Electrolyte and lithium ion battery

Abstract

The invention provides an electrolyte and a lithium ion battery, and relates to the technical field of lithium ion batteries. The electrolyte comprises a lithium salt, an organic solvent, a basic additive and a functional additive, the functional additive comprises a sulfonate-containing compound and a diboron derivative compound. The electrolyte provided by the invention can effectively improve the high and low temperature performance of the battery and improve the safety problem at the same time.

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. Background Art

[0002] The successful application of lithium-ion secondary batteries in power and energy storage has proven their commercial success. Currently, lithium iron phosphate batteries and ternary batteries remain the mainstream lithium-ion battery technology. While lithium iron phosphate batteries' high safety and low cost play a significant role in energy storage and power batteries, their low energy density still limits their application in high-energy-density batteries. Ternary batteries, with their high energy density and excellent rate performance, are widely used in long-range applications.

[0003] Currently, research on the development of lithium-ion battery electrolyte additives has been underway, primarily focusing on functional group splicing, derivatization, and the dual structure of mature additives. However, these efforts often focus on exploring the direction and mechanism of improvement with a single additive, while exploring the synergistic effects of different additives remains lacking.

[0004] Liquid electrolyte formulations based on organic solvents still face a series of problems at high and low temperatures, including gas production, circulating water drop, and safety issues at high temperatures, and high electrolyte viscosity, slow kinetic reactions, and lithium precipitation at low temperatures. Summary of the Invention

[0005] Based on the technical problems existing in the background technology, the present invention proposes an electrolyte and a lithium-ion battery.

[0006] The present invention provides an electrolyte comprising a lithium salt, an organic solvent, a basic additive and a functional additive; the functional additive comprises a sulfonate-containing compound and a diboron derivative compound.

[0007] The present invention proposes the use of sulfonate-containing compounds and diboron derivative compounds as additives for lithium-ion batteries. The two compounds can participate in the film-forming reaction on the surface of the electrode material to form a low-impedance film component, stabilize the highly oxidized structure of the lithium-ion battery positive electrode material, and improve the electrochemical window of the electrolyte, thereby improving the high-temperature and room-temperature performance of the lithium-ion battery.

[0008] Preferably, the sulfonate-containing compound has a structural formula as shown in Formula I,

[0009]

[0010] Wherein R1 is selected from one or more of hydrogen atom, C1-C5 alkane, alkene or alkyne, cyano group, isocyano group, phenyl group and halogen; R2 and R3 are independently selected from one or more of hydrogen atom, C1-C3 alkane, alkene or alkyne, cyano group, isocyano group and halogen.

[0011] Compounds containing sulfonates can improve the SEI film structure and generate lithium sulfate, lithium sulfite, etc. These compounds can quickly conduct lithium ions. At the same time, the sulfur-containing organic components generated can effectively prevent the dissolution of transition metals and effectively improve the high-temperature performance of the battery.

[0012] More preferably, the sulfonate-containing compound is selected from One of them.

[0013] The sulfonate-containing compound used in the present invention contains both cyclic and linear sulfonic acid groups, which further promotes the improvement of high temperature performance.

[0014] The The PubChem CID is 155217737.

[0015] Preferably, the diboron derivative compound has a structural formula as shown in Formula II,

[0016]

[0017] Wherein R4 and R5 are independently selected from one or more of hydrogen atom, C1-C3 alkane, alkene or alkyne, cyano group, isocyano group and halogen.

[0018] The electron-deficient boron atoms in diboron derivative compounds can combine with anions in the electrolyte and intermediate products in the reaction, effectively regulating the SEI composition, enhancing the transmission dynamics of low-temperature lithium ions, reducing impedance, increasing low-temperature discharge efficiency, and thus improving normal and low-temperature performance.

[0019] More preferably, the diboron derivative compound is selected from One of them.

[0020] The diboron derivative compound used in the present invention can serve as an anion receptor, effectively improving the low-temperature kinetics of the electrolyte, removing HF, reducing low-temperature impedance, and improving the normal low-temperature performance of the battery.

[0021] The The CAS number is: 230299-21-5.

[0022] Preferably, the mass ratio of the sulfonate-containing compound to the diboron derivative compound is (0.5-5):(0.15-2.5).

[0023] Preferably, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(fluorosulfonyl imide), and lithium bis(trifluoromethanesulfonyl imide).

[0024] The role of lithium salt is to provide an appropriate amount of lithium source, working synergistically with the solvent to improve battery performance.

[0025] Preferably, the organic solvent is selected from one or more of cyclic or chain carbonates, cyclic or linear carboxylates, and cyclic or linear ethers.

[0026] The role of the organic solvent is to dissolve the solute in the electrolyte, control the conductivity of lithium ions, and reduce gas production under high temperature conditions and solidification under low temperature conditions.

