A 6V ultra-high voltage electrolyte and its preparation method and application

Abstract

The present invention relates to a 6V ultra-high voltage electrolyte and a preparation method and application thereof, belonging to the technical field of lithium ion batteries. The electrolyte is composed of a mixture of a highly antioxidant lithium salt, a cyclic solvent, a chain solvent, a diluent, and a film-forming additive. The electrolyte obtained by the present invention can make the electrochemical window reach above 6V, and form a dense and uniform CEI and SEI film at the positive and negative electrodes, greatly improving the stability of the electrolyte working under high voltage, and significantly improving the high-voltage cycle life of the secondary battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a 6V ultra-high voltage electrolyte and a preparation method and application thereof. Background Art

[0002] In order to meet the growing consumer demand, lithium-ion batteries must achieve higher energy density, longer cycle life, faster charging capability and a wider operating temperature range. In principle, the energy density of the battery can be further improved by increasing the charge cut-off voltage. However, the continuous oxidative decomposition of the electrolyte under high voltage, the excessive growth of the inhomogeneous cathode-electrolyte interface (CEI) and the sluggish interface kinetics are still the key issues that hinder the cathode from achieving high voltage, fast charging and long cycle. The use of highly antioxidant electrolytes and the construction of a stable and fast ion transport electrode / electrolyte interface through additives are effective strategies to solve the above problems. Summary of the invention

[0003] In view of this, the present invention provides a 6V ultra-high voltage electrolyte and a preparation method and application thereof, the main purpose of which is to solve the technical problem that current lithium-ion batteries cannot work normally under ultra-high voltage.

[0004] On the one hand, the present invention provides a 6V ultra-high voltage electrolyte, the components of which include a highly antioxidant lithium salt, a highly antioxidant cyclic solvent, a highly antioxidant chain solvent, a highly antioxidant diluent and a highly antioxidant film-forming additive.

[0005] Optionally, the molar concentration of the highly antioxidant lithium salt in the 6V ultra-high voltage electrolyte is 0.3-4 mol / L, calculated based on the molar amount of the lithium element in the lithium salt.

[0006] Optionally, the mass ratio of the highly antioxidant cyclic solvent, the chain solvent and the diluent in the 6V ultra-high voltage electrolyte is (0-30): (20-90): (0-50).

[0007] Optionally, the amount of the highly antioxidant film-forming additive added to the 6V ultra-high voltage electrolyte is 0.2-10wt%.

[0008] Optionally, the highly antioxidant lithium salt is selected from at least one of phosphate lithium salts, chlorate lithium salts, borate lithium salts and arsenate lithium salts.

[0009] Optionally, the highly antioxidant lithium salt is selected from at least one of lithium hexafluorophosphate, lithium difluorooxalatoborate, lithium tetrafluoroborate, lithium hexafluoroarsenate, and lithium perchlorate.

[0010] Optionally, the highly antioxidant cyclic solvent is selected from at least one of propylene carbonate, butylene carbonate and fluoroethylene carbonate.

[0011] Optionally, the highly antioxidant chain solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, trans-4,5-difluoroethylene carbonate, methyl trifluoroethyl carbonate, bis(2,2,2-trifluoroethyl) carbonate, methyl formate, methyl acetate, methyl trifluoroacetate, ethyl acetate, ethyl trifluoroacetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate and butyl butyrate.

[0012] Optionally, the high antioxidant diluent is selected from at least one of 1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, bis(2,2,2-trifluoroethyl) ether, 1,1,2,2,3,3,4,4-octafluoro-5-(1,1,2,2-tetrafluoroethoxy)pentane, fluorobenzene, fluorinated orthoformate, and 2H,3H-decafluoropentane.

[0013] Optionally, the highly antioxidant film-forming additive is selected from at least one of lithium bis(oxalatoborate), 1,3-propane sultone, and lithium difluorophosphate.

[0014] Optionally, the operating voltage range of the 6V ultra-high voltage electrolyte is 0.001~6V.

