High voltage electrolyte and lithium ion battery thereof

Abstract

The application provides a high-voltage electrolyte and a lithium ion battery thereof. The high-voltage electrolyte comprises a lithium salt, a nonaqueous organic solvent and an additive, and the additive is selected from compounds with structures shown in formula I and formula II, wherein X, Y, Z are each independently selected from C=O or O=S=O. The additive with the structure shown in formula I and formula II is included in the high-voltage electrolyte of the application, and when the additive is applied to a lithium ion battery, the high-temperature storage performance and the high-temperature cycle performance of the lithium ion battery under a high-voltage system can be effectively improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a high-voltage 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 continuous progress of technology, the demand for lithium ion battery performance is also increasing, especially the cycle and storage performance under high voltage. Under high voltage conditions, the stability of the electrolyte is crucial to maintaining battery performance, because high voltage can accelerate the decomposition of the electrolyte and cause oxygen to be generated inside the battery, thereby affecting the cycle stability and safety of the battery.

[0003] Particularly under high voltage conditions, the problem of oxygen evolution inside the battery becomes particularly serious. The evolution of oxygen not only exacerbates the decomposition of the electrolyte, but also leads to an increase in internal pressure and an increase in the risk of thermal runaway. In addition, the increase in interfacial impedance after film formation and the insufficient stability of some additives under high voltage also limit the application of the battery under high voltage conditions. Therefore, improving the high-voltage cycle performance and high-voltage storage performance of lithium ion batteries has become a technical problem that needs to be solved by those skilled in the art.

[0004] To overcome the above problems, new research shows that by using specific substances to improve film quality and provide electrons to inhibit the evolution of oxygen, the performance of the battery can be effectively improved. This method not only reduces the increase in interfacial impedance, but also significantly improves the cycle stability and storage performance of the battery under high voltage, thereby widening the application range of lithium ion batteries in high voltage environments. This innovative solution provides a new direction and possibility for the technical development of lithium ion batteries. SUMMARY

[0005] The purpose of the present application is to provide a high-voltage electrolyte and a lithium ion battery thereof, which can improve the high-temperature storage performance and high-temperature cycle performance of lithium ion batteries under high-voltage systems.

[0006] To achieve the above-mentioned purpose, the present application provides a high-voltage electrolyte, which comprises a lithium salt, a non-aqueous organic solvent and an additive, and the additive comprises a compound having the structure shown in Formula I and Formula II:

[0007]

[0008] wherein X, Y and Z are each independently selected from C=O or O=S=O.

[0009] Compared with the prior art, the high-voltage electrolyte of the application includes a lithium salt, a non-aqueous organic solvent and an additive, the compound shown in 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 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 singlet oxygen to the electrolyte. The compound shown in formula II contains a polycyclic structure. The possible mechanism of action is that this polycyclic substance can reduce the SEI organic components of different polymerization degrees generated by the decomposition of the organic solvent (such as EC) in the electrolyte, directly adding such substances to the electrolyte additives to form a SEI film similar to a macromolecular polymer network, at the same time, such substances can be preferentially oxidized on the surface of the positive electrode sheet to form a thin and uniform dense CEI film, which can prevent the interface side reaction of the electrolyte and the positive electrode, and is beneficial to the transmission of lithium ions (Li+), thereby reducing the impedance of the lithium ion battery, thereby improving the high-temperature cycle performance and high-temperature storage performance of the electrochemical device. When the additives with the structures shown in formula I and formula II are added to the electrolyte at the same time, a good film is formed on the surface of the positive electrode, and at the same time, the structure of the positive electrode material is protected, the release of lattice oxygen is reduced, and the battery can be stably operated at high voltage, thereby improving the high-temperature cycle and high-temperature storage performance.

[0010] As a preferred technical solution, at least one of X, Y and Z is C=O and at least one is O=S=O.

