Modified lithium supplement agent and preparation method thereof, positive pole piece and lithium ion battery

Abstract

The invention relates to the technical field of positive electrode lithium supplementing materials of lithium ion batteries, in particular to a modified lithium supplementing agent and a preparation method thereof, a positive electrode plate and a lithium ion battery, the preparation method comprises the following steps: S1, adding lithium phosphate salt into water, and stirring until the lithium phosphate salt is dissolved to obtain an aqueous solution of a coating layer; s2, dispersing a lithium supplement agent Li2NiO2 into an alcohol solvent, and uniformly stirring to obtain a suspension of Li2NiO2; s3, adding the aqueous solution of the coating layer into the Li2NiO2 suspension, uniformly mixing, and drying to obtain a mixture; and S4, sintering the mixture, cooling, and crushing to obtain the modified lithium supplement agent. The modified lithium supplement agent prepared by the preparation method provided by the invention can obviously reduce the gas production rate after Li2NiO2 is applied to a lithium ion battery in a high-temperature environment.

Description

Technical Field

[0001] The present invention relates to the technical field of positive electrode lithium replenishing materials for lithium ion batteries, and in particular to a modified lithium replenishing agent and a preparation method thereof, a positive electrode sheet and a lithium ion battery. Background Art

[0002] In recent years, the country has introduced a series of policies to encourage and support the development of the energy storage industry, and has formulated detailed storage requirements for new energy wind, solar and solar power generation projects to improve energy utilization and ensure a stable supply of power grids. With the continuous development of my country's new energy industry, energy storage batteries, as an important link in the industry chain, have become increasingly stringent in terms of performance requirements. With the continuous development of photovoltaic technology, its design service life has reached 20-25 years, and correspondingly, higher cycle life requirements have been put forward for its supporting energy storage power stations. In order to ensure the goal of equal life of photovoltaic and storage, the current service life of energy storage batteries needs to meet at least 15,000 weeks.

[0003] Current energy storage batteries are primarily based on lithium iron phosphate systems, with a typical service life of 10,000 to 12,000 cycles. To further extend this service life, battery suppliers are considering lithium replenishment technologies. Among these, positive electrode lithium replenishment technology is the fastest-growing and most mature. During the initial charge, the positive electrode lithium replenisher releases additional lithium, which is stored in the negative electrode to compensate for the gradual loss of active lithium in the later stages of the cycle, thereby extending cycle life.

[0004] The current mainstream positive electrode lithium replenisher Li2NiO2 has high lithium replenishment capacity, strong compatibility with current production lines, and easy battery interface control. It is widely used in long-life energy storage products. During the application process, it was found that the positive electrode lithium replenisher Li2NiO2 will easily react with the electrolyte in a high temperature environment and release gas. The main reason is that after the first delithiation, the lithium replenisher is converted into Li 0.36 NiO2 has an unstable crystal structure and easily releases lattice oxygen, which can be eliminated when negative pressure is drawn during the initial activation process. However, the high-valent Ni (+3 valence to +3.64 valence) in the decomposition product also has strong oxidizing properties, which easily oxidizes the electrolyte and releases gas. Although the proportion of lithium supplement added to the battery is low (2% to 5%), gas will continue to be produced throughout the entire life cycle, which will not only reduce the battery's cycle stability, but also increase the battery's safety risks. Therefore, how to reduce the gas production of Li2NiO2 after it is applied to lithium-ion batteries under high temperature conditions is a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a modified lithium supplement agent and its preparation method, a positive electrode plate and a lithium ion battery. The modified lithium supplement agent prepared by the preparation method provided by the present invention can reduce the gas production of Li2NiO2 after it is applied to lithium ion batteries under high temperature environment.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing a modified lithium supplement agent, the preparation method comprising the following steps:

[0008] S1. Add lithium phosphate salt to water and stir until dissolved to obtain an aqueous solution of the coating layer;

[0009] S2, dispersing the lithium supplement Li2NiO2 in an alcohol solvent and stirring evenly to obtain a Li2NiO2 suspension;

[0010] S3, adding the aqueous solution of the coating layer to the suspension of Li2NiO2, mixing them evenly, and drying to obtain a mixture;

[0011] S4, sintering the mixture, and crushing it after cooling to obtain the modified lithium supplement agent.

