Lithium ion battery electrolyte and lithium ion battery

Abstract

The invention relates to a lithium ion battery electrolyte and a lithium ion battery, the lithium ion battery electrolyte comprises a solvent, an electrolyte salt and an additive, and the additive comprises amido, acylamino and cyano groups. According to the electrolyte disclosed by the invention, the additive containing amido, acylamino and cyano groups is used, so that the high-temperature cycle performance and the high-temperature storage performance of the lithium ion battery can be obviously improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to a lithium ion battery electrolyte and a lithium ion battery. Background Art

[0002] Lithium-ion secondary batteries have the advantages of high operating voltage, light weight, no memory effect, low self-discharge rate, long cycle life, and high energy density. They are currently widely used in mobile phones, computers, electric vehicles, etc. In recent years, out of consideration for environmental protection, electric vehicles have been rapidly developed under the promotion of governments and automobile manufacturers, and lithium-ion secondary batteries have become the ideal power source for the new generation of electric vehicles with their excellent performance.

[0003] At present, based on the fast charging demand of lithium-ion batteries, researchers have developed niobium-based negative electrode materials, especially niobium titanium oxide materials. However, the voltage platform of niobium titanium oxide negative electrode materials is greater than 1V. When paired with conventional lithium iron phosphate or ternary materials, the overall voltage platform of lithium-ion batteries drops significantly, and the energy density is not competitive. Therefore, it is necessary to develop high-voltage positive electrode materials to match them.

[0004] The most researched high-voltage material is nickel-manganese cathode material, which is superior to nickel-cobalt-manganese ternary material in cost and thermal stability. However, the acidic substances produced in lithium-ion batteries will corrode nickel-manganese cathode materials, not only leading to irreversible loss of cathode materials, but also exposing more cathode surface to oxidize electrolyte, and causing manganese ions dissolved from the cathode to migrate to the electrolyte and the cathode to participate in more side reactions, especially significantly deteriorating the high-temperature cycle and storage performance of lithium-ion batteries. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a lithium ion battery electrolyte and a lithium ion battery. The technical problem to be solved by the present invention is achieved by the following technical solutions: An embodiment of the present invention provides a lithium ion battery electrolyte, comprising: a solvent, an electrolyte salt and an additive, wherein the additive comprises an amine group, an amide group and a cyano group, and the structure of the additive is shown in Formula I:

[0006] Formula I Among them, R1 is an alkyl group having 1 to 4 carbon atoms, and R2 is an alkyl group having 1 to 4 carbon atoms or an alkyl group having 1 to 4 carbon atoms substituted with phenyl or an alkenyl group having 2 to 4 carbon atoms substituted with phenyl or a phenyl group or a phenyl group substituted with fluorine or a phenyl group substituted with nitro.

[0007] In one embodiment of the present invention, the additive includes at least one of 3-(4-methylpiperazine-1-yl)-3-oxopropionitrile, 3-(4-ethylpiperazine-1-yl)-3-oxopropionitrile, 3-oxo-3-(4-phenyl-1-piperazine)propionitrile, 3-[4-(2-fluorophenyl)piperazine-1-yl]-3-oxopropionitrile, 3-oxo-3-[4-(2-phenylethyl)piperazine-1-yl]propionitrile, 3-[4-(4-nitrophenyl)piperazine-1-yl]-3-oxopropionitrile and 3-oxo-3-[4-(3-phenylprop-2-enyl)-1-piperazine]propionitrile.

[0008] In one embodiment of the present invention, the content of the additive in the electrolyte is 0.3-2 wt %.

[0009] In one embodiment of the present invention, the solvent includes at least one of carbonates, fluorocarbonates, fluoroethers, nitriles, and sulfones.

[0010] In one embodiment of the present invention, the electrolyte salt includes at least one of LiPF6, LiClO4, LiFSI, LiTFSI, and LiBF4.

[0011] Another embodiment of the present invention provides a lithium-ion battery, comprising: a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the electrolyte is the lithium-ion battery electrolyte described in any of the above embodiments, wherein: The positive electrode sheet and the negative electrode sheet are respectively arranged on both sides of the diaphragm, and the electrolyte infiltrates the positive electrode sheet, the negative electrode sheet and the diaphragm.

[0012] In one embodiment of the present invention, the positive electrode plate includes a positive electrode material, and the positive electrode material includes lithium nickel manganese oxide having a spinel structure.

