WO2022078300A1 - 正极材料及其制备方法、锂离子二次电池 - Google Patents

正极材料及其制备方法、锂离子二次电池 Download PDF

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WO2022078300A1
WO2022078300A1 PCT/CN2021/123122 CN2021123122W WO2022078300A1 WO 2022078300 A1 WO2022078300 A1 WO 2022078300A1 CN 2021123122 W CN2021123122 W CN 2021123122W WO 2022078300 A1 WO2022078300 A1 WO 2022078300A1
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Prior art keywords
coating layer
positive electrode
electrode material
phosphate
primary
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PCT/CN2021/123122
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English (en)
French (fr)
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宋雄
张弘旭
罗亮
杨顺毅
杨才德
黄友元
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BTR Nano Tech Co Ltd
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BTR Nano Tech Co Ltd
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Priority to US17/797,013 priority Critical patent/US20230077131A1/en
Priority to KR1020227013860A priority patent/KR102822620B1/ko
Priority to JP2022519347A priority patent/JP7381733B2/ja
Priority to EP21879344.6A priority patent/EP4086984A4/en
Publication of WO2022078300A1 publication Critical patent/WO2022078300A1/zh
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Definitions

  • the present application relates to the technical field of positive electrode materials, in particular, to a positive electrode material, a preparation method thereof, and a lithium ion secondary battery.
  • Lithium-ion batteries are widely used in electric vehicles and consumer electronic products due to their advantages of high energy density, high output power, long cycle life and low environmental pollution. How to improve the rate performance, thermal stability and cycle stability of lithium batteries has always been the direction of research and development.
  • the present application proposes a positive electrode material, a preparation method thereof, and a lithium ion secondary battery, which can effectively improve the rate performance and cycle stability of the lithium battery and reduce the production cost.
  • the coating layer includes a first coating layer and a second coating layer, the first coating layer is formed on the surface of the primary particle, and the second coating layer is formed on the The surfaces of the secondary particles, the first coating layer and the second coating layer both contain a phosphoric acid compound.
  • N in the Li b Ni x Co y M z N w O 2 includes Co, Mn, Al, Ti, Zr, Sr, Mg, Y, Ba, Cu, W, Nb , at least one of La, Ce, Mo, and Sn.
  • the secondary particles are spherical or quasi-spherical.
  • the average particle size of the primary particles is 200 nm to 800 nm.
  • the average particle size of the secondary particles is 9 ⁇ m ⁇ 15 ⁇ m.
  • the positive electrode material satisfies at least one of the following conditions a to g:
  • the phosphoric acid compound includes at least one of Li 3 PO 4 and LiN k (PO 4 ) r , 0 ⁇ k ⁇ 2, 0 ⁇ r ⁇ 2, N includes Co, Mn, Al, Ti, Zr, Sr , at least one of Mg, Y, Ba, Cu, W, Nb, La, Ce, Mo and Sn;
  • the phosphoric acid compound includes at least one of LiMgPO 4 , LiSrPO 4 , LiAl k (PO 4 ) r , LiCo k (PO 4 ) r and LiZrk (PO 4 ) r ;
  • the raw materials for the preparation of the phosphoric acid compound of the first coating layer include a phosphoric acid metal salt and a lithium compound;
  • the raw materials for preparing the phosphoric acid compound of the first coating layer include phosphate metal salt and lithium compound, and the phosphoric acid metal salt includes Mg 3 (PO4) 2 , Sr 3 (PO4) 2 , AlPO 4 and Zr 3 (PO4 ) at least one of 4 ;
  • the raw materials for preparing the phosphoric acid compound of the first coating layer include metal phosphate and a lithium compound, and the lithium compound includes at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate and lithium oxalate;
  • the preparation raw material of the phosphoric acid compound of described second coating layer comprises hydrogen phosphate
  • the raw materials for preparing the phosphoric acid compound of the second coating layer include hydrogen phosphate, and the hydrogen phosphate includes at least one of SrHPO 4 , Zr(HPO 4 ) 2 , MgHPO 4 and Al(H 2 PO 4 ) 3 A sort of.
  • the positive electrode material satisfies at least one of the following conditions a to g:
  • the phosphate radical content of the phosphoric acid compound in the first coating layer is 0.03wt% to 0.3wt% of the total mass of the positive electrode material before primary coating;
  • the phosphate radical content of the phosphoric acid compound in the second coating layer is 0.1 wt % to 0.7 wt % of the total mass of the positive electrode material before secondary coating;
  • the crystallized phosphate content of the phosphoric acid compound in the first coating layer or the second coating layer is 5wt% to 50wt% of the total mass of phosphate radicals;
  • the thickness of the first coating layer is 0.005 ⁇ m ⁇ 0.05 ⁇ m;
  • the thickness of the second coating layer is 0.02 ⁇ m ⁇ 0.2 ⁇ m;
  • the powder conductivity of the positive electrode material under the pressure of 4kN/cm 2 is greater than 0.02S/cm;
  • the specific surface area of the positive electrode material is 0.2 m 2 /g to 1.5 m 2 /g.
  • the content of phosphate groups in the first coating layer is 0.03wt% to 0.3wt%.
  • the content of phosphate groups in the second coating layer is 0.3wt% to 0.5wt%.
  • the embodiments of the present application also provide a method for preparing a positive electrode material, the method comprising the following steps:
  • the primary sinter includes a plurality of primary particles and a first coating layer forming the surface of the primary particles, the first the coating layer comprises a phosphoric acid compound;
  • the primary sintered product is mixed with hydrogen phosphate to obtain a second mixture, and the second mixture is subjected to secondary sintering to obtain a positive electrode material, wherein the positive electrode material includes secondary particles and a second mixture forming the surface of the secondary particles.
  • the method satisfies at least one of the following conditions a to g:
  • the addition amount of the lithium compound is such that the ratio of the total molar content of Ni, Co and M to the molar content of Li is 1: (0.95-1.05);
  • the lithium compound includes at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate and lithium oxalate;
  • the average particle size of the phosphate metal salt is less than 0.5 ⁇ m
  • the metal element of the metal phosphate is selected from at least one of Co, Mn, Al, Ti, Zr, Sr, Mg, Y, Ba, Cu, W, Nb, La, Ce, Mo and Sn;
  • the hydrogen phosphate salt includes at least one of A 2 HPO 4 and AH 2 PO 4 , and A is selected from Ni, Co, Mn, Al, Na, K, Ca, NH 4 , Ti, Zr, Sr, Mg , at least one of Fe, Li, Y, Ba, Cu, W, Nb, La, Ce, Mo and Sn;
  • the phosphate radical content in the phosphate metal salt is 0.03wt% to 0.3wt% of the total mass of the first mixture
  • the content of phosphate radicals in the hydrogen phosphate salt is 0.1 wt % to 0.7 wt % of the total mass of the second mixture.
  • the method satisfies at least one of the following conditions a to i:
  • the phosphate metal salt includes at least one of Mg 3 (PO4) 2 , Sr 3 (PO4) 2 , AlPO 4 and Zr 3 (PO4) 4 ;
  • the hydrogen phosphate salt includes at least one of SrHPO 4 , Zr(HPO 4 ) 2 , MgHPO 4 and Al(H 2 PO 4 ) 3 ;
  • the phosphoric acid compound includes at least one of Li 3 PO 4 and LiN k (PO 4 ) r , 0 ⁇ k ⁇ 2, 0 ⁇ r ⁇ 2, and N is selected from Co, Mn, Al, Ti, Zr , at least one of Sr, Mg, Y, Ba, Cu, W, Nb, La, Ce, Mo, Sn;
  • the phosphoric acid compound includes at least one of LiMgPO 4 , LiSrPO 4 , LiAl k (PO 4 ) r , LiCo k (PO 4 ) r , and LiZrk (PO 4 ) r ;
  • the crystallized phosphate content of the phosphoric acid compound in the first coating layer or the second coating layer is 5wt% to 50wt% of the total mass of phosphate radicals;
  • the average particle size of the primary particles is 200 nm to 800 nm;
  • the thickness of the first coating layer is 0.005 ⁇ m ⁇ 0.05 ⁇ m;
  • the average particle size of the secondary particles is 9 ⁇ m to 15 ⁇ m;
  • the thickness of the second coating layer is 0.02-0.2 ⁇ m.
  • the first mixture is prepared by the following method:
  • At least one of Ni x Co y M z oxide and Ni x Co y M z hydroxide, the lithium compound and the metal phosphate salt are solid-phase mixed at 10° C. to 50° C. for 0.3 h to 2 h.
  • the method satisfies at least one of the following conditions a to d:
  • the primary sintering is carried out in an oxygen-containing atmosphere
  • the primary sintering is performed in an oxygen-containing atmosphere, and the oxygen content of the oxygen-containing atmosphere for the primary sintering is greater than or equal to 95%;
  • the temperature of the primary sintering is 650°C ⁇ 850°C;
  • the time for the primary sintering is 6h-20h.
  • the method satisfies at least one of the following conditions a to f:
  • the temperature at which the primary sintered product is mixed with hydrogen phosphate is 10°C to 50°C;
  • the mixing time of the primary agglomerate and hydrogen phosphate is 0.3h ⁇ 2h;
  • the secondary sintering is carried out in an oxygen-containing atmosphere
  • the secondary sintering is performed in an oxygen-containing atmosphere, and the oxygen content of the oxygen-containing atmosphere for the secondary sintering is greater than or equal to 95%;
  • the temperature of the secondary sintering is 400°C ⁇ 800°C;
  • the time of the secondary sintering is 5h ⁇ 10h.
  • the embodiments of the present application further provide a lithium ion secondary battery, including the positive electrode material prepared as the above-mentioned positive electrode material or the above-mentioned method for preparing the positive electrode material.
  • the positive electrode material provided by the present application includes secondary particles formed by a plurality of primary particles closely combined, the primary particles have a first coating layer, the secondary particles have a second coating layer, the first coating layer and the second coating layer
  • the material of the coating layer includes phosphoric acid compound, and the phosphoric acid compound coating layer not only has high lithium ion conductivity, but also can reduce the residual alkali on the surface of the positive electrode material.
  • This coating method of coating both the inside and the surface at the same time is conducive to the formation of a space-type, all-round isolated electrolyte network and a Li-ion conductive network.
  • the second coating layer on the surface of the secondary particles can not only protect the surface of the secondary particles from being corroded by the electrolyte, improve thermal stability, but also improve the diffusion rate of lithium ions and reduce the residual alkali on the surface, so that the obtained positive electrode material has high rate performance , High thermal stability, good processability and safety.
  • the first coating layer also has the above-mentioned characteristics.
  • the first coating layer can prevent the secondary particles from being cracked, and the primary particles inside the positive electrode material directly contact the electrolyte to inhibit side reactions, which is conducive to improving the secondary particle.
  • the coating of the primary particles of the positive electrode material and the doping of metal cations are realized in the primary sintering process, and the coating of the secondary particles of the positive electrode material is realized in the secondary sintering process;
  • the water washing treatment in the preparation process of the conventional cathode material is not involved, and the loss of lattice lithium on the surface of the cathode material can be better suppressed, thereby improving its rate performance and cycle stability.
  • the method adopts a non-water washing process, which reduces the water washing steps, the drying process and the generation of sewage, and at the same time can reduce the influence of the water washing process on the consistency of the material quality.
  • the preparation method of the positive electrode material provided by the present application can not only improve the electrochemical performance of the material, but also reduce the production cost and environmental pollution, and is more suitable for large-scale production.
  • the prepared cathode material can effectively improve the rate performance, thermal stability and cycle stability of the lithium battery.
  • FIG. 1 is a process flow diagram of a method for preparing a positive electrode material provided by an embodiment of the present application
  • 2a and 2b are scanning electron microscope pictures of the cathode material of Example 1 under different magnifications
  • 3a and 3b are SEM pictures of the cathode material of Comparative Example 1 under different magnifications
  • FIG. 4 is a rate performance diagram of Example 1 of the present application and Comparative Example 1;
  • FIG. 5 is the differential scanning calorimetry (DSC) curves of Example 1 and Comparative Example 1 of the present application.
  • an embodiment of the present application provides a positive electrode material.
  • the coating layer includes a first coating layer and a second coating layer, the first coating layer is formed on the surface of the primary particle, the second coating layer is formed on the surface of the secondary particle, the first coating layer and the second coating layer are formed on the surface of the secondary particle. Both coating layers contain phosphoric acid compounds.
  • the positive electrode material provided by the present application includes secondary particles formed by closely combining a plurality of primary particles, the primary particles have a first coating layer, the secondary particles have a second coating layer, the first coating layer and the second coating layer
  • the materials of the phosphate compound include phosphoric acid compound, and the phosphoric acid compound coating layer not only has high lithium ion conductivity, but also can reduce the residual alkali on the surface of the positive electrode material. This coating method of coating both the inside and the surface at the same time is conducive to the formation of a space-type, all-round isolated electrolyte network and a Li-ion conductive network.
