High-temperature and high-rate secondary battery containing FEC electrolyte

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a high-temperature and high-rate secondary battery containing FEC electrolyte. The high-temperature and high-rate secondary battery comprises a positive pole piece, a negative pole piece and an electrolyte, the electrolyte comprises a solvent, an auxiliary agent and a lithium salt, wherein the solvent comprises ethylene carbonate, methyl ethyl carbonate and propylene carbonate in a volume ratio of 1: (1.2-1.4): (0.5-0.7); the auxiliary agent is prepared from fluoroethylene carbonate, fluoroethylene carbonate, butane sultone and vinylene carbonate according to the volume ratio of 1 to (1.3 to 1.6) to (0.2 to 0.4) to (1.5 to 1.8); and the auxiliary agent accounts for 2-4% of the total weight of the electrolyte. The secondary battery prepared by the invention is excellent in performance and high in rate, and can still keep relatively high cycle performance at high temperature.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries, and in particular relates to a high-temperature and high-rate secondary battery containing a FEC electrolyte. Background Art

[0002] The electrolyte of lithium-ion batteries used in electric vehicles is one of the key factors in battery performance. The main function of the electrolyte is to provide a medium for ion transmission, ensuring that the lithium ions inside the battery can move efficiently between the positive and negative electrodes. Lithium secondary batteries generate electrical energy through oxidation and reduction reactions when lithium ions are inserted and removed from the positive and negative electrodes. Therefore, lithium secondary batteries are prepared by using materials that can insert and remove lithium ions as negative and positive electrodes, and filling organic electrolytes or polymer electrolytes between the positive and negative electrodes.

[0003] Although lithium secondary batteries perform well in terms of energy density, cycle life and self-discharge rate, they still face some technical and challenges: 1. SEI film instability: The solid electrolyte interface (SEI) film may be unstable in some cases, resulting in internal short circuit or thermal runaway of the battery. 2. Cycle life: As the number of charge and discharge cycles increases, the capacity of the battery will gradually decrease. 3. Energy density: The energy density of the currently commonly used positive and negative electrode materials is limited, and it is difficult to meet the demand for higher energy density. 4. Fast charging capability: lithium dendrites: During fast charging, the deposition rate of lithium ions on the surface of the negative electrode is too fast, and lithium dendrites are easily formed, resulting in internal short circuits and safety hazards in the battery. 5. Environmental adaptability: Under low and high temperature conditions, the conductivity of the electrolyte decreases, the performance of the battery will be affected, and the cycle life and safety of the battery will decrease.

[0004] In the existing technology, by optimizing the types and contents of lithium salts and additives, the irreversible expansion of silicon-based negative electrode sheets can be reduced while the conductivity of the electrolyte is increased, thereby improving the rate charging performance and cycle life of lithium-ion batteries. However, it does not solve the problem of performance loss of lithium-ion batteries at high temperatures and cannot meet the needs of the existing market.

[0005] Therefore, there is an urgent need for a high-temperature and high-rate secondary battery containing FEC electrolyte. Summary of the invention

[0006] The object of the present invention is to provide a high-temperature and high-rate secondary battery containing a FEC electrolyte.

[0007] In order to achieve the above object, the present invention provides the following technical solutions: A high-temperature, high-rate secondary battery containing FEC electrolyte, comprising a positive electrode plate, a negative electrode plate and an electrolyte; the electrolyte comprises a solvent, an auxiliary agent and a lithium salt, the solvent comprises ethylene carbonate, ethyl methyl carbonate and propylene carbonate in a volume ratio of 1: (1.2-1.4): (0.5-0.7); the auxiliary agent comprises fluoroethylene carbonate, fluoroethylene carbonate, butane sultone and vinylene carbonate in a volume ratio of 1: (1.3-1.6): (0.2-0.4): (1.5-1.8); the auxiliary agent accounts for 2-4% of the total weight of the electrolyte.

