Lithium battery electrolyte additive, electrolyte and lithium battery

Abstract

The invention relates to a lithium battery electrolyte additive, an electrolyte and a lithium battery, and belongs to the technical field of lithium batteries, a sulfonyl borate compound is used as the electrolyte additive, the boron-containing compound additive is fully decomposed, compact and stable interfacial films containing boron and sulfur elements are formed on the surfaces of a positive electrode and a negative electrode, and the lithium battery electrolyte additive is formed. The decomposition of the electrolyte is inhibited, the corrosion damage of HF to a positive electrode interface is blocked, meanwhile, the dissolution of transition metal ions and the damage to a negative electrode are inhibited, and the cycle performance of the lithium ion battery is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and specifically, relates to a lithium battery electrolyte additive, an electrolyte, and a lithium battery. Background Art

[0002] Lithium-ion batteries have many advantages such as high working voltage, long cycle life, large energy density, no memory effect, and environmental friendliness, and are currently the secondary batteries with the widest market application range and the most promising development prospects. With the rapid development of China's economy, products such as smart phones, laptops, digital cameras, and video cameras have put forward higher requirements for the safety performance, energy density, cycle life, etc. of lithium-ion batteries, and lithium-ion batteries are facing unprecedented challenges. The development of high-energy-density lithium-ion batteries has become a research hotspot at home and abroad, and increasing the working voltage is an effective way to improve the energy density of lithium-ion batteries. However, during the development and application of high-voltage lithium-ion batteries, the following two problems will be encountered:

[0003] First, the conventional carbonate solvent electrolyte system will undergo irreversible oxidative decomposition when the voltage reaches above 4.2V, and its decomposition products will form a relatively thick dielectric layer on the surfaces of the positive and negative electrodes, resulting in an increase in battery impedance and causing deterioration of the battery cycle performance.

[0004] Second, at high voltages, side reactions will occur at the interface where the positive electrode material contacts the electrolyte. The HF generated by the reaction will damage the positive electrode interface, and at the same time cause the dissolution of transition metal ions. The transition metal ions migrate to the negative electrode and will damage the interface film on the surface of the negative electrode, all of which will cause deterioration of the battery electrochemical performance and a decrease in the cycle performance.

[0005] Therefore, it is necessary to develop a high-voltage electrolyte additive that can preferentially undergo oxidative decomposition, form a stable interface film on both the positive and negative electrode interfaces, inhibit the decomposition of the electrolyte and the migration of transition metal ions, reduce the impedance, and improve the cycle performance of high-voltage lithium-ion batteries. Summary of the Invention

[0006] The purpose of the present invention is to provide a lithium battery electrolyte additive, an electrolyte, and a lithium battery. Using a sulfonyl borate compound as the electrolyte additive, the boron-containing compound additive is fully decomposed to form a tight and stable interface film containing boron and sulfur elements on the surfaces of the positive and negative electrodes, inhibit the decomposition of the electrolyte, block the corrosion and damage of HF to the positive electrode interface, and at the same time inhibit the dissolution of transition metal ions and the damage to the negative electrode, and improve the cycle performance of the lithium-ion battery.

[0007] Technical problems to be solved by the present invention: During the development and application of high-voltage lithium-ion batteries, the following two problems will be encountered: First, the conventional carbonate solvent electrolyte system will undergo irreversible oxidative decomposition when the voltage reaches above 4.2V, and its decomposition products will form a relatively thick dielectric layer on the surfaces of the positive and negative electrodes, resulting in an increase in battery impedance and deterioration of battery cycling performance. Second, at high voltages, side reactions will occur at the interface between the positive electrode material and the electrolyte. The HF generated by the reaction will damage the positive electrode interface, and at the same time cause the dissolution of transition metal ions. The transition metal ions migrate to the negative electrode and will damage the interface film on the surface of the negative electrode, all of which will cause deterioration of the battery's electrochemical performance and a decline in cycling performance.

[0008] The object of the present invention can be achieved by the following technical solutions:

[0009] The present invention provides a lithium battery electrolyte additive, which is a sulfonyl borate compound represented by formula (I):

[0010]

[0011] Among them, R 1 、R 2 independently select any one of C1-5 alkyl groups, cyano groups, carbon-carbon double bonds, sulfonyl groups, benzene rings or carbon-carbon triple bonds. The present invention uses a sulfonyl borate compound as an electrolyte additive to fully decompose the boron-containing compound additive, form a tight and stable interfacial film containing boron and sulfur elements on the surfaces of the positive and negative electrodes, inhibit the decomposition of the electrolyte, block the corrosion and damage of the positive electrode interface by HF, and at the same time inhibit the dissolution of transition metal ions and the damage to the negative electrode, improving the cycling performance of the lithium-ion battery.

