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

Abstract

Disclosed in the present invention is a method for surface modification of a lithium transition metal oxide positive electrode material, comprising: 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. According to the present invention, a coating layer 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

English translation of PCT / CN2022 / 090538 METHOD FOR SURFACE MODIFICATION OF LITHIUM TRANSITION METAL OXIDE POSITIVE ELECTRODE MATERIAL FIELD

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

[0002] A lithium-ion battery has high capacity, discharge platform and compaction density, which is one of the most fully studied and widely used positive electrode materials for the commercial lithium-ion battery. Currently, the common layered lithium-ion batteries include lithium cobalt oxide, low-nickel lithium nickel cobalt manganese oxide and high-nickel lithium nickel cobalt manganese oxide, etc. The lithium cobalt oxide is widely used in 3C fields including a mobile phone, an unmanned aerial vehicle, and a notebook computer, and the lithium nickel cobalt manganese oxide is widely used in the field of new energy vehicles.

[0003] Residual alkali generally refers to residual soluble Li>CO3 and LiOH on a surface of a lithium transition metal oxide powder material. The problem of residual alkali has a great impact on the battery. In the process of making and coating slurry for a rechargeable battery, the high amount of residual alkali content may 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 liable to react with the electrolyte so as to cause the generation of gas, which reduces the safety performance and the cycle performance of the battery. There are two main sources of the residual alkali on the surface of the lithium transition metal oxide powder material: first, during the production process, a lithium salt may volatilize during the high-temperature calcination process, and in order to compensate for the loss of Li during the calcination process, a mixture ratio Li / M (M refers to a transition metal) is generally greater than 1, so that the high-temperature conditions of calcination make a remaining small amount of Li exist in the form of Li>O. During the subsequent cooling process, Li2O may react with CO; and HzO in the air to produce Li>CO3 and LiOH. Second, the active oxygen anions on the surface of the lithium transition metal oxide positive electrode English translation of PCT / CN2022 / 090538 material may react with CO; and HzO in the air to produce COs> and OH". A small amount of Li+ migrates from a body to the surface and produces Li>CO3 and LiOH with CO3* and OH" on the surface of the material, and this process is accompanied by deoxidation of the surface of the material to form a surface oxide layer with a distorted structure. During the cycle of the battery, the residual alkali on a surface layer of the particles easily reacts with the electrolyte to produce gas. The more residual alkali on the surface layer of the material is, the higher the cycle ambient temperature or the voltage is, and thus the more obvious the phenomenon of gas generation is.

[0004] Currently, the method for removing the residual lithium on the surface of a high-nickel lithium nickel cobalt manganese oxide material is mainly by water washing and drying. The residual lithium on the surface is removed by water washing with the soluble characteristics of Li2CO3 and LiOH, and the residual water is removed by heating and drying. However, the process of water washing may increase the cost of use. More importantly, the lithium transition metal oxide material is sensitive to water. If the drying time is too long and the contact time between the material and the water is too long, the lattice lithium on the surface may be lost, which may lead to deterioration of the material structure and serious performance degradation. High-voltage lithium cobalt oxide itself has a low residual alkali content while the surface activity is enhanced under high-temperature and high-voltage, and much residual lithium on the surface of the material may also increase side reactions, which may lead to irreversible capacity loss of the battery, acceleration of the cycle attenuation and flatulence of the battery accompany with cobalt dissolution and oxygen precipitation. In addition, a series of safety hazards may occur.

[0005] By coating other material on the surface of the lithium transition metal oxide material, the amount of the residual alkali on the surface layer of the positive electrode material can be effectively reduced, the generation of gas can be reduced, and the structural stability and the cycle performance are improved. The common coating materials are metal oxides, such as Al;03, La;03, TiO2 or ZrO2. A common coating method is solid-phase coating method, and such coating method can stabilize the structure, reduce the residual lithium, which performs the function of protecting the positive electrode material. However, most pure oxides are electronically insulated, and the coating may increase the electronic conductivity of the positive electrode material and reduce the capacity. In addition, the solid-phase coating has the problem of non-uniform coating and increase of the BET of the surface layer, which English translation of PCT / CN2022 / 090538 increases the battery impedance and reduces the capacity. Although the residual alkali on the surface is reduced, the capacity is affected. SUMMARY

[0006] The present application is directed to solve at least one of the technical problems existing in the above conventional technology. For this, a method for surface modification of a lithium transition metal oxide positive electrode material is provided according to the present application, which can effectively reduce the alkali on a surface of the lithium transition metal oxide positive electrode material, improve the stability of an interface, improve the compaction density and improve the energy density.

