WO2013133017A1

WO2013133017A1 - Method for controlling charging/discharging of lithium-ion secondary cell, and charging/discharging controller

Info

Publication number: WO2013133017A1
Application number: PCT/JP2013/054109
Authority: WO
Inventors: 高橋　宏文; 玲緒小林
Original assignee: 株式会社日立製作所
Priority date: 2012-03-06
Filing date: 2013-02-20
Publication date: 2013-09-12
Also published as: JP2013187960A

Abstract

Provided are a more suitable method for controlling the charging/discharging of a lithium-ion secondary cell, and a charging/discharging controller. The method has a cell-information-acquisition step (S101) for acquiring information related to a lithium-ion secondary cell, a degradation-state-determination step (S102) for determining the state of degradation of the lithium-ion secondary cell on the basis of the information acquired in the cell-information-acquisition step (S101), a relation-selection step (S104) for selecting the relation between the cell voltage and the charging state corresponding to the degradation state determined in the degradation-state determination step (S102) as one of pre-stored relations between the cell voltage and the charging state in a degradation state, and a charging/discharging-voltage-changing step (S105) for changing at least one of a charging-upper-limit voltage and a discharging-lower-limit voltage, on the basis of the relation of the cell voltage and charging state selected in the relation-selection step (S104).

Description

Charge / discharge control method and charge / discharge control apparatus for lithium ion secondary battery

Lithium ion secondary batteries (hereinafter referred to as “batteries” where appropriate) are, for example, ships, railroads, automobiles (electric cars, hybrid electric cars, etc.), electronic devices as batteries capable of increasing energy density and output density. It is widely used in stationary power storage systems. In addition, technologies for storing electric power generated by using natural energy such as wind power and sunlight in a battery and storing electric power from the grid are attracting attention for both home and industrial use. Furthermore, in a smart grid (next-generation power transmission network) using IT (Information Technology) technology, a technology using a battery is attracting attention.

In recent years, there has been a particular demand for higher energy density and longer life in batteries mounted on ships, railways, automobiles, and the like. Accordingly, not only the performance of the battery itself but also the optimization of the usage method including the charge / discharge control of the battery is required. Therefore, for example, a technique described in Patent Document 1 is known as a related technique.

JP 2005-253287 A

In lithium ion secondary batteries, deterioration with time such as a decrease in battery capacity and an increase in internal resistance occurs with use. Therefore, if the battery is continuously used under the same conditions as the battery in the initial state, the usable energy amount (charge / discharge range) may decrease due to the deterioration of the battery over time. Therefore, it is conceivable to expand the charge / discharge range. However, when the charge / discharge range is randomly expanded, overcharge and overdischarge of the lithium ion secondary battery can be caused. When the battery is overcharged and overdischarged, the battery further deteriorates and the life is shortened.

The present invention has been made in view of such circumstances, and an object thereof is to provide a more appropriate charge / discharge control method and charge / discharge control device for a lithium ion secondary battery.

As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by controlling the charge / discharge range of the battery according to the deterioration state of the battery, and have completed the present invention.

According to the present invention, a more appropriate charge / discharge control method and charge / discharge control apparatus for a lithium ion secondary battery can be provided.

It is the (a) block diagram which shows the charging / discharging control apparatus of this embodiment, and (b) the charging / discharging curve memorize | stored previously. It is a flowchart which shows the charging / discharging control method of this embodiment. It is a figure explaining changing a charge upper limit voltage according to a deterioration state. It is a figure explaining the manufacturing method of the battery in an Example. It is a figure explaining the manufacturing method of the battery in an Example. It is a figure explaining the manufacturing method of the battery in an Example. It is a figure explaining the manufacturing method of the battery in an Example. It is the relationship between SOC and voltage corresponding to each deterioration state obtained in the example. It is the relationship between SOC corresponding to each deterioration state and voltage change obtained in the Example. It is the relationship between the capacity | capacitance maintenance factor corresponding to each deterioration state and 50% SOC voltage which were obtained in the Example. It is the relationship between the resistance increase rate corresponding to each deterioration state and 50% SOC voltage obtained in the examples.

Hereinafter, a form for carrying out the present invention (this embodiment) will be described with reference to the drawings as appropriate. First, the structure of the charge / discharge control apparatus of this embodiment is demonstrated, and the charge / discharge control method using this charge / discharge control apparatus is demonstrated.

<Charge / discharge control device>
The charge / discharge control apparatus (charge / discharge control apparatus 100) of this embodiment is applied with respect to the lithium ion secondary battery (battery) 11, as shown to Fig.1 (a). That is, the charge / discharge control apparatus 100 includes a positive electrode (not shown) capable of occluding and releasing lithium ions, a negative electrode (not shown) capable of occluding and releasing lithium ions, and a lithium salt (not shown). It controls charging / discharging of the secondary battery. Specifically, the charge / discharge control device 100 includes a battery information acquisition unit 12, a deterioration state determination unit 13, a charge / discharge curve selection unit (relation selection unit, charge / discharge voltage change unit) 14, a storage unit 15, And a control signal transmission unit 16.

