A type of battery

Abstract

This invention provides a battery comprising a negative electrode and an electrolyte. The negative electrode includes a negative electrode active layer. The electrolyte includes a lithium salt additive and a first additive. The lithium salt additive includes lithium bis(trifluoromethanesulfonyl)imide, and the first additive includes a compound having the structural formula of Formula 1; 0.1 ≤ 100*(a+b)*x / y ≤ 1.8. The battery provided by this invention exhibits excellent high-charge and high-temperature cycle performance.

Description

Technical Field

[0001] This invention relates to a battery, belonging to the field of lithium-ion battery technology. Background Technology

[0002] Currently, lithium-ion batteries are widely used in consumer electronics, new energy vehicles, and other power battery products due to their environmental friendliness, low cost, and high operating voltage. Fast charging performance and lifespan have become primary considerations for users.

[0003] However, current high-energy-density lithium-ion batteries still have the following problems during charging: the internal temperature rises rapidly during battery cycling, which degrades the battery's rate charging performance and shortens its lifespan. Under high-temperature operating environments, the internal temperature of the battery is even higher, and the high-temperature cycling performance of the battery is even worse.

[0004] Therefore, there is an urgent need to develop a battery with high charge-rate and high-temperature cycling performance. Summary of the Invention

[0005] This invention provides a battery with excellent charge-up and high-temperature cycling performance.

[0006] This invention provides a battery comprising a negative electrode and an electrolyte, wherein the negative electrode comprises a negative electrode active layer; the electrolyte comprises a lithium salt additive and a first additive, the lithium salt additive comprising lithium bis(trifluoromethanesulfonyl)imide, and the first additive comprising a compound having a structure of Formula 1:

[0007] Formula 1;

[0008] 0.1≤100*(a+b)*x / y≤1.8;

[0009] Wherein, a is the mass percentage of the lithium bis(trifluoromethanesulfonyl)imide in the electrolyte; b is the mass percentage of the compound having the structure of Formula 1 in the electrolyte; x is the ratio of the total mass of the electrolyte to the discharge capacity of the battery, in g / Ah; and y is the single-sided density of the negative electrode active layer, in mg / cm³. 2 .

[0010] The battery as described above, wherein a / b is (0.5-1.5):(0.3-1).

[0011] In the battery described above, 0.1% ≤ a ≤ 3%;

[0012] And / or, 0.1%≤b≤2%.

[0013] The battery is as described above, where 1 ≤ x ≤ 5;

[0014] And / or, 5≤y≤20.

[0015] In the battery described above, the electrolyte further includes a second additive, which includes at least one of silane additives, vinylene carbonate, and ethylene ethylene carbonate.

[0016] In the battery described above, the silane additive includes at least one compound having the structural formulas of Formula 2 and Formula 3:

[0017]

[0018] Among them, R1-R 10 Each is independently selected from substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted C6-C10 aryl, R1-R 10 The substituents in it include halogens.

[0019] In the battery described above, the second additive has a mass percentage content of 0.1-3% in the electrolyte.

[0020] In the battery described above, the second additive comprises tetravinylsilane, wherein the mass ratio of the lithium bis(trifluoromethanesulfonyl)imide, the compound having the structure of Formula 1, and the tetravinylsilane is (0.5-1.5):(0.3-1):(0.05-0.3).

[0021] In the battery described above, the electrolyte further includes an organic solvent, which includes carbonate solvents and / or carboxylic acid ester solvents;

[0022] The carbonate solvent includes at least one of propylene carbonate, ethylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate.

[0023] The carboxylic acid ester solvent includes at least one of methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

[0024] In the battery described above, the organic solvent includes ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, and ethyl acetate, wherein the mass ratio of ethylene carbonate, methyl ethyl carbonate, and ethyl acetate is (2-3):(1-9):(1-9).

[0025] The battery provided by this invention limits the selection of lithium salt additives and a first additive in the electrolyte, and also limits the relationship between the ratio of the total mass of the lithium salt additive, the first additive, and the electrolyte to the discharge capacity of the battery and the areal density of the negative electrode. Lithium bis(trifluoromethanesulfonyl)imide and the compound of Formula 1 work synergistically to suppress the generation of hydrogen fluoride in the electrolyte, improve the rate charging and high-temperature cycling performance of the battery, and increase the ionic conductivity of the electrolyte, thereby increasing the migration rate of lithium ions. At the same time, it can construct a lower impedance SEI film, improve the transport rate of lithium ions in the SEI film, and improve the lithium plating problem caused by increasing the areal density of the negative electrode during charging. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0027] This invention provides a battery comprising a negative electrode and an electrolyte. The negative electrode includes a negative electrode active layer. The electrolyte includes a lithium salt additive and a first additive. The lithium salt additive includes lithium bis(trifluoromethanesulfonyl)imide, and the first additive includes a compound having the structural formula of Formula 1.

