An electrolyte and a battery

Abstract

This invention provides an electrolyte and a battery. The electrolyte comprises a fluorosulfonamide inner salt having the structure shown in Formula 1, wherein R1 to R5 are each independently selected from C1-C12 alkyl groups, C1-C12 alkyl groups containing halogen atoms, halogen atoms, substituted or unsubstituted aryl groups. The electrolyte provided by this invention can improve the high-temperature cycle performance and high-temperature storage performance of the battery under high voltage.

Description

Technical Field

[0001] This invention relates to an electrolyte, and more particularly to an electrolyte and a battery, belonging to the field of ion batteries. Background Art

[0002] With the development of technology and the increase in market demand, the application fields of lithium-ion batteries are expanding, from consumer electronics to electric vehicles and energy storage systems, and the requirements for battery performance are becoming increasingly stringent. As technology is updated and iterated, electronic products are becoming thinner and lighter, which also places more stringent demands on the energy density of lithium-ion batteries. Under the condition of a fixed lithium battery volume, the energy density can be increased by means of increasing the upper limit voltage.

[0003] However, as the voltage increases (>4.55V), the oxidation of the electrolyte by oxygen released from the positive electrode active material intensifies, leading to solvent decomposition and gas production. Lithium salt decomposition also increases, generating more corrosive substances such as HF, which damage the SEI film and corrode the electrode materials. Simultaneously, transition metal ions from the positive electrode continuously dissolve and migrate to the negative electrode surface, causing further damage to the SEI film. Under high-temperature conditions, solvent decomposition and gas production are further aggravated, and corrosive substances such as HF exhibit even stronger corrosiveness to the SEI film and electrode materials, resulting in deterioration of the battery's high-voltage, high-temperature cycle performance and high-temperature storage performance.

[0004] Therefore, those skilled in the art urgently need to develop a highly stable electrolyte to improve the high-temperature cycling performance and high-temperature storage performance of batteries under high voltage. Summary of the Invention

[0005] This invention provides an electrolyte that can improve the high-temperature cycle performance and high-temperature storage performance of batteries under high voltage.

[0006] This invention provides an electrolyte comprising a fluorosulfonamide inner salt having the structure shown in Formula 1:

[0007]

[0008] R1 to R5 are each independently selected from C1 to C12 alkyl groups, C1 to C12 alkyl groups containing halogen atoms, halogen atoms, substituted or unsubstituted aryl groups.

[0009] In the electrolyte as described above, R1 to R5 are each independently selected from C1 to C6 alkyl groups, C1 to C6 alkyl groups containing fluorine atoms, fluorine atoms, substituted or unsubstituted aryl groups, and when the aryl group has a substituent, the substituent is selected from C1 to C6 alkyl groups.

[0010] In the electrolyte described above, the fluorosulfonamide inner salt comprises one or more compounds of formulas 1-1 to 1-5:

[0011]

[0012] In the electrolyte as described above, the fluorosulfonamide inner salt accounts for 0.1% to 20% of the electrolyte by mass percentage (ml), preferably 0.5% to 10%.

[0013] The electrolyte as described above, wherein the electrolyte comprises a carboxylic acid ester solvent;

[0014] Preferably, the carboxylic acid ester solvent includes at least one of propyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, ethyl propionate, n-propyl propionate, methyl butyrate, ethyl butyrate, and n-ethyl butyrate.

[0015] Preferably, the carboxylic acid ester solvent accounts for 5% to 50% of the mass percentage m2 of the electrolyte.

[0016] The electrolyte as described above, wherein the electrolyte comprises a lithium salt, and the lithium salt comprises a boron-containing lithium salt;

[0017] Preferably, the boron-containing lithium salt comprises lithium difluorooxalate borate;

[0018] Preferably, the boron-containing lithium salt in the electrolyte accounts for 0.1% to 1% of the electrolyte by mass (m3).

[0019] The electrolyte as described above, wherein the electrolyte comprises vinyl sulfate;

[0020] Preferably, the ethylene sulfate in the electrolyte accounts for 0.1% to 1% of the mass of the electrolyte.

