Non-aqueous electrolytes and lithium-ion batteries

Abstract

This invention provides a non-aqueous electrolyte and a lithium-ion battery. The non-aqueous electrolyte comprises a non-aqueous organic solvent, an electrolyte salt, and additives. The additives include compound A (structural formula I) and compound B (structural formula II). In the non-aqueous electrolyte of this invention, compound A is an unsaturated phosphorus-containing compound, and compound B is a carboxylic acid ester compound. Through the synergistic effect of the unsaturated phosphorus-containing compound and the carboxylic acid ester compound, a relatively complete SEI (Sediment Injection) membrane can be formed, providing a stable transport channel for lithium ions during cycling and storage. Furthermore, since the carboxylic acid ester may occupy positions in the SEI membrane, it prevents the phosphorus-containing compound from forming an excessively thick SEI membrane, thus ensuring a uniform SEI membrane thickness and shortening the lithium-ion transport distance. Therefore, through these two effects, the high-temperature storage, cycling, and low-temperature performance of the high-nickel ternary cathode material system battery under high voltage (≥4.35V) can be improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a non-aqueous electrolyte and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries, as a green and environmentally friendly high-energy battery, are currently the most ideal and promising rechargeable batteries in the world. Compared with other batteries, lithium-ion batteries have a series of advantages such as no memory effect, rapid charging and discharging, high energy density, long cycle life, and no environmental pollution. Therefore, they are widely used in small electronic devices such as laptops, cameras, mobile phones, and smartwatches. Today, with the increasing demands on lithium-ion battery capacity from pure electric vehicles, hybrid vehicles, and portable energy storage devices, there is a growing expectation for the development of lithium-ion batteries with higher energy density and power density to achieve energy storage and longer battery life.

[0003] Currently, the industry improves the energy density of lithium-ion batteries by increasing the specific capacity or upper charging voltage of the positive and negative electrode materials. The increase in specific capacity of ternary cathode materials stems from increasing the Ni content or raising the charging voltage. However, the increased nickel content in ternary cathode materials leads to residual alkali and unstable cell structure, resulting in poor cycle performance, significant gas generation during storage, and, after increasing the charging voltage, continuous solvent decomposition in the electrolyte and continuous consumption of additives, poor high-temperature storage and severe gas generation during cycling. One reason may be the imperfection of coating or doping technologies for newly developed ternary cathode materials. Another reason is the matching problem with the electrolyte. Conventional electrolytes in high-nickel ternary cathode material systems are easily oxidized and decomposed on the surface of the battery cathode, especially under high-temperature conditions, which accelerates the oxidation and decomposition of the electrolyte and leads to the deterioration of the cathode material. Therefore, it is necessary to develop an electrolyte that can withstand a high voltage of 4.35V and is compatible with high-nickel ternary cathode materials to achieve excellent electrical performance of lithium-ion batteries. Summary of the Invention

[0004] In view of the above problems, the object of the present invention is to provide a non-aqueous electrolyte and a lithium-ion battery. The additives contained in this non-aqueous electrolyte can form a complete, uniformly thick SEI film with a short transmission distance, thereby improving the low-temperature performance of the battery. Furthermore, the formed SEI film can inhibit the oxidative decomposition of the electrolyte, and in particular, improve the high-temperature storage and cycle performance of high-nickel ternary cathode material system batteries under high voltage (≥4.35V).

[0005] To achieve the above objectives, a first aspect of the present invention provides a non-aqueous electrolyte comprising a non-aqueous organic solvent, an electrolyte salt, and additives. The additives include compound A represented by structural formula I and compound B represented by structural formula II. Specifically, R1 to R3 are each independently selected from substituted or unsubstituted C1 to C6 hydrocarbon groups or alkylsilyl groups; R4 and R7 are each independently selected from substituted or unsubstituted C1 to C6 hydrocarbon groups, alkylsilyl groups, or alkylketene groups; and R5 and R6 are each independently selected from hydrogen, halogens, or substituted or unsubstituted C1 to C6 hydrocarbon groups.