[0012] The modified lithium supplement prepared by the preparation method provided by the present invention can reduce the gas production after Li2NiO2 is applied to lithium ion batteries under high temperature environment.

[0013] Furthermore, the lithium phosphate salt includes one of Li3PO4 and LiH2PO4.

[0014] Furthermore, in step S1, the mass percentage of the lithium phosphate salt in the aqueous solution of the coating layer is 5% to 15%;

[0015] And / or, in step S1, the stirring includes ultrasonic stirring at a water bath temperature of 50-70°C for 0.5-2h.

[0016] Furthermore, in step S2, the alcohol solvent includes one of ethanol and methanol;

[0017] And / or, in step S2, the mass percentage of Li2NiO2 in the Li2NiO2 suspension is 5% to 15%;

[0018] And / or, in step S2, the stirring speed is 500-800 r / min, and the stirring time is 1-3 h.

[0019] Furthermore, the mass ratio of the lithium phosphate salt to the Li2NiO2 is (3-5):100;

[0020] and / or, in step S3, mixing uniformly by ball milling, wherein the ball milling comprises ball milling at 400-500 rpm for 2-4 hours;

[0021] And / or, in step S3, the drying temperature is 70-90° C., and the drying time is 2-4 hours.

[0022] Furthermore, in step S4, the sintering atmosphere includes an air atmosphere;

[0023] And / or, in step S4, the sintering includes a primary sintering and a secondary sintering, the primary sintering temperature is 300-400° C., the primary sintering time is 1-2.5 hours, the secondary sintering temperature is 550-650° C., and the secondary sintering time is 2-3 hours;

[0024] And / or, in step S4, the heating rate of the primary sintering is 5-10°C / min;

[0025] And / or, in step S4, the heating rate of the secondary sintering is 5-10°C / min.

[0026] Furthermore, the D50 particle size of the modified lithium supplement agent is distributed in the range of 11 to 15 μm.

[0027] In a second aspect, the present invention provides a modified lithium supplement agent, which is prepared by the preparation method described in the first aspect.

[0028] In a third aspect, the present invention provides a positive electrode plate, comprising a positive electrode current collector and a positive electrode active layer covering at least one surface of the positive electrode current collector; the positive electrode active layer comprises the modified lithium supplement agent described in the second aspect, or the modified lithium supplement agent prepared by the preparation method described in the first aspect.

[0029] In a fourth aspect, the present invention provides a lithium-ion battery, comprising the positive electrode sheet described in the third aspect.

[0030] Compared with the prior art, the present invention has at least one of the following advantages:

[0031] The modified lithium supplement prepared by the preparation method provided by the present invention can reduce the gas production after Li2NiO2 is applied to lithium ion batteries under high temperature environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 This is a SEM image of the modified lithium supplement agent prepared in Example 1 of the present invention;

[0034] Figure 2 This is a SEM image of the modified lithium supplement agent prepared in Example 2 of the present invention;

[0035] Figure 3 This is the SEM image of conventional Li2NiO2. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Those skilled in the art should understand that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. The process parameters for which specific conditions are not specified in the following examples are generally based on conventional conditions. Unless otherwise specified, all raw materials can be purchased from the market or are commonly used materials in this industry.

[0037] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0038] In a first aspect, the present invention provides a method for preparing a modified lithium supplement agent, the preparation method comprising the following steps:

[0039] S1. Add lithium phosphate salt to water and stir until dissolved to obtain an aqueous solution of the coating layer;

[0040] S2, dispersing the lithium supplement Li2NiO2 in an alcohol solvent and stirring evenly to obtain a Li2NiO2 suspension;

[0041] S3, adding the aqueous solution of the coating layer to the suspension of Li2NiO2, mixing them evenly, and drying to obtain a mixture;

[0042] S4, sintering the mixture, and crushing it after cooling to obtain the modified lithium supplement agent.

[0043] Since the decomposition products of the lithium supplement agent Li2NiO2 will continuously react with the electrolyte, oxidizing the electrolyte to release gas, the present invention considers coating the surface of the lithium supplement agent Li2NiO2 with a protective layer to block the reaction between the electrolyte and the decomposition products of the lithium supplement agent, thereby preventing the occurrence of side reactions and solving the problem of gas production.

