Non-aqueous electrolyte for energy storage devices and energy storage devices

Abstract

This nonaqueous electrolytic solution includes a solute, a nonaqueous solvent, an isocyanate component, and a phenol component. The nonaqueous electrolytic solution is used in a power storage device.

Description

[Technical Field]

[0001] The present disclosure relates to a non-aqueous electrolyte for an electricity storage device and an electricity storage device. [Background Art]

[0002] Electricity storage devices such as lithium primary batteries, lithium ion secondary batteries, and lithium secondary batteries (sometimes referred to as lithium metal secondary batteries, etc.) are increasingly being used outdoors. Therefore, electricity storage devices are required to maintain stable characteristics even when exposed to various environments such as high-temperature environments or extremely low-temperature environments such as sub-zero temperatures.

[0003] Patent Document 1 proposes a non-aqueous organic electrolyte for a lithium primary battery, which uses manganese dioxide as a positive electrode active material and lithium metal or a lithium alloy as a negative electrode active material, wherein an organic compound belonging to dicarboxylic acid esters having a chain structure as an additive is added to a basic electrolyte composed of an organic solvent and a supporting salt.

[0004] Patent Document 2 proposes a non-aqueous electrolyte in which a lithium salt is dissolved in a non-aqueous organic solvent, wherein the non-aqueous electrolyte contains a chain carboxylic acid ester in an amount of 5 to 70% by mass relative to the mass of the non-aqueous electrolyte, and further contains a compound having two or more isocyanate groups.

[0005] Patent Document 3 proposes a non-aqueous electrolyte in which a lithium salt is dissolved in a non-aqueous organic solvent, wherein the non-aqueous electrolyte contains at least one chain ester selected from the group of compounds represented by a specific formula in a total amount of 20 to 80% by mass relative to the mass of the non-aqueous electrolyte, further contains an alkanesulfonic anhydride represented by a specific formula, and still further contains a cyclic carbonate having an unsaturated bond or a fluorine atom. [Prior Art Documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Unexamined Patent Publication No. 2016-46027 [Patent Document 2] Japanese Unexamined Patent Publication No. 2013-175369 [Patent Document 3] Japanese Unexamined Patent Publication No. 2013-211224 [Summary of the Invention] [Problem to be Solved by the Invention]

[0007] In an electricity storage device, the output voltage may decrease under a low-temperature environment. When the output voltage of the electricity storage device decreases, a device mounted with the electricity storage device may fail to operate properly. [Means for Solving the Problem]

[0008] A first aspect of the present disclosure relates to a non-aqueous electrolyte solution used for an electricity storage device, comprising a solute, a non-aqueous solvent, an isocyanate component, and a phenol component.

[0009] A second aspect of the present disclosure relates to an electricity storage device comprising a pair of electrodes and a non-aqueous electrolyte solution, wherein the non-aqueous electrolyte solution comprises a solute, a non-aqueous solvent, an isocyanate component, and a phenol component. [Effects of the Invention]

[0010] A non-aqueous electrolyte solution for an electricity storage device and an electricity storage device that can ensure a high output voltage under a low-temperature environment can be provided. [Brief Description of the Drawings]

[0011] [Figure 1] It is a front view with a partial cross-section of an electricity storage device according to an embodiment of the present disclosure. [Mode for Carrying Out the Invention]

[0012] Novel features of the present invention are described in the appended claims, but the present invention, both in terms of structure and content, and in conjunction with other objects and features of the present invention, will be better understood by the following detailed description in conjunction with the drawings.

[0013] The output of an energy storage device is greatly influenced by the progress of the battery reaction at the interface between the electrode and the non-aqueous electrolyte. In particular, under low-temperature conditions, the diffusivity of ions in the non-aqueous electrolyte decreases, making it difficult for the battery reaction at the interface between the electrode and the non-aqueous electrolyte to proceed. Therefore, under low-temperature conditions, the output characteristics of the energy storage device deteriorate, and the decrease in output voltage tends to become significant. If the decrease in output voltage is large, it may not be possible to secure sufficient voltage to operate the equipment on which the energy storage device is installed. Examples of energy storage devices include batteries and capacitors that utilize non-aqueous electrolytes. Examples of energy storage devices include non-aqueous electrolyte batteries or capacitors that utilize lithium ions as charge carriers (also called carrier ions). Examples of such energy storage devices include lithium primary batteries, lithium-ion secondary batteries, lithium secondary batteries, and lithium-ion capacitors.

[0014] In recent years, the adoption of ICT (Information and Communication Technology), including DX (Digital Transformation), has been accelerating. One example of a device that has become widespread as an ICT tool is the smart meter. A smart meter is a device that transmits data on gas or electricity usage, etc. Devices used for such purposes are required to operate continuously for long periods without maintenance. For example, lithium primary batteries are suitable for long-term use because they have a high energy density and low self-discharge.

[0015] Equipment used for the applications described above is often used outdoors and is frequently exposed to various environments, including high and low temperatures. Therefore, energy storage devices such as lithium primary batteries installed in such equipment are required to have a stable output voltage even when exposed to harsh environments such as high or low temperatures.

[0016] When a non-aqueous electrolyte containing isocyanate components is used in an energy storage device, the high reactivity of the isocyanate groups causes a film derived from the isocyanate components to form on the electrode surface. While this film protects the electrode surface and thus suppresses side reactions between the electrode and the non-aqueous solvent, it increases resistance. This increase in resistance is thought to be due to the rapid growth of the film, resulting in the formation of a thick film on the electrode during or in the early stages after battery assembly. Because this film inhibits the charge-discharge reaction, the effect of improving output in low-temperature environments is limited.

[0017] In view of the foregoing, (1) the non-aqueous electrolyte relating to the first aspect of this disclosure comprises a solute, a non-aqueous solvent, an isocyanate component, and a phenol component. Such a non-aqueous electrolyte is used in energy storage devices.

[0018] The disclosure also includes (2) an energy storage device comprising a pair of electrodes and a non-aqueous electrolyte. In the energy storage device, the non-aqueous electrolyte comprises a solute, a non-aqueous solvent, an isocyanate component, and a phenol component.

[0019] In this disclosure, by using a combination of isocyanate and phenol components in a non-aqueous electrolyte, the rapid film formation on the electrode surface can be suppressed by utilizing the reaction between the isocyanate and phenol components. It is presumed that by forming a moderately high-quality film on the electrode surface derived from both the isocyanate and phenol components, the resistance of the film can be kept low while ensuring protection of the electrode surface, thereby ensuring high ionic conductivity. By forming a high-quality film on the electrode, a high output voltage of the energy storage device can be ensured even in low-temperature environments below -20°C (e.g., -30°C). Phenolic hydroxyl groups correspond to tertiary alcohols, and compared to primary or secondary alcohols, their reactivity with isocyanate groups is low due to steric hindrance of the aromatic ring. Therefore, the reaction between the phenol component and the isocyanate component proceeds relatively slowly. Thus, it is considered that by using a phenol component, a protective film with high quality can be formed while ensuring a certain degree of reactivity of the isocyanate group on the electrode.

