Electrolytes, lithium secondary batteries, and electrical devices

Abstract

The present invention relates to an electrolyte, a lithium secondary battery, and an electrical device. The electrolyte comprises a first solvent, a silane compound containing a carbon-carbon double bond, and a cyclic lithium borate compound, wherein the first solvent contains a cyclic carbonate compound, and based on the total mass of the electrolyte, the mass content W3 of the cyclic carbonate compound, the mass content W1 of the silane compound containing a carbon-carbon double bond, and the mass content W2 of the cyclic lithium borate compound satisfy the condition 0.001 ≤ (W1 + W2) / W3 ≤ 2.67. By using a combination of a silane compound containing a carbon-carbon double bond and a cyclic lithium borate compound, the flexibility and thermal stability of the SEI film can be improved, thereby reducing the degree of gas generation during the cycle and storage processes of the lithium secondary battery, and improving the storage performance, rapid charging performance, and cycle performance of the lithium secondary battery.

Description

[Technical Field]

[0001] (Cross-reference of related applications) This application claims priority to Chinese patent application 202311600919.X, filed on November 28, 2023, with the title of the invention "Electrolyte, Lithium Secondary Battery and Electrical Device," and all contents of the said Chinese patent application are incorporated into this application by reference.

[0002] This application relates to the technical field of lithium batteries, and more particularly to electrolytes, lithium secondary batteries, and electrical devices. [Background technology]

[0003] In recent years, as the range of applications for lithium-ion batteries has expanded, they are widely used in various fields such as energy storage and power systems including hydroelectric, thermal, wind, and solar power plants, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Due to the significant advancements in lithium-ion batteries, the demands on their energy density, cycle performance, and safety have also increased.

[0004] Improving battery power, cycle life, and shelf life has always been an industry goal, but the overall performance of the cell remains low due to electrolyte side reactions at the cathode-anode interface. [Overview of the project]

[0005] This application has been made in view of the above-mentioned problems, and its purpose is to provide an electrolyte that improves the flexibility and thermal stability of the SEI (Solid Electrolyte Interphase) film, thereby reducing the degree of gas generation during the cycling and storage processes of lithium secondary batteries, improving the storage performance, rapid charging performance, and cycling performance of lithium secondary batteries, and comprehensively improving the performance of lithium secondary batteries.

[0006] To achieve the above objective, a first aspect of this application provides an electrolyte for a lithium secondary battery comprising a first solvent, a silane compound containing a carbon-carbon double bond, and a cyclic lithium borate compound, wherein the first solvent comprises a cyclic carbonate compound, the cyclic carbonate compound comprises at least one of ethylene carbonate, fluoroethylene carbonate, and propylene carbonate, and the mass content W3 of the cyclic carbonate compound, the mass content W1 of the silane compound containing a carbon-carbon double bond, and the mass content W2 of the cyclic lithium borate compound satisfy 0.001 ≤ (W1 + W2) / W3 ≤ 2.67 based on the total mass of the electrolyte.

[0007] In any embodiment, the mass content W3 of the cyclic carbonate compound, the mass content W1 of the silane compound containing a carbon-carbon double bond, and the mass content W2 of the cyclic lithium borate compound satisfy 0.005 ≤ (W1 + W2) / W3 ≤ 2, based on the total mass of the electrolyte.

[0008] By controlling the content of cyclic carbonate compounds in the electrolyte within an appropriate range, and by adding silane compounds and cyclic lithium borate compounds containing carbon-carbon double bonds within the above content range, the flexibility and thermal stability of the SEI film can be effectively improved. This balances the storage performance and DC impedance of the lithium secondary battery, thereby comprehensively improving the performance of the lithium secondary battery.

[0009] In any embodiment, the cyclic carbonate compound comprises at least one of ethylene carbonate, fluoroethylene carbonate, and propylene carbonate.

[0010] When a cyclic carbonate compound is used as a solvent in the electrolyte, it exhibits excellent ionic conductivity and film-forming properties.

[0011] In any embodiment, the silane compound containing the carbon-carbon double bond comprises at least one of tetravinylsilane, trivinylethylsilane, divinyldiethylsilane, and vinyltrimethylsilane.

[0012] In any embodiment, the silane compound containing a carbon-carbon double bond includes tetravinylsilane.

[0013] Due to the presence of the carbon-carbon double bond, the silane compound containing a carbon-carbon double bond described above forms a film preferentially over the cyclic carbonate-based compound at the anode, and can generate a polymer component in the SEI film, which improves the flexibility of the SEI film. In addition, the SEI film covers the surface of the anode electrode sheet to reduce the exposure degree of the anode electrode sheet to the electrolyte, reduce side reactions and gas generation, and improve the performance of the lithium secondary battery.

[0014] In any embodiment, the cyclic lithium borate-based compound includes a compound having a structure represented by Formula I,

Chemical Formula

[0015] In any embodiment, the cyclic lithium borate-based compound is

Chemical Formula

[0016] The cyclic lithium borate-based compound described above is reduced and forms a film preferentially over the cyclic carbonate-based compound, and can form a component containing a large amount of lithium salt in the SEI film, which improves the thermal stability of the SEI film, reduces the overall oxidative decomposition degree of the SEI film and the solubility of the SEI film in the solvent of the electrolyte, and improves the storage performance of the lithium secondary battery.

[0017] In any embodiment, based on the total mass of the electrolyte, the mass content W1 of the silane compound containing a carbon-carbon double bond and the mass content W2 of the cyclic lithium borate-based compound satisfy 0.01≦W1 / W2≦200.

[0018] In any embodiment, based on the total mass of the electrolytic solution, the mass content W1 of the silane compound containing a carbon-carbon double bond and the mass content W2 of the cyclic lithium borate-based compound satisfy 0.1≦W1 / W2≦10.