[0021] The present invention provides a battery comprising a positive electrode, a negative electrode, and an electrolyte as described above.

[0022] In the battery described above, the negative electrode sheet includes a negative electrode active material, which includes carbon-based materials and silicon-based materials, and / or the porosity of the negative electrode sheet is 50% to 70%.

[0023] Preferably, the mass percentage m5 of silicon element in the negative electrode active material is 2% to 30%;

[0024] Preferably, the D50 of the silicon-based material is 5μm to 15μm.

[0025] The battery as described above, wherein the positive electrode comprises lithium cobalt oxide material;

[0026] Preferably, the mass percentage m6 of cobalt element in the lithium cobalt oxide material is 54.8% to 63.1%.

[0027] The electrolyte of the present invention contains a fluorosulfonamide inner salt. When the electrolyte containing this fluorosulfonamide inner salt is applied to a battery, on the one hand, the high electronegativity of the fluorine atoms in the fluorosulfonamide inner salt gives the fluorosulfonamide groups strong adsorption on the positive electrode surface, enabling them to preferentially interact with the surface of the positive electrode material to form a dense CEI film. The dense CEI film can improve the high-temperature cycle performance and high-temperature storage performance of the battery under high voltage. On the other hand, the high energy level of the fluorosulfonamide groups in the fluorosulfonamide inner salt gives the positive electrode material strong oxidation resistance, thereby improving the high-temperature cycle performance and high-temperature storage performance of the battery under high voltage. Detailed Implementation

[0028] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] This invention provides an electrolyte comprising a fluorosulfonamide inner salt having the structure shown in Formula 1:

[0030]

[0031] R1 to R5 are each independently selected from C1 to C12 alkyl groups, C1 to C12 alkyl groups containing halogen atoms, halogen atoms, substituted or unsubstituted aryl groups.

[0032] In the embodiments of the present invention, the C1 to C12 alkyl groups refer to chain alkyl groups with 1 to 12 carbon atoms or cycloalkyl groups with 3 to 12 carbon atoms.

[0033] In the embodiments of the present invention, the C1 to C12 alkyl groups containing halogen atoms refer to chain alkyl groups with 1 to 12 carbon atoms substituted by halogen atoms or cycloalkyl groups with 3 to 12 carbon atoms.

[0034] In the embodiments of this invention, halogen atoms refer to fluorine atoms, bromine atoms, iodine atoms, etc.

[0035] In this invention, substituted or unsubstituted aryl refers to an aryl group with or without a substituent. When a substituent is specified as a group having a specific number of carbon atoms, it includes all geometric isomers having that number of carbon atoms.

[0036] For example, R1 to R5 are each independently selected from -CH3, -CH2CH3, -CH2CH2CH3, -CH(CH3)2, -CF3, -CCl3, -CBr3, -CH2CF3, -CH2CH2CF3, -F, -Cl, -I, -C6H5, -C6F5, -C6H4-CH3, -C6H4-F, etc.

[0037] The electrolyte in this invention includes a fluorosulfonamide inner salt, and when the fluorosulfonamide inner salt has the above-mentioned structure, it can improve the high-temperature cycle performance and high-temperature storage performance of the battery under high voltage. The inventors analyzed the principle and believe that the reason may be that, on the one hand, the high electronegativity of the fluorine atoms in the fluorosulfonamide inner salt makes the fluorosulfonamide groups have strong adsorption on the positive electrode surface, and can preferentially interact with the surface of the positive electrode material to form a dense CEI film. This CEI film can effectively mask the positive electrode transition metal sites, protect the positive electrode active material, and avoid damage to the SEI film caused by the dissolution of the positive electrode transition metal; on the other hand, the high energy level of the fluorosulfonamide groups in the fluorosulfonamide inner salt makes the positive electrode material have strong oxidation resistance, thereby improving the high-temperature cycle performance and high-temperature storage performance of the battery under high voltage; in addition, the fluorosulfonamide inner salt can form stable ion pairs in the electrolyte and promote the rapid transport of lithium ions, which helps to reduce the internal resistance of the battery and improve the rate performance and fast charge and discharge capability of the battery.

