Electrolyte suitable for dry-method graphite negative electrode battery and lithium ion battery thereof

Abstract

The invention provides a lithium ion battery electrolyte which comprises a lithium salt, a non-aqueous organic solvent, an additive A diphenyl ether and an additive B tris (trimethylsilyl) amine, the additive A is diphenyl ether containing a benzene ring and an ether group, the additive B is tris (trimethylsilyl) amine with a trimethylsilyl group, and the non-aqueous organic solvent is a non-aqueous solvent. The additive A enables the electrolyte to be rapidly spread and infiltrated on the surface of an electrode, the additive B enables the electrolyte to form a compact SEI film on the surface of a negative electrode, HF generated by side reaction can be removed, the negative electrode is better protected, the additive A and the additive B act together to improve the interface of the negative electrode, and the service life of the negative electrode is prolonged. And the high-temperature cycle performance of the battery can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to an electrolyte suitable for dry-process graphite negative electrode batteries and a lithium ion battery thereof Background Art

[0002] Dry electrodes have the advantages of high production efficiency, low cost, and higher energy density, and have been considered a promising battery technology. However, due to the high compaction density of dry electrodes, the electrode wettability is poor, resulting in large impedance, which affects battery performance. At the same time, due to the poor chemical stability of the dry electrode binder PTFE in the negative electrode environment, side reactions are prone to occur, and PTFE will decompose at high temperatures to produce fluoride ion free radicals and form HF, etc., resulting in poor negative electrode interface and poor cycle performance.

[0003] The existing technology improves the problems of electrode wettability and poor interface by changing the binder structure or modifying the negative electrode, but the existing technology still has shortcomings and the performance of dry-process batteries needs to be further improved.

[0004] Based on this, the present invention invents an electrolyte suitable for dry-process graphite negative electrode battery and a lithium-ion battery thereof to overcome the above-mentioned problems. Summary of the invention

[0005] The invention provides a lithium ion battery electrolyte and a preparation method thereof, which can improve the high temperature cycle performance of the battery.

[0006] The first aspect of the present application provides a lithium ion battery electrolyte, which is mainly composed of the following ingredients: lithium salt, additive A diphenyl ether and additive B tri(trimethylsilyl)amine, and a non-aqueous organic solvent, wherein the additive A is diphenyl ether containing a benzene ring and an ether group, and the additive B is tri(trimethylsilyl)amine having a trimethylsilyl group. The additive A enables the electrolyte to spread and infiltrate the electrode surface quickly, and the additive B enables the electrolyte to form a dense SEI film on the negative electrode surface, while being able to remove HF generated by side reactions, thereby better protecting the negative electrode. The additives A and B work together to improve the negative electrode interface, thereby improving the high temperature cycle performance of the battery.

[0007] Optionally, the mass percentage of the additive A in the electrolyte is 1% to 10%, preferably 5%, and the mass percentage of the additive B in the electrolyte is 0.1% to 2%, preferably 0.5%.

[0008] Optionally, the electrolyte also includes other additives, which are film-forming additives. Optionally, the film-forming additives are lithium difluorooxalatoborate (LiDFOB), vinylene carbonate (VC) and fluoroethylene carbonate (FEC). The mass percentage of the film-forming additives in the electrolyte is 2% to 5%, preferably 3%.

[0009] Optionally, the non-aqueous organic solvent in the electrolyte includes: any one or a combination of at least two of ethylene carbonate (EC), ethyl methyl carbonate (EMC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl acetate (EA), ethyl propionate (EP), propyl propionate (PP), propyl acetate (PA), methyl acetate (MA), and methyl propionate (MP), preferably a combination of 30% of the ethylene carbonate (EC), 35% of the dimethyl carbonate (DMC), and 35% of the ethyl methyl carbonate (EMC).

[0010] Optionally, the electrolyte lithium salt includes any one or a combination of at least two of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiN(SO2F)2), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), lithium fluorosulfonate (LiSO3F) and lithium bis(pentafluoroethanesulfonyl)imide (LiN(SO2C2F5)2), lithium difluorophosphate (LiPO2F2), lithium monofluorophosphate (Li2PO3F), lithium bis(oxalatoborate) (LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(oxalatofluoroborate) (LiODFB), preferably a combination of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI), and the concentration of the lithium salt is 0.8-1.5 mol / L, preferably 1 mol / L.

