WO2025086593A1 - 多元正极材料及其制备方法、正极极片、锂离子电池 - Google Patents

多元正极材料及其制备方法、正极极片、锂离子电池 Download PDF

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WO2025086593A1
WO2025086593A1 PCT/CN2024/091055 CN2024091055W WO2025086593A1 WO 2025086593 A1 WO2025086593 A1 WO 2025086593A1 CN 2024091055 W CN2024091055 W CN 2024091055W WO 2025086593 A1 WO2025086593 A1 WO 2025086593A1
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positive electrode
electrode material
precursor
preparation
cross
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English (en)
French (fr)
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姜华伟
宋顺林
刘亚飞
陈彦彬
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Beijing Easpring Material Technology Co Ltd
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Beijing Easpring Material Technology Co Ltd
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Priority to JP2025534955A priority Critical patent/JP2026501530A/ja
Priority to EP24880972.5A priority patent/EP4614599A4/en
Priority to KR1020257033918A priority patent/KR102958741B1/ko
Publication of WO2025086593A1 publication Critical patent/WO2025086593A1/zh
Priority to US19/237,045 priority patent/US12620591B2/en
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    • C01G53/506—Complex oxides containing nickel and at least one other metal element containing alkali metals, e.g. LiNiO2 containing manganese of the type (MnO2)n-, e.g. Li(NixMn1-x)O2 or Li(MyNixMn1-x-y)O2 containing lithium and cobalt with the molar ratio of nickel with respect to all the metals other than alkali metals higher than or equal to 0.5, e.g. Li(MzNixCoyMn1-x-y-z)O2 with x ≥ 0.5 with the molar ratio of nickel with respect to all the metals other than alkali metals higher than or equal to 0.8, e.g. Li(MzNixCoyMn1-x-y-z)O2 with x ≥ 0.8
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Definitions

  • the present invention relates to the technical field of lithium ion batteries, and in particular to a multi-element positive electrode material and a preparation method thereof, a positive electrode sheet containing the multi-element positive electrode material, and a lithium ion battery containing the positive electrode sheet.
  • Lithium-ion batteries are mainly divided into cylindrical, square and soft-pack types. As a battery for small consumer products, power tools, power batteries and energy storage, lithium-ion batteries have a wide range of applications. Precisely because of the strong demand, its output has grown rapidly, and production technology has advanced by leaps and bounds.
  • the manufacturing process of lithium-ion batteries is relatively complicated, usually including the steps of slurrying, coating, rolling, cutting, injecting, winding and other steps of the positive electrode material. Therefore, it is very important whether the positive electrode material can maintain sufficient stability in each manufacturing process. Among them, in the actual production process of lithium batteries, in order to pursue the energy density of lithium-ion batteries, manufacturers often increase the amount of positive electrode materials used, or use greater pressure in the rolling process, but excessive pressure can easily cause the positive electrode to break, causing the pole piece to be scrapped, and ultimately leading to a higher battery defect rate. From the perspective of the performance of the positive electrode material, the generation of pole piece fragments is largely related to the structure of the positive electrode material itself.
  • the purpose of the present invention is to overcome the problems of existing battery pole pieces that are easy to break, cannot withstand high rolling pressure, and the batteries assembled therefrom have low safety performance, high temperature stability and cycle performance.
  • a multi-element positive electrode material and a preparation method thereof, a positive electrode pole piece and a lithium ion battery are provided.
  • the internal grains of the multi-element positive electrode material are arranged irregularly and non-radially in a disordered manner, so that the multi-element positive electrode material has a higher powder compaction density and processing performance; at the same time, the positive electrode pole piece containing the multi-element positive electrode material can easily withstand a higher rolling pressure and is not prone to pole piece breakage.
  • the first aspect of the present invention provides a multi-element positive electrode material, wherein the multi-element positive electrode material is a secondary particle formed by agglomeration of primary particles, wherein the ratio of the total cross-sectional area of the primary particles having more than 5 grain boundaries to the cross-sectional area of the secondary particles is ⁇ 3:4; and the porosity on the cross-sectional surface of the secondary particles is ⁇ 2%;
  • the grain boundary refers to the contour line of the interface between primary particles with the same structure but different orientations on the cross section of the secondary particle, and the length of the grain boundary is ⁇ 0.1 ⁇ m.
  • the cross section of the secondary particle refers to a cross section after ion milling, preferably a cross section of a particle after ion milling with a cross-sectional diameter equal to DB 50 of the secondary particle.
  • the cross section of the secondary particles used to determine the number of grain boundaries is obtained as follows:
  • Sample preparation a. Cut aluminum foil of about 2 ⁇ 4cm2 and silicon wafer of 1.5 ⁇ 1.5cm2 for use, fold the aluminum foil in half, flatten the two sides, and reserve a gap in the middle for placing the sample; b. Add conductive glue to the positive electrode material powder and mix evenly, then pick up the mixed material and put it into the reserved gap of the aforementioned aluminum foil, then place the aluminum foil on the platform, use a flat plate to compact the periphery of the sample, and then gently press the middle of the sample to obtain the pretreated sample, mark the side of the pretreated sample that contacts the platform as the front side, and the pressed side as the back side; c.
  • measurement stick a conductive tape on the side of the sample stage, fix the sample to be tested on the sample stage, wherein the upper edge of the sample to be tested should be about 1-3mm higher than the sample stage. Then perform ion milling on the sample to be tested on the sample stage. After the milling is completed, apply liquid conductive glue in the gap between the silicon wafer and the sample to be tested to increase the conductivity. Finally, put the treated sample stage into the sample stage bracket dedicated to the electron microscope, fix the position of the sample stage with an inner hexagon, and obtain the cross-sectional sample by electron microscope observation.
  • the ion milling instrument used in the present invention is Hitachi ion milling instrument IM4000PLUS, and the ion milling conditions refer to Table 1:
  • the particles with a cross-sectional diameter equal to the DB 50 of the secondary particles are screened for observation, because such a cross section is a cross section passing through or close to the center of the sphere, which is more representative.
  • the STAGE CONT of the ion milling instrument should first be set to C4 mode, the working time should be adjusted to 40min, the acceleration voltage should be 6kV, the discharge voltage should be adjusted to the maximum, and the air flow should be adjusted to 0.09cm3/min.
  • the powder compaction density of the multi-element positive electrode material is ⁇ 3.4 g/cm 3 .
  • the total residual alkali content of the multi-element positive electrode material satisfies: m(Li 2 CO 3 )+m(LiOH) ⁇ 6000ppm.
  • a second aspect of the present invention provides a method for preparing a multi-element positive electrode material, the method comprising the following steps:
  • M and G are each independently selected from at least one element of Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, B, Al, Co and Y.
  • the precursor is prepared by the following method: in an inert atmosphere, a mixed metal salt solution containing a nickel source, a cobalt source, a manganese source and an optional M-containing dopant is subjected to a co-precipitation reaction with a precipitant, a complexing agent and a dispersant, and the obtained co-precipitation reaction product is washed and dried in sequence to obtain the precursor.
  • the conditions of the coprecipitation reaction include: a temperature selected from 40-80° C., a pH value of 10-13, and a stirring speed selected from 200-550 rpm.
  • the heating rate V1 is selected from 1-6°C/min, preferably from 1-3°C/min, and more preferably from 1-2°C/min; T1 is selected from 400-760°C, preferably from 500-750°C; the insulation time t1 is selected from 2-6h, preferably from 3-5h; the heating rate V2 is selected from 1-6°C/min, preferably from 1-3°C/min; T2 is selected from 710-950°C, preferably from 710-920°C; the insulation time t2 is selected from 5-13h, preferably from 6-12h.
  • the third aspect of the present invention provides a positive electrode plate, wherein the active material layer of the positive electrode plate contains the multi-element positive electrode material provided by the first aspect, or the multi-element positive electrode material prepared by the preparation method provided by the second aspect.
  • a fourth aspect of the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the positive electrode sheet provided by the third aspect.
  • the present invention has the following advantages:
  • the multi-element positive electrode material provided by the present invention has a ratio of the total cross-sectional area of primary particles with more than 5 grain boundaries to the cross-sectional area of secondary particles of ⁇ 3:4.
  • the grain boundaries herein satisfy a length ⁇ 0.1 ⁇ m, and the porosity on the cross-sectional surface of the secondary particles is ⁇ 2%. Therefore, most of the primary particles constituting the secondary particles are closely arranged and have a large number of grain boundaries. It can also be understood that on the cross-sectional surface of the secondary particles, most of the cross-sectional surfaces of the primary particles of the present invention are multi-angular.
  • the multi-element positive electrode material provided by the present invention can disperse and conduct the pressure along the interfaces in multiple directions under extreme compaction, that is, the internal primary particles will creep under pressure.
  • the multi-element positive electrode material is not easy to break.
  • the fracture of the plate can be reduced, so that the multi-element positive electrode material has a higher powder compaction density and processing performance;
  • the preparation method provided by the present invention adopts a precursor with disordered internal grains, and prepares a multi-element positive electrode material with disordered internal grains by optimizing a primary sintering process; specifically, the coprecipitation reaction conditions are controlled to maintain the disordered growth of the seed crystals, so that the primary grains are non-radially disordered and distributed, and a precursor that meets the requirements is prepared; after the above precursor is fully mixed with the lithium source, a double-platform heat preservation sintering process curve is used to allow the lithium source to slowly and fully react with the precursor, and the obtained process product is then coated, and finally a multi-element positive electrode material with fully grown grains and disordered grains is obtained;
  • the multi-element positive electrode material provided by the present invention is used for positive electrode plates.
  • the doping element M When it contains a specific doping element M, the doping element M will be distributed at the interface and will be in an amorphous state.
  • the specific doping element M When squeezed, the specific doping element M can act as a lubricant, making the secondary particles less likely to break and only causing relative displacement, thereby slowing down the occurrence of plate fragmentation. At the same time, it also ensures that the electrical properties of the material are not affected and it is easy to withstand higher rolling pressure and is less likely to produce plate fragmentation.
  • FIG1 is a SEM image of a cross section of the precursor S1 prepared in Preparation Example 1;
  • FIG2 is a SEM image of a cross section of the precursor DS1 obtained in Comparative Preparation Example 1;
  • FIG3 is a SEM image of a cross section of the multi-element positive electrode material P3 prepared in Example 3;
  • FIG4 is a SEM image of a cross section of the multi-element positive electrode material DP3 prepared in Comparative Example 3;
  • FIG5 is an ion milling cross-sectional view of the multi-element positive electrode material P4 prepared in Example 4;
  • FIG6 is an ion milling cross-sectional view of the multi-element positive electrode material DP1 prepared in Comparative Example 1;
  • FIG. 7 is a single-fold cross-sectional SEM image of a positive electrode sheet made from the multi-element positive electrode material P1 of Example 1;
  • FIG8 is a SEM image of a bifold cross-section of a positive electrode sheet made from the multi-element positive electrode material P1 of Example 1;
  • FIG9 is a single-fold cross-sectional SEM image of a positive electrode sheet made from the multi-element positive electrode material DP1 of Comparative Example 1;
  • FIG. 10 is a SEM image of a bifold cross section of a positive electrode sheet made from the multi-element positive electrode material DP1 of Comparative Example 1.
  • the first aspect of the present invention provides a multi-element positive electrode material, wherein the multi-element positive electrode material is a secondary particle formed by agglomeration of primary particles, wherein the ratio of the total cross-sectional area of the primary particles having 5 or more grain boundaries to the cross-sectional area of the secondary particles is ⁇ 3:4; and the porosity on the cross-sectional surface of the secondary particles is ⁇ 2%;
  • the grain boundary refers to the contour line of the interface between primary particles with the same structure but different orientations on the cross section of the secondary particle, and the length of the grain boundary is ⁇ 0.1 ⁇ m.
  • the cross section of the secondary particle refers to the cross section after ion milling, preferably the cross section of the particle after ion milling and having a cross-sectional diameter equal to the DB 50 of the secondary particle.
  • the grain boundary between the primary particles on the cross section of the secondary particle is arranged in a disordered radial direction, and the arrangement form of the primary particles in the cross section of the secondary particle is canine teeth staggered. Under extreme compaction, the secondary particles will creep and are not easy to break.
  • the fracture of the electrode sheet can be reduced.
  • the number of grain boundaries with a length of ⁇ 1.5 ⁇ m accounts for more than 70% of the total number of grain boundaries; further preferably, the number of grain boundaries with a length of ⁇ 1.2 ⁇ m accounts for more than 70% of the total number of grain boundaries; more preferably, the number of grain boundaries with a length selected from 0.2-1.2 ⁇ m accounts for more than 80% of the total number of grain boundaries.
  • the number of grain boundaries with a length of ⁇ 1.5 ⁇ m accounts for more than 70% of the total number of grain boundaries, which means the contour lines of the interfaces between primary particles with the same structure but different orientations on the cross-section of the secondary particles, wherein the number of contour lines with a length of 0.1 ⁇ m ⁇ 1.5 ⁇ m and the total number of contour lines with a length of ⁇ 0.1 ⁇ m account for more than 70%; that is, the number of grain boundaries with a length of 0.1 ⁇ m ⁇ 1.5 ⁇ m and the total number of grain boundaries with a length of ⁇ 0.1 ⁇ m account for more than 70%.