  • the second coating layer on the surface of the secondary particles can not only protect the surface of the secondary particles from being corroded by the electrolyte, improve thermal stability, but also improve the diffusion rate of lithium ions and reduce the residual alkali on the surface, so that the obtained positive electrode material has high rate performance , High thermal stability, good processability and safety.
  • the first coating layer also has the above-mentioned characteristics.
  • the first coating layer can prevent the secondary particles from being cracked, and the primary particles inside the positive electrode material directly contact the electrolyte to inhibit side reactions, which is conducive to improving the secondary particle.
  • the value of b may be, for example, 0.95, 0.98, 1.01, or 1.05, or the like.
  • the value of x may be, for example, 0.8, 0.83, 0.88, 0.91, 0.94, or 0.98, or the like.
  • the value of y+z may be, for example, 0.02, 0.06, 0.09, 0.12, 0.17, or 0.2, and the value of w may be, for example, 0.0001, 0.0005, 0.0010, 0.0015, 0.0020, 0.0025, or 0.0030, and the like. This is not limited.
  • N in the Li b Ni x Co y M z N w O 2 includes Co, Mn, Al, Ti, Zr, Sr, Mg, Y, Ba, Cu, W, Nb, La, Ce, At least one of Mo and Sn.
  • the content of each element in the active material Li b Ni x Co y M z N w O 2 can be measured by a well-known ICP, ICP-MS and other known equipment for qualitative analysis and/or quantitative analysis of each element.
  • the primary particle is a single fine grain
  • the secondary particle is a particle formed by the agglomeration of the primary particle, preferably, the secondary particle is an aggregate of the primary particle, the interior of the secondary particle is compact, and the secondary particle is spherical or quasi-spherical .
  • the average particle size D50 of the primary particles of the active material is 200nm-800nm, for example, it can be 200nm, 300nm, 400nm, 500nm, 600nm, 700nm or 800nm.
  • the average particle size of the secondary particles is 9 ⁇ m-15 ⁇ m, such as 9 ⁇ m, 10 ⁇ m, 11 ⁇ m, 12 ⁇ m, 13 ⁇ m or 15 ⁇ m, etc.
  • the average particle size of the secondary particles is 10 ⁇ m-13 ⁇ m.
  • the thickness of the first cladding layer is 0.005 ⁇ m ⁇ 0.05 ⁇ m, such as 0.005 ⁇ m, 0.01 ⁇ m, 0.015 ⁇ m, 0.02 ⁇ m, 0.025 ⁇ m, 0.03 ⁇ m, 0.035 ⁇ m, 0.04 ⁇ m, 0.045 ⁇ m or 0.05 ⁇ m.
  • the thickness of the first cladding layer can also be other values within the above range, which are not limited here.
  • the thickness of the second cladding layer is 0.02 ⁇ m ⁇ 0.2 ⁇ m, such as 0.02 ⁇ m, 0.03 ⁇ m, 0.05 ⁇ m, 0.08 ⁇ m, 0.1 ⁇ m, 0.13 ⁇ m, 0.15 ⁇ m, 0.18 ⁇ m or 0.2 ⁇ m .
  • the thickness of the second cladding layer can also be other values within the above range, which is not limited here.
  • the phosphoric acid compound includes at least one of Li 3 PO 4 and LiN k (PO 4 ) r , 0 ⁇ k ⁇ 2, 0 ⁇ r ⁇ 2, and N is selected from Co, Mn, Al , at least one of Ti, Zr, Sr, Mg, Y, Ba, Cu, W, Nb, La, Ce, Mo and Sn, specifically, the phosphoric acid compound includes LiMgPO 4 , LiSrPO 4 , LiAl k (PO 4 ) At least one of r , LiCo k (PO 4 ) r and LiZrk (PO 4 ) r , the combination of typical but non-limiting examples are: the phosphoric acid compound can be a combination of Li 3 PO 4 and LiMgPO 4 , Li 3 A combination of PO 4 and LiSrPO 4 .
  • the phosphoric acid compound not only has high lithium ion conductivity, but also can reduce the residual alkali on the surface of the positive electrode material.
  • This coating method of coating both the inside and the surface at the same time is conducive to the formation of a space-type, all-round isolated electrolyte network and a Li-ion conductive network.
  • the raw materials for the preparation of the phosphoric acid compound of the first coating layer include a phosphoric acid metal salt and a lithium compound, which are phosphoric acid compounds formed by a high-temperature reaction between a phosphoric acid metal salt and a lithium compound.
  • the phosphoric acid compound coating and metal cation doping are carried out;
  • the preparation raw materials of the phosphoric acid compound of the second coating layer include hydrogen phosphate; the phosphoric acid compound formed by the high temperature reaction of the hydrogen phosphate.
  • the phosphate content in the first coating layer is 0.03wt% to 0.3wt% of the quality of the positive electrode material before the primary coating, preferably, the phosphate content is 0.075wt% to 0.175wt%, for example, it can be 0.075wt%, 0.1wt%, 0.125wt%, 0.15wt% or 0.175wt%.
  • the phosphate content in the second coating layer is 0.1wt% to 0.7wt% of the mass of the positive electrode material before the secondary coating, preferably, the phosphate content is 0.3wt% to 0.5wt%, for example, it may be 0.3 wt %, 0.35 wt %, 0.4 wt %, 0.45 wt % or 0.5 wt %.
  • the applicant has found through many tests that controlling the phosphate group within the above range enables the primary particles or secondary particles to obtain a good coating effect without reducing the capacity of the positive electrode material.
  • the content of phosphate in the first coating layer is 0.03wt% to 0.3wt%.
  • the content of phosphate in the second coating layer is 0.3 wt % to 0.5 wt %.
  • the primary coating is the first coating treatment of the positive electrode material
  • the secondary coating is the second coating treatment of the positive electrode material
  • the content of crystalline phosphate in the phosphoric acid compound coating layer is 5wt% to 50wt% of the total mass of phosphate, for example, it can be 5wt%, 10wt%, 20wt%, 30wt%, 40wt% or 50wt% %.
  • the content of crystalline phosphate in the first coating layer is controlled at 5wt% to 50wt% to make the coating layer and the surface of the positive electrode material more stable, and the coating of primary particles can prevent secondary particles from cracking, and the primary particles inside the positive electrode material directly Contacting the electrolyte, inhibiting side reactions, is also beneficial to improve the structural stability, thermal stability and long-term cycle stability of the secondary particles. layer, which reduces the transmission resistance of grain boundaries, which is beneficial to improve the rate performance of cathode materials.
  • the positive electrode material is a ternary positive electrode material, and the powder conductivity of the positive electrode material under the pressure of 4kN/cm 2 is greater than 0.02S/cm, which can effectively improve the discharge capacity at a high current rate.
  • the specific surface area of the positive electrode material is 0.2 m 2 /g to 1.5 m 2 /g.
  • the specific surface area of the positive electrode material is 0.3m 2 /g ⁇ 0.8m 2 /g, for example, it can be 0.3m 2 /g, 0.4m 2 /g, 0.5m 2 /g, 0.6m 2 /g, 0.7m 2 /g, 0.8m 2 /g, etc.
  • the present application also provides a method for preparing a positive electrode material, the method comprising the following steps S100-S200:
  • the primary sintered product includes a plurality of primary particles and a first coating layer forming the surface of the primary particles; the first coating layer contains a phosphoric acid compound.
  • the primary particles of the positive electrode material are coated with phosphoric acid compounds and doped with metal cations at the same time during the roasting process; and the primary particle coating can prevent the secondary particles from cracking.
  • the metal cation in the first coating layer can be doped into the positive electrode material during the coating process, which can inhibit the conversion of the positive electrode material from the layered structure to rock salt.
  • the phase structure can inhibit the dissolution of metal ions, and at the same time inhibit the release of lattice oxygen of the material, and improve the safety performance of the material.
  • step of preparing the first mixture comprising the steps of:
  • At least one of Ni x Co y M z oxide and Ni x Co y M z hydroxide, the lithium compound and the metal phosphate salt are solid-phase mixed at 10° C. to 50° C. for 0.3 h to 2 h.
  • the lithium compound is added in an amount such that the ratio of the sum of the molar contents of Ni, Co and M to the molar content of Li is 1: (0.95-1.05). Within this range, the mixing degree of Li/Ni cations can be reduced, and the excessive residual lithium on the surface of the sintered product can be prevented from affecting the processing performance and safety performance.
  • the lithium compound includes at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate and lithium oxalate.
  • the lithium compound is lithium hydroxide.
  • the average particle size of the metal phosphate salt is less than 0.5 ⁇ m, for example, may be 0.001 ⁇ m, 0.01 ⁇ m, 0.05 ⁇ m, 0.1 ⁇ m, 0.15 ⁇ m, 0.2 ⁇ m, 0.25 ⁇ m, 0.3 ⁇ m, 0.35 ⁇ m, 0.4 ⁇ m or 0.45 ⁇ m.
  • the metal element of the metal phosphate is selected from at least one of Co, Mn, Al, Ti, Zr, Sr, Mg, Y, Ba, Cu, W, Nb, La, Ce, Mo and Sn.
  • the metal phosphate can be at least one of SrHPO 4 , Zr(HPO 4 ) 2 , MgHPO 4 and Al(H 2 PO 4 ) 3
  • the typical but non- Limiting examples are:
  • the metal phosphate salt can be SrHPO 4 , or a combination of SrHPO 4 , Zr(HPO 4 ) 2
  • the metal phosphate salt can also include Mg 3 (PO4) 2 , Sr 3 (PO4) 2 , AlPO 4 and at least one of Zr 3 (PO4) 4
  • the typical but non-limiting examples are: phosphate metal salt can be Mg 3 (PO4) 2 , and can also be AlPO 4 and Zr 3 (PO4) 4 Compositions.
  • the phosphate radical content in the phosphate metal salt is 0.03wt% to 0.3wt% of the total mass in the first mixture.
  • it may be 0.03 wt %, 0.05 wt %, 0.1 wt %, 0.15 wt %, 0.2 wt % or 0.3 wt %, etc.
  • the phosphate radical content in the metal phosphate salt is 0.075wt% to 0.175wt% of the total mass in the first mixture.
  • the mixing time is 0.3h ⁇ 2.0h, for example, it can be 0.3h , 0.4h , 0.5h, 0.7h, 0.8h, 1.0h, 1.2h, 1.5h or 2.0h, etc., but not limited to the listed values, and other unlisted values within the numerical range are also applicable.
  • the mixing temperature is 10°C to 50°C, such as 10°C, 15°C, 25°C, 30°C, 35°C, 40°C, 45°C or 50°C, etc., preferably, the mixing temperature is 10°C to 40°C. The applicant has found through many tests that under the mixing conditions, the mixing can be sufficiently uniform, and the side reactions of the mixed raw materials due to excessive temperature can be prevented.
  • the primary sintered product is an active material having a first coating layer
  • M is selected from at least one of Mn or Al
  • N includes Co, Mn, Al, Ti, Zr, Sr, At least one of Mg, Y, Ba, Cu, W, Nb, La, Ce, Mo, and Sn.
  • the first coating layer includes a phosphoric acid compound, the phosphoric acid compound includes at least one of Li 3 PO 4 and LiN k (PO 4 ) r , 0 ⁇ k ⁇ 2, 0 ⁇ r ⁇ 2, N is selected from Co, At least one of Mn, Al, Ti, Zr, Sr, Mg, Y, Ba, Cu, W, Nb, La, Ce, Mo, and Sn.
  • the first mixture is sintered at 650°C to 850°C for 6 hours to 20 hours in an oxygen-containing atmosphere, and pulverized and sieved to obtain a primary sinter, the primary sinter includes a plurality of primary particles, and the primary particles have first cladding.
  • the average particle diameter D50 of the primary particles is 200 nm to 800 nm, and may be, for example, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, or 800 nm.
  • the metal phosphate reacts with the lithium compound at high temperature to form a first coating layer of the primary particles
  • the thickness of the first coating layer is 0.005 ⁇ m ⁇ 0.05 ⁇ m, for example, 0.005 ⁇ m, 0.01 ⁇ m, 0.015 ⁇ m, 0.02 ⁇ m, 0.025 ⁇ m, 0.03 ⁇ m, 0.035 ⁇ m, 0.04 ⁇ m, 0.045 ⁇ m or 0.05 ⁇ m.
  • the thickness of the first cladding layer can also be other values within the above range, which are not limited here.
  • the content of crystallized phosphate in the first coating layer is 5wt% to 50wt% of the total mass of phosphate, such as 5wt%, 10wt%, 15wt%, 20wt%, 30wt%, 40wt% or 50wt%.
