JP7669001B2 - Battery charge/discharge method and battery module - Google Patents

Description

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

For example, various technologies have been developed to increase the storage capacity of lithium-ion secondary batteries installed in 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 that uses 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 or release lithium ions in excess of this amount. Therefore, there is a limit to how much energy density can be improved.

In addition, in recent years, lithium ion secondary batteries (hereinafter referred to as "lithium metal secondary batteries") that use lithium metal as the negative electrode material have been developed. Lithium metal secondary batteries are thought to be capable of achieving a relatively high energy density.

However, lithium metal secondary batteries have the problem that lithium metal dendrites tend to grow easily. In other words, there is concern that dendrites may cause a short circuit between the positive and negative electrodes.

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 multiple protrusions are provided on the surface of the current collector, and lithium can be deposited on the protrusions.

Patent No. 2668678 JP 2022-187895 A

However, in a storage battery that has numerous fine protrusions formed on the surface of the negative electrode current collector and allows lithium ions to be deposited 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 this problem is not limited to lithium ion secondary batteries, but may also occur in other storage batteries that have the above-mentioned negative electrode structure.

The present invention was made in consideration of these problems, and aims to provide a method for charging and discharging a storage battery and a storage battery module that can suppress the decrease in battery capacity.

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,
The method for charging and discharging a storage battery includes repeatedly charging and discharging the battery after charging from an initial uncharged state to an initial charge capacity so that the fine protrusions are not exposed from the metal .

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 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 in a storage battery module that 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 .

In the method of 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. This makes it possible to suppress the decrease in the battery capacity of the storage battery.

In the above 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 repeat charging and discharging so that the fine protrusions are not exposed from the metal. This makes it possible to suppress a decrease in the battery capacity of the storage battery.

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 are capable of suppressing a decrease in battery capacity .

FIG. 2 is a schematic diagram of a storage battery according to the first embodiment. 3 is a schematic diagram of a fine protrusion in the first embodiment. FIG. 4 is a scanning electron microscope photograph of the fine protrusions in the first embodiment. FIG. 4 is a schematic diagram showing deposition of lithium on a negative electrode during charging in the first embodiment. FIG. 4 is a schematic diagram showing the release of lithium from a negative electrode during discharge in the first embodiment. Schematic diagram of a storage battery in its initial or fully discharged state. FIG. 2 is an explanatory diagram illustrating how lithium is deposited on a negative electrode during charging. 4 is a scanning electron microscope photograph showing a state in which lithium is precipitated on a negative electrode of a charged storage battery in the first embodiment. 4 is a diagram showing an example of a charge/discharge pattern of a storage battery in the first embodiment (charge/discharge pattern 2 in an experimental example). 5 is a diagram showing another example of a charge/discharge pattern of the storage battery in the first embodiment. 5 is a diagram showing yet another example of a charge/discharge pattern of the storage battery in the first embodiment. FIG. 4 is a block diagram of the storage battery module during charging in the first embodiment. FIG. 4 is a block diagram of the storage battery module during discharging in the first embodiment. 1 is a diagram showing a charge/discharge pattern 1 in an experimental example. 1 is a graph showing the measurement results of changes in Coulombic efficiency in an experimental example. Schematic diagram of a negative electrode structure of a storage battery in a modified form.

In the above-mentioned method for charging and discharging a storage battery or the above-mentioned 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. This makes it possible to suppress the decrease in the battery capacity of the storage battery.

The lower limit capacity per unit area of the negative electrode current collector may be set to 0.05 mAh/cm ² or more. In this case, a decrease in the battery capacity of the storage battery can be effectively suppressed.

The initial charge capacity per unit area of the negative electrode current collector can be 1.5 mAh/ ^cm2 or more. In this case, the discharge capacity after the initial charge can be sufficiently secured. 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.

The fine protrusions can be carbon nanostructures made of nanographene that stand upright on the surface of the negative electrode current collector. In this case, the performance of the storage battery becomes more stable, and durability and temperature characteristics are likely to be improved.

The fine protrusions can also be made of the same material as the negative electrode current collector. In this case, there is no need for a process to deposit a new material, which has a significant cost advantage.

The micro-projections may have a protruding height from the negative electrode current collector of, for example, about 0.1 to 30 μm. The distance between adjacent micro-projections may be, for example, about 0.1 to 30 μm.

(Embodiment 1)
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for charging and discharging a storage battery and a storage battery module will be described with reference to FIGS.
The method for charging and discharging a storage battery according to the present 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.

In the method of charging and discharging the storage battery 1 of this embodiment, as shown in Figures 4, 5, and 9 to 11 described below, 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. 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.

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 therebetween. 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.

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.

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.

