CN111864263A - Electrolyte for silicon-carbon cathode of lithium ion battery - Google Patents

Abstract

The invention provides a composite electrolyte capable of effectively improving the electrochemical performance of a silicon-carbon-based lithium ion battery. The electrolyte comprises a non-aqueous organic solvent, lithium salt and an electrolyte additive, wherein the electrolyte additive comprises a chain sulfite compound, lithium difluorophosphate and a fluorophosphazene compound, and the content of the electrolyte additive in the electrolyte can be 0.5-12 wt%. The lithium ion battery electrolyte can effectively improve the cycle performance of the silicon-carbon-based lithium ion battery, and the internal resistance change of the battery is small.

Description

Electrolyte for silicon-carbon cathode of lithium ion battery

Technical Field

The invention belongs to the field of lithium ion batteries, and particularly relates to an electrolyte for a silicon-carbon cathode of a lithium ion battery.

Background

Silicon is used as an alloy negative electrode material because the silicon has the highest theoretical specific capacity (4200mAh/g) and lower lithium removal potential (<0.5V) is used as one of the potential choices for upgrading and updating the carbon-based cathode of the lithium ion battery. However, the silicon-based negative electrode has huge volume change and low self conductivity in the charging and discharging processes, so that the battery capacity is rapidly attenuated. And the silicon-based negative electrode material has unstable structure and is easy to generate chemical and electrochemical reactions with electrolyte (the silicon-based negative electrode is in conventional LiPF ₆The stable SEI film is difficult to form in the electrolyte, and the electrode structure is damaged, so that the stable SEI film is continuously formed on the exposed silicon surfaceFormation of a new SEI film, which aggravates corrosion of silicon and capacity degradation), causes structural collapse of an electrode material and decomposition of an electrolyte, resulting in degradation of battery performance. Therefore, optimizing the interface property of the silicon-based negative electrode/electrolyte is very important for improving the performance of the silicon-based lithium ion battery.

Research shows that the addition of the additive into the electrolyte to form the interface film with excellent properties is an effective means for realizing high performance (cycle stability, high and low temperature, safety, multiplying power and the like) of the silicon-based lithium ion battery. Therefore, in order to meet the requirement of high energy density, it is necessary to develop a novel lithium ion battery electrolyte to improve the electrochemical performance of the silicon-carbon based lithium ion battery, so as to meet the market demand.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention provides an electrolyte for a silicon-carbon negative electrode of a lithium ion battery, which can effectively improve the cycle performance of the silicon-carbon-based lithium ion battery, and the electrolyte comprises: a non-aqueous organic solvent, a lithium salt, and an electrolyte additive; wherein the electrolyte additive comprises the following three additives: the first additive is a chain sulfite compound; the second additive is lithium difluorophosphate; the third additive is a fluoro phosphazene compound.

Wherein the chain sulfite compound has a structure shown in a formula (I);

wherein R is₁、R₂Identical or different, independently of one another, from C unsubstituted or substituted by one, two or more halogen_1-12Alkyl, said halogen being selected from F, Cl, Br or I.

According to an embodiment of the invention, R in formula (I)₁、R₂Identical or different, independently of one another, from C unsubstituted or substituted by one, two or more halogen_1-6An alkyl group;

among them, the halogen is preferably F.

Preferably, R in formula (I)₁、R₂Identical or different, independently of one another, from the following groups, unsubstituted or substituted by one, two or more F: methyl, ethyl, propyl, butyl, pentyl.

As an example, the chain sulfite compound is CH₃OSO₂CH₃、CH₃CH₂OSO₂CH₃、CH₃CH₂OSO₂CH₂CH₃、CH₃(CH₂)₂OSO₂CH₂CH₃、CF₂HOSO₂CF₂CF₂H、CF₂HCF₂CH₂OSO₂CF₂CF₂H、CF₃CH₂OSO₂CH₂CF₃、CF₃CFHCF₂CH₂OSO₂CF₂CFHC₃F₇Any one or more of them.

