Battery pack and control circuit

Abstract

To provide a technique for estimating the state of charge of a secondary battery.SOLUTION: A battery pack includes a secondary battery, a strain sensor attached to the secondary battery, and a control circuit, and the strain sensor is capable of detecting the thickness of the secondary battery, and the control circuit calculates a State Of Charge (SOC) value from the relationship between information on the thickness of the secondary battery and the SOC.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a battery pack and a control circuit. [Background technology]

[0002] Patent Document 1 discloses an electrode deterioration determination system that includes a measurement unit that measures the pressure versus time characteristics of a storage battery and an electrode deterioration determination unit that determines electrode deterioration of the storage battery. Patent Document 1 discloses that the electrode deterioration determination unit in the electrode deterioration determination system compares a first pressure versus time characteristic measured by the measurement unit when the electrodes of the storage battery are not deteriorated with a second pressure versus time characteristic measured by the measurement unit.

[0003] Patent Document 2 discloses a battery pack including a battery and a sensor that detects the state of the battery. Patent Document 2 discloses that the sensor of the battery pack has an insulating layer and a resistor formed of a Cr mixed phase film on one side of the insulating layer, and that the state of the battery is detected as a change in the resistance value of the resistor.

[0004] Patent Document 3 discloses an estimation device including an observation value acquisition unit that acquires observation values ​​of the voltage and current of a secondary battery, and a calculation unit that estimates a State Of Charge (SOC) value that indicates the state of charge of the secondary battery. Patent Document 3 discloses that the calculation unit in the estimation device estimates the SOC value that indicates the state of charge of the secondary battery by an estimation calculation that applies a Kalman filter to an equivalent circuit model of the secondary battery, based on the observation values ​​acquired by the observation value acquisition unit. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-147748 [Patent Document 2] Japanese Patent Publication No. 2020-034536 [Patent Document 3] Japanese Patent Application Laid-Open No. 2018-151176 Summary of the Invention [Problem to be solved by the invention]

[0006] In a secondary battery, the state of charge is estimated by, for example, the open circuit voltage (OCV) or current integration.

[0007] The present disclosure provides a technique for estimating the state of charge of a secondary battery. [Means for solving the problem]

[0008] In one aspect of the present disclosure, a battery pack is provided that includes a secondary battery, a strain sensor attached to the secondary battery, and a control circuit, wherein the strain sensor is capable of detecting the thickness of the secondary battery, and the control circuit calculates a State Of Charge (SOC) value from the relationship between information on the thickness of the secondary battery and the SOC. [Effects of the Invention]

[0009] According to the present disclosure, the state of charge of a secondary battery can be estimated. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing an example of a schematic configuration of a battery pack according to a first embodiment. [Figure 2] FIG. 2 is a diagram illustrating an example (part 1) of how a strain sensor is attached to a secondary battery in a battery pack according to the first embodiment. [Figure 3] FIG. 3 is a diagram illustrating an example (part 2) of attaching a strain sensor to a secondary battery in a battery pack according to the first embodiment. [Figure 4] FIG. 4 is a diagram (part 1) illustrating an example of the relationship between the thickness and SOC of the secondary battery in the battery pack according to the first embodiment. [Figure 5]FIG. 5 is a flow diagram (part 1) illustrating an example of processing in the battery pack according to the first embodiment. [Figure 6] FIG. 6 is a diagram (part 2) illustrating an example of the relationship between the thickness and SOC of the secondary battery in the battery pack according to the first embodiment. [Figure 7] FIG. 7 is a flow diagram (part 2) illustrating an example of processing in the battery pack according to the first embodiment. [Figure 8] FIG. 8 is a diagram showing an example of a schematic configuration of a battery pack according to the second embodiment. [Figure 9] FIG. 9 is a perspective view (part 1) illustrating an example of a battery pack according to this embodiment that includes a plurality of secondary batteries. [Figure 10] FIG. 10 is a side view (part 1) illustrating an example of a battery pack according to this embodiment that includes a plurality of secondary batteries. [Figure 11] FIG. 11 is a perspective view (part 2) illustrating an example of a battery pack according to this embodiment that includes a plurality of secondary batteries. [Figure 12] FIG. 12 is a side view (part 2) illustrating an example of a battery pack according to this embodiment that includes a plurality of secondary batteries. [Figure 13] FIG. 13 is a diagram illustrating an example of the relationship between the thickness and SOC of the secondary battery in the battery pack according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes the preferred embodiments of the present invention with reference to the accompanying drawings. In the drawings, the same components are designated by the same reference numerals, and redundant explanations may be omitted.

