Electrolyte and lithium-ion battery

Abstract

To provide an electrolyte that has good oxidation resistance and can suppress an increase in battery resistance.SOLUTION: There is provided an electrolyte for use in a lithium ion battery, the lithium ion battery includes lithium metal as a negative electrode active material, the electrolyte includes an organic electrolyte and an inorganic electrolyte, and the inorganic electrolyte includes a lithium salt and sulfur dioxide (SO2).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to electrolytes and lithium-ion 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 organic electrolyte battery comprising a positive electrode, a negative electrode, an organic electrolyte, and a separator. Patent Document 1 also discloses that the negative electrode is made of lithium metal, a lithium alloy, or a material capable of absorbing and releasing lithium. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-225498 Summary of the Invention [Problem to be solved by the invention]

[0005] Among electrolytes, organic electrolytes generally have the advantage of a high upper limit of the potential window and good oxidation resistance. Furthermore, lithium metal is useful as a negative electrode active material from the viewpoint of improving the energy density of batteries. However, as will be described later, when lithium metal and an organic electrolyte are used, there is a risk of increased resistance due to a coating (Solid Electrolyte Interphase: SEI) formed on the surface of the lithium metal.

[0006] The present disclosure has been made in view of the above circumstances, and has as its main object to provide an electrolyte solution that has good oxidation resistance and can suppress an increase in battery resistance. [Means for solving the problem]

[0007] [1] An electrolyte solution for use in a lithium ion battery, the lithium ion battery containing lithium metal as a negative electrode active material, the electrolyte solution including an organic electrolyte solution and an inorganic electrolyte solution, the inorganic electrolyte solution including a lithium salt and sulfur dioxide (SO2).

[0008] [2] The above lithium salt contains AlCl4 as the anion component. - and BCl4 - The electrolyte solution according to [1], containing at least one of the following:

[0009] [3] The electrolyte solution according to [1] or [2], wherein the proportion of the inorganic electrolyte solution relative to the total of the organic electrolyte solution and the inorganic electrolyte solution is 0.05% by weight or more and 70.0% by weight or less.

[0010] [4] The electrolyte solution according to any one of [1] to [3], wherein the proportion of the inorganic electrolyte solution relative to the total of the organic electrolyte solution and the inorganic electrolyte solution is 0.10 wt % or more and 40.0 wt % or less.

[0011] [5] A lithium ion battery that uses lithium metal as a negative electrode active material and contains the electrolyte 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 that has good oxidation resistance and can suppress an increase in battery resistance. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating a lithium-ion battery according to the present disclosure. [Figure 2] 1 is a graph showing the results of evaluation of oxidation resistance of an electrolyte solution. DETAILED DESCRIPTION OF THE INVENTION

[0014] The electrolyte solution and lithium-ion battery according to the present disclosure will be described in detail below. Note that the drawings shown below are schematic illustrations, and the size and shape of each part are appropriately exaggerated for ease of understanding.

[0015] A. Electrolyte (liquid electrolyte) The electrolyte solution in this disclosure is an electrolyte solution used in a lithium-ion battery. The lithium-ion battery contains lithium metal as a negative electrode active material. The electrolyte solution includes an organic electrolyte solution and an inorganic electrolyte solution. The inorganic electrolyte solution contains a lithium salt and sulfur dioxide (SO2).

[0016] The electrolyte solution of the present disclosure contains a predetermined inorganic electrolyte solution in addition to an organic electrolyte solution, which results in the electrolyte solution having good oxidation resistance and being able to suppress an increase in battery resistance.

[0017] As mentioned above, there are advantages to using organic electrolytes and lithium metal in lithium-ion batteries. However, because lithium metal has a relatively high reactivity, side reactions may occur with the electrolyte. As a result, the organic electrolyte may be reductively decomposed on the surface of the negative electrode active material (lithium metal), forming a film (SEI). In this regard, the increase in interfacial resistance of the negative electrode active material due to the film is expected to depend on the density (insulating properties) and thickness of the film. If the film density is low, the decomposition reaction of the electrolyte will proceed more easily, resulting in an increase in film thickness (film growth). Furthermore, when an organic electrolyte is used, the film formed is thought to be low in density, and as the electrolyte decomposition reaction progresses, the film grows thicker, increasing the interfacial resistance of the negative electrode active material. On the other hand, when an inorganic electrolyte containing sulfur dioxide (SO2) and lithium salt is used, the film formed is thought to be denser, suppressing the progress of the electrolyte decomposition reaction. Even when an inorganic electrolyte solution is used together with an organic electrolyte solution, it is believed that the thin coating resulting from the decomposition of the inorganic electrolyte solution can suppress the formation of a coating of the organic electrolyte solution, thereby preventing the coating from becoming thick. As a result, the electrolyte solution of the present disclosure, which contains an organic electrolyte solution and a predetermined inorganic electrolyte solution, can suppress an increase in battery resistance while obtaining the benefits of the organic electrolyte solution (good oxidation resistance).

