Lithium battery with high energy density, long cycle life and thermal stability and preparation method thereof

Abstract

The application relates to a lithium battery with high energy density, long cycle life and thermal stability and a preparation method thereof, and belongs to the technical field of lithium ion batteries.The raw materials of a positive electrode slurry include a positive electrode active material, a positive electrode dopant, a positive electrode framework material and a first conductive agent, the positive electrode active material includes lithium nickel cobalt manganese oxide, the positive electrode dopant includes lithium iron phosphate, and the positive electrode framework material includes a lithium-rich manganese-based material.The raw materials of a negative electrode slurry include a negative electrode active material and a second conductive agent, the negative electrode active material includes a nano silicon-carbon composite, silicon monoxide and lithium titanate nanoparticles, and the second conductive agent includes graphene-coated graphite.The chemical formula of the silicon monoxide is SiO x , x is 0.8-1.2, the mass ratio of the nano silicon-carbon composite to the silicon monoxide is 1:2-5, and the mass ratio of the lithium iron phosphate to the lithium titanate nanoparticles is 1:0.8-1.2.The lithium battery prepared by the application simultaneously meets the requirements of high energy density, long cycle life and high thermal runaway temperature.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to lithium batteries with high energy density, long cycle life and thermal stability, and their preparation methods. Background Technology

[0002] Existing lithium-ion battery materials suffer from limitations of single-system design. For example, single cathode materials (such as ternary lithium nickel cobalt manganese oxide / NCM) have high energy density but poor cycle performance, while single lithium titanate anode materials have long lifespan but low energy density. On the other hand, single silicon-based anode materials have large capacity but high expansion rate. These limitations can lead to capacity decay, poor cycle performance, and the triggering of thermal runaway reactions in lithium-ion batteries. In particular, thermal runaway accidents in the battery systems of new energy vehicles have occurred frequently in recent years, and thermal safety, a core performance characteristic, has received widespread attention from the whole society. Furthermore, with the continuous development of lithium-ion batteries, the performance requirements for them are becoming increasingly stringent. However, current single-system lithium-ion batteries cannot simultaneously meet the requirements of high energy density, long cycle life, and low thermal runaway rate. Summary of the Invention

[0003] The purpose of this application is to address the shortcomings of existing lithium-ion batteries in simultaneously achieving high energy density, long cycle life, and high thermal runaway temperature. Therefore, this application proposes a lithium battery with high energy density, long cycle life, and thermal stability, along with its fabrication method. This application utilizes lithium-rich manganese-based materials, lithium iron phosphate, lithium nickel cobalt manganese oxide, silicon-carbon materials, silicon suboxide, graphene-coated graphite, and lithium titanate in a synergistic manner, specifically limiting the use of silicon suboxide (SiO₂). x In the given information, x takes a value within a certain range, such that SiO... x The optimal balance between active silicon (Si) and inert silicon oxide (SiO2) is achieved by combining specific silicon suboxide with nano-silicon carbon composites in a certain proportion, which can significantly improve the energy density and cycle life of lithium batteries. At the same time, limiting the amount of lithium iron phosphate and lithium titanate nanoparticles can effectively increase the thermal runaway temperature of lithium batteries, thereby reducing the thermal runaway rate of lithium batteries.

[0004] Firstly, this application provides a high-energy-density, long-life lithium battery with good thermal stability, employing the following technical solution: It includes a positive electrode, a negative electrode, an electrolyte, a separator, and a casing. The positive electrode is obtained by coating a positive electrode slurry onto a positive electrode current collector, and the negative electrode is obtained by coating a negative electrode slurry onto a negative electrode current collector. The raw materials of the positive electrode slurry include a positive electrode active material, a positive electrode dopant, a positive electrode framework material, and a first conductive agent. The positive electrode active material includes lithium nickel cobalt manganese oxide, the positive electrode dopant includes lithium iron phosphate, and the positive electrode framework material includes a lithium-rich manganese-based material. The raw materials of the negative electrode slurry include a negative electrode active material and a second conductive agent. The negative electrode active material includes nano-silicon-carbon composites, silicon suboxide, and lithium titanate nanoparticles. The second conductive agent includes graphene-coated graphite, wherein the chemical formula of the silicon suboxide is SiO₂. x The value of x is 0.8 to 1.2, for example, it can be 0.8, 0.9, 1.0, 1.1 or 1.2; the mass ratio of the nano-silicon-carbon composite to silicon suboxide is 1:2 to 5, for example, it can be 1:2, 1:3, 1:4 or 1:5; the mass ratio of lithium iron phosphate to lithium titanate nanoparticles is 1:0.8 to 1.2, for example, it can be 1:0.8, 1:0.9, 1:1.0, 1:1.1 or 1:1.2.

