JP7410598B2 - Battery control device, battery recovery processing method - Google Patents

Description

The present invention relates to a battery control device and a battery recovery processing method, and particularly relates to a technique for reducing the height of metal precipitates deposited on the negative electrode surface of a battery cell.

In secondary batteries that generate electromotive force by transferring metal ions made of alkali metals and alkaline earth metals between the positive and negative electrodes during charging and discharging, dendrites, which are metal whiskers that grow on the surface of the negative electrode, occur during charging. Due to this formation, a problem often arises in that the positive electrode and the negative electrode are electrically connected and short-circuited. A dendrite is a metal that has grown in a dendritic or acicular shape, and is sometimes called a whisker.

Incidentally, in recent years, as batteries with higher energy density are becoming more popular, metals of the same type as the above-mentioned metal ions, represented by metallic lithium, are formed on the negative electrode current collector in the form of a foil or by vapor deposition to form negative electrode active materials. There is an increasing demand for metal secondary batteries (metallic lithium secondary batteries as a typical example) that are used as metals or in which a metal such as metallic lithium is electrochemically deposited on the negative electrode.

In such metal secondary batteries, metal ions are not occluded or intercalated in the negative electrode active material, so metals such as lithium are constantly deposited on the negative electrode surface. Local electrolytic concentration occurs in response to slight irregularities in the surface, and metal deposition tends to occur more easily in the convex portions, resulting in the above-mentioned whisker-like metal growth.

In order to avoid such problems, for example, as disclosed in Japanese Unexamined Patent Application Publication No. 2014-170741, instead of constant current charging, applying a pulsed current in the opposite direction may suppress or suppress the generation of dendrites. Attempts have been made to perform recovery.

However, the method described in the above-mentioned Japanese Patent Application Publication No. 2014-170741 has the problem that charging takes a long time compared to general constant current charging because it is a mode in which currents in opposite directions are applied alternately in a pulsed manner. was there. This has led to problems such as excessive charging and discharging, which accelerates the deterioration of battery life, or conversely prevents sufficient recovery.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to accurately estimate the height of metal precipitates generated on the negative electrode surface of a metal secondary battery and perform recovery processing according to the estimated value. The purpose of the present invention is to provide a method that can prevent short circuits from occurring without accelerating battery deterioration.

One aspect of the present invention is a battery control device that controls a power storage device equipped with at least one secondary battery cell that includes at least a positive electrode, a negative electrode, and an electrolyte,
a first storage unit that stores an integrated value of the current flowing through the secondary battery cell due to charging;
a precipitation estimation unit that estimates the precipitation height of the current metal precipitate deposited on the negative electrode surface of the secondary battery cell;
a parameter setting unit that sets a parameter for reducing the precipitation height of the metal precipitates when the current precipitation height of the metal precipitates estimated by the precipitation estimation unit is equal to or higher than a predetermined threshold;
an execution unit that executes a recovery process of applying a pulse current to the secondary battery cell based on the parameters set by the parameter setting unit;
a charging rate estimation unit that estimates the current charging rate of the secondary battery cell;
Equipped with
The parameter setting unit sets a current value of the pulsed current based on a processable time for the recovery process, a target value of a precipitation height of metal precipitates due to the recovery process, and the charging rate; This is a battery control device that sets parameters consisting of pulse period and current application time.

Another aspect of the present invention is a battery recovery processing method for controlling a power storage device equipped with at least one secondary battery cell including at least a positive electrode, a negative electrode, and an electrolyte, comprising:
Step (A) of estimating the current precipitation height of metal precipitates deposited on the negative electrode surface of the secondary battery cell based on a pre-stored integrated value of the current flowing through the secondary battery cell due to charging. and,
a step (B) of comparing the current precipitation height of the metal precipitate estimated in the step (B) with a predetermined threshold value of the precipitation height of the metal precipitate;
If the current precipitation height of the metal precipitates estimated in the step (A) is equal to or greater than the threshold value, a step (C) of setting a parameter for reducing the precipitation height of the metal precipitates;
a step (D) of performing a recovery process of applying a pulse current to the secondary battery cell based on the parameters set in the step (C);
a step (E) of estimating the charging rate of the secondary battery cell;
a step (F) of obtaining processing available time for the recovery processing;
including;
The step (C) is
Furthermore, based on the processable time acquired in the step (F) and the current charging rate of the secondary battery cell estimated in the step (E),
This is a battery recovery processing method in which parameters consisting of a current value of the pulse current, a pulse period, and a current application time are set.

According to an aspect of the present invention, by accurately estimating the height of metal precipitates generated on the negative electrode surface of a metal secondary battery and performing recovery processing according to the estimated value, battery deterioration is not accelerated. This can prevent short circuits from occurring.

FIG. 2 is a diagram showing an ideal case regarding the generation of dendrites in a secondary battery cell. It is a figure which shows the actual case about the generation|occurrence|production of dendrite in a secondary battery cell. FIG. 3 is a diagram illustrating the influence of the initial surface quality of the negative electrode surface of a secondary battery cell on the generation of dendrites, and schematically shows the generation of dendrites on one protrusion on the negative electrode surface. FIG. 2 is a diagram illustrating the influence of the initial surface quality of the negative electrode surface of a secondary battery cell on the generation of dendrites, and shows the generation of dendrites on the negative electrode surface having a predetermined surface roughness. FIG. 2 is a diagram illustrating factors that cause dendrites to be unevenly generated on the negative electrode surface of a secondary battery cell. FIG. 2 is a diagram illustrating factors that cause dendrites to be unevenly generated on the negative electrode surface of a secondary battery cell. It is a figure which shows the coefficient table referred when estimating the dendrite height in a secondary battery cell. It is a figure which shows the charging method and recovery process performed when charging a secondary battery cell. FIG. 3 is a diagram illustrating current waveforms in pulse reverse charging (PR charging) and recovery processing (pulse discharging). FIG. 3 is a diagram showing electrical connection relationships when charging a battery module in a charging device. FIG. 3 is a functional block diagram of a cell management unit and a charging control unit when charging a battery module. FIG. 3 is a diagram illustrating the relationship between SOC and voltage of a secondary battery cell. FIG. 2 is a diagram showing the relationship between the SOC of a secondary battery cell and the charging method and recovery process (pulse discharge) that can be performed for the cell. 5 is a flowchart related to an example of overall processing executed by a charging control unit when charging a battery module. 12 is a flowchart relating to an example of detailed processing of the conditioning setting processing in the flowchart of FIG. 11.

