Battery life-prolonging charging optimization method based on PWM (Pulse Width Modulation) waveform

Abstract

The invention discloses a battery life-prolonging charging optimization method based on a PWM waveform. The method comprises the following steps: step 1, determining an initial state of a battery and pre-charging the battery; step 2, a PWM current rising transition stage; 3, a large-current constant-current charging stage; 4, a PWM current reduction transition stage; and step 5, carrying out low-current constant-current full charge and cut-off. According to the main principle of the method, the electrochemical inertia characteristic of a battery system is utilized, an average current which can be perceived and changes smoothly in the battery is generated through a PWM waveform with alternating high-frequency positive and negative currents, and therefore the problems of impact and polarization caused by traditional step currents are effectively avoided while rapid charging is achieved. According to the invention, seamless transition of the charging current between different stages is realized by accurately controlling the duty ratio change rule of the PWM, and an effective scheme is provided for improving the charging acceptance of the battery, prolonging the cycle life and improving the safety.

Description

Technical Field

[0001] This invention belongs to the field of battery performance optimization technology, and relates to a battery charging protocol optimization method, specifically a battery life extension charging optimization method based on PWM waveform. Background Technology

[0002] Lithium-ion batteries, characterized by long range, high energy density, and high power, are widely used in electric transportation, 3C digital products, and other fields. Lithium-ion batteries typically face the need for fast charging, and traditional solutions involve increasing the charging current to achieve high-rate charging or using pulse charging. However, sudden increases or drastic changes in current can cause electrode material cracking and electrolyte decomposition, leading to a rapid decline in battery cycle life. Existing technologies address this by controlling the charging and discharging protocol steps to avoid drastic current changes, but these methods still cannot prevent battery failure caused by current surges.

[0003] Furthermore, methods to improve fast-charging performance by adjusting charge and discharge strategies are easily affected by battery systems and electrode materials, resulting in poor universality. Therefore, there is an urgent need to develop a new fast-charging protocol for lithium-ion batteries to extend battery life under fast-charging conditions. Summary of the Invention

[0004] The purpose of this invention is to provide a battery life-extending charging optimization method based on PWM waveforms to mitigate the impact of current surges on battery life. This method leverages the continuity of PWM waveforms and the inertial characteristics of the battery system. By applying PWM waveform current at the beginning and end of charging to alleviate current surges / drops, it can significantly improve the negative impacts such as the fragmentation of battery active materials caused by current spikes. This invention is a universal adjustment strategy applicable to various types and categories of lithium-ion batteries.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A battery life extension charging optimization method based on PWM waveform includes the following steps:

[0007] Step 1: Initial battery state determination and pre-charging:

[0008] Step 1-1: Take the commercial lithium-ion battery to be charged and test its current voltage value;

[0009] Steps 1-2: When the battery voltage is below 3.0V, the battery is determined to be in a deep discharge state and needs to enter the pre-charge process; for batteries with a voltage above 3.0V, the PWM current ramp-up transition stage can be directly entered; for batteries that need pre-charge, the current voltage value is read, and a constant current charging step is set with a charging current of 0.1~0.5C until the battery voltage rises to 3.0V.

[0010] Step 2, PWM current boost transition stage:

[0011] Step 2-1: Connect the battery that has been pre-charged or has qualified voltage in Step 1 to the bidirectional programmable charge and discharge instrument and temperature sensor, and fix it on the battery charge and discharge test mold.

[0012] Step 2-2: Set the temperature of the constant temperature chamber to a fixed value between 20 and 30°C. After the temperature of the chamber stabilizes, transfer the battery and its mold from Step 2-1 into the chamber and seal the chamber.

[0013] Steps 2-3: Record the battery voltage at the start of the transition phase, set the PWM current boost step, where the reference positive current is set to 0.5~1.5C, the reference negative current is set to 0.0~0.2C, the PWM period is set to 1~50s, the duty cycle is linearly increased from 0% to 100%, and the transition time is 1~5min, to complete the smooth increase of current from the initial value to the target large current value.

[0014] Step 3, High-current constant-current charging stage:

[0015] After the PWM current boosting stage is completed, the base positive current after boosting is 0.5~1.5C, and the cutoff voltage is selected as 4.0~4.1V. High current constant current charging is performed until the cutoff voltage is reached.

[0016] Step 4, PWM current reduction transition stage:

[0017] Step 4-1: After charging the battery with a high current constant current until the battery voltage reaches 4.0~4.1V, let it rest for 10 seconds, and then switch to the PWM current reduction step.

[0018] Step 4-2: Set the PWM current reduction step, where the reference positive current is set to 0.5~1C, the reference negative current is set to -0.5~0.5C, the PWM period is set to 1~50s, the duty cycle is linearly reduced from 100% to 0%, and the transition time is 1~5min, to complete the smooth decrease of current from a large current value to the target small current value.

