Electrolyte and lithium battery

Abstract

The invention discloses an electrolyte and a lithium battery, and additives of the electrolyte comprise a compound as shown in a structural formula 1, a cyclic sulfate compound and a sultone compound, the proportions of the compound as shown in the structural formula 1, the cyclic sulfate compound and the sultone compound in the electrolyte are awt%, bwt% and cwt% respectively, 2.5 b-a is more than or equal to-0.5 and less than or equal to 4, and 2a + c is more than or equal to 5 and less than or equal to 8. In the design, the compound shown in the structural formula 1 can form stable interfacial films on the surfaces of the positive electrode and the negative electrode, oxidative decomposition of an electrolyte at high temperature is reduced, consumption of the electrolyte is inhibited, the high-temperature cycle performance is improved, and the cyclic sulfate compound can reduce film-forming impedance and improve gram volume exertion; the sultone compound can improve the high-temperature storage performance. Therefore, the high-temperature cycle and high-temperature nesting performance of the lithium battery is effectively improved by adjusting the ratio of the compound shown in the structural formula 1, the cyclic sulfate compound and the sultone compound.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery design, and in particular to an electrolyte and a lithium battery. Background Art

[0002] Lithium-ion batteries have the advantages of high operating voltage, long cycle life, low self-discharge and no memory effect. They are widely used in portable electronic devices, electric vehicles and other products.

[0003] With the development of technology, the upper voltage limit of lithium-ion batteries is getting higher and higher to meet the requirements of high energy density. As the upper voltage limit increases, the high-temperature cycle performance deteriorates. In response to this, the doping amount of the positive electrode material is usually increased or the high-temperature cycle performance of the high-voltage system is improved by electrolyte additives, but these in turn deteriorate the capacity of the battery cell.

[0004] Therefore, finding a technical solution that can solve the above technical problems has become an important topic studied by technical personnel in this field. Summary of the invention

[0005] The invention discloses an electrolyte and a lithium battery, which are used to solve the technical problem that the existing method of improving the high-temperature cycle performance of a high-voltage system will deteriorate the capacity of the lithium battery.

[0006] The present invention provides an electrolyte comprising a lithium salt, a solvent and an additive, wherein the additive comprises a compound represented by structural formula 1, a cyclic sulfate ester compound and a sultone compound;

[0007] The compound represented by the structural formula 1, the cyclic sulfate compound and the sultone compound account for awt%, bwt% and cwt% of the electrolyte respectively, wherein -0.5≤2.5ba≤4 and 5≤2a+c≤8 are satisfied;

[0008] Structural formula 1:

[0009]

[0010] Wherein, R1 and R2 are each independently selected from any one of a hydrogen atom, a halogen atom, a vinyl sulfate group, and a vinyl carbonate group.

[0011] Optionally, the ratio a of the compound represented by the structural formula 1 in the electrolyte is 0.1-10, the ratio b of the cyclic sulfates in the electrolyte is 0.1-1.5, and the ratio c of the sultones in the electrolyte is 0.1-5.

[0012] Optionally, the compound of structural formula 1 is selected from at least one of the following compounds:

[0013] Compound 1:

[0014]

[0015] Compound 2:

[0016]

[0017] Compound 3:

[0018]

[0019] Compound 4:

[0020]

[0021] Optionally, the cyclic sulfate ester compound is selected from at least one of vinyl sulfate, propylene sulfate, methyl vinyl sulfate, divinyl sulfate, propylene sulfate, and butylene sulfate;

[0022] The sultone compound is selected from at least one of 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sultone and methylene disulfonate.

[0023] Optionally, the additive further comprises at least one of a cyclic carbonate compound and a nitrile compound, wherein the nitrile compound is selected from at least two of succinonitrile, adiponitrile, 1,3,6-hexanetrinitrile and ethylene glycol bis(propionitrile) ether.

[0024] Optionally, the concentration of lithium salt in the electrolyte is 0.9M to 2M.

