JP4417676B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to improvement of its energy density.

  In recent years, information electronic devices such as personal computers, mobile phones, and PDAs, and audiovisual electronic devices such as video camcorders and mini-disc players are rapidly becoming smaller and lighter and cordless. As a power source for driving these electronic devices, a secondary battery having a high energy density is desired. Non-aqueous electrolyte secondary batteries having a high energy density that cannot be achieved by conventional secondary batteries such as lead acid batteries, nickel cadmium batteries, and nickel metal hydride batteries are becoming mainstream as power sources for driving these batteries.

In lithium ion secondary batteries and lithium ion polymer secondary batteries, which are nonaqueous electrolyte secondary batteries, a material having an average discharge potential with respect to lithium in the range of 3.5 V to 4.0 V is used as the positive electrode active material. . Examples of such materials include lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), a mixture of these positive electrode materials, and a solid solution material containing a plurality of transition metals (LiCo _x Ni _y Mn _z O ₂ or _{Li (Co a Ni b Mn c} ) 2 O 4) , etc. are used. The positive electrode active material is applied to a current collector such as an aluminum, titanium, or stainless steel or a case that also serves as a current collector together with a carbon-based conductive agent or binder, or used after being compression molded. It has been.

  As the negative electrode active material, a carbon material capable of inserting and extracting lithium is preferably used. Carbon materials include artificial graphite, natural graphite, mesophase fired body made from coal / petroleum pitch, non-graphitizable carbon fired by adding oxygen to them, and non-graphitized fired from plastic fired body originally containing oxygen. Carbon is used. The carbon material is used by being applied to a copper foil current collector or an iron / nickel sealing plate or case that also serves as a current collector, or a compression molding, together with a binder. In general, when a graphite material is used, the average potential for releasing lithium ions is about 0.2 V in comparison with the case where non-graphitizable carbon is used. Therefore, in a field where high voltage and voltage flatness are desired. The graphite material is suitable as the negative electrode.

A non-aqueous electrolyte is selected that can withstand the oxidizing atmosphere of the positive electrode that discharges at a high potential of 3.5 V to 4.0 V as described above and can withstand the reducing atmosphere of the negative electrode that is charged and discharged at a potential close to lithium. . At present, a solution in which lithium hexafluorophosphate (LiPF ₆ ) is dissolved in a mixed solvent of ethylene carbonate (EC) and chain carbonate having a high dielectric constant is used. As the chain carbonate, for example, one or more low-viscosity solvents such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are used. Further, propylene carbonate having a high dielectric constant, cyclic carbonates such as γ-butyrolactone, cyclic esters, and the like are also used. Fluorobenzene or the like is also used as a low viscosity solvent other than the above. In a lithium ion polymer secondary battery, a gel electrolyte in which these nonaqueous electrolytes are included as a plasticizer in a polymer component is used.

  From the viewpoint of improving the high-temperature storage characteristics and cycle life characteristics of nonaqueous electrolyte secondary batteries, vinylene carbonate, propane sultone, phenylethylene carbonate vinylethylene carbonate, and the like are used as additives to be included in the nonaqueous electrolyte. In addition, cyclohexylbenzene, biphenylbenzene, diphenyl ether, and the like may be added to the nonaqueous electrolyte from the viewpoint of improving safety during overcharge.

However, the non-aqueous electrolyte secondary battery naturally has a limit capacity due to the maximum capacity density of the positive electrode represented by LiCoO ₂ (about 282 mAh / g) and the maximum capacity density of the negative electrode represented by graphite (about 372 mAh / g). It has been decided. Therefore, in a standard battery with a limited volume, when these materials or materials having a similar crystal structure are used, an improvement in energy density exceeding the limit capacity cannot be expected. Therefore, research on secondary batteries having a novel structure using sodium for the negative electrode, molten salt for the positive electrode, and sodium ion conductive solid electrolyte for the diaphragm has also been conducted (see Non-Patent Document 1).
Matsunaga, “Behavior of Na / Se (IV) Secondary Battery Using AlCl 3 —NaCl Molten Salt”, Electrochemistry and Industrial Physical Chemistry, 1983, Vol. 51, No. 10, p. 847-848

  An object of the present invention is to provide a nonaqueous electrolyte secondary battery that is less expensive than a conventional battery and has a high energy density.

The present invention includes (A) an electrolyte solution obtained by dissolving an alkali metal salt in a nonaqueous solvent, (B) a positive electrode active material made of a redox material dissolved or dispersed in the electrolyte solution, and (C) the positive electrode active material is oxidized. The present invention relates to a positive electrode current collector that provides a field for performing a reduction reaction, and (D) a nonaqueous electrolyte secondary battery including a negative electrode capable of occluding and releasing alkali metal ions, or depositing or dissolving alkali metals.
When the battery is used, the negative electrode is electronically insulated from the positive electrode active material. However, even when the battery is used, the negative electrode and the positive electrode active material may be electronically conductive as long as the amount of self-discharge is permissible, and must be completely electronically insulated. There is no.

