A positive electrode active material having a combination of large and small particles and a method for preparing the same

Abstract

The present application belongs to the field of lithium ion batteries, and discloses a positive electrode active material with large and small particles, which comprises large particle secondary balls and small particle secondary balls, wherein the mass percentage of the large particle secondary balls is not less than 50%; the D50 particle size of the large particle secondary balls is 10-20 mu m, and the D50 particle size of the small particle secondary balls is 2-5 mu m. The doping elements and nickel content of the large and small particles are strictly controlled, and finally a positive electrode material with good comprehensive performance of capacity, cycle and DCR is obtained. The present application also discloses a preparation method of the positive electrode active material with large and small particles, different elements are doped in the precursor stage, the size of the primary particles of the material after sintering is controlled, and the sintering temperature of the large and small particles is indirectly satisfied during the co-sintering process, so that the performance of the co-sintering material of the large and small particles can reach a better level.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries, and particularly relates to a positive electrode active material with a combination of large and small particles and its preparation method. Background Technology

[0002] To improve the compaction density of lithium-ion batteries, the industry commonly uses a combination of large and small particles to prepare electrode sheets, further enhancing energy density. However, large and small secondary particles have different characteristics. Therefore, when heat-treated simultaneously, the small secondary particles may be over-calcined, or the large secondary particles may be under-calcined, leading to performance degradation. Thus, the usual calcination method involves heat-treating the large and small secondary particles separately, and then mixing the heat-treated particles before further heat treatment. The need for several heat treatment processes complicates the preparation of the positive electrode active material and increases manufacturing costs.

[0003] Chinese patent document CN114447289A discloses a method for co-sintering large and small particles. The large secondary spheres contain Al, while the small particles contain Mn, with the Mn content in the large particles being less than that in the small particles. The sintering conditions are controlled by varying the precursor element content, and manganese coats the surface of each large secondary particle, while aluminum coats the surface of each small secondary particle. Chinese patent document CN113823774A discloses a method where the Mn concentration difference between large and small particles is less than 2, which can prevent differences in particle size during co-sintering. This is achieved by adjusting the sintering temperature based on the Mn concentration difference. Both of these patent documents utilize variations in Mn to address the different co-firing characteristics of large and small particles. Mn is essential, but this method is not applicable to products like NCA products that do not require Mn, thus limiting its applicability.

[0004] Chinese patent document CN107785550A discloses a low-temperature coating pretreatment process before co-firing, which is complex. Chinese patent document CN113394385A discloses in-situ coating treatment for precursors with larger particle sizes and pre-oxidation treatment for precursors with smaller particle sizes before co-firing. Both patents require multiple processing steps, increasing the complexity of the actual production process and raising the operational difficulty in practical production requirements.

[0005] Furthermore, the size difference between large and small particles results in their own advantages and disadvantages in performance. Small particles require improved cycle performance, while large particles require improved capacity characteristics. Performance improvement also needs to consider the damping rate (DCR), and the DCR should be minimized when combining large and small particles. Therefore, in the process of preparing cathode materials with a combination of large and small particles, it is necessary to improve the material's capacity and cycle performance while simultaneously reducing its DCR. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, to provide a positive electrode active material with good capacity and cycle performance, and to provide a preparation method that can achieve co-sintering of large and small particles to meet the material characteristic requirements, reduce costs, and is simple to operate.

[0007] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0008] A positive electrode active material with a combination of large and small particles includes large secondary spheres and small secondary spheres, wherein the mass proportion of large secondary spheres in the positive electrode active material is not less than 50%.

[0009] The chemical formula of the large secondary spheres is Li. a Ni b M c M' d O2, where M is one or more of Co, Mn, and Al, M' is a dopant element and M' is selected from one or more of Zr and Sr, 0.9≤a≤1.2, 0.7≤b<1, 0<c≤0.3, 0<d≤0.1;

[0010] The chemical formula of the small secondary spheres is Li e Ni f M g M” h O2, where M is one or more of Co, Mn, and Al, M” is a dopant element and M” is selected from one or more of B, W, Mo, In, Ta, and S, 0.9≤e≤1.2, 0.7≤f<1, 0<g≤0.2, 0<h≤0.1;

[0011] The large secondary spheres have a D50 particle size of 10-20 μm, and the small secondary spheres have a D50 particle size of 2-5 μm.

[0012] In the above-mentioned positive electrode active material with a combination of large and small particles, the mass ratio of the large secondary spheres to the small secondary spheres is preferably (7:3)-(9:1).

[0013] Preferably, f and b satisfy: f > b, and fb < 0.1. Within this range, increasing the Ni content of small particles is more beneficial to the DCR of the co-fired secondary spheres with different sizes.

