Lithium secondary battery and electric device

Abstract

The application provides a lithium secondary battery and a power consumption device. The lithium secondary battery comprises an electrolyte and a negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, the electrolyte comprises a chain carboxylic acid ester and a cyclic carbonate, the mass content W1 of the chain carboxylic acid ester is 5% to 75% based on the total mass of the electrolyte, the mass content W2 of the cyclic carbonate is 2% to 40%, and the thickness of the negative electrode film layer is 10 μm to 100 μm. The lithium secondary battery has excellent fast charging performance and cycle performance.

Description

[0001] This application is a divisional application of the invention patent application with the application date of July 18, 2023, the application number of 202310883089.X, and the invention name of "Lithium secondary battery and power utilization device". TECHNICAL FIELD

[0002] The present application relates to the technical field of lithium batteries, in particular to a lithium secondary battery and a power utilization device. BACKGROUND

[0003] In recent years, secondary batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc., and the requirements for the electrical performance of secondary batteries are constantly improving, and there is an increasingly high expectation for the charging rate of secondary batteries.

[0004] The performance of the electrolyte has a crucial influence on the performance of the secondary battery, and an electrolyte with a suitable component composition can improve the electrical performance or charging rate of the secondary battery, meeting the different performance requirements of batteries in different fields. Therefore, it is still necessary to develop electrolytes to meet the application needs of new generations of electrochemical systems. SUMMARY

[0005] The present application is made in view of the above-mentioned problems, and aims to provide a lithium secondary battery having excellent fast charging performance and cycle performance.

[0006] To achieve the above-mentioned purpose, the first aspect of the present application provides a lithium secondary battery, comprising an electrolyte and a negative electrode sheet, the electrolyte comprising a chain carboxylic acid ester and a cyclic carbonate, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector.

[0007] Wherein, based on the total mass of the electrolyte, the mass content W1 of the chain carboxylic acid ester and the mass content W2 of the cyclic carbonate satisfy: 0.1≤W2 / W1≤2, and the mass content W1 of the chain carboxylic acid ester and the thickness H of the negative electrode film layer satisfy: 0.2≤H / 100W1≤20, the unit of H is μm.

[0008] The chain carboxylic acid ester introduced into the electrolyte can significantly reduce the viscosity of the electrolyte and improve the wettability of the electrolyte to the negative electrode sheet, improve the liquid phase transmission rate of lithium ions and reduce the migration resistance of lithium ions, and significantly improve the fast charging performance of the lithium secondary battery; at the same time, the mass content W1 of the chain carboxylic acid ester and the mass content W2 of the cyclic carbonate and the thickness H of the negative electrode film satisfy the above relationship, which can not only make the passivation layer generated by the reduction of the cyclic carbonate on the surface of the negative electrode sheet to reduce the side reaction between the metal lithium and the chain carboxylic acid ester on the negative electrode sheet side during the cycle of the lithium secondary battery, but also reduce the degree of lithium precipitation on the negative electrode due to insufficient electrolyte infiltration, so that the lithium secondary battery can have both fast charging performance and cycle performance.

[0009] In any embodiment, the electrolyte further comprises a sulfonate compound, and the mass content W1 of the chain carboxylic acid ester and the mass content W3 of the sulfonate compound satisfy: 0.005≤W3 / W1≤0.4, based on the total mass of the electrolyte.

[0010] The sulfonate compound can first oxidize on the positive electrode sheet side of the lithium secondary battery, and the oxide is deposited at the interface of the positive electrode sheet to form a CEI film, which can reduce the degree of oxidation reaction of the chain carboxylic acid ester at high pressure on the positive electrode sheet side, reduce the loss and gas generation degree of the chain carboxylic acid ester, and further improve the fast charging performance and storage performance of the lithium secondary battery.

[0011] In any embodiment, the chain carboxylic acid ester comprises one or more of ethyl formate, ethyl acetate, methyl acetate, methyl propionate, ethyl propionate, propyl propionate, propyl acetate, butyl formate, and methyl butyrate, and optionally comprises one or more of ethyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

[0012] The above chain carboxylic acid ester has a low viscosity due to the number of main chain carbon atoms being less than 5, which can significantly reduce the viscosity of the electrolyte, improve the liquid phase transmission rate of lithium ions, and further improve the conductivity of the electrolyte, which is beneficial to improve the fast charging performance of the lithium secondary battery.

[0013] In any embodiment, the cyclic carbonate comprises one or more of ethylene carbonate, propylene carbonate, and fluorinated ethylene carbonate, and optionally comprises one or more of ethylene carbonate and fluorinated ethylene carbonate.

[0014] The above cyclic carbonates can all be reduced to form a passivation layer on the negative electrode sheet side, reduce the side reaction between the chain carboxylic acid ester and the metal lithium, and improve the cycle performance and storage performance of the lithium secondary battery.

[0015] In any embodiment, the sulfate compound includes one or more of compounds shown in Formula I, Formula II, diethyl sulfate, dimethyl sulfate, dihydro-1,3,2-dioxoheptane-2,2,5,5-tetraoxide, one or more of sulfenyl-(1,3,2-dioxoheptane)-2,2,5,5-tetraoxide,

[0016]

[0017] wherein R1, R2 each independently includes a hydrogen atom, a C 1-6 alkyl group, R3 includes a C 1-6 alkyl group. Optionally, the sulfate compound includes 4,4'-vinylene sulfite, vinyl sulfite, diethyl sulfate, dimethyl sulfate, dihydro-1,3,2-dioxoheptane-2,2,5,5-tetraoxide, one or more of sulfenyl-(1,3,2-dioxoheptane)-2,2,5,5-tetraoxide.

[0018] The above sulfate compound can participate in the formation of CEI film on the positive electrode sheet side, reduce the degree of oxidation reaction of the chain carboxylate, and improve the fast charging performance and storage performance of the battery.

[0019] In any embodiment, the mass content W1 of the chain carboxylate is 5% to 75%, and optionally 20% to 75%, based on the total mass of the electrolyte.

[0020] Controlling the mass content of the chain carboxylate within a suitable range can significantly reduce the viscosity of the electrolyte, improve the liquid phase transmission rate of lithium ions, and thus improve the conductivity of the electrolyte, which is conducive to improving the fast charging performance of the lithium secondary battery, and can also reduce the degree of aggravation of the side reaction between the chain carboxylate and the metal lithium on the negative electrode sheet side.

[0021] In any embodiment, the mass content W2 of the cyclic carbonate is 5% to 40%, and optionally 10% to 30%, based on the total mass of the electrolyte.

[0022] Controlling the mass content of the cyclic carbonate within a suitable range can provide sufficient cyclic carbonate to dissociate the lithium salt in the electrolyte and participate in the formation of a passivation layer on the surface of the negative electrode sheet, thereby improving the conductivity of the electrolyte, and can also reduce the influence of excessive introduction of cyclic carbonate on the viscosity of the electrolyte, thereby comprehensively improving the fast charging performance of the lithium secondary battery.

[0023] In any embodiment, the mass content W3 of the sulfate compound is 0.1% to 2%, and optionally 0.1% to 1%, based on the total mass of the electrolyte.

[0024] The quality content of the sulfate compound is controlled within a proper range, which can provide sufficient sulfate compounds to participate in the formation of the CEI film on the positive electrode sheet side, inhibit the oxidation reaction of the carboxylic acid ester, and improve the fast charging performance of the lithium secondary battery, and can also prevent excessive introduction of the sulfate compound from increasing the production cost of the lithium secondary battery.

[0025] In any embodiment, the thickness of the negative electrode film layer is 10-100 μm, and optionally 20-70 μm.