[0020] Furthermore, compared to using a non-aqueous electrolyte (electrolyte B1) that contains neither isocyanate nor phenol components, using a non-aqueous electrolyte (electrolyte B2) that contains isocyanate but not phenol components improves the output voltage in low-temperature environments, but the effect is very slight. On the other hand, the film-forming ability of the phenol component on the electrode is considered to be low, and when using a non-aqueous electrolyte (electrolyte B3) that contains phenol but not isocyanate, the output voltage in low-temperature environments is lower than when using electrolyte B1. In other words, it can be said that the phenol component itself does not have the effect of improving the output voltage in low-temperature environments. From these findings, it is expected that combining isocyanate and phenol components will not yield much effect in increasing the output voltage in low-temperature environments. However, when isocyanate and phenol components are actually combined, the output voltage in low-temperature environments improves significantly. This is thought to be because the appropriate interaction between the isocyanate and phenol components forms a protective film with excellent film quality derived from both components on the electrode surface, resulting in a synergistic improvement in the output voltage.

[0021] Generally, when an energy storage device is exposed to a high-temperature environment, the reaction between the non-aqueous electrolyte and the electrode becomes more pronounced, making it easier for a film to grow on the electrode and increasing the resistance of the film. If the energy storage device is used in a low-temperature environment after a high-resistance film has formed on the electrode in a high-temperature environment, the output voltage will decrease significantly. In the non-aqueous electrolyte of this disclosure, since an isocyanate component and a phenol component are combined, the resistance of the film formed when the energy storage device is exposed to a high-temperature environment (e.g., during high-temperature storage) can be kept low, and the high ionic conductivity of the film can be easily ensured. Therefore, the decrease in the output voltage of the energy storage device when it is used in a low-temperature environment after being exposed to a high-temperature environment (e.g., after high-temperature storage) can be reduced.

[0022] (3) In (1) or (2) above, the mass ratio of the phenol component to the isocyanate component in the non-aqueous electrolyte (=phenol component / isocyanate component) is 2 × 10 -3 The following is also acceptable.

[0023] (4) In any one of (1) to (3) above, the concentration of the phenol component in the non-aqueous electrolyte may be 10 ppm or less by mass.

[0024] (5) In any one of the above (1) to (4), the concentration of the isocyanate component in the non-aqueous electrolyte may be 10% by mass or less.

[0025] (6) In any one of (1) to (5) above, the isocyanate component may include an isocyanate compound having two or more isocyanate groups.

[0026] (7) In any one of the above (1) to (6), the isocyanate component may include an isocyanate compound containing a ring structure.

[0027] (8) In any one of (1) to (7) above, the phenol component may include a phenol compound having an aromatic ring, at least one phenolic hydroxyl group directly bonded to the aromatic ring, and at least one selected from the group consisting of hydrocarbon groups and alkoxy groups directly bonded to the aromatic ring.

[0028] (9) In (8) above, the phenol compound may have at least an alkyl group as a hydrocarbon group.

[0029] (10) In any one of the above (1) to (9), the solute may include a lithium salt.

[0030] (11) In any one of (1) to (10) above, the energy storage device may be a lithium primary battery comprising a pair of electrodes. One of the pair of electrodes may comprise at least one of metallic lithium and a lithium alloy, and the other electrode may comprise a positive electrode mixture comprising manganese dioxide.

[0031] The non-aqueous electrolyte and energy storage device of this disclosure will be described in more detail below, including items (1) to (11) above. To the extent that it is not technically inconsistent, at least one of items (1) to (11) above may be combined with at least one of the elements described below.

[0032] [Nonaqueous electrolyte] (Isocyanate component) Examples of isocyanate components include isocyanate compounds having an isocyanate group. Typically, isocyanate compounds that dissolve in non-aqueous solvents are used.

[0033] The isocyanate compound may be either an isocyanate compound having one isocyanate group (sometimes referred to as a monoisocyanate compound) or an isocyanate compound having two or more isocyanate groups (sometimes referred to as a polyisocyanate compound). Polyisocyanate compounds readily form a protective film on the electrode surface, as some of the isocyanate groups react with the phenol component, and the remaining isocyanate groups act on the electrode. Therefore, it is preferable that the isocyanate component includes at least a polyisocyanate compound. Polyisocyanate compounds and monoisocyanate compounds may also be used in combination.

[0034] The upper limit of the number of isocyanate groups in the polyisocyanate compound is, for example, 5 or less, and may be 4 or less or 3 or less. The isocyanate component may include at least one selected from the group consisting of diisocyanate compounds having two isocyanate groups and triisocyanate compounds having three isocyanate groups (particularly diisocyanate compounds). In this disclosure, the output voltage in a low-temperature environment can be improved even when the phenol component in the non-aqueous electrolyte is at a very low concentration. Therefore, by using at least one of the diisocyanate compound and the triisocyanate compound (particularly the diisocyanate compound), it becomes easier to balance the reaction with the phenol component and the effect on the electrode, and a protective film with excellent film quality can be formed more easily. For example, the ratio of the diisocyanate compound to the isocyanate component may be, for example, 50% by mass or more, 75% by mass or more, or 90% by mass or more. The ratio of the diisocyanate compound to the isocyanate component is 100% by mass or less.

[0035] The isocyanate compound may be linear or may contain a ring structure. The linear isocyanate compound may be linear or branched. The ring structure may be a hydrocarbon ring or a heterocycle. The ring structure may be an aromatic ring or a non-aromatic ring.

[0036] Aromatic rings may have, for example, 6 to 20 members, or 6 to 10 members. Aromatic rings also include structures (also called bisarene structures) in which multiple aromatic rings, such as biphenyls, bisphenylalkanes, and bisphenyl ethers, are linked by single bonds or primary linking groups (alkylene groups (including alkylidene groups), ether bonds (-O-), etc.). Furthermore, ring structures containing aromatic rings also include ring structures having an aromatic ring and a non-aromatic ring fused to this aromatic ring. Non-aromatic rings include aliphatic hydrocarbon rings and non-aromatic heterocycles. In ring structures, the non-aromatic ring may be a crosslinking ring. Aliphatic hydrocarbon rings also include ring structures corresponding to hydrogenated bisarene structures.

[0037] From the viewpoint of being relatively inexpensive, readily available, and less prone to side reactions, isocyanate compounds containing aromatic or aliphatic hydrocarbon rings, or linear isocyanate compounds may be used.

[0038] In isocyanate compounds containing a ring structure, the isocyanate group may be directly bonded to the ring or bonded to the ring via a secondary linking group. Examples of secondary linking groups include alkylene groups (including alkylidene groups), oxydialkylene groups, and -NH-R- groups (where R is an alkylene group). In the case of an -NH-R- group, the isocyanate group is bonded to R.

[0039] The number of carbon atoms in the alkylene groups of the first and second linking groups, each alkylene group constituting the oxydialkylene group of the second linking group, and the alkylene group represented by R are, for example, 1 to 12, and may be 1 to 10 or 1 to 6.

[0040] In this specification, a heterocycle is a ring that contains a heteroatom (for example, at least one selected from the group consisting of nitrogen, oxygen, and sulfur atoms) as a constituent atom of the ring. The heterocycle may be aromatic or non-aromatic.

[0041] Aromatic isocyanate compounds tend to increase the rate of film formation because the reactivity of the isocyanate group is enhanced by the resonance structure of the aromatic ring. Therefore, it is preferable that the isocyanate component includes at least one selected from the group consisting of chain-like isocyanate compounds (such as aliphatic isocyanate compounds) and isocyanate compounds having an aliphatic ring (such as an aliphatic hydrocarbon ring).

