Method and apparatus for diagnosing battery cells

Abstract

This invention provides a method and apparatus for diagnosing battery cells that can determine the internal state of each individual battery cell. [Solution] The battery pack 1 raises the temperature of multiple battery cells by ripple current while the multiple battery cells are not being charged or discharged, calculates resistance values ​​at multiple frequencies, estimates the positive electrode resistance value and negative electrode resistance value based on the relationship information showing the relationship between the resistance value at AC impedance obtained in advance and the frequency of the positive electrode resistance reaction range and the frequency of the negative electrode resistance reaction range, and the calculated resistance value, and diagnoses the state of each of the multiple battery cells based on the positive electrode resistance value and negative electrode resistance value.

Description

[Technical Field]

[0001] The present disclosure relates to a battery cell diagnostic method and a diagnostic apparatus. [Background Art]

[0002] Patent Document 1 discloses a technology of an internal resistance estimation apparatus that estimates the internal resistance of a power storage device based on a ripple current detected by a current detection unit connected to the power storage device, a temperature detected by a temperature detection unit, and a correlation between the ripple current and the temperature stored in a storage unit. [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. 2011-122835 [Summary of the Invention] [Problems to be Solved by the Invention]

[0004] Incidentally, in Patent Document 1, since the positive electrode resistance and negative electrode resistance of the power storage device change depending on the deterioration state, it is difficult to predict the respective resistance values of the positive electrode and the negative electrode from the relationship between frequency and internal resistance, and there was room for improvement.

[0005] The present disclosure has been made in view of the above, and an object of the present disclosure is to provide a battery cell diagnostic method and a diagnostic apparatus capable of grasping the internal state of each battery cell. [Means for Solving the Problems]

[0006] The battery cell diagnostic method according to this disclosure involves, in a battery cell diagnostic method, raising the temperature of multiple battery cells by ripple current while the multiple battery cells are not being charged or discharged, calculating resistance values ​​at multiple frequencies, estimating positive electrode resistance values ​​and negative electrode resistance values ​​based on relationship information showing the relationship between the resistance value at AC impedance obtained in advance and the frequency of the positive electrode resistance reaction range and the frequency of the negative electrode resistance reaction range, and the calculated resistance values, and diagnosing the state of each of the multiple battery cells based on the positive electrode resistance values ​​and negative electrode resistance values.

[0007] Furthermore, the diagnostic device according to this disclosure comprises a battery pack composed of a plurality of battery cells, a ripple generator that raises the temperature of the plurality of battery cells by supplying a ripple current to the plurality of battery cells when the plurality of battery cells are not being charged or discharged, a voltage detection device that detects the voltage of the plurality of battery cells when the plurality of battery cells are being heated, a relational information recording unit that records relational information showing the relationship between the resistance value at AC impedance acquired in advance and the frequency of the positive electrode resistance reaction range and the frequency of the negative electrode resistance reaction range, and a control device. The control device raises the temperature of the plurality of battery cells by the ripple current when the plurality of battery cells are not being charged or discharged, calculates the resistance values ​​at multiple frequencies, estimates the positive electrode resistance value and the negative electrode resistance value based on the relational information and the calculated resistance value, and diagnoses the state of each of the plurality of battery cells based on the positive electrode resistance value and the negative electrode resistance value. [Effects of the Invention]

[0008] According to this disclosure, the internal state of each battery cell can be understood. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a diagram showing a schematic configuration of a diagnostic device according to one embodiment of the present disclosure. [Figure 2]Figure 2 shows the relationship between the resistance value at AC impedance and the resistance value at ripple current in relational information recorded by the relational information recording unit of a diagnostic device according to one embodiment of the present disclosure. [Figure 3] Figure 3 is a flowchart showing an overview of the process for diagnosing an in-vehicle battery cell executed by a control device according to one embodiment of the present disclosure. [Figure 4] Figure 4 shows the relationship between the resistance value calculated by the control device of a diagnostic device according to one embodiment of the present disclosure and the resistance value when AC impedance is applied. [Modes for carrying out the invention]

[0010] Hereinafter, a method and apparatus for diagnosing battery cells according to one embodiment of the present disclosure will be described with reference to the drawings. Note that the components in the following embodiment include those that are easily substituted or substantially identical to those that are easily substituted by a person skilled in the art.