[0014] Preferably, the positive electrode active material is obtained by sintering a mixture of a precursor of large-particle secondary spheres and a precursor of small-particle secondary spheres, and the doping elements M' and M" are added during the preparation of the precursor.

[0015] Based on a general inventive concept, the present invention also provides a method for preparing a positive electrode active material with a combination of large and small particles, comprising the following steps:

[0016] (1) The metal salt solutions corresponding to the large and small secondary spheres are mixed with the precipitant, complexing agent and metal salt solutions corresponding to the dopant element, respectively, to carry out co-precipitation reaction, and then filtered and dried to prepare the large secondary sphere precursor containing the dopant element M' and the small secondary sphere precursor containing the dopant element M”, respectively.

[0017] (2) The large-particle secondary sphere precursor and the small-particle secondary sphere precursor are mixed together with a lithium source to obtain a mixture, which is then sintered to obtain the positive electrode active material with the combination of large and small particles.

[0018] In the above preparation method, preferably, in step (1), the mixed metal salt solution corresponding to the large and small secondary spheres includes nickel salt and M salt; the precipitant includes one or more of sodium hydroxide and potassium hydroxide; and the complexing agent includes one or more of ammonia, ammonium sulfate and ammonium bicarbonate.

[0019] Preferably, in step (1), the conditions for the coprecipitation reaction are as follows: all the above solutions are added to the reaction vessel at a rate of 0.1-10 L / h, the pH is 9-12, the temperature is 40-80℃, and the stirring speed is 300-600 rpm during the reaction.

[0020] Preferably, in step (2), the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, and lithium nitrate; the ratio of the molar amount of metal elements in the lithium source to the total molar amount of metal elements in the large and small secondary sphere precursors is (0.9-1.2):1.

[0021] Preferably, in step (2), the sintering temperature is 500-1000℃.

[0022] More preferably, the sintering operation includes the following steps:

[0023] S1. The mixture is placed in an oxygen atmosphere for the first sintering. First, it is sintered at 400-550℃ for 1-3 hours, and then the temperature is increased to 600-800℃ at 1-5℃ / min for 8-20 hours. After cooling, it is passed through a 300-mesh sieve to obtain the first sintered product.

[0024] S2. After washing, filtering and drying the first sintering product, a second sintering is carried out in an oxygen atmosphere at a sintering temperature of 300-700℃ and a holding time of 3-20h. After cooling, the product is passed through a 300-mesh sieve to obtain the positive electrode active material with the specified particle size distribution.

[0025] Doping the precursors of large and small secondary spheres with elements that have different effects can improve the problem of different temperatures during the sintering process. Elements that increase the size of primary particles after sintering can be doped into the large-particle precursor, while elements that decrease the size of primary particles after sintering can be doped into the small-particle precursor. The above methods can make the primary particles in the final sintered secondary spheres the same or similar in size. Co-firing can also be achieved for two precursors with different nickel contents.

[0026] The size of the primary particles in secondary spheres is a direct method to determine whether the sintering temperature is appropriate; materials with suitable primary particle sizes can achieve their optimal performance. Generally, the actual sintering temperature for large particles must be higher than that for small particles to achieve the same primary particle size for both. Excessively large primary particle size can affect the migration path of Li ions, while excessively small primary particles may result in incomplete crystallinity during sintering. Doping different elements into the large and small particle precursors can improve material performance and simplify the sintering process. Doping the precursors promotes a more uniform distribution of elements within the material, resulting in more uniform material performance during charge and discharge processes and reducing polarization.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. The positive electrode active material of the present invention, with small particles, incorporates elements that are beneficial to and improve the deficiencies of both large and small secondary spheres. The small particle precursor is doped with elements that improve the cycle performance of the small particles, while the large particle precursor is doped with elements that enhance capacity. These elements work together to balance capacity and cycle performance. Furthermore, by increasing the Ni content of the small secondary spheres, even though the proportion of small particles is not high, the increased Ni content has a significant effect on reducing the overall DCR of the material. In summary, the present invention, through strict control of the doping elements and Ni content of large and small particles, ultimately obtains a positive electrode material with good overall performance in terms of capacity, cycle life, and DCR.

[0029] 2. The preparation method of the present invention can control the size of the primary particles of the sintered material by doping different elements in the precursor stage. The co-sintering process indirectly satisfies that the particles of different sizes have the same sintering temperature. Therefore, the performance of the material co-sintered with large and small particles can reach a better level. It can not only achieve the co-sintering of large and small particles to meet the material characteristic requirements, but also does not need to limit specific elements, has a wide range of applications, and is simple to operate, which can reduce costs. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a SEM image of the positive electrode active material formed by the co-sintering of large and small particles in Example 1.

