Sodium-ion battery extreme temperature range and zero-volt recovery control system and BMS reconfiguration method

Abstract

This invention discloses a sodium-ion battery extreme temperature range and zero-volt recovery control system and BMS reconstruction method, belonging to the field of battery management technology. The system includes: a sodium-ion battery module, a micro-energy self-awakening extraction module, a BMS control unit, a high-frequency AC bidirectional H-bridge inverter topology, a wideband online electrochemical impedance spectroscopy (EIS) measurement module, and an SEI film in-situ reconstruction control module. The method includes: a micro-energy accumulation and black-start stage, using ambient energy to awaken the BMS; a high-frequency AC active heating stage, injecting 30kHz to 90kHz AC current into the battery module to achieve uniform heating from the inside out; an EIS-based internal temperature estimation stage, extracting the impedance spectrum zero-crossing point features and combining an electrothermal coupling model to accurately calculate the core temperature; and an SEI film in-situ dynamic reconstruction stage, using low-rate constant current trickle charging and closed-loop impedance monitoring to repair the solid electrolyte interface film degraded after deep discharge. This achieves extreme temperature range and zero-volt recovery of the sodium-ion battery, improving its reliability and service life in extremely cold regions.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage system and battery management technology. Specifically, it relates to a control system and BMS dynamic reconstruction method that can achieve autonomous system wake-up, non-destructive internal heating, accurate core temperature estimation, and in-situ reconstruction of the solid electrolyte interface film under extreme low temperature (such as -40℃) and zero voltage (0V) dual deadlock conditions. It is mainly aimed at large-capacity wide-temperature-range square sodium-ion cells and their application in scenarios such as energy storage power stations in extremely cold regions. Background Technology

[0002] Sodium-ion batteries, due to their abundant resources, low cost, and the fact that their aluminum current collectors do not oxidize, dissolve, or grow dendrites when deeply discharged to 0V, possess inherently zero-volt safe storage and transportation characteristics, making them an important development direction in the field of large-scale energy storage. However, when sodium-ion battery energy storage systems are left stagnant at 0V for extended periods in extreme low-temperature environments (e.g., -40°C), they face a series of technical challenges, and existing technologies have the following shortcomings: 1. System startup deadlock: In remote mining areas or extremely cold regions without external power grid access, the battery pack terminal voltage is 0V and the ambient temperature is extremely low. Conventional BMS (Battery Management System) will completely shut down due to lack of power and will not be able to start autonomously. Existing solutions that rely on external strong power grids or dedicated heating power supplies fail in passive scenarios.

[0003] 2. Safety charging boundary constraints: When the cell temperature of a sodium-ion battery is below the allowable charging temperature (usually 0°C), directly applying a DC charging current can easily cause metallic sodium to precipitate on the surface of the hard carbon negative electrode, leading to irreversible capacity loss and safety risks. Traditional external thermal management solutions (such as PTC heating and liquid cooling) are difficult to achieve rapid, uniform, and inside-out heating when charging is prohibited.

[0004] 3. Core temperature sensing lag: In thick-gauge battery cells and modules, surface temperature sensors (such as NTC, i.e., negative temperature coefficient thermistors) are limited by thermal resistance, and their readings lag significantly behind the actual core temperature of the battery cell. This lag effect is exacerbated under extremely cold conditions, and relying solely on surface temperature cannot safely and reliably determine the charging conditions.

[0005] 4. Lack of SEI film degradation and recovery: After a battery is deeply discharged to 0V and left to stand for an extended period, the solid electrolyte interphase (SEI) film on the negative electrode surface undergoes localized dissolution and structural degradation, manifested as a decrease in open-circuit voltage and a significant increase in impedance. Existing BMS lacks a dedicated recovery algorithm for this degraded interface; using conventional charging strategies will result in significant capacity loss.

[0006] 5. Insufficient integration of existing technologies: Existing literature discloses high-frequency AC self-heating methods for lithium-ion batteries or battery state estimation algorithms based on impedance spectroscopy, but none of them provide a complete, closed-loop control link from micro-energy wake-up, non-destructive heating, internal temperature estimation to interface reconstruction for the combined extreme conditions of "sodium-ion battery system + extreme cold environment + 0V transport and storage + SEI degradation repair".

