Ternary positive electrode material, preparation method thereof and lithium ion battery

Abstract

The application provides a ternary positive electrode material and a preparation method thereof, and a lithium ion battery, to provide a high-strength ternary positive electrode material, and avoid the problem of cycle performance decline caused by micro-cracks or breakage of the ternary positive electrode material due to lattice shrinkage and expansion in the charging-discharging process. The molecular general formula of the ternary positive electrode material is: Li 1+k Ni c Z d Co e Q f M g O2, -0.03≤k<1.0, c+d+e+f+g+k=1, 0.80≤c≤1.0, 0 The particle environmental stress micro-crack index of the ternary positive electrode material is not greater than (1-2d-2e)120% and not less than (1-2d-2e)30%, wherein S(P) is the specific surface area of the ternary positive electrode material after being pressed by a pressure P of 180-220 MPa, and S(P0) is the specific surface area of the ternary positive electrode material before being pressed.

Description

Technical Field

[0001] This invention relates to the field of cathode materials technology for energy storage batteries, and particularly to a ternary cathode material and its preparation method, and a lithium-ion battery. Background Technology

[0002] Currently, ternary cathode materials are the preferred choice for lithium-ion battery fabrication due to their high energy density. High-nickel ternary cathode materials, in particular, exhibit outstanding energy density. However, because high-nickel ternary cathode materials have a layered structure, during the charging process, the electroneutrality of the layered structure is disrupted as lithium ions are extracted from the lithium layers. The negative charges of adjacent metal layers repel each other, leading to lattice expansion. Simultaneously, with further lithium ion extraction, especially when the discharge voltage exceeds 4.2V, a phase transition from H2 to H3 occurs in the crystal. This reduces the spacing between adjacent metal layers in the layered structure of the high-nickel cathode material, causing a decrease in lattice parameters and resulting in lattice contraction. This cycle of lattice expansion followed by contraction leads to stress accumulation in the crystal, causing microcracks and a rapid deterioration in the cycle performance of the ternary cathode material. Current technologies primarily use coating layers to improve the strength of the ternary cathode material to avoid stress-induced microcracks. However, uneven coating can lead to cracks under stress concentration, resulting in poor cycle performance. Summary of the Invention

[0003] This application provides a ternary cathode material and its preparation method, as well as a lithium-ion battery, to provide a high-strength ternary cathode material and avoid the problem of decreased cycle performance caused by microcracks or breakage due to lattice contraction and expansion of the ternary cathode material during charging and discharging.

[0004] In a first aspect, embodiments of this application provide a ternary cathode material, the molecular formula of which is: Li 1+k Ni c Z d Co e Q f M g O2, -0.03≤k<1.0, c+d+e+f+g+k=1, 0.80≤c≤1.0, 0<d≤0.20, 0.05≤e≤0.20, 0≤f≤0.05, 0≤g≤0.05, Z is Al and / or Mn, Q is a dopant element, Q is selected from at least one of Zr, Sr, Y, Sb, Mo, Mg, Ti, Ba, Ta, and W; M is a coating element, M is selected from at least one of B, W, Ta, Nb, Sn, Ba, Mo, and Ce;

[0005] The ternary cathode material's particle environmental stress microcrack resistance index Not greater than (1-2d-2e) 120%, and not less than (1-2d-2e) 30%; wherein, the microcrack index of the particles under environmental stress is inversely proportional to the particle strength of the ternary cathode material. S(P) is the specific surface area of ​​the ternary cathode material after being pressed by a pressure P of 180-220 MPa, and S(P0) is the specific surface area of ​​the ternary cathode material before pressing.

[0006] The ternary cathode material composed of the aforementioned stoichiometric elements (especially Ni) provided in this application embodiment possesses high particle strength, effectively resisting the structural damage caused by stresses resulting from lattice expansion and / or lattice contraction during charging and discharging. This enhances the particle microcrack resistance index of the ternary cathode material. Not greater than (1-2d-2e) 120%, and not less than (1-2d-2e) This reduces the yield by 30%, effectively avoiding the problem of deteriorated cycle performance caused by microcracks due to stress in ternary cathode materials during the charging-discharging process.

[0007] In one possible implementation, the specific surface area of ​​the ternary cathode material is 0.35-1.3 m². 2 / g.

[0008] In one possible implementation, the coating thickness of the ternary cathode material is 1-20 nm.

[0009] In one possible implementation, the coating thickness variation rate Δδ of the ternary cathode material is ≤4; wherein, .

