CN114506830A - Preparation method of phosphate coated positive electrode active material - Google Patents
Preparation method of phosphate coated positive electrode active material Download PDFInfo
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- CN114506830A CN114506830A CN202011284593.0A CN202011284593A CN114506830A CN 114506830 A CN114506830 A CN 114506830A CN 202011284593 A CN202011284593 A CN 202011284593A CN 114506830 A CN114506830 A CN 114506830A
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- H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
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Abstract
The invention relates to a preparation method of a phosphate-coated positive electrode active material, which comprises the following steps: adding a phosphorus source and ammonia water into deionized water, and mixing to form a coating dispersion liquid, wherein the phosphorus source is one or more of iron phosphate, nickel phosphate, cobalt phosphate, manganese phosphate, copper phosphate and magnesium phosphate; coating the coating dispersion liquid on the surface of a positive active material with a spinel structure, and drying to obtain powder; and sintering the dry powder at 200-600 ℃.
Description
Technical Field
The invention relates to the field of lithium ion batteries, in particular to a preparation method of a phosphate-coated positive active material.
Background
Lithium ion secondaryCompared with other rechargeable battery systems, the battery has the advantages of high working voltage, light weight, small volume, no memory effect, low self-discharge rate, long cycle life, high energy density and the like, and is widely applied to mobile terminal products such as mobile phones, notebook computers, tablet computers and the like. In recent years, electric vehicles have been rapidly developed under the push of governments and automobile manufacturers in various countries from the viewpoint of environmental protection, and lithium ion secondary batteries have become an ideal power source for a new generation of electric vehicles by virtue of their excellent performance. Currently, positive active materials of lithium ion secondary batteries that are of interest can be roughly classified into three categories: with lithium cobaltate (LiCoO)2) A layered material represented by lithium iron phosphate (LiFePO)4) Olivine-type material typified by lithium manganate (LiMn)2O4) Is a typical spinel structure material. Among these materials, spinel-structured materials have been widely studied because of their advantages of environmentally friendly raw materials, low cost, simple process, high safety, good rate capability, and the like.
Manganese-based high voltage materials, as an advanced positive active material, are considered to be the most likely positive active material for the next generation of high performance lithium batteries. Particularly, the theoretical specific capacity of the lithium nickel manganese oxide with the spinel structure is 146.7mAh/g, and the working voltage is 4.7Vvs+The theoretical capacity density can reach 695Wh/kg, and the lithium ion secondary battery material is an ideal material for the lithium ion secondary battery for the electric vehicle in the future. The lithium-rich material with the layered structure has the specific capacity of more than 350mAh/g, and belongs to a future better anode material.
However, with current manganese-based high-voltage materials, H is generated at high voltage due to conventional carbonate-based electrolytes2O (even fresh electrolyte inevitably contains trace amount of H2O)，H2O and conventional carbonate electrolyte (containing LiPF)6) HF is generated by the reaction and further corrodes the surface of the anode material, so that the surface of the anode active material is dissolved, and finally, the active substances are reduced. Meanwhile, for the nickel lithium manganate positive electrode active material, Mn ions dissolved in the positive electrode can migrate to the negative electrode and deposit on the negative electrode, so that solid electrolysis on the surface of the negative electrode is promotedThe interface film (SEI film) decomposes, consuming active lithium in the battery system, resulting in a decline in capacity.
In order to solve the technical problem, people propose to carry out coating modification on the positive electrode active material, wherein the lithium phosphate is adopted for coating, so that a good effect can be achieved, the lithium phosphate is high-pressure resistant, can absorb hydrofluoric acid, does not contain transition metal ions, and has no side effect on the battery. The conventional lithium phosphate coating method includes: (1) mixing a positive electrode material to be coated with lithium phosphate in a solid phase and calcining the mixture to coat the positive electrode material; (2) and coating the positive electrode material to be coated with lithium phosphate by using a sol-gel method. However, in the conventional lithium phosphate coating method, lithium phosphate is difficult to uniformly distribute on the surface of the positive active material due to mismatching of crystal lattices, and meanwhile, the coating effect of the conventional solid phase coating method is influenced by the particle size of the coating material, the larger particle size of the coating material is not beneficial to coating of the coating material, and the coating material needs to be nanocrystallized to obtain smaller particles of the coating material, so that the cost is higher. In the coating process of the sol-gel, organic matters such as citric acid and the like are introduced into the system, the organic matters can be removed only by sintering at a higher temperature, and most of coating materials are agglomerated at the high temperature, so that the subsequent uniform surface coating is not facilitated.
