JP6252220B2 - Sodium ion secondary battery, charge / discharge method and charge / discharge system - Google Patents

Description

  The present invention relates to a sodium ion secondary battery, and relates to a sodium ion secondary battery suitable for charging or discharging at a low temperature.

  In recent years, technology that converts natural energy such as sunlight and wind power into electric energy has attracted attention. In addition, as a battery having a high energy density capable of storing a large amount of electric energy, demand for non-aqueous electrolyte secondary batteries is expanding. Among non-aqueous electrolyte secondary batteries, lithium ion secondary batteries are promising in that they are lightweight and have a high electromotive force. However, since the lithium ion secondary battery uses an organic solvent as an electrolyte component, it has a drawback of low heat resistance. In addition, with the expansion of the non-aqueous electrolyte secondary battery market, the price of lithium resources is also rising. Therefore, development of a sodium ion secondary battery using an ionic liquid as an electrolyte, which has high heat resistance and can be expected to be produced at low cost, is being promoted.

  As an ionic liquid used for a battery, for example, a mixture of sodium bis (fluorosulfonyl) amide (NaFSA) and potassium bis (fluorosulfonyl) amide (KFSA) has been developed as an ionic liquid having a melting point of 90 ° C. or lower. (Patent Document 1). In addition, some ionic liquids containing organic cations are known to be liquid at room temperature.

JP 2011-192474 A

It is known that the ionic liquid has high heat resistance, but has high viscosity at low temperatures. Therefore, a secondary battery using an ionic liquid as an electrolyte is assumed to be used at a temperature higher than room temperature. This is because, generally, when the temperature is high, the viscosity of the ionic liquid decreases and the utilization factor of the active material increases. Also, by mixing a salt having a low-viscosity organic cation with a salt having a high-viscosity sodium ion and increasing the content ratio of the salt having an organic cation, the viscosity of the ionic liquid is reduced, and the active material is used. It is considered desirable to increase the rate.
However, in recent years, applications of secondary batteries have been diversified, and there is a demand for the development of secondary batteries that can be used in a wide temperature range and have high safety.

  A first aspect of the present invention includes a positive electrode having a positive electrode active material and a positive electrode current collector holding the positive electrode active material, a negative electrode active material and a negative electrode having a negative electrode current collector holding the negative electrode active material, and An electrode group including a separator interposed between a positive electrode and the negative electrode, a nonaqueous electrolyte having sodium ion conductivity, and a battery case containing the electrode group and the nonaqueous electrolyte, The water electrolyte includes a first salt of a sodium ion and a first anion, and a second salt of an organic cation and a second anion, and the ratio of the sodium ion in the total of the sodium ion and the organic cation is: It is 30-50 mol%, It is related with the sodium ion secondary battery whose viscosity in 5 degreeC of the said nonaqueous electrolyte is 0.25-1.7 Pa.s.

  The second aspect of the present invention includes a step of detecting the temperature of the sodium ion secondary battery, and a step of starting charging or discharging when the detected temperature is 5 to 40 ° C. The present invention relates to a method for charging and discharging a sodium ion secondary battery.

A third aspect of the present invention, the sodium ion secondary battery, a temperature measuring unit for detecting the temperature of the sodium-ion battery, the charge control device that controls the charging current I _in of the sodium ion secondary battery And a discharge control device that controls the discharge current I _out of the sodium ion secondary battery, and the temperature of the sodium ion secondary battery detected by the temperature measurement unit is 5 to 40 ° C. The present invention relates to a charge / discharge system for a sodium ion secondary battery that starts charging or discharging.

  The sodium ion secondary battery of the present invention can obtain a high utilization rate comparable to that of the active material in a high temperature range even in charge and discharge at a low temperature.

1 is a longitudinal sectional view schematically showing a sodium ion secondary battery according to an embodiment of the present invention. It is a block diagram which shows the outline | summary of the charging / discharging system which concerns on one Embodiment of this invention.

[Description of Embodiment of the Invention]
First, the contents of the embodiments of the invention will be listed and described.
A first aspect of the present invention is (1) a positive electrode having a positive electrode active material and a positive electrode current collector holding the positive electrode active material, a negative electrode active material, and a negative electrode having a negative electrode current collector holding the negative electrode active material, And an electrode group comprising a separator interposed between the positive electrode and the negative electrode, a non-aqueous electrolyte having sodium ion conductivity, and a battery case containing the electrode group and the non-aqueous electrolyte. The non-aqueous electrolyte includes a first salt of a sodium ion and a first anion, and a second salt of an organic cation and a second anion, and the sodium ion occupies the total of the sodium ion and the organic cation. The present invention relates to a sodium ion secondary battery in which the ratio is 30 to 50 mol%, and the viscosity of the nonaqueous electrolyte at 5 ° C. is 0.25 to 1.7 Pa · s. Thereby, for example, even when charging / discharging in a low temperature range of 5 ° C. or higher, preferably 10 ° C. or higher, 40 ° C. or lower, preferably 30 ° C. or lower (more preferably 20 ° C. or lower, particularly preferably 15 ° C. or lower). It becomes possible to obtain the utilization factor of the active material (hereinafter sometimes simply referred to as utilization factor).

  (2) The positive electrode current collector is a first metal porous body having a three-dimensional network structure, the positive electrode has a thickness of 300 μm or more, and the negative electrode current collector has a three-dimensional network shape. When the second metal porous body has a structure and the negative electrode has a thickness of 300 μm or more, the viscosity of the nonaqueous electrolyte at 5 ° C. is preferably 0.25 to 0.8 Pa · s. . In this case, for example, a particularly high utilization factor can be obtained in charge and discharge in a low temperature range of 5 ° C. or more and 40 ° C. or less.

  (3) The total content of the first salt and the second salt in the non-aqueous electrolyte is preferably 80% by mass or more. This is because a further improvement in the utilization rate can be expected.

  (4) It is preferable that the non-aqueous electrolyte contains an organic solvent in a proportion of 10% by mass or less. This is because it is easy to adjust the viscosity in a low temperature range.

  (5) The second aspect of the present invention includes a step of detecting the temperature of the sodium ion secondary battery, and a step of starting charging or discharging when the detected temperature is 5 to 40 ° C. The present invention relates to a method for charging and discharging a sodium ion secondary battery.

(6) The third aspect of the present invention controls the sodium ion secondary battery, a temperature measuring unit for detecting the temperature of the sodium-ion battery, the charging current I _in of the sodium ion secondary battery A charge control device, and a discharge control device that controls a discharge current I _out of the sodium ion secondary battery, wherein the temperature of the sodium ion secondary battery detected by the temperature measurement unit is 5 to 40 ° C. The present invention relates to a charging / discharging system of a sodium ion secondary battery that starts charging or discharging in some cases. Thereby, charge and discharge can be started in a low temperature range of 5 ° C. or higher, preferably 10 ° C. or higher, 40 ° C. or lower, preferably 30 ° C. or lower (more preferably 20 ° C. or lower, particularly preferably 15 ° C. or lower). For example, convenience when used as a power source in a cold region is improved.

