Positive electrode material, preparation method thereof and lithium ion battery

Abstract

The invention relates to the field of lithium ion battery materials, and discloses a positive electrode material, a preparation method thereof and a lithium ion battery. The positive electrode material comprises an equiaxed crystal stacking inner core and a plurality of coating layers coating the equiaxed crystal stacking inner core, in the coating layer, from inside to outside, odd-numbered layers are columnar crystal radial arrangement layers, and even-numbered layers are equiaxed crystal stacking layers; the total layer number of the coating layers is r, r is larger than or equal to 3 and smaller than or equal to 13, and r is an odd number; the chemical composition of the isometric crystal stacking inner core and the isometric crystal stacking layer meets the chemical formula LiNix1My1O2, x1 is larger than or equal to 0.6 and smaller than or equal to 0.98, y1 is larger than or equal to 0.02 and smaller than or equal to 0.4, and x1 + y1 is equal to 1; the chemical composition of the columnar crystal radial arrangement layer meets the chemical formula LiNix2My2LmO2, x < 2 > is larger than or equal to 0.6 and smaller than or equal to 0.98, y < 2 > is larger than or equal to 0.02 and smaller than or equal to 0.4, m is larger than or equal to 0.001 and smaller than or equal to 0.03, and x < 2 > + y < 2 > + m = 1; wherein M is selected from at least one of Co, Mn and Ca; l is a doping element. The positive electrode material is not easy to crack in the charge-discharge cycle process, can well resist electrolyte erosion, and has excellent cycle performance.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion battery materials, and in particular to a positive electrode material and a preparation method thereof, and a lithium ion battery. Background Art

[0002] With the development of the electric vehicle industry, higher energy density has become a key requirement for lithium-ion batteries that provide power. High-nickel cathode materials have become a research hotspot due to their high energy density. However, as the nickel content increases, the cycle performance of cathode materials gradually deteriorates. The failure of high-nickel cathode materials is closely related to the structure of the material and the surface interface properties of the material particles during the charge and discharge cycle. During the charge and discharge cycle, the high-nickel cathode material will undergo phase change. The reciprocating change of the unit cell volume will cause the cathode material particles to crack and pulverize. The instability of the cathode material surface and the erosion of the electrolyte during the cycle will easily induce the surface phase change to generate NiO, making the surface inactive. With the increase of nickel content in the cathode material, the phenomenon of unit cell volume change, particle surface phase change, and side reactions at the interface between particles and electrolyte during the charge and discharge cycle will become more serious, resulting in rapid capacity decay of high-nickel cathode materials during the charge and discharge cycle. The poor cycle performance seriously restricts the application of high-nickel cathode materials.

[0003] Therefore, it is urgent to reduce the cracking phenomenon of the positive electrode material during the charge and discharge cycle and reduce the erosion of the electrolyte on the positive electrode material to improve the cycle performance of the positive electrode material. Summary of the invention

[0004] Aiming at the problem that the existing high-nickel positive electrode material is prone to cracking and being corroded by electrolyte during the charge and discharge cycle, thus resulting in poor cycle performance, the present invention provides a positive electrode material and a preparation method thereof and a lithium ion battery.

[0005] In order to achieve the above-mentioned object, the first aspect of the present invention provides a positive electrode material, the positive electrode material comprising: an equiaxed crystal stacking core, and a plurality of coating layers coating the equiaxed crystal stacking core;

[0006] In the coating layer, from the inside to the outside, the odd-numbered layers are radially arranged layers of columnar crystals, and the even-numbered layers are equiaxed crystal stacking layers; the total number of layers of the coating layer is r, wherein 3≤r≤13, and r is an odd number;

[0007] The chemical compositions of the equiaxed crystal stacking core and the equiaxed crystal stacking layer satisfy the chemical formula LiNi x1 M y1 O2, where 0.6≤x1≤0.98, 0.02≤y1≤0.4, x1+y1=1;

[0008] The chemical composition of the columnar crystal radial arrangement layer satisfies the chemical formula LiNi x2 M y2 Lm O2, where 0.6≤x2≤0.98, 0.02≤y2≤0.4, 0.001≤m≤0.03, x2+y2+m=1;

[0009] Wherein, M is selected from at least one of Co, Mn and Ca; L is a doping element selected from at least one of Al, Zr, Ti, W, B, Mg, Mo, La and Nd.

[0010] A second aspect of the present invention provides a method for preparing a positive electrode material, comprising:

[0011] (1) mixing a salt solution containing Ni and element M, a precipitant, and a complexing agent to obtain a reaction system A; mixing a salt solution containing Ni and element M, a salt solution containing element L, a precipitant, and a complexing agent to obtain a reaction system B;

[0012] (2) reacting part of the reaction system A to obtain a first product stream containing a core precursor; reacting the first product stream with part of the reaction system B to obtain a second product stream containing a first coating product; then reacting the second product stream with part of the reaction system A to obtain a third product stream containing a second coating product; reacting the third product stream with part of the reaction system B to obtain a fourth product stream containing a third coating product; and so on, reacting the obtained product streams alternately with the reaction system A and the reaction system B to obtain a precursor;

[0013] (3) calcining the precursor and the lithium source to obtain a positive electrode material;

[0014] The precursor comprises: a core precursor, and a plurality of coating layer precursors coating the core precursor; the total number of layers of the coating layer precursors is r, wherein 3≤r≤13, and r is an odd number;

[0015] The amount of the salt solution containing Ni and element M, the salt solution containing element L, the precipitant and the complexing agent is such that the chemical composition of the core precursor and the even-numbered coating layer precursors from the inside to the outside satisfies the chemical formula Ni x1 M y1 (OH)2, where 0.6≤x1≤0.98, 0.02≤y1≤0.4, x1+y1=1;

[0016] The chemical composition of the odd-numbered coating layer precursors from the inside to the outside satisfies the chemical formula Ni x2 M y2 L m (OH)2, where 0.6≤x2≤0.98, 0.02≤y2≤0.4, 0.001≤m≤0.03, x2+y2+m=1;

[0017] Wherein, M is selected from at least one of Co, Mn and Ca; L is a doping element selected from at least one of Al, Zr, Ti, W, B, Mg, Mo, La and Nd.

[0018] The third aspect of the present invention provides a positive electrode material prepared by the method described in the second aspect.

[0019] A fourth aspect of the present invention provides a lithium-ion battery comprising the positive electrode material described in the first aspect or the third aspect.

[0020] The positive electrode material provided by the present invention has an equiaxed crystal stacking core and a multilayer structure coated on the outside of the core, and the multilayer structure is arranged alternately from the inside to the outside with a columnar crystal radial arrangement layer and an equiaxed crystal stacking layer, wherein the columnar crystal radial arrangement layer has uniform internal stress, high mechanical strength, and is not easy to crack during the charge and discharge cycle; the alternately arranged multilayer structure can reduce cracking by dispersing stress, and the interlayer boundary can effectively limit the expansion of the formed cracks between different layers, and the outermost columnar crystal radial arrangement layer can reduce the erosion of the electrolyte. Under the synergistic effect of the above factors, the positive electrode material provided by the present invention is not easy to crack during the charge and discharge cycle, can better resist the erosion of the electrolyte, and has excellent cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings:

[0022] Figure 1 This is a schematic diagram of the structure of the positive electrode material P3 prepared in Example 3 of the present invention.

[0023] Description of Reference Numerals

[0024] 1. Equiaxed crystal stacking core 2. Columnar crystal radial arrangement layer

[0025] 3. Equiaxed crystal stacking layer DETAILED DESCRIPTION

[0026] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0027] A first aspect of the present invention provides a positive electrode material, the positive electrode material comprising: an equiaxed crystal stacking core, and a plurality of coating layers coating the equiaxed crystal stacking core;

[0028] In the coating layer, from the inside to the outside, the odd-numbered layers are radially arranged layers of columnar crystals, and the even-numbered layers are equiaxed crystal stacking layers; the total number of layers of the coating layer is r, wherein 3≤r≤13, and r is an odd number;

[0029] The chemical compositions of the equiaxed crystal stacking core and the equiaxed crystal stacking layer satisfy the chemical formula LiNi x1 M y1 O2, where 0.6≤x1≤0.98, 0.02≤y1≤0.4, x1+y1=1;

[0030] The chemical composition of the columnar crystal radial arrangement layer satisfies the chemical formula LiNi x2 M y2 L m O2, where 0.6≤x2≤0.98, 0.02≤y2≤0.4, 0.001≤m≤0.03, x2+y2+m=1;

[0031] Wherein, M is selected from at least one of Co, Mn and Ca; L is a doping element selected from at least one of Al, Zr, Ti, W, B, Mg, Mo, La and Nd.