  • the number of grain boundaries with a length of ⁇ 1.2 ⁇ m accounts for more than 70% of the total number of grain boundaries, which means that the length of the grain boundary is 0.1 ⁇ m ⁇
  • the number of grain boundaries with a length of 1.2 ⁇ m and a total number of grain boundaries with a length ⁇ 0.1 ⁇ m account for more than 70%;
  • the number of grain boundaries with a length of 0.2-1.2 ⁇ m accounts for more than 80% of the total number of grain boundaries, which means the number of grain boundaries with a length of 0.2 ⁇ m ⁇ 1.2 ⁇ m and a total number of grain boundaries with a length ⁇ 0.1 ⁇ m account for more than 80%.
  • the primary particles in the multi-electrode positive electrode material show obvious disordered distribution, and at the same time will not cause cracking of the positive electrode active material particles caused by charging and discharging, and maintain sufficient cycle characteristics.
  • the average aspect ratio of the primary particles is ⁇ 1.5, for example, 0.8, 0.9, 1, 1.02, 1.05, 1.08, 1.1, 1.3, 1.5, and any value in the range of any two values, preferably selected from 1-1.5, more preferably selected from 1-1.1.
  • the primary particles have a smaller average aspect ratio, which is convenient for stacking with each other, and increases the packing density of the primary particles between the secondary particles.
  • the aspect ratio has the same concept as the length-to-width ratio, that is, the ratio of the longest diameter passing through the inside of the particle to the longest diameter perpendicular to it. This parameter is used to describe the particle morphology to determine whether its shape is close to a regular body.
  • the average aspect ratio in the present invention refers to the average value of the aspect ratios of all primary particles on the cross section of the secondary particles.
  • the primary particles having an aspect ratio of 0.9-1.1 account for ⁇ 70%.
  • the primary particles are not easily guided to be arranged radially when agglomerated into secondary particles, and are easy to change the stacking form when under pressure, so that the secondary particles are deformed without breaking.
  • the average particle size DB 50 of the secondary particles and the average particle size DA 50 of the primary particles satisfy: 10 ⁇ DB 50 /DA 50 ⁇ 40, for example, 10, 15, 20, 25, 30, 35, 40, and any value in the range of any two values.
  • the secondary particles are composed of an appropriate amount of primary particles, and are tightly combined with each other, which is convenient for increasing the strength of the secondary particles; at the same time, they have good electrical properties.
  • the secondary particles are spherical or nearly spherical.
  • the average particle size DB50 of the secondary particles is selected from 6-14 ⁇ m, for example, 6 ⁇ m, 8 ⁇ m, 10 ⁇ m, 12 ⁇ m, 14 ⁇ m, and any value in the range of any two values, preferably 8-12 ⁇ m.
  • the average particle size DA50 of the primary particles is selected from 0.1-1.5 ⁇ m , for example, 0.1 ⁇ m, 0.2 ⁇ m, 0.5 ⁇ m, 0.8 ⁇ m, 1 ⁇ m, 1.2 ⁇ m, 1.5 ⁇ m, and any value in the range of any two values, preferably 0.2-1.2 ⁇ m.
  • the average particle size DA50 of the primary particles meets the above range, the primary particles in the multi-element positive electrode material have a smaller average particle size and dense stacking, which is conducive to forming a stable structure, relieving the internal stress during the battery charging and discharging process, and slowing down the generation of microcracks.
  • the multi-element cathode material has a composition shown in Formula I: Li a (Ni x Co y Mn z M b )G c O 2 (I);
  • M and G are each independently selected from at least one element of Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, B, Al, Co and Y.
  • M is selected from at least one element of Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, Al, Co and Y
  • G is selected from at least one element of Mg, Ti, W, Zr, Ce, Er, Si, B and Al.
  • M is selected from at least one element of W, Zr, La and Y;
  • G is selected from at least one element of B, Ti, W, Si and Al.
  • the half-maximum width FWHM (104) of the characteristic diffraction peak of the multinary positive electrode material at the (104) crystal plane is selected from 0.2-0.24, for example, 0.2, 0.22, 0.23, 0.24, and any value in the range of any two numerical values, preferably 0.22-0.24.
  • the multi-electrode cathode material when the half-peak width FWHM (104) of the characteristic diffraction peak of the (104) crystal plane meets the above conditions, the multi-electrode cathode material has better crystallization performance and cycle performance; at the same time, the grains can be fully developed, so that there are more grain boundaries in the primary particles. Based on the fact that the crystal arrangement at the grain boundaries is very irregular, the crystal faces are interlaced and bite each other, so that the multi-electrode cathode material can have a stable structure under normal pressure.
  • the secondary particles are prone to creep under high pressure, thereby Reduce the squeezing of the secondary balls on the aluminum foil pole piece and reduce the breakage of the pole piece.
  • the half-maximum width FWHM (104) of the characteristic diffraction peak of the (104) crystal plane meets the above conditions, there is less adhesion between the secondary particles, which can increase the compaction density of the multi-element positive electrode material and further reduce the occurrence of positive electrode piece breakage.
  • the multi-element positive electrode material has a single ⁇ -NaFeO 2- type layered structure.
  • the powder compaction density of the multi-component positive electrode material is ⁇ 3.4 g/cm 3 .
  • the multi-component positive electrode material provided by the present invention has a relatively high powder compaction density, thereby increasing the energy density of the lithium battery to a certain extent.
  • the total residual alkali content of the multi-element positive electrode material satisfies: m(Li 2 CO 3 )+m(LiOH) ⁇ 6000ppm; further preferably, the total residual alkali content of the multi-element positive electrode material also satisfies: m(Li 2 CO 3 ) ⁇ m(LiOH), and both m(Li 2 CO 3 ) and m(LiOH) are lower than 3000ppm.
  • the lattice structure of the obtained multi-element positive electrode material is stable and complete, which can significantly enhance the structural stability, capacity rate performance and safety performance of the positive electrode material, thereby further improving the cycle stability of the multi-element positive electrode material; at the same time, the reduction in the amount of residual alkali can also reduce the adhesion between particles, increase the compaction density of the material, and further reduce the occurrence of electrode breakage.
  • a second aspect of the present invention provides a method for preparing a multi-element positive electrode material, the method comprising the following steps:
  • M and G are each independently selected from at least one element of Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, B, Al, Co and Y.
  • M is selected from at least one element of Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, Al, Co and Y; further preferably, in formula II, 0.0001 ⁇ 0.02, M is selected from at least one element of W, Zr, La and Y.
  • the inventors of the present invention have found that when a specific doping element M is added to the positive electrode material, it is conducive to the disordered distribution of the primary particles, and the doping element M will be distributed at the interface in an amorphous state. When squeezed, the doping element M can act as a lubricant, making the secondary particles less likely to break, but only relatively displacing. This slows down the occurrence of pole fragments while also ensuring that the electrical properties of the material are not affected.
  • adding a dopant containing the M element during the wet coprecipitation synthesis process of the precursor can, on the one hand, stabilize the internal structure of the material and improve the cycle life of the ternary material, especially the high-nickel ternary material.
  • the doping element M can be more evenly distributed in the positive electrode material, which is conducive to the disordered distribution of the primary particles.
  • the present invention also optimizes the sintering process, specifically, the lithium source and the precursor adopt a double-stage heat preservation one-time sintering process, so that the lithium source slowly and fully reacts with the precursor, and the obtained process product is then coated to finally obtain a multi-element positive electrode material with fully grown grains and disordered grains.
  • D 50 of the precursor is selected from 8-14 ⁇ m; and the specific surface area of the precursor is selected from 3-7 m 2 /g.
  • the precursor is prepared by the following method: in an inert atmosphere, a mixed metal salt solution containing a nickel source, a cobalt source, a manganese source and an optional M-containing dopant is contacted with a precipitant, a complexing agent and a dispersant to carry out a co-precipitation reaction, and the obtained co-precipitation reaction product is sequentially washed and dried to obtain the precursor.
  • the inert atmosphere includes but is not limited to nitrogen atmosphere, argon atmosphere, etc.
  • the coprecipitation reaction conditions include: temperature selected from 40-80°C, pH value 10-13, stirring speed selected from 200-550rpm. More preferably, the coprecipitation reaction conditions include: temperature selected from 50-70°C, pH value 11-12.5, stirring speed selected from 350-500rpm.
  • the pH value and the stirring speed are within the specified range, so that the disordered growth of the seed crystals can be maintained, the primary grains are non-radially disordered, and a precursor with disordered internal grains is obtained.
  • the amounts of the nickel source, cobalt source, manganese source and dopant satisfy n(Ni):n(Co):n(Mn):n(M), 0.3 ⁇ n(Ni) ⁇ 1, 0 ⁇ n(Co) ⁇ 0.5, 0 ⁇ n(Mn) ⁇ 0.5, 0 ⁇ n(M) ⁇ 0.05; further preferably, 0.4 ⁇ n(Ni) ⁇ 0.95, 0.01 ⁇ n(Co) ⁇ 0.2, 0.01 ⁇ n(Mn) ⁇ 0.3, 0 ⁇ n(M) ⁇ 0.02; more preferably, 0.0001 ⁇ n(M) ⁇ 0.02.
  • the concentration of the mixed metal salt solution is 1-3 mol/L in terms of metal elements.
  • the nickel source, cobalt source, manganese source and dopant are each independently selected from at least one of sulfate, chlorate, nitrate and acetate.
  • the nickel source is selected from at least one of nickel sulfate, nickel chlorate, nickel nitrate and nickel acetate
  • the cobalt source is selected from at least one of cobalt sulfate, cobalt chlorate, cobalt nitrate and cobalt acetate
  • the manganese source is selected from at least one of manganese sulfate, manganese chlorate, manganese nitrate and manganese acetate.
  • the dopant is selected from soluble salts containing M, preferably selected from at least one of sulfates, chlorides, hydroxides and carbonates containing M.
  • the dopant is selected from at least one of sulfates, chlorides, hydroxides and carbonates containing Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, B, Al, Co and Y, preferably selected from at least one of sulfates, chlorides, hydroxides and carbonates containing Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, Al, Co and Y, more preferably selected from at least one of sulfates, chlorides, hydroxides and carbonates containing W, Zr, La and Y.
  • the precipitant is selected from NaOH and/or KOH;
  • the complexing agent is selected from at least one of ammonia water, disodium ethylenediaminetetraacetic acid, ammonium nitrate, ammonium chloride and ammonium sulfate;
  • the dispersant is selected from at least one of polyethylene glycol (PEG), polyvinyl alcohol (PVA) and polyglycerol.
  • the precipitant, complexing agent and dispersant are each independently present in the form of aqueous solution; further preferably, the concentration of the precipitant solution is 2-15 mol/L; the concentration of the complexing agent solution is 1-15 mol/L; and the concentration of the dispersant solution is 1-200 g/L.
  • the drying temperature is 105-130°C.
  • the conditions for the primary sintering include: the heating rate V1 is selected from 1-6°C/min, preferably selected from 1-3°C/min, and more preferably selected from 1-2°C/min; T1 is selected from 400-760°C, preferably selected from 500-750°C; the holding time t1 is selected from 2-6h, preferably selected from 3-5h; the heating rate V2 is selected from 1-6°C/min, preferably selected from 1-3°C/min; T2 is selected from 710-950°C, preferably selected from 710-920°C; the holding time t2 is selected from 5-13h, preferably selected from 6-12h.
  • a two-stage platform sintering process is used to prepare a multi-element positive electrode material, so that the multi-element positive electrode material has the advantages of low residual alkali, disordered internal structure, stable structure, etc. That is, in step (2), by setting a suitable heating rate (i.e., V1 and V2), insulation temperature (i.e., T1 and T2) and insulation time (t1 and t2), the material is sintered on two platforms, so that the lithium source and the precursor react fully, and the primary particles grow along various crystal directions after growing up, so as to obtain a pressure-resistant agglomerated positive electrode material with disordered internal structure orientation.
  • a suitable heating rate i.e., V1 and V2
  • insulation temperature i.e., T1 and T2
  • t1 and t2 insulation time
  • the oxygen concentration in the oxygen-containing atmosphere is ⁇ 92 volume % in terms of metal element. In this way, sufficient oxygen concentration ensures that the mixing degree of nickel ions and lithium ions is reduced when the nickel content is high, thereby reducing the residual alkali content of the material.
  • the product of the primary sintering is cooled to room temperature and then crushed to obtain the process product.
  • the crushing includes but is not limited to at least one of a jaw crusher, a roller, a colloid mill, a mechanical mill and a jet mill.
  • the coating agent is selected from at least one of oxides, hydroxides and carbonates containing G, preferably selected from at least one of oxides, hydroxides and carbonates containing Mg, Ti, W, Zr, Ce, Er, Si, B and Al, more preferably selected from at least one of oxides, hydroxides and carbonates containing B, Ti, W, Si and Al.