[0025] Optionally, the lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium difluorooxalatoborate (LiODFB), lithium difluorodioxalatophosphate (LiDFOP), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethylsulfonyl)imide (Li TFSI), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium difluorophosphate (LiPOF2);

[0026] The solvent includes one or more of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethyl propionate (EP), and propyl propionate (PP).

[0027] The present invention provides a lithium battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and the above-mentioned electrolyte.

[0028] Optionally, the total content of S element in the positive electrode sheet and the negative electrode sheet is not less than 150 ppm by mass.

[0029] Optionally, the positive electrode plate includes a positive electrode current collector and a positive electrode film disposed on the positive electrode current collector, and the negative electrode plate includes a negative electrode current collector and a negative electrode film disposed on the negative electrode current collector;

[0030] Wherein, the positive electrode film comprises a positive electrode active material, a positive electrode conductive agent and a positive electrode binder, and the negative electrode film comprises a negative electrode active material, a negative electrode conductive agent and a negative electrode binder;

[0031] The positive electrode active material includes one of lithium cobalt oxide, ternary material, and lithium iron phosphate;

[0032] The negative electrode active material includes one or more of graphite and silicon-containing materials.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] In the electrolyte of the present invention, the compound shown in structural formula 1 contains S element, which can form a stable interface film on the surface of the positive electrode and the negative electrode, forming sulfur-containing organic matter such as Li2SO4, Li2SO3, Li2S, CH3CH(OSO2Li), etc., reducing the reaction activity of the electrode surface, reducing the oxidative decomposition of the electrolyte at high temperature, inhibiting the consumption of the electrolyte, and improving the high-temperature cycle performance. The cyclic sulfate ester compound can reduce the film formation impedance and improve the gram capacity. The sultone compound can improve the high-temperature storage performance. Therefore, by adjusting the ratio between the compound shown in structural formula 1, the cyclic sulfate ester compound, and the sultone compound, the three can produce a synergistic effect, effectively improving the high-temperature cycle and high-temperature nesting performance of the lithium battery, and ensuring the capacity of the lithium battery. DETAILED DESCRIPTION

[0035] The invention discloses an electrolyte and a lithium battery, which are used to solve the technical problem that the existing method of improving the high-temperature cycle performance of a high-voltage system will deteriorate the capacity of the lithium battery.

[0036] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below in conjunction with specific implementation methods. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0037] The present invention provides an electrolyte comprising a lithium salt, a solvent and an additive, wherein the additive comprises a compound represented by structural formula 1, a cyclic sulfate ester compound and a sultone compound;

[0038] The compound represented by the structural formula 1, the cyclic sulfate compound and the sultone compound account for awt%, bwt% and cwt% of the electrolyte respectively, wherein -0.5≤2.5ba≤4 and 5≤2a+c≤8 are satisfied;

[0039] Structural formula 1:

[0040]

[0041] Wherein, R1 and R2 are each independently selected from any one of a hydrogen atom, a halogen atom, a vinyl sulfate group, and a vinyl carbonate group.

[0042] In the electrolyte of the present invention, the compound shown in structural formula 1 contains S element, which can form a stable interface film on the surface of the positive electrode and the negative electrode, forming sulfur-containing organic matter such as Li2SO4, Li2SO3, Li2S, CH3CH(OSO2Li), etc., reducing the reaction activity of the electrode surface, reducing the oxidative decomposition of the electrolyte at high temperature, inhibiting the consumption of the electrolyte, and improving the high-temperature cycle performance. The cyclic sulfate ester compound can reduce the film formation impedance and improve the gram capacity. The sultone compound can improve the high-temperature storage performance. Therefore, by adjusting the ratio between the compound shown in structural formula 1, the cyclic sulfate ester compound, and the sultone compound, the three can produce a synergistic effect, effectively improving the high-temperature cycle and high-temperature nesting performance of the lithium battery, and ensuring the capacity of the lithium battery.