[0011] The second aspect of the present application provides a dry-process graphite negative electrode lithium battery, wherein the lithium battery comprises: a positive electrode sheet, a negative electrode sheet, a lithium battery separator and the electrolyte described in the first aspect of the present invention.

[0012] Optionally, the dry-process graphite negative electrode battery comprises: a positive electrode sheet, a negative electrode sheet, a lithium battery separator and the electrolyte, to form a lithium-ion battery.

[0013] The positive electrode sheet includes a positive electrode active material capable of embedding or de-embedding lithium ions, a conductive agent, a current collector, and a binder capable of combining the positive electrode active material, the conductive agent, and the current collector. Optionally, the positive electrode active material is lithium manganate.

[0014] The negative electrode sheet includes a negative electrode active material capable of inserting or extracting lithium ions, a conductive agent, a current collector, and a binder capable of combining the negative electrode active material, the conductive agent and the current collector.

[0015] The negative electrode active material includes a graphite material, and the graphite material is one or more of crystalline carbon, amorphous carbon, carbon fiber, graphene, hard carbon or soft carbon.

[0016] The present invention provides an electrolyte for a dry-process graphite negative electrode, wherein the electrolyte contains additives, wherein the additives include an additive A containing a benzene ring and an ether group and an additive B having a trimethylsilyl group, namely tri(trimethylsilyl)amine. The additive A can make the electrolyte spread and infiltrate rapidly on the electrode surface, the additive B can ensure and form a dense SEI film on the negative electrode surface, and can remove HF generated by side reactions, thereby better protecting the negative electrode. The additive A and the additive B can work together to improve the negative electrode interface, thereby improving the high-temperature cycle performance of the dry-process graphite negative electrode battery. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] Example

[0019] The embodiment of the present application provides a lithium ion battery electrolyte, the electrolyte comprising: a lithium salt, an additive A diphenyl ether and an additive B tri(trimethylsilyl)amine, and a non-aqueous organic solvent, the additives comprising an additive A diphenyl ether and an additive B tri(trimethylsilyl)amine containing a benzene ring, an ether group and a trimethylsilyl group, the additive A enables the electrolyte to spread and infiltrate rapidly on the electrode surface, the additive B enables the electrolyte to form a dense SEI film on the negative electrode surface, and at the same time removes HF generated by a side reaction, thereby better protecting the negative electrode, and the additive A and the additive B work together to improve the negative electrode interface.

[0020] Optionally, the total mass ratio of the additive A in the electrolyte is 1% to 10%, preferably 5%, and the total mass ratio of the additive B in the electrolyte is 0.1% to 2%, preferably 0.5%.

[0021] Optionally, the electrolyte further comprises a film-forming additive, wherein the film-forming additive is lithium difluorooxalatoborate (LiDFOB), vinylene carbonate (VC) and fluoroethylene carbonate (FEC), and the total mass ratio of the film-forming additive in the electrolyte is 3%.

[0022] Optionally, the non-aqueous organic solvent in the electrolyte includes: any one or a combination of at least two of ethylene carbonate (EC), ethyl methyl carbonate (EMC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl acetate (EA), ethyl propionate (EP), propyl propionate (PP), propyl acetate (PA), methyl acetate (MA), and methyl propionate (MP), preferably a combination of 30% of the ethylene carbonate (EC), 35% of the dimethyl carbonate (DMC), and 35% of the ethyl methyl carbonate (EMC).

[0023] Optionally, the electrolyte lithium salt includes any one or a combination of at least two of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiN(SO2F)2), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), lithium fluorosulfonate (LiSO3F) and lithium bis(pentafluoroethanesulfonyl)imide (LiN(SO2C2F5)2), lithium difluorophosphate (LiPO2F2), lithium monofluorophosphate (Li2PO3F), lithium bis(oxalatoborate) (LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(oxalatofluoroborate) (LiODFB), preferably a combination of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI), and the concentration of the lithium salt is 0.8-1.5 mol / L, preferably 1 mol / L.

[0024] The second aspect of the present application provides a dry-process graphite negative electrode lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, a lithium battery separator and the electrolyte described in the first aspect of the present application.