The term "metal precipitate" in the present disclosure refers to metal ions that move between the positive electrode and the negative electrode in a secondary battery cell and are deposited on the negative electrode during charging and exist in a metallic state. Dendrites are an example of metal precipitates. Examples of the metal include alkali metals and alkaline earth metals, and below, the case of lithium will be explained as an example.
In the present disclosure, "dendritic height" refers to the height of dendrites generated on the negative electrode based on the surface of the negative electrode of the secondary battery cell.
In the present disclosure, "conditioning" refers to a process that prepares the negative electrode surface of a secondary battery cell by lowering the peak height of dendrites that occur on the negative electrode of the secondary battery cell, or by reducing the height difference of the dendrites. means.

Below, first, a method for estimating the amount of increase in the dendrite height of a secondary battery cell (hereinafter referred to as a "battery cell" as appropriate) will be described with reference to FIGS. 1A to 4.
As shown in FIG. 1A, in an ideal case where the negative electrode surface is completely flat, lithium ions are transported uniformly depending on the position on the negative electrode surface, so that precipitation occurs uniformly on the negative electrode surface. In this case, the dendrite height depends on the product of the current density of the charging current (charging current density) and time.
In the case of such an ideal negative electrode surface, if the charging current density is i [A/cm ² ], the charging time is t [s], and the Faraday constant is [C/mol], the amount of lithium precipitated n is as follows. It is expressed by formula (1).

Further, when the atomic weight of lithium is M [g/mol] and the density is ρ [g/cm ² ], the increase amount Δh [cm] in the height of the lithium dendrite is expressed by the following formula (2).

On the other hand, in an actual battery cell, as shown in Figure 1B, the transport of lithium ions is uneven depending on the position of the negative electrode surface due to the surface roughness of the negative electrode. is not uniform. The reason for this can be explained as follows with reference to FIGS. 2A and 2B.

FIG. 2A is a diagram schematically showing one protrusion on the surface of the negative electrode of a battery cell and the concentration distribution of lithium ions in the electrolyte near the surface of the negative electrode. During charging, lithium ions are consumed on the surface of the negative electrode due to a reduction reaction at the negative electrode, so the concentration of lithium ions decreases near the surface of the negative electrode. Therefore, as shown in FIG. 2A, the concentration of lithium ions becomes relatively high around the protrusion protruding toward the positive electrode, and a reaction in which lithium ions are precipitated occurs intensively at the protrusion. As a result, on the negative electrode surface, more dendrites occur in the protruding parts than in the flat parts.
As shown in FIG. 2B, when looking at the entire negative electrode surface, the growth rate of the dendrite height increases at each protrusion on the negative electrode surface. That is, the greater the surface roughness of the negative electrode surface in its initial state, the greater the height of dendrites deposited by subsequent charging current, and as a result, the difference in surface height tends to further increase.

From equation (2) above, it is clear that the amount of increase in dendrite height varies depending on the current density during charging, but assuming that the negative electrode surface has surface roughness, the negative electrode surface Since the concentration distribution of lithium ions is biased, it is necessary to consider the bias in the concentration distribution when estimating the dendrite height. In other words, in the case of low current density, the consumption rate of lithium ions on the electrode surface is low, so as schematically shown in Figure 3A, lithium ions cover the entire negative electrode surface regardless of the surface roughness in the initial state. Easily supplied relatively evenly. Therefore, the height difference on the negative electrode surface due to dendrite precipitation becomes difficult to increase.
On the other hand, in the case of high current density, the consumption rate of lithium ions in a certain period of time is higher than that at low current density, and the transport of lithium ions in the electrolyte becomes insufficient, as shown schematically in Figure 3B. As such, the concentration distribution of lithium ions in the electrolyte tends to be largely biased due to the surface roughness in the initial state. As a result, as described with reference to FIGS. 2A and 2B, the height of the dendrites deposited by the charging current increases, and as a result, the height difference on the surface tends to become larger.

Another factor that causes a bias in the concentration distribution of lithium ions on the surface of the negative electrode is temperature.
In the case of low-temperature charging, the transport speed of lithium ions in the electrolyte is low, and as described with reference to FIGS. 2A and 2B, the concentration distribution of lithium ions in the electrolyte tends to be uneven. Therefore, as the height of the dendrite increases, the height difference on the surface tends to further increase. On the other hand, in the case of high-temperature charging, the transport speed of lithium ions in the electrolyte becomes higher than in the case of low temperature, and the bias in the concentration distribution of lithium ions in the electrolyte is improved.

From the above point of view, in order to accurately estimate the amount of increase in dendrite height under the assumption that the negative electrode surface is not flat, based on the above formula (2), the higher the charging current density, the higher the It is preferable to correct the amount of increase in dendrite height so that it becomes larger as .
Therefore, by setting the current density coefficient x corresponding to the current density during charging (charging current density) and the temperature coefficient y corresponding to the temperature of the battery cell, the amount of increase in dendrite height Δh [cm] can be calculated as follows: It can be expressed as the following equation (3).

FIG. 4 is a diagram showing a coefficient table that is referred to when estimating the dendrite height in a battery cell.
As shown in FIG. 4, the current density coefficients corresponding to the current densities i ₁ , i ₂ , i ₃ ,..., _im (however, i ₁ < i ₂ < i ₃ <...< i _m ) are expressed as x ₁ , x ₂ , x ₃ , ..., x _m , x ₁ <x ₂ <x ₃ <...<x _m . Furthermore, the temperature coefficients corresponding to the temperatures T ₁ , T ₂ , T ₃ ,..., Ti _n (where T ₁ >T ₂ >T ₃ >>>T _n ) are y ₁ , y ₂ , y ₃ ,..., When y _n , y ₁ <y ₂ <y ₃ <...<y _n . That is, the amount of increase in dendrite height is corrected by the current density coefficient x and the temperature coefficient y so that the higher the charging current density is, the greater the increase is, and the lower the temperature is, the greater the increase is.
Note that since the temperature can change over time, the amount of increase in dendrite height can be corrected depending on the temperature history.