The negative electrode is covered with a diaphragm to shield the positive electrode active material and having a A alkali metal ion conductivity.
It is preferable that only the alkali metal ion is allowed to pass through the diaphragm among the elements constituting the component (A) and the component (B).
It is preferable that the component (A) and the component (B) form a liquid or fluid composite.
The positive electrode current collector is preferably made of a metal sheet or a porous carbon sheet exhibiting a dissolution (oxidation) potential of +3 V or more with respect to the potential of the alkali metal constituting the alkali metal salt.

A carbon layer is preferably attached to the surface of the metal sheet.
It is preferable that the negative electrode lead connected to the negative electrode and for taking out current to the outside is shielded from the positive electrode active material.
The positive electrode active material is composed of at least one selected from the group consisting of transition metal salts, sulfur compounds, selenium compounds, tellurium compounds, simple sulfur, simple selenium and simple tellurium that can be partially or wholly dissolved in a non-aqueous solvent. It is preferable.
The negative electrode is preferably made of at least one selected from the group consisting of alkali metal, graphite, amorphous carbon, fullerene, carbon nanotube, alloy, transition metal oxide, transition metal sulfide, silicon and silicon monoxide. .

The alkali metal salt includes imide salt, meside salt, borate, perchlorate, hexafluoroarsenate, chloroaluminate, thiocyanate, iodide, tetrafluoroborate, hexafluorophosphate , A salt in which at least one of fluorine of hexafluorophosphate is replaced with —CF ₃ or —C ₂ F ₅ , and at least one of fluorine of tetrafluoroborate is —CF ₃ or —C ₂ F ₅ It is preferably at least one selected from the group consisting of substituted salts.

The non-aqueous solvent is preferably composed of at least one selected from the group consisting of a polar solvent that is liquid at room temperature and a room temperature molten salt that is ionically dissociated at room temperature.
In one aspect of the present invention, the diaphragm is ing an alkali metal ion conductive solid electrolyte.
In one aspect of the present invention, the alkali metal ion conductive solid electrolyte, including an alkali metal phosphate.
The alkali metal ion conductive solid electrolyte preferably further includes a sulfide salt.

In another aspect of the present invention, the electrolyte solution is seen containing an organic substance having a function of forming a film on the surface of the negative electrode by charging and discharging, the diaphragm is made of said coating.
The organic material is preferably composed of at least one selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, phenyl ethylene carbonate, and propane sultone.
When the electrolyte solution contains the organic substance, an alkali metal ion conductive film is formed on the surface of the negative electrode by the initial charge / discharge, so that the negative electrode and the positive electrode active material are electronically formed in the battery immediately after manufacture. It does not need to be insulated.

  According to the present invention, it is possible to provide a nonaqueous electrolyte secondary battery that is less expensive than a conventional battery and has a high energy density.

  The nonaqueous electrolyte secondary battery of the present invention includes (A) an electrolyte solution obtained by dissolving an alkali metal salt in a nonaqueous solvent, (B) a positive electrode active material comprising a redox material dissolved or dispersed in the electrolyte solution, (C) A positive electrode current collector that provides a field for the positive electrode active material to perform an oxidation-reduction reaction; and (D) a negative electrode capable of occluding and releasing alkali metal ions or depositing and dissolving alkali metals.

  The component (A) and the component (B) usually form a liquid or fluid composite (hereinafter referred to as a positive electrode solution). In the positive electrode solution, chalcogen elements such as sulfur, selenium, and tellurium, which are redox materials, and transition metal salts are dissolved or dispersed, and the redox material functions as a positive electrode active material. The alkali metal salt of the component (A) has a function of maintaining the electrochemical neutrality of the positive electrode solution and stabilizing the oxidation state and reduction state of the redox material by coordination.

  The chalcogen element which is a redox material forms an alkali metal salt and can be dissolved in a non-aqueous solvent. When an alkali metal salt of a chalcogen element is ionically dissociated into an alkali metal ion and a chalcogen ion, the chalcogen element has a negative charge, but is converted into a higher-order oxidation state by charging. The reaction formula (1) when the alkali metal ion is lithium ion and the chalcogen element is sulfur is exemplified below.

