Self-repairing lithium ion battery positive electrode plate, preparation method thereof and lithium ion battery

Abstract

This application relates to a self-healing lithium-ion battery positive electrode sheet and its preparation method, belonging to the field of lithium-ion battery technology. The method includes: placing polyvinyl alcohol, soluble starch, and urea in a solvent and heating them to obtain a homogeneous solution; adding boric acid to the homogeneous solution and ultrasonically treating it to obtain a hydrogel; adding a positive electrode active material to the hydrogel and heating it in a water bath, then drying it to obtain a positive electrode active material; mixing the positive electrode active material, a conductive agent, a binder, and a solvent to form a slurry, coating the slurry onto a positive electrode current collector, and then drying it to obtain a self-healing lithium-ion battery positive electrode sheet. The positive electrode sheet prepared using the method described in this application has high self-healing capability and effectively improved conductivity.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to a self-healing lithium-ion battery positive electrode sheet and its preparation method, and a lithium-ion battery. Background Technology

[0002] Currently, lithium-ion batteries, as high-energy-density storage devices, dominate in electric vehicles, consumer electronics, and wearable devices. However, due to external stress or the effects of high-rate charge-discharge processes on electrode materials, microcracks can form in the positive electrode material due to volume contraction and expansion, and the negative electrode SEI film can have poor stability and be prone to rupture, ultimately affecting the lifespan of lithium batteries and even causing safety issues. To address these problems, some researchers have attempted to mitigate them by optimizing material formulations and improving battery structure design, but these solutions often sacrifice other performance parameters, such as energy density or cost, making comprehensive optimization difficult. Therefore, the concept of self-healing electrolyte materials has been proposed and applied to lithium-ion batteries. However, most of the solid-state self-healing polymer electrolytes currently studied suffer from low conductivity, which is related to the inability of the self-healing components to achieve lithium-ion transport. Summary of the Invention

[0003] The purpose of this application is to address the shortcomings of existing lithium-ion batteries, which struggle to simultaneously achieve self-healing capabilities and low conductivity. This application proposes a self-healing lithium-ion battery positive electrode sheet, its preparation method, and the lithium-ion battery itself. The positive electrode is prepared by coating the positive electrode active material with a specific hydrogel electrolyte repair agent. This positive electrode can automatically fill cracks and regenerate a stable interface layer. Simultaneously, this positive electrode, a polymer with dynamic bonding properties as a negative electrode binder, and an electrolyte containing specific additives are compounded to prepare the lithium-ion battery. This allows the lithium-ion battery to slow down capacity decay and effectively improve conductivity under high-voltage fast charging conditions, while maintaining high-rate charge-discharge performance.

[0004] Firstly, the method for preparing a self-healing lithium-ion battery positive electrode sheet provided in this application adopts the following technical solution: the preparation method includes the following steps: S1. Polyvinyl alcohol, soluble starch and urea are placed in a solvent and heated to obtain a homogeneous solution. Boric acid is added to the homogeneous solution and ultrasonically treated to obtain a hydrogel. S2. Add the positive electrode active material to the hydrogel, heat it in a water bath, and then dry it to obtain the positive electrode active material; S3. The positive electrode active material, conductive agent, binder and solvent are mixed to form a slurry, and the slurry is coated on the positive electrode current collector and then dried to obtain a self-healing lithium-ion battery positive electrode sheet.

