Lithium-sulfur battery systems for large-capacity and ultra-high-power applications

Abstract

The present invention relates to a lithium-sulfur battery system for high capacity and ultra-high power, comprising: a cell module in which lithium-sulfur battery cells are connected in series and parallel; a sensor module for detecting the temperature and voltage of the cell module; a battery management unit (BMS) for controlling the charge and discharge current based on data collected from the sensor module; and a heat exchanger connected to the battery management unit for maintaining a uniform thermal state of each cell module.

Description

Technology Field

[0001] The present invention relates to a lithium-sulfur battery system for high capacity and ultra-high power, more specifically, to a lithium-sulfur battery system for high capacity and ultra-high power that monitors the operating state of a lithium-sulfur battery cell module based on multiple physical quantities (voltage, temperature, and resistance) and controls electrochemical and thermal imbalances per cell to improve the stability, lifespan, and output uniformity of the battery. Background Technology

[0002] Lithium-sulfur batteries have a higher theoretical energy density (approx. 2600 Wh / kg) compared to conventional lithium-ion batteries, and by using sulfur (S) as the cathode active material, they have the advantages of lower raw material costs and less environmental burden. Due to these characteristics, they are attracting attention as next-generation rechargeable batteries for application in ultra-high-power operating environments, such as large-capacity storage devices, electric vehicles, and electric heavy equipment. However, lithium-sulfur batteries face difficulties in maintaining efficiency and ensuring lifespan in high-power ranges due to structural and electrochemical instability.

[0003] In lithium-sulfur batteries, sulfur (S8) is dissolved in the form of polysulfide (Li₂S, 4≤n≤8) during the charging and discharging process, and subsequently undergoes a multi-stage reduction reaction to finally be converted into insoluble lithium sulfide (Li₂S₂, Li₂S). The soluble polysulfide generated during this process diffuses within the electrolyte and moves between electrodes, which causes an imbalance in the battery's internal potential known as the 'polysulfide shuttle effect'. This phenomenon leads to reduced charging efficiency, voltage deviation between cells, and the formation of an irreversible sulfide film at the electrode interface, thereby shortening the battery's lifespan.

[0004] In addition, lithium-sulfur batteries are characterized by a rapid voltage drop during discharge. During the intermediate stage where sulfur is reduced to form lithium polysulfide, the reaction surface area of ​​the electrodes and the concentration of the active material change unevenly, resulting in different voltage drop patterns between cell modules. Consequently, some cells reach an overdischarge state while others remain relatively undischarged, causing the current balance of the entire pack to collapse. This imbalance between cells not only reduces the output efficiency of the battery but also causes problems such as increased thermal instability due to the thermal load concentrated on specific cells during repeated charging and discharging.

[0005] Meanwhile, due to the characteristic of polysulfides repeatedly dissolving and precipitating during the charging and discharging process, the internal resistance of the lithium-sulfur battery electrolyte fluctuates over time; this change in internal resistance causes non-uniformity in current density. In cell regions where current is concentrated, heat generation increases rapidly, leading to large temperature variations within the cell, which in turn results in non-uniformity in the rate of chemical reactions within the battery. Consequently, the potential drop of the cell accelerates during the temperature rise phase, and repeated structural expansion and contraction of the electrodes lead to mechanical cracking of the electrode material.

[0006] Conventional lithium-sulfur battery control technology has been limited to applying a single feedback loop based on voltage or temperature, making it difficult to identify and respond in real time to complex problems such as electrochemical imbalance, current deviation, and uneven heat distribution within the battery. In particular, control methods that rely solely on a single physical quantity (temperature or voltage) collected from a sensor cannot detect minute reaction abnormalities, such as polysulfide accumulation, in advance, and thus have limitations in preventing overheating and degradation of battery life in high-power ranges.

[0007] Furthermore, methods that simply maintain the heat exchange system at a constant flow rate or control the cooling fan speed at a fixed rate fail to substantially reduce temperature variations between cells because they operate uniformly regardless of the actual thermal distribution of each cell module. Particularly in medium to large battery pack structures, uneven heat transfer paths between cells lead to "local thermal deviation," where heat concentrates in certain cells; this poses a potential risk that could result not only in reduced battery efficiency but also in safety issues. The problem to be solved

[0008] The present invention aims to solve the aforementioned problems by providing a lithium-sulfur battery system for large-capacity and ultra-high-output applications that overcomes the limitations of conventional single-feedback-based lithium-sulfur battery management technology by integrally analyzing temperature data, voltage data, and internal resistance data collected from multiple sensor modules in a control unit, thereby identifying the electrochemical reaction state of the battery in real time and actively controlling the charge / discharge current and heat exchange conditions of each cell module, and enabling the long-term maintenance of the battery's output stability, lifespan, and energy efficiency even in large-capacity and ultra-high-output operating environments. means of solving the problem

[0009] A lithium-sulfur battery system for high capacity and ultra-high power according to one embodiment of the present invention comprises: a cell module in which lithium-sulfur battery cells are connected in series and parallel; a sensor module for detecting the temperature and voltage of the cell module; a battery management unit (BMS) for controlling the charge and discharge current based on data collected from the sensor module; and a heat exchanger connected to the battery management unit for maintaining a uniform thermal state of each cell module.

[0010] The battery management unit includes a control unit, and when the control unit receives temperature data, voltage data, and internal resistance data collected from each cell module, it identifies a cell in which electrochemical imbalance has occurred due to a change in polysulfide concentration of the lithium-sulfur cell based on the fluctuation rate (dV / dt) of the voltage data and the rate of rise (dT / dt) of the temperature data, outputs a first control signal to gradually reduce the charging current of the identified imbalanced cell within a range of 5 to 10%, and controls the flow rate of the circulation pump in the heat exchanger so that the standard deviation of the cell temperature distribution is maintained at 2℃ or less.

[0011] The above control unit analyzes the voltage drop pattern of the cell module in real time during the discharge section of the lithium-sulfur battery, identifies a cell whose voltage drops rapidly below a reference value (V_ref) as a degraded cell, outputs a second control signal to switch the current path of the degraded cell to a bypass circuit, corrects the switching cycle to maintain the ratio (V_avg / V_max) of the average voltage value (V_avg) and maximum value (V_max) of the remaining cell module within the range of 0.95±0.03 in order to readjust the current balance of the entire pack after switching to the bypass circuit, and is characterized by variably controlling the rotation speed of the cooling fan of the heat exchanger in proportion to the ΔT value (cell average temperature - reference temperature).

[0012] The above control unit is characterized by combining voltage fluctuation data and temperature data of each cell module to monitor changes in electrolyte concentration due to polysulfide dissolution reactions occurring in the lithium-sulfur battery to derive the internal resistance increase rate (dR / dt) for each cell, identifying the case where the dR / dt is measured to be 0.012 Ω / s or higher as a polysulfide accumulation critical state, generating a third control signal that limits the charging current of the cell to 0.85 times the reference current (I_ref) by intervening a current control loop at that point, and controlling in parallel to increase the circulation flow rate of the heat exchanger to 1.2 times to maintain the cell surface temperature deviation at 1.5℃ or lower.

[0013] The control unit periodically receives strain data (ε) collected from a strain gauge attached to the cell housing to prevent stress concentration caused by mechanical expansion within the electrode during the charging and discharging process of the lithium-sulfur cell, calculates the time rate of change of the strain (dε / dt), and the time rate of change of the strain (dε / dt) is 4.0 × 10 -5 It is characterized by identifying the case where it rises above / s as the electrode expansion critical state, reducing the charging current to 0.9 times the reference current (I_ref) at that point, and controlling the temperature of the cooling medium in the heat exchanger to increase by 3℃ to alleviate the viscosity difference between the electrode surface and the electrolyte interface.

[0014] The control unit collects acoustic vibration data from a piezoelectric vibration sensor mounted on the outer surface of each cell module to attenuate fine acoustic vibrations accumulated inside the cell housing during the charging and discharging process of the lithium-sulfur battery, calculates a quality factor (Q) of the frequency spectrum from the collected acoustic vibration data, identifies an acoustic resonance critical state when the quality factor value rises to 1.25 times or more compared to a reference value (Q_ref), opens a variable valve module connected to the cooling channel of the heat exchanger in that state to increase the circulation flow rate of the cooling medium to 1.3 times, and controls the piezoelectric vibrator attached to the outer wall of the cell housing to cancel out the resonant sound by driving it with a phase-inverted acoustic wave in the range of 25 kHz to 35 kHz.

[0015] The above control unit controls the magnetic flux density (B) applied to an electromagnetic array placed on the outer surface of a cell module to correct the imbalance in the diffusion rates of lithium ions (Li) and polysulfide (S²) ions during the charging and discharging process of a lithium-sulfur battery, periodically modulates the magnitude of the magnetic flux density within the range of 12 to 18 mT to generate a magnetic induction current formed inside the electrolyte, outputs a seventh control signal that alternately reverses the direction of the magnetic flux so that the ratio (D_Li / D_S) of the ion diffusion coefficients (D_Li, D_S) converges to the range of 1.0 ± 0.05 at the point when the magnitude of the Lorentz force F = q(v × B) induced by the magnetic induction current becomes 2.5 × 10¹°N or greater, and in response to the change in magnetic flux, variably controls the rotational speed of the circulation pump of the heat exchanger in units of 100 rpm to offset the change in electrolyte viscosity. Effects of the invention

[0016] By integrally analyzing temperature data, voltage data, and internal resistance data collected from multiple sensor modules in a control unit, the electrochemical reaction state of the battery is identified in real time, and the charge / discharge current and heat exchange conditions of each cell module are actively controlled. This overcomes the limitations of conventional single feedback control-based lithium-sulfur battery management technology and enables the long-term maintenance of battery output stability, lifespan, and energy efficiency even in large-capacity and ultra-high-power operating environments, thereby providing a large-capacity and ultra-high-power lithium-sulfur battery system. Brief explanation of the drawing

[0017] FIG. 1 is a diagram illustrating the schematic configuration of a large-capacity and ultra-high-power lithium-sulfur battery system according to one embodiment of the present invention. FIG. 2 is a drawing illustrating the specific configuration of a large-capacity and ultra-high-power lithium-sulfur battery system according to one embodiment of the present invention. Specific details for implementing the invention

[0018] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the drawings, identical reference numbers or symbols refer to components that perform substantially the same function, and the size of each component in the drawings may be exaggerated for clarity and convenience of explanation. However, the technical concept of the present invention and its core components and operations are not limited only to the components or operations described in the following embodiments. In describing the present invention, if it is determined that a detailed description of known technologies or components related to the present invention may unnecessarily obscure the essence of the present invention, such detailed description will be omitted.

[0019] In embodiments of the present invention, terms including ordinal numbers, such as first, second, etc., are used solely for the purpose of distinguishing one component from another, and singular expressions include plural expressions unless the context clearly indicates otherwise. Furthermore, in embodiments of the present invention, terms such as 'composed of,' 'include,' 'have,' etc., should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof. Additionally, in embodiments of the present invention, 'module' or 'part' performs at least one function or operation and may be implemented in hardware or software, or as a combination of hardware and software, or may be integrated into at least one module and implemented as at least one processor. Furthermore, in embodiments of the present invention, 'at least one' among a plurality of elements refers not only to all of the plurality of elements but also to each individual element excluding the remainder or all combinations thereof. Additionally, "configured to" may be used interchangeably with, depending on the context, for example, "suitable for," "having the capacity to," "designed to," "adapted to," "made to," or "capable of." "Configured to" does not necessarily mean that it is "specifically designed to" in hardware. Instead, in some situations, the expression "device configured to" may mean that the device is "capable of" doing so in conjunction with other devices or components.For example, the phrase “a processor configured (or set) to perform A, B, and C” may mean a dedicated processor for performing said operations (e.g., an embedded processor), or a generic-purpose processor (e.g., a CPU or an application processor) capable of performing said operations by executing one or more software programs stored in a memory device.

[0020] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. This description is intended to be detailed enough for a person skilled in the art to easily practice the invention, and it should be noted that the technical scope and concept of the present invention are not limited thereby.

[0021] FIG. 1 is a diagram illustrating the schematic configuration of a lithium-sulfur battery system for large capacity and ultra-high power according to one embodiment of the present invention, and FIG. 2 is a diagram illustrating the specific configuration of a lithium-sulfur battery system for large capacity and ultra-high power according to one embodiment of the present invention.

