FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION (See section 10, rule 13) “METHOD FOR ESTABLISHING LITHIUM SECONDARY BATTERY CHARGING PROTOCOL, BATTERY MANAGEMENT SYSTEM, BATTERY PACK, AND BATTERY CELL CHARGING DEVICE” LG ENERGY SOLUTION, LTD., Tower1, 108, Yeouidaero, Yeongdeungpo-gu, Seoul 07335, Republic of Korea The following specification particularly describes the invention and the manner in which it is to be performed. 1 [Description] [Title of the Invention] METHOD FOR ESTABLISHING LITHIUM SECONDARY BATTERY CHARGING PROTOCOL, BATTERY MANAGEMENT SYSTEM, BATTERY PACK, 5 AND BATTERY CELL CHARGING DEVICE [Technical Field] [1] This application claims the benefit of priority to Korean Patent Application No. 10- 2022-0147927, filed on Nov. 8, 2022. [2] The present invention relates to a method for establishing a quick charging protocol 10 that considers heat generation and internal resistance due to charging and discharging of a large capacity battery cell, a battery management system capable of establishing such a quick charging protocol, a battery pack including the same, and a charging device for battery cells using the same. [Background Technology of the Invention] 15 [3]In recent years, the demand for portable electronic products such as laptops and portable phones has increased dramatically, and the demand for electric carts, electric wheelchairs, and electric bicycles has also increased, and research on high-performance batteries that can be repeatedly charged and discharged has been actively conducted. In recent years, the demand for hybrid electric vehicles (HEVs) and electric vehicles (EVs) has also 20 been increasing worldwide as carbon energy is gradually depleting and environmental concerns are rising. As a result, more attention and research are being focused on vehicle batteries, which are the core components of HEVs and EVs, and there is an urgent need to develop quick charging technologies that can quickly recharge batteries. Quick charging is a critical capability, especially for EVs that do not have an additional energy source. 2 [4] The process of charging a battery involves introducing current into the battery to build up charge and energy, and this process must be carefully controlled. In general, excessive charging current (C-rate) or charging voltage can permanently degrade the performance of a battery and ultimately cause complete failure, or cause a sudden failure such 5 as a leak or explosion of highly corrosive chemicals. [5] When charging a battery with a constant current, if the current rate of the charging current is small, a very long time is required to fully charge the battery. On the other hand, if the current rate of the charging current is too high, the battery will quickly degrade. Therefore, during constant current charging, it is necessary to gradually adjust the current rate of the 10 charging current according to the state of the battery. [6] A charge map with a "multi-stage constant-current charging protocol" is often utilized to adjust the current rate during constant-current charging in a stepwise manner. The charge map includes at least one data array in which a relationship between a plurality of current rates and a plurality of transition conditions is recorded. Whenever each transition condition is 15 satisfied, the following sequence of current rates can be supplied to the battery as charging current. A current rate (which may also be referred to as a 'C-rate') is the charging current divided by the maximum capacity of the battery, using the unit 'C'. [7]Conventionally, 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) 20 at which Li-plating occurs at the negative electrode for each charging current was established as the charging limit. [8] However, three-electrode cells are difficult to manufacture and require a dedicated charger and discharger to charge and discharge, so there are many constraints such as the completeness of the three-electrode cell, the manufacturing time of the three-electrode cell, 3 the preparation of the dedicated charger and discharger, and the like. In addition, when applying the limited state of charge identified in these three-electrode cells to large capacity battery cells with capacities in the range of 40-200 Ah, there is no technology that reflects the resistance of large capacity battery cells or the heat generation during quick charging. 5 [9]In addition, the method of establishing charging protocols using three-electrode cells is subject to the experimenter's subjectivity as the Li-plating zones are not clearly distinguished as the charging current becomes smaller and as the negative electrode composition becomes more favorable for quick charging, making it difficult to establish charging protocols that exhibit similar voltage profiles in case of deviations in the battery 10 cells. [10] Therefore, it is necessary to develop a technology that derives a charging protocol that does not require manufacturing of a three-electrode cell, but considers the resistance of a large capacity battery cell and the heating state during quick charging. [Description of the Invention] 15 [Technical Problem] [11] The present