Charge-discharge management device, charge-discharge management method, and program

Abstract

To determine the propriety of re-use and safety of lithium-ion secondary batteries.SOLUTION: A charge-discharge management device being the charge-discharge management device which manages charge and discharge of a lithium-ion secondary battery that charges power supplied from a power supply device and supplies power to a load device by discharging the charged power, and includes: a capacity calculation unit that calculates a value of a temporarily reduced battery capacity due to charge and discharge operations performed in a low-temperature environment; a speed calculation unit that calculates a speed of charge and discharge at which the lithium-ion secondary battery can be safely charged / discharged on the basis of the value calculated by the capacity calculation unit; and a speed control unit that controls the speed of charge and discharge of the lithium-ion secondary battery so as to be equal to or less than the speed calculated by the speed calculation unit.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a charge / discharge management device, a charge / discharge management method, and a program. [Background technology]

[0002] It has been known that the safety of lithium ion secondary batteries is significantly reduced when used in a low-temperature environment. In order to use lithium ion secondary batteries safely, there was a technology for determining signs of thermal runaway from the rate of temperature rise of the lithium ion secondary battery, and preventing thermal runaway by stopping charging of the lithium ion secondary battery when there are signs of thermal runaway (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-103077 A Summary of the Invention [Problem to be solved by the invention]

[0004] Even if the above-mentioned technologies are used, it is not possible to prevent the temperature rise of lithium-ion secondary batteries, and no technology has yet been found that allows lithium-ion secondary batteries to be used safely. In particular, technologies that prevent thermal runaway from the rate of temperature rise are insufficient for determining whether or not lithium-ion secondary batteries can be reused and for judging their safety.

[0005] Therefore, an object of the present invention is to provide a charge / discharge management device, a charge / discharge management method, and a program that are capable of determining whether a lithium ion secondary battery can be reused and of determining its safety. [Means for solving the problem]

[0006] (1) One aspect of the present invention is a charge / discharge management device that manages the charging and discharging of a lithium-ion secondary battery that supplies power to a load device by charging with power supplied from a power supply device and discharging the charged power. The charge / discharge management device includes a capacity calculation unit that calculates a value of a battery capacity that is temporarily reduced as a result of charging and discharging in a low temperature environment, a rate calculation unit that calculates a charge / discharge rate at which the lithium-ion secondary battery can be safely charged and discharged based on the value calculated by the capacity calculation unit, and a rate control unit that controls the charge / discharge rate of the lithium-ion secondary battery so that the charge / discharge rate is equal to or lower than the rate calculated by the rate calculation unit.

[0007] (2) In one aspect of the present invention, in the charge / discharge management device described in (1) above, the rate calculation unit calculates a charge / discharge rate at which the lithium ion secondary battery can be safely charged / discharged by substituting a value calculated by the capacity calculation unit into a predetermined arithmetic formula and performing a numerical calculation.

[0008] (3) In one aspect of the present invention, in the charge / discharge management device described in (1) or (2) above, the predetermined calculation formula used by the rate calculation unit is determined based on the minimum value of battery capacity in a low-temperature environment and the temperature rise value when the lithium-ion secondary battery is charged and discharged at a plurality of different rates using the lithium-ion secondary battery whose battery capacity value has decreased as a result of being charged and discharged in a low-temperature environment.

[0009] (4) In one aspect of the present invention, in the charge / discharge management device described in any one of (1) to (3) above, the predetermined arithmetic formula used by the rate calculation unit is to calculate a charge / discharge rate at which the lithium ion secondary battery can be safely charged / discharged by multiplying the square root of the value calculated by the capacity calculation unit by a predetermined coefficient.

[0010] (5) In one aspect of the present invention, in the charge / discharge management device described in any one of (1) to (4) above, the device further includes a temperature acquisition unit that acquires the temperature of the lithium ion secondary battery, and a counting unit that counts the number of times charging / discharging is performed when the acquired temperature is equal to or lower than a predetermined temperature, and the capacity calculation unit calculates the value of the battery capacity that has decreased as a result of charging / discharging in a low-temperature environment by substituting the value counted by the counting unit into a predetermined arithmetic formula and performing numerical calculations.

[0011] (6) In one aspect of the present invention, in the charge / discharge management device described in (5) above, the predetermined temperature refers to room temperature, and is preferably 10 degrees Celsius. When repeatedly charged and discharged between 10 degrees and room temperature, the temperature dependency of the decrease in battery capacity due to charging and discharging is small. However, when repeatedly charged and discharged at a temperature lower than 10 degrees, the rate of decrease in battery capacity is significantly high. Furthermore, some of the decreased battery capacity does not recover even when the temperature is returned to room temperature.

[0012] (7) In one aspect of the present invention, in the charge / discharge management device described in (5) or (6) above, the counting unit counts up the number of times charging or discharging has been performed when the acquired temperature is equal to or lower than a predetermined temperature and the time during which charging or discharging has been performed is equal to or longer than a predetermined time.

[0013] (8) In one aspect of the present invention, in the charge / discharge management device described in any of (5) to (7) above, the counting unit counts up the number of times charging or discharging has been performed when the acquired temperature is equal to or lower than a predetermined temperature and when the battery capacity at which charging or discharging has been performed is equal to or greater than the predetermined battery capacity.