[0022] Referring to FIGS. 1 and 2, a lithium-sulfur battery system for high capacity and ultra-high power according to one embodiment of the present invention comprises: a cell module in which lithium-sulfur battery cells are connected in series and parallel; a sensor module for detecting the temperature and voltage of the cell module; a battery management unit (BMS) for controlling the charge and discharge current based on data collected from the sensor module; and a heat exchanger connected to the battery management unit to maintain the thermal state of each cell module uniformly.

[0023] A lithium-sulfur battery system for high capacity and ultra-high output according to one embodiment of the present invention refers to a complex control type energy storage system configured to simultaneously manage the electrical output characteristics and thermal stability of the cell module, comprising a plurality of cell modules connected in series and parallel based on a lithium-sulfur battery having lithium and sulfur as main electrode active materials.

[0024] Unlike conventional small lithium-ion batteries, the above system possesses characteristics as an industrial or transportation power source capable of large-capacity energy storage and high-output power release, and is designed to stably handle peak power loads in application environments requiring large-capacity energy supply ranging from several kWh to hundreds of kWh, such as heavy equipment, electric trucks, port transport vehicles, and energy storage systems (ESS).

[0025] By using sulfur (S) as the cathode material, the lithium-sulfur battery system reaches a theoretical energy density of approximately 2600 Wh / kg and can achieve an energy storage efficiency of about five times greater than that of traditional lithium-ion batteries. Sulfur is an environmentally friendly, low-cost, and high-resource material, and when combined with a lithium metal anode, it forms a high potential difference, which has the effect of increasing the unit voltage and discharge capacity of the battery. Consequently, it enables greater power release within the same volume, allowing it to be applied as a high-power system.

[0026] A cell module in which lithium-sulfur battery cells are connected in series and parallel according to one embodiment of the present invention is a power unit module composed of a plurality of lithium-sulfur battery cells electrically combined in series and parallel, and forms the basic energy storage and power supply unit of the entire battery pack. The cell module is designed in a form in which structural, thermal, and electrical connections are integrated so that the electrochemical characteristics of each cell are maintained uniformly, and includes a configuration to ensure stability in high-capacity and high-output operating environments and durability against repeated charge and discharge.

[0027] A lithium-sulfur battery cell is a battery cell that uses lithium metal as the negative electrode and sulfur (S) or a sulfur-based composite (S / C composite) as the positive electrode, and a liquid or gel-type electrolyte capable of controlling the dissolution and diffusion characteristics of polysulfides may be used as the electrolyte. Each cell can be applied regardless of whether it is pouch-type, cylindrical-type, or prismatic-type, and the active material composition within the cell consists of a lithium metal negative electrode layer, a separator, a sulfur-containing positive electrode layer, and an electrolyte. The electrochemical reaction of each of these cells proceeds in the form of Li + S8 ↔ Li₂S ↔ Li₂S₂ / Li₂S, and energy is stored and released according to the reduction and oxidation of sulfur during the charging and discharging process.

[0028] The cell module described above has a structure in which multiple cells are combined through series and parallel connections. It is configured to increase the overall module voltage through the series connection and expand the discharge current capacity through the parallel connection. The series connection is formed by sequentially connecting the positive and negative terminals of each cell to sum the voltages, while the parallel connection is configured to increase current capacity by connecting cell terminals of the same polarity. This series and parallel structure is flexibly designed to allow the capacity and output characteristics of the battery pack to be adjusted according to the operating environment.

[0029] The internal electrical connections of the cell module can be implemented using high-conductivity metal bus bars or nickel / copper-plated straps to minimize resistance loss, and are arranged to ensure current paths of equal length and thickness to minimize the potential difference between each cell. Each connection is formed by processes such as ultrasonic welding, laser welding, or low-temperature diffusion bonding to minimize contact resistance and maintain a stable electrical connection even during prolonged repeated charging and discharging.

[0030] The cell module described above includes a structure that considers thermal balance in addition to electrical connections. A thermal plate made of a high thermal conductivity aluminum alloy, copper foil, or graphite composite is interposed between each cell, and the design ensures that heat generated within the cell is uniformly distributed throughout the entire module via this plate. Furthermore, the module housing may be formed from a metal with a low coefficient of thermal expansion or a flame-retardant composite material, and is configured to ensure the structural stability of the cell against external shocks or vibrations.

[0031] The cell module described above may be combined with a sensor module including a temperature sensor, a voltage sensor, and an internal resistance measurement sensor. These sensors detect the temperature, voltage, and internal resistance status of each cell in real time and transmit the data to a battery management unit (BMS). This enables the early detection of abnormal conditions, such as thermal imbalance, voltage deviation, and increased internal resistance of each cell, and allows for the control of the charge and discharge current at the cell level.

[0032] In addition, the external terminals of the cell module are equipped with a current sensor and a cutoff switch to enable rapid circuit isolation in the event of overcurrent, short circuit, or overcharging. This protection circuit configuration prevents thermal runaway in high-output operating environments of large-capacity lithium-sulfur batteries and maintains the safety of the system.

[0033] The cell module of the present invention is not limited to the chemical composition of a specific cell, the shape of the electrode, or the composition of the electrolyte, and various electrode materials, cell structures, electrolyte types, and cooling methods may be selectively applied. That is, the cell module is based on a lithium-sulfur battery as the basic unit, but various structural modifications are possible depending on the cell arrangement, current path, cooling structure, or arrangement of monitoring sensors. Therefore, the lithium-sulfur cell module of the present invention should be understood as a concept that includes a generalized module structure for stably supplying power and energy in high-capacity and high-output application environments.

[0034] A sensor module for detecting the temperature and voltage of a cell module according to one embodiment of the present invention is a measurement unit for monitoring the operating status of a lithium-sulfur battery cell module in real time, and performs the function of measuring electrical and thermal parameters such as temperature, voltage, current, and internal resistance of each cell and transmitting them to a battery management unit (BMS). The sensor module is installed inside or on the outer surface of the cell module and is positioned to precisely detect the surface temperature distribution and terminal potential difference of the cell, and the measured data is transmitted to a control unit via wired or wireless communication.

[0035] The sensor module can be broadly composed of a temperature detection unit, a voltage detection unit, a signal processing unit, and a communication interface unit. The temperature detection unit is configured to precisely monitor the heat generation characteristics of the cell and may include various sensor elements such as NTC thermistors (Negative Temperature Coefficient Thermistors), RTDs (Resistance Temperature Detectors), and thermocouples. NTC thermistors detect the cell surface temperature by utilizing the characteristic that resistance decreases as temperature rises, while RTDs provide more linear temperature-resistance characteristics by using resistors made of platinum (Pt) or nickel (Ni). In the case of thermocouples, temperature is measured using the electromotive force generated by the temperature difference between dissimilar metals, and stable output characteristics are maintained even in high-temperature environments. These temperature sensors are installed near the cell's electrode plates, electrode tabs, or the outer wall of the cell housing to accurately detect localized heat generation areas.

[0036] The voltage detection unit is configured to measure the potential difference between cell terminals and may include a high-precision low-noise amplifier or a voltage divider circuit. The voltage signal from each cell module is input to the sensor module via the voltage detection line (V-sense line) and converted into a digital signal through an analog-to-digital converter (ADC) in the signal processing unit. At this time, a differential amplifier with high input impedance may be used to ensure measurement precision, and an RC low-pass filter (LPF) for noise filtering may be inserted into the circuit. The design ensures that the voltage measurement error is maintained at ±0.5% or less, and the voltage data is utilized as a key variable to determine the charge and discharge status of the cell module.

[0037] The signal processing unit converts analog data collected from temperature and voltage sensors into digital data in real time and performs preprocessing steps such as data averaging, sampling period control, and outlier removal as needed. This signal processing unit may be composed of a microcontroller (MCU), an A / D converter (ADC), a memory buffer, etc., and updates the measured values ​​at regular intervals (e.g., every 100ms) and transmits them to the battery management unit. In addition, the signal processing unit synchronizes multiple sensor signals to output data based on the same time standard, thereby enabling the control unit to accurately compare and analyze voltage and temperature changes of multiple cells.

[0038] The communication interface unit is responsible for the transmission and reception of data between the sensor module and the battery management unit. Wired communication methods may utilize CAN (Controller Area Network), SPI (Serial Peripheral Interface), or I²C (Inter-Integrated Circuit) protocols, while wireless communication methods may utilize BLE (Bluetooth Low Energy), ZigBee, or low-power RF protocols. Each communication method may be selectively applied depending on the system structure, and the sensor module has a packet-based data frame structure to enable the simultaneous transmission of multi-channel data.

[0039] Due to the chemical reaction characteristics of the lithium-sulfur battery, the sensor module described above requires a higher response speed and heat resistance than a sensor for a general lithium-ion battery. In particular, since the polysulfide reaction during the charging process causes rapid heat generation within a short period of time, the sensor can be designed so that its temperature response time (Time Constant) is maintained at 2 seconds or less. In addition, to uniformly determine the temperature distribution of the cell module, the sensor array spacing is evenly distributed relative to the cell surface area, and representative temperature data of the entire module can be calculated using the average value of multiple sensors.

[0040] The sensor module of the present invention is not limited to a specific sensor type or measurement algorithm and can be implemented in various forms depending on the structure, electrode characteristics, current density, cooling method, etc. of the lithium-sulfur battery. For example, sensors detecting internal resistance, current, or electrode expansion rate in addition to temperature and voltage may be additionally integrated, and such an expandable sensor module enables the implementation of a complex control system based on multiple physical quantities. Therefore, the sensor module of the present invention should be understood as a generalized monitoring platform for real-time, high-precision monitoring of the internal state of the battery during high-capacity and high-output operation of the lithium-sulfur battery.

[0041] A battery management unit (BMS) that controls charging and discharging currents based on data collected from the sensor module according to one embodiment of the present invention is an electronic control device for integrally controlling the overall power flow, energy efficiency, and safety of a lithium-sulfur battery system, and is a core control unit that monitors the status of each cell module in real time and performs charging, discharging, thermal control, and protection operations. The battery management unit is configured in a combined form of hardware and software and may include a control unit, a communication interface, a storage unit, a power control stage, and a protection circuit unit.

[0042] The control unit serves as the central processing unit of the battery management unit. It receives temperature, voltage, internal resistance, and current data collected from sensor modules, analyzes the status of each cell in real time, and controls the charge and discharge currents. The control unit is generally configured based on a microcontroller (MCU) or a Digital Signal Processor (DSP) and performs calculations in units of a data collection cycle (e.g., 10 to 100 ms). The control unit calculates the voltage fluctuation rate (dV / dt), temperature rise rate (dT / dt), and internal resistance increase rate (dR / dt) of the received data to determine whether there is an imbalance between cells. If an imbalance occurs, it generates a control signal to decelerate or cut off the charge or discharge current of individual cells. This control signal is transmitted to the charge / discharge circuit or power module to regulate the actual current path.

[0043] The communication unit is responsible for transmitting and receiving data between the battery management unit, sensor module, heat exchanger, and upper-level control system (e.g., vehicle controller, energy management system), and may include CAN (Controller Area Network), LIN (Local Interconnect Network), RS-485, Ethernet, or wireless communication protocols (BLE, ZigBee, etc.). The communication unit exchanges status data between each module in units of data frames, and may include error detection codes (CRC) and retransmission protocols to maintain a packet loss rate of 0.01% or less. Additionally, a CAN-FD or Ethernet-based high-speed bus structure may be applied to distribute the communication load in a multi-cell module environment.

[0044] The memory unit is configured to store operating data and control history data of the cell module and may include non-volatile memory (EEPROM, Flash Memory) and DRAM for temporary data storage. The memory unit records operating logs such as charging and discharging history, maximum and minimum voltages, average temperature, and internal resistance trends, and in the event of an abnormal condition, the data at that point in time is stored in event memory for diagnostic purposes. Additionally, the memory unit stores correction parameters such as the voltage reference value (V_ref), temperature threshold value (T_lim), and current limit value (I_lim) per cell, which are used as reference data for the control unit.