[0010] In one possible implementation, the mass ratio of the coating element to the mass of the ternary cathode material is 0.05 wt%-1 wt%.

[0011] In one possible implementation, the median particle size of the ternary cathode material is 9.5-14 μm.

[0012] In one possible implementation, the ratio of the sum of the masses of lithium carbonate and lithium hydroxide on the surface of the ternary cathode material to the mass of the ternary cathode material is no greater than 0.5 wt%.

[0013] Secondly, embodiments of this application provide a method for preparing a ternary cathode material as described in the first aspect and a possible implementation thereof, comprising:

[0014] For mixtures of ternary precursors, dopants, and lithium sources, the temperature range is 650-800℃. Sintering under the specified conditions for 7-20 hours yields the cathode material Li. 1+k Ni c Z d Co e Q f M g O2; where -0.03≤k<1.0, c+d+e+f+g+k=1, 0.80≤c≤1, 0<d≤0.20, 0.05≤e≤0.20, 0≤f≤0.05, 0≤g≤0.05, Z is Al and / or Mn, Q is a dopant element, and Q is selected from at least one of Zr, Sr, Y, Sb, Mo, Mg, Ti, Ba, Ta, and W.

[0015] In one possible implementation, the lithium source is selected from at least one of LiOH·H2O, LiOH, and Li2CO3, and the molar ratio between the lithium source and the precursor is 0.9-1.1.

[0016] In one possible implementation, the dopant is selected from at least one of H3BO3, ZrO2, SrO, Y2O3, Sb2O3, MoO3, MgO, TiO2, BaCO3, Ta2O5, and WO3.

[0017] One possible implementation, after obtaining the positive electrode material, further includes:

[0018] The cathode material is filtered using a coating solution containing a coating agent to obtain a target filter cake with a water content of 0.05%-20%; wherein the coating solution is alkaline.

[0019] The dried target filter cake is then heated in an atmosphere with a carbon dioxide content of less than 0.1% at 180-800 °C. Sintering under certain conditions yields a cathode material with a coating layer.

[0020] One possible implementation includes, before casting the positive electrode material using a coating solution containing a coating agent, the following steps:

[0021] The positive electrode material to be coated is immersed in deionized water and washed for 1-30 minutes, and then dehydrated to obtain a water-washed filter cake with a water content of 0.05%-30%.

[0022] The process of using a coating solution containing a coating agent to filter the positive electrode material to obtain a target filter cake with a water content of 0.05%-20% includes:

[0023] The target filter cake is obtained by casting the water-washed filter cake with the coating solution.

[0024] In one possible implementation, the solute in the coating solution further includes a soluble lithium salt.

[0025] In one possible implementation, the concentration of hydroxide ions in the coating solution is 0.05-9 mol / L.

[0026] In one possible implementation, the concentration of metal ions in the coating solution is 0.05-1.5 mol / L, and the coating agent in the solute is at least one selected from H3BO3, HBO2, WO3, H2WO4, Ta2O5, WO3, Li2WO4, Nb2O5, and MoO3.

[0027] Thirdly, embodiments of this application provide a lithium-ion battery, comprising:

[0028] The ternary cathode material as described in the first aspect and any possible embodiment, or the ternary cathode material prepared by the method described in the first aspect and any possible embodiment. Attached Figure Description

[0029] Figure 1 A scanning electron microscope image of Embodiment 1 provided for the purposes of this application;

[0030] Figure 2 A scanning electron microscope image of Embodiment 4 provided for the purposes of this application;

[0031] Figure 3 A scanning electron microscope image of Comparative Example 1 provided in this application embodiment;

[0032] Figure 4 The image is a scanning electron microscope image of Comparative Example 2 provided in this application. Detailed Implementation

[0033] To address the problem of insufficient particle strength and low cycle stability in existing ternary cathode materials, this application provides a ternary cathode material with the general molecular formula: Li 1+k Ni c Z d Co e Q f M gO2, -0.03≤k<1, c+d+e+f+g+k=1, 0.80≤c≤1, 0<d≤0.20, 0.05≤e≤0.20, 0≤f≤0.05, 0≤g≤0.05, Z is Al and / or Mn, Q is a doping element selected from at least one of Zr, Sr, Y, Sb, Mo, Mg, Ti, Ba, Ta, and W; M is a coating element selected from at least one of B, W, Ta, Nb, Sn, Ba, Mo, and Ce. This ternary cathode material... Not greater than (1-2d-2e) 120%, and not less than (1-2d-2e) 30%.