invention is designed to solve the above problems, and aims to provide a method for deriving a charging protocol that does not require manufacturing a three-electrode cell in advance to derive a limit state of charge by charging current, a method for deriving a charging protocol that takes into account the resistance of a large capacity 20 battery cell and the heating state during quick charging, a battery management system capable of establishing such a charging protocol, and a battery pack and charging device equipped with such a system. [Technical Solution] 4 [12] According to one embodiment of the present invention, a method of establishing a charging protocol for a lithium secondary battery is provided. The method for establishing a lithium secondary battery charging protocol includes: [13] (a) measuring the open-circuit voltage (Vref) according to the state of charge 5 (SOCx) for a two-electrode battery cell with a positive and negative electrode, when charged with a reference current; [14] (b) measuring the open circuit voltage (Vc) according to the state of charge (SOCx) during charging with each charging current, when the battery cell is charged with different charging currents; 10 [15] (c) substituting the measurements Vref, Vc into Equation 1 below, calculating an internal resistance value (RSOCx) according to the state of charge (SOCx) for each charging current, and collecting an internal resistance profile plotting the internal resistance value according to the state of charge (SOCx) for each charging current; and [16] (d) identifying, from the collected charging current-specific internal 15 resistance profile, each inflection point at which the internal resistance value (RSOCx) changes from an increasing trend to a decreasing trend, determining the lowest resistance value among the inflection points for each charging current as a reference resistance value, and determining, from the internal resistance profile for each charging current, the state of charge having the reference resistance value as a limit state of charge. 20 [17] [Equation 1] [18] Internal resistance value (RSOCx)= (Vc - Vref)/ Ic [19] (In the above Equation 1, Ic means the applied current value for each charging current) 5 [20] In an exemplary embodiment of the present invention, the inflection point may be an inflection point corresponding to a second inflection point when the graph of the internal resistance profile by charging current is viewed as 'W' shaped. [21] In an exemplary embodiment of the present invention, the inflection point 5 may be located within an interval where the state of charge is between SOC 40% and SOC 60%. [22] In an exemplary embodiment of the present invention, the two-electrode battery cell may have a capacity of 40 to 200 Ah. [23] In an exemplary embodiment of the present invention, the reference current 10 in process (a) may be selected from a range of 0.25C to 0.4C. [24] In an exemplary embodiment of the present invention, a plurality of the charging current in process (b) may be selected from a range of 0.2C to 6C. [25] In an exemplary embodiment of the present invention, in the process (b), charging the discharged battery cell to SOC 50% to SOC 100%, may be repeated for each 15 charging current. [26] In an exemplary embodiment of the present invention, the process (b) may apply a charging current, increasing the value of the charging current in a stepwise manner from lower to higher current. [27] The method for establishing a lithium secondary battery charging protocol an 20 exemplary embodiment of the present invention further includes mapping the charging protocol based on the limit state of charge by charging current, wherein the mapping process maps so that each charging current is charged at a corresponding charging current up to a limit state of charge, but the charging current decreases as the state of charge increases. 6 [28] In an exemplary embodiment of the present invention, the mapping process may be mapping to a state of charge interval below 55% SOC. [29] In an exemplary embodiment of the present invention, the process (b) further includes, between each of the steps of measuring an open circuit voltage (Vc) according to the 5 state of charge (SOCx) by each charging current, performing charge/discharge compensation, wherein the charge/discharge compensation may be a process of discharging with a reference current of process (a), and charging and discharging with a reference current again. [30] According to another exemplary embodiment of the present invention, a battery management system is provided. The battery management system includes: a voltage 10 measurement portion configured to measure the open circuit voltage (Vref, Vc) according to the state of charge (SOCx), when charged with a reference current and various numerical charging currents, for a two-electrode battery cell having a positive and negative electrode; [31] a memory portion configured to calculate an internal resistance value, RSOCx, according to the state of charge, SOCx, by substituting the above measured values, Vref, Vc, 15 into Equation 1, and to collect, for each charging current, an internal resistance