Cathode material, preparation method thereof and lithium ion battery

Abstract

The present application 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 stack inner core, and a plurality of coating layers covering the equiaxed crystal stack inner core; from inside to outside, the odd layers in the coating layers are columnar crystal radial arrangement layers, and the even layers are equiaxed crystal stack layers; the total number of the coating layers is r, wherein 3≤r≤13, and r is an odd number; the chemical composition of the equiaxed crystal stack inner core and the equiaxed crystal stack layers satisfies the chemical formula LiNi x1 M y1 O2, wherein 0.6≤x1≤0.98, 0.02≤y1≤0.4, and x1+y1=1; the chemical composition of the columnar crystal radial arrangement layers satisfies the chemical formula LiNi x2 M y2 L m O2, wherein 0.6≤x2≤0.98, 0.02≤y2≤0.4, 0.001≤m≤0.03, and x2+y2+m=1; wherein M is selected from at least one of Co, Mn and Ca; and L is a doping element. The positive electrode material is not prone to cracking during the charge and discharge cycle process, can resist electrolyte corrosion well, and has excellent cycle performance.

Description

TECHNICAL FIELD

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

[0002] With the development of the electric vehicle industry, higher energy density has become a key requirement for lithium ion batteries that provide power, and high-nickel positive electrode materials have become a research hotspot due to their high energy density. However, as the nickel content increases, the cycle performance of the positive electrode material gradually deteriorates. The failure of high-nickel positive electrode materials is closely related to the structure of the material and the interface properties of the surface of the material particles during the charging and discharging cycles. During the charging and discharging cycles, the high-nickel positive electrode material undergoes a phase change, and the repeated changes in the unit cell volume can cause the positive electrode material particles to crack and powder. The instability of the surface of the positive electrode material and the corrosion of the electrolyte during the cycle process can easily induce the formation of NiO through surface phase change, causing the surface layer to be deactivated. As the nickel content in the positive electrode material increases, the phenomena of unit cell volume change, particle surface phase change, and side reactions at the particle-electrolyte interface during the charging and discharging cycles will become more severe, leading to rapid capacity decay of high-nickel positive electrode materials during the charging and discharging cycles, and poor cycle performance seriously restricting the application of high-nickel positive electrode materials.

[0003] Therefore, it is urgent to reduce the cracking of the positive electrode material during the charging and discharging cycles and to reduce the corrosion of the electrolyte on the positive electrode material in order to improve the cycle performance of the positive electrode material. SUMMARY

[0004] The present application provides a positive electrode material, a preparation method thereof and a lithium ion battery to solve the problem of poor cycle performance caused by the cracking of the existing high-nickel positive electrode material during the charging and discharging cycles and the corrosion of the electrolyte.

[0005] To achieve the above-mentioned purpose, the first aspect of the present application provides a positive electrode material, which comprises: an equiaxed crystal stack inner core and a plurality of coating layers covering the equiaxed crystal stack inner core.

[0006] From the inside to the outside, the odd-numbered layers in the coating layer are columnar crystal radial arrangement layers, and the even-numbered layers are equiaxed crystal stack layers; the total number of coating layers is r, wherein 3≤r≤13, and r is an odd number;

[0007] The chemical composition of the equiaxed crystal stack inner core and the equiaxed crystal stack layer satisfies the chemical formula LiNi x1 M y1 O2, wherein 0.6≤x1≤0.98, 0.02≤y1≤0.4, and x1+y1=1;

[0008] The chemical composition of the columnar crystal radial arrangement layer satisfies the chemical formula LiNi x2 M y2 Lm O2, wherein 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] The second aspect of the present application provides a preparation method of 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 in the same way, alternately reacting the obtained product stream with the reaction system A and the reaction system B to obtain a precursor;

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

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

[0015] The feeding 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 inside to outside satisfies the chemical formula Ni x1 M y1 (OH)2, wherein 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 inside to outside satisfies the chemical formula Ni x2 M y2 L m (OH)2, wherein 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 application provides a positive electrode material prepared by the method of the second aspect.

[0019] The fourth aspect of the present application provides a lithium ion battery comprising the positive electrode material of the first aspect or the third aspect.

[0020] The positive electrode material provided by the present application has an equiaxed crystal stack core and a multi-layer structure coated outside the core, and the multi-layer structure is alternately arranged with the columnar crystal radial arrangement layer and the equiaxed crystal stack layer from inside to outside, wherein the structure of the columnar crystal radial arrangement layer is uniform in internal stress and high in mechanical strength, and is not easy to crack during the charging and discharging cycle; the multi-layer structure arranged alternately can disperse stress and reduce cracking, the interlayer boundary can effectively limit the expansion of the formed crack between different layers, and the outermost columnar crystal radial arrangement layer can reduce the corrosion of the electrolyte. Under the synergistic effect of the above factors, the positive electrode material provided by the present application is not easy to crack during the charging and discharging cycle, can better resist electrolyte corrosion, and has excellent cycle performance. BRIEF DESCRIPTION OF DRAWINGS

[0021] The accompanying drawings are included to provide a further understanding of the present application, and constitute a part of the specification, and are used together with the following detailed description to explain the present application, but do not constitute a limitation on the present application. In the drawings:

[0022] Figure 1 Structure schematic diagram of the positive electrode material P3 prepared for the third embodiment of the present application.

