JP2016143546A - Charge/discharge control system for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charge/discharge control system that can suppress deposition of lithium metal on the surface of a negative electrode by suppressing deviation of a salt concentration distribution occurring in electrolytic solution due to high rate charging/discharging.SOLUTION: A charge/discharge control system comprises a lithium ion secondary battery, a salt concentration sensor for detecting the salt concentration in the lithium ion secondary battery, a storage medium for storing a deviation pattern of the salt concentration due to excessive charging/discharging, and a controller for determining a charge excessive state or a discharge excessive state on the basis of the deviation of the salt concentration, and controlling charging/discharging of the lithium ion secondary battery. The controller prohibits charging with a lithium metal deposition limit current value or more when the salt concentration measured by the salt concentration sensor is smaller than a predetermined threshold value.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a charge / discharge control system for a lithium ion secondary battery. More specifically, the present invention relates to a charge / discharge control system capable of suppressing salt concentration unevenness in a lithium ion secondary battery due to high rate charge / discharge.

  Lithium ion secondary batteries are lighter and have higher energy density than existing batteries, and are therefore preferably used as high-output power sources for mounting on vehicles, or power sources for personal computers and portable terminals. For example, an application in which a lithium ion secondary battery is preferably used includes a high output power source for driving a vehicle such as an electric vehicle (EV), a hybrid vehicle (HV), and a plug-in hybrid vehicle (PHV).

  Such a lithium ion secondary battery gradually deteriorates due to repeated charge and discharge, and battery performance such as an increase in internal resistance and a decrease in battery capacity may be deteriorated. Therefore, various battery control methods, battery systems, and the like have been proposed in order to suppress a decrease in battery performance due to repeated charge and discharge. Patent documents 1-4 are mentioned as technical literature about this kind of technique.

Japanese Unexamined Patent Publication No. 2014-3826 JP 2010-218877 A JP 2012-221744 A JP 2010-73657 A

  By the way, for example, when charging a lithium ion secondary battery, lithium metal (dendritic lithium) may be deposited on the negative electrode surface depending on the charging conditions. If lithium metal is deposited on the negative electrode, the battery function tends to be adversely affected, such as a decrease in battery capacity in a short period of time or a short circuit between the positive and negative electrodes. For this reason, a method for appropriately preventing or suppressing lithium metal deposition on the negative electrode surface has been demanded. For example, Patent Document 4 discloses a method for controlling charging conditions in order to avoid precipitation of lithium metal.

  However, according to the conventional method, lithium metal deposition cannot be sufficiently prevented when the lithium ion secondary battery is charged at high rate. The present invention has been created in view of the above circumstances, and its purpose is to suppress the unevenness of lithium salt concentration distribution (salt concentration unevenness) generated in the electrolyte solution by high-rate charge / discharge, thereby reducing lithium on the negative electrode surface. It is to provide a charge / discharge control system capable of suppressing metal deposition.

According to the present invention, a charge / discharge control system for a lithium ion secondary battery is provided. The charge / discharge control system stores a lithium ion secondary battery, a salt concentration sensor that detects a salt concentration inside the lithium ion secondary battery, and a pattern of bias in salt concentration due to excessive discharge and excessive charge. A storage medium; and a control unit that determines whether the battery is overcharged or overdischarged based on an uneven salt concentration and controls charging / discharging of the lithium ion secondary battery.
Here, when the salt concentration measured by the salt concentration sensor is lower than a preset specified value, the control unit uses a pattern of salt concentration bias stored in the storage medium, It is determined whether the decrease in salt concentration is due to an excessive charge state or an excessive discharge state, charging is limited in the excessive charging state, and discharging is limited in the excessive discharging state. Further, the control unit prohibits charging at a current value equal to or higher than a lithium metal deposition limit current value when the salt concentration measured by the salt concentration sensor is further smaller than a predetermined threshold value smaller than the specified value. To do.

  According to the charge / discharge control system having such a configuration, when the salt concentration detected by at least one salt concentration sensor installed in the lithium ion secondary battery is lower than a preset specified value, the charge / discharge of the battery is performed. Is appropriately restricted. When charging / discharging is limited in this way, the reduced salt concentration can be restored to the level of the specified value within a relatively short period of time. According to the charge / discharge control system having such a configuration, the salt concentration in the lithium ion secondary battery is intermittently measured, and the charge / discharge is appropriately limited as necessary. The uneven distribution of the salt concentration in the battery can be eliminated in a relatively short time.

