JP2017228513A - Nonaqueous electrolyte storage element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte storage element capable of suppressing gas generation without deteriorating the characteristics of the storage element.SOLUTION: The nonaqueous electrolyte storage element includes: a positive electrode containing a positive electrode active material capable of inserting or extracting an anion; a negative electrode containing a negative electrode active material; and a nonaqueous electrolytic solution. The positive electrode active material contains a carbon material having a plurality of pores forming a three-dimensional network structure and having a solid electrolyte interface (SEI) substance on its surface.SELECTED DRAWING: None

Description

  The present invention relates to a non-aqueous electrolyte storage element.

  In recent years, with the miniaturization and high performance of portable devices, the characteristics of non-aqueous electrolyte storage elements having a high energy density have been improved and become widespread. Development of non-aqueous electrolyte storage elements with larger capacities and superior safety has been promoted, and installation in electric vehicles and the like has begun.

  Under such circumstances, a so-called dual intercalation type non-aqueous electrolyte storage element is expected to be put to practical use as a storage element having high energy density and suitable for high-speed charge / discharge. Since the dual intercalation type storage element uses a carbonaceous material for the positive electrode, it is possible to operate stably without elution of elements from the positive electrode even under high voltage. Along with this, there is a problem that a large amount of gas is generated. This is presumably because decomposition of the electrolytic solution occurs at the interface between the electrode and the electrolytic solution.

  In order to suppress such decomposition of the electrolyte, in a general lithium secondary battery, a solid electrolyte interface (SEI) made of a decomposition product such as an electrolyte is formed on the negative electrode surface. It has been broken. The SEI is not electrically conductive, but has lithium ion conductivity, and its formation is known to suppress decomposition of the electrolyte.

For example, an assembled battery is subjected to an initial charge (preliminary charge process) until a predetermined potential value is reached, and an aging process is performed for the battery that has been initially charged and held for a predetermined time in a predetermined temperature range. In the initial charging, part of the electrolyte component is intentionally reduced and decomposed, and the negative electrode surface is coated with an SEI film made of the decomposition product. It is disclosed that further reductive decomposition of the electrolyte component can be prevented (see, for example, Patent Document 1).
In addition, by subjecting the negative electrode composition to high-frequency thermal plasma treatment in a plasma gas atmosphere containing BF ₃ , boron alone or a boron-containing functional group containing boron is introduced on the surface of the material. Has been disclosed that can be stably produced on the negative electrode surface (see, for example, Patent Document 2).
Further, it is disclosed that a passivation film containing SEI and polymer electrolyte PEI can be formed on the surface of the positive electrode by heat-treating the positive electrode material at 50 ° C. to 120 ° C. for 1 hour to 2 months in a discharged state (for example, And Patent Document 3).

  An object of this invention is to provide the non-aqueous-electrolyte electrical storage element which can suppress gas generation, without reducing an electrical storage element characteristic.

The nonaqueous electrolyte storage element of the present invention as a means for solving the above problems includes a positive electrode including a positive electrode active material capable of inserting or removing anions, a negative electrode including a negative electrode active material, a nonaqueous electrolyte, A non-aqueous electrolyte storage element comprising:
The positive electrode active material contains a carbon material having a plurality of pores forming a three-dimensional network structure and having a solid electrolyte interface (SEI) material on the surface.

  According to the present invention, it is possible to provide a nonaqueous electrolytic solution storage element capable of suppressing gas generation without deteriorating the storage element characteristics.

FIG. 1 is a schematic view showing an example of the nonaqueous electrolyte storage element of the present invention. FIG. 2 is a schematic view showing another example of the nonaqueous electrolyte storage element of the present invention.

(Non-aqueous electrolyte storage element)
The non-aqueous electrolyte storage element of the present invention is a non-aqueous electrolyte storage element having a positive electrode including a positive electrode active material capable of inserting or removing anions, a negative electrode including a negative electrode active material, and a non-aqueous electrolyte. ,
The positive electrode active material includes a carbon material having a plurality of pores forming a three-dimensional network structure and having a solid electrolyte interface (SEI) material on the surface, and further includes other members as necessary. Become.

The non-aqueous electrolyte storage element of the present invention is a method for forming SEI on the negative electrode of a lithium ion secondary battery in the techniques described in Patent Documents 1 and 2, and does not mention formation of SEI on the surface of the positive electrode. . This is based on the knowledge that the formation of SEI is mainly generated by the reductive decomposition reaction of the electrolytic solution, so that it is difficult to form on the positive electrode surface of a general lithium ion secondary battery.
Further, the non-aqueous electrolyte storage element of the present invention is different from the technique described in Patent Document 3 in that the SEI is formed on the surface of a general negative electrode as shown in Patent Documents 1 and 2, A special SEI formation process is required before forming the positive electrode composite or assembling the electricity storage device. Therefore, it is based on the knowledge that handling at the time of manufacture of an electrical storage element becomes very difficult.

  As a result of intensive studies by the present inventors to solve the above problems, in the dual intercalation type power storage element, on the positive electrode side having a plurality of pores forming a three-dimensional network structure, in the high voltage range. When charging and discharging, gas generation due to decomposition of the electrolyte during charging and in a charged state is a serious problem. In this case, if the SEI can be formed in the positive electrode of the electricity storage device as in the conventional negative electrode, gas generation can be performed while obtaining high capacity without causing gas generation, without reducing capacity and cycle life. It was found that it was possible to suppress.

The non-aqueous electrolyte storage element of the present invention is a system using a carbon material having a plurality of pores forming a three-dimensional network structure as a positive electrode active material, and a solid electrolyte interface (SEI) material on the surface of the positive electrode active material There is no particular limitation on the raw material of the carbon material, its production method, other characteristics, etc. Further, the other constituent elements such as the negative electrode of the power storage element and the electrolytic solution with anion intercalation using the positive electrode are not particularly limited.
Hereafter, it demonstrates in detail for every structural member of the non-aqueous-electrolyte electrical storage element of this invention.

