Method for dividing charge and discharge of secondary battery, battery management system and battery pack including the same

Abstract

The split charging / discharging method of the present invention is a method for charging and discharging a secondary battery in a charge state range of SOCa to SOCb, and includes a charging process for charging the secondary battery and a discharging process for discharging the secondary battery charged by the charging process, and is characterized in that such charging and discharging processes are repeated, and the charging process ends when a measured voltage value of the secondary battery reaches a charge end reference voltage, and the discharging process ends when a measured discharge capacity reaches a value obtained by multiplying the capacity Qc charged in the charging process by the Coulombic efficiency. (However, a

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0141689, filed on October 28, 2022.

[0002] The present invention relates to a method for charging and discharging a secondary battery, a battery management system, and a battery pack including the same.

[0003] More specifically, the present invention relates to a cycle evaluation method for a secondary battery using lithium iron phosphate as a cathode material, in which charging and discharging are repeated while maintaining a constant charging / discharging state section when the secondary battery is repeatedly charged and discharged within a specific range of charging / discharging state section, a battery management system, and a battery pack including the same. [Background technology]

[0004] As technological development and demand for electric vehicles and energy storage systems (ESS) increases, the demand for batteries as energy sources is rapidly increasing, and various research efforts are being conducted on batteries that can meet various requirements. In particular, research on lithium secondary batteries, which have high energy density and excellent life and cycle characteristics as power sources for such devices, is being actively conducted.

[0005] The positive electrode active materials used in lithium secondary batteries include lithium cobalt oxide (LCO), lithium nickel cobalt manganese oxide (LNCMO), and lithium iron phosphate (LFP). Lithium iron phosphate batteries have a lower operating voltage range than the widely used lithium nickel cobalt manganese oxide batteries, but because lithium iron phosphate has an olivine structure, it has the advantage of having more stable operating characteristics than lithium transition metal oxides with a layered or spinel structure.

[0006] FIG. 1 shows the profile of open-circuit voltage as a function of the state of charge (SOC) of a lithium-nickel-cobalt-manganese oxide battery, and FIG. 2 shows the profile of open-circuit voltage as a function of the state of charge (SOC) of a lithium-iron-phosphate battery. Referring to these figures, a lithium-nickel-cobalt-manganese oxide battery has a graph shape in which the voltage increases as the SOC increases, and the SOC can be estimated from the measured open-circuit voltage. In contrast, a lithium-iron-phosphate battery exhibits a flat graph shape in which the voltage change is zero or close to zero even as the SOC increases in a certain SOC range, known as a plateau range. In this plateau range, the SOC cannot be accurately determined from the battery's open-circuit voltage.

[0007] On the other hand, when evaluating the cycle characteristics of a secondary battery or operating it, it is often necessary to repeatedly charge and discharge a specific range of charge (discharge) depths, such as SOC 50% to SOC 100%, which is called split charge and discharge. Specifically, a split charge and discharge method for charging and discharging a charge state range from SOCa to SOCb involves charging the secondary battery while knowing in advance the voltage value corresponding to SOCa and the voltage value corresponding to SOCb. When charging the secondary battery, the secondary battery is charged, and charging is terminated when the secondary battery's voltage reaches the voltage value corresponding to SOCb. When discharging the secondary battery, the secondary battery is discharged, and discharging is terminated when the secondary battery's voltage reaches the voltage value corresponding to SOCa. Because it is easier to measure voltage than SOC during charging and discharging of a secondary battery, charging and discharging are generally terminated based on the measured voltage.

[0008] However, during split charge / discharge of a lithium iron phosphate battery, the SOC cannot be accurately estimated from the voltage measurement value in the plateau section. Therefore, if discharge is terminated based on the voltage value, the discharge may be terminated before reaching the set SOC. Referring to FIG. 2, assuming that the SOC section of split charge / discharge is between SOC 70% and SOC 100%, the battery should be discharged to SOC 70% during discharge. However, because the voltage values ​​measured in the SOC 70% to SOC 95% section are similar, the discharge may be terminated only after discharging to SOC 80%.

