Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device, and belongs to the technical field of energy storage. The secondary battery comprises an electrolyte and a shell; the electrolyte comprises an additive, and the additive comprises at least one of fluoroethylene carbonate, vinylene carbonate and 1, 3-propane sultone; based on the total mass of the electrolyte, the mass content of the additive is X%, and 1.2 < = X < = 30; the shell is made of a steel shell; the shell comprises an air leakage hole, and the area of the air leakage hole is A mm < 2 >; 0.3 < = X / A < = 25 is satisfied. By controlling the components and the content of the electrolyte and the relationship between the electrolyte and the gas release hole, the gas production phenomenon in the formation process can be effectively inhibited, and the qualified rate of battery production is improved.

Description

Technical Field

[0001] The present application belongs to the field of energy storage technology, and specifically relates to a secondary battery and an electronic device. Background Art

[0002] As a rechargeable energy storage device, secondary batteries can store and release electrical energy through electrochemical reactions. They are an indispensable key component of electronic devices, electric vehicles and energy storage systems. With the continuous iteration and upgrading of technology, lithium-ion batteries are widely used due to their high energy density, long cycle life and environmental friendliness.

[0003] In the manufacturing process of lithium-ion batteries, the problem of gas production during formation is a particularly prominent technical problem. The so-called formation refers to the process of initial charging and discharging of the electrode materials inside the battery through a specific electrochemical process before the battery is used for the first time, so as to form a stable solid electrolyte membrane at the interface of the positive and negative electrodes. This process is crucial to ensure battery performance. However, gases are inevitably produced during the formation process. These gases will cause the internal pressure of the battery to increase, affect the safety and performance of the battery, and even reduce the production qualification rate. Especially in a large-scale production environment, the problem of gas production during formation is more significant, which directly affects the overall production efficiency and cost. Therefore, inhibiting gas production during formation and improving the production qualification rate have become an important direction of current technological development. Summary of the invention

[0004] In view of this, the present application provides a secondary battery and an electronic device, which can effectively suppress the gas production during the formation process by controlling the composition and content of the electrolyte and its relationship with the vent holes, thereby improving the qualified rate of battery production and thus improving the overall performance and safety of the battery.

[0005] In a first aspect, the present application provides a secondary battery, comprising an electrolyte and a shell; the electrolyte comprises an additive, the additive comprises at least one of fluoroethylene carbonate, vinylene carbonate, and 1,3-propane sultone; based on the total mass of the electrolyte, the mass content of the additive is X%, 1.2≤X≤30; the shell is made of steel; the shell comprises an air vent, and the area of ​​the air vent is A mm 2 ; 0.3≤X / A≤25. The present application can inhibit formation gas production by controlling the composition and mass content of the electrolyte and controlling the area of ​​the vent hole, reduce overflow and cell pollution caused by gas production, improve production qualification rate, and thus improve the overall performance and safety of the battery.

[0006] In some embodiments, 0.5≤X / A≤20. When the ratio between the mass content of the additive in the electrolyte and the area of ​​the gas leakage hole meets the above range, the gas generation by chemical formation can be further suppressed, and the production qualification rate can be improved.

[0007] In some embodiments, 1≤A≤6. When the area of ​​the air leakage hole meets the above range, the gas generation by chemical formation can be further suppressed, thereby improving the production qualification rate.

[0008] In some embodiments, the housing is provided with a receiving cavity, and the volume of the receiving cavity is 2 cm 3 ~150 cm 3 When the volume of the receiving chamber meets the above range, the gas generation during chemical formation can be further suppressed, thereby improving the production qualification rate.

[0009] In some embodiments, the secondary battery includes a plurality of positive electrode sheets, a plurality of negative electrode sheets, and a plurality of separators, wherein the positive electrode sheets and the negative electrode sheets are alternately stacked, and the separator is disposed between the positive electrode sheets and the negative electrode sheets. The positive and negative electrode sheets of the present application are alternately stacked, so that the wettability is better, and the solid electrolyte membrane formed at the interface of the positive and negative electrodes during the formation stage is more stable, thereby further suppressing the formation gas production and improving the production qualification rate.

