CN110649319A

CN110649319A - High-temperature-resistant electrolyte matched with high-nickel cathode material lithium ion battery

Info

Publication number: CN110649319A
Application number: CN201910995660.0A
Authority: CN
Inventors: 陈仕谋; 冯冬瑾; 王如梦; 刘玉文; 张锁江
Original assignee: Institute of Process Engineering of CAS
Current assignee: Institute of Process Engineering of CAS
Priority date: 2019-10-18
Filing date: 2019-10-18
Publication date: 2020-01-03

Abstract

The invention relates to the field of lithium ion batteries, and discloses a high-temperature-resistant electrolyte matched with a high-nickel anode material lithium ion battery. The electrolyte comprises a composite lithium salt and an organic solvent, wherein the lithium salt is lithium hexafluorophosphate, and the solvent is ethylene carbonate and ethyl methyl carbonate, the ratio of the lithium salt to the solvent is adjusted by constantly changing the concentration of the lithium salt, so that the capacity retention rate of the high-nickel anode material reaches 78.66% after 100 cycles at the high temperature of 60 ℃ under 0.5 ℃, and under the same condition, the capacity retention rate of the conventional electrolyte is only 44.85% left, the high-concentration electrolyte can effectively improve the cycle stability of the battery, the CEI formed in the high-concentration electrolyte is more stable and is not easily dissolved by the solvent, the self-decomposition of the electrolyte on the surface of the electrode material is reduced, and the application range of the lithium ion battery is greatly enlarged.

Description

High-temperature-resistant electrolyte matched with high-nickel cathode material lithium ion battery

Technical Field

The invention belongs to the field of lithium ion batteries, and particularly relates to a high-temperature-resistant electrolyte matched with a high-nickel anode material lithium ion battery.

Background

At present, lithium ion batteries have rapidly occupied most markets in the fields of portable electronic equipment, electric tools, small electric vehicles and the like due to the advantages of high energy density, less self-discharge, environmental protection and the like. At present, the power battery is mainly a lithium iron phosphate battery, but the specific energy of the power battery is limited, so that the pursuit of high specific energy is an important research and development direction of the lithium ion power battery, and the development of the high specific energy power battery such as a high nickel ternary system and the like is accelerated to meet the requirement of a new energy automobile on the driving range. However, in the process of high-temperature cycle and long-cycle service life of the high-nickel ternary material, a phase transformation occurs on the particle surface, oxygen is released, and certain potential safety hazards are caused. In addition, high nickel materials have a relatively high capacity when added, but the shrinkage volume of the particles changes greatly during delithiation. During the circulation process, cracks can occur due to the shrinkage and expansion of crystals, on one hand, the cracks can cause short circuit of electrons, on the other hand, the cracks can cause more negative reactions with the electrolytic liquid on the fresh surface, and the circulation performance and the safety of the whole battery are affected. Therefore, the development of the high-temperature resistant electrolyte matched with the high-nickel cathode material has important significance.

Disclosure of Invention

The invention aims to provide a high-temperature-resistant electrolyte matched with a high-nickel anode material lithium ion battery, so as to overcome the defects of the prior art.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a high-temperature-resistant electrolyte matched with a high-nickel anode material lithium ion battery comprises lithium salt and a solvent. Wherein the total concentration of the lithium salt in the electrolyte is 0.8-3.5 mol/L.

Preferably, the lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis fluorosulfonyl imide and lithium bis fluorooxalato borate.

Preferably, the solvent is one or two of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate and dimethyl carbonate.

Preferably, the solvent is a mixed solvent capable of improving the stability and solubility of the electrolyte.

Preferably, the invention is carried out in an argon-filled glove box having a water content of less than 1PPm and an oxygen content of less than 1PPm, the organic solvent having a water content of less than 1PPm and the lithium salt having a water content of less than 1 PPm.

The beneficial effect of above-mentioned scheme is: by using the high-concentration lithium salt electrolyte provided by the invention, the high-nickel anode material can keep good stability at high temperature, the generation of HF is inhibited, the occurrence of side reaction between the electrolyte and an electrode at high temperature is reduced, and the high-nickel anode material can show good electrochemical performance at high temperature.

