Electrolyte solution of lithium ion battery, lithium ion battery, and electronic appliance

Abstract

To provide an electrolyte solution of a lithium ion battery applicable to a low-temperature environment, in which the operation in a high-temperature environment is improved, both the cycle performance and the preservation performance at high temperature and low temperature are achieved, and the operation performance and safety in various extreme environments are improved.SOLUTION: An electrolyte solution of a lithium ion battery includes a nonaqueous solvent containing linear carboxylic acid ester solvent, lithium salts at least one of which contains sulfur, and an additive containing thiophene, in which the content of thiophene in the electrolyte solution is 0.1 wt% to 3 wt%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to the technical field of power batteries, and in particular to an electrolyte for lithium ion batteries, lithium ion batteries, and electronic devices. [Background technology]

[0002] Lithium-ion batteries are widely used as power sources for electric drive systems, such as electric vehicles, electric bicycles, and power tools. Due to their advantages such as high energy density, long life, and fast charging, they have become a core component of electric drive systems.

[0003] Compared with other types of power batteries, lithium-ion batteries have a significantly higher energy density, but they also pose potential risks in terms of safety and cycle life. In particular, when fully charged, lithium-ion batteries are in a high-temperature environment, which further increases the reactivity of the positive and negative electrodes and the electrolyte inside the battery. As a result, the heat generated by the reaction increases significantly, and a large amount of gas is generated, which makes the lithium-ion battery prone to volume expansion. In severe cases, this can cause an internal short circuit, which can seriously affect the safety of the lithium-ion battery. Summary of the Invention [Problem to be solved by the invention]

[0004] As application scenarios continue to expand, lithium-ion batteries must not only operate normally in normal high-temperature environments, but also adapt to low-temperature environments. In consideration of the above, the present invention proposes a low-temperature electrolyte suitable for low-temperature operating environments. The low-temperature electrolyte employs a low-viscosity linear carboxylic acid ester-based solvent to maintain high ionic conductivity and low interfacial resistance even at low temperatures. At the same time, the use of high-temperature film-forming additives, such as 1,3-propanesultone (PS), is reduced or avoided to avoid an increase in low-temperature resistance. However, such low-temperature electrolytes suffer from the problem of reduced performance in high-temperature environments. The main reasons for this problem are as follows: First, linear carboxylic acid ester-based solvents have poor chemical and electrochemical stability with electrode materials and lithium salts at high temperatures, especially the commonly used lithium salt lithium hexafluorophosphate (LiPF6). Furthermore, they react with byproducts generated by components such as LiPF6, which decompose at high temperatures, resulting in reduction and gas generation. Second, if the amount of high-temperature additives such as PS is too small, it will affect the stability of the solid electrolyte interface (SEI) in high-temperature environments. Therefore, low-temperature electrolytes that are suitable for low-temperature environments often generate a lot of gas in high-temperature environments, causing more serious loss of active lithium and making them unsuitable for high-temperature working environments. [Means for solving the problem]

[0005] The present invention provides a lithium-ion battery electrolyte, a lithium-ion battery, and an electronic device. The lithium-ion battery electrolyte, lithium-ion battery, and electronic device provided by the present invention enable the lithium-ion battery to adapt to low-temperature environments while improving its operation in high-temperature environments, achieving both high-temperature and low-temperature cycle performance and storage performance of the lithium-ion battery, and improving the operation performance and safety of the lithium-ion battery in various extreme environments.

[0006] In order to solve the above technical problems, the present invention provides an electrolyte for a lithium ion battery, comprising the following components:

[0007] a non-aqueous solvent containing a linear carboxylic acid ester solvent;

[0008] a lithium salt containing at least one sulfur salt;

[0009] An additive containing thiophene, wherein the content of thiophene in the electrolyte is 0.1 wt % to 3 wt %.

[0010] In one embodiment of the present invention, the lithium salt includes at least one of lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, lithium methyl((trifluoroboryl)methyl)sulfonate, lithium fluorosulfonate, trifluoromethanesulfonate, and lithium bis(pentafluoroethylsulfonyl)imide.

[0011] In one embodiment of the present invention, the lithium salts mentioned above further comprise lithium hexafluorophosphate and / or lithium difluoroborate.

[0012] In one embodiment of the present invention, the sulfur content in the above-mentioned lithium salt is 26 wt% to 35 wt%.

[0013] In one embodiment of the present invention, the viscosity of the above-mentioned electrolyte at 5°C is 0.5 mm 2 / s~10.0mm 2 / s.

[0014] In one embodiment of the present invention, the non-aqueous solvent includes one or more of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, ethyl propionate, and diethyl carbonate, and the content of the non-aqueous solvent in the electrolyte is 75 wt % to 85 wt %.

