JP6848775B2 - Lithium ion secondary battery system - Google Patents

Description

The present invention relates to a lithium ion secondary battery system.

A lithium ion secondary battery is a battery that can be recharged repeatedly. However, when the lithium ion secondary battery is overcharged, oxidation of the positive electrode and the like occur. As a result, the battery capacity is lowered and the internal resistance is increased, and the performance of the battery is lowered.

Therefore, conventionally, it is performed to detect that the lithium ion secondary battery is in the overcharged state and suppress the overcharge of the lithium ion secondary battery. For example, Patent Document 1 discloses that the charge rate of a lithium ion secondary battery is estimated based on the time change rate of the voltage of the lithium ion secondary battery.

Japanese Unexamined Patent Publication No. 2016-0582245 Japanese Unexamined Patent Publication No. 6-189466

However, the charge / discharge curve of a lithium ion secondary battery typically has hysteresis due to the influence of internal resistance. Therefore, when charging is performed after discharging, the voltage may rise sharply immediately after the start of charging even in a region where the charging rate is low. As a result, the rate of change in voltage with time increases, and there is a risk of erroneously detecting overcharging of the lithium ion secondary battery.

Therefore, in view of the above problems, an object of the present invention is to provide a lithium ion secondary battery system capable of accurately detecting that a lithium ion secondary battery is in an overcharged state.

In order to solve the above problems, in the present invention, a lithium ion secondary battery, a charging device for charging the lithium ion secondary battery, a voltage detecting device for detecting the voltage of the lithium ion secondary battery, and the lithium. A current detection device that detects the current flowing through the ion secondary battery, and a determination that determines whether or not the lithium ion secondary battery is in an overcharged state when the lithium ion secondary battery is charged by the charging device. When the first value obtained by differentiating the voltage with time is larger than the first threshold value and the second value obtained by differentiating the first value with time is positive, the determination unit includes a unit. Alternatively, the third value obtained by differentiating the voltage with the amount of electricity supplied to the lithium ion secondary battery is larger than the second threshold value, and the fourth value obtained by differentiating the third value with time is positive. In this case, a lithium ion secondary battery system for determining that the lithium ion secondary battery is in an overcharged state is provided.

According to the present invention, there is provided a lithium ion secondary battery system capable of accurately detecting that a lithium ion secondary battery is in an overcharged state.

FIG. 1 is a schematic view of a lithium ion secondary battery system according to the first embodiment of the present invention. FIG. 2 is a graph showing a charge / discharge curve of a lithium ion secondary battery. FIG. 3 is a graph showing the time transition of the voltage when charging is started at the point a in FIG. FIG. 4 is a graph showing the time transition of the voltage when charging is started at the point b of FIG. FIG. 5 is a graph showing the time transition of the voltage when charging is started at the point c in FIG. FIG. 6 is a graph showing the time transition of the first value and the second value calculated from the data of the broken line of FIG. FIG. 7 is a graph showing the time transition of the first value and the second value calculated from the solid line data of FIG. FIG. 8 is a graph showing the time transition of the first value and the second value calculated from the data of the broken line of FIG. FIG. 9 is a graph showing the time transition of the first value and the second value calculated from the solid line data of FIG. FIG. 10 is a graph showing the time transition of the first value and the second value calculated from the data of the broken line in FIG. FIG. 11 is a graph showing the time transition of the first value and the second value calculated from the solid line data of FIG. FIG. 12 is a flowchart showing a control routine of the overcharge determination process according to the first embodiment of the present invention. FIG. 13 is a flowchart showing a control routine for charge stop processing according to the first embodiment of the present invention. FIG. 14 is a flowchart showing a control routine of the overcharge determination process according to the second embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, similar components are given the same reference number.

<First Embodiment>
First, the first embodiment of the present invention will be described with reference to FIGS. 1 to 13.

<Configuration of lithium-ion secondary battery system>
FIG. 1 is a schematic view of a lithium ion secondary battery system according to the first embodiment of the present invention. The lithium ion secondary battery system 1 includes a lithium ion secondary battery 2. The lithium ion secondary battery 2 is a secondary battery in which a plurality of battery cells 21 are connected in series, and is also referred to as a battery pack or an assembled battery. Each battery cell 21 has a positive electrode, a negative electrode, and an electrolyte arranged between the positive electrode and the negative electrode. In each battery cell 21, lithium ions move between the positive electrode and the negative electrode via an electrolyte, so that charging and discharging are performed.