[0008] The performance of lithium secondary batteries is mainly affected by the structure of the organic electrolyte and the SEI film formed by the reaction of the organic electrolyte and the electrode. The performance of the commonly used electrolytes on the market after the reaction with the electrodes prepared by the present invention is not ideal. The present invention can improve the rate performance of secondary batteries by synergizing solvents and additives in a specific ratio. Analysis shows that the performance of lithium secondary batteries is affected by the structure of the organic electrolyte and the SEI film formed by the reaction of the organic electrolyte and the electrode. Suitable solvents can improve the lithium ion conductivity of the electrolyte and accelerate the migration speed of lithium ions in the electrolyte. Specific additives can also help inhibit the occurrence of harmful side reactions, such as the growth of lithium dendrites. At the same time, there is a complex interaction between the composition of the electrolyte of the present invention and the surface structure of the electrode prepared by the present invention, which jointly determines the formation and stability of the SEI film. Specific solvents and additives can interact with specific active sites on the surface of the electrode to form a denser and more uniform SEI film, thereby improving the cycle stability and rate performance of the battery.

[0009] Furthermore, the lithium salt includes LiPF 6 and LiAlO 2 .

[0010] Furthermore, the molar concentration of the lithium salt in the electrolyte is 1.5-1.7 mol / L.

[0011] Furthermore, the preparation method of the negative electrode plate comprises the following steps: mixing the silicon-carbon composite material, carbon nanotubes and a binder in a weight ratio of (92-94):3:(3.8-4.2) evenly, coating the mixture on a copper foil with a thickness of 8-10 μm, and obtaining a negative electrode plate.

[0012] Furthermore, the method for preparing the silicon-carbon composite material comprises the following steps: (1) Mix kaolin with 2-4 mol / L nitric acid in a weight ratio of 1:(8-10), stir and react at 50-60°C for 10-12 hours; filter, wash with water until neutral, and dry to obtain acid-treated kaolin; mix acid-treated kaolin, sodium hydroxide, and water in a weight ratio of 1:(0.4-0.7):(8-10), stir and react at 30-40°C for 4-6 hours, filter, wash with water until neutral, and dry to obtain pretreated kaolin; (2) In the presence of cyclohexanol and anhydrous ethanol in a volume ratio of 1: (1.5-1.7) as a solvent, the pretreated kaolin and glucose are uniformly mixed, and after removing the solvent, calcined in an inert atmosphere at a temperature of 600-800°C and a calcination time of 4-6 hours to obtain a silicon-carbon composite material.

[0013] Furthermore, the weight ratio of glucose to kaolin calculated as silicon dioxide is 1:(2-5).

[0014] Furthermore, the particle size of the kaolin is 325 mesh to 500 mesh and is purchased from Shandong Qiyi Chemical Technology Co., Ltd., and the model is ultrafine calcined kaolin.

[0015] Furthermore, the weight ratio of the solvent to kaolin is (12-15):1.

[0016] In the prior art, silicon dioxide is directly added to improve the problem of low specific capacity of graphite as a negative electrode. However, if the size and distribution of the directly added silicon dioxide particles are uneven, it will lead to uneven stress distribution inside the electrode, aggravating the pulverization and shedding of the electrode material, and the service life of the obtained secondary battery is not ideal. The present invention improves the service life of the secondary battery at room temperature by preparing a silicon-carbon composite material using kaolin and an organic carbon source. This is mainly because the present invention uses kaolin as the source of silicon dioxide, and the combination of silicon dioxide and carbon produces a composite structure. Its special morphology reduces the phenomenon of volume expansion during charging and discharging, and the battery prepared therefrom has higher performance stability during charging and discharging. At the same time, the service life of the secondary battery at low temperatures is improved.

[0017] Furthermore, the carbon nanotubes include single-walled carbon nanotubes, multi-walled carbon nanotubes and double-walled carbon nanotubes in a mass ratio of (0.2-0.5):1:(1.5-1.7); the single-walled carbon nanotubes have a diameter of 1-2 nm, a length of 5-30 μm, and a specific surface area of ​​120 m 2 / g, conductivity is 2400s / cm; the diameter of multi-walled carbon nanotubes is 3-6nm, the length is 0.5-1.5μm, and the specific surface area is 50m 2 / g, conductivity is 150s / cm; double-walled carbon nanotubes have a diameter of 2-4nm, a length of 0.5-2μm, and a specific surface area of ​​450m 2 / g, conductivity is 150s / cm.

