Lithium primary battery and non-aqueous electrolyte used therefor

Abstract

This lithium primary battery is provided with a positive electrode, a negative electrode and a nonaqueous electrolyte solution; the positive electrode contains a positive electrode mixture that contains manganese dioxide; the negative electrode contains at least one of lithium metal and a lithium alloy; the nonaqueous electrolyte solution contains an isocyanate compound (a first component), and at least one of a cyclic imide compound and a phthalic acid ester compound (a second component); and the concentration of the isocyanate compound in the nonaqueous electrolyte solution is 5% by mass or less.

Description

Technical Field

[0001] The present disclosure relates to a primary lithium battery and a non-aqueous electrolyte used therefor.

Background Art

[0002] Primary lithium batteries are suitable for long-term use because they have a high energy density and low self-discharge. The adoption of primary lithium batteries as power sources for devices that are used for a long time is progressing. For example, a smart meter is a device that transmits data regarding the usage amount of gas, electricity, etc., and is required to operate without maintenance for a long time. During that time, a primary lithium battery is required to maintain a high internal electromotive force and low internal resistance.

[0003] Patent Document 1 proposes a non-aqueous organic electrolyte for a primary lithium battery including a positive electrode containing a positive electrode material having manganese dioxide as a positive electrode active material and a current collector made of stainless steel, and a negative electrode made of lithium metal or a lithium alloy, wherein LiCF3SO3 is included as a supporting salt and LiB(C2O4)2 is added.

[0004] Patent Document 2 proposes a non-aqueous electrolyte battery having a negative electrode made of a metal lithium, a lithium alloy, or a material capable of occluding and releasing lithium, a positive electrode, and a non-aqueous electrolyte composed of a solvent and a solute dissolved in the solvent, wherein the non-aqueous electrolyte contains a cyclic imide compound.

[0005] Patent Document 3 proposes a non-aqueous electrolyte battery including a negative electrode made of lithium, a lithium alloy, or a carbon material capable of electrochemically occluding and releasing lithium, a positive electrode having manganese dioxide as an active material, and a non-aqueous electrolyte containing a low-boiling solvent, wherein a phthalic acid diester is added as an additive to the non-aqueous electrolyte.

Prior Art Documents

Patent Documents

[0006] Patent Document 1 Japanese Patent Application Laid-Open No. 2015-022985 Patent Document 2 Pamphlet of International Publication No. 2001 / 041247 Patent Document 3 Japanese Patent Application Laid-Open No. 07-22069 SUMMARY OF THE INVENTION

[0007] In order for a primary lithium battery to maintain a high internal electromotive force, it is necessary to protect the positive electrode and the negative electrode with a coating to suppress side reactions or self-discharge. Therefore, as proposed in the above patent documents, studies have been made to include an additive having a protective action in the non-aqueous electrolyte. However, when such an additive is used, the internal resistance may increase or the internal electromotive force may decrease.

[0008] One aspect of the present disclosure relates to a primary lithium battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode includes a positive electrode mixture containing manganese dioxide, the negative electrode includes at least one of metallic lithium and a lithium alloy, the non-aqueous electrolyte includes an isocyanate compound as a first component and at least one of a cyclic imide compound and a phthalic acid ester compound as a second component, and a concentration of the isocyanate compound in the non-aqueous electrolyte is 5% by mass or less.

[0009] Another aspect of the present disclosure relates to a non-aqueous electrolyte used in a primary lithium battery including a positive electrode including a positive electrode mixture containing manganese dioxide, a negative electrode including at least one of metallic lithium and a lithium alloy, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte includes an isocyanate compound as a first component and at least one of a cyclic imide compound and a phthalic acid ester compound as a second component, and a concentration of the isocyanate compound in the non-aqueous electrolyte is 5% by mass or less.

[0010] A primary lithium battery showing a high internal electromotive force and a low internal resistance after initial and high-temperature storage can be obtained.