In order to estimate the amount of increase in dendrite height with higher accuracy, it is preferable to correct the amount of increase in dendrite height determined by the above equation (3) based on the surface roughness of the negative electrode surface in its initial state. This is because the greater the surface roughness of the negative electrode surface in its initial state, the more likely it is that the concentration distribution of lithium ions in the electrolyte will be biased, and the amount of increase in dendrite height will increase accordingly.
For example, as an index of surface roughness, the amount of increase in dendrite height is determined based on at least one selected from the arithmetic mean roughness Ra, ten-point mean roughness Rzjis, and maximum height Rz of the negative electrode surface. It is a good idea to correct this. Note that among the arithmetic mean roughness Ra, the ten-point mean roughness Rzjis, and the maximum height Rz, the maximum height Rz has the greatest influence on the dendrite height. No matter which surface roughness standard is selected, the surface roughness of the negative electrode surface is measured in advance before using the battery cell.

In the battery recovery processing method of one embodiment, the amount of increase in dendrite height is accurately estimated, and a discharge pulse is generated to melt the dendrite and reduce the dendrite height. A discharge pulse is a pulse that causes a current to flow in the discharge direction. In the present disclosure, dissolving the dendrite by applying a discharge pulse is referred to as a "recovery process." The dendrite height reduction amount Δh may be calculated by setting the current density i in each of equations (2) and (3) as the current density in the discharge direction.
In the battery recovery processing method of one embodiment, the current height of dendrites on the negative electrode surface is estimated with high accuracy in order to perform necessary and sufficient recovery processing. In order to accurately estimate the current dendrite height, the integrated value of the current that has flowed through the battery cells up to now and data regarding the history of recovery processing up to now (execution history data) are stored in a storage device. It is preferable. In one embodiment, when a battery cell is connected to a charging device such as a charger, the integrated value of the current that has flowed to the battery cell up to the present and the execution history data up to the present are read from the storage device, and the current Estimate dendrite height.
In the battery recovery processing method of one embodiment, in order to perform the necessary and sufficient recovery processing, a target value of the dendrite height is set, and the recovery processing is executed until the estimated value of the dendrite height reaches the target value.

In the battery recovery processing method of one embodiment, when a battery cell is connected to a charging device, one of normal charging, pulse reverse charging, and recovery processing (pulse discharge) is selectively performed. In one embodiment, the state of charge (SOC) of the battery cell is estimated and, depending on the estimated SOC, a conditioning program (described below) consisting of pulsed reverse charging and/or recovery processing is determined to perform conditioning. Execute.
Normal charging means CCCV charging (Constant Current, Constant Voltage).
Pulse reverse charging (hereinafter referred to as "PR charging" as appropriate) refers to charging in such a way that the absolute value of the product of the current value in the charging direction and the application time exceeds the absolute value of the product of the current value in the discharging direction and the application time. , and a charging method in which pulse current is applied alternately.
The recovery process is to apply a discharge pulse, as described above.

FIG. 5 shows exemplary current density profiles for each of normal charging, PR charging, and recovery processing, and changes in shape of the negative electrode surface due to dendrite precipitation when each is performed. Note that in the current profile shown in FIG. 5, the current in the charging direction is positive, and the current in the discharging direction is negative.
In normal charging, for example, constant current charging, a constant current flows in the charging direction. In this case, since dendrites are generated intensively in the protruding portions of the negative electrode surface, the difference in height of the dendrites increases as normal charging is performed.

An example of a current profile for PR charging is shown in more detail in FIG. Here, i _charge is the current value in the charging direction, i _disch is the current value in the discharging direction, T _pulse is the pulse period, t _charge is the current application time in the charging direction, and t _disch is the current value in the discharging direction. is the current application time, and t _rest1 and t _rest2 are rest times. These values are pulse waveform parameters in PR charging in one embodiment. i _ave is an average current value determined by the pulse waveform. In PR charging, the absolute value of the product of the current value in the charging direction and the application time is set to exceed the absolute value of the product of the current value in the discharging direction and the application time (that is, i _charge ×t _charge > i _disch ×t _disch ), the average current value i _ave is positive (that is, the current in the charging direction).
As shown in Figure 5, in the case of PR charging, the average current value is the current in the charging direction, so the dendrites on the flat part of the negative electrode surface become high, while the effect of suppressing the height of the dendrites on the protruding parts is be. In other words, in the case of PR charging, there is an effect of widening the base without increasing the height of the protrusion.

An example of a current profile for the recovery process is shown in more detail in FIG. Here, i _disch is the current value in the discharging direction, t _disch is the current application time in the discharging direction, and T _pulse is the pulse period. These values are pulse waveform parameters in the recovery process of one embodiment.
The recovery treatment dissolves dendrites over the entire surface of the negative electrode, but as shown in FIG. 5, it has the effect of reducing the height of the dendrites particularly in the protruding portions.

Next, a charging system in which the battery recovery processing method of one embodiment is implemented will be described.
The charging system schematically shown in FIG. 7 is a system in which a battery module 2 (an example of a power storage device) is charged by a charging device 3, and a state in which the battery module 2 is connected to the charging device 3 is shown. The battery module 2 includes a battery cell group 21 to which one or more battery cells are connected, and a cell management unit (CMU) connected to each battery cell of the battery cell group 21. Each battery cell includes at least a positive electrode, a negative electrode, and an electrolyte.

Note that the charging system shown in FIG. 7 is only an example, and the present invention can be applied to a battery pack including two or more battery modules. In addition, although the battery cell group 21 shown in FIG. 7 is an example of a case in which one or more battery cells are connected in series, this is not a limitation, and each battery cell group is composed of battery cells connected in parallel. A plurality of combinations may be connected in series.

The cell management unit 22 is provided to control each battery cell included in the battery module 2. When the battery module 2 is connected to the charging device 3, the cell management unit 22 is connected to a charge control unit 6 (CCU: Charge Control Unit; an example of a battery control device) of the charging device 3. In this state, the cell management unit 22 and the charging control unit 6 are in a communicable state.

