JP2021048088A - Non-aqueous electrolyte power storage element - Google Patents

Abstract

To provide a non-aqueous electrolyte power storage element in which an initial inner resistance under a low temperature is reduced even if a non-aqueous electrolyte contains boron inclusion oxalate complex salt, and the non-aqueous electrolyte at a manufacturing has an excellent liquid filling performance.SOLUTION: An aspect of the present invention comprises: a positive electrode; a negative electrode; and a non-aqueous electrolyte, and the non-aqueous electrolyte contains a cyclic carbonate and boron inclusion oxalate complex salt. The cyclic carbonate contains an ethylene carbonate, and a volume ratio of the ethylene carbonate to the cyclic carbonate is 0.30 or more and 0.80 or less.SELECTED DRAWING: None

Description

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

Non-aqueous electrolyte secondary batteries represented by lithium-ion non-aqueous electrolyte secondary batteries are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. due to their high energy density. The non-aqueous electrolyte secondary battery generally includes an electrode body having a pair of electrodes electrically separated by a separator, and a non-aqueous electrolyte interposed between the electrodes, and transfers ions between the two electrodes. It is configured to charge and discharge by doing so. In addition, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as power storage elements other than non-aqueous electrolyte secondary batteries.

Generally, the non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent, and other components are added as necessary. For example, in Patent Document 1, a boron-containing oxalate complex salt is added to a non-aqueous electrolyte solution, and the film formed on the surface of the negative electrode by decomposing the boron-containing oxalate complex salt is formed into a specific composition to form a lithium secondary battery. Techniques have been proposed for improving durability and the effect of suppressing an increase in internal resistance after a charge / discharge cycle.

JP-A-2007-018945

However, the present inventor has found that when a boron-containing oxalate complex salt is contained in a non-aqueous electrolyte, the initial internal resistance of the non-aqueous electrolyte storage element at a low temperature increases. In the non-aqueous electrolyte power storage element, it is required that the initial internal resistance at a low temperature is reduced. When the non-aqueous electrolyte contains a non-aqueous electrolyte that is solid at room temperature, the crystals precipitated in the liquid injection step during the manufacture of the non-aqueous electrolyte power storage element adhere to the liquid injection nozzle to make the non-aqueous electrolyte liquid injectable. There is a risk of deterioration.

The present invention has been made based on the above circumstances, and even if the non-aqueous electrolyte contains a boron-containing oxalate complex salt, the initial internal resistance at low temperature is reduced and the non-aqueous electrolyte is not produced at the time of production. It is an object of the present invention to provide a non-aqueous electrolyte power storage element having good liquid injection property of a water electrolyte.

One aspect of the present invention made to solve the above problems includes a positive electrode, a negative electrode and a non-aqueous electrolyte, the non-aqueous electrolyte containing a cyclic carbonate and a boron-containing oxalate complex salt, and the cyclic carbonate containing an ethylene carbonate. , A non-aqueous electrolyte storage element in which the volume ratio of the ethylene carbonate to the cyclic carbonate is 0.30 or more and 0.80 or less.

According to the present invention, even if the non-aqueous electrolyte contains a boron-containing oxalate complex salt, the initial internal resistance at low temperature is reduced, and the non-aqueous electrolyte has good liquid injection property at the time of production. A power storage element can be provided.

It is an external perspective view which shows the non-aqueous electrolyte power storage element which concerns on one Embodiment of this invention. It is a schematic diagram which shows the power storage device which was configured by gathering a plurality of non-aqueous electrolyte power storage elements in one Embodiment of this invention.

One aspect of the present invention comprises a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the non-aqueous electrolyte contains a cyclic carbonate and a boron-containing oxalate complex salt, the cyclic carbonate contains an ethylene carbonate, and the ethylene carbonate relative to the cyclic carbonate. It is a non-aqueous electrolyte power storage element having a volume ratio of 0.30 or more and 0.80 or less.