[0013] In one embodiment of the present invention, the lithium nickel manganese oxide is also doped with one or more elements selected from Al, Mg, Fe, Co, Y, Sc, Ru, Cu, Mo, Ce, W, Ta, Zr, Ca, P, S, F, B, Si, and Sr.

[0014] In one embodiment of the present invention, the negative electrode plate comprises a negative electrode material, and the negative electrode material comprises a niobium titanium oxide material.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention adds an additive containing an amine group, an amide group and a cyano group to the electrolyte of a lithium ion battery. The amine group and the amide group can not only react with water and acidic substances in the lithium ion battery, remove the water and acidic substances in the lithium ion battery, prevent the corrosion of the positive electrode material by water and acidic substances, and inhibit the decomposition of the positive electrode material, but also form a dense interface film on the positive electrode through a ring-opening reaction to inhibit the oxidation of the electrolyte at the positive electrode; the cyano group can combine with the transition metal ions on the positive electrode material to stabilize the positive electrode material, complex the metal ions dissolved from the positive electrode, and inhibit the metal ions from migrating to the electrolyte or the negative electrode to participate in side reactions; therefore, the electrolyte of the present invention can significantly improve the high-temperature cycle performance and high-temperature storage performance of the lithium ion battery by using the additive containing an amine group, an amide group and a cyano group. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a curve chart of the 45°C cycle capacity retention rate of Example 2 and Comparative Example 1 provided by the present invention. DETAILED DESCRIPTION

[0017] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0018] A specific embodiment of the present invention provides a lithium ion battery electrolyte. The lithium ion battery electrolyte includes: a solvent, an electrolyte salt and an additive. The additive includes an amine group, an amide group and a cyano group, and the structure of the additive is shown in Formula I:

[0019] Formula I Among them, R1 is an alkyl group having 1 to 4 carbon atoms, and R2 is an alkyl group having 1 to 4 carbon atoms or an alkyl group having 1 to 4 carbon atoms substituted with phenyl or an alkenyl group having 2 to 4 carbon atoms substituted with phenyl or a phenyl group or a phenyl group substituted with fluorine or a phenyl group substituted with nitro.

[0020] Combined with the structural formula of the additives, it can be seen that the amine group in the above additives is -NCH2CH2, the amide group is -CO-NCH2CH2, and the cyano group is -CN.

[0021] Preferably, the additive includes at least one of 3-(4-methylpiperazin-1-yl)-3-oxopropionitrile, 3-(4-ethylpiperazin-1-yl)-3-oxopropionitrile, 3-oxo-3-(4-phenyl-1-piperazine)propionitrile, 3-[4-(2-fluorophenyl)piperazin-1-yl]-3-oxopropionitrile, 3-oxo-3-[4-(2-phenylethyl)piperazin-1-yl]propionitrile, 3-[4-(4-nitrophenyl)piperazin-1-yl]-3-oxopropionitrile and 3-oxo-3-[4-(3-phenylprop-2-enyl)-1-piperazine]propionitrile.

[0022] Preferably, the content of the additive in the electrolyte is 0.3-2wt%, such as 0.3wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, etc., but is not limited to the listed values.

[0023] Practically, the solvent comprises at least one of carbonate, fluorocarbonate, fluoroether, nitrile, and sulfone. Exemplarily, the solvent comprises at least one of ethylene carbonate, propylene carbonate, fluorocarbonate, bisfluorocarbonate, trifluoromethylethylene carbonate, pentafluoroethylethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methylpropyl carbonate, methyl trifluoromethyl carbonate, methyl trifluoroethyl carbonate, ethyl trifluoroethyl carbonate, di(2,2,2-trifluoroethyl) carbonate, bis(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether or 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, acetonitrile, propionitrile, isobutyronitrile, dimethyl sulfone, methyl ethyl sulfone, and sulfolane.

[0024] Preferably, the electrolyte salt includes at least one of LiPF6, LiClO4, LiFSI, LiTFSI, and LiBF4.

[0025] Preferably, the content of the electrolyte salt in the electrolyte is 10-25wt%, such as 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, 25wt%, etc., but is not limited to the listed values.

[0026] If the electrolyte salt content is too low, the battery rate cycle performance will deteriorate; if the electrolyte lithium salt content is too high, the electrolyte viscosity will increase significantly, the conductivity will decrease, and it will be unfavorable for the transmission of lithium ions. The electrolyte salt content of this embodiment is 10-25wt%, which can not only achieve good battery rate cycle performance, but also facilitate the transmission of lithium ions.

