Secondary battery and electric device

Abstract

The invention discloses a secondary battery and an electric device, and belongs to the technical field of batteries. According to the secondary battery provided by the invention, the propionate organic solvent containing propyl propionate and / or ethyl propionate is added into the electrolyte, and meanwhile, the mass percentage a of the silicon-carbon material in the negative electrode active material, the mass percentage b of the hydrogen element in the silicon-carbon material and the mass percentage c of the propionate organic solvent in the electrolyte are controlled; on one hand, the lithium intercalation kinetics of the silicon-carbon material can be accelerated and the transmission capability of lithium ions can be improved on the basis of effectively reducing the side reaction between the silicon-carbon material and an electrolyte under the conditions of normal temperature and high temperature, so that the internal resistance of the secondary battery is reduced, and the cycle performance of the secondary battery under the conditions of normal temperature and high temperature is improved; on the other hand, the excessive increase of the viscosity of the electrolyte under the high voltage condition can be relieved, and the floating charge performance of the secondary battery under the high voltage condition is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a secondary battery and a power utilization device. BACKGROUND

[0002] Currently, the negative electrode material widely used in secondary batteries is graphite material, but the capacity of commercialized graphite negative electrode has approached its theoretical specific capacity (372 mAh / g), and the endurance anxiety is still a key factor restricting consumers to choose new energy vehicles. Under this background, developing new negative electrode materials suitable for high-capacity batteries is an inevitable trend for the development of the secondary battery industry.

[0003] The theoretical specific capacity of silicon-based negative electrode material is as high as 4200 mAh / g, which is 10 times that of traditional graphite material, and can greatly improve the energy density of secondary batteries. New silicon-carbon negative electrodes based on porous carbon have begun to be mass-produced for unmanned aerial vehicles, notebook and mobile phone brands, and the mixing ratio is becoming higher and higher.

[0004] However, the silicon-carbon has poor conductivity, poor rate performance, and low compaction density. As the mixing ratio of silicon-carbon becomes higher and higher, the float performance and cycle performance of the material deteriorate significantly compared with pure graphite. SUMMARY

[0005] The present application aims to solve the technical problem of poor float performance and cycle performance of the secondary battery caused by the addition of silicon-carbon material in the negative electrode material of the secondary battery in the prior art, and proposes a secondary battery and a power utilization device.

[0006] To achieve the above-mentioned purpose, the first aspect of the present application provides a secondary battery, the secondary battery comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector,

[0007] The negative electrode active material layer comprises a negative electrode active material, the negative electrode active material comprising a silicon-carbon material and graphite, and the silicon-carbon material comprising a hydrogen element;

[0008] The electrolyte comprises a propionic acid ester organic solvent, and the propionic acid ester organic solvent comprises at least one of propyl propionate and ethyl propionate;

[0009] The secondary battery satisfies 0.005≤A≤15,

[0010] Wherein A=100×a×b / c;

[0011] a is the mass percentage of the silicon-carbon material based on the mass of the negative electrode active material;

[0012] b is the mass percentage of the hydrogen element in the silicon-carbon material;

[0013] c is the mass percentage of propionate ester organic solvent based on the total mass of electrolyte.

[0014] As an embodiment of the present application, the mass percentage a of silicon-carbon material based on the mass of negative electrode active material is 5-50%.

[0015] As an embodiment of the present application, the mass percentage b of hydrogen element in silicon-carbon material is 0.02-5%.

[0016] As an embodiment of the present application, the mass percentage c of propionate ester organic solvent based on the total mass of electrolyte is 10-70%.

[0017] As an embodiment of the present application, the electrolyte further comprises sulfonic acid pentafluorophenol ester compound; the sulfonic acid pentafluorophenol ester compound comprises at least one of pentafluorophenyl methanesulfonate and pentafluorophenyl propanesulfonate.

[0018] As an embodiment of the present application, the mass percentage d of sulfonic acid pentafluorophenol ester compound based on the total mass of electrolyte is 0.5-3%.

[0019] As an embodiment of the present application, the secondary battery satisfies 0.1≤B≤2.27;

[0020] wherein B=100×a×b+d / a.

[0021] As an embodiment of the present application, the electrolyte further comprises vinyl carbonate substance, and the vinyl carbonate substance comprises at least one of vinyl carbonate and fluorinated vinyl carbonate.

[0022] As an embodiment of the present application, the mass percentage e of vinyl carbonate substance based on the total mass of electrolyte is 1-30%.

[0023] As an embodiment of the present application, the mass ratio m of propionate ester substance and vinyl carbonate substance is 0.1-40.

[0024] As an embodiment of the present application, the silicon-carbon material satisfies 0.049≤C≤0.115,

[0025] wherein C=1 / g-(1-b-f) / 2.25-f / 2.2;

[0026] g is the true density of silicon-carbon material, unit: g / cc;

[0027] f is the mass percentage of silicon element in silicon-carbon material.

[0028] As an embodiment of the present application, the silicon-carbon material has a microporous structure, and the pore volume V of the microporous structure of the silicon-carbon material obtained by nitrogen gas adsorption testing is 0-0.02 cc / g.

[0029] As an embodiment of the present application, the g is ≥ 1.8 g / cc.

[0030] As an embodiment of the present application, the f is 30-70%.

[0031] In a second aspect of the present application, the present application provides an electrical device comprising the secondary battery described in the present application.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] The present application provides a secondary battery, which adds a propionate organic solvent including propyl propionate and / or ethyl propionate to the electrolyte, and controls the mass percentage a of the silicon-carbon material in the negative electrode active material, the mass percentage b of the hydrogen element in the silicon-carbon material, and the mass percentage c of the propionate organic solvent in the electrolyte to satisfy 0.005≤100×a×b / c≤15. On the one hand, it can accelerate the lithium insertion kinetics of the silicon-carbon material on the basis of effectively reducing the side reactions between the silicon-carbon material and the electrolyte at room temperature and high temperature conditions, improve the lithium ion transmission capacity, thereby reducing the internal resistance of the secondary battery and improving the cycle performance of the secondary battery at room temperature and high temperature conditions; on the other hand, it can alleviate the excessive increase of the electrolyte viscosity under high voltage conditions (voltage of 4.5-4.58V) and improve the floating charge performance of the secondary battery at high voltage. DETAILED DESCRIPTION

[0034] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0035] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0036] In this application, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0037] In one embodiment of the present application, a secondary battery is provided, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.