[0005] Through the above technical solutions, the positive electrode material of the lithium battery described in this application utilizes lithium-rich manganese-based materials to provide structural support for ternary materials, suppressing lattice collapse and improving cycle life and thermal stability. Lithium iron phosphate is used to improve thermal stability, and lithium nickel cobalt manganese oxide is used as a high-capacity matrix for the positive electrode material. The negative electrode material of the lithium battery uses silicon-carbon materials as a high-capacity carrier and utilizes silicon suboxide to buffer silicon-carbon expansion, thereby improving capacity retention and thermal stability. Graphene-coated graphite is used to enhance conductivity and mechanical support. At the same time, lithium titanate forms fast ion channels at the interface, enabling the lithium battery to have a high capacity retention under high-rate charge and discharge. The chemical formula of the silicon suboxide is SiO₂. x When x is less than 0.8, the silicon phase ratio is too high, leading to structural instability and insufficient buffering of silicon-carbon material expansion, resulting in reduced lithium battery life and increased safety risks. When x is greater than 1.2, there is an excessive amount of SiO2 phase, and Li... + The low diffusion coefficient in SiO2 leads to a reduced cycle life in lithium batteries; when the mass ratio of the nano-silicon-carbon composite to silicon suboxide is less than 1:2, the proportion of nano-silicon-carbon is too high, resulting in a low SiO2 diffusion coefficient. x The buffer layer is destroyed by silicon expansion, leading to a decrease in the thermal runaway temperature. When the mass ratio of the nano-silicon-carbon composite to silicon suboxide is greater than 1:5, SiO... xExcessive proportion of lithium iron phosphate and lithium titanate nanoparticles, with low-capacity components dominating the negative electrode, leads to a significant reduction in energy density. When the mass ratio of lithium iron phosphate to lithium titanate nanoparticles is less than 1:0.8, the insufficient proportion of lithium titanate nanoparticles will cause cracks in lithium iron phosphate during cycling, thereby reducing the cycle life of the lithium battery. When the mass ratio of lithium iron phosphate to lithium titanate nanoparticles is greater than 1:1.2, the excessive proportion of lithium titanate nanoparticles leads to a significant reduction in the energy density of the lithium battery.

[0006] Optionally, the graphene-coated graphite is GCG, a graphene-coated graphite lithium-ion battery anode material, with an average particle size of 8~10 μm and a specific surface area ≤6.0 m². 2 / g.

[0007] Through the above technical solution, this application uses specific graphene to coat graphite materials, which can effectively overcome the defects of natural graphite anode materials such as poor liquid absorption, low initial efficiency, and short cycle life. It significantly improves the capacity, initial efficiency, and cycle stability of natural graphite materials, and has the characteristics of high specific capacity and long cycle life. As a result, the prepared lithium battery has a long cycle life and a high capacity retention rate under high-rate fast charging conditions.

[0008] Optionally, the mass ratio of the lithium nickel cobalt manganese oxide, the lithium-rich manganese-based material, and the lithium iron phosphate is 5~25:0.5~5:1, specifically, for example, it can be 5:0.5:1, 15:3:1, or 25:5:1.

[0009] The above technical solution combines a certain amount of lithium iron phosphate with lithium nickel cobalt manganese oxide and lithium-rich manganese-based materials to further balance the high energy density, long cycle life and thermal safety of lithium batteries.

[0010] Optionally, the mass ratio of the nano-silicon-carbon composite, the silicon suboxide, the graphene-coated graphite, and the lithium titanate nanoparticles is 4~10:8~50:3~25:1. Specifically, for example, it can be 4:8:3:1, 5:20:10:1, or 10:50:25:1.