The charge / discharge control apparatus 100 includes, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a HDD (Hard Disk Drive), and the like, and a predetermined program developed in the ROM. Is implemented by the CPU.

The battery information acquisition unit 12 acquires the terminal voltage of the battery 11 (hereinafter simply referred to as “voltage” or “battery voltage”), the current flowing through the battery 11, and the charge / discharge time in the battery 11. That is, the battery information acquisition unit 12 acquires information about the battery 11. Specific means for measuring the battery voltage of the battery 11 includes, for example, a voltmeter (not shown). Moreover, as a specific means for measuring the current flowing through the battery 11, for example, an ammeter (not shown) can be cited. Furthermore, examples of the charge / discharge time measurement in the battery 11 include a timer (not shown).

That is, the battery information acquisition unit 12 is connected to, for example, a voltmeter, an ammeter, and a timer. And the battery information acquisition part 12 acquires each information regarding the battery 11, for example using each above-mentioned means. The acquired information is transmitted as an electrical signal to a deterioration state determination unit 13 described later.

The deterioration state determination unit 13 determines the deterioration state (degree of deterioration) of the battery 11 based on the battery information from the battery information acquisition unit 12. That is, the deterioration state determination unit 13 determines the deterioration state of the battery 11 based on the information (battery information) acquired by the battery information acquisition unit 12.

In this embodiment, in order to determine the deterioration state, the deterioration state determination unit 13 calculates the battery capacity of the battery 11 and the internal resistance of the battery 11 based on the voltage, current, and charge / discharge time of the battery 11. ing. Specifically, the battery capacity of the battery 11 is calculated by multiplying the acquired current and charge / discharge time. Further, the internal resistance of the battery 11 is calculated by dividing the acquired voltage change by the current.

The deterioration state determination unit 13 determines the deterioration state of the battery 11 based on the calculated battery capacity and internal resistance of the battery 11. Specifically, in the present embodiment, based on the calculated battery capacity and internal resistance, it is classified into four degradation states (degradation state 1 to degradation state 4). In this case, the degree of degradation is the smallest in the “degraded state 1” and the largest in the “degraded state 4”.

That is, details will be described later. For example, if the calculated battery capacity is in the range of C1 to C2, “deterioration state 1”, if it is in the range of C2 to C3, “deterioration state 2”, and in the range of C3 to C4. For example, “deterioration state 3” is determined, and if it is in the range of C4 to C5, “deterioration state 4” is determined. Further, for example, if the calculated internal resistance is in the range of R1 to R2, “deterioration state 1”, if it is in the range of R2 to R3, “deterioration state 2”, and if in the range of R3 to R4, “deterioration state 3”. If it is within the range of R4 to R5, it is determined as “degradation state 4”. Although not shown, C1 to C5 and R1 to R5 are values that are determined and stored in advance through experiments or the like.

At this time, the deterioration state based on the calculated battery capacity may be different from the deterioration state based on the calculated internal resistance. In such a case, in this embodiment, the one with the smaller degree of deterioration is adopted. For example, when it is determined as “deterioration state 3” based on the battery capacity and “deterioration state 2” is determined based on the internal resistance, the deterioration state transmitted to the charge / discharge curve selection unit 14 is “deterioration state 2”. It becomes. By doing so, it is possible to minimize the number of times of changing the charge upper limit voltage and the discharge lower limit voltage (both will be described later) and to avoid the complexity of the control. Further, when there are a plurality of deterioration states, the change may be made promptly based on them. By doing in this way, control with especially high responsiveness can be performed. In addition, although the thing with a small degree of deterioration was employ | adopted in the above, it is not restricted to this.

That is, in the present embodiment, charge / discharge control of the battery 11 is performed using a plurality of pre-stored charge / discharge curves corresponding to the deterioration state 1 to the deterioration state 4. The deterioration state obtained as a result of the determination is transmitted by the deterioration state determination unit 13 to a charge / discharge curve selection unit 14 described later.

The charge / discharge curve selection unit 14 selects a charge / discharge curve according to the deterioration state of the battery 11 received from the deterioration state determination unit 13 among the charge / discharge curves determined in advance through experiments or the like and stored in the storage unit 15. To do. That is, it corresponds to the deterioration state determined by the deterioration state determination unit 13 among the relationship between the state of charge (SOC; State of 状態 Charge) and the battery voltage (charge / discharge curve in the present embodiment) stored in advance. The relationship between the state of charge and the battery voltage is selected.

Here, the “charge / discharge curve” in the present embodiment is a graph in which the horizontal axis indicates the state of charge (SOC) and the vertical axis indicates the battery voltage V. Examples of such a graph include the graph shown in FIG. Thus, the charge / discharge curve in the deteriorated state stored in advance includes at least one of the charge upper limit voltage and the discharge lower limit voltage that can be charged / discharged in the deteriorated battery 11. And in this embodiment, a charging / discharging curve is defined by the relational expression represented by the following formula | equation (1). Therefore, in FIG. 1B, the definition formula according to the formula (1) is determined and graphed for each of the initial state and the four deterioration states. Details of FIG. 1B will be described later.

