CN112531212A

CN112531212A - Non-aqueous electrolyte with high-temperature characteristic and low impedance, application thereof and lithium ion battery

Info

Publication number: CN112531212A
Application number: CN202011429086.1A
Authority: CN
Inventors: 李轶; 余乐; 王仁和
Original assignee: Envision Power Technology Jiangsu Co Ltd; Envision Ruitai Power Technology Shanghai Co Ltd
Current assignee: Vision Power Technology Hubei Co ltd; Envision Power Technology Jiangsu Co Ltd; Envision Ruitai Power Technology Shanghai Co Ltd
Priority date: 2020-12-09
Filing date: 2020-12-09
Publication date: 2021-03-19
Anticipated expiration: 2040-12-09
Also published as: CN112531212B

Abstract

The invention relates to a non-aqueous electrolyte with high temperature characteristic and low impedance, application thereof and a lithium ion battery. The nonaqueous electrolyte comprises the following components in parts by mass based on the total weight of the nonaqueous electrolyte: 70-90% of non-aqueous organic solvent, 5-20% of electrolyte lithium salt and additive; the additive comprises 0.1-2.5% of lithium difluorophosphate, 0.1-2.5% of propane sultone, 0.5-3% of lithium bis-fluorosulfonyl imide, 0.1-1% of tetravinylsilane and 0.1-1.5% of tris (trimethylsilane) phosphate based on the total weight of the nonaqueous electrolyte. The TVS is used as the high-temperature additive, so that the high-temperature gas production and DCR growth of the electrolyte are inhibited; the TMSP with the reduced impedance is matched for use, the appropriate dosage is balanced, the initial impedance caused by the addition of the TVS is increased, and the purpose of taking high-temperature storage and multiplying power into consideration is achieved for the electrolyte.

Description

Non-aqueous electrolyte with high-temperature characteristic and low impedance, application thereof and lithium ion battery

Technical Field

The invention relates to the technical field of power storage devices, in particular to a non-aqueous electrolyte with high temperature characteristics and low impedance, application thereof and a lithium ion battery.

Background

In recent years, power storage devices, particularly lithium secondary batteries, have been widely used as power sources for small electronic devices such as mobile phones and notebook personal computers, and power sources for electric vehicles and power storage. Among them, laminate batteries or rectangular batteries using a laminate film such as an aluminum laminate film as an outer package member are frequently used in thin electronic devices such as tablet terminals or ultrabooks (ultrabooks) and in some pure electric new energy vehicles, but these batteries are thin flexible packages and therefore easily cause deformation such as swelling due to generation of gas inside the battery cell, which seriously affects normal operation of the electronic devices and modules.

In addition, the rate characteristics of the battery are gradually required to be improved in the new energy automobile market, and particularly, vehicles (such as PHEV and the like) which have requirements on rate performance have a lot of shares in the market, so that the battery is required to have lower impedance; however, the battery with good low impedance characteristic often has high gas production in high temperature storage, and cannot effectively give consideration to high and low temperature performance. Although the high-temperature characteristics of the conventional high-temperature electrolyte are good, the impedance is high, and the multiplying power requirement cannot be met.

On the other hand, in order to improve the capacity of the battery, the high-voltage positive electrode material is an effective way for improving the capacity density of the lithium ion battery, and under high voltage, the electrolyte is easy to decompose, so that gas generation is serious, and the performance of the battery core is seriously influenced.

In order to reduce the battery impedance, the effect of reducing the impedance can be obtained relatively quickly from the perspective of improving the electrolyte. However, the existing low-impedance electrolyte has poor high-temperature characteristics, more high-temperature gas generation and larger increase of stored DCR. Therefore, it is required to develop an electrolyte having good stability under high voltage, good cyclability, less gas production during high-temperature storage, and less DCR increase.

Disclosure of Invention

In order to solve the technical problems, the invention aims to provide a non-aqueous electrolyte with high temperature characteristics and low impedance, application thereof and a lithium ion battery.

The invention discloses a nonaqueous electrolyte which comprises the following components in parts by mass based on the total weight:

70-90% of non-aqueous organic solvent, 5-20% of electrolyte lithium salt except for lithium bis (fluorosulfonyl) imide and additives;

the additive comprises lithium difluorophosphate (LiF) based on the total weight of the nonaqueous electrolyte₂PO₂) 0.1-2.5%, 0.1-2.5% of Propane Sultone (PS), 0.5-3% of lithium bis (fluorosulfonyl) imide (LiFSI), 0.1-1% of Tetravinylsilane (TVS) and 0.1-1.5% of tris (trimethylsilane) phosphate (TMSP).