[0038] In one specific embodiment, R1 to R5 are each independently selected from C1 to C6 alkyl groups, C1 to C6 alkyl groups containing halogen atoms, halogen atoms, substituted or unsubstituted aryl groups. When the aryl group has a substituent, the substituent is selected from C1 to C6 alkyl groups. For example, R1 to R5 are each independently selected from -CH3, -CH2CH3, -CH2CH2CH3, -CH(CH3)2, -CF3, -CH2CF3, -CH2CH2CF3, -CH(CF3)2, -C6H4-CH3, -C6H4CH2CH3, -C6H4CH2CH2CH3, -C6H3(CH3)2, -C6H3(CH2CH3)2, -C6H2(CH3)3, etc.

[0039] In one specific embodiment, the fluorosulfonamide inner salt comprises one or more compounds of Formulas 1-1 to 1-5:

[0040]

[0041] When the above-mentioned compounds are selected as the fluorosulfonamide inner salt, the fluorosulfonamide inner salt makes the cathode material more resistant to oxidation, thereby further improving the battery's high-temperature cycle performance and high-temperature storage performance under high voltage.

[0042] In one specific embodiment, the mass percentage m1 of the fluorosulfonamide internal salt in the electrolyte is 0.1% to 20%, for example, 0.1%, 0.5%, 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, or 20%, etc., preferably, m1 is 0.5% to 10%. When the mass percentage of the fluorosulfonamide internal salt is within the above range, a sufficient amount of the fluorosulfonamide internal salt can form a CEI film of sufficient thickness on the positive electrode surface, making the CEI film more stable, thereby better protecting the positive electrode active material and avoiding damage to the SEI film caused by the dissolution of the positive electrode transition metal; on the other hand, a sufficient amount of the fluorosulfonamide internal salt makes the positive electrode material have stronger oxidation resistance, thereby further improving the high-temperature cycle performance and high-temperature storage performance of the battery under high voltage.

[0043] In one specific embodiment, the electrolyte comprises a carboxylic acid ester solvent; preferably, the carboxylic acid ester solvent comprises at least one selected from propyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, ethyl propionate, n-propyl propionate, methyl butyrate, ethyl butyrate, and n-ethyl butyrate; preferably, the mass percentage m2 of the carboxylic acid ester solvent in the electrolyte is 5% to 50%, for example, 5%, 10%, 20%, 30%, 40%, or 50%. When a carboxylic acid ester solvent is selected and the mass percentage of the solvent is within the above range, the carboxylic acid ester solvent can completely dissolve the fluorosulfonamide internal salt, thereby improving the high-temperature cycle performance, high-temperature storage performance, and low-temperature discharge performance of the battery.

[0044] In one specific embodiment, the electrolyte includes a lithium salt, which includes a boron-containing lithium salt; preferably, the boron-containing lithium salt includes lithium difluorooxalate borate (LiODFB). When LiODFB is selected as the boron-containing lithium salt, lithium difluorooxalate borate can form a dense protective film on the positive electrode surface. This protective film can effectively suppress the oxidation reaction of lithium difluorooxalate borate on the positive electrode at high potentials. This suppression effect increases the stability of lithium-ion batteries using lithium difluorooxalate borate as the electrolyte.

[0045] Preferably, the boron-containing lithium salt accounts for 0.1% to 1% of the electrolyte by mass percentage (m3), for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%. When the mass percentage of boron-containing lithium salt is within the above range, it can form a more stable complex layer at the positive electrode, thereby better protecting the positive electrode active material, improving the high-temperature cycle performance and high-temperature storage performance of the battery, and avoiding side reactions between the boron-containing lithium salt and other components in the battery due to excessive addition, thus preventing the degradation of electrochemical performance.

[0046] In one specific embodiment, the lithium salt further includes one or more of lithium hexafluorophosphate, lithium difluorophosphate, and lithium tetrafluoroborate; preferably, the lithium salt accounts for 5% to 25% of the electrolyte by mass, for example, 5%, 10%, 15%, 20%, or 25%, etc., and preferably, the lithium salt includes lithium hexafluorophosphate (LiPF6). When the mass percentage of the lithium salt is within the above range, the lithium salt can be completely dissolved in the organic solvent to form a highly stable electrolyte, allowing lithium ions to rapidly dissociate and transport in the electrolyte, improving the conductivity of the electrolyte, thereby enhancing the electrochemical performance of the battery.

