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

Abstract

The present invention provides a cobalt-free high-nickel cathode material, a preparation method thereof and an application. The preparation method comprises the following steps: (1) mixing a nickel source and a manganese source according to Ni:Mn = 9-99:1 to obtain a salt solution A, and mixing a nickel source and a manganese source according to Ni:Mn = 2-4:1 to obtain a salt solution B; (2) adding the salt solution A, ammonia water and an alkali solution into a reaction vessel in a co-current manner for a one-step reaction, and then replacing the salt solution A with the salt solution B for a two-step reaction to obtain a cobalt-free high-nickel precursor; (3) mixing the precursor with a lithium source and a dopant, sintering, then performing pickling and flushing, adding a lithium salt solution, performing power-on regeneration and repair, and then mixing with boric acid and sintering to obtain the cobalt-free high-nickel cathode material. The present invention synthesizes a cathode material with a manganese-rich surface and a nickel-rich interior. Combining with a novel pickling and flushing process can improve the structural stability of the material and also improve the lithium ion deintercalation rate and deintercalation amount, thereby obtaining better cycle performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and relates to a cobalt-free high-nickel cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] The trend of electrification in the automotive industry is becoming increasingly obvious. Major global automobile manufacturers have announced their electrification milestones. As the core component of electrification, the demand for power batteries will experience explosive growth, and the demand for cathode materials will continue to increase.

[0003] Currently, the mainstream high-energy density cathode material is the ternary cathode material. Due to the increasing demand for Co element in the ternary cathode material, Co currently accounts for 10% of power batteries. At the same time, the uncertain factors in the development of Co resources will affect the process of electrification. Therefore, it is urgent to develop cobalt-free cathode materials.

[0004] It is worth noting that when the Ni content is above 90%, the role of Co will no longer be obvious. Therefore, cobalt-free NM and NCM will exhibit comparable electrochemical properties.

[0005] CN111916726A discloses a high-nickel ternary cathode material and a preparation method thereof. The preparation method includes: in-situ growing Mg-MOF-74 material on the surface of polystyrene spheres to obtain Mg-MOF-74@PS; impregnating Mg-MOF-74@PS with a solution containing a doping element X to obtain X-Mg-MOF-74@PS; using X-Mg-MOF-74@PS as the core to in-situ grow a nickel-manganese precursor to obtain a nickel-manganese precursor with a core-shell structure; mixing the above nickel-manganese precursor with a lithium source and performing high-temperature lithiation to obtain a hollow nickel-manganese binary cathode material with gradient doping in the inner layer; mixing the above nickel-manganese binary cathode material with ZIF-8 and calcining to obtain a hollow high-nickel cobalt-free cathode material coated with nitrogen-doped graphite carbon.

[0006] CN113809290A discloses a cobalt-free high-nickel cathode material and a preparation method thereof. The method includes the following steps: preparing a soluble salt solution of a coating metal, adding a complexing agent, adjusting the pH, adding a cobalt-free high-nickel cathode material matrix, performing an electroless plating reaction, separating the solid and liquid, drying, and calcining to obtain the cobalt-free high-nickel cathode material.

[0007] The above-mentioned high-nickel cobalt-free cathode materials have problems such as poor cycle stability and high gas generation risk, which limit their practical applications. Summary of the Invention

[0008] The object of the present invention is to provide a cobalt-free high-nickel cathode material, a preparation method thereof and an application. By synthesizing a cathode material with a manganese-rich surface and a nickel-rich interior, and combining a novel pickling and flushing process, the present invention can not only improve the structural stability of the material, but also increase the lithium ion deintercalation rate and the amount of deintercalated lithium, thereby obtaining better cycling performance.

