A lithium-ion battery electrolyte and a lithium-ion battery

Abstract

The present invention relates to a lithium-ion battery electrolyte and a lithium-ion battery. The lithium-ion battery electrolyte includes: a solvent, an electrolyte salt, and an additive, and the additive includes amine groups, amide groups, and cyano groups. By using the additive containing amine groups, amide groups, and cyano groups, the electrolyte of the present invention can significantly improve the high-temperature cycle performance and high-temperature storage performance of the lithium-ion battery.

Description

Technical Field

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

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

[0003] Currently, based on the fast charging requirements of lithium-ion batteries, researchers have developed niobium-based anode materials, especially niobium titanium oxide materials. However, the voltage platform of niobium titanium oxide anode 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 cathode materials to match them.

[0004] Currently, the high-voltage material that has been studied more is the nickel manganese cathode material, whose cost and thermal stability are both superior to those of nickel cobalt manganese ternary materials. However, the acidic substances generated in lithium-ion batteries will corrode the nickel manganese cathode material, which not only causes irreversible loss of the cathode material, but also exposes more of the cathode surface to oxidize the electrolyte, and will also cause the manganese ions dissolved from the cathode to migrate to the electrolyte and the anode 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 problems to be solved by the present invention are realized through the following technical solutions:

[0006] An embodiment of the present invention provides a lithium-ion battery electrolyte, including: 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:

[0007]

[0008] Formula I

[0009] Wherein, R 1 is an alkyl group with 1 to 4 carbon atoms, and R 2 is an alkyl group with 1 to 4 carbon atoms or an alkyl group with 1 to 4 carbon atoms substituted by a phenyl group or an alkenyl group with 2 to 4 carbon atoms substituted by a phenyl group or a phenyl group substituted by a fluorine element or a phenyl group substituted by a nitro group.

[0010] In one embodiment of the present invention, the additive includes at least one of 3-(4-methylpiperazin-1-yl)-3-oxopropanenitrile, 3-(4-ethylpiperazin-1-yl)-3-oxopropanenitrile, 3-oxo-3-(4-phenyl-1-piperazinyl)propanenitrile, 3-[4-(2-fluorophenyl)piperazin-1-yl]-3-oxopropanenitrile, 3-oxo-3-[4-(2-phenylethyl)piperazin-1-yl]propanenitrile, 3-[4-(4-nitrophenyl)piperazin-1-yl]-3-oxopropanenitrile, 3-oxo-3-[4-(3-phenylprop-2-enyl)-1-piperazinyl]propanenitrile.

[0011] In one embodiment of the present invention, the content of the additive in the electrolyte is 0.3-2 wt%.

[0012] In one embodiment of the present invention, the solvent includes at least one of carbonates, fluorinated carbonates, fluoroethers, nitriles, sulfones.

[0013] In one embodiment of the present invention, the electrolyte salt includes LiPF 6 , LiClO 4 , LiFSI, LiTFSI, LiBF 4 and at least one of them.

[0014] Another embodiment of the present invention provides a lithium-ion battery, including: a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. The electrolyte uses the lithium-ion battery electrolyte described in any one of the above embodiments. Among them,

[0015] 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.

[0016] In one embodiment of the present invention, the positive electrode sheet includes a positive electrode material, and the positive electrode material includes lithium nickel manganate with a spinel structure.

[0017] In one embodiment of the present invention, the lithium nickel manganate is further 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, Sr.

[0018] In one embodiment of the present invention, the negative electrode sheet includes a negative electrode material, and the negative electrode material includes a niobium titanium oxide material.

[0019] Compared with the prior art, the beneficial effects of the present invention:

[0020] In the present invention, an additive containing amino, amide and cyano groups is added to the electrolyte of a lithium-ion battery. The amino and amide groups can not only react with water and acidic substances in the lithium-ion battery to remove water and acidic substances in the lithium-ion battery, prevent the corrosion of the cathode material by water and acidic substances, and inhibit the decomposition of the cathode material, but also form a dense interfacial film on the cathode through a ring-opening reaction to inhibit the oxidation of the electrolyte at the cathode; the cyano group can combine with transition metal ions on the cathode material to stabilize the cathode material, complex the metal ions dissolved out from the cathode, and inhibit the migration of metal ions to the electrolyte or the anode 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 an additive containing amino, amide and cyano groups. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a graph showing the cycle capacity retention rate at 45 °C of Example 2 and Comparative Example 1 provided by the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] The following further describes the present invention in detail with specific examples, but the embodiments of the present invention are not limited thereto.