[0034] When the Ni, Co, and Mn elements in this ternary cathode material are in the amounts described above, it exhibits high particle strength and high resistance to environmental stress microcracks. Not greater than (1-2d-2e) 120%, and not less than (1-2d-2e) 30%. When it is in the charging-discharging process, the ternary cathode material has high strength, and its ability to resist stress caused by lattice expansion and contraction is significantly enhanced, which effectively suppresses the occurrence of microcracks in the ternary cathode material, thereby achieving the purpose of improving the cycle stability of the ternary cathode material.

[0035] The above-mentioned particle environmental stress microcrack index refer to: Wherein, S(P) is the specific surface area of ​​the ternary cathode material after being pressed under a pressure of P=180-220Mpa (e.g., P=200Mpa), and S(P0) is the specific surface area of ​​the ternary cathode material before pressing.

[0036] The following explains the S(P) and S(P0) tests mentioned above:

[0037] First, a small amount of the aforementioned ternary cathode material (1-3g) is placed in a stainless steel granule mold, so that the ternary cathode material is relatively evenly distributed in the cylindrical cavity (radius r=6.5mm, height d=20.3mm) of the stainless steel granule mold.

[0038] Then, apply a uniaxial force of 180-220 MPa for 0.5-3 minutes.

[0039] The aforementioned microcrack resistance index of particles under environmental stress is actually determined by calculating the rate of change in the specific surface area of ​​the particles before and after pressing. Therefore, the smaller this rate of change, i.e., the lower the microcrack resistance index of the particles under environmental stress, the greater the particle strength. This microcrack resistance index of particles under environmental stress... For example, it could be: 24%≤ ≤96%; 19.8%≤ ≤79.2%; or 21.4%≤ ≤48.9%.

[0040] Furthermore, the specific surface area of ​​the aforementioned ternary cathode material is 0.35-1.3 m². 2 / g.

[0041] Furthermore, the coating thickness of the aforementioned ternary cathode material is 1-20 nm.

[0042] Furthermore, the coating layer provided in this embodiment of the application has the characteristic of uniform coating; therefore, the coating layer thickness variation rate Δδ of the ternary cathode material is ≤4; wherein, δmax is the maximum thickness of the coating layer on the surface of any particle in the ternary cathode material, δmin is the minimum thickness of the coating layer on the surface of that particle in the ternary cathode material, and δave is the average thickness of the coating layer at Q points on the surface of that particle in the ternary cathode material, including the thickest and thinnest points. Q is an integer greater than or equal to 10.

[0043] Furthermore, the mass ratio of the coating element to the mass of the ternary cathode material is 0.05 wt%-1 wt%.

[0044] Furthermore, the median particle size of the ternary cathode material is 9.5-14 μm.

[0045] Furthermore, the ratio of the sum of the masses of lithium carbonate and lithium hydroxide on the surface of the ternary cathode material to the mass of the ternary cathode material is no greater than 0.5 wt%.

[0046] Based on the same inventive concept, this application provides a method for preparing the above-mentioned ternary cathode material, the method comprising:

[0047] For mixtures of ternary precursors, dopants, and lithium sources, the temperature range is 650-800℃. Sintering under the specified conditions for 7-20 hours yields the positive electrode material i. 1+k Ni c Z d Co e Q f M g O2; where -0.03≤k<1, c+d+e+f+g+k=1, 0.80≤c≤1, 0<d≤0.20, 0.05≤e≤0.20, 0≤f≤0.05, 0≤g≤0.05, Z is Al and / or Mn, Q is a dopant element, and Q is selected from at least one of Zr, Sr, Y, Sb, Mo, Mg, Ti, Ba, Ta, and W.

[0048] The preferred sintering temperature for the mixture of the ternary precursor, dopant, and lithium source is 700-750°C. The sintering time is 7-20 hours, preferably 10-12 hours.

[0049] The above precursors are selected from: Ni c Z d Co e (OH)2 and / or Ni c Z d Co e CO3; where 0.80≤c≤1.0, 0<d≤0.20, 0.05≤e≤0.20, and Z is Al and / or Mn.

[0050] The dopant is at least one of H3BO3, ZrO2, SrO, Y2O3, Sb2O3, MoO3, MgO, TiO2, BaCO3, Ta2O5, and WO3.

[0051] To further enhance the particle strength of the aforementioned ternary cathode material, it can be coated. This coating not only provides higher strength to counteract the stress generated by crystal contraction and expansion during charging and discharging, but also utilizes at least one of the electrochemically active H3BO3, HBO2, WO3, H2WO4, Ta2O5, WO3, Li2WO4, Nb2O5, and MoO3 as a coating agent. 1+ k Ni c Z d Co e Q f M g The capacity and rate performance of O2 have been improved.