[0027] More preferably, the organic solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl methyl carbonate, ethylene carbonate, propylene carbonate, γ-butyrolactone, ethyl propionate, methyl butyrate, butyl acetate, methyl propionate, propyl butyrate, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0028] Preferably, the base additive is selected from one or more of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, 1,3-propane sultone, 1,4-butane sultone, methylene methanesulfonate, and tris(trimethylsilyl)phosphate.

[0029] The role of basic additives is to work synergistically with functional additives to improve electrolyte performance.

[0030] Preferably, the electrolyte comprises, by mass percentage, 6-40% lithium salt, 55-85% organic solvent, 0.5-10% basic additive, and 0.1-15% functional additive.

[0031] The mass percentage of raw materials in the electrolyte within a certain range helps to obtain the electrolyte with the optimal ratio, effectively improving the high and low temperature performance of the battery.

[0032] A lithium-ion battery comprises a positive electrode sheet, a negative electrode sheet, a separator and the above-mentioned electrolyte.

[0033] The beneficial effects of the present invention are:

[0034] The electrolyte provided by the present invention can effectively improve the high and low temperature performance of the battery, enhance the battery rate performance and improve safety issues.

[0035] The sulfonate-containing compound additive and the basic additive used in the present invention act synergistically. On the one hand, they can remove free radicals in the electrolyte and prevent the occurrence of side reactions. On the other hand, they can efficiently participate in the film-forming reaction on the electrode surface to generate organic SEI and CEI films containing sulfur components, reduce the impedance of the film-forming components, reduce the internal resistance of the lithium-ion battery, and show good normal high temperature performance.

[0036] The diboron derivative compound used in the present invention can act as an anion receptor, effectively improving the low-temperature kinetics of the electrolyte, scavenging HF, reducing low-temperature impedance, and enhancing the battery's normal low-temperature performance. In summary, the sulfonate-containing compound and diboron derivative compound combination additive used in the present invention can improve the overall performance of lithium-ion batteries. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is described in detail through specific embodiments.

[0038] Unless otherwise specified, the materials, reagents, etc. used in the following examples and comparative examples can be obtained from commercial sources.

[0039] Example 1

[0040] Preparation of electrolyte: In an inert atmosphere glove box with water / oxygen index <0.1ppm, ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC:DEC:EMC=3:2:5. After mixing, 12wt% LiPF6, 0.5wt% LiODFB and 3wt% VC were added. After the lithium salt was completely dissolved, 2.5wt% and 0.5wt% Mix and stir evenly.

[0041] A lithium-ion battery comprises a positive electrode sheet, a negative electrode sheet, a separator and the above-mentioned electrolyte.

[0042] The preparation method of the lithium-ion battery is as follows: the negative electrode material hard carbon, conductive base SP, binder CMC, and dispersant SBR are mixed in a mass ratio of 94.5:1.5:2:2, and an appropriate amount of deionized water is added to form a uniform paste, which is evenly coated on a 10μm copper foil as a negative electrode current collector and baked at 100℃ for 12h to obtain a negative electrode sheet. 0.75 Co 0.1 Mn 0.15 O2, conductive agent SP, and binder PVDF were mixed in a mass ratio of 95:2:2.5 with an appropriate amount of NMP solvent to form a uniform paste. This paste was evenly coated onto a 12μm aluminum foil serving as the positive electrode current collector and baked at 110°C for 12 hours to produce the positive electrode sheet. The positive electrode sheet, separator, and negative electrode sheet were stacked in sequence to form a lithium-ion battery cell. The battery prepared in this experiment was a 2.4Ah soft-pack cell. After drying, the cell was injected with 8g of electrolyte to produce the corresponding battery sample.

[0043] Examples 2 to 17 and Comparative Examples 1 to 4 were performed by changing the ratio and type of specific substances in the electrolyte, and referring to the preparation method of Example 1 to obtain lithium-ion batteries. The electrolyte formula is shown in Table 1 below.

[0044] Table 1

[0045]

[0046]

[0047]

[0048] The batteries prepared in the above examples and comparative examples were subjected to a room temperature cycle test and a high temperature shelf performance test, respectively.

[0049] (1) 45℃ high temperature cycle test

[0050] At 45°C, the lithium-ion batteries of Examples 1 to 17 and Comparative Examples 1 to 4 were charged to 4.25V using a 1C constant current and constant voltage charge, with a cut-off current of 0.05C; then discharged to 2.8V using a 0.5C constant current charge, and the discharge capacity Q0 was recorded as the initial discharge capacity. After 300 cycles under the same charge and discharge regime while maintaining the ambient temperature constant, the 300th discharge capacity Q was recorded. 300 , then the room temperature discharge capacity retention rate = Q 300 / Q0*100%.

