Electrolyte and lithium ion battery containing the same

Abstract

The present invention relates to the technical field of lithium ion batteries, and discloses an electrolyte and a lithium ion battery containing the electrolyte. The electrolyte contains an ether solvent, an additive A and an additive B; the additive A is a compound containing an S=O bond, and the additive B is a compound having a structural formula shown in formula (1) or formula (2); R is H, an alkyl group or a halogenated alkyl group; R1, R2 and R3 are the same or different, and each is H, an alkyl group, a halogenated alkyl group, a nitro group or a formyl group, and R1, R2 and R3 are not H at the same time; the lithium ion battery containing the electrolyte has good cycle performance;

Description

Technical Field

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

[0002] Due to the need for environmental protection, the power battery industry has developed rapidly around the world, and the production and sales of lithium batteries are increasing year by year. However, as the industrialization of lithium batteries gradually matures, the existing battery system can no longer meet the needs of power batteries. Safer and higher energy density are the inevitable trends in the development of power batteries in the future.

[0003] Lithium metal anodes have become the darling of the battery industry due to their light weight and high energy density. However, lithium metal has a low potential, and there will be serious interface problems when it comes into contact with liquid or solid electrolytes.

[0004] At present, for liquid electrolytes, conventional carbonate systems cannot be used as solvents for lithium metal batteries due to their poor reduction resistance. In contrast, ether solvents have become the first choice for lithium metal batteries due to their lower reduction potential. Although ether electrolytes have good reduction resistance, they have poor oxidation resistance, and oxidation reactions cannot form a good film on the positive electrode. Therefore, people have improved the stability of the electrolyte to the positive electrode material by modifying the ether solvents.

[0005] CN110176630A discloses an electrolyte and an electrochemical device using the same, which utilizes a fluorinated ether substituted with F to improve the stability of the electrolyte to the positive electrode material. However, inevitably, the F substitution makes the reduction resistance of the solvent worse, and increases the side reaction between the solvent and metallic lithium.

[0006] CN103378370A discloses a lithium iodide organic electrolyte for lithium iron battery and its preparation method, wherein sulfone additives or carbonate solvents are added to ether solvents, and both sulfones and carbonates have the function of reducing and forming films at the negative electrode. A good protective film can indeed reduce the side reaction between the lithium metal negative electrode and the electrolyte, but this effect is very limited. The main reason is that the expansion of lithium metal during the cycle is very serious, and the charge and discharge process will be accompanied by the continuous generation and destruction of SEI.

[0007] In addition, ether solvents are also divided into monoethers and polyethers. The complexing ability between monoethers and lithium ions is weak, and desolvation is relatively easy at the electrolyte / electrode interface, but its solubility for lithium salts is too low, resulting in low lithium ion conductivity. Polyethers have a strong complexing ability with lithium ions and a large solubility for lithium salts, but desolvation is difficult at the electrolyte / electrode interface. The current solution is mainly to increase the concentration of lithium salts, resulting in high costs and poor wettability of the electrolyte to other electrode materials.

[0008] In response to the above problems, from the performance point of view, the ideal electrolyte for lithium metal batteries should be: ① able to dissolve sufficient lithium salt; ② the solvent is easily desolvated; ③ does not react with the negative electrode, and ④ can form a stable SEI film on the positive electrode surface.

[0009] Therefore, it is of great significance to research and develop an electrolyte. Summary of the invention

[0010] The purpose of the present invention is to overcome the defects of the prior art such as the side reaction between the electrolyte and the negative electrode, the poor wettability of the electrolyte to the electrode material, the difficulty in desolvation of polyether solvents or the difficulty in lithium deposition, and to provide an electrolyte and a lithium ion battery containing the electrolyte, wherein the lithium ion battery containing the electrolyte has good cycle performance.

[0011] In order to achieve the above-mentioned object, the first aspect of the present invention provides an electrolyte, wherein the electrolyte contains an ether solvent, an additive A and an additive B; wherein the additive A is a compound containing an S=O bond, and the additive B is a compound having a structural formula shown in formula (1) or formula (2);

[0012]

[0013] Wherein, in formula (1), R is H, alkyl or halogenated alkyl;

[0014] Wherein, in formula (2), R1, R2 and R3 are the same or different, and are each H, alkyl, halogenated alkyl, nitro or formyl, and R1, R2 and R3 are not H at the same time.

