Modification method of lithium ion battery positive electrode material

Abstract

The invention provides a lithium ion battery positive electrode material modification method, which comprises: A) mixing a nanometer carrier with a phosphotungstic acid impregnation liquid, impregnating, and drying to obtain nanometer carrier-loaded phosphotungstic acid; b) mixing the lithium nickel manganese oxide material with the nano-carrier loaded phosphotungstic acid, and extracting the mixture by using diethyl ether to obtain an intermediate material; and C) carrying out heat treatment on the intermediate material to obtain the modified lithium nickel manganese oxide composite material. According to the invention, a nano-carrier loaded phosphotungstic acid coated lithium nickel manganese oxide material is adopted, then phosphotungstic acid is extracted by diethyl ether, and the phosphotungstic acid and the nano-carrier form a uniform coating on the surface of the lithium nickel manganese oxide material together. After heat treatment, the lithium nickel manganese oxide composite material coated with nano titanium dioxide / aluminum oxide and tungsten oxide and doped with phosphorus element is obtained, and the high-temperature long-cycle capacity retention ratio of the lithium nickel manganese oxide material is improved through the synergistic effect of titanium dioxide / aluminum oxide, tungsten oxide and phosphorus oxide.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a method for modifying a cathode material of a lithium-ion battery. Background Art

[0002] In the past few decades, science and technology have developed by leaps and bounds, and lithium-ion batteries have achieved very important applications in various fields. With the extensive research on green energy and the further popularization of intelligent technology, people have higher and stricter requirements for the energy density, safety performance, cycle stability, low cost, etc. of lithium-ion batteries. And the cathode material is an indispensable component in the battery. Therefore, the electrochemical performance of the cathode material directly determines the electrochemical performance of the battery. Therefore, the development of cathode materials with high energy density and low cost is the current development trend.

[0003] There are mainly two ways to improve the energy density of the cathode material and reduce the cost: one is to increase the specific capacity of the cathode material. For example, lithium-rich manganese-based materials have the performance advantages of high theoretical capacity, high energy density, and low cost; the other is to increase the de-lithiation potential of the cathode material. For example, lithium nickel manganate has a voltage plateau of 4.7V (vs. Li / Li + ) and a theoretical specific capacity of 146 mAh·g -1 , and it is an excellent alternative material for lithium-ion batteries with low cost and high energy. However, for lithium-rich manganese-based materials, problems such as poor cycle stability, poor electron / ion conductivity, fast voltage decay, and oxygen evolution severely limit their applications; the relatively high voltage causes serious interfacial side reactions when lithium nickel manganate is used as the cathode, resulting in poor cycle high-temperature performance, storage performance, and serious gas generation.

[0004] To solve the problems of the above-mentioned lithium nickel manganate material, surface coating is an effective method. Most common coating materials are particulate substances, and the coating effect is largely affected by the particle size of the coating material. If the coating particles are large, it will lead to low chemical reaction activity and uneven distribution, and the coating effect is not ideal; if the coating particles are too small, agglomeration is likely to occur, and the cathode material cannot be completely coated. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for modifying a cathode material of a lithium-ion battery. The modification method in the present invention can form a uniform coating on the surface of the lithium nickel manganate material and improve the high-temperature long-cycle capacity retention rate of the lithium nickel manganate material.

[0006] The present invention provides a method for modifying a cathode material of a lithium-ion battery, including the following steps:

[0007] A) Mix a nano-carrier with a phosphotungstic acid impregnation solution, dry after impregnation to obtain a phosphotungstic acid supported on the nano-carrier;

[0008] The nano-carrier includes nano-titanium dioxide and / or nano-aluminum oxide;

[0009] B) Mix the lithium nickel manganese oxide material with the phosphotungstic acid supported by the nano-carrier, and extract the mixture with ether to obtain an intermediate material;

[0010] C) Heat-treat the intermediate material to obtain a modified lithium nickel manganese oxide composite material.

[0011] Preferably, the particle size of the nano-carrier is 20 - 100 nm.

[0012] Preferably, the phosphotungstic acid impregnation solution includes phosphotungstic acid and water, and the mass concentration of the phosphotungstic acid impregnation solution is 20 - 50%.