[0011] Through the above technical solutions, nano-silicon-carbon composites, silicon suboxide, graphene-coated graphite, and lithium titanate produce a synergistic effect in a certain proportion, further improving the high energy density, long cycle life, and thermal safety of lithium batteries.

[0012] Optionally, the value of x in the silicon suboxide is 0.9 to 1.0, and the mass ratio of the nano-silicon-carbon composite to silicon suboxide is 1:3 to 4.

[0013] By further limiting the proportion of silicon and oxygen in silicon suboxide and further limiting the mass ratio of nano-silicon-carbon composite to silicon suboxide through the above technical solutions, the cycle life and thermal stability of lithium batteries can be further improved.

[0014] Optionally, the lithium-rich manganese-based material is polycrystalline alumina coated with high-capacity lithium-rich manganese, and the chemical formula of the polycrystalline alumina coated with high-capacity lithium-rich manganese is Li. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2, with an average particle size of 10–13 μm and a specific surface area of ​​1–10 m². 2 / g.

[0015] Through the above technical solution, high-capacity lithium-rich manganese-based polycrystalline alumina with a certain particle size and specific surface area is selected as the cathode skeleton material. The cathode skeleton material, lithium nickel cobalt manganese oxide and lithium iron phosphate are used to prepare the cathode of lithium-ion battery. The lithium-ion battery prepared using the cathode still has a high capacity retention rate under high voltage fast charging conditions.

[0016] Optionally, the lithium nickel cobalt manganese oxide is a zirconium cobalt composite coated lithium nickel cobalt manganese oxide, and the chemical formula of the zirconium cobalt composite coated lithium nickel cobalt manganese oxide is LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 In the zirconium-cobalt composite coated nickel-cobalt-manganese lithium oxide, the total content of nickel, cobalt and manganese is 55-60%.

[0017] Through the above technical solution, lithium nickel cobalt manganese oxide doped with zirconium and coated with cobalt is selected as the positive electrode active material. Zirconium doping can suppress lattice phase transitions, and cobalt coating can construct a conductive network. By limiting the total content of nickel, cobalt and manganese to 55-60%, the capacity and structural stability can be balanced, thereby enabling the prepared lithium battery to achieve comprehensive performance of high energy density, long cycle life and high thermal safety.

[0018] Optionally, the first conductive agent is composed of carbon nanotubes and conductive carbon black in a mass ratio of 1:2 to 3. Specifically, for example, the mass ratio of carbon nanotubes to conductive carbon black can be 1:2, 1:2.5, or 1:3. The raw materials of the positive electrode slurry and the negative electrode slurry also include a binder, which is hydroxybutyrate latex.

[0019] The above technical solution combines carbon nanotubes and conductive carbon black in a mass ratio of 1:2 to 3. The axial conductivity of carbon nanotubes enables rapid electron transport, thereby improving the capacity retention rate of lithium batteries at high rates. At the same time, conductive carbon black buffers volume expansion, inhibits carbon nanotube network breakage, and improves the cycle life of lithium batteries. Hydroxystyrene-butadiene latex can improve interfacial bonding and electrolyte stability.

[0020] In a specific embodiment of the lithium battery described in this application, the positive electrode active material, positive electrode dopant, and positive electrode framework material are collectively referred to as positive electrode material in the positive electrode slurry, and the mass ratio of the positive electrode material, the first conductive agent, and the binder is 70:15:15.

[0021] In a specific embodiment of the lithium battery described in this application, the mass ratio of the negative electrode active material, the second conductive agent, and the binder in the negative electrode slurry is 70:15:15.

[0022] In a specific embodiment of the lithium battery described in this application, the raw materials for both the positive electrode slurry and the negative electrode slurry also include a solvent, which can be a conventional choice in the art.

[0023] Optionally, the electrolyte is a trimethyl phosphate-based electrolyte, and the diaphragm is a glass fiber diaphragm.

[0024] The above technical solution, which uses trimethyl phosphate-based electrolyte and glass fiber separator in synergy, can effectively improve the thermal stability of lithium batteries.

