High-voltage electrolyte and lithium ion battery thereof

Abstract

The invention provides a high-voltage electrolyte and a lithium ion battery thereof. The high-voltage electrolyte comprises a lithium salt, a non-aqueous organic solvent and an additive, the additive is selected from compounds with structures shown in a formula I and a formula II, and X, Y and Z are independently selected from C = O or O = S = O. The high-voltage electrolyte comprises the additives with the structures shown in the formula I and the formula II, and the high-temperature storage performance and the high-temperature cycle performance of the lithium ion battery in a high-voltage system can be effectively improved when the high-voltage electrolyte is applied to the lithium ion battery. # imgabs0 #

Description

Technical Field

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

[0002] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles and large energy storage systems due to their high energy density, long cycle life and wide operating temperature range. With the continuous advancement of technology, the demand for lithium-ion battery performance is also increasing, especially the cycle and storage performance under high voltage environment is more critical. Under high voltage conditions, the stability of the electrolyte is crucial to maintaining battery performance, because high voltage will accelerate the decomposition of the electrolyte and cause oxygen to be generated in the battery, thus affecting the cycle stability and safety of the battery.

[0003] Especially under high voltage conditions, the problem of oxygen dissolution inside the battery becomes particularly serious. The dissolution of oxygen will not only aggravate the decomposition of the electrolyte, but also lead to an increase in the internal pressure of the battery 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 batteries 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 urgently by those skilled in the art.

[0004] To overcome the above problems, new research shows that by using specific substances to improve the film quality and provide electrons to inhibit the dissolution of oxygen, the battery performance can be effectively improved. This method can not only reduce the increase in interface impedance, but also significantly improve the cycle stability and storage performance of the battery under high voltage, thereby broadening the application range of lithium-ion batteries in high voltage environments. This innovative solution provides new directions and possibilities for the technological development of lithium-ion batteries. Summary of the invention

[0005] The object of the present invention is to provide a high voltage electrolyte and a lithium ion battery thereof, wherein the high voltage electrolyte can improve the high temperature storage performance and high temperature cycle performance of the lithium ion battery under a high voltage system.

[0006] To achieve the above object, the present invention provides a high voltage electrolyte, comprising a lithium salt, a non-aqueous organic solvent and an additive, wherein the additive comprises a compound having a structure shown in Formula 1 and Formula 2:

[0007] Wherein, X, Y, and Z are each independently selected from C=O or O=S=O.

[0008] Compared with the prior art, the high-voltage electrolyte of the present invention includes a lithium salt, a non-aqueous organic solvent and an additive. The compound shown in Formula 1 can neutralize the alkalinity of the surface of the positive electrode active material particles on the surface of the positive electrode plate, inhibit the reaction of the solvent in the electrolyte on the surface of the positive electrode plate, and the compound shown in Formula 1 contains selenium, which can lose electrons preferentially compared to the oxygen of the positive electrode, thereby reducing the generation of singlet oxygen at the positive electrode, thereby reducing the oxidation of the electrolyte by singlet oxygen. The compound shown in Formula 2 contains a polycyclic structure. Its possible mechanism of action is that the polycyclic substance can reduce the SEI organic components of different polymerization degrees produced by the decomposition of organic solvents (such as EC) in the electrolyte, and directly add such substances to the electrolyte additives to form SEI components similar to macromolecular polymer networks. At the same time, such substances can be preferentially oxidized on the surface of the positive electrode plate to form a thin, uniform and dense CEI film, which can prevent the interface side reactions between the electrolyte and the positive electrode, and is conducive to the transmission of lithium ions (Li+), reducing the impedance of lithium ion batteries, thereby improving the high-temperature cycle performance and high-temperature storage performance of electrochemical devices. When the additives of the structures shown in Formula 1 and Formula 2 are added to the electrolyte at the same time, a good film is formed on the surface of the positive electrode, and the structure of the positive electrode material is protected at the same time, reducing the release of lattice oxygen. The combined effect enables the battery to operate stably at high voltage, thereby improving high-temperature cycle and high-temperature storage performance. As a preferred technical solution, at least one of X, Y, and Z is C=O and at least one of them is O=S=O.

[0009] As a preferred technical solution, the compound of the structure shown in Formula 2 of the present invention is selected from at least one of Compounds 1 to 4:

[0010] The synthesis method of compounds 1 to 4 can refer to the synthesis method in patent document CN111755753A.

[0011] As a preferred technical solution, the mass percentage of the compound of the structure shown in Formula 1 of the present invention in the high voltage electrolyte is 0.05-5%. As an example, the mass percentage of the compound of 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%, 5.0%.

[0012] As a preferred technical solution, the compound of the structure shown in Formula 2 of the present invention is in a high voltage electrolyte. The mass percentage of the compound of 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%.

[0013] As a preferred technical solution, the mass percentage of the compound with the structure shown in Formula 1 in the high-voltage electrolyte is 0.1-2%, and the mass percentage of the compound with the structure shown in Formula 2 in the high-voltage electrolyte is 0.1-4%.

