A cobalt-free cathode material, its preparation method and application

Abstract

This invention provides a cobalt-free cathode material, its preparation method, and its application. The preparation method includes the following steps: (1) mixing a cobalt-free precursor, a lithium source, and a zirconium source, and then calcining at a low temperature to obtain a calcined material; (2) mixing the calcined material with boric acid, lithium borate, and alumina, and then sintering at a high temperature to obtain the cobalt-free cathode material; the low-temperature calcination temperature is ≤550℃. This invention, by adjusting the sintering temperature and the type of coating material, prepares a lithium-permeable, uniformly grown single-crystal ceramic protective layer, significantly improving the material's capacity and cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and relates to a cobalt-free cathode material, its preparation method, and its application. Background Technology

[0002] With the continuous development and upgrading of electric vehicle performance, manufacturing a cathode material with high capacity and good cycle performance has become a hot research topic. Nickel plays a role in increasing capacity, cobalt can stabilize the layered structure of the material and improve its recycling stability, while manganese can reduce material costs and improve safety and structural stability. However, the high cost of cobalt raw materials leads to high production costs for synthesized materials. Furthermore, current high-nickel materials suffer from high-temperature gas generation and insufficient cycle life; therefore, reducing the cobalt content in materials has become a crucial research topic.

[0003] CN116789187A discloses a high-nickel cobalt-free cathode material and its preparation method. The preparation method of the high-nickel cobalt-free cathode material includes the following steps: preparing zirconium-doped high-nickel cobalt-free nickel-manganese hydroxide; adding zirconium-doped high-nickel cobalt-free nickel-manganese hydroxide, lithium hydroxide, magnesium titanate, and zirconium aluminate to water, mixing evenly, and drying to obtain a mixture; placing the mixture in a pure oxygen atmosphere and holding it at a temperature of 300℃-800℃ for 6-12 hours to obtain high-nickel cobalt-free nickel-manganese lithium oxide; mixing high-nickel cobalt-free nickel-manganese lithium oxide, borosilicate, and tungsten oxide evenly, and then drying and sintering to obtain the target product.

[0004] CN115417461A discloses a cobalt-free high-nickel cathode material and its preparation method. The preparation method of the cobalt-free high-nickel cathode material includes the following steps: S1: mixing a cobalt-free high-nickel precursor, a lithium source, and a dopant uniformly; S2: placing the mixture obtained in S1 into an alumina crucible, transferring it to a calcining furnace, and sintering it under an oxygen atmosphere; S3: crushing and sieving the sintered product obtained in S2 to obtain the cobalt-free high-nickel cathode material.

[0005] The poor structural uniformity of the cobalt-free high-nickel cathode material prepared by the above method results in low capacity and cycle stability, which limits its practical application. Summary of the Invention

[0006] The purpose of this invention is to provide a cobalt-free cathode material, its preparation method, and its application. This invention, by adjusting the sintering temperature and the type of coating material, prepares a lithium-permeable, uniformly grown single crystal with a uniform ceramic protective layer formed by the coating material, which significantly improves the material's capacity and cycle stability.

[0007] To achieve this objective, the present invention employs the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a cobalt-free cathode material, the method comprising the following steps:

[0009] (1) A cobalt-free precursor, a lithium source and a zirconium source are mixed and then calcined at low temperature to obtain a calcined material;

[0010] (2) The calcined material is mixed with boric acid, lithium borate and alumina, and then sintered at high temperature to obtain the cobalt-free cathode material;

[0011] The temperature of the low-temperature calcination is ≤550℃.

[0012] This invention involves calcining a cobalt-free precursor, a lithium source, and a zirconium source at a low temperature of ≤550℃. During the reaction, lithium effectively penetrates into the polycrystalline material by more than 1-2 micrometers. The zirconium oxide generated by the zirconium source adheres to the crystal surface, fixing the lattice and preventing collapse in the electrolyte (this zirconium oxide is not a conventional doping method; strict temperature control is required, as excessively high temperatures can cause zirconium to be incorporated into the precursor). This process not only achieves sufficient lithium penetration but also results in more uniform single-crystal ion growth. Subsequently, boric acid, lithium borate, and alumina are added for high-temperature calcination. Boric acid reacts with residual lithium on the surface of the calcined material to form lithium borate. Lithium borate has a melting point of 760℃. When the high-temperature sintering temperature reaches 760℃, the lithium borate melts and coats the material surface with alumina. After cooling, a "ceramic" protective layer is formed on the material surface, effectively reducing the erosion rate of the electrolyte and significantly improving the material's capacity and cycle stability.

