JP2023017587A - NONAQUEOUS ELECTROLYTE ELECTRIC STORAGE ELEMENT AND MANUFACTURING METHOD THEREOF - Google Patents

Abstract

To provide a non-aqueous electrolyte storage element that suppresses expansion due to charge/discharge cycles and has a large discharge capacity even after charge/discharge cycles.SOLUTION: A non-aqueous electrolyte storage element includes a positive electrode containing a positive electrode active material containing nickel, cobalt, and manganese, and a non-aqueous electrolyte containing an oxalic acid ester represented by the following formula (1). In the formula (1), R1 is an aryl group having 6 to 10 carbon atoms which is unsubstituted or at least a part of hydrogen atoms are substituted with halogen-free substituents. R2 is a hydrocarbon group having 1 to 10 carbon atoms which has no substituent or at least a part of hydrogen atoms of which are substituted with substituents which do not contain halogen.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte storage element and a method for manufacturing the same.

Non-aqueous electrolyte secondary batteries, typified by lithium ion secondary batteries, are widely used in electronic devices such as personal computers, communication terminals, and automobiles because of their high energy density. A non-aqueous electrolyte secondary battery generally has a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between the electrodes. is configured to be charged and discharged by passing the Capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as non-aqueous electrolyte storage elements other than non-aqueous electrolyte secondary batteries.

Lithium-transition metal composite oxides and the like are widely used as positive electrode active materials for non-aqueous electrolyte storage devices. An oxide containing nickel, cobalt and manganese is known as one of positive electrode active materials that are lithium-transition metal composite oxides (see Patent Document 1).

JP-A-2005-346956

The positive electrode active material containing nickel, cobalt and manganese as described above has an advantage of high discharge capacity. In order to further increase the discharge capacity, the use of a positive electrode active material having a high nickel content among the above positive electrode active materials is also being studied. However, the non-aqueous electrolyte storage element having a positive electrode active material containing nickel, cobalt and manganese has insufficient life characteristics, and the non-aqueous electrolyte storage element tends to expand and decrease in discharge capacity during charge-discharge cycles. have inconvenience.

The present invention has been made based on the above circumstances, and an object thereof is to provide a non-aqueous electrolyte storage element having a positive electrode active material containing nickel, cobalt and manganese, which does not expand due to charge-discharge cycles. An object of the present invention is to provide a non-aqueous electrolyte storage element that is suppressed and has a large discharge capacity even after charge-discharge cycles, and a method for manufacturing such a non-aqueous electrolyte storage element.

（式（１）中、Ｒ^１は、置換基を有さない、又は水素原子の少なくとも一部がハロゲンを含まない置換基で置換されている、炭素数６から１０のアリール基である。Ｒ^２は、置換基を有さない、又は水素原子の少なくとも一部がハロゲンを含まない置換基で置換されている、炭素数１から１０の炭化水素基である。） One aspect of the present invention is a non-aqueous electrolyte power storage element that includes a positive electrode containing a positive electrode active material containing nickel, cobalt, and manganese, and a non-aqueous electrolyte containing an oxalate represented by the following formula (1): be.

(In the formula (1), R ¹ is an aryl group having 6 to 10 carbon atoms and having no substituent or having at least part of the hydrogen atoms substituted with a halogen-free substituent. ² is a hydrocarbon group having 1 to 10 carbon atoms which does not have a substituent or at least a part of hydrogen atoms of which are substituted with a substituent which does not contain halogen.)

（式（１）中、Ｒ^１は、置換基を有さない、又は水素原子の少なくとも一部がハロゲンを含まない置換基で置換されている、炭素数６から１０のアリール基である。Ｒ^２は、置換基を有さない、又は水素原子の少なくとも一部がハロゲンを含まない置換基で置換されている、炭素数１から１０の炭化水素基である。） Another aspect of the present invention is to prepare a positive electrode containing a positive electrode active material containing nickel, cobalt and manganese, and to prepare a non-aqueous electrolyte containing an oxalate represented by the following formula (1): A method for manufacturing a non-aqueous electrolyte storage element comprising:

(In the formula (1), R ¹ is an aryl group having 6 to 10 carbon atoms and having no substituent or having at least part of the hydrogen atoms substituted with a halogen-free substituent. ² is a hydrocarbon group having 1 to 10 carbon atoms which does not have a substituent or at least a part of hydrogen atoms of which are substituted with a substituent which does not contain halogen.)

According to one aspect of the present invention, there is provided a non-aqueous electrolyte power storage element having a positive electrode active material containing nickel, cobalt, and manganese, wherein expansion due to charge-discharge cycles is suppressed and discharge capacity is large even after charge-discharge cycles. It is possible to provide an aqueous electrolyte storage device and a method for manufacturing such a non-aqueous electrolyte storage device.

FIG. 1 is an external perspective view showing a non-aqueous electrolyte storage element according to one embodiment of the present invention. FIG. 2 is a schematic diagram showing a power storage device configured by assembling a plurality of non-aqueous electrolyte power storage elements according to one embodiment of the present invention.

First, an overview of the non-aqueous electrolyte storage element and the method for manufacturing the non-aqueous electrolyte storage element disclosed by the present specification will be described.

（式（１）中、Ｒ^１は、置換基を有さない、又は水素原子の少なくとも一部がハロゲンを含まない置換基で置換されている、炭素数６から１０のアリール基である。Ｒ^２は、置換基を有さない、又は水素原子の少なくとも一部がハロゲンを含まない置換基で置換されている、炭素数１から１０の炭化水素基である。） A non-aqueous electrolyte power storage device according to one aspect of the present invention includes a positive electrode containing a positive electrode active material containing nickel, cobalt and manganese, and a non-aqueous electrolyte containing an oxalate ester represented by the following formula (1). It is a non-aqueous electrolyte storage element provided.

(In the formula (1), R ¹ is an aryl group having 6 to 10 carbon atoms and having no substituent or having at least part of the hydrogen atoms substituted with a halogen-free substituent. ² is a hydrocarbon group having 1 to 10 carbon atoms which does not have a substituent or at least a part of hydrogen atoms of which are substituted with a substituent which does not contain halogen.)

