Charging system

Abstract

To inhibit the deposition of lithium metal.SOLUTION: An ECU executes processing including the steps of calculating the negative electrode potential of an unopposed portion (S102) when charging is in progress (YES in S100), executing charging restriction processing (S106) when it is determined that the negative electrode potential is equal to or lower than a threshold value b1 (YES in S104), calculating the negative electrode potential of the unopposed portion (S108), and executing restriction release processing (S112) when it is determined that the negative electrode potential exceeds a threshold value b2 (YES in S110).SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to a charging system.

Background Art

[0002] Japanese Unexamined Patent Application Publication No. 2020-077464 (Patent Document 1) discloses a secondary battery system that executes control to reduce the charging current in order to prevent the deposition of lithium metal when the negative electrode potential calculated using the charging current to the lithium ion battery and the reaction resistance is lower than the deposition potential at which lithium metal is deposited on the negative electrode.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the electrode body of a lithium ion battery as described above, when the negative electrode has a larger shape than the positive electrode, lithium metal may accumulate in the negative electrode portion that does not face the positive electrode when the charge and discharge of the secondary battery are repeated. Therefore, the accumulated lithium metal may move to the negative electrode portion facing the positive electrode when the charge and discharge stop, and lithium metal may be deposited on the negative electrode during subsequent charging.

[0005] The present disclosure has been made to solve the above-described problems, and an object thereof is to provide a charging system that suppresses the deposition of lithium metal.

Means for Solving the Problems

[0006] A charging system according to an aspect of the present disclosure includes a secondary battery having a negative electrode containing a negative electrode active material into which lithium ions are inserted and desorbed, and a positive electrode, and a control device that controls the charging power of the secondary battery. The control device restricts the charging power when the negative electrode potential of the unopposed portion of the negative electrode that does not face the positive electrode becomes equal to or lower than a threshold value.

[0007] By doing so, since the charging power is restricted when the negative electrode potential of the unopposed portion becomes equal to or lower than the threshold value, it is possible to suppress the precipitation of lithium metal on the negative electrode due to the movement of lithium metal from the unopposed portion to the portion facing the positive electrode.

[0008] In one embodiment, the control device estimates the negative electrode potential of the unopposed portion using the control state of the charging power, and restricts the charging power when the estimated negative electrode potential becomes equal to or lower than the threshold value.

[0009] By doing so, it is possible to suppress the precipitation of lithium metal on the negative electrode due to the movement of lithium metal accumulated in the unopposed portion to the portion facing the positive electrode.

[0010] In yet another embodiment, the control device acquires the deterioration state of the secondary battery and sets a threshold value using the acquired deterioration state.

[0011] By doing so, since the charging power is restricted according to the deterioration state of the secondary battery, it is possible to suppress the precipitation of lithium metal on the negative electrode due to the movement of lithium metal accumulated in the unopposed portion to the portion facing the positive electrode.

[0012] In yet another embodiment, the control device releases the restriction on the charging power when the negative electrode potential of the unopposed portion exceeds the threshold value after the restriction on the charging power.

[0013] By doing so, since the restriction on the charging power is released when the accumulation of lithium metal in the unopposed portion is eliminated, it is possible to suppress the charging time from becoming unnecessarily long.

[0014] In yet another embodiment, the control device releases the restriction on the charging power when the restricted time of the charging power exceeds a predetermined time.

[0015] By doing so, since the restriction on the charging power is released when the accumulation of lithium metal in the unopposed portion is eliminated, it is possible to suppress the charging time from becoming unnecessarily long.

Advantages of the Invention

[0016] According to the present disclosure, it is possible to provide a charging system that suppresses the precipitation of lithium metal.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and their description will not be repeated.

[0019] Hereinafter, an example of the configuration of the charging system 1 according to the present embodiment will be described. FIG. 1 is a diagram showing an example of the configuration of the charging system 1. As shown in FIG. 1, the charging system 1 includes a vehicle 200 and a charging stand 2 which is a power supply facility outside the vehicle 200. The vehicle 200 may be any vehicle equipped with a power storage device that can be charged using electric power supplied from an external power source. For example, it may be an electric vehicle or a plug-in hybrid vehicle.