[0028] Formula 1;

[0029] 0.1≤100*(a+b)*x / y≤1.8;

[0030] Where, a is the mass percentage of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte; b is the mass percentage of the compound having the structure of Formula 1 in the electrolyte; x is the ratio of the total mass of the electrolyte to the discharge capacity of the battery, in g / Ah; and y is the single-sided density of the negative electrode active layer, in mg / cm³. 2 .

[0031] It is understood that in this application, the unit for the ratio of the total mass of the electrolyte to the discharge capacity of the battery is g / Ah, and the unit for the single-sided density of the negative electrode active layer is mg / cm³. 2 However, this application does not limit the ratio of discharge capacity or the unit of the single-sided density of the negative electrode active layer. For example, the unit of the single-sided density of the negative electrode active layer can also be g / cm³. 3 When the unit of the ratio of battery discharge capacity is other than g / Ah, and the unit of the single-sided density of the negative electrode active layer is mg / cm³, etc. 2 When using units other than g / Ah and mg / cm³, convert the units to g / Ah and mg / cm³.2 When the resulting formula value is between 0.1 and 1.8, it is also within the scope of protection of this application.

[0032] The battery of the present invention includes a negative electrode sheet, which comprises a negative electrode current collector and a negative electrode active layer disposed on the surface of the negative electrode current collector. The negative electrode active layer comprises a negative electrode active material, a conductive agent, and a binder, wherein the negative electrode current collector is generally copper foil. The present invention does not limit the selection of the negative electrode active material and can select it according to actual needs. For example, carbonaceous materials, silicon-carbon materials, alloy materials, lithium-containing metal composite oxides, etc., can be used as the negative electrode active material. The conductive agent and binder in the negative electrode active layer of the present invention can both be selected from conventional materials in the art.

[0033] According to the above-described solution provided by the present invention, after applying the negative electrode and electrolyte to a lithium-ion battery, the lithium-ion battery exhibits excellent charge-up and high-temperature cycle performance. The inventors analyzed the principle behind this and believe that the reason may be that the charge-up and high-temperature cycle performance of the battery is jointly determined by the negative electrode and the electrolyte. When lithium bis(trifluoromethanesulfonyl)imide and the compound of formula 1 are added to the electrolyte, adjusting the values ​​of a, b, x, and y can optimize the charge-up and high-temperature cycle performance of the battery. Here, a is the mass percentage of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte. The addition of lithium bis(trifluoromethanesulfonyl)imide can inhibit the generation of hydrogen fluoride in the electrolyte and block the continuous decomposition of lithium hexafluorophosphate, thereby effectively improving the high-temperature cycle performance of the battery. Furthermore, it allows for easier dissociation of lithium ions and bis(trifluoromethanesulfonyl)imide anions in the lithium bis(trifluoromethanesulfonyl)imide, thereby significantly improving the ionic conductivity of the electrolyte and enhancing the electrolytic efficiency. The migration rate of lithium ions in the electrolyte improves the battery's charge-up and high-temperature cycling performance; b is the mass percentage of compound 1 in the electrolyte. The addition of compound 1 can participate in the construction of the SEI film, improve the transport rate of lithium ions in the SEI film, and improve the battery's charge-up and high-temperature cycling performance; x is the ratio of the total mass of the electrolyte to the battery's discharge capacity. x can affect the amount of lithium bis(trifluoromethanesulfonyl)imide and compound 1 added to the battery, thereby improving the battery's charge-up and high-temperature cycling performance; y is the single-sided density of the negative electrode active layer. y greatly affects the battery's internal resistance. The larger y is, the greater the resistance to lithium ion transport in the negative electrode active layer, resulting in a larger internal resistance of the battery and a decrease in the battery's charge-up and high-temperature cycling performance. Therefore, based on experience and experiments, it has been found that within a certain range, a, b, and x are positively correlated with the battery's charge-up and high-temperature cycle performance. Dividing the product ((a+b)*x) by the single-sided density y of the negative electrode active layer is for normalization, so that the formula is applicable to batteries with negative electrode active layers of different single-sided densities.