Drawings

FIG. 1 is a graph showing the cycle performance of the electrolytes of example 6 of the present invention and comparative example 1 after 100 cycles at high temperature.

Detailed Description

The present invention will be described in detail with reference to specific examples. It is intended that the present invention shall include all such modifications as fall within the scope of the appended claims without departing from the spirit of the invention.

The electrolyte prepared below was added to the button cell.

Example 1

And finishing the preparation of the electrolyte in the glove box. Wherein lithium hexafluorophosphate is selected as lithium salt, and ethylene carbonate and methyl ethyl carbonate are uniformly mixed according to the volume ratio of 3: 7. Mixing 0.8mol/L LiPF₆Dissolving in mixed solvent, mixing lithium salt and electrolyte, standing for 6 hr.

Example 2

And finishing the preparation of the electrolyte in the glove box. Wherein lithium hexafluorophosphate is selected as lithium salt, and ethylene carbonate and methyl ethyl carbonate are uniformly mixed according to the volume ratio of 3: 7. 1.5mol/L LiPF₆Dissolving in mixed solvent, mixing lithium salt and electrolyte, standing for 6 hr.

Example 3

Completing the electrolyte in a glove boxThe configuration of (2). Wherein lithium hexafluorophosphate is selected as lithium salt, and ethylene carbonate and methyl ethyl carbonate are uniformly mixed according to the volume ratio of 3: 7. 2.0mol/L LiPF₆Dissolving in mixed solvent, mixing lithium salt and electrolyte, standing for 6 hr.

Example 4

And finishing the preparation of the electrolyte in the glove box. Wherein lithium hexafluorophosphate is selected as lithium salt, and ethylene carbonate and methyl ethyl carbonate are uniformly mixed according to the volume ratio of 3: 7. 2.5mol/L LiPF₆Dissolving in mixed solvent, mixing lithium salt and electrolyte, standing for 6 hr.

Example 5

And finishing the preparation of the electrolyte in the glove box. Wherein lithium hexafluorophosphate is selected as lithium salt, and ethylene carbonate and methyl ethyl carbonate are uniformly mixed according to the volume ratio of 3: 7. 3.0mol/L LiPF₆Dissolving in mixed solvent, mixing lithium salt and electrolyte, standing for 6 hr.

Example 6

And finishing the preparation of the electrolyte in the glove box. Wherein lithium hexafluorophosphate is selected as lithium salt, and ethylene carbonate and methyl ethyl carbonate are uniformly mixed according to the volume ratio of 3: 7. 3.5mol/L LiPF₆Dissolving in mixed solvent, mixing lithium salt and electrolyte, standing for 6 hr.

Example 7

And finishing the preparation of the electrolyte in the glove box. Wherein lithium hexafluorophosphate is selected as lithium salt, and ethylene carbonate and methyl ethyl carbonate are uniformly mixed according to the volume ratio of 3: 7. 4.0mol/L LiPF₆Dissolving in mixed solvent, mixing lithium salt and electrolyte, standing for 6 hr.

Comparative example 1

And finishing the preparation of the electrolyte in the glove box. Wherein lithium hexafluorophosphate is selected as lithium salt, and ethylene carbonate and methyl ethyl carbonate are uniformly mixed according to the volume ratio of 3: 7. 1.0mol/L LiPF₆Dissolving in mixed solvent, mixing lithium salt and electrolyte, standing for 6 hr.

Preparing and testing the lithium ion battery:

preparing a positive pole piece: mixing Li (Ni)_0.8Co_0.1Mn_0.1)O₂Powder: conductive carbon black: and mixing PVDF (polyvinylidene fluoride) serving as a binder according to the mass ratio of 8:1:1, uniformly mixing the PVDF with NMP to prepare slurry, uniformly stirring the slurry, coating the slurry on an aluminum foil, drying the aluminum foil in an air-blast drying oven at 80 ℃ for 12 hours, compacting the dried aluminum foil by using a tablet press, cutting the aluminum foil into 14mm pole pieces, and drying the pole pieces in vacuum at 80 ℃ for 12 hours. Weighing and placing into a glove box.