The non-aqueous electrolyte storage element is a non-aqueous electrolyte storage element having a positive electrode active material containing nickel, cobalt and manganese, suppresses expansion due to charge-discharge cycles, and has a large discharge capacity even after charge-discharge cycles. Although the reason why such an effect occurs is not clear, the following reason is presumed. Particles of the positive electrode active material containing nickel, cobalt, and manganese are likely to crack due to repeated charging and discharging, and this cracking is thought to be the main cause of expansion of the non-aqueous electrolyte storage element and reduction in discharge capacity. be done. On the other hand, when a non-aqueous electrolyte containing an oxalate ester represented by the above formula (1) is used, the surface of the positive electrode active material is derived from the oxalate ester, and is characterized by an aryl group possessed by the oxalate ester. It is believed that a film of the origin is formed. In the non-aqueous electrolyte power storage element according to one aspect of the present invention, since such a film is formed on the surface of the positive electrode active material, cracking of the particles of the positive electrode active material containing nickel, cobalt, and manganese is suppressed. , it is presumed that the above effects are exhibited.

The hydrocarbon group having 1 to 10 carbon atoms for R ² is preferably an alkyl group, a cycloalkyl group, an alkenyl group, a cycloalkenyl group or an aryl group. When the hydrocarbon group having 1 to 10 carbon atoms in R ² is one of these groups, the expansion of the non-aqueous electrolyte storage element due to charge-discharge cycles is further suppressed, and the discharge capacity after charge-discharge cycles becomes greater. .

It is preferable that the content of nickel with respect to the total content of nickel, cobalt and manganese in the positive electrode active material is 50 atm % or more. When the content of nickel in the positive electrode active material is increased in this manner, the discharge capacity of the non-aqueous electrolyte storage element can be increased, and the energy density can be increased. On the other hand, particles of a positive electrode active material with a high nickel content are more susceptible to cracking due to repeated charging and discharging, so the improvement effect when one embodiment of the present invention is applied is noticeable.

（式（１）中、Ｒ^１は、置換基を有さない、又は水素原子の少なくとも一部がハロゲンを含まない置換基で置換されている、炭素数６から１０のアリール基である。Ｒ^２は、置換基を有さない、又は水素原子の少なくとも一部がハロゲンを含まない置換基で置換されている、炭素数１から１０の炭化水素基である。） A method for manufacturing a non-aqueous electrolyte storage element according to one aspect of the present invention comprises preparing a positive electrode containing a positive electrode active material containing nickel, cobalt and manganese, and adding an oxalate ester represented by the following formula (1). A method for manufacturing a non-aqueous electrolyte storage element comprising preparing a non-aqueous electrolyte to be contained therein.

(In the formula (1), R ¹ is an aryl group having 6 to 10 carbon atoms and having no substituent or having at least part of the hydrogen atoms substituted with a halogen-free substituent. ² is a hydrocarbon group having 1 to 10 carbon atoms which does not have a substituent or at least a part of hydrogen atoms of which are substituted with a substituent which does not contain halogen.)

According to the manufacturing method, the non-aqueous electrolyte storage element has a positive electrode active material containing nickel, cobalt, and manganese, and the non-aqueous electrolyte is suppressed in expansion due to charge-discharge cycles and has a large discharge capacity even after charge-discharge cycles. A power storage device can be manufactured.

Hereinafter, a non-aqueous electrolyte storage element and a method for manufacturing the non-aqueous electrolyte storage element according to one embodiment of the present invention will be described in order.

<Non-aqueous electrolyte storage element>
A non-aqueous electrolyte storage element according to one embodiment of the present invention has a positive electrode, a negative electrode, and a non-aqueous electrolyte. Hereinafter, a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as a "secondary battery") will be described as an example of a non-aqueous electrolyte storage element. The positive electrode and the negative electrode normally form an electrode assembly alternately stacked or wound with a separator interposed therebetween. This electrode assembly is housed in a container, and the container is filled with a non-aqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Moreover, as a container, a known metal container, resin container, or the like, which is usually used as a container for a secondary battery, can be used.

(positive electrode)
The positive electrode has a positive electrode base material and a positive electrode active material layer disposed directly on the positive electrode base material or via an intermediate layer.

A positive electrode base material has electroconductivity. "Conductive" means that the volume resistivity measured according to JIS-H-0505 (1975) is 10 ⁷ Ω cm or less, and "non-conductive" It means that the volume resistivity is more than 10 ⁷ Ω·cm. Metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof are used as the material of the positive electrode substrate. Among these, aluminum and aluminum alloys are preferable from the viewpoint of the balance between potential resistance, high conductivity and cost. In addition, as a form of forming the positive electrode base material, a foil, a deposited film, and the like can be mentioned, and a foil is preferable from the viewpoint of cost. In other words, aluminum foil is preferable as the positive electrode substrate. Examples of aluminum or aluminum alloy include A1085, A3003, A1N30, etc. defined in JIS-H-4000 (2014) or JIS-H4160 (2006).

The average thickness of the positive electrode substrate is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, even more preferably 8 μm or more and 30 μm or less, and particularly preferably 10 μm or more and 25 μm or less. By setting the average thickness of the positive electrode substrate within the above range, the energy density per volume of the secondary battery can be increased while increasing the strength of the positive electrode substrate. The "average thickness" of the base material refers to a value obtained by dividing the punched mass when a base material having a predetermined area is punched out by the true density and the punched area of the base material. The same applies to the "average thickness" of the negative electrode base material described below.

The intermediate layer is a layer arranged between the positive electrode substrate and the positive electrode active material layer, and contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The structure of the intermediate layer is not particularly limited, and contains, for example, a binder and a conductive agent.

The positive electrode active material layer is a layer formed from a so-called positive electrode mixture containing a positive electrode active material. The positive electrode material mixture forming the positive electrode active material layer may contain optional components such as a conductive agent, a binder, a thickener, and a filler, if necessary.

Positive electrode active materials include positive electrode active materials containing nickel, cobalt and manganese. The content of nickel with respect to the total content of nickel, cobalt and manganese in the positive electrode active material containing nickel, cobalt and manganese may be, for example, 30 atm % or more, preferably 50 atm % or more. On the other hand, the upper limit of the nickel content is, for example, preferably 90 atm%, more preferably 80 atm%, and even more preferably 60 atm%. The lower limit of the content of cobalt with respect to the total content of nickel, cobalt and manganese is preferably 5 atm%, more preferably 10 atm%. On the other hand, the upper limit of the cobalt content is preferably 40 atm %, more preferably 30 atm %. Also, the lower limit of the content of manganese with respect to the total content of nickel, cobalt and manganese is preferably 5 atm%, more preferably 10 atm%. On the other hand, the upper limit of the content of manganese is preferably 70 atm%, more preferably 50 atm%. Energy density can be increased by using a positive electrode active material having such a composition. In addition, when a positive electrode active material having such a composition is used, cracks are likely to occur due to charge/discharge cycles, and the non-aqueous electrolyte storage element tends to swell and the discharge capacity tends to decrease. The advantages of the present invention can be fully enjoyed.