[0032] Figure 2 This is a SEM image of the positive electrode active material formed by the co-sintering of large and small particles in Example 2.

[0033] Figure 3 The image shows a SEM image of the positive electrode active material co-sintered with particles of different sizes in Comparative Example 1.

[0034] Figure 4 The image shows a SEM image of the positive electrode active material co-sintered with particles of different sizes in Comparative Example 2. Detailed Implementation

[0035] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0036] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0037] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0038] Example 1:

[0039] A positive electrode active material with a combination of large and small particles includes large secondary spheres and small secondary spheres, wherein the chemical formula of the large secondary spheres is Li. 1.05 Ni 0.9 Co 0.08 Al 0.02 Zr 0.002 O2, the chemical formula of the small secondary spheres is Li 1.05 Ni 0.92 Co 0.06 Al 0.02 B 0.0005 The preparation method for O2 is as follows:

[0040] (1) Nickel sulfate solution and cobalt sulfate solution were mixed, and sodium aluminate solution dissolved in sodium hydroxide solution, zirconium sulfate solution, ammonia water with a concentration of 0.2 mol / L and sodium hydroxide solution with a concentration of 5.5 mol / L were added. The mixture was fed into the reactor at a rate of 2.0 L / h. During the reaction, the pH was 11, the temperature was 60℃, and the stirring speed was 400 rpm. The molar ratio of Ni, Co, and Al was 0.9:0.08:0.02, and the molar amount of Zr was 0.2 mol%. After aging, centrifugation, and drying, a precursor material with a D50 of 16 μm was obtained. The small particle precursor was synthesized in the same way as the large particle precursor, but the molar ratio of Ni, Co, and Al was 0.91:0.07:0.02. Instead of adding zirconium sulfate solution, boric acid solution was added. The molar amount of B was 0.05 mol%. The reaction was stopped when the D50 reached 2.9 μm. The small particle precursor was then obtained after post-processing.

[0041] (2) Weigh out large-particle Ni precursor doped with 0.2 mol% Zr in a mass ratio of 7.5:2.5. 0.9 Co 0.08 Al 0.02 (OH)2 and Ni precursor particles doped with 0.05 mol% B. 0.92 Co 0.06 Al 0.02 (OH)2, two precursors, and lithium hydroxide were mixed in a high-speed mixer at a metal element molar ratio of 1:1.05. The mixture was then placed in an oxygen atmosphere furnace for the first sintering. The mixture was first sintered at 400℃ for 3 hours, then heated to 710℃ for 12 hours at a heating rate of 5℃ / min. After natural cooling, the matrix material was obtained. The sintered sample was passed through a 300-mesh sieve, and the first sintered product was washed with water. During the washing process, the prepared material was stirred with an electric stirrer and washed with deionized water at a 1:1 ratio for 30 minutes. The product was then filtered, and the filter cake was dried in a vacuum drying oven for 10 hours. The washed and dried sample was then subjected to a second sintering process, held at 650℃ in an oxygen atmosphere furnace for 6 hours, and then naturally cooled. The cooled sample was passed through a 300-mesh sieve to obtain the high-density cathode material.

[0042] like Figure 1 As shown, different elements are doped into the precursor for both large and small secondary spherical particles. After the large and small particles are sintered together, the size of their primary particles is similar.

[0043] Example 2:

[0044] A positive electrode active material with a combination of large and small particles includes large secondary spheres and small secondary spheres, wherein the chemical formula of the large secondary spheres is Li. 1.03 Ni0.9 Co 0.05 Mn 0.05 Sr 0.0013 O2, the chemical formula of the small secondary spheres is Li 1.03 Ni 0.91 Co 0.04 Mn 0.05 B 0.001 The preparation method for O2 is as follows:

[0045] 1) Nickel sulfate solution, cobalt sulfate solution, manganese sulfate solution, strontium hydroxide solution, 0.2 mol / L ammonia solution, and 6.0 mol / L sodium hydroxide solution were fed into a reactor at a rate of 2.0 L / h. During the reaction, the pH was 11, the temperature was 60℃, and the stirring speed was 350 rpm. The molar ratio of Ni, Co, and Mn was 0.9:0.05:0.05, and the molar amount of Sr was 0.13% mol. After aging, centrifugation, and drying, a large-particle precursor with a D50 of 14.5 μm was obtained. The small-particle precursor was synthesized using the same method as the large-particle precursor, but with a Ni, Co, and Mn molar ratio of 0.91:0.04:0.05. Instead of adding strontium hydroxide solution, boric acid solution was added, and the molar amount of B was 0.1 mol%. The reaction was stopped when the D50 reached 3.1 μm, and the small-particle precursor was obtained after post-processing.

