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Abstract

This paper conducts an in-depth study on the thermal runaway problem of lead-acid batteries in forklifts, systematically analyzes the causes of thermal runaway, covering multiple dimensions such as the battery's own structure, charging process, usage environment and daily maintenance. Through the analysis of various influencing factors, targeted and operational preventive measures are proposed, aiming to reduce the risk of thermal runaway of lead-acid batteries in forklifts, ensure the safety and efficient operation of forklifts, and provide reference basis for forklift user enterprises and relevant technical personnel.

Ⅰ. Introduction

In the modern logistics warehousing and industrial production fields, forklifts have become indispensable equipment due to their efficient and flexible cargo handling capabilities. Lead-acid batteries, as the main power source for forklifts, have the advantages of low cost, mature technology and good high-current discharge performance, and are widely used in various types of forklifts. However, lead-acid batteries have the risk of thermal runaway during use. Once thermal runaway occurs, it not only leads to a shortened battery life and a decline in performance, but in severe cases, it may also cause safety accidents such as fires and explosions, threatening the lives of personnel and the property safety of enterprises. Therefore, it is of great practical significance to conduct an in-depth analysis of the causes of thermal runaway of lead-acid batteries in forklifts and formulate effective preventive measures.

Ⅱ. Principle of Thermal Runaway of Lead-Acid Batteries in Forklifts

Thermal runaway refers to the phenomenon where, during the charging process of lead-acid batteries, due to the imbalance between internal heat generation and heat dissipation, the battery temperature continuously rises, triggering a series of chain reactions, and ultimately causing a significant decline in battery performance or even damage. During the normal charging process, chemical reactions occur inside lead-acid batteries, generating a certain amount of heat. At the same time, the battery also dissipates heat to the surrounding environment through the casing. When the heat generation and heat dissipation reach a balance, the battery temperature remains stable. However, when certain factors disrupt this balance, causing the heat generation rate to be greater than the heat dissipation rate, the battery temperature begins to rise. As the temperature rises, the rate of chemical reactions inside the battery accelerates, and the heat generation further increases, forming a vicious cycle. When the temperature rises to a certain extent, components such as the battery plates and separators will deform and get damaged, the decomposition of the electrolyte will intensify, generating a large amount of gas, increasing the internal pressure of the battery, and eventually leading to thermal runaway.

Ⅲ. Analysis of the Causes of Thermal Runaway of Lead-Acid Batteries in Forklifts

(1) Battery itself factors

Plate quality issues: Some lead-acid battery manufacturers, in order to cut costs, use poor-quality lead alloy materials or fail to meet production standards during the plate manufacturing process, resulting in insufficient adhesion of the active substances on the plates and uneven thickness. During the long-term charging and discharging process, the plates are prone to problems such as active material shedding and short circuits, which increase the internal resistance of the battery, increase heat generation, and cause thermal runaway.

Performance defect of the separator: The main function of the separator is to separate the positive and negative plates to prevent short circuits, while allowing ions in the electrolyte to pass through. If the pore size of the separator is too large, its thickness is uneven or its corrosion resistance is poor, it will lead to an uneven distribution of the electrolyte inside the battery, affecting the battery's charging and discharging performance. It may also cause the positive and negative plates to come into direct contact, resulting in a short circuit and generating a large amount of heat.

The electrolyte ratio is unreasonable: The main components of the electrolyte are sulfuric acid and water, and their concentration and purity have a significant impact on the battery performance. If the concentration of the electrolyte is too high or too low, it will affect the chemical reaction efficiency of the battery and cause it to heat up. In addition, if the electrolyte contains impurities, micro-cells will form inside the battery, increasing the internal resistance of the battery and generating additional heat.

(2) Factors during the charging process

Excessively high charging voltage: During the charging process of forklift lead-acid batteries, if the charging voltage is set too high, it will accelerate the chemical reaction rate inside the battery and generate a large amount of heat. At the same time, excessively high voltage will also accelerate the decomposition of water, generating a large amount of hydrogen and oxygen, and increasing the internal pressure of the battery. When the pressure exceeds the opening pressure of the battery safety valve, the gas escapes and takes away some heat. However, if the charging voltage remains too high and the heat generation rate is still greater than the heat dissipation rate, thermal runaway will occur.

Excessive charging current: High current charging can shorten the charging time, but if the charging current is too large, it will cause the active substances on the surface of the battery plates to react rapidly, resulting in severe heating of the plates. In addition, high-current charging will also raise the temperature of the electrolyte inside the battery, accelerate the evaporation and decomposition of the electrolyte, reduce the battery's service life, and increase the risk of thermal runaway.