[0009] To achieve the object of the present invention, the following technical solutions are adopted:

[0010] In the first aspect, the present invention provides a preparation method of a cobalt-free high-nickel cathode material, and the preparation method includes the following steps:

[0011] (1) Mix a nickel source and a manganese source according to Ni:Mn = 9-99:1 with a solvent to obtain a salt solution A, and mix a nickel source and a manganese source according to Ni:Mn = 2-4:1 with a solvent to obtain a salt solution B;

[0012] (2) After adding the salt solution A, ammonia water and an alkali solution into a reaction vessel in a co-current manner for a one-step reaction, then adding the salt solution B, ammonia water and an alkali solution into the reaction vessel in a co-current manner for a two-step reaction, and aging to obtain a cobalt-free high-nickel precursor;

[0013] (3) Mix the cobalt-free high-nickel precursor with a lithium source and a dopant, perform one-step sintering, then perform pickling and flushing, add a lithium salt solution and energize for regeneration and repair, and mix the obtained material with boric acid and perform two-step sintering to obtain the cobalt-free high-nickel cathode material.

[0014] By synthesizing a cathode material with a manganese-rich surface and a nickel-rich interior, the present invention effectively improves the mechanical strength of cobalt-free polycrystalline primary particles, and can make the mirror arrangement of primary particles better, improve the fracture strength of secondary particle spheres, thereby reducing structural damage during battery charge and discharge and improving cycling stability.

[0015] Preferably, the nickel source in step (1) includes nickel sulfate.

[0016] Preferably, the manganese source includes manganese sulfate.

[0017] Preferably, the total molar concentration of metal ions in the salt solution A is 2-4 mol / L, for example: 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L or 4 mol / L, etc.

[0018] Preferably, the total molar concentration of metal ions in the salt solution B is 2-4 mol / L, for example: 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L or 4 mol / L, etc.

[0019] Preferably, the molar concentration of the ammonia water in step (2) is 10 to 12 mol / L, for example: 10 mol / L, 10.5 mol / L, 11 mol / L, 11.5 mol / L, 12 mol / L, etc.

[0020] Preferably, the molar concentration of sodium hydroxide in the lye is 3 to 4 mol / L, for example: 3 mol / L, 3.2 mol / L, 3.5 mol / L, 3.8 mol / L, 4 mol / L, etc.

[0021] Preferably, the flow rates of the salt solution A and the salt solution B are independently 0.2 to 0.4 L / min, for example: 0.2 L / min, 0.25 L / min, 0.3 L / min, 0.35 L / min, 0.4 L / min, etc.

[0022] Preferably, in the reaction systems of the one-step reaction and the two-step reaction, the molar ratio of sodium hydroxide to metal ions is 2 to 4:1, for example: 2:1, 2.5:1, 3:1, 3.5:1, 4:1, etc.

[0023] Preferably, in the reaction systems of the one-step reaction and the two-step reaction, the molar ratio of ammonium ions to metal ions in the ammonia water is 1.2 to 1.5:1, for example: 1.2:1, 1.3:1, 1.4:1, 1.5:1, etc.

[0024] Preferably, the reaction time of the one-step reaction in step (2) is 12 to 20 h, for example: 12 h, 14 h, 16 h, 18 h, 20 h, etc.

[0025] Preferably, the reaction time of the two-step reaction is 2 to 4 h, for example: 2 h, 2.5 h, 3 h, 3.5 h, 4 h, etc.

[0026] Preferably, the temperatures of the one-step reaction and the two-step reaction are independently 40 to 60 °C, for example: 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, etc.

[0027] Preferably, the stirring speeds of the one-step reaction and the two-step reaction are independently 50 to 200 rpm, for example: 50 rpm, 80 rpm, 100 rpm, 150 rpm, 200 rpm, etc.

[0028] Preferably, the aging time is 8 to 12 h, for example: 8 h, 9 h, 10 h, 11 h, 12 h, etc.

[0029] Preferably, washing and drying treatments are carried out after aging.

[0030] Preferably, the Li / M ratio of the lithium source and the cobalt-free high-nickel precursor in step (3) is 1.01-1.06:1, for example: 1.01:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1 or 1.06:1, etc.

[0031] Preferably, the dopant includes any one or a combination of at least two of ZrO2, Al2O3, MgO, Y2O3, TiO2, ZnO, Nb2O5, MoO3, SrCO3, WO3 or Ta2O5.

[0032] Preferably, the doping amount of the dopant is 500-5000 ppm, for example: 500 ppm, 1000 ppm, 2000 ppm, 3000 ppm or 5000 ppm, etc.

[0033] Preferably, the temperature of the one-step sintering in step (3) is 700-800 °C, for example: 700 °C, 720 °C, 750 °C, 780 °C or 800 °C, etc.

