Non-aqueous electrolyte for lithium-ion secondary batteries and lithium-ion secondary batteries

Abstract

To provide a technology that can suppress the growth of precipitated metallic lithium. [Solution] The non-aqueous electrolyte disclosed herein comprises a supporting salt, a non-aqueous solvent, and a compound having a triphenylmethane skeleton. The compound comprises a branched hydrocarbon group and a hydroxyl group. The branched hydrocarbon group is located on a phenyl group in the triphenylmethane skeleton and has three or more carbon atoms. The hydroxyl group is located on the phenyl group and is adjacent to the branched hydrocarbon group.

Description

[Technical Field]

[0001] This disclosure relates to lithium-ion secondary batteries. Specifically, it relates to a non-aqueous electrolyte used in lithium-ion secondary batteries and a lithium-ion secondary battery using said non-aqueous electrolyte. [Background technology]

[0002] Japanese Patent Publication No. 2022-87412 discloses a non-aqueous electrolyte for a lithium-ion secondary battery, comprising a lithium salt as an electrolyte salt, a non-aqueous solvent, and aromatic carboxylic acid compounds and aryl halide compounds as additives. The publication also discloses a lithium-ion secondary battery equipped with this non-aqueous electrolyte. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-87412 [Overview of the project] [Problems that the invention aims to solve]

[0004] Incidentally, there is a need for further development of technologies that can suppress the growth of deposited metallic lithium in lithium-ion secondary batteries. [Means for solving the problem]

[0005] The non-aqueous electrolyte disclosed herein comprises a supporting salt, a non-aqueous solvent, and a compound having a triphenylmethane skeleton. The compound comprises a branched hydrocarbon group and a hydroxyl group. The branched hydrocarbon group is located on a phenyl group in the triphenylmethane skeleton and has three or more carbon atoms. The hydroxyl group is located on the phenyl group and is adjacent to the branched hydrocarbon group. The non-aqueous electrolyte with this configuration can suppress the growth of precipitated metallic lithium.

[0006] The lithium-ion secondary battery disclosed herein comprises a positive electrode, a negative electrode, and any of the non-aqueous electrolytes disclosed herein. Such a configuration provides a lithium-ion secondary battery capable of suppressing the growth of deposited metallic lithium. [Brief explanation of the drawing]

[0007] [Figure 1A] Figure 1A is a first explanatory diagram illustrating the collection of metallic lithium according to one embodiment. [Figure 1B] Figure 1B is a second explanatory diagram illustrating the collection of metallic lithium according to one embodiment. [Figure 1C] Figure 1C is a third explanatory diagram illustrating the collection of metallic lithium according to one embodiment. [Figure 2] Figure 2 is a schematic cross-sectional view showing a lithium-ion secondary battery according to one embodiment. [Figure 3] Figure 3 is a schematic perspective view showing the electrode body of a lithium-ion secondary battery according to one embodiment. [Modes for carrying out the invention]

[0008] Hereinafter, several embodiments of the technology disclosed herein will be described with reference to the drawings. In the following drawings, components and parts that perform the same function are denoted by the same reference numerals. Furthermore, the dimensional relationships (length, width, thickness, etc.) in each figure do not reflect actual dimensional relationships. Matters other than those specifically mentioned herein that are necessary for carrying out the technology disclosed herein (for example, non-aqueous electrolytes for lithium-ion secondary batteries and the general configuration and manufacturing process of lithium-ion secondary batteries that do not characterize this disclosure) can be understood as design matters for those skilled in the art based on the prior art. The technology disclosed herein can be carried out based on the contents disclosed herein and common technical knowledge in the art. Furthermore, the following description is not intended to limit this disclosure to the following forms.

[0009] In this specification, the notation "A~B" indicating a range means "A or more and B or less". It also includes the meanings of "exceeding A" and "less than B". Further, in the following description, the reference numerals X and Y in the drawings represent the short-side direction and the long-side direction orthogonal to the short-side direction of the lithium-ion secondary battery 100, respectively. However, these are merely directions for convenience of explanation and do not limit the installation form of the lithium-ion secondary battery 100 in any way.

