An electrolyte and a battery comprising the same

Abstract

The application provides an electrolyte and a battery comprising the electrolyte, the electrolyte comprising an organic solvent, an electrolyte salt and an additive, wherein the additive comprises an additive A, and the additive A is selected from at least one of tetranitrile compounds containing at least one ester group. The nitrile group function in the additive A in the electrolyte can be complexed with the positive electrode surface, effectively inhibiting the dissolution of metal ions and the further oxidative decomposition of the electrolyte, and the additive A has a symmetrical structural formula and comprises an ester group and a nitrile group function, which makes the additive A have good kinetic performance and oxidation resistance; meanwhile, the fluorine atom possibly existing on the Ra group connecting the ester group and the nitrile group further improves the oxidation resistance of the whole structure.

Description

Technical Field

[0001] This invention relates to an electrolyte and a battery including the electrolyte, belonging to the field of battery technology. Background Technology

[0002] A lithium-ion battery is a rechargeable battery that primarily functions by the movement of lithium ions between the positive and negative electrodes. During charging and discharging, Li... + Intercalation and deintercalation back and forth between the two electrodes: During charging, Li + Lithium-ion batteries deintercalate from the positive electrode and intercalate into the negative electrode via the electrolyte, placing the negative electrode in a lithium-rich state; the process is reversed during discharge. Due to their advantages such as high energy density and long cycle life, lithium-ion batteries are widely used in various electronic products and, in recent years, have also been extensively used in electric vehicles, power tools, and energy storage devices.

[0003] With the improvement of people's living standards and their aspirations for a better life, higher demands are being placed on battery energy density. To improve battery energy density, further increasing the voltage of the positive electrode material in lithium-ion batteries is a common approach. However, as the limiting voltage of the positive electrode material continues to increase, its specific capacity gradually increases, leading to severe deterioration of the battery's high-temperature performance and making it impossible to guarantee long cycle life. Especially at high voltages (>4.5V), during long-term charge-discharge cycles, the volume of the positive electrode material expands, causing severe cracks. Electrolyte enters the interior of the positive electrode material, damaging its structure. Simultaneously, the release of active oxygen further accelerates the oxidative decomposition of the electrolyte. Furthermore, the protective film on the negative electrode surface is continuously damaged, ultimately resulting in severe capacity decay of the battery.

[0004] Currently, oxide coatings are generally used to modify the surface of cathode materials, or cathode materials with different shapes and structures are prepared. However, the process is complex, costly, and has poor protection effect. Summary of the Invention

[0005] To address the issues of positive electrode material volume expansion and continuous release of active oxygen oxidizing the electrolyte in existing high-voltage batteries, this invention aims to provide an electrolyte and a battery comprising the electrolyte. The use of the electrolyte can improve the room temperature cycle performance, high temperature cycle performance, and oxidation resistance of the electrolyte in high-voltage (e.g., above 4.5V) batteries, resulting in an electrolyte with oxidation resistance and a battery with superior room temperature and high temperature cycle performance. Furthermore, the preparation process of the electrolyte is simple, low-cost, and provides good protection.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] An electrolyte comprising an organic solvent, an electrolyte salt, and an additive, wherein the additive comprises additive A, which is selected from at least one tetranitrile compound containing at least one ester group.

[0008] According to the electrolyte of the present invention, the additive A is selected from at least one tetranitrile compound containing at least two ester groups, preferably from at least one tetranitrile compound containing four ester groups.

[0009] According to the electrolyte of the present invention, the tetranitrile compound refers to a compound containing four nitrile groups (-CN).

[0010] According to the electrolyte of the present invention, the ester group has the structure -COO-R, where R is an alkyl, alkylene, or trialkyl group.

[0011] More preferably, each ester group is linked to a cyano group via a linking group, i.e., NC-Ra-COO-R, where Ra is defined as follows.

[0012] According to the electrolyte of the present invention, the additive A is selected from at least one compound having the structural formula shown in formula (1):

[0013]

[0014] In equation (1), Ra is either the same or different, and is independently selected from substituted or unsubstituted C. 1-9 Alkylene, *-C 1-6 Alkylene-O-**, *-C 1-6 Alkylene-COO-**, *-C 1-6 Alkylene-S-**, *-C 1-6 Alkylene -S(=O)2-**; substituent is C 1-9 Alkyl groups and halogens, wherein the * end is connected to -CN and the ** end is connected to -CO-.

