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, a pyridine derivative containing a nitrogen substituent group and an auxiliary film-forming additive. According to the invention, the pyridine derivative containing the nitrogen substituent group and the acidic substance in the electrolyte are subjected to an acid-base neutralization reaction, so that the acidic substance in the electrolyte is removed, and the acidic substance is prevented from corroding the positive electrode material; moreover, the pyridine derivative containing the nitrogen substituent group can be adsorbed on the surface of the positive electrode to prevent the electrolyte from oxidizing the positive electrode and complexing metal ions dissolved out of the positive electrode, so that side reactions on the surfaces of the positive electrode and the negative electrode are inhibited, and the pyridine derivative containing the nitrogen substituent group forms a compact interface film on the surfaces of the positive electrode and the negative electrode through the auxiliary film-forming additive; the side reaction on the surfaces of the positive and negative electrodes is further inhibited, and the high-temperature cycle and storage performance of the lithium ion battery is 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 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 titanium niobate materials. However, the voltage platform of titanium niobate negative electrode materials is greater than 1V. When titanium niobate negative electrode materials are matched with conventional lithium iron phosphate or nickel-cobalt-manganese 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] Lithium nickel manganese oxide is a high-voltage positive electrode material that is currently being studied more frequently. Its cost and thermal stability are superior to nickel-cobalt-manganese ternary materials. However, the acidic substances produced in the electrolyte of lithium-ion batteries will corrode lithium nickel manganese oxide, causing the capacity of lithium-ion batteries to decay rapidly. It will also cause manganese ions to dissolve from the lithium nickel manganese oxide positive electrode material, and the dissolved manganese ions will migrate to the negative electrode, destroying the negative electrode interface, 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:

[0006] A first aspect of the present invention provides a lithium ion battery electrolyte, comprising: a solvent, an electrolyte salt, a pyridine derivative containing a nitrogen substituent, and an auxiliary film-forming additive.

[0007] In one achievable manner, the pyridine derivative containing a nitrogen substituent includes one or more of 4-dimethylaminopyridine, 4-pyrrolidinylpyridine, 1-pyridine-4-piperidine, 4-di-n-propylaminopyridine, 4-dibutylaminopyridine and 4-(4-methylpiperidin-1-yl)pyridine.

[0008] In one achievable manner, the auxiliary film-forming additive includes: one or more of lithium difluorooxalatoborate, lithium dioxalatoborate, lithium dimalonate borate, lithium difluorooxalatophosphate, lithium difluorophosphate, tripropargyl phosphate, vinyl sulfate, fluoroethylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, methylene disulfonate, and succinic anhydride.

[0009] In an achievable manner, the content of the pyridine derivative containing a nitrogen substituent in the lithium ion battery electrolyte is 0.2 to 3 wt %.

[0010] In one achievable manner, the content of the auxiliary film-forming additive in the lithium-ion battery electrolyte is 0.2-2 wt %.

[0011] In one achievable manner, the solvent comprises: one or more of carbonates, fluorocarbonates, fluorocarboxylates, fluoroethers, nitriles, and sulfones;

[0012] The electrolyte salt includes one or more of LiPF6, LiClO4, LiFSI, LiTFSI and LiBF4.

[0013] The second aspect of the present invention provides a lithium ion battery, comprising: a positive electrode sheet, a negative electrode sheet, a separator and the lithium ion battery electrolyte provided by the first aspect of the present invention, wherein:

[0014] The diaphragm is arranged between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet, the negative electrode sheet and the diaphragm are all located in the electrolyte of the lithium-ion battery.

[0015] In one achievable manner, the positive electrode plate includes a positive electrode material;

[0016] The positive electrode material is spinel-type lithium nickel manganese oxide doped with doping elements;

[0017] The doping elements include: one or more doping elements of Al, Mg, Fe, Co, Y, Sc, Ru, Cu, Mo, Ce, W, Nb, Ta, Zr, Ca, P, S, F, B, Si and Sr.

[0018] In one achievable manner, the negative electrode plate includes a niobium-based negative electrode material.

