Wide-temperature-range start-stop sodium ion battery system

Abstract

The invention relates to a wide-temperature-range start-stop sodium-ion battery system in the technical field of sodium-ion batteries, and is characterized in that a sodium-ion battery cell adopts a fluorine-doped modified composite sodium iron phosphate positive electrode material and a sodium-ion low-temperature electrolyte (an ethylene carbonate + dimethyl carbonate + fluoroethylene carbonate ternary solvent system is matched with bis (fluorosulfonyl) imide lithium salt); a high-temperature-resistant polyimide-based ceramic coating diaphragm is adopted, the contraction of the diaphragm at a high temperature is inhibited through a nanoscale aluminum oxide coating, and a full-tab cylindrical battery cell structural design is adopted; the battery management system BMS adopts a heating film and battery parallel architecture, and current-limiting charging is dynamically adjusted in real time based on temperature-SOC two-dimensional parameters; the charging current can be adjusted according to the real-time temperature of the battery module and the state of charge of the sodium ion battery cell, so that the battery module can adapt to a 12V start-stop sodium ion battery in an extreme temperature environment of-35 DEG C to 70 DEG C, and the problems of low-temperature charging efficiency, high-temperature safe operation and BMS intelligent temperature control are solved.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery production technology, specifically relating to a wide-temperature-range start-stop sodium-ion battery system that can cope with extreme high and low temperature environments. Background Technology

[0002] Sodium-ion batteries are also a type of rechargeable secondary energy storage battery. They primarily function by the movement of sodium ions between the positive and negative electrodes. Structurally, sodium-ion batteries are similar to lithium-ion batteries, mainly consisting of a positive electrode, negative electrode, electrolyte, separator, and current collector. Based on whether the main materials directly participate in the electrochemical reaction process, they can be divided into active and inactive materials. Active materials include the positive electrode material, negative electrode material, and electrolyte material; they directly participate in the electrochemical reaction and determine the battery's intrinsic characteristics. During charging, sodium ions released from the positive electrode reach the negative electrode material through the electrolyte, while electrons enter the negative electrode through the external circuit, ensuring a balance of positive and negative charges. During discharging, the situation reverses: electrons enter the positive electrode from the negative electrode through the external circuit, generating current to drive electrical devices.

[0003] Compared to lithium-ion batteries, sodium has a larger ionic radius and atomic mass than lithium. Therefore, for the same amount of electricity stored, sodium-ion batteries have lower volumetric energy density and lower gravimetric energy density than lithium-ion batteries. From a cost perspective, sodium is abundant in nature, with resources approximately 450 times that of lithium, resulting in lower costs. From a safety perspective, the synergistic effect of sodium's intrinsic chemical properties, the inherent properties of electrode materials, and the thermodynamic stability of the battery system reduces the risks of thermal runaway, fire, and explosion. Furthermore, with its abundant resources, low cost, and high safety, sodium-ion batteries are rapidly being adopted as a viable alternative to lithium-ion batteries in energy storage, low-speed electric vehicles, and start-stop power supplies.

[0004] However, sodium-ion battery technology is still immature and faces various problems that urgently need to be solved. For example, existing sodium-ion batteries struggle to meet the high-rate discharge requirements in extremely cold and tropical regions. The charging rate drops significantly below 0°C, especially below -10°C, where the charging capacity can drastically decrease to 0.1C or even lower. Prolonged use in low-temperature environments will significantly shorten the battery's lifespan. To address this issue, new sodium-ion cells and protection boards suitable for vehicle operating conditions have been developed to better meet the needs of all start-stop vehicles. These cells offer significantly improved low-temperature charging capabilities, increasing the charging rate to 2C between 0°C and -10°C, and maintaining a 0.5C charging rate in environments ranging from -10°C to -35°C. However, the battery cycle life remains essentially the same as existing products because the low-temperature charging current in current battery systems cannot be controlled and is directly received by the cell. After prolonged low-temperature cycling, the cell's internal resistance increases, leading to a shortened lifespan. Therefore, there is an urgent need to find a sodium-ion battery system that can adapt to a wider temperature range. Summary of the Invention

[0005] In response to the above situation, the present invention provides a wide-temperature-range start-stop sodium-ion battery system, which can better cope with 12V start-stop sodium-ion batteries in extreme high and low temperature environments, and effectively solves the problems of low-temperature charging efficiency, high-temperature safe operation and intelligent temperature control of battery management system (BMS).