[0042] Isocyanate compounds containing a ring structure tend to yield higher output voltages in low-temperature environments compared with linear isocyanate compounds. Therefore, it is preferable that the isocyanate component includes at least an isocyanate compound containing a ring structure. The isocyanate component may include both an isocyanate compound containing a ring structure and a linear isocyanate compound. As the isocyanate compound containing a ring structure, at least one selected from isocyanate compounds having an aliphatic ring (such as an aliphatic hydrocarbon ring) is preferred, as described above. The ratio of isocyanate compounds containing a ring structure (e.g., an aliphatic ring such as an aliphatic hydrocarbon ring) to the isocyanate component may be 30% by mass or more, 50% by mass or more, or 70% by mass or more. The ratio of isocyanate compounds containing a ring structure (e.g., an aliphatic ring such as an aliphatic hydrocarbon ring) to the isocyanate component is 100% by mass or less.

[0043] Isocyanate compounds include isocyanate compounds having substituents. Isocyanate compounds may have substituents on the main chain, on the side chain, or in the ring structure. Examples of such substituents include hydrocarbon groups (such as saturated hydrocarbon groups like alkyl groups), alkoxy groups, alkoxycarbonyl groups, oxo groups (=O), and halogen atoms (such as fluorine atoms and chlorine atoms). The number of carbon atoms in alkyl and alkoxy groups may be 1 to 6, 1 to 4, or 1 or 2. The number of carbon atoms in an alkoxycarbonyl group may be 2 to 7, 2 to 5, or 2 to 4. Isocyanate compounds may have one substituent or two or more substituents. If an isocyanate compound has two or more substituents, at least two substituents may be the same, or all may be different.

[0044] Examples of monoisocyanate compounds include linear monoisocyanate compounds (alkyl isocyanates, alkoxycarbonyl isocyanates, etc.), monoisocyanate compounds containing aliphatic hydrocarbon rings (cyclohexyl isocyanate, cyclohexylmethyl isocyanate, etc.), and monoisocyanate compounds containing aromatic hydrocarbon rings (phenyl isocyanate, fluorophenyl isocyanate, benzyl isocyanate, etc.). Examples of alkyl isocyanates include alkyl isocyanates with 1 to 10 carbon atoms in the alkyl group (e.g., methyl isocyanate, ethyl isocyanate, propyl isocyanate, butyl isocyanate, pentyl isocyanate, hexyl isocyanate, heptyl isocyanate, octyl isocyanate), and monoisocyanate compounds containing heterocycles. Examples of alkoxycarbonyl isocyanates include alkoxycarbonyl isocyanates in which the alkoxycarbonyl group has 2 to 10 carbon atoms (for example, 2 to 6 carbon atoms) (e.g., methoxycarbonyl isocyanate). Examples of diisocyanate compounds include linear diisocyanate compounds (e.g., alkylene diisocyanates, alkylene diisocyanates having an alkoxycarbonyl group (e.g., lysine diisocyanate)), diisocyanate compounds containing an aliphatic hydrocarbon ring, and diisocyanate compounds containing an aromatic hydrocarbon ring. Examples of alkylene diisocyanates include alkylene diisocyanates in which the alkylene has 2 to 12 (preferably 4 to 10) carbon atoms (e.g., tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, peptamethylene diisocyanate, octamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate).Examples of diisocyanate compounds containing an aliphatic hydrocarbon ring include isophorone diisocyanate, bisisocyanatoalkylcyclohexane [e.g., 1,2-bis(isocyanatomethyl)cyclohexane, 1,3-bis(isocyanatomethyl)cyclohexane, 1,4-bis(isocyanatomethyl)cyclohexane, 1,2-bis(isocyanatoethyl)cyclohexane, 1,3-bis(isocyanatoethyl)cyclohexane, 1,4-bis(isocyanatoethyl)cyclohexane], dicyclohexylmethane-4,4'-diisocyanate, bicyclo[2.2.1]heptane-2,5-diylbis(methylisocyanate), and bicyclo[2.2.1]heptane-2,6-diylbis(methylisocyanate). Examples of diisocyanate compounds containing aromatic hydrocarbon rings include diisocyanatharenes [e.g., phenylenediisocyanate, toluene diisocyanate (2,4-tolylenediisocyanate, 2,6-tolylenediisocyanate, etc.), diisocyanathonaphthalene], diisocyanatoalkylarenes (e.g., xylylenediisocyanate), and isocyanatobisarenes [e.g., bis(4-isocyanatophenyl)methane, 4,4'-diisocyanato-3,3'-dimethylbiphenyl]. Examples of triisocyanate compounds include linear triisocyanate compounds (1,6,11-triisocyanatondecane, lysine triisocyanate, tris(isocyanatohexyl)biuret, etc.), triisocyanate compounds containing aliphatic hydrocarbon rings, and triisocyanate compounds containing non-aromatic heterocycles. Examples of triisocyanate compounds containing non-aromatic heterocycles include triisocyanate compounds having a skeleton derived from isocyanuric acid (such as compounds in which an isocyanatoalkyl group is bonded to the nitrogen atom of isocyanuric acid). The alkyl group of the isocyanatoalkyl group corresponds to the alkylene group of the second linking group.Specific examples of such compounds include 1,3,5-tris(6-isocyanatohexa-1-yl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 1,3,5-tris(6-isocyanatotetra-1-yl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, and 1,3,5-tris(6-isocyanatopenta-1-yl) Examples include triazine-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, tris(6-isocyanatotetra-1-yl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, and tris(6-isocyanatohepta-1-yl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione.

[0045] The isocyanate component may contain one isocyanate compound or two or more isocyanate compounds.

[0046] The concentration of the isocyanate component in the non-aqueous electrolyte is, for example, 15% by mass or less, and may be 12% by mass or less. From the viewpoint of easily securing a higher output voltage in a low-temperature environment, the concentration of the isocyanate component is preferably 11% by mass or less or 10% by mass or less. When the concentration of the isocyanate component is within this range, it is also easier to secure a higher output voltage in a low-temperature environment after high-temperature storage. The concentration of the isocyanate component in the non-aqueous electrolyte may be 0.1% by mass or more, and may be 0.2% by mass or more. From the viewpoint of easily securing a higher output voltage in a low-temperature environment, the concentration of the isocyanate component in the non-aqueous electrolyte is preferably 0.5% by mass or more or 1% by mass or more, and may be 2% by mass or more or 3% by mass or more. These upper and lower limits can be combined arbitrarily. For example, the concentration of the isocyanate component in the non-aqueous electrolyte may be 0.1% by mass or more (or 0.2% by mass or more) and 15% by mass or less, or 0.5% by mass or more and 11% by mass or less (or 10% by mass or less), or 2% by mass or more and 11% by mass or less (or 10% by mass or less). Such concentrations of the isocyanate component are values ​​(in other words, initial values) in the non-aqueous electrolyte used in the assembly of energy storage devices. The concentration of the isocyanate component obtained from the non-aqueous electrolyte collected from the energy storage device may fall within the above range. In energy storage devices, the isocyanate component is consumed for film formation, so for example, the concentration of the isocyanate component in the non-aqueous electrolyte changes during storage or use. Therefore, when analyzing the non-aqueous electrolyte collected from an energy storage device, it is sufficient that the isocyanate component remains in the non-aqueous electrolyte at a concentration above the detection limit. Thus, the upper limit of the concentration of the isocyanate component is within the above range, and the lower limit may be above the detection limit.