Even if the non-aqueous electrolyte storage element contains a boron-containing oxalate complex salt in the non-aqueous electrolyte, the initial internal resistance at low temperature is reduced by containing a predetermined ratio of ethylene carbonate as the cyclic carbonate. The reason for this is not clear, but it can be considered as follows. When the non-aqueous electrolyte contains a boron-containing oxalate complex salt, the flexibility of the coating film formed on the surface of the negative electrode is improved, and it becomes easier to follow the expansion and contraction of the negative electrode due to charging and discharging, and the coating film is stabilized by boron. It is presumed that the non-aqueous electrolyte power storage element can have an effect of suppressing an increase in internal resistance after a charge / discharge cycle. On the other hand, since the film derived from the boron-containing oxalate complex salt has high resistance, it is considered that when such a film is formed on the surface of the negative electrode, the initial internal resistance of the non-aqueous electrolyte storage device at a low temperature increases. In the non-aqueous electrolyte power storage device, by containing ethylene carbonate as a cyclic carbonate in a specific content, an excessive increase in viscosity of the non-aqueous electrolyte is suppressed, and a low resistance film derived from boron-containing oxalate complex salt and ethylene carbonate is formed. Is presumed to be formed on the surface of the negative electrode. Therefore, a non-aqueous electrolyte power storage device in which the initial internal resistance at low temperature is reduced can be obtained.
Further, although the ethylene carbonate is solid at room temperature, the volume ratio of the ethylene carbonate to the cyclic carbonate is 0.30 or more and 0.80 or less, so that in the liquid injection step at the time of manufacturing the non-aqueous electrolyte power storage element. Precipitation of crystals can be suppressed. Therefore, it is possible to suppress a decrease in liquid injection property during manufacturing of the non-aqueous electrolyte power storage element.

The non-aqueous electrolyte preferably further contains lithium tetraborate. Since the non-aqueous electrolyte further contains lithium tetraborate, the initial internal resistance of the non-aqueous electrolyte power storage device at low temperature is further reduced. The reason for this is not clear, but by using the chain lithium tetraborate and the boron-containing oxalate complex salt together, a film derived from lithium tetraborate and a film derived from the boron-containing oxalate complex salt are formed on the surface of the negative electrode in this order. As a result, it is presumed that the resistance of the coating film becomes even lower.

Hereinafter, the non-aqueous electrolyte power storage device according to the embodiment of the present invention will be described in detail.

<Non-aqueous electrolyte power storage element>
The non-aqueous electrolyte power storage device according to the embodiment of the present invention has a positive electrode, a negative electrode, and a non-aqueous electrolyte. Hereinafter, a non-aqueous electrolyte secondary battery will be described as an example of the non-aqueous electrolyte power storage element. The positive electrode and the negative electrode usually form electrode bodies that are alternately superposed by stacking or winding through a separator. The electrode body is housed in a case, and the case is filled with a non-aqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Further, as the above case, a known metal case, resin case or the like which is usually used as a case of a non-aqueous electrolyte secondary battery can be used.

[Positive electrode]
The positive electrode has a positive electrode base material and a positive electrode mixture layer. The positive electrode mixture layer contains a positive electrode active material. The positive electrode mixture layer is laminated directly or via an intermediate layer along at least one surface of the positive electrode base material.

(Positive electrode base material)
The positive electrode base material is a base material having conductivity. As the material of the positive electrode base material, metals such as aluminum, titanium, tantalum, and stainless steel or alloys thereof are used. Among these, aluminum and aluminum alloys are preferable from the viewpoint of balance of potential resistance, high conductivity and cost. Further, examples of the form of the positive electrode base material include foils and thin-film deposition films, and foils are preferable from the viewpoint of cost. That is, aluminum foil is preferable as the positive electrode base material. Examples of aluminum or aluminum alloy include A1085 and A3003 specified in JIS-H4000 (2014). Note that has a "conductive" means that the volume resistivity is measured according to JIS-H-0505 (1975 years) is not more than 1 × 10 ⁷ Ω · cm, "non-conductive "means that the volume resistivity is 1 × 10 ⁷ Ω · cm greater.

(Positive electrode mixture layer)
The positive electrode mixture layer is formed from a so-called positive electrode mixture containing a positive electrode active material. As the positive electrode active material, for example, a known positive electrode active material can be appropriately selected. As the positive electrode active material for a lithium ion secondary battery, a material capable of occluding and releasing lithium ions is usually used. Examples of the positive electrode active material include _{a lithium transition metal composite oxide having an α-NaFeO type 2} crystal structure, a lithium transition metal oxide having a spinel type crystal structure, a polyanion compound, a chalcogen compound, sulfur and the like. Examples of the lithium transition metal composite oxide having an _{α-NaFeO type 2 crystal structure include Li [Li x} Ni _1-x ] O ₂ (0 ≦ x <0.5) and Li [Li _x Ni _γ Co _{(1-). x-γ)} ] O ₂ (0 ≦ x <0.5, 0 <γ <1), Li [Li _x Co _(1-x) ] O ₂ (0 ≦ x <0.5), Li [Li _x Ni _γ Mn _(1-x-γ) ] O ₂ (0 ≦ x <0.5, 0 <γ <1), Li [Li _x Ni _γ Mn _β Co _(1-x-γ-β) ] O ₂ (0 ≦ x <0.5, 0 <γ, 0 <β, 0.5 <γ + β <1), Li [Li _x Ni _γ Co _β Al _(1-x-γ-β) ] O ₂ (0 ≦ Examples thereof include x <0.5, 0 <γ, 0 <β, 0.5 <γ + β <1). Examples of the lithium transition metal oxide having a spinel-type crystal structure include Li _x Mn ₂ O ₄ and Li _x Ni _γ Mn _(2-γ) O ₄ . Examples of the polyanion compound include LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄ F and the like. Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, molybdenum dioxide and the like. The atoms or polyanions in these materials may be partially substituted with atoms or anion species consisting of other elements. The surface of these materials may be coated with other materials. In the positive electrode mixture layer, one of these materials may be used alone, or two or more of these materials may be mixed and used.