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A wide-temperature-range start-stop sodium-ion battery system includes a battery module composed of several sodium-ion cells and a battery management system (BMS) for managing and controlling the battery module. The sodium-ion cells use a composite sodium iron phosphate cathode material and a sodium-ion low-temperature electrolyte, and adopt a full-tab cylindrical cell structure design. The BMS has a built-in parallel charging heating system, a dynamic charging current limiting module, and an intelligent equalization management circuit, which can automatically adjust the charging current according to the real-time temperature of the battery module and the state of charge (SOC) of the sodium-ion cells.

[0007] Furthermore, the composite sodium iron phosphate cathode material undergoes fluorine doping modification to enhance its intrinsic ionic conductivity. The treated composite sodium iron phosphate cathode material retains over 85% of its capacity output at -35℃, representing a 30% improvement in low-temperature performance compared to traditional lithium iron phosphate materials. The anode of the sodium-ion battery cell can utilize mainstream existing carbon-based, titanium-based, organic, and alloy anode materials. Hard carbon anode material is preferred.

[0008] Furthermore, the sodium ion low-temperature electrolyte uses a ternary solvent system of ethylene carbonate (EC) + dimethyl carbonate (DMC) + fluoroethylene carbonate (FEC), combined with lithium bis(fluorosulfonyl)imide (LiFSI) salt. This reduces the viscosity of the electrolyte by 60% at -40℃ and increases the ionic conductivity to over 2 mS / cm.

[0009] Furthermore, the tabs and current collector of the full-tab cylindrical cell are fully connected by laser welding. Compared with the traditional tab structure, the internal resistance of the tabs of the full-tab cylindrical cell can be reduced by 40%, and it can support continuous discharge at a rate of 30C and pulse discharge at a rate of 70C, which can well meet the instantaneous high power requirements of start-stop battery systems.

[0010] Furthermore, the separator of the sodium-ion battery cell is made of high-temperature resistant polyimide (PI)-based ceramic coating, with an upper temperature resistance of up to 180°C, which is 100°C higher than that of traditional PE separators. The separator is further reinforced by a nano-level alumina coating to inhibit separator shrinkage at high temperatures, which can extend the cycle life of the sodium-ion battery cell to more than 3,000 cycles at an ambient temperature of 70°C.

[0011] Furthermore, the battery management system (BMS) includes an MCU main control chip, an AFE acquisition chip, a charge / discharge MOS, and a current limiting circuit module. The MCU main control chip is responsible for data transmission, system judgment, and control functions. The AFE acquisition chip works with the MCU main control chip to be responsible for current and voltage acquisition and charge / discharge control. The charge / discharge MOS is controlled by the MCU main control chip and the AFE acquisition chip and is responsible for charging protection control and discharging protection control. The current limiting circuit module consists of a coil and a MOS switch. The MCU main control chip controls the coil current by controlling the frequency of the MOS switch.

[0012] Furthermore, the parallel charging heating system adopts an architecture that is connected in parallel with the battery module, and the heating film of the parallel charging heating system is a polyimide flexible electrothermal film with a power density of 500W / m².

[0013] When the battery management system (BMS) detects that the battery module temperature is below -10℃, the BMS automatically switches to heating mode, turns on the heating MOS switch, and uses generator energy for heating. In the low temperature range of -35℃ to -10℃, it charges with a current of 0.5C, while the heating film works at maximum power to achieve a heating rate of 3℃ / min. In the low temperature range of -10℃ to 0℃, the BMS switches to a current of 2C for charging, and the power of the heating film decreases linearly with the increase of temperature.