[0027] The specific embodiment of the present invention also provides a lithium-ion battery. The lithium-ion battery includes: a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. The positive electrode sheet and the negative electrode sheet are respectively arranged on both sides of the separator, and the electrolyte infiltrates the positive electrode sheet, the negative electrode sheet and the separator. The electrolyte adopts the lithium-ion battery electrolyte described in the above embodiment.

[0028] In practice, the positive electrode plate includes a positive electrode material, and the positive electrode material includes lithium nickel manganese oxide having a spinel structure. Further, the positive electrode material lithium nickel manganese oxide may be doped with one or more elements selected from Mg, Fe, Co, Y, Sc, Ru, Cu, Mo, Ce, W, Zr, Ca, P, S, F, B, Si, and Sr.

[0029] Preferably, the content of the doping element in lithium nickel manganese oxide is 0-0.2wt%, such as 0wt%, 0.02wt%, 0.05wt%, 0.1wt%, 0.15wt%, 0.2wt%, etc., but is not limited to the listed values.

[0030] Practically, the positive electrode plate includes a conductive agent, a binder and a current collector in addition to the positive electrode material.

[0031] In practice, the negative electrode plate includes a negative electrode material, and the negative electrode material includes a niobium-titanium oxide material.

[0032] Practically, the negative electrode plate includes a conductive agent, a binder and a current collector in addition to the negative electrode material.

[0033] Practically, the conductive agent in the positive electrode sheet and the conductive agent in the negative electrode sheet can be selected from at least one of conductive carbon black, carbon nanotubes, and graphene, but is not limited thereto.

[0034] Practically, the binder in the positive electrode sheet and the binder in the negative electrode sheet can be selected from at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polystyrene-butadiene rubber, copolymers containing polystyrene-butadiene rubber, polyacrylic acid, copolymers containing acrylic acid, polyacrylates, copolymers containing acrylates, polyacrylonitrile, copolymers containing acrylonitrile, nylon, etc., but is not limited thereto.

[0035] Practically, the current collector in the positive electrode sheet and the current collector in the negative electrode sheet can be selected from at least one of aluminum, titanium, copper, nickel, stainless steel, carbon cloth, and carbon paper, but is not limited thereto.

[0036] In practice, the diaphragm is used to isolate electrons and allow metal ions (such as lithium ions) to pass through. The diaphragm can be a traditional electrochemical battery diaphragm, including any one of an organic polymer diaphragm or an inorganic diaphragm. Exemplary, the diaphragm can be selected from but not limited to polyethylene porous film, polypropylene porous film, polyethylene-polypropylene double-layer porous film, polypropylene-polyethylene-polypropylene three-layer porous film, glass fiber porous film, non-woven porous film, electrospinning porous film, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) porous film, polyacrylonitrile porous film. Wherein, the non-woven porous film can be selected from polyimide nanofiber nonwoven fabric, polyethylene terephthalate (PET) nanofiber nonwoven fabric, cellulose nanofiber nonwoven fabric, aramid nanofiber nonwoven fabric, nylon nanofiber nonwoven fabric or polyvinylidene fluoride (PVDF) nanofiber nonwoven fabric. The electrospun porous membrane may be selected from a polyimide electrospun membrane, a polyethylene terephthalate electrospun membrane or a polyvinylidene fluoride electrospun membrane.

[0037] The present invention adds an additive containing an amine group, an amide group and a cyano group to the electrolyte of a lithium ion battery. The amine group and the amide group can not only react with water and acidic substances in the lithium ion battery, remove water and acidic substances in the lithium ion battery, prevent water and acidic substances from corroding the positive electrode material, and inhibit the decomposition of the positive electrode material, but also form a dense interface film on the positive electrode through a ring-opening reaction to inhibit the oxidation of the electrolyte at the positive electrode; the cyano group can combine with the transition metal ions on the positive electrode material to stabilize the positive electrode material, complex the metal ions dissolved from the positive electrode, and inhibit the metal ions from migrating to the electrolyte or the negative electrode to participate in side reactions; therefore, the electrolyte of the present invention can reduce side reactions in the battery, reduce the consumption of lithium ions, thereby reducing the damage to the positive electrode structure, and further significantly improve the high-temperature cycle performance and high-temperature storage performance of the lithium ion battery.