[0019] In any embodiment, based on the total mass of the electrolytic solution, the mass content W1 of the silane compound containing a carbon-carbon double bond and the mass content W2 of the cyclic lithium borate-based compound satisfy 0.5≦W1 / W2≦5.

[0020] When the ratio of the mass content of the silane compound containing a carbon-carbon double bond to the mass content of the cyclic lithium borate-based compound is controlled within an appropriate range, the synergistic effect of the two can comprehensively improve the thermal stability and flexibility of the SEI film, thereby making the storage performance and direct current impedance of the lithium secondary battery compatible, and comprehensively improving the performance of the lithium secondary battery.

[0021] In any embodiment, based on the total mass of the electrolytic solution, the mass content W3 of the cyclic carbonate-based compound satisfies 3%≦W3≦20%.

[0022] In any embodiment, based on the total mass of the electrolytic solution, the mass content W3 of the cyclic carbonate-based compound satisfies 5%≦W3≦20%.

[0023] By controlling the content of the cyclic carbonate-based compound in the electrolytic solution within an appropriate range, the formation of the SEI film and the ionic conductivity of the electrolytic solution can be made compatible, thereby improving the cycle performance of the lithium secondary battery and reducing the degree of gas generation during the storage process.

[0024] In any embodiment, based on the total mass of the electrolytic solution, the mass content W1 of the silane compound containing a carbon-carbon double bond satisfies 0.01%≦W1≦5%.

[0025] In any embodiment, the mass content W1 of the silane compound containing the carbon-carbon double bond, based on the total mass of the electrolyte, satisfies 0.01% ≤ W1 ≤ 3%.

[0026] By controlling the content of silane compounds containing carbon-carbon double bonds in the electrolyte within an appropriate range, the flexibility of the SEI film can be improved, while side reactions and gas generation can be reduced, thereby improving the performance of lithium secondary batteries.

[0027] In any embodiment, the mass content W2 of the cyclic lithium borate compound satisfies 0.01% ≤ W2 ≤ 3% based on the total mass of the electrolyte.

[0028] In any embodiment, the mass content W2 of the cyclic lithium borate compound satisfies 0.1% ≤ W2 ≤ 2% based on the total mass of the electrolyte.

[0029] By controlling the content of cyclic lithium borate compounds in the electrolyte within an appropriate range, the thermal stability of the SEI film can be improved, thereby enhancing the storage performance of lithium secondary batteries.

[0030] In any embodiment, the electrolyte comprises a second solvent, the second solvent comprises a linear carbonate compound, the linear carbonate compound comprises at least one of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, ethyl acetate, methyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

[0031] By adding the above-mentioned second solvent to the electrolyte, the viscosity of the electrolyte can be reduced, the conductivity of the electrolyte can be improved, and the rapid charging performance and cycle life of the battery can be further improved.

[0032] In any embodiment, the electrolytic solution contains a lithium salt, and the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium (fluorosulfonyl)(perfluorobutylsulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide, and the concentration of the lithium salt in the electrolytic solution is 0.8 mol / L to 1.3 mol / L.

[0033] By controlling the concentration of the lithium salt in the electrolytic solution within the above range, the conductivity of the electrolytic solution can be increased, which is advantageous for further improving the cycle life of the battery.

[0034] A second aspect of the present application provides a lithium secondary battery comprising a positive electrode sheet, a negative electrode sheet, and the electrolytic solution according to the first aspect of the present application.

[0035] In any embodiment, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer located on at least one side of the positive electrode current collector, and the positive electrode material layer is Li d [Ni x Co y X1 z M1 1-x-y-z O2, one or more of LiMn2O4, Li2MnO3·(1-a)LiAO2, and LiM2X2O4, where 0.1≦d≦1, X1 includes Mn and / or Al, M1 includes one or more of Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, and Ti, 0≦x<1, 0≦y≦1, 0≦z≦1, x+y+z≦1, A includes one or more of Ni, Co, and Mn, 0<a<1, M2 includes one or more of Fe, Mn, Ni, and Co, and X2O4 h- X2 in the above includes one or more of S, P, As, V, Mo, and W, and h=2 or 3.

[0036] In any embodiment, the positive electrode material layer is Li d [Ni x Co y X1 z M1 1-x-y-zThe formula contains O2, where 0.1 ≤ d ≤ 1, X1 contains Mn and / or Al, M1 contains one or more of Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, Ti, and 0 ≤ x < 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and x + y + z ≤ 1.

[0037] In any embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer located on at least one side of the negative electrode current collector, wherein the negative electrode material layer includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, mesocarbon microbeads, silicon-based materials, and tin-based materials.

[0038] In any embodiment, the negative electrode material layer comprises at least one of artificial graphite and natural graphite.

[0039] A third aspect of this application provides an electrical device including a lithium secondary battery according to the second aspect of this application.

[0040] A secondary battery manufactured using the electrolyte provided in this application has improved cycle performance and storage performance. Accordingly, the electrical device provided in this application also has good performance. [Brief explanation of the drawing]

[0041] [Figure 1] This is a schematic diagram of a secondary battery according to one embodiment of the present application. [Figure 2] Figure 1 is an exploded view of a secondary battery according to one embodiment of this application. [Figure 3] This is a schematic diagram of an electrical device using a secondary battery as a power source according to one embodiment of this application. [Modes for carrying out the invention]

[0042] The following describes in detail embodiments of the electrolyte, lithium secondary battery, and electrical device of this application, with appropriate reference to the drawings. However, unnecessary details may be omitted. For example, detailed explanations of well-known matters and redundant explanations of identical structures may be omitted. This is to avoid unnecessarily verbose explanations, making it easier for those skilled in the art to understand. Furthermore, the drawings and the following explanation are provided to enable those skilled in the art to fully understand this application and are not intended to limit the intent of the claims.