[0014] Furthermore, the dynamic charging current limiting module adopts a current limiting algorithm based on temperature and state of charge (SOC): in the low temperature range of -35℃ to 0℃, the charging current is dynamically adjusted according to the real-time temperature of the battery module, while the state of charge (SOC) of the sodium-ion battery cell is identified at this time. When the real-time temperature of the battery module is in the low-temperature range of -35℃ to -10℃, such as -20℃, the sodium-ion battery cell has a weaker ability to accept current. If the state of charge (SOC) is ≤70%, the BMS will turn off the charging MOS switch and turn on the dynamic charging current limiting module to limit the charging current to 0.5C. If the SOC is >70%, the battery is fully charged, and the BMS will turn off the charging MOS switch and adjust the dynamic charging current limiting module to limit the charging current to 0.3C. When the real-time temperature of the battery module reaches the low temperature range of -10℃ to 0℃, if the SOC ≤ 70%, the battery management system (BMS) will adjust the dynamic charging current limiting module to increase the charging current; when the temperature reaches 0℃ to 70℃, if the SOC ≤ 70%, the BMS will turn off the current limiting module and turn on the charging MOS switch for fast charging, and the charging current can be increased to 2C. Furthermore, at any temperature within the range of -35℃ to 70℃, if the state of charge (SOC) of the sodium-ion battery cell is ≥90%, the BMS will activate the current limiting module to reduce the charging rate, thereby providing overcharge protection.

[0015] Furthermore, the intelligent equalization management circuit adopts a distributed active equalization circuit, with each sodium-ion cell equipped with an independent equalization module, and energy transfer is achieved through a bidirectional DC-DC converter; when the voltage difference between individual cells exceeds 20mV, the equalization module performs energy transfer with a current of 1A to ensure that the consistency deviation of each sodium-ion cell in the battery module is less than 3% throughout the entire life cycle.

[0016] The main innovation of this invention is as follows: 1. The synergistic design of composite cathode materials and low-temperature electrolyte breaks through the -40℃ low-temperature boundary of sodium-ion batteries; 2. Parallel heating architecture improves heating efficiency by 40% and reduces energy loss by 25% compared to traditional series solutions; 3. Dynamic current limiting algorithm enables precise matching of charging current and temperature, extending battery life by more than 30%.

[0017] The present invention also includes other components that enable its normal use, all of which are conventional means in the art. In addition, devices or components not limited in the present invention, such as the positive electrode, negative electrode, tab, electrolyte, diaphragm, current collector, etc. of sodium ion battery cells, all adopt the prior art in the art.

[0018] The beneficial effects of this invention are as follows: The wide-temperature-range start-stop sodium-ion battery system provided by this invention employs a BMS (Battery Management System) design for a charging current-limiting module. This module adjusts the charging current based on temperature and cell state of charge (SOC), effectively protecting the cell. The system is adaptable to 12V start-stop sodium-ion batteries operating in extreme temperature environments ranging from -35℃ to 70℃, solving the problems of low-temperature charging efficiency, high-temperature safe operation, and intelligent temperature control by the battery management system (BMS). The battery possesses high-rate discharge capability and high-rate charging capability under any state of charge at low temperatures. The battery maintains a low-temperature 2C charge-discharge cycle life of over 350 cycles with a capacity retention rate of ≥80%. Attached Figure Description

[0019] Figure 1 This is a block diagram of the electrical architecture of the battery management system (BMS) in this invention. Detailed Implementation

[0020] The present invention will now be clearly described in conjunction with the accompanying drawings and specific embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art based on the embodiments of the present invention without inventive effort to obtain all other embodiments should be included within the scope of protection of the present invention.