[0046] (2) Weigh out large-particle Ni precursors doped with 0.13% mol Sr at a mass ratio of 7:3. 0.9 Co 0.05 Mn 0.05 (OH)2 and small-particle precursor Ni doped with 0.05% mol B. 0.91 Co 0.04 Mn 0.05 (OH)2, two precursors, and lithium hydroxide were mixed in a high-speed mixer at a metal element molar ratio of 1:1.03. The mixture was then placed in an oxygen atmosphere furnace for the first sintering. The mixture was first sintered at 400℃ for 3 hours, then heated to 750℃ for 12 hours at a heating rate of 5℃ / min. After natural cooling, the matrix material was obtained. The sintered sample was passed through a 300-mesh sieve, and the first sintered product was washed with water. During the washing process, the prepared material was stirred with an electric stirrer and washed with deionized water at a 1:1 ratio for 30 minutes. The product was then filtered, and the filter cake was dried in a vacuum drying oven for 10 hours. The washed and dried sample was then subjected to a second sintering process, held at 500℃ in an oxygen atmosphere furnace for 6 hours, and then naturally cooled. The cooled sample was passed through a 300-mesh sieve to obtain the high-density cathode material.

[0047] like Figure 2As shown, different elements are doped into the precursor for both large and small secondary spherical particles. After the large and small particles are sintered together, the size of their primary particles is similar.

[0048] Example 3:

[0049] A positive electrode active material with a combination of large and small particles includes large secondary spheres and small secondary spheres, wherein the chemical formula of the large secondary spheres is Li. 1.03 Ni 0.9 Co 0.07 Al 0.03 Sr 0.001 O2, the chemical formula of the small secondary spheres is Li 1.03 Ni 0.91 Co 0.06 Al 0.03 W 0.0005 The preparation method for O2 is as follows:

[0050] 1) Nickel sulfate solution and cobalt sulfate solution were mixed, and sodium aluminate solution dissolved in sodium hydroxide solution, strontium hydroxide solution, 0.2 mol / L ammonia water, and 5.5 mol / L sodium hydroxide solution were added to the reactor at a rate of 2 L / h. During the reaction, the pH was 11.8, the temperature was 60℃, and the stirring speed was 400 rpm. The molar ratio of Ni, Co, and Al was 0.9:0.07:0.03, and the molar amount of strontium was 0.1 mol%. After aging, centrifugation, and drying, a large-particle precursor with a D50 of 14.5 μm was obtained. The small-particle precursor was synthesized using the same method as the large-particle precursor, but the molar ratio of Ni, Co, and Al was 0.91:0.06:0.03. Instead of adding a strontium-containing solution, sodium tungstate solution was added, and the molar amount of W was 0.05 mol%. The reaction was stopped when the D50 reached 3.2 μm, and the small-particle precursor was obtained after post-processing.

[0051] (2) Weigh out large-particle Ni precursors doped with 0.1% mol Sr in a mass ratio of 7:3. 0.9 Co 0.07 Al 0.03 (OH)2 and small-particle precursor Ni doped with 0.05% mol W. 0.91 Co 0.06 Al 0.03(OH)2, two precursors, and lithium hydroxide were mixed in a high-speed mixer at a metal element molar ratio of 1:1.03. The mixture was then placed in an oxygen atmosphere furnace for the first sintering. The mixture was first sintered at 400℃ for 3 hours, then heated to 715℃ for 12 hours at a heating rate of 5℃ / min. After natural cooling, the matrix material was obtained. The sintered sample was passed through a 300-mesh sieve, and the first sintered product was washed with water. During the washing process, the prepared material was stirred with an electric stirrer and washed with deionized water at a 1:1 ratio for 30 minutes, then filtered. The filter cake was dried in a vacuum drying oven for 10 hours. The washed and dried sample was then subjected to a second sintering process, held at 630℃ in an oxygen atmosphere furnace for 6 hours, and then naturally cooled. The cooled sample was passed through a 300-mesh sieve to obtain the high-density cathode material.

