Apparatus, system, and method for performance estimation of rechargeable batteries

Abstract

The present invention relates to an apparatus, a system, and a method for predicting performance of a secondary battery. The apparatus of the present invention includes a current sensor for measuring a discharge current output from a secondary battery during a discharge period in which the secondary battery is discharged at a constant voltage from a predetermined reference voltage, and a control unit for calculating a relationship between a resistance change and a change in a state of charge during the discharge based on a change in the discharge current over time and the reference voltage. The control unit calculates a resistance value of each of a first resistance, a second resistance, and a third resistance based on the relationship between the resistance change and the change in the SOC during the discharge period, wherein the first resistance is a resistance due to a voltage drop of the secondary battery, the second resistance is a resistance generated due to ion insertion into an active material of the secondary battery during the discharge period, and the third resistance is a polarization resistance generated due to movement of ions in the secondary battery.

Description

TECHNICAL FIELD

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of Korean Patent Application No. 10-2020-0126848, filed on September 29, 2020, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to an apparatus, system, and method for estimating performance of a rechargeable battery. BACKGROUND

[0004] As the demand for lithium rechargeable batteries is changing from small portable electronic devices to medium and large electric vehicles (EVs) and energy storage systems (ESSs), the required battery characteristics are also changing significantly. In addition to the significant increase in requirements for long-term reliability (such as more than 10 years), battery pack-level safety, and price competitiveness safety, which are required compared to existing small batteries, high power characteristics and fast charging performance are also required.

[0005] Recently, attempts have been made to improve output by increasing the movement speed of electrons or increasing the movement speed of ions. For example, there are various attempts such as research related to increasing the electrical conductivity to increase the movement speed of electrons or adding new materials to increase the movement speed of ions (Li + ). Following this, there is a need for a method of measuring or estimating how much the output of a rechargeable battery is improved by increasing the movement speed of electrons or ions (Li + ).

[0006] However, in order to measure the output of a rechargeable battery, since the voltage and current must be measured and controlled at the same time, this is much more difficult than measuring the capacity of a conventional unit battery cell. In addition, this has been pointed out as a problem because, in addition to the selection of a method for measuring the output of a rechargeable battery, the measured value tends to vary greatly depending on the measurement conditions such as output holding time, state of charge (SOC), cutoff condition, and measurement temperature.

[0007] Therefore, there is a need for a method that can easily and accurately estimate how much the output performance or fast charging performance of a rechargeable battery is improved due to the increase in the movement speed of ions. SUMMARY

[0008] TECHNICAL PROBLEM

[0009] The present invention provides an apparatus, system, and method for performance estimation of a rechargeable battery to estimate output improvement of a rechargeable battery according to ion movement speed increase based on polarization resistance (Rpola), which is resistance caused by ion movement.

[0010] The present application provides an apparatus, a system and a method for performance estimation of a rechargeable battery to discharge the rechargeable battery in a constant current (CC) mode and a constant voltage (CV) mode and to quantify a polarization resistance (Rpola) based on a discharge current output from the rechargeable battery in the constant voltage (CV) mode.

[0011] The present application provides an apparatus, a system and a method for performance estimation of a rechargeable battery to determine that the rechargeable battery to be verified exceeds a predetermined output performance when a polarization resistance (Rpola) value is less than a predetermined reference value.

[0012] Technical Solution

[0013] An apparatus of the present application includes a current sensor for measuring a discharge current output from a rechargeable battery during a discharge period in which the rechargeable battery is discharged from a predetermined reference voltage in a constant voltage, and a control unit for calculating a resistance change relationship depending on a change in SOC (State of Charge) during the discharge period based on a change of the discharge current depending on the lapse of time and the reference voltage, wherein the control unit calculates a resistance value of each of a first resistance which is a resistance due to a voltage drop of the rechargeable battery, a second resistance which is a resistance generated due to ion insertion into an active material of the rechargeable battery during the discharge period, and a third resistance which is a polarization resistance generated by movement of ions in the rechargeable battery, based on the resistance change relationship according to the change in SOC during the discharge period.

[0014] In the resistance change relationship depending on the change in SOC during the discharge period, the control unit can calculate a resistance value of the first resistance using a resistance value of a time of the discharge period, a resistance value at an end point of the discharge period as an upper limit value of the second resistance on an extension line connecting a first point corresponding to the resistance value of the discharge period and a second point at which a resistance change rate with respect to the change in SOC exceeds a first reference value in the resistance change relationship with respect to the change in SOC, and a resistance value of the second resistance based on a difference between the upper limit value of the second resistance and the resistance value of the first resistance.

