Battery charge / discharge method and battery module

Abstract

To provide a storage battery charge / discharge method and a storage battery module capable of suppressing the decrease in battery capacity.SOLUTION: A storage battery module 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, and there is provided a charge / discharge method that charges / discharges storage battery 1 that is configured such that metal ions that migrate from the positive electrode side via the electrolyte during charging become metal and deposit on the fine protrusions 22. After charging from an initial uncharged state to an initial charge capacity, charging and discharging are repeated such that the fine protrusions are not exposed from the metal.SELECTED DRAWING: Figure 5

Description

[Technical field]

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

[0002] For example, various technologies have been developed to increase the storage capacity of lithium-ion secondary batteries mounted on electric vehicles and the like. For this purpose, it is desirable for the negative electrode material to be lightweight and capable of absorbing or depositing a large amount of lithium. For example, Patent Document 1 discloses a technology using carbon as the material for the negative electrode active material of lithium-ion secondary batteries. 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 theoretically it is impossible to absorb and release lithium ions in an amount exceeding this. Therefore, there is a limit to the improvement of the energy density.

[0003] Recently, lithium ion secondary batteries (hereinafter referred to as "lithium metal secondary batteries") that have lithium metal as the negative electrode material have been developed. It is believed that lithium metal secondary batteries can achieve a relatively high energy density.

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

[0005] Therefore, the inventors have developed a negative electrode for a lithium ion secondary battery that suppresses the dendrite growth of lithium metal and has sufficient energy density, and have proposed it in Patent Document 2. The negative electrode for the 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. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 2668678 [Patent Document 2] Patent Publication No. 2022-187895 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in a storage battery having a large number of fine protrusions formed on the surface of a negative electrode current collector and capable of depositing lithium ions on the fine protrusions, a problem has been found in that the battery capacity is easily reduced by repeated charging and discharging. It is believed that such a problem may occur not only in lithium ion secondary batteries but also in other storage batteries having the above-mentioned negative electrode structure.

[0008] The present invention has been made in view of the above 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. [Means for solving the problem]

[0009] One aspect of the present invention is 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 a surface of the negative electrode current collector, the method being configured such that metal ions that migrate from a positive electrode side via an electrolyte during charging become metal and are deposited on the fine protrusions, the method comprising: the fine protrusions are carbon nanostructures made of nanographene standing on the surface of the negative electrode current collector covered with an amorphous carbon layer, 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. 。

[0010] The present invention OtherThe 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 to the storage battery, The storage battery is configured to include a negative electrode current collector made of a metal substrate and a large number of fine protrusions formed on a surface of the negative electrode current collector, and metal ions that migrate from the positive electrode side via an electrolyte during charging become metal and are deposited on the fine protrusions; the fine protrusions are carbon nanostructures made of nanographene standing on the surface of the negative electrode current collector covered with an amorphous carbon layer, 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. 。 Effect of the Invention

[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-described 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. 。 [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a schematic diagram of a storage battery in the first embodiment. [Diagram 2] FIG. 3 is a schematic diagram of a fine protrusion in the first embodiment. [Diagram 3]3 is a scanning electron microscope photograph of the fine protrusions in the first embodiment. [Figure 4] FIG. 2 is a schematic diagram showing deposition of lithium on a negative electrode during charging in the first embodiment. [Diagram 5] FIG. 3 is a schematic diagram showing the release of lithium from a negative electrode during discharge in the first embodiment. [Figure 6] Schematic diagram of a storage battery in its initial or fully discharged state. [Figure 7] FIG. 2 is an explanatory diagram illustrating how lithium is deposited on a negative electrode during charging. [Figure 8] 4 is a scanning electron microscope photograph showing a state in which lithium is deposited on the negative electrode of a charged storage battery in the first embodiment. [Figure 9] 4 is a diagram showing an example of a charge / discharge pattern of a storage battery (charge / discharge pattern 2 in an experimental example) in the first embodiment. [Figure 10] 5 is a diagram showing another example of the charge / discharge pattern of the storage battery in the first embodiment. [Figure 11] 5 is a diagram showing yet another example of a charge / discharge pattern of the storage battery in the first embodiment. [Figure 12] FIG. 2 is a block diagram of the storage battery module during charging in the first embodiment. [Figure 13] FIG. 4 is a block diagram of the storage battery module during discharging in the first embodiment. [Figure 14] 1 is a diagram showing a charge / discharge pattern 1 in an experimental example. [Figure 15] 1 is a graph showing the measurement results of changes in Coulombic efficiency in an experimental example. [Figure 16] Schematic diagram of a negative electrode structure of a storage battery in a modified form. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 standing 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 be made of the same material as the negative electrode current collector, in which case no additional material deposition process is required, 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 of a storage battery charging / discharging method and a storage battery module will be described with reference to Figs. 1 to 13. The method for charging and discharging a storage battery according to this embodiment is a method for charging and discharging a storage battery configured as follows. That is, as shown in Fig. 1, the storage battery 1 to be charged 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 configured such that metal ions that migrate from the positive electrode side via the electrolyte 11 during charging become metal and are deposited on the fine protrusions 22.