[0051] (2) 60℃ high temperature shelf performance test

[0052] At 25°C, the lithium-ion batteries of Examples 1-17 and Comparative Examples 1-4 were each charged to 4.25V using a 0.2C constant current and constant voltage charge at a cutoff current of 0.05C. The batteries were then discharged to 2.0V using a 0.2C constant current and constant voltage charge at a cutoff current of 0.05C, and the discharge capacity Q0 was recorded as the initial discharge capacity. The fully charged experimental cells were then placed in a 60°C oven for 7 days. After the high-temperature storage, the experimental cells were removed and discharged to 2.8V using a 0.2C constant current and constant voltage charge at 25°C. The discharge capacity Q1 was recorded. Three experimental cells were tested in parallel and the average value was taken. The high-temperature storage capacity retention rate = Q1 / Q0*100%.

[0053] (3) Normal and low temperature DC resistance (DCR) performance test

[0054] The lithium-ion batteries of Examples 1-17 and Comparative Examples 1-4 were each charged at 0.33C constant current and constant voltage to 100% SOC at 25°C, then discharged at 0.33C constant current to 50% SOC. The battery samples were then allowed to stand at 25°C / -20°C for 3 hours to reach temperature equilibrium, and the end-of-stand voltage was recorded as U0. At 25°C / -20°C, pulse discharge was performed at 3C discharge current I3 for 10 seconds, and the end-of-discharge voltage was recorded as U1. The normal low-temperature DC resistance (DCR) of the battery sample was calculated as (U0-U1) / I3, expressed in milliohms.

[0055] The test results are shown in Table 2.

[0056] Table 2

[0057]

[0058]

[0059] Comparison of the above examples with the comparative examples shows that, compared to conventional additives, the combination of the sulfonate-containing compound and the diboron derivative compound of the present invention can reduce the DC internal resistance of lithium-ion batteries (improvements of ~5% at room temperature and ~15% at low temperature), and improve high-temperature cycling (~5%) and shelf performance (~4%). Comparison of Example 16 with Example 3 shows that increasing EC slightly improves high-temperature performance but degrades low-temperature performance. Comparison of Example 17 with Example 4 shows that the addition of TMSP tris(trimethylsilyl)phosphite further improves both high- and low-temperature performance.

[0060] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0061] Sulfonate-containing compounds participate in film formation, forming a sulfur-containing component that effectively prevents excess metal precipitation and hinders side reactions. Diboron derivatives, on the other hand, contain an electron-deficient group B, which effectively binds to anions and electrolyte intermediates, scavenging HF and improving the low-temperature kinetics of lithium-ion batteries. Combining these two compounds leverages their respective strengths, effectively improving the film composition, thereby reducing the impedance of lithium-ion batteries and significantly improving their high- and low-temperature performance.

[0062] In summary, the electrolyte provided by the present invention significantly improves the high and low temperature performance of lithium-ion batteries.

[0063] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. An electrolyte, characterized in that The invention comprises lithium salt, organic solvent, basic additive and functional additive; the functional additive comprises a sulfonic acid ester-containing compound and a diboron derivative compound.

2. The electrolyte according to claim 1, characterized in that The sulfonate-containing compound has a structural formula as shown in Formula I, Wherein R1 is selected from one or more of hydrogen atom, C1-C5 alkane, alkene or alkyne, cyano group, isocyano group, phenyl group and halogen; R2 and R3 are independently selected from one or more of hydrogen atom, C1-C3 alkane, alkene or alkyne, cyano group, isocyano group and halogen.

3. The electrolyte according to any one of claims 1 or 2, characterized in that The sulfonate-containing compound is selected from One of them.

4. The electrolyte according to claim 1, characterized in that The diboron derivative compound has a structural formula as shown in Formula II. Wherein R4 and R5 are independently selected from one or more of hydrogen atom, C1-C3 alkane, alkene or alkyne, cyano group, isocyano group and halogen.

5. The electrolyte according to any one of claims 1 or 4, characterized in that The diboron derivative compound is selected from One of them.

6. The electrolyte according to claim 1, characterized in that The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(fluorosulfonyl imide), and lithium bis(trifluoromethanesulfonyl imide).

7. The electrolyte according to claim 1, characterized in that The organic solvent is selected from one or more of cyclic or chain carbonates, cyclic or linear carboxylates, and cyclic or linear ethers.

8. The electrolyte according to claim 1, characterized in that The basic additive is selected from one or more of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, 1,3-propane sultone, 1,4-butane sultone, methylene methanesulfonate, and tris(trimethylsilyl)phosphate.

9. The electrolyte according to claim 1, characterized in that Calculated by mass percentage, the invention comprises 6-40% of lithium salt, 55-85% of organic solvent, 0.5-10% of basic additive and 0.1-15% of functional additive.

10. A lithium ion battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte according to any one of claims 1 to 9.

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