Electrolyte and lithium ion secondary battery

Abstract

The present application relates to a kind of electrolyte and lithium ion secondary battery.The electrolyte of the present application includes organic solvent, electrolyte salt and additive, wherein the additive includes one or several of additive A sulfone compound, one or several of additive B borate and one or several of additive C trimethylsilicon compound.The synergistic effect of additive A, additive B and additive C makes the lithium ion battery prepared by using the electrolyte has good retention rate after high temperature cycle, lower internal resistance after high temperature storage and better rate performance under normal temperature cycle.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to an electrolyte and a lithium-ion secondary battery. Background Technology

[0002] Lithium-ion batteries have attracted much attention due to their high specific energy, long cycle life, low self-discharge, and good safety performance. Moreover, as the application of lithium-ion batteries becomes more and more widespread, the performance requirements for lithium-ion batteries are also becoming higher and higher.

[0003] In recent years, cathode materials such as ternary cathode materials and high-voltage lithium cobalt oxide have been found to have low structural stability. During cycling and storage, the interface between the cathode and electrolyte becomes unstable, leading to continuous oxidative decomposition of the electrolyte at the cathode. This causes transition metal ions in the cathode material to dissolve, resulting in structural collapse. Simultaneously, these metal ions migrate to the anode, damaging the anode protective film and thus affecting the performance of the lithium-ion battery. Furthermore, moisture and HF in the electrolyte can damage the protective film at the cathode and anode interface during the charging and discharging process of the lithium-ion battery, generating gas and causing an increase in internal pressure, thus reducing the safety of the lithium-ion battery. Application number 201310144332.2 discloses an electrolyte solvent comprising a sulfone-based compound with a sulfonyl fluoride structure and halogen-containing chain and cyclic carbonates, which improves battery cycle characteristics, storage performance, and expansion performance to some extent. Application No. 201610355485.5 discloses an electrolyte comprising both cyanosulfone compounds and lithium fluorophosphate. The cyanosulfone compounds form a passivation film on the surface of the electrodes in a high-voltage battery, effectively suppressing the reaction between the electrolyte and the electrodes. Simultaneously, lithium fluorophosphate effectively inhibits lithium salt decomposition and improves the film impedance of the electrodes. Through their synergistic effect, the cycle performance and storage performance of the lithium-ion battery are improved. Application No. 201710513306.0 discloses a lithium-ion battery film-forming additive composition containing pteridine compounds and sulfone compounds with specific structures. The above patents all improve lithium-ion battery performance through specific compound combinations. However, with the development of battery applications, the market has placed higher demands on battery lifespan, cycle performance at high voltage and high temperature, and rate discharge performance. This necessitates continuous optimization of electrolytes to provide better-performing electrolytes and lithium-ion batteries. Summary of the Invention

[0004] The purpose of this invention is to provide an electrolyte and a lithium-ion secondary battery that have good retention rate after high-temperature cycling, low internal resistance after high-temperature storage, and good rate performance under room temperature cycling.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] An electrolyte includes an organic solvent, an electrolyte salt, and additives, wherein the additives include additive A, additive B, and additive C.

[0007] The additive A is one or more of the substances shown in structural formula (1), and the structural formula (1) is... R1 is a halogen atom, an alkyl group with 1 to 6 carbon atoms, an alkenyl group with 2 to 6 carbon atoms, an alkynyl group with 2 to 6 carbon atoms, a haloalkyl group with 1 to 6 carbon atoms, a haloalkenyl group with 2 to 6 carbon atoms, or a haloalkynyl group with 2 to 6 carbon atoms; R2 is a group containing a double or triple bond.

[0008] Additive B is a borate.

[0009] The additive C is one or more of the substances shown in structural formula (2), and structural formula (2) is... R3 can be a borate ester group, phosphate ester group, phosphite ester group, isocyanate ester group, heterocyclic group, or amine group.

[0010] In this invention, the amino group is an amino group in which the hydrogen atom is replaced by an alkyl, alkenyl, alkynyl or silyl group.