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

[0020] The lithium ion battery electrolyte provided by the present invention removes the acidic substances in the electrolyte through an acid-base neutralization reaction between a pyridine derivative containing a nitrogen substituent and an acidic substance in the electrolyte, thereby preventing the acidic substance from corroding the positive electrode material; and the pyridine derivative containing a nitrogen substituent can be adsorbed on the surface of the positive electrode to prevent the oxidation of the electrolyte at the positive electrode, and complex the metal ions dissolved from the positive electrode, thereby inhibiting the occurrence of side reactions on the positive and negative electrode surfaces, and the pyridine derivative containing a nitrogen substituent can form a dense interface film on the surface of the positive and negative electrodes through an auxiliary film-forming additive, further inhibiting the occurrence of side reactions on the surface of the positive and negative electrodes, thereby improving the high-temperature cycle and storage performance of the lithium ion battery, especially the combination of the pyridine derivative containing a nitrogen substituent and the auxiliary film-forming additive can greatly produce a synergistic protection effect with a niobium-based negative electrode, generate an interface film containing nitrogen elements on the surface of the niobium-based negative electrode, and improve the stability of the niobium-based negative electrode material. DETAILED DESCRIPTION

[0021] 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.

[0022] A first aspect of the present embodiment provides a lithium-ion battery electrolyte, comprising: a solvent, an electrolyte salt, a pyridine derivative containing a nitrogen substituent, and an auxiliary film-forming additive.

[0023] Specifically, the pyridine derivatives containing nitrogen substituents contain both nitrogen substituents and pyridine groups, and have strong alkalinity. They can not only remove acidic substances in the electrolyte, but also be adsorbed on the surface of the positive electrode to prevent the oxidation of the electrolyte at the positive electrode, and can also complex the metal ions dissolved from the positive electrode, thereby inhibiting the occurrence of side reactions on the positive and negative electrode surfaces. However, it is difficult for pyridine derivatives containing nitrogen substituents to form a dense interface film on the surface of the positive electrode. Therefore, this embodiment uses auxiliary film-forming additives to allow pyridine derivatives containing nitrogen substituents to form a dense interface film on the surface of the positive and negative electrodes, further inhibiting the occurrence of side reactions on the surface of the positive and negative electrodes, so that the lithium-ion battery has excellent high-temperature cycling and storage performance.

[0024] In this embodiment, the pyridine derivative containing a nitrogen substituent includes one or more of 4-dimethylaminopyridine, 4-pyrrolidinylpyridine, 1-pyridine-4-piperidine, 4-di-n-propylaminopyridine, 4-dibutylaminopyridine and 4-(4-methylpiperidin-1-yl)pyridine.

[0025] In this embodiment, the auxiliary film-forming additives include: one or more of lithium difluorooxalatoborate, lithium dioxalatoborate, lithium dimalonate borate, lithium difluorooxalatophosphate, lithium difluorophosphate, tripropargyl phosphate, vinyl sulfate, fluoroethylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, methylene disulfonate, and succinic anhydride.

[0026] In this embodiment, the content of the pyridine derivative containing a nitrogen substituent in the lithium-ion battery electrolyte is 0.2-3wt%, such as 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%. The content of the auxiliary film-forming additive in the lithium-ion battery electrolyte is 0.2-2wt%, such as 0.2%, 0.5%, 1%, 1.5%, 2%.

[0027] In this embodiment, the solvent includes: one or more of carbonate, fluorocarbonate, fluorocarboxylate, fluoroether, nitriles, and sulfones. Preferably, the solvent includes: one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, bisfluoroethylene carbonate, 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 cyclopentane sulfone.

[0028] In this embodiment, the electrolyte salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium tetrafluoroborate (LiBF4). The content of the electrolyte salt in the electrolyte is 10-25wt%, for example, 10%, 12.5%, 15%, 17.5%, 20%, 22.5%, 25%.

[0029] The second aspect of this embodiment provides a lithium-ion battery, comprising: a positive electrode plate, a negative electrode plate, a diaphragm and the lithium-ion battery electrolyte provided by the first aspect of this embodiment, wherein the diaphragm is arranged between the positive electrode plate and the negative electrode plate, and the positive electrode plate, the negative electrode plate and the diaphragm are all located in the lithium-ion battery electrolyte.

