Non-aqueous electrolyte and lithium ion battery containing the same

Abstract

The application discloses a non-aqueous electrolyte, which comprises a lithium salt, a non-aqueous organic solvent and an additive, wherein the additive is a compound as shown in structural formula 1 and / or structural formula 2, R1, R2, R3, R4 and R5 are each independently selected from alkyl with 1-4 carbon atoms and hydrogen, and X is selected from O, S, N and halogen. The additive contains an in-cyclic double bond and adjacent ester groups. In a high-pressure charged state, the structure material preferentially undergoes ring-opening reaction to form a double bond radical, the radical is easy to undergo polymerization reaction with the adjacent ester groups to form a 'net-like' material with different polymerization degrees, and the 'net-like' material is attached to a solid electrolyte interface position. The 'net-like' structure of different polymers can slow down decomposition of the electrolyte caused by material expansion and reduce the dissolution effect of excessive metals, and improve high-temperature storage and high-temperature cycle performance of a non-aqueous electrolyte lithium ion battery. The application further provides a lithium ion battery containing the non-aqueous electrolyte.

Description

Technical Field

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

[0002] Lithium-ion batteries are favored by the market due to their high energy density and low self-discharge. Among them, lithium-ion rechargeable batteries (lithium rechargeable batteries with layered oxide as the main positive electrode material) are widely used because of their large capacity, fast charging speed, and high cycle life. Recent studies have shown that the main reason for the shortened lifespan of lithium-ion rechargeable batteries is that the electrodes are prone to side reactions with the non-aqueous electrolyte under the high temperature and pressure environment inside the battery. These side reactions consume the active materials in the electrode material and the solvent components in the electrolyte. Simultaneously, the gas generated by the side reactions leads to battery volume expansion and overall electrical performance degradation. These side reactions are intertwined and mutually interfere with each other, easily causing battery performance degradation and shortened calendar life. Currently, the main approach to solving the battery problems from the electrolyte perspective is to add functional additives with stabilizing effects to the non-aqueous electrolyte, such as fluorobenzene, cyclohexylbenzene, and cyclohexylfluorobenzene, to inhibit the reaction between the electrode and the non-aqueous electrolyte. However, these stabilizing additives have high viscosity, significantly reducing the fluidity of the electrolyte, thereby affecting the ion transport rate in the electrolyte and reducing battery performance. Summary of the Invention

[0003] The purpose of this invention is to provide a non-aqueous electrolyte that can improve the high-temperature storage performance, high-temperature cycle performance, and low-temperature discharge performance of lithium-ion batteries under high-voltage systems.

[0004] To achieve the above objectives, the present invention provides a non-aqueous electrolyte comprising a lithium salt, a non-aqueous organic solvent, and additives, wherein the additives are compounds represented by structural formula 1 and / or structural formula 2.

[0005]

[0006] Structural Formula 1

[0007]

[0008] Structural Formula 2

[0009] R1, R2, R3, R4, and R5 are each independently selected from alkyl groups with 1 to 4 carbon atoms and hydrogen atoms, and X is selected from O, S, N, and halogen.

[0010] Compared with the prior art, the non-aqueous electrolyte of the present invention includes a lithium salt, a non-aqueous organic solvent, and an additive. The additive is a compound shown in structural formula 1 and / or structural formula 2. The additive contains an intracyclic double bond and an adjacent ester group. Under high voltage charging state, this structure will preferentially undergo a ring-opening reaction to form a double-bonded free radical. This free radical readily undergoes a polymerization reaction with the adjacent ester group to form a "network" material with different degrees of polymerization, which adheres to the solid electrolyte interface. This "network" structure of different polymers can slow down the decomposition of the electrolyte caused by the expansion of the material and reduce the dissolution effect of excess metals, thereby improving the high-temperature storage and high-temperature cycling performance of the non-aqueous electrolyte lithium-ion battery.

[0011] It is understood that the alkyl groups with 1-4 carbon atoms in R1-R5 can be straight-chain, branched, or cyclic alkyl groups. This invention does not limit them. For example, specific examples include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, neopentyl, sec-pentyl, tert-pentyl, n-hexyl, 2-hexyl, etc., but are not limited to these.

[0012] It is understood that R1, R2, R3, R4, and R5 can be the same or different. Preferably, R1, R2, R3, and R4 are selected from the same groups so that structural formula 1 or structural formula 2 can have a symmetrical structure, thereby improving its stability.