Assembling the battery: putting the positive pole piece in the middle of a negative pole shell, sucking a small amount of electrolyte by a dropper, dripping 2-3 drops of electrolyte on the pole piece, putting a diaphragm, dripping 3-4 drops of electrolyte, putting the smooth surface of the lithium piece on the battery downwards, putting the foam nickel and the negative pole shell, and finally pressing the battery to 550Kpa by a battery sealing machine. The resulting assembly was assembled into a CR2025 cell and left to stand for 10 hours before testing.

Setting circulation parameters: standing for 1h at 60 ℃, circulating the battery for 3 circles at 0.2C, then circulating for 97 circles at 0.5C, and adopting a constant-current charging and discharging mode, wherein the upper and lower limits of voltage are 2.5V-4.3V. The test results are shown in table 1 and fig. 1.

TABLE 1

Electrolyte solution	Cycle number of high temperature cycle	High temperature capacity retention ratio
			Example 1	100	40.56％
Example 2	100	60.33％
			Example 3	100	63.47％
Example 4	100	65.32％
			Example 5	100	70.68％
Example 6	100	78.66％
			Example 7	100	76.32％
Comparative example 1	100	44.85％

As can be seen from the test curves of FIG. 1 and the comparison of the data in the above table: compared with the lithium ion battery prepared by the conventional electrolyte, the high-temperature resistant electrolyte matched with the high-nickel anode material lithium ion battery provided by the invention greatly improves the cycle stability of the high-nickel anode material at a high temperature of 60 ℃. After 100 cycles of high-temperature circulation, the capacity retention rate of the conventional electrolyte is only 44.85%, and the capacity retention rate of the high-concentration lithium salt electrolyte is 78.66%, which is far higher than that of the conventional electrolyte. The concentrated electrolyte can ensure that the electrolyte is nonflammable and forms a better CEI film, thereby avoiding the poor passivation capability of common non-flammable solvents, and the high-concentration electrolyte can enhance the interaction between cations and solvent molecules and reduce the volatility of the solvent. The concentrated electrolyte can reduce the occurrence of side reactions, inhibit the generation of HF and improve the cycle performance of the NCM811 cathode material at high temperature.

The above-described embodiments are preferred embodiments of the present invention, and modifications and variations which may occur to those skilled in the art without departing from the spirit and scope of the present invention are intended to be covered by the present invention.

Claims

1. The high-temperature-resistant electrolyte matched with the high-nickel anode material lithium ion battery is characterized by comprising a lithium salt and a non-aqueous organic solvent, wherein the total concentration of the lithium salt is kept to be 0.8-3.5 mol/L.

2. The high-temperature-resistant electrolyte matched with the high-nickel cathode material lithium ion battery of claim 1 is characterized in that: the lithium salt is selected from any one of lithium hexafluorophosphate, lithium bis (oxalato) borate and lithium bis (fluorosulfonyl) imide.

3. The high-temperature-resistant electrolyte matched with the high-nickel cathode material lithium ion battery of claim 1 is characterized in that: the proportion of the positive electrode material, the conductive agent and the binder includes but is not limited to 8:1:1, 7:2:1, 9:0.5: 0.5.

4. The high-temperature-resistant electrolyte matched with the high-nickel cathode material lithium ion battery of claim 1 is characterized in that: the organic solvent is selected from one or more of ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, adiponitrile, succinonitrile, ethyl acetate and sulfolane.

5. The high-temperature-resistant electrolyte matched with the high-nickel cathode material lithium ion battery of claim 1 is characterized in that: the organic solvents are mixed according to the volume ratio or the mass ratio, and the ratio is one or more of 1:1, 3:7 and 5: 2.

6. The high-temperature-resistant electrolyte matched with the high-nickel cathode material lithium ion battery of claim 1 is characterized in that: the lithium ion battery is a Li-Ni-Co-Mn system, preferably Li (Ni)_0.8Co_0.1Mn_0.1)O₂。

7. The high-temperature-resistant electrolyte matched with the high-nickel cathode material lithium ion battery of claim 1 is characterized in that: the test temperature of the lithium ion battery electrolyte is 60 ℃.

8. A lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm and electrolyte, and is characterized in that: a high temperature safety electrolyte as claimed in any preceding claim.