A safe recovery charging method and system for lithium batteries after deep over-discharge.

Abstract

This invention discloses a safe recovery charging method and system for lithium batteries deeply over-discharged. The method first monitors the lithium battery terminal voltage in real time using a high-precision sampling circuit. When the detected voltage is lower than a preset deep over-discharge threshold, the system automatically locks the high-current path and enters a safe recovery mode. In this mode, the drive circuit generates micro-current pulses with dynamic duty cycles and injects them into the battery. During the relaxation monitoring period between pulses, high-frequency sampling is used to acquire voltage drop data to calculate the voltage maintenance slope. The main control unit adaptively adjusts the duty cycle of subsequent pulses based on the electrochemical activity state represented by this slope, activating electrolyte activity while eliminating polarization voltage. The system also integrates NTC full-temperature monitoring and timeout protection. When the voltage recovers to the safe threshold and passes smooth transition verification, it automatically switches to the constant-current fast charging stage, effectively solving the lithium plating and bulging problems caused by direct charging of over-discharged batteries.

Description

Technical Field

[0001] This invention relates to the field of power management and lithium battery charging control technology, and in particular to a safe recovery charging method and system for lithium batteries after deep over-discharge. Background Technology

[0002] Throughout the entire lifecycle of consumer electronics products, the built-in lithium-ion battery often becomes depleted due to long-distance transportation, prolonged storage, or prolonged user inactivity without being turned off. This leads to a deep over-discharge state, with the terminal voltage dropping to 2.0V or even below 1.0V. From an electrochemical mechanism perspective, when the battery voltage is in this dangerous range, the copper foil of the negative electrode current collector approaches its oxidation potential, and the stability of the solid electrolyte interface film on the negative electrode surface decreases significantly. This blocks the ion transport channels inside the battery, resulting in a rapid, non-linear increase in internal resistance.

[0003] Existing power management solutions often lack effective internal state diagnosis mechanisms when dealing with such depleted batteries, typically employing fixed micro-current blind charging or directly initiating standard charging procedures. In actual engineering testing and R&D experiments, it has been found that if a continuous charging current is applied directly to a deeply over-discharged battery with a terminal voltage below 1.0V, even if the current meets standard requirements, lithium ions on the electrode surface cannot be embedded into the crystal lattice in time, rapidly establishing an extremely high concentration polarization overpotential. This overpotential directly drives an irreversible decomposition reaction in the electrolyte, generating a large amount of gas. Macroscopically, the battery rapidly undergoes severe bulging and deformation in the early stages of charging, leading to physical damage to the cell structure. This not only prevents capacity recovery but also poses safety hazards such as leakage and combustion. Furthermore, while some solutions employ trickle charging, they cannot detect the elimination of internal polarization. The fixed current often causes new polarization accumulation before the battery's activity is activated, making it difficult to effectively restore capacity while maintaining the battery's appearance integrity. Summary of the Invention

[0004] One of the objectives of this invention is to provide a safe recovery charging method and system for lithium batteries that have been deeply over-discharged, in order to solve the problems mentioned in the background art.

[0005] In a first aspect, embodiments of the present invention provide a safe recovery charging method for a lithium battery after deep over-discharge, the method comprising:

[0006] Step A: Real-time detection of the terminal voltage of the lithium battery, and comparison of the terminal voltage with a preset deep over-discharge threshold;

[0007] Step B: If the terminal voltage is higher than the deep over-discharge threshold, execute the standard charging process; if the terminal voltage is lower than or equal to the deep over-discharge threshold, determine that the lithium battery is in a deep over-discharge state and enter the safe recovery mode.

[0008] The secure recovery mode includes the following steps:

[0009] Step C: Generate a pulse charging current with a dynamic duty cycle and inject it into the lithium battery. The pulse charging current consists of alternating current injection periods and relaxation monitoring periods.

[0010] Step D: During the relaxation monitoring period, the charging circuit is blocked, the voltage drop data of the lithium battery is obtained by high-frequency sampling, and the voltage maintenance slope is calculated based on the voltage drop data.

[0011] Step E: Compare the voltage maintenance slope with the preset active convergence condition, and dynamically adjust the duty cycle of the pulse charging current in the next pulse cycle according to the comparison result until the terminal voltage rises back to the preset safe recovery threshold.

[0012] Optionally, in step B, the depth over-discharge threshold is set to 2.0V;

[0013] When the lithium battery is determined to be in a deep over-discharge state, the system locks the high-current charging path and only opens the low-current charging path to execute step C.

