A non-aqueous electrolyte and a lithium-ion battery

Abstract

This invention provides a non-aqueous electrolyte and a lithium-ion battery. The non-aqueous electrolyte comprises: an anhydrous organic solvent, a conductive lithium salt electrolyte, and a functional electrolyte additive; the functional electrolyte additive includes additive A; additive A is selected from at least one compound with a core structure as shown in Formula I or Formula II. In the non-aqueous electrolyte provided by this invention, additive A can form a stable interfacial film on the electrode surface, reducing electrolyte decomposition and the accumulation of decomposition products at the electrode interface during long-term battery cycling, thereby suppressing the increase in battery impedance during cycling and improving the long-term cycle life of the battery. Furthermore, the interfacial film formed by additive A has a lower interfacial impedance at low temperatures, while also improving the electrochemical performance of the battery at low temperatures.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery materials, and particularly relates to a non-aqueous electrolyte and a lithium ion battery. BACKGROUND

[0002] With the increasing demand for mobile energy of electric vehicles and portable electronic products, people pay more and more attention to the key performances of lithium ion batteries, such as energy density, endurance, cycle life and wide temperature applicability. Especially when the lithium ion battery is used as a power battery, its long-term cycle life and endurance in cold regions are far from the expected.

[0003] When the electrode material is determined, changing the matching electrolyte is a key element to improve the performance of the battery. During the long-term cycle of the battery, the continuous decomposition of the electrolyte, the dissolution of the transition metal ions and the accumulation of the interface by-products cause the increase of the battery impedance and the increase of the polarization, and finally lead to the rapid decay of the battery capacity. The occurrence of the above-mentioned side reactions is closely related to the instability of the electrode / electrolyte interface. In addition, the sharp increase of the interface impedance of the battery at low temperature is the key reason for the poor low-temperature performance of the battery. Therefore, by designing and optimizing the electrolyte to construct a stable and low-impedance interface film, the cycle life and low-temperature performance of the battery can be improved.

[0004] Functional additives are one of the important components of electrolyte. By designing a reasonable molecular structure, the decomposition of the additive molecules on the electrode surface and the formation of a more stable interface film can reduce the occurrence of side reactions during the cycle; at the same time, the interface components formed by the decomposition of the additive molecules also have lower interface impedance, which can promote the rapid transmission of lithium ions at the interface, especially at low temperature.

[0005] Therefore, the design and development of additive molecules capable of forming a stable interface film with low impedance on the electrode surface are very crucial to solve the problems of poor cycle life of lithium ion power battery and short endurance mileage at low temperature. SUMMARY

[0006] To solve the above problems, the application provides a non-aqueous electrolyte, which comprises: a non-aqueous organic solvent, a conductive lithium salt electrolyte and a functional electrolyte additive.

[0007] The functional electrolyte additive comprises an additive A.

[0008] The additive A is selected from at least one of the compounds with the mother nucleus structure as shown in formula I or formula II:

[0009] Formula I: ;

[0010] Formula II: .

[0011] Preferably, the amount of additive A added is 0.1-5 wt.% of the total mass of the electrolyte.

[0012] Preferably, in Formula I, R is selected from O or N;

[0013] When R is selected from O, there is no substituent R1;

[0014] R1 and R2 may be the same or different, and each is independently selected from hydrogen, halogen, -CN, unsubstituted or optionally substituted C1-C10 alkyl, unsubstituted or optionally substituted aryl or heteroaryl.

[0015] The substituent is selected from one or more of halogen, alkyl, olefin, alkynyl, alkoxy, and cyano groups.

[0016] Preferably, in formula II, R is selected from O or N;

[0017] When R is selected from O, there is no substituent R3;

[0018] R5 is selected from C or N; R3, R4 and R6 may be the same or different, and each is independently selected from hydrogen, halogen, -CN, unsubstituted or optionally substituted C1-C10 alkyl, unsubstituted or optionally substituted aryl or heteroaryl.

[0019] The substituent is selected from one or more of halogen, alkyl, olefin, alkynyl, alkoxy, and cyano groups.

[0020] Preferably, the additive A is selected from at least one of the following compounds: Formula I-1 to Formula I-8 and Formula II-1 to Formula II-4:

[0021] Formula I-1: ;

[0022] Formula I-2: ;

[0023] Formula I-3: ;

[0024] Formula I-4: ;

[0025] Formula I-5: ;

[0026] Formula I-6: ;

[0027] Formula I-7: ;

[0028] Formula I-8: ;

[0029] Formula II-1: ;

[0030] Formula II-2: ;

[0031] Formula II-3: ;

[0032] Formula II-4: .