Disclosure of Invention
Based on this, it is necessary to provide a method for preparing a phosphate-coated positive electrode active material, which enables lithium phosphate to be uniformly distributed on the surface of the positive electrode active material.
The invention provides a preparation method of a phosphate-coated positive electrode active material, which comprises the following steps:
step S10, adding a phosphorus source and ammonia water into deionized water, and mixing to form a coating dispersion liquid, wherein the phosphorus source is one or more of iron phosphate, nickel phosphate, cobalt phosphate, manganese phosphate, copper phosphate and magnesium phosphate;
step S20, coating the coating dispersion liquid on the surface of a positive active material with a spinel structure, and drying to obtain powder; and
and step S30, sintering the dry powder at 200-600 ℃.
In one embodiment, the positive active material has a chemical formula of LiMn2-xAxOyWherein x is more than or equal to 0 and less than or equal to 0.7, y is more than or equal to 3.8 and less than or equal to 4.2, and A is selected from one or more of alkaline earth metal elements, metalloid elements or transition metal elements.
In one embodiment, A is selected from one or more of Li, Mg, Zn, Ni, Mn, Fe, Co, Ti, Y, Sc, Ru, Cu, Mo, Ge, W, Zr, Ca, Ta, Al, Nb, B, Si, F, S, P, and Sr.
In one embodiment, the formula LiMn2-xAxOyWherein A is selected from Co and/or Ti;
preferably, 0. ltoreq. x. ltoreq.0.5;
preferably, the particle size of the positive electrode active material is 0.1 to 30 μm, preferably 0.2 to 10 μm, and more preferably 0.2 to 0.5 μm.
In one embodiment, the coating dispersion further contains a lithium precursor, and the lithium precursor is lithium hydroxide.
In one embodiment, the molar concentration of the ammonia water is 5-50 mol/L, and the mass ratio of the phosphorus source, the ammonia water and the lithium precursor is (1-5): (20-50): (0.1-2).
In one embodiment, the mass ratio of the coating dispersion liquid to the positive electrode active material is (30-300): (20-200).
In one embodiment, step S20 includes the following steps:
placing the positive active material in a closed container with the ambient temperature of 50-200 ℃, and rolling the positive active material by using airflow or mechanical stirring;
spraying the coating dispersion liquid into the closed container at the spraying speed of 1-200 g/s; and
and after the spraying is finished, drying at 100-200 ℃.
In one embodiment, step S20 includes the following steps:
and (3) dipping the positive electrode active material in the coating dispersion liquid, and drying by adopting a spray drying method or a vacuum rake drying method.
In one embodiment, the method of spray drying comprises the steps of:
and spraying the coating dispersion liquid impregnated with the positive electrode active material into a cavity with hot air circulation at the injection speed of 5 g/min-5 kg/min, and staying in the cavity until drying, wherein the temperature of the hot air is 100-200 ℃.
In one embodiment, the method of spray drying comprises the steps of:
and (3) heating the coating dispersion liquid impregnated with the positive electrode active material in a closed container at the temperature of 80-200 ℃, and stirring and vacuumizing while heating to volatilize the solvent.
According to the preparation method of the phosphate-coated positive active material, provided by the invention, phosphate containing metal elements is used as a phosphorus source, ammonia water is used as a solvent to form a coating solution, and the ammonia water can be used for complexing the phosphate to form a complex, so that the phosphate can be more uniformly formed on the surface of the positive active material without agglomeration. Such transition layer is favorable to the coating evenly distributed on spinel structure's positive active material, plays the effect of the positive active material of firm coating and spinel structure, forms stable structure between coating and spinel structure's positive active material.
Drawings
Fig. 1 is a flowchart of a method for preparing a phosphate-coated positive active material according to the present invention.