[0010] In this specification, the "lithium-ion secondary battery" refers to a secondary battery that performs charge and discharge by moving Li ions, which are charge carriers, between the positive electrode and the negative electrode. Secondary batteries generally referred to as lithium secondary batteries (or lithium-ion batteries) are typical examples included in the lithium-ion secondary batteries in this specification. Further, the "active material" in this specification refers to a substance (compound) involved in the intercalation and deintercalation of Li ions on the positive electrode side and the negative electrode side.

[0011] <Non-aqueous electrolyte for lithium-ion secondary battery> First, an embodiment of the non-aqueous electrolyte for a lithium-ion secondary battery disclosed herein will be described. The non-aqueous electrolyte for a lithium-ion secondary battery according to this embodiment contains a supporting salt, a non-aqueous solvent, and a compound having a triphenylmethane skeleton. The above compound contains a branched-chain hydrocarbon group and a hydroxy group. The above branched-chain hydrocarbon group is present on the phenyl group in the triphenylmethane skeleton and has 3 or more carbon atoms. Further, the above hydroxy group is present on the above phenyl group and is adjacent to the above branched-chain hydrocarbon group. Although details will be described later, the above compound functions as a Li collector that collects precipitated metallic lithium. Therefore, according to the non-aqueous electrolyte containing the Li collector, further growth of the precipitated metallic lithium can be suppressed. Hereinafter, each component will be described. In the following description, the above compound will be referred to as the "Li collector".

[0012] As the supporting salt, known lithium salts used as electrolyte salts in the non-aqueous electrolyte of lithium-ion secondary batteries may be used. Examples of lithium salts that can be used include LiPF6, LiBF4, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethane)sulfonimide (LiTFSI), and the like. These can be used alone or in combination of two or more. As the lithium salt, LiPF6 is preferred. The concentration of the lithium salt in the non-aqueous electrolyte is not particularly limited, but is, for example, 0.5 mol / L to 1.5 mol / L, preferably 0.7 mol / L to 1.2 mol / L.

[0013] The non-aqueous solvent is not particularly limited, and known non-aqueous solvents used in the non-aqueous electrolyte of lithium-ion secondary batteries may be used. Examples of non-aqueous solvents include carbonates, ethers, esters, nitriles, sulfones, lactones, and the like. Since the effect of suppressing the growth of deposited metallic lithium is particularly high, it is preferable to include non-aqueous solvents belonging to ethers or carbonates as the non-aqueous solvent. Further, from the viewpoint of easily dissolving the Li collector, it is particularly preferable that the non-aqueous solvent includes a non-aqueous solvent belonging to carbonates.

[0014] Examples of ethers include chain ethers such as dimethoxyethane, diethyl ether, 1,3-dioxolane, glyme, diglyme, triglyme, and tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran, and 2-methyltetrahydrofuran. These can be used alone or in combination of two or more.

[0015] Examples of carbonates include ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyldifluoromethyl carbonate (F-DMC), and trifluorodimethyl carbonate (TFDMC). These can be used individually or in combination of two or more. Among the carbonates, ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are particularly preferred. It is preferable to contain at least one of the three types of carbonates listed above. It is even more preferable to have a mixed solvent containing at least two of the three types of carbonates listed above.

[0016] Although not intended to be interpreted restrictively below, the mechanism by which the Li-collecting material suppresses the growth of metallic lithium deposited on the electrodes of a lithium-ion secondary battery can be considered as follows. Here, Figure 1A is a first explanatory diagram for illustrating the collection of metallic lithium according to one embodiment. Figure 1B is a second explanatory diagram for illustrating the collection of metallic lithium according to one embodiment. Figure 1C is a third explanatory diagram for illustrating the collection of metallic lithium according to one embodiment. Note that Figures 1A to 1C describe a Li-collecting material 90 in which the branched hydrocarbon group 92 is an isopropyl group, but naturally, it is not intended to limit the Li-collecting material disclosed herein to this structure.