[0011] As a preferred technical solution, the compound with the structure shown in formula II in the application is selected from at least one of compound 1 to compound 4:

[0012]

[0013] The synthesis method of compounds 1-4 can refer to the synthesis method in the patent document CN111755753A.

[0014] As a preferred technical solution, the mass percentage of the compound with the structure shown in formula I in the high-voltage electrolyte is 0.05-5%. As an example, the mass percentage of the compound with the structure shown in formula I in the high-voltage 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%.

[0015] As a preferred technical solution, the mass percentage of the compound with the structure shown in formula II in the high-voltage electrolyte is 0.05-5%.

[0016] The mass percentage is 0.05% to 5%. As an example, the mass percentage of the compound with the structure shown in Formula 1 in the high-voltage electrolyte may 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%, and 5.0%.

[0017] As a preferred technical solution, the compound with the structure shown in Formula 1 has a mass percentage of 0.1~2% in the high-voltage electrolyte, and the compound with the structure shown in Formula 2 has a mass percentage of 0.1~4% in the high-voltage electrolyte.

[0018] As a preferred technical solution, the compound with the structure shown in Formula 1 has a mass percentage of 0.1~1% in the high-voltage electrolyte, and the compound with the structure shown in Formula 2 has a mass percentage of 0.5~2% in the high-voltage electrolyte.

[0019] As a preferred technical solution, the lithium salt of the present invention is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2), lithium bis(oxalateborate) (C4BLiO8), lithium difluorophosphate (LiPO2F2), lithium fluorosulfonate (FLiO3S), lithium difluorodioxalate phosphate (LiDODFP), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0020] As a preferred technical solution, the lithium salt in the high-voltage electrolyte of the present invention has a mass percentage of 5-25%, further, the lithium salt has a mass percentage of 8-20%, and more preferably, the lithium salt has a mass percentage of 10-15%. As an example, the mass percentage of lithium salt in the high-voltage electrolyte may be, but is not limited to, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 20%, 22%, 23%, 24%, and 25%.

[0021] As a preferred technical scheme, the non-aqueous organic solvent is 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 (PP), propyl butylate (PRB), ethylene carbonate (EC), propylene carbonate (PCA), butylene carbonate (BC), pentylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), methyl n-propyl carbonate, ethyl n-propyl carbonate, propylene carbonate (PC), 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), and diethylene glycol dimethyl ether (DEGME).

[0022] As a preferred technical scheme, the mass percentage of the non-aqueous organic solvent in the high-voltage electrolyte is 65-90%, preferably, the mass percentage of the non-aqueous organic solvent in the high-voltage electrolyte is 75-89%, more preferably, the mass percentage of the non-aqueous organic solvent in the high-voltage electrolyte is 78-88%. As an example, the mass percentage of the non-aqueous organic solvent in the high-voltage electrolyte can be, but is not limited to, 65%, 70%, 75%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 90%.

[0023] As a preferred technical scheme, the high-voltage electrolyte of the application further comprises an additive, and the additive is at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propane sulfone lactone (PS), ethylene sulfate (DTD), 1,3-propanediol cyclic sulfate (PCS), 1,4-butane sulfone lactone (1,4-BS), triallyl phosphate (TAP), and succinic anhydride (SA).

[0024] The mass percentage of the additive in the high-voltage electrolyte of the application is 0.1-5%, as an example, the mass percentage of the additive in the high-voltage 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%.

[0025] Another aspect of the application provides a lithium ion battery, which comprises a positive electrode material and a negative electrode material, further comprises the high-voltage electrolyte described above, and the maximum charging voltage is 4.53 V.

[0026] As a preferred technical solution, the positive electrode material of the present application is selected from at least one of nickel cobalt manganese oxide, lithium cobaltate or nickel cobalt aluminum oxide. Specifically, the chemical formula of the nickel cobalt manganese oxide can be LiNi x Co y Mn z M (1-x-y-z) O2; the chemical formula of the nickel cobalt aluminum oxide can be LiNi x Co y Al z N (1-x-y-z) O2, wherein M, N are each independently selected from at least one of Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V and Ti, 0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z ≤ 1; the chemical formula of the lithium cobaltate is LiCoO2.