[0005] Through the above technical solution, the hydroxyl groups of polyvinyl alcohol (PVA) and boric acid form dynamic borate bonds in aqueous solution. When subjected to mechanical damage, the borate bonds break and can reversibly recombine upon contact with water or heating, achieving self-repair. The hydroxyl groups of starch molecular chains form a hydrogen-bonded interpenetrating structure with the PVA / boric acid network, enhancing the mechanical strength of the gel. At the same time, the branched structure of starch increases the crosslinking point density, inhibiting crack propagation. Meanwhile, urea-mediated intermolecular hydrogen bonds can enhance toughness, plasticize, and promote dynamic recombination, thereby accelerating the recombination rate after the borate bonds break. The PVA-starch-urea-boric acid system achieves rapid self-repair capability of hydrogel through the dual network of dynamic borate bonds and hydrogen bonds. This hydrogel is used in conjunction with positive electrode active materials to prepare positive electrode active materials. The positive electrode prepared using these positive electrode active materials meets the requirements of lithium-ion battery positive electrodes for interface stability, and the lithium-ion diffusion coefficient is effectively improved, thereby increasing conductivity.

[0006] Optionally, in step S1, based on the total mass of the polyvinyl alcohol, soluble starch, urea, boric acid, and solvent as 100%, the content of the polyvinyl alcohol is 8-12%, specifically, for example, 8%, 9%, 10%, 11%, or 12%; the content of the soluble starch is 1.5-5%, specifically, for example, 1.5%, 2%, 3%, 4%, or 5%; the content of the urea is 4-10%, specifically, for example, 4%, 5%, 6%, 7%, 8%, 9%, or 10%; the content of the boric acid is 0.5-2%, specifically, for example, 0.5%, 1%, 1.5%, or 2%; and the content of the solvent is 75-85%, specifically, for example, 75%, 78%, 80%, 83%, or 85%.

[0007] By further optimizing the proportions of raw materials in the preparation process of the self-healing hydrogel through the above technical solutions, the crack propagation of the prepared lithium-ion battery cathode can be further reduced under high-voltage fast charging conditions, while the battery capacity decay can be further slowed down.

[0008] In a specific embodiment of the preparation method described in this application, in step S1, the solvent can be a conventional choice in the art, as long as it can sufficiently dissolve polyvinyl alcohol, soluble starch and urea. Specifically, the solvent is water.

[0009] In a specific embodiment of the preparation method described in this application, in step S1, the conditions for ultrasonic treatment are: power of 300~500W and time of 5~10 min.

[0010] Optionally, in step S2, the positive electrode active material is alumina-coated lithium-rich manganese-based material, wherein the average particle size of the alumina-coated lithium-rich manganese-based material is 10~13 μm, and the specific surface area is 1~10 m². 2 / g; the mass ratio of the alumina-coated lithium-rich manganese group to the hydrogel is 3~5:10, specifically, for example, it can be 3:10, 3.5:10, 4:10, 4.5:10 or 5:10.

[0011] Through the above technical solution, lithium-rich manganese-based aluminum oxide with a certain particle size and specific surface area is selected as the positive electrode active material. The positive electrode active material is synergistically prepared with a hydrogel with self-healing ability to prepare a lithium-ion battery positive electrode. The lithium-ion battery prepared using this positive electrode can maintain high-rate charge and discharge performance under high-voltage fast charging conditions while reducing the capacity decay rate.

[0012] Optionally, in step S1, the conditions for the heat treatment include: a temperature of 90~95 ℃ and a time of 25~35 min; In step S2, the conditions for water bath heating include: a temperature of 50~60 ℃ and a time of 40~50 min; In step S2, the specific drying method is as follows: the system heated in a water bath is dried for the first time at 75~80 ℃, the system dried for the first time is dried for the second time at 95~105 ℃, and the system dried for the second time is dried for the third time at 115~125 ℃. The drying times for the first, second and third drying are 15~25 min, 55~65 min and 5~15 min, respectively.

[0013] The above technical solution ensures the dissolution of polyvinyl alcohol, soluble starch, and urea by heating at 90-95℃ for 25-35 minutes, while preventing premature decomposition of urea. Water bath heating at 50-60℃ for 40-50 minutes allows the hydrogel to fully wet the surface of the active material particles and complete the dual dynamic cross-linking network of borate ester bonds and hydrogen bonds. The first drying at 75-80℃ removes residual solvent from the colloid surface, the second drying at 95-105℃ deeply removes hydrogen-bonded water, and the third drying at 115-125℃ enhances the crystallinity of the positive electrode active material, thereby improving its mechanical strength and interfacial stability.