[0015] The control unit can calculate a resistance value of the third resistance based on a difference between a resistance value of the end point of the discharge period and the upper limit value of the second resistance.

[0016] The control unit can compare the resistance value of the third resistance with a second reference value to determine an output performance of the rechargeable battery.

[0017] A voltage sensor for measuring a voltage of the rechargeable battery to be transmitted to the control unit can also be included.

[0018] A system of the present application includes a discharger that discharges the rechargeable battery at a constant voltage from a predetermined reference voltage, a current sensor that measures a discharge current output from the rechargeable battery during a discharge period in which the rechargeable battery is discharged, and a control unit that calculates a resistance change relationship depending on a change in SOC (State Of Charge) during the discharge period based on a change in the discharge current depending on the time elapsed and the reference voltage, wherein the control unit calculates a resistance value of each of a first resistance that is a resistance due to a voltage drop of the rechargeable battery, a second resistance that is a resistance generated due to ion insertion into an active material of the rechargeable battery during the discharge period, and a third resistance that is a polarization resistance generated by movement of ions in the rechargeable battery based on the resistance change relationship according to the change in SOC during the discharge period.

[0019] In the resistance change relationship depending on the change in SOC during the discharge period, the control unit can calculate a resistance value at an end point of the discharge period as an upper limit value of the second resistance on an extension line connecting a first point corresponding to the resistance value of the discharge period and a second point at which a resistance change rate with respect to the change in SOC exceeds a first reference value in the resistance change relationship with respect to the change in SOC, using a resistance value of the time of the discharge period as the resistance value of the first resistance, and calculate a resistance value of the second resistance based on a difference between the upper limit value of the second resistance and the resistance value of the first resistance.

[0020] The control unit can calculate a resistance value of the third resistance based on a difference between a resistance value at the end point of the discharge period and the upper limit value of the second resistance.

[0021] The discharger can discharge the rechargeable battery at a predetermined constant current under the control of the control unit to lower a voltage of the rechargeable battery to correspond to the reference voltage.

[0022] A method of the present application includes: controlling a rechargeable battery to discharge at a constant voltage from a predetermined reference voltage; receiving a measurement of a discharge current output from the rechargeable battery during a discharge period in which the rechargeable battery is discharged; calculating a resistance change relationship depending on a change in SOC (State of Charge) during the discharge period based on the discharge current according to a change in time elapse and the reference voltage; and calculating each of a first resistance, a second resistance, and a third resistance, based on the resistance change relationship depending on a change in SOC during the discharge period, the first resistance being a resistance due to a voltage drop of the rechargeable battery, the second resistance being a resistance generated due to ion insertion into an active material of the rechargeable battery during the discharge period, and the third resistance being a polarization resistance generated due to movement of ions in the rechargeable battery.

[0023] The calculation of the resistance values can include: calculating a resistance value of a time of the discharge period as a resistance value of the first resistance; calculating a resistance value at an end point of the discharge period as an upper limit value of the second resistance, and calculating a resistance value of the second resistance based on a difference between the upper limit value of the second resistance on an extension line connecting a first point corresponding to the resistance value of the time of the discharge period and a second point at which a change rate of resistance with respect to the change in SOC exceeds a first reference value based on the resistance change relationship with respect to the change in SOC; and calculating a resistance value of the third resistance based on the resistance value of the end point of the discharge period and the upper limit value of the second resistance.

[0024] Advantageous Effects

[0025] The present application can easily determine whether a rechargeable battery to be verified passes a predetermined output performance having a polarization resistance (Rpola) value expressed in numbers in research and production stages of the rechargeable battery. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a graph illustrating a system for estimating performance of a rechargeable battery according to an exemplary embodiment.

[0027] Figure 2 is a flowchart illustrating a method for estimating performance of a rechargeable battery according to an exemplary embodiment.

[0028] Figure 3 is a graph showing a discharge current measured when a rechargeable battery is discharged at a constant voltage (CV).

[0029] Figure 4 is a graph showing a discharge current measured when a rechargeable battery is discharged at a constant voltage (CV). Figure 3a current-time graph of the battery is converted into a resistance-SOC (state of charge) graph.

[0030] Figure 5 is a graph illustrating a method of calculating a polarization resistance (Rpola) in a graph of a current-time of a battery. Figure 4 is a graph illustrating a method of calculating a polarization resistance (Rpola) in a graph of a current-time of a battery.