[0015] A second aspect of the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is the electrolyte described above.

[0016] Through the above technical solution, the present invention has the following advantages:

[0017] (1) In the present invention, since the additive B has a lower reduction potential and does not react with metallic lithium, the side reaction between the electrolyte and the negative electrode can be reduced;

[0018] (2) In the present invention, since the additive B undergoes oxidative polymerization at a relatively low oxidation potential, a polymer protective layer can be formed on the surface of the positive electrode to prevent the ether solvent used as the main solvent from being oxidized;

[0019] (3) The combined use of additive A, additive B and ether solvents in the present invention can effectively improve the coulombic efficiency of lithium metal batteries. Since additive A participates in the competitive coordination between ether solvents and lithium ions, the desolvation ability of lithium ions is improved, which can overcome the defects of difficult desolvation of polyether solvents or difficult lithium deposition. The structure of additive B has high symmetry and three phenolic sites. Compared with resorcinol or phenol, it can form a polymer film with a higher degree of polymerization and a more uniform product, slowing down the repeated rupture and generation of SEI caused by the expansion of lithium metal during the cycle. DETAILED DESCRIPTION

[0020] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0021] The first aspect of the present invention provides an electrolyte, wherein the electrolyte contains an ether solvent, an additive A and an additive B; wherein the additive A is a compound containing an S=O bond, and the additive B is a compound having a structural formula shown in formula (1) or formula (2);

[0022]

[0023] Wherein, in formula (1), R is H, alkyl or halogenated alkyl;

[0024] Wherein, in formula (2), R1, R2 and R3 are the same or different, and are each H, alkyl, halogenated alkyl, nitro or formyl, and R1, R2 and R3 are not H at the same time.

[0025] According to the present invention, the additive A containing S=O bonds has a strong ability to complex lithium ions. The combination of the additive A containing S=O bonds and the ether solvent can make the additive containing S=O bonds compete with the ether solvent to participate in the solvation of the electrolyte, but there will be a problem of poor oxidation resistance of the positive electrode. Therefore, the inventors of the present invention have found that the introduction of additive B can effectively solve this problem. On the one hand, the reduction potential of the additive B is very low, and there are few side reactions with the lithium negative electrode; on the other hand, the additive B will undergo oxidative polymerization at a relatively low oxidation potential, and can form a polymer protective layer on the surface of the positive electrode, thereby preventing the ether solvent as the main solvent from being oxidized.

[0026] According to the present invention, the inventors of the present invention have found through experiments that the additive B is:

[0027]

[0028] In the present invention, the additive B specifically defined in the present invention is selected, that is, the structure of the additive B has a high symmetry and has three phenolic sites, so that a polymer film with a higher degree of polymerization and a more uniform product can be formed.

[0029] According to the present invention, the oxidation potential of the additive B is 3.0-4.1 V, preferably 3.29-4.05 V. Specifically, for example, it can be 3.0 V, 3.29 V, 3.53 V, 3.6 V, 3.68 V, 3.9 V, 4.05 V, 4.1 V and any value in the range formed by any two of these point values.

[0030] According to the present invention, in the electrolyte, the amount of the additive B is 1-25wt% of the ether solvent, preferably 1.5-10wt%; in the present invention, if the content of additive B is too high, the film is too thick, resulting in an increase in battery impedance; if the content of additive B is too low, the film is insufficient and the integrity of the film on the positive electrode surface cannot be ensured.

[0031] The inventors of the present invention found that: in the present invention, solvent A participates in the competitive coordination between the ether solvent and lithium ions, the desolvation ability of lithium ions is improved, the structure of additive B has high symmetry and three phenolic sites, and compared with resorcinol or phenol, it can form a polymer film with a higher degree of polymerization and a more uniform product, slowing down the repeated rupture and generation of SEI caused by the expansion of lithium metal during the cycle, and the use of additives A and additives B can significantly improve the coulombic efficiency of lithium metal batteries.