[0044] The preparation method provided by the present invention coats Li3PO4 or LiH2PO4 on the surface of Li2NiO2 without significantly reducing the gram capacity of the lithium supplement agent. After coating, the interface stability of the lithium supplement agent Li2NiO2 can be improved, the interface side reaction can be suppressed, the cycle performance of the material can be improved, and the gas production of the material can be reduced. At the same time, Li3PO4 or LiH2PO4, as a lithium salt, is a fast ion conductor and can also improve the kinetic performance of the lithium supplement agent Li2NiO2.

[0045] The modified lithium supplement prepared by the preparation method provided by the present invention can significantly reduce the gas production after Li2NiO2 is applied to lithium ion batteries under high temperature environment.

[0046] In the preparation method of the modified lithium supplement agent, as an optional embodiment, the lithium phosphate salt includes one of Li3PO4 and LiH2PO4.

[0047] In the above-mentioned method for preparing a modified lithium supplement, as an optional embodiment, in step S1, the weight percentage of the lithium phosphate salt in the aqueous solution of the coating layer is 5% to 15%, for example, 5%, 10%, or 15%. If the weight percentage of the lithium phosphate salt is too low and the water content is high, the capacity of the lithium supplement Li2NiO2 can be affected.

[0048] In the preparation method of the modified lithium supplement agent, as an optional embodiment, in step S1, the stirring includes ultrasonic stirring at a water bath temperature of 50-70°C (for example, 50°C, 60°C or 70°C) for 0.5-2h, for example, 0.5h, 1h, 1.5h or 2h.

[0049] In the above-mentioned method for preparing the modified lithium supplement agent, as an optional embodiment, in step S2, the alcohol solvent includes one of ethanol and methanol.

[0050] Based on the uniformity of the dispersion of the lithium supplement agent Li2NiO2, in the above-mentioned preparation method of the modified lithium supplement agent, as an optional embodiment, in step S2, the mass percentage of Li2NiO2 in the Li2NiO2 suspension is 5% to 15%, for example, it can be 5%, 10% or 15%.

[0051] In the above-mentioned method for preparing the modified lithium supplement agent, as an optional embodiment, in step S2, the stirring speed is 500-800 r / min (for example, it can be 500 r / min, 600 r / min, 700 r / min, or 800 r / min), and the stirring time is 1-3 h (for example, it can be 1 h, 2 h or 3 h).

[0052] In the preparation method of the modified lithium supplement agent, as an optional embodiment, the mass ratio of the lithium phosphate salt to the Li2NiO2 is (3-5):100, for example, it can be 3:100, 4:100 or 5:100.

[0053] In the preparation method of the above-mentioned modified lithium supplement agent, as an optional embodiment, in step S3, the mixture is mixed evenly by ball milling, and the ball milling includes ball milling at 400-500 rpm (for example, 500 rpm, 500 rpm, 500 rpm, 500 rpm) for 2-4 h (for example, 2 h, 3 h or 4 h).

[0054] In the preparation method of the modified lithium supplement agent, as an optional embodiment, in step S3, the drying temperature includes 70 to 90°C (for example, 70°C, 80°C or 90°C), and the drying time includes 2 to 4 hours (for example, 2 hours, 3 hours or 4 hours).

[0055] In the above-mentioned method for preparing the modified lithium supplement agent, as an optional embodiment, in step S4, the sintering atmosphere includes an air atmosphere.

[0056] In the preparation method of the modified lithium supplement agent, as an optional embodiment, in step S4, the sintering includes a primary sintering and a secondary sintering, the primary sintering temperature is 300-400°C (for example, 300°C, 320°C, 340°C, 360°C, 380°C or 400°C), the primary sintering time is 1-2.5 hours, and the primary sintering promotes the bonding of the two materials. The secondary sintering temperature is 550-650°C (for example, 550°C, 570°C, 590°C, 610°C, 630°C or 650°C), and the secondary sintering time is 2-3 hours. The secondary sintering can ensure that Li3PO4 or LiH2PO4 is fully covered on the surface of the lithium supplement agent Li2NiO2. If the sintering time is too long, the coated product will further sinter into agglomerates, increasing the particle size of the final product and causing particles to appear during homogenization.