In the present embodiment, the lithium ion secondary battery 2 is an all-solid-state lithium-sulfur (LiS) battery having a bipolar structure. In this case, sulfur is used as the positive electrode material, metallic lithium is used as the negative electrode material, and a solid electrolyte such as ceramics is used as the electrolyte.

The lithium ion secondary battery system 1 further includes a charging device 3 for charging the lithium ion secondary battery 2. The charging device 3 is electrically connected to the positive electrode terminals and the negative electrode terminals at both ends of the lithium ion secondary battery 2. The charging device 3 charges the lithium ion secondary battery 2 using electric power supplied from an external power source such as a commercial power source or electric power supplied from a motor generator.

At the time of charging, a current is supplied from the charging device 3 to the lithium ion secondary battery 2, and the lithium ions move from the positive electrode to the negative electrode of each electric cell 10. As a result, the capacity of the lithium ion secondary battery 2 gradually increases. On the other hand, at the time of discharge, lithium ions move from the negative electrode to the positive electrode of each electric cell 10, and power is supplied from the lithium ion secondary battery 2 to an external load such as an electronic device such as a motor. As a result, the capacity of the lithium ion secondary battery 2 gradually decreases.

The lithium ion secondary battery system 1 further includes a voltage detection device 4, a current detection device 5, a temperature sensor 6, and a control device 7. The voltage detection device 4 is connected in parallel to the lithium ion secondary battery 2 and detects the voltage of the lithium ion secondary battery 2 which is the total voltage of each battery cell 21. The voltage detected by the voltage detection device 4 is input to the control device 7.

The current detection device 5 is connected in series with the lithium ion secondary battery 2 and detects the current flowing through the lithium ion secondary battery 2. Therefore, the current detection device 5 detects the current supplied from the charging device 3 to the lithium ion secondary battery 2 at the time of charging. The current detected by the current detection device 5 is input to the control device 7.

The temperature sensor 6 is provided in the package of the lithium ion secondary battery 2 and detects the temperature of the lithium ion secondary battery 2. The temperature sensor 6 is, for example, a thermistor or a thermocouple. The temperature detected by the temperature sensor 6 is input to the control device 7.

The control device 7 is a microcomputer including a central arithmetic unit (CPU), memories such as ROM and RAM, an input port, and an output port, and controls charging and discharging of the lithium ion secondary battery 2. At the time of charging, the control device 7 controls the charging device 3 based on the outputs of the voltage detecting device 4, the current detecting device 5, the temperature sensor 6, and the like.

<Charge / discharge curve of lithium-ion secondary battery>
FIG. 2 is a graph showing a charge / discharge curve of the lithium ion secondary battery 2. The horizontal axis of the graph shows the capacity of the lithium ion secondary battery 2, and the vertical axis of the graph shows the closed circuit voltage (CCV) of the lithium ion secondary battery 2. In the lithium ion secondary battery 2, an overvoltage due to an internal resistance causes a difference between the closed circuit voltage and the open circuit voltage (OCV). Further, the direction of the current flowing through the lithium ion secondary battery 2 is opposite between the time of charging and the time of discharging. Therefore, as shown in FIG. 2, the closed circuit voltage at the time of charging becomes higher than the closed circuit voltage at the time of discharging, and the charge / discharge curve has hysteresis. Further, since the polarization is not immediately eliminated even after charging or discharging is completed, it takes a long time for the voltage to converge to the open circuit voltage.

FIG. 3 is a graph showing the time transition of the voltage when charging is started at the point a in FIG. The solid line in the figure shows the time transition of the voltage when one battery cell 21 is overcharged, and the broken line in the figure shows the time transition of the voltage when the overcharged battery cell 21 does not exist.

