Non-aqueous electrolyte and lithium-ion battery

Abstract

The present invention provides a non-aqueous electrolyte and a lithium ion battery thereof, the non-aqueous electrolyte comprising a lithium salt, a non-aqueous organic solvent and an additive, the additive comprising an unsaturated ionic liquid salt shown in structural formula I, wherein R1, R2, and R3 each independently represent H, a halogen, a hydrocarbon group having 1-6 carbon atoms, an alkenyl group having 1-6 carbon atoms, an alkynyl group, a phenyl group, a benzyl group, a biphenyl group or hexylamine. The unsaturated ionic liquid salt of the present invention contains a sulfur-oxygen double bond and a carbon-carbon double bond. During the battery cell formation stage, the sulfur-containing unsaturated bond forms an inorganic substance and a carbon-carbon double bond to form a polymer. These effective components can stably improve the interface composition of the battery cell during high-temperature storage and circulation, suppress the damage of harmful components to the electrolyte, thereby significantly improving the high-temperature storage and cycle performance of the battery, and can improve the high-temperature storage performance and high-temperature cycle performance of the high-voltage ternary lithium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a non-aqueous electrolyte and a lithium ion battery thereof. Background Art

[0002] As a green, environmentally friendly, high-energy battery, lithium-ion batteries are currently the world's most ideal and promising rechargeable battery. Compared to other batteries, lithium-ion batteries offer a range of advantages, including no memory effect, rapid charge and discharge, high energy density, long cycle life, and environmental friendliness. Consequently, they are widely used in small electronic devices such as laptops, camcorders, mobile phones, and electronic watches. With the increasing demand for lithium-ion battery capacity in pure electric vehicles, hybrid electric vehicles, and portable energy storage devices, the development of fast-charging lithium-ion batteries is highly anticipated to improve the convenience of our lives.

[0003] Technicians increase the charging speed of lithium-ion batteries by increasing the charging current. However, as the charging speed increases, local lithium deposition occurs. At the same time, because the rate at which lithium ions are embedded in graphite is lower than the rate at which they migrate, a large amount of lithium accumulates, which further exacerbates the deposition of lithium ions and makes it easier for lithium dendrites to form. However, lithium dendrites cause the electrode-electrolyte interface to continuously decompose and regenerate, leading to continuous consumption of the electrolyte and ultimately deteriorating lithium-ion battery performance. In addition, conventional electrolytes in high-nickel batteries are easily oxidized and decomposed on the surface of the battery's positive electrode, especially under fast-charging conditions, which accelerates the oxidative decomposition of the electrolyte and promotes the deterioration of the positive electrode material.

[0004] Therefore, it is necessary to develop a fast-charging electrolyte that can withstand a high voltage of 4.35V to achieve excellent electrical performance of lithium-ion batteries. Summary of the Invention

[0005] In order to solve the above problems, the purpose of the present invention is to provide a non-aqueous electrolyte and a lithium ion battery thereof, which can improve the high-temperature storage performance and high-temperature cycle performance of the ternary lithium ion battery.

[0006] To achieve the above object, the present invention provides a non-aqueous electrolyte in a first aspect, comprising a lithium salt, a non-aqueous organic solvent and an additive, wherein the additive comprises an unsaturated ionic liquid salt represented by structural formula I.

[0007]

[0008] wherein R1, R2, and R3 each independently represent H, halogen, a hydrocarbon group having 1 to 6 carbon atoms, an alkenyl group having 1 to 6 carbon atoms, an alkynyl group, a phenyl group, a benzyl group, a biphenyl group, or caprolactam.

[0009] The addition of the unsaturated ionic liquid salt shown in structural formula I to the non-aqueous electrolyte of the present invention not only reduces the surface activity of the positive electrode and inhibits the oxidative decomposition of the electrolyte, but more importantly, the unsaturated ionic liquid salt contains sulfur-oxygen double bonds and carbon-carbon double bonds. During the battery cell formation stage, the sulfur-containing unsaturated bonds will form inorganic substances and the carbon-carbon double bonds will polymerize to form polymers. These effective components can stably improve the interface composition of the battery cell during high-temperature storage and cycling, inhibit the damage of harmful components to the electrolyte, thereby significantly improving the high-temperature storage performance and high-temperature cycling performance of the battery, and can improve the high-temperature storage performance and high-temperature cycling performance of high-voltage (4.35V) ternary lithium-ion batteries.

