Recovery method and recovery device

Abstract

To improve the recovery of charge / discharge characteristics of a power storage device.SOLUTION: A method for recovering a power storage device having an electrode on which metallic lithium is deposited includes a recovery step of performing a high-temperature preservation process that heats and maintains the power storage device with a storage temperature T within a range of 50°C or more and 70°C or less and a storage time H within a range of 50 hours or more and 700 hours or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This specification discloses a recovery method and a recovery apparatus. [Background technology]

[0002] Conventionally, a battery system has been proposed for automobiles equipped with lithium-ion secondary batteries that maintains the lithium-ion secondary battery at a temperature of 55°C to 65°C using a power supply from an external source while the lithium-ion secondary battery is being charged (see Patent Document 1). This battery system is said to be able to further enhance safety by deactivating metallic lithium. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 4905609 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, the battery system described in Patent Document 1 deactivates metallic lithium, but from the standpoint of restoring battery function, it is still insufficient, and there was a need to further improve the recovery of the energy storage device.

[0005] This disclosure is made to solve these problems, and its main objective is to provide a recovery method and recovery apparatus that can further improve the recovery of the charge and discharge characteristics of energy storage devices. [Means for solving the problem]

[0006] As a result of intensive research to achieve the above object, the inventors of the present invention have found that when a power storage device having an electrode on which metallic lithium is deposited is stored within a specific period of time in a predetermined temperature range, the metallic lithium can be inactivated and the capacity retention rate determined from the discharge capacity can be restored, thus completing the invention of the present disclosure.

[0007] That is, the recovery method of the present disclosure is a method for recovering a power storage device having an electrode on which metallic lithium is deposited, including a recovery step of performing a high-temperature storage treatment of heating and holding the power storage device with the storage temperature T within a range of 50°C or more and 70°C or less and the storage time H within a range of 50 hours or more and 700 hours or less.

[0008] In addition, the recovery device of the present disclosure is a recovery device for a power storage device, including a housing part for housing a power storage device having an electrode on which metallic lithium is deposited, a temperature adjustment part for adjusting the temperature of the housing part, and a control part for controlling the temperature adjustment part to perform a high-temperature storage treatment of heating and holding the power storage device with the storage temperature T within a range of 50°C or more and 70°C or less and the storage time H within a range of 50 hours or more and 700 hours or less. It is equipped with the above.

Effects of the Invention

[0009] In this recovery method and recovery device, the recovery of the charge-discharge characteristics of the power storage device can be further improved. The reason for obtaining such an effect is presumably as follows, for example. In a power storage device such as a lithium-ion secondary battery, metallic lithium may be deposited on the surface of the negative electrode. Most of the metallic lithium deposited on the surface of the negative electrode cannot contribute to the charge-discharge reaction of the battery, so the battery capacity decreases as lithium is deposited on the surface of the negative electrode. In addition, the metallic lithium deposited on the negative electrode is highly active, and the state where metallic lithium is deposited on the negative electrode reduces safety. In the present disclosure, by setting the power storage device having metallic lithium deposited on the surface of the negative electrode within the range of 50°C or higher and 70°C or lower, for example, the metallic lithium can be efficiently deactivated (inactivated), such as by further ionizing the metallic lithium. Further, in the present disclosure, by storing the power storage device within the range of 50 hours or longer and 700 hours or shorter, the discharge capacity can be further recovered, and a decrease due to over-recovery of the discharge capacity can be further suppressed. For this reason, in the present disclosure, it is presumed that the recovery of the charge-discharge characteristics of the power storage device can be further improved.

Brief Description of the Drawings

[0010] [Figure 1] Explanatory drawing showing an outline of the configuration of the recovery system and the power storage device 20. [Figure 2] Discharge curves before and after initial and metallic Li deposition. [Figure 3] Initial capacity, capacity after 20 cycles, and capacity deterioration rate before and after metallic Li deposition. [Figure 4] External appearance photographs of the negative electrode before and after 20 cycles of rapid charge and discharge. [Figure 5] SEM image of the cross section of the negative electrode after 20 cycles of rapid charge and discharge. [Figure 6] Solid 7Li-NMR measurement spectrum of the negative electrode after 20 cycles of rapid charge and discharge. [Figure 7] SEM image of the cross section of the negative electrode stored at 60°C for 1 month after metallic Li deposition. [Figure 8] Solid 7Li-NMR measurement spectrum of the negative electrode stored at 60°C for 1 month after metallic Li deposition. [Figure 9]Cross-sectional SEM image of the negative electrode stored at 60°C for one week after the deposition of metallic Li. [Figure 10] Cross-sectional SEM image of the negative electrode stored at 60°C for three days after the deposition of metallic Li. [Figure 11] Relationship diagram between the storage period at 60°C and the capacity retention rate before and after storage. [Figure 12] It is a relationship diagram between the storage period at 60°C and the capacity recovery rate after storage.

Mode for Carrying Out the Invention

[0011] [Power Storage Device] First, the power storage device to be subjected to the recovery process will be described. The power storage device includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and an ion conduction medium interposed between the positive electrode and the negative electrode and conducting carrier ions. Examples of the carrier ions include Group 1 element ions and Group 2 element ions, and those containing lithium ions may also be used. The power storage device is not particularly limited as long as metallic lithium may be deposited on the electrode, and examples include lithium ion secondary batteries, hybrid capacitors, and pseudo electric double layer capacitors. Hereinafter, for the sake of convenience of explanation, the case where the power storage device is a lithium ion secondary battery having a carbon material as the negative electrode active material and using lithium ions as the carrier ions will be mainly described.

