Solid battery

Abstract

To provide a solid-state battery having high cycle characteristics.SOLUTION: In the solid-state battery of the present disclosure, a positive electrode current collector layer, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector layer are laminated in this order. The negative electrode active material layer of the solid-state battery of the present disclosure includes a gallium-based layer containing gallium or a lithium-gallium alloy, and a magnesium-based layer containing magnesium or a lithium-magnesium alloy. The gallium-based layer is arranged on the solid electrolyte layer side, and the magnesium-based layer is arranged on the negative electrode current collector layer side.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a solid battery.

[0002] With the rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones in recent years, the development of batteries used as their power sources has been emphasized. Also, in the automotive industry and the like, the development of high-output and high-capacity batteries for electric vehicles or hybrid vehicles has been underway.

[0003] Among batteries, lithium secondary batteries contain metallic lithium, which has the largest ionization tendency among metals, in the negative electrode active material layer. Therefore, they are attracting attention because of the large potential difference with the positive electrode active material layer and the ability to obtain a high output voltage.

[0004] In recent years, solid batteries having a solid electrolyte as an electrolyte have also been attracting attention. Compared with batteries using an electrolytic solution, solid batteries are less likely to cause decomposition of the electrolytic solution due to overcharging of the battery and have high cycle characteristics and energy density.

Background Art

[0005] Patent Document 1 discloses a solid battery including a β single-phase alloy of metallic lithium and metallic magnesium as a negative electrode active material.

[0006] Patent Document 2 discloses a secondary battery in which a negative electrode active material layer contains gallium and a resin.

[0007] Patent Document 3 discloses an all-solid-state lithium battery provided with at least one lithium alloy layer selected from among lithium-aluminum alloy, lithium-gallium alloy, lithium-indium alloy, lithium-antimony alloy, and lithium-bismuth alloy at the interface between a solid electrolyte and a lithium negative electrode.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0009] Regarding the cycle characteristics in a solid battery containing a material capable of forming an alloy with metallic lithium as a negative electrode active material, there is still room for improvement.

[0010] Therefore, an object of the present disclosure is to provide a solid battery having high cycle characteristics.

Means for Solving the Problems

[0011] The present inventors have found that the above problems can be solved by the following means. <Aspect 1> A solid battery in which a positive electrode current collector layer, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector layer are laminated in this order, The negative electrode active material layer has a gallium-based layer containing gallium or a lithium gallium alloy, and a magnesium-based layer containing magnesium or a lithium magnesium alloy, The gallium-based layer is disposed on the solid electrolyte layer side, and The magnesium-based layer is disposed on the negative electrode current collector layer side. Solid battery.

Effects of the Invention

[0012] According to the present disclosure, a solid battery having high cycle characteristics can be provided.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the disclosure.

[0015] 《Solid Battery》 In the solid battery of the present disclosure, a positive electrode current collector layer, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector layer are laminated in this order. Further, the negative electrode active material layer of the solid battery of the present disclosure has a gallium-based layer containing gallium or a lithium gallium alloy, and a magnesium-based layer containing magnesium or a lithium magnesium alloy, the gallium-based layer is disposed on the solid electrolyte layer side, and the magnesium-based layer is disposed on the negative electrode current collector layer side.

[0016] As a method for improving the energy density of a solid battery, there is a method of using metallic lithium (Li) as a negative electrode active material and making the anode free. However, the present inventors have found that the cycle characteristics may deteriorate in a solid battery without an anode. Although not intending to be bound by any theory, this is presumably because peeling occurs at the interface between the solid electrolyte layer and the negative electrode active material layer due to the disappearance of Li in the negative electrode active material layer during discharge.