[0014] In a specific embodiment of the preparation method described in this application, in step S3, the conductive agent, binder, solvent, and positive electrode current collector can all be conventionally selected in the art. Specifically, for example, the conductive agent can be superconducting carbon black, the binder can be sodium carboxymethyl cellulose, the solvent can be N-methylpyrrolidone (NMP), and the positive electrode current collector can be aluminum foil; the positive electrode active material, conductive agent, and binder are mixed in a ratio of 7:2:1.

[0015] In step S3, the drying conditions include a temperature of 55~65 ℃ and a time of 3~5 h. In actual operation, after drying, vacuum drying is also included, and the conditions for vacuum drying include a temperature of 55~65 ℃ and a time of 10~14 h.

[0016] Secondly, this application provides a self-healing lithium-ion battery positive electrode sheet prepared according to the preparation method described above.

[0017] Thirdly, this application provides a lithium-ion battery, including a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode is the self-healing lithium-ion battery positive electrode described above. The binder used for the negative electrode includes polyacrylate and polyvinyl alcohol. The electrolyte includes fluorine-containing compounds and rare earth elements.

[0018] Through the above technical solution, the carboxyl groups in polyacrylate and the hydroxyl groups in polyvinyl alcohol form a network with dynamic cross-linking points through hydrogen bonds. This network can be reversibly broken / reassembled under stress, buffering volume changes and maintaining interface integrity. The combination of fluorine-containing compounds and rare earth elements can stabilize the SEI layer and form a protective film. Through the self-healing ability of the positive electrode, the dynamic adaptability of the negative electrode, and the synergistic effect of electrolyte additives, the problem of accelerated battery capacity decay under high voltage fast charging conditions is solved, maintaining high-rate charge and discharge performance, while the conductivity is effectively improved.

[0019] Optionally, the mass ratio of the polyacrylate to the polyvinyl alcohol is 1:0.5 to 1.5, specifically, for example, 1:0.5, 1:1, or 1:1.5; the amount of the fluorinated compound added is 0.3 to 0.8% of the total electrolyte, specifically, for example, 0.3%, 0.5%, or 0.8%; the amount of the rare earth element added is 0.05 to 0.2% of the total electrolyte, specifically, for example, 0.05%, 0.1%, 0.15%, or 0.2%.

[0020] By limiting the ratio of polyacrylate to polyvinyl alcohol within a certain range and synergistically limiting the addition of fluorinated compounds and rare earth elements in the electrolyte, the volume change of the negative electrode can be further buffered, the SEI layer can be stabilized and a protective film can be formed, thereby maintaining the interface integrity and not hindering Li + The penetration of the SEI into the negative electrode will not adversely affect the high-rate performance of the battery.

[0021] Further optionally, the fluorinated compound is lithium hexafluorophosphate, and the rare earth element is a lanthanide element, specifically, for example, selected from one or more of lanthanum, cerium, and gadolinium.

[0022] Through the above technical solution, LiPF6 decomposes to generate LiF, which can fill the defects in the SEI layer. LiPF6 and lanthanide elements form a rare earth oxide / fluoride composite protective film, which enhances mechanical strength, reduces electrolyte decomposition under high voltage, and thus slows down capacity decay.

[0023] Alternatively, the lanthanide element may be lanthanum.

[0024] The above technical solution further limits the lanthanide elements to lanthanum, and the lanthanum ion (La) 3+ ) and fluoride ions (F) produced by the decomposition of lithium hexafluorophosphate (LiPF6) - Combined with the generated LaF3, LaF3 further enhances the stability and mechanical strength of the SEI layer, while also improving rate performance.