[0013] Preferably, the chemical formula of the cobalt-free precursor in step (1) is Ni x M 1-x (OH)2, wherein M includes manganese, 0.8≤x≤0.98.

[0014] Preferably, the lithium source includes hydrated lithium hydroxide and / or lithium hydroxide.

[0015] Preferably, the molar ratio of lithium in the lithium source to metal in the cobalt-free precursor is (1.025 to 1.08):1, for example: 1.025:1, 1.03:1, 1.05:1, 1.06:1 or 1.08:1, etc.

[0016] Preferably, the zirconium source includes zirconium oxide and / or zirconium hydroxide, and more preferably zirconium hydroxide.

[0017] This invention uses zirconium hydroxide and / or zirconium oxide as zirconium source. Zirconium hydroxide decomposes into zirconium oxide at around 500°C and then adheres to the crystal surface, exhibiting a better adhesion effect than zirconium oxide. Therefore, zirconium hydroxide is preferred as the zirconium source here.

[0018] Preferably, based on the mass of the calcined material as 100%, the mass fraction of zirconium in the calcined material is 0.1% to 0.12%, for example: 0.1%, 0.105%, 0.11%, 0.115%, or 0.12%, etc.

[0019] Preferably, the atmosphere of the low-temperature calcination treatment in step (1) includes oxygen.

[0020] Preferably, the heating rate of the low-temperature calcination treatment is 2.5 to 3 °C / min, for example: 2.5 °C / min, 2.6 °C / min, 2.8 °C / min, 2.9 °C / min or 3 °C / min, etc.

[0021] Preferably, the low-temperature calcination treatment includes one-step calcination and two-step calcination.

[0022] This invention employs a two-step calcination process. In the first calcination step, the lithium source is in a molten state and fully integrates and permeates with the precursor, achieving a lithium penetration depth of over 2μm, thus providing a medium for charge transport and transfer. In the second calcination step, the lithium source on the surface further reacts and fuses with the material, and single-crystal particles begin to form on the material surface, ensuring that lithium is not excessively lost during the water washing stage, thus preventing lithium deficiency.

[0023] Preferably, the calcination temperature in the first step is 450-500℃, for example: 450℃, 460℃, 480℃, 490℃ or 500℃.

[0024] Preferably, the holding time for the one-step calcination is 3 to 8 hours, for example: 3 hours, 3.5 hours, 4 hours, 5 hours or 8 hours.

[0025] Preferably, the temperature of the two-step calcination is 500-550℃, for example: 500℃, 510℃, 520℃, 540℃ or 550℃.

[0026] Preferably, the holding time for the two-step calcination is 3 to 8 hours, for example: 3 hours, 3.5 hours, 4 hours, 5 hours or 8 hours.

[0027] Preferably, the holding time for the low-temperature calcination treatment is 9 to 10 hours, for example: 9 hours, 9.2 hours, 9.5 hours, 9.8 hours, or 10 hours.

[0028] Preferably, the calcined material in step (1) is subjected to water washing, pressure filtration and drying treatment.

[0029] Preferably, the water-to-material ratio for the washing process is (2-4):1, for example: 2:1, 2.5:1, 3:1, 3.5:1 or 4:1, etc.

[0030] Preferably, the stirring frequency of the water washing is 10-20Hz, for example: 10Hz, 12Hz, 15Hz, 18Hz or 20Hz.

[0031] Preferably, the washing time is 5 to 10 hours, for example: 5 hours, 6 hours, 8 hours, 9 hours or 10 hours.

[0032] Preferably, the pressure filtration time is 20 to 30 minutes, for example: 20 minutes, 22 minutes, 25 minutes, 28 minutes or 30 minutes.

[0033] Preferably, the pressure of the filter press is 0.1 to 0.3 MPa, for example: 0.1 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa or 0.3 MPa, etc.

[0034] Preferably, the drying temperature is 120-180°C, for example: 120°C, 140°C, 150°C, 160°C or 180°C.

[0035] Preferably, the drying time is 3 to 10 hours, for example: 3 hours, 5 hours, 6 hours, 8 hours or 10 hours.

[0036] Preferably, the mass ratio of boric acid and lithium borate in step (2) is 1:(2-4), for example: 1:2, 1:2.5, 1:3, 1:3.5 or 1:4, etc.