[0017] As an anode-free solid battery, as shown in Patent Document 1, those containing a β single-phase alloy of metallic Li and metallic magnesium (Mg) as a negative electrode active material are known. In addition to such a Mg-based layer containing metallic Mg or a lithium-magnesium (Li-Mg) alloy, the present inventors have found that by disposing a Ga-based layer containing metallic gallium (Ga) or a lithium-gallium (Li-Ga) alloy between the solid electrolyte layer and the Mg-based layer to form a two-layer negative electrode active material layer, the cycle characteristics of a battery including such a negative electrode active material layer are improved. Although not intending to be bound by any theory, this is presumably because even at the end of discharge of the battery, the Ga-based layer is retained between the solid electrolyte layer and the Mg-based layer, thereby suppressing peeling at the interface between the negative electrode active material layer and the solid electrolyte layer.

[0018] The solid battery of the present disclosure has a positive electrode current collector layer, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector layer laminated in this order.

[0019] 〈Positive electrode current collector layer〉 As the positive electrode current collector, a known metal that can be used as a current collector of a solid battery can be used. Examples of such a metal include a metal material containing one or more elements selected from the group consisting of Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Co, Cr, Zn, Ge, and In.

[0020] The form of the positive electrode current collector is not particularly limited and can be various forms such as foil and mesh.

[0021] 〈Positive electrode active material layer〉 The positive electrode active material layer contains a positive electrode active material and may optionally contain a solid electrolyte, a conductive material, a binder, etc.

[0022] (Positive electrode active material) There is no particular limitation on the type of the positive electrode active material, and any material that can be used as the active material of the solid battery can be adopted. The positive electrode active material may contain a lithium element or may not contain a lithium element.

[0023] Examples of the positive electrode active material containing a lithium element include metallic lithium (Li), a lithium alloy, LiCoO2, LiNi x Co 1-x O2 (0 < x < 1), LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiMnO2, hetero-element substituted Li-Mn spinel (e.g., LiMn 1.5 Ni 0.5 O4, LiMn 1.5 Al 0.5 O4, LiMn 1.5 Mg 0.5 O4, LiMn 1.5 Co 0.5 O4, LiMn 1.5 Fe 0.5 O4, and LiMn 1.5 Zn 0.5 O4, etc.), lithium titanate (e.g., Li4Ti5O 12 ), lithium metal phosphate (e.g., LiFePO4, LiMnPO4, LiCoPO4, and LiNiPO4, etc.), LiCoN, Li2SiO3, and Li4SiO4, etc.

[0024] Examples of the lithium alloy include Li-Au, Li-Mg, Li-Sn, Li-Si, Li-Al, Li-Ge, Li-Sb, Li-B, Li-C, Li-Ca, Li-Ga, Li-As, Li-Se, Li-Ru, Li-Rh, Li-Pd, Li-Ag, Li-Cd, Li-Ir, Li-Pt, Li-Hg, Li-Pb, Li-Bi, Li-Zn, Li-Tl, Li-Te, Li-At, and Li-In, etc.

[0025] Examples of the cathode active material that does not contain lithium element include, for example, transition metal oxides (such as V2O5 and MoO3, etc.), sulfur, TiS2, Si, SiO2, and lithium storage intermetallic compounds (such as Mg2Sn, Mg2Ge, Mg2Sb, and Cu3Sb, etc.), etc.

[0026] The shape of the cathode active material is not particularly limited, and it may be particulate.

[0027] A coating layer containing a Li ion conductive oxide may be formed on the surface of the cathode active material. This is because the reaction between the cathode active material and the solid electrolyte can be suppressed.

[0028] Examples of the Li ion conductive oxide include, for example, LiNbO3, Li4Ti5O 12 , and Li3PO4, etc. The thickness of the coating layer is, for example, 0.1 nm or more, and may be 1 nm or more. On the other hand, the thickness of the coating layer is, for example, 100 nm or less, and may be 20 nm or less. The coverage rate of the coating layer on the surface of the cathode active material is, for example, 70% or more, and may be 90% or more.

[0029] (Solid electrolyte) Examples of the solid electrolyte include sulfide solid electrolytes and oxide-based solid electrolytes, etc.

