Lithium secondary battery and electric device

Abstract

The invention provides a lithium secondary battery and a power utilization device. The lithium secondary battery comprises an electrolyte and a negative pole piece, the electrolyte comprises chain carboxylic ester and cyclic carbonate, and the negative pole piece comprises a negative current collector and a negative film layer located on at least one side of the negative current collector; wherein based on the total mass of the electrolyte, the mass content W1 of the chain carboxylic ester and the mass content W2 of the cyclic carbonate meet the condition that 0.1 < = W2 / W1 < = 2, the mass content W1 of the chain carboxylic ester and the thickness H of the negative electrode film layer meet the condition that 0.2 < = H / 100W1 < = 20, and the unit of H is [mu] m. The lithium secondary battery has excellent quick charge performance and cycle performance.

Description

Technical Field

[0001] The present application relates to the technical field of lithium batteries, and in particular to a lithium secondary battery and an electrical device. Background Art

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal, wind and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. The requirements for the electrical performance of secondary batteries are constantly increasing, and there are also higher and higher expectations for the charging rate of secondary batteries.

[0003] The performance of the electrolyte has a key impact on the performance of the secondary battery. An electrolyte with a suitable composition can improve the electrical performance or charging rate of the secondary battery and meet the requirements of different fields for different battery performance. Therefore, it is still necessary to develop electrolytes to meet the application needs of the new generation of electrochemical systems. Summary of the invention

[0004] The present application is made in view of the above-mentioned problems, and its purpose is to provide a lithium secondary battery having excellent fast charging performance and cycle performance.

[0005] In order to achieve the above-mentioned object, the first aspect of the present application provides a lithium secondary battery, comprising an electrolyte and a negative electrode plate, wherein the electrolyte comprises a chain carboxylate and a cyclic carbonate, and the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector;

[0006] Among them, 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, the mass content W1 of the chain carboxylate and the thickness H of the negative electrode film layer satisfy: 0.2≤H / 100W1≤20, and the unit of H is μm.

[0007] The chain carboxylates introduced into the electrolyte can significantly reduce the viscosity of the electrolyte and improve the wettability of the electrolyte to the negative electrode plate, thereby improving the liquid phase transmission rate of lithium ions and reducing the migration resistance of lithium ions, and significantly improving the fast charging performance of the lithium secondary battery; at the same time, the mass content W1 of the chain carboxylates is controlled to satisfy the above-mentioned relationship with the mass content W2 of the cyclic carbonate and the thickness H of the negative electrode film layer, so as to reduce the side reaction between the metallic lithium and the chain carboxylates on the negative electrode plate side during the cycle of the lithium secondary battery, and reduce the degree of lithium precipitation at the negative electrode due to insufficient electrolyte infiltration, so that the lithium secondary battery can have both fast charging performance and cycle performance.

[0008] In any embodiment, the electrolyte further includes a sulfate compound, and 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.

[0009] Sulfate ester compounds can undergo oxidation reaction on the positive electrode side of the lithium secondary battery before chain carboxylates, and the oxides are deposited at the interface of the positive electrode to form a CEI film, which can reduce the degree of oxidation reaction of chain carboxylates under high pressure on the positive electrode side, reduce the loss and gas production of chain carboxylates, and further improve the fast charging performance and storage performance of lithium secondary batteries.

[0010] In any embodiment, the chain carboxylic acid ester includes 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 includes one or more of ethyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

[0011] The above-mentioned chain carboxylic acid ester has a lower viscosity due to its main chain carbon atom number less than 5, which can significantly reduce the viscosity of the electrolyte, increase the liquid phase transmission rate of lithium ions, and then increase the conductivity of the electrolyte, which is beneficial to improving the fast charging performance of lithium secondary batteries.

[0012] In any embodiment, the cyclic carbonate includes one or more of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate, and optionally includes one or more of ethylene carbonate and fluoroethylene carbonate.

[0013] The above-mentioned cyclic carbonates can all be reduced on the negative electrode side to form a passivation layer, thereby reducing the side reaction between the chain carboxylic acid ester and metallic lithium and improving the cycle performance and storage performance of the lithium secondary battery.

[0014] In any embodiment, the sulfate ester compound includes the structural compound shown in Formula I, Formula II, diethyl sulfate, dimethyl sulfate, dihydro-1,3,2-dimethyl sulfate, One or more of thio-(1,3,2-dioxane)-2,2,5,5-tetraoxide,

[0015]

[0016] Among them, R 1 , R 2 Each independently includes hydrogen atoms, C 1-6 The alkyl group R 3 Including C 1-6Optionally, the sulfate ester compound includes 4,4'-disulfate, vinyl sulfate, diethyl sulfate, dimethyl sulfate, dihydro-1,3,2-disulfate, One or more of thio-(1,3,2-dioxane)-2,2,5,5-tetraoxide.

[0017] The above-mentioned sulfate ester compounds can all participate in the formation of the CEI film on the positive electrode side, reduce the degree of oxidation reaction of the chain carboxylic acid ester, and improve the fast charging performance and storage performance of the battery.

[0018] In any embodiment, based on the total mass of the electrolyte, the mass content W1 of the chain carboxylic acid ester is 5% to 75%, and can be optionally 20% to 75%.

[0019] Controlling the mass content of the chain carboxylate within an appropriate range can not only significantly reduce the viscosity of the electrolyte, increase the liquid phase transmission rate of lithium ions, and thereby increase the conductivity of the electrolyte, which is beneficial to improving the fast charging performance of lithium secondary batteries, but also reduce the aggravation of the side reaction between the chain carboxylate and the metallic lithium on the negative electrode side.

[0020] In any embodiment, based on the total mass of the electrolyte, the mass content W2 of the cyclic carbonate is 5% to 40%, and can be optionally 10% to 30%.

[0021] Controlling the mass content of the cyclic carbonate within an appropriate range can not only provide sufficient cyclic carbonate to dissociate the lithium salt in the electrolyte and participate in forming a passivation layer on the surface of the negative electrode, thereby improving the conductivity of the electrolyte, but also reduce the effect of introducing too much cyclic carbonate on the viscosity of the electrolyte, thereby comprehensively improving the fast charging performance of the lithium secondary battery.