  • the conditions for the secondary sintering include: temperature T3 is selected from 300-800°C, preferably selected from 400-700°C; time t3 is selected from 4-10h, preferably selected from 5-8h.
  • the multi-element positive electrode material prepared according to the above preparation method has a composition shown in Formula I: Li a (Ni x Co y Mn z M b )G c O 2 (I);
  • M and G are each independently selected from at least one element of Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, B, Al, Co and Y.
  • M is selected from at least one element of Mg, Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, Al, Co and Y
  • G is selected from at least one element of Mg, Ti, W, Zr, Ce, Er, Si, B and Al.
  • M is selected from at least one element of W, Zr, La and Y;
  • G is selected from at least one element of B, Ti, W, Si and Al.
  • the third aspect of the present invention provides a positive electrode plate, wherein the active material layer of the positive electrode plate contains the multi-element positive electrode material provided by the first aspect, or the multi-element positive electrode material prepared by the preparation method provided by the second aspect.
  • the positive electrode sheet includes a positive electrode current collector and an active material layer loaded on the positive electrode current collector.
  • the active material layer contains not only the multi-element positive electrode material but also a conductive agent, a binder and a dispersant.
  • the positive electrode plate is prepared by the following method: the above-mentioned multi-element positive electrode material, SuperP, CNT and polyvinylidene fluoride (PVDF) are fully mixed with an appropriate amount of N-methylpyrrolidone (NMP) in a mass ratio of 97:1:0.8:1.2 to form a uniform slurry, the slurry is coated on an aluminum foil, and after a drying process, a die-cutting machine is used to punch out a 112mm ⁇ 40mm electrode plate, wherein the multi-element positive electrode material loading is 380 ⁇ 2g/ m2 .
  • NMP N-methylpyrrolidone
  • the method for determining the fragmentation of the electrode piece of the present invention is: the prepared positive electrode pieces are all baked in a vacuum oven at 125°C for more than 8 hours; then the positive electrode pieces are tested and rolled twice to reach the corresponding compaction density; then the electrode pieces are folded with a fixed weight flat plate; finally, an LED point light source is used for light transmission observation. At the same time, the thickness of the positive electrode piece before and after rolling and the length of the positive electrode piece are recorded, and the thickness compression ratio and elongation of the positive electrode piece before and after rolling are calculated. The positive electrode pieces are pressed to different compaction densities respectively, and the light transmission of the electrode piece when it is folded once, twice, three times, and four times under different compaction densities is observed and counted respectively. The fragmentation result of the electrode piece is determined based on whether it is light-transmitting.
  • the present invention can also use the above multi-element positive electrode materials according to the same formula to make battery electrodes, and then apply a certain pressure to the electrode to observe the cross section of the battery electrode under SEM to determine the electrode fragmentation according to the cross section.
  • the ultimate compaction density of the positive electrode sheet is selected from 3.2-3.8 g/cm 3 , for example, 3.2 g/cm 3 , 3.3 g/cm 3 , 3.5 g/cm 3 , 3.6 g/cm 3 , 3.7 g/cm 3 , 3.8 g/cm 3 , and any value in the range consisting of any two values, preferably 3.3-3.7 g/cm 3 .
  • the thickness compression ratio of the positive electrode plate is selected from 25-45%, for example, 25%, 30%, 32%, 35%, 38%, 40%, 45%, and any value in the range of any two values, preferably 30-40%.
  • the elongation of the positive electrode plate is selected from 1.2-3%, for example, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 3%, and any value in the range of any two values, preferably 1.5-2.5%.
  • the positive electrode sheet made of the above-mentioned multi-element positive electrode material can withstand a larger rolling pressure and is not prone to breaking.
  • a fourth aspect of the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the positive electrode sheet prepared according to the third aspect.
  • compositions of the precursor and multi-element cathode materials were measured by ICP method; the instrument used was PE Optima 7000DV, and the test conditions were that 0.1 g of sample was completely dissolved in a mixed acid solution of 3 mL HNO 3 + 9 mL HCl and diluted to 250 mL for testing;
  • the cross section of secondary particles there are two ways to obtain the cross section of secondary particles, namely, one is the SEM image of the cross section as shown in Figures 1-4, and the cross section is obtained by taking a small amount of the material to be tested and placing it on a glass slide, and then squeezing the material with another glass slide, selecting the cross section obtained by squeezing from the center of the secondary particle, and observing the cross section under a scanning electron microscope to obtain the cross section of the secondary particle of the present invention; this method is convenient for three-dimensional observation;
  • the second is the ion milling cross-section as shown in Figures 5-6.
  • the cross-section obtained by this method is convenient for clearly defining the grain boundaries mentioned in this article.
  • the method of obtaining the surface is as follows:
  • Sample preparation a. Cut 2 ⁇ 4cm2 aluminum foil and 1.5 ⁇ 1.5cm 2. Prepare silicon wafers of different specifications, fold the aluminum foil in half, flatten the two sides, and reserve a gap in the middle for placing the sample; b. Add conductive glue to the positive electrode material powder and mix evenly, then pick and place the mixed material in the reserved gap of the aforementioned aluminum foil, then place the aluminum foil on the platform, use a flat plate to compact the periphery of the sample, and then gently press the sample in the middle to obtain the pretreated sample, and mark the side of the pretreated sample that contacts the platform as the front side, and the pressed side as the back side; c.
  • measurement stick a conductive tape on the side of the sample stage, fix the sample to be tested on the sample stage, wherein the upper edge of the sample to be tested should be about 1-3mm higher than the sample stage. Then perform ion milling on the sample to be tested on the sample stage. After the milling is completed, apply liquid conductive glue in the gap between the silicon wafer and the sample to be tested to increase the conductivity. Finally, put the treated sample stage into the sample stage bracket dedicated to the electron microscope, fix the position of the sample stage with an inner hexagon, and obtain the cross-sectional sample by electron microscope observation.
  • the ion milling instrument used in the present invention is Hitachi ion milling instrument IM4000PLUS, and the ion milling conditions refer to Table 1:
  • the STAGE CONT of the ion milling instrument should first be set to C4 mode, the working time should be adjusted to 40 minutes, the acceleration voltage should be 6 kV, the discharge voltage should be adjusted to the maximum, and the airflow should be adjusted to 0.09 cm3/min.
  • the grain boundary determination is based on the ion milling cross-section diagram.
  • the grain boundary is defined as the interface between primary particles with the same structure but different orientations on the cross-section of the secondary particles, and the length of the interface is ⁇ 0.1 ⁇ m.
  • Particle size DA 50 , DB 50 measured by Malvern's Mastersize 2000 laser particle size analyzer
  • compositions and physical properties of the precursors prepared in Preparation Examples 1-5 and Comparative Preparation Examples 1-4 are listed in Table 2.
  • the above solutions were introduced into the reactor in parallel for co-precipitation reaction, the reaction temperature was maintained at 50°C, the reaction pH was 11.2, the stirring speed was 350 rpm, and the precursor S1 was obtained after washing, drying at 120°C and sieving.
  • the SEM of the cross section of the precursor S1 is shown in FIG1 . It can be seen from FIG1 that the precursor S1 is formed by agglomeration of primary crystal grains, and the primary crystal grains on the cross section of the precursor S1 are randomly distributed.
  • the type of dopant was replaced with zirconium chloride
  • the SEM image of the cross section of the above-mentioned precursor S3 is similar to that of FIG1 .
  • a 2 mol/L mixed metal salt solution is prepared, wherein the molar ratios of nickel sulfate, cobalt sulfate, manganese sulfate, sodium tungstate and yttrium sulfate in the mixed metal salt solution are 0.95:0.02:0.0275:0.001:0.0015 respectively, based on the metal elements;
  • No dopant yttrium sulfate is added, that is, a 2 mol/L mixed metal salt solution is prepared, and the molar ratio of nickel sulfate, cobalt sulfate and manganese sulfate in the mixed metal salt solution is 50:20:30 based on metal elements;
  • the conditions of the coprecipitation reaction were replaced by a reaction temperature of 60°C, a reaction pH of 11.7, and a stirring speed of 800 rpm;
  • the SEM image of the cross section of the precursor DS1 is shown in FIG. 2 . It can be seen from FIG. 2 that the precursor DS1 is formed by agglomeration of primary crystal grains, and the primary crystal grains on the cross section of the precursor DS1 are distributed radially.
  • No doping agent zirconium chloride is added; that is, a 2 mol/L mixed metal salt solution is prepared, and the molar ratio of nickel sulfate, cobalt sulfate and manganese sulfate in the mixed metal salt solution is 60:20:20 based on metal elements;
  • the concentration of NaOH solution is 2 mol/L, and the concentration of ammonia water is 2 mol/L;
  • the conditions of the coprecipitation reaction were replaced by a reaction temperature of 55°C, a reaction pH of 13.2, and a stirring speed of 450 rpm;
  • No dopant lanthanum nitrate is added; that is, a 2 mol/L mixed metal salt solution is prepared, and the molar ratio of nickel sulfate, cobalt sulfate and manganese sulfate in the mixed metal salt solution is 81:9:10 based on metal elements;
  • the conditions of the coprecipitation reaction were replaced by a reaction temperature of 58°C, a reaction pH of 13.2, and a stirring speed of 800 rpm;
  • the dispersant is a 10 g/L polyglycerol dispersant aqueous solution
  • the conditions of the coprecipitation reaction were replaced by a reaction temperature of 60°C, a reaction pH of 11.7, and a stirring speed of 600 rpm;
  • preparation examples 1-5 meet the conditions of the coprecipitation reaction by regulating: the temperature is selected from 40-80°C, the pH value is 10-13, the stirring speed is selected from 200-550rpm, and especially in combination with the type of doping element M, the precursor satisfying formula II is formed by agglomeration of primary grains, and the primary grains on the cross section of the precursor are non-radially distributed.
  • step (4) the secondary sintering temperature is replaced with 500°C;
  • FIG3 The SEM image of the cross section of the multi-element positive electrode material P3 is shown in FIG3 .
  • the internal particles of the multi-element positive electrode material P3 are disordered and grow in a non-radial manner.
  • the primary sintering atmosphere is an oxygen atmosphere with an oxygen content of ⁇ 95V%;
  • step (4) the secondary sintering temperature is replaced with 350°C;
  • the ion milling cross-sectional view of the multi-element positive electrode material P4 is shown in FIG5 .
  • the internal particles of the multi-element positive electrode material P4 are disordered and grow in a non-radial manner.
  • step (1) the precursor is the precursor S5 prepared in Preparation Example 5;
  • step (1) the precursor is the precursor DS1 prepared in Comparative Preparation Example 1;
  • the ion milling cross-sectional view of the multi-element positive electrode material DP1 is shown in FIG6 .
  • the internal particles of the multi-element positive electrode material DP1 grow in a radial distribution.
  • step (1) the precursor is the precursor DS2 prepared in Comparative Preparation Example 2;
  • the SEM image of the cross section of the multi-element positive electrode material DP3 is shown in FIG4 .
  • the internal particles of the multi-element positive electrode material DP3 grow in a radial distribution.
  • step (1) the precursor is the precursor DS4 prepared in Comparative Preparation Example 4;
  • step (2) t1 is 0 h
  • step (2) the atmosphere of the primary sintering and the secondary sintering is an oxygen atmosphere with an oxygen content of 85V%;
  • Examples 1-5 adopt the preparation method provided by the present invention, and the multi-element positive electrode material prepared has the advantages of disordered non-radial growth of internal particles, high compaction density, and the pole piece is not easy to break;
  • Examples 1-4 respectively use non-radial doping precursors, and the material powder compaction prepared by the double-platform insulation process is significantly higher than the positive electrode material of Comparative Examples 1-8 treated by the same process with radially distributed precursors.
  • the distribution compaction of the material of Example 5, which is not doped with element M in the precursor stage but added with doping element M in the preparation stage of the positive electrode material, is slightly lower than that of the material of Example 4 prepared by doping element M in the precursor stage.
  • the materials prepared by excessively high heating rates V1 and V2 (Comparative Example 6), high Ni content and insufficient oxygen concentration in the first sintering (Comparative Example 7), and single-platform first sintering process (Comparative Example 5, Comparative Example 8) have significantly higher alkali content and correspondingly lower compaction, which makes it easier to produce breakage when the pole pieces are compacted.
  • the positive electrode sheets made of the multi-element positive electrode materials of the above-mentioned embodiments and comparative examples were subjected to limit compaction and fragmentation tests, and the test results are listed in Table 5.
  • the specific preparation process of the positive electrode sheet the above-mentioned multi-element positive electrode materials, SP, CNT and polyvinylidene fluoride (PVDF) are fully mixed with an appropriate amount of N-methylpyrrolidone (NMP) in a mass ratio of 97:1:0.8:1.2 to form a uniform slurry, the slurry is coated on aluminum foil, and after a drying process, a die-cutting machine is used to punch out 112mm ⁇ 40mm electrode sheets, in which the multi-element positive electrode material loading is 380 ⁇ 2g/ m2 .
