Charging and discharging method of storage battery, and storage battery module

Abstract

Disclosed is a charging and discharging method for charging and discharging a storage battery (1) which includes a negative electrode current collector (21) that is formed of a metal substrate, and a large number of fine protrusions (22) that are formed on the surface of the negative electrode current collector (21), and which is configured such that metal ions moved from the positive electrode side via an electrolyte solution during charging are transformed into a metal and deposited on the fine protrusions (22). After charging the storage battery from the non-charged initial state to the initial charge capacity, charging and discharging are repeated so that the fine protrusions are not exposed from the metal.

Description

Battery charging / discharging method and battery module

[0001] The present invention relates to a method for charging and discharging a storage battery and a storage battery module.

[0002] For example, various technologies have been developed to increase the storage capacity of lithium-ion secondary batteries installed in electric vehicles and the like. Therefore, it is desirable for the negative electrode material to be lightweight and capable of absorbing or depositing a large amount of lithium. A technology using carbon as the negative electrode active material for lithium-ion secondary batteries is disclosed, for example, in Patent Document 1. Graphite is often used as the carbon material. Graphite can absorb and release one lithium ion per six carbon atoms in a six-membered ring. However, it is believed that it is theoretically impossible to absorb and release lithium ions in amounts greater than this. Therefore, there is a limit to how much energy density can be improved.

[0003] Recently, lithium ion secondary batteries (hereinafter referred to as "lithium metal secondary batteries") have been developed, which use lithium metal as the negative electrode material. Lithium metal secondary batteries are thought to be capable of achieving a relatively high energy density.

[0004] However, lithium metal secondary batteries have the problem that lithium metal dendrites tend to grow easily, which raises concerns that dendrites may cause short circuits between the positive and negative electrodes.

[0005] Therefore, the inventors have developed a negative electrode for a lithium ion secondary battery that suppresses dendrite growth of lithium metal and has sufficient energy density, and have proposed it in Patent Document 2. The negative electrode for a lithium ion secondary battery disclosed in Patent Document 2 is configured such that a plurality of protrusions are provided on the surface of a current collector, and lithium can be deposited on the protrusions.

[0006] Japanese Patent No. 2668678 Japanese Patent Application Laid-Open No. 2022-187895

[0007] However, in a storage battery having a large number of fine protrusions formed on the surface of a negative electrode current collector and allowing lithium ions to be deposited on the fine protrusions, a problem has been found in that the battery capacity is prone to decrease with repeated charge and discharge. This problem is not limited to lithium-ion secondary batteries, and is thought to occur in other storage batteries having the above-mentioned negative electrode structure.

[0008] The present invention has been made in view of the above-mentioned problems, and aims to provide a method for charging and discharging a storage battery and a storage battery module that can suppress a decrease in battery capacity.

[0009] One aspect of the present invention is a method for charging and discharging a storage battery that includes a negative electrode current collector made of a metal substrate and a large number of fine protrusions formed on the surface of the negative electrode current collector, and that is configured so that metal ions that migrate from the positive electrode side via an electrolyte during charging become metal and deposit on the fine protrusions, and that, after charging from an initial uncharged state to an initial charge capacity, repeats charging and discharging so that the fine protrusions are not exposed from the metal.

[0010] Another aspect of the present invention is a storage battery module including a storage battery and a charge / discharge control unit that controls charging and discharging of the storage battery, wherein the storage battery includes a negative electrode current collector made of a metal substrate and a large number of fine protrusions formed on the surface of the negative electrode current collector, and is configured so that metal ions that migrate from the positive electrode side via an electrolyte during charging become metal and deposit on the fine protrusions, and the charge / discharge control unit is configured to charge the storage battery from an initial uncharged state to an initial charge capacity, and then repeatedly charge and discharge the battery so that the fine protrusions are not exposed from the metal.

[0011] In the method for charging and discharging the storage battery, after charging from an initial uncharged state to an initial charge capacity, charging and discharging are repeated so that the fine protrusions are not exposed from the metal, thereby suppressing a decrease in the battery capacity of the storage battery.

[0012] In the storage battery module, the charge / discharge control unit is configured to charge the storage battery from an initial uncharged state to an initial charge capacity, and then repeatedly charge and discharge the storage battery so that the fine protrusions are not exposed from the metal, thereby suppressing a decrease in the battery capacity of the storage battery.

[0013] As described above, according to the above aspects, it is possible to provide a method for charging and discharging a storage battery and a storage battery module that can suppress a decrease in battery capacity.