[0010] In some embodiments, the number of positive electrode sheets is B sheets, 4≤B≤20. The number of positive electrode sheets of the present application meets the above range, which can further suppress the formation gas generation and improve the production qualification rate.

[0011] In some embodiments, the compaction density of the positive electrode sheet is C g / cm 3 , 3.2≤C≤5. The compaction density of the positive electrode sheet of the present application meets the above range, which can further suppress the formation of gas and improve the production qualification rate.

[0012] In some embodiments, 3.5≤C≤4.4. The present application further optimizes the compaction density of the positive electrode sheet, which can further suppress the formation of gas and improve the production qualification rate.

[0013] In some embodiments, the electrolyte further comprises a compound of formula II, wherein the compound of formula II comprises at least one of the following compounds: Formula II-1, Formula II-2, Formula II-3, Formula II-4, Formula II-5, Formula II-6, Formula II-7, Formula II-8, Formula II-9, Formula II-10, Formula II-11, Formula II-12; Based on the total mass of the electrolyte, the mass content of the compound of formula II is D%, 5≤D≤50. When the mass content of the compound of formula II in the present application is matched with the electrolyte system and meets the above range, the gas production can be further suppressed and the production qualification rate can be improved.

[0014] In some embodiments, 8≤D≤30. The present application further optimizes the mass content of the compound of formula II, which can further inhibit the formation of gas and improve the production qualification rate.

[0015] In a second aspect, the present application provides an electronic device comprising any of the above-mentioned secondary batteries. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solution and advantages of the present application more clear, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application.

[0017] In order to solve the problems of the prior art, the present application provides a secondary battery in a first aspect, which includes an electrolyte and a shell; the electrolyte includes an additive, and the additive includes at least one of fluoroethylene carbonate, vinylene carbonate, and 1,3-propane sultone; based on the total mass of the electrolyte, the mass content of the additive is X%, 1.2≤X≤30; the material of the shell is a steel shell; the shell includes a vent hole, and the area of ​​the vent hole is A mm 2 ; 0.3≤X / A≤25. The inventors have found that the above-mentioned additives can react before the solvent during the formation process to form a stable solid electrolyte membrane at the interface of the positive and negative electrodes, and can significantly inhibit the generation of gas in a high compaction density (high energy density) system. When the area of ​​the gas leakage holes and the content of the additives are controlled within a specific range, the gas production of the battery cell during formation can be greatly reduced. At the same time, the small amount of gas produced can be discharged through the gas leakage holes in time, reducing the probability of electrolyte overflow, thereby inhibiting the pollution of the battery cell by the gas production during formation and improving the production qualification rate.

[0018] In some embodiments, 1.2≤X≤30, preferably 4≤X≤25, for example, X can be 1.2, 2, 4, 6, 10, 12, 14, 16, 17, 20, 22, 25, 28, 30 or a value in the range formed by any two of these values. The present application regulates the mass content of the additive to meet the above range. The appropriate concentration of the additive in the electrolyte can quickly form a stable solid electrolyte membrane at the interface of the positive and negative electrodes, thereby further inhibiting the formation of gas production and improving the production qualification rate. When the additive content is too high, the gas generated by its own decomposition is too much, which is not conducive to the inhibition of formation of gas production. When the addition amount is too small, the stability of the solid electrolyte membrane formed is poor, and the inhibition of gas production is not significant enough.

[0019] In some embodiments, 0.3≤X / A≤25, preferably 0.5≤X / A≤20, for example, the value of X / A can be 0.3, 0.5, 3, 5, 7, 9, 10, 12, 15, 17, 18, 20, 22, 25 or a value in the range formed by any two of these values. The present application regulates the ratio of the mass content of the additive and the area size of the air leakage hole to meet the above relationship, so that the two can better play a role in cooperation with each other, thereby further inhibiting the formation of gas production and improving the production qualification rate.