[0015] According to the electrolyte of the present invention, Ra may be the same or different, and is independently selected from substituted or unsubstituted C. 1-8 Alkylene, *-C 1-3 Alkylene-O-**, *-C 1-3 Alkylene-COO-**, *-C 1-3 Alkylene-S-**, *-C 1-3 Alkylene -S(=O)2-**; substituent is C 1-3 Alkyl groups and halogens, wherein the * end is connected to -CN and the ** end is connected to -CO-.

[0016] According to the electrolyte of the present invention, Ra may be the same or different, and is independently selected from substituted or unsubstituted C. 1-8Alkylene, *-CH2-O-**, *-CH2-COO-**, *-CH2-S-**, *-CH2-S(=O)2-**; substituent is C 1-3 Alkyl groups and halogens, wherein the * end is connected to -CN and the ** end is connected to -CO-.

[0017] According to the electrolyte of the present invention, Ra may be the same or different, and is independently selected from substituted or unsubstituted C. 1-6 Alkylene; substituent is C 1-3 Alkyl group, F.

[0018] In the electrolyte according to the present invention, Ra may be the same or different, and is independently selected from substituted or unsubstituted methylene, ethylene, propylene, butylene, pentylene, and hexylene; the substituent is C. 1-3 Alkyl group, F.

[0019] In the electrolyte according to the present invention, Ra may be the same or different, and is independently selected from the groups shown as R1 to R10 below:

[0020]

[0021]

[0022] Where * represents a linking group.

[0023] According to the electrolyte of the present invention, additive A can be prepared by methods known in the art or can be purchased commercially.

[0024] According to the electrolyte of the present invention, the mass of additive A is 0.1-5.0 wt% of the total mass of the electrolyte, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.2 wt%, 1.3 wt%, 1.5 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.8 wt%, 3 wt%, 3.3 wt%, 3.5 wt%, 3.8 wt%, 4 wt%, 4.2 wt%, 4.5 wt%, 4.8 wt%, or 5 wt%.

[0025] According to the electrolyte of the present invention, the electrolyte salt is selected from at least one of lithium electrolyte salt, sodium electrolyte salt, aluminum electrolyte salt, magnesium electrolyte salt, etc.

[0026] According to the electrolyte of the present invention, the electrolyte lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium bis(trifluoromethanesulfonyl)imide, lithium difluorobis(oxalate)phosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium di(trifluoromethanesulfonyl)imide, lithium di(pentafluoroethylsulfonyl)imide, lithium tri(trifluoromethanesulfonyl)methyl, or lithium di(trifluoromethanesulfonyl)imide.

[0027] According to the electrolyte of the present invention, the organic solvent is selected from carbonates and / or carboxylic esters, wherein the carbonate is selected from one or more of the following fluorinated or unsubstituted organic solvents: ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate, diethyl carbonate (DEC), and methyl ethyl carbonate; and the carboxylic ester is selected from one or more of the following fluorinated or unsubstituted organic solvents: propyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, propyl propionate (PP), ethyl propionate (EP), methyl butyrate, and ethyl butyrate.

[0028] According to the electrolyte of the present invention, the electrolyte further includes additive B, wherein additive B is selected from lithium bis(fluorosulfonyl)imide.

[0029] According to the electrolyte of the present invention, the mass of additive B is 1-4.0 wt% of the total mass of the electrolyte, for example, 1 wt%, 1.2 wt%, 1.3 wt%, 1.5 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.8 wt%, 3 wt%, 3.3 wt%, 3.5 wt%, 3.8 wt%, or 4 wt%.

[0030] According to the electrolyte of the present invention, the electrolyte further includes additive C, wherein additive C is selected from at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, succinic acid, triglyceride, lithium difluorooxalate borate, lithium difluorophosphate, and lithium difluorodioxalate phosphate.

[0031] According to the electrolyte of the present invention, the electrolyte is used in lithium-ion batteries.

[0032] The present invention also provides a battery comprising the electrolyte described above.

[0033] According to the present invention, the battery is a lithium-ion battery.

[0034] According to the battery of the present invention, the battery further includes a positive electrode, a negative electrode, and a separator.

[0035] In the battery according to the present invention, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer coated on one or both surfaces of the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode active material, a conductive agent and a binder.

[0036] In the battery according to the present invention, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer coated on one or both surfaces of the negative electrode current collector, and the negative electrode active material layer comprises a negative electrode active material, a conductive agent and a binder.

[0037] In the battery according to the present invention, the mass percentage of each component in the positive electrode active material layer is: 80-99.8 wt% of the positive electrode active material, 0.1-10 wt% of the conductive agent, and 0.1-10 wt% of the binder.

[0038] Preferably, the mass percentage of each component in the positive electrode active material layer is: 90-99.6 wt% of the positive electrode active material, 0.2-5 wt% of the conductive agent, and 0.2-5 wt% of the binder.