[0012] In the directions of parallel, right-angle, orthogonal, horizontal, vertical, up-down, left-right, front-back, etc., deviations are permitted to the extent that they do not impair the effects of the embodiments. The shape of the corners is not limited to right angles and may be rounded. Parallel, right-angle, orthogonal, horizontal, and vertical may include approximately parallel, approximately right-angle, approximately orthogonal, approximately horizontal, and approximately vertical, respectively.

[0013] For example, "substantially parallel" means that even if two lines or two surfaces are not completely parallel to each other, they can be treated as parallel as long as it is within the range of manufacturing tolerance. As with "substantially parallel," "substantially right angle," "substantially perpendicular," "substantially horizontal," and "substantially vertical" are also intended to fall under the respective terms as long as the relative position of two lines or two surfaces is within the range of manufacturing tolerance.

[0014] First Embodiment A battery pack according to the first embodiment will be described. The battery pack according to the first embodiment includes a secondary battery, a strain sensor attached to the secondary battery, and a control circuit. The strain sensor in the battery pack according to the first embodiment can detect the thickness of the secondary battery. The control circuit in the battery pack according to the first embodiment calculates a State Of Charge (SOC) value based on the relationship between information about the thickness of the secondary battery and the SOC.

[0015] The battery pack according to the first embodiment will be described in detail with reference to the drawings. Fig. 1 is a diagram showing an outline of a battery pack 1, which is an example of the battery pack according to the first embodiment.

[0016] The battery pack 1 stores electricity by being charged externally. The battery pack 1 also supplies the charged power to devices. Devices in which the battery pack 1 is used include, for example, information devices such as personal computers, smartphones, and tablet terminals, vehicles such as bicycles and automobiles, home appliances, and power storage devices. The battery pack 1 is used by repeatedly charging and discharging. The battery pack 1 includes a secondary battery 10, a strain sensor 20, a control circuit 30, and a charging circuit 40.

[0017] Each component of the battery pack 1 will now be described in detail.

[0018] [Secondary battery 10] The secondary battery 10 is a battery that can be repeatedly charged and discharged, and is, for example, a lithium ion battery.

[0019] [Strain sensor 20] The strain sensor 20 is a sensor that detects strain in an object. The strain sensor 20 is configured, for example, with a resistive film formed on a substrate. The resistance value of the resistive film in the strain sensor 20 is used to detect strain.

[0020] The following describes how the strain sensor 20 is attached to the secondary battery 10. Figures 2 and 3 are diagrams illustrating an example of how the strain sensor 20 is attached to the secondary battery 10 in the battery pack 1, which is an example of the battery pack according to the first embodiment.

[0021] The secondary battery 10 is, for example, a pouch-type lithium ion battery. As shown in Fig. 2, the strain sensor 20 is attached by being directly affixed to the secondary battery 10. Alternatively, as shown in Fig. 3, the strain sensor 20 may be attached by being affixed to a band 11 attached so as to surround the secondary battery 10. As a result, it is possible to detect an increase in the thickness of the secondary battery 10 in any direction.

[0022] The battery pack 1 detects the thickness of the secondary battery 10 by the strain sensor 20. In other words, the battery pack 1 can detect the thickness of the secondary battery 10.

[0023] [Control circuit 30] The control circuit 30 controls charging in the charging circuit 40. The control circuit 30 also calculates the SOC value of the secondary battery 10. Furthermore, the control circuit 30 uses the measurement results of the strain sensor 20 to detect changes in the thickness of the secondary battery 10.

[0024] The control circuit 30 is, for example, a computer, and includes a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), an auxiliary storage device, etc. The CPU operates based on a program stored in the ROM or the auxiliary storage device.

[0025] The control circuit 30 includes a charge control unit 31, an SOC estimation unit 32, a thickness detection unit 33, and a storage unit .