[0047] Qualitative and quantitative analysis of isocyanate components can be performed using a non-aqueous electrolyte and gas chromatography-mass spectrometry (GC-MS) under the following conditions. Equipment: GC (Agilent 7890B), MS (Agilent 5977B) Column: Agilent J&W HP-1 (1μm x 60m) manufactured by Agilent Corporation Column temperature: Increase temperature from 50°C to 110°C at a rate of 5°C / min, and hold at 110°C for 12 minutes. Increase temperature from 110°C to 250°C at a rate of 5°C / min, and hold at 250°C for 7 minutes. Increase temperature from 250°C to 300°C at a rate of 10°C / min, and hold at 300°C for 20 minutes. Split ratio: 1 / 50 Linear speed: 25.3cm / sec. Inlet temperature: 270℃ Interface temperature: 230℃ Injection volume: 0.5μL Mass range: m / z=30~400

[0048] (Phenol components) Examples of phenolic components include phenolic compounds (in other words, aromatic hydroxy compounds) that contain an aromatic ring and at least one phenolic hydroxyl group directly bonded to the aromatic ring. Typically, phenolic compounds that dissolve in non-aqueous solvents are used.

[0049] The aromatic ring may be an aromatic heterocycle, but an aromatic hydrocarbon ring is preferred. Aromatic hydrocarbon rings include arene rings, bisarene rings, etc. Examples of arene rings include arene rings having 6 to 20 carbon atoms (benzene rings, naphthalene rings, anthracene rings, phenanthrene rings, etc.). Examples of bisarene rings include ring structures in which the above arene rings (especially benzene rings, naphthalene rings, etc.) are linked via single bonds or third linking groups. The third linking group is selected, for example, from the groups exemplified for the second linking group. Furthermore, aromatic rings also include fused rings of aromatic rings and non-aromatic rings (alicyclic hydrocarbon rings, heterocycles, etc.). From the viewpoint of easily ensuring appropriate reactivity with the isocyanate component, it is preferable that the phenol component includes a phenol compound having a benzene ring as the aromatic ring. In other words, it is preferable that the phenol component includes phenol or its derivatives (such as phenols with substituents) as the phenol compound.

[0050] A phenolic compound may have one phenolic hydroxyl group or two or more. The number of phenolic hydroxyl groups depends on the number of members in the aromatic ring, but it is 4 Tsu The following are also acceptable: 3 Tsu The following may also be the case: The phenol component may include a phenol compound having one or two phenolic hydroxyl groups.

[0051] Phenol compounds may have substituents directly bonded to the aromatic ring. Examples of such substituents include hydrocarbon groups, alkoxy groups, and alkoxycarbonyl groups. Preferred hydrocarbon groups include aliphatic hydrocarbon groups (such as alkyl groups or cycloalkyl groups) that do not have ethylenically unsaturated bonds, and aralkyl groups such as phenylalkyl groups. The number of carbon atoms in each alkyl group and alkoxy group is, for example, 1 to 10, and may be 1 to 6 or 1 to 5. The number of carbon atoms in the alkoxycarbonyl group is, for example, 2 to 12, and may be 2 to 7. The number of carbon atoms in the cycloalkyl group is, for example, 5 to 10, and may be 5 to 8. Specific examples of alkyl groups include methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, neopentyl, sec-pentyl, 3-pentyl, and tert-pentyl groups. Specific examples of alkoxy groups include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, and tert-butoxy groups. Specific examples of alkoxycarbonyl groups include methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, and butoxycarbonyl groups. Examples of aralkyl groups include phenylalkyl groups with 1 to 4 carbon atoms in the alkyl group (such as benzyl, phenethyl, α-methylbenzyl, and α,α-dimethylbenzyl groups). The phenol component preferably contains a phenol compound having an aromatic ring, at least one phenolic hydroxyl group directly bonded to the aromatic ring, and at least one selected from the group consisting of hydrocarbon groups and alkoxy groups directly bonded to the aromatic ring. When the phenol component contains such a phenol compound, appropriate reactivity with the isocyanate component is easily obtained, and a protective film with excellent film quality is easily formed on the electrode surface. The ratio of such phenol compounds to the phenol component is, for example, 50% by mass or more, and may be 75% by mass or more. The ratio of the above phenol compounds shown in the phenol component is 100% by mass or less. The above phenol compound preferably has at least an alkyl group as the hydrocarbon group.

[0052] The phenol compound may optionally have, for example, a hindered group such as a hindered alkyl group, or a phenylalkyl group whose alkyl moiety is a branched alkyl group. Examples of the hindered alkyl group include hindered alkyl groups having 4 to 10 carbon atoms or 4 to 6 carbon atoms (such as tert-butyl group and tert-pentyl group). Examples of the phenylalkyl group include phenylalkyl groups whose alkyl moiety is a branched alkyl group having 2 to 4 carbon atoms (such as α-methylbenzyl group and α,α-dimethylbenzyl group). The phenol compound may optionally have a hindered group and another substituent (for example, at least one selected from the group consisting of linear alkyl groups and alkoxy groups).

[0053] A preferred phenol compound is represented, for example, by the following formula (1).

Chemical Formula

[0054] Specific examples of phenol compounds include monophenol compounds having one phenolic hydroxyl group [e.g., dibutylhydroxytoluene (also known as 2,6-di-tert-butyl-p-cresol), butylhydroxyanisole (2-tert-butyl-4-methoxyphenol, 3-tert-butyl-4-methoxyphenol, or mixtures thereof), mono, di, or tri(α-methylbenzyl)phenol, sesamol, etc.], and phenol compounds having two or more phenolic hydroxyl groups (bisphenol compounds, polyphenol compounds having multiple hydroxyl groups on one aromatic ring, etc.). Examples of bisphenol compounds include 2,2'-methylenebis(4-methyl-6-tert-butylphenol) and 4,4'-butylidenebis(3-methyl-6-tert-butylphenol). Examples of polyphenol compounds include hydroquinone, resorcinol, catechol, pyrogallol, 2,5-di-tert-butylhydroquinone, 2,5-di-tert-amylhydroquinone, and propyl gallate.

[0055] The phenol component may contain one type of phenol compound, or it may contain two or more types.

[0056] From the viewpoint of easily obtaining appropriate reactivity with isocyanate components and easily forming a protective film with excellent film quality on the electrode surface, it is preferable that the phenol component contains at least a monophenol compound. Specifically, such a monophenol compound is a monophenol compound in which the aromatic ring is a benzene ring, and in particular, in formula (1), R 1 ~R 5 A monophenol compound is preferred in which each of the elements is a hydrogen atom or a substituent. The ratio of the monophenol compound to the phenol component is, for example, 30% by mass or more, may be 50% by mass or more, or 75% by mass or more. The ratio of the monophenol compound to the phenol component is 100% by mass or less.

[0057] Even when present in very low concentrations in the non-aqueous electrolyte, the phenol component acts on the isocyanate component to form a protective film with excellent film quality on the electrode surface. The concentration of the phenol component in the non-aqueous electrolyte is, for example, 200 ppm or less by mass, and may be 150 ppm or less. From the viewpoint of easily securing a higher output voltage in a low-temperature environment, the concentration of the phenol component is preferably 30 ppm or less or 20 ppm or less by mass, more preferably 10 ppm or less, and may be 8 ppm or less. When the concentration of the phenol component is within this range, it is also easier to secure a higher output voltage in a low-temperature environment after high-temperature storage. The concentration of the phenol component in the non-aqueous electrolyte may be 0.001 ppm or more by mass, and may be 0.01 ppm or more. These upper and lower limits can be arbitrarily combined. For example, the concentration of the phenol component in the non-aqueous electrolyte may be between 0.001 ppm and 200 ppm (or 150 ppm or less) by mass, between 0.001 ppm and 10 ppm (or 8 ppm or less), or between 0.01 ppm and 10 ppm (or 8 ppm or less). Such concentrations of the phenol component are values ​​(in other words, initial values) in the non-aqueous electrolyte used in the assembly of energy storage devices. The concentration of the phenol component obtained from the non-aqueous electrolyte sampled from an energy storage device may also fall within the above range. In energy storage devices, the phenol component is consumed together with the isocyanate component for film formation, so the concentration of the phenol component in the non-aqueous electrolyte changes, for example, during storage or use. Therefore, when analyzing the non-aqueous electrolyte sampled from an energy storage device, it is sufficient that the phenol component remains in the non-aqueous electrolyte at a concentration above the detection limit. Thus, the upper limit of the phenol component concentration is within the above range, and the lower limit may be above the detection limit.