[0014] 1 is a schematic diagram of a storage battery according to embodiment 1. FIG. 2 is a schematic diagram of fine protrusions according to embodiment 1. FIG. 3 is a scanning electron microscope photograph of fine protrusions according to embodiment 1. FIG. 4 is a schematic diagram illustrating deposition of lithium on the negative electrode during charging according to embodiment 1. FIG. 5 is a schematic diagram illustrating removal of lithium from the negative electrode during discharge according to embodiment 1. FIG. 6 is a schematic diagram of a storage battery showing an initial state or a completely discharged state. FIG. 7 is an explanatory diagram illustrating how lithium deposits on the negative electrode during charging. FIG. 8 is a scanning electron microscope photograph illustrating a state in which lithium has been deposited on the negative electrode of a charged storage battery according to embodiment 1. FIG. 9 is a diagram illustrating an example of a charge / discharge pattern of a storage battery according to embodiment 1 (charge / discharge pattern 2 in an experimental example). FIG. 10 is a diagram illustrating another example of a charge / discharge pattern of a storage battery according to embodiment 1. FIG. 11 is a diagram illustrating yet another example of a charge / discharge pattern of a storage battery according to embodiment 1. FIG. 12 is a block diagram of a storage battery module during charging according to embodiment 1. FIG. 13 is a block diagram of a storage battery module during discharge according to embodiment 1. FIG. 14 is a diagram illustrating charge / discharge pattern 1 in an experimental example. 10 is a diagram showing the measurement results of the change in coulomb efficiency in an experimental example.

[0015] In the storage battery charging / discharging method or the storage battery module, charging and discharging can be repeated so that the remaining capacity of the storage battery does not fall below a predetermined lower limit capacity, thereby suppressing a decrease in the battery capacity of the storage battery.

[0016] The lower limit capacity per unit area of ​​the negative electrode current collector is 0.05 mAh / cm 2 In this case, the decrease in the battery capacity of the storage battery can be effectively suppressed.

[0017] The initial charge capacity per unit area of ​​the negative electrode current collector is 1.5 mAh / cm 2 In this case, it is possible to ensure a sufficient discharge capacity after the initial charge. Note that the "charge capacity" is the amount of electricity charged in the storage battery, and the "initial charge capacity" is the amount of electricity charged in the storage battery by the initial charge.

[0018] The fine protrusions may be carbon nanostructures made of nanographene that stand upright on the surface of the negative electrode current collector, which may provide more stable performance of the storage battery and improve durability, temperature characteristics, and the like.

[0019] The fine protrusions may also be made of the same material as the negative electrode current collector, which eliminates the need for a process for depositing a new material, resulting in significant cost benefits.

[0020] The fine protrusions may have a protruding height from the negative electrode current collector of, for example, about 0.1 to 30 μm, and the interval between adjacent fine protrusions may be, for example, about 0.1 to 30 μm.

[0021] (Embodiment 1) An embodiment relating to a storage battery charge / discharge method and a storage battery module will be described with reference to Figures 1 to 13. The storage battery charge / discharge method of this embodiment is a method for charging and discharging a storage battery configured as follows. That is, as shown in Figure 1, the storage battery 1 in question includes a negative electrode current collector 21 made of a metal substrate and a large number of fine protrusions 22 formed on the surface of the negative electrode current collector 21. The storage battery 1 is also configured so that metal ions that migrate from the positive electrode side via the electrolyte 11 during charging become metal and deposit on the fine protrusions 22.

[0022] 4, 5, and 9 to 11, after charging from an initial uncharged state to an initial charge capacity, charging and discharging are repeated so as not to expose the fine protrusions 22. To achieve this, charging and discharging are repeated so as not to allow the remaining capacity of the storage battery 1 to fall below a predetermined lower limit capacity.

[0023] In this embodiment, a lithium-ion battery in which lithium (Li) ions are involved in charging and discharging is used as the storage battery 1. FIG. 1 is a schematic diagram of the storage battery 1. As shown in the figure, the storage battery 1 has a negative electrode 2 and a positive electrode 3 facing each other, and a separator 4 disposed therebetween. The negative electrode 2 has a negative electrode current collector 21 and a number of fine protrusions 22. The positive electrode 3 has a positive electrode current collector 31 and a positive electrode active material 32 formed on the inner surface thereof.

