Lithium-ion secondary battery control system, charge / discharge control method, and device equipped with the same

Abstract

To provide a lithium ion secondary battery control system capable of reducing a cycle deterioration of a lithium ion secondary battery, and a device equipped with the system.SOLUTION: A lithium ion secondary battery control system for controlling charging and discharging of a lithium ion secondary battery, includes a detection unit that detects a charge condition of the lithium ion secondary battery, and a computation processing unit. When determining that there is no battery remaining quantity from a charge condition obtained from the detection unit, the computation processing unit calculates a first DC resistance during a charging time subsequent to the no battery remaining quantity condition by using data obtained from the detection unit. When determining a fully-charged condition from the charge condition obtained from the detection unit, the computation processing unit calculates a second DC resistance during a discharging time subsequent to the fully-charged condition by using the data obtained from the detection unit, calculates a DC resistance ratio of the first DC resistance and the second resistance, and performs deterioration determination by using the DC resistance ratio.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a lithium ion secondary battery control system and a device equipped with the same. [Background technology]

[0002] Due to their high energy density, lithium-ion secondary batteries have attracted attention as batteries for a variety of applications, from electrical equipment to vehicles such as railways and automobiles, and even for storing and supplying electricity generated by solar or wind power generation systems. For example, when lithium-ion secondary batteries (hereinafter referred to as "batteries") are installed in electrical equipment, they can significantly improve the mobility of the electrical equipment. Furthermore, when installed in automobiles, such vehicles include zero-emission electric vehicles (EVs) that do not have engines, hybrid electric vehicles (EVs) that are equipped with both engines and secondary batteries, and plug-in hybrid electric vehicles (EVs) that are charged directly from the grid. Lithium-ion secondary batteries are also expected to be used as stationary energy storage systems to supply power in emergencies when the power grid is interrupted.

[0003] For these diverse applications, batteries are required to have excellent durability, such as a low rate of decrease in rechargeable battery capacity even at high ambient temperatures or after repeated charge-discharge cycles, and a high battery retention of capacity (SOHQ) over the long term.

[0004] However, lithium-ion secondary batteries lose their capacity due to cycle degradation caused by exposure to high temperatures or repeated charge-discharge cycles. This capacity loss is more pronounced when exposed to high voltages or when subjected to charge-discharge cycles over a wide voltage range or large currents. Furthermore, this capacity loss varies depending on the environment, usage, and charge-discharge method of the device or system in which the lithium-ion secondary battery is installed.

[0005] A prior art document in this technical field is Patent Document 1. Patent Document 1 discloses that a deterioration characteristic value related to the degree of capacity deterioration of a secondary battery after a predetermined time has elapsed is compared with a threshold value to determine whether or not switching of the charging voltage is necessary, and the charging control circuit sets a second charging voltage value lower than the first charging voltage value in the charger when it determines that the deterioration characteristic value has reached the threshold value. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-109840 Summary of the Invention [Problem to be solved by the invention]

[0007] The method described in Patent Document 1 changes the charging conditions after determining that the full charge capacity, which is a degradation characteristic value related to cycle degradation caused by repeated charge / discharge cycles over a predetermined period of time, has reached a threshold value. Therefore, the likelihood of extending the battery life is low, which is an issue.

[0008] In view of the above problems, the present invention aims to provide a lithium ion secondary battery control system, a charge / discharge control method, and a device equipped with the same, which can limit charge / discharge conditions before the capacity retention rate of a lithium ion secondary battery falls below a predetermined threshold, thereby reducing cycle deterioration. [Means for solving the problem]