An example of a suitable positive electrode active material is a lithium transition metal composite oxide having a layered crystal structure and containing at least nickel, cobalt and manganese, wherein the moles of Li with respect to the total content of Ni, Co and Mn The ratio (Li/Me) is more than 0 and 1.6 or less, the molar ratio of Ni to the total content of Ni, Co, and Mn (Ni/Me) is 0.3 or more and less than 1, the sum of Ni, Co, and Mn Lithium having a molar ratio of Co to the content (Co/Me) of more than 0 and less than 0.5 and a molar ratio of Mn to the total content of Ni, Co, and Mn (Mn/Me) of more than 0 and less than 0.8 Transition metal composite oxides (lithium-nickel-cobalt-manganese composite oxides) can be mentioned.

In the lithium-transition metal composite oxide, Li/Me is preferably 1 or more, and may be 1. Ni/Me is preferably 0.5 or more and 0.9 or less, and more preferably 0.8 or less or 0.6 or less in some cases. Co/Me is preferably 0.05 or more and 0.4 or less, more preferably 0.1 or more and 0.3 or less. Mn/Me is preferably 0.05 or more and 0.7 or less, more preferably 0.1 or more and 0.5 or less.

Another preferred example of the positive electrode active material (lithium transition metal composite oxide) is Li[Li _x Ni _α Mn _β Co _1-x-α-β ]O ₂ (0≦x<0.5, 0.3≦α<1, 0<β<1, 0<1-x-α-β<1). In the above general formula, 0≤x≤0.6 is preferable, and x=0 may be satisfied. Further, 0.5≦α≦0.9 is preferable, and α≦0.8 or α≦0.6 is more preferable in some cases. 0.05≦β≦0.7 is preferred, and 0.1≦β≦0.5 is more preferred. 0.05≦1-x-α-β≦0.4 is preferred, and 0.1≦1-x-α-β≦0.3 is more preferred.

As the positive electrode active material (lithium transition metal composite oxide), for example, LiNi _3/5 Co _1/5 Mn _1/5 O ₂ , LiNi _1/2 Co _1/5 Mn _3/10 O ₂ , LiNi _1/2 Co _3/10 Mn _1/5 O ₂ , LiNi _8/10 Co _1/10 Mn _1/10 O ₂ , LiNi _3/5 Co _1/5 Mn _1/5 O ₂ and the like.

The composition ratio of the lithium-transition metal composite oxide used in this specification refers to the composition ratio when the battery is completely discharged by the following method. First, the non-aqueous electrolyte storage element (secondary battery) is charged at a constant current of 0.05 C until it reaches the charging end voltage for normal use, and is brought into a fully charged state. After resting for 30 minutes, constant current discharge is performed at a current of 0.05C to the lower limit voltage for normal use. Disassemble, remove the positive electrode, assemble a test battery with a metal lithium electrode as the counter electrode, and discharge at a constant current of 10 mA per 1 g of the positive electrode mixture until the positive electrode potential reaches 3.0 V (vs. Li/Li ⁺ ). to adjust the positive electrode to a fully discharged state. Dismantle again and take out the positive electrode. Using dimethyl carbonate, the non-aqueous electrolyte and the like adhering to the taken-out positive electrode are thoroughly washed and dried at room temperature for a whole day and night. The collected lithium-transition metal composite oxide is subjected to measurement. The work from dismantling the non-aqueous electrolyte storage element to collecting the lithium transition metal composite oxide for measurement is performed in an argon atmosphere with a dew point of -60°C or less.

The positive electrode active material layer may contain a positive electrode active material other than the positive electrode active material containing nickel, cobalt, and manganese. As other positive electrode active materials, various materials conventionally used as positive electrode active materials for lithium ion secondary batteries can be used without particular limitation. (Li _x Mn ₂ O ₄ , Li _x Ni _α Mn _(2-α) O ₄ etc.), polyanion compounds (LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄ F, etc.). Elements or polyanions in these positive electrode active materials may be partially substituted with other elements or anion species. These materials may be coated with other materials on their surfaces.

One type of positive electrode active material may be used alone, or two or more types may be mixed and used. The content ratio of the positive electrode active material containing nickel, cobalt and manganese to all positive electrode active materials is preferably 50% by mass or more, more preferably 70% by mass or more, further preferably 90% by mass or more, and substantially 100% by mass. % is more preferred.

The positive electrode active material usually exists in the form of particles. The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. By making the average particle size of the positive electrode active material equal to or more than the above lower limit, manufacturing or handling of the positive electrode active material becomes easy. By setting the average particle size of the positive electrode active material to the above upper limit or less, the electron conductivity of the positive electrode active material layer is improved. Here, the "average particle size" is based on the particle size distribution measured by a laser diffraction/scattering method for a diluted solution in which the particles are diluted with a solvent in accordance with JIS-Z-8825 (2013). Z-8819-2 (2001) means the value at which the volume-based integrated distribution calculated according to 50%.

A pulverizer, a classifier, or the like is used to obtain particles of the positive electrode active material in a predetermined shape. Pulverization methods include, for example, methods using a mortar, ball mill, sand mill, vibrating ball mill, planetary ball mill, jet mill, counter jet mill, whirling jet mill, or sieve. At the time of pulverization, wet pulverization in which water or an organic solvent such as hexane is allowed to coexist can also be used. As a classification method, a sieve, an air classifier, or the like is used as necessary, both dry and wet.

The content of the positive electrode active material in the positive electrode active material layer is preferably 70% by mass or more and 98% by mass or less, more preferably 80% by mass or more and 97% by mass or less, and even more preferably 90% by mass or more and 96% by mass or less. By setting the content of the positive electrode active material within the above range, the discharge capacity of the secondary battery can be increased.

