Lithium-ion secondary battery

Abstract

To provide a lithium ion secondary battery that can suppress "corrosion of the current collecting foil, decomposition of a positive electrode active material, and decomposition of the coating of a negative electrode active material."SOLUTION: To provide an electrolyte solution 30 that contains a borate triester compound that captures fluoride ions in a lithium ion secondary battery 100 including a positive electrode plate 21, a negative electrode plate 25, and an electrolyte solution 30 containing LiPF6.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a lithium-ion secondary battery. [Background technology]

[0002] Patent Document 1 discloses a lithium ion secondary battery comprising a non-aqueous electrolyte solution containing a sultone compound A and a boron compound B. In this lithium ion secondary battery, the action of the sultone compound A can suppress an increase in resistance during storage of the battery. The reason for this is not clear, but it is thought that a coating derived from the sultone compound A is formed on the surface of the electrode (negative electrode or positive electrode) during storage of the battery, and the action of the coating formed during storage of the battery prevents deterioration of the electrodes during storage and suppresses an increase in resistance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-22525

[0004] Furthermore, in this lithium ion secondary battery, the initial resistance of the battery (i.e., the resistance before storage) can be reduced by the action of the boron compound B. The reason for this is not clear, but it is believed to be related to the fact that the boron compound B has a higher reduction reactivity than the sultone compound A. That is, since the boron compound B has a higher reduction reactivity, it is believed to form a coating on the surface of the negative electrode before storage of the battery more quickly than the sultone compound A. It is believed that the initial resistance of the battery (resistance before storage) is reduced by the action of the coating formed before storage of the battery. Summary of the Invention [Problem to be solved by the invention]

[0005] In the past, in an electrolyte containing LiPF6, for example, a small amount of water contained in the electrolyte reacts with LiPF6 to generate HF (hydrogen fluoride). Fluoride ions (F - ) may cause corrosion of the current collector foil constituting the positive or negative electrode plate, decomposition of the positive electrode active material, and decomposition of the coating of the negative electrode active material.

[0006] The present invention has been made in consideration of the above-mentioned current situation, and aims to provide a lithium-ion secondary battery that can suppress "corrosion of the current collecting foil, decomposition of the positive electrode active material, and decomposition of the coating of the negative electrode active material." [Means for solving the problem]

[0007] (1) One aspect of the present invention is a lithium ion secondary battery including a positive electrode plate, a negative electrode plate, and an electrolyte solution containing LiPF6, the electrolyte solution having a function of capturing fluoride ions. At least one of tri(4-chlorophenyl) borate or tri(2,4,6-trifluorophenyl) borate A lithium ion secondary battery comprising:

[0008] In the above-mentioned lithium-ion secondary battery, the electrolyte is "fluoride ions (F - ) Tri(4-chlorophenyl)borate or Tri(2,4,6-trifluorophenyl)borate In such a lithium-ion secondary battery, the electrolyte solution contains Tri(4-chlorophenyl)borate or Tri(2,4,6-trifluorophenyl)borate Since the fluoride ions generated by the ionization of HF can be captured by the above method, it is possible to suppress "corrosion of the current collector foil, decomposition of the positive electrode active material, and decomposition of the coating of the negative electrode active material." In addition, the fluoride ions are Tri(4-chlorophenyl)borate or Tri(2,4,6-trifluorophenyl)borate By coordinating to the boron atom of the boron complex, it is captured by the borate triester compound.

[0011] Also, tri(4-chlorophenyl) borate or tri(2,4,6-trifluorophenyl) borate is a compound that has a particularly high ability to capture fluoride ions. Therefore, in the above-mentioned lithium-ion secondary battery, the fluoride ions generated by the ionization of HF are captured by Tri(4-chlorophenyl)borate or Tri(2,4,6-trifluorophenyl)borateTherefore, in the above-mentioned lithium ion secondary battery, "corrosion of the current collector foil, decomposition of the positive electrode active material, and decomposition of the coating of the negative electrode active material" can be sufficiently suppressed. 。

[0012] (3) The lithium ion secondary battery according to (2), Tri(4-chlorophenyl)borate or Tri(2,4,6-trifluorophenyl)borate is 1.0 mol / L in the electrolyte. More than It is preferable that the lithium ion secondary battery contains the lithium at a concentration of 2.0 mol / L or less.