In the example of FIG. 3, charging is performed after the capacity is reduced by discharging. Immediately after time t0, the voltage rises sharply due to the difference between the closed circuit voltage during discharging and the closed circuit voltage during charging, and the time change rate of the voltage gradually decreases from time t0 to time t1. After the time t1, the rate of change of the voltage with time becomes constant, and the voltage gradually increases with the lapse of the charging time. When one battery cell 21 is overcharged, the voltage suddenly rises again at time t2. This is caused by the capacity of one battery cell 21 approaching the maximum value. After that, at time t3, the rate of change in voltage with time became higher, and it is considered that one battery cell 21 was in an overcharged state.

FIG. 4 is a graph showing the time transition of the voltage when charging is started at the point b of FIG. The solid line in the figure shows the time transition of the voltage when one battery cell 21 is overcharged, and the broken line in the figure shows the time transition of the voltage when the overcharged battery cell 21 does not exist.

In the example of FIG. 4, charging is performed again after the capacity is increased by charging. Immediately after the time t0, the voltage slightly rises due to the overvoltage due to the internal resistance, and the time change rate of the voltage gradually decreases from the time t0 to the time t1. After the time t1, the rate of change of the voltage with time becomes constant, and the voltage gradually increases with the lapse of the charging time. When one battery cell 21 is overcharged, the voltage suddenly rises again at time t2. This is caused by the capacity of one battery cell 21 approaching the maximum value. After that, at time t3, the rate of change in voltage with time became higher, and it is considered that one battery cell 21 was in an overcharged state.

FIG. 5 is a graph showing the time transition of the voltage when charging is started at the point c in FIG. The solid line in the figure shows the time transition of the voltage when one battery cell 21 is overcharged, and the broken line in the figure shows the time transition of the voltage when the overcharged battery cell 21 does not exist.

In the example of FIG. 5, charging is performed after the capacity is reduced by discharging. Further, in the example of FIG. 5, the capacity at the start of charging is larger than that of the example of FIG. Immediately after time t0, the voltage rises sharply due to the difference between the closed circuit voltage during discharging and the closed circuit voltage during charging, and the time change rate of the voltage gradually decreases from time t0 to time t1. After time t1, the rate of change in voltage gradually increases, and the voltage gradually increases with the passage of charging time. When one battery cell 21 is overcharged, the voltage suddenly rises again at time t2. This is caused by the capacity of one battery cell 21 approaching the maximum value. After that, at time t3, the rate of change in voltage with time became higher, and it is considered that one battery cell 21 was in an overcharged state.

<Judgment of overcharge>
In order to suppress overcharging of the lithium ion secondary battery 2, it is necessary to accurately detect that the lithium ion secondary battery 2 is in the overcharged state regardless of the charging start position on the charge / discharge curve. By executing the program stored in the memory, the control device 7 determines whether or not the lithium ion secondary battery 2 is in the overcharged state when the lithium ion secondary battery 2 is charged by the charging device 3. It functions as a judgment unit.

The inventor of the present application has focused on the fact that the voltage rise curve immediately after the start of charging is convex upward and the voltage rise curve at the time of overcharging is convex downward as shown in FIGS. 3 to 5, and the following We have found a method for determining overcharge. In the present embodiment, in the determination unit, the first value obtained by differentiating the voltage of the lithium ion secondary battery 2 with time is larger than the first threshold value, and the second value obtained by differentiating the first value with time is positive. If, it is determined that the lithium ion secondary battery 2 is in the overcharged state. The voltage is detected by the voltage detection device 4.

The first value (ΔV / Δt) is the rate of change in voltage over time, and indicates the amount of change in voltage per unit time. The second value (Δ ² V / Δt ² ) is the rate of change of the first value over time, and indicates the amount of change of the first value per unit time. The second value is equal to the second derivative of the voltage.

FIG. 6 is a graph showing the time transition of the first value and the second value calculated from the data of the broken line of FIG. That is, FIG. 6 shows the time transition of the first value and the second value when charging is started at the point a of FIG. 2 and the overcharged battery cell 21 does not exist. FIG. 7 is a graph showing the time transition of the first value and the second value calculated from the solid line data of FIG. That is, FIG. 7 shows the time transition of the first value and the second value when charging is started at the point a in FIG. 2 and one battery cell 21 is overcharged. In FIGS. 6 and 7, the alternate long and short dash line indicates the first value, and the solid line indicates the second value.