[0037] The amount of lithium borate obtained from the reaction of boric acid and residual lithium is relatively small, so lithium borate needs to be added here to better melt and form a complete coating layer.

[0038] Preferably, the total mass ratio of boric acid and lithium borate to the calcined material is (0.05-0.2):100, for example: 0.05:100, 0.08:100, 0.1:100, 0.15:100 or 0.2:100, etc., and preferably (0.05-0.15):100.

[0039] Preferably, the mass ratio of alumina to calcined material is (0.05-0.2):100, for example: 0.05:100, 0.08:100, 0.1:100, 0.15:100 or 0.2:100, etc.

[0040] Preferably, the heating rate of the high-temperature sintering treatment in step (2) is 4.2 to 4.6 °C / min, for example: 4.2 °C / min, 4.3 °C / min, 4.4 °C / min, 4.5 °C / min or 4.6 °C / min, etc.

[0041] Preferably, the temperature of the high-temperature sintering treatment is >760°C.

[0042] Preferably, the high-temperature sintering treatment temperature is 800-850℃, for example: 800℃, 810℃, 820℃, 840℃ or 850℃, etc.

[0043] Preferably, the holding time for the high-temperature sintering treatment is 9 to 10 hours, for example: 9 hours, 9.2 hours, 9.5 hours, 9.8 hours, or 10 hours.

[0044] As a preferred embodiment of the present invention, the preparation method includes the following steps:

[0045] (1) Mix cobalt-free precursor, lithium source and zirconium oxide, calcine at 450-500℃ for 3-8h at a heating rate of 2.5-3℃ / min, then heat to 500-550℃ and calcine again for 3-8h, and then wash with water, filter and dry to obtain calcined material with a zirconium mass fraction of 0.1-0.12%;

[0046] (2) The calcined material is mixed with boric acid, lithium borate and alumina, wherein the mass ratio of boric acid and lithium borate is 1:(2-4), and sintered at 800-850°C for 9-10 hours at a heating rate of 4.2-4.6°C / min to obtain the cobalt-free cathode material.

[0047] In a second aspect, the present invention provides a cobalt-free cathode material, which is prepared by the method described in the first aspect.

[0048] Thirdly, the present invention provides a positive electrode sheet comprising the cobalt-free positive electrode material as described in the second aspect.

[0049] Fourthly, the present invention provides a lithium-ion battery comprising a positive electrode as described in the third aspect.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] (1) By controlling the temperature of one-step sintering (low-temperature calcination), the present invention allows lithium to be immersed into the shallow layer of the polycrystalline structure, and zirconium oxide to adhere to the polycrystalline surface to stabilize the structure. Boric acid, lithium borate and alumina are then added for high-temperature sintering, which reduces residual alkali and forms a ceramic-like protective layer, thereby further improving the capacity and cycle stability of the material.

[0052] (2) The battery made from the cobalt-free cathode material prepared by the method of the present invention can achieve a first charge-discharge specific capacity of more than 217.3 mAh / g, a first charge-discharge efficiency of more than 93.8%, and a discharge capacity retention rate of more than 82.5% after 100 discharge cycles at 1C. Attached Figure Description

[0053] Figure 1This is a SEM image of the cobalt-free cathode material prepared in Example 1.

[0054] Figure 2 This is a magnified SEM image of the cobalt-free cathode material prepared in Example 1.

[0055] Figure 3 This is an SEM image of the mixture obtained in Example 1.

[0056] Figure 4 This is a magnified SEM image of the mixture obtained in Example 1.

[0057] Figure 5 This is an SEM image of the calcined material prepared in Example 1.

[0058] Figure 6 This is a magnified SEM image of the calcined material prepared in Example 1.

[0059] Figure 7 This is a SEM image of the washed and dried material prepared in Example 1.