[0013] Preferably, the mass ratio of the nano-carrier to the phosphotungstic acid is 1:(0.2 - 1).

[0014] Preferably, the impregnation temperature in step A) is 20 - 30 °C, and the impregnation time in step A) is 20 - 30 hours.

[0015] Preferably, the drying temperature in step A) is 100 - 120 °C, and the drying time in step A) is 3 - 12 hours.

[0016] Preferably, the mass ratio of the lithium nickel manganese oxide material to the phosphotungstic acid supported by the nano-carrier is (4 - 5):1.

[0017] Preferably, in step B), the mass ratio of the mixture to the ether is 1:(1 - 3).

[0018] Preferably, in step B), the extraction time is 1 - 5 h, and the extraction temperature is 15 - 35 °C.

[0019] Preferably, in step C), the heat-treatment temperature is 500 - 850 °C, and the heat-treatment time is 5 - 24 hours.

[0020] The present invention provides a method for modifying a cathode material of a lithium-ion battery, comprising the following steps: A) mixing a nano-carrier with a phosphotungstic acid impregnation solution, drying after impregnation to obtain a nano-carrier loaded with phosphotungstic acid; B) mixing a lithium nickel manganese oxide material with the nano-carrier loaded with phosphotungstic acid, and extracting the mixture with ether to obtain an intermediate material; C) performing heat treatment on the intermediate material to obtain a modified lithium nickel manganese oxide composite material. In the present invention, phosphotungstic acid loaded on a nano-carrier is used to coat the lithium nickel manganese oxide material, and then phosphotungstic acid is extracted with ether. Phosphotungstic acid and ether form a liquid layer to wrap the lithium nickel manganese oxide material, and the ether completely evaporates naturally. Phosphotungstic acid remains on the surface of the lithium nickel manganese oxide, and together with the nano-carrier, a uniform coating is formed on the surface of the lithium nickel manganese oxide material. After heat treatment, a lithium nickel manganese oxide composite material coated with a nano-carrier, tungsten oxide and doped with phosphorus element is obtained. The synergistic effect of nano-titanium dioxide / aluminum oxide, tungsten oxide and phosphorus oxide improves the high-temperature long-cycle capacity retention rate of the lithium nickel manganese oxide material. Detailed implementation mode

[0021] The present invention provides a method for modifying a cathode material of a lithium-ion battery, comprising the following steps:

[0022] A) Mixing a nano-carrier with a phosphotungstic acid impregnation solution, drying after impregnation to obtain a nano-carrier loaded with phosphotungstic acid;

[0023] The nano-carrier includes nano-titanium dioxide and / or nano-aluminum oxide;

[0024] B) Mixing a lithium nickel manganese oxide material with the nano-carrier loaded with phosphotungstic acid, and extracting the mixture with ether to obtain an intermediate material;

[0025] C) Performing heat treatment on the intermediate material to obtain a modified lithium nickel manganese oxide composite material.

[0026] The present invention first prepares phosphotungstic acid loaded on a nano-carrier. First, phosphotungstic acid is added to water and dissolved to obtain a phosphotungstic acid impregnation solution. Then, nano-carrier powder is added to the phosphotungstic acid impregnation solution, and the mixture is stirred evenly while adding. After impregnation, it is dried to obtain a nano-carrier loaded with phosphotungstic acid.

[0027] In the present invention, the mass concentration of the phosphotungstic acid impregnation solution is preferably 20-50%, more preferably 30-40%, such as 20%, 25%, 30%, 35%, 40%, 45%, 50%, and is preferably a range value with any of the above values as the upper or lower limit.

[0028] In the present invention, the nano-carrier is preferably nano-titanium dioxide and / or nano-aluminum oxide. When the nano-carrier is a combination of nano-titanium dioxide and nano-aluminum oxide, the mass ratio of nano-titanium dioxide to nano-aluminum oxide is preferably 1:(2 - 5), more preferably 1:(3 - 4). In the present invention, after low-temperature sintering, part of the nano-aluminum oxide enters the crystal structure of lithium nickel manganate, improving the structural stability and inhibiting the phase change of the material during the charge-discharge cycle.