[0014] The safety recovery threshold is set to 3.0V, which is the critical voltage point for determining whether the lithium battery has escaped the lithium plating risk zone.

[0015] Optionally, in step C, the amplitude of the pulse charging current during the current injection period is constantly limited to 100mA;

[0016] The 100mA amplitude is used to activate the electrolyte activity without causing gas generation and bulging inside the lithium battery;

[0017] The dynamic duty cycle is adjusted within a range of 20% to 80% to ensure that the average charging current is always less than 100mA.

[0018] Optionally, the entire method also includes a temperature safety monitoring step based on an NTC thermistor:

[0019] Real-time acquisition of temperature data fed back by the NTC thermistor attached to the surface of the lithium battery;

[0020] Determine whether the temperature data is within a preset safe charging temperature range, which is 0 degrees Celsius to 45 degrees Celsius.

[0021] If the temperature data exceeds the safe charging temperature range, all charging outputs will be forcibly terminated immediately, regardless of whether the terminal voltage meets the conditions.

[0022] Optionally, the method further includes a timeout fuse protection step:

[0023] Simultaneously, start the security timer when initiating the secure recovery mode;

[0024] If the safety timer reaches the preset maximum recovery time limit and the terminal voltage still fails to recover to the safety recovery threshold, the lithium battery is determined to be physically irreversibly damaged, and the charging circuit is permanently disconnected.

[0025] Optionally, the method further includes a smooth switching step after exiting recovery mode:

[0026] When the terminal voltage reaches the safety recovery threshold for the first time, it does not immediately switch to constant current charging mode, but maintains the current amplitude of 100mA for constant current pre-charging;

[0027] The rate of increase of the terminal voltage is continuously monitored, and the system only switches to the high-current constant-current charging stage when the rate of increase stabilizes within the preset normal range.

[0028] Optionally, in step D, the specific method for calculating the voltage sustaining slope is as follows:

[0029] A first voltage value is collected at the first moment after the start of the relaxation monitoring period, and a second voltage value is collected at the second moment before the end of the relaxation monitoring period.

[0030] The first voltage value, the second voltage value, and multiple intermediate sampling points between them are linearly fitted using the least squares method to obtain the absolute value of the slope of the voltage decline trend line, and the absolute value of the slope is used as the voltage maintenance slope.

[0031] The voltage sustaining slope is used to characterize the polarization elimination rate of the lithium battery after the removal of external excitation.

[0032] Optionally, in step E, the specific logic for dynamically adjusting the duty cycle of the pulse charging current in the next pulse cycle based on the comparison result is as follows:

[0033] If the voltage maintenance slope is greater than the preset slope threshold, it indicates that the lithium battery has a serious false high voltage phenomenon. The control system reduces the duty cycle of the next pulse cycle to prolong the duration of the relaxation monitoring period.

[0034] If the voltage maintenance slope is less than or equal to the slope threshold, it indicates that the lithium battery has good electrochemical activity. The control system gradually increases the duty cycle of the next pulse cycle to accelerate the charging process.

[0035] Optionally, the method further includes a pulse waveform self-test step:

[0036] The actual pulse width of the pulse charging current is monitored in real time using the waveform capture unit inside the system.

[0037] The actual pulse width is compared with the preset theoretical command pulse width;

[0038] If the deviation exceeds the allowable range, a waveform abnormality alarm will be generated and charging will be stopped;

[0039] The waveform self-test step is used to simulate the monitoring function of an external oscilloscope to ensure that the energy density injected into the lithium battery meets the preset safety standards.

[0040] Secondly, embodiments of the present invention provide a safe recovery charging system for a lithium battery after deep over-discharge, the system comprising:

[0041] Voltage acquisition module, used to monitor the terminal voltage of lithium battery in real time;

[0042] The temperature monitoring module is used to obtain the battery temperature via an NTC thermistor;

[0043] The charging drive circuit is capable of outputting a 100mA micro current and pulse modulation.

[0044] The main control logic unit is connected to the voltage acquisition module, the temperature monitoring module, and the charging drive circuit.

[0045] The main control logic unit is configured to perform the method described in any of the first aspects, and is configured to, when the terminal voltage is below 2.0V, use high-frequency sampling to analyze the voltage relaxation characteristics of the pulse gap, and adjust the charging duty cycle accordingly.