[0023] Explanation of reference signs

[0024] 1, equiaxed crystal stack core 2, columnar crystal radial arrangement layer

[0025] 3, equiaxed crystal stack layer DETAILED DESCRIPTION

[0026] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the present application. Any numeric range recited is intended to include all values from the lower value to the upper value. For values that are less than one, one unit in the lower value is considered to be 0.000... with the number of zeros being equal to the least significant digit of the upper value. For values that are greater than one, one unit in the upper value is considered to be 1 with the number of ones being equal to the least significant digit of the lower value. These are not to be taken as the preferred or critical values. The minimum and maximum values of each range are to be included in the range.

[0027] The positive electrode material comprises: an equiaxed crystal stack inner core, and a plurality of cladding layers cladding the equiaxed crystal stack inner core.

[0028] In the cladding layers, from inside to outside, odd layers are columnar crystal radial arrangement layers, and even layers are equiaxed crystal stack layers; the total number of the cladding layers is r, wherein 3≤r≤13, and r is an odd number.

[0029] The chemical composition of the equiaxed crystal stack inner core and the equiaxed crystal stack layers satisfies the chemical formula LiNi x1 M y1 O2, wherein 0.6≤x1≤0.98, 0.02≤y1≤0.4, and x1+y1=1.

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

[0031] 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 application has an inner core and a plurality of cladding layers cladded on the outer surface of the inner core, the inner core and the cladding layers adjacent thereto are in direct contact, the adjacent cladding layers are in direct contact, the plurality of cladding layers form a multilayer structure, and from inside to outside, the cladding layers are alternately arranged in columnar crystal radial arrangement layers and equiaxed crystal stack layers, and the outermost layer is a columnar crystal radial arrangement layer, wherein the inner core and the cladding layers of even layers satisfy the above chemical composition and are all equiaxed crystal stack layers, having the characteristics of small stress and stable structure; the cladding layers of odd layers satisfy the above chemical composition, the doping elements therein can promote the formation of columnar crystals, thereby strengthening the structural stability, and the cladding layers of odd layers are all columnar crystal radial arrangement layers, the mechanical strength of the columnar crystal radial arrangement layers is high, the internal stress of the structure is uniform, the columnar crystal radial arrangement layers are not prone to cracking during the charging and discharging cycle, and the corrosion of electrolyte can be reduced. The multilayer structure arranged alternately as above can disperse stress, reduce cracking caused by the charging and discharging cycle, slow down the expansion speed of cracking, and the interlayer boundary can inhibit the interlayer expansion of cracks. The positive electrode material provided by the application has the above specific structure and chemical composition, so that the cracking phenomenon is greatly reduced during the charging and discharging cycle, and the interface side reaction between the positive electrode material and electrolyte is reduced.

[0033] In the present application, the "equiaxed crystal stack" refers to that in the absence of dopant, the crystal growth has no obvious preferred orientation, each direction grows uniformly to form equiaxed crystal grains, and the stack forms a core and an even number of cladding layers. The "radial arrangement of columnar crystals" refers to that in the presence of dopant, the crystal tends to grow radially to form columnar crystal grains, and an odd number of cladding layers are formed.

[0034] According to the present application, in the positive electrode material, in the chemical formula LiNi x1 M y1 O2, LiNi x2 M y2 L m 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 electrolyte, and make the positive electrode material have better electrochemical performance.

[0035] According to the present application, in the positive electrode material, in the chemical formula LiNi x1 M y1 O2, LiNi x2 M y2 L m O2, x1, y1, x2, y2 and m are in the above defined range, preferably, 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.

[0036] According to the present application, the total number of cladding layers in the positive electrode material should take into account the structural stability of the material and the ease of operation in the preparation process, and should not be too few or too many. If the total number of cladding layers is too few, the structural stability of the positive electrode material is insufficient, and it is difficult to inhibit crack propagation during the cycle process; if the total number of cladding layers is too many, 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 cladding layers r, preferably, 5≤r≤7, and r is an odd number.

[0037] According to the present application, 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 realize a multi-layer structure, and the capacity is low; if the average particle size of the positive electrode material is too large, the structural stability will be poor and the processing performance will be poor.

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

[0039] According to the application, preferably, the radius of the core of the equiaxed crystal stack in the positive electrode material is 1.5-3 μm. If the radius of the core of the equiaxed crystal stack is too small, the core precursor particles grow for a short time during preparation, leading to uneven particle size and possibly poor sphericity of the core, affecting the performance of the overall positive electrode material. If the radius of the core of the equiaxed crystal stack is too large, the stability of the core will be poor, and micro-cracks are likely to occur.

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

[0041] According to the application, for the coating layer in the positive electrode material, preferably, the thickness of the innermost coating layer is 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 application, the thickness of the coating layer gradually decreases from the inside to the outside, which is conducive to the formation of a stable and ordered structure, avoids the formation of cracks that penetrate the particles, and reduces the performance degradation of the positive electrode material caused by electrolyte corrosion.

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

[0043] The positive electrode material provided by the application has significantly reduced cracking and pulverization during the charge and discharge cycle, can better resist electrolyte corrosion, has a high capacity retention rate during the cycle, and has excellent cycle performance compared to conventional high-nickel positive electrode materials.