[0012] The positive electrode may be formed by, for example, mixing a positive electrode active material, a conductive material, and a binder, adding an appropriate solvent to form a paste-like positive electrode mixture, applying and drying it on the surface of a current collector, and compressing it as necessary to increase the electrode density. The positive electrode active material may have a redox potential exceeding 3.0 V with respect to the Li standard potential, preferably 3.5 V or more, more preferably 3.8 V or more, and even more preferably 4.0 V or more. As the positive electrode active material, sulfides containing transition metal elements, oxides containing lithium and transition metal elements, etc. can be used. Specifically, transition metal sulfides such as TiS2, TiS3, MoS3, FeS2, Li (1-x) MnO2 (0 < x < 1, etc., the same hereinafter), Li (1-x)Lithium manganese composite oxides such as Mn2O4, Li (1-x) Lithium cobalt composite oxides such as LiCoO2, Li (1-x) Lithium nickel composite oxides such as LiNiO2, Li (1-x) Ni a Mn b O2 (a + b = 1) or Li (1-x) Ni a Mn b Lithium nickel manganese composite oxides such as LiNiMnO4 (a + b = 2), Li (1-x) Ni a Co b Mn c Lithium nickel cobalt manganese composite oxides such as LiNiCoMnO2 (a + b + c = 1), lithium vanadium composite oxides such as LiV2O3, transition metal oxides such as V2O5, etc. can be used. Also, Li (1-x) Olivine-type lithium manganese phosphate compounds such as LiMnPO4, Li (1-x) Olivine-type lithium cobalt phosphate compounds such as LiCoPO4, Li (1-x) Olivine-type lithium nickel phosphate compounds such as LiNiPO4, etc. can be used. Also, Li (1-x) Inverse spinel-type lithium manganese vanadate compounds such as LiMnVO4, Li (1-x) Inverse spinel-type lithium cobalt vanadate compounds such as LiCoVO4, Li (1-x) Inverse spinel-type lithium nickel vanadate compounds such as LiNiVO4, etc. can be used. The positive electrode active material is preferably an oxide containing one or more of nickel, manganese, and cobalt. For example, LiCoO2, LiNiO2, LiMnO2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc. are preferred.

[0013] As the conductive material for the positive electrode, for example, graphite such as natural graphite (scaly graphite, flake graphite) or artificial graphite, acetylene black, carbon black, Ketjenblack, carbon whiskers, needle coke, carbon fiber, and metals (copper, nickel, aluminum, silver, gold, etc.) can be used. As the binder, for example, fluororesins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluororubber, or thermoplastic resins such as polypropylene and polyethylene, ethylene propylene diene rubber (EPDM), sulfonated EPDM rubber, and natural butyl rubber (NBR) can be used. In addition, aqueous binders such as cellulose-based carboxymethylcellulose (CMC) and aqueous dispersions of styrene-butadiene rubber (SBR) can also be used. As solvents, for example, organic solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran can be used. Alternatively, a dispersant and a thickener may be added to water, and the active material may be slurryed with latex such as SBR. As thickeners, for example, polysaccharides such as carboxymethylcellulose and methylcellulose can be used alone or as a mixture of two or more. As coating methods, for example, roller coating such as applicator roll coating, screen coating, doctor blade method, spin coating, and bar coating can be used, and any thickness and shape can be achieved using any of these. As current collectors, aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymers, conductive glass, etc., can be used, as well as aluminum or copper whose surfaces have been treated with carbon, nickel, titanium, or silver for the purpose of improving adhesion, conductivity, and oxidation resistance. For these, it is also possible to oxidize the surface. Current collectors can take various shapes, including foil, film, sheet, net, punched or expanded, lath, porous, foam, and fiber-forming materials. For example, current collectors with a thickness of 1 to 500 μm are commonly used.

[0014] The negative electrode may be formed, for example, by mixing a negative electrode active material, a conductive material, and a binder, adding a suitable solvent to form a paste-like negative electrode composite, applying and drying it on the surface of a current collector, and compressing it as needed to increase the electrode density, or by tightly bonding the negative electrode active material and the current collector. The negative electrode active material preferably has an oxidation-reduction potential of 3.0V or less, more preferably 2.0V or less, and even more preferably 1.0V or less, based on the Li reference potential. Examples of negative electrode active materials include inorganic compounds such as lithium, lithium alloys, and tin compounds, carbonaceous materials capable of intercalating and releasing lithium ions, composite oxides containing multiple elements, and conductive polymers. Examples of carbonaceous materials include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. An example of a composite oxide is Li4Ti5O 12 Examples include lithium titanium composite oxides such as α and lithium vanadium composite oxides such as LiV2O3. Among these, carbonaceous materials such as graphites are preferred as the negative electrode active material. Furthermore, the conductive material, binder, and solvent used in the negative electrode can be those exemplified for the positive electrode. For the negative electrode current collector, in addition to copper, nickel, stainless steel, titanium, aluminum, calcined carbon, conductive polymers, conductive glass, and Al-Cd alloys, materials can also be used in which the surface of, for example, copper has been treated with carbon, nickel, titanium, or silver for the purpose of improving adhesion, conductivity, and reduction resistance. These can also be oxidized. The shape of the current collector can be the same as that of the positive electrode.

