Non-aqueous electrolyte and lithium ion battery thereof

Abstract

The application provides a non-aqueous electrolyte and a lithium ion battery thereof. The non-aqueous electrolyte comprises a lithium salt, a non-aqueous organic solvent and an additive, the additive comprises a compound A shown in a structural formula I and a compound B shown in a structural formula II, wherein R1 is selected from halogen or alkylphenyl, R2, R3, R4, R5 and R6 are each independently selected from hydrogen, halogen, cyano, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted alkoxy and substituted or unsubstituted sulfonyl. The non-aqueous electrolyte of the application simultaneously comprises the compound A shown in the structural formula I and the compound B shown in the structural formula II, and through the synergistic effect of the two substances, the high-temperature storage performance and the high-temperature fast-charging cycle performance of the lithium ion battery can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a non-aqueous electrolyte and a lithium ion battery thereof. BACKGROUND

[0002] Lithium ion batteries are widely used in portable electronic devices, electric vehicles and large-scale energy storage systems due to their high energy density, long cycle life and wide operating temperature range. With the advancement of technology, people's requirements for the performance of lithium ion batteries are constantly increasing, especially the demand for fast charging performance is increasingly urgent. Fast charging performance often requires electrolyte to have high ionic conductivity, rapid lithium ion desolvation, etc.

[0003] During the charging and discharging process of lithium cobalt oxide batteries, lithium ions in the positive electrode lithium cobalt oxygen layer are deintercalated and intercalated, and reach the negative electrode through the electrolyte and the separator. During fast charging, the battery is under high current density, which can cause the electrolyte in the battery to polarize and the internal resistance to increase, so the ion movement speed in the electrolyte must be fast. At the same time, during fast charging of lithium batteries, the positive electrode material structure is often unstable, even collapses and is destroyed, and transition metal ions are dissolved to catalyze electrolyte decomposition.

[0004] Therefore, it is urgent to develop a non-aqueous electrolyte suitable for lithium cobalt oxide batteries to solve the problems of the prior art. SUMMARY

[0005] The purpose of the present application is to provide a non-aqueous electrolyte and a lithium ion battery thereof, which simultaneously contains compound A represented by structural formula I and compound B represented by structural formula II, and through the synergistic effect of the two substances, the high-temperature fast-charging cycle performance and high-temperature storage performance of the lithium ion battery can be improved.

[0006] To achieve the above purpose, the present application provides a non-aqueous electrolyte, which comprises a lithium salt, a non-aqueous organic solvent and an additive, the additive comprising compound A represented by structural formula I:

[0007]

[0008] and compound B represented by structural formula II:

[0009]

[0010] wherein R1 is selected from halogen or alkylphenyl, R2, R3, R4, R5 and R6 are each independently selected from hydrogen, halogen, cyano, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted alkoxy or substituted or unsubstituted sulfonyl.

[0011] Compared with the prior art, the non-aqueous electrolyte of the application includes a lithium salt, a non-aqueous organic solvent and an additive, the compound shown in structural formula I can neutralize the alkalinity of the surface of the positive active material particles on the surface of the positive electrode sheet, inhibit the reaction of the solvent in the electrolyte on the surface of the positive electrode sheet, and the compound shown in structural formula I contains selenium, which can preferentially lose electrons to oxygen in the positive electrode, thereby reducing the generation of singlet oxygen in the positive electrode, thereby reducing the oxidation of the electrolyte by singlet oxygen. The compound shown in structural formula II is a zwitterionic compound, which interacts with the lithium salt in the electrolyte, accelerates the dissociation of the lithium salt and the acid radical ion, thereby improving the ionic conductivity of the electrolyte, accelerating the transmission speed of lithium ions, greatly reducing the polarization internal resistance under fast charging conditions, thereby improving the fast charging performance; and due to the instability of the S-N bond in the structure of the additive, a stable S-Li bond can be generated in situ when the CEI film is formed, thereby increasing the stability of the CEI film and improving the electrical performance of the battery under high temperature conditions. In addition, the two nitrogen atoms in the structure of the additive have a certain degree of complexation with metal ions in the positive electrode material, making the structure of the positive electrode material more stable. Under the overall conditions, the combination of the two additives combines the advantages of the two additives, thereby improving the high-temperature fast-charging cycle performance and high-temperature storage performance of the lithium ion battery.

