JP2015220038A - Lithium ion secondary battery system and method for charging lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery system improved in charging efficiency at low temperatures without degrading space utilization efficiency inside a battery.SOLUTION: A secondary battery system includes: a lithium ion secondary battery 2; a temperature sensor 4 for measuring an outer surface temperature of the lithium ion secondary battery 2; and a control section 7 configured to control such that, in the case where a measured temperature is less than a predetermined temperature when the lithium ion secondary battery 2 is subjected to charge treatment, the lithium ion secondary battery 2 is charged after having been discharged.

Description

  The present invention relates to a lithium ion secondary battery system and a method for charging a lithium ion secondary battery.

  In recent years, lithium ion secondary batteries have been used as motor driving batteries for electric vehicles (EV) and hybrid electric vehicles (HEV).

  In such a lithium ion secondary battery, there is a problem that the internal resistance of the battery increases at a low temperature, the charging efficiency becomes worse, and the charging time becomes longer than that at room temperature. Conventionally, in order to solve such a problem, there is a technique in which a heater is provided inside a battery pack of a lithium ion secondary battery, and charging is performed after the internal temperature is raised by heating with the heater during charging (Patent Document 1). ).

Japanese Patent Laid-Open No. 10-284133

  However, in the conventional technology, since a heater is provided inside the battery, a space for installing the heater must be secured in the battery casing. For this reason, the volume and weight of the heater occupy the internal space utilization efficiency of the entire battery, which causes a reduction in energy density.

  Accordingly, an object of the present invention is to provide a lithium ion secondary battery system and a charging method for a lithium ion secondary battery that have improved charging efficiency at low temperatures without deteriorating space utilization efficiency inside the battery.

  In order to solve the above problems, a lithium ion secondary battery system of the present invention includes a lithium ion secondary battery, a temperature sensor for measuring the outer surface temperature of the lithium ion secondary battery, and a charging process for the lithium ion secondary battery. When performing, when the temperature measured with the temperature sensor is less than predetermined temperature, it has a control part which controls to charge after discharging.

  The charging method of the secondary battery of the present invention for solving the above-mentioned problem is a step of measuring the outer surface temperature of the lithium ion secondary battery when the lithium ion secondary battery is charged, and the measured temperature. Charging after discharging when the temperature is lower than a predetermined temperature.

  According to the present invention, when a lithium ion secondary battery is charged at a low temperature, it is discharged before charging. As a result, the temperature inside the secondary battery can be raised by the heat generation action caused by the current flowing through the discharge. For this reason, it can charge, after raising the internal temperature of a secondary battery, without providing a heater etc. inside a battery. Therefore, it is possible to improve the charging efficiency without reducing the space utilization efficiency inside the battery.

It is a block diagram for demonstrating the structure of the secondary battery system of this Embodiment 1. FIG. It is a flowchart which shows a charging process procedure. It is a graph which shows the relationship between SOC and the time concerning charging / discharging. It is a flowchart which shows the procedure for considering the resistance increase by a time-dependent change. It is a schematic sectional drawing for demonstrating the whole structure of a non-bipolar type | mold laminated lithium ion secondary battery. It is a schematic sectional drawing for demonstrating the whole structure of a bipolar type laminated | stacked lithium ion secondary battery. FIG. 7 is a perspective view illustrating an appearance of the stacked lithium ion secondary battery illustrated in FIG. 5 or FIG. 6.

  Embodiments to which the present invention is applied will be described below with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may differ from actual ratios.

[Secondary battery system]
FIG. 1 is a block diagram for explaining the configuration of the lithium ion secondary battery system according to the first embodiment.

  The lithium ion secondary battery system (hereinafter referred to as secondary battery system 1) includes a lithium ion secondary battery (hereinafter referred to as secondary battery 2). A voltage sensor 3 that measures the voltage between the positive and negative electrodes of the secondary battery 2, a temperature sensor 4 that measures the outer surface temperature (environmental temperature) of the secondary battery 2, and a voltage / current adjustment that supplies charging power to the secondary battery 2 5, a current sensor 6 that measures the charge / discharge current of the secondary battery 2, and a control unit 7 that controls charge / discharge. The voltage / current adjusting unit 5 is connected to the external power source 8 and receives power supply during charging, while discharging to the external power source 8 side through the voltage / current adjusting unit 5 during discharging (details will be described later).

  Details of each part will be described below.

  The secondary battery 2 is an ordinary lithium ion secondary battery, and is disposed so that a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material face each other with a separator interposed therebetween, and the separator is filled with an electrolyte. ing. The details of the lithium ion secondary battery will be described later.

  The voltage sensor 3 may be a voltmeter, for example, and measures the voltage between the positive electrode and the negative electrode of the secondary battery 2. The attachment position of the voltage sensor 3 is not particularly limited, and may be a position where the voltage between the positive electrode and the negative electrode can be measured in the circuit connected to the secondary battery 2.

  The temperature sensor 4 measures the temperature of the exterior surface of the secondary battery 2. The temperature sensor 4 is attached to the surface of the case (housing) of the secondary battery 2 (see FIG. 7 described later).

  The secondary battery 2 has a form in which a plurality of unit cells are stacked as will be described later. For this reason, it is difficult to measure the internal temperature. Therefore, in the present embodiment, the temperature of the secondary battery 2 is used as a measure by measuring the outer surface temperature of the secondary battery 2. The outer surface temperature is almost the same as the temperature of the single cell near the outermost layer of the laminated battery, even if the internal temperature cannot be expressed accurately.

  The voltage / current adjusting unit 5 adjusts the voltage and current of the electric power from the external power supply 8 based on a command from the control unit 7 and supplies the electric power to the secondary battery 2. Further, the voltage / current adjusting unit 5 discharges the electricity discharged from the secondary battery 2 to the external power source 8 at the time of discharging.

  Here, the external power source 8 is a charging device for an electric vehicle called a power grid used for charging an electric vehicle or the like, and outputs a direct current. Such a charging device for an electric vehicle provides commercial electric power (alternating current) by converting it into direct current of voltage and current necessary for charging the secondary battery 2. The external power supply 8 is provided with a power regeneration function. When the secondary battery 2 is discharged, the external power supply 8 can convert direct current to alternating current and regenerate to a commercial power supply. Note that such a device serving as an external power source may be a well-known charging device with a power regeneration function, and therefore a detailed description thereof is omitted (for example, a charging device with a power regeneration function is a special No. 7-222369 and JP-A-10-080067.

  When the external power supply 8 is not connected to an external power supply device such as a commercial power supply, for example, when charging another secondary battery installed outside as a power source, the secondary battery 2 is discharged to the other secondary battery. It is preferable to store the generated electric power. Thereby, waste of energy can be reduced.

  The current sensor 6 is an ammeter, for example. The current sensor 6 measures the current value of the power supplied from the voltage / current adjusting unit 5 to the secondary battery 2 during charging, and the current value of the power discharged from the secondary battery 2 to the voltage / current adjusting unit 5 during discharging. Measure. The mounting position of the current sensor 6 is not particularly limited and may be a position where the current value at the time of charging / discharging can be measured by being arranged in a circuit that supplies power from the voltage / current adjusting unit 5 to the secondary battery 2. That's fine.

  The control unit 7 is a so-called computer including a CPU 71, a storage unit 72, and the like, for example. When charging the secondary battery 2 during charging, the control unit 7 switches between charging after discharging or immediately charging, and controls the voltage and current supplied during charging according to the procedure described below. The storage unit 72 includes a nonvolatile memory in addition to the RAM used by the CPU 71 as a working area. The nonvolatile memory stores a program for performing the charging process of the present embodiment. In addition, the storage unit 72 stores a relationship between the SOC (remaining battery capacity) of the secondary battery 2 and time in a charging process described later. As such a control part 7, you may make it use ECU (Engine Control Unit) etc. in an electric vehicle, for example.

[Charging process]
A procedure of the charging process in the secondary battery system configured as described above will be described.

  FIG. 2 is a flowchart showing a charging process procedure, and is a process performed by the control unit 7 unless otherwise specified.