[0015] The present invention uses highly antioxidant lithium salts, cyclic solvents, chain solvents, diluents and film-forming additives to jointly regulate the electrolyte solvation structure and the electrode / electrolyte interface, thereby constructing an electrolyte with high antioxidant properties, which can make the electrochemical window reach above 6 V and generate a dense and uniform SEI and CEI film at the positive and negative electrodes, greatly improving the stability of the electrolyte working under high voltage, and significantly improving the high-voltage cycle life of the secondary battery.

[0016] In a second aspect, the present invention provides a method for preparing the above-mentioned 6V ultra-high voltage electrolyte, the method comprising the following steps: The raw materials of highly antioxidant lithium salt, highly antioxidant cyclic solvent, highly antioxidant chain solvent, highly antioxidant diluent and highly antioxidant film-forming additive are mixed according to a proportion to obtain the 6V ultra-high voltage electrolyte.

[0017] In a third aspect, the present invention provides a lithium-ion battery comprising an electrolyte, wherein the electrolyte is the above-mentioned 6V ultra-high voltage electrolyte.

[0018] In a fourth aspect, the present invention provides the use of the above-mentioned 6V ultra-high voltage electrolyte in the preparation of lithium-ion batteries.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention constructs a highly antioxidant electrolyte by using highly antioxidant lithium salts, cyclic solvents, chain solvents, diluents and film-forming additives, which can make the electrochemical window reach above 6 V and is the electrolyte with the highest antioxidant stability to date.

[0020] 2. The 6V ultra-high voltage electrolyte provided by the present invention effectively regulates the electrolyte solvation structure and the electrode / electrolyte interface, generates a dense and uniform SEI and CEI film at the positive and negative electrodes, greatly improves the stability of the electrolyte working under ultra-high voltage, and can significantly improve the high-voltage cycle life of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0022] Figure 1 The linear sweep voltammetry (LSV) curves of Examples 1, 2, and 3 of the present invention and Comparative Examples 1 and 2 are shown; Figure 2 The first charge and discharge curves of Example 1 of the present invention and the comparative example are shown; Figure 3 This is the first charge and discharge curve diagram of Example 2 of the present invention; Figure 4 This is the first charge and discharge curve diagram of Example 3 of the present invention; Figure 5 The cycle performance diagram of Examples 1, 2, 3 of the present invention and Comparative Example 2 in button batteries; Figure 6 Graph showing the capacity and capacity retention rate of Example 3 of the present invention in a 18650 cylindrical lithium-ion battery. DETAILED DESCRIPTION

[0023] The present application is further described below in conjunction with specific embodiments. The following are only a few embodiments of the present application, and are not intended to limit the present application in any form. Although the present application discloses the following preferred embodiments, they are not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the above disclosed technical content to make some changes or modifications are equivalent to equivalent implementation cases and are within the scope of the technical solution.

[0024] Unless otherwise specified, the raw materials in the examples of the present application were purchased from commercial sources and used directly without any special treatment.

[0025] Unless otherwise specified, the analysis methods in the examples all adopt conventional settings and conventional analysis methods of instruments or equipment.

[0026] Example 1 The electrolyte was prepared in a glove box filled with argon (H2O≤0.01ppm, O2≤0.01ppm).

[0027] Taking the mass of the electrolyte as 100%, the electrolyte comprises the following components: LiPF6 16.5%; FEC 15.07%; DMC 22.18%; 1,1,2,2-Tetrafluoroethyl-2,2,2-trifluoroethyl ether (TTE) 46.25%.

[0028] Example 2 The electrolyte was prepared in a glove box filled with argon (H2O≤0.01ppm, O2≤0.01ppm).

[0029] Taking the mass of the electrolyte as 100%, the electrolyte comprises the following components: LiPF6 16.17%; PC 7.83%; FEC 16.71%; DMC 28.12%; Diluent 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TTE) 30.83%; Film-forming additive LiPO2F20.33%.

[0030] Example 3 The electrolyte was prepared in a glove box filled with argon (H2O≤0.01ppm, O2≤0.01ppm).