[0038] The negative electrode active material layer includes a negative electrode active material, the negative electrode active material includes a silicon-carbon material and graphite, and the silicon-carbon material includes hydrogen element;

[0039] The electrolyte includes a propionate organic solvent, and the propionate organic solvent includes at least one of propyl propionate and ethyl propionate;

[0040] The secondary battery satisfies 0.005≤A≤15,

[0041] Where A = 100 × a × b / c;

[0042] a is the mass percentage of silicon-carbon material based on the mass of negative electrode active material;

[0043] b is the mass percentage of hydrogen in the silicon-carbon material;

[0044] c is the mass percentage of the propionate organic solvent based on the total mass of the electrolyte.

[0045] The present application provides a secondary battery, which adds a propionate organic solvent including propyl propionate and / or ethyl propionate to the electrolyte, and controls the mass percentage a of the silicon-carbon material in the negative electrode active material, the mass percentage b of the hydrogen element in the silicon-carbon material, and the mass percentage c of the propionate organic solvent in the electrolyte to satisfy 0.005≤100×a×b / c≤15. On the one hand, it can accelerate the lithium insertion kinetics of the silicon-carbon material on the basis of effectively reducing the side reactions between the silicon-carbon material and the electrolyte at room temperature and high temperature conditions, improve the lithium ion transmission capacity, thereby reducing the internal resistance of the secondary battery and improving the cycle performance of the secondary battery at room temperature and high temperature conditions; on the other hand, it can alleviate the excessive increase of the electrolyte viscosity under high voltage conditions (voltage of 4.5-4.58V) and improve the floating charge performance of the secondary battery at high voltage.

[0046] Specifically, the present application defines that the silicon-carbon material includes hydrogen. Although hydrogen in the silicon-carbon material will inevitably increase the side reaction between the silicon-carbon material and the electrolyte, it can also make the silicon-silicon bond in the silicon-carbon material easier to break, thereby accelerating the lithium insertion dynamics of the silicon-carbon material. In addition, the electrolyte selected in the present application includes a propionate organic solvent, which not only has low viscosity and good fluidity, but can also effectively alleviate the problem of increased electrolyte viscosity and increased internal resistance of the secondary battery at high voltage, thereby damaging the cycle performance of the secondary battery. It can also reduce the probability of side reactions between the silicon-carbon material and the electrolyte caused by the presence of hydrogen in the silicon-carbon material. That is, by controlling the secondary battery to meet 0.01≤100×a×b / c≤14, the present application can effectively improve the floating charge performance and cycle performance of the secondary battery through the synergistic effect between the silicon-carbon material and the electrolyte.

[0047] Exemplarily, A can be any point value or any two-point range value between 0.005-15, such as 0.005, 0.05, 0.1, 0.3, 0.5, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, etc.

[0048] In one embodiment, the secondary battery satisfies 0.2≤A≤1.82, for example, 0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 1.82, etc.

[0049] The research in this application found that when the value of A is further controlled to be 0.2-1.82, an excellent balance can be achieved between reducing the side reactions between the silicon-carbon material and the electrolyte and improving the lithium insertion kinetics, and the increase in electrolyte viscosity under high voltage conditions can be better alleviated, ensuring good transmission of lithium ions, and alleviating the decomposition of the electrolyte under high temperature conditions or the increase in side reactions with the negative electrode active material; that is, further controlling the value of A to be 0.2-1.82 can better improve the floating charge performance of the secondary battery at high voltage and improve the cycle performance of the secondary battery at room temperature and high temperature.

[0050] In one embodiment, based on the mass of the negative electrode active material, the mass percentage a of the silicon-carbon material is 5-50%.

[0051] It should be noted that the mass percentage of silicon-carbon material, measured by the mass of the negative electrode active material, is determined as follows: Under SEM backscattering mode, the contrast and morphology of the graphite and silicon-carbon material in the negative electrode plate show significant differences. Because silicon-carbon material has lower conductivity than graphite, graphite particles appear grayish-dark in SEM images, while silicon-carbon particles appear grayish-bright. Silicon-carbon particles have distinct angular edges, while graphite particles have relatively rounded boundaries. A cross-section of the negative electrode plate along its thickness was imaged using a scanning electron microscope (SEM) at a magnification of 1000x and an area of ​​125 μm × 85 μm. Image J software was then used to calculate the areas of the graphite and silicon-carbon particles, respectively. The area ratio was calculated by dividing the area of ​​the silicon-carbon particles by the area of ​​the graphite particles. Fifty SEM images were analyzed to determine the area ratio, and the 50 area ratios were arithmetic averaged to represent the mass percentage of silicon-carbon material in the negative electrode active material.

[0052] For example, based on the mass of the negative electrode active material, the mass percentage a of the silicon-carbon material can be any point value between 5-50% or any two point range values, such as 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc.

[0053] In one embodiment, the mass percentage a of the silicon-carbon material is 18-40% based on the mass of the negative electrode active material, for example, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, etc.

[0054] This study found that the amount of silicon-carbon material added to the negative electrode active material affects the capacity of the secondary battery. Increasing the amount of silicon-carbon material within a certain range can improve the capacity of the secondary battery, but at the same time, it can reduce the battery's float charge and cycling performance. Selecting a silicon-carbon material addition within a certain range can maintain a good capacity while effectively improving the battery's float charge performance under high voltage conditions and providing excellent cycling performance. In particular, selecting a silicon-carbon material mass percentage (a) of 18-40% based on the mass of the negative electrode active material yields even better overall secondary battery performance.

[0055] In one embodiment, the mass percentage b of hydrogen in the silicon-carbon material is 0.02-5%.

[0056] It should be noted that the test method for the mass percentage of hydrogen in silicon-carbon materials follows the industry standards SN / T 3005-2011, "Determination of Carbon, Hydrogen, Nitrogen, and Sulfur in Organic Chemicals by Elemental Analyzer," and SH / T-0656-1998, "Determination of Carbon, Hydrogen, and Nitrogen in Petroleum Products and Lubricants." The specific testing process involves discharging a secondary battery to 2.5V at a discharge rate of 1C. The secondary battery is then disassembled, and the resulting negative electrode sheet is cleaned and dried with dimethyl carbonate (DMC). The sheet is then heated in a muffle furnace at 500°C under a nitrogen atmosphere for 5 hours. After cooling, the negative electrode is scraped off to obtain the negative electrode active material. The a value is obtained according to the "Test Method for Mass Percentage of Silicon-Carbon Materials." Subsequently, a 1g sample of the negative electrode active material is fully combusted into gas, adsorbed and desorbed, and measured using a thermal conductivity cell to determine the mass percentage of hydrogen in the negative electrode material, b1. Therefore, b = b1 / a, which is the hydrogen content of the silicon-carbon material.

