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 based on 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, the demand for portable electronic products such as laptops and mobile phones has grown dramatically, along with the demand for electric carts, electric wheelchairs, and electric bicycles. This has led to active research into high-performance batteries that can be repeatedly charged and discharged. Furthermore, as carbon energy is gradually depleted and environmental concerns grow, demand for hybrid electric vehicles (HEVs) and electric vehicles (EVs) is gradually increasing worldwide. This has led to increased interest and research being focused on vehicle batteries, a core component of HEVs and EVs, and the development of fast-charging technology that can rapidly charge batteries is becoming increasingly urgent. Fast charging is a particularly important feature for EVs, which lack 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 battery performance and ultimately lead to complete failure or catastrophic failure such as leakage of highly corrosive chemicals or explosion.

[0005] In constant current charging of a battery, if the charging current rate is low, it takes a very long time to fully charge the battery. On the other hand, if the charging current rate is too high, it can cause the battery to deteriorate rapidly. Therefore, it is necessary to gradually adjust the charging current rate according to the battery condition during constant current charging.

[0006] To gradually adjust the current rate during constant-current charging, a charging map with a "multi-stage constant-current charging protocol" is primarily utilized. The charging map includes at least one data array that records the relationship between multiple current rates and multiple transition conditions. Each time a 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 is expressed in units of "C."

[0007] Previously, 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 on the negative electrode for each charging current was determined as the charging limit.

[0008] However, three-electrode cells are difficult to manufacture and require a dedicated charger / discharger for charging and discharging, which means there are many constraints, such as the manufacturing completion level of the three-electrode cell, the manufacturing time of the three-electrode cell, and the preparation of the dedicated charger / discharger.In addition, in the process of applying the limit state of charge confirmed with 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] Furthermore, when establishing a charging protocol using a three-electrode cell, the lithium plating zone becomes less clearly defined as the charging current decreases and the negative electrode composition becomes more favorable for fast charging, and the experimenter's subjectivity becomes an issue. This makes it difficult to establish a charging protocol that shows a similar voltage profile when there is a deviation in the battery cell.

[0010] Therefore, it is necessary to develop technology that derives 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-mentioned 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 that can establish 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, there is provided a method for establishing a charging protocol for a lithium secondary battery, the method comprising: (a) State of charge (SOC) when a two-electrode battery cell with a positive and negative electrode 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 cand calculate the state of charge (SOC) for each charging current. x ) according to the internal resistance (R SOCx ) and calculates the state of charge (SOC) for each charging current. x ) according to the internal resistance (R SOCx ) and collecting an internal resistance profile by plotting the (d) In the internal resistance profile for each charging current collected above, the internal resistance value (R SOCx and determining the lowest resistance value among the inflection points for each charging current as a reference resistance value, and then determining the 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 (R SOCx )=(V c -V ref ) / I C

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

[0015] In an embodiment of the present invention, the inflection point may be a second inflection point when the graph of the internal resistance profile for each charging current has 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 between 40% SOC and 60% SOC.

[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 the 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 step (b) can be selected from a plurality of values ​​within the range of 0.2C to 6C.

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

[0021] In one embodiment of the present invention, in the step (b), the charging current may be applied 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 mapping such that charging is performed at the corresponding charging current until the limit state of charge is reached, and the charging current decreases as the state of charge increases.

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

[0024] In one embodiment of the present invention, the step (b) is performed by calculating the state of charge (SOC) for each charging current. x ) according to the open circuit voltage (V c The method may further include a step of performing charge / discharge compensation between steps of measuring the reference current (a), and the charge / discharge compensation step may include discharging with the reference current of step (a) and then 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 configured to monitor a state of charge (SOC) of a two-electrode battery cell having a positive electrode and a negative electrode when the two-electrode battery cell is charged with a reference current and various charging currents. x ) according to the open circuit voltage (V ref , V c a voltage measurement unit configured to measure the The above measured value V is calculated using the following formula 1. ref , V c Substituting the state of charge (SOC x ) according to the internal resistance (R SOCx ) and calculates 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 according to the temperature is plotted; In the internal resistance profile for each 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 (R SOCx )=(V c -V ref ) / I C