[0022] In any embodiment, based on the total mass of the electrolyte, the mass content W3 of the sulfate ester compound is 0.1% to 2%, and can be optionally 0.1% to 1%.

[0023] Controlling the mass content of sulfate ester compounds within an appropriate range can not only provide sufficient sulfate ester compounds to participate in the formation of CEI film on the positive electrode side, inhibit the oxidation reaction of carboxylic acid esters, and improve the fast charging performance of lithium secondary batteries, but also reduce the increase in the production cost of lithium secondary batteries caused by the introduction of excessive sulfate ester compounds.

[0024] In any embodiment, the thickness of the negative electrode film layer is 10 μm to 100 μm, and can be optionally 20 μm to 70 μm.

[0025] By controlling the thickness of the negative electrode film layer within an appropriate range, both the fast charging performance and energy density of the battery can be taken into account.

[0026] In any embodiment, the electrolyte further comprises a lithium salt, wherein the lithium salt comprises LiPF 6 and LiFSI. In any embodiment, LiPF 6 The molar concentration C1 of LiFSI and the molar concentration C2 of LiFSI satisfy: 0.8mol / L≤C1+C2≤1.3mol / L, which can be optionally 0.8mol / L≤C1+C2≤1.2mol / L.

[0027] In any embodiment, LiPF 6 The molar concentration C1 of LiFSI and the molar concentration C2 of LiFSI satisfy: 1≤C1 / C2≤5, which can be optionally 1≤C1 / C2≤3.

[0028] LiFSI has a high degree of dissociation in the electrolyte, which can greatly improve the room-temperature conductivity of the electrolyte. However, at the same time, LiFSI has the risk of corroding the aluminum foil of the positive electrode current collector. 6 The dissociation degree of LiPF in the electrolyte is not as good as that of LiFSI in the electrolyte, but 6 It has the effect of passivating aluminum foil and inhibiting aluminum foil corrosion. Control the molar concentration of LiFSI and LiPF 6 When the molar concentration satisfies a certain relationship, it can not only improve the conductivity of the electrolyte, which is beneficial to improving the fast charging performance of the lithium secondary battery, but also reduce the risk of corrosion of the aluminum foil and improve the safety of the lithium secondary battery.

[0029] In any embodiment, LiPF 6 The molar concentration C1 of LiFSI is 0.2 mol / L to 1.2 mol / L, and can be optionally 0.2 mol / L to 1.1 mol / L; in any embodiment, the molar concentration C2 of LiFSI is 0.1 mol / L to 1 mol / L, and can be optionally 0.2 mol / L to 1 mol / L.

[0030] Control LiFSI and LiPF separately 6 The molar concentration of is within an appropriate range, which helps to balance the fast charging performance and safety of lithium secondary batteries.

[0031] In any embodiment, the electrolyte further includes an additive, and the additive includes one or more of lithium difluorophosphate, lithium fluorosulfonate, trimethylphosphite, vinylene carbonate, lithium tetrafluoroborate, lithium difluorobisoxalatophosphate, tris(trimethylsiloxy)borate, trimethylfluorosilane, adiponitrile, and succinonitrile, and optionally includes one or more of lithium difluorophosphate, lithium fluorosulfonate, lithium tetrafluoroborate, and lithium difluorooxalatoborate.

[0032] The above additives can participate in the formation of CEI film on the positive electrode side or SEI film on the negative electrode side, reduce the direct contact between the chain carboxylic acid ester and the positive electrode or metal lithium, and thus reduce the consumption of active lithium and the reduction and decomposition of the electrolyte. Lithium difluorophosphate, lithium fluorosulfonate, trimethylphosphite, vinylene carbonate, lithium tetrafluoroborate or lithium difluorobisoxalate phosphate participates in the formation of CEI film on the positive electrode side, and tris (trimethylsiloxy) borate, trimethylfluorosilane, adiponitrile or succinonitrile participates in the formation of SEI film on the negative electrode side.

[0033] In any embodiment, the positive electrode sheet in the lithium secondary battery includes a positive electrode active material, and the positive electrode active material includes Li d [Ni x Co y X1 z M1 1-x-y-z ]O 2-S 、LiMn 2 O 4 , Li 2 MnO 3 ·(1-a)LiAO 2 、LiM2X2O 4 One or more of

[0034] 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<a<1; M2 includes one or more of Fe, Mn, Ni, Co, X2O 4 h- Wherein X2 includes one or more of S, P, As, V, Mo, and W, and h=2 or 3.

[0035] The above-mentioned positive electrode active materials can all be used in combination with an electrolyte to realize a lithium secondary battery with excellent fast charging performance and cycle performance.

[0036] In any embodiment, 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, intermediate phase microcarbon beads, silicon-based materials, and tin-based materials, and optionally includes one or more of artificial graphite and natural graphite.

[0037] The negative electrode film layer having the above-mentioned negative electrode active material can be used in combination with an electrolyte to realize a lithium secondary battery with excellent fast charging performance and cycle performance.

[0038] In any embodiment, the compaction density of the negative electrode film layer is 0.9 g / cm 3 ~1.6g / cm 3 , optional 1.1g / cm 3 ~1.6g / cm 3 .

[0039] Controlling the compaction density of the negative electrode film layer within an appropriate range can not only meet the requirement of sufficient contact between the negative electrode active materials so that the battery has 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, resulting in unfavorable lithium ion insertion and extraction.

[0040] A second aspect of the present application provides an electrical device, comprising the lithium secondary battery of the first aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of a lithium secondary battery according to one embodiment of the present application.

[0042] Figure 2 yes Figure 1 An exploded view of a lithium secondary battery according to an embodiment of the present application is shown.

[0043] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0044] Figure 4 It is a schematic diagram of a battery pack according to one embodiment of the present application.

[0045] Figure 5 yes Figure 5 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0046] Figure 6 Schematic diagram of an electrical device using a lithium secondary battery according to an embodiment of the present application as a power source.

[0047] Description of reference numerals:

[0048] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 lithium secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly DETAILED DESCRIPTION

[0049] Hereinafter, the embodiments of the lithium secondary battery and the electric device of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0050] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0051] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0052] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0053] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0054] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0055] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies 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).