[0043] The “range” disclosed in this application is limited by a lower and upper limit, and a given range is limited by selecting one lower limit and one upper limit, and the boundaries of a particular range are limited by the selected lower and upper limits. Such limited ranges may or may not include endpoint values ​​and can be combined arbitrarily, that is, any lower limit and any upper limit can be combined to form a single range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, the ranges 60-110 and 80-120 are also understood to be predictable. Also, if the minimum range values ​​are 1 and 2 and the maximum range values ​​are 3, 4 and 5, then the ranges 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 are all predictable. In this application, unless otherwise specified, the numerical range “a-b” represents an abbreviated expression for any combination of real numbers between a and b, where both a and b are real numbers. For example, the numerical range "0 to 5" indicates that all real numbers between "0 to 5" are listed in this specification, and "0 to 5" is merely an abbreviated representation of combinations of these numbers. Furthermore, when a parameter is described as being an integer of 2 or more, it is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12.

[0044] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0045] Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0046] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably in order. For example, when the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed in order, or steps (b) and (a) performed in order. For example, when the method further includes step (c), it 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 steps (a), (c) and (b), or steps (c), (a) and (b), or other cases.

[0047] Unless otherwise specified, the terms "includes" and "incorporates" in this application represent open-ended expressions, but may also represent closed-ended expressions. For example, the terms "includes" and "incorporates" may further include or incorporate other components not listed, or may include or incorporate only the listed components.

[0048] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following conditions satisfy the "A or B" condition: 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).

[0049] Cyclic carbonate compounds (e.g., ethylene carbonate) possess excellent ionic conductivity and film-forming properties as solvent components in electrolytes. However, proton hydrogens generated during the oxidation process can attack lithium hexafluorophosphate in the solvent, destroying the SEI film. As a result, the electrolyte undergoes continuous redox decomposition at both the positive and negative electrodes, consuming active lithium and degrading the cell's performance. Furthermore, the oxidative decomposition of cyclic carbonate compounds (e.g., ethylene carbonate) at the positive electrode generates gas, causing the cell to expand, increasing the distance between the positive and negative electrodes, and lengthening the lithium ion migration path. To avoid these defects, it is common practice to reduce the content of cyclic carbonate compounds (e.g., ethylene carbonate) in the electrolyte. However, reducing the content of cyclic carbonate compounds affects not only the ionic conductivity of the electrolyte but also the formation of the SEI film.

[0050] [Electrolyte] To achieve the above objective, this application provides an electrolyte for a lithium secondary battery comprising a first solvent, a silane compound containing a carbon-carbon double bond, and a cyclic lithium borate compound, wherein the first solvent comprises a cyclic carbonate compound, and the cyclic carbonate compound comprises at least one of ethylene carbonate, fluoroethylene carbonate, and propylene carbonate, and the mass content W3 of the cyclic carbonate compound, the mass content W1 of the silane compound containing a carbon-carbon double bond, and the mass content W2 of the cyclic lithium borate compound satisfy 0.001 ≤ (W1 + W2) / W3 ≤ 2.67 based on the total mass of the electrolyte.

[0051] In some embodiments, the mass content W3 of the cyclic carbonate compound, the mass content W1 of the silane compound containing a carbon-carbon double bond, and the mass content W2 of the cyclic lithium borate compound satisfy 0.005 ≤ (W1 + W2) / W3 ≤ 2, based on the total mass of the electrolyte.

[0052] In the electrolyte provided in this application, the silane compound containing a carbon-carbon double bond can effectively form polymer components in the SEI film, thereby improving the flexibility of the SEI film and suppressing the reductive decomposition of the electrolyte to some extent. The cyclic lithium borate compound can improve the thermal stability of the SEI by forming a component containing a large amount of lithium salt in the SEI film. The synergistic effect of both improves the stability and flexibility of the SEI film, thereby reducing the degree of gas generation during the cycle and storage processes of the lithium secondary battery, improving the storage performance and rapid charging performance of the lithium secondary battery, and comprehensively improving the cycle performance of the lithium secondary battery.

[0053] Furthermore, by controlling the content of cyclic carbonate compounds in the electrolyte within an appropriate range, and by adding silane compounds and cyclic lithium borate compounds containing carbon-carbon double bonds within the above content range, the flexibility and thermal stability of the SEI film can be effectively improved. This balances the storage performance and DC impedance of the lithium secondary battery, thereby comprehensively improving the performance of the lithium secondary battery.

[0054] In some embodiments, the cyclic carbonate compound comprises at least one of ethylene carbonate, fluoroethylene carbonate, and propylene carbonate.

[0055] When a cyclic carbonate compound is used as a solvent in the electrolyte, it exhibits excellent ionic conductivity and film-forming properties.

[0056] In some embodiments, the silane compound containing the carbon-carbon double bond comprises at least one of tetravinylsilane, trivinylethylsilane, divinyldiethylsilane, and vinyltrimethylsilane.

[0057] In some embodiments, the silane compound containing the carbon-carbon double bond includes tetravinylsilane.

[0058] Due to the presence of carbon-carbon double bonds, the silane compounds containing the carbon-carbon double bonds can be reduced preferentially to the solvent at the anode to form a film, generating polymer components in the SEI film. This improves the flexibility of the SEI film, and the SEI film also covers the surface of the anode electrode sheet, reducing the degree of exposure of the anode electrode sheet to the electrolyte, thereby reducing side reactions and gas generation, and improving the performance of the lithium secondary battery.

[0059] In some embodiments, the cyclic lithium borate compound comprises a compound having the structure shown in formula I, [ka] In the formula, Y1, Y2, Y3, and Y4 each independently contain at least one oxygen atom and one sulfur atom.

[0060] In some embodiments, the cyclic lithium borate compound [ka] At least one of the following.

[0061] In some selective embodiments, Y1, Y2, Y3, and Y4 in formula I all contain an oxygen atom.

[0062] The above-mentioned cyclic lithium borate-based compounds can be reduced and formed into films preferentially over cyclic carbonate-based compounds, forming components that contain a large amount of lithium salt in the SEI film. This improves the thermal stability of the SEI film, reduces the degree of oxidative decomposition of the entire SEI film and its solubility in the electrolyte solvent, and improves the storage performance of lithium secondary batteries.