[0024] An electrolyte solution 11 is filled between the positive electrode 3 and the negative electrode 2. The electrolyte solution 11 has the property of being able to transfer metal ions involved in charge and discharge between the negative electrode 2 and the positive electrode 3. In this embodiment, the electrolyte solution 11 is composed of a solution in which a lithium salt is dissolved in an organic solvent, and is able to transfer Li ions between the positive electrode 3 and the negative electrode 2. As the lithium salt of the electrolyte solution 11, for example, lithium hexafluorophosphate (LiPF), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfone)imide (LiTFSI), or a mixture thereof can be used. Examples of organic solvents that can be used include ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethoxyethane (DME), diethoxyethane (DEE), triglyme, tetraglyme, tetrafluoroethyl tetrafluoropropyl ester (TTE), bis(2,2,2-trifluoroethyl)ether (BTFE), tris[(trifluoroethoxy)methane] (TFEO), derivatives thereof, and any combinations or mixtures thereof.

[0025] The separator 4 divides the internal space between the positive electrode 3 and the negative electrode 2 into a space on the positive electrode 3 side and a space on the negative electrode 2 side. The separator 4 has electrical insulation and ion conductivity, and electrically insulates the positive electrode 3 from the negative electrode 2 while allowing metal ions (Li ions in this embodiment) transmitted via the electrolyte solution 11 to pass through. The separator 4 is made of, for example, a resin film or nonwoven fabric having a porous structure.

[0026] The positive electrode current collector 31 is made of a metal substrate. In this embodiment, the positive electrode current collector 31 is made of an aluminum substrate. Furthermore, for example, a ternary material can be used as the positive electrode active material 32. For example, the positive electrode active material 32 can be lithium cobalt oxide (LiCoO), LiNiCoMnO (Ni:CO:Mn=8:1:1 (CM-811)), lithium manganese oxide (LMO), lithium nickel oxide (NCA), lithium iron phosphate (LFP), or the like.

[0027] The negative electrode current collector 21 is made of a metal substrate, for example, copper (Cu). More specifically, the negative electrode current collector 21 can be made of copper foil, for example. In this embodiment, the fine protrusions 22 are made of carbon nanostructures formed of nanographene 221, as shown in FIG. 2 . That is, the fine protrusions 22 made of carbon nanostructures stand upright on the surface of the negative electrode current collector 21.

[0028] FIG. 2 schematically illustrates the configuration of the microprotrusions 22 made of carbon nanostructures. Numerous microprotrusions 22 are erected across the entire surface of the negative electrode current collector 21. The carbon nanostructure constituting each microprotrusion 22 has a multilayer structure in which a plurality of (e.g., 5 to 10) nanographenes 221 are stacked in the thickness direction. The nanographenes 221 are sheet-like substances having a thickness equivalent to one carbon atom and composed of a six-membered carbon ring structure, i.e., a hexagonal lattice structure with carbon atoms as vertices. Each microprotrusion 22 is a carbon nanostructure in which these sheet-like nanographenes 221 are stacked in the thickness direction. Numerous microprotrusions 22 are formed on the surface of the negative electrode current collector 21, with the thickness direction of the nanographenes 221 intersecting the normal direction to the surface of the negative electrode current collector 21. In this embodiment, the thickness of the fine protrusions 22 (wall thickness) is, for example, about 2 to 30 nm, and the interval between adjacent fine protrusions 22 is, for example, about 20 to 1000 nm. The height of the fine protrusions 22 is, for example, about 0.1 to 30 μm. The carbon nanostructure is conductive.

[0029] The fine protrusions 22 made of carbon nanostructures can be formed on the surface of the negative electrode current collector 21 by, for example, chemical vapor deposition (CVD). Although not shown, the surface of the negative electrode current collector 21 is covered with a thin amorphous carbon layer. In the CVD method, an amorphous carbon layer is formed on the surface of the negative electrode current collector 21, and then carbon nanostructures are formed so as to extend upward from the amorphous carbon layer as the starting point of growth. FIG. 3 shows a scanning electron microscope photograph of the fine protrusions 22 made of carbon nanostructures (carbon nanowalls) formed on the surface of the negative electrode current collector 21 by CVD. This photograph is taken from the protruding direction of the fine protrusions 22.

[0030] Carbon nanostructures can be formed, for example, in a needle-like, wall-like, pleated, etc. Depending on the state of formation, carbon nanostructures can be, for example, carbon nanowalls, carbon nanoflakes, carbon nanoflowers, carbon nanotrees, carbon nanotubes, carbon nanocacti, carbon nanocords, etc.