  Here, in the case where the salt concentration is lower than the specified value and the salt concentration does not sufficiently recover to the specified value level even if the above-described charge / discharge restriction is performed, the salt concentration is less than the specified value. Is smaller than the predetermined threshold value, charging with a current value equal to or higher than the lithium metal deposition limit current value is prohibited. Thereby, it can prevent or suppress that a lithium metal precipitates in the part with low salt concentration in a lithium ion secondary battery.

  In the present specification, the “salt concentration” refers to the salt concentration in the lithium ion secondary battery. Such a salt may be ionized at least partially or substantially entirely in the electrolyte.

It is explanatory drawing which shows typically the charging / discharging control system which concerns on one Embodiment. It is a figure which illustrates typically salt concentration distribution in a lithium ion secondary battery. It is a flowchart which shows the control processing by the charging / discharging control system which concerns on one Embodiment. It is a graph explaining the relationship between the salt concentration in a lithium ion secondary battery, and a lithium metal precipitation limit electric current value. It is a graph explaining the relationship between the battery temperature of a lithium ion secondary battery, and a salt concentration threshold value. It is a graph which shows the time-dependent change of the salt concentration in the lithium ion secondary battery which concerns on one Example.

  Hereinafter, a charge / discharge control system for a lithium ion secondary battery according to the present invention will be described based on a preferred embodiment with reference to the drawings as appropriate. Note that matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention (for example, battery structures that do not characterize the present invention) are those skilled in the art based on the prior art in the field. It can be grasped as a design item. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

  Here, as a preferred embodiment of the charge / discharge control system, a charge / discharge control system in a lithium ion secondary battery for a vehicle-mounted battery mounted on a hybrid vehicle (HV) will be described as an example. A vehicle to which the charge / discharge control system disclosed herein is preferably applied may be a vehicle that uses electric energy from a battery for all or a part of its power source, and is limited to a hybrid vehicle. Absent. For example, an electric vehicle (EV), a plug-in hybrid vehicle (PHV), a hybrid railway vehicle, a forklift, an electric wheelchair, an electric assist bicycle, an electric scooter, and the like may be used.

  FIG. 1 is an explanatory diagram showing a schematic configuration of the charge / discharge control system 1. As shown in FIG. 1, the charge / discharge control system 1 includes a lithium ion secondary battery 2 that is a target of charge / discharge control processing, a salt concentration sensor 3 installed in the lithium ion secondary battery 2, and a control. Part (controller) 4. The control unit 4 typically includes an input unit 5, an output unit 6, a calculation unit (CPU) 7 and a storage medium (memory) 8.

  The lithium ion secondary battery 2 is a secondary battery that uses lithium (Li) ions as electrolyte ions (charge carriers) and is charged and discharged as lithium ions move between positive and negative electrodes. In FIG. 1, for convenience, the lithium ion secondary battery 2 is used alone, but the lithium ion secondary battery 2 may be used in the form of an assembled battery constructed by arranging a plurality.

  The salt concentration sensor 3 directly detects the lithium salt concentration in the electrolytic solution in the lithium ion secondary battery 2. The salt concentration sensor 3 is electrically connected to the input unit 5 of the control unit 4, and information on the lithium salt concentration in the lithium ion secondary battery 2 detected by the salt concentration sensor 3 is input to the control unit 4. The On the other hand, the salt concentration distribution pattern of the lithium ion secondary battery 2 is stored in advance in the storage medium 8 of the control unit 4. The calculation unit 7 of the control unit 4 compares the salt concentration information input from the salt concentration sensor 3 with the salt concentration distribution pattern stored in advance in the storage medium 8 to thereby compare the lithium ion secondary battery 2. The state of is determined. Based on the determination result, the control unit 4 outputs a command related to charge / discharge control from the output unit 6. The output unit 6 of the control unit 4 is typically electrically connected to a main control device (electronic control unit; ECU) 9 installed in the vehicle. The ECU 9 is connected to the lithium ion secondary battery 2. Charge / discharge control is performed.

  Here, for the sake of convenience, the control unit (controller) 4 and the ECU 9 are separately illustrated in FIG. 1, but the control unit 4 disclosed herein may constitute a part of the ECU 9.