[0015] In one embodiment of the present invention, the non-aqueous solvent includes ethylene carbonate, ethyl methyl carbonate, and ethyl propionate.

[0016] In one embodiment of the present invention, the content of the lithium salt in the above-mentioned electrolyte solution is 10 wt % to 20 wt %.

[0017] The present invention further provides a lithium ion battery containing the above-described lithium ion battery electrolyte.

[0018] The present invention further provides an electronic device including the above-described lithium ion battery. [Effects of the Invention]

[0019] In summary, the present invention provides a lithium-ion battery electrolyte, a lithium-ion battery, and an electronic device that can form a dense, heat-resistant SEI film on the surface of a negative electrode sheet. The SEI film contains sulfonic acid groups, which are more heat-resistant and dense, and have better high-temperature stability. This suppresses reactions between the negative electrode active lithium, the SEI film, and the electrolyte at high temperatures, thereby improving high-temperature storage performance. At the same time, the sulfonic acid groups in the formed SEI film have electronic insulation, better high-temperature stability, and lower electronic conductivity. They also favorably promote the dissociation of sulfonic acid groups from lithium salts and the transport of lithium ions, thereby improving the high-temperature cycle performance of lithium-ion batteries. Therefore, the formation of a dense SEI film can be ensured while maintaining the ionic conductivity of the electrolyte, thereby improving the high-temperature cycle and high-temperature storage performance of lithium-ion batteries. The viscosity of the electrolyte at low temperatures is reduced, allowing the lithium-ion battery to adapt to low-temperature environments while at the same time improving its operation in high-temperature environments, achieving both the cycle performance and storage performance of the lithium-ion battery at both high and low temperatures, and improving the operating performance and safety of the lithium-ion battery in a variety of extreme environments. DETAILED DESCRIPTION OF THE INVENTION

[0020] While the present invention will be described below with reference to specific examples, those skilled in the art will readily understand other advantages and effects of the present invention from the disclosure of this specification. The present invention may also be implemented or applied through other different specific embodiments, and various details of the specification may be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0021] It should be understood that this invention may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0022] The technical solutions of the present invention will be described in more detail with reference to the following embodiments, but it is clear that the described embodiments are only a part, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without any creative work fall within the scope of protection of the present invention.

[0023] The present invention provides a lithium-ion battery. The lithium-ion battery may be, for example, a primary battery or a secondary battery. The secondary battery may be, for example, a pouch-type battery, a prismatic-case battery, or a cylindrical battery. However, the present invention is not limited to this type of lithium-ion battery. Here, a prismatic-case battery will be used as an example to explain specific embodiments of the present invention. In one embodiment of the present invention, the lithium-ion battery includes a housing and a bare cell disposed within the housing. The bare cell includes a positive electrode sheet, a separator, and a negative electrode sheet. The positive electrode sheet, the separator, and the negative electrode sheet are stacked in this order, with the separator positioned between the positive electrode sheet and the negative electrode sheet. The multilayer laminate is obtained by winding or stacking, and then assembled into a battery housing as a bare cell. Finally, an electrolyte is injected into the housing in one or more batches, completely immersing the bare cell in the electrolyte.

[0024] In one embodiment of the present invention, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer applied to at least one surface of the positive electrode current collector. The positive electrode current collector is, for example, a foil material formed by surface-treating nickel, titanium, aluminum, silver, stainless steel, or carbon. In addition to foil materials, the positive electrode current collector may also be in various forms, such as film, mesh, porous, foam, or nonwoven fabric, either alone or in combination. The thickness of the positive electrode current collector is, for example, 8 μm to 15 μm. In this embodiment, the positive electrode current collector is, for example, aluminum foil, and the thickness of the aluminum foil is, for example, 13 μm.

[0025] In one embodiment of the present invention, the positive electrode active material layer includes a positive electrode active material, an adhesive, a conductive agent, etc. Here, the positive electrode active material may be any positive electrode active material suitable for use in a lithium ion secondary battery in a low temperature environment. In one embodiment of the present invention, the positive electrode active material is, for example, lithium iron phosphate (LiFePO4). The adhesive may be any one or more selected from the group consisting of polyvinylidene fluoride (PVDF), poly(ethylene oxide) (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinylether, polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), polyhexafluoropropylene, and polymerized styrene butadiene rubber (SBR). The conductive agent may be any one or more selected from the group consisting of conductive carbon black (Super P), acetylene black, carbon nanotubes, and graphene.

[0026] In one embodiment of the present invention, the positive electrode active material is, for example, LiFePO4, the adhesive is, for example, selected from polyvinylidene fluoride, and the conductive agent is, for example, selected from conductive carbon black. The positive electrode active material, conductive agent, and adhesive are mixed, for example, in a mass ratio of (90-98):(1-5):(1-5), and then an organic solvent is added. The mixture is stirred in a vacuum mixer until the system becomes homogeneous, yielding a positive electrode slurry. Here, the organic solvent is, for example, selected from N-methylpyrrolidone (NMP). The positive electrode slurry is uniformly applied to an aluminum foil, dried at room temperature, and then transferred to an oven for drying. A positive electrode sheet is obtained through processes such as cold pressing and slitting. In other embodiments, the positive electrode sheet may be obtained using any other method for forming a positive electrode sheet.

