A lithium ion battery nonaqueous electrolyte and a lithium ion battery

Abstract

The application relates to a lithium ion battery non-aqueous electrolyte and a lithium ion battery. The lithium ion non-aqueous electrolyte comprises an electrolyte, an organic solvent and an additive, the additive comprises a nitrile additive, and the organic solvent comprises fluoroethylene carbonate and a compound A with the structure of formula I. By adding the nitrile additive and the organic solvent with the specific structure into the electrolyte, the cycle performance of a lithium cobalt oxide lithium ion battery under high voltage conditions is effectively improved, the battery gas generation in the battery charging and discharging process is inhibited, and the high-voltage high-safety goal of the battery cell is achieved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more particularly to a non-aqueous electrolyte for lithium-ion batteries and a lithium-ion battery. Background Technology

[0002] To improve the energy density of LCO batteries, the most direct and effective method is to increase the charging cut-off voltage. Raising the charging cut-off voltage to 4.60 V will increase the discharge capacity by 50%-60%. However, increasing the charging cut-off voltage can lead to problems such as the dissolution of transition metal ions, release of lattice oxygen, stress accumulation, structural changes, and particle cracking within the material structure, resulting in a decline in the battery's electrochemical performance and potentially triggering a series of safety issues.

[0003] Therefore, in-depth research on lithium cobalt oxide lithium-ion batteries, focusing on suppressing electrolyte decomposition under high voltage conditions and improving the structural stability of lithium cobalt oxide under high voltage, thereby enhancing the cycle life of lithium-ion batteries, is of great significance. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a non-aqueous electrolyte for lithium-ion batteries and a lithium-ion battery itself. By adding nitrile additives and organic solvents with specific structures to the electrolyte, the cycle performance of lithium cobalt oxide lithium-ion batteries under high-voltage conditions is effectively improved, battery gas generation during charging and discharging is suppressed, and the goal of high voltage and high safety for the battery cell is achieved.

[0005] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a non-aqueous electrolyte for lithium-ion batteries, the non-aqueous electrolyte comprising an electrolyte, an organic solvent, and additives, wherein the additives include nitrile additives, and the organic solvent comprises fluoroethylene carbonate and compound A having the structure of formula I. , R1 is selected from any one of the following: C1-C10 (e.g., C2, C3, C4, C5, C6, C7, C8, or C9) alkyl, C1-C10 (e.g., C2, C3, C4, C5, C6, C7, C8, or C9) haloalkyl, C6-C30 (e.g., C8, C10, C12, C15, C18, C20, C25, or C28, etc.) aryl, or C6-C30 (e.g., C8, C10, C12, C15, C18, C20, C25, or C28, etc.) haloaryl.

[0006] In this invention, the cycling performance of lithium cobalt oxide lithium-ion batteries under high voltage conditions can be effectively improved by using nitrile additives, compound A and fluoroethylene carbonate solvent, and the battery gas generation during the charging and discharging process can be suppressed, thereby achieving the goal of high voltage and high safety of the battery cell.

[0007] Among them, the nitrile additives contain cyano groups, which have high carbon-nitrogen triple bond energies and are not easily oxidized. Therefore, they have good stability and strong oxidation resistance in the cathode, thereby improving the oxidation resistance of the electrolyte. They can effectively complex cobalt ions in the lithium cobalt oxide cathode material, inhibit the dissolution of transition metals in the cathode, and improve the stability of the cathode material. Fluoroethylene carbonate has excellent dielectric constant and can provide excellent lithium-ion kinetic energy to the electrolyte when used as a solvent. In addition, fluorine carbonate contains fluorine groups, which can improve the high-voltage oxidation stability of the electrolyte. Compound A, being a tertiary carboxylic acid ester, does not have hydrogen atoms on the carbonyl carbon atoms and has three methyl substituents on the carbon atoms. It can eliminate side reactions caused by ortho-hydrogen while improving the oxidation / reduction resistance of the functional groups, thereby improving the stability of the electrolyte and the safety of the battery.

