A high-temperature and high-rate secondary battery with an FEC-containing electrolyte

Abstract

The present invention belongs to the technical field of batteries, and particularly relates to a high-temperature and high-rate secondary battery containing an FEC electrolyte. The high-temperature and high-rate secondary battery includes a positive electrode sheet, a negative electrode sheet, and an electrolyte; the electrolyte includes a solvent, an additive, and a lithium salt, and the solvent includes ethylene carbonate, ethyl methyl carbonate, and propylene carbonate in a volume ratio of 1:(1.2-1.4):(0.5-0.7); the additive 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 additive accounts for 2-4% of the total weight of the electrolyte. The secondary battery prepared by the present invention has excellent performance, has a high rate, and can still maintain a high cycle performance at high temperatures.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and particularly relates to a high-temperature and high-rate secondary battery with an FEC electrolyte. Background Art

[0002] The electrolyte used in lithium-ion batteries for electric vehicles is one of the key factors affecting battery performance. The main function of the electrolyte is to provide a medium for ion transport, ensuring that lithium ions inside the battery can move efficiently between the positive and negative electrodes. A lithium secondary battery generates electrical energy through oxidation and reduction reactions during the insertion and extraction of lithium ions in the positive and negative electrodes. Therefore, a lithium secondary battery is prepared by using substances that can insert and extract lithium ions as the negative and positive electrodes, and filling an organic electrolyte or a polymer electrolyte 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 challenges: 1. Unstable SEI film: The solid electrolyte interface (SEI) film may be unstable in some cases, leading to internal short circuits or thermal runaway in the battery. 2. Cycle life: As the number of charge and discharge cycles increases, the capacity of the battery gradually decreases. 3. Energy density: The energy density of commonly used positive and negative electrode materials is limited, making it difficult to meet the demand for higher energy density. 4. Fast charging ability: Lithium dendrites: During fast charging, the deposition rate of lithium ions on the surface of the negative electrode is too fast, easily forming lithium dendrites, resulting in internal short circuits and safety hazards in the battery. 5. Environmental adaptability: At low and high temperatures, the conductivity of the electrolyte decreases, affecting the performance of the battery, and the cycle life and safety of the battery will decline.

[0004] In the prior art, by optimizing the types and contents of lithium salts and additives, while increasing the conductivity of the electrolyte, the irreversible expansion of the silicon-based negative electrode sheet is reduced, which can improve the rate charging performance and cycle life of lithium-ion batteries, but it does not solve the problem of performance loss of lithium-ion batteries at high temperatures and cannot meet the current market demand.

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

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

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A high-temperature and high-rate secondary battery with an FEC-containing electrolyte includes a positive electrode plate, a negative electrode plate, and an electrolyte; the electrolyte includes a solvent, an additive, and a lithium salt, and the solvent includes ethylene carbonate, ethyl methyl carbonate, and propylene carbonate in a volume ratio of 1:(1.2 - 1.4):(0.5 - 0.7); the additive 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 additive accounts for 2 - 4% of the total weight of the electrolyte.

[0009] The performance of lithium secondary batteries is mainly affected by the structure of the organic electrolyte and the SEI film formed through the reaction of the organic electrolyte and the electrode. The performance after the reaction of the commonly used electrolytes in the market with the electrodes prepared in the present invention is not ideal. In the present invention, by synergistically using solvents and additives in specific ratios, the rate performance of secondary batteries can be improved. The analysis is that the performance of lithium secondary batteries is affected by the structure of the organic electrolyte and the SEI film formed through the reaction of the organic electrolyte and the electrode. Suitable solvents can increase 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 electrodes prepared in 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 electrode surface to form a denser and more uniform SEI film, thereby improving the cycle stability and rate performance of the battery.

[0010] Further, the lithium salt includes LiPF6 and LiAlO2 in a molar ratio of (3 - 5):1.

[0011] Further, the molar concentration of the lithium salt in the electrolyte is 1.5 - 1.7 mol / L.

[0012] Further, the preparation method of the negative electrode plate includes 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), and coating it on a copper foil with a thickness of 8 - 10 μm to obtain the negative electrode plate.