[0057] Exemplarily, the mass percentage b of hydrogen element in the silicon-carbon material can be any point value between 0.02-5% or any two point range values, such as 0.02%, 0.04%, 0.06%, 0.08%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, etc.

[0058] In one embodiment, the mass percentage b of hydrogen in the silicon-carbon material is 0.8-4%, for example, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, etc.

[0059] The present study found that the mass percentage of hydrogen in the silicon-carbon material affects the extent of the side reaction between the silicon-carbon material and the electrolyte, and also affects the difficulty of breaking the silicon-silicon bond in the silicon-carbon material, thereby affecting the lithium insertion kinetics of the silicon-carbon material; when the mass percentage b of the hydrogen in the silicon-carbon material is selected to be 0.02-5%, especially 0.8-4%, the hydrogen content is moderate, which can achieve a good balance between causing side reactions between the silicon-carbon material and the electrolyte and enhancing the lithium insertion kinetics of the silicon-carbon material, thereby effectively improving the overall performance of the secondary battery.

[0060] In one embodiment, based on the total mass of the electrolyte, the mass percentage c of the propionate organic solvent is 10-70%.

[0061] It should be noted that the mass percentage of propionate ester organic solvents, based on the total mass of the electrolyte, is determined as follows: the secondary battery is discharged to 2.5V at a discharge rate of 1C. The secondary battery is then disassembled, and the negative electrode, separator, and positive electrode are cut into 5mm fragments. 2.0mL of DMC is added for extraction and centrifugation. 0.31g of the supernatant is purified by adding alumina adsorbent and 2mL of acetonitrile containing methyl n-heptanoate (0.5mg / mL). GC conditions include an HP-INNOWAX column, a helium flow rate of 1.0mL / min, and a temperature program of 40°C to 230°C. The peak area ratio of the propionate ester organic solvent to the internal standard peak is measured, and its mass percentage is calculated using a calibration curve.

[0062] For example, based on the total mass of the electrolyte, the mass percentage c of the propionate organic solvent can be any point value between 10-70% or any two point range values, such as 10%, 20%, 30%, 40%, 50%, 60%, 70%, etc.

[0063] In one embodiment, the mass percentage c of the propionate organic solvent is 33-55% based on the total mass of the electrolyte, for example, 33%, 35%, 38%, 40%, 43%, 45%, 48%, 50%, 53%, 55%, etc.

[0064] The present application study found that the mass percentage of propionate organic solvents in the electrolyte not only affects the viscosity of the electrolyte and the viscosity growth of the electrolyte under high voltage conditions, but also affects the degree of side reactions between the electrolyte and the silicon-carbon negative electrode material; when the mass percentage c of the propionate organic solvent is 10-70%, especially 33-55%, based on the total mass of the electrolyte, the secondary battery obtained has excellent room temperature and high temperature cycle performance, and the floating charge performance under high voltage conditions is also better.

[0065] In one embodiment, the electrolyte further includes a pentafluorophenol sulfonate compound; the pentafluorophenol sulfonate compound includes at least one of pentafluorophenyl methanesulfonate and pentafluorophenyl propanesulfonate.

[0066] The structural formulas of pentafluorophenyl methanesulfonate and pentafluorophenyl propanesulfonate are shown in Formula I and Formula II, respectively.

[0067]

[0068] The present application has discovered that pentafluorophenol sulfonate compounds inherently have a high reduction potential. By introducing pentafluorophenol sulfonate compounds to replace some of the fluoroethylene carbonate in a secondary battery using silicon-carbon materials as the negative electrode active material, the gas production of the secondary battery in the negative electrode active material system can be reduced, thereby improving the thermal stability of the secondary battery. Furthermore, because the silicon-carbon material contains hydrogen, it can reduce the reaction between the silicon-carbon material and the pentafluorophenol sulfonate compound during cycling and float charging. In particular, it can inhibit the decomposition caused by the contact reaction between the electrolyte and the negative electrode under high temperature conditions, thereby suppressing the increase in the DC internal resistance under high temperature conditions and significantly improving the high-temperature cycling performance of the secondary battery.

[0069] In one embodiment, based on the total mass of the electrolyte, the mass percentage d of the pentafluorophenol sulfonate compound is 0.5-3%.

[0070] It should be noted that the test method for the mass percentage of the pentafluorophenol sulfonate compound based on the total mass of the electrolyte is as follows: discharge the secondary battery to 2.5V at a discharge rate of 1C; then disassemble the secondary battery, cut the negative electrode plate, separator, and positive electrode plate into 5mm fragments, add 2.0mL of DMC for extraction, and centrifuge. Take 0.21g of the supernatant, add 2.0mL of acetonitrile containing pentafluorobromobenzene (0.1mg / mL), dilute and filter. Analyze under the following GC conditions: DB-624 column, helium flow rate of 1.2mL / min, and program temperature rise of 60℃→260℃. The peak area ratio of the propionate organic solvent to the internal standard peak is measured, and its mass percentage can be calculated using the calibration curve.

[0071] Exemplarily, based on the total mass of the electrolyte, the mass percentage d of the pentafluorophenol sulfonate compound can be any point value between 0.5-3% or any two point range values, for example, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, or 3%.

[0072] In one embodiment, the mass percentage d of the pentafluorophenol sulfonate compound is 0.8-1.5% based on the total mass of the electrolyte, for example, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc.

[0073] The research in this application found that pentafluorophenol sulfonate compounds within a specific addition amount range can effectively inhibit the gas production of secondary batteries under high temperature conditions and improve the high-temperature cycle performance of secondary batteries; at the same time, they can also cooperate with the hydrogen element in the silicon-carbon material to control the activity of silicon in the silicon-carbon material, further reduce the side reactions between the electrolyte and the negative electrode, and improve the cycle performance and float charge performance of the secondary battery.

[0074] In one embodiment, the secondary battery satisfies 0.1≤B≤2.27;

[0075] Where B = 100 × a × b + d / a.

[0076] Exemplarily, B can be any point value or any two point range value between 0.1-2.27, such as 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.27, etc.

[0077] In one embodiment, the secondary battery satisfies 0.18≤B≤0.7, for example, 0.18, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, etc.

[0078] The research in this application found that there is an interaction between the addition amount of sulfonic acid pentafluorophenol ester compounds, silicon-carbon materials, and the content of hydrogen elements in the silicon-carbon materials. When the secondary battery is further controlled to meet 0.1≤100×a×b+d / a≤2.27, especially when it meets 0.18≤100×a×b+d / a≤0.7, it can not only reduce the cyclic gas production of the secondary battery, especially the high-temperature cyclic gas production, but also effectively improve and reduce the reaction between the electrolyte and the negative electrode plate; thereby effectively improving the overall performance of the secondary battery.