  Hereinafter, the configuration of the lithium ion secondary battery 2 included in the charge / discharge control system 1 will be briefly described. The lithium ion secondary battery 2 includes a wound electrode body 2a in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound with a separator interposed therebetween, an electrolytic solution, a wound electrode body 2a, and a battery containing the electrolytic solution A case 2b. A positive electrode active material layer is formed on at least one surface of the strip-shaped positive electrode, and a negative electrode active material layer is formed on at least one surface of the strip-shaped negative electrode.

The positive electrode active material layer includes a positive electrode active material. As the positive electrode active material, a material capable of inserting and extracting lithium ions, for example, a lithium-containing compound (for example, a lithium transition metal composite oxide) containing lithium element and one or more transition metal elements is suitably used. Can be used. Such a lithium transition metal oxide is, for example, a lithium nickel composite oxide (eg LiNiO ₂ ), a lithium cobalt composite oxide (eg LiCoO ₂ ), a lithium manganese composite oxide (eg LiMn ₂ O ₄ ), or lithium nickel cobalt manganese. It may be a ternary lithium-containing composite oxide such as a composite oxide (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ).

  The negative electrode active material layer includes a negative electrode active material. As the negative electrode active material, for example, a carbon material such as graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), carbon nanotube, or a combination of these materials is suitably used. .

  As the electrolytic solution (nonaqueous electrolytic solution), a solution in which a supporting salt is dissolved or dispersed in a nonaqueous solvent is employed. As the non-aqueous solvent, various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones can be used without particular limitation. Specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). Such a non-aqueous solvent can be used alone or as a mixed solvent in which two or more are mixed.

In the case of a lithium ion secondary battery, for example, a lithium salt such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N, LiCF ₃ SO ₃ or the like may be used as the supporting salt. it can. Such supporting salts may be used singly or in combination of two or more.

  In such a lithium ion secondary battery 2, when the battery is overcharged beyond a certain level, a phenomenon in which lithium metal (dendritic lithium) is deposited on the negative electrode surface may occur. Such a phenomenon can typically occur when the negative electrode potential is below the lithium deposition potential due to overcharging. Therefore, conventionally, attempts have been made to control the charging conditions of the lithium ion secondary battery in order to prevent the occurrence of such a phenomenon.

  However, according to the study by the present inventors, it has been found that it is difficult to sufficiently suppress lithium metal deposition by the above-described measures by controlling the charging conditions. Specifically, the present inventors disassemble a lithium ion secondary battery that has been subjected to high-rate charge / discharge for a predetermined time, take out the negative electrode in the lithium ion secondary battery, observe the surface, etc. The behavior of metal precipitation was observed. As a result, it was newly found that the uneven distribution of lithium salt concentration in the electrolytic solution that occurs during high-rate charge / discharge (hereinafter also referred to as “salt concentration unevenness”) affects the precipitation of lithium metal. That is, when the lithium salt concentration temporarily decreased in at least a part of the battery due to the occurrence of uneven salt concentration, it was found that lithium metal tends to precipitate mainly in the vicinity of the portion where the salt concentration decreased.

  Here, the salt concentration unevenness due to the high rate charge / discharge in the lithium ion secondary battery will be briefly described. For example, when a lithium ion secondary battery is charged at a high rate, lithium ions are released from the positive electrode active material on the positive electrode side of the battery. For this reason, the lithium salt concentration (or lithium ion concentration) temporarily increases on the positive electrode side. On the other hand, when a lithium ion secondary battery is charged at a high rate, lithium ions are occluded in the negative electrode active material on the negative electrode side of the battery. For this reason, the lithium salt concentration (or lithium ion concentration) temporarily decreases on the negative electrode side. Thus, a temporary bias may occur in the salt concentration distribution in the lithium ion secondary battery. Such a temporary bias in the salt concentration distribution can also occur due to high-rate discharge.

  Thus, when a temporary bias occurs in the lithium salt concentration distribution, the lithium ions tend to move from the higher lithium ion concentration toward the lower lithium ion concentration. However, since the movement speed of lithium ions is finite, if a rapid change occurs in the salt concentration distribution due to high-rate charge / discharge, the movement of lithium ions is not in time. If such usage continues, the salt concentration distribution may remain biased. In this way, uneven salt concentration distribution (uneven salt concentration) can occur in the lithium ion secondary battery due to high-rate charge / discharge.