[0027] In one embodiment of the present invention, the negative electrode sheet includes, for example, a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector. The negative electrode current collector is, for example, one selected from a copper foil current collector, a composite copper foil current collector, a carbon current collector, a foamed copper current collector, or a stainless steel current collector. The thickness of the negative electrode current collector is, for example, 8 μm to 15 μm. In this embodiment, the negative electrode current collector is, for example, copper foil, and the thickness of the copper foil is, for example, 13 μm.

[0028] In one embodiment of the present invention, the negative electrode active material includes a negative electrode active material, a conductive agent, an adhesive, and a thickener. Here, the negative electrode active material is a compound capable of absorbing and releasing lithium ions. In one embodiment of the present invention, the negative electrode active material is selected from carbon materials such as artificial graphite and natural graphite. The adhesive is, for example, one or more selected from polyvinylidene fluoride, poly(ethylene oxide), polyamide, polypropylene, polyacrylate, polyvinyl ether, polymethyl methacrylate, polyhexafluoropropylene, and styrene butadiene rubber. The thickener is, for example, one or more selected from carboxymethyl cellulose sodium (CMC-Na). The conductive agent is, for example, one or more selected from conductive carbon black, acetylene black, ketjen black, carbon nanotubes, and graphene.

[0029] In one embodiment of the present invention, the negative electrode active material is selected from, for example, artificial graphite, the conductive agent is selected from, for example, conductive carbon black, the thickener is selected from, for example, sodium carboxymethyl cellulose, and the adhesive is selected from, for example, styrene butadiene rubber. In one embodiment of the present invention, the artificial graphite, conductive agent, adhesive, and thickener carbon are mixed in a mass ratio of, for example, (90-96):(1-2):(1-3):(2-5), deionized water is added, and the mixture is uniformly mixed in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry is applied to a copper foil, dried at room temperature, and then transferred to an oven for drying. A negative electrode sheet is obtained through processes such as cold pressing and slitting. In other embodiments, the negative electrode sheet may be obtained using any other method for forming a negative electrode sheet.

[0030] In one embodiment of the present invention, the separator is, for example, a polyethylene film (PE), a polypropylene film (PP), a glass fiber film, a composite film, etc. The thickness of the separator is, for example, 9 μm to 15 μm.

[0031] In one embodiment of the present invention, the lithium-ion battery further includes an electrolyte that fills the entire internal space of the battery. The positive electrode sheet, separator, and negative electrode sheet are completely immersed in the electrolyte. The electrolyte functions to conduct ions, provide ion channels, and maintain chemical stability. The components in the electrolyte are broadly classified into non-aqueous solvents, lithium salts, and additives based on their functions and amounts. The non-aqueous solvent dissolves the lithium salt and additives. The lithium salt primarily provides lithium ions to form ion channels. In the overall electrochemical system of a battery, electricity is generated through the directional movement of lithium ions and electrons. Lithium salts significantly affect the energy density, power density, wide electrochemical window, cycle life, and safety performance of a lithium battery. Additives are substances added in small amounts to the electrolyte. There are many types, each with different functions, and they each provide different improvements in, for example, high and low temperature performance, cycle performance, and membrane formation performance.

[0032] In one embodiment of the present invention, the lithium salt includes, for example, lithium hexafluorophosphate (LiPF), and the additive includes, for example, a film-forming additive such as ethylene sulfate (DTD), 1,3-propanesultone (PS), vinylene carbonate (VC), fluoroethylene carbonate (FEC), or vinyl ethylene carbonate (VEC). The non-aqueous solvent includes at least one of cyclic carbonates, linear carbonates, ethers, or carboxylic acid esters. Here, cyclic carbonate solvents can improve electrochemical stability and safety, but have poor compatibility with lithium. Linear carbonate solvents have lower viscosity than cyclic carbonates, better electrochemical stability, and can improve the low-temperature performance of the electrolyte, but cannot be used alone. Ether-based solvents have low dielectric constants and low viscosity, which effectively improve the conductivity of electrolytes, but they have active chemical properties and poor antioxidant properties. Linear carboxylic acid ester-based solvents have low viscosity, which allows electrolytes to maintain high ionic conductivity and low interfacial resistance even at low temperatures. However, to avoid increased low-temperature resistance, the use of high-temperature film-forming additives such as PS must be minimized or avoided. However, such low-temperature electrolytes suffer from performance degradation at high temperatures. Therefore, while lithium-ion batteries can improve low-temperature performance by selecting nonaqueous electrolyte solvents, they cannot simultaneously achieve both low-temperature and high-temperature performance.