Detailed Description
To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
Other than as shown in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients, physical and chemical properties, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about". For example, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can be suitably varied by those skilled in the art in seeking to obtain the desired properties utilizing the teachings disclosed herein. The use of numerical ranges by endpoints includes all numbers within that range and any range within that range, for example, 1 to 5 includes 1, 1.1, 1.3, 1.5, 2, 2.75, 3, 3.80, 4, and 5, and the like.
A core-shell structure is generally defined as an ordered assembly of one material coated with another material by chemical bonding or other forces. The core-shell like structure "core" and "shell" as defined in the present invention are actually integral. The modified lithium nickel manganese oxide material structure comprises two phases, so that the microstructure of a surface layer is different from the microstructure of the interior of the material, the interior of the material formed in the way is called a core, the surface layer is called a shell, and the material with the structure is defined as a material with a core-shell-like structure.
Referring to fig. 1, an embodiment of the present invention provides a method for preparing a phosphate-coated positive active material, including the following steps:
s10, adding a phosphorus source and ammonia water into deionized water, and mixing to form a coating dispersion liquid, wherein the phosphorus source is one or more of iron phosphate, nickel phosphate, cobalt phosphate, manganese phosphate, copper phosphate and magnesium phosphate;
s20, coating the coating dispersion liquid on the surface of the positive active material with a spinel structure, and drying to obtain powder; and
s30, sintering the dry powder at 200-600 ℃.
According to the preparation method of the phosphate-coated positive active material, provided by the invention, phosphate containing metal elements is used as a phosphorus source, ammonia water is used as a solvent to form a coating solution, and the ammonia water can be used for complexing the phosphate to form a complex, so that the phosphate can be more uniformly formed on the surface of the positive active material without agglomeration. Such transition layer is favorable to the coating evenly distributed on spinel structure's positive active material, plays the effect of the positive active material of firm coating and spinel structure, forms stable structure between coating and spinel structure's positive active material.
Preferably, the phosphorus source is cobalt phosphate and/or manganese phosphate.
The chemical formula of the positive active material LiMn2-xAxOyIn the formula, x is more than or equal to 0 and less than or equal to 0.7, y is more than or equal to 3.8 and less than or equal to 4.2, and the A element is a doping element used for replacing the transition metal element Mn. In some embodiments, the doping element A can be represented by the formula Σ Wi Ai, Wi being the atomic percentage of Ai in the entire doping element A, Σ Wi ≦ 1, wherein 1 ≦ i ≦ 16, preferably 1 ≦ i ≦ 5, more preferably 1 ≦ i ≦ 3.
In one embodiment, A is selected from one or more of Li, Mg, Zn, Ni, Mn, Fe, Co, Ti, Y, Sc, Ru, Cu, Mo, Ge, W, Zr, Ca, Ta, Al, Nb, B, Si, F, S, P, and Sr. Preferably, A is selected from Co and/or Ti.
Further preferably, the formula LiMn2-xAxOyWhere 0. ltoreq. x.ltoreq.0.5, in some implementationsIn examples, x is 0, and in some embodiments, 0.1 ≦ x ≦ 0.5.
In a preferred embodiment, the chemical formula of the positive active material is LiMn2O4Or LiNi0.5Mn1.5O4。
The particle size of the positive electrode active material may be any value between 0.1 μm and 30 μm, and may be, for example, 0.2 μm, 0.5 μm, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, preferably 0.2 μm to 10 μm, and more preferably 0.2 μm to 0.5 μm.
In some embodiments, the coating dispersion further comprises a lithium precursor. The lithium precursor can supplement lithium to the interface of the active material, and provides a lithium source for the subsequent generation of lithium phosphate or lithium phosphate salt, preferably, the lithium precursor is lithium hydroxide.
In the phosphate coating layer formed by the preparation method of the phosphate-coated positive electrode active material, the phosphate is lithium phosphate or lithium phosphate containing nickel, cobalt, manganese, copper or magnesium metal elements. Such as LiCoPO4、LiNiPO4、LiMnPO4、LiCuPO4、LiMgPO4And Li3PO4One or more of (a).