[0031] Figure 6 and Figure 7 is a graph illustrating experimental results comparing performance of a rechargeable battery at room temperature and at low temperature.

[0032] Figure 8 and Figure 9 is a graph comparing charge performance of a rechargeable battery based on a polarization resistance (Rpola) when porosity of a negative electrode is different.

[0033] Figure 10 and Figure 11 is a graph comparing output performance of a rechargeable battery based on a polarization resistance (Rpola) when a positive electrode additive is different.

[0034] Figure 12 and Figure 13 is a graph comparing output performance of a rechargeable battery based on a polarization resistance (Rpola) when porosity of a positive electrode is different. DETAILED DESCRIPTION

[0035] Hereinafter, exemplary embodiments disclosed in the present specification will be described in detail with reference to the accompanying drawings. In the present specification, the same or similar components will be denoted by the same or similar reference numerals, and repetitive description thereof will be omitted. The terms "module" and "unit" used in the following description are used only in order to facilitate the description, and thus the terms do not have meanings or roles that distinguish them from each other. In addition, in describing the exemplary embodiments of the present specification, when it is determined that a detailed description of a well-known technology associated with the present invention may obscure the gist of the present invention, the detailed description will be omitted. In addition, the accompanying drawings are provided only to enable the exemplary embodiments disclosed in the present specification to be easily understood, are not to be interpreted as limiting the spirit of the present specification, and it is understood that the present invention includes all modifications, equivalents, and substitutions without departing from the scope and spirit of the present invention.

[0036] The terms including ordinal numbers such as first, second, etc. will be used only to describe various components, and should not be construed to limit the components. The terms are used only to distinguish one component from other components.

[0037] It is to be understood that when a component is referred to as being "connected" or "coupled" to another component, it can be directly connected or coupled to the other component or intervening components can be present. On the other hand, it is to be understood that when a component is referred to as being "directly connected or coupled" to another component, it can be connected or coupled to the other component without other components intervening therebetween.

[0038] It will also be understood that the terms "comprises" or "comprising", when used in this specification, specify the presence of stated features, integers, steps, operations, components, parts, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, components, parts, or combinations thereof.

[0039] Figure 1 is a diagram illustrating a system for estimating performance of a rechargeable battery according to an exemplary embodiment.

[0040] Referring to Figure 1 The performance estimation system 100 of the rechargeable battery can include a rechargeable battery 10, a discharger 20, a voltage sensor 30, a current sensor 40, a relay 50, and a control unit 60.

[0041] The rechargeable battery 10 is a battery composed of at least one electrochemical cell that can be repeatedly charged and discharged. Hereinafter, the rechargeable battery 10 is described as a lithium ion (Li-ion) rechargeable battery that generates electric power through a chemical reaction of lithium, but is not limited thereto, and the rechargeable battery 10 can include a rechargeable battery such as a nickel-cadmium (Ni-Cd) battery, a nickel-hydrogen (NiMH) battery, or the like that can be repeatedly charged and discharged.

[0042] The rechargeable battery can be composed of a positive electrode, a negative electrode, an electrolyte solution, and a separator.

[0043] The positive electrode can coat a mixture of a positive active material, a conductive agent, and a binder mixed on a thin aluminum base material that holds a positive electrode frame. The positive active material is a material containing lithium ions (Li + ) that are unstable in an elemental state, such as lithium oxide in which lithium is combined with oxygen. That is, the positive active material provides lithium ions (Li + ) during charging, and is a material that participates in electrode reactions of an actual battery. The conductive agent functions to increase the conductivity of the positive active material having low conductivity. The binder functions as an adhesive that helps the active material and the conductive agent to be well settled on the aluminum base material.

[0044] For the negative electrode, a negative active material, a conductive agent, and a binder are coated on a copper base material. The negative active material stores lithium ions (Li +), and mainly uses graphite having a stable structure. Graphite has the following multiple conditions that must be possessed by a negative active material: structural stability, low electrochemical reactivity, and the ability to store a large amount of lithium ions (Li + ). The negative active material allows electric current to flow through an external circuit while reversibly absorbing and releasing lithium ions (Li + ) released from the positive electrode.

[0045] The electrolyte solution is a medium that allows lithium ions (Li + ) to move between the positive electrode and the negative electrode. As the electrolyte solution, a material having high ionic conductivity can be used to allow lithium ions (Li + ) to move well. The electrolyte solution can include a salt, a solvent, and an additive. The salt is a passage through which lithium ions (Li + ) can pass, the solvent is an organic liquid used to dissolve the salt, and the additive is a material added in a small amount for a specific purpose.

