All-solid-state secondary battery

Abstract

This all-solid-state secondary battery includes: a positive electrode 11 containing cyanide containing lithium; a negative electrode 13 containing a substance capable of inserting and desorbing lithium at a potential lower than that of the positive electrode; and a chloride solid electrolyte 12 containing lithium.

Description

All-solid-state secondary battery

[0001] This disclosure relates to all-solid-state rechargeable batteries.

[0002] Traditionally, all-solid-state lithium-ion batteries have been developed as secondary batteries for use in electric vehicles, mobile devices, and other applications. All-solid-state lithium-ion batteries are highly safe and have a high energy density.

[0003] Patent No. 6565724, Patent No. 7281296

[0004] All-solid-state lithium-ion batteries are constructed by stacking solid negative electrodes, electrolytes, and positive electrodes, and unlike conventional lithium-ion batteries, they do not use liquid electrolytes containing flammable organic solvents. Therefore, all-solid-state lithium-ion batteries have a low risk of fire and can achieve high safety. In addition, because all components of an all-solid-state lithium-ion battery are solid, it is possible to increase the energy density of the battery by stacking multiple battery cells with high efficiency.

[0005] Solid-state rechargeable batteries are expected to become widespread in a wide range of applications, including large-scale applications such as electric vehicles. If such solid-state rechargeable batteries become widespread, it would be desirable from an environmental perspective to recycle and reuse the constituent materials after the batteries have been used for a certain period and have deteriorated.

[0006] In the all-solid-state lithium secondary batteries of Patent Documents 1 and 2, Li x La3Zr2O 12 (6≦x≦8), (Li 3a ,La 2 / 3-a )(Mg b ,W 1-b Although metal oxide materials such as 3(1 / 6≦a≦1 / 3, 0.4≦b≦0.6) are used as solid electrolytes, chemically stable metal oxides generally do not dissolve in water (neutral) for short periods of time. Furthermore, while Patent Documents 1 and 2 exemplify manganese dioxide (MnO2) and iron oxide as positive electrode active materials, these are also stable metal oxides and therefore do not dissolve in water (neutral).

[0007] Therefore, current recycling of all-solid-state lithium secondary batteries requires complex processes such as heat treatment and dissolution with strong acids like sulfuric acid, and there is a challenge in that the efficiency of recycling has not been considered.

[0008] This disclosure is made in view of the above circumstances and aims to provide an all-solid-state secondary battery with excellent recyclability.

[0009] The all-solid-state secondary battery of this disclosure includes a positive electrode containing a lithium-containing cyanide, a negative electrode containing a substance that allows lithium to be inserted into and removed from at a potential lower than that of the positive electrode, and a lithium-containing chloride solid electrolyte.

[0010] According to this disclosure, it is possible to provide an all-solid-state secondary battery with excellent recyclability.

[0011] Figure 1 is a basic schematic diagram of the all-solid-state secondary battery of this embodiment. Figure 2 is a diagram showing an example of a lithium-containing Prussian blue synthesis method (method 1). Figure 3 is a diagram showing an example of a lithium-containing Prussian blue synthesis method (method 2). Figure 4 is a diagram showing an example of a lithium-containing Prussian blue synthesis method (method 3). Figure 5 is a schematic cross-sectional view showing an example of the structure of an all-solid-state secondary battery. Figure 6 is a diagram showing a method for adjusting the positive electrode of the embodiment. Figure 7 is a diagram showing a method for adjusting the negative electrode of the embodiment. Figure 8 is a graph showing the discharge curve and charge curve during the first discharge of Embodiment 1. Figure 9 is a table showing the battery performance of the embodiment and comparative example. Figure 10 is a table showing the solubility evaluation of the embodiment and comparative example.

[0012] The embodiments of this disclosure will be described below with reference to the figures.

[0013] [Configuration of the secondary battery] Figure 1 is a diagram showing the configuration of an all-solid-state secondary battery according to an embodiment of the present invention. The all-solid-state secondary battery of this embodiment is a secondary battery in which a negative electrode 13, a solid electrolyte 12, and a positive electrode 11 are stacked.