[0060] Figure 8 This is a magnified SEM image of the washed and dried material prepared in Example 1. Detailed Implementation

[0061] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0062] Example 1

[0063] This embodiment provides a cobalt-free cathode material, and the SEM image of the cobalt-free cathode material is shown below. Figure 1-2 As shown, the cobalt-free cathode material is prepared by the following method:

[0064] (1) Ni 0.88 Mn 0.12 The (OH)₂ precursor and lithium hydroxide monohydrate were mixed at a Li:Me(Ni+Mn) ratio of 1.06, and zirconium hydroxide was added. The SEM image of the resulting mixture is shown below. Figure 3-4 As shown, by Figure 3-4 It can be seen that lithium hydroxide and zirconium oxide are dispersed between the precursors. The mixture was heated to 500℃ at a heating rate of 2.8℃ / min and calcined for 6 hours, then heated to 540℃ and calcined for another 3.36 hours to obtain a calcined material with a zirconium content of 0.11% by mass. The SEM image of the calcined material is shown below. Figure 5-6 As shown, by Figure 5-6It can be seen that the dispersed lithium hydroxide has reacted and dissolved, and the added zirconium oxide is no longer scattered in powder form, but is all attached to the polycrystalline surface. After washing with water at 16 Hz for 8 minutes at a water-to-material ratio of 3:1, pressure filtering at 0.2 MPa for 25 minutes, and drying at 150℃ for 6 hours, the SEM image of the dried material is shown below. Figure 7-8 As shown, by Figure 7-8 It can be seen that after washing and drying, obvious single crystal particles appear on the surface, and the residual lithium black spots on the surface are significantly reduced.

[0065] (2) Borides (boric acid: lithium borate 1:3) and alumina were added at 0.1% of the mass of the calcined material, and the material was heated to 820°C at a heating rate of 4.4°C / min and sintered for 9.5 h to obtain the cobalt-free cathode material. The SEM image of the cobalt-free cathode material shows that the single crystal ions of the finished product obtained after the above sintering treatment are significantly increased and the particles are relatively uniform.

[0066] Example 2

[0067] This embodiment provides a cobalt-free cathode material, which is prepared by the following method:

[0068] (1) Ni 0.88 Mn 0.12 (OH)2 precursor and lithium hydroxide monohydrate were mixed in a Li:Me(Ni+Mn) ratio of 1.045. Zirconia was added and the mixture was heated to 450℃ at a heating rate of 2.5℃ / min and calcined for 4.5h. Then the temperature was increased to 550℃ and calcined for another 5.24h to obtain a calcined material with a zirconium content of 0.1%. The material was washed with water at a frequency of 16Hz for 10min at a water-to-material ratio of 2:1, filtered under pressure at 0.1MPa for 20min, and dried at 150℃ for 6h.

[0069] (2) Add 0.05% of boride (boric acid: lithium borate 1:3) and 0.15% of alumina according to the mass of the calcined material, respectively, and sinter at 800℃ for 10h at a heating rate of 4.2℃ / min to obtain the cobalt-free cathode material.

[0070] Example 3

[0071] This embodiment provides a cobalt-free cathode material, which is prepared by the following method:

[0072] (1) Ni 0.88 Mn 0.12(OH)2 precursor and lithium hydroxide monohydrate were mixed in a Li:Me(Ni+Mn) ratio of 1.07. Zirconia was added and the mixture was heated to 500℃ at a heating rate of 3℃ / min and calcined for 5.1h. Then the temperature was increased to 520℃ and calcined for another 4.36h to obtain a calcined material with a zirconium content of 0.12%. The material was washed with water at a frequency of 16Hz for 10min at a water-to-material ratio of 4:1, filtered under pressure at 0.3MPa for 20min, and dried at 120℃ for 10h.

[0073] (2) Borides (boric acid: lithium borate 1:3) and alumina were added at 0.15% of the mass of the calcined material, and the material was sintered at 850°C for 9 hours at a heating rate of 4.6°C / min to obtain the cobalt-free cathode material.

[0074] Example 4

[0075] The only difference between this embodiment and Embodiment 1 is that step (1) is calcined at 550°C for 9.5 hours, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0076] Example 5

[0077] The only difference between this embodiment and embodiment 1 is that the mass ratio of boric acid and lithium borate in step (2) is 1:1, while the other conditions and parameters are exactly the same as in embodiment 1.

[0078] Example 6

[0079] The only difference between this embodiment and embodiment 1 is that the mass ratio of boric acid and lithium borate in step (2) is 1:5, while the other conditions and parameters are exactly the same as in embodiment 1.

[0080] Example 7

[0081] The only difference between this embodiment and embodiment 1 is that the mass ratio of alumina to calcined material in step (2) is 0.02:100, while the other conditions and parameters are exactly the same as in embodiment 1.

[0082] Example 8

[0083] The only difference between this embodiment and embodiment 1 is that the mass ratio of alumina to calcined material in step (2) is 0.3:100, while the other conditions and parameters are exactly the same as in embodiment 1.