According to an embodiment of the invention, the first additive is present in the electrolyte in an amount of 0.2 wt% to 5.0 wt%, preferably 0.1 wt% to 2.0 wt%, such as 0.5 wt%, 1.0 wt%.

The second additive is lithium difluorophosphate LiPF₂O₂。

The content of the second additive in the electrolyte is 0.1 wt% -2.0 wt%, preferably 0.1 wt% -1.0 wt%.

According to the embodiment of the invention, the fluoro phosphazene compound has a structure shown in a formula (III);

Wherein R in formula (III) may be C which is unsubstituted or substituted by one, two or more halogens_1-12Alkyl radical, C_6-20And (4) an aryl group.

Preferably, R is C unsubstituted or substituted by one, two or more halogens_1-6Alkyl, phenyl.

According to an embodiment of the present invention, the third additive is any one or more of methoxy pentafluorocyclotriphosphazene, ethoxy pentafluorocyclotriphosphazene, propoxy pentafluorocyclotriphosphazene, butoxy pentafluorocyclotriphosphazene, isopropoxy pentafluorocyclotriphosphazene, isobutoxy pentafluorocyclotriphosphazene, 2,2, 2-trifluoroethoxy pentafluorocyclotriphosphazene, phenoxy pentafluorocyclotriphosphazene, 4-fluorophenoxy pentafluorocyclotriphosphazene.

According to an embodiment of the invention, the third additive is present in the electrolyte in an amount of 0.1 wt% to 5 wt%, preferably 0.5 wt% to 2 wt%, such as 1.0 wt%, 1.5 wt%.

According to an embodiment of the present invention, the electrolyte additive may be present in the electrolyte in an amount of 0.5 wt% to 12 wt%, preferably 0.5 wt% to 5 wt%, e.g. 2.5 wt%, 3.5 wt%.

According to an embodiment of the present invention, the non-aqueous organic solvent is selected from any one or more of ethylene carbonate, ethyl propyl carbonate, diethyl carbonate, methyl propyl carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate; preferably, the non-aqueous organic solvent is any two or three of the above solvents, more preferably a mixture of Ethylene Carbonate (EC) and dimethyl carbonate (DMC), or a mixture of dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC), or a mixture of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC).

According to an embodiment of the invention, the lithium salt is selected from LiPF₆、LiBF₄、LiClO₄、LiAsF₆And LiBOB (lithium bis (oxalato) borate).

According to an embodiment of the present invention, the concentration of the lithium salt in the electrolyte may be 0.3 to 1.2mol/L, for example, 1 mol/L.

The invention also provides a preparation method of the electrolyte, which comprises the step of mixing the non-aqueous organic solvent, the lithium salt and the electrolyte additive, wherein the electrolyte additive comprises chain sulfite compounds, lithium difluorophosphate and fluoro-phosphazene compounds

The invention also provides application of the electrolyte, which is applied to a lithium ion battery.

Preferably, the electrolyte is applied to a lithium ion battery adopting a silicon-carbon cathode.

The invention also provides a lithium ion battery, which comprises the electrolyte.

According to the embodiment of the invention, the lithium ion battery further comprises a pole piece, a separation film and a lithium piece.

Terms and definitions

The term "C_1-12Alkyl is understood to preferably mean a straight-chain or branched saturated monovalent hydrocarbon radical having from 1 to 12 carbon atoms, preferably C_1-6An alkyl group. Said C is_1-6Alkyl is a straight-chain or branched saturated monovalent hydrocarbon radical having 1,2, 3, 4, 5 or 6 carbon atoms, such as methyl, ethyl, propyl, butyl, pentyl, hexyl, isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, 2-methylbutyl, 1-methylbutyl, 1-ethylpropyl, 1, 2-dimethylpropyl, neopentyl, 1-dimethylpropyl, 4-methylpentyl, 3-methylpentyl, 2-methylpentyl, 1-methylpentyl, 2-ethylbutyl, 1-ethylbutyl, 3-dimethylbutyl, 2-dimethylbutyl, 1-dimethylbutyl, 2, 3-dimethylbutyl, 1, 3-dimethylbutyl, or 1, 2-dimethylbutyl, and the like, or isomers thereof.