  This charging process is performed in a state where the secondary battery system 1 is connected to the external power source 8 and charging power can be supplied to the secondary battery 2. The charging process is controlled using a constant current / constant voltage charging method in which charging is performed with a constant current until the voltage of the secondary battery 2 reaches a predetermined voltage, and after the voltage reaches a predetermined voltage. Yes. On the other hand, during discharging, the external power source 8 is assumed to be driven with a constant current.

  The charging process according to the present embodiment is performed when the total charging time is faster than when immediate charging is started when the charging process is started at a temperature lower than a predetermined temperature (referred to as a threshold temperature). Is to charge once discharged. Hereinafter, the charging process will be described with reference to FIG.

  First, the control unit 7 acquires the current temperature from the temperature sensor 4 and the current voltage from the voltage sensor 3 (S1).

  Subsequently, the control unit 7 determines whether or not the acquired current temperature is lower than the threshold temperature (S2). If the temperature is not lower than the threshold temperature (S2: NO), power from the external power supply 8 to the voltage / current adjusting unit 5 is introduced and normal charging is performed as it is (S8). Step S8 is the same as normal charging, and the charging process is terminated if the SOC of the secondary battery 2 reaches a predetermined amount (so-called fully charged state) or if there is an instruction to stop the charging operation. All of this processing is completed when charging is completed.

  On the other hand, if the temperature is lower than the threshold temperature in step S2 (S2: YES), the current SOC is obtained from the current voltage acquired in step S1, and the post-discharge charging is performed based on the relationship between the current temperature and the SOC. Is selected (S3). This selection process will be described later.

  As a result of the selection in step S3, if it is not post-discharge charging (that is, immediate charging) (S4: NO), the process immediately proceeds to normal charging operation (S8) without discharging, and the control unit 7 performs normal charging. Execute the process.

  On the other hand, in the case of charging after discharging (S4: YES), the control unit 7 instructs the voltage / current adjusting unit 5 to start discharging (S5). In response to this instruction, the voltage / current adjusting unit 5 starts discharging. In this embodiment, the voltage / current adjusting unit 5 directly connects the secondary battery 2 and the external power supply 8 to regenerate the power of the secondary battery 2 by the external power supply 8 in this embodiment.

  Thereafter, the control unit 7 estimates the current internal temperature of the secondary battery 2 from the current value (S6).

  This internal temperature is estimated based on the current value I, voltage value V, and elapsed time t from the start of discharge.

The calorific value Q = I ² R × Δt = IV × Δt (I is current, R is internal resistance of the secondary battery 2, Δt is minute time, and V is voltage). Therefore, if the current value and voltage value are known, the heat generation amount Q when the minute time Δt has elapsed can be known. Then, if the calorific value Q is divided by the heat capacity HC of the secondary battery 2, the temperature increase ΔT = Q / HC per minute time Δt can be obtained. By performing this calculation every minute time Δt from the start of discharge, a temperature rise amount ΔT for each minute time Δt, that is, a temperature rise amount that changes every moment can be obtained. The current temperature T can be obtained by integrating (ΣΔT) this amount of temperature increase ΔT from the discharge start temperature (that is, the temperature measured in step S1). That is, current temperature T = discharge start temperature T0 + ΣΔT.

Here, the internal resistance of the secondary battery 2 changes because the temperature inside the secondary battery 2 changes due to discharge. For this reason, the value of I ² R = IV also changes with time. Therefore, it is preferable to measure the current value I and the voltage value V by shortening the time interval with as little change as possible, that is, the minute time Δt. However, the minute time Δt is a time for obtaining the temperature rise amount ΔT. For this reason, if the minute time Δt is too small, the calculation efficiency is poor. Therefore, the secondary battery having a large battery volume (that is, the heat capacity HC is large) has a low rate of temperature rise, and therefore the minute time Δt is made somewhat longer. On the other hand, a secondary battery with a small battery volume (that is, with a small heat capacity HC) has a high rate of temperature rise, so it is better to make the minute time Δt as short as possible. From such a viewpoint, it is preferable to set the minute time Δt so that the error of the estimated temperature value is as small as possible.

  Subsequently, the control unit 7 determines whether or not the estimated temperature is equal to or higher than the threshold temperature (S7). If the estimated temperature is not equal to or higher than the threshold temperature (S7: NO), the process returns to step S5. Steps S5 and S7 will be repeated until the temperature exceeds the threshold temperature, and the discharge continues during that time. On the other hand, if the temperature is equal to or higher than the threshold temperature (S7: YES), the routine proceeds to a normal charging operation (S8). Thereafter, the control unit 7 performs a normal charging process and ends the charging process.

  Instead of estimating the internal temperature in step S6, it may be determined based on whether or not the current temperature of the temperature sensor 4 is equal to or higher than a threshold temperature. However, the temperature sensor 4 can only know the temperature of the battery casing surface, and does not accurately represent the temperature inside the secondary battery 2. Further, since the temperature of the outer surface is measured, the temperature measured by the temperature sensor 4 is inevitably lower than the internal temperature (since the environmental temperature around the battery is lower than the threshold temperature, the secondary battery 2 as a whole This process is performed at a temperature lower than the threshold temperature, so entering this process is when the ambient temperature is lower than the threshold temperature). For this reason, as already explained, it is possible to more quickly determine that the internal temperature of the secondary battery 2 has reached the threshold temperature, and the transition from the discharged state to the charge can be made faster by estimating the internal temperature. it can.

[Selection between charge after discharge or immediate charge]
Next, a process for selecting whether charging after discharge or immediate charging in step S3 will be described. There are two ways to do this.

(First selection method)
In the first selection method, the relationship between the charging processing start temperature, the SOC, and the time required for charging / discharging is stored in advance, and either the case of charging after discharge or the case of immediate charging is faster. It is judged whether it can be charged. Here, the charging processing start temperature is not the temperature at the time of actually starting charging, but the temperature at the time of starting processing necessary for charging, and in this embodiment, at the time of step S1. It will be the temperature of.

  FIG. 3 is a graph showing the relationship between the SOC and the time required for charging and discharging. In the figure, the vertical axis represents SOC and the horizontal axis represents time. This graph shows a case where an immediate charge process is performed from a temperature lower than the threshold temperature (dotted line) and a case where charge after discharge is performed (solid line). In the figure, t0 is the time when processing is started, t1 is the time when the threshold temperature is reached by discharging in the case of charging after discharging, t2 is the time when the curve of charging after discharging and the curve of immediate charging intersect, and charging after charging The time when the battery is fully charged is t3, and the time when the battery is fully charged by immediate charging is t4.

  From this graph, in the case of immediate charging from a certain temperature lower than the threshold temperature (dotted line), the SOC gradually increases and reaches full charging. On the other hand, when charging is performed after discharging (solid line), the SOC decreases at one end. Then, charging is started from the time (t1) when the temperature reaches the threshold temperature. Comparing the dotted line and the solid line, it can be seen that the time until full charge (SOC 100%) is reached is faster in the case of charge after discharge (solid line). However, from time t0 to t2, it can be seen that the immediate charge (dotted line) can increase the SOC in a shorter time.

  Therefore, in the process of step S3, whether to perform post-discharge charging or immediate charge is selected using this graph.

  As a selection criterion, for example, the user may desire full charge. In the case of full charge, it can be seen that full charge can be achieved more quickly by selecting post-discharge charge from the graph of FIG. Therefore, in this case, charging after discharging is selected.

  As another selection criterion, for example, there is a case where the user has little time margin and wants to charge in a limited time. In such a case, if the time that the user spends on charging (predesignated time) is not less than t0 and less than t2 in the graph, the charging is immediately performed. On the other hand, in the case of t2 or more, charging is performed after discharging.