profile plotting the internal resistance value according to the state of charge, SOCx; [32] a control portion configured to, in the collected internal resistance profile by charging current, identify each inflection point at which the internal resistance value (RSOCx) changes from an increasing trend to a decreasing trend, determine the lowest resistance value 20 among the inflection points for each charging current as a reference resistance value, and determine, from the internal resistance profile for each charging current, the state of charge having the reference resistance value as a limit state of charge. [33] [Equation 1] [34] Internal resistance value (RSOCx)= (Vc - Vref)/ Ic 7 [35] (In the above Equation 1, Ic means the applied current value for each charging current) [36] In an exemplary embodiment of the present invention, the control portion may determine a second inflection point as the inflection point when the graph of the internal 5 resistance profile by charging current is viewed as 'W' shaped. [37] A battery management system according to an exemplary embodiment of the present invention may further include a connecting portion configured to be connected to a charging portion capable of supplying a charging current to the battery cells, according to a charging protocol established by the control portion. 10 [38] According to another exemplary embodiment of the present invention, a battery pack is provided. The battery pack includes the battery management system. [39] According to another exemplary embodiment of the present invention, a battery pack charging device is provided, and the battery pack charging device includes: the battery management system; and a charging unit configured to supply a charging current to 15 the battery cell according to a charging protocol created to reflect the limit state of charge by charging current. [Advantageous Effects] [40] A method of setting charging protocol, a battery management system, and a charging device mounting the same according to the present invention have the effect of 20 providing a charging protocol that reflects resistance and heat directly from a large capacity battery cell, without the need to manufacture a cumbersome three-electrode cell. [Brief Description of the Drawings] [41] FIG. 1 is a flowchart to illustrate a method of establishing a charging protocol according to an exemplary embodiment of the present invention. 8 [42] FIG. 2 is a diagram illustrating an internal resistance profile by charging current collected according to an exemplary embodiment of the present invention. [43] FIG. 3 is an illustration of an exemplary configuration of a battery pack including a battery management system according to an exemplary embodiment of the present 5 invention. [44] FIG. 4 is a diagram schematically illustrating a battery pack including a battery management system according to an exemplary embodiment of the present invention. [45] FIG. 5 is a block diagram of a charging device for battery cells according to an exemplary embodiment of the present invention. 10 [46] FIG. 6 is a graph illustrating a limit state of charge by charging current derived according to Example 1 and Comparative Examples 1,2. [47] FIG. 7 is a diagram illustrating the results of measuring the open circuit voltage according to the state of charge according to Experimental Example 1. [48] FIG. 8 is a diagram illustrating an internal resistance profile by charging 15 current derived according to Example 2. [49] FIG. 9 is a diagram illustrating the results for partial charging currents in FIG. 8. [50] FIG. 10 is a diagram illustrating an internal resistance profile by charging current derived according to Example 3. 20 [Best Mode for Carrying out the Invention] [51] The terms and words used in this specification and claims are not to be construed in their ordinary or dictionary sense, but are to be construed in a sense and concept 9 consistent with the technical idea of the present invention, based on the principle that the inventor may properly define the concept of a term to best describe his invention. [52] Accordingly, it is to be understood that the embodiments described herein and the configurations illustrated in the drawings are only the most preferred embodiments of 5 the present invention and do not represent all of the technical ideas of the present invention, and that there may be various equivalents and variations that may be substituted for them at the time of filing the application. [53] In addition, in describing the invention, detailed descriptions of related known configurations or features are omitted where it is determined that such detailed 10 descriptions would obscure the essence of the present invention. [54] Throughout the specification, when a part is said to "include" a component, it means that it may further include other components, not that it excludes other components, unless specifically stated to the contrary. [55] In addition, terms such as control portion as used in the specification refer to 15 a unit that handles at least one function or operation, which may be implemented in hardware or software, or a combination of hardware and software. [56] In addition, throughout the specification, when a part is said to be "connected" to another part, this includes not only "directly connected" but also "indirectly connected" with other elements in between. 