The term "C_6-20Aryl "is understood to preferably mean a mono-, bi-or tricyclic hydrocarbon ring having a monovalent or partially aromatic character with 6 to 20 carbon atoms, preferably" C_6-14Aryl ". The term "C_6-14Aryl "is to be understood as preferably meaning a mono-, bi-or tricyclic hydrocarbon ring having a monovalent or partially aromatic character with 6, 7, 8, 9, 10, 11, 12, 13 or 14 carbon atoms (" C_6-14Aryl group "), in particular a ring having 6 carbon atoms (" C₆Aryl "), such as phenyl; or biphenyl, or is a ring having 9 carbon atoms ("C₉Aryl radicals "), e.g. indeneFull or indenyl, or a ring having 10 carbon atoms ("C)₁₀Aryl radicals), such as tetralinyl, dihydronaphthyl or naphthyl, or rings having 13 carbon atoms ("C₁₃Aryl radicals), such as the fluorenyl radical, or a ring having 14 carbon atoms ("C)₁₄Aryl), such as anthracenyl.

The above for the term "alkyl", e.g. "C_1-12The definition of alkyl "applies equally to compounds containing" C_1-12Other terms for alkyl ", e.g. the term" halogen-substituted C_1-12Alkyl groups "and the like.

The invention has the beneficial effects that:

the invention provides a composite electrolyte for improving the electrochemical performance of a silicon-carbon-based lithium ion battery. The electrolyte for the silicon-carbon cathode of the lithium ion battery comprises a non-aqueous organic solvent, a lithium salt and an electrolyte additive, wherein the electrolyte additive comprises a chain sulfite compound, lithium difluorophosphate and a fluorophosphazene compound, and the content of the electrolyte additive in the electrolyte can be 0.5-12 wt%. The lithium ion battery electrolyte can effectively improve the cycle performance of the silicon-carbon-based lithium ion battery, and the internal resistance change of the battery is small.

Detailed Description

The present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.

The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.

Example 1

Preparing an electrolyte: in a glove box filled with argon (moisture)<1ppm, oxygen content<1ppm), mixing Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) according to the mass ratio of 1:1:1 to prepare 1mol/L LiPF₆Solution, then sequentially adding 0.5 wt% CF₃CH₂OSO₂CH₂CF₃And 1.0 wt% of lithium difluorophosphate, and stirring the mixture uniformly to obtain the lithium ion battery electrolyte of example 1.

Preparing a pole piece: the negative active material silicon carbon material SiC600, the conductive agent acetylene black and the aqueous binder 133 are fully stirred and uniformly mixed in a water system according to the mass ratio of 80:10:10, coated on a current collector Cu foil, and dried and cold-pressed to obtain the pole piece.

Preparing a lithium ion battery: and placing the processed pole piece, the isolating membrane and the lithium piece in sequence, assembling the pole piece, the isolating membrane and the lithium piece into a CR2025 button cell, and injecting the prepared electrolyte.

Example 2

Preparing an electrolyte: in a glove box filled with argon (moisture)<1ppm, oxygen content<1ppm), mixing Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) according to the mass ratio of 1:1:1 to prepare 1mol/L LiPF₆Solution, then 1.0 wt% CH was added in sequence₃CH₂OSO₂CH₂CH₃And 1.0 wt% of lithium difluorophosphate, and stirring the mixture uniformly to obtain the lithium ion battery electrolyte of example 2.