[0022] In the method of charging and discharging the storage battery 1 of this embodiment, after charging from an initial uncharged state to an initial charge capacity, charging and discharging are repeated so that the fine protrusions 22 are not exposed from the metal, as shown in Fig. 4, Fig. 5, and Fig. 9 to Fig. 11 described later. To achieve this, charging and discharging are repeated so that the remaining capacity of the storage battery 1 does not 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 a 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 between them. The negative electrode 2 has a negative electrode current collector 21 and a large 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 11 is filled between the positive electrode 3 and the negative electrode 2. The electrolyte 11 has a property of being able to transmit metal ions involved in charging and discharging between the negative electrode 2 and the positive electrode 3. In this embodiment, the electrolyte 11 is composed of a solution in which a lithium salt is dissolved in an organic solvent, and is able to transmit Li ions between the positive electrode 3 and the negative electrode 2. As the lithium salt of the electrolyte 11, for example, lithium hexafluorophosphate (LiPF6), 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 and 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 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. The positive electrode active material 32 may be, for example, a ternary material. For example, the positive electrode active material 32 may be lithium cobalt oxide (LiCoO 2 ), LiNiCoMnO 2 (Ni:CO:Mn=8:1:1 (CM-811), lithium manganese oxide (LMO), lithium nickel oxide (NCA), lithium iron phosphate (LFP), etc. can be used.

[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 a carbon nanostructure made of nanographene 221, as shown in FIG. 2. That is, the fine protrusions 22 made of a carbon nanostructure stand upright on the surface of the negative electrode current collector 21.

[0028] FIG. 2 shows a schematic configuration of the fine protrusions 22 made of carbon nanostructures. A large number of fine protrusions 22 are erected over the entire surface of the negative electrode current collector 21. The carbon nanostructure constituting each fine protrusion 22 has a multilayer structure in which a plurality of (for example, 5 to 10 layers) nanographenes 221 are stacked in the thickness direction. The nanographenes 221 are sheet-like substances having a thickness of one carbon atom, which are constituted by a six-membered carbon ring structure, that is, a hexagonal lattice structure with carbon atoms as vertices. Each fine protrusion 22 is constituted by a carbon nanostructure in which the sheet-like nanographenes 221 are stacked in the thickness direction. A large number of the fine protrusions 22 are formed on the surface of the negative electrode current collector 21 in a state in which the thickness direction of the nanographenes 221 intersects with the normal direction of the surface of the negative electrode current collector 21. In this embodiment, the thickness (wall thickness) of the fine protrusions 22 is, for example, about 2 to 30 nm, and the distance 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 the 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 the CVD method. 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, etc. ,mosquito It could be a nano-cactus, a carbon nano-cord, etc.