[0018] 1.Inorganic electrolyte The inorganic electrolyte in this disclosure contains a lithium salt and sulfur dioxide (SO2).

[0019] The cation component in the lithium salt is typically Li + The anion component in the lithium salt is, for example, AlCl4 - , GaCl4 - , BF4 - , BCl4 - and InCl4 - Among these, chloride anions such as AlCl4 - and GaCl4 - The lithium salt may contain one type of anion component or two or more types of anion components.

[0020] The composition of the inorganic electrolyte can be expressed as LiX-αSO2, where X is an anion component and α is a number satisfying 0.5≦α≦10. α may be 1.0 or greater, 3.0 or greater, or 5.0 or greater. On the other hand, α may be 8.0 or less, or 6.0 or less. The inorganic electrolyte can be prepared by injecting SO2 gas into a lithium salt material (e.g., a mixture of LiCl and AlCl4).

[0021] The proportion (weight ratio) of the inorganic electrolyte solution relative to the total of the organic electrolyte solution and the inorganic electrolyte solution is not particularly limited, but is, for example, 0.05% by weight or more. The proportion of the inorganic electrolyte solution may be 0.1% by weight or more, 1.0% by weight or more, 5.0% by weight or more, or 10.0% by weight or more. On the other hand, the proportion of the inorganic electrolyte solution is, for example, 70.0% by weight or less. The proportion of the inorganic electrolyte solution may be 50.0% by weight or less, 40.0% by weight or less, 30.0% by weight or less, or 20.0% by weight or less.

[0022] The proportion (volume ratio) of the inorganic electrolyte solution relative to the total of the organic electrolyte solution and the inorganic electrolyte solution is not particularly limited, but is, for example, 0.05% by volume or more. The proportion of the inorganic electrolyte solution may be 0.1% by volume or more, 1.0% by volume or more, 5.0% by volume or more, 10.0% by volume or more, or 20.0% by volume or more. On the other hand, the proportion of the inorganic electrolyte solution is, for example, 70.0% by volume or less. The proportion of the inorganic electrolyte solution may be 50.0% by volume or less, 40.0% by volume or less, or 30.0% by volume or less.

[0023] 2.Organic electrolyte The organic electrolyte solution in the present disclosure may be, for example, an electrolyte solution containing a supporting salt and an organic solvent.

[0024] Examples of supporting salts include inorganic lithium salts such as LiPF6, LiBF4, LiClO4, and LiAsF6; and organic lithium salts such as LiCF3SO3, LiN(SO2CF3)2, LiN(SO2C2F5)2, and LiC(SO2CF3)3. Examples of organic solvents include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The organic electrolyte may contain only one type of supporting salt and one type of organic solvent, or two or more types.

[0025] 3. Electrolyte The ionic conductivity of the electrolyte is preferably high. The ionic conductivity at 25°C is, for example, 0.1 mS / cm or more. The ionic conductivity may be 1.0 mS / cm or more, 3.0 mS / cm or more, 5.0 mS / cm or more, or even 7.0 mS / cm or more. On the other hand, the ionic conductivity at 25°C may be, for example, 15.0 mS / cm or less, or 10.0 mS / cm or less.

[0026] The electrolyte solution of the present disclosure is used in lithium ion batteries, which will be described later.

[0027] B. Lithium-ion battery FIG. 1 is a schematic cross-sectional view illustrating a lithium-ion battery according to the present disclosure. The lithium-ion battery 10 shown in FIG. 1 includes 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. The lithium-ion battery 10 also includes a positive electrode current collector 4 that collects electrons from the positive electrode active material layer 1, and a negative electrode current collector 5 that collects electrons from the negative electrode active material layer 2. In particular, the lithium-ion battery 10 contains lithium metal as the negative electrode active material. The lithium-ion battery 10 also contains the above-described electrolyte solution. In the lithium-ion battery, it is preferable that the negative electrode active material layer, the positive electrode active material layer, and the electrolyte layer all contain the above-described electrolyte solution.