[0020] In some embodiments, 1≤A≤6, preferably 1.5≤A≤5.2, for example, A can be 1, 1.1, 1.5, 2, 2.2, 2.8, 3, 3.8, 4, 4.8, 5, 5.2, 5.7, 6 or a value in the range formed by any two of these values. The area size of the vent hole is adjusted to meet the above range, which can better cooperate with the mass content of the additive in the electrolyte, further inhibit the formation of gas, and improve the production qualification rate.

[0021] In some embodiments, the shell is made of steel, and the strength of the steel is ≥300MPa.

[0022] In some embodiments, the housing is provided with a receiving cavity, the volume of the receiving cavity is 2 cm 3 ~150 cm 3 , preferably 4 cm 3 ~120 cm 3 For example, the volume value of the receiving chamber can be 2, 12, 14, 25, 41, 48, 67, 75, 86, 94, 111, 121, 134, 142, 150 or a value within the range formed by any two of these values. The present application regulates the volume of the receiving chamber to limit the total amount of active material in the battery cell to a specific range, thereby further suppressing the formation of gas and improving the production qualification rate.

[0023] In some embodiments, the secondary battery includes a plurality of positive electrode sheets, a plurality of negative electrode sheets and a plurality of separators, wherein the positive electrode sheets and the negative electrode sheets are alternately stacked, and the separator is disposed between the positive electrode sheets and the negative electrode sheets. The positive electrode sheets and the negative electrode sheets of the present application are alternately stacked, so that the electrolyte can enter the interior in time for replenishment, the wettability is better, and the solid electrolyte film formed at the interface of the positive and negative electrodes during the formation stage is more stable, thereby further suppressing the formation gas production and improving the production qualification rate.

[0024] In some embodiments, the number of positive electrode sheets is B sheets, 4≤B≤20, preferably 6≤B≤18, for example, the value of B can be 4, 6, 7, 8, 10, 11, 12, 13, 15, 17, 18, 20 or a value in the range formed by any two of these values. The present application regulates the number of positive electrode sheets to meet the above range, which can ensure that the battery cell has good wettability, and the electrolyte can be evenly distributed to all the sheets after injection, thereby further suppressing the formation of gas and improving the production qualification rate.

[0025] In some embodiments, the compaction density of the positive electrode sheet is C g / cm 3 , 3.2≤C≤5, preferably 3.5≤C≤4.4, for example, the value of C can be 3.2, 3.4, 3.5, 3.6, 3.9, 4.0, 4.1, 4.2, 4.4, 4.6, 4.7, 4.9, 5 or a value in the range formed by any two of these values. The application regulates the compaction density of the positive electrode sheet to meet the above range, which can ensure that the battery cell has good wetting and liquid storage properties, thereby further inhibiting formation gas production and improving the production qualification rate.

[0026] In some embodiments, the electrolyte further comprises a compound of formula II, wherein the compound of formula II comprises at least one of the following compounds: Formula II-1, Formula II-2, Formula II-3, Formula II-4, Formula II-5, Formula II-6, Formula II-7, Formula II-8, Formula II-9, Formula II-10, Formula II-11, Formula II-12; Based on the total mass of the electrolyte, the mass content of the compound of formula II is D%, 5≤D≤50, preferably 8≤D≤30, for example, D can be 5, 8, 12, 14, 17, 20, 23, 27, 30, 33, 37, 45, 50 or a value within the range composed of any two of these values. For a battery system with a high compaction density of the pole piece, the higher compaction density causes the secondary particles of the active material to break, and then the active reaction area of ​​the active material and the electrolyte increases, causing the side reaction to intensify and the gas production to be serious. The present application adopts the compound of formula II in combination with the above-mentioned electrolyte system, which can form a more stable solid electrolyte membrane at the positive and negative electrode interface, reduce the side reaction of the electrolyte at the positive and negative electrode interface during the cycle, improve the stability of the electrolyte at the positive and negative electrodes, and reduce the generation of gas, thereby further suppressing the formation of gas and improving the production qualification rate.