[0014] (9) One aspect of the present invention is a charge / discharge management method for managing the charging / discharging of a lithium ion secondary battery that supplies power to a load device by charging with power supplied from a power supply device and discharging the charged power, the charge / discharge management method including a capacity calculation step for calculating a value of a battery capacity that is temporarily reduced as a result of charging / discharging in a low temperature environment, a rate calculation step for calculating a charge / discharge rate at which the lithium ion secondary battery can be safely charged / discharged based on the value calculated in the capacity calculation step, and a rate control step for controlling the charge / discharge rate of the lithium ion secondary battery so that the charge / discharge rate is equal to or lower than the rate calculated in the rate calculation step.

[0015] (10) One aspect of the present invention is a program for causing a computer to manage the charging and discharging of a lithium ion secondary battery that supplies power to a load device by charging with power supplied from a power supply device and discharging the charged power, the program executing a capacity calculation step of calculating a value of the battery capacity that is temporarily reduced as a result of charging and discharging in a low temperature environment, a rate calculation step of calculating a charging and discharging rate at which the lithium ion secondary battery can be safely charged and discharged based on the value calculated in the capacity calculation step, and a rate control step of controlling the charging and discharging rate of the lithium ion secondary battery so that it is equal to or lower than the rate calculated in the rate calculation step. Effect of the Invention

[0016] According to the present invention, it is possible to provide a charge / discharge management device, a charge / discharge management method, and a program that are capable of determining whether a lithium ion secondary battery can be reused and of determining its safety. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram for explaining a power storage system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a functional configuration diagram showing an example of a functional configuration of the charge / discharge management device according to the present embodiment. [Diagram 3]FIG. 4 is a diagram showing an example of a formula for calculating a battery capacity according to the embodiment; [Figure 4] FIG. 11 is a diagram showing changes in a formula for calculating battery capacity according to the embodiment when a constant is changed. [Diagram 5] FIG. 4 is a diagram showing an example of a formula for controlling a charge / discharge rate according to the embodiment; [Figure 6] FIG. 11 is a diagram showing the change in the formula for controlling the charge / discharge rate according to the embodiment when the constants are changed. [Figure 7] 5 is a flowchart showing an example of a count-up process of the number of times of charging and discharging in the charge and discharge management method according to the embodiment. [Figure 8] 5 is a flowchart showing an example of control of a charge / discharge rate in the charge / discharge management method according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] [Embodiment] Hereinafter, the charge / discharge management device, charge / discharge management method, and program according to the aspects of the present invention will be described in detail with reference to the accompanying drawings, with preferred embodiments presented. Note that the aspects of the present invention are not limited to these embodiments, and include those with various modifications or improvements. In other words, the components described below include those that a person skilled in the art can easily imagine, and those that are substantially the same, and the components described below can be appropriately combined. In addition, various omissions, substitutions, or modifications of the components can be made without departing from the gist of the present invention. In addition, in the following drawings, the scale and number of each structure may be different from the scale and number of the actual structure in order to make each configuration easier to understand.

[0019] FIG. 1 is a diagram for explaining the power storage system according to the present embodiment. First, an overview of the power storage system 1 will be described with reference to the diagram. The power storage system 1 is configured to include at least a lithium ion secondary battery 10, a charge / discharge management device 30, a load device 40, and a power supply device 50. The power storage system 1 is applied to a device that generates power using the power supply device 50, charges the generated power into the lithium ion secondary battery 10, and discharges the charged power to the load device 40, thereby driving the load device 40. Specifically, the power storage system 1 may be used in a hybrid vehicle (HV), an electric vehicle (EV), a plug-in hybrid vehicle (PHV), or the like, or may be used for stationary purposes. Note that the present embodiment is not limited to an example in which the power storage system 1 is applied to these vehicles, and can be widely applied to other systems in which the lithium ion secondary battery 10 is used.

[0020] The lithium ion secondary battery 10 charges with power supplied from a power supply device 50 and supplies power to a load device 40 by discharging the charged power. In other words, the lithium ion secondary battery 10 is a chargeable and dischargeable secondary battery. The lithium ion secondary battery 10 is a lithium ion secondary battery (lithium ion battery) among secondary batteries that can charge and discharge power. The lithium ion secondary battery 10 is an example of a non-aqueous power storage element. The lithium ion secondary battery 10 contains a carbon-based material and LTO (Li4Ti5O 12 , lithium titanate) is used. Specifically, the lithium ion secondary battery 10 may be one in which lithium cobalt oxide is used as the material of the positive electrode and a carbon material is used as the material of the negative electrode. As another example, the material used for the positive electrode generally includes nickel-based, cobalt-based, manganese-based, ternary-based, and iron-based (e.g., iron phosphate-based) materials. Also, a specific example of the carbon-based material used for the negative electrode is graphite.

[0021] The power supply device 50 generates power. The power generated by the power supply device 50 is charged to the lithium ion secondary battery 10 via the charge / discharge management device 30. Specifically, the power supply device 50 may be a generator that generates power using an engine mounted on an automobile. The power supply device 50 may also be a general term for a power supply source that supplies power from a power system to the lithium ion secondary battery 10 via an outlet or a power cable.

[0022] The load device 40 is driven by power supplied from the lithium ion secondary battery 10. DC power is supplied from the lithium ion secondary battery 10 to the load device 40. The load device 40 may be a load that is driven by consuming the supplied DC current as is, or may be a load that converts the DC power into AC power and then consumes the converted AC power. Specifically, the load device 40 may be a motor mounted on an automobile.