[0009] Therefore, a method of terminating discharge based on capacity may be proposed as an alternative, but this does not reflect capacity degradation as charge-discharge cycles progress, and therefore the charge-discharge interval may not be maintained constant when charging and discharging are repeated.

[0010] Therefore, there is a need to develop technology that can repeatedly charge and discharge a lithium iron phosphate battery while maintaining a constant charge and discharge interval during split charge and discharge. Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention provides a method for repeating charge and discharge while maintaining a constant charge and discharge interval during split charge and discharge of a lithium iron phosphate battery.

[0012] Another object of the present invention is to provide a charge / discharge method that takes into account capacity degradation during split charge / discharge of the lithium iron phosphate battery. [Means for solving the problem]

[0013] The method for divided charge and discharge of a secondary battery according to an embodiment of the present invention is a method for divided charge and discharge of a secondary battery that charges and discharges a secondary battery within a state-of-charge range of SOCa to SOCb, including a charging process of charging the secondary battery and a discharging process of discharging the secondary battery charged by the charging process, and repeating such charging and discharging processes. In the charging process, charging ends when the measured voltage value of the secondary battery reaches the charging end reference voltage. In the discharging process, discharging ends when the measured discharge capacity reaches a value obtained by multiplying the capacity Qc charged in the charging process by the Coulomb efficiency. (However, a < b, where a is a value of 0% or more and less than 100%, and b is a value greater than 0% and 100% or less).

[0014] (However, a < b, where a is a value of 0% or more and less than 100%, and b is a value greater than 0% and 100% or less)

[0015] In one embodiment of the present invention, the secondary battery is a secondary battery containing lithium iron phosphate as a cathode active material of the cathode.

[0016] In one embodiment of the present invention, the Coulomb efficiency can be a value calculated by substituting the charge capacity and discharge capacity measured in an arbitrary charge-discharge cycle for the secondary battery to be charged and discharged into the following formula 1.

[0017] Formula 1: Coulomb efficiency = (discharge capacity × 100) / charge capacity

[0018] In one embodiment of the present invention, SOCa can be set within the state-of-charge range of the plateau region where the rate of change of voltage with respect to the change in capacity of the secondary battery (dV / dQ) is 0.

[0019] In one embodiment of the present invention, SOCb can be set outside the state-of-charge range of the plateau region.

[0020] In one embodiment of the present invention, the charging end reference voltage can be set to the voltage value corresponding to SOCb in the voltage profile according to the state of charge of the secondary battery to be charged and discharged.

[0021] In one embodiment of the present invention, the charging and discharging processes may each further include measuring one or more of the voltage, current, temperature, capacity, and resistance of the secondary battery.

[0022] A battery management system according to one embodiment of the present invention includes a sensing unit that measures one or more of the voltage, current, temperature, capacity, and resistance of a secondary battery, and a control unit that controls the secondary battery to charge and discharge in accordance with a built-in charge and discharge control algorithm. The charge and discharge control algorithm is configured to repeatedly charge and discharge the secondary battery through charge state intervals of SOCa to SOCb, and to terminate charging when the measured voltage value of the secondary battery reaches a charge termination reference voltage during charging, and to terminate discharging when the measured discharge capacity reaches a value obtained by multiplying the charged capacity Qc during the charging process by the Coulomb efficiency.

[0023] In one embodiment of the present invention, the coulombic efficiency may be a value calculated by substituting the charge capacity and discharge capacity measured in any charge / discharge cycle of the secondary battery to be charged / discharged into the following formula 1.

[0024] Equation 1: Coulombic efficiency = (discharge capacity x 100) / charge capacity

[0025] The battery management system according to an embodiment of the present invention may further include a memory unit that stores the coulomb efficiency of the secondary battery, a charge end reference voltage, and measurements measured by the sensing unit.

[0026] In one embodiment of the present invention, the charge / discharge control algorithm may be configured to set the SOCa within a state of charge range of a plateau section where the rate of change of voltage with respect to capacity change (dV / dQ) of the secondary battery is zero.