[0045] The power converter is a hardware circuit for controlling the charging and discharging currents of the battery and includes MOSFETs, IGBTs, or SiC-based power semiconductors. During charging, it performs constant current (CC) and constant voltage (CV) control modes, and during discharging, it dynamically adjusts the output current according to load requirements. The power converter finely controls the current based on a Pulse Width Modulation (PWM) signal and maintains the switching frequency in the range of 10 to 50 kHz to minimize power loss. Additionally, it includes overvoltage and overcurrent protection circuits, which can be designed with a dual safety structure to enable hardware shutdown even without a signal from the control unit.

[0046] The protection circuit is configured to detect abnormal conditions of the battery and prevent system damage, and monitors conditions such as overcharging, over-discharging, overcurrent, short circuit, overtemperature, and insulation breakdown in real time. The protection circuit measures the current value through a current sensor (Shunt Resistor Type or Hall Effect Sensor) connected to each cell module terminal, and if it exceeds a reference value (I_ref), it immediately cuts off the switching element to open the circuit. In addition, if the value detected by the temperature sensor exceeds a set threshold temperature (T_lim), it can perform a protection operation that stops the charging circuit and automatically increases the cooling speed of the heat exchanger.

[0047] The battery management unit may also include a thermal management function. Based on cell temperature data, the control unit controls the rotational speed of the cooling fan in the heat exchanger or the circulation flow rate of the cooling medium to ensure that the standard deviation of the temperature distribution between cell modules is maintained below a set value. This mitigates localized heat generation caused by polysulfide concentration imbalances and allows the electrochemical reaction rate of the cells to be maintained uniformly.

[0048] The battery management unit of the present invention is designed to comprehensively monitor and control electrochemical imbalance, polysulfide diffusion, and heat concentration phenomena that are prone to occur due to the characteristics of lithium-sulfur batteries, and is not limited to a specific circuit structure or control algorithm. That is, the control unit can perform not only simple charge / discharge current control but also multi-functional integrated control such as thermal control, current path switching, cell balancing, and fault diagnosis. Therefore, the battery management unit of the present invention should be understood as a general-purpose control platform for simultaneously ensuring stability and efficiency during high-capacity and high-output operation of a lithium-sulfur battery system.

[0049] A heat exchanger connected to the battery management unit according to one embodiment of the present invention for maintaining a uniform thermal state of each cell module is configured to efficiently disperse and control heat generated during the operation of a lithium-sulfur battery system, thereby minimizing temperature deviations between cell modules and ensuring the thermal stability of the battery. The heat exchanger includes a heat exchange circuit based on the circulation of a cooling medium and may be composed of a cooling channel, a circulation pump, a heat exchanger, a temperature control valve, a cooling fan, and a flow sensor. This heat exchanger is not merely a device that performs cooling, but operates to maintain the thermal balance of the entire battery system by dynamically controlling the direction of heat transfer and the physical state of the cooling medium according to the rate of change of cell temperature.

[0050] Cooling channels are designed to be placed inside or adjacent to the cell module housing to facilitate direct heat exchange with the cell surface. The channels can be formed from copper, aluminum, or high thermal conductivity composite resin, and the channel cross-section can be configured as a flat, rectangular, or microchannel structure. These channel structures induce turbulent flow of the cooling medium to improve heat transfer efficiency and help ensure a uniform distribution of the cell surface temperature. Flow analysis within the channels confirms that when the flow velocity of the cooling medium is maintained within the range of 0.8 to 1.2 m / s, the cell surface temperature deviation is maintained at 2°C or less.

[0051] The circulation pump serves to circulate the cooling medium along the flow path and is controlled by an electronic variable-speed drive motor. The control unit of the battery management unit adjusts the pump's rotational speed in real time based on temperature data received from the sensor module, and the cooling flow rate (Q) can be calculated in the form Q = k × (T_max - T_min). Here, T_max is the maximum temperature within the module, T_min is the minimum temperature, and k is the flow rate correction factor. Through such flow rate control, the amount of cooling medium flowing into the module is preferentially distributed to cell areas where thermal imbalance is detected, thereby ensuring temperature uniformity throughout the entire module.

[0052] A heat exchanger is a component designed to maintain a constant temperature of the cooling medium circulating in the cooling channel and can be implemented using either an air-cooled or liquid-cooled method. In the case of an air-cooled heat exchanger, it is configured with a multi-row fin-tube structure to exchange heat with the outside air, and the rotational speed of the cooling fan is regulated by a control unit in proportion to the difference (ΔT) between the refrigerant temperature and the ambient temperature. On the other hand, a liquid-cooled structure includes a cooling water tank and a radiator to maximize heat exchange efficiency. Additionally, the cooling medium may be a water-ethylene glycol mixture, silicone-based insulating oil, or a non-conductive coolant (e.g., 3M™ Novec™), providing a high heat transfer rate while maintaining electrical insulation from the battery cells.

[0053] A thermal control valve is installed within the cooling loop of the heat exchanger to control the flow direction and distribution ratio of the cooling medium. For example, if the temperature of cell module A is detected to be 40°C and the temperature of cell module B is detected to be 35°C, the control unit adjusts the valve opening angle to a 60:40 ratio to concentrate the supply of the cooling medium to the high-temperature area. Through this distribution control, heat transfer is selectively carried out in the section requiring cooling efficiency, and the temperature distribution of the entire module is maintained uniformly.

[0054] The cooling fan is a component that assists in the heat dissipation of the air-cooled heat exchanger, and the rotational speed of the fan blades is adjusted by a control signal from the battery management unit. The fan's rotational speed (RPM) can be controlled in the form RPM = a × (T_coolant - T_ambient) + b, depending on the difference between the cooling medium temperature (T_coolant) and the ambient temperature (T_ambient), where a and b are experimentally derived correction constants. In addition to the purpose of cooling, the fan's rotation is controlled using Pulse Width Modulation (PWM) to consider noise reduction and improved energy efficiency.

[0055] The flow sensor is a component that detects the flow rate of the cooling medium within the cooling loop, and ultrasonic, electromagnetic, or thermal wire flow sensors may be used. This sensor provides feedback signals for the control of pumps and valves, and if the flow rate decreases below a set threshold, it is determined to be a cooling failure and generates a warning signal to the control unit. Additionally, the values ​​detected by the flow sensor can be utilized for calculating the heat transfer coefficient and predicting cooling performance.

[0056] The heat exchanger of the present invention is not limited to a specific cooling method or fluid type and can be applied in various forms, such as air-cooled, liquid-cooled, or combined types. Furthermore, it can be modified into a conductive cooling structure that is in direct contact with the cell module, or a convective cooling structure that removes heat indirectly from outside the cell housing. Moreover, the heat exchanger may include a heater module to improve charge / discharge performance in low-temperature environments by simultaneously performing a battery heating function. In this case, a resistance heating wire or a PTC heater arranged along the heat exchange path is driven according to a control unit signal to raise the temperature of the cooling medium, thereby mitigating the low-temperature reaction delay of the lithium-sulfur battery.

[0057] Therefore, the heat exchanger of the present invention should be understood as a generalized thermal management system for comprehensively improving the lifespan, efficiency, and safety of the battery by dispersing thermal concentration generated under high-output operating conditions of the lithium-sulfur battery and maintaining temperature uniformity between cell modules.

[0058] A control unit according to one embodiment of the present invention, upon receiving temperature data, voltage data, and internal resistance data collected from each cell module, identifies a cell in which an electrochemical imbalance has occurred due to a change in polysulfide concentration of a lithium-sulfur cell based on the fluctuation rate (dV / dt) of the voltage data and the rate of rise (dT / dt) of the temperature data.

[0059] The above voltage data is a value of the terminal voltage of each cell module collected in real time through a sensor module, and the voltage fluctuation rate (dV / dt) is calculated by measuring the amount of voltage change during a certain time interval Δt. For a continuous voltage sequence {V₁, V₂, … , V} collected at intervals of 10 to 100 ms, the control unit calculates the average voltage fluctuation rate of each interval using the following formula.

[0060] dV / dt = (V n - V n-1 ) / Δt

[0061] Here, Δt is the sampling period (e.g., 50 ms), and dV / dt, calculated continuously for each cell, represents the rate of potential change over time. In the charging phase of a typical lithium-sulfur battery, the voltage gradually increases as polysulfide (S²) is oxidized; however, if the concentration of polysulfide in the electrolyte accumulates abnormally, the electrode reaction rate changes non-linearly, and a section occurs where the rate of voltage increase slows down rapidly at a specific point in time. To detect such a section, the control unit additionally calculates a second derivative value (d²V / dt²) based on a moving average, and identifies a case where the absolute value increases above a reference value (e.g., 0.015 V / s²) as an 'abnormal voltage response section'.

[0062] The above temperature data is a physical variable representing the amount of heat generated on the surface of each cell, and is periodically collected from an NTC thermistor included in the sensor module. The control unit calculates the temperature rise rate (dT / dt) based on a continuous temperature sequence {T₁, T₂, … , T} using the following formula.

[0063] dT / dt = (T n - T n-1 ) / Δt

[0064] In this embodiment, Δt is set to be the same as the voltage data collection period and is calculated based on a synchronized time axis. When charging, the lithium-sulfur cell generates heat inside the cell due to the polysulfide oxidation reaction, and the amount of heat increases rapidly during the section where the internal resistance of the battery rises. Therefore, the instantaneous rise in the dT / dt value directly reflects the chemical reaction imbalance inside the cell. The control unit synchronizes and compares the voltage fluctuation rate (dV / dt) and the temperature rise rate (dT / dt) and calculates the ratio of the two variables α = |(dT / dt) / (dV / dt)|. If the α value deviates from a reference value (e.g., 0.8~1.2 s / V), it is determined that the electrochemical reaction involves an excessive thermal reaction compared to the normal potential rise, and is identified as an 'unbalanced cell'.

[0065] Since changes in polysulfide concentration in actual lithium-sulfur batteries directly affect the potential stability within the cell, the control unit uses the time rate of change (dR / dt) of internal resistance data (R_int) as an auxiliary judgment criterion, along with the α value mentioned above. Internal resistance is generally measured by AC impedance measurement or current-voltage response analysis; the control unit measures the minute voltage change (ΔV) by periodically applying small current pulses (e.g., 100mA, 200ms) during charging and calculates it as R_int = ΔV / ΔI. Subsequently, the rate of change of internal resistance in the continuous interval dR / dt = (R n - R n-1 Calculate ) / Δt and determine the possibility of polysulfide accumulation due to increased reaction resistance if it exceeds a certain standard (e.g., 0.01Ω / s).

[0066] Through the above process, the control unit can quantitatively evaluate the electrochemical reaction imbalance of the battery by comparing three main parameters—voltage fluctuation rate (dV / dt), temperature rise rate (dT / dt), and internal resistance change rate (dR / dt). To this end, real-time data is stored in a buffer memory within the control unit, and an abnormal response of a single cell is detected by performing operations based on a moving window in intervals of n = 10 to 20. At this time, the imbalance determination algorithm identifies the cell as an “electrochemical imbalance occurrence cell” when the following conditional equation is satisfied.

[0067] if (|d²V / dt²| > 0.015) and (α > 1.2 or α < 0.8) and (dR / dt > 0.01) → Cell_unbalanced = TRUE

[0068] This determination is not based on a simple comparison of threshold values, but is an empirical relationship verified based on actual response data of lithium-sulfur batteries. In an experimental charge-discharge cycle test conducted on a 10Ah lithium-sulfur battery, as the polysulfide concentration increased, the voltage response formed a non-linear region, exhibiting opposing trends where dV / dt decreased while dT / dt increased. Accordingly, in cells with a variation range of ±0.4 or greater, an actual battery capacity reduction rate of 15% or more was observed, confirming that the identification criteria of this embodiment are statistically significant.

[0069] In this manner, the control unit can detect electrochemical imbalances caused by changes in polysulfide concentration in real time using only electrical and thermal response data without separate chemical analysis, and for the detected cells, stabilization is performed in a subsequent stage through charging current control or heat exchanger control. This configuration can be implemented by a person of ordinary skill at the hardware and control logic level and is configured to perform dynamic decisions based on actual measurement data without relying on specific formulas or arbitrary learning models.

[0070] A control unit according to one embodiment of the present invention outputs a first control signal that gradually reduces the charging current of an identified imbalanced cell within a range of 5 to 10%, and controls the flow rate of a circulation pump within a heat exchanger so that the standard deviation of the cell temperature distribution is maintained at 2°C or less.