[0056] The conductivity of the electrolyte seriously affects the battery performance. For example, for lithium batteries, lower conductivity can lead to adverse phenomena such as reduced fast charging performance of lithium batteries. Low-viscosity solvents are introduced into the electrolyte to reduce the viscosity of the electrolyte system, increase the lithium ion transfer rate, and thus increase the conductivity of the electrolyte. However, the introduction of low-viscosity solvents will bring other adverse effects, such as side reactions between the low-viscosity solvent chain carboxylic acid ester and the precipitated metallic lithium, which consumes part of the metallic lithium and produces gas, seriously affecting the battery's cycle performance and storage performance. Therefore, it is necessary to design a new battery that can take into account both fast charging performance and cycle performance.

[0057] [Lithium secondary battery]

[0058] Based on this, the present application proposes a lithium secondary battery, which includes an electrolyte and a negative electrode plate, the electrolyte includes a chain carboxylate and a cyclic carbonate, and the negative electrode plate includes a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector;

[0059] Among them, 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, the mass content W1 of the chain carboxylic acid ester and the thickness H (μm) of the negative electrode film layer satisfy: 0.2≤H / 100W1≤20, and the unit of H is μm.

[0060] In this article, the term "chain carboxylic acid ester" refers to a carboxylic acid ester with a main chain carbon number of less than 5. Generally speaking, the longest carbon chain in the chain organic compound is the main chain. Herein, exemplary chain carboxylic acid esters include 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 include one or more of ethyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

[0061] Herein, "W2 / W1" refers to the ratio between W2 and W1.

[0062] Herein, “H / 100W1” refers to the ratio between the thickness H and 100 times W1, and the unit of H is μm.

[0063] In some embodiments, the cyclic carbonate includes one or more of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate, and may optionally include one or more of ethylene carbonate and fluoroethylene carbonate.

[0064] In some embodiments, based on the total mass of the electrolyte, the ratio of the mass content W1 of the linear carboxylate to the mass content W2 of the cyclic carbonate can be selected to be 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 the range consisting of any two of the above points.

[0065] In some embodiments, the mass content W1 of the chain carboxylic acid ester in the electrolyte and the thickness H of the negative electrode film layer, that is, H / 100W1, can be selected as 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 the range formed by any two of the above points.

[0066] Chain carboxylates have low viscosity and low melting point. The introduction of chain carboxylates into the electrolyte can significantly reduce its viscosity, which is beneficial to improving the liquid phase transmission rate of lithium ions, thereby improving the electrical conductivity of the electrolyte, and is beneficial to improving the fast charging performance of lithium secondary batteries; however, chain carboxylates are also prone to side reactions with metallic lithium precipitated from the negative electrode side, which not only consumes chain carboxylates and metallic lithium, affecting the cycle performance of the battery, but also produces gas, causing flatulence of the lithium secondary battery, affecting the transmission of lithium ions and the storage performance of the lithium secondary battery.

[0067] The cyclic carbonate added to the electrolyte can be reduced to form a passivation layer on the surface of the negative electrode plate, reducing the degree of side reactions between the metal lithium and the chain carboxylic acid ester on the negative electrode plate side, and improving the cycle performance and storage performance of the lithium secondary battery. Controlling the dosage relationship of the chain carboxylic acid ester and the cyclic carbonate ester can not only improve the conductivity of the electrolyte, but also help 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.

[0068] In addition, in order to improve the energy density of lithium secondary batteries, the coating thickness of the active material of the negative electrode gradually becomes thicker, resulting in the gradual deterioration of the wettability of the electrolyte. Poor electrolyte infiltration will cause the "broken bridge" phenomenon in lithium ion transmission. During charging, the area where the negative electrode plate is not infiltrated is an invalid area, and lithium precipitation may occur in the area where the negative electrode plate is infiltrated, resulting in a sharp deterioration in the battery cycle performance and safety performance. However, after the introduction of chain carboxylates into the electrolyte, the reduction in electrolyte viscosity is conducive to the improvement of the wettability of the electrolyte to the negative electrode plate, thereby reducing the migration resistance of lithium ions and improving the fast charging performance of lithium secondary batteries. The thickness of the negative electrode film layer needs to be controlled within an appropriate range to take into account the requirements of energy density and fast charging performance. By controlling the mass content of the chain carboxylic acid ester and the thickness of the negative electrode film layer in the negative electrode plate to satisfy the above relationship, on the one hand, the electrolyte can quickly infiltrate the negative electrode film layer and increase the migration rate of lithium ions, thereby meeting the fast charging performance requirements of the lithium secondary battery. At the same time, it can reduce the degree of lithium precipitation at the negative electrode due to insufficient electrolyte infiltration, and reduce the impact of lithium dendrites on the cycle performance and storage performance of the lithium secondary battery. On the other hand, it can also reduce the degree of aggravation of side reactions caused by excessive chain carboxylates or meet the energy density requirements of the lithium secondary battery.

[0069] Herein, the term “fast charging performance” refers to the capacity retention rate of a lithium secondary battery under high-rate charging.

[0070] In some embodiments, the electrolyte further includes a sulfate compound, and 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. In some embodiments, 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 W3 / W1, which can be 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 consisting of any two of the above points.

[0071] In some embodiments, the sulfate ester compounds include compounds of formula I, formula II, compounds of the structures shown, diethyl sulfate, dimethyl sulfate, dihydro-1,3,2-dimethyl sulfate, One or more of thio-(1,3,2-dioxane)-2,2,5,5-tetraoxide,

[0072]

[0073] Among them, R 1 , R 2 Each independently includes hydrogen atoms, C 1-6 The alkyl group R 3 Including C 1-6 The alkyl group, the C 1-6 The alkyl group includes one or more of methyl, ethyl, propyl, isopropyl and n-butyl.

[0074] Optionally, the sulfate ester compounds include 4,4'-vinyl sulfate, vinyl sulfate, diethyl sulfate, dimethyl sulfate, dihydro-1,3,2-disulfate, One or more of thio-(1,3,2-dioxane)-2,2,5,5-tetraoxide.

[0075] In this article, dihydro-1,3,2-dihydro The CAS number of thio-(1,3,2-dioxane)-2,2,5,5-tetraoxide is 496-45-7.

