CN103594729B - A kind of electrolyte for lithium ion battery - Google Patents

Abstract

The invention discloses a kind of electrolyte for lithium ion battery, this electrolyte comprises organic solvent, lithium salts and additive, described additive is additive (I) fluorine-containing sulfimide lithium, additive (II) carbonats compound or sulfonates compounds and additive (III) phosphate compounds; Wherein, additive (I): additive (II): additive (III) in the electrolytic solution shared weight ratio is 1:0.2 ~ 6:0.01 ~ 5, and in described electrolyte, additive (I) accounts for the percentage by weight of all electrolyte is 0.01%-10%.The present invention has carried out rational quality ratio optimization to additive contained in electrolyte, meets the performance requirement of lithium ion battery in low temperature discharge and high temperature circulation process; This electrolyte can form stable fine and close passivating film (SEI film) on lithium battery Carbon anode surface, prevents the further decomposition of solvent and lithium salts, improves the performance of battery significantly.

Description

A kind of electrolyte solution for lithium ion battery

technical field

The invention relates to the technical field of lithium-ion batteries, in particular to an electrolyte solution for lithium-ion batteries added with fluorine-containing lithium sulfonylimide, carbonate or sulfonate compounds and phosphoric acid ester compounds.

Background technique

Lithium-ion batteries are mainly composed of positive electrode, negative electrode, electrolyte and separator. The electrolyte, as a key material, plays the role of transmitting lithium ions and conducting current in lithium-ion batteries. It is a bridge connecting positive and negative electrode materials. Its performance determines the performance of lithium-ion batteries. At present, the electrolyte of lithium-ion batteries is mainly composed of organic solvents, lithium salts and additives. The organic solvent is usually a mixture of cyclic carbonate solvents (such as ethylene carbonate, propylene carbonate) and linear carbonate solvents (such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate); LiPF ₆ is a conductive salt; and there are many kinds of additives, which are usually selected according to different uses. It accounts for a small proportion in the electrolyte, but it has been extensively researched and developed due to its obvious functions.

During the first charging process of lithium-ion batteries, a layer of SEI film will be formed on the surface of the negative electrode. In a low-temperature environment, if the formed SEI film is too thick and the film resistance is high, lithium ions cannot migrate through, and lithium precipitation will occur; during high-temperature cycling, if the formed SEI film is not dense and stable, the SEI film will Gradually dissolve or rupture, causing the exposed negative electrode to continue to react with the electrolyte, which consumes the electrolyte and reduces the battery capacity. It can be seen that the quality of the SEI film is crucial to the performance of lithium-ion batteries. Due to different additives or different amounts of the same additive in the electrolyte, the quality of the formed SEI film will be different, and the film impedance will also be different. Therefore, it is necessary to improve the quality of the SEI film by adjusting the additives and their amounts to realize high-performance lithium-ion batteries.

A lot of research has been done on this issue. A non-aqueous electrolyte solution for lithium ion batteries and its corresponding lithium ion battery (CN103151559A) discloses a lithium salt containing LiN(SO ₂ F) ₂ , fluoroethylene carbonate (FEC) and triallyl phosphate An electrolyte solution in which ester is an additive. When LiN(SO ₂ F) ₂ is used as a lithium salt, the amount of LiN(SO 2 F) 2 used is large, and the HF content in the electrolyte will inevitably be high, and it will also be detrimental to the high-temperature cycle performance of the battery. If LiN(SO ₂ F) ₂ is used as an additive, while improving the high-temperature cycle performance of the battery, it can also avoid the occurrence of high HF content. In addition, the effect of additive amount on battery performance is not studied in this patent. More importantly, our research found that triallyl phosphate has poor low-temperature performance.

Contents of the invention

The purpose of the present invention is to solve the above-mentioned technical problems and provide an electrolyte that can form a stable and dense passivation film on the surface of the carbon negative electrode of a lithium battery.

In order to realize the above-mentioned purpose of the invention, the technical scheme adopted in the present invention is:

An electrolyte solution for a lithium-ion battery, including an organic solvent, a lithium salt and additives, the additives including additive (I), additive (II) and additive (III);

The additive (I) is lithium fluorine-containing sulfonylimide, and its structural formula is:

Among them, R1 and R2 are fluorine atoms or hydrocarbon groups in which more than one hydrogen atom is replaced by fluorine atoms;

The additive (II) is a carbonate compound or a sulfonate compound;

The additive (Ⅲ) is a phosphoric acid ester compound with the structural formula:

Wherein, R1, R2 and R3 are independently selected from hydrocarbon groups with 1-8 carbon atoms;

The weight ratio of the additive (I): additive (II): additive (III) in the electrolyte solution is 1:0.2-6:0.01-5, and the weight ratio of the additive (I) in the electrolyte solution is 1:0.2-6:0.01-5. The percentage is 0.01%-10%.

Among them, preferably, the weight ratio of the additive (I): additive (II): additive (III) in the electrolyte solution is 1:0.5-4:0.02-3.