[Details of the embodiment of the invention]
Embodiments of the present invention will be specifically described below. In addition, this invention is not limited to the following content, but is shown by the claim, and it is intended that all the changes within the meaning and range equivalent to a claim are included.

[Nonaqueous electrolyte]
The non-aqueous electrolyte includes a first salt of a sodium ion and a first anion, and a second salt of an organic cation and a second anion (hereinafter, the ionic liquid is combined with the first salt and the second salt) May be called).

  Sodium ion concentration is 30-50 mol% with respect to the cation contained in a nonaqueous electrolyte, ie, the sum total of an organic cation and a sodium ion. When the sodium ion concentration is within this range, a high utilization rate can be achieved when the battery is operated in a low temperature range of 5 to 40 ° C. The sodium ion concentration is preferably 35 to 45 mol%.

  The non-aqueous electrolyte has a viscosity at 5 ° C. of 0.25 to 1.7 Pa · s, preferably 0.25 to 1.2 Pa · s, and preferably 0.25 to 0.8 Pa · s. It is more preferable. Usually, a secondary battery using an ionic liquid as an electrolyte has a low ionic liquid viscosity, for example, in a high temperature range of 60 ° C. or higher under conditions where the viscosity of the ionic liquid is low. It is made to use. However, if the sodium ion concentration is 30 to 50 mol% and the viscosity of the nonaqueous electrolyte at 5 ° C is in the range of 0.25 to 1.7 Pa · s, the battery is operated in a low temperature range of 5 to 40 ° C. When used, a high utilization rate is obtained. The present invention has been achieved based on such new findings.

The viscosity is measured using an E-type viscometer according to JIS Z 8803 “Method for measuring viscosity of liquid”. The viscosity is a rotor having an angle of 1 ° and a radius of 24 mm. The shear rate is 38.3 s ⁻¹ (rotation speed 10), 76.6 s ⁻¹ (rotation speed 20), 191.5 s ⁻¹ (rotation speed 50). ) And an average value of numerical values measured at 383 s ⁻¹ (rotation speed 100). The same applies hereinafter.

  When the electrodes (positive electrode and negative electrode) are thickened, the utilization factor is easily affected by the viscosity of the nonaqueous electrolyte. The viscosity of the nonaqueous electrolyte at 5 ° C. is preferably 0.25 to 0.8 Pa · s when the electrode thickness is 300 μm or more, particularly 300 to 500 μm. When the electrode thickness exceeds 500 μm, it is preferably 0.25 to 0.3 Pa · s. An electrode having a thickness of 300 μm or more can be obtained, for example, by using a metal porous body as a current collector, as will be described later. Even when such a thick electrode is used, a high utilization factor can be achieved in a low temperature region by using the non-aqueous electrolyte.

  The total content of the first salt and the second salt (that is, the ionic liquid) is preferably 80% by mass or more, and more preferably 90% by mass or more of the nonaqueous electrolyte. By making the content of the ionic liquid 80% by mass or more of the non-aqueous electrolyte, the ion concentration becomes high and it becomes easy to obtain a high utilization rate in a low temperature range.

  Although the ionic liquid may occupy 100% by mass of the nonaqueous electrolyte, an organic solvent may be contained as an additive in a proportion of 10% by mass or less, preferably 8% by mass or less. As an organic solvent, a carbonate compound is preferable. Examples of the carbonate compound include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), chain carbonates such as diethyl carbonate (DEC) and dimethyl carbonate (DMC), and fluorine-containing carbonate compounds such as fluoroethylene carbonate. It is done. By containing the carbonate compound or the fluorine-containing carbonate compound, it becomes easy to adjust the viscosity of the nonaqueous electrolyte at 5 ° C. to 0.25 to 1.7 Pa · s. Moreover, it is preferable that the minimum of the ratio of an organic solvent is 3 mass%.

  The first salt preferably contains a salt of sodium ion and a fluorine-containing amide anion (first anion). The second salt preferably contains a salt of an organic cation and a fluorine-containing amide anion (second anion). This is because a non-aqueous electrolyte with high ion conductivity can be obtained.

Preferred examples of the fluorine-containing amide anion include an anion having a bis (sulfonyl) amide skeleton and a fluorine atom in the sulfonyl group (fluorine-containing bis (sulfonyl) amide anion). Fluorine-containing bis (sulfonyl) of the amide anion, bis (fluorosulfonyl) amide anion ^{(FSA -: bis (fluorosulfonyl)} amide anion)); bis (trifluoromethylsulfonyl) amide anion ^{(TFSA -: bis (trifluoromethylsulfonyl)} amide anion ), Bis (pentafluoroethylsulfonyl) amide anion, bis (perfluoroalkylsulfonyl) amide anion (PFSA ⁻ : bis (perfluoroalkylsulfonyl) amide anion) such as (fluorosulfonyl) (trifluoromethylsulfonyl) amide anion it can.

As the first anion or the second anion, in addition to the fluorine-containing amide anion, an anion of a fluorine-containing acid [anion of fluorine-containing phosphate such as hexafluorophosphate ion (PF ₆ ⁻ ); tetrafluoroborate ion (BF ₄ ^-), such as an anion of a fluorine-containing boric acid, etc.], the anion of chlorine-containing acid [perchloric acid ion (ClO ₄ ^-), etc.], anion [bis oxyacid having oxalate group (oxalato) borate ion (B (C Oxalatoborate ions such as ₂ O ₄ ) ₂ ⁻ ); Oxalatoborate ions such as tris (oxalato) phosphate ions (P (C ₂ O ₄ ) ₃ ⁻ )], anion of fluoroalkanesulfonic acid [trifluoromethanesulfone Acid ion (CF ₃ SO ₃ ⁻ ) and the like].

  The first anion and the second anion may be the same or different. Moreover, each of the first salt and the second salt may be a single salt or a combination of a plurality of types of salts. Furthermore, the non-aqueous electrolyte may contain a salt of a metal cation other than sodium ion such as lithium, potassium, rubidium and cesium and an anion in addition to the first salt and the second salt. That is, the kind of salt which comprises a nonaqueous electrolyte is not restricted to 2 types.

  Examples of organic cations include nitrogen-containing cations; sulfur-containing cations; phosphorus-containing cations. Nitrogen-containing cations include cations derived from aliphatic amines, alicyclic amines, and aromatic amines (for example, quaternary ammonium cations), and organic cations having nitrogen-containing heterocycles (that is, cyclic amines). Examples thereof include derived cations).

The quaternary ammonium cations such as tetramethyl ammonium cation, trimethyl ammonium cation, hexyl trimethyl ammonium cation, tetraethylammonium cation (TEA ^+: tetraethylammonium cation), preparative Riechiru methyl ammonium cation ^{(TEMA +: t riethyl methyl ammonium} cation And tetraalkylammonium cations (such as tetra-C _1-10 alkylammonium cations).

Examples of the sulfur-containing cation include tertiary sulfonium cations such as trialkylsulfonium cations such as trimethylsulfonium cation, trihexylsulfonium cation, and dibutylethylsulfonium cation (for example, tri-C _1-10 alkylsulfonium cation). .