[0015] As the ion conducting medium, non-aqueous electrolytes containing supporting salts or non-aqueous gel electrolytes can be used. Examples of solvents for non-aqueous electrolytes include carbonate compounds, ester compounds, ether compounds, nitrile compounds, amide compounds, furan compounds, sulfolane compounds, and dioxolane compounds, which can be used individually or in mixtures. Specifically, examples of carbonate compounds include cyclic carbonate compounds such as ethylene carbonate (EC), propylene carbonate, vinylene carbonate, butylene carbonate, and chloroethylene carbonate, as well as linear carbonate compounds such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethyl-n-butyl carbonate, methyl-t-butyl carbonate, di-i-propyl carbonate, and t-butyl-i-propyl carbonate. Furthermore, examples of ester compounds include cyclic ester compounds such as γ-butyllactone and γ-valerolactone, and linear ester compounds such as methyl formate, methyl acetate, ethyl acetate, and methyl butyrate. Examples of ether compounds include dimethoxyethane, ethoxymethoxyethane, and diethoxyethane; examples of nitrile compounds include acetonitrile and benzonitrile; examples of amide compounds include dimethylacetamide (DMA) and dimethylformamide; examples of furan compounds include tetrahydrofuran and methyltetrahydrofuran; examples of sulfolane compounds include sulfolane and tetramethylsulfolane; and examples of oxolane compounds include 1,3-dioxolane and methyldioxolane. These can be used individually or in combination. Of these, a mixture of cyclic carbonate compounds and linear carbonate compounds, such as DMC-EC, DEC-EC, and DMC-EMC-EC, is preferred as the solvent for the non-aqueous electrolyte. Examples of supporting salts include inorganic salts such as LiPF6, LiBF4, LiAsF6, and LiClO4, and organic salts such as LiCF3SO3, LiN(CF3SO2)2, and LiC(CF3SO2)3, which can be used individually or in combination.The supporting salt is preferably concentrated in the electrolyte at a concentration of 0.1 mol / L or more and 5 mol / L or less, and more preferably at a concentration of 0.5 mol / L or more and 2 mol / L or less. In addition, instead of a liquid ion conducting medium, an ion-conducting polymer, an inorganic solid electrolyte, a mixed material of an organic polymer electrolyte and an inorganic solid electrolyte, or an inorganic solid powder bound by an organic binder can be used as the ion conducting medium.

[0016] This energy storage device may include a separator between the positive and negative electrodes. The separator is not particularly limited as long as its composition can withstand the operating range of the energy storage device, but examples include polymer nonwoven fabrics such as polypropylene nonwoven fabrics, and thin microporous membranes of olefin resins such as polyethylene. These may be used individually or in combination.

[0017] The shape of this energy storage device is not particularly limited, but examples include coin-shaped, button-shaped, sheet-shaped, laminated, cylindrical, flat, and rectangular shapes. It may also be a large one used in electric vehicles, etc. Figure 1 is an explanatory diagram showing an example of the recovery system 10 and energy storage device 20 of this embodiment. The energy storage device 20 comprises a positive electrode sheet 23 in which a positive electrode composite material 22 is formed on a current collector 21, a negative electrode sheet 26 in which a negative electrode composite material 25 is formed on the surface of a current collector 24, a separator 28 provided between the positive electrode sheet 23 and the negative electrode sheet 26, and a non-aqueous electrolyte 29 that fills the space between the positive electrode sheet 23 and the negative electrode sheet 26. In this energy storage device 20, the separator 28 is sandwiched between the positive electrode sheet 23 and the negative electrode sheet 26, these are wound up and inserted into a cylindrical case 32, and a positive electrode terminal 34 connected to the positive electrode sheet 23 and a negative electrode terminal 36 connected to the negative electrode sheet 26 are arranged to form the device.

[0018] (Recovery method) The recovery method for a power storage device according to this disclosure is a method for recovering a power storage device having electrodes on which metallic lithium is deposited. This recovery method includes a recovery step. In the recovery step, a high-temperature storage treatment is performed in which the power storage device is heated and held at a storage temperature T within the range of 50°C to 70°C and a storage time H within the range of 50 hours to 700 hours. In the recovery step, it is preferable to perform the high-temperature storage treatment on a power storage device in an open-circuit state. In particular, it is preferable to perform the high-temperature storage treatment on a power storage device with its terminals disconnected from the circuit.

[0019] In the recovery process, it is preferable to perform an adjustment process to adjust the remaining state of charge (SOC) of the energy storage device to a range of 30% to 70% before performing the high-temperature storage treatment. Adjusting the remaining SOC to this range makes it easier to remove, for example, metallic lithium deposited on the electrodes. The remaining SOC is preferably 40% or more, more preferably 45% or more. It is also preferably 60% or less, more preferably 55% or less. Setting the remaining SOC to an intermediate range makes it possible to obtain the high-temperature storage effect more reliably. Note that this adjustment process may be omitted in the recovery process.