[0038] For the convenience of understanding the present invention, the present invention lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0039] In the embodiments and comparative examples of the present invention, the materials used to prepare the electrolyte are as follows: Solvents: propylene carbonate (PC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC); Electrolyte salt: LiPF6; Additives: 3-(4-methylpiperazin-1-yl)-3-oxopropionitrile (A1), 3-oxo-3-(4-phenyl-1-piperazine)propionitrile (A2), 3-[4-(2-fluorophenyl)piperazin-1-yl]-3-oxopropionitrile (A3).

[0040] The electrolytes in Examples 1 to 6 of the present invention were prepared according to the following preparation method: First, in a glove box, slowly add electrolyte salt to the mixed solution of solvent, add additives after the temperature in the container drops to room temperature, mix well, and prepare an electrolyte. The content and type of each additive in the electrolyte are shown in Table 1, where the content of the additive is the weight percentage based on the total weight of the electrolyte. The content of electrolyte salt LiPF6 in the electrolyte is 14wt%, and the mass ratio of each solvent EC:PC:EMC:DEC is 2:2:3:3. In addition, 3-(4-methylpiperazine-1-yl)-3-oxopropionitrile is represented as "A1" in Table 1, 3-oxo-3-(4-phenyl-1-piperazine)propionitrile is represented as "A2" in Table 1, and 3-[4-(2-fluorophenyl)piperazine-1-yl]-3-oxopropionitrile is represented as "A3" in Table 1.

[0041] Comparative Example 1 An electrolyte was prepared according to the following preparation method: First, in a glove box, slowly add electrolyte salt to the mixed solution of solvents, mix well, and prepare an electrolyte solution. The content of electrolyte salt LiPF6 in the electrolyte solution is 14wt%, and the mass ratio of each solvent EC:PC:EMC:DEC is 2:2:3:3.

[0042] Table 1: Composition of additives in the electrolytes of Examples 1 to 6 and Comparative Example 1

[0043] Preparation of lithium-ion batteries: The electrolytes obtained in the examples and comparative examples were respectively applied to lithium ion batteries for performance testing, wherein the lithium ion batteries were prepared by the following steps: (1) Preparation of positive electrode sheet The positive electrode material is lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4), binder (polyvinylidene fluoride), and conductive agent (conductive carbon black) are mixed in a mass ratio of 95:2:3, and N-methylpyrrolidone (NMP) is added and stirred to form a positive electrode slurry. Then the positive electrode slurry is evenly coated on the aluminum foil, and the coated aluminum foil is dried at room temperature and transferred to a 130°C oven for drying, followed by cold pressing, trimming, cutting, and striping, and then welding the pole ears to form a positive electrode sheet.

[0044] (2) Negative electrode sheet preparation The negative electrode material niobium titanium oxide (TiNb2O7), binder (polyvinylidene fluoride), and conductive agent (conductive carbon black) are dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 95:2:3 and mixed evenly to form a negative electrode slurry. The negative electrode slurry is then evenly coated on the current collector copper foil, then dried at 130°C, and then cold pressed, trimmed, cut, and striped, and the tabs are welded to form a negative electrode sheet.

[0045] (3) Preparation of lithium-ion button cells After the positive electrode sheet, negative electrode sheet and electrolyte are prepared, they are placed in a button battery shell to assemble a lithium-ion button battery.

[0046] The lithium-ion battery obtained above was subjected to lithium-ion battery performance tests, including the following performance tests: (1) Lithium-ion battery 45°C cycle test First, the lithium-ion battery is left to stand in an environment of 45°C, then charged to 3.5V at a constant current of 1C, further charged to a current of 0.05C at a constant voltage of 3.5V, left to stand again, and then discharged to 1V at a constant current of 2C. This is a charge and discharge cycle process, and the discharge capacity obtained is the discharge capacity Ca of the lithium-ion battery. After that, 25 charge and discharge cycles are performed, and the discharge capacity of the 25th cycle is recorded as Cb.

[0047] The capacity retention rate (%) of the lithium-ion battery after 25 cycles = Cb / Ca.

[0048] (2) Lithium-ion battery storage test at 60°C First, the lithium-ion battery was placed in an environment of 25°C for 30 minutes; it was charged to 3.5V at a constant current of 1C, and further charged to a current of 0.05C at a constant voltage of 3.5V; the lithium-ion battery was then stored in an oven at 60°C, taken out after 60 days of storage, and the remaining power (State Of Charge, SOC) of the battery was adjusted to a full discharge state; the battery was then disassembled, the negative electrode plate was taken out, and the content of metallic manganese in the negative electrode plate was tested by an inductively coupled plasma (ICP) method.