[0007] Therefore, there is an urgent need for an intelligent control system and method that can solve the aforementioned extreme temperature range and zero-volt recovery problems. It should be noted that even when a sodium-ion battery is deeply discharged to a terminal voltage of 0V, a very small amount of sodium-intercalated state still exists in the hard carbon of its negative electrode. Based on the equilibrium potential characteristics of sodium-ion batteries, a residual potential of not less than 0.1V can be provided. This weak potential is sufficient to be utilized by a DC-DC circuit with an extremely low start-up voltage. Summary of the Invention

[0008] To overcome the shortcomings of the prior art, this invention provides a sodium-ion battery extreme temperature range and zero-volt deep recovery control system and BMS dynamic reconfiguration method to achieve autonomous wake-up, safe heating, precise temperature control and electrochemical interface repair of the battery pack under dual extreme conditions of -40℃ and 0V.

[0009] The technical solution provided by this invention is as follows: A sodium-ion battery extreme temperature range and zero-volt recovery control system includes: Sodium-ion battery module: It consists of multiple square sodium-ion cells with a rated voltage of 3.0V and a rated capacity of 50Ah to 300Ah, covering a wide temperature range.

[0010] The micro-energy self-awakening extraction module has its input terminals connected to a piezoelectric vibration energy harvester and / or an extremely weak light MPPT (maximum power point tracking) photovoltaic thin-film module, used to collect weak mechanical vibrations or light energy from the environment. Internally, it includes a DC-DC boost circuit with an extremely low start-up voltage threshold (≤0.3V) and an onboard supercapacitor for boosting and storing the collected energy. Furthermore, even when a sodium-ion battery is deeply discharged to its terminal voltage of 0V, a very small amount of sodium-intercalated states still exist in the hard carbon of its negative electrode, providing a residual potential of not less than 0.1V. This weak potential is sufficient to be utilized by the extremely low start-up voltage DC-DC circuit in this invention, thereby achieving micro-energy extraction.

[0011] The BMS control unit includes a microcontroller (MCU) and its low-power wake-up circuit. Its power supply is connected to the supercapacitor, and it switches from standby to operating state when the voltage reaches the MCU wake-up threshold, performing a black-start self-test. During the self-test phase, the BMS only activates the basic internal register bus and sensor interface, without driving external contactors. The BMS control unit is also configured to draw residual potential from the sodium-ion battery module via a DC-DC converter circuit and store this potential in the supercapacitor to further boost the supercapacitor voltage to a preset operating voltage threshold.

[0012] High-frequency AC bidirectional H-bridge inverter topology: It consists of four silicon carbide (SiC) field-effect transistors, a series energy storage inductor L, and a parasitic inductor Lp. Its output terminal is connected in parallel to both ends of the battery module. It is used to inject a high-frequency AC current within a preset frequency range (30kHz to 90kHz) into the battery module under the control of the BMS to suppress concentration polarization and avoid sodium deposition.

[0013] Wideband online electrochemical impedance spectroscopy (EIS) module: Connected to the battery module and BMS control unit, it is used to apply small perturbation voltage or current, acquire voltage and current responses in the frequency range of 100Hz to 1kHz, and calculate electrochemical impedance spectroscopy (EIS) data.

[0014] SEI film in-situ reconstruction control module: Connected to BMS control unit and external microgrid power supply or photovoltaic MPPT output terminal, it is used to control trickle charging at a small rate constant current (0.05C~0.1C) when the battery module is detected to have a zero-volt static history mark, and combine impedance feedback to realize in-situ reconstruction of SEI film.

[0015] The BMS control unit manages the coordinated operation of the above modules through a state machine, enabling black start, autonomous heating, internal temperature estimation, and zero-volt depth recovery at -40℃ and 0V.

[0016] A sodium-ion battery extreme temperature range and zero-volt recovery BMS reconfiguration method, applied to the above system, specifically: 1. Micro-energy accumulation and black start phase: When the battery terminal voltage is 0V and the ambient temperature is below the charging prohibition temperature (such as 0℃), ambient energy is collected, boosted and stored in the supercapacitor; when the voltage reaches the MCU wake-up threshold (such as 1.8V), the BMS is started and enters the low power self-test mode.