[0011] This invention combines additive A (sulfone compounds), additive B (borate compounds), and additive C (compounds with trimethylsilyl groups) to achieve good cycle performance and rate discharge performance even at high voltages, resulting in a significant improvement in service life.

[0012] Preferably, in the structural formula (1), the halogenation in R1 refers to partial or complete halogenation.

[0013] Preferably, in the structural formula (1), the halogenation in R1 refers to fluorination, bromination or chlorination.

[0014] Preferably, in the structural formula (1), R1 is a halogen atom, an alkenyl group with 2 to 5 carbon atoms, or an alkynyl group with 2 to 5 carbon atoms, and R2 is a group containing a double bond or a triple bond.

[0015] More preferably, in the structural formula (1), R1 is F, vinyl, propenyl, butenyl, ethynyl, propynyl or butynyl, and R2 is a group containing a double bond or a triple bond.

[0016] Preferably, in the structural formula (1), R2 is an alkynyl, alkenyl, heterocyclic or -R-R', wherein R is an alkylene group with 1 to 5 carbon atoms or a haloalkylene group with 1 to 5 carbon atoms, and R' is a cyano, carbonyl, sulfonyl, sulfinyl or heterocyclic.

[0017] More preferably, in the structural formula (1), R2 is an alkynyl group with 2 to 6 carbon atoms, an alkenyl group with 2 to 6 carbon atoms, an N-containing five-membered heterocyclic group, or -R-R', wherein R is an alkyl group with 1 to 4 carbon atoms or a haloalkyl group with 1 to 4 carbon atoms, and R' is a cyano group, carbonyl group, sulfonyl group, sulfinyl group, or an N-containing five-membered heterocyclic group.

[0018] Preferably, in the structural formula (1), the halogenation in R2 refers to partial or complete halogenation.

[0019] Preferably, in the structural formula (1), the halogenation in R2 refers to fluorination, bromination or chlorination.

[0020] More preferably, in the structural formula (1), R2 is a vinyl, propenyl, butenyl, ethynyl, propynyl, butynyl, or a five-membered heterocyclic group containing an N-substituted alkyl group, or -R-R', wherein R is an alkylene group with 1 to 4 carbon atoms or a haloalkylene group with 1 to 4 carbon atoms, and R' is a cyano, carbonyl, sulfonyl, sulfinyl, or...

[0021] Preferably, R3 is a silyl-substituted borate ester group, a silyl-substituted phosphate ester group, a silyl-substituted phosphite ester group, an isocyanate ester group, an N-heterocyclic lactone group, an alkyl group with 1 to 6 carbon atoms, an alkenyl group with 2 to 6 carbon atoms, an alkynyl group with 2 to 6 carbon atoms, or an amino group with silyl-substituted amine group.

[0022] More preferably, the silane substitution refers to partial or complete substitution.

[0023] More preferably, when R3 in the structural formula (2) is an amino group, the amino group is -NRaRb, wherein Ra is vinyl, propylene or butenyl, and Rb is trimethylsilyl.

[0024] In this invention, the substitution is either a complete substitution or a partial substitution.

[0025] According to some preferred embodiments, the additive B is one or more of lithium tetrafluoroborate, lithium dioxalate borate, and lithium difluorooxalate borate.

[0026] According to some preferred embodiments, the substance represented by structural formula (1) is

[0027] According to some preferred embodiments, the substance represented by structural formula (2) is

[0028] Preferably, the additive A is added at a mass of 0.5% to 3% of the total mass of the electrolyte, for example, 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8% or 3%.

[0029] More preferably, the mass of additive A is 0.8% to 2.0% of the total mass of the electrolyte.

[0030] Preferably, the additive B is added at a mass of 0.1% to 2% of the total mass of the electrolyte, for example, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.6%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, or 2%.

[0031] More preferably, the mass of additive B is 0.3% to 1.5% of the total mass of the electrolyte.

[0032] Preferably, the additive C is added at a mass of 0.1% to 2% of the total mass of the electrolyte, for example, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.6%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, or 2%.