  • the oxygen content in the oxygen-containing atmosphere is ⁇ 95%, preferably, the primary sintering temperature is 720°C to 800°C, and the primary sintering temperature can be, for example, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C, or 800°C, etc., but are not limited to the listed values, and other unrecited values within the numerical range are also applicable.
  • the applicant has found through many experiments that sufficient oxygen can promote the oxidation of divalent nickel to trivalent nickel, reduce the mixed discharge of Li/Ni cations, and improve the capacity of the positive electrode material. cause material to decompose.
  • the primary sintering time can be, for example, 6h, 8h, 10h, 12h, 15h, 18h or 20h, etc., but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
  • the applicant has found through many experiments that a layered structure and a uniform primary particle coating layer can be effectively formed, and then various performance indicators of the positive electrode material can be taken into account.
  • the particle size of the metal phosphate salt it is beneficial to form a uniform first coating layer on the surface of the primary particles, and the content of crystallized phosphate in the first coating layer is controlled at 5wt% ⁇ 50wt% % makes the combination of the coating layer and the surface of the positive electrode material more stable, and the coating of the primary particles can prevent the secondary particles from cracking.
  • Stability, thermal stability and long cycle stability at the same time, due to the formation of a phosphate compound coating layer with high ionic conductivity at the grain boundary between the primary particles, the transmission resistance of the grain boundary is reduced, which is beneficial to improve the rate performance of the cathode material. .
  • the positive electrode material includes secondary particles and a second coating layer forming the surface of the secondary particles, the secondary particles are aggregates of primary particles, and the second coating layer contains a phosphoric acid compound.
  • the coating of the primary particles of the active material and the doping of metal cations are realized in the first sintering process, and the secondary particles of the active material are realized in the second sintering process of the second mixture. wrap.
  • the method does not involve the water washing treatment in the preparation process of the conventional positive electrode material, and can better suppress the loss of the lattice lithium on the surface of the positive electrode material, thereby improving its rate performance and cycle stability.
  • the method adopts a non-water washing process, which reduces the water washing steps, the drying process and the generation of sewage, and at the same time can reduce the influence of the water washing process on the consistency of the material quality.
  • the mixing time is 0.3h-2.0h, for example, it can be 0.3h, 0.4h, 0.5h, 0.7h, 0.8h, 1.0h, 1.2h, 1.5h or 2.0h, etc., but not limited to the listed values, and other unlisted values within the numerical range are also applicable.
  • the mixing temperature is 10°C to 50°C, such as 10°C, 15°C, 25°C, 30°C, 35°C, 40°C, 45°C or 50°C, etc., preferably, the mixing temperature is 10°C to 40°C. The applicant has found through many tests that under the mixing conditions, the mixing can be sufficiently uniform, and the side reactions of the mixed raw materials due to excessive temperature can be prevented.
  • the average particle size of the hydrogen phosphate is less than 10 ⁇ m, for example, can be 0.01 ⁇ m, 0.1 ⁇ m, 1 ⁇ m, 2 ⁇ m, 4 ⁇ m, 5 ⁇ m, 8 ⁇ m or 9 ⁇ m, etc., but not limited to the listed numerical values, other values within the numerical range The same applies to non-recited values.
  • the hydrogen phosphate salt includes at least one of A 2 HPO 4 and AH 2 PO 4 , and A is selected from Ni, Co, Mn, Al, Na, K, Ca, NH 4 , Ti, Zr, Sr, Mg, Fe , at least one of Li, Y, Ba, Cu, W, Nb, La, Ce, Mo, and Sn. Typical but non-limiting examples of such combinations are: the combination of MgHPO 4 and NH 4 H 2 PO 4 , the combination of (NH 4 ) 2 HPO 4 and Al(H 2 PO 4 ) 3 and the like.
  • the phosphate radical content in the hydrogen phosphate is 0.1wt% to 0.7wt% of the total mass in the second mixture, for example, it can be 0.31wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt% , 0.6 wt % or 0.7 wt %.
  • the content of phosphate radicals in the hydrogen phosphate salt is 0.3 wt % to 0.5 wt % of the total mass in the second mixture.
  • the second mixture is placed in an oxygen-containing atmosphere for secondary sintering at 400° C. ⁇ 800° C. for 5 h ⁇ 10 h, and the cathode material is obtained by crushing and sieving.
  • the positive electrode material includes a plurality of secondary particles, which are aggregates of primary particles.
  • the average particle size of the secondary particles is 9 ⁇ m-15 ⁇ m, such as 9 ⁇ m, 10 ⁇ m, 11 ⁇ m, 12 ⁇ m, 13 ⁇ m or 15 ⁇ m, etc.
  • the average particle size of the secondary particles is 10 ⁇ m-13 ⁇ m.
  • the thickness of the second coating layer is 0.02 ⁇ m ⁇ 0.2 ⁇ m, for example, may be 0.02 ⁇ m, 0.03 ⁇ m, 0.05 ⁇ m, 0.08 ⁇ m, 0.1 ⁇ m, 0.13 ⁇ m, 0.15 ⁇ m, 0.18 ⁇ m or 0.2 ⁇ m.
  • the thickness of the second cladding layer can also be other values within the above range, which is not limited here.
  • the hydrogen phosphate reacts with the residual lithium on the surface of the primary sinter at a high temperature to form the second coating layer, and the content of the crystallized phosphate in the second coating layer is 5wt% to 50wt% of the total mass of phosphate radicals %.
  • the oxygen content in the oxygen-containing atmosphere in the secondary sintering is greater than or equal to 95%, and the secondary sintering temperature is 400°C to 800°C, such as 400°C, 500°C, 550°C, 600°C, 650°C, 700°C or 800°C etc., preferably, the sintering temperature is 500°C to 700°C, but it is not limited to the listed numerical values, and other unlisted numerical values within the numerical range are also applicable.
  • the phosphoric acid compound can be more uniformly and firmly coated on the surface of the primary sinter, and at the same time, it is conducive to the reaction between hydrogen phosphate and the residual lithium on the surface of the primary sinter, reducing the The residual alkali forms a phosphoric acid compound with high lithium ion conductivity, which improves the processing performance and rate performance, and does not cause the decomposition of the fired product and the precipitation of lithium.
  • the secondary sintering time is 5h-10h, such as 5h, 6h, 7h, 8h, 9h or 10h, etc., but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
  • the applicant has found through many experiments that a uniform second coating layer and a phosphoric acid compound with high lithium ion conductivity can be formed, and then various performance indicators of the positive electrode material can be taken into account.
  • the mixing method used in this embodiment may be mechanical mixing, such as a high mixer or a VC mixer.
  • M is selected from at least one of Mn and Al;
  • N includes Co, Mn, Al, Ti, Zr, Sr, Mg, Y, Ba, Cu, W, Nb , at least one of La, Ce, Mo, and Sn.
  • a first coating layer is formed on the surface of the primary particle, and a second coating layer is formed on the surface of the secondary particle.
  • the first coating layer and the second coating layer are both phosphoric acid compounds, and the phosphoric acid compounds are at least Including at least one of Li 3 PO 4 and LiN k (PO 4 ) r , 0 ⁇ k ⁇ 2, 0 ⁇ r ⁇ 2, N is selected from Co, Mn, Al, Ti, Zr, Sr, Mg, Y, At least one of Ba, Cu, W, Nb, La, Ce, Mo, and Sn.
  • the preparation method of the positive electrode material provided by the present application realizes the coating of the primary particles of the positive electrode material and the doping of metal cations in the primary sintering process, and realizes the coating of the secondary particles of the positive electrode material in the secondary sintering process; this method does not involve
  • the water washing treatment during the preparation of conventional cathode materials can better suppress the loss of lattice lithium on the surface of cathode materials, thereby improving their rate performance and cycle stability.
  • the method adopts a non-water washing process, which reduces the water washing steps, the drying process and the generation of sewage, and at the same time can reduce the influence of the water washing process on the consistency of the material quality.
  • the embodiments of the present application further provide a lithium ion secondary battery, including the positive electrode material prepared as the above-mentioned positive electrode material or the above-mentioned method for preparing the positive electrode material.
  • a preparation method of a positive electrode material comprising the following steps:
  • (1) Mix the precursor Ni 0.88 Co 0.09 Al 0.03 (OH) 2 , lithium hydroxide and SrHPO 4 with an average particle size D50 of 0.2 ⁇ m in a high-mixer uniformly. obtaining a first mixture, wherein Li/(Ni+Co+Al) 1.05, and the phosphate content is 0.3wt% of the total mass of the first mixture;
  • the positive electrode material obtained in this embodiment includes a plurality of secondary particles, and the secondary particles are aggregates of a plurality of primary particles; a first coating layer is formed on the surface of the primary particle, and a second coating layer is formed on the surface of the secondary particle.
  • the average particle size of the primary particles is 0.6 ⁇ m, the average particle size of the secondary particles is 12 ⁇ m, and the material of the primary particles is Li 1.05 Ni 0.88 Co 0.09 Al 0.03 Sr 0.0026 O 2 ;
  • the thickness of the first coating layer is 0.04 ⁇ m , the materials of the first coating layer are Li 3 PO 4 and LiSrk (PO 4 ) r ;
  • the secondary particles are the aggregates of the primary particles after coating the first coating layer, and the thickness of the second coating layer is 0.06 ⁇ m ;
  • the material of the second coating layer is Li 3 PO 4 and LiAl k (PO 4 ) r .
  • Table 1 shows the performance test results of the positive electrode material S1 prepared in Example 1.
  • (1) Mix the precursor Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 , lithium hydroxide and Zr(HPO 4 ) 2 with an average particle size D50 of 0.4 ⁇ m in a high-mixer uniformly, and control the mixing temperature to 25°C, The mixing time is 2h to obtain a first mixture, wherein Li/(Ni+Co+Al) 1.03, and the phosphate content is 0.2wt% of the total mass of the first mixture;
  • the positive electrode material obtained in this embodiment includes a plurality of secondary particles, and the secondary particles are aggregates of a plurality of primary particles; a first coating layer is formed on the surface of the primary particle, and a second coating layer is formed on the surface of the secondary particle.
  • the average particle diameter of the primary particles is 0.7 ⁇ m
  • the average particle diameter of the secondary particles is 11.5 ⁇ m
  • the material of the primary particles is Li 1.03 Ni 0.83 Co 0.11 Mn 0.06 Zr 0.0009 O 2
  • the thickness of the first coating layer is 0.02 ⁇ m
  • the materials of the first coating layer are Li 3 PO 4 and LiZrk (PO 4 ) r
  • the secondary particles are the aggregates of the primary particles after coating the first coating layer, and the thickness of the second coating layer is 0.10 ⁇ m
  • the substance of the second coating layer is Li 3 PO 4 .
  • the first mixture was sintered at 650°C in an atmosphere with an oxygen content of ⁇ 95% for 20 hours, pulverized and sieved to obtain a phosphoric acid compound-coated primary sinter LiNi 0.88 Co 0.09 Al 0.03 Mg 0.0009 Zr 0.0004 O 2 , and primary sintering It is doped with Mg and Zr.
  • the positive electrode material obtained in this embodiment includes a plurality of secondary particles, and the secondary particles are aggregates of a plurality of primary particles; a first coating layer is formed on the surface of the primary particle, and a second coating layer is formed on the surface of the secondary particle; wherein , the average particle size of primary particles is 0.3 ⁇ m, the average particle size of secondary particles is 12 ⁇ m, the material of primary particles is LiNi 0.88 Co 0.09 Al 0.03 Mg 0.0009 Zr 0.0004 O 2 ; the thickness of the first coating layer is 0.01 ⁇ m, The substances of the first coating layer are Li 3 PO 4 , LiMg k (PO 4 ) r and LiZrk (PO 4 ) r ; the secondary particles are the aggregates of the primary particles coated with the first coating layer, and the second The thickness of the cladding layer is 0.15 ⁇ m; the substance of the second cladding layer is Li 3 PO 4 .
  • the positive electrode material obtained in this embodiment includes a plurality of secondary particles, and the secondary particles are aggregates of a plurality of primary particles; a first coating layer is formed on the surface of the primary particle, and a second coating layer is formed on the surface of the secondary particle; wherein , the average particle size of the primary particles is 0.5 ⁇ m, the average particle size of the secondary particles is 12 ⁇ m, the material of the primary particles is LiNi 0.88 Co 0.09 Al 0.03 Sr 0.0003 O 2 , the thickness of the first coating layer is 0.008 ⁇ m, the first The materials of the coating layer are Li 3 PO 4 and LiSrk (PO 4 ) r ; the secondary particles are the aggregates of the primary particles after coating the first coating layer, and the thickness of the second coating layer is 0.18 ⁇ m; The substances of the two cladding layers are Li 3 PO 4 and LiZrk (PO 4 ) r .
