Non-aqueous lithium battery electrolyte and non-aqueous lithium battery

Abstract

In order to solve the problem that the battery performance of a lithium battery is reduced under high voltage, the non-aqueous lithium battery electrolyte and the non-aqueous lithium battery are provided, the non-aqueous lithium battery electrolyte comprises an organic solvent and a lithium salt, the organic solvent is composed of carbonic ester compounds, and the carbonic ester compounds comprise first carbonic ester and second carbonic ester, the first carbonic ester is dimethyl 2, 5-dioxaadipate and / or diethyl 2, 5-dioxaadipate, and the mass content of the first carbonic ester in the electrolyte is not less than 20%; the second carbonate ester includes a chain carbonate ester and a cyclic carbonate ester other than the first carbonate ester, and at least one of the chain carbonate ester and the cyclic carbonate ester contains a halogen. The electrolyte is simple in formula, generation of dendritic crystals and damage to a negative electrode can be reduced, dissolution of metal ions is inhibited, stable positive and negative electrode films can be generated, decomposition of the electrolyte is prevented, and the electrolyte has excellent cycle performance under the high voltage of 5V.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a non-aqueous lithium battery electrolyte and a non-aqueous lithium battery. Background Technology

[0002] With the rapid advancements in electric vehicle technology, lower-cost and higher-energy-density lithium-ion batteries have become a key research focus. One effective method to improve the energy density of lithium-ion batteries is the development of high-voltage lithium-ion batteries. Currently, increasing voltage poses a significant challenge to battery electrolyte solvents. Traditional electrolyte solvents, due to their chemical windows, are easily decomposed by the electrodes when the operating voltage increases, thus accelerating electrolyte consumption and reducing battery performance. Solvents suitable for high voltage also present a series of problems, such as poor conductivity, high viscosity, and incompatibility with the negative electrode.

[0003] Patent CN105826607B discloses that by using ester dimers and fluorinated ethers, a high voltage target can be achieved, with the maximum normal operating voltage increased to 4.4V–5.0V and good cycle performance of the lithium-ion battery. However, the electrolyte composition is complex and requires the synergistic effect of multiple additives. Summary of the Invention

[0004] The purpose of this invention is to provide a non-aqueous lithium battery electrolyte and a non-aqueous lithium battery that have a simple formulation and can still have good cycle performance under high voltage.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A non-aqueous lithium battery electrolyte includes an organic solvent and a lithium salt. The organic solvent is composed of carbonate compounds, which include a first carbonate and a second carbonate. The first carbonate is dimethyl 2,5-dioxadipic acid and / or diethyl 2,5-dioxadipic acid, and the mass content of the first carbonate in the electrolyte is not less than 20%.

[0007] The second carbonate includes chain carbonates other than the first carbonate and cyclic carbonates, wherein at least one of the chain carbonates and cyclic carbonates contains a halogen.

[0008] First carbonate has high viscosity and poor solubility for lithium salts, so it is usually used as an additive and the amount added is generally no more than 20%. This invention creatively uses first carbonate as the main solvent and combines it with cyclic carbonate and chain carbonate. By adding cyclic carbonate, the viscosity and conductivity of first carbonate can be synergistically adjusted, and by adding chain carbonate, the solubility of lithium salt in the solvent system can be synergistically adjusted. Therefore, the electrolyte of this invention can significantly improve the cycle performance of lithium batteries at high voltages even without adding any additives, maintaining ultra-high cycle performance at a high voltage of 5V.

[0009] Preferably, the mass content of the first carbonate in the electrolyte is 20% to 30%, for example, 20%, 25%, or 30%.

[0010] Preferably, the mass content of the chain carbonate in the electrolyte is greater than the mass content of the cyclic carbonate in the electrolyte, and the mass content of the cyclic carbonate in the electrolyte is 10% to 30%, for example 10%, 15%, 20%, 25%, or 30%.

[0011] Preferably, the cyclic carbonate is selected from one or more of ethylene carbonate and fluoroethylene carbonate.

[0012] Preferably, the chain carbonate is selected from one or more of methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, fluoromethyl ethyl carbonate, dimethyl fluorocarbonate, diethyl fluorocarbonate, and methyl propyl fluorocarbonate.