[0011] [Configuration of the diagnostic device] Figure 1 is a diagram showing the schematic configuration of a diagnostic device according to one embodiment of the present disclosure. The diagnostic device 1 shown in Figure 1 comprises a secondary battery 10, a ripple generation device 20, a voltage detection device 30, a related information recording unit 40, and a control device 50.

[0012] The secondary battery 10 is a battery pack composed of multiple battery cells 11, and is mounted in a vehicle. The secondary battery 10 is made using rechargeable batteries such as lithium-ion batteries and nickel-metal hydride batteries. Furthermore, the secondary battery 10 has an internal resistance 12. This internal resistance 12 has a temperature dependence of the secondary battery 10 and also has the characteristic of changing significantly depending on the frequency of the current flowing through the secondary battery 10.

[0013] The ripple generator 20 is electrically connected to the secondary battery 10. Under the control of the control device 50, the ripple generator 20 generates a ripple current of a predetermined frequency in the secondary battery 10. Specifically, the ripple generator 20 raises the temperature of the secondary battery 10 from the inside by generating a ripple current in the secondary battery 10 (ripple heating). The ripple generator 20 is configured using at least one power semiconductor switching element, and under the control of the control device 50, generates a ripple current in the secondary battery 10 by switching the power semiconductor switching element on or off.

[0014] The voltage detection device 30 is configured using a voltage sensor or the like, detects the voltage of the secondary battery 10, and outputs the detection result to the control device 50.

[0015] The relational information recording unit 40 records relational information for each battery cell 11, showing the relationship between the resistance value at AC impedance and the frequency of the positive electrode resistance reaction region and the frequency of the negative electrode resistance reaction region, which has been acquired in advance. Figure 2 is a diagram showing the relationship between the resistance value at AC impedance and the resistance value at ripple current in the relational information recorded by the relational information recording unit 40. In Figure 2, the vertical axis shows the resistance value at AC impedance ([Z][Ω]), and the horizontal axis shows the frequency (Hz). Also in Figure 2, curve L1 shows the resistance value at AC impedance (weak current), straight line D1 shows the positive electrode DC resistance reaction region, and straight line D2 shows the negative electrode DC resistance reaction region. Furthermore, the amount of heat generated Q of the secondary battery 10 is explained under the condition that the self-heating (operating temperature) is within 20 degrees Celsius from the perspective of the safety and durability of the capacitors constituting the ripple generation device 20. In addition, Figure 2 shows an example of the relationship between the resistance value at AC impedance of one battery cell 11 and the frequency of the positive electrode resistance reaction region and the frequency of the negative electrode resistance reaction region.

[0016] As shown by curve L1 in FIG. 2, the relationship information associates resistance values at alternating current impedance with frequencies. Further, as shown by straight line D1 and straight line D2, resistance values of the positive electrode DC resistance reaction region and the negative electrode DC resistance reaction region of the battery cell 11 are associated with each frequency. Note that FIG. 2 is merely an example, and data obtained in advance for the positive electrode DC resistance reaction region and the negative electrode DC resistance reaction region for each state of the SOC (State Of Charge), temperature, cell design factor tolerance (basis weight, density, etc.) and deterioration state of the battery cell 11 is recorded as relationship information in the relationship information recording unit 40.

[0017] Returning to FIG. 1, the description of the configuration of the diagnostic device 1 will be continued. The control device 50 is configured using a memory and hardware such as a CPU (Central Processing Unit). The control device 50 controls the ripple generator 20 to cause a ripple current to be generated in the secondary battery 10, thereby heating the secondary battery 10 from the inside. Specifically, based on the frequency characteristics of the impedance of the secondary battery 10, the control device 50 controls the ripple generator 20 to cause the secondary battery 10 to generate a ripple current in a frequency region where the absolute value of the impedance of the secondary battery 10 relatively decreases.