[0031] Taking the mass of the electrolyte as 100%, the electrolyte comprises the following components: LiPF6 16.5%; FEC 15%; DMC 60.5%; Diluent 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TTE) 5%; Film-forming additive LiPO2F21%; Film-forming additive LiBOB 1%; Film-forming additive 1,3-PS 2%.

[0032] Comparative Example 1 The electrolyte was prepared in a glove box filled with argon (H2O≤0.01ppm, O2≤0.01ppm).

[0033] Taking the mass of the electrolyte as 100%, the electrolyte comprises the following components: LiPF6 16.5%; EC 15%; DMC 53%; EMC 9%; Film-forming additive VC 2%; Film-forming additive FEC 2%; Overcharge additive BP 0.5%; Overcharge additive CHB 2%.

[0034] Comparative Example 2 The electrolyte was prepared in a glove box filled with argon (H2O≤0.01ppm, O2≤0.01ppm).

[0035] Taking the mass of the electrolyte as 100%, the electrolyte comprises the following components: LiPF6 16.5%; EC 15%; DMC 54.5%; EMC 10%; Film-forming additive VC 2%; Film-forming additive FEC 2%.

[0036] Example 4 (Cylindrical battery) The positive electrode active material used in the lithium-ion battery described in this embodiment is lithium nickel manganese oxide, the negative electrode active material is graphite, and the electrolyte is the electrolyte described in Example 3.

[0037] In the positive electrode of the lithium-ion battery described in this embodiment, the positive electrode current collector is aluminum foil, the conductive agent is SP, and the binder is PVDF; wherein the mass ratio of the positive electrode active material, the conductive agent, and the binder is 94.9:3.5:1.6; In the negative electrode of the lithium-ion battery described in this embodiment, the negative electrode current collector is copper foil, the conductive agent is SP, the binder is CMC and SBR, and the mass ratio of the negative electrode active material, the conductive agent and the binder is 94.7:1.5:3.8; The preparation method of the lithium ion battery described in this embodiment: (a) mixing lithium nickel manganese oxide, a conductive agent, a binder, an additive lithium carbonate and a solvent NN-dimethylpyrrolidone to obtain a positive electrode slurry, coating the mixture on a positive electrode current collector, drying, rolling, slitting and sheeting to obtain a positive electrode; Wherein, taking the mass of the positive electrode slurry as 100%, the positive electrode slurry includes the following components: Lithium nickel manganese oxide 50%-70%; Conductive agent 0.1%-5%; Binder 0.1%-5%; Additives 0.3%-2%; Solvent 20%-40%; (b) mixing graphite, a conductive agent, a binder and a solvent of deionized water to obtain a negative electrode slurry, coating the mixture on a negative electrode current collector, drying, rolling, slitting and sheeting to obtain a negative electrode; Wherein, taking the mass of the negative electrode slurry as 100%, the negative electrode slurry includes the following components: Graphite 50-60%; Conductive agent 0.1-1%; Binder 0.1-3%; Solvent 30-50%; (c) The positive electrode in step (a), the negative electrode in step (b) and the polyethylene separator are wound, shelled, injected, sealed, pre-charged, formed, aged and capacity divided to obtain the lithium-ion battery.

[0038] Example 5 (Button Battery) The assembly process of lithium||lithium nickel manganese oxide button battery is carried out in the order of positive electrode shell, positive electrode sheet, electrolyte, diaphragm, electrolyte, metal lithium sheet, gasket, and negative electrode shell. After the battery is completed, it is packaged and left to stand at room temperature for 6 hours before the electrochemical performance test.

[0039] The preparation method of the lithium nickel manganese oxide electrode is the same as that of Example 4. After drying, the electrode is die-cut into a positive electrode with a diameter of 14 mm.

[0040] Figure 1 It is the electrochemical stability window test diagram of the electrolytes of Examples 1, 2, 3 and Comparative Examples 1 and 2. It can be seen from the figure that the electrolytes of Examples 1, 2, 3 have a wide electrochemical stability window, the highest oxidation potential reaches 6V, and the oxidation resistance is strong, and can be applied to high-voltage battery systems.