[0047] In one specific embodiment, the electrolyte includes vinyl sulfate (DTD). The addition of a fluorosulfonamide inner salt to the electrolyte can form a stable protective film on the positive electrode surface, protecting the positive electrode active material and improving the battery's high-temperature cycle performance and high-temperature storage performance under high voltage. However, the conductivity of this protective film is not high enough, leading to increased battery impedance and deterioration of the battery's low-temperature discharge performance. To improve the battery's low-temperature discharge performance, this embodiment of the invention adds DTD to the electrolyte. DTD can change the coordination environment between the positive electrode metal ions and the fluorosulfonamide inner salt, reduce the activity of the metal ions, reduce the reaction between the metal ions and other components in the electrolyte, avoid accelerated oxidative decomposition of the electrolyte solvent, and reduce impedance, thereby reducing the impedance of the positive electrode and improving the battery's low-temperature discharge performance. Moreover, DTD can participate in the construction of the SEI film, effectively improving the flexibility and stability of the SEI film, preventing SEI film rupture caused by volume changes of the negative electrode material during charging and discharging, thereby improving the battery's cycle performance.

[0048] Preferably, the mass percentage (m4) of DTD in the electrolyte is 0.1% to 1%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%. When the mass percentage of DTD is within the above range, DTD can better reduce the impedance of the positive electrode and improve the flexibility and stability of the SEI film. At the same time, it can avoid the side reactions between DTD and other components in the electrolyte caused by excessive DTD, thereby enabling the battery to exhibit higher low-temperature discharge performance and cycle performance.

[0049] This invention provides a battery comprising a positive electrode, a negative electrode, and the aforementioned electrolyte. This battery exhibits excellent high-temperature cycling performance and high-temperature storage performance under high voltage.

[0050] In one specific embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder. The negative electrode current collector is generally copper foil. The negative electrode active material includes carbon-based materials and silicon-based materials. When the negative electrode active material includes both carbon-based and silicon-based materials, the silicon-based material can improve the energy density of the battery, while the carbon-based material can suppress the expansion problem caused by the silicon-based material and improve the diffusion rate and transport rate of lithium ions in silicon particles, thereby ensuring the cycle performance of the battery.

[0051] Preferably, the mass percentage m5 of silicon in the negative electrode active material is 2% to 30%, for example, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, or 30%. When the mass percentage of silicon in the negative electrode active material is within the above range, the conductivity of the negative electrode sheet is high, and the expansion rate of the negative electrode active material layer is low during battery charging and discharging, avoiding the problems of powdering and shedding of the negative electrode active material layer, thereby improving the cycle performance and safety performance of the battery.

[0052] Specifically, the mass percentage of silicon in the negative electrode active material can be obtained by inductively coupled plasma spectroscopy (ICP).

[0053] Preferably, the D50 of the silicon-based material is 5μm to 15μm, for example, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, or 15μm. When the D50 of the silicon-based material is within the above range, it allows the silicon particles to have a certain buffer space when the volume changes, reducing the risk of material breakage and improving the cycle stability of the battery.

[0054] Specifically, the testing method for the D50 of silicon-based materials includes the following steps:

[0055] The battery was disassembled, the negative electrode was removed, and the silicon-carbon negative electrode powder on the current collector was scraped off. The scraped powder sample was ground and sieved to control the average particle size within a certain range (e.g., 320 mesh, about 40 μm) and ensure uniform particle distribution. Then, the sample was scanned with an X-ray diffractometer to obtain the D50 of the silicon-based material.

[0056] In a specific embodiment, the porosity of the negative electrode sheet is 50% - 70%, such as 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68% or 70%, etc. The increase in porosity means that the proportion of unoccupied pore space in the negative electrode material increases, which helps to increase the specific surface area of the material. The increase in specific surface area provides more active sites for the insertion and extraction of lithium ions, thereby increasing the energy storage capacity of the battery. At the same time, it provides a certain buffer space to reduce the stress and strain generated by the volume change of the negative electrode material, thereby improving the cycle stability of the battery.