[0017] First, as shown in Figure 1A, the non-aqueous electrolyte 80 for the lithium-ion secondary battery according to this embodiment contains a Li-collecting material 90 having a triphenylmethane skeleton. Furthermore, at least one phenyl group in the triphenylmethane skeleton has a branched hydrocarbon group 92 and a hydroxyl group adjacent to the branched hydrocarbon group 92. Next, as shown in Figure 1B, the oxygen atom of the hydroxyl group of the Li-collecting material 90 becomes radicalized in the non-aqueous electrolyte 80. The Li-collecting material 90 changes into a radical 90A in the non-aqueous electrolyte 80. The radicalized oxygen atom (hereinafter also referred to as "oxygen radical") reacts with metallic lithium deposited on the surface of the negative electrode 60, for example, and collects lithium elements (lithium radicals). Then, as shown in Figure 1C, the radical 90A changes into a sparingly soluble lithium adduct 90B in the non-aqueous electrolyte 80 and precipitates.

[0018] Generally, compounds containing radicals are known to be unstable and highly reactive. On the other hand, the radical 90A has a bulky (sterically hindered) branched hydrocarbon group 92 adjacent to the oxygen radical. This suitably reduces and stabilizes the reactivity of the oxygen radical. That is, because the oxygen radical and the branched hydrocarbon group 92 are adjacent, the oxygen atom can maintain the oxygen radical state. Then, the metallic lithium and the oxygen radical react to produce a lithium adduct 90B. The lithium adduct 90B can exist inside the lithium-ion secondary battery 100 without reverting back to metallic lithium. Here, unlike metallic lithium, the lithium adduct 90B does not grow in a dendritic manner. That is, metallic lithium becomes lithium adduct 90B, and its growth is suppressed. This suitably prevents metallic lithium deposited on the negative electrode 60 from growing, passing through the separator sheet 70, and coming into contact with the positive electrode 50, thus preventing an internal short circuit. In this way, the battery performance of the lithium-ion secondary battery 100 can be suitably improved.

[0019] The following describes specific examples of Li-collecting materials having the above-mentioned effects. Note that the following examples are not intended to limit this disclosure to these specific examples. As described above, the Li-collecting material has a triphenylmethane skeleton. The Li-collecting material includes a branched hydrocarbon group and a hydroxyl group. The branched hydrocarbon group is located on a phenyl group in the triphenylmethane skeleton and has three or more carbon atoms. The hydroxyl group is located on the phenyl group and is adjacent to the branched hydrocarbon group. In the Li-collecting material, on the phenyl group, there is a carbon atom to which the hydroxyl group is attached adjacent to the carbon atom to which the branched hydrocarbon group is attached. Here, the branched hydrocarbon group and the hydroxyl group may be present on only one phenyl group, on two phenyl groups, or on three phenyl groups of the triphenylmethane skeleton. Furthermore, the branched hydrocarbon group and the hydroxyl group may be present as one pair, or as two or more pairs on a single phenyl group. In this disclosure, the term "triphenylmethane skeleton" encompasses the skeleton shown in the following chemical formula (1) and the skeleton shown in the following chemical formula (2).

[0020] [ka]

[0021] [ka]

[0022] An example of a lithium-collecting material is the one shown in the following general formula (3). Here, R in the following general formula (3) is independently one of the following: a hydrogen atom, a linear hydrocarbon group (linear alkyl group), a branched-chain hydrocarbon group (branched-chain alkyl group) having 3 or more carbon atoms, a phenyl group, a benzyl group, a halogen atom, a hydroxyl group, two CH2N(CH2COOH) groups, a sulfone group, or a carboxyl group. Furthermore, at least one phenyl group in the following general formula (3) contains a branched-chain hydrocarbon group and a hydroxyl group adjacent to the said branched-chain hydrocarbon group.