[0032] The positive electrode material provided by the present invention has a core and a plurality of coating layers coated on the outer surface of the core, the core is in direct contact with the coating layer adjacent to it, the adjacent coating layers are in direct contact with each other, the plurality of coating layers form a multilayer structure, and are arranged alternately from the inside to the outside in a columnar crystal radial arrangement layer and an equiaxed crystal stacking layer, and the outermost layer is a columnar crystal radial arrangement layer, wherein the core and the coating layers of the even number layers meet the above chemical composition, and are all equiaxed crystal stacking layers, with the characteristics of small stress and stable structure; the coating layers of the odd number layers meet the above chemical composition, and the doping elements therein can promote the formation of columnar crystals, thereby enhancing the structural stability, and the coating layers of the odd number layers are all columnar crystal radial arrangement layers, the columnar crystal radial arrangement layers have high mechanical strength, uniform stress in the structure, are not easy to crack during the charge and discharge cycle, and can reduce the erosion of the electrolyte. The above-mentioned alternately arranged multilayer structure can reduce the cracking caused by the charge and discharge cycle by dispersing stress, slow down the expansion speed of the cracking, and the interlayer boundary can inhibit the interlayer expansion of the crack. The positive electrode material provided by the present invention has the above-mentioned specific structure and chemical composition, thereby greatly reducing the cracking phenomenon during the charge and discharge cycle and reducing the interface side reaction with the electrolyte.

[0033] In the present invention, the "equiaxed crystal stacking" means that in the absence of a dopant, the crystal growth has no obvious preferred orientation, grows uniformly in all directions, forms equiaxed grains, and stacks to form a core and an even-numbered coating layer. The "columnar radial arrangement" means that in the presence of a dopant, the crystal tends to grow radially to form columnar grains and form an odd-numbered coating layer.

[0034] According to the present invention, in the positive electrode material, in the chemical formula LiNi x1 M y1 O2、LiNi x2 M y2 L m In O2, preferably, the doping element L can be selected from at least one of Al, Zr, Ti, W and B, which can better stabilize the crystal structure, inhibit the reaction of transition metal ions with the electrolyte, and make the positive electrode material have better electrochemical properties.

[0035] According to the present invention, in the positive electrode material, in the chemical formula LiNi x1 M y1 O2、LiNi x2 M y2 L m In O2, x1, y1, x2, y2, and m, on the basis of satisfying the above-mentioned limited ranges, are preferably 0.8≤x1≤0.95, 0.05≤y1≤0.2; 0.8≤x2≤0.95, 0.05≤y2≤0.2, and 0.005≤m≤0.02.

[0036] According to the present invention, the total number of coating layers in the positive electrode material should take into account both the structural stability of the material and the ease of operation of the preparation process, and should not be too small or too large. If the total number of coating layers is too small, the structural stability of the positive electrode material is insufficient, and it is difficult to suppress crack propagation during the cycle; if the total number of coating layers is too large, it will increase the complexity of the preparation process, increase the cost, and it is difficult to further improve the performance of the positive electrode material. For the total number of coating layers r, preferably, 5≤r≤7, and r is an odd number.

[0037] According to the present invention, preferably, the average particle size of the positive electrode material is 6-24 μm. If the average particle size of the positive electrode material is too small, it is difficult to achieve a multilayer structure and the capacity is low; if the average particle size of the positive electrode material is too large, the structural stability and processing performance will deteriorate.

[0038] In the present invention, the average particle size refers to D50, which can be measured by a laser particle size analyzer.

[0039] According to the present invention, in the positive electrode material, preferably, the radius of the core of the equiaxed crystal stacking is 1.5-3 μm. If the radius of the core of the equiaxed crystal stacking is too small, the growth time of the core precursor particles is short during the preparation stage, resulting in uneven particle size, and may also cause poor core sphericity, affecting the performance of the overall positive electrode material; if the radius of the core of the equiaxed crystal stacking is too large, the stability of the core will deteriorate and microcracks will easily occur.

[0040] In the present invention, the radius of the inner core of the equiaxed crystal stacking is measured by ion beam milling (CP) combined with scanning electron microscopy (SEM). Specifically, the particles of the positive electrode material (particles with a size close to D50 are selected) are cross-sectioned by ion beam milling, and then the radius of the inner core is measured from the above cross-section by scanning electron microscopy.

[0041] According to the present invention, in the positive electrode material, for the coating layer, preferably, the innermost coating layer has a thickness of 0.6-2.9 μm, and the thickness of each layer decreases by 0.1-0.8 μm from the inside to the outside. In the present invention, the thickness of the coating layer gradually decreases from the inside to the outside, which is conducive to forming a stable and orderly structure, avoiding the formation of cracks penetrating the particles, and reducing the performance degradation of the positive electrode material caused by electrolyte erosion.

[0042] In the present invention, the thickness of the coating layer is measured by ion beam milling (CP) combined with scanning electron microscopy (SEM). Specifically, the particles of the positive electrode material (particles with a size close to D50 are selected) are cross-sectioned by ion beam milling, and then the thickness of each coating layer is measured from the above cross-section by scanning electron microscopy.

[0043] Compared with conventional high-nickel positive electrode materials, the positive electrode material provided by the present invention has greatly reduced cracking and pulverization during the charge and discharge cycle, can better resist electrolyte erosion, has a high capacity retention rate during the cycle, and has excellent cycle performance.

[0044] A second aspect of the present invention provides a method for preparing a positive electrode material, comprising:

[0045] (1) mixing a salt solution containing Ni and element M, a precipitant, and a complexing agent to obtain a reaction system A; mixing a salt solution containing Ni and element M, a salt solution containing element L, a precipitant, and a complexing agent to obtain a reaction system B;

[0046] (2) reacting part of the reaction system A to obtain a first product stream containing a core precursor; reacting the first product stream with part of the reaction system B to obtain a second product stream containing a first coating product; then reacting the second product stream with part of the reaction system A to obtain a third product stream containing a second coating product; reacting the third product stream with part of the reaction system B to obtain a fourth product stream containing a third coating product; and so on, reacting the obtained product streams alternately with the reaction system A and the reaction system B to obtain a precursor;

[0047] (3) calcining the precursor and the lithium source to obtain a positive electrode material;

[0048] The precursor comprises: a core precursor, and a plurality of coating layer precursors coating the core precursor; the total number of layers of the coating layer precursors is r, wherein 3≤r≤13, and r is an odd number;

[0049] The amount of the salt solution containing Ni and element M, the salt solution containing element L, the precipitant and the complexing agent is such that the chemical composition of the core precursor and the even-numbered coating layer precursors from the inside to the outside satisfies the chemical formula Ni x1 M y1 (OH)2, where 0.6≤x1≤0.98, 0.02≤y1≤0.4, x1+y1=1;

[0050] The chemical composition of the odd-numbered coating layer precursors from the inside to the outside satisfies the chemical formula Ni x2 M y2 L m (OH)2, where 0.6≤x2≤0.98, 0.02≤y2≤0.4, 0.001≤m≤0.03, x2+y2+m=1;

[0051] Wherein, M is selected from at least one of Co, Mn and Ca; L is a doping element selected from at least one of Al, Zr, Ti, W, B, Mg, Mo, La and Nd.

[0052] According to the present invention, in step (1), the salt solution containing element L provides the doping element L. Preferably, L can be selected from at least one of Al, Zr, Ti, W and B, which can better stabilize the crystal structure, inhibit the reaction of transition metal ions with the electrolyte, and make the prepared positive electrode material have better electrochemical properties.

[0053] According to the present invention, in step (1), the salt solution containing Ni and element M can be prepared by co-preparing nickel salt, salt containing M and water. Preferably, the total metal ion concentration in the salt solution containing Ni and element M is 1-3 mol / L.

[0054] According to the present invention, in step (1), the salt solution containing element L can be prepared by mixing salt containing L and water. Preferably, the concentration of doping element ions in the salt solution containing element L is 0.2-1 mol / L.

[0055] In the present invention, the nickel salt, the salt containing M, and the salt containing L are broadly defined, and the water-soluble salts capable of providing Ni, the element M, and the element L used in the positive electrode material precursor can be prepared by conventional coprecipitation methods in the art.