[0046] The separator is a porous polymer film that physically prevents the positive electrode from contacting the negative electrode. In addition, lithium ions (Li + ) can move through the pores formed in the separator. For example, if the positive electrode directly contacts the negative electrode, the battery can short circuit or explode.

[0047] The performance required for the rechargeable battery 10 varies depending on its use environment. For example, the output performance of the rechargeable battery 10 is the ability to provide electric energy per unit time. For example, the electric energy required to perform an image on a smartphone is greater than the electric energy required to perform a telephone call, and at this time, the output of the rechargeable battery 10 that provides electric energy to the smartphone is also determined accordingly. For example, if the movement speed of electrons or the movement speed of lithium ions (Li + ) increases, the output that the rechargeable battery 10 can provide can also increase.

[0048] In order to estimate the output performance or the rapid charging performance of the rechargeable battery 10, the discharger 20 can discharge the rechargeable battery 10 at a constant voltage (CV) from a predetermined reference voltage after discharging it at a constant current (CC). The discharger 20 can discharge the rechargeable battery 10 under the control of the control unit 60, but is not limited thereto, and can discharge the rechargeable battery 10 according to a predetermined procedure by including a separate discharging circuit, a current sensor, and a voltage sensor.

[0049] At this time, the reference voltage, which is an inflection point for changing the discharge mode from the constant current (CC) mode to the constant voltage (CV) mode, can be set to well observe the lithium ions (Li +The voltage value of the polarization resistor generated by the movement of the rechargeable battery 10 or the voltage value corresponding to the SOC (state of charge) at which its output performance is to be checked. In addition, when the SOC of the rechargeable battery 10 reaches a predetermined SOC value, the discharger 20 can terminate the discharge of the rechargeable battery 10.

[0050] Voltage sensor 30 can measure the voltage of rechargeable battery 10 at predetermined time intervals or in real time and send it to control unit 60.

[0051] The current sensor 40 can measure the discharge current as the current output from the rechargeable battery 10 and send it to the control unit 60. According to an exemplary embodiment, the current sensor 40 can measure the discharge current as the current output from the rechargeable battery 10 to be sent to the control unit 60 at predetermined time intervals or in real time during a discharge period in which the rechargeable battery 10 is discharged at a constant voltage (CV) from a predetermined reference voltage.

[0052] Under the control of the control unit 60, the relay 50 electrically connects or disconnects the rechargeable battery 10 from the discharger 20. For example, the control unit 60 may send a control signal to turn on the relay 50 to connect the rechargeable battery 10 and the discharger 20, thereby causing the rechargeable battery 10 to discharge continuously for a predetermined time.

[0053] The control unit 60 calculates the resistance change relationship depending on the change in state of charge (SOC) during the discharge period based on the change in discharge current over time and a reference voltage. Additionally, the control unit 60 can calculate each of a first resistance, a second resistance, and a third resistance based on the resistance change relationship depending on the change in state of charge (SOC) during the discharge period. The first resistance is the resistance caused by the voltage drop of the rechargeable battery 10, and the second resistance is the resistance changed based on the change in state of charge (SOC) during the discharge period. + The resistance generated by lithium ions (Li) inserted into the active material of the rechargeable battery, wherein the third resistance is generated in the rechargeable battery 10 by lithium ions (Li) inserted into the active material of the rechargeable battery 10. + The polarization resistance is generated by the movement of (). For a more detailed description, [it will be discussed in...] Figures 2 to 5 Let's explain it together.

[0054] Figure 2 This is a flowchart illustrating a method for estimating the performance of a rechargeable battery according to an exemplary embodiment. Figure 3 It is a graph showing the discharge current measured when a rechargeable battery is discharged at a constant voltage (CV). Figure 4 It is Figure 3 The current-time curve is converted into a resistance-SOC (state of charge) curve, and... Figure 5 This is to explain Figure 4a graph of the method of calculating the polarization resistance (Rpola).

[0055] Referring to Figure 2 First, the control unit 60 controls the discharger 20 to discharge the rechargeable battery 10 at a constant current (CC) so that the voltage of the rechargeable battery 10 is lowered to a predetermined reference voltage (S110).