[0007] According to one aspect of the present application, a method for surface modification of a lithium transition metal oxide positive electrode material is provided according to the present application, which includes 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; where the first additive is a lithium-containing phosphate, and the second additive is an acidic solution of Y3* salt or AIP* salt; S2: adding a third additive dropwise into the first slurry and stirring to obtain a second slurry, where the third additive is an acidic solution of TiO? salt or ZrO?" salt; S3: adding a fourth additive dropwise into the second slurry and stirring to obtain a third slurry, where the fourth additive is an alkaline solution of ALO? salt; S4: centrifuging the third slurry and drying to obtain an intermediate product; mixing the intermediate product with a large-particle positive electrode material and sintering to obtain a surface-modified lithium transition metal oxide material.

[0008] In some embodiments of the present application, an addition amount of the first additive is 0.001% to 0.05% of a mass of the lithium transition metal oxide, a molar ratio of Li+ in the first additive, Y?* or AI** in the second additive, TiO** or ZrO?* in the third additive and A1O? in the fourth additive is (0.1-0.5): (0.5-1.5): (0.5-1.5): (2.5-7.5).

[0009] In some embodiments of the present application, a chemical formula composition of the lithium transition metal oxide is LiCoxM;.xO2, and M represents 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 block English translation of PCT / CN2022 / 090538 material obtained by sintering a precursor and a lithium source for the first time with a conventional process, and pulverizing the block material so as to obtain a powder material, with a particle size Dv50 ranging from 3pm to 22um.

[0010] In some embodiments of the present application, in step S1, a solid-liquid mass ratio of the lithium transition metal oxide to water is 1: (0.2-4), and more preferably 1:1.2.

[0011] In some embodiments of the present application, in step S1, the lithium-containing phosphate is at least one of lithium-containing orthophosphate, lithium-containing hydrogen phosphate, or lithium-containing metaphosphate, and more preferably at least one of lithium-containing orthophosphate and lithium-containing metaphosphate.

[0012] In some embodiments of the present application, the acidic solution in the second additive and / or the third additive is selected from at least one of sulfuric acidic solution, hydrochloric acidic solution, acetic acidic solution, nitric acidic solution, citric acidic solution or oxalic acidic solution.

[0013] In some embodiments of the present application, in step S1, a stirring speed ranges from 100r / min to 300r / min, and a stirring time ranges from 5min to 30min.

[0014] In some embodiments of the present application, in step S2, a stirring speed ranges from 100r / min to 1000r / min, and a stirring time ranges from Smin to 30min.

[0015] In some embodiments of the present application, 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.

[0016] In some embodiments of the present application, a concentration of Y** or AI** in the second additive ranges from 0.001mol / L to 0.3mol / L; a concentration of TiO* or ZrO? in the third additive ranges from 0.002mol / L to 0.4mol / L; and a concentration of AlO% in the fourth additive ranges from 0.001mol / L to 0.3mol / L.

[0017] In some embodiments of the present application, the large-particle positive electrode material is at least one of lithium cobalt oxide, high-nickel lithium nickel cobalt manganese oxide and low-nickel lithium nickel cobalt manganese oxide; a particle size Dv50 of the large-particle positive electrode material ranges from 10pm to 22um; and a mass ratio of the intermediate product to the large-particle positive electrode material is (2-10):1, and more preferably (3-9):1. English translation of PCT / CN2022 / 090538

[0018] In some embodiments of the present application, in step S4, a temperature for sintering ranges from 600 degrees Celsius to 950 degrees Celsius; preferably, a time for sintering ranges from 5h to 10h.

[0019] In some embodiments of the present application, in step S4, a centrifugation speed ranges from 1000r / min to 3000r / min.

[0020] In some embodiments of the present application, a dropping time of the third additive and the fourth additive ranges from 3min to 10min.

[0021] In some embodiments of the present application, in step S4, the drying is vacuum drying, and a drying temperature ranges from 100 degrees Celsius to 110 degrees Celsius, a drying time ranges from 3h to 10h, and a vacuum degree is maintained ranging from -0.02MPa to -0.4MPa.

[0022] In some embodiments of the present application, in step S4, a mixing rate ranges from 300r / min to 1000r / min, and a time ranges from 5min to 30min.