[0012] Further, R1 is selected from halogen or methylphenyl, R2, R3, R4, R5, R6 are each independently selected from hydrogen, halogen, cyano, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted C2-C10 alkynyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C1-C10 sulfonyl.

[0013] Further, R1 is selected from halogen or methylphenyl, R2, R3, R4, R5, R6 are each independently selected from hydrogen, halogen, cyano, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted C2-C10 alkynyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C1-C10 sulfonyl.

[0014] Further, the compound B of the application is selected from at least one of compounds 1-11:

[0015]

[0016]

[0017] Specifically, compound 1 can be prepared according to the following synthesis route:

[0018]

[0019] The synthesis route of compound 2-9 can refer to compound 1, which is different in that the compound with Cas number 110-86-1 in the synthesis route of compound 1 is respectively replaced by the following compounds:

[0020]

[0021]

[0022] Compound 10 can be prepared according to the following synthesis route:

[0023]

[0024] Compound 11 can be prepared according to the following synthesis route:

[0025]

[0026] Further, the mass percentage of compound A in the non-aqueous electrolyte is 0.05-5%, and the mass percentage of compound B in the non-aqueous electrolyte is 0.05-5%. As an example, the mass percentage of compound A in the non-aqueous electrolyte can be, but is not limited to, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%. The mass percentage of compound B in the non-aqueous electrolyte can be, but is not limited to, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%.

[0027] Further, the mass percentage of compound A in the non-aqueous electrolyte is 0.1-2%, and the mass percentage of compound B in the non-aqueous electrolyte is 0.1-4%.

[0028] Further, the mass percentage of compound A in the non-aqueous electrolyte is 0.1-1%, and the mass percentage of compound B in the non-aqueous electrolyte is 0.1-2%.

[0029] Further, the lithium salt of the present application is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium trifluoromethylsulfonate (LiCF3SO3), lithium bis-trifluoromethylsulfonimide (LiN(CF3SO2)2), lithium bis(oxalato)borate (C4BLiO8), lithium difluorophosphate (LiPO2F2), lithium fluorosulfonate, lithium difluoro(oxalato)borate (LiODFB), lithium lower aliphatic carboxylate, lithium difluoro dioxalato phosphate (LiDODFP), and lithium bisfluorosulfonylimide (LiFSI). The lithium lower aliphatic carboxylate includes, but is not limited to, lithium chloroborane, lithium tetraphenylborate, lithium imide salt, etc. As an example, the lithium salt is lithium hexafluorophosphate (LiPF6), but is not limited thereto. Further, the lithium salt is a mixture of lithium hexafluorophosphate and lithium bis(oxalato)borate, but is not limited thereto.

[0030] Further, the mass percentage of the lithium salt in the non-aqueous electrolyte solution of the present application is 5 to 25%, further, the mass percentage of the lithium salt in the non-aqueous electrolyte solution is 8 to 20%, more preferably, the mass percentage of the lithium salt in the non-aqueous electrolyte solution is 10 to 15%, as an example, the mass percentage of the lithium salt in the non-aqueous electrolyte solution can be, but is not limited to, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 20%, 22%, 23%, 24%, 25%.

[0031] Further, the non-aqueous organic solvent of the present application is selected from at least one of carboxylic acid ester, carbonate, and ether compound.