[0012] Preferably, the lithium battery electrolyte additive has at least one of the following compounds 1 to compound 11:

[0013]

[0014] The present invention provides a lithium battery electrolyte, which is composed of a lithium salt, an organic solvent and the above-mentioned lithium battery electrolyte additive, and the mass of the lithium battery electrolyte additive accounts for 0.01-5% of the total mass of the lithium battery electrolyte.

[0015] As a preferred embodiment of the present invention, the organic solvent is selected from one or more of carbonate organic solvents, carboxylate organic solvents, phosphate organic solvents, fluorinated ether organic solvents, fluorinated ester organic solvents, and ether organic solvents.

[0016] As a preferred embodiment of the present invention, the lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium tris(trifluoromethanesulfonyl)methyl, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, or lithium tetrafluoro(oxalato)phosphate, and the molar concentration range of the lithium salt in the lithium battery electrolyte is 0.05 - 3 mol / L.

[0017] The present invention also provides a lithium battery, which includes a positive electrode, a negative electrode, a separator, and the above-mentioned lithium battery electrolyte.

[0018] As a preferred embodiment of the present invention, the positive electrode material is LiNi 0.5 Mn 1.5 O 4 、LiCoO 2 、LiCoPO 4 、LiNiPO 4 、LiNi x Co y Mn 1-x-y O 2 、and LiNi x Co y Al 1-x-y O 2 at least one of them, and the negative electrode material is at least one of graphite, mesophase carbon microspheres, silicon-carbon, or metallic lithium.

[0019] Advantages of the present invention:

[0020] In the technical solution of the present invention, the additive of the lithium battery electrolyte provided is a sulfonyl borate compound. The HOMO value of this compound is higher than that of common electrolyte solvents, and it can be preferentially oxidized to form a stable oxide film at the positive electrode interface, protecting the positive electrode material and slowing down the structural damage. At the same time, the LUMO value of this additive is less than that of common electrolyte solvents, and it can preferentially undergo reduction decomposition on the surfaces of negative electrodes such as graphite, silicon negative electrodes, and metallic lithium prior to the solvents, forming a more stable SEI film, which can effectively improve the cycling performance of high-voltage lithium batteries. Specific embodiments

[0021] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts fall within the scope of protection of the present invention.

[0022] Example 1

[0023] A lithium battery electrolyte is composed of a lithium salt, an organic solvent, and an additive. The lithium salt LiPF6 Dissolved in an organic solvent composed of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), the mass ratio of EC, DMC, and EMC is 3:2:5, the lithium salt concentration is 1 mol / L, and Compound 1 accounting for 3% of the total mass of the electrolyte is added.

[0024] A lithium battery, comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the electrolyte is the lithium-ion battery electrolyte sample prepared above.

[0025] The preparation method of the lithium battery in this embodiment includes: mixing the negative electrode material graphite, conductive agent SP, binder CMC, and dispersant SBR according to a mass ratio of 94.5:1.5:1.5:2.5, adding an appropriate amount of deionized water, mixing into a uniform paste, and then uniformly coating it on a 9-μm copper foil, and drying to obtain the negative electrode sheet. For the positive electrode material LiNi 0.5 Co 0.2 Mn 0.3 O 2 、conductive agent SP, and binder PVDF are mixed according to a mass ratio of 96:2:2, adding an appropriate amount of NMP solvent, mixing into a uniform paste, and then uniformly coating it on a 16-μm aluminum foil, and drying to obtain the positive electrode sheet. The positive electrode sheet, separator, and negative electrode sheet are wound on a winding machine in sequence to obtain a lithium-ion battery core, and the battery prepared in this experiment is a 2.5 Ah cylindrical battery. After drying the core, 5 g of the electrolyte is injected to obtain the corresponding battery sample.

[0026] Example 2

[0027] A lithium battery manufactured by the same method as in Example 1, the electrolyte is composed of lithium salt LiPF 6 Dissolved in an organic solvent composed of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), the mass ratio of EC, DMC, and EMC is 3:2:5, the lithium salt concentration is 1 mol / L, and Compound 2 accounting for 3% of the total mass of the electrolyte is added.