[0009] One example of the present invention is a lithium ion secondary battery control system that controls the charging and discharging of a lithium ion secondary battery, and includes a detection unit that detects the charging state of the lithium ion secondary battery, and an arithmetic processing unit. When the arithmetic processing unit determines that there is no remaining battery power from the charging state from the detection unit, it calculates a first DC resistance during charging from an empty state using data from the detection unit, and when the arithmetic processing unit determines that the battery is fully charged from the charging state from the detection unit, it calculates a second DC resistance during discharging from the fully charged state using data from the detection unit, calculates a DC resistance ratio between the first DC resistance and the second DC resistance, and uses the DC resistance ratio to determine deterioration. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a lithium ion secondary battery control system, a charge / discharge control method, and an apparatus equipped with the same, which are capable of reducing cycle deterioration of a lithium ion secondary battery. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a graph showing the change in capacity retention rate over charge-discharge cycles under various cycle test conditions that are the basis for the examples. [Figure 2] FIG. 2 is a diagram showing the conditions of each cycle test in FIG. 1. [Figure 3] FIG. 1 is a graph showing the change in DC resistance at full charge with respect to charge / discharge cycles under various cycle test conditions that are the premise of the examples. [Figure 4] FIG. 10 is a diagram showing the battery capacity dependency of DC resistance before and after a cycle test in an example. [Figure 5] FIG. 1 is a graph showing the change in the ratio of the DC resistance during charging with no remaining battery charge to the DC resistance during discharging in a fully charged state with respect to the charge-discharge cycles under each cycle test condition in Examples. [Figure 6] 1 is a configuration diagram of a lithium ion secondary battery control system according to an embodiment. [Figure 7] FIG. 10 is a diagram showing experimental results of a cycle test in an example. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the embodiment is not limited to the following content, and can be arbitrarily modified and implemented within the scope of the gist of the present invention. [Example]

[0013] First, a conventional method for detecting the degradation state of a lithium-ion secondary battery, which is the premise of this embodiment, will be described. SOH (States of Health) is a value that indicates the degradation state of a battery. When a battery deteriorates, changes in characteristics generally occur, such as an increase in internal resistance or a decrease in the capacity at full charge (capacity retention rate) compared to the initial state. A common method is to calculate the SOH from these characteristics that have changed due to deterioration or the ratio of these changed characteristics to the initial characteristics. The calculated SOH can be reflected in other calculations to detect the battery state taking degradation information into account, and can also be used as an index for determining the battery's lifespan. Examples of the degradation state include changes in the capacity retention rate and DC resistance.

[0014] However, SOH is a transition from the past to the present when the equipment is in use, and while it is possible to track the user's usage environment history of the equipment, it is not possible to determine whether accelerated deterioration will occur under future usage environments.

[0015] As described above, a conventional method for detecting the degradation state of a battery is to evaluate the degradation characteristics under standard usage conditions in advance, and determine that degradation has occurred when it is determined that the capacity retention rate, which is related to cycle degradation caused by repeated charge-discharge cycles over a predetermined period of time, falls below a preset threshold. After the degradation state is detected, subsequent degradation can be reduced by changing the charging conditions, such as setting a lower end-of-charge voltage.

[0016] FIG. 1 shows the change in capacity retention rate over charge / discharge cycles under various cycle test conditions, which are the premise of this example. The cycle test conditions shown in FIG. 1 are also shown in FIG. 2. As shown in FIG. 2, the cycle test conditions are varied by changing the ambient temperature, charge rate, discharge rate, upper limit voltage, and number of test cycles. Here, the charge / discharge rate refers to the magnitude of the current when a certain battery is energized. When a certain battery is discharged from a fully charged state at a certain current, the current value at which the battery is completely discharged in one hour (the state of charge (SOC) reaches 0%) is defined as 1 C.

[0017] In Figure 1, under cycle test conditions Cy#5 and Cy#9, it can be observed that as cycle degradation caused by repeated charge / discharge cycles progresses, battery degradation, i.e., the decline in capacity retention, accelerates. This degradation is significantly affected by the battery's charge / discharge environment, which in turn is significantly influenced by the user's usage patterns of the device in which the battery is installed.

[0018] Meanwhile, Figure 3 shows the change in DC resistance at full charge with respect to the charge / discharge cycles under each cycle test condition that is the premise of this example. The cycle test conditions are as shown in Figure 2. Figure 3 shows that the DC resistance increases with the number of cycles of the battery, i.e., with increased degradation, but does not show any accelerated degradation as seen in Figure 1.

[0019] FIG. 4 shows the battery capacity dependence of DC resistance before and after the cycle test in this example. FIG. 4 shows the results for cycle test condition Cy#9, with the open circles representing the results before the cycle test and the closed circles representing the results after 600 cycles, when the capacity retention rate had dropped to 60%. As shown in FIG. 4, the cycle test resulted in an overall increase in DC resistance and a decrease in battery capacity. Here, attention is focused on the shape of the graph in FIG. 4. It can be seen that the shape on the right side, where the state of charge is 0% (SOC 0%), is almost the same before and after the cycle test, with a parallel shift, whereas the shape on the left side, where the state of charge is 100% (SOC 100%), changes significantly.