[0046] The present invention has achieved the following beneficial effects:

[0047] This invention, by constructing a pulse charging strategy based on relaxation feature feedback, changes the energy injection method of traditional DC charging and effectively solves the safety problem during the recovery process of deeply over-discharged batteries. The system utilizes the power-off relaxation time during the pulse gap to allow lithium ions accumulated on the electrode surface to diffuse into the material interior. This physical mechanism significantly reduces concentration polarization, fundamentally suppressing electrolyte decomposition and gas generation caused by local overpotential. Experimental data shows that this method can ensure the battery maintains a flat appearance during the low-voltage recovery phase, significantly reducing the risk of physical bulging and ensuring the integrity of the cell structure.

[0048] This invention utilizes high-frequency sampling technology to capture the voltage drop trajectory during pulse gaps in real time, and accurately quantifies the electrochemical activity of the battery by calculating the voltage maintenance slope. This closed-loop feedback mechanism allows the system to dynamically adjust the pulse duty cycle based on the battery's current actual accepting capacity. When battery activity is poor, the system automatically increases the relaxation time to allow ion diffusion; after activity recovery, it appropriately increases the energy injection ratio. This adaptive adjustment avoids artificially high voltages caused by blind charging, ensuring that every unit of injected energy is effectively stored, achieving a dynamic balance between charging efficiency and safety. Simultaneously, the system's real-time monitoring capability of the output pulse waveform ensures that the energy injection density meets design standards.

[0049] Furthermore, this invention integrates a comprehensive hardware-level safety protection system, enhancing system reliability. Through real-time monitoring of the pulse waveform and continuous temperature tracking by the NTC thermistor, the system ensures that the charging process always operates within a safe temperature range of 0 to 45 degrees Celsius. If any waveform abnormality or temperature exceeding the limit is detected, the circuit is immediately cut off, preventing low-temperature lithium plating or high-temperature thermal runaway. Combined with smooth switching logic after voltage recovery, this eliminates current surges during mode transitions, extending the battery's cycle life after deep over-discharge recovery.

[0050] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings.

[0051] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0052] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0053] Figure 1 This is a schematic diagram of a safe recovery charging system for a lithium battery with deep over-discharge according to an embodiment of the present invention;

[0054] Figure 2 This is a flowchart of a method for safely recovering and charging a lithium battery after deep over-discharge, as described in an embodiment of the present invention. Detailed Implementation

[0055] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0056] This invention provides a safe recovery charging method and system for lithium batteries after deep over-discharge. The core of this method lies in addressing the applicability failure of traditional constant current charging strategies in deep over-discharge scenarios by constructing a micro-current pulse closed-loop control system based on electrochemical relaxation feedback. This system uses microsecond-level time slicing technology to deconstruct the charging process into two orthogonal dimensions: energy injection and state diagnosis. It utilizes the voltage drop characteristics between pulses to reconstruct the battery's internal state of health (SOH).

[0057] Before detailing the method flow of this invention, it is necessary to first clarify the hardware basis for implementing this method. The safe recovery charging method disclosed in this invention operates in the power management unit (PMU) of a portable electronic device or a standalone high-reliability battery management system (BMS). To meet the precise control requirements for deeply over-discharged batteries (terminal voltages may be as low as 0V-2.0V), this embodiment constructs as follows: Figure 1 The hardware architecture shown mainly includes the following core functional modules:

[0058] High-precision differential voltage acquisition module: Given that the terminal voltage of deeply over-discharged batteries is at an extremely low level (e.g., 0.5V), conventional single-ended ADCs (analog-to-digital converters) often suffer from large nonlinear errors and low signal-to-noise ratios in the low-range segment. This system specifically employs an instrumentation amplifier with a high common-mode rejection ratio (CMRR > 100dB) as the front end to construct a fully differential sampling link. This link is directly connected across the positive and negative terminals of the lithium battery and strictly follows the Kelvin connection wiring rule, effectively separating the current loop from the voltage sampling loop physically to minimize the interference of PCB trace impedance and connector contact resistance on the voltage measurement accuracy in high-current paths.

[0059] In addition, the voltage acquisition module integrates a high-resolution (at least 12-bit, preferably 16-bit) SAR or Sigma-Delta ADC. To capture transient voltage relaxation characteristics, the ADC sampling rate is configured to be no less than 1 ksps (i.e., 1000 samples per second). A second-order Butterworth low-pass filter (LPF) with a cutoff frequency of 2 kHz is also configured in the signal conditioning circuit to filter out PWM switching noise and ambient power frequency interference, ensuring that the acquired voltage data accurately and purely reflects the battery's open-circuit voltage (OCV) trend.

