JP2019099388A - Solution, electrolyte and lithium ion battery containing the same - Google Patents

Abstract

To provide an electrolyte excellent in high temperature properties.SOLUTION: The present invention provides an electrolyte containing a compound represented by the following formula (1) of 0.1 mass ppm-180000 mass ppm (where, R, R, Rmay be the same or different to denote fluorine or a C1-6 fluorinated alkyl group, M denotes an alkali metal).SELECTED DRAWING: None

Description

  The present invention relates to a solution, an electrolyte, and a lithium ion battery including the same.

The fluorosulfonyl imide salt or a derivative thereof is useful as an intermediate of a compound having an N (SO ₂ F) group or an N (SO ₂ F) ₂ group. In addition, it is useful in various applications such as being used as additives to electrolytes of electrolytes, batteries or capacitors, selective electrophilic fluorinating agents, photo acid generators, thermal acid generators, near infrared absorption dyes, etc. It is a compound (patent document 1).

International Publication No. 2011/149095

  However, the electrolyte contained in the battery or capacitor is frequently subjected to high temperatures during use. Therefore, the electrolytic solution is required to have good high-temperature characteristics, but the electrolytic solution using a fluorosulfonylimide salt or a derivative thereof has room for improvement from the viewpoint of high-temperature characteristics.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a solution suitable for use at high temperature, an electrolytic solution excellent in high temperature characteristics, and a lithium ion battery using the same.

（一般式（１）中、Ｒ^１、Ｒ^２、Ｒ^３はそれぞれフッ素又は炭素数１〜６のフッ化アルキル基を表す。） The solution of the present invention contains 0.1 mass ppm to 180,000 mass ppm of a compound represented by the following formula (1).

(In general formula (1), R ¹ , R ² and R ³ each represent fluorine or a fluorinated alkyl group having 1 to 6 carbon atoms.)

The solution of the present invention preferably further contains 0.1 mass ppm to 10,000 mass ppm of LiFSO ₃ .

The solution of the present invention preferably further comprises at least one compound selected from the group consisting of LiPF ₆ , LiBF ₄ , and LiN (SO ₂ C _n F _{2n + 1} ) ₂ (n is an integer of 0 to 6).

  The solution of the present invention preferably contains 1 mass ppm to 90 mass% of lithium bis (fluorosulfonyl) imide.

In the solution of the present invention, it is preferable that all of R ¹ , R ² and R ³ in the above formula (1) are a fluorine atom.

  The electrolyte of the present invention contains the above solution.

  The lithium ion battery of the present invention contains the above-mentioned electrolytic solution.

  ADVANTAGE OF THE INVENTION According to this invention, the solution suitable for the use in high temperature, the electrolyte solution which is excellent in high temperature characteristics, and a lithium ion battery using the same can be provided.

  Hereinafter, embodiments of the present invention will be described in detail.

（一般式（１）中、Ｒ^１、Ｒ^２、Ｒ^３はそれぞれフッ素又は炭素数１〜６のフッ化アルキル基を表す。） The solution of the present embodiment contains 0.1 mass ppm to 180,000 mass ppm of a compound represented by the following formula (1). In addition, in this specification, content of each component in a solution is represented by the ratio (mass ppm etc.) with respect to the whole quantity of a solution.

(In general formula (1), R ¹ , R ² and R ³ each represent fluorine or a fluorinated alkyl group having 1 to 6 carbon atoms.)

  Examples of applications of the solution include electrolytes such as batteries and capacitors, selective electrophilic fluorinating agents, photoacid generators, thermal acid generators, near infrared absorbing dyes, antistatic agents, and the like. In particular, since the solution contains a component excellent in heat resistance, it is suitable for use in a high temperature environment.

As R ¹ , R ² and R ³ , the fluorinated alkyl group having 1 to 6 carbon atoms may be linear or branched. The fluorinated alkyl group having 1 to 6 carbon atoms may be one in which one or more hydrogen atoms of the alkyl group having 1 to 6 carbon atoms are substituted with a fluorine atom, and all hydrogen atoms are substituted with a fluorine atom It may be a perfluoroalkyl group.

It is lithium N, N-bis (fluorosulfonyl) imide sulfamoyl fluoride represented by following formula (2) that all of R < ¹ >, R < ² > and R < ³ > are fluorine atoms.

  The content of the compound of the above formula (1) in the solution is preferably 1 mass ppm to 20000 mass ppm, and more preferably 10 ppm to 10000 mass ppm, from the viewpoint of further enhancing the high temperature characteristics of the battery.

