Electrolyte and lithium ion battery

Abstract

This application provides an electrolyte and a lithium-ion battery. The electrolyte includes an electrolyte, a solvent, and an additive. The electrolyte includes lithium bis(fluorosulfonyl)imide, with a mass percentage of lithium bis(fluorosulfonyl)imide of A% (based on the mass of the electrolyte), 8≤A≤20; the additive includes a compound represented by Formula I, with a mass percentage of the compound represented by Formula I of B% (based on the mass of the electrolyte), 0.1≤B≤5. The electrolyte includes LiFSI and the compound represented by Formula I, and the mass percentages of LiFSI and the compound represented by Formula I are regulated within the scope of this application. The synergistic effect of the two improves the high-temperature performance of the lithium-ion battery, reduces the occurrence of exothermic reactions during the evolution of thermal runaway in the lithium-ion battery, and improves the thermal stability of the lithium-ion battery. #imgabs0#

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to an electrolyte and a lithium-ion battery. Background Art

[0002] Lithium-ion batteries are widely used in consumer electronics, power batteries, and energy storage batteries due to their advantages such as high energy density, long cycle life, and lack of memory effect. However, safety issues such as fire and explosion caused by lithium-ion batteries have gradually attracted social attention. In particular, the development trend of large-capacity and large-size lithium-ion batteries such as 280Ah has exacerbated the occurrence of safety accidents. Thermal runaway is a common and key factor in lithium-ion battery safety issues. When the heat generation rate in the lithium-ion battery exceeds the heat dissipation rate, thermal runaway is triggered, and side reactions spontaneously increase the temperature of the lithium-ion battery. At relatively high temperatures, severe redox exothermic reactions may be triggered, generating large amounts of heat and causing runaway and dangerous conditions. Therefore, how to reduce the occurrence of exothermic reactions during the evolution of thermal runaway and improve the safety performance of lithium-ion batteries has become an urgent problem to be solved. Summary of the Invention

[0003] The purpose of this application is to provide an electrolyte and a lithium-ion battery that improve the high-temperature performance of the lithium-ion battery while reducing the occurrence of exothermic reactions during the evolution of thermal runaway, thereby improving the thermal stability of the lithium-ion battery and thus improving the safety performance of the lithium-ion battery. The specific technical solution is as follows:

[0004] A first aspect of the present application provides an electrolyte, comprising an electrolyte, a solvent, and an additive, wherein the electrolyte comprises lithium bis(fluorosulfonyl)imide, wherein the mass percentage of the lithium bis(fluorosulfonyl)imide is A%, 8≤A≤20, preferably, 10≤A≤15, based on the mass of the electrolyte; and the additive comprises a compound represented by formula I:

[0005] ,

[0006] R1 and R2 are each independently selected from phenyl, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C2-C6 alkenyl, and when substituted, the substituent is selected from halogen; based on the mass of the electrolyte, the mass percentage of the compound of formula I is B%, 0.1≤B≤5, preferably, 0.5≤B≤2.

[0007] In some embodiments of the present application, the compound represented by Formula I includes at least one of the following compounds:

[0008] .

[0009] In some embodiments of the present application, the additive includes a second additive selected from at least one of vinyl sulfate and methylene disulfonate, and the mass percentage of the second additive based on the mass of the electrolyte is C%, and 0.5≤C≤3. In some embodiments of the present application, the electrolyte includes an auxiliary salt selected from at least one of LiPF6, LiSO3CF3, LiBF4, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2, and LiPF4C2O4, and the mass percentage of the auxiliary salt based on the mass of the electrolyte is D%, and 0.1≤D≤2.

[0010] In some embodiments of the present application, the solvent includes a cyclic organic solvent and / or a chain organic solvent, the cyclic organic solvent is selected from at least one of ethylene carbonate and propylene carbonate, and the chain organic solvent is selected from at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate and methylpropyl carbonate.

[0011] The second aspect of the present application provides a lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte provided by the first aspect of the present application, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector, the negative electrode material layer comprises a negative electrode active material, and the negative electrode active material comprises graphite; the lithium-ion battery satisfies the relationship: 0.82≤(A+X) / B 2 ≤2050, preferably, 5≤(A+X) / B 2 ≤175, where X is the surface density of the single-sided negative electrode material layer, in mg / cm 2 .

[0012] In some embodiments of the present application, 5≤X≤12, preferably, 7≤X≤9.

[0013] Beneficial effects of this application:

[0014] The present application provides an electrolyte and a lithium ion battery. The electrolyte includes an electrolyte, a solvent, and an additive. The electrolyte includes lithium bis(fluorosulfonyl)imide, and the mass percentage of lithium bis(fluorosulfonyl)imide based on the mass of the electrolyte is A%, 8≤A≤20; the additive includes a compound represented by Formula I, and the mass percentage of the compound represented by Formula I based on the mass of the electrolyte is B%, 0.1≤B≤5. The electrolyte includes LiFSI and the compound represented by Formula I, and the mass percentages of LiFSI and the compound represented by Formula I are regulated within the scope of the present application. The synergistic effect of the two is beneficial to improving the high-temperature performance of the lithium ion battery, while also helping to reduce the occurrence of exothermic reactions during the evolution of thermal runaway of the lithium ion battery, thereby improving the thermal stability of the lithium ion battery.

