METHOD FOR ESTABLISHING CHARGING PROTOCOL FOR LITHIUM SECONDARY BATTERY, BATTERY MANAGEMENT SYSTEM, BATTERY PACK, AND BATTERY CELL CHARGING DEVICE

Abstract

The method for establishing a charging protocol for a lithium secondary battery according to the present invention is a method for determining a state of charge (SOC) when a two-electrode battery cell is charged with a reference current. x ) according to the open circuit voltage (V ref ) and when the battery cell is charged with different charging currents, the state of charge (SOC) x ) according to the open circuit voltage (V c ) and the measured value V ref , V c By substituting the above, the state of charge (SOC x ) according to the internal resistance (R SOCx ) and calculate the state of charge (SOC) for each charging current. x ) to collect an internal resistance profile by plotting the internal resistance value according to the charging current. SOCx determining the lowest resistance value among the inflection points for each charging current as a reference resistance value, and then determining a state of charge having the reference resistance value in the internal resistance profile for each charging current as a limit state of charge. [Formula 1] Internal resistance value (R SOCx )=(V c -V ref ) / I C (In the above formula 1, Ic means the current value applied for each charging current)

Description

[Technical field]

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2022-0147927, filed on November 8, 2022.

[0002] The present invention relates to a method for establishing a rapid charging protocol that reflects the heat generation and internal resistance associated with charging and discharging of large-capacity battery cells, a battery management system capable of establishing such a rapid charging protocol, a battery pack including the same, and a charging device for battery cells using the same. [Background technology]

[0003] In recent years, as the demand for portable electronic products such as laptops and mobile phones has increased dramatically, as has the demand for electric carts, electric wheelchairs, and electric bicycles, there has been active research into high-performance batteries that can be repeatedly charged and discharged. In addition, as carbon energy is gradually depleted and environmental concerns have grown recently, the demand for hybrid electric vehicles (HEVs) and electric vehicles (EVs) is gradually increasing worldwide. As a result, much attention and research is being focused on vehicle batteries, which are a core component of HEVs and EVs, and there is an urgent need to develop fast-charging technology that can quickly charge batteries. Fast charging is a very important feature, especially for EVs that do not have an additional energy source.

[0004] The process of charging a battery involves applying current to the battery to store charge and energy, and such a process must be carefully controlled. In general, excessive charging current (C-rate) or charging voltage can permanently degrade the battery's performance and ultimately induce complete failure or catastrophic failure such as leakage of highly corrosive chemicals or explosion.

[0005] In constant current charging of a battery, if the current rate of the charging current is small, it takes a very long time to fully charge the battery. On the other hand, if the current rate of the charging current is too high, there is a side effect that the battery deteriorates rapidly. Therefore, it is necessary to gradually adjust the current rate of the charging current according to the state of the battery during constant current charging.

[0006] In order to adjust the current rate during constant current charging stepwise, a charging map having a "multi-stage constant-current charging protocol" is mainly utilized. The charging map includes at least one data array in which the relationship between multiple current rates and multiple transition conditions is recorded. Each time each transition condition is satisfied, the current rate of the subsequent sequence can be supplied to the battery as the charging current. The current rate (which may also be referred to as "C-rate") is the charging current divided by the maximum capacity of the battery, and the unit is "C".

[0007] In the past, in order to derive such a multi-stage constant current charging protocol, a 50mAh mono-cell type three-electrode cell was manufactured and the state of charge (SOC) at which lithium plating occurs at the negative electrode according to the charging current was set as the charging limit.

[0008] However, since three-electrode cells are difficult to manufacture and require charging and discharging using a dedicated charger, there are many constraints, such as the manufacturing completion of the three-electrode cells, the manufacturing time of the three-electrode cells, and the preparation of the dedicated charger, etc. In addition, in the process of applying the limit state of charge confirmed in such three-electrode cells to large-capacity battery cells with capacities of 40 to 200 Ah, there was no technology that could reflect the resistance of large-capacity battery cells or heat generation during fast charging.

[0009] In addition, in the method of establishing a charging protocol using a three-electrode cell, the lithium plating section becomes less clearly defined as the charging current becomes smaller and as the negative electrode composition becomes more favorable for fast charging, and the subjective judgment of the experimenter becomes involved. As a result, when there is a deviation in the battery cell, it is difficult to establish a charging protocol that shows a similar voltage profile.

[0010] Therefore, there is a need to develop technology that can derive a charging protocol that takes into account the resistance of large-capacity battery cells and the heat generation state during fast charging, while eliminating the need to manufacture three-electrode cells. Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been devised to solve the above problems, and aims to provide a method for deriving a charging protocol that takes into account the resistance of large-capacity battery cells and the heat generation state during fast charging, without the need to manufacture three-electrode cells in advance to derive the limiting state of charge for each charging current, a battery management system capable of establishing such a charging protocol, a battery pack equipped with the same, and a charging device. [Means for solving the problem]

[0012] According to one embodiment of the present invention, a method for establishing a charging protocol for a lithium secondary battery is provided. The method for establishing a charging protocol for a lithium secondary battery includes: (a) State of charge (SOC) when a two-electrode battery cell with positive and negative electrodes is charged at a reference current x ) according to the open circuit voltage (V ref ) and (b) When the battery cell is charged with different charging currents, the state of charge (SOC) x ) according to the open circuit voltage (V c ) and (c) The above measured value V is calculated using the following formula 1. ref , V cBy substituting the above, the state of charge (SOC x ) according to the internal resistance (R SOCx ) and calculate the state of charge (SOC) for each charging current. x ) according to the internal resistance (R SOCx ) to collect an internal resistance profile; (d) In the internal resistance profile by charging current collected above, the internal resistance value (R SOCx determining the lowest resistance value among the inflection points for each charging current as a reference resistance value, and then determining a state of charge having the reference resistance value in the internal resistance profile for each charging current as a limit state of charge.