In the example of FIG. 6, the first value decreases from time t0 to time t1 and becomes constant after time t1. On the other hand, the second value becomes negative from time t0 to time t1 and becomes zero after time t1. In the example of FIG. 7, the first value decreases from time t0 to time t1, becomes constant from time t1 to time t2, increases after time t2, and exceeds the first threshold value Th1 at time t3. On the other hand, the second value becomes negative from time t0 to time t1, becomes zero from time t1 to time t2, and becomes positive after time t2.

Immediately after the time t0 in FIGS. 6 and 7, the first value is larger than the first threshold value Th1. However, the second value is negative. Therefore, it is determined that the lithium ion secondary battery 2 is not in the overcharged state. On the other hand, at time t3 in FIG. 7, the first value is larger than the first threshold Th1 and the second value is positive. Therefore, it is determined that the lithium ion secondary battery 2 is in the overcharged state.

FIG. 8 is a graph showing the time transition of the first value and the second value calculated from the data of the broken line of FIG. That is, FIG. 8 shows the time transition of the first value and the second value when charging is started at the point b of FIG. 2 and the overcharged battery cell 21 does not exist. FIG. 9 is a graph showing the time transition of the first value and the second value calculated from the solid line data of FIG. That is, FIG. 9 shows the time transition of the first value and the second value when charging is started at the point b of FIG. 2 and one battery cell 21 is overcharged. In FIGS. 8 and 9, the alternate long and short dash line indicates the first value, and the solid line indicates the second value.

In the example of FIG. 8, the first value decreases from time t0 to time t1 and becomes constant after time t1. On the other hand, the second value becomes negative from time t0 to time t1 and becomes zero after time t1. In the example of FIG. 9, the first value decreases from time t0 to time t1, becomes constant from time t1 to time t2, increases after time t2, and exceeds the first threshold value Th1 at time t3. On the other hand, the second value becomes negative from time t0 to time t1, becomes zero from time t1 to time t2, and becomes positive after time t2.

In FIG. 8, the first value is smaller than the first threshold Th1 and the second value is negative or zero. Therefore, it is determined that the lithium ion secondary battery 2 is not in the overcharged state. On the other hand, at time t3 in FIG. 9, the first value is larger than the first threshold Th1 and the second value is positive. Therefore, it is determined that the lithium ion secondary battery 2 is in the overcharged state.

FIG. 10 is a graph showing the time transition of the first value and the second value calculated from the data of the broken line in FIG. That is, FIG. 10 shows the time transition of the first value and the second value when charging is started at the point c of FIG. 2 and the overcharged battery cell 21 does not exist. FIG. 11 is a graph showing the time transition of the first value and the second value calculated from the solid line data of FIG. That is, FIG. 11 shows the time transition of the first value and the second value when charging is started at the point c in FIG. 2 and one battery cell 21 is overcharged. In FIGS. 10 and 11, the alternate long and short dash line indicates the first value, and the solid line indicates the second value.

In the example of FIG. 10, the first value decreases from time t0 to time t1 and gradually increases after time t1. On the other hand, the second value becomes negative from time t0 to time t1 and becomes positive after time t1. In the example of FIG. 11, the first value decreases from time t0 to time t1, increases from time t1 to time t2, increases sharply after time t2, and exceeds the first threshold Th1 at time t3. .. On the other hand, the second value becomes negative from time t0 to time t1, becomes positive from time t1 to time t2, and becomes a larger positive value after time t2.

Immediately after the time t0 in FIGS. 10 and 11, the first value is larger than the first threshold value Th1. However, the second value is negative. Therefore, it is determined that the lithium ion secondary battery 2 is not in the overcharged state. Further, at time t1 to time t2 in FIGS. 10 and 11, the second value is positive. However, the first value is smaller than the first threshold Th1. Therefore, it is determined that the lithium ion secondary battery 2 is not in the overcharged state. On the other hand, at time t3 in FIG. 11, the first value is larger than the first threshold Th1 and the second value is positive. Therefore, it is determined that the lithium ion secondary battery 2 is in the overcharged state.

Therefore, according to the determination method in the present embodiment, it is possible to suppress erroneous detection of overcharge when charging is performed after discharging, and it is possible to accurately determine that the lithium ion secondary battery is in the overcharged state. Can be detected.