  Furthermore, as another selection criterion, for example, there is a case where it is desired to charge to a SOC desired by the user (a SOC designated in advance). The SOC desired by the user is a case where, for example, in an electric vehicle, it is sufficient to be able to charge as many kilometers as possible. In such a case, the desired distance is converted into the SOC to obtain the SOC desired by the user. In the graph shown in FIG. 3, until the time point t <b> 2 when the post-discharge charge curve and the immediate charge curve intersect, the instant charge reaches that SOC faster regardless of the SOC. On the other hand, when the SOC is higher than the time point t2 at which the curve for charging after discharge and the curve for immediate charging intersect, charging after discharging reaches faster. Therefore, if the SOC desired by the user is higher than the SOC at time t2 when the curve for charging after discharging and the curve for immediate charging intersect, charging after discharging is selected.

  In order to make such a selection, a plurality of graphs as shown in FIG. 3 are prepared with different charging processing start temperatures at temperatures lower than the threshold temperature. For example, when the use limit temperature of the secondary battery 2 is −40 ° C. and the threshold temperature is 0 ° C., a graph is created in increments of 10 ° C. That is, there are three graphs: a charging process start temperature—10 ° C., a charging process start temperature—20 ° C., and a charging process start temperature—30 ° C. And when the temperature (namely, charging process start temperature) measured by step S1 is 0 degreeC-15 degreeC, the graph of -10 degreeC is used. When the temperature in step S1 is −15 ° C. to −25 ° C., a graph of −20 ° C. is used. When the temperature in step S1 is −25 ° C. to −40 ° C., a graph of −30 ° C. is used. Of course, such a graph is not limited to increments of 10 ° C., and by narrowing the increment, the selection between post-discharge charging and immediate charging can be controlled more finely.

  Note that the SOC at the start of the charging process when creating such a graph needs to be started from an SOC that can be discharged until the threshold temperature is reached (details will be described later). For this reason, the determination in step S3 is also made based on whether or not the SOC at the start of the charging process is a value that can be raised to the threshold temperature. Referring to FIG. 3, when the SOC at the start of the charging process is lower than the difference in SOC at the time point t1 of the threshold temperature from the SOC value at the start of the charging process on this graph, the immediate charging is performed. On the other hand, if the SOC at the start of the charging process is higher than the SOC difference at the time point t1 from the SOC at the start of the charging process on the graph to the threshold temperature, charging is performed after discharging. Note that if the lower limit of the SCO reached by discharge is extremely lowered, the secondary battery is likely to deteriorate. For this reason, it is assumed that the amount of stored electricity remains. Therefore, a lower limit is set for the SCO that is reached during discharge. For example, it is about 20%. The lower limit value is not limited as long as it is appropriately set according to the characteristics of the secondary battery. The same applies to other graphs created for each charge processing start temperature.

  As described above, in the first selection method, whether to perform post-discharge charging or immediate charging is selected using a graph indicating the relationship between the SOC and the time required for charging / discharging that has been created in advance. The graph indicating the relationship between the SOC and the time required for charging / discharging is created by, for example, an experiment using an actual battery or a simulation. Such a graph is actually stored as numerical data that can be calculated by the control unit 7.

  Thus, by performing charge control using the graph showing the relationship between the SOC and the time required for charging and discharging, it is possible to perform faster charging that matches the battery characteristics.

  As a modified example of the first selection method, the relationship between the SOC and time that changes from time to time as shown in FIG. The SOC relationship may be stored as a range, and charging after discharging or immediate charging may be selected. For example, when the threshold temperature is −10 ° C., if the current SOC is 20% (lower limit) to less than 40%, the post-discharge charging is selected, and if the current SOC is 40% or more, immediate charging is performed. And so on.

(Second selection method)
Next, the second selection method will be described. In the second selection method, the amount of current required to reach the threshold temperature, the SOC to be reached thereby, and the time required for it, and the time required to reach a predetermined SOC when charged from the reached SOC are determined. Calculate and estimate. Then, the estimation result is compared with the time stored in advance at the time of the immediate charge at the low temperature to select the post-discharge charge or the immediate charge.

  As described in the estimation of the current temperature (S3 described above), the calorific value Q and the temperature increase ΔT have the following relationships (1) and (2).

Calorific value Q = I ² R × t (1)
Temperature rise ΔT = Q / HC (2)
In the formula, I is current, R is internal resistance of the secondary battery 2, t is time, and HC is heat capacity.

  On the other hand, the SOC can be obtained from the following (3) threshold, where q is the charge entered and exited by charging and discharging, and FC is the full charge capacity.

SOC (%) = q / FC × 100 (3)
However, current I = charge q / time t.

  Here, it is assumed that the discharge current I = constant and the internal resistance R = constant. Moreover, the internal resistance R = constant is a value when the temperature is lower than the threshold temperature. Then, from the above equations (1) and (2), the amount of current necessary for raising the current temperature to the threshold temperature is obtained. Then, from the equation (3), the SOC at the end of discharge (at the time when the threshold temperature is reached) can be calculated from the SOC at the start of discharge (at the time below the threshold temperature). At this time, since the time until the amount of current is obtained is also known, the time required to raise the threshold temperature is known.

  Further, the amount of charge from the SOC at the time when the calculated threshold temperature is reached to full charge is assumed to be constant when charging is performed at room temperature (that is, above the threshold temperature) (3) above. ) Calculate from the formula.

  As a result, the discharge time required to raise the temperature to the threshold temperature and the time required to fully charge from the SOC reached after reaching the threshold temperature are known. That is, it is possible to calculate the time required to fully charge when charging is started after discharging.

  On the other hand, when the temperature is lower than the threshold temperature, the time from the start of immediate charging until full charging is different depending on the temperature. Therefore, it is necessary to obtain in advance an experiment (or simulation). This is as shown by the dotted line in FIG. Therefore, when the temperature is lower than the threshold temperature, the time until the battery is fully charged by immediate charging is obtained in advance and stored in the storage unit 72. For example, for each temperature lower than the threshold temperature, the time required for full charge when the temperature differs in increments of 10 ° C. such as −10 ° C., −20 ° C., and −30 ° C. is stored. Of course, it may not be in increments of 10 ° C.

  Then, the battery is immediately charged from the temperature corresponding to the calculated time to the calculated threshold temperature + the time required from the SOC after discharge to full charge (charge after discharge) and the current temperature (temperature of S1) stored in advance. Compare the time required for full charge (immediate charge).

Again, for comparison, the charge time at the charge processing start temperature stored in advance is compared with the charge time close to the temperature measured in step S1. For example, when the use limit temperature of the secondary battery 2 is −40 ° C. and the threshold temperature is 0 ° C., the temperature measured in step S1 (that is, the charging processing start temperature) is −10 ° C. when the temperature is 0 ° C. to 15 ° C. Use the charging time with immediate charging. When the temperature in step S1 is −15 ° C. to −25 ° C., the charging time by immediate charging of −20 ° C. is used. When the temperature in step S1 is −25 ° C. to −40 ° C., the charging time by immediate charging at −30 ° C. is used. Of course, the temperature of such immediate charging is not limited to 10 ° C increments, and if this interval is narrowed, the selection between post-discharge charging and immediate charging can be controlled more finely. in this case,
As a result of the comparison, if charging after discharging is faster, charging is performed after discharging, and if charging is performed immediately, charging is performed immediately.

  Also in this second selection method, it is possible to select the post-discharge charge or the immediate charge according to the charge time (preliminarily designated time) or SOC (predesignated SOC) desired by the user.

  When the user selects a desired time as a reference, the charging is switched from discharging to charging at that time, and charging is performed after discharging when the obtained SOC is higher than the SOC obtained for immediate charging. In this case, it is necessary to store in the storage unit 72 in advance the SOC that arrives at each of a plurality of predetermined temperatures that are lower than the predetermined temperature and that has reached each elapsed time since the start of immediate charging.

  In this case, first, it is determined whether or not the temperature can be raised above the threshold temperature within the time desired by the user. If the temperature can be raised above the threshold temperature within the time desired by the user, charging is performed from there and the SOC when the time desired by the user is reached is obtained. And it compares with SOC by the immediate charge close | similar to the user's desired time from the SOC at the time of the immediate charge for every elapsed time memorize | stored beforehand. As a result, if the SOC of the post-discharge charge is higher in the same time charge, the post-discharge charge is selected.