[0018] The present invention improves the capacity recovery rate of a secondary battery after use at high temperature by adding carbon nanotubes with specific parameters and ratios. The carbon nanotubes of the present invention can form a three-dimensional network structure, improve the porosity and specific surface area of ​​the electrode material, and facilitate the rapid transmission of lithium ions. At high temperatures, the diffusion rate of lithium ions will be affected. The three-dimensional network structure of the carbon nanotubes can provide more transmission paths, accelerate the diffusion of lithium ions, and improve the high temperature performance and capacity recovery rate of the battery. At the same time, the synergistic effect of the carbon nanotubes and the silicon-carbon composite material of the present invention can comprehensively improve the conductivity, mechanical properties and stability of the SEI film of the electrode, thereby significantly improving the capacity recovery rate of the battery at high temperatures.

[0019] Graphite layers are connected by van der Waals forces, the interlayer force is small and the interlayer spacing is smaller than the crystal plane interlayer spacing of graphite intercalation compounds, which causes the graphite interlayer spacing to change during the charge and discharge process, resulting in graphite flakes peeling and pulverization, resulting in unsatisfactory electrical cycle performance; secondly, due to the structural defects of graphite itself, there are many active groups on its surface, which makes natural graphite have poor compatibility with solvents. Domestic research institutions have used phenolic resin to modify natural graphite. Although this modification method can improve the specific capacity and recycling rate of graphite materials, it still has the following serious defects: (1) Phenolic resin is easy to form an adhesive system that is easy to settle during stirring or volatilization, resulting in uneven coating on the graphite surface; (2) The surface of the graphite coated with phenolic resin once will have holes, and some places are not even coated, resulting in graphite exposed to the outside. Contact with the electrolyte will cause the generation of irreversible capacity, thereby reducing the graphite cycle performance.

[0020] Furthermore, the binder comprises sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 1: (1.2-1.5).

[0021] Furthermore, the preparation method of the positive electrode plate comprises the following steps: uniformly mixing nickel cobalt manganese hydroxide, polyvinylidene fluoride and carbon black in a weight ratio of (90-92):5:(4-6), and coating the mixture on an aluminum foil with a thickness of 10-12 μm to obtain a positive electrode plate.

[0022] Compared with the prior art, the advantages and beneficial effects of the present invention are: 1. The electrolyte system of the present invention can form a stable solid electrolyte interface (SEI) film by adding an appropriate amount of FEC-containing additives, reduce the occurrence of side reactions, ensure the compatibility of FEC with positive and negative electrode materials, avoid adverse reactions, and improve the cycle stability, thermal stability and overall safety of the secondary battery by introducing FEC as an electrolyte additive.

[0023] 2. The present invention can improve the rate performance of the secondary battery by synergizing the solvent and the auxiliary agent in a specific ratio.

[0024] 3. The present invention improves the service life of the secondary battery at room temperature by using kaolin and an organic carbon source to prepare a silicon-carbon composite material; at the same time, it improves the service life of the secondary battery at low temperature.

[0025] 4. The present invention improves the capacity recovery rate of the secondary battery after use at high temperature by adding carbon nanotubes with specific parameters and proportions. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] The raw materials used in the following examples of the present invention are all commercially available products: Nickel Cobalt Manganese Hydroxide, Ni 0.6 Co 0.2 Mn 0.2 (OH) 2 , purchased from Dalian Ruiyuan Power Co., Ltd.

[0028] Example 1 This embodiment provides a high-temperature and high-rate secondary battery containing a FEC electrolyte, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte.

[0029] The electrolyte includes a solvent, an auxiliary agent and a lithium salt. The solvent includes ethylene carbonate, ethyl methyl carbonate and propylene carbonate in a volume ratio of 1:1.3:0.6; the auxiliary agent includes fluoroethylene carbonate, fluoroethylene carbonate, butane sultone and vinylene carbonate in a volume ratio of 1:1.4:0.3:1.7; the auxiliary agent accounts for 3% of the total weight of the electrolyte. The lithium salt includes LiPF 6 and LiAlO 2 The molar concentration of the lithium salt in the electrolyte is 1.6 mol / L.

[0030] The preparation method of the negative electrode plate comprises the following steps: mixing a silicon-carbon composite material, carbon nanotubes and a binder in a weight ratio of 93:3:4 evenly, coating the mixture on a copper foil with a thickness of 9 μm, and obtaining a negative electrode plate. The binder comprises sodium carboxymethyl cellulose and styrene-butadiene rubber in a weight ratio of 1:1.4.