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 ₂ ), LiNiCoMnO ₂ (Ni:CO:Mn=8:1:1 (CM-811), lithium manganate (LMO), lithium nickel oxide (NCA), lithium iron phosphate (LFP), or the like.

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 made 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.

Figure 2 shows a schematic configuration of the micro-projections 22 made of carbon nanostructures. A large number of micro-projections 22 are erected over the entire surface of the negative electrode current collector 21. The carbon nanostructure constituting each micro-projection 22 has a multi-layer structure in which a plurality of (e.g., 5 to 10 layers) of nanographene 221 are stacked in the thickness direction. Nanographene 221 is a sheet-like substance having a thickness of one carbon atom, which is composed of a six-membered carbon ring structure, that is, a hexagonal lattice structure with carbon atoms as vertices. Each micro-projection 22 is constituted by a carbon nanostructure in which the sheet-like nanographene 221 is stacked in the thickness direction. A large number of micro-projections 22 are formed on the surface of the negative electrode current collector 21 with the thickness direction of the nanographene 221 intersecting with the normal direction of the surface of the negative electrode current collector 21. In this embodiment, the thickness of the micro-projections 22 (wall thickness) is, for example, about 2 to 30 nm, and the distance between adjacent micro-projections 22 is, for example, about 20 to 1000 nm. The height of the micro-projections 22 is, for example, about 0.1 to 30 μm. The carbon nanostructure is conductive.

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 viewed from the protruding direction of the fine protrusions 22.

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 nanocacti, carbon nanocords, etc.

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, several tens of nm, and are formed by the reaction of the electrolyte 11 with an electrolyte, Li compounds, Li ions, etc. 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.

Next, the battery reaction during charging and discharging of the storage battery 1 will be described.
The chemical reactions occurring during charging and discharging in 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.
LiCoO ₂ ⇔ Li _1-x CoO ₂ + xLi ⁺ + xe ^- (1)

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

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 ⁺ ) move from the positive electrode 3 to the negative electrode 2, and lithium metal is precipitated on the negative electrode 2. During discharging, as shown in Fig. 5, the lithium metal precipitated on the negative electrode 2 becomes lithium ions and moves to the positive electrode 3.

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 arrangement. When charging is further continued, this regular arrangement of lithium atoms piles up, and a lithium metal layer with excellent crystallinity is precipitated on the many fine protrusions 22. Since lithium metal is precipitated in an orderly manner in this way, the generation of dendrites can be prevented.

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

During discharge, as shown in FIG. 5, the lithium that has accumulated on the negative electrode 2 is released as lithium ions 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).

As shown in the experimental example described later, if the battery is discharged too much and too much lithium is released from the negative electrode 2, the decrease in battery capacity is accelerated. It is believed that the deterioration of the negative electrode 2 progresses when the fine protrusions 22 are exposed to the electrolyte 11. 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. 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.

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 account variations. In this embodiment, for example, the lower limit capacity per unit area of the negative electrode current collector 21 is preferably set to 0.05 mAh/ ^cm2 or more, and more preferably set to 0.08 mAh/ ^cm2 or more.

As shown in FIG. 9, the method of charging and discharging the storage battery 1 of this embodiment involves charging from an initial uncharged 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. Note that 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.

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/ ^cm2 or more. The first charge is performed, for example, by the manufacturer of the storage battery 1 before shipping.

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 5 mAh (3.8 mAh/cm ² ), and the lower limit capacity is 1 mAh (0.75 mAh/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 predetermined cutoff voltage (e.g., 3.5 V). This allows the battery to be discharged until the remaining capacity after discharge approaches the lower limit capacity of 1 mAh. Thereafter, charging and discharging are repeated while preventing the capacity from falling below this lower limit capacity.

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. However, the charge and discharge pattern is not limited to this. For example, the initial charge capacity can be set lower than 5 mAh, as in the charge and discharge patterns shown in FIG. 10 and FIG. 11.

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

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 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. For this purpose, 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 so as 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.

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 they are omitted here.

The charge/discharge control unit 52 is configured, for example, by 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.

The switch unit 54 is composed of, for example, a switch element capable of controlling the opening and closing of a current. The switch unit 54 is provided in 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 and discharging of the storage battery 1 is completed.

The current measurement unit 55 is, for example, configured with 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.

The voltage measurement unit 56 is, for example, configured with 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.

The storage battery module 5 configured as described above is configured so that the charge/discharge control unit 52 executes the above-mentioned charge/discharge method when charging/discharging the storage battery 1. In other words, 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.

The remaining capacity (amount of charged electricity) and charging 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.

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.

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.

The lower limit capacity per unit area of the negative electrode current collector 21 is set to be equal to or greater than 0.05 mAh/cm ^2. This makes it possible to effectively suppress a decrease in the battery capacity of the storage battery 1.