[0029] In the present invention, the average particle size of the nano-carrier is preferably 20 - 100 nm, more preferably 20 - 50 nm, such as 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, and is preferably a range value with any of the above values as the upper or lower limit; the mass ratio of the nano-carrier to phosphotungstic acid is preferably 1:(0.2 - 1), more preferably 1:(0.45 - 0.7), such as 1:0.2, 1:0.25, 1:0.3, 1:0.35, 1:0.4, 1:0.45, 1:0.5, 1:0.55, 1:0.6, 1:0.65, 1:0.7, 1:0.75, 1:0.8, 1:0.85, 1:0.9, 1:0.95, 1:1, and is preferably a range value with any of the above values as the upper or lower limit.

[0030] In the present invention, the temperature of the impregnation is preferably 20 - 30 °C, more preferably 25 - 30 °C. Specifically, in the examples of the present invention, the impregnation can be carried out at room temperature. The time of the impregnation is preferably 20 - 30 hours, more preferably 24 - 26 hours.

[0031] In the present invention, the drying is preferably carried out in a vacuum drying oven. The temperature of the drying is preferably 100 - 120 °C, more preferably 100 - 110 °C, such as 100 °C, 105 °C, 110 °C, 115 °C, 120 °C, and is preferably a range value with any of the above values as the upper or lower limit; the time of the drying is preferably 3 - 12 hours, more preferably 6 - 10 hours.

[0032] In the phosphotungstic acid supported by the nano-carrier obtained after drying, the mass fraction of phosphotungstic acid (the percentage of phosphotungstic acid in the total mass of phosphotungstic acid and the carrier) is preferably 20 - 50 wt%, more preferably 30 - 40 wt%.

[0033] After obtaining the phosphotungstic acid supported by the nanocarrier, the present invention mixes lithium nickel manganate with the phosphotungstic acid supported by the nanocarrier to obtain a mixture, and then mixes the mixture with diethyl ether. The phosphotungstic acid is extracted by the diethyl ether, and the phosphotungstic acid and the diethyl ether form a liquid layer to wrap the lithium nickel manganate material. At room temperature, the diethyl ether volatilizes, and the phosphotungstic acid remains on the surface of the lithium nickel manganate, realizing the uniform coating of the phosphotungstic acid on the surface of the lithium nickel manganate. At the same time, the nanocarrier as the carrier of the phosphotungstic acid is also uniformly coated on the surface of the lithium nickel manganate.

[0034] In the present invention, the lithium nickel manganate material is LiNi 0.5 Mn 1.5 O 4 , and the mass ratio of the lithium nickel manganate material to the phosphotungstic acid supported by the nanocarrier is preferably (4 - 5):1, such as 4:1, 4.1:1, 4.2:1, 4.3:1, 4.4:1, 4.5:1, 4.6:1, 4.7:1, 4.8:1, 4.9:1, 5:1, and is preferably a range value with any of the above values as the upper or lower limit.

[0035] In the present invention, the mass ratio of the mixture to the diethyl ether is preferably 1:(1 - 3), more preferably 1:(1.5 - 2.5), such as 1:1, 1:1.5, 1:2, 1:2.5, 1:3, and is preferably a range value with any of the above values as the upper or lower limit.

[0036] In the present invention, the temperature of the extraction is preferably 15 - 35°C, more preferably 20 - 25°C, and the time of the extraction is preferably 1 - 5 hours, more preferably 2 - 3 h.

[0037] After completing the extraction to obtain the intermediate material, the present invention sinters the intermediate material to obtain a modified lithium nickel manganate composite material.

[0038] In the present invention, phosphotungstic acid is a substance with a low melting point and is easily decomposed during the heat treatment process. The phosphorus and tungsten elements undergo chemical reactions again to generate phosphorus oxides and tungsten oxides. The nanocarrier and tungsten oxides form a coating layer on the surface of the lithium nickel manganate material, and the phosphorus element enters the surface lattice of the lithium nickel manganate material to form P - O bonds, realizing surface doping.