[0021] Example 1 A wide-temperature-range start-stop sodium-ion battery system includes a battery module composed of several sodium-ion cells and a battery management system (BMS) for managing and controlling the battery module. The sodium-ion cells use a composite sodium iron phosphate cathode material and a sodium-ion low-temperature electrolyte, and adopt a full-tab cylindrical cell structure design. The BMS has a built-in parallel charging heating system, a dynamic charging current limiting module, and an intelligent equalization management circuit, which can automatically adjust the charging current according to the real-time temperature of the battery module and the state of charge (SOC) of the sodium-ion cells.

[0022] The composite sodium iron phosphate cathode material is further modified by fluorine doping to improve its intrinsic ionic conductivity. The treated composite sodium iron phosphate cathode material can still maintain more than 85% of its capacity output at -35℃, which is 30% better than the low-temperature performance of traditional lithium iron phosphate materials. The anode of the sodium-ion battery cell is preferably made of hard carbon anode material.

[0023] The sodium ion low-temperature electrolyte uses a ternary solvent system of ethylene carbonate (EC), dimethyl carbonate (DMC), and fluoroethylene carbonate (FEC), combined with lithium bis(fluorosulfonyl)imide (LiFSI) salt. This reduces the electrolyte viscosity by 60% and increases the ionic conductivity to over 2 mS / cm at -40°C. A battery cell equipped with this electrolyte can be charged to 80% in 10 minutes at -35°C, representing a three-fold increase in charging speed compared to traditional electrolytes.

[0024] The tabs and current collector of the full-tab cylindrical cell are fully connected by laser welding. Compared with the traditional tab structure, the internal resistance of the tabs of the full-tab cylindrical cell can be reduced by 40%, and it can support continuous discharge at a rate of 30C and pulse discharge at a rate of 70C, which can well meet the instantaneous high power requirements of start-stop battery systems.

[0025] The separator of the sodium-ion battery cell is made of high-temperature resistant polyimide (PI)-based ceramic coating, with an upper temperature resistance of up to 180°C, which is 100°C higher than that of traditional PE separators. The separator is further reinforced by a nano-alumina coating to inhibit separator shrinkage at high temperatures, which can extend the cycle life of the sodium-ion battery cell to more than 3,000 cycles at an ambient temperature of 70°C.

[0026] Example 2 like Figure 1 As shown in Example 1, the Battery Management System (BMS) includes an MCU main control chip, an AFE acquisition chip, a charge / discharge MOS, and a current limiting circuit module. The MCU main control chip uses an APM32E103RET6 microcontroller chip, and the AFE acquisition chip uses a DVC1110 battery pack monitoring chip. The MCU main control chip is responsible for data transmission, system judgment, and control functions. The AFE acquisition chip works with the MCU main control chip (using an AND control relationship) to be responsible for current and voltage acquisition and charge / discharge control. The charge / discharge MOS is controlled by the MCU main control chip and the AFE acquisition chip and is responsible for charging protection control and discharging protection control. The current limiting circuit module consists of a coil and a MOS switch. The MCU main control chip controls the coil current by controlling the frequency of the MOS switch.

[0027] The parallel charging heating system adopts an architecture that is connected in parallel with the battery module. The heating film of the parallel charging heating system is a polyimide flexible electrothermal film with a power density of 500W / m².

[0028] When the Battery Management System (BMS) detects that the battery module temperature is below -10℃, the BMS automatically switches to heating mode, and the heating film begins to heat the battery module, turning on the heating MOS switch. Heating is powered by the generator. In the low temperature range of -35℃ to -10℃, it charges at 0.5C, and the heating film operates at maximum power to achieve a temperature rise rate of 3℃ / min. In the low temperature range of -10℃ to 0℃, the BMS switches to 2C charging, and the heating film power decreases linearly with the temperature increase, ensuring that the battery module temperature rises above 0℃ within 10 minutes.

[0029] The dynamic charging current limiting module adopts a current limiting algorithm based on temperature and state of charge (SOC): in the low temperature range of -35℃ to 0℃, the charging current is dynamically adjusted according to the real-time temperature of the battery module, and the state of charge (SOC) of the sodium-ion battery cell is identified at this time.

