Method for surface modification of lithium transition metal oxide positive electrode material

Abstract

The invention relates to a method for surface modification of a lithium transition metal oxide cathode material, comprising the following steps: adding a first additive, a second additive, and a lithium transition metal oxide to water to obtain a first slurry, the first additive being a lithium-containing phosphate, and the second additive being an acidic solution of a Y3+ or Al3+ salt; dropwise adding a third additive to the firs slurry to obtain a second slurry, the third additive being an acidic solution of a TiO2+ or ZrO2+ salt; dropwise adding a fourth additive to the second slurry to obtain a third slurry, the fourth additive being an acidic solution of a AlO2- salt; and performing centrifugation and drying on the third slurry to obtain an intermediate product, mixing the intermediate product with a large-particle positive electrode material, and performing sintering to obtain a surface-modified lithium transition metal oxide material. The coating layer according to the present invention is uniform in composition and controllable in thickness, the phenomenon of an uneven surface of a solid phase structure can be improved, a spinel structure substance is generated on the surface of the material during a cycle process, the high-pressure resistance performance of the material is improved, and the cycle performance of the lithium transition metal oxide positive electrode material is improved.

Description

Method for surface modification of lithium transition metal oxide positive electrode material Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a method for surface modification of a lithium transition metal oxide positive electrode material. Background Art

[0002] Lithium-ion batteries, with their high capacity, discharge platform, and compaction density, are one of the most thoroughly researched and widely used commercial lithium-ion battery cathode materials. Commonly used layered lithium-ion batteries include lithium cobalt oxide, low-nickel lithium nickel cobalt manganese oxide, and high-nickel lithium nickel cobalt manganese oxide. Lithium cobalt oxide is widely used in 3C applications such as mobile phones, drones, and laptops, while lithium nickel cobalt manganese oxide is widely used in new energy vehicles.

[0003] Residual alkali usually refers to the residual soluble Li2CO3 and LiOH on the surface of lithium transition metal oxide powder materials. The residual alkali problem has a great impact on batteries. In the process of making and coating rechargeable batteries, high residual alkali will make the slurry unstable, accelerate the gelation of the slurry, and reduce the uniformity of the battery. In addition, the residual alkali on the surface of the positive electrode material is easy to react with the electrolyte to cause gas production, which reduces the safety and cycle performance of the battery. There are two main sources of residual alkali on the surface of lithium transition metal oxide powder: First, during the production process, lithium salts will volatilize to a certain extent during high-temperature calcination. In order to compensate for the loss of Li during the calcination process, the ingredient ratio Li / M>1 (M refers to transition metal) is usually used. In this way, the high temperature conditions of calcination make the remaining small amount of Li exist in the form of Li2O. In the subsequent cooling process, Li2O will react with CO2 and H2O in the air to produce Li2CO3 and LiOH. Second, the active oxygen anions on the surface of the lithium transition metal oxide positive electrode material will react with CO2 and H2O in the air to produce CO3 2- and OH - , a small amount of Li + Migrate from the bulk to the surface and react with CO3 on the surface of the material 2- and OH - Li2CO3 and LiOH are formed. This process is accompanied by deoxidation of the material surface to form a surface oxide layer with a distorted structure. During the cycle of the battery, the residual alkali on the surface of the particles easily reacts with the electrolyte to produce gas. The more residual alkali on the surface of the material, the higher the cycle environment temperature or the higher the voltage, the more obvious the gas production phenomenon.

[0004] Currently, the main method for removing residual lithium from the surface of high-nickel lithium cobalt manganese oxide materials is through water washing and then drying. Taking advantage of the solubility of Li2CO3 and LiOH, they are washed with water to remove residual lithium on the surface, and then heated and dried to remove residual moisture. However, the water washing process increases the cost of use. More importantly, lithium transition metal oxide materials are sensitive to moisture. If the drying time is too long and the material is in contact with moisture for too long, the lattice lithium on its surface will be lost, resulting in deterioration of the material structure and severe performance degradation. High-voltage lithium cobalt oxide itself has a low residual alkali content, but under high temperature and high voltage, the surface activity is enhanced. The large amount of residual lithium on the surface of the material will also aggravate side reactions, resulting in cobalt dissolution, oxygen precipitation, etc., which will cause irreversible capacity loss in the battery, accelerated cycle decay and accompanied by battery bloating, and there are also a series of safety hazards.