[0014] The all-solid-state secondary battery of the present embodiment includes a positive electrode 11 containing a cyanide containing lithium, a negative electrode 13 containing a substance capable of inserting and extracting lithium at a potential lower than that of the positive electrode 11, and a chloride solid electrolyte 12 containing lithium.

[0015] The positive electrode 11 may contain Prussian blue (Li2FeFe(CN)6) containing lithium as the cyanide.

[0016] The substance capable of inserting and extracting lithium in the negative electrode 13 also includes a substance capable of alloying and dealloying lithium. As the substance, a metal material such as In or a carbon-based material can be used for the negative electrode 13. Specifically, the negative electrode 13 may contain metallic indium or a carbon material.

[0017] For the chloride solid electrolyte 12, a water-soluble lithium-containing chloride material having lithium ion conductivity can be used. The chloride solid electrolyte 12 may contain lithium chloride-aluminum (LiAlCl4) or lithium chloride-iron (Li2FeCl4). [[ID=X]] [[ID=Y]]

[0018] The above components of the secondary battery of the present embodiment will be described below.

[0019] (1) Positive electrode The positive electrode 11 of the present embodiment includes at least a positive electrode active material and may include the following solid electrolyte powder, conductive assistant, binder, and current collector.

[0020] (1-1) Positive electrode active material The positive electrode active material in the present embodiment contains a cyanide containing lithium. The cyanide is a complex having cyanide (CN ― )). Examples of the cyanide containing lithium include Li x M1[M2(CN)6] y (M1, M2 are at least one transition metal selected from the group consisting of Mn, Fe, Co, Ni, Cu, Mo, 0 < x ≤ 1, 2 / 3 ≤ y ≤ 1) can be used. From the viewpoint of solubility in water, for example, Prussian blue Li2FeFe(CN)6 containing lithium is suitable as the cyanide containing lithium.

[0021] The synthesis of Prussian blue can be carried out, for example, by the method described in previously published report 1 (Energy Storage Materials 60 (2023) 102803), as shown in Figures 2-4. The preferred addition ratio of Prussian blue is 30-60% (by weight) of the total electrode of the positive electrode 11.

[0022] First, as shown in Figure 2, 10 g of potassium ferricyanide (K3Fe(CN)6) is dissolved in 400 mL of deionized water (S11), and 400 mL of deionized water is added to this solution (S12). The solution from S12 is stirred for a predetermined time (for example, 12 hours), centrifuged, and the substance after centrifugation is washed (S13-S15). In the washing in S15, for example, the substance is washed three times with deionized water and three times with ethanol. The substance after washing is dried overnight to synthesize iron(III) ferricyanide (FeFe(CN)6) (S16).

[0023] Next, as shown in Figure 3, 10 mmol of perylene was added to dimethoxyethane (DME) solvent and stirred in a glove box at room temperature (S21). Then, 10 mmol of metallic lithium was added and stirred for a predetermined time (e.g., 6 hours) to prepare a perylene-lithium / DME solution (S22).

[0024] Next, as shown in Figure 4, the FeFe(CN)6 powder prepared in Figure 2 was added to 10 mL of DME solvent, stirred and dispersed to obtain a solution (S31). The perylene-lithium / DME solution prepared in Figure 3 was then added to this solution, stirred for a predetermined time (e.g., 2 hours), centrifuged, and washed to obtain Li2FeFe(CN)6 powder (S32-S34). The perylene-lithium / DME solution was added so that Li / Fe = 1.0 (molar ratio). In the washing step in S34, the mixture was washed with DME a predetermined number of times (e.g., 3 times) until the supernatant liquid became clear.

[0025] (1-2) Solid electrolyte powder In order to ensure ion conduction paths in the positive electrode, it is necessary to mix the solid electrolyte powder into the positive electrode. The solid electrolyte powder is the powder of the solid electrolyte described later. It is preferable to use a chloride solid electrolyte as the solid electrolyte.