[0026] The thickness of the negative electrode film layer is controlled within a proper range, which can simultaneously take into account the fast charging performance and energy density of the battery.

[0027] In any embodiment, the electrolyte further comprises a lithium salt, and the lithium salt comprises LiPF6 and LiFSI. In any embodiment, the molar concentration C1 of LiPF6 and the molar concentration C2 of LiFSI satisfy: 0.8 mol / L≤C1+C2≤1.3 mol / L, and optionally 0.8 mol / L≤C1+C2≤1.2 mol / L.

[0028] In any embodiment, the molar concentration C1 of LiPF6 and the molar concentration C2 of LiFSI satisfy: 1≤C1 / C2≤5, and optionally 1≤C1 / C2≤3.

[0029] LiFSI has a high dissociation degree in the electrolyte, which can greatly improve the room temperature conductivity of the electrolyte, but at the same time, LiFSI has the risk of corroding the negative electrode current collector aluminum foil. LiPF6 has a lower dissociation degree in the electrolyte than LiFSI, but LiPF6 has the effect of passivating aluminum foil and inhibiting aluminum foil corrosion. When the molar concentration of LiFSI and the molar concentration of LiPF6 satisfy a certain relationship, the conductivity of the electrolyte can be improved, which is beneficial to improving the fast charging performance of the lithium secondary battery, and the risk of aluminum foil corrosion can be reduced, which improves the safety of the lithium secondary battery.

[0030] In any embodiment, the molar concentration C1 of LiPF6 is 0.2-1.2 mol / L, and optionally 0.2-1.1 mol / L; and in any embodiment, the molar concentration C2 of LiFSI is 0.1-1 mol / L, and optionally 0.2-1 mol / L.

[0031] Controlling the molar concentrations of LiFSI and LiPF6 within a proper range can help to take into account the fast charging performance and safety of the lithium secondary battery.

[0032] In any embodiment, the electrolyte further comprises an additive, the additive comprising one or more of lithium difluorophosphate, lithium fluorosulfate, trimethyl phosphite, vinylene carbonate, lithium tetrafluoroborate, lithium difluorobisoxalate phosphate, tris(trimethylsiloxy)borate, trimethylfluorosilane, adiponitrile, succinonitrile, optionally comprising one or more of lithium difluorophosphate, lithium fluorosulfate, lithium tetrafluoroborate, lithium difluorobisoxalate phosphate.

[0033] Any of the above additives can participate in the formation of a CEI film on the positive electrode tab side or a SEI film on the negative electrode tab side, reducing the direct contact of the chain carboxylate with the positive electrode tab or metallic lithium, and in turn reducing the consumption of active lithium and the reduction decomposition of the electrolyte. Lithium difluorophosphate, lithium fluorosulfate, trimethyl phosphite, vinylene carbonate, lithium tetrafluoroborate, or lithium difluorobisoxalate phosphate participate in the formation of a CEI film on the positive electrode tab side, and tris(trimethylsiloxy)borate, trimethylfluorosilane, adiponitrile, or succinonitrile participate in the formation of a SEI film on the negative electrode tab side.

[0034] In any embodiment, the positive electrode tab in the lithium secondary battery comprises a positive electrode active material, the positive electrode active material comprising Li d [Ni x Co y X1 z M1 1-x-y-z ]O 2-S , LiMn2O4, Li2MnO3·(1-a)LiAO2, LiM2X2O4, wherein a is 0.1 to 0.9, and A comprises one or more of Ni, Co, Mn.

[0035] wherein 0.1≤d≤1, 0≤S≤2, X1 comprises Mn and / or Al, M1 comprises one or more of Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Zr, Sr, V, Ti, 0≤x<1, 0≤y≤1, 0≤z≤1, x+y+z≤1; A comprises one or more of Ni, Co, Mn, 0<a<1; M2 comprises one or more of Fe, Mn, Ni, Co, and X2O4 h- X2 in X2O4 comprises one or more of S, P, As, V, Mo, W, and h = 2 or 3.

[0036] Any of the above positive electrode active materials can be used in combination with the electrolyte to achieve a lithium secondary battery with excellent fast-charging performance and cycle performance.

[0037] In any embodiment, the negative electrode film layer comprises a negative electrode active material, the negative electrode active material comprising one or more of artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microbeads, silicon-based materials, tin-based materials, optionally comprising one or more of artificial graphite, natural graphite.

[0038] The negative electrode film layer with the negative electrode active material described above can be used in combination with an electrolyte to achieve a lithium secondary battery with excellent fast charging performance and cycle performance.

[0039] In any embodiment, the compaction density of the negative electrode film layer is 0.9 g / cm 3 ~1.6 g / cm 3 , and optionally 1.1 g / cm 3 ~1.6 g / cm 3 .

[0040] Controlling the compaction density of the negative electrode film layer within a suitable range can not only meet the requirement of sufficient contact between the negative electrode active materials to enable the battery to have excellent electron transmission performance and energy density, but also reduce the risk of the pores between the negative electrode active materials being crushed during the preparation process, which is not conducive to the embedding and extraction of lithium ions.

[0041] The second aspect of the present application provides a power consumption device comprising the lithium secondary battery of the first aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 is a schematic diagram of a lithium secondary battery of an embodiment of the present application.

[0043] Figure 2 is an exploded view of the lithium secondary battery of an embodiment of the present application shown in Figure 1

[0044] Figure 3 is a schematic diagram of a battery module of an embodiment of the present application.

[0045] Figure 4 is a schematic diagram of a battery pack of an embodiment of the present application.

[0046] Figure 5 is an exploded view of the battery pack of an embodiment of the present application shown in Figure 5

[0047] Figure 6 is a schematic diagram of a power consumption device using the lithium secondary battery of an embodiment of the present application as a power source.

[0048] BRIEF DESCRIPTION OF DRAWINGS

[0049] 1 battery pack; 2 upper box body; 3 lower box body; 4 battery module; 5 lithium secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly DETAILED DESCRIPTION

[0050] ​​Hereinafter, embodiments of the lithium secondary battery and the electric device of the present application will be specifically described with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters known well, repeated description of substantially identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to sufficiently understand the present application, and are not intended to limit the subject matter recited in the claims.

[0051] The ranges disclosed herein are defined by their lower and upper limits. Ranges can be defined by selecting either the lower or the upper limit. The selected lower and upper limits define the range. Ranges defined by their lower and upper limits can be either inclusive or exclusive of the end values. Ranges can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if a range is listed as 60-120 and 80-110, it is understood that the range 60-110 and 80-120 are also contemplated. Furthermore, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" indicates a shorthand way of describing each and every intervening real number with the range with "a" and "b" being real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, and "0-5" is merely a shorthand way of describing these numerical combinations. Also, when a parameter is stated to be an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0052] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0053] If not specifically stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0054] If not specifically stated, all steps of the present application can be performed in sequence or randomly, and preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method can further comprise step (c), which means that step (c) can be added to the method in any sequence. For example, the method can comprise steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b), etc.

[0055] As used herein, the terms "comprises," "comprising," "includes," "including" and the like can be used in an inclusive sense, i.e., the process or product including additional steps or components, or the like. Alternatively, the terms "comprises", "comprising", "includes", "including" and the like can be used in an exclusive sense, i.e., the process or product excluding additional steps or components, or the like.

