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Introduction

Lead-acid batteries, as a type of energy storage device with a long history and wide application, play a key role in many fields due to their advantages such as mature technology, low cost, and good high-current discharge performance. From the starting power supply of automobiles to the power support of industrial equipment, from emergency lighting systems to the energy storage links of renewable energy, lead-acid batteries can be seen everywhere. However, under high-load operation conditions, lead-acid batteries are confronted with numerous challenges, and their stability is severely tested. High-load operation usually means that batteries need to provide a large amount of electrical energy in a short period of time or discharge continuously for a long time. This harsh working condition will accelerate the aging of batteries and cause a series of problems that affect their stability, such as capacity attenuation, voltage fluctuations, and thermal runaway. In-depth research on the stability of lead-acid batteries in high-load operations is of great practical significance for ensuring the reliable operation of related equipment and systems, extending the service life of batteries, and improving energy utilization efficiency.

The working principle and structure of lead-acid batteries

Working principle

The working process of lead-acid batteries is based on complex REDOX reactions. During discharge, the lead on the negative plate reacts with the sulfuric acid in the electrolyte. The lead atoms lose two electrons to form lead sulfate. The electrons flow through the external circuit to the positive electrode, creating a current. Lead dioxide on the positive plate gains electrons under the action of sulfuric acid and combines with sulfate ions and hydrogen ions, also generating lead sulfate and water. The charging process is the reverse reaction of discharging. By inputting electrical energy through an external power source, lead sulfate is respectively reduced to lead and lead dioxide on the positive and negative plates, and the concentration of sulfuric acid gradually recovers. This reversible chemical reaction process realizes the mutual conversion between electrical energy and chemical energy, providing stable power output for the equipment.

Structural composition

Lead-acid batteries are mainly composed of positive and negative plates, separators, electrolyte, casings and other parts. The positive and negative plates are the core components of a battery, usually made of lead-antimony alloy, lead-calcium alloy, etc., and coated with active substances on their surfaces. The active material of the positive plate is lead dioxide, which is dark brown. The active material of the negative plate is spongy lead, which is bluish-gray in color. The separator is located between the positive and negative plates, serving to isolate the positive and negative electrodes and prevent short circuits. At the same time, it allows ions in the electrolyte to pass through. Commonly used separator materials include microporous rubber and glass fiber.

The influence of high-load operation on the stability of lead-acid batteries

Capacity attenuation

During high-load operations, lead-acid batteries frequently undergo deep charging and discharging, which can lead to the gradual shedding and passivation of the active substances inside the battery. As the number of charge and discharge cycles increases, the lead sulfate crystals on the positive and negative plates keep growing, becoming coarse and difficult to be completely restored to the active material during the charging process, thereby reducing the effective reaction area of the battery and gradually reducing its capacity. Studies show that when the discharge depth of lead-acid batteries reaches over 80%, their cycle life will be significantly shortened and the capacity attenuation rate will accelerate significantly.

Voltage fluctuation

When operating under high load, the discharge current of the battery is relatively large, which will generate a significant ohmic voltage drop and polarization voltage drop inside the battery. Ohmic voltage drop is the voltage loss caused by the resistance inside the battery. The greater the discharge current, the greater the ohmic voltage drop. Polarization voltage drop is the voltage drop caused by the electrochemical reaction rate inside the battery failing to keep up with the current demand, resulting in the potential of the electrode surface deviating from the equilibrium potential. The existence of these two types of voltage drops causes significant fluctuations in the output voltage of the battery during high-load discharge, making it difficult to maintain stability. When the equipment has high requirements for the stability of the power supply voltage, such voltage fluctuations may affect the normal operation of the equipment, such as causing unstable motor speed and abnormal operation of electronic devices.

Thermal effect and risk of thermal runaway

Under high-load operation, the chemical reaction rate inside lead-acid batteries increases, generating a large amount of heat. Meanwhile, the ohmic heat caused by high-current discharge will further increase the temperature of the battery. If the battery's heat dissipation conditions are poor and the heat cannot be dissipated in time, the battery temperature will continue to rise. When the temperature rises to a certain extent, the rate of chemical reactions inside the battery will further accelerate, generating more heat and forming a vicious cycle. This is what is called thermal runaway. Thermal runaway can cause a sharp increase in the internal pressure of the battery, which may lead to serious accidents such as battery casing rupture, electrolyte leakage, fire and even explosion, posing a huge threat to personnel safety and equipment.

Plate corrosion and deformation

When operating under high load, the electrochemical environment inside the battery becomes more complex and harsh. During the charging and discharging process, the positive plate will be corroded to a certain extent due to the REDOX reaction of lead dioxide. Especially under high charging voltage and high-temperature environments, the corrosion rate of the plates will increase significantly. Long-term corrosion will gradually thin the thickness of the plates, reduce their mechanical strength, and even cause them to break. Meanwhile, the large current generated during high-load discharge will create significant stress inside the plates, causing them to deform. Corrosion and deformation of the plates can damage the internal structure of the battery, affect its performance and stability, and further shorten its service life.