Reaction formula (1)
Li ₂ S ⇔ 2Li ⁺ + S ^2-
S ^2- ⇔ S + 2e ^{-
2Li + + S + 2A - ⇔} 2Li + + S 2+ (2A -) + 2e -
^{2Li + + S 2+ (2A -} ) + 2A - ⇔ 2Li + + S 4+ (4A -) + 2e -
^{S 2- + 4A - ⇔ S 4+} (4A -) + 6e - ( Total reaction)
Here, LiA is a lithium salt of component (A) dissolved in a solvent, and is ion-dissociated as follows.
LiA → Li ^{+ +} A ^-

  As described above, when lithium sulfide is used, a total of six electron reactions can be obtained. Other alkali metal salts of chalcogen elements can also be used as redox materials as in the case where the chalcogen element is sulfur.

  The transition metal salt, which is a redox material, is ionically dissociated into a positively charged transition metal ion (cation) and anion in the cathode solution. Transition metal ions cannot perform as many electron reactions as chalcogen elements, but can vary the operating voltage of the battery depending on the type of transition metal. The reaction formula (2) when the transition metal ion is Co is illustrated below. Again, LiA represents the lithium salt of component (A) dissolved in the solvent.

Reaction formula (2)
_{Co (N (CF 3 SO 2} ) 2) 2 ⇔ Co 2+ + 2 (N (CF 3 SO 2) 2 -)
^{Li + + Co 2+ + A -} ⇔ Li + + Co 3+ A - + e -

In addition to the above, the redox materials in the cathode solution include simple powders such as sulfur, selenium and tellurium, and thiocyanates such as iron thiocyanate (Fe (SCN) ₂ ) and cobalt thiocyanate ( Co (SCN) ₂ ) Etc. can be used. In addition, any transition metal salt containing an anion of a lithium salt that is currently known can be used without particular limitation.

  The positive electrode current collector is a place where the redox material in the positive electrode solution is oxidized / reduced to exchange electrons, so that the reaction area of the positive electrode current collector is preferably as large as possible depending on the reaction rate. From the perspective of securing a large reaction area and promoting the electronic reaction of the redox material, carbon particles having a large specific surface area are attached to the surface of a current collector made of a metal sheet instead of a single metal plate to form a carbon layer. It is effective to form.

  The positive electrode current collector is preferably as stable as possible at a potential of +3 V or higher with respect to the potential of the alkali metal constituting the alkali metal salt. That is, the metal sheet constituting the positive electrode current collector preferably has a dissolution potential of +3 V or higher with respect to the potential of the alkali metal. For example, tungsten, molybdenum, easy and inexpensive aluminum, austenitic stainless steel, titanium, and the like are suitable as the positive electrode current collector. Alternatively, the positive electrode current collector may be formed of a sintered metal powder having a high specific surface area, a carbon powder, a carbon sheet made of a carbon material having a large specific surface area such as graphite powder, and the like.

  A laminate sheet composed of a resin film and a positive electrode current collector can also be used so that it can also serve as a battery exterior material. Further, the exterior material can be made of glass, ceramics, or the like. In that case, it is necessary to connect a lead made of the same material to the positive electrode current collector and draw it out of the exterior.

  A material that can occlude and release alkali metal can be used for the negative electrode without any particular limitation. Moreover, the alkali metal itself which melt | dissolves and produces | generates reprecipitation, producing | generating an alkali metal ion can also be used. Materials that can occlude and release alkali metals include carbon materials such as graphite, amorphous carbon, fullerene, and carbon nanotubes with large capacities, metals that can occlude and release alkali metals such as silicon, tin, lead, aluminum, and bismuth, Alloys that can occlude and release alkali metals, transition metal oxides such as tungsten oxide, vanadium oxide, lithium titanate, lithium vanadate, transition metal sulfides such as molybdenum disulfide and titanium disulfide, silicon, silicon monoxide, etc. Can be mentioned. Moreover, lithium, sodium, etc. can be used as an alkali metal. These negative electrode materials may be used in combination of two or more.

  As the non-aqueous solvent constituting the component (A), it is preferable to use a polar solvent that is liquid at room temperature (for example, 25 ° C.), a room temperature molten salt that is ion-dissociated at room temperature (for example, 25 ° C.), or the like. However, when a non-aqueous solvent composed of a mixture of two or more compounds is used, the mixture may be liquid at room temperature, and may contain a solid compound at room temperature.

  The polar solvent that can be used is not particularly limited as long as it is currently used for a lithium ion secondary battery or a lithium primary battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate, cyclic carboxylic acid esters such as γ-butyrolactone, γ-valerolactone, tetrahydrofuran, etc. Cyclic ethers can be used. Also, those having a relatively high dielectric constant such as glymes, lactones, sulfolanes can be used.

  As the room temperature molten salt, an ionic liquid in which an organic cation and an organic or inorganic anion are combined can be used. Here, as the organic cation, tetrahexylammonium (THA), 1-hexyl-3-methylimidazolium (HMI), 1,2-dimethyl-3-propylimidazolium (DMPI), 1-ethyl-3-methyl Imidazolium (EMI), 1-butyl-3-methylimidazolium (BMI), or the like can be used. As the organic or inorganic anion, bistrifluoromethanesulfonylimide anion (TFSI), hexafluorophosphate anion (PF6), tetrafluoroborate anion (BF4), or the like can be used.