[0023] [ka]

[0024] Here, regarding R in the above chemical formula (3), the number of carbon atoms in the chain hydrocarbon group is, for example, 1 to 6, preferably 1 to 4, and more preferably 1 to 3. Examples of chain hydrocarbon groups include methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, etc. The number of carbon atoms in the branched chain hydrocarbon group is 3 or more, as described above. The number of carbon atoms in the branched chain hydrocarbon group is, for example, 3 to 15, preferably 3 to 10, and more preferably 3 to 6. Preferred examples of branched chain hydrocarbon groups include isopropyl group, isobutyl group, sec-butyl group, tert-butyl group, isopentyl group, neopentyl group, tert-pentyl group, cyclopentyl group, 2-ethylbutyl group, cyclohexyl group, etc. Among these, isopropyl group, isobutyl group, sec-butyl group, and tert-butyl group are particularly preferred. Examples of halogen atoms include fluorine atom, chlorine atom, bromine atom, iodine atom, etc. In particular, it is preferable that the atom be one of chlorine, fluorine, or bromine.

[0025] Examples of other Li-trapping materials include those represented by the following general formula (4). Here, each R in the following general formula (4) is independently a hydrogen atom, a chain hydrocarbon group (chain alkyl group), a branched chain hydrocarbon group having 3 or more carbon atoms (branched alkyl group), a phenyl group, a benzyl group, a halogen atom, a hydroxy group, a CH2N(CH2COOH)2 group, a sulfone group, or a carboxy group. R in the following general formula (4) a is one of an oxygen atom, an amino group, an NHX group, NX 1 X 2 group. X, X 1 、X 2 is a hydrocarbon group (alkyl group) or a phenyl group which may have a substituent. Note that X 1 、X 2 may be the same substituent or different substituents. X, X 1 、X 2 is an amino group, an NHX group, NX 1 X 2 group, it exists in the form of an ammonium cation. Also, on at least one phenyl group in the following general formula (4), it contains a branched chain hydrocarbon group and a hydroxy group adjacent to the branched chain hydrocarbon group.

[0026]

Chemical formula

[0027] Here, regarding R in the above chemical formula (4), the number of carbon atoms in the chain hydrocarbon group is, for example, 1 to 6, preferably 1 to 4, and more preferably 1 to 3. Examples of chain hydrocarbon groups include methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, etc. The number of carbon atoms in the branched chain hydrocarbon group is 3 or more, as described above. The number of carbon atoms in the branched chain hydrocarbon group is, for example, 3 to 15, preferably 3 to 10, and more preferably 3 to 6. Preferred examples of branched chain hydrocarbon groups include isopropyl group, isobutyl group, sec-butyl group, tert-butyl group, isopentyl group, neopentyl group, tert-pentyl group, cyclopentyl group, 2-ethylbutyl group, cyclohexyl group, etc. Among these, isopropyl group, isobutyl group, sec-butyl group, and tert-butyl group are particularly preferred. Examples of halogen atoms include fluorine atom, chlorine atom, bromine atom, iodine atom, etc. In particular, it is preferable that the atom be one of chlorine, fluorine, or bromine.

[0028] R in the above chemical formula (4) a X, X 1 , X 2 Regarding the hydrocarbon group, it may be linear or branched. The number of carbon atoms in the hydrocarbon group is, for example, 1 to 6, preferably 1 to 4, and more preferably 1 to 3. Examples of hydrocarbon groups include methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, phenyl group, and benzyl group. The phenyl group may or may not have substituents. If the phenyl group has substituents, examples of substituents include hydrocarbon groups with 1 to 6 carbon atoms, hydroxyl groups, halogen atoms, etc.

[0029] In addition, in the above chemical formulas (3) and (4), the sulfone group (-SO3H) and carboxyl group (-COOH) may exist in a state where the hydrogen atom of the hydroxyl group is substituted by the salt. Examples of such salts include alkali metal salts, alkaline earth metal salts, and ammonium salts. Examples of alkali metal salts include lithium salts, sodium salts, and potassium salts. Examples of alkaline earth metal salts include magnesium salts and calcium salts.