[0028] Example 3

[0029] A lithium battery manufactured by the same method as in Example 1, the electrolyte is composed of lithium salt LiPF 6 Dissolved in an organic solvent composed of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), the mass ratio of EC, DMC, and EMC is 3:2:5, the lithium salt concentration is 1 mol / L, and Compound 3 accounting for 3% of the total mass of the electrolyte is added.

[0030] Example 4

[0031] A lithium battery manufactured by the same method as in Example 1, the electrolyte is composed of lithium salt LiPF 6Dissolved in an organic solvent composed of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), the mass ratio of EC, DMC, and EMC is 3:2:5, the lithium salt concentration is 1 mol / L, and Compound 4 accounting for 3% of the total mass of the electrolyte is added.

[0032] Example 5

[0033] A lithium battery manufactured by the same method as in Example 1, the electrolyte consists of lithium salt LiPF 6 Dissolved in an organic solvent composed of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), the mass ratio of EC, DMC, and EMC is 3:2:5, the lithium salt concentration is 1 mol / L, and Compound 5 accounting for 3% of the total mass of the electrolyte is added.

[0034] Example 6

[0035] A lithium battery manufactured by the same method as in Example 1, the electrolyte consists of lithium salt LiPF 6 Dissolved in an organic solvent composed of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), the mass ratio of EC, DMC, and EMC is 3:2:5, the lithium salt concentration is 1 mol / L, and Compound 6 accounting for 3% of the total mass of the electrolyte is added.

[0036] Example 7

[0037] A lithium battery manufactured by the same method as in Example 1, the electrolyte consists of lithium salt LiPF 6 Dissolved in an organic solvent composed of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), the mass ratio of EC, DMC, and EMC is 3:2:5, the lithium salt concentration is 1 mol / L, and Compound 7 accounting for 3% of the total mass of the electrolyte is added.

[0038] Example 8

[0039] A lithium battery manufactured by the same method as in Example 1, the electrolyte consists of lithium salt LiPF 6 Dissolved in an organic solvent composed of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), the mass ratio of EC, DMC, and EMC is 3:2:5, the lithium salt concentration is 1 mol / L, and Compound 8 accounting for 3% of the total mass of the electrolyte is added.

[0040] Example 9

[0041] A lithium battery manufactured by the same method as in Example 1, the electrolyte consists of lithium salt LiPF 6Dissolved in an organic solvent composed of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), the mass ratio of EC, DMC, and EMC is 3:2:5, the lithium salt concentration is 1 mol / L, and Compound 9 accounting for 3% of the total mass of the electrolyte is added.

[0042] Example 10

[0043] A lithium battery manufactured by the same method as in Example 1, the electrolyte consists of lithium salt LiPF 6 Dissolved in an organic solvent composed of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), the mass ratio of EC, DMC, and EMC is 3:2:5, the lithium salt concentration is 1 mol / L, and Compound 10 accounting for 3% of the total mass of the electrolyte is added.

[0044] Example 11

[0045] A lithium battery manufactured by the same method as in Example 1, the electrolyte consists of lithium salt LiPF 6 Dissolved in an organic solvent composed of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), the mass ratio of EC, DMC, and EMC is 3:2:5, the lithium salt concentration is 1 mol / L, and Compound 11 accounting for 3% of the total mass of the electrolyte is added.

[0046] Example 12

[0047] A lithium battery manufactured by the same method as in Example 1, the electrolyte consists of lithium salt LiPF 6 Dissolved in an organic solvent composed of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), the mass ratio of EC, DMC, and EMC is 3:2:5, the lithium salt concentration is 1 mol / L, and Compound 1 accounting for 1.5% of the total mass of the electrolyte is added.

[0048] Example 13

[0049] A lithium battery manufactured by the same method as in Example 1, the difference is that the electrolyte lithium salt is composed of a mixture of LiPF 6 and LiBF 4 (mass ratio 1:1), dissolved in an organic solvent composed of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), the mass ratio of EC, DMC, and EMC is 3:2:5, the lithium salt concentration is 1 mol / L, and Compound 1 accounting for 3% of the total mass of the electrolyte is added.