The content of the positive electrode active material in the positive electrode mixture layer is not particularly limited, but the lower limit thereof is preferably 50% by mass, more preferably 80% by mass, and even more preferably 90% by mass. On the other hand, as the upper limit of this content, 99% by mass is preferable, and 98% by mass is more preferable.

(Other optional ingredients)
The positive electrode mixture forming the positive electrode mixture layer contains optional components such as a conductive agent, a binder, a thickener, and a filler, if necessary.

The conductive agent is not particularly limited as long as it is a conductive material. Examples of the conductive agent include carbonaceous materials, metals, conductive ceramics and the like. Examples of the carbonaceous material include graphitized carbon, non-graphitized carbon, graphene-based carbon and the like. Examples of non-graphitized carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), and fullerenes. Examples of the shape of the conductive agent include powder and fibrous. As the conductive agent, one of these materials may be used alone, or two or more of these materials may be mixed and used. Further, these materials may be used in combination. For example, a material in which carbon black and CNT are composited may be used. Among these, carbon black is preferable from the viewpoint of electron conductivity and coatability, and acetylene black is particularly preferable.

Examples of the binder include fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), thermoplastic resins such as polyethylene, polypropylene, and polyimide; ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, and styrene. Elastomers such as butadiene rubber (SBR) and fluororubber; polysaccharide polymers and the like can be mentioned.

Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium, it is preferable to deactivate the functional group by methylation or the like in advance.

The filler is not particularly limited. Examples of the main component of the filler include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, and glass.

(Middle layer)
The intermediate layer is a coating layer on the surface of the positive electrode base material, and contains conductive particles such as carbon particles to reduce the contact resistance between the positive electrode base material and the positive electrode mixture layer. The composition of the intermediate layer is not particularly limited, and can be formed by, for example, a composition containing a resin binder and conductive particles.

[Negative electrode]
The negative electrode has a negative electrode base material and a negative electrode mixture layer. The negative electrode mixture layer contains a negative electrode active material. The negative electrode mixture layer is laminated directly or via an intermediate layer along at least one surface of the negative electrode base material.

(Negative electrode base material)
The negative electrode base material is a base material having conductivity. As the material of the negative electrode base material, metals such as copper, nickel, stainless steel and nickel-plated steel or alloys thereof are used, and copper or a copper alloy is preferable. Further, examples of the form of the negative electrode base material include foils and thin-film deposition films, and foils are preferable from the viewpoint of cost. That is, a copper foil is preferable as the negative electrode base material. Examples of the copper foil include rolled copper foil and electrolytic copper foil.

(Negative electrode mixture layer)
The negative electrode mixture layer is laminated directly along at least one surface of the negative electrode base material or via an intermediate layer. The negative electrode mixture layer is formed from a so-called negative electrode mixture containing a negative electrode active material.

As the negative electrode active material, a material capable of occluding and releasing lithium ions is usually used. Specific anode active material, for example Si, a metal or a metalloid such as Sn; Si oxide, Ti oxide, a metal oxide such as Sn oxide or semi-metal _{oxide; Li 4 Ti 5 O 12,} LiTiO _2, TiNb titanium-containing oxide such as ₂ O _7; polyphosphate compound; silicon carbide; non-graphitizable carbon (hard carbon), and the non-graphitic carbon such as easily graphitizable carbon (soft carbon), graphite, etc. Examples include carbon materials. In the negative electrode mixture layer, one of these materials may be used alone, or two or more of these materials may be mixed and used.

The content of the negative electrode active material in the negative electrode mixture layer is not particularly limited, but the lower limit thereof is preferably 50% by mass, more preferably 80% by mass, and even more preferably 90% by mass. On the other hand, as the upper limit of this content, 99% by mass is preferable, and 98% by mass is more preferable.

(Other optional ingredients)
The positive electrode mixture forming the negative electrode mixture layer contains optional components such as a conductive agent, a binder, a thickener, and a filler, if necessary.

The conductive agent, binder, thickener, and filler can be selected from the materials exemplified by the positive electrode.