[0060] Full-temperature-range high-sensitivity temperature monitoring module: The core of this module is an NTC (negative temperature coefficient) thermistor attached to the hot spots on the lithium battery surface (such as the base of the tabs or the center of the cell). To achieve accurate measurement across the entire temperature range (-20℃ to +60℃), the drive circuit uses a constant current source excitation method instead of a simple voltage divider resistor method to improve linearity at low temperatures. The ADC reads the voltage drop across the NTC and converts it into a resistance value. Then, the microcontroller uses the built-in Steinhart-Hart equation to calculate the precise thermodynamic temperature. (Unit: Kelvin):

[0061] ;

[0062] in, These are the inherent material characteristic constants of the NTC thermistor. Ultimately, the system will... Convert to Celsius ( The data refresh rate is set to 10Hz to ensure that transient temperature rises caused by micro-short circuits inside the battery can be captured.

[0063] High dynamic response micro-current charging drive circuit: This is the actuator of the system, and its topology differs from that of traditional linear charging ICs. This embodiment uses a synchronous rectified Buck-Boost converter with high-frequency switching capability, or a precision linear constant current source array composed of high-precision operational amplifiers and power MOSFETs. This circuit is designed to have an extremely wide output dynamic range: it can output a large current of up to 2A for normal fast charging, and can also stably output a micro-current as low as 10mA for deep recovery.

[0064] More importantly, the control terminal of this drive circuit is directly controlled by the high-frequency PWM signal of the main control unit, possessing a microsecond-level switching response speed (rise / fall time < 1µs). This means that the circuit can generate square wave pulse currents with steep edges, constant amplitude, and precisely adjustable duty cycle. A high-precision current sensing resistor is also connected in series at the circuit output, forming a hardware-level current negative feedback loop to ensure that the output current will not exceed the hardware-set safety limit (e.g., 150mA) at any time (including during software crashes).

[0065] Specifically, this embodiment constructs a hardware architecture with VBUS-priority power supply and dual-channel physical isolation. First, the power network is configured with an independent LDO that draws power directly from the external charger input (VBUS), prioritizing power to the main control unit and drive circuitry to ensure the system can still wake up normally even when the battery voltage is 0V. Second, the charging drive circuit is topologically divided into two parallel paths: the main channel is a high-current loop based on synchronous rectification Buck-Boost, and the secondary channel is a low-current loop based on a precision linear source. Both have independent power MOSFETs connected in series at their outputs. When entering the safe recovery mode, the main control unit forcibly pulls the gate of the main channel MOSFET through hardware logic, physically cutting off the high-current path and only conducting the secondary channel, thereby minimizing the risk of large current injection due to software overload.

[0066] Furthermore, to facilitate the waveform self-test in step S15, a high-speed hysteresis comparator is connected in parallel to the output of the current sensing resistor in the drive circuit. This comparator compares the analog voltage signal across the current sensing resistor with a preset reference voltage in real time, shaping the analog current pulse into a digital logic level signal (PWM feedback), and physically connecting this digital signal to the timer input capture pin of the main control unit. This hardware design allows the MCU to accurately measure the actual output current pulse width, just like an external oscilloscope, rather than simply reading the software instruction value.

[0067] Central Control Logic Unit: This unit consists of a 32-bit microcontroller (MCU) or digital signal processor (DSP) with an embedded floating-point unit (FPU). It internally runs a real-time operating system (RTOS) or a high-efficiency bare-metal state machine, embedding the single-pulse fault diagnosis algorithm, voltage relaxation trend evolution analysis algorithm, and PID closed-loop adaptive control algorithm involved in this invention. This unit electrically connects and interacts with the aforementioned modules via I2C, SPI bus, or GPIO.

[0068] More importantly, based on the aforementioned sophisticated hardware platform, embodiments of the present invention provide a safe method for recharging. (Refer to...) Figure 2 The flowchart shown illustrates that this method mainly includes the following steps:

[0069] Step S11: Full-time voltage scan and electrochemical state determination;

[0070] After the system powers on and resets, the main control logic unit first initiates a full-time voltage scan task. The voltage acquisition module continuously and in real-time captures the terminal voltage of the lithium battery with a period of 1ms. To obtain high-confidence voltage data, the system introduces a sliding window extreme value removal and averaging filtering algorithm: a FIFO queue of length N (e.g., N=20) is established to store the latest 20 sampling points in real time. Each time new data is acquired, the maximum and minimum values ​​in the queue are removed, and the arithmetic mean of the remaining data is calculated, which is then used as the valid terminal voltage value at the current moment. .