[0052] Example 4:

[0053] A positive electrode active material with a combination of large and small particles includes large secondary spheres and small secondary spheres, wherein the chemical formula of the large secondary spheres is Li. 1.03 Ni 0.9 Co 0.07 Al 0.03 Zr 0.0015 O2, the chemical formula of the small secondary spheres is Li 1.03 Ni 0.92 Co 0.05 Al 0.03 W 0.001 Ti 0.001 The preparation method for O2 is as follows:

[0054] 1) Nickel sulfate solution and cobalt sulfate solution were mixed, and sodium aluminate solution dissolved in sodium hydroxide solution, zirconium sulfate solution, ammonia water with a concentration of 0.2 mol / L and sodium hydroxide solution with a concentration of 5.0 mol / L were added to the reactor at a rate of 2.2 L / h. During the reaction, the pH was 11, the temperature was 55℃ and the stirring speed was 400 rpm. The molar ratio of Ni, Co and Al was 0.9:0.07:0.03 and the molar amount of zirconium was 0.15 mol%. After aging, centrifugation and drying, a precursor with a D50 of 14.5 μm was obtained. The small particle precursor is synthesized using the same method as the large particle precursor, but the metal molar ratio of Ni, Co, and Al is 0.91:0.06:0.03. Instead of adding zirconium sulfate solution, sodium tungstate and titanic acid solution are added simultaneously. The molar amount of W is 0.1 mol%, and the molar amount of Ti is 0.1 mol%. The reaction is stopped when D50 reaches 3.2 μm, and the small particle precursor is obtained after post-processing.

[0055] (2) Weigh out large-particle Ni precursors doped with 0.15% mol Zr at a mass ratio of 7:3. 0.9 Co 0.07 Al 0.03 (OH)2 and small-particle precursor Ni doped with 0.1% mol W and 0.1% mol Ti 0.92 Co 0.05 Al 0.03 (OH)2, two precursors, and lithium hydroxide were mixed in a high-speed mixer at a metal element molar ratio of 1:1.03. The mixture was then placed in an oxygen atmosphere furnace for the first sintering. The mixture was first sintered at 400℃ for 3 hours, then heated to 710℃ for 12 hours at a heating rate of 5℃ / min. After natural cooling, the matrix material was obtained. The sintered sample was passed through a 300-mesh sieve, and the first sintered product was washed with water. During the washing process, the prepared material was stirred with an electric stirrer and washed with deionized water at a 1:1 ratio for 30 minutes. The product was then filtered, and the filter cake was dried in a vacuum drying oven for 10 hours. The washed and dried sample was then subjected to a second sintering process, held at 600℃ in an oxygen atmosphere furnace for 6 hours, and then naturally cooled. The cooled sample was passed through a 300-mesh sieve to obtain the high-density cathode material.

[0056] Example 5:

[0057] A positive electrode active material with a combination of large and small particles includes large secondary spheres and small secondary spheres, wherein the chemical formula of the large secondary spheres is Li. 1.03 Ni 0.9 Co 0.07 Al 0.03 Zr 0.0015 O2, the chemical formula of the small secondary spheres is Li 1.03 Ni 0.925 Co 0.045 Al 0.03 W 0.0015 Mg 0.001 The preparation method for O2 is as follows:

[0058] 1) Nickel sulfate solution and cobalt sulfate solution were mixed, and sodium aluminate solution dissolved in sodium hydroxide solution, zirconium sulfate solution, ammonia water with a concentration of 0.2 mol / L, and sodium hydroxide solution with a concentration of 5.5 mol / L were added to the reactor at a rate of 2.5 L / h. During the reaction, the pH was 11.5, the temperature was 55℃, and the stirring speed was 400 rpm. The molar ratio of Ni, Co, and Al was 0.9:0.07:0.03, and the molar amount of zirconium was 0.15 mol% of the total molar amount of metal. After aging, centrifugation, and drying, a precursor with a D50 of 14.5 μm was obtained. The small particle precursor is synthesized using the same method as the large particle precursor, but with a metal molar ratio of Ni:Co:Al of 0.91:0.07:0.02. Magnesium sulfate solution and sodium tungstate solution are added during the preparation process, with W molar amount of 0.15 mol% and Mg molar amount of 0.1 mol%. The reaction is stopped when D50 reaches 3.2 μm, and the small particle precursor is obtained after post-processing.

[0059] (2) Weigh out large-particle Ni precursors doped with 0.15% mol Zr at a mass ratio of 7:3. 0.9 Co 0.07 Al 0.03 (OH)2 and small-particle Ni precursor doped with 0.15% mol W and 0.1% mol Mg 0.925 Co 0.045 Al 0.03 (OH)2, two precursors, and lithium hydroxide were mixed in a high-speed mixer at a metal element molar ratio of 1:1.03. The mixture was then placed in an oxygen atmosphere furnace for the first sintering. The mixture was first sintered at 400℃ for 3 hours, then heated to 710℃ for 12 hours at a heating rate of 5℃ / min. After natural cooling, the matrix material was obtained. The sintered sample was passed through a 300-mesh sieve, and the first sintered product was washed with water. During the washing process, the prepared material was stirred with an electric stirrer and washed with deionized water at a 1:1 ratio for 30 minutes. The product was then filtered, and the filter cake was dried in a vacuum drying oven for 10 hours. The washed and dried sample was then subjected to a second sintering process, held at 550℃ in an oxygen atmosphere furnace for 6 hours, and then naturally cooled. The cooled sample was passed through a 300-mesh sieve to obtain the high-density cathode material.