[0033] Preferably, it also includes additive B;

[0034] Additive B is a film-forming additive;

[0035] Preferably, the film-forming additive is selected from vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, and 1,3-ethylene carbonate. Propanesulfonate lactone, 1,3 At least one of propylene sulfonate lactone, vinyl sulfite, vinyl sulfate, propylene sulfate, methane disulfonate, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, lithium difluorophosphate, lithium bis(oxalate)borate, lithium difluorooxalate borate, and lithium difluorooxalate phosphate.

[0036] Preferably, the amount of additive B is 0.1-5 wt.% of the total mass of the electrolyte.

[0037] Preferably, the non-aqueous organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, propyl acetate, ethyl propionate, and propyl propionate.

[0038] Preferably, the conductive lithium salt electrolyte is selected from one or more of lithium perchlorate, lithium hexafluorophosphate, lithium bis(oxalate)borate, lithium difluoro(oxalate)borate, lithium tetrafluoroborate, lithium difluoro(oxalate)phosphate, lithium bis(fluoro)sulfonylimide, and lithium bis(trifluoromethanesulfonylimide).

[0039] Preferably, the concentration of lithium salt in the non-aqueous electrolyte is 0.5-2 mol / L.

[0040] In addition, to solve the above problems, the present invention also provides a lithium-ion battery, including a positive electrode, a negative electrode and a separator, and a non-aqueous electrolyte as described above.

[0041] This invention provides a non-aqueous electrolyte and a lithium-ion battery. The non-aqueous electrolyte comprises: an anhydrous organic solvent, a conductive lithium salt electrolyte, and a functional electrolyte additive; the functional electrolyte additive includes additive A; additive A is selected from at least one compound with a core structure as shown in Formula I or Formula II. Additive A can form a stable interfacial film on the electrode surface, reducing electrolyte decomposition and the accumulation of decomposition products at the electrode interface during long-term battery cycling, thereby suppressing the increase in battery impedance during cycling and improving the long-term cycle life of the battery. Furthermore, the interfacial film formed by additive A has lower interfacial impedance at low temperatures, while also improving the electrochemical performance of the battery at low temperatures. Detailed Implementation

[0042] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Unless otherwise defined below, all technical and scientific terms used in the specific embodiments of this invention are intended to have the same meaning as commonly understood by those skilled in the art. While it is believed that the following terms will be well understood by those skilled in the art, the following definitions are set forth to better explain the invention.

[0044] As used in this invention, the terms “comprising,” “including,” “having,” “containing,” or “involving” are inclusive or open-ended and do not exclude other unlisted elements or method steps. The term “consisting of” is considered a preferred embodiment of the term “comprising.” If a group is defined below as comprising at least a certain number of embodiments, this should also be understood to disclose a group that preferably consists only of those embodiments.

[0045] When referring to a singular noun, the indefinite or definite article used, such as "a" or "a kind of," "the," includes the plural form of the noun.

[0046] The term "approximately" in this invention refers to an accuracy range that, as would be understood by those skilled in the art, still guarantees the technical effects of the features in question. This term typically indicates a deviation from the indicated value of ±10%, preferably ±5%.

[0047] Furthermore, the terms first, second, third, (a), (b), (c), and similar terms used in the specification and claims are for distinguishing similar elements and are not necessary for the order of description or chronological sequence. It should be understood that such terms are interchangeable in appropriate contexts, and the embodiments described in this invention can be implemented in a different order than that described or illustrated in this invention.

[0048] The following is provided merely to aid in understanding the invention. These definitions should not be construed as having a scope less than that understood by those skilled in the art.

[0049] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but this does not constitute any limitation on the present invention. Any limited modifications made by any person within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0050] This embodiment provides a non-aqueous electrolyte, comprising: an anhydrous organic solvent, a conductive lithium salt electrolyte, and a functional electrolyte additive;

[0051] The functional electrolyte additive includes additive A;

[0052] The additive A is selected from at least one of the compounds with the core structure shown in Formula I or Formula II:

[0053] Wherein, Equation I is Formula II is .

[0054] The above-mentioned non-aqueous electrolyte includes anhydrous organic solvent, conductive lithium salt electrolyte and functional electrolyte additive, wherein additive A can be one or more compounds with a core of Formula I or Formula II.

[0055] Furthermore, the amount of additive A added is 0.1-5 wt.% of the total mass of the electrolyte.

[0056] Furthermore, in Equation I, R is selected from O or N;

[0057] When R is selected from O, there is no substituent R1;

[0058] R1 and R2 may be the same or different, and each is independently selected from hydrogen, halogen, -CN, unsubstituted or optionally substituted C1-C10 alkyl, unsubstituted or optionally substituted aryl or heteroaryl.