[0039] Among them, the nanocarrier and tungsten oxides are uniformly coated on the surface of the lithium nickel manganate, playing a role in isolating the electrolyte, preventing the matrix material from being eroded by acidic substances such as HF generated by the decomposition of the electrolyte and the oxidation of carbonate solvents under high pressure, thereby inhibiting the adverse side reactions between the electrode and the electrolyte and improving the stability of the electrode - interface structure during the cycling process; at the same time, the P - O bond has the characteristic of having a larger bond energy than the Mn - O bond. Although phosphorus is a non - metal element, it exists in the form of P 5+ , occupying part of the Mn in the lattice 3+The position is used to enhance the stability of the crystal structure of the material, ensure that the crystal does not undergo structural deformation and phase transformation during repeated ion deintercalation processes, and improve the cycling performance of the material.

[0040] In the present invention, the temperature of the heat treatment is preferably 500 - 850 °C, more preferably 650 - 800 °C, such as 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, 720 °C, 750 °C, 780 °C, 800 °C, 820 °C, 850 °C, preferably a range value with any of the above-mentioned values as the upper or lower limit; the time of the heat treatment is preferably 5 - 24 hours, more preferably 10 - 20 hours.

[0041] The present invention provides a method for modifying a cathode material for a lithium-ion battery, comprising the following steps: A) mixing a nanocarrier with a phosphotungstic acid impregnation solution, drying after impregnation to obtain a phosphotungstic acid supported on the nanocarrier; B) mixing a lithium nickel manganese oxide material with the phosphotungstic acid supported on the nanocarrier, and extracting the mixture with diethyl ether to obtain an intermediate material; C) performing heat treatment on the intermediate material to obtain a modified lithium nickel manganese oxide composite material. In the present invention, phosphotungstic acid supported on a nanocarrier is used to coat the lithium nickel manganese oxide material, and then phosphotungstic acid is extracted with diethyl ether. Phosphotungstic acid and diethyl ether form a liquid layer to wrap the lithium nickel manganese oxide material. Since diethyl ether has high volatility and can volatilize at room temperature, it can be completely volatilized during the extraction process of 1 - 5 h, and phosphotungstic acid remains on the surface of the lithium nickel manganese oxide, forming a uniform coating on the surface of the lithium nickel manganese oxide material together with the nanocarrier. After heat treatment, a lithium nickel manganese oxide composite material with a nanocarrier, tungsten oxide coating, and phosphorus element doping, the carrier, tungsten oxide, and phosphorus oxide act synergistically to improve the high-temperature long-cycle capacity retention rate of the lithium nickel manganese oxide material.

[0042] To further illustrate the present invention, the following is a detailed description of a method for modifying a cathode material for a lithium-ion battery provided by the present invention in combination with examples, but it should not be construed as a limitation of the protection scope of the present invention.

[0043] In the following examples, the raw materials are nano-titanium dioxide with a CSA number of 13463 - 67 - 7 sold by Aladdin Industrial Corporation, nano-aluminum oxide with a CAS number of 1344 - 28 - 1, and phosphotungstic acid with a CAS number of 12067 - 99 - 1.

[0044] Example 1

[0045] Weigh 30 g of phosphotungstic acid, add deionized water to dissolve it to make an impregnation solution. Weigh 70 g of titanium dioxide powder with a particle size of 30 nm, then slowly add it to the impregnation solution, stirring while adding until it is uniform, and impregnate it at room temperature for 24 hours. After impregnation, place it in a vacuum drying oven at 110 °C and dry it for 6 hours to obtain nano-titanium dioxide supported phosphotungstic acid with a phosphotungstic acid loading of 30 wt%.

[0046] Lithium nickel manganese oxide and phosphotungstic acid supported on nano-titanium dioxide are mixed in a weight ratio of 4.5:1 to obtain a uniform mixture. Then, ether is added in a ratio of 1:2 by weight of the mixture to ether. The ether extracts the phosphotungstic acid, forming a mixture of lithium nickel manganese oxide, phosphotungstic acid, and nano-titanium dioxide. Then, it is heat-treated at 750 °C for 15 h to form a lithium nickel manganese oxide composite material.

[0047] Example 2

[0048] Weigh 40 g of phosphotungstic acid, add deionized water to dissolve it, and make an impregnation solution. Weigh 60 g of titanium dioxide powder with a particle size of 50 nm, and then slowly add it to the impregnation solution, stirring while adding until it is uniform. It is impregnated at room temperature for 24 hours. After impregnation, it is placed in a vacuum drying oven at 105 °C and dried for 8 hours to obtain nano-titanium dioxide supported phosphotungstic acid with a phosphotungstic acid loading of 40 wt%.