  FIG. 2 schematically shows a lithium salt concentration distribution in a general prismatic lithium ion secondary battery. The two broken lines in FIG. 2 indicate the lithium salt concentration distribution when the lithium ion secondary battery is excessively charged and the lithium salt concentration distribution when the battery is excessively discharged.

  According to the example shown in FIG. 2, when the lithium ion secondary battery is in an overcharged state, in the central portion of the winding electrode body 2 a of the lithium ion secondary battery 2 in the winding axis direction (horizontal direction in the figure). The lithium salt concentration is relatively high, and the lithium salt concentration tends to be relatively low at both ends in the winding axis direction (horizontal direction in the figure). That is, when the lithium ion secondary battery is overcharged, a lithium salt (or lithium ion) is provided at the center in the winding axis direction (horizontal direction in the figure) of the wound electrode body 2a of the lithium ion secondary battery 2. Is easy to gather.

  On the other hand, when the lithium ion secondary battery is in an excessive discharge state, the lithium salt concentration is relatively low at the center portion of the lithium ion secondary battery 2 in the winding axis direction (horizontal direction in the figure), The lithium salt concentration tends to be relatively high at both ends in the winding axis direction. That is, when the lithium ion secondary battery is excessively discharged, lithium salts (or lithium ions) are formed at both ends in the winding axis direction (horizontal direction in the drawing) of the wound electrode body 2a of the lithium ion secondary battery 2. Is easy to gather.

  As described above, a typical pattern of uneven salt concentration tends to differ depending on whether the lithium ion secondary battery is in an excessively charged state or an excessively discharged state. Therefore, the state of the battery at that time can be determined by measuring the salt concentration of the lithium ion secondary battery in use (during charging / discharging) and comparing it with the knowledge related to such salt concentration unevenness.

According to the charge / discharge control system 1 disclosed herein, the salt concentration sensor 3 is installed inside the lithium ion secondary battery 2. The salt concentration sensor 3 directly detects the salt concentration (or ion concentration) in the electrolytic solution in the lithium ion secondary battery 2.
Such salt concentration sensors 3 are installed at three or more locations in the lithium ion secondary battery 2 and each independently measures the salt concentration. By setting the salt concentration sensor 3 to be installed at three or more locations, the salt concentration distribution pattern in the lithium ion secondary battery 2 can be appropriately acquired. The number of salt concentration sensors 3 installed in the lithium ion secondary battery 2 is preferably 3 or more, for example, 4 or more, or 5 or more. The salt concentration sensor 3 is preferably arranged so as to equally divide the winding axis direction (horizontal direction in the drawing) of the wound electrode body 2a.

  FIG. 1 shows an installation example of the salt concentration sensor 3 in the lithium ion secondary battery 2. FIG. 1 shows an example in which three salt concentration sensors 3 are installed inside a prismatic lithium ion secondary battery 2. Specifically, the salt concentration sensor 3 is at both ends of the wound electrode body 2a of the lithium ion secondary battery 2 in the winding axis direction (horizontal direction in the figure) and in the height direction (perpendicular to the winding axis direction). One in the center of each direction, and one in the center in the winding axis direction and the height direction (three in total).

The salt concentration sensor 3 measures the concentration of lithium salt (or lithium ion concentration) dissolved in the electrolyte near the measurement location. As the salt concentration sensor 3 disclosed herein, for example, a fine line sensor is preferably employed. For example, LiFePO ₄ , Li ₄ Ti ₅ O ₁₂ , LiCoPO ₄ , LiMnPO ₄ or the like can be suitably used as a constituent material of the salt concentration difference detection electrode in the salt concentration sensor 3.

  Next, with reference to the flowchart of FIG. 3, the charge / discharge control process of the lithium ion secondary battery 2 according to the present invention will be described. When the charging / discharging control process of the lithium ion secondary battery 2 disclosed herein is started, the salt concentration sensor 3 installed in the lithium ion secondary battery 2 measures the salt concentration (S101). Here, if the salt concentration is not lower than the preset specified value (S102: No), the process returns to the step of measuring the salt concentration (S101) again. If the salt concentration is lower than the specified value as a result of measuring the salt concentration (S102: Yes), the control unit 4 determines the salt concentration distribution pattern stored in the storage medium 8 and the salt concentration sensor 3 in advance. Is compared with the salt concentration data indicated by (2), and it is specified whether the state of the lithium ion secondary battery 2 at that time is an excessive charge state or an excessive discharge state (S103).