[0031] The preparation method of the silicon-carbon composite material comprises the following steps: (1) Mix kaolin with 3 mol / L nitric acid in a weight ratio of 1:9, stir and react at 55°C for 11 hours; filter, wash with water until neutral, and dry to obtain acid-treated kaolin; mix acid-treated kaolin, sodium hydroxide, and water in a weight ratio of 1:0.6:9, stir and react at 35°C for 5 hours, filter, wash with water until neutral, and dry to obtain pretreated kaolin; (2) In the presence of cyclohexanol and anhydrous ethanol in a volume ratio of 1:1.6 as a solvent, the pretreated kaolin and glucose were evenly mixed. After removing the solvent, the mixture was calcined in an inert atmosphere at a temperature of 700°C and a time of 5 h to obtain a silicon-carbon composite material.

[0032] The weight ratio of the solvent to the kaolin is 13:1. The weight ratio of the glucose to the kaolin in terms of silicon dioxide is 1:4. The particle size of the kaolin is 325 mesh to 500 mesh. It was purchased from Shandong Qiyi Chemical Technology Co., Ltd. and the model is ultrafine calcined kaolin.

[0033] The carbon nanotubes include single-walled carbon nanotubes, multi-walled carbon nanotubes and double-walled carbon nanotubes in a mass ratio of 0.4:1:1.6; the single-walled carbon nanotubes have a diameter of 1-2 nm, a length of 5-30 μm, and a specific surface area of ​​120 m 2 / g, conductivity is 2400s / cm; the diameter of multi-walled carbon nanotubes is 3-6nm, the length is 0.5-1.5μm, and the specific surface area is 50m 2 / g, conductivity is 150s / cm; double-walled carbon nanotubes have a diameter of 2-4nm, a length of 0.5-2μm, and a specific surface area of ​​450m 2 / g, conductivity is 150s / cm; The preparation method of the positive electrode plate comprises the following steps: uniformly mixing nickel cobalt manganese hydroxide, polyvinylidene fluoride and carbon black in a weight ratio of 91:5:5, and coating the mixture on an aluminum foil with a thickness of 11 μm to obtain a positive electrode plate.

[0034] Example 2 This embodiment provides a high-temperature and high-rate secondary battery containing FEC electrolyte, including a positive electrode plate, a negative electrode plate and an electrolyte.

[0035] The electrolyte includes a solvent, an auxiliary agent and a lithium salt. The solvent includes ethylene carbonate, ethyl methyl carbonate and propylene carbonate in a volume ratio of 1:1.2:0.7; the auxiliary agent includes fluoroethylene carbonate, fluoroethylene carbonate, butane sultone and vinylene carbonate in a volume ratio of 1:1.3:0.4:1.8; the auxiliary agent accounts for 2% of the total weight of the electrolyte. The lithium salt includes LiPF 6 and LiAlO 2The molar concentration of the lithium salt in the electrolyte is 1.5 mol / L.

[0036] The preparation method of the negative electrode plate comprises the following steps: mixing a silicon-carbon composite material, carbon nanotubes and a binder in a weight ratio of 92:3:3.8 evenly, coating the mixture on a copper foil with a thickness of 9 μm, and obtaining a negative electrode plate. The binder comprises sodium carboxymethyl cellulose and styrene-butadiene rubber in a weight ratio of 1:1.2.

[0037] The preparation method of the silicon-carbon composite material comprises the following steps: (1) Mix kaolin with 4 mol / L nitric acid at a weight ratio of 1:10, stir and react at 60°C for 10 hours; filter, wash with water until neutral, and dry to obtain acid-treated kaolin; mix acid-treated kaolin, sodium hydroxide, and water at a weight ratio of 1:0.4:10, stir and react at 40°C for 6 hours, filter, wash with water until neutral, and dry to obtain pretreated kaolin; (2) In the presence of cyclohexanol and anhydrous ethanol in a volume ratio of 1:1.5 as a solvent, the pretreated kaolin and glucose were evenly mixed. After removing the solvent, the mixture was calcined in an inert atmosphere at a temperature of 600°C and a time of 6 hours to obtain a silicon-carbon composite material.

