Lithium battery

Abstract

To materialize a lithium battery excellent in discharge characteristics at low temperature.SOLUTION: A lithium battery 100 includes a battery element 10 for a lithium battery, having: a positive electrode 11 obtained by using manganese dioxide; a negative electrode 12 obtained by using lithium; and a separator 13 provided therebetween. The lithium battery 100 further includes: an exterior body 30 in which the battery element 10 is housed; and electrolyte solution 20 housed in the exterior body 30. The electrolytic solution 20 includes: a nonaqueous electrolytic solution component including a lithium electrolyte salt and a fluorine-free organic solvent; and an inorganic acid ester compound having a fluoroalkyl group.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to lithium batteries. [Background technology]

[0002] Known batteries that use an electrolyte include lithium ion batteries (also called "lithium secondary batteries") and lithium batteries (also called "lithium primary batteries"). For example, a lithium battery is known that includes a positive electrode, a negative electrode containing lithium, a separator therebetween, and an electrolyte solution. With regard to such lithium batteries, a technology is known in which a carbonaceous material-containing layer is provided on the surface of the negative electrode to suppress reaction between the surface of the negative electrode and the electrolyte solution (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-140648 Summary of the Invention [Problem to be solved by the invention]

[0004] One type of lithium battery is known, which has a battery element including a manganese dioxide positive electrode, a lithium negative electrode, and a separator disposed between the positive and negative electrodes, housed together with an electrolyte in an outer casing such as a film or a can. Such lithium batteries are used for a variety of applications, including meter communication and various backup power sources, and are expected to exhibit high discharge characteristics over a wide operating temperature range. However, lithium batteries using conventional electrolytes often fail to exhibit sufficient discharge characteristics in low-temperature environments, such as temperatures below 0°C, such as -40°C.

[0005] In one aspect, the present invention aims to provide a lithium battery that has excellent discharge characteristics at low temperatures. [Means for solving the problem]

[0006] In one embodiment, there is provided a lithium battery including a battery element for a lithium battery having a positive electrode using manganese dioxide, a negative electrode using lithium, and a separator provided between the positive electrode and the negative electrode, an exterior housing in which the battery element is housed, and an electrolyte solution housed in the exterior housing, wherein the electrolyte solution includes a non-aqueous electrolyte solution component containing a lithium electrolyte salt and a fluorine-free organic solvent, and an inorganic acid ester compound having a fluoroalkyl group. [Effects of the Invention]

[0007] In one aspect, it becomes possible to realize a lithium battery with excellent discharge characteristics at low temperatures. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating an example of a lithium battery. [Figure 2] FIG. 1 is a diagram showing an example of a pulse discharge graph of a lithium battery. DETAILED DESCRIPTION OF THE INVENTION

[0009] First, an example of a lithium battery will be described. A lithium battery (lithium primary battery) has a configuration in which a battery element for a lithium battery, which has, for example, a positive electrode using manganese dioxide, a negative electrode using lithium, and a separator provided between the positive electrode and the negative electrode, is housed in an exterior body together with an electrolyte. Known forms of lithium batteries include thin batteries that use a bag-shaped laminate film as the exterior body, as well as coin batteries, cylindrical batteries, prismatic batteries, and the like that use a can of a predetermined shape as the exterior body.

[0010] FIG. 1 is a diagram illustrating an example of a lithium battery. FIG. 1(A) is a schematic plan view of a main part of an example of a lithium battery. FIG. 1(B) is a schematic cross-sectional view of a main part of an example of a lithium battery. FIG. 1(B) is a schematic cross-sectional view taken along line II of FIG. 1(A).

[0011] 1(A) and 1(B) is an example of a thin lithium battery. The lithium battery 100 includes a battery element 10, an electrolyte 20, and an exterior body 30. The battery element 10 is a battery element for a lithium battery, and as shown in FIG. 1(B), has a positive electrode 11, a negative electrode 12, and a separator 13 provided between them.

[0012] The positive electrode 11 uses a positive electrode material containing a positive electrode active material. Manganese dioxide is used as the positive electrode active material. The positive electrode material may include, in addition to the positive electrode active material, a conductive agent such as a carbon material, and organic components such as a binder and a solvent. Such materials may be kneaded with the positive electrode active material to form a positive electrode material (positive electrode mixture). The positive electrode 11 may include a current collector such as a stainless steel expanded metal, on which the positive electrode material is laminated. For example, the positive electrode 11 is formed by applying a slurry-like positive electrode material to the current collector, drying it, and pressing it. As shown in FIGS. 1(A) and 1(B), a positive electrode tab 11a made of a strip of metal or the like is connected to the positive electrode 11 for external connection.