[0025] Secondly, this application provides a method for preparing the high energy density, long lifespan, and thermal stability lithium battery described above, the method comprising the following steps: S1. Preparation of positive electrode slurry: The first conductive agent and binder are added to the solvent and mixed to form a first mixed system. Then, lithium nickel cobalt manganese oxide, lithium-rich manganese-based material and lithium iron phosphate are added to the first mixed system in sequence and mixed evenly to obtain positive electrode slurry. Negative electrode slurry preparation: Silicon powder and nano-silica are mixed at an O:Si atomic ratio of 0.8~1.2, and then ball-milled to obtain SiO2. x The silicon suboxide with x values ​​ranging from 0.8 to 1.2 is ball-milled with the nano-silicon carbon composite to obtain a composite material. The composite material is then added to a mixing system containing a binder and a solvent to form a second mixing system. The lithium titanate nanoparticles and graphene-coated graphite are added to the second mixing system and mixed evenly to obtain a negative electrode slurry. S2. The positive electrode slurry is coated onto the positive electrode current collector and then dried to obtain a positive electrode sheet; the negative electrode slurry is coated onto the negative electrode current collector and then dried to obtain a negative electrode sheet. S3. Assemble the positive electrode, negative electrode, electrolyte, separator and casing to prepare a lithium battery.

[0026] Through the above technical solutions, when preparing the positive electrode slurry, the first conductive agent and binder are mixed first, and then lithium nickel cobalt manganese oxide, lithium-rich manganese-based material and lithium iron phosphate are added in sequence. This can optimize the dispersion uniformity and conductive network connectivity of the electrode slurry, thereby improving the energy density and cycle life of the lithium battery. When preparing the negative electrode slurry, silicon suboxide and nano-silicon carbon composite are first prepared into a composite material, which can pre-buffer silicon carbon expansion, thereby effectively improving the capacity retention and thermal stability of the lithium battery.

[0027] In summary, this application includes at least one of the following beneficial technical effects: 1. The lithium battery described in this application improves the overall performance of the lithium battery by using a composite of lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium-rich manganese-based materials, nano-silicon-carbon composites, silicon suboxide, lithium titanate nanoparticles, and graphene-coated graphite, and enhances the SiO2 content. x The optimal balance between active silicon (Si) and inert silicon oxide (SiO2) is achieved by using specific silicon suboxide and nano-silicon carbon composites in a certain proportion, which can significantly improve the energy density and cycle life of lithium batteries. At the same time, limiting the amount of lithium iron phosphate and lithium titanate nanoparticles can effectively increase the thermal runaway temperature of lithium batteries, thereby reducing the thermal runaway rate of lithium batteries. The raw materials of the lithium battery described in this application are simple and do not require additional complex processes to prepare materials. The lithium battery prepared has stable performance. 2. In the lithium battery preparation method described in this application, when preparing the positive electrode slurry, the first conductive agent and the binder are mixed first, and then other raw materials are added, which can effectively improve the energy density and cycle life of the lithium battery. When preparing the negative electrode slurry, silicon suboxide and nano-silicon carbon composite are first prepared into a composite material, which can pre-buffer silicon carbon expansion, thereby effectively improving the capacity retention rate and thermal stability of the lithium battery. Detailed Implementation

[0028] The present application will be further described in detail below with reference to specific embodiments.

[0029] The following examples further illustrate the high energy density, long cycle life, and thermal stability lithium battery and its preparation method described in this application. These 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.

[0030] 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.