Phosphorus-containing cations include quaternary phosphonium cations, for example, tetraalkylphosphonium cations such as tetramethylphosphonium cation, tetraethylphosphonium cation, tetraoctylphosphonium cation (for example, tetra C _1-10 alkylphosphonium cation); triethyl (methoxymethyl) ) Alkyl (alkoxyalkyl) phosphonium cations such as phosphonium cation, diethylmethyl (methoxymethyl) phosphonium cation, trihexyl (methoxyethyl) phosphonium cation (for example, tri-C _1-10 alkyl (C _1-5 alkoxy C _1-5 alkyl)) Phosphonium cation, etc.). In the alkyl (alkoxyalkyl) phosphonium cation, the total number of alkyl groups and alkoxyalkyl groups bonded to the phosphorus atom is 4, and the number of alkoxyalkyl groups is preferably 1 or 2.

  In addition, as for carbon number of the alkyl group couple | bonded with the nitrogen atom of the quaternary ammonium cation, the sulfur atom of the tertiary sulfonium cation, or the phosphorus atom of the quaternary phosphonium cation, 1-8 are preferable, and 1-4 are further 1, 2, or 3 is particularly preferable.

  Here, the organic cation is preferably an organic cation having a nitrogen-containing heterocycle. An ionic liquid comprising an organic cation having a nitrogen-containing heterocycle is promising as a non-aqueous electrolyte because of its high heat resistance and low viscosity. Examples of the nitrogen-containing heterocyclic skeleton of the organic cation include pyrrolidine, imidazoline, imidazole, pyridine, piperidine and the like, 5- to 8-membered heterocycles having 1 or 2 nitrogen atoms as ring constituent atoms; Examples thereof include 5- to 8-membered heterocycles having 1 or 2 nitrogen atoms and other heteroatoms (oxygen atoms, sulfur atoms, etc.).

  Note that the nitrogen atom which is a constituent atom of the ring may have an organic group such as an alkyl group as a substituent. Examples of the alkyl group include alkyl groups having 1 to 10 carbon atoms such as a methyl group, an ethyl group, a propyl group, and an isopropyl group. 1-8 are preferable, as for carbon number of an alkyl group, 1-4 are more preferable, and it is especially preferable that it is 1, 2 or 3.

  Among organic cations having a nitrogen-containing heterocycle, organic cations having a pyrrolidine skeleton are particularly promising as nonaqueous electrolytes because of their high heat resistance and low production costs. The organic cation having a pyrrolidine skeleton preferably has two of the above alkyl groups on one nitrogen atom constituting the pyrrolidine ring. The organic cation having a pyridine skeleton preferably has one alkyl group on one nitrogen atom constituting the pyridine ring. Moreover, it is preferable that the organic cation which has an imidazole skeleton has one said alkyl group respectively in two nitrogen atoms which comprise an imidazole ring.

Specific examples of the organic cation having a pyrrolidine skeleton include 1,1-dimethylpyrrolidinium cation, 1,1-diethylpyrrolidinium cation, 1-ethyl-1-methylpyrrolidinium cation, 1-methyl-1- propyl pyrrolidinium cation ^{(P13 +: 1-methyl-} 1-propylpyrrolidinium cation), 1- methyl-1-butyl pyrrolidinium cation ^{(MBPY +: 1- methyl -1- butyl} pyrrolidinium cation), 1- ethyl -1 -Propylpyrrolidinium cation and the like. Of these, pyrrolidinium cations having a methyl group and an alkyl group having 2 to 4 carbon atoms, such as P13 ⁺ and MBPY ^+, are preferable because of particularly high electrochemical stability.

  Specific examples of the organic cation having a pyridine skeleton include 1-alkylpyridinium cations such as 1-methylpyridinium cation, 1-ethylpyridinium cation, and 1-propylpyridinium cation. Of these, pyridinium cations having an alkyl group having 1 to 4 carbon atoms are preferred.

Specific examples of the organic cation having an imidazole skeleton include 1,3-dimethylimidazolium cation, 1-ethyl-3-methylimidazolium cation (EMI ⁺ : 1-ethyl-3-methylimidazolium cation), and 1-methyl-3. -Propylimidazolium cation, 1-butyl-3-methylimidazolium cation (BMI ⁺ : 1-buthyl-3-methylimidazolium cation), 1-ethyl-3-propylimidazolium cation, 1-butyl-3-ethylimidazolium And cations. Of these, an imidazolium cation having a methyl group such as EMI ⁺ or BMI ⁺ and an alkyl group having 2 to 4 carbon atoms is preferable.

As a specific example of the combination of the first salt and the second salt,
(I) a first salt of sodium ion and FSA ⁻ (Na · FSA), and a second salt of P13 ⁺ and FSA ⁻ (P13 · FSA),
(Ii) a first salt of sodium ion and TFSA ⁻ (Na · TFSA), and a second salt of P13 ⁺ and TFSA ⁻ (P13 · TFSA),
(Iii) a first salt of sodium ion and FSA ⁻ (Na · FSA), and a second salt of EMI ⁺ and FSA ⁻ (EMI · FSA),
(Iv) a first salt of sodium ion and TFSA ⁻ (Na · TFSA), and a second salt of EMI ⁺ and TFSA ⁻ (EMI · TFSA),
(V) a first salt of sodium ion and FSA ⁻ (Na · FSA), a second salt of EMI ⁺ and FSA ⁻ (EMI · FSA), and a second salt of P13 ⁺ and FSA ⁻ (P13 · FSA), and the like.

[Positive electrode]
The positive electrode includes a positive electrode current collector and a positive electrode active material layer held by the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material as an essential component, and may include a conductive carbon material, a binder, and the like as optional components.

The positive electrode active material may be any material that electrochemically occludes and releases sodium ions, and sodium-containing metal oxides are preferably used. A sodium containing metal oxide may be used individually by 1 type, and may be used in combination of multiple types. The average particle size of the sodium-containing metal oxide particles (particle size D _{50 at} 50% cumulative volume of volume particle size distribution, the same shall apply hereinafter) is preferably 2 μm or more and 20 μm or less.

As the sodium-containing metal oxide, for example, sodium chromite (NaCrO ₂ ) can be used. In sodium chromite, a part of Cr or Na may be substituted with other elements. For example, the general formula: Na _1-x M ¹ _x Cr _1-y M ² _y O ₂ (0 ≦ x ≦ 2 / 3, 0 ≦ y ≦ 0.7, M ¹ and M ² are each independently a metal element other than Cr and Na). In the above general formula, x preferably satisfies 0 ≦ x ≦ 0.5, and M ¹ and M ² are at least one selected from the group consisting of Ni, Co, Mn, Fe and Al, for example. Preferably there is. M ¹ is an element occupying Na site and M ² is an element occupying Cr site. Such a compound can be produced at a low cost and is excellent in reversibility of structural change accompanying charge / discharge. Thereby, it is possible to obtain a sodium molten salt battery having further excellent charge / discharge cycle characteristics.