[0063] In some embodiments, the mass content W1 of the silane compound containing the carbon-carbon double bond and the mass content W2 of the cyclic lithium borate compound satisfy 0.01 ≤ W1 / W2 ≤ 200, based on the total mass of the electrolyte.

[0064] In some embodiments, the mass content W1 of the silane compound containing the carbon-carbon double bond and the mass content W2 of the cyclic lithium borate compound satisfy 0.1 ≤ W1 / W2 ≤ 10, based on the total mass of the electrolyte.

[0065] In some embodiments, the mass content W1 of the silane compound containing the carbon-carbon double bond and the mass content W2 of the cyclic lithium borate compound satisfy 0.5 ≤ W1 / W2 ≤ 5, based on the total mass of the electrolyte.

[0066] If the W1 / W2 value is too low, the content of silane compounds containing carbon-carbon double bonds is too low, making it difficult to improve the flexibility of the SEI film. On the other hand, if the W1 / W2 value is too high, the content of cyclic lithium borate compounds is too low, making it difficult to improve the thermal stability of the SEI film. Therefore, by controlling the ratio of the mass content of silane compounds containing carbon-carbon double bonds to cyclic lithium borate compounds within an appropriate range, the synergistic effect of both can comprehensively improve the thermal stability and flexibility of the SEI film. This allows for a balance between the storage performance and DC impedance of the lithium secondary battery, thereby comprehensively improving the performance of the lithium secondary battery.

[0067] In some embodiments, the mass content W3 of the cyclic carbonate compound satisfies 3% ≤ W3 ≤ 20% based on the total mass of the electrolyte.

[0068] In some embodiments, the mass content W3 of the cyclic carbonate compound satisfies 5% ≤ W3 ≤ 20% based on the total mass of the electrolyte.

[0069] If the content of cyclic carbonate compounds in the electrolyte is less than 3%, the conductivity of the electrolyte becomes too low, affecting the battery's cycle performance. On the other hand, if the content of cyclic carbonate compounds in the electrolyte is higher than 20%, oxidative decomposition and gas generation impair battery performance. Therefore, by controlling the content of cyclic carbonate compounds in the electrolyte within an appropriate range, it is possible to achieve both SEI film formation and ionic conductivity of the electrolyte, thereby improving the cycle performance of lithium secondary batteries and reducing the degree of gas generation during the storage process.

[0070] In some embodiments, the mass content W1 of the silane compound containing the carbon-carbon double bond, based on the total mass of the electrolyte, satisfies 0.01% ≤ W1 ≤ 5%.

[0071] In some embodiments, the mass content W1 of the silane compound containing the carbon-carbon double bond, based on the total mass of the electrolyte, satisfies 0.01% ≤ W1 ≤ 3%.

[0072] If the content of silane compounds containing carbon-carbon double bonds in the electrolyte is less than 0.01%, the film formation effect cannot be effectively achieved. On the other hand, if the content of silane compounds containing carbon-carbon double bonds in the electrolyte is higher than 5%, the film formation impedance becomes too high, affecting the rapid charging performance of the battery. Therefore, by controlling the content of silane compounds containing carbon-carbon double bonds in the electrolyte within an appropriate range, the flexibility of the SEI film can be improved, side reactions and gas generation can be reduced, and the performance of the lithium secondary battery can be improved.

[0073] In some embodiments, the mass content W2 of the cyclic lithium borate compound satisfies 0.01% ≤ W2 ≤ 3% based on the total mass of the electrolyte.

[0074] In some embodiments, the mass content W2 of the cyclic lithium borate compound satisfies 0.1% ≤ W2 ≤ 2% based on the total mass of the electrolyte.

[0075] If the content of cyclic lithium borate compounds in the electrolyte is less than 0.01%, the effect of effective film formation cannot be achieved. On the other hand, if the content of cyclic lithium borate compounds in the electrolyte is higher than 3%, the viscosity of the electrolyte increases, which may reduce the conductivity of the electrolyte. Therefore, by controlling the content of cyclic lithium borate compounds in the electrolyte within an appropriate range, the thermal stability of the SEI film can be improved, thereby improving the storage performance of lithium secondary batteries.

[0076] In some embodiments, the electrolyte comprises a second solvent, the second solvent comprises a linear carbonate compound, the linear carbonate compound comprises at least one of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, ethyl acetate, methyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

[0077] By adding the above-mentioned second solvent to the electrolyte, the viscosity of the electrolyte can be reduced, the conductivity of the electrolyte can be improved, and the rapid charging performance and cycle life of the battery can be further improved.

[0078] In some embodiments, the electrolyte contains a lithium salt, the lithium salt comprising at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium fluorosulfonyl(perfluorobutylsulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide, and the concentration of the lithium salt in the electrolyte is 0.8 mol / L to 1.3 mol / L.

[0079] In some embodiments, the concentration of the lithium salt in the electrolyte is within the range of 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, or any two of the above concentrations.

[0080] By controlling the concentration of the lithium salt in the electrolyte within the above range, the conductivity of the electrolyte can be increased, which is advantageous for further improving the cycle life of the battery.

[0081] The present application further provides a lithium secondary battery comprising a positive electrode sheet, a negative electrode sheet, and the electrolyte according to the first aspect of the present application. During charging and discharging of the battery, active ions repeatedly intercalate and deintercalate between the positive electrode sheet and the negative electrode sheet. The electrolyte serves to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, and mainly functions to prevent short circuit between the positive and negative electrodes while allowing ions to pass therethrough.

[0082] [Positive Electrode Sheet] The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer located on at least one side of the positive electrode current collector.

[0083] As an example, the positive electrode current collector has two surfaces facing each other in the thickness direction of itself, and the positive electrode material layer is provided on either one or both of the two opposing surfaces of the positive electrode current collector.