(In Formula (1), n is an integer greater than or equal to 3, _ak is a constant, x is a variable showing the charge condition of the said lithium ion secondary battery.)

By using such a definition equation having a large order, charge / discharge can be controlled more accurately.

As the charge / discharge curve, it is preferable to use a so-called SOC-OCV (Open Circuit Voltage) curve that is ideally obtained by intermittent charge or intermittent discharge. However, in this embodiment, when the speed at the time of charging or discharging is sufficiently low (for example, about 1/50 (0.02) CA), charging obtained at the time of charging or discharging at such a low speed is performed. It was considered that a curve or a discharge curve (that is, a charge / discharge curve) can be regarded as the SOC-OCV curve. In addition, even when the speed at the time of charging or discharging is high, the present embodiment can be similarly applied by considering an error from the SOC-OCV curve. Such an error can be determined by, for example, experiments.

The graph shown in FIG. 1B is an SOC-V graph in the initial state of the battery 11 and an SOC-V graph in the deteriorated state 1 to the deteriorated state 4 obtained by the study of the present inventors. However, the graphs shown in FIG. 1B are all schematically shown in order to explain the present embodiment, and do not necessarily match the actual graph shape.

As shown in FIG. 1B, in the battery 11, when the deterioration progresses from the initial state, V changes even with the same SOC. Although details will be described later, as shown in FIG. 9, the change in V becomes remarkable when the SOC is about 40% to 90%.

In order to use the battery efficiently, it is necessary to accurately determine the deterioration state (that is, the degree of deterioration) of the battery that is the target of charge / discharge control, and charge / discharge according to the deterioration state. Two important points are the determination of a guideline (parameter) for appropriately controlling the parameters. In view of such circumstances, the present inventors have found that the amount of change (increase) in V due to deterioration strongly correlates with basic battery performance such as battery capacity and internal resistance. The inventors have also found that the relationship between SOC and V changes due to deterioration of the battery 11.

That is, a relationship was found between quantitative performance factors such as battery capacity and internal resistance, and qualitative performance factors of the battery such as the relationship between SOC and V. By performing the charge / discharge control of this embodiment based on these findings, it is possible to appropriately control even a deteriorated battery without falling into a disorderly charge / discharge range.

The charge / discharge curve selection unit 14 also determines an upper limit voltage (charge upper limit voltage) that can be charged and a lower limit voltage (discharge lower limit voltage) that can be discharged based on the selected charge / discharge curve. That is, based on the relationship between the charge state and the battery voltage selected by the charge / discharge curve selection unit 14 (charge / discharge curve in the present embodiment), at least one of the charge upper limit voltage and the discharge lower limit voltage is changed.

The specific method of determining the charge upper limit voltage and the discharge lower limit voltage will be described later with reference to FIG. The charge upper limit voltage and the discharge lower limit voltage thus determined are transmitted by the charge / discharge curve selection unit 14 to the control signal transmission unit 16 described later. In addition, the deterioration state of the battery 11 received by the charge / discharge curve selection unit 14 is stored in the storage unit 15.

The control signal transmission unit 16 transmits the received charge upper limit voltage and discharge lower limit voltage to the controller 11 a that controls charging / discharging of the battery 11. The controller 11a controls the voltage applied to the battery 11 and the flowing current. That is, the controller 11a energizes the battery 11 so that the charging lower limit voltage and the discharging lower limit voltage received from the control signal transmission unit 16 (that is, determined by the charge / discharge control device 100) are obtained. Yes.

<Charging / discharging control method>
Next, a charge / discharge control method of the battery 11 by the charge / discharge control apparatus 100 shown in FIG. 1 will be described with reference to FIG. The charge / discharge control method of this embodiment is a method for controlling charge / discharge of a lithium ion secondary battery including a positive electrode capable of occluding and releasing lithium ions, a negative electrode capable of occluding and releasing lithium ions, and a lithium salt. .

First, the battery information acquisition unit 12 acquires information about the battery 11 (battery information; battery voltage, current, and charge / discharge time) (step S101; battery information acquisition step). Then, the battery information acquisition unit 12 transmits the acquired battery information of the battery 11 to the deterioration state determination unit 13.

The deterioration state determination unit 13 calculates the battery capacity and internal resistance of the battery 11 based on the received voltage and current of the battery 11. Then, based on the calculated battery capacity and internal resistance, the deterioration state of the battery 11 is determined (step S102; deterioration state determination step). That is, the deterioration state determination unit 13 determines the deterioration state of the battery 11 based on the information acquired in step S101.

In this determination, when the deterioration state determined based on the battery capacity is different from the deterioration state determined based on the internal resistance, in the present embodiment, the degree of deterioration is light as described above. Shall be adopted. Then, the deterioration state obtained by the determination is transmitted to the charge / discharge curve selection unit 14 by the deterioration state determination unit 13.