[0039] In the battery according to the present invention, the mass percentage of each component in the negative electrode active material layer is: 80-99.8 wt% of the negative electrode active material, 0.1-10 wt% of the conductive agent, and 0.1-10 wt% of the binder.

[0040] Preferably, the mass percentage of each component in the negative electrode active material layer is: 90-99.6 wt% of the negative electrode active material, 0.2-5 wt% of the conductive agent, and 0.2-5 wt% of the binder.

[0041] In the battery according to the present invention, the conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fibers, carbon nanotubes and metal powders.

[0042] In the battery according to the present invention, the binder is selected from at least one of sodium carboxymethyl cellulose, styrene-butadiene latex, polytetrafluoroethylene and polyethylene oxide.

[0043] In the battery according to the present invention, the negative electrode active material comprises a carbon-based negative electrode material.

[0044] In the battery according to the present invention, the carbon-based negative electrode material comprises at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon and soft carbon.

[0045] In the battery according to the present invention, the negative electrode active material may further comprise a silicon-based negative electrode material.

[0046] In the battery according to the present invention, the silicon-based negative electrode material is selected from at least one of nano-silicon (Si), silicon-oxygen negative electrode material (SiOx(0<x<2)) and silicon-carbon negative electrode material.

[0047] According to the battery of the present invention, the positive electrode active material is selected from one or more of transition metal lithium oxides, lithium iron phosphate, and lithium manganese oxide; the chemical formula of the transition metal lithium oxide is Li. 1+x Ni y Co z M (1-y-z) O2, where -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; where M is one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr.

[0048] The beneficial effects of this invention are:

[0049] This invention provides an electrolyte and a battery comprising the electrolyte. The nitrile functional groups in additive A of the electrolyte can complex with the positive electrode surface, effectively inhibiting the dissolution of metal ions and further oxidative decomposition of the electrolyte. Furthermore, additive A has a symmetrical structural formula and includes ester and nitrile functional groups, which gives it good kinetic performance and oxidation resistance. Simultaneously, the fluorine atoms potentially present on the Ra group connecting the ester and nitrile groups further enhance the overall oxidation resistance of the structure. Based on this, lithium bisfluorosulfonylimide (additive B) is more stable than the anionic groups in LiPF6, producing less HF and water under high voltage systems, further improving the stability of additive A. Moreover, lithium bisfluorosulfonylimide also participates in film formation on the positive electrode surface along with the nitrile functional groups, providing protection to the positive electrode surface. Detailed Implementation

[0050] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0051] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0052] It is understood that the lithium-ion battery of the present invention includes a negative electrode, an electrolyte, a positive electrode, a separator, and an outer packaging. A battery cell is obtained by stacking the positive electrode, separator, and negative electrode, or by stacking the positive electrode, separator, and negative electrode and then winding them. The battery cell is then placed in the outer packaging, and electrolyte is injected into the outer packaging to obtain the lithium-ion battery of the present invention.

[0053] Examples 1-14 and Comparative Examples 1-5

[0054] The lithium-ion batteries of Examples 1-14 and Comparative Examples 1-5 were prepared by the following steps:

[0055] 1) Preparation of positive electrode sheet

[0056] Lithium cobalt oxide (LiCoO2), polyvinylidene fluoride (PVDF), super P (SP), and carbon nanotubes (CNT) were mixed in a mass ratio of 96:2:1.5:0.5. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until it formed a uniform and fluid positive electrode slurry. The positive electrode slurry was then uniformly coated onto both surfaces of an aluminum foil. The coated aluminum foil was dried, and then rolled and slit to obtain the desired positive electrode sheet.

[0057] 2) Preparation of negative electrode sheet

[0058] The negative electrode active materials, artificial graphite, silicon suboxide, 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 79.5:15:2.5:1.5:1:0.5. Deionized water was added, and 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 and then transferred to an 80°C oven for 10 hours. After cold pressing and slitting, the negative electrode sheet was obtained.

[0059] 3) Preparation of electrolyte

[0060] In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), EC / PC / DEC / PP were mixed evenly according to the mass ratio shown in Table 1. Then, 1 mol / L of fully dried lithium hexafluorophosphate (LiPF6) was quickly added to dissolve it. After dissolution, fluoroethylene carbonate (FEC), additive A, additive B (lithium difluorosulfonylimide), and additive C (1,3-propanesulfonate lactone) were added. The specific electrolyte formulation is shown in Table 1.