[0027] In one embodiment of the present invention, the charge / discharge control algorithm may be configured to set the SOCb outside the state of charge range of the plateau section.

[0028] In one embodiment of the present invention, the charge end reference voltage can be set to a voltage value corresponding to SOCb in a voltage profile according to the state of charge of the secondary battery to be charged or discharged.

[0029] The battery management system according to the present invention may further include a switching unit that turns on and off an electrical connection between the secondary battery and the charger.

[0030] A battery pack according to one embodiment of the present invention includes a battery management system according to the present invention and a plurality of secondary batteries each including lithium iron phosphate as a positive electrode active material of a positive electrode. [Effects of the Invention]

[0031] The split charge / discharge method, battery management system, and battery pack according to the present invention are effective in maintaining a constant charge / discharge interval while repeating charge / discharge during split charge / discharge of a lithium iron phosphate battery.

[0032] Furthermore, the split charge / discharge method, battery management system, and battery pack of the present invention can charge and discharge a lithium iron phosphate battery while reflecting capacity degradation during split charge / discharge. [Brief explanation of the drawings]

[0033] [Figure 1] 1 is a graph showing a profile of an open circuit voltage according to the state of charge (SOC) of a lithium nickel cobalt manganese oxide battery. [Figure 2] 1 is a graph showing a profile of an open circuit voltage according to a state of charge of a lithium iron phosphate battery. [Figure 3] 1 is a graph showing the capacity retention rate and coulombic efficiency of a lithium iron phosphate battery according to charge / discharge cycles. [Figure 4] 1 is a diagram illustrating the concept of a split charge / discharge method according to the present invention. [Figure 5] 1 is a flowchart of a split charge / discharge method according to an embodiment of the present invention. [Figure 6] 3 is a conceptual diagram for explaining the concept of capacity discharged during a discharging process according to the present invention; FIG. [Figure 7] 1 is a diagram illustrating an example configuration of a battery pack including a battery management system according to an embodiment of the present invention. [Figure 8] 1 is a block diagram illustrating a battery management system according to an embodiment of the present invention; [Figure 9] FIG. 2 is a schematic diagram of a battery pack including a battery management system according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0034] The terms and words used in this 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 the inventor can appropriately define the concepts of terms in order to best describe his own invention.

[0035] Therefore, the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments 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.

[0036] Furthermore, in the description of the present invention, if it is determined that a detailed description of related publicly known structures or functions may obscure the gist of the present invention, the detailed description will be omitted.

[0037] Throughout the specification, when a part is said to "comprise" a certain element, this does not mean that it excludes other elements, unless specifically stated to the contrary, and it means that it may further include other elements.

[0038] Also, terms such as the control unit described in the specification mean a unit that processes at least one function or operation, which can be embodied by hardware, software, or a combination of hardware and software.

[0039] Also, throughout the specification, when a certain part is "connected" to another part, this includes not only the case of being "directly connected", but also the case of being "indirectly connected" with other elements interposed therebetween.

[0040] In defining the "plateau region" in this specification, for descriptive techniques, it is defined as the charging state region where the rate of change of voltage with respect to the change in the capacity of the secondary battery (dV / dQ) is 0, but the plateau region also includes the charging state region where the rate of change of voltage with respect to the change in capacity (dV / dQ) is close to 0.

[0041] FIG. 4 is a drawing for explaining the concept of the split charge-discharge method according to the present invention. The dotted line in FIG. 4 shows a charge-discharge method that repeatedly charges a secondary battery with SOC of 0% until it reaches SOC of 100% and then fully discharges the fully charged secondary battery until it reaches SOC of 0%.

[0042] The solid line in FIG. 4 shows a method of repeatedly charging and discharging the secondary battery in a charging state range of SOCa to SOCb (where a < b, a is a value of 0% or more and less than 100%, and b is a value greater than 0% and 100% or less). The charge-discharge method according to the solid line in FIG. 4 ends charging when the charging state of the secondary battery reaches SOCb during charging, ends discharging when the charging state of the secondary battery reaches SOCa during discharging, and is a charge-discharge method that repeats such charge-discharge. Such a charge-discharge method is called split charge-discharge.