[0057] In the preparation method of the modified lithium supplement agent, as an optional embodiment, in step S4, the heating rate of the primary sintering is 5-10°C / min, for example, it can be 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min or 10°C / min.

[0058] In the preparation method of the modified lithium supplement agent, as an optional embodiment, in step S4, the heating rate of the secondary sintering is 5-10°C / min, for example, it can be 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min or 10°C / min.

[0059] In the preparation method of the modified lithium supplement agent, as an optional embodiment, the D50 particle size distribution of the modified lithium supplement agent is 11 to 15 μm.

[0060] In a second aspect, the present invention provides a modified lithium supplement agent, which is prepared by the preparation method described in the first aspect.

[0061] In the above-mentioned modified lithium supplement agent, as an optional embodiment, the modified lithium supplement agent includes Li2NiO2 and lithium phosphate salt, and the lithium phosphate salt is coated on the surface of the Li2NiO2.

[0062] In a third aspect, the present invention provides a positive electrode plate, comprising a positive electrode current collector and a positive electrode active layer covering at least one surface of the positive electrode current collector; the positive electrode active layer comprises the modified lithium supplement agent described in the second aspect, or the modified lithium supplement agent prepared by the preparation method described in the first aspect.

[0063] Those skilled in the art can add the modified lithium supplement agent to the positive electrode slurry according to the existing method and prepare a positive electrode sheet. As an example, the preparation method of the positive electrode sheet is: mixing the modified lithium supplement agent with the positive electrode active material, the conductive agent and the binder to obtain the positive electrode slurry, and coating the positive electrode slurry on the positive electrode current collector, baking it, and obtaining the positive electrode sheet. Among them, the currently common positive electrode active materials have significantly improved positive electrode sheet effects after adding the modified lithium supplement agent of the present invention. For example, the above-mentioned positive electrode active materials include but are not limited to any one or more of lithium iron phosphate, lithium nickel cobalt manganese oxide and lithium-rich manganese-based materials.

[0064] In the above-mentioned positive electrode sheet, as an optional embodiment, the positive electrode active layer also includes a positive electrode active material, and the mass ratio of the positive electrode active material to the modified lithium supplement agent is 100:(0.5~5), for example, it can be 100:0.5, 100:1, 100:2, 100:3, 100:4 or 100:5.

[0065] In a fourth aspect, the present invention provides a lithium-ion battery, comprising the positive electrode sheet described in the third aspect.

[0066] The present invention will be further described in detail below with reference to specific examples and comparative examples.

[0067] Example 1

[0068] This embodiment provides a method for preparing a modified lithium supplement agent, comprising the following steps:

[0069] Take 1.2g Li3PO4 and dissolve it in 12g deionized water, ultrasonicate it in a water bath at 60℃ for 30min to obtain an aqueous solution of Li3PO4; then add 28.8g lithium supplement Li2NiO2 to 288g ethanol solution, stir at high speed, stirring at 600r / min, stir for 60min to obtain a uniform suspension (dispersion); then add the aqueous solution of Li3PO4 to the dispersion of lithium supplement Li2NiO2, put it into a ball mill, ball mill at a speed of 400rpm for 2h, with a ball-to-material ratio of 10:1 (mass ratio), to obtain a uniform Li3PO4 The method comprises the following steps: preparing a mixture of coated lithium supplement agent Li2NiO2; baking the mixture in a forced air drying oven at 90°C for 2 hours to ensure that the material is dried and the solvent (water and ethanol) is removed; sintering the dried mixture at high temperature in an air atmosphere in two stages, first heating to 300°C at 5°C / min, sintering at 300°C for 1.5 hours, then heating to 560°C at 5°C / min, sintering at 560°C for 2.5 hours, and then naturally cooling to room temperature; finally, mechanically crushing the sintered product to ensure that the D50 particle size of the final product is 13.7um to obtain a modified lithium supplement agent.

[0070] Figure 1 This is the SEM image of the modified lithium supplement prepared in the embodiment of the present invention. Figure 1 It can be seen that the surface of Li2NiO2 is covered with fine particles.