[0020] The vehicle 200 includes an ECU (Electronic Control Unit) 100 which is a control device, a battery 214, an inverter 216, an MG (Motor Generator) 218, and an inlet 220.

[0021] The battery 214 is a rechargeable power storage device, and includes, for example, a secondary battery such as a lithium-ion battery having a liquid electrolyte or a solid electrolyte.

[0022] The inverter 216 is configured to be able to convert the DC power of the battery 214 and the AC power of the MG 218 bidirectionally according to a control signal from the ECU 100.

[0023] The MG 218 is a drive source for driving the drive wheels of the vehicle 200, and is configured by, for example, a three-phase AC rotating electric machine or the like.

[0024] The inlet 220 has a shape to which the connector 17 of the charging stand 2 can be attached. The inlet 220 is electrically connected to the battery 214.

[0025] Sensors 102, 104, and 106 for acquiring the voltage, current, and temperature of the battery 214 are connected to the ECU 100. The ECU 100 includes a CPU (Central Processing Unit) and a memory (both not shown). Based on the signals received from each sensor and information such as maps and programs stored in the memory, the ECU 100 controls each device so that the vehicle 200 reaches a desired state.

[0026] The ECU 100 has a function of sequentially calculating the State of Charge (SOC) of the battery 214 based on the detection values of the respective sensors 102, 104, and 106. As a method for calculating the SOC, various known methods can be adopted, such as a method based on current value integration (Coulomb count) or a method based on the estimation of the open circuit voltage (OCV). The ECU 100 is configured to be communicable with the communication unit 13 of the charging stand 2 described later.

[0027] The charging stand 2 includes a communication unit 13, a control unit 14, a charging unit 15, a cable 16, and a connector 17. The charging stand 2 includes, for example, a rapid charger that completes charging in a shorter time than normal charging by supplying charging power higher than normal charging.

[0028] The communication unit 13 performs wired communication with the ECU 100 of the vehicle 200 via the cable 16 when the connector 17 is connected to the inlet 220 of the vehicle 200. The wired communication includes, for example, power line communication, CAN (Control Area Network) communication, or LAN communication. Note that the communication unit 13 may communicate with the ECU 100 of the vehicle 200 by wireless communication of various standards (for example, Wifi).

[0029] The control unit 14 controls the operation of the charging unit 15 (for example, charging voltage, charging current, and charging power). The control unit 14 includes, for example, a CPU and a memory (both not shown). The control unit 14 controls the charging unit 15 based on information received from the vehicle 200 using the communication unit 13 (such as required power described later) and information such as maps and programs stored in the memory. When the connector 17 is attached to the inlet 220, the control unit 14 acquires information about the battery 214 (for example, information about SOC, charging voltage, and required power) or transmits information about the charging stand 2 (for example, available time and available charging power) using the communication unit 13.

[0030] The charging unit 15 converts AC power from the utility power supply 400 into DC power according to a control signal from the control unit 14. One end of the cable 16 is connected to the charging unit 15. A connector 17 is connected to the other end of the cable 16.

[0031] The connector 17 has a shape that can be attached to the inlet 220. When the connector 17 is attached to the inlet 220, DC power can be supplied from the charging unit 15 to the battery 214 according to a control signal from the control unit 14.

[0032] For example, when the connector 17 is connected to the inlet 220 of the stopped vehicle 200, the charging stand 2 operates the charging unit 15 to convert AC power from the utility power supply 400 into DC power and supplies the converted DC power to the battery 214. The ECU 100 transmits information about the SOC and the required power calculated using the detection values of the sensors 102, 104, 106 to the control unit 14 during charging of the battery 214. For example, when the SOC is calculated, the ECU 100 calculates the required power corresponding to the calculated SOC, the full charge capacity of the battery 214, or the battery temperature of the battery 214, etc., and transmits information about the SOC and the required power, etc. to the control unit 14.