[0034] Preferably, the time of the one-step sintering is 8-16 h, for example: 8 h, 10 h, 12 h, 15 h or 16 h, etc.

[0035] Preferably, the detergent for pickling and flushing includes any one or a combination of at least two of carbonic acid, acetic acid, silicic acid, hypochlorous acid, hydrocyanic acid, sulfurous acid, phosphoric acid or nitrous acid.

[0036] Preferably, the concentration of the detergent is 0.2-0.5 mol / L, for example: 0.2 mol / L, 0.3 mol / L, 0.4 mol / L or 0.5 mol / L, etc.

[0037] Preferably, the number of times of pickling and flushing is 2-4 times.

[0038] Preferably, the mass ratio of the detergent to the material for each pickling and flushing is 0.5-0.8:1, for example: 0.5:1, 0.6:1, 0.7:1 or 0.8:1, etc.

[0039] Compared with the traditional stirring water washing process, the present invention greatly reduces the surface residual alkali and improves the cycle stability of the cathode material by designing the flushing pickling process. On the other hand, a certain number of cavities will be generated in the cathode material during the flushing pickling process, and these cavities contribute to improving the lithium ion deintercalation rate and deintercalation amount, thereby improving the cycle performance.

[0040] Preferably, the solute of the lithium salt solution includes any one or a combination of at least two of lithium acetate, lithium carbonate, lithium nitrate, lithium hydroxide, lithium oxalate or lithium sulfate.

[0041] Preferably, the concentration of the lithium salt solution is 1 to 2 mol / L, such as: 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, or 2 mol / L, etc.

[0042] Preferably, the current density of the energization is 3 to 6 A / cm 2 , such as: 3 A / cm 2 , 3.5 A / cm 2 , 4 A / cm 2 , 5 A / cm 2 or 6 A / cm 2 etc.

[0043] Preferably, the energization time is 3 to 6 h, such as: 3 h, 4 h, 5 h, or 6 h, etc.

[0044] Preferably, during the regeneration and repair process, the mass of the repair material is 20 to 60% of the mass of the repair solution, such as: 20%, 30%, 40%, 50%, or 60%, etc.

[0045] The process of self-repairing lithium in the present invention effectively compensates for the lithium-deficient "dead zones" where insertion and extraction fail to occur, greatly reducing the loss of lithium during the insertion and extraction processes, thereby improving the cycle stability.

[0046] Preferably, the addition amount of boric acid in step (3) is 500 to 3000 ppm, such as: 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, or 3000 ppm, etc.

[0047] The internal doping and surface B process of the present invention effectively improve the structural stability and surface stability of the cobalt-free high-nickel cathode material, and improve the cycle stability of the cobalt-free high-nickel cathode material.

[0048] Preferably, the temperature of the two-step sintering is 200 to 300 °C, such as: 200 °C, 220 °C, 250 °C, 280 °C, or 300 °C, etc.

[0049] Preferably, the time of the two-step sintering is 5 to 8 h, such as: 5 h, 6 h, 7 h, or 8 h, etc.

[0050] In the second aspect, the present invention provides a cobalt-free high-nickel cathode material, which is prepared by the method as described in the first aspect.

[0051] In the third aspect, the present invention provides a positive electrode plate, which comprises the cobalt-free high-nickel cathode material as described in the second aspect.

[0052] In the fourth aspect, the present invention provides a lithium-ion battery, which comprises the positive electrode plate as described in the third aspect.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] (1) By synthesizing a cathode material with a manganese-rich surface and a nickel-rich interior, the present invention effectively improves the mechanical strength of the cobalt-free polycrystalline primary particles, and enables a better mirror arrangement of the primary particles, thereby enhancing the fracture strength of the secondary particle spheres, reducing structural damage during battery charge and discharge, and improving cycle stability.

[0055] (2) By designing a flushing pickling process compared to the traditional stirring-based water washing process, the present invention significantly reduces the surface residual alkali, improves the cycle stability of the cathode material. On the other hand, the flushing pickling process generates certain cavities in the cathode material, which helps to increase the lithium ion deintercalation rate and the amount of deintercalated lithium, thus improving the cycle performance.