Further, the control device 7 sets the upper limit value of the charge rate (SOC: State Of Charge) of the lithium ion secondary battery 2 by executing the program stored in the memory, and the charge rate reaches the upper limit value. Then, it functions as a charging stop unit for stopping the charging of the lithium ion secondary battery 2. When it is determined that the lithium ion secondary battery 2 is in the overcharged state, the charging stop unit stops charging the lithium ion secondary battery 2 and updates the upper limit of the charging rate to the current charging rate. .. As a result, it is possible to prevent the lithium ion secondary battery 2 from being overcharged again. The charge rate SOC is the ratio of the current capacity of the lithium ion secondary battery 2 to the maximum capacity of the lithium ion secondary battery 2 in the initial state.

<Overcharge judgment processing>
Hereinafter, the control executed by the lithium ion secondary battery system 1 will be described with reference to the flowcharts of FIGS. 12 and 13. FIG. 12 is a flowchart showing a control routine of the overcharge determination process according to the first embodiment of the present invention. This control routine is repeatedly executed by the control device 7. The control device 7 functions as a determination unit by executing this control routine.

First, in step S101, it is determined whether or not the lithium ion secondary battery 2 is being charged. If it is determined that the lithium ion secondary battery 2 is not being charged, this control routine ends. On the other hand, if it is determined that the lithium ion secondary battery 2 is being charged, this control routine proceeds to step S102.

In step S102, the voltage V of the lithium ion secondary battery 2 is acquired. The voltage V is detected by the voltage detection device 4.

Next, in step S103, the first value A1 (ΔV / Δt) and the second value A2 (Δ ² V / Δt ² ) are calculated. Here, the first value A1 is calculated by dividing the amount of change ΔV (ΔV = V (t + Δt) −V (t)) of the voltage V in the minute time Δt by the minute time Δt. The second value A2 is calculated by dividing the amount of change ΔA1 (ΔA1 = A1 (t + Δt) −A1 (t)) of the first value A1 in the minute time Δt by the minute time Δt.

Then, in step S104, it is determined whether or not the first value A1 is larger than the first threshold Th1. The first threshold Th1 is experimentally or theoretically predetermined and is a value greater than zero. When it is determined that the first value A1 is equal to or less than the first threshold value Th1, the control routine ends. On the other hand, when it is determined that the first value A1 is larger than the first threshold value Th1, the control routine proceeds to step S105.

In step S105, it is determined whether or not the second value A2 is positive. When it is determined that the second value A2 is zero or less, this control routine ends. On the other hand, if it is determined that the second value A2 is positive, the control routine proceeds to step S106.

In step S106, it is determined that the lithium ion secondary battery 2 is in the overcharged state. Then, in step S107, the overcharge flag Foc is set to 1. The initial value of the overcharge flag Foc is zero. After step S107, this control routine ends.

<Charging stop processing>
FIG. 13 is a flowchart showing a control routine for charge stop processing according to the first embodiment of the present invention. This control routine is repeatedly executed by the control device 7. The control device 7 functions as a charging stop unit by executing this control routine.

First, in step S201, it is determined whether or not the charging / discharging of the lithium ion secondary battery 2 is stopped. When it is determined that the charging / discharging of the lithium ion secondary battery 2 is stopped, this control routine proceeds to step S202. In step S202, the voltage V of the lithium ion secondary battery 2, the current I flowing through the lithium ion secondary battery 2, and the temperature T of the lithium ion secondary battery 2 are acquired. The voltage V is detected by the voltage detection device 4, the current I is detected by the current detection device 5, and the temperature T is detected by the temperature sensor 6.

Next, in step S203, the initial value SOCin of the charge rate is calculated. The initial value SOCin is an estimated value of the charging rate before charging is started. First, the internal resistance is calculated from the temperature T using a map that describes the relationship between the internal resistance and the temperature T. Next, the value obtained by multiplying the internal resistance by the current I is calculated as an overvoltage. After the charging is stopped, the value obtained by subtracting the overvoltage from the voltage V is calculated as the open circuit voltage. On the other hand, after the discharge is stopped, the value obtained by adding the overvoltage to the voltage V is calculated as the open circuit voltage. Next, the charge rate is calculated from the open circuit voltage using the map in which the relationship between the charge rate and the open circuit voltage is described, and the calculated charge rate is set to the initial value SOCin. Each map is stored in a memory (for example, ROM) of the control device 7. After step S203, this control routine ends.