[0033] The battery 214 is composed of a plurality of battery cells connected in series or in parallel. The battery cell is formed, for example, by laminating an electrode body (hereinafter referred to as a laminate) including a positive electrode including a positive electrode active material layer, a separator, and a negative electrode including a negative electrode active material layer into which lithium ions are inserted and desorbed, and a liquid or solid electrolyte. FIG. 2 is a diagram showing an example of the configuration of the laminate of the battery cell.

[0034] As shown in FIG. 2, the battery cell 214a is configured with a separator 30 provided between a positive electrode 10 and a negative electrode 20. A positive electrode tab 12 is connected to the positive electrode 10. Further, a negative electrode tab 22 is connected to the negative electrode 20. The battery 214 is formed by connecting the positive electrode tab 12 and the negative electrode tab 22 to the negative electrode tab 22 of one adjacent battery cell 214a and the positive electrode tab 12 of the other adjacent battery cell 214a, respectively.

[0035] Also, the negative electrode 20 has a shape larger than that of the positive electrode 10 and has a portion that does not face the positive electrode 10 (hereinafter referred to as the non-facing portion). Specifically, at least both ends of the negative electrode 20 in the vertical direction of the paper surface of FIG. 2 are configured such that the negative electrode 20 is positioned outside both ends of the positive electrode 10. FIG. 3 is a diagram for explaining the positional relationship between the positive electrode and the negative electrode. As shown in FIG. 3, a part of the regions 24, 26 (hatched regions in FIG. 3) on the end side of the negative electrode 20 become non-facing portions that do not face the positive electrode 10.

[0036] During charging of the lithium-ion battery, when the absorption and diffusion of lithium ions in the negative electrode 20 cannot catch up with the supply of lithium ions from the positive electrode 10, lithium metal may precipitate on the surface of the negative electrode. The precipitation of lithium metal in the negative electrode 20 causes the negative electrode 20 to expand and the capacity retention rate to decrease. Therefore, it is required to limit the charging current so that lithium metal does not precipitate.

[0037] Therefore, for example, it is conceivable to execute control such as limiting the charging current using the negative electrode potential so that the negative electrode potential does not reach the potential at which lithium metal precipitates on the negative electrode 20 (precipitation potential). However, when the non-facing portion of the negative electrode 20 of the lithium-ion battery as described above is formed, during repeated charge and discharge of the battery 214, the lithium metal absorbed by the negative electrode 20 may move to and accumulate in the non-facing portion. Therefore, when the accumulated lithium metal moves to the facing portion with the positive electrode 10 when the charge and discharge stop, lithium metal may precipitate on the surface of the negative electrode during subsequent charging.

[0038] FIG. 4 is a diagram for explaining an example of changes in the amount of lithium metal during charge and discharge. FIG. 4 shows an example of the distribution of the absorption amount of lithium metal in each of the negative electrode 20 and the positive electrode 10 during charging, during standing, and during discharging.

[0039] (A) of FIG. 4 shows an example of the distribution of the absorption amount of lithium metal corresponding to each part of the negative electrode 20 and the absorption amount of lithium metal corresponding to each part of the positive electrode 10 when the battery 214 is being charged. The threshold value a1 indicates the threshold value of the absorption amount at which lithium metal is deposited in the negative electrode 20. The threshold value a2 indicates the threshold value of the absorption amount at which lithium metal is deposited in the positive electrode 10. As shown in (A) of FIG. 4, when the battery 214 is being charged, since lithium ions move to the negative electrode 20, the absorption amount of lithium metal in the negative electrode 20 increases, and the absorption amount of lithium metal in the positive electrode 10 decreases. At this time, lithium metal is also absorbed on the side closer to the facing part even in the non-facing part of the negative electrode 20.

[0040] (B) of FIG. 4 shows an example of the distribution of the absorption amount of lithium metal corresponding to each part of the negative electrode 20 and the absorption amount of lithium metal corresponding to each part of the positive electrode 10 when the charged battery 214 is standing. As shown in (B) of FIG. 4, when the battery 214 is standing, a part of the lithium metal that was absorbed on the side closer to the non-facing part in the facing part of the negative electrode 20 and the positive electrode 10 moves to the non-facing part, so that the absorption amount of lithium metal in the non-facing part of the negative electrode 20 increases.