[0056] According to the present invention, in step (1), the precipitant may be selected from at least one of sodium hydroxide, sodium carbonate and sodium bicarbonate. According to a preferred embodiment of the present invention, the precipitant is fed in the form of an aqueous solution of the precipitant. Preferably, in the aqueous solution of the precipitant, the molar concentration of the precipitant is 1-15 mol / L (for example, when the precipitant is sodium carbonate, the molar concentration of Na2CO3 in the aqueous solution of the precipitant is 1-15 mol / L).

[0057] According to the present invention, the amount of the precipitant added is sufficient to completely precipitate the metal ions in the salt solution, and the hydroxide contained in the remaining precipitant after precipitation or the hydroxide produced by hydrolysis is sufficient to maintain the pH required for the reaction in step (2).

[0058] According to the present invention, in step (1), the complexing agent can be selected from at least one of ammonia water, ammonium bicarbonate and ammonium sulfate, preferably ammonia water with a concentration of 1-15 mol / L.

[0059] According to the present invention, preferably, the amount of the complexing agent added is such that the ammonia values ​​(NH3 and NH4) of the reaction system A and the reaction system B are + The content) is independently 2-20 g / L.

[0060] According to the present invention, in step (1), the reaction system A is used to prepare the core precursor (ultimately forming the core of the positive electrode material), and is used to prepare the coating precursor of the even-numbered layers (ultimately forming the even-numbered coating layers in the positive electrode material). The reaction system B is used to prepare the coating precursor of the odd-numbered layers (ultimately forming the odd-numbered coating layers in the positive electrode material).

[0061] According to the present invention, in step (2), a "alternative doping" reaction method is adopted to form a precursor with a multilayer structure. Specifically, firstly, part of the reaction system A is reacted to prepare a core precursor; when the generated core precursor reaches the target particle size, the first product flow containing the core precursor (that is, the product system obtained after the reaction of the part of the reaction system A) is mixed and reacted with part of the reaction system B, and the first layer of "coating layer precursor" is coated on the surface of the core precursor to obtain the first coated product; when the first coated product reaches the target particle size (that is, the target thickness of the first layer of "coating layer precursor"), the second product flow containing the first coating product (that is, the product system obtained after the reaction of the first product flow and part of the reaction system B) is mixed and reacted with part of the reaction system A, and the second layer of "coating layer precursor" is coated on the surface of the first coating product to obtain the second coated product; when When the second coated product reaches the target particle size (i.e., the target thickness of the second layer of "coating layer precursor"), the third product flow containing the second coated product (i.e., the product system obtained after the second product flow and part of the reaction system A react) is mixed and reacted with part of the reaction system B, and the third layer of "coating layer precursor" is coated on the surface of the second coated product to obtain the third coated product; when the third coated product reaches the target particle size (i.e., the target thickness of the third layer of "coating layer precursor"), the fourth product flow containing the third coated product (i.e., the product system obtained after the third product flow and part of the reaction system B react) is mixed and reacted with part of the reaction system A; and so on, the obtained product flow is alternately reacted with the reaction system A and the reaction system B to obtain a precursor. By adopting this reaction mode, the formed precursor has a "core" (core precursor) and multiple coating layer precursors coating the "core", wherein the total number of coating layer precursors is an odd number, and the odd-numbered coating layer precursors are doped with element L.

[0062] According to the present invention, in step (2), for the precursor, in the chemical formula Ni x1 M y1 (OH)2 and Ni x2 M y2 L m In (OH)2, x1, y1, x2, y2, and m preferably satisfy the above-defined ranges, and are 0.8≤x1≤0.95, 0.05≤y1≤0.2; 0.8≤x2≤0.95, 0.05≤y2≤0.2, and 0.005≤m≤0.02. This enables the positive electrode material to have a better structure and better electrical properties.

[0063] According to the present invention, in step (2), preferably, the radius of the core precursor is 1.5-3 μm.

[0064] According to the present invention, in step (2), preferably, in the coating layer precursor, the thickness of the innermost layer is 0.6-2.9 μm, and the thickness of each layer decreases by 0.1-0.8 μm from the inner to the outer.

[0065] According to the present invention, in step (2), preferably, the average particle size of the precursor is 6-24 μm.

[0066] In the present invention, the radius of the core precursor can be measured by a laser particle size analyzer. Specifically, the radius of the core precursor = D50 内核前驱物 / 2.

[0067] In the present invention, the thickness of the coating layer precursor can be measured by a laser particle size analyzer. Specifically, the thickness of the coating layer precursor = (D50 包覆后的颗粒 -D50 包覆前的颗粒 ) / 2

[0068] In the present invention, the average particle size (D50) of the precursor can be measured by a laser particle size analyzer.

[0069] According to the present invention, in step (2), the reaction conditions include: pH 9.8-12.5, ammonia value 2-20 g / L, and temperature 50-70°C.

[0070] According to the present invention, in step (2), specifically, for preparing the core precursor and the coating layer precursor of the even-numbered layers, the reaction conditions adopted include: pH of 11-12.5, ammonia value of 2-20 g / L, and temperature of 55-70°C; for preparing the coating layer precursor of the odd-numbered layers, the reaction conditions adopted include: pH of 9.8-12, ammonia value of 3-20 g / L, and temperature of 50-60°C.

[0071] According to the present invention, in step (2), each reaction is carried out under a protective atmosphere to avoid oxidation of the product, preferably under a nitrogen atmosphere.

[0072] According to the present invention, in step (3), the amount of the precursor and the lithium source is such that the chemical composition of the core and the even-numbered coating layer of the positive electrode material obtained by calcination satisfies the chemical formula LiNi x1 M y1 O2, where 0.6≤x1≤0.98, 0.02≤y1≤0.4, x1+y1=1;

[0073] The chemical composition of the odd-numbered coating layer satisfies the chemical formula LiNi x2 M y2 L mO2, where 0.6≤x2≤0.98, 0.02≤y2≤0.4, 0.001≤m≤0.03, x2+y2+m=1.

[0074] According to the present invention, in step (3), the type of the lithium source is relatively broad, and conventional lithium sources for preparing positive electrode materials in the art can be selected, preferably lithium hydroxide.

[0075] According to the present invention, in step (3), the calcination is divided into low-temperature sintering and high-temperature sintering performed sequentially.

[0076] According to the present invention, preferably, the conditions for low temperature sintering include: a heating rate of 2-8°C / min, a constant temperature of 400-620°C, and a constant temperature time of 2-8h;

[0077] According to the present invention, preferably, the conditions for high temperature sintering include: a heating rate of 2-8° C. / min, a constant temperature of 650-950° C., and a constant temperature time of 8-20 h.

[0078] According to the present invention, in step (3), the calcination is carried out in air or oxygen atmosphere.

[0079] The positive electrode material preparation method provided by the present invention adopts the reaction mode of "alternative doping" so that the prepared positive electrode material has an equiaxed crystal stacking core and a plurality of coating layers covering the equiaxed crystal stacking core; wherein, in the coating layers, from inside to outside, the odd-numbered layers are columnar crystal radially arranged layers, the even-numbered layers are equiaxed crystal stacking layers, and the outermost layer is a columnar crystal radially arranged layer. The positive electrode material prepared by the method is not easy to crack during the charge and discharge cycle, can better resist electrolyte erosion, and has excellent cycle performance.

[0080] The third aspect of the present invention provides a positive electrode material prepared by the method described in the second aspect.

[0081] According to the present invention, the positive electrode material prepared by the method described in the second aspect has the same chemical composition, structure and performance as the positive electrode material described in the first aspect of the present invention, and will not be described in detail here.

[0082] A fourth aspect of the present invention provides a lithium-ion battery comprising the positive electrode material described in the first aspect or the third aspect.

[0083] The lithium ion battery provided by the present invention adopts the positive electrode material provided by the present invention, so that the battery has the advantages of high energy density and good cycle performance.

[0084] The present invention will be described in detail below by way of examples. In the following examples and comparative examples, unless otherwise specified, all are conventional methods; the reagents and materials, unless otherwise specified, can be obtained from commercial sources.