In embodiment 2, the preparation of the electrode plate and the preparation of the lithium ion battery are basically the same as those in embodiment 1, and are not described again.

Example 3

Preparing an electrolyte: in a glove box filled with argon (moisture)<1ppm, oxygen content<1ppm), mixing Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) according to the mass ratio of 1:1:1 to prepare 1mol/L LiPF₆Solution, then sequentially adding 0.5 wt% CF₃CH₂OSO₂CH₂CF₃And 1.0 wt% of 4-fluorophenoxy pentafluorocyclotriphosphazene, and uniformly stirring to obtain the lithium ion battery electrolyte of example 3.

In embodiment 3, the preparation of the electrode plate and the preparation of the lithium ion battery are basically the same as those in embodiment 1, and are not described again.

Example 4

Preparing an electrolyte: under the condition of filling with argonGlove box (moisture)<1ppm, oxygen content<1ppm), mixing Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) according to the mass ratio of 1:1:1 to prepare 1mol/L LiPF₆Solution, then 0.5 wt% CH was added in sequence₃OSO₂CH₃And 2.0 wt% of ethoxy pentafluorocyclotriphosphazene, and uniformly stirring to obtain the lithium ion battery electrolyte of example 4.

In embodiment 4, the preparation of the electrode plate and the lithium ion battery are basically the same as that in embodiment 1, and are not described again.

Example 5

Preparing an electrolyte: in a glove box filled with argon (moisture)<1ppm, oxygen content<1ppm), mixing Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) according to the mass ratio of 1:1:1 to prepare 1mol/L LiPF₆And (3) adding 1.0 wt% of lithium difluorophosphate and 1.0 wt% of 4-fluorophenoxy pentafluorocyclotriphosphazene into the solution in sequence, and uniformly stirring to obtain the lithium ion battery electrolyte of the embodiment 5.

In example 5, the preparation of the electrode sheet and the preparation of the lithium ion battery are basically the same as those in example 1, and are not described again.

Example 6

Preparing an electrolyte: in a glove box filled with argon (moisture)<1ppm, oxygen content<1ppm), mixing Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) according to the mass ratio of 1:1:1 to prepare 1mol/L LiPF ₆Solution, then sequentially adding 1.0 wt% CF₃CH₂OSO₂CH₂CF₃1.0 wt% of lithium difluorophosphate and 1.5 wt% of 2,2, 2-trifluoroethoxy pentafluorocyclotriphosphazene, and uniformly stirring to obtain the lithium ion battery electrolyte of example 6.

In example 6, the preparation of the electrode sheet and the preparation of the lithium ion battery are basically the same as those in example 1, and are not described again.

Example 7

Preparing an electrolyte: in a glove box filled with argon (moisture)<1ppm, oxygen content<1ppm), mixing Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) according to the mass ratio of 1:1:1 to prepare 1mol/L LiPF₆Solution, then sequentially adding 0.5 wt% CF₃CH₂OSO₂CH₂CF₃1.0 wt% of lithium difluorophosphate and 1.0 wt% of 4-fluorophenoxy pentafluorocyclotriphosphazene, and stirring uniformly to obtain the lithium ion battery electrolyte of example 7.

In example 7, the preparation of the electrode sheet and the preparation of the lithium ion battery are basically the same as those in example 1, and are not described again.

Comparative example 1

Preparing an electrolyte: in a glove box filled with argon (moisture)<1ppm, oxygen content<1ppm), mixing Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) according to the mass ratio of 1:1:1 to prepare 1mol/L LiPF₆And (3) solution.

In comparative example 1, the preparation of the pole piece and the preparation of the lithium ion battery are basically the same as those in example 1, and are not described again.

The batteries prepared in examples 1 to 7 and comparative example 1 were allowed to stand at normal temperature for one day and then subjected to electrochemical performance test.

The cycle performance results are shown in Table 1 when the test piece was cycled at 0.2C rate for 200 weeks at 0.005-2.0V.