[0038] The weight ratio of the solvent to the kaolin is 12: 1. The weight ratio of the glucose to the kaolin in terms of silicon dioxide is 1: 5. The particle size of the kaolin is 325 mesh to 500 mesh. It was purchased from Shandong Qiyi Chemical Technology Co., Ltd. and the model is ultrafine calcined kaolin.

[0039] The carbon nanotubes include single-walled carbon nanotubes, multi-walled carbon nanotubes and double-walled carbon nanotubes in a mass ratio of 0.2:1:1.7; the single-walled carbon nanotubes have a diameter of 1-2 nm, a length of 5-30 μm, and a specific surface area of ​​120 m 2 / g, conductivity is 2400s / cm; the diameter of multi-walled carbon nanotubes is 3-6nm, the length is 0.5-1.5μm, and the specific surface area is 50m 2 / g, conductivity is 150s / cm; double-walled carbon nanotubes have a diameter of 2-4nm, a length of 0.5-2μm, and a specific surface area of ​​450m 2 / g, conductivity is 150s / cm; The preparation method of the positive electrode plate comprises the following steps: uniformly mixing nickel cobalt manganese hydroxide, polyvinylidene fluoride and carbon black in a weight ratio of 92:5:6, and coating the mixture on an aluminum foil with a thickness of 11 μm to obtain a positive electrode plate.

[0040] Comparative Example 1 The difference between this comparative example and Example 1 is that the solvent comprises ethylene carbonate, ethyl methyl carbonate and propylene carbonate in a volume ratio of 1:1:1.

[0041] Comparative Example 2 The difference between this comparative example and Example 1 is that the auxiliary agent includes fluoroethylene carbonate, fluoroethylene carbonate, butane sultone and vinylene carbonate in a volume ratio of 1:1:1:1.

[0042] Comparative Example 3 The difference between this comparative example and Example 1 is that the kaolin is not pretreated.

[0043] Comparative Example 4 The difference between this comparative example and Example 1 is that the carbon nanotubes include single-walled carbon nanotubes, multi-walled carbon nanotubes and double-walled carbon nanotubes in a mass ratio of 1:1:1; the single-walled carbon nanotubes have a diameter of 1-2 nm, a length of 5-30 μm, and a specific surface area of ​​120 m 2 / g, conductivity is 2400s / cm; the diameter of multi-walled carbon nanotubes is 3-6nm, the length is 0.5-1.5μm, and the specific surface area is 50m 2 / g, conductivity is 150s / cm; double-walled carbon nanotubes have a diameter of 2-4nm, a length of 0.5-2μm, and a specific surface area of ​​450m 2 / g, conductivity is 150s / cm.

[0044] Comparative Example 5 The difference between this comparative example and Example 1 is that kaolin is replaced by halloysite, which is purchased from Lingshou County Zhengxu Mineral Products Processing Plant, 325 mesh.

[0045] The preparation method of the silicon-carbon composite material comprises the following steps: (1) Mixing halloysite with 3 mol / L nitric acid in a weight ratio of 1:9, stirring and reacting at 55°C for 11 hours; filtering, washing with water until neutral, and drying to obtain acid-treated kaolin; mixing acid-treated kaolin, sodium hydroxide, and water in a weight ratio of 1:0.6:9, stirring and reacting at 35°C for 5 hours, filtering, washing with water until neutral, and drying to obtain pretreated halloysite; (2) In the presence of cyclohexanol and anhydrous ethanol in a volume ratio of 1:1.6 as a solvent, the pretreated halloysite and glucose were uniformly mixed. After removing the solvent, the mixture was calcined in an inert atmosphere at a temperature of 700°C and a time of 5 h to obtain a silicon-carbon composite material.

[0046] The weight ratio of the glucose to the halloysite calculated as silicon dioxide is 1:4.

[0047] Comparative Example 6 The difference between this comparative example and Example 1 is that the diameter of the single-walled carbon nanotube is 4-6 nm, the length is 20-30 μm, and the specific surface area is 80 m 2 / g, conductivity is 2500s / cm; double-walled carbon nanotubes have a diameter of 5-8nm, a length of 1-4μm, and a specific surface area of ​​300m 2 / g, conductivity is 100s / cm; the diameter of multi-walled carbon nanotubes is 10-20nm, the length is 2-4μm, and the specific surface area is 27m 2 / g, conductivity is 90s / cm. It was purchased from Jiangsu Xianfeng Nanomaterial Technology Co., Ltd.