[0020] Therefore, in this embodiment, the ratio of the DC resistance at a charging rate of 0% to the DC resistance at a charging rate of 100% is calculated, and this DC resistance ratio is used as an index for determining deterioration diagnosis, and for example, this DC resistance ratio is used to determine deterioration. Furthermore, this DC resistance ratio is used as a trigger for changing the charge / discharge conditions. Details of this will be explained below.

[0021] 5 is a graph showing the change in the ratio of the DC resistance during charging with no remaining battery power (0% SOC) to the DC resistance during discharging with full charge (100% SOC) for each charge-discharge cycle under each cycle test condition in this example. The cycle test conditions are as shown in FIG.

[0022] In Figure 5, for cycle test conditions Cy#5 and Cy#9, where the capacity retention rate accelerated and deteriorated midway through the cycles in Figure 1, the DC resistance ratio dropped significantly at 100 cycles. In contrast, for cycle test conditions Cy#1 and Cy#2, where the capacity retention rate showed moderate deterioration over time in Figure 1, the DC resistance ratio dropped gradually. On the other hand, for cycle test condition Cy#3, where the capacity retention rate showed little change in Figure 1, the DC resistance ratio remained almost constant.

[0023] Let's compare Figures 1 and 5. The capacity retention curve (SOH) shown in Figure 1, which is the conventional method, allows us to estimate battery life under conditions where accelerated degradation, such as inflection points, does not occur. By implementing control to suppress battery degradation when a set threshold is reached, we can expect to extend battery life to some extent. However, under conditions where rapid acceleration occurs, such as cycle test conditions Cy#5 and Cy#9, significant degradation is already present when the threshold is reached, and this method fails to extend battery life. On the other hand, by using the DC resistance ratios at 0% and 100% charge rates shown in Figure 5, we can detect cycle conditions where rapid degradation occurs at an early stage. For example, while signs of degradation appear after 300 cycles in Figure 1, signs of degradation can be detected around 100 cycles in Figure 5.

[0024] Next, a lithium ion secondary battery control system for controlling charging and discharging of the lithium ion secondary battery in this embodiment will be described.

[0025] FIG. 6 is a configuration diagram of a lithium-ion secondary battery control system according to this embodiment. In FIG. 6, a lithium-ion secondary battery control system 101 includes an arithmetic processing unit 107 that performs various calculations, a charge / discharge control circuit 105 that serves as an analog interface, a current measurement unit 110, a voltage measurement unit 111, and a switch 112. The arithmetic processing unit 107 is a signal processing device, typically comprising a CPU (processor) and memory resources such as a storage device and memory. Specifically, the arithmetic processing unit 107 performs software processing to realize various functions by loading programs stored in a storage device into the memory and executing the loaded programs with the CPU. As shown in FIG. 6, the arithmetic processing unit 107 includes a degradation diagnosis unit 102, a battery state storage unit 103, and a DC resistance calculation unit 104. An external load 108 is connected to a lithium-ion secondary battery 106 via a switch 112, and a charging power source 109 for charging the battery 106 is also connected via the switch 112.

[0026] The lithium-ion secondary battery control system 101 can be installed as an external load 108 in electrical equipment, vehicles such as trains and automobiles, and even in power storage systems that store power generated by solar power generation, wind power generation, etc. For example, in electrical equipment, the system is effective in rechargeable vacuum cleaners and other devices that are subject to harsh environments for batteries. This is because rechargeable vacuum cleaners require high-rate discharge due to high power and a wide voltage range for charge / discharge cycles, from full charge to empty.

[0027] Next, a description will be given of the charge / discharge control process for the lithium ion secondary battery using the DC resistance ratios at a charging rate of 0% and a charging rate of 100% in this embodiment.