[0043] Specifically, the ratio a of the compound represented by the structural formula 1 to the electrolyte is 0.1 to 10, preferably, a is preferably 0.2 to 5, and in some specific embodiments, a can be 0.3, 0.6, 1.2, 1.6, etc.;

[0044] The ratio b of the cyclic sulfate to the electrolyte is 0.1 to 1.5. In some specific embodiments, b can be 0.5, 0.6, 1.4, 1.5, etc.;

[0045] The ratio c of the sultones in the electrolyte is 0.1 to 5. In some specific embodiments, c can be 0.1, 0.2, 3, 4, 5, etc.

[0046] Furthermore, the compound represented by structural formula 1 can be selected from at least one of the following compounds:

[0047] Compound 1:

[0048]

[0049] Compound 2:

[0050]

[0051] Compound 3:

[0052]

[0053] Compound 4:

[0054]

[0055] Specifically, the cyclic sulfate compound in this embodiment is selected from at least one of vinyl sulfate, propylene sulfate, methyl vinyl sulfate, divinyl sulfate, propylene sulfate, and butylene sulfate;

[0056] Among them, the cyclic sulfate ester compound is preferably vinyl sulfate, which accounts for 0.1-1.5wt% of the electrolyte. In some specific embodiments, the proportion of vinyl sulfate in the electrolyte can be 0.2wt%, 0.5wt%, 0.6wt%, 1.2wt%, 1.4wt%, etc.

[0057] Specifically, the sultone compound in this embodiment is selected from at least one of 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sultone or methylene disulfonate;

[0058] Among them, the sultone compound is preferably 1,3-propane sultone, and its proportion in the electrolyte is 0.5-5wt%. In some specific embodiments, the proportion of 1,3-propane sultone in the electrolyte can be 0.5wt%, 0.7wt%, 0.9wt%, 2.0wt%, etc.

[0059] Furthermore, the additive of the present invention also includes at least one of a cyclic carbonate compound and a nitrile compound.

[0060] Specifically, the nitrile compound is selected from at least two of succinonitrile, adiponitrile, 1,3,6-hexanetrinitrile, and ethylene glycol bis(propionitrile) ether.

[0061] Furthermore, the concentration of the lithium salt in the electrolyte of the present invention is 0.9M to 2M, preferably, the concentration of the lithium salt is 1.0M to 1.3M, and in some specific embodiments, the concentration of the lithium salt can be 1.1M, 1.2M, etc.

[0062] Specifically, the lithium salt in the present invention includes one or more of lithium hexafluorophosphate (LiPF6), lithium difluorooxalatoborate (LiODFB), lithium difluorodioxalatophosphate (LiDFOP), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFS I), and lithium difluorophosphate (LiPOF2);

[0063] The solvent in the present invention includes one or more of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethyl propionate (EP), and propyl propionate (PP).

[0064] The present invention provides a lithium battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and the above-mentioned electrolyte.

[0065] It should be noted that the positive electrode sheet, the negative electrode sheet, and the separator in the present invention are wound or stacked into a battery cell, which is then placed in a shell and the above-mentioned electrolyte is injected into the shell to produce a lithium battery.

[0066] Furthermore, in the positive electrode sheet and the negative electrode sheet of the present invention, the total content of S element accounts for no less than 150 ppm by mass.

[0067] It should be noted that the compound shown in structural formula 1, cyclic sulfate compounds, and sultone compounds all contain the S element and can form films at the positive and negative electrodes to form sulfur-containing organic substances such as Li 2SO4, Li 2SO3, Li2S, and CH3CH(OSO2Li). The S element content can reflect the film-forming effect.

[0068] Further, the positive electrode plate includes a positive electrode current collector and a positive electrode film arranged on the positive electrode current collector, and the negative electrode plate includes a negative electrode current collector and a negative electrode film arranged on the negative electrode current collector;

[0069] Wherein, the positive electrode film comprises a positive electrode active material, a positive electrode conductive agent and a positive electrode binder, and the negative electrode film comprises a negative electrode active material, a negative electrode conductive agent and a negative electrode binder;

[0070] The positive electrode active material includes one of lithium cobalt oxide, ternary material, and lithium iron phosphate;

[0071] The negative electrode active material includes one or more of graphite and silicon-containing materials (such as silicon carbon).