[0031] In FIG. 1 , solid electrolyte interphase (SEI) films 121 and 122 are formed between the negative electrode 2 and the electrolyte solution 11, and between the positive electrode 3 and the electrolyte solution 11. The SEI films 121 and 122 are extremely thin films, e.g., several tens of nanometers thick, and are formed by a reaction between the electrolyte solution 11 and an electrolyte, a Li compound, or Li ions. The SEI film 121 on the negative electrode 2 side is formed on the surface of a lithium metal layer deposited on the negative electrode 2. Therefore, as the thickness of the lithium metal layer deposited on the negative electrode 2 increases or decreases with charge and discharge, the position of the SEI film 121 also moves up and down. The SEI film 121 does not allow the electrolyte solution 11 to pass through, but allows lithium ions to pass through. The SEI film is omitted in other figures (e.g., FIG. 4 ).

[0032] Next, the battery reaction during charging and discharging of the storage battery 1 will be described. The chemical reaction during charging and discharging of the storage battery 1 can be expressed, for example, by the following reaction formula. When the positive electrode active material 32 is LiCoO2, the reaction formula in the positive electrode 3 is expressed by the following formula (1). x represents the proportion of reacting atoms and is a real number greater than 0 and less than 1. LiCoO2 ⇔ Li 1-x CoO2 + xLi + + xe - ...(1)

[0033] On the other hand, the reaction formula at the negative electrode 2 is expressed by the following formula (2): Li + + e - ⇔ Li ... (2)

[0034] In the above formulas (1) and (2), the reaction from the left side to the right side is the reaction during charging, and the reaction from the right side to the left side is the reaction during discharging. That is, during charging, as shown in FIG. 4, lithium ions (Li + ) moves to the negative electrode 2, and lithium metal is deposited on the negative electrode 2. During discharge, as shown in FIG. 5, the lithium metal deposited on the negative electrode 2 becomes lithium ions and moves to the positive electrode 3.

[0035] In the storage battery 1 of this embodiment, when charging is performed from an uncharged initial state (a state in which no lithium is present on the negative electrode 2 as shown in FIG. 6), a large number of lithium atoms are sequentially precipitated and accumulated, with the fine protrusions 22 of the negative electrode 2 acting as nuclei, as shown in FIG. 7. Lithium is first precipitated along the surface of the fine protrusions 22. Therefore, a large number of lithium atoms are precipitated in an orderly array. As charging proceeds further, this orderly array of lithium atoms piles up, and a lithium metal layer with excellent crystallinity is precipitated on the many fine protrusions 22. Because lithium metal is precipitated in an orderly manner in this way, the formation of dendrites can be prevented.

[0036] FIG. 8 shows an electron microscope photograph of a cross section of the negative electrode 2 of a charged storage battery 1 in a state where a lithium metal layer is deposited. The lithium metal layer shown in the figure has a height of about 30 μm. For ease of understanding, the charging capacity (charged electricity amount) shown here is 9 mAh. In this embodiment, the area of ​​the negative electrode current collector is 1.327 cm. 2 Therefore, the photograph shown in Figure 8 shows a charge capacity per unit area of ​​6.8 mAh / cm 2 In the figure, the fine protrusions 22 are barely visible, but they have a height of about 1 μm.

[0037] During discharge, as shown in Fig. 5, the lithium accumulated on the negative electrode 2 becomes lithium ions and is released into the electrolyte 11. At this time, lithium is left on the negative electrode 2 to the extent that the fine protrusions 22 are not exposed. In other words, the lithium is not released from the negative electrode 2 to expose the fine protrusions 22 (for example, the state shown in Fig. 6).

[0038] This is because, as will be shown in the experimental examples described later, excessive discharge and excessive release of lithium from the negative electrode 2 accelerates the decrease in battery capacity. This is thought to be due to the exposure of the fine protrusions 22 to the electrolyte 11, which accelerates deterioration of the negative electrode 2. Therefore, in the charge / discharge method for the storage battery 1 of this embodiment, as shown in FIG. 9 , the remaining capacity of the storage battery 1 is maintained at a certain level or higher during discharge so that the fine protrusions 22 are not exposed. To achieve this, the cutoff voltage during discharge is set so that the remaining capacity of the storage battery 1 does not fall below a predetermined lower limit capacity.

[0039] As described above, the lower limit capacity is set to a value that does not expose the fine protrusions 22. This lower limit capacity can be set according to the height of the fine protrusions 22. In other words, the lower limit capacity is set so that the amount (thickness) of lithium metal deposited on the negative electrode 2 exceeds the height of many fine protrusions 22, taking into consideration variations. In this embodiment, for example, the lower limit capacity per unit area of ​​the negative electrode current collector 21 is 0.05 mAh / cm. 2 It is preferable to set it at or above, and more preferably 0.08 mAh / cm2 The above is the setup.