[0013] It is understandable that halogens are one of F, Cl, and Br, but are not limited to these.

[0014] In some embodiments, the compound represented by structural formula 2 is selected from at least one of compound 11, compound 12, compound 13, and compound 14.

[0015]

[0016] Compound 11 (CAS: 1710-1-7)

[0017]

[0018] Compound 12 (CAS: 20416-03-9)

[0019]

[0020] Compound 13 (CAS: 6579-15-3)

[0021]

[0022] Compound 14 (CAS: 1186078-10-3).

[0023] In some embodiments, the compound represented by structural formula 1 is selected from at least one of compound 21 and compound 22.

[0024]

[0025] Compound 21 (CAS: 2703-15-3)

[0026]

[0027] Compound 22 (CAS: 66405-70-7).

[0028] In some embodiments, the mass percentage of the additive of the present invention in the non-aqueous electrolyte is 0.05-5%, preferably 0.1-4%, and more preferably 0.1-3%. As an example, the mass percentage of the additive in the non-aqueous electrolyte may be, but is not limited to, 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, or 3%.

[0029] In some embodiments, the mass percentage of the lithium salt in the non-aqueous electrolyte is 5-20%, preferably 8-15%, and more preferably 10-15%. As an example, the mass percentage of the lithium salt in the non-aqueous electrolyte may be, but is not limited to, 10%, 11%, 12%, 13%, 14%, or 15%.

[0030] In some embodiments, the lithium salt of the present invention is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate, lithium difluorooxalatoborate, lithium difluorodi(oxalato)phosphate, and lithium bis(fluorosulfonyl)imide. As an example, the lithium salt is lithium hexafluorophosphate (LiPF6) or lithium bis(oxalato)borate (LiBOB). In a preferred embodiment, the lithium salt is a mixture of two or more compounds, such as a mixture of lithium hexafluorophosphate (LiPF6) and lithium bis(oxalato)borate (LiBOB), or a mixture of lithium hexafluorophosphate and lithium trifluoromethanesulfonate, which can achieve better high-temperature cycling performance.

[0031] In some embodiments, the non-aqueous organic solvent of the present invention is at least one of chain carbonates, cyclic carbonates, carboxylic acid esters, fluorinated ethers, fluorinated carbonates, fluorinated carboxylic acid esters, and fluorinated sulfones. Further, the non-aqueous organic solvent is selected from ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), n-butyl acetate (n-Ba), γ-butyrolactone (γ-Bt), n-propyl propionate (n-PP), ethyl propionate (EP), ethyl butyrate (Eb), dimethyl fluorocarbonate, diethyl fluorocarbonate, fluoroethylene carbonate, n-propyl fluoropropionate, ethyl fluoropropionate, fluoropropylene carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, ethyl fluorobutyrate, fluorosulfonate, dimethyl difluorocarbonate, diethyl difluorocarbonate, difluoroethylene carbonate.

[0032] In some embodiments, the mass percentage of the non-aqueous organic solvent in the non-aqueous electrolyte of the present invention is 65-90%, preferably 70-88%, and more preferably 80-88%. As an example, the mass percentage of the non-aqueous organic solvent in the non-aqueous electrolyte can be, but is not limited to, 80%, 82%, 85%, 86%, 87%, 88%.

[0033] Correspondingly, the present invention also provides a lithium-ion battery, including a positive electrode material, a negative electrode material, and the above non-aqueous electrolyte. Due to the inclusion of this non-aqueous electrolyte, the lithium-ion battery has good high-temperature storage performance, high-temperature cycling performance, and low-temperature discharge performance.

[0034] In some embodiments, the positive electrode material is at least one of lithium cobalt oxide, nickel cobalt manganese oxide, or nickel cobalt aluminum oxide.

[0035] Among them, the chemical formula of nickel cobalt manganese oxide is LiNi

[0036] , Co y Mn z M (1-x-y-z) O2; the chemical formula of nickel cobalt aluminum oxide is 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, and x + y + z ≤ 1; the chemical formula of lithium cobalt oxide is LiCoO2.

[0036] In some embodiments, 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 suboxide. Detailed Implementation

[0037] To better illustrate the purpose, technical solution, and beneficial effects of the present invention, specific embodiments are provided below to further illustrate the purpose, technical solution, and beneficial effects of the present invention. However, these embodiments do not constitute any limitation on the present invention. Unless otherwise specified, specific conditions may be followed according to conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the reagents or instruments used are all conventional products that can be obtained commercially.