[0033] More preferably, the additive C is added at a mass of 0.3% to 1.5% of the total mass of the electrolyte.

[0034] Preferably, the organic solvent is one or more of carbonates, carboxylic esters, ethers, sulfones, sulfoxides, and benzene compounds.

[0035] More preferably, the organic solvent includes one or more of fluorocarbonates, fluorocarboxylic esters, fluoroethers, fluorosulfons, fluorosulfoxides, and fluorobenzenes, as well as one or more of other carbonates, carboxylic esters, ethers, sulfons, and sulfoxides.

[0036] More preferably, the organic solvent is a mixture of two or more of the following: fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethyl carbonate, fluoroethyl sulfone, tetrafluoroethyl tetrafluoropropyl ether, trifluoroethyl hexafluoropropyl ether, dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, methyl ethyl carbonate, ethylene glycol dimethyl ether, γ-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, sulfolane, methyl ethyl sulfone, dimethyl sulfoxide, and fluorobenzene.

[0037] Preferably, the organic solvent is added at a mass of 70% to 85% of the total mass of the electrolyte, for example, 70%, 72%, 74%, 76%, 78%, 80%, 81%, 82%, 83%, 84%, or 85%.

[0038] More preferably, the mass of the organic solvent added is 80% to 85% of the total mass of the electrolyte.

[0039] Preferably, the electrolyte salt includes lithium hexafluorophosphate and selectively includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0040] Preferably, the mass of the electrolyte salt is 10% to 25% of the total mass of the electrolyte, for example, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, or 25%.

[0041] More preferably, the mass of lithium hexafluorophosphate fed is 10% to 15% of the total mass of the electrolyte, for example, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%.

[0042] Preferably, the additive further includes other additives, which are one or more of the following: cyclic carbonates containing double bonds, cyclic carbonates containing halogens, sulfonates, sulfates, sulfites, acid anhydrides, benzene compounds, fluorobenzene compounds, nitrile compounds, phosphate esters, phosphites, boron compounds, amine compounds, silicon-containing compounds, and heterocyclic compounds.

[0043] More preferably, the other additives include, but are not limited to, one or more of fluoroethylene carbonate, 1,3-propanesulfonic acid lactone, and vinyl sulfate.

[0044] Preferably, the other additives are added at a mass of 0.5% to 5% of the total mass of the electrolyte, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5.0%.

[0045] More preferably, the other additives are added at a mass of 1% to 3% of the total mass of the electrolyte.

[0046] The present invention also provides a lithium-ion secondary battery, wherein the lithium-ion secondary battery includes the electrolyte.

[0047] Specifically, the lithium-ion secondary battery includes a casing, a battery cell housed within the casing, and a non-aqueous electrolyte; the battery cell includes a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode, and the non-aqueous electrolyte is the electrolyte as described above.

[0048] Preferably, the positive electrode includes a positive electrode current collector and a positive electrode material located on the surface of the positive electrode current collector.

[0049] Furthermore, the positive electrode material includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The positive electrode active material is a common type LiNi. x Co y Mn (1-x-y) O2, ordinary LiNi x Co y Al (1-x-y) O2, ordinary LiCoO2, high-voltage LiNi x Co y Mn (1-x-y) O2, high-voltage LiCoO2, wherein 0 < x < 1, 0 < y < 1 and x + y < 1. The positive electrode conductive agent is acetylene black or carbon nanotubes, and the positive electrode binder is polyvinylidene fluoride.

[0050] Preferably, the negative electrode includes a negative electrode current collector and a negative electrode material located on the surface of the negative electrode current collector.

[0051] Furthermore, the negative electrode material includes a negative electrode active material and a negative electrode binder, and optionally a negative electrode conductive agent. The negative electrode conductive agent may be the same as or different from the positive electrode conductive agent, and both are commonly used conductive agents in the art. The negative electrode active material and negative electrode binder can be conventionally used negative electrode active materials and negative electrode binders in the art, such as lithium metal, metal oxides, lithium-aluminum alloys, graphite and modified carbon materials, silicon and its silicon-oxygen-carbon, and silicon-carbon. Preferably, the negative electrode active material is silicon-oxygen-carbon or graphite, the negative electrode conductive material is superconducting carbon black, and the negative electrode binder is styrene-butadiene rubber.

