Battery management system, battery pack including the same, and method for diagnosing whether or not secondary battery has deteriorated

Abstract

The present invention provides a battery management system for diagnosing whether a secondary battery having a positive electrode containing lithium iron phosphate as a positive electrode active material has degraded, the battery management system including: a sensing unit configured to measure a voltage and an open circuit voltage of the secondary battery; a memory unit configured to store the open circuit voltage measured by the sensing unit; and a control unit configured to determine that the secondary battery has degraded when an amount of change in the open circuit voltage according to the charge / discharge cycles of the secondary battery satisfies the following condition 1 for five or more charge / discharge cycles. [Condition 1] V n-1 -V n <0.002V (In the above condition 1, V n-1 is the open circuit voltage of the battery measured in the n-1th charge / discharge cycle, and V n is the open circuit voltage of the battery measured at the nth charge / discharge cycle, where n is any integer.

Description

[Technical field]

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2022-0150244, filed on November 11, 2022.

[0002] The present invention relates to a battery management system for diagnosing whether a secondary battery having a positive electrode containing lithium iron phosphate has degraded, a battery pack including the same, and a method for diagnosing whether the secondary battery has degraded. [Background technology]

[0003] In recent years, the demand for portable electronic products such as laptops, video cameras, and mobile phones has increased dramatically, and the development of electric vehicles, energy storage batteries, robots, satellites, and other products has progressed in earnest. As a result, research into high-performance batteries that can be repeatedly charged and discharged is being actively conducted.

[0004] Batteries currently in commercial use include nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, and lithium secondary batteries. Among these, lithium secondary batteries are attracting attention due to their advantages over nickel-based batteries, such as almost no memory effect, freedom to charge and discharge, a very low self-discharge rate, and high energy density.

[0005] Such lithium secondary batteries degrade, such as decreasing capacity and energy, through repeated charging and discharging. When a battery degrades, cycle performance such as capacity retention rate decreases, shortening the battery's life and reducing usability. Therefore, it is necessary to diagnose whether a secondary battery in use has degraded, and to restore batteries that have been diagnosed as degraded.

[0006] There are various techniques for diagnosing the deterioration state of a battery. For example, the following patent document discloses obtaining information on the deterioration state of a battery from a Q-dV / dQ curve of the battery by utilizing Differential Voltage Analysis (DVA). The Q-dV / dQ curve can be expressed as a graph having a Q axis and a dV / dQ axis, where Q is the amount of charge, V is the voltage, dV is the amount of change in V over a predetermined time, dQ is the amount of change in Q over the predetermined time, and dV / dQ is the ratio of dV to dQ.

[0007] However, this technique is not suitable for determining whether or not a secondary battery having a positive electrode in which lithium iron phosphate is used as a positive electrode active material has degraded. FIG. 1 is a graph showing the voltage as a function of the capacity of a secondary battery having a positive electrode in which lithium iron phosphate is used as a positive electrode active material. Referring to FIG. 1, it can be seen that a secondary battery including lithium iron phosphate as a positive electrode active material has a flat voltage even when the charge / discharge capacity changes due to the structural characteristics of lithium iron phosphate. This phenomenon occurs due to the stability of the lithium iron phosphate structure itself with an olivine structure and the similarity of the crystal structure of LiFePO4 in a discharged state and FePO4 in a charged state. Therefore, the secondary battery including lithium iron phosphate as a positive electrode active material cannot be determined to be degraded or to what extent by differential voltage analysis, and therefore, technological development for this purpose is required. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to provide a battery management system and method for diagnosing whether a secondary battery containing lithium iron phosphate as a positive electrode active material has degraded due to repeated charging and discharging, and a battery pack including the same. [Means for solving the problem]

[0009] The present invention provides a battery management system for diagnosing whether a secondary battery having a positive electrode containing lithium iron phosphate as a positive electrode active material has degraded, the battery management system including: a sensing unit configured to measure a voltage and an open circuit voltage of the secondary battery; a memory unit configured to store the open circuit voltage measured by the sensing unit; and a control unit configured to determine that the secondary battery has degraded when an amount of change in the open circuit voltage according to the charge / discharge cycles of the secondary battery satisfies the following condition 1 for five or more charge / discharge cycles.

[0010] [Condition 1] V n-1 -V n <0.002V

[0011] (In the above condition 1, V n-1 is the open circuit voltage of the battery measured in the n-1th charge / discharge cycle, and V n is the open circuit voltage of the battery measured at the nth charge / discharge cycle, where n is any integer.