<Positive electrode>
The positive electrode is not particularly limited as long as it contains a positive electrode storage material (positive electrode active material or the like), and can be appropriately selected according to the purpose. For example, a positive electrode material having a positive electrode active material on a positive electrode current collector is used. And a positive electrode provided.
There is no restriction | limiting in particular as a shape of the said positive electrode, According to the objective, it can select suitably, For example, flat form etc. are mentioned.

-Positive electrode material-
There is no restriction | limiting in particular as said positive electrode material, According to the objective, it can select suitably, For example, a positive electrode active material is included at least, and also a conductive support agent, a binder, a thickener, etc. are included as needed.

--- Positive electrode active material-
The positive electrode active material includes a carbon material having a plurality of pores forming a three-dimensional network structure and having a solid electrolyte interface (SEI) material on the surface.

---- Carbon material ---
The “carbon material having a plurality of pores (mesopores) forming a three-dimensional network structure” is a pair of positive and negative electrolyte ions on both sides of the surface where the mesopores (cavities) and the carbon material portion are in contact with each other. A capacitor in which a charge double layer is formed. For this reason, the movement of the electrolyte ions present in pairs is faster than the subsequent movement of the generated electrolyte ions after sequentially reacting with the polar active material. It is understood that the size depends on the size of the surface area of the mesopores in which positive and negative electrolyte ion pairs exist.

Looking at the crystallinity of the carbon material, the time constant of the capacitor (slow response at the time of charging / discharging) depends not only on the capacitance of the non-aqueous electrolyte but also on the resistance value of the carbon material part in ohmic contact with the capacitor. It depends. Furthermore, since both electrolyte ions involve a chemical reaction that repeats bond separation with the polar active material for each, the carbon material may be deteriorated. The crystallinity of the carbon material is preferably determined as appropriate so that the carbon material has a strength that can withstand this deterioration.
In addition, it is not necessary that all the carbonaceous parts have a crystal structure, an amorphous part may exist in part, and all may be amorphous.

  In the carbon material, mesopores are essential, but micropores are not essential. Therefore, the micropores may or may not exist, but the organic substance as the carbon material forming source usually carbonizes by releasing a volatile substance during carbonization. Accordingly, since micropores are usually left as a release trace, it is difficult to obtain one having no micropores. In contrast, mesopores are usually formed intentionally. For example, as known, acid (alkali) soluble metal, metal oxide, metal salt, metal-containing organic material and carbon material or organic material that is its raw material are molded together, then acid In many cases, the traces of the muscle parts dissolved by (alkali) become mesopores.

Here, in this specification, those having a pore diameter of less than 2 nm are referred to as micropores, and those having a pore diameter of 2 nm to 50 nm are referred to as mesopores. Since the size of the electrolyte ions is 0.5 nm or more and 2 nm or less, it is difficult to say that the micropores contribute much to the movement of ions. Therefore, mesopores are important for the smooth movement of ions. Incidentally, the pore size of activated carbon, which is the same carbonaceous material, is said to be about 1 nm on average, and in the case of activated carbon, it is regarded as one of all adsorption accompanied by exotherm (decrease in enthalpy) without exception.
The mesopores of the size preferably form a three-dimensional network structure. If the hole has a three-dimensional network structure, ions move smoothly.

The BET specific surface area of the carbon material, preferably at least ^{50 m} 2 / g, more preferably ^{50 m} 2 / g or more 2,000 m ² / g or less, more preferably 800 m ² / g or more 1,800 m ² / g or less.
When the BET specific surface area is 50 m ² / g or more, a sufficient amount of pores are formed and ions are sufficiently inserted, so that the capacity can be increased. Further, when the BET specific surface area is 2,000 m ² / g or less, mesopores are sufficiently formed and ion insertion is not hindered, so that the capacity can be increased.
The BET specific surface area can be obtained, for example, by using a BET (Brunauer, Emmett, Teller) method from the measurement result of the adsorption isotherm by an automatic specific surface area / pore distribution measuring device (TriStar II 3020, manufactured by Shimadzu Corporation). it can.

The pore volume of the carbon material is preferably 0.2 mL / g or more and 2.3 mL / g or less, and more preferably 0.2 mL / g or more and 1.7 mL / g or less. When the pore volume is 0.2 mL / g or more, mesopores rarely become independent pores, and a large discharge capacity can be obtained without hindering the movement of anions. On the other hand, if the pore volume of the carbon material is 2.3 mL / g or less, the carbon structure is not bulky, the energy density is increased as an electrode, and the discharge capacity per unit volume can be increased. Further, the carbonaceous wall forming the pores is not thin, and it is advantageous in that the shape of the carbonaceous wall can be maintained even after repeated occlusion and release of anions, and charge / discharge characteristics are improved. .
The pore volume of the carbon material is determined by, for example, using the BJH (Barrett, Joyner, Hallender) method from the measurement results of the adsorption isotherm by an automatic specific surface area / pore distribution measuring device (TriStar II 3020, manufactured by Shimadzu Corporation). Can be sought.

  As said carbon material, what was manufactured suitably may be used and a commercial item may be used. As said commercial item, Knobel (trademark) (made by Toyo Tanso Co., Ltd.) etc. are mentioned, for example.