[0056] For example, if the movement speed of lithium ions (Li + ) is increased by changing the positive electrode additive, the porosity of the positive electrode, the negative electrode active material, etc., the output of the rechargeable battery 10 is also increased. When the rechargeable battery 10 is continuously discharged for a predetermined time and the state of charge (SOC) of the rechargeable battery 10 is lowered and reaches a certain value (e.g., SOC 30%, etc.), a section in which the output performance is rapidly reduced can occur. At this time, the researcher, etc. can want to check how much the output performance of the rechargeable battery 10 is improved in the corresponding section by changing the positive electrode additive, the porosity of the positive electrode, the negative electrode active material, etc. At this time, the starting point of the section can be set to the state of charge (SOC) of the rechargeable battery 10. In addition, the voltage value corresponding to the state of charge (SOC) can be set as the reference voltage.

[0057] Next, the control unit 60 controls the discharger 20 to discharge the rechargeable battery 10 at a constant voltage (CV) (S120).

[0058] According to an exemplary embodiment, the control unit 60 can set a discharge section for discharging the rechargeable battery 10 at a constant voltage (CV) based on the state of charge (SOC) of the rechargeable battery 10. For example, when the real-time state of charge (SOC) of the rechargeable battery 10 reaches a first state of charge (SOC) (e.g., SOC 35%), the control unit 60 controls the discharger 20 so that the discharge of the rechargeable battery 10 at a constant voltage (CV) starts. In addition, when the real-time state of charge (SOC) of the rechargeable battery 10 reaches a second state of charge (SOC) (e.g., SOC 20%), the control unit 60 controls the discharger 20 so that the discharge of the rechargeable battery 10 at a constant voltage (CV) is turned off. That is, the control unit 60 can discharge the rechargeable battery 10 at a constant voltage (CV) in a discharge section in which the starting point is set to SOC 35% and the ending point is set to SOC 20%. At this time, the time corresponding to the discharge section is defined as a discharge period.

[0059] Next, the control unit 60 receives a measured value of the discharge current output from the rechargeable battery during the discharge period from the current sensor (S130).

[0060] According to an exemplary embodiment, the current sensor 40 measures a discharge current to be transmitted to the control unit 60 of the current output from the rechargeable battery 10 at a predetermined time interval or in real time during a discharge period in which the rechargeable battery 10 is discharged at a constant voltage (CV) from a predetermined reference voltage.

[0061] Figure 3 A graph calculated according to the passage of time of the discharge current is shown in an experimental condition in which the rechargeable battery 10 is discharged at a constant voltage (CV) starting at a state of charge (SOC) of 35% and a reference voltage of 2.5 V and the discharge of the rechargeable battery 10 is completed when the state of charge (SOC) reaches 20%. The control unit 60 can calculate the measured value of the discharge current received from the current sensor with a graph as shown in Figure 3

[0062] Next, the control unit 60 calculates a polarization resistance Rpola(S140) generated by the movement of lithium ions (Li + ) based on the discharge current according to the passage of time.

[0063] According to an exemplary embodiment, if the rechargeable battery 10 is discharged at a constant voltage CV, i.e., discharged while maintaining a constant voltage, a current change as shown in Figure 3 can be observed. In addition, the control unit 60 can estimate the SOC at each point in the graph of Figure 3 During the discharge period, since the voltage is constant, the current change depending on the passage of time can be viewed in Figure 3 and the SOC value corresponding to each time can be known, and the control unit 60 can derive a resistance change relationship according to the SOC change during the discharge period. For example, the control unit 60 can calculate the resistance change relationship with a graph as shown in Figure 4 Figure 3

[0064] Figure 5 is a graph showing a method of calculating the polarization resistance Rpola in the graph shown in Figure 4 First, the control unit 60 can calculate a resistance value of a first resistance Rohmic of a resistance due to a voltage drop of the rechargeable battery 10 based on a resistance change relationship depending on the SOC change during the discharge period. The resistance of the first resistance Rohmic corresponds to a summation value of resistance values of a resistance Rohm derived from the electrical characteristics of the rechargeable battery 10, a charge transfer resistance Rct, and a resistance Rocv due to an open circuit voltage (OCV).

[0065] ​​​For example, when the rechargeable battery 10 is discharged at a constant voltage CV, the first resistance Rohmic can be represented in about 0.1 seconds. Accordingly, in the graph of the resistance change with respect to the SOC, the control unit 60 can use the resistance value generated at the discharge period (more accurately, after 0.1 seconds from the time) as the resistance value of the first resistance Rohmic. Figure 5

[0066] The control unit 60 calculates a second resistance (Rdiff) that is a resistance generated when ions are inserted into the active material of the rechargeable battery 10. Also, in other words, the second resistance Rdiff can be defined as a resistance Rdiff caused by diffusion of the electrolyte.