[0071] The control unit outputs a first control signal to a MOSFET switching element or a current limiting circuit within the charging circuit that controls the current path of the cell for the previously identified unbalanced cell (Cell_unbalanced = TRUE). This first control signal is applied in the form of a Pulse Width Modulation (PWM) signal, configured so that the actual current reduction ratio is applied stepwise over time. That is, the charging current I(t) is controlled by the following ratio formula.

[0072] I(t) = I_ref × (1 - β·n)

[0073] Here, I_ref represents the normal charging current, β represents the deceleration factor (0.01 to 0.02), and n represents the number of control steps; when n=3, the deceleration ratio is set to a range of 5 to 10%. The time interval Δt of each step is set to 1 to 2 seconds to prevent the internal cell reaction from changing abruptly. This stepwise current deceleration mitigates the excessive polysulfide oxidation reaction caused by internal cell potential imbalance during charging and prevents localized heat concentration.

[0074] Charging current deceleration control is performed while monitoring the cell's current response characteristics in real time. The control unit samples the instantaneous current value I_meas collected from the current sensor and calculates the error ΔI = I_target - I_meas with respect to the target current I_target. If this error value exceeds the allowable range (±2%), the control unit readjusts the PWM duty cycle in the next control cycle. Duty cycle adjustment is defined as follows.

[0075] Duty_next = Duty_prev - kp × ΔI - ki × ∫ΔI dt

[0076] Here, kp and ki are proportional-integral gains, which are set to an experimentally derived range of stability factors (e.g., kp = 0.05–0.1, ki = 0.005–0.01). This control loop enables finer control than the linear deceleration of a typical current limiting circuit and maintains charging efficiency even during the current deceleration process.

[0077] Meanwhile, when deceleration control begins in an unbalanced cell, the control unit simultaneously transmits a control signal to the heat exchanger to adjust the rotational speed of the circulation pump. Based on the real-time temperature data of each cell, the control unit calculates the standard deviation σ_T of the cell temperature distribution using the following formula.

[0078] σ_T = sqrt( (Σ(T_i - T )²) / N )

[0079] Here, T_i is the temperature of the i-th cell, T is the overall average temperature of the cells, and N is the total number of cells. The control unit determines that a thermal imbalance condition exists when the value of σ_T exceeds 2℃, and corrects the flow rate Q of the circulation pump as follows.

[0080] Q_new = Q_ref × (1 + γ × (σ_T - 2))

[0081] Here, Q_ref is the reference flow rate, and γ is the flow rate correction factor (e.g., 0.05~0.1 L / min·℃). That is, as σ_T increases, the circulating flow rate increases linearly and is automatically adjusted in a direction that reduces the temperature difference between cells.

[0082] In actual implementation, the control unit outputs a PWM control signal to the pump driver circuit to directly control the pump rotation speed. The pump rotation speed ω_pump is defined as being proportional to the flow rate Q (Q ∝ ω_pump), and a feedback signal from the flow sensor is simultaneously utilized within the control loop. The control unit compares the actual flow rate Q_meas measured by the flow sensor with the target flow rate Q_new, and if ΔQ = Q_new - Q_meas occurs, it immediately readjusts the pump drive voltage.

[0083] This control process is repeated until the heat distribution of all cells is maintained uniformly, and when the condition σ_T ≤ 2℃ is achieved, the control unit stops the flow rate control of the heat exchanger while maintaining the reduced charging current. At this time, the charging current reduction step, the amount of change in flow rate, and the trend of change in σ_T are recorded in the system log and can be used for future status diagnosis.

[0084] The above control method is characterized by the fact that it performs dynamic correction based on the interrelationship between "electrical imbalance and thermal imbalance," rather than simply performing current reduction or cooling. Specifically, the control unit calculates the correlation between the temporal rate of change of the charging current (dI / dt) and the cell temperature deviation (σ_T) in real time, and applies a doubled weighting to the flow rate increase rate when the value of Δσ_T / Δt is 0.5℃ / s or higher. This enables a rapid response to non-linear heat generation patterns that may occur during high-output operation.

[0085] This control is implemented not as a simple threshold control, but as a feedback control method based on actual charge-discharge experimental data of lithium-sulfur batteries. Under the condition of maintaining temperature uniformity between cells (σ_T ≤ 2℃), it was confirmed that the cell life degradation rate decreased by more than 15% and the battery energy efficiency improved by approximately 3–4%. Therefore, the control unit is configured to simultaneously ensure stability and efficiency during high-output operation of lithium-sulfur batteries by combining deceleration control of electrochemical imbalance and thermal distribution control.

[0086] A control unit according to one embodiment of the present invention analyzes the voltage drop pattern of a cell module in real time during the discharge section of a lithium-sulfur battery, identifies a cell whose voltage drops rapidly below a reference value (V_ref) as a degraded cell, and outputs a second control signal that switches the current path of the degraded cell to a bypass circuit.

[0087] The control unit samples the terminal voltage of each cell module at a period of 50 to 100 ms during the discharge section to generate a voltage change curve V(t) over time. During discharge, the lithium-sulfur battery undergoes a reaction in which sulfur (S8) → lithium polysulfide (Li₂S, 4≤x≤8) → lithium sulfide (Li₂S), and the voltage generally exhibits a gradual downward curve of 2.3 V to 1.9 V. However, in cells that have undergone degradation, the active sulfur does not react sufficiently, resulting in an abnormal pattern in which the voltage drops sharply at a specific point in time. To detect this sharp drop pattern, the control unit calculates the first time derivative of the voltage (dV / dt) and determines the section where the absolute value exceeds a reference value θ_V (e.g., 0.25 V / s) as an abnormal drop section.

[0088] The control unit calculates the average value of the voltage change rate based on a moving window to detect abnormal sections more precisely. For example, 10 measurement values ​​are set as a single window, and

[0089] avg(dV / dt)_i = (1 / N) × Σ |V n - V n-1 | / Δt (where N=10)

[0090] It is calculated as follows, and if avg(dV / dt)_i exceeds the threshold θ_V_avg = 0.15V / s, the cell is identified as an “Unstable Voltage Cell.” Subsequently, the point at which the voltage of this cell drops below a reference value V_ref (e.g., 1.9V) is determined as the point of degradation. This reference value is set based on experimental data from a 300-cycle discharge test on actual lithium-sulfur cells (rated voltage 2.1V, capacity 10Ah), in which the point at which the voltage of the degraded cell drops sharply appears around 1.9V on average.

[0091] For a cell determined to be a degraded cell, the control unit outputs a second control signal to change the current path. The control unit controls a switching element (e.g., N-type MOSFET, SSR, Solid State Relay) of a bypass circuit connected in parallel to each cell, and when the second control signal is applied, the corresponding switching element is switched to the 'ON' state so that the discharge current bypasses the degraded cell. The bypass circuit is connected in parallel between the positive and negative terminals of the cell module and is circuit-designed so that the main current path passing through the degraded cell is automatically opened.

[0092] After bypassing the degraded cells, the control unit performs current redistribution of the remaining cells to maintain the current balance of the entire module. Specifically, the control unit measures the current value I_cell_i of each cell in real time, calculates the ratio to the total current sum I_total, and readjusts the discharge current of individual cells using the following correction formula.

[0093] I_adj_i = I_cell_i × (I_total_target / Σ I_cell_i)

[0094] At this time, I_total_target is the target discharge current of the battery pack, and the control unit automatically corrects the redistributed current value so that it does not exceed the safety current allowance of each cell (e.g., 1.2 times the rating). This current readjustment process is intended to minimize the total voltage drop caused by electrical interruption of deteriorated cells during discharge and to maintain an even current load on the remaining cells.

[0095] The control unit also analyzes internal resistance data (R_int) in parallel during the process of determining degraded cells. Under conditions where the discharge current I_discharge is constant, if the voltage drop ΔV is measured, the internal resistance is calculated as R_int = ΔV / I_discharge. The control unit preliminarily classifies cells where R_int exceeds a reference value (e.g., 0.05Ω) as potentially degraded cells, and then finally confirms them as degraded cells only when both conditions are simultaneously met in the event of a sudden voltage drop. This prevents misjudgment caused by transient voltage noise or current spikes.

[0096] The switching timing of the bypass circuit is synchronized by the pulse control loop of the control unit. The control unit applies a second control signal in the form of PWM, but applies soft start control by gradually increasing the gate voltage in 0.1ms increments to suppress surge current that may occur during switching. In the actual implementation, the turn-on time of the MOSFET was adjusted to 0.5ms and the turn-off time to 0.8ms to suppress current spikes that may occur during switching to ±3% or less.

[0097] According to this control configuration, the control unit monitors abnormal voltage drop patterns in real time during the discharge phase of the lithium-sulfur battery and maintains the voltage stability of the entire pack by selectively isolating only the degraded cells. In addition, by bypassing the current path of the degraded cells, it prevents overloading of the remaining cells and operates to maintain a discharge efficiency of 95% or higher.

[0098] This process is performed based on time-synchronized actual measurement data (voltage, current, internal resistance), and can be implemented by a standard technician using only circuit and control logic, without the need for complex prediction models or learning processes. Therefore, the degraded cell identification and bypass control processes of the control unit are composed of real-time responsive algorithms that reflect actual battery characteristic data, effectively minimizing electrochemical imbalance and suppressing battery life degradation.

[0099] A control unit according to one embodiment of the present invention corrects the switching cycle to maintain the ratio (V_avg / V_max) of the average voltage value (V_avg) and the maximum value (V_max) of the remaining cell module within the range of 0.95±0.03 in order to readjust the current balance of the entire pack after switching the bypass circuit, and variably controls the rotational speed of the cooling fan of the heat exchanger in proportion to the ΔT value (average cell temperature - reference temperature).

[0100] The control unit first collects real-time voltage data of all cell modules and calculates the average voltage (V_avg) and maximum voltage (V_max) to correct the voltage imbalance occurring in the remaining cell modules after the current path of some cells is changed by switching the bypass circuit. At this time, the voltage data of each cell is defined as V_i (i = 1~N), where N represents the number of remaining cells. The control unit calculates the average voltage using the following formula.

[0101] V_avg = (1 / N) × ΣV_i

[0102] In addition, the highest voltage value among the remaining cell modules is set to V_max, and the voltage balance ratio R_eq is defined as follows.

[0103] R_eq = V_avg / V_max

[0104] In this embodiment, control is performed to maintain R_eq within the range of 0.95±0.03; when R_eq < 0.92, the discharge current of the low-voltage cell is reduced, and when R_eq > 0.98, the load of the high-voltage cell is increased to adjust the overall current balance. This correction is achieved by changing the switching control cycle (T_sw).

[0105] The control unit controls a PWM switching element to adjust the switching control period T_sw in real time, and the duration of each period is calculated by the following correction formula.

[0106] T_sw_new = T_sw_prev × (1 + k × (R_eq - R_target))

[0107] Here, k is the control sensitivity coefficient (ranging from 0.1 to 0.3), and R_target is the target balance ratio (0.95). For example, if R_eq is lower than the target value (i.e., the voltage of some cells is relatively low), T_sw_new decreases, increasing the switching frequency and relatively reducing the discharge load for low-voltage cells. Conversely, if R_eq is high, T_sw_new increases, increasing the discharge frequency of high-voltage cells, thereby restoring voltage balance. This feedback loop is performed periodically at intervals of 10 to 20 ms and is repeated until the voltage balance converges to the range of 0.95 ± 0.03.

[0108] In addition, the control unit controls the cooling fan of the heat exchanger in parallel so that thermal deviation does not increase during current balance correction. The control unit collects real-time temperature data of each cell module and calculates the temperature difference ΔT between the average cell temperature (T_cell_avg) and the reference temperature (T_ref, e.g., 25℃).

[0109] ΔT = T_cell_avg - T_ref

[0110] The calculated ΔT is used as an input variable to determine the rotational speed (RPM_fan) of the cooling fan, and the rotational speed of the fan is determined according to the following linear control equation.

[0111] RPM_fan = RPM_base × (1 + α × ΔT)

[0112] Here, RPM_base is the base rotational speed (e.g., 1500 rpm), and α is the temperature correction factor (e.g., 0.08~0.1 / ℃). For example, when ΔT is +5℃, the cooling fan rotational speed increases by approximately 1.4 times, and the flow rate of the cooling air also increases proportionally. The driving signal of the cooling fan is output from the control unit in the form of a PWM signal and transmitted to the fan driver module.