[0071] Subsequently, the system retrieves the preset parameter depth over-discharge threshold stored in the EEPROM. In this embodiment, the threshold is strictly set to 2.0V.

[0072] Explanation of the physical meaning of the 2.0V threshold: The negative electrode current collector in lithium-ion batteries is typically copper foil. From an electrochemical potential perspective, the oxidation potential of copper is approximately 3.4V (relative to...). When the battery is fully charged, the negative electrode potential is close to 0V (relative to the battery's charge level). The copper foil is in an absolutely stable region. However, as the battery is over-discharged, the negative electrode potential gradually increases. When the battery terminal voltage drops below 1.5V-2.0V, the negative electrode potential may approach the oxidation potential of copper, causing the copper foil to undergo an oxidation reaction. The copper ions produced dissolve in the electrolyte. Simultaneously, the SEI film (solid electrolyte interphase) on the negative electrode surface undergoes severe decomposition and reconstruction under low pressure. Therefore, 2.0V is the physical dividing line for determining whether a qualitative change has occurred in the battery's internal chemical system and whether it has entered a high-risk zone.

[0073] like This indicates that although the battery is in a depleted state, its internal structure is intact, the SEI film is stable, and it is capable of accepting regular charging. The system then executes the standard charging procedure, such as starting the CC (constant current)-CV (constant voltage) charging algorithm to replenish the energy with maximum efficiency.

[0074] like The system immediately determines that the battery is in a deep over-discharge state. In this state, the battery's internal resistance increases sharply, and the ion channels are blocked. If a conventional high current (such as 5V / 2A) is applied directly at this time, according to Ohm's law, a huge overpotential will be generated at the battery terminals, causing lithium deposition on the negative electrode surface and electrolyte decomposition to produce gas, which macroscopically manifests as the battery bulging instantly.

[0075] Therefore, once a deep over-discharge is detected, the system immediately triggers the highest priority safety interrupt, locks the high current path at the hardware level (i.e., forcibly pulls down the gate signal of the main power transistor), only opens the dedicated micro-current charging path, and enters the safety recovery mode.

[0076] Step S12: Microcurrent pulse excitation and dynamic energy injection;

[0077] After entering safe recovery mode, the system no longer outputs continuous DC current, but instead generates pulse charging current with dynamic duty cycle.

[0078] Specifically, the main control logic unit controls the charging drive circuit to output a series of fixed-frequency (e.g.) A square wave pulse current. Each pulse cycle... It is strictly divided into two time periods, and their mathematical relationship is defined as follows:

[0079] ;

[0080] ;

[0081] in, During the current injection period, the drive circuit is turned on to inject a current of constant amplitude into the battery. During the relaxation monitoring period, the drive circuit is turned off, the loop is open, and the current is zero. This parameter represents the pulse duty cycle and will be dynamically adjusted as a controlled variable in subsequent steps. It's important to define specifically that when the system first enters the safety recovery mode and generates the first pulse cycle (i.e., n=1), since voltage relaxation feedback data has not yet been acquired, the main control logic unit will initialize the duty cycle... The default setting is the lower limit of the adjustment range (i.e., 20%). This soft-start strategy ensures that the energy injection in the first cycle is at the most moderate level, avoiding impact on the fragile electrode interface.

[0082] The selection criteria for the 100mA current amplitude: In this embodiment, the pulse current amplitude is constantly limited to 100mA. This value was chosen based on a balance between activation efficiency and safety.

[0083] Specifically, on the one hand, under deep over-discharge conditions, the SEI film on the electrode surface may thicken or passivate, requiring a certain electric field strength (overpotential) to drive lithium ions through the interface barrier. If the current is too small (e.g., <10mA), the electric field is insufficient, ion migration is extremely slow, and the recovery time will be as long as several hours, which does not meet the requirements of user experience.

[0084] On the other hand, if the current is too large (e.g., >200mA), the excessive polarization voltage will cause the side reaction rate to increase exponentially, triggering gas production.

[0085] Furthermore, a current density of 100mA (for a typical 300-5000mAh battery) falls within the range that allows for activation without causing excessive stress.

[0086] Regarding the design of dynamic duty cycle: pulse duty cycle It is not fixed, but designed to be dynamically adjustable between 20% and 80%.

[0087] Setting a 20% lower limit is to ensure that there is at least 200ms of charging time in each cycle to maintain the most basic energy input.

[0088] Setting an 80% upper limit ensures at least 200ms of relaxation time per cycle. This relaxation time is crucial, as it allows lithium ions to diffuse from the electrode surface into the depths of the internal crystal lattice, minimizing concentration polarization and preventing the accumulation of polarization voltage.

