CN110994024A

CN110994024A - Electrolyte additive, electrolyte and lithium ion battery

Info

Publication number: CN110994024A
Application number: CN201911239579.6A
Authority: CN
Inventors: 李枫; 张昌明; 杜冬冬; 梁永鹏; 胡大林
Original assignee: Huizhou Highpower Technology Co Ltd
Current assignee: Huizhou Highpower Technology Co Ltd
Priority date: 2019-12-06
Filing date: 2019-12-06
Publication date: 2020-04-10
Anticipated expiration: 2039-12-06
Also published as: CN110994024B

Abstract

The invention discloses an electrolyte additive, an electrolyte and a lithium ion battery, wherein the electrolyte additive comprises 2- (2, 2-dicyanovinyl) -4-vinyl-1, 3-dioxolane and barbituric acid. The electrolyte additive can be applied to battery electrolyte, can form a stable passive film on a positive electrode and a negative electrode, has excellent toughness, can ensure that the positive electrode and the negative electrode can cover active sites under a long-time high-temperature condition without damage, and improves the floating charge performance and the overcharge performance of the battery.

Description

Electrolyte additive, electrolyte and lithium ion battery

Technical Field

The invention relates to the technical field of batteries, in particular to an electrolyte additive, an electrolyte and a lithium ion battery.

Background

Lithium ion batteries are widely used in consumer electronics and energy storage and power batteries because of their high energy, long cycle life, and low self-discharge. With the wide application of lithium ion batteries, the temperature adaptability and safety performance of the lithium ion batteries become an important index of the lithium ion batteries. The stability of a lithium ion battery is influenced by many factors, wherein the electrolyte, as an important component of the lithium ion battery, has a great influence on the environmental suitability and safety performance of the lithium ion battery.

The electrolyte generally comprises a carbonate solvent with a low flash point, lithium hexafluorophosphate and other additives, and because the solvent components have the characteristics of flammability and explosiveness, potential safety hazards are easily generated when the battery is overcharged, overdischarged or in some extreme use cases, and fire or even explosion events occur. When the lithium ion battery is overcharged, the voltage of the battery rapidly rises along with the increase of polarization, so that irreversible change of a positive electrode active material structure and oxidative decomposition of electrolyte can be caused, a large amount of gas is generated, a large amount of heat is released, the internal pressure and the temperature of the battery rapidly rise, and potential safety hazards such as explosion, combustion and the like exist. In addition, the current lithium ion battery generally has the problem of poor floating charge cycle performance at high temperature.

Disclosure of Invention

The present invention is directed to solving at least one of the problems of the prior art. Therefore, the electrolyte additive, the electrolyte and the lithium ion battery are provided, the electrolyte additive can be applied to the battery electrolyte, a stable passive film can be formed on a positive electrode and a negative electrode, the passive film is excellent in toughness, the positive electrode and the negative electrode can be enabled not to be damaged when covering active sites under a long-time high-temperature condition, and the float charge performance and the overcharge performance of the battery are improved.

The technical scheme adopted by the invention is as follows:

in a first aspect of the invention, an electrolyte additive is provided, comprising an additive a and an additive B; the additive A is 2- (2, 2-dicyanovinyl) -4-vinyl-1, 3-dioxolane (DCKVEA for short), and the structural formula is as follows:

the additive B is barbituric acid, and the structural formula of the additive B is as follows:

according to some embodiments of the invention, the mass ratio of the additive A to the additive B is (0.05-10): (0.01-5).

According to some embodiments of the invention, the mass ratio of the additive A to the additive B is (0.1-5): (0.1-2).

In a second aspect of the invention, there is provided an electrolyte comprising an electrolytic lithium salt, an organic solvent and any one of the electrolyte additives provided in the first aspect of the invention.

According to some embodiments of the invention, the electrolyte additive is present in the electrolyte in an amount of 0.06% to 15% by weight. Specifically, the mass percentage content of the additive A in the electrolyte additive in the electrolyte can be 0.05-10%, and preferably 0.1-5%; the mass percentage of the additive B in the electrolyte can be 0.01-5%, preferably 0.1-2%.

