Electrolytic solution and battery

Abstract

To provide an electrolytic solution with good thermal stability.SOLUTION: The present disclosure solves the above problems by providing an electrolytic solution containing a first salt, a second salt, and SO2, and the first salt is a LiAl halide salt containing at least LiAlCl4, and the second salt is an ionic liquid containing a sulfonyl group.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to electrolytes and batteries. [Background technology]

[0002] In recent years, the development of batteries has been actively pursued. For example, in the automotive industry, development of batteries for use in electric vehicles (BEVs), plug-in hybrid vehicles (PHEVs), and hybrid electric vehicles (HEVs) is underway. Furthermore, development of components and materials for use in these batteries is also underway.

[0003] For example, Patent Document 1 discloses an electrolyte for a sulfur dioxide-based secondary battery that contains sulfur dioxide (SO2), an alkali metal salt, and an iodide additive. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-056107 Summary of the Invention [Problem to be solved by the invention]

[0005] Electrolytes containing sulfur dioxide (SO2) (SO2-based electrolytes) have good ionic conductivity and are expected to contribute to reducing battery resistance. However, SO2-based electrolytes have low thermal stability and are prone to volatilization during battery use. As a result, batteries using SO2-based electrolytes may experience a decline in battery performance due to the volatilization of the electrolyte.

[0006] The present disclosure has been made in view of the above circumstances, and has as its main object to provide an electrolyte solution having good thermal stability. [Means for solving the problem]

[0007] [1] An electrolyte solution containing a first salt, a second salt, and SO2, The first salt is a LiAl halide salt containing at least LiAlCl4, The second salt is an ionic liquid containing a sulfonyl group.

[0008] [2] The electrolyte solution according to [1], wherein the ionic liquid has an ionic conductivity of 1.5 mS / cm or more at 25°C.

[0009] [3] The electrolyte solution according to [1] or [2], wherein the viscosity of the ionic liquid at 25°C is 200 mPa or less.

[0010] [4] The electrolyte solution according to any one of [1] to [3], wherein the ionic liquid contains at least one of bis(trifluoromethanesulfonyl)amide (TFSA) and bis(fluorosulfonyl)amide (FSA) as an anion component.

[0011] [5] A battery having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, A battery in which the positive electrode active material layer, the negative electrode active material layer, and the electrolyte layer contain the electrolytic solution according to any one of [1] to [4]. [Effects of the Invention]

[0012] The present disclosure has the effect of providing an electrolyte solution with good thermal stability. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating a battery according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0014] The electrolyte and battery according to the present disclosure will be described in detail below.

[0015] A. Electrolyte The electrolytic solution of the present disclosure contains a first salt, a second salt, and SO. In particular, the first salt of the present disclosure is a LiAl halide salt containing at least LiAlCl, and the second salt is an ionic liquid containing a sulfonyl group.

[0016] The electrolyte solution of the present disclosure contains the predetermined first and second salts and SO2, and therefore has good thermal stability.

[0017] Patent Document 1 discloses an SO2-based electrolyte containing a lithium salt (LiAl halide salt) such as LiAlCl4 and SO2. While such SO2-based electrolytes have good ionic conductivity, they are prone to volatilization during battery use due to the low boiling point of SO2 and the low boiling point of the electrolyte. If the electrolyte volatilizes during battery use and the amount of electrolyte decreases, battery resistance may increase. In response to this issue, the present inventors have discovered that adding an ionic liquid containing a sulfonyl group as a second salt can lower the boiling point of the electrolyte and suppress volatilization. While the details of the mechanism by which volatilization of the electrolyte is suppressed are unclear, it is presumed that the interaction between SO2 in the electrolyte and the sulfonyl group in the ionic liquid suppresses volatilization of SO2 and the electrolyte.

