Electrolyte and lithium ion battery thereof

Abstract

This invention provides an electrolyte and a lithium-ion battery thereof. The lithium-ion battery includes a positive electrode, a negative electrode, and an electrolyte. The maximum charging voltage is 4.4V. The positive electrode comprises a nickel-cobalt-manganese oxide material, specifically a high-nickel-cobalt-manganese oxide (LiNi) material. x Co y Mn (1‑x‑y) M z O2, wherein 0.6≤x<0.9, x+y≤1, 0≤z<0.08, and M is any one of Al, Mg, Zr, and Ti. The electrolyte includes lithium salt, organic solvent, and additives. The additives include compounds having the structure shown in Formula II or Formula III: Formula II Formula III Wherein, R1-R3 are each independently selected from H, substituted or unsubstituted C1-C3 alkyl groups, and R1 is the same as R3; X is selected from -S-, -O-, -NH-, -SO-, or -SO2-. The additive in the electrolyte of this invention is an adamantane derivative, which can form a stable lithium nitride-rich interface film on the positive electrode surface. This film has good lithium-ion conductivity, so the lithium-ion battery of this invention has better high-temperature cycling and low-temperature discharge performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more particularly to an electrolyte and a lithium-ion battery thereof. Background Technology

[0002] In lithium-ion batteries, commonly used cathode materials include lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium iron phosphate, lithium-rich composite oxides, and ternary composite oxides. Cathode materials used in power lithium-ion batteries mainly include lithium iron phosphate, lithium manganese oxide, and ternary materials. Among them, ternary materials have high electrochemical capacity, good cycle performance, low cost, and ternary synergistic effect. They also have the advantages of lithium cobalt oxide, lithium manganese oxide, and lithium nickel oxide, thus becoming a hot topic in research and development and production.

[0003] Ternary materials, especially high-nickel ternary materials, are prone to irreversible H2-H3 phase transitions under high voltage and high temperature, leading to oxygen evolution. This instability at the electrolyte and electrode interfaces results in poor high-temperature storage performance and severe gas generation during cycling. Conventional carbonate electrolytes will oxidize and decompose on the surface of the battery's positive electrode at a high voltage of 4.4V, especially under high temperature 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 an electrolyte that can withstand a high voltage of 4.4V in order to achieve excellent performance of lithium-ion batteries. Summary of the Invention

[0005] The purpose of this invention is to provide an electrolyte and lithium-ion battery that can reduce the surface activity of the positive electrode and inhibit the oxidative decomposition of the electrolyte, thereby improving the high-temperature storage and cycle performance of high-voltage (4.4V) ternary lithium-ion batteries.

[0006] To achieve the above objectives, the present invention provides an electrolyte comprising a lithium salt, an organic solvent, and an additive, wherein the additive comprises a compound as shown in structural formula I, structural formula II, or structural formula III:

[0007]

[0008] R1-R4 are each independently selected from H, substituted or unsubstituted C1-C6 hydrocarbon groups; X is selected from heteroatoms or polyatomic groups containing heteroatoms.

[0009] Compared with existing technologies, the additive of the present invention has an adamantane derivative structure, possibly because the adamantane derivative structure is relatively stable and easily adsorbed onto the electrode surface, forming an inert layer to protect the electrode-electrolyte interface. The nitrogen element in the structure of the present invention readily forms a stable lithium nitride-rich interfacial film at the electrode interface. This film has excellent lithium-ion conduction channels, preventing collapse of lithium-ion channels during cycling and thus improving cycle performance. Simultaneously, the introduction of side-chain functional groups into the adamantane derivative enriches the composition of the electrode / electrolyte interfacial film.

[0010] Preferably, R1 is the same as R3. By introducing at least one pair of symmetrical side chains, the stability of SEI can be further improved, the structural stability of the interface film can be improved, thereby achieving the purpose of improving the storage and cycle performance of lithium-ion batteries.

[0011] Preferably, R1-R4 are each independently selected from H, substituted or unsubstituted C1-C3 alkyl groups; X is selected from -S-, -O-, -NH-, -SO- or -SO2-.

[0012] Preferably, R1-R4 are each independently selected from H and methyl; X is selected from -S-.

[0013] Preferably, R1-R4 are each independently selected from H and methyl; X is selected from -SO2-.