[0013] In some embodiments, the second carbonate is fluoroethylene carbonate, methyl ethyl carbonate, and fluoromethyl ethyl carbonate, wherein the sum of the mass contents of the fluoroethylene carbonate and fluoromethyl ethyl carbonate in the electrolyte is greater than the mass content of the methyl ethyl carbonate in the electrolyte, the mass content of the fluoroethylene carbonate in the electrolyte is 10-30%, the mass content of the methyl ethyl carbonate in the electrolyte is 10-30%, and the mass content of the fluoromethyl ethyl carbonate in the electrolyte is 15-40%.

[0014] Furthermore, the mass content of the fluoroethylene carbonate in the electrolyte is A, the mass content of the methyl ethyl carbonate in the electrolyte is B, and the mass content of the fluoroethylene carbonate in the electrolyte is C, wherein A + C > 2B.

[0015] In some embodiments, the second carbonate is fluoroethylene carbonate and fluoroethyl carbonate, wherein the mass content of fluoroethyl carbonate in the electrolyte is greater than the mass content of fluoroethylene carbonate in the electrolyte, the mass content of fluoroethylene carbonate in the electrolyte is 20-30%, and the mass content of fluoroethyl carbonate in the electrolyte is 30-40%.

[0016] Preferably, the electrolyte further includes additives selected from one or more of lithium bis(trimethylsilyl)phosphate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, vinyl sulfate, vinylene carbonate, and succinic anhydride. The addition of additives can further improve battery performance.

[0017] Preferably, the additive accounts for 0.1-5% of the total mass of the electrolyte, more preferably 0.5-4%, and even more preferably 0.5-3%.

[0018] In some embodiments, the additive includes lithium bis(trimethylsilyl)phosphate, wherein the lithium bis(trimethylsilyl)phosphate is present in the electrolyte at a mass content of 1.1-2%, preferably 1.5-2%.

[0019] In some embodiments, the additive includes succinic anhydride, wherein the succinic anhydride is present in the electrolyte at a mass content of 0.1-1%, more preferably 0.4-0.6%.

[0020] In some embodiments, the additive includes lithium difluorooxalate borate, wherein the lithium difluorooxalate borate in the electrolyte is present in a mass content of 0.1-1%, more preferably 0.4-0.6%.

[0021] Preferably, the lithium salt is selected from one or more of LiPF6, LiTFSI, LiBF4, LiClO4, LiCH3SO3, LiSCN, LiNO3, LiO3SCF2CF3, LiAsF6, and LiAlCl4.

[0022] Preferably, the concentration of the lithium salt in the electrolyte is 0.5–2 mol / L, more preferably 0.5–1.5 mol / L, and even more preferably 0.8–1.2 mol / L.

[0023] The present invention also provides a non-aqueous lithium battery comprising the electrolyte as described above.

[0024] Preferably, the non-aqueous lithium battery further includes a positive electrode, a negative electrode, and a separator.

[0025] In some embodiments, the positive electrode active material is lithium nickel manganese oxide.

[0026] In some embodiments, the negative electrode active material is selected from lithium, graphite, hard carbon, soft carbon, Li-S alloy, Li-S-O alloy, Sn, SnO, SnO2 tin-based composite material, spinel-structured lithiated TiO2, Li4Ti5O 12 One or more of the following: Li-Al alloy, silicon, Li-Si alloy, Li-Si-O alloy, silicon-based composite material, and tin-silicon composite material.

[0027] In some embodiments, the diaphragm includes a substrate and a coating, wherein the substrate is made of polyethylene and / or polypropylene, and the coating is an organic material and / or a metal oxide.

[0028] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0029] The electrolyte formulation of this invention is simple, can reduce dendrite formation and damage to the negative electrode, inhibit the dissolution of metal ions, and can generate stable positive and negative electrode films, preventing electrolyte decomposition. It also has excellent cycle performance at a high voltage of 5V. Detailed Implementation

[0030] The present invention will be further described below with reference to embodiments. However, the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific applications, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0031] Unless otherwise specified, all raw materials mentioned below are commercially available products or can be prepared using existing methods. Specifically, AB-1 represents dimethyl 2,5-dioxahexanoate, AB-2 represents diethyl 2,5-dioxahexanoate, FEC represents fluoroethylene carbonate (4-fluoro-1,3-dioxolane-2-one), EMC represents methyl ethyl carbonate, FEMC represents fluoromethyl ethyl carbonate (methyltrifluoroethyl carbonate), EC represents ethylene carbonate, DFEA represents 2,2-difluoroethyl acetate, LiTMSP represents lithium bis(trimethylsilyl)phosphate, LiDFOB represents lithium difluorooxalate borate, and SA represents succinic anhydride.