[0013] In the above-mentioned lithium ion secondary battery, Tri(4-chlorophenyl)borate or Tri(2,4,6-trifluorophenyl)borate The concentration of 1.0 mol / L More than The value is within the range of 2.0 mol / L or less. Tri(4-chlorophenyl)borate or Tri(2,4,6-trifluorophenyl)borate to 1.0 mol / L More than By including fluoride in the amount of 0.1 to 1.0%, the effect of capturing fluoride ions generated by the ionization of HF can be increased. Tri(4-chlorophenyl)borate or Tri(2,4,6-trifluorophenyl)borate Even if the concentration is increased to more than 2.0 mol / L, the fluoride ion capture effect remains unchanged. Tri(4-chlorophenyl)borate or Tri(2,4,6-trifluorophenyl)borate Even if the concentration is increased above 2.0 mol / L, Tri(4-chlorophenyl)borate or Tri(2,4,6-trifluorophenyl)borate This means adding Tri(4-chlorophenyl)borate or Tri(2,4,6-trifluorophenyl)borate Therefore, the electrolyte is Tri(4-chlorophenyl)borate or Tri(2,4,6-trifluorophenyl)borate It is preferable that the content of the fluoride is in the range of 1.0 to 2.0 mol / L. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view of a lithium-ion secondary battery according to an embodiment. [Diagram 2] FIG. 2 is a plan view of a positive electrode plate of the lithium ion secondary battery. [Diagram 3] FIG. 2 is a plan view of a negative electrode plate of the lithium ion secondary battery. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Next, a lithium ion secondary battery 100 according to an embodiment will be described with reference to the drawings. The lithium ion secondary battery 100 includes an exterior body 10 made of a laminate film 11, an electrode assembly 20 and an electrolyte 30 housed inside the exterior body 10, and a positive electrode terminal 40 and a negative electrode terminal 50 extending from the inside of the exterior body 10 to the outside (see FIG. 1). Most of the electrolyte 30 is impregnated inside the electrode assembly 20.

[0016] The exterior body 10 is formed by overlapping a pair of rectangular laminate films 11 and heat-welding the peripheral portions of these laminate films 11. Therefore, the exterior body 10 is composed of a storage section 10c that stores the electrode body 20 and the electrolyte 30 therein, and a sealing section 10d that is a square ring in a plan view and is located on the peripheral portion of the storage section 10c to airtightly seal the storage section 10c (see FIG. 1). The laminate film 11 that constitutes the exterior body 10 is a three-layer laminate film composed of a metal foil 12 and a pair of resin films 13 laminated on both sides of the metal foil 12.

[0017] The electrode body 20 includes a rectangular positive electrode plate 21, a rectangular negative electrode plate 25, and a rectangular separator 29 interposed therebetween, which are stacked in the thickness direction CH.

[0018] The positive electrode plate 21 includes a positive electrode current collector foil 22 made of aluminum foil, and a positive electrode active material layer 23 laminated on the surface of the positive electrode current collector foil 22 (see FIG. 2). The positive electrode active material layer 23 includes positive electrode active material particles and a binder. In this embodiment, lithium transition metal composite oxide particles, specifically, lithium nickel cobalt manganese composite oxide particles, are used as the positive electrode active material particles. In addition, polyvinylidene fluoride (PVDF) is used as the binder. Note that at one end (the left end in FIG. 2) of the positive electrode plate 21, the positive electrode active material layer 23 does not exist on the surface of the positive electrode current collector foil 22, and the positive electrode current collector foil 22 is exposed, forming a positive electrode current collector part 22b. A positive electrode terminal 40, which will be described later, is electrically connected to this positive electrode current collector part 22b.

[0019] The negative electrode plate 25 includes a negative electrode current collector foil 26 made of copper foil, and a negative electrode active material layer 27 laminated on the surface of the negative electrode current collector foil 26 (see FIG. 3). The negative electrode active material layer 27 includes negative electrode active material particles and a binder. In this embodiment, graphite particles are used as the negative electrode active material particles. Note that at the other end (the right end in FIG. 3) of the negative electrode plate 25, the negative electrode active material layer 27 is not present on the surface of the negative electrode current collector foil 26, and the negative electrode current collector foil 26 is exposed, forming a negative electrode current collector part 26b. A negative electrode terminal 50, which will be described later, is electrically connected to this negative electrode current collector part 26b.

[0020] The positive electrode terminal 40 is made of aluminum and has an elongated shape. One end of the positive electrode terminal 40 is connected to the positive electrode current collecting portion 22b of the positive electrode plate 21 constituting the electrode body 20, and is disposed within the housing portion 10c of the exterior body 10 (see FIGS. 1 and 2). The positive electrode terminal 40 extends to the outside of the exterior body 10 through the seal portion 10d of the exterior body 10.

