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Introduction

In modern logistics and industrial production, forklifts, as important material handling equipment, have a crucial power source. Lead-acid batteries have become one of the commonly used power sources for forklifts due to their advantages such as mature technology, low cost, and good high-current discharge performance. A thorough understanding of the structural composition and performance parameters of forklift lead-acid batteries is of great significance for the correct selection, use and maintenance of batteries, as well as for improving the operational efficiency of forklifts and reducing operating costs.

The structural composition of lead-acid batteries for forklifts

Plate

Grid: The plate is one of the core components of a lead-acid battery, composed of a grid and active material. The grid serves to support the active substance and conduct current, and is usually made of lead alloy. Common grid materials include lead-antimony alloy, lead-calcium alloy, etc. Lead-antimony alloy grid plates have good casting performance and electrical conductivity. However, during the charging and discharging process, antimony elements will migrate towards the negative plate, resulting in an increase in hydrogen evolution from the negative plate and accelerating the battery's water loss. The lead-calcium alloy grid has a high hydrogen evolution overpotential, which can effectively reduce battery water loss and extend battery life. It is widely used in modern forklift lead-acid batteries. The structural design of the grid is also very crucial. The shape and size of the grid will affect the adhesion of active substances and the internal resistance of the battery. A reasonable grid structure can improve the utilization rate of active substances and enhance the charging and discharging performance of batteries.

The active material: The main active material of the positive plate is lead dioxide, which is brownish in color. During the discharge process, lead dioxide reacts with sulfuric acid, converting into lead sulfate and releasing electrons, thereby generating an electric current. The active material of the negative plate is spongy pure lead, which is bluish-gray in color. During discharge, lead reacts with sulfuric acid to form lead sulfate while losing electrons. During the charging process, the lead sulfate on the positive and negative plates is respectively reduced to lead dioxide and spongy lead. The quality and performance of active substances directly affect the capacity and lifespan of batteries. To enhance the performance of active substances, some additives are often added. For instance, adding barium sulfate, carbon fiber, etc. to the cathode active substance can improve the structural stability and conductivity of the active substance. Adding humic acid and other substances to the negative electrode active material can prevent sulfation of the negative plate and improve the charging and discharging performance of the battery.

Partition board

The separator is located between the positive and negative plates. Its main function is to prevent short circuits between the positive and negative plates and at the same time allow ions in the electrolyte to pass freely, forming an ionic conductive channel. The partition material should have good insulation performance, high porosity, low resistance, as well as excellent chemical stability and mechanical strength. Common partition materials include microporous rubber, microporous plastic and glass fiber, etc.

Microporous rubber separators: They have high mechanical strength and good acid resistance, but their production process is complex, the cost is high, and the porosity is relatively low, which limits the ion transport speed.

Microporous plastic separators: Made mainly of polypropylene and polyethylene, they have the advantages of low cost, light weight, high porosity and low resistance, and are widely used in forklift lead-acid batteries. The pore size and pore distribution of the microporous plastic separator are uniform, which can effectively prevent the migration of active substances and improve the safety and stability of the battery.

Glass fiber partition: It has high chemical stability and thermal stability and can withstand large current impacts. Its fibrous structure can adsorb the electrolyte, reduce the stratification of the electrolyte, and improve the charging and discharging performance of the battery. In some high-performance forklift lead-acid batteries, it is often the case that glass fiber separators are used in combination with other separator materials to fully leverage the advantages of different materials.

Electrolyte

The electrolyte is an important medium for lead-acid batteries to achieve the mutual conversion of electrical energy and chemical energy. It is usually prepared by mixing pure sulfuric acid and distilled water in a certain proportion. The role of the electrolyte in a battery mainly lies in two aspects: First, it participates in the electrochemical reactions of the battery. During the charging and discharging process, sulfuric acid reacts with the active substances on the positive and negative plates, achieving the conversion of electrical energy to chemical energy. The second is to conduct ions, forming a conductive circuit inside the battery.