[0018] 1. First Salt The first salt is a LiAl halide salt containing at least LiAlCl4. The first salt may contain only LiAlCl4, or may contain other compounds (other salts). In other words, the first salt may be a salt consisting of two or more types of salts. The first salt may also be a eutectic salt.

[0019] The proportion of LiAlCl4 in the first salt may be 100 mol% or less than 100 mol%. In the latter case, the proportion of LiAlCl4 is, for example, 50 mol% or more and 99 mol% or less.

[0020] An example of a salt other than LiAlCl4 is LiAlX4 (X is any of F, Br, and I). The salt other than LiAlCl4 may be one type or two or more types.

[0021] 2. Second Salt The second salt is an ionic liquid containing a sulfonyl group. An ionic liquid is a liquid salt having a cation component and an anion component, and refers to a salt that is liquid at, for example, 100°C or less. The melting point of the second salt (ionic liquid) may be 70°C or less, 50°C or less, or 40°C or less. The second salt may exist in the electrolyte in a liquid state or a solid state.

[0022] The ionic liquid may be a monocationic ionic liquid having one cation structure, or a dicationic ionic liquid having two cation structures, in which the two cation structures may be the same or different.

[0023] Examples of cationic components include pyridinium cations such as N-ethyl-N-methylpyrrolidinium (P12), N-methyl-N-propylpyrrolidinium (P13), and N-butyl-N-methylpyrrolidinium (P14); sulfonium cations such as methyldiethylsulfonium; phosphonium cations such as methyltributylphosphonium; ammonium cations such as butyltriethylammonium; imidazolium cations such as 1-allyl-3-butylimidazolium; and piperidinium cations such as 1-butyl-1-methylpiperidinium. The second salt may contain one type of cationic component, or two or more types of cationic components.

[0024] The sulfonyl group in an ionic liquid is usually contained in an anion component. Examples of an anion component having a sulfonyl group include bis(trifluoromethanesulfonyl)amide (TFSA), bis(fluorosulfonyl)amide (FSA), fluorosulfonyl(trifluoromethanesulfonylamide) (FTA), bis(pentafluoroethanesulfonyl)imide (BETI), and trifluoromethylsulfonyl (Tf). An ionic liquid may contain one type of anion component, or two or more types of anion components. When an ionic liquid contains two or more types of anion components, the ionic liquid may contain an anion component that does not have a sulfonyl group. Examples of anion components that do not have a sulfonyl group include hexafluorophosphate ion (PF6 - ), tetrafluoroborate ion (BF4 - ), and halogen ions (Cl - , Br - , I - ) are listed.

[0025] The electrolyte may contain one type of second salt, or may contain two or more types of second salts.

[0026] The ionic conductivity of the ionic liquid (second salt) at 25°C is not particularly limited, but is preferably high. This is because the ionic conductivity of the electrolyte is improved. The ionic conductivity of the ionic liquid at 25°C is, for example, 1.5 mS / cm or more, or may be 2.0 mS / cm or more, or 2.5 mS / cm or more, or even 3.0 mS / cm or more. On the other hand, the ionic conductivity is, for example, 6.0 mS / cm or less, or may be 5.5 mS / cm or less, or even 5.0 mS / cm or less.

[0027] Furthermore, the viscosity of the ionic liquid at 25°C is not particularly limited, but is preferably low, as this facilitates handling of the electrolyte. The viscosity is, for example, 200 mPa or less, or may be 150 mPa or less, 100 mPa or less, or 70 mPa or less. On the other hand, the viscosity may be, for example, 30 mPa or more, or 50 mPa or more.

[0028] The proportion of the second salt in the electrolytic solution is not particularly limited, but may be, for example, 5% by weight or more, or 10% by weight or more, while the proportion of the second salt is, for example, 30% by weight or less, or may be 25% by weight or less, or may be 20% by weight or less.

[0029] 3. Electrolyte The electrolytic solution contains SO2 in addition to the first salt and the second salt. The proportion of SO2 in the electrolytic solution is not particularly limited, but may be, for example, 0.5 to 3 molar parts, or 0.8 to 2 molar parts, relative to the first salt (1 molar part).