[0052] It should be noted that the coating layers on the surface of the cathode materials corresponding to the above-mentioned coating agents are all fast ion conductors. Compared with the existing coatings that have no electrochemical activity (e.g., zirconium oxide) and coatings that have low electrochemical activity and are not bulk ion conductors, fast ion conductors as coating layers can effectively improve the capacity and rate performance of ternary cathode materials with coating layers.

[0053] The above-mentioned coating methods include, but are not limited to, dry coating and wet coating.

[0054] When coating is performed by dry coating, the coating agent can be mixed with the above-mentioned cathode material and then sintered to obtain a ternary cathode material with a coating layer.

[0055] However, if the coating layer of the ternary cathode material has a severely uneven coating, or even if the coating layer is extremely thin in some local areas on the surface of the ternary cathode material, stress concentration may occur in these local areas during the charging and discharging process of the lithium-ion battery, leading to microcracks on the surface of the ternary cathode material particles, thus resulting in poor particle strength improvement. To overcome this problem, in one embodiment of this application, the coating agent is pretreated to have a finer particle size, thereby promoting the uniformity of mixing between the coating agent and the ternary cathode material, and thus improving the uniformity of the coating layer.

[0056] However, when the particle size is fine, agglomeration is a common problem. Therefore, to avoid the problem of uneven coating due to agglomeration of the aforementioned fine-particle coating agents when coating ternary cathode materials, in one embodiment of this application, the cathode material to be coated is filtered using a coating solution containing the coating agent in the solute to obtain a target filter cake with a water content of 0.05%-20%; wherein the coating solution is alkaline; the dried target filter cake is then subjected to an atmosphere with a carbon dioxide content of less than 0.1% at 180-800 °C. Sintering is carried out under the following conditions for 5-36 hours to obtain a positive electrode material with a coating layer. The preferred atmosphere is a vacuum or a pure oxygen atmosphere.

[0057] The preferred sintering temperature for the target filter cake is 200-600°C. The preferred sintering time is 10-24 hours.

[0058] The hydroxide ion concentration in the above-mentioned coating solution is 0.05-9 mol / L; preferably, it is 0.2-2.0 mol / L.

[0059] The equipment used for dewatering the target filter cake can be a vacuum filter, a centrifuge, or a filter press, and the moisture content of the obtained target filter cake is preferably 1%-12%.

[0060] Furthermore, the drying equipment can be a plow dryer, a double cone dryer, or a vibrating dryer. The drying temperature can be 50-300°C. Preferably, 100-250 The drying time can be 3-15 hours; preferably, 5-8 hours.

[0061] Furthermore, since the residual alkali on the surface of the ternary cathode material is mainly soluble in NaOH and Na2CO3 in water, compared to washing away the residual alkali of the ternary cathode material with a coating solution containing the aforementioned dissolving coating agent, it is preferable to use deionized water to wash away the residual alkali of the ternary cathode material in this embodiment. Therefore, in one embodiment of this application, before filtering the cathode material with a coating solution containing the coating agent, the cathode material is first immersed in deionized water for 1-30 minutes and then dehydrated to obtain a water-washed filter cake with a water content of 0.05%-30%. Then, the water-washed filter cake is filtered with the coating solution to obtain the aforementioned target filter cake.

[0062] In this embodiment, the washing time is preferably 5-10 minutes. During washing, the mass ratio of deionized water to the ternary cathode material with the coating layer is 0.3-3; preferably 1-1.5. The moisture content of the washed filter cake is preferably 2%-15%.

[0063] It should be noted that the water content of the washed filter cake in this embodiment should not be too high, otherwise it will be difficult to achieve the effect of uniform coating of the coating agent by the coating solution through wetting.

[0064] Correspondingly, the moisture content of the target filter cake should not be too high, otherwise too much coating agent will adhere to the surface of the ternary cathode material, which will lead to a significant decrease in the performance (e.g., capacity, rate performance) of the ternary cathode material with the coating layer due to the coating layer being too thick.

[0065] Furthermore, to prevent lithium ion deposition and chemical reaction between the coating agent and the lithium layer in the layered structure of the cathode material during the sintering of the target filter cake, when the coating agent transforms into a coating layer covering the surface of the cathode material, one embodiment of this application involves lithium replenishment to the cathode material before casting with the coating agent. Specifically, this can be achieved by dissolving a soluble lithium salt in the coating solution, ensuring that the solute in the coating solution also includes the soluble lithium salt, thereby achieving lithium replenishment.