  It can be made into a solution by dissolving the compound of Formula (1) in a solvent. The solvent is not particularly limited as long as it is a solvent used for electrolytic solutions such as capacitors and lithium ion batteries, but, for example, dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, diethyl carbonate, propylene carbonate, butylene carbonate, methyl ethyl Examples thereof include carbonates such as carbonate, esters such as γ-butyrolactone and methyl formate, and ethers such as 1,2-dimethoxyethane and tetrahydrofuran. These solvents may be used alone or in combination of two or more.

The compound of the formula (1) may be independently dissolved in a solvent to form an electrolytic solution, but LiFSO ₃ , LiPF ₆ , LiBF ₄ , and LiN (SO ₂ C _n F _{2n + 1} ) ₂ (n = 0 to 6) In combination with at least one compound selected from the group consisting of Among these, LiFSO ₃ , LiPF ₆ or LiN (SO ₂ F) ₂ (lithium (bisfluorosulfonyl) imide, also called LiFSI) is preferable. It is preferable that the solution of this embodiment contains 1 mass ppm-90 mass% of lithium bis (fluoro sulfonyl) imides.

When the electrolytic solution contains LiFSO ₃ , the content is 0.1 mass ppm to 10000 mass ppm from the viewpoint of suppressing the increase in resistance of the battery and suppressing the decrease in ion conductivity and the increase in viscosity of the electrolytic solution. Preferably, 10 mass ppm to 5000 mass ppm is more preferable, and 100 mass ppm to 2000 mass ppm is more preferable.

  When the electrolytic solution contains LiFSI, the content is preferably 1 mass ppm to 900000 mass ppm from the viewpoint of improving ion conductivity and suppressing corrosion of the current collector such as aluminum, and is preferably 10000 mass ppm to 400000. It is more preferable that it is mass ppm, and it is further more preferable that it is 30000 mass ppm-150,000 mass ppm.

The compound of the above formula (1) can be obtained by heating the solid of the compound represented by the formula (XSO ₂ ) (XSO ₂ ) NLi. In the compound, X is selected to correspond to the above R ¹ , R ² and R ³ , and (XSO ₂ ) (XSO ₂ ) NLi according to the structure of the desired compound represented by the formula (1) One or two or more of the compounds represented by can be used as appropriate. For example, the compound of the above formula (2) is obtained by heating a solid of LiFSI. As heating temperature, 150 degreeC or more is preferable, It is more preferable in it being 155 degreeC or more, It is more preferable in it being 155 degreeC-160 degreeC. There is no restriction | limiting in particular as heating time, For example, it is preferable in it being 30 minutes or more, and it is more preferable in it being 1 hour-120 hours.

  When a solid of LiFSI is heated to synthesize a compound of the above formula (2), substantially all of LiFSI can be converted to a compound of the above formula (2) by heating for a sufficiently long time. Only a part can also be converted to the compound of the above formula (2). When only a part is converted, the solid after heating is a mixture (electrolyte composition) containing LiFSI and the compound of the above formula (2), and can be dissolved in a solvent to form an electrolyte.

  Although the mechanism by which the compound of the above formula (2) is generated when heating a solid of LiFSI is not necessarily clear, the present inventors, for example, have a reaction represented by the following reaction formula. It is believed that the compound is formed.

  As bis (fluorosulfonyl) imide salt which is a raw material, a commercially available thing may be used and what was synthesize | combined may be used. The alkali metal bis (fluorosulfonyl) imide salt is, for example, a cation of an ammonium bis (fluorosulfonyl) imide obtained by the reaction of ammonia and bis (chlorosulfonyl) imide using a hydroxide salt of an alkali metal or the like. It can also be obtained by conducting an exchange reaction.

  The electrolyte solution of the present embodiment is excellent in high temperature characteristics such as the cycle capacity retention ratio at high temperature, and thus can be suitably used for a capacitor, a lithium ion battery, and the like.

  There is no restriction | limiting in particular as a concrete structure of a lithium ion battery, A general structure is employable. The positive electrode can include a commonly used positive electrode material such as a composite oxide of Li and a transition metal, and the negative electrode can be a commonly used negative electrode material such as graphite, an oxide of Si or Sn, etc. Can be included.

  Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited thereto.

