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Introduction

In the fields of modern logistics and industrial production, forklifts, as key handling equipment, the stability and durability of their power supply are of vital importance. Lead-acid batteries have occupied an important position in the selection of power sources for forklifts due to their advantages such as low cost, mature technology and good high-current discharge performance. However, as the usage time increases, lead-acid batteries in forklifts generally face the problem of capacity attenuation, which not only affects the working efficiency and endurance of forklifts but may also lead to an increase in operating costs. An in-depth analysis of the reasons for the capacity attenuation of lead-acid batteries in forklifts is of great significance for improving their performance and prolonging their service life.

Analysis of the Reasons for Capacity Attenuation of Lead-Acid Batteries in Forklifts

Plate-related factors

Plate sulfation: Plate sulfation is a common and significant cause of capacity attenuation in forklift lead-acid batteries. When a battery is in a state of undercharging for a long time, that is, when it is not fully charged, the lead sulfate produced during discharge cannot be completely converted back into the active material, and a layer of white, hard and poorly conductive lead sulfate crystals will gradually form on the surface of the plates. These crystalline particles will clog the pores of the plates, hindering the full contact and reaction between the electrolyte and the active substances on the plates, thereby increasing the internal resistance of the battery and reducing its capacity. In addition, frequent deep discharges and long-term use in a low-temperature environment will also accelerate the sulfation process of the plates. For instance, for forklifts operating outdoors in cold winters, if the insulation measures for the battery are not in place, the sulfation of the plates is often more severe.

Plate corrosion: It mainly occurs on the positive plate. During the charge and discharge cycles of the battery, lead dioxide on the positive plate undergoes oxidation-reduction reactions with sulfuric acid. The environment where the plates are located is strongly acidic and has a relatively high potential. As the number of cycles increases, the positive plate grid material will gradually be corroded, resulting in damage to the grid structure and a reduction in the effective cross-sectional area. This, in turn, increases the connection resistance between the active material on the plates and the grid, intensifies the shedding of the active material, and leads to a decline in battery capacity. Excessively high charging voltage or temperature will significantly accelerate the corrosion rate of the positive plate. For instance, when the charging voltage exceeds the specified range, the corrosion rate of the positive plate may increase several times, significantly shortening the battery's service life.

Plate active material shedding: During the operation of forklifts, frequent acceleration, deceleration, and jolting and vibration can cause mechanical stress to the plates. Meanwhile, the internal stress generated by the volume change of the active material on the plates during the charging and discharging process can also cause damage to the plates. Over a long period of accumulation, the active substances on the plates will gradually soften, fall off and deposit at the bottom of the battery. The reduction of active substances directly leads to a decrease in the total amount of substances involved in the electrochemical reaction, and the battery capacity naturally declines. In severe cases, the detached active substances may cause short circuits between the plates, further damaging the battery.

Factors related to electrolyte

Electrolyte water loss: During the charging process of lead-acid batteries, especially when overcharged, an electrolytic reaction of water occurs, generating hydrogen and oxygen that escape from the battery interior, causing the water content in the electrolyte to gradually decrease. After the electrolyte loses water, the concentration of sulfuric acid relatively increases, and the density of the electrolyte increases. This will accelerate the corrosion of the plates, increase the internal resistance of the battery at the same time, reduce the charging and discharging performance of the battery, and cause capacity attenuation. In addition, high-temperature environments will accelerate the rate of water loss in the electrolyte. For instance, for forklifts operating in high-temperature environments during summer, if the battery is not replenished with water in a timely manner for maintenance, the loss of electrolyte water will be even more severe.

Electrolyte contamination: The working environment of forklifts is complex. If impurities such as metal ions (iron, copper, etc.), organic substances or dust are mixed into the electrolyte, it will trigger a series of adverse chemical reactions. These impurities may form micro-batteries on the surface of the plates, leading to intensified local self-discharge and consuming the effective capacity of the battery. For instance, when the electrolyte contains iron ions, the iron ions will undergo a reduction reaction on the negative plate, consuming the active material of the negative plate and accelerating the corrosion of the positive plate at the same time, thereby affecting the overall performance and capacity of the battery.

Charging and discharging related factors

Overcharging: Overcharging occurs when the charging voltage is too high or the charging time is too long, exceeding the battery's normal acceptance capacity. When overcharged, in addition to the normal charging reaction inside the battery, there will also be a large amount of water electrolysis and side reactions on the plates, generating excessive gases (hydrogen and oxygen), which leads to water loss in the battery, accelerated corrosion of the plates, and shedding of active substances, seriously damaging the battery performance and causing irreversible capacity decline. Long-term overcharging may also cause the battery to heat up severely, leading to thermal runaway and even safety issues such as battery bulging and explosion.