[0027] In the present application, the electrolyte may also include other organic solvents. The present application does not particularly limit the types of other organic solvents, as long as the purpose of the present application can be achieved, for example, it may include but is not limited to ether compounds, dimethyl sulfoxide, 1,2-dioxolane, cyclopentane, methyl cyclopentane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate or other organic solvents. The above-mentioned ether compounds may include but are not limited to ethylene glycol dimethyl ether, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or at least one of tetrahydrofuran.

[0028] The secondary battery of the present application is not particularly limited, and may include, but is not limited to, a lithium-ion secondary battery (also called a lithium-ion battery) or a sodium-ion secondary battery.

[0029] The secondary battery of the present application includes a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is selected from any of the above electrolytes; the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector; the above-mentioned "negative electrode active material layer located on at least one surface of the negative electrode current collector" means that the negative electrode active material layer can be located on one surface of the negative electrode current collector along its own thickness direction, or on two surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the surface of the negative electrode current collector, or it can be a partial area of ​​the surface of the negative electrode current collector. This application has no special restrictions, as long as the purpose of this application can be achieved.

[0030] The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or composite current collector (such as carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.). In the present application, there is no particular restriction on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the purpose of the present application can be achieved.

[0031] The negative electrode active material layer in the present application may also include a negative electrode binder and a negative electrode conductor, or the negative electrode active material layer may also include a negative electrode binder, a negative electrode conductor and a thickener. The present application does not particularly limit the type of negative electrode binder in the negative electrode active material layer, as long as the purpose of the present application can be achieved. For example, the negative electrode binder may include but is not limited to at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified styrene-butadiene rubber (SBR) or polyurethane. In some embodiments, the polyolefin binder includes at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol or polyacrylic acid. The present application does not particularly limit the type of negative electrode conductor in the negative electrode active material layer, as long as the purpose of the present application can be achieved. In some embodiments, the negative electrode conductor includes carbon-based materials, such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black or carbon fiber; metal-based materials, such as metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof. The present application does not particularly limit the type of thickener, as long as the purpose of the present application can be achieved. For example, the thickener may include but is not limited to at least one of sodium carboxymethyl cellulose or carboxymethyl cellulose. The present application does not particularly limit the mass ratio of the negative electrode active material, the negative electrode conductive agent, the negative electrode binder, and the thickener in the negative electrode active material layer. Those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.

[0032] In the present application, the positive electrode includes a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode active material layer located on at least one surface of the positive electrode current collector" means that the positive electrode active material layer can be located on one surface of the positive electrode current collector along its own thickness direction, or on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the surface of the positive electrode current collector, or it can be a partial area of ​​the surface of the positive electrode current collector. This application has no special restrictions, as long as the purpose of this application can be achieved.

[0033] The present application has no particular restrictions on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector). The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate.

[0034] The positive electrode active material layer of the present application includes a positive electrode active material. The present application has no particular limitation on the type of the positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include lithium nickel cobalt manganese oxide (LiNi 0.90 Co 0.05 Mn 0.05 O2 (NCM955), NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel lithium manganese oxide, spinel lithium nickel manganese oxide and lithium titanate. In the present application, the positive active material may also contain non-metallic elements, such as non-metallic elements including at least one of fluorine, phosphorus, boron, chlorine, silicon or sulfur. In the present application, there is no particular restriction on the thickness of the positive current collector and the positive active material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the positive current collector is 5μm to 20μm, and the thickness of the single-sided positive active material layer is 30μm to 120μm.

[0035] In the present application, the positive electrode active material layer may further include a positive electrode binder and a positive electrode conductor. The present application does not particularly limit the type of positive electrode binder in the positive electrode active material layer, as long as the purpose of the present application can be achieved. For example, the positive electrode binder may include but is not limited to polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified styrene-butadiene rubber (SBR) or at least one of polyurethane. In some embodiments, the polyolefin binder includes at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol or polyacrylic acid.