[0005] Coating other materials on the surface of lithium transition metal oxide materials can effectively reduce the amount of residual alkali on the surface of the positive electrode material, reduce gas production, and improve structural stability and cycle performance. Common coating materials are metal oxides, such as A12O3, La2O3, TiO2, ZrO2, etc. The commonly used coating method is solid-phase coating. This type of coating method can stabilize the structure, reduce residual lithium, and play a role in protecting the positive electrode material. However, most pure oxides are electronically insulating, and coating will increase the electronic conductivity impedance of the positive electrode material and reduce the capacity. At the same time, solid-state coating has the problem of uneven coating, increased surface BET, increased battery impedance, and reduced capacity. Although the surface residual alkali is reduced, the capacity is affected.

[0006] Summary of the Invention

[0007] The present invention aims to address at least one of the technical problems existing in the aforementioned prior art. To this end, the present invention provides a method for surface modification of lithium transition metal oxide cathode materials, which can effectively reduce the surface base of the lithium transition metal oxide, improve interfacial stability, enhance voltage cycling capability, increase compaction density, and increase energy density.

[0008] According to one aspect of the present invention, a method for surface modification of a lithium transition metal oxide positive electrode material is provided, comprising the following steps:

[0009] S1: Add the first additive, the second additive and the lithium transition metal oxide into water and stir to obtain a first slurry; the first additive is lithium phosphate, the second additive is Y 3+ or Al 3+ Acidic solutions of salts;

[0010] S2: Add a third additive dropwise to the first slurry and stir to obtain a second slurry. The third additive is TiO 2+ or ZrO 2+ Acidic solutions of salts;

[0011] S3: Add the fourth additive dropwise to the second slurry and stir to obtain a third slurry. The fourth additive is AlO2 - alkaline solutions of salt;

[0012] S4: centrifuging the third slurry and drying it to obtain an intermediate product, mixing the intermediate product with a large-particle positive electrode material, and sintering them to obtain a surface-modified lithium transition metal oxide material.

[0013] In some embodiments of the present invention, the amount of the first additive added is 0.1-5% of the mass of the lithium transition metal oxide, and the Li + , Y in the second additive 3+ or Al 3+ , TiO in the third additive 2+ or ZrO 2+ , AlO2 in the fourth additive - The molar ratio is (0.1-0.5):(0.5-1.5):(0.5-1.5):(2.5-7.5).

[0014] In some embodiments of the present invention, the chemical formula of the lithium transition metal oxide is LiCo x M 1-x O2, wherein M is at least one of Mn, Al, Zr, Ti, Mg, La, Ni, or Mg, and 1 ≥ x ≥ 0.10. The lithium transition metal oxide refers to a powder obtained by pulverizing a precursor and a lithium source in a conventional process to obtain a bulk material, having a particle size Dv50 of 3-22 μm.

[0015] In some embodiments of the present invention, in step S1, the solid-liquid mass ratio of the lithium transition metal oxide to water is 1:(0.2-4), more preferably 1:1.2.

[0016] In some embodiments of the present invention, in step S1, the lithium-containing phosphate is at least one of lithium-containing orthophosphate, lithium-containing hydrogenphosphate, or lithium-containing metaphosphate, and is more preferably at least one of lithium-containing orthophosphate or lithium-containing metaphosphate.

[0017] In some embodiments of the present invention, the acidic solution in the second additive and / or the third additive is selected from at least one of a sulfuric acid solution, a hydrochloric acid solution, an acetic acid solution, a nitric acid solution, a citric acid solution or an oxalic acid solution.

[0018] In some embodiments of the present invention, in step S1, the stirring speed is 100-300 r / min, and the stirring time is 5-30 min.

[0019] In some embodiments of the present invention, in step S2, the stirring speed is 100-1000 r / min, and the stirring time is 5-30 min.

[0020] In some embodiments of the present invention, the alkaline solution in the fourth additive is selected from at least one of sodium hydroxide solution, potassium hydroxide solution, lithium hydroxide solution or ammonia solution.

