Secondary battery and electronic device

Abstract

The application 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; the additive comprises at least one of fluoroethylene carbonate, vinylene carbonate and 1,3-propane sultone; the mass content of the additive is X% based on the total mass of the electrolyte, and 1.2<=X<=30; the material of the shell is a steel shell; the shell comprises a gas escape hole, the area of the gas escape hole is A mm 2 ; and 0.3<=X / A<=25 is met. Through control of the components and content of the electrolyte and the relationship between the electrolyte and the gas escape hole, the application can effectively inhibit the gas generation phenomenon in the formation process and improve the qualified rate of battery production.

Description

Technical Field

[0001] This application belongs to the field of energy storage technology, specifically relating to a secondary battery and electronic device. Background Technology

[0002] As rechargeable energy storage devices, secondary batteries can store and release electrical energy through electrochemical reactions, making them an indispensable key component in electronic devices, electric vehicles, and energy storage systems. With continuous technological iteration and upgrades, 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, gas generation during formation is a particularly prominent technical challenge. Formation refers to the initial charge-discharge treatment of the electrode materials inside the battery through a specific electrochemical process before its first use, thereby forming a stable solid electrolyte film at the positive and negative electrode interfaces. This process is crucial for ensuring battery performance. However, gas generation is inevitable during formation, which increases the internal pressure of the battery, affecting its safety and performance, and even reducing the production yield. This gas generation problem is particularly pronounced in large-scale production environments, directly impacting overall production efficiency and cost. Therefore, suppressing formation gas generation and improving the production yield has become an important direction for current technological development. Summary of the Invention

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

[0005] In a first aspect, this application provides a secondary battery, comprising an electrolyte and a casing; the electrolyte includes additives, the additives being at least one selected from fluoroethylene carbonate, vinylene carbonate, and 1,3-propane sulpholactone; based on the total mass of the electrolyte, the mass content of the additives is X%, 1.2 ≤ X ≤ 30; the casing is made of steel; the casing includes a vent, the area of ​​which is A mm. 2 0.3≤X / A≤25. This application, by controlling the composition and mass content of the electrolyte, and in conjunction with controlling the area of ​​the vent, can suppress gas generation during formation, reduce leakage and cell contamination caused by gas generation, improve the production qualification rate, and thus enhance the overall performance and safety of the battery.

[0006] In some embodiments, 0.5 ≤ X / A ≤ 20. When the ratio of the mass content of the additive in the electrolyte to the size of the vent area meets the above range, gas generation during formation can be further suppressed, and the production qualification rate can be improved.

[0007] In some implementations, 1 ≤ A ≤ 6. When the area of ​​the vent hole meets the above range, it can further suppress gas formation and improve the production qualification rate.

[0008] In some embodiments, the housing has a receiving cavity with a volume of 2 cm³. 3 ~150 cm 3 When the volume of the containment cavity meets the above range, it can further suppress the formation of gas and improve the production qualification rate.

[0009] In some embodiments, the secondary battery includes a plurality of positive electrode plates, a plurality of negative electrode plates, and a plurality of separators, with the positive and negative electrode plates alternately stacked, and the separators disposed between the positive and negative electrode plates. The alternating stacking of the positive and negative electrode plates in this application results in better wettability and a more stable solid electrolyte film formed at the positive and negative electrode interface during the formation stage, thereby further suppressing gas generation during formation and improving the production yield.

[0010] In some embodiments, the number of positive electrode plates is B, where 4 ≤ B ≤ 20. The number of positive electrode plates in this application meets the above range, which can further suppress gas generation during formation and improve the production yield.

[0011] In some embodiments, the compaction density of the positive electrode sheet is C g / cm³. 3 3.2≤C≤5. The compaction density of the positive electrode sheet in this application meets the above range, which can further suppress gas generation during formation and improve the production qualification rate.