[0015] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0017] Figure 1 The differential scanning calorimetry (DSC) exothermic test curves of Examples 1-3 of the present application are as follows;

[0018] Figure 2 The differential scanning calorimetry (DSC) exothermic test curves of Comparative Examples 1-4 of the present application;

[0019] Figure 3 This is a diagram showing the high temperature cycle performance test results of Examples 1-3 and Comparative Examples 1-4 of the present application. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings of this application to clearly and completely describe the technical solutions in this application. Obviously, the embodiments described are only some of the embodiments of this application, rather than all of them. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0021] A first aspect of the present application provides an electrolyte, comprising an electrolyte, a solvent, and an additive. The electrolyte comprises lithium bis(fluorosulfonyl)imide (LiFSI). Based on the mass of the electrolyte, the mass percentage of lithium bis(fluorosulfonyl)imide is A%, 8≤A≤20, preferably, 10≤A≤15. For example, the mass percentage of lithium bis(fluorosulfonyl)imide may be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a range consisting of any two of these values. The additive comprises a compound represented by Formula I:

[0022] ,

[0023] R1 and R2 are each independently selected from phenyl, substituted or unsubstituted C1-C6 alkyl, or substituted or unsubstituted C2-C6 alkenyl. When substituted, the substituent is selected from halogen, preferably, the substituent is selected from fluorine atom. Based on the mass of the electrolyte, the mass percentage of the compound represented by Formula I is B%, 0.1≤B≤5, preferably, 0.5≤B≤2. For example, the mass percentage of the compound represented by Formula I can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range consisting of any two of these values.

[0024] LiFSI has good thermal stability and high ion conductivity. It is currently used primarily as an electrolyte additive, generally at a level of 3% to 5%, to improve the high-temperature performance of lithium-ion batteries. However, despite its inherent thermal stability, LiFSI can react with charged negative electrode materials (such as lithiated graphite) at high temperatures during lithium-ion battery operation if extreme failure occurs, releasing significant heat and triggering thermal runaway, posing a risk of explosion.

[0025] The inventors have found that the electrolyte includes LiFSI and the compound shown in Formula I, and the mass percentage of LiFSI and the compound shown in Formula I is regulated within the scope of the present application. The synergistic effect of the two is beneficial to improving the high-temperature performance of the lithium-ion battery, reducing the occurrence of exothermic reactions during the evolution of thermal runaway, and improving the thermal stability of the lithium-ion battery. On the one hand, the electrolyte includes LiFSI as the main electrolyte, with a mass percentage of 8% to 20% in the electrolyte, which is beneficial for improving the thermal stability of the electrolyte itself and the high-temperature performance of the lithium-ion battery. In addition, when the compound represented by Formula I is added to the electrolyte, at the early stage of thermal runaway evolution of the lithium-ion battery, at a temperature greater than or equal to 150°C, the compound represented by Formula I triggers a ring-opening polymerization reaction through lithiated graphite to form a polymer, forming a highly thermally stable polymer film on the surface of the negative electrode, thereby targetedly repairing the solid electrolyte interface film (SEI film) that breaks with increasing temperature and effectively suppressing the exothermic reaction between LiFSI and lithiated graphite, thereby reducing the occurrence of exothermic reactions during the thermal runaway evolution process, effectively raising the critical temperature for thermal runaway, improving the thermal stability of the lithium-ion battery, and thus improving the safety performance of the lithium-ion battery. "High temperature" as used in this application refers to a temperature greater than or equal to 45°C.

[0026] If the value of A% is too small, for example, less than 8%, the lithium salt concentration in the electrolyte is too low, which is not conducive to lithium ion transmission; when the value of A is too large, for example, greater than 20%, the lithium salt concentration is too high, which will increase the overall viscosity of the electrolyte and affect the cycle performance of the lithium ion battery. When the value of B is too small, for example, less than 0.1%, the amount of the compound shown in Formula I added is too small, which cannot effectively inhibit the exothermic reaction between LiFSI and lithiated graphite, which is not conducive to improving the thermal stability of the lithium ion battery; when the value of B is too large, for example, greater than 5%, the amount of the compound shown in Formula I added to the electrolyte is too large, which will lead to excessive viscosity of the electrolyte, which is not conducive to the active metal ions (such as Li + ) transmission, affecting the cycle performance of lithium-ion batteries.

[0027] In some embodiments of the present application, the compound represented by Formula I includes at least one of the following compounds:

[0028] .

[0029] The electrolyte includes the compound represented by formula I within the above range, which is conducive to the compound represented by formula I triggering a ring-opening polymerization reaction through lithiated graphite at a temperature greater than or equal to 150°C, performing ring-opening polymerization to form a polymer, and forming a polymer film with high thermal stability on the surface of the negative electrode, thereby targetedly repairing the solid electrolyte interface film (SEI film) that breaks with increasing temperature, and effectively inhibiting the exothermic reaction between LiFSI and lithiated graphite, thereby reducing the occurrence of exothermic reaction during the evolution of thermal runaway, effectively increasing the critical temperature for thermal runaway, and further improving the thermal stability of the lithium-ion battery.

[0030] Preferably, when the compound represented by Formula I contains a halogen group, such as a F group, it can participate in the formation of the SEI film, making the SEI film rich in fluorides, such as LiF. LiF has a high Young's modulus, high surface energy, and abundant lithium ion flux. It can effectively disperse local current, regulate lithium nucleation in a uniform and low-volume manner, and reduce the tendency of moss-like dendrite growth, thereby improving the cycling stability and safety of lithium-ion batteries and extending their lifespan.

[0031] Preferably, when the compound represented by Formula I contains an alkenyl group, a polymerization reaction can occur on the electrode surface. During the initial charging of a lithium-ion battery, the double bonds in the additive are catalytically opened on the electrode surface, causing polymerization to form a protective polymer film, which is part of the SEI membrane. This film effectively prevents direct contact between the electrolyte and the electrode material, reduces side reactions in the electrode material, and improves the safety performance of the lithium-ion battery.