[0030] The melting point of the electrolyte is preferably, for example, 25° C. or lower. The ionic conductivity of the electrolyte at 25° C. is preferably, for example, 20 mS / cm or higher.

[0031] The electrolyte solution of the present disclosure is typically used in batteries, which will be described later. The electrolyte solution of the present disclosure can be produced by injecting SO gas into the first salt described above to prepare a precursor solution, and then adding the ionic liquid described above to this precursor solution.

[0032] B.Battery FIG. 1 is a schematic cross-sectional view illustrating a battery according to the present disclosure. Note that FIG. 1 is a schematic illustration of the battery according to the present disclosure, and the size and shape of each part are appropriately exaggerated for ease of understanding. The battery 10 shown in FIG. 1 has a positive electrode active material layer 1, a negative electrode active material layer 2, and an electrolyte layer 3 disposed between the positive electrode active material layer 1 and the negative electrode active material layer 2. In particular, in the battery 10 according to the present disclosure, the positive electrode active material layer 1, the negative electrode active material layer 2, and the electrolyte layer 3 contain the above-described electrolyte solution.

[0033] In the battery according to the present disclosure, the positive electrode active material layer, the negative electrode active material layer, and the electrolyte layer contain the above-described electrolytic solution, and therefore an increase in battery resistance due to volatilization of the electrolytic solution is suppressed.

[0034] 1.Cathode active material layer The positive electrode active material layer contains at least a positive electrode active material and the above-mentioned electrolyte solution.

[0035] The positive electrode active material may be, for example, an oxide active material. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 and LiNi 0.8 Co 0.15 Al 0.05 Examples of the active material include rock salt layer type active materials such as O2, spinel type active materials such as LiMn2O4, and olivine type active materials such as LiFePO4. Sulfur (S) may also be used as the positive electrode active material.

[0036] The positive electrode active material is, for example, in the form of particles. 50 ) is, for example, 0.5 μm or more and 50 μm or less. 50 ) refers to the volume cumulative particle size measured by a laser diffraction / scattering particle size distribution analyzer. The proportion of the positive electrode active material in the positive electrode active material layer is, for example, 50% by weight or more and 80% by weight or less.

[0037] The positive electrode active material layer may contain only the above-described electrolytic solution as the electrolyte. Alternatively, the positive electrode active material layer may contain other electrolytes. The other electrolytes are described in "3. Electrolyte Layer." The positive electrode active material layer may also contain at least one of a conductive material and a binder.

[0038] Examples of binders include rubber-based binders such as butadiene rubber (BR), acrylate butadiene rubber (ABR), and styrene butadiene rubber (SBR), as well as fluorine-containing binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). The proportion of the binder in the positive electrode active material layer is, for example, 0.5% by weight or more and 10% by weight or less.

[0039] The thickness of the positive electrode active material layer is not particularly limited, but is, for example, 0.1 μm or more and 1000 μm or less.

[0040] 2.Negative electrode active material layer The negative electrode active material layer contains at least the negative electrode active material and the above-mentioned electrolyte solution.

[0041] Examples of negative electrode active materials include Si-based active materials. Si-based active materials are active materials containing Si element. Examples of Si-based active materials include simple Si, Si alloys, and Si oxides. The Si alloy preferably contains Si element as a main component. The proportion of Si element in the Si alloy is, for example, 50 mol% or more, or may be 70 mol% or more, or even 90 mol% or more. On the other hand, the proportion of Si element in the Si alloy is, for example, 99 mol% or less. Examples of Si alloys include Si-Al based alloys, Si-Sn based alloys, Si-In based alloys, Si-Ag based alloys, Si-Pb based alloys, Si-Sb based alloys, Si-Bi based alloys, Si-Mg based alloys, Si-Ca based alloys, Si-Ge based alloys, and Si-Pb based alloys. The Si alloy may be a binary alloy or a multi-component alloy of 3 or more components. Examples of Si oxides include SiO.