[0030] Examples of the sulfide solid electrolyte include, for example, Li2S-P2S5, Li2S-SiS2, LiX-Li2S-SiS2, LiX-Li2S-P2S5, LiX-Li2O-Li2S-P2S5, LiX-Li2S-P2O5, LiX-Li3PO4-P2S5, and Li3PS4. Note that the description of "Li2S-P2S5" means a material obtained using a raw material composition containing Li2S and P2S5, and the same applies to other descriptions. Further, "X" in the above LiX indicates a halogen element. LiX may be contained in one or more kinds in the raw material composition containing LiX. When two or more kinds of LiX are contained, the mixing ratio of the two or more kinds is not particularly limited.

[0031] Examples of the oxide-based solid electrolyte include, for example, Li 6.25 La3Zr2A l0.25 O 12 , Li3PO4, and Li 3+x PO 4-x N x (0 < x ≦ 3) and the like.

[0032] The ratio of the solid electrolyte in the positive electrode active material layer is not particularly limited, but may be, for example, 1 mass% to 80 mass% when the total mass of the positive electrode active material layer is 100 mass%.

[0033] (Conductive material) As the conductive material, known materials can be used, and examples thereof include carbon materials and metal particles. Examples of the carbon material include at least one selected from the group consisting of carbon black such as acetylene black and furnace black, carbon nanotubes, and carbon nanofibers. Among them, from the viewpoint of electron conductivity, at least one selected from the group consisting of carbon nanotubes and carbon nanofibers is preferable. The carbon nanotubes and carbon nanofibers may be VGCF (vapor grown carbon fiber). Examples of the metal particles include particles such as Ni, Cu, Fe, and SUS.

[0034] The content of the conductive material in the positive electrode active material layer is not particularly limited.

[0035] (Binder) Examples of the binder include acrylonitrile-butadiene rubber (ABR), butadiene rubber (BR), polyvinylidene fluoride (PVdF), and styrene-butadiene rubber (SBR).

[0036] The content of the binder in the positive electrode active material layer is not particularly limited.

[0037] The thickness of the positive electrode active material layer is not particularly limited.

[0038] 〈Solid electrolyte layer〉 The solid electrolyte layer contains a solid electrolyte and optionally a binder.

[0039] (Solid electrolyte) For the solid electrolyte, reference can be made to the above description regarding the positive electrode active material layer of the present disclosure.

[0040] The solid electrolyte can be used alone or in combination of two or more. When using two or more solid electrolytes, they may be mixed, or layers of two or more solid electrolytes may be formed respectively to form a multilayer structure.

[0041] The proportion of the solid electrolyte in the solid electrolyte layer is not particularly limited, but for example, it may be 50% by mass or more, 60% by mass or more and 100% by mass or less, or 70% by mass or more and 100% by mass or less, or even 100% by mass.

[0042] (Binder) The solid electrolyte layer can also contain a binder from the viewpoint of exhibiting plasticity or the like. Regarding the binder, reference can be made to the above description regarding the positive electrode active material layer of the present disclosure. However, from the viewpoint of facilitating high power output and forming a solid electrolyte layer having a solid electrolyte that prevents excessive aggregation and is uniformly dispersed, the binder contained in the solid electrolyte layer may be 5% by mass or less.

[0043] The thickness of the solid electrolyte layer is not particularly limited and is usually 0.1 μm or more and 1 mm or less.

[0044] 〈Negative electrode active material layer〉 The negative electrode active material layer has a Ga-based layer and an Mg-based layer.

[0045] (Gallium-based layer) The Ga-based layer contains metallic Ga or a Li-Ga alloy as a negative electrode active material.

[0046] The metallic Ga may be metallic Ga itself or a material obtained by vapor depositing metallic Ga or the like.

[0047] The Li-Ga alloy may be an alloy generated by charging the solid battery including the negative electrode active material layer of the present disclosure, or an alloy prepared separately.

