A high voltage electrolyte and a battery comprising the same

Abstract

The present invention belongs to the technical field of lithium-ion batteries, and specifically relates to a high-voltage electrolyte and a battery including the electrolyte. The electrolyte provided by the present invention contains a triynylborazine compound as a first additive. The triynylborazine compound can undergo an electropolymerization reaction on the surface of the positive electrode to form a polymer interface film rich in boron and nitrogen structures. The polymer interface film has good flexibility and high oxidation resistance, can inhibit the reaction between the electrolyte and the positive electrode, and protect the electrolyte from excessive consumption. At the same time, the generated polymer interface film contains rich B atoms and N atoms, effectively reducing the interfacial impedance while further improving the stability of the interface film, thereby significantly improving the cycle storage performance of the battery.

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 battery comprising the electrolyte. Background Art

[0002] Since the 1990s, with the rapid development of digital electronic devices and power tools, lithium-ion batteries and related industries have also experienced rapid growth, attracting increasing market attention. As customer demand continues to rise, performance requirements for lithium-ion batteries, such as operating voltage, energy density, service life, and charging speed, continue to increase. However, at high voltages, the stability of positive and negative electrode materials decreases, and side reactions between electrolytes and positive and negative electrode materials intensify, resulting in lithium-ion battery cycle performance and safety performance failing to meet customer demands.

[0003] The electrolyte is like the blood of lithium-ion batteries. As an important component of lithium-ion batteries, its stability and oxidation resistance play an important role in improving the performance of lithium-ion batteries. Generating a stable electrolyte interface film and inhibiting further reaction between the electrolyte and the positive electrode material are key technical elements for improving high-voltage lithium-ion batteries. Therefore, it is necessary to develop a high-voltage electrolyte that can improve the cyclic storage performance of lithium-ion batteries at high voltage. Summary of the Invention

[0004] The purpose of the present invention is to improve the problem of poor cycling and storage performance of batteries under high voltage in the prior art, and to provide a high-voltage electrolyte and a battery including the electrolyte. Under high voltage, the electrolyte can take into account low-temperature performance while achieving good normal and high-temperature cycling performance and high-temperature storage performance.

[0005] The object of the present invention is achieved through the following technical solutions:

[0006] An electrolyte comprises a lithium salt, an organic solvent and an additive, wherein the additive comprises a first additive selected from triynyl borazane compounds.

[0007] According to an embodiment of the present invention, the trialkynyl borazine compound includes an alkynyl group (-C≡C-) and a boron nitrogen group (-NB-).

[0008] According to an embodiment of the present invention, the triynyl borazine compound is selected from at least one of the structural formulas shown in Formula I:

[0009]

[0010] wherein R1, R2, R3, R4, R5, and R6 are the same or different and are independently selected from hydrogen, halogen, cyano, sulfonic acid, sulfonyl, substituted or unsubstituted C 1～10Alkyl, substituted or unsubstituted C 2～10 Alkenyl, substituted or unsubstituted C 6～26 Aryl, substituted or unsubstituted C 1～10 Alkoxy, substituted by halogen, cyano, C 1～10 alkyl.

[0011] According to an embodiment of the present invention, R1, R2, R3, R4, R5, and R6 are the same or different and are independently selected from hydrogen atoms, halogens, cyano groups, sulfonic acid groups, sulfonyl groups, substituted or unsubstituted C 1～6 Alkyl, substituted or unsubstituted C 2～6 Alkenyl, substituted or unsubstituted C 6～10 Aryl, substituted or unsubstituted C 1～6 Alkoxy, substituted by halogen, cyano, C 1～6 alkyl.

[0012] According to an embodiment of the present invention, R1, R2, R3, R4, R5, and R6 are the same or different and are independently selected from hydrogen atoms, halogens, cyano groups, sulfonic acid groups, sulfonyl groups, substituted or unsubstituted C 1～3 Alkyl, substituted or unsubstituted C 2～3 Alkenyl, substituted or unsubstituted C 6～8 Aryl, substituted or unsubstituted C 1～3 Alkoxy, substituted by halogen, cyano, C 1～3 alkyl.