When the battery module 2 is connected to the charging device 3, a closed circuit to which the battery cell group 21 is connected is formed. A current sensor 7 is provided on the closed circuit in the charging device 3 to detect the current flowing through the closed circuit.
The charging control unit 6 acquires the current value detected by the current sensor 7, acquires the voltage value of each battery cell from the battery module 2, and controls charging of the battery module 2.

Next, the configurations of the charging control unit 6 and the cell management unit 22 in the charging system of one embodiment will be described with reference to FIG. 8. FIG. 8 is a functional block diagram of the charging control unit 6 and the cell management unit 22.

Referring to FIG. 8, the cell management unit 22 includes a controller 221, a storage section 222, a cell monitoring section 223, and a communication section 224.
The controller 221 includes a microcomputer, ROM (Read Only Memory), RAM (Random Access Memory), and the like. In the controller 221, the microcomputer executes a predetermined program, so that, for example, the integrated charging value (integrated value of the current flowing through each battery cell due to normal charging; described later) received from the charging control unit 6 via the communication unit 224. ) and execution history data are written into the storage unit 222.

The storage unit 222 is, for example, a nonvolatile storage device such as a flash memory, and stores the integrated charging value and execution history data received from the charging control unit 6, as described above.

The cell monitoring unit 223 detects the inter-terminal voltage of each battery cell in the battery cell group 21, and performs battery cell balancing as necessary. The method of battery cell balancing is not particularly limited, and may be passive balancing or active balancing.

The communication unit 224 is a communication interface unit that communicates with the charging control unit 6 according to a predetermined protocol.
For example, after communication with the charging control unit 6 of the charging device 3 is established, the communication unit 224 transmits the integrated charging value and execution history data of each battery cell stored in the storage unit 222 to the charging control unit 6. do. The communication unit 224 also receives the integrated charging value and execution history data of each battery cell from the charging control unit 6 .

Referring to FIG. 8, charging control unit 6 includes a controller 61, a storage section 62, a display section 63, a communication section 64, and a temperature sensor 65 (an example of a temperature detection section).
The controller 61 includes a microcomputer, ROM, RAM, etc. The controller 61 functions as a charging processing section 611, a dendrite height estimation section 612, an SOC estimation section 613, a conditioning setting section 614, and a conditioning execution section 615 when the microphone computer executes a predetermined program.

The charging processing unit 611 executes various processes while the battery module 2 is connected to the charging device 3.
For example, the charging processing unit 611 displays the SOC of the battery module 2 on the display unit 63 based on the voltage value of the battery cell group 21 obtained from the cell management unit 22 while the battery module 2 is being charged.

The charging processing unit 611 writes in the storage unit 62 an integrated value of the current flowing through each battery cell during normal charging (hereinafter referred to as a “charge integrated value”). The charge integrated value is information necessary to accurately estimate the dendrite height. The charge integrated value is calculated by multiplying the current flowing through the current sensor 7 by time.
The charging processing unit 611 appropriately records data regarding the execution history of the recovery process executed by the conditioning execution unit 615 (execution history data) in the storage unit 62 (an example of a second storage unit). In the example shown in FIG. 6, the execution history data includes the current value _idisch of the pulse waveform in the recovery process, the current application time _tdisch in the discharge direction, the pulse period _Tpulse , and the time (or number of pulses) at which the recovery process was executed. ).
When the series of processes after the battery module 2 is connected is completed, the charging processing unit 611 transmits the integrated charging value and execution history data written in the storage unit 62 to the cell management unit 22 via the communication unit 64. do.

Upon receiving the integrated charging value and execution history data, the cell management unit 22 adds the received integrated charging value and execution history data to the integrated charging value and execution history data recorded in the storage unit 222, respectively. In other words, the storage unit 222 stores the accumulated charging integrated value and execution history data.

For example, the storage unit 222 of the cell management unit 22 stores the cumulative charging value and execution history data obtained from the first to N-1 connections with the charging device 3. Then, when the cell management unit 22 connects to the charging device 3 for the Nth time, it transmits the first to N-1th charging integrated value and execution history data to the charging control unit 6. When the N-th processing in the charging device 3 is completed, the charging control unit 6 transmits the N-th charging integrated value and the execution history data to the cell management unit 22, and the cell management unit 22 receives the N-th charging integrated value and the execution history data. The value and execution history data are written to the storage unit 222.
In this way, the storage section 222 of the cell management unit 22 cumulatively stores past integrated charge values and execution history data. Therefore, even if the battery module 2 is not always connected to the same charging device 3, the charging device 3 can acquire the past cumulative charging value and execution history data of each battery cell, and the dendrite height estimation unit 612 Height can be estimated with high accuracy.

The dendrite height estimating unit 612 (an example of a precipitation estimating unit) estimates the current height of dendrites generated on the negative electrode surface of each battery cell.
The dendrite height estimation method of one embodiment estimates the dendrite height of a battery cell based on the cumulative charge value and execution history data of each battery cell acquired from the cell management unit 22. The amount of increase in dendrite height based on past charging history is determined from the charging integrated value, and the amount of decrease in dendrite height is determined from past execution history data. Therefore, by subtracting the reduction amount based on the past execution history data from the dendrite height based on the past charging history (that is, the integrated value of the increase in dendrite height), the current dendrite height of the battery cell can be calculated. It can be calculated. At this time, as shown in equation (3), it is preferable to correct the amount of increase in dendrite height using the current density coefficient x and the temperature coefficient y.

The SOC estimating unit 613 (an example of a charging rate estimating unit) estimates the SOC, which is the current charging rate of each battery cell. The SOC estimating unit 613 performs estimation based on, for example, the current value detected by the current sensor 7 and the voltage value of each battery cell, but is not limited to a specific estimation method and may employ any method. You can also do it.