[0026] The solid electrolyte powder needs to be as fine as possible and uniformly dispersed in the positive electrode. Therefore, the solid electrolyte powder and other positive electrode materials are crushed and mixed using a ball mill. The addition ratio of the solid electrolyte powder is preferably 30-50% (by weight) of the entire positive electrode 11.

[0027] (1-3) Conductive additives For conductive additives, carbon can be used, for example. Specifically, carbon blacks such as Ketjenblack and acetylene black, activated carbon, graphites, and carbon fibers can be used. These carbons can be obtained, for example, as commercially available products or by known synthesis. The additive ratio of the conductive additive is preferably 5 to 30% (by weight) of the entire electrode of the positive electrode 11.

[0028] (1-4) Binding agent The positive electrode 11 may contain a binding agent. Specific examples of binding agents include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber, ethylene propylene diene rubber, and natural rubber. The binding agent addition ratio is preferably 5-30% (by weight) of the entire electrode of the positive electrode 11.

[0029] (1-5) Current collector The current collector may be a current collector comprising at least one selected from the group consisting of aluminum, copper, iron, and titanium, or a nonwoven fabric current collector containing carbon.

[0030] (1-6) Method for manufacturing a positive electrode A positive electrode 11 can be manufactured by pressing a mixture obtained by grinding and mixing a positive electrode active material (e.g., Li2FeFe(CN)6 powder), a solid electrolyte powder, a conductive additive powder (e.g., carbon powder), and a binder powder. Alternatively, the positive electrode 11 can also be manufactured by rolling the mixture in a roll press, processing it into a sheet, and pressing it onto a current collector.

[0031] Alternatively, the positive electrode 11 can be manufactured by applying a slurry containing dispersed positive electrode active material to a current collector, or by impregnating the current collector with the slurry, and then drying the coated or impregnated current collector. Here, by applying a cold press or hot press to the electrode (positive electrode 11) after drying, the strength of the electrode can be increased, and a more stable positive electrode 11 can be manufactured.

[0032] (1-7) Determination of a recyclable positive electrode material Considering recyclability, it is preferable to avoid using substances other than water-soluble substances as the positive electrode material. Therefore, by optimizing the electrode composition and / or current collection method, the positive electrode 11 could be constructed using only a positive electrode active material, chloride solid electrolyte powder, and a conductive additive (carbon), as will be explained in the examples described later.

[0033] Here, chloride solid electrolyte powder exhibits superior deformability compared to oxide solid electrolyte powder. Therefore, chloride solid electrolyte powder has the effect of binding the positive electrode active material and conductive additive, eliminating the need for binders like those used in conventional fluoropolymer resins.

[0034] Furthermore, even if a current collector (current collecting material) is used, if the other materials are water-soluble, the active material will dissolve when the electrodes are immersed in water (neutral), making it easy to recover the current collector, which can then be recycled. Similarly, the carbon used as a conductive additive can also be easily recovered by filtration or centrifugation, and the carbon can be recycled as well.

[0035] (2) Negative electrode The negative electrode 13 of this embodiment contains at least a negative electrode active material and may also contain the following solid electrolyte powder, conductive additive, binder, and current collector.

[0036] (2-1) Anode active material The anode active material of this embodiment contains a material capable of inserting and extracting lithium at a potential lower than that of the cathode 11. As said material, for example, a metal indium foil capable of alloying with lithium, a carbon material, etc. can be used. The carbon material is graphite (natural graphite, artificial graphite) used in general lithium secondary batteries, amorphous hard carbon which is one type of carbon black, etc. The addition ratio of the carbon material as the anode active material is preferably 30 to 60% (weight ratio) of the entire electrode of the anode 13.

[0037] (2-2) Solid electrolyte powder When using a powder material such as a carbon material as the anode active material, it is necessary to mix the solid electrolyte powder into the anode in order to ensure an ion conduction path in the anode. The solid electrolyte powder is the powder of the solid electrolyte described later. It is preferable to use a chloride solid electrolyte for the solid electrolyte.