According to some embodiments of the present invention, the electrolyte lithium salt is an organic lithium salt or an inorganic lithium salt, for example, the electrolyte lithium salt may be selected from at least one of hexafluorophosphate (e.g., lithium hexafluorophosphate), hexafluoroarsenate (e.g., lithium hexafluoroarsenate), perchlorate (e.g., lithium perchlorate), trifluorosulfonyl lithium, difluoro (trifluoromethylsulfonyl) imide lithium, bis (fluorosulfonyl) imide lithium, tris (trifluoromethylsulfonyl) methide lithium.

According to some embodiments of the invention, the electrolyte lithium salt is selected from a fluorine-containing element and/or a lithium-containing element compound.

According to some embodiments of the invention, the concentration of the electrolyte lithium salt in the electrolyte solution is 0.5 to 2 mol/L. The electrolyte lithium salt concentration is too low, the conductivity of the electrolyte is low, and the multiplying power and the cycle performance of the whole battery system can be influenced; the concentration of the electrolyte lithium salt is too high, the viscosity of the electrolyte is too high, and the multiplying power of the whole battery system is also influenced. Preferably, the concentration of the electrolyte lithium salt in the electrolyte is 0.9-1.3 mol/L.

According to some embodiments of the present invention, the organic solvent is an organic complex solvent, and may be specifically selected from at least two of Ethylene Carbonate (EC), Propylene Carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), methyl formate, ethyl propionate, Propyl Propionate (PP), methyl butyrate, and tetrahydrofuran.

In a third aspect of the invention, there is provided a lithium ion battery comprising any one of the electrolytes provided in the second aspect of the invention. Specifically, the lithium ion battery includes a positive electrode sheet, a negative electrode sheet, a separator disposed between the positive electrode sheet and the negative electrode sheet, and an electrolyte.

The positive plate comprises a positive current collector and a positive active material layer positioned on the positive current collector. The material of the positive electrode active material layer generally includes a positive electrode active material, a conductive agent, and a binder; the positive electrode active material can be selected from lithium cobaltate (LiCoO)₂) Lithium nickel manganese cobalt ternary material, lithium iron phosphate (LiFePO)₄) Lithium manganate (LiMn)₂O₄) At least one of (1).

The negative plate comprises a negative current collector and a negative active material layer arranged on the negative current collector. The material of the negative active material layer generally includes a negative active material selected from natural graphite, artificial graphite, mesophase micro carbon spheres (abbreviated as MCMB), hard carbon, soft carbon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, and the like, a conductive agent, and a binder₂Spinel-structured lithiated TiO₂-Li₄Ti₅O₁₂And Li-Al alloy.

The embodiment of the invention has the beneficial effects that:

the embodiment of the invention provides an electrolyte additive, which comprises an additive A and an additive B, wherein the additive A is specifically 2- (2, 2-dicyanovinyl) -4-vinyl-1, 3-dioxolane, and the additive B is barbituric acid; the electrolyte additive can be applied to battery electrolyte, wherein the additive A and the additive B can form a stable passive film on the positive and negative electrodes of the battery through synergistic action, the passive film has excellent toughness, can ensure that the positive and negative electrodes of the battery cover active sites under long-time high-temperature conditions without being damaged, and can obviously improve the repeated high-temperature floating charge performance of the battery at high temperature and improve the floating charge performance and overcharge performance of the battery under the action of cyano-group complex metal elements in the additive A.

Detailed Description

The concept and technical effects of the present invention will be clearly and completely described below in conjunction with the embodiments to fully understand the objects, features and effects of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and those skilled in the art can obtain other embodiments without inventive effort based on the embodiments of the present invention, and all embodiments are within the protection scope of the present invention.