[0031] In FIG. 1, between the negative electrode 2 and the electrolyte 11, and between the positive electrode 3 and the electrolyte 11, SEI (Solid Electrolyte Interphase) films 121 and 122 are formed. The SEI films 121 and 122 are extremely thin films, for example, about several tens of nm, and are formed by a reaction between the electrolyte 11 and an electrolyte, a Li compound, Li ions, or the like. The SEI film 121 on the negative electrode 2 side is formed on the surface of the lithium metal layer deposited on the negative electrode 2. Therefore, when the thickness of the lithium metal layer deposited on the negative electrode 2 increases or decreases with charging and discharging, the position of the SEI film 121 also moves up and down. The SEI film 121 does not allow the electrolyte 11 to pass through, but allows lithium ions to pass through. In other figures (such as FIG. 4), the SEI film is omitted.

[0032] Next, the battery reaction during charging and discharging of the storage battery 1 will be described. The chemical reactions occurring during charging and discharging of the storage battery 1 can be expressed by, for example, the following reaction formula: 2 In this case, the reaction formula at 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. LiCoO 2 ⇔ Li 1-x Chief of Staff 2 + 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 that was 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 initial uncharged 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 around the fine protrusions 22 of the negative electrode 2 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 a regular alignment. As charging proceeds further, this regular alignment of lithium atoms piles up, and a lithium metal layer with excellent crystallinity is precipitated on the many fine protrusions 22. Since lithium metal precipitates in an orderly manner in this manner, the generation 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 has been 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 cm2. 2 Therefore, the photo 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, 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 shown in the experimental example described later, excessive discharge and release of too much lithium from the negative electrode 2 accelerates the decrease in battery capacity. It is believed that the exposure of the fine protrusions 22 to the electrolyte 11 accelerates the deterioration of the negative electrode 2. Therefore, in the method of charging and discharging the storage battery 1 of this embodiment, as shown in FIG. 9, the remaining capacity of the storage battery 1 is kept at a certain level or higher during discharge so that the fine protrusions 22 are not exposed. For this purpose, 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 at which the fine protrusions 22 are not exposed. 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. 2It is preferable to set it at or above 0.08 mAh / cm 2 The above is all that is set.

[0040] In the method of charging and discharging the storage battery 1 of this embodiment, after charging from an uncharged initial 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, as shown in Fig. 9. 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, and lithium is deposited on the negative electrode 2 as shown in FIGS. 5 and 4. The method of 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 1mAh (0.75mAh / cm 2 ) First, the battery is charged from the initial state to an initial charge capacity of 5 mAh. From this state, the battery is discharged until the discharge voltage reaches a specified 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. After that, charging and discharging are repeated while preventing the capacity from falling below this lower limit capacity.

[0043] In the example shown in Fig. 9, the initial charge capacity is set to 5 mAh, and the battery is discharged until the remaining capacity 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 to the initial charge capacity, charging and discharging are repeated so as not to fall below the lower limit capacity (1 mAh in these examples). To achieve this, the cut-off voltage during discharging is set as described above according to the assumed lower limit capacity. In this embodiment, the cut-off voltage is set to, for example, 3.5 V.

[0045] The storage battery module 5 of this embodiment includes the storage battery 1 and a charge / discharge control unit 52, as shown in FIGS. 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 initial uncharged state to an initial charge capacity, and then repeat charging and discharging 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 repeat charging and discharging 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 to achieve the above-mentioned charging and discharging method. In other words, the charge / discharge control unit 52 controls a discharge circuit, for example, when discharging the storage battery 1, so that discharging is stopped before the remaining capacity falls below a predetermined lower limit capacity.

[0046] As shown in Figs. 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 a circuit in the storage battery module 5. The external terminals 511, 512 are connected to an external power source 61 or a load 62. That is, when the storage battery 1 is charged, the external terminals 511, 512 are connected to the power source 61 as shown in Fig. 12, and when the storage battery 1 is discharged, the external terminals 511, 512 are connected to the load 62 as shown in Fig. 13. Note that various elements such as a power conversion unit are interposed between the external terminals 511, 512 and the storage battery 1 as necessary, but are omitted 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 execute 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 during charging / discharging of the storage battery 1, and is opened when charging / discharging of the storage battery 1 is completed.