[0013] The negative electrode 12 uses a negative electrode material containing a negative electrode active material. The negative electrode active material is lithium, for example, metallic lithium or a lithium alloy. The negative electrode 12 may include a current collector such as copper foil, on which lithium, the negative electrode material, is laminated. For example, the negative electrode 12 is formed by attaching the lithium, the negative electrode material, to a current collector. For external connection, a negative electrode tab 12a made of a strip of metal or the like is connected to the negative electrode 12, as shown in FIGS. 1(A) and 1(B).

[0014] As shown in FIG. 1(B), the positive electrode 11 and the negative electrode 12 are disposed so as to face each other with a separator 13 interposed therebetween. The facing positive electrode 11 and negative electrode 12 are separated by the separator 13. The separator 13 may be a polyolefin-based or cellulose-based porous film, a woven fabric, a nonwoven fabric, or the like. Alternatively, the separator 13 may be made of ceramic or the like.

[0015] 1(A) and 1(B), the positive electrode 11, negative electrode 12, and separator 13 of the battery element 10 are housed in an exterior body 30, for example, an exterior body 30 formed by laminating the edges of two exterior films 30a together to form a bag, so that the tips of the positive electrode tab 11a and the negative electrode tab 12a protrude. For the exterior film 30a of the exterior body 30, a laminate film is used in which insulating layers of polyamide, polypropylene, or the like are laminated on both sides of a metal layer of aluminum, stainless steel, or the like.

[0016] The exterior body 30 contains the battery element 10 and an electrolyte solution 20 that serves as a conductive medium for lithium ions. For example, the battery element 10 is housed together with the electrolyte solution 20 in a bag-shaped exterior body 30 formed by welding the edges of three sides of two rectangular exterior films 30a and leaving one side open, with the positive electrode tab 11a and negative electrode tab 12a protruding outside the exterior body 30, and the open side is welded. The battery element 10 is impregnated with the electrolyte solution 20, and the electrolyte solution 20 permeates into the battery element 10. Using this method, a lithium battery 100 as shown in FIGS. 1(A) and 1(B) is manufactured, i.e., a lithium battery 100 in which the battery element 10 and the electrolyte solution 20 are housed in the exterior body 30 and the positive electrode tab 11a and negative electrode tab 12a protrude outside the exterior body 30.

[0017] When the lithium battery 100 is discharged, lithium ions are conducted and taken into the positive electrode 11 from the negative electrode 12 via the separator 13. In the lithium battery 100, the discharge operation is realized by such lithium ion conduction.

[0018] Here, a lithium battery 100 in the form of a thin battery is illustrated as an example of a lithium battery. However, other known lithium batteries include coin-shaped batteries in which a battery element having a positive electrode, a negative electrode, and a separator between them is housed together with an electrolyte in a coin-shaped battery can (also referred to as an "external can"), and cylindrical or prismatic batteries in which the battery element is housed together with an electrolyte in a cylindrical or prismatic battery can. In any form of lithium battery, the battery element may include two or more separator layers, and the positive electrode and negative electrode may be arranged so as to face each other with a separator interposed therebetween (i.e., two or more positive or negative electrodes). Furthermore, the battery element may be one in which a predetermined number of positive electrodes, negative electrodes, and separators are stacked in one direction in a predetermined order, or one in which the stacked layers are wound or folded.

[0019] In the following description, one or both of the positive electrode and negative electrode (for example, the positive electrode 11 and negative electrode 12 of the lithium battery 100) in the battery element of various lithium batteries including the lithium battery 100 will also be referred to as "electrode".

[0020] Various types of lithium batteries such as the lithium battery 100 are used for a variety of purposes, such as meter communication and various backup power sources, and have a wide operating temperature range, with the dischargeable temperature range being set to a wide temperature range from minus several tens of degrees Celsius to plus several tens of degrees Celsius. It is desirable for lithium batteries to exhibit high discharge characteristics over such a wide temperature range.

[0021] Conventionally, known electrolytes for lithium batteries, such as the electrolyte 20 of the lithium battery 100, contain a lithium electrolyte salt, such as lithium trifluoromethanesulfonate, and an organic solvent, such as ethylene carbonate, propylene carbonate, or 1,2-dimethoxyethane. However, lithium batteries using such conventional electrolytes sometimes fail to provide sufficient discharge characteristics in low-temperature environments, for example, in low-temperature environments below 0°C, such as −40°C, which is within the dischargeable temperature range.