Preparation of electrolyte

Ethylene Carbonate (EC), diethyl carbonate (DEC) and Propylene Carbonate (PC) were mixed in a mass ratio of 1:1:1, and the mixture was uniformly mixed to obtain an organic solvent. Then adding additive A and additive B (see table 1 for details) in different proportions, mixing uniformly, adding lithium hexafluorophosphate (LiPF)₆) The required mass of lithium hexafluorophosphate was calculated from the concentration of lithium salt of 1.1mol/L, and the mixture was stirred uniformly to obtain 10 kinds of comparative example electrolytes L1# -L5 # and example electrolytes L6# -L10 #, which were stored in a sealed state at room temperature for future use. In the electrolyte of each example and comparative example, the additive A2- (2, 2-dicyanovinyl) -4-vinyl-1, 3-dioxolane (DCKVEA for short) and the additive B barbituric acid are matched to form the corresponding electrolyte additive.

TABLE 1 contents of additive A and additive B in comparative and example electrolytes

Note: the mass percentages of additive a and additive B in the electrolyte are given in table 1.

Preparation of (II) lithium ion battery

(1) Preparing a positive plate: the positive electrode active material lithium cobaltate (LiCoO)₂) The conductive agent Carbon Nano Tube (CNT) and the adhesive polyvinylidene fluoride (PVDF) are fully stirred and mixed in N-methyl pyrrolidone (NMP) solvent according to the weight ratio of 97:1.5:1.5 to form uniform anode slurry; coating the slurry on an Al foil of a positive current collector, drying and cold pressing to obtain a positive plate。

(2) Preparing a negative plate: fully stirring and mixing a negative active material graphite, a conductive agent acetylene black, a binder Styrene Butadiene Rubber (SBR), a thickening agent carboxymethyl cellulose sodium salt (CMC) and deionized water solvent according to a weight ratio of 95:2:2:1 to form uniform negative electrode slurry; and coating the slurry on a Cu foil of a negative current collector, drying and cold pressing to obtain the negative plate.

(3) Assembling: the method comprises the steps of stacking a positive plate, a diaphragm (a PE porous polymer film) and a negative plate in sequence, arranging the diaphragm between the positive plate and the negative plate to play a role in isolation, then winding to form a bare cell, then placing the bare cell into an outer packaging bag, respectively injecting the prepared electrolyte solution L1-L10 into a dried battery, then performing vacuum-pumping packaging, standing, formation, shaping and other processes, and correspondingly preparing the lithium ion battery C1-C10.

Specifically, the lithium ion batteries C1# to C10# prepared by the method and the corresponding proportion and the electrolyte of the embodiment have no difference in other aspects except for different electrolyte additives.

(III) Battery Performance test

1. High temperature float charge test of battery

The lithium ion battery C1-C10 # prepared in the method is respectively subjected to a floating charge test, and the specific test method comprises the following steps: testing the thickness of the battery core at room temperature, standing at 45 +/-2 ℃ for 2h, charging to full charge according to a standard charging mode, standing for 5min, discharging for 1h at 0.05C, standing for 5min, repeating the charging and discharging, taking out the battery core after 400 weeks, 800 weeks and 1200 weeks respectively to test the thermal state thickness, observing the appearance of the battery every day, and stopping the test when lithium pockmarks appear; and calculating the expansion rate of the battery cell by the following method:

the expansion rate of the battery core is (thickness in the high-temperature floating charging process-thickness before entering the box)/(thickness before entering the box) 100%.

The float charge test of the battery was performed by the above method, and the obtained results are shown in table 2 below.