[0023] According to a preferred embodiment of the present application, at least the following beneficial effects are obtained:

[0024] 1. a liquid-phase surface modification is adopted according to the present application, lithium ions, phosphate ions or metaphosphate ions is introduced in the liquid-phase coating process of the lithium transition metal oxide, which can inhibit the precipitation of lithium ions in the structure of the lithium transition metal oxide to a certain extent, and effectively reduce the source of residual alkali, and stabilize a structure of a matrix of the surface layer.

[0025] 2. additives are added stepwise and hydrolyzed synchronously, and Al(OH)3; and Zr(OH)4 or Ti(OH). and Al(OH);PO; complexes are formed on the surface of the material and distributed uniformly, so as to avoid excessive contact time between the material and the water and improve the lack of lattice lithium on the surface.

[0026] 3. the method of electrode configuration with large and small particles is adopted, the intermediate product and the large particle are mixed and then sintered at a high temperature, the hydroxide and complexes are in dehydration to obtain a coating layer by A203 and TiO2 or ZrO; and Al(PO3)3 with a uniform composition and a controllable thickness. The coating layer is compact and smooth, which can effectively reduce the residual alkali content on the surface. In addition, the presence of amphiphilic substances on the surface layer can improve English translation of PCT / CN2022 / 090538 the generation of gas, and increase the compaction density and energy density.

[0027] 4. the coating layer according to the present application has a uniform composition and a controllable thickness, which can improve the surface non-uniformity of the solid-phase structure, reduce the BET of the interface, reduce the contact area of the interface and the electrolyte, reduce the occurrence of the side reactions, and produce a substance with a spinel structure on the surface of the material during the cycle process, improve the high-voltage resistance of the material, and improve the cycle performance of the lithium transition metal oxide positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0001] The present application will be further described hereinafter in conjunction with the drawings and embodiments, inwhich:

[0028] FIG. 1 is an SEM diagram of a material of a third slurry after drying in Embodiment 1 of the present application;

[0029] FIG. 2 is an SEM diagram of a material after sintering in Embodiment 1 of the present application;

[0030] FIG. 3 is an SEM diagram after dry mixing of Comparative Example 1 of the present application;

[0031] FIG. 4 is an SEM diagram after dry mixing and sintering of Comparative Example 1 of the present application; and

[0032] FIG. 5 shows the cycle performance of Embodiment 1, Embodiment 2, Comparative Example 1 and Comparative Example 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] Hereinafter, the concept of the present application and the generated technical effects will be described clearly and completely with reference to the embodiments, so as to fully understand the purpose, features and effects of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments, Based on the embodiments of the present application, any other English translation of PCT / CN2022 / 090538 embodiments, made by the person skilled in the art without any creative efforts, will fall into the protection scope of the present application.

[0034] Embodiment 1

[0035] In this embodiment, a surface-modified lithium transition metal oxide positive electrode material is prepared, and the specific process is as follows:

[0036] (1) a deionized water of 50kg is poured into a washing kettle, and a sulfuric acid solution of a first additive LiPO3 and a second additive Alo(SO4); with a concentration of Al** of 0.2mol / L therein are added into the deionized water and stirred uniformly, and then a LiCoO; sintered powder material (a particle size Dv50 is 8um) is added in the deionized water with a solid-liquid mass ratio of 1:0.8, and an addition amount of the first additive is 0.02wt% of the mass of the added LiCoO; sintered powder material, so that a uniform first slurry is formed by stirring at a high speed of 200r / min;

[0037] (2) a TiOSOs sulfuric acid solution with a concentration of TiO** of 0.2mol / L is added dropwise into the first slurry, and a dropping time is controlled for Smin, stirring at a high speed of 500r / min for 10min after dropping is completed, so as to obtain a second slurry;

[0038] (3) a NaAlO: sodium hydroxide solution with a concentration of AlO? of 0.3mol / L is added dropwise into the second slurry, and a dropping time is controlled for 10min, stirring at a high speed of 500r / min for 10min after dropping is completed, so as to obtain a third slurry; the second additive, the third additive and the fourth additive are added with an amount of Lit: AI**:TiO**: A10%=0.5:1:1:2.5 based on the addition amount of the first additive;

[0039] (4) the third slurry is placed in a high-mixing drying equipment for vacuum drying after centrifugation and separation, where a high-mixing speed is 10r / min, a drying temperature is 105 degrees Celsius; a drying time is 8h, and a vacuum degree is set to -0.05MPa; the dried material is mixed with LiCoO; with a particle size Dv50 of 18um at a high speed of 500r / min, a time of 15min, a ratio of 8:1, which are placed in a box furnace, ventilated with compressed air with a ventilation volume of 5m?h, and are heated to 850 degrees Celsius for 8h, and cooled naturally to room temperature, so as to obtain a LiCoO2 material coated with TiO,, Al,O3 and AI(PO3)s.