[ ¹⁹ F-NMR measurement]
In the following, measurement of ¹⁹ F-NMR was performed under the following conditions.
Measuring device: VNMRS 600 (manufactured by VARIAN)
Heavy solvent: acetonitrile-d ₃
Analysis concentration: sample concentration; 12% by mass, internal standard: 3.6% by mass
Accumulated number of times: 16 times

Synthesis Example 1
[Fluorosulfonylimide Synthesis Step (Fluorination Step)]
Under a nitrogen stream, 990 g of butyl acetate was charged into a Pyrex (registered trademark) reaction vessel A (having an inner volume of 5 L) equipped with a stirrer. To the charged butyl acetate, 110 g (514 mmol) of bis (chlorosulfonyl) imide was added dropwise at room temperature (25 ° C.).

  55.6 g (540 mmol, 1.05 equivalents relative to bis (chlorosulfonyl) imide) of zinc fluoride is added in one portion to the obtained butyl acetate solution of bis (chlorosulfonyl) imide at room temperature, and zinc fluoride Stir at room temperature for 6 hours until complete dissolution. The resulting solution is referred to as solution A.

[Cation Exchange Step 1-Synthesis of Ammonium Salt]
In a Pyrex (registered trademark) reaction vessel B (3 L content) equipped with a stirrer, 297 g (4360 mmol, 8.49 equivalents relative to bis (chlorosulfonyl) imide) of 25 mass% ammonia water was charged. Solution A was added dropwise to the reaction vessel B at room temperature while stirring the ammonia water. After completion of the addition of the solution A, the stirring was stopped, and the reaction system was divided into two layers of an aqueous layer and an organic layer. The aqueous layer containing by-products such as zinc chloride was removed to obtain a butyl acetate solution of ammonium bis (fluorosulfonyl) imide which is an organic layer.

The ¹⁹ F-NMR measurement was performed using the obtained organic layer as a sample (internal standard substance: trifluoromethylbenzene). In the chart of the obtained ¹⁹ F-NMR, a peak (δ 56.0 ppm) derived from ammonium bis (fluorosulfonyl) imide was observed. ^From the measurement results of ¹⁹ F-NMR, the concentration of ammonium bis (fluorosulfonyl) imide in the organic layer was determined by the following internal standard method. That is, by comparing the amount of trifluoromethylbenzene added as an internal standard substance, and the integral value of the peak derived from this with the integral value of the peak derived from ammonium bis (fluorosulfonyl) imide, in the sample The content of ammonium bis (fluorosulfonyl) imide was determined. The concentration of ammonium bis (fluorosulfonyl) imide in the organic layer is determined from the determined content of ammonium bis (fluorosulfonyl) imide and the concentration (sample concentration) of the organic layer in the sample for which ¹⁹ F-NMR measurement was performed. Calculated. Thus, the crude yield of ammonium bis (fluorosulfonyl) imide was calculated to be 416 mmol.

[Cation Exchange Step 2-Synthesis of Lithium Salt]
Add 133 g (834 mmol in terms of Li) of a 15% by mass aqueous solution of lithium hydroxide so that the amount of lithium is 2 equivalents with respect to ammonium bis (fluorosulfonyl) imide contained in the obtained organic layer, and Stir for 10 minutes. Thereafter, the aqueous layer was removed from the reaction system to obtain a butyl acetate solution of lithium bis (fluorosulfonyl) imide which is an organic layer. Hereinafter, lithium bis (fluorosulfonyl) imide is also referred to as LiFSI.

Using the obtained organic layer as a sample, it was confirmed by ICP emission spectrometry that the proton of fluorosulfonylimide was exchanged to a lithium ion.
In addition, ¹⁹ F-NMR measurement was performed using the obtained organic layer as a sample (internal standard substance: trifluoromethylbenzene). The peak of LiFSI was observed in the chart of the obtained ¹⁹ F-NMR. The concentration of LiFSI in the organic layer was determined by the internal standard method described above. The concentration of LiFSI in the organic layer was 7% by mass (yield of organic layer: 994 g, yield of LiFSI: 69.6 g).

[Concentration step]
A portion of the solvent was distilled off from the organic layer obtained in the above-mentioned cation exchange step 2 under reduced pressure using a rotary evaporator ("REN-1000", manufactured by IWAKI) to obtain 162 g of a concentrated solution of LiFSI (Concentration: 43% by mass).