[0017] 2. High-frequency AC active heating stage: After confirming that the temperature is below the safe charging threshold, the DC circuit is cut off, and the H-bridge topology is driven to inject a high-frequency AC current of 30kHz to 90kHz into the battery module. According to the formula... Dynamically adjust the root mean square value of the current This allows electrical energy to be primarily converted into Joule heat and polarization heat, achieving a uniform temperature rise from the inside out. Among these, For total heat generation, Let f be the real part of the high-frequency impedance at frequency f and temperature T. This is the heat compensation amount for the electrochemical reaction.

[0018] 3. Internal temperature estimation stage based on EIS: A sweep frequency signal is injected into the battery module during the heating gap, the response is acquired, and a fast Fourier transform is performed to obtain the Nyquist plot. The zero-crossing frequency when the imaginary part of the impedance crosses from a negative value to a positive value on the real axis and the corresponding real part of the impedance are extracted and input into a pre-calibrated electrothermal coupling reduced-order model to calculate the true temperature of the cell core; when the core temperature reaches the heating stop temperature (e.g., 5℃), high-frequency heating is stopped.

[0019] 4. SEI Membrane In-situ Dynamic Reconstruction Stage: After the core temperature reaches a safe range and a zero-volt static history marker is detected, the external power supply is controlled to perform trickle charging at a constant current rate of 0.05C to 0.1C. The EIS module is continuously used to monitor the surface film impedance and charge transfer impedance. When the surface film impedance value falls back to the preset health reference range and its rate of change approaches zero, the reconstruction is deemed complete, the reconstruction lock is released, and the system switches to normal charge and discharge operation mode. The preset health reference range can be calibrated according to the electrochemical impedance spectrum at the time of battery manufacturing, for example, the surface film impedance does not exceed 125% of the initial value.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. It has achieved autonomous black start capability without relying on the external power grid under the dual extreme conditions of -40℃ extreme cold and 0V voltage.

[0021] 2. The high-frequency AC internal heating method effectively avoids the risk of sodium precipitation caused by DC charging at low temperatures, and achieves rapid and uniform heating from the inside out.

[0022] 3. The accurate estimation of the core temperature of the battery cell was achieved by using online EIS features and an electrothermal coupling model, which effectively compensated for the hysteresis error of surface temperature measurement and improved the reliability of thermal management control.

[0023] 4. An in-situ dynamic reconstruction algorithm for SEI film degradation after 0V deep static storage was proposed. The algorithm achieved near-non-destructive repair of the battery interface state through closed-loop impedance verification, which significantly extended the effective service life of the battery under extreme conditions.

[0024] 5. It provides a complete, state machine-driven four-stage control strategy, forming a fully automated recovery process from extreme deadlock state to normal grid-connected operation, with high engineering compatibility and prospects for standardized testing.

[0025] Other features and advantages of the invention will be set forth in the following description or may be learned by practicing the invention. Attached Figure Description

[0026] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0027] Figure 1 This is a schematic diagram of the hardware architecture of the sodium-ion battery extreme temperature range and zero-volt recovery control system provided in an embodiment of the present invention.

[0028] Figure 2 The flowchart shows the four-stage state machine control process for the sodium-ion battery extreme temperature range and zero-volt recovery BMS reconfiguration method provided in this embodiment of the invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solution of this invention will be described in detail below with reference to a specific embodiment. It should be understood that this embodiment is only for explaining this invention and is not intended to limit the scope of this invention. Example 1:

[0030] This embodiment provides a sodium-ion battery extreme temperature range and zero-volt deep recovery control system, applied to a 100kWh energy storage power station in a high-altitude mining area. The power station uses 3.0V / 200Ah wide-temperature-range square sodium-ion cells, configured as a 1-parallel-N-series battery module. After being transported at -40℃ with 0V and left to stand for 3 months, the system needs to be restored to grid-connected operation under conditions without external power.