Further preferably, the weight ratio of the additive (I): additive (II): additive (III) in the electrolyte solution is 1:1-3:0.05-2.

Wherein, both R1 and R2 in the additive (I) are fluorine. The molecular formula of the additive (I) is Li[N(SO ₂ F) ₂ ](LiFSI), namely lithium bisfluorosulfonyl imide.

Wherein, the additive (II) is vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, chloroethylene ethylene carbonate, propane sultone or butane sultone, preferably chlorocarbonic acid vinyl ester.

Wherein, R1, R2 and R3 in the additive (III) are all propenyl groups. The molecular formula of additive (Ⅲ) is (C ₃ H ₅ O) ₃ PO, ie triallyl phosphate.

Wherein, the organic solvent is one or more combinations of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate or propyl methyl carbonate.

Wherein, the lithium salt in the electrolyte is one or more combinations of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium difluorooxalate borate or lithium hexafluoroarsenate.

The beneficial effects of the present invention are:

(1) Provide a new lithium-ion battery electrolyte, and optimize the mass ratio of the additives contained in the electrolyte to meet the performance requirements of lithium-ion batteries during low-temperature discharge and high-temperature cycle;

(2) The electrolyte can form a stable and dense passivation film (SEI film) on the surface of the carbon negative electrode of the lithium battery, which prevents the further decomposition of the solvent and lithium salt, and significantly improves the performance of the battery.

Detailed ways

In order to describe in detail the technical content, structural features, achieved objectives and effects of the present invention, the following will be described in detail in conjunction with the embodiments.

The electrolyte solution of the present invention can be applied in non-aqueous electrolyte secondary lithium ion batteries such as square batteries, cylindrical batteries, button batteries, soft pack batteries and the like.

The electrolytic solution of the present invention includes an organic solvent, lithium salt and additives, the additives are additive (I) fluorine-containing lithium sulfonylimide, additive (II) carbonate compound or sulfonate compound and additive (III) phosphate ester Compounds; wherein, the weight ratio of additive (I): additive (II): additive (III) in the electrolyte is 1: 0.2 to 6: 0.01 to 5, and the additive (I) in the electrolyte accounts for all the electrolyte The weight percentage of liquid is 0.01%-10%. The organic solvent is one or more combinations of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate or propyl methyl carbonate. The lithium salt in the electrolyte is one or more combinations of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium difluorooxalate borate or lithium hexafluoroarsenate.

The additive (I) is lithium bistrifluoromethanesulfonyl imide (LiN(CF ₃ SO ₂ ) ₂ , lithium bisfluorosulfonyl imide (LiN(SO ₂ F) ₂ ), (fluorosulfonyl)( Lithium n-perfluorobutylsulfonyl)imide (Li[(SO ₂ F)(nC ₄ F ₉ SO ₂ )N], lithium (fluorosulfonyl)(trifluoromethylsulfonyl)imide Li[N( SO ₂ F)(CF ₃ SO ₂ )], preferably lithium bisfluorosulfonyl imide (LiFSI). The additive (II) is vinylene carbonate (VC), vinyl ethylene carbonate (VEC ), fluoroethylene carbonate (FEC), chlorinated vinyl ester (ClEC), propane sultone (PS), butane sultone, preferably fluoroethylene carbonate (FEC); The additive (Ⅲ) is a phosphoric acid ester compound, which is one of triethylene phosphate, triallyl phosphate, triethyl phosphate, tripropyl phosphate and tributyl phosphate, preferably triallyl phosphate ( (C ₃ H ₅ O) ₃ PO).

Below in conjunction with embodiment the present invention is described in detail:

The preparation of the electrolyte was carried out in a dry box with a dew point controlled below -40°C. The configuration process is as follows: mix ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) according to the mass ratio of EC:DMC:EMC=1:1:1, and then add 1.1mol/ L of LiPF ₆ , after fully stirring and mixing, then add the additives in sequence according to the designed formula ratio, and then fully stir and mix again to obtain the required electrolyte. Please see the following table 1 for the proportioning of specific comparative examples and embodiments:

Table 1 electrolyte comparative example and the formula table of embodiment (ratio is mass percent)

Additive Ⅰ Additive II Additive III Comparative example 1 LiFSI: 1% Comparative example 2 FEC: 1% Comparative example 3 Triallyl Phosphate: 0.1%

Comparative example 4 LiFSI: 1% FEC: 1% Comparative example 5 FEC: 1% Triallyl Phosphate: 0.1% Comparative example 6 LiFSI: 1% Triallyl Phosphate: 0.1% Example 1 LiFSI: 1% FEC: 1% Triallyl Phosphate: 0.1% Example 2 LiFSI: 1% FEC: 1% Triallyl Phosphate: 1% Example 3 LiFSI: 1% FEC: 1% Triallyl Phosphate: 3% Example 4 LiFSI: 2% FEC: 1% Triallyl Phosphate: 0.1% Example 5 LiFSI: 4% FEC: 1% Triallyl Phosphate: 0.1% Example 6 LiFSI: 1% FEC: 2% Triallyl Phosphate: 0.1% Example 7 LiFSI: 1% FEC: 3% Triallyl Phosphate: 0.1%