[0032] Preferably, when the compound shown in Formula I contains a phenyl group, the phenyl group has a conjugated π electron structure and can interact with the electrode surface in a π-π manner. This interaction can enhance the adsorption of the additive on the electrode surface, allowing the additive to better perform its function. Taking the graphite negative electrode as an example, the additive containing the phenyl group can be tightly adsorbed on the graphite surface. During the charge and discharge process of the lithium ion battery, even if the electrolyte is affected by factors such as internal battery pressure and temperature changes, the additive can also firmly adhere to the electrode surface, stabilize the electrode-electrolyte interface, reduce side reactions at the interface, and thus improve the cycle life and safety performance of the lithium ion battery.

[0033] In some embodiments of the present application, the additive includes a second additive selected from at least one of diethylenetriaminetetradecanoate (DTD) and methylene dimethyl disulfonate (MMDS). The weight percentage of the second additive, based on the weight of the electrolyte, is C%, with 0.5 ≤ C ≤ 3. For example, the weight percentage of the second additive can be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, or a range consisting of any two of these values. The second additive has a lower LUMO energy level, which makes it easier for it to be electron-reduced and form a film on the graphite electrode side. For example, DTD can coordinate with lithium salts and alkali metal ions in the solvent to form stable complexes in the electrolyte. These complexes then form part of the solid electrolyte interface film (SEI film) on the electrode surface or modify and supplement the SEI film. MMDS can participate in the formation and stabilization of the SEI film on the electrode surface, improve the thermal stability of the electrolyte, reduce its decomposition rate at high temperatures, and enhance the structural stability of the electrode material at high temperatures, reducing the adverse effects of high temperatures on battery performance. In short, both are conducive to further increasing the stability of the SEI film, so that the SEI film can effectively inhibit the peeling of graphite, thereby improving the stability of the graphite negative electrode and achieving stable and reversible Li + Deintercalation further improves the thermal stability of lithium-ion batteries.

[0034] In some embodiments of the present application, the electrolyte includes an auxiliary salt, and the auxiliary salt is selected from at least one of LiPF6, LiSO3CF3, LiBF4, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2 and LiPF4C2O4. Based on the mass of the electrolyte, the mass percentage of the auxiliary salt is D%, and 0.1≤D≤2. For example, the mass percentage of the auxiliary salt can be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or a range consisting of any two values ​​therein. The electrolyte includes an auxiliary salt within the scope of this application and regulates the mass percentage of the auxiliary salt within this range, which is conducive to assisting the formation of the SEI film and further improving the cycle performance of the lithium-ion battery.

[0035] In some embodiments of the present application, the solvent includes a cyclic organic solvent and / or a chain organic solvent, the cyclic organic solvent being selected from at least one of ethylene carbonate and propylene carbonate, and the chain organic solvent being selected from at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and methylpropyl carbonate. The electrolyte including a solvent within the above range can impart an appropriate viscosity, high ionic conductivity, and good electrochemical stability to the electrolyte, further improving the high-temperature performance and thermal stability of the lithium-ion battery.

[0036] In some embodiments of the present application, the electrolyte comprises lithium bis(fluorosulfonyl)imide, the compound represented by Formula I, and the aforementioned solvent. The weight percentages of lithium bis(fluorosulfonyl)imide and the compound represented by Formula I are as described above, and the weight percentage of the solvent is 75% to 91%, based on the mass of the electrolyte. The electrolyte comprising lithium bis(fluorosulfonyl)imide, the compound represented by Formula I, and the aforementioned solvent, when applied to a lithium-ion battery, is beneficial for improving the high-temperature performance and thermal stability of the lithium-ion battery.

[0037] In some embodiments of the present application, the electrolyte comprises lithium bis(fluorosulfonyl)imide, a compound represented by Formula I, a second additive, and the aforementioned solvent. The weight percentages of lithium bis(fluorosulfonyl)imide, the compound represented by Formula I, and vinylene carbonate are as described above, and the weight percentage of the solvent is 72% to 91%, based on the mass of the electrolyte. The electrolyte comprising lithium bis(fluorosulfonyl)imide, the compound represented by Formula I, vinylene carbonate, and the aforementioned solvent, when applied to a lithium-ion battery, is beneficial for further improving the high-temperature performance and thermal stability of the lithium-ion battery.

[0038] In some embodiments of the present application, the electrolyte comprises lithium bis(fluorosulfonyl)imide, a compound represented by Formula I, a secondary salt, and the aforementioned solvent. The weight percentages of lithium bis(fluorosulfonyl)imide, the compound represented by Formula I, and the secondary salt are as described above, and the weight percentage of the aforementioned solvent is 73% to 91%, based on the mass of the electrolyte. The electrolyte comprising lithium bis(fluorosulfonyl)imide, the compound represented by Formula I, the secondary salt, and the aforementioned solvent, when applied to a lithium-ion battery, is beneficial for further improving the high-temperature performance and thermal stability of the lithium-ion battery.

[0039] In some embodiments of the present application, the electrolyte comprises lithium bis(fluorosulfonyl)imide, a compound represented by Formula I, a second additive, a secondary salt, and the aforementioned solvent. The weight percentages of lithium bis(fluorosulfonyl)imide, the compound represented by Formula I, vinylene carbonate, and the secondary salt are as described above, and the weight percentage of the aforementioned solvent is 70% to 91%, based on the mass of the electrolyte. The electrolyte comprising lithium bis(fluorosulfonyl)imide, the compound represented by Formula I, vinylene carbonate, the secondary salt, and the aforementioned solvent, when applied to a lithium-ion battery, is beneficial for further improving the high-temperature performance and thermal stability of the lithium-ion battery.