[0056] As used herein, the term "or" is both inclusive and exclusive unless expressly indicated otherwise or indicated exclusively by context. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0057] The conductivity of the electrolyte seriously affects the performance of the battery. For example, for a lithium battery, lower conductivity can cause the lithium battery to have reduced fast charging performance and other undesirable phenomena. To reduce the viscosity of the electrolyte system and improve the lithium ion transmission rate, and thus the conductivity of the electrolyte, a low-viscosity solvent is introduced into the electrolyte. However, the introduction of a low-viscosity solvent can have other adverse effects, such as the occurrence of side reactions between the low-viscosity solvent chain carboxylate and the extracted metal lithium, which consumes part of the metal lithium and generates gas, seriously affecting the cycle performance and storage performance of the battery. Therefore, it is necessary to design a new battery that can balance fast charging performance and cycle performance.

[0058] [lithium secondary battery]

[0059] Based on this, the present application provides a lithium secondary battery, the lithium secondary battery comprising an electrolyte and a negative electrode sheet, the electrolyte comprising a chain carboxylate and a cyclic carbonate, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector;

[0060] wherein, based on the total mass of the electrolyte, the mass content W1 of the chain carboxylate and the mass content W2 of the cyclic carbonate satisfy: 0.1≤W2 / W1≤2, and the mass content W1 of the chain carboxylate and the thickness H (μm) of the negative electrode film layer satisfy: 0.2≤H / 100W1≤20, the unit of H being μm.

[0061] In this document, the term "chain carboxylate" refers to a carboxylate with a main chain of less than 5 carbon atoms. Typically, the longest carbon chain in a chain organic compound is the main chain. In this document, exemplary chain carboxylates include one or more of ethyl formate, ethyl acetate, methyl acetate, methyl propionate, ethyl propionate, propyl propionate, propyl acetate, butyl formate, methyl butyrate, and optionally one or more of ethyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate.

[0062] In the present text, "W2 / W1" refers to the ratio between W2 and W1.

[0063] In the present text, "H / 100W1" refers to the ratio between the thickness H and 100 times W1, and the unit of H is μm.

[0064] In some embodiments, the cyclic carbonate includes one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, and optionally includes one or more of ethylene carbonate, fluoroethylene carbonate.

[0065] In some embodiments, the ratio between the mass content W1 of the chain carboxylic acid ester and the mass content W2 of the cyclic carbonate, based on the total mass of the electrolyte, can be optionally 0.1, 0.2, 0.4, 0.5, 0.6, 0.8, 1, 1.1, 1.2, 1.4, 1.5, 1.6, 1.8, 2, or a value in a range constituted by any two of the above.

[0066] In some embodiments, the ratio between the mass content W1 of the chain carboxylic acid ester in the electrolyte and the thickness H of the negative electrode film layer, i.e. H / 100W1, can be optionally 0.2, 0.4, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or a value in a range constituted by any two of the above.

[0067] The chain carboxylic acid ester has a lower viscosity and a lower melting point. The introduction of the chain carboxylic acid ester into the electrolyte can significantly reduce the viscosity thereof, which is conducive to improving the liquid-phase transmission rate of lithium ions, and in turn improving the conductivity of the electrolyte, which is conducive to improving the fast-charging performance of the lithium secondary battery. However, the chain carboxylic acid ester is also prone to side reactions with the metal lithium extracted from the negative electrode tab, which not only consumes the chain carboxylic acid ester and the metal lithium, affecting the cycle performance of the battery, but also produces gas, causing the lithium secondary battery to swell, affecting the transmission of lithium ions and the storage performance of the lithium secondary battery.

[0068] The cyclic carbonate added to the electrolyte can be reduced to form a passivation layer on the surface of the negative electrode tab, reducing the degree of side reactions between the metal lithium on the side of the negative electrode tab and the chain carboxylic acid ester, and improving the cycle performance and storage performance of the lithium secondary battery. Controlling the amount relationship between the chain carboxylic acid ester and the cyclic carbonate can not only improve the conductivity of the electrolyte, but also help to inhibit the side reactions between the chain carboxylic acid ester and the metal lithium, so that the lithium secondary battery has good fast-charging performance, cycle performance and storage performance.

[0069] In addition, in order to improve the energy density of the lithium secondary battery, the active material coating thickness of the negative electrode is gradually thickened, resulting in gradually poor wettability of the electrolyte. Poor wettability of the electrolyte can cause the lithium ion transfer to exhibit a "broken bridge" phenomenon. During charging, the places of the negative electrode tab that are not wetted are invalid areas, and the places of the negative electrode tab that are wetted can cause lithium precipitation, resulting in rapid deterioration of the cycle performance and safety performance of the battery. However, after the introduction of the chain carboxylic acid ester into the electrolyte, the reduction of the viscosity of the electrolyte is conducive to the improvement of the wettability of the electrolyte to the negative electrode tab, thereby reducing the migration resistance of the lithium ion and improving the fast charging performance of the lithium secondary battery. The thickness of the negative electrode film layer needs to be controlled within a suitable range to balance the demand for energy density and the demand for fast charging performance. Controlling the mass content of the chain carboxylic acid ester and the thickness of the negative electrode film layer in the negative electrode tab to satisfy the above relationship, on the one hand, the electrolyte can quickly wet the negative electrode film layer, improve the migration rate of the lithium ion, that is, meet the demand for fast charging performance of the lithium secondary battery, while reducing the degree of negative electrode lithium precipitation caused by insufficient electrolyte wetting, reducing the influence of lithium dendrite on the cycle performance and storage performance of the lithium secondary battery, on the other hand, it can also reduce the degree of side reaction caused by excessive chain carboxylic acid ester or meet the demand for energy density of the lithium secondary battery.

[0070] In the present document, the term "fast charging performance" refers to the capacity retention rate of the lithium secondary battery under high-rate charging.

[0071] In some embodiments, the electrolyte further comprises a sulfonate compound, and the mass content W1 of the chain carboxylic acid ester and the mass content W3 of the sulfonate compound satisfy: 0.005≤W3 / W1≤0.4, based on the total mass of the electrolyte. In some embodiments, the mass content W1 of the chain carboxylic acid ester and the mass content W3 of the sulfonate compound satisfy W3 / W1 can be selected as 0.005, 0.006, 0.008, 0.01, 0.02, 0.04, 0.05, 0.06, 0.08, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, or a value in the range formed by any two of the above.

[0072] In some embodiments, the sulfonate compound comprises one or more of compounds shown in formula I, formula II, diethyl sulfonate, dimethyl sulfonate, dihydro-1,3,2-dioxane-2,2,5,5-tetraoxide, and the like. sulfur-based-(1,3,2-dioxane)-2,2,5,5-tetraoxide,

[0073]

[0074] wherein R1, R2 each independently comprises a hydrogen atom, C 1-6 alkyl, R3 comprises C1-6 alkyl groups include one or more of methyl, ethyl, propyl, isopropyl, n-butyl. 1-6 alkyl groups include one or more of methyl, ethyl, propyl, isopropyl, n-butyl.

[0075] Optionally, the sulfuric ester compound includes one or more of 4,4'-dithioethylene sulfate, ethylene sulfate, diethyl sulfate, dimethyl sulfate, dihydro-1,3,2-dithiino-2,2,5,5-tetraoxide. Optionally, the sulfuric ester compound includes one or more of 4,4'-dithioethylene sulfate, ethylene sulfate, diethyl sulfate, dimethyl sulfate, dihydro-1,3,2-dithiino-2,2,5,5-tetraoxide.

[0076] In this context, dihydro-1,3,2-dithiino-2,2,5,5-tetraoxide has a CAS number of 496-45-7. In this context, dihydro-1,3,2-dithiino-2,2,5,5-tetraoxide has a CAS number of 496-45-7.