The molar concentration of the ammonia water is 5-50 mol/L. The ammonia water is used as a solvent, is volatile, and can effectively avoid introducing other impurities in the sintering process.
The molar ratio of the phosphorus source to the ammonia water to the lithium precursor can be (1-5): (20-50): (0.1-2).
The coating dispersion liquid and the positive electrode active material may be in a mass ratio of (30-300): (20-200).
In step S20, there are various methods of forming the coating dispersion liquid on the surface of the positive electrode active material having a spinel structure and drying the coating dispersion liquid to obtain a powder.
In an embodiment, the method for preparing the dry powder may include the following steps:
s21, placing the positive electrode active material in a closed container with the ambient temperature of 50-200 ℃, and rolling the positive electrode active material by using airflow or mechanical stirring;
s23, spraying the coating dispersion liquid into the closed container at a spraying speed of 1 g/S-200 g/S; and
s25, drying at 100-200 ℃ after spraying.
In the liquid phase synthesis method, because of solid-liquid contact, continuous interface reaction exists among all phases, and in order to avoid influence caused by the interface reaction, better modification can be realized by effectively controlling the interface reaction, and the positive active material with better electrochemical performance is prepared. Preferably, the method of spraying the coating dispersion liquid on the surface of the positive active material can control the solid-liquid interface reaction time and accurately control the thickness of the coating dispersion liquid formed on the positive active material, so that the method has a better modification effect, and the prepared phosphate coating positive active material has better electrochemical performance.
Preferably, in step S23, the coating dispersion has a solid content of 20% to 40% and the spray speed is 1g/S to 10 g/S. The thickness of the coating dispersion liquid formed on the positive electrode active material can be adjusted by adjusting the solid content of the coating dispersion liquid and the spraying speed of the coating dispersion liquid, and the solid content of the coating dispersion liquid and the spraying speed of the coating dispersion liquid in the range can improve the electrochemical performance of the positive electrode active material.
The ambient temperature of the closed container is preferably 80 to 120 ℃.
In another embodiment, the method for preparing the dry powder may include the steps of:
and S22, dipping the positive electrode active material in the coating dispersion liquid, and drying by adopting a spray drying method or a vacuum rake drying method.
Further, when the dry powder is prepared in step S22, the coating dispersion liquid preferably further includes an easily evaporable stabilizer. In step S22, the solid phase and the liquid phase in the coating dispersion liquid are likely to be layered or settled during the drying process, and the addition of the stabilizer can effectively avoid the separation of the solid phase and the liquid phase, which is beneficial to the uniform distribution of the coating dispersion liquid on the surface of the positive active material, so that the doping interface of the finally prepared positive active material is more uniform.
The stabilizer may include one or more of polyvinyl alcohol, polyethylene glycol, acrylonitrile multipolymer, polybutyl acrylate, and polyacrylonitrile.
In one embodiment, step S22 is performed by spray drying, which includes the following steps:
s24, spraying the coating dispersion liquid impregnated with the positive electrode active material into a cavity with hot air circulation at a spraying speed of 5 g/min-5 kg/min, and staying in the cavity until drying, wherein the temperature of the hot air is 100-200 ℃.
The above-mentioned spray drying method can spray the coating dispersion liquid impregnated with the positive electrode active material into extremely fine mist-like droplets, and the droplets can be rapidly vaporized in a hot air circulation to form a dried powder. Therefore, the method has higher efficiency of preparing dry powder.
In another embodiment, step S22 is performed by a vacuum rake drying method, which includes the following steps:
and S28, heating the coating dispersion liquid impregnated with the positive electrode active material in a closed container at the temperature of 80-200 ℃, and stirring and vacuumizing while heating to volatilize the solvent.
The vacuum rake drying method can control the interface condition of the modified material by controlling the heating temperature and the stirring speed, and adjust the interface reaction between the phosphorus source and the anode active material to be modified, so that the finally formed phosphate is coated more uniformly.
The heating temperature of the vacuum rake drying method can be 80-200 ℃, and preferably 100-150 ℃. The stirring speed may be 20 to 400 revolutions per minute, preferably 50 to 100 revolutions per minute.