[0031] 1. System hardware configuration, such as Figure 1 As shown: Micro-energy self-awakening extraction module: Multiple miniature piezoelectric vibrating plates (collecting wind vibrations and environmental micro-vibrations) and a 10cm×10cm extremely low-light MPPT photovoltaic film (illuminance as low as 10Lux) are deployed outside the energy storage cabinet. The module uses a commercial inductive DC-DC boost converter chip (such as LTC3108) with a start-up voltage threshold of 0.28V, and a 1F / 5.5V supercapacitor is connected in parallel at the output.

[0032] BMS control unit: Uses an ultra-low power ARM Cortex-M0+ core MCU with a deep sleep current of 0.5μA and a wake-up voltage threshold of 1.8V. The MCU's VCC pin is directly connected to the supercapacitor.

[0033] The high-frequency AC bidirectional H-bridge inverter topology consists of four 1200V / 40A silicon carbide MOSFETs (such as C3M0065090J), a 10μH energy storage inductor L, and a PCB layout parasitic inductance Lp (approximately 50nH). The H-bridge output is connected in parallel across the positive and negative terminals of a single battery module (voltage 0V).

[0034] Wideband online EIS module: Integrated on the BMS motherboard, it includes a 16-bit resolution ADC (analog-to-digital converter) and multiplexer, which can apply disturbance signals of 1mV to 10mV with a frequency range of 0.1Hz to 10kHz.

[0035] 2. Implementation steps of BMS refactoring method, such as... Figure 2 As shown: Step 1, Micro-energy accumulation and black start: Under initial conditions of -40℃ / 0V, all contactors disconnect, and the BMS is completely powered down. The piezoelectric element and photovoltaic film continuously harvest energy at an average power of approximately 50μW, which is then boosted to approximately 2V via DC-DC converter to charge the supercapacitor. After approximately 6 hours, the supercapacitor voltage slowly climbs to 1.8V. The MCU is then awakened and immediately enters a black-start self-test sub-mode: the MCU only activates the internal RC oscillator and base register, sampling the onboard NTC temperature (displaying -40℃) and battery pack voltage (displaying 0V) at extremely low power (approximately 1mA). In this state, the MCU does not drive any external relays or H-bridge MOSFETs to avoid current surges that could cause system crashes. Subsequently, the MCU controls an internal ultra-low dropout linear regulator (LDO) to draw power from the supercapacitor and uses an isolated flyback converter to draw microampere leakage current from the battery pack parallel bus using the weak residual potential of the battery (even if the battery terminal voltage shows 0V, a very small amount of sodium intercalation remains in the hard carbon of the negative electrode, which can provide a residual potential of not less than 0.1V). This further stabilizes and boosts the supercapacitor voltage to 3.3V, and the BMS enters a fully awake state.

[0036] Step 2, High-frequency AC active heating: After the BMS confirms that the battery pack open circuit voltage is 0V and the NTC temperature is -40℃, it determines that it is in an "extreme cold +0V" deadlock state, and the state machine switches to the high-frequency preheating sub-mode.

[0037] Parameter settings: The MCU H-bridge switching frequency is set to 60kHz (within the preferred range of 30-90kHz), initial target. It is 120A (corresponding to 0.6C, below the range of 1.17-1.56C, for safe starting; where C represents the rated capacity rate of the battery, taking a 200Ah cell as an example, 1C corresponds to 200A).

[0038] Excitation application: The MCU sends a complementary PWM (Pulse Width Modulation) signal to drive the four SiC MOSFETs of the H-bridge to conduct alternately, generating a 60kHz AC current with a peak-to-peak voltage of approximately 48V across the battery module. This AC current is forced to flow through the battery's internal ohmic resistance, generating endogenous Joule heating. Because the frequency is much higher than the diffusion characteristic frequency, sodium ions undergo reverse polarization before they can be inserted into / extracted from the hard carbon anode, eliminating the risk of sodium deposition.

[0039] Dynamic adjustment: The BMS calls the EIS module every 2 seconds to measure the real impedance at 60kHz. Initial measurements The resistance is 4.5 mΩ. Based on the preset heating rate of 6℃ / min and the formula... (In this example) (This item is relatively small and can be ignored; it should generally be included.) The MCU will... The temperature was gradually increased to 260A (corresponding to 1.3C). The battery module temperature then steadily increased.