On the other hand, if it is determined in step S201 that the lithium ion secondary battery 2 is being charged or discharged, this control routine proceeds to step S204. In step S204, it is determined whether or not the lithium ion secondary battery 2 is being charged. If it is determined that the lithium ion secondary battery 2 is not being charged, this control routine ends. On the other hand, if it is determined that the lithium ion secondary battery 2 is being charged, this control routine proceeds to step S205.

In step S205, the current I flowing through the lithium ion secondary battery 2 is acquired. The current I is detected by the current detection device 5. Next, in step S206, the current charge rate SOCcu of the lithium ion secondary battery 2 is calculated. The amount of increase in SOC after the start of charging is calculated based on the integrated value (ΣI) of the current I, and the value obtained by adding the amount of increase in SOC to the initial value SOCin is set in the current charging rate SOCcu.

Next, in step S207, it is determined whether or not the overcharge flag Foc is 1. If it is determined that the overcharge flag Foc is zero, the control routine proceeds to step S208. In step S208, it is determined whether or not the current charge rate SOCcu is equal to or higher than the upper limit value SOCup of the charge rate. When it is determined that the current charge rate SOCcu is lower than the upper limit value SOCup, this control routine ends.

On the other hand, if it is determined in step S207 that the overcharge flag Foc is 1, the control routine proceeds to step S209. In step S209, the upper limit value SOCup is updated to the current SOCcu, and the overcharge flag Foc is set to zero. The initial value of the upper limit value SOCup is, for example, 100%.

Then, in step S210, charging of the lithium ion secondary battery 2 is stopped. Specifically, the current supply from the charging device 3 to the lithium ion secondary battery 2 is stopped. After step S210, this control routine ends.

If it is determined in step S208 that the current charge rate SOCcu is equal to or greater than the upper limit value SOCup, the control routine proceeds to step S210. In step S210, charging of the lithium ion secondary battery 2 is stopped. After step S210, this control routine ends.

If a sufficient time has passed since the charging / discharging of the lithium ion secondary battery 2 was stopped, the voltage V may be set as the open circuit voltage in step S203.

<Second embodiment>
The configuration and control of the lithium ion secondary battery system in the second embodiment are basically the same as those in the lithium ion secondary battery system in the first embodiment, except for the points described below. Therefore, the second embodiment of the present invention will be described below focusing on parts different from the first embodiment.

In vehicles that use the lithium-ion secondary battery 2 as the power source for the motor (hybrid vehicle (HV), plug-in hybrid vehicle (PHV), electric vehicle (EV), etc.), the lithium-ion secondary battery 2 is used by regenerative energy or the like. It will be charged. In this case, the current supplied to the lithium ion secondary battery 2 may fluctuate during charging. The amount of change in voltage during charging is affected by the amount of change in current. Further, when one or more battery cells 21 are in an overcharged state, the amount of change in the voltage of the lithium ion secondary battery 2 becomes large with respect to the amount of change in the amount of electricity supplied to the lithium ion secondary battery 2.

Therefore, in the second embodiment, the determination unit determines that the third value obtained by differentiating the voltage of the lithium ion secondary battery 2 with the amount of electricity supplied to the lithium ion secondary battery 2 is larger than the second threshold value. When the fourth value obtained by differentiating the third value with time is positive, it is determined that the lithium ion secondary battery 2 is in the overcharged state. The voltage is detected by the voltage detection device 4. The amount of electricity is calculated by integrating the time with the current detected by the current detection device 5.

The third value (ΔV / ΔQ) indicates the amount of change in voltage per unit amount of electricity. The fourth value (Δ (ΔV / ΔQ) / Δt) is the rate of change of the third value over time, and indicates the amount of change of the third value per unit time.