(Middle layer)
The intermediate layer is a coating layer on the surface of the negative electrode base material, and contains conductive particles such as carbon particles to reduce the contact resistance between the negative electrode base material and the negative electrode mixture layer. Similar to the above positive electrode, the structure of the intermediate layer is not particularly limited, and can be formed by, for example, a composition containing a resin binder and conductive particles.

[Non-aqueous electrolyte]
The non-aqueous electrolyte usually contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. In the non-aqueous electrolyte power storage device according to the present embodiment, the non-aqueous solvent contains a cyclic carbonate. Further, the non-aqueous electrolyte power storage device according to the present embodiment contains a boron-containing oxalate complex salt as an additive.

(Non-aqueous solvent)
The non-aqueous electrolyte contains a cyclic carbonate as a non-aqueous solvent.

<Cyclic carbonate>
The cyclic carbonate contains ethylene carbonate. The lower limit of the volume ratio of the ethylene carbonate to the cyclic carbonate is 0.30, preferably 0.33, more preferably 0.36, still more preferably 0.40, still more preferably 0.45, and 0. .50 is particularly preferred. On the other hand, the upper limit of the volume ratio of the ethylene carbonate is 0.80, preferably 0.78, more preferably 0.76, further preferably 0.74, still more preferably 0.72, and 0.70. Is particularly preferable. When the volume ratio of the ethylene carbonate to the cyclic carbonate is in the above range, the initial internal resistance of the non-aqueous electrolyte power storage element at a low temperature is reduced, and the liquid injection property of the non-aqueous electrolyte during production is good. It becomes.

Cyclic carbonates other than ethylene carbonate (EC) include propylene carbonate (PC), butylene carbonate (BC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), and styrene. Examples thereof include carbonate, catechol carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate and the like. Among these, propylene carbonate, butylene carbonate, vinylethylene carbonate, and propylene carbonate, butylene carbonate, vinylethylene carbonate, which are liquid at room temperature and have low volatility, are liquid from the viewpoint of suppressing crystallization of ethylene carbonate having a melting point higher than normal temperature and improving liquid injection property. Fluorethylene carbonate is preferable, and propylene carbonate having a wide potential window is particularly preferable.

The lower limit of the volume ratio of the cyclic carbonate to the non-aqueous solvent is preferably 10%, more preferably 15%. On the other hand, the upper limit of the volume ratio of the cyclic carbonate is preferably 50%, more preferably 45%. When the volume ratio of the cyclic carbonate to the non-aqueous solvent is in the above range, the dielectric constant can be improved, the solubility of the electrolyte salt can be improved, and the ionic conductivity can be improved.

<Other non-aqueous solvents>
As the other non-aqueous solvent, a known non-aqueous solvent usually used as a non-aqueous solvent for a general non-aqueous electrolyte for a power storage device can be used. Examples of other non-aqueous solvents include chain carbonates, esters, ethers, amides, sulfones, lactones, nitriles and the like. Among these, as the other non-aqueous solvent, it is preferable to use at least a chain carbonate. Examples of the chain carbonate include ethyl methyl carbonate (EMC), ethyl carbonate (DEC), dimethyl carbonate (DMC), diphenyl carbonate and the like. Among these, ethyl methyl carbonate (EMC), ethyl carbonate (DEC), diphenyl carbonate and the like have a low melting point, and coagulation of a non-aqueous electrolyte at an extremely low temperature. Ethyl methyl carbonate is preferable from the viewpoint of suppressing the above.

(Electrolyte salt)
As the electrolyte salt, a known electrolyte salt usually used as an electrolyte salt of a general non-aqueous electrolyte for a power storage element can be used. Examples of the electrolyte salt include lithium salt, sodium salt, potassium salt, magnesium salt, onium salt and the like, but lithium salt is preferable.

Examples of the lithium salt include inorganic lithium salts such _{as LiPF 6} , LiPO ₂ F ₂ , LiBF ₄ , LiClO _{4 , LiSO 3} CF ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiC (SO ₂ C ₂ F ₅ ) _{3, and the} like. Examples thereof include a lithium salt having a hydrocarbon group in which hydrogen is substituted with fluorine. Among these, an inorganic lithium salt is preferable, and LiPF ₆ is more preferable.

As the lower limit of the content of the electrolyte salt in the non-aqueous solution, 0.1 mol / dm ³ is preferable, 0.3 mol / dm ³ is more preferable, 0.5 mol / dm ³ is further preferable, and 0.7 mol / dm ³ is preferable. Especially preferable. On the other hand, the upper limit is not particularly limited, but is preferably 2.5 mol / dm ^3, more preferably 2 mol / dm ^3, more preferably 1.5 mol / dm ^3. The non-aqueous solution means a state in which an electrolyte salt is dissolved in a non-aqueous solvent, and means a state before an additive such as a boron-containing oxalate complex salt is dissolved.