Excessive charging time: When the battery is fully charged, if it is charged for a long time, overcharging will occur inside the battery. When overcharged, the main chemical reaction inside the battery is the decomposition of water, generating a large amount of hydrogen and oxygen, and releasing a significant amount of heat at the same time. Long-term overcharging will cause the battery temperature to keep rising, eventually leading to thermal runaway.

Charging equipment failure: The performance and stability of charging equipment have a direct impact on the battery charging process. If the voltage regulation device, current control device and other components of the charging equipment malfunction and fail to accurately control the charging voltage and current, it will lead to abnormal battery charging and cause thermal runaway. In addition, if the cooling system of the charging device malfunctions, such as a damaged fan or blocked heat dissipation holes, the heat generated by the charging device itself cannot be dissipated in time, which will also affect the charging safety of the battery.

(3) Environmental factors of use

Excessively high ambient temperature: When forklifts operate or charge in high-temperature environments, the ambient temperature around the battery is relatively high, which will affect the battery's heat dissipation effect. The heat dissipation of batteries mainly occurs through heat conduction, heat convection and heat radiation. When the ambient temperature is too high, the temperature difference between the battery and the environment decreases, the heat dissipation efficiency drops, causing heat accumulation inside the battery and easily leading to thermal runaway.

Poor ventilation: If the battery compartment of the forklift is not designed properly, with the ventilation openings being too small or blocked, or if there are no good ventilation facilities in the charging area, the heat and gas generated by the battery during charging and discharging cannot be discharged in time. The accumulation of heat and gas in the battery compartment not only affects the battery's heat dissipation but also increases the internal pressure of the battery, raising the risk of thermal runaway.

(4) Daily maintenance factors

The electrolyte level is too low: During the use of lead-acid batteries, the electrolyte will gradually decrease due to evaporation and chemical reactions. If the electrolyte is not replenished in time, causing the electrolyte level to be too low, the plates will be exposed to the air, and the active substances on the plates will not be able to fully contact the electrolyte, affecting the charging and discharging performance of the battery. At the same time, the exposed parts of the plates will heat up due to oxidation, increasing the possibility of thermal runaway.

Battery surface dirt: If a large amount of dust, electrolyte stains and other dirt accumulate on the battery surface, it will form a conductive path, causing an increase in battery self-discharge and generating additional heat. In addition, dirt can also affect the heat dissipation on the battery surface, causing the battery temperature to rise.

Lack of regular inspection and maintenance: Many forklift user enterprises do not attach sufficient importance to the daily inspection and maintenance of lead-acid batteries. They fail to regularly test parameters such as battery voltage, electrolyte density, and temperature, nor do they promptly identify and address potential battery issues. For instance, if problems such as sulfation of battery plates and loose connectors are not detected and resolved in time, they will gradually deteriorate and eventually lead to thermal runaway.

Ⅳ. Preventive Measures for Thermal Runaway of Lead-Acid Batteries in Forklifts

(1) Optimize the quality of the battery itself

Strictly control the quality of battery production: Battery manufacturers should strengthen the management of raw material procurement and select reliable lead alloy materials, separators, electrolytes and other raw materials. Meanwhile, strictly control the production process to ensure the precision and quality of the plate manufacturing process, enhance the adhesion and uniformity of the active substances on the plates, and guarantee that the pore size, thickness and corrosion resistance of the separators meet the standard requirements. Strengthen product quality inspection, conduct strict performance tests and quality checks on each batch of batteries produced, and prevent substandard products from entering the market.

Improving battery structure design: R&D personnel can enhance the heat dissipation performance and safety of batteries by improving their structure design. Adopting new separator materials and structures, the insulation performance and ion conduction performance of the separator are improved, and the internal resistance of the battery is reduced. Temperature sensors and pressure sensors are installed inside the battery to monitor the temperature and pressure changes of the battery in real time. When the dangerous threshold is reached, measures are taken promptly for protection.

(2) Standardize the management of the charging process

Set charging parameters reasonably: According to the model, specification and user manual of the forklift lead-acid battery, set the charging voltage, current and charging time reasonably. During the charging process, strictly follow the specified parameters for charging to avoid overcharging and charging with high current. Under normal circumstances, the charging voltage should be controlled at approximately 1.2 to 1.3 times the battery's rated voltage, and the charging current should not exceed 0.1C of the battery's rated capacity. The charging time is determined based on the remaining battery power and the charging current. Once the battery is fully charged, charging should be stopped promptly.