[0060] Comparative Example 1:

[0061] The preparation method of a positive electrode active material includes the following steps:

[0062] Weigh out large-particle precursor Ni at a mass ratio of 7.5:2.5. 0.9 Co 0.08 Al 0.02 (OH)2 and small particle precursor Ni0.91 Co 0.07 Al 0.02 (OH)2, with a large particle D50 of 14.5 μm and a small particle D50 of 3.5 μm, was mixed with lithium hydroxide in a high-speed mixer at a metal element molar ratio of 1:1.04. The mixture was then placed in an oxygen atmosphere furnace for the first sintering. The initial sintering was at 400℃ for 3 h, followed by sintering at 720℃ for 12 h at a heating rate of 5℃ / min. After natural cooling, the matrix material was obtained. The sintered sample was passed through a 300-mesh sieve, and the first sintered product was washed with water. During the washing process, the prepared material was stirred with an electric stirrer and washed with deionized water at a 1:1 ratio for 30 min, then filtered. The filter cake was dried in a vacuum drying oven for 10 h. The washed and dried sample underwent a second sintering process, held at 600℃ in an oxygen atmosphere furnace for 6 h, and then naturally cooled. The cooled sample was passed through a 300-mesh sieve to obtain the high-density cathode material.

[0063] like Figure 3 As shown, after sintering, there is a significant difference in the primary particle size between large and small particles without other doping.

[0064] Comparative Example 2:

[0065] The preparation method of a positive electrode active material includes the following steps:

[0066] Weigh out the large-particle precursor Ni according to a mass ratio of 7:3. 0.9 Co 0.05 Mn 0.05 (OH)2 and small particle precursor Ni 0.91 Co 0.04 Mn 0.05 (OH)2, with a large particle D50 of 14.5 μm and a small particle D50 of 3.1 μm, was mixed with lithium hydroxide in a high-speed mixer at a metal element molar ratio of 1:1.03. The mixture was then placed in an oxygen atmosphere furnace for the first sintering. The initial sintering was at 400℃ for 3 h, followed by sintering at 750℃ for 12 h at a heating rate of 5℃ / min. After natural cooling, the matrix material was obtained. The sintered sample was passed through a 300-mesh sieve, and the first sintered product was washed with water. During the washing process, the prepared material was stirred with an electric stirrer and washed with deionized water at a 1:1 ratio for 30 min, then filtered. The filter cake was dried in a vacuum drying oven for 10 h. The washed and dried sample underwent a second sintering process, holding at 500℃ in an oxygen atmosphere furnace for 6 h, followed by natural cooling. The cooled sample was then passed through a 300-mesh sieve to obtain the high-density cathode material.

[0067] like Figure 4 As shown, after sintering, there is a significant difference in the primary particle size between large and small particles without other doping.

[0068] Comparative Example 3:

[0069] The preparation method of a positive electrode active material includes the following steps:

[0070] (1) Nickel sulfate solution, cobalt sulfate solution, manganese sulfate solution, zirconium sulfate solution, 0.15 mol / L ammonia water, and 6.0 mol / L sodium hydroxide solution were fed into a reaction vessel at a certain rate, with a metal molar ratio of 0.9:0.05:0.05 and 0.15% mol zirconium solution. After aging, centrifugation, and drying, a large-particle precursor with a D50 of 14.0 μm was obtained. The small-particle precursor was synthesized in the same way as the large-particle precursor, prepared with a metal molar ratio of 0.91:0.04:0.05 and 0.15% mol zirconium solution was added. The reaction was stopped when the D50 reached 3.3 μm, and the small-particle precursor was obtained after post-processing.

[0071] (2) Weigh out 0.15% mol of Zr-doped large-particle Ni precursor at a mass ratio of 7:3. 0.9 Co 0.05 Mn 0.05 (OH)2 and small-particle precursor Ni doped with 0.15% mol of Zr. 0.91 Co 0.04 Mn 0.05 (OH)2, two precursors, and lithium hydroxide were mixed in a high-speed mixer at a metal element molar ratio of 1:1.05. The mixture was then placed in an oxygen atmosphere furnace for the first sintering. The mixture was first sintered at 400℃ for 3 hours, then heated to 745℃ for 12 hours at a heating rate of 5℃ / min. After natural cooling, the matrix material was obtained. The sintered sample was passed through a 300-mesh sieve, and the first sintered product was washed with water. During the washing process, the prepared material was stirred with an electric stirrer and washed with deionized water at a 1:1 ratio for 30 minutes, then filtered. The filter cake was dried in a vacuum drying oven for 10 hours. The washed and dried sample was then subjected to a second sintering process, held at 500℃ in an oxygen atmosphere furnace for 6 hours, and then naturally cooled. The cooled sample was passed through a 300-mesh sieve to obtain the high-density cathode material.