[0058] The mass ratio of the phenol component to the isocyanate component (=phenol component / isocyanate component) is 2 × 10⁻⁶ -3 The following is true: 1.5 × 10 -3 The following is also acceptable: From the viewpoint of easily securing a higher output voltage in low-temperature environments, the mass ratio of the phenol component / isocyanate component should be 1 × 10⁻⁶.-3 The following is preferable: 0.7 × 10 -3 The following or 0.5 × 10 -3 The following is more preferable: The mass ratio of the phenol component to the isocyanate component is 0.3 × 10⁻⁶. -3 The following is also acceptable. In this case, it is easier to ensure a higher output voltage in a low-temperature environment after high-temperature storage. The mass ratio of the phenol component / isocyanate component is, for example, 0.001 × 10⁻⁶. -3 It may be greater than or equal to 0.002 × 10 -3 The above values ​​may also be used. These upper and lower limits can be combined arbitrarily. The mass ratio of the phenol component to the isocyanate component is, for example, 0.001 × 10⁻⁶. -3 The above 2 x 10 -3 The following (or 1.5 × 10 -3 Below), 0.001 × 10 -3 The above 1 x 10 -3 The following (or 0.5 × 10 -3 (Below), or 0.001 × 10 -3 The above is 0.3 × 10 -3 The following is also acceptable.

[0059] Qualitative and quantitative analysis of phenol components can be performed using a non-aqueous electrolyte and GC-MS under the same conditions as for the analysis of isocyanate components.

[0060] (Non-aqueous solvent) Examples of non-aqueous solvents include ethers, esters (such as carboxylic acid esters), and carbonate esters. These may be linear or cyclic compounds. Examples of linear ethers include dimethyl ether and 1,2-dimethoxyethane (DME). Examples of cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of linear carboxylic acid esters include formate esters (such as ethyl formate), acetate esters (such as methyl acetate, ethyl acetate, and propyl acetate), and propionic acid esters (such as methyl propionate, ethyl propionate, and methyl fluoropropionate). Examples of cyclic carboxylic acid esters include γ-butyrolactone and γ-valerolactone. Examples of linear carbonate esters include diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate. Examples of cyclic carbonate esters include propylene carbonate (PC) and ethylene carbonate (EC). The non-aqueous electrolyte may contain one non-aqueous solvent, or a combination of two or more non-aqueous solvents.

[0061] From the viewpoint of improving the discharge characteristics of the energy storage device, the non-aqueous solvent preferably contains a cyclic carbonate ester with a high boiling point and a chain ether with low viscosity at low temperatures. The cyclic carbonate ester preferably contains at least one selected from the group consisting of PC and EC. The chain ether preferably contains, for example, DME.

[0062] (solute) Examples of solutes include salts of cations (carrier ions) that act as charge carriers in non-aqueous electrolytes and anions that are counterions of cations. For example, in energy storage devices where lithium ions are used as carrier ions (such as lithium primary batteries, lithium-ion secondary batteries, lithium-ion capacitors, etc.), lithium salts are used as solutes. The solute of a non-aqueous electrolyte may also contain lithium salts.

[0063] Examples of lithium salts include LiClO4, LiBF4, LiPF6, and LiR a SO3 (e.g., LiCF3SO3), LiFSO3, imide salts (LiN(SO2R) b )(SO2R c ), LiN(FSO2)2, etc.), LiC(SO2R d )(SO2R e )(SO2R f Examples include LiPO2F2 and oxalate complex salts. a ~R f Each of these is an alkyl fluoride. The number of carbon atoms in the alkyl fluoride is, for example, 1 to 12, and may be 1 to 6 or 1 to 4. b and R c These may be the same (e.g., LiN(CF3SO2)2, LiN(C2F5SO2)2) or different (e.g., LiN(CF3SO2)(C4F9SO2)). d ~R f At least two of these may be the same, and all may be different. Examples of oxalate complex salts include bisoxalate borate lithium (LiB(C2O4)2), LiBF2(C2O4), LiPF4(C2O4), and LiPF2(C2O4)2. Examples of lithium salts include LiAlCl4, LiAlF4, LiAsF6, LiSbF6, LiTaF6, LiNbF6, LiSiF6, LiCH3BF3, LiCN, LiSCN, LiCF3CO2, and LiB 10 Cl 10 LiNO3, LiNO2, lithium lower aliphatic carboxylates, lithium halides (such as LiCl), and borates (such as lithium bis(1,2-benzenediolate(2-)-O,O')borate) may be used. The non-aqueous electrolyte may contain one lithium salt or a combination of two or more. The lithium salt is selected, for example, depending on the type of energy storage device and the components contained in the electrodes.

[0064] (others) The concentration of the solute (or carrier ion) contained in the non-aqueous electrolyte may be, for example, between 0.1 mol / L and 3.5 mol / L. The solute concentration is selected according to, for example, the type and capacity of the energy storage device. For example, in a lithium primary battery, the solute concentration may be within the above range, or it may be between 0.2 mol / L and 2.0 mol / L.

[0065] The non-aqueous electrolyte may contain additives other than isocyanate and phenol components, as needed. Examples of additives include propanesultone, propensultone, ethylene sulfate, tristrimethylsilyl phosphite, tristrimethylsilyl phosphate, vinylene carbonate, fluoroethylene carbonate, vinylethylene carbonate, adiponitrile, and succinonitrile. The total concentration of such additives in the non-aqueous electrolyte is, for example, 5 mol / L or less. The total concentration of additives may be 0.003 mol / L or higher. Furthermore, even if the non-aqueous electrolyte does not contain alkanesulfonic anhydrides or its concentration is less than 0.001% by mass, a high output voltage can still be ensured. Alkanesulfonic anhydrides include, for example, alkanesulfonic anhydrides that may contain fluorine atoms and alkanedisulfonic anhydrides that may contain fluorine atoms.

[0066] Depending on the type of energy storage device, the non-aqueous electrolyte may, if necessary, be a non-flowing gel electrolyte in which a gelling agent or matrix material is combined with the non-aqueous electrolyte.

[0067] [Energy storage devices] The energy storage device includes a pair of electrodes and a non-aqueous electrolyte. The non-aqueous electrolyte used is the one described above. The components of the energy storage device other than the non-aqueous electrolyte are described in more detail below.

[0068] One electrode of a pair is capable of electrochemically dissolving or releasing carrier ions (such as lithium ions), while the other electrode is capable of electrochemically depositing or intercepting carrier ions (such as lithium ions). In this specification, the ability to intercept carrier ions also includes the ability to adsorb carrier ions. In a secondary battery or capacitor, each electrode is capable of electrochemically dissolving and depositing carrier ions, or electrochemically releasing and intercepting (or desorbing and adsorbing) carrier ions. Each electrode may contain an active material having such a function.