[0012] In one embodiment of the present invention, the sensing unit may be configured to measure a voltage of the secondary battery during discharge, and measure an open circuit voltage of the secondary battery each time the measured voltage reaches a reference discharge voltage.

[0013] In one embodiment of the present invention, the sensing unit may be configured to measure the open circuit voltage of the secondary battery during rest after the secondary battery reaches a reference discharge voltage.

[0014] In an embodiment of the present invention, the sensing unit may be configured to measure an open circuit voltage of the secondary battery every time one charge / discharge cycle of the secondary battery is completed.

[0015] A battery management system according to another embodiment of the present invention may further include a switching unit that turns on and off an electrical connection between the secondary battery and the charger.

[0016] The present invention provides a battery pack including the above battery management system and a plurality of secondary batteries.

[0017] In one embodiment of the present invention, the secondary battery may contain, as the negative electrode active material, 50 to 100% of a graphite-based negative electrode active material based on the total weight of the negative electrode active material.

[0018] The method for diagnosing degradation of a secondary battery according to the present invention is a method for diagnosing the presence or absence of degradation of a secondary battery having a positive electrode containing lithium iron phosphate as a positive electrode active material, and includes the steps of (A) measuring the voltage of the secondary battery during discharge while repeatedly charging and discharging the secondary battery, and measuring the open circuit voltage of the secondary battery each time the measured voltage reaches a reference discharge voltage, and (B) determining that the secondary battery has degraded if the amount of change in the open circuit voltage satisfies the following condition 1 for five or more charge and discharge cycles.

[0019] [Condition 1] V n-1 -V n <0.002V

[0020] (In the above condition 1, V n-1 is the open circuit voltage of the battery measured in the n-1th charge / discharge cycle, and V n is the open circuit voltage of the battery measured at the nth charge / discharge cycle, where n is any integer.

[0021] In one embodiment of the present invention, the above step (A) may include a step of measuring the open circuit voltage of the secondary battery during rest after the secondary battery reaches a reference discharge voltage.

[0022] In one embodiment of the present invention, the step (A) may include a step of measuring an open circuit voltage of the secondary battery every time one charge / discharge cycle of the secondary battery is completed. Effect of the Invention

[0023] In a secondary battery having a positive electrode containing lithium iron phosphate as the positive electrode active material, the potential difference of the negative electrode appears as the open circuit voltage of the secondary battery, which has the effect of making it possible to diagnose the degradation of the secondary battery from the amount of change in the open circuit voltage that accompanies the progress of charge and discharge cycles. [Brief description of the drawings]

[0024] [Figure 1] 1 is a graph showing voltage depending on capacity of a secondary battery including a positive electrode in which lithium iron phosphate is used as a positive electrode active material. [Diagram 2] 1 is a diagram illustrating an example of a configuration of a battery pack including a battery management system according to an embodiment of the present invention. [Diagram 3] 1 is a block diagram illustrating a battery management system according to an embodiment of the present invention; [Figure 4] 4 is a graph showing an example of a measured value of an open circuit voltage according to a charge / discharge cycle calculated by a battery management system 100 according to an embodiment of the present invention. [Diagram 5] FIG. 2 is a schematic diagram of a battery pack including a battery management system according to another embodiment of the present invention. [Figure 6] 10 is a flowchart illustrating an exemplary method for diagnosing degradation of a secondary battery according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the attached drawings. Before that, the terms and words used in the specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention based on the principle that an inventor can appropriately define the concept of a term to best describe his own invention.

[0026] Therefore, the embodiment described in this specification and the configurations shown in the drawings are merely the most preferred embodiment of the present invention and do not represent the entire technical idea of ​​the present invention, and there may be various equivalents and modifications that can replace them at the time of this application.

[0027] Throughout the specification, when a part "includes" a certain component, this does not exclude other components, unless otherwise specified to the contrary, but means that other components may be further included. Furthermore, terms such as "control unit" described in the specification mean a unit that processes at least one function or operation, and may be embodied in hardware, software, or a combination of hardware and software.

[0028] Furthermore, throughout the specification, when a part is said to be "connected" to another part, this includes not only the case where the part is "directly connected" to another part, but also the case where the part is "indirectly connected" through another element between them.

[0029] FIG. 2 is a diagram illustrating an example of a configuration of a battery pack including a battery management system according to an embodiment of the present invention.

[0030] 2, a battery pack 1000 may be provided so as to be installable in an electric system (e.g., an electric vehicle). The battery management system 100 according to the present invention is electrically connected to a battery module 10 including a plurality of secondary batteries 11, and may diagnose the state of each of the plurality of secondary batteries.