[0025] In order to explain the technical content, structural features, achieved objectives and effects of the technical solution in detail, the following is a detailed description in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0026] The preparation methods of all the embodiments and comparative examples of lithium batteries are as follows:

[0027] (1) Preparation of positive electrode

[0028] The positive electrode active material, the conductive agent and the binder are mixed and coated on the aluminum foil to form the positive electrode plate, and the positive electrode active material is lithium manganate.

[0029] (2) Preparation of negative electrode sheet

[0030] At least one of the negative electrode active material, the conductive agent and the binder is subjected to fiberization treatment to form a fiberized material, and the mixed material is covered on the surface of the current collector to form a negative electrode sheet.

[0031] (3) Preparation of electrolyte

[0032] First, the organic solvent is mixed for about 30 minutes, and the organic solvent includes 30% of ethylene carbonate (EC), 35% of dimethyl carbonate (DMC), and 35% of ethyl methyl carbonate (EMC); lithium salt is slowly added and stirred for 30 minutes; the contents of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) in the electrolyte are 0.8 mol / L and 0.2 mol / L, respectively, and then a film-forming additive is added and stirred for 30 minutes again to make the solution uniformly mixed. The film-forming additive is lithium difluorooxalatoborate (LiDFOB), vinylene carbonate (VC) and fluoroethylene carbonate (FEC), and the total mass ratio of the film-forming additive in the electrolyte is 3%, and then additive A diphenyl ether is added and stirred for 1 hour, and then additive B tri(trimethylsilyl)amine is added, and the preparation of the electrolyte is completed after stirring for one hour. The addition amount of additive A diphenyl ether and additive B tri(trimethylsilyl)amine is mixed according to the relevant parameters shown in Table 1.

[0033] (4) Diaphragm

[0034] PE separator is selected as the separator of lithium battery.

[0035] (5) Preparation method of lithium metal battery

[0036] The positive electrode sheet, electrolyte, separator and negative electrode sheet prepared by the above preparation method are stacked in sequence to prepare a lithium battery.

[0037] Comparative Example 1

[0038] In the comparative example of the present application, the preparation of the electrolyte includes the following steps: first, the organic solvent is mixed for about 30 minutes. Wherein, in terms of the total mass percentage of the organic solvent, the organic solvent includes 30% of ethylene carbonate (EC), 35% of dimethyl carbonate (DMC), and 35% of ethyl methyl carbonate (EMC). Then slowly add the lithium salt and continue stirring for 30 minutes. Wherein, the contents of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) in the electrolyte are 0.8 mol / L and 0.2 mol / L, respectively, and then a film-forming agent is added, and the solution is stirred again for 30 minutes to mix evenly to complete the configuration of the electrolyte. Wherein, the film-forming additives are lithium difluorooxalate borate (LiDFOB), vinylene carbonate (VC) and fluoroethylene carbonate (FEC), and the total mass ratio of the film-forming additives in the electrolyte is 3%.

[0039] The preparation of the positive electrode sheet includes the following steps: mixing the positive electrode active material, the conductive agent and the binder, coating them on the aluminum foil to form the positive electrode sheet. The positive electrode active material is lithium manganate.

[0040] The preparation of the negative electrode sheet includes the following steps: performing a fiberization treatment on at least one of the negative electrode active material, the conductive agent and the binder to form a fiberized material, and covering the mixed material on the surface of the current collector to form a negative electrode sheet.

[0041] PE separator is selected as the separator for lithium metal batteries.

[0042] The preparation of the battery comprises the following steps: the positive electrode sheet, electrolyte, separator and negative electrode sheet prepared by the above preparation method are stacked in sequence to prepare a lithium battery.

[0043] Comparative Example 2

[0044] In another comparison of the present application, only the additive A diphenyl ether is added without adding the additive B tri(trimethylsilyl)amine, and the capacity retention rate is lower than that of Example 1.

[0045] Comparative Example 3

[0046] In Comparative Example 3, only tri(trimethylsilyl)amine, the additive B, was added without diphenyl ether, the capacity retention rate was also lower than that of Example 1. This shows that the effect of using tri(trimethylsilyl)amine alone is not good, and after using it in combination with diphenyl ether, they can synergistically improve the battery performance.