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

[0028] In one embodiment of the present invention, when the graph shape of the internal resistance profile for each charging current is assumed to be "W" shaped, 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 cells 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 in accordance with a charging protocol created to reflect the limit state of charge for each charging current. [Effects 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 generation from a large-capacity battery cell, without the need to manufacture three-electrode cells, which are complicated to manufacture. [Brief explanation 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. [Figure 2] 1 is a graph showing internal resistance profiles according to charging currents collected according to an embodiment of the present invention. [Figure 3] 1 is a diagram illustrating an example configuration of a battery pack including a battery management system according to an embodiment of the present invention. [Figure 4] 1 is a diagram schematically illustrating a battery pack including a battery management system according to an embodiment of the present invention. [Figure 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 the open circuit voltage according to the state of charge in Experimental Example 1. [Figure 8] 10 is a graph showing internal resistance profiles for different charging currents derived in Example 2. [Figure 9] 9 is a graph showing results for some of the charging currents in FIG. 8. [Figure 10]10 is a graph showing an internal resistance profile according to a charging current derived from Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0034] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concepts of terms in order to best describe his own invention.

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

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

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

[0038] Furthermore, the term "controller" or the like used in the specification means a unit that processes at least one function or operation, and this 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 "directly connected" but also "indirectly connected" with another element in between.

[0040] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now 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 the state of charge (SOC) of a two-electrode battery cell having a positive electrode and a negative electrode when the two-electrode battery cell 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 and calculate the state of charge (SOC) for each charging current. x ) according to the internal resistance (R SOCx ) and calculates the state of charge (SOC) for each charging current. x ) according to the internal resistance (R SOCx ) and collecting an internal resistance profile by plotting the (d) In the internal resistance profile for each charging current collected above, the internal resistance value (R SOCx and determining the lowest resistance value among the inflection points for each charging current as a reference resistance value, and then determining the 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 (R SOCx )=(V c -V ref ) / I C

[0044] (In the above formula 1, Ic represents 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 by 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 difference in open circuit voltage (V c -V ref ) divided by the applied current (Ic) was defined as the internal resistance.

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

[0048] That is, since the reference resistance values ​​of the battery cells may differ depending on the manufacturing history of the battery cells, but the limit state of charge for each charging current having the reference resistance values ​​is at a similar level, the method for establishing a charging protocol of the present invention has the effect of providing a method for establishing a uniform reference charging protocol despite the deviations between the battery cells. Furthermore, the limit state of charge that reflects the capacity and internal resistance of the battery cell for each charging current can be derived using the reference resistance values.

[0049] In the present invention, the battery cell refers to a two-electrode battery cell having a negative electrode and a positive electrode, which is a physically separable independent cell. As an example, a pouch-type lithium polymer cell can be considered 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, halides, etc. may 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, similar to that of Li, and lithium plating occurs in the negative electrode to form a metal plating film due to the characteristics of lithium ions due to an increase in resistance or an increase in current. Therefore, a safe charging protocol is established by a method of determining the charging state at which lithium plating occurs in 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 in order to determine the limiting charging state for each charging current, then analyze the internal resistance profile to determine the reference resistance value, and determine the charging state indicating the reference resistance value in the internal resistance profile as the limiting charging state. 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 the 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, and the state of charge (SOC) is measured. x ) according to the open circuit voltage (V ref ) is a process of measuring the charging current. In this specification, the current applied in the process (a) is defined as a reference current. The charging current value of this reference current may be 0.25C to 0.4C. 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) is maintained. x ) according to the open circuit voltage (V c In the present invention, in charging a battery cell, various charging currents are applied to measure the state of charge (SOC). x ) according to the open circuit voltage (V c ) is measured for each charging 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, 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 measured.

[0059] During the charging process for one charging current value, the target battery cells 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 cells reach an SOC of 50% to 100%. x ) according to the open circuit voltage (V c) is measured. This process is then repeated for each charging current.

[0060] 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 0.5 C, 0.75 C, 1.0 C, 1.25 C, 1.5 C, 1.75 C, 2.0 C, 2.25 C, 2.5 C, 2.75 C, and 3.0 C, the open-circuit voltage corresponding to the state of charge is measured repeatedly while applying the charging current in the order listed above. That is, after measuring the open-circuit voltage corresponding to the state of charge with a charging current of 0.5 C, the battery cell is discharged and then the open-circuit voltage corresponding to the state of charge with a charging current of 0.75 C is measured. This process is repeated for each of the charging currents of 1.0 C, 1.25 C, 1.5 C, 1.75 C, 2.0 C, 2.25 C, 2.5 C, 2.75 C, and 3.0 C.