  The above concentrated solution (162 g) was added to a 500 mL separable flask equipped with a dropping funnel and a condenser and a receiver. The pressure in the separable flask was reduced to 667 Pa using a vacuum pump, and the separable flask was immersed in an oil bath heated to 55 ° C. Next, the concentrated solution in the separable flask was slowly heated with stirring to distill the reaction solvent from the fluorosulfonylimide synthesis step, which is the reaction solvent. The total volume of 1,2,4-trimethylbenzene as a poor solvent was added to the separable flask as a poor solvent in the same amount as the total amount of liquid collected in the distillation receiver within 10 minutes after the start of distillation. Thereafter, by continuing to add the same volume of 1,2,4-trimethylbenzene to the separable flask every 10 minutes, the reaction solution is further concentrated, and the butyl acetate in the system (reaction solvent (reaction solvent is removed). Crystals of LiFSI were precipitated by changing the mixing ratio of (1) and 1,2,4-trimethylbenzene. After repeating the above operation until the supernatant in the separable flask became clear, the flask was cooled to room temperature, and the obtained suspension of LiFSI crystals was filtered to obtain crystals of LiFSI. The time from the start of heating of the concentrated solution to the end of the concentration step was 6 hours, and the time required for the start of crystal precipitation was 2 hours.

  Next, the obtained crystals were washed with a small amount of hexane, and then transferred to a flat bottom vat, and dried under reduced pressure at 667 Pa at 55 ° C. for 12 hours to obtain white crystals of LiFSI (yield: 65.4 g).

  An acetonitrile solution of the obtained LiFSI white crystals was prepared. The compound contained in the produced | generated fluoro sulfonyl imide salt was measured using the said acetonitrile solution as a measurement sample using a gas chromatograph mass spectrometer. As a result of measurement, the crystals contained 539 ppm by weight of butyl acetate and 136 ppm by weight of 1,2,4-trimethylbenzene as a residual solvent.

  Further, 0.1 g of the obtained LiFSI white crystal was mixed with 9.9 g of ultrapure water to prepare an aqueous solution having a concentration of 1 mass%. The chlorine content derived from the halogenated hydrocarbon contained in the measurement sample was measured using the aqueous solution as a measurement sample using an ICP emission spectrophotometer (ICPE-9000: manufactured by Shimadzu Corporation). The quantitative limit (lower limit value) of the above-mentioned ICP emission spectrometer is 0.1 mass ppm.

  It can be judged from the isotope peak, the molecular weight and the fragment that the chlorine detected by the ICP emission spectrometer is derived from the halogenated hydrocarbon by the analysis by the gas chromatograph mass spectrometer. When the structure was confirmed from the measurement result by the gas chromatograph mass spectrometer, the content of the halogenated hydrocarbon was 35 mass ppm or less, and the content of chlorine derived from the halogenated hydrocarbon was 10 mass ppm or less.

Synthesis Example 2
14.3 g (0.55 mol) of LiF was weighed and charged into a PFA (made of fluorine resin) reaction vessel. While cooling the reaction vessel with ice, 90.47 g (0.50 mol) of liquid bis (fluorosulfonyl) imide (HFSI) was added to prepare a slurry reaction mixture. The reaction mixture was heated to 140 ° C., and lithium fluoride was dissolved to obtain a liquid reaction solution. The temperature of the reaction solution was maintained at 140 ° C., and the reaction was carried out for 15 minutes. The reaction solution was further heated under reduced pressure at 10 hPa and 140 ° C. to 145 ° C. for 2 hours, and then heated at 140 ° C. for 24 hours in a nitrogen blowing environment at normal pressure. As a result, 72 g of an electrolyte composition was obtained.

Example 1
100 g of LiFSI obtained by the method of Synthesis Example 1 was charged into a PFA (made of fluorine resin) reaction vessel. A thermometer was inserted into the interior, and heated in a nitrogen-blowing state until the internal melt temperature reached 150 ° C., and heated while maintaining 150 ° C. for 2 hours. Thereafter, the mixture was naturally cooled to obtain 95.4 g of an electrolyte composition. The electrolyte composition was analyzed by ¹⁹ F-NMR as a sample (internal standard substance: benzenesulfonyl fluoride, δ 68.9 ppm, singlet, hereinafter, benzenesulfonyl fluoride was used as an internal standard). As a result, in addition to the peak derived from LiFSI (δ 55.4 ppm, singlet) and the peak derived from LiFSO ₃ (δ 4 0.1 ppm, singlet), the peak is δ 64.67 ppm (triplet: J = 7.6 Hz), δ 58 respectively It was observed at .77 ppm (doublet: J = 7.6 Hz). The area ratio of the peak at δ 64.67 ppm to the peak at δ 58.77 ppm was 1: 2. From these facts, the peak at δ 64.67 ppm and the peak at δ 58.77 ppm are lithium N, N-bis (fluorosulfonyl) imidosulfamoyl fluoride (one of the compounds represented by the above formula (1) Hereinafter, it is considered to be derived respectively from the fluorine bonded to the central S of LiFSISF) and the fluorine bonded to S at both ends. The content of LiFSISF in the above-mentioned electrolyte composition determined by the above-mentioned internal standard method was 1,400 mass ppm. In addition, the content of LiFSO ₃ determined in the same manner was 6900 mass ppm.