[0030] When the real-time temperature of the battery module is in the low-temperature range of -35℃ to -10℃, such as -20℃, the sodium-ion battery cell has a weaker ability to accept current. If the state of charge (SOC) is ≤70%, the BMS will turn off the charging MOS switch and turn on the dynamic charging current limiting module to limit the charging current to 10A (or 0.5C). If the SOC is >70%, the battery is fully charged, and the BMS will turn off the charging MOS switch and adjust the dynamic charging current limiting module to limit the charging current to 5A (or 0.3C).

[0031] While the user is driving, the alternator continuously charges the battery cells with a small current, protecting the cells and replenishing the power consumed during startup every 10-20 minutes, thus optimizing battery cell charging. During vehicle operation, the BMS activates the parallel heating film switch, drawing power from the alternator, causing the high-power heating film to heat up rapidly.

[0032] When the real-time temperature of the battery module reaches the low temperature range of -10℃ to 0℃, if the SOC ≤ 70%, the battery management system (BMS) will adjust the dynamic charging current limiting module to increase the charging current; when the temperature reaches 0℃ to 70℃, if the SOC ≤ 70%, the BMS will turn off the current limiting module and turn on the charging MOS switch for fast charging, and the charging current can be increased to 2C. Furthermore, at any temperature within the range of -35℃ to 70℃, if the state of charge (SOC) of the sodium-ion battery cell is ≥90%, the BMS will activate the current limiting module to reduce the charging rate, thereby providing overcharge protection.

[0033] The intelligent equalization management circuit adopts a distributed active equalization circuit, with each sodium-ion cell equipped with an independent equalization module, which realizes energy transfer through a bidirectional DC-DC converter. When the voltage difference between individual cells exceeds 20mV, the equalization module performs energy transfer with a current of 1A to ensure that the consistency deviation of each sodium-ion cell in the battery module is less than 3% throughout the entire life cycle.

[0034] Example 3 Based on the wide-temperature-range start-stop sodium-ion battery system provided in the above embodiments, a low-temperature start-up test was conducted on the 12V start-stop battery system equipped with the present invention at an environment of -35°C: Initial state: Battery temperature -35℃, SOC=20%; Heating starts: The BMS activates the heating film, heating at 700W power while charging at 0.5C current; When the temperature reaches -10℃: switch to 2C charging, the heating film power drops to 300W; Temperature rises to 0℃: turn off the heating film, and charge to 95% with 3C current, total time 8 minutes.

[0035] Example 4 Based on the wide-temperature-range start-stop sodium-ion battery system provided in the above embodiments, the 12V start-stop battery system equipped with the present invention was subjected to 3000 high-temperature cycle tests in a 60°C high-temperature chamber: Charging strategy: Adopts "CC-CV (constant current-constant voltage)" mode, with a charging cutoff voltage of 4.0V; Discharge strategy: Discharge to 2.0V with a 2C current; Test results: Capacity retention rate 70%, internal resistance growth rate ≤15%, no thermal runaway phenomenon.

[0036] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A wide-temperature-range start-stop sodium-ion battery system, comprising a battery module composed of several sodium-ion cells, and a battery management system for managing and controlling the battery module, characterized in that: The sodium-ion battery cell uses a composite sodium iron phosphate cathode material and a sodium-ion low-temperature electrolyte, and adopts a full-tab cylindrical cell structure design. The battery management system has a built-in parallel charging heating system, a dynamic charging current limiting module, and an intelligent equalization management circuit, which can automatically adjust the charging current according to the real-time temperature of the battery module and the state of charge of the sodium-ion battery cell.

2. The wide-temperature-range start-stop sodium-ion battery system according to claim 1, characterized in that: The composite sodium iron phosphate cathode material is further modified by fluorine doping to improve its intrinsic ionic conductivity. The treated composite sodium iron phosphate cathode material can still maintain high capacity output at an ambient temperature of -35℃.