[0043] Although secondary batteries are repeatedly used for charge and discharge, it is known that in order to use secondary batteries for a long time, it is more advantageous to repeat split charge-discharge as described above rather than repeatedly performing full charge and full discharge.

[0044] Therefore, such a split charge / discharge method must not only be set as a charge / discharge condition for performance evaluation of the secondary battery, but also be set so that the secondary battery is charged / discharged according to the split charge / discharge method even after the product is shipped.

[0045] However, as described above, when split charging and discharging is performed on a secondary battery containing lithium iron phosphate as a positive electrode active material of the positive electrode, it is difficult to accurately determine the state of charge of the battery from the voltage measurement value due to the presence of a plateau section. Therefore, when discharging is terminated based on the voltage measurement value, the discharge may be terminated before the intended state of charge is reached.

[0046] Therefore, the present invention proposes a discharge termination criterion in the discharge process when a secondary battery having a positive electrode containing lithium iron phosphate is charged and discharged in divided cycles.

[0047] The secondary battery to which the split charge / discharge method according to the present invention is applied includes lithium iron phosphate as a positive electrode active material, which may be a compound represented by the following Chemical Formula 1:

[0048] [Chemical formula 1] Li 1+a Fe 1-x M x (PO 4-b )X b

[0049] (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.)

[0050] For example, the lithium iron phosphate may be LiFePO4.

[0051] Figure 5 is a flowchart of a split charge and discharge method according to an embodiment of the present invention. Referring to Figure 5, the split charge and discharge method of the secondary battery according to the present invention includes a charging process of charging the secondary battery in a state of charge interval from SOCa to SOCb, and a discharging process of discharging the secondary battery charged by the above charging process. Such charging and discharging processes are repeated. The above charging process ends charging when the measured voltage value of the secondary battery reaches the charging end reference voltage. The above discharging process ends discharging when the measured discharge capacity reaches a value obtained by multiplying the capacity Qc charged in the above charging process by the Coulomb efficiency.

[0052] (However, a < b, where a is a value of 0% or more and less than 100%, and b is a value greater than 0% and 100% or less)

[0053] The above charging process is a process of charging the secondary battery until the state of charge of the secondary battery reaches SOCb by charging. The charging process of the present invention is configured to end charging when the voltage measured during charging of the secondary battery reaches the charging end reference voltage.

[0054] In one specific example, the above charging end reference voltage can be set to the voltage value corresponding to SOCb in the voltage profile according to the state of charge of the secondary battery to be charged and discharged.

[0055] Specifically, it will be described with reference to Figure 2. For example, assuming that SOCb is SOC100%, the voltage corresponding to SOC100% in the voltage profile according to the state of charge shown in Figure 2 is about 3.35V. Therefore, the charging end reference voltage is 3.35V, and when the voltage of the secondary battery measured in the charging process reaches 3.35V, the charging ends.

[0056] The charge termination reference voltage may be a value set from a voltage profile corresponding to a state of charge obtained by previously charging and discharging a secondary battery to be charged / discharged. That is, the charging process of the present invention charges the secondary battery, monitors the measured voltage of the secondary battery, and terminates the charge when the measured voltage reaches a predetermined charge termination reference voltage.

[0057] Furthermore, since the charging process of the present invention includes a process of comparing the measured voltage with a preset charge termination reference voltage, it may include a process of measuring the voltage of the secondary battery in real time or periodically during the charging process.

[0058] The SOCb is preferably set within a state of charge range where the rate of change of voltage with respect to capacity change of the secondary battery (dV / dQ) is not zero. This is because if the SOCb is set within a state of charge section where the rate of change of voltage with respect to capacity change of the secondary battery (dV / dQ) is zero, charging may be terminated before the target SOCb is reached. Here, the state of charge section where the rate of change of voltage with respect to capacity change of the secondary battery (dV / dQ) is zero refers to the above-mentioned plateau section, and the state of charge section where the rate of change of voltage with respect to capacity change of the secondary battery (dV / dQ) is not zero refers to a state of charge section other than the plateau section.