[0057] Specifically, the test method for the porosity of the negative electrode sheet includes the following steps: disassemble the battery, take out the electrode sheet and dry it, then use CT technology on the negative electrode sheet to obtain the three-dimensional structure and morphological information inside the negative electrode sheet, including the size, shape and distribution of pores, etc. Then, through three-dimensional reconstruction and data analysis, parameters such as porosity can be accurately calculated.

[0058] In a specific embodiment, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on the surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, a conductive agent and a binder. Among them, the positive electrode current collector is generally a copper foil. The positive electrode active material includes lithium cobalt oxide material. The selection of lithium cobalt oxide material in the embodiments of the present invention can effectively improve the specific capacity of the battery.

[0059] Specifically, the mass percentage content of cobalt element in the lithium cobalt oxide material is obtained by inductively coupled plasma spectroscopy (ICP) testing.

[0060] Preferably, the mass percentage content m6 of cobalt element in the lithium cobalt oxide material is 54.8% - 63.1%, such as 54.8%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62% or 63.1%, etc. When the mass percentage content of cobalt element in lithium cobalt oxide is within the above range, it can improve the specific capacity of the battery and avoid problems such as capacity decline and poor cycle performance caused by the system expansion of the positive electrode material, thereby ensuring that the battery reaches higher electrochemical performance under high-capacity conditions.

[0061] In a specific embodiment, the carbon-based material includes at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon and soft carbon; and / or, the silicon-based material is selected from at least one of nano-silicon (Si), silicon oxide negative electrode material (SiOx(0 < x < 2)) and silicon-carbon negative electrode material.

[0062] In one specific embodiment, the electrolyte further includes conventional additives, including at least one selected from vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, vinyl sulfate, succinate, glutaronitrile, adiponitrile, heptaonitrile, octanoic acid, sebaconitrile, 1,3,6-hexanetrionitrile, glycerol trionitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,3-propanesulfonic acid lactone, and propenyl-1,3-sulfonic acid lactone.

[0063] In one specific embodiment, the negative electrode active material layer further includes a conductive agent and a binder; the positive electrode active material layer further includes a conductive agent and a binder.

[0064] In one specific embodiment, the conductive agent includes at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, and metal powder.

[0065] In one specific embodiment, the adhesive includes at least one of sodium carboxymethyl cellulose, styrene-butadiene latex, polytetrafluoroethylene, and polyethylene oxide.

[0066] In one specific embodiment, the battery further includes a separator, which is known in the art to be used in batteries and is stable to the electrolyte used, and may be configured as needed.

[0067] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. 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.

[0068] The present invention will be further described below through specific embodiments and comparative examples. Unless otherwise specified, the reagents, materials and instruments used below are all conventional reagents, materials and instruments, all of which are commercially available, and the reagents and materials involved can also be synthesized by conventional synthetic methods.

[0069] Example 1

[0070] The battery provided in this embodiment is prepared through the following steps:

[0071] 1. Preparation of electrolyte: In an argon-filled glove box (H2O<0.1ppm, O2<0.1ppm), ethylene carbonate (EC) / propylene carbonate (PC) / diethyl carbonate (DEC) / n-propyl propionate (PP) were mixed evenly in a mass ratio of 8 / 8 / 15 / 50. Then, 13 wt% of fully dried lithium hexafluorophosphate (LiPF6) based on the total mass of the electrolyte was quickly added to the mixture. After dissolution, 4 wt% of 1,3-propanesulfonate lactone (PS) and 8 wt% of fluoroethylene carbonate based on the total mass of the electrolyte were added. Fluorosulfonamide inner salt, LiODFB and DTD were added according to the additives shown in Table 1. After mixing evenly, the electrolyte was prepared.