[0069] Isocyanate components tend to act on active materials or conductive agents contained in electrodes to form a protective film. In particular, when the electrode contains at least one element selected from the group consisting of lithium (Li), silicon (Si), and carbonaceous materials, the isocyanate components contained in the non-aqueous electrolyte readily act on the Li, Si, or carbonaceous materials in the electrode to form a film with excellent film quality derived from the isocyanate and phenol components. Furthermore, when the electrode contains polyvalent metals with an oxidation state of 2 or higher (such as at least one element selected from the group consisting of manganese (Mn), nickel (Ni), and cobalt (Co)), the isocyanate groups readily act on these elements contained in the electrode to provide a protective effect. Therefore, in energy storage devices using electrodes containing at least one element selected from the group consisting of Li, Si, and carbonaceous materials; energy storage devices using electrodes containing at least one element selected from the group consisting of Mn, Ni, and Co; or energy storage devices in which one electrode contains at least one element selected from the group consisting of Li, Si, and carbonaceous materials, and the other electrode contains at least one element selected from the group consisting of Mn, Ni, and Co, the effect of suppressing the decrease in output voltage in low-temperature environments when using the above-mentioned non-aqueous electrolyte is particularly significant. Examples of carbonaceous materials include graphite materials, carbon black, and activated carbon. Examples of energy storage devices using such electrodes include lithium primary batteries, lithium-ion secondary batteries, lithium secondary batteries, and lithium-ion capacitors. The non-aqueous electrolyte of this disclosure is particularly suitable for use in these energy storage devices. In lithium secondary batteries, the negative electrode may initially contain only a current collector, but during charging, the isocyanate component acts on the metallic lithium deposited on the current collector to form a film with excellent film quality derived from the isocyanate component and phenol component.

[0070] (One electrode) In an energy storage device, one electrode may be, for example, a negative electrode. The other electrode may be, for example, a positive electrode. The configuration of each electrode is determined, for example, according to the type of energy storage device.

[0071] (Negative electrode) In lithium primary batteries, the negative electrode only needs to contain metallic lithium or a lithium alloy, and metallic lithium and lithium alloy It may contain both. A composite of metallic lithium and a lithium alloy may also be used.

[0072] Lithium alloys may contain elements other than lithium, such as aluminum, tin, silicon, magnesium, indium, lead, and zinc. Examples of lithium alloys include Li-Al alloys, Li-Sn alloys, Li-Ni-Si alloys, Li-Pb alloys, Li-Mg alloys, Li-Zn alloys, Li-In alloys, and Li-Al-Mg alloys. The content of metallic elements other than lithium in the lithium alloy may be between 0.05% by mass and 15% by mass, from the viewpoint of ensuring discharge capacity and stabilizing internal resistance.

[0073] Lithium metal, lithium alloys, or composites thereof are molded into any shape and thickness depending on the shape, dimensions, and performance specifications of the lithium primary battery.

[0074] In the case of coin-type batteries, a hoop-shaped piece of metallic lithium or lithium alloy may be punched out into a disc shape and used as the negative electrode. In the case of cylindrical batteries, a sheet of metallic lithium or lithium alloy may be used as the negative electrode. The sheet can be obtained, for example, by extrusion molding.

[0075] In both lithium-ion secondary batteries and lithium-ion capacitors, the negative electrode includes a negative electrode active material capable of intercalating and releasing lithium ions or dissolving or depositing lithium ions. The negative electrode may also include a negative electrode current collector that holds the negative electrode active material. The negative electrode may, for example, include a negative electrode mixture containing the negative electrode active material and a negative electrode current collector that holds the negative electrode mixture. Examples of negative electrode active materials include lithium metal, lithium alloys, carbonaceous materials (graphite materials, soft carbon, hard carbon, amorphous carbon, etc.), Si-containing materials (elemental Si, Si alloys, and Si compounds (oxides, nitrides, carbides, etc.)), Sn-containing materials (elemental Sn, Sn alloys, and Sn compounds, etc.). The negative electrode may contain one type of negative electrode active material or two or more types. From the viewpoint of easily forming a film with excellent film quality derived from isocyanate and phenol components, a negative electrode may be used that contains a negative electrode active material that includes at least one selected from the group consisting of Li element, Si element (such as Si-containing material), and carbonaceous material. In addition to the negative electrode active material, the negative electrode mixture may also contain a binder (such as fluororesin, olefin resin, polyamide resin, polyimide resin, acrylic resin, or rubbery polymer), a thickener (such as carboxymethylcellulose or its salt), a conductive agent (such as carbon black or carbon fiber), etc. The negative electrode can be formed, for example, by applying a paste containing the materials of the negative electrode mixture to a negative electrode current collector. The negative electrode may also be formed by depositing the negative electrode active material onto the negative electrode current collector.

[0076] In lithium secondary batteries, the negative electrode includes a current collector. Examples of current collectors include conductive sheets formed from conductive materials other than lithium metal and lithium alloys. At least one of a negative electrode composite layer and a lithium-containing layer (also referred to as a base layer) may be formed on the surface of the current collector. The negative electrode composite layer is formed, for example, by applying a paste containing negative electrode active material to at least a portion of the surface of the negative electrode current collector. The base layer is a pre-prepared layer containing metallic lithium or a lithium alloy. The lithium alloy may contain, in addition to lithium, at least one element selected from the group consisting of, for example, aluminum, magnesium, indium, and zinc. From the viewpoint of easily forming a film with excellent film quality derived from isocyanate and phenol components, a negative electrode including a lithium-containing base layer may be used.

[0077] (positive electrode) The positive electrode includes a positive electrode mixture. The positive electrode may also include a positive electrode current collector that holds the positive electrode mixture. The positive electrode mixture includes a positive electrode active material. The positive electrode mixture may further include a binder, a conductive agent, and the like.

[0078] In lithium primary batteries, the positive electrode active material includes, for example, manganese dioxide. A positive electrode containing manganese dioxide as the positive electrode active material exhibits relatively high voltage and excellent pulse discharge characteristics. Manganese dioxide may be in a mixed crystal state containing multiple crystalline states. The positive electrode may also contain manganese oxides other than manganese dioxide. Examples of manganese oxides other than manganese dioxide include MnO, Mn3O4, Mn2O3, and Mn2O7. It is sufficient that the main component of the manganese oxide contained in the positive electrode (for example, 50% by mass or more) is manganese dioxide.

[0079] A portion of the manganese dioxide contained in the positive electrode may be doped with lithium. A small amount of lithium doping can ensure high capacity. Manganese dioxide and manganese dioxide doped with a small amount of lithium are Li xIt can be represented as MnO2 (0 ≤ x ≤ 0.05). Manganese dioxide also includes manganese oxides represented by such formulas. The average composition of all manganese oxides contained in the positive electrode is Li x The MnO2(0≦x≦0.05) is sufficient. The ratio of Li x should be 0.05 or less in the initial discharge state of the lithium primary battery. The ratio of Li x increases as the discharge of the lithium primary battery progresses. Theoretically, the oxidation state of manganese in manganese dioxide is tetravalent, but the average oxidation state of manganese is allowed to fluctuate slightly from tetravalent.

[0080] The positive electrode may contain manganese dioxide as well as other positive electrode active materials used in lithium primary batteries. Examples of other positive electrode active materials include graphite fluoride. However, the proportion of manganese dioxide in the total positive electrode active material is preferably 90% by mass or more.

[0081] Examples of binders include fluororesins, rubber particles, and acrylic resins.

[0082] Examples of conductive materials include conductive carbonaceous materials. Examples of conductive carbonaceous materials include natural graphite, artificial graphite, carbon black, and carbon fibers.