[0042] The Si-based active material may have a diamond-type crystalline phase, a clathrate I crystalline phase, or a clathrate II crystalline phase. In the clathrate I or II crystalline phase, multiple Si elements form a polyhedron (cage) containing pentagons or hexagons. This polyhedron has spaces inside that can encapsulate metal ions such as Li ions, thereby suppressing volumetric changes during charging and discharging. The Si-based active material may also have voids inside the primary particles. These voids can suppress volumetric changes in the active material and cracking of the negative electrode active material layer. The porosity is not particularly limited, but is, for example, 4% or more and 40% or less. The presence of voids in the primary particles and the porosity can be confirmed by observation with a scanning electron microscope (SEM).

[0043] The negative electrode active material layer may contain only the above-mentioned electrolytic solution as the electrolyte. On the other hand, the negative electrode active material layer may contain other electrolytes. The other electrolytes are described in "3. Electrolyte Layer." Furthermore, the negative electrode active material layer may contain at least one of a conductive material and a binder, as necessary. The conductive material and the binder are the same as those described in "1. Positive electrode active material layer."

[0044] The thickness of the negative electrode active material layer is not particularly limited, but is, for example, 0.1 μm or more and 1000 μm or less.

[0045] 3. Electrolyte layer The electrolyte layer contains at least the above-described electrolytic solution as an electrolyte, and may also contain other electrolytes as an electrolyte.

[0046] Examples of electrolytes other than the above-mentioned electrolytic solutions include solid electrolytes. Examples of solid electrolytes include organic solid electrolytes such as gel electrolytes, and inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes. In addition, the battery may contain an electrolytic solution other than the above-mentioned electrolytic solutions.

[0047] The electrolyte layer may contain a binder as needed. The binder is the same as that described in "1. Positive electrode active material layer." The thickness of the electrolyte layer is not particularly limited, but is, for example, 0.1 μm or more and 1000 μm or less.

[0048] 4. Other configurations As shown in Fig. 1, a battery 10 according to the present disclosure typically includes a positive electrode current collector 4 that collects electrons from a positive electrode active material layer 1 and a negative electrode current collector 5 that collects electrons from a negative electrode active material layer 2. Examples of materials for the positive electrode current collector include stainless steel, aluminum, nickel, iron, titanium, and carbon. Examples of materials for the negative electrode current collector include stainless steel, copper, nickel, and carbon.

[0049] The battery according to the present disclosure may also include an exterior body that houses the above-described components. Examples of the exterior body include a laminate-type exterior body and a case-type exterior body.

[0050] 5.Battery The battery in the present disclosure is typically a lithium ion secondary battery. The battery in the present disclosure may be a liquid battery or a solid battery. When the electrolyte layer in the battery contains a solid electrolyte (e.g., an inorganic solid electrolyte) in addition to the electrolytic solution, the battery can be considered a solid battery.

[0051] Examples of applications of the battery include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered automobiles, diesel-powered automobiles, etc. The battery of the present disclosure may also be used as a power source for mobile objects other than vehicles (for example, trains, ships, and aircraft), or as a power source for electrical appliances such as information processing devices.