[0022] Here, the discharge characteristics of a lithium battery include, for example, continuous discharge characteristics and pulse discharge characteristics. Continuous discharge characteristics are the characteristics of a lithium battery when continuously discharged at a constant current, i.e., when connected to a load through which a predetermined current flows continuously. Continuous discharge characteristics can also be said to be the characteristics of a lithium battery when continuously discharged at a low rate. Pulse discharge characteristics are the characteristics of a lithium battery when pulsed or sudden discharge occurs from a no-load state, i.e., when connected to a load through which a predetermined current flows in pulsed or sudden manner from a no-load state where the battery is not connected to a load. Pulse discharge characteristics can also be said to be the characteristics of a high-rate pulsed or sudden discharge.

[0023] Lithium batteries using the above-described conventional electrolyte, especially those in the final stages of discharge capacity (e.g., when approximately 80% of the design capacity has been consumed, i.e., approximately 80% discharge depth), tend to exhibit insufficient pulse discharge characteristics in low-temperature environments, and the voltage when transitioning from a no-load state (i.e., when connected to a load) to a loaded state (i.e., immediately after the start of discharge from the no-load state) tends to drop sharply and temporarily. If the voltage immediately after the start of discharge from the no-load state drops sharply and falls below the reference voltage of the product in which the lithium battery is used, the product may prematurely determine that the lithium battery is dead, even if there is still battery capacity remaining. For example, this may lead to a situation where the product prematurely determines that the battery is dead during the initial stages of starting the product in a low-temperature environment.

[0024] In order to prevent the product from prematurely determining that the battery is dead in a low-temperature environment, it is effective to improve the pulse discharge characteristics of the lithium battery at low temperatures, i.e., to suppress the sudden drop in voltage immediately after the start of discharge from a no-load state. However, lithium batteries using conventional electrolytes, especially those at the end of their discharge capacity, do not have sufficient pulse discharge characteristics at such low temperatures, making it difficult to prevent the product from prematurely determining that the battery is dead.

[0025] In view of these points, an electrolyte solution for a lithium battery having the composition shown below is used to realize a lithium battery having excellent discharge characteristics at low temperatures, particularly at low temperatures in the final discharge capacity state.

[0026] That is, the electrolyte used in this lithium battery is an electrolyte containing a non-aqueous electrolyte component including a lithium electrolyte salt and a fluorine-free organic solvent, and an inorganic acid ester compound having a fluoroalkyl group.

[0027] The lithium electrolyte salt of the electrolyte solution may be, for example, lithium trifluoromethanesulfonate, which is a type of lithium salt. Other lithium salts may be used for the lithium electrolyte salt of the electrolyte solution, such as lithium bis(fluorosulfonyl)imide. One type of lithium salt may be used for the lithium electrolyte salt of the electrolyte solution, or two or more types of lithium salts may be used.

[0028] The fluorine-free organic solvent of the electrolyte solution is, for example, an organic compound that does not contain fluorine atoms in the molecule, such as ethylene carbonate, propylene carbonate, 1,2-dimethoxyethane, etc. The fluorine-free organic solvent of the electrolyte solution may be one type of organic compound that does not contain fluorine atoms, or two or more types of organic compounds that do not contain fluorine atoms.

[0029] For example, a mixture of three organic compounds, ethylene carbonate, propylene carbonate, and 1,2-dimethoxyethane, in a predetermined ratio (volume ratio, etc.) is used as the fluorine-free organic solvent for the electrolyte. A lithium electrolyte salt, for example, lithium trifluoromethanesulfonate, is dissolved in such a fluorine-free organic solvent to a predetermined concentration, thereby preparing a non-aqueous electrolyte component.

[0030] The non-aqueous electrolyte component is a component that can function by itself as an electrolyte (nonaqueous electrolyte) for a lithium battery. As long as the non-aqueous electrolyte solution mainly contains a lithium electrolyte salt and a fluorine-free organic solvent, it may contain other components different from these, such as a solvent or inevitable impurities.

[0031] Here, an inorganic acid ester compound having a fluoroalkyl group is further added to the nonaqueous electrolyte solution components as described above, i.e., the nonaqueous electrolyte solution components containing a predetermined lithium electrolyte salt and a fluorine-free organic solvent, to form an electrolyte solution for a lithium battery.