[0008] In other words, the electrolyte provided by this invention contains nitrile additives, compound A, and fluoroethylene carbonate solvent. These three compounds work synergistically to improve the electrolyte's antioxidant capacity, inhibit the dissolution of transition metal ions from the cathode material, and improve its cycling performance under high voltage.

[0009] Preferably, the nitrile additive includes any one or a combination of at least two of butadionitrile, glutaronitrile, adiponitrile, trans-butenedionitrile, trans-hexenedionitrile, 1,2-di(cyanoethoxy)ethane, 1,3,6-hexanetrionitrile, or 1,2,3-tri(cyanoethoxy)propane.

[0010] Preferably, the nitrile additive has a mass percentage of 0.5%-5% in the non-aqueous electrolyte of the lithium-ion battery, for example, it can be 1%, 1.5%, 2%, 2.5%, 3% or 4%, etc.

[0011] Preferably, the halogenated halogen atom includes any one or a combination of at least two of fluorine, chlorine, bromine or iodine.

[0012] Preferably, the C1-C10 alkyl group includes any one of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, n-hexyl, 2-methylpentyl, 3-methylpentyl, 2,3-dimethylpentyl, 2,2-dimethylpentyl, n-heptyl, 2-methylhexyl, 3-methylhexyl, 3,3-dimethylpentyl, 2,3-dimethylpentyl, 2,4-dimethylpentyl, 3-ethylpentyl, or 2,2,3-trimethylbutyl.

[0013] Preferably, the C1-C10 haloalkyl group includes at least one halogen atom, for example, it may be 2, 3, 4, 5 or 6, etc.

[0014] Preferably, the C6-C30 aryl group includes at least one benzene ring, for example, it can be 2, 3, 4, 5 or 6 rings, etc.

[0015] Preferably, the C6-C30 haloaryl group includes at least one halogen atom, such as 2, 3, 4, 5 or 6.

[0016] Preferably, the C6-C30 halogenated aryl group includes at least one benzene ring, for example, it can be 2, 3, 4, 5 or 6 rings, etc.

[0017] Preferably, compound A comprises methyl trimethylacetate and / or ethyl trimethylacetate.

[0018] Preferably, the mass percentage of compound A in the non-aqueous electrolyte of the lithium-ion battery is 5%-80%, for example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 50%, 60% or 70%, etc.

[0019] Preferably, the additive also includes lithium salt additives.

[0020] Preferably, the lithium salt additive includes any one or a combination of at least two of lithium difluorosulfonate (LiFSI), lithium difluorooxalate borate (LiODFB), lithium tetrafluoroborate borate (LiBF4), lithium bis(oxalate borate) (LiBOB), lithium difluorophosphate (LiPO2F2), or lithium difluorobis(oxalate borate) (LiDFOP).

[0021] Preferably, the lithium salt additive has a mass percentage content of 0.1%-4.0% in the non-aqueous electrolyte of the lithium-ion battery, for example, it can be 0.2%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0% or 3.5%, and more preferably 0.2%-3.0%.

[0022] Preferably, the additive also includes a film-forming additive.

[0023] Preferably, the film-forming additive comprises any one or a combination of at least two of the following: vinylene carbonate (VC), 1,3-propanesulfonate lactone (PS), vinylene sulfate (ES), vinyl sulfate (DTD), methanedisulfonate methylene (MMDS), vinylene carbonate (VEC), fluoroethylene carbonate (FEC), tri(trimethylsilane) phosphate (TMSP), or tri(trimethylsilane) borate (TMSB).

[0024] Preferably, the film-forming additive has a mass percentage content of 0.5%-11% in the non-aqueous electrolyte of the lithium-ion battery, for example, it can be 1.2%, 3.8%, 5.9%, 8.2%, 9.0% or 9.5%.

[0025] Preferably, the electrolyte comprises a lithium salt electrolyte.