[0036] The present application has no particular restrictions on the type of positive electrode conductive agent in the positive electrode active material layer, as long as the purpose of the present application can be achieved. In some embodiments, the positive electrode conductive agent includes carbon-based materials, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black or carbon fiber; metal-based materials, such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof. The present application has no particular restrictions on the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode active material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved. For example, the loading amount of the positive electrode active material in the positive electrode sheet is 4.0 mg / cm 2 Up to 10.0 mg / cm 2 .

[0037] In order to prevent short circuit, a separator is usually provided between the positive electrode and the negative electrode of the secondary battery. In this case, the electrolyte of the present application is usually used after being infiltrated into the separator.

[0038] There is no particular restriction on the material and shape of the isolation membrane, as long as the effect of the present application is not significantly impaired. The isolation membrane may be a resin, glass fiber, inorganic substance, etc. formed of a material that is stable to the electrolyte of the present application. In some embodiments, the isolation membrane includes a porous sheet or a non-woven fabric-like material with excellent liquid retention. Examples of materials for resin or glass fiber isolation membranes may include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, polyether sulfone, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The materials of the above isolation membranes may be used alone or in any combination.

[0039] The separator may also be a material formed by laminating the above materials, examples of which include, but are not limited to, a three-layer separator formed by laminating polypropylene, polyethylene, and polypropylene in this order.

[0040] Examples of inorganic materials may include, but are not limited to, oxides such as aluminum oxide and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (eg, barium sulfate, calcium sulfate, etc.). The form of the inorganic material may include, but is not limited to, granular or fibrous.

[0041] The separator may be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabrics, woven fabrics, microporous films, etc. In the thin film form, the separator has a pore size of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm. In addition to the above-mentioned independent thin film separators, the following separators can also be used: a separator formed by forming a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or the negative electrode using a resin-based adhesive, for example, a separator formed by using a fluororesin as an adhesive to form a porous layer on both sides of the positive electrode with alumina particles having a particle size of 90% less than 1 μm.

[0042] The thickness of the separator is arbitrary. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. When the thickness of the separator is within the above range, insulation and mechanical strength can be ensured, and the rate characteristics and energy density of the secondary battery can be ensured.

[0043] The secondary battery of the present application also includes a packaging bag for containing a positive electrode, a negative electrode, a separator and an electrolyte, as well as other components known in the art in the secondary battery, and the present application does not limit the above other components. The present application does not specifically limit the packaging bag, and it can be a packaging bag known in the art, as long as it can achieve the purpose of the present application.

[0044] The preparation process of the secondary battery of the present application includes but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly of the stacked structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, an overcurrent protection element, a guide plate, etc. can also be placed in the packaging bag as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging.

[0045] In a second aspect, the present application provides an electronic device comprising any of the above-mentioned secondary batteries.

[0046] In some embodiments, the electronic devices of the present application include, but are not limited to, laptop computers, pen-type computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini CDs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

[0047] The scheme of the present application is described below by taking lithium-ion batteries as an example in combination with the following specific embodiments. Unless otherwise specified, the raw materials used in the following embodiments are all from ordinary commercial products, and the devices or equipment used are all purchased from conventional market sales channels. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0048] Test Method Gas production test: After the battery cell is filled with liquid, the vent hole is sealed, the initial thickness of the battery cell is measured, the battery cell is placed at 70℃ for 30 minutes, and charged to 4.3V at a charging rate of 0.3C. The thickness of the battery cell after formation is immediately tested. The growth of thickness is used to characterize the amount of gas generated during formation. The greater the thickness growth, the more gas generated during formation. Thickness growth rate = (thickness after formation - initial thickness) / initial thickness × 100%.