[0032] The inorganic acid ester compound having a fluoroalkyl group may be, for example, a carbonate ester having a fluoroalkyl group or a phosphate ester having a fluoroalkyl group. Alternatively, the inorganic acid ester compound having a fluoroalkyl group may be, for example, a carbonate ester having a fluoroalkyl group and a phosphate ester having a fluoroalkyl group.

[0033] Here, the carbonate ester having a fluoroalkyl group is a compound represented by the following formula (1a). O=C(OR 1 )2···(1a) In the above formula (1a), two R 1 one of the R is a fluoroalkyl group containing at least one fluorine atom, and two R 1 The remaining one of the two R in the above formula (1a) is an alkyl group or a fluoroalkyl group containing at least one fluorine atom. 1 The elemental composition and structure of each of the may be independent of each other.

[0034] As an example, bis(2,2,2-trifluoroethyl)carbonate as shown in the following formula (1) is used as the carbonate ester added to the non-aqueous electrolyte component of the electrolyte.

[0035] [ka]

[0036] To the non-aqueous electrolyte component of the electrolyte, one type of carbonate ester having a fluoroalkyl group may be added, or two or more types of carbonate esters having a fluoroalkyl group may be added.

[0037] Furthermore, as the phosphate ester having a fluoroalkyl group, a compound represented by the following formula (2a) is used. O=P(OR 2 )3···(2a) In the above formula (2a), three R 2 one of the R is a fluoroalkyl group containing at least one fluorine atom, and three R 2 The remaining two of the three R in the above formula (2a) are each an alkyl group or a fluoroalkyl group containing at least one fluorine atom. 2 The elemental composition and structure of each of the may be independent of each other.

[0038] As an example, tris(2,2,2-trifluoroethyl)phosphate as shown in the following formula (2) is used as the phosphate ester added to the non-aqueous electrolyte component of the electrolyte.

[0039] [ka]

[0040] One type of phosphoric acid ester having a fluoroalkyl group may be added to the non-aqueous electrolyte component of the electrolyte, or two or more types of phosphoric acid esters having a fluoroalkyl group may be added.

[0041] In the above-described electrolyte solution, i.e., in which an inorganic acid ester compound having a fluoroalkyl group is added to non-aqueous electrolyte components containing a lithium electrolyte salt and a fluorine-free organic solvent, the inorganic acid ester compound is added to the non-aqueous electrolyte components in an amount corresponding to 2 to 20% by volume of the non-aqueous electrolyte components. In other words, the inorganic acid ester compound having a fluoroalkyl group is contained in the electrolyte in an amount ranging from 2 to 20% by volume relative to the volume of the non-aqueous electrolyte components. Alternatively, when the ratio of the volume V1 of the non-aqueous electrolyte components to the volume V2 of the inorganic acid ester compound having a fluoroalkyl group is V1:V2 = 100:X, the inorganic acid ester compound is added to the non-aqueous electrolyte components so that X is 2 to 20.

[0042] In conventional lithium batteries that do not contain an inorganic acid ester compound having a fluoroalkyl group and that use a non-aqueous electrolyte solution containing lithium electrolyte salt and a fluorine-free organic solvent, by-products generated in the electrolyte during discharge or storage can adhere to the electrode surface, particularly the surface of lithium used in the negative electrode. The adhesion of such by-products to the electrode surface can cause an increase in the electrode's internal resistance and a decrease in voltage during pulse discharge. Lithium batteries that use lithium in the negative electrode and manganese dioxide in the positive electrode are often installed outdoors for applications such as gas meters and water meters and are exposed to low-temperature environments. In such low-temperature environments, by-products adhering to the electrode surface can easily increase the electrode's internal resistance and decrease voltage during pulse discharge. Therefore, as described above, lithium batteries using conventional electrolytes, especially those near the end of their discharge capacity, experience a significant drop in voltage immediately after the start of discharge in low-temperature environments, increasing the likelihood that the product will determine that the battery is dead early.

[0043] In contrast, in a lithium battery using an electrolyte solution in which an inorganic acid ester compound having a fluoroalkyl group as described above is further added to nonaqueous electrolyte components containing a lithium electrolyte salt and a fluorine-free organic solvent, adhesion of by-products to the electrode surface is suppressed. This is thought to be because the strong electronegativity of the fluorine atoms in the fluoroalkyl group of the inorganic acid ester compound added to the electrolyte solution causes the by-products in the electrolyte solution to be captured by the inorganic acid ester compound, thereby suppressing adhesion of the by-products to the electrode surface. Suppressing adhesion of by-products to the electrode surface suppresses an increase in the internal resistance of the electrode and inhibits lithium ion conduction during discharge, i.e., inhibiting the generation of lithium ions from the negative electrode and their incorporation into the positive electrode. Therefore, voltage drop during pulse discharge is suppressed, and the voltage drop immediately after the start of discharge from a no-load state is suppressed.