[0071] Example 2

[0072] This embodiment provides a method for preparing a modified lithium supplement agent, comprising the following steps:

[0073] 1.2g of LiH2PO4 was dissolved in 12g of deionized water and ultrasonicated in a 60°C water bath for 30min to obtain an aqueous solution of LiH2PO4; 28.8g of lithium supplement Li2NiO2 was then added to 288g of ethanol solution and stirred at a high speed of 700r / min for 60min to obtain a uniformly mixed suspension (dispersion); the aqueous solution of LiH2PO4 was then added to the dispersion of lithium supplement Li2NiO2 and ball milled at 450rpm for 2h with a ball-to-material ratio of 10:1 (mass ratio) to obtain LiH2PO4. The method comprises the following steps: preparing a mixture of uniformly coated lithium supplement agent Li2NiO2; baking the mixture in a forced air drying oven at 90°C for 2 hours to ensure that the material is dried and the solvent (water and ethanol) is removed; sintering the dried mixture at high temperature in an air atmosphere in two stages, first heating to 330°C at a rate of 5°C / min, sintering at 330°C for 1.5 hours, then heating to 600°C at a rate of 5°C / min, sintering at 600°C for 2.5 hours, and then naturally cooling to room temperature; finally, mechanically crushing the sintered product to ensure that the D50 particle size of the final product is 12.5um to obtain a modified lithium supplement agent.

[0074] Figure 2 This is the SEM image of the modified lithium supplement prepared in the embodiment of the present invention. Figure 2 It can be seen that the surface of Li2NiO2 is covered by fine particles, and the surface coating is fine and uniform.

[0075] Example 3

[0076] This embodiment provides a method for preparing a modified lithium supplement agent, comprising the following steps:

[0077] 1.2g of Li3PO4 was dissolved in 12g of deionized water and ultrasonicated in a water bath at 60°C for 30min to obtain an aqueous solution of Li3PO4. 28.8g of lithium supplement Li2NiO2 was then added to 288g of ethanol solution and stirred at high speed (700r / min) for 60min to obtain a uniformly mixed suspension (dispersion). The aqueous solution of Li3PO4 was then added to the dispersion of lithium supplement Li2NiO2 and ball milled at 400rpm for 2h with a ball-to-material ratio of 10:1 (mass ratio) to obtain Li3PO4. The method comprises the following steps: preparing a mixture of uniformly coated lithium supplement agent Li2NiO2; baking the mixture in a forced air drying oven at 90°C for 2 hours to ensure that the material is dried and the solvent (water and ethanol) is removed; sintering the dried mixture at high temperature in an air atmosphere in two stages, first heating to 400°C at a rate of 5°C / min, sintering at 400°C for 1 hour, then heating to 650°C at a rate of 5°C / min, sintering at 650°C for 2 hours, and then naturally cooling to room temperature; finally, mechanically crushing the sintered product to ensure that the D50 particle size of the final product is 13.2um to obtain a modified lithium supplement agent.

[0078] Comparative Example 1

[0079] Compared with Examples 1-3, the difference is that Li3PO4 or LiH2PO4 is not coated on the surface of the lithium supplement agent Li2NiO2, and the lithium supplement agent provided in this comparative example is Li2NiO2.

[0080] Figure 3 This is the SEM image of the conventional lithium supplement Li2NiO2. The surface of pure Li2NiO2 is smooth. Figure 1 and Figure 2 After comparison, it was found that after the surface was coated, the particles became rough and the surface of the particles was evenly coated with small particles.

[0081] Comparative Example 2

[0082] The preparation method of the modified lithium supplement agent provided in this comparative example is basically the same as that in Example 1, except that 28.8 g of lithium supplement agent Li2NiO2 is directly added to the aqueous solution of Li3PO4, and then placed in a ball mill for milling.

[0083] Comparative Example 3

[0084] The preparation method of the modified lithium supplement agent provided in this comparative example is basically the same as that in Example 1, except that 1.2 g of Li3PO4 is dispersed in 12 g of ethanol, and the mixture is ultrasonicated in a 60°C water bath for 30 min to obtain an ethanol solution of Li3PO4; then 28.8 g of the lithium supplement agent Li2NiO2 is directly added to the ethanol solution of Li3PO4, and then the mixture is placed in a ball mill for ball milling.

[0085] Comparative Example 4

[0086] The preparation method of the modified lithium supplement provided in this comparative example is basically the same as that in Example 1, except that 1.2 g of Li3PO4 is dispersed in 300 g of ethanol and ultrasonicated in a 60°C water bath for 30 min to obtain an ethanol solution of Li3PO4; then 28.8 g of the lithium supplement agent Li2NiO2 is directly added to the ethanol solution of Li3PO4, and then the mixture is placed in a ball mill for ball milling.