  However, referring to the graph of FIG. 3, the post-discharge charge becomes faster in the time after t2. Therefore, simply, the time t2 may be stored for each charging process start temperature, and the post-charging discharge may be selected only when the time desired by the user is longer than the time t2.

  When the SOC desired by the user is used as a reference, the situation is almost the same. First, the time until the user arrives at the desired SOC is compared with the time until the SOC at the time of instant charging stored in advance is compared. If the post-discharge charge is faster, the post-discharge charge is selected.

  Also in this case, referring to the graph of FIG. 3, the post-discharge charge becomes faster after time t2. Accordingly, even when charging is performed until the SOC desired by the user is reached, the SOC at t2 is stored for each charging processing start temperature, and the SOC desired by the user is t2. If it is higher than the SOC, the post-discharge post-charge may be selected.

  In the second selection method as well, when discharging, it is necessary to start from an SOC that can be discharged until the threshold temperature is reached. In addition, the lower limit value is set for the SOC reached by the discharge as in the first selection method.

  Here, the reason for starting from the SOC that can be discharged until the threshold temperature is reached will be described.

  There is a case where the SOC at the time when the charging process is started does not reach a storage amount enough to reach the threshold temperature. In such a case, in the second selection method, it is determined how much the temperature rises when discharged to the lower limit value of SOC. At this time, even if the SOC at the time of starting the charging process is discharged to the lower limit value, if the threshold temperature is not reached, immediate charging is performed. This is because when the SOC at the time when the charging process is started is discharged to the lower limit value, the threshold temperature is not reached, which is the same as charging at a low temperature where charging efficiency is low. Moreover, since charging is performed after the SOC is lowered by discharge, the time required for the discharge is added. For this reason, the temperature has not risen sufficiently, and while the charging efficiency is poor, it is necessary to charge the portion where the SOC has further decreased. For this reason, charging after discharging cannot be faster than immediate charging.

  In the second selection method, since the time required for charging / discharging is obtained by calculation, it is not necessary to store a graph (including numerical data based thereon) in advance as in the first selection method. Therefore, the capacity of the storage unit 72 in the control device can be small compared to the first selection method.

[Deformation]
As described above, the selection in step S3 is influenced by the internal resistance of the secondary battery. On the other hand, it is known that a lithium ion secondary battery gradually increases in internal resistance while being used.

  In the present embodiment, an increase in resistance due to a change with time may be taken into account before step S3 described above.

  FIG. 4 is a flowchart showing a procedure for taking into account an increase in resistance due to a change with time. This flowchart is a procedure inserted between steps S2 and S3 of the flowchart shown in FIG.

  In order to take into account the increase in resistance due to changes over time, it is necessary to perform processing before step S3. Therefore, here, after step S2, as shown in FIG. 4, the control unit 7 determines whether or not to rewrite the resistance (S21). For this determination, for example, an index that can be used to know a change with time of the battery based on the usage time of the battery, the number of times of charging and discharging, and the like is used. Then, for example, rewriting is performed when the usage time has elapsed, or rewriting is performed when the number of charge / discharge times is reached, and the like is stored in the storage unit 72 in advance.

  If rewriting is not necessary in this step S21 (S21: NO), the process proceeds to step S3 as it is.

  If it is determined in step S21 that rewriting is necessary (S21: YES), the following selection is made depending on whether the first selection method or the second selection method is used in the selection of S3. Processing is performed (S22).

  When the first selection method described above is used, the charge / discharge time in the graph shown in FIG. 3 is delayed according to the change with time. In other words, if the SOC is the same, the charging / discharging time until the SOC is reached is delayed. Specifically, the curve of the graph is shifted in the direction of delaying along the time axis (rightward in FIG. 3) at a predetermined rate.

  In addition, when the second selection method is used, the internal resistance R used for the calculation is multiplied by a predetermined increase coefficient α to obtain the value of the internal resistance R that has increased with time.

  The delay amount in the case of the first selection method and the increase coefficient α in the case of the second selection method are obtained by experiments or simulations.

  Then, after the influence of the change over time is taken into consideration according to each method in step S22, the control unit 7 moves to step S3, and selects between post-discharge charge and immediate charge as already described.

  As a result, even in a secondary battery that has been used for a long time, it is possible to select whether to perform post-discharge charging or immediate charging in consideration of the effect of increased internal resistance due to changes over time. .

  In FIG. 4, the process of inserting steps S21 and S22 between S2 and S3 and the process below may be anywhere before S3. Preferably, it is provided immediately before step S3. Thereby, use time and the frequency | count of charging / discharging can be reflected correctly to the process of step S3.

[Secondary battery]
Hereinafter, a laminated lithium ion secondary battery will be described as an example of the secondary battery 2.

(Non-bipolar lithium ion secondary battery)
FIG. 5 is a schematic cross-sectional view for explaining the overall structure of a non-bipolar, stacked lithium ion secondary battery.

  The lithium ion secondary battery 10 that is the secondary battery 2 shown in FIG. 5 has a configuration in which the power generation element 17 is housed and sealed using the battery exterior material 22. Here, the power generation element 17 is a positive electrode plate in which the positive electrode active material layer 12 is formed on both surfaces of the positive electrode current collector 11, the electrolyte layer 13, and both surfaces of the negative electrode current collector 14 (for the lowermost layer and the uppermost layer of the power generation element). The negative electrode plate in which the negative electrode active material layer 15 is formed on one side) is laminated. When laminating, the positive electrode active material layer 12 on one surface of one positive electrode plate and the negative electrode active material layer 15 on one surface of one negative electrode plate adjacent to the one positive electrode plate face each other with the electrolyte layer 13 therebetween. The electrolyte layer 13 and the negative electrode plate are stacked in this order.

  As a result, the adjacent positive electrode active material layer 12, electrolyte layer 13, and negative electrode active material layer 15 constitute one unit cell layer 16. Therefore, it can be said that the lithium ion secondary battery 10 has a configuration in which a plurality of single battery layers 16 are stacked and electrically connected in parallel. Note that the positive electrode active material layer 12 is formed on only one side of the outermost positive electrode current collector 11 a located in both outermost layers of the power generation element 17. In addition, you may change arrangement | positioning of a positive electrode plate and a negative electrode plate. In that case, the outermost layer negative electrode current collector (not shown) is positioned on both outermost layers of the power generation element 17, and the negative electrode active material layer 15 is formed only on one side also in the case of the outermost layer negative electrode current collector. To be.

  The positive electrode tab 18 and the negative electrode tab 19 that are electrically connected to the electrode plates (the positive electrode plate and the negative electrode plate) are connected to the positive electrode current collector 11 and the negative electrode current collector of each electrode plate via the positive electrode terminal lead 20 and the negative electrode terminal lead 21. It is attached to the body 14 by ultrasonic welding or resistance welding. Thus, the positive electrode tab 18 and the negative electrode tab 19 that are electrically connected to the positive electrode current collector 11 and the negative electrode current collector 14 have a structure exposed to the outside of the battery exterior material 22.

  From the viewpoint of such an electrode structure, the lithium ion secondary battery 10 is referred to as a non-bipolar lithium ion secondary battery, in contrast to the structure shown in FIG.

(Bipolar lithium ion secondary battery)
FIG. 6 is a schematic cross-sectional view for explaining the entire structure of a bipolar and stacked lithium ion secondary battery according to another embodiment. Here, the bipolar type is used as a term corresponding to the non-bipolar type.

  A lithium ion secondary battery 30 shown in FIG. 6 has a structure in which a power generation element 37 in which a charge / discharge reaction actually proceeds is sealed inside a battery outer packaging material 42. As shown in FIG. 6, the power generation element 37 of the bipolar secondary battery 30 includes an electrolyte layer 35 sandwiched between two or more bipolar electrodes 34, and a positive electrode active material of adjacent bipolar electrodes 34. The layer 32 and the negative electrode active material layer 33 are opposed to each other with the electrolyte layer 35 interposed therebetween. Here, the bipolar electrode 34 has a structure in which the positive electrode active material layer 32 is provided on one surface of the current collector 31 and the negative electrode active material layer 33 is provided on the other surface. That is, in the bipolar secondary battery 30, the bipolar electrode 34 having the positive electrode active material layer 32 on one side of the current collector 31 and the negative electrode active material layer 33 on the other side is provided with the electrolyte layer 35. A power generation element 37 having a structure in which a plurality of layers are stacked via a gap is provided.