  When the lithium ion secondary battery 2 is in an overcharged state, the control unit 4 restricts charging of the lithium ion secondary battery 2 (S104). On the other hand, when the lithium ion secondary battery 2 is in an excessive discharge state, the control unit 4 limits the discharge of the lithium ion secondary battery 2 (S105). By limiting charging or discharging in this manner, salt concentration unevenness is eliminated and the salt concentration tends to increase. When the salt concentration recovers due to the restriction of charging or discharging and becomes larger than the specified value (S106: Yes), the restriction of charging or discharging is released, and the process returns to the step of salt concentration measurement (S101).

Note that the above-described restriction of charging or discharging refers to lowering a current value in charging or discharging or prohibiting charging or discharging. Specifically, the charge limit, lowering the upper limit of the current value I _C that is allowed in the charging to an appropriate value, or means to inhibit charging. The restriction of discharge refers to lowering the upper limit of the current value _ID allowed for discharge to an appropriate value or prohibiting discharge.

  Here, only when the salt concentration is higher than a predetermined threshold (S107: No), when the salt concentration does not recover to the specified level due to the restriction of charging or discharging (S106: No), After returning to step S103 again and determining whether the lithium ion secondary battery 2 is in an excessively charged state or an excessively discharged state, charging or discharging is limited again accordingly.

  By repeatedly performing the processing so far (ie, S101 to S107), the salt concentration unevenness of the lithium ion secondary battery 2 due to the high-rate charge / discharge can be appropriately eliminated within a relatively short period of time. Such treatment not only prevents or suppresses lithium metal precipitation due to uneven salt concentration, but also suppresses an increase in internal resistance.

When the salt concentration does not recover to the predetermined specified value due to the restriction of the charge or discharge, and further becomes smaller than the predetermined threshold value smaller than the specified value (S107: Yes), the control unit 4 Charging at a current value equal to or higher than the lithium metal deposition limit current value A (hereinafter also referred to as “I _lim-A ”) is prohibited (S108). This is because when the salt concentration is smaller than the threshold value, lithium metal precipitation is likely to occur on the negative electrode surface.

Here, in this specification, the lithium metal deposition limit current value (hereinafter also referred to as “I _lim ”) refers to a limit current value at which the lithium metal can be charged without being deposited. The lithium metal deposition limit current value I _lim may vary depending on the salt concentration in the lithium ion secondary battery, as shown in FIG. Specifically, when the salt concentration decreases, the lithium metal deposition limit current value I _lim tends to decrease. The lithium metal deposition limit current value A (I _lim-A ) described above is the lithium metal deposition limit current value I in a state where the salt concentration is not lowered (that is, a state where the salt concentration is a predetermined value set in advance). _It means _lim .

As the salt concentration threshold, an appropriate value is set according to the application, use conditions, components, and the like of the charge / discharge control system used. For example, in the graph of FIG. 4, it is preferable to set the salt concentration at which the lithium metal deposition limit current value I _lim starts to decrease as the threshold value when the salt concentration is lowered from a preset specified value.

  Further, for example, the threshold value is preferably set according to the battery temperature when the battery is used. FIG. 5 shows a correlation diagram between the threshold value and the battery temperature of the lithium ion secondary battery according to a preferred embodiment. As shown in FIG. 5, it is preferable that the threshold value be set larger as the battery temperature increases.

According to the charge / discharge control processing with such a configuration, when the salt concentration falls below the threshold value, charging at a current value equal to or higher than I _lim-A is prohibited, so that lithium metal deposition is prevented in the portion where the salt concentration is lowered. Or suppressed. In addition, by repeatedly performing the charge / discharge control process having such a configuration, a decrease in salt concentration or salt concentration unevenness of the lithium ion secondary battery 2 due to high-rate charge / discharge can be suppressed. Therefore, a decrease in battery performance (for example, an increase in internal resistance) caused by salt concentration unevenness can be suppressed.

  Hereinafter, an example when the charge / discharge control system according to one embodiment disclosed herein is implemented will be described. FIG. 6 shows the change over time of the salt concentration of the lithium ion secondary battery that is charge / discharge controlled by the charge / discharge control system disclosed herein. Specifically, when a lithium ion secondary battery is charged and discharged at a high rate, among the salt concentration sensors installed inside the battery, a salt concentration sensor installed at the winding axial end of the wound electrode body is It is a time-dependent change of the lithium salt concentration measured.