[0052] Preferably, the high voltage of the lithium battery is 4.2V or higher.

[0053] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0054] This invention utilizes a combination of additives A (sulfone compounds), B (borate compounds), and C (trimethylsilicon compounds) as electrolyte additives. This combination enables the formation of an excellent passivation film on the positive and negative electrode surfaces during the charging and discharging process of the lithium-ion secondary battery. This suppresses interfacial activity between the electrolyte and materials, while simultaneously reducing the acidity in the electrolyte, minimizing corrosion of the passivation film. The improved interfacial stability between the electrolyte and materials results in good rate performance at room temperature cycling, good rate retention after high-temperature cycling, and low internal resistance after high-temperature storage, thus extending the battery's lifespan. Detailed Implementation

[0055] The present invention will be further described below with reference to embodiments. However, the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific applications, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0056] With the expanding application scenarios of lithium batteries, there is a need to further improve the rate performance of lithium-ion secondary batteries under normal temperature cycling and the capacity retention rate after high temperature cycling. Furthermore, it is necessary to further suppress the increase in internal resistance after high-temperature storage and extend battery life. Therefore, the inventors of this invention conducted in-depth research and numerous experiments, ultimately proposing an electrolyte and a lithium-ion secondary battery using this electrolyte.

[0057] The present invention will be further described below with reference to embodiments. However, the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific applications, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0058] Electrolyte preparation:

[0059] In the specific embodiments of this invention, the battery electrolyte is prepared in a glove box according to the formulations described in Tables 1 and 2. The substances mentioned in the tables are: ethylene carbonate (EC), dimethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), ethyl propionate (EP), fluoroethylene carbonate (FEC), lithium difluorosulfonyl imide (LiFSI), lithium difluorophosphate (LiDFP), 1,3-propanesulfonate lactone (PS), ethylene sulfate (DTD), and lithium hexafluorophosphate (LiPF6).

[0060] Table 1

[0061]

[0062]

[0063] Table 2

[0064]

[0065]

[0066]

[0067]

[0068] The additives A1-A8, B1-B3, and C1-C6 involved in Tables 1 and 2 are as follows:

[0069]

[0070]

[0071] B1: Lithium tetrafluoroborate, B2: Lithium dioxolaneborate, B3: Lithium difluorooxolaneborate;

[0072]

[0073] Battery manufacturing:

[0074] The electrolytes obtained from Comparative Examples 1-24 and Examples 1-30 were injected into 550mAh polymer pouch batteries of the same batch of LiCoO2(LCO)||silicon-oxygen-carbon, and the following tests were performed respectively. The data are shown in Table 3.

[0075] 1) Test the capacity retention rate L-C1% of the battery after 500 charge-discharge cycles at 45℃ with a voltage between 2.75-4.35V and a current of 1C (discharge capacity after 500 cycles / average discharge capacity of the first 5 cycles * 100).

[0076] 2) Test the internal resistance growth rate LR% of a fully charged battery at 4.35V after being left at 85℃ for 4 hours ((internal resistance before leaving - internal resistance after leaving) / internal resistance before leaving * 100);

[0077] 3) Test the capacity retention rate L-C3% of the battery after 300 charge-discharge cycles at room temperature (25℃) with voltage between 2.75-4.35V and current of 3C (discharge capacity after 300 cycles / average discharge capacity of the first 5 cycles * 100).

[0078] The electrolytes obtained from Comparative Examples 25–48 and Examples 31–60 were injected into the same batch of LiNi. 0.6 Co 0.2 Mn 0.2In a 1Ah polymer pouch cell containing O2(NCM622)||graphite, the following tests were performed, and the data are shown in Table 4.