  • NMP N-methylpyrrolidone
  • Method for determining the broken pieces of the electrode bake the prepared positive electrode pieces in a vacuum oven at 125°C for more than 8 hours; then test the positive electrode pieces Roll the plate twice to reach the corresponding compaction density; then fold the plate with a fixed weight; finally, use an LED point light source for light transmission observation. At the same time, record the thickness of the positive electrode plate before and after rolling and the length of the positive electrode plate, and calculate the thickness compression ratio and elongation of the positive electrode plate before and after rolling. Press the positive electrode plate to different compaction densities, and observe and count the light transmission of the plate when it is folded once, twice, three times, and four times at different compaction densities. Determine the fragmentation result of the positive electrode plate based on whether it is light-transmitting.
  • the positive electrode sheet made of the multi-element positive electrode material P1 of Example 1 is subjected to extreme pressing, and the corresponding limit compaction densities when single folded and double folded are opaque are 3.64g/ cm3 and 3.57g/ cm3 respectively (taking Example 1 as an example, the corresponding limit compaction density of the positive electrode sheet A2 when the first single fold is opaque, and the corresponding limit compaction density of the positive electrode sheet A4 when the first double fold is opaque) ;
  • the positive electrode sheet made of the multi-element positive electrode material P2 of Example 2 is subjected to extreme pressing, and the corresponding limit compaction densities when single folded and double folded are opaque are 3.66g/ cm3 and 3.62g/ cm3 respectively;
  • the positive electrode sheet made of the multi-element positive electrode material P3 of Example 3 is subjected to extreme pressing, and the corresponding limit compaction densities when single folded and double folded are opaque are 3.77g/ cm3 and 3.59g/ cm3 respectively.
  • the positive electrode sheet made of the multi-element positive electrode material P4 of Example 4 was subjected to extreme compression, and the corresponding extreme compaction densities when single-folded and double-folded were opaque were 3.71 g/cm 3 and 3.57 g/cm 3 respectively.
  • the compaction densities of these material sheets were higher than the corresponding comparative examples.
  • FIG7 single fold
  • FIG8 double fold
  • the secondary particles are easy to soften, which is equivalent to removing a part of the rolling pressure, thereby reducing the squeezing of the secondary balls on the aluminum foil sheet and reducing the breakage of the sheet.
  • the electrical properties of the battery can still meet the use requirements well.

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Abstract

一种多元正极材料及其制备方法、以及使用上述多元正极材料的正极极片和锂离子电池。该多元正极材料为一次颗粒团聚而成的二次颗粒，其中，具有5条以上晶界数量的一次颗粒的剖面总面积与二次颗粒的剖面面积比值≥3:4；所述二次颗粒的剖面上的孔隙率≤2％；其中，晶界是指结构相同而取向不同的一次颗粒之间的界面在所述二次颗粒的剖面上的轮廓线，且所述晶界的长度≥0.1μm。多元正极材料的内部晶粒为无规则非径向无序排列，使得多元正极材料具有较高的粉末压实密度和加工性能；同时，含有该多元正极材料的正极极片容易承受较高的辊压压力，不易产生极片断片。

Description

多元正极材料及其制备方法、正极极片、锂离子电池
优先权信息
本发明请求2023年10月25日向中国国家知识产权局提交的专利申请202311394203.9的优先权和权益，并且通过参照将其全文并入此处。
技术领域
本发明涉及锂离子电池技术领域，具体涉及一种多元正极材料及其制备方法，一种含有该多元正极材料的正极极片，以及一种含有该正极极片的锂离子电池。
背景技术
锂离子电池主要分为圆柱、方形和软包几类。作为从小型消费类到电动工具再到动力电池包括储能在内，锂离子电池有着广泛的应用领域。正是因为需求强烈，其产量有着迅猛的增长，生产技术更是突飞猛进。
锂离子电池的制作过程较为繁琐，通常包括将正极材料进行匀浆、涂布、辊压、裁切、注液、卷绕等步骤，因此正极材料在各项制作工序中能否保持足够的稳定性十分重要。其中，在锂电池实际生产过程中，厂家为追求锂离子电池的能量密度，往往会加大正极材料的使用量，或者在辊压工序采用更大的压力，但过大的压力容易出现正极片断片的现象，造成极片报废，最终导致较高的电池不良率。从正极材料的性能角度考虑，极片断片的产生，与正极材料自身的结构关系较大。
一般来说，设计正极材料时为了改善循环性能，会有意识的设计成剖面为径向分布的材料，但在制作电池极片过程中，当采用较大辊压压力获取足够的能量密度时，此类正极材料会将受到的压力均沿径向传导至涂抹正极的铝箔极片上，相同的受压方向经扩大后极易导致极片断裂，大大降低了电池极片的不良率。这种现象也会影响电池的电性能，特别是电池的安全性能、高温稳定性和循环性能，无法满足电动汽车电池高安全性的要求。
发明内容
本发明的目的是为了克服现有电池极片存在易断片，无法承受高辊压压力，以及其组装的电池存在较低的安全性能、高温稳定性和循环性能等问题，提供一种多元正极材料及其制备方法、一种正极极片和一种锂离子电池，该多元正极材料的内部晶粒为无规则非径向无序排列，使得多元正极材料具有较高的粉末压实密度和加工性能；同时，含有该多元正极材料的正极极片容易承受较高的辊压压力，不易产生极片断片。
为了实现上述目的，本发明第一方面提供一种多元正极材料，所述多元正极材料为一次颗粒团聚而成的二次颗粒，其中，具有5条以上晶界数量的一次颗粒的剖面总面积与二次颗粒的剖面面积比值≥3:4；所述二次颗粒的剖面上的孔隙率≤2％；
其中，晶界是指结构相同而取向不同的一次颗粒之间的界面在所述二次颗粒的剖面上的轮廓线，且所述晶界的长度≥0.1μm。
在本发明中，没有特殊情况说明下，所述二次颗粒的剖面是指经离子研磨的剖面，优选是指经离子研磨且截面直径等于所述二次颗粒的DB50的颗粒的剖面。
在本发明中，用于确定晶界数量的二次颗粒的剖面的获取方式如下：
S1、制样：a、剪取2×4cm2左右的铝箔和1.5×1.5cm2规格的硅片备用，将铝箔对折，两边压平，中部预留空隙用于放置样品；b、向正极材料粉末内加入导电胶混合均匀，然后将混合物料挑放至前述铝箔的预留空隙中，接着将铝箔放置于平台上，用平板先将样品的周边压实，再轻轻按压中部的样品，得预处理样品，标记预处理样品中接触所述平台的一面为正面，按压面为背面；c、将预处理样品在100℃的温度下干燥60min，干燥完成后取出预处理样品，切掉预处理样品上没有样品的多余部分铝箔，然后在样品充足的部位处从背面垂直切开样品；d、取上述硅片，用胶水将切好的预处理样品的背面粘在硅片上，如此样品中较为平整的正面可以紧贴挡板并正向面对离子束，在粘贴时，应保证铝箔的切面突出于 硅片的边缘或与之平齐，例如突出60μm以上，得待测样品。
S2、测定：在样品台侧边粘上导电胶带，将待测样品固定在样品台上，其中待测样品的上边缘应高出样品台1-3mm左右。然后对样品台上的待测样品进行离子研磨处理，研磨完成后，再在待测样品中硅片和样品的间隙内涂抹液体导电胶以增加导电性。最后，将处理后的样品台放入电镜专用的样品台支架上，用内六方固定紧样品台位置，通过电镜观察获取截面样品，其中，本发明中采用的离子研磨仪为日立离子研磨仪IM4000PLUS，离子研磨条件参阅表1：
表1
其中，基于上述方法获取的离子研磨剖面图上，筛选出截面直径与二次颗粒的DB50相等的颗粒进行观察，因为，这样的截面是经过或靠近球心的截面，更加具有代表性，其中在进行离子研磨时，应首先将离子研磨仪的STAGE CONT到C4模式，调节工作时间为40min，加速电压为6kV，放电电压调为最大，气流调整为0.09cm3/min。电镜的测试条件为采用低电压背散模式，电压＝1kV，WD＝2.5mm，放大倍数为10k。
优选地，所述多元正极材料的粉末压实密度≥3.4g/cm3。
优选地，所述多元正极材料的总残碱含量满足：m(Li2CO3)+m(LiOH)＜6000ppm。
本发明第二方面提供一种多元正极材料的制备方法，所述制备方法包括以下步骤：
(1)将具有式II所示组成的前驱体和锂源进行混合，得到混合物I，所述前驱体由一次晶粒团聚而成，且所述前驱体的剖面上的一次晶粒非径向分布；
(2)在含氧气氛中，将所述混合物I进行一次烧结，得到过程品；所述一次烧结的条件包括：以V1的升温速率升温至T1，恒温t1；再以V2的升温速率升温至T2，恒温t2；
(3)将所述过程品和可选的含G的包覆剂进行混合，得到混合物II；