Next, the charge / discharge curve selection unit 14 determines whether or not the received deterioration state has changed from the deterioration state of the battery 11 before the predetermined time has elapsed (step S103). In the first flow, the “deterioration state of the battery 11 before elapse of a predetermined time” is the “initial state” of the battery 11 (that is, immediately after the battery is manufactured; see FIG. 1B). If the deterioration state has changed (Yes in step S103), the charge / discharge curve selection unit 14 reads out and selects the charge / discharge curve corresponding to the deterioration state after the change from the storage unit 15 (step S104). ; Relationship selection step). That is, the charge / discharge curve selection unit 14 stores the charge corresponding to the deterioration state determined in step S102 out of the relationship between the charge state in the deterioration state and the battery voltage (charge / discharge curve in the present embodiment) stored in advance. Select the relationship between state and battery voltage.

On the other hand, if the deterioration state has not changed (No direction of step S103), the charge / discharge curve selection unit 14 waits for a predetermined time (step S106). Thereafter, the charge / discharge curve selection unit 14 transmits a signal to the battery information acquisition unit 12 so that steps S101 to S103 are performed again.

After the charge / discharge curve corresponding to the deteriorated state after the change is selected (step S104 described above), the charge upper limit voltage and the discharge lower limit voltage are changed (step S105; charge / discharge voltage change step). That is, the charge / discharge curve selection unit 14 changes at least one of the upper limit charge voltage and the lower limit discharge voltage based on the relationship between the charge state and the battery voltage selected in step S104 (charge / discharge curve in the present embodiment). To do.

Specifically, in step S105, the charge / discharge curve selection unit 14 determines the changed charge upper limit voltage and discharge lower limit voltage. Then, the charge / discharge curve selection unit 14 instructs the control signal transmission unit 16 to transmit a signal that becomes the charge upper limit voltage and the discharge lower limit voltage. Thereby, the control signal transmission part 16 transmits a control signal with respect to the controller 11a, and the charge upper limit voltage and the discharge lower limit voltage of the charge / discharge voltage of the battery 11 are changed.

As a more specific change method, when changing the charge upper limit voltage, the charge upper limit voltage before the change is changed so as to approach the charge upper limit voltage that can be charged in the deteriorated battery 11, and the discharge lower limit voltage is changed. When changing, the discharge lower limit voltage before the change is changed to be close to the dischargeable lower limit voltage in the deteriorated battery 11.

Here, the charge upper limit voltage and the discharge lower limit voltage will be described. As an example, a case where a lithium ion secondary battery is used in the range of SOC 25% to 75% is taken up. However, the SOC is a value defined by the user and cannot be actually measured. Therefore, charge / discharge is controlled using the charge / discharge curve in the initial state and using, for example, voltages corresponding to 25% and 75% as an index. Specifically, for example, in a battery used with an SOC in the range of 25% to 75%, the discharge lower limit voltage is a voltage corresponding to SOC 25%, and the charge upper limit voltage is a voltage corresponding to SOC 75%.

However, as described above, as the battery deteriorates, the corresponding voltage changes (increases) even with the same SOC (see FIG. 1B). Therefore, even if the battery is deteriorated, when charging / discharging is performed at a constant charging upper limit voltage and discharging lower limit voltage, charging / discharging is performed in which the actual battery state is not considered at all. This may shorten the battery life. Moreover, the design battery capacity which can use a battery may not fully be used.

Therefore, the charge upper limit voltage and the discharge lower limit voltage are changed according to the deterioration state of the battery. This point will be specifically described with reference to FIG. FIG. 3 shows an enlarged graph of the SOC 50% to 100% portion in the charge / discharge curves of the initial state and the deteriorated state 1. As shown in FIG. 3, in the initial state, the voltage corresponding to SOC 70% is V1. On the other hand, when the deterioration progresses to the deterioration state 1, the voltage corresponding to SOC 70% increases to V2.

When charging to SOC 70% in the initial state without considering the deterioration state of the battery, the charging upper limit voltage becomes constant at V1. Accordingly, even when the battery is deteriorated (in the case of deterioration state 1), the upper limit voltage for charging is constant at V1, and therefore, when the charging is finished at this voltage, the SOC increases only to 55%. Become. That is, the charging ends even though the upper limit of the SOC of the battery that can be charged still has room.

Therefore, in order to avoid such a situation, the charging upper limit voltage is changed. That is, as shown in FIG. 3, when the deterioration changes to the deterioration state 1, the charging upper limit voltage is also changed to V2 accordingly. At this time, the charge upper limit voltage is not necessarily set to V2, and the charge upper limit voltage may be changed so as to approach V2. By doing in this way, it can charge to about 70% of SOC same as an initial state, without complete | finishing charge by SOC55%. That is, even if the battery deteriorates, it is possible to avoid a decrease in usable battery capacity.

In FIG. 3, only the graphs of the initial state and the deterioration state 1 are shown for simplification of illustration, but the same applies to other deterioration states. Further, for the sake of simplification of explanation, only the change of the charge upper limit voltage has been described, but the change of the discharge lower limit voltage can be similarly changed.