[0076] In this context, when R in Formula I 1 Selected from hydrogen atoms, R 2 Selected from The obtained substance is 4,4'-vinyl sulfate.

[0077] It is understandable that when a lithium secondary battery is charged, under high voltage, the chain carboxylic acid ester is prone to undergo oxidation reaction at the interface of the positive electrode plate to produce gas, which is the phenomenon of "oxidation and gas production". This is because the transition metal ions in the positive electrode plate have a catalytic effect, and the chain carboxylic acid ester is prone to undergo oxidation reaction under the catalytic effect of the transition metal ions when in contact with the positive electrode plate. However, the introduction of sulfate ester compounds can lead to sulfate ester compounds taking precedence over chain carboxylic acid esters in undergoing oxidation reaction at the interface of the positive electrode plate, and the oxidation products are deposited at the interface of the positive electrode plate, that is, forming a CEI film. The formation of the CEI film can isolate the chain carboxylic acid ester from direct contact with the positive electrode plate, which can reduce the degree of oxidation reaction of the chain carboxylic acid ester on the positive electrode plate side, reduce the loss of chain carboxylic acid esters and the degree of gas production, and further improve the fast charging performance and storage performance of lithium secondary batteries.

[0078] In some embodiments, based on the total mass of the electrolyte, the mass content W1 of the chain carboxylic acid ester is 5% to 75%, and can be 20% to 75%. In some embodiments, based on the total mass of the electrolyte, the mass content W1 of the chain carboxylic acid ester can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or a value in the range consisting of any two of the above points.

[0079] Controlling the mass content of the chain carboxylate within an appropriate range can not only significantly reduce the viscosity of the electrolyte, increase the liquid phase transmission rate of lithium ions, and thereby increase the conductivity of the electrolyte, which is beneficial to improving the fast charging performance of lithium secondary batteries, but also reduce the aggravation of the side reaction between the chain carboxylate and the metallic lithium on the negative electrode side.

[0080] In some embodiments, based on the total mass of the electrolyte, the mass content W2 of the cyclic carbonate is 5% to 40%, optionally 10% to 30%. In some embodiments, based on the total mass of the electrolyte, the mass content W2 of the cyclic carbonate can be 5%, 8%, 10%, 12%, 15%, 17%, 20%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, or a numerical value in the range consisting of any two of the above points.

[0081] Controlling the mass content of the cyclic carbonate within an appropriate range can not only provide sufficient cyclic carbonate to dissociate the lithium salt in the electrolyte and participate in forming a passivation layer on the surface of the negative electrode, thereby improving the conductivity of the electrolyte, but also reduce the effect of introducing too much cyclic carbonate on the viscosity of the electrolyte, thereby comprehensively improving the fast charging performance of the lithium secondary battery.

[0082] In some embodiments, based on the total mass of the electrolyte, the mass content W3 of the sulfate ester compound is 0.1% to 2%, and can be 0.1% to 1%. In some embodiments, based on the total mass of the electrolyte, the mass content W3 of the sulfate ester compound can be 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 the range consisting of any two of the above points.

[0083] Controlling the mass content of sulfate ester compounds within an appropriate range can not only provide sufficient sulfate ester compounds to participate in the formation of CEI film on the positive electrode side, inhibit the oxidation reaction of carboxylic acid esters, and improve the fast charging performance of lithium secondary batteries, but also reduce the increase in the production cost of lithium secondary batteries caused by the introduction of excessive sulfate ester compounds.

[0084] In some embodiments, the thickness of the negative electrode film layer is 10 μm to 100 μm, and can be 20 μm to 70 μm. In some embodiments, the thickness of the negative electrode film layer can be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, or a value in the range formed by any two of the above points.

[0085] By controlling the thickness of the negative electrode film layer within an appropriate range, both the fast charging performance and energy density of the battery can be taken into account.

[0086] In some embodiments, the electrolyte further includes linear carbonates, and the linear carbonates include at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate.

[0087] In some embodiments, the electrolyte further comprises a lithium salt, wherein the lithium salt comprises LiPF 6 and / or LiFSI.

[0088] In some embodiments, LiPF 6 The molar concentration C1 of LiFSI and the molar concentration C2 of LiFSI satisfy: 0.8mol / L≤C1+C2≤1.3mol / L, which can be optionally 0.8mol / L≤C1+C2≤1.2mol / L.

[0089] In some embodiments, LiPF 6 The molar concentration C1 of LiFSI satisfies C1+C2 and can be 0.8mol / L, 0.85mol / L, 0.9mol / L, 0.95mol / L, 1.0mol / L, 1.05mol / L, 1.1mol / L, 1.15mol / L, 1.2mol / L, 1.25mol / L, 1.3mol / L, or a value in the range formed by any two of the above points.

[0090] In some embodiments, LiPF 6 The molar concentration C1 of LiPF and the molar concentration C2 of LiFSI satisfy: 1≤C1 / C2≤5, which may be 1≤C1 / C2≤3. 6 The molar concentration C1 of LiFSI and the molar concentration C2 of LiFSI satisfy C1 / C2, which can be selected as 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or a value in the range formed by any two of the above points.

[0091] LiFSI has a high degree of dissociation in the electrolyte, which can greatly improve the room-temperature conductivity of the electrolyte, but LiFSI has the risk of corroding aluminum foil. 6 The dissociation degree of LiPF in the electrolyte is not as good as that of LiFSI in the electrolyte, but 6 It has the effect of passivating aluminum foil and inhibiting aluminum foil corrosion. Control the molar concentration of LiFSI and LiPF 6 When the molar concentration satisfies a certain relationship, it can not only improve the conductivity of the electrolyte, which is beneficial to improving the fast charging performance of the lithium secondary battery, but also reduce the risk of corrosion of the aluminum foil and improve the safety of the lithium secondary battery.