[0013] [Formula 1] Internal resistance value (R SOCx )=(V c -V ref ) / I C

[0014] (In the above formula 1, Ic means the current value applied for each charging current)

[0015] In an embodiment of the present invention, the inflection point may be an inflection point corresponding to a second inflection point when the graph shape of the internal resistance profile for each charging current is assumed to be a "W" shape.

[0016] In one embodiment of the present invention, the inflection point may be located within a range where the state of charge is SOC 40% to SOC 60%.

[0017] In one embodiment of the present invention, the capacity of the two-electrode battery cell may be 40 to 200 Ah.

[0018] In one embodiment of the present invention, the reference current in step (a) may be selected within the range of 0.25C to 0.4C.

[0019] In one embodiment of the present invention, the charging current in the above step (b) can be selected from a plurality of currents within the range of 0.2C to 6C.

[0020] In an embodiment of the present invention, the above step (b) may be performed by repeatedly charging the discharged battery cell until the SOC reaches 50% to 100% for each charging current.

[0021] In one embodiment of the present invention, the step (b) may apply the charging current by increasing the charging current value stepwise from a low current to a high current.

[0022] The method for establishing a charging protocol according to an embodiment of the present invention may further include a step of mapping a charging protocol based on a limit state of charge for each charging current, and the mapping step may be to map the charging protocol so that the charging current is charged at the corresponding charging current until the charging current is below the limit state of charge for each charging current, and the charging current is decreased as the state of charge increases.

[0023] In one embodiment of the present invention, the mapping process may be mapping up to a state of charge section of SOC 55% or less.

[0024] In one embodiment of the present invention, the step (b) is a step of calculating the state of charge (SOC) for each charging current. x ) according to the open circuit voltage (V c The method further includes a step of performing charge / discharge compensation between the steps of measuring the current density, and the charge / discharge compensation step may include discharging with the reference current of the step (a) and charging and discharging with the reference current again.

[0025] According to another embodiment of the present invention, a battery management system is provided, which is capable of detecting a state of charge (SOC) when a two-electrode battery cell having a positive electrode and a negative electrode is charged with a reference current and various values ​​of charging current. x ) according to the open circuit voltage (V ref , V c A voltage measurement unit configured to measure The above measured value V is added to the following formula 1. ref , V c Substituting the above, the state of charge (SOC x ) according to the internal resistance (R SOCx ) and calculate the state of charge (SOC) for each charging current. x A memory unit configured to collect an internal resistance profile in which the internal resistance value is plotted according to the temperature of the sample. In the internal resistance profile by charging current collected above, the internal resistance value (R SOCx and a control unit configured to check each inflection point where the internal resistance profile changes from an increasing trend to a decreasing trend, determine the lowest resistance value among the inflection points for each charging current as a reference resistance value, and then determine a state of charge having the reference resistance value in the internal resistance profile for each charging current as a limit state of charge.

[0026] [Formula 1] Internal resistance value (R SOCx )=(V c -V ref ) / I C

[0027] (In the above formula 1, Ic means the current value applied for each charging current)

[0028] In an embodiment of the present invention, when the graph shape of the internal resistance profile for each charging current is assumed to be a "W" shape, the control unit may determine a second inflection point as the inflection point.

[0029] A battery management system according to one embodiment of the present invention may further include a connection unit configured to be connected to a charging unit that can supply a charging current to the battery cell according to a charging protocol established by the control unit.

[0030] According to another embodiment of the present invention, there is provided a battery pack, the battery pack including the battery management system described above.

[0031] According to another embodiment of the present invention, a battery cell charging device is provided, the battery cell charging device including the battery management system and a charging unit configured to supply a charging current to the battery cell according to a charging protocol created to reflect a limit state of charge for each charging current. Effect of the Invention

[0032] The charging protocol setting method, battery management system, and charging device equipped with the same according to the present invention have the effect of providing a charging protocol that immediately reflects the resistance and heat generated from a large-capacity battery cell, without the need to manufacture three-electrode cells, which are complicated to manufacture. [Brief description of the drawings]

[0033] [Figure 1] 4 is a flowchart illustrating a method for establishing a charging protocol according to an embodiment of the present invention. [Diagram 2] 1 is a graph showing an internal resistance profile according to a charging current collected according to an embodiment of the present invention. [Diagram 3] 1 is a diagram illustrating an example of a configuration of a battery pack including a battery management system according to an embodiment of the present invention. [Figure 4] 1 is a diagram illustrating a battery pack including a battery management system according to an embodiment of the present invention. [Diagram 5] 1 is a block diagram of a battery cell charging device according to an embodiment of the present invention; [Figure 6] 1 is a graph showing limiting states of charge for different charging currents derived from Example 1 and Comparative Examples 1 and 2. [Figure 7] 1 is a graph showing the results of measuring an open circuit voltage according to a state of charge in Experimental Example 1. [Figure 8] 1 is a graph showing an internal resistance profile for each charging current derived in Example 2. [Figure 9] 9 is a graph showing results for some of the charging currents in FIG. 8. [Figure 10]13 is a graph showing an internal resistance profile according to a charging current derived from Example 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] The terms and words used in this specification and the claims should not be interpreted 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 the terms in order to best describe his own invention.

[0035] Therefore, the embodiment described in this specification and the configurations shown in the drawings are merely the most preferred embodiment of the present invention and do not represent the entire technical idea of ​​the present invention, and there may be various equivalents and modifications that can replace them at the time of this application.

[0036] In addition, in the description of the present invention, if it is determined that a specific description of related publicly known configurations 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 to exclude other elements, but means that it may further include other elements, unless specifically stated to the contrary.

[0038] Furthermore, the term "controller" or the like used in the specification means a unit that processes at least one function or operation, and may be embodied in hardware, software, or a combination of hardware and software.

[0039] Furthermore, throughout this specification, when a part is said to be "connected" to another part, this includes not only the case where the part is "directly connected" to another part, but also the case where the part is "indirectly connected" through another element between them.