[0059] After the charging process, a discharging process is performed, and a resting period may be included between charging and discharging. The resting period is when the secondary battery is left standing without charging or discharging. The resting period may be 20 minutes to 2 hours, and the duration of the resting period may be selected within a suitable range taking into account the charge / discharge characteristics and purpose of the battery.

[0060] The discharging process is a process in which the secondary battery, which has reached a state of charge of SOCb through the charging process, is discharged until the state of charge reaches SOCa.

[0061] In a divided charge / discharge method for charging / discharging in the state of charge range from SOCa to SOCb, if SOCa is set within the state of charge range of the plateau section where the rate of change of voltage with respect to capacity change (dV / dQ) of the secondary battery is 0, discharging may be terminated before reaching SOCb if the discharge end point is set based on the voltage as in the charging process. Therefore, in the discharging process, a method of discharging the same amount of capacity charged in the previous charging process can be considered, but this has the problem of not reflecting deterioration due to the accumulation of charge / discharge cycles.

[0062] In the present invention, charge and discharge are repeated while maintaining a constant charge / discharge state interval while reflecting capacity degradation due to accumulation of charge / discharge cycles during the discharge process, and discharge is terminated when the discharge capacity measured during the discharge process reaches a value obtained by multiplying the capacity Qc charged during the charge process by the coulombic efficiency. That is, the discharge process is terminated when the capacity discharged is equal to the value obtained by multiplying the capacity Qc charged during the charge process by the coulombic efficiency.

[0063] Figure 3 is a graph showing the capacity retention rate and coulombic efficiency of a lithium iron phosphate battery as a function of charge / discharge cycles. As shown in Figure 3, the discharge capacity gradually decreases due to degradation as the number of charge / discharge cycles increases. Meanwhile, the coulombic efficiency remains constant even as the number of charge / discharge cycles increases.

[0064] In the discharging process of the split charge / discharge method, if the secondary battery is discharged to the same capacity as that charged in the previous charge process, capacity degradation due to the accumulation of charge / discharge cycles cannot be reflected. Therefore, in the split charge / discharge method according to the present invention, discharging is terminated when the discharge capacity of the secondary battery measured in the discharging process reaches a value obtained by multiplying the capacity (Qc) charged in the previous charge process by the coulombic efficiency. Terminating the discharge in this manner completes one charge / discharge cycle. Then, to proceed with the next charge / discharge cycle, the secondary battery can be subjected to the above charging process again, and a rest period may be provided between the discharge and charge processes.

[0065] 6 is a conceptual diagram illustrating the concept of the capacity discharged in the discharging process according to the present invention. As described above, since the coulombic efficiency remains constant even if the number of charge / discharge cycles accumulates, the capacity Qd to be discharged in the discharging process is set to a value obtained by multiplying the charge capacity Qc charged in the previous charging process by the coulombic efficiency.

[0066] The discharging process of the present invention may further include a process of measuring the discharged capacity of the secondary battery while discharging the secondary battery to discharge the discharge capacity Qd. The method of measuring the discharged capacity through the discharging process may use various known technical methods.

[0067] The Coulombic efficiency can be set before carrying out the charge / discharge method of the present invention, and can be a value calculated by substituting the charge capacity and discharge capacity measured in any charge / discharge cycle of the secondary battery to be charged / discharged into the above formula 1.

[0068] Equation 1: Coulombic efficiency = (discharge capacity x 100) / charge capacity

[0069] In the split charge / discharge method of the present invention, the discharge end point is determined based on the capacity corresponding to the coulombic efficiency of the immediately preceding charge capacity, rather than the voltage during discharge, so that the discharge can be terminated when the target state of charge is reached.

[0070] Furthermore, even if the capacity of the secondary battery decreases with the accumulation of charge / discharge cycles, the Coulombic efficiency of the secondary battery is maintained constant, and the discharge capacity Qd to be discharged during the discharge process is calculated using the Coulombic efficiency, so that the capacity degradation due to repeated charge / discharge can be reflected. As a result, charge / discharge can be repeated while maintaining a constant charge / discharge interval.