[0030] Li-collecting materials can be used individually or in combination of two or more. Suitable examples of Li-collecting materials include thymol blue, bromothymol blue, and methylthymol blue. Here, chemical formulas (5) to (7) below represent thymol blue, bromothymol blue, and methylthymol blue, respectively.

[0031] [ka]

[0032] [ka]

[0033] [ka]

[0034] The concentration of the Li-collecting material in the non-aqueous electrolyte is not particularly limited, as long as the effects of the technology disclosed herein are achieved. Up to a certain concentration of the Li-collecting material, the effect of suppressing the growth of precipitated metallic lithium increases as the concentration increases. However, once the concentration of the Li-collecting material exceeds a certain value, the effect of suppressing the growth of precipitated metallic lithium saturates. For this reason, the concentration of the Li-collecting material in the non-aqueous electrolyte is, for example, 0.05 mmol / L or more, preferably 0.1 mmol / L or more, and more preferably 0.2 mmol / L or more. Furthermore, the upper limit of the concentration of the Li-collecting material in the non-aqueous electrolyte is, for example, 2 mmol / L or less, preferably 1.5 mmol / L or less (for example 1.2 mmol / L or less), and more preferably 1.1 mmol / L or less. When two or more types of Li-collecting materials are used in combination, the total concentration of these can be used as the concentration of the Li-collecting material.

[0035] The non-aqueous electrolyte for the lithium-ion secondary battery according to this embodiment may contain various additives such as gas generating agents (e.g., biphenyl (BP), cyclohexylbenzene (CHB)), film-forming agents, dispersants, and thickeners, as long as they do not significantly impair the effects of the disclosure. The concentration of additives in the non-aqueous electrolyte is, for example, 0.01 mmol / L to 1 mmol / L, and preferably 0.05 mmol / L to 0.5 mmol / L.

[0036] The non-aqueous electrolyte 80 for lithium-ion secondary batteries according to this embodiment can be used in the lithium-ion secondary battery 100 according to a known method. By using the non-aqueous electrolyte 80 for lithium-ion secondary batteries according to this embodiment in the lithium-ion secondary battery 100, the growth of deposited metallic lithium can be suppressed in the lithium-ion secondary battery 100.

[0037] <Lithium-ion rechargeable battery> Next, the lithium-ion secondary battery according to this embodiment will be described. Here, Figure 2 is a schematic cross-sectional view showing a lithium-ion secondary battery according to one embodiment. Figure 3 is a schematic perspective view showing the electrode body of the lithium-ion secondary battery according to one embodiment. As shown in Figure 2, the lithium-ion secondary battery 100 according to this embodiment includes a positive electrode 50, a negative electrode 60, and a non-aqueous electrolyte 80. With this configuration, it is possible to provide a lithium-ion secondary battery 100 that can suppress the growth of deposited metallic lithium. The individual components will be described below.

[0038] The lithium-ion secondary battery 100 shown in Figure 2 is a sealed battery constructed by housing a flat-shaped wound electrode body 20 and a non-aqueous electrolyte 80 in a flat, rectangular battery case (i.e., outer container) 30. The battery case 30 is provided with a positive electrode terminal 42 and a negative electrode terminal 44 for external connection, and a thin-walled safety valve 36 that is set to release the internal pressure when the internal pressure of the battery case 30 rises above a predetermined level. The battery case 30 is also provided with an inlet (not shown) for injecting the non-aqueous electrolyte 80. The positive electrode terminal 42 is electrically connected to a positive electrode current collector plate 42a. The negative electrode terminal 44 is electrically connected to a negative electrode current collector plate 44a. As the material of the battery case 30, for example, a lightweight metal material with good thermal conductivity such as aluminum is used.