Preferably, the additive includes lithium difluorophosphate (LiF), based on the total weight of the nonaqueous electrolytic solution₂PO₂)0.1-2.5 percent of Propane Sultone (PS), 0.1-2.5 percent of bis-fluorosulfonyl imide Lithium (LiFSI), 0.5-3 percent of Tetravinylsilane (TVS) and 0.3-1 percent of tris (trimethylsilane) phosphate (TMSP).

If the content of TVS exceeds 1.0%, the effect of inhibiting gas production is not obviously improved, and the impedance of the electrolyte is increased; the content of TMSP is more than 1.5%, the effect gain of impedance reduction of the electrolyte is insignificant, and the high temperature characteristics become poor.

Furthermore, the additive also comprises vinyl sulfate (DTD), wherein the mass fraction of the vinyl sulfate in the nonaqueous electrolyte is less than 2%.

Furthermore, the additive also comprises Vinylene Carbonate (VC), wherein the vinylene carbonate accounts for less than 1% of the mass fraction of the non-aqueous electrolyte.

Further, the non-aqueous organic solvent is selected from one or more of Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC), Propylene Carbonate (PC), diethyl carbonate (DEC) and dimethyl carbonate (DMC).

Further, the non-aqueous organic solvent is selected from the group consisting of ethylene carbonate, ethylmethyl carbonate, diethyl carbonate and propylene carbonate.

Further, the mass ratio of the ethylene carbonate, the ethyl methyl carbonate, the diethyl carbonate and the propylene carbonate is 1-5:2-7:1-6: 0-4.

Preferably, the non-aqueous organic solvent is selected from the group consisting of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate, the mass ratio of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate and propylene carbonate being 3:5: 2.

According to the invention, a carbonate solvent is selected as a non-aqueous organic solvent, so that the lithium ion conductivity is relatively excellent, the viscosity of a solvent system is relatively low, the dynamic performance is relatively good, and a stable SEI film is favorably formed; meanwhile, the boiling point of the mixed solvent is high, the chemical window is stable, and the high-temperature performance is considered.

Further, the electrolyte lithium salt includes lithium hexafluorophosphate (LiPF)₆) And/or lithium bistrifluoromethanesulfonylimide (LiTFSi).

According to the invention, the used inorganic salts such as lithium difluorophosphate and LiFeSi are added into the non-aqueous electrolyte, so that an organic-inorganic electrolyte film can be formed on the surface of the negative electrode together with decomposition products of solvents such as EC and the like, SEI film damage caused by dissolution and migration of transition elements in the positive electrode to the negative electrode is reduced, and the generation of reducing gas is reduced. Meanwhile, lithium salt additives can replace part of electrolyte lithium salt (such as LiPF)₆) Reduction of PF₅Thereby reducing damage to the electrolyte membrane and the positive and negative electrode materials. The PS can inert active point positions on the surface of the anode material and slow down the oxidative decomposition reaction of the electrolyte. The tetravinyl silane has high unsaturation degree, wherein double bond groups can capture free radicals generated by electropolymerization for polymerization to form a film, and an electrolyte film can autonomously finish electropolymerization due to poor electronic conductance of a Si-containing part so as to control the thickness of the film. The film formed in this way can protect the negative electrode, and has considerable stability, so that the battery has good high-temperature performance. The higher DCR impedance brought by electronic conductance can be balanced by adjusting the solvent ratio, adjusting the additive composition. Tris (trimethylsilane) phosphate forms a CEI film on the surface of the positive electrode, has good permeability to lithium ions and can reduce impedance, but is easily decomposed at high temperature, resulting in deterioration of high-temperature characteristics of the battery cell. The absence of any additive in the nonaqueous electrolyte of the present invention does not provide the desired effect, particularly by the addition of tetraethyleneSilane improves high temperature characteristics, and tris (trimethylsilane) phosphate reduces the increase in resistance caused by tetravinylsilane, thereby improving rate characteristics.

The second purpose of the invention is to disclose the application of the non-aqueous electrolyte as the electrolyte of a high-voltage lithium ion battery, wherein the charging voltage of the high-voltage lithium ion battery is less than or equal to 5V.

Further, the high-temperature preservation temperature range of the high-voltage lithium ion battery is 45-80 ℃.