Select high-quality charging equipment: Choose charging equipment that is reliable in quality and stable in performance, and ensure that the charging equipment has complete voltage regulation, current control and protection functions. Regularly maintain and service the charging equipment, check whether the voltage regulation device, current control device, heat dissipation system and other components of the charging equipment are working properly, and replace the damaged parts in time. At the same time, the number of charging devices should be reasonably configured based on the quantity of batteries and their usage frequency to avoid malfunctions caused by excessive use of the charging devices.

Adopting intelligent charging technology: With the continuous development of technology, intelligent charging technology has gradually been applied in the field of lead-acid battery charging. Intelligent charging devices can automatically adjust the charging voltage and current based on the real-time status of the battery, enabling the switching of multiple charging modes such as constant current charging, constant voltage charging, and float charging, thereby enhancing charging efficiency and extending the battery's service life. In addition, intelligent charging devices can also be connected to the monitoring system through the network to achieve remote monitoring and management, and promptly detect and handle problems that occur during the charging process.

(3) Improve the environmental conditions for use

Control the ambient temperature: Try to avoid forklifts operating and charging for long periods in high-temperature environments. If it is unavoidable, some cooling measures can be taken, such as installing air conditioners, fans and other cooling equipment in the working area and charging area to lower the ambient temperature. At the same time, when designing the battery compartment of a forklift, heat insulation measures should be taken into account to reduce the impact of ambient temperature on the battery.

Strengthen ventilation management: Ensure that the ventilation openings in the forklift battery compartment are unobstructed, and regularly clean the dust and debris from the ventilation openings. In the charging area, good ventilation facilities should be set up, such as installing exhaust fans and ventilation ducts, to ensure air circulation in the charging area and promptly expel the heat and gas generated by the battery during charging and discharging. In addition, temperature and gas monitoring devices can be installed inside the battery compartment to monitor the temperature and gas concentration in real time. When the dangerous threshold is reached, the ventilation equipment will be automatically activated for ventilation.

(4) Strengthen daily maintenance and upkeep

Regularly check the electrolyte level: Develop a strict battery maintenance plan and regularly check the electrolyte level. When the electrolyte level drops below the minimum mark, distilled water or dedicated lead-acid battery electrolyte should be replenished in a timely manner. When replenishing the electrolyte, be careful not to exceed the highest scale line to prevent the electrolyte from overflowing. Meanwhile, regularly test the density of the electrolyte and adjust the concentration of the electrolyte based on the test results to ensure that the performance of the electrolyte meets the requirements.

Keep the battery surface clean: Regularly clean the battery surface, wipe the dust and electrolyte stains on the battery surface with a damp cloth, and avoid using corrosive cleaning agents. During the cleaning process, be careful to prevent moisture from entering the battery interior. After cleaning, ensure that the battery surface is dry. In addition, it is necessary to regularly inspect the battery's connectors, terminal blocks and other parts to ensure a firm connection and prevent sparks and heat caused by poor contact.

Establish battery maintenance files: Establish detailed maintenance files for the lead-acid batteries of each forklift, recording information such as the purchase date, usage time, charging frequency, regular inspection data, and maintenance conditions of the batteries. By analyzing the maintenance files, problems and potential risks of the battery can be identified in a timely manner, and targeted maintenance measures can be formulated to extend the service life of the battery. Meanwhile, maintaining the archives can also provide a reference basis for battery replacement and management.

V. Conclusion

Thermal runaway of lead-acid batteries in forklifts is caused by the combined effect of multiple factors such as the battery's own factors, charging process factors, usage environment factors and daily maintenance factors. Through in-depth analysis of these reasons, we can take a series of preventive measures, such as optimizing the quality of the battery itself, standardizing the management of the charging process, improving the usage environment conditions and strengthening daily maintenance and care, to effectively reduce the risk of thermal runaway. In practical applications, forklift user enterprises should attach great importance to the safety management of lead-acid batteries, strengthen the training of operators and maintenance personnel, enhance their safety awareness and operational skills, strictly follow relevant standards and norms for battery use and maintenance, ensure the safe and stable operation of forklift lead-acid batteries, and provide reliable power support for the production and operation activities of enterprises.

The above article analyzes the thermal runaway problem of lead-acid batteries in forklifts from multiple aspects and provides preventive measures. If you think some parts need further refinement or have any other supplementary requirements, please feel free to let us know at any time.