Brief Description of the Drawings

[0011]

Figure 1

Embodiments for Carrying Out the Invention

[0012] The primary lithium battery according to the present disclosure includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive electrode mixture containing manganese dioxide (for example, a manganese oxide represented by Li x MnO2 (0 ≦ x ≦ 0.05)). The negative electrode includes at least one of metallic lithium and a lithium alloy. The non-aqueous electrolyte includes an isocyanate compound as a first component and at least one of a cyclic imide compound and a phthalic acid ester compound as a second component.

[0013] The second component is considered to have an effect of suppressing an increase in the internal resistance of the primary lithium battery after high-temperature storage. The second component forms a stable film having lithium ion conductivity on the surface of the negative electrode. Thereby, the active negative electrode surface is protected, and excessive film formation on the negative electrode surface due to side reactions is avoided. However, its effect is insufficient, and it considerably increases the initial internal resistance and also considerably increases the internal resistance after high-temperature storage. In addition, the second component tends to decrease the initial electromotive force of the primary lithium battery and promote self-discharge. Such a phenomenon is a phenomenon associated with side reactions of the second component at the positive electrode, and is considered to proceed with elution of Mn from the positive electrode active material.

[0014] On the other hand, when the non-aqueous electrolyte contains the first component and the second component, a decrease in the initial electromotive force and self-discharge of the primary lithium battery are significantly suppressed. Also, an increase in the internal resistance after high-temperature storage is significantly suppressed. This is considered to be because a composite film derived from both the first component and the second component is formed on the surface of the manganese dioxide contained in the positive electrode. The composite film is considered to suppress side reactions of the second component at the positive electrode and suppress a decrease in the initial electromotive force of the positive electrode and the progress of self-discharge.

[0015] When only the first component is used without using the second component, conversely, the open-circuit voltage of the lithium primary battery decreases after initial use and high-temperature storage, and the increase in internal resistance after high-temperature storage also becomes remarkable. This is presumably because a composite film containing a component derived from the second component is not formed on the positive electrode, and side reactions involving the decomposition of the first component proceed excessively. That is, the side reaction of the first component at the positive electrode is specifically suppressed when the second component coexists. Also, when the second component coexists with the first component, the side reaction of the second component at the positive electrode is also suppressed. As a result, the decrease in the initial open-circuit voltage and the progress of self-discharge are significantly alleviated.

[0016] The concentration of the isocyanate compound in the non-aqueous electrolyte is limited to 5% by mass or less. When the concentration of the isocyanate compound in the non-aqueous electrolyte exceeds 5% by mass, it becomes difficult to suppress side reactions involving the isocyanate compound. Therefore, after high-temperature storage, the open-circuit voltage decreases significantly and the internal resistance also increases. The concentration of the isocyanate compound in the non-aqueous electrolyte may be 4% by mass or less, 3% by mass or less, or 2% by mass or less. Also, from the viewpoint of more significantly suppressing the decrease in the initial open-circuit voltage and the progress of self-discharge, the concentration of the isocyanate compound in the non-aqueous electrolyte may be, for example, 0.01% by mass or more, 0.1% by mass or more, or 0.5% by mass or more. When limiting the range, these upper and lower limits can be arbitrarily combined.

[0017] When attempting to form a better-quality composite film, it is desirable to control the mass ratio of the first component to the second component contained in the non-aqueous electrolyte to be 1 / 3 or more and 50 or less, and it may be 1 / 2 or more and 10 or less, 1 / 2 or more and 7 or less, or 1 or more and 5 or less. Thereby, the balance of the composition of the composite film is improved, and it becomes possible to further manifest the effect of suppressing the decrease in the initial open-circuit voltage and self-discharge.

[0018] The concentration of the second component in the non-aqueous electrolyte is, for example, 3% by mass or less, may be 1.5% by mass or less, or may be 1% by mass or less. Also, the concentration of the second component in the non-aqueous electrolyte is, for example, 0.01% by mass or more, may be 0.1% by mass or more, or may be 0.3% by mass or more. When limiting the range, these upper and lower limits can be arbitrarily combined.