A third object of the present invention is to provide a lithium ion battery comprising: a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and the nonaqueous electrolytic solution of the present invention;

the positive electrode includes a positive electrode active material;

the negative electrode comprises a negative current collector and a negative diaphragm arranged on the negative current collector, and the negative diaphragm comprises a negative active material, a negative conductive agent and a binder.

Further, the anode active material is a ternary anode material, and the structural formula of the ternary anode material is LiNi_xCo_yMn_zL_(1-x-y-z)O₂Wherein, L is Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, W or Fe, x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, and x + y + z is more than or equal to 0.5 and less than or equal to 1.

Further, the negative electrode active material is selected from a carbon-based negative electrode active material or a graphite-based negative electrode active material; the negative electrode conductive agent is selected from one or more of acetylene black, conductive carbon black, carbon fiber, carbon nanotube and Ketjen black.

Further, the lithium ion battery is a pouch-type (soft pack) secondary battery.

Further, the carbon-based negative electrode active material is selected from one or more of crystalline carbon, amorphous carbon, and a carbon composite material.

Further, the graphite-based negative electrode active material is selected from natural graphite and/or artificial graphite.

By the scheme, the invention at least has the following advantages:

the non-aqueous electrolyte disclosed by the invention controls the gas generation of the electrolyte when the electrolyte is stored at high temperature (45-80 ℃) under high voltage (up to 5V) through the combination of various additives. TVS is used as a high-temperature additive, so that high-temperature gas generation and DCR growth of the electrolyte are inhibited; the TMSP with the reduced impedance is matched for use, the appropriate dosage is balanced, the initial impedance caused by the addition of the TVS is increased, and the purpose of taking high-temperature storage and multiplying power into consideration is achieved for the electrolyte.

The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clearly understood and to implement them in accordance with the contents of the description, the following description is made with reference to the preferred embodiments of the present invention and the accompanying detailed drawings.

Drawings

Fig. 1 is a result of a gas volume change test after high-temperature storage of different lithium secondary batteries;

fig. 2 is a DCR variation test result after high-temperature storage of different lithium secondary batteries;

fig. 3 is a DCR test result at 50% SOC state of different lithium secondary batteries at 25 ℃.

Detailed Description

The following examples are given to further illustrate the embodiments of the present invention. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.

Example 1

1. Preparation of nonaqueous electrolyte:

mixing EC/EMC/DEC into a non-aqueous organic solvent according to the mass ratio of about 3:5:2, and mixing the non-aqueous organic solvent with 14 wt% of LiPF₆After the aqueous solutions were mixed, and 1 wt% of lithium difluorophosphate, 1 wt% of LiFSi, 1 wt% of DTD, 1 wt% of PS, 0.2 wt% of VC, 0.2 wt% of TVS, and 0.5wtTMSP were added with respect to 100 parts by weight of the nonaqueous electrolyte solution, thereby obtaining a nonaqueous electrolyte solution. The obtained nonaqueous electrolyte solution contained 81.1% by mass of a nonaqueous organic solvent and LiPF₆Is 14% by mass.

2. Preparation of lithium secondary battery:

97 wt% of NCM (LiNi) as a positive electrode active material based on the total weight of the positive electrode material_xCo_yMn_1-x-yO₂X is more than or equal to 0.3, y is less than or equal to 0.3, and 1-x-y is less than or equal to 0.5), 2 wt% of carbon black serving as a conductive agent and 1 wt% of PVDF serving as a binder are added into a solvent NMP to prepare positive mixture slurry. And coating the positive electrode mixture slurry on a positive electrode current collector, drying, and rolling and die cutting to obtain a positive electrode material. The thickness of the positive electrode current collector was about 15 μm, and the material thereof was aluminum foil.

An anode mixture slurry was prepared by dissolving 98 wt% of artificial graphite as an anode active material, 1 wt% of SBR as a binder, and 1 wt% of CMC as a thickener in water, based on the total weight of the anode material. And coating the negative electrode mixture slurry on a negative electrode current collector, drying, and rolling and die-cutting the negative electrode mixture slurry to obtain a negative electrode material. Wherein the thickness of the negative electrode current collector is 8 μm, and the material is copper foil.

The prepared positive electrode material and negative electrode material are used together with a diaphragm to manufacture a laminated soft package battery by a conventional method, wherein the diaphragm is three layers, namely PP, PE and PP in sequence. Then, the nonaqueous electrolytic solution prepared in step 1 is injected to complete the production of the lithium secondary battery.