[0040] Step 3, Core temperature estimation based on EIS: During the intervals of high-frequency heating (heating is paused for 200ms every 5 seconds), the BMS executes an internal temperature estimation sub-mode.

[0041] Frequency sweep and FFT: The EIS module applies a frequency sweep sine wave from 100Hz to 1kHz to the battery module. After acquiring the response voltage and current, the MCU performs a fast Fourier transform and plots the Nyquist plot.

[0042] Feature extraction: The algorithm automatically searches for points in the graph where the imaginary part of the impedance (-jZ) changes from negative to positive across zero. At -40℃, the frequency of this zero-crossing point is approximately 380Hz, corresponding to a real impedance of 3.8mΩ; as heating progresses, when the estimated core temperature reaches 0℃, the zero-crossing point frequency drifts to 520Hz, and the real part drops to 2.1mΩ.

[0043] Solution and Judgment: Input the above features (zero-crossing frequency and real part) into the offline calibrated electrothermal coupling reduced-order model. , Indicates the core temperature of the battery cell. The zero-crossing frequency, This represents the real part of the impedance at that frequency. Surface temperature, This represents the functional relationship determined by the offline calibrated electrothermal coupling reduced-order model. The model outputs the real-time core temperature. When the model outputs... When the temperature reaches 5℃ (at which point the surface NTC reading is -15℃, lagging by 20℃), the MCU determines that heating is complete, immediately stops the high-frequency PWM output, and ends the heating phase.

[0044] Step 4, in-situ dynamic reconstruction of the SEI membrane: The BMS confirmed that the core temperature was >5℃, but detected a "0V idle for >7 days" flag in the system status flag. Therefore, instead of entering the normal charging mode, the state machine jumped to the REFORMATION sub-mode.

[0045] Micro-current polarization: The BMS controls the external bidirectional energy storage converter (PCS) via the communication bus, commanding it to trickle charge the battery pack with a constant current of 0.05C (10A). The battery pack voltage slowly rises from 0V.

[0046] Closed-loop impedance verification: During charging, the BMS calls the EIS module every 30 seconds to monitor the surface film impedance at 1kHz. ) and charge transfer impedance ( Initially, verification yielded... The SEI was up to three times higher (3.6 mΩ) than the initial healthy baseline (1.2 mΩ), indicating severe SEI degradation. As charging proceeded, film-forming additives in the electrolyte (such as FEC, i.e., fluoroethylene carbonate) reformed a dense SEI on the hard carbon surface at the reduction potential. Continuous monitoring revealed that... The value gradually decreased to 1.3 mΩ within 2 hours, and the rate of change was calculated three times consecutively. All were below 0.01 mΩ / min.

[0047] Condition removal and grid connection: MCU judgment The voltage has fallen back to the healthy baseline range (<1.5mΩ) and the rate of change is close to zero, indicating that SEI reconstruction is complete. The BMS clears the "0V history" flag, controls the main positive / main negative contactor to close, and the system state machine switches to normal operating mode. At this time, the battery pack voltage has recovered to 2.8V and can accept charging according to the standard charging protocol (0.5C constant current constant voltage). After testing, the capacity has recovered to 98% of the initial value, and the internal resistance has been fully restored.

[0048] Through the above four-stage closed-loop control, this embodiment successfully achieved the fully automatic recovery of the sodium-ion battery energy storage system from a deadlock state of -40℃ or 0V to safe and efficient grid-connected operation, verifying the effectiveness and reliability of the technical solution of the present invention under extreme conditions.