Conditioning setting section 614 (an example of a parameter setting section) executes conditioning setting processing for reducing the dendrite height based on the current dendrite height estimated by dendrite height estimating section 612. In the conditioning setting process, a conditioning program for reducing dendrite height is determined.
The conditioning program refers to a series of processes planned for performing conditioning, and includes, for example, at least one of the available processing time and the target value of dendrite height, and each battery estimated by the SOC estimation unit 613. It is determined based on the SOC of the cell. Note that the "processable time" is the time during which recovery processing can be executed. For example, if the charging device 3 side is set to charge until the charging end time, the time between the current time and the charging end time becomes the processable time.

The conditioning program of one embodiment is configured by either recovery processing or PR charging, or a combination of recovery processing and PR charging. When the conditioning program is configured by a combination of recovery processing and PR charging, the conditions for switching between recovery processing and PR charging may be set, for example, depending on the current SOC of the battery cell.

After determining a conditioning program, the conditioning setting unit 614 sets parameters of a pulse waveform of recovery processing and/or PR charging included in the determined conditioning program.
In the case of PR charging, the parameters set by the conditioning setting unit 614 include a current value i _charge in the charging direction, a current value i _disch in the discharging direction, a pulse period T _pulse , and a current application time t in the charging direction shown in FIG. _charge and the current application time _tdisch in the discharge direction. In the case of the recovery process, the parameters set by the conditioning setting unit 614 are the current value i _disch in the discharging direction, the current application time t _disch in the discharging direction, and the pulse period T _pulse shown in FIG.

In one embodiment, the priority order of parameter settings in the recovery process is the current value in the discharge direction, the current application time in the discharge direction, and the pulse period. The larger the current value in the discharge direction, the greater the effect of dissolving dendrites, so it is preferable to increase the current value in the discharge direction as much as possible. Next, it is preferable to set the current application time in the discharge direction so as to secure the amount of discharge electricity that reaches the target value of the dendrite height (that is, to obtain the amount of dendrite dissolution).
The pulse period consists of a current application time in the discharge direction and a rest time. Here, the rest time is the time required to eliminate the charge state distribution of the positive electrode active material in the thickness direction of the positive electrode, so the pulse period is given priority because it includes factors other than reducing the dendrite height. It is preferable to set the order after the current value in the discharge direction and the current application time in the discharge direction.

The priority order of parameter settings in PR charging can also be considered in the same way as in recovery processing. That is, the larger the current value is, the greater the effect of widening the base without increasing the height of the protrusion formed by dendrites on the surface of the negative electrode, and therefore, first, it is preferable to set the current value as large as possible. Next, it is preferable to set the current application time in the charging direction so as to ensure a charging amount of electricity that reaches the target SOC.

The conditioning execution unit 615 (an example of an execution unit) executes the conditioning program based on the conditioning program determined by the conditioning setting unit 614 and the pulse waveform parameters set for the recovery process and/or PR charging included in the program. , performs conditioning on each battery cell.

Here, the SOC conditions under which each of normal charging, PR charging, and recovery processing can be executed will be described with reference to FIGS. 9 and 10.
FIG. 9 is a diagram illustrating the relationship between the SOC and voltage of a battery cell. In FIG. 9, the SOC lower limit threshold SOC _L is a threshold for determining whether the recovery process (pulse discharge) can be executed. If pulse discharge is performed when the current SOC of the battery cell is too low, the voltage of the battery cell will further decrease and the positive electrode may deteriorate due to overdischarge. Therefore, it is preferable to set a lower limit threshold SOC _L of the battery cell and avoid executing pulse discharge when the current SOC is smaller than the lower limit threshold SOC _L.
In FIG. 9, the upper limit threshold value SOC _H of the SOC is a threshold value for determining whether PR charging can be performed. If PR charging is performed when the current SOC of the battery cell is too high, the positive electrode and electrolyte may deteriorate. Therefore, it is preferable to set the upper limit threshold value SOC _H of the battery cell and avoid executing PR charging when the current SOC of the battery cell is larger than the upper limit threshold value SOC _H.
Note that normal charging (CCCV charging) is possible no matter what value the current SOC of the battery cell is (however, CV charging is performed at a high SOC).

FIG. 10 is a diagram showing the relationship between the SOC of a battery cell and the charging method and recovery process that can be executed for the battery cell, and shows the contents explained with reference to FIG. 9 in an organized manner.
In one embodiment, a current SOC of a battery cell is obtained and a conditioning program is determined taking into account constraints based on the obtained current SOC. In this case, in one embodiment, a predetermined first value Th1 and a predetermined second value Th2 (Th2>Th1) are set between the lower limit threshold SOC _L and the upper threshold SOC _H.

For example, the conditioning program (program P2 described below) of one embodiment is configured to first perform PR charging to increase the SOC to a second value Th2, and then execute the recovery process. This conditioning program is selected for efficient conditioning when, for example, the current SOC of the battery cell is very close to the lower threshold SOC _L. A first value Th1 is set to determine the degree of proximity of the current SOC to the lower limit threshold SOC _L.

A conditioning program (program P1 described below) of one embodiment is configured to perform a recovery process. This conditioning program is performed, for example, when the current SOC of the battery cell is between the lower threshold SOC _L and the upper threshold SOC _{H and is not very close to the lower threshold SOC L (} that is, the current SOC is at the first value Th1 and the upper threshold SOC _H ).

The conditioning setting unit 614 of one embodiment selects one of the conditioning programs from among a plurality of conditioning programs prepared in advance, depending on the current SOC of the battery cell.

The storage unit 62 (an example of a first storage unit or a second storage unit) is, for example, a nonvolatile storage device such as a flash memory. As described above, the storage unit 62 stores, for example, charging routine data in which the daily charging start time and charging end time are defined, and the cumulative charging value and execution history data of each battery cell.
The storage unit 62 stores data on the surface roughness of the negative electrode surface of each battery cell. It is preferable that the surface roughness data of the negative electrode surface be measured and written in the storage section 62 before starting to use the battery module 2. The surface roughness data of the negative electrode surface is referred to by the dendrite height estimation unit 612 when estimating the dendrite height.

The display unit 63 includes a display panel such as an LCD (Liquid Crystal Panel) panel and a display drive circuit, and displays images generated by the controller 61 on the display panel.