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

[0064] In the above step (a), the reference current is set to 0.33C for a battery cell with an SOC of 0%. A charging current of 0.33C is applied, and the open circuit voltage (V ref ) is measured at SOC 5%, SOC 10%... (omitted)... SOC 100%. ref ) is measured.

[0065] In the step (b), for example, a 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 step (a). x ) according to the open circuit voltage (V c ) is measured.

[0066] Specifically, the battery cell charged at 0.33C in step (a) is discharged to an SOC level of 0% with a discharge current of 0.33C, and then charged to an SOC level of 100% by applying the lowest charging current of 0.5C in step (b). While charging the battery cell in this manner, the open circuit voltage (V) is measured at each SOC 5% interval (SOC 5%, SOC 10%, ... SOC 100%). c ) is measured. In this way, the open circuit voltage (V c After the process of measuring the voltage Vcc is completed, a charge / discharge compensation process can be performed by discharging at 0.33C, and then charging and discharging at 0.33C.

[0067] After that, the same process is carried out for a charging current of 0.75C, which is higher than the 0.5C, and then the above process is repeated while gradually increasing the charging current value to measure 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) to the above equation 1. ref , V c Substituting the state of charge (SOC x ) according to the internal resistance (R SOCx ) and calculates the state of charge (SOC) for each charging current. x ) and collect 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 process (c) 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 process (b), and the measured open circuit voltage value is substituted into Equation 1 by the above process (c) to calculate the internal resistance corresponding to the state of charge for each charging current. 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 step (d) is a step of analyzing the internal resistance profile for each charging current shown in FIG. 2 and determining the reference resistance value and the limit state of charge for each charging current.

[0071] Referring to Figure 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, the internal resistance profile for a 1.5C charge current shows a first inflection point where the internal resistance changes from a decreasing trend to an increasing trend at a state of charge (SOC) of approximately 30%, and a second inflection point where the internal resistance changes from an increasing trend to a decreasing trend at a state of charge (SOC) of approximately 55%. Each internal resistance profile for a 2.0C to 3C charge current also shows a second inflection point where the internal resistance changes from an increasing trend to a decreasing trend as the state of charge increases. In the present invention, the smallest internal 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 at the second inflection point in the internal resistance profile for a charging current of 1.5 C is approximately 3.67 mΩ, the internal resistance value at the second inflection point in the internal resistance profile for a charging current of 2.0 C is approximately 3.67 mΩ, the internal resistance value at the second inflection point in the internal resistance profile for a charging current of 2.5 C is approximately 3.71 mΩ, the internal resistance value at the second inflection point in the internal resistance profile for a charging current of 2.75 C is approximately 4.0 mΩ, and the internal resistance value at the second inflection point in the internal resistance profile for a charging current of 3.0 C is approximately 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 performed to obtain the internal resistance value (R SOCx ) is checked, 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 corresponding to the reference resistance value in the charging current profile is determined as the limit state of charge. Referring to FIG. 2, a dotted line parallel to the x-axis with an internal resistance value of 3.67 mΩ can be drawn 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 can be determined as the limit state of charge. Specifically, since the x-axis coordinate at the point where the dotted line intersects with the internal resistance profile for a 3.0 C charging current is approximately SOC 38%, the limit state of charge corresponding to a 3.0 C charging current is determined as approximately SOC 38%.

[0076] As described above, in the internal resistance profile for each charging current, the SOC on the x-axis coordinate at 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 from 2.75C to 1.5C is determined in this manner, the limiting state of charge 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%.

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

[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 limiting 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 as follows may be as follows:

[0081] SOC 0% to SOC 38% charge range: 3.0C

[0082] SOC 38% to SOC 41% charge range: 2.75C

[0083] SOC 41% to SOC 45% charge range: 2.5C

[0084] SOC 45% to SOC 55% charge range: 2.0C

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

[0086] SOC 0% to SOC 35% charge range: 3.0C

[0087] SOC 35% to SOC 45% charge range: 2.5C

[0088] SOC 45% to SOC 55% charge range: 1.5C

[0089] In one embodiment, the mapping process may be mapping up to a charge state interval where the charge state is 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 a charging protocol can be established according to the present invention for a state of charge range of SOC 60% or less, specifically in the state of charge range of SOC 55% or less. For a state of charge range outside 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 referenced.