[0013] According to an embodiment of the present invention, R1, R2, R3, R4, R5, and R6 are the same or different and are independently selected from hydrogen atom, methyl group, and phenyl group.

[0014] According to an embodiment of the present invention, the compound represented by formula I is selected from at least one of the following structural formulas:

[0015]

[0016] According to an embodiment of the present invention, the mass of the first additive accounts for 0.1 to 10 wt % of the total mass of the electrolyte, preferably 0.5 to 3 wt %, for example, 0.1 wt %, 0.2 wt %, 0.3 wt %, 0.4 wt %, 0.5 wt %, 0.6 wt %, 0.7 wt %, 0.8 wt %, 0.9 wt %, 1 wt %, 1.2 wt %, 1.3 wt %, 1.5 wt %, 1.6 wt %, 1.8 wt %, 2 wt %, 2.2 wt %, 2.4 wt %, 2.5 wt %, 2.6 wt %, 2.8 wt %, 3 wt %, 3.3 wt %, 3.5 wt %, 3.8 wt %, 4 wt %, 4.2 wt %, 4.5 wt %, 4.8 wt %, 5 wt %, 6 wt %, 7 wt %, 8 wt %, 9 wt % or 10 wt %.

[0017] According to an embodiment of the present invention, the lithium salt is at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPF2O2), lithium difluorobis(oxalatophosphate) (LiPF2(C2O4)2), lithium tetrafluorooxalatophosphate (LiPF4C2O4), lithium oxalatophosphate (LiPO2C2O4), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl imide) (LiTFSI) and lithium bis(fluorosulfonyl imide) (LiFSI).

[0018] According to an embodiment of the present invention, the mass of the lithium salt accounts for 10-15 wt% of the total mass of the electrolyte, for example, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, or 15 wt%.

[0019] According to an embodiment of the present invention, the organic solvent is selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), propyl propionate (PP), ethyl acetate (EA), ethyl butyrate (EB) and gamma-butyrolactone (GBL).

[0020] According to an embodiment of the present invention, the mass of the organic solvent accounts for 20-60 wt% of the total mass of the electrolyte, for example, 20 wt%, 25 wt%, 30 wt%, 40 wt%, 55 wt% or 60 wt%.

[0021] According to an embodiment of the present invention, the additive further includes a second additive, which is selected from at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propane sultone (PS), vinyl sulfate (DTD), methylene methanedisulfonate (MMDS), propene sultone (PST), maleic anhydride, diglycolic anhydride, succinic anhydride, succinonitrile (SN), adiponitrile (ADN), ethylene glycol bis(propionitrile) ether (EGBE) and hexane tricarbonitrile (HTCN).

[0022] According to an embodiment of the present invention, the mass of the second additive accounts for 0.1 to 15 wt% of the total mass of the electrolyte, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.2 wt%, 1.3 wt%, 1.5 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.8 wt%, 3 wt%, 3.3 wt%, 3.5 wt%, 3.8 wt%, 4 wt%, 4.2 wt%, 4.5 wt%, 4.8 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, and 15 wt%.

[0023] The present invention also provides a battery, comprising the above-mentioned electrolyte.

[0024] According to an embodiment of the present invention, the battery is a lithium-ion battery.

[0025] According to an embodiment of the present invention, the battery further includes a positive electrode sheet, a negative electrode sheet, and a separator spaced between the positive electrode sheet and the negative electrode sheet.

[0026] According to an embodiment of the present invention, the charge cut-off voltage of the battery is greater than 4.48V.