Comparative example 1

A lithium secondary battery was fabricated in the same manner as in example 1, except that TVS and TMSP were not used in the nonaqueous electrolytic solution. Specifically, the nonaqueous electrolyte consists of the following components in percentage by mass based on the total weight of the nonaqueous electrolyte:

71.8 wt% of non-aqueous organic solvent (EC/EMC/DEC in a mass ratio of about 3:5:2), LiPF₆14 wt%, 1 wt% lithium difluorophosphate, 1 wt% LiFSI, 1 wt% DTD, 1 wt% PS, 0.2 wt% VC.

Comparative example 2

A lithium secondary battery was fabricated in the same manner as in example 1, except that TVS was not used for the nonaqueous electrolytic solution. Specifically, the nonaqueous electrolyte consists of the following components in percentage by mass based on the total weight of the nonaqueous electrolyte:

81.3 wt% of non-aqueous organic solvent (EC/EMC/DEC in a mass ratio of about 3:5:2), LiPF₆14%, 1 wt% lithium difluorophosphate, 1 wt% LiFSI, 1 wt% DTD, 1 wt% PS, 0.2 wt% VC, 0.5 wt% TMSP。

Comparative example 3

A lithium secondary battery was fabricated in the same manner as in example 1, except that TMSP was not used for the nonaqueous electrolytic solution. Specifically, the nonaqueous electrolyte consists of the following components in percentage by mass based on the total weight of the nonaqueous electrolyte:

81.6 wt% of non-aqueous organic solvent (EC/EMC/DEC in a mass ratio of about 3:5:2), LiPF₆14 wt%, 1 wt% lithium difluorophosphate, 1 wt% LiFSI, 1 wt% DTD, 1 wt% PS, 0.2 wt% VC, 0.2 wt% TVS.

Comparative example 4

A lithium secondary battery was produced in the same manner as in example 1, except that the contents of the respective materials in the nonaqueous electrolytic solution were different. Specifically, the nonaqueous electrolyte consists of the following components in percentage by mass based on the total weight of the nonaqueous electrolyte:

79.8 wt% of non-aqueous organic solvent (EC/EMC/DEC in a mass ratio of about 3:5:2), LiPF₆14%, 1 wt% lithium difluorophosphate, 1 wt% LiFSI, 1 wt% DTD, 1 wt% PS, 0.2 wt% VC, 1.5 wt% TVS, 0.5wt TMSP.

Comparative example 5

79.6% of non-aqueous organic solvent (EC/EMC/DEC in a mass ratio of about 3:5:2), LiPF₆14 wt%, 1 wt% lithium difluorophosphate, 1 wt% LiFSI, 1 wt% DTD, 1 wt% PS, 0.2 wt% VC, 0.2 wt% TVS, 2 wt% TMSP.

The physical property characteristic values of the electrolyte such as conductivity, density and the like in example 1 of the present invention and comparative examples 1 to 5 are shown in the following table:

TABLE 1 Property characteristics such as conductivity and density of different electrolytes

	Electrical conductivity of	Density of
			Example 1	7.9	1.205
Comparative example 1	7.81	1.190
			Comparative example 2	8.15	1.1201
Comparative example 3	7.5	1.196
			Comparative example 4	7.04	1.216
Comparative example 5	8.31	1.221

Example 2

A lithium secondary battery was produced in the same manner as in example 1 except that the nonaqueous electrolytic solution TVS content was 0.1 wt% and the TMSP content was 0.3 wt%. Specifically, the nonaqueous electrolyte consists of the following components in percentage by mass based on the total weight of the nonaqueous electrolyte:

81.4 wt% of non-aqueous organic solvent (EC/EMC/DEC in a mass ratio of about 3:5:2), LiPF₆14 wt%, 1 wt% lithium difluorophosphate, 1 wt% LiFSI, 1 wt% DTD, 1 wt% PS, 0.2 wt% VC, TVS0.1wt%, TMSP0.3 wt%.

Example 3

The nonaqueous electrolyte consists of the following components in parts by mass based on the total weight of the nonaqueous electrolyte:

89.5 wt% of a non-aqueous organic solvent (EC/EMC/DEC in a mass ratio of about 3:5:2), LiPF₆8.7 wt%, 0.1 wt% lithium difluorophosphate, 0.6 wt% LiFSI, 0.3 wt% PS, 0.5 wt% TVS, 0.3 wt% TMSP0.

Example 4

70.5 wt% of non-aqueous organic solvent (EC/EMC/DEC in a mass ratio of about 3:5:2), LiPF ₆20 wt%, 2.5 wt% lithium difluorophosphate, 3 wt% LiFSI, 2 wt% PS, 1 wt% TVS, 1 wt% TMSP.