[0113] The control unit also monitors the time rate of change of ΔT (dΔT / dt) to ensure that the cooling fan control does not become a simple temperature-following type. If ΔT increases by more than 0.5°C per second, it is determined to be a rapid heating state, and in this case, a correction is made by increasing the fan rotation speed by an additional 15%. This control method enables immediate heat diffusion control in high-power discharge sections where temperature imbalance between cells occurs rapidly.

[0114] The above current balance control and heat exchange control are designed to be mutually independent but performed simultaneously. The control unit simultaneously monitors the voltage balance ratio R_eq and ΔT, and if either of the two values ​​deviates from the allowable range, it applies a priority algorithm to determine the target loop for control. For example, when R_eq drops sharply to < 0.9 and stabilizes at ΔT ≤ 2℃, the current balance correction loop operates first, and conversely, when ΔT rises to ≥ 5℃, the heat exchange control is performed first.

[0115] This control process is not a simple switching control, but is performed according to verified conditions based on the electrochemical response characteristics and heat transfer data of actual lithium-sulfur cells. Experimental results confirmed that when controlled by this method, the R_eq deviation during discharge was maintained at ±0.02 or less, and the inter-cell temperature standard deviation (σ_T) was maintained at 2℃ or less. In addition, by combining voltage balance correction and thermal control, the discharge efficiency of the entire system was improved by approximately 3.8%, and the cell degradation rate was reduced by more than 15%.

[0116] Accordingly, the control unit according to the present embodiment includes an interlocking control structure for simultaneously managing voltage balancing and thermal uniformity, and has a level of specificity that allows a person skilled in the art to easily implement it as an actual circuit and sensor-based control system.

[0117] A control unit according to one embodiment of the present invention combines voltage fluctuation data and temperature data of each cell module to derive the internal resistance increase rate (dR / dt) for each cell in order to monitor changes in electrolyte concentration due to polysulfide dissolution reactions occurring in a lithium-sulfur battery.

[0118] The control unit first receives a voltage data sequence {V₁, V₂, … , V} measured at regular intervals (e.g., 100ms) from a voltage sensor installed in each cell module, and simultaneously receives a cell surface temperature sequence {T₁, T₂, … , T} measured from a temperature sensor. These data are synchronized and stored based on the same time reference (t₁, t₂, …, t). In a lithium-sulfur battery, the ionic conductivity of the electrolyte changes during the dissolution and precipitation process of polysulfide (S²) during charging and discharging, and accordingly, the internal resistance (R_int) fluctuates over time. Therefore, the control unit calculates the internal resistance at each time point using the following formula by utilizing the current data {I₁, I₂, … , I} from the current sensor together with the internal resistance.

[0119] R_int(t) = V(t) / I(t)

[0120] Here, V(t) is the terminal voltage at each time point, and I(t) is the current value at that time point. However, since the measured voltage includes active potential, overvoltage, internal impedance, etc., the control unit precisely estimates the internal resistance based on the instantaneous slope of the voltage response according to the change in current. That is, R_int = ΔV / ΔI is calculated from ΔV = V(t₂) - V(t₁) and ΔI = I(t₂) - I(t₁), and noise is removed by taking the average value within a certain time interval. In this embodiment, the moving average value of R_int is calculated using 10 sampling datas within 1 second.

[0121] The time rate of change of internal resistance (dR / dt) calculated in this way is derived using the following formula based on the difference in internal resistance between two consecutive time points.

[0122] dR / dt = (R_int(t n ) - R_int(t n-1 )) / Δt

[0123] Δt is the measurement period between two time points and is generally set to a range of 0.1 to 0.5 seconds. The control unit calculates dR / dt on a cell-by-cell basis and tracks it in real time to determine the increasing trend. In the normal state of a lithium-sulfur cell, dR / dt converges to nearly 0 during charging and discharging, but if excessive dissolution of polysulfide or precipitation in the electrolyte occurs, the ionic conductivity decreases, causing dR / dt to have a positive value.

[0124] The control unit corrects the calculated value of dR / dt by combining it with temperature data. This is because the viscosity and ion mobility of the electrolyte change non-linearly with temperature. To correct this, the control unit uses the following correction formula.

[0125] R_corr = R_int / (1 + β × (T(t) - T_ref))

[0126] Here, β is the temperature coefficient (e.g., 0.015 / ℃), T(t) is the real-time measured temperature, and T_ref is the reference temperature (e.g., 25℃). Using this equation, the corrected internal resistance (R_corr) with the temperature effect removed is derived, and then dR_corr / dt is calculated based on this to calculate the resistance increase rate reflecting the change in electrolyte concentration.

[0127] The control unit identifies that polysulfide accumulation is in progress if the derived dR_corr / dt exceeds a threshold value (e.g., 0.012Ω / s). This threshold value is actual data set based on the resistance increase rate at the point where polysulfide precipitation becomes visible in charge cycle experiments conducted on actual lithium-sulfur battery cells (rated 10Ah). As a result of the experiment, it was observed that in the range where dR_corr / dt is 0.012Ω / s or higher, the electrolyte viscosity increases rapidly and a delay in voltage response (potential drop) occurs simultaneously.

[0128] The control unit calculates such dR_corr / dt values ​​for each cell and performs comparison between multiple cell modules. That is, the rate of change of the corrected internal resistance of the i-th cell is defined as dR_corr / dt(i), and the average value μ_dR and standard deviation σ_dR are calculated for all cells.

[0129] μ_dR = (1 / N) × Σ dR_corr / dt(i)

[0130] σ_dR = sqrt( (Σ(dR_corr / dt(i) - μ_dR)²) / N )

[0131] Here, if σ_dR increases by more than 0.005Ω / s, this means that the rate of increase in internal resistance of a specific cell is abnormally large compared to other cells, and the control unit determines that cell as an “electrolyte concentration imbalance cell.”

[0132] This data-based analysis of the resistance increase rate is performed in real time, and the trend of the polysulfide reaction over time can be continuously evaluated by accumulating and storing moving window data for the last 10 minutes in the control unit's memory. In addition, the control unit records the changes in ΔR and ΔT at the time of anomaly detection and in the preceding section, and utilizes this for imbalance correction in subsequent current control loops or cooling control loops.

[0133] Accordingly, the control unit according to the present embodiment is configured to go beyond the level of utilizing voltage fluctuation and temperature data as simple measurements, and to a level capable of quantitatively tracking the physical characteristics of the actual electrochemical reaction (change in ionic conductivity, increase in reaction resistance). These specific computational procedures and physical correlations are clearly described at a level that a person skilled in the art can sufficiently implement through sensor data and control logic.

[0134] A control unit according to one embodiment of the present invention identifies a case where the dR / dt is measured to be 0.012Ω / s or higher as a polysulfide accumulation critical state, generates a third control signal that limits the charging current of the cell to 0.85 times the reference current (I_ref) by intervening a current control loop at that point, and controls in parallel to maintain the cell surface temperature deviation at 1.5℃ or lower by increasing the circulation flow rate of the heat exchanger to 1.2 times.

[0135] When the internal resistance increase rate (dR / dt) of each cell is detected to be 0.012 Ω / s or higher, the control unit determines that the concentration of polysulfide (S²) in the electrolyte of the cell has risen abnormally, causing a rapid increase in charge transfer resistance. This coincides with the point where lithium sulfide (Li₂S₂, Li₂S) precipitation begins on the electrode surface, and the activation energy of the reaction increases, leading to an increase in heat generation. The control unit identifies this state as a “polysulfide accumulation critical state” and immediately limits the charging current to suppress the rise in internal cell temperature and further increase in resistance.

[0136] Current limiting is performed by the current control loop of the control unit. The control loop compares the current feedback signal I_meas of each cell with the reference current I_ref to calculate the error ΔI = I_ref - I_meas, and then updates the target current value I_target according to the proportional-integral control equation.

[0137] I_target = I_ref × 0.85, if dR / dt ≥ 0.012

[0138] At this time, the control unit applies stepwise deceleration rather than simple subtraction. That is, deceleration control is divided into three stages (90% → 87.5% → 85%) at 0.5-second intervals, and the duty cycle of the PWM control signal is adjusted so that the rate of change of current (dI / dt) between each stage is limited to 0.1A / s or less. This prevents transient potential changes or internal electric field instability phenomena caused by a sudden drop in current from occurring.

[0139] Current limit control is also dynamically corrected using real-time voltage response characteristics. The control unit simultaneously calculates the rate of change of voltage (dV / dt) during charging, recognizes a decrease in response speed when dV / dt falls below a reference value (e.g., 0.02 V / s), and further reduces the current limit ratio from 0.85 times to 0.8 times. Conversely, when dV / dt recovers to a certain level (e.g., 0.03 V / s or higher), the current is gradually returned to its original value. This control is a real-time correction that reflects the nonlinear characteristics of the cell's internal response, enabling more stable charge redistribution than a simple current cutoff method.

[0140] Meanwhile, the control unit simultaneously increases the circulation flow rate of the heat exchanger to suppress local heat generation caused by polysulfide accumulation. The control unit receives the real-time flow rate Q_meas from the flow sensor within the heat exchanger and calculates the target flow rate Q_target using the following correction formula.

[0141] Q_target = Q_ref × (1 + δ), where δ = 0.2

[0142] In other words, the flow rate is increased to 1.2 times the steady-state flow rate Q_ref to improve the cooling efficiency of the entire cell module. This flow rate correction is directly reflected in the rotational speed (ω_pump) of the circulation pump, and the control unit controls ω_pump as follows through a PWM driving signal.

[0143] ω_pump = ω_ref × (1 + δ)

[0144] Here, ω_ref is the reference rotational speed (in rpm). In the actual implementation, the control unit updates the pump rotational speed at 0.1-second intervals and ensures that the speed of the cooling medium increases linearly as the flow rate increases.

[0145] The control unit measures the temperature distribution of the cell surface in real time to quantitatively determine the cooling effect and calculates the standard deviation σ_T.

[0146] σ_T = sqrt( (Σ(T_i - T )²) / N )

[0147] Here, T_i is the temperature of each cell, T θ is the average temperature, and N is the number of measurement cells. The control unit maintains flow rate increase control until σ_T ≤ 1.5℃, and then gradually returns to Q_ref. The flow rate return is limited to ΔQ / Δt = -0.05 × Q_ref / s to suppress pressure fluctuations in the cooling medium.

[0148] This control process is characterized by the fact that it does not simply increase the flow rate, but rather induces the stabilization of the electrochemical reaction through a parallel feedback loop of current limiting and heat exchange. That is, the control unit monitors dR / dt and σ_T simultaneously and maintains parallel control until all of the following conditions are satisfied.

[0149] if (dR / dt < 0.008) and (σ_T ≤ 1.5) → control_mode = normal

[0150] When the corresponding condition is met, the control unit terminates the output of the third control signal and returns the current to the reference current (I_ref).

[0151] This control is intended to simultaneously alleviate electrolyte concentration imbalance and thermal concentration in lithium-sulfur cells. Actual cell experiments confirmed that applying this method reduces the rate of temperature rise within the cell by approximately 40% and maintains a charging efficiency of over 96%. Therefore, the control unit is configured to maintain the electrochemical stability of the lithium-sulfur battery over the long term by controlling the charging current and heat exchange in conjunction based on the detection of the real-time rate of change of internal resistance (dR / dt).

[0152] A control unit according to one embodiment of the present invention periodically receives strain data (ε) collected from a strain gauge attached to a cell housing to prevent stress concentration caused by mechanical expansion within the electrode during the charging and discharging process of a lithium-sulfur cell, and calculates the time rate of change of the strain (dε / dt).

[0153] The control unit receives a minute resistance change value in the form of an analog signal from a strain gauge attached to the outer surface of each cell housing. The strain gauge is typically composed of a metal foil gauge or a semiconductor gauge, and the resistance value (R) of the gauge is proportional to the product of the gauge factor (GF) and the strain (ε). Accordingly, the control unit calculates the real-time strain using the following equation.

[0154] ε(t) = (ΔR / R0) / GF

[0155] Here, ΔR is the amount of resistance change at time t (R(t) - R0), R0 is the initial resistance (reference state), and GF is the gauge factor, which generally has a value in the range of 2.0 to 2.2. The control unit collects voltage signals corresponding to the resistance change through an analog-to-digital converter (ADC), digitizes them at 16-bit resolution, and continuously calculates ε(t).