[0027] Beneficial effects of the present invention:

[0028] The electrolyte provided by the present invention adds a triynyl borazine compound as a first additive. The triynyl borazine compound can undergo an electropolymerization reaction on the surface of the positive electrode to generate a polymer interface film rich in boron and nitrogen structure. The polymer interface film has good flexibility and high oxidation resistance, can inhibit the reaction between the electrolyte and the positive electrode, and protect the electrolyte from being over-consumed. At the same time, the generated polymer interface film contains rich B atoms and N atoms, which effectively reduces the interfacial impedance while further improving the stability of the interface film. After the second additive is added, it can act together with the first additive on the surface of the positive and negative electrodes to generate a stable SEI film to isolate the active material from the electrolyte side reaction. Therefore, through the synergistic effect of the first additive and the second additive, the film formation stability of the positive and negative electrodes is significantly improved, and the low temperature performance, normal high temperature cycle performance and high temperature storage performance of the battery at high voltage are significantly improved. DETAILED DESCRIPTION

[0029] The preparation method of the present invention will be described in further detail below with reference to specific examples. It should be understood that the following examples are merely illustrative and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are encompassed within the scope of protection intended by the present invention.

[0030] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the reagents, materials, etc. used in the following examples are all commercially available unless otherwise specified.

[0031] The preparation method of a lithium-ion battery includes:

[0032] [Cathode sheet preparation]

[0033] The positive electrode active material lithium cobalt oxide (LCO), the binder polyvinylidene fluoride (PVDF), the conductive carbon black and the single-walled carbon nanotubes are mixed in a weight ratio of 97.2:1.5:1.2:0.1, N-methylpyrrolidone (NMP) is added, and the mixture is stirred under the action of a vacuum mixer until the mixed system becomes a positive electrode slurry with uniform fluidity; the positive electrode slurry is evenly coated on the current collector aluminum foil; the coated aluminum foil is baked in an oven with 5 different temperature gradients, and then dried in an oven at 120°C for 8 hours, and then rolled and cut to obtain the required positive electrode sheet.

[0034] [Anode sheet preparation]

[0035] The negative electrode active material graphite, thickener sodium carboxymethyl cellulose (CMC-Na), binder styrene-butadiene rubber, and conductive agent acetylene black are mixed in a weight ratio of 97:1:1:1, deionized water is added, and a negative electrode slurry is obtained under the action of a vacuum mixer; the negative electrode slurry is evenly coated on a high-strength carbon-coated copper foil to obtain an electrode sheet; the obtained electrode sheet is dried at room temperature and then transferred to an 80°C oven for drying for 10 hours, and then rolled and slit to obtain a negative electrode sheet.

[0036] [Electrolyte preparation]

[0037] In a glove box filled with inert gas (H2O <10ppm, O2 <5ppm), ethylene carbonate, propylene carbonate, and diethyl carbonate were mixed in a mass ratio of EC:PC:DEC = 1:1:3. Lithium hexafluorophosphate (LiPF6) was then slowly added to the mixed solution. After passing the moisture and free acid tests, a basic electrolyte was obtained. Different amounts of lithium salts and additives listed in Table 1 were added to the basic electrolyte to obtain the electrolytes of the corresponding Examples and Comparative Examples.

[0038] [Battery Manufacturing]

[0039] The positive electrode sheet, separator (9-micron thick PP film), and negative electrode sheet prepared above are stacked in order, ensuring that the separator is between the positive and negative electrode sheets to play an isolating role. The bare battery cell is placed in an aluminum-plastic film outer packaging, and the electrolyte prepared above is injected into the dried battery. The battery is packaged, allowed to stand, formed, shaped, and capacity divided to complete the preparation of the lithium-ion soft-pack battery.

[0040] Examples 1 to 12 and Comparative Examples 1 to 4

[0041] Batteries of Examples 1 to 12 and Comparative Examples 1 to 4 were prepared according to the above preparation method. The difference between different Examples and Comparative Examples lies only in the composition of the electrolyte, as shown in Table 1 below.

[0042] Table 1 Composition of lithium salts and additives in the electrolytes of Examples and Comparative Examples

[0043]

[0044]

[0045] The lithium ion batteries obtained in Examples 1 to 12 and Comparative Examples 1 to 4 were subjected to relevant performance tests.