[0031] Silicon powder: Purchased from Shanghai Xiaohuang Nanotechnology Co., Ltd. Nano silica: Purchased from Zhejiang Chongchuan New Material Technology Co., Ltd., product number ZC-SIO2-N20; Zirconium-cobalt composite coated lithium nickel cobalt manganese oxide (positive electrode active material): purchased from Shenzhen Kejing Zhida Technology Co., Ltd., chemical formula LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 The total content of O2, nickel, cobalt and manganese is 58.5%; Polycrystalline alumina coated with high-capacity lithium-rich manganese-based cathode 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; Lithium iron phosphate: Purchased from Shenzhen Kejing Zhida Technology Co., Ltd., model number T01; Nano-silicon-carbon composite: Purchased from Shenzhen Kejing Zhida Technology Co., Ltd., model number SL45B-SC; Lithium titanate nanoparticles: Purchased from Shenzhen Kejing Zhida Technology Co., Ltd., model number LTO-2; Graphene-coated graphite (second conductive agent): Purchased from Angxing New Carbon Materials Changzhou Co., Ltd., product name: Graphene-coated graphite lithium-ion battery anode material GCG, average particle size 9 μm, specific surface area 6.0 m². 2 / g; Conductive carbon black (conductive agent): superconducting carbon black, purchased from Shenzhen Kejing Zhida Technology Co., Ltd., model ECP-600JD; Carbon nanotubes (conductive agent): Purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., product number 100253; Hydroxy-butadiene styrene latex (adhesive): Purchased from Shenzhen Kejing Zhida Technology Co., Ltd., model MS-451B-SBR; 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; Separator: Fiberglass diaphragm, purchased from Oulage (Chongqing) New Materials Co., Ltd., model GF / D6227; Housing: Purchased from Shenzhen Kejing Zhida Technology Co., Ltd., sheet-like aluminum-plastic film; Electrolyte: LiPF6, trimethyl phosphate and triethyl phosphate are prepared in a volume ratio of 1:1:1.

[0032] Examples 1-8 and Comparative Examples 1-8 describe lithium batteries with high energy density, long lifespan, and thermal stability, and their preparation methods.

[0033] Example 1 (i) A lithium battery with high energy density, long life and thermal stability, comprising a positive electrode, a negative electrode, an electrolyte, a separator and a casing, wherein the positive electrode is obtained by coating a positive electrode slurry onto an aluminum foil, and the negative electrode is obtained by coating a negative electrode slurry onto a copper foil. The raw materials of the positive electrode slurry include zirconium cobalt composite coated lithium nickel cobalt manganese oxide, polycrystalline alumina coated high-capacity lithium-rich manganese-based oxide, lithium iron phosphate, a first conductive agent and hydroxybutyrate latex, wherein the mass ratio of zirconium cobalt composite coated lithium nickel cobalt manganese oxide, polycrystalline alumina coated high-capacity lithium-rich manganese-based oxide and lithium iron phosphate is 15:3:1, the first conductive agent is composed of carbon nanotubes and conductive carbon black in a mass ratio of 1:2, and the mass ratio of the positive electrode material (zirconium cobalt composite coated lithium nickel cobalt manganese oxide, polycrystalline alumina coated high-capacity lithium-rich manganese-based oxide and lithium iron phosphate), the first conductive agent and hydroxybutyrate latex is 70:15:15; The raw materials for the negative electrode slurry include negative electrode active materials and graphene-coated graphite. The negative electrode active materials include nano-silicon-carbon composites, silicon suboxide, and lithium titanate nanoparticles. The silicon suboxide is prepared by mixing silicon powder and nano-silica at an O:Si atomic ratio of 1.0, and then ball-milling the mixture in a SPEX 8000M high-energy ball mill for 8 hours to obtain SiO₂. 1.0 The mass ratio of silicon suboxide, nano-silicon carbon composite, silicon suboxide, graphene-coated graphite, and lithium titanate nanoparticles is 5:20:10:1; among which, the mass ratio of lithium iron phosphate to lithium titanate nanoparticles is 1:1. (II) A method for preparing a lithium battery with high energy density, long lifespan, and thermal stability, the method comprising the following steps: S1. Preparation of positive electrode slurry: The first conductive agent and hydroxybutyrate latex are added to deionized water and mixed to form a first mixed system. Then, lithium nickel cobalt manganese oxide, lithium-rich manganese-based material and lithium iron phosphate are added to the first mixed system in sequence and mixed evenly to obtain a positive electrode slurry. The solid content of the positive electrode slurry is 30%. Negative electrode slurry preparation: The silicon suboxide and nano-silicon carbon composite were ball-milled in a planetary ball mill for 10 h to obtain a composite material. The composite material was added to deionized water containing hydroxybutyrate latex and mixed to form a second mixing system. The lithium titanate nanoparticles and graphene-coated graphite were added to the second mixing system and mixed evenly to obtain a negative electrode slurry with a solid content of 30%. S2. The positive electrode slurry is coated onto an aluminum foil and then dried to obtain a positive electrode sheet; the negative electrode slurry is coated onto a copper foil and then dried to obtain a negative electrode sheet. S3. The positive electrode, negative electrode, electrolyte, separator and casing are used to fabricate a soft-pack lithium-ion battery using a soft-pack stacking process, and the performance of the battery is tested.