The conductive agent is not particularly limited as long as it is a conductive material. Such conductive agents include, for example, carbonaceous materials; metals; and conductive ceramics. Carbonaceous materials include graphite, carbon nanofibers, pitch-based carbon fibers, carbon black, graphene-based carbon, and the like. Examples of carbon black include furnace black, acetylene black, and ketjen black. Graphene-based carbon includes graphene, carbon nanotube (CNT), fullerene, and the like. Among these, carbonaceous materials are preferable from the viewpoint of conductivity and coatability. Among them, acetylene black and ketjen black are preferable. Examples of the shape of the conductive agent include powder, sheet, fiber, and the like. As the conductive agent, one type of these materials may be used alone, or two or more types may be mixed and used. Also, these materials may be combined for use. For example, a composite material of carbon black and CNT may be used.

The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more and 40% by mass or less, more preferably 2% by mass or more and 10% by mass or less. By setting the content of the conductive agent within the above range, the energy density of the secondary battery can be increased.

Binders include fluorine resins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), thermoplastic resins such as polyethylene, polypropylene, polyacryl, and polyimide; ethylene-propylene-diene rubber (EPDM), sulfonated EPDM. , styrene-butadiene rubber (SBR), fluororubber, and other elastomers; polysaccharide polymers;

The content of the binder in the positive electrode active material layer is preferably 0.5% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 6% by mass or less. By setting the binder content within the above range, the positive electrode active material can be stably retained.

Examples of thickening agents include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. Moreover, when the thickener has a functional group that reacts with lithium, it is preferable to deactivate the functional group in advance by methylation or the like. In one aspect of the present invention, it may be preferable that the positive electrode active material layer does not contain the thickener.

A filler is not specifically limited. Fillers include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, aluminum oxide, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide and aluminosilicate, magnesium hydroxide, calcium hydroxide, and water. Hydroxides such as aluminum oxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, talc, montmorillonite, boehmite, and zeolite , apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, mica, and other mineral resource-derived substances or artificial products thereof. In one aspect of the present invention, it may be preferable that the positive electrode active material layer does not contain a filler.

The positive electrode active material layer contains typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba, and the like. typical metal elements, transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, W are used as positive electrode active materials, conductive agents, binders, thickeners, fillers It may be contained as a component other than

(negative electrode)
The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed directly on the negative electrode substrate or via an intermediate layer. The intermediate layer of the negative electrode can have the same structure as the intermediate layer of the positive electrode.

The negative electrode substrate can have the same structure as the positive electrode substrate, but as a material, metals such as copper, nickel, stainless steel, nickel-plated steel, alloys thereof, carbonaceous materials, etc. are used. Or a copper alloy is preferable. That is, copper foil is preferable as the negative electrode substrate. Examples of the copper foil include rolled copper foil and electrolytic copper foil.

The average thickness of the negative electrode substrate is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, even more preferably 4 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. By setting the average thickness of the negative electrode substrate within the above range, the energy density per volume of the secondary battery can be increased while increasing the strength of the negative electrode substrate.

The negative electrode active material layer is generally formed from a so-called negative electrode mixture containing a negative electrode active material. In addition, the negative electrode mixture forming the negative electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, a filler, and the like, if necessary. Optional components such as a conductive agent, a binder, a thickener, and a filler can be the same as those used for the positive electrode active material layer. The negative electrode active material layer may be a layer consisting essentially of a negative electrode active material such as metal Li.

The negative electrode active material layer contains typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba, and the like. and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W are used as negative electrode active materials, conductive agents, binders, and thickeners. You may contain as a component other than a sticky agent and a filler.

The negative electrode active material can be appropriately selected from known negative electrode active materials. For example, as a negative electrode active material for lithium ion secondary batteries, a material capable of intercalating and deintercalating lithium ions is usually used. Examples of the negative electrode active material include metal Li; metals or metalloids such as Si and Sn; metal oxides and metalloid oxides such as Si oxide, Ti oxide and Sn oxide; Li ₄ Ti ₅ O ₁₂ ; Titanium-containing oxides such as LiTiO _{2 and} TiNb ₂ O ₇ ; polyphosphate compounds; silicon carbide; carbon materials such as graphite and non-graphitizable carbon (easily graphitizable carbon or non-graphitizable carbon) be done. Among these materials, graphite and non-graphitic carbon are preferred. In the negative electrode active material layer, one type of these materials may be used alone, or two or more types may be mixed and used.

“Graphite” refers to a carbon material having an average lattice spacing (d ₀₀₂ ) of the (002) plane of 0.33 nm or more and less than 0.34 nm as determined by X-ray diffraction before charging/discharging or in a discharged state. Graphite includes natural graphite and artificial graphite. Artificial graphite is preferable from the viewpoint that a material with stable physical properties can be obtained.

“Non-graphitic carbon” refers to a carbon material having an average lattice spacing (d ₀₀₂ ) of the (002) plane of 0.34 nm or more and 0.42 nm or less as determined by X-ray diffraction before charging/discharging or in a discharged state. . Non-graphitizable carbon includes non-graphitizable carbon and graphitizable carbon. Examples of non-graphitic carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, and alcohol-derived materials.

Here, the “discharged state” of the carbon material means a state in which the carbon material, which is the negative electrode active material, is discharged such that lithium ions that can be inserted/extracted are sufficiently released during charge/discharge. For example, in a half-cell using a negative electrode containing a carbon material as a negative electrode active material as a working electrode and metal Li as a counter electrode, the open circuit voltage is 0.7 V or higher.

The term “non-graphitizable carbon” refers to a carbon material having a d ₀₀₂ of 0.36 nm or more and 0.42 nm or less.

“Graphitizable carbon” refers to a carbon material having a d ₀₀₂ of 0.34 nm or more and less than 0.36 nm.

When the form of the negative electrode active material is particles (powder), the average particle size of the negative electrode active material can be, for example, 1 nm or more and 100 μm or less. When the negative electrode active material is, for example, a carbon material, a titanium-containing oxide, or a polyphosphate compound, the average particle size may preferably be 1 μm or more and 100 μm or less, and may be more preferably 3 μm or more and 40 μm or less, further preferably 20 μm or less. . When the negative electrode active material is Si, Sn, Si oxide, Sn oxide, or the like, the average particle size may preferably be 1 nm or more and 1 μm or less. By making the average particle size of the negative electrode active material equal to or larger than the above lower limit, the manufacturing or handling of the negative electrode active material becomes easy. By setting the average particle size of the negative electrode active material to the above upper limit or less, the conductivity of the negative electrode active material layer is improved. A pulverizer, a classifier, or the like is used to obtain powder with a predetermined particle size. The pulverization method and the powder class method can be selected from, for example, the methods exemplified for the positive electrode. Moreover, when the negative electrode active material is a metal such as metal Li, its form may be foil-like or plate-like.