[0079] In one embodiment, the electrolyte further includes ethylene carbonate substances, and the ethylene carbonate substances include at least one of ethylene carbonate and fluoroethylene carbonate.

[0080] The present study found that further introduction of ethylene carbonate substances, especially at least one of ethylene carbonate and fluoroethylene carbonate, can help improve the interfacial stability of the secondary battery during the cycle process, and further improve the cycle performance and high-temperature performance of the secondary battery.

[0081] In one embodiment, based on the total mass of the electrolyte, the mass percentage e of the ethylene carbonate substance is 1-30%.

[0082] It should be noted that the mass percentage of ethylene carbonate substances, based on the total mass of the electrolyte, is determined as follows: the secondary battery is discharged to 2.5V at a discharge rate of 1C. The secondary battery is then disassembled, and the negative electrode, separator, and positive electrode are cut into 5mm fragments. Extraction is performed with 2.0mL of DMC, followed by centrifugation. 0.41g of the supernatant is purified by adding molecular sieves and activated carbon. Then, 1mL of chloroform containing diethyl phthalate (1.0mg / mL) is added and the mixture is filtered. GC conditions include a DB-1701 column, a helium flow rate of 1.2mL / min, and a temperature program of 80°C to 230°C. The peak area ratio of the ethylene carbonate substance to the internal standard peak is measured, and its mass percentage is calculated using a calibration curve.

[0083] Exemplarily, based on the total mass of the electrolyte, the mass percentage e of the ethylene carbonate substance can be any point value between 1-30% or any two point range values, such as 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, etc.

[0084] In one embodiment, the mass percentage e of the ethylene carbonate substance is 12-16% based on the total mass of the electrolyte, for example, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, etc.

[0085] The present application has found that adding ethylene carbonate substances within the above-mentioned mass percentage range to the electrolyte of the present application can alleviate the problem of more obvious expansion during the secondary battery cycle or float charge caused by the increased addition of silicon-carbon materials in the negative electrode active material by improving the interface stability; at the same time, it can also alleviate the problem of increased side reactions caused by excessive ethylene carbonate substances; that is, by limiting the mass percentage e of ethylene carbonate substances in the electrolyte to 1-30%, especially 12-16%, the comprehensive performance of the secondary battery obtained in the present application is better.

[0086] In one embodiment, the mass ratio m of the propionate substance to the ethylene carbonate substance is 0.1-40.

[0087] Exemplarily, the mass ratio m of the propionate ester substance and the ethylene carbonate substance can be any point value or any two point range values ​​between 0.1-40, such as 0.1, 0.5, 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, etc.

[0088] In one embodiment, the mass ratio m of the propionate ester substance to the ethylene carbonate substance is 2.75-3.44, for example, 2.75, 2.80, 2.85, 2.90, 2.95, 3.00, 3.05, 3.10, 3.15, 3.20, 3.25, 3.30, 3.35, 3.40, 3.44, etc.

[0089] The present study found that further controlling the mass ratio of acrylic acid esters and ethylene carbonate substances within an appropriate range can improve the interfacial stability while minimizing the impact on the viscosity of the electrolyte, thereby effectively improving the high temperature performance, cycle performance and floating charge performance of the secondary battery.

[0090] In one embodiment, the silicon-carbon material satisfies 0.049≤C≤0.115,

[0091] Where C = 1 / g-(1-bf) / 2.25-f / 2.2;

[0092] g is the true density of silicon carbon material, in g / cc;

[0093] f is the mass percentage of silicon element in the silicon-carbon material.

[0094] Exemplarily, C may be any point value or any two point range value between 0.049-0.115, such as 0.049, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.115, etc.

[0095] The research in this application found that by making the true density of the silicon-carbon material and the mass percentage of the silicon element in the silicon-carbon material meet 0.049≤1 / g-(1-bf) / 2.25-f / 2.2≤0.115, the ion diffusion capacity and electron conduction capacity of the silicon-carbon material can be better improved, thereby better improving the cycle performance of the secondary battery.

[0096] In one embodiment, the silicon-carbon material has a microporous structure, and the pore volume V of the microporous structure of the silicon-carbon material measured by nitrogen gas adsorption method is 0-0.02 cc / g, wherein the microporous structure is a pore with a pore diameter of less than 2 nm.

[0097] It should be noted that the silicon-carbon material has a microporous structure. The specific testing process for the pore volume of the microporous structure of the silicon-carbon material using the nitrogen gas adsorption method is as follows: a secondary battery is discharged to 2.5V at a discharge rate of 1C; the secondary battery is then disassembled, and the resulting negative electrode sheet is cleaned and dried with dimethyl carbonate (DMC). It is then kept in a muffle furnace at 500°C under a nitrogen atmosphere for 5 hours. After cooling, the negative electrode of the negative electrode sheet is scraped off to obtain the negative electrode active material. The a value can be obtained according to the "Test Method for Mass Percentage of Silicon-Carbon Materials". A 0.1g sample of the negative electrode active material is weighed and placed in a 1 / 2-inch bulb-shaped tube (the diameter of the spherical part is 12mm). After pre-treatment at 200°C for 2 hours, the sample is placed in an instrument (TriStar 3030, Micromeritics, USA) for testing. The adsorption gas used is nitrogen (purity: 99.999%). The test conditions are 77K. The pore volume V1 cc / g is calculated using the density functional theory (DFT) model. Graphite is a crystalline material and does not have a microporous structure. The micropore volume of graphite is 0cc / g. Therefore, the measured pore volume is that of the silicon-carbon material, so V=V1 / a is the pore volume of the silicon-carbon negative electrode material.

[0098] Exemplarily, the silicon-carbon material has a microporous structure, and the pore volume V of the microporous structure of the silicon-carbon material obtained by nitrogen gas adsorption testing can be any point value or any two-point range value between 0-0.02cc / g, such as 0cc / g, 0.01cc / g, 0.012cc / g, 0.014cc / g, 0.016cc / g, 0.018cc / g, 0.02cc / g, etc.

[0099] The research in this application found that since most silicon-carbon materials are obtained by coating after porous carbon deposition, by further limiting the pore volume of the micropores of the silicon-carbon material within the above-mentioned range, the gas production and side reactions during the preparation of the slurry can be reduced, while at the same time ensuring a sufficient number of lithium ion channels to ensure the kinetic performance of the secondary battery.