[0026] Preferably, the electrolyte comprises LiPF6.

[0027] Preferably, the electrolyte has a mass percentage content of 2%-22% in the non-aqueous electrolyte of the lithium-ion battery, for example, it can be 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 16%, 18% or 20%, etc.

[0028] Preferably, the fluoroethylene carbonate has a mass percentage content of 5%-80% in the non-aqueous electrolyte of the lithium-ion battery, for example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 50%, 60% or 70%, etc.

[0029] Preferably, the mass ratio of compound A to fluoroethylene carbonate is (1-6):1, for example, it can be 2:1, 3:1, 3.5:1, 4:1 or 5:1, etc.

[0030] Preferably, the organic solvent has a mass percentage content of 75%-94% in the non-aqueous electrolyte of the lithium-ion battery, for example, it can be 76%, 81%, 82%, 86%, 90% or 91%, etc.

[0031] In a second aspect, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, wherein the electrolyte is a non-aqueous electrolyte for lithium-ion batteries as described in the first aspect.

[0032] Preferably, the positive electrode comprises a positive electrode active material, a conductive agent, and a binder.

[0033] Preferably, the positive electrode active material includes LiCoO2 and LiNi. x Co y Mn z L (1-x-y-z) O2 or LiNi x' L' y' Mn (2-x'-y') Any one or at least two of O4 Wherein, L is any one or a combination of at least two of Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, or Fe; 0.5≤x≤1 (e.g., it can be 0.6, 0.7, 0.75, 0.8, or 0.9, etc.), 0≤y<1 (e.g., it can be 0.2, 0.4, 0.5, 0.6, or 0.8, etc.), 0≤z≤1 (e.g., it can be 0.2, 0.4, 0.5, 0.6, or 0.8, etc.), and 0<x+y+z≤1 (e.g., it can be 0.2, 0.4, 0.5, 0.6, or 0.8, etc.). L' includes any one or at least two of Co, Al, Sr, Mg, Ti, Ca, Zr, Zn, Si or Fe, 0 < x' ≤ 1 (e.g., it can be 0.2, 0.4, 0.5, 0.6 or 0.8, etc.), and 0.01 ≤ y' ≤ 0.2 (e.g., it can be 0.05, 0.08, 0.1, 0.12 or 0.15, etc.).

[0034] Preferably, the positive electrode active material includes LiCoO2.

[0035] Preferably, the negative electrode comprises a negative electrode active material.

[0036] Preferably, the negative electrode active material includes any one or a combination of at least two of the following: natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, graphene, graphdiene, lithium metal, nano-carbon, carbon nanotubes, elemental silicon, silicon oxide, silicon / copper oxide composite, AG composite, silicon alloy, elemental tin, tin oxide, tin-carbon composite, tin alloy, or lithium titanate. More preferably, it includes any one or a combination of at least two of the following: elemental silicon, silicon oxide, silicon / copper oxide composite, or silicon alloy.

[0037] Preferably, the membrane material includes any one or a combination of at least two of polyethylene, polypropylene, or composite ceramic membrane.

[0038] Compared with the prior art, the present invention has at least the following beneficial effects: The electrolyte provided by this invention contains nitrile additives, compound A, and fluoroethylene carbonate. These three compounds work synergistically to improve the electrolyte's antioxidant capacity, inhibit the dissolution of transition metal ions from the cathode material, and improve its cycle performance under high voltage, thus meeting the application requirements of lithium cobalt oxide batteries under high voltage. Detailed Implementation

[0039] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0040] Examples 1-8, Comparative Examples 1-9 Examples 1-8 and Comparative Examples 1-9 respectively provide a non-aqueous electrolyte for lithium-ion batteries and its preparation method. The composition and amount of the non-aqueous electrolyte are shown in Table 1, where the amount of each component in Table 1 is the mass percentage in the electrolyte.