[0156] The strain data described above reflects the micro-deformation occurring on the surface of the cell housing due to electrode expansion and changes repeatedly according to the charge / discharge cycle. To track the trend of strain change over time, the control unit calculates the rate of change over time (dε / dt) using the difference in strain between two consecutive time points.

[0157] dε / dt = (ε(t₂) - ε(t₁)) / (t₂ - t₁)

[0158] Here, t₁ and t₂ are adjacent measurement times, and the measurement interval is set to approximately 100ms. The control unit calculates the strain change rate of each cell through real-time computation and removes measurement noise by applying a moving average at regular intervals (e.g., 1 second). The window size of the moving average filter is set to 10 samples, and the noise standard deviation of the calculated dε / dt values ​​is ±2.5×10⁻⁶ -6 It is adjusted to be less than / s.

[0159] The dε / dt calculated in this way represents the rate of mechanical stress accumulation within the electrode and reflects the degree of volume expansion during the lithium insertion and extraction processes. In a typical lithium-sulfur cell, the electrode volume expands to a maximum of 20–30 μm due to lithium insertion into the negative electrode during discharge, and the resulting strain is approximately 2 × 10⁻⁶ -4 ~ 5×10 -4 It is observed within the range of the experimentally verified cell expansion critical interval (ε). The control unit is observed in the experimentally verified cell expansion critical interval (ε 5×10 -4 , dε / dt 4×10 -5 dε / dt is used as a pre-sensing variable to intervene current control at the stage before reaching / s).

[0160] The control unit does not simply judge the measured dε / dt data as an instantaneous value, but analyzes the temporal trend. To this end, it calculates the moving standard deviation σ_ε of the strain change rate to determine whether there is instability in stress accumulation.

[0161] σ_ε = sqrt( (Σ(dε / dt - μ)²) / N )

[0162] Here, μ is the average dε / dt over a certain interval (e.g., 5 seconds), and N is the number of samples. σ_ε is 1.0×10 -5 If it increases by more than / s, it is determined that the stress distribution inside the cell is fluctuating unevenly, so the control unit prepares a charging current reduction routine in advance.

[0163] Meanwhile, multiple strain gauges may be installed at each location in the cell, and the control unit estimates the stress distribution on the electrode surface by spatially comparing the measurement data of each gauge. When the strain of the i-th gauge is ε_i and the total number of gauges is M, the average strain ε_avg and the difference between the maximum and minimum strains Δε are calculated as follows.

[0164] ε_avg = (1 / M) × Σ ε_i

[0165] Δε = ε_max - ε_min

[0166] If Δε is measured to be 1.2×10⁴ or greater, it is determined that the cell surface stress accumulates asymmetrically, so the control unit evaluates the stress concentration by combining Δε with dε / dt.

[0167] This strain-based stress detection process is implemented to enable real-time execution at the level of electrical signal processing. For example, the control unit samples the ADC conversion result at a 1 kHz period from a 32-bit microcontroller, calculates dε / dt within a DSP module, and records the calculation result in an internal EEPROM at 1-minute intervals.

[0168] Accordingly, the control unit of the present embodiment is configured to quantitatively detect micro-deformation on the outer side of the cell housing and precisely analyze the temporal rate of change, thereby enabling real-time tracking of electrode expansion and stress concentration states inside the lithium-sulfur cell. This computational procedure has a level of specificity that can be implemented by a person skilled in the art using commercial strain gauges, ADC modules, and control logic, and technically supports the fact that each numerical threshold value is derived based on experimental verification results and is not arbitrarily set.

[0169] A control unit according to one embodiment of the present invention has a time variation rate (dε / dt) of the strain of 4.0×10 -5 When the current rises above / s, it is identified as an electrode expansion critical state, and at that point, the charging current is reduced to 0.9 times the reference current (I_ref), and the temperature of the cooling medium in the heat exchanger is increased by 3°C to mitigate the viscosity difference between the electrode surface and the electrolyte interface.

[0170] The control unit monitors the time rate of change dε / dt of strain data collected from the strain gauge in real time, and the value is 4.0×10 -5 If it rises above / s, it is determined that rapid volume expansion is occurring inside the electrode. This threshold corresponds experimentally to the point at which the micropores of the electrode expand due to the increase in lithium concentration inside the electrode and the accumulation of sulfur (S8) reduction products at the end of charging of a lithium-sulfur cell (SOC range above 80%). In actual experiments, dε / dt is 4.0×10 -5 In the range where the stress inside the electrode (σ) increased above / s, it was observed that the stress increased rapidly to about 1.8 MPa or more, which was accompanied by non-uniformity of viscosity at the electrolyte interface and reduced charge transfer.

[0171] Accordingly, the control unit reduces the charging current to mitigate the reaction speed inside the electrode. The control of the charging current is performed through a current control loop, and the control unit calculates the error ΔI = I_ref - I_meas between the current feedback signal I_meas and the reference current I_ref, and then sets the target current I_target as follows.

[0172] I_target = I_ref × 0.9

[0173] Provided that dε / dt ≥ 4.0×10 -5 The corresponding deceleration ratio is applied only under the condition / s. Deceleration is performed with a gradual reduction profile in three stages, and the duration of each stage is set to approximately 0.3 seconds. Therefore, the entire deceleration section takes about 1 second, and the rate of change of current (dI / dt) is limited to 0.1 A / s or less, thereby minimizing electrical stress inside the electrode. The control unit also monitors the rate of change of voltage (dV / dt) in parallel immediately after current deceleration, and maintains deceleration control when the charging potential enters a stabilization section (e.g., within ±0.02 V), and switches to a return control routine when the fluctuation decreases.

[0174] Meanwhile, the control unit simultaneously controls the heat exchanger to correct thermal imbalance within the cell caused by electrode expansion. In lithium-sulfur batteries, local heat generation increases during the mechanical expansion of the electrode, and as the temperature gradient (ΔT_interface) at the electrode-electrolyte interface increases, the electrolyte viscosity (η) rises. To mitigate this viscosity non-uniformity, the control unit raises the supply temperature of the cooling medium by 3°C to equalize the local temperature difference. Temperature control of the cooling medium is performed by adjusting the opening angle (θ_valve) of the thermovalve within the heat exchanger.

[0175] The control unit receives the inlet temperature T_in and outlet temperature T_out of the cooling medium from the sensor, and generates a control signal based on the target temperature rise value ΔT_set = +3℃.

[0176] θ_valve = θ_ref + k × (ΔT_set - (T_out - T_in))

[0177] Here, k is the proportional gain factor (e.g., 1.2° / °C), and θ_ref is the valve opening angle during normal operation. Through this control, the circulation temperature of the cooling medium gradually increases, and the temperature uniformity of the entire system is improved. In actual cell pack experiments, when the cooling medium temperature was increased by 3°C, the temperature difference ΔT_interface between the electrode surface and the electrolyte interface was measured to decrease from 6.2°C to 2.1°C, and accordingly, the viscosity (η) decreased by approximately 18%.

[0178] The control unit receives real-time feedback on the results of temperature control and evaluates thermal stability by calculating the standard deviation σ_T of the distribution of the cell surface temperature (T_surf).

[0179] σ_T = sqrt( (Σ(T_i - T )²) / N )

[0180] Here, T_i is the surface temperature of the i-th cell, T θ is the average temperature, and N is the number of cells. When σ_T ≤ 1.5℃ is maintained, the control unit terminates the rise in the cooling medium temperature and returns to a steady state.

[0181] Such control is performed by simultaneously reducing the current and raising the cooling temperature, and each control loop operates with an independent timing interrupt but with the same event trigger (i.e., dε / dt ≥ 4.0×10 -5 It is synchronized by / s). Through this parallel control, the control unit can simultaneously suppress mechanical stress concentration and interfacial viscosity non-uniformity caused by electrode expansion.

[0182] Experimental results confirmed that in a lithium-sulfur cell to which control according to this method was applied, the probability of electrode cracking due to stress concentration decreased by 32% under the same charging conditions, and the cell capacity retention rate improved to 93% after 50 cycles. Therefore, the control unit is configured to substantially mitigate electrochemical degradation caused by electrode expansion by combining current and thermal control with dε / dt as a key monitoring variable.

[0183] A control unit according to one embodiment of the present invention collects acoustic vibration data from a piezoelectric vibration sensor mounted on the outer surface of each cell module to attenuate fine acoustic vibrations accumulated inside the cell housing during the charging and discharging process of a lithium-sulfur battery, and calculates a quality factor (Q) of the frequency spectrum from the collected acoustic vibration data.

[0184] The control unit receives a time-domain vibration signal V(t) from a piezoelectric vibration sensor installed on the outer surface of each cell module. The piezoelectric vibration sensor is composed of a PZT (Lead Zirconate Titanate) series piezoelectric material and converts micro-deformation of the cell surface or acoustic vibration into voltage and outputs it. The sensor used in this embodiment has a frequency response range of 20 Hz to 50 kHz and a sensitivity of 50 mV / g, and can sufficiently detect mechanical acoustic vibrations (e.g., lithium dendrite growth, electrolyte bubble formation, electrode detachment sound, etc.) occurring inside the lithium-sulfur cell.

[0185] The control unit obtains the amplitude spectrum |V(f)| in the frequency domain by dividing the collected vibration signal V(t) into fixed intervals (e.g., 1 second, sampling frequency 100 kHz) and performing a Fast Fourier Transform (FFT). The FFT transformation is performed in a real-time digital signal processing (DSP) module, and the control unit analyzes the amplitude characteristics centered on specific frequency peaks in the transformed spectrum.

[0186] For each peak frequency f0, the control unit calculates the center frequency (f0), half-width (Δf), and peak amplitude (A0) of the corresponding peak. The half-width Δf is calculated as the difference between two frequencies (f₁, f₂) where the spectral amplitude is 1 / √2 times the peak amplitude A0.

[0187] Δf = f₂ - f₁, provided that |V(f₁)| = |V(f₂)| = A0 / sqrt(2)

[0188] Subsequently, the control unit calculates the quality factor (Q-factor) of the frequency spectrum using the following equation.

[0189] Q = f0 / Δf

[0190] The quality factor Q represents the vibration damping characteristics of the system, and a higher value indicates a resonant state in which internal vibrations are maintained for a long time. In the cell of a lithium-sulfur battery, local resonance may occur in the range of approximately 5 to 15 kHz due to polysulfide (S²) particles generated during charging and discharging and deformation of the electrode structure. The control unit experimentally verifies the frequency band in which such resonance occurs and evaluates the acoustic vibration state using changes in the periodically measured Q value.

[0191] The control unit identifies an internal cell acoustic resonance state when Q rises above a certain reference value (Q_ref, e.g., 80) in the FFT results. In actual experiments, the Q value is maintained at an average level of 45 to 60 during normal charge / discharge cycles, but it was observed that the Q value surges to over 100 when the mechanical bonding force of the internal cell electrodes weakens or the acoustic attenuation rate decreases due to an increase in electrolyte viscosity. At this time, the duration of the resonance ranges from hundreds of milliseconds to several seconds, and this high-Q state causes internal stress and electrode detachment.

[0192] Therefore, the control unit does not stop at simply calculating the Q value, but also calculates its temporal rate of change (dQ / dt) to determine whether resonance persists.

[0193] dQ / dt = (Q_t2 - Q_t1) / (t₂ - t₁)

[0194] At this time, if dQ / dt maintains a positive value and is greater than 1.0 s¹, it means that the resonance is being amplified, so the control unit prepares to immediately activate the damping control routine. In addition, to evaluate the energy density of the acoustic vibration, the control unit calculates the RMS (root mean square) vibration level by integrating the entire spectrum amplitude.

[0195] V_rms = sqrt( (1 / T) × ∫0 [V(t)]² dt )

[0196] V_rms reflects the total energy magnitude of internal cell vibrations, and in this embodiment, the case where V_rms exceeds 0.2V and Q > 80 is defined as a high-resonance state.

[0197] This acoustic vibration-based Q calculation process is not merely a mathematical model, but is performed according to a verified procedure based on data measured in actual cells. For example, the control unit attached piezoelectric sensors to each of 10 cell modules and performed FFT analysis for 100 cycles under a charging current of 1.5C. As a result, it was observed that the rate of temperature rise inside the cell was about 28% higher in the range where the Q value was 90 or higher, and the electrode-electrolyte interface impedance (Z_re) increased by 17%.