[0026] (Charging control unit 31) The charging control unit 31 controls the charging of the secondary battery 10. The charging control unit 31 controls the charging circuit 40 to control the charging of the secondary battery 10.

[0027] An example of charging control of the secondary battery 10 by the charging control unit 31 will be described. The charging control unit 31 first performs constant current charging (CC charging) at a constant current. Then, when the open circuit voltage reaches a predetermined voltage value, the charging control unit 31 performs constant voltage charging (CV charging) at a constant voltage. Then, during constant voltage charging, the charging control unit 31 stops charging when the charging current falls below the predetermined current value.

[0028] (SOC estimation unit 32) The SOC estimation unit 32 calculates the SOC value of the secondary battery 10 using the thickness of the secondary battery 10 detected by the thickness detection unit 33. The SOC estimation unit 32 receives information on the thickness of the secondary battery 10 from the thickness detection unit 33. The SOC estimation unit 32 calculates the SOC value using the relationship between the SOC and the thickness or the integrated value of the thickness (thickness information) detected by the thickness detection unit 33. The SOC estimation unit 32 is an example of a calculation unit.

[0029] (Thickness detection unit 33) The thickness detection unit 33 detects the thickness of the secondary battery 10. The thickness detection unit 33 acquires information about strain from the strain sensor 20. The thickness detection unit 33 detects the thickness of the secondary battery 10 based on the measurement results of the strain sensor 20.

[0030] [Charging circuit 40] The charging circuit 40 supplies power to charge the secondary battery 10. The charging circuit 40 charges the secondary battery 10 with a current or voltage based on the control of the charging control section 31 in the control circuit 30.

[0031] <Processing in the SOC Estimation Unit> [First Processing Example] As the processing in the SOC estimation unit, the first processing example will be described in detail. First, the relationship between the thickness in the secondary battery 10 and the thickness of the secondary battery 10 will be described. FIG. 4 is a diagram for explaining an example of the relationship between the thickness of the secondary battery 10 and the SOC in the battery pack 1 which is an example of the battery pack according to the first embodiment.

[0032] In FIG. 4, the horizontal axis is the SOC value in the secondary battery 10, and the vertical axis is the open circuit voltage (OCV) in the secondary battery 10 or the thickness (T) of the secondary battery 10. In FIG. 4, since the thickness (T) changed by charging of the secondary battery is represented, the starting point is 0. FIG. 4 is a graph showing, as an example, the case where the secondary battery 10 is a lithium ion battery using iron phosphate for the negative electrode. The line LV indicates the open circuit voltage (OCV) in the secondary battery 10. The line LT indicates the thickness (T) in the secondary battery 10.

[0033] As shown in FIG. 4, in the case of a lithium ion battery using iron phosphate for the negative electrode, the open circuit voltage (OCV) changes rapidly with respect to the SOC when the SOC value is near 0% and when the SOC value is near 95%. On the other hand, the open circuit voltage (OCV) changes little with respect to the SOC and is substantially constant in the range where the SOC value is from 10% to 80%. That is, in the relationship between the open circuit voltage (OCV) and the SOC, there is a region where the change in the open circuit voltage (OCV) is small even when the SOC value increases. Here, the region where the change is small is a region where there are portions with large changes before and after this region, the amount of change is small with respect to the portions with large changes, and it appears flat as a whole.

[0034] Therefore, when estimating the SOC using the open circuit voltage (OCV), particularly in the range from 10% to 80%, the error in the estimated SOC value may become large.

[0035] On the other hand, as shown in FIG. 4, the thickness (T) monotonically increases as the SOC value increases.

[0036] Therefore, by estimating the SOC using the thickness (T), the SOC value can be estimated with high accuracy.

[0037] The processing in the SOC processing unit will be described below. Fig. 5 is a flow chart illustrating an example of processing in the battery pack 1, which is an example of a battery pack according to the first embodiment.

[0038] (Step S10) First, the SOC estimation unit 32 in the battery pack 1 continuously acquires the thickness of the secondary battery 10 from the thickness detection unit 33 for a predetermined period, for example, 10 seconds (offset value calculation step). The SOC estimation unit 32 acquires the thickness of the secondary battery 10, for example, at a sampling period of 2 seconds.