[0089] Step S13: High-frequency sampling and single-sample feature extraction during relaxation.

[0090] During the relaxation monitoring period Internally, when the external excitation is removed, the battery enters the electrochemical relaxation process. At this time, the change in battery terminal voltage is no longer subject to Ohm's law (…). It does not govern the internal polarization of the battery, but rather reflects the dynamic characteristics of polarization elimination within the battery.

[0091] The system enters After the initial period, a programmable delay (e.g., 10ms to 20ms) is executed. This delay not only avoids the inductive spike oscillation at the moment of MOSFET turn-off, but more importantly, it avoids the instantaneous voltage jump caused by the disappearance of ohmic internal resistance, ensuring that the subsequently acquired voltage data can accurately reflect the elimination process of concentration polarization inside the battery. Then, the voltage acquisition module immediately starts a high-speed sampling mode (e.g., 2ksps) to intensively capture the falling trajectory of the battery terminal voltage.

[0092] The system extracts key feature points from the collected voltage sequence and constructs single-sample data of voltage relaxation for the current period.

[0093] Based on this data, the system performs voltage sustaining slope calculation. Specifically, it selects the relaxation monitoring period. Internal collection There are 10 effective voltage sample points, of which For the first The timestamp of each sampling point This corresponds to the voltage value. It must be noted that changes in the pulse duty cycle will affect the relaxation monitoring period. The length changes (e.g., fluctuating between 200ms and 800ms). This is to ensure that the slope calculated for different periods... It is mathematically comparable, and the system sets a value independent of A fixed sampling time window of length. Specifically, regardless of the current... Regardless of the duration, the system only extracts 100ms after the end of the delay period (20ms). The data from 20ms to 120ms after the start of sampling are fitted. This window duration is set based on the minimum relaxation time under the maximum duty cycle, ensuring that the sampling process is always completed within the effective relaxation period, and that the calculation results only reflect the battery polarization state rather than the time variable. To eliminate interference from high-frequency sampling noise, the system uses the least squares method to perform linear fitting on these discrete points and calculates the absolute value of the slope of the voltage drop trend line. :

[0094] ;

[0095] The slope The polarization elimination rate of the battery after the removal of external excitation was accurately characterized. A large value means that the voltage drops sharply after power is cut off, indicating that the injected charge only created a virtual high double-layer potential on the surface (virtual charging); if A smaller value indicates that the charge has been effectively absorbed by the electrode material and that internal diffusion is smooth (actual charge).

[0096] Step S14: Closed-loop feedback control based on live convergence conditions;

[0097] The main control logic unit will calculate in real time With the preset active convergence condition (i.e., slope threshold) The comparison is performed, and the duty cycle of the next pulse cycle is dynamically adjusted using a piecewise iterative function. :

[0098] ;

[0099] in, This represents the duty cycle for the current period. For a single adjustment step size (e.g., 5%); and These are the lower limit (20%) and upper limit (80%) of the duty cycle, respectively.

[0100] Specifically, if This indicates severe battery polarization, causing the system to execute deceleration logic (reducing the duty cycle) and prolonging the relaxation time. To await ion diffusion; if This indicates that the battery is in good condition and the system is executing acceleration logic (increasing the duty cycle) to improve charging efficiency within a safe range.

[0101] This cycle-by-cycle dynamic adjustment ensures that the charging intensity always matches the actual state of the battery.

[0102] It should be noted that the preset slope threshold It is obtained in advance and embedded in the system through the following calibration steps:

[0103] Select a standard lithium battery of the same model (SOH=100%) and discharge it to 2.0V at room temperature; apply a 100mA pulse current set by this system; during the relaxation monitoring period (after the delay), record the baseline value of the slope of the voltage natural drop. The calibration process also follows the aforementioned 100ms fixed sampling time window rule, and the pulse duty cycle applied during testing is fixed at 50%. This system will... The slope threshold is set to 1.2 to 1.5 times. In this embodiment, for a typical cylindrical lithium-ion battery with a nominal capacity of 3000mAh (e.g., a conventional power battery of model 18650 or 21700), the threshold kth is ultimately set to 2.5mV / s. When the measured slope... When the voltage exceeds this threshold, it means that the voltage drops too quickly and the internal polarization of the battery has not yet been eliminated.

[0104] Step S15: Comprehensive security protection mechanism;

[0105] In addition to the main process mentioned above, this system also runs multiple security monitoring tasks in parallel.