[0034] Therefore, the specific physical meaning of the formula 100*(a+b)*x / y is actually the degree of matching between the negative electrode and the electrolyte in the battery. Experiments show that when 100*(a+b)*x / y is in the range of 0.1-1.8, the matching between the negative electrode and the electrolyte is optimal. Lithium bis(trifluoromethanesulfonyl)imide and the compound of formula 1 work synergistically to inhibit the generation of hydrogen fluoride in the electrolyte and block the continuous decomposition of lithium hexafluorophosphate, thereby effectively improving the high-temperature cycle performance of the battery. Furthermore, it makes it easier for lithium ions and bis(trifluoromethanesulfonyl)imide anions in lithium bis(trifluoromethanesulfonyl)imide to dissociate, thus significantly improving the ionic conductivity of the electrolyte. The conductivity improves the migration rate of lithium ions in the electrolyte, thereby enhancing the battery's charge-time and high-temperature cycling performance. It also accelerates the ring-opening polymerization of compound 1, constructing a lower impedance SEI film, thus increasing the lithium ion transport rate within the SEI film. Furthermore, the appropriate molar amounts of lithium bis(trifluoromethanesulfonyl)imide and the SEI-forming compound 1 ensure that the SEI film is formed without any excess lithium bis(trifluoromethanesulfonyl)imide and compound 1, minimizing the impact of hydrogen fluoride on the battery and maximizing lithium ion migration and transport rates. This results in excellent charge-time and high-temperature cycling performance. If the value of 100*(a+b)*x / y is too large or too small, it will lead to an improper match between the negative electrode and the electrolyte, resulting in insufficient stability or excessive impedance of the formed SEI film. Simultaneously, the high resistance to lithium ion transport in the negative electrode active layer reduces the lithium ion transport and migration rates, thus affecting the battery's charge-time and high-temperature cycling performance.

[0035] In one specific embodiment, a / b is (0.5-1.5):(0.3-1), for example, a / b is 0.5:0.3, 0.5:0.5, 0.5:1, 1:0.3, 1:0.5, 1:1, 1.5:0.3, 1.5:0.5, or 1.5:1, etc. When a / b is within the above range, lithium bis(trifluoromethanesulfonyl)imide and the compound of formula 1 can further synergistically reduce the hydrofluoric acid content in the electrolyte and further improve the migration rate and transport rate of lithium ions, forming a lower impedance SEI film, thereby making the battery's charge-recharge and high-temperature cycle performance better.

[0036] In one specific embodiment, 0.1% ≤ a ≤ 3%, for example, a is 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, or 3%, etc. When the mass percentage of lithium bis(trifluoromethanesulfonyl)imide is within the above range, lithium bis(trifluoromethanesulfonyl)imide can better synergize with the compound of Formula 1, further suppressing the formation of hydrogen fluoride in the electrolyte, and simultaneously increasing the migration and transport rates of lithium ions in the electrolyte, thereby significantly improving the battery's charge-up and high-temperature cycle performance. Further, the mass percentage of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte is 0.5-1.5%.

[0037] In one specific embodiment, 0.1% ≤ b ≤ 2%, for example, b is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%, etc. When the mass percentage of compound 1 is within the above range, compound 1 can be better matched with lithium bis(trifluoromethanesulfonyl)imide, resulting in lower hydrogen fluoride formation in the electrolyte and faster dissociation of lithium bis(trifluoromethanesulfonyl)imide, leading to faster lithium ion migration in the electrolyte. Simultaneously, the constructed SEI film has lower impedance and a higher lithium ion transport rate, thereby improving the battery's charge-up and high-temperature cycling performance.

[0038] In one specific embodiment, 1 ≤ x ≤ 5, for example, x is 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5. When the ratio of the total mass of the electrolyte to the discharge capacity of the battery is within the above range, the molar amount of the compound of formula 1 that can form the SEI film can be controlled within a suitable range, which enables lithium bis(trifluoromethanesulfonyl)imide to further synergize with the compound of formula 1, further reducing the acidity of the electrolyte and increasing the migration rate of lithium ions, and generating an SEI film with lower impedance, thereby further improving the battery's charge-up and high-temperature cycle performance.