[0038] The solid electrolyte powder needs to be as fine a powder as possible and uniformly dispersed in the anode. Therefore, the solid electrolyte powder and other anode materials are pulverized and mixed using a ball mill. The addition ratio of the solid electrolyte powder is preferably 40 to 70% (weight ratio) of the entire electrode of the anode 13.

[0039] (2-3) Binder The anode 13 may contain a binder. Specifically, examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber, ethylene-propylene-diene rubber, natural rubber, etc. The addition ratio is preferably 5 to 30% (weight ratio) of the entire electrode.

[0040] (2-4) Current collector The anode 13 may be formed of a current collector containing at least one selected from the group consisting of copper and titanium, or a non-woven fabric current collector containing carbon. These current collectors can be obtained, for example, as commercially available products.

[0041] (2-5) Method for manufacturing the anode When using metal indium for the anode active material, the anode 13 can be manufactured by purchasing a commercially available metal indium foil and cutting it into a predetermined shape of a battery jig described later.

[0042] When a carbon material is used as the negative electrode active material, the negative electrode 13 can be manufactured by crushing and mixing the negative electrode active material (e.g., natural graphite powder), solid electrolyte powder, and binder powder, and then pressing the mixture. Alternatively, the negative electrode 13 can also be manufactured by rolling the mixture in a roll press, processing it into a sheet, and then pressing it onto a current collector.

[0043] Alternatively, the negative electrode 13 can be manufactured by applying a slurry containing dispersed positive electrode active material to a current collector, or by impregnating the current collector with the slurry, and then drying the coated or impregnated current collector. Here, by applying cold pressing or hot pressing to the electrode (negative electrode 13) after drying, the strength of the electrode can be increased, and a more stable negative electrode 13 can be manufactured.

[0044] (2-6) Determination of anode material with recyclability Considering recyclability, it is preferable to avoid using substances other than water-soluble substances as anode material. Therefore, by optimizing the electrode composition and / or current collection method, when a carbon material is used as the anode active material, the anode 13 could be constructed using only the anode active material (for example, natural graphite) and chloride solid electrolyte powder, as described in the examples.

[0045] Here, chloride solid electrolyte powder exhibits superior deformability compared to oxide solid electrolyte powder. Therefore, chloride solid electrolyte powder has the effect of binding the negative electrode active material, and by using chloride solid electrolyte powder, the use of binders like those found in conventional fluororesins becomes unnecessary.

[0046] Furthermore, even if a current collector (current collecting material) is used, if the other materials are water-soluble, the active material will dissolve when the electrodes are immersed in water (neutral), making it easy to recover the current collector, and the recovered current collector can be recycled.

[0047] (3) Solid Electrolyte A lithium-containing chloride solid electrolyte is used for the solid electrolyte 12. Specifically, a lithium-ion conductive and water-soluble lithium-containing chloride material can be used. Examples of solid electrolytes 12 include LiAlCl4, Li2FeCl4, Li2CoCl4, Li2CrCl4, Li 10 Mg7Cl24 , Li4Mn3Cl 10 , can be used. From the viewpoint of conductivity and stability, it is desirable to use lithium aluminum chloride (LiAlCl4) or lithium iron chloride (Li2FeCl4).

[0048] (3-1) Method for preparing solid electrolytes Solid electrolyte 12 was synthesized, for example, in the case of LiAlCl4, using a planetary ball mill (PL-7 manufactured by Fritsch). Specifically, commercially available anhydrous LiCl powder and commercially available anhydrous AlCl3 powder were mixed in a molar ratio of 1:1 in a glove box under an argon atmosphere, and the mixture was packed into a dedicated pot together with zirconia balls (10 mm in diameter), and ball milling was performed at 600 rpm for 12 hours. X-ray diffraction measurements of the obtained powder showed a peak pattern that matched that reported previously, confirming that LiAlCl4 had been synthesized. Li2FeCl4 could also be synthesized in the same manner.