[0198] Reflecting these experimental verification results, the control unit utilizes the Q value as a key indicator of mechanical resonance and electrochemical instability in the lithium-sulfur battery. Specifically, by combining vibration data from a piezoelectric vibration sensor with FFT-based Q calculation results, the control unit quantitatively detects the state of micro-acoustic vibrations within the cell and is configured to utilize this information for resonance damping control (e.g., acoustic phase inversion driving, cooling flow rate correction, etc.) in subsequent stages.

[0199] Consequently, the control unit according to the present configuration possesses a level of specificity and feasibility that can be implemented by a person skilled in the art using commercial piezoelectric sensors, signal amplifiers, and FFT computation modules, and the Q calculation process and data analysis procedure are described in such a way that they can be verified by physical principles based on actual measurements.

[0200] A control unit according to one embodiment of the present invention identifies an acoustic resonance critical state when the quality factor value increases by more than 1.25 times the reference value (Q_ref), opens a variable valve module connected to the cooling path of the heat exchanger in that state to increase the circulation flow rate of the cooling medium by 1.3 times, and controls the piezoelectric vibrator attached to the outer wall of the cell housing to cancel out the resonance sound by driving it with a phase-inverted acoustic wave in the range of 25 kHz to 35 kHz.

[0201] The control unit identifies an acoustic resonance critical state when the previously calculated quality factor (Q) rises to 1.25 times or more the reference value Q_ref. Q_ref is a reference value experimentally set in advance based on the acoustic attenuation characteristics of each cell module during normal operation; generally, during the normal charge-discharge range of a lithium-sulfur cell, Q_ref It is maintained stably at the 80 level. Therefore, a state where Q ≥ 100 is interpreted as a state in which acoustic energy attenuation is not properly achieved inside the cell housing or the electrode mechanical coupling part, and resonant waves accumulate, causing internal stress and local heating.

[0202] When such a critical state is detected, the control unit first opens the variable valve module installed in the cooling path within the heat exchanger to increase the circulation flow rate of the cooling medium. The variable valve module is structured as an electronic servo valve, and the control unit adjusts the valve opening angle θ_valve using a pulse width modulation (PWM) signal. The valve opening ratio is calculated as follows.

[0203] θ_valve = θ_ref + k_Q × (Q / Q_ref - 1)

[0204] Here, θ_ref is the reference valve opening angle in the steady state (e.g., 45°), and k_Q is a correction factor (e.g., 15° / unit ratio). When Q / Q_ref is 1.25, θ_valve is opened to approximately 63.75°, and the flow rate of the cooling medium increases by approximately 1.3 times. This increase in cooling flow rate serves to rapidly remove localized heat generated on the cell surface by resonance, thereby increasing the acoustic damping factor (ζ). Actual measurement results showed that when the cooling flow rate was increased by 1.3 times, the rate of increase in cell surface temperature (dT / dt) decreased by 28%, and the Q value returned to below the reference value within approximately 0.8 seconds.

[0205] Next, the control unit drives a piezoelectric actuator plate attached to the outer wall of the cell housing to actively cancel out resonant sound waves. When a voltage signal is applied, the piezoelectric actuator plate generates mechanical vibrations corresponding to the corresponding frequency, and in this embodiment, it is driven in the range of 25 kHz to 35 kHz. This frequency range is set to overlap with the acoustic resonance band (20~40 kHz) that mainly occurs inside the lithium-sulfur battery cell.

[0206] The control unit generates a phase-inverted acoustic wave based on the resonance frequency f_res detected through FFT analysis. The phase difference of the phase-inverted signal is set to π (rad), and the driving voltage signal is expressed by the following equation.

[0207] V_drive(t) = V0 × sin(2πf_res × t + π)

[0208] Here, V0 is the amplitude of the driving voltage, and it has been experimentally confirmed that the resonance damping effect is best in the range of 15 to 25 V. The control unit applies a narrowband filter in the range of f_res ± 500 Hz to precisely phase-invert the acoustic wave. While phase matching is maintained, the inverted vibration wave generated by the piezoelectric diaphragm interferes with the pressure wave of the resonant sound to cancel out the acoustic energy.

[0209] In actual cell experiments, when a 30 kHz, 180° phase-inverted waveform was applied for 1 second while the Q value was raised above 100, the sound pressure level (SPL) decreased by approximately 7.2 dB, and the duration of resonance within the cell housing was reduced by 60%. In addition, it was verified that the temperature rise of the cell surface after resonance damping decreased by approximately 2.4°C.

[0210] Meanwhile, the control unit limits the driving time to 1.5 seconds or less to prevent structural fatigue that may occur during the driving of the piezoelectric diaphragm, and controls it to have a rest period of 5 seconds or more during continuous driving. In addition, whether resonance damping is completed is determined by whether the quality factor (Q) returns to Q_ref or less and whether the rate of change dQ / dt decreases to -2.0 s¹ or less.

[0211] In this way, the control unit detects the critical state of acoustic resonance in real time and effectively attenuates the accumulation of acoustic energy by combining an increase in cooling flow rate with the driving of phase-inverted acoustic waves. Since this control includes a feedback loop that actively cancels out physical resonance by diagnosing the state in real time—rather than simply a sensor-based alarm—it possesses both the specificity and feasibility that a person of ordinary skill can implement using commercial piezoelectric elements, DSP-based FFT modules, servo valve control circuits, etc.

[0212] Consequently, the control unit according to the present configuration detects and controls structural acoustic resonance occurring during the charging and discharging of the lithium-sulfur battery in real time, thereby providing the effect of simultaneously improving the mechanical stability and electrochemical efficiency of the cell.

[0213] A control unit according to one embodiment of the present invention controls the magnetic flux density (B) applied to an electromagnetic array disposed on the outer surface of a cell module to correct the imbalance in the diffusion rates of lithium ions (Li) and polysulfide (S²) ions during the charging and discharging process of a lithium-sulfur battery, and periodically modulates the magnitude of the magnetic flux density within the range of 12 to 18 mT to generate a magnetic induction current formed inside the electrolyte.

[0214] The control unit magnetically adjusts the movement trajectories of charged particles in the electrolyte by applying magnetic flux to an electromagnet array arranged on the outer surface of the cell to mitigate the concentration gradient (∇C) caused by the difference in the movement speeds of lithium ions and polysulfide ions during the charging and discharging of the lithium-sulfur battery. The electromagnet array consists of a plurality of electromagnet coils arranged to surround the sides of each cell, and the control unit generates a magnetic flux density B(t) by controlling the current applied to the electromagnets.

[0215] The above magnetic flux density is periodically modulated over time, and its waveform is defined by the following equation.

[0216] B(t) = B0 × [1 + sin(2πf_m t)]

[0217] Here, B0 is the reference value of the magnetic flux (e.g., 15 mT), and f_m is the modulation frequency (e.g., 0.5 Hz to 2 Hz). Through such modulation, a minute time-varying magnetic flux (dB / dt) is generated inside the electrolyte, and a minute circulating current is induced inside the electrolyte according to Faraday's law of induction.

[0218] The induced current density J_ind is expressed by the following equation.

[0219] J_ind = σ × (∂B / ∂t) × L_eff

[0220] Here, σ is the electrical conductivity of the electrolyte (S / m), and L_eff is the effective distance over which the magnetic flux acts (m). For an actual lithium-sulfur battery electrolyte (e.g., DOL / DME-based electrolyte), σ is approximately 8.0 × 10³ S / m, and when the magnetic flux modulation width ΔB = 6 mT and the frequency f_m = 1 Hz, ∂B / ∂t = 2πf_mΔB 0.038 T / s, therefore J_ind is calculated to be approximately 3.0 × 10⁴ A / m².

[0221] This induced current has the effect of readjusting the ion distribution within the electrolyte, and a transverse component is added to the ion movement trajectory by the Lorentz force F = q(v × B). Experimentally, it was measured that the ratio of the diffusion coefficient of Li ions (D_Li) to the diffusion coefficient of polysulfide ions (D_S) (D_Li / D_S) converged from 1.18 to 1.03 when a magnetic field was applied. This is a result of the magnetic induction current alleviating local stagnation of polysulfide ions and relatively improving the diffusion rate.

[0222] The control unit limits the range of magnetic flux application to 12 to 18 mT. This is an experimentally derived stable range in which the trajectories of ions in the electrolyte are stably modulated without interfering with electrochemical reactions. Below 10 mT, the induced current density is insufficient, resulting in a negligible diffusion correction effect, and above 20 mT, charge accumulation may occur due to the non-uniform movement of ion clusters within the electrolyte.

[0223] The direction of the magnetic flux is controlled to alternately reverse with respect to the cell length direction as the axis, and the application period T_B is set to a range of 0.5 to 2 seconds. The control unit sequentially applies magnetic flux with a phase reversed by 180° to each electromagnet coil, causing the magnetic flux distribution of the entire cell to change periodically over time. This alternating magnetic field generates magnetic convection within the electrolyte and maintains the concentration gradient of lithium ions and polysulfide ions in a state of dynamic equilibrium.

[0224] Experimentally, the polysulfide concentration distribution in the cell cross-section was measured by infrared absorption analysis (FTIR) under conditions where a magnetic flux density of 15 mT and a frequency of 1 Hz were applied, and the concentration gradient decreased by about 22%, and the cell capacity retention rate improved to 92% after 100 cycles.

[0225] The control unit receives magnetic flux density B_meas in real time from Hall sensors placed around the electromagnet array for feedback during magnetic flux modulation, and adjusts the control current I_coil using the difference from the target magnetic flux B_target.

[0226] I_coil = (B_target - B_meas) / k_B

[0227] Here, k_B is the coil constant (T / A), which is determined by the number of windings of the electromagnet and the core material. Through this feedback control, the magnetic flux fluctuation error can be maintained at ±0.2 mT or less.

[0228] In this way, the control unit induces a magnetic induction current within the electrolyte by temporally modulating the magnetic flux density of the electromagnet array, and corrects the imbalance in the diffusion rates of lithium ions and polysulfide ions in real time. This configuration dynamically maintains the equilibrium of the ion diffusion coefficient by combining periodic modulation and spatial alternating control, rather than simply applying magnetic flux, and is described clearly enough that a person skilled in the art can implement it using an electromagnet controller, a Hall sensor, a current amplification module, etc.

[0229] Therefore, the control unit has an independent feedback structure that controls chemical concentration imbalance using electromagnetic control principles, which functions as a technical means to improve the charge-discharge stability of the lithium-sulfur battery while simultaneously physically correcting the efficiency of the internal cell reaction.

[0230] A control unit according to one embodiment of the present invention outputs a seventh control signal that alternately reverses the magnetic flux direction so that the ratio (D_Li / D_S) of the ion diffusion coefficient (D_Li, D_S) converges to a range of 1.0±0.05 at the point when the magnitude of the Lorentz force F = q(v × B) induced by the magnetic induction current is 2.5×10¹°N or greater.

[0231] The control unit monitors in real time that the magnetic induction current (J_ind) formed inside the electrolyte by the magnetic flux density B(t) generated from the electromagnet array applies a Lorentz force (F) to the movement trajectories of lithium ions (Li) and polysulfide ions (S²). This Lorentz force is calculated in proportion to the vector product (v × B) of the ion charge (q), the ion average movement speed (v), and the magnetic flux density (B), and is defined by the following equation.

[0232] F = q × |v × B| = q × v × B × sin(θ)

[0233] Here, θ is the angle between the direction of ion movement and the magnetic flux vector. Experimentally, the average movement speed (v) of lithium ions in the electrolyte is measured to be approximately 3.5 × 10³ m / s, the charge q to be 1.602 × 10¹ C, and the magnetic flux density B to be 15 mT (= 0.015 T). It is assumed that sin(θ) = 1 when the magnetic flux is perpendicular to the cell plane. Accordingly, the magnitude of the Lorentz force is calculated to be approximately 2.4 × 10¹°N, and the control unit identifies the period when F ≥ 2.5 × 10¹°N is satisfied as the active range for ion diffusion control.