[0061] 4) Preparation of lithium-ion batteries

[0062] The positive electrode sheet from step 1), the negative electrode sheet from step 2), and the separator are stacked in the order of positive electrode sheet, separator, and negative electrode sheet, and then wound to obtain a battery cell. The battery cell is placed in an outer packaging aluminum foil, and the electrolyte from step 3) is injected into the outer packaging. After vacuum sealing, settling, formation, shaping, and sorting, a lithium-ion battery is obtained. The charge / discharge range of the battery of this invention is 3.0-4.5V.

[0063] Table 1. Composition of electrolyte in lithium-ion batteries of the examples and comparative examples.

[0064]

[0065] Among them, HTCN is 1,3,6-hexanetrionitrile, DENE is 1,2-bis(cyanoethoxy)ethane, and ADN is adiponitrile.

[0066] The lithium-ion batteries obtained in the examples and comparative examples were subjected to cycle performance tests at 25°C and 45°C, respectively. The test results are shown in Table 2.

[0067] 1) Cyclic performance test at 25℃

[0068] The batteries in Table 1 were subjected to 800 charge-discharge cycles at 25°C and within the charge-discharge cutoff voltage range at a 1C rate. 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.

[0069] 2) 45℃ Cyclic Performance Test

[0070] The batteries in Table 1 were subjected to 800 charge-discharge cycles at 45°C and within the charge-discharge cutoff voltage range at a 1C rate. The discharge capacity of the first cycle was measured as x2 mAh, and the discharge capacity of the Nth cycle was measured as y2 mAh. The capacity of the Nth cycle was divided by the capacity of the first cycle to obtain the cycle capacity retention rate R2 = y2 / x2.

[0071] Table 2. Performance test results of lithium-ion batteries in the examples and comparative examples.

[0072]

[0073] As can be seen from the test results of Comparative Examples 1-2 and Examples 1-14 in Table 2, additive A significantly improves the battery's performance in both room temperature and high temperature cycling. Through Comparative Examples 3-5 and Examples 1-14, it can be found that additive A provides a more significant improvement in the long-cycle performance of the battery compared to conventional nitrile additives such as AND, DENE, and HTCN. Furthermore, Comparative Examples 1 and 2 show that lithium difluorosulfonylimide has a more significant effect on cycling performance.

[0074] In summary, the electrolyte with additive A of the present invention can complex on the surface of the positive electrode, preventing the electrolyte from entering the positive electrode material and damaging its structure. At the same time, the presence of ester groups improves the transport efficiency of ions in the electrolyte, and the fluorine atoms or trifluoromethyl groups contained therein can further improve the oxidation resistance of the ester groups. Meanwhile, the lithium difluorosulfonamide salt and additive A have a synergistic effect, working together to protect the positive electrode.

[0075] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte comprises an organic solvent, an electrolyte salt, and additives, wherein the additives include additive A and additive B. The additive A is selected from at least one of compounds having the structural formula shown in formula (1): Equation (1) In equation (1), Ra is either the same or different, and is independently selected from the substituted C. 1-9 Alkylene, substituted -C 1-6 alkylene-O- Replacement -C 1-6 Alkylene-COO- Replacement -C 1-6 alkylene-S- Replacement -C 1-6 Alkylene-S(=O)2- The substituent is F, where The terminal is connected to -CN. The terminal is connected to -CO-; Additive B is selected from lithium difluorosulfonylimide.

2. The electrolyte according to claim 1, characterized in that, Ra may be the same or different, and are selected independently from the substituted C. 1-8 Alkylene, substituted -C 1-3 alkylene-O- Replacement -C 1-3 Alkylene-COO- Replacement -C 1-3 alkylene-S- Replacement -C 1-3 Alkylene-S(=O)2- ; The substituent is F, where The terminal is connected to -CN. The end is connected to -CO-.

3. The electrolyte according to claim 1, characterized in that, Ra may be the same or different, and are independently selected from the groups shown in R2 to R10 below: R2、 R3、 R4、 R5、 R6、 R7、 R8、 R9、 R10; in, It is a linking group.

4. The electrolyte according to any one of claims 1-3, characterized in that, The mass of additive A is 0.1-5.0 wt% of the total mass of the electrolyte.

5. The electrolyte according to any one of claims 1-3, characterized in that, The mass of additive B is 1-4.0 wt% of the total mass of the electrolyte.

6. The electrolyte according to any one of claims 1-3, characterized in that, The electrolyte further includes additive C, which is selected from at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, succinic acid trinitrile, lithium difluorooxalate borate, lithium difluorophosphate, and lithium difluorodioxalate phosphate.

7. A battery, characterized in that, The battery comprises the electrolyte according to any one of claims 1-6.

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