[0092] In some embodiments, LiPF 6The molar concentration C1 of LiFSI is 0.2 mol / L to 1.2 mol / L, and may be 0.2 mol / L to 1.1 mol / L. The molar concentration C2 of LiFSI is 0.1 mol / L to 1 mol / L, and may be 0.2 mol / L to 1 mol / L. In some embodiments, LiPF 6 The molar concentration C1 of LiFSI can be selected as 0.2mol / L, 0.3mol / L, 0.4mol / L, 0.5mol / L, 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L, 1.0mol / L, 1.1mol / L, 1.2mol / L, or a value in the range formed by any two of the above points, and the molar concentration C2 of LiFSI can be selected as 0.1mol / L, 0.2mol / L, 0.3mol / L, 0.4mol / L, 0.5mol / L, 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L, 1mol / L, or a value in the range formed by any two of the above points.

[0093] Control LiFSI and LiPF separately 6 The molar concentration is within an appropriate range, taking into account both the fast charging performance and safety of the lithium secondary battery.

[0094] In some embodiments, the electrolyte further includes additives, and the additives include one or more of lithium difluorophosphate, lithium fluorosulfonate, trimethylphosphite, vinylene carbonate, lithium tetrafluoroborate, lithium difluorobisoxalatophosphate, tris(trimethylsiloxy)borate, trimethylfluorosilane, adiponitrile, and succinonitrile, and optionally include one or more of lithium difluorophosphate, lithium fluorosulfonate, lithium tetrafluoroborate, and lithium difluorooxalatoborate.

[0095] The above additives can participate in the formation of CEI film on the positive electrode side or SEI film on the negative electrode side, reducing the direct contact between the chain carboxylic acid ester and the positive electrode or metal lithium, thereby reducing the consumption of active lithium and the reduction decomposition of the electrolyte. Lithium difluorophosphate, lithium fluorosulfonate, trimethylphosphite, vinylene carbonate, lithium tetrafluoroborate or lithium difluorobisoxalate phosphate participates in the formation of CEI film on the positive electrode side, which is beneficial to reduce the oxidative decomposition of the electrolyte on the positive electrode side, thereby reducing the cathode interface 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 flatulence of the battery cell, reduce the consumption of active lithium, and improve the life of the battery cell. Tris (trimethylsilyl) borate, trimethylfluorosilane, adiponitrile or succinonitrile participates in the formation of SEI film on the negative electrode side, which is beneficial to reduce the reduction decomposition of the electrolyte on the negative electrode side, reduce gas production, and improve the electrical performance of the battery.

[0096] In some embodiments, the conductivity of the electrolyte is 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.

[0097] The conductivity of the electrolyte is within an appropriate range, which can take into account the fast charging performance and storage performance of the lithium secondary battery. If the electrolyte has too low conductivity, the fast charging performance of the lithium secondary battery will be seriously affected; if the electrolyte has too high conductivity, it will lead to an increase in gas production, which is not conducive to the storage performance of the lithium secondary battery.

[0098] In some embodiments, the filling coefficient of the lithium secondary battery is 1.5 g / Ah to 4.0 g / Ah. In some embodiments, the filling coefficient of the lithium secondary battery can be selected as 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 in the range formed by any two of the above points.

[0099] In this article, the term "filling factor" is the ratio of electrolyte mass (g) to cell capacity (Ah).

[0100] Controlling the injection coefficient of lithium secondary batteries within an appropriate range can not only provide enough electrolyte to meet the needs of lithium secondary batteries, but also release a certain amount of space to accommodate more positive electrode active materials / negative electrode active materials, thereby improving the energy density of lithium secondary batteries, or release a certain amount of space for gas transfer, thereby reducing the internal pressure of the lithium secondary battery shell and improving the service life and safety of lithium secondary batteries.

[0101] [Positive electrode]

[0102] 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, wherein the positive electrode film layer includes a positive electrode active material.

[0103] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0104] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0105] In some embodiments, the positive electrode active material may be a positive electrode active material for a battery known in the art. As an example, the positive electrode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0106] In some embodiments, the positive electrode active material includes Li d [Ni x Co y X1 z M1 1-x-y-z ]O 2-S 、LiMn 2 O 4 , Li 2 MnO 3 ·(1-a)LiAO 2 、LiM2X2O 4 One or more of

[0107] 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<a<1; M2 includes one or more of Fe, Mn, Ni, Co, X2O 4 h- Wherein X2 includes one or more of S, P, As, V, Mo, and W, and h=2 or 3.

[0108] The above-mentioned positive electrode active materials can all be used in combination with an electrolyte to realize a lithium secondary battery with excellent fast charging performance and cycle performance.

[0109] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0110] In some embodiments, the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0111] In some embodiments, the compaction density of the positive electrode film layer of the positive electrode sheet is 3.3 g / cm 3 ~3.7g / cm 3 .

[0112] In this article, the compaction density of the positive electrode film layer can be tested by any known test method. As an example, the compaction density of the film layer of the positive electrode sheet is obtained by calculation, taking a positive electrode sheet with a unit area of ​​S, weighing it as M1, the mass of the aluminum foil under the unit area S as M2, measuring the thickness of the positive electrode sheet H1, and the thickness of the aluminum foil as H2, then the compaction density of the positive electrode film layer = (M1-M2) / ((H1-H2)×S).

[0113] The compaction density of the positive electrode film layer is within a suitable range, which can take into account both the DC impedance and the energy density of the lithium secondary battery.

[0114] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0115] [Negative electrode]

[0116] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector and containing at least a negative electrode active material.

[0117] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0118] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may 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 substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0119] 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, intermediate phase microcarbon beads, silicon-based materials, and tin-based materials, and optionally includes one or more of artificial graphite and natural graphite.

[0120] The negative electrode film layer with the above negative electrode active material can be used in combination with the electrolyte to realize a lithium secondary battery with excellent fast charging performance and cycle performance. In addition, since artificial graphite or natural graphite has a large gram capacity, and the graphite structure is stable and has a small expansion and contraction rate when lithium is inserted and extracted, artificial graphite or natural graphite has greater advantages as a negative electrode active material.

[0121] In some embodiments, the compaction density of the negative electrode film layer is 0.9 g / cm 3 ~1.6g / cm 3 , optional 1.1g / cm 3 ~1.6g / cm 3 In some embodiments, the compaction density of the negative electrode film layer may be 0.9 g / cm 3 , 0.95g / cm 3 , 1.0g / cm 3 , 1.05g / cm 3 , 1.1g / cm 3 , 1.15g / cm 3 , 1.2g / cm 3 , 1.25g / cm 3 , 1.3g / cm 3 , 1.35g / cm 3 , 1.4g / cm 3 , 1.45g / cm 3 , 1.5g / cm 3 , 1.55g / cm 3 , 1.6g / cm 3 , or a value in the range formed by any two of the above points.