[0014] Preferably, the additive is selected from one or more of compounds 1 to 5:

[0015]

[0016] Preferably, the additive accounts for 0.1%-5.0% of the total mass of the electrolyte, specifically but not limited to 0.1%, 0.2%, 0.5%, 1%, 2%, 3%, 4%, and 5%.

[0017] Preferably, the lithium salt is one or more of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium methanesulfonate, lithium trifluoromethanesulfonate (LiCF3SO3), lithium dioxalate borate (C4BLiO8), lithium difluorooxalate borate (C2BF2LiO4), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalate) phosphate (LiDFBP), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0018] Preferably, the concentration of the lithium salt is 0.5M-1.5M, specifically but not limited to 0.5M, 0.8M, 1.0M, 1.3M, and 1.5M.

[0019] Preferably, the organic solvent is one or more of chain carbonates, cyclic carbonates, carboxylic acid esters, ether compounds, and heterocyclic compounds. Specifically, the organic solvent is selected from at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), butyl acetate (n-BA), γ-butyrolactone (GBL), propyl propionate (n-PP), ethyl propionate (EP), and ethyl butyrate (EB).

[0020] Preferably, the electrolyte further includes additives, which include one or more of vinylene carbonate (VC), vinylene carbonate (VEC), fluoroethylene carbonate (FEC), vinyl sulfite (ES), 1,3-propanesulfonate lactone (PS), and vinyl sulfate (DTD). The additives used account for 0.1%-5% of the total mass of the electrolyte.

[0021] In another aspect, the present invention provides a lithium-ion battery, including a positive electrode and a negative electrode, and also including the electrolyte described above.

[0022] Preferably, the positive electrode comprises a nickel-cobalt-manganese oxide material, specifically, the nickel-cobalt-manganese oxide material is a high-nickel-cobalt-manganese oxide LiNi. x Co y Mn (1-x-y) M z O2, where 0.6≤x<0.9, x+y≤1, 0≤z<0.08, and M is any one of Al, Mg, Zr, and Ti. Detailed Implementation

[0023] 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.

[0024] The present invention will be described in detail below. In the present invention, a lithium-ion battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode is a high-nickel cobalt-manganese oxide (LiNiO2). x Co y Mn (1-x-y) M zO2, wherein 0.6≤x<0.9, x+y≤1, M is one of Al, Mg, Zr, Ti, 0≤z<0.08, preferably x=0.6, y=0.2, M is Zr, z=0.03. The negative electrode is a carbon negative electrode material, a silicon negative electrode material, or a silicon-carbon negative electrode material, preferably a silicon-carbon negative electrode material (10% Si). The electrolyte includes lithium salt, organic solvent, additives, and auxiliaries, with additives accounting for 0.1%-5.0% of the total electrolyte mass. The auxiliaries are one or more of vinylene carbonate (VC), vinylene carbonate (VEC), fluoroethylene carbonate (FEC), vinyl sulfite (ES), 1,3-propanesulfonate lactone (PS), and vinyl sulfate (DTD), accounting for 0.1%-5% of the total electrolyte mass. The lithium salt is one or more of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium methanesulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), lithium dioxalatoborate (C4BLiO8), lithium difluorooxalatoborate (C2BF2LiO4), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalato)phosphate (LiDFBP), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), wherein the concentration of the lithium salt is 0.5M-1.5M. The organic solvent is selected from one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), butyl acetate (n-BA), γ-butyrolactone (GBL), propyl propionate (n-PP), ethyl propionate (EP), and ethyl butyrate (EB).

[0025] Example 1

[0026] Electrolyte preparation:

[0027] In a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm), ethyl propionate (EP), dimethyl carbonate (DMC), and propylene carbonate (PC) were mixed thoroughly in a mass ratio of 1:1:1 to obtain a mixed solvent, which was then used as an organic solvent. Additives and auxiliaries were added to obtain a mixed solution. The mixed solution was sealed and packaged and frozen in a freezer (-4°C) for 2 hours. After being removed, lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution in a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm). After thorough mixing, the electrolyte was prepared.

[0028] Preparation of positive electrode:

[0029] Ternary material LiNi 0.6 Co 0.2 Mn 0.2 Zr 0.03O2, conductive agent SuperP, binder PVDF, and carbon nanotubes (CNTs) were mixed uniformly at a mass ratio of 97.5:1.5:1:1 to prepare a lithium-ion battery positive electrode slurry of a certain viscosity. This slurry was then coated onto aluminum foil used for current collectors, with a coating weight of 324 g / m². 2 After drying at 85℃, the material is cold-pressed; then it is trimmed, cut into pieces, and slit. After slitting, it is dried at 85℃ for 4 hours under vacuum conditions, and then the tabs are welded to produce a lithium-ion battery positive electrode sheet that meets the requirements.