[0067] Referring to Figure 5 , the control unit 60 can calculate the resistance (for example, 9 ohms) at the end point P3 of the discharge period on the extension line S, which connects the first point P1 corresponding to the start point of the discharge period and the second point P2 at which the resistance change rate with respect to the SOC change exceeds the first reference value in the resistance change relationship with respect to the SOC change, as an upper limit value of the second resistance Rdiff. The control unit 60 can calculate the resistance (for example, 7.8 ohms) of the second resistance Rdiff based on the difference (9-1.2=7.8 ohms) between the upper limit value of the second resistance Rdiff and the resistance (for example, 1.2 ohms) of the first resistance Rohmic. Here, the second point P2 can be defined as a point at which the slope suddenly changes in the resistance change relationship graph according to the SOC change, that is, a point at which the slope exceeds the first predetermined reference value.

[0068] The control unit 60 calculates a third resistance Ppola that is a polarization resistance caused by ion movement in the rechargeable battery. Referring to Figure 5 , the control unit 60 can calculate the resistance (for example, 5.8 ohms) of the third resistance Ppola based on the difference (14.8-9=5.8 ohms) between the resistance (for example, 14.8 ohms) of the end point P4 of the discharge period and the upper limit value (for example, 9 ohms) of the second resistance.

[0069] Next, the control unit 60 compares the polarization resistance Rpola value with a reference value (S150).

[0070] According to an exemplary embodiment, if there is a performance index expected from a completely assembled rechargeable battery, the polarization resistance Rpola value corresponding to the performance index can be calculated as the reference value. Then, the control unit 60 can compare the polarization resistance Rpola value of the measured electrode with the reference value to determine whether the rechargeable battery including the electrode to be verified passes the reference performance (pass) or fails (fail). ​

[0071] Next, if the polarization resistance Rpola value is less than the reference value (S150, Yes), the control unit 60 determines that the performance of the rechargeable battery including the corresponding electrode passes the performance index expected from the fully assembled rechargeable battery (pass) (S160).

[0072] Next, if the polarization resistance Rpola value is greater than the reference value (S215, No), the control unit 60 determines that the performance of the rechargeable battery including the corresponding electrode does not pass the performance index expected from the fully assembled rechargeable battery (fail) (S170).

[0073] Figures 6 to 13 is an experimental result showing the correlation between the polarization resistance Rpola and the output performance.

[0074] Figure 6 and Figure 7 shows experimental results for comparing the performance of rechargeable batteries at room temperature and at low temperature.

[0075] Figure 6 is derived by performing a constant voltage CV discharge test on each of a plurality of electrodes A, B, C, and D at room temperature (e.g., 25°C) and a predetermined initial condition (15C and 2.5V), and demonstrates a resistance change relationship according to SOC change during a discharge period. Figure 7 is derived by performing a constant voltage CV discharge test on each of a plurality of electrodes A, B, C, and D at low temperature (e.g., -10°C) and a predetermined initial condition (5.5C and 2.5V), and demonstrates a resistance change relationship according to SOC change during a discharge period. The plurality of electrodes A, B, C, D, and other conditions are the same, only the temperature and the initial condition are different, and the discharge test is performed. The discharge test discharges the rechargeable battery at a constant current CC and a constant voltage CV, and measures a discharge current output from the rechargeable battery during a discharge period, which is a period during which the rechargeable battery is discharged at a constant voltage CV.

[0076] [Table 1]

[0077]

[0078] Table 1 demonstrates the values of the end-of-discharge current (End I) and the polarization resistance Rpola of the continuous discharge output of each of the plurality of electrodes A, B, C, and D, which are calculated based on Figure 6 and Figure 7 Referring to Table 1, it can be seen that the lower the polarization resistance (Rpola) value (A > B > C > D), the higher the end-of-discharge current (End I) value, regardless of the temperature and the initial condition. At this time, the higher the end-of-discharge current (End I) value, the better the continuous discharge output performance of the rechargeable battery.

[0079] Therefore, it can be confirmed that the polarization resistance (Rpola) is a factor indicating the performance of the rechargeable battery regardless of the temperature.

[0080] Figure 8 and Figure 9 is a graph comparing the charge performance of the rechargeable battery based on the polarization resistance (Rpola) when the porosity of the negative electrode is different. Specifically, Figure 8 and Figure 9 is an exemplary graph showing the correlation between the polarization resistance (Rpola) and the end-of-charge SOC.