[0034] Example 2 The procedure was carried out as described in Example 1, except that the silicon suboxide was prepared as follows: silicon powder and nano-silica were mixed at an O:Si atomic ratio of 0.8, and then ball-milled in a SPEX 8000M high-energy ball mill for 8 hours to obtain SiO2. 0.8 The mass ratio of silicon suboxide, nano-silicon-carbon composite, silicon suboxide, graphene-coated graphite, and lithium titanate nanoparticles is 4:8:3:1.

[0035] Example 3 The procedure was carried out as described in Example 1, except that the silicon suboxide was prepared as follows: silicon powder and nano-silica were mixed at an O:Si atomic ratio of 1.2 and then ball-milled in a SPEX 8000M high-energy ball mill for 8 hours to obtain SiO2. 1.2 The mass ratio of silicon suboxide, nano-silicon carbon composite, silicon suboxide, graphene-coated graphite, and lithium titanate nanoparticles is 10:50:25:1.

[0036] Example 4 The method was implemented as in Example 1, except that the mass ratio of lithium iron phosphate to lithium titanate nanoparticles was 1:0.8.

[0037] Example 5 The method was implemented as in Example 1, except that the mass ratio of lithium iron phosphate to lithium titanate nanoparticles was 1:1.2.

[0038] Example 6 The method was implemented in accordance with Example 1, except that the mass ratio of zirconium cobalt composite coated lithium nickel cobalt manganese oxide, polycrystalline alumina coated high-capacity lithium-rich manganese-based oxide, and lithium iron phosphate was 5:0.5:1.

[0039] Example 7 The method was implemented in accordance with Example 1, except that the mass ratio of zirconium cobalt composite coated lithium nickel cobalt manganese oxide, polycrystalline alumina coated high-capacity lithium-rich manganese-based lithium iron phosphate and lithium iron phosphate was 25:5:1.

[0040] Example 8 The method of Example 1 was followed, except that the first conductive agent was composed of carbon nanotubes and conductive carbon black in a mass ratio of 1:3.

[0041] Comparative Example 1 The procedure was carried out as described in Example 1, except that the silicon suboxide was prepared as follows: silicon powder and nano-silica were mixed at an O:Si atomic ratio of 0.6, and then ball-milled in a SPEX 8000M high-energy ball mill for 8 hours to obtain the chemical formula SiO. 0.6 Silica suboxide.

[0042] Comparative Example 2 The procedure was carried out as described in Example 1, except that the silicon suboxide was prepared as follows: silicon powder and nano-silica were mixed at an O:Si atomic ratio of 1.4 and then ball-milled in a SPEX 8000M high-energy ball mill for 8 hours to obtain SiO2. 1.4 Silica suboxide.

[0043] Comparative Example 3 The method was implemented in accordance with Example 1, except that the mass ratio of the nano-silicon-carbon composite, silicon suboxide, graphene-coated graphite, and lithium titanate nanoparticles was 20:20:10:1.

[0044] Comparative Example 4 The method was implemented in accordance with Example 1, except that the mass ratio of the nano-silicon-carbon composite, silicon suboxide, graphene-coated graphite, and lithium titanate nanoparticles was 5:30:10:1.

[0045] Comparative Example 5 The method was implemented as in Example 1, except that the mass ratio of lithium iron phosphate to lithium titanate nanoparticles was 1:0.6.

[0046] Comparative Example 6 The method was implemented as in Example 1, except that the mass ratio of lithium iron phosphate to lithium titanate nanoparticles was 1:1.4.

[0047] Comparative Example 7 The process is carried out in accordance with Example 1, except that in the preparation of the positive electrode slurry for the lithium battery, the first conductive agent, hydroxystyrene-butadiene latex, lithium nickel cobalt manganese oxide, lithium-rich manganese-based material and lithium iron phosphate are added to deionized water and mixed evenly to obtain the positive electrode slurry, wherein the solid content of the positive electrode slurry is 30%.