[0032] Experimental group 1

[0033] A method for preparing a lithium-ion battery, comprising: preparing LiNi 0.5 Mn 1.5 O4 (LNMO), conductive additive Super-P, and binder PVDF are mixed evenly in NMP at a mass ratio of 90:5:5. The mixture is then coated onto an aluminum foil current collector, with a coating density of 360 g / m². 2A positive electrode was prepared, and a high-voltage lithium-ion battery was assembled using polyethylene (PE) as the base film (12μm) and an alumina coating (2μm) coated on both sides of the base film as a separator, and artificial graphite as the negative electrode.

[0034] Lithium salt LiPF6 was dissolved in a mixed solvent containing AB-1 / AB-2, FEC, EMC, and FEMC to obtain the basic electrolyte Base1. The mass ratios of LiPF6, AB-1 / AB-2, FEC, EMC, and FEMC in Base1 are shown in Table 1. Then, additives were selectively added to Base1 to obtain the electrolyte. The additives and their mass percentages in the electrolyte are shown in Table 1. Finally, the prepared electrolyte was injected into the aforementioned high-voltage lithium-ion battery for cycle performance testing.

[0035] Cyclic performance test method: The lithium-ion batteries obtained in the examples and comparative examples were charged and discharged at room temperature (25°C) at a rate of 0.5C within the charge and discharge dielectric voltage range (3-5V). The discharge capacity of the first week was measured as x mAh, and the discharge capacity of the Nth week was measured as y mAh. The capacity of the Nth week was divided by the capacity of the first week to obtain the cycle capacity retention rate of the Nth week, R = y / x × 100%.

[0036] Table 1

[0037]

[0038] Adding a primary carbonate (AB-1 / AB-2) to the electrolyte can improve battery cycle performance to some extent, but the improvement is limited when added in small amounts (below 20%). Increasing the primary carbonate content to 20% or more of the total mass of the base electrolyte can significantly improve battery cycle performance, but this has no effect on cycle performance when other solvents in the electrolyte are used improperly. The synergistic effect of the primary carbonate with cyclic carbonates (FEC) and chain carbonates (EMC and / or FEMC) further enhances battery cycle performance. Adding a small amount of LiTMSP to the electrolyte further improves cycle performance.

[0039] Experimental group 2

[0040] High-voltage lithium-ion batteries were prepared according to experimental group 1.

[0041] Lithium salt LiPF6 was dissolved in a mixed solvent containing the solvents shown in Table 2 to obtain the base electrolyte Base2. The mass ratio of lithium salt to each solvent in the base electrolyte Base2 is shown in Table 2. Then, additives were added to the base electrolyte Base2 to obtain the electrolyte. The mass percentage of additives in the electrolyte is shown in Table 2. Finally, the prepared electrolyte was injected into the high-voltage lithium-ion battery described above, and cycle performance tests were conducted according to Experimental Group 1.

[0042] Table 2

[0043]

[0044] As shown in Table 2, in Comparative Examples 2-1 and 2-2 containing fluorinated carboxylate esters (DFEA), the cycle retention decreased compared to Examples 1-2, 1-5, and 1-11 to 1-14 which did not contain fluorinated carboxylate esters. Therefore, it can be demonstrated that the addition of carboxylate esters does not improve battery cycle performance when the electrolyte contains more first carbonate esters, while the battery cycle performance is better when cyclic carbonate esters (FEC / EC), chain carbonate esters (EMC and / or FEMC), and first carbonate esters are used simultaneously in the organic solvent.

[0045] For Examples 2-1, which use halogen-free cyclic carbonates (EC) as solvents, and Examples 1-5 and Examples 1-11 to 1-14, which use halogen-containing cyclic carbonates (FEC), the battery cycle performance is better.

[0046] Experimental group 3

[0047] High-voltage lithium-ion batteries were prepared according to experimental group 1.

[0048] Lithium salt LiPF6 was dissolved in a mixed solvent containing AB-1, FEC, EMC, and FEMC to obtain the basic electrolyte Base3. The mass ratio of LiPF6, AB-1, FEC, EMC, and FEMC in the basic electrolyte Base3 is shown in Table 3. Then, additives were added to the basic electrolyte Base3 to obtain the electrolyte. The additives and their mass percentage in the electrolyte are shown in Table 3. Finally, the prepared electrolyte was injected into the high-voltage lithium-ion battery described above, and cycle performance tests were conducted according to Experimental Group 1.