[0039] The thickness detection unit 33 detects the thickness of the secondary battery 10 from the output of the strain sensor 20. The thickness detection unit 33 outputs the detected thickness to the SOC estimation unit 32.

[0040] The SOC estimation unit 32 calculates the average value of the thickness for 10 seconds, and then stores the calculated average value as an initial value (offset value).

[0041] The process of step S10 may be performed after the secondary battery 10 is completely discharged. The process operation of step S10 is an example of a first operation, and the predetermined period in step S10 is an example of a first time.

[0042] The processing from step S20 onwards is carried out while the secondary battery 10 is being charged.

[0043] (Step S20) Next, the SOC estimation unit 32 acquires the thickness from the thickness detection unit 33 (thickness acquisition step). The SOC estimation unit 32 acquires the thickness of the secondary battery 10 from the thickness detection unit 33, for example, with a sampling period of 2 seconds.

[0044] (Step S30) Next, the SOC estimation unit 32 subtracts the initial value (offset value) calculated in step S10 from the thickness acquired in step S20 to correct the offset (offset correction step). As a result, the amount of change in thickness of the secondary battery 10 due to charging can be calculated.

[0045] (Step S40) Next, the SOC estimation unit 32 calculates the SOC value using the thickness that has been offset-corrected in step S30, based on the relationship between the thickness and the SOC as shown in FIG. 4, which is stored in the memory unit 34 (SOC value calculation step).

[0046] (Step S50) Next, the SOC estimator 32 determines whether the SOC value calculated in step S40 is equal to or greater than a threshold value (threshold value determination step). The threshold value corresponds to, for example, the voltage at the portion of the relationship between the open circuit voltage (OCV) and the SOC where the open circuit voltage (OCV) appears flat even as the SOC increases. If the SOC value is equal to or greater than the threshold value (YES in step S50), the SOC estimator 32 proceeds to step S60. If the SOC value is less than the threshold value (NO in step S50), the SOC estimator 32 proceeds to step S70. The threshold value is an example of a first value. That is, the SOC estimator 32 determines whether the SOC value is equal to or greater than a first value. Here, it is preferable to set the first value to approximately 90% as shown in FIG. 4. The open circuit voltage (OCV) tends to increase sharply when the SOC value is 90% or greater. On the other hand, the thickness (T) increases monotonically, allowing for accurate estimation of the SOC in the region close to full charge. As a result, unnecessary charging can be reduced, contributing to energy conservation.

[0047] (Step S60) If the SOC value is equal to or greater than the threshold value (YES in step S50), the SOC estimator 32 transmits a signal to the charge controller 31 to stop charging the secondary battery 10 (process change step). Then, the SOC estimator 32 proceeds to step S70. The signal transmitted by the SOC estimator 32 is an example of a first signal.

[0048] (Step S70) Next, the SOC estimation unit 32 determines whether to continue the processing (processing determination step). If the processing is to be continued (YES in step S70), the SOC estimation unit 32 returns to step S20 and repeats the processing. If the processing is not to be continued (NO in step S70), the SOC estimation unit 32 ends the processing.

[0049] [Second processing example] As the processing in the SOC estimation unit, a second processing example will be described in detail. First, the relationship between the thickness of the secondary battery 10 and the thickness of the secondary battery 10 will be described. Fig. 6 is a diagram illustrating an example of the relationship between the thickness and SOC of the secondary battery 10 in the battery pack 1, which is an example of the battery pack according to the first embodiment.

[0050] In FIG. 4, the horizontal axis represents the SOC value of the secondary battery 10, and the vertical axis represents the open circuit voltage (OCV2) of the secondary battery 10 or the thickness (T2) of the secondary battery 10. FIG. 6 is a graph showing an example in which the secondary battery 10 is a lithium-ion battery that uses iron phosphate for the negative electrode. Line LV2 represents the open circuit voltage (OCV2) of the secondary battery 10. Line LT2 represents the thickness (T2) of the secondary battery 10. Note that in FIG. 6, the starting point is 0 because it represents the change in thickness (T2) of the secondary battery due to charging.