[0044] As described above, the lithium battery uses an electrolyte containing a non-aqueous electrolyte solution containing a lithium electrolyte salt and a fluorine-free organic solvent, to which an inorganic acid ester compound having a fluoroalkyl group has been added. The use of an electrolyte containing such an inorganic acid ester compound having a fluoroalkyl group improves the discharge characteristics of the lithium battery at low temperatures compared to conventional electrolytes without such an inorganic acid ester compound. For example, the discharge characteristics at low temperatures below 0°C, such as −40°C, and the pulse discharge characteristics in such low-temperature environments are improved. More specifically, the voltage drop immediately after the start of discharge from a no-load state in a low-temperature environment is suppressed. This prevents the voltage of the lithium battery from falling below the reference voltage of the product at an early stage, such as when the product is started up, even when the product is placed in a low-temperature environment or even when the lithium battery reaches the end of its discharge capacity in such a low-temperature environment. This effectively prevents the product from prematurely determining that the lithium battery is dead. The above electrolyte allows for the realization of a lithium battery with excellent low-temperature discharge characteristics.

[0045] The electrolyte solutions of Examples, Comparative Examples and Conventional Examples, lithium batteries using the electrolyte solutions, and the results of their characteristic evaluations will be described below. Example 1 (positive electrode) Manganese dioxide was used as the positive electrode active material, and this was mixed with a conductive agent, a binder, etc. to obtain a slurry positive electrode material. The obtained positive electrode material was applied to a sheet of stainless steel expanded metal that would serve as a positive electrode current collector, and after drying and pressing, a positive electrode portion and a positive electrode terminal portion were cut out. A positive electrode tab with a heat-sealing resin was resistance-welded to the positive electrode terminal portion to obtain a positive electrode with the positive electrode tab connected.

[0046] (Negative electrode) A lithium attachment portion and a negative electrode terminal portion were cut out from the copper foil serving as the negative electrode current collector, and cut pieces of metallic lithium were attached to the lithium attachment portion as the negative electrode material or negative electrode active material. A negative electrode tab with a heat-sealing resin was resistance-welded to the negative electrode terminal portion, thereby obtaining a negative electrode with the negative electrode tab connected.

[0047] (separator) A polypropylene separator was used as the separator. (electrolyte) Lithium trifluoromethanesulfonate (LiCF3SO3) was used as the lithium electrolyte salt. Ethylene carbonate (also referred to as "EC"), propylene carbonate (also referred to as "PC"), and 1,2-dimethoxyethane (also referred to as "DME") were used as the fluorine-free organic solvent. Bis(2,2,2-trifluoroethyl)carbonate (also referred to as "TFEC"), as shown in formula (1) above, was used as the inorganic acid ester compound having a fluoroalkyl group.

[0048] To prepare the electrolyte solution, first, a fluorine-free organic solvent containing EC, PC, and DME was prepared. The volume ratios of EC, PC, and DME in the fluorine-free organic solvent can be, for example, 5% to 20% by volume for EC, 5% to 20% by volume for PC, and 60% to 90% by volume for DME. As an example, a fluorine-free organic solvent was prepared containing 10% by volume of EC, 10% by volume of PC, and 80% by volume of DME. Next, lithium trifluoromethanesulfonate, a lithium electrolyte salt, was dissolved in the prepared fluorine-free organic solvent to a salt concentration of 0.6 M (mol / L) to prepare a solution containing the lithium electrolyte salt and the fluorine-free organic solvent, i.e., a nonaqueous electrolyte component. Then, TFEC was added to the prepared nonaqueous electrolyte component in amounts corresponding to 2%, 5%, 10%, and 20% by volume, based on 100% by volume of the nonaqueous electrolyte component, respectively. In this way, four types of electrolyte solutions (electrolyte solutions of Example 1) with different amounts of TFEC added were obtained.