The method for producing the carbon material is not particularly limited and may be appropriately selected depending on the intended purpose. For example, the carbon material is formed by molding a muscle material having a three-dimensional network structure and an organic material as a carbon material forming source. Examples thereof include a method of dissolving the muscle material with an acid or alkali after carbonization. In this case, the trace which melt | dissolved the said muscle material becomes a several mesopore which forms a three-dimensional network structure, and can form intentionally.
There is no restriction | limiting in particular as said reinforcing material, According to the objective, it can select suitably, For example, a metal, a metal oxide, a metal salt, a metal containing organic substance etc. are mentioned. Among these, acid or alkali-soluble ones are preferable.
The organic substance is not particularly limited as long as it can be carbonized, and can be appropriately selected according to the purpose. In addition, since the said organic substance discharge | releases a volatile substance at the time of carbonization, since a micropore is formed as an emission trace, it is difficult to manufacture the carbon material which does not have a micropore at all.

--- Solid electrolyte interface (SEI) material ---
In the present invention, in order to suppress decomposition of the electrolytic solution and suppress gas generation, a solid electrolyte interface (SEI) made of a decomposable product such as an electrolytic solution is formed on the surface of the positive electrode. The SEI material is not electrically conductive but has lithium ion conductivity, and its formation is known to suppress decomposition of the electrolyte.
The solid electrolyte interface (SEI) material can be formed on the surface of the positive electrode by subjecting the produced storage element to an aging treatment under predetermined conditions.
In the aging treatment, for example, the obtained electric storage element is held in a constant temperature bath at 40 ° C. for 5 hours, charged to 4.5 V at a 1/5 C rate, and then left for 5 hours, at a 1/5 C rate. This is done by discharging to 1.5V.
Examples of the solid electrolyte interface (SEI) material include lithium fluoride, lithium carbonate, lithium oxide, an organic lithium compound, and an organic polymer. Among these, lithium fluoride is preferable from the viewpoint of high stability.
The fact that a solid electrolyte interface (SEI) substance (for example, lithium fluoride) is formed on the surface of the positive electrode is confirmed by X-ray photoelectron spectroscopy (XPS) having a peak in the range of 685 eV to 687 eV. can do.

The solid electrolyte interface (SEI) ratio of the positive electrode surface is preferably 58% or less, more preferably 3% or more and 58% or less, and further preferably 13% or more and 58% or less.
When the solid electrolyte interface (SEI) ratio on the positive electrode surface is 58% or less, the effect of suppressing gas generation can be obtained without impairing the performance of the storage element.

The solid electrolyte interface (SEI) ratio on the positive electrode surface can be determined, for example, as follows.
The storage element is disassembled after the aging treatment is completed, and the positive electrode is washed with a dimethyl carbonate (DMC) solution. The positive electrode after cleaning is subjected to surface elemental analysis under non-air exposure using X-ray photoelectron spectroscopy (XPS) (manufactured by Shimadzu Kratos Co., Ltd., AXIS-Ultra). Note that Al monochromatic X-ray is used as an excitation source, measurement output is 105 W, measurement mode is Hybrid mode, and path energy is 20 eV.
Formation of lithium fluoride (LiF) can be confirmed from having a peak (F peak) in the range of 685 eV or more and 687 eV or less.
In addition, surface analysis is performed in the same manner for an unused positive electrode as a storage element, and the ratio of the positive electrode active material on the surface of the unused positive electrode is calculated from the C peak derived from the positive electrode active material existing at 284 eV in the unused positive electrode. To do. By subtracting the ratio of the positive electrode active material on the positive electrode surface from this value, the SEI ratio on the positive electrode surface can be calculated.

  By forming a plasma treatment on the carbon material that is the positive electrode active material, the formation of a solid electrolyte interface (SEI) material can be increased. The plasma treatment can be performed, for example, in an inert gas atmosphere under a treatment condition of a container internal pressure of 40 Pa, an output of 300 W, and a frequency of 13.56 MHz for 30 minutes.

--Binder and thickener--
The binder and thickener are not particularly limited as long as they are materials that are stable with respect to the solvent and electrolyte used during electrode production and the applied potential, and can be appropriately selected according to the purpose. Fluorine binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), ethylene-propylene-butadiene rubber (EPBR), styrene-butadiene rubber (SBR), isoprene rubber, acrylate latex, carboxymethylcellulose (CMC) , Methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyacrylic acid, polyvinyl alcohol, alginic acid, oxidized starch, phosphoric acid starch, casein and the like. These may be used individually by 1 type and may use 2 or more types together. Among these, fluorine-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), acrylate latex, and carboxymethyl cellulose (CMC) are preferable.

--Conductive aid--
Examples of the conductive aid include metal materials such as copper and aluminum, and carbonaceous materials such as carbon black, acetylene black, and carbon nanotubes. These may be used individually by 1 type and may use 2 or more types together.

-Positive electrode current collector-
There is no restriction | limiting in particular as a material of the said positive electrode electrical power collector, a shape, a magnitude | size, and a structure, According to the objective, it can select suitably.
The material of the positive electrode current collector is formed of a conductive material and is not particularly limited as long as it is stable with respect to the applied potential, and can be appropriately selected according to the purpose. Examples include stainless steel, nickel, aluminum, titanium, and tantalum. Among these, stainless steel and aluminum are particularly preferable.
There is no restriction | limiting in particular as a shape of the said positive electrode electrical power collector, According to the objective, it can select suitably.
The size of the positive electrode current collector is not particularly limited as long as it is a size that can be used for a non-aqueous electrolyte storage element, and can be appropriately selected according to the purpose.

<Method for producing positive electrode>
The positive electrode is applied to the positive electrode current collector in a slurry form by adding the binder, the thickener, the conductive additive, a solvent and the like to the positive electrode active material as necessary. It can be manufactured by drying. There is no restriction | limiting in particular as said solvent, According to the objective, it can select suitably, For example, an aqueous solvent, an organic solvent, etc. are mentioned. Examples of the aqueous solvent include water and alcohol. Examples of the organic solvent include N-methyl-2-pyrrolidone (NMP) and toluene.
In addition, the positive electrode active material can be roll-formed as it is to form a sheet electrode, or can be formed into a pellet electrode by compression molding.