[0051] As shown in FIG. 6, in the case of a lithium ion battery using iron phosphate in the negative electrode, the open circuit voltage (OCV) has a similar tendency to the example shown in FIG.

[0052] On the other hand, as shown in FIG. 6, the thickness (T2) does not increase monotonically as the SOC value increases, but decreases when the SOC is around 70 to 80%.

[0053] The processing in the SOC processing unit will be described for the case where the thickness does not monotonically increase with respect to the SOC as shown in Fig. 6. Fig. 7 is a flow diagram illustrating the processing in the battery pack 1, which is an example of the battery pack according to the first embodiment.

[0054] Compared to the first processing example, the second processing example differs in that step S135 is newly added and step S140 is provided instead of step S40. For the steps common to the first processing example and the second processing example, the explanation of the first processing example should be referred to, and detailed explanations thereof will be omitted here.

[0055] (Step S135) The SOC estimation unit 32 integrates the thickness after the offset correction in step S30 over time to obtain a thickness accumulation value (thickness integration step). The thickness accumulation value is obtained by, for example, trapezoidal approximation of the two sampled thicknesses to obtain an accumulation value that is an integral value of the thickness over time. That is, the SOC estimation unit 32 time-integrates the result of measuring the thickness of the secondary battery 10 by the thickness detection unit 33 while charging is being performed. Then, the SOC estimation unit 32 calculates the cumulative change in the thickness of the secondary battery 10 by performing time integration.

[0056] That is, the SOC estimation unit 32 performs time integration of the thickness at predetermined time intervals during charging. The SOC estimation unit 32 can calculate the cumulative change in thickness of the secondary battery 10 by performing time integration. The cumulative change (cumulative value of thickness) calculated by the SOC estimation unit 32 monotonically increases. For example, as shown in FIG. 6, the cumulative value of thickness is represented by the area between the line LT2 and the horizontal axis. That is, even if the thickness of the secondary battery 10 decreases by around 70 to 80%, the cumulative value of the thickness of the secondary battery 10 monotonically increases.

[0057] (Step S140) Next, the SOC estimation unit 32 calculates the SOC value using the cumulative thickness value obtained in step S135 based on the relationship between the cumulative thickness value and the SOC stored in the storage unit 34 (SOC value calculation step). Note that the relationship between the cumulative thickness value and the SOC is an example of the first relationship.

[0058] According to the second processing example, the SOC can be calculated even when the relationship between the thickness and the SOC is not such that the thickness increases monotonically with respect to the SOC. Note that the second processing example can also be applied when the thickness increases monotonically with respect to the SOC.

[0059] According to the battery pack of the first embodiment, the state of charge of the secondary battery can be estimated.

[0060] The control circuit 30 may transmit the calculated SOC value to an external device when a request signal is input. The first value is preferably set to an SOC value of approximately 90%, based on the same concept as in FIG. 4. The open circuit voltage (OCV) tends to increase sharply when the SOC value is 90% or higher. Meanwhile, the cumulative value of the thickness (T) increases monotonically, allowing for accurate estimation of the SOC in the region close to full charge. This reduces unnecessary charging, contributing to energy conservation.

[0061] Second Embodiment The battery pack according to the second embodiment uses the SOC value calculated in the battery pack according to the first embodiment, and further corrects the SOC value calculated by a different calculation method.

[0062] The battery pack according to the second embodiment will be described in detail with reference to the drawings. Figure 8 is a diagram showing an outline of a battery pack 2, which is an example of the battery pack according to the second embodiment.

[0063] The battery pack 2 includes a secondary battery 10, a strain sensor 20, a control circuit 130, and a charging circuit 140. Note that for the same configuration as the battery pack 1, the description of the battery pack 1 should be referred to, and the description will be omitted here.

[0064] The control circuit 130 includes a charge control unit 31, an SOC estimation unit 132, a thickness detection unit 33, and a storage unit 134.

[0065] The SOC estimation unit 132 acquires current and voltage information from the charging circuit 140 in addition to the SOC estimation unit 32, and calculates the SOC value. The charging circuit 140 outputs charging-time information to the SOC estimation unit 132. For example, the SOC estimation unit 132 calculates an integrated current value using the charging-time information acquired from the charging circuit 140. The SOC estimation unit 132 then estimates the SOC value using the integrated current value. Alternatively, the SOC estimation unit 132 may process the charging-time information acquired from the charging circuit 140 using a Kalman filter to estimate the SOC value.