[0072] 2. Preparation of negative electrode sheet: The negative electrode active material artificial graphite, silicon carbon material (D50 of 15μm), sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP), and single-walled carbon nanotubes (SWCNTs) were mixed in a mass ratio of 94.5:2.5:1.5:1:0.5, and deionized water was added. The mixture was stirred in a vacuum mixer to obtain a negative electrode active slurry. The negative electrode active slurry was uniformly coated on both surfaces of a copper foil. The coated copper foil was dried at room temperature, then transferred to an 80℃ oven for drying for 10 hours. After cold pressing and slitting, the negative electrode sheet was obtained.

[0073] 3. Preparation of the positive electrode sheet: Lithium cobalt oxide (LiCoO2, D50 15.54 μm, D90 28.89 μm), polyvinylidene fluoride (PVDF), SP (superP), and carbon nanotubes (CNT) are mixed in a mass ratio of 96:2:1.5:0.5. N-methylpyrrolidone (NMP) is added, and the mixture is stirred under vacuum until a uniform and fluid positive electrode slurry is formed. The positive electrode slurry is uniformly coated onto both surfaces of an aluminum foil. The coated aluminum foil is dried, and then rolled and slit to obtain the desired positive electrode sheet.

[0074] 4. Battery fabrication: The positive electrode, negative electrode, and separator are stacked in the order of positive electrode, separator, and negative electrode, and then wound to obtain a battery cell. The battery cell is placed in an outer packaging aluminum foil, and electrolyte is injected into the outer packaging. After vacuum sealing, settling, formation, shaping, and sorting, the battery is obtained. The charge / discharge range of the battery of this invention is 3.0-4.58V.

[0075] Examples 2 to 52, Comparative Examples 1 and 2: The differences from Example 1 are shown in Table 1. Except for the differences shown in Table 1, all other conditions are the same. Among them, the structure of the pyridine propane sulfonic acid inner salt in Comparative Example 1 is as follows:

[0076] The mass percentage of cobalt in the lithium cobalt oxide material was determined by ICP, as shown in Table 1.

[0077] The porosity of the negative electrode was obtained by true density testing, as shown in Table 1.

[0078] True density meter method for testing porosity:

[0079] The sample is placed in a true density meter, and the mass of the sample is measured using a weighing device.

[0080] The true volume of a sample is determined by gas expansion displacement methods (such as using helium).

[0081] Calculate the true density, which is the mass divided by the actual volume.

[0082] Measure apparent density:

[0083] Place the sample into the container and measure the mass of the entire container.

[0084] Apparent density is calculated by measuring the volume of the container and the mass of the sample.

[0085] Calculate porosity: According to the porosity formula: porosity = (apparent density - true density) / apparent density × 100%, substitute the true density and apparent density into the formula to calculate the porosity.

[0086] Table 1

[0087]

[0088]

[0089]

[0090] Test case

[0091] The lithium-ion batteries obtained in the examples and comparative examples were subjected to high-temperature cycle performance tests, high-temperature storage performance tests, low-temperature discharge performance tests, and rate tests, respectively. The test results are shown in Table 2.

[0092] 1) High-temperature cycling performance test at 45℃

[0093] The batteries prepared in the examples and comparative examples were subjected to 600 charge-discharge cycles at 45°C and a 1C rate within the charge-discharge cutoff voltage range. The discharge capacity of the first cycle was measured as x1 mAh, and the discharge capacity of the Nth cycle was measured as y1 mAh. The capacity of the Nth cycle was divided by the capacity of the first cycle to obtain the cycle capacity retention rate R1 = y1 / x1. See Table 2 for details.

[0094] 2) Cyclic performance test at 25℃

[0095] The batteries prepared in the examples and comparative examples were subjected to 600 charge-discharge cycles at 25°C and a 1C rate within the charge-discharge cutoff voltage range. The discharge capacity of the first cycle was measured as x1 mAh, and the discharge capacity of the Nth cycle was measured as y1 mAh. The capacity of the Nth cycle was divided by the capacity of the first cycle to obtain the cycle capacity retention rate R1 = y1 / x1. See Table 2 for details.