Density: The density of the electrolyte has a significant impact on the performance of the battery. Generally speaking, the density of the electrolyte in forklift lead-acid batteries is between 1.28 and 1.30g/cm³ at 25℃. Excessively high density will accelerate the corrosion of the plates and shorten the battery life. If the density is too low, the capacity and charging and discharging performance of the battery will be affected. Under different usage environments and working conditions, the density of the electrolyte needs to be adjusted according to the actual situation. For instance, in cold regions, appropriately increasing the density of the electrolyte can enhance the low-temperature performance of the battery. In hot regions, the density of the electrolyte should be appropriately reduced to minimize water loss and plate corrosion of the battery.

Purity: The purity of the electrolyte is crucial to the performance of the battery. If sulfuric acid contains impurities such as iron, copper, chlorine, etc., chemical reactions will occur inside the battery, leading to increased self-discharge, accelerated corrosion of the plates and other problems, seriously affecting the service life of the battery. Therefore, the sulfuric acid used to prepare the electrolyte must be high-purity sulfuric acid specifically designed for storage batteries, and the distilled water should also meet the corresponding purity standards.

Shell

The casing is a protective component of lead-acid batteries, used to accommodate internal components such as plates, separators and electrolyte. The casing should have good mechanical strength, acid corrosion resistance, heat resistance and sealing performance to ensure that the battery can operate safely and reliably under various environmental conditions.

Materials: Common shell materials include hard rubber, engineering plastics, etc. The hard rubber shell has good acid resistance and mechanical strength, but it is relatively heavy and has a complex production process. Engineering plastic casings have the advantages of light weight, simple molding process and low cost. Moreover, their acid resistance and mechanical properties can also meet the usage requirements of batteries. Therefore, they are widely used in modern forklift lead-acid batteries.

Structural design: The structural design of the casing should take into account factors such as the installation, maintenance and heat dissipation of the battery. Generally speaking, the top of the shell is provided with a liquid filling hole for adding electrolyte and distilled water. At the same time, there is also an exhaust hole to discharge the gas produced by the battery during charging and discharging, preventing the internal pressure of the battery from being too high. In addition, the shape and size of the casing should match the battery installation space of the forklift to ensure that the battery is firmly installed and avoid shaking and collision during the operation of the forklift.

Other components

Terminal post: The terminal post is the component that connects the battery to the external circuit, and it is divided into the positive terminal post and the negative terminal post. The terminal posts are usually made of lead or lead alloys, and their surfaces have undergone special treatment to enhance their electrical conductivity and anti-corrosion performance. To facilitate the distinction between the positive and negative poles, the positive pole column is usually painted red, while the negative pole column is painted blue or black.

Connection strip: The connection strip is used to connect multiple single-cell batteries in series to obtain the required battery voltage. The material of the connecting strip is the same as that of the terminal post. Its cross-sectional area should be reasonably selected based on the battery capacity and discharge current to ensure that the connecting strip can withstand sufficient current and reduce resistance and heat generation.

Performance parameters of lead-acid batteries for forklifts

Rated voltage

The basic unit of a lead-acid battery is a single-cell battery, and the rated voltage of each single-cell battery is approximately 2V. Forklift lead-acid batteries are usually composed of multiple single-cell batteries connected in series to meet the different voltage requirements of forklifts. The common rated voltages of lead-acid batteries for forklifts include 24V, 36V, 48V, 80V, etc. Rated voltage is one of the important performance parameters of a battery. It determines the voltage level that the battery can provide under normal working conditions and directly affects the design and operation of the forklift's electrical system.

Rated capacity

Rated capacity refers to the amount of electricity that a battery can release under specified discharge conditions, with the unit being ampere-hours (Ah). Rated capacity is an important indicator for measuring a battery's ability to store electrical energy. It reflects the duration for which a battery can continuously discharge at a certain discharge current. The rated capacity of lead-acid batteries for forklifts is usually selected based on the operating conditions and operational requirements of the forklift. Common capacity ranges from 100Ah to 1500Ah.