[0021] In some embodiments of the present invention, the second additive Y 3+ or Al 3+ The concentration of TiO in the third additive is 0.001-0.3 mol / L; 2+ or ZrO 2+ The concentration of AlO2 in the fourth additive is 0.002-0.4 mol / L; - The concentration is 0.001-0.3mol / L.

[0022] In some embodiments of the present invention, the large-particle positive electrode material is at least one of lithium cobalt oxide, high-nickel nickel cobalt manganese oxide, and low-nickel nickel cobalt manganese oxide; the particle size Dv50 of the large-particle positive electrode material is 10-22 μm; the mass ratio of the intermediate product to the large-particle positive electrode material is (2-10):1, and further preferably (3-9):1.

[0023] In some embodiments of the present invention, in step S4, the sintering temperature is 600-950° C., and preferably, the sintering time is 5-10 hours.

[0024] In some embodiments of the present invention, in step S4, the centrifugal speed is 1000-3000 r / min.

[0025] In some embodiments of the present invention, the third additive and the fourth additive are added dropwise for 3-10 minutes.

[0026] In some embodiments of the present invention, in step S4, the drying is performed by vacuum drying, the drying temperature is 100-110° C., the drying time is 3-10 h, and the vacuum degree is maintained at -0.02 to -0.4 MPa.

[0027] In some embodiments of the present invention, in step S4, the mixing rate is 300-1000 r / min and the mixing time is 5-30 min.

[0028] According to a preferred embodiment of the present invention, there are at least the following beneficial effects:

[0029] 1. The present invention adopts liquid phase surface modification and introduces lithium ions, phosphate ions or metaphosphate ions during the liquid phase coating process of lithium transition metal oxide, which inhibits the precipitation of lithium ions in the lithium transition metal oxide structure to a certain extent, effectively reduces the source of residual alkali, and stabilizes the surface matrix structure.

[0030] 2. Add additives step by step and hydrolyze them simultaneously to form Al(OH)3, Zr(OH)4 or Ti(OH)4 and Al(OH)2PO3 complexes and other substances on the surface of the material and distribute them evenly, so as to avoid prolonged contact time between the material and water and improve the lattice lithium deficiency phenomenon on the surface.

[0031] 3. The method of extreme matching of large and small particles is adopted to match the intermediate product with the large particles and then sinter them at high temperature. The hydroxide and the complexing substance lose water to obtain a coating layer of Al2O3, TiO2 or ZrO2 and Al(PO3)3 with uniform composition and controllable thickness. The coating layer is dense and smooth, which can effectively reduce the residual alkali content on the surface. The presence of amphoteric substances on the surface improves the gas production phenomenon and increases the compaction density and energy density.

[0032] 4. The coating layer of the present invention has uniform composition and controllable thickness, which can improve the surface unevenness of the solid phase structure, reduce the interface BET, reduce the contact area between the interface and the electrolyte, reduce the occurrence of side reactions, and generate spinel structure substances on the surface of the material during the cycle, thereby improving the material's high-voltage resistance and thus improving the cycle performance of the lithium transition metal oxide positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0034] FIG1 is a SEM image of the material after drying of the third slurry in Example 1 of the present invention;

[0035] FIG2 is a SEM image of the sintered material of Example 1 of the present invention;

[0036] FIG3 is a SEM image of comparative example 1 of the present invention after dry mixing;

[0037] FIG4 is a SEM image of the dry-mixed sintered comparative example 1 of the present invention;

[0038] FIG5 shows the cycle performance of Example 1, Example 2, Comparative Example 1 and Comparative Example 2. DETAILED DESCRIPTION

[0039] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0040] Example 1

[0041] This example prepares a surface-modified lithium transition metal oxide positive electrode material, and the specific process is as follows:

[0042] (1) Pour 50kg of deionized water into the water washing kettle, then add the first additive LiPO3 and the second additive Al2(SO4)3 sulfuric acid solution into the deionized water. 3+ The concentration of the first additive is 0.2 mol / L, and the mixture is stirred evenly. Then, the first additive is added according to the solid-liquid mass ratio of LiCoO2-calcined powder (particle size Dv50 is 8 μm) and deionized water of 1:0.8, and the amount of the first additive is 0.02 wt% of the mass of the added LiCoO2-calcined powder. The mixture is stirred at a high speed of 200 r / min to form a uniform first slurry.