[0025] Optionally, the conductive agent used in the positive electrode and the negative electrode is a graphene / carbon nanotube composite material, wherein the graphene sheet diameter in the graphene / carbon nanotube composite material is 5~15 μm, the outer diameter of the carbon nanotube is 5~15 nm, and the electrical conductivity of the graphene / carbon nanotube composite material is 300~600 S / cm.

[0026] By employing the above technical solutions and using specific graphene / carbon nanotube composite materials as positive and negative electrode conductive agents, the internal resistance of the battery can be significantly reduced, the rate performance and cycle life can be improved, and the self-healing ability of the positive electrode, the dynamic adaptability of the negative electrode and specific electrolyte additives can be combined to slow down the capacity decay rate of lithium-ion batteries under high voltage fast charging conditions, effectively improve the conductivity, and maintain high rate charge and discharge performance.

[0027] In specific embodiments of the lithium-ion battery described in this application, the separator can be a conventional choice in the art. In a preferred embodiment, the separator is a polyimide lithium-ion battery separator.

[0028] In summary, this application includes at least one of the following beneficial technical effects: 1. In the preparation process of the self-healing lithium-ion battery positive electrode sheet described in this application, the hydroxyl groups of polyvinyl alcohol (PVA) and boric acid form dynamic borate ester bonds in an aqueous solution to achieve self-healing. The starch molecular chain improves the mechanical strength and inhibits crack propagation. Urea accelerates the recombination rate of the dynamic borate ester bonds. Through the synergistic system of polyvinyl alcohol, starch, urea and boric acid, the hydrogel achieves rapid self-healing capability. The hydrogel is then used together with the positive electrode active material to prepare the positive electrode active material. The battery positive electrode prepared using this positive electrode active material meets the requirements of lithium-ion battery positive electrode for interface stability, and the lithium-ion diffusion coefficient is effectively improved, thereby improving the conductivity. 2. In a preferred embodiment, by selecting alumina with a certain particle size and specific surface area to coat lithium-rich manganese-based material as the positive electrode active material, lithium-ion batteries can maintain high-rate charge and discharge performance under high-voltage fast charging conditions while reducing the capacity decay rate. 3. The lithium-ion battery described in this application uses polyacrylate and polyvinyl alcohol as a composite binder for the negative electrode. The polyacrylate and polyvinyl alcohol form a network with dynamic cross-linking points, which buffers volume changes and maintains interface integrity. The addition of fluorine-containing compounds and rare earth elements to the electrolyte can stabilize the SEI layer and form a protective film without affecting the battery's rate performance. Through the self-healing ability of the positive electrode, the dynamic adaptability of the negative electrode, and the synergistic effect of electrolyte additives, the problem of accelerated battery capacity decay under high voltage fast charging conditions is solved, maintaining high rate charge and discharge performance, while the conductivity is effectively improved. 4. In a preferred embodiment, by limiting the rare earth element to lanthanum, the stability and mechanical strength of the SEI layer of the lithium-ion battery can be further enhanced, while the ionic conductivity and rate performance can be improved. Detailed Implementation

[0029] The present application will be further described in detail below with reference to specific embodiments.

[0030] The following examples further illustrate the self-healing lithium-ion battery positive electrode sheet and its preparation method, as well as the lithium-ion battery described in this application. The examples are implemented based on the technical solution of this application, providing detailed implementation methods and specific operating procedures; however, the scope of protection of this application is not limited to the following examples.