[0096] 3) Low-temperature discharge performance test

[0097] The voltage, internal resistance, and thickness of the lithium-ion battery were tested at 0℃, and then left to stand for 10 minutes. The battery was then discharged at 1C to the lower limit voltage of 3.0V, and left to stand for 10 minutes. It was then fully charged at 1C in a constant temperature chamber with a cutoff current of 0.025C, and left to stand for 10 minutes. Finally, it was discharged at 3C in a constant temperature chamber to the cutoff voltage of 3.0V, and left to stand for 10 minutes. The discharge capacity Q1 and the initial discharge capacity Q0 were recorded. The discharge capacity retention rate was calculated by Q1 / Q0×100%. See Table 2 for details.

[0098] 4) Ratio Testing

[0099] The voltage, internal resistance, and thickness of the lithium-ion battery were tested at 25℃, and then left to stand for 10 minutes. The battery was then discharged at 1C to the lower limit voltage of 3.0V and left to stand for 10 minutes. It was then fully charged at 1C in a constant temperature chamber with a cutoff current of 0.025C and left to stand for 10 minutes. Finally, it was discharged at 3C in a constant temperature chamber to the cutoff voltage of 3.0V and left to stand for 10 minutes. The discharge capacity Q2 and the initial discharge capacity Q0 were recorded. The discharge capacity retention rate was calculated by Q2 / Q0×100%. See Table 2 for details.

[0100] Table 2

[0101]

[0102]

[0103]

[0104] As shown in Table 2, based on Example 1, Comparative Example 1 and Comparative Example 2, the electrolyte can include fluorosulfonamide inner salts, which can improve the high-temperature cycling performance and high-temperature storage performance of the battery under high voltage.

[0105] As can be seen from the comparison of Examples 1-5, when the amount of fluorosulfonamide inner salt is in the range of 0.5% to 20%, the high-temperature cycle performance and high-temperature storage performance of the battery under high voltage can be improved.

[0106] According to the comparison of Examples 1 and 6-9, when the mass percentage m4 of DTD in the electrolyte is in the range of 0.1% to 1%, DTD can better reduce the impedance of the positive electrode and make the SEI film more flexible and stable. At the same time, it can avoid the side reaction between DTD and other components in the electrolyte caused by excessive DTD, thereby making the battery exhibit higher low-temperature discharge performance and cycle performance.

[0107] According to the comparison of Examples 1 and 10-13, when the mass percentage m2 of the carboxylic acid ester solvent in the electrolyte is in the range of 5% to 50%, the carboxylic acid ester solvent can completely dissolve the fluorosulfonamide internal salt, which is beneficial to the improvement of the battery's high-temperature cycle performance, high-temperature storage performance and low-temperature discharge performance.

[0108] According to the comparison of Examples 1 and 18-21, when the mass percentage m3 of boron-containing lithium salt in the electrolyte is in the range of 0.1% to 1%, the boron-containing lithium salt can form a more stable complex layer on the positive electrode, thereby better protecting the positive electrode active material and improving the high-temperature cycle performance and high-temperature storage performance of the battery.

[0109] According to the comparison of Examples 1 and 22-26, when the mass percentage m5 of silicon element in the negative electrode active material is in the range of 2% to 30%, the conductivity of the negative electrode sheet is high, and the expansion rate of the negative electrode active material layer is low during the battery charging and discharging process, thus avoiding the problem of powdering and shedding of the negative electrode active material layer, thereby improving the cycle performance and safety performance of the battery.

[0110] As can be seen from the comparison of Examples 1 and 27-30, when the D50 of the silicon-based material is in the range of 5μm to 15μm, the silicon particles can have a certain buffer space when the volume changes, reducing the risk of material breakage and improving the cycle stability of the battery.

[0111] According to the comparison of Examples 1 and 31-34, when the porosity of the negative electrode sheet is in the range of 50% to 70%, the energy storage capacity and cycle stability of the battery can be improved.

[0112] According to the comparison of Examples 1 and 35-38, when the mass percentage m6 of cobalt element in the lithium cobalt oxide material is in the range of 54.8% to 63.1%, the specific capacity of the battery can be improved, and the problems of capacity reduction and deterioration of cycle performance caused by the expansion of the cathode material system can be avoided, thereby ensuring that the battery achieves high electrochemical performance under high capacity conditions.