[0040] FIG. 1 is an SEM diagram of the material of the third slurry after centrifugation and drying, and it can be seen from the SEM that there are apparent traces of uniform coating on English translation of PCT / CN2022 / 090538 the surface layer of the material; FIG. 2 is an SEM diagram of the material after sintering, and it can be seen from FIG. 2 that the surface becomes smooth and dense after sintering is completed.

[0041] Embodiment 2

[0042] In this embodiment, a surface-modified lithium transition metal oxide positive electrode material is prepared, and the specific process is as follows:

[0043] (1) a deionized water of 50kg is poured into a washing kettle, and a sulfuric acid solution of a first additive Li;PO3 and a second additive Al,Cls with a concentration of Al** of 0.1mol / L therein are added into the deionized water and stirred uniformly, and then a LiCoO2 sintered powder material (a particle size Dv50 is 10um) is added in the deionized water with a solid-liquid mass ratio of 1:3, and an addition amount of the first additive is 0.01wt% of the mass of the added LiCoO sintered powder material, so that a uniform first slurry is formed by stirring at a high speed of 300r / min;

[0044] (2) a TiOSO: sulfuric acid solution with a concentration of TiO** of 0.lmol / L is added dropwise into the first slurry, and a dropping time is controlled for 7min, stirring at a high speed of 500r / min for 10min after dropping is completed, so as to obtain a second slurry;

[0045] 3) a NaAlO; sodium hydroxide solution with a concentration of AIO* of 0.3mol / L is added dropwise into the second slurry, and a dropping time is controlled for 8min, stirring at a high speed of 500r / min for 10min after dropping is completed, so as to obtain a third slurry; the second additive, the third additive and the fourth additive are added with an amount of Li*:AP*: TiO: A10% =0.3:1:1:3 based on the addition amount of the first additive;

[0046] (4) the third slurry is placed in a high-mixing drying equipment for vacuum drying after centrifugation and separation, where a high-mixing speed is 10r / min, a drying temperature is 110 degrees Celsius; a drying time is 3h, a vacuum degree is set to -0.04MPa; the dried material is mixed with LiCoO; with a particle size Dv50 of 18um at a high speed of 300r / min, a time of 10min, a ratio of 6:1, which are placed in a box furnace, ventilated with compressed air with a ventilation volume of 5Sm*h, and are heated to 800 degrees Celsius for 8h, and cooled naturally to room temperature, so as to obtain a LiCoO, material coated with TiOa, Al,03 and Al(PO3)s.

[0047] Embodiment 3 English translation of PCT / CN2022 / 090538

[0048] In this embodiment, a surface-modified lithium transition metal oxide positive electrode material is prepared, and the specific process is as follows:

[0049] (1) a deionized water of 50kg is poured into a washing kettle, and a sulfuric acid solution of a first additive Li;POs and a second additive Y2(SO4); with a concentration of Y* of 0.05mol / L therein are added into the deionized water and stirred uniformly, and then a LiNio8sMno sO: (a particle size Dv50 is 3um ) powder material is added with a solid-liquid mass ratio of the high-nickel ternary material sintered powder material (a particle size Dv50 is 3pm) and deionized water of 1:5, an addition amount of the first additive is 0.01wt% of the mass of the added sintered powder material, so that a uniform first slurry is formed by stirring at a high speed of 200r / min;

[0050] (2) a ZrOSOs sulfuric acid solution with a concentration of ZrO** of 0.05mol / L is added dropwise into the first slurry, and a dropping time is controlled for 6min, stirring at a high speed of 500r / min for 10min after dropping is completed, so as to obtain a second slurry;

[0051] 3) a NaAlO; sodium hydroxide solution with a concentration of AlO?* of 0.2mol / L is added dropwise into the second slurry, and a dropping time is controlled for 10min, stirring at a high speed of 500r / min for 10min after dropping is completed, so as to obtain a third slurry; the second additive, the third additive and the fourth additive are added with an amount of Lit: Y**: ZrO: A10%=0.3:1:1:5 based on the addition amount of the first additive;