  • Example 5 Using the preparation method and process steps of Example 1, the difference between Example 5 and Example 1 is that the second mixture is sintered at 400° C. in an atmosphere with an oxygen content of ⁇ 95% for 8 hours.
  • the positive electrode material obtained in this embodiment includes a plurality of secondary particles, and the secondary particles are aggregates of a plurality of primary particles; a first coating layer is formed on the surface of the primary particle, and a second coating layer is formed on the surface of the secondary particle.
  • the average particle size of the primary particles is 0.6 ⁇ m, the average particle size of the secondary particles is 12 ⁇ m, and the material of the primary particles is Li 1.05 Ni 0.88 Co 0.09 Al 0.03 Sr 0.0026 O 2 ;
  • the thickness of the first coating layer is 0.04 ⁇ m , the materials of the first coating layer are Li 3 PO 4 and LiSrk (PO 4 ) r ;
  • the secondary particles are the aggregates of the primary particles after coating the first coating layer, and the thickness of the second coating layer is 0.1 ⁇ m ;
  • the material of the second coating layer is Li 3 PO 4 and LiAl k (PO 4 ) r .
  • Example 7 Using the preparation method and process steps of Example 1, the difference between Example 7 and Example 1 is that Sr 3 (PO 4 ) 2 is used in step (1).
  • Example 1 Using the preparation method and process steps of Example 1, the difference between Comparative Example 1 and Example 1 is that SrHPO 4 is not added in step (1), and Al(H 2 PO 4 ) 3 is not added in step (2).
  • Comparative Example 3 is different from Example 1 in that the median particle size of SrHPO 4 used in step (1) is 10 ⁇ m.
  • Example 1 Using the preparation method and process steps of Example 1, the difference between Comparative Example 4 and Example 1 is that Al(H 2 PO 4 ) 3 in step (3) is replaced by AlPO 4 , and all other operations and raw material ratios are the same as Example 1 is the same.
  • Table 1 shows the performance test results of the positive electrode material D4 prepared in Comparative Example 4.
  • the morphology of the cathode material was analyzed by scanning electron microscope, and its scanning electron microscope picture was obtained.
  • the electrochemical performance of the prepared cathode material was evaluated by using a button half cell.
  • the specific method is as follows: the cathode material, SP and polyvinylidene fluoride (PVDF) were weighed in a mass ratio of 96:2:2, and added at a solid content of 50%.
  • N-methylpyrrolidone was prepared into a viscous slurry with a high-speed disperser, uniformly coated on aluminum foil with a scraper, dried in an oven at 80°C, rolled, and cut into a positive electrode sheet with a diameter of 14 mm.
  • a lithium sheet with a diameter of 16 mm was used as the negative electrode, Celgard polyethylene PP film was used as the diaphragm, and LiPF6 carbonate (DEC/EC volume ratio 1:1) solution with a concentration of 1 mol/L was used as the electrolyte. Assemble in the glove box.
  • the capacity, the first coulombic efficiency, and the rate performance were tested at 25°C and 3.0V to 4.3V.
  • the reference capacity was set to 200mA/g, and the current density corresponding to 1C was 200mA/g.
  • the positive electrode material particles were cut by an ion beam cutter, and then the cross-section of the cut particles was scanned by a high-precision electron energy spectrometer.
  • a NETZSCH scanning calorimeter was used to test the thermal stability of the electrode material in a closed high-pressure crucible at 5°C/min under nitrogen atmosphere, and a differential scanning calorimeter curve was obtained. The active material scraped from the fully charged electrode sheet after 2.5 weeks.
  • the structural composition of the cathode material was tested by Bruker X-ray diffractometer, and then the content of crystalline phosphate in the phosphate compound of the coating layer was obtained by refined calculation of the X-ray pattern.
  • the high-precision four-probe instrument MCP-T700 is used to test the powder conductivity of the positive electrode material, which can test the conductivity of the powder material under different pressures.
  • the positive electrode material obtained in Example 1 forms a uniform coating layer on the surface of the secondary particles, and the gaps between the primary particles are filled with phosphoric acid compounds, so that the contact at the grain boundaries is very close, and The coating layer is very tightly bound to the cathode material.
  • the surface of the secondary particles of the positive electrode material obtained in Comparative Example 1 is relatively smooth and has no coating layer; at the same time, the gap between the primary particles is large, and the electrolyte is easily penetrated into the interior of the secondary particles.
  • the rate performance of the positive electrode material obtained in Example 1 is better than that of Comparative Example 1, indicating that the rate performance of the positive electrode material without coating the primary particles with a phosphoric acid compound is significantly worse.
  • Example 1 the decomposition temperature and heat release of the positive electrode material in Example 1 are better than those in Comparative Example 1, indicating that coating the primary particles and secondary particles of the positive electrode material with a phosphoric acid compound is beneficial to improve the thermal stability of the positive electrode material.
  • the electrochemical properties of the cathode materials prepared in Examples 1 to 5 of the present application are all excellent, the discharge capacity is above 205mAh/g, the first coulombic efficiency can reach about 90%, the rate performance is good, and the long cycle performance is outstanding. , the surface lithium content is low.
