NON-AQUEOUS ELECTROLYTE SOLUTION FOR SODIUM ION SECONDARY BATTERY, AND SODIUM ION SECONDARY BATTERY

Abstract

The present invention is aimed at providing: a non-aqueous electrolyte solution for a sodium ion secondary battery, with which a sodium ion secondary battery having a low resistance and showing a limited amount of gas generation after a durability test can be provided; and a sodium ion secondary battery obtained by using the same. The non-aqueous electrolyte solution for a sodium ion secondary battery comprises: a non-aqueous solvent; NaPF.sub.6; and a compound represented by the following Formula (1) (wherein, R.sub.1 and R.sub.2 each independently represent a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms, and n represents 0 or 1), and a ratio of the content of the compound represented by Formula (1) with respect to the content of NaPF.sub.6, [compound represented by Formula (1)]/[NaPF.sub.6] (molar ratio), is 0.001 to 1.5:

##STR00001##

Claims

1. A non-aqueous electrolyte solution for a sodium ion secondary battery, comprising: a non-aqueous solvent; NaPF.sub.6; and a compound represented by the following Formula (1), wherein a ratio of the content of the compound represented by Formula (1) with respect to the content of NaPF.sub.6, [compound represented by Formula (1)]/[NaPF.sub.6](molar ratio), is 0.001 to 1.5: ##STR00004## wherein, R.sub.1 and R.sub.2 each independently represent a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms, and n represents 0 or 1.

2. The non-aqueous electrolyte solution for a sodium ion secondary battery according to claim 1, comprising the compound represented by Formula (1) in an amount of 0.01 parts by mass to 10 parts by mass with respect to 100 parts by mass of the non-aqueous solvent.

3. The non-aqueous electrolyte solution for a sodium ion secondary battery according to claim 1, comprising 0.001 mol/L to 5.0 mol/L of NaPF.sub.6 in the non-aqueous solvent.

4. The non-aqueous electrolyte solution for a sodium ion secondary battery according to claim 1, comprising a cyclic carbonate as the non-aqueous solvent.

5. A sodium ion secondary battery, comprising: a positive electrode; a negative electrode; and an electrolyte solution, wherein the non-aqueous electrolyte solution for a sodium ion secondary battery according to claim 1 is used as the electrolyte solution.

6. The sodium ion secondary battery according to claim 5, wherein the negative electrode comprises porous carbon.

Description

EXAMPLES

[0104] The present invention will now be described more concretely by way of Examples and Reference Examples; however, the present invention is not restricted thereto within the gist of the present invention.

Example 1-1

[Production of Positive Electrode]

[0105] Na.sub.2CO.sub.3, Ni.sub.2CO.sub.3, Mn.sub.3O.sub.4, and Fe.sub.2O.sub.3 were weighed such that the resulting composite metal compound would have a formulation of NaNi.sub.0.3Mn.sub.0.3Fe.sub.0.4O.sub.2, and these materials were dispersed in an ethanol solvent and subsequently wet-pulverized to a median diameter d50 of 0.4 μm or less using Pico Grain Mill (PCM-L, manufactured by Asada Iron Works, Co., Ltd.) to obtain a mixture of metal-containing compounds. It is noted here that, at the time of the weighing, 5% by mole of Na.sub.2CO.sub.3 was further added, taking into consideration the loss during the production. The thus obtained mixture was dried by evaporation, loaded to an alumina crucible, and then fired in the air atmosphere at 900° C. for 24 hours using an electric furnace, whereby a composite metal oxide, O.sub.3-type NaNi.sub.0.3Mn.sub.0.3Fe.sub.0.4C.sub.2, was obtained.

[0106] The thus obtained composite metal oxide as a positive electrode active material, an acetylene black (HS-100, manufactured by Denka Co., Ltd.) as a conductive material, and a polyvinylidene fluoride (#7500, manufactured by Kureha Corporation) as a binder were weighed at a mass ratio of 95:5:5 and dispersed in an NMP solvent to obtain a slurry. The thus obtained slurry was applied onto an aluminum foil using a coating machine. The resulting coated polar plate was rolled using a rolling machine, punched out in a rectangular shape of 30 mm×40 mm, and then processed into the state of an electrode, whereby a test electrode was obtained.