[0056] (3) The internal doping and surface B process of the cobalt-free high-nickel cathode material of the present invention effectively improve the structural stability and surface stability of the cobalt-free high-nickel cathode material, and enhance the cycle stability of the cobalt-free high-nickel cathode material.

[0057] (4) The cobalt-free high-nickel cathode material of the present invention can achieve a capacity retention rate of over 97.1% after 50 cycles at 1C, the total residual alkali amount of the material can reach below 2300 ppm, and the diffusion coefficient during the deintercalation process at a charging voltage of 3.8V can reach 2.12*10 - 12 cm 2 / s or less. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 is a schematic diagram of the device for flushing washing and self-repairing used in Example 1 of the present invention, 1 - vacuum pump, 2 - water bucket, 3 - drainage area, 4 - filter membrane, 5 - base, 6 - electrode rod, 7 - electrode rod, 8 - feeding area, 9 - base, 10 - detergent or repair liquid.

[0059] Figure 2 is a schematic diagram of the Mn distribution of the cobalt-free high-nickel cathode material prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0060] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0061] Example 1

[0062] This example provides a cobalt-free high-nickel cathode material, and the preparation method of the cobalt-free high-nickel cathode material is as follows:

[0063] (1) Prepare 2M (i.e., 2 mol / L) salt solution A by mixing nickel sulfate hexahydrate (NiSO4·6H2O) and manganese sulfate monohydrate (MnSO4·H2O) in a ratio of 9:1, and prepare 2M salt solution B by mixing them in a ratio of 3:1. In addition, prepare 10.25M ammonia water as a complexing agent and 4M sodium hydroxide solution;

[0064] (2) Add 2000 mL of salt solution A, 120 mL of ammonia water, and 1000 mL of sodium hydroxide to a nitrogen-filled reaction kettle at a flow rate of 200 mL / min and stir and react at a certain temperature for 12 h. Then add 1000 mL of salt solution B, 60 mL of ammonia water, and 500 mL of sodium hydroxide to the nitrogen-filled reaction kettle at a flow rate of 200 mL / min and continue to stir for 2 h at a certain temperature. After aging and standing for 10 h, take the precipitate, wash it with pure water, filter it, and dry it at 110 °C to obtain the prepared cobalt-free high-nickel precursor;

[0065] (3) Mix 120 g of the cobalt-free high-nickel precursor, 54.28 of lithium hydroxide, and 0.2365 g of Y2O3 agent evenly, put them into an oxygen-filled atmosphere furnace and sinter at 730 °C for 12 h. After the temperature drops to room temperature, sieve it. Put 100 g of the prepared material into a flushing washer and flush it three times, with 50 g of 0.2M oxalic acid solution used each time. After washing, pour 200 g of 1M lithium oxalate solution, and apply 3A / cm 2 Electrify for 6 h. After the electrification is completed, filter the material and put it into a vacuum drying oven at 150 °C to dry for more than 12 h. Take 100 g of the dried material and mix it evenly with 0.4575 g of boric acid, put it into an oxygen-filled atmosphere furnace and sinter at 300 °C for 5 h. After the temperature drops to room temperature, sieve it to obtain the cobalt-free high-nickel cathode material. The schematic diagram of the device used for flushing and self-repair is as Figure 1 shown. The schematic diagram of the Mn distribution of the cobalt-free high-nickel cathode material is as Figure 2 shown. It can be seen from Figure 2 that the present invention successfully synthesizes a high-nickel cathode material with a manganese-rich surface, making the synthesized cobalt-free high-nickel cathode material have a 3.5% improvement in cycle compared with the commercially available high-nickel cobalt-free cathode, and the particle strength is significantly increased.

