ELECTROLYTE SOLUTION AND METHOD FOR PRODUCING SULFATE SALT

Abstract

A method for producing a compound of formula (1) R.sup.11X.sup.11—SO.sub.3M.sup.11, which includes reacting a compound of formula (3) R.sup.31O—SO.sub.2—OR.sup.32 and a metal alkoxide, wherein R.sup.11, X.sup.11 and M.sup.11 are as defined herein.

Claims

1. A method for producing a compound represented by the following formula (1), comprising: reacting a compound represented by the following formula (3) and a metal alkoxide, the formula (1) being R.sup.11X.sup.11—SO.sub.3M.sup.11 wherein R.sup.11 is a C1-C6 linear or branched alkyl group, a C2-C6 linear or branched alkenyl group, a C2-C6 linear or branched alkynyl group, a C3-C6 cycloalkyl group, a C3-C6 cycloalkenyl group, or a C3-C6 alkylsilyl group, the alkyl group, the cycloalkyl group, and the alkylsilyl group may have a halogen atom which substitutes for a hydrogen atom bonding to a carbon atom, may have a cyclic structure, and may have an ether bond or a thioether bond; X.sup.11 is O; and M.sup.11 is at least one selected from the group consisting of Li, Na, K, and Cs, and the formula (3) being R.sup.31O—SO.sub.2—OR.sup.32 wherein R.sup.31 and R.sup.32 may be the same as or different from each other, and are individually a C1-C6 linear or branched alkyl group, a C2-C6 linear or branched alkenyl group, a C2-C6 linear or branched alkynyl group, a C3-C6 cycloalkyl group, a C3-C6 cycloalkenyl group, or a C3-C6 alkylsilyl group, the alkyl group, the cycloalkyl group, and the alkylsilyl group may have a halogen atom which substitutes for a hydrogen atom bonding to a carbon atom, may have a cyclic structure, and may have an ether bond or a thioether bond.

2. The production method according to claim 1, wherein, in the formula (1), R.sup.11 is a C1-C6 linear or branched alkyl group or a C3-C6 cycloalkyl group; and M.sup.11 is Li.

3. The production method according to claim 1, wherein, in the formula (3), R.sup.31 and R.sup.32 may be the same as or different from each other, and are individually a C1-C6 linear or branched alkyl group or a C3-C6 cycloalkyl group.

4. The production method according to claim 1, wherein the metal alkoxide is a lithium alkoxide.

5. The production method according to claim 1, wherein the metal alkoxide is at least one selected from the group consisting of lithium methoxide and lithium ethoxide.

6. The production method according to claim 4, further comprising reacting an alcohol with lithium metal to provide a lithium alkoxide.

7. The production method according to claim 1, wherein the reaction is caused by adding 0.7 to 1.5 mol of the metal alkoxide relative to 1 mol of the compound represented by the formula (3).

Description

EXAMPLES

[0383] The present invention will be described with reference to, but not limited to, examples.

(Method for Producing Lithium Monoalkyl Sulfate)

Synthesis Example 1: Production of Lithium Monomethyl Sulfate

[0384] A 2-L glass reactor was charged with 400 g (3.2 mol) of dimethyl sulfate, and the temperature was controlled by water bath such that the internal temperature was 25° C. A dropping funnel was charged with 1.23 kg (3.2 mol) of a 10 mass % lithium methoxide/methanol solution, and the solution was added dropwise to the system such that the internal temperature was 40° C. or lower. The reaction solution was slightly cloudy immediately after the dropwise addition. The reaction solution was then stirred for one hour at the same temperature, resulting in removal of the cloudiness.

[0385] The resulting reaction solution was analyzed by gas chromatography (GC), and no peak derived from the material, i.e., dimethyl sulfate, was observed.

[0386] Components such as methanol and dimethyl ether which is a by-product, occupying most part of the reaction solution, were distilled off at a reduced pressure of 200 Pa and an internal temperature of 60° C., and then the above compounds and others were further distilled off at a reduced pressure of 30 Pa and an internal temperature of 150° C. Thereby, 370 g of white solid was obtained.