[0046] (1) High temperature cycle performance test:

[0047] At 45°C, the divided battery was charged to 4.48V at 0.7C constant current and constant voltage, with a cut-off current of 0.05C, and then discharged to 3.0V at 0.5C constant current. This cycle was repeated for 500 cycles, and the capacity retention rate at the 500th cycle was calculated. The calculation formula is as follows: 500th cycle capacity retention rate (%) = (500th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0048] (2) Normal temperature cycle performance test:

[0049] At 25°C, the divided battery was charged to 4.48V at 0.7C constant current and constant voltage, with a cut-off current of 0.05C, and then discharged to 3.0V at 0.5C constant current. This cycle was repeated for 500 cycles, and the capacity retention rate at the 500th cycle was calculated. The calculation formula is as follows: Capacity retention rate at the 500th cycle (%) = (discharge capacity at the 500th cycle / discharge capacity at the first cycle) × 100%.

[0050] (3) 60℃ 14-day high temperature storage test:

[0051] The battery was charged and discharged once at 0.5C at room temperature (4.48V-3.0V), and the discharge capacity C0 of the battery before storage was recorded. The battery was then charged to a fully charged state of 4.48V at constant current and constant voltage. The thickness d1 of the battery before high-temperature storage was measured using a PPG battery thickness gauge (500g). The battery was placed in a 60°C constant temperature box and stored for 14 days. After the storage was completed, the battery was taken out and the thermal thickness d2 of the battery after storage was measured. The thickness expansion rate of the battery after storage at 60°C for 14 days was calculated. After the battery was cooled at room temperature for 24 hours, the battery was again discharged to 3.0V at 0.5C at a constant current and constant voltage, and then charged to 4.48V at 0.5C at a constant current and constant voltage. The discharge capacity C1 and charge capacity C2 of the battery after storage were recorded, and the capacity retention rate and capacity recovery rate of the battery after storage at 60°C for 14 days were calculated as follows:

[0052] Thickness expansion ratio after storage at 60°C for 14 days = (d2-d1) / d1*100%;

[0053] Capacity retention after 14 days storage at 60°C = C1 / C0*100%;

[0054] After storage at 60°C for 14 days, the capacity recovery rate = C2 / C0*100%.

[0055] (4) Low temperature discharge performance test: Under 25℃ environmental conditions, discharge the divided battery at 0.5C to 3.0V and let it sit for 5 minutes; then charge it at 0.2C to 4.48V. When the cell voltage reaches 4.48V, change to 4.48V constant voltage charging until the charging current is less than or equal to the given cutoff current 0.05C and let it sit for 5 minutes; transfer the fully charged cell to a high and low temperature box, set at -10℃, and let it sit for 120 minutes after the box temperature reaches the target; then discharge it at 0.2C to a termination voltage of 3.0V and let it sit for 5 minutes; then adjust the high and low temperature box temperature to 25℃±3℃, and let it sit for 60 minutes after the box temperature reaches the target; charge it at 0.2C to 4.48V. When the cell voltage reaches 4.48V, change to 4.48V constant voltage charging until the charging current is less than or equal to the given cutoff current 0.05C; let it sit for 5 minutes; calculate the -10℃ low temperature discharge 3.0V capacity retention rate. The calculation formula is as follows: -10℃ discharge to 3.0V capacity retention rate (%) = (-10℃ discharge to 3.0V discharge capacity / 25℃ discharge to 3.0V discharge capacity) × 100%.

[0056] Table 2 Performance test results of batteries of Examples and Comparative Examples

[0057]

[0058] Comparison of the test results of Comparative Example 4 and Examples 1-12 in Table 2 shows that the addition of the first additive in the examples can effectively improve the room-temperature and high-temperature cycle performance and high-temperature storage thickness expansion rate of the lithium-ion battery, effectively inhibit gas production, and improve the capacity retention rate and capacity recovery rate of the lithium-ion battery after high-temperature storage. At the same time, the low-temperature performance of the lithium-ion battery can be taken into account at a certain dosage.