[0013] Further, the preparation method of the silicon-carbon composite material includes the following steps:

[0014] (1) Mix kaolin with nitric acid at a weight ratio of 1:(8 - 10) and 2 - 4 mol / L, stir and react at 50 - 60 °C for 10 - 12 h; filter, wash with water until neutral, and dry to obtain acid-treated kaolin. Mix the acid-treated kaolin, sodium hydroxide, and water at a weight ratio of 1:(0.4 - 0.7):(8 - 10), stir and react at 30 - 40 °C for 4 - 6 h, filter, wash with water until neutral, and dry to obtain pretreated kaolin.

[0015] (2) Under the condition that cyclohexanol and absolute ethanol with a volume ratio of 1:(1.5 - 1.7) are used as solvents, mix the pretreated kaolin and glucose evenly. After removing the solvents, calcine in an inert atmosphere at a calcination temperature of 600 - 800 °C for 4 - 6 h to obtain a silicon-carbon composite material.

[0016] Further, the weight ratio of glucose to kaolin calculated as silica is 1:(2 - 5).

[0017] Further, the particle size of the kaolin is 325 mesh - 500 mesh. It is purchased from Shandong Qiyi Chemical Technology Co., Ltd., and the model is ultra-fine calcined kaolin.

[0018] Further, the weight ratio of the solvent to kaolin is (12 - 15):1.

[0019] In the prior art, adding silica directly is used to improve the problem of low specific capacity of graphite as the negative electrode. However, if the size and distribution of the directly added silica particles are uneven, it will lead to uneven stress distribution inside the electrode, exacerbate the pulverization and shedding of the electrode material, and the service life of the prepared secondary battery is not ideal. In the present invention, a silicon-carbon composite material is prepared by using kaolin and an organic carbon source, which improves the service life of the secondary battery at room temperature. This is mainly because the present invention uses kaolin as the source of silica, and the combination of silica and carbon produces a composite structure, and its special morphology alleviates the phenomenon of volume expansion during charge and discharge, and the battery prepared with it has higher performance stability during charge and discharge. At the same time, it improves the service life of the secondary battery at low temperature.

[0020] Further, the carbon nanotubes include single-walled carbon nanotubes, multi-walled carbon nanotubes, and double-walled carbon nanotubes with a mass ratio of (0.2 - 0.5):1:(1.5 - 1.7); the diameter of the single-walled carbon nanotubes is 1 - 2 nm, the length is 5 - 30 μm, the specific surface area is 120 m 2 / g, and the conductivity is 2400 s / cm; the diameter of the multi-walled carbon nanotubes is 3 - 6 nm, the length is 0.5 - 1.5 μm, the specific surface area is 50 m 2 / g, and the conductivity is 150 s / cm; the diameter of the double-walled carbon nanotubes is 2 - 4 nm, the length is 0.5 - 2 μm, and the specific surface area is 450 m2 / g, with a conductivity of 150 s / cm.

[0021] By adding carbon nanotubes with specific parameters and ratios, the present invention improves the capacity recovery rate of secondary batteries after use at high temperatures. The carbon nanotubes of the present invention can form a three-dimensional network structure, increasing the porosity and specific surface area of the electrode material, which is conducive to the rapid transmission of lithium ions. At high temperatures, the diffusion rate of lithium ions will be affected. The three-dimensional network structure of carbon nanotubes can provide more transmission paths, accelerating the diffusion of lithium ions and improving the high-temperature performance and capacity recovery rate of the battery. At the same time, the synergistic effect of carbon nanotubes and the silicon-carbon composite material of the present invention can comprehensively improve the conductivity, mechanical properties of the electrode, and the stability of the SEI film, thus significantly improving the capacity recovery rate of the battery at high temperatures.

[0022] The graphite layers are combined by van der Waals forces. The intermolecular forces are small and the layer spacing is smaller than the crystal layer spacing of graphite intercalation compounds. As a result, during the charge and discharge process, the graphite layer spacing changes, causing the graphite flakes to exfoliate and pulverize, resulting in unsatisfactory electrical cycling performance. Secondly, due to the structural defects of graphite itself, there are many active groups on its surface, making the compatibility between natural graphite and solvents poor. Some domestic research institutions use phenolic resin to modify natural graphite once. Although this modification method can improve the specific capacity and cycling rate of graphite materials, there are still the following serious defects: (1) During the stirring or volatilization process of phenolic resin, it is easy to form an adhesive system that is prone to sedimentation, resulting in uneven coating on the graphite surface; (2) There will be holes on the surface of the graphite coated with phenolic resin once, and in some places, there is even no coating, resulting in the exposure of graphite, which will cause the generation of irreversible capacity when contacting with the electrolyte, thus reducing the cycling performance of graphite.