[0100] In one embodiment, the g is ≥ 1.8 g / cc.

[0101] It should be noted that the specific testing process for the true density of the silicon-carbon material is as follows: a secondary battery is discharged to 2.5V at a discharge rate of 1C; the secondary battery is then disassembled, and the resulting negative electrode sheet is cleaned and dried with dimethyl carbonate (DMC). The sheet is then insulated in a muffle furnace at 500°C under a nitrogen atmosphere for 5 hours. After cooling, the negative electrode is scraped off to obtain the negative electrode active material. The a value can be obtained according to the "Test Method for Mass Percentage of Silicon-Carbon Materials." A 1.0g sample is weighed, vacuum-dried at 120°C for 12 hours, and then degassed in a true density meter sample cell at 150°C for 4 hours. The test conditions are: helium pressure of 19.5 psig. After 10 cycles, the true density is measured as g1 g / cc. The true density of graphite is 2.26 g / cc, so g = a / (1 / g1 - (1-a) / 2.26), which is the true density of the silicon-carbon negative electrode material.

[0102] In one embodiment, 1.9≤g≤2.1.

[0103] The present application has found that by controlling the true density of the silicon-carbon material within the above range, it is possible to ensure that the silicon-carbon interface is tightly bonded while containing closed pores for accommodating silicon-carbon expansion, thereby effectively improving the cycle performance of the secondary battery.

[0104] In one embodiment, the f is 30-70%.

[0105] It should be noted that the test method for the mass percentage of silicon in silicon-carbon materials is as follows: discharge a secondary battery to 2.5V at a discharge rate of 1C; then disassemble the secondary battery, clean and dry the resulting negative electrode with dimethyl carbonate (DMC), and then heat it in a muffle furnace at 500°C under a nitrogen atmosphere for 5 hours. After cooling, scrape the negative electrode from the negative electrode to obtain the negative electrode active material. The a value can be obtained according to the "Test Method for Mass Percentage of Silicon-Carbon Materials." Weigh 1.0g of the negative electrode active material, place it in a muffle furnace, heat it to 1000°C (heating rate 10°C / min), hold it for 1 hour, cool it to 100°C in the muffle furnace, remove it, place it in a desiccator, and weigh its mass m1 after cooling. Calculate the silicon content f = 28*(m1-(1-a)) / 60 / a.

[0106] Exemplarily, the g may be any point value between 30-70% or any two point range values, such as 30%, 40%, 50%, 60%, 70%, etc.

[0107] The present application has found that by controlling the mass percentage of silicon in the silicon-carbon material within the above range, sufficient silicon-silicon bonds can be broken to enhance the lithium ion transmission capacity, thereby improving the overall performance of the secondary battery.

[0108] In one embodiment, the Dv50 particle size of the silicon-carbon material is 4-12 μm; and the Dv50 particle size of the graphite is 4-12 μm.

[0109] It should be noted that the preparation method of the silicon-carbon material includes the following steps:

[0110] S1. Preparation of porous carbon: pre-carbonize the phenolic resin at 400-500°C, carbonize it at 500-600°C, and then activate it with water vapor at 800-1000°C to form pores. The porous carbon is obtained by controlling the activation time to 5-24 hours.

[0111] S2. Silane deposition and pre-coating: The porous carbon is placed in a fluidized bed for silane deposition, with a silane concentration of 5-50%, nitrogen as the other gas component, a deposition time of 6-24 hours, and a deposition temperature of 400-500°C. Then, acetylene gas is switched to pre-coating, with an acetylene concentration of 10-90%, nitrogen as the other gas component, a pre-coating time of 1-12 hours, and a pre-coating temperature of 400-500°C. After cooling, a semi-finished silicon-carbon material is obtained;

[0112] S3. Coating: Place the semi-finished silicon-carbon material into a rotary kiln for coating. The acetylene concentration is 10-90%, and the other gas components are nitrogen. The coating time is 1-24 hours, and the coating temperature is 500-600°C. After cooling, the silicon-carbon material is obtained.

[0113] It should be noted that the change in the mass percentage of hydrogen element in the silicon-carbon material is achieved by adjusting the activation pore-forming temperature of water vapor in step S1, the deposition temperature in step S2, the silane concentration in step S2, the acetylene concentration in the pre-coating in step S2, the acetylene concentration in step S3, etc. For example, when the activation pore-forming temperature of water vapor in S1 is lowered, the deposition temperature in step S2 is lowered, the silane concentration in step S2 is increased, the acetylene concentration in the pre-coating in step S2 is increased, the pre-coating temperature in step S2 is lowered, and the acetylene concentration in step S3 is increased, the mass percentage of hydrogen element in the silicon-carbon material will increase.

[0114] It should be noted that by adjusting the activation time in step S1, the silane concentration in step S2 and the silane deposition time, the mass and percentage of the silicon element in the silicon-carbon material can be changed. For example, when the activation time in step S1 is increased, the silane concentration in step S2 is increased and the silane deposition time is increased, the mass percentage of the silicon element in the silicon-carbon material will increase.

[0115] It should be noted that the change of the mass percentage of hydrogen element in the silicon-carbon material can realize the change of the true density of the silicon-carbon material by adjusting the silane concentration and the silane deposition time in step S2, the acetylene concentration in the pre-coating in step S2, and the acetylene concentration in step S3, for example, when the silane concentration and the silane deposition time in step S2 are increased, the acetylene concentration in the pre-coating in step S2 is reduced, and the acetylene concentration in step S3 is reduced, the true density of the silicon-carbon material will increase.

[0116] It should be noted that the change of the pore volume of the microporous structure of the silicon-carbon material can be realized by adjusting the acetylene concentration, coating temperature, and time in step S3, for example, when the acetylene concentration, coating temperature, and time in step S3 are reduced, the pore volume of the microporous structure of the silicon-carbon material will increase.

[0117] In an embodiment, the negative electrode active material layer further comprises a negative electrode conductive agent, a negative electrode thickening agent, and a negative electrode binder.

[0118] The selection of the negative electrode conductive agent is not limited in the present application, and any known negative electrode conductive agent can be used. For example, it can be carbon black SP, single-walled carbon nanotube SWCNT, etc.

[0119] The selection of the negative electrode thickening agent is not limited in the present application, and any known negative electrode thickening agent can be used. For example, it can be carboxymethyl cellulose (CMC), lithium carboxymethyl cellulose (CMC-Li), etc.

[0120] The selection of the negative electrode binder is not limited in the present application, and any known negative electrode binder can be used. For example, it can be styrene-butadiene rubber (SBR), polyacrylic acid (PAA), etc.