[0019] In addition, in the non-aqueous electrolyte contained in the initial battery after the start of use or the electrolyte before being injected into the battery, the concentrations (mass %) of the first component and the second component may be within the above ranges. After the start of use, in a lithium primary battery used for a considerable period, the concentrations of the first component and the second component in the non-aqueous electrolyte can change. Therefore, in the non-aqueous electrolyte collected from such a lithium primary battery, it is sufficient that the first component and the second component remain at a concentration above the detection limit. In the non-aqueous electrolyte collected from a battery other than the initial battery after the start of use, the content of the first component may be, for example, 0.0001% by mass or more, and the content of the second component may be, for example, 0.0001% by mass or more. Also in this case, in order to reflect the initial mass ratio, the mass ratio of the first component to the second component can fall within the range of 1 / 3 or more and 50 or less.

[0020] Among the second components, cyclic imide compounds are more preferable. The content rate of the cyclic imide compound in the second component may be 50% by mass or more, may be 70% by mass or more, or may be 90% by mass or more.

[0021] (Isocyanate compound) The isocyanate compound has, for example, at least one isocyanate group and an aliphatic hydrocarbon group having 1 to 20 carbon atoms or an aromatic hydrocarbon group having 6 to 20 carbon atoms. The aliphatic hydrocarbon group and the aromatic hydrocarbon group constituting the isocyanate compound may have a substituent. The substituent may be a group that can exist stably, for example, a halogen atom or a nitrile group. The aliphatic group may be an alicyclic aliphatic group or a linear or branched aliphatic group. The aromatic hydrocarbon group is a hydrocarbon group having one or more aromatic rings, and may also be a group in which an aromatic ring and an aliphatic group are linked.

[0022] The isocyanate compound may be a monoisocyanate compound having one isocyanate group, a diisocyanate compound having two isocyanate groups, or a polyisocyanate compound having three or more isocyanate groups. The number of isocyanate groups in the isocyanate compound may be five or less, or four or less. The diisocyanate compound is considered to produce a composite film with lower resistance than the monoisocyanate compound and a more homogeneous composite film than the triisocyanate. In addition, the diisocyanate compound has a high ability to form a composite film even in a small amount and is excellent in stability within the battery.

[0023] Specific examples of the isocyanate compound include methyl isocyanate, ethyl isocyanate, propyl isocyanate, butyl isocyanate, pentyl isocyanate, hexyl isocyanate, heptyl isocyanate, octyl isocyanate, cyclohexane isocyanate, phenyl isocyanate, fluorophenyl isocyanate, methoxycarbonyl isocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, peptamethylene diisocyanate, octamethylene diisocyanate, 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, isophorone diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, xylylene diisocyanate, phenyl diisocyanate, toluene diisocyanate, diisocyanatonaphthalene, o-tolidine diisocyanic acid, lysine diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, bis(4-isocyanatophenyl)methane, 1,6,11-triisocyanatoundecane, 1,3,5-tris(6-isocyanatohex-1-yl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 1,3,5-tris(6-isocyanatotetr-1-yl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 1,3,5-tris(6-isocyanatopent-1-yl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 1,3,5-tris(6-isocyanatotetr-1-yl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 1,3,5-tris(6-isocyanatohept-1-yl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, and the like. These may be used alone or in combination of two or more.

[0024] Among them, OCN-C nH 2n -NCO (where n is an integer from 1 to 10), such as hexamethylene diisocyanate, compounds having an alicyclic diyl group (e.g., 1,3-bis(isocyanatomethyl)cyclohexane, dicyclohexylmethane-4,4'-diisocyanate, bicyclo[2.2.1]heptane-2,5-diylbis(methyl isocyanate), bicyclo[2.2.1]heptane-2,6-diylbis(methyl isocyanate), isophorone diisocyanate), 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, hexyl isocyanate, etc. are easily available. Among these, at least one selected from the group consisting of hexyl isocyanate, hexamethylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, and isophorone diisocyanate is preferred, and these may account for 50% by mass or more, further 70% by mass or more, or 90% by mass or more of the isocyanate compound.