[0023] The detailed 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. Among them, the additive includes amino, amide and cyano groups, and the structure of the additive is shown in Formula I:

[0024]

[0025] Formula I

[0026] Wherein, R 1 is an alkyl group with 1 to 4 carbon atoms, and R 2 is an alkyl group with 1 to 4 carbon atoms or an alkyl group with 1 to 4 carbon atoms substituted by a phenyl group or an alkenyl group with 2 to 4 carbon atoms substituted by a phenyl group or a phenyl group substituted by a fluorine element or a phenyl group substituted by a nitro group.

[0027] Combined with the structural formula of the additive, it can be seen that the amino group in the above additive is -NCH 2 CH 2 , the amide group is -CO-NCH 2 CH 2 , and the cyano group is -CN.

[0028] Desirably, the additive includes at least one of 3-(4-methylpiperazin-1-yl)-3-oxopropanenitrile, 3-(4-ethylpiperazin-1-yl)-3-oxopropanenitrile, 3-oxo-3-(4-phenyl-1-piperazin)propanenitrile, 3-[4-(2-fluorophenyl)piperazin-1-yl]-3-oxopropanenitrile, 3-oxo-3-[4-(2-phenylethyl)piperazin-1-yl]propanenitrile, 3-[4-(4-nitrophenyl)piperazin-1-yl]-3-oxopropanenitrile, 3-oxo-3-[4-(3-phenylprop-2-enyl)-1-piperazin]propanenitrile.

[0029] Preferably, the content of the additive in the electrolyte is 0.3-2 wt%, such as 0.3 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, etc., but is not limited to the listed values.

[0030] Desirably, the solvent includes at least one of carbonates, fluorinated carbonates, fluoroethers, nitriles, sulfones. Exemplarily, the solvent includes at least one of ethylene carbonate, propylene carbonate, fluorinated ethylene carbonate, difluorinated ethylene carbonate, trifluoromethyl carbonate, pentafluoroethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl trifluoromethyl carbonate, methyl trifluoroethyl carbonate, ethyl trifluoroethyl carbonate, bis(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, sulfolane.

[0031] Desirably, the electrolyte salt includes LiPF 6 、LiClO 4 、LiFSI, LiTFSI, LiBF 4 and at least one of them.

[0032] Preferably, the content of the electrolyte salt in the electrolyte is 10-25 wt%, such as 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, 25 wt%, etc., but is not limited to the listed values.

[0033] If the content of the electrolyte salt is too low, the battery rate cycling performance will deteriorate; if the content of the electrolyte lithium salt is too high, the viscosity of the electrolyte will increase significantly and the conductivity will decrease, which is not conducive to the transport of lithium ions. The content of the electrolyte salt in this embodiment is 10-25 wt%, which can not only achieve good battery rate cycling performance, but also is conducive to the transport of lithium ions.

[0034] The specific implementation manner of the present invention also provides a lithium-ion battery. The lithium-ion battery includes: a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. Among them, the positive electrode plate and the negative electrode plate are respectively arranged on both sides of the separator, and the electrolyte infiltrates the positive electrode plate, the negative electrode plate, and the separator. The electrolyte adopts the lithium-ion battery electrolyte described in the above implementation manner.

[0035] Implementably, the positive electrode plate includes a positive electrode material, and the positive electrode material includes lithium nickel manganese oxide with a spinel structure. Further, the lithium nickel manganese oxide of the positive electrode material can also 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, Sr.

[0036] Preferably, the content of the doped element in the lithium nickel manganese oxide is 0 to 0.2 wt%, such as 0 wt%, 0.02 wt%, 0.05 wt%, 0.1 wt%, 0.15 wt%, 0.2 wt%, etc., but not limited to the listed values.

[0037] Implementably, in addition to the positive electrode material, the positive electrode plate further includes a conductive agent, a binder, and a current collector.

[0038] Implementably, the negative electrode plate contains a negative electrode material, and the negative electrode material includes niobium titanium oxide material.

[0039] Implementably, in addition to the negative electrode material, the negative electrode plate further includes a conductive agent, a binder, and a current collector.

[0040] Implementably, the conductive agent in the positive electrode plate and the conductive agent in the negative electrode plate can both be selected from at least one of conductive carbon black, carbon nanotubes, and graphene, but not limited thereto.

[0041] Implementably, the binder in the positive electrode plate and the binder in the negative electrode plate can both be selected from at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polystyrene-butadiene rubber, a copolymer containing polystyrene-butadiene rubber, polyacrylic acid, a copolymer containing acrylic acid, polyacrylate, a copolymer containing polyacrylate, polyacrylonitrile, a copolymer containing acrylonitrile, nylon, etc., but not limited thereto.