[0077] In this context, when R1in formula I is selected from a hydrogen atom, and R2is selected from The resulting substance is 4,4'-dithioethylene sulfate.

[0078] It can be understood that when the lithium secondary battery is charged, the chain carboxylic ester is prone to oxidation reaction at the interface of the positive electrode sheet under high pressure, i.e., the "oxidation gas production" phenomenon, which is due to the catalytic effect of transition metal ions in the positive electrode sheet, and the chain carboxylic ester is prone to oxidation reaction under the catalytic effect of the transition metal ions in contact with the positive electrode sheet. However, the introduction of the sulfuric ester compound can cause the sulfuric ester compound to be superior to the chain carboxylic ester in preferentially undergoing oxidation reaction at the interface of the positive electrode sheet, and the oxidation product is deposited at the interface of the positive electrode sheet, i.e., a CEI film is formed, the formation of the CEI film can isolate the direct contact of the chain carboxylic ester with the positive electrode sheet, reduce the degree of oxidation reaction of the chain carboxylic ester on the side of the positive electrode sheet, reduce the loss and gas production degree of the chain carboxylic ester, and further improve the fast charging performance and storage performance of the lithium secondary battery.

[0079] In some embodiments, the mass content W1 of the chain carboxylic ester is 5% to 75%, and can be selected to be 20% to 75%, based on the total mass of the electrolyte. In some embodiments, the mass content W1 of the chain carboxylic ester can be selected to be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or a value in a range formed by any two of the above.

[0080] Controlling the mass content of the chain carboxylic ester within a suitable range can not only significantly reduce the viscosity of the electrolyte, improve the liquid phase transmission rate of lithium ions, and thus improve the conductivity of the electrolyte, but also help to improve the fast charging performance of the lithium secondary battery, and reduce the degree of aggravation of the side reaction between the chain carboxylic ester and the metal lithium on the side of the negative electrode sheet.

[0081] In some embodiments, the mass content W2 of the cyclic carbonate is 5% to 40%, optionally 10% to 30%, based on the total mass of the electrolyte. In some embodiments, the mass content W2 of the cyclic carbonate is optionally 5%, 8%, 10%, 12%, 15%, 17%, 20%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, or a value within a range defined by any two of the above values, based on the total mass of the electrolyte.

[0082] Controlling the mass content of the cyclic carbonate within a suitable range can provide sufficient cyclic carbonate to dissociate the lithium salt in the electrolyte and participate in the formation of a passivation layer on the surface of the negative electrode sheet, thereby improving the conductivity of the electrolyte, while reducing the impact of excessive cyclic carbonate on the viscosity of the electrolyte, and comprehensively improving the fast-charging performance of the lithium secondary battery.

[0083] In some embodiments, the mass content W3 of the sulfate compound is 0.1% to 2%, optionally 0.1% to 1%, based on the total mass of the electrolyte. In some embodiments, the mass content W3 of the sulfate compound is optionally 0.1%, 0.2%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.1%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, or a value within a range defined by any two of the above values, based on the total mass of the electrolyte.

[0084] Controlling the mass content of the sulfate compound within a suitable range can provide sufficient sulfate compound to participate in the formation of a CEI film on the positive electrode sheet side, inhibit the oxidation reaction of carboxylic acid ester, and improve the fast-charging performance of the lithium secondary battery, while excessive introduction of the sulfate compound can increase the production cost of the lithium secondary battery.

[0085] In some embodiments, the thickness of the negative film layer is 10 μm to 100 μm, optionally 20 μm to 70 μm. In some embodiments, the thickness of the negative film layer is optionally 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, or a value within a range defined by any two of the above values.

[0086] Controlling the thickness of the negative film layer within a suitable range can simultaneously consider the fast-charging performance and energy density of the battery.

[0087] In some embodiments, the electrolyte further comprises a linear carbonate, and the linear carbonate comprises at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate.

[0088] In some embodiments, the electrolyte further comprises a lithium salt, and the lithium salt comprises LiPF6 and / or LiFSI.

[0089] In some embodiments, the molar concentration C1 of LiPF6 and the molar concentration C2 of LiFSI satisfy: 0.8 mol / L≤C1+C2≤1.3 mol / L, and optionally 0.8 mol / L≤C1+C2≤1.2 mol / L.

[0090] In some embodiments, the molar concentration C1 of LiPF6 and the molar concentration C2 of LiFSI satisfy: C1+C2 is optionally 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 0.95 mol / L, 1.0 mol / L, 1.05 mol / L, 1.1 mol / L, 1.15 mol / L, 1.2 mol / L, 1.25 mol / L, 1.3 mol / L, or a value in a range defined by any two of the above.

[0091] In some embodiments, the molar concentration C1 of LiPF6 and the molar concentration C2 of LiFSI satisfy: 1≤C1 / C2≤5, and optionally 1≤C1 / C2≤3. In some embodiments, the molar concentration C1 of LiPF6 and the molar concentration C2 of LiFSI satisfy: C1 / C2 is optionally 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or a value in a range defined by any two of the above.

[0092] LiFSI has a high degree of dissociation in the electrolyte, which can greatly improve the room temperature conductivity of the electrolyte. However, LiFSI has the risk of corroding aluminum foil. LiPF6 has a lower degree of dissociation in the electrolyte than LiFSI, but LiPF6 has the effect of passivating aluminum foil and inhibiting aluminum foil corrosion. When the molar concentration of LiFSI and the molar concentration of LiPF6 satisfy a certain relationship, the conductivity of the electrolyte can be improved, which is beneficial to improving the fast charging performance of the lithium secondary battery, and the risk of aluminum foil corrosion can be reduced, thereby improving the safety of the lithium secondary battery.

[0093] In some embodiments, the molar concentration C1 of LiPF6 is 0.2-1.2 mol / L, and the molar concentration C2 of LiFSI is 0.1-1 mol / L. In some embodiments, the molar concentration C1 of LiPF6 is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2 mol / L, or a value within a range defined by any two of the above values, and the molar concentration C2 of LiFSI is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 mol / L, or a value within a range defined by any two of the above values.

[0094] Controlling the molar concentrations of LiFSI and LiPF6 respectively within appropriate ranges can balance the fast-charging performance and safety of the lithium secondary battery.

[0095] In some embodiments, the electrolyte further comprises an additive, which comprises one or more of lithium difluorophosphate, lithium fluorosulfate, trimethyl phosphite, vinylene carbonate, lithium tetrafluoroborate, lithium difluorobisoxalate phosphate, tris(trimethylsiloxy)borate, trimethylfluorosilane, adiponitrile, and succinonitrile, and optionally comprises one or more of lithium difluorophosphate, lithium fluorosulfate, lithium tetrafluoroborate, and lithium difluorobisoxalate phosphate.

[0096] The above additives can participate in the formation of a CEI film on the positive electrode tab side or a SEI film on the negative electrode tab side, reduce the direct contact of the chain carboxylate with the positive electrode tab or metal lithium, and further reduce the consumption of active lithium and the reduction decomposition of the electrolyte. Lithium difluorophosphate, lithium fluorosulfate, trimethyl phosphite, vinylene carbonate, lithium tetrafluoroborate, or lithium difluorobisoxalate phosphate participate in the formation of a CEI film on the positive electrode tab side, which is conducive to reducing the oxidative decomposition of the electrolyte on the positive electrode tab side, thereby reducing the cathode interfacial impedance, facilitating the rapid release of lithium ions, and improving the fast-charging performance. The reduction in the degree of oxidative decomposition can also reduce the swelling of the battery cell and reduce the consumption of active lithium, thereby improving the life of the battery cell. Tris(trimethylsiloxy)borate, trimethylfluorosilane, adiponitrile, or succinonitrile participate in the formation of a SEI film on the negative electrode tab side, which is conducive to reducing the reduction decomposition of the electrolyte on the negative electrode tab side, reducing gas production, and improving the electrical performance of the battery.