  The adjacent positive electrode active material layer 32, electrolyte layer 35, and negative electrode active material layer 33 constitute one unit cell layer 36. Therefore, it can be said that the bipolar secondary battery 30 has a configuration in which the single battery layers 36 are stacked. In addition, an insulating layer (seal part) 43 is disposed in the periphery of the unit cell layer 36 in order to prevent liquid junction due to leakage of the electrolyte from the electrolyte layer 35. By providing the insulating layer 43, the adjacent current collectors 31 can be insulated, and a short circuit due to contact between adjacent electrodes (the positive electrode active material layer 32 and the negative electrode active material layer 33) can be prevented.

  The positive electrode 34a and the negative electrode 34b located in the outermost layer of the power generation element 37 may not have a bipolar electrode structure. For example, a structure in which the positive electrode active material layer 32 or the negative electrode active material layer 33 only on one side necessary for the current collectors 31a and 31b may be arranged. Specifically, as shown in FIG. 5, a positive electrode active material layer 32 may be formed only on one side of the positive electrode side outermost layer current collector 31 a located in the outermost layer of the power generation element 37. Good. Similarly, the negative electrode active material layer 33 may be formed on only one surface of the negative electrode side outermost layer current collector 31b located in the outermost layer of the power generation element 37. In the bipolar lithium ion secondary battery 30, current collector plates 38 a and 39 b are provided on the outer sides of the positive electrode side outermost layer current collector 31 a and the negative electrode side outermost layer current collector 31 b at the upper and lower ends, respectively. The current collecting plates 38 a and 39 b are extended to be a positive electrode tab 38 and a negative electrode tab 39, respectively. The current collecting plates 38a and 39b may be joined via a positive terminal lead and a negative terminal lead as necessary. Further, the positive electrode side outermost layer current collector 31 a may be extended to form a positive electrode tab 38, which may be derived from a laminate sheet that is the battery exterior material 42. Similarly, the negative electrode side outermost layer current collector 31b may be extended to form a negative electrode tab 39, which may be similarly derived from a laminate sheet that is the battery outer packaging material 42.

  Further, the bipolar lithium ion secondary battery 30 may have a structure in which the power generation element 37 is sealed in the battery outer packaging material 42 under reduced pressure, and the positive electrode tab 38 and the negative electrode tab 39 are taken out of the battery outer packaging material 42. This is because such a structure can prevent external impact and environmental degradation during use. The basic configuration of the bipolar lithium ion secondary battery 30 can be said to be a configuration in which a plurality of stacked unit cell layers 36 are connected in series.

(Appearance shape)
FIG. 7 is a perspective view showing the appearance of the stacked lithium ion secondary battery shown in FIG. 5 or FIG. It is also called a flat secondary battery because of its external shape.

  As shown in FIG. 7, the laminated flat lithium ion secondary battery 50 has a rectangular flat shape, and a positive electrode tab 58 and a negative electrode tab 59 for taking out electric power from both sides thereof. Has been pulled out. The power generation element 57 is encased by the battery outer packaging material 52 of the lithium ion secondary battery 50, and the periphery thereof is heat-sealed. The power generation element 57 is sealed with the positive electrode tab 58 and the negative electrode tab 59 pulled out to the outside. Has been. Here, the power generation element 57 corresponds to the power generation elements 17 and 37 of the non-bipolar or bipolar lithium ion secondary batteries 10 and 30 shown in FIGS. A plurality of single battery layers (single cells) 16 composed of the electrolyte layer 13 and the negative electrode layer 15 are laminated.

  And in this embodiment, the temperature sensor 4 is affixed on the exterior member surface of this laminated flat lithium ion secondary battery 50. Thereby, the present temperature of the secondary battery 2 required as the secondary battery system 1 is measured.

  7 is not particularly limited, and the positive electrode tab 58 and the negative electrode tab 59 may be pulled out from the same side, or the positive electrode tab 58 and the negative electrode tab 59 may be removed. It is not limited to the form shown in FIG. 7, for example, it may be divided into a plurality of parts and taken out from each side.

  Next, the detail of each member in the lithium ion secondary battery of the above forms is demonstrated.

[Current collector]
The current collector is made of a conductive material. The material constituting the current collector is not particularly limited as long as it has conductivity. For example, conventionally known materials such as metals and conductive polymers can be appropriately used. Specifically, at least one selected from the group consisting of Fe, Cr, Ni, Mn, Ti, Mo, V, Nb, Al, Cu, Ag, Au, Pt and carbon, for example, two or more The current collector material such as stainless steel made of the above alloy can be preferably used. In the present embodiment, a Ni / Al clad material, a Cu / Al clad material, or a plating material obtained by combining these current collector materials can be preferably used. The current collector may be a current collector in which the surface of a metal (excluding Al) as the current collector material is coated with Al as the other current collector material. Moreover, you may use the electrical power collector which bonded together the metal foil which is two or more said electrical power collector materials depending on the case.

  The thickness of the current collector is not particularly limited, but any current collector is usually about 1 to 100 μm, preferably about 1 to 50 μm. However, even if it is outside the above range, it is included in the technical scope of the present invention as long as it does not impair the effects of the present invention.

  In addition to the foil using the said material, you may use a collector comprised from the mesh using the said material, an expanded grid (expanded metal), a punched metal, etc. other than the foil using the said material. . The mesh opening, wire diameter, number of meshes, etc. are not particularly limited, and conventionally known ones can be used.

  As the positive electrode current collector 11 of the non-bipolar battery 10, Al, Ni, stainless steel (SUS), or the like can be used. Al is preferable in that it can be easily processed into a thin film and is inexpensive. As a method for supporting the positive electrode active material layer (positive electrode mixture) on the positive electrode current collector, a method of pressure molding, or pasting using a solvent or the like, coating and drying on the current collector, pressing, etc. The method of adhering is mentioned. The method of supporting the positive electrode active material layer (positive electrode mixture) on the positive electrode current collector can also be applied to the method of supporting the negative electrode active material layer (negative electrode mixture) on the negative electrode current collector.

[Positive electrode active material layer (positive electrode mixture)]
The positive electrode active material layer (positive electrode mixture) is a layer that is formed on the current collector and includes a positive electrode active material that plays a central role in the charge / discharge reaction. Examples of the positive electrode active material layer (positive electrode mixture) include a positive electrode active material, a conductive material (also referred to as a conductive auxiliary agent) for increasing electrical conductivity, a binder, and the like. Moreover, the compounding ratio of these components is not particularly limited, and can be adjusted by appropriately referring to known knowledge about existing lithium ion secondary batteries.

(Positive electrode active material)
As already described, the lithium ion secondary battery uses, for example, a ternary positive electrode active material as the positive electrode active material.

Examples of the positive electrode active material include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni, Co, Mn) O ₂ , Li ₂ MnO ₃ , Li ₂ MnO ₃ —LiMO ₂ (M = Co, Ni, etc.) ) Lithium-transition metal composite oxides such as solid solutions and those in which some of these transition metals are substituted with other elements, lithium-transition metal phosphate compounds, lithium-transition metal sulfate compounds, and the like. In some cases, two or more positive electrode active materials may be used in combination. Preferably, a lithium-transition metal composite oxide is used as the positive electrode active material from the viewpoint of capacity and output characteristics.

More specifically, a part of Ni in LiNiO ₂ and LiNiO ₂ is substituted with another element such as Co or Al, LiCoO ₂ , Li (Ni, Co, Mn) O ₂ (= LiNixCoyMnzO ₂ ; x + y + z = 1), etc., hexagonal layered structure such as Li ₂ MnO ₃ , Li ₂ MnO ₃ —LiMO ₂ (M = Co, Ni, etc.) solid solution (close-packed) layered rock salt type, rock salt type For example, a positive electrode active material having a layered structure) may be used.