[0059] Comparative Examples 1-4 show that when the amount of the first additive is within an appropriate range (0.5-2 wt%), the cycling and high-temperature storage performance are improved while also taking into account the low-temperature performance. However, when the amount is excessive (3 wt%), the low-temperature discharge performance deteriorates. This may be due to the excessive amount of the additive (Formula I) forming the polymer film, which affects the lithium ion conduction and leads to the deterioration of the lithium battery performance.

[0060] By comparing Example 2 with Examples 8-9 and Example 11 with Comparative Example 4, it can be seen that the first additive can better balance the performance of the battery when combined with the second additive. This may be because the simultaneous addition of the first additive and the second additive can generate a stable positive and negative electrode interface film, thereby avoiding the occurrence of interfacial side reactions during long cycles.

[0061] In summary, it can be seen that the present invention provides a high-voltage electrolyte and a lithium-ion battery using the electrolyte, which effectively improves the room-temperature and high-temperature cycle performance and high-temperature storage performance while taking into account the low-temperature performance at high voltage, showing extremely high application potential.

[0062] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. An electrolyte, characterized in that: The electrolyte includes a lithium salt, an organic solvent and an additive, wherein the additive includes a first additive and a second additive, wherein the first additive is selected from triynyl borazane compounds; and the second additive is selected from fluoroethylene carbonate (FEC) and vinylene carbonate (VC); The triynyl borazine compound is selected from at least one of the compounds having the structural formula shown in Formula I: wherein R1, R2, R3, R4, R5, and R6 are the same or different and are independently selected from hydrogen, halogen, cyano, sulfonic acid, sulfonyl, substituted or unsubstituted C 1～10 Alkyl, substituted or unsubstituted C 2～10 Alkenyl, substituted or unsubstituted C 6～26 Aryl, substituted or unsubstituted C 1～10 Alkoxy, substituted by halogen, cyano, C 1～10 alkyl.

2. The electrolyte according to claim 1, characterized in that R1, R2, R3, R4, R5, R6 are the same or different and are independently selected from hydrogen atom, halogen, cyano, sulfonic acid, sulfonyl, substituted or unsubstituted C 1～6 Alkyl, substituted or unsubstituted C 2～6 Alkenyl, substituted or unsubstituted C 6～10 Aryl, substituted or unsubstituted C 1～6 Alkoxy, substituted by halogen, cyano, C 1～6 alkyl.

3. The electrolyte according to claim 2, characterized in that The compound represented by formula I is selected from at least one of the following structural formulas:

4. The electrolyte according to any one of claims 1 to 3, characterized in that The mass of the first additive accounts for 0.1 to 10 wt % of the total mass of the electrolyte.

5. The electrolyte according to claim 4, characterized in that The mass of the first additive accounts for 0.5-3 wt% of the total mass of the electrolyte.

6. The electrolyte according to any one of claims 1 to 3, characterized in that The lithium salt is at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPF2O2), lithium difluorobis(oxalatophosphate) (LiPF2(C2O4)2), lithium tetrafluorooxalatophosphate (LiPF4C2O4), lithium oxalatophosphate (LiPO2C2O4), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl imide) (LiTFSI) and lithium bis(fluorosulfonyl imide) (LiFSI).

7. The electrolyte according to any one of claims 1 to 3, characterized in that The additives further include a third additive, which is selected from at least one of 1,3-propane sultone (PS), vinyl sulfate (DTD), methylene methanedisulfonate (MMDS), propene sultone (PST), maleic anhydride, diglycolic anhydride, succinic anhydride, succinonitrile (SN), adiponitrile (ADN), ethylene glycol bis(propionitrile) ether (EGBE) and hexane tricarbonitrile (HTCN).

8. A battery, characterized in that: The battery comprises the electrolyte according to any one of claims 1 to 7.

9. The battery according to claim 8, characterized in that The charging cut-off voltage of the battery is above 4.48V.

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