[0021] The negative electrode terminal 50 is made of copper and has an elongated shape. One end of the negative electrode terminal 50 is connected to the negative electrode current collecting portion 26b of the negative electrode plate 25 constituting the electrode body 20, and is disposed in the housing portion 10c of the exterior body 10 (see FIGS. 1 and 3). The negative electrode terminal 50 extends to the outside of the exterior body 10 through the seal portion 10d of the exterior body 10. The negative electrode terminal 50 extends to the opposite side to the positive electrode terminal 40.

[0022] The electrolytic solution 30 is a non-aqueous electrolytic solution containing an organic solvent and LiPF6. In this embodiment, the organic solvent is a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a weight ratio of 3:3:4. The concentration of LiPF6 in the electrolytic solution 30 is 1.16 mol / L.

[0023] In the past, in electrolytes containing LiPF6, a small amount of water contained in the electrolyte reacted with LiPF6 to generate HF (hydrogen fluoride). HF was ionized to generate fluoride ions (F -) may cause corrosion of the current collector foil constituting the positive or negative electrode plate, decomposition of the positive electrode active material, and decomposition of the coating of the negative electrode active material.

[0024] In contrast, the electrolyte 30 of the present embodiment contains fluoride ions (F - ) is included. Therefore, in the lithium ion secondary battery 100 of this embodiment, the borate triester compound contained in the electrolyte 30 can capture fluoride ions generated by the ionization of HF. This makes it possible to suppress "corrosion of the current collector foil, decomposition of the positive electrode active material, and decomposition of the coating of the negative electrode active material." The fluoride ions are captured by the borate triester compound by forming a coordinate bond with the boron atom of the borate triester compound.

[0025] As the borate triester compound, for example, trialkyl borate, triphenyl borate, tri(alkylated phenyl) borate, and tri(halogenated phenyl) borate can be used. Among these, as the trialkyl borate, for example, triethyl borate, tris(hexafluoroisopropyl) borate, and trioctadecyl borate can be used. As the tri(alkylated phenyl) borate, for example, tri-o-tolyl borate and tri(2,4,6-trimethylphenyl) borate can be used. As the tri(halogenated phenyl) borate, for example, tri(4-chlorophenyl) borate and tri(2,4,6-trifluorophenyl) borate can be used.

[0026] Among these, tri(halogenated phenyl) borate is a compound that has a particularly high fluoride ion trapping ability among borate triester compounds. Therefore, by using an electrolyte solution 30 containing tri(halogenated phenyl) borate as the electrolyte solution 30, the fluoride ions generated by the ionization of HF can be efficiently trapped by the tri(halogenated phenyl) borate. This makes it possible to sufficiently suppress "corrosion of the current collector foil, decomposition of the positive electrode active material, and decomposition of the coating of the negative electrode active material." In addition, it is preferable to use tri(4-chlorophenyl) borate, tri(2,4,6-trifluorophenyl) borate, etc. as the tri(halogenated phenyl) borate.

[0027] <Example 1> In the lithium ion secondary battery 100 of Example 1, an electrolyte solution 30 containing a trialkyl borate as a borate triester compound is used. More specifically, triethyl borate represented by the following chemical formula 1 is used as the trialkyl borate. The concentration of triethyl borate in the electrolyte solution 30 is 1.0 mol / L.

[0028] [ka]

[0029] <Example 2> In the lithium ion secondary battery 100 of Example 2, an electrolyte solution 30 containing triphenyl borate as a borate triester compound is used. Triphenyl borate is a compound represented by the following chemical formula 2. The concentration of triphenyl borate in the electrolyte solution 30 is 1.0 mol / L.

[0030] [ka]

[0031] <Example 3> In the lithium ion secondary battery 100 of Example 3, an electrolyte solution 30 containing tri(alkylated phenyl) borate as a borate triester compound is used. More specifically, tri-o-tolyl borate represented by the following chemical formula 3 is used as the tri(alkylated phenyl) borate. The concentration of tri-o-tolyl borate in the electrolyte solution 30 is 1.0 mol / L.

[0032] [ka]

[0033] <Examples 4 to 7> In the lithium ion secondary batteries 100 of Examples 4 to 7, an electrolyte solution 30 containing tri(halogenated phenyl) borate is used as a borate triester compound. More specifically, tri(4-chlorophenyl) borate represented by the following chemical formula 4 is used as the tri(halogenated phenyl) borate.