[0066] The SOC estimator 132 calculates a final SOC value using the SOC value calculated using the thickness information and the SOC value calculated using the information from the charging circuit 140 during charging. For example, the SOC estimator 132 may calculate the final SOC value by correcting the SOC value calculated using the information from the charging circuit 140 during charging with the SOC value calculated using the thickness information. Alternatively, for example, the SOC estimator 132 may calculate the final SOC value by correcting the SOC value calculated using the thickness information with the SOC value calculated using the information from the charging circuit 140 during charging. Furthermore, for example, the SOC estimator 132 may calculate the final SOC value by averaging the SOC value calculated using the information from the charging circuit 140 during charging and the SOC value calculated using the thickness information. When calculating the average value, the SOC estimator 132 may use an arithmetic average or a weighted average.

[0067] The battery pack according to the second embodiment allows the state of charge of the secondary battery to be estimated, and also allows the SOC value to be estimated with higher accuracy.

[0068] Furthermore, although the above description has been given of a lithium ion battery using iron phosphate for the negative electrode, it is particularly effective when a ternary lithium ion battery is used as the secondary battery in the battery pack according to this embodiment.

[0069] The following describes the relationship between the thickness of a ternary lithium ion battery and the thickness of the secondary battery 10. Fig. 13 is a diagram illustrating the relationship between the thickness and SOC when a ternary lithium ion battery is used as the secondary battery in the battery pack according to this embodiment.

[0070] 13, the horizontal axis represents the SOC value of the ternary lithium-ion battery, and the vertical axis represents the open circuit voltage (OCV3) of the ternary lithium-ion battery or the thickness (T3) of the ternary lithium-ion battery. Line LV3 represents the open circuit voltage (OCV3) of the ternary lithium-ion battery. Line LT3 represents the thickness (T3) of the ternary lithium-ion battery.

[0071] As shown in FIG. 13, in the case of a ternary lithium-ion battery, the open circuit voltage (OCV3) increases monotonically with the SOC value. That is, the open circuit voltage (OCV3) does not have a region where the change is small (a region that appears flat). Furthermore, the thickness (T3) increases monotonically with the SOC value. Therefore, by estimating the SOC using the open circuit voltage (OCV3) and the thickness (T3), the SOC value can be estimated with high accuracy. Note that the SOC may also be estimated using only the thickness (T3).

[0072] <<Variations>> The battery pack according to this embodiment may include a plurality of secondary batteries. Fig. 9 is a perspective view illustrating a secondary battery unit 110, which is an example of a battery pack according to this embodiment that includes a plurality of secondary batteries. Fig. 10 is a side view illustrating a secondary battery unit 110, which is an example of a battery pack according to this embodiment that includes a plurality of secondary batteries.

[0073] 9 and 10, the secondary battery unit 110 includes six secondary batteries 111. The number of secondary batteries is not limited to six, and may be determined appropriately based on the capacity, drive current, etc.

[0074] The secondary battery unit 110 includes a plurality of secondary batteries 111 arranged in the horizontal direction in Fig. 10. That is, the secondary battery units 110 form a group of secondary batteries arranged in the horizontal direction in Fig. 10. The horizontal direction in Fig. 10 is an example of a first direction.

[0075] The secondary battery unit 110 includes a band 112 that bundles together a plurality of secondary batteries 111. The band 112 secures a top surface 110A and both side surfaces (side surface 110B and side surface 110C) of the secondary battery unit 110. That is, the band 112 secures the top surface and both side surfaces of the secondary battery group.

[0076] The band 112 has a plate member 112a arranged on the top surface 110A of the secondary battery unit 110. The band 112 also has a plate member 112b connected to an end of the plate member 112a and arranged on the side surface 110B of the secondary battery unit 110. The band 112 also has a plate member 112c connected to an end of the plate member 112a and arranged on the side surface 110C of the secondary battery unit 110 opposite to the side surface 110B.

[0077] The strain sensor 20 is attached by being stuck to the plate member 112a. That is, the strain sensor 20 is disposed on the upper surface of the plurality of secondary batteries.