[0040] 9, the method of charging and discharging the storage battery 1 of this embodiment involves charging from an uncharged initial state to an initial charge capacity, and then repeating charge and discharge so that the remaining capacity does not fall below a predetermined lower limit capacity. In this specification, the lower limit capacity, remaining capacity, charge capacity, etc. per unit area of ​​the negative electrode current collector 21 may also be simply referred to as the lower limit capacity, remaining capacity, charge capacity, etc.

[0041] In the initial state, as shown in Fig. 6, no lithium is present in the negative electrode 2. From this initial state, the storage battery 1 is first charged, causing lithium to deposit on the negative electrode 2 as shown in Figs. 5 and 4. The method for depositing lithium on the negative electrode 2 is as described above. The deposited lithium metal layer then completely covers the fine protrusions 22 of the negative electrode 2. The initial charge capacity per unit area of ​​the negative electrode current collector 21 during this first charge is 1.5 mAh / cm 2 The initial charging is performed, for example, by the manufacturer of the storage battery 1 before shipping.

[0042] FIG. 9 shows an example of a charge / discharge pattern of the method for charging / discharging the storage battery 1 of this embodiment. In this example, the initial charge capacity is set to 5 mAh (3.8 mAh / cm 2 ), and the lower limit capacity is 1 mAh (0.75 mAh / cm 2 ) First, from the initial state, the battery is charged up to an initial charge capacity of 5 mAh. From this state, the battery is discharged until the discharge voltage reaches a predetermined cutoff voltage (e.g., 3.5 V). This allows the battery to be discharged until the remaining capacity after discharge approaches a lower limit capacity of 1 mAh. Thereafter, charging and discharging are repeated while preventing the remaining capacity from falling below this lower limit capacity.

[0043] 9 shows a charge / discharge pattern in which the initial charge capacity is set to 5 mAh and the remaining capacity is discharged until it approaches the lower limit capacity, but the charge / discharge pattern is not limited to this. For example, the initial charge capacity can be set lower than 5 mAh, as in the charge / discharge patterns shown in FIGS. 10 and 11.

[0044] In either case, after charging up to the initial charge capacity, charging and discharging are repeated so that the capacity does not fall below the lower limit capacity (1 mAh in these examples). To achieve this, the cutoff voltage during discharging is set as described above according to the assumed lower limit capacity. In this embodiment, the cutoff voltage is set to, for example, 3.5 V.

[0045] As shown in FIGS. 12 and 13 , the storage battery module 5 of this embodiment includes the storage battery 1 and a charge / discharge control unit 52. The charge / discharge control unit 52 controls charging and discharging of the storage battery 1. The charge / discharge control unit 52 is configured to charge the storage battery 1 from an uncharged initial state to an initial charge capacity, and then repeatedly charge and discharge the storage battery 1 so that the fine protrusions 22 are not exposed from the lithium metal. To achieve this, the charge / discharge control unit 52 is configured to repeatedly charge and discharge the storage battery 1 so that the remaining capacity of the storage battery 1 does not fall below a predetermined lower limit capacity. That is, the charge / discharge control unit 52 controls the charging and discharging of the storage battery 1 so as to achieve the above-described charge / discharge method. In other words, the charge / discharge control unit 52 controls a discharge circuit, for example, during discharging of the storage battery 1, so that discharging is stopped before the remaining capacity falls below the predetermined lower limit capacity.

[0046] As shown in Figures 12 and 13, the storage battery module 5 has a pair of external terminals 511, 512, a charge / discharge control unit 52, a switch unit 54, a current measurement unit 55, and a voltage measurement unit 56. The external terminals 511, 512 are connected to the positive electrode 3 and the negative electrode 2 of the storage battery 1, respectively, via circuits within the storage battery module 5. The external terminals 511, 512 are connected to an external power supply 61 or a load 62. That is, when the storage battery 1 is being charged, the external terminals 511, 512 are connected to the power supply 61 as shown in Figure 12, and when the storage battery 1 is being discharged, the external terminals 511, 512 are connected to the load 62 as shown in Figure 13. Note that various elements, such as a power conversion unit, may be interposed between the external terminals 511, 512 and the storage battery 1 as needed, but are not illustrated here.

[0047] The charge / discharge control unit 52 is configured by, for example, a microprocessor. The charge / discharge control unit 52 controls the switch unit 54 and the like in the storage battery module 5 to perform charge / discharge control of the storage battery 1.