[0085] Example 1

[0086] (1) nickel sulfate, cobalt sulfate and manganese sulfate are prepared into a salt solution (the total metal ion concentration is 2 mol / L); aluminum sulfate, boric acid and water are prepared into a dopant solution (the doping element ion concentration is 0.5 mol / L, wherein the molar ratio of doping element Al:B is 1:1); the precipitant is a NaOH aqueous solution (the NaOH concentration is 6 mol / L); the complexing agent is ammonia water with a concentration of 8 mol / L;

[0087] The salt solution, precipitant and complexing agent are mixed to obtain reaction system A; the salt solution, dopant solution, precipitant and complexing agent are mixed to obtain reaction system B;

[0088] (2) When a portion of the reaction system A is reacted and the D50 of the obtained core precursor reaches 3.4 μm, the first product flow containing the core precursor is mixed with a portion of the reaction system B and reacted to coat the surface of the core precursor with a first coating layer precursor to obtain a first coating product; when the D50 of the obtained first coating product reaches 6.4 μm, the second product flow containing the first coating product is mixed with a portion of the reaction system A and reacted to coat the surface of the first coating product with a second coating layer precursor to obtain a second coating product; when the D50 of the second coating product reaches 6.4 μm, the second product flow containing the first coating product is mixed with a portion of the reaction system A and reacted to coat the surface of the first coating product with a second coating layer precursor to obtain a second coating product; When D50 reaches 9 μm, the third product flow containing the second coated product is mixed with part of the reaction system B and reacted, and the third coating layer precursor is coated on the surface of the second coated product to obtain a third coated product; when the D50 of the third coated product reaches 11.2 μm, the fourth product flow containing the third coated product is mixed with part of the reaction system A and reacted; and so on, the obtained product flow is alternately reacted with the reaction system A and the reaction system B to obtain a slurry containing the precursor, and the slurry is washed, filtered, dried, sieved and iron-removed to obtain a precursor;

[0089] The reaction conditions used to prepare the core precursor and the even-numbered layer precursor are as follows: pH 11.5, ammonia value 10 g / L, temperature 60°C, and nitrogen as the protective gas; the reaction conditions used to prepare the odd-numbered layer precursor are as follows: pH 11, ammonia value 10 g / L, temperature 55°C, and nitrogen as the protective gas;

[0090] In the obtained precursor, the core precursor is Ni 0.9 Co 0.05 Mn 0.05 (OH)2, the total number of layers of the coating layer precursors covering the core precursor is 7; among them, the coating layer precursors of the even-numbered layers from the inside to the outside are Ni 0.9 Co 0.05Mn 0.05 (OH)2, the odd-numbered coating layer precursor is Ni 0.882 Co 0.049 Mn 0.049 B 0.01 Al 0.01 (OH)2; the radius of the core precursor is 1.7 μm, and the thickness of the coating layer precursor from the inside to the outside is 1.5 μm, 1.3 μm, 1.1 μm, 0.9 μm, 0.7 μm, 0.5 μm, and 0.3 μm;

[0091] (3) The precursor obtained in step (2) is uniformly mixed with lithium hydroxide, and the resulting mixture is placed in a sintering furnace. In an oxygen atmosphere, the temperature is increased to 500° C. at a heating rate of 6° C. / min and kept at the constant temperature for 4 h; then the temperature is increased to 850° C. at a heating rate of 4° C. / min and kept at the constant temperature for 15 h to obtain a positive electrode material (denoted as P1);

[0092] P1 has an equiaxed crystal stacking core LiNi 0.9 Co 0.05 Mn 0.05 O2, and 7 layers of coating covering the core; among them, from the inside to the outside, the odd-numbered layers are LiNi 0.882 Co 0.049 Mn 0.049 B 0.01 Al 0.01 O2, is a columnar crystal radially arranged layer; the even-numbered layers are LiNi 0.9 Co 0.05 Mn 0.05 O2, is an equiaxed crystal stacking layer;

[0093] The average particle size of P1 is 16 μm, wherein the radius of the inner core is 1.7 μm, and the thickness of the coating from the inside to the outside is 1.5 μm, 1.3 μm, 1.1 μm, 0.9 μm, 0.7 μm, 0.5 μm, and 0.3 μm.

[0094] Example 2

[0095] (1) nickel sulfate, cobalt sulfate, manganese sulfate and water are prepared into a salt solution (the total metal ion concentration is 2 mol / L); tungsten carbonate, titanium isopropoxide and water are prepared into a dopant solution (the doping element ion concentration is 0.5 mol / L, wherein the molar ratio of the doping element W:Ti is 1:1); the precipitant is a NaOH aqueous solution (the NaOH concentration is 6 mol / L); the complexing agent is ammonia water with a concentration of 8 mol / L;

[0096] The salt solution, precipitant and complexing agent are mixed to obtain reaction system A; the salt solution, dopant solution, precipitant and complexing agent are mixed to obtain reaction system B;

[0097] (2) reacting a portion of the reaction system A, and when the D50 of the obtained core precursor reaches 3.6 μm, mixing and reacting a first product stream containing the core precursor with a portion of the reaction system B, and coating the surface of the core precursor with a first coating layer precursor, to obtain a first coating product; when the D50 of the obtained first coating product reaches 6.6 μm, mixing and reacting a second product stream containing the first coating product with a portion of the reaction system A, and coating the surface of the first coating product with a second coating layer precursor, to obtain a second coating product; when the D50 of the second coating product reaches 6.6 μm, When D50 reaches 9.2 μm, the third product flow containing the second coated product is mixed with part of the reaction system B and reacted, and the third coating layer precursor is coated on the surface of the second coated product to obtain a third coated product; when D50 of the third coated product reaches 11.4 μm, the fourth product flow containing the third coated product is mixed with part of the reaction system A and reacted; and so on, the obtained product flow is alternately reacted with the reaction system A and the reaction system B to obtain a slurry containing the precursor, and the slurry is washed, filtered, dried, sieved and iron-removed to obtain a precursor;

[0098] The reaction conditions used to prepare the core precursor and the even-numbered layer precursor are as follows: pH 11.5, ammonia value 10 g / L, temperature 60°C, and nitrogen as the protective gas; the reaction conditions used to prepare the odd-numbered layer precursor are as follows: pH 11, ammonia value 10 g / L, temperature 55°C, and nitrogen as the protective gas;

[0099] In the obtained precursor, the core precursor is Ni 0.9 Co 0.05 Mn 0.05 (OH)2, the total number of layers of the coating layer precursors covering the core precursor is 5; among them, the coating layer precursors of even numbers from the inside to the outside are Ni 0.9 Co 0.05 Mn 0.05 (OH)2, the odd-numbered coating layer precursor is Ni 0.891 Co 0.0495 Mn 0.0495 W 0.005 Ti 0.005 (OH)2; the radius of the core precursor is 1.8 μm, and the thickness of the coating layer precursor from the inside to the outside is 1.5 μm, 1.3 μm, 1.1 μm, 0.9 μm, and 0.6 μm;

[0100] (3) The precursor obtained in step (2) is uniformly mixed with lithium hydroxide, and the resulting mixture is placed in a sintering furnace. In an oxygen atmosphere, the temperature is increased to 500° C. at a heating rate of 6° C. / min and kept at the constant temperature for 4 h; then the temperature is increased to 850° C. at a heating rate of 4° C. / min and kept at the constant temperature for 15 h to obtain a positive electrode material (denoted as P2);

[0101] P2 has an equiaxed crystal stacking core LiNi 0.9 Co 0.05 Mn 0.05 O2, and 5 layers of coating covering the core; among them, from the inside to the outside, the odd-numbered layers are LiNi 0.891 Co 0.0495 Mn 0.0495 W 0.005 Ti 0.005 O2, is a columnar crystal radially arranged layer; the even-numbered layers are LiNi 0.9 Co 0.05 Mn 0.05 O2, is an equiaxed crystal stacking layer;

[0102] The average particle size of P2 is 14.4 μm, wherein the radius of the inner core is 1.8 μm, and the thickness of the coating from the inside to the outside is 1.5 μm, 1.3 μm, 1.1 μm, 0.9 μm, and 0.6 μm.