[0091] In the conventional method for 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 corresponding to the negative electrode potential was determined as the limit state of charge. However, the present invention does not require the manufacture of a three-electrode cell, and can directly 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 an embodiment of the present invention, and FIG. 4 is a diagram illustrating a battery pack including a battery management system according to an embodiment of the present invention.

[0093] 3, the battery pack 1 may include battery cells 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 cells 10 and controls and manages them to prevent overcharging, over-discharging, etc.

[0094] Here, the battery cell 10 refers to a two-electrode battery cell having a negative electrode and a positive electrode, and is a physically separable independent cell. As an example, a pouch-type lithium polymer cell can be considered 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 of the battery cell 10. 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 ) can 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 state of charge (SOC x ) according to the internal resistance (R SOCx ) and calculates 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 (R SOCx )=(V c -V ref ) / I C

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

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

[0103] In one specific example, when the graph shape of the internal resistance profile for each charging current is 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 can 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. 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 the switching unit (SW) to control the 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 heat generation due to rapid charging.

[0108] 5 is a block diagram of a battery cell charging device 1000 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 cells 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. Specific descriptions of the voltage measurement unit 1110, the memory unit 1120, and the control unit 1130 have been described in detail above, so further detailed descriptions will be omitted.

[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 40Ah and SOC 0% at a charging current of 0.33C, the voltage measurement unit measures the open circuit voltage (V) of the battery cell at SOC 2.5% intervals. ref ) is measured and stored in the memory unit.

[0114] Then, the control unit controls the charge / discharge unit to discharge the battery cell at a discharge current of 0.33 C and then apply a charge current of 1.5 C to the discharged battery cell. The voltage measurement unit measures the open circuit voltage (V) of the battery cell at an SOC 2.5% state of charge interval when the battery cell is charged at 1.5 C. c ) and the memory unit stores it. Then, the control unit controls the charge / discharge unit to discharge the charged battery cell at a discharge current of 0.33C and to charge and discharge at 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 stored in the memory unit.

[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 state of charge (SOC x ) according to the internal resistance (R SOCx ) and calculates 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 (R SOCx )=(V c -V ref ) / I C

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

[0120] The control unit calculates the internal resistance value (R SOCx The inflection points where the resistance value (3.67 mΩ) changes from an increasing trend to a decreasing trend were identified, and the lowest resistance value (3.67 mΩ) among the inflection points for each charging current was determined as the reference resistance value. The state of charge having the reference resistance value in the profile for each charging current was determined as the limiting 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°C, and the limiting state of charge (SOC) was derived for each charging current. 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 at a charging current set in 0.25C increments in the range of 1.0C to 2.75C, and determining the SOC at the point where the negative electrode potential no longer decreases and begins to stabilize.

[0124] <Comparative Example 2>

[0125] The limiting 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., and the results are shown in FIG.

[0126] 6, it can be seen that the limit state of charge values ​​for different charging currents derived in Example 1 are very similar to the limit state of charge values ​​for different charging currents derived in Comparative Example 2. This confirms that the limit state of charge derived in accordance with 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 to improve rapid charging capability were prepared.

[0129] The 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) was established for the battery cell of Manufacturing Example 1, which took 28.4 minutes to charge, and a charging protocol (second charging protocol) was established for the battery cell of Manufacturing Example 2, which took 21.7 minutes to charge.

[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 exhibit similar voltage profiles. This demonstrates that the method for establishing a charging protocol according to the present invention is effective in enabling the establishment of protocols that use similar states of charge for battery cells with different electrode compositions.

[0132] <Example 2>

[0133] A battery cell having a capacity of 40 Ah and different electrode composition and manufacturing history from those in Example 1 above, with an SOC of 0%, was charged at a charging current of 0.33 C. The voltage measurement unit measured the open circuit voltage (V ref ) is measured and stored in the memory unit.