[0049] Lithium nickel manganese oxide and phosphotungstic acid supported on nano-titanium dioxide are mixed in a weight ratio of 4:1 to obtain a uniform mixture. Then, ether is added in a ratio of 1:2.5 by weight of the mixture to ether. The ether extracts the phosphotungstic acid, forming a mixture of lithium nickel manganese oxide, phosphotungstic acid, and nano-titanium dioxide. Then, it is heat-treated at 780 °C for 12 h to form a lithium nickel manganese oxide composite material.

[0050] Example 3

[0051] Weigh 30 g of phosphotungstic acid, add deionized water to dissolve it, and make an impregnation solution. Weigh 70 g of aluminum oxide powder with a particle size of 30 nm, and then slowly add it to the impregnation solution, stirring while adding until it is uniform. It is impregnated at room temperature for 24 hours. After impregnation, it is placed in a vacuum drying oven at 110 °C and dried for 6 hours to obtain nano-aluminum oxide supported phosphotungstic acid with a phosphotungstic acid loading of 30 wt%.

[0052] Lithium nickel manganese oxide and phosphotungstic acid supported on nano-aluminum oxide are mixed in a weight ratio of 4.5:1 to obtain a uniform mixture. Then, ether is added in a ratio of 1:2 by weight of the mixture to ether. The ether extracts the phosphotungstic acid, forming a mixture of lithium nickel manganese oxide, phosphotungstic acid, and nano-aluminum oxide. Then, it is heat-treated at 750 °C for 15 h to form a lithium nickel manganese oxide composite material.

[0053] Example 4

[0054] Weigh 30 g of phosphotungstic acid, add deionized water to dissolve it, and make an impregnation solution. Weigh 1 part of titanium dioxide powder with a particle size of 30 nm and 3.5 parts of aluminum oxide powder with a particle size of 30 nm, totaling 70 g. Then slowly add the impregnation solution, stirring continuously until it is uniform, and impregnate at room temperature for 24 hours. After impregnation, place it in a vacuum drying oven at 110 °C for 6 hours to obtain nano-aluminum oxide / titanium dioxide supported phosphotungstic acid with a phosphotungstic acid loading of 30 wt%.

[0055] Mix lithium nickel manganate and nano-aluminum oxide / titanium dioxide supported phosphotungstic acid in a weight ratio of 4.5:1 to obtain a uniform mixture. Then add diethyl ether in a ratio of 1:2 by weight of the mixture to diethyl ether. The diethyl ether extracts the phosphotungstic acid, forming a mixture of lithium nickel manganate, phosphotungstic acid, and nano-aluminum oxide / titanium dioxide. Then perform heat treatment at 750 °C for 15 h to form a lithium nickel manganate composite material.

[0056] Comparative Example 1

[0057] The difference between this comparative example and Example 1 is only that: in this comparative example, 60 wt% nano-titanium dioxide supported phosphotungstic acid is prepared, and other conditions are the same.

[0058] Comparative Example 2

[0059] The difference between this comparative example and Example 1 is only that: in this comparative example, lithium nickel manganate and nano-titanium dioxide supported phosphotungstic acid are mixed in a weight ratio of 7:1, and other conditions are the same.

[0060] Comparative Example 3

[0061] The difference between this comparative example and Example 1 is only that: in this comparative example, lithium nickel manganate and nano-titanium dioxide supported phosphotungstic acid are mixed in a weight ratio of 2:1, and other conditions are the same.

[0062] Comparative Example 4

[0063] The difference between this comparative example and Example 1 is only that: in this comparative example, titanium dioxide powder with a particle size of 200 nm is used, and other conditions are the same.

[0064] Comparative Example 5

[0065] The difference between this comparative example and Example 1 is only that: in this comparative example, titanium dioxide powder with a particle size of 5 nm is used, and other conditions are the same.

[0066] Comparative Example 6

[0067] The difference between this comparative example and Example 1 is only that: in this comparative example, there is no coating layer, and other conditions are the same.