[0044] The second aspect of the application provides a preparation method of a positive electrode material, comprising:

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

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

[0047] (3) the precursor and a lithium source are calcined 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 the coating layer precursors is r, wherein 3≤r≤13, and r is an odd number.

[0049] The feeding 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 inside to outside satisfies the chemical formula Ni x1 M y1 (OH)2, wherein 0.6≤x1≤0.98, 0.02≤y1≤0.4, and x1+y1=1.

[0050] The chemical composition of the odd-numbered coating layer precursors from inside to outside satisfies the chemical formula Ni x2 M y2 L m (OH)2, wherein 0.6≤x2≤0.98, 0.02≤y2≤0.4, 0.001≤m≤0.03, and 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 application, 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 electrolyte, and make the prepared positive electrode material have better electrochemical performance.

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

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

[0055] In the present application, the nickel salt, the M-containing salt, and the L-containing salt can be prepared by using water-soluble salts capable of providing Ni, the element M, and the element L, respectively, in a conventional coprecipitation method for preparing the positive electrode material precursor.

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

[0057] According to the present application, the amount of the precipitant fed is capable of completely precipitating the metal ions in the salt solution, and the hydroxyl ions contained in the remaining precipitant after precipitation or the hydroxyl ions produced by the hydrolysis of the remaining precipitant are capable of maintaining the required pH for the reaction in step (2).

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

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

[0060] According to the present application, in step (1), the reaction system A is used for preparing the inner core precursor (which is finally formed into the inner core of the positive electrode material) and for preparing the even-numbered layer coating precursor (which is finally formed into the even-numbered layer coating of the positive electrode material). The reaction system B is used for preparing the odd-numbered layer coating precursor (which is finally formed into the odd-numbered layer coating of the positive electrode material).

[0061] According to the application, in step (2), the precursor with a multi-layer structure is formed by using a reaction mode of "intermittent doping". Specifically, part of the reaction system A is first reacted to prepare an inner core precursor; when the generated inner core precursor reaches a target particle size, the first product stream containing the inner core precursor (i.e., the product system obtained after the reaction of the part of the reaction system A) is mixed with part of the reaction system B and reacts to coat a first layer of "coating layer precursor" on the surface of the inner core precursor, obtaining the first coating product; when the first coating product reaches a target particle size (i.e., reaches a target thickness of the first layer of "coating layer precursor"), the second product stream containing the first coating product (i.e., the product system obtained after the reaction of the first product stream and part of the reaction system B) is mixed with part of the reaction system A and reacts to coat a second layer of "coating layer precursor" on the surface of the first coating product, obtaining the second coating product; when the second coating product reaches a target particle size (i.e., reaches a target thickness of the second layer of "coating layer precursor"), the third product stream containing the second coating product (i.e., the product system obtained after the reaction of the second product stream and part of the reaction system A) is mixed with part of the reaction system B and reacts to coat a third layer of "coating layer precursor" on the surface of the second coating product, obtaining the third coating product; when the third coating product reaches a target particle size (i.e., reaches a target thickness of the third layer of "coating layer precursor"), the fourth product stream containing the third coating product (i.e., the product system obtained after the reaction of the third product stream and part of the reaction system B) is mixed with part of the reaction system A and reacts; and so on, the obtained product stream is alternately reacted with the reaction system A and the reaction system B to obtain the precursor. By using this reaction mode, the formed precursor has an "inner core" (the inner core precursor) and multiple coating layer precursors coating the "inner core", wherein the total number of the coating layer precursors is odd, and the odd number of coating layer precursors are element L-doped.

[0062] According to the application, in step (2), for the precursor, in the chemical formula Ni x1 M y1 (OH)2and Ni x2 M y2 L m (OH)2, x1, y1, x2, y2, and m preferably satisfy 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 on the basis of satisfying the above defined range. This can make the positive electrode material have a more optimal structure and better electrical performance.

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

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

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

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

[0067] In the present application, the thickness of the cladding layer precursor can be determined by a laser particle size analyzer, specifically, the thickness of the cladding layer precursor = (D50 包覆后的颗粒 -D50 包覆前的颗粒 ) / 2

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

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

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

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

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

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

[0074] According to the present application, in step (3), the type of the lithium source is limited to be wide, and the conventional lithium source for preparing the positive electrode material in the art can be selected, and preferably, lithium hydroxide is selected.

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

[0076] According to the present application, preferably, the conditions of the low-temperature sintering include: the heating rate is 2-8℃ / min, the constant temperature is 400-620℃, and the constant temperature time is 2-8h.

[0077] According to the present application, preferably, the conditions of the high-temperature sintering include: the heating rate is 2-8℃ / min, the constant temperature is 650-950℃, and the constant temperature time is 8-20h.

[0078] According to the present application, in step (3), the calcination is performed in an air or oxygen atmosphere.

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

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

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

[0082] The fourth aspect of the present application provides a lithium ion battery containing the positive electrode material of the first aspect or the third aspect.

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

[0084] The present application will be described in detail below by way of examples. In the following examples and comparative examples, if not otherwise specified, the methods are conventional methods; and the reagents and materials, if not otherwise specified, can be obtained from commercial channels.