[0043] (2) Add TiO2 dropwise to the first slurry. 2+ A 0.2 mol / L TiOSO4 sulfuric acid solution was added, and the addition time was controlled to 5 min. After the addition was completed, high-speed stirring was continued at 500 r / min for 10 min to obtain a second slurry;

[0044] (3) Add AlO2 dropwise to the second slurry - A NaAlO2 sodium hydroxide solution with a concentration of 0.3 mol / L was added, and the addition time was controlled to 10 min. After the addition was completed, high-speed stirring was continued at 500 r / min for 10 min to obtain a third slurry;

[0045] Based on the addition amount of the first additive, the second additive, the third additive and the fourth additive are added according to Li + :Al 3+ :TiO 2+ :AlO2 - =0.5:1:1:2.5 added;

[0046] (4) The third slurry was centrifuged and placed in a high-mix drying equipment for vacuum drying, wherein the high-mix speed was 10 r / min, the drying temperature was 105°C, the drying time was 8 h, and the vacuum degree was set to -0.05 MPa; the dried material was mixed with LiCoO2 with a particle size Dv50 of 18 μm at a high speed of 500 r / min, for 15 min, in a ratio of 8:1, and placed in a box furnace with compressed air and a ventilation volume of 5 m 3 / h, heated to 850℃ and kept warm for 8h, and naturally cooled to room temperature to obtain LiCoO2 material coated with TiO2, Al2O3, and Al(PO3)3.

[0047] Figure 1 shows the SEM image of the material after centrifugation and drying of the third slurry. It can be seen from the SEM that there are obvious traces of uniform coating on the surface of the material; Figure 2 is the SEM image of the material after sintering. It can be seen from Figure 2 that the surface becomes smooth and dense after sintering is completed.

[0048] Example 2

[0049] This example prepares a surface-modified lithium transition metal oxide positive electrode material, and the specific process is as follows:

[0050] (1) Pour 50kg of deionized water into the water washing kettle, then add the first additive Li3PO4 and the second additive Al2Cl3 sulfuric acid solution into the deionized water. 3+ The concentration of the first additive is 0.1 mol / L, and the mixture is stirred evenly. Then, the first additive is added according to a solid-liquid mass ratio of 1:3 between LiCoO2 calcined powder (particle size Dv50 is 10 μm) and deionized water. The amount of the first additive is 0.01 wt% of the mass of the added LiCoO2 calcined powder. The mixture is stirred at a high speed of 300 r / min to form a uniform first slurry.

[0051] (2) Add TiO2 dropwise to the first slurry. 2+ A 0.1 mol / L TiOSO4 sulfuric acid solution was added, and the addition time was controlled to 7 min. After the addition was completed, high-speed stirring was continued at 500 r / min for 10 min to obtain a second slurry;

[0052] (3) Add AlO2 dropwise to the second slurry - A NaAlO2 sodium hydroxide solution with a concentration of 0.3 mol / L was added, and the addition time was controlled to 8 min. After the addition was completed, high-speed stirring was continued at 500 r / min for 10 min to obtain a third slurry;

[0053] Based on the addition amount of the first additive, the second additive, the third additive and the fourth additive are added according to Li + :Al 3+ :TiO 2+ :AlO2- =0.3:1:1:3 added;

[0054] (4) The third slurry was centrifuged and placed in a high-mix drying equipment for vacuum drying, wherein the high-mix speed was 10 r / min, the drying temperature was 110°C, the drying time was 3 h, and the vacuum degree was set to -0.04 MPa; the dried material was mixed with LiCoO2 with a particle size Dv50 of 18 μm at a high speed of 300 r / min, for 10 min, in a ratio of 6:1, and placed in a box furnace with compressed air and a ventilation volume of 5 m 3 / h, heated to 800℃ and kept warm for 8h, and naturally cooled to room temperature to obtain LiCoO2 material coated with TiO2, Al2O3, and Al(PO3)3.