The communication unit 64 is a communication interface unit that communicates with the cell management unit 22 according to a predetermined protocol.
After connecting the battery module 2 to the charging device 3 and establishing communication with the cell management unit 22, the communication unit 64 receives the past integrated charge value and execution history data of each battery cell from the cell management unit 22. . Further, after the series of processing after the battery module 2 is connected is completed, the communication unit 64 transmits the charging integrated value and the execution history data written in the storage unit 62 to the cell management unit 22.

Temperature sensor 65 includes, for example, a thermocouple, and detects the temperature of battery module 2 . The temperature value detected by the temperature sensor 65 is sequentially taken into the controller 61.
The dendrite height estimation unit 612 is necessary when correcting the amount of increase in dendrite height by referring to a coefficient table from the temperature value detected by the temperature sensor 65 and the current value detected by the current sensor 7. Obtain the current density coefficient x and temperature coefficient y.

Next, the operation of the charging system of one embodiment will be described with reference to FIGS. 11 and 12.
FIG. 11 is a flowchart relating to an example of the overall process executed by the charging control unit 6 when charging each battery cell of the battery module 2. FIG. 12 is a flowchart relating to an example of detailed processing of the conditioning setting processing in the flowchart of FIG. 11.
In the following description, it is assumed that the battery module 2 is connected to the charging device 3 for the Nth time.

When the battery module 2 is connected to the charging device 3, communication is first established between the battery module 2 and the charging device 3. At this time, the charging control unit 6 of the charging device 3 receives the past integrated charging value and execution history data of each battery cell from the cell management unit 22 of the battery module 2 (step S2). That is, when connecting to the charging device 3 for the Nth time, the charging integrated value and execution history data acquired from the first to N-1th connections to the charging device 3 are received from the cell management unit 22.

Next, the charging control unit 6 acquires execution history data after the battery module 2 is connected to the charging device 3 from the storage unit 62 (step S4). Immediately after the battery module 2 is connected to the charging device 3, the recovery process for each battery cell is not executed, so no execution history data is stored in the storage unit 62.

The charging control unit 6 estimates the dendrite height of each battery cell based on the integrated charging value and the execution history data (step S6). Immediately after the battery module 2 is connected to the charging device 3 for the Nth time, the charging control unit 6 controls the dendrite height (that is, the dendrite height from the first time to N- The battery cell is Calculate the current dendrite height.

If the dendrite height estimated in step S6 is less than the predetermined threshold (step S8: NO), there is no need to perform recovery processing to dissolve the dendrites, so the charging control unit 6 controls the battery module 2 to Then, it is decided to perform normal charging (step S10). The predetermined threshold value in step S8 is preferably a value obtained by subtracting a certain margin from the distance between the positive electrode and the negative electrode of each battery cell, from the viewpoint of preventing a short circuit between the positive electrode and the negative electrode due to the growth of dendrites. This margin is appropriately determined based on variations in the thickness of the separator, initial surface roughness of the negative electrode surface, planned charging current rate, amount of electricity, and the like. Since the growth rate of dendrites tends to increase as the dendrite height increases, it is necessary to ensure a sufficient margin.
Note that in step S10, it may be determined to perform PR charging instead of normal charging. Since PR charging requires more time to raise the SOC than normal charging, it is better to perform normal charging when the SOC of the battery module 2 is relatively low.

If the dendrite height estimated in step S6 is greater than or equal to the predetermined threshold (step S8: YES), it is necessary to perform conditioning of the battery cells, so the process proceeds to step S12 and subsequent steps.

First, the charging control unit 6 estimates the SOC of each battery cell in order to determine a conditioning program (step S12). Next, the charging control unit 6 refers to the charging routine data stored in the storage unit 62 and obtains the available processing time (step S14). For example, the time from the current time to the charging end time specified in the charging routine data is the processable time.

In step S14, the available processing time may be determined as follows. That is, charging control unit 6 first calculates a predicted charging time until charging is completed (for example, reaching the target SOC) based on the SOC estimated in step S12. Then, the processable time is determined by subtracting the predicted charging time from the total amount of time during which charging and recovery processing can be performed (for example, the time from the current time to the charging end time specified in the charging routine data). Good too. This makes it possible to perform conditioning while charging each battery cell to a desired SOC.
If the processable time is less than or equal to the predetermined threshold (step S16: YES), the charging control unit 6 determines that there is not enough time to perform the recovery process and ends the process. For example, if the time obtained by subtracting the estimated charging time from the above sum is less than or equal to a predetermined threshold, it is determined that there is not enough time and the process ends.

If the processable time is greater than the predetermined threshold (step S16: NO), conditioning is performed as follows.
That is, the charging control unit 6 first sets a target value for the dendrite height (step S18). The target value of the dendrite height can be any value less than the threshold value that is the reference for the determination in step S8. The target value of the dendrite height may be set to zero, for example.
Next, charging control unit 6 executes conditioning setting processing (step S20). In the conditioning setting process, a conditioning program is determined, and parameters of the recovery process and/or PR charging pulse waveform included in the determined conditioning program are set.

An example of the conditioning setting process is shown in FIG.
In the flowchart of FIG. 12, the charging control unit 6 first sets a first value Th1 and a second value Th2 (Th1<Th2) between the lower limit threshold SOC _L and the upper threshold SOC _H (step S30). The first value Th1 and the second value Th2 set conditions for switching between recovery processing and PR charging based on the current SOC of the battery cell.
The first value Th1 and the second value Th2 may be fixed values, but in order to achieve the highest efficiency, they are estimated in step S12 using at least one of the processing time, the target value, and the current dendrite height. The first value Th1 and the second value Th2 may be determined based on the SOC.
For example, if the processing time is short or the amount of dendrite dissolved required to reach the target value is small, it is better to perform PR charging to raise the SOC and then perform recovery processing by large pulse discharge. However, it may be possible to reduce the dendrite height in a shorter time by performing a recovery process using a small pulse discharge.

