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Introduction

As a widely used handling equipment in industries such as logistics and warehousing, the power source of forklifts is of vital importance. Lead-acid batteries have become the commonly used power source for forklifts due to their advantages such as low cost, mature technology and good high-rate discharge performance. However, lead-acid batteries have the phenomenon of self-discharge, which not only affects their performance and lifespan, but also increases the usage cost and maintenance workload. An in-depth analysis of the self-discharge phenomenon of lead-acid batteries in forklifts is of great significance for improving the operational efficiency of forklifts and reducing operating costs.

Self-discharge phenomenon and principle

Description of self-discharge phenomenon

Even if the lead-acid battery of a forklift is not connected to a load and is in an open circuit state, its power will gradually decrease over time, which is manifested as a drop in voltage and a reduction in capacity. If a fully charged forklift battery is left idle for a period of time and its working time is significantly shortened when used again, failing to meet the normal operation requirements, this is a direct manifestation of self-discharge.

The principle of negative electrode self-discharge

The active material of the negative electrode is spongy lead. In the sulfuric acid electrolyte, its electrode potential is more negative than that of hydrogen, and a reaction of hydrogen displacement occurs, that is, lead auturysis. Hydrogen evolution overpotential affects the autolysis rate of lead. If there are metal impurities with low hydrogen overpotential values (such as platinum, copper, bismuth, etc.) on the surface of the negative electrode, they will form corrosion micro-cells with the active material of the negative electrode, accelerating the autolysis of lead and increasing the self-discharge rate. Meanwhile, the oxygen released from the positive electrode diffuses to the negative electrode to react with lead, which also leads to some lead being unable to be completely converted into active substances during charging, causing self-discharge.

The principle of positive electrode self-discharge

Lead dioxide, the active material of the positive electrode, will undergo autolysis in sulfuric acid solution. The rate of autolysis is controlled by the rate of oxygen release. Factors such as impurities in the electrode and electrolyte, ambient temperature, composition of the grid alloy, and concentration of the electrolyte all have an impact on it. For instance, if there are easily oxidized organic substances in the electrolyte, self-discharge will occur on the positive plate, consuming active substances and releasing gases such as carbon dioxide.

Factors influencing self-discharge

Battery materials and manufacturing processes

1. ** Grid material ** : The sealing of valve-regulated lead-acid batteries without leakage and their good storage performance are largely attributed to the grid material. If lead-calcium alloy grids are adopted, self-discharge can be reduced because their corrosion resistance is superior to that of traditional lead-antimony alloys, which can decrease the self-discharge caused by grid corrosion. The composition and structure of different grid alloys have a significant impact on the self-discharge of batteries.

2. ** Purity of Active substances ** : The high content of harmful impurities in active substance additives, separators, and sulfuric acid electrolyte is an important reason for the high self-discharge of batteries. Impurities such as iron, manganese, chlorine, antimony, etc. can form local micro-batteries inside the battery, causing self-discharge. For instance, if the iron ions in the electrolyte exceed the standard, oxidation-reduction reactions will occur between the positive and negative electrodes, accelerating the loss of electrical charge. The manufacturing process also affects self-discharge, such as the uniformity of the plate paste application and the curing process. If the paste application is uneven, it will lead to inconsistent contact between the active substance and the electrolyte, causing local self-discharge.

Environmental factors

1. ** Temperature ** : Temperature has a significant impact on the self-discharge rate. Valve-regulated sealed lead-acid batteries have an average daily self-discharge rate of approximately 0.1% in an environment of 25-45 ℃. The lower the temperature, the smaller the self-discharge. Low temperatures are conducive to battery storage. For every 10℃ increase in temperature, the self-discharge rate may increase by 1 to 2 times. At high temperatures, the chemical reaction rate inside the battery accelerates, and the reaction between the active substances of the positive and negative electrodes and the electrolyte intensifies, resulting in a significant increase in self-discharge. In the hot summer, when forklifts are parked outdoors for a long time, the battery self-discharge accelerates and the power loss is serious.

2. ** Humidity ** : In a high-humidity environment, moisture in the air may enter the battery interior and react with the electrolyte or electrode materials, increasing self-discharge. Moisture may also cause rust or corrosion of the external metal components of the battery, forming local conductive paths and triggering self-discharge. If the forklift operates in a damp warehouse, the battery casing is prone to moisture, which may cause abnormal self-discharge.

Factors related to electrolyte

1. ** Electrolyte concentration ** : Tests show that for valve-regulated lead-acid batteries (with grid material Pb-Ca-Sn) stored at 10℃, the self-discharge rate increases with the increase of electrolyte density, and the positive plate is more affected. If the density of the electrolyte increases by 0.01g/cm³, the self-discharge rate of the positive plate increases by 0.06% per day, and that of the negative plate increases by approximately 0.03%. However, some studies have shown that for VRLA batteries with lead-calcium grid materials as the negative plates, the self-discharge is the most severe when the electrolyte density is 1.250g/cm³ at room temperature. When the density increases to 1.35g/cm³, the self-discharge reaction rate decreases instead. The reason is that the high-density electrolyte forms a fine lead sulfate protective layer on the plates, which hinders the self-discharge reaction.