[0049] (Cell preparation) A laminate, which was formed by stacking a positive electrode with a positive electrode tab, a separator, and a negative electrode with a negative electrode tab in this order, was housed together with an electrolyte in a separately prepared exterior case made of a laminate film so that the positive and negative electrode tabs protruded, and the exterior case was sealed. The following procedure, for example, can be used to house the laminate and the electrolyte in the exterior case and seal the exterior case so that the positive and negative electrode tabs protrude outside the exterior case. That is, three sides of two rectangular laminate films (exterior films) facing each other are welded to form a bag-shaped exterior case with one side open. The laminate is housed in the bag-shaped exterior case so that the positive and negative electrode tabs protrude, and the electrolyte is then injected and housed inside, and the open side of the bag-shaped exterior case on the side where the positive and negative electrode tabs protrude is sealed. For example, this procedure is used to house the laminate and the electrolyte in the exterior case so that the positive and negative electrode tabs protrude outside the exterior case.

[0050] Using the above-mentioned procedure, four types of lithium batteries (lithium batteries of Example 1) with different electrolyte solutions were obtained using the four types of electrolyte solutions prepared above. The cell size of the lithium batteries was 7 cm long x 7 cm wide x 1 cm thick.

[0051] <Example 2> In Example 2, lithium trifluoromethanesulfonate was used as the lithium electrolyte salt of the electrolyte solution, EC, PC, and DME were used as the fluorine-free organic solvents, and tris(2,2,2-trifluoroethyl)phosphate (also referred to as "TTFPa") as shown in the above formula (2) was used as the inorganic acid ester compound having a fluoroalkyl group.

[0052] A non-aqueous electrolyte solution containing lithium trifluoromethanesulfonate, a lithium electrolyte salt with a salt concentration of 0.6 M, and a fluorine-free organic solvent containing EC, PC, and DME (volume ratio of EC:PC:DME=10:10:80) was prepared by adding TTFPa in amounts corresponding to 2 vol%, 5 vol%, 10 vol%, and 20 vol% relative to 100 vol% of the non-aqueous electrolyte solution. In this way, four types of electrolyte solutions (electrolyte solutions of Example 2) with different amounts of TTFPa added were obtained.

[0053] Four types of lithium batteries (lithium batteries of Example 2) each having a different electrolyte solution were obtained in the same manner as in Example 1, except that these four types of electrolyte solutions were used. <Comparative Example 1> In Comparative Example 1, lithium trifluoromethanesulfonate was used as the lithium electrolyte salt of the electrolyte solution, EC, PC, and DME were used as the fluorine-free organic solvents, and trimethyl phosphate (also referred to as "TMP"), which does not have a fluoroalkyl group and is shown in the following formula (3), was used as the inorganic acid ester compound.

[0054] [ka]

[0055] A non-aqueous electrolyte solution containing lithium trifluoromethanesulfonate, a lithium electrolyte salt with a salt concentration of 0.6 M, and a fluorine-free organic solvent containing EC, PC, and DME (volume ratio of EC:PC:DME=10:10:80), was prepared by adding TMP in amounts corresponding to 2 vol%, 5 vol%, 10 vol%, and 20 vol% relative to 100 vol% of the non-aqueous electrolyte solution. In this way, four types of electrolyte solutions (electrolyte solutions of Comparative Example 1) with different amounts of TMP added were obtained.

[0056] Four types of lithium batteries (lithium batteries of Comparative Example 1) each having a different electrolyte solution were obtained in the same manner as in Example 1, except that these four types of electrolyte solutions were used. <Comparative Example 2> In Comparative Example 2, lithium trifluoromethanesulfonate was used as the lithium electrolyte salt of the electrolyte solution, EC, PC, and DME were used as the fluorine-free organic solvents, and triethyl phosphate (also referred to as "TEP"), which does not have a fluoroalkyl group and is shown in the following formula (4), was used as the inorganic acid ester compound.

[0057] [ka]

[0058] A non-aqueous electrolyte solution containing lithium trifluoromethanesulfonate, a lithium electrolyte salt with a salt concentration of 0.6 M, and a fluorine-free organic solvent containing EC, PC, and DME (volume ratio of EC:PC:DME=10:10:80) was prepared by adding TEP in amounts of 2 vol%, 5 vol%, 10 vol%, and 20 vol% relative to 100 vol% of the non-aqueous electrolyte solution. In this way, four types of electrolyte solutions (electrolyte solutions of Comparative Example 2) with different amounts of TEP added were obtained.

[0059] Four types of lithium batteries (lithium batteries of Comparative Example 2) each having a different electrolyte solution were obtained in the same manner as in Example 1, except that these four types of electrolyte solutions were used. <Conventional example> The conventional electrolyte solution used was lithium trifluoromethanesulfonate with a salt concentration of 0.6 M as the lithium electrolyte salt, and EC, PC, and DME (volume ratio of EC:PC:DME=10:10:80) as the fluorine-free organic solvent, and did not contain any inorganic acid ester compounds, i.e., a solution corresponding to the above-mentioned non-aqueous electrolyte components.