[0066] The aforementioned soluble lithium salt must be a lithium salt that does not introduce cationic impurities, such as lithium hydroxide or lithium carbonate, to ensure that the metal ion content on the surface of the aforementioned ternary cathode material with a coating layer is 0.05wt%-1wt%, preferably 0.1wt%-0.5wt%. When the metal ion content in the coating layer is within the above range, the cathode material with the coating layer exhibits excellent cycle performance while also maintaining superior capacity, rate capability, and other electrochemical properties.

[0067] The solvent of the coating solution can be deionized water, and the solute may also include ammonia. The concentration of the metal ion corresponding to the coating element in the coating solution is 0.05-1.5 mol / L, preferably 0.1-1.0 mol / L.

[0068] The following describes the details through Examples 1-10 and Comparative Examples 1-5.

[0069] Example 1

[0070] S1, for 1000g of precursor Ni 0.90 Co 0.05 Al 0.05 A mixture of (OH)₂ and 479g LiOH·H₂O was heated in an oxygen atmosphere at 730°C. Under the specified conditions, sintering for 11 hours yielded the positive electrode material Li. 1.035 Ni 0.90 Co 0.05 Al 0.05 O2.

[0071] The cathode material has an average particle size of 10.5 μm and a specific surface area of ​​0.25 m². 2 / g.

[0072] S2. Wash 500g of the above positive electrode material with 500g of deionized water for 10min. Then, filter the liquid obtained by washing with a Buchner filtration flask for 30min to obtain a primary filter cake with a water content of 10%.

[0073] S3. The coating solution is evenly poured into the first filter cake and filtered by vacuum to obtain a second filter cake with a moisture content of 8%.

[0074] The coating solution was obtained by dissolving 3.75 g of lithium hydroxide (LiOH·H2O) in 150 mL of pure water and adding 6.95 g of tungsten oxide (WO3) to make the tungsten ion concentration in the aqueous solution 0.20 mol / L.

[0075] S4. Place the secondary filter cake into a double cone vacuum dryer at 120°C. The washed and dried material was obtained after drying for 6 hours.

[0076] S5. Place the dried material in an oxygen atmosphere, at 2 The heating rate was increased to 300 / min. The material was kept at this temperature for 10 hours to obtain the heat-treated material. Passing it through a 325-mesh sieve yielded a high-nickel material with a coating. Please refer to the SEM image of this high-nickel material. Figure 1 .

[0077] Example 2

[0078] In step S3, the coating solution is prepared by dissolving 7.50 g of lithium hydroxide (LiOH·H2O) in 150 mL of pure water and adding 13.90 g of tungsten oxide (WO3) to make the tungsten ion concentration in the aqueous solution 0.40 mol / L.

[0079] Except for the coating solution, which is different from that in Example 1, all other steps are the same as in Example 1.

[0080] Example 3

[0081] In step S3, the coating solution is prepared by dissolving 3.75 g of lithium hydroxide (LiOH·H2O) in 150 mL of pure water and adding 4.32 g of molybdenum oxide (MoO3) to make the molybdenum ion concentration in the aqueous solution 0.40 mol / L.

[0082] Except for the coating solution, which is different from that in Example 1, all other steps are the same as in Example 1.

[0083] Example 4

[0084] In step S3, the coating solution is prepared by dissolving 15.0 g of lithium hydroxide (LiOH·H2O) in 150 mL of pure water and adding 2.78 g of tungsten oxide (WO3) to make the tungsten ion concentration in the aqueous solution 0.80 mol / L.

[0085] Except for the coating solution, which differs from that in Example 1, all other steps are the same as in Example 1. Please refer to the SEM image of this high-nickel material for further details. Figure 2 .

[0086] Example 5

[0087] Except for the fact that the moisture content of the secondary filter cake in step S4 is 16%, the other implementation steps are the same as in Example 1.

[0088] Example 6

[0089] S1, for 1000g of precursor Ni 0.83 Co 0.6 Mn 0.11 A mixture of (OH)2 and 482g LiOH·H2O was heated in an oxygen atmosphere at 770°C. Under the specified conditions, sintering for 11 hours yielded the positive electrode material Li. 1.035 Ni 0.83 Co 0.6 Mn 0.11 O2.

[0090] The cathode material has an average particle size of 10.5 μm and a specific surface area of ​​0.25 m². 2 / g.