[0084] In some embodiments, the positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer located on at least one side of the positive electrode current collector, and the positive electrode material layer comprises Li d [Ni x Co y X1 z M1 1-x-y-z O2, one or more of LiMn2O4, Li2MnO3·(1-a)LiAO2, and LiM2X2O4, wherein 0.1≦d≦1, X1 comprises Mn and / or Al, M1 comprises one or more of Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, and Ti, 0≦x<1, 0≦y≦1, 0≦z≦1, x+y+z≦1, A comprises one or more of Ni, Co, and Mn, 0<a<1, M2 comprises one or more of Fe, Mn, Ni, and Co, X2O4 h- X2 therein comprises one or more of S, P, As, V, Mo, and W, and h=2 or 3.

[0085] In some embodiments, the positive electrode material layer is Li d [Ni x Co y X1 z M1 1-x-y-z The formula contains O2, where 0.1 ≤ d ≤ 1, X1 contains Mn and / or Al, M1 contains one or more of Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, Ti, and 0 ≤ x < 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and x + y + z ≤ 1.

[0086] In some embodiments, a metal foil or a composite current collector can be used as the positive electrode current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer material substrate (for example, a substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0087] In some embodiments, the positive electrode material layer selectively further comprises a binder. For 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.

[0088] In some embodiments, the cathode material layer selectively further comprises a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0089] In some embodiments, the positive electrode sheet can be manufactured as follows: The above components for manufacturing the positive electrode sheet, such as a positive electrode material layer, a conductive agent, a binder, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, the positive electrode slurry is applied to a positive electrode current collector, and the positive electrode sheet can be obtained through processes such as oven drying and cold pressing.

[0090] [Negative electrode sheet] The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer located on at least one side of the negative electrode current collector.

[0091] For example, the negative electrode current collector has two opposing surfaces in its own thickness direction, and the negative electrode material layer is provided on one or both of the two opposing surfaces of the negative electrode current collector.

[0092] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer located on at least one side of the negative electrode current collector, wherein the negative electrode material layer includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, mesocarbon microbeads, silicon-based materials, and tin-based materials.

[0093] In some embodiments, the negative electrode material layer includes at least one of artificial graphite and natural graphite.

[0094] In some embodiments, a metal foil or a composite current collector can be used as the negative electrode current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys) on a polymer material substrate (for example, a substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0095] In some embodiments, the negative electrode material layer selectively further comprises a binder. The binder may be at least one selected from 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).

[0096] In some embodiments, the negative electrode material layer further selectively comprises a conductive agent. The conductive agent may be at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0097] In some embodiments, the negative electrode material layer further comprises other additives, such as a selective thickener (e.g., sodium carboxymethylcellulose (CMC-Na)).

[0098] In some embodiments, the negative electrode sheet can be manufactured as follows: The above-mentioned components for manufacturing the negative electrode sheet, such as a negative electrode material layer, a conductive agent, a binder, and any other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry, the negative electrode slurry is applied to a negative electrode current collector, and the negative electrode sheet can be obtained through processes such as oven drying and cold pressing.

[0099] [Separator] In some embodiments, the secondary battery further includes a separator. In this application, the type of separator is not particularly limited, and any known porous structure separator having good chemical and mechanical stability can be selected.

[0100] In some embodiments, the material of the separator may be at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. If the separator is a multilayer composite film, the materials of each layer may be the same or different, and are not particularly limited.

[0101] In some embodiments, the positive electrode sheet, negative electrode sheet, and separator can be assembled into an electrode assembly by a winding process or a lamination process.

[0102] [Secondary battery] In some embodiments, the secondary battery may include an outer casing. This casing can be used to enclose the electrode assembly and electrolyte.

[0103] In some embodiments, the casing of the secondary battery may be a rigid case, such as a hard plastic case, an aluminum case, or a steel case. The casing of the secondary battery may also be a soft pack, such as a pouch-type soft pack. The material of the soft pack may be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0104] In this application, the shape of the secondary battery is not particularly limited and may be cylindrical, rectangular, or any other shape. For example, Figure 1 shows a rectangular secondary battery 5 as an example.

[0105] In some embodiments, referring to Figure 2, the exterior may include a case 51 and a cover plate 53. Here, the case 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and side plates surround the case 51 to form a housing cavity. The case 51 has an opening that communicates with the housing cavity, and the cover plate 53 can cover the opening to seal the housing cavity. The positive electrode sheet, negative electrode sheet and separator can be formed into an electrode assembly 52 by a winding process or a lamination process. The electrode assembly 52 is sealed within the housing cavity. The electrolyte is impregnated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and a person skilled in the art can select according to the specific actual needs.

[0106] [Electrical equipment] This application further provides an electrical device including a lithium secondary battery provided herein. The secondary battery, battery module, or battery pack may be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), trains, ships and satellites, energy storage systems, etc.

[0107] The aforementioned electrical device can be selected as a secondary battery, battery module, or battery pack, depending on its intended use.

[0108] Figure 3 shows an example of an electrical device. This electrical device may be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the requirements for high power output and high energy density of secondary batteries, this electrical device may use a battery pack or battery module.

[0109] Other examples of devices may include mobile phones, tablet computers, and laptop computers. These devices are typically required to be lightweight and thin, and may use rechargeable batteries as a power source. [Examples]

[0110] Examples of the present application are described below. The examples described below are illustrative and are for interpretive purposes only, and should not be understood as limiting this application. Unless otherwise specified in the examples, specific techniques or conditions are followed in accordance with the techniques or conditions or product specifications described in the literature in the art. Unless otherwise specified, the reagents or equipment used are common commercially available products.