[0039] In one specific embodiment, 5 ≤ y ≤ 20, for example, y is 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20. When the single-sided density of the battery's negative electrode active layer is within the above range, the lithium-ion transport rate in the battery is higher, which can reduce the amount of Formula 1 compound and lithium bis(trifluoroimide) added, avoid excessive internal resistance of the battery, form a more stable SEI film, and thus the battery exhibits higher charge-rate and high-temperature cycling performance.

[0040] In one specific embodiment, the electrolyte further includes a second additive, which includes at least one of silane additives, vinylene carbonate, and ethylene ethylene carbonate. When the second additive is selected from the above-mentioned compounds, it can synergistically interact with lithium bis(trifluoromethanesulfonyl)imide and the compound of formula 1. The second additive can participate in the construction of the CEI film, resulting in lower impedance and higher stability of the CEI film, inhibiting side reactions such as solvent decomposition that occur when organic solvents come into contact with the positive electrode active material, and can also participate in the construction of the SEI film, further reducing the impedance of the SEI film and greatly improving the lithium-ion transport speed, thereby further improving the battery's charge-up and high-temperature cycle performance.

[0041] In one specific embodiment, the silane additive includes at least one compound having the structural formulas of Formula 2 and Formula 3:

[0042]

[0043] Among them, R1-R 10 Each is independently selected from substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted C6-C10 aryl, R1-R 10 The substituents in it include halogens.

[0044] The substituted or unsubstituted C1-C10 alkyl groups of this invention refer to alkyl chains with 1-10 carbon atoms that have substituents or unsubstituted groups, or cycloalkyl chains with 3-10 carbon atoms that have substituents or unsubstituted groups; the substituted or unsubstituted C2-C10 alkenyl groups of this invention refer to alkenyl chains with 2-10 carbon atoms that have substituents or unsubstituted groups, or cycloalkenyl chains with 3-10 carbon atoms that have substituents or unsubstituted groups; the substituted or unsubstituted C2-C10 alkynyl groups of this invention refer to alynyl chains with 2-10 carbon atoms that have substituents or unsubstituted groups, or cycloalynyl chains with 3-10 carbon atoms that have substituents or unsubstituted groups; the substituted or unsubstituted C6-C10 aryl groups of this invention refer to aryl groups with 6-10 carbon atoms that have substituents or unsubstituted groups; when specified as a hydrocarbon group with a specific number of carbon atoms, it includes all geometric isomers having that number of carbon atoms. R1-R 10 The substituents in the form include halogens, such as fluorine, chlorine, bromine, iodine, etc. 10 Each can be independently selected from -CH3, -CH2CH3, -CF3, -CH=CH2, -CH=CF2, -CHC-CH3, -CC-CCl3, -C6H5, -C6H4F, -C6H4-CCl3, etc.

[0045] When the second additive includes the aforementioned silane additives, the silane additives can further synergize with lithium bis(trifluoromethanesulfonyl)imide and the compound of formula 1, resulting in higher stability of the battery's CEI film. This effectively inhibits solvent decomposition caused by contact between the solvent and the positive electrode material, thereby further improving the battery's high-temperature cycle performance. When the silane additives contain unsaturated groups, they can combine with gases generated by solvent decomposition, thereby suppressing battery gas expansion.

[0046] In one specific embodiment, the second additive has a mass percentage content of 0.1-3% in the electrolyte, for example, the mass percentage content of the second additive in the electrolyte is 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, or 3%, etc. When the mass percentage content of the second additive is within the above range, the second additive can have a better synergistic effect with lithium bis(trifluoromethanesulfonyl)imide and the compound of formula 1, which can generate SEI film and CEI film with lower impedance and higher stability, further improve the lithium ion transport rate, and suppress the decomposition reaction of the electrolyte to a greater extent. At the same time, it can reduce the generation of hydrogen fluoride in the electrolyte and improve the migration rate of lithium ions in the electrolyte, thereby making the battery's charge-up and high-temperature cycle performance better.