[0012] In some embodiments, 3.5 ≤ C ≤ 4.4. This application further optimizes the compaction density of the positive electrode sheet, which can further suppress gas generation during formation and improve the production yield.

[0013] In some embodiments, the electrolyte further includes a compound of formula II, which includes at least one of the following compounds:

[0014] Formula II-1 Formula II-2 Formula II-3

[0015] Formula II-4 Formula II-5 Formula II-6

[0016] Formula II-7 Formula II-8

[0017] Formula II-9 Formula II-10

[0018] Formula II-11 Formula II-12;

[0019] Based on the total mass of the electrolyte, the mass content of compound II is D%, 5 ≤ D ≤ 50%. When compound II is used in conjunction with the electrolyte system, and its mass content meets the above range, it can further suppress gas formation and improve the production yield.

[0020] In some embodiments, 8 ≤ D ≤ 30. This application further optimizes the mass content of the compound of formula II, which can further suppress formation gas production and improve the production yield.

[0021] Secondly, this application provides an electronic device including any of the aforementioned secondary batteries. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0023] To address the problems of the prior art, this application provides a secondary battery in a first aspect, comprising an electrolyte and a casing; the electrolyte includes additives, the additives being at least one selected from fluoroethylene carbonate, vinylene carbonate, and 1,3-propane sulpholactone; based on the total mass of the electrolyte, the mass content of the additives is X%, 1.2 ≤ X ≤ 30; the casing is made of steel; the casing includes a vent, the area of ​​which is A mm. 2 0.3≤X / A≤25. The inventors discovered that the above-mentioned additives can react before the solvent during the formation process, forming a stable solid electrolyte film at the positive and negative electrode interfaces. In high-density (high-energy-density) systems, they can significantly suppress gas generation. When the vent area and additive content are controlled within a specific range, the amount of gas generated during cell formation can be greatly reduced. At the same time, the small amount of gas generated can be discharged in time through the vent, reducing the probability of electrolyte overflow, thereby suppressing the contamination of the cell by formation gas and improving the production qualification rate.

[0024] In some embodiments, 1.2 ≤ X ≤ 30, preferably 4 ≤ X ≤ 25. For example, X can be a value within the range of 1.2, 2, 4, 6, 10, 12, 14, 16, 17, 20, 22, 25, 28, 30, or any combination of these values. This application controls the mass content of the additive to meet the above range. A suitable concentration of the additive in the electrolyte can quickly form a stable solid electrolyte film at the positive and negative electrode interfaces, thereby further suppressing gas formation and improving the production yield. When the additive content is too high, too much gas is generated from its own decomposition, which is not conducive to suppressing gas formation. When the amount added is too low, the stability of the formed solid electrolyte film is poor, and the suppression of gas formation is not significant enough.

[0025] 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 any value within the range of any two of these values. The ratio of the additive's mass content to the vent area size, as described in this application, conforms to the above relationship, enabling them to better cooperate and further suppress gas formation, thereby improving the production qualification rate.

[0026] In some embodiments, 1 ≤ A ≤ 6, preferably 1.5 ≤ A ≤ 5.2. For example, A can be a value within the range of 1, 1.1, 1.5, 2, 2.2, 2.8, 3, 3.8, 4, 4.8, 5, 5.2, 5.7, 6, or any two of these values. Adjusting the size of the vent hole to meet the above range allows for better coordination with the mass content of additives in the electrolyte, further suppressing gas formation and improving the production yield.

[0027] In some embodiments, the shell is made of steel with a strength ≥300MPa.

[0028] In some embodiments, the housing is provided with a receiving cavity, the volume of which is 2 cm³. 3 ~150 cm 3 Preferably 4 cm 3 ~120 cm 3 For example, the volume of the containment cavity can be 2, 12, 14, 25, 41, 48, 67, 75, 86, 94, 111, 121, 134, 142, 150, or a value within any two of these ranges. This application regulates the volume of the containment cavity to limit the total amount of active material in the battery cell to a specific range, thereby further suppressing gas formation and improving the production yield.