[0111] 1. Manufacturing method Example 1 1) Electrolyte In an argon-atmosphered glove box (H2O content < 10 ppm, O2 content < 1 ppm), ethylene carbonate (EC), the first solvent, and ethyl methyl carbonate (EMC), the second solvent, were mixed, and 1 mol / L lithium LiPF6 salt was dissolved. Then, tetravinylsilane and lithium fluoromalonic acid (difluoro)borate (Y1 to Y4 in formula I are all O) were added, and the mixture was uniformly stirred to produce an electrolyte. Based on the total mass of the electrolyte, the mass content W3 of the first solvent was 10%, the mass content W1 of tetravinylsilane was 2%, and the mass content W2 of lithium fluoromalonic acid (difluoro)borate was 1%.

[0112] 2) Manufacturing of positive electrode sheets LiNi 0.5 Co 0.2 Mn 0.3O2, acetylene black (a conductive agent), and polyvinylidene fluoride (PVDF) (a binder) were thoroughly stirred and mixed in an N-methylpyrrolidone solvent system in a weight ratio of 90:5:5 until homogeneous, to obtain a positive electrode slurry with a solid content of 50 wt%. The positive electrode slurry was uniformly applied to the aluminum foil of the positive electrode current collector, and after air-drying the aluminum foil at room temperature, it was transferred to an 85°C oven for oven drying, followed by cold pressing. Subsequently, the foil was trimmed, sliced, and slit, and then oven-dried under vacuum conditions at 85°C for 4 hours to produce a positive electrode sheet.

[0113] 3) Manufacturing of negative electrode sheets A negative electrode slurry with a solid content of 30 wt% was prepared by uniformly mixing artificial graphite, the negative electrode active material, with Super P, a conductive agent, sodium carboxymethylcellulose (CMC-Na), a thickener, and styrene-butadiene rubber (SBR), a binder, in deionized water in a mass ratio of 80:15:3:2. The negative electrode slurry was applied to the copper foil of the current collector, and after the copper foil was air-dried at room temperature, it was transferred to an 85°C oven for oven drying, followed by cold pressing, edge cutting, thinning, and slitting. Finally, the negative electrode sheet was produced by oven drying at 120°C under vacuum conditions for 12 hours.

[0114] 4) Separator A 16 μm polyethylene (PE) porous polymer film was used as the separator.

[0115] 5) Battery manufacturing The positive electrode sheet, separator, and negative electrode sheet were stacked in this order, with the separator acting to separate them, and then wound to obtain a bare cell. Tabs were welded on, the bare cell was set in an outer casing, the electrolyte manufactured above was injected into the dried cell, and packaging, standing, chemical conversion, molding, and capacity testing were performed to complete the manufacturing of a pouch-type lithium secondary battery (pouch-type lithium secondary battery: thickness 4.0 mm, width 60 mm, length 140 mm).

[0116] The secondary batteries of Examples 2-21 and Comparative Examples 1-4 were manufactured in the same manner as the secondary battery of Example 1, except that the composition of the battery electrode sheet and product parameters were adjusted. Details of the different product parameters are shown in Table 1.

[0117] 2. Performance measurement 1, Electrolyte 1) Ionic conductivity The ionic conductivity of the electrolyte was measured according to the method described in HG-T 4067-2015. The specific procedure was as follows: Pretreatment: The liquid to be measured was taken and kept at a constant temperature for measurement, while the temperature of the standard solution was kept constant at 25°C (deviation ±0.1°C). Measurement: The instrument was calibrated by measuring two standard solutions at 25°C. After calibration, the electrode was cleaned, and then the sample was measured. The electrode was placed vertically in the solution to be measured, and the measurement was started by clicking. After the data stabilized for 10 seconds or more, the measurement results were recorded.

[0118] 2) Method for measuring the solvent content in the electrolyte The method for measuring the solvent content in the electrolyte was carried out in accordance with GB / T9722-2006. The specific method was as follows: A standard solution was prepared, and the standard solution and sample were automatically injected directly into the FID for detection. The type of additive was determined based on the peak position, and the additive content in the electrolyte was calculated based on the peak area.

[0119] 3) Method for measuring the content of additives (lithium salts) in the electrolyte The method for measuring the salt additive content was carried out in accordance with GB / T6040-2002. The specific method was as follows: A fixed amount of electrolyte was weighed (the concentration of the diluent was in the center of the standard curve), diluted to a fixed volume of 100 mL with ultrapure water, automatically injected into an ion chromatograph for detection, the type of additive was determined based on the peak position, and the additive content was determined based on the peak area.

[0120] 4) Method for measuring the mass content W3 of cyclic carbonate compounds, W1 of silane compounds containing carbon-carbon double bonds, and W2 of cyclic lithium borate compounds in the electrolyte. Based on the standard GB / T9722-2006 "General Rules for Gas Chromatography of Chemical Reagents," the organic components in the electrolyte were qualitatively and quantitatively analyzed by gas chromatography to obtain the mass content W3 of cyclic carbonate compounds, the mass content W1 of silane compounds containing carbon-carbon double bonds, and the mass content W2 of cyclic lithium borate compounds in the electrolyte.

[0121] 2, battery 1) DC impedance At 25°C, the battery cell was adjusted to a charge state of 50% SOC and left standing for 30 minutes. The battery voltage U1 (V) at this time was recorded. The battery was then discharged at 4C for 30 seconds, and the battery voltage U2 (V) at this time was recorded. The corresponding discharge current I (mA) was 4 × battery design capacity (mAh). The DC impedance DCR (mΩ) was (U1 - U2) / I.

[0122] 2) Cycle performance The manufactured lithium secondary battery was charged at 25°C at a rate of 1C to 4.4V with a constant current, then charged at a constant voltage of 0.05C, left for 10 minutes, and then discharged at a rate of 1C to 2.8V with a constant current. The discharge capacity C0 was recorded, and 300 cycles were performed according to the above charge / discharge process. The discharge capacity after 300 cycles was defined as C1, and the battery's cycle capacity retention rate was calculated as C1 / C0 × 100%.