  A mixed solvent of an organic solvent that does not ionically dissociate and an ionic liquid can also be used. Note that there is no particular problem even if a solid exists in the cathode solution due to solubility.

The alkali metal salt constituting the component (A) includes an imide salt (XN (SO ₂ C _n F _{2n + 1} ) (SO ₂ C _m F _{2m + 1} ) (X is an alkali metal, n and m are 0 or more) n = m)), meside salt (XC (SO ₂ C _k F _{2k + 1} ) (SO ₂ C _m F _{2m + 1} ) (SO ₂ C _n F _{2n + 1} ) (X is an alkali metal) , K, m, n are 1 or more, k = n = m may be sufficient)), borate having BO ₄ skeleton, perchlorate (XClO ₄ ), hexafluoroarsenate (XAsF ₆ ) , Chloroaluminate (XAlCl ₄ ), thiocyanate (XSCN), iodide (XI), tetrafluoroborate (XBF ₄ ), hexafluorophosphate (LiPF ₆ etc.), hexafluorophosphate at least one salt is replaced by -CF ₃ or -C ₂ F _5, salts of at least one of fluorine tetrafluoroborate salt was replaced by -CF ₃ or -C ₂ F _5, LiCF ₃ SO of fluorine ₃ and its derivatives can be used. In addition, as an alkali metal (X), although lithium is preferable, sodium, potassium, etc. can also be used. Depending on the type of alkali metal (X), a redox material in the positive electrode solution, an alkali metal ion conductive diaphragm, or the like may be selected.

  The diaphragm present at the interface between the positive electrode solution and the negative electrode can be used without particular limitation as long as it has alkali metal ion conductivity and low electron conductivity.

Since the positive electrode solution is liquid or fluid, in the present invention, in order to reliably prevent electrical contact between the negative electrode and the positive electrode active material, it has a function of passing an alkali metal ion and shielding the positive electrode active material. Ru Ttei covering the negative electrode with a septum. As such a diaphragm, an alkali metal ion conductive solid electrolyte is suitable. For example, a solid electrolyte composed of an alkali metal phosphate or an alkali metal phosphate containing nitrogen, a solid electrolyte composed of an alkali metal phosphate and a sulfide salt (for example, Li ₂ S-SiS ₂ ), an alkali metal phosphate And a solid electrolyte composed of alkali metal silicate (for example, Li ₃ PO ₄ -Li ₄ SiO ₄ system when the alkali metal is lithium), alkali metal sulfide and other sulfides (for example, B ₂ S ₃ , P ₂ A solid electrolyte (Li ₂ SB ₂ S ₃ system, Li ₂ SP ₂ S ₅ system) composed of S ₅ ) can be used.

  The alkali metal iodide salt forms an alkali metal ion conductive film made of iodide on the negative electrode surface. Accordingly, the alkali metal iodide is a suitable material that provides both an alkali metal salt that is a constituent of the positive electrode solution and an alkali metal ion conductive diaphragm.

  In the case where the expansion and contraction of the negative electrode volume is large, it is useful to use an alkali metal ion conductive polymer electrolyte instead of the positive electrode solution. For example, a gel polymer electrolyte in which a positive electrode solution made of a redox material, a nonaqueous solvent and an alkali metal salt and a polymer material are combined can be used. The polymer material is preferably a polymer having an ethylene oxide chain or a propylene oxide chain, a polymer having a skeleton derived from an organic solvent such as ethylene carbonate or lactone.

  By including an organic substance having a function of forming a film on the negative electrode surface in the positive electrode solution, a diaphragm (film) having a function of passing alkali metal ions and shielding the positive electrode active material may be formed on the negative electrode surface. it can. As such an organic substance, vinylene carbonate (VC), vinyl ethylene carbonate (VEC), phenyl ethylene carbonate (PhEC), propane sultone (PS), or the like can be used.

  When the negative electrode lead for taking out an electric current outside is connected to the negative electrode, it is preferable that the negative electrode lead is also shielded from the positive electrode active material. For example, the portion of the negative electrode lead that may come into contact with the positive electrode active material may be covered with a diaphragm made of an alkali metal ion conductive solid electrolyte, or the entire negative electrode lead may be covered with an insulating material such as a resin. It is valid.

The present invention may be applied to non-aqueous electrolyte secondary batteries having any shape such as a cylindrical shape, a square shape, a laminate sheet tare type, and a coin type. What is necessary is just to change suitably the form of a positive electrode and a negative electrode according to the shape of a battery. In any form, if at least a part of each of the negative electrode and the positive electrode current collector is immersed in the positive electrode solution, the nonaqueous electrolyte secondary battery of the present invention can be charged and discharged.
Hereinafter, the present invention will be specifically described based on examples.