[0068] Comparative Example 7

[0069] The difference between this comparative example and Example 1 is that the same mass of phosphotungstic acid is used in this comparative example to replace the nano-titanium dioxide-loaded phosphotungstic acid in Example 1, and other conditions are the same.

[0070] Comparative Example 8

[0071] The difference between this comparative example and Example 1 is that in this comparative example, nano-titanium dioxide with a particle size of 30 nm of the same mass is used to replace the nano-titanium dioxide loaded with phosphotungstic acid in Example 1, and other conditions are the same.

[0072] Comparative Example 9

[0073] The difference between this comparative example and Example 1 is that in this comparative example, phosphotungstic acid is not extracted with ether, but lithium nickel manganese oxide and nano titanium dioxide-supported phosphotungstic acid are mixed at a weight ratio of 4.5:1, and a uniform mixture is directly heat-treated at 750° C. for 15 hours to form a lithium nickel manganese oxide composite material. Other conditions are the same.

[0074] Comparative Example 10

[0075] The difference between this comparative example and Example 1 is that nano-titanium dioxide loaded with phosphotungstic acid is not used for extraction and coating in this comparative example. The specific implementation is as follows:

[0076] Weigh 30 g of phosphotungstic acid and 70 g of titanium dioxide powder with a particle size of 30 nm, and mix them to obtain a mixture of phosphotungstic acid and nano-titanium dioxide.

[0077] Lithium nickel manganese oxide is mixed with a mixture of phosphotungstic acid and nano titanium dioxide in a weight ratio of 4.5:1 to obtain a uniform mixture, and heat-treated at 750° C. for 15 hours to form a lithium nickel manganese oxide composite material.

[0078] The nickel-manganese-oxide lithium composite material assembled battery obtained in the embodiment and the comparative example was subjected to electrochemical performance testing, and the specific steps were as follows:

[0079] The main raw materials used in preparing battery samples are: acetylene carbon black with CAS number 1333-86-4, polytetrafluoroethylene with CAS number 24937-79-9, N-methylpyrrolidone with CAS number 872-50-4, diaphragm 2500 sold by Celgard, battery shell CR2025 sold by Shenzhen Tiancheng Co., Ltd., and pure lithium sheet sold by Tianjin Zhongneng Co., Ltd.; the main equipment used in preparing battery samples are: ARE-310 mixer sold by THINKY, Super series of super purification glove boxes sold by Shanghai Michelona Co., Ltd., and CT3002A battery testing system sold by Wuhan Blue Electric Electronics Co., Ltd.; electrochemical performance test conditions: 3.0~4.95V@0.1C.

[0080] Specific steps for preparing the battery: 1) Lithium nickel manganese oxide composite, acetylene black, and polyvinylidene fluoride are mixed in a weight ratio of 90:5:5, and N-methylpyrrolidone is added dropwise, with the addition amount being based on wetting the surface of the mixture; 2) Use a stirrer to stir into a uniform slurry, coat it, and dry it; 3) Put the processed electrode sheet into a glove box and assemble it into a battery; 4) Place it on a battery system test cabinet for testing. The results are shown in Table 1.

[0081] Table 1 Electrochemical performance test of lithium nickel manganese oxide composite materials in examples and comparative examples

[0082]

[0083]

[0084] It can be seen from the data in the above table that: for Comparative Example 1 and Comparative Example 3, the specific capacity at the first cycle and the capacity retention rate of long cycles are both less than those of Example 1. When the addition amount of nano-titanium dioxide supported phosphotungstic acid is too much, the specific capacity and the capacity retention rate will be reduced. The possible reason is that when the addition amount of phosphorus element is too much, the crystallinity of the material is affected, the crystal structure is unstable, and the capacity retention rate of long cycles decreases; a relatively thick coating layer is formed by nano-titanium dioxide and tungsten oxide, which inhibits the insertion and extraction of lithium ions, resulting in a decrease in specific capacity.