In order to identify the molecular structure, the electrolyte composition of Example 1 was dissolved in ultrapure water to form a 0.5 mass% aqueous solution, and the aqueous solution was analyzed by LC-MS. The analysis conditions are as follows.
HPLC: LC 30A System (manufactured by Shimadzu Corporation)
Mobile phase: solvent A (0.1 mass% formic acid aqueous solution), solvent B (methanol), A: B = 20: 80 (volume ratio)
Flow rate: 0.1 ml / min
Column temperature: 40 ° C
Detector: Absorbance detector (190 nm to 800 nm)
Injection volume: 1 μL
MS: Q Exactive (Thermo Fisher Scientific)
Ionization method: Electrospray ionization (ESI)
Probe heater temperature: 330 ° C
Capillary temperature: 330 ° C
In LC-MS, all were ionized without performing peak separation. Among the ones ionized in the first step, MS / MS measurement was performed on the main peak, and the anion part of LiFSISF was identified from the pattern of fragment ions.

As a result of mass spectrometry by ESI method, a molecular ion peak was detected at m / z = 260.89. In addition, as a result of MS / MS measurement, fragment ions were detected at m / z = 96.96 (O ₂ NFS) and m / z = 177.93 (O ₃ N ₂ F ₂ S ₂ ). The structural formula satisfying the formation of these fragment ions is the anion shown in formula (2).

Example 2
100 g of LiFSI obtained by the method of Synthesis Example 1 was charged into a PFA (made of fluorine resin) reaction vessel. A thermometer was inserted inside, and the temperature was maintained until the internal melt temperature reached 150 ° C. in a nitrogen-blowing state, and heating was continued for an additional 108 hours at 150 ° C. Thereafter, the mixture was naturally cooled to obtain 95.2 g of an electrolyte composition.

Comparative Example 1
100 g of LiFSI obtained by the method of Synthesis Example 1 was charged into a PFA (made of fluorine resin) reaction vessel. A thermometer was inserted inside, and the temperature was maintained until the internal melt temperature reached 145 ° C. in a nitrogen-blowing state, and heating was continued for a further 10 minutes at 145 ° C. Thereafter, the mixture was naturally cooled to obtain 95.6 g of an electrolyte composition.

The electrolyte compositions of Examples 1 and 2 and Comparative Example 1 were each analyzed by ¹⁹ F-NMR, and the content of each component was determined by the internal standard method described above. The results are shown in Table 1. In Table 1, as Comparative Example 2, with respect to LiFSI obtained by the method of Synthesis Example 1, ¹⁹ F-NMR analysis was carried out without heat treatment.

LiPF ₆ and the electrolyte compositions of Examples 1 and 2 and Comparative Examples 1 and 2 were respectively dissolved in a solvent (EC: MEC = 3: 7 (volume ratio)) to 10 mL of electrolytes 1, 2 and C1 and C2 Was prepared. The concentration of LiPF _{6 in} the electrolytes 1, 2, C1 and C2 is 0.6 M, and the concentrations of FSI anions in the electrolyte compositions of Examples 1, 2 and Comparative Examples 1 and 2 are 0.6 M respectively. Were added to each electrolyte solution. In addition, LiPF ₆ used the commercial item.
Table 2 shows the actual weight values of the electrolyte composition and the contents of LiFSISF and LiFSO ₃ in the electrolytic solution calculated from the analysis results of Table 1.

The ¹⁹ F-NMR measurement was performed using the electrolytic solution 2 as a sample. When the content of LiFSISF was determined by the above-mentioned internal standard method using the measurement results, it became 6800 mass ppm, and showed almost the same value as the calculated value in Table 2.