Example 1
FIG. 1 shows a longitudinal sectional view of a nonaqueous electrolyte secondary battery produced in the example. This battery was produced as follows.
(A) Production of Battery Case A bag-like case 2 was produced from a tungsten sheet serving both as a positive electrode current collector and an exterior. A carbon layer 3 containing carbon black as a main component was formed on the inner surface of the case 2. Here, a mixed paste (CB: PVdF: NMP weight ratio of 100: 10: 100) containing carbon black (CB), polyvinylidene fluoride (PVdF), and N-methyl-2-pyrrolidone (NMP) is made of tungsten. After coating on one side of the sheet by screen printing, it was dried at 100 ° C. to fix the carbon layer to the tungsten sheet.

(B) Preparation of cathode solution The cathode solution 4 was prepared by dissolving a cathode active material made of a redox material in an electrolyte solution. In the electrolyte solution, a mixed non-aqueous solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1: 1 and lithium bistrifluoromethanesulfonylimide (LiN (SO ₂ CF ₃ ) ₂ ) as an alkali metal salt is 4 mol / liter. What was dissolved in the concentration of was used. Lithium sulfide (Li ₂ S) as a redox material was dissolved in the electrolyte solution thus obtained at a concentration of 1 mol / liter to obtain a cathode solution 4.

(C) Production of negative electrode 3 parts by weight of an aqueous dispersion of styrene butadiene rubber as a binder is added to 100 parts by weight of amorphous carbon (Carbontron P manufactured by Kureha Chemical Industry Co., Ltd.), which is a negative electrode active material. Part was added and kneaded to obtain a paste-like negative electrode mixture. This paste-like negative electrode mixture was applied to both surfaces of a current collector made of copper foil, then dried and rolled to form an active material layer, whereby negative electrode 7 was obtained.

Next, the negative electrode 7 cut into a predetermined shape is introduced into a sputtering apparatus and sputtered using a solid electrolyte target made of lithium phosphate (Li ₃ PO ₄ ), and a 2 μm-thickness diaphragm is formed on the surface of the negative electrode 7. 6 was formed. The composition of lithium phosphate constituting the diaphragm was approximately Li _2.9 PO _3.3 N _0.36 . Thereafter, a part of the negative electrode mixture was peeled off from the end portion of the negative electrode current collector, and one end of the nickel negative electrode lead 1 was joined to the current collector exposed portion by resistance welding. The negative electrode lead was entirely covered with insulating tape 8 except for the other end.

(D) Production of Battery Next, the negative electrode was inserted into the case 2 and the positive electrode solution 4 was further injected. At this time, the joining portion between the negative electrode lead and the negative electrode current collector at one end of the negative electrode was set to be below the liquid surface of the positive electrode. Thereafter, the other end of the negative electrode lead 1 was pulled out from the opening of the case 2, and the opening was bonded with an insulating gasket 5 made of polyphenylene sulfide.
The dimensions of the obtained battery were 30 mm in width, 50 mm in total height, 5.3 mm in thickness, and the design capacity of the battery was 800 mAh. Hereinafter, the design capacity of all the batteries was also set to 800 mAh.

  The battery was charged at a constant current of 0.08 A at an ambient temperature of 20 ° C. until the battery voltage reached 4.5 V, paused for 20 minutes, then discharged at a discharge current of 0.08 A and a final voltage of 2. Charging / discharging which discharges to 0V was performed once. The voltage of the battery before the start of discharge was 3.7V. This battery was referred to as the battery of Example 1.

Example 2
A battery was produced in the same manner as in Example 1, except that lithium tetrafluoroborate (LiBF ₄ ) was used as the alkali metal salt of the electrolyte solution constituting the positive electrode solution. This battery was referred to as the battery of Example 2.

Example 3
A battery was produced in the same manner as in Example 1 except that lithium thiocyanate (LiSCN) was used as the alkali metal salt of the electrolyte solution constituting the positive electrode solution. This battery was referred to as the battery of Example 3.

Example 4
A battery was produced in the same manner as in Example 1 except that lithium bisfluoroethylsulfonylimide (LiN (SO ₂ C ₂ F ₅ ) ₂ ) was used as the alkali metal salt of the electrolyte solution constituting the positive electrode solution. . This battery was referred to as the battery of Example 4.

Example 5
A battery was fabricated in the same manner as in Example 1 except that a mixed solvent having a volume ratio of 1: 3 of propylene carbonate and dimethyl carbonate was used as the nonaqueous solvent for the electrolyte solution constituting the positive electrode solution. This battery was referred to as the battery of Example 5.