[0387] The purity of lithium monomethyl sulfate calculated by the internal standard method utilizing 1H-NMR was 99 mass % or more, and the sulfate ion concentration calculated by the external standard method utilizing ion chromatograph was 6200 mass ppm. The moisture concentration calculated by the coulometric Karl Fischer titration method was 103 mass ppm.

Synthesis Example 2: Production of Lithium Monoethyl Sulfate

[0388] A 2-L glass reactor was charged with 500 g (3.2 mol) of diethyl sulfate, and the temperature was controlled by water bath such that the internal temperature was 25° C. A dropping funnel was charged with 1.26 kg (3.3 mol) of a 10 mass % lithium methoxide/methanol solution, and the solution was added dropwise to the system such that the internal temperature was 40° C. or lower. The reaction solution was slightly cloudy immediately after the dropwise addition. The reaction solution was then stirred for five hours at the same temperature, resulting in removal of the cloudiness.

[0389] The resulting reaction solution was analyzed by gas chromatography (GC), and no peak derived from the material, i.e., diethyl sulfate, was observed.

[0390] Components such as methanol and ethyl methyl ether which is a by-product in the reaction solution were distilled off at a reduced pressure of 200 Pa and an internal temperature of 60° C., and then the above compounds and others were further distilled off at a reduced pressure of 30 Pa and an internal temperature of 150° C. Thereby, 420 g of white solid was obtained.

[0391] The purity of lithium monoethyl sulfate calculated by the internal standard method utilizing .sup.1H-NMR was 99 mass % or more, and the sulfate ion concentration calculated by the external standard method utilizing ion chromatograph was 2 mass ppm. The moisture concentration calculated by the coulometric Karl Fischer titration method was 148 mass ppm.

Synthesis Example 3: Production of Lithium Mono-n-Butyl Sulfate

[0392] A 200-mL glass reactor was charged with 50 g (0.24 mol) of di-n-butyl sulfate, and the temperature was controlled by water bath such that the internal temperature was 25° C. A dropping funnel was charged with 95 g (0.25 mol) of a 10 mass % lithium methoxide/methanol solution, and the solution was added dropwise to the system such that the internal temperature was 40° C. or lower. Immediately after the dropwise addition, the reaction solution was heated up to 40° C., and then stirred for five hours at the same temperature.

[0393] The resulting reaction solution was analyzed by gas chromatography (GC), and no peak derived from the material, i.e., di-n-butyl sulfate, was observed.

[0394] Components such as methanol and butyl methyl ether which is a by-product in the reaction solution were distilled off at a reduced pressure of 200 Pa and an internal temperature of 60° C., and then the above compounds and others were further distilled off at a reduced pressure of 30 Pa and an internal temperature of 150° C. Thereby, 35 g of white solid was obtained.

[0395] The purity of lithium mono-n-butyl sulfate calculated by the internal standard method utilizing 1H-NMR was 98 mass % or more, and the sulfate ion concentration calculated by the external standard method utilizing ion chromatograph was 25 mass ppm. The moisture concentration calculated by the coulometric Karl Fischer titration method was 170 mass ppm.

Comparative Synthesis Example 1

[0396] A 300-mL glass reactor was charged with 50 g (0.32 mol) of diethyl sulfate, and the temperature was controlled by water bath such that the internal temperature was 25° C. Then, 126 g (3.9 mol) of methanol was added dropwise to the system through a dropping funnel, and no generation of heat was observed. The system was then stirred at the same temperature for five hours.

[0397] The resulting reaction solution was analyzed by gas chromatography (GC), and diethyl sulfate and methanol were detected at the peak ratio calculated from the ratio between the amounts thereof prepared. This confirmed no progress of the reaction.

Experiment 1 (Evaluation of 4.4 V Grade Lithium Battery)

[0398] Electrolyte solutions of Examples 1 to 21 and electrolyte solutions of Comparative Examples 1 to 6 were prepared as follows and lithium ion secondary batteries were produced using the resulting electrolyte solutions. The resistance increasing rates and the cycle capacity retention ratios of the respective batteries were evaluated.