Batteries 1, 2 and C1, and C2 were produced using electrolytes 1, 2 and C1, and C2, respectively, and the high temperature performance evaluation of the battery was performed. As a cell used for high temperature performance evaluation, a laminate battery of 1000 mAh design using LiNi _0.5 Co _0.2 Mn _0.3 O ₂ as a positive electrode, graphite as a negative electrode, and a polyethylene (PE) separator was used.
The cells of the above specification were aged under the following conditions to complete batteries 1, 2 and C1 and C2.

[Aging condition 1]
One hour after pouring each electrolyte solution of electrolytes 1, 2 and C1 and C2 into the cell, constant current constant voltage charge of 4.2 V and 200 mA was applied to the cell for 90 minutes. Then left for 72 hours. After that, the excess laminate was released, and degassing was performed by vacuum welding again. After degassing, constant current constant voltage charging of 4.2 V and 500 mA was performed for 5 hours, and after 10 minutes of rest, constant current discharge was performed at 200 mA to a closed circuit voltage of 2.75 V. After 10 minutes of rest, constant current constant voltage charging of 4.2 V and 500 mA was further performed for 5 hours. After 10 minutes of rest, constant current discharge was performed at 1000 mA to a closed circuit voltage of 2.75V. All aging was performed in a 25 ° C. environment.

[45 ° C cycle characteristic 1]
The charge and discharge cycle test of 500 cycles was performed under the following conditions for each of Batteries 1, 2 and C1 and C2.
Charge conditions: Constant voltage charge of 4.2 V and 1000 mA was performed at 45 ° C. until the current value became 20 mA. Then, it rested at 45 ° C. for 10 minutes.
Discharge conditions: A constant current discharge of 1000 mA was performed at 45 ° C. until the closed circuit voltage was 2.75V. Then, it rested at 45 ° C. for 10 minutes.

  After completion of the 500 cycles, charging was performed at a constant current constant voltage of 4.2 V and 1000 mA under a 25 ° C. environment until the current value became 20 mA. Rest for 10 minutes at 25 ° C. Thereafter, the battery was discharged at 25 ° C. at a level of 20 mA at which the resistance can be ignored until the closed circuit voltage becomes 2.75V. After the end of the discharge, the ratio of the obtained discharge capacity to the initial discharge capacity (initial discharge capacity after aging) was calculated as a capacity retention rate. Table 3 shows the results.

Batteries 1 and 2 containing LiFSISF had higher capacity retention of high temperature cycle than batteries C1 and C2 not containing LiFSISF. In addition, since the batteries 1 and 2 have a higher 20 mA discharge capacity after cycling than the batteries C1 and C2, it can be seen that there is less Li which is deposited and deactivated on the negative electrode.
The battery C1 containing LiFSO ₃ and the battery C 2 not containing LiFSO ₃ were almost the same in capacity retention rate and 20 mA discharge capacity. In addition, the battery 2 having a large LiFSISF content was superior to the battery 1 in the capacity retention rate and the 20 mA discharge capacity. From this, it is considered that the effect of improving the cycle capacity retention rate at high temperature was obtained by containing LiFSISF in the electrolytic solution.

Example 3
100 g of LiFSI obtained by the method of Synthesis Example 1 was charged into a PFA (made of fluorine resin) reaction vessel. A thermometer was inserted into the interior, and heated in a nitrogen-blowing state until the internal melt temperature reached 150 ° C., and heated at a temperature maintained at 150 ° C. for 10 minutes. Thereafter, the mixture was naturally cooled to obtain 95.6 g of an electrolyte composition.

Example 4
100 g of LiFSI obtained by the method of Synthesis Example 1 was charged into a PFA (made of fluorine resin) reaction vessel. A thermometer was inserted into the interior, and heated in a nitrogen-blowing state until the internal melt temperature reached 150 ° C., with heating maintained at 150 ° C. for 30 minutes. Thereafter, the mixture was naturally cooled to obtain 95.5 g of an electrolyte composition.

Example 5
100 g of LiFSI obtained by the method of Synthesis Example 1 was charged into a PFA (made of fluorine resin) reaction vessel. A thermometer was inserted inside, and the temperature was maintained until the internal melt temperature reached 150 ° C. in a nitrogen-blowing state, and the state was maintained at 150 ° C. for 17 hours. Thereafter, the mixture was naturally cooled to obtain 95.4 g of an electrolyte composition.