[0031] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0032] Polyvinyl alcohol: Purchased from Shanghai Aladdin Reagent Co., Ltd., product number P752227; Soluble starch: Purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., product number S104452; Superconducting carbon black: Purchased from Shenzhen Kejing Zhida Technology Co., Ltd., model ECP-600JD; Sodium carboxymethyl cellulose (binder): Purchased from Shenzhen Kejing Zhida Technology Co., Ltd., MS-Daicel2200 (Japan Daicel) high-performance CMC sodium carboxymethyl cellulose; Polyacrylate: Purchased from Shanghai Yingxin Laboratory Equipment Co., Ltd., item number TX2216-500g; Aluminum foil: Purchased from Shenzhen Kejing Zhida Technology Co., Ltd., ultra-high gyrnet aluminum foil; Copper foil: Purchased from Shenzhen Kejing Zhida Technology Co., Ltd., battery-specific carbon-coated copper foil; The diaphragm was purchased from Shenzhen Kejing Zhida Technology Co., Ltd., and is a PE substrate coated with double-sided polyimide diaphragm. Electrolyte: Purchased from Suzhou Duoduo Chemical Technology Co., Ltd., Product No.: LB-370; Negative electrode active material: Purchased from Shenzhen Kejing Zhida Technology Co., Ltd., porous silicon-carbon lithium battery negative electrode material; Lithium manganese oxide MS-WJ-2100 (positive electrode active material): purchased from Shenzhen Kejing Zhida Technology Co., Ltd. Alumina-coated lithium-rich manganese-based cathode active material: purchased from Shenzhen Kejing Zhida Technology Co., Ltd., with an average particle size of 10~13 μm and a specific surface area of ​​1~10 m². 2 / g; Graphene / carbon nanotube composite material (conductive agent): Purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., item number 105035, graphene sheet diameter 5~15 μm, carbon nanotube outer diameter 5~15 nm, electrical conductivity 300~600 S / cm.

[0033] Examples 1-7 and Comparative Examples 1-2 illustrate the preparation of positive electrode sheets for lithium-ion batteries.

[0034] Example 1 A method for preparing a self-healing positive electrode sheet for a lithium-ion battery, the method comprising the following steps: S1. Place 10% polyvinyl alcohol, 3% soluble starch and 5% urea in 80% deionized water and heat at 92 °C for 30 min. Continue stirring for 30 min to obtain a homogeneous solution. Add 2% boric acid to the homogeneous solution and sonicate at 500 W for 5 min to obtain a hydrogel. S2. Add lithium manganese oxide MS-WJ-2100 (positive electrode active material) to the hydrogel and heat it in a water bath at 60 °C for 45 min. Dry the system after water bath heating at 75 °C for 20 min, then dry it a second time at 100 °C for 60 min, and finally dry it a third time at 120 °C for 10 min to obtain the positive electrode active material. The mass ratio of lithium manganese oxide MS-WJ-2100 to the hydrogel is 5:10. S3. The positive electrode active material, superconducting carbon black (conductive agent) and sodium carboxymethyl cellulose (binder) are mixed in a mass ratio of 8:1:1, and the mixture is added to N-methylpyrrolidone and stirred for 24 h to obtain a slurry. The solid content of the slurry is 30%. The slurry is coated on aluminum foil and then vacuum dried at 80 °C for 12 h to obtain a self-healing lithium-ion battery positive electrode sheet.

[0035] Example 2 The method of Example 1 is followed, except that in step S2, all of the lithium manganese oxide MS-WJ-2100 (positive electrode active material) is replaced with lithium-rich manganese-based material coated with alumina.

[0036] Example 3 The procedure was carried out in accordance with Example 2, except that the mass ratio of the lithium-rich manganese-based aluminum oxide coating to the hydrogel was 3:10.

[0037] Example 4 The procedure was carried out as described in Example 3, except that in step S1, 12% polyvinyl alcohol, 1.5% soluble starch and 4% urea were placed in 82% deionized water and heated at 92 °C for 30 min, and stirred for another 30 min to obtain a homogeneous solution. 0.5% boric acid was added to the homogeneous solution and ultrasonically treated at 500 W for 5 min to obtain a hydrogel.

[0038] Example 5 The procedure was carried out as described in Example 3, except that in step S1, 8% polyvinyl alcohol, 5% soluble starch and 10% urea were placed in 76% deionized water and heated at 92 °C for 30 min, and stirred for another 30 min to obtain a homogeneous solution. 1% boric acid was added to the homogeneous solution and ultrasonically treated at 500 W for 5 min to obtain a hydrogel.

