A high-energy lithium-ion battery electrolyte and a lithium-ion battery

Abstract

The present invention discloses a lithium ion battery electrolyte and a lithium ion battery with high specific energy, relating to the technical field of lithium ion batteries, wherein the electrolyte comprises the following components: a lithium salt, an organic solvent, a film-forming additive, and a borate additive; the borate additive is a 2,5-dialkyl-1-oxolane trimethylsilyl borate compound, and its structural formula is: wherein R1 and R2 are each independently selected from an aryl group, a nitrile group, a C1-C3 alkyl group, a C1-C3 alkenyl group or a C1-C3 fluoroalkyl group. The electrolyte of the present invention preferentially generates a dense and stable passivation film on the silicon negative electrode during the battery formation process, suppressing decomposition on the silicon negative electrode active point during the electrolyte circulation process; simultaneously, a similar polymer solid electrolyte film can be generated to suppress the continuous consumption of the electrolyte caused by the expansion of silicon particles during the circulation process, reduce the interfacial impedance, and thus improve the cycle stability of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a lithium ion battery electrolyte and a lithium ion battery with high specific energy. Background Art

[0002] With the popularization of mobile Internet devices such as smartphones and laptops, the promotion of electric vehicles such as electric bicycles and electric motorcycles, and the development of aerospace technologies such as drones and space probes, lithium-ion batteries are facing higher development requirements, and small size and high energy density have become the research and development direction of high-energy-density lithium-ion batteries.

[0003] Currently, the most promising direction for high-energy-density lithium-ion battery applications is the silicon-carbon material system. However, silicon-carbon anodes also have many problems: the volume expansion and contraction of silicon particles during intercalation and deintercalation leads to particle pulverization, shedding, and electrochemical performance failure; the continuous growth of the solid electrolyte layer (SEI) on the surface of silicon particles due to continuous side reactions with the electrolyte, resulting in poor cycling performance of high-energy-density batteries using silicon-carbon anode materials. Summary of the Invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a high-energy-density lithium-ion battery electrolyte and a lithium-ion battery. The electrolyte contains a borate additive, which can preferentially form a dense and stable passivation film on the silicon negative electrode. The oxygen atoms generated by the BO-Si fracture react with the active points of the silicon negative electrode to reduce its activity, thereby achieving the effect of inhibiting the decomposition of the electrolyte at the active points of the silicon negative electrode during the circulation process. At the same time, the side-opening reaction of the pentyl ring can generate a polymer-like solid electrolyte membrane. The solid electrolyte membrane has good ionic conductivity and strong flexibility. It can inhibit the continuous consumption of electrolyte caused by the expansion of silicon particles during the cycle, reduce the interfacial impedance, and thus improve the cycle stability of the lithium-ion battery with a high-energy-density battery cell system.

[0005] The present invention proposes a high-energy-density lithium-ion battery electrolyte comprising the following components: a lithium salt, an organic solvent, a film-forming additive, and a borate additive; the borate additive is a 2,5-dialkyl-1-oxolanetrimethylsilane borate compound, the structural formula of which is shown in Formula (I):

[0006]

[0007] Wherein, R1 and R2 are each independently selected from an aryl group, a nitrile group, a C1-C3 alkyl group, a C1-C3 alkenyl group or a C1-C3 fluoroalkyl group.

[0008] Preferably, in the electrolyte, the content of the borate additive is 0.1-5 wt%.

[0009] Preferably, the lithium salt is selected from one or more of lithium chloride, lithium fluoride, lithium nitrate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bisoxalatoborate, lithium difluorooxalatoborate, and lithium difluorophosphate.

[0010] Preferably, the content of the lithium salt in the electrolyte is 10-15%.

[0011] Preferably, the organic solvent is selected from one or a combination of dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, ethyl formate, ethyl acetate, ethyl propionate, ethyl butyrate, methyl propionate, and tetrahydrofuran.

[0012] Preferably, the content of the organic solvent in the electrolyte is 75-85%.

[0013] Preferably, the film-forming additive is selected from one or a combination of more than one of vinyl sulfate, vinylene carbonate, propylene sulfite, fluoroethylene carbonate, cyclohexylbenzene, and vinyl ethylene carbonate.

[0014] Preferably, the content of the film-forming additive in the electrolyte is 1-5%.

[0015] Another object of the present invention is to provide a lithium-ion battery comprising a positive electrode, a negative electrode, a separator and the above-mentioned electrolyte.

[0016] Beneficial effects: The present invention adds a borate additive 2,5-dialkyl-1-oxopentacyclotrimethylsilyl borate to the electrolyte, thereby preferentially generating a dense and stable passivation film on the silicon negative electrode during the battery formation process. The oxygen atoms generated by the BO-Si fracture react with the active points of the silicon negative electrode to reduce its activity, thereby achieving the effect of inhibiting the decomposition of the electrolyte on the active points of the silicon negative electrode during the circulation process; at the same time, the side-opening reaction of the pentane ring can generate a polymer-like solid electrolyte membrane, which has good ionic conductivity and strong flexibility, can inhibit the continuous consumption of electrolyte caused by the expansion of silicon particles during the cycle, reduce the interface impedance, and thus improve the cycle stability of the lithium-ion battery with a high-energy-density cell system. DETAILED DESCRIPTION

[0017] The technical solution of the present invention is described in detail below through specific embodiments.