  Of course, positive electrode active materials other than those described above may be used.

(Conductive material)
The conductive material (also referred to as a conductive auxiliary agent) refers to an additive blended to improve the conductivity of the positive electrode active material layer (positive electrode mixture). The conductive aid is not particularly limited, and a conventionally known one can be used. Examples thereof include carbon materials such as carbon black such as natural graphite, artificial graphite, cokes, and acetylene black, graphite, and carbon fiber. As the conductive material, each may be used alone, or for example, artificial graphite and carbon black may be mixed and used. When the conductive assistant is included, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery.

(binder)
The binder is added to the active material layer for the purpose of maintaining the electrode structure (three-dimensional network) by binding the active materials to each other or the active material and the current collector or conductive additive.

  Examples of the binder include polyvinylidene fluoride (hereinafter sometimes referred to as PVDF), polytetrafluoroethylene (hereinafter also referred to as PTFE), tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride-based copolymer. Polymers such as copolymers, hexafluoropropylene / vinylidene fluoride copolymers, tetrafluoroethylene / perfluorovinyl ether copolymers, polyvinyl acetate, polyimide, acrylic resins, and other thermoplastic resins, epoxy resins, polyurethane resins, and Examples thereof include thermosetting resins such as urea resins, and rubber materials such as styrene butadiene rubber (SBR). These may be used alone or in combination of two or more. These binders used in the production process are those dissolved or dispersed in a solvent in which the binder is soluble or dispersible, such as N-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP) and water. You can also

  A fluororesin and a polyolefin resin as a binder, the ratio of the fluororesin in the positive electrode active material layer (positive electrode mixture) is 1 to 10% by mass, and the ratio of the polyolefin resin is 0.1 to 10% by mass. Thus, it is desirable to use in combination with the positive electrode active material powder of this embodiment. This is preferable because it has excellent binding properties with the current collector and can further improve the safety of the lithium ion secondary battery against external heating as typified by a heating test.

(Supporting salt)
The supporting salt (lithium salt) _{include, LiPF 6, LiBF 4, LiClO} 4, LiAsF 6, LiTaF 6, LiAlCl 4, inorganic acid anion salts such as _{Li 2 B10Cl 10; LiCF 3 SO} 3, Li Organic acid anion salts such as (CF ₃ SO ₂ ) ₂ N and Li (C ₂ F ₅ SO ₂ ) ₂ N can be mentioned. These supporting salts may be used alone or in combination of two or more.

(Other details of cathode active material)
The average particle size of the positive electrode active material is not particularly limited. However, if the average particle size is too large, the reaction surface area of the active material becomes small, or lithium ion conduction inside the active material particles limits the lithium ion conduction in the active material layer. From such a viewpoint, the average particle diameter of the active material is preferably 0.1 to 100 μm, more preferably 1 to 50 μm, and further preferably 1 to 20 μm. However, forms outside these ranges can also be employed. In addition, the value measured by the laser diffraction type particle size distribution measurement (laser diffraction scattering method) shall be employ | adopted for the average particle diameter of an active material.

  The content of the positive electrode active material in the positive electrode active material layer (positive electrode mixture) is preferably 70 to 98% by mass, more preferably 80 to 98% by mass with respect to the total mass of the positive electrode active material layer. . If the content of the positive electrode active material is in the above range, it is preferable because the energy density can be increased.

  The thickness of the positive electrode active material layer (thickness on one side of the current collector) is preferably 20 to 500 μm, more preferably 20 to 300 μm, and still more preferably 20 to 150 μm.

[Negative electrode active material layer]
The negative electrode active material layer in the negative electrode is a layer that is formed on the current collector and includes a negative electrode active material that bears the center of the charge / discharge reaction and Li particles. The negative electrode active material layer is composed of a negative electrode active material, and, if necessary, a conductive material (also referred to as a conductive auxiliary agent) for increasing electrical conductivity, a binder, an electrolyte (polymer matrix, ion conductive polymer, electrolytic solution, etc.), Examples thereof include a support salt (electrolyte salt) and the like for increasing ion conductivity. In addition, the blending ratio of these components is not particularly limited, and can be adjusted by appropriately referring to known knowledge about the lithium ion secondary battery.

(Negative electrode active material)
The negative electrode active material used for the negative electrode active material layer is preferably carbon (carbon) and a material that can be doped / undoped with lithium. Examples of carbon include graphite-based carbon materials such as natural graphite, artificial graphite, and expanded graphite, and carbon materials such as carbon black, activated carbon, carbon fiber, coke, soft carbon, and hard carbon. In some cases, two or more negative electrode active materials may be used in combination.

  However, in the case where the negative electrode active material itself is a substance or composition that does not cause metal deposition, for example, a lithium transition metal-composite oxide having a partial composition does not make sense to apply this embodiment. This is because if the metal (particularly lithium) does not precipitate in the negative electrode, there will be no reduction in capacity.

  However, the negative electrode is not limited to carbon (carbon), and this embodiment is suitable when a material or composition that causes the deposition of metal (particularly lithium) in the negative electrode is used.

(Conductive material, binder)
As the conductive material and the binder, those described in the section of the positive electrode active material layer can be used similarly. In particular, when a negative electrode active material having no conductivity such as a material alloyed with lithium is used, the conductive material is effectively used. Note that when a conductive metal / alloy, carbon material, or the like is used for the negative electrode active material, the conductive material can be omitted.

  The average particle diameter of the negative electrode active material is not particularly limited. However, if the average particle diameter is too large, the reaction surface area of the active material may be reduced, or lithium ion conduction inside the active material particles may limit the lithium ion conduction in the active material layer. From such a viewpoint, the average particle diameter of the active material is preferably 0.1 to 20 μm. However, forms outside these ranges can also be employed. In this application, the average particle diameter of the active material is a value measured by a laser diffraction / scattering particle size distribution analyzer.

[Electrolyte layer]
The electrolyte (layer) includes an electrolyte and, if necessary, an organic solvent (plasticizer) and a separator.

  As the electrolyte, for example, a liquid electrolyte or a polymer electrolyte is used and should not be limited. Various conventionally known electrolytic solutions can be appropriately used, but a non-aqueous electrolyte is particularly preferable.

(Liquid electrolyte)
The liquid electrolyte (electrolytic salt and an organic solvent), for _{example, LiPF 6, LiBF 4, LiClO} 4, LiAsF 6, LiTaF 6, LiAlCl 4, Li 2 B 10 Cl 10 inorganic acid anion salts such as, LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, Li (C ₂ F ₅ SO ₂ ) ₂ N (also referred to as LiBETI) and the like, at least one kind of supporting salt (electrolyte salt) Cyclic carbonates such as propylene carbonate and ethylene carbonate; chain carbonates such as dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate; tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-dibutoxyethane, etc. Ethers; lactones such as γ-butyrolactone; nitriles such as acetonitrile; esters such as methyl propionate; amides such as dimethylformamide; at least one or more selected from methyl acetate and methyl formate Can be used in which a plasticizer (organic solvent) such as an aprotic solvent is mixed. However, it is not necessarily limited to these.

(Polymer electrolyte)
On the other hand, the polymer electrolyte is classified into a gel electrolyte containing an electrolytic solution and an intrinsic polymer electrolyte containing no electrolytic solution.

  The gel electrolyte is a solid polymer electrolyte having ion conductivity and containing an electrolyte used in a conventionally known lithium ion secondary battery, and further, in a polymer skeleton having no lithium ion conductivity. In addition, an electrolyte holding solution is also included. Examples of the solid polymer electrolyte having ion conductivity include known solid polymer electrolytes such as polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. This solid polymer electrolyte having ion conductivity is used as an intrinsic (all solid) polymer electrolyte.