[0066] Example 2

[0067] This example provides a cobalt-free high-nickel cathode material, and the preparation method of the cobalt-free high-nickel cathode material is as follows:

[0068] (1) Prepare 2M salt solution A by mixing nickel sulfate hexahydrate (NiSO4·6H2O) and manganese sulfate monohydrate (MnSO4·H2O) in a ratio of 20:1, and prepare 2M salt solution B by mixing them in a ratio of 3.5:1. In addition, prepare 11M ammonia water as a complexing agent and 3.8M sodium hydroxide solution;

[0069] (2) Add 2000 mL of salt solution A, 120 mL of ammonia water, and 1000 mL of sodium hydroxide to a nitrogen-filled reaction kettle at a flow rate of 300 mL / min, stir and react at a certain temperature for 12 h. Then, add 1000 mL of salt solution B, 60 mL of ammonia water, and 500 mL of sodium hydroxide to the nitrogen-filled reaction kettle at a flow rate of 300 mL / min, continue to stir for 2 h at a certain temperature, age and stand for 10 h. Take the precipitate, wash it with pure water, filter it, and dry it at 110 °C to obtain the prepared cobalt-free high-nickel precursor;

[0070] (3) Take 120 g of the cobalt-free high-nickel precursor, 54.28 of lithium hydroxide, and 0.3267 g of Nb2O5 agent, mix them evenly, put them into an oxygen-filled atmosphere furnace, sinter at 730 °C for 12 h. After the temperature drops to room temperature, sieve. Put 100 g of the prepared material into a flushing washer, flush it three times, and use 50 g of 0.3 M acetic acid solution for each flushing. After washing, pour 200 g of 1 M lithium oxalate solution, and apply 4 A / cm 2 Electrify for 5 h. After the electrification is completed, filter the material and put it into a vacuum drying oven at 150 °C to dry for more than 12 h. Take 100 g of the dried material, mix it evenly with 0.4575 g of boric acid, put it into an oxygen-filled atmosphere furnace, sinter at 280 °C for 6 h. After the temperature drops to room temperature, sieve to obtain the cobalt-free high-nickel cathode material.

[0071] Example 3

[0072] The difference between this example and Example 1 is only that the molar concentration of ammonia water is 8 M, and other conditions and parameters are exactly the same as those in Example 1.

[0073] Example 4

[0074] The difference between this example and Example 1 is only that the molar concentration of ammonia water is 14 M, and other conditions and parameters are exactly the same as those in Example 1.

[0075] Example 5

[0076] The difference between this example and Example 1 is only that the time of the second-step reaction is 1 h, and other conditions and parameters are exactly the same as those in Example 1.

[0077] Example 6

[0078] The difference between this example and Example 1 is only that the time of the second-step reaction is 10 h, and other conditions and parameters are exactly the same as those in Example 1.

[0079] Example 7

[0080] This embodiment is only different from Embodiment 1 in that the detergent used for pickling and flushing is 20 g, and other conditions and parameters are exactly the same as those in Embodiment 1.

[0081] Example 8

[0082] This embodiment is only different from Embodiment 1 in that the detergent used for pickling and flushing is 100 g, and other conditions and parameters are exactly the same as those in Embodiment 1.

[0083] Example 9

[0084] This embodiment is only different from Embodiment 1 in that the current density is 10 A / cm 3 , and other conditions and parameters are exactly the same as those in Embodiment 1.

[0085] Example 10

[0086] This embodiment is only different from Embodiment 1 in that the current density is 0.5 A / cm 3 , and other conditions and parameters are exactly the same as those in Embodiment 1.

[0087] Comparative Example 1

[0088] This comparative example provides a cobalt-free high-nickel cathode material, and the preparation method of the cobalt-free high-nickel cathode material is as follows:

[0089] (1) Take 120 g of commercially available cobalt-free high-nickel precursor (Ni 0.95 Mn 0.05 (OH)2), 54.28 of lithium hydroxide and 0.2365 g of Y2O3, mix them evenly, and then put them into an oxygen-filled atmosphere furnace and sinter at 730 °C for 12 h. After the temperature drops to room temperature, sieve them;

[0090] (2) Put 100 g of the prepared material into a flushing and washing device, flush it three times, and the water consumption for each flushing is 50 g. After washing, put the material into a vacuum drying oven at 150 °C and dry it for more than 12 h. Take 100 g of the dried material and mix it evenly with 04575 g of boric acid, and then put it into an oxygen-filled atmosphere furnace and sinter at 300 °C for 5 h. After the temperature drops to room temperature, sieve to obtain the cobalt-free high-nickel cathode material.