[Production of Negative Electrode]

[0107] A test electrode was produced using a porous carbon material (LN0010, manufactured by AT Electrode Co., Ltd.) and a copper foil as a negative electrode active material and a current collector, respectively. The above-described porous carbon material as a negative electrode active material, a carbon black (Super P, manufactured by TIMCAL Ltd.) as a conductive material, and a polyvinylidene fluoride (#1120, manufactured by Kureha Corporation) as a binder were weighed at a mass ratio of 95:2:3 and dispersed in an NMP solvent to obtain a slurry. The thus obtained slurry was applied onto a copper foil using a coating machine. The resulting coated polar plate was rolled using a rolling machine, punched out in a rectangular shape of 32 mm×42 mm, and then processed into the state of an electrode, whereby a test electrode was obtained.

[Preparation of Electrolyte Solution]

[0108] An electrolyte solution (manufactured by Kishida Chemical Co., Ltd.), in which NaPF.sub.6 as an electrolyte was dissolved at a ratio of 1 mol/L in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio=30:70), was used as a basic electrolyte solution. Ethylene sulfate (compound (1-1)) in an amount of 1.43 parts by mass was mixed with respect to 100 parts by mass of the mixed solvent to prepare an electrolyte solution of Example 1.

[Battery Production]

[0109] A battery element was prepared by laminating the above-obtained positive electrode and negative electrode along with a polypropylene separator in the order of the negative electrode, the separator, and the positive electrode. This battery element was inserted into a pouch made of a laminated film obtained by coating both sides of an aluminum sheet (thickness: 40 pm) with a resin layer, with the terminals of the positive and negative electrodes protruding out of the pouch. Thereafter, the above-prepared electrolyte solution was injected into the pouch, and the pouch was vacuum-sealed, whereby a sheet-form battery of Example 1-1, which would be brought into a fully-charged state at 4.0 V, was produced.

[Battery Evaluation]

[0110] The thus obtained sodium ion secondary battery was charged to 4.0 V at 25° C. and a constant current equivalent to 0.1 C, and then discharged to 1.5 V at a constant current of 0.1 C. Two cycles of these operations were performed to stabilize the battery. Subsequently, the battery was charged to 4.0 V at a constant current equivalent to 0.1 C, and the impedance was measured at a temperature of -20° C. with a voltage amplitude of 10 mV and a frequency range of 100,000 Hz to 0.001 Hz. Using an analysis program ZView (ver. 3.2b), the negative electrode resistance and the positive electrode resistance were separated from on the thus obtained results of the impedance measurement. As a durability test, the battery was charged to 4.0 V at 60° C. and a constant current equivalent to 1 C, and then discharged to 1.5 V at a constant current of 1 C. These operations were performed for a total of 100 cycles, and the change in the battery volume was measured based on the Archimedes' principle.

Comparative Example 1-1

[0111] A sheet-form battery was produced in the same manner as in Example 1-1 except that the compound (1-1) was not mixed, and the sheet-form battery was evaluated under the same conditions as in Example 1-1.

Comparative Example 1-2

[0112] A sheet-form battery was produced in the same manner as in Example 1-1, except that a positive electrode, in which LiNi.sub.1/3Mn.sub.1/3Co.sub.1/3O, was used as the positive electrode active material along with a carbon black as the conductive material and a polyvinylidene fluoride as the binder at a mass ratio of 90:7:3, was used and LiPF.sub.6 was used as the electrolyte in place of NaPF.sub.6. Further, this sheet-form battery was evaluated under the same conditions as in Example 1-1, except that the discharge voltage was changed to 3.0 V.

Comparative Example 1-3

[0113] A sheet-form battery was produced in the same manner as in Comparative Example 1-2 except that the compound (1-1) was not mixed, and the sheet-form battery was evaluated under the same conditions as in Example 1-1.

Comparative Example 1-4

[0114] A sheet-form battery was produced in the same manner as in Comparative Example 1-2, except that a negative electrode, in which graphite was used as the negative electrode active material along with sodium carboxymethyl cellulose (an aqueous dispersion having a concentration of 1% by mass) as a thickening agent and a styrene-butadiene rubber (an aqueous dispersion having a concentration of 50% by mass) as the binder at a mass ratio of 97.5:1.5:1, was used. This sheet-form battery was evaluated under the same conditions as in Comparative Example 1-2.