[0027] As a preferred technical solution, 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 of the present application is artificial graphite, but is not limited thereto. DETAILED DESCRIPTION

[0028] In order to better illustrate the purpose, technical solution 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.

[0029] Example 1

[0030] (1) Preparation of high-voltage electrolyte

[0031] In an argon-filled glove box (O2<1 ppm, H2O<1 ppm), ethylene carbonate (EC), methyl ethyl carbonate (EMC) and diethyl carbonate (DEC) were mixed in a weight ratio of EC: EMC: DEC = 1: 1: 1 to prepare 86.5 g of non-aqueous organic solvent, then 0.5 g of structural formula I and 0.5 g of compound 1 were added as additives, dissolved and fully stirred, then 12.5 g of lithium hexafluorophosphate was added, and the mixture was uniformly mixed to obtain a high-voltage electrolyte.

[0032] (2) Preparation of positive electrode

[0033] 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, the mixed slurry was coated on both sides of an aluminum foil, then dried and rolled to obtain a positive electrode sheet.

[0034] (3) Preparation of negative electrode

[0035] The artificial graphite, conductive agent Super P, thickening agent CMC, and adhesive SBR (styrene-butadiene rubber emulsion) are mixed in a mass ratio of 95:1.5:1.0:2.5 to form a slurry, which is uniformly mixed. After the mixed slurry is coated on both sides of a copper foil, the copper foil is dried and rolled to obtain a negative electrode sheet.

[0036] (4) Preparation of a lithium ion battery

[0037] The positive electrode, the separator, and the negative electrode are wound to form a soft-pack battery cell, which is packaged with a polymer aluminum-plastic film. The high-voltage electrolyte prepared above is filled into the soft-pack battery cell. After a formation process and a capacity distribution process, a lithium ion battery with a capacity of 4000 mAh is prepared.

[0038] The high-voltage electrolyte formulations of Examples 1-13 and Comparative Examples 1-3 are shown in Table 1. The steps of preparing the high-voltage electrolyte and the lithium ion battery of Examples 2-13 and Comparative Examples 1-3 are the same as those of Example 1.

[0039] Table 1: High-voltage electrolyte formulations of Examples 1-13 and Comparative Examples 1-3

[0040]

[0041] The lithium ion batteries prepared in Examples 1-13 and Comparative Examples 1-3 are subjected to high-temperature storage tests and high-temperature cycle tests, respectively. The specific test conditions are as follows, and the performance test results are shown in Table 2.

[0042] Lithium ion battery high temperature storage performance test

[0043] At room temperature (25°C), the lithium ion battery is subjected to one 0.3C / 0.3C charge and discharge (the battery discharge capacity is recorded as C0), and the upper limit voltage is 4.53 V. The battery is placed in a 60°C oven for 7 days, and then taken out and placed in a 25°C environment for 0.3C discharge. The discharge capacity is recorded as C1. The lithium ion battery is then subjected to one 0.3C / 0.3C charge and discharge (the battery discharge capacity is recorded as C2). The capacity retention rate and the capacity recovery rate of the lithium ion battery are calculated using the following formula:

[0044]

[0045]

[0046] Lithium ion battery high temperature cycle performance test

[0047] The lithium ion battery was placed in a 45℃ constant temperature oven, and was allowed to stand for 30 minutes to reach a constant temperature. The lithium ion battery was charged at 1C constant current to 4.53V, then charged at 4.53V constant voltage to 0.05C, then discharged at 1C constant current to 3.0V, and the first circle discharge capacity of the battery was recorded as C0, which was one charge-discharge cycle. Then the 2C / 1C charge and discharge were carried out at 45℃ 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.