20 [57] [58] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. [59] FIG. 1 is a flowchart to illustrate a method of establishing a charging protocol according to an exemplary embodiment of the present invention. 10 [60] Referring to FIG. 1, a method of establishing a charging protocol according to an exemplary embodiment of the present invention includes (a) measuring the open-circuit voltage (Vref) according to the state of charge (SOCx) for a two-electrode battery cell with a positive and negative electrode, when charged with a reference current; 5 [61] (b) measuring the open circuit voltage (Vc) according to the state of charge (SOCx) during charging with each charging current, when the battery cell is charged with different charging currents; [62] (c) substituting the measurements Vref, Vc into Equation 1 below, calculating an internal resistance value (RSOCx) according to the state of charge (SOCx) for each charging 10 current, and collecting an internal resistance profile plotting the internal resistance value according to the state of charge (SOCx) for each charging current; and [63] (d) identifying, from the collected charging current-specific internal resistance profile, each inflection point at which the internal resistance value (RSOCx) changes from an increasing trend to a decreasing trend, determining the lowest resistance value among 15 the inflection points for each charging current as a reference resistance value, and determining, from the internal resistance profile for each charging current, the state of charge having the reference resistance value as a limit state of charge. [64] [Equation 1] [65] Internal resistance value (RSOCx)= (Vc - Vref)/ Ic 20 [66] (In the above Equation 1, Ic means the applied current value for each charging current) [67] The method for establishing a charging protocol for a lithium secondary battery according to the present invention introduces the concept of an internal resistance by charging current to reflect the resistance and heating of large capacity battery cells. In the 11 present invention, this internal resistance is defined as the resistance of the overvoltage generated during charging divided by the applied current at a given state of charge (SOCx). [68] When the open-circuit voltage according to the state of charge is measured while performing quick charging and slow charging, the open-circuit voltage (Vc) in the case 5 of quick charging is higher than the open-circuit voltage (Vref) in the case of slow charging, even at the same state of charge, and the present invention defines the internal resistance as the difference in the open-circuit voltage (Vc - Vref) according to different charging currents divided by the applied current (Ic). [69] The inventors of the present invention have analyzed internal resistance 10 profiles plotting internal resistance values according to the state of charge by charging current (Ic) and found that the internal resistance profiles by charging current (Ic) generally have a graph shape in which, in an initial state of charge interval, the internal resistance value decreases, then increases, then decreases again, then increases, and among these inflection points that change from an increasing trend to a decreasing trend, the state of charge 15 representing the reference resistance value with the lowest resistance value is determined as the limit state of charge, and the limit state of charge by charging current reflects the resistance or heating state of a large capacity battery cell, and discovered a characteristic that appears at a similar level in battery cells with the same capacity, even if footprint is different, thereby leading to the present invention. 20 [70] In other words, if the battery cells have different footprints, the reference resistance values of the battery cells may vary, but the limit state of charge by charging current with the reference resistance value is similar, so the charging protocol establishment method of the present invention has the effect of presenting a method for establishing a charging protocol based on the same criteria despite deviations between battery cells. 12 Furthermore, through the reference resistance value, a limit state of charge that reflects the capacity and internal resistance of the battery cell can be derived for each charge current. [71] [72] In the present invention, the battery cell is a two-electrode battery cell having 5 a negative electrode and a positive electrode, which is a single, physically separable cell. In one example, a pouch-type lithium polymer cell may be considered as a battery cell 10. Further, the battery cell may be a large capacity battery cell having a capacity in the range of 40 to 200 Ah. [73] As a positive electrode active material comprising the positive electrode of 10 the battery cell 10, a lithium-containing transition metal oxide may be used. For example, LiCoC2, LiNiO2, LiMnO2, LiMn2O4, Li(NiaCobMnc)O2 (0