[0085] Example 1

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

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

[0088] (2) Part of the above reaction system A was reacted, and when the D50 of the obtained inner core precursor reached 3.4 μm, a first product stream containing the inner core precursor was mixed with part of the reaction system B and reacted to coat a first layer of coating layer precursor on the surface of the inner core precursor, thereby obtaining a first coating product; when the D50 of the obtained first coating product reached 6.4 μm, a second product stream containing the first coating product was mixed with part of the reaction system A and reacted to coat a second layer of coating layer precursor on the surface of the first coating product, thereby obtaining a second coating product; when the D50 of the second coating product reached 9 μm, a third product stream containing the second coating product was mixed with part of the reaction system B and reacted to coat a third layer of coating layer precursor on the surface of the second coating product, thereby obtaining a third coating product; when the D50 of the third coating product reached 11.2 μm, a fourth product stream containing the third coating product was mixed with part of the reaction system A and reacted; in this way, the obtained product stream was alternately reacted with the reaction system A and the reaction system B to obtain a slurry containing the precursor, and the slurry was washed, filtered, dried, sieved and de-ironed to obtain the precursor;

[0089] The reaction conditions for preparing the inner core precursor and the even-numbered layers of coating layer precursor were as follows: pH was 11.5, ammonia value was 10 g / L, temperature was 60℃, and nitrogen was used as the protective gas; the reaction conditions for preparing the odd-numbered layers of coating layer precursor were as follows: pH was 11, ammonia value was 10 g / L, temperature was 55℃, and nitrogen was used as the protective gas;

[0090] The obtained precursor comprised an inner core precursor Ni 0.9 Co 0.05 Mn 0.05 (OH)2, and a total of 7 layers of coating layer precursor coated on the inner core precursor; wherein the even-numbered layers of coating layer precursor from the inside to the outside were Ni 0.9 Co 0.05Mn 0.05 (OH)2, the odd-numbered layers of the coating layer precursor are Ni 0.882 Co 0.049 Mn 0.049 B 0.01 Al 0.01 (OH)2; the radius of the inner core precursor is 1.7 μm, and the thickness of the coating layer precursor from inside to 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) uniformly mixing the precursor obtained in step (2) with lithium hydroxide, and placing the obtained mixture in a sintering furnace, and heating to 500 ℃ at a heating rate of 6 ℃ / min in an oxygen atmosphere, and keeping the temperature for 4 h; then heating to 850 ℃ at a heating rate of 4 ℃ / min, and keeping the temperature for 15 h, to obtain a positive electrode material (denoted as P1);

[0092] P1 has an equiaxed crystal stack inner core LiNi 0.9 Co 0.05 Mn 0.05 O2, and 7 layers of coating layers covering the inner core; wherein, from inside to outside, the odd-numbered layers are LiNi 0.882 Co 0.049 Mn 0.049 B 0.01 Al 0.01 O2, which are radially arranged layers of columnar crystals; the even-numbered layers are LiNi 0.9 Co 0.05 Mn 0.05 O2, which are equiaxed crystal stack layers;

[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 layer from inside to 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) preparing a salt solution (the total metal ion concentration is 2 mol / L) by using nickel sulfate, cobalt sulfate, manganese sulfate, and water; preparing a dopant solution (the dopant element ion concentration is 0.5 mol / L, wherein the molar ratio of the dopant elements W:Ti is 1:1) by using tungsten carbonate, titanium isopropoxide, and water; the precipitating agent is an aqueous NaOH solution (the NaOH concentration is 6 mol / L); the complexing agent is ammonia water with a concentration of 8 mol / L;

[0096] Mixing the above salt solution, precipitating agent, and complexing agent to obtain a reaction system A; mixing the above salt solution, dopant solution, precipitating agent, and complexing agent to obtain a reaction system B;

[0097] (2) when the D50 of the obtained core precursor reaches 3.6 μm, the first product stream containing the core precursor is mixed with part of the reaction system B and reacts to coat the first layer of coating precursor on the surface of the core precursor, obtaining a first coating product; when the D50 of the obtained first coating product reaches 6.6 μm, the second product stream containing the first coating product is mixed with part of the reaction system A and reacts to coat the second layer of coating precursor on the surface of the first coating product, obtaining a second coating product; when the D50 of the second coating product reaches 9.2 μm, the third product stream containing the second coating product is mixed with part of the reaction system B and reacts to coat the third layer of coating precursor on the surface of the second coating product, obtaining a third coating product; when the D50 of the third coating product reaches 11.4 μm, the fourth product stream containing the third coating product is mixed with part of the reaction system A and reacts; in this way, the obtained product stream is alternately mixed 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 de-ironed to obtain the precursor;

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

[0099] The obtained precursor contains the core precursor Ni 0.9 Co 0.05 Mn 0.05 (OH)2, and the total number of the layers of coating precursor coating the core precursor is 5; the even-numbered layer of coating precursor from the inside to the outside is Ni 0.9 Co 0.05 Mn 0.05 (OH)2, and the odd-numbered layer of coating 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 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) uniformly mixing the precursor obtained in step (2) with lithium hydroxide, and placing the mixture into a sintering furnace, and heating to 500℃ at a heating rate of 6℃ / min in an oxygen atmosphere, and keeping the temperature for 4h; then heating to 850℃ at a heating rate of 4℃ / min, and keeping the temperature for 15h, to obtain a positive electrode material (denoted as P2);

[0101] P2 has an equiaxed crystal stack core LiNi 0.9 Co 0.05 Mn 0.05 O2, and 5 layers of coating layers covering the core; wherein, from inside to outside, the odd layers are LiNi 0.891 Co 0.0495 Mn 0.0495 W 0.005 Ti 0.005 O2, which are radially arranged layers of columnar crystals; and the even layers are LiNi 0.9 Co 0.05 Mn 0.05 O2, which are equiaxed crystal stack layers.