[0014] As a preferred technical solution, the mass percentage of the compound with the structure shown in Formula 1 in the high-voltage electrolyte is 0.1-1%, and the mass percentage of the compound with the structure shown in Formula 2 in the high-voltage electrolyte is 0.5-2%.

[0015] 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(oxalatoborate) (C4BLiO8), lithium difluorophosphate (LiPO2F2), lithium fluorosulfonate (FLiO3S), lithium difluorobis(oxalatophosphate) (LiDODFP) and lithium bis(fluorosulfonyl imide) (LiFSI).

[0016] As a preferred technical solution, the mass percentage of the lithium salt of the present invention in the high-voltage electrolyte is 5-25%. Further, the mass percentage of the lithium salt in the high-voltage electrolyte is 8-20%. More preferably, the mass percentage of the lithium salt in the high-voltage electrolyte is 10-15%. By way of example, the mass percentage of the 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%.

[0017] As a preferred technical solution, the non-aqueous organic solvent of the present invention is selected from 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), butyl propionate (PRB), 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), At least one of 1,3-dioxolane (DOL), 1,4-dioxolane (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).

[0018] As a preferred technical solution, the mass percentage of the non-aqueous organic solvent in the high-voltage electrolyte of the present invention is 65-90%, preferably, the mass percentage of the non-aqueous organic solvent in the high-voltage electrolyte is 75-89%, and 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 may be, but is not limited to, 65%, 70%, 75%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 90%.

[0019] As a preferred technical solution, the high-voltage electrolyte of the present invention also includes an auxiliary agent, which is selected from at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propane sultone (PS), diethylene sulfate (DTD), 1,3-propylene glycol cyclosulfate (PCS), 1,4-butane sultone (1,4-BS), triallyl phosphate (TAP), and succinic anhydride (SA).

[0020] The mass percentage of the additive of the present invention in the high voltage electrolyte is 0.1-5%. By way of example, the mass percentage of the additive in the high voltage electrolyte may 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%, and 5.0%.

[0021] Another aspect of the present invention provides a lithium-ion battery, comprising a positive electrode material and a negative electrode material, and also comprising the above-mentioned high-voltage electrolyte, and the maximum charging voltage is 4.53V.

[0022] As a preferred technical solution, the positive electrode material of the present invention is selected from at least one of nickel cobalt manganese oxide, lithium cobaltate or nickel cobalt aluminum oxide. Specifically, the chemical formula of nickel cobalt manganese oxide may be LiNi x Co y Mn z M (1-x-y-z) O2; the chemical formula of nickel cobalt aluminum oxide may be LiNi x Co y Al z N (1-x-y-z) O2, where M and 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 lithium cobaltate is LiCoO2.

[0023] As a preferred technical solution, the negative electrode material of the present invention is selected from at least one of artificial graphite, natural graphite, lithium titanate, silicon carbon composite material and silicon monoxide. By way of example, the negative electrode material of the present invention is artificial graphite, but is not limited thereto. Detailed implementation manners

[0024] To better illustrate the purpose, technical solution and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the following implementation methods are further explanatory descriptions of the present invention and should not be regarded as limitations to the present invention.

[0025] Example 1 (1) Preparation of high-voltage electrolyte In a glove box filled with argon (O2 < 1 ppm, H2O < 1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed according to a weight ratio of EC:EMC:DEC = 1:1:1 to obtain 86.5 g of a non-aqueous organic solvent. Then, 0.5 g of structural formula I and 0.5 g of compound 1 were added as additives. After dissolution and thorough stirring, 12.5 g of lithium hexafluorophosphate was added. After mixing evenly, a high-voltage electrolyte was obtained.

[0026] (2) Preparation of positive electrode LiCoO2, binder PVDF, and conductive agent SuperP were mixed evenly according to a mass ratio of 95:1:4 to form a lithium-ion battery positive electrode slurry with a certain viscosity. After the mixed slurry was coated on both sides of the aluminum foil, it was dried and roll-pressed to obtain a positive electrode sheet.

[0027] (3) Preparation of negative electrode Artificial graphite, conductive agent SuperP, thickener CMC, and adhesive SBR (styrene-butadiene rubber latex) are made into slurry in a mass ratio of 95:1.5:1.0:2.5, mixed evenly, coated on both sides of copper foil with the mixed slurry, and then dried and rolled to obtain a negative electrode sheet.

[0028] (4) Preparation of lithium-ion batteries The positive electrode, the separator and the negative electrode are wound into a soft-pack battery cell, which is packaged with a polymer aluminum-plastic film and filled with the prepared lithium-ion battery high-voltage electrolyte. After the processes of formation and capacity division, a lithium-ion battery with a capacity of 4000mAh is manufactured.

[0029] The high voltage electrolyte formulations of Examples 1-13 and Comparative Examples 1-3 are shown in Table 1, wherein the steps of preparing the high voltage electrolyte and preparing the lithium ion battery in Examples 2-13 and Comparative Examples 1-3 are the same as those in Example 1.