[0087] Comparative Example 5

[0088] The preparation method of the modified lithium supplement agent provided in this comparative example is basically the same as that in Example 1, except that 1.2g of Li3PO4 and 28.8g of lithium supplement agent Li2NiO2 are dry ball milled and then sintered. The dry ball milling includes dry ball milling 1.2g of Li3PO4 and 28.8g of lithium supplement agent Li2NiO2 in a mixture of argon and oxygen (oxygen partial pressure of 180ppm) at a speed of 100rpm for 8h to obtain a mixed product, wherein the ball-to-material ratio is 10:1 (mass ratio).

[0089] Comparative Example 6

[0090] The preparation method of the modified lithium supplement agent provided in this comparative example is basically the same as that of Example 1, except that 1.2 g of Li3PO4 is dissolved in 58.8 g of deionized water.

[0091] Comparative Example 7

[0092] The preparation method of the modified lithium supplement agent provided in this comparative example is basically the same as that of Example 1, except that only one sintering is performed, the temperature is raised to 560°C at 5°C / min, sintered at 560°C for 4 hours, and then naturally cooled to room temperature.

[0093] Performance Testing

[0094] Make the lithium supplement into a battery and evaluate its performance:

[0095] ① Preparation of lithium supplement electrode: Mix the lithium supplement Li2NiO2 material in the above implementation and comparative examples with PVDF and SP at a ratio of 8:1:1 to prepare a slurry, and coat it on the surface of 13um aluminum foil on both sides. The single-side coating density is 10.0±0.2mg / cm 2 ; Dry the coated electrode and roll it to 91±2um (total thickness of the electrode);

[0096] ② Preparation of negative electrode sheet: Take the commonly used graphite negative electrode on the market (charge capacity> 360mAh / g, discharge capacity> 350mAh / g), mix graphite: SP: CMC: SBR = 96.0%: 1.2%: 1.2%: 1.6% to prepare a mixed slurry, and coat it on the surface of 6um copper foil on both sides, with a single-side coating density of 10.3±0.2mg / cm 2 ; Dry the coated electrode and roll it to 135±2um (total thickness of the electrode); positive and negative electrode charge NP ratio = 1.06;

[0097] ③ Assembly: Cut the positive electrode sheet into 50mm*60mm small pieces, and the negative electrode into 55mm*65mm small pieces. Take 10 positive electrode sheets and 11 negative electrode sheets to make a laminated soft-pack battery; bake until the moisture content of the positive and negative electrodes is less than 200ppm;

[0098] ④ Liquid injection activation: inject 6g electrolyte, seal the bottle; age at high temperature 45℃ for 24h, and then activate it;

[0099] ⑤The activation process is as follows:

[0100] 1) Let stand for 4 hours;

[0101] 2) Charge at 0.1C constant current and constant voltage to 4.2V, with a cut-off current of 0.05C. Record the charge capacity and calculate the charge capacity in grams. The results are shown in Table 1.

[0102] 3) Let it stand for 10 minutes;

[0103] ⑥45℃ cycle test:

[0104] 1) Let stand for 10 minutes; 2) Charge at 0.5C constant current and constant voltage to 4.2V, with a cut-off current of 0.05C; 3) Let stand for 10 minutes; 4) Discharge at 0.5C constant current to 2.5V; 5) Cycle 1) to 4) for 500 cls;

[0105] ⑦55℃ 7day high temperature storage test:

[0106] Take the activated battery cell (100% SOC) and place it in a 55°C environment for 7 days. Measure the battery volume before and after storage to confirm the difference in gas production.

[0107] The test results are shown in Table 1.

[0108] Table 1

[0109]

[0110] From Table 1, we can see at least the following points:

[0111] (1) It can be seen from Examples 1-3 and Comparative Example 1 that after coating, the charge capacity is equivalent to that of Comparative Example 1, and the coating has little effect on the material capacity. Secondly, the cycle trend of the improved examples is significantly better than that of Comparative Example 1 when cycled at high temperature of 45°C. The gas production after storage at 55°C for 7 days is also significantly reduced, and the gas production is suppressed. This shows that the coating has an improving effect on the stability of the lithium supplement.