[0055] Example 3

[0056] This example prepares a surface-modified lithium transition metal oxide positive electrode material, and the specific process is as follows:

[0057] (1) Pour 50 kg of deionized water into the water washing kettle, then add the first additive LiPO3 and the second additive Y2(SO4)3 sulfuric acid solution into the deionized water. 3+ The concentration is 0.05mol / L, stir evenly, and then add LiNi according to the solid-liquid mass ratio of high nickel ternary material calcined powder and deionized water of 1:5 0.85 Co 0.10 Mn 0.05 O2 (particle size Dv50 is 3 μm) powder, the amount of the first additive added is 0.01wt% of the mass of the added first calcined powder, and the mixture is stirred at a high speed of 200 r / min to form a uniform first slurry;

[0058] (2) Add ZrO to the first slurry 2- A ZrOSO4 sulfuric acid solution with a concentration of 0.05 mol / L was added dropwise for 6 min. After the addition was completed, high-speed stirring was continued at 500 r / min for 10 min to obtain a second slurry;

[0059] (3) Add AlO2 dropwise to the second slurry - A NaAlO2 sodium hydroxide solution with a concentration of 0.2 mol / L was added, and the addition time was controlled to 10 min. After the addition was completed, high-speed stirring was continued at 500 r / min for 10 min to obtain a third slurry;

[0060] Based on the addition amount of the first additive, the second additive, the third additive and the fourth additive are added according to Li + :Y 3+ :ZrO 2+ :AlO2 -=0.3:1:1:5 added;

[0061] (4) The third slurry was centrifuged and placed in a high-mix drying equipment for vacuum drying, wherein the high-mix speed was 10 r / min, the drying temperature was 120°C, the drying time was 3 h, and the vacuum degree was set to -0.05 MPa; the dried material was mixed with LiNi with a particle size Dv50 of 10 μm. 0.85 Co 0.10 Mn 0.05 The large particles of O2 high nickel ternary material were mixed at high speed, with a speed of 50r / min, a time of 20min, and a ratio of 7:1. The mixing process was protected by nitrogen. The mixed material was placed in a muffle furnace, heated to 600℃ and kept warm for 3h under oxygen environment, and naturally cooled to room temperature to obtain LiNi coated with ZrO2, Y2O3, and Al(PO3)3. 0.85 Co 0.10 Mn 0.05 O2 high nickel ternary material.

[0062] Comparative Example 1

[0063] In this comparative example, the LiCoO2 powder in Example 1 was uniformly mixed with nano-Al2O3, nano-TiO2, and nano-LiPO3 at high speed. The addition amounts of Ti element, Al element, and LiPO3 were the same as those in Example 1. Compressed air was passed through the box-type furnace with a ventilation volume of 5m 3 / h, heated to 850℃ and kept warm for 8h, and naturally cooled to room temperature to obtain LiCoO2 material coated with TiO2, Al2O3, and Al(PO3)3.

[0064] Figure 3 is an SEM image of the comparative example after dry mixing. It can be seen from the figure that after dry mixing, there are many large particles dispersed unevenly on the surface. Figure 4 is an SEM image of the sintered product of the comparative example. It can be seen from the figure that there are obvious granular substances on the surface of the material.

[0065] Comparative Example 2

[0066] In this comparative example, LiPO3 is not added in step (1) of Example 1. Instead, TiOSO4 sulfuric acid solution, Al2(SO4)3 sulfuric acid solution and NaAlO2 sodium hydroxide solution are directly added. In step (4), large-particle lithium cobalt oxide is not added. The remaining addition amounts and other steps are the same as those of Example 1, and a LiCoO2 material coated with TiO2 and Al2O3 is obtained.

[0067] Comparative Example 3

[0068] In this comparative example, the LiNi 0.85 Co 0.10 Mn 0.05The primary O2 powder is washed, centrifuged, and dried, and then mixed evenly with nano-Al2O3, nano-TiO2, and nano-LiPO3 at high speed. The addition amount of Ti element, Al element, and LiPO3 and the large particles are the same as those in Example 3. Compressed air is passed through the box furnace with a ventilation volume of 5m 3 / h, heated to 600℃ and kept warm for 3h, and naturally cooled to room temperature to obtain LiNi coated with TiO2, Al2O3, and Al(PO3)3 0.85 Co 0.10 Mn 0.05 O2 material.