[0052] (4) the third slurry after centrifugation and separation is placed in a high-mixing drying equipment for vacuum drying, where a high-mixing speed is 10r / min, a drying temperature is 120 degrees Celsius; a drying time is 3h, a vacuum degree is set to -0.05MPa; the dried material is mixed with a LiNiossMnoosO2 high-nickel ternary material of large particle with a particle size Dv50 of 10um at a high speed of 50r / min, a time of 20min, a ratio of 7:1, which are protected by nitrogen during the mixing process, the mixture is placed in a muffle furnace, and is heated to 600 degrees Celsius for 3h under an oxygen environment, and cooled naturally to room temperature, so as to obtain a LiNio.ssC00.10Mno0sO2 high-nickel ternary material coated with ZrO, Y203 and AI(PO3)s.

[0053] Comparative Example 1

[0054] In this comparative example, the LiCoO, powder material in Embodiment 1 is mixed uniformly with nano Al;Os, nano TiO; and nano LiPOj at a high speed, the addition amounts English translation of PCT / CN2022 / 090538 of Ti element, Al element and LiPOs are the same with those in Embodiment 1, the box furnace is filled with compressed air with a ventilation volume of Sm, and is heated to 850 degrees Celsius and kept for 8h, and cooled naturally to room temperature, so as to obtain a LiCoO; material coated with TiO2, Al,O3 and AL(PO3)3.

[0055] FIG. 3 is an SEM diagram after dry mixing of the present comparative example. It can be seen from the figure that there are relatively more large particles in the surface layer which are dispersed non-uniformly after dry mixing. FIG. 4 is an SEM diagram of a sintered product of the present comparative example. It can be seen from the figure that there are particulate substances on the surface layer of the material apparently.

[0056] Comparative Example 2

[0057] In this comparative example, LiPOj is not added at step (1) of Embodiment 1, and TiOSOy sulfuric acid solution, Al2(SO4)3 sulfuric acid solution and NaAlO; sodium hydroxide solution are directly added, a lithium cobalt oxide of large particle is not added at step (4), other addition amounts and steps are the same with those in Embodiment 1, so as to obtain a LiCoO, material coated with TiO; and Al,Os.

[0058] Comparative Example 3

[0059] In this comparative example, the LiNiossMno.0sO2 primary powder in Embodiment 3 is mixed uniformly with nano Al;O3, nano TiO; and nano LiPOs at a high speed after water washing, centrifugation and drying, the addition amount of Ti element, Al element, LiPO3 and the large particle is the same with those in Embodiment 3, the box furnace is filled with compressed air with a ventilation volume of Sm*h, and is heated to 600 degrees Celsius and kept for 3h, and cooled naturally to room temperature, so as to obtain a LiNiggsMnoesO2 material coated with TiO3, Al,03 and AI(PO3)s.

[0060] Comparative Example 4

[0061] In Comparative Example 4, an Al2(SO.); sulfuric acid solution is not added at step (1) of Embodiment 1, and TiOSOs sulfuric acid solution, LiPO; solution and NaAlO; sodium hydroxide solution are directly added, and the addition amounts and other steps are the same with those in Embodiment 1. Comparative Example 5

[0062] In Comparative Example 5, TiOSOs sulfuric acid solution is not added at step (2) of English translation of PCT / CN2022 / 090538 Embodiment I, only NaAlO; sodium hydroxide solution is added, a lithium cobalt oxide of large particle is not added at step (4) and the addition amounts and other steps are the same with those in Embodiment 1. Comparative Example 6

[0063] In Comparative Example 6, substantially the same method as in Embodiment 3 is applied, and the main difference is that no large particle is added at step (4). Comparative Example 7

[0064] In this comparative example, a lithium transition metal oxide positive electrode material is prepared. The difference with Embodiment 1 is that only the first additive LiPO; is added at step (1) so as to obtain the first slurry, the second additive, the third additive and the fourth additive are added simultaneously so as to obtain the second slurry, and a LiCoO2 material coated with TiOz, A103 and Al(POa); is obtained by sintering finally. Test Example

[0065] Residual alkali test: tests to the residual alkali on the surface of the coated positive electrode material obtained in Embodiments 1 to 3 and Comparative Examples 1 to7 are conducted, respectively. The test method for the residual alkali is a company-defined method. The specific steps of the test are as follows: a sample of 30.00g is weighed, a deionized water of 100.00g is added, a magnet is added, stirring at a speed of 600rpm for 30min, standing for 15min, suction filtration is performed after standing, the filtrate is transferred to a disposable plastic cup, 50ml of which is pipetted and is titrated with 0.05mol / L hydrochloric acid standard solution. Calibration of 0.05mol / L hydrochloric acid standard solution: sodium carbonate of 3g that has been dried at 270 degrees Celsius is weighed, deionized water is added to dissolve the sodium carbonate with a constant volume 500ml, 10ml is pipetted for calibration, and a calibration result shows the residual lithium content.