<Others>
As described above, the charge / discharge control method and the charge / discharge control apparatus according to the present embodiment have been described. As the lithium ion secondary battery to which the embodiment can be applied, a positive electrode capable of occluding and releasing lithium ions, and occluding and releasing lithium ions. The specific configuration is not particularly limited as long as it includes a possible negative electrode and a lithium salt. For example, the battery may be a battery using a non-aqueous electrolyte or a battery containing a lithium ion polymer. Further, the battery may be a battery including a solid electrolyte or a battery including an ionic liquid. A separator may also be used as necessary.

In the present embodiment, the battery voltage is constantly monitored, and when the voltage deviates from the range between the charge upper limit voltage and the discharge lower limit voltage, a signal for stopping charge / discharge is output or a signal notifying the abnormality Is preferably output. In such a case, when the deterioration state is changed, it is more preferable that the voltage (threshold value) for outputting the signal is also changed.

Therefore, the charge / discharge control apparatus 100 includes a signal output unit (not shown) that outputs a signal when it is detected that the voltage of the battery 11 has reached a predetermined voltage when the battery 11 is charged / discharged. The predetermined voltage detected by the signal output unit is at least one of a charge upper limit voltage and a discharge lower limit voltage. That is, when the voltage of the battery 11 exceeds the charging upper limit voltage (that is, in the case of overcharging), the signal output unit outputs a signal notifying abnormality. In addition, when the voltage of the battery 11 falls below the discharge lower limit voltage (that is, in the case of overdischarge), the signal output unit outputs a signal notifying the abnormality.

Furthermore, the signal output unit is configured to output a predetermined voltage (charge upper limit voltage and discharge lower limit voltage) when outputting the signal when at least one of the charge upper limit voltage and the discharge lower limit voltage is changed by the charge / discharge curve selection unit 14. ) Is also changing. Note that the predetermined voltage is not limited to the charge upper limit voltage and the discharge lower limit voltage, and a voltage close to the charge upper limit voltage and the discharge lower limit voltage may be used as a threshold value.

Furthermore, the above-described embodiment can be arbitrarily modified without departing from the gist of the present invention.

For example, in order to determine the deterioration state of the battery 11, the battery information acquisition unit 12 measures the voltage, current, and charge / discharge time as the battery information. If the deterioration state of the battery 11 can be determined, the battery information includes There is no limitation to these.

Furthermore, in the above-described embodiment, the battery capacity and the internal resistance are calculated based on the battery information when determining the deterioration state. However, only one of the calculated values may be used. That is, for example, when determining the deterioration state using only the battery capacity, the capacity maintenance rate (value obtained by dividing the battery capacity after deterioration by the battery capacity in the initial state) has become a predetermined value or less. In this case, the deterioration state may be changed. However, from the viewpoint of more accurate control, it is preferable to use both to determine the deterioration state.

For example, although the present embodiment has been described in an example in which four deterioration states are stored in the charge / discharge curve stored in the storage unit 15, three or less deterioration states may be stored. The above deterioration state may be stored. However, by storing more deterioration states, the charge upper limit voltage and the discharge lower limit voltage can be changed more accurately. Therefore, it is preferable to store as many deterioration states as possible.

Further, for example, in the above-described embodiment, a charge / discharge curve (graph; relational expression between SOC and V) is used as an indicator of the deterioration state, but only the charge upper limit voltage and the discharge lower limit voltage are used. Also good. That is, the deterioration state may be defined using only the values of both the upper limit charge voltage and the lower discharge limit voltage as indicators of the deterioration state. Thereby, the memory capacity of the memory | storage part 15 can be reduced and a process can be simplified.

Furthermore, for example, in the above-described embodiment, both the charge upper limit voltage and the discharge lower limit voltage are changed, but only one of them may be changed. For example, if the change amount of the charge upper limit voltage or the discharge lower limit voltage is small even if the deterioration state changes, the smaller change amount may not be changed. Furthermore, if both the change amounts are small, it is possible to not change both (in this case, the process proceeds in the No direction in step S103 in FIG. 2). As a result, the processing can be simplified.

Further, for example, the predetermined time in step S106 described with reference to FIG. 2 can be arbitrarily set. However, from the viewpoint of performing control with higher accuracy, the predetermined time is preferably short. Moreover, you may make it identify with the frequency | count of charging / discharging of the battery 11, for example, without specifying with predetermined time.

Next, the present embodiment will be described more specifically with examples.

<Production of lithium ion secondary battery>
A rocking chair type lithium ion secondary battery was produced.

· Layered LiMO ₂ as the positive electrode the positive electrode active material (M _represents Ni _0.5 Co 0.2 _{Mn 0.3)} and, with acetylene black as a conductive material, polyvinylidene fluoride as a binder and (PVdF) Was mixed with N-methylpyrrolidone (NMP) as a solvent so that the weight ratio was 93: 4: 3 to prepare a positive electrode mixture slurry. And this positive mix slurry was apply | coated to 15-micrometer-thick aluminum foil, and it dried in air | atmosphere. The positive electrode obtained by drying was molded by a roll press, and cut into a shape in which a collector foil exposed portion (described later with reference to FIG. 4) was added to 45 mm × 70 mm to produce a positive electrode.