[0121] In an embodiment, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder.

[0122] The selection of the positive electrode active material is not limited in the present application, and any known positive electrode active material can be used. For example, it can be a lithium cobaltate positive electrode, a NCM ternary positive electrode, etc.

[0123] The selection of the positive electrode conductive agent is not limited in the present application, and any known positive electrode conductive agent can be used. For example, it can be carbon black SP, single-walled carbon nanotube SWCNT, etc.

[0124] The selection of the positive electrode binder is not limited in the present application, and any known positive electrode binder can be used. For example, it can be polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), etc.

[0125] In an embodiment, the electrolyte further comprises a lithium salt.

[0126] The present application has no limitation on the choice of lithium salt, and any known lithium salt may be used, such as lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), bis(trifluoromethanesulfonyl imide) (LiTFSI), and the like.

[0127] In one embodiment, the separator of the secondary battery is disposed between the positive electrode and the negative electrode.

[0128] The present application has no limitation on the separator, and any known separator may be used.

[0129] Illustratively, the diaphragm includes any one of a PE diaphragm, a PP diaphragm, and a composite of PE and PP.

[0130] In one embodiment of the present application, the present application provides an electric device, and the electric device includes the secondary battery described in the present application.

[0131] Example 1

[0132] An embodiment of the present application provides a secondary battery, wherein a method for preparing the secondary battery comprises the following steps:

[0133] (1) Preparation of electrolyte

[0134] In an environment with a water content of less than 10 ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of EC:EMC:DEC=30:50:20, and after mixing evenly, lithium salt LiPF6 is added, and after dissolving and fully stirring, propyl propionate and ethyl propionate are added, followed by adding pentafluorophenyl methanesulfonate and fluoroethylene carbonate, and mixing evenly to obtain an electrolyte, wherein the content of LiPF6 is 13%, the content of ethyl propionate is 10%, the content of propyl propionate is 30%, the content of pentafluorophenyl methanesulfonate is 1%, and the content of fluoroethylene carbonate is 1%, and all contents refer to the mass content in the electrolyte;

[0135] (2) Preparation of positive electrode sheet

[0136] The positive electrode active material, lithium cobalt oxide, the conductive agent, conductive carbon black, and the binder, polyvinylidene fluoride (PVDF), were dissolved in an N-methylpyrrolidone (NMP) solution in a weight ratio of 97:1.4:1.6 to form a positive electrode slurry, wherein the solid content of the positive electrode slurry was 72 wt %. An 8 μm thick aluminum foil was used as a positive electrode current collector, and the positive electrode slurry was coated on both sides of the positive electrode current collector. After drying, cold pressing, and slitting, the positive electrode sheets were obtained.

[0137] (3) Preparation of negative electrode sheet

[0138] Preparation of silicon-carbon materials:

[0139] S1. Preparation of porous carbon: Phenolic resin was pre-carbonized at 460°C, carbonized at 570°C, and then activated with water vapor at 850°C to form pores. The porous carbon was obtained by controlling the activation time to 18 hours.

[0140] S2, Silane Deposition and Pre-coating: The porous carbon was placed in a fluidized bed for silane deposition, with a silane concentration of 15%, nitrogen as the other gas component, a deposition time of 12 hours, and a deposition temperature of 450°C. Then, acetylene gas was switched to pre-coating, with an acetylene concentration of 50%, nitrogen as the other gas component, a coating time of 3 hours, and a coating temperature of 480°C. After cooling, a semi-finished silicon-carbon material was obtained;

[0141] S3. Coating: Place the semi-finished silicon-carbon material into a rotary kiln for coating. The acetylene concentration is 50%, and the other gas components are nitrogen. The coating time is 11 hours and the coating temperature is 550° C. After cooling, the silicon-carbon material is obtained.

[0142] The negative electrode active material is composed of artificial graphite particles with a Dv50 of 10.3 μm and a silicon-carbon material with a Dv50 of 8.0 μm. The silicon-carbon material has a hydrogen mass percentage b of 2%, a true density f of 1.8 g / cc, a silicon content f of 50%, and a micropore volume V of 0.01 cc / g. The artificial graphite and silicon-carbon material are mixed in a mass ratio of 90:10 to form the negative electrode active material.

[0143] The negative electrode active material, styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) were fully stirred and mixed in an appropriate amount of deionized water at a weight ratio of 97:2:1 to form a uniform negative electrode slurry, wherein the solid content of the negative electrode slurry was 35 wt%. The slurry was coated on a 6 μm thick negative electrode current collector copper foil and dried at 85°C. During the cold pressing process, the compaction density of the negative electrode sheet was controlled to be 1.65 g / cm by controlling the cold pressing pressure. 3 The thickness of the negative electrode active material layer is 62 μm, and then after cutting and slitting, it is dried under vacuum conditions at 120°C for 12 hours to obtain a negative electrode sheet;

[0144] (4) Preparation of diaphragm

[0145] A 7 μm thick polyethylene (PE) porous polymer film was used as the separator;

[0146] (5) Preparation of soft-pack lithium batteries

[0147] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to act as a barrier. The electrode assembly is then wound to form an electrode assembly. The electrode assembly is then placed in an aluminum-plastic film package, dehydrated at 80°C, and then injected with the aforementioned electrolyte and packaged. The secondary battery is then produced through a series of processes, including formation, degassing, and shaping.

[0148] Examples 2-4

[0149] The present embodiment provides a secondary battery, which differs from Example 1 in that the amount of silicon-carbon material added to the negative electrode active material, the type of silicon-carbon material (changing the type refers to changing the mass percentage of hydrogen and silicon elements in the silicon-carbon material, as well as changing the true density and micropore volume of the silicon-carbon material), and the amount of propionate esters, pentafluorophenol sulfonate compounds, and ethylene carbonate substances added to the electrolyte are adjusted to achieve the parameters in Table 1;

[0150] The difference between the types of silicon-carbon materials in Example 2 and Example 1 is mainly due to the change of the silane concentration (18%) and the pre-coating temperature (490° C.) in the silicon-carbon material preparation step S2, while the other preparation parameters of the silicon-carbon material remain unchanged;

[0151] The difference between the types of silicon-carbon materials in Example 3 and Example 1 is mainly due to the changes in the activation temperature (820° C.) in step S1 of the silicon-carbon material preparation, the silane concentration (10%) and the pre-coating concentration (60%) in step S2, and the coating temperature (530° C.) in step S3. The preparation parameters of other silicon-carbon materials remain unchanged.