[0066] Battery preparation: the positive electrode material, polyvinylidene fluoride, and conductive carbon are mixed in a mass ratio of 90:5:5, N-methylpyrrolidone (NMP) is added, slurry is made by stirring so as to be coated on an aluminum foil, and a positive electrode sheet is made by drying at 80 degrees Celsius. The prepared positive electrode sheet, the lithium sheet, electrolyte and a diaphragm are configured to be raw materials to constitute a CR2430 button battery in a glove box. English translation of PCT / CN2022 / 090538

[0067] Capacity test: 4 parallel samples of the batteries made in Comparative Examples 1 to7 and Embodiments 1 to 3 are taken, and charging to a voltage of V1 at a constant current rate of 0.1C at room temperature of 25 degrees Celsius, and further charging until the current is lower than 0.05C under the constant voltage of V1, so as to be in a full charge state of V1. Discharging to V2 at a constant current rate of 0.1C is performed, so as to obtain the discharge capacity. The discharge capacity at the rate of 0.1C is obtained by the following calculation formula: discharge gram capacity=discharge capacity / mass of positive electrode material.

[0068] Cycle performance test: it is carried out by a combination of charge, discharge and storage at room temperature 25 degrees Celsius, that is, storage is performed after one charge and one discharge, and then the charge and discharge test is performed again and this cycle is repeating. Cycle capacity retention ratio=(discharge capacity of 50th cycle / discharge capacity of first cycle)*100%.

[0069] Different lithium transition metal oxides have different requirements for the charge and discharge voltage in the capacity test and the cycle test, which are specifically as follows:

[0070] In case that the lithium transition metal oxide is LiNiggsC00.10Mng.050, the test ot the discharge gram capacity is conducted at a rate of 3.0 to 4.25V@0.2C of the charge-discharge voltage, and the text to the cycle performance is conducted at a rate of 3.0 to 4.25V@0.1C of the charge-discharge voltage, the results are shown in Table 1. Charge Discharge | 10 times 1 ratio 4.25v / 1.0c Charge Discharge | 10 times 50-cycles gram gram discharge gram 3 Powder i capacity Residual Number capacity | capacity | CE% capacity compaction retention alkali % (mAh / g) (mAh / g) (mAh / g) . glem?® ratio | 4.25v / 0.2c | 4.25v / 0.2¢ 4.25v / 1.0c a an FET or oy rem ay 5 Rta A Embodiment 3 243 217.6 89.54 202 98% 3.6 0.0110 Embodiment 3 | 243 217.6 | 89.54 | 202 98% 3.6 | 0.0110 Comparative Co Co | oo oo oo . | 87.70 | 198 95% 355 | 0.0220 | - 236 212 | 87.70 | 198 95% 3.55 Example 3 Comparative Lomparative 240 216.8 | 88.63 | 200 97% 3.36 | 0.0130 | Example 6

[0071] According to the analysis to Table 1, the residual alkali content of Comparative Example 3 is substantially the same with that of Embodiment 3, which indicates that water English translation of PCT / CN2022 / 090538 washing can effectively reduce the residual alkali content on the surface of the high-nickel lithium nickel cobalt manganese oxide material. Compared with Embodiment 3, the battery capacity and the first effect are reduced, the capacity retention ratio after 50 cycles is significantly reduced, which is mainly because the Li* added in the process of water washing in Embodiment 3 can inhibit the excessive precipitation of Li* in the a matrix of the material and stabilize the structure of the matrix, so that the capacity and the first effect remain stable. In addition, due to the presence of double hydrolysis, the surface layer is uniformly coated, and the 50-cycle capacity retention ratio is relatively high. On the contrary, a conventional solid-phase coating is used by the high-nickel lithium nickel cobalt manganese oxide material in Comparative Example 3, which increases the BET of the surface layer, and weakens the ability to inhibit the precipitation of Li* in the material and reduces the capacity. In addition, due to the precipitation of Li*, more residual alkali is produced, the contact area of which with the electrolyte is increased, side reactions are increased, and the cycle performance is decreased. The compaction density of the large-particle powder added in Embodiment 3 and Comparative Example 3 is 3.6g / cm’® and 3.55g / cm?’, respectively, and no large particle is added in Comparative Example 6 with the compaction density of powder in 3.36g / cm?, which is significantly lower than those of the samples added with the large particle.