(Boron-containing oxalate complex salt)
The non-aqueous electrolyte contains a boron-containing oxalate complex salt. The oxalate complex salt refers to a salt containing a complex ion having an oxalate ligand. When the non-aqueous electrolyte contains a boron-containing oxalate complex salt, it is possible to have an effect of suppressing an increase in internal resistance of the non-aqueous electrolyte power storage element after a charge / discharge cycle.

Examples of the boron-containing oxalate complex salt include lithium difluorooxalatoborate (LiFOB) represented by the following formula (1), lithium bisoxalatoborate (LiBOB) represented by the following formula (2), and the like.

The lower limit of the content of the boron-containing oxalate complex salt in the non-aqueous electrolyte is preferably 0.01% by mass, more preferably 0.02% by mass, and even more preferably 0.1% by mass. On the other hand, as the upper limit of this content, 3.0% by mass is preferable, 2.0% by mass is more preferable, and 1.0% by mass is further preferable. When the content of the boron-containing oxalate complex salt is in the above range, the effect of suppressing the increase in internal resistance after the charge / discharge cycle can be further improved. Here, the content of the boron-containing oxalate complex salt means the mass of the boron-containing oxalate complex salt with respect to the mass of the non-aqueous solution. When a plurality of types of boron-containing oxalate complex salts are contained, the content of the boron-containing oxalate complex salt means the total mass of the plurality of boron-containing oxalate complex salts with respect to the mass of the non-aqueous solution.

(Lithium tetraborate)
The non-aqueous electrolyte preferably further contains _{lithium tetraborate (Li 2} B ₄ O _7). When the non-aqueous electrolyte further contains lithium tetraborate, the initial internal resistance of the non-aqueous electrolyte power storage element at a low temperature can be further reduced.

The lower limit of the content of lithium tetrabolate in the non-aqueous electrolyte is preferably 0.01% by mass, more preferably 0.10% by mass, and even more preferably 0.30% by mass. On the other hand, as the upper limit of this content, 2.00% by mass is preferable, 1.00% by mass is more preferable, and 0.70% by mass is further preferable. When the content of the lithium tetraborate is in the above range, the initial internal resistance of the non-aqueous electrolyte power storage device at a low temperature can be further reduced.

(Other additives)
In addition to lithium tetraborate, the non-aqueous electrolyte further contains vinylene carbonate, lithium difluorophosphate (LiDFP), 4,4'-bis (2,2-dioxo-1,3,2-dioxathiolane), or a combination thereof. It is preferable to do so. The non-aqueous electrolyte further contains vinylene carbonate, lithium difluorophosphate, 4,4'-bis (2,2-dioxo-1,3,2-dioxathiolane) or a combination thereof, thereby causing Li on the negative electrode. Since the precipitation of dendrite can be suppressed, the initial internal resistance of the non-aqueous electrolyte power storage element at a low temperature can be further reduced.

The lower limit of the content of vinylene carbonate in the non-aqueous electrolyte is preferably 0.05% by mass, more preferably 0.10% by mass. On the other hand, the upper limit of this content is preferably 1.5% by mass, more preferably 1.00% by mass. When the content of vinylene carbonate is in the above range, the initial internal resistance of the non-aqueous electrolyte power storage device at a low temperature can be further reduced.

The lower limit of the content of lithium difluorophosphate in the non-aqueous electrolyte is preferably 0.1% by mass, more preferably 0.2% by mass. On the other hand, the upper limit of this content is preferably 2.0% by mass, more preferably 1.0% by mass. When the content of lithium difluorophosphate is in the above range, the initial internal resistance of the non-aqueous electrolyte power storage device at a low temperature can be further reduced.

The lower limit of the content of 4,4'-bis (2,2-dioxo-1,3,2-dioxathiolane) in the non-aqueous electrolyte is preferably 0.3% by mass, more preferably 0.5% by mass. .. On the other hand, the upper limit of this content is preferably 2.0% by mass, more preferably 1.5% by mass. When the content of 4,4'-bis (2,2-dioxo-1,3,2-dioxathiolane) is in the above range, the initial internal resistance of the non-aqueous electrolyte power storage device at low temperature can be further reduced.

The non-aqueous electrolyte includes the non-aqueous solvent, the electrolyte salt, the boron-containing oxalate complex salt, and any components such as lithium tetraborate, vinylene carbonate, and lithium difluorophosphate, 4,4, as long as the effects of the present invention are not impaired. It may contain other components other than'-bis (2,2-dioxo-1,3,2-dioxathiolane) and the like. Examples of the other components include various additives contained in a general non-aqueous electrolyte for a non-aqueous electrolyte power storage device. However, the content of these other components is preferably 5% by mass or less, more preferably 1% by mass or less.