[0091] Comparative Example 2

[0092] This comparative example provides a cobalt-free high-nickel cathode material, and the preparation method of the cobalt-free high-nickel cathode material is as follows:

[0093] (1) Prepare 2M salt solution A by mixing nickel sulfate hexahydrate (NiSO4·6H2O) and manganese sulfate monohydrate (MnSO4·H2O) in a ratio of 9:1, and prepare 2M salt solution B by mixing them in a ratio of 3:1. In addition, prepare 10.25M ammonia water as a complexing agent and 4M sodium hydroxide solution;

[0094] (2) Add 2000 mL of salt solution A, 120 mL of ammonia water, and 1000 mL of sodium hydroxide to a nitrogen-filled reactor at a flow rate of 200 mL / min, stir and react at a certain temperature for 12 h. Then add 1000 mL of salt solution B, 60 mL of ammonia water, and 500 mL of sodium hydroxide to the nitrogen-filled reactor at a flow rate of 200 mL / min, continue to stir for 2 h at a certain temperature, age and stand for 10 h. Take the precipitate, wash it with pure water, filter and dry it at 110 °C for a certain period of time to obtain the prepared cobalt-free high-nickel precursor;

[0095] (3) Take 120 g of the cobalt-free high-nickel precursor, 54.28 of lithium hydroxide, and 0.2365 g of Y2O3 agent, mix them evenly, put them into an oxygen-filled atmosphere furnace, sinter at 730 °C for 12 h. After the temperature drops to room temperature, sieve and take 100 g of the material and put it into a magnetic stirrer, add 50 g of water, wash for 15 min. After washing, put the material into a vacuum drying oven at 150 °C and dry for more than 12 h. Take 100 g of the dried material and mix it evenly with 0.4575 g of boric acid, put it into an oxygen-filled atmosphere furnace, sinter at 300 °C for 5 h. After the temperature drops to room temperature, sieve to obtain the cobalt-free high-nickel cathode material.

[0096] Performance test:

[0097] Using a lithium metal sheet as the negative electrode, take the cobalt-free high-nickel cathode materials prepared in the examples and comparative examples, prepare the positive electrode plates. The prepared positive electrode plates use NMP as the solvent, and the positive electrode, binder (PVDF), and conductive agent (SP) are mixed evenly in a ratio of 92:4:4 and then coated on the aluminum foil. The solid content of the PVDF glue solution is 6.05%, the thickness of the aluminum foil is 12 μm, the purity is above 99%, and the electrode plate is compacted to 3.3 g / cm 3 , assemble a coin-type half-cell in a vacuum glove box with a Celgand2325 separator, calculate the de-lithium diffusion coefficient, and perform a potentiostatic intermittent titration through an electrochemical workstation. The specific calculation formula is as follows:

[0098]

[0099] The charging cut-off voltage is 4.3 V, the discharging cut-off voltage is 3.0 V, and the nominal specific capacity is 200 mAh / g. The electrochemical performance test results are shown in Table 1:

[0100] Table 1

[0101]

[0102]

[0103] As can be seen from Table 1, it can be obtained from Examples 1-2 that the capacity retention rate of the battery made of the cobalt-free high-nickel cathode material of the present invention can reach more than 97.1% at 1C for 50 weeks, the total residual alkali amount of the material can reach below 2300 ppm, and the diffusion coefficient during the delithiation process at 3.8V charging can reach 2.12*10 -12 cm 2 / s or less.

[0104] It can be obtained by comparing Example 1 with Examples 3-4 that during the coprecipitation reaction (i.e., the one-step reaction and the two-step reaction), the concentration of ammonia water will affect the performance of the high-nickel cobalt-free cathode material. Controlling the concentration of ammonia water at 10-12 mol / L results in better performance of the cobalt-free high-nickel cathode material. When the concentration of ammonia water used is too low, the specific surface area of the underlying core precursor during the synthesis process is too large, which is not conducive to the formation of the manganese-rich shell in the later stage, resulting in poor structural stability of the synthesized cathode material. When the concentration of ammonia water is too high, the reaction is incomplete, and too many metal ions are complexed, so that a precursor with a manganese-rich surface structure cannot be formed, resulting in metal segregation in the synthesized cathode and poor structural stability.