[0032] According to the present invention, the additive A is selected from one or more of sulfones, sulfates, sultones and cyclic disulfonate compounds; preferably, the additive A is selected from one or more of vinyl sulfate, vinyl sulfite, 4-methyl-vinyl sulfate, 4-fluoro-vinyl sulfate, propane sultone, propene sultone, methylene disulfonate, ethylene disulfonate, sulfolane, 3-methyl sulfolane and 2,4-dimethyl sulfolane.

[0033] According to the present invention, in the electrolyte, the amount of the additive A is 1-20wt% of the ether solvent, preferably 1.5-6wt%; in the present invention, the content of the additive A is limited to the aforementioned range, which can ensure that there is enough additive A to compete with the ether solvent to form a solvate, and can minimize the side reaction between the electrolyte and metallic lithium. The reduction potential of the additive A is higher than that of the ether solvent, and too much A will increase the side reaction between the electrolyte and the negative electrode.

[0034] According to the present invention, the ether solvent is a chain ether compound containing two ether oxygen groups; preferably, the ether solvent is selected from one or more of dimethoxymethane, dimethoxyethane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether and propylene glycol dimethyl ether.

[0035] The inventors of the present invention have found that: the polyether solvents have the defect that it is difficult to desolvate or difficult to deposit lithium. In the present invention, a chain ether compound containing two etheroxy groups is used, which also belongs to the polyether solvent, but in the present invention, the electrolyte also contains additives A and additives B. The combination of additives A, additive B and the chain ether compound containing two etheroxy groups can improve desolvation, that is, it can dissolve more lithium salts, thereby overcoming the defect that it is difficult to desolvate or difficult to deposit lithium of the polyether solvents used in the prior art.

[0036] According to the present invention, the electrolyte further contains a lithium salt; preferably, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(fluorosulfonyl imide) and lithium bis(trifluoromethylsulfonyl imide).

[0037] According to the present invention, in the electrolyte, the concentration of the lithium salt in terms of Li is 0.7-3 mol / L, preferably 1.2-2.5 mol / L. In the present invention, the concentration of the lithium salt is controlled within the aforementioned range, which can not only ensure that the viscosity of the electrolyte is not too high, but also reduce the solvation effect of the solvent, reduce the co-embedding of the solvent or facilitate the deposition of lithium ions.

[0038] A second aspect of the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is the electrolyte described above.

[0039] According to the present invention, the material of the positive electrode is selected from one or more of lithium iron phosphate, lithium cobalt oxide, ternary materials and lithium manganese oxide; preferably, the material of the positive electrode is selected from one or more of lithium cobalt oxide, ternary materials and lithium iron phosphate.

[0040] According to the present invention, the material of the negative electrode is selected from one or more of metallic lithium, lithium alloys, graphite and Si-containing materials; preferably, the material of the negative electrode is selected from metallic lithium.

[0041] The present invention will be described in detail below through examples.

[0042] In the following examples and comparative examples:

[0043] (1) Cycle performance and initial efficiency testing

[0044] The lithium-ion battery was tested for charge and discharge cycles at 0.5C at 25°C with a voltage range of 3.0-4.2V.

[0045] First efficiency = first discharge capacity / first charge capacity cycle × 100%;

[0046] Capacity retention after 100 cycles = (discharge capacity after 100 cycles / initial discharge capacity) × 100%.

[0047] (2) Product Source

[0048] The additive raw materials are all commercially available products of Shanghai Jizhi Biochemical Technology Co., Ltd. The specific CAS numbers are shown in Table 1:

[0049] Table 1

[0050]

[0051]

[0052] Example 1

[0053] This embodiment is intended to illustrate a lithium-ion battery prepared using the electrolyte of the present invention.

[0054] (1) Preparation of electrolyte

[0055] In 100 g of dimethoxyethane (DME) solvent, 6 g of dried additive A, 4-methylvinyl sulfate, and 4 g of additive B were added. The oxidation potential of the additive B was 3.68 V. The structural formula of the additive B used is as follows, denoted as B1.

[0056]

[0057] Then, lithium bis(fluorosulfuryl)imide (LiFSI) was added to prepare an electrolyte with a concentration of 1.5 M, and the electrolyte was recorded as E1.

[0058] (2) Preparation of lithium-ion batteries

[0059] Lithium metal negative electrode: A 40 μm thick lithium metal strip is rolled onto a Cu current collector to obtain a negative electrode lithium metal strip, which is then cut into a 44 mm long and 20 mm wide negative electrode sheet.