[0039] As shown in Figures 2 and 3, the wound electrode body 20 has a configuration in which a positive electrode sheet 50 and a negative electrode sheet 60 are superimposed on each other via two elongated separator sheets 70 and wound in the longitudinal direction. The positive electrode sheet 50 has a configuration in which a positive electrode active material layer 54 is formed along the longitudinal direction on one or both sides (here, both sides) of an elongated positive electrode current collector 52. The negative electrode sheet 60 has a configuration in which a negative electrode active material layer 64 is formed along the longitudinal direction on one or both sides (here, both sides) of an elongated negative electrode current collector 62. The portion 52a where the positive electrode active material layer is not formed (i.e., the portion where the positive electrode current collector 52 is exposed without the positive electrode active material layer 54 being formed) and the portion 62a where the negative electrode active material layer is not formed (i.e., the portion where the negative electrode current collector 62 is exposed without the negative electrode active material layer 64 being formed) are formed to protrude outward from both ends of the winding axis direction of the wound electrode body 20 (i.e., the sheet width direction perpendicular to the longitudinal direction). The positive electrode current collector plate 42a and the negative electrode current collector plate 44a are joined to the positive electrode active material layer not formed portion 52a and the negative electrode active material layer not formed portion 62a, respectively.

[0040] The positive electrode sheet 50 and the negative electrode sheet 60 can be the same as those used in conventional lithium-ion secondary batteries, without any particular limitations. A typical embodiment is shown below.

[0041] Examples of positive electrode current collectors 52 constituting the positive electrode sheet 50 include aluminum foil. The positive electrode active material layer 54 contains at least positive electrode active material. Examples of positive electrode active material include lithium transition metal oxides (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNiO2, LiCoO2, LiFeO2, LiMn2O4, LiNi 0.8 Co 0.15 Al 0.5 O2, LiLiLi 0.5 Mn 1.5Examples include O4, lithium transition metal phosphate compounds (e.g., LiFePO4), etc. The positive electrode active material layer 54 may contain components other than the active material, such as conductive materials and binders. Suitable conductive materials include carbon black such as acetylene black (AB) and other carbon materials (e.g., graphite). Suitable binders include polyvinylidene fluoride (PVDF), etc.

[0042] The negative electrode current collector 62 constituting the negative electrode sheet 60 can be, for example, copper foil. The negative electrode active material layer 64 contains at least negative electrode active material. As the negative electrode active material, carbon materials such as graphite, hard carbon, and soft carbon can be used, with graphite being preferred. The negative electrode active material layer 64 may contain components other than the active material, such as a binder and a thickener. As a binder, for example, styrene-butadiene rubber (SBR) can be used. As a thickener, for example, carboxymethylcellulose (CMC) can be used.

[0043] Examples of separator sheets 70 include porous sheets (films) made of resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. Such porous sheets may have a single-layer structure or a laminated structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). A heat-resistant layer (HRL) may be provided on the surface of the separator sheet 70.

[0044] The non-aqueous electrolyte 80 used is the non-aqueous electrolyte of the lithium-ion secondary battery according to the present embodiment described above. Note that Figure 2 does not precisely show the amount of non-aqueous electrolyte 80 injected into the battery case 30.

[0045] The lithium-ion secondary battery 100 can be used for various applications. Suitable applications include power supplies for vehicles such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). The lithium-ion secondary battery 100 can also be used as a storage battery for small power storage devices. The lithium-ion secondary battery 100 can typically be used in the form of a battery pack, where multiple batteries are connected in series and / or parallel.

[0046] As an example, a rectangular lithium-ion secondary battery 100 equipped with a flattened wound electrode body 20 has been described. However, lithium-ion secondary batteries can also be configured as lithium-ion secondary batteries equipped with a stacked electrode body (i.e., an electrode body in which multiple positive electrodes and multiple negative electrodes are stacked alternately). Furthermore, lithium-ion secondary batteries can also be configured as cylindrical lithium-ion secondary batteries, laminated lithium-ion secondary batteries, and the like.