-Negative electrode Graphite, carboxymethyl cellulose (CMC) as a binder, and styrene-butadiene rubber (SBR) were mixed with water as a solvent so that the weight ratio was 98: 1: 1, and a negative electrode mixture slurry was prepared. Prepared. And this negative mix slurry was apply | coated to the 10-micrometer-thick copper foil, and it dried in air | atmosphere. The negative electrode obtained by drying was molded by a roll press and cut into a shape obtained by adding a current collector foil exposed portion (described later with reference to FIG. 4) to 45 mm × 70 mm to produce a negative electrode.

-Separator The separator used was a separator having a total thickness of 0.03 mm in which polypropylene, polyethylene, and polypropylene were laminated in three layers. The positive electrode was sandwiched between two separators, and three sides were thermally welded to form a bag.
Electrolyte solution As an electrolyte solution, lithium hexafluorophosphate (LiPF ₆₎ was added to an organic solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 2 so as to be 1.0 mol / L. ) Was used.

And the positive electrode 1 and the negative electrode 2 which were accommodated in the bag-shaped separator 3 were laminated | stacked, and the laminated body was obtained. And in this laminated body, the positive electrode terminal 5 and the negative electrode terminal 6 were connected to the part (current collector foil exposed part) of the positive electrode 1 and the negative electrode 2 exposed to the outside by ultrasonic welding, respectively, and FIG. The electrode body 4 shown was obtained. Next, as shown in FIG. 5, the electrode body 4 is disposed between the two heat-weldable sheets 7, and portions other than the electrolyte solution injection portion of the sheet 7 are heat-welded, so that FIG. The electrode placement container 9 shown was obtained.

Then, the electrolyte solution was injected into the electrode-arranged container 9. After injecting the electrolytic solution, the opening 11 was thermally welded to produce the battery 11 shown in FIG. Then, an electrolyte impregnation time of 8 hours was provided after sealing, and then the battery 11 subjected to the following test was charged and discharged for 3 cycles at a current value of 0.5 CA at a voltage range of 4.2 V to 2.5 V. Completed.

<Acquisition of battery performance and discharge curve during cycle load test>
In the completed battery 11, data on the battery capacity and internal resistance (battery capacity) and the discharge curve at 1/50 (0.02) CA were obtained. Thereafter, a cycle load test was performed in which the SOC was continuously charged and discharged at a current value of 2 CA in the range of SOC 25% to 75%. Each time a predetermined number of cycles (500 times) passed, battery capacity, internal resistance, and a discharge curve at 1/50 CA were acquired, and the battery performance and discharge curve for each deterioration state were accumulated. These accumulations were performed a total of 4 times. In this embodiment, the “discharge curve at 1/50 CA” is regarded as the “SOC-OCV curve” because the discharge rate is sufficiently slow.

The initial state and the discharge curve obtained each time after starting the cycle load test are shown in FIG. In FIG. 8, the deterioration state 1 is a discharge curve acquired after 1000 cycles, the deterioration state 2 is a discharge curve acquired after 2000 cycles, the deterioration state 3 is a discharge curve acquired after 3000 cycles, and the deterioration state 4 is 4000 cycles. The discharge curve acquired later is represented. Hereinafter, the same applies to other graphs. As shown in FIG. 8, it can be seen that the voltage generally increases as the deterioration progresses (that is, the number at the end of the deterioration state is large. The same applies hereinafter).

Also, FIG. 9 shows the difference (voltage change) between the voltage in the initial state and the voltage in the deteriorated state 1 to 4 in each SOC. As shown in FIG. 9, it can be seen that the difference from the initial state increases as the deterioration progresses. In particular, when the SOC was 60%, the difference was particularly large compared to other SOCs.

Furthermore, FIG. 10 shows the relationship between the battery capacity maintenance rate (capacity maintenance rate) and the voltage (50% SOC voltage) at 50% SOC for each deterioration state. FIG. 11 shows the relationship between the rate of increase in internal resistance (resistance increase rate) and the voltage (50% SOC voltage) at which 50% SOC is obtained for each deterioration state. As shown in FIG. 10, it can be seen that as the deterioration progresses, the capacity retention rate decreases and the 50% SOC voltage increases. In particular, when the deterioration progresses to the deterioration state 4, the battery capacity is reduced to 75% of the battery capacity in the initial state. Further, as shown in FIG. 11, it can be seen that as the deterioration progresses, the resistance increase rate increases and the 50% SOC voltage also increases.

The equation of the discharge curve in the initial state (relational equation between SOC and V) is shown in the following equation (2). Further, the equation of the discharge curve in the deteriorated state 4 is shown in the following equation (3). In addition, both the following formulas (2) and (3) are obtained by approximating experimental values by the least square method.