Example 6
100 g of LiFSI obtained by the method of Synthesis Example 1 was charged into a PFA (made of fluorine resin) reaction vessel. A thermometer was inserted inside, and the temperature was maintained until the temperature of the internal melt reached 150 ° C. in a nitrogen-blowing state, and maintained at 150 ° C. for 36.5 hours. Thereafter, the mixture was naturally cooled to obtain 95.0 g of an electrolyte composition.

The electrolyte compositions of Examples 3 to 6 were each analyzed by ¹⁹ F-NMR, and the content of each component was determined by the internal standard method described above. The results are shown in Table 4.

Each of LiPF ₆ and the electrolyte compositions of Examples 3 to 6 was dissolved in a solvent (EC: MEC = 3: 7 (volume ratio)) to prepare 10 mL of electrolytes 3 to 6, respectively. The concentration of LiPF ₆ in the electrolytic solution 3-6 is 0.6M, the electrolyte compositions of Examples 3-6, the concentration of the FSI anion is added to the electrolyte solution so that 0.6M, respectively. In addition, LiPF ₆ used the commercial item.
The measured values of the actual electrolyte composition and the contents of LiFSISF and LiFSO ₃ in the electrolyte solution calculated from the analysis results of Table 4 are shown in Table 5.

The ¹⁹ F-NMR measurement was performed using the electrolytic solution 6 as a sample. When the content of LiFSISF was determined by the above-mentioned internal standard method using the measurement results, it became 2200 mass ppm, and showed almost the same value as the calculated value of Table 5.

Batteries 3 to 6 and C3 were produced using electrolytic solutions 3 to 6 and electrolytic solution C2, respectively, and high temperature performance evaluation of the batteries was performed. As a cell used for high temperature performance evaluation, a 30 mAh design laminate battery using LiNi _1/3 Co _1/3 Mn _1/3 O ₂ as a positive electrode, graphite as a negative electrode, and a polyethylene (PE) separator was used.
The cells of the above specification were aged under the following conditions to complete batteries 3 to 6 and C3.

[Aging Condition 2]
One hour after pouring each electrolyte solution of electrolyte solution 3-6 and C2 into the cell, constant current constant voltage charge of 4.2 V and 6 mA was performed on the cell for 90 minutes. Then left for 72 hours. After that, the excess laminate was released, and degassing was performed by vacuum welding again. After degassing, constant current constant voltage charging of 4.2 V and 15 mA was performed for 5 hours, and after 10 minutes of rest, constant current discharge was performed at 6 mA to a closed circuit voltage of 2.75 V. After 10 minutes of rest, constant current constant voltage charging of 4.2 V and 15 mA was further performed for 5 hours. After 10 minutes of rest, constant current discharge was performed at 30 mA to a closed circuit voltage of 2.75V. All aging was performed at 25 ° C.

[45 ° C cycle characteristic 2]
The charge and discharge cycle test of 1000 cycles was performed on each of the batteries 3 to 6 and C3 under the following conditions.
Charge conditions: Constant voltage charge of 4.2 V and 30 mA was performed at 45 ° C. until the current value became 0.6 mA. Then, it rested at 45 ° C. for 10 minutes.
Discharge conditions: A constant current discharge of 30 mA was performed at 45 ° C. until the closed circuit voltage became 2.75V. Then, it rested at 45 ° C. for 10 minutes.
The ratio of the discharge capacity of the 1000th cycle to the discharge capacity of the 1st cycle was calculated and used as the capacity retention rate.

In the batteries 3 to 6, the content of LiFSISF contained in the electrolytic solution was large in this order, and the capacity retention rate after 1000 cycles was high in this order. Further, comparing the batteries 3 and 4, the battery 4 having the same LiFSO ₃ content but having a large amount of LiFSISF shows a better result regarding the capacity retention rate. From these facts, it is considered that the inclusion of LiFSISF has an effect of improving the cycle capacity retention rate at high temperature.

[Measurement of initial discharge capacity]
The capacity of the battery after aging was checked at 25 ° C. under the following conditions.
Discharge: A constant current discharge was performed at 6 mA until the closed circuit voltage was 2.75 V, and then rested for 10 minutes.
Charging: After performing constant current constant voltage charging at 4.2 V and 30 mA until the current value reached 0.6 mA, it was rested for 10 minutes.
Discharge: A constant current discharge was performed at 30 mA until the closed circuit voltage stopped at 2.75 V, and the discharge capacity was measured.
The discharge capacity obtained in this manner was taken as the initial discharge capacity.