(Preparation of Electrolyte Solution)

[0399] An acyclic carbonate(s) and a cyclic carbonate(s) were mixed in a ratio shown in Table 1 under dry argon atmosphere. To this solution was added dry lithium monoalkyl sulfate in an amount shown in Table 1, and dry LiPF.sub.6 was further added so as to be a concentration of 1.0 mol/L. Thereby, a non-aqueous electrolyte solution was obtained. The amounts of the additives such as lithium monoalkyl sulfate blended were expressed by mass % relative to the acyclic carbonate(s) and the cyclic carbonate(s).

[0400] The compounds in the tables are as follows.

Acyclic Carbonates

[0401] a: dimethyl carbonate

[0402] b: ethylmethyl carbonate

[0403] c: diethyl carbonate

[0404] d: CF.sub.3CH.sub.2OCOOCH.sub.3

[0405] e: CF.sub.3CH.sub.2OCOOCH.sub.2CF.sub.3

Cyclic Carbonates

[0406] EC: ethylene carbonate

[0407] FEC: 4-fluoro-1,3-dioxolan-2-one

Additives

[0408] F: C.sub.2H.sub.5OSO.sub.3Li

[0409] G: CH.sub.3CH.sub.2CH.sub.2OSO.sub.3Li

[0410] H: CH.sub.3CH.sub.2CH.sub.2CH.sub.2OSO.sub.3Li

[0411] I: CH.sub.3 (CH.sub.2).sub.11OSO.sub.3Na

[0412] J: (CH.sub.3).sub.2NSO.sub.3Li

[0413] K: (C.sub.2H.sub.5).sub.2NSO.sub.3Li

(Production of Negative Electrode)

[0414] Powder of artificial graphite used as a negative electrode active material, an aqueous dispersion of carboxymethyl cellulose sodium (concentration of carboxymethyl cellulose sodium: 1 mass %) used as a thickening agent, and an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber: 50 mass %) used as a binder were mixed in a water solvent to prepare a negative electrode mixture slurry. The solid content ratio of the negative electrode active material, the thickening agent, and the binder was 97.6/1.2/1.2 (mass % ratio). The slurry was uniformly applied to 20-μm-thick copper foil, followed by drying, and then the workpiece was compression-molded with a press. Thereby, a negative electrode was prepared.

(Production of Positive Electrode)

[0415] LiCoO.sub.2 used as a positive electrode active material, acetylene black used as a conductive material, and a dispersion of polyvinylidene fluoride (PVdF) in N-methyl-2-pyrrolidone used as a binder were mixed to prepare a positive electrode mixture slurry. The solid content ratio of the positive electrode active material, the conductive material, and the binder was 92/3/5 (mass % ratio). The positive electrode mixture slurry was uniformly applied to a 20-μm-thick current collector made of aluminum foil, followed by drying, and then the workpiece was compression-molded with a press. Thereby, a positive electrode was prepared.

(Production of Lithium Ion Secondary Battery)

[0416] The above prepared negative electrode, a polyethylene separator, and the above prepared positive electrode were stacked in the given order to provide a battery element.

[0417] A bag made of a laminate film in which an aluminum sheet (thickness: 40 μm) was coated with a resin layer on each side was prepared. The above battery element was placed in the bag in such a manner that the terminals of the positive electrode and negative electrode stuck out of the bag. One of the electrolyte solutions of Examples 1 to 21 and Comparative Examples 1 to 6 was poured into the bag and the bag was vacuum sealed. Thereby, a lithium ion secondary battery in a sheet form was produced.