[0023] Further, the binder includes sodium carboxymethyl cellulose and styrene-butadiene rubber with a mass ratio of 1: (1.2 - 1.5).

[0024] Further, the preparation method of the positive electrode sheet includes the following steps: mixing nickel cobalt manganese hydroxide, polyvinylidene fluoride, and carbon black with a weight ratio of (90 - 92): 5: (4 - 6) evenly, and coating it on an aluminum foil with a thickness of 10 - 12 μm to obtain the positive electrode sheet.

[0025] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0026] 1. In the electrolyte system of the present invention, by adding an appropriate amount of FEC-containing additive, a stable solid electrolyte interface (SEI) film can be formed, reducing the occurrence of side reactions, ensuring the compatibility of FEC with the positive and negative electrode materials, avoiding adverse reactions, and improving the cycling stability, thermal stability, and overall safety of secondary batteries by introducing FEC as an electrolyte additive.

[0027] 2. By synergistically using a solvent and an auxiliary agent with specific ratios, the present invention can improve the rate performance of secondary batteries.

[0028] 3. By using kaolin and an organic carbon source to prepare a silicon-carbon composite material, the present invention improves the service life of secondary batteries at room temperature; meanwhile, the service life of secondary batteries at low temperature is also improved.

[0029] 4. By adding carbon nanotubes with specific parameters and ratios, the present invention improves the capacity recovery rate of secondary batteries after use at high temperature. Specific Embodiments

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0031] All raw materials used in the following embodiments of the present invention are commercially available products:

[0032] Nickel cobalt manganese hydroxide, Ni 0.6 Co 0.2 Mn 0.2 (OH)2, purchased from Dalian Ruiyuan Power Co., Ltd.

[0033] Example 1

[0034] This example provides a high-temperature and high-rate secondary battery with an FEC electrolyte, including a positive electrode sheet, a negative electrode sheet, 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 with a volume ratio of 1:1.3:0.6; the auxiliary agent includes fluoroethylene carbonate, fluoroethylene carbonate, butanesultone, and vinylene carbonate with 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 LiPF6 and LiAlO2 with a molar ratio of 4:1. The molar concentration of the lithium salt in the electrolyte is 1.6 mol / L.

[0036] The preparation method of the negative electrode sheet includes the following steps: mixing a silicon-carbon composite material, carbon nanotubes, and a binder with a weight ratio of 93:3:4 evenly, and coating it on a copper foil with a thickness of 9 μm to obtain a negative electrode sheet. The binder includes sodium carboxymethyl cellulose and styrene-butadiene rubber with a mass ratio of 1:1.4.

[0037] The preparation method of the silicon-carbon composite material includes the following steps:

[0038] (1) Mix kaolin and 3 mol / L nitric acid at a weight ratio of 1:9, react with stirring at 55 °C for 11 h; filter, wash with water until neutral, and dry to obtain acid-treated kaolin. Mix the acid-treated kaolin, sodium hydroxide, and water at a weight ratio of 1:0.6:9, react with stirring at 35 °C for 5 h, filter, wash with water until neutral, and dry to obtain pretreated kaolin.

[0039] (2) Under the condition that cyclohexanol and absolute ethanol with a volume ratio of 1:1.6 are used as solvents, mix the pretreated kaolin and glucose evenly. After removing the solvents, calcine in an inert atmosphere at a calcination temperature of 700 °C for 5 h to obtain a silicon-carbon composite material.

[0040] The weight ratio of the solvent to kaolin is 13:1. The weight ratio of glucose to kaolin calculated as silicon dioxide is 1:4. The particle size of the kaolin is 325 mesh - 500 mesh. It is purchased from Shandong Qiyi Chemical Technology Co., Ltd., and the model is ultrafine calcined kaolin.