[0041] (C) of FIG. 4 shows an example of the distribution of the absorption amount of lithium metal corresponding to each part of the negative electrode 20 and the absorption amount of lithium metal corresponding to each part of the positive electrode 10 when the battery 214 after standing is being discharged. As shown in (C) of FIG. 4, when the battery 214 is being discharged, since lithium ions move to the positive electrode 10, the absorption amount of lithium metal in the positive electrode 10 increases, and the absorption amount of lithium metal in the negative electrode 20 decreases. At this time, a part of the lithium metal absorbed in the non-facing part of the negative electrode 20 moves to the positive electrode 10, and the rest remains and accumulates in the non-facing part.

[0042] In (D) of FIG. 4, an example of the distribution of the amount of lithium metal absorbed at each part of the negative electrode 20 and the amount of lithium metal absorbed at each part of the positive electrode 10 when the battery 214 is left standing after discharging is shown. As shown in FIG. 4(D), when the battery 214 is left standing, a part of the lithium metal absorbed in the non-facing part of the negative electrode 20 moves to the facing part with the positive electrode 10, so that the amount of lithium metal absorbed in the facing part of the negative electrode 20 increases.

[0043] In FIG. 4(E), an example of the distribution of the amount of lithium metal absorbed at each part of the negative electrode 20 and the amount of lithium metal absorbed at each part of the positive electrode 10 when the battery 214 after standing is charged is shown. As shown in FIG. 4(E), when the battery 214 is charged, since lithium ions move to the negative electrode 20 again, the amount of lithium metal absorbed in the negative electrode 20 increases, and the amount of lithium metal absorbed in the positive electrode 10 decreases. At this time, the lithium metal that has moved from the non-facing part to the facing part of the negative electrode 20 and the lithium metal that has moved from the positive electrode 10 cause a sharp increase in the lithium metal in the negative electrode 20 near the non-facing part. As a result, when the amount of lithium metal absorbed exceeds the threshold value a1, lithium metal is deposited on the surface of the negative electrode 20.

[0044] Therefore, in the present embodiment, the ECU 100 acquires the negative electrode potential of the non-facing part using the control state of the charging power, and limits the charging power when the acquired negative electrode potential is equal to or lower than the threshold value.

[0045] By doing so, it is possible to suppress the deposition of lithium metal on the negative electrode 20 due to the movement of lithium metal from the non-facing part to the facing part.

[0046] Hereinafter, an example of the process executed in the ECU 100 will be described with reference to FIG. 5. FIG. 5 is a flowchart showing an example of the process executed in the ECU 100. A series of processes shown in this flowchart are repeatedly executed at predetermined intervals.

[0047] In step 100 (hereinafter referred to as step S), the ECU 100 determines whether it is in the charging state. For example, the ECU 100 may determine that it is in the charging state when the connector 17 is connected to the inlet 220, or may determine that it is in the charging state when the current supplied to the battery 214 is equal to or greater than a threshold value. If it is determined that it is in the charging state (YES in S100), the process proceeds to S102.

[0048] In S102, the ECU 100 calculates the negative electrode potential of the unopposed portion of the negative electrode 20 using the control state of the charging power. For example, the ECU 100 may calculate the negative electrode potential of the unopposed portion using a map showing the relationship between a plurality of parameters indicating the control state and the negative electrode potential of the unopposed portion, and the values obtained as the plurality of parameters. The map showing the relationship between the plurality of parameters and the negative electrode potential of the unopposed portion is adapted, for example, by experiments or the like. The plurality of parameters includes at least any one of the control value of the charging power, the SOC, the number of charging times, the charging time up to the present time, the charging time in a predetermined period up to the present time, the most recent idle time, and the temperature at the present time. Note that the ECU 100 may set a reference value of the negative electrode potential of the unopposed portion using a map showing the relationship between any one of the plurality of parameters and the negative electrode potential of the unopposed portion, and calculate the negative electrode potential of the unopposed portion by correcting it using other parameters. Thereafter, the process proceeds to S104.