[0018] To facilitate understanding of the present invention, the present invention will be described more comprehensively below with reference to specific embodiments.

[0019] Comparative Example 1

[0020] Preparation of electrolyte:

[0021] In an argon-filled glove box (water <0.1ppm, oxygen <0.1ppm), ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 30:20:50, and then 13.5% by mass of lithium hexafluorophosphate (LiPF6) was slowly added while stirring slowly until it was completely dissolved. Then, 3% by mass of vinylene carbonate was added and stirred evenly to prepare the basic electrolyte.

[0022] Example 1

[0023] Preparation of high specific energy electrolyte:

[0024] In an argon-filled glove box (water <0.1ppm, oxygen <0.1ppm), ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 30:20:50, and then 13.5% by mass of lithium hexafluorophosphate (LiPF6) was slowly added while slowly stirring until it was completely dissolved. Then, 3% by mass of vinylene carbonate and 1% by mass of borate additive 1 were added, and the mixture was stirred evenly to obtain a high specific energy electrolyte.

[0025] Among them, the structural formula of borate additive 1 is:

[0026] Example 2

[0027] The high specific energy electrolyte in this embodiment is different from that in Example 1 only in the borate additive, which is 1% by mass of the borate additive 2. The remaining components, contents and preparation methods are the same as those in Example 1.

[0028] Among them, the structural formula of borate additive 2 is:

[0029] Example 3

[0030] The high specific energy electrolyte in this embodiment is different from that in Example 1 only in the borate additive, which is 1% by mass of the borate additive 3. The remaining components, contents and preparation methods are the same as those in Example 1.

[0031] Among them, the structural formula of the borate ester additive 3 is:

[0032] Example 4

[0033] The high specific energy electrolyte in this embodiment is different from that in Example 1 only in the borate additive, which is 1% by mass of the borate additive 4. The remaining components, contents and preparation methods are the same as those in Example 1.

[0034] Among them, the structural formula of borate additive 4 is:

[0035] Example 5

[0036] The high specific energy electrolyte in this embodiment is different from that in Example 1 only in the borate additive, which is 1% by mass of the borate additive 5. The other components, contents and preparation methods are the same as those in Example 1.

[0037] Among them, the structural formula of the borate ester additive 5 is:

[0038] Example 6

[0039] The high specific energy electrolyte in this embodiment is different from that in Example 1 only in the borate additive 6 having a mass fraction of 1%. The remaining components, contents and preparation methods are the same as those in Example 1.

[0040] Among them, the structural formula of borate additive 6 is:

[0041] Example 7

[0042] The high specific energy electrolyte in this embodiment is different from that in Example 1 only in the borate additive, which is 1% by mass of the borate additive 7. The remaining components, contents and preparation methods are the same as those in Example 1.

[0043] Among them, the structural formula of borate additive 7 is:

[0044] Example 8

[0045] The high specific energy electrolyte in this embodiment is different from that in Example 1 only in the borate additive 8 having a mass fraction of 1%. The remaining components, contents and preparation methods are the same as those in Example 1.

[0046] Among them, the structural formula of borate additive 8 is:

[0047] Example 9

[0048] The high specific energy electrolyte in this embodiment differs from that in Example 1 only in the borate additive 9 with a mass fraction of 1%. The remaining components, contents and preparation methods are the same as those in Example 1.

[0049] Among them, the structural formula of borate additive 9 is:

[0050] Example 10

[0051] The high specific energy electrolyte in this embodiment is different from that in Example 1 only in the borate additive 10 with a mass fraction of 1%. The other components, contents and preparation methods are the same as those in Example 1.

[0052] The structural formula of the borate additive 10 is:

[0053] Example 11

[0054] The high specific energy electrolyte in this embodiment is different from that in Example 1 only in the borate additive, which is 0.1% by mass of the borate additive 1. The remaining components, contents and preparation methods are the same as those in Example 1.

[0055] Example 12

[0056] The high specific energy electrolyte in this embodiment is different from that in Example 1 only in the borate additive 8 having a mass fraction of 3%. The remaining components, contents and preparation methods are the same as those in Example 1.

[0057] Example 13

[0058] The high specific energy electrolyte in this embodiment is different from that in Example 1 only in the borate additive 8 having a mass fraction of 5%. The remaining components, contents and preparation methods are the same as those in Example 1.