For example, when the negative electrode active material layer is formed of a negative electrode mixture, the content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 98% by mass or less. preferable. By setting the content of the negative electrode active material within the above range, it is possible to achieve both high energy density and manufacturability of the negative electrode active material layer. When the negative electrode active material is a metal such as metal Li, the content of the negative electrode active material in the negative electrode active material layer may be 99% by mass or more, and may be 100% by mass.

(separator)
The separator can be appropriately selected from known separators. As the separator, for example, a separator consisting only of a base material layer, a separator having a heat-resistant layer containing heat-resistant particles and a binder formed on one surface or both surfaces of the base material layer, or the like can be used. The base layer of the separator may contain heat-resistant particles. Examples of the shape of the base layer of the separator include woven fabric, non-woven fabric, and porous resin film. Among these materials, a porous resin film is preferred from the viewpoint of strength, and a non-woven fabric is preferred from the viewpoint of retention of the non-aqueous electrolyte. As the material for the base layer of the separator, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of shutdown function, and polyimide, aramid, and the like are preferable from the viewpoint of oxidative decomposition resistance. A material obtained by combining these resins may be used as the base material layer of the separator.

The heat-resistant particles contained in the heat-resistant layer and the base layer preferably have a mass reduction of 5% or less when the temperature is raised from room temperature to 500 ° C. in an air atmosphere of 1 atm, and the temperature is raised from room temperature to 800 ° C. It is more preferable that the weight loss during heating is 5% or less. An inorganic compound can be given as a material whose mass loss is not more than a predetermined value when the temperature is raised. Inorganic compounds such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, oxides such as aluminosilicate; magnesium hydroxide, calcium hydroxide, water Hydroxides such as aluminum oxide; Nitrides such as aluminum nitride and silicon nitride; Carbonates such as calcium carbonate; Sulfates such as barium sulfate; covalent crystals such as silicon and diamond; mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica; . As the inorganic compound, a single substance or a composite of these substances may be used alone, or two or more of them may be mixed and used. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferable from the viewpoint of the safety of the electric storage device.

The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and preferably 20% by volume or more from the viewpoint of discharge performance. Here, the "porosity" is a volume-based value and means a value measured with a mercury porosimeter.

A polymer gel composed of a polymer and a non-aqueous electrolyte may be used as the separator. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polyethylene carbonate, polypropylene carbonate, polyvinyl carbonate, polyalkyl methacrylates such as polymethyl methacrylate, polyalkyl acrylates such as polymethyl acrylate, polyvinyl ethylene carbonate, polyvinyl Acetate, polyvinylpyrrolidone, polymaleic acid and derivatives thereof, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, etc., copolymers of monomers constituting these polymers, and polymers of these polymers Mixtures are included. Moreover, these polymers may be combined with an inorganic salt or an ionic liquid. The use of polymer gel has the effect of suppressing liquid leakage. As the separator, a polymer gel may be used in combination with the porous resin film or non-woven fabric as described above.

(Non-aqueous electrolyte)
The non-aqueous electrolyte contains oxalic acid ester. A non-aqueous electrolyte is usually a non-aqueous electrolytic solution further containing a non-aqueous solvent and an electrolyte salt dissolved in this non-aqueous solvent. The oxalic acid ester usually exists in a dissolved state in a non-aqueous solvent.

The oxalic acid ester contained in the non-aqueous electrolyte is a compound represented by the following formula (1).

In formula (1), R ¹ is an aryl group having 6 to 10 carbon atoms which is unsubstituted or at least part of hydrogen atoms are substituted with halogen-free substituents. R ² is a hydrocarbon group having 1 to 10 carbon atoms which is unsubstituted or at least part of hydrogen atoms are substituted with halogen-free substituents.

An aryl group having 6 to 10 carbon atoms in which at least part of the hydrogen atoms are substituted with halogen atoms also does not correspond to R ¹ . Similarly, a hydrocarbon group having 1 to 10 carbon atoms in which at least part of the hydrogen atoms are substituted with halogen atoms does not correspond to R ² . Thus, the oxalic acid ester represented by formula (1) does not contain halogen. By including the oxalic acid ester represented by the above formula (1), which is a compound that does not contain halogen, in the non-aqueous electrolyte, the generation of gas accompanying the charge-discharge cycle, and the non-aqueous electrolyte storage element derived from the generation of gas bulge and the like can be suppressed. That is, in the non-aqueous electrolyte storage element according to one embodiment of the present invention, both the generation of gas and cracking of the positive electrode active material particles accompanying charge-discharge cycles are suppressed, and as a result, expansion accompanying charge-discharge cycles is suppressed. is suppressed, and the discharge capacity is large even after charge-discharge cycles.

The aryl group having 6 to 10 carbon atoms for R ¹ includes a phenyl group, a tolyl group, a naphthyl group and the like.

Examples of the substituent that the aryl group having 6 to 10 carbon atoms in R ¹ may have include a hydroxy group, a carboxy group, a cyano group, an alkoxy group and the like.

R ¹ is preferably an unsubstituted aryl group having 6 to 10 carbon atoms. Among unsubstituted aryl groups having 6 to 10 carbon atoms, a phenyl group is more preferred.

The hydrocarbon group having 1 to 10 carbon atoms for R ² includes aliphatic hydrocarbon groups and aromatic hydrocarbon groups having 1 to 10 carbon atoms. Aliphatic hydrocarbon groups include aliphatic chain hydrocarbon groups and aliphatic cyclic hydrocarbon groups.

Examples of aliphatic chain hydrocarbon groups include alkyl groups having 1 to 10 carbon atoms such as methyl, ethyl, propyl, butyl and hexyl groups, and 2 to 10 carbon atoms such as ethenyl (vinyl) and propenyl. 10 alkenyl groups, and alkynyl groups having 2 to 10 carbon atoms such as ethynyl and propynyl groups.