[0047] In one specific embodiment, the second additive comprises tetravinylsilane, lithium bis(trifluoromethanesulfonyl)imide, a compound having the structure of Formula 1, and the tetravinylsilane in a mass ratio of (0.5-1.5):(0.3-1):(0.05-0.3), for example, a mass ratio of 0.5:0.3:0.05, 0.5:0.5:0.05, 0.5:1:0.05, 0.5:0.3:0.15, 0.5 :0.3:0.3, 0.5:0.5:0.15, 0.5:0.5:0.3, 0.5:1:0.15, 0.5:1:0.3, 1:0.3:0.05, 1:0.5:0.05, 1:1:0.05, 1:0.3:0.15, 1:0.3:0.3, 1:0.5:0.15, 1:0.5:0.3, 1:1:0.15 or 1:1:0.3, etc. When the mass ratio of lithium bis(trifluoromethanesulfonyl)imide, compound of formula 1, and tetravinylsilane is within the above range, lithium bis(trifluoromethanesulfonyl)imide, compound of formula 1, and tetravinylsilane exhibit better synergistic effects, further reducing the content of acidic substances in the electrolyte and increasing the migration rate of lithium ions to a greater extent. At the same time, it can generate SEI film and CEI film with lower impedance and better stability, thereby making the battery exhibit better charge-over-charge and high-temperature cycle performance.

[0048] In one specific embodiment, the electrolyte further includes an organic solvent, which includes carbonate solvents and / or carboxylic acid ester solvents; the carbonate solvent includes at least one selected from propylene carbonate, ethylene carbonate, butenyl carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate; the carboxylic acid ester solvent includes at least one selected from methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. When the organic solvent of the present invention includes the above-mentioned solvents, the electrolyte has a lower viscosity and a higher ionic conductivity, which is beneficial to improving the migration rate of lithium ions, thereby improving the battery's charge-up and high-temperature cycle performance. Furthermore, the above-mentioned organic solvents, when used in combination with various additives, can further improve the stability and oxidation resistance of the electrolyte, and to a greater extent avoid the decomposition reaction of the electrolyte, thereby further improving the battery's charge-up and high-temperature cycle performance.

[0049] In one specific embodiment, the organic solvent includes ethylene carbonate, methyl ethyl carbonate, and ethyl acetate, with a mass ratio of (2-3):(1-9):(1-9), for example, a mass ratio of 2:1:1, 2:5:1, 2:9:1, 2:1:5, 2:1:9, 2:5:5, 2:5:9, 2:9:5, 2:9:9, 3:1:1, 3:5:1, 3:9:1, 3:1:5, 3:1:9, 3:5:5, 3:5:9, 3:9:5, or 3:9:9. When the organic solvent includes the above solvents and the mass ratio is within the above range, the viscosity of the electrolyte is more suitable, and the ionic conductivity is higher, resulting in a higher lithium ion migration rate, thereby achieving better cycle performance of the battery. Furthermore, when used in combination with the above additives, the stability and oxidation resistance of the electrolyte can be further improved, thus resulting in better high-temperature cycle performance of the battery.

[0050] In one specific embodiment, the electrolyte further includes a lithium salt, comprising lithium hexafluorophosphate and / or lithium bisfluorosulfonylimide. The addition of the lithium salt improves the conductivity and stability of the electrolyte, thereby enhancing the battery's cycle performance. The molar concentration of the lithium salt in the electrolyte is 0.3-2 mol / L, for example, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, or 2 mol / L. When the lithium salt is within the above range, the conductivity and stability of the electrolyte can be further improved, thereby further enhancing the battery's charge-time performance and high-temperature cycle performance. Furthermore, the molar concentration of lithium salt in the electrolyte is 0.3-1.5 mol / L.

[0051] In one specific embodiment, the battery of the present invention further includes a positive electrode and a separator, specifically:

[0052] The positive electrode sheet includes a positive current collector and a positive active layer disposed on the surface of the positive current collector. The positive active layer includes a positive active material, a conductive agent, and a binder. The positive current collector is typically aluminum foil, and the positive active material is selected from lithium transition metal oxides, such as LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, and Li... 1+a Mn 1-x M x O2, LiCo 1-x M x O2, LiFe 1-x M x PO4, LiMn 1-x O4, M is selected from one or more of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B, and F, 0≤a<0.2, 0≤x<1.

[0053] The conductive agent and binder in the positive electrode active layer can be conventional materials in this field.

[0054] The separator is a type of membrane known in the art that can be used in batteries and is stable to the electrolyte used. Specifically, it may include one or more of polyolefins, aromatic polyamides, polytetrafluoroethylene, and polyethersulfone. Further, the separator includes one or both of polyethylene and polypropylene. Moreover, the separator can be obtained by sequentially laminating multiple layers of materials; for example, the separator includes sequentially laminated polypropylene layers, polyethylene layers, and polypropylene layers.