[0048] Comparative Example 8 The process is carried out in accordance with Example 1, except that in the preparation of the negative electrode slurry for the lithium battery, the silicon suboxide, nano-silicon carbon composite, lithium titanate nanoparticles, graphene-coated graphite and hydroxyl styrene-butadiene latex are added to deionized water and mixed evenly to obtain the negative electrode slurry. The solid content of the positive electrode slurry is 30%.

[0049] Test case Energy density test: Weigh the lithium battery and record the weight as m; place the battery in a fixture and apply a force of 3000 N. Charge the individual cells at a constant current of 0.33 C to 3.65 V, then continue charging at a constant voltage of 3.65 V until the current drops to 0.05 C and is cut off; let stand for 30 min, then discharge at a constant current of 0.33 C to 2.5 V, let stand for 30 min, and repeat this cycle 3 times; calculate the discharge capacity (in Ah) and energy E (average of three cycles), discharge energy density = E / m (in Wh / kg); Cyclic performance test: At 25 ℃, the LAND-CT2001A battery test system was used to conduct 5C rate cycle tests and record the capacity retention rate after 1000 cycles. The charging was performed in constant current-constant voltage mode (1C) and the discharging was performed in constant current mode until the cutoff voltage. The test voltage was 4.3V. Thermal runaway performance test: The lithium battery was placed in an oven and heated at 200 ℃, 300 ℃ and 400 ℃ for 30 min respectively to test the thermal runaway performance of the lithium battery.

[0050] The lithium batteries prepared in Examples 1-8 and Comparative Examples 1-8 were subjected to energy density testing, cycle performance testing, and thermal runaway performance testing, respectively. The test results are shown in Table 1. Table 1

[0051] As can be seen from Table 1, the lithium batteries obtained using the raw materials and preparation methods described in this application simultaneously meet the requirements of high energy density, long cycle life, and high thermal runaway temperature. In Comparative Examples 1 and 2, the O:Si atomic ratio was not within the range of 0.8 to 1.2 when preparing silicon suboxide, making it difficult for the prepared lithium batteries to simultaneously meet the requirements of high energy density, long cycle life, and high thermal runaway temperature. In Comparative Examples 3 and 4, the ratio of nano-silicon-carbon composite to silicon suboxide was not within the range of 1:2 to 5, making it difficult for the prepared lithium batteries to simultaneously meet the requirements of high energy density, long cycle life, and high thermal runaway temperature. In Comparative Examples 5 and 6, the ratio of lithium iron phosphate to lithium titanate nanoparticles was not within the range of 1:0.8 to 1.2, making it difficult for the prepared lithium batteries to simultaneously meet the requirements of high energy density, long cycle life, and high thermal runaway temperature. In Comparative Examples 7 and 8, the raw materials of the positive electrode slurry or negative electrode slurry were mixed together during the preparation of the lithium batteries, and the feeding steps of this application were not followed. Therefore, the prepared lithium batteries also failed to simultaneously meet the requirements of high energy density, long cycle life, and high thermal runaway temperature.

[0052] 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 lithium battery with high energy density, long lifespan, and good thermal stability, comprising a positive electrode, a negative electrode, an electrolyte, a separator, and a casing, wherein the positive electrode is obtained by coating a positive electrode slurry onto a positive electrode current collector, and the negative electrode is obtained by coating a negative electrode slurry onto a negative electrode current collector, characterized in that, The raw materials of the positive electrode slurry include positive electrode active material, positive electrode dopant, positive electrode framework material and first conductive agent. The positive electrode active material includes lithium nickel cobalt manganese oxide, the positive electrode dopant includes lithium iron phosphate, and the positive electrode framework material includes lithium-rich manganese-based material. The raw materials for the negative electrode slurry include a negative electrode active material and a second conductive agent. The negative electrode active material includes nano-silicon-carbon composite, silicon suboxide, and lithium titanate nanoparticles. The second conductive agent includes graphene-coated graphite, wherein the chemical formula of the silicon suboxide is SiO₂. x x takes the value of 0.8 to 1.2, the mass ratio of the nano-silicon-carbon composite to silicon suboxide is 1:2 to 5, and the mass ratio of lithium iron phosphate to lithium titanate nanoparticles is 1:0.8 to 1.