[0049] In S104, the ECU 100 determines whether the negative electrode potential of the unopposed portion becomes equal to or less than a threshold value b1. The threshold value b1 is a value set using the threshold value a1 of the absorption amount at which the above-described lithium metal is deposited, and is predetermined by experiments or the like. The threshold value b1 is set, for example, so that the amount of lithium metal supplied from the positive electrode 10 by subsequent charging and the amount of lithium metal moving from the unopposed portion to the opposed portion do not exceed the threshold value a1 of the absorption amount at which the lithium metal is deposited. If it is determined that the negative electrode potential of the unopposed portion becomes equal to or less than the threshold value b1 (YES in S104), the process proceeds to S106.

[0050] In S106, the ECU 100 executes charge limit processing. The charge limit processing may include, for example, processing to reduce and limit the charging power to a predetermined value or less, or alternatively, processing to reduce and limit the charging power by a predetermined ratio. The predetermined value or the predetermined ratio is set so that the amount of lithium metal does not exceed the threshold value a1 depending on the amount of lithium metal supplied from the positive electrode 10 even when lithium metal moves from the non-opposing portion to the opposing portion. Thereafter, the process proceeds to S108. Note that the predetermined value or the predetermined ratio may be a value that varies depending on the voltage of the battery 214, the type of the vehicle 200, and the like.

[0051] In S108, the ECU 100 calculates the negative electrode potential of the non-opposing portion in the negative electrode 20. Since the calculation method is the same as the calculation method described in S102, detailed description thereof will not be repeated. Thereafter, the process proceeds to S110.

[0052] In S110, the ECU 100 determines whether or not the negative electrode potential of the non-opposing portion in the negative electrode 20 exceeds the threshold value b2. The threshold value b2 is, for example, a predetermined value larger than the threshold value b1. When it is determined that the negative electrode potential of the non-opposing portion exceeds the threshold value b2 (YES in S110), the process proceeds to S112.

[0053] In S112, the ECU 100 executes restriction release processing. The restriction release processing may include, for example, processing to set the charging power to a value according to the required power. Thereafter, the process ends. Note that when it is determined that charging is not in progress (NO in S100), or when it is determined that it is larger than the threshold value b1 (in S104), this process ends. Also, when it is determined that it is equal to or less than the threshold value b2 (NO in S110), the process returns to S108.

[0054] An example of the operation of the ECU 100 based on the above structure and flowchart will be described.

[0055] For example, when the connector 17 is attached to the inlet 220 and external charging is executed, if it is determined that charging is in progress (YES in S100), the negative electrode potential of the unopposed portion of the negative electrode 20 is calculated using a plurality of parameters indicating the control state of the charging power (S102). If the calculated negative electrode potential of the unopposed portion is not less than the threshold value b1 (NO in S104), since the amount of lithium metal absorbed in the unopposed portion of the negative electrode 20 is small, charge and discharge of the battery 214 are possible while suppressing the precipitation of lithium metal.

[0056] On the other hand, when the charge and discharge of the battery 214 are repeated and the amount of lithium metal absorbed in the unopposed portion of the negative electrode 20 increases, the negative electrode potential of the unopposed portion decreases. When the negative electrode potential of the unopposed portion becomes less than or equal to the threshold value b1 (YES in S104), a charge limit process is executed. As a result, when the charging power supplied to the battery 214 decreases, the amount of lithium metal moving from the positive electrode 10 to the negative electrode 20 also decreases. As a result, even if the lithium metal absorbed in the unopposed portion moves to the opposed portion, precipitation of lithium metal on the negative electrode surface is suppressed. When lithium metal moves from the unopposed portion to the opposed portion, the negative electrode potential will increase. During the execution of the charge limit process, the negative electrode potential is calculated (S108). When it is determined that the calculated negative electrode potential exceeds the threshold value b2 (YES in S110), a limit release process is executed (S112), so the limit on the charging power is released. Therefore, charging of the battery 214 according to the required power is performed.