TABLE 2 Floating Charge test results for batteries

As can be seen from table 1 and table 2 above, lithium ion battery C2# employs the electrolyte of comparative example L2# in which 11% DCKVEA alone is added, and the swelling of the battery is improved, but the battery shows a lithium separation pock after only 23 days of float charging, as compared to lithium ion battery C1 #. The batteries C6# to C10# respectively and correspondingly adopt electrolytes L6# to L10#, and the electrolytes L6# to L10# respectively adopt DCKVEA and barbituric acid with specific proportion to form an electrolyte additive, so that the gas expansion condition of the batteries and the pits on the surfaces of the batteries are improved; however, when the content of DCKVEA in the electrolyte exceeds 10% or the barbituric acid content is increased to 6%, the surface lithium separation pock of the battery is not improved but not improved, or even worsened, and particularly, when 11% of DCKVEA and 6% of barbituric acid are added to the electrolyte L5#, pock occurs in the corresponding battery C5# battery after being tested for only 15 days, because DCKVEA and barbituric acid can form films on the positive and negative electrodes of the battery, and DCKVEA can complex transition metal ions, and plays a role in protecting the positive and negative electrodes, thereby preventing the system from generating gas, but when the content of DCKVEA and barbituric acid is too high, the ion transport kinetics is insufficient due to the increase of the viscosity of the electrolyte, and the battery separates lithium.

2. Battery process testing

The overcharge test is respectively carried out on the lithium ion batteries C1# to C10# prepared in the above, and the specific test method comprises the following steps: and assembling the batteries with the capacity grading to be 72-degree breaker, charging the batteries to 200% SOC at a constant current at 1C, and keeping the cut-off voltage at 18.5V. The battery is regarded as passing when it is not ignited and not exploded. The overcharge test of the battery was performed by the above method, and the results are shown in table 3 below.

TABLE 3 Battery overcharge test results

Battery numbering	The electrolyte used	Overcharge pass rate
			Battery C1#	Comparative example electrolyte L1#	0/10
Battery C2#	Comparative example electrolyte L2#	0/10
			Battery C3#	Comparative example electrolyte L3#	0/10
Battery C4#	Comparative example electrolyte L4#	3/10
			Battery C5#	Comparative example electrolyte L5#	0/10
Battery C6#	Examples electrolyte L6#	10/10
			Battery C7#	Examples electrolyte L7#	5/10
Battery C8#	Examples electrolyte L8#	9/10
			Battery C9#	Examples electrolyte L9#	7/10
Battery C10#	Examples electrolyte L10#	5/10

As can be seen from table 1 and table 3, when 11% DCKVEA was added to the electrolyte of the battery C1# and the battery C2# alone, the overcharge of the batteries was not improved; the electrolyte of the batteries C6# -C10 # is added with appropriate amount of DCKVEA and barbituric acid, and the overcharge pass rate of the batteries is obviously improved. However, when the DCKVEA in the electrolyte of the battery exceeds 10% or the barbituric acid content is increased to 6%, the charge passage rate of the battery is reduced, and particularly, 11% of DCKVEA and 6% of barbituric acid are added to the electrolyte of the battery C5# to overcharge all the cells to NG.

Claims

1. The electrolyte additive is characterized by comprising an additive A and an additive B; the additive A is 2- (2, 2-dicyanovinyl) -4-vinyl-1, 3-dioxolane, and the additive B is barbituric acid.

2. The electrolyte additive according to claim 1, wherein the mass ratio of the additive A to the additive B is (0.05-10): (0.01-5).

3. The electrolyte additive according to claim 2, wherein the mass ratio of the additive A to the additive B is (0.1-5): (0.1-2).

4. An electrolytic solution, characterized by comprising an electrolytic lithium salt, an organic solvent, and the electrolyte additive according to any one of claims 1 to 3.

5. The electrolyte of claim 4, wherein the electrolyte additive is present in the electrolyte in an amount of 0.06-15% by weight.

6. The electrolyte of claim 4, wherein the electrolytic lithium salt is an organic lithium salt or an inorganic lithium salt.

7. The electrolyte of claim 6, wherein the electrolyte lithium salt is selected from a fluorine-containing compound and/or a lithium-containing compound.

8. The electrolyte according to claim 6, wherein the concentration of the electrolyte lithium salt in the electrolyte is 0.5 to 2 mol/L.

9. The electrolyte of claim 4, wherein the organic solvent is selected from at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl propionate, propyl propionate, methyl butyrate, and tetrahydrofuran.

10. A lithium ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator provided between the positive electrode sheet and the negative electrode sheet, and the electrolyte solution according to any one of claims 4 to 9.