<Negative electrode>
The negative electrode is not particularly limited as long as it contains a negative electrode storage material (negative electrode active material or the like), and can be appropriately selected according to the purpose. For example, a negative electrode material having a negative electrode active material on a negative electrode current collector is used. And a negative electrode provided.
There is no restriction | limiting in particular as a shape of the said negative electrode, According to the objective, it can select suitably, For example, flat form etc. are mentioned.

-Negative electrode material-
The negative electrode material includes at least a negative electrode active material, and further includes a conductive additive, a binder, a thickener, and the like as necessary.

-Negative electrode active material-
The negative electrode active material is not particularly limited as long as it can occlude and release cations in a non-aqueous solvent system, and can be appropriately selected according to the purpose. For example, it can occlude and release lithium ions as cations. Examples thereof include a carbonaceous material, a metal oxide, a metal or metal alloy that can be alloyed with lithium, a composite alloy compound of lithium and an alloy containing a metal that can be alloyed with lithium and lithium, and lithium nitride metal.

There is no restriction | limiting in particular as said carbonaceous material, According to the objective, it can select suitably, For example, graphite (graphite), the thermal decomposition thing of organic substance on various thermal decomposition conditions, etc. are mentioned.
Examples of the graphite (graphite) include coke, artificial graphite, and natural graphite. Among these, artificial graphite and natural graphite are preferable.
Examples of the metal oxide include antimony tin oxide and silicon monoxide.
Examples of the metal or metal alloy include lithium, aluminum, tin, silicon, and zinc.
Examples of the composite alloy compound with lithium include lithium titanate.
Examples of the lithium metal nitride include cobalt lithium nitride.
As said negative electrode active material, 1 type may be used individually and 2 or more types may be used together. Among these, from the viewpoint of safety and cost, at least one of a carbonaceous material and lithium titanate is preferable.

--Binder and thickener--
The binder and thickener are not particularly limited as long as they are materials that are stable with respect to the solvent and electrolyte used during electrode production and the applied potential, and can be appropriately selected according to the purpose. Fluorine binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), ethylene-propylene-butadiene rubber (EPBR), styrene-butadiene rubber (SBR), isoprene rubber, acrylate latex, carboxymethylcellulose (CMC) , Methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyacrylic acid, polyvinyl alcohol, alginic acid, oxidized starch, phosphoric acid starch, casein and the like. These may be used individually by 1 type and may use 2 or more types together. Among these, fluorine-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) are preferable.

--Conductive aid--
Examples of the conductive aid include metal materials such as copper and aluminum, and carbonaceous materials such as carbon black, acetylene black, and carbon nanotubes. These may be used individually by 1 type and may use 2 or more types together.

-Negative electrode current collector-
There is no restriction | limiting in particular as a material, a shape, a magnitude | size, and a structure of the said negative electrode collector, According to the objective, it can select suitably.
The material of the negative electrode current collector is formed of a conductive material and is not particularly limited as long as it is stable with respect to the applied potential, and can be appropriately selected according to the purpose. Steel, nickel, aluminum, copper, etc. are mentioned. Among these, stainless steel, copper, and aluminum are particularly preferable.
There is no restriction | limiting in particular as a shape of the said negative electrode electrical power collector, According to the objective, it can select suitably.
The size of the negative electrode current collector is not particularly limited as long as it is a size that can be used for a non-aqueous electrolyte storage element, and can be appropriately selected according to the purpose.

<Method for producing negative electrode>
The negative electrode is coated on the negative electrode current collector with a negative electrode material made into a slurry by adding the binder and thickener, the conductive additive, a solvent, etc. to the negative electrode active material, if necessary. It can be manufactured by drying. As the solvent, the same solvent as that for the positive electrode can be used.
In addition, the negative electrode active material added with the binder, the thickener, the conductive auxiliary agent and the like is roll-formed as it is to form a sheet electrode, a pellet electrode by compression molding, a method such as vapor deposition, sputtering, plating, etc. A thin film of the negative electrode active material may be formed on the negative electrode current collector.

<Non-aqueous electrolyte>
The non-aqueous electrolyte is an electrolyte obtained by dissolving an electrolyte salt in a non-aqueous solvent.

-Non-aqueous solvent-
There is no restriction | limiting in particular as said non-aqueous solvent, Although it can select suitably according to the objective, An aprotic organic solvent is suitable.
As the aprotic organic solvent, carbonate-based organic solvents such as chain carbonates and cyclic carbonates are used, and low viscosity solvents are preferred. Among these, a chain carbonate is preferable from the viewpoint that the electrolyte salt has a high dissolving power.
Examples of the chain carbonate include dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC). Among these, dimethyl carbonate (DMC) is preferable.
The content of the DMC is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 70% by mass or more and more preferably 83% by mass or more with respect to the non-aqueous solvent. If the content of the DMC is less than 70% by mass, the amount of the cyclic substance having a high dielectric constant increases when the remaining solvent is a cyclic substance (cyclic carbonate, cyclic ester, etc.) having a high dielectric constant. When a non-aqueous electrolyte solution having a high concentration of 3M or more is produced, the viscosity becomes too high, which may cause problems in terms of penetration of the non-aqueous electrolyte solution into the electrode and ion diffusion.
Examples of the cyclic carbonate include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate (VC), and fluoroethylene carbonate (FEC).
When a mixed solvent combining ethylene carbonate (EC) as the cyclic carbonate and dimethyl carbonate (DMC) as the chain carbonate is used, the mixing ratio of ethylene carbonate (EC) and dimethyl carbonate (DMC) is particularly There is no restriction | limiting, According to the objective, it can select suitably.