[0040] In some embodiments of the present application, the additive further comprises vinylene carbonate (VC), and the mass percentage of vinylene carbonate is 0.5% to 5% based on the mass of the electrolyte. For example, the mass percentage of vinylene carbonate can be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, or a range consisting of any two of these values. In addition to the electrolyte comprising LiFSI and the compound represented by Formula 1, VC is further introduced, and the mass percentage of VC is regulated within the scope of the present application. Compared to other additives, VC can be reduced to form a stable SEI film on the negative electrode surface before other additives, mitigating the occurrence of thermal failure in the early stages of thermal runaway, further suppressing the exothermic reaction between LiFSI and lithiated graphite, and further improving the high-temperature performance and thermal stability of the lithium-ion battery.

[0041] The second aspect of the present application provides a lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte provided by the first aspect of the present application, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector, the negative electrode material layer comprises a negative electrode active material, and the negative electrode active material comprises graphite; the lithium-ion battery satisfies the relationship: 0.82≤(A+X) / B 2 ≤2050, preferably, 5≤(A+X) / B 2 ≤175, where X is the surface density of the single-sided negative electrode material layer, in mg / cm 2 For example, (A+X) / B 2The value of can be 0.82, 1, 5, 10, 100, 175, 200, 500, 800, 1000, 1200, 1500, 1800, 2000, 2050, or a range consisting of any two of these values. It should be noted that the "areal density of a single-sided negative electrode material layer" described in this application refers to the mass of the negative electrode material layer per unit area on one side of the negative electrode current collector.

[0042] The unit of the surface density of the single-sided negative electrode material layer is mg / cm 2 However, this application does not limit the unit of the surface density of the single-sided negative electrode material layer. For example, the unit of the surface density of the single-sided negative electrode material layer can also be g / m 2 、g / cm 2 , mg / m 2 When the unit of the surface density of the single-sided negative electrode material layer is mg / cm 2 If the unit is other than mg / cm, the unit should be converted to mg / cm 2 When the value of the formula obtained is between 0.82 and 2050, it is also within the protection scope of this application.

[0043] After a lithium-ion battery is charged, the negative electrode graphite is embedded with lithium to become lithiated graphite. The LiFSI in the electrolyte reacts with the lithiated graphite to generate heat. The inventors have discovered that by using the electrolyte provided by the first aspect of this application and regulating the values ​​of A, B, and X to satisfy the above relationship, this not only improves the high-temperature performance of the lithium-ion battery but also helps suppress the exothermic reaction between LiFSI and lithiated graphite, thereby reducing the occurrence of exothermic reactions during the evolution of thermal runaway. This effectively raises the critical temperature for thermal runaway and improves the thermal stability of the lithium-ion battery.

[0044] When (A+X) / B 2 When the value of is greater than 2050, it indicates that the mass percentage of LiFSI and the density of the negative electrode material layer are large, that is, the heat generated by the reaction between LiFSI and the negative electrode active material lithiated graphite is large, while the mass percentage of the compound represented by Formula I is relatively small, which cannot effectively inhibit the exothermic reaction between LiFSI and lithiated graphite, which is not conducive to improving the thermal stability of the lithium-ion battery; when (A+X) / B 2 When the value is less than 0.82, it indicates that the mass percentage of the compound represented by Formula I is relatively large, which is beneficial to suppress the exothermic reaction between LiFSI and lithiated graphite. However, if the amount of the compound represented by Formula I is too large, the viscosity of the electrolyte will be too large, which will affect the transport of active metal ions (such as Li + ), and affects the capacity of lithium-ion batteries.

[0045] In some embodiments of the present application, 5 mg / cm 2 ≤X≤12mg / cm 2, preferably, 7 mg / cm 2 ≤X≤9mg / cm 2 For example, the surface density of a single-sided negative electrode material layer can be 5 mg / cm 2 , 6mg / cm 2 , 7mg / cm 2 , 8mg / cm 2 , 9mg / cm 2 、10mg / cm 2 、11mg / cm 2 , 12mg / cm 2 By regulating the surface density of the single-sided negative electrode material layer within the scope of the present application, it is beneficial to reduce the exothermic reaction between LiFSI and lithiated graphite and improve the thermal stability of the lithium-ion battery.

[0046] In the present application, the negative electrode active material includes graphite, and the graphite is selected from at least one of natural graphite and artificial graphite. In some embodiments of the present application, the negative electrode active material is entirely selected from graphite. In other embodiments of the present application, the negative electrode active material may also include but is not limited to silicon-based materials, soft carbon, hard carbon, or mesophase microcarbon beads, and the silicon-based material may include but is not limited to at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, or silicon alloys.

[0047] In the present application, the negative electrode plate includes a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector. The above-mentioned "negative electrode material layer is arranged on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be arranged on one surface of the negative electrode current collector along the thickness direction of itself, or can be arranged on two surfaces of the negative electrode current collector along the thickness direction of itself. It should be noted that the "surface" here can be the entire area of ​​the surface of the negative electrode current collector, or it can be a partial area of ​​the surface of the negative electrode current collector. This application has no special restrictions, as long as the purpose of this application can be achieved. This application has no special restrictions on the negative electrode current collector, as long as the purpose of this application can be achieved. For example, the negative electrode current collector can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel or foam copper, aluminum foil or a composite negative electrode current collector. The composite negative electrode current collector may comprise a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The polymer substrate may be made of, but not limited to, at least one of polypropylene (PP), polyethylene terephthalate (PET), or polybutylene terephthalate (PBT). The metal layer may be made of, but not limited to, at least one of copper, a copper alloy, nickel, or a nickel alloy. The thickness of the negative electrode material layer and the negative electrode current collector are not particularly limited in this application, as long as they can achieve the objectives of this application. For example, the thickness of a single-sided negative electrode material layer is 30 to 70 μm, and the thickness of the negative electrode current collector is 3 to 10 μm.