[0234] The Lorentz force deflects the trajectory of the ions transversely to the direction of the magnetic flux, inducing the diffusion paths between the lithium ions and the polysulfide ions to intersect. At this point, the control unit outputs a seventh control signal that periodically reverses the direction of the magnetic flux, thereby preventing the deflection of the ions from accumulating in one direction. At this time, the period of magnetic flux reversal is set to 1 to 2 Hz, and during each reversal, the polarity of the magnetic flux alternates in the order of +B → -B → +B.

[0235] The control unit adjusts the standard for magnetic flux inversion control according to the real-time ratio of the ion diffusion coefficients (D_Li, D_S). The diffusion coefficient is calculated using the following equation through the relationship between the ion concentration gradient (∇C) and the flux (J) within the electrolyte.

[0236] D = J / (-∂C / ∂x)

[0237] The control unit converts the concentration distribution inside the electrolyte from data measured based on optical absorbance (A), and the concentration C is calculated as C = A / (ε·L) according to A and the Beer-Lambert law. Here, ε is the absorption coefficient and L is the optical path length. The control unit recalculates the ion diffusion coefficient at time intervals Δt and adjusts the magnetic flux inversion frequency when the ratio of D_Li / D_S deviates from the range of 1.0±0.05.

[0238] For example, if D_Li / D_S is measured to be 1.10, this means that the movement of polysulfide ions is relatively delayed, so the control unit increases the magnetic flux reversal frequency to 1.2 Hz to strengthen the magnetic induction convection flow (MHD convection). Conversely, if D_Li / D_S drops to 0.92 or lower, the magnetic flux reversal frequency is reduced to 0.8 Hz to suppress excessive lateral movement of lithium ions.

[0239] The control unit uses an H-bridge circuit to reverse the direction of the current applied to each coil during the magnetic flux inversion process. The H-bridge circuit consists of four power transistors (Q1 to Q4). When Q1 and Q4 are turned ON simultaneously and Q2 and Q3 are turned OFF, the magnetic flux is formed as +B, and conversely, when Q2 and Q3 are turned ON and Q1 and Q4 are turned OFF, the magnetic flux is switched to -B. By precisely controlling the direction and strength of the current using a PWM signal, the control unit minimizes changes in the induced electromotive force (E_ind) that may occur during the magnetic flux inversion process.

[0240] Through such magnetic flux reversal control, the ion concentration distribution within the electrolyte undergoes periodic cross-convection, and the imbalance in the migration speeds of lithium ions and polysulfide ions is adjusted in real time. Actual cell experiments confirmed that when the Lorentz force F is maintained at 2.5 × 10¹°N or higher and the magnetic flux reversal period is 1.2 Hz, the D_Li / D_S ratio converges to a level of 1.03. In addition, under the same conditions, the cell capacity reduction rate decreased by 11% after 100 cycles, and the concentration deviation (ΔC / C_avg) within the cell stabilized at 18% or less.

[0241] The control unit can simultaneously mitigate local deposition of polysulfide ions and asymmetric diffusion of lithium ions within a lithium-sulfur battery by performing such magnetic induction-based diffusion correction control in real time. This control method possesses a level of specificity and feasibility that can be implemented by a person skilled in the art using an electromagnet array, a Hall sensor, a current control circuit, and an FFT analysis module, and can be described in the specification based on physical principles derived from experimental data.

[0242] Therefore, the control unit is configured to actively adjust the ion distribution within the electrolyte using minute magnetodynamic effects induced by the Lorentz force, and to fundamentally prevent problems such as electrode corrosion, capacity reduction, and cell expansion caused by diffusion imbalance.

[0243] A control unit according to one embodiment of the present invention controls the rotational speed of the circulation pump of the heat exchanger in units of 100 rpm in response to the change in magnetic flux to offset the change in electrolyte viscosity.

[0244] The control unit detects in real time the phenomenon in which the viscosity (η) of the electrolyte changes slightly due to the generation of magnetic induction current within the electrolyte when the magnetic flux density (B) in the electromagnet array is modulated over time. The electrolyte of a lithium-sulfur battery is generally a mixed system containing a DOL / DME (1,3-dioxolane / 1,2-dimethoxyethane)-based solvent and a salt such as LiTFSI, and has the characteristic that its viscosity changes depending on temperature (T) and magnetic flux (B). The viscosity η can be expressed as follows by considering the temperature-dependent equation of the Arrhenius form and the magnetic field influence term.

[0245] η(T, B) = η0 × exp(E / (R × T)) × (1 + β × B²)

[0246] Here, η0 is the viscosity at the reference temperature (25℃), E is the activation energy (J / mol), R is the gas constant, and β is the magnetic field influence coefficient. Experimental results showed that when B = 15 mT was applied, β = 1.2 × 10³, which means the viscosity increased by about 0.18%.

[0247] The control unit calculates the rate of change in viscosity (dη / dt) of the electrolyte in real time based on the above equation. When the magnetic flux is periodically reversed, the greater the time rate of change of magnetic flux (∂B / ∂t), the greater the microcirculation flow within the electrolyte, and consequently, the shear stress increases, causing the viscosity to change non-linearly. The control unit indirectly estimates the real-time rate of change in viscosity of the electrolyte using data from the current sensor and the temperature sensor.

[0248] dη / dt (∂η / ∂T) × (dT / dt) + (∂η / ∂B) × (dB / dt)

[0249] Here, (∂η / ∂B) = 2βBη0, (∂η / ∂T) = -(E / (R × T²)) × η0 × exp(E / (R × T)). Through this, the instantaneous rise or fall of the electrolyte viscosity at the point of magnetic flux reversal is quantitatively calculated.

[0250] If the viscosity change rate calculated in this way increases by more than the reference value of 0.0025 mPa·s / s, the control unit increases the rotational speed of the circulation pump of the heat exchanger in steps of 100 rpm. The relationship between the pump rotational speed N_pump and the cooling flow rate Q_cool is defined as follows.

[0251] Q_cool = k_p × N_pump

[0252] Here, k_p is the flow coefficient of the pump (L / min·rpm¹), which is set to 0.012 L / min·rpm¹ in this embodiment. Therefore, if N_pump is increased by 100 rpm, the cooling flow rate increases by 1.2 L / min, and the temperature of the electrolyte decreases by about 1.5℃. This cooling effect reduces the viscosity η of the electrolyte by about 0.3% and offsets the increase in viscosity caused by the application of magnetic flux.

[0253] The control unit outputs a PWM-based current control signal to control the rotational speed of the circulation pump. The PWM duty cycle (D_duty) is set to be proportional to the viscosity change rate (dη / dt) and is calculated using the following control formula.

[0254] D_duty = D0 + k_η × (dη / dt)

[0255] Here, D0 is the reference duty ratio (e.g., 60%), and k_η is the viscosity control gain factor, which is set to 2000 s / mPa. When dη / dt is 0.0025 mPa·s / s, D_duty increases to about 65%, increasing the pump current by about 0.3A, and consequently increasing the rotational speed by 100 rpm.

[0256] The pump speed is adjusted in real time with every magnetic flux reversal cycle, and the control unit maintains the rotational speed of the pump drive motor within an error of ±5 rpm by verifying the Hall sensor feedback signal. This feedback loop is implemented as a non-linear control structure that reflects the correlation between the viscosity of the electrolyte and temperature in real time.

[0257] Experimental results showed that when the pump rotation speed was corrected and controlled in increments of 100 rpm under conditions of a magnetic flux inversion frequency of 1 Hz and a magnetic flux density of 15 mT, the variation range of the electrolyte viscosity decreased by approximately 19% from 0.26 mPa·s to 0.21 mPa·s, and the stable range of the diffusion coefficient (D_Li / D_S) converged to ±0.04. This demonstrates that the asymmetry of the ion migration speed was suppressed as the temperature balance and viscosity constancy of the electrolyte were maintained.

[0258] Based on this configuration, the control unit variably controls the circulation pump of the heat exchanger in real time to physically offset changes in electrolyte viscosity caused by alternating magnetic flux variations. This control method does not simply maintain a constant cooling rate, but includes a physical correction loop that dynamically adjusts the cooling flow rate by considering the rheological characteristics of the electrolyte according to changes in magnetic flux.

[0259] Consequently, the control unit of the present embodiment stabilizes the change in electrolyte viscosity within a certain range even during magnetic induction control of the lithium-sulfur battery, and is designed to simultaneously secure the balance of ion movement and the efficiency of the electrode reaction, thereby ensuring specificity and reproducibility at a level achievable by a person skilled in the art.

Claims

Claim 1 A lithium-sulfur battery system for high capacity and ultra-high output comprises: a cell module in which lithium-sulfur battery cells are connected in series and parallel; a sensor module for detecting the temperature and voltage of the cell module; a battery management unit (BMS) for controlling charge / discharge currents based on data collected from the sensor module; and a heat exchanger connected to the battery management unit for maintaining a uniform thermal state of each cell module; wherein the battery management unit includes a control unit, and the control unit, upon receiving temperature data, voltage data, and internal resistance data collected from each cell module, identifies a cell in which an electrochemical imbalance has occurred due to a change in polysulfide concentration of the lithium-sulfur cell based on the fluctuation rate (dV / dt) of the voltage data and the rate of rise (dT / dt) of the temperature data, outputs a first control signal for stepwise deceleration of the charging current of the identified imbalanced cell within a range of 5 to 10%, and controls the flow rate of a circulation pump within the heat exchanger so that the standard deviation of the cell temperature distribution is maintained at 2°C or less. Lithium-sulfur battery system for large capacity and ultra-high power. Claim 2 delete Claim 3 A lithium-sulfur battery system for large capacity and ultra-high output according to claim 1, wherein the control unit analyzes the voltage drop pattern of a cell module in real time during the discharge section of a lithium-sulfur battery, identifies a cell whose voltage drops rapidly below a reference value (V_ref) as a degraded cell, outputs a second control signal to switch the current path of the degraded cell to a bypass circuit, corrects the switching cycle to maintain the ratio (V_avg / V_max) of the average voltage value (V_avg) and maximum value (V_max) of the remaining cell module within the range of 0.95±0.03 in order to readjust the current balance of the entire pack after switching to the bypass circuit, and variably controls the rotational speed of the cooling fan of the heat exchanger in proportion to the ΔT value (average cell temperature - reference temperature). Claim 4 A lithium-sulfur battery system for large capacity and ultra-high output according to claim 3, wherein the control unit combines voltage fluctuation data and temperature data of each cell module to monitor changes in electrolyte concentration due to polysulfide dissolution reactions occurring in the lithium-sulfur battery to derive an internal resistance increase rate (dR / dt) for each cell, identifies a case where dR / dt is measured to be 0.012 Ω / s or higher as a polysulfide accumulation critical state, generates a third control signal that limits the charging current of the cell to 0.85 times the reference current (I_ref) by intervening a current control loop at that point, and controls in parallel to increase the circulation flow rate of the heat exchanger by 1.2 times to maintain the cell surface temperature deviation at 1.5℃ or lower. Claim 5 In paragraph 4, the control unit periodically receives strain data (ε) collected from a strain gauge attached to the cell housing to prevent stress concentration due to mechanical expansion within the electrode during the charging and discharging process of the lithium-sulfur cell, calculates the time rate of change of the strain (dε / dt), and the time rate of change of the strain (dε / dt) is 4.0 × 10 -5 A lithium-sulfur battery system for large capacity and ultra-high power, characterized by identifying an electrode expansion critical state when the current rises above / s, reducing the charging current to 0.9 times the reference current (I_ref) at that point, and controlling the temperature of the cooling medium in the heat exchanger to increase by 3℃ to alleviate the viscosity difference between the electrode surface and the electrolyte interface. Claim 6 A lithium-sulfur battery system for large capacity and ultra-high output according to claim 5, wherein the control unit collects acoustic vibration data from a piezoelectric vibration sensor mounted on the outer surface of each cell module to attenuate fine acoustic vibrations accumulated inside the cell housing during the charging and discharging process of the lithium-sulfur battery, calculates a quality factor (Q) of the frequency spectrum from the collected acoustic vibration data, identifies an acoustic resonance critical state when the quality factor value rises by more than 1.25 times compared to a reference value (Q_ref), opens a variable valve module connected to the cooling path of the heat exchanger in that state to increase the circulation flow rate of the cooling medium by 1.3 times, and controls the piezoelectric vibrator attached to the outer wall of the cell housing to cancel out the resonance sound by driving it with a phase-inverted acoustic wave in the range of 25 kHz to 35 kHz.

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