[0020] In the recovery process, the storage temperature T is within the range of 50°C to 70°C, but preferably 55°C or higher, and preferably 65°C or lower. A storage temperature T of 50°C or higher allows for a more reliable recovery effect, while a temperature of 70°C or lower is preferable because it can more effectively suppress, for example, the decomposition of the electrolyte. In the recovery process, the storage time H is within the range of 50 hours to 700 hours, but preferably 70 hours or higher, more preferably 100 hours or higher, and even more preferably 150 hours or higher. Furthermore, a storage time H of 600 hours or lower is more preferable, more preferably 500 hours or higher, even more preferably 400 hours or lower, and may also be 360 ​​hours or lower. A storage time H of 50 hours or higher makes it easier to obtain a recovery effect, while a storage time of 700 hours or lower is preferable because it reduces the likelihood of adverse effects after metallic lithium decomposition, such as an increase in Li in the coating.

[0021] (Recovery device) The recovery device of this disclosure will be described below with reference to the drawings. The recovery device of this disclosure may be a device that performs the recovery method described above. As shown in Figure 1, the recovery device 10 comprises a control device 11 and a processing unit 16. The processing unit 16 comprises a storage unit 17, a temperature adjustment unit 18 and a remaining capacity adjustment unit 19.

[0022] The control device 11 is configured as a computer that controls the entire device and comprises a control unit 12, a storage unit 13, an input device 14, and a display unit 15. The control unit 12 is configured as a microprocessor centered on a CPU. The control device 11 controls the temperature adjustment unit 18 to perform a high-temperature storage process in which the energy storage device 20 having electrodes with deposited metallic lithium is heated and held, with the storage temperature T set to a range of 50°C to 70°C and the storage time H set to a range of 50 hours to 700 hours. The control unit 12 shall perform the high-temperature storage process by adopting any of the conditions described in the recovery method described above. The storage unit 13 is a device that stores various data such as processing programs, such as an HDD. The input device 14 includes a keyboard and mouse, etc., for the operator to input various commands. The display unit 15 is a liquid crystal screen that displays various information.

[0023] The housing section 17 is a housing having a housing space for housing energy storage devices 20 having electrodes with metallic lithium deposited on them. One or more energy storage devices 20 are housed in the housing section 17. The temperature control section 18 adjusts the temperature of the internal space of the housing section 17 and includes, for example, a heating section and, if necessary, a cooling section. The processing section 16 may be a constant temperature bath. The remaining capacity adjustment section 19 adjusts the remaining capacity of the energy storage devices 20 housed in the housing section 17 and may be a charge / discharge device. The remaining capacity adjustment section 19 has a connection cord (not shown), and the operator may adjust the remaining capacity (SOC) of the energy storage device 20 by connecting this connection cord to the terminals of the energy storage device 20. Note that the recovery device 10 may not have a remaining capacity adjustment section 19, and the remaining capacity (SOC) of the energy storage device 20 may be adjusted at another processing facility, or this adjustment of the remaining capacity (SOC) may be omitted.

[0024] The recovery method and recovery device described above can further improve the recovery of the charge and discharge characteristics of energy storage devices. The reason for this effect is presumed to be, for example, as follows: In energy storage devices such as lithium-ion secondary batteries, metallic lithium may be deposited on the negative electrode surface. Much of the metallic lithium deposited on the negative electrode surface cannot contribute to the battery's charge and discharge reaction, so the battery capacity decreases as lithium is deposited on the negative electrode surface. In addition, metallic lithium deposited on the negative electrode is highly reactive, and the state in which metallic lithium is deposited on the negative electrode reduces safety. In the recovery method and recovery device of this disclosure, by keeping the energy storage device with metallic lithium deposited on the negative electrode surface in a temperature range of 50°C to 70°C, the metallic lithium can be efficiently deactivated, for example, by further ionizing it. By deactivating the metallic lithium deposited on the electrodes of the energy storage device, the safety of the battery can be improved. Furthermore, if metallic lithium can be ionized, it becomes possible to recover the battery capacity. Furthermore, this recovery method and device allows for greater recovery of discharge capacity and suppression of the decrease due to over-recovery of discharge capacity by storing the energy storage device for a period of 50 to 700 hours. Therefore, it is presumed that this recovery method and device can further improve the recovery of the charge and discharge characteristics of the energy storage device.

[0025] It goes without saying that this disclosure is not limited in any way to the embodiments described above, and can be implemented in various forms as long as they fall within the technical scope of this disclosure.

[0026] This disclosure may be any of the following [1] to [6]. [1] A method for restoring an energy storage device having electrodes on which metallic lithium is deposited, A recovery method comprising a recovery step of performing a high-temperature storage treatment in which the energy storage device is heated and held at a storage temperature T within the range of 50°C to 70°C and a storage time H within the range of 50 hours to 700 hours. [2] The recovery method according to [1], wherein in the recovery step, the high-temperature storage treatment is performed for a storage time H of 70 hours or more and 360 hours or less. [3] The recovery method according to [1] or [2], wherein the recovery step involves performing an adjustment process to adjust the remaining capacity (SOC) of the energy storage device to a range of 30% or more and 70% or less before the high-temperature storage treatment. [4] The recovery method according to any one of [1] to [3], wherein the recovery step is performed with the storage temperature T of the energy storage device within the range of 55°C to 65°C. [5] The recovery method according to any one of [1] to [4], wherein in the recovery step, the energy storage device is subjected to the high-temperature storage treatment in an open-circuit state after being removed from the circuit. [6] A recovery device for an energy storage device, A housing section for housing an energy storage device having electrodes with metallic lithium deposited on them, A temperature adjustment unit for adjusting the temperature of the housing section, A control unit controls the temperature adjustment unit to perform a high-temperature storage process that heats and maintains the energy storage device within a storage temperature T range of 50°C to 70°C and a storage time H range of 50 hours to 700 hours. A recovery device. [Examples]

[0027] The following describes experimental examples that specifically examine the recovery method and recovery apparatus for the energy storage device of this disclosure. Experimental examples 2-4 and 7-9 correspond to embodiments of this disclosure, experimental examples 1 and 5 correspond to comparative examples, and experimental examples 6 and 10-12 correspond to reference examples.