In step S30, the sintering may be performed under oxygen, air, nitrogen, an atmosphere containing a reducing gas (e.g., hydrogen), or an inert atmosphere (e.g., argon). Preferably, the specific operation of the sintering process is as follows: heating to 200-600 ℃ at a heating rate of 0.5-10 ℃/min, sintering for 0.5-10 h, and cooling to room temperature at a cooling rate of 0.5-10 ℃/min.
The invention further provides a phosphate-coated positive electrode active material obtained by the preparation method of the phosphate-coated positive electrode active material.
The phosphate-coated positive active material includes lithium-containing compound particles having a spinel structure and a phosphate coating layer coated on the surfaces thereof. The lithium-containing compound particles have a transition layer containing a diffusion element that enters the lithium-containing compound particles due to sintering.
In one embodiment, the lithium-containing compound particles have the chemical formula LiMn2-xAxOyWherein x, y and A are as defined above.
In one embodiment, the diffusion element is one or more of Ni, Co, Mn, Cu and Mg.
The phosphate in the phosphate coating layer may be LiCoPO4、LiNiPO4、LiMnPO4、LiCuPO4、LiMgPO4And Li3PO4One or more of (a).
In some embodiments, the phosphate is Li3PO4The diffusion element is one or more of Ni, Co, Mn and Cu. In other embodiments, the phosphate is LiMgPO4And the diffusion element is Mg.
The thickness of the phosphate coating layer may be any value between 1nm and 50nm, and for example, the phosphate coating layer further includes 2nm, 5nm, 8nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm and 45nm, and preferably 5nm to 15 nm.
The coverage of the phosphate coating layer on the surface of the lithium-containing compound particle may be any value between 1% and 100%. In some embodiments, the phosphate coating has a coverage on the surface of the lithium-containing compound particles from a low endpoint value of 10%, 20%, 30%, 40%, 50%, or 60% to a high endpoint value of 50%, 60%, 70%, 80%, or 90%. For example, in some preferred embodiments, the phosphate coating has a coverage of 20% to 90% on the surface of the lithium-containing compound particles, and in some more preferred embodiments, 60% to 80%.
In some embodiments, the phosphate coating may consist of a single layer of phosphate particles. In some embodiments, the particle size of the phosphate particles is from 1nm to 50nm, and in some preferred embodiments the particle size of the phosphate particles is from 5nm to 20 nm.
The thickness of the transition layer may be any value between 0.1 μm and 15 μm, and further includes, for example, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, and 14 μm.
In some preferred embodiments, the thickness of the transition layer is 100nm to 250 nm.
The transition layer may be distributed between 0nm and 10nm, preferably between 0nm and 5nm, from the surface of the lithium-containing compound particle.
The phosphate-coated cathode active material provided according to the present invention, wherein the phosphate coating layer and the transition layer may be measured by any method known in the art. For example, the type of the phosphate coating layer can be determined by X-ray diffraction spectrum and X-ray photoelectron spectrum, and the distribution and content of each element in the transition layer can be measured by X-ray energy spectrum line scanning of a spherical aberration correction transmission electron microscope.
Further, the invention also provides a positive electrode of the lithium ion secondary battery, which comprises a positive electrode current collector and a positive electrode active material layer positioned on the positive electrode current collector, wherein the positive electrode active material layer comprises the phosphate-coated positive electrode active material.
As the positive electrode current collector, a conductive member formed of a highly conductive metal as used in a positive electrode of a lithium ion secondary battery of the related art is preferable. For example, aluminum or an alloy including aluminum as a main component may be used. The shape of the positive electrode current collector is not particularly limited, since it may vary depending on the shape of the lithium ion secondary battery, etc. For example, the positive electrode collector may have various shapes such as a rod shape, a plate shape, a sheet shape, and a foil shape.
The positive active material layer further includes a conductive additive and a binder.
The conductive additive may be a conductive additive that is conventional in the art, and the present invention is not particularly limited thereto. For example, in some embodiments, the conductive additive is carbon black (e.g., acetylene black or Ketjen black).