[0091] S2. Wash 500g of the above positive electrode material with 500g of deionized water for 10min. Then, filter the liquid obtained by washing with a Buchner filtration flask for 30min to obtain a primary filter cake with a water content of 10%.

[0092] S3. The coating solution is evenly poured into the first filter cake and filtered by vacuum to obtain a second filter cake with a moisture content of 8%.

[0093] The coating solution was obtained by dissolving 3.75 g of lithium hydroxide (LiOH·H2O) in 150 mL of pure water and adding 6.95 g of tungsten oxide (WO3) to make the tungsten ion concentration in the aqueous solution 0.20 mol / L.

[0094] S4. Place the secondary filter cake into a double cone vacuum dryer at 120°C. The washed and dried material was obtained after drying for 6 hours.

[0095] S5. Place the dried material in an oxygen atmosphere, at 2 The heating rate was increased to 300 / min. After heat treatment for 10 hours, the heat-treated material is obtained. Passing it through a 325-mesh sieve yields a high-nickel material with a coating layer.

[0096] Example 7

[0097] In step S3, the coating solution is prepared by dissolving 7.50 g of lithium hydroxide (LiOH·H2O) in 150 mL of pure water and adding 13.90 g of tungsten oxide (WO3) to make the tungsten ion concentration in the aqueous solution 0.40 mol / L.

[0098] Except for the coating solution, which is different from that in Example 6, all other steps are the same as in Example 6.

[0099] Example 8

[0100] In step S3, the coating solution is prepared by dissolving 3.75 g of lithium hydroxide (LiOH·H2O) in 150 mL of pure water and adding 0.66 g of metaboric acid (HBO2) to make the boron ion concentration in the aqueous solution 0.10 mol / L.

[0101] Except for the coating solution, which is different from that in Example 7, all other steps are the same as in Example 7.

[0102] Example 9

[0103] S5. Place the dried material in an oxygen atmosphere, at 2 The heating rate was increased to 350 / min. After heat treatment for 10 hours, the heat-treated material is obtained. Passing it through a 325-mesh sieve yields a high-nickel material with a coating layer.

[0104] Except for step S5, which is different from that in Example 8, all other steps are the same as in Example 8.

[0105] Example 10

[0106] Except for step S5, which is different from that in Example 8, all other steps are the same as in Example 8.

[0107] S5. Place the dried material in an oxygen atmosphere, at 2 The heating rate was increased to 400 / min. After heat treatment for 10 hours, the heat-treated material is obtained. Passing it through a 325-mesh sieve yields a high-nickel material with a coating layer.

[0108] Comparative Example 1

[0109] Except for step S3, which is different from that in Example 8, all other steps are the same as in Example 1.

[0110] S3. Pour 150ml of pure water evenly into the filter cake once, and then filter by vacuum to obtain a secondary filter cake with a moisture content of 8%.

[0111] Please refer to the SEM image of the obtained high-nickel material. Figure 3 .

[0112] Comparative Example 2

[0113] Steps S1-S2 are the same as in Example 1.

[0114] S3. Pour 150ml of pure water evenly into the filter cake once, and then filter by vacuum to obtain a secondary filter cake with a moisture content of 8%.

[0115] S4. Place the secondary filter cake into a double cone vacuum dryer at 120°C. The material was dried under the specified conditions for 6 hours to obtain the washed and dried material.

[0116] S5. Add 0.8 g of nano tungsten oxide (WO3) and 0.23 g of lithium hydroxide (LiOH·H2O) to the 400-water-washed and dried material, and mix them evenly with a high-speed mixer.

[0117] S6. The mixture obtained in S5 is placed in an oxygen atmosphere at 22... The heating rate was increased to 300 / min. The material was kept at this temperature for 10 hours to obtain the heat-treated material. Passing it through a 325-mesh sieve yielded a high-nickel material with a coating. Please refer to the SEM image of this high-nickel material. Figure 4 .

[0118] Comparative Example 3

[0119] Steps S1-S2 are the same as in Example 1.

[0120] S3. Pour 150ml of pure water evenly into the filter cake once, and then filter by vacuum to obtain a secondary filter cake with a moisture content of 8%.

[0121] S4. Place the secondary filter cake into a double cone vacuum dryer at 120°C. The material was dried under the specified conditions for 6 hours to obtain the washed and dried material.

[0122] S5. Add 0.76 g of metaboric acid (HBO2) and 0.23 g of lithium hydroxide (LiOH·H2O) to the 400-water-washed and dried material, and mix them evenly with a high-speed mixer.