[0081] According to the exemplary embodiment, the quantified polarization resistance is correlated with the end-of-charge SOC, which is one of the factors of the charge performance of the rechargeable battery. For example, if the porosity of the negative electrode increases, the moving speed of the ions increases and the polarization resistance decreases, and as a result, the end-of-charge SOC also increases. That is, when the rechargeable battery 10 is continuously charged, the quantified polarization resistance can be used as an index to predict the performance of the end-of-charge SOC point. The experimental results for this are as follows.

[0082] Referring to Figure 8 and Figure 9 , the first electrode A has a porosity of 26%, and the second electrode B has a porosity of 30%.

[0083] [Table 2]

[0084] Negative electrode porosity A(26％) B(30％) Rpola (milliohm) 2 3.7

[0085] Table 2 shows the polarization resistance Rpola values of the first electrode A and the second electrode B calculated by the method described in Figure 9 Figure 5

[0086] Referring to Figure 8 and Table 2, it can be confirmed that the polarization resistance Rpola value of the first electrode A is less than that of the second electrode B, and the end-of-charge SOC value of the first electrode A is less than that of the second electrode B.

[0087] Figure 10 and Figure 11 is a graph comparing the output performance of the rechargeable battery based on the polarization resistance Rpola when the positive electrode additive is different. Specifically, Figure 10 and Figure 11 is an exemplary graph exemplifying the correlation between the polarization resistance Rpola and the end-of-discharge current I.

[0088] ​​According to an exemplary embodiment, the quantified polarization resistance is related to an end-of-discharge current end I, which is one of output performance factors during discharging of the rechargeable battery. For example, if the movement speed of ions is increased by adding the positive electrode additive, the polarization resistance decreases, and as a result, the end-of-discharge current (end I) also increases. That is, when the rechargeable battery 10 is continuously discharged, the quantified polarization resistance can be used as an index to predict the output performance at the end of discharging. Experimental results for this are as follows.

[0089] Figure 10 A graph showing the discharge current value depending on the lapse of time is shown as the discharge test result of the first electrode A to which no positive electrode additive is added and the second electrode B to which the positive electrode additive is added. Figure 11 is a graph showing the change in resistance based on the change in SOC of the first electrode A and the second electrode B. Figure 10

[0090] [Table 3]

[0091]

[0092] Table 3 shows the polarization resistance (Rpola) values of the first electrode A and the second electrode B calculated by the method described in Figure 11 Figure 5

[0093]

[0094] Figure 12 and Figure 13 are graphs comparing the output performance of the rechargeable battery based on the polarization resistance Rpola when the porosity of the positive electrode is different. Specifically, Figure 12 and Figure 13 are other exemplary graphs showing the correlation between the polarization resistance Rpola and the end-of-discharge current end I.

[0095] ​​​​According to an exemplary embodiment, the quantified polarization resistance is related to the end-of-discharge current end, which is one of the output performance factors during discharging of the rechargeable battery. For example, when the porosity of the positive electrode increases, the moving speed of ions increases and the polarization resistance decreases, as a result, the end-of-discharge current end also increases. That is, when the rechargeable battery 10 is continuously discharged, the quantified polarization resistance can be used as an index to predict the output performance at the end of discharging. Experimental results for this are as follows.

[0096] Figure 12 A graph showing the discharge current value according to the lapse of time, which is a discharge test result for a plurality of electrodes A, B, and C having different porosities of the positive electrode, is shown. Figure 13 is a graph showing the change in resistance based on the change in SOC of the plurality of electrodes A, B, and C. Figure 12 The porosity of the first electrode A is 21%, the porosity of the second electrode B is 23%, and the porosity of the third electrode C is 30%.

[0097] [Table 4]

[0098]

[0099] Table 4 shows the polarization resistance Rpola and the end-of-discharge current end of the plurality of electrodes A, B, and C calculated by the method described in Figure 13 with reference to the graph. Figure 5 With reference to Table 4, when the polarization resistance (Rpola) value decreases (A > B > C) due to the increase in porosity and the increase in ion conductivity, the end-of-discharge current (end) increases (A < B < C).