  • Example 1 and Comparative Example 2 in Table 1 show that whether the primary particles or the secondary particles are not coated with the phosphoric acid compound, the surface residual alkali of the prepared positive electrode material is on the high side, and the rate performance, discharge Capacity and cycle performance are greatly affected.
  • the data comparison between Example 1 and Comparative Example 3 shows that the particle size of metal phosphate (SrHPO 4 ) is equal to 10 ⁇ m, and the particle size is too large, which is not conducive to the formation of a uniform first coating layer on the surface of primary particles by metal phosphate.
  • the residual alkali on the surface of the positive electrode material is high, and the rate performance, discharge capacity, and cycle performance are greatly affected. It can be seen from the comparison of the data of Example 1 and Comparative Example 4 that when hydrogen phosphate is not used for the secondary coating, the residual alkali on the surface of the obtained positive electrode material is seriously high and cannot pass the processability test.

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Abstract

本申请涉及正极材料领域，提供一种正极材料及其制备方法、锂离子二次电池，正极材料包括二次粒子，所述二次粒子包括多个一次粒子，所述一次粒子包含活性物质，所述活性物质的化学通式为Li bNi xCo yM zN wO 2，其中，0.95≤b≤1.05，0.8≤x<1，0<y+z≤0.2，x+y+z＝1，0.0001≤w≤0.003；M选自Mn及Al中的至少一种；N为金属；及包覆层，所述包覆层包括第一包覆层和第二包覆层，所述第一包覆层形成于所述一次粒子的表面，所述第二包覆层形成于所述二次粒子的表面，所述第一包覆层和第二包覆层均包含磷酸化合物。本申请的正极材料及其制备方法、锂离子二次电池，低成本、可规模化生产，能够有效提高锂电池的倍率性能及循环稳定性。

Description

正极材料及其制备方法、锂离子二次电池
本申请要求于2020年10月12日提交中国专利局，申请号为2020110949367，申请名称为“高镍正极材料及其制备方法、锂离子二次电池”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及正极材料技术领域，具体地讲，涉及正极材料及其制备方法、锂离子二次电池。
背景技术
锂离子电池由于具备能量密度大、输出功率高、循环寿命长和环境污染小等优点而被广泛应用于电动汽车以及消费类电子产品中。如何提高锂电池的倍率性能、热稳定性及循环稳定性一直是研发人员的探索方向。
现有的正极材料在经过长循环后，颗粒裂化使得内部结构容易直接暴露，影响正极材料的长循环稳定性，影响锂电池的倍率性能。
基于此，亟需开发一种正极材料，以提高锂电池的倍率性能及循环稳定性。
申请内容
鉴于此，本申请提出正极材料及其制备方法、锂离子二次电池，能够有效提高锂电池的倍率性能及循环稳定性，降低生产成本。
本申请实施例提供一种正极材料，所述正极材料包括二次粒子，所述二次粒子包括多个一次粒子，所述一次粒子包含活性物质，所述活性物质的化学通式为Li bNi xCo yM zN wO 2，其中，0.95≤b≤1.05，0.8≤x<1，0<y+z≤0.2，x+y+z＝1，0.0001≤w≤0.003；M选自Mn及Al中的至少一种；N为金属；
及包覆层，所述包覆层包括第一包覆层和第二包覆层，所述第一包覆层形成于所述一次粒子的表面，所述第二包覆层形成于所述二次粒子的表面，所述第一包覆层和第二包覆层均包含磷酸化合物。
在一种可行的实施方式中，所述Li bNi xCo yM zN wO 2中的N包括Co、Mn、Al、Ti、Zr、Sr、Mg、Y、Ba、Cu、W、Nb、La、Ce、Mo及Sn中的至少一种。
在一种可行的实施方式中，所述二次粒子呈球形或者类球形。
在一种可行的实施方式中，所述一次粒子的平均粒径为200nm～800nm。
在一种可行的实施方式中，所述二次粒子的平均粒径为9μm～15μm。
在一种可行的实施方式中，所述正极材料满足以下条件a～g的至少一者：
a、所述磷酸化合物包括Li 3PO 4及LiN k(PO 4) r中的至少一种，0<k≤2，0<r≤2，N包括Co、Mn、Al、Ti、Zr、Sr、Mg、Y、Ba、Cu、W、Nb、La、Ce、Mo及Sn中的至少一种；
b、所述磷酸化合物包括LiMgPO 4、LiSrPO 4、LiAl k(PO 4) r、LiCo k(PO 4) r和LiZr k (PO 4) r中的至少一种；
c、所述第一包覆层的磷酸化合物的制备原料包括磷酸金属盐和锂化合物；
d、所述第一包覆层的磷酸化合物的制备原料包括磷酸金属盐和锂化合物，所述磷酸金属盐包括Mg 3(PO4) 2、Sr 3(PO4) 2、AlPO 4和Zr 3(PO4) 4中的至少一种；
e、所述第一包覆层的磷酸化合物的制备原料包括磷酸金属盐和锂化合物，所述锂化合物包括碳酸锂、氢氧化锂、醋酸锂、硝酸锂及草酸锂中的至少一种；
f、所述第二包覆层的磷酸化合物的制备原料包括磷酸氢盐；
g、所述第二包覆层的磷酸化合物的制备原料包括磷酸氢盐，所述磷酸氢盐包括SrHPO 4、Zr(HPO 4) 2、MgHPO 4和Al(H 2PO 4) 3中的至少一种。
在一种可行的实施方式中，所述正极材料满足以下条件a～g的至少一者：
a、所述第一包覆层中的磷酸化合物的磷酸根含量为一次包覆前的正极材料的总质量的0.03wt％～0.3wt％；
b、所述第二包覆层中的磷酸化合物的磷酸根含量为二次包覆前的正极材料的总质量的0.1wt％～0.7wt％；
c、所述第一包覆层或所述第二包覆层中的磷酸化合物的晶化磷酸根含量为磷酸根总质量的5wt％～50wt％；
d、所述第一包覆层的厚度为0.005μm～0.05μm；
e、所述第二包覆层的厚度为0.02μm～0.2μm；
f、所述正极材料在4kN/cm 2加压下的粉体电导率大于0.02S/cm；
g、所述正极材料的比表面积为0.2m 2/g～1.5m 2/g。
在一种可行的实施方式中，以正极材料的质量为100％计，第一包覆层中的磷酸根含量为0.03wt％～0.3wt％。
在一种可行的实施方式中，以正极材料的质量为100％计，第二包覆层中的磷酸根含量为0.3wt％～0.5wt％。
第二方面，本申请实施例还提供一种正极材料的制备方法，所述方法包括以下步骤：
将第一混合物进行一次烧结，得到一次烧结物，其中，所述第一混合物包括Ni xCo yM z氧化物及Ni xCo yM z氢氧化物中的至少一种、锂化合物及磷酸金属盐，x+y+z＝1，M选自Mn或Al中的至少一种，所述一次烧结物包括多个一次粒子及形成所述一次粒子表面的第一包覆层，所述第一包覆层包含磷酸化合物；及
将所述一次烧结物与磷酸氢盐混合，得到第二混合物，将所述第二混合物进行二次烧结，得到正极材料，所述正极材料包括二次粒子及形成所述二次粒子表面的第二包覆层，所述二次粒子包括多个聚集的一次粒子，所述第二包覆层包含磷酸化合物。
在一种可行的实施方式中，所述方法满足以下条件a～g的至少一者：
a、所述锂化合物的添加量为：使得Ni、Co及M的摩尔含量总和与Li的摩尔含量比值为1：(0.95～1.05)；
b、所述锂化合物包括碳酸锂、氢氧化锂、醋酸锂、硝酸锂及草酸锂中的至少一种；
c、所述磷酸金属盐的平均粒径小于0.5μm；
d、所述磷酸金属盐的金属元素选自Co、Mn、Al、Ti、Zr、Sr、Mg、Y、Ba、Cu、W、Nb、La、Ce、Mo及Sn中的至少一种；
e、所述磷酸氢盐包括A 2HPO 4、AH 2PO 4中的至少一种，A选自Ni、Co、Mn、Al、Na、K、Ca、NH 4、Ti、Zr、Sr、Mg、Fe、Li、Y、Ba、Cu、W、Nb、La、Ce、Mo及Sn中的至少一种；
f、所述磷酸金属盐中的磷酸根含量为所述第一混合物总质量的0.03wt％～0.3wt％；
g、所述磷酸氢盐中的磷酸根含量为所述第二混合物总质量的0.1wt％～0.7wt％。
在一种可行的实施方式中，所述方法满足以下条件a～i的至少一者：
a、所述磷酸金属盐包括Mg 3(PO4) 2、Sr 3(PO4) 2、AlPO 4和Zr 3(PO4) 4中的至少一种；
b、所述磷酸氢盐包括SrHPO 4、Zr(HPO 4) 2、MgHPO 4和Al(H 2PO 4) 3中的至少一种；
c、所述磷酸化合物至少包括Li 3PO 4及LiN k(PO 4) r中的至少一种，0<k≤2，0<r≤2，N选自Co、Mn、Al、Ti、Zr、Sr、Mg、Y、Ba、Cu、W、Nb、La、Ce、Mo、Sn中的至少一种；
d、所述磷酸化合物包括LiMgPO 4、LiSrPO 4、LiAl k(PO 4) r、LiCo k(PO 4) r、LiZr k(PO 4) r中的至少一种；
e、所述第一包覆层或所述第二包覆层中的磷酸化合物的晶化磷酸根含量为磷酸根总质量的5wt％～50wt％；
f、所述一次粒子的平均粒径为200nm～800nm；
g、所述第一包覆层的厚度为0.005μm～0.05μm；
h、所述二次粒子的平均粒径为9μm～15μm；
i、所述第二包覆层的厚度为0.02～0.2μm。
在一种可行的实施方式中，所述第一混合物包括以下方法制备：
将Ni xCo yM z氧化物及Ni xCo yM z氢氧化物中的至少一种、锂化合物及磷酸金属盐在10℃～50℃下固相混合0.3h～2h。
在一种可行的实施方式中，所述方法满足以下条件a至d的至少一者：
a、所述一次烧结在含氧气氛下进行；
b、所述一次烧结在含氧气氛下进行，所述一次烧结的含氧气氛的氧气含量大于等于95％；
c、所述一次烧结的温度为650℃～850℃；
d、所述一次烧结的时间为6h～20h。
在一种可行的实施方式中，所述方法满足以下条件a至f的至少一者：
a、所述一次烧结物与磷酸氢盐混合的温度为10℃～50℃；
b、所述一次烧结物与磷酸氢盐混合的时间为0.3h～2h；
c、所述二次烧结在含氧气氛下进行；
d、所述二次烧结在含氧气氛下进行，所述二次烧结的含氧气氛的氧气含量大于等于95％；
e、所述二次烧结的温度为400℃～800℃；
f、所述二次烧结的时间为5h～10h。
本申请实施例还提供一种锂离子二次电池，包括如上述正极材料或如上述正极材料的制备方法制备的正极材料。
本申请的技术方案至少具有以下有益的效果：
首先，本申请提供的正极材料包括由多个一次粒子紧密结合形成的二次粒子，一次粒子具有第一包覆层，二次粒子具有第二包覆层，第一包覆层与第二包覆层的材质均包括磷酸化合物，磷酸化合物包覆层不仅具有高锂离子电导，同时能降低正极材料表面残碱。这种内部和表面同时包覆的包覆方式有利于形成空间型、全方位隔离电解液网络和锂离子导电网络。二次粒子表面的第二包覆层不仅能保护二次颗粒表面不被电解液腐蚀，提高热稳定性，且能提升锂离子扩散速率，降低表面残碱，使得获得的正极材料兼顾高倍率性能、高热稳定性、良好的加工性能以及安全性。第一包覆层同样具有上述特点，除此之外，第一包覆层还能防止二次粒子发生裂化时，正极材料内部一次粒子直接接触电解液，抑制副反应，这有利于提高二次粒子的结构稳定性、热稳定性和长循环稳定性，再者由于在一次粒子间的晶界处形成了具有高离子电导的磷酸化合物包覆层，降低了晶界传输阻抗，有利于提高正极材料的倍率性能。因此，这种内外结合的包覆方式协同改善正极材料的结构稳定性、热稳定性、安全性、倍率性能、长循环性能以及加工性能。
其次，本申请提供的正极材料的制备方法，在一次烧结过程中实现对正极材料的一次粒子包覆和金属阳离子掺杂，在二次烧结过程中实现对正极材料二次粒子包覆；本方法不涉及常规正极材料制备过程中的水洗处理，能更好的抑制正极材料表面晶格锂的损失，从而改善其倍率性能和循环稳定性。并且，本方法采用非水洗工艺，减少了水洗工步、干燥工序以及污水产生，同时能降低水洗过程对材料品质一致性的影响。
本申请提供的正极材料的制备方法，不仅能改善材料的电化学性能，同时能降低生产成本和环境污染，更加适合大规模生产。制备得到正极材料，能够有效提高锂电池的倍率性能、热稳定性及循环稳定性。
附图说明
图1为本申请实施例提供的正极材料的制备方法的工艺流程图；
图2a和图2b为实施例1的正极材料在不同放大倍率下的扫描电镜图片；
图3a和图3b为对比例1的正极材料在不同放大倍率下的扫描电镜图片；
图4为本申请实施例1与对比例1的倍率性能图；
图5为本申请实施例1与对比例1的差式扫描热曲线(DSC)。
具体实施方式
以下所述是本申请实施例的优选实施方式，应当指出，对于本技术领域的普通技术人员来说，在不脱离本申请实施例原理的前提下，还可以做出若干改进和润饰， 这些改进和润饰也视为本申请实施例的保护范围。