[0113] As can be seen from Examples 1 and 39-42, when the above-mentioned compounds are selected as the fluorosulfonamide inner salt, the fluorosulfonamide inner salt makes the cathode material more resistant to oxidation, thereby further improving the high-temperature cycle performance and high-temperature storage performance of the battery under high voltage.

[0114] As can be seen from the comparison of Examples 1 and 43-44, when the lithium salt contains boron-containing lithium salt, it is beneficial to improve the stability of the battery.

[0115] As can be seen from the comparison of Examples 1, 43 and 45, the presence of DTD in the electrolyte can improve the high-temperature cycle performance of the battery.

[0116] As can be seen from Examples 1 and 46-53, the above-mentioned carboxylic acid ester solvents can completely dissolve the fluorosulfonamide inner salt, thereby improving the battery's high-temperature cycle performance, high-temperature storage performance, and low-temperature discharge performance.

[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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. An electrolyte, characterized in that, This includes fluorosulfonamide inner salts, wherein the fluorosulfonamide inner salt has any one of the following structures: ； R1 to R5 are each independently selected from C1 to C12 alkyl groups, C1 to C12 alkyl groups containing halogen atoms, halogen atoms, substituted or unsubstituted aryl groups.

2. The electrolyte according to claim 1, characterized in that, R1 to R5 are each independently selected from C1 to C6 alkyl groups, C1 to C6 alkyl groups containing fluorine atoms, fluorine atoms, substituted or unsubstituted aryl groups, wherein when the aryl group has a substituent, the substituent is selected from C1 to C6 alkyl groups.

3. The electrolyte according to claim 2, characterized in that, The fluorosulfonamide inner salt includes compounds shown in Formulas 1-3 below: 。 4. The electrolyte according to any one of claims 1-3, characterized in that, The fluorosulfonamide inner salt accounts for 0.1% to 20% of the mass percentage (m1) of the electrolyte.

5. The electrolyte according to claim 4, characterized in that, The value of m1 is 0.5% to 10%.

6. The electrolyte according to any one of claims 1-3, characterized in that, The electrolyte includes carboxylic acid ester solvents.

7. The electrolyte according to claim 6, characterized in that, The carboxylic acid ester solvent includes at least one of propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, ethyl propionate, n-propyl propionate, methyl butyrate, ethyl butyrate, and n-ethyl butyrate.

8. The electrolyte according to claim 6, characterized in that, The carboxylic acid ester solvent accounts for 5% to 50% of the mass percentage (m2) of the electrolyte.

9. The electrolyte according to any one of claims 1-3, characterized in that, The electrolyte includes a lithium salt, which includes a boron-containing lithium salt.

10. The electrolyte according to claim 9, characterized in that, The boron-containing lithium salt includes lithium difluorooxalate borate.

11. The electrolyte according to claim 9, characterized in that, The boron-containing lithium salt in the electrolyte accounts for 0.1% to 1% of the electrolyte by mass (m3).

12. The electrolyte according to any one of claims 1-3, characterized in that, The electrolyte includes vinyl sulfate.

13. The electrolyte according to claim 12, characterized in that, The ethylene sulfate in the electrolyte accounts for 0.1% to 1% of the mass of the electrolyte.

14. A battery, characterized in that, It includes a positive electrode, a negative electrode, and the electrolyte according to any one of claims 1-13.

15. The battery according to claim 14, characterized in that, The negative electrode sheet includes a negative electrode active material, which includes carbon-based materials and silicon-based materials, and / or the porosity of the negative electrode sheet is 50%~70%.

16. The battery according to claim 15, characterized in that, The mass percentage (m5) of silicon in the negative electrode active material is 2% to 30%.

17. The battery according to claim 15, characterized in that, The D50 of the silicon-based material is 5μm~15μm.

18. The battery according to claim 14, characterized in that, The positive electrode includes lithium cobalt oxide material.

19. The battery according to claim 18, characterized in that, The mass percentage (m6) of cobalt in the lithium cobalt oxide material is 54.8% to 63.1%.

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