TABLE 1 comparison of the cycle performance of the lithium ion batteries obtained in examples 1 to 7 and comparative example 1

As can be seen from Table 1, the use of the electrolyte additive comprising the chain sulfite compound, the lithium difluorophosphate and the fluorophosphazene compound obviously improves the cycle performance of the silicon-carbon-based lithium ion battery.

The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. The utility model provides an electrolyte for lithium ion battery silicon carbon negative pole, its cycling performance that can effectively improve silicon carbon based lithium ion battery which characterized in that, the electrolyte includes: a non-aqueous organic solvent, a lithium salt, and an electrolyte additive; wherein the electrolyte additive comprises the following three additives: the first additive is a chain sulfite compound; the second additive is lithium difluorophosphate; the third additive is a fluoro phosphazene compound.

2. The electrolyte according to claim 1, wherein the chain sulfite compound has a structure represented by formula (I);

wherein R is₁、R₂Identical or different, independently of one another, from C unsubstituted or substituted by one, two or more halogen_1-12Alkyl, said halogen being selected from F, Cl, Br or I.

3. The electrolyte of claim 2, wherein R in formula (I)₁、R₂Identical or different, independently of one another, from C unsubstituted or substituted by one, two or more halogen_1-6An alkyl group;

wherein the halogen is preferably F;

preferably, R in formula (I)₁、R₂Identical or different, independently of one another, from the following groups, unsubstituted or substituted by one, two or more F: methyl, ethyl, propyl, butyl, pentyl.

4. The electrolyte according to any one of claims 1 to 3, wherein the first additive is present in the electrolyte in an amount of 0.2 to 5.0 wt.%, preferably 0.1 to 2.0 wt.%;

the content of the second additive in the electrolyte is 0.1 wt% -2.0 wt%, preferably 0.1 wt% -1.0 wt%.

5. The electrolyte of any one of claims 1-4, wherein the fluorinated phosphazene compound has a structure represented by formula (III);

Wherein R in formula (III) may be C which is unsubstituted or substituted by one, two or more halogens_1-12Alkyl radical, C_6-20An aryl group;

preferably, said R is C, unsubstituted or substituted by one, two or more halogens_1-6Alkyl, phenyl.

6. The electrolyte of any one of claims 1 to 5, wherein the third additive is present in the electrolyte in an amount of 0.1 wt% to 5 wt%, preferably 0.5 wt% to 2 wt%;

the content of the electrolyte additive in the electrolyte is 0.5 wt% -12 wt%, preferably 0.5 wt% -5 wt%.

7. The electrolyte of any one of claims 1 to 6, wherein the non-aqueous organic solvent is selected from any one or more of ethylene carbonate, ethyl propyl carbonate, diethyl carbonate, methyl propyl carbonate, propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate; preferably, the non-aqueous organic solvent is any two or three of the above solvents, more preferably a mixture of Ethylene Carbonate (EC) and dimethyl carbonate (DMC), or a mixture of dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC), or a mixture of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC);

The lithium salt is selected from LiPF₆、LiBF₄、LiClO₄、LiAsF₆Any one or more of LiBOB (lithium bis (oxalato) borate);

in the electrolyte, the concentration of the lithium salt is 0.3-1.2 mol/L.

8. The method for preparing the electrolyte according to any one of claims 1 to 7, characterized in that it comprises: mixing the non-aqueous organic solvent, the lithium salt and the electrolyte additive, wherein the electrolyte additive comprises the chain sulfite compound, lithium difluorophosphate and the fluorophosphazene compound.

9. Use of the electrolyte of any of claims 1-7 in a lithium ion battery;

preferably, the electrolyte is applied to a lithium ion battery adopting a silicon-carbon cathode.

10. A lithium ion battery comprising the electrolyte of any one of claims 1-7;

preferably, the lithium ion battery further comprises a pole piece, a separation film and a lithium piece.