[0019] Step 5: Small current constant current full charge and cutoff:

[0020] Step 5-1: After the PWM current reduction transition is completed, switch to the small current constant current charging step. Based on the cutoff current when the duty cycle is 100% after the PWM current reduction, set the charging current to 0.1~0.3C, continuously monitor the battery voltage, and stop charging immediately when the battery voltage reaches 4.2V.

[0021] Step 5-2: Keep the temperature sensor from step 2-1 on throughout the entire process and output the temperature detection results to monitor the thermal behavior during charging.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. This invention proposes for the first time a PWM waveform charging system based on alternating positive and negative currents, which effectively smooths the current switching curve through the high-frequency averaging effect and significantly reduces the current surge in traditional methods.

[0024] 2. This invention utilizes the inertial characteristics of the battery system to simulate a continuously changing current environment using high-frequency PWM commands, fundamentally solving the problems of increased battery polarization and internal stress concentration caused by sudden current changes.

[0025] 3. This invention combines high-current fast charging with low-current charging and achieves seamless connection through PWM, which greatly improves the gentleness of the charging process while ensuring charging speed.

[0026] 4. This invention introduces a controllable negative pulse for instantaneous depolarization, providing relaxation time for lithium-ion migration and insertion, effectively improving charging efficiency and battery acceptance.

[0027] 5. This invention does not require modification of the battery body structure; it can be achieved simply by optimizing the charging control process, making it easy to integrate and apply in existing battery management systems. Attached Figure Description

[0028] Figure 1 This is a schematic diagram illustrating the optimization principle of the charging protocol based on PWM waveform;

[0029] Figure 2 This is a fast charging protocol with optimized PWM waveform in the embodiment;

[0030] Figure 3 This is a graph showing the battery capacity retention rate under different charging modes based on actual measurements.

[0031] Figure 4 These are electron microscope images of electrode particles after battery cycling under different charging modes. Detailed Implementation

[0032] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0033] This invention provides a battery life-extending charging optimization method based on PWM waveforms to mitigate the damage to batteries caused by high-current surges during fast charging, thereby extending battery life. The main principle of this method is to utilize the electrochemical inertia characteristics of the battery system. Through a high-frequency alternating positive and negative current PWM waveform, a smoothly varying average current that is perceptible within the battery is generated. This effectively avoids the impact and polarization problems caused by traditional step currents while achieving fast charging. By precisely controlling the duty cycle variation of the PWM, this invention achieves seamless transitions between different stages of the charging current, providing an effective solution for improving battery charging acceptance, cycle life, and safety. Specifically, it includes the following steps:

[0034] Step 1: Initial battery state determination and pre-charging:

[0035] Step 1-1: Take a commercial lithium-ion battery to be charged and test its current voltage value. The size and type of the commercial lithium-ion battery to be charged are one of the following: cylindrical battery 18650, 21700, 4680, pouch battery, square battery, and button battery; the battery system is one of the following: nickel-cobalt-manganese ternary lithium-ion battery, lithium cobalt oxide battery, and lithium metal battery.

[0036] Steps 1-2: When the battery voltage is below 3.0V, the battery is determined to be in a deep discharge state and needs to enter the pre-charge process; for batteries with a voltage above 3.0V, the PWM current ramp-up transition stage can be directly entered; for batteries that need pre-charge, the current voltage value is read, and a constant current charging step is set with a charging current of 0.1~0.5C until the battery voltage rises to 3.0V.

[0037] Step 2, PWM current boost transition stage:

[0038] Step 2-1: Connect the battery that has been pre-charged or has qualified voltage in Step 1 to the bidirectional programmable charge / discharge instrument and the temperature sensor, and fix it on the battery charge / discharge test mold. The bidirectional programmable charge / discharge instrument is either a high-precision linear power supply or a high-frequency switching power supply. The temperature sensor connection is either an external bonding connection or an internal implanted connection.

[0039] Step 2-2: Set the temperature of the constant temperature chamber to a fixed value between 20 and 30°C. After the temperature of the chamber stabilizes, transfer the battery and its mold from Step 2-1 into the chamber and seal the chamber.

[0040] Steps 2-3: Record the battery voltage at the start of the transition phase, set the PWM current boost step, where the reference positive current is set to 0.5~1.5C, the reference negative current is set to 0.0~0.2C, the PWM period is set to 1~50s, the duty cycle is linearly increased from 0% to 100%, and the transition time is 1~5min, to complete the smooth increase of current from the initial value to the target large current value.