[0049] Table 3

[0050]

[0051]

[0052] As shown in Table 3, compared to Examples 1-4 without additives, the addition of one or more of LiTMSP, LiDFOB, and SA (Examples 3-1 to 3-5) can further improve the cycle performance of the battery. For LiTMSP, when its addition amount is less than or equal to 1%, the improvement effect on battery cycle performance is not significant, so its addition amount is preferably 1.1-2%; for SA, when its addition amount is greater than or equal to 1%, the improvement effect on battery cycle performance is not significant, so its addition amount is preferably 0.3-0.8%.

[0053] The present invention has been described in detail above, with the aim of enabling those skilled in the art to understand and implement the invention. However, this description should not be construed as limiting the scope of protection of the invention. All equivalent changes or modifications made in accordance with the spirit and essence of the invention should be included within the scope of protection of the invention.

Claims

1. A nonaqueous lithium battery electrolyte comprising an organic solvent and a lithium salt, characterized in that: The organic solvent is composed of carbonate compounds, which include a first carbonate and a second carbonate. The first carbonate is dimethyl 2,5-dioxadipic acid and / or diethyl 2,5-dioxadipic acid, and the mass content of the first carbonate in the electrolyte is not less than 20%. The second carbonate includes chain carbonates other than the first carbonate and cyclic carbonates, wherein at least one of the chain carbonates and cyclic carbonates contains a halogen.

2. The non-aqueous lithium battery electrolyte according to claim 1, characterized in that: The first carbonate has a mass content of 20-30% in the electrolyte.

3. The non-aqueous lithium battery electrolyte according to claim 1, characterized in that: The mass content of the chain carbonate in the electrolyte is greater than the mass content of the cyclic carbonate in the electrolyte, and the mass content of the cyclic carbonate in the electrolyte is 10-30%.

4. The non-aqueous lithium battery electrolyte according to claim 1, characterized in that: The cyclic carbonate is selected from one or more of ethylene carbonate and fluoroethylene carbonate; and / or, The chain carbonate is selected from one or more of methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl ethyl fluorocarbonate, dimethyl fluorocarbonate, diethyl fluorocarbonate, and methyl propyl fluorocarbonate.

5. The non-aqueous lithium battery electrolyte according to claim 4, characterized in that: The second carbonate is fluoroethylene carbonate, methyl ethyl carbonate, and fluoromethyl ethyl carbonate. The sum of the mass contents of the fluoroethylene carbonate and fluoromethyl ethyl carbonate in the electrolyte is greater than the mass content of the methyl ethyl carbonate in the electrolyte. The mass content of the fluoroethylene carbonate in the electrolyte is 10-30%, the mass content of the methyl ethyl carbonate in the electrolyte is 10-30%, and the mass content of the fluoromethyl ethyl carbonate in the electrolyte is 15-40%.

6. The non-aqueous lithium battery electrolyte according to claim 4, characterized in that: The second carbonate is fluoroethylene carbonate and fluoroethyl methyl carbonate, wherein the mass content of fluoroethyl methyl carbonate in the electrolyte is greater than the mass content of fluoroethylene carbonate in the electrolyte, the mass content of fluoroethylene carbonate in the electrolyte is 20-30%, and the mass content of fluoroethyl methyl carbonate in the electrolyte is 30-40%.

7. The non-aqueous lithium battery electrolyte according to claim 1, characterized in that: The electrolyte also includes additives selected from one or more of lithium bis(trimethylsilyl)phosphate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, vinyl sulfate, vinylene carbonate, and succinic anhydride.

8. The non-aqueous lithium battery electrolyte according to claim 7, characterized in that: The additive accounts for 0.1% to 5% of the total mass of the electrolyte.

9. The non-aqueous lithium battery electrolyte according to claim 1, characterized in that: The lithium salt is selected from one or more of LiPF6, LiTFSI, LiBF4, LiClO4, LiCH3SO3, LiSCN, LiNO3, LiO3SCF2CF3, LiAsF6, and LiAlCl4; and / or, The concentration of the lithium salt in the electrolyte is 0.5–2 mol / L.

10. A non-aqueous lithium battery, characterized in that: The non-aqueous lithium battery comprises the electrolyte according to any one of claims 1 to 9.

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