[0060] A conventional lithium battery was obtained in the same manner as in Example 1, except that such an electrolyte solution was used. <Characteristics evaluation> (Pulse discharge characteristics of lithium batteries) Pulse discharge was carried out on the lithium batteries using the electrolytes of Example 1-2, Comparative Example 1-2, and the conventional example. Before pulse discharge, each lithium battery was previously discharged to 80% of its design capacity (80% depth of discharge). The pulse discharge was carried out in a chamber at a temperature of -40°C, and the load conditions were a current value of 16.1 mA and a time of 1 s (second). Under these load conditions, pulse discharge was carried out on the lithium batteries using the electrolytes of Example 1-2, Comparative Example 1-2, and the conventional example, and the voltage (minimum voltage) during the pulse discharge was measured.

[0061] An example of a pulse discharge graph for a lithium battery is shown in FIG. 2. When the above-described pulse discharge is performed on a lithium battery, a pulse discharge graph such as that shown in FIG. 2 is obtained. As an example, FIG. 2 shows pulse discharge graphs for lithium batteries using the electrolyte of Example 1 (TFEC content: 10% by volume) and the conventional electrolyte. As shown in FIG. 2, both the lithium batteries using the electrolyte of Example 1 and the conventional electrolyte exhibit a discharge behavior in which the voltage drops during the load period (1 second from the start of discharge) during pulse discharge. As can be seen from FIG. 2, the lithium battery using the conventional electrolyte exhibits a larger voltage drop immediately after the start of discharge than the lithium battery using the electrolyte of Example 1. If the voltage drop immediately after the start of discharge falls below the specified reference voltage of a product using the lithium battery, the product is likely to determine that the battery is dead, even though there is still some battery capacity remaining.

[0062] 2 shows lithium batteries using the electrolyte of Example 1 and the conventional electrolyte, but the above-mentioned pulse discharge was carried out for all of the lithium batteries using the electrolytes of Example 1-2, Comparative Example 1-2, and the conventional electrolyte, and the minimum voltage during the load period was measured. The measurement results are shown in Table 1.

[0063] [Table 1]

[0064] From Table 1, it can be seen that in the lithium battery using the conventional electrolyte corresponding to the non-aqueous electrolyte components, the minimum voltage during pulse discharge (the voltage immediately after the start of discharge) was 1.56V. In contrast, in the lithium battery using the electrolyte solution of Example 1, in which TFEC was added to the non-aqueous electrolyte components, the minimum voltage during pulse discharge was 1.88 V when the TFEC content was 2 vol%, 2.04 V when it was 5 vol%, 2.02 V when it was 10 vol%, and 1.97 V when it was 20 vol%.In other words, in the range of TFEC content from 2 vol% to 20 vol%, the minimum voltage during pulse discharge was higher than the minimum voltage during pulse discharge of the lithium battery using the electrolyte solution of the conventional example.

[0065] Furthermore, in the lithium battery using the electrolyte solution of Example 2 in which TTFPa was added to the non-aqueous electrolyte components, the minimum voltage during pulse discharge was 1.94 V when the amount of TTFPa added was 2 vol%, 1.91 V when it was 5 vol%, 1.89 V when it was 10 vol%, and 1.85 V when it was 20 vol%, and this was higher than the minimum voltage during pulse discharge of the lithium battery using the electrolyte solution of the conventional example in the range of TTFPa added from 2 vol% to 20 vol%.

[0066] On the other hand, in the lithium battery using the electrolyte solution of Comparative Example 1 in which TMP was added to the non-aqueous electrolyte components, the minimum voltage during pulse discharge was 1.52 V when the TMP addition amount was 2 vol%, 1.58 V when it was 5 vol%, 1.51 V when it was 10 vol%, and 1.52 V when it was 20 vol%. In other words, within the range of TMP addition from 2 vol% to 20 vol%, the minimum voltage during pulse discharge was lower than that of the lithium battery using the electrolyte solution of the conventional example, or no sufficient improvement was observed.