[0085] The specific capacity at the first cycle in the data of Comparative Example 2 is similar, and the capacity retention rate after 100 cycles of specific capacity decreases. Considering that the addition amount of nano-titanium dioxide supported phosphotungstic acid is reduced, it means that both the coating layer and the phosphorus doping amount are reduced. After multiple cycles, the interfacial side reaction between the electrolyte and the electrode intensifies, and the crystal structure also changes to varying degrees, and the electrical performance of the lithium nickel manganese oxide composite material deteriorates; in the data of Comparative Example 6, no nano-titanium dioxide supported phosphotungstic acid is added, but the specific capacity at the first cycle is similar, while the capacity retention rate drops significantly, indicating that the addition of nano-titanium dioxide supported phosphotungstic acid is of great significance for slowing down the decrease of the capacity retention rate; however, in Comparative Example 9, although nano-titanium dioxide supported phosphotungstic acid is added, but diethyl ether is not used to extract phosphotungstic acid, and phosphotungstic acid does not play a role in the nickel manganese composite material, resulting in a significant reduction in the capacity retention rate.

[0086] From the data of Comparative Example 4 and Comparative Example 5, it can be seen that increasing or decreasing the particle size of titanium dioxide will reduce the long-cycle capacity retention rate. In Comparative Example 7 and Comparative Example 8, if phosphotungstic acid or nano-titanium dioxide is added alone, the performance improvement is not as good as that of nano-titanium dioxide loaded with phosphotungstic acid. Considering the corrosion-resistant isolation performance and stable crystal structure performance of its composite oxide structure are better; although phosphotungstic acid and nano-titanium dioxide are added simultaneously in Comparative Example 10, it is not nano-titanium dioxide loaded with phosphotungstic acid, and no further extraction treatment is carried out on it, resulting in a serious decline in the capacity retention rate. At the same time, combining the above examples and comparative examples for analysis, nano-titanium dioxide loaded with phosphotungstic acid and extraction are two important factors essential for preparing lithium nickel manganate with excellent electrochemical performance.

[0087] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and retouches can be made, and these improvements and retouches should also be regarded as the protection scope of the present invention.

Claims

1. A method for modifying a positive electrode material of a lithium ion battery, comprising the following steps: A) mixing the nanocarrier with the phosphotungstic acid impregnation solution, and drying after impregnation to obtain the phosphotungstic acid loaded on the nanocarrier; The nano-carrier comprises nano-titanium dioxide and / or nano-aluminum oxide; B) mixing the lithium nickel manganese oxide material with the phosphotungstic acid supported by the nanocarrier, and extracting the mixture with ether to obtain an intermediate material; C) heat treating the intermediate material to obtain a modified lithium nickel manganese oxide composite material.

2. The method for modifying the positive electrode material of a lithium ion battery according to claim 1, characterized in that: The particle size of the nanocarrier is 20-100 nm.

3. The method for modifying the positive electrode material of a lithium ion battery according to claim 1, characterized in that: The phosphotungstic acid impregnation solution comprises phosphotungstic acid and water, and the mass concentration of the phosphotungstic acid impregnation solution is 20-50%.

4. The method for modifying the positive electrode material of a lithium ion battery according to claim 3, characterized in that: The mass ratio of the nano-carrier to phosphotungstic acid is 1:(0.2-1).

5. The method for modifying the positive electrode material of a lithium ion battery according to claim 1, characterized in that: The immersion temperature in step A) is 20-30° C., and the immersion time in step A) is 20-30 hours.

6. The method for modifying the positive electrode material of a lithium ion battery according to claim 1, characterized in that: The drying temperature in step A) is 100-120° C., and the drying time in step A) is 3-12 hours.

7. The method for modifying the positive electrode material of a lithium ion battery according to claim 1, characterized in that: The mass ratio of the lithium nickel manganese oxide material to the phosphotungstic acid supported by the nano-carrier is (4-5):

1.

8. The method for modifying the positive electrode material of a lithium ion battery according to claim 1, characterized in that: In the step B), the mass ratio of the mixture to diethyl ether is 1:(1-3).

9. The method for modifying the positive electrode material of a lithium ion battery according to claim 1, characterized in that: In the step B), the extraction time is 1 to 5 hours and the extraction temperature is 15 to 35°C.

10. The method for modifying the positive electrode material of a lithium ion battery according to claim 1, characterized in that: In the step C), the heat treatment temperature is 500 to 850° C. and the heat treatment time is 5 to 24 hours.

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