[0025] (Cyclic imide compound) The cyclic imide compound only needs to have a diacylamine ring (imide ring). Another ring (second ring) may be condensed with the imide ring. The second ring may be an aromatic ring, a saturated or unsaturated aliphatic ring. The second ring may contain at least one heteroatom. Examples of the heteroatom include an oxygen atom, a sulfur atom, a nitrogen atom, etc. The non-aqueous electrolyte may contain one kind of cyclic imide compound or may contain two or more kinds.

[0026] The cyclic imide compound may be contained in the non-aqueous electrolyte in the form of an imide having a free NH group, in the form of a tertiary amine, or in the form of an anion or a salt. Even when the cyclic imide compound is contained in the form of a tertiary amine, an anion, or a salt, in this specification, the concentration of the first component in the non-aqueous electrolyte is taken as the value converted to the concentration of the first component having a free NH group.

[0027] The cyclic imide compound may be an N-substituted imide compound having a substituent on the nitrogen atom of the imide. Examples of such substituents include a hydroxy group, an alkyl group, an alkoxy group, a halogen atom, and the like. Examples of the alkyl group include C1-C4 alkyl groups, which may be a methyl group, an ethyl group, or the like. Examples of the alkoxy group include C1-C4 alkoxy groups, which may be a methoxy group, an ethoxy group, or the like. Examples of the halogen atom include a chlorine atom, a fluorine atom, and the like.

[0028] The cyclic imide compound may be a hydrogenated product, for example, a hydrogenated product of phthalimide.

[0029] Specific examples of the cyclic imide compound include phthalimide, hexahydrophthalimide, N-methylphthalimide, N-hydroxyphthalimide, N-hydroxymethylphthalimide, N-(2-hydroxyethyl)phthalimide, N-fluorophthalimide, N-(phenylthio)phthalimide, N-(cyclohexylthio)phthalimide, N-(propanthio)butafluorophthalimide, succinimide, N-hydroxysuccinimide, N-fluorosuccinimide, cyclohex-3-ene-1,2-dicarboximide, cyclohexane-1,2-dicarboximide, N-(phenylthio)imide, and the like. These may be used alone or in combination of two or more. Among them, at least one selected from the group consisting of phthalimide, hexahydrophthalimide, N-methylphthalimide, N-hydroxyphthalimide, N-hydroxymethylphthalimide, N-(2-hydroxyethyl)phthalimide, N-fluorophthalimide, succinimide, N-hydroxysuccinimide and N-fluorosuccinimide is preferable.

[0030] The cyclic imide compound is more preferably at least one selected from the group consisting of phthalimide and N-substituted phthalimide. These compounds may account for 50% by mass or more, further 70% by mass or more, or 90% by mass or more of the cyclic imide compound. Further, the cyclic imide compound preferably contains at least phthalimide. Phthalimide may account for 50% by mass or more, further 70% by mass or more, or 90% by mass or more of the cyclic imide compound.

[0031] (Phthalic acid ester compound) The phthalic acid ester compound includes phthalic acid esters and their derivatives. The derivative may have a substituent bonded to the aromatic ring derived from phthalic acid. Examples of such a substituent include a hydroxy group, an alkyl group, an alkoxy group, a halogen atom, etc. Examples of the alkyl group include a C1-C4 alkyl group, which may be a methyl group, an ethyl group, etc. Examples of the alkoxy group include a C1-C4 alkoxy group, which may be a methoxy group, an ethoxy group, etc. Examples of the halogen atom include a chlorine atom, a fluorine atom, etc.

[0032] The phthalic acid ester compound may be a monoester, but a diester is desirable. As the alcohol constituting the ester with phthalic acid (or its derivative), a C1-C20 (preferably C1-C6) saturated or unsaturated aliphatic alcohol is desirable.

[0033] Specific examples of the phthalic acid ester compound include dimethyl phthalate, diethyl phthalate, diallyl phthalate, dibutyl phthalate, diisobutyl phthalate, bis(2-ethylhexyl) phthalate, etc. These may be used alone or in combination of two or more. These may account for 50% by mass or more, further 70% by mass or more, or 90% by mass or more of the phthalic acid ester compound.