As the non-aqueous solvent, an ester organic solvent such as a cyclic ester or a chain ester, an ether organic solvent such as a cyclic ether or a chain ether, or the like can be used as necessary.
Examples of the cyclic ester include γ-butyrolactone (γ-BL), 2-methyl-γ-butyrolactone, acetyl-γ-butyrolactone, and γ-valerolactone.
Examples of the chain ester include propionic acid alkyl ester, malonic acid dialkyl ester, acetic acid alkyl ester (methyl acetate (MA), ethyl acetate, etc.), formic acid alkyl ester (methyl formate (MF), ethyl formate, etc.) and the like. Can be mentioned.
Examples of the cyclic ether include tetrahydrofuran, alkyltetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran, 1,3-dioxolane, alkyl-1,3-dioxolane, 1,4-dioxolane, and the like.
Examples of the chain ether include 1,2-dimethoxyethane (DME), diethyl ether, ethylene glycol dialkyl ether, diethylene glycol dialkyl ether, triethylene glycol dialkyl ether, and tetraethylene glycol dialkyl ether.

-Electrolyte salt-
As the electrolyte salt, a lithium salt is preferably used.
The lithium salt is not particularly limited as long as it is dissolved in a non-aqueous solvent and exhibits high ionic conductivity. For example, lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), chloride Lithium (LiCl), lithium borofluoride (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium bistrifluoromethylsulfonylimide (LiN (CF ₃ SO ₂ ) ₂ ), lithium bispentafluoroethylsulfonylimide (LiN (C ₂ F ₅ SO ₂ ) ₂ ) and the like. These may be used individually by 1 type and may use 2 or more types together. Among these, at least one of LiPF ₆ and LiBF ₄ is particularly preferable from the viewpoint of the amount of occlusion of anions in the carbon electrode.
The concentration of the electrolyte salt is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 0.5 mol / L or more and 6 mol / L or less in the nonaqueous solvent, and has a storage element capacity and output. From the point of coexistence of 2 mol / L or more and 4 mol / L or less is more preferable.

<Separator>
The separator is provided between the positive electrode and the negative electrode in order to prevent a short circuit between the positive electrode and the negative electrode.
There is no restriction | limiting in particular as a material, a shape, a magnitude | size, and a structure of the said separator, According to the objective, it can select suitably.
Examples of the material of the separator include paper such as kraft paper, vinylon mixed paper, synthetic pulp mixed paper, cellophane, polyethylene graft membrane, polyolefin nonwoven fabric such as polypropylene melt blown nonwoven fabric, polyamide nonwoven fabric, glass fiber nonwoven fabric, and micropore membrane. Can be mentioned. Among these, those having a porosity of 50% or more are preferable from the viewpoint of holding the electrolytic solution.
As the shape of the separator, a non-woven fabric system having a higher porosity is more preferable than a thin film type having micropores.
There is no restriction | limiting in particular as average thickness of the said separator, Although it can select suitably according to the objective, 20 micrometers or more and 100 micrometers or less are preferable. When the average thickness is less than 20 μm, the retained amount of the electrolytic solution may be reduced, and when it exceeds 100 μm, the energy density is reduced.
There is no restriction | limiting in particular as long as the magnitude | size of the said separator is a magnitude | size which can be used for a non-aqueous electrolyte electrical storage element, It can select suitably according to the objective.
The separator may have a single layer structure or a laminated structure.

<Method for Manufacturing Nonaqueous Electrolyte Storage Element>
The non-aqueous electrolyte storage element of the present invention is manufactured by assembling the positive electrode, the negative electrode, the non-aqueous electrolyte, and, if necessary, a separator into an appropriate shape. Furthermore, other components such as an outer can can be used as necessary. There is no restriction | limiting in particular as a method of assembling the said non-aqueous electrolyte electrical storage element, It can select suitably from the methods employ | adopted normally.

  There is no restriction | limiting in particular about the shape of the nonaqueous electrolyte electrical storage element of this invention, According to the use, it can select suitably from various shapes employ | adopted generally. Examples of the shape include a cylinder type in which a sheet electrode and a separator are spiral, a cylinder type having an inside-out structure in which a pellet electrode and a separator are combined, and a coin type in which a pellet electrode and a separator are stacked.

  Here, an example of the nonaqueous electrolyte storage element is shown in FIG. The non-aqueous electrolyte storage element 10 shown in FIG. 1 includes a positive electrode 1, a negative electrode 2, a separator 3 holding a non-aqueous electrolyte, an outer can 4, a positive electrode lead wire 6, and a negative electrode lead wire 5. And other members as necessary. Specific examples of the non-aqueous electrolyte storage element 10 include a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte capacitor.

FIG. 2 is a schematic diagram for easily explaining the basic configuration of the non-aqueous electrolyte storage element 10.
The positive electrode 11 includes, for example, a positive electrode current collector 20 made of aluminum, carbon 21 as a positive electrode active material fixed on the positive electrode current collector 20, a binder 22 that connects the carbons 21, and a conductive material between the carbons 21. It has a conductive aid 23 indicated by a black circle for providing a pass.
The negative electrode 12 includes, for example, a copper negative electrode current collector 24, a negative electrode active material 25 made of a carbonaceous material fixed on the negative electrode current collector 24, a binder 22 that holds the negative electrode active materials 25 together, A conductive assistant 23 indicated by a black circle for providing a conductive path between the active materials 25 is included.
A separator 13 is disposed between the positive electrode 11 and the negative electrode 12, and a nonaqueous electrolytic solution 26 is disposed. Reference numeral 27 denotes ions. Charging / discharging is performed by inserting or desorbing ions between the carbon layers.
For example, when LiPF ₆ is used as the electrolyte, the charge / discharge reaction of the dual intercalation type non-aqueous electrolyte storage element is PF ₆ from the non-aqueous electrolyte to the positive electrode as shown in the following reaction formula. ^When- is inserted and Li ⁺ is inserted into the negative electrode, charging is performed, and PF ₆ ⁻ is desorbed from the positive electrode and Li ⁺ is desorbed from the negative electrode into the nonaqueous electrolytic solution.