[0023] The charge / discharge management device 30 acquires the battery temperature of the lithium ion secondary battery 10, and further acquires an upper limit temperature setting value. The battery temperature of the lithium ion secondary battery 10 may be acquired from a temperature measuring unit (not shown) provided around the lithium ion secondary battery 10, or may be acquired from a temperature measuring unit (not shown) provided inside the lithium ion secondary battery 10. The upper limit temperature setting value is a predetermined constant. The upper limit temperature setting value is stored in a storage unit (not shown). The upper limit temperature setting value may be a different value for each type (model) of the lithium ion secondary battery 10. The upper limit temperature setting value is an upper limit temperature for determining that a low temperature environment exists when the temperature is equal to or lower than this set temperature.

[0024] Furthermore, the charge / discharge management device 30 acquires a plurality of setting values ​​(shown as setting values ​​a to c) used for charge / discharge management. These setting values ​​are predetermined constants. These setting values ​​are stored in a storage unit (not shown). The charge / discharge management device 30 performs control related to the charging and discharging of the lithium ion secondary battery 10 based on these acquired values.

[0025] The lithium ion secondary battery 10 may have different electrode materials, sizes, etc. depending on the type and model. When the electrode materials, sizes, etc. differ depending on the type and model, it is preferable to apply values ​​according to the type and model of the lithium ion secondary battery 10 as the above-mentioned set values ​​(set values ​​a to c). In the following description, when it is said that the electrode materials, sizes, etc. differ depending on the type (model) of the lithium ion secondary battery 10, specifically, this may refer to different types, sizes, etc. of the electrodes.

[0026] In the following description, it is assumed that power is not directly supplied from the power supply device 50 to the load device 40. Power generated by the power supply device 50 is temporarily charged into the lithium ion secondary battery 10, and is then discharged from the lithium ion secondary battery 10 to the load device 40. Note that the present embodiment is not limited to this example, and power may be directly supplied from the power supply device 50 to the load device 40.

[0027] FIG. 2 is a functional configuration diagram showing an example of the functional configuration of the charge / discharge management device according to the present embodiment. With reference to the same figure, an example of the functional configuration of the charge / discharge management device 30 will be described. The charge / discharge management device 30 includes a processing unit 31 and a storage unit 32. The processing unit 31 includes a current value acquisition unit 311, a temperature acquisition unit 312, a charge / discharge count unit 313, a capacity calculation unit 314, a speed calculation unit 315, and a speed control unit 316. Each of these functional units is realized, for example, by using an electronic circuit. Each functional unit may include a storage means such as a semiconductor memory or a magnetic hard disk device, as necessary. Each function may be realized by a computer having a CPU (Central Processing Unit) and software. All or a part of each functional unit may be realized by hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field-Programmable Gate Array). All or a part of each functional unit may be realized by a combination of software and hardware.

[0028] The storage unit 32 stores an upper limit temperature setting value and a plurality of setting values ​​used for charge / discharge management. These setting values ​​are determined in advance for each type (model) of the lithium ion secondary battery 10. In other words, the storage unit 32 stores an upper limit temperature setting value and a plurality of setting values ​​used for charge / discharge management for each type (model) of the lithium ion secondary battery 10 in association with each other. The storage unit 32 acquires the battery identification information ID of the lithium ion secondary battery 10 and outputs a setting value based on the acquired battery identification information ID to the processing unit 31. The battery identification information ID of the lithium ion secondary battery 10 may be acquired from the lithium ion secondary battery 10 as, for example, a digital signal.

[0029] The processing unit 31 acquires various set values ​​from the storage unit 32. The processing unit 31 acquires, for example, the battery identification information ID of the lithium ion secondary battery 10, and acquires various set values ​​according to the acquired battery identification information ID from the storage unit 32. The processing unit 31 also acquires the current value charged to the lithium ion secondary battery 10 or the current value discharged from the lithium ion secondary battery 10, and the temperature of the lithium ion secondary battery 10. The processing unit 31 performs control regarding charging and discharging of the lithium ion secondary battery 10 based on these acquired values. Specifically, the control regarding charging and discharging of the lithium ion secondary battery 10 is control regarding the charging and discharging speed, and may be control that determines an upper limit value of the charging and discharging speed and limits the charging and discharging speed within the determined upper limit value. Below, the functions of each functional unit included in the processing unit 31 will be described.

[0030] The current value acquiring unit 311 acquires a current value I from the current measuring unit 61. The current value I is the current value of the power charged from the power supply device 50 to the lithium ion secondary battery 10 or the current value of the power discharged from the lithium ion secondary battery 10 to the load device 40. The current measuring unit 61 measures the current value of the power charged from the power supply device 50 to the lithium ion secondary battery 10 or the current value of the power discharged from the lithium ion secondary battery 10 to the load device 40, and outputs the measured value as the current value I to the current value acquiring unit 311. The current value I may include information on the direction of the current (i.e., charging or discharging). The current value acquiring unit 311 outputs a digital value indicating the acquired current value I to the charge / discharge count counting unit 313 as current value information II.