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

[0103] Example 3

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

[0105] Mixing the above salt solution, precipitant and complexing agent to obtain a reaction system A; mixing the above salt solution, dopant solution, precipitant and complexing agent to obtain a reaction system B;

[0106] (2) when the D50 of the obtained core precursor reaches 4 μm, the first product stream containing the core precursor is mixed with part of the reaction system B and reacts to coat the first layer of coating precursor on the surface of the core precursor, obtaining a first coating product; when the D50 of the obtained first coating product reaches 7.2 μm, the second product stream containing the first coating product is mixed with part of the reaction system A and reacts to coat the second layer of coating precursor on the surface of the first coating product, obtaining a second coating product; when the D50 of the second coating product reaches 10 μm, the third product stream containing the second coating product is mixed with part of the reaction system B and reacts to coat the third layer of coating precursor on the surface of the second coating product, obtaining a third coating product; when the D50 of the third coating product reaches 12.4 μm, the fourth product stream containing the third coating product is mixed with part of the reaction system A and reacts; in this way, the obtained product stream is alternately mixed 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 de-ironed to obtain the precursor;

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

[0108] The obtained precursor comprises a core precursor Ni 0.9 Co 0.05 Mn 0.05 (OH)2, and the total number of layers of the coating precursor coating the core precursor is 3; wherein the even-numbered layer of coating precursor from the inside to the outside is Ni 0.9 Co 0.05 Mn 0.05 (OH)2, the odd-numbered layer of coating 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 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 obtained mixture is placed in a sintering furnace, heated to 500°C at a heating rate of 6°C / min under an oxygen atmosphere, and kept at 500°C for 4 h; then heated to 850°C at a heating rate of 4°C / min, and kept at 850°C for 15 h, to obtain a positive electrode material (denoted as P3);

[0110] As shown in Figure 1 P3 has an equiaxed crystal stack core LiNi 0.9 Co 0.05 Mn 0.05 O2, and 3 layers of cladding layers cladding the core; wherein, from inside to outside, the odd layers are LiNi 0.882 Co 0.049 Mn 0.049 B 0.01 Al 0.01 O2, which are columnar crystal radial arrangement layers; the even layers are LiNi 0.9 Co 0.05 Mn 0.05 O2, which are equiaxed crystal stack layers;

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

[0112] Example 4

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

[0114] Mix the above salt solution, precipitant and complexing agent to obtain reaction system A; mix the above salt solution, dopant solution, precipitant and complexing agent to obtain reaction system B;

[0115] (2) when the D50 of the obtained core precursor reaches 4 μm, the first product stream containing the core precursor is mixed with part of the reaction system B and reacts to coat the first layer of coating precursor on the surface of the core precursor, obtaining a first coating product; when the D50 of the obtained first coating product reaches 7.2 μm, the second product stream containing the first coating product is mixed with part of the reaction system A and reacts to coat the second layer of coating precursor on the surface of the first coating product, obtaining a second coating product; when the D50 of the second coating product reaches 10 μm, the third product stream containing the second coating product is mixed with part of the reaction system B and reacts to coat the third layer of coating precursor on the surface of the second coating product, obtaining a third coating product; when the D50 of the third coating product reaches 12.4 μm, the fourth product stream containing the third coating product is mixed with part of the reaction system A and reacts; in this way, the obtained product stream is alternately mixed 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 de-ironed to obtain the precursor;

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

[0117] The obtained precursor comprises a core precursor Ni 0.9 Co 0.05 Mn 0.05 (OH)2, and the total number of layers of the coating precursor coating the core precursor is 5; wherein the even-numbered layer of coating precursor from the inside to the outside is Ni 0.9 Co 0.05 Mn 0.05 (OH)2, and the odd-numbered layer of coating 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 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 obtained mixture is placed in a sintering furnace, heated to 500°C at a heating rate of 6°C / min under an oxygen atmosphere, and kept at 500°C for 4 h; then heated to 850°C at a heating rate of 4°C / min, and kept at 850°C for 15 h, to obtain a positive electrode material (denoted as P4).