The aliphatic cyclic hydrocarbon group includes a cycloalkyl group having 3 to 10 carbon atoms, preferably 5 to 10 carbon atoms such as cyclopropyl group, cyclobutyl group, cyclohexyl group, cyclooctyl group, cyclopropenyl group, cyclohexenyl group, A cycloalkenyl group having 3 to 10 carbon atoms, preferably 6 to 10 carbon atoms such as a cyclooctenyl group, and a cycloalkynyl group having 6 to 10 carbon atoms, preferably 8 to 10 carbon atoms such as a cyclooctynyl group.

Aromatic hydrocarbon groups include aryl groups having 6 to 10 carbon atoms such as phenyl, tolyl and naphthyl groups.

Examples of the substituent which the hydrocarbon group having 1 to 10 carbon atoms in R ² may have include a hydroxy group, a carboxy group, a cyano group, an alkoxy group and the like.

The hydrocarbon group having 1 to 10 carbon atoms for R ² is preferably an alkyl group, a cycloalkyl group, an alkenyl group, a cycloalkenyl group and an aryl group. That is, R ² is preferably an alkyl group, a cycloalkyl group, an alkenyl group, a cycloalkenyl group, an aryl group, or a group in which at least some of these hydrogen atoms are substituted with a halogen-free substituent. R ² is also preferably an unsubstituted hydrocarbon group having 1 to 10 carbon atoms. Furthermore, R ² is more preferably an alkyl group, a cycloalkyl group, an alkenyl group, a cycloalkenyl group, or an aryl group, all of which are unsubstituted, and more preferably an unsubstituted aryl group. Among unsubstituted aryl groups, a phenyl group is particularly preferred.

When R ¹ and R ² are such groups, the film formed on the surface of the positive electrode active material is considered to be better, and the capacity retention rate of the non-aqueous electrolyte storage element after charge-discharge cycles is further increased. And expansion can be suppressed more.

The oxalic acid ester represented by the above formula (1) is 2-propynylphenyl oxalate (an oxalic acid ester in which R ¹ in formula (1) is a phenyl group and R ² is a 2-propynyl group). preferably other than

The content of the oxalic acid ester represented by the above formula (1) in the non-aqueous electrolyte is preferably 0.1% by mass or more and 5% by mass or less, more preferably 0.3% by mass or more and 3% by mass or less. 0.5% by mass or more and 1% by mass or less is more preferable. By setting the content of the oxalic acid ester represented by the above formula (1) to the above lower limit or more, a sufficient amount of coating is formed on the surface of the positive electrode active material, and the non-aqueous electrolyte storage element expands due to charge-discharge cycles. is further suppressed, and the discharge capacity after charge-discharge cycles becomes larger. On the other hand, by setting the content to the above upper limit or less, excessive film formation on the surface of the positive electrode active material is suppressed, and the discharge capacity of the non-aqueous electrolyte storage element after charge-discharge cycles is increased.

As the non-aqueous solvent, a known non-aqueous solvent that is usually used as a non-aqueous solvent for a general non-aqueous electrolyte for an electric storage device can be used. Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, esters, ethers, amides, sulfones, lactones, nitriles and the like.

As the non-aqueous solvent, it is preferable to use at least a cyclic carbonate or a chain carbonate, and it is more preferable to use a combination of a cyclic carbonate and a chain carbonate. By using a cyclic carbonate, it is possible to promote the dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. By using a chain carbonate, the viscosity of the non-aqueous electrolyte can be kept low. When a cyclic carbonate and a chain carbonate are used together, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate:chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

Cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), styrene carbonate , catechol carbonate, etc. Among them, EC is preferable.

Examples of chain carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), diphenyl carbonate, trifluoroethylmethyl carbonate, bis(trifluoroethyl) carbonate and the like. Among them, EMC and DMC are preferred.

As the electrolyte salt, a known electrolyte salt that is usually used as an electrolyte salt for a general non-aqueous electrolyte for electric storage elements can be used. Examples of electrolyte salts include lithium salts, sodium salts, potassium salts, magnesium salts, onium salts and the like, with lithium salts being preferred.

Lithium salts include inorganic lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ and LiN(SO ₂ F) ₂ , LiSO ₃ CF ₃ , LiN(SO ₂ CF ₃ ) ₂ and LiN(SO ₂ C ₂ F ₅ ). ₂ , LiN( _SO2CF3 )( _SO2C4F9 ) _{, LiC(SO2CF3)3 , LiC ( SO2C2F5 )3 and other lithium salts} having a fluorohydrocarbon group can be mentioned. Among these, inorganic lithium salts are preferred, LiPF ₆ and LiN(SO ₂ F) ₂ are more preferred, and LiPF ₆ is even more preferred.

The content of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol/dm ³ or more and 2.5 mol/dm ³ or less, more preferably 0.3 mol/dm ³ or more and 2.0 mol/dm ³ or less, and 0.5 mol/dm 3 or more and 2.0 mol/dm 3 or less. dm ³ or more and 1.7 mol/dm ³ or less is more preferable, and 0.7 mol/dm ³ or more and 1.5 mol/dm ³ or less is particularly preferable. By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

The non-aqueous electrolyte may contain additives other than the oxalic acid ester represented by the above formula (1). Other additives include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, dibenzofuran; -Partial halides of the above aromatic compounds such as cyclohexylfluorobenzene and p-cyclohexylfluorobenzene; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride ; ethylene sulfite, propylene sulfite, dimethyl sulfite, dimethyl sulfate, ethylene sulfate, sulfolane, dimethylsulfone, diethylsulfone, dimethylsulfoxide, diethylsulfoxide, tetramethylenesulfoxide, diphenylsulfide, 4,4'-bis(2,2-dioxo- 1,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, perfluorooctane, trimethylsilyl borate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphate, tetrakistrimethylsilyl titanate and the like. These additives may be used singly or in combination of two or more.

The content of other additives contained in the nonaqueous electrolyte is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 7% by mass or less, with respect to the entire nonaqueous electrolyte. 0.2% by mass or more and 5% by mass or less is more preferable, and 0.3% by mass or more and 3% by mass or less is particularly preferable. By setting the content of the additive in the above range, it is possible to improve capacity retention performance or charge/discharge cycle performance after high-temperature storage, and further improve safety.

The shape of the non-aqueous electrolyte storage element of the present embodiment is not particularly limited, and examples thereof include cylindrical batteries, rectangular batteries, flat batteries, coin batteries, button batteries, and the like.