现有的正极材料在经过长循环后，颗粒裂化使得内部结构容易直接暴露，影响正极材料的长循环稳定性，影响锂电池的倍率性能。为了提高锂离子电池的倍率性能及循环稳定性，本申请实施例提供了一种正极材料。
所述正极材料包括：二次粒子，二次粒子包括多个一次粒子，一次粒子包含活性物质，活性物质的化学通式为Li bNi xCo yM zN wO 2，其中，0.95≤b≤1.05，0.8≤x<1，0<y+z≤0.2，x+y+z＝1，0.0001≤w≤0.003；M选自Mn及Al中的至少一种；N为金属；及包覆层，包覆层包括第一包覆层和第二包覆层，第一包覆层形成于一次粒子的表面，第二包覆层形成于二次粒子的表面，第一包覆层和第二包覆层均包含磷酸化合物。
本申请提供的正极材料包括由多个一次粒子紧密结合形成的二次粒子，一次粒子具有第一包覆层，二次粒子具有第二包覆层，第一包覆层与第二包覆层的材质均包括磷酸化合物，磷酸化合物包覆层不仅具有高锂离子电导，同时能降低正极材料表面残碱。这种内部和表面同时包覆的包覆方式有利于形成空间型、全方位隔离电解液网络和锂离子导电网络。二次粒子表面的第二包覆层不仅能保护二次颗粒表面不被电解液腐蚀，提高热稳定性，且能提升锂离子扩散速率，降低表面残碱，使得获得的正极材料兼顾高倍率性能、高热稳定性、良好的加工性能以及安全性。第一包覆层同样具有上述特点，除此之外，第一包覆层还能防止二次粒子发生裂化时，正极材料内部一次粒子直接接触电解液，抑制副反应，这有利于提高二次粒子的结构稳定性、热稳定性和长循环稳定性，再者由于在一次粒子间的晶界处形成了具有高离子电导的磷酸化合物包覆层，降低了晶界传输阻抗，有利于提高正极材料的倍率性能。因此，这种内外结合的包覆方式协同改善正极材料的结构稳定性、热稳定性、安全性、倍率性能、长循环性能以及加工性能，同时，这种双包覆层结构可提高材料的颗粒强度，抑制正极材料在极片制作过程中的开裂。
具体地，b的值例如可以是0.95、0.98、1.01或1.05等。x的值例如可以是0.8、0.83、0.88、0.91、0.94或0.98等。y+z的值例如可以是0.02、0.06、0.09、0.12、0.17或0.2等，w的值例如可以是0.0001、0.0005、0.0010、0.0015、0.0020、0.0025或0.0030等。在此不做限定。
可选地，所述Li bNi xCo yM zN wO 2中的N包括Co、Mn、Al、Ti、Zr、Sr、Mg、Y、Ba、Cu、W、Nb、La、Ce、Mo及Sn中的至少一种。
需要说明的是，活性物质Li bNi xCo yM zN wO 2中各元素含量可以通过公知的ICP、ICP-MS等公知的各元素进行定性分析和/或定量分析的仪器来测定。
一次粒子为单个细小晶粒，二次粒子为一次粒子团聚后形成的颗粒，优选地，所述二次粒子是一次粒子的聚集体，二次粒子内部紧实，二次粒子呈球形或者类球形。
本申请提供的正极材料经过扫描电子显微镜(SEM)和粒度测试共同检测后，得出活性物质的一次粒子的平均粒径D50为200nm～800nm，例如可以是200nm、300nm、400nm、500nm、600nm、700nm或800nm。
二次粒子的平均粒径为9μm～15μm，例如可以是9μm、10μm、11μm、12μm、13μm 或15μm等，优选地，二次粒子的平均粒径为10μm-13μm。申请人通过多次试验发现，二次粒子的平均粒径控制在9μm～15μm这个范围内时，能够避免在二次粒子在循环过程中发生裂化的问题，有利于提高二次粒子的结构稳定性、热稳定性和长循环稳定性。
在其中一些实施例中，第一包覆层的厚度为0.005μm～0.05μm，例如可以是0.005μm、0.01μm、0.015μm、0.02μm、0.025μm、0.03μm、0.035μm、0.04μm、0.045μm或0.05μm。第一包覆层的厚度也可以上述范围内的其他数值，在此不做限定。
在其中一些实施例中，第二包覆层的厚度为0.02μm～0.2μm，例如可以是0.02μm、0.03μm、0.05μm、0.08μm、0.1μm、0.13μm、0.15μm、0.18μm或0.2μm。第二包覆层的厚度也可以上述范围内的其他数值，在此不做限定。
在其中一些实施例中，所述磷酸化合物包括Li 3PO 4及LiN k(PO 4) r中的至少一种，0<k≤2，0<r≤2，N选自Co、Mn、Al、Ti、Zr、Sr、Mg、Y、Ba、Cu、W、Nb、La、Ce、Mo及Sn中的至少一种，具体地，磷酸化合物包括LiMgPO 4、LiSrPO 4、LiAl k(PO 4) r、LiCo k(PO 4) r和LiZr k(PO 4) r中的至少一种，所述组合典型但非限制性实例有：磷酸化合物可以是Li 3PO 4和LiMgPO 4的组合、Li 3PO 4和LiSrPO 4的组合。
该磷酸化合物不仅具有高锂离子电导率，同时能降低正极材料表面残碱。这种内部和表面同时包覆的包覆方式有利于形成空间型、全方位隔离电解液网络和锂离子导电网络。
具体地，第一包覆层的磷酸化合物的制备原料包括磷酸金属盐和锂化合物，为由磷酸金属盐与锂化合物高温反应形成的磷酸化合物，目的是在焙烧过程中同时对正极材料的一次粒子进行磷酸化合物包覆和金属阳离子掺杂；第二包覆层的磷酸化合物的制备原料包括磷酸氢盐；由磷酸氢盐高温反应形成的磷酸化合物。
其中，所述第一包覆层中的磷酸根含量为一次包覆前的正极材料质量的0.03wt％～0.3wt％，优选地，磷酸根含量为0.075wt％～0.175wt％，例如可以是0.075wt％、0.1wt％、0.125wt％、0.15wt％或0.175wt％。
所述第二包覆层中的磷酸根含量为二次包覆前的正极材料质量的0.1wt％～0.7wt％，优选地，磷酸根含量为0.3wt％～0.5wt％，例如可以是0.3wt％、0.35wt％、0.4wt％、0.45wt％或0.5wt％。申请人通过多次试验发现，将磷酸根控制在上述范围内，使得一次粒子或二次粒子能够获得良好的包覆效果，又不至于降低正极材料的容量。
在一些实施方式中，以正极材料的质量为100％计，第一包覆层中的磷酸根含量为0.03wt％～0.3wt％。
在一些实施方式中，以正极材料的质量为100％计，第二包覆层中的磷酸根含量为0.3wt％～0.5wt％。
需要说明的是，一次包覆为正极材料的第一次包覆处理，二次包覆为正极材料的第二次包覆处理。
本申请提供的正极材料，磷酸化合物包覆层中的晶化磷酸根含量为磷酸根总质量的5wt％～50wt％，例如可以是5wt％、10wt％、20wt％、30wt％、40wt％或50wt％。第一包覆层中晶化磷酸根含量控制在5wt％～50wt％使得包覆层与正极材料表面结合 更加稳固，而一次粒子包覆能防止二次颗粒发生裂化时，正极材料内部一次粒子直接接触电解液，抑制副反应，也有利于提高二次粒子的结构稳定性、热稳定性和长循环稳定性，同时由于在一次粒子间的晶界处形成了具有高离子电导的磷酸化合物包覆层，降低了晶界传输阻抗，有利于提高正极材料的倍率性能。
正极材料为三元正极材料，正极材料在4kN/cm 2加压下的粉体电导率大于0.02S/cm，能够有效提高高电流速率下的放电容量。
正极材料的比表面积为0.2m 2/g～1.5m 2/g。优选地，正极材料的比表面积为0.3m 2/g～0.8m 2/g，例如可以是0.3m 2/g、0.4m 2/g、0.5m 2/g、0.6m 2/g、0.7m 2/g、0.8m 2/g等。申请人通过多次试验发现，
本申请还提供一种正极材料的制备方法，所述方法包括以下步骤S100～S200：
S100、将第一混合物进行一次烧结，得到一次烧结物，其中，所述第一混合物包括Ni xCo yM z氧化物及Ni xCo yM z氢氧化物中的至少一种、锂化合物及磷酸金属盐，x+y+z＝1，M选自Mn或Al中的至少一种；
其中，一次烧结物包括多个一次粒子及形成一次粒子表面的第一包覆层；第一包覆层包含磷酸化合物。通过添加磷酸金属盐成份，以在焙烧过程中同时对正极材料的一次粒子进行磷酸化合物包覆和金属阳离子掺杂；而一次粒子包覆能防止二次颗粒发生裂化时，正极材料内部一次粒子直接接触电解液，抑制副反应，这有利于提高二次粒子的结构稳定性、热稳定性和长循环稳定性，同时由于在一次粒子间的晶界处形成了具有高离子电导的磷酸化合物包覆层，降低了晶界传输阻抗，有利于提高正极材料的倍率性能，第一包覆层中的金属阳离子在包覆过程中可掺杂进入正极材料内部，抑制正极材料由层状结构转变为岩盐相结构，抑制金属离子溶出，同时抑制材料晶格氧的释放，提升材料安全性能。
还包括制备第一混合物的步骤，包括以下步骤：
将Ni xCo yM z氧化物及Ni xCo yM z氢氧化物中的至少一种、锂化合物及磷酸金属盐在10℃～50℃下固相混合0.3h～2h。
在具体实施例中，所述锂化合物的添加量为：使得Ni、Co及M的摩尔含量总和与Li的摩尔含量比值为1：(0.95～1.05)。在此范围内，能够降低Li/Ni阳离子混排度，又能够防止烧结产物的表面残锂过高影响加工性能和安全性能。
具体地，所述锂化合物包括碳酸锂、氢氧化锂、醋酸锂、硝酸锂及草酸锂中的至少一种。优选地，锂化合物为氢氧化锂。
所述磷酸金属盐的平均粒径小于0.5μm，例如可以是0.001μm、0.01μm、0.05μm、0.1μm、0.15μm、0.2μm、0.25μm、0.3μm、0.35μm、0.4μm或0.45μm。
所述磷酸金属盐的金属元素选自Co、Mn、Al、Ti、Zr、Sr、Mg、Y、Ba、Cu、W、Nb、La、Ce、Mo及Sn中的至少一种。所述组合典型但非限制性实例有：所述磷酸金属盐可以是SrHPO 4、Zr(HPO 4) 2、MgHPO 4和Al(H 2PO 4) 3中的至少一种，所述典型但非限制性实例有：磷酸金属盐可以是SrHPO 4，还可以是SrHPO 4、Zr(HPO 4) 2的组合物，所述磷酸金属盐还可以包括Mg 3(PO4) 2、Sr 3(PO4) 2、AlPO 4和Zr 3(PO4) 4中的至少一种，所述典型但非限制性实例有：磷酸金属盐可以是Mg 3(PO4) 2，还可以 是AlPO 4和Zr 3(PO4) 4的组合物。
所述磷酸金属盐中的磷酸根含量为所述第一混合物中总质量的0.03wt％～0.3wt％。例如可以是0.03wt％、0.05wt％、0.1wt％、0.15wt％、0.2wt％或0.3wt％等。优选地，所述磷酸金属盐中的磷酸根含量为所述第一混合物中总质量的0.075wt％～0.175wt％。申请人通过多次试验发现，将磷酸根含量控制在此范围内，既可以获得良好一次粒子包覆效果，又不至于降低正极材料的容量。
在将Ni xCo yM z氧化物或Ni xCo yM z氢氧化物、锂化合物以及磷酸金属盐进行混合过程中，混合时间为0.3h～2.0h，例如可以是0.3h、0.4h、0.5h、0.7h、0.8h、1.0h、1.2h、1.5h或2.0h等，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。混合温度为10℃～50℃，例如10℃、15℃、25℃、30℃、35℃、40℃、45℃或50℃等，优选地，混合温度为10℃～40℃。申请人通过多次试验发现，在该混合条件下，既可以充分混合均匀，又可以防止温度过高导致混合原料发生副反应。
需要说明的是，一次烧结物为具有第一包覆层的活性物质，活性物质的通式为Li bNi xCo yM zN wO 2，其中，0.95≤b≤1.05，0.8≤x<1，0<y+z≤0.2，x+y+z＝1，0.0001≤w≤0.003；M选自Mn或Al中的至少一种；N包括Co、Mn、Al、Ti、Zr、Sr、Mg、Y、Ba、Cu、W、Nb、La、Ce、Mo及Sn中的至少一种。
第一包覆层包括磷酸化合物，所述磷酸化合物至少包括Li 3PO 4及LiN k(PO 4) r中的至少一种，0<k≤2，0<r≤2，N选自Co、Mn、Al、Ti、Zr、Sr、Mg、Y、Ba、Cu、W、Nb、La、Ce、Mo及Sn中的至少一种。
可选地，将所述第一混合物置于含氧气氛下于650℃～850℃一次烧结6h～20h，经粉碎、过筛得到一次烧结物，一次烧结物包括多个一次粒子，一次粒子具有第一包覆层。
一次粒子的平均粒径D50为200nm～800nm，例如可以是200nm、300nm、400nm、500nm、600nm、700nm或800nm。
在本实施例中，所述磷酸金属盐与所述锂化合物高温反应形成一次粒子的第一包覆层，所述第一包覆层的厚度为0.005μm～0.05μm，例如可以是0.005μm、0.01μm、0.015μm、0.02μm、0.025μm、0.03μm、0.035μm、0.04μm、0.045μm或0.05μm。第一包覆层的厚度也可以上述范围内的其他数值，在此不做限定。
第一包覆层中的晶化磷酸根含量为磷酸根总质量的5wt％～50wt％，例如可以是5wt％、10wt％、15wt％、20wt％、30wt％、40wt％或50wt％。
所述含氧气氛中的氧气含量≥95％，优选地，一次烧结温度为720℃～800℃，一次烧结温度例如可以是720℃、730℃、740℃、750℃、760℃、770℃、780℃、790℃或800℃等，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。申请人通过多次试验发现，充足的氧气能促进二价镍向三价镍氧化，降低Li/Ni阳离子混排，提升正极材料容量，同时，此温度范围有利于形成层状结构，又不至于导致材料分解。
一次烧结时间例如可以是6h、8h、10h、12h、15h、18h或20h等，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。申请人通过多次试验发现，能有效形成层状结构和均匀的一次粒子包覆层，进而兼顾正极材料的各项性 能指标。