[0030] Preparation of negative electrode:

[0031] Artificial graphite and silicon are mixed at a mass ratio of 90:10, and then combined with conductive agent SuperP, thickener CMC, and binder SBR (styrene-butadiene rubber latex) at a mass ratio of 95:1.5:1.0:2.5 to form a slurry. The mixture is thoroughly mixed, coated onto both sides of copper foil, dried, and rolled to obtain the negative electrode sheet, thus producing a lithium-ion battery negative electrode sheet that meets the requirements.

[0032] Preparation of lithium-ion batteries:

[0033] The positive electrode, negative electrode, and separator prepared according to the above process are stacked to form a lithium-ion battery with a thickness of 4.7 mm, a width of 55 mm, and a length of 60 mm. The battery is then vacuum-baked at 75°C for 10 hours and injected with the above-mentioned electrolyte. After standing for 24 hours, it is charged to 4.45V with a constant current of 0.1C (180 mA), and then charged at a constant voltage of 4.45V until the current drops to 0.05C (90 mA). It is then discharged to 3.0V at 0.2C (180 mA), and this charge-discharge cycle is repeated twice. Finally, the battery is charged to 3.8V at 0.2C (180 mA) to complete the fabrication of the lithium-ion battery.

[0034] The composition of the electrolytes in Examples 1-20 and Comparative Examples 1-8 is shown in Table 1. The preparation processes of the electrolytes, positive electrode sheets, negative electrode sheets, and lithium-ion batteries in Examples 2-20 and Comparative Examples 1-8 are the same as those in Example 1.

[0035] Table 1: Composition of the electrolytes in the examples and comparative examples

[0036]

[0037]

[0038] In the comparative examples above, the structural formula of compound A is:

[0039]

[0040] The lithium-ion batteries prepared in Examples 1-20 and Comparative Examples 1-8 were tested for high-temperature storage, cycle performance and low-temperature discharge performance under the following conditions, and the results are shown in Table 2.

[0041] Room temperature cycle test: Under room temperature (25℃) conditions, the lithium-ion battery is charged and discharged once at 1.0C / 1.0C (battery discharge capacity is C0), with an upper limit voltage of 4.4V. Then, under room temperature conditions, it is charged and discharged for 500 cycles at 1.0C / 1.0C (battery discharge capacity is C1), and the capacity retention rate is calculated.

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

[0043] High-temperature cycling test: Under high temperature (45℃) conditions, the lithium-ion battery is charged and discharged once at 1.0C / 1.0C (battery discharge capacity is C0), with an upper limit voltage of 4.4V. Then, it is charged and discharged for 500 cycles at 1.0C / 1.0C under normal temperature conditions (battery discharge capacity is C1), and the capacity retention rate is calculated.

[0044] Capacity retention rate = (C1 / C0) * 100%

[0045] High-temperature storage test: Under normal temperature (25℃) conditions, the lithium-ion battery was charged and discharged once at 0.3C / 0.3C (the battery discharge capacity was recorded as C0), with an upper limit voltage of 4.4V; the battery was placed in a 60℃ oven for 15 days, then removed and placed in a 25℃ environment for 0.3C discharge, with the discharge capacity recorded as C1; then the lithium-ion battery was charged and discharged once at 0.3C / 0.3C (the battery discharge capacity was recorded as C2), and the capacity retention rate and capacity recovery rate were calculated.

[0046] Capacity retention rate = (C1 / C0) * 100%

[0047] Capacity recovery rate = (C2 / C0) * 100%

[0048] Low-temperature discharge test: Under normal temperature (25℃) conditions, the lithium-ion battery was charged and discharged once at 0.3C / 0.3C (the battery discharge capacity was recorded as C0), with an upper limit voltage of 4.4V; then the battery was charged to 4.4V under constant current and constant voltage conditions at 0.5C, and the battery was placed in a -20℃ oven for 4 hours. The battery was then discharged at 0.3C at -20℃ (the discharge capacity was recorded as C1), with a cutoff voltage of 3.0V. The low-temperature discharge rate was then calculated.