The non-aqueous electrolyte can be obtained by dissolving any component such as the electrolyte salt, the boron-containing oxalate complex salt, and lithium tetrabolate in the non-aqueous solvent.

[Separator]
As the separator, for example, a woven fabric, a non-woven fabric, a porous resin film, or the like is used. Among these, a porous resin film is preferable from the viewpoint of strength, and a non-woven fabric is preferable from the viewpoint of liquid retention of a non-aqueous electrolyte. As the main component of the separator, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of strength, and polyimide and aramid are preferable from the viewpoint of oxidative decomposition resistance. Moreover, you may combine these resins.

An inorganic layer may be arranged between the separator and the electrode (usually the positive electrode). This inorganic layer is a porous layer also called a heat-resistant layer or the like. Further, a separator having an inorganic layer formed on one surface of the porous resin film can also be used. The inorganic layer is usually composed of inorganic particles and a binder, and may contain other components.

[Specific configuration of power storage element]
FIG. 1 shows a schematic view of a rectangular non-aqueous electrolyte storage element 1 (non-aqueous electrolyte secondary battery), which is an embodiment of the non-aqueous electrolyte storage element according to the present invention. The figure is a perspective view of the inside of the case. In the non-aqueous electrolyte power storage element 1 shown in FIG. 1, the electrode body 2 is housed in the case 3. The electrode body 2 is formed by winding a positive electrode having a positive electrode mixture layer and a negative electrode having a negative electrode mixture layer through a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode current collector 4', and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode current collector 5'. Further, a non-aqueous electrolyte is injected into the case 3.

The configuration of the non-aqueous electrolyte power storage element according to the present invention is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), and a flat battery.

[Manufacturing method of non-aqueous electrolyte power storage element]
In the method for producing a non-aqueous electrolyte power storage element according to an embodiment of the present invention, a step of accommodating a positive electrode and a negative electrode in a case and a non-aqueous electrolyte containing the above-mentioned cyclic carbonate and boron-containing oxalate complex salt are injected into the above case. It is provided with a liquiding process. The positive electrode can be obtained by laminating the positive electrode mixture layer directly on the positive electrode base material or via an intermediate layer. The positive electrode mixture layer is laminated by applying the positive electrode mixture paste to the positive electrode base material. Further, the negative electrode can be obtained by laminating the negative electrode mixture layer directly on the negative electrode base material or via an intermediate layer, similarly to the positive electrode. The negative electrode mixture layer is laminated by applying the negative electrode mixture paste to the negative electrode base material. The positive electrode mixture paste and the negative electrode mixture paste may contain a dispersion medium. As the dispersion medium, for example, an aqueous solvent such as water or a mixed solvent mainly composed of water; an organic solvent such as N-methylpyrrolidone or toluene can be used.

Further, the method for manufacturing the non-aqueous electrolyte power storage element includes, for example, laminating the negative electrode and the positive electrode via a separator as another step. An electrode body is formed by laminating the negative electrode and the positive electrode via a separator.

The method of accommodating the negative electrode and the positive electrode in the case and the method of injecting the non-aqueous electrolyte into the case can be performed by a known method. A non-aqueous electrolyte power storage element can be obtained by sealing the liquid injection port after the liquid injection. Details of each element constituting the non-aqueous electrolyte power storage element obtained by the above manufacturing method are as described above.

According to the method for manufacturing the non-aqueous electrolyte power storage device, the initial internal resistance at low temperature is reduced while having the effect of suppressing the increase in internal resistance after the charge / discharge cycle due to the inclusion of the boron-containing oxalate complex salt. A non-aqueous electrolyte power storage element can be manufactured.

[Other Embodiments]
The non-aqueous electrolyte power storage device of the present invention is not limited to the above embodiment.

Further, in the above embodiment, the embodiment in which the non-aqueous electrolyte power storage element is a non-aqueous electrolyte secondary battery has been mainly described, but other non-aqueous electrolyte power storage elements may be used. Examples of other non-aqueous electrolyte storage elements include capacitors (electric double layer capacitors, lithium ion capacitors) and the like. Examples of the non-aqueous electrolyte secondary battery include a lithium ion non-aqueous electrolyte secondary battery.

Further, although the winding type electrode body is used in the above embodiment, a laminated electrode body formed from a laminated body obtained by stacking a plurality of sheet bodies including a positive electrode, a negative electrode and a separator may be provided.