[0038] Example 1

[0039] (1) Preparation of non-aqueous electrolyte

[0040] In an argon-filled glove box (O2 < 1 ppm, H2O < 1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a weight ratio of EC:EMC:DEC = 1:1:1 to obtain 87 g of non-aqueous organic solvent. Then, 0.5 g of compound 11 was added as an additive, dissolved, and stirred thoroughly. After that, 12.5 g of lithium hexafluorophosphate was added and mixed evenly to obtain a non-aqueous electrolyte.

[0041] (2) Preparation of positive electrode

[0042] LiCoO2, binder PVDF and conductive agent SuperP are mixed evenly at a mass ratio of 95:1:4 to prepare a lithium-ion battery positive electrode slurry with a certain viscosity. The mixed slurry is coated on both sides of aluminum foil, dried and rolled to obtain the positive electrode sheet.

[0043] (3) Preparation of negative electrode

[0044] Artificial graphite was mixed with conductive agent SuperP, thickener CMC, and binder SBR (styrene-butadiene rubber latex) in a mass ratio of 95:1.5:1.0:2.5 to form a slurry. The mixture was then coated on both sides of copper foil, dried, and rolled to obtain the negative electrode sheet.

[0045] (4) Preparation of lithium-ion batteries

[0046] The positive electrode, separator, and negative electrode are wound together to form a soft-pack battery cell, which is then packaged in a polymer aluminum-plastic film and filled with the prepared non-aqueous electrolyte for lithium-ion batteries. After formation, capacity testing, and other processes, a lithium-ion battery with a capacity of 4920mAh is produced.

[0047] The non-aqueous electrolyte formulations for Examples 2-11 and Comparative Examples 1-2 are shown in Table 1. The steps for preparing the electrolyte and manufacturing the battery are the same as in Example 1.

[0048] Table 1 Formulation of non-aqueous electrolyte

[0049]

[0050] The lithium-ion batteries prepared in Examples 1-11 and Comparative Examples 1-2 were subjected to low-temperature discharge performance tests, high-temperature storage tests, and high-temperature cycling tests, respectively. The specific test conditions are as follows, and the performance test results are shown in Table 2.

[0051] Low temperature discharge performance test of lithium ion battery

[0052] Under normal temperature (25℃) conditions, a lithium-ion battery is subjected to a single 0.5C / 0.5C charge and discharge cycle (discharge capacity denoted as C0), with an upper limit voltage of 4.53V. The battery is then charged to 4.53V under constant current and constant voltage conditions at 0.5C. The lithium-ion battery is then placed in a -20℃ low-temperature chamber for 6 hours and discharged at -20℃ at 0.5C (discharge capacity denoted as C1). The low-temperature discharge rate of the lithium-ion battery is calculated using the following formula:

[0053] Low-temperature discharge rate = (C1 / C0) * 100%

[0054] High temperature storage performance test of lithium ion battery

[0055] Under normal temperature (25℃) conditions, a lithium-ion battery was subjected to one 0.3C / 0.3C charge and discharge cycle (battery discharge capacity recorded as C0), with an upper limit voltage of 4.53V. The battery was then placed in an 85℃ oven for 12 hours, removed, and placed in a 25℃ environment for a 0.3C discharge, with the discharge capacity recorded as C1. Finally, the lithium-ion battery was subjected to one 0.3C / 0.3C charge and discharge cycle (battery discharge capacity recorded as C2). The capacity retention rate and capacity recovery rate of the lithium-ion battery were calculated using the following formulas:

[0056] Capacity retention rate = (C1 / C0) * 100%

[0057] Capacity recovery rate = (C2 / C0) * 100%

[0058] High temperature cycle performance test of lithium ion battery

[0059] Place the lithium-ion battery in a 45°C constant temperature chamber and let it stand for 30 minutes to allow the battery temperature to reach the set temperature. Charge the battery at a constant current of 1C until the voltage reaches 4.53V, then charge it at a constant voltage of 4.53V until the current reaches 0.05C, and then discharge it at a constant current of 1C until the voltage reaches 3.0V. Record the first discharge capacity of the battery as C0. This constitutes one charge-discharge cycle. Then, perform 300 cycles of 1C / 1C charge and discharge at 45°C, recording the discharge capacity as C1. Calculate the capacity retention rate of the lithium-ion battery using the following formula.