[0071] The split charge / discharge method of the present invention may include a step of comparing a measured voltage of the secondary battery with a preset charge termination reference voltage to terminate charging, and a step of comparing a measured discharge capacity of the secondary battery with a value obtained by multiplying the charged capacity in a previous charging step by the coulombic efficiency to terminate discharging.

[0072] As described above, the split charge / discharge method of the present invention requires the voltage measurement and discharge capacity measurement to determine the end points of the charge and discharge processes. Therefore, the charge and discharge processes may each further include a step of measuring one or more of the voltage, current, temperature, capacity, and resistance of the secondary battery.

[0073] Here, temperature is a factor for correcting for differences in voltage or capacitance due to temperature differences, and current and resistance can be measured to calculate voltage or capacitance through current and resistance measurements when it is difficult to measure voltage or capacitance directly.

[0074] Hereinafter, a battery management system according to another embodiment of the present invention will be described.

[0075] FIG. 7 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, and FIG. 8 is a block diagram illustrating a battery management system according to an embodiment of the present invention.

[0076] 2, a battery pack 1000 may be provided so as to be installable in an electrical system (e.g., an electric vehicle). A 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 can control charging and discharging of each of the plurality of secondary batteries according to a charge and discharge control algorithm according to the present invention.

[0077] Furthermore, 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. 7 shows 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. 7. Similarly, the number of secondary batteries 11 included in the battery module 10 is not limited to the number shown in Fig. 7.

[0078] As described above, the secondary battery included in the battery module and battery pack of the present invention contains lithium iron phosphate as a positive electrode active material, which has been described above in detail and will not be described further.

[0079] Referring to FIG. 8, a battery management system 100 according to an embodiment of the present invention may include a sensing unit 110, a memory unit 120, and a control unit 130.

[0080] The sensing unit 110 may be configured to measure one or more of the voltage, current, temperature, capacity, and resistance of the secondary battery. That is, the sensing unit 110 may be configured to measure one or more of the voltage, current, temperature, capacity, and resistance of each of the secondary batteries 11 included in the battery module 10.

[0081] 7, 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 charging may be measured. 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 the voltage of the second secondary battery C2 via the second sensing line SL2 and the third sensing line SL3. The sensing unit 110 may also measure the voltage of the third secondary battery C3 via the third sensing line SL3 and the fourth sensing line SL4, and the voltage of the fourth secondary battery C4 via the fourth sensing line SL4 and the fifth sensing line SL5.

[0082] The sensing unit 110 may include a voltage sensor (not shown). The voltage sensor is electrically connected to the positive and negative terminals 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 also include a current sensor and a resistance sensor (not shown). These current and resistance sensors may be configured to measure the current of the secondary battery at predetermined time intervals while the secondary battery is being charged or discharged.

[0083] The memory unit 120 may be operably coupled to the sensing unit 110. The memory unit 120 is configured to store the coulombic efficiency of the secondary battery to be charged / discharged, the charge termination reference voltage, and the measurement values ​​measured by the sensing unit.

[0084] The coulombic efficiency can be a value calculated by substituting the charge capacity and discharge capacity measured in any charge / discharge cycle of the secondary battery to be charged / discharged into the following formula 1.

[0085] Equation 1: Coulombic efficiency = (discharge capacity x 100) / charge capacity

[0086] The charge end reference voltage may be a voltage value corresponding to SOCb in a voltage profile according to the state of charge of the secondary battery to be charged / discharged.

[0087] The measurement value measured by the sensing unit may be one or more of voltage, current, capacity, temperature, and resistance measured by the sensing unit during charging and discharging according to a charge / discharge control algorithm. These measurement values ​​are data necessary to understand the state of charge of the secondary battery to be charged or discharged.

[0088] The memory unit 120 is not particularly limited in type as long as it is a known information storage means capable of recording, erasing, and updating data. For example, the memory unit 120 may include at least one type of storage medium selected from the group consisting of flash memory, hard disk, solid state disk (SSD), silicon disk drive (SDD), multimedia card micro, random access memory (RAM), static random access memory (SRAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), and programmable read-only memory (PROM).