[0103] Example 3

[0104] (1) nickel sulfate, cobalt sulfate, manganese sulfate and water are prepared into a salt solution (the total metal ion concentration is 2 mol / L); aluminum sulfate, boric acid and water are prepared into a dopant solution (the doping element ion concentration is 0.5 mol / L, wherein the molar ratio of doping element Al:B is 1:1); the precipitant is a NaOH aqueous solution (the NaOH concentration is 6 mol / L); the complexing agent is ammonia water with a concentration of 8 mol / L;

[0105] The salt solution, precipitant and complexing agent are mixed to obtain reaction system A; the salt solution, dopant solution, precipitant and complexing agent are mixed to obtain reaction system B;

[0106] (2) reacting a portion of the reaction system A, and when the D50 of the obtained core precursor reaches 4 μm, mixing and reacting the first product stream containing the core precursor with a portion of the reaction system B, coating the surface of the core precursor with a first coating layer precursor, and obtaining a first coating product; when the D50 of the obtained first coating product reaches 7.2 μm, mixing and reacting the second product stream containing the first coating product with a portion of the reaction system A, coating the surface of the first coating product with a second coating layer precursor, and obtaining a second coating product; when the D50 of the second coating product reaches 7.2 μm, When D50 of the third coated product reaches 10 μm, the third product flow containing the second coated product is mixed with part of the reaction system B and reacted, and the third coating layer precursor is coated on the surface of the second coated product to obtain a third coated product; when D50 of the third coated product reaches 12.4 μm, the fourth product flow containing the third coated product is mixed with part of the reaction system A and reacted; and so on, the obtained product flow is alternately reacted with the reaction system A and the reaction system B to obtain a slurry containing the precursor, and the slurry is washed, filtered, dried, sieved and iron-removed to obtain a precursor;

[0107] The reaction conditions used to prepare the core precursor and the even-numbered layer precursor are as follows: pH 11.5, ammonia value 10 g / L, temperature 60°C, and nitrogen as the protective gas; the reaction conditions used to prepare the odd-numbered layer precursor are as follows: pH 11, ammonia value 10 g / L, temperature 55°C, and nitrogen as the protective gas;

[0108] In the obtained precursor, the core precursor is Ni 0.9 Co 0.05 Mn 0.05 (OH)2, the total number of layers of the coating layer precursors covering the core precursor is 3; among them, the coating layer precursors of the even-numbered layers from the inside to the outside are Ni 0.9 Co 0.05 Mn 0.05 (OH)2, the odd-numbered coating layer precursor is Ni 0.882 Co 0.049 Mn 0.049 B 0.01 Al 0.01 (OH)2; the radius of the core precursor is 2 μm, and the thickness of the coating layer precursor from the inside to the outside is 1.6 μm, 1.4 μm, and 1.2 μm;

[0109] (3) The precursor obtained in step (2) is uniformly mixed with lithium hydroxide, and the resulting mixture is placed in a sintering furnace. In an oxygen atmosphere, the temperature is increased to 500° C. at a heating rate of 6° C. / min and kept at the constant temperature for 4 h; then the temperature is increased to 850° C. at a heating rate of 4° C. / min and kept at the constant temperature for 15 h to obtain a positive electrode material (denoted as P3);

[0110] like Figure 1 As shown, P3 has an equiaxed crystal stacking core LiNi 0.9 Co 0.05 Mn 0.05 O2, and three layers of coating covering the core; among them, from the inside to the outside, the odd-numbered layers are LiNi 0.882 Co 0.049 Mn 0.049 B 0.01 Al 0.01 O2, is a columnar crystal radially arranged layer; the even-numbered layers are LiNi 0.9 Co 0.05 Mn 0.05 O2, is an equiaxed crystal stacking layer;

[0111] The average particle size of P3 is 12.4 μm, wherein the radius of the inner core is 2 μm, and the thickness of the coating layers from the inside to the outside are 1.6 μm, 1.4 μm, and 1.2 μm.

[0112] Example 4

[0113] (1) nickel sulfate, cobalt sulfate, manganese sulfate and water are prepared into a salt solution (the total metal ion concentration is 2 mol / L); aluminum sulfate, zirconium sulfate and water are prepared into a dopant solution (the doping element ion concentration is 0.5 mol / L, wherein the molar ratio of doping element Zr:Al is 1:2); the precipitant is a NaOH aqueous solution (the NaOH concentration is 6 mol / L); the complexing agent is ammonia water with a concentration of 8 mol / L;

[0114] The salt solution, precipitant and complexing agent are mixed to obtain reaction system A; the salt solution, dopant solution, precipitant and complexing agent are mixed to obtain reaction system B;

[0115] (2) reacting a portion of the reaction system A, and when the D50 of the obtained core precursor reaches 4 μm, mixing and reacting the first product stream containing the core precursor with a portion of the reaction system B, coating the surface of the core precursor with a first coating layer precursor, and obtaining a first coating product; when the D50 of the obtained first coating product reaches 7.2 μm, mixing and reacting the second product stream containing the first coating product with a portion of the reaction system A, coating the surface of the first coating product with a second coating layer precursor, and obtaining a second coating product; when the D50 of the second coating product reaches 7.2 μm, When D50 of the third coated product reaches 10 μm, the third product flow containing the second coated product is mixed with part of the reaction system B and reacted, and the third coating layer precursor is coated on the surface of the second coated product to obtain a third coated product; when D50 of the third coated product reaches 12.4 μm, the fourth product flow containing the third coated product is mixed with part of the reaction system A and reacted; and so on, the obtained product flow is alternately reacted with the reaction system A and the reaction system B to obtain a slurry containing the precursor, and the slurry is washed, filtered, dried, sieved and iron-removed to obtain a precursor;

[0116] The reaction conditions used to prepare the core precursor and the even-numbered layer precursor are as follows: pH 11.5, ammonia value 10 g / L, temperature 60°C, and nitrogen as the protective gas; the reaction conditions used to prepare the odd-numbered layer precursor are as follows: pH 11, ammonia value 10 g / L, temperature 55°C, and nitrogen as the protective gas;

[0117] In the obtained precursor, the core precursor is Ni 0.9 Co 0.05 Mn 0.05 (OH)2, the total number of layers of the coating layer precursors covering the core precursor is 5; among them, the coating layer precursors of even numbers from the inside to the outside are Ni 0.9 Co 0.05 Mn 0.05 (OH)2, the odd-numbered coating layer precursor is Ni 0.873 Co 0.0485 Mn 0.0485 Zr 0.01 Al 0.02 (OH)2; the radius of the core precursor is 2 μm, and the thickness of the coating layer precursor from the inside to the outside is 1.6 μm, 1.4 μm, 1.2 μm, 1 μm, and 0.8 μm;

[0118] (3) The precursor obtained in step (2) is uniformly mixed with lithium hydroxide, and the resulting mixture is placed in a sintering furnace. In an oxygen atmosphere, the temperature is increased to 500° C. at a heating rate of 6° C. / min and maintained at the temperature for 4 h; then the temperature is increased to 850° C. at a heating rate of 4° C. / min and maintained at the temperature for 15 h to obtain a positive electrode material (denoted as P4);

[0119] P4 has an equiaxed crystal stacking core LiNi 0.9 Co 0.05 Mn 0.05 O2, and 5 layers of coating covering the core; among them, from the inside to the outside, the odd-numbered layers are LiNi 0.873 Co 0.0485 Mn 0.0485 Zr 0.01 Al 0.02 O2, is a columnar crystal radially arranged layer; the even-numbered layers are LiNi 0.9 Co 0.05 Mn 0.05 O2, is an equiaxed crystal stacking layer;

[0120] The average particle size of P4 is 16 μm, wherein the radius of the inner core is 2 μm, and the thickness of the coating from the inside to the outside is 1.6 μm, 1.4 μm, 1.2 μm, 1 μm, and 0.8 μm.

[0121] Example 5

[0122] (1) nickel sulfate, cobalt sulfate, manganese sulfate and water are prepared into a salt solution (the total metal ion concentration is 2 mol / L); magnesium sulfate and water are prepared into a dopant solution (the doping element ion concentration is 0.5 mol / L); the precipitant is a NaOH aqueous solution (the NaOH concentration is 6 mol / L); the complexing agent is ammonia water with a concentration of 8 mol / L;

[0123] The salt solution, precipitant and complexing agent are mixed to obtain reaction system A; the salt solution, dopant solution, precipitant and complexing agent are mixed to obtain reaction system B;

[0124] (2) reacting a portion of the reaction system A, and when the D50 of the obtained core precursor reaches 3.6 μm, mixing and reacting a first product stream containing the core precursor with a portion of the reaction system B, and coating the surface of the core precursor with a first coating layer precursor, to obtain a first coating product; when the D50 of the obtained first coating product reaches 6.6 μm, mixing and reacting a second product stream containing the first coating product with a portion of the reaction system A, and coating the surface of the first coating product with a second coating layer precursor, to obtain a second coating product; when the D50 of the second coating product reaches 6.6 μm, When D50 reaches 9.2 μm, the third product flow containing the second coated product is mixed with part of the reaction system B and reacted, and the third coating layer precursor is coated on the surface of the second coated product to obtain a third coated product; when D50 of the third coated product reaches 11.4 μm, the fourth product flow containing the third coated product is mixed with part of the reaction system A and reacted; and so on, the obtained product flow is alternately reacted with the reaction system A and the reaction system B to obtain a slurry containing the precursor, and the slurry is washed, filtered, dried, sieved and iron-removed to obtain a precursor;