[0049] Production qualification rate: After the battery cell is filled with electrolyte, the vent hole is kept unobstructed with the outside air (not sealed), and the battery cell is placed at 70℃ for 30 minutes, and charged to 4.3V at a charging rate of 0.3C. During this process, the number of cells with electrolyte overflowing from the vent hole is recorded. The cells without electrolyte overflow are qualified cells. Production qualification rate = qualified cells / total cells × 100%.

[0050] Example 1-1 <Preparation of Electrolyte> In a dry argon atmosphere glove box, lithium hexafluorophosphate (LiPF6) as a supporting electrolyte was dissolved in a solution containing diethyl carbonate and an additive, wherein the additive was fluoroethylene carbonate. Based on the mass of the electrolyte, the mass content of lithium hexafluorophosphate was 10%, the mass content of the additive was as shown in Table 1 below, and the remainder was diethyl carbonate.

[0051] <Preparation of negative electrode sheet> Silicon carbon particles and graphite particles are mixed in a mass ratio of 1:4 to obtain a negative electrode active material; the negative electrode active material, negative electrode conductive agent Super P, thickener sodium carboxymethyl cellulose (CMC), and negative electrode binder styrene butadiene rubber (SBR) are mixed in a mass ratio of 95:2:1:2, and then deionized water is added as a solvent to prepare a negative electrode slurry with a solid content of 60wt%, and the negative electrode slurry is evenly coated on a negative electrode current collector copper foil with a thickness of 10µm, dried, and cold pressed to obtain a negative electrode sheet.

[0052] <Preparation of positive electrode sheet> The positive electrode active material lithium cobalt oxide (LiCoO2), the positive electrode binder polyvinylidene fluoride (PVDF), and the positive electrode conductive agent Super P were mixed in a mass ratio of 97:1.6:1.4, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75wt%, and stirred evenly. The positive electrode slurry was evenly coated on a positive electrode current collector aluminum foil with a thickness of 10μm, dried, and cold pressed to obtain a positive electrode sheet.

[0053] <Diaphragm> A polyethylene-polypropylene composite film with a thickness of 7 μm was used.

[0054] <Preparation of lithium-ion batteries> The positive electrode sheets and negative electrode sheets prepared above are stacked in order, so that the separator is located between the positive electrode sheets and the negative electrode sheets to play a barrier role, and then alternately stacked in order and fixed to obtain an electrode assembly with a laminated structure. The number of positive electrode sheets is 3, and the compaction density of the positive electrode sheets is 5.5 g / cm 3 The lithium-ion battery also includes a shell, the shell is made of steel, and the strength of the steel shell is 300MPa; the shell includes a vent hole, the area of ​​the vent hole is shown in Table 1 below; the shell is provided with a receiving cavity, the volume of the receiving cavity is 160 cm 3 The electrode assembly obtained above is placed in the receiving cavity, placed in a vacuum oven at 85°C for 12 hours to remove moisture, injected with the prepared electrolyte, and a lithium-ion battery is obtained through vacuum packaging, standing, and formation processes.

[0055] The main difference between the embodiments and comparative examples in Table 1 and Embodiment 1-1 is that the parameters shown in Table 1 are adjusted.

[0056] Table 1

[0057] As can be seen from Table 1, the present application controls the composition and mass content of the electrolyte to meet 1.2≤X≤30, and controls the area of ​​the vent holes so that the ratio of the mass content of the additive to the area of ​​the vent holes meets 0.3≤X / A≤25, which can inhibit gas production and improve the production qualification rate. In particular, when the mass content of the additive is regulated to meet 4≤X≤25, and the ratio of the mass content of the additive to the area of ​​the vent holes meets 0.5≤X / A≤20, gas production can be further inhibited and the production qualification rate can be improved.

[0058] The main difference between each embodiment in Table 2 and embodiments 1-11 lies in the volume of the receiving cavity. The volume of the receiving cavity of each embodiment is shown in Table 2.

[0059] Table 2

[0060] As can be seen from Table 2, the present application controls the volume of the receiving cavity to be 2 cm 3 ~150 cm 3 , which can further inhibit the formation of gas and improve the production qualification rate.