[0122] Controlling the compaction density of the negative electrode film layer within an appropriate range can not only meet the requirement of sufficient contact between the negative electrode active materials so that the battery has 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, resulting in unfavorable lithium ion insertion and extraction.

[0123] In some embodiments, the negative electrode film layer may further include a binder. The binder may 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).

[0124] In some embodiments, the negative electrode film layer may further include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0125] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0126] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0127] [Isolation film]

[0128] In some embodiments, the lithium secondary battery further includes a separator, which can be any known porous structure separator with good chemical stability and mechanical stability.

[0129] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different.

[0130] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0131] In some embodiments, the lithium secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0132] In order to alleviate the problem of expansion force of secondary battery cells, expansion space can be reserved for the cells in the design. 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 cell thickness in the battery to the thickness of the inner cavity of the shell.

[0133] In some embodiments,. In some embodiments, the group margin of the lithium secondary battery can be selected as 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, or a value in the range consisting of any two of the above points.

[0134] Controlling the group margin of the lithium secondary battery within an appropriate range, that is, providing enough space to accommodate the electrode assembly and providing 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.

[0135] In some embodiments, the outer packaging of the lithium secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the lithium secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed.

[0136] The shape of the lithium secondary battery in this application can be cylindrical, square or any other shape. For example, Figure 1 The lithium secondary battery 5 is a square structure as an example.

[0137] In some embodiments, reference Figure 2 , the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may 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 connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the lithium secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0138] In some embodiments, lithium secondary batteries can be assembled into a battery module. The number of lithium secondary batteries contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0139] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of lithium secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of lithium secondary batteries 5 may be fixed by fasteners.

[0140] Optionally, the battery module 4 may further include a housing having a housing space, and the plurality of lithium secondary batteries 5 are housed in the housing space.

[0141] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0142] Figure 4 and Figure 5 1 is a battery pack 1 as an example. Figure 4 and Figure 5The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0143] In addition, the present application also provides an electrical device, which includes at least one of the lithium secondary battery, battery module, or battery pack provided in the present application. The lithium secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.

[0144] As the electrical device, a lithium secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

[0145] Figure 6 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the power consumption device's requirements for high power and high energy density of lithium secondary batteries, a battery pack or a battery module can be used.

[0146] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a lithium secondary battery may be used as a power source.

[0147] Example

[0148] 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 should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0149] 1. Preparation method

[0150] Example 1

[0151] 1) Electrolyte

[0152] In an argon atmosphere glove box (H 2 O content <10ppm, O 2content <1ppm), 5g of ethyl formate, 10g of ethylene carbonate, and 71.13g of ethyl methyl carbonate were mixed evenly to obtain a mixed solvent. Then lithium salt lithium hexafluorophosphate (LiPF 6 ) and lithium salt lithium bis(fluorosulfonyl)imide (LiFSI) were added to the above-mentioned mixed solvent to make the molar concentrations of the two to be 0.7 mol / L (8.75 g) and 0.3 mol / L (4.62 g), respectively, and stirred evenly, and then 0.5 g of 4,4'-disulfuric acid vinyl ester was added and stirred evenly to prepare an electrolyte.

[0153] 2) Preparation of positive electrode

[0154] The positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3 O 2 , conductive agent Super P, and binder polyvinylidene fluoride (PVDF) are used to prepare positive electrode slurry in N-methylpyrrolidone (NMP); the solid content in the positive electrode slurry is 50wt%, and the solid content of LiNi 0.5 Co 0.2 Mn 0.3 O 2 The mass ratio of Super P and PVDF is 8:1:1. The positive electrode slurry is coated on the negative electrode current collector aluminum foil and dried at 85°C and then cold pressed. Then, after trimming, cutting and striping, it is dried at 85°C under vacuum for 4 hours to make a positive electrode sheet.

[0155] 3) Preparation of negative electrode sheet

[0156] Graphite as the negative electrode active material, conductive agent Super P, thickener carboxymethyl cellulose (CMC), and adhesive styrene butadiene rubber (SBR) are mixed evenly in deionized water to prepare a negative electrode slurry; the solid content in the negative electrode slurry is 30wt%, and the mass ratio of graphite, Super P, CMC and adhesive styrene butadiene rubber (SBR) in the solid component is 80:15:3:2. The negative electrode slurry is coated on the negative electrode current collector copper foil and dried at 85°C, and then cold pressed, trimmed, cut, and striped, and then dried at 120°C under vacuum conditions for 12h to prepare a negative electrode sheet with a negative electrode film thickness of 50μm.

[0157] 4) Isolation film

[0158] A 16 μm polyethylene film (PE) was used as the isolation membrane.

[0159] 5) Preparation of batteries

[0160] The positive electrode sheet, the isolation film, and the negative electrode sheet are stacked in order, so that the isolation film is placed in the middle of the positive and negative electrode sheets to isolate the positive and negative electrode sheets, and the bare battery cell is wound, and the pole ears are welded. The bare battery cell is placed in an outer package, and the prepared electrolyte is injected into the dried battery cell. After packaging, standing, formation, shaping, capacity testing and other processes, the lithium secondary battery product of Example 1 is obtained.

[0161] The secondary batteries of Examples 2 to 29 and the secondary batteries of Comparative Examples 1 to 6 are prepared in a similar manner to the secondary battery of Example 1, but the composition and product parameters of the battery electrodes are adjusted. The different product parameters are detailed in Tables 1 and 2;

[0162] The size of W1, W2, and W3, as well as the mass content of the additives, can be adjusted by adjusting the mass content of ethyl methyl carbonate in the electrolyte.

[0163] 2. Performance Test

[0164] 1. Compaction density of negative electrode film layer

[0165] The compaction density of the film layer of the negative electrode sheet is obtained by calculation: take a negative electrode sheet of unit area s, weigh it as m1, the mass of the copper foil under unit area s is m2, measure the thickness h1 of the negative electrode sheet, the thickness of the copper foil is h2, and the compaction density of the film layer of the negative electrode sheet = (m1-m2) / ((h1-h2)×s).