[0125] The reaction conditions used to prepare the core precursor and the even-numbered layer precursor are as follows: pH 11.5, ammonia value 10 g / L, temperature 60°C, and nitrogen as the protective gas; the reaction conditions used to prepare the odd-numbered layer precursor are as follows: pH 11, ammonia value 10 g / L, temperature 55°C, and nitrogen as the protective gas;

[0126] In the obtained precursor, the core precursor is Ni 0.9 Co 0.05 Mn 0.05 (OH)2, the total number of layers of the coating layer precursors covering the core precursor is 5; among them, the coating layer precursors of even numbers from the inside to the outside are Ni 0.9 Co 0.05 Mn 0.05 (OH)2, the odd-numbered coating layer precursor is Ni 0.882 Co 0.049 Mn 0.049 Mg 0.02 (OH)2; the radius of the core precursor is 1.8 μm, and the thickness of the coating layer precursor from the inside to the outside is 1.5 μm, 1.3 μm, 1.1 μm, 0.9 μm, and 0.6 μm;

[0127] (3) The precursor obtained in step (2) is uniformly mixed with lithium hydroxide, and the resulting mixture is placed in a sintering furnace. In an oxygen atmosphere, the temperature is increased to 500° C. at a heating rate of 6° C. / min and kept at the constant temperature for 4 h; then the temperature is increased to 850° C. at a heating rate of 4° C. / min and kept at the constant temperature for 15 h to obtain a positive electrode material (denoted as P5);

[0128] P5 has an equiaxed crystal stacking core LiNi 0.9 Co 0.05 Mn 0.05 O2, and 5 layers of coating covering the core; among them, from the inside to the outside, the odd-numbered layers are LiNi 0.882 Co 0.049 Mn 0.049 Mg 0.02 O2, is a columnar crystal radially arranged layer; the even-numbered layers are LiNi 0.9 Co 0.05 Mn 0.05 O2, is an equiaxed crystal stacking layer;

[0129] The average particle size of P5 is 14.4 μm, wherein the radius of the inner core is 1.8 μm, and the thickness of the coating from the inside to the outside is 1.5 μm, 1.3 μm, 1.1 μm, 0.9 μm, and 0.6 μm.

[0130] Example 6

[0131] (1) nickel sulfate, cobalt sulfate, manganese sulfate and water are prepared into a salt solution (the total metal ion concentration is 2 mol / L); sodium molybdate, lanthanum nitrate and water are prepared into a dopant solution (the doping element ion concentration is 0.5 mol / L, wherein the molar ratio of the doping element Mo:La is 1:1); the precipitant is a NaOH aqueous solution (the NaOH concentration is 6 mol / L); the complexing agent is ammonia water with a concentration of 8 mol / L;

[0132] The salt solution, precipitant and complexing agent are mixed to obtain reaction system A; the salt solution, dopant solution, precipitant and complexing agent are mixed to obtain reaction system B;

[0133] (2) reacting a portion of the reaction system A, and when the D50 of the obtained core precursor reaches 4 μm, mixing and reacting the first product stream containing the core precursor with a portion of the reaction system B, coating the surface of the core precursor with a first coating layer precursor, and obtaining a first coating product; when the D50 of the obtained first coating product reaches 7.2 μm, mixing and reacting the second product stream containing the first coating product with a portion of the reaction system A, coating the surface of the first coating product with a second coating layer precursor, and obtaining a second coating product; when the D50 of the second coating product reaches 7.2 μm, When D50 of the third coated product reaches 10 μm, the third product flow containing the second coated product is mixed with part of the reaction system B and reacted, and the third coating layer precursor is coated on the surface of the second coated product to obtain a third coated product; when D50 of the third coated product reaches 12.2 μm, the fourth product flow containing the third coated product is mixed with part of the reaction system A and reacted; and so on, the obtained product flow is alternately reacted with the reaction system A and the reaction system B to obtain a slurry containing the precursor, and the slurry is washed, filtered, dried, sieved and iron-removed to obtain a precursor;

[0134] The reaction conditions used to prepare the core precursor and the even-numbered layer precursor are as follows: pH 11.5, ammonia value 10 g / L, temperature 60°C, and nitrogen as the protective gas; the reaction conditions used to prepare the odd-numbered layer precursor are as follows: pH 11, ammonia value 10 g / L, temperature 55°C, and nitrogen as the protective gas;

[0135] In the obtained precursor, the core precursor is Ni 0.9 Co 0.05 Mn 0.05 (OH)2, the total number of layers of the coating layer precursors covering the core precursor is 7; among them, the coating layer precursors of the even-numbered layers from the inside to the outside are Ni 0.9 Co 0.05 Mn 0.05 (OH)2, the odd-numbered coating layer precursor is Ni 0.886 Co 0.0495 Mn 0.0495 Mo 0.005 La 0.005 (OH)2; the radius of the core precursor is 2 μm, and the thickness of the coating layer precursor from the inside to the outside is 1.6 μm, 1.4 μm, 1.1 μm, 0.9 μm, 0.7 μm, 0.5 μm, and 0.3 μm;

[0136] (3) The precursor obtained in step (2) is uniformly mixed with lithium hydroxide, and the resulting mixture is placed in a sintering furnace. In an oxygen atmosphere, the temperature is increased to 500° C. at a heating rate of 6° C. / min and kept at the constant temperature for 4 h; then the temperature is increased to 850° C. at a heating rate of 4° C. / min and kept at the constant temperature for 15 h to obtain a positive electrode material (denoted as P6);

[0137] P6 has an equiaxed crystal stacking core LiNi 0.9 Co 0.05 Mn 0.05 O2, and 7 layers of coating covering the core; among them, from the inside to the outside, the odd-numbered layers are LiNi 0.886 Co 0.0495 Mn 0.0495 Mo 0.005 La 0.005 O2, is a columnar crystal radially arranged layer; the even-numbered layers are LiNi 0.9 Co 0.05 Mn 0.05 O2, is an equiaxed crystal stacking layer;

[0138] The average particle size of P6 is 17 μm, wherein the radius of the inner core is 2 μm, and the thickness of the coating from the inside to the outside is 1.6 μm, 1.4 μm, 1.1 μm, 0.9 μm, 0.7 μm, 0.5 μm, and 0.3 μm.

[0139] Example 7

[0140] (1) nickel sulfate, cobalt sulfate, manganese sulfate and water are prepared into a salt solution (the total metal ion concentration is 2 mol / L); magnesium sulfate, lanthanum nitrate and water are prepared into a dopant solution (the doping element ion concentration is 0.5 mol / L, wherein the molar ratio of the doping element Mg:La is 1:1); the precipitant is a NaOH aqueous solution (the NaOH concentration is 6 mol / L); the complexing agent is ammonia water with a concentration of 8 mol / L;

[0141] The salt solution, precipitant and complexing agent are mixed to obtain reaction system A; the salt solution, dopant solution, precipitant and complexing agent are mixed to obtain reaction system B;

[0142] (2) When a portion of the reaction system A is reacted and the D50 of the obtained core precursor reaches 3.6 μm, the first product stream containing the core precursor is mixed with a portion of the reaction system B and reacted to coat the surface of the core precursor with a first coating layer precursor to obtain a first coating product; when the D50 of the obtained first coating product reaches 7 μm, the second product stream containing the first coating product is mixed with a portion of the reaction system A and reacted to coat the surface of the first coating product with a second coating layer precursor to obtain a second coating product; when the D50 of the second coating product reaches 7 μm, the second product stream containing the first coating product is mixed with a portion of the reaction system A and reacted to coat the surface of the first coating product with a second coating layer precursor to obtain a second coating product; When the D50 of the third coated product reaches 10.2 μm, the third product flow containing the second coated product is mixed with part of the reaction system B and reacted, and the third coating layer precursor is coated on the surface of the second coated product to obtain a third coated product; when the D50 of the third coated product reaches 13.2 μm, the fourth product flow containing the third coated product is mixed with part of the reaction system A and reacted; and so on, the obtained product flow is alternately reacted with the reaction system A and the reaction system B to obtain a slurry containing the precursor, and the slurry is washed, filtered, dried, sieved and iron-removed to obtain a precursor;

[0143] The reaction conditions used to prepare the core precursor and the even-numbered layer precursor are as follows: pH 11.5, ammonia value 10 g / L, temperature 60°C, and nitrogen as the protective gas; the reaction conditions used to prepare the odd-numbered layer precursor are as follows: pH 11, ammonia value 10 g / L, temperature 55°C, and nitrogen as the protective gas;