[0028] (Battery making) Spheroidal natural graphite particles (average particle size 10 μm) were used as the negative electrode active material, and a mixture of styrene-butadiene rubber (SBR) and carboxymethylcellulose (CMC) was used as the aqueous binder. Ultrapure water was used as the solvent. The spheroidal natural graphite particles, SBR, and CMC were weighed in a mass ratio of 98:1:1. The spheroidal natural graphite particles and CMC were mixed and stirred, then ultrapure water and SBR were added and mixed and stirred. This mixture was then applied to a 10 μm thick negative electrode current collector (copper foil) with a basis weight of 7.8 mg / cm². 2 The mixture was applied in this manner. Then, it was dried in a vacuum at 120°C for 6 hours, and rolled using a roll press to create a composite material density of 1.3 g / cm³ on the negative electrode current collector. 3 A negative electrode sheet was fabricated with a negative electrode composite layer formed thereon. Next, the positive electrode active material LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were weighed in a mass ratio of 92:5:3. These materials were dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a paste-like composition for forming a positive electrode composite layer. This was then applied to a 15 μm thick positive electrode current collector (aluminum foil) with a composite weight of 14.5 mg / cm². 2 The mixture was applied in this manner. Then, it was dried in a vacuum at 120°C for 6 hours, and rolled using a roll press to achieve a composite material density of 2.8 g / cm³ on the positive electrode current collector. 3 A positive electrode sheet was fabricated with a positive electrode composite layer. The composite layer of the positive electrode sheet was partially peeled off, and an aluminum positive electrode terminal was attached by ultrasonic welding. Similarly, the composite layer of the negative electrode sheet was partially peeled off, and a nickel negative electrode terminal was attached by ultrasonic welding. An aluminum laminate cell was fabricated by connecting the positive electrode sheet and the negative electrode sheet, each with its respective terminals attached, via a single-layer polyethylene separator. As the non-aqueous electrolyte, a solution of 1M LiPF6 dissolved in a non-aqueous solvent with a volume ratio of EC, DMC, and EMC of 3:4:3 was used. The following evaluations were performed using the 20mAh class aluminum laminate cell fabricated in this manner.

[0029] (Deposition of metallic lithium and evaluation of batteries) Laminate cells were subjected to charging and discharging in an environment of 20°C. First, to evaluate the battery capacity, the cells were charged with a constant current (2mA) to 4.1V, followed by constant voltage charging at 4.1V for 3 hours. Then, they were discharged with a constant current (2mA) to 3V, followed by constant voltage discharge at 3V for 1 hour. Two cycles of the above constant current charge and discharge were performed, and the discharge capacity of the second cycle was taken as the initial capacity. The batteries whose capacity had been confirmed underwent a rapid charge and discharge cycle to deposit metallic lithium on the negative electrode surface. Constant current charging was performed at 4.5C to 4.1V, followed by constant voltage charging at 4.1V for 10 minutes. Then, constant current discharge was performed at 0.5C to 3V, followed by constant voltage discharge at 3V for 3 hours. After 20 cycles of the above rapid charge and discharge, the capacity after metallic lithium deposition was confirmed under the same conditions as the initial capacity confirmation.

[0030] (Deactivation and capacity recovery treatment of deposited lithium metal and battery evaluation) After depositing metallic lithium in batteries through 20 rapid charge-discharge cycles, the batteries were adjusted to a State of Charge (SOC) of 50% (battery voltage 3.7V). The batteries were then kept in a 60°C constant temperature bath to deactivate the deposited metallic lithium and restore battery capacity. The capacity after the cycles was then confirmed under the same conditions as the initial capacity check.

[0031] (Preparation of analytical samples) Batteries that had undergone metallic lithium deposition, deactivation, and capacity recovery treatment were charged to 4.1V with a constant current (2mA), followed by constant voltage charging at 4.1V for 3 hours to reach a fully charged state (SOC 100%) and used as analytical samples. Subsequently, the electrodes were disassembled, the negative electrode was removed, washed with dimethyl carbonate (DMC) in a glove box under an inert Ar gas atmosphere, and dried.

[0032] (Observation of precipitation morphology) To investigate the deposition state of metallic Li on the negative electrode, SEM observation was performed. Sampling was carried out in a glove box under an inert Ar gas atmosphere, and the sample was introduced into the SEM chamber without exposure to the atmosphere using an air-free transfer method. SEM observation was performed using a Hitachi High-Tech S-4300.