[0029] In some embodiments, the secondary battery includes a plurality of positive electrode plates, a plurality of negative electrode plates, and a plurality of separators, wherein the positive and negative electrode plates are alternately stacked, and the separators are disposed between the positive and negative electrode plates. The alternating stacking of the positive and negative electrode plates in this application allows the electrolyte to enter and replenish the interior in a timely manner, resulting in better wettability and a more stable solid electrolyte film formed at the positive and negative electrode interface during the formation stage. This further suppresses gas generation during formation and improves the production yield.

[0030] In some embodiments, the number of positive electrode plates is B, where 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 any value within the range of any two of these values. This application controls the number of positive electrode plates to meet the above range, ensuring good wettability of the battery cell. After electrolyte injection, the electrolyte can be evenly distributed to all electrodes, thereby further suppressing gas formation and improving the production yield.

[0031] In some embodiments, the compaction density of the positive electrode sheet is C g / cm³. 3 The density of C is 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 any value within the range of any two of these values. This application regulates the compaction density of the positive electrode sheet to meet the above range, ensuring that the battery cell has good wetting and liquid storage properties, thereby further suppressing gas generation during formation and improving the production qualification rate.

[0032] In some embodiments, the electrolyte further includes a compound of formula II, which includes at least one of the following compounds:

[0033] Formula II-1 Formula II-2 Formula II-3

[0034] Formula II-4 Formula II-5 Formula II-6

[0035] Formula II-7 Formula II-8

[0036] Formula II-9 Formula II-10

[0037] Formula II-11 Formula II-12;

[0038] Based on the total mass of the electrolyte, the mass content of compound 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 any value within the range of any two of these values. For battery systems with high compaction density of the electrodes, the high compaction density leads to secondary particle breakage of the active material, which in turn increases the active reaction area between the active material and the electrolyte, exacerbating side reactions and causing severe gas production. This application uses compound II in combination with the above-mentioned electrolyte system to form a more stable solid electrolyte film at the positive and negative electrode interfaces, reducing side reactions of the electrolyte at the positive and negative electrode interfaces during cycling, improving the stability of the electrolyte at the positive and negative electrodes, reducing gas production, thereby further suppressing gas production during formation and improving the production yield.

[0039] In this application, the electrolyte may also include other organic solvents. This application does not particularly limit the types of other organic solvents, as long as they can achieve the purpose of this application. For example, they may include, but are not limited to, at least one of ether compounds, dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate, or other organic solvents. The aforementioned ether compounds may include, but are not limited to, at least one of 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 tetrahydrofuran.

[0040] The secondary battery in this application is not particularly limited, and may include, but is not limited to, lithium-ion secondary batteries (also known as lithium-ion batteries) or sodium-ion secondary batteries.

[0041] The secondary battery of this application includes a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte is selected from any of the electrolytes mentioned above; 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 aforementioned "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 it can be located 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 part of the surface of the negative electrode current collector. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0042] This application does not impose any particular restrictions on the negative electrode current collector, as long as it achieves the purpose of this application. 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 collectors (e.g., carbon-copper composite current collectors, nickel-copper composite current collectors, titanium-copper composite current collectors, etc.). In this application, there are no particular restrictions on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as they achieve the purpose of this application.

[0043] The negative electrode active material layer in this application may further include a negative electrode binder and a negative electrode conductive agent, or the negative electrode active material layer may further include a negative electrode binder, a negative electrode conductive agent, and a thickener. This application does not particularly limit the type of negative electrode binder in the negative electrode active material layer, as long as it can achieve the purpose of this application. 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, polyenol, or polyacrylic acid. This application does not particularly limit the type of negative electrode conductive agent in the negative electrode active material layer, as long as it can achieve the purpose of this application. In some embodiments, the negative 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 powder or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof. This application does not impose any particular limitation on the type of thickener, as long as it can achieve the purpose of this application. For example, the thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or carboxymethyl cellulose. This application does not impose any particular limitation on the mass ratio of negative electrode active material, negative electrode conductive agent, negative electrode binder, and thickener in the negative electrode active material layer. Those skilled in the art can select according to actual needs, as long as it can achieve the purpose of this application.