<High-Temperature Cycle Capacity Retention Ratio>

[0418] The above produced secondary battery in the state of being sandwiched and pressurized between plates was subjected to constant current-constant voltage charge (hereinafter, referred to as CC/CV charge) (0.1 C cut off) to 4.4 V at a current corresponding to 0.2 C at 60° C. Then, the battery was discharged to 3 V at a constant current of 0.2 C. This process was counted as one cycle. The initial discharge capacity was determined from the discharge capacity of the third cycle. Here, 1 C means a current value required for discharging the reference capacity of a battery in an hour. For example, 0.2 C indicates a 1/5 current value thereof. The cycle was again repeated, and the discharge capacity after 100 cycles was defined as the capacity after cycles. The ratio of the discharge capacity after 100 cycles to the initial discharge capacity was determined, which was regarded as a cycle capacity retention ratio (%).

(Discharge capacity after 100 cycles)/(initial discharge capacity)×100=cycle capacity retention ratio (%)

<Resistance Increasing Rate>

[0419] A charge and discharge cycle under predetermined charge and discharge conditions (charge at 0.2 C and a predetermined voltage until the charge current reached 1/10 C, and discharge at a current corresponding to 1 C to 3.0 V) was defined as one cycle. The resistance after three cycles and the resistance after 100 cycles were determined. The measurement temperature was 25° C. The resistance increasing rate after 100 cycles was determined by the following formula.

[0420] Table 1 shows the results.

Resistance increasing rate (%)=(resistance (Ω) after 100 cycles)/(resistance (Ω) after three cycles)×100

TABLE-US-00001 TABLE 1 Components constituting electrolyte solution Cyclic Acrylic carbonate Cyclic carbonate Additive capacity Resistance Mixing ratio Mixing ratio Mixing ratio retention increasing Structure (vol %) Structure (vol %) Structure (mass %) ratio (%) rate (%) Example 1  Component (b) 70 EC 30 Component (F) 2.0 93 134 Example 2  Component (b) 70 EC 30 Component (F)  0.001 88 153 Example 3  Component (b) 70 EC 30 Component (F)  0.01 90 146 Example 4  Component (b) 70 EC 30 Component (F) 0.1 91 142 Example 5  Component (b) 70 EC 30 Component (F) 0.5 92 138 Example 6  Component (b) 70 EC 30 Component (F) 1.0 82 137 Example 7  Component (b) 70 EC 30 Component (F) 5.0 91 132 Example 8  Component (b) 70 EC 30 Component (F) 10.0  90 131 Example 9  Component (a) 70 EC 30 Component (F) 2.0 80 153 Example 10 Component (c) 70 EC 30 Component (F) 3.0 91 141 Example 11 Component (a) 70 FEC 30 Component (F) 2.0 90 144 Example 12 Component (b) 70 FEC 30 Component (F) 2.5 92 141 Example 13 Component (c) 70 FEC 30 Component (F) 2.5 92 139 Example 14   Component (a) + 24 + 45 EC 30 Component (F) 1.0 91 145 Component (b) Example 15 Component (b) 70 EC + FEC 20 + 10 Component (F) 2.0 91 141 Example 16 Component (b) 50 EC 50 Component (F) 2.0 88 137 Example 17 Component (b) 70 EC 30 Component (G) 2.0 90 140 Example 18 Component (b) 60 EC + FEC 15 + 5    Component (F) + 2.0 + 2.0 91 137 Component (G) Example 19 Component (b) 70 EC 30 Component (H) 3.0 88 142 Example 20 Component (b) 70 EC 30 Component (J)  0.5 90 145 Example 21 Component (b) 70 EC 30 Component (K) 0.5 91 142 Comparative Component (b) 70 EC 30 — 0   87 165 Example 1  Comparative Component (b) 70 EC 30 Component (F) 13.0  72 194 Example 2  Comparative Component (b) 70 EC 30 Component (H) 15.0  64 187 Example 3  Comparative Component (b) 60 EC + FEC 20 + 20   Component (G) + 8.0 + 8.0 68 178 Example 4  Component (H) Comparative Component (b) 60 FEC 40 — 0   86 170 Example 5  Comparative Component (b) 70 EC 30 Component (I)  2.0 84 180 Example 6 

[0421] The table shows that the lithium ion secondary batteries produced using the electrolyte solutions of Examples 1 to 21 had a lower resistance increasing rate than the lithium ion secondary batteries produced using the electrolyte solutions of Comparative Examples 1 to 6.