[0041] The carbon nanotubes include single-walled carbon nanotubes, multi-walled carbon nanotubes, and double-walled carbon nanotubes with a mass ratio of 0.4:1:1.6; the diameter of the single-walled carbon nanotubes is 1 - 2 nm, the length is 5 - 30 μm, the specific surface area is 120 m 2 / g, and the conductivity is 2400 s / cm; the diameter of the multi-walled carbon nanotubes is 3 - 6 nm, the length is 0.5 - 1.5 μm, the specific surface area is 50 m 2 / g, and the conductivity is 150 s / cm; the diameter of the double-walled carbon nanotubes is 2 - 4 nm, the length is 0.5 - 2 μm, the specific surface area is 450 m 2 / g, and the conductivity is 150 s / cm;

[0042] The preparation method of the positive electrode plate includes the following steps: Mix nickel cobalt manganese hydroxide, polyvinylidene fluoride, and carbon black at a weight ratio of 91:5:5, and coat it on an aluminum foil with a thickness of 11 μm to obtain a positive electrode plate.

[0043] Example 2

[0044] This example provides a high-temperature and high-rate secondary battery containing FEC electrolyte, including a positive electrode plate, a negative electrode plate, and an electrolyte.

[0045] The electrolyte includes a solvent, an additive, and a lithium salt. The solvent includes ethylene carbonate, ethyl methyl carbonate, and propylene carbonate with a volume ratio of 1:1.2:0.7. The additive includes fluoroethylene carbonate, fluoroethylene carbonate, butane sultone, and vinylene carbonate with a volume ratio of 1:1.3:0.4:1.8. The additive accounts for 2% of the total weight of the electrolyte. The lithium salt includes LiPF6 and LiAlO2 with a molar ratio of 3:1. The molar concentration of the lithium salt in the electrolyte is 1.5 mol / L.

[0046] The preparation method of the negative electrode sheet includes the following steps: Mix a silicon-carbon composite material, carbon nanotubes, and a binder with a weight ratio of 92:3:3.8 evenly, and coat it on a copper foil with a thickness of 9 μm to obtain the negative electrode sheet. The binder includes sodium carboxymethyl cellulose and styrene-butadiene rubber with a mass ratio of 1:1.2.

[0047] The preparation method of the silicon-carbon composite material includes the following steps:

[0048] (1) Mix kaolin with 4 mol / L nitric acid at a weight ratio of 1:10, stir and react at 60 °C for 10 h; filter, wash with water until neutral, and dry to obtain acid-treated kaolin. Mix the acid-treated kaolin, sodium hydroxide, and water at a weight ratio of 1:0.4:10, stir and react at 40 °C for 6 h, filter, wash with water until neutral, and dry to obtain pretreated kaolin;

[0049] (2) Under the condition that cyclohexanol and absolute ethanol with a volume ratio of 1:1.5 are used as solvents, mix the pretreated kaolin and glucose evenly. After removing the solvents, calcine in an inert atmosphere at a calcination temperature of 600 °C for 6 h to obtain the silicon-carbon composite material.

[0050] The weight ratio of the solvent to kaolin is 12:1. The weight ratio of glucose to kaolin calculated as silica is 1:5. The particle size of the kaolin is 325 mesh - 500 mesh. It is purchased from Shandong Qiyi Chemical Technology Co., Ltd., and the model is ultra-fine calcined kaolin.

[0051] The carbon nanotubes include single-walled carbon nanotubes, multi-walled carbon nanotubes, and double-walled carbon nanotubes with a mass ratio of 0.2:1:1.7. The diameter of the single-walled carbon nanotubes is 1 - 2 nm, the length is 5 - 30 μm, the specific surface area is 120 m 2 / g, and the conductivity is 2400 s / cm; the diameter of the multi-walled carbon nanotubes is 3 - 6 nm, the length is 0.5 - 1.5 μm, the specific surface area is 50 m 2 / g, and the conductivity is 150 s / cm; the diameter of the double-walled carbon nanotubes is 2 - 4 nm, the length is 0.5 - 2 μm, the specific surface area is 450 m 2 / g, and the conductivity is 150 s / cm;

[0052] The preparation method of the positive electrode plate comprises the following steps: mixing nickel cobalt manganese hydroxide, polyvinylidene fluoride and carbon black with a weight ratio of 92:5:6 evenly, and coating them on an aluminum foil with a thickness of 11 μm to obtain the positive electrode plate.

[0053] Comparative Example 1

[0054] The difference between this comparative example and Example 1 is that the solvent comprises ethylene carbonate, ethyl methyl carbonate and propylene carbonate with a volume ratio of 1:1:1.