[0031] The temperature acquisition unit 312 acquires the temperature T of the lithium ion secondary battery 10 from the temperature measurement unit 62. The temperature T of the lithium ion secondary battery 10 may be, for example, the temperature around the lithium ion secondary battery 10 or the temperature inside the lithium ion secondary battery 10. The temperature measurement unit 62 is provided near the lithium ion secondary battery 10 or inside the lithium ion secondary battery 10. The temperature measurement unit 62 measures the temperature T of the lithium ion secondary battery 10 and outputs the measured temperature T to the temperature acquisition unit 312. The temperature acquisition unit 312 outputs a digital value indicating the acquired temperature T to the charge / discharge count count unit 313 as temperature information TI.

[0032] The charge / discharge counting unit 313 acquires current value information II from the current value acquiring unit 311, and acquires temperature information TI from the temperature acquiring unit 312. The charge / discharge counting unit 313 performs a counting process based on the acquired information. Specifically, the charge / discharge counting unit 313 counts the number of times charging / discharging has been performed when the acquired temperature is equal to or lower than a predetermined temperature. For example, the charge / discharge counting unit 313 performs a count-up operation when either charging or discharging has been performed at a temperature equal to or lower than the predetermined temperature. The predetermined temperature may be, for example, 1 degree Celsius, 10 degrees Celsius, or the like.

[0033] The determination of whether charging or discharging has been performed may be made based on whether the time during which charging or discharging has been performed is equal to or greater than a predetermined threshold. In this case, the charge / discharge count unit 313 determines that charging or discharging has been performed when the magnitude of the current acquired by the current value acquisition unit 311 is equal to or greater than a predetermined threshold and the direction of the current is constant for a predetermined period of time or more. That is, when the acquired temperature is equal to or less than a predetermined temperature and the time during which charging or discharging has been performed is equal to or greater than a predetermined period of time, the charge / discharge count unit 313 counts up the number of times charging or discharging has been performed.

[0034] In addition, the determination of whether or not either charging or discharging has been performed may be performed based on whether or not the battery capacity when charging or discharging is continued is equal to or greater than a predetermined threshold. The charge / discharge counting unit 313 calculates the battery capacity by the product of the current value and the time. In this case, the charge / discharge counting unit 313 calculates the battery capacity based on the magnitude of the current acquired by the current value acquiring unit 311, and determines that charging or discharging has been performed when the battery capacity is equal to or greater than a predetermined threshold. That is, when the acquired temperature is equal to or less than a predetermined temperature, the charge / discharge counting unit 313 counts up the number of times charging or discharging has been performed when the battery capacity at which charging or discharging has been performed is equal to or greater than a predetermined battery capacity. Note that the charge / discharge counting unit 313 may perform calculations directly from the current value instead of converting the current value to the amount of power once.

[0035] When the charge / discharge counting unit 313 performs a count-up operation as a result of either charging or discharging being performed at a temperature equal to or lower than a predetermined temperature, the charge / discharge counting unit 313 stores information indicating that the count-up operation has been performed as the number-of-times information NI in the storage unit 32. The number-of-times information NI may include information on the number of times that charging and discharging were performed at a temperature equal to or lower than the predetermined temperature. The number-of-times information NI may also include information for counting up a counter stored in the storage unit 32.

[0036] In the following description, the charge / discharge counting unit 313 may be simply referred to as a counting unit.

[0037] The capacity calculation unit 314 acquires the coefficient b and the coefficient c from the storage unit 32. The capacity calculation unit 314 also acquires the number of times information NI from the storage unit 32. The number of times information NI includes information on the number of times charging and discharging have been performed at a predetermined temperature or lower. The capacity calculation unit 314 calculates the value of the battery capacity of the lithium ion secondary battery 10 based on the acquired information. More specifically, the value of the battery capacity calculated by the capacity calculation unit 314 may be a value of the battery capacity that is temporarily reduced as a result of charging and discharging in a low temperature environment. The values ​​of the coefficient b and the coefficient c acquired from the storage unit 32 may be values ​​that are predetermined for each model of the lithium ion secondary battery 10.

[0038] The capacity calculation unit 314 calculates the value of the battery capacity that has decreased as a result of charging and discharging in a low-temperature environment by directly performing numerical calculations by substituting the value counted by the charge / discharge count unit 313 into a predetermined arithmetic expression. The predetermined arithmetic expression is, for example, expressed by the following formula (1).

[0039]

number

[0040] Here, N in formula (1) is the number of times the lithium ion secondary battery has been charged and discharged in a low temperature environment (for example, in an environment below 10 degrees Celsius). Also, D in formula (1) is the battery capacity of the lithium ion secondary battery 10 that has decreased in that environment. Note that the battery capacity of the lithium ion secondary battery 10 decreases in a low temperature environment, and the battery capacity recovers when the temperature environment returns to normal (for example, when it exceeds 10 degrees Celsius). It can also be said that D is the minimum battery capacity (hereinafter may be referred to as minimum capacity) that the lithium ion secondary battery 10 has ever experienced.

[0041] The coefficient b in formula (1) corresponds to the multiplier of N (specifically, b in the formula), and may be in the range of b=0.15-0.2, for example, depending on the model of the lithium-ion secondary battery 10. The coefficient c in formula (1) corresponds to the coefficient of N (specifically, k in the formula), and may be in the range of k=30-55, for example, depending on the model of the lithium-ion secondary battery 10.