[0042] Implementably, the current collector in the positive electrode plate and the current collector in the negative electrode plate can both be selected from at least one of aluminum, titanium, copper, nickel, stainless steel, carbon cloth, and carbon paper, but not limited thereto.

[0043] Operably, the separator is used to isolate electrons and allow metal ions (such as lithium ions) to pass through. The separator can be a conventional electrochemical cell separator, including either an organic polymer separator or an inorganic separator. Exemplarily, the separator can be selected from, but not limited to, any one of a polyethylene porous membrane, a polypropylene porous membrane, a polyethylene - polypropylene bilayer porous membrane, a polypropylene - polyethylene - polypropylene trilayer porous membrane, a glass fiber porous membrane, a non - woven fabric porous membrane, an electrospun porous membrane, a polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - HFP) porous membrane, and a polyacrylonitrile porous membrane. Among them, the non - woven fabric porous membrane can be selected from a polyimide nanofiber non - woven fabric, a polyethylene terephthalate (PET) nanofiber non - woven fabric, a cellulose nanofiber non - woven fabric, an aramid nanofiber non - woven fabric, a nylon nanofiber non - woven fabric, or a polyvinylidene fluoride (PVDF) nanofiber non - woven fabric. The electrospun porous membrane can be selected from a polyimide electrospun membrane, a polyethylene terephthalate electrospun membrane, or a polyvinylidene fluoride electrospun membrane.

[0044] In the present invention, an additive containing amino, amide, and cyano groups is added to the electrolyte of a lithium - ion battery. The amino and amide groups can not only react with water and acidic substances in the lithium - ion battery to remove water and acidic substances in the lithium - ion battery, prevent the corrosion of the cathode material by water and acidic substances, and inhibit the decomposition of the cathode material, but also form a dense interfacial film on the cathode through a ring - opening reaction to inhibit the oxidation of the electrolyte at the cathode; the cyano group can combine with transition metal ions on the cathode material to stabilize the cathode material, complex the metal ions dissolved out from the cathode, and inhibit the migration of metal ions to the electrolyte or the anode to participate in side reactions; therefore, by using the additive containing amino, amide, and cyano groups, 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 cathode structure, and further significantly improving the high - temperature cycle performance and high - temperature storage performance of the lithium - ion battery.

[0045] To facilitate the understanding of the present invention, the following examples are listed. Those skilled in the art should understand that the examples are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0046] In the examples and comparative examples of the present invention, the materials for preparing the electrolyte are as follows:

[0047] Solvents: propylene carbonate (PC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC);

[0048] Electrolyte salt: LiPF 6 ;

[0049] Additives: 3-(4-methylpiperazin-1-yl)-3-oxopropanenitrile (A1), 3-oxo-3-(4-phenylpiperazin-1-yl)propanenitrile (A2), 3-[4-(2-fluorophenyl)piperazin-1-yl]-3-oxopropanenitrile (A3).

[0050] The electrolytes in Examples 1 to 6 of the present invention were all prepared according to the following preparation method:

[0051] First, in a glove box, an electrolyte salt was slowly added to a mixed solution of solvents. After the temperature in the container dropped to room temperature, an additive was added. After mixing evenly, an electrolyte was prepared. 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 electrolyte salt LiPF 6 has a content of 14 wt% in the electrolyte, and the mass ratio of each solvent EC:PC:EMC:DEC is 2:2:3:3. In addition, 3-(4-methylpiperazin-1-yl)-3-oxopropanenitrile is denoted as "A1" in Table 1, 3-oxo-3-(4-phenylpiperazin-1-yl)propanenitrile is denoted as "A2" in Table 1, and 3-[4-(2-fluorophenyl)piperazin-1-yl]-3-oxopropanenitrile is denoted as "A3" in Table 1.

[0052] The electrolyte in Comparative Example 1 was prepared according to the following preparation method:

[0053] First, in a glove box, an electrolyte salt was slowly added to a mixed solution of solvents. After mixing evenly, an electrolyte was prepared. Among them, the electrolyte salt LiPF 6 has a content of 14 wt% in the electrolyte, and the mass ratio of each solvent EC:PC:EMC:DEC is 2:2:3:3.