[0030] Table 1 High voltage electrolyte formula table of Examples 1 to 13 and Comparative Examples 1 to 3

[0031] The lithium ion batteries prepared in Examples 1 to 13 and Comparative Examples 1 to 3 were subjected to high temperature storage test and high temperature cycle test respectively. The specific test conditions are as follows. The performance test results are shown in Table 2.

[0032] Lithium-ion battery high temperature storage performance test At room temperature (25°C), the lithium-ion battery is charged and discharged at 0.3C / 0.3C (the battery discharge capacity is recorded as C0), and the upper limit voltage is 4.53V; the battery is placed in a 60°C oven for 7 days, the battery is taken out, and the battery is placed in a 25°C environment for 0.3C discharge, and the discharge capacity is recorded as C1; then the lithium-ion battery is charged and discharged at 0.3C / 0.3C (the battery discharge capacity is recorded as C2), and the capacity retention rate and capacity recovery rate of the lithium-ion battery are calculated using the following formula:

[0033]

[0034] Lithium-ion battery high temperature cycle performance test Place the lithium-ion battery in a 45℃ constant temperature box and let it stand for 30 minutes to make the lithium-ion battery reach a constant temperature. Charge it at a constant current of 1C to a voltage of 4.53V, then charge it at a constant voltage of 4.53V to a current of 0.05C, and then discharge it at a constant current of 1C to a voltage of 3.0V. Record the first discharge capacity of the battery as C0, which is a charge and discharge cycle. Then charge and discharge at 2C / 1C for 300 cycles at 45℃, record the discharge capacity as C1, and use the following formula to calculate the capacity retention rate of the lithium-ion battery.

[0035]

[0036] Table 2 Performance test results of Examples 1 to 13 and Comparative Examples 1 to 3

[0037] From the results in Table 2, it can be seen that compared with Comparative Examples 1 to 3, the lithium-ion batteries of Examples 1 to 13 have more excellent high-temperature storage performance and high-temperature cycle performance at a high voltage of 4.53V. Since in the battery, the compounds 1 to 4 shown in Formula 2 can be preferentially oxidized on the surface of the positive electrode to form a thin, uniform and dense CEI film, it is beneficial to the lithium ion (Li + ) transmission, reducing the impedance of lithium-ion batteries. At the same time, the compound shown in Formula 1 can be adsorbed on cobalt ions on the surface of the positive electrode through the cyano group to inhibit the dissolution of cobalt. At the same time, when the positive electrode is deeply delithiated, its selenium atoms can provide electrons to reduce the precipitation of lattice oxygen into singlet oxygen, thereby reducing the oxidation of singlet oxygen to the electrolyte and reducing the catalytic decomposition of cobalt dissolution to the electrolyte. The simultaneous use of the compounds shown in Formula 1 and Formula 2 can work synergistically, improving the fragmentation and dissolution phenomenon on the positive electrode surface and forming a good CEI film, thereby effectively improving the high-temperature storage performance and high-temperature cycle performance of the battery at a high voltage of 4.53V.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention is described in detail with reference to the preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A high voltage electrolyte comprising a lithium salt, a non-aqueous organic solvent and an additive, characterized in that: The additive is selected from the compounds shown in Formula 1 and Formula 2: Wherein, X, Y, and Z are each independently selected from C=O or O=S=O.

2. The high voltage electrolyte according to claim 1, characterized in that: At least one of X, Y, and Z One is C=O and at least one is O=S=O.

3. The high voltage electrolyte according to claim 1, characterized in that: The compound of the structure shown in Formula 2 is selected from at least one of Compounds 1 to 4: 。 4. The high voltage electrolyte according to claim 1, characterized in that: The mass percentage of the compound of the structure represented by Formula 1 in the high-voltage electrolyte is 0.05-5%, and the mass percentage of the compound of the structure represented by Formula 2 in the high-voltage electrolyte is 0.05-5%.

5. The high voltage electrolyte according to claim 4, characterized in that: The mass percentage of the compound of the structure represented by Formula 1 in the high-voltage electrolyte is 0.1-2%, and the mass percentage of the compound of the structure represented by Formula 2 in the high-voltage electrolyte is 0.1-4%.

6. The high voltage electrolyte according to claim 1, characterized in that: The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bistrifluoromethanesulfonyl imide, lithium bisoxalatoborate, lithium difluorophosphate, lithium fluorosulfonate, lithium difluorobisoxalatophosphate and lithium bisfluorosulfonyl imide.

7. The high voltage electrolyte according to claim 1, characterized in that: 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, pentyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl 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, and diethylene glycol dimethyl ether.

8. The high voltage electrolyte according to claim 7, characterized in that: The invention also includes an auxiliary agent, which is selected from at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, vinyl sulfate, 1,3-propylene glycol 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: It also includes the high-voltage electrolyte according to any one of claims 1 to 8, and the maximum charging voltage is 4.53V.

10. The lithium ion battery according to claim 9, characterized in that: 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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