If the current SOC of the battery cell (hereinafter appropriately referred to as " _{SOC_P} ") is larger than the upper limit threshold SOC _H (step S32: YES), the charging control unit 6 performs PR as shown in FIG. Charging is avoided. Therefore, the program P1 that executes the recovery process is selected as the conditioning program (step S34), and parameters of the pulse waveform of the recovery process are set (step S36).
When the _{SOC_P} of the battery cell is smaller than the lower limit threshold SOC _L , the charging control unit 6 is prevented from immediately performing the recovery process (pulse discharge) as shown in FIG. 10 . Therefore, as a conditioning program, a program P2 that first performs PR charging to increase the SOC to the second value Th2 and then executes recovery processing is selected (step S40), and parameters of the pulse waveform of PR charging and recovery processing are selected. is set (step S42).

When the SOC _{_P} of the battery cell is between the lower limit threshold SOC _L and the upper threshold SOC _H , the charging control unit 6 performs conditioning that is selected depending on whether the SOC _{_P} of the battery cell is larger than the first value Th1. The programs are different. If the SOC _{_P} of the battery cell is less than or equal to the first value Th1, it is close to the lower limit threshold SOC _L , so PR charging is performed first to increase the SOC to the second value Th2, and then the recovery process is executed. Program P2 is selected (step S46), and pulse waveform parameters for PR charging and recovery processing are set (step S48). On the other hand, if the _{SOC_P} of the battery cell is larger than the first value Th1, the program P1 for executing the recovery process is selected (step S50), and parameters of the pulse waveform of the recovery process are set (step S52).

Referring again to FIG. 11, after performing the conditioning setting process, the charging control unit 6 performs the following steps based on the conditioning program (P1 or P2) selected according to the _{SOC_P} of the battery cell and the set parameters: Conditioning is performed on each battery cell (step S22).
The time period for performing conditioning using the selected conditioning program can be set as appropriate. The time for performing conditioning may be several minutes, one hour or more, or the time until the charging end time specified in the charging routine data.
When the charging control unit 6 executes the recovery process during conditioning, the charging control unit 6 writes the execution history data in the storage unit 62.

When the conditioning is completed, charging control unit 6 determines whether the estimated value of the dendrite height has reached the target value set in step S18 (step S24). Here, in step S6, since the dendrite height before conditioning has been estimated, the target dendrite height is achieved by subtracting the dendrite height reduction amount calculated based on the conditioning execution result. It is possible to determine whether the value has been reached.
As a result, if the dendrite height has not reached the target value (step S24: NO), the process returns to step S4.

When returning to step S4, charging control unit 6 acquires execution history data (step S4). This execution history data is data cumulatively written in the storage unit 62 when the battery module 2 is connected to the charging device 3 for the Nth time. Then, the charging control unit 6 estimates the dendrite height based on the cumulative charge value and execution history data from the first time to the N-1th time acquired in step S2, and the Nth time execution history data (step S6 ).
Steps S4 and S6 do not need to be performed if they have already been executed in step S24 before returning to step S4. The dendrite height estimated in step S6 (that is, the dendrite height after being reduced by performing conditioning before returning to step S4) is again compared with a predetermined threshold (step S8). As a result, if the dendrite height is still greater than or equal to the predetermined threshold, the process proceeds to step S12 and subsequent steps to execute the recovery process again. If the dendrite height estimated in step S6 is less than the predetermined threshold, the process proceeds to step S10.

As described above, unless the dendrite height reaches the target value (step S24: NO), the processes of steps S4 to S24 are repeated during the N-th connection of the battery module 2 to the charging device 3.
For example, when repeating steps S4 to S24 executes conditioning for the Mth time (step S22), the process returns to step S4 after storing the time required for performing the conditioning for the Mth time. Returning to step S4, estimation of dendrite height (step S6) and estimation of SOC (step S12) are performed. If the dendrite height is less than the predetermined threshold, the M+1st conditioning is not performed (step S10). Further, the available processing time is obtained based on the time required to perform the Mth conditioning (step S14), and if the available processing time is less than or equal to a predetermined threshold, the M+1st conditioning is not performed (step S16: YES). . Furthermore, if the estimated value of SOC is too low (for example, if it is below the lower limit threshold SOC _L ), recovery processing cannot be executed immediately.
Accordingly, in one embodiment, the method performs the M+1 conditioning (particularly the recovery process) based on the time taken to perform the M conditioning, the current SOC of each battery cell, and the dendrite height of each battery cell. Decide whether or not to implement.

While the processes of steps S4 to S24 are repeated, the integrated charge value at the M-th connection of the battery module 2 to the charging device 3 (when step S10 is executed) and the execution history data (when the recovery process is executed at step S20) case) is stored in the storage section 62 of the charging control unit 6.

After the dendrite height reaches the target value (step S24: YES), there is no need to perform further conditioning, so the process ends. Although not shown in FIG. 11, if there is sufficient time from the current time at the time of termination to the charging termination time, the charging control unit 6 may perform normal charging or PR charging on the battery module 2. good.

When the charging end time is reached, the integrated charging value written in the storage section 62 of the charging control unit 6 and the execution history data (if steps S4 to S24 are repeated N times, (cumulative execution history data) is transmitted to the battery module 2 as the N-th charge integrated value and execution history data. The battery module 2 writes the received N-th charge integrated value and execution history data into the storage unit 222. Thereby, the storage unit 222 of the battery module 2 stores the charging integrated value and the execution history data acquired from the first to Nth connections with the charging device 3.

As explained above, according to the charging system of one embodiment, when a battery module including one or more battery cells is connected to a charging device, the past cumulative charge value stored for each battery cell is , past conditioning execution history data are acquired on the charging device side, and the dendrite height of each battery cell can be estimated based on the acquired data. At this time, the dendrite height of each battery cell can be estimated with high accuracy by correcting the dendrite height based on at least one of the current density coefficient, the temperature coefficient, and the surface roughness of the negative electrode surface.
According to the charging system of one embodiment, when the charging device is connected to the battery module, at least one of target values of processing time for conditioning and dendrite height, and an estimated value of SOC of each battery cell. Based on this, an appropriate conditioning program is determined. Therefore, it is possible to efficiently condition each battery cell. In other words, it is possible to prevent the battery from being overcharged and discharged, which may accelerate the deterioration of the battery's life, or conversely prevent it from being able to recover sufficiently.