[0123] 3) Storage performance The manufactured lithium secondary battery was charged at 25°C at a rate of 1C to 4.4V with a constant current, then charged at 0.05C with a constant voltage, left for 5 minutes, and then discharged at 1C at a constant current to 2.8V, recording the discharge capacity D0. Next, the lithium secondary battery was stored at 60°C for 30 days, removed, returned to 25°C, discharged at 1C at a constant current to 2.8V, left for 2 hours, then charged at 1C to 4.4V, then charged at 0.05C with a constant voltage, left for 2 hours, and then discharged at 1C to 2.8V, recording the discharge capacity D1. The discharge capacity retention rate was D1 / D0 × 100%.

[0124] 3. Analysis of the test results of each example and comparative example. Batteries for each example and comparative example were manufactured according to the method described above, and each performance parameter was measured. The results are shown in Table 1 below.

[0125] [Table 1]

[0126] [Table 2]

[0127] [Table 3]

[0128] The electrolytes of Examples 1 to 18 all contain a first solvent, a silane compound containing a carbon-carbon double bond, and a cyclic lithium borate compound. Lithium secondary batteries containing these electrolytes all exhibit low DC impedance and excellent storage and cycle performance.

[0129] The electrolyte in Comparative Example 1 does not contain a silane compound containing a carbon-carbon double bond. As can be seen from the comparison between Examples 1 to 18 and Comparative Example 1, by adding a silane compound containing a carbon-carbon double bond to the electrolyte, the DC impedance can be effectively reduced, and the storage performance and cycle performance of the lithium secondary battery can be improved.

[0130] The electrolyte in Comparative Example 2 does not contain a cyclic lithium borate compound. As can be seen from the comparison between Examples 1-18 and Comparative Example 2, adding a cyclic lithium borate compound to the electrolyte can effectively reduce DC impedance and improve the storage performance and cycle performance of lithium secondary batteries.

[0131] In the electrolytes of Examples 1 to 18, the mass content W3 of the cyclic carbonate compound, the mass content W1 of the silane compound containing a carbon-carbon double bond, and the mass content W2 of the cyclic lithium borate compound satisfy 0.001 ≤ (W1 + W2) / W3 ≤ 2.67 and 0.01 ≤ W1 / W2 ≤ 200. Lithium secondary batteries containing these electrolytes all exhibit low DC impedance and excellent storage and cycle performance.

[0132] In the electrolyte of Comparative Example 3, the value of (W1+W2) / W3 does not satisfy the range of 0.001 ≤ (W1+W2) / W3 ≤ 2.67. As can be seen from the comparison between Examples 1 to 18 and Comparative Example 3, by controlling the content of cyclic carbonate compounds, silane compounds containing carbon-carbon double bonds, and cyclic lithium borate compounds in the electrolyte within an appropriate range, it is possible to simultaneously achieve the cycle performance, storage performance, and DC impedance of the lithium secondary battery, thereby comprehensively improving the performance of the lithium secondary battery.

[0133] As can be seen from Examples 1 to 5, by controlling the mass content W3 of the first solvent, ethylene carbonate, to 3% to 20%, all lithium secondary batteries can have low DC impedance and excellent storage and cycle performance. The mass content W3 of ethylene carbonate in Comparative Example 3 was 2%, and as can be seen from the comparison between Examples 1 to 5 and Comparative Example 3, by controlling the mass content W3 of the first solvent, ethylene carbonate, to within the range of 3% to 20%, the DC impedance can be effectively reduced and the storage and cycle performance of the lithium secondary battery can be improved.

[0134] As can be seen from Examples 1, 6-9, by controlling the mass content W1 of the silane compound containing a carbon-carbon double bond to 0.01%-5%, lithium secondary batteries can all have low DC impedance and excellent storage and cycle performance.

[0135] As can be seen from Examples 1, 10-13, by controlling the mass content W2 of the cyclic lithium borate compound to 0.01%-3%, lithium secondary batteries can all have low DC impedance and excellent storage and cycle performance.

[0136] As can be seen from Examples 1, 14-17, lithium secondary batteries can all have low DC impedance and excellent storage and cycle performance by using various different types of first solvents (e.g., ethylene carbonate, fluoroethylene carbonate), or various different types of silane compounds containing carbon-carbon double bonds (e.g., tetravinylsilane, trivinylethylsilane, vinyltrimethylsilane), or various different types of cyclic lithium borate compounds (e.g., compounds in which Y1, Y2, Y3, and Y4 in formula I are all oxygen atoms, or compounds in which Y1 and Y2 in formula I are sulfur atoms and Y3 and Y4 are oxygen atoms).

[0137] As can be seen from Examples 1 and 18, by using different types of negative electrode active materials (e.g., artificial graphite, mesocarbon microbeads), lithium secondary batteries can all have low DC impedance and excellent storage and cycle performance.

[0138] It should be noted that this application is not limited to the embodiments described above. The embodiments described above are merely illustrative, and all embodiments having substantially the same technical idea and achieving the same function and effect within the scope of the technical solution of this application are included in the technical scope of this application. Furthermore, other forms that are constructed by adding various modifications to the embodiments that a person skilled in the art could conceive of, and by combining some of the components of the embodiments, are also included in the scope of this application, without departing from the gist of this application. [Explanation of Symbols]

[0139] 5 Secondary battery 51 cases 52 Electrode assembly 53 Cover Plate

Claims

1. The first solvent comprises a silane compound containing a carbon-carbon double bond and a cyclic lithium borate compound, wherein the first solvent comprises a cyclic carbonate compound, and the cyclic carbonate compound comprises at least one of ethylene carbonate, fluoroethylene carbonate, and propylene carbonate. An electrolyte for a lithium secondary battery, characterized in that, on a basis of the total mass of the electrolyte, the mass content W3 of the cyclic carbonate compound, the mass content W1 of the silane compound containing a carbon-carbon double bond, and the mass content W2 of the cyclic lithium borate compound satisfy the condition 0.001 ≤ (W1 + W2) / W3 ≤ 2.