[0049] For filling solid electrolyte powder into all-solid-state secondary batteries, the batteries can be manufactured by uniformly spreading a predetermined amount of fixed electrolyte powder on the negative electrode or positive electrode and then pressing it.

[0050] (4) Other battery components In addition to the above components, the all-solid-state secondary battery of this embodiment may include structural components such as a battery case and other elements required for a secondary battery. Conventional known components can be used for these.

[0051] (5) Method for manufacturing an all-solid-state secondary battery As described above, the all-solid-state secondary battery of this embodiment includes at least a positive electrode 11, a negative electrode 13, and a solid electrolyte 12, and as illustrated in Figure 1, the solid electrolyte 12 is arranged between the positive electrode 11 and the negative electrode 13 so as to be in contact with the positive electrode 11 and the negative electrode 13.

[0052] Figure 5 is a schematic cross-sectional view showing an example of the structure of an all-solid-state secondary battery according to this embodiment. The illustrated all-solid-state secondary battery can be manufactured by stacking a negative electrode 13, a solid electrolyte 12, and a positive electrode 11 in order using a dedicated jig. The dedicated jig includes a metal jig 21 for the positive electrode side, a metal jig 22 for the negative electrode side, and a PTFE (polytetrafluoroethylene) jig 23 for fixing the all-solid-state secondary battery from both sides. A positive electrode terminal 24 is installed on the metal jig 21, and a negative electrode terminal 25 is installed on the metal jig 22.

[0053] Furthermore, the all-solid-state secondary battery disclosed herein is not limited to the secondary battery shown in Figure 5, and may be modified as appropriate without altering the purpose and scope of this disclosure.

[0054] (6) Battery Recycling Method The all-solid-state secondary battery of this embodiment can be disassembled and broken down, placed in deionized water or the like, and water-soluble metal resources can be recovered by neutralization and precipitation or filtration and centrifugation. Known methods can be used for the extraction process of these metal resources.

[0055] Furthermore, for insoluble current collectors (current collecting materials), if the other materials are water-soluble, the positive electrode active material and negative electrode active material will dissolve when the electrodes are immersed in water (neutral), making it easy to recover the current collector and recycle it. Similarly, carbon can also be easily recovered and recycled by filtration or centrifugation.

[0056] [Examples 1-4] Examples of the all-solid-state secondary battery according to this embodiment will be described in detail below. In this embodiment, an all-solid-state secondary battery was manufactured using the dedicated jig shown in Figure 5.

[0057] For the positive electrode (positive electrode active material) in Examples 1-4, lithium-containing Prussian blue (Li2FeFe(CN)6) was used as a lithium-containing cyanide. For the solid electrolyte in Examples 1 and 2, lithium-aluminum chloride (LiAlCl4) was used, and for the solid electrolyte in Examples 3 and 4, lithium-iron chloride (Li2FeCl4) was used. For the negative electrode (negative electrode active material) in Examples 1 and 3, metallic indium was used, and for the negative electrode (negative electrode active material) in Examples 2 and 4, natural graphite was used.

[0058] The battery configurations of Examples 1-4 are shown in Figure 9. It should be noted that this disclosure is not limited to those shown in the following examples, and can be modified as appropriate without altering its essence.

[0059] (Preparation of Solid Electrolyte) The solid electrolyte powder was synthesized using a planetary ball mill (PL-7, manufactured by Fritsch). Specifically, commercially available anhydrous LiCl powder and commercially available anhydrous AlCl3 powder were mixed in a molar ratio of 1:1 in a glove box under an argon atmosphere, and the mixture was packed into a dedicated pot along with zirconia balls (10 mm in diameter) and subjected to ball milling at 600 rpm for 12 hours. X-ray diffraction measurements of the obtained powder showed a peak pattern that matched that of the previously reported 2 (ACS Materials Lett. 2020, 2, 8, 880-886), confirming that it was synthesized in a single phase.