[0040] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0041] FIG. 1 is a flowchart of a method for establishing a charging protocol for a lithium secondary battery according to one embodiment of the present invention.

[0042] Referring to FIG. 1, a method for establishing a charging protocol according to an embodiment of the present invention includes: (a) determining a state of charge (SOC) when a two-electrode battery cell having a positive electrode and a negative electrode is charged with a reference current; x ) according to the open circuit voltage (V ref ) and (b) When the battery cell is charged with different charging currents, the state of charge (SOC) x ) according to the open circuit voltage (V c ) and (c) The above measured value V is calculated using the following formula 1. ref , V c By substituting the above, the state of charge (SOC x ) according to the internal resistance (R SOCx ) and calculate the state of charge (SOC) for each charging current. x ) according to the internal resistance (R SOCx ) to collect an internal resistance profile; (d) In the internal resistance profile by charging current collected above, the internal resistance value (R SOCx determining the lowest resistance value among the inflection points for each charging current as a reference resistance value, and then determining a state of charge having the reference resistance value in the internal resistance profile for each charging current as a limit state of charge.

[0043] [Formula 1] Internal resistance value (R SOCx )=(V c -V ref ) / I C

[0044] (In the above formula 1, Ic means the current value applied for each charging current)

[0045] The method for establishing a charging protocol for a lithium secondary battery according to the present invention introduces the concept of internal resistance for each charging current to reflect the resistance and heat generation of a large-capacity battery cell. In the present invention, such internal resistance is determined based on the state of charge (SOC x ) is defined as the resistance to the overvoltage that occurs during charging divided by the applied current.

[0046] When measuring the open circuit voltage according to the charging state while performing fast charging and slow charging, the open circuit voltage (V c ) is the open circuit voltage (V ref ), but the present invention is based on the open circuit voltage difference (V c -V ref The internal resistance was defined as the value obtained by dividing the resistance by the applied current (Ic).

[0047] The inventors of the present invention analyzed an internal resistance profile in which internal resistance values ​​according to the state of charge for each charging current (Ic) were plotted. As a result, the internal resistance profile for each charging current (Ic) generally has a graph shape in which the internal resistance value changes from a decreasing trend to an increasing trend in the initial state of charge section, and then decreases again and then increases. Among the inflection points where the trend changes from an increasing trend to a decreasing trend, the state of charge showing the reference resistance value having the lowest resistance value was determined as the limit state of charge. The inventors discovered that the limit state of charge for each charging current reflects the resistance and heat generation state of a large-capacity battery cell and appears at a similar level in battery cells with the same capacity even if the manufacturing history (footprint) is different, which led to the present invention.

[0048] That is, when the manufacturing history of the battery cells is different, the reference resistance values ​​of the battery cells may appear differently, but the limit state of charge for each charging current having the reference resistance value is at a similar level, so that the method of establishing a charging protocol of the present invention has an effect of providing a method of establishing a same reference charging protocol despite the deviation between the battery cells. Also, the limit state of charge reflecting the capacity and internal resistance of the battery cell for each charging current can be derived from the reference resistance value.

[0049] In the present invention, the battery cell means a two-electrode battery cell having a negative electrode and a positive electrode, and is one independent cell that can be physically separated. As an example, one pouch-type lithium polymer cell can be regarded as the battery cell 10. The battery cell can be a large-capacity battery cell having a capacity of 40 to 200 Ah.

[0050] The positive electrode active material constituting the positive electrode of the battery cell 10 may be a lithium-containing transition metal oxide. For example, LiCoC2, LiNiO2, LiMnO2, LiMn2O4, Li(Ni a Co b Mn c )O2(0 <a<1、0<b<1、0<c<1、a+b+c=1)、Li x (Ni a Co b Mn c Al d )O2(0.5 <x<1.3、0.6<a<1、0<b<0.2、0<c<0.1、0<d<0.1、a+b+c+d=1)、LiNi 1-y Co y O2, LiCo 1-y Mn y O2, LiNi 1-y Mn y O2(0≦y<1), Li(Ni a Co b Mn c )O4(0 <a<2、0<b<2、0<c<2、a+b+c=2)、LiMn 2-z Ni z O4, LiMn 2-z Co zO4 (0 < z < 2), LiCoPO4, LiFePO4, or two or more of these may be used. In addition to such oxides, sulfides, selenides, and halides can be mentioned.

[0051] As the negative electrode active material constituting the negative electrode, carbon-based materials such as graphite or activated carbon, or substances such as silicon oxide (SiO x ) are used.

[0052] In the case of a negative electrode active material using a carbon-based material, the potential is very low, about the same as that of Li, and lithium plating (Li-plating), which forms a metallic plating film due to the characteristics of lithium ions at the negative electrode due to an increase in resistance or an increase in current, occurs. Therefore, a safe charging protocol is established in a method of determining the charging state at which lithium plating occurs at the negative electrode as the limiting charging state.

[0053] The method for establishing the rapid charging protocol of the present invention is to first obtain each internal resistance profile for each charging current, then analyze the internal resistance profile to determine a reference resistance value, and determine the charging state indicating the reference resistance value in the internal resistance profile as the limiting charging state in order to determine the limiting charging state for each charging current. Here, the internal resistance profile for each charging current can be obtained through the above processes (a) to (c).

[0054] The above processes (a) and (b) are processes of obtaining the open circuit voltage according to the charging state while charging the battery cell for each charging current of various numerical values for calculating the internal resistance value defined by the present invention.

[0055] As described above, the internal resistance value in the present invention is a value obtained by dividing the overvoltage applied at the charging state by the current, and the overvoltage is the difference in the open circuit voltage due to the difference between the reference current and the charging current.