[0041] The preparation method of the non-aqueous electrolyte includes the following steps: The electrolyte was prepared in a Michelona glove box (filled with argon gas, with less than 10 ppm of gaseous water). First, the organic solvent was mixed evenly in proportion, then the film-forming additive was added, and finally the electrolyte was added. The mixture was mixed until the electrolyte had no bottom residue and was clear and turbid, thus obtaining the non-aqueous electrolyte with normal color. It was then stored in a -10°C refrigerator.

[0042] Table 1 Application Example 1-8, Comparative Application Example 1-9 Application Examples 1-8 and Comparative Application Examples 1-9 each provide a lithium-ion battery and its preparation method. The lithium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is a non-aqueous electrolyte provided in Examples 1-8 and Comparative Examples 1-9, respectively.

[0043] The method for preparing the lithium-ion battery includes the following steps: (1) Preparation of positive electrode: Polyvinylidene fluoride (PVDF) is uniformly dissolved in N-methylpyrrolidone (NMP), then the conductive agent Super P is added and mixed thoroughly. Then, the positive electrode active material LiCoO2 powder is gradually added (wherein, the mass ratio of LiCoO2 powder, PVDF and conductive agent Super P is 97.4:1.3:1.3, to obtain positive electrode slurry (the solid content of the positive electrode slurry is 63.1%)). The positive electrode slurry is coated on the current collector, and then dried, rolled and slit to obtain a positive electrode that can be directly stacked.

[0044] (2) Preparation of negative electrode: Artificial graphite, conductive carbon and sodium carboxymethyl cellulose in a mass ratio of 95.9:2.9:1.2 are fed and premixed. The mixture is stirred at 250 rpm for 140 min to obtain negative electrode slurry. The negative electrode slurry is then transferred to deionized water for dispersion. After being mixed evenly, the negative electrode slurry is sieved (180 mesh). Finally, the sieved negative electrode slurry is coated onto the negative electrode current collector. After drying, rolling and slitting, a negative electrode that can be directly stacked is obtained.

[0045] (3) Cell manufacturing: The slit positive and negative electrodes are stacked on a stacking machine, and the separator is made of three layers of PP / PE / PP material to form a soft-pack cell.

[0046] (4) Electrolyte injection, formation and aging: After the cell is dried at high temperature, the non-aqueous electrolyte of Examples 1-8 and Comparative Examples 1-9 is injected into the soft-pack cell; after the electrolyte is injected, the lithium-ion battery is first packaged, the surface cleaning process is completed, and it is placed at room temperature for one day; the formation is carried out by step formation method. The first step formation current is 0.05C, constant current charging for 2 hours, the second step formation current is 0.1C, constant current charging until the voltage reaches 3.85V; after formation, it is aged at 50°C for one day, cooled to room temperature for final sealing, and the lithium-ion battery is obtained.

[0047] Test methods After the lithium-ion battery is assembled, it is left at room temperature for 10 hours to allow the electrolyte to fully wet the battery electrodes before being subjected to the following tests.

[0048] (1) 25℃ ambient temperature cycle test: constant current charge and discharge is performed in a constant temperature room at 25℃ with a current density of 1C at the rated capacity. The cycle number is 800. The test voltage range is 3V-4.5V. The charging cut-off current is 0.05C. After the test, the capacity retention rate of the 800th cycle is calculated based on the discharge capacity of the first cycle.

[0049] The formula for calculating capacity retention after 800 cycles at ambient temperature is as follows: Capacity retention rate after 800 cycles (%) = (Discharge capacity after 800 cycles at room temperature / Initial discharge capacity) * 100%.

[0050] (2) 45℃ high temperature cycle test: constant current charge and discharge is performed in a constant temperature 45℃ forced air oven with a current density of 1C at the rated capacity. The cycle number is 600 times, the test voltage range is 3V-4.5V, the charging cut-off current is 0.05C, and after the test, the capacity retention rate of the 600th cycle is calculated based on the discharge capacity of the first cycle.