[0044] In this application, the positive electrode comprises 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 aforementioned "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 thickness direction, or it can be located on two surfaces of the positive electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the positive electrode current collector, or it can be a partial surface area; this application has no particular limitation, as long as the purpose of this application is achieved.

[0045] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil, or composite current collectors (such as aluminum-carbon composite current collectors). Composite current collectors can be formed by forming metallic materials (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer substrate.

[0046] The positive electrode active material layer of this application includes a positive electrode active material. This application does not have specific limitations on the type of positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material may include lithium nickel cobalt manganese oxide (LiNi). 0.90 Co 0.05 Mn 0.05 At least one of the following: 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-type lithium manganese oxide; spinel-type lithium nickel manganese oxide; and lithium titanate. In this application, the positive electrode active material may also contain non-metallic elements, such as at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. In this application, there are no particular limitations on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the purpose of this application is achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the single-sided positive electrode active material layer is 30 μm to 120 μm.

[0047] In this application, the positive electrode active material layer may further include a positive electrode binder and a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode binder in the positive electrode active material layer, as long as it achieves the purpose of this application. For example, the positive 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, polyvinyl alcohol, or polyacrylic acid.

[0048] This application does not impose any particular limitation on the type of positive electrode conductive agent in the positive electrode active material layer, as long as it can achieve the purpose of this application. 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 powder or metal fiber of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof. This application does not impose any particular limitation on the mass ratio of positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode active material layer. Those skilled in the art can choose according to actual needs, as long as it can achieve the purpose of this application. For example, the loading of positive electrode active material in the positive electrode sheet is 4.0 mg / cm³. 2 Up to 10.0 mg / cm 2 .

[0049] To prevent short circuits, a separator is typically placed between the positive and negative electrodes of a secondary battery. In this case, the electrolyte of this application is typically used after penetrating into the separator.

[0050] There are no particular limitations on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application. The separator can be a resin, glass fiber, inorganic material, etc., formed from a material that stabilizes the electrolyte of this application. In some embodiments, the separator includes a porous sheet or non-woven fabric-like material with excellent liquid retention properties. Examples of materials for resin or glass fiber separators may include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-mentioned separator materials can be used alone or in any combination.

[0051] The separator can also be a material formed by laminating the above-mentioned materials, examples of which include, but are not limited to, a three-layer separator formed by laminating polypropylene, polyethylene, and polypropylene in that order.

[0052] Examples of inorganic materials may include, but are not limited to, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.). Inorganic materials may be in, but are not limited to, particulate or fibrous forms.

[0053] The separator can be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabrics, woven fabrics, and microporous membranes. 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: separators formed by using a resin-based adhesive to form a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive and / or negative electrodes. For example, a separator formed by using fluororesin as an adhesive to form a porous layer of alumina particles with a particle size of less than 1 μm on both sides of the positive electrode.

[0054] 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 ranges, insulation and mechanical strength can be ensured, and the rate characteristics and energy density of the secondary battery can be ensured.

[0055] The secondary battery of this application also includes a packaging bag for containing the positive electrode, negative electrode, separator, and electrolyte, as well as other components known in the art for secondary batteries. This application does not limit the aforementioned other components. This application does not have any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0056] The preparation process of the secondary battery in this application includes, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, then fixing the four corners of the entire stacked structure with tape to obtain the electrode assembly of the stacked structure, placing the electrode assembly into a packaging bag, injecting electrolyte into the packaging bag and sealing it to obtain the secondary battery. In addition, overcurrent protection components, conductive plates, etc., can also be placed in the packaging bag as needed to prevent pressure rise and overcharging / discharging inside the secondary battery.