[0144] In the obtained precursor, the core precursor is Ni 0.9 Co 0.05 Mn 0.05 (OH)2, the total number of layers of the coating layer precursors covering the core precursor is 3; among them, the coating layer precursors of the even-numbered layers from the inside to the outside are Ni 0.9 Co 0.05 Mn 0.05 (OH)2, the odd-numbered coating layer precursor is Ni 0.882 Co 0.049 Mn 0.049 Mg 0.01 La 0.01 (OH)2; the radius of the core precursor is 1.8 μm, and the thickness of the coating layer precursor from the inside to the outside is 1.7 μm, 1.6 μm, and 1.5 μm;

[0145] (3) The precursor obtained in step (2) was uniformly mixed with lithium hydroxide, and the resulting mixture was placed in a sintering furnace. In an oxygen atmosphere, the temperature was increased to 500° C. at a heating rate of 6° C. / min and kept at the constant temperature for 4 h; then the temperature was increased to 850° C. at a heating rate of 4° C. / min and kept at the constant temperature for 15 h to obtain a positive electrode material (denoted as P7);

[0146] P7 has an equiaxed crystal stacking core LiNi 0.9 Co 0.05 Mn 0.05 O2, and three layers of coating covering the core; among them, from the inside to the outside, the odd-numbered layers are LiNi 0.882 Co 0.049 Mn 0.049 Mg 0.01 La 0.01 O2, is a columnar crystal radially arranged layer; the even-numbered layers are LiNi 0.9 Co 0.05 Mn 0.05 O2, is an equiaxed crystal stacking layer;

[0147] The average particle size of P7 is 13.2 μm, wherein the radius of the inner core is 1.8 μm, and the thickness of the coating layers from the inside to the outside are 1.7 μm, 1.6 μm, and 1.5 μm.

[0148] Example 8

[0149] (1) nickel sulfate, cobalt sulfate, manganese sulfate and water are prepared into a salt solution (the total metal ion concentration is 2 mol / L); aluminum sulfate and water are prepared into a dopant solution (the doping element ion concentration is 0.5 mol / L); the precipitant is a NaOH aqueous solution (the NaOH concentration is 6 mol / L); the complexing agent is ammonia water with a concentration of 8 mol / L;

[0150] The salt solution, precipitant and complexing agent are mixed to obtain reaction system A; the salt solution, dopant solution, precipitant and complexing agent are mixed to obtain reaction system B;

[0151] (2) reacting a portion of the reaction system A, and when the D50 of the obtained core precursor reaches 4 μm, mixing and reacting the first product stream containing the core precursor with a portion of the reaction system B, and coating the surface of the core precursor with a first coating layer precursor to obtain a first coating product; when the D50 of the obtained first coating product reaches 7.6 μm, mixing and reacting the second product stream containing the first coating product with a portion of the reaction system A, and coating the surface of the first coating product with a second coating layer precursor to obtain a second coating product; when the D50 of the second coating product reaches 7.6 μm, When D50 reaches 11 μm, the third product flow containing the second coated product is mixed with part of the reaction system B and reacted, and the third coating layer precursor is coated on the surface of the second coated product to obtain a third coated product; when D50 of the third coated product reaches 14 μm, the fourth product flow containing the third coated product is mixed with part of the reaction system A and reacted; and so on, the obtained product flow is alternately reacted with the reaction system A and the reaction system B to obtain a slurry containing the precursor, and the slurry is washed, filtered, dried, sieved and iron-removed to obtain a precursor;

[0152] The reaction conditions used to prepare the core precursor and the even-numbered layer precursor are as follows: pH 11.5, ammonia value 10 g / L, temperature 60°C, and nitrogen as the protective gas; the reaction conditions used to prepare the odd-numbered layer precursor are as follows: pH 11, ammonia value 10 g / L, temperature 55°C, and nitrogen as the protective gas;

[0153] In the obtained precursor, the core precursor is Ni 0.9 Co 0.05 Mn 0.05 (OH)2, the total number of layers of the coating layer precursors covering the core precursor is; among which, the coating layer precursors of even numbers from the inside to the outside are Ni 0.9 Co 0.05 Mn 0.05 (OH)2, the odd-numbered coating layer precursor is Ni 0.873 Co 0.0485 Mn 0.0485 Al 0.03 (OH)2; the radius of the core precursor is 2 μm, and the thickness of the coating layer precursor from the inside to the outside is 1.8 μm, 1.7 μm, and 1.5 μm;

[0154] (3) The precursor obtained in step (2) is uniformly mixed with lithium hydroxide, and the resulting mixture is placed in a sintering furnace. In an oxygen atmosphere, the temperature is increased to 500° C. at a heating rate of 6° C. / min and kept at the constant temperature for 4 h; then the temperature is increased to 850° C. at a heating rate of 4° C. / min and kept at the constant temperature for 15 h to obtain a positive electrode material (denoted as P8);

[0155] P8 has an equiaxed crystal stacking core LiNi 0.9 Co 0.05 Mn 0.05 O2, and three layers of coating covering the core; among them, from the inside to the outside, the odd-numbered layers are LiNi 0.873 Co 0.0485 Mn 0.0485 Al 0.03 O2, is a columnar crystal radially arranged layer; the even-numbered layers are LiNi 0.9 Co 0.05 Mn 0.05 O2, is an equiaxed crystal stacking layer;

[0156] The average particle size of P8 is 14 μm, wherein the radius of the inner core is 2 μm, and the thickness of the coating from the inside to the outside is 1.8 μm, 1.7 μm, and 1.5 μm.

[0157] Comparative Example 1

[0158] (1) nickel sulfate, cobalt sulfate, manganese sulfate and water are prepared into a salt solution (total metal ion concentration is 2 mol / L); the precipitant is a NaOH aqueous solution (NaOH concentration is 6 mol / L); the complexing agent is ammonia water with a concentration of 8 mol / L; the salt solution, precipitant and complexing agent are mixed to obtain a reaction system A;

[0159] (2) The reaction system A is reacted under the following reaction conditions: pH 11.5, ammonia value 10 g / L, temperature 60°C, and nitrogen as protective gas; the reaction is stopped when the D50 of the product reaches 16 μm to obtain a slurry containing the precursor, and the slurry is washed, filtered, dried, sieved, and iron removed to obtain a precursor Ni 0.9 Co 0.05 Mn 0.05 (OH)2;

[0160] (3) The precursor obtained in step (2) is uniformly mixed with lithium hydroxide, and the resulting mixture is placed in a sintering furnace. In an oxygen atmosphere, the temperature is increased to 500° C. at a heating rate of 6° C. / min and kept at the constant temperature for 4 h; then the temperature is increased to 850° C. at a heating rate of 4° C. / min and kept at the constant temperature for 15 h to obtain a positive electrode material (denoted as D1);

[0161] D1 is LiNi 0.9 Co 0.05 Mn 0.05 O2, average particle size is 16μm.

[0162] Comparative Example 2

[0163] (1) nickel sulfate, cobalt sulfate and manganese sulfate are prepared into a salt solution (the total metal ion concentration is 2 mol / L); aluminum sulfate, boric acid and water are prepared into a dopant solution (the doping element ion concentration is 0.5 mol / L, wherein the molar ratio of doping element Al:B is 1:1); the precipitant is a NaOH aqueous solution (the NaOH concentration is 6 mol / L); the complexing agent is ammonia water with a concentration of 8 mol / L;

[0164] The salt solution, dopant solution, precipitant and complexing agent are mixed to obtain a reaction system B;

[0165] (2) The reaction system B is reacted under the following reaction conditions: pH 11, ammonia value 10 g / L, temperature 55°C, and nitrogen as protective gas; the reaction is stopped when the D50 of the product reaches 14.5 μm to obtain a slurry containing the precursor, and the slurry is washed, filtered, dried, sieved, and iron removed to obtain a precursor Ni 0.882 Co 0.049 Mn 0.049 B 0.01 Al 0.01 (OH)2;

[0166] (3) The precursor obtained in step (2) is uniformly mixed with lithium hydroxide, and the resulting mixture is placed in a sintering furnace. In an oxygen atmosphere, the temperature is increased to 500° C. at a heating rate of 6° C. / min and kept at the constant temperature for 4 h; then the temperature is increased to 850° C. at a heating rate of 4° C. / min and kept at the constant temperature for 15 h to obtain a positive electrode material (denoted as D2);

[0167] D2 is LiNi 0.882 Co 0.049 Mn 0.049 B 0.01 Al 0.01 O2, average particle size is 14.5μm.