[0051] The formula for calculating the capacity retention rate after 600-cycle high-temperature cycling is as follows: Capacity retention rate after 600 cycles (%) = (Discharge capacity after 600 high-temperature cycles / Initial discharge capacity) * 100%.

[0052] (3) High-temperature gas generation performance test of lithium-ion battery: Constant current charging and discharging was performed at a current density of 1C at the rated capacity in a constant temperature chamber of 25℃, followed by constant voltage charging at 4.5V until the current was 0.05C. After the battery was fully charged, the initial volume of the battery was tested using the water displacement method. The battery was stored in an oven at 60℃ for 7 days, and then removed. The battery was left to stand at 25℃ for 60 minutes, and the volume of the battery was tested using the water displacement method.

[0053] Perform storage tests following the steps outlined above, up to 28 days. Using the battery volume tested before storage as a baseline, calculate the battery's volume expansion rate over storage time.

[0054] High-temperature storage volume expansion rate on day 28 = (Volume after high-temperature storage on day 28 - Initial battery volume / Initial battery volume) * 100%.

[0055] The test results are shown in Table 2.

[0056] Table 2 The test results show that: (1) As can be seen from Application Examples 1-8, by adding nitrile additives, compound A, and fluoroethylene carbonate solvent to the electrolyte, the present invention enables the secondary lithium-ion battery to have good capacity retention at room temperature and high capacity retention at high temperature, and can greatly suppress the volume expansion of the battery during storage. The lithium cobalt oxide lithium-ion battery assembled with the electrolyte has a capacity retention rate of 91.3%-96.3% under the test conditions of 25°C and 1C, a capacity retention rate of 84.9%-90.4% under the test conditions of 45°C and 1C, and a volume expansion rate of 6.1%-9.2% after storage at 60°C for 28 days.

[0057] (2) By comparing Application Example 1 with Application Examples 2-4, it can be seen that the present invention improves the performance of lithium-ion batteries by further limiting the mass ratio of compound A to fluoroethylene carbonate.

[0058] (3) By comparing Application Example 1 with Comparative Application Examples 1-9, it can be seen that if the combination of nitrile additives, compound A and fluoroethylene carbonate solvent is not used, the overall performance of the battery will be significantly worse.

[0059] In summary, this invention effectively improves the cycle performance of lithium cobalt oxide lithium-ion batteries under high voltage conditions and suppresses battery gas generation during charging and discharging by adding nitrile additives and organic solvents with specific structures to the electrolyte, thereby achieving the goal of high voltage and high safety for the battery cells.

[0060] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A non-aqueous electrolyte for lithium-ion batteries, characterized in that, The lithium-ion non-aqueous electrolyte comprises lithium salt, the organic solvent fluoroethylene carbonate, and compound A. Compound A, having the structure of formula I, is as follows. ， R1 is selected from any one of C1-C10 alkyl, C1-C10 haloalkyl, C6-C30 aryl, or C6-C30 haloaryl.

2. The non-aqueous electrolyte for lithium-ion batteries according to claim 1, characterized in that, The nitrile additives include any one or a combination of at least two of the following: butadionitrile, glutaronitrile, adiponitrile, trans-butenedionitrile, trans-hexenedionitrile, 1,2-di(cyanoethoxy)ethane, 1,3,6-hexanetrionitrile, or 1,2,3-tri(cyanoethoxy)propane. Preferably, the nitrile additive has a mass percentage content of 0.5%-5% in the non-aqueous electrolyte of the lithium-ion battery.