[0056] In the above step (a), the battery cell is charged with a reference current, which is a relatively low charging current serving as a reference, and the state of charge (SOC x ) according to the open circuit voltage (V ref In the present specification, the current applied in the above process (a) is defined as a reference current. The charging current value of the reference current may be 0.25C to 0.4C. More specifically, the charging current may be 0.25C to 0.33C.

[0057] In the above step (b), the battery cell is charged with a charging current that is relatively higher than the reference current, and the state of charge (SOC x ) according to the open circuit voltage (V c In the present invention, the state of charge (SOC) is measured by applying various charging currents during charging of the battery cell. x ) according to the open circuit voltage (V c The process of measuring the charge current is repeated for each charge current.

[0058] In one specific example, the charging current applied in the step (b) may be selected from a range of 0.2C to 6C, more specifically, from a range of 0.33C to 6C. For example, the charging current may be selected from a range of 0.5C to 3.0C at intervals of 0.25C. In this case, charging is performed at each of the charging currents of 0.5C, 0.75C, 1.0C, 1.25C, 1.5C, 1.75C, 2.0C, 2.25C, 2.5C, 2.75C, and 3.0C, and the state of charge (SOC) is measured at each charging current. x ) according to the open circuit voltage (V c ) may be included in the process.

[0059] During the charging process for one charging current value, the battery cells to be charged are those with a state of charge of 0% to 5% (SOC 0% to 5%), which is close to a fully discharged state, and are charged until the battery cell reaches SOC 50% to 100% (SOC x ) according to the open circuit voltage (V c) is measured. This process is then repeated for each charging current.

[0060] At this time, the charging current is applied by increasing the charging current value stepwise from low to high. For example, when the charging current is set to 0.5C, 0.75C, 1.0C, 1.25C, 1.5C, 1.75C, 2.0C, 2.25C, 2.5C, 2.75C, and 3.0C, the open circuit voltage corresponding to the charging state is repeatedly measured while applying the charging current in the above-mentioned order. That is, after performing the process of measuring the open circuit voltage corresponding to the charging state with a charging current of 0.5C, the battery cell is discharged, and then the open circuit voltage corresponding to the charging state is measured with a charging current of 0.75C. This process is repeated for each of 1.0C, 1.25C, 1.5C, 1.75C, 2.0C, 2.25C, 2.5C, 2.75C, and 3.0C.

[0061] In one specific example, the above step (b) calculates the state of charge (SOC) according to the charging current. x ) according to the open circuit voltage (V c The method may further include a step of performing charge / discharge compensation between each step of measuring the current (a), and the charge / discharge compensation step may include a step of discharging with the reference current of the step (a) and charging and discharging with the reference current again.

[0062] This charge / discharge compensation process has the effect of removing the influence accumulated on the battery cell due to the previous charging experiment.

[0063] The above steps (a) and (b) will now be described with reference to specific embodiments.

[0064] In the above step (a), the reference current is set to 0.33C for a battery cell with a SOC of 0%, and a charging current of 0.33C is applied. The open circuit voltage (V ref ) is measured at each open circuit voltage (V ref ) is measured.

[0065] In the above step (b), the charging current value is set in the range of 0.5C to 3.0C at intervals of 0.25C, and the state of charge (SOC) is measured while applying the set charging current to the battery cell as in the above step (a). x ) according to the open circuit voltage (V c ) is measured.

[0066] Specifically, the battery cell charged at 0.33C according to the above process (a) is discharged to a level of SOC0% with a discharge current of 0.33C, and then the battery cell is charged to a level of SOC100% while applying a charge current of 0.5C, which is the lowest charge current value, according to the above process (b). While charging the battery cell in this manner, the open circuit voltage (V c In this way, the open circuit voltage (V c After the process of measuring the capacitance, the battery is discharged at 0.33C, and then a charge / discharge compensation process is performed in which the battery is charged and discharged at 0.33C.

[0067] After that, the above process is repeated for a charging current of 0.75C, which is higher than the 0.5C, and then the charging current is increased stepwise to obtain the state of charge (SOC x ) according to the open circuit voltage (V c ) is measured.

[0068] The above step (c) is performed by adding the measured value V measured through steps (a) and (b) in the above formula 1. ref , V c Substituting the above, the state of charge (SOC x ) according to the internal resistance (R SOCx ) and calculate the state of charge (SOC) for each charging current. x This is a process of collecting an internal resistance profile by plotting the internal resistance value according to the temperature.

[0069] 2 is a diagram showing an internal resistance profile for each charging current collected by the above (c) process according to an embodiment of the present invention. The open circuit voltage corresponding to the state of charge for each charging current (1.5C, 2.0C, 2.5C, 2.75C, 3C) is measured by the above (b) process, and the measured open circuit voltage value is substituted into the above Equation 1 by the above (c) process to calculate the internal resistance value corresponding to the state of charge for each charging current, and the state of charge is plotted on the x-axis and the internal resistance value on the y-axis, thereby obtaining an internal resistance profile in which the internal resistance value corresponding to the state of charge is plotted as shown in FIG. 2.

[0070] The above step (d) is a step of analyzing the internal resistance profile for each charging current shown in FIG. 2 to determine a reference resistance value and a limit state of charge for each charging current.

[0071] Referring to FIG. 2, the state of charge (SOC x ) according to the internal resistance (R SOCx ) shows a decreasing trend in the initial charging state section, then changes to an increasing trend, then decreases again, then changes to an increasing trend. 。

[0072] Specifically, in the internal resistance profile of a charging current of 1.5C, a first inflection point appears where the internal resistance value changes from a decreasing trend to an increasing trend at a charging state where the SOC is about 30%, and a second inflection point appears where the internal resistance value changes from an increasing trend to a decreasing trend at a charging state where the SOC is about 55%. In each internal resistance profile of charging currents of 2.0C to 3C, a second inflection point where the internal resistance value changes from an increasing trend to a decreasing trend as the charging state increases is also observed. In the present invention, the smallest resistance value among the internal resistance values ​​at the second inflection point is determined as the reference resistance value.