[0048] This application does not specifically limit the types of negative electrode conductive agents and negative electrode binders, as long as they can achieve the objectives of this application. For example, the negative electrode conductive agent may include, but is not limited to, at least one of superconducting carbon black (Super P), acetylene black, Ketjen black, carbon nanotubes, graphene, or carbon fibers. The carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or nanofibers. For example, the negative electrode binder may include, but is not limited to, 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), or carboxymethyl chitosan (CMCS). This application does not specifically limit the mass ratio of the negative electrode active material, negative electrode conductive agent, and negative electrode binder in the negative electrode material layer. Those skilled in the art may select the ratio based on actual needs, as long as it can achieve the objectives of this application. In some embodiments of this application, the negative electrode material layer may also include a thickener, which may include, but is not limited to, sodium carboxymethyl cellulose (CMC). The present application does not particularly limit the mass ratio of the negative electrode active material, negative electrode conductive agent, negative electrode binder, and thickener in the negative electrode material layer. Those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0049] In this application, there are no particular limitations on the method for preparing the negative electrode sheet, as long as the objectives of this application can be achieved. For example, the negative electrode sheet can be prepared by the following method: negative electrode active material, negative electrode conductive agent, and negative electrode binder are added to deionized water and stirred uniformly to obtain a negative electrode slurry with a solid content of 45 wt% to 70 wt%. The negative electrode slurry is evenly coated on both surfaces of the negative electrode current collector and dried to obtain a negative electrode sheet coated with a negative electrode material layer on both sides. The negative electrode sheet is then cold pressed and cut to obtain the negative electrode sheet.

[0050] In the present application, a lithium-ion battery includes a positive electrode plate, which includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be disposed on one surface of the positive electrode current collector along its own thickness direction, or it can be disposed on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the positive electrode current collector surface or a partial area of ​​the positive electrode current collector surface. This application is not particularly limited, as long as the purpose of this application can be achieved. The positive electrode material layer includes a positive electrode active material. This application does not specifically limit the positive electrode active material, as long as it can achieve the objectives of this application. For example, the positive electrode active material may include, but is not limited to, at least one of lithium nickel cobalt manganese oxide (such as NCM811, NCM712, NCM622, NCM523, or NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, a lithium-rich manganese-based material, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium iron manganese phosphate, or lithium titanate. This application does not specifically limit the positive electrode current collector, as long as it can achieve the objectives of this application. For example, the positive electrode current collector may be aluminum foil, aluminum alloy foil, or a composite positive electrode current collector. The composite positive electrode current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. The polymer base layer may include, but is not limited to, at least one of polypropylene (PP), polyethylene terephthalate (PET), or polybutylene terephthalate (PBT). The metal layer may include, but is not limited to, at least one of aluminum, an aluminum alloy, nickel, or a nickel alloy. The present application has no particular limitation on the thickness of the positive electrode material layer and the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the single-sided positive electrode material layer is 50 μm to 250 μm, and the thickness of the positive electrode current collector is 7 μm to 15 μm.

[0051] The positive electrode material layer may also include a positive electrode conductive agent and a positive electrode binder. This application does not particularly limit the types of the positive electrode conductive agent and the positive electrode binder, as long as the purpose of this application can be achieved. For example, the positive electrode conductive agent may include, but is not limited to, at least one of superconducting carbon black (Super P), acetylene black, Ketjen black, carbon nanotubes, graphene, or carbon fibers. For example, the positive electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or fluorine-containing acrylate resin. This application does not particularly limit the mass ratio of the positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application can be achieved.

[0052] In this application, there are no particular restrictions on the method for preparing the positive electrode sheet, as long as the objectives of this application can be achieved. For example, the positive electrode sheet can be prepared by the following method: a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder are mixed, N-methylpyrrolidone (NMP) is added, and the mixture is stirred uniformly to obtain a positive electrode slurry having a solid content of 50 wt% to 85 wt%. The positive electrode slurry is evenly coated on both surfaces of the positive electrode current collector, and after drying, a positive electrode sheet coated on both sides with a positive electrode material layer is obtained. The positive electrode sheet is then cold pressed and cut to obtain the positive electrode sheet.

[0053] The lithium-ion battery of the present application also includes a diaphragm to separate the positive electrode plate and the negative electrode plate, prevent internal short circuit of the battery, allow electrolyte ions to pass freely, and do not affect the electrochemical charge and discharge process. The present application has no particular restrictions on the type of diaphragm, and any porous structure diaphragm with good chemical stability and mechanical stability can be selected. For example, the material of the diaphragm may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The type of diaphragm may include but is not limited to at least one of woven membrane, non-woven membrane (non-woven fabric), microporous membrane, composite membrane, rolled membrane or spinning membrane. The diaphragm can be a single-layer film or a multi-layer composite film. In the present application, the thickness of the diaphragm is not particularly limited, as long as the purpose of the present application can be achieved, for example, the thickness can be 5μm to 20μm.