[0041] Step 3, High-current constant-current charging stage:

[0042] After the PWM current ramp-up transition phase is completed, a high-current constant-current charging process is performed with a base positive current of 0.5~1.5C and a cutoff voltage of 4.0~4.1V, until the cutoff voltage is reached. The PWM waveform is one of the following: a square wave, a triangular wave, or a sine wave with alternating positive and negative currents. The duty cycle of the PWM changes according to one of the following: linear change, nonlinear change, or S-curve change.

[0043] Step 4, PWM current reduction transition stage:

[0044] Step 4-1: After charging the battery with a high current constant current until the battery voltage reaches 4.0~4.1V, let it rest for 10 seconds, and then switch to the PWM current reduction step.

[0045] Step 4-2: Set the PWM current reduction step, where the reference positive current is set to 0.5~1C, the reference negative current is set to -0.5~0.5C, the PWM period is set to 1~50s, the duty cycle is linearly reduced from 100% to 0%, and the transition time is 1~5min, to complete the smooth decrease of current from a large current value to the target small current value.

[0046] Step 5: Small current constant current full charge and cutoff:

[0047] Step 5-1: After the PWM current reduction transition is completed, switch to the small current constant current charging step. Based on the cutoff current when the duty cycle is 100% after the PWM current reduction, set the charging current to 0.1~0.3C, continuously monitor the battery voltage, and stop charging immediately when the battery voltage reaches 4.2V.

[0048] Step 5-2: Keep the temperature sensor from step 2-1 running synchronously throughout the process and output the temperature detection results to monitor the thermal behavior during charging. The temperature detection results can be used for one or more of the following: battery thermal model construction, real-time feedback adjustment of charging strategy, and charging safety early warning.

[0049] Example:

[0050] This embodiment provides a multi-stage constant current charging method for batteries based on smooth PWM waveforms. The principle of the method is as follows: Figure 1 As shown, the specific implementation steps are as follows:

[0051] (1) Initial state determination of the battery: Take a commercial 18650 nickel-cobalt-manganese ternary lithium-ion battery to be charged, with a rated capacity of 3500mAh, and test the current voltage. The voltage value is 2.95V. This voltage value is lower than the set 3.0V judgment standard, and the battery is determined to be in a deep discharge state. The pre-charge process needs to be performed.

[0052] (2) Setup of the battery pre-charging and PWM current ramp-up transition device: Assemble the pre-charged battery onto the battery fixture, with the two terminals of the battery tightly pressed together by conductive copper pillars. Connect both ends of the fixture to a bidirectional programmable DC power supply via wires. After testing the open-circuit voltage and confirming that the circuit connection is normal, connect the thermocouple temperature sensor. The sensor probe is tightly attached to the middle of the battery casing with high-temperature tape, and the other end is connected to the data acquisition instrument. After completing the device connection, move the entire device into a constant temperature chamber that has been preheated to 25°C and stabilized. Set the constant current charging step with a charging current of 0.2C, i.e., 700mA, to charge the battery with a constant current until the battery voltage recovers to 3.0V.

[0053] (3) Setting and Execution of PWM Current Increase Transition Step: Record the battery voltage as 3.00V at the start of the transition phase. Set the PWM current increase step, where the reference positive current is set to 1C (3500mA), the reference negative current is set to 0.2C (700mA), and the PWM period is set to 10s. Set the duty cycle to linearly increase from 0 to 100% at a rate of 10%, that is, the duty cycle increases by 10% every 10 seconds, and the total transition time is 100s. Activate this step to make the average charging current smoothly increase from 700mA to 3500mA, such as... Figure 2 As shown.

[0054] (4) High-current constant-current charging stage: After the PWM current ramp-up transition is completed, the high-current constant-current charging step is immediately started. The charging current is set to 1C, i.e., 3500mA. The battery voltage is continuously monitored. When the battery voltage reaches 4.0V, this stage ends immediately.

[0055] (5) Setting and executing the PWM current reduction transition step: Set the PWM current reduction step, where the reference positive current is set to 1C (3500mA), the reference negative current is set to -0.2C (-700mA), and the PWM period is set to 10s. Set the duty cycle to decrease linearly from 100% to 30% at a rate of 10%, that is, the duty cycle decreases by 10% every 10 seconds, and the total transition time is 70s. Enable this step to make the average charging current smoothly decrease to a low current.

[0056] (6) Low-current constant-current full charge and cutoff: After the PWM current reduction transition is completed, the low-current constant-current charging step is entered. The charging current is set to 0.2C, i.e., 700mA. The battery voltage is continuously monitored. When the battery voltage reaches 4.2V, all charging processes are stopped immediately, and charging ends.

[0057] (7) Data acquisition and processing: Keep the temperature sensor on synchronously throughout the process, and set the acquisition frequency to 0.1Hz. Record current, voltage and temperature data synchronously.