[0084] Comparative Example 1

[0085] The only difference between this comparative example and Example 1 is that the calcination temperature in step (1) is 580°C, while the other conditions and parameters are exactly the same as in Example 1.

[0086] Comparative Example 2

[0087] The only difference between this comparative example and Example 1 is that lithium borate is not added in step (2), while the other conditions and parameters are exactly the same as in Example 1.

[0088] Performance testing:

[0089] The cobalt-free cathode material, binder, conductive agent, and solvent prepared in the examples and comparative examples were mixed uniformly with solvent in a certain order and under certain conditions to form a stable suspension. This suspension was then coated, dried, and rolled into cathode sheets. These sheets were then assembled into 2032 coin cells in a glove box with a cathode shell, a cathode shell, gasket, spring, separator, and electrolyte. The cells were tested using a Blue Electric testing system, charging at 0.1C to 4.3V, discharging at 0.1C constant current to 3.0V, then charging at 1C to 4.3V, and discharging at 1C to 3.0V, for 100 cycles. The test results are shown in Table 1.

[0090] Table 1

[0091]

[0092]

[0093] As can be seen from Table 1, and from Examples 1-3, the battery made of the cobalt-free cathode material prepared by the method of the present invention can achieve a first charge-discharge specific capacity of over 217.3 mAh / g, a first charge-discharge efficiency of over 93.8%, and a capacity retention rate of over 82.5% after 100 discharge cycles at 1C.

[0094] Comparing Examples 1 and 4, it can be seen that the present invention uses a two-step calcination process. In the first step of calcination, the lithium source is in a molten state and fully combines and penetrates with the precursor, so that the penetration depth of lithium reaches more than 2μm, providing a medium for charge transport and transfer. In the second step of calcination, the lithium source on the surface further reacts and fuses with the material, and single crystal particles begin to form on the material surface, ensuring that lithium is not excessively lost during the water washing stage, thus preventing lithium deficiency.

[0095] A comparison of Examples 1 and 5-6 shows that the ratio of boric acid to lithium borate affects the performance of the cobalt-free cathode material during its preparation. Maintaining a mass ratio of boric acid to lithium borate of 1:2 to 4 results in a cobalt-free cathode material with better performance. If the proportion of boric acid is too high, it will lead to higher impurities in the material, reducing its overall capacity. If the proportion of boric acid is too low, it will result in higher residual lithium on the material surface, making it prone to absorbing water and forming a "jelly-like" substance during the battery slurry preparation stage. After a certain number of cycles, this can also cause the battery to bulge.

[0096] A comparison of Examples 1 and 7-8 shows that the amount of alumina added affects the performance of the cobalt-free cathode material described in this invention. Controlling the mass ratio of alumina to calcined material to 0.05–0.2:100 yields a cobalt-free cathode material with better performance. Excessive alumina addition not only leads to higher impurities and reduced capacity but also results in a thicker "ceramic layer," affecting charge transport and transfer, thus causing lower capacity. Conversely, insufficient alumina addition results in a thinner "ceramic layer," which cannot effectively slow down electrolyte corrosion, leading to poorer cycle performance.

[0097] Comparing Example 1 and Comparative Example 1, it can be seen that the present invention calcines a cobalt-free precursor, a lithium source, and zirconium oxide at a low temperature of ≤550℃. During the reaction, lithium effectively penetrates into the polycrystalline interior by more than 1-2 micrometers. The zirconium oxide generated by the zirconium source adheres to the crystal surface, fixing the crystal lattice and preventing collapse in the electrolyte (here, zirconium oxide is not a conventional doping method; temperature must be strictly controlled, as excessively high temperatures will cause zirconium to be doped into the precursor and damage the crystal structure). This process not only achieves sufficient lithium penetration but also results in more uniform single-crystal ion growth.

[0098] As can be seen from the comparison between Example 1 and Comparative Example 2, the present invention uses boric acid and lithium borate in combination, which can not only reduce the residual lithium on the material surface, but also generate a complete protective layer, effectively reduce the erosion rate of the electrolyte, and significantly improve the capacity and cycle stability of the material.