[0078] The strain sensor 20 may be attached by being stuck to at least one of the plate members 112b and 112c of the band 112. Fig. 11 is a perspective view illustrating a secondary battery unit 110, which is an example of a battery pack according to this embodiment, including multiple secondary batteries. Fig. 12 is a side view illustrating a secondary battery unit 110, which is an example of a battery pack according to this embodiment, including multiple secondary batteries.

[0079] 11 and 12, the strain sensor 20 is attached by being adhered to each of the plate members 112b and 112c. That is, the strain sensor 20 is disposed on the side surfaces of the plurality of secondary batteries.

[0080] 11 and 12, the strain sensor 20 is attached to each of the plate members 112b and 112c, but may be attached to either one of the plate members 112b and 112c. Also, the strain sensor 20 may be attached to at least one of the plate members 112a, 112b, and 112c.

[0081] It should be noted that the embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive, and the above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope and spirit of the appended claims.

[0082] [Appendix 1] A battery pack comprising a secondary battery, a strain sensor attached to the secondary battery, and a control circuit, wherein the strain sensor is capable of detecting the thickness of the secondary battery, and the control circuit calculates an SOC value from the relationship between information on the thickness of the secondary battery and the SOC, and when the SOC value becomes equal to or greater than a first value, transmits a signal to stop charging the secondary battery. [Appendix 2] A battery pack comprising a secondary battery, a strain sensor attached to the secondary battery, and a control circuit, wherein the strain sensor is capable of detecting the thickness of the secondary battery, and the control circuit calculates an SOC value from the relationship between information on the thickness of the secondary battery and an SOC, and transmits the SOC value when a request signal is input. [Explanation of symbols]

[0083] 1, 2 battery pack, 10, 111 secondary battery, 11, 112 band, 20 strain sensor, 30, 130 control circuit, 31 charge control unit, 32, 132 SOC estimation unit, 33 thickness detection unit, 40, 140 charging circuit, 110 secondary battery unit, 110A top surface, 110B, 110C side surface

Claims

1. A secondary battery; a strain sensor attached to the secondary battery; a control circuit; the strain sensor is capable of detecting a thickness of the secondary battery; the control circuit calculates an SOC value from the relationship between information on the thickness of the secondary battery and the SOC; Battery pack.

2. the control circuit is capable of calculating a cumulative change in the thickness of the secondary battery by integrating, over time, the results of measurements of the thickness of the secondary battery by the strain sensor at predetermined time intervals during charging; The battery pack according to claim 1 .

3. Further comprising a storage unit, a first relationship between the secondary battery and a cumulative change in thickness of the secondary battery is stored in the storage unit; the control circuit determines an SOC value from a cumulative change of the secondary battery using the first relationship. The battery pack according to claim 2 .

4. the control circuit performs a first operation of averaging the results of measurements of the thickness of the secondary battery by the strain sensor over a first time period and using the averaged results as an initial value of a cumulative change in the thickness of the secondary battery; The battery pack according to claim 3 .

5. the control circuit performs the first operation after the secondary battery is completely discharged; The battery pack according to claim 4.

6. The secondary battery is a lithium ion battery using iron phosphate as a negative electrode. The battery pack according to any one of claims 1 to 5.

7. The control circuit transmits a first signal when the SOC value is equal to or greater than a first value, and the first value is located in a region where the change in OCV is small even when the SOC value increases in the relationship between OCV and SOC. The battery pack according to any one of claims 1 to 6.

8. A plurality of the secondary batteries are provided, further comprising a band for bundling the plurality of secondary batteries; The strain sensor is attached to the band. The battery pack according to any one of claims 1 to 7.

9. the plurality of secondary batteries form a secondary battery group arranged in a first direction; the bands fix the top surface and both side surfaces of the secondary battery group; The battery pack according to claim 8.

10. The strain sensor is disposed on the upper surface. The battery pack according to claim 9.

11. The strain sensor is disposed on the side surface. The battery pack according to claim 9.

12. A calculation unit is included, the calculation unit receives information on the thickness of the secondary battery and calculates an SOC value from the relationship between the thickness and the SOC of the secondary battery; Control circuit.

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