[0168] Comparative Example 3

[0169] According to the method of Example 1, the difference is that in step (2), the reaction order of the core precursor and the reaction system B and the reaction system A is exchanged, that is, the core precursor first reacts with part of the reaction system A, and the obtained product then reacts with part of the reaction system B, and so on, and the reactions are performed alternately. The other steps and conditions are the same as those in Example 1, and a positive electrode material (denoted as D3) is obtained;

[0170] P3 has an equiaxed crystal stacking core LiNi 0.9 Co 0.05 Mn 0.05 O2, and 7 layers of coating covering the core; among them, from the inside to the outside, the odd-numbered layers are LiNi 0.9 Co 0.05 Mn0.05 O2, is an equiaxed crystal stacking layer; the even-numbered layers are LiNi 0.882 Co 0.049 Mn 0.04 9B 0.01 Al 0.01 O2, is a radially arranged layer of columnar crystals;

[0171] The average particle size of D3 is 16 μm, wherein the radius of the inner core is 1.7 μm, and the thickness of the coating from the inside to the outside is 1.5 μm, 1.3 μm, 1.1 μm, 0.9 μm, 0.7 μm, 0.5 μm, and 0.3 μm.

[0172] Test Case

[0173] Assemble lithium-ion batteries using the above-mentioned cathode materials P1-P8 and D1-D3:

[0174] Positive electrode: The positive electrode material (P1-P8, D1-D3), conductive agent (Carbon ECP), binder (PVDF 761) and dispersant (NMP) are uniformly mixed (wherein the weight ratio of positive electrode material: conductive agent: binder is 96:2:2) to obtain positive electrode slurry, and the positive electrode slurry is uniformly coated on a clean aluminum foil, and then baked and pressed to obtain a positive electrode sheet;

[0175] Negative electrode: The negative electrode material (graphite), conductive agent (Carbon ECP), binder (SBR), and thickener (CMC) are weighed in a weight ratio of 95:1:2:2, and mixed evenly in deionized water to obtain a negative electrode slurry, and the negative electrode slurry is evenly coated on a clean copper foil, and then baked and pressed to obtain a negative electrode sheet;

[0176] Diaphragm: Celgard PP2075 diaphragm (Celgard, USA);

[0177] Electrolyte: 1 mol / L LiPF6 solution (wherein the solvent is a mixture of EC, PC, EP, and PP in a weight ratio of 1:1:2:6) is used as the electrolyte;

[0178] The positive electrode, negative electrode, separator and electrolyte are assembled in sequence to obtain lithium-ion batteries (respectively denoted as B1-B8 and DB1-DB3).

[0179] The above batteries B1-B8 and DB1-DB3 were tested for capacity retention at 0.2C charge and discharge for 500 cycles at 25°C and a voltage of 2.7-4.2V. The results are shown in Table 1.

[0180] Table 1

[0181]

[0182] It can be seen from the data in Table 1 that the lithium ion batteries B1-B8 using the positive electrode materials P1-P8 provided by the present invention are cycled for 500 cycles under the above test conditions, and the capacity retention rate is greater than 85%, showing excellent cycle performance. This is because P1-P8 adopts the positive electrode material structure and chemical composition of the present invention, with stable structure and excellent electrical properties. The cracking phenomenon is greatly reduced during the charge and discharge cycle, and it can better resist electrolyte erosion. Compared with D1-D3, the cycle performance is significantly improved.

[0183] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A positive electrode material, characterized in that: The positive electrode material comprises: an equiaxed crystal stacking core, and a plurality of coating layers coating the equiaxed crystal stacking core; In the coating layer, from the inside to the outside, the odd-numbered layers are radially arranged layers of columnar crystals, and the even-numbered layers are equiaxed crystal stacking layers; the total number of layers of the coating layer is r, wherein 3≤r≤13, and r is an odd number; The chemical compositions of the equiaxed crystal stacking core and the equiaxed crystal stacking layer satisfy the chemical formula LiNi x1 M y1 O2, where 0.6≤x1≤0.98, 0.02≤y1≤0.4, x1+y1=1; The chemical composition of the columnar crystal radial arrangement layer satisfies the chemical formula LiNi x2 M y2 L m O2, where 0.6≤x2≤0.98, 0.02≤y2≤0.4, 0.001≤m≤0.03, x2+y2+m=1; Wherein, M is selected from at least one of Co, Mn and Ca; L is a doping element selected from at least one of Al, Zr, Ti, W, B, Mg, Mo, La and Nd.

2. The positive electrode material according to claim 1, wherein L is selected from at least one of Al, Zr, Ti, W and B; And / or, 0.8≤x1≤0.95, 0.05≤y1≤0.2; 0.8≤x2≤0.95, 0.05≤y2≤0.2, 0.005≤m≤0.

02.

3. The positive electrode material according to claim 1 or 2, wherein 5≤r≤7, and r is an odd number.

4. The positive electrode material according to any one of claims 1 to 3, wherein The average particle size of the positive electrode material is 6-24 μm; And / or, the radius of the inner core of the equiaxed crystal stacking is 1.5-3 μm; And / or, in the coating layer, the thickness of the innermost layer is 0.6-2.9 μm, and the thickness of each layer decreases by 0.1-0.8 μm from the inner to the outer.

5. A method for preparing a positive electrode material, comprising: (1) mixing a salt solution containing Ni and element M, a precipitant, and a complexing agent to obtain a reaction system A; mixing a salt solution containing Ni and element M, a salt solution containing element L, a precipitant, and a complexing agent to obtain a reaction system B; (2) reacting a portion of the reaction system A to obtain a first product stream containing a core precursor; The first product stream is reacted with a part of the reaction system B to obtain a second product stream containing a first coated product; then the second product stream is reacted with a part of the reaction system A to obtain a third product stream containing a second coated product; Then, the third product stream is reacted with a part of the reaction system B to obtain a fourth product stream containing the third coated product; By analogy, the obtained product stream is reacted alternately with reaction system A and reaction system B to obtain a precursor; (3) calcining the precursor and the lithium source to obtain a positive electrode material; The precursor comprises: a core precursor, and a plurality of coating layer precursors coating the core precursor; the total number of layers of the coating layer precursors is r, wherein 3≤r≤13, and r is an odd number; The amount of the salt solution containing Ni and element M, the salt solution containing element L, the precipitant and the complexing agent is such that the chemical composition of the core precursor and the even-numbered coating layer precursors from the inside to the outside satisfies the chemical formula Ni x1 M y1 (OH)2, where 0.6≤x1≤0.98, 0.02≤y1≤0.4, x1+y1=1; The chemical composition of the odd-numbered coating layer precursors from the inside to the outside satisfies the chemical formula Ni x2 M y2 L m (OH)2, where 0.6≤x2≤0.98, 0.02≤y2≤0.4, 0.001≤m≤0.03, x2+y2+m=1; Wherein, M is selected from at least one of Co, Mn and Ca; L is a doping element selected from at least one of Al, Zr, Ti, W, B, Mg, Mo, La and Nd.

6. The method according to claim 5, wherein: The precipitant is selected from at least one of sodium hydroxide, sodium carbonate and sodium bicarbonate; And / or, the complexing agent is selected from at least one of ammonia water, ammonium bicarbonate and ammonium sulfate; And / or, in step (2), the reaction conditions include: pH 9.8-12.5, ammonia value 2-20 g / L, and temperature 50-70°C.

7. The method according to claim 5 or 6, wherein: The average particle size of the precursor is 6-24 μm; and / or, the radius of the core precursor is 1.5-3 μm; And / or, in the coating layer precursor, the thickness of the innermost layer is 0.6-2.9 μm, and the thickness of each layer decreases by 0.1-0.8 μm from the inner to the outer.

8. The method according to any one of claims 5 to 7, wherein: The calcination is divided into low temperature sintering and high temperature sintering which are carried out in sequence; Preferably, the conditions for low-temperature sintering include: a heating rate of 2-8°C / min, a constant temperature of 400-620°C, and a constant temperature time of 2-8h; Preferably, the high temperature sintering conditions include: a heating rate of 2-8°C / min, a constant temperature of 650-950°C, and a constant temperature time of 8-20h.

9. A positive electrode material obtained by the method according to any one of claims 5 to 8.

10. A lithium ion battery comprising the positive electrode material according to any one of claims 1 to 4 and 9.

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