[0119] P4 has an equiaxed crystal stack core LiNi 0.9 Co 0.05 Mn 0.05 O2, and 5 layers of cladding layers cladding the core; wherein, from inside to outside, the odd layers are LiNi 0.873 Co 0.0485 Mn 0.0485 Zr 0.01 Al 0.02 O2, and the even layers are LiNi 0.9 Co 0.05 Mn 0.05 O2, and the even layers are LiNi

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

[0121] Example 5

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

[0123] Mix the above salt solution, precipitant and complexing agent to obtain reaction system A; mix the above salt solution, dopant solution, precipitant and complexing agent to obtain reaction system B;

[0124] (2) when the D50 of the obtained core precursor reaches 3.6 μm, the first product stream containing the core precursor is mixed with part of the reaction system B and reacts to coat the first layer of coating precursor on the surface of the core precursor, to obtain a first coating product; when the D50 of the obtained first coating product reaches 6.6 μm, the second product stream containing the first coating product is mixed with part of the reaction system A and reacts to coat the second layer of coating precursor on the surface of the first coating product, to obtain a second coating product; when the D50 of the second coating product reaches 9.2 μm, the third product stream containing the second coating product is mixed with part of the reaction system B and reacts to coat the third layer of coating precursor on the surface of the second coating product, to obtain a third coating product; when the D50 of the third coating product reaches 11.4 μm, the fourth product stream containing the third coating product is mixed with part of the reaction system A and reacts; in this way, the obtained product stream is alternately mixed 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 de-ironed to obtain the precursor;

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

[0126] The obtained precursor contains the core precursor Ni 0.9 Co 0.05 Mn 0.05 (OH)2, and the total number of the layers of coating precursor coating the core precursor is 5; the even-numbered layer of coating precursor from the inside to the outside is Ni 0.9 Co 0.05 Mn 0.05 (OH)2, the odd-numbered layer of coating 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 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 obtained mixture is placed in a sintering furnace, heated to 500°C at a heating rate of 6°C / min under an oxygen atmosphere, and kept at 500°C for 4 h; then heated to 850°C at a heating rate of 4°C / min, and kept at 850°C for 15 h, to obtain a positive electrode material (denoted as P5);

[0128] P5 has an equiaxed crystal stack core LiNi 0.9 Co 0.05 Mn 0.05 O2, and 5 layers of cladding layers cladding the core; wherein, from inside to outside, the odd layers are LiNi 0.882 Co 0.049 Mn 0.049 Mg 0.02 O2, and the even layers are LiNi 0.9 Co 0.05 Mn 0.05 O2, and the even layers are LiNi

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

[0130] Example 6

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

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

[0133] (2) when the D50 of the obtained core precursor reaches 4 μm, mixing the first product stream containing the core precursor with part of the reaction system B and allowing the mixture to react to coat the first layer of coating precursor on the surface of the core precursor, thereby obtaining a first coating product; when the D50 of the obtained first coating product reaches 7.2 μm, mixing the second product stream containing the first coating product with part of the reaction system A and allowing the mixture to react to coat the second layer of coating precursor on the surface of the first coating product, thereby obtaining a second coating product; when the D50 of the second coating product reaches 10 μm, mixing the third product stream containing the second coating product with part of the reaction system B and allowing the mixture to react to coat the third layer of coating precursor on the surface of the second coating product, thereby obtaining a third coating product; when the D50 of the third coating product reaches 12.2 μm, mixing the fourth product stream containing the third coating product with part of the reaction system A and allowing the mixture to react; in this way, the obtained product stream is alternately mixed 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 de-ironed to obtain the precursor;

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

[0135] In the obtained precursor, the core precursor is Ni 0.9 Co 0.05 Mn 0.05 (OH)2, and the total number of layers of the coating precursor coating the core precursor is 7; the even-numbered layer of coating precursor from the inside to the outside is Ni 0.9 Co 0.05 Mn 0.05 (OH)2, and the odd-numbered layer of coating 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 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) uniformly mixing the precursor obtained in step (2) with lithium hydroxide, and placing the mixture into a sintering furnace, and heating to 500 DEG C at a heating rate of 6 DEG C / min under an oxygen atmosphere, and keeping the temperature for 4 h; then heating to 850 DEG C at a heating rate of 4 DEG C / min, and keeping the temperature for 15 h, to obtain a positive electrode material (denoted as P6);

[0137] P6 has an equiaxed crystal stack core LiNi 0.9 Co 0.05 Mn 0.05 O2, and 7 layers of coating layers covering the core; wherein, from inside to outside, the odd layers are LiNi 0.886 Co 0.0495 Mn 0.0495 Mo 0.005 La 0.005 O2, which are radially arranged layers of columnar crystals; and the even layers are LiNi 0.9 Co 0.05 Mn 0.05 O2, which are equiaxed crystal stack layers;

[0138] The average particle size of P6 is 17 μm, wherein the radius of the core is 2 μm, and the thicknesses of the coating layers from inside to outside are 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) preparing a salt solution (total metal ion concentration is 2 mol / L) by mixing nickel sulfate, cobalt sulfate, manganese sulfate and water; preparing a dopant solution (doping element ion concentration is 0.5 mol / L, wherein the molar ratio of doping elements Mg:La is 1:1) by mixing magnesium sulfate, lanthanum nitrate and water; the precipitant is NaOH aqueous solution (NaOH concentration is 6 mol / L); the complexing agent is ammonia water with a concentration of 8 mol / L;

[0141] Mixing the above salt solution, precipitant and complexing agent to obtain a reaction system A; mixing the above salt solution, dopant solution, precipitant and complexing agent to obtain a reaction system B;