[0055] The present invention will be further described in detail below through specific embodiments.

[0056] Example 1

[0057] The battery of the present invention is prepared by the following steps:

[0058] 1. Preparation of electrolyte: Prepare electrolyte in a glove box filled with 99.999% pure argon gas, control the moisture content in the glove box to ≤0.1ppm, and control the temperature to room temperature. After thoroughly mixing the organic solvent, add lithium salt, lithium salt additive, and first additive and mix thoroughly. After mixing evenly, the electrolyte is obtained.

[0059] The lithium salts include lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, with a molar concentration of 1 mol / L for lithium hexafluorophosphate and 0.2 mol / L for lithium bis(fluorosulfonyl)imide. The organic solvents include ethylene carbonate, methyl ethyl carbonate, and ethyl acetate in a mass ratio of 3:4:3. The lithium salt additives include lithium bis(trifluoromethanesulfonyl)imide, with a mass percentage of 0.5%. The first additive includes a compound having the structure of Formula 1, with a mass percentage of 0.5%.

[0060] 2. Preparation of the positive electrode sheet: The positive electrode active material lithium nickel cobalt manganese oxide (purchased from Zhenhua New Materials), conductive agent carbon black, conductive agent carbon nanotubes, and binder polyvinylidene fluoride are dispersed in the solvent N-methylpyrrolidone at a mass ratio of 94.5:3.5:0.5:1.5 to obtain the positive electrode active layer slurry; the positive electrode active layer slurry is uniformly coated on the surface of the positive electrode current collector aluminum foil, and after drying, rolling, baking, slitting, and spot welding of the tabs, the positive electrode sheet is obtained, with a total thickness of 90 μm.

[0061] 3. Preparation of the negative electrode sheet: Graphite (purchased from Jiangxi Zichen), carbon black (conductive agent), polyvinylidene fluoride (PVDF) and sodium carboxymethyl cellulose (CMC) were dispersed in deionized water at a mass ratio of 94.5:2:2:1.5 and stirred evenly to obtain a negative electrode active layer slurry. The negative electrode active layer slurry was uniformly coated on the surface of the copper foil of the negative electrode current collector. After drying, rolling, baking, slitting, and spot welding of the tabs, the negative electrode sheet was obtained. The total thickness of the negative electrode sheet was 128 μm, and the single-sided density of the negative electrode active layer was 8 mg / cm³. 2 .

[0062] 4. Stack the prepared positive electrode, negative electrode, and separator in sequence, place the separator between the positive and negative electrode sheets, and wind them to obtain the battery cell. Place the battery cell in the outer packaging, and inject 8g of electrolyte into the battery cell in a glove box. After encapsulation, formation, aging, and capacity testing, the lithium-ion battery is completed. Its rated capacity is 2Ah, so the ratio of the total mass of the electrolyte to the battery's discharge capacity, x, is 4g / Ah. Specifically, the capacity obtained by fully charging the battery at 1C and then discharging it at 1C is 2Ah.

[0063] The preparation methods of the batteries provided in Examples 2-22 and Comparative Examples 1-5 are basically the same as those in Example 1, and the specific parameters are shown in Table 1.

[0064] The preparation methods of the batteries provided in Examples 23-41 are basically the same as those in Example 1, except for the preparation of the electrolyte: the electrolyte is prepared in a glove box filled with 99.999% pure argon gas, the moisture content in the glove box is controlled at ≤0.1ppm, and the temperature is controlled at room temperature. After the organic solvent is fully mixed, lithium salt, lithium salt additive, first additive, and second additive are added and fully mixed. After uniform mixing, the electrolyte is obtained. Specific parameters are shown in Table 1.

[0065] Table 1

[0066]

[0067]

[0068]

[0069]

[0070]

[0071]

[0072]

[0073] Test case

[0074] The lithium-ion batteries prepared in the examples and comparative examples were tested for their double charge cycle performance and high-temperature performance. The test methods are as follows:

[0075] Double charge cycle performance test method: At 25℃, charge to 4.4V with 5C constant current and constant voltage, let stand for 5 minutes, and then discharge to 2.75V with 1C constant current. After 500 cycles, calculate the capacity retention rate. Calculation method: Capacity retention rate (%) = (500th discharge capacity / 1st discharge capacity) × 100%.