[0067] Furthermore, in the lithium battery using the electrolyte solution of Comparative Example 2 in which TEP was added to the non-aqueous electrolyte components, the minimum voltage during pulse discharge was 1.63 V when the TEP addition amount was 2 vol%, 1.58 V when it was 5 vol%, 1.54 V when it was 10 vol%, and 1.54 V when it was 20 vol%. In the range of TEP addition amount from 2 vol% to 20 vol%, the minimum voltage during pulse discharge was lower than the minimum voltage during pulse discharge of the lithium battery using the electrolyte solution of the conventional example, or no sufficient improvement was observed.

[0068] These results suggest that lithium batteries using electrolytes containing inorganic acid ester compounds with fluoroalkyl groups, such as TFEC or TTFPa, as non-aqueous electrolyte components exhibit a reduced voltage drop during pulse discharge at low temperatures compared to lithium batteries using electrolytes without such inorganic acid ester compounds. The inorganic acid ester compounds with fluoroalkyl groups, which contain highly electronegative fluorine atoms, capture by-products in the electrolyte, preventing their adhesion to the electrode surface and the resulting inhibition of discharge. Table 1 indicates that adding an inorganic acid ester compound with a fluoroalkyl group (TFEC or TTFPa) in an amount ranging from 2% to 20% by volume relative to 100% by volume of the non-aqueous electrolyte components effectively suppresses voltage drop during pulse discharge at temperatures as low as -40°C.

[0069] By using a non-aqueous electrolyte containing an inorganic acid ester compound having a fluoroalkyl group as a component of the electrolyte for a lithium battery, even when the product using the lithium battery is placed in a low-temperature environment, or even when the lithium battery reaches the end of its discharge capacity in such a low-temperature environment, the voltage of the lithium battery can be effectively prevented from falling below the reference voltage of the product at an early stage, such as when the product is started up, which would cause the product to prematurely determine that the battery is dead. This electrolyte allows for the realization of a lithium battery with excellent discharge characteristics at low temperatures.

[0070] Here, TFEC and TTFPa are exemplified as inorganic acid ester compounds having a fluoroalkyl group that are added to the non-aqueous electrolyte components. In addition to TFEC and TTFPa, one or more of various inorganic acid ester compounds having a fluoroalkyl group (such as compounds represented by the above formula (1a) or formula (2a)) can be added to the non-aqueous electrolyte components. This achieves the same effect as above, namely, the inorganic acid ester compound having a fluoroalkyl group can suppress adhesion of by-products to the electrode surface and the resulting inhibition of discharge, thereby suppressing voltage drops during pulse discharge at low temperatures.

[0071] In addition, while the electrolyte solution containing lithium trifluoromethanesulfonate as the lithium electrolyte salt and the lithium battery using the same are exemplified here, the same effects as those described above can also be obtained for electrolyte solutions containing one or more lithium salts other than lithium trifluoromethanesulfonate and lithium batteries using the same by adding various inorganic acid ester compounds having a fluoroalkyl group to the electrolyte solution.

[0072] In addition, the present invention provides an electrolyte solution containing a fluorine-free organic solvent containing EC, PC, and DME, and a lithium battery using the same. In addition, the same effects as those described above can be obtained for an electrolyte solution containing a fluorine-free organic solvent containing any one of EC, PC, and DME, or one or more compounds other than EC, PC, and DME, and a lithium battery using the same, by adding various inorganic acid ester compounds having a fluoroalkyl group to the electrolyte solution. [Explanation of symbols]

[0073] 10 Battery element 11 Positive electrode 11a Positive electrode tab 12 Negative electrode 12a Negative electrode tab 13 Separator 20 Electrolyte 30 Exterior body 30a exterior film 100 lithium batteries

Claims

1. a battery element for a lithium battery, the battery element having a positive electrode using manganese dioxide, a negative electrode using lithium, and a separator provided between the positive electrode and the negative electrode; an exterior body that houses the battery element; an electrolyte solution contained in the exterior body; Including, The electrolyte solution is a non-aqueous electrolyte solution component containing a lithium electrolyte salt and a non-fluorine-containing organic solvent; an inorganic acid ester compound having a fluoroalkyl group; Contains lithium batteries.

2. 2. The lithium battery according to claim 1, wherein the inorganic acid ester compound is contained in an amount of 2% by volume or more and 20% by volume or less relative to the volume of the non-aqueous electrolyte solution components.

3. 2. The lithium battery according to claim 1, wherein the inorganic acid ester compound is a carbonate ester having a fluoroalkyl group.

4. 2. The lithium battery according to claim 1, wherein the inorganic acid ester compound is a phosphate ester having a fluoroalkyl group.

5. 2. The lithium battery according to claim 1, wherein the dischargeable temperature range includes −40° C.

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