[0072] Comparative Example 4:

[0073] A positive electrode active material with a combination of large and small particles includes large secondary spheres and small secondary spheres, wherein the chemical formula of the large secondary spheres is Li. 1.04 Ni 0.9 Co 0.08 Al0.02 O2, the chemical formula of the small secondary spheres is Li 1.04 Ni 0.91 Co 0.07 Al 0.02 O2 (containing 0.1 mol% W dopant) is prepared by the following steps:

[0074] (1) Nickel sulfate solution and cobalt sulfate solution were mixed, and sodium aluminate solution, sodium tungstate solution, ammonia water with a concentration of 0.2 mol / L, and sodium hydroxide solution with a concentration of 5.5 mol / L were added to the reactor at a certain rate for reaction. The metal molar ratio was 0.91:0.07:0.02, and the molar amount of W was 0.1 mol%. After aging, centrifugation, and drying, a precursor with a D50 of 3 μm was obtained. The synthesis method of the large particle precursor was the same as that of the small particle precursor, but the metal molar ratio was 0.90:0.08:0.02, and sodium tungstate solution was not added during the preparation process. The reaction was stopped when the D50 reached 14.5 μm, and the large particle precursor was obtained after post-processing.

[0075] (2) Weigh out the large-particle precursor Ni according to a mass ratio of 7.5:2.5. 0.9 Co 0.08 Al 0.02 (OH)2 and small-particle precursor Ni doped with 0.1 mol% W. 0.91 Co 0.07 Al 0.02 (OH)2, two precursors, and lithium hydroxide were mixed in a high-speed mixer at a metal element molar ratio of 1:1.04. The mixture was then placed in an oxygen atmosphere furnace for the first sintering. The mixture was first sintered at 400℃ for 3 hours, then heated to 710℃ for 12 hours at a heating rate of 5℃ / min. After natural cooling, the matrix material was obtained. The sintered sample was passed through a 300-mesh sieve, and the first sintered product was washed with water. During the washing process, the prepared material was stirred with an electric stirrer and washed with deionized water at a 1:1 ratio for 30 minutes, then filtered. The filter cake was dried in a vacuum drying oven for 10 hours. The washed and dried sample was then subjected to a second sintering at 600℃ in an oxygen atmosphere furnace for 6 hours, followed by natural cooling. The cooled sample was then passed through a 300-mesh sieve to obtain the high-density cathode material.

[0076] Comparative Example 5:

[0077] The preparation method of a positive electrode active material includes the following steps:

[0078] Weigh out the large-particle precursor Ni according to a mass ratio of 7:3. 0.9 Co 0.05 Mn 0.05(OH)2 and small particle precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2, with a large particle D50 of 14.0 μm and a small particle D50 of 3.0 μm, was mixed with lithium hydroxide in a high-speed mixer at a metal element molar ratio of 1:1.03. The mixture was then placed in an oxygen atmosphere furnace for the first sintering. The initial sintering was at 400℃ for 3 hours, followed by sintering at 750℃ for 12 hours at a heating rate of 5℃ / min. After natural cooling, the matrix material was obtained. The sintered sample was passed through a 300-mesh sieve, and the first sintered product was washed with water. During the washing process, the prepared material was stirred with an electric stirrer and washed with deionized water at a 1:1 ratio for 30 minutes, then filtered. The filter cake was dried in a vacuum drying oven for 10 hours. The washed and dried sample underwent a second sintering process, holding at 500℃ in an oxygen atmosphere furnace for 6 hours and then naturally cooled. The cooled sample was passed through a 300-mesh sieve to obtain the high-density cathode material.