2.

2. The lithium battery with high energy density, long lifespan, and thermal stability according to claim 1, characterized in that, The graphene-coated graphite used is GCG, a graphene-coated graphite lithium-ion battery anode material, with an average particle size of 8~10 μm and a specific surface area ≤6.0 m². 2 / g.

3. The lithium battery with high energy density, long lifespan, and thermal stability according to claim 1, characterized in that, The mass ratio of the lithium nickel cobalt manganese oxide, the lithium-rich manganese-based material, and the lithium iron phosphate is 5~25:0.5~5:

1.

4. The lithium battery with high energy density, long lifespan, and thermal stability according to claim 1 or 2, characterized in that, The mass ratio of the nano-silicon-carbon composite, the silicon suboxide, the graphene-coated graphite, and the lithium titanate nanoparticles is 4~10:8~50:3~25:

1.

5. The lithium battery with high energy density, long lifespan, and thermal stability according to claim 1, characterized in that, The value of x in the silicon suboxide is 0.9~1.0, and the mass ratio of the nano-silicon-carbon composite to silicon suboxide is 1:3~4.

6. The lithium battery with high energy density, long lifespan, and thermal stability according to claim 1, characterized in that, The lithium-rich manganese-based material is a polycrystalline alumina-coated high-capacity lithium-rich manganese-based material, and the chemical formula of the polycrystalline alumina-coated high-capacity lithium-rich manganese-based material is Li. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2, with an average particle size of 10–13 μm and a specific surface area of ​​1–10 m². 2 / g.

7. The lithium battery with high energy density, long lifespan, and thermal stability according to claim 1, characterized in that, The lithium nickel cobalt manganese oxide is a zirconium cobalt composite coated lithium nickel cobalt manganese oxide, and the chemical formula of the zirconium cobalt composite coated lithium nickel cobalt manganese oxide is LiNi. 1 / 3Co 1 / 3 Mn 1 / 3 In the zirconium-cobalt composite coated nickel-cobalt-manganese lithium oxide, the total content of nickel, cobalt and manganese is 55-60%.

8. The lithium battery with high energy density, long lifespan, and thermal stability according to claim 1, characterized in that, The first conductive agent is composed of carbon nanotubes and conductive carbon black in a mass ratio of 1:2~3; The raw materials for both the positive and negative electrode slurries also include a binder, which is hydroxybutyrate latex.

9. The lithium battery with high energy density, long lifespan, and thermal stability according to claim 1, characterized in that, The electrolyte is a trimethyl phosphate-based electrolyte, and the diaphragm is a glass fiber diaphragm.

10. A method for preparing a lithium battery with high energy density, long lifespan, and thermal stability as described in any one of claims 1 to 9, characterized in that, The preparation method includes the following steps: S1. Preparation of positive electrode slurry: The first conductive agent and binder are added to the solvent and mixed to form a first mixed system. Then, lithium nickel cobalt manganese oxide, lithium-rich manganese-based material and lithium iron phosphate are added to the first mixed system in sequence and mixed evenly to obtain positive electrode slurry. Negative electrode slurry preparation: Silicon powder and nano-silica are mixed at an O:Si atomic ratio of 0.8~1.2, and then ball-milled to obtain SiO2. x The silicon suboxide with x values ​​ranging from 0.8 to 1.2 is ball-milled with the nano-silicon carbon composite to obtain a composite material. The composite material is then added to a mixing system containing a binder and a solvent to form a second mixing system. The lithium titanate nanoparticles and graphene-coated graphite are added to the second mixing system and mixed evenly to obtain a negative electrode slurry. S2. The positive electrode slurry is coated onto the positive electrode current collector and then dried to obtain a positive electrode sheet; the negative electrode slurry is coated onto the negative electrode current collector and then dried to obtain a negative electrode sheet. S3. Assemble the positive electrode, negative electrode, electrolyte, separator and casing to prepare a lithium battery.

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