Comparative Example 1-5

[0115] A sheet-form battery was produced in the same manner as in Comparative Example 1-4 except that the compound (1-1) was not mixed, and the sheet-form battery was evaluated under the same conditions as in Comparative Example 1-2.

Example 1-2

[Production of Positive Electrode]

[0116] Na.sub.2CO.sub.3, Ni.sub.2CO.sub.3, and Mn.sub.3O.sub.4 were weighed such that the resulting composite metal compound would have a formulation of Na.sub.2/3Ni.sub.1/3Mn.sub.2/3O.sub.2, and these materials were dispersed in an ethanol solvent and subsequently wet-pulverized to a median diameter d50 of 0.4 μm or less using Pico Grain Mill (PCM-L, manufactured by Asada Iron Works, Co., Ltd.) to obtain a mixture of metal-containing compounds. It is noted here that, at the time of the weighing, 10% by mole of Na.sub.2CO.sub.3 was further added, taking into consideration the loss during the production. The thus obtained mixture was dried by evaporation, loaded to an alumina crucible, and then fired in the air atmosphere at 1,000° C. for 24 hours using an electric furnace, whereby a composite metal oxide, P2-type Na.sub.2/3Ni.sub.1/3Mn.sub.2/3O.sub.2, was obtained. The thus obtained composite metal oxide as a positive electrode active material, an acetylene black (HS-100, manufactured by Denka Co., Ltd.) as a conductive material, and a polyvinylidene fluoride (#7500, manufactured by Kureha Corporation) as a binder were weighed at a mass ratio of 95:5:5 and dispersed in an NMP solvent to obtain a slurry. The thus obtained slurry was applied onto an aluminum foil using a coating machine. The resulting coated polar plate was rolled using a rolling machine, punched out in a rectangular shape of 30 mm x 40 mm, and then processed into the state of an electrode, whereby a test electrode was obtained.

[Production of Negative Electrode]

[0117] An active carbon material (specific surface area: 1,700 m.sup.2/g, average particle size: 10 pm) was heat-treated at 2,100° C. for 1 hour under an argon gas atmosphere in a furnace to obtain a negative electrode active material. This heat-treated active carbon material obtained as a negative electrode active material and a polyvinylidene fluoride (#1120, manufactured by Kureha Corporation) as a binder were weighed at a mass ratio of 9:1 and dispersed in an NMP solvent to obtain a slurry. The thus obtained slurry was applied onto a copper foil using a coating machine. The resulting coated polar plate was rolled using a rolling machine, punched out in a rectangular shape of 32 mm×42 mm, and then processed into the state of an electrode, whereby a test electrode was obtained.

[0118] A sheet-form battery was produced in the same manner as in Example 1-1 except that the positive and negative electrodes produced by the above-described methods were used as test electrodes, and the sheet-form battery was evaluated under the same conditions as in Example 1-1.

Example 1-3

[0119] A sheet-form battery was produced in the same manner as in Example 1-2 except that an electrolyte solution, in which 1.60 parts by mass of 1,2-propylene sulfate (compound (1-2)) was mixed without the compound (1-1), was used. This sheet-form battery was evaluated under the same conditions as in Example 1-2.

Comparative Example 1-6

[0120] A sheet-form battery was produced in the same manner as in Example 1-2 except that the compound (1-1) was not mixed, and the sheet-form battery was evaluated under the same conditions as in Example 1-2.