[0031] In addition, the battery management system 100 according to the present invention may be included in a battery pack 1000 together with the battery module 10. Although Fig. 2 illustrates an example in which one battery module 10 and one battery management system 100 are included in the battery pack 1000, the number of battery modules 10 and battery management systems 100 included in the battery pack 1000 is not limited to the number shown in Fig. 2. Similarly, the number of secondary batteries 11 included in the battery module 10 is not limited to the number shown in Fig. 2.

[0032] A secondary battery included in the battery module and battery pack of the present invention will be described. The secondary battery to be diagnosed for degradation by the battery management system 100 of the present invention includes lithium iron phosphate as a positive electrode active material of the positive electrode. A lithium secondary battery using lithium iron phosphate as a positive electrode active material includes a plateau section in which the voltage change is zero or close to zero despite the capacity change accompanying charge and discharge in a specific capacity section in a capacity-voltage graph in which the voltage corresponds to the capacity. In the conventional technology, there is no method for diagnosing the degradation of a secondary battery using lithium iron phosphate. The present invention provides a battery management system capable of diagnosing the degradation of such a secondary battery and a battery pack including the same.

[0033] In an exemplary embodiment, the lithium iron phosphate may be a compound of Formula 1:

[0034] [Chemical formula 1] Li 1+a Fe 1-x M x (PO 4-b )X b

[0035] (In the above chemical formula 1, M includes any one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X includes any one or more elements selected from the group consisting of F, S, and N, and a, b, and x are -0.5≦a≦0.5, 0≦b≦0.1, and 0≦x≦0.5, respectively.)

[0036] For example, the lithium iron phosphate can be LiFePO4.

[0037] In an exemplary embodiment, the negative electrode constituting the secondary battery of the present invention may include a graphite-based negative electrode active material as a negative electrode active material, and specifically, the graphite-based negative electrode active material may be included in an amount of 50 wt% to 100 wt% based on the total weight of the negative electrode active material. The graphite-based negative electrode active material also changes the potential of the negative electrode in response to changes in the state of charge (SOC) or depth of discharge (DOD) and the negative electrode potential. That is, in the case of a negative electrode including a graphite-based negative electrode active material, a correlation graph between the state of charge (SOC) or depth of discharge (DOD) and the negative electrode potential does not include a plateau section in which the potential of the negative electrode does not change in response to changes in the state of charge or depth of discharge, so that a secondary battery including a negative electrode including a graphite-based negative electrode active material is suitable for applying the degradation diagnosis method of the present invention.

[0038] Specific examples of such graphite-based negative electrode active materials include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, low crystalline carbon, and high crystalline carbon, and composites containing metallic compounds and carbonaceous materials, etc. Low crystalline carbon includes soft carbon and hard carbon, and high crystalline carbon includes natural graphite, kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature fired carbon such as petroleum or coal tar pitch derived cokes.

[0039] A specific configuration of the battery management system 100 will be described with reference to Fig. 3. Fig. 3 is a block diagram illustrating a battery management system according to an embodiment of the present invention.

[0040] Referring to FIG. 3, the battery management system 100 may include a sensing unit 110, a memory unit 120, and a control unit 130.

[0041] The sensing unit 110 may be configured to measure the voltage of the secondary batteries 11 included in the battery module 10. That is, the sensing unit 110 may be configured to measure the voltage of each of the secondary batteries 11 included in the battery module 10.

[0042] For example, in the embodiment shown in FIG. 2, the sensing unit 110 may measure the voltages of the first secondary battery C1, the second secondary battery C2, the third secondary battery C3, and the fourth secondary battery C4 included in the battery module 10 during discharging. Specifically, the sensing unit 110 may measure the voltage of the first secondary battery C1 via the first sensing line SL1 and the second sensing line SL2, and measure the voltage of the second secondary battery C2 via the second sensing line SL2 and the third sensing line SL3. In addition, the sensing unit 110 may measure the voltage of the third secondary battery C3 via the third sensing line SL3 and the fourth sensing line SL4, and measure the voltage of the fourth secondary battery C4 via the fourth sensing line SL4 and the fifth sensing line SL5.

[0043] The sensing unit 110 is also configured to measure an open circuit voltage (OCV) of the secondary battery 11. That is, the sensing unit 110 is configured to measure both the voltage and the open circuit voltage of the secondary battery 11. The sensing unit 110 is also configured to measure the voltage of the secondary battery when the secondary battery is charged and discharged, and is configured to measure the open circuit voltage of the secondary battery 11 to determine degradation.