[0059] The electrolytes in Comparative Example 1 and Examples 1 to 13 were respectively prepared into lithium ion batteries, and the specific preparation steps were as follows:

[0060] Preparation of positive electrode:

[0061] The active material lithium nickel cobalt manganese oxide (NCM811), the conductive agent super conductive carbon (SP), and the binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in an N-methyl-2-pyrrolidone solvent system in a mass ratio of 97:1:2. The slurry is then coated on the current collector Al foil. The positive electrode sheet is obtained by slitting, die-cutting, and rolling. Its compaction density is 3.45g / cm3.

[0062] Preparation of negative electrode sheet:

[0063] The silicon-carbon negative electrode (SiOC600), conductive agent super conductive carbon (SP), binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are thoroughly stirred and mixed in a deionized water solvent system in a mass ratio of 95:1:2:2. The slurry is then coated on the current collector Cu foil. After slitting, rolling, and die-cutting, the negative electrode sheet is obtained, and its compaction density is 1.6g / cm3.

[0064] The separator used was a 12 μm polypropylene (PP) base film coated with a 4 μm nano-aluminum oxide coating.

[0065] The positive electrode sheet, separator and negative electrode sheet are stacked in sequence according to the process of laminated battery to obtain a bare cell, and then the bare cell is pre-packaged in an aluminum-plastic film, injected with the prepared electrolyte and then packaged to obtain the required soft-pack battery.

[0066] Electrical performance test:

[0067] The above-mentioned soft-pack batteries were formed and capacitated using a battery test cabinet. The formation process consisted of charging at a constant current of 0.02C to 3.0V, charging at a constant current of 0.1C to 3.4V, and finally charging at a constant current of 0.2C to 3.7V. The aging process involved stagnation at 45°C for 12 hours. The capacitation process involved charging at a constant current and voltage of 0.33C to 4.25V, followed by a cutoff current of 0.05C and then discharging at a constant current of 0.33C to 2.75V, repeated three times. The batteries were then cycled at room temperature for 800 cycles at a constant current and voltage of 1C / 1C, with a voltage range of 2.75-4.25V. After cycling, the battery impedance was measured using an internal resistance meter, and the battery thickness was measured using a vernier caliper. The internal resistance growth rate was equal to the difference between the pre- and post-cycle internal resistance divided by the pre-cycle internal resistance, and the thickness growth rate was equal to the difference between the pre- and post-cycle thickness divided by the pre-cycle thickness. The internal resistance growth rate and thickness growth rate of the batteries were compared, and the specific results are shown in Table 1.

[0068] Table 1 Battery cycle performance test results

[0069]

[0070] Comparing the test results of Examples 1-10 and Comparative Example 1, it can be seen that the electrolyte containing the high-energy-density additive 2,5-dialkyl-1-oxolanetrimethylsilyl borate provided by the present invention significantly improved the initial charge and discharge coulombic efficiency and capacity retention rate in the soft-pack battery cycle test, reduced the internal resistance and battery thickness, suppressed the impedance growth caused by the electrolyte reaction with the lithiated silicon negative electrode during the cycle, and at the same time, to a certain extent, protected the silicon negative electrode from repeated lithium insertion and deintercalation caused by particle fragmentation and differentiation, thereby improving the battery's cycle stability. This shows that the electrolyte provided by the present invention is an excellent high-energy-density lithium-ion battery electrolyte.

[0071] 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. A lithium ion battery electrolyte, characterized in that Includes the following components: Lithium salt, organic solvent, film-forming additive, borate additive; the borate additive is a 2,5-dialkyl-1-oxolane trimethylsilyl borate compound, and its structural formula is shown in formula (I): Wherein, R1 and R2 are each independently selected from an aryl group, a nitrile group, a C1-C3 alkyl group, a C1-C3 alkenyl group or a C1-C3 fluoroalkyl group.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that In the electrolyte, the mass content of the borate ester additive is 0.1-5 wt%.

3. The lithium ion battery electrolyte according to claim 1 or 2, characterized in that The lithium salt is selected from at least one of lithium chloride, lithium fluoride, lithium nitrate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bisoxalatoborate, lithium difluorooxalatoborate, and lithium difluorophosphate.

4. The lithium-ion battery electrolyte according to claim 1 or 2, characterized in that In the electrolyte, the mass content of the lithium salt is 10-15%.

5. The lithium ion battery electrolyte according to claim 1 or 2, characterized in that The organic solvent is selected from at least one of dimethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, ethyl formate, ethyl acetate, ethyl propionate, ethyl butyrate, methyl propionate, and tetrahydrofuran.

6. The lithium-ion battery electrolyte according to claim 1 or 2, characterized in that In the electrolyte, the content of the organic solvent is 75-85%.

7. The lithium-ion battery electrolyte according to claim 1 or 2, characterized in that The film-forming additive is selected from at least one of vinyl sulfate, vinylene carbonate, propylene sulfite, fluoroethylene carbonate, cyclohexylbenzene, and vinyl ethylene carbonate.

8. The lithium-ion battery electrolyte according to claim 1 or 2, characterized in that In the electrolyte, the mass content of the film-forming additive is 1-5%.

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

Images