[0152] The difference between the types of silicon-carbon materials in Example 4 and Example 1 is mainly due to the changes in the activation temperature (820° C.) in step S1 of the silicon-carbon material preparation, the silane concentration (8%) and the pre-coating concentration (55%) in step S2, while the other preparation parameters of the silicon-carbon material remain unchanged.

[0153] When the amount of the ethylene carbonate substance added to the electrolyte is changed, the mass percentage of the fluoroethylene carbonate in the electrolyte is kept unchanged.

[0154] Examples 5-6

[0155] The embodiment of the present application provides a secondary battery, which differs from the embodiment 1 in that the amount of silicon-carbon material added to the negative electrode active material layer is adjusted to achieve the parameters in Table 1.

[0156] Examples 7-8

[0157] The embodiment of the present application provides a secondary battery, which differs from Example 1 in that the type of silicon-carbon material is adjusted to achieve changes in the hydrogen content, silicon content, true density and pore volume of the silicon-carbon material to achieve the parameters in Table 1.

[0158] Examples 9-10

[0159] The embodiment of the present application provides a secondary battery, which differs from the embodiment 1 in that the amount of propionate organic solvent added to the electrolyte is adjusted to achieve the parameters in Table 1.

[0160] Examples 11-12

[0161] The embodiment of the present application provides a secondary battery, which differs from the embodiment 1 in that the amount of pentafluorophenol sulfonate compound added is adjusted to achieve the parameters in Table 1.

[0162] Examples 13-14

[0163] The embodiment of the present application provides a secondary battery, which differs from embodiment 1 in that the amount of ethylene carbonate added is adjusted (keeping the mass percentage of fluoroethylene carbonate in the electrolyte unchanged) to achieve the parameters in Table 1.

[0164] Example 15

[0165] The embodiment of the present application provides a secondary battery, which differs from embodiment 1 in that propyl propionate is not added, and its amount is supplemented with ethyl propionate to achieve the parameters in Table 1.

[0166] Example 16

[0167] The embodiment of the present application provides a secondary battery, which differs from the embodiment 1 in that pentafluorophenyl propanesulfonate is used instead of pentafluorophenyl methanesulfonate to achieve the parameters in Table 1.

[0168] Example 17

[0169] The embodiment of the present application provides a secondary battery, which differs from embodiment 1 in that fluoroethylene carbonate is not added and the amount thereof is supplemented with ethylene carbonate to achieve the parameters in Table 1.

[0170] Example 18

[0171] The embodiment of the present application provides a secondary battery, which differs from embodiment 1 in that no pentafluorophenol sulfonate compound is added and ethyl methyl carbonate is used to make up the amount sufficient to achieve the parameters in Table 1.

[0172] Example 19

[0173] The embodiment of the present application provides a secondary battery, which differs from the embodiment 1 in that no ethylene carbonate substance is added and the amount of ethyl methyl carbonate is supplemented to achieve the parameters in Table 1.

[0174] Comparative Example 1-2

[0175] The comparative example of the present application provides a secondary battery, which differs from Example 1 in that the amount of silicon-carbon material added to the negative electrode active material, the type of silicon-carbon material (changing the type changes the content of hydrogen and silicon elements in the silicon-carbon material, as well as the true density and micropore volume of the silicon-carbon material), and the amount of propionate esters, pentafluorophenol sulfonate compounds, and ethylene carbonate substances added to the electrolyte are adjusted to achieve the parameters in Table 1;

[0176] When the amount of the ethylene carbonate substance added to the electrolyte is changed, the mass percentage of the fluoroethylene carbonate in the electrolyte is kept unchanged.

[0177] Comparative Example 3

[0178] The comparative example of the present application provides a secondary battery, which differs from Example 1 in that no propionate organic solvent is introduced and the amount of ethyl methyl carbonate is supplemented to achieve the parameters in Table 1.

[0179] Comparative Example 4

[0180] The comparative example of the present application provides a secondary battery, which differs from Example 1 in that the type of silicon-carbon material is changed so that the silicon-carbon material does not contain hydrogen element to achieve the parameters in Table 1.

[0181] The a, b, c, A, d, B, e, g, f, C, V, the mass ratio m of the propionate ester substance and the ethylene carbonate substance, the type of the acrylic acid ester organic solvent, the type of the pentafluorophenol sulfonate compound, and the type of the ethylene carbonate substance in the secondary batteries in the Examples and Comparative Examples are shown in Table 1-2;

[0182] Among them, the propionate organic solvent 1: a mixture of propyl propionate and ethyl propionate in a mass ratio of 1:3;

[0183] Propionate organic solvent 2: ethyl propionate;

[0184] Pentafluorophenol sulfonate compound 1: pentafluorophenyl methanesulfonate;

[0185] Pentafluorophenol sulfonate compound 2: pentafluorophenyl propanesulfonate;

[0186] Ethylene carbonate substance 1: ethylene carbonate and fluoroethylene carbonate, with a mass ratio of 10:1;

[0187] Ethylene carbonate substance 2: Ethylene carbonate.

[0188] Table 1

[0189] a b c A d B e m Example 1 10％ 2％ 40％ 0.500 1.0％ 0.30 14.5％ 2.76 Example 2 12％ 1％ 55％ 0.218 0.8％ 0.19 16.0％ 3.44 Example 3 15％ 4％ 33％ 1.818 1.5％ 0.70 12.0％ 2.75 Example 4 45％ 5％ 15％ 15.000 1.0％ 2.27 14.5％ 1.03 Example 5 5％ 2％ 40％ 0.250 1.0％ 0.30 14.5％ 2.76 Example 6 50％ 2％ 40％ 2.500 1.0％ 1.02 14.5％ 2.76 Example 7 10％ 0.02％ 40％ 0.005 1.0％ 0.10 14.5％ 2.76 Example 8 10％ 5％ 40％ 1.250 1.0％ 0.60 14.5％ 2.76 Example 9 10％ 2％ 10％ 2.000 1.0％ 0.30 14.5％ 0.69 Example 10 10％ 2％ 70％ 0.286 1.0％ 0.30 14.5％ 4.83 Example 11 10％ 2％ 40％ 0.500 0.5％ 0.25 14.5％ 2.76 Example 12 10％ 2％ 40％ 0.500 3.0％ 0.50 14.5％ 2.76 Example 13 10％ 2％ 40％ 0.500 1.0％ 0.30 1.0％ 40.00 Example 14 10％ 2％ 40％ 0.500 1.0％ 0.30 20.0％ 2.00 Example 15 10％ 2％ 40％ 0.500 1.0％ 0.30 14.5％ 2.76 Example 16 10％ 2％ 40％ 0.500 1.0％ 0.30 14.5％ 2.76 Example 17 10％ 2％ 40％ 0.500 1.0％ 0.30 14.5％ 2.76 Example 18 10％ 2％ 40％ 0.500 0.0％ 0.20 14.5％ 2.76 Example 19 10％ 2％ 40％ 0.500 1.0％ 0.30 0.0％ / Comparative Example 1 8％ 0.02％ 60％ 0.003 1.0％ 0.13 14.5％ 4.14 Comparative Example 2 48％ 5％ 14％ 17.143 1.0％ 2.42 14.5％ 0.97 Comparative Example 3 10％ 2％ 0％ / 1.0％ 0.30 14.5％ 0.00 Comparative Example 4 10％ 0％ 40％ 0.000 1.0％ 0.10 14.5％ 2.76