[0079] Table 1: Performance Comparison of Cathode Materials in Examples 1-5 and Comparative Examples 1-5

[0080]

[0081] Table 1 shows a comparison of the performance of the cathode materials in Examples 1-5 and Comparative Examples 1-5. The results show that in the comparative examples, due to the inability to precisely control the sintering temperature required for large and small particles during the co-sintering process, the overall performance of the secondary spheres after sintering could not reach optimal levels. In the examples, by doping different elements in the precursor stage, the size of the primary particles could be controlled, and the co-sintering process indirectly ensured that large and small particles had the same sintering temperature. Therefore, the performance of the material could reach better levels when large and small particles were co-sintered appropriately. In Example 2, different elements were doped into large and small particles, resulting in improved capacity and cycle performance compared to Comparative Example 2. Similar results can be seen in Examples 3 and Comparative Example 3. Examples 1-5 show a more significant performance improvement compared to the comparative examples, which is due to the simultaneous doping of appropriate elements into both large and small particles, which is beneficial for further performance improvement. Meanwhile, in Comparative Example 5, the Ni content was the same for both large and small particles, resulting in a higher DCR compared to other test results.

Claims

1. A positive electrode active material of a size particle combination, characterized by, The positive electrode active material comprises large-particle secondary balls and small-particle secondary balls, and the mass percentage of the large-particle secondary balls in the positive electrode active material is not less than 50%; The large particle secondary ball has a chemical formula of Li a Ni b M c M’ d O2, wherein M is one or more of Co, Mn, Al, M’ is a doping element and M’ is selected from one or more of Zr, Sr, 0.9≤a≤1.2, 0.7≤b<1, 0 c≤0.3, 0 d≤0.

1. The small particle secondary ball has a chemical formula of Li e Ni f M g M” h O2, wherein M is one or more of Co, Mn, Al, M" is a doping element and M" is selected from one or more of B, W, Mo, In, Ta, S, 0.9≤e≤1.2, 0.7≤f<1, 0 The f and b satisfy: f>b, and f-b<0.

1. The D50 particle size of the large-particle secondary balls is 10-20 μm, and the D50 particle size of the small-particle secondary balls is 2-5 μm.

2. The size fractioned positive electrode active material according to claim 1, characterized by, The mass ratio of the large-particle secondary balls to the small-particle secondary balls is (7:3)-(9:1).

3. The size fractioned positive electrode active material according to any one of claims 1-2, characterized in that, The positive electrode active material is obtained by sintering a mixture of a precursor of the large-particle secondary balls and a precursor of the small-particle secondary balls, and the doping elements M' and M" are added in the preparation process of the precursors.

4. A method for producing the positive electrode active material of the size particle combination according to any one of claims 1 to 3, characterized by, The method comprises the following steps: (1) mixing the metal salt solutions corresponding to the large-particle secondary balls and the small-particle secondary balls respectively with a precipitant, a complexing agent and metal salt solutions corresponding to the doping elements, performing a co-precipitation reaction, and then filtering and drying to respectively prepare a large-particle secondary ball precursor containing the doping element M' and a small-particle secondary ball precursor containing the doping element M"; (2) mixing the large-particle secondary ball precursor and the small-particle secondary ball precursor with a lithium source to obtain a mixture, and sintering to obtain the positive electrode active material with large and small particles.

5. The preparation method according to claim 4, characterized in that, In step (1), the metal salt solutions corresponding to the large-particle secondary balls and the small-particle secondary balls both comprise nickel salt and M salt; the precipitant comprises one or more of sodium hydroxide and potassium hydroxide; and the complexing agent comprises one or more of ammonia, ammonium sulfate and ammonium bicarbonate.

6. The preparation method according to claim 4, characterized in that, In step (1), the co-precipitation reaction is performed under the following conditions: the solution is added to the reaction container at a speed of 0.1-10 L / h, the pH during the reaction is 9-12, the temperature is 40-80 ℃, and the stirring speed is 300-600 rpm.

7. The preparation method according to claim 4, characterized in that, In step (2), the lithium source is selected from one or more of lithium carbonate, lithium hydroxide and lithium nitrate; and the ratio of the molar amount of the metal element of the lithium source to the total molar amount of the metal elements of the large-particle secondary ball precursor and the small-particle secondary ball precursor is (0.9-1.2):

1.

8. The production method according to any one of claims 4 to 7, characterized by, In step (2), the sintering temperature is 500-1000 ℃.

9. The production method according to claim 8, characterized by, The specific operation of the sintering comprises the following steps: S1, placing the mixture in an oxygen atmosphere to perform a first sintering, first sintering at 400-550 ℃ for 1-3 h, then increasing the temperature to 600-800 ℃ at a rate of 1-5 ℃ / min and sintering for 8-20 h, and then sieving through a 300-mesh sieve to obtain a first sintering product; S2, washing, filtering and drying the first sintering product, and then performing a second sintering in an oxygen atmosphere, the sintering temperature is 300-700 ℃, the holding time is 3-20 h, and then sieving through a 300-mesh sieve to obtain the positive electrode active material with large and small particles.

Images