The lithium secondary batteries prepared above were tested for performance:

(1) the gas product volume change after high-temperature storage is as follows: charging the lithium secondary battery to 4.3V, and storing at 60 ℃ for 56 days; before storage, the volume of the lithium secondary battery was measured on days 7, 14, 28, 42 and 56 (the test method was to calculate the buoyancy by putting into water and then calculate the volume by archimedes' drainage method), and the change in volume after high-temperature storage of the battery for each day was calculated as a percentage (volume for the corresponding day/initial volume-1) × 100%) based on the number before storage. The experiment was performed at 100% SOC.

(2) DCR change after high temperature storage: charging the lithium secondary battery to 4.3V, and storing at 60 ℃ for 56 days; before storage, DCR in 50% SOC state was measured on days 7, 14, 28, and 56, and DCR change after high-temperature storage of the battery corresponding to each day was calculated as percentage (DCR/initial DCR-1) × 100% for corresponding day) based on the before-storage. Storage was performed at 100% SOC and DCR was tested at 50% SOC.

(3) The DCR was measured at an initial 50% SOC state of the cell at a test temperature of 25 ℃.

The results of the gas production volume change after high-temperature storage are shown in fig. 1. The results of the DCR change after high temperature storage are shown in fig. 2. As can be seen from the results of fig. 1-2, the volume expansion (gas production) was low after the storage at high temperature in examples 1 and 2, and the DCR growth was low after the storage at the temperature maintained for 56 days, which resulted in good high temperature characteristics, and the DCR growth was high in comparative example 4. As is clear from the results of fig. 1 and 2, the formulation of the present invention has both excellent high-temperature characteristics and rate characteristics. Meanwhile, as is clear from the results of fig. 3, examples 1 and 2 had low initial DCR (impedance). In consideration of comprehensive performance, examples 1 and 2 can give consideration to both high-temperature characteristics and low impedance.

The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, it should be noted that, for those skilled in the art, many modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.

Claims

1. The nonaqueous electrolyte is characterized by comprising the following components in parts by mass based on the total weight of the nonaqueous electrolyte:

the additive comprises 0.1-2.5% of lithium difluorophosphate, 0.1-2.5% of propane sultone, 0.5-3% of lithium bis-fluorosulfonyl imide, 0.1-1% of tetravinylsilane and 0.1-1.5% of tris (trimethylsilane) phosphate, based on the total weight of the nonaqueous electrolyte.

2. The nonaqueous electrolytic solution of claim 1, wherein: the additive also comprises vinyl sulfate, and the vinyl sulfate accounts for less than 2% of the mass fraction of the nonaqueous electrolyte.

3. The nonaqueous electrolytic solution of claim 1, wherein: the additive also comprises vinylene carbonate, wherein the vinylene carbonate accounts for less than 1% of the mass fraction of the nonaqueous electrolyte.

4. The nonaqueous electrolytic solution of claim 1, wherein: the non-aqueous organic solvent is one or more selected from ethylene carbonate, ethyl methyl carbonate, propylene carbonate, diethyl carbonate and dimethyl carbonate.

5. The nonaqueous electrolytic solution of claim 1, wherein: the non-aqueous organic solvent is selected from the group consisting of ethylene carbonate, ethylmethyl carbonate, diethyl carbonate and propylene carbonate.

6. The nonaqueous electrolytic solution of claim 5, wherein: the mass ratio of the ethylene carbonate to the ethyl methyl carbonate to the diethyl carbonate to the propylene carbonate is 1-5:2-7:1-6: 0-4.

7. The nonaqueous electrolytic solution of claim 1, wherein: the electrolyte lithium salt includes lithium hexafluorophosphate and/or lithium bistrifluoromethanesulfonylimide.

8. Use of the nonaqueous electrolytic solution of any one of claims 1 to 7 as an electrolytic solution for a high-voltage lithium ion battery having a charge voltage of 5V or less.

9. A lithium ion battery, comprising: a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and the nonaqueous electrolytic solution of any one of claims 1 to 7;

the positive electrode includes a positive electrode active material;

10. According to the claimsThe lithium ion battery of claim 9, wherein the positive active material is a ternary positive material having a structural formula of LiNi_xCo_yMn_zL_(1-x-y-z)O₂Wherein, L is Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, W or Fe, x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, and x + y + z is more than or equal to 0.5 and less than or equal to 1.