Over-discharge: During the operation of a forklift, if the battery is over-discharged, that is, the discharge voltage is lower than the specified terminal voltage, a large amount of active substances on the plates will be converted into lead sulfate. Moreover, due to the excessive depth of discharge, the generated lead sulfate particles are coarse and difficult to be completely converted back into active substances in the subsequent charging process, resulting in sulfation of the plates, increased internal resistance of the battery, and reduced capacity. Frequent over-discharge is particularly damaging to batteries and will greatly shorten their service life. For instance, some forklift operators continue to use the battery when its power is nearly exhausted. If this continues for a long time, it will accelerate the battery capacity decline.

Unreasonable charging and discharging currents: Excessive charging and discharging currents can cause multiple types of damage to the battery. When the charging current is too large, the chemical reaction rate inside the battery is too fast, which can lead to local overheating, accelerated water loss of the electrolyte, and at the same time, it may cause the active material on the plates to fall off due to rapid expansion and contraction. If the discharge current is too large, it will cause the battery voltage to drop too rapidly in an instant, affecting the normal working performance of the forklift. Moreover, due to the uneven reaction on the surface of the plates during the discharge process, it is easy to cause local sulfation of the plates, thereby reducing the battery capacity. For instance, when a forklift starts at full load or climbs a slope, the instantaneous discharge current is relatively large. If it frequently operates under such conditions, it will have an adverse effect on the battery capacity.

Environmental factors for forklift usage

Temperature influence: Lead-acid batteries are relatively sensitive to the temperature of the operating environment. In a low-temperature environment, the viscosity of the electrolyte increases, the ion diffusion rate slows down, resulting in a decrease in the electrochemical reaction rate, an increase in the internal resistance of the battery, and a reduction in the actual output capacity. Generally speaking, for every 10℃ drop in temperature, the battery capacity decreases by approximately 10% to 15%. For instance, the battery capacity of forklifts operating outdoors in the cold northern regions during winter is significantly lower than that under normal temperature conditions. In high-temperature environments, the chemical reactions inside the battery accelerate, and problems such as electrolyte water loss and plate corrosion intensify, which can also lead to a rapid decline in battery capacity. Moreover, high temperatures may also trigger the risk of battery thermal runaway, seriously threatening the safety and lifespan of the battery.

Vibration and shock: During the process of handling goods, forklifts are inevitably subject to various vibrations and shocks. These mechanical external forces acting on the battery can cause damage to components such as the plates and connecting parts. If the active material on the plates may become loose or fall off due to vibration, and the connection parts may become loose or have poor contact, etc., it will affect the electrical performance of the battery and lead to a decrease in capacity. Forklifts that are used for a long time in poor road conditions or in working environments with frequent starts, stops and turns suffer more significant damage from vibration and shock to their batteries.

Factors for battery maintenance and care

Inadequate daily inspection: If forklift operators or maintenance personnel do not conduct regular inspections of the battery as required, problems such as low electrolyte level, damaged battery casing, and corrosion of terminal posts cannot be detected in a timely manner. If these problems accumulate over a long period of time, they will gradually deteriorate, affecting the normal performance of the battery and leading to capacity attenuation. For instance, when the electrolyte level is too low and not replenished in time, it will accelerate the sulfation and corrosion of the plates. Severe corrosion of the terminal post will increase the contact resistance and affect the charging and discharging efficiency.

Improper maintenance methods: When maintaining lead-acid batteries, if incorrect methods are adopted, it can also damage the battery's performance. For instance, when replenishing the electrolyte, if the added liquid is not distilled water or a special supplementary solution but ordinary tap water, impurities in the water will contaminate the electrolyte, causing battery failure. In addition, when cleaning the battery surface, if metal tools are used, it may scratch the battery casing or cause a short circuit between the positive and negative terminals, affecting the normal use of the battery. Moreover, not charging in accordance with the prescribed charging system and arbitrarily changing charging parameters will also have a negative impact on battery capacity.

Conclusion

The capacity attenuation of forklift lead-acid batteries is a complex process caused by the combined effect of multiple factors, involving multiple aspects such as plates, electrolyte, charging and discharging operations, usage environment, and maintenance. Sulfidation, corrosion of the plates and shedding of active substances have changed the physical and chemical properties of the plates, affecting the progress of electrochemical reactions. The loss of water and contamination of the electrolyte disrupted the chemical balance inside the battery. Unreasonable charging and discharging behaviors directly damage the structure and performance of the battery. The harsh usage environment and improper maintenance further accelerate the battery capacity decline. To effectively delay the capacity attenuation of lead-acid batteries in forklifts and extend their service life, it is necessary to take comprehensive measures from multiple aspects such as optimizing the operating conditions of forklifts, strictly standardizing charging and discharging operations, strengthening daily maintenance and care, and improving the working environment of batteries, to ensure that lead-acid batteries maintain good performance and stability in forklift applications and reduce operating costs. Improve the efficiency of logistics and industrial production.