[0047] 25℃ cycle test: The battery is tested at 25℃, as follows: the divided battery is charged to 4.2V with 1C constant current and constant voltage, with a cut-off rate of 0.05C; then discharged to 3V with 1C constant current. After such charge / discharge cycles, the capacity retention rate after the target number of cycles is calculated to evaluate its cycle performance. Among them, the target number of cycles at 25℃ is 500 times.

[0048] Contact angle test: Use a contact angle meter to gently release the electrolyte droplet and let it fall on the surface of the negative electrode to be tested. Use a camera or image acquisition system to capture the image of the droplet on the solid surface, and use data analysis tools to measure the contact angle formed between the droplet and the solid surface.

[0049] As shown in Table 1, the examples and comparative examples were carried out according to the different contents of additive A, additive B, and lithium salt concentrations.

[0050] Table 1

[0051]

[0052] The present invention provides an electrolyte for a dry-process graphite negative electrode, wherein the electrolyte contains additives, wherein the additives include an additive A, diphenyl ether, containing a benzene ring, an ether group and a trimethylsilyl group, and an additive B, tri(trimethylsilyl)amine. The additive A can make the electrolyte spread and infiltrate quickly on the electrode surface, the additive B can ensure and form a dense SEI film on the negative electrode surface, and can remove HF generated by side reactions, thereby better protecting the negative electrode. The additive A and the additive B can work together to improve the negative electrode interface, thereby improving the high-temperature cycle performance of the battery.

[0053] The above description is merely an exemplary embodiment of the present invention and is not intended to limit the protection scope of the present invention. The protection scope of the present invention is determined by the appended claims.

Claims

1. An electrolyte, characterized in that: The electrolyte is mainly prepared from the following components: electrolyte lithium salt, additive A diphenyl ether and additive B tris(trimethylsilyl)amine and non-aqueous organic solvent, wherein: The concentration of the electrolyte lithium salt in the electrolyte is 0.8-1.5 mol / L.

2. The electrolyte according to claim 1, characterized in that The mass percentage of the additive A in the electrolyte is 0.1% to 10%.

3. The electrolyte according to claim 1, characterized in that The mass percentage of the additive B in the electrolyte is 0.1% to 2%.

4. The electrolyte according to claim 1, characterized in that The non-aqueous organic solvent is any one of ethylene carbonate (EC), ethyl methyl carbonate (EMC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl acetate (EA), ethyl propionate (EP), propyl propionate (PP), propyl acetate (PA), methyl acetate (MA), and methyl propionate (MP), or a combination of at least two or more thereof in any proportion.

5. The electrolyte according to claim 1, characterized in that The electrolyte lithium salt is one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bisfluorosulfonyl imide (LiN(SO2F)2), lithium bistrifluoromethanesulfonyl imide (LiN(SO2CF3)2), lithium fluorosulfonate (LiSO3F) and lithium bis(pentafluoroethanesulfonyl)imide (LiN(SO2C2F5)2), lithium difluorophosphate (LiPO2F2), lithium monofluorophosphate (Li2PO3F), lithium bis(oxalatoborate) (LiBOB), lithium bis(fluorosulfonyl imide) (LiFSI), and lithium bis(oxalatofluoroborate) (LiODFB), or a mixture of two or more thereof in any proportion.

6. The electrolyte according to claim 1, characterized in that: The other additives are lithium difluorooxalatoborate (LiDFOB), vinylene carbonate (VC) and fluoroethylene carbonate (FEC), and the content of the other additives is 2% to 5% of the total weight of the electrolyte.

7. A dry-process graphite negative electrode lithium-ion battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, a lithium battery separator and the electrolyte according to any one of claims 1 to 6.

8. A dry-process graphite negative electrode lithium-ion battery according to claim 7, characterized in that: The negative electrode sheet includes a negative electrode active material capable of inserting or extracting lithium ions, a conductive agent, a current collector, and a binder capable of combining the negative electrode active material, the conductive agent and the current collector.

9. A dry-process graphite negative electrode lithium-ion battery according to claim 8, characterized in that: The negative electrode active material includes a graphite material, and the graphite material is one or more of crystalline carbon, amorphous carbon, carbon fiber, graphene, hard carbon or soft carbon.

10. A dry-process graphite negative electrode lithium-ion battery according to claim 8, characterized in that: The binder is polytetrafluoroethylene (PTFE).

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