[0083] Examples of materials for the positive electrode current collector include stainless steel, aluminum, and titanium.

[0084] In the case of a coin-type battery, the positive electrode may be constructed by attaching a ring-shaped positive electrode current collector with an L-shaped cross-section to a positive electrode mixture pellet, or the positive electrode may be constructed using only the positive electrode mixture pellet. The positive electrode mixture pellet can be obtained, for example, by compression molding and drying a wet positive electrode mixture prepared by adding an appropriate amount of water to the positive electrode active material and additives.

[0085] In the case of a cylindrical battery, a positive electrode can be used that comprises a sheet-shaped positive electrode current collector and a positive electrode mixture layer held by the positive electrode current collector. As the sheet-shaped positive electrode current collector, a metal foil may be used, or a perforated current collector may be used. Examples of perforated current collectors include expanded metal, net, and punched metal. The positive electrode mixture layer can be obtained, for example, by coating the above-mentioned wet positive electrode mixture onto the surface of the sheet-shaped positive electrode current collector or filling the positive electrode current collector with it, applying pressure in the thickness direction, and drying it.

[0086] In lithium-ion secondary batteries, the positive electrode active material can be a composite oxide containing lithium and a transition metal, for example. Examples of transition metals include Ni, Co, and Mn. Examples of composite oxides include Li a CoO2, Li a KiO2, Li a MnO2, Li a Co b1 Ni 1-b1 O2, Li a Co b1 M 1-b1 O c1 Li a Ni 1-b1 M b1 O c1 Li a Mn2O4, Li a Mn 2-b1 M b1 O4 is an example. Here, a = 0 to 1.2, b1 = 0 to 0.9, and c1 = 2.0 to 2.3. M is at least one selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B. Note that the a value, which indicates the molar ratio of lithium, increases or decreases with charging and discharging. As a composite oxide, Li a Ni b2 M 1-b2O2 (where 0 < a ≦ 1.2, 0.3 ≦ b2 ≦ 1, and M is at least one selected from the group consisting of Mn, Co and Al) may be used. The positive electrode active material may include one type, or two or more types. From the viewpoint of easily forming a coating film excellent in film quality derived from an isocyanate component and a phenol component, a positive electrode including a positive electrode active material containing a polyvalent metal (in particular, at least one selected from the group consisting of Mn, Ni, and Co) may be used.

[0087] In a lithium secondary battery, examples of the positive electrode active material include lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, and transition metal sulfides. Examples of the transition metal element contained in the lithium-containing transition metal oxide include at least one selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W. From the viewpoint of easily forming a coating film excellent in film quality derived from an isocyanate component and a phenol component, the lithium-containing transition metal oxide may contain, as a transition metal element, at least one selected from the group consisting of Mn, Ni, and Co. The lithium-containing transition metal oxide may contain a typical metal (for example, at least one selected from the group consisting of Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, and Bi, etc., particularly at least Al).

[0088] In a lithium ion capacitor, for example, the positive electrode contains a carbonaceous material as an active material as an essential component, and may optionally contain a binder, a conductive agent, and the like. As the carbonaceous material, for example, activated carbon, carbon nanotubes, graphite, graphene and the like are used.

[0089] Examples of binders and conductive agents used in the positive electrodes of lithium-ion secondary batteries and lithium-ion capacitors include the components exemplified for lithium primary batteries. In the case of these energy storage devices, the positive electrode is prepared in the same manner as in the case of lithium primary batteries. For example, the positive electrode is prepared by applying a paste or slurry containing the components of the positive electrode mixture to the surface of the positive electrode current collector, and then drying and compressing the coating.

[0090] (Separator) The energy storage device may include a separator interposed between a pair of electrodes. Examples of separators include nonwoven fabrics, microporous films, or laminates thereof. The thickness of the separator is, for example, 5 μm or more and 100 μm or less.

[0091] Nonwoven fabrics are composed of fibers including, for example, polypropylene, polyphenylene sulfide, and polybutylene terephthalate. Microporous membranes include, for example, polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymer.

[0092] (others) The structure of the energy storage device is not particularly limited. The structure may be selected according to the type of energy storage device. For example, the energy storage device may be coin-shaped, consisting of a disc-shaped positive electrode and a disc-shaped negative electrode stacked with a separator in between. The energy storage device may also be cylindrical, comprising a group of electrodes consisting of a strip-shaped positive electrode and a strip-shaped negative electrode wound in a spiral shape with a separator in between.

[0093] Figure 1 shows a cross-sectional front view of a part of a cylindrical energy storage device according to one embodiment. The energy storage device 10 houses an electrode group in which a positive electrode 1 and a negative electrode 2 are wound around a separator 3, together with a non-aqueous electrolyte (not shown) in a battery case 9. A sealing plate 8 is fitted to the opening of the battery case 9. A positive electrode lead 4 connected to the current collector 1a of the positive electrode 1 is connected to the sealing plate 8. A negative electrode lead 5 connected to the negative electrode 2 is connected to the battery case 9. An upper insulating plate 6 and a lower insulating plate 7 are arranged above and below the electrode group, respectively.

[0094] [Examples] The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0095] Examples 1-10 and Comparative Examples 1-3 A lithium primary battery was fabricated as an energy storage device using the following procedure.

[0096] (Fabrication of the positive electrode) As the positive electrode, 100 parts by mass of electrolytic manganese dioxide was mixed with 5 parts by mass of Ketjenblack, a conductive agent, 5 parts by mass of polytetrafluoroethylene, a binder, and an appropriate amount of pure water to prepare a wet positive electrode mixture.

[0097] Next, a positive electrode precursor was prepared by filling a positive electrode current collector made of 0.1 mm thick expanded metal of stainless steel (SUS444) with the positive electrode mixture. The positive electrode precursor was then dried and rolled to a thickness of 0.4 mm using a roll press, and cut into sheets measuring 3.5 cm in length and 20 cm in width to obtain the positive electrode. Subsequently, a portion of the filled positive electrode mixture was peeled off, and a lead made of SUS444 was resistance-welded to the portion of the positive electrode current collector that was exposed.

[0098] (Fabrication of the negative electrode) A negative electrode was obtained by cutting a 300 μm thick metallic lithium foil into pieces measuring 3.7 cm in length and 22 cm in width. Nickel leads were welded to predetermined locations on the negative electrode.

[0099] (Fabrication of electrode groups) An electrode array was fabricated by winding the positive and negative electrodes so that they faced each other with a separator in between. A 25 μm thick microporous film made of polypropylene was used as the separator.

[0100] (Preparation of non-aqueous electrolyte) PC, EC, and DME were mixed in a volume ratio of 3:2:5. LiCF3SO3 was dissolved in the mixed solvent to a concentration of 0.5 mol / L, and the isocyanate and phenol components shown in Table 1 were dissolved to the concentrations shown in Table 1 to prepare a non-aqueous electrolyte. In Comparative Example 1, neither the isocyanate nor the phenol component was used. In Comparative Example 2, the isocyanate component was used, and in Comparative Example 3, the phenol component was used.

[0101] (Assembly of energy storage devices) The electrode group was housed in a cylindrical battery case that also served as the negative electrode terminal. An iron case (outer diameter 17 mm, height 45.5 mm) was used for the battery case. Next, a non-aqueous electrolyte was injected into the battery case, and the opening of the battery case was closed using a metal sealing body that also served as the positive electrode terminal. The other end of the positive electrode lead was connected to the sealing body, and the other end of the negative electrode lead was connected to the inner bottom surface of the battery case. In this way, a test energy storage device (lithium primary battery) was fabricated. The design capacity of the lithium primary battery is 2000 mAh.