[0166] 2. Battery fast charging performance

[0167] The prepared battery was discharged to 2.8 V at 1C, then allowed to stand for 5 min, charged to 4.25 V at 0.5C, and the charge capacity C0 was recorded. Then, it was discharged to 2.8 V at 1C and allowed to stand for 5 min, and then charged to 4.25 V at 2C, and the charge capacity C1 was recorded. The battery charge capacity retention rate = C1 / C0×100%.

[0168] 3. Battery cycle performance

[0169] At 25°C, the prepared battery was charged to 4.25V at a constant current of 1C, then charged at a constant voltage of 4.25V until the current dropped to 0.05C, and after standing for 10 minutes, discharged to 2.8V at a constant current of 1C. This was the first charge / discharge cycle of the battery, and the discharge capacity at this time was recorded as the discharge capacity of the first cycle of the battery (C0); the above steps were repeated for the same battery, and the process capacity of the battery after the 300th cycle (C1), the capacity retention rate after 300 cycles = C1 / C0×100%. The test process of the comparative example and other embodiments is the same as above.

[0170] 4. Battery storage gas production performance

[0171] At 25°C, the prepared full battery was allowed to stand for 30 minutes, then charged to 4.2V at a constant current rate of 0.1C, and then charged to 0.05C at a constant voltage at 4.2V. After standing for 5 minutes, the volume V1 of the battery cell was tested by the water drainage method. After storage at 60°C for 30 days, the battery cell was taken out, cooled to 25°C, charged to 4.2V at 0.1C, and then charged to 0.05C at a constant voltage. The volume V2 of the battery was tested by the water drainage method, and the volume expansion rate of the battery = (V2-V1) / V1×100%.

[0172] III. Analysis of test results of various embodiments and comparative examples

[0173] The batteries of the embodiments and comparative examples were prepared according to the above method, and various performance parameters were measured. The results are shown in Tables 1 and 2 below.

[0174] Table 1

[0175]

[0176]

[0177] Table 2

[0178]

[0179]

[0180] The lithium secondary batteries of Examples 1 to 29 all include an electrolyte and a negative electrode plate, the electrolyte includes a chain carboxylate and a cyclic carbonate, the negative electrode plate includes a negative electrode collector and a negative electrode film layer located on at least one side of the negative electrode 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, the mass content W1 of the chain carboxylate and the thickness H of the negative electrode film layer satisfy: 0.2≤H / 100W1≤20, and the unit of H is μm.

[0181] From the comparison of Examples 1 to 7, Examples 22 to 24 and Comparative Examples 1 to 4, it can be seen that, 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 are controlled to 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, which is beneficial to improving the fast charging performance and cycle performance of the lithium secondary battery, as well as reducing the storage gas production rate of the lithium secondary battery and improving its storage performance.

[0182] From the comparison between Examples 2 to 6, 23 to 24 and Examples 1, 7 and 23, it can be seen that, based on the total mass of the electrolyte, further controlling the mass content W1 of the linear carboxylic acid ester and the mass content W2 of the cyclic carbonate to satisfy: 0.1≤W2 / W1≤1.5 is beneficial to further improve the storage performance of the battery.

[0183] As can be seen from Examples 1 to 4, based on the total mass of the electrolyte, the mass content W1 of the chain carboxylic acid ester is controlled to be 5% to 75%, so that the lithium secondary battery has excellent fast charging performance, cycle performance and storage performance. As can be seen from the comparison between Examples 2 to 4 and Example 1, based on the total mass of the electrolyte, further controlling the mass content W1 of the chain carboxylic acid ester to be 20% to 75% is conducive to further improving the fast charging performance, cycle performance and storage performance of the lithium secondary battery.

[0184] As can be seen from Examples 2, 5 to 7, based on the total mass of the electrolyte, the mass content W2 of the cyclic carbonate is controlled to be 5% to 40%, so that the lithium secondary battery has excellent fast charging performance, cycle performance and storage performance. From the comparison of Examples 2 and 6 with Examples 5 and 7, it can be seen that based on the total mass of the electrolyte, further controlling the mass content W2 of the cyclic carbonate to be 5% to 30% is beneficial to further improve the fast charging performance, cycle performance and storage performance of the lithium secondary battery.

[0185] It can be seen from Examples 2 and 22 to 24 that the thickness of the negative electrode film layer is controlled to be 10 μm to 100 μm so that the lithium secondary battery has excellent fast charging performance, cycle performance and storage performance.

[0186] As can be seen from Examples 2, 8 to 11, controlling LiPF 6 The molar concentration C1 of LiFSI and the molar concentration C2 of LiFSI satisfy: 1≤C1 / C2≤5, so that the lithium secondary battery has excellent fast charging performance, cycle performance and storage performance. From the comparison between Examples 2, 8, 10 to 11 and Example 9, it can be seen that further controlling the LiPF 6 The molar concentration C1 of LiFSI and the molar concentration C2 of LiFSI satisfy: 1≤C1 / C2≤3, which is beneficial to further improve the fast charging performance, cycle performance and storage performance of lithium secondary batteries.

[0187] As can be seen from Examples 2, 5 to 7, and 12 to 14, the chain carboxylic acid ester may be ethyl formate or methyl acetate, the cyclic carbonate may be ethylene carbonate or fluoroethylene carbonate, and the sulfate compound may be 4,4'-disulfate or a substance represented by the structure of Formula I (R 1 =b, R 2 =b, R 3= methyl), can make the lithium secondary battery have excellent fast charging performance, cycle performance and storage performance. It can also be seen from Examples 2, 5 to 7, 12 to 14 that based on the total mass of the electrolyte, the mass content W2 of the cyclic carbonate is controlled to be 5% to 40%, which can take into account the fast charging performance, cycle performance and storage performance of the lithium secondary battery.

[0188] As can be seen from Examples 12 to 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 (R 1 =b, R 2 =b, R 3 = methyl), can also make the lithium secondary battery have excellent fast charging performance, cycle performance and storage performance.