[0054] Table 1: Composition of each additive in the electrolytes of Examples 1 to 6 and Comparative Example 1

[0055]

[0056] Preparation of lithium-ion battery:

[0057] The electrolytes obtained in the examples and comparative examples were respectively applied to lithium-ion batteries for performance testing. Among them, the lithium-ion batteries were prepared by the following steps:

[0058] (1) Preparation of the positive electrode sheet

[0059] The positive electrode material lithium nickel manganate (LiNi 0.5 Mn 1.5 O 4) The binder (polyvinylidene fluoride), conductive agent (conductive carbon black) are mixed according to a mass ratio of 95:2:3, and N-methylpyrrolidone (NMP) is added and stirred to make the positive electrode paste. Then the positive electrode paste is evenly coated on the aluminum foil, and the coated aluminum foil is air-dried at room temperature and then transferred to an oven at 130 °C for drying. Subsequently, after cold pressing, trimming, slicing, and slitting, the tab is welded to make the positive electrode plate.

[0060] (2) Preparation of negative electrode plate

[0061] The negative electrode material niobium titanium oxide (TiNb 2 O 7 )), binder (polyvinylidene fluoride), and conductive agent (conductive carbon black) are dissolved in N-methylpyrrolidone (NMP) and mixed evenly according to a mass ratio of 95:2:3 to make the negative electrode paste. Then the negative electrode paste is evenly coated on the current collector copper foil, and then dried at 130 °C, and then cold pressed, trimmed, sliced, and slitted, and the tab is welded to make the negative electrode plate.

[0062] (3) Preparation of lithium-ion coin cell

[0063] After preparing the above positive electrode plate, negative electrode plate and electrolyte, they are assembled into a lithium-ion coin cell by loading them into a coin cell case.

[0064] The obtained lithium-ion battery is subjected to lithium-ion battery performance tests, including the following performance tests:

[0065] (1) 45 °C cycle test of lithium-ion battery

[0066] First, after the lithium-ion battery is left standing in an environment of 45 °C, it is charged at a constant current of 1C to 3.5V, further charged at a constant voltage of 3.5V until the current is 0.05C, left standing again, and then discharged at a constant current of 2C to 1V. This is a charge-discharge cycle process, and the obtained discharge capacity is the discharge capacity Ca of the lithium-ion battery. Then, 25 charge-discharge cycle processes are carried out, and the discharge capacity of the 25th cycle is recorded as Cb.

[0067] The capacity retention rate (%) of the lithium-ion battery after 25 cycles = Cb / Ca.

[0068] (2) 60 °C storage test of lithium-ion battery

[0069] First, the lithium-ion battery is left standing in an environment of 25 °C for 30 minutes; it is charged at a constant current of 1C to 3.5V, and further charged at a constant voltage of 3.5V until the current is 0.05C; then the lithium-ion battery is stored in an oven at 60 °C, taken out after 60 days of storage, and the remaining state of charge (SOC) of the battery is adjusted to a fully discharged state; then the battery is disassembled, the negative electrode sheet is taken out, and the inductively coupled plasma (ICP) method is used to test the content of metallic manganese in the negative electrode sheet.

[0070] The performance test data of the lithium-ion batteries in the embodiments and comparative examples of the present invention are shown in Table 2.

[0071] Table 2: Performance test results of lithium-ion batteries

[0072]

[0073] Please refer to Figure 1 , Figure 1 is the curve graph of the 45 °C cycle capacity retention rate of Example 2 and Comparative Example 1 provided by the present invention. Combining Figure 1 , the test results of Examples 1 to 4 and the test results of Comparative Example 1 in the above Table 2, it can be concluded that by adding additive A1 to the electrolyte, the 45 °C cycle capacity retention rate and the content of metallic manganese in the negative electrode during storage at 60 °C of the lithium-ion battery are significantly improved; this is because additive A1 can combine with water and acid, and inhibit the decomposition of the cathode material catalyzed by water and acid, protect the positive and negative electrode interfaces and inhibit the decomposition of the electrolyte to generate gas and the consumption of active lithium ions. In addition, additive A1 can also complex the metallic manganese ions dissolved from the cathode and inhibit their deposition on the negative electrode. However, when the content of additive A1 is too high, it will cause the interfacial film formed on the positive and negative electrodes to be too thick, thus hindering the transmission of lithium ions and further affecting the performance of the cycle.

[0074] From the test results of Example 2 and the test results of Examples 5 to 6 in the above Table 2, it can be seen that different types of additives A1, A2, and A3 have different degrees of improvement on the performance of the lithium battery.

[0075] The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, several simple deductions or substitutions can be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A lithium ion battery electrolyte, characterized in that: The electrolyte is applied to lithium ion batteries of nickel manganese oxide and niobium titanium oxide systems, and comprises: 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: 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; The positive electrode plate includes a positive electrode material, and the positive electrode material includes lithium nickel manganese oxide having a spinel structure; The negative electrode plate includes a negative electrode material, and the negative electrode material includes a niobium titanium oxide material.

7. The lithium-ion battery according to claim 6, 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.

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