[0052] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0053] [Example 1] The electrolyte solution was prepared as follows. First, a mixture of LiCl and AlCl4 was prepared in a 1:1 molar ratio. This mixture was placed in a flask, and SO2 gas was sprayed into it. This resulted in a first solution containing a first salt (LiAlCl4) and SO2. The amount of SO2 gas was adjusted to a molar ratio of 100% relative to the first salt. The first solution was filtered to separate it into a solid component and a liquid component, and the liquid component was collected as a second solution. The second salt (P13TFSA: N-methyl-N-propylpyrrolidinium bistrifluoromethanesulfonylamide) was added to the second solution, and the mixture was stirred at room temperature for 1 hour. This resulted in an electrolyte solution. The P13TFSA was added in an amount equivalent to 20 wt% of the electrolyte solution. This electrolyte solution was used as a sample for the evaluation described below. The physical properties of the ionic liquid (P13TFSA) used, along with the second salts used in Examples 2 and 3, are listed in Table 1. The melting point was measured by differential scanning calorimetry (DSC), the ionic conductivity was measured by impedance analysis, and the viscosity was measured using a viscometer. The viscosity and ionic conductivity of the second salt (P12TFSA) in Example 2 were not measured because it was a solid at room temperature.

[0054] [Examples 2 and 3] An electrolyte solution was prepared in the same manner as in Example 1, except that P12TFSA (N-ethyl-N-methylpyrrolidinium bistrifluoromethanesulfonylamide) or P14TFSA (N-butyl-N-methylpyrrolidinium bistrifluoromethanesulfonylamide) was used as the ionic liquid.

[0055] [Comparative Example 1] The second solution was used as a sample (electrolytic solution) and evaluated as described below.

[0056] [Table 1]

[0057] [evaluation] (Weight reduction rate) The volatilization amount (weight loss rate) of the electrolyte solutions of Examples 1 to 3 and Comparative Example 1 was measured using a Rigaku differential thermal and thermogravimetric simultaneous analyzer (TG-DTA8122). Specifically, each electrolyte solution was kept at 40°C for 10 hours, and the weight change before and after the keeping was calculated as the weight loss rate. The results are shown in Table 2.

[0058] (ionic conductivity) The ionic conductivity was measured by an AC impedance method for the electrolyte solutions of Comparative Example 1 and Examples 1 to 3. The results are shown in Table 2.

[0059] [Table 2]

[0060] As shown in Table 2, the weight loss rate was reduced in all Examples, and it was confirmed that volatilization of the electrolyte solution was suppressed and thermal stability was improved compared to Comparative Example 1. In particular, volatilization was significantly suppressed in Example 1. As shown in Table 1, the second salt used in Example 2 is solid within the normal temperature range of a battery, and therefore is expected to have lower ionic conductivity than the second salt used in Examples 1 and 3. Therefore, from the viewpoint of the ionic conductivity of the electrolyte solution, the electrolyte solutions of Examples 1 and 3 are considered more preferable. Note that the ionic conductivity of the electrolyte solutions of Examples 1 to 3 was lower than that of Comparative Example 1, but still showed good ionic conductivity. In particular, when the battery is used for a long period of time, the batteries using the electrolyte solutions of Examples 1 to 3 are considered more effective in that an increase in battery resistance due to a decrease in the electrolyte solution can be more effectively suppressed. [Explanation of symbols]

[0061] 1 ...positive electrode active material layer 2 ...Negative active material layer 3 ...Electrolyte layer 4 ...positive electrode current collector 5 ...Negative electrode current collector 10 …batteries

Claims

1. A first salt, a second salt, and SO ２ and an electrolyte solution containing The first salt is at least LiAlCl ４ LiAl halide salts comprising: The electrolyte, wherein the second salt is an ionic liquid containing a sulfonyl group.

2. 2. The electrolyte solution according to claim 1, wherein the ionic liquid has an ionic conductivity of 1.5 mS / cm or more at 25°C.

3. The electrolyte solution according to claim 1 , wherein the ionic liquid has a viscosity at 25° C. of 200 mPa or less.

4. 2. The electrolyte solution according to claim 1, wherein the ionic liquid contains, as an anion component, at least one of bis(trifluoromethanesulfonyl)amide (TFSA) and bis(fluorosulfonyl)amide (FSA).

5. A battery having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, A battery, wherein the positive electrode active material layer, the negative electrode active material layer, and the electrolyte layer contain the electrolytic solution according to any one of claims 1 to 4.

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