[0028] 6, first, arithmetic processing unit 107 outputs a signal to charge / discharge control circuit 105 to connect switch 112 to charging power supply 109, thereby causing current to flow through battery 106 and starting charging. Furthermore, data on the state of charge of battery 106 measured by a state-of-charge detection unit consisting of voltage measurement unit 111 and current measurement unit 110 is converted into a digital value by charge / discharge control circuit 105 and sent to arithmetic processing unit 107. As a result, arithmetic processing unit 107 performs constant-current, constant-voltage charging while monitoring the state of charge of battery 106. Then, when the data on the state of charge of battery 106 from charge / discharge control circuit 105 satisfies predetermined conditions, arithmetic processing unit 107 determines that battery 106 is fully charged and outputs a signal to charge / discharge control circuit 105 to open switch 112. Then, the calculation processing unit 107 outputs a signal to the charge / discharge control circuit 105 to connect the switch 112 to an external load, and the DC resistance calculation unit 104 calculates the DC resistance from the data of the voltage measurement unit 111 and the current measurement unit 110, determines the DC resistance when the battery is discharged from a fully charged state, and records the calculated DC resistance in the battery state memory unit 103.

[0029] Furthermore, when the calculation processing unit 107 detects that the measurement value received from the charge / discharge control circuit 105 by the voltage measurement unit 111 is a set lower limit voltage due to a decrease in the remaining battery charge caused by the external load 108, the calculation processing unit 107 determines that there is no remaining battery charge and sends a signal to the charge / discharge control circuit 105 to open the switch 112. When a start signal for the charging power supply 109 is input, the calculation processing unit 107 outputs a signal to the charge / discharge control circuit 105 to connect the switch 112 to the charging power supply, and calculates the DC resistance from the data of the voltage measurement unit 111 and the current measurement unit 110 in the DC resistance calculation unit 104, determines the DC resistance during charging from a state where there is no remaining battery charge, and records the calculated DC resistance in the battery state storage unit 103.

[0030] The deterioration diagnosis unit 102, in which the calculation processing unit 107 reads the DC resistance when the battery is empty and the DC resistance when the battery is fully charged from the battery state storage unit 103, calculates the DC resistance ratio between them, and when the DC resistance ratio becomes equal to or less than a threshold, transitions to processing to limit the charge and discharge conditions. The processing to limit the charge and discharge conditions may, for example, be processing to lower the upper limit charge voltage or processing to lower the charge and discharge current.

[0031] Here, the DC resistance of a battery is measured by loading a constant current (I) onto the battery and calculating it using Ohm's law from the voltage difference before and after the load. Specifically, if the difference between the voltage before the load and the voltage after, say, 10 seconds of load is ΔV, then DC resistance R can be expressed as R = ΔV / I, and is calculated using this formula. Therefore, strictly speaking, DC resistance when the battery is empty is not the DC resistance when the battery is empty, but the DC resistance when charging from an empty battery state (SOC 0%). Similarly, DC resistance when fully charged is not the DC resistance when fully charged, but the DC resistance when discharging from a fully charged state (SOC 100%).

[0032] The DC resistance from the fully charged state and the DC resistance from the empty state do not have to be strictly measured from the fully charged state or the empty state. For example, as shown in Fig. 4, the DC resistance from the fully charged state or the empty state after a predetermined time has elapsed may be measured within a range in which a significant difference in the left and right shapes before and after the cycle test is maintained.

[0033] Fig. 7 shows the experimental results of the cycle test in this example. In Fig. 7, Experiment 1 corresponds to cycle test condition Cy#5 in Fig. 1, and the battery was mounted in the lithium ion secondary battery control system shown in Fig. 6, charged and discharged, and the battery characteristics were evaluated by the method described below.

[0034] The battery was charged at 25°C with a current equivalent to 0.5 CA up to 4.20 V, then subjected to constant voltage charging at 4.20 V until the current reached 0.04 CA. After a 30-minute rest, the battery was discharged at a constant current equivalent to 1 CA down to 3.0 V. The discharge capacity at this time was taken as the initial capacity. The DC resistance ratio between the initial empty battery and the fully charged battery was 3.2.

[0035] Next, the battery was charged at 25°C with a current equivalent to 2.0 CA up to 4.20 V, and then constant voltage charging was performed at 4.20 V until the current reached 0.04 CA. After a 30-minute break, the battery was discharged at a constant current equivalent to 4 CA down to 3.0 V, and then the battery was left for 60 minutes.