[0060] The positive electrode uses LiCoO2 material. LiCoO2, acetylene black, and polyvinylidene fluoride (PVDF) are mixed in N-methylpyrrolidone at a mass ratio of 100:3:2, dispersed at high speed to make positive electrode slurry, coated on aluminum foil current collector, dried, and then die-cut into pole pieces. The positive electrode piece is 43mm long, 19mm wide, and 120μm thick.

[0061] Preparation of laminated lithium-ion battery: The cut positive and negative electrodes are alternately laminated, with a 45mm wide 9+2 ceramic separator inserted in a Z shape in the middle. The number of electrodes is 33. After being placed in an aluminum-plastic film, the edges are sealed, baked, and the electrolyte is injected to make a lithium-ion battery L1.

[0062] Example 2

[0063] This embodiment is intended to illustrate a lithium-ion battery prepared using the electrolyte of the present invention.

[0064] A lithium ion battery was prepared in the same manner as in Example 1, except that in step (1), "additive B1" was replaced with additive B2, the oxidation potential of the additive B2 was 4.05 V, and the structural formula of the additive B2 was as follows:

[0065]

[0066] The resulting lithium-ion battery was labeled L2.

[0067] Example 3

[0068] This embodiment is intended to illustrate a lithium-ion battery prepared using the electrolyte of the present invention.

[0069] A lithium ion battery was prepared in the same manner as in Example 1, except that in step (1), "additive A vinyl sulfate" was replaced by "propane sultone", and "additive B1" was replaced by additive B3, the oxidation potential of the additive B3 was 3.90 V, and the structural formula of the additive B3 was as follows:

[0070]

[0071] The resulting lithium-ion battery was labeled L3.

[0072] Example 4

[0073] This embodiment is to illustrate the lithium ion battery prepared by using the electrolyte of the present invention.

[0074] A lithium ion battery was prepared in the same manner as in Example 1, except that in step (1), "additive B1" was replaced with additive B4, the oxidation potential of the additive B4 was 3.29 V, and the structural formula of the additive B4 was as follows:

[0075]

[0076] The resulting lithium-ion battery was labeled L4.

[0077] Example 5

[0078] This embodiment is to illustrate the lithium ion battery prepared by using the electrolyte of the present invention.

[0079] A lithium ion battery was prepared in the same manner as in Example 1, except that in step (1), "additive B1" was replaced with additive B5, the oxidation potential of the additive B5 was 3.60 V, and the structural formula of the additive B5 was as follows:

[0080]

[0081] The resulting lithium-ion battery was labeled L5.

[0082] Example 6

[0083] This embodiment is to illustrate the lithium ion battery prepared by using the electrolyte of the present invention.

[0084] A lithium ion battery was prepared in the same manner as in Example 1, except that in step (1), the "additive B1" was replaced with an additive B6, the oxidation potential of the additive B6 was 3.53 V, and the structural formula of the additive B6 was as follows:

[0085]

[0086] The resulting lithium-ion battery was labeled L6.

[0087] Example 7

[0088] This embodiment is to illustrate the lithium ion battery prepared by using the electrolyte of the present invention.

[0089] A lithium ion battery was prepared in the same manner as in Example 1, except that: in step (1), "additive A is 4-methylvinyl sulfate, 6 g" was replaced with "additive A is 4-methylvinyl sulfate, 15 g";

[0090] The resulting lithium-ion battery was labeled L7.

[0091] Example 8

[0092] This embodiment is to illustrate the lithium ion battery prepared by using the electrolyte of the present invention.

[0093] A lithium ion battery was prepared in the same manner as in Example 1, except that: in step (1), "Additive B 4 g" was replaced with "Additive B 1 g";

[0094] The resulting lithium-ion battery was labeled L8.

[0095] Comparative Example 1

[0096] A lithium ion battery was prepared in the same manner as in Example 1, except that the electrolyte did not contain the additive B, and electrolyte DE1 was obtained.

[0097] The resulting lithium-ion battery was labeled DL1.

[0098] Comparative Example 2

[0099] A lithium-ion battery was prepared in the same manner as in Example 1, except that in step (1), "dimethoxyethane" was replaced with "di(trifluoromethoxy)ethane" to obtain electrolyte DE2.