[0054] In the present application, the lithium-ion battery also includes a shell for accommodating the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte, as well as other components known in the field of lithium-ion batteries. This application does not limit the above-mentioned other components. This application has no special restrictions on the shell, and it can be a shell known in the art, as long as it can achieve the purpose of this application. For example, the shell can be a hard shell or a flexible shell. The material of the hard shell can be metal. This application does not limit the type of metal. A metal hard shell known in the art can be used, as long as it can achieve the purpose of this application. The flexible shell can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0055] The preparation process of the lithium-ion battery of the present application is well known to those skilled in the art and is not particularly limited in the present application. For example, the preparation process of the lithium-ion battery may include but is not limited to the following steps: stacking the positive electrode sheets, the separator and the negative electrode sheets in order, and winding, folding and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a lithium-ion battery. Alternatively, stacking the positive electrode sheets, the separator and the negative electrode sheets in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly with a stacked structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a lithium-ion battery. In addition, as needed, overcurrent protection elements, guide plates, etc. may be placed in the shell to prevent pressure rise and overcharge and discharge inside the lithium-ion battery.

[0056] The batteries of the present application may include battery cells, battery modules, and battery packs. Battery cells can be assembled into battery modules, which can contain one or more battery cells. A person skilled in the art can select the specific number based on the application and capacity of the battery module. The battery modules of the present application can also be assembled into battery packs, which can contain one or more battery modules. A person skilled in the art can select the specific number based on the application and capacity of the battery pack.

[0057] Example

[0058] The following examples and comparative examples are provided to further illustrate the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are by weight. In the following examples and comparative examples, all reagents, materials, and instruments used are commercially available unless otherwise specified.

[0059] Test methods and equipment:

[0060] High temperature cycle performance test

[0061] The lithium-ion battery was placed in a 45°C constant temperature chamber and allowed to rest for 4 hours. The battery was then charged at a constant current of 1C to a voltage of 3.65V. The battery was then charged at a constant voltage of 3.65V to a current of 0.05C. The battery was then discharged at a constant current of 1C to a voltage of 2.00V. The initial discharge capacity was recorded as C1. This constituted one charge-discharge cycle. The above charge-discharge cycle was repeated 500 times, and the discharge capacity after the 500th cycle was recorded as C2. The charge-discharge cycle test instrument was a Xinwei BTS.

[0062] 45℃ capacity retention rate (%) = C2 / C1×100%; the high-temperature cycle performance of lithium-ion batteries is evaluated by the 45℃ capacity retention rate. The greater the capacity retention rate, the better the high-temperature cycle performance of the lithium-ion battery.

[0063] High temperature storage performance test

[0064] The lithium-ion battery was placed in a 25°C environment and charged at a constant current of 1C to 3.65V, then charged at a constant voltage of 3.65V to a current of 0.05C. The thickness of the lithium-ion battery was measured and recorded as D1. The lithium-ion battery was then placed in a 60°C explosion-proof oven and left to stand for 30 days. The lithium-ion battery was taken out and the thickness of the battery was measured again after it was completely cooled and recorded as D2. The thickness change rate .

[0065] Heat release test

[0066] The lithium-ion battery was placed at 25°C and charged at a constant current of 1C to 3.65 V. It was then charged at a constant voltage of 3.65 V to a current of 0.05C, bringing the battery to a full charge. The battery was then disassembled in an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), and the negative electrode sheet was removed and cut. 3 mg of the negative electrode sheet and 5 μl of the corresponding electrolyte were weighed and placed in a DSC high-pressure crucible (27 μl, NETZSCH). The crucible was then sealed using a press to obtain the sample. The sample was then subjected to differential scanning calorimetry (DSC) using a NETZSCH DSC214 differential scanning calorimeter. The temperature was increased from 25°C to 400°C at a rate of 10°C / min. The main exothermic peak temperature was recorded, and the heat released from 150°C to 350°C was calculated by calculating the peak area. The larger the value of the main exothermic peak temperature, the higher the temperature point at which thermal runaway occurs, and the later the point at which thermal runaway occurs, that is, the better the thermal stability.

[0067] Example 1-1

[0068] <Preparation of Electrolyte>

[0069] In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 32:4:52.2 to form a base solvent. The electrolyte, lithium bis(fluorosulfonyl)imide (LiFSI), the compound represented by Formula 1-1, and vinylene carbonate were then added to the base solvent and mixed uniformly to form an electrolyte. Based on the mass of the electrolyte, the mass percentage of LiFSI was 8%, the mass percentage of the compound represented by Formula 1-1 was 1.3%, and the mass percentage of vinylene carbonate was 2.5%. The balance was the base solvent, with the mass percentage of EC being 32%, the mass percentage of PC being 4%, and the mass percentage of EMC being 52.2%.

[0070] <Preparation of negative electrode sheet>

[0071] The negative electrode active material artificial graphite, conductive agent Super P, binder sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) were mixed in a mass ratio of 95:1.5:1.5:2, and deionized water was added as a solvent to prepare a slurry with a solid content of 49wt%. After stirring evenly with a vacuum mixer, the negative electrode slurry was obtained. The negative electrode slurry was evenly coated on both surfaces of a negative electrode current collector copper foil with a thickness of 9μm, dried at 85℃ and cold pressed to obtain a negative electrode sheet with a double-sided negative electrode material layer. The surface density of the single-sided negative electrode material layer is 8mg / cm 2 The thickness of the single-sided negative electrode material layer is 50 μm, and then it is trimmed, cut into pieces, and divided into strips. After dividing into strips, it is dried at 85°C under vacuum conditions for 4 hours, and the tabs are welded to obtain negative electrode sheets with specifications of 660 mm × 59 mm for use.