[0123] S6. The mixture obtained in S5 is placed in an oxygen atmosphere at 22... The heating rate was increased to 300 / min. After heat treatment for 10 hours, the heat-treated material is obtained. Passing it through a 325-mesh sieve yields a high-nickel material with a coating layer.

[0124] Comparative Example 4

[0125] In step S3, the coating solution is prepared by dissolving 30.00 g of lithium hydroxide (LiOH·H2O) in 150 mL of pure water and adding 55.60 g of tungsten oxide (WO3) to make the tungsten ion concentration in the aqueous solution 1.60 mol / L.

[0126] Except for the coating solution, which is different from that in Example 1, all other steps are the same as in Example 1.

[0127] Comparative Example 5

[0128] In step S3, the coating solution is prepared by dissolving 30.0 g of lithium hydroxide (LiOH·H2O) in 150 mL of pure water and adding 55.60 g of tungsten oxide (WO3) to make the tungsten ion concentration in the aqueous solution 1.60 mol / L.

[0129] Except for the coating solution, which is different from that in Example 6, all other steps are the same as in Example 6.

[0130] The differences in the implementation steps of Examples 1-10 and Comparative Examples 1-5 are shown in Table 1.

[0131] Table 1

[0132]

[0133] The coating thickness and coating thickness variation rate Δδ of the ternary cathode materials obtained in Examples 1-10 and Comparative Examples 1-5 were tested. Here, δave is the average coating thickness at 10 points on the same particle surface, including the thickest and thinnest points. Test data are shown in Table 2.

[0134] Table 2

[0135]

[0136] It can be seen that the coating thickness variation rate of Examples 1-10 is less than 4. Compared with Examples 1 and 6, Comparative Examples 4 and 5 show that the coating thickness variation rate of Examples 1 and 6 is lower, and both exhibit good coating uniformity.

[0137] Furthermore, the particle strength of the ternary cathode materials obtained in Examples 1-10 and Comparative Examples 1-5 was tested (test data are shown in Table 2), and lithium-ion batteries were prepared.

[0138] In this case, a slurry (with a solid content of 60%~63%) obtained by mixing the ternary cathode material from Examples 1-10 and Comparative Examples 1-5 with a conductive agent and a binder at a mass ratio of 96.5%:1.5%:2% was coated onto a cathode film with a diameter of 15 mm, and the coating density was 17±1 mg / cm³. 2 Membrane compaction density: 3.2-3.4 g / cm³; coating thickness: 250 μm; nominal specific capacity: 180 mAh / g.

[0139] The 0.2C discharge capacity of the above lithium-ion batteries was tested, and the capacity retention rate after 100 cycles under 0.2C conditions with a discharge voltage window of 4.25-2.5V was also tested. The test data are shown in Table 3.

[0140] Table 3

[0141]

[0142] Compared with Examples 8-10 and Comparative Example 3, the coating effect is more uniform when using a coating solution. Furthermore, compared to Comparative Example 3, Examples 8-10 achieve primary particle coating, meaning the coating agent enters the cathode material along with the solvent, thus achieving secondary uniform coating within the particles. Therefore, it achieves a more thorough stress buffering effect. Correspondingly, the particles of Examples 8-10 have a lower environmental stress microcrack index and a higher cycle capacity retention rate.

[0143] Comparing Examples 6 and 7, the coating solution concentration and coating amount increased sequentially. Clearly, a higher coating amount provides better stress buffering. Therefore, the particles in Example 7 exhibit a smaller environmental stress microcrack index ΔA and a higher cycle capacity retention rate.

[0144] Comparing the sintering temperatures of Examples 8-10, it can be seen that as the sintering temperature increases sequentially, the coating layer can achieve a more uniform coating effect at higher coating temperatures. At the same time, the coating layer can fill the pores between the primary particles, resulting in a lower specific surface area S(P0) before pressing. The uniform and stable coating layer filling these pores further provides a buffering effect for stress, thereby reducing the microcrack index of the particles against environmental stress, i.e., increasing the particle strength, and the cycle capacity retention rate is also improved accordingly.

[0145] Compared to Example 4, the concentration of the coating liquid in Comparative Example 4 is higher, so the coating amount in Comparative Example 4 is higher than that in Example 4. Its particle environmental stress microcrack index ΔA is much lower than that in Example 4. Correspondingly, the cycle capacity retention rate of Comparative Example 4 is higher than that of Example 4. However, due to the larger (thicker) coating layer in Comparative Example 4, its capacity shows a significant loss compared to Example 4.