[0033] (Determination of the total amount of Li in the negative electrode) The total amount of Li in the negative electrode was quantified using inductively coupled plasma atomic emission spectrometry (ICP-OES). The negative electrode, taken from a cycled battery, was immersed in a small amount of water to remove the negative electrode mixture from the current collector. After removing the current collector, 10 mL of 6 M hydrochloric acid was added to heat and dissolve the Li in the negative electrode mixture. The solution was filtered and then diluted to a certain volume, and the amount of Li was measured using ICP-OES. The results are shown converted to the amount of Li per electrode.

[0034] (Analysis of the compound state of Li in the negative electrode) The compound state of Li in the negative electrode was analyzed by solid-state 7Li nuclear magnetic resonance (NMR) spectroscopy. The sample was prepared in an Ar gas atmosphere glove box. The negative electrode (7mm x 7mm) was detached from the current collector, and its entire volume was packed into an NMR zirconia rotor. Transfer of the sample tube to the apparatus and measurement were performed under an inert atmosphere. 7 Li-NMR measurements were performed using a Bruker AVANCE400 with the single-pulse method. 7 In Li-NMR, the chemical shift differs depending on the compound state of Li. 7 The FFT spectra obtained from Li-MNR measurements were used to represent deposited metallic Li, charged Li intercalated between graphite layers (charged Li), and coated Li. The amount of Li was organized into the three states of metallic Li, charged Li, and coated Li, and the total amount of Li in the negative electrode was estimated by determining it using ICP-OES.

[0035] [Experimental Example 1] (Deposition of metallic lithium) (Capacity retention rate and morphology of deposited metallic lithium) Figure 2 shows the discharge curves after 20 cycles of rapid charge-discharge (metallic lithium deposition) in the initial and rapid charge-discharge cycles. Figure 3 shows the initial capacity, capacity after 20 cycles, and capacity degradation rate. The fabricated test battery had an initial capacity of 19.8 mAh, which decreased to 15.1 mAh (= capacity retention rate of 76%) after 20 rapid charge-discharge cycles, and the capacity degradation rate was 24%. Figure 4 shows photographs of the negative electrode before and after 20 rapid charge-discharge cycles, with Figure 4A being before the cycles and Figure 4B being after 20 cycles. The negative electrode before the cycles was black, whereas after 20 rapid charge-discharge cycles, although some yellow Li portions in the negative electrode were observed, it was confirmed that gray metallic Li had deposited almost entirely over the negative electrode. Figure 5 is an SEM image of the cross-section of the negative electrode after 20 rapid charge-discharge cycles. As shown in Figure 5, solidified metallic Li precipitated and densely accumulated on the surface of the negative electrode, with a thickness of 10-15 μm.

[0036] (Analysis of the state of lithium in the negative electrode) The total amount of Li in the negative electrode after a rapid charge-discharge cycle was quantified by ICP-OES and was 0.54 mg / cm³. 2 Figure 6 shows the negative electrode after 20 rapid charge-discharge cycles, solid 7 This spectrum was obtained by Li-NMR measurement. Solid state at graphite anode. 7 From the chemical shifts of the Li-NMR spectra [1,2], the three states of metallic Li, charged Li, and coated Li were assigned, and their quantitative ratios are shown in Table 1 from the waveform separation of each spectrum. Furthermore, the results of the analysis of the total amount of Li by ICP-OES and the solid state are also shown. 7 Based on the results of Li-NMR and ICP-OES, the amount of Li in each state per negative electrode was estimated and is shown in Table 1. All charged Li is Li → Li + +e -Assuming that it is involved in the reaction, the relationship between the amount of Li that can participate in charging and discharging (charged Li) and the battery capacity (mAh) in the charge-discharge cycle determined from the analysis was approximately 1:1. Table 1 shows the results of converting the amount of electricity in each state of metallic Li, charged Li, and coated Li in the negative electrode after rapid charging and discharging. The amount of electricity of charged Li was estimated to be 15.1 mAh, which was the same value as the discharge capacity obtained from electrochemical measurements. In addition, the amounts of electricity of deposited metallic Li and coated Li were 3.1 mAh and 2.65 mAh, respectively.

[0037] [Table 1]

[0038] [Experimental Example 2] (Storage treatment at 60°C for 1 month) (Capacity retention rate and morphology of deposited metallic lithium) Test batteries, in which metallic lithium was deposited through 20 rapid charge-discharge cycles, were adjusted to a State of Charge (SOC) of 50% (battery voltage 3.7V). Then, a high-temperature storage treatment was performed, in which the batteries were kept in a 60°C constant temperature bath for one month in an open-circuit state to deactivate the deposited metallic lithium and restore the battery's capacity. Figure 7 shows a cross-sectional SEM image of the negative electrode after metallic lithium deposition and storage at 60°C for one month. It was found that the metallic lithium formed after rapid charge-discharge disappeared after storage at 60°C for one month. While the initial capacity was 20.0 mAh, the capacity after metallic lithium deposition following 20 rapid charge-discharge cycles was 14.5 mAh, with a capacity retention rate of 73%. However, after storage at 60°C for one month, the capacity became 14.9 mAh, with a capacity retention rate of 75%. The capacity recovery rate R(%) = Rk / Rs × 100, obtained by dividing the capacity retention rate Rk after the storage test by the capacity retention rate Rs before the storage test, was 103% in Experimental Example 2. Figure 8 shows the solid negative electrode after metallic Li deposition and storage at 60°C for one month. 7These are Li-NMR measurement spectra. Table 2 shows the results of determining the quantitative ratios from the waveform separation of each spectrum. Table 2 also shows the results of the total Li content analysis by ICP-OES, and the estimated Li content per negative electrode for each state based on the solid-state 7Li-NMR and ICP-OES results. As shown in Figure 8, metallic lithium was not detected by NMR, and after storage at 60°C for one month, the electric charge of charged Li and coated Li became 15.2 mAh and 5.3 mAh, respectively, indicating an increase in coated lithium.