Example 6
Except that trimethylpropylammonium-bistrifluoromethylsulfonylimide (TMPA-TFSI), which is an ionic liquid (room temperature molten salt), was used as a non-aqueous solvent for the electrolyte solution constituting the positive electrode solution. A battery was produced by this method. This battery was referred to as the battery of Example 6.

Example 7
A battery was produced in the same manner as in Example 1 except that graphite (NG-7 manufactured by Kansai Thermal Chemical Co., Ltd.) was used as the negative electrode active material. This battery was referred to as the battery of Example 7.

Example 8
A battery was produced in the same manner as in Example 1 except that metallic lithium was used as the negative electrode active material. This battery was referred to as the battery of Example 8.

Example 9
A battery was fabricated in the same manner as in Example 1 except that a 4 μm thick silicon film formed by vapor deposition on a copper foil current collector was used as the negative electrode active material. This battery was referred to as the battery of Example 9.

Example 10
A battery was produced in the same manner as in Example 1 except that lithium titanate (Li ₄ Ti ₅ O ₁₂ ) was used as the negative electrode active material. This battery was referred to as the battery of Example 10.

Example 11
A battery was fabricated in the same manner as in Example 1, except that silicon monoxide (SiO) (manufactured by Sumitomo Titanium Co., Ltd.) was used as the negative electrode active material. This battery was referred to as the battery of Example 11.

Example 12
A battery was produced in the same manner as in Example 1 except that molybdenum disulfide (MoS ₂ ) (manufactured by Kojundo Chemical Laboratory Co., Ltd.) was used as the negative electrode active material. This battery was referred to as the battery of Example 12.

Example 13
Lithium sulfide (Li ₂ S), silicon sulfide (SiS ₂ ) and lithium phosphate (Li ₃ PO ₄ ) were melt mixed and then solidified to obtain an amorphous material. A battery was fabricated in the same manner as in Example 1 except that vapor deposition was performed using this amorphous material instead of lithium phosphate to form a diaphragm on the negative electrode surface. This battery was referred to as the battery of Example 13. The composition of the amorphous material constituting the diaphragm was approximately 0.63 Li ₂ S-0.36 SiS ₂ -0.01 Li ₃ PO ₄ (numbers represent molar ratios).

Example 14
Dimethyl carbonate in which LiN (SO ₂ CF ₃ ) ₂ was dissolved was mixed with polyethylene oxide so that the Li / O ratio was 1/12 to prepare a lithium ion conductive polymer electrolyte. A battery was produced in the same manner as in Example 1 except that the surface of the negative electrode was coated with this polymer electrolyte, and the membrane was irradiated with ultraviolet rays and subjected to three-dimensional crosslinking to form a diaphragm. This battery was referred to as the battery of Example 14.

Example 15
A battery was produced in the same manner as in Example 1 except that 5% by weight of vinylene carbonate was added to the positive electrode solution. Thereafter, the battery was charged at 80 mA for 2 hours, and then discharged at 80 mA until the battery voltage reached 2V. This battery was referred to as the battery of Example 15.

Example 16
A battery was produced in the same manner as in Example 1 except that the redox material (positive electrode active material) of the positive electrode solution was replaced with iron tetrafluoroborate (Fe (BF ₄ ) ₂ ). This battery was referred to as the battery of Example 16.

Example 17
A battery was produced in the same manner as in Example 1 except that the redox material of the positive electrode solution was replaced with lithium selenide (Li ₂ Se). This battery was referred to as the battery of Example 17.

Example 18
A battery was produced in the same manner as in Example 1 except that the redox material of the positive electrode solution was replaced with lithium telluride (Li ₂ Te). This battery was referred to as the battery of Example 18.

Example 19
A battery was produced in the same manner as in Example 1 except that the negative electrode covered with the diaphragm was further covered with a polyethylene microporous membrane (manufactured by Tonen Corporation). This battery was referred to as the battery of Example 19.

Example 20
A battery was produced in the same manner as in Example 1 except that an iron sheet was used as the exterior and current collector. This battery was referred to as the battery of Example 20.

<< Comparative Example 1 >>
A battery was produced in the same manner as in Example 1 except that the alkali metal ion conductive diaphragm was not formed on the negative electrode surface, and only the negative electrode was covered with the polyethylene microporous film used in Example 19. . This battery was referred to as the battery of Comparative Example 1.

[Evaluation]
The operation test of the battery was performed as follows.
Charge and discharge at a constant current charge of 0.08A at an ambient temperature of 20 ° C until the battery voltage reaches 5V, and after a 20-minute pause, the battery is discharged to a final voltage of 2.0V at a discharge current of 0.08A. Was repeated 10 cycles, and the discharge capacity at the 10th cycle was determined as the battery capacity. Table 1 shows the capacity of each battery.