Further, sodium manganate (Na _2/3 Fe _1/3 Mn _2/3 O ₂ or the like) can be used as the sodium-containing metal oxide. A part of Fe, Mn or Na of sodium iron manganate may be substituted with other elements. For example, the general _{formula: Na 2/3-x M} 3 x Fe 1/3-y Mn 2/3-z M 4 y + z O 2 (0 ≦ x <2 / 3,0 ≦ y <1/3, It is preferable that 0 ≦ z ≦ 1/3, M ³ and M ⁴ are each independently a metal element other than Fe, Mn and Na. In the above general formula, x preferably satisfies 0 ≦ x ≦ 1/3. M ³ represents, for example Ni, is preferably at least one selected from the group consisting of C o Contact and Al, M ⁴ is at least one selected Ni, from the group consisting of Co and Al Is preferred. M ³ is an Na site, and M ⁴ is an element occupying an Fe or Mn site.

Furthermore, we as the sodium-containing metal _{oxides, Na 2 FePO 4 F, NaVPO} 4 F, NaCoPO 4, NaNiPO 4, also _{NaMnPO 4, NaMn 1.5 Ni 0.5 O} 4, NaMn 0.5 Ni 0.5 O 2 are used.

  Examples of the conductive carbon material included in the positive electrode include graphite, carbon black, and carbon fiber. Of the conductive carbon materials, carbon black is particularly preferable because it can easily form a sufficient conductive path when used in a small amount. Examples of carbon black include acetylene black, ketjen black, and thermal black. The amount of the conductive carbon material is preferably 2 to 15 parts by mass and more preferably 3 to 8 parts by mass per 100 parts by mass of the positive electrode active material.

  The binder serves to bind the positive electrode active materials to each other and fix the positive electrode active material to the positive electrode current collector. As the binder, fluororesin, polyamide, polyimide, polyamideimide and the like can be used. As the fluororesin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, or the like can be used. The amount of the binder is preferably 1 to 10 parts by mass and more preferably 3 to 5 parts by mass per 100 parts by mass of the positive electrode active material.

  As the positive electrode current collector, a metal foil, a non-woven fabric made of metal fibers, a porous metal sheet, or the like is used. The metal constituting the positive electrode current collector is preferably aluminum or an aluminum alloy because it is stable at the positive electrode potential, but is not particularly limited. When using an aluminum alloy, it is preferable that metal components (for example, Fe, Si, Ni, Mn, etc.) other than aluminum are 0.5 mass% or less. The thickness of the metal foil serving as the positive electrode current collector is, for example, 10 to 50 μm, and the thickness of the metal fiber nonwoven fabric or the metal porous sheet is, for example, 100 to 600 μm.

  Among them, the positive electrode current collector is preferably a porous body of a first metal having a three-dimensional network structure in terms of filling property, retainability, and current collecting property of the positive electrode active material. It is preferable that aluminum is included. The porous body containing aluminum can be obtained by forming a coating layer of aluminum or an aluminum alloy on the surface of a foamed resin or a nonwoven fabric serving as a base material and then removing the base material. By removing the substrate, the inside of the skeleton of the porous body can be made hollow. The porous body preferably has a hollow inside of the skeleton in that it is lightweight. The porous body preferably has communication holes, and the porosity is preferably 30% or more and 98% or less, and more preferably 90 to 98%. As a commercially available aluminum porous body, “Aluminum Celmet” (registered trademark) manufactured by Sumitomo Electric Industries, Ltd. can be used.

[Negative electrode]
The negative electrode includes a negative electrode current collector and a negative electrode active material layer held by the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material as an essential component, and may include a conductive carbon material, a binder, and the like as optional components.

  For the negative electrode active material layer, a metal that is alloyed with sodium or a material that electrochemically occludes and releases sodium ions can be used as the negative electrode active material. For example, zinc, a zinc alloy, tin, a tin alloy, silicon, a silicon alloy, etc. can be mentioned as a metal alloyed with sodium.

  When these materials are used, the negative electrode active material layer can be obtained, for example, by attaching or pressing a metal sheet to the negative electrode current collector. Alternatively, the metal may be gasified and attached to the negative electrode current collector by a vapor phase method such as vacuum deposition or sputtering, or the metal fine particles may be collected by an electrochemical method such as plating. You may make it adhere to an electric body. According to the vapor phase method or the plating method, a thin and uniform negative electrode active material layer can be formed.

In addition, as a material for electrochemically storing and releasing sodium ions, sodium-containing titanium compounds, non-graphitizable carbon (hard carbon), and the like are preferably used from the viewpoint of thermal stability and electrochemical stability. . As the sodium-containing titanium compound, sodium titanate is preferable, and more specifically, it is preferable to use at least one selected from the group consisting of Na ₂ Ti ₃ O ₇ and Na ₄ Ti ₅ O ₁₂ . Moreover, you may substitute a part of Ti or Na of sodium titanate with another element. For example, Na _{2 -x} M ⁵ _x Ti _{3 -y} M ⁶ _y O ₇ (0 ≦ x ≦ 3/2, 0 ≦ y ≦ 8/3, M ⁵ and M ⁶ are independently other than Ti and Na A metal element, for example, at least one selected from the group consisting of Ni, Co, Mn, Fe, Al, and Cr), Na _4-x M ⁷ _x Ti _5-y M ⁸ _y O ₁₂ ( 0 ≦ x ≦ 11/3, 0 ≦ y ≦ 14/3, M ⁷ and M ⁸ are each independently a metal element other than Ti and Na, for example, from Ni, Co, Mn, Fe, Al and Cr It is also possible to use at least one selected from the group consisting of A sodium containing titanium compound may be used individually by 1 type, and may be used in combination of multiple types. Sodium-containing titanium compounds may be used in combination with non-graphitizable carbon. M ⁵ and M ⁷ are Na sites, and M ⁶ and M ⁸ are elements occupying Ti sites.

Non-graphitizable carbon is a carbon material that does not develop a graphite structure even when heated in an inert atmosphere. Fine graphite crystals are arranged in random directions, and nanostructured between crystal layers. A material having a void in the order. Since the diameter of a typical alkali metal sodium ion is 0.95 angstrom, the size of the void is preferably sufficiently larger than this. The average particle diameter of the non-graphitizable carbon may be, for example, 3 to 20 μm, and 5 to 15 μm enhances the filling property of the negative electrode active material in the negative electrode and causes side reactions with the electrolyte (ionic liquid). Desirable from the viewpoint of suppression. The specific surface area of the non-graphitizable carbon may together to ensure the acceptance of the sodium ions, from the viewpoint of suppressing side reactions with the electrolyte, if for example 1~10m ² / g, 3~8m ² / It is preferable that it is g. Non-graphitizable carbon may be used alone or in combination of two or more.

  As the binder and the conductive carbon material used for the negative electrode, the materials exemplified as the constituent elements of the positive electrode can be used. The amount of the binder is preferably 1 to 10 parts by mass and more preferably 3 to 5 parts by mass per 100 parts by mass of the negative electrode active material. The amount of the conductive carbon material is preferably 5 to 15 parts by mass and more preferably 5 to 10 parts by mass per 100 parts by mass of the negative electrode active material.