[0044] The secondary battery deteriorates due to repeated charging and discharging, and the sensing unit 110 may be configured to measure the voltage of the secondary battery 11 while the secondary battery 11 is being charged and discharged, and to measure the open circuit voltage of the secondary battery 11 every time one charge / discharge cycle is completed in order to collect data for deterioration diagnosis. Here, one charge / discharge cycle may be defined as a process of charging the secondary battery 11 in a discharged state and discharging the secondary battery 11 in a charged state.

[0045] The sensing unit 110 may measure the open circuit voltage of each secondary battery 11 every time the voltage of the secondary battery measured during N (N is an integer equal to or greater than 2) charge / discharge cycles of the secondary battery reaches a reference discharge voltage. Here, the reference discharge voltage may be a voltage previously set and stored by a user or the like to enable the sensing unit 110 to measure the open circuit voltage. That is, the reference discharge voltage is a reference value for measuring the open circuit voltage of the secondary battery 11 by the sensing unit 110, and may provide a time when the sensing unit 110 should measure the open circuit voltage of the secondary battery 11. For example, the reference discharge voltage may be 2.5 V. However, the reference discharge voltage is not limited thereto.

[0046] The sensing unit 110 may be configured to measure the voltage of a number of secondary batteries 11 during discharge, and to measure the open circuit voltage of the secondary battery 11 each time the measured voltage of the secondary battery 11 reaches the reference discharge voltage. The sensing unit 110 may be configured to measure the open circuit voltage of the secondary battery during rest after the secondary battery 11 reaches the reference discharge voltage. Here, during rest means a certain period of time after the secondary battery has finished discharging until it is charged for the next charge / discharge cycle. As a non-limiting example, the open circuit voltage may be measured 1 second after the end of discharging, more specifically within 3 seconds or 1 minute, and more specifically within 5 seconds or 30 seconds.

[0047] For example, in the embodiment shown in Fig. 2, it is assumed that the reference discharge voltage for each of the secondary batteries 11 is set to Vs [V]. In this case, when the voltage of the first secondary battery C1 reaches Vs due to discharging, the sensing unit 110 may measure the open circuit voltage of the first secondary battery C1. Similarly, when each of the voltages of the second secondary battery C2, the third secondary battery C3, and the fourth secondary battery C4 reaches Vs, the sensing unit 110 may measure the open circuit voltage of the secondary battery that has reached Vs.

[0048] In one specific example, the sensing unit 110 may include a voltage sensor (not shown). The voltage sensor is electrically connected to a positive terminal and a negative terminal of the secondary battery 11. The voltage sensor may be installed in a charge / discharge path of the secondary battery. The sensing unit 110 may further include a current sensor (not shown). The current sensor may be configured to measure the current of the secondary battery at predetermined time intervals while the secondary battery is being charged or discharged.

[0049] The memory unit 120 may be operably coupled to the sensing unit 110. The memory unit 120 may be configured to store an open circuit voltage measurement value measured by the sensing unit 110 and store various other sensing information. The memory unit 120 may also store data and programs necessary for each component of the battery management system 100 to operate and function, or data generated during the process of the operation and function.

[0050] The memory unit 120 may be configured to store the open circuit voltage of the secondary battery 11 measured every time a charge / discharge cycle is completed while repeatedly charging and discharging. As an example, the memory unit 120 may be configured to store the open circuit voltage value measured every time a charge / discharge cycle is performed in a manner of storing an open circuit voltage V1 measured when a reference discharge voltage is reached during a discharge process of a first charge / discharge cycle for the secondary battery 11, and storing an open circuit voltage V2 measured when a reference discharge voltage is reached during a discharge process of a second charge / discharge cycle for the secondary battery 11.

[0051] The memory unit 120 is not particularly limited in type as long as it is a known information storage means that is known to be capable of recording, erasing, and updating data. As an example, the memory unit 120 may include at least one type of storage medium among a flash memory type, a hard disk type, a solid state disk type (SSD type), a silicon disk drive type (SDD type), a multimedia card micro type, a random access memory (RAM), a static random access memory (SRAM), a read-only memory (ROM), an electrically erasable programmable read-only memory (EEPROM), and a programmable read-only memory (PROM).

[0052] The control unit 130 may receive the open circuit voltage measured by the sensing unit 110. The control unit 130 may be configured to transmit and receive electrical signals to and from the memory unit 120 within the battery management system 100, and may receive open circuit voltage data corresponding to the charge / discharge cycles stored in the memory unit 120.