[0042] 3 is a diagram showing an example of a formula for calculating the battery capacity according to this embodiment. With reference to the figure, an example of a formula used by the capacity calculation unit 314 to calculate the battery capacity will be described. The figure shows the correspondence relationship between the number of charge / discharge cycles at or below a predetermined temperature and the minimum capacity when specific coefficients b and c are applied to formula (1). In the figure, the specific temperature is specifically 1 degree Celsius.

[0043] The capacity calculation unit 314 applies the number of times indicated in the number of times information NI to a graph as shown in the figure, and calculates the minimum capacity. The coefficients b and c in the figure may be determined based on the test results of a test performed in advance for each type (model) of the lithium ion secondary battery 10. In the test, the lithium ion secondary battery 10 is charged and discharged at a predetermined temperature (for example, 1 degree Celsius in the example shown in the figure) or lower, and a correspondence relationship between the number of times charging and discharging is performed at that temperature and the minimum capacity at that time is obtained. The coefficients b and c may be determined based on the correspondence relationship.

[0044] Fig. 4 is a diagram showing the change when the constants are changed in the formula for calculating the battery capacity according to the present embodiment. In both Fig. 4(A) and Fig. 4(B), specific values ​​are substituted for the coefficients b and c of the graph shown in Fig. 3. Fig. 4(A) shows a graph in the case where b=0.2 and k=30 in the formula (1). Fig. 4(B) shows a graph in the case where b=0.15 and k=55 in the formula (1). It is preferable that the coefficients b and c are set to, for example, about halfway between the graph shown in Fig. 4(A) and the graph shown in Fig. 4(B), as shown in Fig. 3.

[0045] Returning to FIG. 2, the capacity calculation unit 314 outputs the minimum capacity calculated based on the number of times indicated in the number information NI to the speed calculation unit 315 as capacity information DI.

[0046] The rate calculation unit 315 acquires the capacity information DI calculated by the capacity calculation unit 314. The rate calculation unit 315 also acquires the coefficient a from the storage unit 32. Based on the acquired information, the rate calculation unit 315 calculates the maximum charge / discharge rate at which the lithium ion secondary battery 10 can safely charge / discharge. The maximum charge / discharge rate at which the lithium ion secondary battery 10 can safely charge / discharge may be specifically indicated by a C rate (rate rate). The value of the coefficient a acquired from the storage unit 32 may be a value that is predetermined for each model of the lithium ion secondary battery 10.

[0047] The rate calculation unit 315 calculates a charge / discharge rate at which the battery can be safely charged / discharged by directly calculating a numerical value by substituting the minimum capacity value calculated by the capacity calculation unit 314 into a predetermined calculation formula. The constants of the predetermined calculation formula used by the rate calculation unit 315 are determined by a test using the lithium ion secondary battery 10 whose battery capacity value has decreased due to charging / discharging in a low-temperature environment (for example, 10 degrees Celsius or lower). In the test, a correspondence relationship between the minimum battery capacity value in a low-temperature environment and the temperature rise value when charging / discharging at a plurality of different rates is obtained. More specifically, the predetermined calculation formula used by the rate calculation unit 315 may be a formula that calculates a charge / discharge rate at which the lithium ion secondary battery 10 can be safely charged / discharged by multiplying the square root of the value calculated by the capacity calculation unit 314 by a predetermined coefficient. More specifically, the predetermined calculation formula is expressed by the following formula (2).

[0048]

number

[0049] Here, C in formula (2) is the charge rate and discharge rate, specifically the C rate. Furthermore, D in formula (2) is the minimum capacity. The coefficient a in formula (2) corresponds to the multiplier of D, and may be set to, for example, about a=0.24 depending on the model of the lithium ion secondary battery 10. Note that in this embodiment, the multiplier of D is set to 0.5, but the multiplier may be determined depending on the type and model of the lithium ion secondary battery 10. Furthermore, formula (2) may be a line that rises to the right and passes through the origin, and any formula may be used depending on the test results.

[0050] 5 is a diagram showing an example of a formula for controlling the charge / discharge rate according to the present embodiment. With reference to the figure, an example of a formula used by the rate calculation unit 315 to calculate a charge / discharge rate at which charging / discharging can be performed safely will be described. The figure shows an example in which a specific coefficient a is applied to the formula (2), and as shown in the figure, the graph shows the correspondence relationship between the minimum capacity and the charge / discharge rate.

[0051] The rate calculation unit 315 applies the minimum capacity value calculated by the capacity calculation unit 314 to the graph as shown in the figure, and calculates the charge / discharge rate at which charging / discharging can be performed safely. The coefficient a in the figure may be determined based on the results of tests performed in advance for each type (model) of the lithium ion secondary battery 10. In the test, a plurality of lithium ion secondary batteries 10 of the same type (model) are used, which have different minimum battery capacities due to different numbers of charging / discharging in a low-temperature environment, and safety is tested for each charge / discharge rate. Among the points plotted on the graph shown in the figure, the different plot symbols represent different degrees of temperature rise, and the points with dots in circles (i.e., points above the line of formula (2)) are points where heat generation is large. Among the points plotted on the graph shown in the figure, the points with white circles (i.e., points below the line of formula (2)) are points where heat generation is small, and the points with black circles are points where heat generation is not generated. That is, by charging and discharging at a rate lower than the line of equation (2), heat generation in the lithium ion secondary battery 10 can be suppressed.