[0036] The DC resistance ratio was determined initially and every 20 cycles. The threshold DC resistance ratio at which charge / discharge limiting control was initiated was set to 2.5. Specifically, after 100 cycles, the DC resistance ratio fell below the threshold, and charge / discharge limiting control was initiated by limiting the upper charge voltage to 4.10 V. Testing was continued from 101 to 1000 cycles. To assess capacity retention, the battery was charged at 25°C with a current equivalent to 0.5 CA up to 4.20 V every 100 cycles, followed by constant voltage charging at 4.20 V until the current reached 0.04 CA. After a 30-minute rest, the battery was discharged at a constant current equivalent to 1 CA down to 3.0 V, and the discharge capacity was measured to determine the capacity retention relative to the initial capacity. The resulting capacity retention was 80%.

[0037] Next, in Figure 7, Experiment 2 corresponds to cycle test condition Cy#9 in Figure 1, and the cycle test conditions were charging at 40°C with a current equivalent to 1.0 CA up to 4.20 V, followed by constant voltage charging at 4.20 V until the current reached 0.04 CA. After a 30-minute break, constant current discharge was performed at a constant current equivalent to 6 CA down to 3.0 V, followed by a 60-minute break.

[0038] The DC resistance ratio was determined initially and every 20 cycles, as in Experiment 1, and the threshold for the DC resistance ratio at which charge / discharge limiting control was initiated was set to 2.5. Specifically, the DC resistance ratio fell below the threshold after 40 cycles, and charge / discharge limiting control was initiated by limiting the upper charge voltage to 4.10 V, and the test was continued from the 41st cycle to the 1000th cycle. The capacity retention rate was evaluated in the same manner as in Experiment 1, and the result was a capacity retention rate of 76%.

[0039] Next, in Figure 7, Experiment 3 corresponds to cycle test condition Cy#5 in Figure 1, and the cycle test conditions were the same as those of Experiment 1: charging at 25°C with a current equivalent to 2.0 CA up to 4.20 V, followed by constant voltage charging at 4.20 V until the current reached 0.04 CA. After a 30-minute break, constant current discharge was performed at a constant current equivalent to 4 CA down to 3.0 V, followed by a 60-minute break. This cycle was repeated 1,000 times. The DC resistance ratio was not determined, and charge / discharge limit control was not performed. The resulting capacity retention rate was 59%.

[0040] Next, in Figure 7, Experiment 4 corresponds to cycle test condition Cy#9 in Figure 1. The cycle test conditions were the same as those in Experiment 2: charging at 40°C with a current equivalent to 1.0 CA up to 4.20 V, followed by constant-voltage charging at 4.20 V until the current reached 0.04 CA. After a 30-minute break, constant-current discharging was performed at a constant current equivalent to 6 CA down to 3.0 V, followed by a 60-minute break. This cycle was attempted for 1,000 cycles, but the capacity retention rate reached 60% at 600 cycles, so the test was stopped. The DC resistance ratio was not determined, and charge / discharge limit control was not performed.

[0041] As shown in Figure 7, Experiments 1 and 2, which performed DC resistance ratio determination and charge / discharge limit control based on the DC resistance ratio, completed the 1000-cycle test without showing a rapid change in capacity retention, and maintained a high capacity retention even after 1000 cycles. In contrast, Experiments 3 and 4, which did not perform DC resistance ratio determination or charge / discharge limit control, showed a rapid decrease in capacity retention around 300 to 400 cycles, indicating an increased rate of degradation, as shown in cycle test conditions Cy#5 and Cy#9 in Figure 1. As such, determination based on DC resistance ratio is more sensitive than conventional determination based on capacity retention, allowing for early detection of lithium-ion secondary battery degradation.

[0042] As described above, according to this embodiment, a detection unit is provided that detects whether a lithium-ion secondary battery is empty or fully charged, and measures the DC resistance at SOC 0% when charging from an empty state and the DC resistance at SOC 100% when discharging from a fully charged state, and performs deterioration diagnosis using the ratio of these resistances, and restricts the charge / discharge conditions when this ratio falls below a certain value. In this way, by controlling the battery charge / discharge conditions, it is possible to provide a lithium-ion secondary battery control system, a charge / discharge control method, and a device equipped with the same that can reduce cycle deterioration of the lithium-ion secondary battery and extend its lifespan.