[0072] The technical solution of the present invention is further described in detail below in conjunction with several preferred embodiments. This embodiment is implemented on the premise of the technical solution of the invention, and a detailed implementation method and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

[0073] Unless otherwise specified, the experimental materials used in the following examples can be purchased from conventional biochemical reagent companies.

[0074] Lithium battery manufacturing

[0075] Production of positive electrode:

[0076] The positive electrode active material lithium cobalt oxide (Li CoO2), the conductive agent CNT (carbon nanotube), and the adhesive PVDF (polyvinylidene fluoride) are fully stirred and mixed in NMP (N-methylpyrrolidone) solvent at a weight ratio of 97:1.5:1.5. The slurry is coated on the positive electrode collector (aluminum foil), and after drying, cold pressing, slitting, sheeting, welding, and lug gluing, a positive electrode sheet that meets the winding requirements is made.

[0077] Negative electrode production:

[0078] The negative electrode active material graphite negative electrode, conductive agent SP (conductive carbon black), thickener CMC (carboxymethyl cellulose), and adhesive SBR (styrene-butadiene rubber) are mixed in a proper amount of deionized water solvent at a mass ratio of 96.3:1:1.2:1.5 to form a uniform negative electrode slurry. The slurry is applied to the negative electrode collector (copper foil), and then dried, cold pressed, stripped, welded, and glued to the tabs to form a negative electrode sheet that meets the winding requirements.

[0079] Preparation of electrolyte:

[0080] The preparation steps of the electrolyte are as follows: EC: PC: DEC: EP: PP are mixed in a mass ratio of 15: 15: 15: 15: 40 as a solvent. After uniform mixing, Li PF6 is slowly added to obtain a mixed solution with a Li PF6 concentration of 1.2 mol / L. After the lithium salt is completely dissolved, the corresponding additive is added to obtain the electrolyte.

[0081] Examples 1-9 and Comparative Examples 1-8: All are high-voltage system electrolytes that take into account both high and low temperatures, mainly composed of lithium hexafluorophosphate and solvents. Take the baked battery cells to be filled with liquid (water content <120ppm), and inject the electrolytes of Examples 1-9 and Comparative Examples 1-8 respectively. Then, according to the normal process, stand still, form, seal twice, and test by volume.

[0082]

[0083]

[0084]

[0085] Lithium-ion battery performance test

[0086] 45℃ cycle test: Charge to 4.53V at 0.8C constant current and constant voltage at 45℃, cut-off current 0.05C, stand for 10min, discharge to 3.0V at 0.5C, record discharge capacity C0 as the initial value, repeat 500 cycles. Finally, the capacity C500 after 500 cycles is obtained, and the capacity retention rate = C500 / C0.

[0087] 45℃ nested cycle test: charge to 4.53V at 0.8C constant current and constant voltage at 45℃, cut-off current 0.05C, stand for 24h, discharge to 3.0V at 0.5C, record discharge capacity C0 as the initial value, repeat for 55 cycles. The final capacity after 55 cycles is C55, and the capacity retention rate = C55 / C0.

[0088] Test Results

[0089]

[0090]

[0091]

[0092] The test results of Comparative Examples 1 to 4 show that as the compound shown in Structural Formula 1 is increased and 1,3-propane sultone is reduced, the 45°C cycle and nesting are improved, but the capacity performance is deteriorated, which is presumably mainly related to the excessively high film formation impedance of the compound shown in Structural Formula 1.

[0093] The test results of Comparative Examples 6 to 8 show that as the amount of vinyl sulfate added increases, the capacity is significantly improved.

[0094] The test results of Comparative Examples 3 and 5 show that reducing the content of 1,3-propane sultone will deteriorate storage and easily produce gas. This is related to the fact that 1,3-propane sultone can form sulfite film-forming products at the positive and negative electrodes, which helps to improve high-temperature storage.