[0053] The control unit 130 may be configured to calculate the amount of change in each open circuit voltage measured according to the charge / discharge cycle from the memory unit 120, and may be configured to determine that the secondary battery has degraded if the amount of change in the open circuit voltage satisfies the following condition 1 and remains satisfied for five or more charge / discharge cycles.

[0054] [Condition 1] V n-1 -V n <0.002V

[0055] (In the above condition 1, V n-1 is the open circuit voltage of the battery measured in the n-1th charge / discharge cycle, and V nis the open circuit voltage of the battery measured at the nth charge / discharge cycle, where n is any integer.

[0056] That is, the control unit 130 calculates the open circuit voltage (V n-1 ) and the open circuit voltage (V n ) is less than 0.002 V, and if such a change in open circuit voltage satisfies the above condition 1 for at least five charge / discharge cycles, it can be determined that the secondary battery has degraded.

[0057] 4 is a graph showing an example of a measured value of an open circuit voltage according to a charge / discharge cycle calculated by the battery management system 100 according to an embodiment of the present invention. The control unit 130 may generate the graph shown in FIG. 4 from the open circuit voltage data stored in the memory unit 120. The graph of FIG. 4 shows a relationship between the number of charge / discharge cycles and the open circuit voltage, and as the charge / discharge cycles proceed, the open circuit voltage gradually decreases and the amount of change in the voltage gradually decreases, and after about 1500 cycles, the amount of change in the open circuit voltage approaches 0.

[0058] Lithium iron phosphate with an olivine structure is more stable in terms of structural changes due to degeneration or deterioration than positive electrode active materials with a spinel or layered structure, and therefore lithium iron phosphate does not have a large change in voltage during charging and discharging. Therefore, in secondary batteries equipped with a positive electrode containing lithium iron phosphate, the voltage of the secondary battery is often determined by the potential difference of the negative electrode. In other words, in lithium iron phosphate-based secondary batteries, it is easy to grasp the potential difference of the negative electrode from the measured open circuit voltage.

[0059] Therefore, in order to diagnose the degradation of a secondary battery having a lithium iron phosphate positive electrode, the present invention can determine whether the negative electrode has degraded by determining that the secondary battery has degraded if the change in open circuit voltage of the secondary battery measured during the rest stage after discharge during the progress of a charge / discharge cycle is less than 0.002 V during a certain number of cycles.

[0060] In a lithium secondary battery having a positive electrode in which the lithium iron phosphate is used as a positive electrode active material, a phenomenon in which lithium is charged in a non-facing portion of the negative electrode that does not face the positive electrode due to a difference in the charge / discharge speed between the positive electrode and the negative electrode as the charge / discharge cycles are accumulated. The non-facing portion of the negative electrode that does not face the positive electrode exists because the negative electrode is cut larger than the positive electrode, and typically the edge of the negative electrode becomes the non-facing portion. If this phenomenon in which lithium is charged in the non-facing portion occurs continuously, lithium required for charging and discharging accumulates in the non-facing portion, reducing the capacity of the battery, and also causing safety issues due to lithium precipitation.

[0061] A secondary battery using lithium iron phosphate as the positive electrode active material can grasp the potential difference of the negative electrode through the behavior of the open circuit voltage. When the reduction in soluble lithium deepens and the battery degrades due to the charging of lithium to the non-facing portion of the negative electrode, the potential of the negative electrode does not change for a certain number of charge / discharge cycles or more. Therefore, the present invention can diagnose whether or not the secondary battery has degraded due to the charging of lithium to the non-facing portion through the behavior of the open circuit voltage of the secondary battery.

[0062] The control unit 130 may selectively include a processor, an application-specific integrated circuit (ASIC), other chipsets, logic circuits, registers, a communication modem, a data processing device, etc., known in the art, for executing various control logics performed in the battery management system 100 according to an embodiment of the present invention. In addition, when the control logic is embodied in software, the control unit 130 may be embodied as a collection of program modules. In this case, the program modules may be stored in a memory unit and executed by a processor. For example, the control unit 130 is a processor provided in the battery management system 100 according to an embodiment of the present invention, and may provide the determined presence or absence of degradation of the secondary battery 11 to a user through an output device such as a display device. In addition, the control unit 130 may provide a replacement or a warning alarm of the secondary battery 11 to a user through an external notification device based on the determination result regarding the presence or absence of degradation of the secondary battery 11.