[0057] Secondly, this application provides an electronic device including any of the aforementioned secondary batteries.

[0058] In some embodiments, the electronic devices of this application include, but are not limited to, laptop computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc.

[0059] The following uses a lithium-ion battery as an example to illustrate the solution of this application with specific embodiments. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available 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 methods described below. In addition, unless otherwise specified, "parts" and "%" are quality bases.

[0060] Test methods

[0061] Chemical formation gas production test:

[0062] After the cell is filled with electrolyte, the vent hole is sealed, the initial thickness of the cell is measured, the cell is placed in a 70℃ environment and left to stand for 30 minutes, and charged to 4.3V with a charging rate of 0.3C. The thickness of the cell after formation is immediately tested. The amount of gas produced during formation is characterized by the increase in thickness. The greater the increase in thickness, the more gas is produced during formation.

[0063] Thickness growth rate = (thickness after formation - initial thickness) / initial thickness × 100%.

[0064] Production pass rate:

[0065] After the battery cell is filled with electrolyte, the vent hole is kept open to the outside air (not sealed). The battery cell is placed in a 70℃ environment and left to stand for 30 minutes. It is then charged to 4.3V at a charging rate of 0.3C. During this process, the number of battery cells that have electrolyte overflowed from the vent hole is recorded. Battery cells that have no electrolyte overflow are qualified battery cells.

[0066] Production pass rate = qualified cells / total cells × 100%.

[0067] Example 1-1

[0068] <Preparation of Electrolyte>

[0069] In a dry argon atmosphere glove box, lithium hexafluorophosphate (LiPF6), serving as the supporting electrolyte, was dissolved in a solution containing diethyl carbonate and an additive, namely fluoroethylene carbonate. Based on the mass of the electrolyte, the mass content of lithium hexafluorophosphate was 10%, the mass content of the additive is shown in Table 1 below, and the balance was diethyl carbonate.

[0070] <Preparation of Negative Electrode Sheets>

[0071] Silicon carbon particles and graphite particles were mixed at a mass ratio of 1:4 to obtain the 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) were mixed at a mass ratio of 95:2:1:2. Deionized water was added as a solvent to prepare a negative electrode slurry with a solid content of 60wt%. The negative electrode slurry was uniformly coated on a negative electrode current collector copper foil with a thickness of 10µm, dried, and cold-pressed to obtain the negative electrode sheet.

[0072] <Preparation of the positive electrode>

[0073] Lithium cobalt oxide (LiCoO2), the positive electrode active material, polyvinylidene fluoride (PVDF), the positive electrode binder, and Super P, the positive electrode conductive agent, were mixed in a mass ratio of 97:1.6:1.4. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%, and the mixture was stirred evenly. The positive electrode slurry was uniformly coated onto a 10 μm thick aluminum foil for the positive electrode current collector, dried, and cold-pressed to obtain the positive electrode sheet.

[0074] <Septum>

[0075] A polyethylene-polypropylene composite film with a thickness of 7 μm was used.

[0076] <Preparation of Lithium-ion Batteries>

[0077] The prepared positive and negative electrode sheets are stacked sequentially, with the separator positioned between them to act as a barrier. These are then stacked alternately in sequence and fixed to obtain a stacked electrode assembly. The positive electrode consists of three sheets with a compaction density of 5.5 g / cm³. 3 The lithium-ion battery also includes a casing made of steel with a strength of 300 MPa; the casing includes a vent, the area of ​​which is shown in Table 1; the casing has a receiving cavity with a volume of 160 cm³. 3 The electrode assembly obtained above is placed in the receiving cavity and dried in a vacuum oven at 85°C for 12 hours to remove moisture. The prepared electrolyte is then injected, and the lithium-ion battery is obtained through vacuum sealing, settling, and formation processes.

[0078] 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 accordingly.