(4)在含氧气氛中，将所述过程品或混合物II进行二次烧结，得到多元正极材料；
其中，(NiαCoβMnγMδ)(OH)2(II)，0.3≤α＜1，0＜β＜0.5，0＜γ＜0.5，0≤δ≤0.05，且α+β+γ+δ＝1；M和G各自独立地选自Mg、Ti、W、V、Ta、Zr、La、Ce、Er、Sr、Si、B、Al、Co和Y中的至少一种元素。
优选地，所述前驱体由以下方法制得：在惰性气氛中，将含有镍源、钴源、锰源和可选的含M的掺杂剂的混合金属盐溶液，与沉淀剂、络合剂和分散剂进行共沉淀反应，得到的共沉淀反应产物依次进行洗涤、干燥，得到所述前驱体。
优选地，所述共沉淀反应的条件包括：温度选自40-80℃，pH值为10-13，搅拌转速选自200-550rpm。
优选地，步骤(2)中，所述一次烧结的条件包括：
升温速率V1选自1-6℃/min，优选选自1-3℃/min，更优选选自1-2℃/min；T1选自400-760℃，优选选自500-750℃；保温时间t1选自2-6h，优选选自3-5h；升温速率V2选自1-6℃/min，优选选自1-3℃/min；T2选自710-950℃，优选选自710-920℃；保温时间t2选自5-13h，优选选自6-12h。
本发明第三方面提供一种正极极片，所述正极极片的活性物质层含有第一方面提供的多元正极材料，或者，第二方面提供的制备方法制得的多元正极材料。
本发明第四方面提供一种锂离子电池，所述锂离子电池含有第三方面提供的正极极片。
相比现有技术，本发明具有以下优势：
(1)本发明提供的多元正极材料具有5条以上晶界数量的一次颗粒的剖面总面积与二次颗粒的剖面面积比值≥3:4，此处所述晶界满足长度≥0.1μm，且二次颗粒的剖面上的孔隙率≤2％，因此，组成二次颗粒的一次颗粒大部分紧密排列具有较多的晶界，也可以理解为在二次颗粒的剖面上，本发明的一次颗粒的截面大部分呈多棱角形。基于截面为多棱角一次颗粒的紧密排列特征从而使得本发明提供的多元正极材料在极限压实下，可以将受到的压力沿着多方向的界面分散传导，即内部一次颗粒受压会发生蠕 变而不容易破碎，当将该结构的多元正极材料用于正极极片时，可减少极片的断裂，使得多元正极材料具有较高的粉末压实密度和加工性能；
(2)本发明提供的制备方法，采用内部晶粒无序排列的前驱体，并通过优化一次烧结工艺，制备同样内部晶粒无序排列的多元正极材料；具体而言，控制共沉淀反应条件保持晶种的无序生长，使一次晶粒非径向无序分布，制备出满足要求的前驱体；将上述前驱体与锂源充分混合后，通过双平台保温烧结工艺曲线，使得锂源缓慢充分与前驱体反应，得到的过程品再进行包覆，最终得到晶粒充分生长且晶粒杂乱无章的多元正极材料；
(3)将本发明提供的多元正极材料用于正极极片，当含有特定掺杂元素M时，掺杂元素M会分布于界面处，呈无定型状态，受挤压时，特定掺杂元素M可以起到润滑剂的作用，使二次颗粒不易破裂，只是发生相对位移，进而减缓极片断片发生，同时也保证材料的电性能不受影响容易承受较高的辊压压力，不易产生极片断片。
附图说明
图1是制备例1制得的前驱体S1剖面的SEM图；
图2是对比制备例1制得的前驱体DS1剖面的SEM图；
图3是实施例3制得的多元正极材料P3剖面的SEM图；
图4是对比例3制得的多元正极材料DP3剖面的SEM图；
图5是实施例4制得的多元正极材料P4的离子研磨剖面图；
图6是对比例1制得的多元正极材料DP1的离子研磨剖面图；
图7是由实施例1的多元正极材料P1制得的正极极片单折剖面SEM图；
图8是由实施例1的多元正极材料P1制得的正极极片双折剖面SEM图；
图9是由对比例1的多元正极材料DP1制得的正极极片单折剖面SEM图；
图10是由对比例1的多元正极材料DP1制得的正极极片双折剖面SEM图。
发明详细描述
在本文中所披露的范围的端点和任何值都不限于该精确的范围或值，这些范围或值应当理解为包含接近这些范围或值的值。对于数值范围来说，各个范围的端点值之间、各个范围的端点值和单独的点值之间，以及单独的点值之间可以彼此组合而得到一个或多个新的数值范围，这些数值范围应被视为在本文中具体公开。
本发明第一方面提供一种多元正极材料，所述多元正极材料为一次颗粒团聚而成的二次颗粒，其中，具有5条以上晶界数量的一次颗粒的剖面总面积与二次颗粒的剖面面积比值≥3:4；所述二次颗粒的剖面上的孔隙率≤2％；
其中，晶界是指结构相同而取向不同的一次颗粒之间的界面在所述二次颗粒的剖面上的轮廓线，且所述晶界的长度≥0.1μm。
在本发明中，没有特殊情况说明下，所述二次颗粒的剖面是指经离子研磨的剖面，优选是指经离子研磨且截面直径等于所述二次颗粒的DB50的颗粒的剖面。其中，当晶界满足上述条件时，所述二次颗粒的剖面上一次颗粒间的晶界径向无序排列，二次颗粒的剖面中一次颗粒的排布形式为犬齿交错，在极限压实下，二次颗粒会发生蠕变而不容易破碎，将所述多元正极材料用于正极极片时，可减少极片的断裂。
在本发明的一些实施方式中，优选地，所述晶界的长度≤1.5μm的晶界数量占晶界总数量的70％以上；进一步优选地，所述晶界的长度≤1.2μm的晶界数量占晶界总数量的70％以上；更优选地，所述晶界的长度选自0.2-1.2μm的晶界数量占晶界总数量的80％以上。
在本发明中，所述晶界的长度≤1.5μm的晶界数量占晶界总数量的70％以上是指结构相同而取向不同的一次颗粒之间的界面在所述二次颗粒的剖面上的轮廓线，其中，0.1μm≤轮廓线的长度≤1.5μm的数量，与轮廓线的长度≥0.1μm的总数量占比在70％以上；即，0.1μm≤晶界的长度≤1.5μm的数量，与晶界的长度≥0.1μm的总数量占比在70％以上。
同理，所述晶界的长度≤1.2μm的晶界数量占晶界总数量的70％以上是指0.1μm≤晶界的长度≤ 1.2μm的数量，与晶界的长度≥0.1μm的总数量占比在70％以上；所述晶界的长度选自0.2-1.2μm的晶界数量占晶界总数量的80％以上是指0.2μm≤晶界的长度≤1.2μm的数量，与晶界的长度≥0.1μm的总数量占比在80％以上。
在本发明的一些实施方式中，优选地，所述二次颗粒的晶界密度≥1.8，例如，1.8、2、2.2、2.5、2.8、3，以及任意两个数值组成的范围中的任意值，优选为2-3；其中，所述晶界密度＝所述二次颗粒的剖面上一次颗粒间的界面数/所述二次颗粒的剖面上一次颗粒的数量。
在本发明中，当所述晶界的长度和占比，以及晶界密度满足上述保护范围，尤其是优选保护范围时，所述多元正极材料中的一次颗粒呈现明显的无序分布，同时不会引起由充放电引起的正极活性物质颗粒的开裂，保持足够的循环特性。
在本发明的一些实施方式中，优选地，所述一次颗粒的平均长径比≤1.5，例如，0.8、0.9、1、1.02、1.05、1.08、1.1、1.3、1.5，以及任意两个数值组成的范围中的任意值，优选选自1-1.5，更优选选自1-1.1。当满足上述条件时，一次颗粒具有较小的平均长径比，便于相互间堆积，增加二次颗粒间的一次颗粒的堆积致密。
在本发明中，长径比与长宽比的概念相同，即经过颗粒内部的最长径，和与其相垂直的最长径之比，此参数用来表述颗粒形貌，以判断其形状是否接近于正形体。本发明所述平均长径比是指在二次颗粒的剖面上所有一次颗粒的长径比的平均值。
在本发明的一些实施方式中，进一步优选地，所述一次颗粒的长径比选自0.9-1.1的数量占比≥70％。当满足上述条件时，一次颗粒在团聚为二次颗粒时不易被引导为径向排列，在受压时易于改变堆积形式，使二次颗粒发生形变而不会破碎。
在本发明的一些实施方式中，优选地，所述二次颗粒的平均粒径DB50与所述一次颗粒的平均粒径DA50满足：10≤DB50/DA50≤40，例如，10、15、20、25、30、35、40，以及任意两个数值组成的范围中的任意值。在本发明中，当DA50与DB50满足上式时，二次颗粒由适量的一次颗粒组成，且彼此之间结合紧密，便于增加二次颗粒的强度；同时又具有较好的电性能。
在本发明中，所述二次颗粒为球形或近球形。优选地，所述二次颗粒的平均粒径DB50选自6-14μm，例如，6μm、8μm、10μm、12μm、14μm，以及任意两个数值组成的范围中的任意值，优选为8-12μm。
在本发明的一些实施方式中，优选地，所述一次颗粒的平均粒径DA50选自0.1-1.5μm，例如，0.1μm、0.2μm、0.5μm、0.8μm、1μm、1.2μm、1.5μm，以及任意两个数值组成的范围中的任意值，优选为0.2-1.2μm。当一次颗粒的平均粒径DA50满足上述范围时，多元正极材料中的一次颗粒具有较小的平均粒径和致密的堆积，这有利于形成稳定的结构，缓解电池充放电过程中的内部应力，减缓微裂纹的生成。
在本发明的一些实施方式中，优选地，所述多元正极材料具有式I所示的组成：Lia(NixCoyMnzMb)GcO2(I)；
其中，1≤a≤1.2，0≤b≤0.05，0≤c≤0.05，0.3≤x＜1，0＜y＜0.5，0＜z＜0.5，且x+y+z+b＝1；M和G各自独立地选自Mg、Ti、W、V、Ta、Zr、La、Ce、Er、Sr、Si、B、Al、Co和Y中的至少一种元素。
在本发明的一些实施方式中，进一步优选地，式I中，1≤a≤1.1，0＜b≤0.02，0＜c≤0.02，0.4≤x≤0.95，0.01≤y≤0.2，0.01≤z≤0.3；M选自Mg、Ti、W、V、Ta、Zr、La、Ce、Er、Sr、Si、Al、Co和Y中的至少一种元素；G选自Mg、Ti、W、Zr、Ce、Er、Si、B和Al中的至少一种元素。
在本发明的一些实施方式中，更优选地，式I中，0.0001≤b≤0.02，0.0001≤c≤0.02，M选自W、Zr、La和Y中的至少一种元素；G选自B、Ti、W、Si和Al中的至少一种元素。
在本发明的一些实施方式中，优选地，在XRD衍射图谱中，所述多元正极材料在(104)晶面的特征衍射峰的半峰宽FWHM(104)选自0.2-0.24，例如，0.2、0.22、0.23、0.24，以及任意两个数值组成的范围中的任意值，优选为0.22-0.24。
在本发明中，一方面，当(104)晶面的特征衍射峰的半峰宽FWHM(104)满足上述条件时，多元正极材料具有更好的结晶性能和循环性能；同时，晶粒可以得到充分的发育，使一次颗粒内具有较多的晶界，基于晶界处的晶体排列是非常不规则的，晶面犬牙交错，互相咬合，因此，当在常规压力下可使多元正极材料具有稳定的结构，同时因为晶界处的强度相对低，因此，二次颗粒在高压下容易发生蠕变，从而 减少二次球对铝箔极片的挤压，减少极片的断片。另一方面，当(104)晶面的特征衍射峰的半峰宽FWHM(104)满足上述条件时，二次颗粒之间的黏连少，可以增加多元正极材料的压实密度，进一步降低正极极片的断裂发生。
在本发明的一些实施方式中，优选地，所述多元正极材料具有单一的α-NaFeO2型层状结构。
在本发明的一些实施方式中，优选地，所述多元正极材料的粉末压实密度≥3.4g/cm3。本发明提供的多元正极材料具有较高的粉末压实密度，从而可以在一定程度上增加锂电池的能量密度。
在本发明的一些实施方式中，优选地，所述多元正极材料的总残碱含量满足：m(Li2CO3)+m(LiOH)＜6000ppm；进一步优选地，所述多元正极材料的总残碱含量还满足：m(Li2CO3)＜m(LiOH)，且m(Li2CO3)与m(LiOH)均低于3000ppm。
在本发明中，当所述多元正极材料的总残碱含量满足上述条件时，所获得的多元正极材料的晶格结构稳定且完整，能够显著增强正极材料的结构稳定性、容量倍率性能及安全性能，从而进一步提升多元正极材料循环稳定性能；同时，残碱量的降低也可以减少颗粒之间的黏连，增加材料的压实密度，进一步的降低极片的断裂发生。
本发明第二方面提供一种多元正极材料的制备方法，所述制备方法包括以下步骤：
(1)将具有式II所示组成的前驱体和锂源进行混合，得到混合物I，所述前驱体由一次晶粒团聚而成，且所述前驱体的剖面上的一次晶粒非径向分布；
(2)在含氧气氛中，将所述混合物I进行一次烧结，得到过程品；所述一次烧结的条件包括：以V1的升温速率升温至T1，恒温t1；再以V2的升温速率升温至T2，恒温t2；
(3)将所述过程品和可选的含G的包覆剂进行混合，得到混合物II；
(4)在含氧气氛中，将所述过程品或混合物II进行二次烧结，得到多元正极材料；
其中，(NiαCoβMnγMδ)(OH)2(II)，0.3≤α＜1，0＜β＜0.5，0＜γ＜0.5，0≤δ≤0.05，且α+β+γ+δ＝1；M和G各自独立地选自Mg、Ti、W、V、Ta、Zr、La、Ce、Er、Sr、Si、B、Al、Co和Y中的至少一种元素。
在本发明的一些实施方式中，优选地，式II中，0.4≤α≤0.95，0.01≤β≤0.2，0.01≤γ≤0.3，0＜δ≤0.02，且α+β+γ+δ＝1，M选自Mg、Ti、W、V、Ta、Zr、La、Ce、Er、Sr、Si、Al、Co和Y中的至少一种元素；进一步优选地，式II中，0.0001≤δ≤0.02，M选自W、Zr、La和Y中的至少一种元素。