FIG. 1 shows a non-aqueous electrolyte storage element 1 as an example of a square battery. In addition, the same figure is taken as the figure which saw through the inside of a container. An electrode body 2 having a positive electrode and a negative electrode wound with a separator sandwiched therebetween is housed in a rectangular container 3 . The positive electrode is electrically connected to the positive electrode terminal 4 via a positive electrode lead 41 . The negative electrode is electrically connected to the negative terminal 5 via a negative lead 51 .

<Configuration of power storage device>
The non-aqueous electrolyte storage element of the present embodiment is a power source for automobiles such as electric vehicles (EV), hybrid vehicles (HEV), and plug-in hybrid vehicles (PHEV), power sources for electronic devices such as personal computers and communication terminals, or electric power It can be installed in a storage power source or the like as a power storage unit (battery module) configured by assembling a plurality of non-aqueous electrolyte power storage elements. In this case, the technology according to one embodiment of the present invention may be applied to at least one non-aqueous electrolyte storage element included in the storage unit.

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. The power storage device 30 includes a bus bar (not shown) electrically connecting two or more non-aqueous electrolyte power storage elements 1, a bus bar (not shown) electrically connecting two or more power storage units 20, and the like. good too. The power storage unit 20 or the power storage device 30 may include a state monitoring device (not shown) that monitors the state of one or more non-aqueous electrolyte power storage elements.

<Method for producing non-aqueous electrolyte storage element>
The electric storage device is preferably manufactured by the following method. That is, a method for manufacturing a non-aqueous electrolyte storage element according to an embodiment of the present invention comprises preparing a positive electrode containing a positive electrode active material containing nickel, cobalt and manganese, and Providing a non-aqueous electrolyte containing the acid ester.

Providing a positive electrode containing a positive electrode active material containing nickel, cobalt and manganese may be preparing a positive electrode containing a positive electrode active material containing nickel, cobalt and manganese. The positive electrode can be produced by a known method using a positive electrode mixture paste containing the positive electrode active material. The positive electrode mixture paste usually contains a binder and a dispersion medium in addition to the positive electrode active material, and further contains other components as necessary. An organic solvent is usually used as the dispersion medium. Examples of the organic solvent include polar solvents such as N-methyl-2-pyrrolidone (NMP), acetone, and ethanol, and nonpolar solvents such as xylene, toluene, and cyclohexane. Polar solvents are preferred, and NMP is more preferred. The positive electrode material mixture paste can be obtained by mixing the components described above. The positive electrode is obtained by applying this positive electrode material mixture paste to the surface of the positive electrode substrate and drying it. In addition, you may prepare a positive electrode by methods other than producing. The specific and preferred form of the positive electrode prepared in the manufacturing method is the same as the positive electrode provided in the non-aqueous electrolyte storage element described above.

Preparing the non-aqueous electrolyte containing the oxalate ester represented by the above formula (1) may be preparing the non-aqueous electrolyte containing the oxalate ester represented by the above formula (1). . The non-aqueous electrolyte can be prepared by mixing each component of the non-aqueous electrolyte. That is, the non-aqueous electrolyte can be obtained by dissolving the components such as the oxalic acid ester represented by the above formula (1) and the electrolyte salt in, for example, a non-aqueous solvent. The non-aqueous electrolyte may be prepared by a method other than preparation. The specific and preferred form of the non-aqueous electrolyte prepared in the manufacturing method is the same as the non-aqueous electrolyte provided in the non-aqueous electrolyte storage element described above.

The manufacturing method usually further comprises providing a negative electrode. Furthermore, the manufacturing method includes, for example, forming an alternately stacked electrode body by laminating or winding the positive electrode and the negative electrode with a separator interposed therebetween, housing the positive electrode and the negative electrode (electrode body) in a container, It may comprise injecting a non-aqueous electrolyte into the container and the like. Usually, the non-aqueous electrolyte is injected into the container after the electrode assembly is placed in the container, but this order may be reversed. After these steps, a non-aqueous electrolyte storage element can be obtained by sealing the injection port. Also, initial charge/discharge may be performed after the injection port is sealed. It is presumed that during initial charging and discharging, some of the components of the non-aqueous electrolyte, such as the oxalic acid ester represented by the above formula (1), are decomposed to form a film on the surface of the positive electrode active material.

<Other embodiments>
The present invention is not limited to the above embodiments, and various modifications may be made without departing from the gist of the present invention. For example, the configuration of another embodiment can be added to the configuration of one embodiment, and part of the configuration of one embodiment can be replaced with the configuration of another embodiment or a known technique. Furthermore, some of the configurations of certain embodiments can be deleted. Also, well-known techniques can be added to the configuration of a certain embodiment.

In the above embodiment, the nonaqueous electrolyte storage element is used as a chargeable/dischargeable nonaqueous electrolyte secondary battery, but the type, shape, size, capacity, etc. of the nonaqueous electrolyte storage element are arbitrary. The non-aqueous electrolyte storage device of the present invention can also be applied to capacitors such as various non-aqueous electrolyte secondary batteries, electric double layer capacitors, and lithium ion capacitors.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples.

[Example 1]
(Preparation of positive electrode)
Using LiNi _1/2 Co _1/5 Mn _3/10 O ₂ as a positive electrode active material particle, acetylene black as a conductive agent, polyvinylidene fluoride as a binder, and N-methyl-pyrrolidone (NMP) as a dispersion medium, a positive electrode mixture was prepared. agent paste was prepared. The mass ratios of the positive electrode active material, conductive agent, and binder were 93% by mass, 4% by mass, and 3% by mass (in terms of solid content), respectively. This positive electrode mixture paste was intermittently applied to both surfaces of an aluminum foil serving as a positive electrode base material, leaving a non-coated portion (positive electrode active material layer non-forming region), and dried to prepare a positive electrode active material layer. After that, roll pressing was performed to obtain a positive electrode.

(Preparation of negative electrode)
A negative electrode mixture paste was prepared using graphite as a negative electrode active material, styrene-butadiene rubber (SBR) as a binder, carboxymethyl cellulose (CMC) as a thickener, and water as a dispersion medium. The graphite used was a mixture of natural graphite and artificial graphite at a mass ratio of 1:1. The mass ratios of the negative electrode active material, the binder, and the thickener were 98% by mass, 1% by mass, and 1% by mass (in terms of solid content), respectively. This negative electrode mixture paste was intermittently applied to both surfaces of a copper foil as a negative electrode base material, leaving a non-coated portion (a negative electrode active material layer non-formation region), and dried to prepare a negative electrode active material layer. After that, roll pressing was performed to obtain a negative electrode.