[0049] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A sodium-ion battery extreme temperature range and zero-volt recovery control system, characterized in that, include: Sodium-ion battery modules consist of multiple wide-temperature-range square sodium-ion cells; The micro-energy self-awakening extraction module has its input end connected to an environmental energy harvester. It contains a DC-DC boost circuit with a start-up voltage threshold of ≤0.3V and a supercapacitor for harvesting and storing environmental energy. The BMS control unit includes a microcontroller and its low-power wake-up circuit. The power supply terminal is connected to the supercapacitor and is used to perform a black-start self-test when the voltage reaches the wake-up threshold. The BMS control unit is also configured to: draw residual potential from the sodium-ion battery module through a DC-DC converter circuit and store the potential in the supercapacitor to further increase the voltage of the supercapacitor to a preset operating voltage threshold. The high-frequency AC bidirectional H-bridge inverter topology consists of four silicon carbide field-effect transistors and a series energy storage inductor L. Its output terminal is connected in parallel to both ends of the battery module to inject a high-frequency AC current of 30kHz to 90kHz into the battery module under the control of the BMS. A wideband online electrochemical impedance spectroscopy module is connected to the battery module and BMS control unit to apply perturbation signals and acquire electrochemical impedance spectroscopy data. The SEI film in-situ reconstruction control module is connected to the BMS control unit and external power supply. It is used to control a small-rate constant current charging when a zero-volt static history marker is detected and combine it with impedance feedback to realize the in-situ reconstruction of the SEI film. The BMS control unit manages the coordinated operation of the above modules through a state machine.

2. The control system according to claim 1, characterized in that, The DC-DC boost circuit has a startup voltage threshold of ≤0.3V, which is used to achieve boost startup when the sodium-ion battery module terminal voltage is 0V and a residual potential of not less than 0.1V can be provided.

3. The control system according to claim 1, characterized in that, The BMS control unit is configured during the black-start self-test phase to activate only the internal register bus and sensor interface, while keeping all external contactors and high-power relays in the off state to avoid power supply failure due to current surges.

4. The control system according to claim 1, characterized in that, The high-frequency AC bidirectional H-bridge inverter topology includes: four silicon carbide field-effect transistors, a series energy storage inductor L, and parasitic inductance generated by the circuit layout; its output is connected in parallel to the positive and negative terminals of the sodium-ion battery module to form a closed high-frequency AC circuit.

5. The control system according to claim 1, characterized in that, The switching frequency of the high-frequency alternating current is controlled within the range of 30kHz to 90kHz.

6. A method for reconfiguring a sodium-ion battery in extreme temperature ranges and at zero volt recovery using a BMS based on the system described in any one of claims 1-5, characterized in that, Includes the following stages: Micro-energy accumulation and black start phase: When the battery terminal voltage is 0V and the ambient temperature is below 0℃, the ambient energy is collected, boosted and stored in the supercapacitor. When the voltage reaches the microcontroller wake-up threshold, the BMS is started and enters the low power self-test mode. High-frequency AC active heating stage: The DC circuit is cut off, and the H-bridge topology is driven to inject a high-frequency AC current of 30kHz to 90kHz into the battery module. The root mean square value of the current is dynamically adjusted according to the real part of the impedance measured in real time, so that the electrical energy is converted into Joule heat and polarization heat, and the temperature rises uniformly from the inside to the outside. The internal temperature estimation stage based on EIS: a sweep frequency signal is injected into the battery module during the heating gap, the response is collected and a fast Fourier transform is performed to obtain the Nyquist plot, the zero-crossing frequency when the imaginary part of the impedance changes from negative to positive and the real part of the impedance corresponding to that point are extracted, and the pre-calibrated electrothermal coupling reduced-order model is input to calculate the true temperature of the cell core. When the core temperature reaches 5℃, high-frequency heating is stopped. SEI film in-situ dynamic reconstruction stage: After the core temperature reaches 5℃ and the zero-volt static history mark is detected, the external power supply is controlled to perform trickle charging at a small rate constant current. The EIS module is continuously called to monitor the surface film impedance and charge transfer impedance. When the surface film impedance value falls back to the preset health benchmark range and its rate of change approaches zero, the reconstruction is determined to be complete, and the system switches to normal charging and discharging operation mode.

7. The method according to claim 6, characterized in that, During the in-situ dynamic reconstruction stage of the SEI film, the small-rate constant current is 0.05C to 0.1C, and the trickle charging process continues until the surface film impedance value falls back to the preset health benchmark range.

8. The method according to claim 6, characterized in that, In the in-situ dynamic reconstruction stage of the SEI film, the comprehensive conditions for determining the completion of reconstruction are: the absolute value of the surface film impedance falls back to the preset healthy reference range, and the surface film impedance is measured three times continuously at a fixed time interval of 10 seconds to 60 seconds, and the change rate of the surface film impedance measured each time is less than 0.01mΩ / min.

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