The test batteries are all ternary batteries, the battery design capacity is 900mAh, the positive electrode active material is nickel cobalt manganese oxide LiNi0.5Co0.2Mn0.3O2, and the negative electrode is natural graphite. In the comparative examples and examples, 4 batteries were filled with each electrolyte solution. Carry out the formation according to the following steps: 0.05C constant current charging for 3 minutes, 0.2C constant current charging for 5 minutes, 0.5C constant current charging for 25 minutes, after shelving for 1 hour, it is shaped and sealed, and then further charged at a constant current of 0.2C to 4.2V, and left at room temperature for 24 hours Afterwards, discharge to 3.0V with a constant current of 0.2C. After the battery formation is completed, two batteries are selected to perform charge and discharge cycles at a high temperature of 45°C at a rate of 1C, and the remaining two batteries are discharged at a rate of 0.5C at -30°C. The specific test results are shown in Table 2. The test results of the two batteries show that the performance test results of the same electrolyte in different batteries are relatively consistent and have good stability. (Remarks: Low temperature efficiency at -30°C = discharge capacity at 0.5C at -30°C/discharge capacity at 0.5C at room temperature, capacity retention at 500 cycles = discharge capacity after 500 cycles/discharge capacity at the first cycle)

Low-temperature discharge efficiency and high-temperature cycle capacity retention of table 2 comparative examples and examples

-30℃ discharge efficiency Capacity retention at 45°C for 500 cycles Comparative example 1 61.5% 55.0% Comparative example 2 55.1% 52.0% Comparative example 3 35.8% 48.0% Comparative example 4 63.9% 65.0% Comparative example 5 48.8% 72.5% Comparative example 6 56.8% 66.7% Example 1 71.2% 80.3%

Example 2 70.1% 82.1% Example 3 67.4% 83.5% Example 4 72.5% 81.2% Example 5 72.8% 78.5% Example 6 71.8% 84.2% Example 7 70.3% 81.3%

It can be seen from Table 2 that the discharge efficiency at -30°C and the capacity retention rate at 45°C for 500 cycles of Comparative Example 3 are both very low, but after combining with FEC (Comparative Example 5), it can be seen that the cycle performance at 45°C has been significantly improved. Due to the better low temperature performance of LiFSI (comparative example 1), it can be seen that after combining with FEC and triallyl phosphate (example 1, 2, 3, 4, 5, 6, 7), the low temperature discharge performance is improved Obviously, at the same time, the high-temperature cycle performance has also been improved to varying degrees. In the examples, compared with examples 1, 2, 3, 4, 5, and 7, the low-temperature discharge efficiency and high-temperature cycle performance of example 6 are better, indicating that the combination of three additives under this ratio is the most optimal. Excellent.

The above is only an embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by the description of the present invention, or directly or indirectly used in other related technical fields, shall be the same as The theory is included in the patent protection scope of the present invention.

Claims (6)

1. for an electrolyte for lithium ion battery, comprise organic solvent, lithium salts and additive, it is characterized in that, described additive is made up of additive (I), additive (II) and additive (III);

Described additive (I) is fluorine-containing sulfimide lithium, and structural formula is:

Wherein, R ¹, R ²for the alkyl that fluorine atom or more than one hydrogen atom are replaced by fluorine atoms;

Described additive (II) is carbonats compound or sulfonates compounds;

Described additive (III) is phosphate compounds, and structural formula is:

Wherein, R ₁, R ₂and R ₃independently be selected from the alkyl that carbon number is 1-8;

In described electrolyte, additive (I) accounts for the percentage by weight of all electrolyte is 0.01%-10%;

Described additive (I): additive (II): additive (III) in the electrolytic solution shared weight ratio is 1:(1 ~ 3): (0.05 ~ 2).

2. the electrolyte for lithium ion battery according to claim 1, is characterized in that, R in described additive (I) ¹and R ²be fluorine.

3. the electrolyte for lithium ion battery according to claim 1, it is characterized in that, described additive (II) is vinylene carbonate, vinyl ethylene carbonate, fluorinated ethylene carbonate, chlorocarbonic acid vinyl acetate, propane sultone or butane sultones.

4. the electrolyte for lithium ion battery according to claim 1, is characterized in that, R in described additive (III) ₁, R ₂and R ₃be acrylic.

5. the electrolyte for lithium ion battery according to claim 1, it is characterized in that, described organic solvent is one or more combinations in ethylene carbonate, propene carbonate, butylene, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate or methyl propyl carbonate.

6. the electrolyte for lithium ion battery according to claim 1, it is characterized in that, in described electrolyte, lithium salts is one or more combinations in lithium hexafluoro phosphate, lithium perchlorate, LiBF4, di-oxalate lithium borate, two fluorine Lithium bis (oxalate) borate or hexafluoroarsenate lithium.