[0072] In case that the lithium transition metal oxide is the high-voltage lithium cobalt oxide, the text to the discharge gram capacity is conducted at a rate of 3.0 to 4.55V@0.1C of the charge-discharge voltage, and the text to the cycle performance is conducted at a rate of 3.0 to 4.65V@0.5C of the charge-discharge voltage, and the results are shown in Table 2. | Discharge 3 times Charge gram discharge l. oT | Powder gram oo ro | capacity Number |, ~~ | capacity 3 Capacity | CE% | gram capacity | retention (mAh / o) | 50-cycles 3 Powder } capacity . Residual compaction retention alkali % ofem? (mAh / g) ~ (mAhg) 1 gem? ratio 4.55v / 0.1c | 4.65v / 0.5¢ | capacity | mang) | Embodiment 1 | 210.1 198.6 | 94.52 | 219.1 83% 4.22 | 0.0016 Embodiment 2 | 209.2 197.9 | 94.59 | 218.2 81% 4.23 | 0.0012 Comparative | Co I | Co Co Co | ! 208.6 196.6 | 94.24 | 215.6 68% 4.18 | 0.0015 Example 1 English translation of PCT / CN2022 / 090538 Comparative - ' 210.1 198.5 | 94.47 | 219.7 50% 4.01 | 0.0050 Example 2 Comparative Lomparative > I 2105 1946 | ora4 | 2147 55% 416 | 0.0080 Example 4 Comparative - ! 209.6 195.6 | 93.32 | 215.1 65% 4.05 | 0.0025 Example 5 Comparative - ' 210.6 196.6 | 93.35 | 216.1 69% 4.09 | 0.0045 Example 7

[0073] According to the analysis to Table 1, compared with Embodiment 1, the discharge capacity and the retention ratio of 50-cycles of the product in Comparative Example 1 are both reduced, which is related to the coating method of the surface of the lithium cobalt oxide material. Mainly due to solid-phase coating, it leads to a non-uniform coating on the surface of the material, a phenomenon of BET being larger, the increasing of side reactions of the electrolyte, and lose of lithium salt, which further leads to a decrease in capacity, first effect and cycle performance of the material.

[0074] Compared with Embodiment 1, the primary discharge capacity and three times discharge capacity in Comparative Example 2 are slightly reduced, and the cycle decreases significantly. The reason is that the surface layer lacks the protection of Al(PO3); in a spinel structure, and the stability of the surface layer is weakened, which leads to an increase in residual alkali on the surface layer, side reactions with the electrolyte, and the loss of the lithium salt, so that the cycle decreases significantly.

[0075] Compared with Embodiment 1, the discharge capacity and 50-cycles retention ratio of the sample in Comparative Example 4 are both decreased. The reason is that the multi hydrolysis of the surface layer cannot be achieved due to the lack of an Alx(POx)s sulfuric acid solution, so that the excessive residual alkali cannot be inhibited, and the coating of the surface is damaged, which deteriorates the material performance.

[0076] Compared with Embodiment 1, the discharge capacity and 50-cycles retention ratio of the sample in Comparative Example 5 are both decreased. The reason is that the double hydrolysis of the surface layer cannot be achieved due to the lack of a TiSO; sulfuric acid solution. Also, the function of Ti is to increase the capacity, and thus the capacity decreases English translation of PCT / CN2022 / 090538 significantly due to the lack of Ti. Due to the presence of NaAlO; sodium hydroxide solution, Al(SO4); sulfuric acid solution and LiPOs solution, the precipitation of lithium of the sample is inhibited, so that the increase of the residual alkali on the surface is not apparent.

[0077] Compared with Embodiment 1, the discharge capacity and 50-cycles retention ratio of the sample in Comparative Example 7 are both decreased. The reason is that TIO, AI**, AIO? ionic solutions are hydrolyzed simultaneously under the same condition, and since the various ionic conditions are inconsistent, and the hydrolysis is liable to be incomplete, which makes the ratio of elements on the surface easy unbalance and affects the uniformity and consistency of the coating.