[0055] Comparative Example 2

[0056] The difference between this comparative example and Example 1 is that the auxiliary agent comprises fluoroethylene carbonate, fluoroethylene carbonate, butanesultone and vinylene carbonate with a volume ratio of 1:1:1:1.

[0057] Comparative Example 3

[0058] The difference between this comparative example and Example 1 is that kaolin is not pretreated.

[0059] Comparative Example 4

[0060] The difference between this comparative example and Example 1 is that the carbon nanotubes comprise single-walled carbon nanotubes, multi-walled carbon nanotubes and double-walled carbon nanotubes with a mass ratio of 1:1:1; the diameter of the single-walled carbon nanotubes is 1 - 2 nm, the length is 5 - 30 μm, the specific surface area is 120 m 2 / g, and the conductivity is 2400 s / cm; the diameter of the multi-walled carbon nanotubes is 3 - 6 nm, the length is 0.5 - 1.5 μm, the specific surface area is 50 m 2 / g, and the conductivity is 150 s / cm; the diameter of the double-walled carbon nanotubes is 2 - 4 nm, the length is 0.5 - 2 μm, the specific surface area is 450 m 2 / g, and the conductivity is 150 s / cm.

[0061] Comparative Example 5

[0062] The difference between this comparative example and Example 1 is that kaolin is replaced by halloysite. Purchased from Zhengxu Mineral Products Processing Factory, Lingshou County, 325 mesh.

[0063] The preparation method of the silicon-carbon composite material comprises the following steps:

[0064] (1) Mix halloysite with a weight ratio of 1:9 and 3 mol / L nitric acid, stir and react at 55 °C for 11 h; filter, wash with water until neutral, and dry to obtain acid-treated kaolin. Mix acid-treated kaolin, sodium hydroxide and water with a weight ratio of 1:0.6:9, stir and react at 35 °C for 5 h, filter, wash with water until neutral, and dry to obtain pretreated halloysite;

[0065] (2) Under the condition that cyclohexanol and absolute ethanol with a volume ratio of 1:1.6 are used as solvents, the pretreated halloysite and glucose are mixed evenly. After removing the solvents, they are calcined in an inert atmosphere at a calcination temperature of 700 °C for 5 h to obtain a silicon-carbon composite material.

[0066] The weight ratio of the glucose to the halloysite calculated as silica is 1:4.

[0067] Comparative Example 6

[0068] The difference between this comparative example and Example 1 is that the diameter of the single-walled carbon nanotubes is 4 - 6 nm, the length is 20 - 30 μm, the specific surface area is 80 m 2 / g, and the conductivity is 2500 s / cm; the diameter of the double-walled carbon nanotubes is 5 - 8 nm, the length is 1 - 4 μm, the specific surface area is 300 m 2 / g, and the conductivity is 100 s / cm; the diameter of the multi-walled carbon nanotubes is 10 - 20 nm, the length is 2 - 4 μm, the specific surface area is 27 m 2 / g, and the conductivity is 90 s / cm. They are purchased from Jiangsu Xianfeng Nano Materials Technology Co., Ltd.

[0069] Performance Test

[0070] The secondary batteries prepared in Examples 1 - 2 and Comparative Examples 1 - 6 are subjected to performance tests.

[0071] 1. Assemble a high-temperature high-rate secondary battery, including a positive electrode plate, a negative electrode plate, and an electrolyte. The battery adopts a stacked structure, with an actual capacity of 6 Ah, a battery thickness of 6.5 mm, and a working voltage range of 2.5 - 4.2 V. After the battery assembly is completed, first charge and discharge at a small current of 0.1C for 3 weeks for activation, and then measure the room-temperature rate performance of the battery (where "C" is a unit representing the charge or discharge rate, called the "rate" (C-rate); for example, 0.1C means charging and discharging at a rate of 0.1 times the rated capacity of the battery).)

[0072] The results are shown in Table 1.

[0073] Table 1 Detection Results of Room-Temperature Rate Performance

[0074] 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

[0075] 2. Discharge capacity at -20 °C: After charging at a constant current and constant voltage (CC - CV) of 25 A and 4.2 V for 3 hours at room temperature, after standing at -20 °C for 4 hours, use a current of 25 A and discharge at a constant current (CC) until 2.7 V, and then measure the available capacity (%) relative to the initial capacity.