  As the negative electrode current collector, a metal foil, a non-woven fabric made of metal fibers, a porous metal sheet, or the like is used. As the metal, a metal that is not alloyed with sodium can be used. Among these, aluminum, an aluminum alloy, copper, a copper alloy, nickel, a nickel alloy, and the like are preferable because they are stable at the negative electrode potential. Of these, aluminum and aluminum alloys are preferable in terms of excellent lightness. As the aluminum alloy, for example, an aluminum alloy similar to that exemplified as the positive electrode current collector may be used. The thickness of the metal foil serving as the negative electrode current collector is, for example, 10 to 50 μm, and the thickness of the metal fiber nonwoven fabric or metal porous sheet is, for example, 100 to 600 μm.

  Among these, the negative electrode current collector is preferably a porous body of a second metal having a three-dimensional network structure in terms of the filling property, retention property, and current collecting property of the negative electrode active material. Preferably it contains copper or aluminum. For example, a copper porous body can be obtained by forming a copper coating layer on the surface of a foamed resin or a nonwoven fabric serving as a base material and then removing the base material. By removing the substrate, the inside of the skeleton of the porous body can be made hollow. The porous body preferably has a hollow inside of the skeleton in that it is lightweight. The porous body preferably has communication holes, and the porosity is preferably 30% or more and 98% or less, and more preferably 90 to 98%. As the commercially available second metal porous body, “Celmet” (registered trademark) of copper or aluminum manufactured by Sumitomo Electric Industries, Ltd. can be used.

[Separator]
A separator can be disposed between the positive electrode and the negative electrode. The separator material may be selected in consideration of the operating temperature of the battery, but from the viewpoint of suppressing side reactions with the nonaqueous electrolyte, polyolefin, glass fiber, fluororesin, alumina, polyphenylene sulfite (PPS), etc. Is preferably used. In addition, when using the separator made from polyolefin, it is preferable to provide a heat-resistant layer. The heat resistant layer may contain, for example, a heat resistant resin such as inorganic particles or aramid (aromatic polyamide).

  The thickness of the separator is preferably 10 μm to 500 μm, more preferably 20 to 50 μm. If it is the thickness of this range, since an internal short circuit can be prevented effectively and the volume occupation rate of the separator which occupies for an electrode group can be restrained low, a high capacity | capacitance density can be obtained.

[Electrode group]
The sodium ion secondary battery is used in a state where the electrode group including the positive electrode and the negative electrode and the nonaqueous electrolyte are accommodated in a battery case. The electrode group is formed by laminating or winding a positive electrode and a negative electrode with a separator interposed therebetween. At this time, while using a metal battery case, by making one of the positive electrode and the negative electrode conductive with the battery case, a part of the battery case can be used as the first external terminal. On the other hand, the other of the positive electrode and the negative electrode is connected to a second external terminal led out of the battery case in a state insulated from the battery case, using a lead piece or the like.

Next, the structure of the sodium ion secondary battery according to one embodiment of the present invention will be described. However, the structure of the sodium ion secondary battery according to the present invention is not limited to the following structure.
FIG. 1 is a longitudinal sectional view schematically showing a configuration of a sodium ion secondary battery according to an embodiment of the present invention.

  The sodium ion secondary battery 100 includes a stacked electrode group 11, a non-aqueous electrolyte (not shown), and a rectangular aluminum battery case 10 that houses these. The battery case 10 includes a bottomed container body 12 having an upper opening and a lid 13 that closes the upper opening. When assembling the sodium ion secondary battery 100, first, the electrode group 11 is configured and inserted into the container body 12 of the battery case 10.

  Thereafter, a step of injecting a nonaqueous electrolyte into the container body 12 and impregnating the nonaqueous electrolyte into the gaps of the separator 1, the positive electrode 2 and the negative electrode 3 constituting the electrode group 11 is performed. Alternatively, the non-aqueous electrolyte may be impregnated with the electrode group, and then the electrode group including the non-aqueous electrolyte may be accommodated in the container body 12.

  An external positive terminal (not shown) penetrating the sealing plate 13 is provided near one side of the lid 13, and an external negative terminal 15 penetrating the sealing plate 13 is positioned near the other side of the sealing plate 13. Is provided. Each terminal is preferably insulated from the case. In the center of the sealing plate 13, a safety valve 16 is provided for releasing the gas generated inside when the internal pressure of the electronic case 10 rises.

  The stacked electrode group 11 is composed of a plurality of positive electrodes 2, a plurality of negative electrodes 3, and a plurality of separators 1 interposed between them, each having a rectangular sheet shape. In FIG. 1, the separator 1 is formed in a bag shape so as to surround the positive electrode 2, but the form of the separator is not particularly limited. The plurality of positive electrodes 2 and the plurality of negative electrodes 3 are alternately arranged in the stacking direction in the electrode group 11.

  A positive electrode lead piece 2 c may be formed at one end of each positive electrode 2. The plurality of positive electrodes 2 are connected in parallel by bundling the positive electrode lead pieces 2 c of the plurality of positive electrodes 2 and connecting them to the external positive terminal 14 provided on the lid portion 13 of the battery case 10. Similarly, a negative electrode lead piece 3 c may be formed at one end of each negative electrode 3. The plurality of negative electrodes 3 are connected in parallel by bundling the negative electrode lead pieces 3 c of the plurality of negative electrodes 3 and connecting them to the external negative terminal 15 provided on the lid portion 13 of the battery case 10. The bundle of the positive electrode lead pieces 2c and the bundle of the negative electrode lead pieces 3c are desirably arranged on the left and right sides of one end face of the electrode group 11 so as to avoid mutual contact.

  Both the external positive terminal 14 and the external negative terminal 15 are columnar, and at least a portion exposed to the outside has a screw groove. A nut 7 is fitted in the screw groove of each terminal, and the nut 7 is fixed to the lid portion 13 by rotating the nut 7. A flange portion 8 is provided in a portion of each terminal accommodated in the battery case, and the flange portion 8 is fixed to the inner surface of the lid portion 13 via a washer 9 by the rotation of the nut 7.

[Charging / Discharging System]
The charge / discharge of the sodium ion secondary battery can be performed by, for example, a charge / discharge system as shown in FIG. The charge / discharge system includes a sodium ion secondary battery 100, a temperature measurement unit (temperature sensor) 101 that detects the temperature of the sodium ion secondary battery 100, and a charge control that controls the charging current I _in of the sodium ion secondary battery 100. A control unit 107 including a device (charge circuit) 102 and a discharge control device (discharge circuit) 103 that controls the discharge current I _out of the sodium ion secondary battery 100. The charge / discharge system may include a heater 105 or a cooling device (not shown) as necessary. The heater 105 preferably includes a heating control device 106 that controls the amount of heat supplied to the sodium ion secondary battery 100. The sodium ion secondary battery 100 is used as a power source for the external load 108.