本发明的发明人研究发现，当在正极材料中添加特定掺杂元素M时，有助于一次颗粒的无序分布，而且掺杂元素M会分布于界面处，呈无定型状态，受挤压时，掺杂元素M可以起到润滑剂的作用，使二次颗粒不易破裂，只是发生相对位移，这样在减缓极片断片发生的同时，也保证材料的电性能不受影响。而相比在配混料时加入含M元素的掺杂剂，在制备前驱体湿法共沉淀合成过程中加入含M元素的掺杂剂，一方面可稳定材料内部结构，提升三元材料特别是高镍三元材料的循环寿命，另一方面，掺杂元素M可以更加均匀的分布在正极材料中，利于一次颗粒的无序分布。
同时，本发明还优化烧结工艺，具体将锂源和前驱体采用双阶段保温的一次烧结工艺，使得锂源缓慢充分地与前驱体反应，得到的过程品再进行包覆，最终得到晶粒充分生长且晶粒杂乱无章的多元正极材料。
在本发明的一些实施方式中，优选地，所述前驱体的D50选自8-14μm；所述前驱体的比表面积选自3-7m2/g。
在本发明的一些实施方式中，优选地，所述前驱体和锂源的用量满足n(Ni+Co+Mn+M):n(Li)＝1：1-1.2，优选满足n(Ni+Co+Mn+M):n(Li)＝1：1-1.1。
在本发明的一些实施方式中，优选地，所述前驱体由以下方法制得：在惰性气氛中，将含有镍源、钴源、锰源和可选的含M的掺杂剂的混合金属盐溶液，与沉淀剂、络合剂和分散剂接触并进行共沉淀反应，得到的共沉淀反应产物依次进行洗涤、干燥，得到所述前驱体。
在本发明中，没有特殊情况说明下，惰性气氛包括并不局限于氮气气氛、氩气气氛等。
在本发明的一些实施方式中，优选地，所述共沉淀反应的条件包括：温度选自40-80℃，pH值为10-13，搅拌转速选自200-550rpm。更为优选地，所述共沉淀反应的条件包括：温度选自50-70℃，pH值为11-12.5，搅拌转速选自350-500rpm。
在本发明中，通过控制所述共沉淀反应的条件，尤其是通过添加掺杂元素M，将pH值和搅拌转速在指定范围内，从而可以保持晶种无序生长，使一次晶粒非径向无序分布，得到内部晶粒无序排列的前驱体。
在本发明的一些实施方式中，优选地，所述混合金属盐溶液中，所述镍源、钴源、锰源和掺杂剂的用量满足n(Ni):n(Co):n(Mn):n(M)，0.3≤n(Ni)＜1，0＜n(Co)＜0.5，0＜n(Mn)＜0.5，0≤n(M)≤0.05；进一步优选地，0.4≤n(Ni)≤0.95，0.01≤n(Co)≤0.2，0.01≤n(Mn)≤0.3，0＜n(M)≤0.02；更优选地，0.0001≤n(M)≤0.02。
在本发明的一些实施方式中，优选地，以金属元素计，所述混合金属盐溶液的浓度为1-3mol/L。
在本发明的一些实施方式中，优选地，所述镍源、钴源、锰源和掺杂剂各自独立地选自硫酸盐、氯酸盐、硝酸盐和醋酸盐中的至少一种。在本发明中，所述镍源选自硫酸镍、氯酸镍、硝酸镍和醋酸镍中的至少一种；所述钴源选自硫酸钴、氯酸钴、硝酸钴和醋酸钴中的至少一种；所述锰源选自硫酸锰、氯酸锰、硝酸锰和醋酸锰中的至少一种。
在本发明的一些实施方式中，优选地，所述掺杂剂选自含M的可溶性盐，优选选自含M的硫酸盐、氯化物、氢氧化物和碳酸盐中的至少一种。
在本发明的一种具体实施方式中，所述掺杂剂选自含Mg、Ti、W、V、Ta、Zr、La、Ce、Er、Sr、Si、B、Al、Co和Y的硫酸盐、氯化物、氢氧化物和碳酸盐中的至少一种，优选选自含Mg、Ti、W、V、Ta、Zr、La、Ce、Er、Sr、Si、Al、Co和Y的硫酸盐、氯化物、氢氧化物和碳酸盐中的至少一种，更优选选自含W、Zr、La和Y的硫酸盐、氯化物、氢氧化物和碳酸盐中的至少一种。
在本发明的一种具体实施方式中，所述沉淀剂选自NaOH和/或KOH；所述络合剂选自氨水、乙二胺四乙酸二钠、硝酸铵、氯化铵和硫酸铵中的至少一种；所述分散剂选自聚乙二醇(PEG)、聚乙烯醇(PVA)和聚甘油中的至少一种。
在本发明的一种具体实施方式中，所述沉淀剂、络合剂和分散剂各自独立地以水溶液形式存在；进一步优选地，沉淀剂溶液的浓度为2-15mol/L；络合剂溶液的浓度为1-15mol/L；分散剂溶液的浓度为1-200g/L。
在本发明中，所述洗涤旨在除去共沉淀反应产物表面残留的物质；所述干燥旨在除去共沉淀反应产物表面残留的水分等，优选地，所述干燥的温度为105-130℃。
在本发明的一些实施方式中，优选地，步骤(2)中，所述一次烧结的条件包括：升温速率V1选自1-6℃/min，优选选自1-3℃/min，更优选选自1-2℃/min；T1选自400-760℃，优选选自500-750℃；保温时间t1选自2-6h，优选选自3-5h；升温速率V2选自1-6℃/min，优选选自1-3℃/min；T2选自710-950℃，优选选自710-920℃；保温时间t2选自5-13h，优选选自6-12h。
在本发明中，采用两段平台烧结工艺制备多元正极材料，使得多元正极材料具有残碱低、内部结构无序、结构稳定等优点。即，步骤(2)中，通过设置合适的升温速率(即，V1和V2)、保温温度(即，T1和T2)及保温时间(t1和t2)，物料经过两个平台的烧结处理，使得锂源与前驱体充分反应，一次颗粒长大后沿各个晶向生长，得到内结构无序取向的耐压团聚型正极材料。
在本发明的一些优选实施方式中，优选地，以金属元素计，当所述前驱体中镍含量≥60mol％时，所述含氧气氛中氧气浓度≥92体积％。这样设置，充足的氧浓度保证镍含量较高情况下减少镍离子和锂离子的混排程度，从而降低材料的残碱量。
在本发明的一些实施方式中，优选地，将所述一次烧结的产物冷却至室温，再进行破碎，得到所述过程品。在本发明中，所述破碎包括并不局限于颚破、对辊、胶体磨、机械磨和气流磨中的至少一种。
在本发明的一些实施方式中，优选地，步骤(3)中，所述过程品和包覆剂的用量满足n(Ni+Co+Mn+M):n(G)＝1：n(G)，其中，0≤n(G)≤0.05，优选0＜n(G)≤0.02，更优选0.0001≤n(G)≤0.02。
在本发明的一些实施方式中，优选地，所述包覆剂选自含有G的氧化物、氢氧化物和碳酸盐中的至少一种，优选选自含有Mg、Ti、W、Zr、Ce、Er、Si、B和Al的氧化物、氢氧化物和碳酸盐中的至少一种，更优选选自含有B、Ti、W、Si和Al的氧化物、氢氧化物和碳酸盐中的至少一种。
在本发明的一些实施方式中，优选地，步骤(4)中，所述二次烧结的条件包括：温度T3选自300-800℃，优选选自400-700℃；时间t3选自4-10h，优选选自5-8h。
在本发明中，按照上述制备方法制得的所述多元正极材料具有式I所示的组成：Lia(NixCoyMnzMb)GcO2  (I)；
其中，1≤a≤1.2，0≤b≤0.05，0≤c≤0.05，0.3≤x＜1，0＜y＜0.5，0＜z＜0.5，且x+y+z+b＝1；M和G各自独立地选自Mg、Ti、W、V、Ta、Zr、La、Ce、Er、Sr、Si、B、Al、Co和Y中的至少一种元素。
在本发明的一些实施方式中，优选地，式I中，1≤a≤1.1，0＜b≤0.02，0＜c≤0.02，0.4≤x≤0.95，0.01≤y≤0.2，0.01≤z≤0.3；M选自Mg、Ti、W、V、Ta、Zr、La、Ce、Er、Sr、Si、Al、Co和Y中的至少一种元素；G选自Mg、Ti、W、Zr、Ce、Er、Si、B和Al中的至少一种元素。
在本发明的一些实施方式中，进一步优选地，式I中，0.0001≤b≤0.02，0.0001≤c≤0.02，M选自W、Zr、La和Y中的至少一种元素；G选自B、Ti、W、Si和Al中的至少一种元素。
本发明第三方面提供一种正极极片，所述正极极片的活性物质层含有第一方面提供的多元正极材料，或者，第二方面提供的制备方法制得的多元正极材料。
在本发明中，没有特殊情况说明下，所述正极极片包括正极集流体和负载在正极集流体上的活性物质层。
在本发明的一些实施方式中，所述活性物质层不仅含有所述多元正极材料，还含有导电剂、粘结剂和分散剂。
在本发明的一种具体实施方式中，所述正极极片由以下方法制得：将上述多元正极材料、SuperP、CNT和聚偏二氟乙烯(PVDF)按照97：1：0.8：1.2的质量比与适量的N-甲基吡咯烷酮(NMP)充分混合形成均匀的浆料，将浆料涂覆在铝箔上，经过烘干工序后，使用模切机冲裁为112mm×40mm的极片，其中，所述多元正极材料负载量为380±2g/m2。
本发明判定极片断片的方法是：将制备好的正极极片均经过125℃真空烘箱8h以上烘烤；然后测试正极极片进行两次辊压达到相应压实密度；再用固定重量平板压折极片；最后采用LED点光源进行透光观察。同时记录辊压前后正极极片厚度以及正极极片长度，计算正极极片辊压前后厚度压缩比和延伸率。将正极极片分别压至不同的压实密度，分别观察并统计不同压实密度下极片单折、双折、三折、四折时的透光情况。根据是否透光确定极片的断片结果。
本发明除了上述方法判断极片断片情况外，还可以将上述多元正极材料按相同的配方，制作成电池极片，再对极片施加一定压力后在SEM观察电池极片的剖面。根据剖面状况判断极片的断片情况。
在本发明的一些实施方式中，优选地，所述正极极片的极限压实密度选自3.2-3.8g/cm3，例如，3.2g/cm3、3.3g/cm3、3.5g/cm3、3.6g/cm3、3.7g/cm3、3.8g/cm3，以及任意两个数值组成的范围中的任意值，优选为3.3-3.7g/cm3。
在本发明的一些实施方式中，优选地，所述正极极片的厚度压缩比选自25-45％，例如，25％、30％、32％、35％、38％、40％、45％，以及任意两个数值组成的范围中的任意值，优选为30-40％。
在本发明的一些实施方式中，优选地，所述正极极片的延伸率选自1.2-3％，例如，1.2％、1.5％、1.8％、2％、2.2％、2.5％、3％，以及任意两个数值组成的范围中的任意值，优选为1.5-2.5％。
在本发明中，由含有上述多元正极材料制得的正极极片，能承受较大的辊压压力，不容易出现断片现象。
本发明第四方面提供一种锂离子电池，所述锂离子电池含有第三方面制得的正极极片。
以下将通过实施例对本发明进行详细描述。
(1)前驱体和多元正极材料的组成均采用ICP方法测得；所用仪器为PE Optima 7000DV，测试条件为0.1g样品完全溶解于3mL HNO3+9mL HCl的混合酸溶液中，稀释至250mL进行测试；
(2)二次颗粒的剖面获取：在本发明中，二次颗粒的剖面获取包括两种，即，其一为如图1-4所述的剖面的SEM图，其剖面的获取方式为：将待测试材料取少许放置于载玻片上，再用另一片载玻片挤压材料，选取从二次颗粒的球心挤压开获取的截面，将该截面在扫描电镜下观测获得本发明所属的二次颗粒的剖面；该方式为便于立体观测；
其二为如图5-6所述的离子研磨剖面图，该方式获取的剖面便于清晰界定本文所提到的晶界，其剖 面的获取方式如下：
S1、制样：a、剪取2×4cm2左右的铝箔和1.5×1.5cm2规格的硅片备用，将铝箔对折，两边压平，中部预留空隙用于放置样品；b、向正极材料粉末内加入导电胶混合均匀，然后将混合物料挑放至前述铝箔的预留空隙中，接着将铝箔放置于平台上，用平板先将样品的周边压实，再轻轻按压中部的样品，得预处理样品，标记预处理样品中接触所述平台的一面为正面，按压面为背面；c、将预处理样品在100℃的温度下干燥60min，干燥完成后取出预处理样品，切掉预处理样品上没有样品的多余部分铝箔，然后在样品充足的部位处从背面垂直切开样品；d、取上述硅片，用胶水将切好的预处理样品的背面粘在硅片上，如此样品中较为平整的正面可以紧贴挡板并正向面对离子束，在粘贴时，应保证铝箔的切面突出于硅片的边缘或与之平齐，例如突出60μm以上，得待测样品。
S2、测定：在样品台侧边粘上导电胶带，将待测样品固定在样品台上，其中待测样品的上边缘应高出样品台1-3mm左右。然后对样品台上的待测样品进行离子研磨处理，研磨完成后，再在待测样品中硅片和样品的间隙内涂抹液体导电胶以增加导电性。最后，将处理后的样品台放入电镜专用的样品台支架上，用内六方固定紧样品台位置，通过电镜观察获取截面样品，其中本发明中采用的离子研磨仪为日立离子研磨仪IM4000PLUS，离子研磨条件参阅表1：
表1
其中，基于上述方法获取的离子研磨剖面图上，需要根据本发明限定的二次颗粒的平均粒径，筛选出截面直径为8-12μm的颗粒进行观察，因为，在该直径范围内的截面经过或靠近球心，更加具有代表性，其中在进行离子研磨时，应首先将离子研磨仪的STAGE CONT到C4模式，调节工作时间为40min，加速电压为6kV，放电电压调为最大，气流调整为0.09cm3/min。电镜的测试条件为采用低电压背散模式，电压＝1kV，WD＝2.5mm，放大倍数为10k。