[0033] The present invention provides an electrolyte solution for a lithium ion battery, comprising at least a non-aqueous solvent, a lithium salt, and an additive, wherein the additive comprises a thiophene represented by the following formula: [ka]

[0034] In one embodiment of the present invention, the thiophene content in the electrolyte is, for example, 0.1 wt% to 3 wt%, or, for example, 0.5 wt% to 1 wt%, including the endpoints. A low thiophene content affects the sulfur content at the negative electrode solid electrolyte interface (SEI) during the film formation process, which affects the density of the SEI film and ultimately affects high-temperature stability. A high thiophene content reduces the ionic conductivity of the electrolyte, increases polarization, and significantly increases the direct current resistance (DCR). Therefore, the thiophene content is controlled to ensure improved high-temperature performance of lithium-ion batteries.

[0035] In one embodiment of the present invention, at least one of the lithium salts contains sulfur, or includes, for example, a sulfur-containing lithium salt or a mixture of a sulfur-containing lithium salt and a sulfur-free lithium salt, where the sulfur-containing lithium salt is defined as a lithium salt containing sulfur element in its molecular formula. In this embodiment, the sulfur-free lithium salt is, for example, at least one selected from lithium hexafluorophosphate (LiPF) or lithium difluoroborate (LiODFB), and the sulfur-containing lithium salt is at least one selected from lithium bisfluorosulfonimide (LiFSI), lithium bistrifluoromethanesulfonimide (LiTFSI), lithium methyl ((trifluoroboryl)methyl)sulfonate, lithium fluorosulfonate, trifluoromethanesulfonate (CFSOLi), lithium bis(pentafluoroethylsulfonyl)imide (LiBETI), and the like. When the electrolyte contains both thiophene and a sulfur-containing lithium salt, the sulfur-containing aromatic ring in the thiophene interacts with the graphite in the anode through π-π stacking. The interaction between the sulfur in the thiophene and the sulfur-containing anion in the sulfur-containing lithium salt induces cooperation between the lithium salt and the thiophene, resulting in the formation of a dense, heat-resistant SEI film on the surface of the anode sheet. The SEI film contains sulfonic acid groups, which have better heat resistance and high temperature stability, and inhibits reactions between the anode active lithium, the SEI film, and the electrolyte at high temperatures, improving high-temperature storage performance at 60°C. At the same time, the sulfonic acid groups in the formed SEI film have electronic insulation, better high-temperature stability, and lower electronic conductivity. They also favorably promote the dissociation of the sulfonic acid groups from the lithium salt and the transport of lithium ions, thereby improving high-temperature cycling performance at 45°C.

[0036] In one embodiment of the present invention, the lithium salt content in the lithium salt-containing electrolyte is, for example, 10 wt% to 20 wt%, and the sulfur content in the lithium salt is, for example, 26 wt% to 35 wt%. That is, the mass of sulfur in the lithium salt accounts for 26 wt% to 35 wt% of the total mass of the lithium salt. In one embodiment of the present invention, the lithium salt in the electrolyte may be entirely sulfur-containing lithium salt, or a mixture of sulfur-containing and sulfur-free lithium salts may be selected. This controls the sulfur content in the lithium salt, ensures the density of the SEI film, and ensures the high-temperature performance of lithium-ion batteries. A low sulfur content in the lithium salt affects the sulfur content in the SEI film formation process. This means that the amount of highly polar sulfur-containing functional groups, such as sulfonic acid groups and sulfonylimide groups, in the formed SEI film is reduced, leading to a decrease in the solvent removal ability, thermodynamic stability, and density of the SEI film, which ultimately affects the high-temperature stability of lithium-ion batteries. When the sulfur content in the lithium salt is high, the density of the SEI film is favorable, resulting in a high high-temperature cycle retention rate. However, if the density of the SEI film is too high, the desolvation process and conduction of lithium ions will be affected to some extent, resulting in a high DCR growth rate. Therefore, the sulfur content in the lithium salt is controlled to ensure that the sulfur-containing anions in the lithium salt and the sulfur-containing aromatic ring in the thiophene have a synergistic effect, thereby improving high-temperature performance.