在第一次烧结过程中，通过控制磷酸金属盐的粒径，有利于在一次粒子表面形成均匀的第一包覆层，且第一包覆层中晶化磷酸根含量控制在5wt％～50wt％使得包覆层与正极材料表面结合更加稳固，而一次粒子包覆能防止二次颗粒发生裂化时，正极材料内部一次粒子直接接触电解液，抑制副反应，也有利于提高二次粒子的结构稳定性、热稳定性和长循环稳定性，同时由于在一次粒子间的晶界处形成了具有高离子电导的磷酸化合物包覆层，降低了晶界传输阻抗，有利于提高正极材料的倍率性能。
S200、将所述一次烧结物与磷酸氢盐混合，得到第二混合物，将所述第二混合物二次烧结，得到正极材料。
该正极材料包括二次粒子及形成所述二次粒子表面的第二包覆层，所述二次粒子是一次粒子的聚集体，第二包覆层包含磷酸化合物。
本申请提供的正极材料的制备方法，在第一次烧结过程中实现对活性物质的一次粒子包覆和金属阳离子掺杂，在将第二混合物二次烧结过程中实现对活性物质的二次粒子包覆。本方法不涉及常规正极材料制备过程中的水洗处理，能更好的抑制正极材料表面晶格锂的损失，从而改善其倍率性能和循环稳定性。并且，本方法采用非水洗工艺，减少了水洗工步、干燥工序以及污水产生，同时能降低水洗过程对材料品质一致性的影响。
在一些实施例中，在将所述一次烧结物与磷酸氢盐混合，得到第二混合物过程中，混合时间为0.3h～2.0h，例如可以是0.3h、0.4h、0.5h、0.7h、0.8h、1.0h、1.2h、1.5h或2.0h等，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。混合温度为10℃～50℃，例如10℃、15℃、25℃、30℃、35℃、40℃、45℃或50℃等，优选地，混合温度为10℃～40℃。申请人通过多次试验发现，在该混合条件下，既可以充分混合均匀，又可以防止温度过高导致混合原料发生副反应。
其中，所述磷酸氢盐的平均粒径小于10μm，例如可以是0.01μm、0.1μm、1μm、2μm、4μm、5μm、8μm或9μm等，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。所述磷酸氢盐包括A 2HPO 4、AH 2PO 4中的至少一种，A选自Ni、Co、Mn、Al、Na、K、Ca、NH 4、Ti、Zr、Sr、Mg、Fe、Li、Y、Ba、Cu、W、Nb、La、Ce、Mo、Sn中的至少一种。所述组合典型但非限制性实例有：MgHPO 4和NH 4H 2PO 4的组合，(NH 4) 2HPO 4和Al(H 2PO4) 3的组合等。
所述磷酸氢盐中的磷酸根含量为所述第二混合物中总质量的0.1wt％～0.7wt％，例如可以是0.31wt％、0.2wt％、0.3wt％、0.4wt％、0.5wt％、0.6wt％或0.7wt％。优选地，所述磷酸氢盐中的磷酸根含量为所述第二混合物中总质量的0.3wt％～0.5wt％。申请人通过多次试验发现，将磷酸根控制在该范围内，可以获得良好二次粒子包覆效果，又不至于降低正极材料的容量。
在具体实施方式中，将第二混合物置于含氧气氛下于400℃～800℃二次烧结5h～10h，经粉碎、过筛得到正极材料。正极材料包括多个二次粒子，二次粒子是一次粒子的聚集体。
二次粒子的平均粒径为9μm～15μm，例如可以是9μm、10μm、11μm、12μm、13μm 或15μm等，优选地，二次粒子的平均粒径为10μm-13μm。申请人通过多次试验发现，二次粒子的平均粒径控制在9μm～15μm这个范围内时，能够避免在二次粒子在循环过程中发生裂化的问题，有利于提高二次粒子的结构稳定性、热稳定性和长循环稳定性。
所述第二包覆层的厚度为0.02μm～0.2μm，例如可以是0.02μm、0.03μm、0.05μm、0.08μm、0.1μm、0.13μm、0.15μm、0.18μm或0.2μm。第二包覆层的厚度也可以上述范围内的其他数值，在此不做限定。具体地，所述磷酸氢盐与所述一次烧结物表面残余锂高温反应形成所述第二包覆层，第二包覆层中的晶化磷酸根含量为磷酸根总质量的5wt％～50wt％。
二次烧结中的含氧气氛中的氧气含量≥95％，二次烧结温度为400℃～800℃，例如可以是400℃、500℃、550℃、600℃、650℃、700℃或800℃等，优选地，烧结温度为500℃～700℃，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。申请人通过多次试验发现，在该烧结温度范围内，能使磷酸化合物更加均匀、牢固地包覆在一次烧结物的表面，同时，有利于磷酸氢盐与一次烧结物表面残余锂反应，降低残碱形成高锂离子电导磷酸化合物，改善加工性能和倍率性能，又不至于使烧成物发生分解和锂析出。
二次烧结时间为5h-10h，例如可以是5h、6h、7h、8h、9h或10h等，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。申请人通过多次试验发现，能形成均匀第二包覆层和高锂离子电导磷酸化合物，进而兼顾正极材料的各项性能指标。
可选地，本实施例中采用的混合方式可以为机械混合，例如高混机或VC混合机等。
本申请提供的正极材料，其活性物质的通式为Li bNi xCo yM zN wO 2，其中，0.95≤b≤1.05，0.8≤x<1，0<y+z≤0.2，x+y+z＝1，0.0001≤w≤0.003；M选自Mn及Al中的至少一种；N包括Co、Mn、Al、Ti、Zr、Sr、Mg、Y、Ba、Cu、W、Nb、La、Ce、Mo及Sn中的至少一种。
所述一次粒子的表面形成有第一包覆层，所述二次粒子的表面形成有第二包覆层，第一包覆层、第二包覆层均为磷酸化合物，所述磷酸化合物至少包括Li 3PO 4及LiN k(PO 4) r中的至少一种，0<k≤2，0<r≤2，N选自Co、Mn、Al、Ti、Zr、Sr、Mg、Y、Ba、Cu、W、Nb、La、Ce、Mo及Sn中的至少一种。
本申请提供的正极材料的制备方法，在一次烧结过程中实现对正极材料的一次粒子包覆和金属阳离子掺杂，在二次烧结过程中实现对正极材料二次粒子包覆；本方法不涉及常规正极材料制备过程中的水洗处理，能更好的抑制正极材料表面晶格锂的损失，从而改善其倍率性能和循环稳定性。并且，本方法采用非水洗工艺，减少了水洗工步、干燥工序以及污水产生，同时能降低水洗过程对材料品质一致性的影响。
本申请实施例还提供一种锂离子二次电池，包括如上述正极材料或如上述正极材料的制备方法制备的正极材料。
下面分多个实施例对本申请实施例进行进一步的说明。其中，本申请实施例不 限定于以下的具体实施例。在不变主权利的范围内，可以适当的进行变更实施。
实施例1
一种正极材料的制备方法，包括以下步骤：
(1)将前驱体Ni 0.88Co 0.09Al 0.03(OH) 2、氢氧化锂以及平均粒径D50为0.2μm的SrHPO 4在高混机中混合均匀，控制混合温度为30℃，混合时间1h，得到第一混合物，其中，Li/(Ni+Co+Al)＝1.05，磷酸根含量为第一混合物总质量的0.3wt％；
(2)将第一混合物在750℃氧气含量≥95％的气氛下烧结10h，经粉碎、过筛得到磷酸化合物包覆的一次烧结物Li 1.05Ni 0.88Co 0.09Al 0.03Sr 0.0026O 2，一次烧结物中掺杂有Sr。
(3)将上述一次烧结物Li 1.05Ni 0.88Co 0.09Al 0.03Sr 0.0026O 2与磷酸二氢盐Al(H 2PO 4) 3在高混机中混合均匀，控制混合温度为30℃，混合时间1h，得到第二混合物，其中，磷酸根含量为第二混合物总质量的0.1wt％；
(4)将第二混合物在700℃氧气含量≥95％的气氛下烧结5h，经粉碎、过筛得到磷酸化合物包覆的正极材料Li 1.05Ni 0.88Co 0.09Al 0.03Sr 0.0026O 2。
本实施例得到的正极材料包括多个二次粒子，二次粒子为多个一次粒子聚集体；一次粒子表面形成有第一包覆层，二次粒子的表面形成有第二包覆层。其中，一次粒子的平均粒径为0.6μm，二次粒子的平均粒径为12μm，一次粒子的材质是Li 1.05Ni 0.88Co 0.09Al 0.03Sr 0.0026O 2；第一包覆层的厚度为0.04μm，第一包覆层的物质是Li 3PO 4及LiSr k(PO 4) r；二次粒子是包覆第一包覆层后的一次粒子的聚集体，第二包覆层厚度为0.06μm；第二包覆层的物质是Li 3PO 4及LiAl k(PO 4) r。
实施例1制备得到的正极材料的扫描电子显微镜图片如图1a和图1b所示。
实施例1制备得到的正极材料S1进行性能测试的结果见表1。
实施例2
(1)将前驱体Ni 0.83Co 0.11Mn 0.06(OH) 2、氢氧化锂以及平均粒径D50为0.4μm的Zr(HPO 4) 2在高混机中混合均匀，控制混合温度为25℃，混合时间2h，得到第一混合物，其中，Li/(Ni+Co+Al)＝1.03，磷酸根含量为第一混合物总质量的0.2wt％；
(2)将第一混合物在800℃氧气含量≥95％的气氛下烧结20h，经粉碎、过筛得到磷酸化合物包覆的一次烧结物Li 1.03Ni 0.83Co 0.11Mn 0.06Zr 0.0009O 2，一次烧结物中掺杂有Zr。
(3)将上述一次烧结物Li 1.03Ni 0.83Co 0.11Mn 0.06Zr 0.0009O 2与磷酸二氢盐NH 4H 2PO 4在高混机中混合均匀，控制混合温度为25℃，混合时间2h，得到第二混合物，其中，磷酸根含量为第二混合物总质量的0.3wt％；
(4)将第二混合物在600℃氧气含量≥95％的气氛下烧结8h，经粉碎、过筛得到磷酸化合物包覆的正极材料Li 1.03Ni 0.83Co 0.11Mn 0.06Zr 0.0009O 2。
本实施例得到的正极材料包括多个二次粒子，二次粒子为多个一次粒子聚集体；一次粒子表面形成有第一包覆层，二次粒子的表面形成有第二包覆层。其中，一次 粒子的平均粒径为0.7μm，二次粒子的平均粒径为11.5μm，一次粒子的材质是Li 1.03Ni 0.83Co 0.11Mn 0.06Zr 0.0009O 2，第一包覆层的厚度为0.02μm，第一包覆层的物质是Li 3PO 4及LiZr k(PO 4) r；二次粒子是包覆第一包覆层后的一次粒子的聚集体，第二包覆层厚度为0.10μm；第二包覆层的物质是Li 3PO 4。
实施例2制备得到的正极材料S2进行性能测试的结果见表1。
实施例3
(1)将前驱体Ni 0.88Co 0.09Al 0.03(OH) 2、氢氧化锂以及平均粒径D50为0.05μm的MgHPO 4和中值粒径为0.4μm的Zr(HPO 4) 2在高混机中混合均匀，控制混合温度为20℃，混合时间1.5h，得到第一混合物，其中，Li/(Ni+Co+Al)＝1.00，磷酸根含量为第一混合物总质量的0.1wt％；
(2)将第一混合物在650℃氧气含量≥95％的气氛下烧结20h，经粉碎、过筛得到磷酸化合物包覆的一次烧结物LiNi 0.88Co 0.09Al 0.03Mg 0.0009Zr 0.0004O 2，一次烧结物中掺杂有Mg与Zr。
(3)将上述一次烧结物LiNi 0.88Co 0.09Al 0.03Mg 0.0009Zr 0.0004O 2与磷酸二氢盐(NH 4) 2HPO 4在高混机中混合均匀，控制混合温度为20℃，混合时间1.5h，得到第二混合物，其中，磷酸根含量为第二混合物总质量的0.5wt％；
(4)将第二混合物在500℃氧气含量≥95％的气氛下烧结10h，经粉碎、过筛得到磷酸化合物同时包覆一次粒子和二次粒子的正极材料LiNi 0.88Co 0.09Al 0.03Mg 0.0009Zr 0.0004O 2。
本实施例得到的正极材料包括多个二次粒子，二次粒子为多个一次粒子聚集体；一次粒子表面形成有第一包覆层，二次粒子的表面形成有第二包覆层；其中，一次粒子的平均粒径为0.3μm，二次粒子的平均粒径为12μm，一次粒子的材质是LiNi 0.88Co 0.09Al 0.03Mg 0.0009Zr 0.0004O 2；第一包覆层的厚度为0.01μm，第一包覆层的物质是Li 3PO 4、LiMg k(PO 4) r及LiZr k(PO 4) r；二次粒子是包覆第一包覆层后的一次粒子的聚集体，第二包覆层的厚度为0.15μm；第二包覆层的物质是Li 3PO 4。
实施例3制备得到的正极材料S3进行性能测试的结果见表1。
实施例4
(1)将前驱体Ni 0.88Co 0.09Al 0.03(OH) 2、氢氧化锂以及平均粒径D50为0.2μm的SrHPO 4在高混机中混合均匀，控制混合温度为15℃，混合时间2h，得到第一混合物，其中，Li/(Ni+Co+Al)＝0.95，磷酸根含量为第一混合物总质量的0.03wt％；
(2)将第一混合物在730℃氧气含量≥95％的气氛下烧结6h，经粉碎、过筛得到磷酸化合物包覆的一次烧结物LiNi 0.88Co 0.09Al 0.03Sr 0.0003O 2，一次烧结物中掺杂有Sr。
(3)将上述一次烧结物LiNi 0.88Co 0.09Al 0.03Sr 0.0003O 2与磷酸二氢盐NH 4H 2PO 4和磷酸氢盐Zr(HPO 4) 2在高混机中混合均匀，控制混合温度为15℃，混合时间2h，得到第二混合物，其中，磷酸根含量为第二混合物总质量的0.7wt％；
(4)将第二混合物在550℃氧气含量≥95％的气氛下烧结10h，经粉碎、过筛得到磷酸化合物包覆的正极材料LiNi 0.88Co 0.09Al 0.03Sr 0.0003O 2。
本实施例得到的正极材料包括多个二次粒子，二次粒子为多个一次粒子聚集体；一次粒子表面形成有第一包覆层，二次粒子的表面形成有第二包覆层；其中，一次粒子的平均粒径为0.5μm，二次粒子的平均粒径为12μm，一次粒子的材质是LiNi 0.88Co 0.09Al 0.03Sr 0.0003O 2，第一包覆层的厚度为0.008μm，第一包覆层的物质是Li 3PO 4及LiSr k(PO 4) r；二次粒子是包覆第一包覆层后的一次粒子的聚集体，第二包覆层的厚度为0.18μm；第二包覆层的物质是Li 3PO 4及LiZr k(PO 4) r。