  Examples of the polymer having no lithium ion conductivity used in the gel electrolyte include polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC), polyacrylonitrile (PAN), and polymethyl methacrylate (PMMA). However, it is not necessarily limited to these. PAN, PMMA, and the like, which are in a class with little ion conductivity, can be used as the above polymer having ion conductivity, but are used here as a polymer gel electrolyte. This is exemplified as a polymer having no lithium ion conductivity.

  In addition, when an electrolyte layer is comprised from a liquid electrolyte or a gel electrolyte, you may use a separator for an electrolyte layer. Specific examples of separators include, for example, fluororesins, polyolefins such as polyethylene and polypropylene, nylon (registered trademark of DuPont, USA), microporous films made of aromatic aramids, nonwoven fabrics, woven fabrics, etc. The material which has is mentioned. The thickness of the separator is preferably as thin as possible as long as the mechanical and chemical strength is maintained from the viewpoint of increasing the volume energy density of the battery and reducing the internal resistance, and is preferably 5 to 200 μm.

  The intrinsic polymer electrolyte has a structure in which a supporting salt (lithium salt) is dissolved in a matrix polymer that is a solid polymer electrolyte having ion conductivity, and does not include an organic solvent that is a plasticizer. Therefore, when the electrolyte layer is composed of an intrinsic polymer electrolyte, there is no fear of liquid leakage from the battery, and the reliability of the battery can be improved.

  In addition, various additives may be included in the electrolyte layer (electrolytic solution).

[Insulation layer (seal part)]
The insulating layer (seal part) 43 is formed by contact between adjacent current collectors in the lithium ion secondary battery, in particular, the bipolar battery 30 shown in FIG. 2, or a slight unevenness at the end of the laminated electrode. In order to prevent a short circuit from occurring, it is disposed in the periphery of the unit cell layer 36. The insulating layer 43 only needs to have insulating properties, sealing properties against falling off of the solid electrolyte, sealing properties against moisture permeation from the outside (sealing properties), heat resistance at the battery operating temperature, and the like. For example, urethane resin, epoxy resin, polyethylene resin, polypropylene resin, polyimide resin, rubber and the like can be used. Of these, urethane resins and epoxy resins are preferred from the viewpoints of corrosion resistance, chemical resistance, ease of production (film forming properties), economy, and the like.

[tab]
As the material of the tabs (positive electrode tabs 18 and 38 and negative electrode tabs 19 and 39), aluminum, copper, nickel, stainless steel, alloys thereof, or the like can be used. These are not particularly limited, and known materials conventionally used as tabs can be used.

[Exterior body]
In the lithium ion secondary batteries 10 and 30, in order to prevent external impact and environmental degradation during use, the entire power generation element on which the electrolyte holding layer is formed is attached to the battery exterior materials 22 and 42 or a battery case (not shown). ) Is desirable. As the exterior material, a conventionally known metal can case can be used, and a bag-like case that can cover a power generation element using a laminate sheet containing aluminum can be used. Since the laminate sheet has a high degree of freedom in shape, it can be suitably applied to a battery using a negative electrode material having a large expansion and contraction in addition to being easily mounted in a narrow space.

  Since the metal can case type exterior body has strength, it can absorb even if the power generation element in the can expands and contracts somewhat, and the thickness of the cell does not change. Moreover, it is possible to obtain a can case having a desired strength and size by examining the material of the can, the design of the plate thickness, the clearance between the outer can and the power generation element, and the like.

  The polymer-metal composite laminate sheet is not particularly limited, and a conventionally known sheet formed by arranging a metal film between polymer films and laminating and integrating the whole can be used. Specifically, it is arranged as an outer protective layer (laminated outermost layer) made of a polymer film, a metal film layer, a heat-sealing layer (laminated innermost layer) made of a polymer film, and the whole is laminated and integrated. Is mentioned.

  In particular, it is preferable to use an aluminum laminate film outer package having a high degree of freedom in shape. Aluminum laminate refers to a laminate containing aluminum. Specific examples of the aluminum laminate film include, but are not limited to, a three-layer laminate film in which polypropylene (PP), aluminum, and nylon are laminated in this order.

  The secondary battery having the form described above is used as the secondary battery 2 in the secondary battery system 1 already described.

[Effect of the embodiment]
Next, functions and effects of the embodiment described above will be described.

  (1) In the present embodiment, discharging is performed before charging at a low temperature at which charging efficiency is degraded. As a result, the temperature inside the secondary battery 2 rises, so that the charging efficiency is improved and the charging time can be shortened.

  The temperature change inside the secondary battery 2 due to charging / discharging has the influence of not only Joule heat due to current flow but also reaction heat accompanying charging / discharging. In the lithium ion secondary battery, the reaction heat is an endothermic reaction during charging and an exothermic reaction during discharging. Therefore, at the low temperature, when charging is started as it is, the temperature is not increased immediately because charging is an endothermic reaction, and the charging efficiency is poor because the temperature remains low for a while after charging. On the other hand, since the reaction is exothermic at the time of discharge, the inside of the secondary battery 2 generates heat at the start of discharge. Therefore, the internal temperature of the secondary battery 2 can be raised by first discharging at a low temperature, thereby improving the charging efficiency and consequently shortening the entire charging time.

  In particular, secondary batteries containing non-aqueous electrolytes have lower electrolyte conductivity and higher battery resistance than aqueous electrolytes, and battery resistance at low temperatures is several or tens of times lower than normal temperatures. Therefore, if the temperature is kept low, the charging time becomes long. Therefore, it is very effective in a lithium ion secondary battery containing a nonaqueous electrolyte.

  In addition, in the present embodiment, in order to raise the temperature inside the secondary battery 2 at a low temperature, a heating device such as a heater is not used unlike the prior art, so that the space efficiency is not deteriorated. Therefore, since it can be set as large as possible when installing the secondary battery 2 in a limited space such as an automobile, the energy density for the battery installation space can be increased.

  (2) In the present embodiment, the temperature inside the secondary battery 2 is estimated from the voltage and current during discharge. Usually, since a temperature sensor cannot be arranged inside the secondary battery 2, it is difficult to know an accurate internal temperature. Thus, in the second embodiment, by estimating this, switching from discharging to charging can be performed more quickly.

  (3) In the present embodiment, the relationship between the SOC and charge / discharge time associated with charge / discharge is stored in advance, and charging is performed after discharge only when charging after discharge is not faster based on the relationship. did. Depending on the SOC and battery temperature, there are a range in which charging after discharge is faster and a range in which immediate charging is faster. For this reason, it becomes possible to charge more quickly by selecting any one based on the relationship between the SOC accompanying charge / discharge and the charge / discharge time.

  Then, using the relationship between the SOC and the charge / discharge time associated with the charge / discharge, a faster charging method can be selected in accordance with a designated time, for example, a time desired by the user. In some cases, such as charging an electric vehicle, a time for occupying a charging place and a facility (charging device) necessary for charging may be determined. In such a case, charging can be performed so as to achieve the maximum SOC within the determined time.

  Further, by using the relationship between the SOC and the charge / discharge time associated with this charge / discharge, it becomes possible to select a faster charging method according to the designated SOC, for example, the SOC desired by the user. For example, in the case of charging an electric vehicle, it is possible to perform charging more quickly so that the vehicle can run a certain distance from now on.

(4) In the present embodiment, it is possible to select whether or not post-discharge charging is faster than immediate charging by calculation. By calculating, it is not necessary to memorize | store the relationship between SOC accompanying charging / discharging and charging / discharging time beforehand. For this reason, even if the capacity of the storage unit is small, it is possible to select a charging method that is faster according to the time and SOC desired by the user. Even in the case of this calculation, (5) In this embodiment, the internal resistance that changes with time is taken into account. This is because, in the first selection method for selecting whether charging after discharge or immediate charging, the charge / discharge time until the same SOC is reached is delayed in the relationship between the SOC and the charge / discharge time. In the second selection method, the calculation is performed by increasing the internal resistance by applying a predetermined increase coefficient to the internal resistance. As a result, the charging process can be speeded up in response to changes over time of the secondary battery.

  The embodiments and examples to which the present invention is applied have been described above, but the present invention is not limited to these embodiments and examples.