[0037] In one embodiment of the present invention, the non-aqueous solvent may be, for example, a cyclic carbonate, a chain carbonate, or a linear carboxylic acid ester solvent, or may be, for example, one or a combination of at least two of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethyl propionate (EP), or diethyl carbonate (DEC), and the content of the non-aqueous solvent in the electrolyte is, for example, 75 wt% to 85 wt%. In one embodiment of the present invention, the non-aqueous solvent may be, for example, a mixture of ethylene carbonate, ethyl methyl carbonate, and ethyl propionate, and the mass ratio of the ethylene carbonate, ethyl methyl carbonate, and ethyl propionate is, for example, 1:(4-6):(4-6). The electrolyte contains low-temperature electrolyte solvents such as the chain carbonate solvent ethylene carbonate and the linear carboxylic acid ester solvent ethyl propionate, which can avoid problems such as a decrease in ionic conductivity and wettability of the electrolyte, which is advantageous for the operation of lithium ion batteries at low temperatures. In one embodiment of the present invention, the viscosity of the electrolyte at 5°C is, for example, 0.5 mm 2 / s~10.0mm 2 Therefore, when the electrolyte solution obtained by the present invention is applied to a lithium ion battery, it enables the lithium ion battery to adapt to low temperature environments and at the same time improves its operation in high temperature environments, ultimately achieving both high and low temperature cycle performance and storage performance of the lithium ion battery, and improving the operation performance and safety of the lithium ion battery in various extreme environments.

[0038] In one embodiment of the present invention, when preparing an electrolyte solution, the content of stable gases such as nitrogen and argon in a glove box is 99.999%, the actual oxygen content in the glove box is 0.1 ppm or less, and the water content is 0.1 ppm or less. After uniformly mixing the nonaqueous solvent by mass, a thoroughly dried lithium salt is added to the nonaqueous solvent, and additives are added to prepare a nonaqueous electrolyte solution for a lithium ion battery. Here, the contents of the lithium salt and additives, excluding the nonaqueous solvent, are expressed as weight percentages calculated based on the total weight of the electrolyte solution.

[0039] In one embodiment of the present invention, the positive electrode sheet, separator, and negative electrode sheet are arranged in this order. The separator is positioned between the positive electrode sheet and the negative electrode sheet to provide insulation. A bare cell is obtained by rolling or stacking. The bare cell is placed in a housing, dried in a vacuum oven, and then sealed after the electrolyte solution prepared in the present invention is injected. A lithium-ion secondary battery is obtained by at least the steps of leaving, chemical conversion, and grading.

[0040] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Appropriate modifications can be made within the scope of the present invention, and all such modifications fall within the technical scope of the present invention.

[0041] Example 1

[0042] Preparation of electrolyte solution: In an argon glove box with a water content of less than 1 ppm, 7 g of ethylene carbonate, 38 g of ethyl methyl carbonate, and 38 g of ethyl propionate were mixed. Then, a dry lithium mixture containing 2 g of lithium hexafluorophosphate, 1 g of lithium difluoroborate, 11 g of lithium bisfluorosulfonimide, and 2 g of lithium bistrifluoromethanesulfonimide was added to the mixed solvent. After the mixed lithium salts were dissolved, 1 g of thiophene was added and mixed uniformly to obtain an electrolyte solution. The sulfur content of the mixed lithium salts in the resulting electrolyte solution was 26.3 wt%, and the viscosity of the electrolyte solution at 5°C was 1.93 mm. 2 / s.

[0043] Preparation of positive electrode sheet: LiFePO4, polyvinylidene fluoride, and conductive carbon black were mixed in a mass ratio of 98:1:1, and then N-methylpyrrolidone was added and stirred in a vacuum mixer until the system was homogeneous, obtaining positive electrode slurry. The positive electrode slurry was evenly applied to aluminum foil, dried at room temperature, transferred to an oven, dried, cold pressed, slit, and other processes to obtain a positive electrode sheet.

[0044] Preparation of negative electrode sheet: Artificial graphite, conductive carbon black, sodium carboxymethylcellulose, and styrene-butadiene rubber were mixed in a mass ratio of 96:1:1:2, and deionized water was added. The mixture was mixed uniformly in a vacuum mixer to obtain negative electrode slurry. The negative electrode slurry was applied to copper foil, dried at room temperature, and then transferred to an oven for drying. After cold pressing and slitting, the negative electrode sheet was obtained.

[0045] Separator selection: A 12 μm polyethylene film was selected as the separator.

[0046] Preparation of battery: A positive electrode sheet, a separator, and a negative electrode sheet were stacked in this order so that the separator was positioned between the positive electrode sheet and the negative electrode sheet to provide insulation. This was then placed in a rectangular case and dried in a vacuum oven. The electrolyte solution prepared above was then poured into the case and sealed to form an electrolyte, resulting in a lithium-ion secondary battery.

[0047] The battery cells were filled and formed in a glove box with a dew point controlled below -40°C. The above-mentioned electrolyte was then injected into the battery through the filling port. The amount of electrolyte needed to fill the voids in the battery was sufficient. The initial charge and formation process was then performed as follows: Charging at a constant current of 0.05C for 3 minutes, then at a constant current of 0.2C for 5 minutes, then at a constant current of 0.5C for 25 minutes, then at a constant current of 0.5C for 1 hour, followed by charging to 3.65V at a constant current of 0.2C. After 24 hours of rest at room temperature, the battery was discharged to 2.5V at a constant current of 0.2C.