[0052] FIG. 6 is a diagram showing the change when the constants are changed in the formula for controlling the charge / discharge rate according to the present embodiment. In both FIG. 6(A) and FIG. 6(B), a specific value is substituted for the coefficient a in the graph shown in FIG. 5. FIG. 6(A) shows a graph in the case where a=0.2 in the formula (1). FIG. 6(B) shows a graph in the case where a=0.242 in the formula (1). As shown in FIG. 5, it is preferable to set the coefficient a to, for example, about halfway between the graph shown in FIG. 6(A) and the graph shown in FIG. 6(B).

[0053] Returning to FIG. 2, the rate calculation unit 315 outputs the maximum value of the charge / discharge rate calculated based on the minimum capacity to the rate control unit 316 as maximum rate information Ci.

[0054] The rate control unit 316 controls the rate of charging and discharging of the lithium ion secondary battery 10 so that the rate is equal to or lower than the rate calculated by the rate calculation unit 315 .

[0055] Next, a series of steps of the charge / discharge management method according to this embodiment will be described with reference to FIGS.

[0056] 7 is a flowchart showing an example of the count-up process of the number of times of charging and discharging in the charge and discharge management method according to the present embodiment. With reference to the same figure, an example of the count-up process of the number of times of charging and discharging performed by the charge and discharge counting unit 313 will be described.

[0057] (Step S11) First, the charge / discharge counting unit 313 determines whether or not the temperature around the lithium ion secondary battery is 10 degrees Celsius or less, based on the temperature information TI acquired from the temperature acquiring unit 312. If the temperature is not 10 degrees Celsius or less, the charge / discharge counting unit 313 does not proceed to the next process. If the temperature is 10 degrees Celsius or less, the charge / discharge counting unit 313 advances the process to step S13.

[0058] (Step S13) Next, the charge / discharge counting unit 313 judges whether or not charging / discharging has been performed in the environment of 10 degrees or less. The judgment of whether or not charging / discharging has been performed is performed based on the current value information II acquired from the current value acquiring unit 311. For example, the charge / discharge counting unit 313 may judge that charging / discharging has been performed based on the current value indicated in the current value information II and the battery capacity calculated based on the time during which charging or discharging has been performed. When the charge / discharge counting unit 313 judges that charging / discharging has been performed, it advances the process to step S15. When the condition is not met, such as when charging / discharging has not been performed in the environment of 10 degrees or less, or when the temperature rises above 10 degrees during charging / discharging, the process returns to step S11.

[0059] (Step S15) Next, the charge / discharge counting unit 313 counts up the number of charge / discharge cycles in the low-temperature environment. The counted number of charge / discharge cycles in the low-temperature environment is stored in the storage unit 32.

[0060] 8 is a flowchart showing an example of charge / discharge rate control in the charge / discharge management method according to the present embodiment. With reference to the drawing, an example of the overall flow of charge / discharge rate control performed by the charge / discharge management device 30 will be described.

[0061] (Step S21) First, the charge / discharge management device 30 determines whether or not the lithium ion secondary battery 10 included in the power storage system 1 has experience of use in a low temperature environment. The determination of whether or not the lithium ion secondary battery 10 has experience of use in a low temperature environment may be determined by the charge / discharge counting unit 313, and may be performed based on information stored in the storage unit 32. If the lithium ion secondary battery 10 has not been used in a low temperature environment, the charge / discharge management device 30 advances the process to step S22. If the lithium ion secondary battery 10 has experience of use in a low temperature environment, the charge / discharge management device 30 advances the process to step S23.

[0062] (Step S22) If there is no experience of use in a low-temperature environment, the charge / discharge management device 30 does not control the charge / discharge rate based on the number of times of charge / discharge in a low-temperature environment.

[0063] (Step S23) If the battery has experience of use in a low-temperature environment, the charge / discharge management device 30 controls the charge / discharge rate based on the number of times the battery has been charged / discharged in a low-temperature environment. Steps S23 to S26 are performed as detailed processing for controlling the charge / discharge rate based on the number of times the battery has been charged / discharged in a low-temperature environment. First, the charge / discharge management device 30 acquires the type (identification information, etc.) of the lithium-ion secondary battery 10.

[0064] (Step S24) Next, the capacity calculation unit 314 acquires coefficients (coefficients b and c in FIG. 2) corresponding to the acquired model of the lithium ion secondary battery 10 from the storage unit 32. The capacity calculation unit 314 calculates the minimum capacity in a low-temperature environment based on the number of charge / discharge cycles in a low-temperature environment calculated by the process described with reference to FIG. 7 and the acquired coefficients.

[0065] (Step S25) Next, the rate calculation unit 315 acquires a coefficient (coefficient a in FIG. 2) corresponding to the acquired model of the lithium ion secondary battery 10 from the storage unit 32. The rate calculation unit 315 calculates a charge / discharge rate (specifically, C rate) at which charging / discharging can be performed safely, based on the minimum capacity calculated in step S24 and the acquired coefficient.

[0066] (Step S26) Next, the rate control unit 316 controls the charging and discharging of the lithium ion secondary battery 10 so that the rate is equal to or lower than the C rate calculated in step S25.