[0039] Example 6 The process was carried out in accordance with Example 3, except that in step S2, lithium-rich manganese oxide coated with alumina was added to the hydrogel, and the system was heated in a water bath at 60 °C for 45 min. The system after water bath heating was then dried at 100 °C for 120 min to obtain the positive electrode active material.

[0040] Example 7 The method is implemented in accordance with Example 3, except that in step S3, all superconducting carbon black is replaced with graphene / carbon nanotube composite material.

[0041] Comparative Example 1 The method is implemented in accordance with Example 3, except that in step S1, all 5% urea is replaced with 5% soluble starch, that is, 10% polyvinyl alcohol and 8% soluble starch are placed in 80% deionized water.

[0042] Comparative Example 2 The method is implemented in accordance with Example 3, except that in step S1, all 3% soluble starch is replaced with 3% urea, that is, 10% polyvinyl alcohol and 8% urea are placed in 80% deionized water.

[0043] Application Example 1 The soft-pack lithium-ion battery is manufactured using a soft-pack stacking process. The specific method is as follows: (1) Preparation of negative electrode sheet: The porous silicon-carbon lithium battery negative electrode material, binder (polyacrylate and polyvinyl alcohol in a mass ratio of 1:1) and graphene / carbon nanotube composite material are mixed in a mass ratio of 8:1:1. The mixture is added to deionized water and stirred for 24 h to obtain a slurry. The solid content of the slurry is 30%. The slurry is coated on copper foil and dried in an oven at 80 °C for 12 h to obtain the negative electrode sheet. (2) The positive electrode sheet described in Example 7, the negative electrode sheet described in Example 1, and the double-sided polyimide separator coated on the PE substrate are stacked, assembled, and baked until the moisture content is qualified. An electrolyte containing lithium hexafluorophosphate and lanthanum is injected, wherein the amount of lithium hexafluorophosphate added is 0.5% of the total electrolyte and the amount of lanthanum added is 0.1% of the total electrolyte. After hot pressing formation and high temperature standing, the battery is packaged, and after capacity testing, it is placed at room temperature to obtain a soft-pack finished battery. The electrochemical performance of the battery is tested.

[0044] Application Example 2 The method is implemented in accordance with Application Example 1, except that in the preparation of the negative electrode sheet in step (1), the mass ratio of polyacrylate to polyvinyl alcohol is 1:0.5.

[0045] Application Example 3 The method is implemented in accordance with Application Example 1, except that in the preparation of the negative electrode sheet in step (1), the mass ratio of polyacrylate to polyvinyl alcohol is 1:1.5.

[0046] Application Example 4 The method is implemented in accordance with Application Example 1, except that in step (2), the amount of lithium hexafluorophosphate added is 0.3% of the total electrolyte and the amount of lanthanum added is 0.05% of the total electrolyte.

[0047] Application Example 5 The method is implemented in accordance with Application Example 1, except that in step (2), the amount of lithium hexafluorophosphate added is 0.8% of the total electrolyte and the amount of lanthanum added is 0.2% of the total electrolyte.

[0048] Application Example 6 The application is carried out in the manner described in Example 1, except that in step (2), all lanthanum is replaced with cerium.

[0049] Application Examples 7-12: Implemented in the same manner as Application Example 1, except that the positive electrode sheet described in Example 7 is replaced with the positive electrode sheet described in Examples 1-6 respectively. That is, Application Example 7 uses the positive electrode sheet described in Example 1, Application Example 8 uses the positive electrode sheet described in Example 2, Application Example 9 uses the positive electrode sheet described in Example 3, Application Example 10 uses the positive electrode sheet described in Example 4, Application Example 11 uses the positive electrode sheet described in Example 5, and Application Example 12 uses the positive electrode sheet described in Example 6.