[0048] The switch unit 54 is configured, for example, by a switch element capable of controlling the opening and closing of a current. The switch unit 54 is provided on the wiring between the external terminal 511 and the storage battery 1, and opens and closes under the control of the charge / discharge control unit 52. The switch unit 54 is closed while the storage battery 1 is being charged or discharged, and is opened when the charging or discharging of the storage battery 1 is completed.

[0049] The current measurement unit 55 is configured, for example, by an element that functions as a current sensor, and detects the magnitude of the current charging current. The current measurement unit 55 outputs a signal proportional to the current charging current to the charge / discharge control unit 52. The charge / discharge control unit 52 executes charge / discharge control based on the detection result of the current measurement unit 55.

[0050] The voltage measurement unit 56 is configured, for example, by an element that functions as a voltage sensor, and detects the current voltage of the storage battery 1. The voltage measurement unit 56 outputs a signal proportional to the voltage of the storage battery 1 to the charge / discharge control unit 52. The charge / discharge control unit 52 uses the detection result of the voltage measurement unit 56 for charge / discharge control as appropriate.

[0051] In the storage battery module 5 configured as described above, the charge / discharge control unit 52 executes the above-described charge / discharge method when charging or discharging the storage battery 1. That is, after charging from the initial state to the initial charge capacity, the charge / discharge control unit 52 controls charge / discharge so that charge / discharge is repeated so that the remaining capacity does not fall below a predetermined lower limit capacity.

[0052] The remaining capacity (charged electricity amount) and charge capacity of the storage battery 1 can be calculated using information such as the charging current, the accumulated charging time, the discharging current, and the accumulated discharging time.

[0053] Next, the effects of this embodiment will be described. In the method for charging and discharging the storage battery 1, after charging from an uncharged initial state to an initial charge capacity, charging and discharging are repeated so that the fine protrusions 22 are not exposed from the lithium metal. To this end, charging and discharging are repeated so that the remaining capacity does not fall below a predetermined lower limit capacity. This makes it possible to suppress a decrease in the battery capacity of the storage battery 1.

[0054] In the storage battery module 5, the charge / discharge control unit 52 is configured to charge the storage battery from an initial uncharged state to an initial charge capacity, and then repeatedly charge and discharge the storage battery so that the remaining capacity of the storage battery does not fall below a predetermined lower limit capacity. This makes it possible to suppress a decrease in the battery capacity of the storage battery 1.

[0055] The lower limit capacity per unit area of ​​the negative electrode current collector 21 is 0.05 mAh / cm 2 As a result, the decrease in the battery capacity of the storage battery 1 can be effectively suppressed.

[0056] The initial charge capacity per unit area of ​​the negative electrode current collector 21 is 1.5 mAh / cm 2 This makes it possible to ensure a sufficient discharge capacity after the initial charge.

[0057] Furthermore, the fine protrusions 22 are formed by carbon nanostructures standing upright on the surface of the negative electrode current collector 21. This makes the performance of the storage battery more stable, and the durability, temperature characteristics, and the like are likely to be improved.

[0058] As described above, according to the present embodiment, it is possible to provide a method for charging and discharging a storage battery and a storage battery module that can suppress a decrease in battery capacity.

[0059] (Experimental Example) In this example, the effect of suppressing a decrease in battery capacity by the method of charging and discharging the storage battery 1 shown in the first embodiment was confirmed.

[0060] That is, the decrease in coulomb efficiency was compared between a case where a charge / discharge method (charge / discharge pattern 1 described below) in which charge / discharge was repeated so that the remaining capacity was significantly below the above-mentioned lower limit capacity during discharge, and a case where the charge / discharge method (charge / discharge pattern 2 described below) shown in embodiment 1 was performed. Note that the configuration of the storage battery itself is the same as that shown in embodiment 1 in both cases.

[0061] As shown in FIG. 14, charge / discharge pattern 1 is a charging / discharging pattern in which the battery is charged from an initial state (uncharged state) to a discharge of 4 mAh (3 mAh / cm 2 ) is charged. Here, 1 mA (0.75 mA / cm 2) for 4 hours, resulting in a charge of 4 mAh. Then, the battery is discharged at a constant current of 1 mA. Discharge is continued until the discharge voltage reaches the cutoff voltage of 2.0 V. This allows the battery to discharge until it has almost no remaining capacity after discharge. The battery is then charged to 4 mAh and then discharged until the discharge voltage reaches the cutoff voltage of 2.0 V, and this cycle of alternating charge and discharge is repeated. However, as the cycles are repeated, the internal impedance of the battery increases, resulting in an increase in the charging voltage during constant current charging. After the charging voltage reaches a predetermined voltage (here, 4.75 V), charging is continued at that constant voltage. During this process, the charging current decreases over time, and charging is terminated when it reaches, for example, 0.2 mA or less. In this manner, the change in coulombic efficiency during each cycle of repeated charging and discharging is measured.