3. The wide-temperature-range start-stop sodium-ion battery system according to claim 1, characterized in that: The sodium ion low-temperature electrolyte uses a ternary solvent system of ethylene carbonate + dimethyl carbonate + fluoroethylene carbonate, combined with lithium difluorosulfonyl imide salt.

4. A wide-temperature-range start-stop sodium-ion battery system according to claim 1, characterized in that: The tabs and current collector of the full-tab cylindrical battery cell are fully connected by laser welding, supporting 30C high-rate continuous discharge and 70C high-rate pulse discharge.

5. A wide-temperature-range start-stop sodium-ion battery system according to claim 1, characterized in that: The sodium-ion battery cell uses a high-temperature resistant polyimide-based ceramic coating membrane, and a nano-scale alumina coating is used to suppress membrane shrinkage at high temperatures, which can effectively extend the cycle life of the sodium-ion battery cell at an ambient temperature of 70°C.

6. A wide-temperature-range start-stop sodium-ion battery system according to claim 1, characterized in that: The battery management system includes an MCU main control chip, an AFE acquisition chip, a charge / discharge MOS, and a current limiting circuit module. The MCU main control chip is responsible for data transmission, system judgment, and control functions. The AFE acquisition chip works with the MCU main control chip to be responsible for current and voltage acquisition and charge / discharge control. The charge / discharge MOS is controlled by the MCU main control chip and the AFE acquisition chip and is responsible for charging protection control and discharging protection control. The current limiting circuit module consists of a coil and a MOS switch. The MCU main control chip controls the frequency of the MOS switch to control the magnitude of the coil current.

7. A wide-temperature-range start-stop sodium-ion battery system according to claim 1, characterized in that: The parallel charging and heating system adopts an architecture connected in parallel with the battery module. The heating film of the parallel charging and heating system is a flexible polyimide electric heating film. When the battery management system detects that the battery module temperature is below -10℃, the battery management system controls the heating film to switch to heating mode. In the low temperature range of -35℃ to -10℃, the battery management system switches to charging with a current of 0.5C, and the heating film works at maximum power to achieve a heating rate of 3℃ / min. In the low temperature range of -10℃ to 0℃, the battery management system switches to charging with a current of 2C, and the power of the heating film decreases linearly with the increase of temperature.

8. A wide-temperature-range start-stop sodium-ion battery system according to claim 1, characterized in that: The dynamic charging current limiting module adopts a current limiting algorithm based on both temperature and state of charge. When the real-time temperature of the battery module is in the low-temperature range of -35℃ to -10℃, if the state of charge of the sodium-ion battery cell is ≤70%, the battery management system turns off the charging MOS switch and turns on the dynamic charging current limiting module to limit the charging current to 0.5C; if the state of charge of the sodium-ion battery cell is >70%, the power is sufficient, the battery management system turns off the charging MOS switch and adjusts the dynamic charging current limiting module to limit the charging current to 0.3C. When the real-time temperature of the battery module reaches the low temperature range of -10℃ to 0℃, if the state of charge of the sodium-ion battery cell is ≤70%, the battery management system adjusts the dynamic charging current limiting module to increase the charging current. When the temperature reaches 0℃~70℃, if the state of charge of the sodium-ion battery cell is ≤70%, the battery management system will turn off the current limiting module and turn on the charging MOS switch for fast charging, and the charging current can be increased to 2C. Furthermore, at any temperature within the range of -35℃ to 70℃, if the state of charge of the sodium-ion battery cell is ≥90%, the battery management system will activate the current limiting module to reduce the charging rate, thereby providing overcharge protection.

9. A wide-temperature-range start-stop sodium-ion battery system according to claim 1, characterized in that: The intelligent equalization management circuit adopts a distributed active equalization circuit, with each sodium-ion cell equipped with an independent equalization module, which realizes energy transfer through a bidirectional DC-DC converter. When the voltage difference between individual cells exceeds 20mV, the equalization module performs energy transfer with a current of 1A to ensure that the consistency deviation of each sodium-ion cell in the battery module is less than 3% throughout the entire life cycle.

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