[0048] Examples of the method for generating a Li-Ga alloy by charging the solid battery include the following method. First, a battery precursor having a positive electrode active material layer containing at least one positive electrode active material selected from the group consisting of metallic Li, Li alloys, and Li compounds, a solid electrolyte layer, a metallic Ga layer, and a negative electrode current collector layer in this order is prepared. By charging this battery precursor, a Li-Ga alloy is obtained by reacting Li ions that have moved from the positive electrode active material layer to the metallic Ga layer with the metallic Ga in the metallic Ga layer. From the viewpoint of alloying all of the metallic Ga in the metallic Ga layer with metallic Li, the precursor battery may be charged and discharged a plurality of times. The number of charge and discharge cycles is not particularly limited and can be appropriately set according to the thickness of the metallic Ga layer.

[0049] The Ga-based layer is disposed on the solid electrolyte layer side. By disposing the Ga-based layer between the solid electrolyte layer and the Mg-based layer described later to form a two-layer negative electrode active material layer, the cycle characteristics of a battery including such a negative electrode active material layer are improved.

[0050] The Ga-based layer may contain, as a main component, metallic Ga or a Li-Ga alloy as a negative electrode active material, and may also contain other conventionally known negative electrode active materials. In the present disclosure, the main component means a component contained in an amount of 50% by mass or more when the total mass of the Ga-based layer is 100% by mass.

[0051] (Magnesium-based layer) The Mg-based layer contains metallic Mg or a Li-Mg alloy.

[0052] The metallic Mg may be metallic Mg itself or a material obtained by vapor depositing metallic Mg or the like.

[0053] The Li-Mg alloy may be an alloy formed by charging a solid battery including the negative electrode active material layer of the present disclosure, or may be an alloy prepared separately.

[0054] Regarding the method of forming a Li-Mg alloy by charging a solid battery, reference can be made to the above description regarding the method of forming a Li-Ga alloy of the present disclosure.

[0055] The Mg-based layer is disposed on the negative electrode current collector layer side.

[0056] The Mg-based layer may contain, as a main component, metallic Mg or a Li-Mg alloy as a negative electrode active material, and may also contain other conventionally known negative electrode active materials. In the present disclosure, the main component means a component contained in an amount of 50% by mass or more when the total mass of the Mg-based layer is 100% by mass.

[0057] (Solid electrolyte, conductive material, and binder) The negative electrode active material layer may contain a solid electrolyte, a conductive material, a binder, and the like. For the solid electrolyte, the conductive material, and the binder, reference can be made to the above description regarding the positive electrode active material layer of the present disclosure.

[0058] The thickness of the negative electrode active material layer is not particularly limited, but may be 30 nm or more and 50 μm or less.

[0059] 〈Negative electrode current collector layer〉 The negative electrode current collector may be a material that does not alloy with Li, and examples thereof include SUS, copper, nickel, and the like.

[0060] Examples of the form of the negative electrode current collector include a foil shape and a plate shape.

[0061] The planar shape of the negative electrode current collector is not particularly limited, and examples thereof include a circular shape, an elliptical shape, a rectangular shape, and an arbitrary polygonal shape.

[0062] The thickness of the negative electrode current collector varies depending on the shape, but may be, for example, 1 μm to 50 μm, or 5 μm to 20 μm.

Examples

[0063] 《Fabrication of the cell》 〈Fabrication of the positive electrode active material layer〉 Using butyl butyrate as a solvent, a positive electrode composite slurry was prepared at a weight composition ratio of lithium nickelate (NCA): solid electrolyte: binder: conductive assistant = 84.7:13.4:0.6:1.27, coated on an aluminum (Al) foil with a coating gap of 225 μm, then pre-dried at 60 °C, and finally fully dried at 165 °C for 1 hour. Thus, a positive electrode active material layer with a basis weight of 18.7 mg / cm 2 , and a designed capacity of 3.0 mAh / cm 2 was obtained.