Initial state: V = 24.21y ⁶ -83.20y ⁵ + 108.9y ⁴ -66.82y ³ + 19.44y ² -1.833y + 3.485 (2)
Deterioration state 4: V = -3.194y ⁶ + 13.86y ⁵ -23.08y ⁴ + 18.79y ³ -7.393y ² + 1.869y + 3.329 (3)
However, y is a variable representing the state of charge (SOC) of the battery 11, and is a value satisfying the following formula (4).

Although both the above formulas (1) and (2) are 6th order, good approximation is performed by setting them to the 3rd order or higher (that is, n in the above formula (1) is 3 or higher). I was able to.

<Examples 1 and 2 and Comparative Examples 1 and 2>
Table 1 below shows the charge upper limit voltage, the discharge lower limit voltage, and the usable SOC range (ΔSOC) when the SOC range used is about 25% to 75%. Regarding the SOC of each example and each comparative example, the upper limit value of the SOC used by the upper stage and the lower limit value of the SOC used by the lower stage.

In Table 1, Example 1 is a case where both 75% SOC voltage and 25% SOC voltage are changed from the initial state to the deteriorated state 4. That is, the charge upper limit voltage is changed from 3.877V to 3.917V, and the discharge lower limit voltage is changed from 3.548V to 3.550V.

Further, Example 2 is a case where the 75% SOC voltage is changed from the initial state toward the value of the deterioration state 4 and the 25% SOC voltage is changed to the deterioration state 4. That is, the charge upper limit voltage is changed from 3.877 V to 3.899 V, and the discharge lower limit voltage is changed from 3.548 V to 3.550 V.

Furthermore, Comparative Example 1 is a case where the initial value was not changed. That is, neither the charge upper limit voltage nor the discharge lower limit voltage is changed.

In Comparative Example 2, the 75% SOC voltage is not changed from the initial stage, but the discharge lower limit voltage is changed so as to be in the same usable SOC range as the initial stage. That is, the discharge lower limit voltage is changed from 3.548V to 3.528V without changing the charge upper limit voltage.

As shown in Table 1, the 75% SOC voltage in the initial state was 3.877V, and the 25% SOC voltage was 3.548V. On the other hand, in the deterioration state 4, they were 3.917V and 3.550V, respectively.

Thus, since the change in the 75% SOC voltage is particularly large, it is preferable to change at least the 75% SOC voltage in a direction approaching 3.877 V to 3.917 V, that is, in a direction in which the voltage is increased. Therefore, as shown in Examples 1 and 2, the 75% SOC voltage is changed. In the change, in the first embodiment, the charge upper limit voltage itself in the deteriorated state 4 is changed. Moreover, in Example 2, although it is not the charge upper limit voltage itself of the degradation state 4, the charge upper limit voltage is changed so that the said charge upper limit voltage may be approached. By changing as described above, the usable SOC range (ΔSOC) can be expanded as compared with Comparative Example 1 in which the charge upper limit voltage is not changed.

Moreover, when the range is expanded, both the SOC at the time of the upper charge limit voltage and the SOC at the lower limit of the discharge voltage are included in the SOC use range (25% to 75%) designed in advance. Therefore, the usable SOC range can be expanded without causing overcharge and overdischarge.

On the other hand, in Comparative Example 2, the SOC at the discharge lower limit voltage was 20.6%. This deviates from the SOC design range (25% to 75%) designed in advance, indicating that overdischarge has occurred. Accordingly, it has been found that overdischarge occurs when an attempt is made to make the usable range comparable to the initial state without considering deterioration.

<Examples 3 and 4 and Comparative Example 3>
Table 2 below shows the charge upper limit voltage, the discharge lower limit voltage, and the usable SOC range (ΔSOC) when the SOC range used is about 30% to 70% in the manufactured battery. Regarding the SOC of each example and comparative example, the upper limit value of the SOC used by the upper stage and the lower limit value of the SOC used by the lower stage.

In Table 2, Example 3 is a case where both the 70% SOC voltage and the 30% SOC voltage are changed from the initial state to the deteriorated state 4. That is, the charge upper limit voltage is changed from 3.820V to 3.872V, and the discharge lower limit voltage is changed from 3.578V to 3.576V.

In Example 4, the 70% SOC voltage is changed from the initial state to the deteriorated state 4 and the 30% SOC voltage is not changed. That is, the charge upper limit voltage is changed from 3.820V to 3.872V, and the discharge lower limit voltage is maintained at 3.578V.

As shown in Table 2, the 70% SOC voltage in the initial state was 3.820V, and the 30% SOC voltage was 3.578V. On the other hand, in the deterioration state 4, they were 3.872V and 3.576V, respectively.

As described above, since the change in the 70% SOC voltage is particularly large, it is preferable to change at least the 70% SOC voltage in a direction approaching 3.820V to 3.872V, that is, a direction in which the voltage is increased. Therefore, as shown in Examples 3 and 4, the 70% SOC voltage is changed. At the time of the change, the charge upper limit voltage itself in the deterioration state 4 is changed. By changing in this way, the usable SOC range (ΔSOC) can be expanded as compared with Comparative Example 3 in which the charging upper limit voltage is not changed.