[0079] 1) Test the capacity retention rate N-C1% (discharge capacity after 500 cycles / average discharge capacity of the first 5 cycles * 100) of the battery at 45℃ with voltage between 2.75-4.35V and current of 1C for 500 cycles.

[0080] 2) Test the internal resistance growth rate NR% of a fully charged 4.3V battery after being left at 85℃ for 4 hours ((internal resistance before leaving - internal resistance after leaving) / internal resistance before leaving * 100);

[0081] 3) Test the capacity retention rate N-C3% of the battery after 300 charge-discharge cycles at room temperature (25℃) with voltage between 2.75-4.35V and current of 3C (discharge capacity after 300 cycles / average discharge capacity of the first 5 cycles * 100).

[0082] Experimental results:

[0083] Table 3

[0084]

[0085]

[0086]

[0087] Table 3 shows that in the 550mAh polymer soft-pack battery of LiCoO2(LCO)||silicon-oxygen-carbon, the combined use of additives A (sulfone compounds), B (borate compounds), and C (trimethylsilicon compounds) significantly improves the battery's performance in room temperature, high temperature cycling, and high temperature storage compared to using these three compounds alone or in pairs.

[0088] Table 4

[0089]

[0090]

[0091]

[0092] Table 4 shows that, similarly, in LiNi 0.6 Co 0.2 Mn 0.2 In the 1Ah polymer soft-pack battery of O2(NCM622)||graphite, the combined use of additives A (sulfone compounds), B (borate compounds), and C (trimethylsilicon compounds) significantly improves the battery's performance in room temperature, high temperature cycling, and high temperature storage compared to using these three compounds alone or in pairs.

[0093] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. An electrolyte comprising an organic solvent, an electrolyte salt, and additives, characterized in that: The additives mentioned include additive A, additive B, and additive C. The additive A is one or more of the substances shown in structural formula (1), and the structural formula (1) is... ， Wherein, R1 is a halogen atom; R2 is an N-containing five-membered heterocyclic group substituted with a haloalkyl group. Additive B is lithium difluorooxalate borate. The additive C is , The organic solvent is composed of ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl propionate, and fluoroethylene carbonate. The electrolyte is used in lithium-ion secondary batteries with LiCoO2 as the positive electrode active material and silicon-oxygen-carbon as the negative electrode active material.

2. The electrolyte according to claim 1, characterized in that: The substance shown in the structural formula (1) is .

3. The electrolyte according to claim 1, characterized in that: The additive A is added at a rate of 0.5% to 3% of the total mass of the electrolyte. The additive B is added at a mass of 0.1% to 2% of the total mass of the electrolyte. The additive C is added at a mass of 0.1% to 2% of the total mass of the electrolyte.

4. The electrolyte according to claim 3, characterized in that: The additive A is added at a rate of 0.8% to 2.0% of the total mass of the electrolyte. The additive B is added at a mass of 0.3% to 1.5% of the total mass of the electrolyte. The additive C is added at a mass of 0.3% to 1.5% of the total mass of the electrolyte.

5. The electrolyte according to claim 1, characterized in that: The content of the organic solvent is 70% to 85% of the total mass of the electrolyte.

6. The electrolyte according to claim 1, characterized in that: The electrolyte salt includes lithium hexafluorophosphate and selectively includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalate phosphate, and lithium tetrafluorooxalate phosphate. The mass of the electrolyte salt added is 10% to 25% of the total mass of the electrolyte.

7. The electrolyte according to claim 6, characterized in that: The mass of lithium hexafluorophosphate added is 10% to 15% of the total mass of the electrolyte.

8. The electrolyte according to claim 1, characterized in that: The additives also include 1,3-propanesulfonate lactone; The mass of 1,3-propanesulfonic acid lactone fed into the electrolyte is 0.5% to 5% of the total mass of the electrolyte.

9. A lithium-ion secondary battery, characterized in that: The lithium-ion secondary battery includes the electrolyte according to any one of claims 1 to 8, wherein the positive electrode active material of the lithium-ion secondary battery is LiCoO2 and the negative electrode active material is silicon-oxygen-carbon.

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