TABLE-US-00001 TABLE 1 Amount Additive/ Initial Volume Positive electrode Negative electrode (parts by NaPF.sub.6 NaPF.sub.6 resis- change Examples active material active material Additive mass) mol/L molar ratio tance ratio ratio Example 1-1 NaNi.sub.0.3Mn.sub.0.3Fe.sub.0.4O.sub.2 Porous carbon material Compound (1-1) 1.43 1.00 0.14 0.39 0.74 Comparative NaNi.sub.0.3Mn.sub.0.3Fe.sub.0.4O.sub.2 Porous carbon material — — 1.00 0 1.00 1.00 Example 1-1 Comparative LiNi.sub.1/3Mn.sub.1/3Co.sub.1/3O.sub.2 Porous carbon material Compound (1-1) 1.43 0 — 1.05 1.00 Example 1-2 Comparative LiNi.sub.1/3Mn.sub.1/3Co.sub.1/3O.sub.2 Porous carbon material — — 0 — 1.00 1.00 Example 1-3 Comparative LiNi.sub.1/3Mn.sub.1/3Co.sub.1/3O.sub.2 Graphite Compound (1-1) 1.43 0 — 1.89 0.86 Example 1-4 Comparative LiNi.sub.1/3Mn.sub.1/3Co.sub.1/3O.sub.2 Graphite — — 0 — 1.00 1.00 Example 1-5 Example 1-2 Na.sub.2/3Ni.sub.1/3Mn.sub.2/3O.sub.2 Heat-treated activated carbon Compound (1-1) 1.43 1.00 0.14 0.55 — Example 1-3 Na.sub.2/3Ni.sub.1/3Mn.sub.2/3O.sub.2 Heat-treated activated carbon Compound (1-2) 1.60 1.00 0.14 0.61 — Comparative Na.sub.2/3Ni.sub.1/3Mn.sub.2/3O.sub.2 Heat-treated activated carbon — — 1.00 0 1.00 — Example 1-6

[0121] Table 1 shows the types of active materials, the type of additive, the resistance ratio, and the volume change ratio for each of the evaluated batteries. The initial resistance ratio represents a ratio of the negative electrode resistance without an additive with respect to the negative electrode resistance with an additive in a battery system using the same positive and negative electrode active materials, and was calculated by the following formula:

[Initial resistance ratio]=[(Negative electrode resistance with additive)/(Negative electrode resistance without additive)]

[0122] The volume change ratio represents a ratio of the change in the battery volume without an additive with respect to the change in the battery volume with an additive in a battery system using the same positive and negative electrode active materials, and was calculated by the following formula:

[Volume change ratio]=[(Change in battery volume with additive)/(Change in battery volume without additive)]

[0123] In all of Example 1-1 and Comparative Examples 1-1 to 1-3, a porous carbon material was used as a negative electrode active material and, according to the results shown in Table 1, an effect of reducing the negative electrode resistance by an addition of the compound (1-1) was not confirmed in these lithium ion secondary batteries. It is seen, however, that an addition of the compound (1-1) provided an excellent effect of reducing the negative electrode resistance in the sodium ion secondary batteries.

[0124] Further, in both Comparative Examples 1-4 and 1-5, NaPF.sub.6 was not incorporated and the effects of the present invention were not exerted and, according to the results shown in Table 1, it is seen that an addition of the compound (1-1) tended to increase the negative electrode resistance in these lithium ion secondary batteries in which graphite was used as a negative electrode active material.

[0125] In other words, these results indicate that the use of the same compound as an additive has different effects depending on the battery system. With regard to the point that even the same compound has different effects on the negative electrode resistance between a sodium ion secondary battery and a lithium ion secondary battery, the reaction mechanism thereof is not clear; however, it is believed to be of a lithium ion secondary battery system in the initial negative electrode formation process. It is presumed that, in the process of the formation of a negative electrode coating film in a sodium ion secondary battery, the compound (1) reduces the negative electrode resistance by inhibiting the formation of an inorganic coating film.

[0126] From a comparison between Example 1-2 and Comparative Example 1-6 in which positive and negative electrode active materials for a sodium secondary battery that are different from those of Example 1-1 were used, it is seen that an addition of the compound (1-1) greatly reduces the negative electrode resistance. From a comparison between Example 1-3 and Comparative Example 1-6, it is seen that the compound (1-2) having a chemical structure similar to that of the compound (1-1) can also provide the same effect.

[0127] From the above-described comparisons, a sodium ion secondary battery having a low resistance can be provided by using the non-aqueous electrolyte solution of the present invention for a sodium ion secondary battery.