[0034] For the analysis of the non-aqueous electrolyte (first component and second component), for example, liquid chromatography mass spectrometry (LC / MS) can be used, and ultraviolet spectroscopic analysis (UV) may be performed together with mass spectrometry (MS).

[0035] Hereinafter, the lithium primary battery according to the present disclosure will be described more specifically.

[0036] [Lithium Primary Battery] (Positive Electrode) The positive electrode contains a positive electrode mixture. The positive electrode mixture contains a positive electrode active material. The positive electrode active material contains manganese dioxide. A positive electrode containing manganese dioxide as a positive electrode active material exhibits a relatively high voltage and excellent pulse discharge characteristics. The manganese dioxide may be in a mixed crystal state including a plurality of crystal states. The positive electrode may contain manganese oxides other than manganese dioxide. Examples of manganese oxides other than manganese dioxide include MnO, Mn3O4, Mn2O3, Mn2O7, etc. It is sufficient that the main component (for example, 50% by mass or more) of the manganese oxide contained in the positive electrode is manganese dioxide.

[0037] A part of the manganese dioxide contained in the positive electrode may be doped with lithium. If the doping amount of lithium is small, a high capacity can be ensured. Manganese dioxide and manganese dioxide doped with a small amount of lithium can be represented by Li x MnO2 (0 ≤ x ≤ 0.05). It is sufficient that the average composition of the entire manganese oxide contained in the positive electrode is Li x MnO2 (0 ≤ x ≤ 0.05). The ratio x of Li may be 0.05 or less in the initial state of discharge of the lithium primary battery. The ratio x of Li increases as the discharge of the lithium primary battery progresses. The oxidation number of manganese contained in manganese dioxide is theoretically tetravalent, but a slight increase or decrease in the average oxidation number of manganese is allowed.

[0038] The positive electrode can contain, in addition to manganese dioxide, 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.

[0039] The BET specific surface area of manganese dioxide can be, for example, 10 m 2 / g or more and 40 m 2 / g or less. When the BET specific surface area of manganese dioxide is in such a range, a higher self-discharge suppression effect can be obtained in a lithium primary battery. Also, the positive electrode mixture layer can be easily formed.

[0040] The BET specific surface area of manganese dioxide may be measured by a known method. For example, it is measured based on the BET method using a specific surface area measuring device (for example, manufactured by Mounttech Co., Ltd.). For example, manganese dioxide separated from the positive electrode taken out from the battery may be used as the measurement sample.

[0041] The median particle diameter of manganese dioxide may be 10 μm or more and 40 μm or less. When the median particle diameter is in such a range, in a lithium primary battery, the effect of suppressing self-discharge is further enhanced, and it is easy to ensure high current collection performance in the positive electrode. The median particle diameter of manganese dioxide is, for example, the median value of the volume-based particle size distribution determined by the quantitative laser diffraction / scattering method (qLD method). For example, Li x MnO2 separated from the positive electrode taken out from the battery may be used as the measurement sample. For the measurement, for example, SALD-7500nano manufactured by Shimadzu Corporation is used.

[0042] The positive electrode mixture may contain, in addition to the positive electrode active material, a binder, a conductive agent, and the like. Examples of the binder include fluororesin, rubber particles, and acrylic resin.

[0043] Examples of the conductive agent include conductive carbon materials. Examples of the conductive carbon materials include natural graphite, artificial graphite, carbon black, and carbon fiber.

[0044] The positive electrode may further include a positive electrode current collector that holds a positive electrode mixture. Examples of the material of the positive electrode current collector include stainless steel, aluminum, titanium, and the like.

[0045] In the case of a coin-shaped battery, a ring-shaped positive electrode current collector with an L-shaped cross-section may be attached to the positive electrode mixture pellet to form the positive electrode, or the positive electrode may be composed of only the positive electrode mixture pellet. The positive electrode mixture pellet can be obtained, for example, by compression molding a wet positive electrode mixture prepared by adding an appropriate amount of water to a positive electrode active material and an additive, and then drying it.