[0105] It can be obtained by comparing Example 1 with Examples 5-6 that the time of the two-step reaction will affect the performance of the cobalt-free cathode material. If the time of the two-step reaction is too short, the surface core-shell layer is not completely formed, resulting in the relatively nickel-rich cathode inside being exposed on the outer surface, resulting in poor cycle stability. If the time of the two-step reaction is too long, the manganese-rich surface layer increases, resulting in a decrease in capacity, and the manganese-rich surface layer cathode on the outer surface falls off in the later stage, and the cycle becomes poor.

[0106] It can be obtained by comparing Example 1 with Examples 7-8 that when the amount of washing agent used is too low, the residual lithium on the surface after the first calcination cannot be completely washed away, resulting in a high content of residual alkali on the surface of the synthesized cobalt-free high-nickel polycrystalline cathode, resulting in poor cycle stability. When the amount of washing agent used is too high, too much acid seriously damages the surface of the cobalt-free high-nickel cathode material, resulting in poor cycle stability.

[0107] It can be obtained by comparing Example 1 with Examples 9-10 that when a relatively large current density is used for the self-repair process, it will cause the collapse of the layered structure of part of the cathode material, and the diffusion of Li + ions is hindered, and the cycle becomes poor. When the applied current density is too low, the driving force for the self-repair Li + repair process is low, resulting in a large number of defects on the surface of the cathode material, resulting in poor cycle performance.

[0108] The schematic diagram of the Mn distribution of the cobalt-free high-nickel cathode material described in Example 1 of the present invention is asFigure 2 As shown in Figure 2 Combining the comparison between Example 1 and Comparative Example 1 in Table 1, it can be seen that the high-nickel cathode material with a manganese-rich surface is successfully synthesized in the present invention, so that the cobalt-free high-nickel cathode material synthesized has a 3.5% increase in cycle performance compared with the commercially available high-nickel cobalt-free cathode, and the particle strength is significantly increased.

[0109] From the comparison between Example 1 and Comparative Example 2, it can be obtained that, compared with the traditional stirring water washing process, the present invention designs a flushing pickling process, which greatly reduces the surface residual alkali and improves the cycle stability of the cathode material. On the other hand, certain cavities will be generated in the cathode material during the flushing pickling process, and these cavities contribute to improving the lithium ion deintercalation rate and the amount of deintercalated lithium, thus making the cycle performance better. The process of self-healing lithium effectively replenishes the lithium-deficient "dead zone" where lithium insertion and extraction fail to occur, greatly reducing the loss of lithium during the insertion and extraction processes, thereby improving the cycle stability.

[0110] The applicant declares that the above description is only the specific implementation manner 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 thought of by any person skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A preparation method of a cobalt-free high-nickel cathode material, characterized in that, The preparation method includes the following steps: (1) Mix a nickel source and a manganese source with a solvent according to Ni:Mn = 9 - 99:1 to obtain salt solution A, and mix a nickel source and a manganese source with a solvent according to Ni:Mn = 2 - 4:1 to obtain salt solution B; (2) Add salt solution A, ammonia water, and an alkali solution into a reaction vessel in a parallel flow for a one-step reaction, and then add salt solution B, ammonia water, and an alkali solution into the reaction vessel in a parallel flow for a two-step reaction. The reaction time of the one-step reaction is 12 - 20 h, and the reaction time of the two-step reaction is 2 - 4 h. After aging, a cobalt-free high-nickel precursor is obtained; (3) Mix the cobalt-free high-nickel precursor with a lithium source and a dopant, perform one-step sintering, then perform pickling and flushing, and then add it to a lithium salt solution and apply electricity for regeneration and repair. The current density of the applied electricity is 3-6 A / cm 2 ; Mix the obtained material with boric acid and perform two-step sintering to obtain the cobalt-free high-nickel cathode material.

2. The preparation method according to claim 1, characterized in that, The nickel source described in step (1) includes nickel sulfate.

3. The preparation method according to claim 1, characterized in that, The manganese source includes manganese sulfate.

4. The preparation method according to claim 1, characterized in that, The total molar concentration of metal ions in the salt solution A is 2 - 4 mol / L.