[0134] Then, the control unit discharges the battery cell at a discharge current of 0.33 C, and then controls the charge / discharge unit to apply a charge current of 0.5 C to the discharged battery cell. The voltage measurement unit measures the open circuit voltage (V) of the battery cell every time the battery cell reaches a 2.5% state of charge when it is charged at 0.5 C. c ) and the memory unit stores it. Then, the control unit controls the charge / discharge unit to discharge the charged battery cell at a discharge current of 0.33C and to charge and discharge at 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 stored in the memory unit.

[0136] The memory section also calculates the measured value V ref , V c Substituting the state of charge (SOC x ) according to the internal resistance (R SOCx ) and calculates 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 (R SOCx )=(V c -V ref ) / I C

[0138] (In the above formula 1, Ic represents 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 where 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 the same model as in Example 2 was prepared, and the internal resistance (R SOCx) was calculated, and internal resistance profiles were collected for each charging current. The results are shown in FIG. 10. Then, for the internal resistance profile shown in FIG. 10, the reference resistance value was determined in the same manner as in Example 2. As a result, the reference resistance value was confirmed to be 4.24 mΩ.

[0142] 8 to 10, it can be seen that although the reference resistance values ​​confirmed in Examples 2 and 3 are different, the limit states of charge for each charging current are at similar levels. Therefore, the method for establishing a charging protocol according to the present invention can confirm that the limit states of charge for each charging current are similar even when the reference resistance values ​​are different, thereby providing the same standard charging protocol regardless of deviations 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 charging current listed in Table 1 of Example 1. The battery cell was fully charged to an SOC of 100% according to the mapped charge / discharge protocol, and then fully discharged to an SOC of 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 100% SOC at a constant current of 0.33 C, the fully charged battery cell was fully discharged to 0% SOC 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, and the results are shown in Table 3.

[0150] <Experimental Example 3: Evaluation of capacity retention rate>

[0151] After charging and discharging according to the methods of Example 4 and Comparative Example 3 and repeating 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 charging according to the charging method of Comparative Example 3. Furthermore, the capacity retention rate when charging according to the charging protocol of Example 4 was at the same level as the capacity retention 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 with a reference current. ｘ ) according to the open circuit voltage (V ｒｅｆ ) and (b) When the two-electrode battery cell is charged with different charging currents, the state of charge (SOC) during charging is measured at each charging current. ｘ ) according to the open circuit voltage (V ｃ ) and (c) The measured value V is calculated by the following formula 1: ｒｅｆ , and the measured value V ｃ Substituting the above, the state of charge (SOC) for each charging current is calculated. ｘ ) according to 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 value according to the (d) In the collected internal resistance profile for each charging current, the internal resistance value (R ＳＯＣｘ and determining the lowest resistance value among the inflection points for each charging current as a reference resistance value, and then determining the state of charge having the reference resistance value in the internal resistance profile for each charging current as a limiting 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 of the internal resistance profile for each charging current has 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 40% and 60% SOC.

4. 2. The method for establishing a charging protocol for a lithium secondary battery according to claim 1, wherein the capacity of the two-electrode battery cell is 40 to 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. 2. 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 step (b) is repeated for each charging current, charging the discharged battery cell until the SOC reaches 50% to 100%.

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 a mapping step of mapping a charging protocol based on a limit state of charge for each charging current, 2. The method of claim 1, wherein the mapping step is performed such that charging is performed at a 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.

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 charged state interval of SOC 55% or less.

11. The step (b) calculates the state of charge (SOC) for each charging current. ｘ ) according to the open circuit voltage (V ｃ ) measuring the charge and discharge compensation step, 2. The method for establishing a charging protocol for a lithium secondary battery according to claim 1, wherein the charge / discharge compensation step comprises discharging at the reference current of step (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 values ​​of charging current, the state of charge (SOC) ｘ ) according to the open circuit voltage (V ｒｅｆ , V ｃ a voltage measurement unit configured to measure the The measured value V is calculated by the following formula 1. ｒｅｆ , and the measured value V ｃ Substituting the state of charge (SOC ｘ ) according to 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; 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 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 ) / 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 the graph of the internal resistance profile for each charging current has a “W” shape.

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

15. A battery pack including 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 in accordance with a charging protocol created to reflect the limit state of charge for each charging current.

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