  For example, as a secondary battery, a laminated flat lithium ion secondary battery has been described as an example, but a wound lithium ion battery or a cylindrical flat battery is deformed to form a rectangular flat battery. There is no particular limitation such as a simple shape.

  In the present invention, 0 ° C. is exemplified as a threshold temperature at which it is determined that charging efficiency is deteriorated in the secondary battery. However, this temperature varies depending on the characteristics and size of the battery and is appropriately set according to the battery characteristics. Will do.

  In addition, it goes without saying that the present invention can be variously modified based on the configuration described in the claims.

1 Secondary battery system,
2, 10, 30 Lithium ion secondary battery (secondary battery),
3 Voltage sensor,
4 Temperature sensor,
5 Voltage current adjustment part,
6 Current sensor,
7 Control unit,
8 Secondary battery holder,
11 positive electrode current collector,
12, 32 positive electrode active material layer,
13, 35 electrolyte layer,
14 negative electrode current collector,
15, 33 negative electrode active material layer,
16, 36 cell layer,
17, 37 Power generation element,
18, 38 positive electrode tab,
19, 39 negative electrode tab,
20 positive terminal lead,
21 negative terminal lead,
22 Battery exterior material,
30 Bipolar lithium ion secondary battery,
31 Bipolar lithium-ion secondary battery current collector,
31a The outermost layer current collector on the positive electrode side,
31b The outermost layer current collector on the negative electrode side,
34 Bipolar electrode,
34a positive electrode,
34b negative electrode,
38a Current collector plate further outside the positive electrode side outermost layer current collector,
39a Current collector plate further outside the negative electrode side outermost layer current collector,
43 Insulating layer (seal part),
50 Flat type lithium ion secondary battery,
52 Battery exterior material (laminate film),
57 power generation element 58 positive electrode tab,
59 Negative electrode tab.

Claims (14)

A lithium ion secondary battery;
A temperature sensor for measuring an outer surface temperature of the lithium ion secondary battery;
When performing a charging process on the lithium ion secondary battery, if the temperature measured by the temperature sensor is less than a predetermined temperature, a control unit that controls to charge after discharging,
A secondary battery system comprising:   The controller obtains the internal temperature of the lithium ion secondary battery from the voltage and current of the lithium ion secondary battery during the discharge, and when the internal temperature becomes equal to or higher than the predetermined temperature, the discharge The secondary battery system according to claim 1, wherein the charging is terminated and the charging is switched to the charging. A storage unit that stores a relationship between SOC and time associated with charge / discharge obtained in advance for each different charge start temperature;
The control unit refers to the relationship between SOC and time associated with charging / discharging according to the charging processing start temperature stored in the storage unit, and charges after the discharging for a predetermined time Compared with the SOC that reaches the specified time and the SOC that is reached when the battery is immediately charged during the specified time, the SOC that reaches the specified time is higher when the battery is charged after the discharge. 3. The secondary battery system according to claim 1, wherein charging is controlled after the discharging. A storage unit that stores a relationship between SOC and time associated with charge / discharge obtained in advance for each different charge start temperature;
The control unit refers to the relationship between SOC and time associated with charging / discharging according to the charging processing start temperature stored in the storage unit, and becomes a SOC designated in advance when charging after the discharging. When the time until the designated SOC is reached in the case of immediate charging is shorter than the time until the designated SOC is charged after the discharge, The secondary battery system according to claim 1, wherein the secondary battery system is controlled to be charged after the discharging.   The said control part increases the time required for charging / discharging in the relationship between SOC and time accompanying charging / discharging memorize | stored in the said memory | storage part according to a time-dependent change of a secondary battery. Or the secondary battery system of 4. For each temperature at which the charging process start temperature is different, the storage unit stores in advance the SOC that is reached for each elapsed time since the start of immediate charging;
The controller is
The amount of current required to reach the predetermined temperature (a), the SOC reached by the discharge (b), the time required for the discharge (c), and the SOC reached by the discharge from the time designated in advance Calculate and estimate the SOC (d) that arrives at the time obtained by subtracting the time (c),
Corresponding to the specified time in the immediate charge at a temperature close to the temperature measured by the temperature sensor among the reached SOC (d) and the SOC reached for each elapsed time stored in the storage unit 3. The secondary control according to claim 1, wherein, when the estimated SOC (d) is higher by the estimation than the SOC that is reached in a time to be Battery system. For each temperature at which the charging process start temperature is different, the storage unit stores in advance the time from the start of charging until the predetermined SOC is reached,
The controller is
The amount of current required to reach the predetermined temperature (a), the SOC reached by the discharge (b), the time required for the discharge (c), the SOC specified in advance when charging from the SOC reached by the discharge Calculate and estimate the time (e) required to reach
It is close to the temperature measured by the temperature sensor from the time obtained by adding the time (c) and the time (d) and the time to reach the predetermined SOC by the immediate charging stored in the storage unit. Compared with the time to reach the predetermined SOC by immediate charging at a temperature, the time until reaching the designated SOC is the time obtained by adding the time (c) and the time (d). 3. The secondary battery system according to claim 1, wherein the secondary battery system is controlled to be charged after the discharging in a short time. 4.   The secondary battery system according to claim 6, wherein the control unit performs the calculation by increasing an internal resistance of the secondary battery according to a change with time. When charging the lithium ion secondary battery,
Measuring an outer surface temperature of the lithium ion secondary battery;
Charging after discharging when the measured temperature is below a predetermined temperature;
A method for charging a secondary battery, comprising:   From the voltage and current of the lithium ion secondary battery during the discharge, the internal temperature of the lithium ion secondary battery is obtained, and when the internal temperature becomes equal to or higher than the predetermined temperature, the discharge is terminated and the The method for charging a secondary battery according to claim 9, wherein the charging is switched to charging. Store the relationship between SOC and time associated with charge / discharge obtained in advance for each different charge processing start temperature,
Referring to the relationship between the SOC and time associated with the charging / discharging, the SOC that is reached when charging after the discharging during a pre-specified time, and the case where the charging is performed immediately during the specified time 11. The charging according to claim 9, wherein when the SOC that is reached during the specified time is higher after the discharge than when the SOC is compared with the SOC, the charging is performed after the discharging. How to charge the next battery. Store the relationship between SOC and time associated with charge / discharge obtained in advance for each different charge processing start temperature,
With reference to the relationship between the SOC and time associated with the charging / discharging, the time until the SOC specified in advance when charging after the discharging, and the time until the SOC specified when charging immediately 11. The secondary battery according to claim 9, wherein the battery is charged after the discharge when the time until the designated SOC is reached is shorter after the discharge. Charging method. For each temperature at which the charging process start temperature is different, the SOC that arrives at every elapsed time since the start of immediate charging is stored in advance,
The amount of current required to reach the predetermined temperature (a), the SOC reached by the discharge (b), the time required for the discharge (c), and the SOC reached by the discharge from the time designated in advance Calculate and estimate the SOC (d) that arrives at the time obtained by subtracting the time (c),
Corresponding to the specified time in the immediate charge at a temperature close to the temperature measured by the temperature sensor among the reached SOC (d) and the SOC reached for each elapsed time stored in the storage unit 11. The method of charging a secondary battery according to claim 9, wherein if the reached SOC (d) is higher by the estimation than the SOC that is reached in a time to perform charging, the battery is charged after the discharging. . For each temperature at which the charging process start temperature is different, the time from when charging is started until the predetermined SOC is reached is stored in advance.
The amount of current required to reach the predetermined temperature (a), the SOC reached by the discharge (b), the time required for the discharge (c), specified when charging from the SOC reached by the discharge Calculate and estimate the time (e) required to reach the SOC,
It is close to the temperature measured by the temperature sensor from the time obtained by adding the time (c) and the time (d) and the time to reach the predetermined SOC by the immediate charging stored in the storage unit. Compared with the time to reach the predetermined SOC by immediate charging at a temperature, the time until reaching the designated SOC is the time obtained by adding the time (c) and the time (d). The method of charging a secondary battery according to claim 9 or 10, wherein the battery is charged after the discharging in a short time.