67.

2. The electrolyte according to claim 1, characterized in that, on a basis of the total mass of the electrolyte, the mass content W3 of the cyclic carbonate compound, the mass content W1 of the silane compound containing a carbon-carbon double bond, and the mass content W2 of the cyclic lithium borate compound satisfy 0.005 ≤ (W1 + W2) / W3 ≤ 2.

3. The electrolyte according to claim 1 or 2, characterized in that the silane compound containing the carbon-carbon double bond comprises at least one of tetravinylsilane, trivinylethylsilane, divinyldiethylsilane, and vinyltrimethylsilane.

4. The electrolyte according to any one of claims 1 to 3, characterized in that the silane compound containing the carbon-carbon double bond contains tetravinylsilane.

5. The cyclic lithium borate compound includes a compound having the structure shown in formula I, 【Chemistry 1】 In the formula, Y １ , Y ２ , Y ３ , Y ４ The electrolyte according to any one of claims 1 to 4, characterized in that each of them independently contains at least one of an oxygen atom and a sulfur atom.

6. The aforementioned lithium cyclic borate compound 【Chemistry 2】 The electrolyte according to any one of claims 1 to 5, characterized by comprising at least one of the following.

7. The electrolyte according to any one of claims 1 to 6, characterized in that, on a total mass basis of the electrolyte, the mass content W1 of the silane compound containing the carbon-carbon double bond and the mass content W2 of the cyclic lithium borate compound satisfy 0.01 ≤ W1 / W2 ≤ 200.

8. The electrolyte according to any one of claims 1 to 7, characterized in that, on a total mass basis of the electrolyte, the mass content W1 of the silane compound containing the carbon-carbon double bond and the mass content W2 of the cyclic lithium borate compound satisfy 0.1 ≤ W1 / W2 ≤ 10.

9. The electrolyte according to any one of claims 1 to 8, characterized in that, on a total mass basis of the electrolyte, the mass content W1 of the silane compound containing the carbon-carbon double bond and the mass content W2 of the cyclic lithium borate compound satisfy 0.5 ≤ W1 / W2 ≤ 5.

10. The electrolyte according to any one of claims 1 to 9, characterized in that, on a basis of the total mass of the electrolyte, the mass content W3 of the cyclic carbonate compound satisfies 3% ≤ W3 ≤ 20%.

11. The electrolyte according to any one of claims 1 to 10, characterized in that, on a basis of the total mass of the electrolyte, the mass content W3 of the cyclic carbonate compound satisfies 5% ≤ W3 ≤ 20%.

12. The electrolyte according to any one of claims 1 to 11, characterized in that, on a basis of the total mass of the electrolyte, the mass content W1 of the silane compound containing the carbon-carbon double bond satisfies 0.01% ≤ W1 ≤ 5%.

13. The electrolyte according to any one of claims 1 to 12, characterized in that, on a total mass basis of the electrolyte, the mass content W1 of the silane compound containing the carbon-carbon double bond satisfies 0.01% ≤ W1 ≤ 3%.

14. The electrolyte according to any one of claims 1 to 13, characterized in that, on a basis of the total mass of the electrolyte, the mass content W2 of the cyclic lithium borate compound satisfies 0.01% ≤ W2 ≤ 3%.

15. The electrolyte according to any one of claims 1 to 14, characterized in that, on a basis of the total mass of the electrolyte, the mass content W2 of the cyclic lithium borate compound satisfies 0.1% ≤ W2 ≤ 2%.

16. The electrolyte comprises a second solvent, and the second solvent comprises a linear carbonate compound. The electrolyte according to any one of claims 1 to 15, characterized in that the linear carbonate compound comprises at least one of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, ethyl acetate, methyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

17. The electrolyte contains a lithium salt, and the lithium salt contains at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium fluorosulfonyl (perfluorobutylsulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide. The electrolyte according to any one of claims 1 to 16, characterized in that the concentration of the lithium salt in the electrolyte is 0.8 mol / L to 1.3 mol / L.

18. A lithium secondary battery characterized by comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte according to any one of claims 1 to 17.

19. The positive electrode sheet includes a positive current collector and a positive electrode material layer located on at least one side of the positive current collector, and the positive electrode material layer comprises Li ｄ [Ni ｘ Co ｙ X1 ｚ M1 １－ｘ－ｙ－ｚ O ２ , LiMn ２ O ４ , Li ２ MnO ３ ·(1-a)LiAO ２ , LiM2X2O ４ contains one or more of the above. In the formula, 0.1 ≤ d ≤ 1, X1 contains Mn and / or Al, M1 contains one or more of Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, Ti, 0 ≤ x < 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, x + y + z ≤ 1, A contains one or more of Ni, Co, Mn, 0 < a < 1, M2 contains one or more of Fe, Mn, Ni, Co, X2O ４ ｈ－ The lithium secondary battery according to claim 18, characterized in that X2 inside includes one or more of S, P, As, V, Mo, and W, and h = 2 or 3.

20. The positive electrode material layer is Li ｄ [Ni ｘ Co ｙ X1 ｚ M1 １－ｘ－ｙ－ｚ ]O ２ The lithium secondary battery according to claim 19, wherein the formula includes, where 0.1 ≤ d ≤ 1, X1 includes Mn and / or Al, M1 includes one or more of Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, Ti, and 0 ≤ x < 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, x + y + z ≤ 1.

21. The lithium secondary battery according to any one of claims 18 to 20, wherein the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer located on at least one side of the negative electrode current collector, and the negative electrode material layer includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, mesocarbon microbeads, silicon-based material, and tin-based material.

22. The lithium secondary battery according to claim 21, characterized in that the negative electrode material layer contains at least one of artificial graphite and natural graphite.

23. An electrical device characterized by comprising a lithium secondary battery according to any one of claims 18 to 22.

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