[0142] (2) when the D50 of the obtained core precursor reaches 3.6 μm, the first product stream containing the core precursor is mixed with part of the reaction system B and reacts to coat the first layer of coating precursor on the surface of the core precursor, obtaining 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 part of the reaction system A and reacts to coat the second layer of coating precursor on the surface of the first coating product, obtaining a second coating product; when the D50 of the second coating product reaches 10.2 μm, the third product stream containing the second coating product is mixed with part of the reaction system B and reacts to coat the third layer of coating precursor on the surface of the second coating product, obtaining a third coating product; when the D50 of the third coating product reaches 13.2 μm, the fourth product stream containing the third coating product is mixed with part of the reaction system A and reacts; in this way, the obtained product stream is alternately mixed 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 de-ironed to obtain the precursor;

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

[0144] The obtained precursor is a core precursor Ni 0.9 Co 0.05 Mn 0.05 (OH)2, and the total number of layers of the coating precursor coating the core precursor is 3; the even-numbered layer of coating precursor from the inside to the outside is Ni 0.9 Co 0.05 Mn 0.05 (OH)2, and the odd-numbered layer of coating 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 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) is uniformly mixed with lithium hydroxide, and the obtained mixture is placed in a sintering furnace, heated to 500°C at a heating rate of 6°C / min under an oxygen atmosphere, and kept at 500°C for 4 h; then heated to 850°C at a heating rate of 4°C / min, and kept at 850°C for 15 h, to obtain a positive electrode material (denoted as P7);

[0146] P7 has an equiaxed crystal stack core LiNi 0.9 Co 0.05 Mn 0.05 O2, and 3 layers of coating layers covering the core; wherein, from inside to outside, the odd layers are LiNi 0.882 Co 0.049 Mn 0.049 Mg 0.01 La 0.01 O2, which are radially arranged layers of columnar crystals; the even layers are LiNi 0.9 Co 0.05 Mn 0.05 O2, which are equiaxed crystal stack layers;

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

[0148] Example 8

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

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

[0151] (2) when the D50 of the obtained core precursor reaches 4 μm, the first product stream containing the core precursor is mixed with part of the reaction system B and reacts to coat the first layer of coating precursor on the surface of the core precursor, obtaining a first coating product; when the D50 of the obtained first coating product reaches 7.6 μm, the second product stream containing the first coating product is mixed with part of the reaction system A and reacts to coat the second layer of coating precursor on the surface of the first coating product, obtaining a second coating product; when the D50 of the second coating product reaches 11 μm, the third product stream containing the second coating product is mixed with part of the reaction system B and reacts to coat the third layer of coating precursor on the surface of the second coating product, obtaining a third coating product; when the D50 of the third coating product reaches 14 μm, the fourth product stream containing the third coating product is mixed with part of the reaction system A and reacts; in this way, the obtained product stream is alternately mixed 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 de-ironed to obtain the precursor;

[0152] The reaction conditions for preparing the core precursor and the even-numbered layer of coating precursor are as follows: pH is 11.5, ammonia value is 10 g / L, temperature is 60℃, and nitrogen is used as the protective gas; the reaction conditions for preparing the odd-numbered layer of coating precursor are as follows: pH is 11, ammonia value is 10 g / L, temperature is 55℃, and nitrogen is used 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 precursor coating the core precursor is; wherein the even-numbered layer of coating precursor from the inside to the outside is Ni 0.9 Co 0.05 Mn 0.05 (OH)2, the odd-numbered layer of coating 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 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 obtained mixture is placed in a sintering furnace, heated to 500℃ at a heating rate of 6℃ / min under an oxygen atmosphere, and kept at 500℃ for 4 h; then heated to 850℃ at a heating rate of 4℃ / min, and kept at 850℃ for 15 h, to obtain a positive electrode material (denoted as P8);

[0155] P8 has an equiaxed crystal stack core LiNi 0.9 Co 0.05 Mn 0.05 O2, and 3 layers of coating layers covering the core; wherein, from inside to outside, the odd layers are LiNi 0.873 Co 0.0485 Mn 0.0485 Al 0.03 O2, and the even layers are LiNi 0.9 Co 0.05 Mn 0.05 O2, which is an equiaxed crystal stack layer.

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

[0157] Comparative Example 1

[0158] (1) A salt solution (total metal ion concentration of 2 mol / L) was prepared by mixing nickel sulfate, cobalt sulfate, manganese sulfate and water; the precipitating agent was an aqueous NaOH solution (NaOH concentration of 6 mol / L); the complexing agent was ammonia water with a concentration of 8 mol / L; the above salt solution, precipitating agent and complexing agent were mixed to obtain a reaction system A;

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

[0160] (3) The precursor obtained in step (2) was uniformly mixed with lithium hydroxide, and the obtained mixture was placed in a sintering furnace, heated to 500°C at a heating rate of 6°C / min under an oxygen atmosphere, and kept at 500°C for 4 h; then heated to 850°C at a heating rate of 4°C / min, and kept at 850°C 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, with an average particle size of 16 μm.

[0162] Comparative Example 2

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

[0164] Mix the above salt solution, dopant solution, precipitant and complexing agent to obtain a reaction system B;

[0165] (2) React the reaction system B to obtain a slurry containing a precursor, and wash, filter, dry, sieve and remove iron from the slurry to obtain the precursor Ni 0.882 Co 0.049 Mn 0.049 B 0.01 Al 0.01 (OH)2.