2. ** Electrolyte contamination ** : Electrolyte contamination by impurities will significantly increase the self-discharge rate. The sources of impurities include being mixed in during use and dissolution of battery components, etc. When adding water to a forklift battery, if water containing impurities is used, it will contaminate the electrolyte and cause self-discharge.

The harm of self-discharge to forklift lead-acid batteries

Capacity loss and shortened battery life

Self-discharge directly leads to battery capacity loss. After a forklift is fully charged and left idle for a period of time, the actual available capacity decreases and the driving range shortens. For forklifts that need to operate continuously for long periods of time, this may lead to insufficient battery power during operation, affecting work efficiency and even preventing the forklift from completing the scheduled handling tasks. Frequent charging not only increases labor intensity but also accelerates battery aging.

Battery life is reduced

Long-term self-discharge causes an imbalance in the internal chemical reactions of the battery, intensifies the loss of active substances, and aggravates problems such as sulfation of the plates and corrosion of the grids, seriously shortening the battery's service life. Shortened battery life means that batteries need to be replaced more frequently, increasing equipment maintenance costs and downtime, and affecting the normal production and operation of enterprises.

Affect the performance stability of forklifts

Self-discharge causes unstable battery voltage, which will affect the starting performance and operational stability of forklifts. When starting a forklift, there may be insufficient voltage, difficulty in starting, and unstable power output during operation, which affects the accuracy and safety of goods handling. For forklift operation scenarios with high requirements for operational accuracy, such as handling goods in a precision instrument warehouse, performance fluctuations caused by battery self-discharge may lead to serious consequences.

Measures to reduce self-discharge

Optimize battery design and manufacturing

1. ** Select high-quality materials ** : Use high-purity active substances, low-impurity electrolytes and corrosion-resistant grid materials to reduce self-discharge from the source. If high-purity lead-calcium alloy grids are used, the self-discharge caused by grid corrosion can be effectively reduced. Strictly control the impurity content in the electrolyte to prevent micro-battery reactions caused by impurities.

2. ** Improve manufacturing process ** : By improving the manufacturing process of the plates, ensure the uniformity of the paste coating and enhance the consistency of the contact between the plates and the electrolyte; Optimize the curing process, enhance the bonding force between the active material and the plates, and reduce self-discharge caused by the shedding of the active material. During the battery assembly process, ensure that all components are tightly connected and have good insulation to avoid internal short circuits that may cause self-discharge.

Strengthen the management of battery usage and maintenance

1. ** Reasonable charging ** : In accordance with the requirements of the battery manual, adopt appropriate charging methods and parameters to avoid overcharging and undercharging. Overcharging can cause the battery to heat up, accelerate internal chemical reactions and increase self-discharge. Undercharging will cause sulfation of the plates, intensifying self-discharge. Regularly perform equalization charging on the battery to ensure that the power of each individual battery in the battery pack is consistent, reducing self-discharge imbalance caused by power differences.

2. ** Regular Maintenance and inspection ** : Regularly inspect the battery's appearance to ensure that the battery casing is undamaged and there is no leakage of the electrolyte. Promptly clean the dust and electrolyte stains on the battery surface to prevent self-discharge caused by surface conductivity. Regularly test the density and liquid level of the electrolyte, replenish distilled water in time or adjust the density of the electrolyte to ensure the stable performance of the electrolyte. It is also necessary to conduct regular capacity tests on the batteries to keep track of their health conditions, and promptly identify and handle batteries with abnormal self-discharge.

Improve the usage environment conditions

1. ** Control temperature ** : Try to park the forklift in a place with a suitable temperature and avoid parking it for a long time in high or low temperature environments. In high-temperature environments, the battery temperature can be reduced and self-discharge can be decreased by installing ventilation and heat dissipation devices. In low-temperature environments, insulation measures can be taken, such as installing insulation covers on the battery to maintain its normal performance and reduce the self-discharge rate.

2. ** Keep dry ** : Ensure that the forklift operates and is parked in a dry environment to prevent the battery from getting damp. When working in a humid environment, protective measures can be taken for the battery, such as using a waterproof cover to prevent water from entering the battery and causing self-discharge. For indoor working environments such as warehouses, dehumidification equipment can be installed to control the environmental humidity.

Conclusion

The self-discharge phenomenon of lead-acid batteries in forklifts is influenced by multiple factors, which has many adverse effects on battery performance, lifespan and forklift operation. By deeply understanding the principle and influencing factors of self-discharge, and taking effective measures from aspects such as optimizing battery design and manufacturing, strengthening usage and maintenance management, and improving usage environmental conditions, the self-discharge rate can be significantly reduced, battery performance and service life can be enhanced, the efficient and stable operation of forklifts can be ensured, and the operating costs of enterprises can be lowered. With the development of technology, in the future, it is expected that through the research and development of new materials, process innovation and other means, the self-discharge problem of lead-acid batteries will be further solved, promoting the continuous improvement of forklift power systems.