[0059] The substituent is selected from one or more of halogen, alkyl, olefin, alkynyl, alkoxy, and cyano groups.

[0060] The above can be referred to in the table below for details:

[0061]

[0062] Furthermore, in Equation II, R is selected from O or N;

[0063] When R is selected from O, there is no substituent R3;

[0064] R5 is selected from C or N; R3, R4 and R6 may be the same or different, and each is independently selected from hydrogen, halogen, -CN, unsubstituted or optionally substituted C1-C10 alkyl, unsubstituted or optionally substituted aryl or heteroaryl.

[0065] The substituent is selected from one or more of halogen, alkyl, olefin, alkynyl, alkoxy, and cyano groups.

[0066] Furthermore, the additive A is selected from at least one of the following compounds: Formula I-1 to Formula I-8 and Formula II-1 to Formula II-4:

[0067]

[0068] Furthermore, additive B is selected from vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, 1,3-ethylene carbonate, etc. Propanesulfonate lactone, 1,3 At least one of propylene sulfonate lactone, vinyl sulfite, vinyl sulfate, propylene sulfate, methane disulfonate, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, lithium difluorophosphate, lithium bis(oxalate)borate, lithium difluorooxalate borate, and lithium difluorooxalate phosphate.

[0069] As mentioned above, the combined use of additive A and additive B can further improve the cycle life and electrochemical performance of the battery at low temperatures. This is because, when additive B and additive A jointly participate in interfacial film formation, they can stabilize the electrode-electrolyte interface and reduce interfacial parasitic reactions during cycling.

[0070] Furthermore, the amount of additive B added accounts for 0.1-5 wt.% of the total mass of the electrolyte.

[0071] Furthermore, the non-aqueous organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, propyl acetate, ethyl propionate, and propyl propionate.

[0072] Furthermore, the conductive lithium salt electrolyte is selected from one or more of lithium perchlorate, lithium hexafluorophosphate, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium tetrafluoroborate, lithium difluorobis(oxalate)phosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

[0073] Furthermore, the concentration of lithium salt in the non-aqueous electrolyte is 0.5-2 mol / L.

[0074] In addition, this application also provides a lithium-ion battery, including a positive electrode, a negative electrode, and a separator, as well as a non-aqueous electrolyte as described above.

[0075] The above-mentioned positive electrode is a positive electrode sheet containing a positive electrode active material. The positive electrode active material used is selected from lithium transition metal oxides, including LiMPO4 (M=Fe, Mn, Co) and Li1+xNiyCozM1-y-zO2 (-0.1≤x≤1, 0≤y, z≤1 and 0≤y+z≤1); where M can be selected from one or more of the elements Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Zn, Ga, Y, Zr, Nb, Mo, Sn, and Ba.

[0076] In addition, the positive electrode also contains an Al current collector, a PVDF binder, and acetylene black and / or carbon nanotube conductive agent.

[0077] The aforementioned negative electrode sheet includes a negative electrode active material. The negative electrode active material used is selected from one or more of graphite, Si, SiOx, lithium titanate, and lithium metal.

[0078] The aforementioned negative electrode sheet also includes Cu current collector, CMC thickener, SBR binder, and acetylene black and / or carbon nanotube conductive agent.

[0079] The membrane described above can be selected from polyethylene (PE), polypropylene (PP), and membranes formed by coating their surfaces with alumina ceramic or / and PVDF.

[0080] The present invention will be further illustrated below with specific embodiments. However, it should be understood that these embodiments are merely for the purpose of more detailed illustration and should not be construed as limiting the present invention in any way.

[0081] 1. Preparation method of non-aqueous electrolyte:

[0082] (1) Mix ethylene carbonate and ethyl methyl carbonate in a glove box filled with argon gas at a mass ratio of 3:7 until homogeneous;

[0083] (2) Slowly add 12.5 wt.% of lithium hexafluorophosphate to form a 1 mol / L lithium hexafluorophosphate electrolyte;

[0084] (3) Add functional additives (specific components and contents are shown in Table 1) and mix evenly to obtain electrolyte.

[0085] 2. Preparation methods of lithium-ion batteries:

[0086] (1) LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) active material, PVDF binder, acetylene black conductive agent, and carbon nanotube conductive agent were mixed in a weight ratio of 95:2.5:2.0:0.5, and N was added. Methylpyrrolidone (NMP) was stirred until homogeneous to form a positive electrode slurry;

[0087] (2) The above positive electrode slurry was coated onto an aluminum foil current collector and dried in a vacuum drying oven at 120 °C for 8 h. Then, it was rolled and slit to obtain the positive electrode sheet. Graphite and sodium carboxymethyl cellulose (CMC) were then added. Na), styrene-butadiene rubber (SBR), and acetylene black were mixed in a mass ratio of 96:0.5:2.5:1, and deionized water was added and stirred evenly to obtain the negative electrode slurry.