[0030] In this embodiment, the positive electrode plate includes a positive electrode material. The positive electrode material is spinel-type lithium nickel manganese oxide doped with doping elements. The doping elements include: one or more of Al, Mg, Fe, Co, Y, Sc, Ru, Cu, Mo, Ce, W, Nb, Ta, Zr, Ca, P, S, F, B, Si and Sr.

[0031] In one achievable manner, the negative electrode sheet includes: one of: a carbon negative electrode material, a silicon negative electrode material, a lithium metal negative electrode material, a lithium titanate negative electrode material, and a niobium-based negative electrode material.

[0032] In this embodiment, the negative electrode plate includes a niobium-based negative electrode material. The specific surface area of ​​the niobium-based negative electrode material is 0.2 to 10 m 2 / g, for example, 0.2m 2 / g, 0.5m 2 / g, 1m 2 / g, 2m 2 / g, 3m 2 / g, 5m 2 / g, 7m 2 / g, 10m 2 / g. Furthermore, the niobium-based negative electrode material includes at least one of titanium niobate, tungsten niobate, nickel niobate and niobates containing elements such as P, V, Ta, Cu, Mo, etc., among which titanium niobate is preferred.

[0033] In the present embodiment, the diaphragm can be a conventional electrochemical battery diaphragm, which can isolate electrons and allow metal ions (such as lithium ions) to pass through; it can also be any one of an organic polymer diaphragm or an inorganic diaphragm. Exemplarily, the diaphragm can be selected from any one of a polyethylene porous film, a polypropylene porous film, a polyethylene-polypropylene double-layer porous film, a polypropylene-polyethylene-polypropylene three-layer porous film, a glass fiber porous film, a non-woven porous film, an electrospun porous film, a PVDF-HFP porous film, and a polyacrylonitrile porous film. Further, the non-woven diaphragm can be listed as polyimide nanofiber non-woven fabric, polyethylene terephthalate (PET) nanofiber non-woven fabric, cellulose nanofiber non-woven fabric, aramid nanofiber non-woven fabric, nylon nanofiber non-woven fabric, and polyvinylidene fluoride (PVDF) nanofiber non-woven fabric. Electrospinning porous membranes can be listed as polyimide electrospun membranes, polyethylene terephthalate electrospun membranes, and polyvinylidene fluoride electrospun membranes.

[0034] The preparation method of the lithium ion battery electrolyte provided in this embodiment includes:

[0035] In a glove box, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed in a mass ratio of 2:2:3:3 to obtain a mixed solvent, LiPF6 electrolyte salt was slowly added to the mixed solvent, and mixed evenly, and after the temperature of the mixed solvent dropped to room temperature, a nitrogen-containing substituted pyridine derivative and an auxiliary film-forming additive were added to prepare an electrolyte. The mass content of the electrolyte salt in the electrolyte was 14%.

[0036] The method for preparing a lithium-ion battery provided in this embodiment includes:

[0037] Preparation of positive electrode sheet: The positive electrode material lithium nickel manganese oxide (LiNi 0.5 Mn 1.5O4), polyvinylidene fluoride, and 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.

[0038] Preparation of negative electrode sheet: Titanium niobate negative electrode material, polyvinylidene fluoride, and conductive carbon black are dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 95:2:3 and mixed evenly to form negative electrode slurry. Then the negative electrode slurry is 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 negative electrode sheets.

[0039] The positive electrode sheet, negative electrode sheet and separator are wound into a bare battery cell and then loaded into an aluminum-plastic film. Then, they are baked at 100°C to remove water, and then the electrolyte is injected and sealed. After standing, hot and cold pressing, formation, exhaust, and capacity separation, a lithium-ion battery is obtained.