[0067] [Summary of the embodiment] As described above, the charge / discharge management device 30 manages the charge / discharge of the lithium ion secondary battery 10. The lithium ion secondary battery 10 charges with power supplied from the power supply device 50 and supplies power to the load device 40 by discharging the charged power. The charge / discharge management device 30 includes a capacity calculation unit 314 to calculate a value of the battery capacity that is temporarily decreased due to charging / discharging in a low-temperature environment, includes a rate calculation unit 315 to calculate a charge / discharge rate (e.g., C rate) at which the lithium ion secondary battery 10 can safely charge / discharge based on the value calculated by the capacity calculation unit 314, and includes a rate control unit 316 to control the charge / discharge rate of the lithium ion secondary battery 10 so that it is equal to or lower than the rate calculated by the rate calculation unit 315.

[0068] Here, if the lithium ion secondary battery 10 has deteriorated due to repeated charging and discharging in a low-temperature environment, the charging and discharging speed at which the battery can be safely used will be slow. Therefore, according to this embodiment, the safety of the lithium ion secondary battery 10 can be determined based on the calculated charging and discharging speed. Also, according to this embodiment, it may be possible to determine whether the lithium ion secondary battery 10 can be reused.

[0069] The inventors have discovered that a reliable safety assessment can be made by evaluating the thermal stability of a lithium-ion secondary battery 10 that has a usage history of being charged and discharged in a low-temperature environment using a scanning adiabatic calorimeter. The inventors have also discovered that a reliable safety assessment can be made based on the results of mapping this safety assessment. By using a management device (i.e., charge / discharge management device 30) incorporating this mapping data to control the charge rate and discharge rate, it has become possible to safely use the lithium-ion secondary battery 10.

[0070] Furthermore, according to the above-described embodiment, the rate calculation unit 315 substitutes the value calculated by the capacity calculation unit 314 into a predetermined arithmetic expression to perform direct numerical calculation, thereby calculating the charge / discharge rate at which the lithium-ion secondary battery 10 can be safely charged / discharged. The capacity calculation unit 314 can obtain the charge / discharge rate from the minimum capacity of the lithium-ion secondary battery 10 by using the predetermined arithmetic expression. Therefore, according to the present embodiment, a safe charge / discharge rate can be easily calculated based on the history of charging / discharging performed in a low-temperature environment.

[0071] According to the above-described embodiment, the predetermined arithmetic expression used by the rate calculation unit 315 is determined based on the minimum value of the battery capacity in a low-temperature environment and the temperature rise value when charging and discharging are performed at a plurality of different rates using the lithium-ion secondary battery 10 whose battery capacity value has decreased due to charging and discharging in a low-temperature environment. That is, according to the present embodiment, a constant is determined for each lithium-ion secondary battery 10 by performing experiments in advance. The charge and discharge management device 30 can easily calculate a safe charge and discharge rate based on the predetermined constant and the history of charging and discharging performed in a low-temperature environment.

[0072] According to the embodiment described above, the predetermined arithmetic expression used by the rate calculation unit 315 is a formula that calculates a charge / discharge rate at which the lithium ion secondary battery 10 can be safely charged / discharged by multiplying the square root of the value calculated by the capacity calculation unit 314 by a predetermined coefficient. That is, the predetermined arithmetic expression is specifically the above-mentioned formula (2). By using formula (2), the capacity calculation unit 314 can obtain the charge / discharge rate from the minimum capacity of the lithium ion secondary battery 10. Therefore, according to the embodiment, a safe charge / discharge rate can be easily calculated based on the history of charging / discharging in a low-temperature environment.

[0073] According to the above-described embodiment, the charge / discharge management device 30 further includes the current value acquisition unit 311 to acquire the temperature of the lithium ion secondary battery 10, and further includes the charge / discharge count unit 313 to count the number of times that charging / discharging has been performed when the acquired temperature is equal to or lower than a predetermined temperature. The capacity calculation unit 314 substitutes the value counted by the charge / discharge count unit 313 into a predetermined arithmetic expression, and performs direct numerical calculation to calculate the value of the battery capacity that has decreased as a result of charging / discharging in a low-temperature environment. Here, the predetermined arithmetic expression is specifically the above-described formula (1). By using formula (1), the capacity calculation unit 314 can obtain the battery capacity (i.e., the minimum capacity) that has temporarily decreased as a result of charging / discharging in a low-temperature environment from the number of times that charging / discharging has been performed in a low-temperature environment. Therefore, according to the present embodiment, a safe charge / discharge rate can be easily calculated based on the number of times that charging / discharging has been performed in a low-temperature environment.

[0074] Furthermore, according to the above-described embodiment, the charge / discharge counting unit 313 counts up the number of times charging / discharging has been performed if the temperature acquired by the temperature acquiring unit 312 is equal to or lower than a predetermined temperature and if the time during which charging or discharging has been performed continuously is equal to or longer than a predetermined time. That is, according to this embodiment, the charge / discharge counting unit 313 does not count a short-term charge / discharge as one charge / discharge. Therefore, according to this embodiment, it is possible to more accurately determine the degree of deterioration of the battery and calculate a safe charge / discharge rate.