[0062] As shown in FIG. 9 , in charge / discharge pattern 2, the battery is charged to 5 mAh from its initial state (uncharged state). Here, charging is performed for 5 hours at a constant current of 1 mA, resulting in 5 mAh charging. Then, discharging is performed for 4 hours at a constant current of 1 mA. As a result, the remaining capacity of the battery 1 after discharge approaches 1 mAh (lower limit capacity). The battery 1 is then charged to 4 mAh and then discharged until the discharge voltage reaches a cutoff voltage of 3.5 V. This cycle of charging and discharging is then repeated alternately. However, as with charge / discharge pattern 1, once the charging voltage reaches a predetermined voltage (here, 4.75 V), charging is performed at this constant voltage. During this cycle, the charging current decreases over time, but charging is terminated when it drops below, for example, 0.2 mA. The cutoff voltage (here, 3.5 V) is set so that the remaining capacity of the battery does not fall below the lower limit capacity (here, 1 mAh) during this cycle of charging and discharging. The change in coulombic efficiency during each cycle of repeated charging and discharging is measured.

[0063] The measurement results of the change in Coulomb efficiency for each cycle for charge / discharge pattern 1 and charge / discharge pattern 2 are shown in Figure 15. In this figure, the horizontal axis represents the number of cycles, and the vertical axis represents Coulomb efficiency. As can be seen from this figure, in the case of charge / discharge pattern 1, the Coulomb efficiency fell below 80% after around 78 cycles, whereas in the case of charge / discharge pattern 2, the Coulomb efficiency was maintained at 80% up to roughly 120 cycles.

[0064] From the results of this example, it was confirmed that the charge / discharge method of embodiment 1 can suppress the decrease in battery capacity due to repeated charge / discharge.

[0065] In the above embodiment, a method for charging and discharging the storage battery 1 in which the fine protrusions 22 are made of carbon nanostructures has been described, but the invention according to the present disclosure is not limited to this. For example, even in a storage battery in which the fine protrusions 22 are made of the same material as the negative electrode current collector 21, the decrease in battery capacity can be suppressed by applying the charging and discharging method according to the present disclosure.

[0066] In such a storage battery, for example, the negative electrode current collector 21 can be made of copper foil, and the fine protrusions 22 can also be made of copper. For example, the surface of the copper foil constituting the negative electrode current collector 21 can be modified to form the fine protrusions 22 on the surface of the copper foil. Specifically, as shown schematically in FIG. 16 , the surface of a copper substrate that forms the negative electrode current collector 21 can be irradiated with hydrogen plasma to form the fine protrusions 22 made of copper. This is done by irradiating the surface of the negative electrode current collector 21 made of a copper substrate with hydrogen plasma, knocking out copper particles from the surface of the copper substrate (negative electrode current collector 21). The knocked out particles then re-adhere to the surface of the copper substrate and fuse with the surface of the copper substrate, thereby forming the fine protrusions 22. This technology has been previously proposed by the present inventors and is disclosed in Japanese Patent Application Laid-Open No. 2022-187895.

[0067] Various other methods and modes for forming the fine protrusions may also be employed. For example, a large number of fine protrusions may be formed by depositing metal on the surface of the negative electrode current collector using an electrolytic deposition method.

[0068] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments within the scope of the present invention.

[0069] The features of the present invention are as follows. [1] A method for charging and discharging a storage battery comprising a negative electrode current collector made of a metal substrate and a large number of fine protrusions formed on the surface of the negative electrode current collector, wherein metal ions migrated from the positive electrode side via an electrolyte during charging become metal and deposit on the fine protrusions, the method comprising, after charging from an uncharged initial state to an initial charge capacity, repeating charge and discharge so that the fine protrusions are not exposed from the metal. [2] The method for charging and discharging a storage battery according to [1], after charging from an uncharged initial state to an initial charge capacity, repeating charge and discharge so that the remaining capacity does not fall below a predetermined lower limit capacity. [3] The lower limit capacity per unit area of ​​the negative electrode current collector is 0.05 mAh / cm 2 [4] The initial charge capacity per unit area of ​​the negative electrode current collector is 1.5 mAh / cm 2

[0016] The method for charging and discharging a storage battery according to [2] or [3], wherein the fine protrusions are carbon nanostructures made of nanographene that stand upright on the surface of the negative electrode current collector.