[0106] Specifically, the system monitors the battery temperature in real time. Based on the characteristics of lithium batteries, which are prone to lithium plating at low temperatures and thermal runaway at high temperatures, the system has set a strict safe charging temperature range (0℃-45℃).

[0107] like The system forcibly prohibits charging to prevent lithium plating from puncturing the diaphragm.

[0108] like The system forcibly prohibits charging to prevent thermal runaway.

[0109] Furthermore, for batteries with internal physical short circuits or broken tabs, the voltage cannot recover regardless of activation. To prevent endless, ineffective charging of such batteries (which could lead to overheating), the system starts a hardware watchdog timer when entering recovery mode.

[0110] If the preset maximum recovery time (e.g., 60 minutes) is reached and the voltage still has not recovered to 3.0V, the system determines that the battery has suffered irreversible physical damage. At this point, the system executes a logic fuse to permanently cut off the charging circuit and locks the fault state, no longer responding to any charging requests.

[0111] In addition, to prevent hardware failures (such as PWM generator crashes or MOSFET breakdowns) from causing abnormal output waveforms (such as becoming a continuous high current), the system uses an input capture unit to read back the waveform of the output current in real time.

[0112] The system compares the commanded pulse width with the actual pulse width. If the deviation exceeds the allowable range (e.g., ...), ... If the system detects a hardware failure, it will immediately trigger an alarm and cut off the power.

[0113] Step S16: Smooth switching and mode exit;

[0114] After the aforementioned pulse recovery process, when the battery terminal voltage steadily rises to the safe recovery threshold (3.0V) at the end of the relaxation period, it indicates that the battery has successfully left the danger zone. At this time, the negative electrode potential has moved away from the lithium plating region, and the SEI film has been completely repaired.

[0115] However, in order to avoid the voltage surge caused by switching from a micro current of 100mA to a large current of 1A instantly, this system introduces smooth switching logic.

[0116] Specifically, when the voltage reaches 3.0V, the system does not immediately switch to high-current mode, but instead enters the constant-current pre-charge transition region. In this region, the system maintains a 100mA amplitude, but stops pulse modulation and switches to constant-current charging with a 100% duty cycle.

[0117] The system continuously monitors the voltage rise rate. Only when Once the voltage stabilizes within the normal range (excluding the possibility of a voltage drop due to artificially high voltage), the system officially unlocks the high-current path, controlling the current to linearly climb to the standard fast-charging setting value, thus completing the entire recovery process. In this embodiment, the normal range is set to 0.02V / min to 0.05V / min. This rate indicates that the battery is undergoing a stable electrochemical intercalation reaction rather than simple physical capacitive polarization, at which point the system officially switches to the high-current constant-current charging stage.

[0118] It should be noted that the specific parameters such as 2.0V, 3.0V, and 100mA in this specification are preferred experimental values ​​determined for a typical lithium-ion battery with a nominal capacity of 3000mAh. For batteries with different chemical systems (such as lithium iron phosphate and ternary lithium) or different capacities, those skilled in the art can make adaptive adjustments to the above parameters according to the technical concept of this invention, which still falls within the protection scope of this invention.

[0119] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for safe recovery charging of a lithium battery after deep overdischarge, characterized in that, The method includes: Step A: Real-time detection of the terminal voltage of the lithium battery, and comparison of the terminal voltage with a preset deep over-discharge threshold; Step B: If the terminal voltage is higher than the deep over-discharge threshold, execute the standard charging process; if the terminal voltage is lower than or equal to the deep over-discharge threshold, determine that the lithium battery is in a deep over-discharge state and enter the safe recovery mode. The secure recovery mode includes the following steps: Step C: Generate a pulse charging current with a dynamic duty cycle and inject it into the lithium battery. The pulse charging current consists of alternating current injection periods and relaxation monitoring periods. Step D: During the relaxation monitoring period, the charging circuit is blocked, the voltage drop data of the lithium battery is obtained by high-frequency sampling, and the voltage maintenance slope is calculated based on the voltage drop data. Step E: Compare the voltage maintenance slope with the preset active convergence condition, and dynamically adjust the duty cycle of the pulse charging current in the next pulse cycle according to the comparison result until the terminal voltage rises back to the preset safe recovery threshold.

2. The method for safe recovery charging of a lithium battery after deep over-discharge according to claim 1, characterized in that, In step B, the depth over-discharge threshold is set to 2.0V; When the lithium battery is determined to be in a deep over-discharge state, the system locks the high-current charging path and only opens the low-current charging path to execute step C. The safety recovery threshold is set to 3.0V, which is the critical voltage point for determining whether the lithium battery has escaped the lithium plating risk zone.