[0075] Furthermore, according to the above-described embodiment, the charge / discharge counting unit 313 counts up the number of times charging / discharging has been performed when the temperature acquired by the temperature acquiring unit 312 is equal to or lower than a predetermined temperature and the battery capacity at which charging or discharging has been performed is equal to or higher than a predetermined battery capacity. That is, according to this embodiment, the charge / discharge counting unit 313 does not count a charging / discharging as one time when the battery capacity at which charging / discharging is performed is small. Therefore, according to this embodiment, it is possible to more accurately determine the degree of deterioration of the battery and calculate a safe charging / discharging rate.

[0076] In addition, all or part of the functions of each unit of the charge / discharge management device 30 in the above-mentioned embodiment may be realized by recording a program for realizing these functions in a computer-readable recording medium, reading the program recorded in the recording medium into a computer system, and executing it. Note that the "computer system" here includes hardware such as an OS and peripheral devices.

[0077] In addition, the term "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, and storage units such as hard disks built into computer systems. Furthermore, the term "computer-readable recording medium" may also include those that dynamically hold a program for a short period of time, such as a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line, and those that hold a program for a certain period of time, such as a volatile memory inside a computer system that serves as a server or client in such cases. Furthermore, the above program may be one that realizes part of the above-mentioned functions, or may be one that can realize the above-mentioned functions in combination with a program already recorded in the computer system.

[0078] Although an embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. [Explanation of symbols]

[0079] 1...power storage system, 10...lithium ion secondary battery, 30...charge / discharge management device, 40...load device, 50...power supply device, 61...current measurement unit, 62...temperature measurement unit, 31...processing unit, 32...storage unit, 311...current value acquisition unit, 312...temperature acquisition unit, 313...charge / discharge counting unit, 314...capacity calculation unit, 315...speed calculation unit, 316...speed control unit

Claims

1. A charge / discharge management device that manages the charging / discharging of a lithium ion secondary battery that charges with power supplied from a power supply device and supplies power to a load device by discharging the charged power, a capacity calculation unit that calculates a temporarily decreased battery capacity value due to charging and discharging in a low temperature environment; a rate calculation unit that calculates a charge / discharge rate at which the lithium ion secondary battery can be safely charged / discharged based on the value calculated by the capacity calculation unit; a rate control unit that controls the rate of charging and discharging of the lithium ion secondary battery so that the rate is equal to or lower than the rate calculated by the rate calculation unit; A charge and discharge management device comprising:

2. The rate calculation unit calculates a rate at which the lithium ion secondary battery can be safely charged and discharged by substituting the value calculated by the capacity calculation unit into a predetermined arithmetic expression and performing a numerical calculation. The charge / discharge management device according to claim 1 .

3. The predetermined calculation formula used by the rate calculation unit is determined based on a minimum value of battery capacity in a low-temperature environment and a temperature rise value when the lithium-ion secondary battery is charged and discharged at a plurality of different rates using the lithium-ion secondary battery whose battery capacity has decreased due to charging and discharging in a low-temperature environment. The charge / discharge management device according to claim 2 .

4. The predetermined formula used by the rate calculation unit is a formula for calculating a rate at which the lithium ion secondary battery can be safely charged and discharged by multiplying the square root of the value calculated by the capacity calculation unit by a predetermined coefficient. The charge / discharge management device according to claim 2 .

5. a temperature acquisition unit that acquires a temperature of the lithium ion secondary battery; A counting unit that counts the number of times that charging and discharging are performed when the acquired temperature is equal to or lower than a predetermined temperature, The capacity calculation unit calculates a value of the battery capacity that has decreased as a result of charging and discharging in a low-temperature environment by substituting the value counted by the counting unit into a predetermined arithmetic formula and performing a numerical calculation. The charge / discharge management device according to any one of claims 1 to 4.

6. The predetermined temperature is 10 degrees Celsius. The charge / discharge management device according to claim 5 .

7. The counting unit counts up the number of times charging or discharging has been performed when the acquired temperature is equal to or lower than a predetermined temperature and when the time during which charging or discharging has been performed is equal to or longer than a predetermined time. The charge / discharge management device according to claim 5 .

8. The counting unit counts up the number of times charging or discharging has been performed when the acquired temperature is equal to or lower than a predetermined temperature and when the battery capacity at which charging or discharging has been performed is equal to or higher than a predetermined battery capacity. The charge / discharge management device according to claim 5 .

9. A charge / discharge management method for managing the charge / discharge of a lithium ion secondary battery that supplies power to a load device by charging the battery with power supplied from a power supply device and discharging the charged power, comprising: A capacity calculation step of calculating a value of a battery capacity that is temporarily decreased due to charging and discharging in a low temperature environment; a rate calculation step of calculating a rate at which the lithium ion secondary battery can be safely charged and discharged based on the value calculated in the capacity calculation step; a rate control step of controlling the charge / discharge rate of the lithium ion secondary battery so that the rate is equal to or lower than the rate calculated in the rate calculation step; A charge and discharge management method comprising the steps of:

10. On the computer, A program for managing the charging and discharging of a lithium ion secondary battery that supplies power to a load device by charging the battery with power supplied from a power supply device and discharging the charged power, A capacity calculation step of calculating a value of a battery capacity that is temporarily decreased due to charging and discharging in a low temperature environment; a rate calculation step of calculating a rate at which the lithium ion secondary battery can be safely charged and discharged based on the value calculated in the capacity calculation step; a rate control step of controlling the charge / discharge rate of the lithium ion secondary battery so that the rate is equal to or lower than the rate calculated in the rate calculation step; A program that executes the following.

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