Electrolyte and lithium ion battery

Abstract

The invention relates to an electrolyte and a lithium ion battery. The main purpose of the present invention is to provide an electrolyte solution which has good oxidation resistance and is capable of suppressing an increase in battery resistance. The present disclosure solves the problem by providing an electrolyte solution for a lithium ion battery containing lithium metal as a negative electrode active material, the electrolyte solution containing an organic electrolyte solution and an inorganic electrolyte solution, the inorganic electrolyte solution containing a lithium salt and sulfur dioxide (SO2).

Description

Technical Field

[0001] This disclosure relates to electrolytes and lithium-ion batteries. Background Technology

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

[0003] For example, Patent Document 1 discloses an organic electrolyte battery comprising a positive electrode, a negative electrode, an organic electrolyte, and a separator. Furthermore, Patent Document 1 discloses that the aforementioned negative electrode is composed of lithium metal, a lithium alloy, or a material capable of absorbing and releasing lithium.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2010-225498 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] Among electrolytes, organic electrolytes generally have the advantages of a high upper limit of the potential window and good oxidation resistance. Furthermore, from the viewpoint of improving the high energy density of batteries, lithium metal can be used as a material for the negative electrode active material. On the other hand, as will be discussed later, when using lithium metal and organic electrolytes, the resistance may increase due to the solid electrolyte interphase (SEI) film formed on the surface of the lithium metal.

[0009] This disclosure was made in view of the above-mentioned circumstances, and its main purpose is to provide an electrolyte with good oxidation resistance and the ability to suppress the increase of battery resistance.

[0010] Methods for solving problems

[0011] [1] Electrolyte is an electrolyte used in lithium-ion batteries, wherein the lithium-ion battery contains lithium metal as the negative electrode active material, and the electrolyte includes organic electrolyte and inorganic electrolyte, wherein the inorganic electrolyte contains lithium salt and sulfur dioxide SO2.

[0012] [2] According to the electrolyte described in [1], wherein the lithium salt contains AlCl4 - and BCl4 - At least one of them is an anionic component.

[0013] [3] According to the electrolyte of [1] or [2], wherein the proportion of the inorganic electrolyte is more than 0.05% by weight and less than 70.0% by weight relative to the total of the organic electrolyte and the inorganic electrolyte.

[0014] [4] The electrolyte according to any one of [1] to [3], wherein the proportion of the inorganic electrolyte is 0.10% by weight or more and 40.0% by weight or less relative to the total of the organic electrolyte and the inorganic electrolyte.

[0015] [5] A lithium-ion battery is a lithium-ion battery that uses lithium metal as the negative electrode active material and contains an electrolyte according to any one of [1] to [4].

[0016] The effects of the invention

[0017] This disclosure achieves the effect of providing an electrolyte with good oxidation resistance and the ability to suppress the increase of battery resistance. Attached Figure Description

[0018] Figure 1 A schematic cross-sectional view of the lithium-ion battery disclosed herein is shown as an example.

[0019] Figure 2 A coordinate graph showing the results of the evaluation of the electrolyte's oxidation resistance.

[0020] Explanation of reference numerals in the attached figures

[0021] 1…Positive electrode active material layer

[0022] 2…Negative electrode active material layer

[0023] 3…Electrolyte layer

[0024] 4…Positive current collector

[0025] 5… Negative current collector

[0026] 10…Lithium-ion batteries Detailed Implementation

[0027] The electrolyte and lithium-ion battery of this disclosure are described in detail below. Furthermore, the following figures are schematic and the size and shape of the parts are exaggerated as appropriate for ease of understanding.

[0028] A. Electrolyte (liquid electrolyte)

[0029] The electrolyte disclosed herein is an electrolyte for use in lithium-ion batteries. The lithium-ion battery contains lithium metal as the negative electrode active material. The electrolyte comprises organic electrolytes and inorganic electrolytes. The inorganic electrolyte contains lithium salt and sulfur dioxide (SO2).

[0030] In addition to an organic electrolyte, the electrolyte disclosed herein also contains a specified inorganic electrolyte. As a result, the electrolyte of this disclosure exhibits good oxidation resistance and can suppress the increase in battery resistance.