[0046] In the case of a cylindrical battery, a positive electrode including a sheet-shaped positive electrode current collector and a positive electrode mixture layer held by the positive electrode current collector can be used. As the sheet-shaped positive electrode current collector, a porous current collector is preferable. Examples of the porous current collector include expanded metal, net, and punching metal. The positive electrode mixture layer can be obtained, for example, by applying the above-mentioned wet positive electrode mixture to the surface of the sheet-shaped positive electrode current collector or filling it into the positive electrode current collector, applying pressure in the thickness direction, and then drying it.

[0047] (Negative electrode) The negative electrode only needs to contain metallic lithium or a lithium alloy, and may contain both metallic lithium and lithium metal. A composite of metallic lithium and a lithium alloy may also be used.

[0048] Examples of the lithium alloy include Li-Al alloy, Li-Sn alloy, Li-Ni-Si alloy, Li-Pb alloy, Li-Mg alloy, Li-Zn alloy, Li-In alloy, Li-Al-Mg alloy, and the like. From the viewpoint of ensuring discharge capacity and stabilizing internal resistance, the content of the metal element other than lithium contained in the lithium alloy is preferably 0.05 to 15% by mass.

[0049] Metallic lithium, a lithium alloy, or a composite thereof is formed into an arbitrary shape and thickness according to the shape, dimensions, standard performance, etc. of the lithium primary battery.

[0050] In the case of a coin-shaped battery, a hoop-shaped metallic lithium, lithium alloy, etc. may be punched into a disc shape and used as the negative electrode. In the case of a cylindrical battery, a sheet of metallic lithium, lithium alloy, etc. may be used as the negative electrode. The sheet can be obtained, for example, by extrusion molding.

[0051] (Non-aqueous electrolyte) The non-aqueous electrolyte contains a first component (isocyanate compound) and a second component (at least one of a cyclic imide compound and a phthalic acid ester compound), a non-aqueous solvent, and a lithium salt or lithium ions. At least one of the first component and the second component may be a lithium salt and may be capable of generating lithium ions.

[0052] (Non-aqueous solvent) Examples of the non-aqueous solvent include ethers, esters, carbonic esters, etc. More specifically, dimethyl ether, γ-butyrolactone, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, etc. can be used. The non-aqueous solvent may be used alone or in combination of two or more.

[0053] From the viewpoint of improving the discharge characteristics of the lithium primary battery, it is preferable that the non-aqueous solvent contains a cyclic carbonate with a high boiling point and a chain ether with a low viscosity at low temperatures. The cyclic carbonate preferably contains at least one selected from the group consisting of propylene carbonate (PC) and ethylene carbonate (EC), and PC is particularly preferable. The chain ether preferably contains, for example, dimethoxyethane (DME).

[0054] (Lithium salt) Examples of the lithium salt include LiCF3SO3, LiClO4, LiBF4, LiPF6, LiRaSO3 (Ra is a C1 - C4 fluoroalkyl group), LiFSO3, LiN(SO2Rb)(SO2Rc) (Rb and Rc are each independently a C1 - C4 fluoroalkyl group), LiN(FSO2)2, LiPO2F2, LiB(C2O4)2, and LiBF2(C2O4). The non-aqueous electrolyte may contain one of these lithium salts or two or more of them.

[0055] (Others) The concentration of the lithium salt (or lithium ions) contained in the non-aqueous electrolyte is, for example, 0.2 - 2.0 mol / L, and may be 0.3 - 1.5 mol / L.

[0056] The non-aqueous electrolyte may contain an additive as needed. Examples of the additive include propane sultone, vinylene carbonate, etc. The total concentration of such additives contained in the non-aqueous electrolyte is, for example, 0.003 - 5 mol / L.

[0057] (Separator) The primary lithium battery usually includes a separator interposed between the positive electrode and the negative electrode. Examples of the separator include non-woven fabric, microporous membrane, or a laminate thereof. The thickness of the separator is, for example, 5 μm or more and 100 μm or less.