3. The method for safe recovery charging of a lithium battery after deep over-discharge according to claim 1, characterized in that, In step C, the amplitude of the pulse charging current during the current injection period is constantly limited to 100mA; The 100mA amplitude is used to activate the electrolyte activity without causing gas generation and bulging inside the lithium battery; The dynamic duty cycle is adjusted within a range of 20% to 80% to ensure that the average charging current is always less than 100mA.

4. The method for safe recovery charging of a lithium battery after deep over-discharge according to claim 1, characterized in that, The entire method also includes a temperature safety monitoring step based on an NTC thermistor: Real-time acquisition of temperature data fed back by the NTC thermistor attached to the surface of the lithium battery; Determine whether the temperature data is within a preset safe charging temperature range, which is 0 degrees Celsius to 45 degrees Celsius. If the temperature data exceeds the safe charging temperature range, all charging outputs will be forcibly terminated immediately, regardless of whether the terminal voltage meets the conditions.

5. A method for safe recovery charging of a lithium battery after deep over-discharge according to claim 1, characterized in that, The method also includes a timeout fuse protection step: Simultaneously, start the security timer when initiating the secure recovery mode; If the safety timer reaches the preset maximum recovery time limit and the terminal voltage still fails to recover to the safety recovery threshold, the lithium battery is determined to be physically irreversibly damaged, and the charging circuit is permanently disconnected.

6. A method for safe recovery charging of a lithium battery after deep over-discharge according to claim 3, characterized in that, The method also includes a smooth switching step after exiting recovery mode: When the terminal voltage reaches the safety recovery threshold for the first time, it does not immediately switch to constant current charging mode, but maintains the current amplitude of 100mA for constant current pre-charging; The rate of increase of the terminal voltage is continuously monitored, and the system only switches to the high-current constant-current charging stage when the rate of increase stabilizes within the preset normal range.

7. A method for safe recovery charging of a lithium battery after deep over-discharge according to claim 1, characterized in that, In step D, the specific method for calculating the voltage sustaining slope is as follows: A first voltage value is collected at the first moment after the start of the relaxation monitoring period, and a second voltage value is collected at the second moment before the end of the relaxation monitoring period. The first voltage value, the second voltage value, and multiple intermediate sampling points between them are linearly fitted using the least squares method to obtain the absolute value of the slope of the voltage decline trend line, and the absolute value of the slope is used as the voltage maintenance slope. The voltage sustaining slope is used to characterize the polarization elimination rate of the lithium battery after the removal of external excitation.

8. A method for safe recovery charging of a lithium battery after deep over-discharge according to claim 7, characterized in that, In step E, the specific logic for dynamically adjusting the duty cycle of the pulse charging current in the next pulse cycle based on the comparison result is as follows: If the voltage maintenance slope is greater than the preset slope threshold, it indicates that the lithium battery has a serious false high voltage phenomenon. The control system reduces the duty cycle of the next pulse cycle to prolong the duration of the relaxation monitoring period. If the voltage maintenance slope is less than or equal to the slope threshold, it indicates that the lithium battery has good electrochemical activity. The control system gradually increases the duty cycle of the next pulse cycle to accelerate the charging process.

9. A method for safe recovery charging of a lithium battery after deep over-discharge according to claim 1, characterized in that, The method also includes a pulse waveform self-test step: The actual pulse width of the pulse charging current is monitored in real time using the waveform capture unit inside the system. The actual pulse width is compared with the preset theoretical command pulse width; If the deviation exceeds the allowable range, a waveform abnormality alarm will be generated and charging will be stopped; The waveform self-test step is used to simulate the monitoring function of an external oscilloscope to ensure that the energy density injected into the lithium battery meets the preset safety standards.

10. A safe recovery charging system for a lithium battery after deep over-discharge, characterized in that, The system includes: Voltage acquisition module, used to monitor the terminal voltage of lithium battery in real time; The temperature monitoring module is used to obtain the battery temperature via an NTC thermistor; The charging drive circuit is capable of outputting a 100mA micro current and pulse modulation. The main control logic unit is connected to the voltage acquisition module, the temperature monitoring module, and the charging drive circuit. The main control logic unit is configured to perform the method as described in any one of claims 1 to 9, and is configured to, when the terminal voltage is below 2.0V, use high-frequency sampling to analyze the voltage relaxation characteristics of the pulse gap, and adjust the charging duty cycle accordingly.

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