[0047] [Example Test] The following describes examples of tests relating to the technology disclosed herein. Note that these test examples are not intended to limit the scope of the technology disclosed herein.

[0048] A. First test In this experiment, thymol blue (CAS: 76-61-9), shown in chemical formula (5) above, was prepared as the lithium adsorbent. The solubility and lithium adsorbent performance of this lithium adsorbent were then investigated. The specific experimental procedure is as follows.

[0049] First, 1000 mL of non-aqueous solvent (EMC: ethyl methyl carbonate) was placed in an Eppendorf tube. Then, 100 mg of thymol blue and 0.5 g of lithium foil were added, and the mixture was shaken with a stirrer (shaking time: 3 minutes, shaking speed: 700 rpm). The amount of thymol blue dissolved at this time was 0.1 mg / mL (0.2 mmol / L). As a result, a red compound was formed, and the amount of lithium foil remaining in the non-aqueous solvent decreased to about 0.4 g. From this, it was found that the lithium collecting material (in this case, thymol blue) reduces the amount of metallic lithium in the non-aqueous solvent by collecting lithium foil (metallic lithium).

[0050] B. Second Examination This study investigated the effectiveness of lithium-ion scavenging materials in actual lithium-ion secondary batteries. The lithium-ion secondary battery (test example) prepared for this study is described below.

[0051] 1. Examples of each test (1) Test example 1 In Test Example 1, a lithium-ion secondary battery was fabricated without adding a Li collecting material. Specifically, first, the positive electrode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 A paste for the positive electrode composite was prepared by mixing O2, a conductive material (acetylene black), and a binder (PVdF) in a ratio of 90:8:2 and dispersing the mixture in a dispersion medium (NMP: N-methylpyrrolidone). This paste was then applied to both sides of a positive electrode current collector (aluminum foil), and after drying and rolling, a sheet-like positive electrode was produced. The size of the positive electrode was 47 mm x 45 mm. An aluminum positive electrode terminal was then connected to this positive electrode.

[0052] Next, in this test example, a negative electrode composite paste was prepared by mixing a negative electrode active material (graphite) and a binder (SBR) in a ratio of 98:2 and dispersing them in a dispersion medium (NMP). This paste was then applied to both sides of a negative electrode core (copper foil), and a sheet-like negative electrode was produced by drying and rolling. The size of the negative electrode was 49 mm x 47 mm. Copper negative electrode terminals were then connected to this negative electrode.

[0053] Next, a laminate was fabricated by placing a microporous separator made of polypropylene (size: 51 mm x 49 mm) between the positive and negative electrodes. This laminate was then placed inside a bag-shaped separator and then inside a laminated outer casing. After injecting a non-aqueous electrolyte into the outer casing, the opening of the laminated outer casing was heat-sealed and activated to construct a lithium-ion secondary battery for evaluation testing (Test Example 1). In this test, a non-aqueous electrolyte was used, which contained a mixed solvent with EC, EMC, and DMC in a volume ratio of 3:3:4, and LiPF6 as a supporting salt at a concentration of approximately 1.16 mol / L.

[0054] (2) Test examples 2 and 3 In Test Examples 2 and 3, lithium-ion secondary batteries for evaluation were constructed under the same conditions as in Test Example 1, except that a lithium-collecting agent (in this case, thymol blue) was added. The specific concentrations of the lithium-collecting agent in the non-aqueous electrolyte are shown in Table 1.

[0055] 2. Evaluation Test Next, in this test example, the amount of metallic Li deposited was measured by performing charge-discharge tests on lithium-ion secondary batteries of Test Examples 1 to 3. Specifically, for each lithium-ion secondary battery of Test Example, 100 charge-discharge cycles were performed in a -10°C environment, where a constant current of 5C was used to charge from 3V to 4.2V, followed by a 2-minute pause, and then a constant current of 5C (CC discharge) was used to discharge from 4.2V to 3V, followed by a 2-minute pause. After the charge-discharge cycles, the batteries were disassembled, and the area (mm²) of the region where metallic Li was deposited on the surface of the negative electrode active material layer (Li deposition region) was visually inspected. 2The following measurements were taken. The measurement results are shown in Table 1.