[0061] In particular, when the volume of the receiving chamber is 4 cm 3 ~120 cm 3 When the reaction is carried out, the gas production can be further suppressed and the production qualification rate can be improved.

[0062] The main differences between each embodiment in Table 3 and embodiments 2-3 are the number of positive electrode sheets and the compaction density of the positive electrode sheets. The number of positive electrode sheets and the compaction density of the positive electrode sheets of each embodiment are shown in Table 3.

[0063] Table 3

[0064] As can be seen from Table 3, the present application controls the number of positive electrode sheets to meet 4≤B≤20, preferably 6≤B≤18, which can further suppress the formation gas production and improve the production qualification rate. The present application controls the compaction density of the positive electrode sheets to meet 3.2≤C≤5, preferably 3.5≤C≤4.4, which is conducive to improving the wettability and the stability of the solid electrolyte membrane formed at the positive and negative electrode interfaces, thereby further suppressing the formation gas production and improving the production qualification rate.

[0065] The main difference between each embodiment in Table 4 and embodiments 3-7 is that the electrolyte is prepared according to a method comprising the following steps: In a dry argon atmosphere glove box, the compound of formula II is dissolved in a solution containing lithium hexafluorophosphate, diethyl carbonate and an additive, wherein the additive is fluoroethylene carbonate. Based on the mass of the electrolyte, the mass contents of lithium hexafluorophosphate and the additive are the same as those in Examples 3-7, the type and mass content of the compound of formula II are shown in Table 4 below, and the remainder is diethyl carbonate.

[0066] Table 4

[0067] As can be seen from Table 4, the present application can further suppress the formation of gas and improve the production qualification rate by adding the compound of formula II to the electrolyte and adjusting the mass content of the compound of formula II to satisfy 5≤D≤50, preferably 8≤D≤30.

[0068] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the principles of the present application should be included in the protection scope of the present application.

Claims

1. A secondary battery, characterized in that: The invention comprises an electrolyte and a shell; the electrolyte comprises an additive, and the additive comprises at least one of fluoroethylene carbonate, vinylene carbonate, and 1,3-propane sultone; Based on the total mass of the electrolyte, the mass content of the additive is X%, 1.2≤X≤30; The shell is made of steel; the shell includes an air leakage hole, and the area of ​​the air leakage hole is A mm 2 ;0.3≤X / A≤25.

2. The secondary battery according to claim 1, characterized in that: 0.5≤X / A≤20.

3. The secondary battery according to claim 1, characterized in that: 1≤A≤6。 4. The secondary battery according to claim 3, characterized in that The housing is provided with a receiving cavity, the volume of which is 2 cm 3 ~150 cm 3 .

5. The secondary battery according to claim 1, characterized in that: The secondary battery comprises a plurality of positive electrode sheets, a plurality of negative electrode sheets and a plurality of separators. The positive electrode sheets and the negative electrode sheets are alternately stacked, and the separator is arranged between the positive electrode sheets and the negative electrode sheets.

6. The secondary battery according to claim 5, characterized in that: The number of the positive electrode plates is B plates, 4≤B≤20.

7. The secondary battery according to claim 5, characterized in that The compaction density of the positive electrode sheet is C g / cm 3 , 3.2≤C≤5.

8. The secondary battery according to claim 7, characterized in that: 3.5≤C≤4.4。 9. The secondary battery according to claim 1, characterized in that The electrolyte further comprises a compound of formula II, wherein the compound of formula II comprises at least one of the following compounds: Formula II-1, Formula II-2, Formula II-3, Formula II-4, Formula II-5, Formula II-6, Formula II-7, Formula II-8, Formula II-9, Formula II-10, Formula II-11, Formula II-12; Based on the total mass of the electrolyte, the mass content of the compound of formula II is D%, 5≤D≤50.

10. The secondary battery according to claim 9, characterized in that: 8≤D≤30。 11. An electronic device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 10.

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