[0166] (3) Uniformly mix the precursor obtained in step (2) with lithium hydroxide, and place the mixture in a sintering furnace, heat to 500°C at a heating rate of 6°C / min under an oxygen atmosphere, and keep the temperature constant for 4 h; then heat to 850°C at a heating rate of 4°C / min, and keep the temperature constant 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, and the average particle size is 14.5 μm.

[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 then the obtained product reacts with part of the reaction system B, and so on. The other steps and conditions are the same as those in Example 1 to obtain a positive electrode material (denoted as D3);

[0170] P3 has an equiaxed crystal stack core LiNi 0.9 Co 0.05 Mn 0.05 O2, and 7 layers of coating layers covering the core; wherein, from inside to outside, the odd layers are LiNi 0.9 Co 0.05 Mn0.05 O2, the even layers are LiNi 0.882 Co 0.049 Mn 0.04 9B 0.01 Al 0.01 O2, the even layers are LiNi

[0171] The average particle size of D3 is 16 μm, wherein the radius of the core is 1.7 μm, and the thickness of the coating layers from inside to 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 Example

[0173] The lithium ion batteries were assembled using the above positive electrode 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 dispersing agent (NMP) were uniformly mixed (wherein the weight ratio of the positive electrode material: conductive agent: binder was 96:2:2), to obtain a positive electrode slurry, and the positive electrode slurry was uniformly coated on a clean aluminum foil, and was baked and pressed to obtain a positive electrode sheet;

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

[0176] Separator: Celgard PP2075 separator (American Celgard Company) was used;

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

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

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

[0180] Table 1

[0181]

[0182] As shown in Table 1, the lithium ion batteries B1-B8 using the positive electrode materials P1-P8 provided by the application have a capacity retention rate greater than 85% after 500 cycles under the above test conditions, and exhibit excellent cycle performance. This is because the P1-P8 uses the positive electrode material structure and chemical composition of the application, the structure is stable, the electrical performance is excellent, the cracking phenomenon is greatly reduced during the charge-discharge cycle process, and can better resist electrolyte corrosion, and the cycle performance is significantly improved compared with D1-D3.

[0183] The preferred embodiments of the application are described in detail above, but the application is not limited thereto. Within the technical concept of the application, various simple modifications can be made to the technical solutions of the application, including the combination of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the application and fall within the protection scope of the application.

Claims

1. A positive electrode material, characterized in that, The cathode material includes: an equiaxed crystal stacked core, and a plurality of coating layers covering the equiaxed crystal stacked core; In the coating layer, from the inside out, the odd-numbered layers are columnar crystal radially arranged layers, and the even-numbered layers are equiaxed crystal stacked layers; the total number of coating layers is r, where 3≤r≤13, and r is an odd number; The chemical composition of the equiaxed crystal stacked core and the equiaxed crystal stacked layer satisfies 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 radially arranged columnar crystal 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 cathode 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 cathode material according to claim 1 or 2, wherein, 5≤r≤7, and r is an odd number.

4. The cathode material according to claim 1 or 2, wherein, The average particle size of the cathode material is 6-24 μm; And / or, the radius of the equiaxed crystal stacked core 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 inside to the outside.

5. The cathode material according to claim 3, wherein, The average particle size of the cathode material is 6-24 μm; And / or, the radius of the equiaxed crystal stacked core 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 inside to the outside.

6. A method for preparing the cathode material according to any one of claims 1-5, comprising: (1) Mix the salt solution containing Ni and element M, the precipitant, and the complexing agent to obtain reaction system A; mix the salt solution containing Ni and element M, the salt solution containing element L, the precipitant, and the complexing agent to obtain reaction system B; (2) A portion of the reaction system A is reacted to obtain the first product stream containing the kernel precursor; The first product stream is reacted with a portion of reaction system B to obtain a second product stream containing the first coated product; then the second product stream is reacted with a portion of reaction system A to obtain a third product stream containing the second coated product. The third product stream is then reacted with a portion of reaction system B to obtain a fourth product stream containing the third coated product. By alternating the product streams, reaction systems A and B are carried out to obtain precursors. (3) The precursor and lithium source are calcined to obtain the cathode material; The precursor includes a core precursor and multiple coating layer precursors covering the core precursor; the total number of coating layer precursors is r, where 3≤r≤13, and r is an odd number. The amounts of the Ni- and element M salt solution, the element L salt solution, the precipitant, and the complexing agent added are such that the chemical composition of the core precursor and the even-numbered coating layer precursor from the inside out 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 out 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.

7. The method according to claim 6, 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, 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 ℃.

8. The method according to claim 6 or 7, wherein, The average particle size of the precursor is 6-24 μm; And / or, the radius of the kernel 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 inside to the outside.

9. The method according to claim 6 or 7, wherein, The calcination process is divided into sequential low-temperature sintering and high-temperature sintering. The conditions for low-temperature sintering include: a heating rate of 2-8℃ / min, a constant temperature of 400-620℃, and a constant temperature time of 2-8h. The conditions for high-temperature sintering include: a heating rate of 2-8℃ / min, a constant temperature of 650-950℃, and a constant temperature time of 8-20h.

10. A lithium-ion battery comprising the positive electrode material according to any one of claims 1-5.

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