From the results shown in Table 1, in Examples 1 to 15 and Examples 17 to 19, battery capacities close to the designed capacities were obtained. Therefore, reaction formula (1) or (2) or an electrochemical reaction similar thereto It is thought that the valence of sulfur changed from -2 to +4. Further, from the results of Examples 17 and 18, lithium chalcogenide lithium selenide (Li ₂ Se) and lithium telluride (Li ₂ Te) were also carried out in which the redox material of the cathode solution was lithium sulfide (Li ₂ S). It turns out that it reacts similarly to the case of Examples 1-15.

On the other hand, in Example 16 using iron tetrafluoroborate (Fe (BF ₄ ) ₂ ), the battery capacity is less than half that of lithium sulfide. This is because the lithium valence of lithium sulfide fluctuates hexavalently, whereas the iron of Fe (BF ₄ ) ₂ has an oxidation number of Fe (II) to Fe (III), and at most Fe (IV). I think the cause is that it cannot change.
However, even in Example 16, a higher capacity can be expected as compared with a non-aqueous electrolyte secondary battery that has been put into practical use.

  From the results of Examples 2 to 4, it can be seen that the type of lithium salt constituting the electrolyte solution hardly affects the battery capacity. This is presumably because the reaction utilization rate (yield) of the redox material is low, so that the lithium salt is ionically dissociated to the extent that it can provide a sufficient amount of anions with respect to the amount of cations in a high oxidation state.

  In Examples 7 to 12 in which the type of the negative electrode active material was changed, various capacities were obtained. This is believed to be due to the irreversible capacity inherent in each material. For example, in the case of graphite used in Example 7, compared with the amorphous carbon used in Example 1, the irreversible capacity is about 1/3 per unit weight. For this reason, it is considered that Example 7 using graphite had a slight increase in capacity. Similarly, when lithium metal is used for the negative electrode active material, the capacity increases.

  Silicon of Example 9 and silicon monoxide of Example 11 are known as materials having high ability to occlude and release lithium, but in the above example, they are designed to make maximum use of capacity. Absent. Since these irreversible capacities are larger than those of carbon and graphite, the battery capacities are decreased.

In Example 10 using lithium titanate (Li ₄ Ti ₅ O ₁₂ ) and Example 12 using molybdenum disulfide (MoS ₂ ) as the negative electrode active material, amorphous carbon, graphite, and lithium metal were used. Compared with Examples 1, 7 and 8 using the battery, the battery voltage was lowered. This is presumably because the potential of lithium titanate or molybdenum disulfide causing a lithium elimination reaction in the negative electrode is 1.5 V or more on average with respect to the potential of lithium metal. However, oxides such as lithium titanate and silicon monoxide and sulfides such as molybdenum disulfide are known to have good cycle life, and in applications where a relatively low potential is allowed, Sufficient performance can be expected.

  Example 1 using a mixed solvent of ethylene carbonate and ethyl methyl carbonate, Example 5 using a mixed solvent of propylene carbonate and dimethyl carbonate, and trimethylpropylammonium-bistri which is a kind of ionic liquid (room temperature molten salt) From the results of Example 6 using fluoromethylsulfonylimide (TMPA-TFSI), the nonaqueous solvent of the cathode solution does not give a large difference in battery performance, and sufficient battery capacity is ensured regardless of the seed flow of the nonaqueous solvent. I understand that I can do it. Moreover, since it is thought that an ionic liquid is easy to carry out ion dissociation, it is thought that the use of an ionic liquid rather than a general polar non-aqueous solvent can expect high performance.

  From Examples 1-20, it turns out that the alkali metal ion conductive diaphragm which covers the negative electrode surface has sufficient ion conductivity, and has prevented the short circuit with the redox material of a positive electrode liquid, and a negative electrode effectively. In addition, Example 14 shows that the polymer electrolyte is also effective as a diaphragm.

  In Example 15 in which vinylene carbonate was contained in the positive electrode solution, it was confirmed that vinylene carbonate was decomposed on the negative electrode surface during charging of the battery and a film was formed on the negative electrode surface. However, the vinylene carbonate-derived coating contains a slight amount of sulfur, which is considered to reduce the capacity.

  Example 19 in which an alkali metal ion conductive diaphragm and a polyethylene microporous membrane separator were used together was not different from Example 1 in terms of battery capacity. However, when an impact is applied to the battery, it is considered to play a role of reinforcing the thin alkali metal ion conductive diaphragm.

  In the battery of Comparative Example 2 that did not have an alkali metal ion conductive diaphragm, the voltage did not increase from the beginning of charging, and showed very little capacity at the 10th cycle. This is presumably because −2 valent sulfur, which is a redox material in the positive electrode solution, is oxidized during charging but migrates to the negative electrode surface and is reduced.