[0102] (evaluation) Immediately after assembly, the energy storage device was discharged at 25°C with a constant current of 2.5mA until the depth of discharge (DOD) reached 75%. The discharged battery was then placed in a -30°C environment. Subsequently, the battery was discharged with a pulsed current of 200mA for 1 second, and the battery voltage (open-circuit voltage) V during the pulsed discharge was measured. The lowest open-circuit voltage during the 1-second current flow was defined as the initial output voltage in the low-temperature environment.

[0103] The energy storage devices were stored at 70°C for 120 days immediately after assembly. Using the stored energy storage devices, the battery voltage (open-circuit voltage) V after pulse discharge was measured in a low-temperature environment using the same procedure as for the initial output voltage described above. This voltage was defined as the output voltage in a low-temperature environment after high-temperature storage. The output voltage of each energy storage device is expressed as a relative value with the initial output voltage of the energy storage device in Comparative Example 1 set to 100.

[0104] The results are shown in Table 1. In Table 1, E1 to E10 are the batteries of Examples 1 to 10, and C1 to C3 are the batteries of Comparative Examples 1 to 3.

[0105] [Table 1]

[0106] As shown in Table 1, compared to C1, which uses a non-aqueous electrolyte containing neither isocyanate nor phenol components, C2, which uses an isocyanate component, shows a 1.7% increase in the initial output voltage under low-temperature conditions. On the other hand, C3, which uses a phenol component, shows a 4.6% decrease in the initial output voltage under low-temperature conditions compared to C1. In other words, the phenol component alone does not increase the output voltage under low-temperature conditions; in fact, it significantly decreases the output voltage. Due to the large decrease in output voltage caused by the phenol component, the results for C1 to C3 suggest that when using a non-aqueous electrolyte containing both isocyanate and phenol components, the initial output voltage under low-temperature conditions will be lower than that of C1, which contains neither component (approximately 100 + 1.7 - 4.6 = 97.1%). However, in reality, when using a non-aqueous electrolyte containing both isocyanate and phenol components, the initial output voltage under low-temperature conditions is 103.6% (E1), which is an improvement compared to C1 and an increase of 6.5% compared to the predicted value. Furthermore, the output voltage under low-temperature conditions after high-temperature storage shows a similar trend to the initial output voltage. Specifically, for C1 to C3, when using a non-aqueous electrolyte containing both isocyanate and phenol components, the output voltage under low-temperature conditions after high-temperature storage is expected to be around 90.1 + (93.5 - 90.1) + (81.6 - 90.1) = 85%. However, in E1, it actually increased to 99.3%, a 9.2% increase compared to C1 and a 14.3% increase compared to the expected value. This excellent effect is thought to be due to the synergistic effect obtained through the interaction of the isocyanate and phenol components, which cannot be obtained when each is used individually.

[0107] From the perspective of easily securing a higher initial output voltage in a low-temperature environment, the mass ratio of phenol component / isocyanate component in the non-aqueous electrolyte is 1 × 10⁻⁶. -3 The following is preferable: 0.7 × 10 -3 The following or 0.5 × 10 -3 The following is more preferable: 0.3 × 10 -3The following are even more preferable (comparison between E1 and E10). From a similar viewpoint, the concentration of the phenol component in the non-aqueous electrolyte is preferably 30 ppm or less or 20 ppm or less, and more preferably 10 ppm or less (comparison between E1 and E10).

[0108] From the viewpoint of easily securing a higher output voltage in a low-temperature environment after high-temperature storage, the concentration of the isocyanate component in the non-aqueous electrolyte is preferably 10% by mass or less (comparison between E7 and E8).

[0109] Furthermore, compared to linear isocyanate compounds, isocyanate compounds containing a ring structure tend to yield higher initial output voltages in low-temperature environments (comparison between E1 and E5 and E2, E3, E6, and E7).

[0110] In this example, a lithium primary battery was used as the energy storage device, but similar or comparable effects can be obtained with other energy storage devices (e.g., lithium-ion secondary batteries, lithium-ion capacitors).

[0111] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention. [Industrial applicability]

[0112] The non-aqueous electrolyte of this disclosure is useful as a non-aqueous electrolyte for energy storage devices. Energy storage devices using the non-aqueous electrolyte of this disclosure are suitably used, for example, as the main power supply for various meters and as a memory backup power supply. Examples of energy storage devices include lithium primary batteries, lithium-ion secondary batteries, lithium secondary batteries, and lithium-ion capacitors. However, the applications of the non-aqueous electrolyte and energy storage devices are not limited to these. [Explanation of Symbols]

[0113] 1 positive electrode 1a Positive electrode current collector 2 negative electrode 3 Separators 4 Positive lead 5. Negative lead 6. Upper insulating plate 7 Lower insulating plate 8 Sealing plate 9 Battery case 10 Energy storage devices

Claims

1. Solute and, Non-aqueous solvents and At least one isocyanate component selected from the group consisting of hexamethylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, and isophorone diisocyanate, It comprises at least one phenol component selected from the group consisting of 2,6-di-tert-butyl-p-cresol and butylhydroxyanisole, The concentration of the isocyanate component is 0.2% by mass or more and 10% by mass or less. The concentration of the phenol component is 0.001 ppm or more and 150 ppm or less by mass. A non-aqueous electrolyte used in an energy storage device, wherein the mass ratio of the phenol component to the isocyanate component (= phenol component / isocyanate component) is between 0.002 × 10⁻³ and 1.5 × 10⁻³.

2. The non-aqueous electrolyte according to claim 1, wherein the concentration of the phenol component is 10 ppm or less by mass.

3. The non-aqueous electrolyte according to claim 1 or 2, wherein the solute comprises a lithium salt.

4. The energy storage device is a lithium primary battery including a pair of electrodes, One of the pair of electrodes includes at least one of metallic lithium and a lithium alloy. The other electrode is a non-aqueous electrolyte according to claim 1 or 2, comprising a positive electrode mixture containing manganese dioxide.

5. It comprises a pair of electrodes and a non-aqueous electrolyte, The aforementioned non-aqueous electrolyte is Solute and, Non-aqueous solvents and At least one isocyanate component selected from the group consisting of hexamethylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, and isophorone diisocyanate, It comprises at least one phenol component selected from the group consisting of 2,6-di-tert-butyl-p-cresol and butylhydroxyanisole, In the aforementioned non-aqueous electrolyte, The concentration of the isocyanate component is 0.2% by mass or more and 10% by mass or less. The concentration of the phenol component is 0.001 ppm or more and 150 ppm or less by mass. An energy storage device in which the mass ratio of the phenol component to the isocyanate component (= phenol component / isocyanate component) is between 0.002 × 10⁻³ and 1.5 × 10⁻³.

6. One electrode of the pair of electrodes is capable of electrochemically dissolving or releasing lithium ions, and the other electrode is capable of electrochemically depositing or intercalating lithium ions. The energy storage device according to claim 5, wherein the non-aqueous electrolyte contains a lithium salt.

7. The aforementioned one electrode includes at least one selected from the group consisting of lithium, silicon, and carbonaceous materials. The energy storage device according to claim 6, wherein the other electrode comprises at least one element selected from the group consisting of manganese, nickel, and cobalt.

8. The aforementioned electrode includes at least one of metallic lithium and a lithium alloy. The other electrode comprises a positive electrode mixture containing manganese dioxide, The energy storage device according to claim 6 or 7, wherein the battery is a lithium primary battery.

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