[0048] Performance Testing The secondary batteries prepared in Examples 1-2 and Comparative Examples 1-6 were subjected to performance tests.

[0049] 1. Assemble the high-temperature and high-rate secondary battery, including the positive electrode sheet, the negative electrode sheet and the electrolyte. The battery adopts a laminated structure, with an actual capacity of 6Ah, a battery thickness of 6.5mm, and an operating voltage range of 2.5-4.2V. After the battery is assembled, it is first activated by charging and discharging at a low current of 0.1C for 3 weeks, and then the battery's room-temperature rate performance is measured (where "C" is a unit representing the charging or discharging rate, called "rate" (C-rate); for example, 0.1C means charging and discharging at a rate of 0.1 times the rated capacity of the battery.) The results are shown in Table 1.

[0050] Table 1 Room temperature rate performance test results 0.3C 0.5C 1.0C 2.0C 3.0C Example 1 100 99.3 99.1 98.9 98.1 Example 2 100 99.2 99.0 98.7 98.0 Comparative Example 1 100 98.5 97.8 97.2 95.7 Comparative Example 2 100 98.4 97.9 97.3 95.9 Comparative Example 3 100 98.6 98.1 97.5 96.2 Comparative Example 4 100 98.7 98.0 97.6 96.0 Comparative Example 5 100 98.3 97.6 97.0 95.3 Comparative Example 6 100 98.8 98.2 97.5 96.1 2. -20℃ discharge capacity: After charging at 25A, 4.2V, constant current constant voltage (CC-CV) for 3 hours at room temperature, place at -20℃ for 4 hours, discharge to 2.7V with a current of 25A at constant current (CC), and measure the available capacity (%) relative to the initial capacity.

[0051] Capacity recovery rate after 30 days at 60°C: After charging at 4.2V, 25A constant current and constant voltage (CC-CV) for 3 hours at room temperature, the battery was placed at 60°C for 30 days, and then discharged to 2.7V with a constant current (CC) of 25A, and the recovery rate (%) relative to the initial capacity was measured.

[0052] Normal temperature life: After charging at 4.2V, 50A constant current constant voltage (CC-CV) for 3 hours at room temperature, discharge 500 times at 2.7V, 25A current until 2.7V. At this time, the first discharge capacity is set as C, and the 500th discharge capacity is divided by the first discharge capacity to calculate the capacity retention rate (%) during life.

[0053] The results are shown in Table 2.

[0054] Table 2 Performance test results Capacity recovery rate after 30 days at 60°C% Capacity maintenance rate during life % -20℃ discharge capacity% Example 1 94.1 94.2 92.0 Example 2 93.2 93.4 90.6 Comparative Example 1 82.7 81.8 76.8 Comparative Example 2 81.5 83.1 75.2 Comparative Example 3 85.3 84.9 78.3 Comparative Example 4 86.0 85.7 80.5 Comparative Example 5 78.3 85.6 74.7 Comparative Example 6 87.8 86.3 82.4 It can be seen from the above performance test results that the secondary batteries of Examples 1-2 have excellent performance, especially the comprehensive performance of Example 1 is the most outstanding, which is mainly due to the synergistic effect of the positive electrode, the negative electrode and the electrolyte.

[0055] However, the comparative examples are significantly worse than the embodiments in terms of corresponding performance tests because they do not adopt the necessary technical solutions. The solvent ratio is changed in comparative example 1, and the auxiliary agent ratio is changed in comparative example 2. It can be seen from the results that the rate performance of the secondary battery is reduced. In comparative example 3, kaolin is not pretreated, and in comparative example 5, kaolin is replaced with halloysite. It can be seen that the service life of the secondary battery at room temperature is reduced; the service life of the secondary battery at low temperature is also reduced. The ratio of carbon nanotubes in comparative example 4 is different, and the parameters of carbon nanotubes in comparative example 6 are different, which will affect the capacity recovery rate of the secondary battery after use at high temperature. The above experimental results further prove the importance of the technical solution defined in the present invention for its technical effect.