[0050] Application Comparative Example 1 The application is carried out in the manner described in Example 1, except that the positive electrode sheet described in Example 7 is replaced with the positive electrode sheet described in Comparative Example 1.

[0051] Application Comparative Example 2 The application is carried out in the manner described in Example 1, except that the positive electrode sheet described in Example 7 is replaced with the positive electrode sheet described in Comparative Example 2.

[0052] Application Comparative Example 3 The application is carried out in the manner described in Example 1, except that in step (1), the adhesive (polyacrylate and polyvinyl alcohol in a mass ratio of 1:1) is completely replaced with sodium carboxymethyl cellulose.

[0053] Application Comparative Example 4 The application is carried out in the manner described in Example 1, except that in step (1), all polyacrylate is replaced with polyvinyl alcohol.

[0054] Application Comparative Example 5 The application is carried out in the manner described in Example 1, except that in step (1), all polyvinyl alcohol is replaced with polyacrylate.

[0055] Application Comparative Example 6 The method is implemented in accordance with Application Example 1, except that in step (2), an electrolyte containing lithium hexafluorophosphate is injected, wherein the amount of lithium hexafluorophosphate added is 0.6% of the total amount of electrolyte.

[0056] Application Comparative Example 7 The method is implemented in accordance with Application Example 1, except that in step (2), an electrolyte containing lanthanum is injected, wherein the amount of lanthanum added is 0.6% of the total amount of electrolyte.

[0057] Test case Self-healing performance (crack repair rate) test: A 2 μm wide crack was pre-fabricated on the surface of the prepared electrode using focused ion beam (FIB) and placed on a 60 ℃ hot stage under a pressure of 5 MPa for 10 min. The crack morphology was observed by scanning electron microscopy (SEM), and the crack width change rate was analyzed using image analysis software (ImageJ). The crack repair rate was calculated according to the formula (initial width - repaired width) / initial width × 100%. Electrode resistance test: Peel the electrode from the current collector surface with insulating tape and test the electrode resistivity with a four-probe tester; Cyclic performance test: At 25 ℃, the LAND-CT2001A battery test system was used to conduct 10C and 20C rate cycle tests respectively, and the capacity retention rate after 500 cycles was recorded. The charging mode was constant current-constant voltage (1C), and the discharging mode was constant current to the cutoff voltage. The test voltage was 4.3V.

[0058] The crack repair rate and resistivity of the positive electrode sheets prepared in Examples 1-7 and Comparative Examples 1-2 were measured respectively, and the test results are shown in Table 1. Table 1

[0059] As can be seen from Table 1, the positive electrode sheets obtained by the preparation method of the self-healing lithium-ion battery positive electrode sheet described in this application in Examples 1 to 7 utilize the PVA-starch-urea-boric acid system to achieve rapid self-healing ability of the hydrogel through a dynamic borate ester bond + hydrogen bond double network, and effectively improve the lithium-ion diffusion coefficient, thereby improving the conductivity. Therefore, they all have high crack repair rate and low resistivity (good conductivity). In contrast, Comparative Examples 1 and 2 only use starch or urea to form a dynamic borate ester bond and hydrogen bond single network with PVA and boric acid. Although the hydrogel still has a certain self-healing ability, the repair effect is poor and the conductivity is poor.

[0060] The cycle performance of batteries prepared using Examples 1-12 and Comparative Examples 1-7 was tested respectively, and the test results are shown in Table 2. Table 2

[0061] As can be seen from the results in Table 2, the lithium-ion batteries prepared using the composition of the lithium-ion batteries described in this application in Application Examples 1-12 still have high cycle capacity retention at high rates. However, Application Comparative Examples 1-2 did not use the positive electrode sheet prepared in this application, resulting in poor high-rate performance of the prepared lithium-ion batteries. In Application Comparative Examples 3-5, the binder used in preparing the negative electrode sheet was not a combination of polyacrylate and polyvinyl alcohol, thus the high-rate performance of the prepared lithium-ion batteries was relatively poor. In Comparative Examples 6-7, no compound containing fluorine compounds and rare earth elements was added to the electrolyte during battery preparation, therefore the high-rate performance of the prepared lithium-ion batteries was slightly worse.