The binder may be a binder conventional in the art, and the present invention is not particularly limited thereto, and may be composed of polyvinylidene fluoride (PVDF), or carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR). In some embodiments, the binder is polyvinylidene fluoride (PVDF).
Still further, the present invention also provides a lithium ion secondary battery comprising:
the positive electrode as described above;
a negative electrode including a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector;
a separator and an electrolyte.
As a current collector of the negative electrode,
the negative electrode, separator and electrolyte may employ negative electrode current collectors, separators and electrolyte materials that are conventional in the art, and the present invention is not particularly limited thereto.
The negative electrode current collector may be copper, and the shape of the negative electrode current collector is also not particularly limited, and may be rod-shaped, plate-shaped, sheet-shaped, and foil-shaped, and may vary depending on the shape of the lithium ion secondary battery, and the like. The negative active material layer includes a negative active material, a conductive additive, and a binder. The negative active material, conductive additive and binder are also conventional in the art. In some embodiments, the negative active material is metallic lithium. The conductive additives and binders are as described above and will not be described in detail here.
The separator may be a separator used in a general lithium ion secondary battery, and examples thereof include a microporous film made of polyethylene or polypropylene; a multi-layer film of a porous polyethylene film and polypropylene; nonwoven fabrics formed of polyester fibers, aramid fibers, glass fibers, and the like; and a base film formed by adhering ceramic fine particles such as silica, alumina, and titania to the surfaces thereof. In some embodiments, the separator is a three layer film of PP/PE/PP coated on both sides with alumina.
The electrolyte may include an electrolyte and a non-aqueous organic solvent. The electrolyte is preferably LiPF6、LiBF4、LiSbF6、LiAsF6. The non-aqueous organic solvent can be carbonate, ester and ether. Among them, carbonates such as Ethylene Carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC) and ethylmethyl carbonate (EMC) can be preferably used. In some embodiments, the electrolyte is LiPF6The non-aqueous electrolyte of Ethylene Carbonate (EC)/dimethyl carbonate (DMC) with the concentration of 1mol/L, wherein the volume ratio of EC to DMC is 1: 1.
The following are specific examples, which are intended to provide further detailed description of the present invention and to assist those skilled in the art and researchers in understanding the present invention, and the technical conditions and the like are not intended to limit the present invention. Any modification made within the scope of the claims of the present invention is within the scope of the claims of the present invention.
Example 1
(1) 0.3g of nickel phosphate, 0.15g of lithium hydroxide and 25mL of ammonia water (molar concentration: 2mol/L) were uniformly mixed to form a coating dispersion.
(2) Mixing 10g LiMn2O4The (particle size is 200nm) is placed in a reaction chamber with the ambient temperature of 100 ℃, and the positive active material LiMn is made by airflow2O4And (4) rolling.
(3) And (2) spraying the coating dispersion liquid in the step (1) into a reaction bin from a nozzle with the diameter of 1 mu m-1 mm, so that the coating dispersion liquid is formed on the surface of the positive active material.
(4) And after the coating liquid is sprayed, directly drying at 120 ℃ to obtain dry powder.
(5) And (4) sintering the dried powder in the step (4) in the air at 450 ℃ for 3 hours to obtain the phosphate coated positive electrode active material.
Example 2
(1) 0.3g of nickel phosphate, 0.1g of lithium hydroxide and 25mL of aqueous ammonia (molar concentration: 2mol/L) were uniformly mixed to form a coating dispersion.
(2) Mixing 10g LiMn2O4(particle diameter of 200nm) was immersed in the coating dispersion in step (1), and then the immersion solution was sprayed from a nozzle having a diameter of 1 μm to 1mm into a chamber having circulation of hot air at a temperature of 100 ℃.
(3) And after the coating liquid is sprayed, drying at 100 ℃ to obtain dry powder.
(4) And (4) sintering the dried powder in the step (3) in the air at 450 ℃ for 3 hours to obtain the phosphate coated positive electrode active material.
Example 3
(1) 0.3g of nickel phosphate, 0.1g of lithium hydroxide and 25mL of aqueous ammonia (molar concentration: 2mol/L) were uniformly mixed to form a coating dispersion.