[0100] The resulting lithium-ion battery was labeled DL2.

[0101] Comparative Example 3

[0102] A lithium-ion battery was prepared in the same manner as in Example 1, except that in step (1), "Additive A is 4-methylvinyl sulfate, 6 g" was replaced with "Additive A is 4-methylvinyl sulfate, 25 g" to obtain electrolyte DE3.

[0103] The resulting lithium-ion battery was labeled DL3.

[0104] Comparative Example 4

[0105] A lithium ion battery was prepared in the same manner as in Example 1, except that in step (1), "Additive B 4 g" was replaced with "Additive B 0.2 g", to prepare electrolyte DE4.

[0106] The resulting lithium-ion battery was labeled DL4.

[0107] Comparative Example 5

[0108] A lithium-ion battery was prepared in the same manner as in Example 1, except that in step (1), "concentration is 1.5 M" was replaced by "concentration is 4 M" to prepare electrolyte DE5.

[0109] The resulting lithium-ion battery was labeled DL5.

[0110] Comparative Example 6

[0111] A lithium ion battery was prepared in the same manner as in Example 1, except that in step (1), "the additive B used" was replaced by "the additive B6 used", and the structural formula of the additive B6 was as follows:

[0112]

[0113] The prepared lithium-ion battery was labeled DL6.

[0114] Test Case

[0115] The lithium ion batteries prepared in Examples 1-8 and Comparative Examples 1-6 were tested for cycle performance and initial efficiency. The results are shown in Table 2.

[0116] Table 2

[0117]

[0118]

[0119]

[0120] From the results in Table 2, we can see that:

[0121] Corresponding lithium-ion batteries were prepared using different electrolytes. From the results of the initial efficiency and cycle performance tests on the lithium-ion batteries, the performance of the lithium-ion batteries in the present invention is better than that of the lithium-ion batteries in the comparative examples.

[0122] Specifically, different additives B are added to the electrolytes of Examples 1-3, specifically:

[0123] The electrolyte of Comparative Example 1 does not contain additive B. It can be seen that the initial efficiency and capacity retention rate after 100 cycles of the lithium-ion batteries corresponding to L1-L3 are better than those of DL1. The electrolyte of Comparative Example 2 does not contain additive B, and the solvent is replaced with a highly fluorinated diether. It can be seen that the performance of DL2 is also significantly inferior to that of L1-L3. Since the highly fluorinated ether in Comparative Example 2 has stronger oxidation resistance, the capacity retention rate after 100 cycles is slightly higher than that of Comparative Example 1. However, the excessively high degree of fluorination, although the resistance to positive electrode oxidation is improved, the resistance to negative electrode reduction is reduced, and the side reactions with the electrolyte increase accordingly, resulting in the initial efficiency still being low.

[0124] From the results of Example 1 and Comparative Example 3, since the amount of additive A added in Comparative Example 3 is too large, 25g, additive A still undergoes a certain degree of reduction at the negative electrode, resulting in poor initial efficiency and cycle performance of the DL3 lithium-ion battery. From the comparison of Example 1 and Comparative Example 4, since the amount of additive B added in Comparative Example 4 is too small, a complete protective film cannot be formed at the positive electrode, so the performance of the DL4 lithium-ion battery is inferior to that of L1.

[0125] From the comparison between Example 1 and Comparative Example 5, it can be seen that in Comparative Example 5, due to the excessively high lithium salt concentration (4M), on the one hand, the viscosity of the electrolyte increases and the wettability to the electrode material becomes poor, and on the other hand, the lithium salt also undergoes a certain degree of reduction at the negative electrode. Therefore, the performance of the DL5 lithium-ion battery is not as good as that of the L1.

[0126] From the comparison between Example 1 and Comparative Example 6, it can be seen that in Comparative Example 6, pyrogallol is used as an additive. Although it has quite good lithium-ion battery performance under appropriate lithium salt concentration and additive concentration, the three hydroxyl groups of pyrogallol are close to each other and the steric hindrance during polymerization is large. Therefore, the performance of DL6 lithium-ion battery is inferior to that of L1.