[0063] The battery management system of the present invention has the effect of being able to diagnose the deterioration of a secondary battery by utilizing the characteristic that in a secondary battery having a positive electrode containing lithium iron phosphate as the positive electrode active material, the potential difference of the negative electrode appears as the open circuit voltage of the secondary battery, and by regarding the deterioration of the negative electrode as deterioration of the secondary battery from the change in the open circuit voltage that accompanies the progress of the charge and discharge cycle.

[0064] 5 is a schematic diagram of a battery pack 2000 including a battery management system according to another embodiment of the present invention. Referring to FIG. 5, the battery management system 200 may further include a switching unit 240 and an interface unit 250 for turning on and off an electrical connection between the secondary battery 11 and the charger.

[0065] The switching unit 240 may include a switch 241 and a switch driver 242. The switch 241 is disposed in a current path for charging and discharging the secondary battery 11. The secondary battery 11 can be charged and discharged while the switch 241 is turned on. The switch 241 may be a mechanical relay that is turned on and off by the magnetic force of a coil, or a semiconductor switch such as a metal oxide semiconductor field effect transistor (MOSFET). The charging and discharging of the secondary battery 11 is interrupted while the switch 241 is turned off. In one embodiment, the switch 241 may be turned on in response to a first control signal and turned off in response to a second control signal.

[0066] The switch driver 242 may be electrically connected to the switch 241 and the control unit 230, and may be configured to selectively output a first control signal or a second control signal to the switch 241 in response to an instruction from the control unit 230. The control unit 230 may instruct the switch driver 242 to turn on or off the switch 241 when at least one of predetermined events occurs.

[0067] The interface unit 250 is configured to support wired or wireless communication between the control unit 230 and a host controller 2 (e.g., ECU: Electronic Control Unit) of the electrical system 1. The wired communication may be, for example, CAN (Controller Area Network) communication, and the wireless communication may be, for example, ZigBee or Bluetooth (registered trademark) communication. Of course, the type of communication protocol is not particularly limited as long as it supports wired or wireless communication between the control unit 230 and the host controller 2.

[0068] The interface unit 250 may include an output device (not shown) such as a display or a speaker that provides a user with a form that can be recognized as a result of the process related to the deterioration state of the secondary battery 11 performed by the control unit 230. The interface unit 250 may include an input device (not shown) such as a mouse or a keyboard that can receive and input data from a user.

[0069] 6 is a flowchart showing an exemplary method for diagnosing degradation of a secondary battery according to another embodiment of the present invention. Referring to FIG. 6, the method for diagnosing degradation of a secondary battery according to the present invention includes the steps of (A) measuring a voltage during discharge of the secondary battery while repeatedly charging and discharging the secondary battery, and measuring an open circuit voltage of the secondary battery every time the measured voltage reaches a reference discharge voltage, and (B) determining that the secondary battery has degraded if a change in the open circuit voltage satisfies the following condition 1 for five or more charge and discharge cycles:

[0070] [Condition 1] V n-1 -V n <0.002V

[0071] (In the above condition 1, V n-1 is the open circuit voltage of the battery measured in the n-1th charge / discharge cycle, and V n is the open circuit voltage of the battery measured at the nth charge / discharge cycle, where n is any integer.

[0072] The secondary battery to which the method for diagnosing deterioration of a secondary battery according to the present invention is applied is as described above.

[0073] The above-mentioned process (A) is a process of collecting data for diagnosing whether or not the secondary battery has deteriorated. The deterioration diagnosis method according to the present invention is a process of measuring an open circuit voltage for each charge / discharge cycle while performing charge / discharge cycles of the secondary battery, and collecting open circuit voltages corresponding to the number of charge / discharge cycles.

[0074] Therefore, the above process (A) includes a process of measuring the open circuit voltage of the secondary battery every time one charge / discharge cycle of the secondary battery is completed. At this time, the measurement of the open circuit voltage may be during a pause until the next charge after the secondary battery reaches the reference discharge voltage.

[0075] The above-mentioned process (B) is a process of diagnosing whether the secondary battery has degraded or not based on the amount of change in the open circuit voltage according to the charge / discharge cycle collected through the process (A). Specifically, it includes a process of determining that the secondary battery has degraded when a condition that the difference between the open circuit voltage of the battery measured in the n-1th charge / discharge cycle and the voltage of the battery measured in the nth charge / discharge cycle is less than 0.002 V is satisfied for five charge / discharge cycles.

[0076] Referring to FIG. 6, the above-mentioned (A) process includes a process of measuring the voltage and the open circuit voltage of the secondary battery while repeatedly charging and discharging the secondary battery.