[0006]

[0007] In the non-aqueous electrolyte of this invention, compound A is an unsaturated phosphorus-containing compound, and compound B is a carboxylic acid ester compound. The carboxylic acid ester compound has a low redox potential, but the SEI film it forms has poor thermal stability and is discontinuous, providing incomplete protection of the electrode interface and easily generating gas at high temperatures. The protective layer formed by the unsaturated phosphorus-containing compound has better thermal stability and is continuous, but the electrode cycling performance is weak, and the pores in the SEI film are prone to collapse during long cycles. This invention, through the synergistic effect of the unsaturated phosphorus-containing compound and the carboxylic acid ester compound, can form a relatively complete SEI interface film, providing a stable transport channel for lithium ions during cycling and storage. Furthermore, since the carboxylic acid ester may occupy space in the SEI film, it prevents the phosphorus-containing compound from forming an excessively thick SEI film, thus ensuring a uniform SEI film thickness and shortening the lithium ion transport distance. Therefore, through these two effects, the high-temperature storage, cycling, and low-temperature performance of high-nickel ternary cathode material battery systems at high voltages (≥4.35V) can be improved.

[0008] As a technical solution of the present invention, R1 to R3 are each independently selected from C1 to C3 alkyl, C2 to C3 alkenyl, C2 to C3 alkynyl, and trialkylsilyl; R4 and R7 are each independently selected from C1 to C3 alkyl, perfluorinated C1 to C3 alkyl, trialkylsilyl, and C1 to C3 alkylketone; and R5 and R6 are each independently selected from hydrogen or fluorine.

[0009] As a technical solution of the present invention, compound A is selected from at least one of compounds one to nine.

[0010]

[0011] As a technical solution of the present invention, compound B is selected from at least one of compounds ten to fifteen.

[0012]

[0013] As one technical solution of the present invention, compound A accounts for 0.1% to 5.0% of the total mass of the non-aqueous organic solvent, electrolyte salt, and additive. As an example, the proportion of compound A in the total mass of the non-aqueous organic solvent, electrolyte salt, and additive may be, but is not limited to, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, and 5.0%.

[0014] As one technical solution of the present invention, compound B accounts for 0.1% to 5.0% of the total mass of the non-aqueous organic solvent, electrolyte salt, and additive. As an example, the proportion of compound B to the total mass of the non-aqueous organic solvent, electrolyte salt, and additive may be, but is not limited to, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, and 5.0%.

[0015] As a technical solution of the present invention, the electrolyte salt accounts for 6-15% of the total mass of the non-aqueous organic solvent, the electrolyte salt, and the additive. Preferably, the electrolyte salt accounts for 8-15%. As an example, the electrolyte salt percentage may be, but is not limited to, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%. The electrolyte salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2), lithium dioxolane borate (C4BLiO8), lithium difluorooxolane borate (C2BF2LiO4), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxolane) phosphate (LiDFBP), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0016] As a technical solution of the present invention, the non-aqueous organic solvent is at least one selected from chain carbonates, cyclic carbonates, and carboxylic acid esters. Preferably, the non-aqueous organic solvent is a mixture of chain carbonates and cyclic carbonates. As an example, the non-aqueous organic solvent is selected from at least one selected from ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), butyl acetate (n-Ba), γ-butyrolactone (γ-Bt), propyl propionate (n-Pp), ethyl propionate (EP), and ethyl butyrate (Eb). The non-aqueous organic solvent accounts for ≥80% of the total mass of the non-aqueous organic solvent, electrolyte salt, and additives, preferably ≥85%. As an example, the non-aqueous organic solvent accounts for, but is not limited to, ≥80%, ≥81%, ≥82%, ≥83%, ≥84%, ≥85%, ≥86%, ≥87%, ≥88%, ≥89%, or ≥90% of the total mass of the non-aqueous organic solvent, electrolyte salt, and additives.

[0017] As a technical solution of the present invention, the additive further includes compound C. Compound C is selected from at least one of vinylene carbonate (VC), ethylene ethylene carbonate (VEC), fluoroethylene carbonate (FEC), vinyl sulfite (ES), 1,3-propanesulfonate lactone (PS), and vinyl sulfate (DTD). Compound C accounts for 0.1 to 10.0% of the total mass of the non-aqueous organic solvent, electrolyte salt, and additive. Preferably, compound C accounts for 0.1 to 6.0% of the total mass of the non-aqueous organic solvent, electrolyte salt, and additive. As an example, the proportion of compound C to the sum of the masses of the non-aqueous organic solvent, electrolyte salt, and additives may be, but is not limited to, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 6.0%, 7.0%, 8.0%, 9.0%, and 10.0%.

[0018] A second aspect of this invention provides a lithium-ion battery, comprising a positive electrode material, a negative electrode material, and a non-aqueous electrolyte. This lithium-ion battery exhibits superior cycle life and high-temperature storage performance, which is beneficial for the further industrialization of lithium-ion batteries.