[0010] As a preferred technical solution, the unsaturated ionic liquid salt represented by structural formula I is selected from at least one of compound 1 to compound 20:

[0011]

[0012]

[0013]

[0014]

[0015] The synthesis of compound 1 can be prepared by referring to the following route:

[0016]

[0017] In the synthesis process of Compound 2-Compound 20, Compound 2-Compound 20 can be obtained by replacing Compound A with Compound B-Compound T. The structural formulas of Compound A-Compound T are as follows:

[0018]

[0019] As a preferred technical solution, the mass percentage of the unsaturated ionic liquid salt represented by structural formula I in the non-aqueous electrolyte is 0.1-5%, specifically but not limited to 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, and 5%.

[0020] As a preferred technical solution, the lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium methanesulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethylsulfonyl)imide (LiN(CF3SO2)2), lithium bis(oxalatoborate) (C4BLiO8), lithium difluorooxalatoborate (C2BF2LiO4), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFBP), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0021] As a preferred technical solution, the mass percentage of the lithium salt of the present invention in the non-aqueous electrolyte is 10-20%, specifically 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0022] As a preferred technical solution, the non-aqueous organic solvent is at least one of a linear carbonate, a cyclic carbonate, a carboxylate, an ether, and a heterocyclic compound. More preferably, the non-aqueous organic solvent is 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).

[0023] As a preferred technical solution, the mass percentage of the non-aqueous organic solvent of the present invention in the non-aqueous electrolyte is 60-85%, specifically 60%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 80%, 85%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] As a preferred technical solution, the non-aqueous electrolyte further includes an auxiliary agent, wherein the auxiliary agent is selected from at least one of vinylene carbonate (VC), vinylene carbonate (VEC), fluoroethylene carbonate (FEC), ethylene sulfite (ES), 1,3-propane sultone (PS), and diethylene sulfate (DTD). Preferably, the weight percentage of the auxiliary agent in the non-aqueous electrolyte is 0.0512%, and more preferably, the weight percentage of the auxiliary agent in the non-aqueous electrolyte is 1.10%.

[0025] The second aspect of the present invention provides a lithium-ion battery, comprising a positive electrode material, a negative electrode material and an electrolyte, wherein the electrolyte is the aforementioned non-aqueous electrolyte. The lithium-ion battery of the present invention can effectively improve the high-temperature storage performance and high-temperature cycling performance of the lithium-ion battery because the additive of the non-aqueous electrolyte comprises an unsaturated ionic liquid salt shown in Structural Formula I.

[0026] As a preferred technical solution, the positive electrode material is selected from nickel cobalt manganese oxides. More preferably, the chemical formula of the nickel cobalt manganese oxide is LiNi x Co y Mn (1-x-y) M z O2, wherein, 0.6 < x < 0.9, x + y ≤ 1, M is one of Al, Mg, Zr, Ti, and 0 ≤ z < 0.08.

[0027] As a preferred technical solution, the negative electrode material is one of a carbon negative electrode material, a silicon negative electrode material or a silicon-carbon negative electrode material. Detailed Embodiments

[0028] The following specific examples are used to further illustrate the purpose, technical solutions and beneficial effects of the present invention, but do not constitute any limitation to the present invention. For those not specified in the examples, conventional conditions or conditions recommended by the manufacturer can be followed. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial channels.

[0029] Example 1

[0030] Preparation of non-aqueous electrolyte: In an argon atmosphere, an electrolyte is prepared in a vacuum glove box with a water content < 1 ppm. In a dry argon atmosphere glove box, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed according to a weight ratio of EC:PC:EMC:DEC = 2:1:5:2 to obtain a non-aqueous organic solvent. Then, additives and auxiliaries are added, dissolved and stirred thoroughly, and then a lithium salt is added. After mixing evenly, an electrolyte is obtained. The specific contents are shown in Table 1.

[0031] The electrolyte formulations of Examples 2 to 13 and Comparative Example 1 are shown in Table 1. The steps for preparing the electrolyte are the same as those in Example 1.

[0032] Table 1 Electrolyte components of each example

[0033]

[0034]

[0035] With a maximum charging voltage of 4.35V for LiNi8Co1Mn1M 0.3O2 was used as the positive electrode material, and a silicon-carbon negative electrode material (10% Si) was used as the negative electrode material. Lithium-ion batteries were prepared using the electrolytes of Examples 1-13 and Comparative Example 1 according to a conventional lithium battery preparation method. The normal temperature cycle performance, high temperature cycle performance, and high temperature storage performance tests were performed respectively. The test conditions are as follows. The test results are shown in Table 2:

[0036] High temperature storage performance test:

[0037] At room temperature (25°C), the lithium-ion battery is charged and discharged at 0.5C / 0.5C (the discharge capacity is recorded as C0), with an upper limit voltage of 4.35V. Then, the battery is charged to 4.35V under 0.5C constant current and constant voltage conditions, and the battery thickness d0 is measured. The lithium-ion battery is placed in a 60°C high temperature box for 30 days, and the battery thickness d1 is measured after it is taken out. The battery is discharged at 0.5C at 25°C (the discharge capacity is recorded as C1). The lithium-ion battery is charged and discharged at 0.5C / 0.5C (the discharge capacity is recorded as C2) at room temperature (25°C), 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 formula:

[0038] Capacity retention rate = C1 / C0*100%

[0039] Capacity recovery rate = C2 / C0*100%

[0040] Thickness expansion rate = d1 / d0*100%

[0041] Normal temperature rate cycle test:

[0042] At room temperature (25°C), the lithium-ion battery is charged and discharged at 1.0C / 1.0C once (the battery discharge capacity is C0), with an upper limit voltage of 4.35V, and then charged and discharged at 4.0C / 1.0C for 500 cycles at room temperature (the battery discharge capacity is C1).

[0043] Capacity retention rate = (C1 / C0)*100%

[0044] High temperature cycle test:

[0045] Under high temperature (45℃) conditions, the lithium-ion battery is charged and discharged at 1.0C / 1.0C once (the battery discharge capacity is C0), with an upper limit voltage of 4.35V, and then charged and discharged at 1.0C / 1.0C for 500 cycles at room temperature (the battery discharge capacity is C1). The capacity retention rate = (C1 / C0)*100%

[0046] Table 2 Lithium-ion battery performance test results

[0047]

[0048] As can be seen from the results in Table 2, the high-temperature storage performance and high-temperature cycle performance of Examples 1-13 are significantly better than those of Comparative Example 1. This may be due to the addition of an unsaturated ionic liquid salt shown in structural formula I to the non-aqueous electrolyte. The unsaturated ionic liquid salt contains sulfur-oxygen double bonds and carbon-carbon double bonds. During the battery cell formation stage, the sulfur-containing unsaturated bonds will form inorganic substances and the carbon-carbon double bonds will polymerize to form polymers. These effective components can stably improve the interface composition of the battery cell during high-temperature storage and cycling, inhibit the damage of harmful components to the electrolyte, thereby significantly improving the high-temperature storage performance and high-temperature cycle performance.

[0049] 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, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents 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 an electrolyte, characterized in that: The positive electrode material is selected from nickel cobalt manganese oxides, and the chemical formula of the nickel cobalt manganese oxides is LiNi x Co y Mn (1-x-y) M z O2, where 0.6 < x < 0.9, x + y ≤ 1, M is one of Al, Mg, Zr, and Ti, 0 ≤ z < 0.08, the maximum charging voltage of the lithium ion battery is 4.35 V, the electrolyte includes a lithium salt, a non-aqueous organic solvent, and an additive, and the additive includes at least one of compound 1, compound 2, compound 5, compound 6, compound 7, compound 8, compound 9, compound 11, compound 12, compound 13, compound 14, compound 15, compound 16, compound 17, compound 18, compound 20, and the unsaturated ionic liquid salt shown in structural formula I wherein R1, R2, and R3 each independently represent H, halogen, alkenyl having 1 to 6 carbon atoms, alkynyl, phenyl, biphenyl, or caprolactam.

2. The lithium-ion battery according to claim 1, wherein The unsaturated ionic liquid salt represented by structural formula I is selected from at least one of compound 3, compound 4, compound 10 and compound 19:

3. The lithium-ion battery according to claim 1, wherein The mass percentage of the unsaturated ionic liquid salt represented by structural formula I in the electrolyte is 0.1-5%.

4. The lithium-ion battery according to claim 1, wherein The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium methanesulfonate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethylsulfonyl imide), lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate, lithium difluorobis(oxalatophosphate), lithium bis(fluorosulfonyl imide), and lithium bis(trifluoromethylsulfonyl imide.

5. The lithium-ion battery according to claim 1, wherein The non-aqueous organic solvent is at least one of chain carbonates, cyclic carbonates, carboxylates, ethers and heterocyclic compounds.

6. The lithium-ion battery according to claim 5, wherein The non-aqueous organic solvent is at least one selected from the group consisting of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, butyl acetate, γ-butyrolactone, propyl propionate, ethyl propionate and ethyl butyrate.

7. The lithium-ion battery according to claim 1, wherein The invention also includes an auxiliary agent, which is selected from at least one of vinylene carbonate, vinylene carbonate, fluoroethylene carbonate, vinyl sulfite, 1,3-propane sultone, and vinyl sulfate.

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