[0076] Capacity recovery rate after 30 days at 60°C: After charging at a constant current and constant voltage (CC-CV) of 4.2V and 25A for 3 hours at room temperature, it is placed at 60°C for 30 days. Then, after discharging at a constant current (CC) of 25A to 2.7V, the recovery rate (%) relative to the initial capacity is measured.

[0077] Room temperature life: After charging at a constant current and constant voltage (CC-CV) of 4.2V and 50A for 3 hours at room temperature, it is repeatedly discharged 500 times until 2.7V with a current of 2.7V and 25A. 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 the life.

[0078] The results are shown in Table 2.

[0079] Table 2 Performance test results

[0080] Capacity recovery rate (%) after 30 days at 60°C Capacity retention rate during life (%) Discharge capacity at -20°C (%) 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

[0081] From the above performance test results, it can be seen that the performance of the secondary batteries in Examples 1-2 is excellent. In particular, the comprehensive performance of Example 1 is the most prominent, which is mainly due to the synergistic effect of the positive electrode, negative electrode, and electrolyte.

[0082] In the comparative examples, because the necessary technical solutions were not adopted, their performance in the corresponding performance tests was significantly worse than that of the examples. In Comparative Example 1, the solvent ratio was changed, and in Comparative Example 2, the additive ratio was changed. It can be seen from the results that the rate performance of the secondary battery decreased. In Comparative Example 3, kaolin was not pretreated, and in Comparative Example 5, kaolin was replaced with halloysite. It can be seen that the service life of the secondary battery at room temperature decreased; the service life of the secondary battery at low temperature also decreased. In Comparative Example 4, the ratio of carbon nanotubes was different, and in Comparative Example 6, the parameters of carbon nanotubes were different, which would affect the capacity recovery rate after the secondary battery was used at high temperature. The above experimental results further prove the importance of the technical solutions defined in the present invention for its technical effects.

[0083] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A high-temperature and high-rate secondary battery with an FEC electrolyte, characterized in that it includes a positive electrode plate, a negative electrode plate and an electrolyte; the electrolyte includes a solvent, an additive and a lithium salt; the solvent includes ethylene carbonate, ethyl methyl carbonate and propylene carbonate in a volume ratio of 1:(1.2 - 1.4):(0.5 - 0.7); the additive includes fluoroethylene carbonate, butane sultone and vinylene carbonate in a volume ratio of (2.3 - 2.6):(0.2 - 0.4):(1.5 - 1.8); the additive accounts for 2 - 4% of the total weight of the electrolyte; the preparation method of the negative electrode plate includes 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), and coating it on a copper foil with a thickness of 8 - 10 μm to obtain a negative electrode plate; the preparation method of the silicon-carbon composite material includes 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 h; 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 h, filter, wash with water until neutral, and dry to obtain pretreated kaolin; (2) Under the condition that cyclohexanol and absolute ethanol in a volume ratio of 1:(1.5 - 1.7) are used as solvents, mix pretreated kaolin and glucose evenly, remove the solvent, and then calcine in an inert atmosphere. The calcination temperature is 600 - 800 °C, and the calcination time is 4 - 6 h to obtain a silicon-carbon composite material; 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; 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 diameter of the single-walled carbon nanotubes is 1 - 2 nm, the length is 5 - 30 μm, the specific surface area is 120 m 2 / g, and the conductivity is 2400 s / cm; the diameter of the multi-walled carbon nanotubes is 3 - 6 nm, the length is 0.5 - 1.5 μm, the specific surface area is 50 m 2 / g, and the conductivity is 150 s / cm; the diameter of the double-walled carbon nanotubes is 2 - 4 nm, the length is 0.5 - 2 μm, the specific surface area is 450 m 2 / g, and the conductivity is 150 s / cm.

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

3. The high-temperature and high-rate secondary battery with an FEC electrolyte according to claim 1, characterized in that the particle size of the kaolin is 325 mesh - 500 mesh.

4. The high-temperature and high-rate secondary battery with an FEC electrolyte according to claim 1, characterized in that the weight ratio of the solvent to kaolin is (12 - 15):

1.

5. The high-temperature and high-rate secondary battery with an FEC electrolyte according to claim 1, characterized in that the binder includes sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 1:(1.2 - 1.5).