[0064] 〈Fabrication of the solid electrolyte layer〉 Using butyl butyrate as a solvent, a solid electrolyte slurry was prepared at a weight composition ratio of solid electrolyte: binder = 92.6:7.4. After coating it on a release film with a coating gap of 325 μm, it was pre-dried at room temperature for about 3 hours and then fully dried at 165°C for 1 hour. Two pieces with a diameter of φ14.5 mm were punched out from the dried coated foil, and the coated surfaces were overlapped and pressed at 7 t. After pressing, the release film was peeled off to obtain a self-supporting sulfide solid electrolyte layer.

[0065] 〈Preparation of negative electrode active material layer〉 As the negative electrode active material layer, a gallium (Ga) vapor-deposited foil (thickness: 0.84 μm), a magnesium (Mg) vapor-deposited foil (thickness: 1.0 μm), and a Ga-Mg two-layer vapor-deposited foil (thickness of Ga vapor-deposited foil: 1.0 μm, thickness of Mg vapor-deposited foil: 1.0 μm) were prepared.

[0066] 〈Assembly of cell〉 (Comparative Example 1) The prepared positive electrode active material layer was punched out with a diameter of φ11.28 mm. Also, the Ga vapor-deposited foil as the negative electrode active material layer was punched out with a diameter of φ14.5 mm. The prepared self-supporting solid electrolyte layer with a diameter of φ14.5 mm was placed between the positive electrode active material layer and the negative electrode active material layer, and it was vacuum-sealed in a laminate film using an Al foil as the positive electrode current collector and Ni as the negative electrode current collector. The sealed cell was isotropically pressed at 392 MPa using cold isostatic pressing (CIP) to fabricate a laminate cell. A spring was inserted to use a constant-pressure jig to constrain the fabricated cell at 1 MPa so that the restraint pressure would be constant regardless of the volume change of the cell. Thereby, the cell of Comparative Example 1 was obtained.

[0067] (Comparative Example 2) A cell of Comparative Example 2 was obtained in the same manner as in Comparative Example 1 except that the negative electrode active material layer was made of Mg vapor-deposited foil.

[0068] (Example 1) A cell of Example 1 was obtained in the same manner as in Comparative Example 1 except that the negative electrode active material layer was made of a Ga-Mg two-layer vapor-deposited foil. Note that the Ga vapor-deposited foil was placed on the solid electrolyte layer side and the Mg vapor-deposited foil was placed on the negative electrode current collector layer side.

[0069] 《Evaluation》 〈Measurement of charge-discharge curve〉 In the range of cut-off voltage 4.2 V - 3.0 V, at constant current (current density: 0.15 mA / cm 2 , equivalent to 0.05C) - constant voltage (cut-off current density: 0.03 mA / cm 2 , equivalent to 0.01C) test, the first charge-discharge of the constrained cell was carried out at 60 °C, and the charge-discharge curve was obtained.

[0070] 〈SEM-EDX measurement〉 Regarding the cross-section of the Ga-Mg bilayer deposited foil after the first charge at 60 °C, SEM observation and EDX mapping in secondary electron images were performed at an applied voltage of 5 kV.

[0071] 〈Measurement of cycle characteristics〉 After the first charge-discharge at 60 °C, also in the range of cut-off voltage 4.2 V - 3.0 V, at 25 °C, at constant current (current density: 0.60 mA / cm 2 , equivalent to 0.05C) - constant voltage (only during charging, cut-off current density: 0.03 mA / cm 2 , equivalent to 0.01C) test, the cycle characteristics were measured. However, since Ga has a low melting point (melting point: 29.7 °C), for the cycle characteristic test of the cell in Comparative Example 1 with the negative electrode active material layer as a Ga-deposited foil, the first charge-discharge was also carried out at 25 °C.

[0072] 《Results》 〈Measurement results of charge-discharge curve〉 The 60 °C first charge-discharge curves at a current density of 0.15 mA / cm 2 (~C / 20) for the cells of each example are shown in Figure 1.