[0069] Comparative Example 4

[0070] Comparative Example 4: In step (1) of Example 1, Al2(SO4)3 sulfuric acid solution is not added, and TiOSO4 sulfuric acid solution, LiPO3 solution and NaAlO2 sodium hydroxide solution are directly added. The addition amount and other steps are the same as those in Example 1.

[0071] Comparative Example 5

[0072] In Comparative Example 5, in step (2) of Example 1, no TiOSO4 sulfuric acid solution is added, and only NaAlO2 sodium hydroxide solution is added. At the same time, in step (4), the large-particle lithium cobalt oxide is not added. The addition amount and other steps are the same as in Example 1.

[0073] Comparative Example 6

[0074] Comparative Example 6 adopts substantially the same method as Example 3, the main difference being that no large particles are added in step (4).

[0075] Comparative Example 7

[0076] This comparative example prepares a lithium transition metal oxide positive electrode material. The difference from Example 1 is that in step (1), only the first additive LiPO3 is added to obtain a first slurry, and the second additive, the third additive and the fourth additive are added simultaneously to obtain a second slurry, and finally sintering is performed to obtain a LiCoO2 material coated with TiO2, Al2O3, and Al(PO3)3.

[0077] Test example

[0078] Residual alkali test: The surface residual alkali of the coated positive electrode materials obtained in Examples 1-3 and Comparative Examples 1-7 was tested respectively. The residual alkali test method was the company's own method. The specific test steps are as follows: Weigh 30.00g of sample, add 100.00g of deionized water, add a magnet, stir at 600rpm for 30min, let it stand for 15min, and then filter. The filtrate is transferred to a disposable plastic cup, and 50ml is transferred and titrated with 0.05mol / L hydrochloric acid standard solution. 0.05mol / L hydrochloric acid standard solution calibration: Weigh 3g of sodium carbonate that has been dried at 270℃, add deionized water to dissolve, adjust the volume to 500ml, and transfer 10ml for calibration. The calibration result gives the residual lithium content.

[0079] Battery preparation: The positive electrode material, polyvinylidene fluoride, and conductive carbon were mixed in a mass ratio of 90:5:5, NMP (N-methylpyrrolidone) was added, and the mixture was stirred to form a slurry, which was then coated on aluminum foil and dried at 80°C to form a positive electrode sheet. The prepared positive electrode sheet, lithium sheet, electrolyte, and separator were used as raw materials to assemble CR2430 button batteries in a glove box.

[0080] Capacity Test: Four replicate samples of the batteries prepared in Comparative Examples 1-7 and Examples 1-3 were charged at room temperature (25°C) at a constant current rate of 0.1C to a voltage of V1. The samples were then charged at a constant voltage of V1 until the current dropped below 0.05C, reaching the fully charged state V1. The discharge capacity was then determined by discharging the battery at a constant current rate of 0.1C to V2. The discharge capacity in grams at a rate of 0.1C was calculated using the following formula: Discharge capacity in grams = Discharge capacity / Mass of positive electrode material.

[0081] Cycling performance test: At room temperature (25°C), the battery was tested using a combination of charge-discharge and storage. This test cycle consisted of a single charge-discharge cycle followed by storage and then another charge-discharge cycle. Cycling capacity retention = (discharge capacity at the 50th cycle / discharge capacity at the first cycle) × 100%.

[0082] Different lithium transition metal oxides have different requirements for charge and discharge voltage in capacity testing and cycle testing, as follows:

[0083] Lithium transition metal oxide is LiNi 0.85 Co 0.10 Mn 0.05 When O2 is used, the discharge capacity is tested at a charge and discharge voltage of 3.0~4.25V@0.2C rate, and the cycle performance is tested at a charge and discharge voltage of 3.0~4.25V@1.0C rate. The results are shown in Table 1.