[0100] While the present application has been described in connection with what is presently considered to be the actual exemplary embodiments, it is to be understood that the application is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. An apparatus for performance estimation of a rechargeable battery, the apparatus comprising: A current sensor is used to measure the discharge current output from the rechargeable battery during a discharge period in which the rechargeable battery discharges from a predetermined reference voltage at a constant voltage. as well as The control unit calculates the resistance change relationship depending on the state of charge (SOC) during the discharge period, based on the change of the discharge current over time and the reference voltage. The control unit calculates the resistance value of each of the first, second, and third resistors based on the resistance change relationship according to the SOC change during the discharge period. The first resistor is the resistance caused by the voltage drop of the rechargeable battery, the second resistor is the resistance generated during the discharge period due to ion insertion into the active material of the rechargeable battery, and the third resistor is the polarization resistance generated due to the movement of ions in the rechargeable battery. Wherein, in the resistance change relationship that depends on the SOC change during the discharge period, the control unit: The resistance value at the beginning of the discharge period is used as the resistance value of the first resistor. The resistance value at the end of the discharge period on the extended line is calculated as the upper limit of the second resistance. The extended line connects a first point and a second point. The first point corresponds to the start of the discharge period. At the second point, in the resistance change relationship with respect to the SOC change, the resistance change rate with respect to the SOC change exceeds the first reference value, and... The resistance value of the second resistor is calculated based on the difference between the upper limit of the second resistor and the resistance value of the first resistor.

2. The apparatus according to claim 1, wherein, The control unit calculates the resistance value of the third resistor based on the difference between the resistance value at the end of the discharge period and the upper limit value of the second resistor.

3. The apparatus according to claim 2, wherein, The control unit compares the resistance value of the third resistor with a second reference value to determine the output performance of the rechargeable battery.

4. The apparatus according to claim 1, further comprising: A voltage sensor is used to measure the voltage of the rechargeable battery to be sent to the control unit.

5. A system for performance estimation of a rechargeable battery, the system comprising: A discharger that discharges the rechargeable battery from a predetermined reference voltage at a constant voltage. A current sensor that measures the discharge current output from the rechargeable battery during a discharge period of the rechargeable battery. as well as The control unit calculates the resistance change relationship depending on the state of charge (SOC) during the discharge period, based on the change of the discharge current over time and the reference voltage. The control unit calculates the resistance value of each of the first, second, and third resistors based on the resistance change relationship according to the SOC change during the discharge period. The first resistor is the resistance caused by the voltage drop of the rechargeable battery, the second resistor is the resistance generated during the discharge period due to ion insertion into the active material of the rechargeable battery, and the third resistor is the polarization resistance generated due to the movement of ions in the rechargeable battery. Wherein, in the resistance change relationship that depends on the SOC change during the discharge period, the control unit: The resistance value at the beginning of the discharge period is used as the resistance value of the first resistor. The resistance value at the end of the discharge period on the extended line is calculated as the upper limit of the second resistance. The extended line connects to a first point and a second point. The first point corresponds to the start of the discharge period. At the second point, in the resistance change relationship with respect to the SOC change, the resistance change rate with respect to the SOC change exceeds the first reference value, and... The resistance value of the second resistor is calculated based on the difference between the upper limit of the second resistor and the resistance value of the first resistor.

6. The system according to claim 5, wherein, The control unit calculates the resistance value of the third resistor based on the difference between the resistance value at the end of the discharge period and the upper limit value of the second resistor.

7. The system according to claim 5, wherein, The discharger, under the control of the control unit, discharges the rechargeable battery at a predetermined constant current to reduce the voltage of the rechargeable battery to a level corresponding to the reference voltage.

8. A method for performance estimation of a rechargeable battery, the method comprising the following steps: Control the rechargeable battery to discharge from a predetermined reference voltage at a constant voltage; Receive a measurement of the discharge current output from the rechargeable battery during the discharge period of the rechargeable battery. The resistance change relationship, which depends on the change in the state of charge (SOC) during the discharge period, is calculated based on the change in the discharge current over time and the reference voltage. as well as Based on the resistance change relationship depending on the SOC change during the discharge period, each of the first, second, and third resistance values ​​is calculated. The first resistance is the resistance caused by the voltage drop of the rechargeable battery, the second resistance is the resistance generated during the discharge period due to ion insertion into the active material of the rechargeable battery, and the third resistance is the polarization resistance generated due to the movement of ions within the rechargeable battery. The steps for calculating the resistance value include: The resistance value at the beginning of the discharge period is calculated as the resistance value of the first resistor; The resistance value at the end of the discharge period on the extended line is calculated as the upper limit of the second resistance, and the resistance value of the second resistance is calculated based on the difference between the upper limit of the second resistance and the resistance value of the first resistance. The extended line connects a first point and a second point. The first point corresponds to the start of the discharge period. At the second point, based on the resistance change relationship with respect to the SOC change, the resistance change rate with respect to the SOC change exceeds a first reference value; and The resistance value of the third resistor is calculated based on the difference between the resistance value at the end of the discharge period and the upper limit value of the second resistor.

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