[0019] As one technical solution of this invention, the positive electrode material is a nickel-cobalt-manganese oxide material. The chemical formula of the nickel-cobalt-manganese oxide material is LiNi. x Co y Mn (1-x-y) M zO2, 0.6≤x≤0.9, x+y<1, 0≤z<0.08, M is one of Al, Mg, Zr and Ti. Preferably, x=0.6, y=0.2, M is Zr and z=0.03, or x=0.8, y=0.1, M is Zr and z=0.02.

[0020] As one technical solution of the present invention, the negative electrode material is selected from at least one of carbon-based negative electrode materials, titanium-based oxide negative electrode materials, and silicon-based negative electrode materials.

[0021] As one technical solution of the present invention, the negative electrode material can be selected from artificial graphite, natural graphite, hard carbon, soft carbon, lithium titanate, Si material, silicon oxide material or silicon carbon material (10wt.% Si). Detailed Implementation

[0022] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0023] Where specific conditions are not specified in the examples, they can be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available standard products.

[0024] Example 1

[0025] (1) Preparation of non-aqueous electrolyte: The electrolyte was prepared in a vacuum glove box with a moisture content of <1ppm under an argon atmosphere. In a dry argon atmosphere glove box, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed in a weight ratio of EC:PC:EMC:DEC = 2:1:5:2. Then, compound 1 was added, dissolved and stirred thoroughly, and lithium hexafluorophosphate was added. After mixing evenly, the electrolyte was obtained.

[0026] (2) Preparation of the positive electrode: LiNi 0.8 Co 0.1 Mn 0.1 Zr 0.03 O2, binder PVDF and conductive agent SuperP are mixed evenly in a mass ratio of 97:1:2 to prepare a lithium-ion battery positive electrode slurry of a certain viscosity. The mixed slurry is coated on both sides of aluminum foil, dried and rolled to obtain the positive electrode sheet.

[0027] (3) Preparation of negative electrode: Silicon carbon negative electrode material (10wt.% Si) is mixed with conductive agent SuperP, thickener CMC and binder SBR (styrene-butadiene rubber emulsion) in a mass ratio of 96:1:1:2 to form a slurry. The mixture is uniformly mixed and coated on both sides of copper foil. After drying and rolling, the negative electrode sheet is obtained.

[0028] (4) Preparation of lithium-ion battery: The positive electrode, separator and negative electrode are stacked to form a square cell, which is packaged with polymer and filled with the non-aqueous electrolyte of lithium-ion battery prepared above. After formation, capacity testing and other processes, a lithium-ion battery with a capacity of 1400mAh is made.

[0029] The electrolyte formulations for Examples 1-22 and Comparative Examples 1-9 are shown in Table 1. The steps for preparing the electrolytes and batteries for Examples 2-22 and Comparative Examples 1-9 are the same as those for Example 1.

[0030] Table 1 Electrolyte components of each embodiment and comparative example

[0031]

[0032]

[0033] The lithium-ion batteries prepared in Examples 1-22 and Comparative Examples 1-9 were subjected to room temperature cycling tests, high temperature cycling tests, high temperature storage tests, and low temperature discharge tests, respectively. The specific test conditions are as follows, and the test results are shown in Table 2.

[0034] (1) Room temperature cycling test

[0035] Under normal temperature (25℃) conditions, the lithium-ion battery is subjected to one 1.0C / 1.0C charge and discharge cycle (battery discharge capacity is C0), with an upper limit voltage of 4.35V. Then, it is subjected to 500 cycles of 1.0C / 1.0C charge and discharge under normal temperature conditions (battery discharge capacity is C1).

[0036] Capacity retention rate = (C1 / C0) * 100%.

[0037] (2) High-temperature cycling test of lithium-ion batteries

[0038] Under high temperature (45℃) conditions, the lithium-ion battery was subjected to one 1.0C / 1.0C charge and discharge cycle (battery discharge capacity C0), with an upper limit voltage of 4.35V. Then, it was subjected to 300 cycles of 1.0C / 1.0C charge and discharge at room temperature (battery discharge capacity C1).

[0039] Capacity retention rate = (C1 / C0) * 100%

[0040] (3) High-temperature storage test

[0041] Under normal temperature (25℃) conditions, a lithium-ion battery is subjected to one 0.5C / 0.5C charge and discharge cycle (discharge capacity denoted as C0), with an upper limit voltage of 4.35V. Then, the battery is charged to 4.35V under constant current and constant voltage conditions at 0.5C, and the battery thickness d0 is measured. The lithium-ion battery is placed in a 60℃ high-temperature chamber for 30 days, and its thickness d1 is measured. It is then discharged at 0.5C at 25℃ (discharge capacity denoted as C1), and further subjected to one 0.5C / 0.5C charge and discharge cycle under normal temperature (25℃) conditions (discharge capacity denoted as C2), with an upper limit voltage of 4.35V. The capacity retention rate, capacity recovery rate, and thickness expansion rate of the lithium-ion battery are calculated using the following formulas.