[0073] 2, the internal resistance value of the second inflection point in the internal resistance profile of the charging current of 1.5 C is about 3.67 mΩ, the internal resistance value of the second inflection point in the internal resistance profile of the charging current of 2.0 C is about 3.67 mΩ, the internal resistance value of the second inflection point in the internal resistance profile of the charging current of 2.5 C is about 3.71 mΩ, the internal resistance value of the second inflection point in the internal resistance profile of the charging current of 2.75 C is about 4.0 mΩ, and the internal resistance value of the second inflection point in the internal resistance profile of the charging current of 3.0 C is about 4.25 mΩ. Therefore, the reference resistance value of the battery cell having the internal resistance profile of FIG. 2 is determined to be 3.67 mΩ, which is the smallest of these internal resistance values.

[0074] In this way, the above process (d) is carried out to obtain the internal resistance value (R SOCx Each inflection point where the resistance value changes from an increasing trend to a decreasing trend is identified, and the smallest resistance value among the inflection points for each charging current is determined as the reference resistance value.

[0075] After the reference resistance value is determined, the state of charge having the reference resistance value in the profile for each charging current is determined as the limit state of charge. Referring to FIG. 2, a dotted line having an internal resistance value of 3.67 mΩ is drawn parallel to the x-axis on the graph showing the internal resistance profile, and the x-axis value at the point where the dotted line intersects with the internal resistance profile may be determined as the limit state of charge. More specifically, since the x-axis coordinate of the point where the internal resistance profile for a 3.0C charging current intersects with the dotted line is about SOC 38%, the limit state of charge corresponding to the 3.0C charging current is determined as about SOC 38%.

[0076] As described above, in the internal resistance profile for each charging current, the SOC on the x-axis coordinate of the point where the y-axis coordinate has the reference resistance value is determined as the limiting state of charge for that charging current. When the limiting state of charge for each charging current of 2.75C to 1.5C is determined in this manner, the limiting state of charge for the charging current of 2.75C is about SOC 41%, the limiting state of charge for the charging current of 2.5C is about SOC 45%, the limiting state of charge for the charging current of 2.0C is about SOC 55%, and the limiting state of charge for the charging current of 1.5C is about SOC 55%.

[0077] In one specific example, the inflection point may be a second inflection point when the graph shape of the internal resistance profile for each charging current is assumed to be a "W" shape. In one embodiment, the second inflection point may be located within a range where the state of charge is SOC 40% to SOC 60%.

[0078] In one embodiment, the method for establishing a charging protocol according to the present invention may further include mapping a charging protocol based on a limit state of charge for each charging current.

[0079] In one embodiment, the mapping process may be performed such that, for each charging current, charging is performed at the corresponding charging current until the charging current reaches a limit state of charge or less, and the charging current decreases as the state of charge increases.

[0080] Referring to FIG. 2, the limit state of charge for a charging current of 3.0C is approximately SOC 38%, for a charging current of 2.75C is approximately SOC 41%, for a charging current of 2.5C is approximately SOC 45%, for a charging current of 2.0C is approximately SOC 55%, and for a charging current of 1.5C is approximately SOC 55%. Based on this, one embodiment of a charging protocol mapped thereto may be as follows:

[0081] SOC0%~SOC38% charge state range: 3.0C

[0082] SOC38%~SOC41% charge state range: 2.75C

[0083] SOC41%~SOC45% charge state range: 2.5C

[0084] SOC45%~SOC55% charge state range: 2.0C

[0085] However, the charging protocol mapped according to the present invention is not limited thereto. The charging protocol according to another embodiment may be as follows.

[0086] SOC0%~SOC35% charge state range: 3.0C

[0087] SOC35%~SOC45% charge range: 2.5C

[0088] SOC45%~SOC55% charge state range: 1.5C

[0089] In one embodiment, the mapping process may be mapping to a charge state interval of 55% or less.

[0090] According to an exemplary embodiment of the present invention, the reference resistance value appears in the state of charge range of SOC 50% to SOC 60%, specifically in the state of charge range of SOC 50% to SOC 55%, so that in the state of charge range of SOC 60% or less, specifically in the state of charge range of SOC 55% or less, a charging protocol can be established according to the present invention. In the case of a state of charge range beyond the above range, charging can be performed according to a referable conventional charging protocol, or a charging protocol derived using a conventional three-electrode cell can be referred to.

[0091] In the conventional method of establishing a charging protocol, a three-electrode cell with a capacity of 50 mAh was manufactured in advance to derive the limit state of charge, and the lithium plating point according to the negative electrode potential was derived as the limit state of charge. However, the present invention does not require the manufacture of a three-electrode cell, and can immediately derive the limit state of charge for a large-capacity two-electrode battery cell with a capacity of 40 to 200 Ah by calculating the internal resistance value.

[0092] FIG. 3 is a diagram illustrating an exemplary configuration of a battery pack including a battery management system according to one embodiment of the present invention, and FIG. 4 is a diagram illustrating a battery pack including a battery management system according to one embodiment of the present invention.

[0093] 3, the battery pack 1 may include a battery cell 10 and a battery management system 100. The battery management system 100 is a battery management system that monitors the voltage, current, temperature, etc. of the battery cell 10 and controls and manages the battery cell 10 to prevent overcharging, overdischarging, etc.

[0094] Here, the battery cell 10 means a two-electrode battery cell having a negative electrode and a positive electrode, and is an independent cell that can be physically separated. As an example, one pouch-type lithium polymer cell can be regarded as the battery cell 10. The battery cell 10 can be a large-capacity battery cell having a capacity of 40 to 200 Ah.

[0095] The battery pack 1 may also include a battery module having one or more battery cells 10 connected in series and / or parallel.

[0096] Referring to FIG. 3, the battery management system according to the present invention may include a voltage measurement unit 110, a memory unit 120, and a control unit .