Experiment 2 (Evaluation of 4.9 V Grade Lithium Battery)

[0422] Electrolyte solutions of Examples 22 to 41 and electrolyte solutions of Comparative Examples 7 to 15 were prepared as follows and lithium ion secondary batteries were produced using the resulting electrolyte solutions. The resistance increasing rates and the cycle capacity retention ratios of the respective batteries were evaluated.

(Preparation of Electrolyte Solution)

[0423] An acyclic carbonate(s) and a cyclic carbonate(s) were mixed in a ratio shown in Table 2 under dry argon atmosphere. To this solution was added dry lithium monoalkyl sulfate in an amount shown in Table 2, and dry LiPF.sub.6 was further added so as to be a concentration of 1.0 mol/L. Thereby, a non-aqueous electrolyte solution was obtained. The amounts of the additives such as lithium monoalkyl sulfate blended were expressed by mass % relative to the acyclic carbonate(s) and the cyclic carbonate(s).

[0424] The components shown in Table 2 are the same as those in Table 1.

(Production of Negative Electrode)

[0425] Powder of artificial graphite used as a negative electrode active material, an aqueous dispersion of carboxymethyl cellulose sodium (concentration of carboxymethyl cellulose sodium: 1 mass %) used as a thickening agent, and an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber: 50 mass %) used as a binder were mixed in a water solvent to prepare a negative electrode mixture slurry. The solid content ratio of the negative electrode active material, the thickening agent, and the binder was 97.6/1.2/1.2 (mass % ratio). The slurry was uniformly applied to 20-μm-thick copper foil, followed by drying, and then the workpiece was compression-molded with a press. Thereby, a negative electrode was prepared.

(Production of Positive Electrode)

[0426] LiNi.sub.0.5Mn.sub.1.5O.sub.4 used as a positive electrode active material, acetylene black used as a conductive material, and a dispersion of polyvinylidene fluoride (PVdF) in N-methyl-2-pyrrolidone used as a binder were mixed to prepare a positive electrode mixture slurry. The solid content ratio of the positive electrode active material, the conductive material, and the binder was 92/3/5 (mass % ratio). The positive electrode mixture slurry was uniformly applied to a 20-μm-thick current collector made of aluminum foil, followed by drying, and then the workpiece was compression-molded with a press. Thereby, a positive electrode was prepared.

(Production of Lithium Ion Secondary Battery)

[0427] The above prepared negative electrode, a polyethylene separator, and the above prepared positive electrode were stacked in the given order to provide a battery element.

[0428] A bag made of a laminate film in which an aluminum sheet (thickness: 40 μm) was coated with a resin layer on each side was prepared. The above battery element was placed in the bag in such a manner that the terminals of the positive electrode and negative electrode stuck out of the bag. One of the electrolyte solutions of Examples 22 to 41 and Comparative Examples 7 to 15 was poured into the bag and the bag was vacuum sealed. Thereby, a lithium ion secondary battery in a sheet form was produced.

<High-Temperature Cycle Capacity Retention Ratio>

[0429] The above produced secondary battery in the state of being sandwiched and pressurized between plates was subjected to constant current-constant voltage charge (hereinafter, referred to as CC/CV charge) (0.1 C cut off) to 4.9 V at a current corresponding to 0.2 C at 60° C. Then, the battery was discharged to 3 V at a constant current of 0.2 C. This process was counted as one cycle. The initial discharge capacity was determined from the discharge capacity of the third cycle. Here, 1 C means a current value required for discharging the reference capacity of a battery in an hour. For example, 0.2 C indicates a 1/5 current value thereof. The cycle was again repeated, and the discharge capacity after 100 cycles was defined as the capacity after cycles. The ratio of the discharge capacity after 100 cycles to the initial discharge capacity was determined, which was regarded as a cycle capacity retention ratio (%).