[0089] The control unit 130 is equipped with a charge / discharge control algorithm and controls the secondary battery to charge and discharge in accordance with the charge / discharge control algorithm.

[0090] The charge / discharge control algorithm is configured to repeatedly charge and discharge the secondary battery in charge state intervals of SOCa to SOCb, and to terminate charging when the measured voltage value of the secondary battery reaches a charge termination reference voltage during charging, and to terminate discharging when the measured discharge capacity reaches a value obtained by multiplying the capacity Qc charged during the charging process by the coulomb efficiency during discharging.

[0091] (However, a < b, where a is a value of 0% or more and less than 100%, and b is greater than 0% and 100% or less.)

[0092] The charge-discharge control algorithm of the present invention can be configured such that the SOCa is set within the range of the state of charge in the plateau region where the rate of change of voltage with respect to the change in the capacity of the secondary battery (dV / dQ) is 0.

[0093] Also, the charge-discharge control algorithm can be configured such that the SOCb is set outside the range of the state of charge in the plateau region.

[0094] The control unit 130 can receive the Coulomb efficiency, the charge end reference voltage, and the measured value from the memory unit 120 in order to determine the charge end point and the discharge end point. The control unit 130 can be configured to be able to transmit and receive electrical signals to and from the memory unit 120 within the battery management system 100.

[0095] The control unit 130 can be configured to calculate the discharge capacity Qd that serves as a reference for the discharge capacity to be discharged during the discharge process. That is, the control unit 130 can receive the charge capacity Qc charged during the previous charge process and the Coulomb efficiency from the memory unit 120, and substitute the capacity Qd to be discharged during the discharge process into Equation 2 below for calculation.

[0096] Equation 2: Qd = Qc × Coulomb efficiency

[0097] The control unit 130 can selectively include a processor, an ASIC (Application-Specific Integrated Circuit), other chip sets, logic circuits, registers, communication modems, data processing devices, etc. known in the art in order to execute various control logics performed in the battery management system 100 according to an embodiment of the present invention. Also, when the control logic is implemented by software, the control unit 130 can be implemented as a set of program modules. At this time, the program modules can be stored in the memory unit and executed by the processor.

[0098] 9 is a schematic diagram of a battery pack including a battery management system 200 according to another embodiment of the present invention. Referring to FIG. 9, the battery management system 200 may further include a switching unit 240 and an interface unit 250 that turn on and off an electrical connection between the secondary battery 11 and the charger.

[0099] 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. While the switch 241 is turned on, charging and discharging of the secondary battery 11 is possible. 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 MOSFET (Metal Oxide Semiconductor Field Effect Transistor). While the switch 241 is turned off, charging and discharging of the secondary battery 11 is suspended. The switch 241 may be turned on in response to a first control signal and may be turned off in response to a second control signal.

[0100] 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.

[0101] 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, a Controller Area Network (CAN) communication, and the wireless communication may be, for example, ZigBee or Bluetooth 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.

[0102] The interface unit 250 may include an output device (not shown) such as a display or a speaker that provides a user-recognizable result of the process related to the charge / discharge 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 the user.

[0103] The above-described embodiments of the present invention can be realized not only through the battery management system 100 and method, but also through a program that realizes functions corresponding to the configuration of the embodiments of the present invention or a recording medium on which the program is recorded. Such realization can be easily realized by a person skilled in the technical field to which the present invention belongs based on the description of the above-described embodiments.

[0104] 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.