<Overcharge judgment processing>
FIG. 14 is a flowchart showing a control routine of the overcharge determination process according to the second embodiment of the present invention. This control routine is repeatedly executed by the control device 7. The control device 7 functions as a determination unit by executing this control routine.

First, in step S301, it is determined whether or not the lithium ion secondary battery 2 is being charged. If it is determined that the lithium ion secondary battery 2 is not being charged, this control routine ends. On the other hand, if it is determined that the lithium ion secondary battery 2 is being charged, this control routine proceeds to step S302.

In step S302, the voltage V of the lithium ion secondary battery 2 and the current I flowing through the lithium ion secondary battery 2 are acquired. The voltage V is detected by the voltage detection device 4, and the current I is detected by the current detection device 5.

Next, in step S303, the third value A3 (ΔV / ΔQ) and the fourth value A4 (Δ (ΔV / ΔQ) / Δt) are calculated. Here, the third value A3 is the change amount ΔV (ΔV = V (t + Δt) −V (t)) of the voltage V in the minute time Δt and the change amount ΔQ (ΔQ = Q (ΔQ = Q)) of the electric energy Q in the minute time Δt. It is calculated by dividing by t + Δt) −Q (t)). Further, the fourth value A4 is calculated by dividing the amount of change ΔA3 (ΔA3 = A3 (t + Δt) −A3 (t)) of the third value A3 in the minute time Δt by the minute time Δt.

Then, in step S304, it is determined whether or not the third value A3 is larger than the second threshold Th2. The second threshold Th2 is experimentally or theoretically predetermined and is a value greater than zero. When it is determined that the third value A3 is equal to or less than the second threshold value Th2, this control routine ends. On the other hand, when it is determined that the third value A3 is larger than the second threshold value Th2, the control routine proceeds to step S305.

In step S305, it is determined whether or not the fourth value A4 is positive. When it is determined that the fourth value A4 is equal to or less than zero, this control routine ends. On the other hand, if it is determined that the fourth value A4 is positive, the control routine proceeds to step S306.

In step S306, it is determined that the lithium ion secondary battery 2 is in the overcharged state. Then, in step S307, the overcharge flag Foc is set to 1. The initial value of the overcharge flag Foc is zero. After step S307, the control routine ends.

In the second embodiment as well, the control routine for the charge stop process of FIG. 13 is executed in the same manner as in the first embodiment.

<Other Embodiments>
Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and modifications can be made within the scope of the claims. For example, if lithium ions can be transferred between the electrodes and the charge / discharge curve has hysteresis, any material can be used as the positive electrode, the negative electrode, and the electrolyte.

However, when sulfur is used as the positive electrode material or silicon is used as the negative electrode material, the hysteresis of the charge / discharge curve becomes large, and the time for the voltage to converge to the open circuit voltage after discharge becomes long. Therefore, it is particularly effective to apply the present invention to a lithium ion secondary battery in which sulfur is used as the positive electrode material or a lithium ion secondary battery in which silicon is used as the negative electrode material.

1 Lithium-ion secondary battery system 2 Lithium-ion secondary battery 3 Charging device 4 Voltage detection device 5 Current detection device 7 Control device

Claims (1)

Lithium-ion secondary battery and
A charging device for charging the lithium ion secondary battery and
A voltage detection device that detects the voltage of the lithium-ion secondary battery, and
A current detection device that detects the current flowing through the lithium ion secondary battery, and
A determination unit that determines whether or not the lithium ion secondary battery is in an overcharged state when the lithium ion secondary battery is charged by the charging device .
A charging stop unit for setting an upper limit value of the charging rate of the lithium ion secondary battery and stopping charging of the lithium ion secondary battery when the charging rate reaches the upper limit value is provided.
When the first value obtained by differentiating the voltage with time is larger than the first threshold value and the second value obtained by differentiating the first value with time is positive, the determination unit determines the voltage. When the third value differentiated by the amount of electricity supplied to the lithium ion secondary battery is larger than the second threshold value and the fourth value obtained by differentiating the third value with time is positive, the lithium is said. Judging that the ion secondary battery is overcharged,
When it is determined that the lithium ion secondary battery is in an overcharged state, the charging stop unit stops charging the lithium ion secondary battery and updates the upper limit value to the current charging rate . Lithium-ion secondary battery system.

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