[0058] The non-woven fabric is composed of fibers including, for example, polypropylene, polyphenylene sulfide, polybutylene terephthalate, etc. The microporous membrane contains, for example, polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymer.

[0059] The structure of the primary lithium battery is not particularly limited. The primary lithium battery may be a coin-shaped battery formed by laminating a disc-shaped positive electrode and a disc-shaped negative electrode with a separator interposed therebetween. The primary lithium battery may also be a cylindrical battery including an electrode group formed by winding a strip-shaped positive electrode and a strip-shaped negative electrode in a spiral shape with a separator interposed therebetween.

[0060] FIG. 1 shows a front view of a cross-section of a cylindrical primary lithium battery according to an embodiment. In the primary lithium battery 10, an electrode group in which a positive electrode 1 and a negative electrode 2 are wound with a separator 3 therebetween is housed in a battery case 9 together with a non-aqueous electrolyte (not shown). A sealing plate 8 is attached 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 case 9. Upper and lower insulating plates 6 and 7 are disposed above and below the electrode group, respectively.

[0061] [Examples] Hereinafter, the present disclosure will be specifically described based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0062] 《Examples 1 to 8 and Comparative Examples 1 to 5》 (Fabrication of Positive Electrode) As the positive electrode, 100 parts by mass of electrolytic manganese dioxide, 5 parts by mass of Ketjen black as a conductive agent, 5 parts by mass of polytetrafluoroethylene as a binder, and an appropriate amount of pure water were added and kneaded to prepare a wet positive electrode mixture. The median particle diameter of the electrolytic manganese dioxide was in the range of 25 μm to 27 μm, and the BET specific surface area was in the range of 15 to 20 m 2 / g.

[0063] Next, the positive electrode mixture was filled into a positive electrode current collector made of expanded metal with a thickness of 0.1 mm made of stainless steel (SUS444) to prepare a positive electrode precursor. Thereafter, the positive electrode precursor was dried and rolled by a roll press until the thickness became 0.4 mm, and then cut into a sheet shape with a length of 3.5 cm and a width of 20 cm to obtain a positive electrode. Subsequently, a part of the filled positive electrode mixture was peeled off, and a lead made of SUS444 was resistance-welded to the exposed part of the positive electrode current collector.

[0064] (Fabrication of Negative Electrode) A negative electrode was obtained by cutting a metallic lithium foil with a thickness of 300 μm into a size of 3.7 cm in length and 22 cm in width. A nickel lead was connected by welding to a predetermined position of the negative electrode.

[0065] (Fabrication of Electrode Assembly) An electrode assembly was fabricated by winding the positive electrode and the negative electrode so as to face each other with a separator interposed therebetween. As the separator, a microporous membrane made of polypropylene with a thickness of 25 μm was used.

[0066] (Preparation of Non-aqueous Electrolyte) PC, EC, and DME were mixed at a volume ratio of 4:2:4. LiCF3SO3 was dissolved in the mixed solvent to a concentration of 0.5 mol / L, and the first component and the second component shown in Table 1 were dissolved so that each component had the concentration shown in Table 1 to prepare a non-aqueous electrolyte.

[0067] (Assembly of Lithium Primary Battery) The electrode assembly 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 as the battery case. Next, after injecting the non-aqueous electrolyte into the battery case, 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 lithium primary battery for testing was fabricated. The designed capacity of the lithium primary battery is 2000 mAh. In Table 1, A1 to A8 are the batteries of Example 1 to 8, and B1 to B5 are the batteries of Comparative Example 1 to 5.

[0068] For batteries A1 to A8 and batteries B1 to B5, the open circuit voltage (OCV) and the internal resistance (IR) were measured immediately after assembly (initial) and after high-temperature storage. The IR was determined by measuring the alternating current resistance value (ACR) by the two-terminal method in an environment at 25°C. The measurement frequency of the alternating current was set to 1 kHz. The OCV and IR after high-temperature storage were measured after storing the battery at 70°C for 100 days. The results are shown in Table 2.