  In this system, the temperature of the sodium ion secondary battery 100 detected by the temperature measurement unit 101 is 5 ° C or higher, preferably 10 ° C or higher, 40 ° C or lower, preferably 30 ° C or lower (more preferably 20 ° C or lower, When the temperature is particularly preferably 15 ° C. or lower, the charging control device 102 or the discharging control device 103 controls the charging or discharging to start. This is because even when charging and discharging are performed in such a low temperature range, a high utilization rate can be achieved.

[Charging / discharging method]
The charging / discharging method of a sodium ion secondary battery has the process of detecting the temperature of a sodium ion secondary battery, and the process of starting charge or discharge, when the detected temperature is 5-40 degreeC. For example, when the temperature of the sodium ion secondary battery before starting charging (or discharging) is lower than 5 ° C, it is 5 ° C or higher, preferably 10 ° C or higher, 40 ° C or lower, preferably 30 ° C or lower with a heater or the like. After heating to (more preferably 20 ° C. or less, particularly preferably 15 ° C. or less), charging (or discharging) is started. This is because even when charging and discharging are performed in such a low temperature range, a high utilization rate can be achieved. The temperature of the sodium ion secondary battery at the start of charging (or discharging) is 5 ° C or higher, preferably 10 ° C or higher, 40 ° C or lower, preferably 30 ° C or lower, more preferably 20 ° C or lower, and particularly preferably 15 ° C. It should just be below ° C and does not prevent exceeding 40 ° C during charge (or during discharge). The temperature during charging (or discharging) is preferably 25 to 40 ° C., and the temperature of the sodium ion secondary battery is preferably controlled by a heating control device or the like.

  In addition, this system and this charging / discharging method do not exclude starting charge or discharge in the temperature exceeding 40 degreeC or a high temperature range (for example, 60 degreeC or more). For example, charging may be started in a low temperature range and discharging may be started in a high temperature range.

[Example]
Next, based on an Example, this invention is demonstrated more concretely. However, the following examples do not limit the present invention.

<< Examples 1 to 5 >>
(Preparation of positive electrode)
85 parts by mass of NaCrO ₂ (positive electrode active material) having an average particle diameter of 10 μm, 10 parts by mass of acetylene black (conductive carbon material) and 5 parts by mass of polyvinylidene fluoride (binder) are used as a dispersion medium. -Dispersed in pyrrolidone (NMP) to prepare a positive electrode paste. The obtained positive electrode paste was applied to one side of an aluminum foil having a thickness of 20 μm, dried, rolled, and cut into a predetermined size to produce a positive electrode having a positive electrode active material layer having a thickness of 65 μm. The positive electrode was punched into a coin shape having a diameter of 12 mm.

(Preparation of negative electrode)
96 parts by mass of non-graphitizable carbon (negative electrode active material) having an average particle diameter of 9 μm, a specific surface area of 6 m ² / g, and a true density of 1.52 g / cm ³ and 4 parts by mass of polyamideimide (binder) are added to N-methyl. A negative electrode paste was prepared by dispersing in 2-pyrrolidone (NMP). The obtained negative electrode paste was applied to one side of a 18 μm thick copper foil, sufficiently dried, and rolled to produce a negative electrode having a total thickness of 78 μm having a negative electrode active material layer having a thickness of 60 μm. The negative electrode was punched into a coin shape having a diameter of 14 mm.

(Separator)
A polyolefin separator having a heat-resistant layer having a thickness of 50 μm and a porosity of 90% was prepared. The separator was also punched into a coin shape with a diameter of 16 mm.

(Nonaqueous electrolyte)
As shown in Table 1, the first salt and the second salt, and further the third component were mixed to prepare nonaqueous electrolytes a to e having a sodium ion concentration of 40 mol% in all cations. In the nonaqueous electrolyte c, the mixing ratio (molar ratio, P13 · FSA: EMI · FSA) of P13 · FSA and EMI · FSA was 1: 1.

(Production of sodium ion secondary batteries A to E)
The coin-type positive electrode, negative electrode, and separator were sufficiently dried by heating at 90 ° C. or higher under a reduced pressure of 0.3 Pa. Thereafter, a coin-type positive electrode is placed on a shallow cylindrical SUS / Al clad container, and a coin-type negative electrode is placed thereon via a coin-type separator. Each of a to e was injected into the container. Thereafter, the opening of the container was sealed with a shallow cylindrical SUS sealing plate having an insulating gasket on the periphery. Thereby, a pressure was applied to the electrode group consisting of the positive electrode, the separator, and the negative electrode between the bottom surface of the container and the sealing plate to ensure contact between the members. Thus, coin-type sodium ion secondary batteries A to E having a design capacity of 1.5 mAh were produced. The capacity ratio C _n / C _p was 0.85 for all.

Each of the sodium ion secondary batteries A to E was cooled to 10 ° C. in a constant temperature room. Table 2 shows the viscosity of each non-aqueous electrolyte at 5 ° C. For reference, the viscosity of each non-aqueous electrolyte at 10 ° C. is also shown in Table 2. The viscosity was measured according to JIS Z 8803 “Method for measuring viscosity of liquid”. Specifically, using an E-type viscometer equipped with a rotor having an angle of 1 ° and a radius of 24 mm, shear rates of 38.3 s ⁻¹ (rotation speed 10), 76.6 s ⁻¹ (rotation speed 20), 191. Measurement was performed at 5 s ⁻¹ (rotation speed 50) and 383 s ⁻¹ (rotation speed 100), and the average value of the obtained numerical values was obtained to obtain the viscosity of the present invention. The same applies hereinafter.

  Moreover, in the state where the temperature of each of the sodium ion secondary batteries A to E was stabilized, the following conditions (1) and (2) were charged and discharged as one cycle. The discharge capacity of each sodium ion secondary battery was measured. The discharge capacity of the battery A at a temperature of 60 ° C. and a discharge current of 0.1 C was 100% utilization relative to the design capacity. In view of this, in the battery A, the discharge capacity at a temperature of 60 ° C. and a discharge current of 0.1 C was assumed to be 100%, and each utilization factor was shown as a relative value. The same applies to Examples 7 to 16 below. The viscosity of the nonaqueous electrolyte a at 60 ° C. was 0.06 Pa · s. The results are shown in Table 3.

(1) Charge to 0.05 V with a charge current of 0.05 C. (2) Discharge to 1.5 V with a discharge current of 0.1 C, 0.2 C, or 0.5 C. To discharge at 1 C means to discharge a battery having a nominal capacity at a current value at which discharge is completed in 10 hours after rated charging / discharging.

Example 6
The utilization factor was calculated in the same manner as in Example 1 except that the sodium ion secondary battery A was cooled to 5 ° C. The results are shown in Table 3.

  For reference, the utilization factor was calculated in the same manner as in Example 1 except that the sodium ion secondary battery A was cooled to 0 ° C. At this time, the viscosity of the nonaqueous electrolyte a at 0 ° C. was 1.65 Pa · s. The results are shown in Table 3.