[0034] [ka]

[0035] However, the concentrations of tri(4-chlorophenyl)borate in the electrolytic solution 30 are different in Examples 4 to 7. Specifically, in Example 4, the concentration of tri(4-chlorophenyl)borate in the electrolytic solution 30 is 1.0 mol / L. In Example 5, the concentration of tri(4-chlorophenyl)borate in the electrolytic solution 30 is 0.1 mol / L. In Example 6, the concentration of tri(4-chlorophenyl)borate in the electrolytic solution 30 is 2.0 mol / L. In Example 7, the concentration of tri(4-chlorophenyl)borate in the electrolytic solution 30 is 5.0 mol / L.

[0036] <Comparative Example 1> The lithium ion secondary battery of Comparative Example 1 is the same as the lithium ion secondary batteries 1 of Examples 1 to 7 except that the electrolyte does not contain a borate triester compound.

[0037] <Evaluation test of fluoride ion trapping ability> The lithium ion secondary batteries of Examples 1 to 7 and Comparative Example 1 were evaluated for their fluoride ion trapping ability. First, the following cycle charge / discharge was performed on each lithium ion secondary battery. Specifically, each lithium ion secondary battery was charged at a constant current of 1 C from a state in which the battery voltage value was set to 3.0 V until the battery voltage value reached 4.3 V. Subsequently, constant current discharge was performed at a constant current of 0.5 C until the battery voltage value reached 3.0 V. With this charge / discharge cycle being regarded as one cycle, five cycles of charge / discharge were performed on each lithium ion secondary battery.

[0038] Thereafter, each lithium ion secondary battery was disassembled, and the concentration of fluoride ions contained in the negative electrode plate 25 was measured by IC (ion chromatography) analysis. In this test, the IC analysis was performed as follows.

[0039] First, the lithium ion secondary battery 100 of Example 1, which has been subjected to the above-mentioned cycle charge and discharge, is disassembled, and the negative electrode plate 25 is taken out. Then, a square test piece having a length of 30 mm and a width of 30 mm is cut out from the taken-out negative electrode plate 25. Next, the cut-out test piece is immersed in acetonitrile. Then, ultrasonic vibration is applied to the acetonitrile in which the test piece is immersed, and the negative electrode active material layer 27 is peeled off from the negative electrode current collector foil 26, and the fluoride ions contained in the test piece are dissolved in the acetonitrile to obtain an acetonitrile solution. Next, the acetonitrile solution is filtered to obtain a filtrate containing fluoride ions. The filtrate is subjected to IC analysis to measure the fluoride ion concentration.

[0040] In this test, an ion chromatograph (ICS-600) manufactured by Nippon Dionex Corporation was used as the IC analyzer. The fluoride ion concentration was expressed as a mass % concentration relative to the negative electrode active material contained in the test piece. The fluoride ion concentrations (mass %) of the lithium ion secondary batteries of Examples 2 to 7 and Comparative Example 1 were also measured in the same manner. The results are shown in Table 1.

[0041] [Table 1]

[0042] As shown in Table 1, the fluoride ion concentration after the above-mentioned cycle charge / discharge was 0.42% by mass in the lithium ion secondary battery of Comparative Example 1. In contrast, the fluoride ion concentrations after the above-mentioned cycle charge / discharge were 0.40% by mass or less in the lithium ion secondary batteries of Examples 1 to 7, which were lower than that of Comparative Example 1.

[0043] The reason is that the lithium ion secondary batteries 100 of Examples 1 to 7 use, as the electrolyte, an electrolyte solution 30 containing a borate triester compound, unlike the lithium ion secondary battery of Comparative Example 1. It can be said that the lithium ion secondary batteries 100 of Examples 1 to 7 were able to capture fluoride ions generated by the ionization of HF by the borate triester compound contained in the electrolyte solution 30. Therefore, it can be said that the lithium ion secondary batteries 100 of Examples 1 to 7 are able to suppress "corrosion of the current collector foil, decomposition of the positive electrode active material, and decomposition of the coating of the negative electrode active material" compared to the lithium ion secondary battery of Comparative Example 1.

[0044] Further, the test results will be examined in detail. First, the results of the lithium ion secondary battery 100 of Examples 1 to 4 will be compared. Although the types of borate triester compounds added to the electrolyte 30 are different in Examples 1 to 4, the amounts added (concentrations) are all equal to 1.0 mol / L. Specifically, as the borate triester compound, trialkyl borate is used in Example 1, triphenyl borate in Example 2, tri(alkylated phenyl) borate in Example 3, and tri(halogenated phenyl) borate in Example 4. Comparing the fluoride ion concentrations after cycle charging and discharging for Examples 1 to 4, Examples 1 to 3 had fluoride ion concentrations of 0.30 mass% or more, whereas Example 4 had fluoride ion concentrations of 0.23 mass%, which was the lowest value among the four Examples (see Table 1).