The present invention can also be realized as a power storage device including a plurality of the above-mentioned non-aqueous electrolyte power storage elements. In this case, the technique of the present invention may be applied to at least one non-aqueous electrolyte power storage element included in the power storage device. Further, an assembled battery can be constructed by using a single or a plurality of non-aqueous electrolyte power storage elements (cells) of the present invention, and a power storage device can be further configured by using the assembled battery. The power storage device can be used as a power source for automobiles such as electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid vehicles (PHEV). Further, the power storage device can be used for various power supply devices such as an engine starting power supply device, an auxiliary power supply device, and an uninterruptible power supply (UPS).

FIG. 2 shows an example of a power storage device 30 in which a power storage unit 20 in which two or more electrically connected non-aqueous electrolyte power storage elements 1 are assembled is further assembled. Even if the power storage device 30 includes a bus bar (not shown) that electrically connects two or more non-aqueous electrolyte power storage elements 1 and a bus bar (not shown) that electrically connects two or more power storage units 20. Good. The power storage unit 20 or the power storage device 30 may include a condition monitoring device (not shown) that monitors the state of one or more power storage elements.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

[Examples 1 to 5, Comparative Examples 1 to 4 and Reference Examples 1 to 2]
(Negative electrode)
A coating liquid (negative electrode mixture paste) containing graphite as a negative electrode active material, styrene-butadiene rubber as a binder, and carboxymethyl cellulose as a thickener and using water as a dispersion medium was prepared. The mixing ratio of the negative electrode active material, the binder, and the thickener was 98: 1: 1 in terms of mass ratio. The coating liquid was applied to both sides of a copper foil base material having a thickness of 10 μm and dried to form a negative electrode mixture layer to obtain negative electrodes of Examples, Comparative Examples, Reference Example 1 and Reference Example 2.
(Non-aqueous electrolyte)
_{LiPF 6} dissolved in 1.4 mol / dm ³ in a non-aqueous solvent in which ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) were mixed at the volume ratios shown in Tables 1 to 3 was dissolved. As a non-aqueous solution, an additive having a content shown in Tables 1 to 3 (content per mass when the mass of the non-aqueous solution was 100) was dissolved to obtain a non-aqueous electrolyte. As the additive, lithium difluorooxalate borate (LiFOB) was used as the boron-containing oxalate complex salt. Other additives include lithium tetraborate (Li ₂ B ₄ O ₇ ), 4,4'-bis (2,2-dioxo-1,3,2-dioxathiolane), vinylene carbonate (VC), lithium difluoroborate (2,2-dioxo-1,3,2-dioxathiolane). LiDFP) was used.
(Positive electrode)
A positive electrode containing NCM (LiNi _0.6 Mn _0.2 Co _0.2 O ₂ ) having an α-NaFeO _{type 2} crystal structure as a positive electrode active material was prepared. The positive electrode contains the above-mentioned positive electrode active material, polyvinylidene fluoride (PVDF) as a binder, and acetylene black as a conductive agent, and uses N-methyl-2-pyrrolidone (NMP) as a dispersion medium. Positive electrode mixture paste) was prepared. The mixing ratio of the positive electrode active material, the binder, and the conductive agent was 93: 3: 4 in terms of mass ratio. The coating liquid was applied to both sides of the positive electrode base material, dried, and pressed to form a positive electrode mixture layer. An aluminum foil having a thickness of 15 μm was used as the positive electrode base material.

(Manufacturing of non-aqueous electrolyte power storage element)
Next, the positive electrode and the negative electrode were laminated via a separator made of a polyethylene base material and an inorganic layer formed on the polyethylene base material to prepare an electrode body. This electrode body was housed in a square electric tank can made of aluminum, and a positive electrode terminal and a negative electrode terminal were attached. After injecting the non-aqueous electrolyte into the inside of this case (square electric tank can), the non-aqueous electrolyte was sealed to obtain the non-aqueous electrolyte power storage elements of Examples, Comparative Examples, Reference Example 1 and Reference Example 2.

[Evaluation]
(Initial internal resistance at low temperature)
The initial internal resistance of the non-aqueous electrolyte power storage device at low temperature was determined as follows. First, the non-aqueous electrolyte power storage elements were constantly charged with a charging current of 1.0 C to a voltage of 50% SOC (State of Charge) in a constant temperature bath at 25 ° C., and then charged at a constant voltage. The charging termination condition was until the total charging time reached 5 hours. After setting the SOC of the non-aqueous electrolyte storage element to 50% under the above conditions, the non-aqueous electrolyte storage element was placed in a constant temperature bath at −10 ° C. and allowed to stand for 5 hours. Next, the current is discharged at the discharge current values of 0.1C, 0.2C, and 0.3C for 10 seconds, and the voltage 10 seconds after the start of discharge is plotted on the vertical axis and the discharge current value is plotted on the horizontal axis. -From the graph of the voltage characteristic, the value of DCR (direct current resistance), which is a value corresponding to the gradient, was obtained. This value was taken as the initial internal resistance at low temperature. As for the reference example, the DCR value at 25 ° C. was also determined by the same method except that the measurement was performed in a constant temperature bath at 25 ° C.