[0031] As mentioned above, there are advantages to using organic electrolytes and lithium metal in lithium-ion batteries. However, lithium metal has relatively high reactivity, which may lead to side reactions between the lithium metal and the electrolyte. As a result, the organic electrolyte may be reduced and decomposed on the surface of the negative electrode active material (lithium metal), forming a thin-film interphase (SEI). Regarding the increase in interfacial resistance of the negative electrode active material caused by the SEI, it is assumed that this depends on the density (insulation) and thickness of the SEI. It is assumed that if the density of the SEI is low, the electrolyte decomposition reaction is more likely to occur, leading to an increase in the thickness of the SEI (coating growth). Furthermore, it is believed that when using organic electrolytes, the resulting SEI has low density, and due to the electrolyte decomposition reaction, the SEI grows thicker, increasing the interfacial resistance of the negative electrode active material. On the other hand, it is speculated that when using inorganic electrolytes containing sulfur dioxide (SO2) and lithium salts, the resulting SEI has high density, which can suppress the electrolyte decomposition reaction. It is believed that even when inorganic electrolytes are used together with organic electrolytes, the thin film caused by the decomposition of the inorganic electrolyte can inhibit the formation of a film with the organic electrolyte, thus preventing the film from thickening. As a result, if the electrolyte of this disclosure contains both an organic electrolyte and a specified inorganic electrolyte, it is possible to suppress the increase in battery resistance while obtaining the advantages of organic electrolytes (good oxidation resistance).

[0032] 1. Inorganic electrolyte

[0033] The inorganic electrolyte disclosed herein contains lithium salt and sulfur dioxide (SO2).

[0034] As the cationic component in lithium salts, typically Li + As an anionic component in lithium salts, AlCl4 can be cited as an example. - GaCl4 - BF4 - BCl4 - and InCl4 - Isochloride anions. Among these, AlCl4 is preferred. - and GaCl4 - Lithium salts may contain one or more anionic components.

[0035] The composition of the inorganic electrolyte can be represented as LiX-αSO2. X is the anionic component, and α is a number satisfying 0.5 ≤ α ≤ 10. α can be 1.0 or higher, 3.0 or higher, or 5.0 or higher. On the other hand, α can be 8.0 or lower, or 6.0 or lower. The inorganic electrolyte can be prepared by injecting SO2 gas into a lithium salt material (e.g., a mixture of LiCl and AlCl4).

[0036] There is no particular limitation on the proportion (by weight) of the inorganic electrolyte relative to the total of the organic and inorganic electrolytes; for example, it may be 0.05% by weight or more. The proportion of inorganic electrolyte 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 inorganic electrolyte may be, for example, 70.0% by weight or less. The proportion of inorganic electrolyte 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.

[0037] There is no particular limitation on the proportion (volume ratio) of inorganic electrolyte relative to the total of organic and inorganic electrolytes, but it is, for example, 0.05% by volume or more. The proportion of inorganic electrolyte can 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 inorganic electrolyte can be, for example, 70.0% by volume or less. The proportion of inorganic electrolyte can be 50.0% by volume or less, 40.0% by volume or less, or 30.0% by volume or less.

[0038] 2. Organic electrolyte

[0039] Examples of organic electrolytes disclosed herein include electrolytes containing a supporting salt and an organic solvent.

[0040] 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), butyl carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC). The supporting salt and organic solvent in an organic electrolyte can each be one type or two or more.

[0041] 3. Electrolyte

[0042] The preferred electrolyte has high ionic conductivity. For example, the ionic conductivity at 25°C is 0.1 mS / cm or higher. The ionic conductivity can be 1.0 mS / cm or higher, 3.0 mS / cm or higher, 5.0 mS / cm or higher, or 7.0 mS / cm or higher. On the other hand, the ionic conductivity at 25°C is, for example, 15.0 mS / cm or lower, or 10.0 mS / cm or lower.

[0043] The electrolyte disclosed herein is used in lithium-ion batteries. Details regarding lithium-ion batteries will be discussed later.