Analysis methods for the stability of lead-acid batteries in high-load operations

Electrical performance test

By testing and analyzing the electrical performance parameters of lead-acid batteries during high-load operation, the stability status of the batteries can be intuitively understood. Commonly used electrical performance test indicators include voltage, current, capacity, internal resistance, etc. Using professional battery testing equipment, such as battery charge and discharge testers, it is possible to simulate high-load operation conditions and conduct charge and discharge tests on batteries at different rates. During the discharge process, the terminal voltage changes of the battery are monitored in real time, and the voltage-time curve is plotted. The voltage stability of the battery is evaluated based on the slope and fluctuation of the curve. By measuring the capacity of the battery at different stages, the capacity attenuation rate can be calculated to determine the health status of the battery. Internal resistance is an important parameter reflecting the internal condition of a battery. It can be measured by the AC impedance method or the DC discharge method. An increase in internal resistance usually indicates that there are problems inside the battery, such as plate corrosion and active material shedding, which will affect the stability of the battery.

Thermal analysis

Thermal analysis is crucial for studying the thermal stability of lead-acid batteries in high-load operations. Infrared thermal imagers can be used to monitor the temperature distribution on the battery surface in real time, and to visually observe whether there is local overheating during the charging and discharging process of the battery. By embedding temperature sensors at different positions inside the battery, the temperature changes inside the battery can be accurately measured. The heat dissipation power of the battery can be measured by using devices such as heat flow meters. Combined with the battery's heat generation model, the thermal equilibrium state of the battery during high-load operation can be analyzed. In addition, thermal stability tests on batteries can be conducted through devices such as accelerated calorimeters to simulate the thermal behavior of batteries under extreme conditions and assess the risk of thermal runaway.

Strategies for enhancing the stability of lead-acid batteries in high-load operations

Optimize the charging strategy

Adopting a reasonable charging strategy can effectively reduce the damage to the battery during high-load operations and enhance its stability. The traditional constant current - constant voltage charging method may not meet the charging requirements of the battery in high-load operation scenarios, which is prone to cause undercharging or overcharging phenomena. Therefore, intelligent charging algorithms, such as pulse charging and segmented charging, can be adopted. Pulse charging, by intermittently applying pulse current, can effectively eliminate battery polarization, improve charging efficiency, and reduce the shedding of active materials and the corrosion of plates. Segmented charging dynamically adjusts the charging current and voltage based on the characteristics of the battery at different charging stages, ensuring that the battery maintains the best charging state throughout the entire charging process. For instance, at the initial stage of charging, a relatively large current is used to rapidly increase the battery's charge. When the battery voltage approaches the full charge voltage, the current is gradually reduced to switch to constant voltage charging to prevent overcharging. Meanwhile, in coordination with the battery management system, the charging process is monitored and controlled in real time. The charging strategy is adjusted promptly based on parameters such as the battery's temperature, voltage, and current to ensure the battery is charged safely and efficiently.

Improvement of battery materials and structures

Developing new battery materials and optimizing battery structures are the fundamental ways to enhance the stability of lead-acid batteries. In terms of plate materials, high-performance lead alloys such as lead-calcium-tin-aluminum alloys are adopted, which can enhance the corrosion resistance and mechanical strength of the plates, and reduce corrosion and deformation of the plates during high-load operations. In terms of active substances, by adding new materials such as graphene and carbon nanotubes, the conductivity and structural stability of the active substances are improved, thereby enhancing the charging and discharging performance and cycle life of the battery. In terms of separator materials, the development of separators with higher ionic conductivity and better mechanical properties, such as new composite fiber separators, can effectively reduce the internal resistance of the battery, prevent short circuits between the positive and negative plates, and enhance the stability of the battery. In terms of battery structure design, a compact and lightweight design concept is adopted to optimize the internal spatial layout of the battery, improve the uniformity of electrolyte distribution, and enhance the battery's heat dissipation capacity and shock resistance.

Battery balancing technology

In a battery pack composed of multiple lead-acid batteries, due to the differences among individual batteries, inconsistency problems such as unbalanced voltage and inconsistent capacity are prone to occur during high-load operation. This will accelerate the overall aging of the battery pack and affect its stability. Battery balancing technology can effectively solve this problem. Common battery balancing methods include passive balancing and active balancing. Passive equalization is achieved by paralleling resistors in each battery. When the battery voltage is higher than the average voltage, the resistors consume the excess energy in the form of heat, thus achieving voltage equalization of the batteries. Active balancing utilizes energy storage components such as inductors and capacitors to transfer energy from batteries with higher voltages to those with lower voltages, achieving dynamic energy distribution among batteries. It offers higher balancing efficiency and better results. By adopting advanced battery balancing technology, it can ensure that each battery in the battery pack is in good working condition, fully exerting the performance of the battery pack, extending its service life, and enhancing stability during high-load operations.

Conclusion

Lead-acid batteries are confronted with numerous stability issues such as capacity attenuation, voltage fluctuations, thermal effects and thermal runaway risks, as well as plate corrosion and deformation during high-load operations. These problems seriously affect the performance and service life of the batteries, restricting their application in related fields. By adopting various analysis methods such as electrical performance testing, thermal analysis, structural analysis, and life prediction models, a thorough understanding of the stability status of batteries during high-load operations can be achieved, providing a basis for taking targeted improvement measures. Strategies such as optimizing charging strategies, improving thermal management systems, enhancing battery materials and structures, and applying battery balancing technologies can effectively improve the stability of lead-acid batteries during high-load operations, extend battery service life, increase energy utilization efficiency, and ensure the reliable operation of related equipment and systems. In the future, with the continuous advancement of technology, further in-depth research on the stability mechanism of lead-acid batteries under high-load operation and the development of more advanced technologies and methods will help promote the efficient and safe application of lead-acid batteries in more fields, enabling them to continue to play an important role in energy storage and conversion.