[0084] Table 1

[0085]

[0086]

[0087] Table 1 shows that the residual alkali content of Comparative Example 3 is basically the same as that of Example 3, indicating that water washing can effectively reduce the residual alkali content on the surface of high nickel nickel cobalt lithium manganese oxide material. The battery capacity and initial efficiency are both reduced compared with Example 3, and the 50-week cycle capacity retention rate is significantly reduced. This is mainly because the Li + Can inhibit the material matrix Li + Excessive precipitation stabilizes the matrix structure, resulting in stable capacity and first efficiency. Due to the presence of double hydrolysis, the surface is evenly coated, and the 50-week capacity retention rate is high. The high-nickel nickel cobalt manganese oxide material in Comparative Example 3 adopts conventional solid phase coating, which increases the surface BET and inhibits Li + The precipitation ability is weakened and the capacity is reduced. At the same time, due to the + The precipitation produces more residual alkali, which increases the contact area with the electrolyte, increases side reactions, and reduces the cycle performance. The compacted densities of Example 3 and Comparative Example 3 with large-particle powder are 3.6 and 3.55 g / cm respectively. 3 In Comparative Example 6, no large particles were added, and the powder compaction density was 3.36 g / cm 3 Significantly lower than the sample with large particles added.

[0088] When the lithium transition metal oxide is high-voltage lithium cobalt oxide, the discharge capacity is tested at a charge and discharge voltage of 3.0 to 4.55 V at a 0.1C rate, and the cycle performance is tested at a charge and discharge voltage of 3.0 to 4.65 V at a 0.5C rate. The results are shown in Table 2.

[0089] Table 2

[0090]

[0091]

[0092] Table 2 analysis shows that compared with Example 1, the discharge capacity and 50-week cycle of the product of Comparative Example 1 are reduced. This is related to the coating method on the surface of the lithium cobalt oxide material. It is mainly due to solid-state coating, uneven coating on the material surface, increased BET, increased occurrence of electrolyte side reactions, loss of lithium salt, and subsequent reduction in material capacity, first efficiency, and cycle performance.

[0093] Compared with Example 1, the first-discharge capacity and the third-discharge capacity of the battery in Comparative Example 2 are slightly reduced, and the cycle life is significantly reduced. The reason is that the surface lacks the protection of Al(PO3)3 with a spinel structure, and the surface stability is weakened, resulting in an increase in residual alkali on the surface, an increase in side reactions with the electrolyte, and an increase in lithium salt loss, which significantly reduces the cycle life.

[0094] Compared with Example 1, the discharge capacity and 50-cycle retention rate of the sample in Comparative Example 4 are reduced. The reason is that due to the lack of Al2(SO4)3 sulfuric acid solution, surface hydrolysis cannot be achieved, so that excess residual alkali cannot be suppressed, the surface coating is damaged, and the material properties are deteriorated.

[0095] Compared with Example 1, the discharge capacity and 50-week cycle retention rate of the sample in Comparative Example 5 are reduced. The reason is that due to the lack of TiOSO4 sulfuric acid solution, double hydrolysis of the surface cannot be achieved. At the same time, the role of Ti is to increase the capacity, and the lack of Ti significantly reduces the capacity. Due to the presence of NaAlO2 sodium hydroxide solution, Al2(SO4)3 sulfuric acid solution and LiPO3 solution, the lithium precipitation of the sample is inhibited, so the increase of surface residual alkali is not obvious.

[0096] Comparison of Example 7 with Example 1 shows that the discharge capacity and 50-cycle retention rate of the sample are both reduced. The reason is that TiO 2+ 、Al 3+ 、AlO2 - The ionic solutions are hydrolyzed at the same time under the same conditions, but the conditions of various ions are inconsistent, so the hydrolysis is not easy to be complete, which makes the ratio of surface elements easily unbalanced, affecting the uniformity and consistency of the coating.

[0097] In Table 2, the compaction densities of Comparative Examples 2 and 4 are 4.01 and 4.05, respectively. Large particles are added to Examples 1 and 2 and Comparative Examples 1 and 4, and the obtained powder compaction densities are 4.22, 4.23, 4.18, and 4.16, respectively. The compaction density of the samples with the addition of large particles is significantly improved, and thus the energy density is improved.