[0099] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a cobalt-free cathode material, characterized in that, The preparation method includes the following steps: (1) A cobalt-free precursor, a lithium source and a zirconium source are mixed and then calcined at low temperature to obtain a calcined material; (2) The calcined material is mixed with boric acid, lithium borate and alumina, and then sintered at high temperature to obtain the cobalt-free cathode material; The temperature of the low-temperature calcination is ≤550℃; The chemical formula of the cobalt-free precursor in step (1) is Ni x M 1-x (OH)2, wherein M includes manganese, 0.8≤x≤0.98, and the calcined material is subjected to water washing, pressure filtration and drying treatment; In step (2), the mass ratio of boric acid to lithium borate is 1:(2~4), the total mass of boric acid and lithium borate to the mass ratio of calcined material is (0.05~0.2):100, the mass ratio of alumina to calcined material is (0.05~0.2):100, and the temperature of the high-temperature sintering treatment is >760℃.

2. The preparation method according to claim 1, characterized in that, The lithium source includes hydrated lithium hydroxide and / or lithium hydroxide.

3. The preparation method according to claim 1, characterized in that, The molar ratio of lithium in the lithium source to metal in the cobalt-free precursor is (1.025~1.08):

1.

4. The preparation method according to claim 1, characterized in that, The zirconium source includes zirconium oxide and / or zirconium hydroxide.

5. The preparation method according to claim 1, characterized in that, The zirconium source is zirconium hydroxide.

6. The preparation method according to claim 1, characterized in that, Based on the mass of the calcined material as 100%, the mass fraction of zirconium in the calcined material is 0.1% to 0.12%.

7. The preparation method according to claim 1, characterized in that, The atmosphere for the low-temperature calcination treatment in step (1) includes oxygen.

8. The preparation method according to claim 1, characterized in that, The heating rate of the low-temperature calcination treatment is 2.5~3℃ / min.

9. The preparation method according to claim 1, characterized in that, The low-temperature calcination treatment includes one-step calcination and two-step calcination.

10. The preparation method according to claim 9, characterized in that, The calcination temperature in the first step is 450~500℃.

11. The preparation method according to claim 9, characterized in that, The holding time for the first calcination step is 3-8 hours.

12. The preparation method according to claim 9, characterized in that, The temperature for the two-step calcination is 500~550℃.

13. The preparation method according to claim 9, characterized in that, The holding time for the two-step calcination is 3 to 8 hours.

14. The preparation method according to claim 1, characterized in that, The holding time for the low-temperature calcination treatment is 9-10 hours.

15. The preparation method according to claim 1, characterized in that, The water-to-material ratio for the washing process is (2~4):

1.

16. The preparation method according to claim 1, characterized in that, The stirring frequency of the water washing is 10~20Hz.

17. The preparation method according to claim 1, characterized in that, The washing time is 5-10 hours.

18. The preparation method according to claim 1, characterized in that, The pressure filtration time is 20-30 minutes.

19. The preparation method according to claim 1, characterized in that, The pressure of the filter press is 0.1~0.3MPa.

20. The preparation method according to claim 1, characterized in that, The drying temperature is 120~180℃.

21. The preparation method according to claim 1, characterized in that, The drying time is 3 to 10 hours.

22. The preparation method according to claim 1, characterized in that, The total mass ratio of boric acid and lithium borate to the mass of the calcined material is (0.05~0.15):

100.

23. The preparation method according to claim 1, characterized in that, The heating rate of the high-temperature sintering treatment in step (2) is 4.2~4.6℃ / min.

24. The preparation method according to claim 1, characterized in that, The high-temperature sintering treatment is performed at a temperature of 800~850℃.

25. The preparation method according to claim 1, characterized in that, The holding time for the high-temperature sintering treatment is 9-10 hours.

26. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) Mix cobalt-free precursor, lithium source and zirconium oxide, calcine at 450~500℃ for 3~6h at a heating rate of 2.5~3℃ / min, then heat to 500~550℃ and calcine again for 3~6h, and then wash with water, filter and dry to obtain calcined material with a zirconium mass fraction of 0.1~0.12%; (2) The calcined material is mixed with boric acid, lithium borate and alumina, wherein the mass ratio of boric acid and lithium borate is 1:(2~4), and sintered at 800~850℃ for 9~10h at a heating rate of 4.2~4.6℃ / min to obtain the cobalt-free cathode material.

27. A cobalt-free cathode material, characterized in that, The cobalt-free cathode material is prepared by the method described in any one of claims 1-26.

28. A positive electrode plate, characterized in that, The positive electrode comprises the cobalt-free positive electrode material as described in claim 27.

29. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode as described in claim 28.

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