[0050] Example 14

[0051] A lithium battery manufactured by the same method as in Example 1, the electrolyte consists of lithium salt LiPF 6Dissolved in an organic solvent composed of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC), the mass ratio of PC, EC, and DEC is 1:1:3, the lithium salt concentration is 1 mol / L, and Compound 1 accounting for 3% of the total mass of the electrolyte is added.

[0052] Comparative Example 1

[0053] The lithium-ion battery manufactured by the same method as in Example 1, the electrolyte is composed of lithium salt LiPF 6 Dissolved in an organic solvent composed of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), the mass ratio of EC, DMC, and EMC is 3:2:5, the lithium salt concentration is 1 mol / L, and vinylene carbonate (VC) accounting for 2% of the total mass of the electrolyte is added.

[0054] Comparative Example 2

[0055] The lithium-ion battery manufactured by the same method as in Example 1, the electrolyte is composed of lithium salt LiPF 6 Dissolved in an organic solvent composed of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC), the mass ratio of PC, EC, and DEC is 1:1:3, the lithium salt concentration is 1 mol / L, and tris(trimethylsilyl) borate (TMSB) accounting for 0.5% of the total mass of the electrolyte is added.

[0056] Comparative Example 3

[0057] The lithium-ion battery manufactured by the same method as in Example 1, the electrolyte is composed of lithium salt LiPF 6 Dissolved in an organic solvent composed of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), the mass ratio of EC, DMC, and EMC is 3:2:5, the lithium salt concentration is 1 mol / L, and fluoroethylene carbonate (FEC) accounting for 3% of the total mass of the electrolyte is added.

[0058] Performance testing

[0059] At room temperature, using a high-precision lithium battery charge and discharge device, for the assembled battery cell, test its cycle stability at 1C charge and discharge for 100 times in the voltage range of 3.0 - 4.5V.

[0060] Table 1

[0061]

[0062]

[0063] It can be seen from the data in Table 1 that the lithium-ion battery provided by the present invention has excellent cycle performance.

[0064] In the description of the specification, the descriptions referring to terms such as "one embodiment", "example", "specific example", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0065] The above content is only an example and explanation of the present invention. Those skilled in the art of the present technology can make various modifications or supplements to the described specific embodiments or use similar methods for substitution, as long as they do not deviate from the invention or exceed the scope defined by the claims of the present invention, they shall fall within the protection scope of the present invention.

Claims

1. A lithium battery electrolyte additive, characterized in that: It is a sulfonyl borate compound having the formula (I): Wherein, R1 and R2 are independently selected from any one of C1-5 alkyl, cyano, carbon-carbon double bond, sulfonyl, benzene ring or carbon-carbon triple bond.

2. The lithium battery electrolyte additive according to claim 1, characterized in that: The lithium battery electrolyte additive comprises at least one of the following compounds 1 to 11:

3. A lithium battery electrolyte, characterized in that: The invention is composed of a lithium salt, an organic solvent and the lithium battery electrolyte additive according to any one of claims 1 to 2.

4. A lithium battery electrolyte according to claim 3, characterized in that: The mass of the lithium battery electrolyte additive accounts for 0.01-5% of the total mass of the lithium battery electrolyte.

5. A lithium battery electrolyte according to claim 3, characterized in that: The organic solvent is selected from one or more of carbonate organic solvents, carboxylate organic solvents, phosphate organic solvents, fluorinated ether organic solvents, fluorinated ester organic solvents, and ether organic solvents.

6. A lithium battery electrolyte according to claim 3, characterized in that: The lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium trifluoromethylsulfonate, lithium bis(trifluoromethylsulfonyl)imide, tris(trifluoromethylsulfonyl)methyl lithium, lithium bis(oxalatoborate), lithium difluorooxalatoborate or lithium tetrafluorooxalatophosphate.

7. A lithium battery electrolyte according to claim 3, characterized in that: The molar concentration of the lithium salt in the lithium battery electrolyte is 0.05-3 mol / L.

8. A lithium battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and the lithium battery electrolyte according to any one of claims 3 to 7.

9. A lithium battery according to claim 8, characterized in that: The positive electrode material is LiNi 0.5 Mn 1.5 O4, LiCoO2, LiCoPO4, LiNiPO4, LiNi x Co y Mn 1-x-y O2, and LiNi x Co y Al 1-x-y At least one of O2.

10. A lithium battery according to claim 8, characterized in that: The negative electrode material is at least one of graphite, mesophase carbon microbeads, silicon carbon or metallic lithium.

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