[0098] As shown in Figure 5, the Li + Cationic fusion agent, thereby effectively inhibiting the Li + Precipitation effectively reduces the source of residual alkali and protects the stability of the lithium transition metal oxide powder matrix structure; introduces polyhydrolyzed substances to form Al(OH)3, Ti(OH)4, Zr(OH)4 and Al(OH)2PO3 complexes on the surface of the material to avoid long contact time between the material and water, and improve the surface lattice lithium deficiency phenomenon; then after high-temperature sintering, the hydroxide and the complex lose water to form a metal oxide or phosphate coating layer, which can effectively reduce the surface residual alkali content; in the initial stage of the 3.0-4.65V@0.5C cycle, the surface coating material will decompose into a spinel-like structure material, the spinel structure material has high pressure resistance, and improves the 50-week capacity retention rate of the material; since comparative examples 1 and 2 do not adopt the schemes of embodiments 1 and 2, the surface coating is not dense and has poor cycle performance.

[0099] While the embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to the embodiments described above. Various modifications may be made within the scope of knowledge possessed by a person skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof may be combined with one another unless there is a conflict.

Claims

1. A method for surface modification of a lithium transition metal oxide cathode material, characterized in that, it comprises the following steps: S1: adding a first additive, a second additive and a lithium transition metal oxide into water and stirring to obtain a first slurry; the first additive is a lithium-containing phosphate, the second additive is Y 3+ or Al 3+ Acidic solutions of salts; S2: Add a third additive dropwise to the first slurry and stir to obtain a second slurry. The third additive is an acidic solution of a TiO 2+ or ZrO 2+ salt; S3: Add a fourth additive dropwise to the second slurry and stir to obtain a third slurry. The fourth additive is an alkaline solution of AlO 2 - salt; S4: Centrifuge and dry the third slurry to obtain an intermediate product, mix the intermediate product with large-particle cathode material, and sinter to obtain a surface-modified lithium transition metal oxide material.

2. The method according to claim 1, characterized in that, The addition amount of the first additive is 0.001-0.05% of the mass of the lithium transition metal oxide, and Li in the first additive + , Y in the second additive 3+ or Al 3+ , TiO in the third additive 2+ or ZrO 2+ , AlO in the fourth additive 2 - has a molar ratio of (0.1-0.5):(0.5-1.5):(0.5-1.5):(2.5-7.5).

3. The method according to claim 1, characterized in that, The chemical formula of the lithium transition metal oxide is LiCo x M 1-x O 2 , where M is at least one of Mn, Al, Zr, Ti, Mg, La, Ni or Mg, and 1≥x≥0.

10.

4. The method according to claim 1, characterized in that, In step S1, the solid-liquid mass ratio of the lithium transition metal oxide to water is 1:(0.2 - 4).

5. The method according to claim 1, characterized in that, In step S1, the lithium-containing phosphate is at least one of lithium orthophosphate, lithium hydrogen phosphate, or lithium metaphosphate.

6. The method according to claim 1, characterized in that, The acidic solution in the second additive and / or the third additive is selected from at least one of sulfuric acid solution, hydrochloric acid solution, acetic acid solution, nitric acid solution, citric acid solution, or oxalic acid solution.

7. The method according to claim 1, characterized in that, The alkaline solution in the fourth additive is selected from at least one of sodium hydroxide solution, potassium hydroxide solution, lithium hydroxide solution, or ammonia water solution.

8. The method according to claim 1, characterized in that, The concentration of Y 3+ or Al 3+ in the second additive is 0.001 - 0.4 mol / L; the concentration of TiO 2+ or ZrO 2+ in the third additive is 0.002 - 0.4 mol / L; the concentration of AlO 2 - in the fourth additive is 0.001 - 0.3 mol / L.

9. The method according to claim 1, characterized in that, The large-particle cathode material is at least one of lithium cobaltate, high-nickel nickel cobalt manganese oxide, or low-nickel nickel cobalt manganese oxide; the particle size Dv50 of the large-particle cathode material is 10 - 22 μm; the mass ratio of the intermediate product to the large-particle cathode material is (2 - 10):

1.

10. The method according to claim 1, characterized in that, In step S4, the sintering temperature is 600 - 950 °C, preferably, the sintering time is 5 - 10 h.