[0097] In some embodiments, the electrolyte has a conductivity of 9 mS.cm to 15 mS.cm at 25°C. The conductivity of the electrolyte can be obtained by a detection method known in the art.

[0098] The electrolyte has a conductivity within a suitable range, which can take into account both the fast-charging performance and the storage performance of the lithium secondary battery. If the electrolyte has too low a conductivity, the fast-charging performance of the lithium secondary battery is seriously affected; if the electrolyte has too high a conductivity, the gas generation rate will increase, which is not conducive to the storage performance of the lithium secondary battery.

[0099] In some embodiments, the lithium secondary battery has a liquid injection coefficient of 1.5 g / Ah to 4.0 g / Ah. In some embodiments, the lithium secondary battery has a liquid injection coefficient of 1.5 g / Ah, 2 g / Ah, 2.5 g / Ah, 3 g / Ah, 3.5 g / Ah, 4.0 g / Ah, or a value within a range defined by any two of the above values.

[0100] In this document, the term "liquid injection coefficient" is the ratio of the mass of the electrolyte (g) to the capacity of the cell (Ah).

[0101] Controlling the liquid injection coefficient of the lithium secondary battery within a suitable range can provide sufficient electrolyte to meet the needs of the lithium secondary battery, and also release a certain space to accommodate more positive / negative active materials, thereby improving the energy density of the lithium secondary battery, or release a certain space for gas transfer, thereby reducing the internal pressure of the lithium secondary battery shell and improving the service life and safety of the lithium secondary battery.

[0102] [Positive electrode sheet]

[0103] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including a positive electrode active material.

[0104] As an example, the positive electrode current collector has two opposite surfaces in the thickness direction thereof, and the positive electrode film layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0105] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0106] In some embodiments, the positive active material can employ a positive active material for a battery known in the art. As an example, the positive active material can include at least one of a lithium-containing phosphate of olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive active material for a battery can also be used. These positive active materials can be used alone only or in combination of two or more.

[0107] In some embodiments, the positive active material includes Li d [Ni x Co y X1 z M1 1-x-y-z ]O 2-S , LiMn2O4, Li2MnO3·(1-a)LiAO2, LiM2X2O4, one or more of

[0108] wherein 0.1≤d≤1, 0≤S≤2, X1 includes Mn and / or Al, M1 includes one or more of Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Zr, Sr, V, Ti, 0≤x<1, 0≤y≤1, 0≤z≤1, x+y+z≤1; A includes one or more of Ni, Co, Mn, 0 h- X2 includes one or more of S, P, As, V, Mo, W, and h=2 or 3.

[0109] The above positive active materials can be used in combination with an electrolyte to achieve a lithium secondary battery having excellent fast charging performance and cycle performance.

[0110] In some embodiments, the positive film layer can further optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0111] In some embodiments, the positive film layer can further optionally include a conductive agent. As an example, the conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0112] In some embodiments, the positive film layer of the positive electrode tab has a compacted density of 3.3 g / cm 3 ~ 3.7 g / cm 3 .

[0113] In this context, the compaction density of the positive electrode film layer can be tested using any known testing method. As an example, the compaction density of the positive electrode film layer is calculated by taking a positive electrode sheet having a unit area S, weighing M1, measuring the thickness H1 of the positive electrode sheet, and measuring the thickness H2 of the aluminum foil. The compaction density of the positive electrode film layer is then calculated as (M1-M2) / ((H1-H2) x S).

[0114] The compaction density of the positive electrode film layer is within a suitable range, which can take into account the DC impedance and the energy density of the lithium secondary battery.

[0115] In some embodiments, the positive electrode sheet can be prepared by dispersing the components described above for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector; and drying, cold-pressing, and the like to obtain the positive electrode sheet.

[0116] [Negative electrode sheet]

[0117] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector and containing at least a negative electrode active material.

[0118] As an example, the negative electrode current collector has two opposing surfaces in the thickness direction thereof, and the negative electrode film layer is disposed on either one or both of the two opposing surfaces of the negative electrode current collector.

[0119] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. 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 material base layer (e.g., a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0120] In some embodiments, the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, mesocarbon microbeads, silicon-based materials, tin-based materials, and optionally one or more of artificial graphite and natural graphite.

[0121] The negative electrode film layer with the negative electrode active material described above can be used in combination with an electrolyte to achieve a lithium secondary battery with excellent fast-charging performance and cycle performance. Moreover, since artificial graphite or natural graphite has a large specific capacity, and the graphite structure has the characteristics of stability and small expansion and contraction rate during lithium intercalation and deintercalation, artificial graphite or natural graphite has greater advantages as a negative electrode active material.

[0122] In some embodiments, the compaction density of the negative electrode film layer is 0.9 g / cm 3 ~ 1.6 g / cm 3 , and optionally 1.1 g / cm 3 ~ 1.6 g / cm 3 . In some embodiments, the compaction density of the negative electrode film layer is optionally 0.9 g / cm 3 , 0.95 g / cm 3 , 1.0 g / cm 3 , 1.05 g / cm 3 , 1.1 g / cm 3 , 1.15 g / cm 3 , 1.2 g / cm 3 , 1.25 g / cm 3 , 1.3 g / cm 3 , 1.35 g / cm 3 , 1.4 g / cm 3 , 1.45 g / cm 3 , 1.5 g / cm 3 , 1.55 g / cm 3 , 1.6 g / cm 3 , or a value in the range defined by any two of the above.

[0123] Controlling the compaction density of the negative electrode film layer within an appropriate range can not only meet the need for sufficient contact between the negative electrode active materials to enable the battery to have excellent electron transport performance and energy density, but also reduce the risk of the pores between the negative electrode active materials being crushed during the preparation process, which is not conducive to lithium ion intercalation and deintercalation.

[0124] In some embodiments, the negative electrode film layer can optionally further include a binder. The binder can include at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0125] In some embodiments, the negative electrode film layer can optionally further include a conductive agent. The conductive agent can include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0126] In some embodiments, the negative electrode film layer can further optionally include other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0127] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and after drying, cold pressing, and the like, the negative electrode sheet can be obtained.

[0128] [Separator]

[0129] In some embodiments, the lithium secondary battery further includes a separator. Any known porous structure separator with good chemical stability and mechanical stability can be selected.

[0130] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of the layers can be the same or different.

[0131] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be used to prepare an electrode assembly by a winding process or a stacking process.

[0132] In some embodiments, the lithium secondary battery can include an outer package. The outer package can be used to package the above-mentioned electrode assembly and the electrolyte.

[0133] In order to alleviate the problem of the swelling force of the secondary battery cell, the cell can be designed to have a reserved swelling space. Specifically, the group margin of the lithium secondary battery is controlled to be 82% to 95%, and the group margin is the percentage of the thickness of the cell in the thickness of the inner cavity of the shell.

[0134] In some embodiments, the group margin of the lithium secondary battery can be selected to be 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, or a value in the range formed by any two of the above.

[0135] Controlling the group margin of the lithium secondary battery within an appropriate range provides sufficient space to accommodate the electrode assembly and also provides a certain space for gas transfer, reduces the internal pressure of the lithium secondary battery shell, and improves the service life and safety of the lithium secondary battery.