(2) Mixing 10g LiMn2O4And (2) dipping the coating dispersion liquid (with the particle size of 200nm) in the step (1), then putting the dipping solution into a closed cavity for heating, stirring and vacuumizing while heating, wherein the heating temperature is 120 ℃, and the stirring speed is 60 revolutions per minute, so that the solvent is volatilized, and the dry powder is obtained.
(3) And (3) sintering the dried powder in the step (2) in the air at 450 ℃ for 3 hours to obtain the phosphate coated positive electrode active material.
Example 4
Substantially the same as in example 1 except that LiMn was used2O4Replacement with LiNi0.5Mn1.5O4。
Example 5
The preparation method was substantially the same as that of example 1 except that nickel phosphate was replaced with cobalt phosphate.
Example 6
Substantially the same as in example 1 except that nickel phosphate was replaced with manganese phosphate.
Example 7
The preparation method was substantially the same as that of example 1 except that nickel phosphate was replaced with copper phosphate.
Example 8
Substantially the same as in example 1 except that nickel phosphate was replaced with magnesium phosphate.
Comparative example 1
The procedure was substantially the same as in example 1, except that aqueous ammonia was not added.
Performance testing
The phosphate-coated positive active materials prepared in examples 1 to 8 were assembled into a button cell according to the following procedure.
(1) Preparing a positive electrode plate, dispersing the positive active material prepared in the example, carbon black as a conductive additive and polyvinylidene fluoride (PVDF) as a binder in N-methyl adjacent pyrrole (NMP) according to a weight ratio of 80:10:10, and uniformly mixing to prepare uniform positive electrode slurry. Uniformly coating the uniform positive electrode slurry on an aluminum foil current collector with the thickness of 15 mu m, drying at 55 ℃ to form a pole piece with the thickness of 100 mu m, and rolling the pole piece under a roller press (the pressure is about 1MPa 1.5 cm)2) Cutting the anode plate into round pieces with the diameter of 14mm, then placing the round pieces in a vacuum oven to be dried for 6 hours at the temperature of 120 ℃, naturally cooling the round pieces, taking out the round pieces and placing the round pieces in a glove box to be used as anode pieces.
(2) Assembling lithium ion secondary battery
And (2) in a glove box filled with inert atmosphere, taking metal carp as a negative electrode of the battery, placing a PP/PE/PP diaphragm coated with alumina on two sides between the positive electrode and the negative electrode, dropwise adding 1M common carbonate electrolyte, taking the positive electrode piece prepared in the step (1) as a positive electrode, and assembling into a button battery with the model of CR 2032.
High-temperature cycle testing:
and standing the prepared button cell for 10 hours at room temperature (25 ℃), then carrying out charge-discharge activation on the button cell, and then carrying out charge-discharge cycle test on the prepared button cell by adopting a blue cell charge-discharge tester. The method comprises the steps of firstly cycling at a rate of 0.1C for 1 week under the condition of room temperature (25 ℃), and then continuing cycling at a rate of 0.2C for 4 weeks, wherein the charging and discharging voltage range of the battery is controlled to be 3V-4.3V. Then, the button cell is transferred to a high-temperature environment of 55 ℃, the circulation is continued for 50 weeks at the multiplying power of 0.2C, and the charging and discharging voltage range of the cell is controlled to be still 3V-4.3V.
In the performance test of the button cell prepared from the positive active material of the example 2, the charge and discharge voltage of the cell is controlled to be 3.5V-4.9V.
And adopting the positive active material LiMn before coating2O4、LiNi0.5Mn1.5O4As a control, the measured data are shown in Table 1.
TABLE 1 electrochemical Properties of Positive electrode active Material of examples of the present invention
From the data in the above table, it can be seen that LiMn is compared to the original positive electrode active material2O4、LiNi0.5Mn1.5O4And in contrast to the comparative example 1, the positive active materials prepared in the embodiments 1 to 8 of the present invention have better electrochemical properties.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
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| CN120376597A (en) * | 2025-04-03 | 2025-07-25 | 中创新航科技集团股份有限公司 | Positive electrode active material, positive electrode plate and lithium ion battery |
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