[0040] Furthermore, in this embodiment, the types and contents of the pyridine derivatives containing nitrogen substituents and the auxiliary film-forming additives are changed, and several electrolytes are prepared by the above-mentioned preparation method, which are recorded as Examples 1 to 12. A control group is set up and recorded as Comparative Examples 1 to 2. The electrolytes shown in Examples 1 to 12 and Comparative Examples 1 to 2 are prepared into lithium-ion batteries according to the above-mentioned preparation method, and are matched with titanium niobate negative electrode materials with different specific surface areas. The contents of each component in Examples 1 to 12 and Comparative Examples 1 to 2 and the specific surface area of ​​the titanium oxide negative electrode material are shown in Table 1. In Table 1, DMAP is 4-dimethylaminopyridine, PP is 4-pyrrolidinopyridine, PST is 1,3-propylene sultone, and LiDFOB is lithium difluorooxalatoborate. The following performance tests were carried out on the lithium-ion batteries of Examples 1 to 12 and Comparative Examples 1 to 2:

[0041] (1) Lithium-ion battery 45℃ 1C / 1C cycle test

[0042] First, let the lithium-ion battery stand for 30 minutes at 45°C, discharge it to 1.5V at a constant current of 1C, and then stand for 5 minutes; then charge it to 3.6V at a constant current of 1C, further charge it to a current of 0.1C at a constant voltage of 3.6V, and then stand for 5 minutes, and then discharge it to 1.5V at a constant current of 1C. This is a charge and discharge cycle process, and the obtained discharge capacity is the discharge capacity Ca of the lithium-ion battery. After that, 500 charge and discharge cycles are performed, and the discharge capacity of the 500th cycle is recorded as Cb. The capacity retention rate (%) of the lithium-ion battery after 500 cycles = Cb / Ca.

[0043] (2) Lithium-ion battery 60°C storage test:

[0044] First, let the lithium-ion battery stand at 25°C for 30 minutes; charge it to 3.6V at a constant current of 1C, and further charge it to 0.1C at a constant voltage of 3.6V; then test the volume of the battery using the drainage method, which is the volume before storage V A The lithium-ion battery was then stored at 60°C and the volume of the test battery was taken out every 10 days. It was then charged to 3.6V at a constant current of 1C and further charged to a current of 0.1C at a constant voltage of 3.6V. The battery was taken out after 50 days of storage at 60°C and the volume of the test battery was V B . Lithium-ion battery storage volume expansion rate at 60°C (%) = (V B -V A ) / V A .

[0045] After being stored at 60°C for 50 days, the test battery was taken out and its volume was measured, and then the battery SOC was adjusted to the full discharge state; then the battery was disassembled, the negative electrode active plate was taken out, and the ICP method was used to test the content of metallic manganese in the negative electrode plate.

[0046] The performance test results of Examples 1 to 12 and Comparative Examples 1 to 2 are shown in Table 2.

[0047] Table 1: Content of each component in Examples 1 to 12 and Comparative Examples 1 to 2

[0048]

[0049] Table 2: Lithium-ion battery performance test results

[0050]

[0051]

[0052] It can be concluded from Example 2, Comparative Example 1 and Comparative Example 2 that by adding a pyridine derivative containing a nitrogen substituent and an auxiliary film-forming additive to the electrolyte at the same time, both the high-temperature cycle and high-temperature storage performances are significantly improved.

[0053] It can be concluded from Examples 1 to 4 that as the content of the pyridine derivative containing nitrogen substituents increases, various performances are improved to varying degrees, but when the content is too high, the cycle performance will deteriorate. It is speculated that when the content of the pyridine derivative containing nitrogen substituents is too high, the excess pyridine derivative containing nitrogen substituents will adsorb lithium ions, hindering the insertion and extraction of lithium ions, which is not conducive to the performance of the cycle performance.

[0054] It can be concluded from Example 2, Examples 5 to 7, and Comparative Example 2 that as the content of the auxiliary film-forming additive increases, various performances are also improved to varying degrees. However, when the content is too high, the interface film formed on the surface of the positive and negative electrodes is too thick, which will also hinder the insertion and extraction of lithium ions, and will also consume more lithium ions, resulting in a decrease in overall performance.

[0055] It can be concluded from Example 2 and Examples 8 to 9 that different combinations of the contents and types of pyridine derivatives containing nitrogen substituents and auxiliary film-forming additives can achieve different performance improvement effects, and R&D personnel can flexibly adjust according to project requirements.