[0032] Specifically, the carboxylic acid ester includes, but is not limited to, at least one of γ-butyrolactone (γ-Bt), γ-valerolactone (GVL), δ-valerolactone (DVL), methyl acetate (MA), ethyl acetate (EA), ethyl propionate (EP), butyl acetate (n-Ba), propyl propionate (n-PP), butyl propionate (PRB).

[0033] Specifically, the carbonate includes, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PCA), butylene carbonate (BC), pentylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl n-propyl carbonate, ethyl n-propyl carbonate, propylene carbonate (PC).

[0034] Specifically, the ether compound includes, but is not limited to, at least one of 1,3-dioxolane (DOL), 1,4-dioxane (DX), crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), 2-trifluoromethyltetrahydrofuran (2-CF3-THF), dimethoxymethane (DMM), diethoxymethane (DEM), ethoxymethoxymethane (DCE), ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether (EDB), diethylene glycol dimethyl ether (DEGME).

[0035] Further, the mass percentage of the non-aqueous solvent in the non-aqueous electrolyte is 65-90%, preferably, the mass percentage of the non-aqueous organic solvent in the non-aqueous electrolyte is 75-89%, more preferably, the mass percentage of the non-aqueous organic solvent in the non-aqueous electrolyte is 78-88%. As an example, the mass percentage of the non-aqueous organic solvent in the non-aqueous electrolyte can be, but is not limited to, 65%, 70%, 75%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 90%.

[0036] Further, the non-aqueous electrolyte of the present application further comprises an additive, and the additive is selected from at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propane sultone (PS), vinyl sulfate (DTD), 1,3-propanediol cyclic sulfate (PCS), 1,4-butane sultone (1,4-BS), triallyl phosphate (TAP) and succinic anhydride (SA).

[0037] Further, the mass percentage of the additive in the non-aqueous electrolyte of the present application is 0.1-5%, as an example, the mass percentage of the additive in the non-aqueous electrolyte can be, but is not limited to, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%.

[0038] Another aspect of the present application provides a lithium ion battery, which comprises a positive electrode material and a negative electrode material, and further comprises the above-mentioned non-aqueous electrolyte.

[0039] Further, the positive electrode material of the present application is selected from lithium cobaltate, which has a chemical formula of LiCoO2.

[0040] Further, the negative electrode material of the present application is selected from at least one of artificial graphite, natural graphite, lithium titanate, silicon-carbon composite material and silicon monoxide. As an example, the negative electrode material is artificial graphite, but is not limited thereto. DETAILED DESCRIPTION

[0041] To better illustrate the purpose, technical solutions and beneficial effects of the present application, the present application will be further described below in conjunction with specific examples. It should be noted that the following implementation of the method is a further explanation and description of the present application, and should not be regarded as a limitation of the present application.

[0042] Example 1

[0043] (1) Preparation of non-aqueous electrolyte

[0044] In an argon-filled glove box (O2<1 ppm, H2O<1 ppm), 86.5 g of non-aqueous organic solvent was prepared by mixing ethylene carbonate (EC), methyl ethyl carbonate (EMC) and diethyl carbonate (DEC) in a weight ratio of EC: EMC: DEC = 1: 1: 1, then 0.5 g of compound A and 0.5 g of compound 1 were added as additives, and after dissolution and sufficient stirring, 12.5 g of lithium hexafluorophosphate was added, and the mixture was uniformly mixed to obtain a non-aqueous electrolyte.

[0045] (2) Preparation of positive electrode

[0046] LiCoO2, adhesive PVDF and conductive agent SuperP were mixed in a mass ratio of 95:1:4 to prepare a lithium ion battery positive electrode slurry with a certain viscosity, and then the mixed slurry was coated on both sides of an aluminum foil, dried and rolled to obtain a positive electrode sheet.

[0047] (3) Preparation of negative electrode

[0048] A slurry was prepared by mixing artificial graphite, conductive agent SuperP, thickening agent CMC and adhesive SBR (styrene-butadiene rubber emulsion) in a mass ratio of 95:1.5:1.0:2.5, and then the mixed slurry was coated on both sides of a copper foil, dried and rolled to obtain a negative electrode sheet.