The initial charge capacity per unit area of the negative electrode current collector 21 is set to 1.5 mAh/cm ² or more, thereby making it possible to ensure a sufficient discharge capacity after the initial charge.

The fine protrusions 22 are made of 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 tends to improve durability, temperature characteristics, etc.

As described above, this embodiment provides a method for charging and discharging a storage battery and a storage battery module that can suppress the decrease in battery capacity.

(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.

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 is repeated so that the remaining capacity during discharging falls significantly below the lower limit capacity described above, and a case where the charge/discharge method shown in embodiment 1 (charge/discharge pattern 2 described below) was performed. Note that the configuration of the storage battery itself is the same as that shown in embodiment 1 in both cases.

As shown in Fig. 14, in charge/discharge pattern 1, the storage battery is charged to 4 mAh (3 mAh/ ^cm2 ) from its initial state (uncharged state). Here, charging is performed for 4 hours at a constant current of 1 mA (0.75 mA/ ^cm2 ), resulting in 4 mAh charging. Thereafter, discharging is performed at a constant current of 1 mA. Discharging is performed until the discharge voltage reaches the cutoff voltage of 2.0 V. This causes the storage battery to discharge until the remaining capacity after discharging is almost depleted.
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 predetermined voltage (here, 4.75 V), charging is performed at the constant voltage. At this time, the charging current decreases over time, and charging is terminated when it becomes, for example, 0.2 mA or less. In this way, the change in coulombic efficiency in each cycle when charging and discharging are repeated is measured.

As shown in FIG. 9, in the charge/discharge pattern 2, the battery is charged to 5 mAh from its initial state (uncharged state). Here, the battery is charged to 5 mAh by charging at a constant current of 1 mA for 5 hours. Then, the battery is discharged at a constant current of 1 mA for 4 hours. As a result, the remaining capacity of the battery 1 after discharge is close to 1 mAh (lower limit capacity). Then, the battery 1 is charged to 4 mAh, and then discharged until the discharge voltage reaches the cutoff voltage of 3.5 V. This alternate charging and discharging is repeated. However, as in the case of the charge/discharge pattern 1, after the charging voltage reaches a predetermined voltage (here, 4.75 V), charging is performed at the constant voltage of the voltage. At this time, the charging current decreases over time, but charging is terminated when it becomes, for example, 0.2 mA or less. In this repeated charging and discharging, 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). In this way, the change in the coulombic efficiency in each cycle when the charging and discharging are repeated is measured.

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

The results of this example confirmed that the charge/discharge method of embodiment 1 can suppress the decrease in battery capacity due to repeated charging and discharging.

In the above embodiment, a method for charging and discharging a 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.

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

In addition, various other methods and configurations for forming the fine protrusions can be used. For example, a large number of fine protrusions can be formed by depositing metal on the surface of the negative electrode current collector using electrolytic deposition.

The present invention is not limited to the above-described embodiments, and can be applied to various embodiments without departing from the spirit of the present invention.

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 a surface of the negative electrode current collector; wherein metal ions transferred 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,
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] The method for charging and discharging a storage battery according to [1] or [2], 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.
[4] The method for charging and discharging a storage battery according to [3] , wherein the lower limit capacity per unit area of the negative electrode current collector is 0.05 mAh/ ^cm2 or more.
[5] The method for charging and discharging a storage battery according to [3] or [4] , wherein the initial charge capacity per unit area of the negative electrode current collector is 1.5 mAh/ ^cm2 or more.
[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 storage battery module described in [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] The storage battery module described in [6] or [7], wherein the charge/discharge control unit is configured to charge 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 storage battery module according to [8] , wherein the lower limit capacity per unit area of the negative electrode current collector is 0.05 mAh/ ^cm2 or more.
[10] The storage battery module according to [8] or [9] , wherein the initial charge capacity per unit area of the negative electrode current collector is 1.5 mAh/ ^cm2 or more.

1 Storage battery 11 Electrolyte 2 Negative electrode 21 Negative electrode current collector 22 Fine protrusion

Claims (10)

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. 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. 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 method for charging and discharging a storage battery according to claim 3 , wherein the lower limit capacity per unit area of the negative electrode current collector is 0.05 mAh/ ^cm2 or more. 5. The method for charging and discharging a storage battery according to claim 4 , wherein the initial charge capacity per unit area of the negative electrode current collector is 1.5 mAh/ ^cm2 or more. 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. 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. 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 storage battery module according to claim 8 , wherein the lower limit capacity per unit area of the negative electrode current collector is 0.05 mAh/ ^cm2 or more. 9. The storage battery module according to claim 8 , wherein the initial charge capacity per unit area of the negative electrode current collector is 1.5 mAh/ ^cm2 or more.

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