[0077] Repeated charging and discharging of a secondary battery means repeating a charge-discharge cycle several times, with a process of charging a secondary battery in a discharged state and then discharging the secondary battery in a charged state being counted as one charge-discharge cycle.

[0078] In one charge / discharge cycle, the voltage of the secondary battery may be measured during the process of charging the secondary battery and then discharging the charged secondary battery, and the voltage measurement of the secondary battery may be performed at regular time intervals.

[0079] While monitoring whether or not the measured voltage of the secondary battery reaches the reference discharge voltage, discharging of the secondary battery and voltage measurement are continued until the measured voltage value of the secondary battery reaches the reference discharge voltage.

[0080] If the measured voltage reaches the reference discharge voltage, the discharge of the secondary battery is terminated and the secondary battery is put into a resting state. The resting state means that the supply of current for charging and discharging the secondary battery is stopped. Then, in this resting state after discharging, the open circuit voltage of the secondary battery is measured.

[0081] In an exemplary embodiment, the charge / discharge method of the above process (A) may be a charge / discharge method applicable to a secondary battery, and non-limiting examples include a constant current (CC) method, a constant voltage (CV) method, a constant power (CP) method, and a CC-CV method and a CP-CV method that are combinations of these. A suitable charge / discharge method may be selected depending on the type of secondary battery. For example, a CP charge / discharge method may be selected for a secondary battery for an ESS. The charge / discharge rate (C rate, CP rate) is not particularly limited, and a suitable range of charge / discharge rate may be selected in consideration of the charge / discharge characteristics of the electrodes.

[0082] As shown in FIG. 4, as the charge / discharge cycle of the secondary battery is performed, the change in the open circuit voltage of the secondary battery gradually decreases, and as a result, the change in the open circuit voltage becomes less than 0.002V.

[0083] In the present invention, the determination of whether a secondary battery has degraded is based on the amount of change in the open circuit voltage. Specifically, when the condition that the amount of change between the open circuit voltage of the battery measured in the n-1th charge / discharge cycle and the open circuit voltage of the battery measured in the nth charge / discharge cycle is less than 0.002 V is satisfied for at least five charge / discharge cycles, the secondary battery is determined to have degraded.

[0084] The present invention will be described in more detail below with reference to examples. However, the following examples are merely for the purpose of illustrating the present invention, and the scope of the present invention is not limited to these examples alone.

[0085] <Example>

[0086] (The process of collecting open circuit voltage for each charge / discharge cycle of a secondary battery) A battery cell was prepared having a negative electrode made of 100% artificial graphite as the negative electrode active material and a positive electrode made of 100% LiFePO4 as the positive electrode active material. The battery cell was charged to 3.65V at a 1CP rate and discharged to 2.5V at a 1CP rate. During the discharge of the battery cell, the voltage of the battery cell was monitored and the discharge was terminated when the voltage of the battery cell was 2.5V. Five seconds after the discharge was terminated, the open circuit voltage of the battery cell was measured and the result was stored as V1.

[0087] After that, charge and discharge are repeated n times in the same manner as above, and the open circuit voltages measured for each charge and discharge cycle are V2, V3...V n Saved as .

[0088] (The process of determining whether secondary batteries have deteriorated or not) While repeatedly charging and discharging the battery cell, measure the open circuit voltage (V n-1 ) and the open circuit voltage (V n ) and if the difference in open circuit voltage was less than 0.002V five times, charging and discharging of the battery cell was terminated and the battery cell was determined to have degenerated.

[0089] <Experimental Example 1: Confirmation of lithium in the negative electrode that does not face the positive electrode>

[0090] In the battery cell determined to be degraded according to the above embodiment, the battery case was opened and the electrode assembly housed therein was disassembled to obtain the negative electrode. As a result of observing the negative electrode, it was confirmed that lithium was deposited on the non-facing portion. From these results, it is believed that the degradation diagnosis method according to the present invention can diagnose that lithium has accumulated in the negative electrode at a portion not facing the positive electrode.

[0091] <Experimental Example 2: Confirmation of Capacity Retention Rate>

[0092] Discharge capacity 1 was measured in the first charge / discharge cycle for the battery cell of the above example. Discharge capacity 2 was measured in the charge / discharge cycle in which the battery cell was determined to have degenerated according to the above example. Then, the capacity retention rate was calculated according to the following Equation 1.