[0049] (4) Preparation of lithium ion battery

[0050] The positive electrode, the separator and the negative electrode were wound to form a soft pack cell, which was packaged with a polymer aluminum plastic film, and the prepared non-aqueous electrolyte of the lithium ion battery was filled, and after processes such as formation and capacity distribution, a lithium ion battery with a capacity of 4000 mAh was prepared.

[0051] The non-aqueous electrolyte formulations of Examples 1-20 and Comparative Examples 1-3 are shown in Table 1, wherein the steps of preparing the non-aqueous electrolyte and the lithium ion battery of Examples 2-20 and Comparative Examples 1-3 are the same as those of Example 1.

[0052] Table 1 Non-aqueous electrolyte formulation table of Examples 1-20 and Comparative Examples 1-3

[0053]

[0054] The lithium ion batteries prepared from Examples 1-20 and Comparative Examples 1-3 were subjected to high-temperature storage test and high-temperature fast-charging cycle test, respectively. The specific test conditions are as follows, and the performance test results are shown in Table 2.

[0055] High temperature storage performance test

[0056] At room temperature (25°C), the lithium ion battery was subjected to one 0.3C / 0.3C charging and discharging (the battery discharge capacity was recorded as C0), and the upper limit voltage was 4.53V. The battery was placed in a 60°C oven for 7 days, and then taken out and placed in a 25°C environment. The battery was subjected to 0.3C discharging, and the discharge capacity was recorded as C1. Then the lithium ion battery was subjected to one 0.3C / 0.3C charging and discharging (the battery discharge capacity was recorded as C2). The capacity retention rate and the capacity recovery rate of the lithium ion battery were calculated using the following formula:

[0057]

[0058]

[0059] High temperature fast charging cycle performance test

[0060] The lithium ion battery was placed in a 45°C constant-temperature oven for 30 minutes, and then subjected to 2C constant-current charging to a voltage of 4.53V, followed by 4.53V constant-voltage charging to a current of 0.05C, and then 1C constant-current discharging to a voltage of 3.0V. The first-cycle discharge capacity of the battery was recorded as C0, which was one charge-discharge cycle. Then the battery was subjected to 2C / 1C charging and discharging at 45°C for 300 cycles, and the discharge capacity was recorded as C1. The capacity retention rate of the lithium ion battery was calculated using the following formula.

[0061]

[0062] Table 2 Performance test results of Examples 1-20 and Comparative Examples 1-3

[0063]

[0064] As can be seen from the results of Table 2, compared with Comparative Examples 1-3, the lithium ion batteries of Examples 1-20 have good high-temperature storage performance and high-temperature fast-charging cycle performance at a high voltage of 4.53 V. It is possible that, in the battery, the compound B shown in structural formula II is a zwitterion compound, the sulfonimide group and the pyridine ring are contained in the structure of the additive, the negative charge is mainly concentrated on the nitrogen atom connected to the sulfur atom, and the positive charge is concentrated on the nitrogen atom on the pyridine ring, and the sulfonimide group and the pyridine ring are connected by a carbonyl group, which makes the additive interact with the lithium salt in the electrolyte, accelerates the dissociation of the lithium salt and the acid radical ion, and thus improves the ionic conductivity of the electrolyte; and because of the instability of the S-N bond in the structure of the additive, it can generate a stable S-Li bond in situ when forming the SEI film, thereby increasing the stability of the SEI film; in addition, the two nitrogen atoms in the structure of the additive have a certain degree of complexation with Li + 、Co 3+ , which makes the structure of lithium cobaltate more stable. At the same time, the compound shown in structural formula I can be adsorbed on cobalt ions on the positive electrode surface through the cyano group, inhibit the dissolution of cobalt, and at the same time, the selenium atom can provide electrons to reduce the lattice oxygen to be precipitated as singlet oxygen when the positive electrode is deeply delithiated, thereby reducing the oxidation of the electrolyte by singlet oxygen and the catalytic decomposition of the electrolyte by cobalt dissolution. The use of compound A shown in structural formula I and compound B shown in structural formula II can have a synergistic effect, which can stabilize the positive electrode of the battery, improve the broken dissolution phenomenon on the positive electrode surface, form a stable CEI film, improve the conductivity of the electrolyte, and facilitate the migration of lithium ions, thereby improving the high-temperature storage performance and high-temperature fast-charging cycle performance of the battery.