[0049] Low-temperature discharge rate = (C1 / C0) * 100%

[0050] Table 2: Performance Test Results of Lithium-ion Batteries

[0051]

[0052] As shown in Table 2, compared to Comparative Examples 1-4, the low-temperature discharge performance, cycle performance, and high-temperature storage performance of the lithium-ion batteries in Examples 1-20 were significantly improved after using the additives of the present invention. This may be because the adamantane derivatives have a relatively stable structure and are easily adsorbed on the electrode surface, forming an inert layer to protect the electrode-electrolyte interface. The nitrogen element in the structure described in the present invention easily forms a stable lithium nitride-rich interface film at the electrode interface. This film has good lithium-ion conduction channels and does not cause the collapse of lithium-ion channels during cycling, thus improving cycle performance. At the same time, the introduction of side-chain functional groups into the adamantane derivatives can enrich the composition of the electrode / electrolyte interface film.

[0053] Compared to Comparative Examples 5-8, Examples 1-20 showed better cycle performance, high-temperature storage performance, and low-temperature discharge performance. This may be because the SEI film formed by Compound A has a relatively simple elemental composition, so the high-temperature storage and low-temperature performance of the lithium-ion battery were not significantly improved.

[0054] A comparison of Examples 1-9 and Examples 10-20 shows that adding additives to the additives of this invention results in better cycle performance and high-temperature storage performance. A comparison of Examples 10-14 shows that when a VC / VEC mixed additive is used in the electrolyte, the lithium-ion battery of this invention exhibits better cycle performance and high-temperature storage performance. When FEC and ES are used as additives, it has better low-temperature discharge performance.

[0055] As shown in Examples 1-5 and Examples 14-18, compounds 1 and 3 lack side-chain structures, resulting in slightly weaker performance. Compounds 2 and 4 have one side chain, leading to better performance compared to compounds 1 and 3. Compound 5 has a symmetrical side chain, thus exhibiting the best performance. Compound 5 demonstrates the best low-temperature discharge rate, high-temperature storage, and cycle performance, likely due to its superior stability of its symmetrical structure and abundant SEI interface elements, further improving the battery's cycle and storage performance. As shown in Examples 5-8 and Examples 18-20, the performance of compound 5 decreases with increasing usage, possibly due to an excessively thick adsorption layer or SEI interface, leading to increased internal impedance and deteriorated battery performance.

[0056] 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, a negative electrode, and an electrolyte, characterized in that, The maximum charging voltage is 4.4V, and the positive electrode comprises a nickel-cobalt-manganese oxide material, wherein the nickel-cobalt-manganese oxide material is a high-nickel-cobalt-manganese oxide LiNi. x Co y Mn (1-x-y) M z O2, wherein 0.6≤x<0.9, x+y≤1, 0≤z<0.08, and M is any one of Al, Mg, Zr, and Ti; the electrolyte comprises a lithium salt, an organic solvent, and additives, wherein the additives comprise compounds having the structure shown in Formula II or Formula III. Structural Form II Structural Form III R1-R3 are each independently selected from H, substituted or unsubstituted C1-C3 alkyl groups, and R1 is the same as R3; X is selected from -S-, -O-, -NH-, -SO- or -SO2-.

2. The lithium-ion battery according to claim 1, characterized in that, The additive is selected from one or more of the following compounds 3 to 5: Compound 3 Compound 4 and Compound 5.

3. The lithium-ion battery according to claim 1, characterized in that, The additive accounts for 0.1%-5.0% of the total mass of the electrolyte.

4. The lithium-ion battery according to claim 1, characterized in that, The lithium salt is one or more of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium methanesulfonate, lithium trifluoromethanesulfonate, lithium dioxalate borate, lithium difluorooxalate borate, lithium difluorophosphate, lithium difluorobis(oxalate) phosphate, lithium difluorosulfonylimide, and lithium di(trifluoromethanesulfonylimide).

5. The lithium-ion battery according to claim 1, characterized in that, The organic solvent is one or more of chain carbonates, cyclic carbonates, carboxylic acid esters, ether compounds, and heterocyclic compounds.

6. The lithium-ion battery according to claim 1, characterized in that, It also includes additives, which include one or more of vinylene carbonate, vinylene carbonate, fluorovinyl carbonate, vinyl sulfite, 1,3-propanesulfonate lactone, and vinyl sulfate.

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