[0049] The performance test data of the lithium ion batteries of the embodiments of the present invention and the comparative examples are shown in Table 2.

[0050] Table 2: Lithium-ion battery performance test results

[0051] See also Figure 1 , Figure 1 The curve diagram of the 45°C cycle capacity retention rate of Example 2 and Comparative Example 1 provided by the present invention, combined with Figure 1, It can be concluded from the test results of Examples 1 to 4 in Table 2 and the test results of Comparative Example 1 that by adding additive A1 to the electrolyte, the 45°C cycle capacity retention rate and the 60°C storage negative electrode metal manganese content of the lithium-ion battery are significantly improved; this is because additive A1 can bind water and acid, and inhibit the decomposition of the positive electrode material catalyzed by water and acid, protect the positive and negative electrode interfaces, and inhibit the decomposition of the electrolyte to produce gas and the consumption of active lithium ions. In addition, additive A1 can also complex the metal manganese ions dissolved from the positive electrode and inhibit its deposition at the negative electrode. However, when the content of additive A1 is too high, the interface film formed on the surface of the positive and negative electrodes will be too thick, thereby hindering the transmission of lithium ions and affecting the performance of the cycle performance.

[0052] From the test results of Example 2 and Examples 5-6 in Table 2 above, it can be seen that different types of additives A1, A2, and A3 improve the performance of lithium batteries to varying degrees.

[0053] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A lithium ion battery electrolyte, characterized in that: include: Solvent, electrolyte salt and additive, the additive includes amine group, amide group and cyano group, and the structure of the additive is shown in Formula I: Formula I Among them, R1 is an alkyl group having 1 to 4 carbon atoms, and R2 is an alkyl group having 1 to 4 carbon atoms or an alkyl group having 1 to 4 carbon atoms substituted with phenyl or an alkenyl group having 2 to 4 carbon atoms substituted with phenyl or a phenyl group or a phenyl group substituted with fluorine or a phenyl group substituted with nitro.

2. The lithium ion battery electrolyte according to claim 1, characterized in that: The additive includes at least one of 3-(4-methylpiperazine-1-yl)-3-oxopropionitrile, 3-(4-ethylpiperazine-1-yl)-3-oxopropionitrile, 3-oxo-3-(4-phenyl-1-piperazine)propionitrile, 3-[4-(2-fluorophenyl)piperazine-1-yl]-3-oxopropionitrile, 3-oxo-3-[4-(2-phenylethyl)piperazine-1-yl]propionitrile, 3-[4-(4-nitrophenyl)piperazine-1-yl]-3-oxopropionitrile and 3-oxo-3-[4-(3-phenylprop-2-enyl)-1-piperazine]propionitrile.

3. The lithium ion battery electrolyte according to claim 1, characterized in that The content of the additive in the electrolyte is 0.3-2wt%.

4. The lithium ion battery electrolyte according to claim 1, characterized in that: The solvent includes at least one of carbonates, fluorocarbons, fluoroethers, nitriles and sulfones.

5. The lithium ion battery electrolyte according to claim 1, characterized in that: The electrolyte salt includes at least one of LiPF6, LiClO4, LiFSI, LiTFSI, and LiBF4.

6. A lithium ion battery, characterized in that: include: A positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the electrolyte is a lithium-ion battery electrolyte as claimed in any one of claims 1 to 5, wherein: The positive electrode sheet and the negative electrode sheet are respectively arranged on both sides of the diaphragm, and the electrolyte infiltrates the positive electrode sheet, the negative electrode sheet and the diaphragm.

7. The lithium-ion battery according to claim 6, characterized in that: The positive electrode plate includes a positive electrode material, and the positive electrode material includes lithium nickel manganese oxide with a spinel structure.

8. The lithium-ion battery according to claim 7, characterized in that: The lithium nickel manganese oxide is also doped with one or more elements selected from Al, Mg, Fe, Co, Y, Sc, Ru, Cu, Mo, Ce, W, Ta, Zr, Ca, P, S, F, B, Si, and Sr.

9. The lithium-ion battery according to claim 6, characterized in that: The negative electrode plate includes a negative electrode material, and the negative electrode material includes a niobium titanium oxide material.

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