[0048] Example 2

[0049] The mass of thiophene was 0.1 g, and the other steps were the same as in Example 1.

[0050] Example 3

[0051] The mass of thiophene is 0.25 g, and the other steps are the same as in Example 1.

[0052] Example 4

[0053] The mass of thiophene is 0.5 g, and the other steps are the same as in Example 1.

[0054] Example 5

[0055] The mass of thiophene is 0.75 g, and the other steps are the same as in Example 1.

[0056] Example 6

[0057] The mass of thiophene is 1.5 g, and the other steps are the same as in Example 1.

[0058] Example 7

[0059] The mass of thiophene is 3 g, and the other steps are the same as in Example 1.

[0060] Example 8

[0061] The composition of the mixed lithium salt was 3 g of lithium hexafluorophosphate, 0.5 g of lithium difluoroborate, and 12.5 g of lithium bisfluorosulfonimide, where the sulfur content in the mixed lithium salt was 26.8 wt %, and the other operations were the same as in Example 4.

[0062] Example 9

[0063] The composition of the mixed lithium salt was 3.5 g of lithium hexafluorophosphate and 12.5 g of lithium bisfluorosulfonimide, where the sulfur content in the mixed lithium salt was 26.8 wt %, and the other operations were the same as in Example 4.

[0064] Example 10

[0065] The composition of the mixed lithium salt was 2 g of lithium hexafluorophosphate and 14 g of lithium bisfluorosulfonimide, where the sulfur content in the mixed lithium salt was 30.0 wt %, and the other operations were the same as in Example 4.

[0066] Example 11

[0067] The composition of the mixed lithium salt was 16 g of lithium bisfluorosulfonimide, where the sulfur content in the mixed lithium salt was 34.2 wt %, and the other operations were the same as in Example 4.

[0068] Comparative Example 1

[0069] No thiophene was added, and the other steps were the same as in Example 1.

[0070] Comparative Example 2

[0071] The mass of thiophene is 6 g, and the other steps are the same as in Example 1.

[0072] Comparative Example 3

[0073] The composition of the mixed lithium salt was 16 g of lithium hexafluorophosphate, no other lithium salt was used, the sulfur content in the mixed lithium salt was 0%, and the other operations were the same as in Example 1.

[0074] Comparative Example 4

[0075] The composition of the mixed lithium salt was 7 g of lithium hexafluorophosphate, 1 g of lithium difluoroborate, 7 g of lithium bisfluorosulfonimide, and 1 g of lithium bistrifluoromethanesulfonimide, and the sulfur content in the mixed lithium salt was 16.4 wt %. The other procedures were the same as in Example 1.

[0076] In the present invention, in Examples 1 to 11 and Comparative Examples 1 to 4, lithium ion batteries were manufactured by changing the ratio of the electrolyte solution, and the performance of the lithium ion batteries was tested. The results are shown in Table 1.

[0077] In one embodiment of the present invention, when performing a 5°C viscosity test on an electrolyte, the Ubbelohde viscometer was placed on a horizontal table and inspected for dirt or damage. Next, the Ubbelohde viscometer was cleaned using a dimethyl carbonate (DMC) solution. The Ubbelohde viscometer was turned on and placed in the electrolyte to be measured. A predetermined time was allowed for the electrolyte temperature to stabilize at 5°C and for the Ubbelohde viscometer to be completely immersed in the electrolyte. Next, the position of the scale line was adjusted using the adjustment screw so that it was flush with the liquid surface. The Ubbelohde viscometer was removed from the electrolyte and quickly rotated 180°. The distance traveled by the scale line within 60 seconds was recorded, and the viscosity of the liquid was calculated. After use, the Ubbelohde viscometer was cleaned, disinfected, and maintained with pure water or another appropriate solution, and then stored in a dry, well-ventilated place.

[0078] In one embodiment of the present invention, a 45°C cycle performance test was performed by charging the formed battery to 3.65 V at 45°C using a 3C constant current and constant voltage, and then discharging to 2.5 V using a 3C constant current. After 500 charge / discharge cycles, the discharge capacity retention rate at the 500th cycle was calculated.

[0079] In one embodiment of the present invention, the DCR test for storage at 60°C was performed by charging the formed battery to 3.65V at a constant current and voltage of 1C at room temperature, then discharging it to 50% SOC (State of Charge) at 1C, and then discharging it at 3C for 10 seconds to test the DCR, which was recorded as DCR0. Then, the battery was discharged to 2.5V at 1C, and then charged to 3.65V at a constant current and voltage of 1C, and stored at 60°C for 30 days. After the battery was cooled to room temperature, the DCR was tested using the same conditions, and the DCR was recorded as DCR0. 15 The DCR growth rate was recorded as (DCR 15 / DCR0-1)×100%.