[0042] Capacity retention rate = C1 / C0 * 100%

[0043] Capacity recovery rate = C2 / C0 * 100%

[0044] Thickness expansion rate = d1 / d0 * 100%

[0045] Low temperature discharge test

[0046] Under normal temperature (25℃) conditions, the lithium-ion battery was subjected to a 0.5C / 0.5C charge-discharge cycle (battery cutoff voltage 3.0V, discharge capacity C0), with an upper limit voltage of 4.35V (cutoff current 0.05C). Then, the battery was fully charged to 4.35V at 0.5C at 25℃ (cutoff current 0.05C), and then transferred to -20℃ for 4 hours, followed by a 0.5C discharge to 3.0V, with a discharge capacity of C1.

[0047] Capacity retention rate = (C1 / C0) * 100%

[0048] Table 2. Performance test results of lithium-ion batteries

[0049]

[0050]

[0051] As shown in Table 2, based on Comparative Examples 1-9, Examples 1-22 of the present invention, by combining Compound A (unsaturated phosphorus-containing compound) with Compound B (carboxylic acid ester compound), can improve the high-temperature storage, cycling and low-temperature performance of high-nickel ternary cathode material system batteries under high voltage (≥4.35V).

[0052] Comparing Examples 5-7, it can be seen that when compound B is compound thirteen, the battery performance is better, which may be related to the fact that compound thirteen contains more fluorine.

[0053] Comparative examples 8-16 show that when the substituents in compound A contain unsaturated double or triple bonds, the resulting battery exhibits better high-temperature performance.

[0054] Comparing Examples 3 and 17-22, it is evident that the battery performance is better when compound C (VC, FEC, PS, DTD, etc.) is added to compounds A and B. This may be because the P=S in compound A is easily oxidized, readily forming a sulfur- and phosphorus-containing interface. However, this SEI interface may be relatively dense, resulting in significant lithium-ion transport resistance during cycling, and thus the improvement in cycle performance is not significant. Compound B contains an ether structure, which can improve electrolyte wettability. Simultaneously, compound B can form a thinner fluorine-containing SEI, reducing interfacial impedance, but its improvement on storage performance is not significant. By introducing additives such as VC, FEC, PS, and DTD, a more complete SEI can be formed at the battery interface, providing more comprehensive protection for the electrode surface and greatly reducing side reactions in the battery materials and electrolyte during cycling, thereby improving battery performance.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A lithium-ion battery, comprising a positive electrode material, a negative electrode material, and a non-aqueous electrolyte, characterized in that, The positive electrode material is a nickel-cobalt-manganese oxide material, and the chemical formula of the nickel-cobalt-manganese oxide material is LiNi. x Co y Mn (1-x-y) M z O2, 0.6≤x≤0.9, x+y<1, 0≤z<0.08, M is one of Al, Mg, Zr and Ti, the non-aqueous electrolyte comprises a non-aqueous organic solvent, an electrolyte salt and additives, the additives comprise compound A and compound thirteen as shown in structural formula I, compound A accounts for 0.1~5.0% of the total mass of the non-aqueous organic solvent, the electrolyte salt and the additives, and compound thirteen accounts for 0.1~5.0% of the total mass of the non-aqueous organic solvent, the electrolyte salt and the additives. R1 to R3 are each independently selected from substituted or unsubstituted C1 to C6 hydrocarbon groups or alkylsilyl groups.

2. The lithium-ion battery according to claim 1, characterized in that, R1 to R3 are each independently selected from C1 to C3 alkyl, C2 to C3 alkenyl, C2 to C3 alkynyl, and trialkylsilyl.

3. The lithium-ion battery according to claim 1, characterized in that, Compound A is selected from at least one of compounds one through nine. 。 4. The lithium-ion battery according to claim 1, characterized in that, The electrolyte salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium dioxarate borate, lithium difluorooxarate borate, lithium difluorophosphate, lithium difluorobis(oxarate) phosphate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

5. The lithium-ion battery according to claim 1, characterized in that, The non-aqueous organic solvent is selected from at least one of chain carbonates, cyclic carbonates, and carboxylic acid esters.

6. The lithium-ion battery according to claim 1, characterized in that, The additive also includes compound C, which is selected from at least one of vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, ethylene sulfite, 1,3-propanesulfonate lactone, and ethylene sulfate.

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