[0018] Here, the amount of heat generated by the secondary battery 10 when a ripple current flows through the secondary battery 10 will be described. When the amount of heat generated by the secondary battery 10 is Q, the ripple current is I, and the resistance value of the internal resistance 12 is R, the following formula (1) holds. Q=I 2 ×R ···(1) According to formula (1), the control device 50 can increase the temperature of the secondary battery 10 more by increasing the ripple current I generated using the ripple generator 20.

[0019] Further, the control device 50 controls the ripple generation device 20 in a state where the plurality of battery cells 11 are not charged or discharged, thereby increasing the temperature of the plurality of battery cells 11 by the ripple current of the ripple generation device 20, and calculates resistance values at a plurality of frequencies. Then, the control device 50 estimates a positive electrode resistance value and a negative electrode resistance value based on the relationship information recorded by the relationship information recording unit 40 and the calculated resistance value, and diagnoses the state of each of the plurality of battery cells 11 based on the positive electrode resistance value and the negative electrode resistance value.

[0020] [Processing of the diagnostic method for vehicle-mounted battery cells] Next, the processing of the diagnostic method for vehicle-mounted battery cells executed by the control device 50 will be described. FIG. 3 is a flowchart showing an outline of the processing of the diagnostic method for vehicle-mounted battery cells executed by the control device 50.

[0021] As shown in FIG. 3, first, the control device 50 controls the ripple generation device 20 to increase the temperature of the secondary battery 10 in a state where the plurality of battery cells 11 of the secondary battery 10 are not charged or discharged, thereby acquiring the voltage (voltage fluctuation) for each frequency of each of the plurality of battery cells 11 of the secondary battery 10 detected by the voltage detection device 30 during the temperature increase (step S101). Here, the state where the plurality of battery cells 11 of the secondary battery 10 are not charged or discharged refers to a state where the vehicle equipped with the secondary battery 10 is stopped.

[0022] Subsequently, the control device 50 calculates a resistance value from the voltage for each frequency of each of the plurality of battery cells 11 of the secondary battery 10 acquired from the voltage detection device 30 (step S102). Specifically, the control device 50 calculates the resistance value by dividing the voltage of the battery cell 11 acquired from the voltage detection device 30 by a value obtained by dividing the amplitude number of the frequency by 2 (resistance = voltage ÷ (amplitude amount / 2)). Specifically, as shown by curve L2 in FIG. 4, the control device 50 calculates the resistance value from the voltage change under the ripple current (strong current) for each frequency. Here, "for each frequency" refers to, for example, 100 Hz, 500 Hz, 10000 Hz, etc.

[0023] Subsequently, the control device 50 compares the resistance value calculated in step S102 with the relational information recorded by the relational information recording unit 40 (step S103). Specifically, the control device 50 compares the relational information for each battery cell 11 recorded by the relational information recording unit 40 with the resistance value characteristics for each frequency calculated in step S102 to see if they match the resistance value characteristics under AC impedance (weak current). For example, in the case shown in Figure 4, the control device 50 compares the relational information with the characteristics of curve L1 based on the characteristics of curve L2 (curve characteristics).

[0024] Next, the control device 50 estimates the positive electrode resistance and negative electrode resistance based on the relational information recorded by the relational information recording unit 40 and the resistance value calculated in step S102 (step S104). Specifically, the control device 50 estimates the positive electrode resistance and negative electrode resistance of the battery cell 11 from the positive electrode DC resistance reaction region of the straight line D1 and the negative electrode DC resistance reaction region of the straight line D2, which are associated with the curve L1 in Figure 4, which has been matched with curve L2. In the case shown in Figure 4, the control device 50 estimates the positive electrode resistance to be 15 ([Z][Ω]) and the negative electrode resistance to be 10 ([Z][Ω]).