[0028] 1.Negative electrode active material layer The negative electrode active material layer contains lithium metal as the negative electrode active material. Here, in this specification, "lithium metal" means a metal containing lithium. Therefore, lithium metal includes simple lithium, an alloy containing lithium metal (lithium alloy), an oxide of lithium metal, and an oxide of lithium alloy.

[0029] Examples of lithium alloys include Li-Au, Li-Mg, Li-Sn, Li-Al, Li-B, Li-C, Li-Ca, Li-Ga, Li-Ge, Li-As, Li-Se, Li-Ru, Li-Rh, Li-Pd, Li-Ag, Li-Cd, Li-In, Li-Sb, Li-Ir, Li-Pt, Li-Hg, Li-Pb, Li-Bi, Li-Zn, Li-Tl, Li-Te, and Li-At. Only one type of lithium alloy may be used, or two or more types may be used.

[0030] The negative electrode active material layer may contain at least one of an electrolyte, a conductive additive, and a binder. In particular, the negative electrode active material layer preferably contains the above-mentioned electrolytic solution as the electrolyte. Examples of conductive additives include carbon materials, metal particles, and conductive polymers. Examples of carbon materials include particulate carbon materials such as acetylene black (AB) and fibrous carbon materials such as carbon nanotubes (CNT). Examples of binders include rubber-based binders such as butadiene rubber (BR) and fluorine-containing binders such as polyvinylidene fluoride (PVDF).

[0031] The negative electrode active material layer may also be a layer formed by a precipitation reaction of metallic lithium. In other words, the lithium-ion battery of the present disclosure may be a battery that utilizes a precipitation / dissolution reaction of metallic lithium as the negative electrode reaction. Although not specifically illustrated, a battery that utilizes a precipitation / dissolution reaction of metallic lithium as the negative electrode reaction has, in this order, a negative electrode current collector, a metal layer containing a metal capable of alloying with lithium, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector. By charging such a battery, the metal in the metal layer alloys with lithium, forming a negative electrode active material layer containing lithium metal. Examples of metals that can be alloyed with lithium include the metals described above in the lithium alloy section.

[0032] 2. Positive electrode active material layer The positive electrode active material layer contains at least a positive electrode active material and preferably contains the above-mentioned electrolyte solution.

[0033] Examples of the positive electrode active material include oxide active materials, such as LiCoO2, LiMnO2, LiNiO2, LiVO2, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 Examples of oxide active materials include rock salt layered active materials such as LiMnO, LiTiO, etc. 12 and Li(Ni 0.5 Mn 1.5 )O4, etc. Other examples of oxide active materials include olivine active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0034] The positive electrode active material layer may contain at least one of an electrolyte, a conductive additive, and a binder. In particular, the positive electrode active material layer preferably contains the above-mentioned electrolytic solution as the electrolyte. The conductive additive and the binder are the same as those described in "1. Negative electrode active material layer."

[0035] 3. Electrolyte layer The electrolyte layer is disposed between the positive electrode active material layer and the negative electrode active material layer and contains at least an electrolyte. The electrolyte layer preferably contains the above-mentioned electrolytic solution as the electrolyte.

[0036] The electrolyte layer may be a layer in which a separator is impregnated with an electrolytic solution. The separator may be made of either an organic or inorganic material. Specific examples include porous membranes made of polyethylene (PE), polypropylene (PP), cellulose, polyvinylidene fluoride, polyamide, polyimide, etc., nonwoven fabrics such as resin nonwoven fabrics and glass fiber nonwoven fabrics, and ceramic porous membranes. The separator may have a single-layer structure or a laminated structure.

[0037] 4. Other configurations The lithium-ion battery in this disclosure typically has a positive electrode current collector and a negative electrode current collector. Materials for the positive electrode current collector include, for example, SUS, aluminum, nickel, iron, titanium, and carbon. Materials for the negative electrode current collector include, for example, SUS, copper, nickel, and carbon.

[0038] The lithium-ion battery according to the present disclosure may also include an exterior housing that houses the above-described components. Examples of the exterior housing include a laminate-type exterior housing and a case-type exterior housing.

[0039] 5. Lithium-ion battery The lithium ion battery in the present disclosure is typically a liquid battery. The lithium ion battery may be a primary battery or a secondary battery, but a secondary battery is preferred because it can be repeatedly charged and discharged and is useful, for example, as an in-vehicle battery.