  As shown in Table 3, if a non-aqueous electrolyte having a viscosity of 0.25 to 1.7 Pa · s at 5 ° C. is used, the discharge was performed under a very low temperature condition of 10 ° C. However, it can be seen that the utilization rate at a discharge current of 0.1 C is 70% or more, which is a good result. In particular, in batteries B, D, and E using non-aqueous electrolytes having a viscosity at 5 ° C. of 0.8 Pa · s or less, the utilization factor at 10 ° C. and a discharge current of 0.1 C is 90% or more. The utilization rate at 2C was 80% or more, which was a good result.

  Among them, the battery D had a utilization factor of 90% or more when discharged at a discharge current of 0.1 C and 0.2 C at 10 ° C. Furthermore, the battery D achieves a very high utilization rate of 60% or more even under conditions of 10 ° C. and a discharge current of 0.5C. The nonaqueous electrolyte of the battery D has a viscosity at 5 ° C. of 0.25 Pa · s or more, and the viscosity of a general nonaqueous electrolyte mainly composed of an organic solvent (the viscosity at 5 ° C. is 0.01 Pa · s). It should be noted that the viscosity is very high compared to s or less).

<< Examples 6 to 10 >>
Sodium ion secondary batteries F to J were produced in the same manner as in Example 1 except that the positive and negative electrodes shown below were used, and the utilization rate at a discharge current of 0.1 C or 0.2 C at 10 ° C. Was calculated. The results are shown in Table 4.

(Preparation of positive electrode)
85 parts by mass of NaCrO ₂ (positive electrode active material) having an average particle diameter of 10 μm, 10 parts by mass of acetylene black (conductive carbon material) and 5 parts by mass of polyvinylidene fluoride (binder) are used as a dispersion medium. -Dispersed in pyrrolidone (NMP) to prepare a positive electrode slurry. A positive electrode slurry was filled into a porous aluminum body (manufactured by Sumitomo Electric Industries, Ltd., aluminum cermet, thickness 1 mm, porosity 90%), dried, and rolled with a roller press to obtain a positive electrode having a thickness of 400 μm.

(Preparation of negative electrode)
96 parts by mass of non-graphitizable carbon (negative electrode active material) having an average particle diameter of 9 μm, a specific surface area of 6 m ² / g, and a true density of 1.52 g / cm ³ and 4 parts by mass of polyamideimide (binder) are added to N-methyl. A negative electrode slurry was prepared by dispersing in 2-pyrrolidone (NMP). A negative electrode slurry was filled in a copper porous body (manufactured by Sumitomo Electric Industries, Ltd., copper cermet, thickness 1 mm, porosity 85%), dried, and rolled with a roller press to obtain a negative electrode having a thickness of 350 μm.

  As shown in Table 4, even when the positive electrode is thick, by using a non-aqueous electrolyte having a viscosity at 5 ° C. of 0.25 to 1.7 Pa · s, the utilization factor is 0.1 C for the discharge current. In some cases, good results of 65% or more were obtained. In particular, in the batteries H, I, and J using nonaqueous electrolytes having a viscosity at 5 ° C. of 0.25 to 0.8 Pa · s, the utilization factor at 0.1 C was 80% or more. Moreover, the utilization factor at 0.2C was 50% or more, which was a good result.

<< Examples 11 to 14 >>
Sodium ion secondary batteries K to N were prepared in the same manner as in Example 1 except that the positive electrode and negative electrode shown below were used, and the utilization rate at a discharge current of 0.1 C or 0.2 C at 25 ° C. Was calculated. The results are shown in Table 5. The viscosity at 25 ° C. of each non-aqueous electrolyte used for reference is also shown in Table 5.

(Preparation of positive electrode)
85 parts by mass of NaCrO ₂ (positive electrode active material) having an average particle diameter of 10 μm, 10 parts by mass of acetylene black (conductive carbon material) and 5 parts by mass of polyvinylidene fluoride (binder) are used as a dispersion medium. -Dispersed in pyrrolidone (NMP) to prepare a positive electrode slurry. A positive electrode slurry was filled into a porous aluminum body (manufactured by Sumitomo Electric Industries, Ltd., aluminum cermet, thickness 1 mm, porosity 90%), dried, and rolled with a roller press to obtain a positive electrode having a thickness of 600 μm.

(Preparation of negative electrode)
96 parts by mass of non-graphitizable carbon (negative electrode active material) having an average particle diameter of 9 μm, a specific surface area of 6 m ² / g, and a true density of 1.52 g / cm ³ and 4 parts by mass of polyamideimide (binder) are added to N-methyl. A negative electrode slurry was prepared by dispersing in 2-pyrrolidone (NMP). A negative electrode slurry was filled in a copper porous body (manufactured by Sumitomo Electric Industries, Ltd., copper cermet, thickness 1 mm, porosity 85%), dried, and rolled with a roller press to obtain a negative electrode having a thickness of 550 μm.

  As shown in Table 5, even when the positive electrode is thicker, by using a non-aqueous electrolyte having a viscosity at 5 ° C. of 0.25 to 1.7 Pa · s, it can be used at a discharge current of 0.1 C. The rate was 70% or more, and good results were shown.

<< Comparative Example 2 >>
A sodium ion secondary battery O was produced in the same manner as in Example 1 except that the nonaqueous electrolyte f in which Na · FSA and P13 · FSA were mixed so that the sodium ion concentration was 10% was used. The utilization factor when the discharge current at 10 ° C. was 0.1 C or 0.2 C was calculated. The results are shown in Table 6. The viscosity at 5 ° C. of the nonaqueous electrolyte f is also shown in Table 6.

Example 15
A sodium ion secondary battery P was produced in the same manner as in Example 1 except that the nonaqueous electrolyte g in which Na · FSA and P13 · FSA were mixed so that the sodium ion concentration was 30% was used. The utilization factor when the discharge current at 10 ° C. was 0.1 C or 0.2 C was calculated. The results are shown in Table 6. The viscosity at 5 ° C. of the nonaqueous electrolyte g is also shown in Table 6.

Example 16
A sodium ion secondary battery Q was produced in the same manner as in Example 1 except that the nonaqueous electrolyte h in which Na · FSA and EMI · FSA were mixed so that the sodium ion concentration was 50% was used. The utilization factor when the discharge current at 10 ° C. was 0.1 C or 0.2 C was calculated. The results are shown in Table 6. The viscosity of the nonaqueous electrolyte h at 5 ° C. is also shown in Table 6.

  In the case of the battery O having a sodium ion concentration of 10 mol%, the viscosity at 5 ° C. was very low, and when the discharge current was 0.1 C, the utilization rate was close to 80%. However, when the discharge current was 0.2 C, the utilization rate was greatly reduced. On the other hand, in the case of the batteries P and Q having a sodium ion concentration of 30 to 50 mol%, the viscosity at 5 ° C. was high, but good utilization was obtained at discharge currents of 0.1 C and 0.2 C.

  The sodium ion secondary battery according to the present invention is useful as a power source for various applications because a high utilization rate can be obtained even in charge and discharge at low temperatures.