[0093] Formula 1: (discharge capacity 2×100) / discharge capacity 1

[0094] The calculated capacity retention rate was 83%. Generally, a secondary battery with a capacity retention rate of 80% is considered to be degraded, but the degradation diagnosis method according to the present invention is analyzed to be effective for degrading a secondary battery in which lithium iron phosphate is used as a positive electrode active material.

[0095] The above-described embodiments of the present invention are not limited to the battery management system 100 and method, but may also be implemented through a program for implementing functions corresponding to the configurations of the embodiments of the present invention or a recording medium having the program recorded thereon. Such implementation may be easily implemented by a person skilled in the art based on the description of the above-described embodiments.

[0096] Although the present invention has been described above with reference to limited embodiments and drawings, the present invention is not limited thereto, and it is of course possible for a person having ordinary skill in the art to which the present invention pertains to make various modifications and variations within the technical spirit of the present invention and the equivalent scope of the claims set forth below.

[0097] Furthermore, the present invention described above is not limited to the above-described embodiments and accompanying drawings, and may be variously substituted, modified, and altered by a person having ordinary knowledge in the technical field to which the present invention pertains, without departing from the technical spirit of the present invention. In order to allow for various modifications, the present invention may be configured by selectively combining all or part of each embodiment. [Explanation of symbols]

[0098] 1: Electrical system 2: Upper controller 10: Battery module 11: Secondary battery 1000, 2000: Battery pack 100, 200: Battery management system 110, 210: Sensing unit 120, 220: Memory section 130, 230: control unit 240: Switching section 250: Interface section

Claims

1. A battery management system for diagnosing whether or not a secondary battery having a positive electrode containing lithium iron phosphate as a positive electrode active material is degraded, a sensing unit configured to measure a voltage and an open circuit voltage of the secondary battery; a memory unit configured to store the open circuit voltage measured by the sensing unit; A battery management system including: and a control unit configured to determine that the secondary battery has degraded when an amount of change in an open circuit voltage according to a charge / discharge cycle of the secondary battery satisfies the following condition 1 for five or more charge / discharge cycles: [Condition 1] V ｎ－１ -V ｎ <0.002V (In the above condition 1, V ｎ－１ is the open circuit voltage of the battery measured in the n-1th charge / discharge cycle, and V ｎ is the open circuit voltage of the battery measured at the nth charge / discharge cycle, where n is any integer.

2. The battery management system according to claim 1 , wherein the sensing unit is configured to measure a voltage of the secondary battery during discharging, and to measure an open circuit voltage of the secondary battery each time the measured voltage reaches a reference discharge voltage.

3. The battery management system according to claim 2 , wherein the sensing unit is configured to measure an open circuit voltage of the secondary battery during a rest period after the secondary battery reaches a reference discharge voltage.

4. The battery management system according to claim 1 , wherein the sensing unit is configured to measure an open circuit voltage of the secondary battery every time one charge / discharge cycle of the secondary battery is completed.

5. The battery management system according to claim 1 , further comprising a switching unit for turning on and off an electrical connection between the secondary battery and the charger.

6. A battery management system according to claim 1; A battery pack including a plurality of secondary batteries.

7. The battery pack according to claim 6, wherein the secondary battery contains, as a negative electrode active material, 50 to 100% of a graphite-based negative electrode active material based on a total weight of the negative electrode active material contained in the negative electrode.

8. A method for diagnosing the presence or absence of degradation of a secondary battery having a positive electrode containing lithium iron phosphate as a positive electrode active material, comprising: (A) a step of measuring a voltage of the secondary battery during discharge while repeatedly charging and discharging the secondary battery, and measuring an open circuit voltage of the secondary battery every time the measured voltage reaches a reference discharge voltage; (B) determining that the secondary battery has degraded if the amount of change in open circuit voltage satisfies the following condition 1 for five or more charge / discharge cycles: [Condition 1] V ｎ－１ -V ｎ <0.002V (In the above condition 1, V ｎ－１ is the open circuit voltage of the battery measured in the n-1th charge / discharge cycle, and V ｎ is the open circuit voltage of the battery measured at the nth charge / discharge cycle, where n is any integer.

9. 9. The method of claim 8, wherein the step (A) includes a step of measuring an open circuit voltage of the secondary battery during rest after the secondary battery reaches a reference discharge voltage.

10. 9. The method of claim 8, wherein the step (A) comprises the step of measuring an open circuit voltage of the secondary battery every time one charge / discharge cycle of the secondary battery is completed.

11. 9. The method for diagnosing degradation of a secondary battery according to claim 8, wherein the secondary battery contains 50 to 100% of a graphite-based negative electrode active material as a negative electrode active material.

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