(3)晶界的测定标准：在本发明中，晶界判定依据离子研磨剖面图进行判定，晶界的定义为在二次颗粒的剖面上，结构相同而取向不同的一次颗粒之间的界面，且所述界面的长度≥0.1μm；
(4)形貌测试：通过日本日立HITACHI公司S-4800型号的扫描电子显微镜测试得到；
(5)粒度DA50、DB50：通过Malvern公司的Mastersize2000型号的激光粒度仪测试得到；
(6)压实密度：通过百特公司BT-30型号的振实密度测试仪测试得到。
制备例1-5和对比制备例1-4制得的前驱体的组成和物性参数均列于表2。
制备例1
配制2mol/L的混合金属盐溶液，以金属元素计，上述混合金属盐溶液中硫酸镍、硫酸钴、硫酸锰和硫酸钇的摩尔比分别为0.5：0.2：0.2985：0.0015；配制3mol/L的NaOH溶液，配制3mol/L的氨水，配制10g/L的PVA分散剂水溶液；
在氮气保护氛围下，将上述几种溶液以并流的方式通入反应釜中进行共沉淀反应，保持反应温度为50℃，反应pH值为11.2，搅拌转速为350rpm，经洗涤、120℃烘干、过筛，得到前驱体S1。
其中，上述前驱体S1剖面的SEM如图1所示，由图1可知，上述前驱体S1由一次晶粒团聚而成，且上述前驱体S1剖面上一次晶粒为无序状分布。
制备例2
按照制备例1的方法，不同的是，
将掺杂剂的种类替换为氯化锆；
配制2mol/L的混合金属盐溶液，以金属元素计，上述混合金属盐溶液中硫酸镍、硫酸钴、硫酸锰和 氯化锆的摩尔比分别为0.6：0.2：0.1985：0.0015；
搅拌转速改为450rpm，分散剂的种类替换为10g/L的PEG1000分散剂水溶液；
其余条件相同，得到前驱体S2。
其中，上述前驱体S2剖面的SEM图与图1类似。
制备例3
按照制备例1的方法，不同的是，
将掺杂剂的种类替换为硝酸镧；
配制2mol/L的混合金属盐溶液，以金属元素计，上述混合金属盐溶液中硫酸镍、硫酸钴、硫酸锰和硝酸镧的摩尔比分别为0.81：0.09：0.0985：0.0015；
氨水的浓度替换为4mol/L；
共沉淀反应的条件替换为反应温度为55℃，反应pH值为11.7，搅拌转速为450rpm；
其余条件相同，得到前驱体S3。
其中，上述前驱体S3剖面的SEM图与图1类似。
制备例4
按照制备例1的方法，不同的是，
将掺杂剂的种类替换为钨酸钠和硫酸钇；
配制2mol/L的混合金属盐溶液，以金属元素计，上述混合金属盐溶液中硫酸镍、硫酸钴、硫酸锰、钨酸钠和硫酸钇的摩尔比分别为0.95：0.02：0.0275：0.001：0.0015；
NaOH的浓度替换为4mol/L；
分散剂采用10g/L的PEG1000分散剂水溶液；
共沉淀反应的反应pH值替换为12.1，搅拌转速替换为400rpm；
其余条件相同，得到前驱体S4。
其中，上述前驱体S4剖面的SEM图与图1类似。
制备例5
按照制备例4的方法，不同的是，不加入掺杂剂(钨酸钠和硫酸钇)，
即，配制2mol/L的混合金属盐溶液，以金属元素计，上述混合金属盐溶液中硫酸镍、硫酸钴和硫酸锰的摩尔比分别为0.95:0.02:0.03；
其余条件相同，得到前驱体S5；
其中，上述前驱体S5剖面的SEM图与图1类似。
对比制备例1
按照制备例1的方法，不同的是，
不加入掺杂剂硫酸钇，即，配制2mol/L的混合金属盐溶液，以金属元素计，上述混合金属盐溶液中硫酸镍、硫酸钴、硫酸锰的摩尔比为50:20:30；
将共沉淀反应的条件替换为反应温度为60℃，反应pH值为11.7，搅拌转速为800rpm；
其余条件相同，得到前驱体S1。
其中，上述前驱体DS1剖面的SEM图如图2所示，由图2可知，上述前驱体DS1由一次晶粒团聚而成，且上述前驱体DS1剖面上一次晶粒呈径向分布。
对比制备例2
按照制备例2的方法，不同的是，
不加入掺杂剂氯化锆；即，配制2mol/L的混合金属盐溶液，以金属元素计，上述混合金属盐溶液中硫酸镍、硫酸钴、硫酸锰的摩尔比为60:20:20；
NaOH溶液的浓度为2mol/L，氨水的浓度为2mol/L；
将共沉淀反应的条件替换为反应温度为55℃，反应pH值为13.2，搅拌转速为450rpm；
其余条件相同，得到前驱体DS2。
其中，上述前驱体DS2剖面的SEM图与图2类似。
对比制备例3
按照制备例3的方法，不同的是，
不加入掺杂剂硝酸镧；即，配制2mol/L的混合金属盐溶液，以金属元素计，上述混合金属盐溶液中硫酸镍、硫酸钴、硫酸锰的摩尔比为81:9:10；
共沉淀反应的条件替换反应温度为58℃，反应pH值为13.2，搅拌转速为800rpm；
其余条件相同，得到前驱体DS3。
其中，上述前驱体DS3剖面的SEM图与图2类似。
对比制备例4
按照制备例4的方法，不同的是，
不加入掺杂剂钨酸钠和硫酸钇；即，配制2mol/L的混合金属盐溶液，以金属元素计，上述混合金属盐溶液中硫酸镍、硫酸钴、硫酸锰的摩尔比为95:2:3；
分散剂为10g/L的聚甘油分散剂水溶液；
共沉淀反应的条件替换反应温度为60℃，反应pH值为11.7，搅拌转速为600rpm；
其余条件相同，得到前驱体DS4。
其中，上述前驱体DS4剖面的SEM图与图2类似。
表2
续表2
注：*-前驱体剖面上一次晶粒分布。
续表2
通过表2数据可知，相比对比制备例1-4，制备例1-5通过调控共沉淀反应的条件满足：温度选自40-80℃，pH值为10-13，搅拌转速选自200-550rpm，尤其结合掺杂元素M的种类，使得满足式II的前驱体由一次晶粒团聚而成，且前驱体的剖面上的一次晶粒非径向分布。
实施例1-5和对比例1-8的工艺参数均列于表3，且制得的多元正极材料的组成和物性参数均列于表4。
实施例1
(1)将制备例1得到的前驱体S1和碳酸锂进行混合，得到混合物I；其中，上述前驱体S1和碳酸锂的用量满足n(Ni+Co+Mn+Y):n(Li)＝1:1.05；
(2)在空气气氛中，将上述混合物I进行一次烧结，以V1＝5℃/min的升温速率升温至T1＝730℃，恒温t1＝3h；再以V2＝5℃/min的升温速率升温至T2＝920℃，恒温t2＝9h，自然降温至室温，用破碎设备破碎后过筛，得到内部结构无序的过程品；
(3)将上述过程品与MgO进行混合，得到均匀包覆的混合物II，上述过程品和MgO的用量满足n(Ni+Co+Mn+Y):n(Mg)＝1:0.0012；
(4)在空气气氛中，将上述混合物II进行二次烧结(温度为700℃，时间为6h)，得到多元正极材料P1。
实施例2
按照实施例1的方法，不同的是，
步骤(1)中，前驱体采用制备例2制得的前驱体S2；上述前驱体S2和碳酸锂的用量满足n(Ni+Co+Mn+Zr):n(Li)＝1:1.06；
步骤(2)中，一次烧结的气氛为氧气气氛，氧含量≥92V％；
一次烧结的条件替换为以V1＝4℃/min的升温速率升温至T1＝710℃，恒温t1＝3h；再以V2＝4℃/min的升温速率升温至T2＝860℃，恒温t2＝10h；
步骤(3)中，包覆剂的种类替换为Al2O3，上述过程品和Al2O3的用量满足n(Ni+Co+Mn+Zr):n(Al)＝1:0.001；
其余条件相同，得到多元正极材料P2。
实施例3
按照实施例1的方法，不同的是，
步骤(1)中，前驱体采用制备例3制得的前驱体S3；上述前驱体S3和氢氧化锂的用量满足n(Ni+Co+Mn+La):n(Li)＝1:1.02；
步骤(2)中，一次烧结的气氛为氧气气氛，氧含量≥95V％；
一次烧结的条件替换为以V1＝2℃/min的升温速率升温至T1＝600℃，恒温t1＝4h；再以V2＝2℃/min的升温速率升温至T2＝785℃，恒温t2＝8h；
步骤(3)中，包覆剂的种类替换为CeO2，上述过程品和CeO2的用量满足n(Ni+Co+Mn+La):n(Ce)＝1:0.0008；
步骤(4)中，二次烧结的温度替换为500℃；
其余条件相同，得到多元正极材料P3。
其中，上述多元正极材料P3剖面的SEM图如图3所示，由图3可知，上述多元正极材料P3的内部颗粒杂乱无序，呈非径向生长。
实施例4
按照实施例1的方法，不同的是，
步骤(1)中，前驱体采用制备例4制得的前驱体S4；上述前驱体S4和氢氧化锂的用量满足n(Ni+Co+Mn+W+Y):n(Li)＝1:1.03；
步骤(2)中，一次烧结的气氛为氧气气氛，氧含量≥95V％；
一次烧结的条件替换为以V1＝2℃/min的升温速率升温至T1＝600℃，恒温t1＝4h；再以V2＝2℃/min的升温速率升温至T2＝725℃，恒温t2＝8h；
步骤(3)中，包覆剂的种类替换为B2O3，上述过程品和B2O3的用量满足n(Ni+Co+Mn+W+Y):n(B)＝1:0.001；
步骤(4)中，二次烧结的温度替换为350℃；
其余条件相同，得到多元正极材料P4。
其中，上述多元正极材料P4的离子研磨剖面图如图5所示，由图5可知，上述多元正极材料P4的内部颗粒杂乱无序，呈非径向生长。
实施例5
按照实施例4的方法，不同的是，
步骤(1)中，前驱体采用制备例5制得的前驱体S5；
掺杂剂采用氧化钨和氧化钇，其中，上述前驱体S5、氧化钨、氧化钇和氢氧化锂的用量满足：n(Ni):n(Co):n(Mn):n(W)n(Y):n(Li)＝0.95:0.02:0.0275:0.001:0.0015:1.03。
其余条件相同，得到多元正极材料P5。
对比例1
按照实施例1的方法，不同的是，
步骤(1)中，前驱体采用对比制备例1制得的前驱体DS1；
其余条件相同，得到多元正极材料DP1。
其中，上述多元正极材料DP1的离子研磨剖面图如图6所示，由图6可知，上述多元正极材料DP1的内部颗粒呈径向分布生长。
对比例2
按照实施例2的方法，不同的是，
步骤(1)中，前驱体采用对比制备例2制得的前驱体DS2；
其余条件相同，得到多元正极材料DP2。
对比例3
按照实施例3的方法，不同的是，
步骤(1)中，前驱体采用对比制备例3制得的前驱体DS3；
其余条件相同，得到多元正极材料DP3。
其中，上述多元正极材料DP3剖面的SEM图如图4所示，由图4可知，上述多元正极材料DP3的内部颗粒呈径向分布生长。
对比例4
按照实施例4的方法，不同的是，
步骤(1)中，前驱体采用对比制备例4制得的前驱体DS4；
其余条件相同，得到多元正极材料DP4。
对比例5
按照实施例1的方法，不同的是，
步骤(2)中，t1为0h；
其余条件相同，得到多元正极材料DP5。
对比例6
按照实施例2的方法，不同的是，
步骤(2)中，一次烧结的条件替换为：以V1＝7℃/min的升温速率升温至T1＝710℃，恒温t1＝3h；再以V2＝7℃/min的升温速率升温至T2＝860℃，恒温t2＝10h；
其余条件相同，得到多元正极材料DP6。
对比例7
按照实施例3的方法，不同的是，
步骤(2)中，一次烧结和二次烧结的气氛为氧含量为85V％的氧气气氛；
其余条件相同，得到多元正极材料DP7。
对比例8
按照实施例4的方法，不同的是，
步骤(2)中，一次烧结的条件替换为：以V1＝7℃/min的升温速率升温至T1＝600℃；再以V2＝7℃/min的升温速率升温至T2＝725℃，恒温t2＝7h；
其余条件相同，得到多元正极材料DP8。
表3

注：1-以金属元素计，锂源和前驱体的摩尔比；
2-以金属元素计，上述前驱体和掺杂剂的摩尔比；
3-以金属元素计，上述过程品和包覆剂的摩尔比。
续表3
续表3

表4
续表4

注：4-具有5条以上晶界数量的一次颗粒的剖面总面积与二次颗粒的剖面面积比值≥3:4，记为√；否则，记为×；5-二次颗粒的剖面上的孔隙率；6-二次颗粒的晶界密度＝二次颗粒的剖面上一次颗粒间的界面数/二次颗粒的剖面上一次颗粒的数量；7-晶界的长度≤1.5μm的晶界数量占晶界总数量的占比；8-一次颗粒的长径比选自0.9-1.1的数量占比。
续表4
由表2-4数据可知，相比对比例1-8，实施例1-5采用本发明提供的制备方法，制得的多元正极材料具有内部颗粒杂乱无序非径向生长、压实密度高，极片不易产生断片的优点；实施例1-4分别采用非放射状的掺杂型前驱体，通过双平台保温工艺制备出的材料粉末压实明显高于用径向分布前驱体相同工艺处理的对比例1-8的正极材料。在前驱体阶段不掺杂元素M而在制备正极材料阶段添加掺杂元素M的实施例5材料的分布压实比在前驱体阶段掺杂元素M制备出的实施例4材料略低。
另外，过高的升温速率V1和V2(对比例6)、Ni含量高而一次烧结氧浓度不足(对比例7)和单平台的一次烧结工艺(对比例5、对比例8)所制备的材料，碱量明显偏高，相应的压实也较低，在极片压实时更容易产生断片现象。
测试例1
将上述实施例和对比例的多元正极材料制得的正极极片进行极限压实和断片测试，测试结果均列于表5。