[0079] Table 1

[0080]

[0081] As shown in Table 1, this application, by controlling the composition and mass content of the electrolyte to meet the condition of 1.2 ≤ X ≤ 30, and in conjunction with controlling the area of ​​the vent, ensures that the ratio of the additive mass content to the vent area is 0.3 ≤ X / A ≤ 25, thereby suppressing gas formation and improving the production yield. In particular, when the additive mass content is controlled to meet the condition of 4 ≤ X ≤ 25, and the ratio of the additive mass content to the vent area is 0.5 ≤ X / A ≤ 20, gas formation can be further suppressed, and the production yield can be improved.

[0082] The main difference between the embodiments in Table 2 and embodiments 1-11 is the volume of the receiving cavity. The volume of the receiving cavity in each embodiment is shown in Table 2.

[0083] Table 2

[0084]

[0085] As shown in Table 2, this application controls the volume of the receiving cavity to be within 2 cm³. 3 ~150 cm 3 This can further suppress gas formation and improve the production qualification rate.

[0086] Specifically, when the volume of the receiving cavity is 4 cm 3 ~120 cm 3 At the same time, it can further suppress gas formation and improve the production qualification rate.

[0087] The main differences between the embodiments 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 in each embodiment are shown in Table 3.

[0088] Table 3

[0089]

[0090] As shown in Table 3, by controlling the number of positive electrode sheets to satisfy 4≤B≤20, preferably 6≤B≤18, this application can further suppress gas generation during formation and improve the production yield. By controlling the compaction density of the positive electrode sheets to satisfy 3.2≤C≤5, preferably 3.5≤C≤4.4, this application can improve wettability and the stability of the solid electrolyte film formed at the positive and negative electrode interfaces, thereby further suppressing gas generation during formation and improving the production yield.

[0091] The main difference between the examples in Table 4 and Examples 3-7 is that the electrolyte is prepared according to the method including the following steps:

[0092] In a dry argon atmosphere glove box, the compound of formula II was dissolved in a solution containing lithium hexafluorophosphate, diethyl carbonate, and an additive, namely fluoroethylene carbonate. Based on the mass of the electrolyte, the mass content of lithium hexafluorophosphate and the additive was the same as in Examples 3-7. The types and mass contents of the compound of formula II are shown in Table 4 below, with the balance being diethyl carbonate.

[0093] Table 4

[0094]

[0095] As shown in Table 4, this application can further suppress gas formation and improve the production qualification rate by adding compound of formula II to the electrolyte and adjusting the mass content of compound of formula II to meet the requirements of 5≤D≤50, preferably 8≤D≤30.

[0096] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the principles of this application should be included within the protection scope of this application.

Claims

1. A secondary battery characterized by comprising: The electrolyte comprises an additive, and the additive comprises fluoroethylene carbonate; The mass content of the additive is X% based on the total mass of the electrolyte, and 1.2≤X≤30; The material of the shell is steel shell; the shell comprises a deflation hole, the area of the deflation hole is A mm 2 ; 4≤X / A≤25; the shell is provided with a receiving cavity, the volume of the receiving cavity is 120 cm 3 ~150 cm 3 ; 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 arranged in a stack, and the separators are arranged between the positive electrode sheets and the negative electrode sheets. The compacted density of the positive electrode plate is C g / cm 3 , 3.2≤C≤4.4; The electrolyte further comprises a compound of Formula II, and the compound of Formula II comprises at least one of the following compounds: Formula II-5, Formula II-12; The mass content of the compound of Formula II is D% based on the total mass of the electrolyte, and 5≤D≤50.

2. The secondary battery according to claim 1, characterized by 4≤X / A≤20.

3. The secondary battery according to claim 1, characterized by 3≤A≤6。 4. The secondary battery according to claim 1, characterized by The number of the positive electrode sheets is B, and 4≤B≤20.

5. The secondary battery according to claim 1, characterized by 8≤D≤30。 6. An electronic device, comprising: The secondary battery of any one of claims 1 to 5.

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