Although the embodiments of the battery control device and battery recovery processing method of the present invention have been described above, the present invention is not limited to the above embodiments. Moreover, various improvements and changes can be made to the embodiments described above without departing from the spirit of the present invention. For example, the individual technical features described in each of the embodiments and modifications described above can be combined as appropriate, as long as there is no technical contradiction.

The present invention is related to patent application No. 2020-209859 filed with the Japan Patent Office on December 18, 2020, and the entire contents of this application are incorporated by reference into this specification.

2...Battery module 21...Battery cell group 22...Cell management unit (CMU)
221...Controller 222...Storage unit 223...Cell monitoring unit 224...Communication unit 3...Charging device 6...Charging control unit (CCU)
61...Controller 611...Charging processing section 612...Dendrite height estimation section 613...SOC estimation section 614...Conditioning setting section 615...Conditioning execution section 62...Storage device 63...Display section 64...Communication section 65...Temperature sensor 7...Current sensor

Claims (13)

A battery control device that controls a power storage device equipped with at least one secondary battery cell including at least a positive electrode, a negative electrode, and an electrolyte,
a first storage unit that stores an integrated value of the current flowing through the secondary battery cell due to charging;
a precipitation estimation unit that estimates the precipitation height of the current metal precipitate deposited on the negative electrode surface of the secondary battery cell;
a parameter setting unit that sets a parameter for reducing the precipitation height of the metal precipitates when the current precipitation height of the metal precipitates estimated by the precipitation estimation unit is equal to or higher than a predetermined threshold;
an execution unit that executes a recovery process of applying a pulse current in the discharge direction of the secondary battery cell based on the parameters set by the parameter setting unit;
a charging rate estimation unit that estimates the current charging rate of the secondary battery cell;
Equipped with
The parameter setting unit sets a current value of the pulsed current based on a processable time for the recovery process, a target value of a precipitation height of metal precipitates due to the recovery process, and the charging rate; Setting parameters consisting of pulse period and current application time,
Battery control device. further comprising a temperature detection unit that measures the temperature of the secondary battery cell;
A battery control device according to claim 1. further comprising a second storage unit that stores an execution history of the recovery process for the secondary battery cell;
A battery control device according to claim 1 or 2. In the negative electrode, one type of element selected from alkali metals or alkaline earth metals is present in a metallic state as a negative electrode active material.
A battery control device according to any one of claims 1 to 3. A battery recovery processing method for controlling a power storage device equipped with at least one secondary battery cell including at least a positive electrode, a negative electrode, and an electrolyte, the method comprising:
Step (A) of estimating the current precipitation height of metal precipitates deposited on the negative electrode surface of the secondary battery cell based on a pre-stored integrated value of the current flowing through the secondary battery cell due to charging. and,
a step (B) of comparing the current precipitation height of the metal precipitate estimated in the step (A) with a predetermined threshold value of the precipitation height of the metal precipitate;
If the current precipitation height of the metal precipitates estimated in the step (B) is equal to or greater than the threshold value, a step (C) of setting a parameter for reducing the precipitation height of the metal precipitates;
a step (D) of performing a recovery process of applying a pulse current in the discharge direction of the secondary battery cell based on the parameters set in the step (C);
a step (E) of estimating the charging rate of the secondary battery cell;
a step (F) of obtaining processing available time for the recovery processing;
including;
The step (C) is
Furthermore, based on the processable time acquired in the step (F) and the current charging rate of the secondary battery cell estimated in the step (E),
setting parameters consisting of a current value of the pulsed current, a pulse period, and a current application time;
Battery recovery processing method. correcting the precipitation height of the metal precipitate estimated in the step (A) based on the temperature history of the secondary battery cell;
The battery recovery processing method according to claim 5. The negative electrode of the secondary battery cell contains, as a negative electrode active material, one element selected from alkali metals or alkaline earth metals in a metallic state,
In addition to the integrated value of the secondary battery cell, the surface roughness of the negative electrode surface in the initial state is selected from arithmetic mean roughness Ra, ten-point mean roughness Rzjis, and maximum height Rz. correcting the precipitation height of the metal precipitate estimated in the step (A) based on at least one;
The battery recovery processing method according to claim 5 or 6. The step (A) is based on a pre-stored execution history of the recovery process for the secondary battery cell, based on the current precipitation height of the metal precipitate determined from the integrated value of the secondary battery cell. including subtracting the determined reduction in the height of the metal precipitate;
A battery recovery processing method according to any one of claims 5 to 7. When the current charging rate of the secondary battery cell is less than or equal to a first value predetermined for the fully charged state of the secondary battery cell , the absolute value of the product of the current value in the charging direction and the application time is Charge the secondary battery cell until the charging rate of the secondary battery cell reaches a predetermined second value by applying pulse current alternately so as to exceed the absolute value of the product of the current value in the discharge direction and the application time. and
performing each step of the step (C) and the step (D) after the charging rate of the secondary battery cell reaches the second value;
A battery recovery processing method according to any one of claims 5 to 8. The processable time obtained in the step (F), the target value of the precipitation height of the metal precipitate by the recovery process , the current precipitation height of the metal precipitate, and the estimated value in the step (E). determining the first value and the second value based on the current charging rate of the secondary battery cell;
The battery recovery processing method according to claim 9. The battery recovery processing method includes, as a step performed after performing the M-th recovery processing,
a step (G) of storing the time required for the M-th recovery process;
a step (H) of estimating the current charging rate of the secondary battery cell and the current precipitation height of the metal precipitate;
The time required for the M-th recovery process stored in the step (G), the current charging rate of the secondary battery cell estimated in the step (H), and the current precipitation of metal precipitates. a step (I) of determining whether or not to perform the M+1 recovery process based on the height;
further including,
The battery recovery processing method according to any one of claims 5 to 10. a step (J) of calculating a predicted charging time based on the current charging rate of the secondary battery cell estimated in the step (E);
a step (K )and,
The battery recovery processing method according to any one of claims 5 to 11, further comprising: When it is determined that the time obtained by subtracting the predicted charging time from the total sum is insufficient, or whether the current precipitation height of metal precipitates is the same as the target value of the precipitation height of metal precipitates due to the recovery treatment. , or when it is determined that the value has fallen below the target value, the subsequent recovery process is not performed;
The battery recovery processing method according to claim 12.

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