(Presence or absence of crystal precipitation)
As an evaluation of the stability of the non-aqueous electrolyte, the presence or absence of crystal precipitation from the non-aqueous electrolyte was confirmed as follows. In a dry room having a dew point of −40 ° C. to −50 ° C. at room temperature, 100 μL of a non-aqueous electrolyte was added dropwise onto a glass plate and left for 60 minutes. The state of the non-aqueous electrolyte after being left to stand was visually observed to confirm the presence or absence of crystal precipitation.

As a reference example, Table 1 below shows the evaluation results of the effect of the presence or absence of the boron-containing oxalate complex salt in the non-aqueous electrolyte on the initial internal resistance of the non-aqueous electrolyte power storage device at a low temperature. For DCR, the measured values at 25 ° C. and −10 ° C., and the ratio (%) when the measured value of Reference Example 1 is 100% are shown.

Next, Table 2 below shows the effects of the mixing ratio of the non-aqueous solvent on the initial internal resistance of the non-aqueous electrolyte power storage device at low temperatures and the evaluation results of the presence or absence of crystal precipitation. Further, for DCR, the ratio (%) when the measured value at −10 ° C. and the measured value of Comparative Example 1 are set to 100% is shown.

Further, Table 3 below shows the evaluation results of each additive's effect of suppressing the initial internal resistance of the non-aqueous electrolyte power storage device at a low temperature and the presence or absence of crystal precipitation. Further, for DCR, the ratio (%) when the measured value at −10 ° C. and the measured value of Comparative Example 1 are set to 100% is shown.

As shown in Reference Example 1 and Reference Example 2 in Table 1, it can be seen that when the non-aqueous electrolyte contains a boron-containing oxalate complex salt, the initial internal resistance of the non-aqueous electrolyte storage device at a low temperature increases.

As shown in Table 2, in Examples 1 to 3 in which the volume ratio of ethylene carbonate to cyclic carbonate in the non-aqueous electrolyte is 0.30 or more and 0.80 or less, the non-aqueous electrolyte contains a boron-containing oxalate complex salt. It can be seen that the initial internal resistance of the non-aqueous electrolyte power storage element at a low temperature is reduced.
In Comparative Example 4 in which the cyclic carbonate was composed only of ethylene carbonate, the initial internal resistance of the non-aqueous electrolyte storage element at a low temperature was reduced, but when left untreated, the non-aqueous electrolyte changed to ethylene carbonate, or ethylene carbonate and LiPF. Precipitation of crystals presumed to be a complex of _{6 was confirmed.} From this, it is considered that in Comparative Example 4, the liquid injection property may be deteriorated due to the precipitated crystals adhering to the liquid injection nozzle in the liquid injection step at the time of manufacturing the non-aqueous electrolyte power storage element.

As shown in Examples 3 to 5 of Table 3, the non-aqueous electrolyte _{further contains lithium tetrabolate (Li 2} B ₄ O ₇ ), vinylene carbonate (VC) or lithium difluorophosphate (LiDFP) as additives. Then, it can be seen that the initial internal resistance of the non-aqueous electrolyte power storage element at a low temperature is further reduced. In particular, in Example 5 in which the non-aqueous electrolyte contains lithium tetrabolate as an additive, the initial internal resistance of the non-aqueous electrolyte power storage device at a low temperature is remarkably reduced.

As described above, in the non-aqueous electrolyte storage element, even if the non-aqueous electrolyte contains a boron-containing oxalate complex salt, the initial internal resistance at low temperature is reduced, and the non-aqueous electrolyte injection during production is performed. It was shown to be good in sex.

INDUSTRIAL APPLICABILITY The present invention is suitably used as a non-aqueous electrolyte power storage element such as a non-aqueous electrolyte secondary battery used as a power source for personal computers, electronic devices such as communication terminals, automobiles, and the like.

1 Non-aqueous electrolyte power storage element 2 Electrode body 3 Case 4 Positive terminal 4'Positive current collector 5 Negative terminal 5'Negative negative current collector 20 Power storage unit 30 Power storage device

Claims (2)

Equipped with positive electrode, negative electrode and non-aqueous electrolyte,
The non-aqueous electrolyte contains a cyclic carbonate and a boron-containing oxalate complex salt.
The cyclic carbonate contains ethylene carbonate and contains
A non-aqueous electrolyte power storage device in which the volume ratio of the ethylene carbonate to the cyclic carbonate is 0.30 or more and 0.80 or less. The non-aqueous electrolyte power storage element according to claim 1, wherein the non-aqueous electrolyte further contains lithium tetraborate.

Images