[0049] The current measuring unit 55 is configured by, for example, an element that realizes the function of a current sensor, and detects the magnitude of the current charging current. The current measuring 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 measuring unit 55.

[0050] The voltage measurement unit 56 is configured, for example, by an element that realizes the function of 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 appropriately uses the detection result of the voltage measurement unit 56 for charge / discharge control.

[0051] The storage battery module 5 configured as described above is configured so that the charge / discharge control unit 52 executes the above-described charge / discharge method when charging / 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 charging / discharging so that charging / discharging 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 initial uncharged 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 repeat charging and discharging 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] Moreover, 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 are capable of suppressing a decrease in battery capacity.

[0059] (Experimental Example) In this example, the effect of suppressing the 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 charging / discharging was repeated so that the remaining capacity was significantly below the lower limit capacity described above during discharging was performed, 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, the 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 ) charging. Here, 1mA (0.75m A / cm 2 ) for 4 hours to charge the battery to 4 mAh. After that, discharge it at a constant current of 1 mA. Discharge it until the discharge voltage reaches the cutoff voltage of 2.0 V. This allows the battery to discharge until there is almost no remaining capacity after discharge. Thereafter, the storage battery 1 is charged to 4 mAh, and then discharged until the discharge voltage reaches the cut-off voltage of 2.0 V, and this cycle is repeated alternately. However, as the cycle is repeated, the internal impedance of the battery increases, and the charging voltage rises when charging at a constant current. After the charging voltage reaches a specified voltage (here, 4.75 V), charging is continued at that constant voltage. At this time, the charging current decreases over time, but when it falls to, for example, 0.2 mA or less, chargingIn this manner, the change in coulomb efficiency during each cycle of repeated charging and discharging is measured.

[0062] As shown in FIG. 9, in charge / discharge pattern 2, the storage 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 charging to 5 mAh. After that, discharging is performed for 4 hours at a constant current of 1 mA. As a result, the remaining capacity of the storage battery 1 after discharging becomes close to 1 mAh (lower limit capacity). Thereafter, the storage battery 1 is charged to 4 mAh, and then discharged until the discharge voltage reaches the cut-off voltage of 3.5 V, and this charging and discharging are repeated alternately. However, as in the case of charge / discharge pattern 1, once the charging voltage reaches a predetermined voltage (here, 4.75 V), charging is performed at the constant voltage of that voltage. At this time, the charging current decreases over time, but when it becomes equal to or lower than 0.2 mA, for example, charging The cutoff voltage (here, 3.5V) is set so that the remaining capacity of the storage battery does not fall below the lower limit capacity (here, 1mAh) during this repeated charging and discharging. In this way, the change in coulombic efficiency in each cycle when charging and discharging are repeated is measured.

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

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

[0065] In the above embodiment, the 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 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 collector 21 is modified to form the fine protrusions 22 on the surface of the copper foil. Specifically, as shown in FIG. 16, the fine protrusions 22 made of copper can be formed by irradiating the surface of the copper substrate that becomes the negative electrode collector 21 with hydrogen plasma. This is because the copper particles are knocked out from the surface of the copper substrate (negative electrode collector 21) by irradiating the surface of the negative electrode collector 21 made of a copper substrate with hydrogen plasma, and the knocked out particles are redeposited on the surface of the copper substrate and fused to the surface of the copper substrate, thereby forming the fine protrusions 22. This technology has been disclosed in JP 2022-187895, which has already been proposed by the present inventors.