[0112] (2) Comparing Example 1 with Comparative Examples 2-4, it can be seen that directly adding Li2NiO2 to the Li3PO4 solution will cause the cycle performance of the obtained lithium supplement at 45°C to decrease, and the gas production after storage at 55°C for 7 days will also increase significantly. The applicant speculates that the reason may be uneven coating.

[0113] (3) Comparing Example 1 with Comparative Example 5, it can be seen that the dry ball milling method results in a lower gram capacity of the obtained lithium supplement, a decrease in the cycle performance at 45°C, and a significant increase in the gas production after storage at 55°C for 7 days.

[0114] (4) Comparison of Example 1 with Comparative Example 6 shows that when the water content in the Li3PO4 solution is too high, the capacity of the lithium supplement agent will be affected, resulting in a decrease in the cycle performance of the obtained lithium supplement agent at 45°C and a significant increase in the gas production after storage at 55°C for 7 days.

[0115] (5) Comparing Example 1 with Comparative Example 7, it can be seen that using only one sintering step and sintering at a higher temperature will cause the cycle performance of the obtained lithium supplement to decrease at 45°C, and the gas production after storage at 55°C for 7 days will also increase significantly.

[0116] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a modified lithium supplement agent, characterized in that: The preparation method comprises the following steps: S1. Add lithium phosphate salt to water and stir until dissolved to obtain an aqueous solution of the coating layer; S2, dispersing the lithium supplement Li2NiO2 in an alcohol solvent and stirring evenly to obtain a Li2NiO2 suspension; S3, adding the aqueous solution of the coating layer to the suspension of Li2NiO2, mixing them evenly, and drying to obtain a mixture; S4, sintering the mixture, and crushing it after cooling to obtain the modified lithium supplement agent.

2. The method for preparing the modified lithium supplement agent according to claim 1, wherein The lithium phosphate salt includes one of Li3PO4 and LiH2PO4.

3. The preparation method of the modified lithium supplement agent according to claim 1, characterized in that: In step S1, the mass percentage of the lithium phosphate salt in the aqueous solution of the coating layer is 5% to 15%; And / or, in step S1, the stirring includes ultrasonic stirring at a water bath temperature of 50-70°C for 0.5-2h.

4. The method for preparing the modified lithium supplement agent according to claim 1, wherein In step S2, the alcohol solvent includes one of ethanol and methanol; And / or, in step S2, the mass percentage of Li2NiO2 in the Li2NiO2 suspension is 5% to 15%; And / or, in step S2, the stirring speed is 500-800 r / min, and the stirring time is 1-3 h.

5. The method for preparing the modified lithium supplement agent according to claim 1, wherein The mass ratio of the lithium phosphate salt to the Li2NiO2 is (3-5):100; and / or, in step S3, mixing uniformly by ball milling, wherein the ball milling comprises ball milling at 400-500 rpm for 2-4 hours; And / or, in step S3, the drying temperature is 70-90° C., and the drying time is 2-4 hours.

6. The method for preparing the modified lithium supplement agent according to claim 1, wherein: In step S4, the sintering atmosphere includes an air atmosphere; And / or, in step S4, the sintering includes a primary sintering and a secondary sintering, the primary sintering temperature is 300-400° C., the primary sintering time is 1-2.5 hours, the secondary sintering temperature is 550-650° C., and the secondary sintering time is 2-3 hours; And / or, in step S4, the heating rate of the primary sintering is 5-10°C / min; And / or, in step S4, the heating rate of the secondary sintering is 5-10°C / min.

7. The method for preparing the modified lithium supplement agent according to any one of claims 1 to 6, characterized in that: The D50 particle size of the modified lithium supplement agent is distributed between 11 and 15 μm.

8. A modified lithium supplement agent, characterized in that: The modified lithium supplement agent is prepared by the preparation method according to any one of claims 1 to 7.

9. A positive electrode plate, comprising a positive electrode current collector and a positive electrode active layer covering at least one surface of the positive electrode current collector, characterized in that: The positive electrode active layer comprises the modified lithium supplement agent according to claim 8, or the modified lithium supplement agent prepared by the preparation method according to any one of claims 1 to 7.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode sheet according to claim 9.

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