[0058] (8) Charging effect verification: The cycle life of the battery using the charging method of this embodiment is compared with that of the same model using traditional 1C constant current charging. Under the same external environment, the capacity retention rate of the two batteries is tested as follows: Figure 3 As shown. Electron microscopy imaging was also performed on the electrode particles of the two cycled batteries, and the results are as follows. Figure 4 As shown, the battery using this method exhibits higher capacity retention while effectively mitigating the problem of electrode particle breakage, verifying the good effect of this method in reducing current surges and delaying performance degradation.

Claims

1. A battery life-extending charging optimization method based on PWM waveform, characterized in that... The method includes the following steps: Step 1: Initial battery state determination and pre-charging: Step 1-1: Take the commercial lithium-ion battery to be charged and test its current voltage value; Steps 1-2: When the battery voltage is below 3.0V, the battery is determined to be in a deep discharge state and needs to enter the pre-charge process; for batteries with a voltage above 3.0V, the PWM current ramp-up transition stage can be directly entered. Step 2, PWM current boost transition stage: Step 2-1: Connect the battery that has been pre-charged or has qualified voltage in Step 1 to the bidirectional programmable charge and discharge instrument and temperature sensor, and fix it on the battery charge and discharge test mold. Step 2-2: Set the temperature of the constant temperature chamber to a fixed value between 20 and 30°C. After the temperature of the chamber stabilizes, transfer the battery and its mold from Step 2-1 into the chamber and seal the chamber. Steps 2-3: Record the battery voltage at the start of the transition phase, set the PWM current boost step, where the reference positive current is set to 0.5~1.5C, the reference negative current is set to 0.0~0.2C, the PWM period is set to 1~50s, the duty cycle is linearly increased from 0% to 100%, and the transition time is 1~5min, to complete the smooth increase of current from the initial value to the target large current value. Step 3, High-current constant-current charging stage: After the PWM current boosting stage is completed, the base positive current after boosting is 0.5~1.5C, and the cutoff voltage is selected as 4.0~4.1V. High current constant current charging is performed until the cutoff voltage is reached. Step 4, PWM current reduction transition stage: Step 4-1: After charging the battery with a high current constant current until the battery voltage reaches 4.0~4.1V, let it rest for 10 seconds, and then switch to the PWM current reduction step. Step 4-2: Set the PWM current reduction step, where the reference positive current is set to 0.5~1C, the reference negative current is set to -0.5~0.5C, the PWM period is set to 1~50s, the duty cycle is linearly reduced from 100% to 0%, and the transition time is 1~5min, to complete the smooth decrease of current from a large current value to the target small current value. Step 5: Small current constant current full charge and cutoff: Step 5-1: After the PWM current reduction transition is completed, switch to the small current constant current charging step. Based on the cutoff current when the duty cycle is 100% after the PWM current reduction, set the charging current to 0.1~0.3C, continuously monitor the battery voltage, and stop charging immediately when the battery voltage reaches 4.2V. Step 5-2: Keep the temperature sensor from step 2-1 on throughout the entire process and output the temperature detection results to monitor the thermal behavior during charging.

2. The battery life extension charging optimization method based on PWM waveform according to claim 1, characterized in that... In step 1-1, the size and type of the commercial lithium-ion battery to be charged are one of the following: cylindrical battery 18650, 21700, 4680, pouch battery, square battery, and button battery.

3. The battery life extension charging optimization method based on PWM waveform according to claim 1, characterized in that... In step 1-1, the battery system is one of the following: nickel-cobalt-manganese ternary lithium-ion battery, lithium cobalt oxide battery, or lithium metal battery.

4. The battery life extension charging optimization method based on PWM waveform according to claim 1, characterized in that... In steps 1-2, for batteries that need to be pre-charged, the current voltage value is read, and a constant current charging step is set with a charging current of 0.1~0.5C until the battery voltage rises to 3.0V.

5. The battery life extension charging optimization method based on PWM waveform according to claim 1, characterized in that... In step 2-1, the bidirectional programmable charge / discharge device is either a high-precision linear power supply or a high-frequency switching power supply.

6. The battery life extension charging optimization method based on PWM waveform according to claim 1, characterized in that... In step 2-1, the temperature sensor connection can be either an external bonding connection or an internal implanted connection.

7. The battery life extension charging optimization method based on PWM waveform according to claim 1, characterized in that... In step 3-1, the PWM waveform is one of the following: a square wave, a triangle wave, or a sine wave with alternating positive and negative currents.

8. The battery life extension charging optimization method based on PWM waveform according to claim 1, characterized in that... In step 3-1, the duty cycle of the PWM changes according to one of the following: linear change, nonlinear change, or S-curve change.

9. The battery life extension charging optimization method based on PWM waveform according to claim 1, characterized in that... In step 5-2, the temperature detection results are used for one or more of the following: battery thermal model construction, real-time feedback adjustment of charging strategy, and charging safety early warning.

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