[0057] As described above, according to the charging system 1 according to the present embodiment, when the negative electrode potential of the unopposed portion of the negative electrode 20 obtained using the control state of the charging power is less than or equal to the threshold value b1, the charging power is limited. Therefore, it is possible to suppress the precipitation of lithium metal on the negative electrode 20 due to the movement of lithium metal from the unopposed portion to the opposed portion facing the positive electrode 10. Therefore, it is possible to provide a charging system that suppresses the precipitation of lithium metal.

[0058] Furthermore, when the negative electrode potential of the unopposed portion becomes equal to or lower than the threshold value during external charging (rapid charging) where the amount of lithium metal movement increases, the charging power amount is restricted. Therefore, precipitation of lithium metal in the negative electrode 20 due to the lithium metal absorbed in the unopposed portion can be suppressed.

[0059] Furthermore, when the negative electrode potential of the unopposed portion exceeds the threshold value b2, the restriction on the charging power is released. Therefore, it is possible to suppress the charging time from becoming unnecessarily long.

[0060] Hereinafter, modified examples will be described.

[0061] In the above-described embodiment, it has been described that when it is determined that the negative electrode potential in the unopposed portion exceeds the threshold value b2 during the execution of the charge restriction process, the restriction release process is executed. However, for example, when the execution time of the charge restriction process exceeds a predetermined time, the restriction release process may be executed. The predetermined time is set using the time predicted to exceed the threshold value b2 by the execution of the charge restriction process after the negative electrode potential becomes equal to or lower than the threshold value b1, and is adapted by experiments or the like, for example. Even in this case, it is possible to suppress the charging time from becoming unnecessarily long.

[0062] Furthermore, in the above-described embodiment, it has been described that the negative electrode potential of the unopposed portion of the negative electrode 20 is calculated during external charging (rapid charging) and it is determined whether or not it is equal to or lower than the threshold value b1. However, it is not particularly limited to during external charging. For example, the ECU 100 may calculate the negative electrode potential of the unopposed portion during at least any one of normal charging (charging that can be performed using a household power supply), discharging, standing, and regeneration, and determine whether or not it is equal to or lower than the threshold value. When the negative electrode potential of the unopposed portion is equal to or lower than the threshold value, the charge restriction process may be executed when the charge control is started.

[0063] Furthermore, in the above-described embodiment, the threshold value b1 has been described as a predetermined value. However, the threshold value b1 may be determined, for example, according to the deterioration state (fully charged capacity) of the battery 214 or the battery cell. The threshold value b1 may be set to increase, for example, when the fully charged capacity drops by a predetermined value or more from the initial value.

[0064] Note that the above-described modifications may be implemented by appropriately combining all or part of them.

[0065] The embodiments disclosed this time should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims be included.

Explanation of Reference Numerals

[0066] 1 Charging system, 2 Charging stand, 10 Positive electrode, 12 Positive electrode tab, 13 Communication unit, 14 Control unit, 15 Charging unit, 16 Cable, 17 Connector, 20 Negative electrode, 22 Negative electrode tab, 24, 26 Regions, 30 Separator, 100 ECU, 102, 104, 106 Sensors, 200 Vehicle, 214 Battery, 214a Battery cell, 216 Inverter, 218 MG, 220 Inlet, 400 Utility power supply.

Claims

1. A secondary battery having a negative electrode containing a negative electrode active material into which lithium ions are inserted and extracted, and a positive electrode, and a control device for controlling the charging power of the secondary battery, wherein the control device limits the charging power when the negative electrode potential of an unopposed portion of the negative electrode that does not face the positive electrode becomes equal to or lower than a threshold value. A charging system.

2. The control device estimates the negative electrode potential of the unopposed portion using the control state of the charging power, and limits the charging power when the estimated negative electrode potential becomes equal to or lower than the threshold value. The charging system according to claim 1.

3. The control device acquires the deterioration state of the secondary battery and sets the threshold value using the acquired deterioration state. The charging system according to claim 1.

4. The control device releases the limitation of the charging power when the negative electrode potential of the unopposed portion exceeds the threshold value after the limitation of the charging power. The charging system according to claim 1.

5. The control device releases the limitation of the charging power when the limitation time of the charging power exceeds a predetermined time. The charging system according to claim 1.

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