[0065] Further, as can be seen from the comparison of Examples 1-11, adjusting different functional substituents on the pyridine ring will have different degrees of influence on the performance of the lithium ion battery. More specifically, when compound A is used in combination with compound 9, the performance of the lithium ion battery is optimal, which is probably because the fluorosulfonyl group introduced by compound 9 is a strong electron-withdrawing group that can make the charge on the pyridine ring more dispersed, making the structure of the compound more stable. In addition, during the charging and discharging cycle of the battery, the S-C bond is homolytically cleaved to generate a fluorosulfonyl radical, and the fluorosulfonyl radical is highly active and will capture oxygen atoms in the electrolyte solvent to generate lithium fluorosulfate. Lithium fluorosulfate has a simple molecular structure, high stability, and high conductivity, thereby improving the high-temperature performance of the lithium ion battery.

[0066] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application, and although the present application has been described in detail with reference to the preferred embodiments, it is not limited to the listed in the embodiments, and those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A nonaqueous electrolyte comprising a lithium salt, a nonaqueous organic solvent, and an additive, characterized in that, The additive includes a compound A shown in structural formula I: and a compound B shown in structural formula II: wherein R1 is selected from halogen or alkylphenyl, R2, R3, R4, R5, R6 are each independently selected from hydrogen, halogen, cyano, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted alkoxy or substituted or unsubstituted sulfonyl.

2. The nonaqueous electrolyte according to claim 1, wherein R1 is selected from halogen or methylphenyl, R2, R3, R4, R5, R6 are each independently selected from hydrogen, halogen, cyano, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted C2-C10 alkynyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C1-C10 sulfonyl.

3. The nonaqueous electrolyte according to claim 1, characterized by The compound B is selected from at least one of compounds 1-11: 。 4. The nonaqueous electrolyte according to claim 1, characterized by The mass percentage of the compound A in the non-aqueous electrolyte is 0.05-5%, and the mass percentage of the compound B in the non-aqueous electrolyte is 0.05-5%.

5. The nonaqueous electrolyte according to claim 1, wherein The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethylsulfonate, lithium bistrifluoromethylsulfonylimide, lithium bisoxalateborate, lithium difluorophosphate, lithium fluorosulfate, lithium difluorooxalateborate, lithium lower aliphatic carboxylate, lithium difluorodioxalate phosphate and lithium bisfluorosulfonylimide.

6. The non-aqueous electrolyte according to claim 5, wherein the mass percentage of the lithium salt in the non-aqueous electrolyte is 5-25%.

7. The nonaqueous electrolyte according to claim 1, wherein The non-aqueous organic solvent is selected from at least one of carboxylic acid ester, carbonate and ether compound.

8. The nonaqueous electrolyte according to claim 1, wherein The additive further includes an auxiliary agent selected from at least one of fluorinated ethylene carbonate, vinylene carbonate, 1,3-propane sultone, ethylene sulfate, 1,3-propanediol cyclic sulfate, 1,4-butane sultone, triallyl phosphate and succinic anhydride.

9. A lithium-ion battery comprising a positive electrode material and a negative electrode material, characterized in that, The non-aqueous electrolyte according to any one of claims 1-8 is further included.

10. The lithium-ion battery of claim 9, wherein, The positive electrode material is selected from lithium cobaltate.

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