[0088] (3) The above negative electrode slurry is uniformly coated on the copper foil current collector and dried in a vacuum drying oven at 80 °C for 10 h. Then, the negative electrode sheet is obtained by rolling and slitting.

[0089] (4) Assemble the prepared positive and negative electrode sheets and PP separator into a bare cell without electrolyte injection, and place the bare cell in an outer aluminum-plastic film and inject the prepared electrolyte.

[0090] (5) After the lithium-ion battery is injected with liquid, it undergoes vacuum sealing, standing, formation, shaping, and capacity testing, and then undergoes corresponding electrochemical tests.

[0091] 3. Performance testing methods:

[0092] (1) Room temperature cycle stability test: The battery is placed in a constant temperature environment of 25℃ and cycled at 1C / 1C charge / discharge rate. The voltage range is 3.0-4.2 V. The charge / discharge cycle is 500 times. The capacity retention rate is the battery discharge capacity on the 500th cycle / the battery discharge capacity on the first cycle.

[0093] (2) Low-temperature performance test: After capacity grading, the battery was cycled 3 times at 1C rate at room temperature to obtain the discharge capacity of the battery at 1C rate at room temperature, and then the battery was charged to full capacity at 1C rate. The fully charged battery was placed at -20℃ for 4 hours and then discharged at 0.5C rate. The low-temperature discharge capacity retention rate = discharge capacity at low temperature / 1C discharge capacity at room temperature; After capacity grading, the battery was charged and discharged at -10℃ at 0.2C rate. The low-temperature cycle capacity retention rate = discharge capacity of the 50th cycle / discharge capacity of the first cycle.

[0094] Example:

[0095] Using the above-described electrolyte preparation method, and based on additives A and B listed in the table below, a non-aqueous electrolyte was prepared, and lithium-ion batteries were then prepared using the above-described lithium-ion battery preparation method.

[0096]

[0097] Using the above performance testing methods, a comparative test was conducted on the embodiments and comparative examples, and the results are shown in the table below:

[0098]

[0099] Conclusion: The data above shows that adding additive A to the electrolyte can significantly improve the battery's cycle stability at room temperature. Furthermore, this type of additive can also improve the battery's low-temperature discharge capacity retention and low-temperature cycle performance. Moreover, the combined use of additive A and additive B can further enhance the battery's cycle life and electrochemical performance at low temperatures.

[0100] The above describes preferred embodiments and corresponding examples of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, including but not limited to adjustments in proportions, processes, and dosages. These modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A non-aqueous electrolyte, characterized in that, The application relates to a non-aqueous electrolyte for lithium ion batteries, which comprises: a non-aqueous organic solvent, a conductive lithium salt electrolyte and a functional electrolyte additive; the functional electrolyte additive comprises an additive A and an additive B; the additive amount of the additive A is 0.1wt.%-5wt.% of the total mass of the non-aqueous electrolyte; the additive B is a film-forming additive; The additive A is selected from at least one of the following compounds of formulae 1-2 to 1-7, and formulae II-1, II-2 and IV-4: formula 1-2: ; formula 1-3: ; formula 1-4: ; formula 1-5: ; formula 1-6: ; formula 1-7: ; formula II-1 : ; formula II-2: ; formula II-4: ; The film-forming additive is selected from at least one of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1,3 propylene sulfite, 1 2. The nonaqueous electrolyte of claim 1, wherein the additive amount of the additive 1 is 0.1-5wt.% of the total mass of the electrolyte.

3. The nonaqueous electrolyte of claim 1, wherein the non-aqueous organic solvent is selected from one or more of the following: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, propyl acetate, ethyl propionate and propyl propionate.

4. The nonaqueous electrolyte of claim 1, wherein the conductive lithium salt electrolyte is selected from one or more of the following: lithium perchlorate, lithium hexafluorophosphate, lithium bisoxalate borate, lithium difluoro oxalate borate, lithium tetrafluoroborate, lithium difluorobisoxalate phosphate, lithium bisfluorosulfonimide and lithium bis-trifluoromethylsulfonimide.

5. The nonaqueous electrolyte according to claim 4, wherein the concentration of lithium salt in the non-aqueous electrolyte is 0.5mol / L-2mol / L.

6. A lithium-ion battery, characterized by the application further relates to a lithium ion battery, which comprises a positive electrode, a negative electrode and a separator, and the non-aqueous electrolyte as described in any one of claims 1-5.

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