[0097] The voltage measurement unit 110 is configured to measure state information of the battery cell 10, including at least one of the voltage and the state of charge. The voltage measurement unit 110 according to the embodiment of the present invention measures the state of charge (SOC) when the battery cell is charged with a reference current and various charging currents in order to calculate the internal resistance of the two-electrode battery cell 10 having a positive electrode and a negative electrode. x ) according to the open circuit voltage (V ref , V c ) is configured to measure

[0098] In one specific example, the voltage measurement unit 110 measures the state of charge (SOC) when a reference current is applied to the battery cell 10. x ) according to the open circuit voltage (V ref ) and measure the state of charge (SOC) when various values ​​of charging current (Ic) set at intervals of 0.25C, such as 0.25C-0.5C-0.75C...-2.75C-3.0C, are applied to the battery cell 10. x ) according to the open circuit voltage (V c ) can be configured to measure the open circuit voltage (V c ) may be measured at SOC 2.5% intervals, SOC 5% intervals, or SOC 10% intervals.

[0099] The memory unit 120 calculates the measured value V ref , V c Substituting the above, the state of charge (SOC x ) according to the internal resistance (R SOCx ) and calculate the state of charge (SOC) for each charging current. x ) according to the internal resistance (R SOCx ) to collect an internal resistance profile.

[0100] [Formula 1] Internal resistance value (R SOCx )=(V c -V ref ) / I C

[0101] (In the above formula 1, Ic means the current value applied for each charging current)

[0102] The control unit 130 determines the internal resistance value (R SOCx The method is configured to check each inflection point where the internal resistance changes from an increasing trend to a decreasing trend, determine the lowest resistance value among the inflection points as a reference resistance value, and then determine a state of charge having the reference resistance value in an internal resistance profile for each charging current as a limit state of charge.

[0103] In one specific example, when the graph shape of the internal resistance profile for each charging current is assumed to be a "W" shape, the control unit 130 may determine a second inflection point as the inflection point.

[0104] In the embodiment of FIG. 2, the battery management system 100 of the present invention may further include a connection unit 140 configured to be connected to a charging unit 200 that may supply a charging current to the battery cells according to a charging protocol established by the control unit.

[0105] The charging unit 200 may be connected to the battery pack 1. Then, the charging unit 200 connected to the battery pack 1 may supply a charging current to the battery cell 10 according to a charging protocol established by the control unit.

[0106] The battery management system 100 may control the operation of a switching unit (SW) to control charging and discharging of the battery cells 10 or / and the battery module.

[0107] The battery management system according to the present invention has an advantage that the measurement unit, memory unit and control unit can charge the battery cells according to a charging protocol that reflects the resistance of the large-capacity battery cells and the heat generated by rapid charging.

[0108] 5 is a block diagram of a battery cell charging device according to an embodiment of the present invention. Referring to FIG. 5, the battery cell charging device 1000 according to the present invention includes a battery management system 1100 and a charging unit 1300 configured to supply a charging current to the battery cell according to a charging protocol created by reflecting the limit state of charge for each charging current.

[0109] The battery management system 1100 may include a voltage measurement unit 1110, a memory unit 1120, and a control unit 1130. The voltage measurement unit 1110, the memory unit 1120, and the control unit 1130 have been described in detail above, and therefore will not be described in detail again.

[0110] The charging unit 1300 is configured to supply a charging current to the battery cell 10 according to a charging protocol established by the control unit 1130.

[0111] Hereinafter, the battery management system and the method for establishing a charging protocol according to the present invention, which derive a limiting state of charge corresponding to a charging current and establish a charging protocol, will be described in detail with specific examples.

[0112] <Example 1>

[0113] While charging a battery cell with a capacity of 40 Ah and SOC 0% with a charging current of 0.33 C, the voltage measurement unit measures the open circuit voltage (V ref ) is measured and the memory unit stores it.

[0114] Thereafter, the control unit controls the charge / discharge unit to discharge the battery cell with a discharge current of 0.33 C and then to apply a charge current of 1.5 C to the discharged battery cell. The voltage measurement unit measures the open circuit voltage (V c ) and the memory unit stores it. Then, the control unit controls the charge / discharge unit to discharge the charged battery cell with a discharge current of 0.33C and to charge and discharge the battery cell with a discharge current of 0.33C.

[0115] The control unit repeats the above procedure with different charging current values ​​and controls the charge / discharge unit to increase the applied charging current stepwise, such as 1.5C-2.0C-2.5C-2.75C-3.0C. The voltage measurement unit measures the state of charge (SOC) for each charging current as described above.x ) according to the open circuit voltage (V c ) is measured and the memory unit stores it.

[0116] The battery cells were charged and discharged in a chamber set at 25 degrees Celsius.

[0117] The memory section also calculates the measured value V ref , V c Substituting the above, the state of charge (SOC x ) according to the internal resistance (R SOCx ) and calculate the state of charge (SOC) for each charging current. x ) according to the internal resistance (R SOCx ) was plotted to collect the internal resistance profile, and the results are shown in Figure 2.

[0118] [Formula 1] Internal resistance value (R SOCx )=(V c -V ref ) / I C

[0119] (In the above formula 1, Ic means the current value applied for each charging current)

[0120] The control unit determines the internal resistance value (R SOCx ) was confirmed, and the lowest resistance value (3.67 mΩ) among the inflection points for each charging current was determined as the reference resistance value. Then, the state of charge having the reference resistance value in the profile for each charging current was determined as the limit state of charge, which is shown in Table 1 and FIG. 6.

[0121] [Table 1]

[0122] <Comparative Example 1>

[0123] Using a three-electrode cell, which is the conventional method for establishing a charging protocol, charging and discharging were performed at a temperature of 25 degrees Celsius, and the limiting state of charge was derived for each charging current, and the charging protocol established based on this is shown in Figure 6. The limiting state of charge was determined by measuring the negative electrode potential (CCV) according to the state of charge (SOC) of the three-electrode cell while charging a 50mAh mono cell with a charging current set at 0.25C intervals in the range of 1.0C to 2.75C, and the state of charge at the point where the negative electrode potential does not decrease and begins to become constant.