3. The non-aqueous electrolyte for lithium-ion batteries according to claim 1 or 2, characterized in that, The halogenated halogen atom includes any one or a combination of at least two of fluorine, chlorine, bromine or iodine; Preferably, the C1-C10 alkyl group includes any one of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, n-hexyl, 2-methylpentyl, 3-methylpentyl, 2,3-dimethylpentyl, 2,2-dimethylpentyl, n-heptyl, 2-methylhexyl, 3-methylhexyl, 3,3-dimethylpentyl, 2,3-dimethylpentyl, 2,4-dimethylpentyl, 3-ethylpentyl, or 2,2,3-trimethylbutyl. Preferably, the C1-C10 haloalkyl group includes at least one halogen atom; Preferably, the C6-C30 aryl group includes at least one benzene ring; Preferably, the C6-C30 haloaryl group includes at least one halogen atom; Preferably, the C6-C30 haloaryl group includes at least one benzene ring; Preferably, compound A comprises methyl trimethylacetate and / or ethyl trimethylacetate; Preferably, the mass percentage of compound A in the non-aqueous electrolyte of the lithium-ion battery is 5%-80%.

4. The non-aqueous electrolyte for lithium-ion batteries according to any one of claims 1-3, characterized in that, The additives also include lithium salt additives; Preferably, the lithium salt additive includes any one or a combination of at least two of lithium difluorosulfonate, lithium difluorooxalate borate, lithium tetrafluoroborate borate, lithium bis(oxalate) borate, lithium difluorophosphate, or lithium difluorobis(oxalate) phosphate. Preferably, the lithium salt additive has a mass percentage content of 0.1%-4.0% in the non-aqueous electrolyte of the lithium-ion battery, and more preferably 0.2%-3.0%.

5. The non-aqueous electrolyte for lithium-ion batteries according to any one of claims 1-4, characterized in that, The additives also include film-forming additives; Preferably, the film-forming additive comprises any one or a combination of at least two of the following: vinylene carbonate, 1,3-propanesulfonate lactone, vinylene sulfate, vinyl sulfate, methanedisulfonate, vinylene carbonate, fluoroethylene carbonate, tris(trimethylsilane) phosphate, or tris(trimethylsilane) borate. Preferably, the film-forming additive has a mass percentage content of 0.5%-11% in the non-aqueous electrolyte of the lithium-ion battery.

6. The non-aqueous electrolyte for lithium-ion batteries according to any one of claims 1-5, characterized in that, The electrolyte includes a lithium salt electrolyte; Preferably, the electrolyte comprises LiPF6; Preferably, the electrolyte has a mass percentage content of 2%-22% in the non-aqueous electrolyte of the lithium-ion battery.

7. The non-aqueous electrolyte for lithium-ion batteries according to any one of claims 1-6, characterized in that, The fluoroethylene carbonate has a mass percentage content of 5%-80% in the non-aqueous electrolyte of lithium-ion batteries. Preferably, the mass ratio of compound A to fluoroethylene carbonate is (1-6):

1.

8. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, wherein the electrolyte is a non-aqueous electrolyte for lithium-ion batteries as described in any one of claims 1-7.

9. The lithium-ion battery according to claim 8, characterized in that, The positive electrode includes a positive electrode active material, a conductive agent, and a binder; Preferably, the positive electrode active material includes LiCoO2 and LiNi. x Co y Mn z L (1-x-y-z) O2 or LiNi x' L' y' Mn (2- x'-y') Any one or at least two of O4 Where L is any one or a combination of at least two of Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, or Fe; 0.5≤x≤1, 0≤y<1, 0≤z≤1, 0<x+y+z≤1, L' includes any one or at least two of Co, Al, Sr, Mg, Ti, Ca, Zr, Zn, Si or Fe, 0 < x' ≤ 1, 0.01 ≤ y' ≤ 0.2; Preferably, the positive electrode active material includes LiCoO2.

10. The lithium-ion battery according to claim 8 or 9, characterized in that, The negative electrode includes a negative electrode active material; Preferably, the negative electrode active material includes any one or a combination of at least two of the following: natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, graphene, graphynylene, lithium metal, nano-carbon, carbon nanotubes, elemental silicon, silicon oxide, silicon / copper oxide composite, AG composite, silicon alloy, elemental tin, tin oxide, tin-carbon composite, tin alloy, or lithium titanate. Preferably, the membrane material includes any one or a combination of at least two of polyethylene, polypropylene, or composite ceramic membrane.

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