Example 2-1

[Production of Positive Electrode]

[0128] Na.sub.2CO.sub.3, Ni.sub.2CO.sub.3, and Mn.sub.3O.sub.4 were weighed such that the resulting composite metal compound would have a formulation of Na.sub.2/3Ni.sub.1/3Mn.sub.2/3O.sub.2, and these materials were dispersed in an ethanol solvent and subsequently wet-pulverized to a median diameter d50 of 0.4 μm or less using Pico Grain Mill (PCM-L, manufactured by Asada Iron Works, Co., Ltd.) to obtain a mixture of metal-containing compounds. It is noted here that, at the time of the weighing, 10% by mole of Na.sub.2CO.sub.3 was further added, taking into consideration the loss during the production. The thus obtained mixture was dried by evaporation, loaded to an alumina crucible, and then fired in the air atmosphere at 1,000° C. for 24 hours using an electric furnace, whereby a composite metal oxide, P2-type Na.sub.2/3Ni.sub.1/3Mn.sub.2/3O.sub.2, was obtained. The thus obtained composite metal oxide as a positive electrode active material, an acetylene black (HS-100, manufactured by Denka Co., Ltd.) as a conductive material, and a polyvinylidene fluoride (#7500, manufactured by Kureha Corporation) as a binder were weighed at a mass ratio of 95:5:5 and dispersed in an NMP solvent to obtain a slurry. The thus obtained slurry was applied onto an aluminum foil using a coating machine. The resulting coated polar plate was rolled using a rolling machine, punched out in a rectangular shape of 30 mm×40 mm, and then processed into the state of an electrode, whereby a test electrode was obtained.

[Production of Negative Electrode]

[0129] An active carbon material (specific surface area: 1,700 m.sup.2/g, average particle size: 10 μm) was heat-treated at 2,100° C. for 1 hour under an argon gas atmosphere in a furnace to obtain a negative electrode active material. This heat-treated active carbon material obtained as a negative electrode active material and a polyvinylidene fluoride (#1120, manufactured by Kureha Corporation) as a binder were weighed at a mass ratio of 9:1 and dispersed in an NMP solvent to obtain a slurry. The thus obtained slurry was applied onto a copper foil using a coating machine. The resulting coated polar plate was rolled using a rolling machine, punched out in a rectangular shape of 32 mm×42 mm, and then processed into the state of an electrode, whereby a test electrode was obtained.

[Preparation of Electrolyte Solution]

[0130] An electrolyte solution was prepared by dissolving ethylene sulfate (compound (1-1)) and NaPF.sub.6 in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio=30:70) as shown in the row of Example 2-1 in Table 2.

[Battery Production]

[0131] A battery element was prepared by laminating the above-obtained positive electrode and negative electrode along with a polyethylene separator in the order of the negative electrode, the separator, and the positive electrode. This battery element was inserted into a pouch made of a laminated film obtained by coating both sides of an aluminum sheet (thickness: 40 μm) with a resin layer, with the terminals of the positive and negative electrodes protruding out of the pouch. Thereafter, the above-prepared electrolyte solution was injected into the pouch, and the pouch was vacuum-sealed, whereby a sheet-form battery of Example 2-1, which would be brought into a fully-charged state at 4.0 V, was produced.

[Battery Evaluation]

[0132] The thus obtained sodium ion secondary battery was charged to 4.0 V at 25° C. and a constant current equivalent to 0.1 C, and then discharged to 1.5 V at a constant current of 0.1 C. Two cycles of these operations were performed to stabilize the battery. Subsequently, the battery was charged to 4.0 V at a constant current equivalent to 0.1 C, and the impedance was measured at a temperature of 25° C. with a voltage amplitude of 10 mV and a frequency range of 100,000 Hz to 0.001 Hz to check the resistance of the battery. As a durability test, the battery charged to 4.0 V was stored at 60° C. for one week, and the change in the battery volume was measured based on the Archimedes' principle.

Example 2-2

[0133] A sheet-form battery was produced in the same manner as in Example 2-1 except that an electrolyte solution was prepared by dissolving ethylene sulfate (compound (1-1)) and NaPF.sub.6 in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio =30:70) as shown in the row of Example 2-2 in Table 2, and the sheet-form battery was evaluated under the same conditions as in Example 2-1.