[0073] As shown in Fig. 1, the charge capacity and the discharge capacity were 213 - 215 mAh / g and 179 - 189 mAh / g, respectively, based on the positive electrode active material. In the cell of Comparative Example 1 using a Ga-deposited foil as the negative electrode active material layer, the cell voltage was lower than that of the Mg-deposited foil in the region of 3.2 V - 3.5 V at the initial stage of charging and in the region of 3.6 V - 3.0 V at the final stage of discharge. From this, it is suggested that in the cell of Comparative Example 1, before the precipitation of metallic lithium (Li) at the negative electrode potential of ~0 V vs Li, Li insertion into and alloying with Ga occur at the initial stage of charging, and Li desorption from Ga occurs at the final stage of charging.

[0074] On the other hand, in the cell of Example 1 using a Ga-Mg bilayer deposited foil as the negative electrode active material layer, an additional reversible capacity was observed in the discharge curve at 3.5 V or less, compared with the cell of Comparative Example 2 using a Mg-deposited foil as the negative electrode active material layer, and the reversible capacity derived from the constant voltage step at the lower cutoff voltage of 3.0 V decreased. From this, it is suggested that the presence of the Ga layer in the Ga-Mg bilayer deposited foil does not cause a decrease in the cell voltage at the initial stage of charging and enables more Li desorption in the constant current step at the final stage of discharge.

[0075] 〈SEM-EDX Measurement Results〉 The results of cross-sectional SEM secondary electron images and EDX mapping analysis after the first charge-discharge at 60 °C of the cell of Example 1 using a Ga-Mg bilayer deposited foil as the negative electrode active material layer are shown in Figs. 2 and 3.

[0076] As shown in Figs. 2 and 3, distributions rich in Mg, Ga, and S were confirmed in order from the bottommost negative electrode current collector layer. This indicates that the Ga-based layer exists between the Mg-based layer and the solid electrolyte layer even after Li insertion and desorption due to the first charge-discharge. This Ga-based layer is considered to serve as a Li desorption reaction field at the final stage of discharge and contribute to the maintenance of the negative electrode active material layer-solid electrolyte interface and the increase in the reversible capacity in the constant current step.

[0077] 〈Measurement Results of Cycle Characteristics〉 For the cells of each example, after the first charge-discharge, 0.60 mA / cm 2The results of the 25 °C cycle characteristics at (~C / 5) are shown in Fig. 4. Also, the reversible capacity after 50 cycles is shown in Table 1.

[0078]

Table 1

[0079] As shown in Fig. 4 and Table 1, the cell of Example 1 using a Ga-Mg bilayer vapor-deposited foil as the negative electrode active material layer had a larger reversible capacity than the cells of the comparative examples, and was about twice as large as that of Comparative Example 2, which had a larger reversible capacity among the comparative examples, both in terms of the reversible capacity after 1 cycle and the reversible capacity after 50 cycles.

[0080] Also, as shown in Fig. 4 and Table 1, the cell of Comparative Example 2 using a Mg vapor-deposited foil had a larger reversible capacity than the cell of Comparative Example 1 using a Ga vapor-deposited foil as the negative electrode active material layer. From this, in the cell including the negative electrode active material layer of the present disclosure, providing the Mg vapor-deposited foil on the negative electrode current collector layer side and providing the Ga vapor-deposited foil, which is the second negative electrode active material layer, between the Mg vapor-deposited foil and the solid electrolyte layer is considered to be the factor that improved the reversible capacity.

Claims

【Claim 1】 A solid-state battery in which a positive electrode current collector layer, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector layer are laminated in this order, wherein the negative electrode active material layer has a gallium-based layer containing gallium or a lithium gallium alloy, and a magnesium-based layer containing magnesium or a lithium magnesium alloy, the gallium-based layer is disposed on the solid electrolyte layer side, and the magnesium-based layer is disposed on the negative electrode current collector layer side. Solid-state battery.

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