[0017] The method for charging and discharging a storage battery according to any one of [1] to [4], wherein the fine protrusions are made of the same material as the negative electrode current collector.

[0018] The method for charging and discharging a storage battery according to any one of [1] to [5], wherein the fine protrusions are made of the same material as the negative electrode current collector.

[0019] A storage battery module including a storage battery and a charge / discharge control unit that controls charging and discharging of the storage battery, wherein the storage battery includes a negative electrode current collector made of a metal substrate and a large number of fine protrusions formed on the surface of the negative electrode current collector, and wherein metal ions that migrate from the positive electrode side via an electrolyte during charging become metal and deposit on the fine protrusions, and the charge / discharge control unit is configured to charge the storage battery from an initial, uncharged state to an initial charge capacity, and then repeatedly charge and discharge the battery so that the fine protrusions are not exposed from the metal. [8] The storage battery module according to [7], wherein the charge / discharge control unit is configured to charge the storage battery from an initial uncharged state to an initial charge capacity, and then repeatedly charge and discharge the storage battery so that the remaining capacity of the storage battery does not fall below a predetermined lower limit capacity. [9] The lower limit capacity per unit area of ​​the negative electrode current collector is 0.05 mAh / cm 2

[10] The storage battery module according to [8], wherein the initial charge capacity per unit area of ​​the negative electrode current collector is 1.5 mAh / cm 2 The battery module according to [8] or [9], wherein the fine protrusions are carbon nanostructures made of nanographene that stand upright on the surface of the negative electrode current collector.

[11] The battery module according to any one of [7] to

[10] , wherein the fine protrusions are made of the same material as the negative electrode current collector.

[12] The battery module according to any one of [7] to

[10] , wherein the fine protrusions are made of the same material as the negative electrode current collector.

Claims

1. A method for charging and discharging a storage battery comprising a negative electrode current collector made of a metal substrate and a large number of fine protrusions formed on the surface of the negative electrode current collector, wherein metal ions that migrate from the positive electrode side via the electrolyte during charging become metal and deposit on the fine protrusions, and after charging from an initial uncharged state to an initial charge capacity, the method for charging and discharging a storage battery repeats charging and discharging so that the fine protrusions are not exposed from the metal.

2. A method for charging and discharging a storage battery as described in claim 1, wherein after charging from an initial uncharged state to an initial charge capacity, charging and discharging are repeated so that the remaining capacity does not fall below a predetermined lower limit capacity.

3. The lower limit capacity per unit area of ​​the negative electrode current collector is 0.05 mAh / cm 2 The method for charging and discharging a storage battery according to claim 2 .

4. The initial charge capacity per unit area of ​​the negative electrode current collector is 1.5 mAh / cm 2 The method for charging and discharging a storage battery according to claim 2 or 3.

5. A method for charging and discharging a storage battery as described in claim 1 or 2, wherein the fine protrusions are carbon nanostructures made of nanographene that stand upright on the surface of the negative electrode current collector.

6. The method for charging and discharging a storage battery according to claim 1 or 2, wherein the fine protrusions are made of the same material as the negative electrode current collector.

7. A storage battery module comprising a storage battery and a charge / discharge control unit that controls charging and discharging to the storage battery, wherein the storage battery comprises a negative electrode collector made of a metal substrate and a number of fine protrusions formed on a surface of the negative electrode collector, and is configured so that metal ions that migrate from the positive electrode side via the electrolyte during charging become metal and precipitate on the fine protrusions, and the charge / discharge control unit is configured to charge the storage battery from an initial uncharged state to an initial charge capacity, and then repeatedly charge and discharge the battery so that the fine protrusions are not exposed from the metal.

8. The storage battery module according to claim 7, wherein the charge / discharge control unit is configured to charge the storage battery from an initial uncharged state to an initial charge capacity, and then repeat charging and discharging so that the remaining capacity of the storage battery does not fall below a predetermined lower limit capacity.

9. The lower limit capacity per unit area of ​​the negative electrode current collector is 0.05 mAh / cm 2 The storage battery module according to claim 8 .

10. The initial charge capacity per unit area of ​​the negative electrode current collector is 1.5 mAh / cm 2 The storage battery module according to claim 8 or 9.

11. A storage battery module as described in claim 7 or 8, wherein the fine protrusions are carbon nanostructures made of nanographene that stand upright on the surface of the negative electrode current collector.

12. The storage battery module according to claim 7 or 8, wherein the fine protrusions are made of the same material as the negative electrode current collector.

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