正极极片的具体制备过程：分别将上述多元正极材料、SP、CNT和聚偏二氟乙烯(PVDF)按照97:1:0.8:1.2的质量比与适量的N-甲基吡咯烷酮(NMP)充分混合形成均匀的浆料，将浆料涂覆在铝箔上，经过烘干工序后，使用模切机冲裁为112mm×40mm的极片，其中多元正极材料负载量为380±2g/m2。
判定极片断片的方法：将制备好的正极极片均经过125℃真空烘箱8h以上烘烤；然后测试正极极片 进行两次辊压达到相应压实密度；再用固定重量平板压折极片；最后采用LED点光源进行透光观察。同时记录辊压前后正极极片厚度以及正极极片长度，计算正极极片辊压前后厚度压缩比和延伸率。将正极极片分别压至不同的压实密度，分别观察并统计不同压实密度下极片单折、双折、三折、四折时的透光情况。根据是否透光确定正极极片的断片结果。
表5


续表5


注：～表示该条件下透光后就不在进行测试。
由表5数据可知，由实施例1的多元正极材料P1制得的正极极片进行极限压制，单折和双折不透光时对应的极限压实密度分别为3.64g/cm3、3.57g/cm3(以实施例1为例，初次单折不透光时对应的正极极片A2对应的极限压实密度，初次双折不透光时对应的正极极片A4对应的极限压实密度)；由实施例2的多元正极材料P2制得的正极极片进行极限压制，单折和双折不透光时对应的极限压实密度分别为3.66g/cm3、3.62g/cm3；由实施例3的多元正极材料P3制得的正极极片进行极限压制，单折和双折不透光时对应的极限压实密度分别为3.77g/cm3、3.59g/cm3；由实施例4的多元正极材料P4制得的正极极片进行极限压制，单折和双折不透光时对应的极限压实密度分别为3.71g/cm3、3.57g/cm3。这些材料极片压实密度均高于对应的对比例结果。
由实施例1的多元正极材料P1制得的正极极片进行极限压实后横截面的SEM图，如图7(单折)-图8(双折)所示，较高的极限压实下，二次颗粒易软化，相当于卸掉一部分辊压压力，从而减少二次球对铝箔极片的挤压，减少极片的断片，同时电池的电性仍可较好的满足使用要求；
由对比例1的多元正极材料DP1制得的正极极片进行极限压实后横截面的SEM图，如图9(单折)-图10(双折)所示，即使二次颗粒在受到较小的极限压实时，多元正极材料DP1内部结构的放射状分布导致其二次球不易变形，将作用于其上的压力直接传递到铝箔上，引起铝箔的断裂。
以上详细描述了本发明的优选实施方式，但是，本发明并不限于此。在本发明的技术构思范围内，可以对本发明的技术方案进行多种简单变型，包括各个技术特征以任何其它的合适方式进行组合，这些简单变型和组合同样应当视为本发明所公开的内容，均属于本发明的保护范围。

Claims (29)

  1. 一种多元正极材料，其特征在于，所述多元正极材料为一次颗粒团聚而成的二次颗粒，其中，具有5条以上晶界数量的一次颗粒的剖面总面积与二次颗粒的剖面面积比值≥3:4；所述二次颗粒的剖面上的孔隙率≤2％；
    其中，晶界是指结构相同而取向不同的一次颗粒之间的界面在所述二次颗粒的剖面上的轮廓线，且所述晶界的长度≥0.1μm。
  2. 根据权利要求1所述的多元正极材料，其中，所述晶界的长度≤1.5μm的晶界数量占晶界总数量的70％以上；
    优选地，所述晶界的长度≤1.2μm的晶界数量占晶界总数量的70％以上；
    进一步优选地，所述晶界的长度选自0.2-1.2μm的晶界数量占晶界总数量的80％以上。
  3. 根据权利要求1或2所述的多元正极材料，其中，所述二次颗粒的晶界密度≥1.8，优选选自2-3，其中，所述晶界密度＝所述二次颗粒的剖面上一次颗粒间的界面数/所述二次颗粒的剖面上一次颗粒的数量。
  4. 根据权利要求1-3任一项所述的多元正极材料，其中，所述一次颗粒的平均长径比≤1.5，优选选自1-1.5，更优选选自1-1.1；
    优选地，所述一次颗粒的长径比选自0.9-1.1的数量占比≥70％。
  5. 根据权利要求1-4中任意一项所述的多元正极材料，所述二次颗粒的平均粒径DB50与所述一次颗粒的平均粒径DA50满足：10≤DB50/DA50≤40；
    和/或，所述二次颗粒的平均粒径DB50选自6-14μm，优选为8-12μm；
    和/或，所述一次颗粒的平均粒径DA50选自0.1-1.5μm，优选为0.2-1.2μm。
  6. 根据权利要求1-5中任意一项所述的多元正极材料，其中，所述多元正极材料具有式I所示的组成：Lia(NixCoyMnzMb)GcO2   (I)；
    其中，1≤a≤1.2，0≤b≤0.05，0≤c≤0.05，0.3≤x＜1，0＜y＜0.5，0＜z＜0.5，且x+y+z+b＝1；M和G各自独立地选自Mg、Ti、W、V、Ta、Zr、La、Ce、Er、Sr、Si、B、Al、Co和Y中的至少一种元素；
    优选地，式I中，1≤a≤1.1，0＜b≤0.02，0＜c≤0.02，0.4≤x≤0.95，0.01≤y≤0.2，0.01≤z≤0.3；M选自Mg、Ti、W、V、Ta、Zr、La、Ce、Er、Sr、Si、Al、Co和Y中的至少一种元素；G选自Mg、Ti、W、Zr、Ce、Er、Si、B和Al中的至少一种元素；
    进一步优选地，式I中，0.0001≤b≤0.02，0.0001≤c≤0.02，M选自W、Zr、La和Y中的至少一种元素；G选自B、Ti、W、Si和Al中的至少一种元素。
  7. 根据权利要求1-6中任意一项所述的多元正极材料，其中，在XRD衍射图谱中，所述多元正极材料具有(104)晶面的特征衍射峰，且(104)晶面的特征衍射峰的半峰宽FWHM(104)选自0.2-0.24。
  8. 根据权利要求1-7中任意一项所述的多元正极材料，其中，所述多元正极材料具有单一的α-NaFeO2型层状结构。
  9. 根据权利要求1-8中任意一项所述的多元正极材料，其中，所述多元正极材料的粉末压实密度≥3.4g/cm3。
  10. 根据权利要求1-9中任意一项所述的多元正极材料，其中，所述多元正极材料的总残碱含量满足：m(Li2CO3)+m(LiOH)＜6000ppm；
    和/或，所述多元正极材料的总残碱含量还满足：m(Li2CO3)＜m(LiOH)，且m(Li2CO3)与m(LiOH)均低于3000ppm。
  11. 一种多元正极材料的制备方法，其特征在于，所述制备方法包括以下步骤：
    (1)将具有式II所示组成的前驱体和锂源进行混合，得到混合物I，所述前驱体由一次晶粒团聚而成，且所述前驱体的剖面上的一次晶粒非径向分布；
    (2)在含氧气氛中，将所述混合物I进行一次烧结，得到过程品；所述一次烧结的条件包括：以V1的升温速率升温至T1，恒温t1；再以V2的升温速率升温至T2，恒温t2；
    (3)将所述过程品和可选的含G的包覆剂进行混合，得到混合物II；
    (4)在含氧气氛中，将所述过程品或混合物II进行二次烧结，得到多元正极材料；
    其中，(NiαCoβMnγMδ)(OH)2   (II)，0.3≤α＜1，0＜β＜0.5，0＜γ＜0.5，0≤δ≤0.05，且α+β+γ+δ＝1；M和G各自独立地选自Mg、Ti、W、V、Ta、Zr、La、Ce、Er、Sr、Si、B、Al、Co和Y中的至少一种元素。
  12. 根据权利要求11所述的制备方法，其中，步骤(1)中，所述前驱体的D50选自8-14μm。
  13. 根据权利要求11或12所述的制备方法，其中，所述前驱体的比表面积选自3-7m2/g。
  14. 根据权利要求11-13任一项所述的制备方法，其中，所述前驱体和锂源的用量满足n(Ni+Co+Mn+M):n(Li)＝1：1-1.2，优选满足n(Ni+Co+Mn+M):n(Li)＝1：1-1.1。
  15. 根据权利要求11-14任一项所述的制备方法，其中，所述前驱体由以下方法制得：在惰性气氛中，将含有镍源、钴源、锰源和可选的含M的掺杂剂的混合金属盐溶液，与沉淀剂、络合剂和分散剂接触并进行共沉淀反应，得到的共沉淀反应产物依次进行洗涤、干燥，得到所述前驱体；
    优选地，所述共沉淀反应的条件包括：温度选自40-80℃，pH值为10-13，搅拌转速选自200-550rpm；
    进一步优选地，所述共沉淀反应的条件包括：温度选自50-70℃，pH值为11-12.5，搅拌转速选自350-500rpm。
  16. 根据权利要求15所述的制备方法，其中，所述混合金属盐溶液中，所述镍源、钴源、锰源和掺杂剂的用量满足n(Ni):n(Co):n(Mn):n(M)，0.3≤n(Ni)＜1，0＜n(Co)＜0.5，0＜n(Mn)＜0.5，0≤n(M)≤0.05；
    优选地，0.4≤n(Ni)≤0.95，0.01≤n(Co)≤0.2，0.01≤n(Mn)≤0.3，0＜n(M)≤0.02；
    进一步优选地，0.0001≤n(M)≤0.02。
  17. 根据权利要求11-16中任意一项所述的制备方法，其中，步骤(2)中，所述一次烧结的条件包括：
    升温速率V1选自1-6℃/min，优选选自1-3℃/min，更优选选自1-2℃/min；T1选自400-760℃，优选选自500-750℃；保温时间t1选自2-6h，优选选自3-5h；
    升温速率V2选自1-6℃/min，优选选自1-3℃/min；T2选自710-950℃，优选选自710-920℃；保温时间t2选自5-13h，优选选自6-12h。
  18. 根据权利要求11-17中任意一项所述的制备方法，其中，以金属元素计，当所述前驱体中镍含量≥60mol％时，所述含氧气氛中氧气浓度≥92体积％。
  19. 根据权利要求11-18中任意一项所述的制备方法，其中，将所述一次烧结的产物冷却至室温，再进行破碎，得到所述过程品。
  20. 根据权利要求11-19中任意一项所述的制备方法，其中，步骤(3)中，所述过程品和包覆剂的用量满足n(Ni+Co+Mn+M):n(G)＝1：n(G)，其中，0≤n(G)≤0.05，优选0＜n(G)≤0.02，更优选0.0001≤n(G)≤0.02。
  21. 根据权利要求11-20中任意一项所述的制备方法，其中，所述包覆剂选自含有G的氧化物、氢氧化物和碳酸盐中的至少一种；优选选自含有Mg、Ti、W、Zr、Ce、Er、Si、B和Al的氧化物、氢氧化物和碳酸盐中的至少一种，更优选选自含有B、Ti、W、Si和Al的氧化物、氢氧化物和碳酸盐中的至少一种。
  22. 根据权利要求11-21中任意一项所述的制备方法，其中，步骤(4)中，所述二次烧结的条件包括：温度T3选自300-800℃，优选选自400-700℃；时间t3选自4-10h，优选选自5-8h。
  23. 根据权利要求11-22中任意一项所述的制备方法，其中，步骤(4)中，所述多元正极材料具有式I所示的组成：
    Lia(NixCoyMnzMb)GcO2   (I)；
    其中，1≤a≤1.2，0≤b≤0.05，0≤c≤0.05，0.3≤x＜1，0＜y＜0.5，0＜z＜0.5，且x+y+z+b＝1；M和G各自独立地选自Mg、Ti、W、V、Ta、Zr、La、Ce、Er、Sr、Si、B、Al、Co和Y中的至少一种元素；
    优选地，式I中，1≤a≤1.1，0＜b≤0.02，0＜c≤0.02，0.4≤x≤0.95，0.01≤y≤0.2，0.01≤z≤0.3；M选自Mg、Ti、W、V、Ta、Zr、La、Ce、Er、Sr、Si、Al、Co和Y中的至少一种元素；G选自Mg、 Ti、W、Zr、Ce、Er、Si、B和Al中的至少一种元素；
    进一步优选地，式I中，0.0001≤b≤0.02，0.0001≤c≤0.02，M选自W、Zr、La和Y中的至少一种元素；G选自B、Ti、W、Si和Al中的至少一种元素。
  24. 一种正极极片，其特征在于，所述正极极片的活性物质层含有权利要求1-10中任意一项所述的多元正极材料，或者，权利要求11-23中任意一项所述的制备方法制得的多元正极材料。
  25. 根据权利要求24所述的正极极片，其中，所述正极极片中，所述多元正极材料的负载量为380±2g/m2。
  26. 根据权利要求24或25所述的正极极片，其中，所述正极极片的极限压实密度选自3.2-3.8g/cm3，优选为3.3-3.7g/cm3。
  27. 根据权利要求24-26任一项所述的正极极片，其中，所述正极极片的厚度压缩比选自25-45％，优选为30-40％。
  28. 根据权利要求24-27任一项所述的正极极片，其中，所述正极极片的延伸率选自1.2-3％，优选为1.5-2.5％。
  29. 一种锂离子电池，其特征在于，所述锂离子电池含有权利要求24-28中任意一项所述的正极极片。
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