Example 2-3

[0134] A sheet-form battery was produced in the same manner as in Example 2-1 except that an electrolyte solution was prepared by dissolving ethylene sulfate (compound (1-1)) and NaPF.sub.6 in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio=30:70) as shown in the row of Example 2-3 in Table 2, and the sheet-form battery was evaluated under the same conditions as in Example 2-1.

Example 2-4

[0135] A sheet-form battery was produced in the same manner as in Example 2-1 except that an electrolyte solution was prepared by dissolving ethylene sulfate (compound (1-1)) and NaPF.sub.6 in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio=30:70) as shown in the row of Example 2-4 in Table 2, and the sheet-form battery was evaluated under the same conditions as in Example 2-1.

Comparative Example 2-1

[0136] A sheet-form battery was produced in the same manner as in Example 2-1 except that an electrolyte solution was prepared by dissolving ethylene sulfate (compound (1-1)) and NaPF.sub.6 in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio =30:70) as shown in the row of Comparative Example 2-1 in Table 2, and the sheet-form battery was evaluated under the same conditions as in Example 2-1.

Comparative Example 2-2

[0137] A sheet-form battery was produced in the same manner as in Example 2-1 except that an electrolyte solution was prepared by dissolving ethylene sulfate (compound (1-1)) and NaPF.sub.6 in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio =30:70) as shown in Table 2, and the sheet-form battery was evaluated under the same conditions as in Example 2-1.

TABLE-US-00002 TABLE 2 Compound (1-1) Compound (1-1) NaPF.sub.6 Compound (1-1)/NaPF.sub.6 Amount Initial resis- Volume Examples mol/L mol/L molar ratio (parts by mass) tance ratio change ratio Example 2-1 0.01 1.50 0.01  0.10 0.84 0.84 Example 2-2 0.10 1.00 0.10  1.10 0.74 0.34 Example 2-3 0.40 0.70 0.57  4.40 0.82 0.26 Example 2-4 1.00 0.80 1.25 10.30 0.94 0.53 Comparative 0.00 1.00 0.00  0.00 1.00 1.00 Example 2-1 Comparative 2.00 1.00 2.00 18.70 1.24 1.13 Example 2-2

[0138] Table 2 shows the amounts in moles of ethylene sulfate (compound (1-1)) and NaPF.sub.6, the ethylene sulfate/NaPF.sub.6 molar ratio, the initial resistance ratio, and the volume change ratio for each of the evaluated batteries. The initial resistance ratio represents a ratio of the negative electrode resistance without an additive with respect to the negative electrode resistance with an additive in a battery system using the same positive and negative electrode active materials, and was calculated by the following formula:

[Initial resistance ratio]=[(Negative electrode resistance with additive)/(Negative electrode resistance without additive)]

[0139] The volume change ratio represents a ratio of the change in the battery volume without an additive with respect to the change in the battery volume with an additive in a battery system using the same positive and negative electrode active materials, and was calculated by the following formula:

[Volume change ratio]=[(Change in battery volume with additive)/(Change in battery volume without additive)]

[0140] From the results of Examples 2-1 to 2-4, it is apparent that the battery resistance and the change in the battery volume after the durability test were both smaller than those of Comparative Example 2-1 as long as the value of ethylene sulfate/NaPF.sub.6 (molar ratio) was in a specific range. Further, as shown in Comparative Example 2-2, it is seen that, when the value of ethylene sulfate/NaPF.sub.6 (molar ratio) was larger than a specific range, the initial resistance was higher and the change in the battery volume after the durability test was larger than in Comparative Example 2-1 where ethylene sulfate was not added. In other words, as long as the molar ratio of ethylene sulfate/NaPF.sub.6 is in an appropriate range, a sodium ion secondary battery having a low initial resistance and a small change in the battery volume after a durability test can be provided.

INDUSTRIAL APPLICABILITY

[0141] The non-aqueous electrolyte solution for a sodium ion secondary battery according to one embodiment of the present invention and the sodium ion secondary battery according to another embodiment of the present invention can be used in a variety of known applications. Specific examples thereof include: power sources for electric tools and portable electronics such as smartphones; emergency power storage systems for houses and the like; power sources for transport equipment such as electric vehicles; power sources for load leveling; and natural energy storage power sources.