[0190] Table 2

[0191]

[0192]

[0193] The performance tests of the secondary batteries prepared in the examples and comparative examples include the following aspects:

[0194] 1. High temperature cycle performance test:

[0195] The test temperature was 45°C. The battery was charged at a constant current of 0.7C to 4.53V, then charged at a constant voltage of 0.025C. After a 5-minute rest, the battery was discharged at 0.7C to 3.0V. The capacity obtained in this step was used as the initial capacity. Cyclic testing was repeated at 0.7C for charge and discharge. The capacity at each step was compared to the initial capacity to determine the capacity retention rate. The number of cycles required to achieve 80% capacity retention was recorded as the battery's high-temperature cycling performance.

[0196] 2. Room Temperature Cycling Performance Test: The test temperature is 25°C. Charge the battery to 4.53V at a constant current of 0.7C, charge it to 0.025C at a constant voltage, let it rest for 5 minutes, and then discharge it to 3.0V at 0.7C. The capacity obtained in this step is regarded as the initial capacity. The battery is cycled at 0.7C for charging and discharging. The capacity at each step is compared with the initial capacity to obtain the capacity retention rate. The number of cycles until the capacity retention rate reaches 90% is recorded as the room temperature cycling performance of the battery.

[0197] 3. Float charge performance test under high voltage: The battery was discharged to 3.0V at 0.7C at 25°C, then charged to 4.53V at 0.7C, and then charged to 0.05C at a constant voltage at 4.53V. The thickness of the lithium-ion battery was tested and recorded as d0. Then, it was placed in a 45°C oven and charged at a constant voltage of 4.53V for 50 days. The thickness change was monitored and the final thickness was recorded as d. The thickness expansion rate of the lithium-ion battery during float charge = (d-d0) / d0×100%. The expansion rate is used as the float charge performance of the battery.

[0198] The results are shown in Table 3;

[0199] Table 3

[0200]

[0201]

[0202] As can be seen from Table 3, when the technical solution provided by the present application is adopted, the obtained product has good cycle performance, high temperature performance and float charge performance; specifically, the obtained product has a high temperature cycle number of more than 501 cycles, a room temperature cycle number of more than 653 cycles, and a float charge performance of less than 33.82%;

[0203] It can be seen from Examples 1-19 and Comparative Examples 1-2 that when the secondary battery does not meet the range of A, the high-temperature cycle, normal-temperature cycle and float charge performance of the obtained secondary battery are significantly reduced; it can be seen from Examples 1-19 and Comparative Example 3 that when no propionate organic solvent is added to the electrolyte, the high-temperature cycle, normal-temperature cycle and float charge performance of the obtained secondary battery are significantly reduced; it can be seen from Examples 1-19 and Comparative Example 4 that when the silicon-carbon material does not include hydrogen element, the obtained secondary battery cannot achieve the purpose of this application.

[0204] Finally, it should be noted that the above embodiments are intended to illustrate the technical solutions of the present application rather than to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, characterized in that: The negative electrode active material layer includes a negative electrode active material, the negative electrode active material includes a silicon-carbon material and graphite, and the silicon-carbon material includes hydrogen element; The electrolyte includes a propionate organic solvent, and the propionate organic solvent includes at least one of propyl propionate and ethyl propionate; The secondary battery satisfies 0.005≤A≤15, Where A = 100 × a × b / c; a is the mass percentage of silicon-carbon material based on the mass of negative electrode active material; b is the mass percentage of hydrogen in the silicon-carbon material; c is the mass percentage of the propionate organic solvent based on the total mass of the electrolyte.

2. The secondary battery according to claim 1, wherein At least one of the following is met: (1) The mass percentage a of the silicon-carbon material is 5-50% based on the mass of the negative electrode active material; (2) The mass percentage b of hydrogen element in the silicon-carbon material is 0.02-5%; (3) Based on the total mass of the electrolyte, the mass percentage c of the propionate organic solvent is 10-70%.

3. The secondary battery according to claim 1, wherein The electrolyte further includes pentafluorophenol sulfonate compounds; the pentafluorophenol sulfonate compounds include at least one of pentafluorophenyl methanesulfonate and pentafluorophenyl propanesulfonate.

4. The secondary battery according to claim 3, wherein Based on the total mass of the electrolyte, the mass percentage d of the pentafluorophenol sulfonate compound is 0.5-3%.

5. The secondary battery according to claim 4, wherein The secondary battery satisfies 0.1≤B≤2.27; Where B = 100 × a × b + d / a.

6. The secondary battery according to claim 1, wherein The electrolyte also includes ethylene carbonate substances, and the ethylene carbonate substances include at least one of ethylene carbonate and fluoroethylene carbonate.

7. The secondary battery according to claim 6, characterized in that Based on the total mass of the electrolyte, the mass percentage e of the ethylene carbonate substance is 1-30%.

8. The secondary battery according to claim 6, wherein The mass ratio m of the propionate substance to the ethylene carbonate substance is 0.1-40.

9. The secondary battery according to claim 1, wherein The silicon-carbon material satisfies 0.049≤C≤0.115, Where C = 1 / g-(1-bf) / 2.25-f / 2.2; g is the true density of silicon carbon material, in g / cc; f is the mass percentage of silicon element in silicon-carbon material; And / or, the silicon-carbon material has a microporous structure, and a pore volume V of the microporous structure of the silicon-carbon material measured by a nitrogen gas adsorption method is 0-0.02 cc / g.

10. The secondary battery according to claim 9, wherein The g is ≥ 1.8 g / cc; And / or, said f is 30-70%.

11. An electrical device, characterized in that: The electric device comprises the secondary battery according to any one of claims 1 to 10.

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