[0072] <Preparation of positive electrode sheet>

[0073] The positive electrode active material lithium iron phosphate (LiFePO4), the positive electrode conductive agent Super P and the positive electrode binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96:2:2, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 55wt%. After vacuum stirring, the positive electrode slurry was obtained. The positive electrode slurry was evenly coated on both surfaces of the positive electrode current collector aluminum foil with a thickness of 12μm, dried at 85℃ and cold pressed to obtain a positive electrode sheet with a double-sided positive electrode material layer. Among them, the surface density of the single-sided positive electrode material layer is 17.5mg / cm 2 The thickness of the single-sided positive electrode material layer is 76.5μm. The process is then trimmed, cut, and slit. After slitting, the strips are dried at 85°C for 4 hours under vacuum conditions, and the tabs are welded to obtain positive electrode sheets with a size of 540mm×55mm for later use.

[0074] <Preparation of Separator>

[0075] A 16-µm-thick polypropylene (PP) porous membrane (provided by Shenzhen Xingyuan Materials Technology Co., Ltd.) was used as the separator.

[0076] <Preparation of lithium-ion batteries>

[0077] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, with the separator positioned between the positive and negative electrode sheets to act as a separator, and then wound to form an electrode assembly. The electrode assembly is then placed in an aluminum-plastic film packaging bag and vacuum-baked at 85°C for 48 hours. The prepared electrolyte is then injected, and the lithium-ion battery is produced through vacuum packaging, standing, formation, and shaping.

[0078] Example 1-2 to Example 1-5

[0079] Except that in <Preparation of Electrolyte>, the mass percentage of LiFSI A% is adjusted according to Table 1, the mass percentage of solvent EMC is changed accordingly, and the mass percentages of other components remain unchanged, the rest are the same as Example 1-1.

[0080] Example 1-6 to Example 1-11

[0081] Except that in <Preparation of Electrolyte>, the mass percentage of the compound represented by Formula I is adjusted by B% according to Table 1, the mass percentage of the solvent EMC is changed accordingly, and the mass percentages of the other components remain unchanged, the rest are the same as in Examples 1-3.

[0082] Example 1-12 to Example 1-14

[0083] Except that the type of the compound represented by Formula I was adjusted according to Table 1 in <Preparation of Electrolyte>, the rest was the same as in Example 1-3.

[0084] Example 1-15 to Example 1-18

[0085] Except that the surface density of the single-sided negative electrode material layer is adjusted according to Table 1 in the "Preparation of Negative Electrode Sheet", the rest is the same as that of Example 1-3.

[0086] Example 1-19 to Example 1-23

[0087] Except for adjusting the relevant parameters according to Table 1, wherein, when the mass percentage A% of LiFSI and the mass percentage B% of the compound represented by Formula I change, the mass percentage of the solvent EMC changes accordingly, and the mass percentages of the other components remain unchanged, the rest are the same as Examples 1-3.

[0088] Example 2-1 to Example 2-5

[0089] The preparation was the same as in Examples 1-3, except that the second additive was added and its mass percentage (C%) was adjusted according to Table 2 in the "Electrolyte Preparation" section. The mass percentage of the solvent EMC was changed accordingly, while the mass percentages of the other components remained unchanged. Here, vinyl sulfate is abbreviated as DTD, and methylene dimethyl sulfonate is abbreviated as MMDS.

[0090] Example 2-6 to Example 2-12

[0091] In the preparation of the electrolyte, the auxiliary salt was added according to Table 2 and the mass percentage of the auxiliary salt was adjusted to D%, the mass percentage of the solvent EMC was changed accordingly, and the mass percentages of the other components remained unchanged. The rest was the same as in Examples 1-3.

[0092] Example 2-13

[0093] Except that in <Preparation of Electrolyte>, auxiliary salt was added according to Table 2, the mass percentage of solvent EMC changed accordingly, and the mass percentages of other components remained unchanged, the rest were the same as Example 2-2.

[0094] Comparative Example 1-1 and Comparative Example 1-2

[0095] Except that in <Preparation of Electrolyte>, the mass percentage of LiFSI is adjusted A% according to Table 1, the mass percentage of solvent EMC is changed accordingly, and the mass percentages of other components remain unchanged, the rest are the same as Examples 1-3.

[0096] Comparative Examples 1-3

[0097] Except that all LiSFI was replaced by LiPF6 in <Preparation of Electrolyte>, the rest was the same as Example 1-3.

[0098] Comparative Examples 1-4

[0099] Except that the compound represented by formula I is not added in the preparation of the electrolyte, the mass percentage of the solvent EMC is changed accordingly, and the mass percentages of the other components remain unchanged, the rest are the same as in Examples 1-3.

[0100] Comparative Examples 1-5

[0101] Except that the mass percentage of the compound represented by Formula I is adjusted in <Preparation of Electrolyte>, the mass percentage of the solvent EMC is changed accordingly, and the mass percentages of the other components remain unchanged, the rest are the same as Examples 1-3.

[0102] The relevant parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 and 2.

[0103] Table 1

[0104]

[0105] Note: “ / ” in Table 1 indicates that there is no corresponding substance or parameter.