[0039] [Table 2]

[0040] [Experimental Example 3] (Storage treatment at 60°C for 1 week) (Capacity retention rate and morphology of deposited metallic lithium) Experimental Example 3 was conducted in the same manner as Experimental Example 2, except that the test battery was kept in a constant temperature bath at 60°C for one week in an open-circuit state during the high-temperature storage treatment. Figure 9 is an SEM image of the cross-section of the negative electrode after metallic lithium deposition and storage at 60°C for one week. It was found that the metallic lithium formed after rapid charging and discharging disappeared when stored at 60°C for one week. In Experimental Example 3, the capacity retention rate after metallic lithium deposition was 76%, the capacity retention rate after high-temperature storage was 84%, and the capacity recovery rate was 111%.

[0041] [Experimental Example 4] (Storage treatment at 60°C for 3 days) (Capacity retention rate and morphology of deposited metallic lithium) Experimental Example 4 was conducted in the same manner as Experimental Example 2, except that the test battery was kept in a constant temperature bath at 60°C for 3 days in an open-circuit state during the high-temperature storage treatment. Figure 10 shows a cross-sectional SEM image of the negative electrode after metallic lithium deposition and storage at 60°C for 3 days. It was found that the metallic lithium formed after rapid charging and discharging remained, although the amount of metallic lithium decreased, after storage at 60°C for 3 days. In Experimental Example 4, the capacity retention rate after metallic lithium deposition was 65%, the capacity retention rate after high-temperature storage was 83%, and the capacity recovery rate was 128%.

[0042] [Experimental Example 5] (Deposition of metallic lithium) (Capacity retention rate and morphology of deposited metallic lithium) Experimental Example 5 involved performing 20 rapid charge-discharge cycles (metallic lithium deposition) under the same conditions as Experimental Example 1, and showing a capacity retention rate of 68% after 20 rapid charge-discharge cycles.

[0043] [Experimental Example 6] (Storage treatment at 60°C for 1 day) Experimental Example 6 was conducted in the same manner as Experimental Example 2, except that the test battery was kept in a constant temperature bath at 60°C for one day in an open-circuit state during high-temperature storage treatment. The capacity retention rate after 20 rapid charge-discharge cycles was 61%, while the capacity retention rate after storage at 60°C for one day was 88%, and the capacity recovery rate after storage at 60°C was 145%.

[0044] [Experimental Example 7] (Storage treatment at 60°C for 1 week) Experimental Example 7 was conducted in the same manner as Experimental Example 2, except that the test battery was kept in a constant temperature bath at 60°C for one week in an open-circuit state during high-temperature storage treatment. The capacity retention rate after 20 rapid charge-discharge cycles was 68%, while the capacity retention rate after storage at 60°C for one week was 78%, and the capacity recovery rate after storage at 60°C was 115%.

[0045] [Experimental Example 8] (Storage treatment at 60°C for 2 weeks) Experimental Example 8 was conducted in the same manner as Experimental Example 2, except that the test battery was kept in a constant temperature bath at 60°C for two weeks in an open-circuit state during high-temperature storage treatment. The capacity retention rate after 20 rapid charge-discharge cycles was 79%, while the capacity retention rate after storage at 60°C for one week was 81%, and the capacity recovery rate after storage at 60°C was 103%.

[0046] [Experimental Example 9] (Storage treatment at 60°C for 2 weeks) Experimental Example 9 was conducted in the same manner as Experimental Example 2, except that the test battery was kept in a constant temperature bath at 60°C for two weeks in an open-circuit state during high-temperature storage treatment. The capacity retention rate after 20 rapid charge-discharge cycles was 73%, while the capacity retention rate after storage at 60°C for one week was 80%, and the capacity recovery rate after storage at 60°C was 110%.

[0047] [Experimental Example 10] (Storage treatment at 60°C for 1 month) In the high-temperature storage treatment, test batteries that had deposited metallic lithium through 20 rapid charge-discharge cycles were adjusted to a State of Charge (SOC) of 50% (battery voltage 3.7V). The test batteries were then kept in a 60°C constant temperature bath for one month in an open-circuit state to deactivate the deposited metallic lithium and restore battery capacity. While the capacity retention rate after 20 rapid charge-discharge cycles was 79%, the capacity retention rate after 1 month of storage at 60°C was 76%, and the capacity recovery rate after 60°C storage was 96%.

[0048] [Experimental Example 11] (Storage treatment at 60°C for 2 months) In the high-temperature storage treatment, test batteries that had deposited metallic lithium through 20 rapid charge-discharge cycles were adjusted to a State of Charge (SOC) of 50% (battery voltage 3.7V). The open-circuit test batteries were then kept in a 60°C constant temperature bath for two months to deactivate the deposited metallic lithium and restore battery capacity. While the capacity retention rate after 20 rapid charge-discharge cycles was 77%, the capacity retention rate after 2 months of storage at 60°C was 73%, and the capacity recovery rate after 60°C storage was 95%.