  As is apparent from FIG. 6, the salt concentration in the electrolyte solution in the lithium ion secondary battery increased or decreased with the use of the battery (high rate charge / discharge). Hereinafter, the portions where the salt concentration is lower than a preset specified value are classified as (A) to (D) in the order of elapsed time, and each portion will be described.

  (A) Since the salt concentration has started to decrease below a predetermined value set in advance, the control unit compares the salt concentration distribution pattern stored in advance in the storage medium with the salt concentration data indicated by the salt concentration sensor, It was determined whether the salt concentration decrease was due to excessive charge or excessive discharge. As a result, since it was determined that the lithium ion secondary battery was in an overcharged state, charging of the battery was limited. After a while, the salt concentration began to increase and the charge control was terminated because the salt concentration was restored to the specified value.

  (B) Next, since the salt concentration again falls below the specified value, the control unit, as in the case of (a) above, displays the salt concentration distribution pattern and the salt concentration sensor stored in advance in the storage medium. The salt concentration data shown was compared to determine whether the salt concentration decrease was due to excessive charge or excessive discharge. As a result, the lithium ion secondary battery was determined to be in an overdischarged state, and thus the discharge of the battery was limited. After a while, the salt concentration began to increase and the discharge control was completed because the salt concentration was restored to the specified value.

  (C) Next, since the salt concentration again falls below the specified value, the control unit, as in the cases (a) and (b) above, reads the pattern of the salt concentration distribution stored in advance in the storage medium. The salt concentration data indicated by the salt concentration sensor was compared to determine whether such a decrease in salt concentration was due to excessive charge or excessive discharge. As a result, since it was determined that the lithium ion secondary battery was in an excessive discharge state, the discharge of the battery was limited. However, the salt concentration continued to decrease without increasing thereafter.

(D) Since the salt concentration became smaller than the predetermined threshold value, charging at a current value equal to or higher than the lithium deposition limit current value A (I _lim-A ) was prohibited. Then, the salt concentration began to rise. After a while, since the salt concentration became higher than the threshold value, the prohibition of charging at a current value equal to or higher than the lithium deposition limit current value A (I _lim-A ) was lifted.

  The lithium ion secondary battery after performing high-rate charge / discharge as shown in FIG. 6 continuously for 500 hours was disassembled, the negative electrode sheet was taken out, and the surface thereof was visually observed. As a result, it was confirmed that lithium metal was not deposited on the negative electrode surface after high-rate charge / discharge.

As is clear from the results of the above examples, according to the charge / discharge control system disclosed herein, it was confirmed that the salt concentration unevenness in the battery due to the high-rate charge / discharge is properly eliminated within a relatively short period of time. It was done. In addition, since charging at a current value equal to or higher than the lithium deposition limit current value A (I _lim-A ) was not performed in a state where the salt concentration was below the threshold value in at least a part of the battery, It was confirmed that the lithium metal precipitation in was suppressed.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims of the present application includes various modifications and changes of the specific examples illustrated above.

DESCRIPTION OF SYMBOLS 1 Charging / discharging control system 2 Lithium ion secondary battery 3 Salt concentration sensor 4 Control part (controller)
8 Storage media (memory)

Claims (1)

A lithium ion secondary battery, a salt concentration sensor for detecting a salt concentration inside the lithium ion secondary battery, a storage medium for storing a pattern of bias in salt concentration due to excessive discharge and excessive charge, and a salt concentration A controller that determines whether the battery is excessively charged or excessively discharged due to bias and controls charging / discharging of the lithium ion secondary battery, and
The control unit, when the salt concentration measured by the salt concentration sensor is lower than a preset specified value,
Using the pattern of salt concentration bias stored in the storage medium, determine whether the decrease in salt concentration is due to an excessive charge state or an excessive discharge state,
In the overcharged state, limiting charging,
In the excessive discharge state, limiting discharge,
Furthermore, the control unit, when the salt concentration measured by the salt concentration sensor is further smaller than a predetermined threshold smaller than the specified value,
Prohibit charging at a current value greater than the lithium metal deposition limit current value,
A charge / discharge control system for a lithium ion secondary battery.

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