[0136] In some embodiments, the outer package of the lithium secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. The outer package of the lithium secondary battery can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, or the like can be listed.

[0137] The shape of the lithium secondary battery according to the present application can be cylindrical, square, or any other shape. For example, Figure 1 is a square structure lithium secondary battery 5 as an example.

[0138] In some embodiments, referring to Figure 2 , the outer package can include a shell 51 and a cover plate 53. The shell 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be provided on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the lithium secondary battery 5 can be one or more, and the skilled person in the art can select according to the specific actual needs.

[0139] In some embodiments, the lithium secondary battery can be assembled into a battery module, and the number of lithium secondary batteries contained in the battery module can be one or more, and the specific number can be selected by the skilled person in the art according to the application and capacity of the battery module.

[0140] Figure 3 is a battery module 4 as an example. Referring to Figure 3 , in the battery module 4, a plurality of lithium secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be used. Further, the plurality of lithium secondary batteries 5 can be fixed by fasteners.

[0141] Optionally, the battery module 4 can also include a housing having a receiving space, and the plurality of lithium secondary batteries 5 are received in the receiving space.

[0142] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by the skilled person in the art according to the application and capacity of the battery pack.

[0143] Figure 4 and Figure 5 is a battery pack 1 as an example. Referring to Figure 4 and Figure 5In the battery pack 1, a battery case and a plurality of battery modules 4 disposed in the battery case can be included. The battery case includes an upper case 2 and a lower case 3, and the upper case 2 can be disposed on the lower case 3 to form an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery case in any manner.

[0144] In addition, the present application also provides a power consuming device including at least one of the lithium secondary battery, the battery module, or the battery pack provided by the present application. The lithium secondary battery, the battery module, or the battery pack can be used as a power source of the power consuming device, or can be used as an energy storage unit of the power consuming device. The power consuming device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0145] As the power consuming device, the lithium secondary battery, the battery module, or the battery pack can be selected according to the use requirement thereof.

[0146] Figure 6 The power consuming device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the lithium secondary battery for the power consuming device, the battery pack or the battery module can be used.

[0147] The power consuming device is a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and the lithium secondary battery can be used as a power source.

[0148] Embodiment

[0149] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application. If the specific technology or condition is not indicated in the embodiments, the technology or condition described in the literature in the art or according to the product instruction is used. If the reagent or instrument is not indicated by the manufacturer, it is a conventional product that can be obtained by market purchase.

[0150] I. Preparation method

[0151] Embodiment 1

[0152] 1) Electrolyte

[0153] In an argon atmosphere glove box (H2O content <10 ppm, O2 content <1 ppm), 5 g of ethyl formate, 10 g of ethylene carbonate, 71.13 g of methyl ethyl carbonate were mixed uniformly to obtain a mixed solvent. Then lithium salt lithium hexafluorophosphate (LiPF6) and lithium salt lithium bisfluorosulfonylimide (LiFSI) were added in the above mixed solvent, so that the molar concentrations of the two were 0.7 mol / L (8.75 g) and 0.3 mol / L (4.62 g), respectively, and stirred uniformly, followed by adding 0.5 g of 4,4'-vinylene disulfate and stirring uniformly. An electrolyte was prepared.

[0154] 2) Preparation of positive electrode sheet

[0155] LiNi 0.5 Co 0.2 Mn 0.3 O2, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) were mixed in N-methyl pyrrolidone (NMP) to prepare a positive electrode slurry; the solid content in the positive electrode slurry was 50 wt%, and the mass ratio of LiNi 0.5 Co 0.2 Mn 0.3 O2, Super P, and PVDF was 8:1:1. The positive electrode slurry was coated on a negative electrode current collector aluminum foil and dried at 85°C, followed by cold pressing, then edge cutting, sheet cutting, and striping, and then dried at 85°C under vacuum conditions for 4 h to prepare a positive electrode sheet.

[0156] 3) Preparation of negative electrode sheet

[0157] Graphite as a negative electrode active material, conductive agent Super P, thickening agent carboxymethyl cellulose (CMC), and adhesive styrene butadiene rubber (SBR) were mixed uniformly in deionized water to prepare a negative electrode slurry; the solid content in the negative electrode slurry was 30 wt%, and the mass ratio of graphite, Super P, CMC, and adhesive styrene butadiene rubber (SBR) in the solid components was 80:15:3:2. The negative electrode slurry was coated on a negative electrode current collector copper foil and dried at 85°C, followed by cold pressing, edge cutting, sheet cutting, and striping, and then dried at 120°C under vacuum conditions for 12 h to prepare a negative electrode sheet with a negative electrode film layer thickness of 50 μm.

[0158] 4) Isolation film

[0159] A 16 μm polyethylene film (PE) was used as the isolation film.

[0160] 5) Preparation of battery

[0161] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, the separator is between the positive and negative electrode sheets to separate the positive and negative electrode sheets, and a bare battery cell is obtained by winding. The bare battery cell is welded with the tab, placed in an outer package, and the electrolyte prepared above is injected into the dried battery cell. Then, the battery cell is subjected to packaging, standing, formation, shaping, capacity testing, and other processes to obtain the lithium secondary battery product of Example 1.

[0162] The secondary batteries of Examples 2-29 and the secondary batteries of Comparative Examples 1-6 are prepared in a similar manner to the secondary battery of Example 1, but the composition of the battery electrode sheet and the product parameters are adjusted. The different product parameters are shown in Tables 1 and 2.

[0163] In the formula, the mass of the carbonic acid methyl ethyl ester in the electrolyte can be adjusted to adjust the sizes of W1, W2, and W3, and the mass content of the additive.

[0164] II. Performance Test

[0165] 1. Compaction density of the negative electrode film layer

[0166] The compaction density of the negative electrode film layer is calculated. The mass of the negative electrode sheet per unit area s is m1, the mass of the aluminum foil per unit area s is m2, the thickness of the negative electrode sheet is h1, and the thickness of the aluminum foil is h2. The compaction density of the negative electrode film layer is (m1-m2) / ((h1-h2)xs).

[0167] 2. Fast charging performance of the battery

[0168] The prepared battery is discharged at 1C to 2.8V, then rested for 5 min, charged at 0.5C to 4.25V, and the charging capacity C0 is recorded. Then, the battery is discharged at 1C to 2.8V and rested for 5 min, and then charged at 2C to 4.25V, and the charging capacity C1 is recorded. The battery charging capacity retention rate is C1 / C0x100%.

[0169] 3. Cycle performance of the battery

[0170] At 25°C, the prepared battery is charged at 1C constant current to 4.25V, then charged at 4.25V constant voltage until the current drops to 0.05C, rested for 10 min, and then discharged at 1C constant current to 2.8V. This is the first charge / discharge cycle of the battery, and the discharge capacity of this cycle is recorded as the discharge capacity of the first cycle (C0). The above steps are repeated for the same battery, and the process capacity of the battery after 300 cycles (C1) is recorded. The capacity retention rate after 300 cycles is C1 / C0x100%. The test process of the comparative examples and other examples is the same as above.

[0171] 4. Storage gas production performance of the battery

[0172] After the prepared full battery is left to stand for 30 minutes at 25℃, it is charged at a constant current to 4.2V at a rate of 0.1C, then charged at a constant voltage to 0.05C at 4.2V, left to stand for 5 minutes, then the volume V1 of the battery is tested by the drainage method, after storage for 30 days at 60℃, the battery is taken out and cooled to 25℃, then charged to 4.2V at a rate of 0.1C, then charged at a constant voltage to 0.05C, the volume V2 of the battery is tested by the drainage method, and the volume expansion rate of the battery is (V2-V1) / V1*100%.