[0060] Capacity retention rate = (C1 / C0) * 100%

[0061] Table 2. Performance test results of lithium-ion batteries

[0062]

[0063] As shown in Table 2, Examples 1 to 4, with oxygen as the basic structural material, exhibited good high-temperature cycling performance, mainly due to the electron-donating properties of oxygen, resulting in a "network" structure with stronger polymerization and toughness. Examples 5 to 6, with sulfur as the basic structural material, exhibited good low-temperature discharge characteristics, mainly due to the good electronic conductivity of sulfur, which can accelerate electron transport and improve low-temperature performance under low-temperature conditions. Examples 7 to 8, with nitrogen-containing basic structural material, exhibited good high-temperature storage characteristics, mainly due to the electronic covalent nature of nitrogen, which reflects the covalent bonds of other metal ions, better adsorbs dissolved cobalt ions, and exhibits better storage performance. Among them, Example 11 contains two structural materials and two functional groups, and the two materials exhibit a synergistic effect, showing the best high and low temperature performance.

[0064] The data from Example 5 illustrates that X is an oxygen-containing material with an intracyclic double bond and an adjacent ester group. Under high voltage and charge, this type of material preferentially undergoes a ring-opening reaction to form a double-bonded free radical. This free radical readily undergoes a polymerization reaction with the adjacent ester group to form a "network" of different degrees of polymerization, which adheres to the solid electrolyte interface. This "network" structure of different polymers enhances the toughness of the cathode material and exhibits significant high-temperature storage performance.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A non-aqueous electrolyte, characterized in that, It includes lithium salts, non-aqueous organic solvents, and additives, said additives being compounds represented by structural formula 1 and / or structural formula 2. Structural Formula 1 Structural Formula 2 In this structure, R1, R2, R3, R4, and R5 are each independently selected from alkyl groups with 1 to 4 carbon atoms and hydrogen atoms. In structural formula 1, X is selected from N, and in structural formula 2, X is selected from O and S.

2. The non-aqueous electrolyte as described in claim 1, characterized in that, The compound represented by structural formula 2 is selected from at least one of compound 11, compound 12, compound 13, and compound 14. Compound 11 Compound 12 Compound 13 Compound 14.

3. The non-aqueous electrolyte as described in claim 1, characterized in that, The compound represented by structural formula 1 is selected from at least one of compound 21 and compound 22. Compound 21 Compound 22.

4. The non-aqueous electrolyte as described in claim 1, characterized in that, The additive is present in the non-aqueous electrolyte at a mass percentage of 0.05-5%.

5. The non-aqueous electrolyte as described in claim 1, characterized in that, The lithium salt constitutes 5-20% of the mass of the non-aqueous electrolyte.

6. The non-aqueous electrolyte as described in claim 1, characterized in that, The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate-borate), lithium difluorophosphate, lithium difluorooxalate-borate, lithium difluorodioxalate-phosphate, and lithium bis(oxalate-imide).

7. The non-aqueous electrolyte as described in claim 1, characterized in that, The non-aqueous organic solvent is at least one of the following: chain carbonate, cyclic carbonate, carboxylic acid ester, fluoroether, fluorocarbonate, fluorocarboxylic acid ester, and fluorosulfone.

8. The non-aqueous electrolyte as described in claim 7, characterized in that, The non-aqueous organic solvent is selected from at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, butyl acetate, γ-butyrolactone, propyl propionate, ethyl propionate, ethyl butyrate, dimethyl fluorocarbonate, diethyl fluorocarbonate, ethylene fluorocarbonate, propyl fluoropropionate, ethyl fluoropropionate, propylene fluorocarbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, ethyl fluorobutyrate, fluorosulfonate, dimethyl difluorocarbonate, diethyl difluorocarbonate, and ethylene difluorocarbonate.

9. A lithium-ion battery, comprising a positive electrode material and a negative electrode material, characterized in that, It also includes the non-aqueous electrolyte as described in any one of claims 1 to 8.

10. The lithium-ion battery as described in claim 9, characterized in that, The cathode material is at least one of lithium cobalt oxide, nickel cobalt manganese oxide, or nickel cobalt aluminum oxide.

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