<Application>
The use of the non-aqueous electrolyte storage element of the present invention is not particularly limited and can be used for various purposes. For example, a notebook computer, pen input personal computer, mobile personal computer, electronic book player, mobile phone, mobile fax, mobile phone Copy, portable printer, headphone stereo, video movie, LCD TV, handy cleaner, portable CD, mini-disc, walkie-talkie, electronic notebook, calculator, memory card, portable tape recorder, radio, motor, lighting equipment, toy, game machine, clock , Power supplies for strobes, cameras, electric bicycles, electric tools, and backup power supplies.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

Example 1
<Preparation of positive electrode>
Porous carbon (manufactured by Toyo Tanso Co., Ltd., Knobell) is used as the positive electrode active material, acetylene black (Denka black powder, manufactured by Denka Co., Ltd.) as the conductive additive, and carboxymethyl cellulose (Daicel 2200, Daicel Chemical Industries) as the thickener. Co., Ltd.) and acrylate latex (TRD202A, manufactured by JSR Co., Ltd.) as a binder are mixed so that the mass% of solid content is 85.0: 6.2: 6.3: 2.5, respectively. The slurry adjusted to an appropriate viscosity by adding water was applied to one side of a 20 μm thick aluminum foil using a doctor blade.
The average weight per unit area (mass of the carbon active material powder in the coated positive electrode) after drying was 3 mg / cm ² . This was punched out to a diameter of 16 mm to obtain a positive electrode.
The porous carbon (manufactured by Toyo Tanso Co., Ltd., Knobel) has a plurality of pores forming a three-dimensional network structure, a BET specific surface area of 1,730 m ² / g, and a pore volume of 2.27 mL / g. It is.

<Production of negative electrode>
Artificial graphite (manufactured by Hitachi Chemical Co., Ltd., MAGD) is used as the negative electrode active material, acetylene black (Denka black powder, manufactured by Denka Co., Ltd.) as the conductive auxiliary agent, SBR system (EX1215, manufactured by Denka Co., Ltd.) as the binder, And carboxymethyl cellulose (Daicel 2200, manufactured by Daicel Chemical Industries, Ltd.) as thickeners were mixed in such a way that the mass percentage of solid content was 90.9: 4.5: 2.7: 1.8, A slurry adjusted to an appropriate viscosity by adding water was applied to one side of a copper foil having a thickness of 18 μm using a doctor blade.
The average weight per unit area (mass of carbon active material powder in the coated positive electrode) after drying was 10 mg / cm ² . This was punched out to a diameter of 16 mm to obtain a negative electrode.

<Separator>
Two separators prepared by punching glass filter paper (GA100, manufactured by ADVANTEC) to a diameter of 16 mm were prepared.

<Non-aqueous electrolyte>
As a non-aqueous electrolyte, a 2 mol / L LiBF ₄ solution was prepared using a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) in a volume ratio of 1: 1: 1. .

<Production of electricity storage element>
After the said positive electrode, the said negative electrode, and the said separator were vacuum-dried at 150 degreeC for 4 hours, the 2032 type coin cell was assembled in the dry argon glove box, and the electrical storage element was obtained.

<Aging process>
The obtained electricity storage device was kept in a constant temperature bath at 40 ° C. for 5 hours, charged to 4.5 V at a 1/5 C rate, then left for 5 hours, and discharged to 1.5 V at a 1/5 C rate ( Aging process). As described above, the nonaqueous electrolytic solution storage element of Example 1 was produced.

(Example 2)
In Example 1, except that 1% by mass of vinylene carbonate (VC, additive A) was added to the nonaqueous electrolytic solution, a power storage device was produced in the same manner as in Example 1, and an aging treatment was performed in the same manner. A non-aqueous electrolyte storage element of Example 2 was produced.

(Example 3)
In Example 1, a power storage device was produced in the same manner as in Example 1 except that 1% by mass of fluoroethylene carbonate (FEC, additive B) was added to the nonaqueous electrolytic solution, and aging treatment was performed in the same manner. Then, a non-aqueous electrolyte storage element of Example 3 was produced.

Example 4
In Example 1, a porous carbon (Toyo Tanso Co., Ltd., Knobel), which is a positive electrode active material, was plasma-treated under a reduced pressure of 40 Pa (treated in an inert gas atmosphere, output 300 W, frequency 13.56 MHz for 30 minutes). A non-aqueous electrolyte electricity storage device of Example 4 was produced in the same manner as in Example 1, except that a battery that had been subjected to the above treatment was produced.
The porous carbon (Toyo Tanso Co., Ltd., Knobel) plasma-treated under a reduced pressure of 40 Pa has a plurality of pores forming a three-dimensional network structure, and has a BET specific surface area of 1,730 m ² / g, The pore volume is 2.27 mL / g.

(Example 5)
A power storage device was produced in the same manner as in Example 4 except that 1% by mass of vinylene carbonate (VC, additive A) was added to the non-aqueous electrolyte using the same positive electrode as in Example 4, and aging was similarly performed. The non-aqueous electrolyte storage element of Example 5 was produced by performing the treatment.