[0105] Furthermore, the present invention described above is susceptible to various substitutions, modifications, and alterations by a person having ordinary knowledge in the technical field to which the present invention pertains, within the scope of not departing from the technical concept of the present invention, and therefore is not limited to the above-described embodiments and the accompanying drawings, and may be configured by selectively combining all or part of each embodiment so that various modifications can be made. [Explanation of symbols]

[0106] 1: Electrical system 2: Upper controller 10: Battery module 11: Secondary battery 1000: 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 method for dividing a secondary battery into charge and discharge states of charge of a secondary battery from SOCa to SOCb, comprising: a charging process for charging a secondary battery and a discharging process for discharging the secondary battery charged by the charging process, and repeating such charging and discharging processes; The charging process is terminated when the measured voltage value of the secondary battery reaches a charge termination reference voltage; The method for split charging and discharging a secondary battery, wherein the discharging process is terminated when the measured discharge capacity reaches a value obtained by multiplying the capacity Qc charged in the charging process by the coulomb efficiency. (where a<b, a is a value equal to or greater than 0% and less than 100%, and b is a value greater than 0% and equal to or less than 100%)

2. The method for split charging and discharging a secondary battery according to claim 1 , wherein the secondary battery contains lithium iron phosphate as a positive electrode active material of a positive electrode.

3. 2. The method for dividing a secondary battery into charge and discharge cycles according to claim 1, wherein the coulombic efficiency is a value calculated by substituting the charge capacity and discharge capacity measured in any charge and discharge cycle of the secondary battery to be charged and discharged into the following formula 1: Equation 1: Coulombic efficiency = (discharge capacity x 100) / charge capacity

4. 2. The method of claim 1, wherein the SOCa is set within a state of charge range of a plateau section in which a rate of change in voltage relative to a capacity change (dV / dQ) of the secondary battery is zero.

5. 2. The method for split charging and discharging a secondary battery according to claim 1, wherein the SOCb is set outside a state of charge range of a plateau section in which a rate of change in voltage relative to a capacity change (dV / dQ) of the secondary battery is zero.

6. 2. The method for split charging and discharging a secondary battery according to claim 1, wherein the charge end reference voltage is set to a voltage value corresponding to an SOCb in a voltage profile according to a state of charge of the secondary battery to be charged or discharged.

7. The charging and discharging processes are each The method for split charging and discharging a secondary battery according to claim 1 , further comprising measuring one or more of the voltage, current, temperature, capacity, and resistance of the secondary battery.

8. a sensing unit that measures one or more of the voltage, current, temperature, capacity, and resistance of the secondary battery; a control unit that controls the secondary battery to be charged and discharged in accordance with a charge and discharge control algorithm installed therein; The charge / discharge control algorithm The secondary battery is repeatedly charged and discharged through a charge state interval of SOCa to SOCb, and During charging, charging ends when the measured voltage of the secondary battery reaches the charge end reference voltage. The battery management system is configured to terminate discharge when the measured discharge capacity reaches a value obtained by multiplying the coulombic efficiency by the capacity Qc charged during the charging process. (where a<b, a is a value equal to or greater than 0% and less than 100%, and b is a value greater than 0% and equal to or less than 100%)

9. 9. The battery management system according to claim 8, wherein the coulombic efficiency is a value calculated by substituting the charge capacity and discharge capacity measured in an arbitrary charge / discharge cycle of the secondary battery to be charged / discharged into the following formula 1: Equation 1: Coulombic efficiency = (discharge capacity x 100) / charge capacity

10. The battery management system of claim 8 , further comprising a memory unit that stores the coulomb efficiency of the secondary battery, a charge termination reference voltage, and the measurement values ​​measured by the sensing unit.

11. The charge / discharge control algorithm 9. The battery management system according to claim 8, wherein the SOCa is set within a state of charge range of a plateau section in which a rate of change of voltage with respect to a capacity change (dV / dQ) of the secondary battery is zero.

12. The charge / discharge control algorithm The battery management system according to claim 8 , configured to set the SOCb outside a state of charge range of a plateau section in which a rate of change of voltage with respect to a capacity change (dV / dQ) of the secondary battery is zero.

13. The battery management system according to claim 8 , wherein the charge end reference voltage is set to a voltage value corresponding to an SOCb in a voltage profile according to a state of charge of the secondary battery to be charged or discharged.

14. The battery management system according to claim 8 , further comprising a switching unit that turns on and off an electrical connection between the secondary battery and the charger.

15. A battery management system according to claim 8; and a plurality of secondary batteries each containing lithium iron phosphate as a positive electrode active material of a positive electrode.

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