[0106] It can be seen from Examples 1-1 to 1-23 and Comparative Examples 1-1 to 1-5 that the electrolyte includes lithium bis(fluorosulfonyl)imide and the compound of Formula I within the scope of the present application, and regulating the mass percentage of lithium bis(fluorosulfonyl)imide and the compound of Formula I within the scope of the present application, the lithium-ion battery can have a higher 45°C capacity retention rate, a lower thickness change rate, a higher exothermic peak temperature and a lower heat release, indicating that the lithium-ion battery has good high-temperature performance and good thermal stability. The mass percentage of lithium bis(fluorosulfonyl)imide in Comparative Examples 1-1 and 1-2 is not within the scope of the present application, and its lithium-ion batteries have a lower 45°C capacity retention rate and a higher thickness change rate. The electrolyte of Comparative Example 1-3 is lithium hexafluorophosphate, and its lithium-ion battery has a lower 45°C capacity retention rate and a higher thickness change rate. Comparative Example 1-4 does not include the additive shown in Formula I, and its lithium-ion battery has a lower exothermic peak temperature and a higher heat release. From Figure 1 and Figure 2 It can be seen that the main exothermic peak temperature of Examples 1-3 is 284.5°C, and the main exothermic peak temperature of Comparative Examples 1-4 is 209.8°C. Figure 3 It can be seen that the cycle capacity retention rate of Comparative Examples 1-4 at 45°C is lower than that of Examples 1-3, and the capacity decay is faster. The mass percentage of the compound represented by Formula I in Comparative Examples 1-5 is not within the scope of this application, and the lithium-ion batteries thereof have a low 45°C capacity retention rate and a high thickness change rate. This indicates that the electrolyte does not meet the scope of this application, and the high-temperature cycle performance and thermal stability of the lithium-ion battery cannot be taken into account simultaneously.

[0107] The type of compound represented by Formula I generally affects the high-temperature performance and thermal stability of lithium-ion batteries. As can be seen from Examples 1-3, 1-12, and 1-14, lithium-ion batteries using compounds represented by Formula I within the scope of this application exhibit high capacity retention at 45°C, low thickness change, high exothermic peak temperature, and low heat release, demonstrating that lithium-ion batteries have both good high-temperature performance and good thermal stability.

[0108] The areal density of a single-sided negative electrode material layer typically affects the high-temperature performance and thermal stability of a lithium-ion battery. As can be seen from Examples 1-3, 1-15, and 1-18, by regulating the areal density of the single-sided negative electrode material layer within the scope of this application, the lithium-ion battery exhibits a higher 45°C capacity retention rate, a lower thickness change rate, a higher exothermic peak temperature, and a lower heat release, demonstrating that the lithium-ion battery has both good high-temperature performance and good thermal stability.

[0109] The relationship between the mass percentage of lithium bis(fluorosulfonyl)imide (A%), the mass percentage of the compound represented by Formula I (B%), and the surface density (X) of the single-sided negative electrode material layer will affect the high-temperature performance and thermal stability of the lithium-ion battery. As can be seen from Examples 1-1 to 1-23, by adjusting (A+X) / B 2 The value of is within the scope of the present application, and the lithium-ion battery has a higher 45°C capacity retention rate, a lower thickness change rate, a higher exothermic peak temperature and a lower heat release, indicating that the lithium-ion battery has good high-temperature performance and good thermal stability.

[0110] Table 2

[0111]

[0112] Note: “ / ” in Table 2 indicates that there is no corresponding substance or parameter.

[0113] The type and weight percentage of the second additive typically affect the high-temperature performance and thermal stability of lithium-ion batteries. As can be seen from Examples 1-3 and 2-1 to 2-5, when the electrolyte includes the second additive within the scope of this application and the weight percentage of the second additive is adjusted within the scope of this application, the lithium-ion batteries exhibit high 45°C capacity retention, low thickness change, high exothermic peak temperature, and low heat release, demonstrating that the lithium-ion batteries have good high-temperature performance and good thermal stability.

[0114] The type and mass percentage of auxiliary salts generally affect the high-temperature performance and thermal stability of lithium-ion batteries. As can be seen from Examples 1-3, 2-2, 2-6, and 2-13, when the electrolyte includes auxiliary salts within the scope of this application and the mass percentage of the auxiliary salts is adjusted within the scope of this application, the lithium-ion batteries exhibit high 45°C capacity retention, low thickness change, high exothermic peak temperature, and low heat release, demonstrating that the lithium-ion batteries have good high-temperature performance and good thermal stability.

[0115] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein: The electrolyte comprises an electrolyte, a solvent and an additive, wherein the electrolyte comprises lithium bis(fluorosulfonyl)imide, and the mass percentage of the lithium bis(fluorosulfonyl)imide is A%, 8≤A≤20 based on the mass of the electrolyte; The additive includes a compound shown in formula I: , R1 and R2 are each independently selected from phenyl, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C2-C6 alkenyl, and when substituted, the substituent is selected from halogen; based on the mass of the electrolyte, the mass percentage of the compound represented by formula I is B%, 0.1≤B≤5; The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes graphite; the lithium ion battery satisfies the relationship: 5≤(A+X) / B 2 ≤175, where 5≤X≤12, X is the surface density of the single-sided negative electrode material layer, in mg / cm 2 .

2. The lithium-ion battery according to claim 1, wherein The electrolyte satisfies at least one of the following conditions: （1）10≤A≤15； （2）0.5≤B≤2。 3. The lithium ion battery according to claim 1, wherein The compound represented by formula I includes at least one of the following compounds: ; ; .

4. The lithium ion battery according to claim 1, wherein The additive includes a second additive, the second additive is selected from at least one of vinyl sulfate and methylene disulfonate, and based on the mass of the electrolyte, the mass percentage of the second additive is C%, and 0.5≤C≤3.

5. The lithium ion battery according to claim 1, wherein The electrolyte includes an auxiliary salt, which is selected from at least one of LiPF6, LiSO3CF3, LiBF4, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2 and LiPF4C2O4. Based on the mass of the electrolyte, the mass percentage of the auxiliary salt is D%, and 0.1≤D≤2.

6. The lithium-ion battery according to claim 1, wherein The solvent includes a cyclic organic solvent and / or a chain organic solvent, the cyclic organic solvent is selected from at least one of ethylene carbonate and propylene carbonate, and the chain organic solvent is selected from at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate and methylpropyl carbonate.

7. The lithium-ion battery according to claim 1, wherein 7≤X≤9。

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