[0060] Furthermore, Li2FeCl4 could also be synthesized in the same manner. X-ray diffraction measurements of the obtained powder confirmed that it matched the peak pattern described in previous report 3 (Adv. Energy Sustainability Res. 2020, 1, 2000025), demonstrating that it could be synthesized in a single phase.

[0061] (Preparation of the positive electrode) The positive electrode active material, Li2FeFe(CN)6, was synthesized by known methods shown in Figures 2-4. First, iron(III) ferricyanide (FeFe(CN)6) was synthesized using commercially available potassium ferricyanide (K3Fe(CN)6) as a raw material, as shown in Figure 2. Next, a perylene-lithium / DME solution was prepared using commercially available perylene, dimethoxyethane (DME), and metallic lithium foil as raw materials, as shown in Figure 3.

[0062] Next, using the method shown in Figure 4, the FeFe(CN)6 prepared in Figure 2 was added to a DME solvent, stirred, and dispersed to obtain a solution. The perylene-lithium / DME solution prepared in Figure 3 was then added, stirred, centrifuged, and washed to obtain Li2FeFe(CN)6 powder. The obtained powder's X-ray diffraction pattern matched that shown in a previous report (Energy Storage Materials 60 (2023) 102803), confirming that it was obtained as a single phase.

[0063] The positive electrode was prepared by the method shown in Figure 6. Specifically, the positive electrode active material, Li2FeFe(CN)6 powder, the conductive additive, acetylene black (DenkaBlack, manufactured by Denka), and solid electrolyte powder (Examples 1 and 2: LiAlCl4, Examples 3 and 4: Li2FeCl4) were adjusted so that the final composition was 40:10:50 by weight ratio to obtain the positive electrode mixture.

[0064] Specifically, Li2FeFe(CN)6 powder and acetylene black (AB) were ground and mixed using a ball mill (S41). The ball mill was rotated at 400 rpm for 1 hour. Solid electrolyte powder (LiAlCl4 or Li2FeCl4) was added to this mixture (Li2FeFe(CN)6-AB) and mixed in a mortar (S42). This yielded positive electrode mixtures (Li2FeFe(CN)6-AB-LiAlCl4, Li2FeFe(CN)6-AB-Li2FeCl4).

[0065] (Preparation of the negative electrode) In Examples 1 and 3, the negative electrode was prepared by cutting out a circle with a diameter of 10 mm from a metallic indium foil (made by Nilaco, 100 μm thick) to fit a dedicated jig.

[0066] In Examples 2 and 4, the negative electrode was prepared using the method shown in Figure 7. Specifically, the negative electrode active material, natural graphite (Sigma-Aldrich), and the solid electrolyte powder (Example 2: LiAlCl4, Example 4: Li2FeCl4) were mixed so that the final composition was 50:50 by weight. More precisely, the natural graphite and the solid electrolyte powder (LiAlCl4 or Li2FeCl4) were crushed and mixed using a ball mill (S51) to obtain the negative electrode mixture (natural graphite-LiAlCl4, natural graphite-Li2FeCl4). The ball mill was rotated at 400 rpm for 1 hour.

[0067] (Fabrication of secondary batteries) All-solid-state secondary batteries were fabricated using the special jig shown in Figure 5. First, metallic indium foil (negative electrode metal) or negative electrode mixture was filled into the space in the center of the special jig (a cavity and opening for housing the positive electrode, electrolyte, and negative electrode). In the case of metallic indium foil, a circular foil was placed in the opening. In the case of natural graphite, 40 mg of negative electrode mixture was uniformly filled into the opening and pressed at 200 MPa.

[0068] Next, 100 mg of solid electrolyte powder (LiAlCl4 or Li2FeCl4) was uniformly packed onto the negative electrode and pressed at 500 MPa. Finally, 40 mg of positive electrode compound was uniformly packed onto the solid electrolyte and pressed at 200 MPa. This allowed for the formation of an all-solid-state secondary battery within the dedicated jig shown in Figure 5.