[0043] The present invention provides a lithium-ion secondary battery control system and a device equipped with the same that can reduce cycle degradation of lithium-ion secondary batteries, thereby reducing the amount of resources required. This reduces carbon emissions and prevents global warming, contributing to the realization of the Sustainable Development Goals (SDGs), particularly item 7, energy.

[0044] Furthermore, the present invention is not limited to the above-described embodiment, and includes various modifications. For example, the above-described embodiment has been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to an embodiment having all of the described configurations. [Explanation of symbols]

[0045] 101: Lithium ion secondary battery control system, 102: Degradation diagnosis unit, 103: Battery state storage unit, 104: DC resistance calculation unit, 105: Charge / discharge control circuit, 106: Lithium ion secondary battery (battery), 107: Arithmetic processing unit, 108: External load, 109: Charging power supply, 110: Current measurement unit, 111: Voltage measurement unit, 112: Switch

Claims

1. A lithium ion secondary battery control system that controls charging and discharging of a lithium ion secondary battery, a detection unit that detects the state of charge of the lithium ion secondary battery; A calculation processing unit is provided, The arithmetic processing unit when it is determined that the battery is empty based on the charging state from the detection unit, calculating a first DC resistance during charging from an empty battery state using data from the detection unit; When the charge state detected by the detection unit is determined to be fully charged, a second DC resistance during discharge from the fully charged state is calculated using data from the detection unit; A lithium ion secondary battery control system, comprising: a DC resistance ratio between the first DC resistance and the second DC resistance; and a deterioration determination using the DC resistance ratio.

2. 2. The lithium ion secondary battery control system according to claim 1, a battery state storage unit; a switch for turning on and off the connection between the lithium ion secondary battery and the external load and the charging power source; The arithmetic processing unit When it is determined that the battery is depleted, the switch is connected to the charging power source, and the first DC resistance is calculated and recorded in the battery state storage unit; When it is determined that the battery is fully charged, the switch is connected to the external load, and the second DC resistance is calculated and recorded in the battery state storage unit; A lithium ion secondary battery control system characterized by reading the first DC resistance and the second DC resistance from the battery state memory unit, calculating the DC resistance ratio, and determining deterioration using the DC resistance ratio.

3. 2. The lithium ion secondary battery control system according to claim 1, The lithium ion secondary battery control system is characterized in that the arithmetic processing unit limits charge and discharge conditions when the DC resistance ratio is equal to or less than a threshold value.

4. 2. The lithium ion secondary battery control system according to claim 1, The lithium ion secondary battery control system is characterized in that the detection unit is a voltage measurement unit and a current measurement unit.

5. 4. The lithium ion secondary battery control system according to claim 3, The lithium ion secondary battery control system is characterized in that the restriction on the charge and discharge conditions is to lower an upper limit charge voltage.

6. 4. The lithium ion secondary battery control system according to claim 3, The lithium ion secondary battery control system is characterized in that the restriction on the charge and discharge conditions is to reduce the charge and discharge current.

7. A method for controlling charging and discharging of a lithium ion secondary battery, comprising: calculating a first DC resistance when charging the lithium ion secondary battery from an empty state and a second DC resistance when discharging the lithium ion secondary battery from a fully charged state; calculating a DC resistance ratio between the first DC resistance and the second DC resistance; A charge / discharge control method for a lithium ion secondary battery, characterized in that deterioration is determined using the DC resistance ratio.

8. 8. The method for controlling charge and discharge of a lithium ion secondary battery according to claim 7, A method for controlling charging and discharging of a lithium ion secondary battery, comprising restricting charging and discharging conditions when the DC resistance ratio is equal to or less than a threshold value.

9. 9. The method for controlling charge and discharge of a lithium ion secondary battery according to claim 8, The method for controlling charging and discharging of a lithium ion secondary battery is characterized in that the restriction of the charging and discharging conditions is performed by lowering the upper limit charging voltage or lowering the charging and discharging current.

10. An electric device equipped with the lithium ion secondary battery control system according to claim 1.

11. A rechargeable vacuum cleaner equipped with the lithium ion secondary battery control system according to claim 1.

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