In addition, when the range is expanded, both the SOC at the time of the charge upper limit voltage and the SOC at the time of the discharge lower limit voltage are included in the SOC use range (30% to 70%) designed in advance (Example) 3 and 4). Therefore, the usable SOC range can be expanded without causing overcharge and overdischarge.

On the other hand, in Comparative Example 3, the SOC at the charge upper limit voltage was 64.1%. This indicates that there is still a margin with respect to the upper limit value (70%) of the SOC usage range designed in advance. Therefore, in the comparative example 3, the SOC use range designed beforehand cannot be fully utilized.

As described above, according to the embodiments, the present invention can provide a more appropriate charge / discharge control method and charge / discharge control device for a lithium ion secondary battery. In the above embodiment, only the case of a specific SOC range is described. However, by using a table or a relational expression of relation values between SOC and V, the same calculation is performed for any SOC range, and deterioration occurs. It is possible to determine the direction of voltage change associated with.

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Bag-like separator 4 Electrode body 5 Positive electrode terminal 6 Negative electrode terminal 7 Thermal welding sheet 8 Thermal welding part 10 Battery 11a Controller 12 Battery information acquisition part 13 Degradation state determination part 14 Charging / discharging curve selection part 15 Storage part 16 Control Signal transmission unit 100 Charge / discharge control device

Claims

A method for controlling charging and discharging of a lithium ion secondary battery comprising a positive electrode capable of occluding and releasing lithium ions, a negative electrode capable of occluding and releasing lithium ions, and a lithium salt,
A battery information acquisition step of acquiring information about the lithium ion secondary battery;
A deterioration state determination step of determining a deterioration state of the lithium ion secondary battery based on the information acquired in the battery information acquisition step;
A relationship selection step for selecting a relationship between the charge state and the battery voltage corresponding to the deterioration state determined in the deterioration state determination step, among the relationship between the charge state and the battery voltage stored in advance in the deterioration state;
A charge / discharge voltage changing step for changing at least one of the upper limit charge voltage and the lower discharge limit voltage based on the relationship between the state of charge and the battery voltage selected in the relationship selection step;
The charge / discharge control method of a lithium ion secondary battery characterized by having.
In the deterioration state determining step,
The charging of the lithium ion secondary battery according to claim 1, wherein the deterioration state is determined using at least one of a battery capacity and an internal resistance of the lithium ion secondary battery. Discharge control method.
The relationship between the charge state and the battery voltage in the deteriorated state stored in advance includes at least one of a charge upper limit voltage and a discharge lower limit voltage of the lithium ion secondary battery in the deteriorated state. The charge / discharge control method of a lithium ion secondary battery according to claim 1 or claim 2.
In the charge / discharge voltage changing step,
When changing the charging upper limit voltage, change the charging upper limit voltage before the change so as to approach the charging upper limit voltage that can be charged in the deteriorated lithium ion secondary battery,
When changing the discharge lower limit voltage, the discharge lower limit voltage before the change is changed so as to approach the dischargeable lower limit voltage in the deteriorated lithium ion secondary battery. 4. A charge / discharge control method for a lithium ion secondary battery according to item 3.
The relationship between the state of charge and the battery voltage in the deteriorated state stored in advance is defined by a relational expression represented by the following formula (1), according to claim 1 or 2, Charge / discharge control method for lithium ion secondary battery.

(In Formula (1), n is an integer greater than or equal to 3, ak is a constant, x is a variable showing the charge condition of the said lithium ion secondary battery.)
A device for controlling charge / discharge of a lithium ion secondary battery comprising a positive electrode capable of inserting and extracting lithium ions, a negative electrode capable of inserting and extracting lithium ions, and a lithium salt,
A battery information acquisition unit for acquiring information about the lithium ion secondary battery;
A deterioration state determination unit that determines a deterioration state of the lithium ion secondary battery based on the information acquired by the battery information acquisition unit;
A relationship selection unit that selects a relationship between the charge state and the battery voltage corresponding to the deterioration state determined by the deterioration state determination unit from among the relationship between the charge state and the battery voltage in the deterioration state stored in advance;
Based on the relationship between the state of charge and the battery voltage selected by the relationship selection unit, a charge / discharge voltage change unit that changes at least one of the charge upper limit voltage and the discharge lower limit voltage;
A charge / discharge control device for a lithium ion secondary battery, comprising:
The battery further comprises a signal output unit that outputs a signal when detecting that the voltage of the lithium ion secondary battery has reached a predetermined voltage during charging / discharging of the lithium ion secondary battery. The charge / discharge control apparatus of the lithium ion secondary battery of Claim 6.
The charging / discharging control device for a lithium ion secondary battery according to claim 7, wherein the predetermined voltage detected by the signal output unit is at least one of a charging upper limit voltage and a discharging lower limit voltage. .
The signal output unit changes a predetermined voltage when outputting a signal when changing at least one of a charge upper limit voltage and a discharge lower limit voltage by the charge / discharge voltage changing unit. The charge / discharge control device for a lithium ion secondary battery according to claim 7 or 8.