[0146] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A ternary cathode material, characterized in that, The general molecular formula of the ternary cathode material is: Li 1+ k Ni c Z d Co e Q f M g O2, -0.03≤k<1.0, c+d+e+f+g+k=1, 0.80≤c<1.0, 0<d≤0.20, 0.05≤e≤0.20, 0≤f≤0.05, 0<g≤0.05, Z is Al and / or Mn, Q is a dopant element, Q is selected from at least one of Zr, Sr, Y, Sb, Mo, Mg, Ti, Ba, Ta, and W; M is a coating element, M is selected from at least one of B, W, Ta, Nb, Sn, Ba, Mo, and Ce; The coating thickness variation rate Δδ of the ternary cathode material is ≤4; where... δmax is the maximum thickness of the coating layer on the surface of any particle in the ternary cathode material, δmin is the minimum thickness of the coating layer on the surface of the particle in the ternary cathode material, and δave is the average thickness of the coating layer on the surface of the particle in the ternary cathode material, including the thickest and thinnest points, at a total of Q points, where Q is an integer greater than or equal to 10. The ternary cathode material's particle environmental stress microcrack resistance index Not greater than (1-2d-2e) 120%, and not less than (1-2d-2e) 30%; of which, S(P) is the specific surface area of ​​the ternary cathode material after being pressed by a pressure P of 180-220 MPa, and S(P0) is the specific surface area of ​​the ternary cathode material before pressing.

2. The ternary cathode material as described in claim 1, characterized in that, The specific surface area of ​​the ternary cathode material is 0.35-1.3 m². 2 / g.

3. The ternary cathode material as described in claim 1, characterized in that, The mass ratio of the coating element to the mass of the ternary cathode material is 0.05wt%-1wt%.

4. The ternary cathode material as described in claim 1, characterized in that, The median particle size of the ternary cathode material is 9.5-14 μm.

5. The ternary cathode material as described in claim 4, characterized in that, The ratio of the sum of the masses of lithium carbonate and lithium hydroxide on the surface of the ternary cathode material to the mass of the ternary cathode material is no greater than 0.5 wt%.

6. A method for preparing the ternary cathode material according to any one of claims 1-5, characterized in that, include: For mixtures of ternary precursors, dopants, and lithium sources, the temperature range is 650-800℃. Sintering under the specified conditions for 7-20 hours yields the cathode material Li. 1+k Ni c Z d Co e Q f M g O2, wherein the dopant includes Q; Wherein, -0.03≤k<1.0, c+d+e+f+g+k=1, 0.80≤c<1, 0<d≤0.20, 0.05≤e≤0.20, 0≤f≤0.05, 0≤g≤0.05, Z is Al and / or Mn, Q is a dopant element, and Q is selected from at least one of Zr, Sr, Y, Sb, Mo, Mg, Ti, Ba, Ta, and W.

7. The method as described in claim 6, characterized in that, After obtaining the positive electrode material, the process further includes: The cathode material is filtered using a coating solution containing a coating agent to obtain a target filter cake with a water content of 0.05%-20%; wherein the coating solution is alkaline. The dried target filter cake is then heated in an atmosphere with a carbon dioxide content of less than 0.1% at 180-800 °C. Sintering under certain conditions yields a cathode material with a coating layer.

8. The method as described in claim 7, characterized in that, Before the process of casting the positive electrode material using a coating solution containing a coating agent in the solute, the following steps are included: The positive electrode material to be coated is immersed in deionized water and washed for 1-30 minutes, and then dehydrated to obtain a water-washed filter cake with a water content of 0.05%-30%. The process of using a coating solution containing a coating agent to filter the positive electrode material to obtain a target filter cake with a water content of 0.05%-20% includes: The target filter cake is obtained by casting the water-washed filter cake with the coating solution.

9. The method as described in claim 8, characterized in that, The solute in the coating solution also includes soluble lithium salt.

10. The method as described in claim 7, characterized in that, The concentration of hydroxide ions in the coating solution is 0.05-9 mol / L.

11. The method as described in claim 7, characterized in that, The concentration of metal ions in the coating solution is 0.05-1.5 mol / L, and the coating agent in the solute is at least one of H3BO3, HBO2, WO3, H2WO4, Ta2O5, WO3, Li2WO4, Nb2O5, and MoO3.

12. A lithium-ion battery, characterized in that, include: The ternary cathode material as described in any one of claims 1-5, or the ternary cathode material prepared by the method described in any one of claims 6-11.

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