[0124] <Comparative Example 2>

[0125] The limit state of charge for each charging current was determined in the same manner as in Comparative Example 1, except that the temperature was set to 35° C. in Comparative Example 1, and the results are shown in FIG.

[0126] 6, it can be seen that the limit state of charge value for each charging current derived from Example 1 is very similar to the limit state of charge value for each charging current derived from Comparative Example 2. This confirms that the limit state of charge derived according to the method for establishing a charging protocol of the present invention can reflect the resistance and heat generation of a large-capacity battery cell.

[0127] <Experimental Example 1>

[0128] The battery cell used in Example 1 (Production Example 1) and a battery cell (Production Example 2) in which the composition of the negative electrode in the battery cell of Production Example 1 was changed so as to have excellent quick charging capability were prepared.

[0129] A limiting state of charge for each charging current was derived and a charging protocol was established for the battery cells of Manufacturing Example 1 and Manufacturing Example 2 in the same manner as in Example 1. As a result, a charging protocol (first charging protocol) taking 28.4 minutes for charging was established for the battery cell of Manufacturing Example 1, and a charging protocol (second charging protocol) taking 21.7 minutes for charging was established for the battery cell of Manufacturing Example 2.

[0130] The battery cell of Manufacturing Example 1 was charged according to the first charging protocol, and the open circuit voltage was measured according to the state of charge, and the results are shown in Figure 7. The battery cell of Manufacturing Example 2 was also charged according to the second charging protocol, and the open circuit voltage was measured according to the state of charge, and the results are shown in Figure 7.

[0131] 7, it can be seen that the battery cell of Manufacturing Example 1 and the battery cell of Manufacturing Example 2 show similar voltage profiles. This shows that the method for establishing a charging protocol according to the present invention has the effect of enabling the establishment of a protocol using a similar state of charge for battery cells having different electrode compositions.

[0132] <Example 2>

[0133] The battery cell has a capacity of 40 Ah, and has a different electrode composition and manufacturing history from those in Example 1. The battery cell has an SOC of 0%. While charging the battery cell with a charging current of 0.33 C, the voltage measuring unit measures the open circuit voltage (V ref ) is measured and the memory unit stores it.

[0134] Thereafter, the control unit controls the charge / discharge unit to discharge the battery cell with a discharge current of 0.33 C, and then to apply a charge current of 0.5 C to the discharged battery cell. The voltage measurement unit measures the open circuit voltage (V c ) and the memory unit stores it. Then, the control unit controls the charge / discharge unit to discharge the charged battery cell with a discharge current of 0.33C and to charge and discharge the battery cell with a discharge current of 0.33C.

[0135] The control unit repeats the above process with different charging current values ​​and controls the charge / discharge unit to increase the applied charging current stepwise, such as 0.75C-1.0C-1.25C-1.5C-2.0C-2.25C-2.5C-2.75C-3.0C. The voltage measurement unit measures the state of charge (SOC) for each charging current as described above. x ) according to the open circuit voltage (V c ) is measured and the memory unit stores it.

[0136] The memory section also calculates the measured value V ref , V c Substituting the above, the state of charge (SOC x ) according to the internal resistance (R SOCx ) and calculate the state of charge (SOC) for each charging current. x ) according to the internal resistance (R SOCx ) to collect the internal resistance profile.

[0137] [Formula 1] Internal resistance value (R SOCx )=(V c -V ref ) / I C

[0138] (In the above formula 1, Ic means the current value applied for each charging current)

[0139] The results are shown in Figures 8 and 9. The control unit then calculates the internal resistance (R SOCx The inflection points at which the resistance value changes from an increasing trend to a decreasing trend were identified, and the lowest resistance value among the inflection points was determined as the reference resistance value. As a result, the reference resistance value was confirmed to be 4.00 mΩ.

[0140] <Example 3>

[0141] A battery cell having a capacity of 40 Ah and of the same model as in Example 2 was prepared, and the internal resistance (R SOCx) was calculated, and an internal resistance profile was collected for each charging current. The results are shown in FIG. 10. Then, in the internal resistance profile shown in FIG. 10, a reference resistance value was determined in the same manner as in Example 2. As a result, it was confirmed that the reference resistance value was 4.24 mΩ.

[0142] 8 to 10, it can be seen that although the reference resistance values ​​confirmed in Example 2 and Example 3 are different, the limit state of charge for each charging current is at a similar level. Thus, the method for establishing a charging protocol according to the present invention can confirm that the limit state of charge for each charging current is similar even when the reference resistance values ​​are different, and thus has the effect of providing the same reference charging protocol despite the deviation of the battery cells.

[0143] <Example 4>

[0144] A battery cell (capacity: 40 Ah) having the same specifications as the battery cell used in Example 1 was connected to an electrochemical charger / discharger. A charge / discharge protocol was mapped as shown in Table 2 below based on the limit state of charge for each charge current listed in Table 1 of Example 1. The battery cell was fully charged to SOC 100% according to the mapped charge / discharge protocol, and then the fully charged battery cell was fully discharged to SOC 0% at a constant current of 0.33 C.

[0145] [Table 2]

[0146] <Comparative Example 3>

[0147] A battery cell (capacity: 40 Ah) having the same specifications as the battery cell used in Example 1 was connected to an electrochemical charger / discharger. After being fully charged to SOC 100% at a constant current of 0.33 C, the fully charged battery cell was fully discharged to SOC 0% at a constant current of 0.33 C.

[0148] <Experimental Example 2: Measurement of charge / discharge time>

[0149] The time required for charging was measured for each of the cases where charging was performed according to the method of Example 4 and the method of Comparative Example 3. The results are shown in Table 3.