[0045] From this result, it can be said that it is more preferable to use the borate tri(halogenated phenyl) of Example 4 as the borate triester compound. Among borate triester compounds, the borate tri(halogenated phenyl) is a compound that has a particularly high fluoride ion trapping ability. By using the electrolyte 30 containing the borate tri(halogenated phenyl) as the electrolyte of the lithium ion secondary battery, it can be said that the fluoride ions generated by the ionization of HF can be efficiently trapped by the borate tri(halogenated phenyl). This can be said to sufficiently suppress "corrosion of the current collector foil, decomposition of the positive electrode active material, and decomposition of the coating of the negative electrode active material". In Example 4, the borate tri(halogenated phenyl) was used as the borate tri(halogenated phenyl), but the borate tri(2,4,6-trifluorophenyl) may be used.

[0046] Next, the test results of Examples 4 to 7 are compared. Examples 4 to 7 have in common the use of tri(halogenated phenyl) borate as the borate triester compound, but the concentrations are different. Specifically, the concentration of tri(halogenated phenyl) borate is 0.1 mol / L in Example 5, 1.0 mol / L in Example 4, 2.0 mol / L in Example 6, and 5.0 mol / L in Example 7. Comparing the fluoride ion concentration after cycle charging and discharging for Examples 1 to 4, Example 5 had a fluoride ion concentration of 0.40 mass%, while Examples 4, 6, and 7 had a fluoride ion concentration of 0.23 mass% or less, which were extremely low values ​​(see Table 1).

[0047] From this result, it can be said that the effect of capturing fluoride ions generated by ionization of HF can be increased by adding triborate (halogenated phenyl) at a ratio of 1.0 mol / L or more to the electrolyte of a lithium ion secondary battery. However, as can be seen from the test results of Examples 6 and 7, even if the concentration of triborate (halogenated phenyl) is increased to more than 2.0 mol / L, the effect of capturing fluoride ions does not change. Therefore, even if the concentration of triborate (halogenated phenyl) is increased to more than 2.0 mol / L, more triborate (halogenated phenyl) than necessary is added, which results in a waste of triborate (halogenated phenyl). Therefore, it can be said that it is preferable to add triborate (halogenated phenyl) at a ratio within the range of 1.0 to 2.0 mol / L to the electrolyte. In other words, it can be said that the concentration of triborate (halogenated phenyl) in the electrolyte of a lithium ion secondary battery is preferably set to a value within the range of 1.0 to 2.0 mol / L.

[0048] Although the present invention has been described above with reference to an embodiment, it goes without saying that the present invention is not limited to the above embodiment and can be modified as appropriate without departing from the spirit of the present invention.

[0049] For example, in Example 1, triethyl borate was used as the trialkyl borate, but it is not limited thereto, and other trialkyl borates such as tris(hexafluoroisopropyl) borate and trioctadecyl borate may be used. In Example 3, tri-o-tolyl borate was used as the tri(alkylated phenyl) borate, but it is not limited thereto, and other tri(alkylated phenyl) borate such as tri(2,4,6-trimethylphenyl) borate may be used. In Examples 4 to 7, tri(4-chlorophenyl) borate was used as the tri(halogenated phenyl) borate, but it is not limited thereto, and other tri(halogenated phenyl) borate such as tri(2,4,6-trifluorophenyl) borate may be used. [Explanation of symbols]

[0050] 10 Exterior body 20 Electrode body 21 Positive electrode plate 25 Negative plate 30 Electrolyte 40 Positive terminal 50 Negative terminal 100 Lithium-ion secondary battery

Claims

1. A positive electrode plate, a negative electrode plate, and LiPF ６ and an electrolyte solution containing the lithium ion secondary battery, The electrolyte contains at least one of tri(4-chlorophenyl)borate and tri(2,4,6-trifluorophenyl)borate that captures fluoride ions. Lithium-ion secondary battery.

2. 2. The lithium ion secondary battery according to claim 1, The tri(4-chlorophenyl) borate or the tri(2,4,6-trifluorophenyl) borate is contained in the electrolyte at a concentration in the range of more than 1.0 mol / L and not more than 2.0 mol / L. Lithium-ion secondary battery.

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