[0056] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A high-temperature and high-rate secondary battery containing a FEC electrolyte, characterized in that: Including positive electrode sheet, negative electrode sheet and electrolyte; The electrolyte comprises a solvent, an auxiliary agent and a lithium salt; The solvent comprises ethylene carbonate, ethyl methyl carbonate and propylene carbonate in a volume ratio of 1: (1.2-1.4): (0.5-0.7); The auxiliary agent includes fluoroethylene carbonate, fluoroethylene carbonate, butane sultone and vinylene carbonate in a volume ratio of 1: (1.3-1.6): (0.2-0.4): (1.5-1.8); The auxiliary agent accounts for 2-4% of the total weight of the electrolyte.

2. The high-temperature and high-rate secondary battery containing FEC electrolyte according to claim 1, characterized in that: The lithium salt includes LiPF6 and LiAlO2 in a molar ratio of (3-5):1; the molar concentration of the lithium salt in the electrolyte is 1.5-1.7 mol / L.

3. The high-temperature and high-rate secondary battery containing FEC electrolyte according to claim 1, characterized in that: The preparation method of the negative electrode plate comprises the following steps: mixing a silicon-carbon composite material, carbon nanotubes and a binder in a weight ratio of (92-94):3:(3.8-4.2) evenly, coating the mixture on a copper foil with a thickness of 8-10 μm, and obtaining a negative electrode plate.

4. The high-temperature and high-rate secondary battery containing FEC electrolyte according to claim 3, characterized in that: The preparation method of the silicon-carbon composite material comprises the following steps: (1) Mix kaolin with 2-4 mol / L nitric acid in a weight ratio of 1:(8-10), stir and react at 50-60°C for 10-12 hours; filter, wash with water until neutral, and dry to obtain acid-treated kaolin; mix acid-treated kaolin, sodium hydroxide, and water in a weight ratio of 1:(0.4-0.7):(8-10), stir and react at 30-40°C for 4-6 hours, filter, wash with water until neutral, and dry to obtain pretreated kaolin; (2) In the presence of cyclohexanol and anhydrous ethanol in a volume ratio of 1: (1.5-1.7) as a solvent, the pretreated kaolin and glucose are uniformly mixed, and after removing the solvent, calcined in an inert atmosphere at a temperature of 600-800°C and a calcination time of 4-6 hours to obtain a silicon-carbon composite material.

5. The high-temperature and high-rate secondary battery containing FEC electrolyte according to claim 4, characterized in that: The weight ratio of glucose to kaolin calculated as silicon dioxide is 1:(2-5).

6. The high-temperature and high-rate secondary battery containing FEC electrolyte according to claim 4, characterized in that: The particle size of the kaolin is 325 meshes to 500 meshes.

7. The high-temperature and high-rate secondary battery containing FEC electrolyte according to claim 4, characterized in that: The weight ratio of the solvent to kaolin is (12-15):

1.

8. The high-temperature and high-rate secondary battery containing FEC electrolyte according to claim 3, characterized in that: The carbon nanotubes include single-walled carbon nanotubes, multi-walled carbon nanotubes and double-walled carbon nanotubes in a mass ratio of (0.2-0.5):1:(1.5-1.7); the single-walled carbon nanotubes have a diameter of 1-2 nm, a length of 5-30 μm, and a specific surface area of ​​120 m 2 / g, conductivity is 2400s / cm; the diameter of multi-walled carbon nanotubes is 3-6nm, the length is 0.5-1.5μm, and the specific surface area is 50m 2 / g, conductivity is 150s / cm; double-walled carbon nanotubes have a diameter of 2-4nm, a length of 0.5-2μm, and a specific surface area of ​​450m 2 / g, conductivity is 150s / cm.

9. The high-temperature and high-rate secondary battery containing FEC electrolyte according to claim 3, characterized in that: The binder comprises sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 1: (1.2-1.5).

10. The high-temperature and high-rate secondary battery containing FEC electrolyte according to claim 1, characterized in that: The preparation method of the positive electrode plate comprises the following steps: uniformly mixing nickel cobalt manganese hydroxide, polyvinylidene fluoride and carbon black in a weight ratio of (90-92):5:(4-6), and coating the mixture on an aluminum foil with a thickness of 10-12 μm to obtain a positive electrode plate.