[0062] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application.

Claims

1. A method for preparing a self-healing positive electrode sheet for a lithium-ion battery, characterized in that, The preparation method includes the following steps: S1. Polyvinyl alcohol, soluble starch and urea are placed in a solvent and heated to obtain a homogeneous solution. Boric acid is added to the homogeneous solution and ultrasonically treated to obtain a hydrogel. S2. Add the positive electrode active material to the hydrogel, heat it in a water bath, and then dry it to obtain the positive electrode active material; S3. The positive electrode active material, conductive agent, binder and solvent are mixed to form a slurry, and the slurry is coated on the positive electrode current collector and then dried to obtain a self-healing lithium-ion battery positive electrode sheet.

2. The method for preparing the self-healing lithium-ion battery positive electrode sheet according to claim 1, characterized in that, In step S1, based on the total mass of the polyvinyl alcohol, soluble starch, urea, boric acid and solvent as 100%, the content of the polyvinyl alcohol is 8-12%, the content of the soluble starch is 1.5-5%, the content of the urea is 4-10%, the content of the boric acid is 0.5-2%, and the content of the solvent is 75-85%.

3. The method for preparing the self-healing lithium-ion battery positive electrode sheet according to claim 1 or 2, characterized in that, In step S2, the positive electrode active material is alumina-coated lithium-rich manganese-based material, wherein the average particle size of the alumina-coated lithium-rich manganese-based material is 10~13 μm, and the specific surface area is 1~10 m². 2 / g; The mass ratio of the alumina-coated lithium-rich manganese group to the hydrogel is 3~5:

10.

4. The method for preparing the self-healing lithium-ion battery positive electrode sheet according to claim 1 or 2, characterized in that, In step S1, the conditions for the heat treatment include: a temperature of 90~95 ℃ and a time of 25~35 min; In step S2, the conditions for water bath heating include: a temperature of 50~60 ℃ and a time of 40~50 min; In step S2, the specific drying method is as follows: the system heated in a water bath is dried for the first time at 75~80 ℃, the system dried for the first time is dried for the second time at 95~105 ℃, and the system dried for the second time is dried for the third time at 115~125 ℃. The drying times for the first, second and third drying are 15~25 min, 55~65 min and 5~15 min, respectively.

5. A self-healing lithium-ion battery positive electrode sheet prepared according to the preparation method of any one of claims 1 to 4.

6. A lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, characterized in that, The positive electrode is the self-healing lithium-ion battery positive electrode as described in claim 5, the binder used for the negative electrode includes polyacrylate and polyvinyl alcohol, and the electrolyte includes fluorine-containing compounds and rare earth elements.

7. The lithium-ion battery according to claim 6, characterized in that, The mass ratio of the polyacrylate to the polyvinyl alcohol is 1:0.5~1.5; The amount of the fluorine-containing compound added is 0.3-0.8% of the total amount of the electrolyte, and the amount of the rare earth element added is 0.05-0.2% of the total amount of the electrolyte.

8. The lithium-ion battery according to claim 7, characterized in that, The fluorine-containing compound is lithium hexafluorophosphate, and the rare earth element is a lanthanide element.

9. The lithium-ion battery according to claim 8, characterized in that, The lanthanide element mentioned is lanthanum.

10. The lithium-ion battery according to claim 6, characterized in that, The positive electrode and the negative electrode use a graphene / carbon nanotube composite material as the conductive agent, wherein the graphene sheet diameter is 5~15 μm, the carbon nanotube outer diameter is 5~15 nm, and the electrical conductivity of the graphene / carbon nanotube composite material is 300~600 S / cm.

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