[0056] [Table 1]

[0057] As shown in Table 1, in Test Examples 2 and 3, the area of ​​the Li deposition region was confirmed to be smaller compared to Test Example 1. This indicates that adding a Li adsorbent to a non-aqueous electrolyte can suppress the deposition of metallic Li. Furthermore, it was found that a concentration of at least 0.2 mmol / L of the Li adsorbent in the non-aqueous electrolyte is preferable.

[0058] As described above, specific embodiments of the technology disclosed herein include those described in the following sections.

[0059] Section 1: Supporting salts, Non-aqueous solvents and Compounds having a triphenylmethane skeleton, Includes, The aforementioned compound, A branched hydrocarbon group having 3 or more carbon atoms is present on the phenyl group in the triphenylmethane skeleton, A hydroxyl group present on the phenyl group and adjacent to the branched hydrocarbon group, A non-aqueous electrolyte for lithium-ion secondary batteries, including [specific component].

[0060] Section 2: The non-aqueous electrolyte according to claim 1, wherein the branched hydrocarbon group comprises at least one selected from the group consisting of isopropyl group, isobutyl group, sec-butyl group and tert-butyl group.

[0061] Section 3: The non-aqueous electrolyte according to claim 1 or 2, wherein the compound is at least one selected from the group consisting of thymol blue, bromothymol blue, and methylthymol blue.

[0062] Section 4: The non-aqueous solvent is a non-aqueous electrolyte according to any one of items 1 to 3, wherein the non-aqueous solvent includes a non-aqueous solvent belonging to the carbonate class.

[0063] Section 5: The non-aqueous electrolyte according to any one of items 1 to 4, wherein the concentration of the compound is at least 0.2 mmol / L.

[0064] Item 6: Positive electrode and, The negative electrode and, A non-aqueous electrolyte as described in any one of items 1 to 5, Lithium-ion rechargeable batteries, including those mentioned above. [Explanation of Symbols]

[0065] 20 Wound electrode body 30 Battery Cases 36 Safety valve 42 Positive terminal 42a Positive electrode current collector plate 44 Negative terminal 44a Negative current collector plate 50 Positive electrode sheets (positive electrode) 52 Positive electrode current collector 52a Portion where positive electrode active material layer is not formed 54 Cathode active material layer 60 Negative electrode sheets (negative electrode) 62 Negative electrode current collector 62a Part where negative electrode active material layer is not formed 64 Negative electrode active material layer 70 Separator Sheets (Separators) 80 Nonaqueous electrolyte 90 Li trapping material (compound) 100 Lithium-ion rechargeable batteries

Claims

1. Supporting salts, Non-aqueous solvents and Compounds having a triphenylmethane skeleton, Includes, The aforementioned compound, A branched hydrocarbon group having 3 or more carbon atoms is present on the phenyl group in the triphenylmethane skeleton, A hydroxyl group present on the phenyl group and adjacent to the branched hydrocarbon group, A non-aqueous electrolyte for lithium-ion secondary batteries, including [specific component].

2. The non-aqueous electrolyte according to claim 1, wherein the branched hydrocarbon group comprises at least one selected from the group consisting of isopropyl group, isobutyl group, sec-butyl group and tert-butyl group.

3. The non-aqueous electrolyte according to claim 1, wherein the compound is at least one selected from the group consisting of thymol blue, bromothymol blue, and methylthymol blue.

4. The non-aqueous electrolyte according to claim 1, wherein the non-aqueous solvent includes a non-aqueous solvent belonging to the carbonate class.

5. The non-aqueous electrolyte according to claim 1, wherein the concentration of the compound is at least 0.2 mmol / L.

6. Positive electrode and, The negative electrode and, A non-aqueous electrolyte according to any one of claims 1 to 5, Lithium-ion rechargeable batteries, including those mentioned above.

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