[0150] <Experimental Example 3: Evaluation of Capacity Retention Rate>

[0151] The batteries were charged and discharged according to the methods of Example 4 and Comparative Example 3, and after 200 cycles of charging and discharging, the capacity retention rates calculated according to the following formula 1 are shown in Table 3.

[0152] Equation 1: (Discharge capacity at 200 cycles x 100) / Discharge capacity at first cycle

[0153] [Table 3]

[0154] Referring to Table 3, the time required for charging according to the charging protocol of Example 4 was significantly reduced compared to the time required for charging according to the charging method of Comparative Example 3. In addition, the capacity maintenance rate when charging according to the charging protocol of Example 4 is at the same level as the capacity maintenance rate when charging according to the charging method of Comparative Example 3, and it can be confirmed that the charging protocol derived according to the present invention does not cause capacity degradation of the battery cell. [Explanation of symbols]

[0155] 1: Battery pack 10: Battery cell 100: Battery Management System 110: Voltage measurement unit 120: Memory section 130: Control unit 200: Charging part

Claims

1. (a) State of charge (SOC) when a two-electrode battery cell having a positive electrode and a negative electrode is charged at a reference current. ｘ ) depending on the open circuit voltage (V ｒｅｆ ) measuring the (b) When the battery cell is charged with different charging currents, the state of charge (SOC) ｘ ) depending on the open circuit voltage (V ｃ ) measuring the (c) The measured value V ｒｅｆ , V ｃ By substituting the above, the state of charge (SOC) for each charging current is calculated. ｘ The internal resistance value (R ＳＯＣｘ ) and calculate the state of charge (SOC) for each charging current. ｘ collecting an internal resistance profile by plotting the internal resistance as a function of the (d) In the collected internal resistance profile for each charging current, the internal resistance value (R ＳＯＣｘ determining the lowest resistance value among the inflection points for each charging current as a reference resistance value, and then determining a state of charge having the reference resistance value in an internal resistance profile for each charging current as a limit state of charge. [Formula 1] Internal resistance value (R ＳＯＣｘ )=(V ｃ -V ｒｅｆ ) / Ic (In the above formula 1, Ic represents the current value applied for each charging current.)

2. 2. The method for establishing a charging protocol for a lithium secondary battery according to claim 1, wherein the inflection point is a second inflection point when the graph shape of the internal resistance profile for each charging current is assumed to be a "W" shape.

3. The method for establishing a charging protocol for a secondary battery according to claim 1 , wherein the inflection point is located within a range in which the state of charge is between SOC 40% and SOC 60%.

4. The method for establishing a charging protocol for a lithium secondary battery as claimed in claim 1, wherein the capacity of the two-electrode battery cell is 40-200 Ah.

5. 2. The method for establishing a charging protocol for a lithium secondary battery according to claim 1, wherein the reference current in step (a) is selected within a range of 0.25C to 0.4C.

6. The method for establishing a charging protocol for a lithium secondary battery according to claim 1, wherein the charging current in step (b) is selected from a plurality of values ​​within the range of 0.2 C to 6 C.

7. 2. The method of claim 1, wherein in step (b), a process of charging the discharged battery cell from SOC 50% to SOC 100% is repeated for each charging current.

8. 2. The method for establishing a charging protocol for a lithium secondary battery according to claim 1, wherein in step (b), the charging current is applied by increasing the charging current value stepwise from a low current to a high current.

9. The method further includes mapping a charging protocol based on a limiting state of charge for each charging current; 2. The method of claim 1, wherein the mapping step is performed such that the charging current is charged at the corresponding charging current until the charging current is equal to or lower than a limiting state of charge, and the charging current is decreased as the state of charge increases.

10. The mapping process includes: The method for establishing a charging protocol for a lithium secondary battery according to claim 9, wherein mapping is performed up to a charging state interval of SOC 55% or less.

11. The step (b) calculates the state of charge (SOC) for each charging current. ｘ ) depending on the open circuit voltage (V ｃ The method further includes a step of performing charge / discharge compensation between each step of measuring the current, 2. The method for establishing a charging protocol for a lithium secondary battery according to claim 1, wherein the charge / discharge compensation process comprises discharging at the reference current of the process (a), and then charging and discharging at the reference current again.

12. When a two-electrode battery cell having a positive electrode and a negative electrode is charged with a reference current and various charging currents, the state of charge (SOC ｘ ) depending on the open circuit voltage (V ｒｅｆ , V ｃ A voltage measurement unit configured to measure The measured value V ｒｅｆ , V ｃ Substituting the above, the state of charge (SOC ｘ The internal resistance value (R ＳＯＣｘ ) and calculate the state of charge (SOC) for each charging current. ｘ A memory unit configured to collect an internal resistance profile in which the internal resistance value is plotted according to the temperature of the sample. In the collected internal resistance profile for each charging current, the internal resistance value (R ＳＯＣｘ a control unit configured to check each inflection point where the internal resistance profile changes from an increasing trend to a decreasing trend, determine the lowest resistance value among the inflection points for each charging current as a reference resistance value, and then determine a state of charge having the reference resistance value in an internal resistance profile for each charging current as a limit state of charge. [Formula 1] Internal resistance value (R ＳＯＣｘ )=(V ｃ -V ｒｅｆ ) / Ic (In the above formula 1, Ic represents the current value applied for each charging current.)

13. The battery management system of claim 12 , wherein the control unit determines a second inflection point as the inflection point when a graph shape of the internal resistance profile for each charging current is assumed to be a “W” shape.

14. The battery management system according to claim 12 , further comprising a connection unit configured to be connected to a charging unit that supplies a charging current to the battery cells according to a charging protocol established by the control unit.

15. A battery pack comprising the battery management system of claim 12.

16. A battery management system according to claim 12; a charging unit configured to supply a charging current to the battery cell according to a charging protocol created to reflect the limit state of charge for each charging current.

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