[0080] Table 1 shows the performance test results of the lithium ion batteries of Examples 1 to 11 and Comparative Examples 1 to 4. [Table 1]

[0081] As shown in Table 1, comparing Examples 1 to 11 with Comparative Examples 1 to 4, the electrolytes exhibited low viscosities at 5°C, thereby satisfying the low-temperature operation of lithium-ion batteries. Comparing Examples 1 to 11 with Comparative Example 1, after adding thiophene to the electrolyte, the sulfur-containing aromatic ring in the thiophene and the graphite in the negative electrode conjugate through π-π bonds. The interaction between the sulfur in the thiophene and the sulfur-containing anions in the sulfur-containing lithium salt induces cooperation between the lithium salt and the thiophene, resulting in the formation of a dense, heat-resistant SEI film on the surface of the negative electrode sheet. The SEI film has high high-temperature resistance and contains dense, electrically insulating sulfonic acid groups, which enhances the high-temperature capacity retention of lithium-ion batteries. Furthermore, the sulfonic acid groups improve high-temperature stability while also promoting the dissociation of lithium salts and the transport of lithium ions, thereby reducing the high-temperature storage DCR growth rate. In the absence of thiophene, the sulfur-containing lithium salt is liberated in the electrolyte and is less likely to participate in film formation on the surface of the negative electrode sheet. Therefore, the SEI film has poor stability at high temperatures, resulting in a reduced capacity retention rate and an increased DCR growth rate during high-temperature storage.

[0082] As shown in Table 1, when Examples 1 to 11 are compared with Comparative Example 3, it can be seen that when the electrolyte does not contain a sulfur-containing lithium salt involved in film formation on the surface of the negative electrode sheet, the SEI film is less stable at high temperatures, the high-temperature capacity retention rate decreases, and the high-temperature storage DCR growth rate increases. Therefore, by using thiophene and a sulfur-containing lithium salt simultaneously, a dense SEI film can be formed, and the high-temperature performance of the lithium-ion battery can be improved.

[0083] As shown in Table 1, comparing Examples 1 to 7, when the sulfur content in the lithium salt is fixed, increasing the thiophene dosage affects the technical effect. As the thiophene dosage increases, the high-temperature capacity retention of the lithium-ion battery initially increases and then decreases, and the high-temperature storage DCR growth rate initially decreases and then increases. Therefore, reducing the thiophene dosage affects the sulfur content during the SEI film formation process, which affects the density of the SEI film and ultimately its high-temperature stability. Increasing the thiophene dosage reduces the ionic conductivity of the electrolyte and significantly increases the high-temperature storage DCR. Therefore, the thiophene dosage must be controlled to ensure improved lithium-ion battery performance.

[0084] As shown in Table 1, comparing Example 4 with Examples 8 and 9, when the ratio of lithium salts used in the mixed lithium salts is different but the sulfur content and thiophene dosage are the same, the high-temperature capacity retention rate and high-temperature storage DCR growth rate of the lithium-ion batteries are similar. Therefore, when the thiophene content and sulfur content in the mixed lithium salts are the same, the density of the formed SEI films and their high-temperature stability are similar.

[0085] As shown in Table 1, comparing Examples 1, 8, 10, and 11, when the sulfur content of the mixed lithium salts is different, it can be seen that increasing the sulfur content in the lithium salt results in similar high-temperature capacity retention of the lithium-ion battery, but an increased high-temperature storage DCR growth rate. The resulting SEI film has favorable density, resulting in a high high-temperature cycle retention rate. However, if the SEI film is too dense, the desolvation process and conduction of lithium ions are affected to some extent, resulting in a high high-temperature storage DCR growth rate. Here, Example 11 examines the extreme situation where only the high-sulfur lithium salt LiFSI is used. Here, the SEI film has favorable density, resulting in a high high-temperature cycle retention rate, but the desolvation process and conduction of lithium ions are affected to some extent, resulting in a high high-temperature storage DCR growth rate. Therefore, controlling the sulfur content in the lithium salt can simultaneously improve the high-temperature cycle and high-temperature storage performance of the lithium-ion battery.

[0086] As shown in Table 1, comparing Examples 1 to 11 with Comparative Example 2, it can be seen that the addition of an excessive amount of thiophene reduces the electrolyte's ability to dissociate and conduct lithium ions, increases polarization, and increases the high-temperature storage DCR growth rate. Comparing Examples 1 to 11 with Comparative Example 4, it can be seen that a low sulfur content in the mixed lithium salt results in a low sulfur content during the SEI film formation process, which fails to effectively improve the density and strength of the SEI film, resulting in a low high-temperature capacity retention rate and a high high-temperature storage DCR growth rate.