[0127] From the comparison between Example 1, Example 2 and Example 4, the difference is that different additives B are used. Judging from the lithium-ion battery test data of these three additives, L3 has the best performance and L2 has the worst performance, that is, the effect of NO2 substitution is not as good as CH3 substitution. This should be related to the fact that NO2 is a strong electron-withdrawing group. After substitution, the positive electrode film-forming potential of the additive is reduced, while the stability to the negative electrode becomes worse.

[0128] From the comparison between Example 1, Example 5 and Example 6, the difference is that different additives B are used. From the lithium-ion battery test data of these three additives, L6 has the best performance, followed by L5, and L1 is the worst. This shows that the replacement of H on the phenolic group by CH3 can have a beneficial effect on the performance of lithium-ion batteries. This should be mainly because the phenolic group itself is slightly acidic. The more phenolic hydroxyl groups there are, the stronger the acidity is, and the more unfavorable it is to the performance of lithium-ion batteries.

[0129] In summary, from the comparison between Example 1, Example 2 and Example 4, and from the comparison between Example 1, Example 5 and Example 6, whether it is the substitution of H on the phenolic group or the substitution of the benzene ring on the pyrogallol, the introduction of electron-donating groups can often bring better results. This is mainly because the introduction of electron-donating groups can reduce the oxidation potential, which is beneficial for the additive to form a film on the positive electrode as early as possible. At the same time, the substituted additive is also resistant to negative electrode reduction.

[0130] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. An electrolyte, characterized in that: The electrolyte contains an ether solvent, an additive A and an additive B; wherein the additive A is a compound containing an S=O bond, and the additive B is a compound having a structure represented by formula (1) or formula (2); Wherein, in formula (1), R is H, alkyl or halogenated alkyl; Wherein, in formula (2), R1, R2 and R3 are the same or different, and are each H, alkyl, haloalkyl, nitro or formyl, and R1, R2 and R3 are not H at the same time; The amount of the additive A is 1-20 wt % of the ether solvent, and the amount of the additive B is 1-25 wt % of the ether solvent.

2. The electrolyte according to claim 1, wherein The additive B is:

3. The electrolyte according to claim 1 or 2, wherein In the electrolyte, the amount of the additive B is 1.5-10 wt % of the ether solvent.

4. The electrolyte according to claim 1, wherein The additive A is selected from one or more of sulfones, sulfates, sultones and cyclic disulfonate compounds.

5. The electrolyte according to claim 4, wherein The additive A is selected from one or more of vinyl sulfate, vinyl sulfite, 4-methyl-vinyl sulfate, 4-fluoro-vinyl sulfate, propane sultone, propene sultone, methylene disulfonate, ethylene dimethyl disulfonate, sulfolane, 3-methylsulfolane and 2,4-dimethylsulfolane.

6. The electrolyte according to claim 1 or 5, wherein In the electrolyte, the amount of the additive A is 1.5-6 wt % of the ether solvent.

7. The electrolyte according to claim 1, wherein The ether solvent is a chain ether compound containing two ether oxygen groups.

8. The electrolyte according to claim 7, wherein The ether solvent is selected from one or more of dimethoxymethane, dimethoxyethane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether and propylene glycol dimethyl ether.

9. The electrolyte according to claim 1, wherein The electrolyte also contains a lithium salt.

10. The electrolyte according to claim 9, wherein The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(fluorosulfonyl imide) and lithium bis(trifluoromethylsulfonyl imide).

11. The electrolyte according to claim 10, wherein In the electrolyte, the concentration of the lithium salt in terms of Li is 0.7-3 mol / L.

12. A lithium ion battery, comprising a positive electrode, a negative electrode and an electrolyte, characterized in that: The electrolyte is the electrolyte described in any one of claims 1 to 11.

13. The lithium ion battery according to claim 12, wherein: The material of the positive electrode is selected from one or more of lithium iron phosphate, lithium cobalt oxide, ternary material, lithium manganese phosphate and lithium manganese oxide.

14. The lithium ion battery according to claim 13, wherein: The material of the positive electrode is selected from one or more of lithium cobalt oxide, ternary materials and lithium iron phosphate.

15. The lithium ion battery according to claim 12, wherein: The material of the negative electrode is selected from one or more of metallic lithium, lithium alloy, graphite and Si-containing materials.

16. The lithium ion battery according to claim 15, wherein: The material of the negative electrode is metallic lithium.

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