实施例4制备得到的正极材料S4进行性能测试的结果见表1。
实施例5
采用实施例1的制备方法及工艺步骤，实施例5与实施例1不同的是，将第二混合物在400℃氧气含量≥95％的气氛下烧结8h。
本实施例得到的正极材料包括多个二次粒子，二次粒子为多个一次粒子聚集体；一次粒子表面形成有第一包覆层，二次粒子的表面形成有第二包覆层。其中，一次粒子的平均粒径为0.6μm，二次粒子的平均粒径为12μm，一次粒子的材质是Li 1.05Ni 0.88Co 0.09Al 0.03Sr 0.0026O 2；第一包覆层的厚度为0.04μm，第一包覆层的物质是Li 3PO 4及LiSr k(PO 4) r；二次粒子是包覆第一包覆层后的一次粒子的聚集体，第二包覆层厚度为0.1μm；第二包覆层的物质是Li 3PO 4及LiAl k(PO 4) r。
实施例6
采用实施例1的制备方法及工艺步骤，实施例6与实施例1不同的是，Li/(Ni+Co+Al)＝0.99。
实施例7
采用实施例1的制备方法及工艺步骤，实施例7与实施例1不同的是，(1)步骤中采用的是Sr 3(PO4) 2。
对比例1
采用实施例1的制备方法及工艺步骤，对比例1与实施例1不同的是，步骤(1)中不添加SrHPO 4，步骤(2)中不添加Al(H 2PO 4) 3。
对比例1制备得到的正极材料D1进行性能测试的结果见表1。
对比例1制备得到的正极材料的扫描电子显微镜图片如图2a和图2b所示。
对比例2
采用实施例1的制备方法及工艺步骤，对比例2与实施例1不同的是，步骤(2)中不添加Al(H 2PO 4) 3。
对比例2制备得到的正极材料D2进行性能测试的结果见表1。
对比例3
采用实施例1的制备方法及工艺步骤，对比例3与实施例1不同的是，步骤(1)中采用SrHPO 4的中值粒径为10μm。
对比例3制备得到的正极材料D3进行性能测试的结果见表1。
对比例4
采用实施例1的制备方法及工艺步骤，对比例4与实施例1不同的是，将步骤(3)中Al(H 2PO 4) 3替换为AlPO 4，其他所有的操作和原料配比与实施例1相同。
对比例4制备得到的正极材料D4进行性能测试的结果见表1。
测试方法
采用扫描电子显微镜对正极材料进行形貌分析，得到其扫描电子显微镜图片。
采用扣式半电池对所制备正极材料进行电化学性能评估，具体方法如下：将正极材料、SP及聚偏氟乙烯(PVDF)按96:2:2质量比称取，按固含量50％加入N-甲基吡咯烷酮，用高速分散机调成粘稠状浆料，用刮刀均匀涂覆在铝箔上，在80℃烘箱烘烤干后，进行辊压，裁成直径14mm的正极片。以直径16mm的锂片为负极片，以Celgard聚乙烯PP膜为隔膜，以浓度为1mol/L的LiPF6的碳酸酯(DEC/EC体积比1:1)溶液为电解液，在充满氩气的手套箱内进行组装。
采用LAND电池测试系统，在25℃，3.0V～4.3V下进行容量、首次库伦效率、和倍率性能测试，参比容量设置为200mA/g，1C对应电流密度为200mA/g。
采用电位滴定仪测试正极材料表面的锂化合物总量，具体通过盐酸滴定，再通过消耗的盐酸量换算成锂化合物量，计算出残碱含量。
采用离子束切割仪将正极材料颗粒切开，再利用高精度电子能谱仪对切开颗粒的截面进行元素线扫描，从而根据线扫描元素分布曲线计算出磷酸化合物包覆层的分布位置。
采用耐驰差式扫描热仪，以5℃/min，氮气气氛下，密闭高压坩埚中对电极材料进行热稳定性测试，得到差式扫描热曲线，上述电极材料为扣电在0.1C下循环2.5周后满电状态的电极片上刮取的活性物质。
采用布鲁克X射线衍射仪测试正极材料结构组成，再经过X射线图谱精修计算获得包覆层磷酸化合物中晶化磷酸根的含量。
采用高精度四探针仪MCP-T700测试正极材料的粉体电导率，可测试不同压力下，粉体材料的电导率。
上述性能测试的结果如下：
表1.性能比对结果表
Figure PCTCN2021123122-appb-000001
Figure PCTCN2021123122-appb-000002
如图1a和图1b可以看出，实施例1得到的正极材料在二次粒子表面形成了均匀的包覆层，且一次粒子间的间隙被磷酸化合物填充，使得晶界处接触非常紧密，且包覆层与正极材料结合非常紧密。
如图2a和图2b可以看出，对比例1得到的正极材料二次粒子表面相对较光滑，无包覆层；同时，一次粒子间间隙较大，电解液容易浸透至二次粒子内部。
如图3所示，实施例1得到的正极材料的倍率性能优于对比例1，说明不对一次粒子进行磷酸化合物包覆的正极材料的倍率性能明显变差。
如图4所示，实施例1对应正极材料的分解温度及放热量优于对比例1，说明对正极材料的一次粒子和二次粒子进行磷酸化合物包覆有利于提升正极材料的热稳定性。
如表1可知，本申请实施例1～5制备得到的正极材料的电化学性能均较优，放电容量在205mAh/g以上，首次库伦效率可达90％左右，倍率性能良好，长循环性能突出，表面锂含量较低。
表1中实施例1和对比例2的数据对比可知，无论是一次粒子还是二次粒子不进行磷酸化合物包覆时，所制备的正极材料的表面残碱都有偏高，且倍率性能、放电容量、循环性能都受到较大的影响。实施例1和对比例3的数据对比可知，磷酸金属盐(SrHPO 4)粒径等于10μm，粒径过大，不利于磷酸金属盐在一次粒子表面形成均匀的第一包覆层，所制备的正极材料的表面残碱都有偏高，且倍率性能、放电容量、循环性能都受到较大的影响。实施例1与对比例4的数据对比可知，当二次包覆不采用磷酸氢盐时，得到的正极材料表面残碱严重偏高，无法通过加工性能测试。

Claims (13)

  1. 一种正极材料，其特征在于，所述正极材料包括：
    二次粒子，所述二次粒子包括多个一次粒子，所述一次粒子包含活性物质，所述活性物质的化学通式为Li bNi xCo yM zN wO 2，其中，0.95≤b≤1.05，0.8≤x<1，0<y+z≤0.2，x+y+z＝1，0.0001≤w≤0.003；M选自Mn及Al中的至少一种；N为金属；及
    包覆层，所述包覆层包括第一包覆层和第二包覆层，所述第一包覆层形成于所述一次粒子的表面，所述第二包覆层形成于所述二次粒子的表面，所述第一包覆层和第二包覆层均包含磷酸化合物。
  2. 根据权利要求1所述的正极材料，其特征在于，所述Li bNi xCo yM zN wO 2中的N包括Co、Mn、Al、Ti、Zr、Sr、Mg、Y、Ba、Cu、W、Nb、La、Ce、Mo及Sn中的至少一种。
  3. 根据权利要求1或2所述的正极材料，其特征在于，其满足以下条件a～c的至少一者：
    a.所述二次粒子呈球形或者类球形；
    b.所述一次粒子的平均粒径为200nm～800nm；
    c.所述二次粒子的平均粒径为9μm～15μm。
  4. 根据权利要求1～3任一项所述的正极材料，其特征在于，其满足以下条件a～g的至少一者：
    a、所述磷酸化合物包括Li 3PO 4及LiN k(PO 4) r中的至少一种，0<k≤2，0<r≤2，N包括Co、Mn、Al、Ti、Zr、Sr、Mg、Y、Ba、Cu、W、Nb、La、Ce、Mo及Sn中的至少一种；
    b、所述磷酸化合物包括LiMgPO 4、LiSrPO 4、LiAl k(PO 4) r、LiCo k(PO 4) r和LiZr k(PO 4) r中的至少一种；
    c、所述第一包覆层的磷酸化合物的制备原料包括磷酸金属盐和锂化合物；
    d、所述第一包覆层的磷酸化合物的制备原料包括磷酸金属盐和锂化合物，所述磷酸金属盐包括Mg 3(PO4) 2、Sr 3(PO4) 2、AlPO 4和Zr 3(PO4) 4中的至少一种；
    e、所述第一包覆层的磷酸化合物的制备原料包括磷酸金属盐和锂化合物，所述锂化合物包括碳酸锂、氢氧化锂、醋酸锂、硝酸锂及草酸锂中的至少一种；
    f、所述第二包覆层的磷酸化合物的制备原料包括磷酸氢盐；
    g、所述第二包覆层的磷酸化合物的制备原料包括磷酸氢盐，所述磷酸氢盐包括SrHPO 4、Zr(HPO 4) 2、MgHPO 4和Al(H 2PO 4) 3中的至少一种。
  5. 根据权利要求1～4任一项所述的正极材料，其特征在于，其满足以下条件a～g的至少一者：
    a、所述第一包覆层中的磷酸化合物的磷酸根含量为一次包覆前的正极材料的总质量的0.03wt％～0.3wt％；
    b、所述第二包覆层中的磷酸化合物的磷酸根含量为二次包覆前的正极材料的总质量的0.1wt％～0.7wt％；
    c、所述第一包覆层或所述第二包覆层中的磷酸化合物的晶化磷酸根含量为磷酸 根总质量的5wt％～50wt％；
    d、所述第一包覆层的厚度为0.005μm～0.05μm；
    e、所述第二包覆层的厚度为0.02μm～0.2μm；
    f、所述正极材料在4kN/cm 2加压下的粉体电导率大于0.02S/cm；
    g、所述正极材料的比表面积为0.2m 2/g～1.5m 2/g。
  6. 根据权利要求1～5任一项所述的正极材料，其特征在于，其满足以下条件a～b的至少一者：
    a.以正极材料的质量为100％计，第一包覆层中的磷酸根含量为0.03wt％～0.3wt％；
    b.以正极材料的质量为100％计，第二包覆层中的磷酸根含量为0.3wt％～0.5wt％。
  7. 一种正极材料的制备方法，其特征在于，所述方法包括以下步骤：
    将第一混合物进行一次烧结，得到一次烧结物，其中，所述第一混合物包括Ni xCo yM z氧化物及Ni xCo yM z氢氧化物中的至少一种、锂化合物及磷酸金属盐，x+y+z＝1，M选自Mn或Al中的至少一种，所述一次烧结物包括多个一次粒子及形成所述一次粒子表面的第一包覆层，所述第一包覆层包含磷酸化合物；及
    将所述一次烧结物与磷酸氢盐混合，得到第二混合物，将所述第二混合物进行二次烧结，得到正极材料，所述正极材料包括二次粒子及形成所述二次粒子表面的第二包覆层，所述二次粒子包括多个聚集的一次粒子，所述第二包覆层包含磷酸化合物。
  8. 根据权利要求7所述的制备方法，其特征在于，其满足以下条件a～g的至少一者：
    a、所述锂化合物的添加量为：使得Ni、Co及M的摩尔含量总和与Li的摩尔含量比值为1：(0.95～1.05)；
    b、所述锂化合物包括碳酸锂、氢氧化锂、醋酸锂、硝酸锂及草酸锂中的至少一种；
    c、所述磷酸金属盐的平均粒径小于0.5μm；
    d、所述磷酸金属盐的金属元素选自Co、Mn、Al、Ti、Zr、Sr、Mg、Y、Ba、Cu、W、Nb、La、Ce、Mo及Sn中的至少一种；
    e、所述磷酸氢盐包括A 2HPO 4、AH 2PO 4中的至少一种，A选自Ni、Co、Mn、Al、Na、K、Ca、NH 4、Ti、Zr、Sr、Mg、Fe、Li、Y、Ba、Cu、W、Nb、La、Ce、Mo及Sn中的至少一种；
    f、所述磷酸金属盐中的磷酸根含量为所述第一混合物总质量的0.03wt％～0.3wt％；
    g、所述磷酸氢盐中的磷酸根含量为所述第二混合物总质量的0.1wt％～0.7wt％。
  9. 根据权利要求7或8所述的制备方法，其特征在于，其满足以下条件a～i的至少一者：
    a、所述磷酸金属盐包括Mg 3(PO4) 2、Sr 3(PO4) 2、AlPO 4和Zr 3(PO4) 4中的至少一种；
    b、所述磷酸氢盐包括SrHPO 4、Zr(HPO 4) 2、MgHPO 4和Al(H 2PO 4) 3中的至少一种；
    c、所述磷酸化合物至少包括Li 3PO 4及LiN k(PO 4) r中的至少一种，0<k≤2，0<r≤2， N选自Co、Mn、Al、Ti、Zr、Sr、Mg、Y、Ba、Cu、W、Nb、La、Ce、Mo、Sn中的至少一种；
    d、所述磷酸化合物包括LiMgPO 4、LiSrPO 4、LiAl k(PO 4) r、LiCo k(PO 4) r、LiZr k(PO 4) r中的至少一种；
    e、所述第一包覆层或所述第二包覆层中的磷酸化合物的晶化磷酸根含量为磷酸根总质量的5wt％～50wt％；
    f、所述一次粒子的平均粒径为200nm～800nm；
    g、所述第一包覆层的厚度为0.005μm～0.05μm；
    h、所述二次粒子的平均粒径为9μm～15μm；
    i、所述第二包覆层的厚度为0.02～0.2μm。
  10. 根据权利要求7～9任一项所述的制备方法，其特征在于，所述第一混合物包括以下方法制备：
    将Ni xCo yM z氧化物及Ni xCo yM z氢氧化物中的至少一种、锂化合物及磷酸金属盐在10℃～50℃下固相混合0.3h～2h。
  11. 根据权利要求7～10任一项所述的制备方法，其特征在于，其满足以下条件a至d的至少一者：
    a、所述一次烧结在含氧气氛下进行；
    b、所述一次烧结在含氧气氛下进行，所述一次烧结的含氧气氛的氧气含量大于等于95％；
    c、所述一次烧结的温度为650℃～850℃；
    d、所述一次烧结的时间为6h～20h。
  12. 根据权利要求7～11任一项所述的制备方法，其特征在于，其满足以下条件a至f的至少一者：
    a、所述一次烧结物与磷酸氢盐混合的温度为10℃～50℃；
    b、所述一次烧结物与磷酸氢盐混合的时间为0.3h～2h；
    c、所述二次烧结在含氧气氛下进行；
    d、所述二次烧结在含氧气氛下进行，所述二次烧结的含氧气氛的氧气含量大于等于95％；
    e、所述二次烧结的温度为400℃～800℃；
    f、所述二次烧结的时间为5h～10h。
  13. 一种锂离子二次电池，其特征在于，包括如权利要求1-6任一项所述正极材料或如权利要求7～12任一项所述正极材料的制备方法制备的正极材料。
PCT/CN2021/123122 2020-10-12 2021-10-11 正极材料及其制备方法、锂离子二次电池 Ceased WO2022078300A1 (zh)

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