[0173] III. Analysis of test results of each embodiment and comparative example

[0174] The batteries of each embodiment and comparative example are prepared according to the above method, and each performance parameter is measured, and the results are shown in Tables 1 and 2 below.

[0175] Table 1

[0176]

[0177]

[0178] Table 2

[0179]

[0180]

[0181] The lithium secondary battery of each of embodiments 1 to 29 comprises an electrolyte and a negative electrode sheet, the electrolyte comprises a chain carboxylate and a cyclic carbonate, and the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector; wherein, based on the total mass of the electrolyte, the mass content W1 of the chain carboxylate and the mass content W2 of the cyclic carbonate satisfy: 0.1≤W2 / W1≤2, and the mass content W1 of the chain carboxylate and the thickness H of the negative electrode film layer satisfy: 0.2≤H / 100W1≤20.

[0182] As can be seen from the comparison of embodiments 1 to 7 and embodiments 22 to 24 with comparative examples 1 to 4, based on the total mass of the electrolyte, controlling the mass content W1 of the chain carboxylate and the mass content W2 of the cyclic carbonate to satisfy: 0.1≤W2 / W1≤2, and the mass content W1 of the chain carboxylate and the thickness H of the negative electrode film layer to satisfy: 0.2≤H / 100W1≤20, is beneficial to improving the fast-charging performance, cycle performance of the lithium secondary battery, and reducing the storage gas generation rate of the lithium secondary battery, and improving the storage performance thereof.

[0183] As can be seen from the comparison of Examples 2-6, 23-24 and Examples 1, 7, 23, further controlling the mass content W1 of the chain carboxylate and the mass content W2 of the cyclic carbonate to satisfy 0.1≤W2 / W1≤1.5 based on the total mass of the electrolyte is beneficial to further improve the storage performance of the battery.

[0184] As can be seen from Examples 1-4, controlling the mass content W1 of the chain carboxylate to be 5%-75% based on the total mass of the electrolyte can make the lithium secondary battery have excellent fast charging performance, cycle performance and storage performance. As can be seen from the comparison of Examples 2-4 and Example 1, further controlling the mass content W1 of the chain carboxylate to be 20%-75% based on the total mass of the electrolyte is beneficial to further improve the fast charging performance, cycle performance and storage performance of the lithium secondary battery.

[0185] As can be seen from Examples 2, 5-7, controlling the mass content W2 of the cyclic carbonate to be 5%-40% based on the total mass of the electrolyte can make the lithium secondary battery have excellent fast charging performance, cycle performance and storage performance. As can be seen from the comparison of Examples 2, 6 and Examples 5, 7, further controlling the mass content W2 of the cyclic carbonate to be 5%-30% based on the total mass of the electrolyte is beneficial to further improve the fast charging performance, cycle performance and storage performance of the lithium secondary battery.

[0186] As can be seen from Examples 2, 22-24, controlling the thickness of the negative electrode film layer to be 10-100 μm can make the lithium secondary battery have excellent fast charging performance, cycle performance and storage performance.

[0187] As can be seen from Examples 2, 8-11, controlling the molar concentration C1 of LiPF6 and the molar concentration C2 of LiFSI to satisfy 1≤C1 / C2≤5 can make the lithium secondary battery have excellent fast charging performance, cycle performance and storage performance. As can be seen from the comparison of Examples 2, 8, 10-11 and Example 9, further controlling the molar concentration C1 of LiPF6 and the molar concentration C2 of LiFSI to satisfy 1≤C1 / C2≤3 is beneficial to further improve the fast charging performance, cycle performance and storage performance of the lithium secondary battery.

[0188] As can be seen from Examples 2, 5-7, 12-14, the chain carboxylate can be ethyl formate or methyl acetate, the cyclic carbonate can be vinyl carbonate or fluorinated vinyl carbonate, and the sulfate compound can be 4,4'-vinylene disulfate or the substance shown in formula I (R1=b, R2=b), all of which can make the lithium secondary battery have excellent fast charging performance, cycle performance and storage performance. As can be seen from Examples 2, 5-7, 12-14, controlling the mass content W2 of the cyclic carbonate to be 5%-40% based on the total mass of the electrolyte can take into account the fast charging performance, cycle performance and storage performance of the lithium secondary battery.

[0189] As can be seen from Examples 12-18, the chain carboxylic acid ester can be selected from methyl acetate, ethyl acetate, methyl propionate, ethyl propionate or propyl acetate, the cyclic carbonate can be selected from ethylene carbonate or fluoroethylene carbonate, and the sulfate compound can be selected from the substance shown in the structure of Formula I (R1 = b, R2 = b), so as to make the lithium secondary battery have excellent fast charging performance, cycle performance and storage performance.

[0190] As can be seen from Examples 1-4 and 19-21, based on the total mass of the electrolyte, the mass content W1 of the chain carboxylic acid ester and the mass content W3 of the sulfate compound satisfy: 0.005≤W3 / W1≤0.4, so as to make the lithium secondary battery have excellent fast charging performance, cycle performance and storage performance. As can be seen from the comparison of Examples 1-4 and 20-21 with Example 19, based on the total mass of the electrolyte, further controlling the mass content W1 of the chain carboxylic acid ester and the mass content W3 of the sulfate compound to satisfy: 0.005≤W3 / W1≤0.25, is beneficial to improve the fast charging performance, cycle performance and storage performance of the lithium secondary battery.

[0191] As can be seen from Examples 1-4 and 19-21, based on the total mass of the electrolyte, controlling the mass content W3 of the sulfate compound to be 0.1%-2% can make the lithium secondary battery have excellent fast charging performance, cycle performance and storage performance.

[0192] As can be seen from the comparison of Examples 25-26 with Example 2, introducing the additives lithium difluorophosphate or lithium fluorosulfonate into the electrolyte is beneficial to improve the fast charging performance, cycle performance and storage performance of the battery.

[0193] As can be seen from Examples 2, 27-29, controlling the compaction density of the negative electrode film layer to be 0.9g / cm 3 -1.6g / cm 3 , so as to make the lithium secondary battery have excellent fast charging performance, cycle performance and storage performance. As can be seen from the comparison of Examples 2, 28-29 with Example 27, further controlling the compaction density of the negative electrode film layer to be 1.1g / cm 3 -1.6g / cm 3 , is beneficial to further improve the fast charging performance, cycle performance and storage performance of the battery.

[0194] Note that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration, function, and effect as the technical idea of the present application are included in the technical scope of the present application. Furthermore, other modes constructed by applying various modifications to the embodiments, or by combining part of the configurations of the embodiments, which can be conceived by those skilled in the art without departing from the spirit of the present application, are also included in the scope of the present application.

Claims

1. A lithium secondary battery, characterized by comprising: The electrolyte, the positive electrode sheet and the negative electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, and the negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, The electrolyte comprises a chain carboxylic acid ester, a cyclic carbonate and a sulfate compound, the mass content W1 of the chain carboxylic acid ester is 20% to 50% based on the total mass of the electrolyte, the mass content W2 of the cyclic carbonate is 15% to 35%, and the mass content W3 of the sulfate compound is 0.1% to 2%, the sulfate compound comprises one or more of compounds represented by Formula I, Formula II, diethyl sulfate, dimethyl sulfate, dihydro-1,3,2-dioxane-2,2,5,5-tetraoxide sulfur-based-(1,3,2-dioxane)-2,2,5,5-tetraoxide, Formula I Formula II Among them, R1 and R2 each independently include hydrogen atoms and C atoms. 1-6 alkyl groups, (a) (b) or (c); R3 includes C 1-6 Alkyl groups; The thickness of the negative electrode film layer is 10 µm to 100 µm. The electrolyte further comprises lithium salt, the lithium salt comprising LiPF6 and LiFSI, the sum of the molar concentrations of LiPF6 and LiFSI being 0.8 mol / L to 1.3 mol / L, the ratio of the molar concentrations of LiPF6 and LiFSI being 1 to 5, the molar concentration of LiPF6 being 0.2 mol / L to 1.2 mol / L, and the molar concentration of LiFSI being 0.1 mol / L to 1 mol / L.