  1: separator, 2: positive electrode, 2a: positive electrode current collector, 2b: positive electrode active material layer, 2c: positive electrode lead piece, 3: negative electrode, 3a: negative electrode current collector, 3b: negative electrode active material layer, 3c: negative electrode lead 7: nut, 8: collar, 9: washer, 10: battery case, 11: electrode group, 12: container body, 13: lid, 14: external positive terminal, 15: external negative terminal, 16: safety valve , 100: lithium ion secondary battery, 101: temperature measurement unit, 102: charge control device, 103: discharge control device, 104: power supply, 105: heater, 106: heating control device, 107: control unit, 108: external load

Claims (10)

A positive electrode having a positive electrode active material and a positive electrode current collector holding the positive electrode active material;
A negative electrode having a negative electrode active material and a negative electrode current collector holding the negative electrode active material; and
An electrode group comprising a separator interposed between the positive electrode and the negative electrode;
A non-aqueous electrolyte having sodium ion conductivity;
A battery case containing the electrode group and the non-aqueous electrolyte, and
The non-aqueous electrolyte includes a first salt of a sodium ion and a first anion, and a second salt of an organic cation and a second anion,
The ratio of the sodium ion to the total of the sodium ion and the organic cation is 30 to 50 mol%,
The positive electrode current collector is a first metal porous body having a three-dimensional network structure;
The positive electrode has a thickness of 300 μm or more;
The negative electrode current collector is a second metal porous body having a three-dimensional network structure;
The negative electrode has a thickness of 300 μm or more;
A sodium ion secondary battery in which the non-aqueous electrolyte has a viscosity at 5 ° C of 0.25 to 0.8 Pa · s. A positive electrode having a positive electrode active material and a positive electrode current collector holding the positive electrode active material;
A negative electrode having a negative electrode active material and a negative electrode current collector holding the negative electrode active material; and
An electrode group comprising a separator interposed between the positive electrode and the negative electrode;
A non-aqueous electrolyte having sodium ion conductivity;
A battery case containing the electrode group and the non-aqueous electrolyte, and
The non-aqueous electrolyte includes a first salt of a sodium ion and a first anion, and a second salt of an organic cation and a second anion,
The ratio of the sodium ion to the total of the sodium ion and the organic cation is 30 to 50 mol%,
The non-aqueous electrolyte has a viscosity at 5 ° C. of 0.25 to 1.7 Pa · s,
A sodium ion secondary battery, wherein either the first anion or the second anion contains an anion of fluorine-containing phosphate or anion of fluorine-containing boric acid . The positive electrode current collector is a first metal porous body having a three-dimensional network structure;
The positive electrode has a thickness of 300 μm or more;
The negative electrode current collector is a second metal porous body having a three-dimensional network structure;
The negative electrode has a thickness of 300 μm or more;
The sodium ion secondary battery according to claim 2 , wherein the nonaqueous electrolyte has a viscosity at 5 ° C. of 0.25 to 0.8 Pa · s.   4. The sodium ion secondary battery according to claim 1, wherein a total content of the first salt and the second salt in the non-aqueous electrolyte is 80% by mass or more. The sodium ion secondary battery according to any one of claims 1 to 4 , wherein the non-aqueous electrolyte contains an organic solvent at a ratio of 10% by mass or less. A positive electrode having a positive electrode active material and a positive electrode current collector holding the positive electrode active material;
A negative electrode having a negative electrode active material and a negative electrode current collector holding the negative electrode active material; and
An electrode group comprising a separator interposed between the positive electrode and the negative electrode;
A non-aqueous electrolyte having sodium ion conductivity;
A battery case containing the electrode group and the non-aqueous electrolyte, and
The non-aqueous electrolyte includes a first salt of a sodium ion and a first anion, and a second salt of an organic cation and a second anion,
The ratio of the sodium ion to the total of the sodium ion and the organic cation is 30 to 50 mol%,
The non-aqueous electrolyte has a viscosity at 5 ° C. of 0.25 to 1.7 Pa · s,
The sodium ion secondary battery in which the non-aqueous electrolyte contains an organic solvent in a proportion of 10% by mass or less. Detecting the temperature of the sodium ion secondary battery according to any one of claims 1 to 6 ;
And a step of starting charging or discharging when the detected temperature is 5 to 40 ° C., a method for charging and discharging a sodium ion secondary battery. A method for charging and discharging a sodium ion secondary battery, comprising:
The sodium ion secondary battery is
A positive electrode having a positive electrode active material and a positive electrode current collector holding the positive electrode active material, a negative electrode having a negative electrode active material and a negative electrode current collector holding the negative electrode active material, and interposed between the positive electrode and the negative electrode An electrode group comprising a separator,
A non-aqueous electrolyte having sodium ion conductivity;
A battery case containing the electrode group and the non-aqueous electrolyte, and
The non-aqueous electrolyte includes a first salt of a sodium ion and a first anion, and a second salt of an organic cation and a second anion,
The ratio of the sodium ion to the total of the sodium ion and the organic cation is 30 to 50 mol%,
The non-aqueous electrolyte has a viscosity at 5 ° C. of 0.25 to 1.7 Pa · s,
Detecting the temperature of the sodium ion secondary battery;
And a step of starting charging or discharging when the detected temperature is 5 to 40 ° C., a method for charging and discharging a sodium ion secondary battery. The sodium ion secondary battery according to any one of claims 1 to 6 ,
A temperature measuring unit for detecting the temperature of the sodium ion secondary battery;
A charge control device for controlling the charging current I _in of the sodium ion secondary battery;
A discharge control device for controlling the discharge current I _out of the sodium ion secondary battery,
The charging / discharging system of a sodium ion secondary battery which starts charge or discharge when the temperature of the said sodium ion secondary battery detected by the said temperature measurement part is 5-40 degreeC. A charge / discharge system for a sodium ion secondary battery,
The sodium ion secondary battery is
A positive electrode having a positive electrode active material and a positive electrode current collector holding the positive electrode active material, a negative electrode having a negative electrode active material and a negative electrode current collector holding the negative electrode active material, and interposed between the positive electrode and the negative electrode An electrode group comprising a separator,
A non-aqueous electrolyte having sodium ion conductivity;
A battery case containing the electrode group and the non-aqueous electrolyte, and
The non-aqueous electrolyte includes a first salt of a sodium ion and a first anion, and a second salt of an organic cation and a second anion,
The ratio of the sodium ion to the total of the sodium ion and the organic cation is 30 to 50 mol%,
The non-aqueous electrolyte has a viscosity at 5 ° C. of 0.25 to 1.7 Pa · s,
A temperature measuring unit for detecting the temperature of the sodium ion secondary battery;
A charge control device for controlling the charging current I _in of the sodium ion secondary battery;
A discharge control device for controlling the discharge current I _out of the sodium ion secondary battery,
The charging / discharging system of a sodium ion secondary battery which starts charge or discharge when the temperature of the said sodium ion secondary battery detected by the said temperature measurement part is 5-40 degreeC.

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