[45 ° C trickle charge cycle]
After the initial discharge capacity was measured for batteries 3 to 6 and C3, a total of 300 trickle charge cycles were performed under the following conditions.
<Cycle conditions up to 1 to 100 cycles>
Charging: constant current constant voltage charging at 4.2 V and 30 mA until the current value became 6 mA at 45 ° C., and then rested for 3 hours.
Discharge: A constant current discharge was performed at 45 ° C. for 15 minutes at 15 mA, and then rested for 5 minutes.
<Cycle conditions up to 101 to 300 cycles>
Charging: constant current constant voltage charging at 4.35 V and 30 mA until the current value became 6 mA at 45 ° C., and then rested for 3 hours.
Discharge: A constant current discharge was performed at 45 ° C. for 15 minutes at 15 mA, and then rested for 5 minutes.

After performing the trickle charge cycle of 300 cycles at 45 ° C. under the above conditions, the discharge capacity after 300 cycles was measured in the same procedure as the initial capacity measurement.
The capacity retention ratio after 300 cycles is shown in Table 7.

In the batteries 3 to 6, the content of LiFSISF contained in the electrolytic solution was large in this order, and the capacity retention rate after the trickle charge cycle was high in this order. Further, comparing the batteries 3 and 4, the batteries 4 having the same LiFSO ₃ content in the electrolytic solution but having a large amount of LiFSISF show better results in terms of capacity retention. From these facts, it is considered that the capacity retention rate after the trickle charge cycle at high temperature is improved by containing LiFSISF in the electrolytic solution.

LiPF ₆ and the electrolyte compositions of Examples 3 to 6 and Comparative Example 2 were respectively dissolved in a solvent (EC: MEC = 3: 7 (volume ratio)) to prepare 10 mL of electrolytes 7 to 10 and C4. The concentration of LiPF ₆ in the electrolytes 7 to 10 and C 4 is 0.95 M, and each of the electrolyte compositions of Examples 3 to 6 and Comparative Example 2 has a concentration of 0.05 M of FSI anion. Added to In addition, LiPF ₆ used the commercial item.
Table 8 shows the measured values of the actual electrolyte composition and the contents of LiFSISF and LiFSO ₃ in the electrolytic solution calculated from the analysis results of Table 4.

A cell was assembled in the same manner as the battery 3 using the electrolytes 7 to 10 and C4. These cells were aged under the condition of the above-mentioned aging condition 2 to complete batteries 7 to 10 and C4.
The batteries 7 to 10 and C4 were tested under the conditions of 45 ° C. cycle characteristic 2 to determine the capacity retention rate. The results are shown in Table 9.

In the batteries 7 to 10, the content of LiFSISF contained in the electrolytic solution was large in this order, and the capacity retention rate after the trickle charge cycle was high in this order. Further, comparing the batteries 7 and 8, the battery 8 having the same LiFSO ₃ content in the electrolytic solution but having a large amount of LiFSISF shows a better result regarding the capacity retention rate. From these facts, it is considered that the capacity retention ratio after the cycle test at high temperature is improved by the inclusion of LiFSISF in the electrolytic solution.

As described above, the use of the electrolyte composition containing a predetermined amount of FSISF improved the high temperature cycle characteristics of the battery.
Although this is not necessarily clear as this reason, the present inventor thinks as follows. The formation of a coating on the surface of the positive and negative electrodes by decomposition and adsorption of the FSISF anion suppresses the oxidation / reduction decomposition of the electrolyte at high temperatures, thereby suppressing the generation of decomposition products and the deposition on the negative electrode. I think for the sake of.

Claims (7)

The solution which contains 0.1 mass ppm-180,000 mass ppm of compounds represented by following formula (1).

(In general formula (1), R ¹ , R ² and R ³ each represent fluorine or a fluorinated alkyl group having 1 to 6 carbon atoms.) The solution according to claim 1, further comprising 0.1 mass ppm to 10000 mass ppm of LiFSO ₃ . The compound according to claim 1 or 2, further comprising at least one compound selected from the group consisting of LiPF ₆ , LiBF ₄ , and LiN (SO ₂ C _n F _{2n + 1} ) ₂ (n is an integer of 0 to 6). solution.   Furthermore, the solution as described in any one of Claims 1-3 containing 1 mass ppm-90 mass% of lithium bis (fluoro sulfonyl) imides. R _{1, R} 2, _{R 3} is either a fluorine atom, a solution according to any one of claims 1-4.   The electrolyte solution containing the solution as described in any one of Claims 1-5.   A lithium ion battery comprising the electrolytic solution according to claim 6.