[0076] High-temperature cycling performance test method: At 45℃, charge to 4.4V with 1C constant current and constant voltage, let stand for 5 minutes, and then discharge to 2.75V with 1C constant current. After 500 cycles, calculate the capacity retention rate. Calculation method: Capacity retention rate (%) = (500th discharge capacity / 1st discharge capacity) × 100%.

[0077] The test results are shown in Table 2.

[0078] Table 2

[0079]

[0080]

[0081] Table 2 shows that, based on the comparison of Examples 1-41 and Comparative Examples 1-5, when 100*(a+b)*x / y satisfies the range of 0.1-0.8, it helps to improve the battery's double charge cycle performance and high-temperature cycle performance. Based on the comparison of Examples 1-16 and Examples 17-22, and Examples 23-25 ​​and Examples 26-31, when 0.1%≤a≤3%, 0.1%≤b≤2%, 1≤x≤5, 5≤y≤20, and a / b is (0.5-1.5):(0.3-1), the battery's double charge cycle performance and high-temperature cycle performance are superior. Through the comparison of Examples 23-25 ​​and Examples 32-36, it is known that tetravinylsilane is selected as the second additive. Furthermore, when the mass ratio of lithium bis(trifluoromethanesulfonyl)imide, the compound having the structure of Formula 1, and tetravinylsilane is in the range of (0.5-1.5):(0.3-1):(0.05-0.3), the battery's charge cycle performance and high-temperature cycle performance can be further improved. According to the comparison of Examples 23, 37, and 38, when the mass ratio of ethylene carbonate, methyl ethyl carbonate, and ethyl acetate is in the range of (2-3):(1-9):(1-9), the battery's charge cycle performance and high-temperature cycle performance are even better. According to the comparison of Examples 23, 39-41, when the molar concentration of lithium salt is 0.3-2 mol / L, the battery's charge cycle performance and high-temperature cycle performance are even higher. The battery provided by this invention has excellent charge cycle performance and high-temperature cycle performance.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery, characterized in that, The battery includes a negative electrode and an electrolyte, the negative electrode including a negative electrode active layer; the electrolyte including a lithium salt additive and a first additive, the lithium salt additive including lithium bis(trifluoromethanesulfonyl)imide, and the first additive including a compound having the structure of Formula 1: 0.1≤100*(a+b)*x / y≤1.8; Wherein, a is the mass percentage of the lithium bis(trifluoromethanesulfonyl)imide in the electrolyte; b is the mass percentage of the compound having the structure of Formula 1 in the electrolyte; x is the ratio of the total mass of the electrolyte to the discharge capacity of the battery, in g / Ah; and y is the single-sided density of the negative electrode active layer, in mg / cm³. 2 ; a / b is (0.5-1.5):(0.3-1).

2. The battery according to claim 1, characterized in that, 0.1％≤a≤3％； And / or, 0.1% ≤ b ≤ 2%.

3. The battery according to claim 2, characterized in that, 1≤x≤5； And / or, 5≤y≤20.

4. The battery according to claim 3, characterized in that, The electrolyte also includes a second additive, which includes at least one of silane additives, vinylene carbonate, and ethylene ethylene carbonate.

5. The battery according to claim 4, characterized in that, The silane additives include at least one compound having the structural formulas 2 and 3: Among them, R1-R 10 Each is independently selected from substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted C6-C10 aryl, R1-R 10 The substituents in it include halogens.

6. The battery according to claim 5, characterized in that, The second additive has a mass percentage content of 0.1-3% in the electrolyte.

7. The battery according to claim 6, characterized in that, The second additive comprises tetravinylsilane, wherein the mass ratio of the lithium bis(trifluoromethanesulfonyl)imide, the compound having the structure of Formula 1, and the tetravinylsilane is (0.5-1.5):(0.3-1):(0.05-0.3).

8. The battery according to claim 7, characterized in that, The electrolyte further includes an organic solvent, which includes carbonate solvents and / or carboxylic acid ester solvents; The carbonate solvent includes at least one of propylene carbonate, ethylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate. The carboxylic acid ester solvent includes at least one of methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

9. The battery according to claim 8, characterized in that, The organic solvent includes ethylene carbonate, methyl ethyl carbonate, and ethyl acetate, wherein the mass ratio of ethylene carbonate, methyl ethyl carbonate, and ethyl acetate is (2-3):(1-9):(1-9).

Images