[0069] (Battery Performance Measurement) The all-solid-state secondary batteries prepared according to the above procedure were subjected to battery performance measurements in a constant temperature chamber maintained at 30°C. The battery cycle test was performed using a charge / discharge measurement system (VMP-3, Bio Logic), with a current density of 20 μA / cm² per effective area of ​​the battery. ２ When the negative electrode was metallic indium, the charging termination voltage was set to 3.6V and the discharge termination voltage to 1.4V. When the negative electrode was natural graphite, the charging termination voltage was set to 4.2V and the discharge termination voltage to 2.0V, and the tests were performed under constant current charging and discharging conditions.

[0070] The charge / discharge capacity was expressed as a value per unit weight (mAh / g) of the positive electrode active material (Li2FeFe(CN)6).

[0071] (Battery Performance) Figure 8 shows the discharge curve during the first discharge and the charge curve during the first charge for Example 1. Figure 9 shows the initial average discharge voltage and initial discharge capacity, and the discharge capacity at 10 and 30 cycles for Examples 1 to 4. The average discharge voltage was defined as the battery voltage at the midpoint of the discharge capacity.

[0072] In Example 1, as shown in Figures 8 and 9, the initial average discharge voltage was 2.4V and the initial discharge capacity was 155mAh / g. The discharge capacities after 10 and 30 cycles were 145mAh / g and 139mAh / g, respectively. Although a decrease of approximately 10% in discharge capacity was observed after 30 cycles, the all-solid-state secondary battery in Example 1 was confirmed to function as a secondary battery capable of charge-discharge cycles.

[0073] As shown in Figure 9, the other embodiments 2 to 4 also demonstrated that, although there was some capacity reduction due to the cycle, they functioned as rechargeable batteries capable of charge-discharge cycles.

[0074] [Comparative Examples 1 and 2] Figure 9 shows the battery configurations of Comparative Examples 1 and 2. In these comparative examples, an oxide solid electrolyte was used instead of a chloride solid electrolyte to create an all-solid-state secondary battery.

[0075] Specifically, a commercially available oxide solid electrolyte, the LICGC disk (LICGC: Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2-based solid electrolyte, Ohara SP-01, 180 μm thick), was used as the solid electrolyte.

[0076] For the positive electrode, commercially available positive electrode active material LiCoO2 (manufactured by Sigma-Aldrich) and LICGC powder (PW-01, manufactured by Ohara, with an average particle size of 0.4 μm) were used. Specifically, the positive electrode was prepared using the same method as in Examples 1 to 4, by adjusting the final composition of LiCoO2 powder, a metal oxide, as the positive electrode active material; acetylene black (manufactured by Denka Black), a conductive additive; and LICGC powder, an oxide solid electrolyte, to a weight ratio of 40:10:50, thereby obtaining a positive electrode mixture.

[0077] The negative electrode was made of metallic indium foil or natural graphite powder, as in Examples 1-4. The natural graphite powder was mixed with LICGC powder in the same manner as in Examples 2 and 4 to obtain the negative electrode mixture. Specifically, the negative electrode mixture was obtained by mixing natural graphite (Sigma-Aldrich), which is the negative electrode active material, and LICGC powder, which is an oxide solid electrolyte powder, so that the final composition was 50:50 by weight.

[0078] The fabrication and evaluation methods for the all-solid-state secondary battery in this comparative example were carried out in the same manner as in Examples 1 to 4. However, the charge and discharge termination voltages were set to 3.7V and 2.4V, respectively, in Comparative Example 1, and to 4.3V and 3.0V, respectively, in Comparative Example 2.

[0079] Figure 9 shows the initial average discharge voltage and initial discharge capacity of the all-solid-state secondary battery in this comparative example, as well as the discharge capacity after 10 and 30 charge-discharge cycles. In both Comparative Example 1 and Comparative Example 2, a decrease in discharge capacity of approximately 70% and 65%, respectively, was observed after 30 discharge cycles, indicating lower battery performance stability compared to Examples 1 to 4.