[0067] In addition, various other methods and modes for forming the fine protrusions may be adopted. 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 without departing from the gist 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 number of fine protrusions formed on a surface of the negative electrode current collector; wherein metal ions that migrate from the positive electrode side via an electrolyte during charging become metal and are deposited on the fine protrusions, the fine protrusions are carbon nanostructures made of nanographene standing on the surface of the negative electrode current collector covered with an amorphous carbon layer, The method for charging and discharging a storage battery includes repeatedly charging and discharging the storage battery after charging the storage battery from an initial uncharged state to an initial charge capacity so that the fine protrusions are not exposed from the metal. [2] The method for charging and discharging a storage battery according to [1], wherein the carbon nanostructure is at least one of a carbon nanowall, a carbon nanoflake, a carbon nanoflower, a carbon nanotree, a carbon nanotube, a carbon nanocactus, and a carbon nanocord. [3] After charging from an initial uncharged state to the initial charge capacity, charging and discharging are repeated so that the remaining capacity does not fall below a specified lower limit capacity. [1] or [2] A method for charging and discharging the storage battery described above. [4] The lower limit capacity per unit area of ​​the negative electrode current collector is 0.05 mAh / cm 2 That's all. [3] A method for charging and discharging the storage battery described in claim 1. [5] The initial charge capacity per unit area of ​​the negative electrode current collector is 1.5 mAh / cm 2 That's all. [3] or [4] A method for charging and discharging the storage battery described in claim 1. [6] A storage battery module including a storage battery and a charge / discharge control unit that controls charging and discharging to the storage battery, The storage battery is configured to include a negative electrode current collector made of a metal substrate and a large number of fine protrusions formed on a surface of the negative electrode current collector, and metal ions that migrate from the positive electrode side via an electrolyte during charging become metal and are deposited on the fine protrusions; the fine protrusions are carbon nanostructures made of nanographene standing on the surface of the negative electrode current collector covered with an amorphous carbon layer, 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. [7] The carbon nanostructure is at least one of a carbon nanowall, a carbon nanoflake, a carbon nanoflower, a carbon nanotree, a carbon nanotube, a carbon nanocactus, and a carbon nanocord; [6] The storage battery module described in [8] 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 the storage battery so that the remaining capacity of the storage battery does not fall below a predetermined lower limit capacity. [6] or [7] The storage battery module described in [9] The lower limit capacity per unit area of ​​the negative electrode current collector is 0.05 mAh / cm 2 That's all. [8] The storage battery module described in

[10] The initial charge capacity per unit area of ​​the negative electrode current collector is 1.5 mAh / cm 2 That's all. [8] or [9] The storage battery module described in [Explanation of symbols]

[0070] 1. Storage battery 11 Electrolyte 2 negative electrode 21 Negative electrode current collector 22 Fine protrusions

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 a surface of the negative electrode current collector; wherein metal ions that migrate from a positive electrode side via an electrolyte during charging become metal and are deposited on the fine protrusions, the method comprising the steps of: the fine protrusions are carbon nanostructures made of nanographene standing on the surface of the negative electrode current collector covered with an amorphous carbon layer, The method for charging and discharging a storage battery includes repeatedly charging and discharging the storage battery after charging the storage battery from an initial uncharged state to an initial charge capacity so that the fine protrusions are not exposed from the metal.

2. The method for charging and discharging a storage battery according to claim 1 , wherein the carbon nanostructure is at least one of a carbon nanowall, a carbon nanoflake, a carbon nanoflower, a carbon nanotree, a carbon nanotube, a carbon nanocactus, and a carbon nanocord.

3. 3. The method for charging and discharging a storage battery according to claim 1, further comprising the step of repeating charging and discharging the storage battery after charging the storage battery from an initial uncharged state to an initial charge capacity so that the remaining capacity does not fall below a predetermined lower limit capacity.

4. 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 3 .

5. 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 4 .

6. A storage battery module including a storage battery and a charge / discharge control unit that controls charging and discharging to the storage battery, The storage battery is configured to include a negative electrode current collector made of a metal substrate and a large number of fine protrusions formed on a surface of the negative electrode current collector, and metal ions that migrate from the positive electrode side via an electrolyte during charging become metal and are deposited on the fine protrusions; the fine protrusions are carbon nanostructures made of nanographene standing on the surface of the negative electrode current collector covered with an amorphous carbon layer, 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.

7. The battery module according to claim 6 , wherein the carbon nanostructure is at least one of a carbon nanowall, a carbon nanoflake, a carbon nanoflower, a carbon nanotree, a carbon nanotube, a carbon nanocactus, and a carbon nanocord.

8. 8. The storage battery module according to claim 6, 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 .

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