[0025] Subsequently, the control device 50 diagnoses the state of the battery cell 11 based on the positive and negative electrode resistance values ​​of the battery cell 11 estimated in step S104 (step S105), and performs optimization for each battery cell (step S106). Specifically, the control device 50 diagnoses the degree of positive electrode degradation of the battery cell 11 as the state of the battery cell 11 based on the positive and negative electrode resistance values ​​of the battery cell 11, and performs optimization to equalize the energy capacity of each of the multiple battery cells 11. As a result, the control device 50 can predict the negative electrode potential by separating the negative electrode resistance value of the battery cell 11, and optimize the charging current value that should be controlled for the battery cell 11. Furthermore, the control device 50 can estimate the amount of positive electrode degradation by separating the positive electrode resistance value of the battery cell 11, and can perform safety control and Li deposition control optimization according to the degradation state. After step S106, the control device 50 terminates this process.

[0026] According to the embodiment described above, the control device 50 estimates the positive and negative electrode resistance values ​​based on relational information showing the relationship between the resistance value at AC impedance and the frequency of the positive electrode resistance reaction range and the frequency of the negative electrode resistance reaction range, and the resistance values ​​calculated at multiple frequencies by raising the temperature of the multiple battery cells 11 with ripple current when the multiple battery cells 11 are not being charged or discharged. Based on these positive and negative electrode resistance values, the internal state of each of the multiple battery cells 11 can be understood in order to diagnose the state of each of the multiple battery cells 11.

[0027] Furthermore, according to one embodiment, by separating the positive electrode resistance value of the battery cell 11, the amount of positive electrode degradation can be estimated, and safety control can be implemented according to the degradation state.

[0028] Further effects and modifications can be readily derived by those skilled in the art. Broader aspects of the present invention are not limited to the specific details and representative embodiments expressed and described above. Accordingly, various modifications are possible without departing from the spirit or scope of the overall concept of the invention as defined by the appended claims and their equivalents.

[0029] Although some embodiments of this application have been described in detail above with reference to the drawings, these are illustrative examples, and the present invention can be implemented in various other forms with modifications and improvements based on the knowledge of those skilled in the art, starting with the embodiments described in the disclosure section of the present invention. [Explanation of Symbols]

[0030] 1. Diagnostic device 10 Secondary battery 20 Ripple Generator 30 Voltage detection device 40. Related Information Recording Section 50 Control device 11 battery cells

Claims

1. In a method for diagnosing battery cells, With multiple battery cells in a state where they are not being charged or discharged, the temperature of the multiple battery cells is raised by ripple current, and the resistance values ​​at multiple frequencies are calculated. Based on the relationship information showing the relationship between the resistance value at AC impedance obtained in advance and the frequencies of the positive electrode resistance reaction range and the negative electrode resistance reaction range, and the resistance value calculated above, the positive electrode resistance value and the negative electrode resistance value are estimated. Based on the positive electrode resistance value and the negative electrode resistance value, the state of each of the plurality of battery cells is diagnosed. Methods for diagnosing battery cells.

2. A method for diagnosing a battery cell according to claim 1, The state in which the aforementioned multiple battery cells are not being charged or discharged is, The vehicle is stopped. Methods for diagnosing battery cells.

3. A method for diagnosing a battery cell according to claim 1, Based on the diagnosed state of each of the plurality of battery cells, optimization is performed to equalize the energy capacity of each of the plurality of battery cells. Methods for diagnosing battery cells.

4. A battery pack composed of multiple battery cells, A ripple generator that raises the temperature of the plurality of battery cells by supplying a ripple current to the plurality of battery cells when the plurality of battery cells are not being charged or discharged, A voltage detection device that detects the voltage of the plurality of battery cells when the temperature of the plurality of battery cells rises, A relational information recording unit records relational information showing the relationship between the resistance value at AC impedance acquired in advance and the frequencies of the positive electrode resistance reaction range and the negative electrode resistance reaction range, Control device and Equipped with, The control device is With multiple battery cells in a state where they are not being charged or discharged, the temperature of the multiple battery cells is raised by the ripple current, and the resistance values ​​at multiple frequencies are calculated. Based on the aforementioned related information and the calculated resistance values, the positive electrode resistance value and the negative electrode resistance value are estimated. Based on the positive electrode resistance value and the negative electrode resistance value, the state of each of the plurality of battery cells is diagnosed. Diagnostic equipment.

Images