[0080] This indicates that LICGC, a metal oxide, has a lower bonding ability with the active material (positive electrode active material, negative electrode active material) than chloride solid electrolytes, and that repeated charge-discharge cycles cause the active material to expand and contract, reducing its adhesion to the solid electrolyte and thus degrading battery performance.

[0081] [Solubility Evaluation] After performance evaluation of the all-solid-state secondary batteries of Examples 1-4 and Comparative Examples 1 and 2, the batteries were removed from the dedicated jig, placed in 100 ml of deionized water (neutral), and stirred for 1 hour using a magnetic stirrer. The solubility of each component was then evaluated.

[0082] Figure 10 shows the evaluation results for Examples 1-4 and Comparative Examples 1-2. Here, solubility was evaluated and determined by observing the presence or absence of precipitate and by evaluating the ionic species contained in the aqueous solution by ICP emission spectrometry.

[0083] In all of Examples 1-4 and Comparative Examples 1 and 2, it was found that the indium and natural graphite in the negative electrode, and the acetylene black, a conductive additive in the positive electrode, did not dissolve. However, since these substances can be recovered relatively easily by filtration or centrifugation, this is not considered to be a major obstacle to battery recycling.

[0084] In Comparative Examples 1 and 2, the oxide-based cathodes using metal oxides and oxide solid electrolytes, and the oxide solid electrolytes, were insoluble in water and remained unchanged. In contrast, in Examples 1-4, it was confirmed that the cyanide-based cathodes containing cyanide and chloride solid electrolytes, and the chloride solid electrolytes, were completely soluble.

[0085] Therefore, considering the ease of battery recycling, it is clear that the battery configurations of Examples 1-4, which use chloride solid electrolytes, are more advantageous than Comparative Examples 1 and 2, which use oxide solid electrolytes.

[0086] As described above, the all-solid-state secondary battery of this embodiment is a secondary battery that is easy to recycle and has excellent recyclability. Specifically, by using water-soluble materials for the positive electrode active material and solid electrolyte of the all-solid-state secondary battery of this embodiment, a heat treatment process is unnecessary, and resources can be recovered using a milder, near-neutral aqueous solution instead of a strong acid such as sulfuric acid. Although the negative electrode and the conductive additive of the positive electrode do not dissolve in the aqueous solution, these substances can be recovered relatively easily by filtration or centrifugation. As a result, the all-solid-state secondary battery of this embodiment can contribute to reducing environmental impact or costs.

[0087] Conventional lithium secondary battery recycling methods involve complex processes, such as recovering black mass obtained by heat-treating used batteries in an electric furnace as cobalt sulfate by dissolving and extracting it in sulfuric acid, or recovering it as lithium carbonate using a carbonate precipitation reaction.

[0088] Furthermore, the all-solid-state secondary battery of this embodiment exhibits excellent charge-discharge characteristics (cycle characteristics).

[0089] The all-solid-state secondary battery of this embodiment can be effectively used as a power source for various electronic devices such as small devices, sensors, and mobile devices, or as a power source for large devices such as electric vehicles.

[0090] This disclosure is not limited to the embodiments described above, and various modifications and combinations are possible within the technical concept of this disclosure.

[0091] 11: Positive electrode 12: Solid electrolyte 13: Negative electrode 21: Positive electrode side metal jig 22: Negative electrode side metal jig 23: PTFE jig 24: Positive electrode terminal 25: Negative electrode terminal

Claims

1. An all-solid-state secondary battery comprising: a positive electrode containing a lithium-containing cyanide; a negative electrode containing a substance that allows lithium to be inserted and removed at a potential lower than that of the positive electrode; and a lithium-containing chloride solid electrolyte.

2. The all-solid-state secondary battery according to claim 1, wherein the positive electrode contains lithium-containing Prussian blue (Li2FeFe(CN)6).

3. The all-solid-state secondary battery according to claim 1, wherein the chloride solid electrolyte comprises lithium-aluminum chloride (LiAlCl4) or lithium-iron chloride (Li2FeCl4).

4. The all-solid-state secondary battery according to claim 1, wherein the negative electrode comprises metallic indium or a carbon material.

Images