2. The lithium secondary battery according to claim 1, characterized by The chain carboxylic acid ester comprises one or more of ethyl formate, ethyl acetate, methyl acetate, methyl propionate, ethyl propionate, propyl propionate, propyl acetate, butyl formate, and methyl butyrate. The cyclic carbonate comprises one or more of ethylene carbonate, propylene carbonate, and fluorinated ethylene carbonate.

3. The lithium secondary battery according to claim 1, characterized by The chain carboxylic acid ester comprises one or more of ethyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, and propyl propionate; and the cyclic carbonate comprises ethylene carbonate and / or fluorinated ethylene carbonate.

4. The lithium secondary battery according to claim 1, characterized by The electrolyte satisfies one of the following conditions: (1) the electrolyte comprises ethyl formate in a mass content of 5% to 50%, based on the total mass of the electrolyte; (2) the electrolyte comprises methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, or propyl acetate in a mass content of 10% to 20%, based on the total mass of the electrolyte; (3) the electrolyte comprises ethylene carbonate in a mass content of 5% to 40%, based on the total mass of the electrolyte; (4) the electrolyte comprises fluorinated ethylene carbonate in a mass content of 2% to 30%, based on the total mass of the electrolyte.

5. The lithium secondary battery according to any one of claims 1 to 4, characterized by, The thickness of the negative electrode film layer is 20 µm to 80 µm.

6. The lithium secondary battery according to any one of claims 1 to 4, characterized by The thickness of the negative electrode film layer is 20 µm to 70 µm.

7. The lithium secondary battery according to any one of claims 1 to 4, characterized by, The ratio W2 / W1 of the mass content W2 of the cyclic carbonate to the mass content W1 of the chain carboxylic acid ester, based on the total mass of the electrolyte, is 0.1 to 2.

8. The lithium secondary battery according to any one of claims 1 to 4, characterized by, W2 / W1 is 0.25 to 1.5 or 1.5 to 2.

9. The lithium secondary battery according to any one of claims 1 to 4, characterized by, The ratio H / 100W1 between the thickness H of the negative electrode film layer and the mass content W1 of the chain carboxylic acid ester satisfies 0.2 ≤ H / 100W1 ≤ 20, H being in µm.

10. The lithium secondary battery according to any one of claims 1 to 4, characterized by, The ratio H / 100W1 is 0.2 to 10.

11. The lithium secondary battery according to any one of claims 1 to 4, characterized by, W3 is 0.1% to 1%.

12. The lithium secondary battery according to any one of claims 1 to 4, characterized by, The sulfuric acid ester compound includes 4,4' vinylene sulfite, vinyl sulfite, diethyl sulfate, dimethyl sulfate, dihydro-1,3,2-dioxane-2,2,5,5-tetraoxide. one or more of thio-(1,3,2-dioxane)-2,2,5,5-tetraoxide.

13. The lithium secondary battery according to any one of claims 1 to 4, characterized by, The ratio of the mass content W3 of the sulfate compound to the mass content W1 of the chain carboxylic acid ester is 0.005 to 0.

4.

14. The lithium secondary battery according to any one of claims 1 to 4, characterized by, The ratio of the mass content W3 of the sulfate compound to the mass content W1 of the chain carboxylic acid ester is 0.005 to 0.

1.

15. The lithium secondary battery according to any one of claims 1 to 4, characterized by, The sum of the molar concentrations of LiPF6 and LiFSI is 0.8 mol / L to 1.2 mol / L; and / or, The ratio of the molar concentrations of LiPF6 and LiFSI is 1 to 3.

16. The lithium secondary battery according to any one of claims 1 to 4, characterized by, The molar concentration of LiPF6 is 0.2-1.1 mol / L, and the molar concentration of LiFSI is 0.2-1 mol / L.

17. The lithium secondary battery according to any one of claims 1 to 4, characterized by, The electrolyte further comprises a linear carbonate, and the linear carbonate comprises at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate.

18. The lithium secondary battery according to claim 17, characterized by The linear carbonate comprises methyl ethyl carbonate.

19. The lithium secondary battery according to any one of claims 1 to 4, characterized by, The electrolyte further comprises an additive, and the additive comprises one or more of lithium difluorophosphate, lithium fluorosulfonate, trimethyl phosphite, vinylene carbonate, lithium tetrafluoroborate, lithium difluorobisoxalate phosphate, tris(trimethylsiloxy)borate, trimethylfluorosilane, adiponitrile, and succinonitrile.

20. The lithium secondary battery according to claim 19, characterized by The additive comprises one or more of lithium difluorophosphate, lithium fluorosulfonate, lithium tetrafluoroborate, and lithium difluorobisoxalate phosphate.

21. The lithium secondary battery according to any one of claims 1 to 4, characterized by, The positive electrode film layer includes a positive electrode active material including Li d [Ni x Co y X1 z M1 1-x-y-z ]O 2-S one or more of LiMn2O4, Li2MnO3-(1-a)LiAO2, LiM2X2O4, wherein 0.1≤d≤1, 0≤S≤2, X1comprises Mn and / or Al, M1comprises one or more of Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Zr, Sr, V, Ti, 0≤x<1, 0≤y≤1, 0≤z≤1, x+y+z≤1; A comprises one or more of Ni, Co, Mn, 0 h- X2comprises one or more of S, P, As, V, Mo, W, h=2 or 3.

22. The lithium secondary battery according to any one of claims 1 to 4, characterized by, The negative electrode film layer comprises a negative electrode active material, and the negative electrode active material comprises one or more of artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microbeads, silicon-based materials, and tin-based materials.

23. The lithium secondary battery according to claim 22, characterized by The negative electrode active material comprises one or more of artificial graphite and natural graphite.

24. The lithium secondary battery according to any one of claims 1 to 4, characterized by, The lithium secondary battery satisfies at least one of the following: (1) the compaction density of the negative electrode film layer is 0.9 g / cm 3 1.6 g / cm 3 ; (2) the compacted density of the positive electrode film layer is 3.3 g / cm 3 3.7 g / cm 3 ; (3) the electrolyte has an electrical conductivity of 9-15 mS.cm at 25°C; (4) the lithium secondary battery has a liquid injection coefficient of 1.5-4.0 g / Ah; (5) the lithium secondary battery has a group margin of 82-95%.

25. The lithium secondary battery according to any one of claims 1 to 4, characterized by, The lithium secondary battery satisfies at least one of the following: (1) the compaction density of the negative electrode film layer is 1.1 g / cm 3 1.6 g / cm 3 ; (2) the lithium secondary battery has a liquid injection coefficient of 2-4.0 g / Ah; (3) the lithium secondary battery has a group margin of 85-95%.

26. The lithium secondary battery according to any one of claims 1 to 4, characterized by, The lithium secondary battery comprises a separator film, and the positive electrode sheet, the negative electrode sheet, and the separator film are formed into an electrode assembly through a winding process or a stacking process.

27. An electrical device, comprising: The lithium secondary battery comprises the lithium secondary battery according to any one of claims 1-26.

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