[0056] It can be concluded from Examples 10 to 12 that if the specific surface area of ​​the titanium niobate negative electrode material is too small, the cycle performance of the lithium-ion battery will deteriorate, but the high-temperature storage performance will improve. If the specific surface area is too large, there will be too many side reactions, and the high-temperature cycle and storage performance will deteriorate. R&D personnel need to select a suitable specific surface area of ​​the titanium niobate negative electrode material according to project requirements.

[0057] The lithium ion battery electrolyte provided in the present embodiment removes the acidic substances in the electrolyte through an acid-base neutralization reaction between the pyridine derivative containing nitrogen substituents and the acidic substances in the electrolyte, thereby preventing the acidic substances from corroding the positive electrode material; and the pyridine derivative containing nitrogen substituents can be adsorbed on the surface of the positive electrode to prevent the oxidation of the electrolyte at the positive electrode, and complex the metal ions dissolved from the positive electrode, thereby inhibiting the occurrence of side reactions on the positive and negative electrode surfaces, and the pyridine derivative containing nitrogen substituents can form a dense interface film on the surface of the positive and negative electrodes through the auxiliary film-forming additive, further inhibiting the occurrence of side reactions on the surface of the positive and negative electrodes, and improving the high-temperature cycle and storage performance of the lithium ion battery. In particular, the combination of the pyridine derivative containing nitrogen substituents and the auxiliary film-forming additive can greatly produce a synergistic protection effect with the niobium-based negative electrode, and produce an interface film containing nitrogen elements on the surface of the niobium-based negative electrode, thereby improving the stability of the niobium-based negative electrode material.

[0058] 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 scope of protection of the present invention.

Claims

1. A lithium ion battery electrolyte, characterized in that: include: Solvent, electrolyte salt, pyridine derivative containing nitrogen substituent and auxiliary film-forming additive.

2. The lithium ion battery electrolyte according to claim 1, characterized in that: The pyridine derivative containing a nitrogen substituent includes one or more of 4-dimethylaminopyridine, 4-pyrrolidinylpyridine, 1-pyridine-4-piperidine, 4-di-n-propylaminopyridine, 4-dibutylaminopyridine and 4-(4-methylpiperidin-1-yl)pyridine.

3. The lithium ion battery electrolyte according to claim 1, characterized in that The auxiliary film-forming additives include: one or more of lithium difluorooxalatoborate, lithium dioxalatoborate, lithium dimalonate borate, lithium difluorooxalatophosphate, lithium difluorophosphate, tripropargyl phosphate, vinyl sulfate, fluoroethylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, methylene disulfonate, and succinic anhydride.

4. The lithium ion battery electrolyte according to claim 1, characterized in that: The content of the pyridine derivative containing a nitrogen substituent in the lithium ion battery electrolyte is 0.2-3 wt %.

5. The lithium ion battery electrolyte according to claim 1, characterized in that: The content of the auxiliary film-forming additive in the lithium-ion battery electrolyte is 0.2-2 wt %.

6. The lithium ion battery electrolyte according to claim 1, characterized in that: The solvent includes: one or more of carbonates, fluorocarbonates, fluorocarboxylates, fluoroethers, nitriles, and sulfones; The electrolyte salt includes one or more of LiPF6, LiClO4, LiFSI, LiTFSI and LiBF4.

7. A lithium ion battery, characterized in that: include: A positive electrode sheet, a negative electrode sheet, a separator and a lithium ion battery electrolyte according to any one of claims 1 to 6, wherein: The diaphragm is arranged between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet, the negative electrode sheet and the diaphragm are all located in the lithium-ion battery electrolyte.

8. The lithium-ion battery according to claim 7, characterized in that: The positive electrode sheet includes a positive electrode material; The positive electrode material is spinel-type lithium nickel manganese oxide doped with doping elements; The doping elements include one or more of Al, Mg, Fe, Co, Y, Sc, Ru, Cu, Mo, Ce, W, Nb, Ta, Zr, Ca, P, S, F, B, Si and Sr.

9. The lithium-ion battery according to claim 7, characterized in that: The negative electrode plate includes a niobium-based negative electrode material.

10. The lithium ion battery according to claim 9, characterized in that: The specific surface area of ​​the niobium-based negative electrode material is 0.2 to 10 m 2 / g.

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