[0078] The compaction density of Comparative Examples 2 and 4 in Table 2 are 4.01 and 4.05, respectively. Large particle is added in Embodiments 1 and 2 and Comparative Examples land 4, and the compaction densities of which are 4.22, 4.23, 4.18 and 4.16, respectively. The compaction density of the sample added with large particle is significantly improved, and thus the energy density is improved.

[0079] It can be seen from FIG. 5 that Li* cationic fusion agent is introduced during the liquid-phase coating of Embodiments 1 and 2, which effectively inhibits the precipitation of Li* in the structure of the lithium transition metal oxide powder, effectively reduces the source of residual alkali, and keep the stability of the structure of the matrix of the lithium transition metal oxide powder. Multi polyhydrolysated substances are introduced to form Al(OH)s, Ti(OH)4, Zr(OH): and Al(OH)2PO3 complexes on the surface of the material, which avoids excessive contact time between the material and the water and improve the lack of lattice lithium on the surface. After high-temperature sintering, the hydroxide and complex substances are in in dehydration so as to form a metal oxide or phosphate coating layer, which can effectively reduce the residual alkali content on the surface. In an initial stage of the 3.0 to 4.65V@0.5C cycle, the coating substance on the surface may decompose into a substance with a spinel structure, and the substance with the spinel structure has a high-voltage resistance, which improves the 50-cycles capacity retention ratio of the material. Since the solutions of the Embodiments 1 and 2 are not adopted by Comparative Examples 1 and 2, the coating of the surface in Comparative Examples 1 and 2 is not dense and has a poor cycle performance.

[0080] The embodiments of the present application have been described in detail with English translation of PCT / CN2022 / 090538 reference to the attached drawings, but the present application is not limited to the above embodiments, and various changes can be made without departing from the purpose of the present application within the knowledge possessed by those skilled in the art. In addition, in a case of no conflict, the embodiments of the present application and features in the embodiments may be combined with each other.

Claims

English translation of PCT / CN2022 / 090538 CLAIMS 1. A method for surface modification of a lithium transition metal oxide positive electrode material, wherein the method 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; wherein the first additive is a lithium-containing phosphate, and the second additive is an acidic solution of Y3* salt or AIP* salt; S2: adding a third additive dropwise into the first slurry and stirring to obtain a second slurry, wherein the third additive is an acidic solution of TiO?* salt or ZrO?" salt; S3: adding a fourth additive dropwise into the second slurry and stirring to obtain a third slurry, wherein the fourth additive is an alkaline solution of ALO? salt; S4: centrifuging the third slurry and drying to obtain an intermediate product; mixing the intermediate product with a large-particle positive electrode material and sintering to obtain a surface-modified lithium transition metal oxide material.

2. The method according to claim 1, wherein an addition amount of the first additive is 0.001% to 0.05% of a mass of the lithium transition metal oxide, a molar ratio of Li* in the first additive, Y** or AI* in the second additive, TiO?" or ZrO?" in the third additive, and AIO? in the fourth additive is (0.1-0.5): (0.5-1.5): (0.5-1.5): (2.5-7.5).

3. The method according to claim 1, wherein a chemical formula composition of the lithium transition metal oxide is LiCoxM1.xO2, wherein M represents at least one of Mn, Al, Zr, Ti, Mg, La, Ni or Mg, and 12x=0.

10.

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

5. The method according to claim 1, wherein in step S1, the lithium-containing English translation of PCT / CN2022 / 090538 phosphate is at least one of lithium-containing orthophosphate, lithium-containing hydrogen phosphate, or lithium-containing metaphosphate.

6. The method according to claim 1, wherein 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, wherein 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.

8. The method according to claim 1, wherein a concentration of Y3* or AI** in the second additive ranges from 0.001mol / L to 0.4mol / L; a concentration of TiO?* or ZrO? in the third additive ranges from 0.002mol / L to 0.4mol / L; and a concentration of AlO? in the fourth additive ranges from 0.001mol / L to 0.3mol / L.

9. The method according to claim 1, wherein the large-particle positive electrode material is at least one of lithium cobalt oxide, high-nickel lithium nickel cobalt manganese oxide and low-nickel lithium nickel cobalt manganese oxide; a particle size Dv50 of the large-particle positive electrode material ranges from 10um to 22um; and a mass ratio of the intermediate product to the large-particle positive electrode material is (2-10):

1.

10. The method according to claim 1, wherein in step S4, a temperature for sintering ranges from 600 degrees Celsius to 950 degrees Celsius; preferably, a time for sintering ranges from 5h to 10h.