[0044] B. Lithium-ion batteries

[0045] Figure 1 A schematic cross-sectional view of the lithium-ion battery disclosed herein is shown as an example. Figure 1 The lithium-ion battery 10 shown 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. Furthermore, the lithium-ion battery 10 includes: a positive electrode current collector 4 for collecting electrons from the positive electrode active material layer 1, and a negative electrode current collector 5 for collecting electrons from the negative electrode active material layer 2. Specifically, the lithium-ion battery 10 contains lithium metal as the negative electrode active material. Additionally, the lithium-ion battery 10 contains the aforementioned electrolyte. In a lithium-ion battery, it is preferable that the entire negative electrode active material layer, the positive electrode active material layer, and the electrolyte layer contain the aforementioned electrolyte.

[0046] 1. Negative electrode active material layer

[0047] The negative electrode active material layer contains lithium metal as the negative electrode active material. Here, "lithium metal" as used in this specification refers to a metal containing lithium. Therefore, lithium metal includes elemental lithium, lithium metal alloys (lithium alloys), lithium metal oxides, and lithium alloy oxides.

[0048] 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. A lithium alloy can be of one type or two or more types.

[0049] 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 aforementioned electrolyte 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 (CNTs). Examples of binders include rubber-based binders such as butadiene rubber (BR) and fluorinated binders such as polyvinylidene fluoride (PVDF).

[0050] Furthermore, the negative electrode active material layer can be a layer formed by the deposition reaction of metallic lithium. That is, the lithium-ion battery of this disclosure can be a battery that uses the deposition and dissolution reaction of metallic lithium as the negative electrode reaction. Although not specifically illustrated, a battery that uses the deposition and dissolution reaction of metallic lithium as the negative electrode reaction sequentially comprises: a negative electrode current collector, a metal layer containing a metal that can form an alloy with lithium, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector. When such a battery is charged, the metal of the metal layer alloys with lithium, forming a negative electrode active material layer containing lithium metal. As a metal that can form an alloy with lithium, the metals described in the above-mentioned lithium alloys can be listed.

[0051] 2. Positive electrode active material layer

[0052] The positive electrode active material layer contains at least a positive electrode active material. Furthermore, the positive electrode active material layer preferably contains the electrolyte described above.

[0053] Examples of positive electrode active materials include oxide active materials. Examples of oxide active materials include LiCoO2, LiMnO2, LiNiO2, LiVO2, and LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 and other layered rock salt active substances. Other examples of oxide active substances include LiMn2O4 and Li4Ti5O. 12 and Li(Ni 0.5 Mn 1.5 Spinel-type active materials such as O4. Other examples of oxide-type active materials include olivine-type active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0054] In addition, the positive electrode active material layer may include at least one of an electrolyte, a conductive additive, and a binder. In particular, the positive electrode active material layer preferably contains the aforementioned electrolyte as the electrolyte. The conductive additive and binder are the same as those described in "1. Negative Electrode Active Material Layer".

[0055] 3. Electrolyte layer

[0056] An electrolyte layer is disposed between the positive electrode active material layer and the negative electrode active material layer, and contains at least an electrolyte. Preferably, the electrolyte layer contains the aforementioned electrolyte solution as the electrolyte.

[0057] The electrolyte layer can be a layer impregnated with electrolyte in the membrane. The membrane material can be organic or inorganic. Specifically, examples include porous membranes made of polyethylene (PE), polypropylene (PP), cellulose, polyvinylidene fluoride, polyamide, polyimide, etc., resin nonwoven fabrics, glass fiber nonwoven fabrics, ceramic porous membranes, etc. Furthermore, the membrane can be a single-layer structure or a multilayer structure.

[0058] 4. Other components

[0059] The lithium-ion battery disclosed herein typically has a positive current collector and a negative current collector. Examples of materials used as the positive current collector include SUS, aluminum, nickel, iron, titanium, and carbon. On the other hand, examples of materials used as the negative current collector include SUS, copper, nickel, and carbon.

[0060] Furthermore, the lithium-ion battery disclosed herein may include an outer packaging body that houses the aforementioned components. Examples of such outer packaging bodies include laminated outer packaging bodies and shell-type outer packaging bodies.