[0049] [Experimental Example 12] (Storage treatment at 60°C for 2 months) In the high-temperature storage treatment, test batteries that had deposited metallic lithium through 20 rapid charge-discharge cycles were adjusted to a State of Charge (SOC) of 50% (battery voltage 3.7V). The test batteries were then kept in a 60°C constant temperature bath for two months in an open-circuit state to deactivate the deposited metallic lithium and restore battery capacity. While the capacity retention rate after 20 rapid charge-discharge cycles was 80%, the capacity retention rate after 2 months of storage at 60°C was 73%, and the capacity recovery rate after 60°C storage was 92%.

[0050] Figure 11 shows the relationship between the storage period at 60°C and the capacity retention rate before and after storage. Figure 12 shows the relationship between the storage period at 60°C and the capacity recovery rate after storage. The measurement results for experimental examples 1 to 12 are summarized in Table 3. As shown in Figure 11, when stored at 60°C for more than one day, the discharge capacity increased rapidly and a significant increase in the capacity retention rate was observed. On the other hand, when the storage period was 400 hours or more, the increase in the capacity retention rate changed to a decrease, and it was found that when the storage period was even longer, more than 600 hours, the capacity retention rate tended to decrease due to the high-temperature storage treatment. Also, as shown in Figure 12, when stored at 60°C for more than one day, the capacity recovery rate showed a high value of 145%, but it was found to gradually decrease thereafter with increasing storage period. Furthermore, it was found that when the storage period at 60°C was 2 months, it showed a value below the capacity retention rate at which metallic lithium deposition occurred due to rapid charge and discharge. On the other hand, as shown in Table 3, the metallic lithium deposited on the electrodes formed after rapid charging and discharging was found to decrease further with high-temperature storage treatment at 60°C and disappear completely after one week of storage.

[0051] From the results of the above experimental examples 1 to 12, it was inferred that the high-temperature storage treatment is preferably performed at a storage temperature T within the range of 50°C to 70°C, more preferably within the range of 55°C to 65°C. Furthermore, it was inferred that the high-temperature storage treatment is preferably performed for a storage time H within the range of 50 hours to 700 hours, more preferably within the range of 70 hours to 500 hours, and even more preferably within the range of 360 hours or less. In addition, it was inferred that it is preferable to adjust the remaining capacity (SOC) of the energy storage device before the high-temperature storage treatment, and that it is preferable to adjust it to a range of 30% to 70%, more preferably within the range of 40% to 60%, and even more preferably within the range of 45% to 55%. Furthermore, since charging and discharging are possible when the terminals of the energy storage device are connected to the circuit, it was inferred that it is preferable to perform the high-temperature storage treatment in an open circuit state, especially when the terminals are disconnected from the circuit.

[0052] [Table 3]

[0053] It goes without saying that this disclosure is not limited in any way to the embodiments described above, and can be implemented in various forms as long as they fall within the technical scope of this disclosure. [Industrial applicability]

[0054] This invention is applicable to the field of the battery industry. [Explanation of Symbols]

[0055] 10 Recovery device, 11 Control device, 12 Control unit, 13 Memory unit, 14 Input device, 15 Display unit, 16 Processing unit, 17 Housing unit, 18 Temperature control unit, 19 Remaining capacity adjustment unit, 20 Energy storage device, 21 Current collector, 22 Positive electrode composite layer, 23 Positive electrode sheet, 24 Current collector, 25 Negative electrode composite layer, 26 Negative electrode sheet, 28 Separator, 29 Non-aqueous electrolyte, 32 Cylindrical case, 34 Positive electrode terminal, 36 Negative electrode terminal.

Claims

1. A method for restoring an energy storage device having electrodes on which metallic lithium is deposited, A recovery method comprising: performing an adjustment process to adjust the remaining capacity (SOC) of the energy storage device to a range of 40% to 70%; and then performing a high-temperature storage process to heat and hold the energy storage device at a storage temperature T of 60°C to 70°C and a storage time H of 50 hours to 360 hours.

2. The recovery method according to claim 1, wherein in the recovery step, the high-temperature storage treatment is performed for a storage time H of 70 hours or more and 360 hours or less.

3. The recovery method according to claim 1 or 2, wherein in the recovery step, the high-temperature storage treatment is performed within the range of 60°C to 65°C for the storage temperature T of the energy storage device.

4. The recovery method according to claim 1 or 2, wherein in the recovery step, the energy storage device is subjected to the high-temperature storage treatment in an open-circuit state after being removed from the circuit.

5. The recovery method according to claim 1 or 2, wherein in the recovery step, the remaining capacity SOC of the energy storage device is adjusted to a range of 45% or more and 55% or less in the adjustment process.

6. A recovery device for energy storage devices, A housing section for housing an energy storage device having electrodes with metallic lithium deposited on them, A temperature adjustment unit for adjusting the temperature of the housing section, A control unit controls the temperature adjustment unit to perform a high-temperature storage process, which involves performing an adjustment process to adjust the remaining capacity (SOC) of the energy storage device to a range of 40% to 70%, and then performing a high-temperature storage process to heat and hold the energy storage device at a storage temperature T of 60°C to 70°C and a storage time H of 50 hours to 360 hours. A recovery device.

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