[0095] The test results of Examples 1 to 3 show that when the content of 1,3-propane sultone is very high, simply adding the compound shown in the structural formula does not significantly improve the high temperature, and at the same time deteriorates the capacity, which may be related to the large negative electrode film formation impedance. Comparing the test results of Examples 3 to 5, 9, it is found that Example 5 has the best performance, with no significant deterioration in capacity and a significant improvement in high temperature cycles, which is related to the ratio between the compound shown in structural formula 1, vinyl sulfate, and 1,3-propane sultone.

[0096] In summary, by adjusting the ratio between the compound shown in Structural Formula 1, the cyclic sulfate compound and the sultone compound, the three can produce a synergistic effect, effectively improving the high-temperature cycle and high-temperature nesting performance of the lithium battery and ensuring the capacity of the lithium battery.

[0097] The above is a detailed introduction to an electrolyte and a lithium battery provided by the present invention. For a person skilled in the art, according to the concept of the embodiments of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. An electrolyte, characterized in that: It includes a lithium salt, a solvent and an additive, wherein the additive includes a compound shown in structural formula 1, a cyclic sulfate ester compound and a sultone compound; The compound represented by the structural formula 1, the cyclic sulfate compound and the sultone compound account for awt%, bwt% and cwt% of the electrolyte respectively, wherein -0.5≤2.5ba≤4 and 5≤2a+c≤8 are satisfied; Structural formula 1: Wherein, R1 and R2 are each independently selected from any one of a hydrogen atom, a halogen atom, a vinyl sulfate group, and a vinyl carbonate group.

2. The electrolyte according to claim 1, characterized in that The ratio a of the compound represented by the structural formula 1 to the electrolyte is 0.1 to 10, the ratio b of the cyclic sulfates to the electrolyte is 0.1 to 1.5, and the ratio c of the sultones to the electrolyte is 0.1 to 5.

3. The electrolyte according to claim 1, characterized in that The compound of structural formula 1 is selected from at least one of the following compounds: Compound 1: Compound 2: Compound 3: Compound 4:

4. The electrolyte according to claim 1, characterized in that The cyclic sulfate compound is selected from at least one of vinyl sulfate, propylene sulfate, methyl vinyl sulfate, divinyl sulfate, propylene sulfate, and butylene sulfate; The sultone compound is selected from at least one of 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sultone and methylene disulfonate.

5. The electrolyte according to claim 4, characterized in that The additive further comprises at least one of cyclic carbonate compounds and nitrile compounds, wherein the nitrile compounds are selected from at least two of succinonitrile, adiponitrile, 1,3,6-hexanetrinitrile and ethylene glycol bis(propionitrile) ether.

6. The electrolyte according to claim 1, characterized in that The concentration of lithium salt in the electrolyte is 0.9M to 2M.

7. The electrolyte according to claim 1, characterized in that The lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium difluorooxalatoborate (LiODFB), lithium difluorobisoxalatophosphate (LiDFOP), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium difluorophosphate (LiPOF2); The solvent includes one or more of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethyl propionate (EP), and propyl propionate (PP).

8. A lithium battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte as claimed in any one of claims 1 to 7.

9. The lithium battery according to claim 8, characterized in that: In the positive electrode sheet and the negative electrode sheet, the total content of S element accounts for no less than 150 ppm by mass.

10. The lithium battery according to claim 8, characterized in that: The positive electrode sheet includes a positive electrode current collector and a positive electrode film disposed on the positive electrode current collector, and the negative electrode sheet includes a negative electrode current collector and a negative electrode film disposed on the negative electrode current collector; Wherein, the positive electrode film comprises a positive electrode active material, a positive electrode conductive agent and a positive electrode binder, and the negative electrode film comprises a negative electrode active material, a negative electrode conductive agent and a negative electrode binder; The positive electrode active material includes one of lithium cobalt oxide, ternary material, and lithium iron phosphate; The negative electrode active material includes one or more of graphite and silicon-containing materials.

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