[0041] Figure 2 The first charge and discharge curves of Example 1 and Comparative Example 1 of the present invention are shown in FIG. 1 . It can be seen from the figure that Example 1 can make the 4.9V nickel manganese oxide positive electrode work normally, while Comparative Example 1 cannot work normally.

[0042] Figure 3 and Figure 4 The first charge and discharge curves of Example 2 and Example 3 of the present invention are shown in the figure. It can be seen from the figure that both Example 2 and Example 3 can make the 4.9V nickel manganese oxide positive electrode work normally.

[0043] Figure 5 The graph is a cycle performance graph of Examples 1, 2, 3 of the present invention and Comparative Example 2 in a lithium||lithium nickel manganese oxide button cell. It can be seen from the graph that Example 3 has the best cycle performance, with a capacity retention rate of 69% after 250 cycles, while the capacity retention rate of Comparative Example 2 is only 50% after 100 cycles.

[0044] Figure 6 This is a diagram of the capacity and capacity retention rate of Example 3 of the present invention in a 18650 cylindrical lithium-ion battery. It can be seen from the figure that the capacity retention rate of Example 3 is still as high as 78% after 600 cycles at a high voltage of 4.8V.

[0045] The embodiments described above are part of the embodiments of the present invention, rather than all of the embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Claims

1. A 6V ultra-high voltage electrolyte, characterized in that: The components of the 6V ultra-high voltage electrolyte include a highly resistant lithium salt, a highly resistant cyclic solvent, a highly resistant chain solvent, a highly resistant diluent and a highly resistant film-forming additive; The highly antioxidant lithium salt is selected from at least one of phosphate lithium salts, chlorate lithium salts, borate lithium salts and arsenate lithium salts; the highly antioxidant lithium salt is selected from at least one of lithium hexafluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium hexafluoroarsenate and lithium perchlorate; the highly antioxidant cyclic solvent is selected from at least one of propylene carbonate, butylene carbonate and fluoroethylene carbonate; the highly antioxidant chain solvent is selected from dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, trans-4,5-difluoroethylene carbonate, methyl trifluoroethyl carbonate, bis (2,2,2-trifluoroethyl) carbonate, methyl formate, methyl acetate, methyl trifluoroacetate, ethyl acetate, ethyl trifluoroacetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, At least one of butyl butyrate; the highly antioxidant diluent is selected from 1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, bis(2,2,2-trifluoroethyl) ether, 1,1,2,2,3,3,4,4-octafluoro-5-(1,1,2,2-tetrafluoroethoxy)pentane, fluorobenzene, fluorinated orthoformate, 2H,3H-decafluoropentane; the highly antioxidant film-forming additive is selected from at least one of lithium bis(oxalatoborate), 1,3-propane sultone, and lithium difluorophosphate.

2. A 6V ultra-high voltage electrolyte according to claim 1, characterized in that: The molar concentration of the highly antioxidant lithium salt is 0.3-4 mol / L, calculated based on the molar amount of the lithium element in the lithium salt.

3. A 6V ultra-high voltage electrolyte according to claim 1, characterized in that: The mass ratio of the highly antioxidant cyclic solvent, the chain solvent and the diluent is (0-30): (0-90): (0-50).

4. A 6V ultra-high voltage electrolyte according to claim 1, characterized in that: The addition amount of the highly antioxidant film-forming additive is 0.2-10wt%.

5. A 6V ultra-high voltage electrolyte according to claim 1, characterized in that: The operating voltage range of the lithium-ion battery electrolyte is 0.001~6V.

6. The method for preparing a 6V ultra-high voltage electrolyte according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: mixing raw materials of highly antioxidant lithium salt, highly antioxidant cyclic solvent, highly antioxidant chain solvent, highly antioxidant diluent and highly antioxidant film-forming additive according to a proportion to obtain the 6V ultra-high voltage electrolyte.

7. Use of an ultra-high voltage electrolyte in a lithium-ion battery, the lithium-ion battery electrolyte according to any one of claims 1 to 6 being employed.

Images