[0087] The present invention further provides an electronic device including the lithium ion battery used to supply at least one of the above-described electric energy sources. The electronic device includes vehicles, mobile phones, portable devices, laptops, ships, spacecraft, electric toys, power tools, and the like. In one embodiment of the present invention, the vehicle is, for example, a new energy vehicle, which may be a pure electric vehicle, a hybrid vehicle, or a range-extended vehicle. The aerospace vehicle includes an airplane, a rocket, a space shuttle, and a spaceship. The electric toys include game consoles, electric car toys, electric ship toys, electric plane toys, and other stationary or mobile electric toys. The power tools include metal cutting power tools, grinding power tools, assembly power tools, and railroad power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers. Since this electronic device includes the above-described lithium ion battery, it also has the advantages of the above-described lithium ion battery, but these will not be described in detail here. [Industrial Applicability]

[0088] In summary, the present invention provides a lithium-ion battery electrolyte, a lithium-ion battery, and an electronic device, which can form a dense, heat-resistant SEI film on the surface of a negative electrode sheet by adding thiophene and a lithium salt, including a sulfur-containing lithium salt, to the electrolyte. The SEI film contains sulfonic acid groups, which are more heat-resistant and dense, and have better high-temperature stability. This suppresses reactions between the negative electrode active lithium, the SEI film, and the electrolyte at high temperatures, thereby improving high-temperature storage performance. At the same time, the sulfonic acid groups in the formed SEI film have electronic insulation, better high-temperature stability, and lower electronic conductivity. They also favorably promote dissociation of the sulfonic acid group-lithium salt and lithium ion transport, thereby improving high-temperature cycling performance. Controlling the sulfur content in the thiophene and lithium salt allows for the formation of a dense SEI film, while ensuring the ionic conductivity of the electrolyte and improving the high-temperature cycling and high-temperature storage performance of the lithium-ion battery. By controlling the selection of the non-aqueous solvent, the viscosity of the electrolyte at low temperatures can be reduced, allowing the lithium-ion battery to simultaneously satisfy the operation in both low-temperature and high-temperature environments, expanding the application scenarios of the lithium-ion battery and improving the safety of the lithium-ion battery in extreme environments.

[0089] The above description is merely a preferred embodiment of the present application and merely describes the technical principles used. Those skilled in the art should understand that the scope of the present invention is not limited to the technical solution formed by the specific combination of the above technical features, but also includes other technical solutions formed by any combination of the above technical features or features equivalent thereto, for example, by replacing the above features with technical features having similar functions (but not limited to) disclosed in the present application, without departing from the inventive concept of the present invention.

[0090] Except for the technical features described in the specification, the remaining technical features are well-known to those skilled in the art, so in order to highlight the innovative features of the present invention, the remaining technical features will not be described in detail here.

Claims

1. An electrolyte for a lithium ion battery, a non-aqueous solvent containing a linear carboxylic acid ester solvent; a lithium salt containing at least one sulfur salt; an additive containing thiophene, wherein the content of the thiophene in the electrolyte solution is 0.1 wt % to 3 wt %; An electrolyte for a lithium ion battery, comprising the components:

2. 2. The electrolyte solution for a lithium ion battery according to claim 1, wherein the lithium salt includes at least one of lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, lithium methyl((trifluoroboryl)methyl)sulfonate, lithium fluorosulfonate, trifluoromethanesulfonate, and lithium bis(pentafluoroethylsulfonyl)imide.

3. 3. The electrolyte solution for a lithium ion battery according to claim 2, wherein the lithium salt further comprises lithium hexafluorophosphate and / or lithium difluoroborate.

4. 2. The electrolyte solution for a lithium ion battery according to claim 1, wherein the sulfur content in the lithium salt is 26 wt % to 35 wt %.

5. The viscosity of the electrolyte at 5°C is 0.5 mm ２ / s to 10.0 mm ２ 2. The electrolyte solution for a lithium ion battery according to claim 1, wherein the electrolyte is:

6. 2. The electrolyte solution for a lithium ion battery according to claim 1, wherein the non-aqueous solvent contains one or more of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, ethyl propionate, and diethyl carbonate, and the content of the non-aqueous solvent in the electrolyte solution is 75 wt % to 85 wt %.

7. 7. The electrolyte solution for a lithium ion battery according to claim 6, wherein the non-aqueous solvent includes ethylene carbonate, ethyl methyl carbonate, and ethyl propionate.

8. 2. The electrolyte for a lithium ion battery according to claim 1, wherein the content of the lithium salt in the electrolyte is 10 wt % to 20 wt %.

9. A lithium ion battery comprising the electrolyte solution of any one of claims 1 to 8.

10. An electronic device comprising the lithium ion battery according to claim 9.

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