(Preparation of separator)
A polyethylene microporous film having a thickness of 20 μm was prepared as a separator.

(Preparation of non-aqueous electrolyte)
Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) were mixed at volume ratios of 25% by volume, 5% by volume and 70% by volume, respectively, to obtain solvents. LiPF ₆ was dissolved in this solvent at a concentration of 1.0 mol/dm ³ to prepare a base electrolyte. Furthermore, a non-aqueous electrolyte was prepared by mixing 0.5% by mass of diphenyl oxalate as an oxalic acid ester with respect to 100% by mass of the base electrolyte.

(Preparation of non-aqueous electrolyte storage element)
The positive electrode, the negative electrode, and the separator were laminated and wound in a flat shape. After that, the positive electrode active material layer non-formed region of the positive electrode and the negative electrode active material layer non-formed region of the negative electrode are welded to the positive electrode lead and the negative electrode lead, respectively, and sealed in a rectangular container. A non-aqueous electrolyte was injected and sealed. Thus, the non-aqueous electrolyte storage element of Example 1 was produced.

[Comparative Examples 1 to 4]
Each of the non-aqueous electrolyte storage elements of Comparative Examples 1 to 4 was carried out in the same manner as in Example 1, except that the non-aqueous electrolyte was mixed with the oxalate ester of the type shown in Table 1 or was not mixed with the oxalate ester. got "-" in the table indicates that the corresponding component was not mixed.

[evaluation]
(initial charge/discharge)
Each obtained non-aqueous electrolyte storage element was subjected to constant-current and constant-voltage charging at 25° C. with a charging current of 1 C and a charge termination voltage of 4.25 V. The termination condition of charging was until the total charging time reached 3 hours. A rest period of 10 minutes was then provided. Initial charge/discharge was performed by performing constant current discharge at a discharge current of 1C and a discharge final voltage of 2.75V.

(Charge-discharge cycle test)
The following charge/discharge cycle test was performed on each non-aqueous electrolyte storage element after the initial charge/discharge. At 45° C., constant-current and constant-voltage charging was performed with a charging current of 1 C and a charging end voltage of 4.25 V. The termination condition of charging was until the total charging time reached 3 hours. A rest period of 10 minutes was then provided. Constant current discharge was performed with a discharge current of 1 C and a discharge final voltage of 2.75 V, followed by a rest period of 10 minutes. This charging/discharging was carried out for 700 cycles.

(Measurement of discharge capacity after charge-discharge cycle test)
After the charge-discharge cycle test, each non-aqueous electrolyte storage element was charged and discharged in the same manner as the initial charge-discharge, and the discharge capacity after the charge-discharge cycle test was measured. A relative value was determined using the discharge capacity of the non-aqueous electrolyte storage element of Comparative Example 1, in which the non-aqueous electrolyte does not contain an oxalic acid ester, as a reference (100%). Table 1 shows the results.

(Thickness measurement after charge-discharge cycle test)
The thickness (container thickness) of each non-aqueous electrolyte storage element after the charge-discharge cycle test was measured with a micrometer. A relative value was obtained with the thickness of the non-aqueous electrolyte storage element of Comparative Example 1, in which the non-aqueous electrolyte does not contain an oxalic acid ester, as a reference (100%). Table 1 shows the results.

As shown in Table 1, the non-aqueous electrolyte storage element of Example 1, which includes a non-aqueous electrolyte containing diphenyl oxalate, which is an oxalate ester represented by the above formula (1), is mixed with an oxalate ester. Compared to the non-aqueous electrolyte storage element of Comparative Example 1, which has a non-aqueous electrolyte that does not contain a non-aqueous electrolyte, the thickness after charge-discharge cycles was small and the discharge capacity was large. On the other hand, each of the non-aqueous electrolyte storage elements of Comparative Examples 2 to 4, which includes a non-aqueous electrolyte containing other oxalate ester, is the non-aqueous electrolyte storage element of Comparative Example 1, which includes a non-aqueous electrolyte containing no oxalate ester. Compared with the element, the thickness after the charge/discharge cycle was large, the discharge capacity was small, and conversely, the results were worse. The effect of suppressing the expansion of the non-aqueous electrolyte storage element due to charge-discharge cycles and increasing the discharge capacity even after the charge-discharge cycles is a unique effect that occurs only when the non-aqueous electrolyte contains a specific oxalic acid ester. You can say that.

INDUSTRIAL APPLICABILITY The present invention can be applied to electronic devices such as personal computers and communication terminals, non-aqueous electrolyte storage elements used as power sources for automobiles and the like.

1 Non-aqueous electrolyte storage element 2 Electrode body 3 Container 4 Positive electrode terminal 41 Positive electrode lead 5 Negative electrode terminal 51 Negative electrode lead 20 Storage unit 30 Storage device

Claims (4)

a positive electrode containing a positive electrode active material comprising nickel, cobalt and manganese;
A non-aqueous electrolyte storage element comprising: a non-aqueous electrolyte containing an oxalic acid ester represented by the following formula (1).

(In the formula (1), R ¹ is an aryl group having 6 to 10 carbon atoms and having no substituent or having at least part of the hydrogen atoms substituted with a halogen-free substituent. ² is a hydrocarbon group having 1 to 10 carbon atoms which does not have a substituent or at least a part of hydrogen atoms of which are substituted with a substituent which does not contain halogen.) 2. The nonaqueous electrolyte power storage element according to claim 1, wherein the hydrocarbon group having 1 to 10 carbon atoms in ^R2 is an alkyl group, a cycloalkyl group, an alkenyl group, a cycloalkenyl group or an aryl group. 3. The non-aqueous electrolyte storage element according to claim 1, wherein the content of said nickel relative to the total content of said nickel, cobalt and manganese in said positive electrode active material is 50 atm % or more. Preparing a positive electrode containing a positive electrode active material containing nickel, cobalt and manganese; and preparing a non-aqueous electrolyte containing an oxalate represented by the following formula (1). Production method.

(In the formula (1), R ¹ is an aryl group having 6 to 10 carbon atoms and having no substituent or having at least part of the hydrogen atoms substituted with a halogen-free substituent. ² is a hydrocarbon group having 1 to 10 carbon atoms which does not have a substituent or at least a part of hydrogen atoms of which are substituted with a substituent which does not contain halogen.)

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