(Example 6)
The electricity storage device of Example 1 was kept in a constant temperature bath at 40 ° C. for 5 hours as an aging treatment, charged to 4.4 V at a 1/5 C rate, then left for 5 hours, and up to 1.8 V at a 1/5 C rate. A nonaqueous electrolyte storage element of Example 6 was produced in the same manner as Example 1 except that the battery was discharged.

(Example 7)
The electricity storage device of Example 5 was kept in a constant temperature bath at 40 ° C. for 5 hours as an aging treatment, charged to 4.7 V at a 1/5 C rate, and then left for 5 hours, to 1.5 V at a 1/5 C rate. A nonaqueous electrolyte storage element of Example 7 was produced in the same manner as Example 5 except that the battery was discharged.

(Example 8)
The electricity storage device of Example 1 was held in a constant temperature bath at 40 ° C. for 5 hours as an aging treatment, charged to 3.5 V at a 1/5 C rate, and then left for 5 hours, to 2.0 V at a 1/5 C rate. A nonaqueous electrolyte storage element of Example 8 was produced in the same manner as Example 1 except that the battery was discharged.

Example 9
The electricity storage device of Example 5 was kept in a constant temperature bath at 40 ° C. for 5 hours as an aging treatment, charged to 5.4 V at a 1/5 C rate, and then left for 5 hours, to 1.5 V at a 1/5 C rate. A nonaqueous electrolyte storage element of Example 9 was produced in the same manner as Example 5 except that the battery was discharged.

(Comparative Example 1)
A nonaqueous electrolyte electricity storage device of Comparative Example 1 was produced in the same manner as Example 1 except that the electricity storage device of Example 1 was kept in a thermostat at 23 ° C. for 5 hours instead of the aging treatment.

  Next, various characteristics of each nonaqueous electrolyte storage element obtained were evaluated as follows. The results are shown in Table 2.

<Confirmation of LiF formation and calculation of SEI ratio on positive electrode surface>
Each power storage element was disassembled after completion of the aging treatment, and the positive electrode was washed with a dimethyl carbonate (DMC) solution. The positive electrode was subjected to surface elemental analysis using X-ray photoelectron spectroscopy (XPS) (Shimadzu Kratos Co., Ltd., AXIS-Ultra) without exposure to the atmosphere. Note that Al monochromatic X-ray was used as an excitation source, measurement output was 105 W, measurement mode was Hybrid mode, and path energy was 20 eV.
Formation of lithium fluoride (LiF) was confirmed by having a peak (F peak) in the range of 685 eV or more and 687 eV or less.
In addition, surface analysis was performed in the same manner for a positive electrode that was not used as a storage element. In the unused positive electrode, the ratio of the positive electrode active material on the surface of the unused positive electrode was calculated from the C peak derived from the positive electrode active material present at 284 eV. From this value, the SEI ratio of the positive electrode surface was calculated by subtracting the ratio of the positive electrode active material on the positive electrode surfaces of Examples 1 to 9 and Comparative Example 1.

<Measurement of initial capacity and capacity maintenance ratio>
Each storage element after the aging treatment was charged to 4.4 V at a 5C rate at 40 ° C., then rested for 5 minutes, and discharged to 1.8 V was repeated 100 times. Using the discharge capacity at the 10th time as the initial capacity value, the capacity retention rate at the 100th time with respect to the initial capacity was calculated.
In addition, the charging / discharging test used the automatic battery evaluation apparatus of 1024B-7V0.1A-4 (made by Electrofield Co., Ltd.).

<Measurement of gas generation amount>
The amount of gas generation was measured for each power storage device using ECC-Press-DL manufactured by EL-CELL. At this time, based on the pressure after completion of the aging treatment, the pressure after repeating the operation of charging to 4.4 V at a 5C rate at 40 ° C., resting for 5 minutes, and discharging to 1.8 V 100 times. Was converted to volume and measured as the amount of gas generated.

  Next, Table 1 summarizes the configuration conditions of the electricity storage elements of Examples 1 to 9 and Comparative Example 1.

From the results of Tables 1 and 2, in Examples 1 to 9, SEI was confirmed on the surface of the positive electrode, and further, a peak derived from LiF expressed at 685 eV to 687 eV by XPS was confirmed. Therefore, lithium fluoride (LiF) It was found that the SEI containing was formed.
In Example 1-9, about the reason why SEI was formed on the positive electrode surface, when Example 1 and Comparative Example 1 having the same electrode configuration were compared, in Example 1, holding at 40 ° C. and charge / discharge as aging treatment As a result, the anion insertion into the positive electrode and the cation insertion into the negative electrode, which are peculiar to the dual intercalation type, occurred, and isolated Li ions and F ions were generated in the electricity storage device. Thus, it is considered that SEI containing LiF was formed.
Focusing on the amount of gas generated, it was found that in Comparative Example 1 in which SEI was not formed on the surface of the positive electrode, a large amount of gas of 320 μL was generated after the 40 ° C. charge / discharge test. On the other hand, in Examples 1-9 in which SEI was formed on the positive electrode surface, it was found that the amount of gas generation could be suppressed without changing the initial capacity and capacity retention rate.
In Example 9, although the gas generation amount was reduced, the initial capacity and the capacity retention rate were reduced. This is presumably because the excessive formation of the solid electrolyte interface (SEI) component on the surface of the positive electrode led to an increase in the resistance of the electricity storage device, which deteriorated the electricity storage device characteristics. In the configuration of the electricity storage device of the present invention, it is considered that a range of 58% or less is preferable as the SEI ratio on the surface of the positive electrode that can obtain the effect of suppressing gas generation without impairing the electricity storage performance. Further, in Example 8 where the SEI ratio on the positive electrode surface is the lowest, the gas generation amount slightly decreased. Thus, it was found that the formation of SEI as a protective film has an effect on the gas generation amount reduction. In Example 1 in which the SEI ratio on the positive electrode surface was 13%, a remarkable gas generation amount reduction was confirmed as compared with Comparative Example 1. Therefore, as the SEI ratio on the positive electrode surface effective in reducing gas generation, From 13% to 58%, it is considered desirable.
In Example 2 and Example 3, addition of additive A or additive B promotes reductive decomposition on the negative electrode surface in the aging treatment, and SEI is also formed on the negative electrode surface. The amount is thought to have decreased.
In particular, in Examples 4 and 5 in which plasma treatment was performed on the positive electrode carbon material, the SEI ratio on the positive electrode surface was particularly high, and a significant gas generation suppression effect was obtained. The reason for this is considered that the plasma treatment of the positive electrode carbon material was effective. As a result of the removal of functional groups on the surface of the carbon material such as carboxyl groups and hydroxyl groups by the plasma treatment, the reaction in which SEI such as lithium fluoride is formed is promoted rather than the decomposition reaction of these functional groups. Conceivable.