[0189] It can be seen from Examples 1 to 4 and 19 to 21 that, 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 ester compound are controlled to satisfy: 0.005≤W3 / W1≤0.4, which can make the lithium secondary battery have excellent fast charging performance, cycle performance and storage performance. It can be seen from the comparison of Examples 1 to 4 and 20 to 21 with Example 19 that, 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 ester compound to satisfy: 0.005≤W3 / W1≤0.25 is beneficial to improving the fast charging performance, cycle performance and storage performance of the lithium secondary battery.

[0190] It can be seen from Examples 1 to 4 and 19 to 21 that, based on the total mass of the electrolyte, controlling the mass content W3 of the sulfate ester compound to 0.1% to 2% can enable the lithium secondary battery to have excellent fast charging performance, cycle performance and storage performance.

[0191] From the comparison between Examples 25 to 26 and Example 2, it can be seen that the introduction of the additive lithium difluorophosphate or lithium fluorosulfonate into the electrolyte is beneficial to improving the fast charging performance, cycle performance and storage performance of the battery.

[0192] It can be seen from Examples 2, 27 to 29 that the compaction density of the negative electrode film is controlled to be 0.9 g / cm 3 ~1.6g / cm 3 , so that the lithium secondary battery has excellent fast charging performance, cycle performance and storage performance. From the comparison between Examples 2, 28 to 29 and Example 27, it can be seen that the compaction density of the negative electrode film layer is further controlled to be 1.1 g / cm 3 ~1.6g / cm 3 , which will help further improve the battery's fast charging performance, cycle performance and storage performance.

[0193] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A lithium secondary battery, characterized in that: The invention comprises an electrolyte and a negative electrode plate, wherein the electrolyte comprises a chain carboxylate and a cyclic carbonate, and the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector; Among them, 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, the mass content W1 of the chain carboxylate and the thickness H of the negative electrode film layer satisfy: 0.2≤H / 100W1≤20, and the unit of H is μm.

2. The lithium secondary battery according to claim 1, characterized in that: The electrolyte further includes a sulfate compound. 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 the following relationship: 0.005≤W3 / W1≤0.

4.

3. The lithium secondary battery according to claim 2, characterized in that: The chain carboxylic acid ester includes 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 includes one or more of ethyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, and propyl propionate; and / or The cyclic carbonate includes one or more of ethylene carbonate, propylene carbonate and fluoroethylene carbonate, and optionally includes one or more of ethylene carbonate and fluoroethylene carbonate; and / or The sulfate compounds include compounds of formula I and formula II, diethyl sulfate, dimethyl sulfate, dihydro-1,3,2-dimethyl sulfate, One or more of thio-(1,3,2-dioxane)-2,2,5,5-tetraoxide, Wherein, R1 and R2 each independently include a hydrogen atom, a C 1-6 The alkyl group R3 includes C 1-6 The alkyl group Optionally, the sulfate ester compound includes 4,4'-dithiovinyl sulfate, vinyl sulfate, diethyl sulfate, dimethyl sulfate, dihydrogen-1,3,2-disulfate, One or more of thio-(1,3,2-dioxane)-2,2,5,5-tetraoxide.

4. The lithium secondary battery according to any one of claims 1 to 3, characterized in that: Based on the total mass of the electrolyte, the mass content W1 of the chain carboxylic acid ester is 5% to 75%, and can be optionally 20% to 75%; Based on the total mass of the electrolyte, the mass content W2 of the cyclic carbonate is 5% to 40%, and can be optionally 10% to 30%; and / or Based on the total mass of the electrolyte, the mass content W3 of the sulfate ester compound is 0.1% to 2%, and can be optionally 0.1% to 1%.

5. The lithium secondary battery according to any one of claims 1 to 4, characterized in that: The thickness of the negative electrode film layer is 10 μm to 100 μm, and can be optionally 20 μm to 70 μm.

6. The lithium secondary battery according to any one of claims 1 to 5, characterized in that: The electrolyte also includes a lithium salt, and the lithium salt includes LiPF6 and LiFSI; wherein, The molar concentration C1 of LiPF6 and the molar concentration C2 of LiFSI satisfy: 0.8 mol / L≤C1+C2≤1.3 mol / L, which may be 0.8 mol / L≤C1+C2≤1.2 mol / L; and / or, The molar concentration C1 of LiPF6 and the molar concentration C2 of LiFSI satisfy: 1≤C1 / C2≤5, which can be optionally 1≤C1 / C2≤3.

7. The lithium secondary battery according to claim 6, characterized in that: The molar concentration C1 of LiPF6 is 0.2mol / L to 1.2mol / L, and can be selected as 0.2mol / L to 1.1mol / L; The molar concentration C2 of LiFSI is 0.1 mol / L to 1 mol / L, and can be optionally 0.2 mol / L to 1 mol / L.

8. The lithium secondary battery according to any one of claims 1 to 7, characterized in that: The electrolyte also includes additives, which include one or more of lithium difluorophosphate, lithium fluorosulfonate, trimethylphosphite, vinylene carbonate, lithium tetrafluoroborate, lithium difluorobisoxalatophosphate, tris(trimethylsilyloxy)borate, trimethylfluorosilane, adiponitrile, and succinonitrile, and can optionally include one or more of lithium difluorophosphate, lithium fluorosulfonate, lithium tetrafluoroborate, and lithium difluorooxalatoborate.

9. The lithium secondary battery according to any one of claims 1 to 8, characterized in that: The positive electrode sheet in the lithium secondary battery includes a positive electrode active material, and the positive electrode 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 or more, 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<a<1; M2 includes one or more of Fe, Mn, Ni, Co, X2O4 h- Wherein X2 includes one or more of S, P, As, V, Mo, and W, and h=2 or 3.

10. The lithium secondary battery according to any one of claims 1 to 9, characterized in that: 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, intermediate phase micro carbon beads, silicon-based materials, and tin-based materials, and optionally includes one or more of artificial graphite and natural graphite.

11. The lithium secondary battery according to any one of claims 1 to 10, characterized in that: The compaction density of the negative electrode film layer is 0.9 g / cm 3 ~1.6g / cm 3 , optional 1.1g / cm 3 ~1.6g / cm 3 .

12. An electrical device, characterized in that: A lithium secondary battery comprising the lithium secondary battery according to any one of claims 1 to 11.

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