[0040] The use of the lithium-ion battery in the present disclosure is not particularly limited, but examples include a power source for a vehicle. Examples of vehicles include a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), an electric vehicle (BEV), a gasoline-powered vehicle, and a diesel-powered vehicle. In particular, the lithium-ion battery is preferably used as a driving power source for a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), or an electric vehicle (BEV). The lithium-ion battery in the present disclosure may also be used as a power source for mobile objects other than vehicles (for example, trains, ships, and aircraft). The battery in the present disclosure may also be used as a power source for electrical appliances such as information processing devices.

[0041] 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]

[0042] [Example 1] (Preparation of Electrolyte) DST3 manufactured by Mitsubishi Chemical Corporation was prepared as an organic electrolyte solution. DST3 is an electrolyte solution prepared by adding 1M LiPF6 to a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). LiCl and AlCl4 were weighed out to a molar ratio of 1:1 and mixed in a flask under an inert atmosphere. SO2 gas was sprayed onto this mixture to obtain a liquid component. The obtained liquid component was subjected to solid-liquid separation by filtration, and the liquid component was recovered as an inorganic electrolyte solution. The organic electrolyte solution and inorganic electrolyte solution were weighed out and mixed to a weight ratio of 99.9:0.1. This produced an electrolyte solution.

[0043] (Preparation of measurement cell) Lithium metal was attached to both electrodes of a cube cell (SB-1A) manufactured by EC Frontier, and the above-mentioned electrolyte solution was added to the inside to prepare a measurement cell.

[0044] [Examples 2 to 5 and Comparative Examples 1 and 2] An electrolyte solution was prepared in the same manner as in Example 1, except that the organic electrolyte solution and the inorganic electrolyte solution were mixed in the ratio shown in Table 1, and a measurement cell was prepared.

[0045] [evaluation] (Measurement of resistance increase rate) Each measurement cell was placed in a thermostatic bath at 25°C and allowed to soak. Then, impedance measurements were performed at regular intervals. The time-dependent change in the resistance increase rate per interface (interface resistance was equivalent to half) was obtained, and the resistance increase rate was calculated from the slope. The results are shown in Table 1.

[0046] (Evaluation of oxidation resistance of electrolyte) The oxidation resistance of the organic and inorganic electrolyte solutions was evaluated using the measurement cells prepared in Comparative Examples 1 and 2. Specifically, the evaluation was based on the behavior of the oxidation current when the potential was swept toward the oxidation side. The results are shown in Figure 2.

[0047] [Table 1]

[0048] As shown in Table 1, when an electrolyte containing an inorganic electrolyte was used, the rate of increase in resistance was significantly suppressed. On the other hand, as shown in Figure 2, the inorganic electrolyte had a large current value on the oxidation side, confirming that it had lower chemical stability (oxidation resistance) than an organic electrolyte. This is thought to be due to the decomposition reaction of the lithium salt contained in the inorganic electrolyte. From this, it was confirmed that organic electrolytes and electrolytes containing inorganic electrolytes have the advantages of organic electrolytes (good oxidation resistance) while also being able to suppress the increase in battery resistance. [Explanation of symbols]

[0049] 1...Cathode active material layer 2...Negative electrode active material layer 3...electrolyte layer 4...Positive electrode current collector 5...Negative electrode current collector 10...Lithium-ion battery

Claims

1. An electrolyte for use in a lithium ion battery, the lithium ion battery containing lithium metal as a negative electrode active material, the electrolyte including an organic electrolyte and an inorganic electrolyte, the inorganic electrolyte including a lithium salt and sulfur dioxide (SO ). 2 ) an electrolyte solution containing

2. The lithium salt contains AlCl as an anion component. 4 - and BCl 4 - The electrolyte solution according to claim 1, comprising at least one of the following:

3. 2. The electrolyte solution according to claim 1, wherein the proportion of the inorganic electrolyte solution relative to the total of the organic electrolyte solution and the inorganic electrolyte solution is 0.05% by weight or more and 70.0% by weight or less.

4. 2. The electrolyte solution according to claim 1, wherein the proportion of the inorganic electrolyte solution relative to the total of the organic electrolyte solution and the inorganic electrolyte solution is 0.10% by weight or more and 40.0% by weight or less.

5. A lithium ion battery using lithium metal as a negative electrode active material, the lithium ion battery containing the electrolyte solution according to any one of claims 1 to 4.

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