(Discharge capacity after 100 cycles)/(initial discharge capacity)×100=cycle capacity retention ratio (%)

<Resistance Increasing Rate>

[0430] A charge and discharge cycle under predetermined charge and discharge conditions (charge at 0.2 C and a predetermined voltage until the charge current reached 1/10 C, and discharge at a current corresponding to 1 C to 3.0 V) was defined as one cycle. The resistance after three cycles and the resistance after 100 cycles were determined. The measurement temperature was 25° C. The resistance increasing rate after 100 cycles was determined by the following formula.

Resistance increasing rate (%) after 100 cycles=(resistance (Ω) after 100 cycles)/(resistance (Ω) after three cycles)×100

TABLE-US-00002 TABLE 2 Components constituting electrolyte solution Cyclic Acrylic carbonate Cyclic carbonate Additive capacity Resistance Mixing ratio Mixing ratio Mixing ratio retention increasing Structure (mass %) Structure (mass %) Structure (mass %) ratio (%) rate (%) Example 22 Component (d) 60 FEC 40 Component (F) 2.0 89 150 Example 23 Component (d) 60 FEC 40 Component (F)  0.001 83 158 Example 24 Component (d) 60 FEC 40 Component (F)  0.01 85 154 Example 25 Component (d) 60 FEC 40 Component (F) 0.1 86 152 Example 26 Component (d) 60 FEC 40 Component (F) 0.5 87 151 Example 27 Component (d) 60 FEC 40 Component (F) 1.0 87 151 Example 28 Component (d) 60 FEC 40 Component (F) 5.0 86 146 Example 29 Component (d) 60 FEC 40 Component (F) 10.0  85 147 Example 30 Component (e) 60 FEC 40 Component (F) 2.0 85 150 Example 31   Component (d) + 30 + 30 FEC 40 Component (F) 3.0 86 150 Component (e) Example 32   Component (d) + 55 + 5  EC + FEC 10 + 30 Component (F) 4.0 87 155 Component (e) Example 33   Component (b) + 10 + 60 FEC 30 Component (F) 2.0 85 156 Component (d) Example 34   Component (b) + 15 + 35 FEC 50 Component (F) 2.5 83 154 Component (d) Example 35   Component (b) + 10 + 60 FEC 30 Component (F) 2.5 87 154 Component (e) Example 36   Component (a) + 25 + 45 EC 30 Component (F) 1.0 86 156 Component (b) Example 37 Component (d) 70 FEC 30 Component (G) 2.0 85 161 Example 38 Component (d) 80 EC + FEC  5 + 15   Component (F) + 2.0 + 2.0 86 150 Component (G) Example 39 Component (d) 70 FEC 30 Component (H) 2.0 83 156 Example 40 Component (d) 60 FEC 40 Component (J)  0.5 82 158 Example 41 Component (d) 60 FEC 40 Component (K) 0.5 86 156 Comparative Component (b) 70 EC 30 — 0   40 218 Example 7  Comparative Component (d) 80 FEC 40 — 0   79 160 Example 8  Comparative Component (d) 70 FEC 30 Component (H) 18.0  59 190 Example 9  Comparative  Component (d) + 55 + 5  FEC 40 Component (F) 20.0  71 174 Example 10 Component (e) Comparative Component (b) 60 EC + FEC 20 + 20   Component (G) + 8.0 + 8.0 63 183 Example 11 Component (H) Comparative Component (b) 60 FEC 40 — 0   84 174 Example 12 Comparative Component (b) 70 EC 30 Component (I)  2.0 36 224 Example 13 Comparative Component (d) 70 FEC 30 Component (F) 13.0  77 180 Example 14 Comparative Component (d) 70 FEC 30 Component (F) 15.0  75 185 Example 15

[0431] The table shows that the lithium ion secondary batteries produced using the electrolyte solutions of Examples 22 to 41 had a lower resistance increasing rate than the lithium ion secondary batteries produced using the electrolyte solutions of Comparative Examples 7 to 15.

INDUSTRIAL APPLICABILITY

[0432] The electrolyte solution of the present invention can be suitably used as an electrolyte solution for electrochemical devices such as lithium ion secondary batteries.