5. The preparation method according to claim 1, characterized in that, The total molar concentration of metal ions in the salt solution B is 2 - 4 mol / L.

6. The preparation method according to claim 1, characterized in that, The molar concentration of ammonia water in step (2) is 10 - 12 mol / L.

7. The preparation method according to claim 1, characterized in that, The molar concentration of sodium hydroxide in the alkali solution is 3 - 4 mol / L.

8. The preparation method according to claim 1, characterized in that, The flow rates of the salt solution A and the salt solution B are independently 0.2 - 0.4 L / min.

9. The preparation method according to claim 1, wherein, In the reaction systems of the one-step reaction and the two-step reaction, the molar ratio of sodium hydroxide to metal ions is 2 - 4:

1.

10. The preparation method according to claim 1, wherein In the reaction systems of the one-step reaction and the two-step reaction, the molar ratio of ammonium ions in ammonia water to metal ions is 1.2 - 1.5:

1.

11. The preparation method according to claim 1, characterized in that, The temperatures of the one-step reaction and the two-step reaction in step (2) are independently 40 - 60 °C.

12. The preparation method according to claim 1, characterized in that, The stirring speeds of the one-step reaction and the two-step reaction are independently 50 - 200 rpm.

13. The preparation method according to claim 1, characterized in that, The aging time is 8 - 12 h.

14. The preparation method according to claim 1, wherein, After aging, washing and drying treatments are carried out.

15. The preparation method according to claim 1, characterized in that, In step (3), the Li / M ratio of the lithium source and the cobalt-free high-nickel precursor is 1.01 - 1.06:

1.

16. The preparation method according to claim 1, characterized in that, The dopant includes any one or a combination of at least two of ZrO2, Al2O3, MgO, Y2O3, TiO2, ZnO, Nb2O5, MoO3, SrCO3, WO3, or Ta2O5.

17. The preparation method according to claim 1, characterized in that, The doping amount of the dopant is 500 - 5000 ppm.

18. The preparation method according to claim 1, characterized in that, The temperature of the one-step sintering in step (3) is 700 - 800 °C.

19. The preparation method according to claim 1, characterized in that, The time of the one-step sintering is 8 - 16 h.

20. The preparation method according to claim 1, characterized in that, The detergent for pickling and flushing includes any one or a combination of at least two of carbonic acid, acetic acid, silicic acid, hypochlorous acid, hydrocyanic acid, sulfurous acid, phosphoric acid, or nitrous acid.

21. The preparation method according to claim 20, characterized in that, The concentration of the detergent is 0.2 - 0.5 mol / L.

22. The preparation method according to claim 1, characterized in that, The number of pickling and flushing times is 2 - 4 times.

23. The preparation method according to claim 1, characterized in that, The mass ratio of the detergent to the material for each pickling and flushing is 0.5 - 0.8:

1.

24. The preparation method according to claim 1, characterized in that, The solute of the lithium salt solution includes any one or a combination of at least two of lithium acetate, lithium carbonate, lithium nitrate, lithium hydroxide, lithium oxalate, or lithium sulfate.

25. The preparation method according to claim 1, characterized in that The concentration of the lithium salt solution is 1 - 2 mol / L.

26. The preparation method according to claim 1, characterized in that, The energization time is 3 - 6 h.

27. The preparation method according to claim 1, characterized in that, During the regeneration and repair process, the mass of the repair material is 20 - 60% of the mass of the repair solution.

28. The preparation method according to any one of claims 1-27, characterized in that, The addition amount of boric acid in step (3) is 500 - 3000 ppm.

29. The preparation method according to any one of claims 1-27, characterized in that, The temperature of the two-step sintering is 200 - 300 °C.

30. The preparation method according to any one of claims 1 to 27, characterized in that, The time of the two-step sintering is 5 - 8 h.

31. A cobalt-free high-nickel cathode material, characterized in that, The cobalt-free high-nickel cathode material is prepared by the method described in any one of claims 1-30.

32. A positive electrode sheet, characterized in that, The cathode electrode sheet contains the cobalt-free high-nickel cathode material described in claim 31.

33. A lithium-ion battery, characterized in that, The lithium-ion battery contains the cathode electrode sheet described in claim 32.

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