[0069]

Table 1

[0070]

Table 2

[0071] In batteries A1 to A8 in which the non-aqueous electrolyte contains the first component and the second component and the concentration of the first component is 5% by mass or less, the initial OCV is higher and the internal resistance is lower than those of batteries B1 to B5. Also, in batteries A1 to A8, the decrease in OCV after high-temperature storage is smaller and the increase in IR is significantly reduced compared to batteries B1 to B5.

[0072] In battery B5 in which the non-aqueous electrolyte contains the first component and the second component but the concentration of the first component exceeds 5% by mass, the OCVs before and after high-temperature storage are relatively good, but the increase in the initial IR and the IR after high-temperature storage is large. This is considered to be due to the excess of the first component.

[0073] In battery B1 in which the non-aqueous electrolyte contains the first component but does not contain the second component, the decrease in OCV after high-temperature storage was large and the increase in IR was remarkable. Also, the evaluation result of battery B1 was further lower than that of battery B2 which uses neither the first component nor the second component. From this, it can be seen that the first component alone does not exhibit the effect of maintaining good OCV and IR after high-temperature storage, and a synergistic effect is exhibited when used in combination with the second component.

[0074] In batteries B3 and B4 in which the non-aqueous electrolyte contains the second component but does not contain the first component, there is a tendency to lower the IR, but it is not sufficient. Also, in batteries B3 and B4, the initial OCV is low. From this, it can be seen that it is difficult to obtain a primary lithium battery in which the second component alone exhibits a high OCV and a low IR both initially and after high-temperature storage.

Industrial Applicability

[0075] In the primary lithium battery of the present disclosure, for example, it is suitably used as the main power source of various meters and the memory backup power source. However, the applications of the primary lithium battery are not limited thereto.

Explanation of Signs

[0076] 1 Positive electrode 1a Positive electrode current collector 2 Negative electrode 3 Separator 4 Positive electrode lead 5 Negative electrode lead 6 Upper insulating plate 7 Lower insulating plate 8 Sealing plate 9 Battery case 10 Primary lithium battery

Claims

1. A primary lithium battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode contains a positive electrode mixture containing manganese dioxide, the negative electrode contains at least one of metallic lithium and a lithium alloy, the non-aqueous electrolyte contains an isocyanate compound as a first component and at least one of a cyclic imide compound and a phthalic acid ester compound as a second component, and the concentration of the isocyanate compound in the non-aqueous electrolyte is 5% by mass or less.

2. The primary lithium battery according to claim 1, wherein the mass ratio of the first component to the second component contained in the non-aqueous electrolyte is 1 / 3 or more and 50 or less.

3. The primary lithium battery according to claim 1 or 2, wherein the isocyanate compound has at least one isocyanate group and an aliphatic hydrocarbon group having 1 to 20 carbon atoms or an aromatic hydrocarbon group having 6 to 20 carbon atoms.

4. The primary lithium battery according to any one of claims 1 to 3, wherein the isocyanate compound contains at least one selected from the group consisting of hexyl isocyanate, hexamethylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, and isophorone diisocyanate.

5. The primary lithium battery according to any one of claims 1 to 4, wherein the cyclic imide compound contains at least one selected from the group consisting of phthalimide and N-substituted phthalimide.

6. The primary lithium battery according to claim 5, wherein the cyclic imide compound contains at least phthalimide.

7. The primary lithium battery according to any one of claims 1 to 6, wherein the phthalic acid ester compound contains dimethyl phthalate.

8. A non-aqueous electrolyte used in a primary lithium battery comprising a positive electrode containing a positive electrode mixture containing manganese dioxide, a negative electrode containing at least one of metallic lithium and a lithium alloy, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte contains an isocyanate compound as a first component and at least one of a cyclic imide compound and a phthalic acid ester compound as a second component, and the concentration of the isocyanate compound in the non-aqueous electrolyte is 5% by mass or less.

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