  As described above, the present invention is inexpensive and can be applied to a non-aqueous electrolyte secondary battery with high energy density, and also has a variety of battery voltages that can be easily designed according to the application.

It is a longitudinal cross-sectional view of an example of the nonaqueous electrolyte secondary battery of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Negative electrode lead 2 Case 3 Carbon layer 4 Positive electrode liquid 5 Insulating gasket 6 Diaphragm 7 Negative electrode 8 Insulating tape

Claims (17)

(A) an electrolyte solution obtained by dissolving an alkali metal salt in a non-aqueous solvent,
(B) a positive electrode active material comprising a redox material dissolved or dispersed in the electrolyte solution;
(C) The positive electrode current collector a positive electrode active material to provide a place for performing a redox reaction, and (D) Ri Do alkali metal ion occluding and releasing, or alkali metal anode capable precipitation and dissolution of ,
The negative electrode is covered with a diaphragm having alkali metal ion conductivity and shielding the positive electrode active material;
The diaphragm is made of an alkali metal ion conductive solid electrolyte,
The non-aqueous electrolyte secondary battery in which the alkali metal ion conductive solid electrolyte contains an alkali metal phosphate . (A) an electrolyte solution obtained by dissolving an alkali metal salt in a non-aqueous solvent,
(B) a positive electrode active material comprising a redox material dissolved or dispersed in the electrolyte solution;
(C) a positive electrode current collector that provides a field for the positive electrode active material to perform a redox reaction; and
(D) Negative electrode capable of occluding and releasing alkali metal ions or depositing and dissolving alkali metals
Consists of
The negative electrode is covered with a diaphragm having alkali metal ion conductivity and shielding the positive electrode active material;
The non-aqueous electrolyte secondary battery in which the electrolyte solution includes an organic substance having a function of forming a film on the surface of the negative electrode by charging and discharging, and the diaphragm is formed of the film. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the diaphragm allows only alkali metal ions to pass among elements constituting the component (A) and the component (B). 4. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the component (A) and the component (B) form a liquid or fluid composite. The positive electrode current collector, wherein the non-aqueous electrolyte secondary alkali metal salt comprising a metal sheet or a porous carbon sheet showing a dissolution potential above + 3V with respect to the alkali metal of potential constituting the claim 1 or 2, wherein battery. The nonaqueous electrolyte secondary battery according to claim 5, wherein the positive electrode current collector is made of the metal sheet, and a carbon layer is attached to a surface of the metal sheet. An anode lead is connected to the negative electrode, the negative electrode lead nonaqueous electrolyte secondary battery according to claim 1 or 2 wherein is shielded from the positive electrode active material for drawing current to the outside. The positive electrode active material can be partially or wholly soluble in the non-aqueous solvent and is at least selected from the group consisting of transition metal salts, sulfur compounds, selenium compounds, tellurium compounds, simple sulfur, simple selenium and simple tellurium. The nonaqueous electrolyte secondary battery according to claim 1 or 2, comprising one type. 2. The negative electrode is made of at least one selected from the group consisting of alkali metal, graphite, amorphous carbon, fullerene, carbon nanotube, alloy, transition metal oxide, transition metal sulfide, silicon and silicon monoxide. Or the nonaqueous electrolyte secondary battery of 2. The alkali metal salt is an imide salt, meside salt, borate, perchlorate, hexafluoroarsenate, chloroaluminate, thiocyanate, iodide, tetrafluoroborate, hexafluorophosphate , A salt in which at least one of fluorine of hexafluorophosphate is replaced with —CF ₃ or —C ₂ F ₅ , and at least one of fluorine of tetrafluoroborate is —CF ₃ or —C ₂ F ₅ at least one non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein is selected from the group consisting of replacement salt. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous solvent is at least one selected from the group consisting of a polar solvent that is liquid at room temperature and a room temperature molten salt that is ionically dissociated at room temperature. The nonaqueous electrolyte secondary battery according to claim 2 , wherein the diaphragm includes an alkali metal ion conductive solid electrolyte. The alkali metal ion-conducting solid electrolyte, non-aqueous electrolyte secondary battery of claim 1 2 further comprising an alkali metal phosphate. The alkali metal ion-conducting solid electrolyte, according to claim 1 or 1 3 non-aqueous electrolyte secondary battery according further comprises a sulfide salt.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the electrolyte solution contains an organic substance having a function of forming a film on the surface of the negative electrode by charging and discharging. The organic material is, vinylene carbonate, vinyl ethylene carbonate, claim 2 or 1 5 non-aqueous electrolyte secondary battery according composed of at least one selected from the group consisting of phenyl ethylene carbonate and propane sultone. The diaphragm, the non-aqueous electrolyte secondary battery of claim 1 5 further comprising the film.

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