[0048]

[0049] Table 2 Performance test results of examples 1-13 and comparative examples 1-3

[0050]

[0051] From the results in Table 2, it can be seen that the lithium ion batteries of examples 1-13 have more excellent high-temperature storage performance and high-temperature cycle performance at 4.53V high voltage compared with comparative examples 1-3. Since in the battery, compounds 1-4 shown in formula two can be preferentially oxidized on the surface of the positive electrode sheet to form a thin and uniform and dense CEI film, which is conducive to the transmission of lithium ions (Li + ), and reduces the impedance of the lithium ion battery. At the same time, the compound shown in formula one can be adsorbed on cobalt ions on the positive electrode surface through the cyano group, inhibiting the dissolution of cobalt, and at the same time, when the positive electrode is deeply delithiated, the selenium atom can provide electrons to reduce the lattice oxygen to singlet oxygen, thereby reducing the oxidation of the electrolyte by singlet oxygen and the catalytic decomposition of the electrolyte by cobalt dissolution. The use of compounds shown in formula one and formula two can have a synergistic effect, which can improve the broken dissolution phenomenon on the surface of the positive electrode and form a good CEI film, thereby effectively improving the high-temperature storage performance and high-temperature cycle performance of the battery at 4.53V high voltage.

[0052] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not intended to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, it is not limited to the examples listed in the embodiments. Those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A high voltage electrolyte comprising a lithium salt, a nonaqueous organic solvent and an additive, characterized in that, The additive comprises a compound of a structure shown in Formula I and Formula II: At least one of X, Y, Z is C=O and at least one is O=S=O.

2. The high voltage electrolyte of claim 1, wherein, The compound of the structure shown in Formula II is selected from at least one of Compound 1~Compound 4: 。 3. The high voltage electrolyte of claim 1, wherein, The mass percentage of the compound of the structure shown in Formula I in the high-voltage electrolyte is 0.05~5%, and the mass percentage of the compound of the structure shown in Formula II in the high-voltage electrolyte is 0.05~5%.

4. The high voltage electrolyte of claim 3, wherein, The mass percentage of the compound of the structure shown in Formula I in the high-voltage electrolyte is 0.1~2%, and the mass percentage of the compound of the structure shown in Formula II in the high-voltage electrolyte is 0.1~4%.

5. The high voltage electrolyte of claim 1, wherein, The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethylsulfonate, lithium bis-trifluoromethylsulfonimide, lithium bis(oxalato)borate, lithium difluorophosphate, lithium fluorosulfonate, lithium difluorodioxalate phosphate, and lithium bisfluorosulfonimide.

6. The high voltage electrolyte of claim 1, wherein, The non-aqueous organic solvent is selected from at least one of γ-butyrolactone, γ-valerolactone, δ-valerolactone, methyl acetate, ethyl acetate, ethyl propionate, butyl acetate, propyl propionate, butyl propionate, ethylene carbonate, propylene carbonate, butylene carbonate, pentylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl n-propyl carbonate, ethyl n-propyl carbonate, propylene carbonate, 1,3-dioxolane, 1,4-dioxane, crown ether, tetrahydrofuran, 2-methyltetrahydrofuran, 2-trifluoromethyltetrahydrofuran, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol dimethyl ether.

7. The high voltage electrolyte of claim 1, wherein, The assistant also includes at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sulfone lactone, ethylene sulfate, 1,3-propanediol cyclic sulfate, 1,4-butane sulfone lactone, triallyl phosphate, succinic anhydride.

8. A lithium-ion battery comprising a positive electrode material and a negative electrode material, characterized in that, The high-voltage electrolyte also includes at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sulfone lactone, ethylene sulfate, 1,3-propanediol cyclic sulfate, 1,4-butane sulfone lactone, triallyl phosphate, succinic anhydride.

9. The lithium-ion battery of claim 8, wherein, The positive electrode material is selected from at least one of nickel cobalt manganese oxide, lithium cobaltate, or nickel cobalt aluminum oxide.

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