[0061] 5. Lithium-ion batteries

[0062] The lithium-ion battery disclosed herein is typically a liquid-based battery. Furthermore, the lithium-ion battery can be a primary battery or a secondary battery, with a secondary battery being preferred. This is because it can be repeatedly charged and discharged, and can be used, for example, as a battery for automotive applications.

[0063] The applications of the lithium-ion batteries disclosed herein are not particularly limited; for example, they can be used as power sources for vehicles. Examples of vehicles include hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline vehicles, and diesel vehicles. In particular, the lithium-ion batteries are preferably used as power sources for driving hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or battery electric vehicles (BEVs). Furthermore, the lithium-ion batteries of this disclosure can be used as power sources for mobile bodies other than vehicles (e.g., railways, ships, and aircraft). Additionally, the batteries of this disclosure can be used as power sources for electrical appliances such as information processing devices.

[0064] It should be noted that this disclosure is not limited to the embodiments described above. The embodiments described above are illustrative examples, and technical solutions with substantially the same structure and achieving the same effect as those described in the patent claims of this disclosure are all included within the technical scope of this disclosure.

[0065] Example

[0066] [Example 1]

[0067] (Preparation of electrolyte)

[0068] As the organic electrolyte, DST3 manufactured by Mitsubishi Chemical Corporation was prepared. DST3 is an electrolyte in which 1 M of LiPF6 was added to a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). LiCl and AlCl4 were weighed to achieve a 1:1 molar ratio and mixed in a flask under an inactive atmosphere. SO2 gas was injected into the mixture to obtain a liquid component. The obtained liquid component was filtered, and solid-liquid separation was performed. The liquid component was recovered as an inorganic electrolyte. The organic electrolyte and inorganic electrolyte were weighed at a weight ratio of 99.9:0.1 and mixed. Thus, an electrolyte was prepared.

[0069] (Determining the fabrication of battery cells)

[0070] Lithium metal was attached to the two electrodes of a cube cell (SB-1A) manufactured by EC Frontier, and then the electrolyte described above was added inside. This prepared the measurement cell.

[0071] [Examples 2-5 and Comparative Examples 1-2]

[0072] Except that the organic electrolyte and inorganic electrolyte were mixed in the proportions shown in Table 1, the electrolyte was prepared in the same manner as in Example 1, and the battery cell was prepared for testing.

[0073] [evaluate]

[0074] (Determination of the rate of increase in resistance)

[0075] Each battery cell was homogenized in a 25°C constant temperature bath. Impedance measurements were then performed at regular intervals. The rate of increase in resistance at each interface (interface resistance equivalent to half) over time was recorded, and the rate of increase in resistance was calculated from its slope. The results are shown in Table 1.

[0076] (Evaluation of the electrolyte's oxidation resistance)

[0077] The oxidation resistance of organic and inorganic electrolytes was evaluated using the test cell cells fabricated in Comparative Examples 1 and 2. Specifically, the evaluation was based on the behavior of the oxidation current at the oxidation-side scan potential. The results are shown below. Figure 2 .

[0078] Table 1

[0079]

[0080] As shown in Table 1, the increase in resistivity was significantly suppressed when using an electrolyte containing inorganic electrolyte. On the other hand, as... Figure 2 As shown, the inorganic electrolyte exhibits a higher current value on the oxidation side, confirming its lower chemical stability (oxidation resistance) compared to organic electrolytes. This is attributed to the decomposition reaction of the lithium salts contained in the inorganic electrolyte. Therefore, it is confirmed that an electrolyte containing both organic and inorganic electrolytes possesses the advantages of organic electrolytes (good oxidation resistance) and can suppress the increase in battery resistance.

Claims

1. Electrolyte, which is used in lithium-ion batteries, wherein the lithium-ion battery contains lithium metal as the negative electrode active material, and the electrolyte includes organic electrolyte and inorganic electrolyte, wherein the inorganic electrolyte contains lithium salt and sulfur dioxide (SO2).

2. The electrolyte according to claim 1, wherein, The lithium salt contains AlCl4. - and BCl4 - At least one of them is an anionic component.

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

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

5. A lithium-ion battery, which uses lithium metal as the negative electrode active material, and contains the electrolyte according to any one of claims 1 to 4.

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