  From the above results, in the non-aqueous electrolyte storage element of the dual intercalation type, the positive electrode active material has a plurality of pores forming a three-dimensional network structure, and a solid electrolyte interface (SEI) material is formed on the surface. It has been found that by including the carbon material, it is possible to provide a power storage element capable of suppressing gas generation without deteriorating the characteristics of the power storage element.

Aspects of the present invention are as follows, for example.
<1> A non-aqueous electrolyte storage element having a positive electrode including a positive electrode active material capable of inserting or removing anions, a negative electrode including a negative electrode active material, and a non-aqueous electrolyte,
The non-aqueous electrolyte storage element, wherein the positive electrode active material contains a carbon material having a plurality of pores forming a three-dimensional network structure and having a solid electrolyte interface (SEI) material on the surface. .
<2> The nonaqueous electrolyte storage element according to <1>, wherein the solid electrolyte interface (SEI) substance includes lithium fluoride.
<3> The nonaqueous electrolyte storage element according to any one of <1> to <2>, wherein the positive electrode has a peak in a range of 685 eV to 687 eV by X-ray photoelectron spectroscopy (XPS).
<4> The nonaqueous electrolyte storage element according to any one of <1> to <3>, wherein a solid electrolyte interface (SEI) ratio of the positive electrode surface is 58% or less.
<5> The nonaqueous electrolyte storage element according to any one of <1> to <4>, wherein a solid electrolyte interface (SEI) ratio of the positive electrode surface is 13% to 58%.
<6> The above <1> to <5>, wherein the BET specific surface area of the carbon material is 50 m ² / g or more, and the pore volume of the carbon material is 0.2 mL / g or more and 2.3 mL / g or less. The nonaqueous electrolyte storage element according to any one of the above.
<7> The nonaqueous electrolyte storage element according to any one of <1> to <6>, wherein the pore diameter is 2 nm or more and 50 nm or less.
<8> The nonaqueous electrolyte storage element according to any one of <1> to <7>, wherein the nonaqueous electrolyte contains at least one of LiPF ₆ and LiBF ₄ .
<9> The nonaqueous electrolyte storage element according to any one of <1> to <8>, wherein the nonaqueous solvent contained in the nonaqueous electrolyte is an aprotic organic solvent.
<10> The nonaqueous electrolyte storage element according to <9>, wherein the aprotic organic solvent is a chain carbonate.
<11> The nonaqueous electrolyte storage element according to any one of <1> to <10>, wherein the negative electrode active material is at least one of a carbonaceous material and lithium titanate.
<12> The nonaqueous electrolyte storage element according to any one of <1> to <11>, wherein a separator is provided between the positive electrode and the negative electrode.
<13> The nonaqueous electrolyte storage element according to <12>, wherein the separator has an average thickness of 20 μm to 100 μm.

According to the nonaqueous electrolyte storage element according to any one of <1> to <13>, the conventional problems can be solved and the object of the present invention can be achieved.

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Exterior can 5 Negative electrode lead wire 6 Positive electrode lead wire 10 Nonaqueous electrolyte storage element

Japanese Patent No. 5408509 Japanese Patent No. 4754109 Japanese Patent No. 3128588

Claims (9)

A non-aqueous electrolyte storage element having a positive electrode including a positive electrode active material capable of inserting or removing anions, a negative electrode including a negative electrode active material, and a non-aqueous electrolyte,
The non-aqueous electrolyte storage element, wherein the positive electrode active material contains a carbon material having a plurality of pores forming a three-dimensional network structure and having a solid electrolyte interface (SEI) material on the surface.   The non-aqueous electrolyte storage element according to claim 1, wherein the solid electrolyte interface (SEI) material includes lithium fluoride.   The non-aqueous electrolyte storage element according to claim 1, wherein the positive electrode has a peak in a range of 685 eV to 687 eV by X-ray photoelectron spectroscopy (XPS).   4. The non-aqueous electrolyte storage element according to claim 1, wherein a solid electrolyte interface (SEI) ratio on the surface of the positive electrode is 58% or less.   5. The nonaqueous electrolyte storage element according to claim 1, wherein a solid electrolyte interface (SEI) ratio of the positive electrode surface is 13% or more and 58% or less. The BET specific surface area of the carbon material is 50 m ² / g or more, and the pore volume of the carbon material is 0.2 mL / g or more and 2.3 mL / g or less. Non-aqueous electrolyte storage element. The non-aqueous electrolyte storage element according to claim 1, wherein the non-aqueous electrolyte contains at least one of LiPF ₆ and LiBF ₄ .   The non-aqueous electrolyte storage element according to claim 1, wherein the negative electrode active material is at least one of a carbonaceous material and lithium titanate. The nonaqueous electrolyte storage element according to claim 1, further comprising a separator between the positive electrode and the negative electrode.