Factors affecting rated capacity

Discharge current: The greater the discharge current of a battery, the less electricity it can actually discharge, that is, the rated capacity will decrease. This is because when a large current is discharged, the chemical reaction rate inside the battery increases, causing lead sulfate to form rapidly on the surface of the plates, blocking the pores of the plates and reducing the contact area between the electrolyte and the active substance, thereby lowering the battery's capacity.

Electrolyte temperature: The electrolyte temperature also has a significant impact on battery capacity. Within a certain range, as the temperature rises, the chemical reaction rate of the battery accelerates, the viscosity of the electrolyte decreases, the ion diffusion rate increases, and the capacity of the battery will increase accordingly. Conversely, when the temperature drops, the battery capacity will decrease. Generally speaking, the optimal operating temperature range for lead-acid batteries is 25℃ to 40℃. When the temperature drops below 0℃, the battery capacity may decrease to less than 50% of the rated capacity.

Battery usage and maintenance: Reasonable usage and maintenance can maintain the rated capacity of the battery. For instance, regular equalization charging of the battery, avoiding overdischarge and overcharging, and timely replenishment of the electrolyte, etc., all help to extend the battery's service life and maintain its rated capacity. Frequent over-discharge, long-term non-charging or insufficient charging, and electrolyte deficiency and other poor usage and maintenance habits can lead to problems such as sulfation of battery plates and shedding of active substances, gradually reducing battery capacity.

Discharge characteristic

Discharge curve: The discharge curve describes the relationship between voltage and time during the battery's discharge process. The discharge curve of forklift lead-acid batteries usually presents three stages: in the initial stage, the battery voltage drops relatively slowly, and at this time, the battery is in a stable discharge state; In the middle stage, the voltage drop rate accelerates and the battery capacity is gradually released. In the final stage, the voltage drops sharply. When the voltage drops to the terminal voltage, the battery discharge ends. The discharge curves of lead-acid batteries for forklifts of different types and capacities may vary. By analyzing the discharge curve, the discharge performance and remaining power of the battery can be understood, providing a basis for the rational use of forklifts and battery maintenance.

Terminal voltage: The terminal voltage refers to the lowest voltage value that a battery is allowed to drop during discharge. When the battery voltage drops to the terminal voltage, the discharge should be stopped immediately; otherwise, it will cause excessive discharge of the battery, damage the plates and shorten the battery life. The magnitude of the terminal voltage is related to factors such as the type of battery, discharge current and usage environment. In actual use, the terminal voltage should be reasonably set according to the working conditions of the forklift and the characteristics of the battery to ensure the safety and service life of the battery.

Charging characteristics

Charging curve: The charging curve reflects the relationship between voltage, current and charge quantity of the battery during the charging process and over time. The charging process of lead-acid batteries in forklifts is generally divided into three stages: constant current charging stage, constant voltage charging stage and float charging stage. During the constant current charging stage, the charging current remains constant and the battery voltage gradually rises. When the battery voltage reaches the set constant voltage value, it enters the constant voltage charging stage, at which point the charging current gradually decreases. When the charging current drops to a certain value, it enters the float charging stage, where the battery is supplemented with a small current to maintain a fully charged state. By controlling the charging curve, the battery can complete the charging process quickly and efficiently under the premise of ensuring safety, while avoiding damage to the battery caused by overcharging.

Charging efficiency: Charging efficiency refers to the ratio of the actual amount of electricity stored in a battery during the charging process to the amount of electricity input during charging. The charging efficiency of lead-acid batteries is generally between 70% and 90%, and its magnitude is related to factors such as the charging method, charging current, and electrolyte temperature. Improving charging efficiency can reduce charging energy consumption, shorten charging time and enhance the utilization efficiency of forklifts. Adopting reasonable charging algorithms, such as pulse charging and intelligent charging technologies, can effectively improve the charging efficiency. At the same time, maintaining an appropriate electrolyte temperature also helps to improve the charging efficiency.

Cycle life

Cycle life refers to the number of charge and discharge cycles a battery can undergo under certain charge and discharge conditions. When the capacity of a battery drops to 80% of its rated capacity, it is considered to have reached the end of its service life. The number of charge and discharge cycles experienced at this point is the cycle life.

Factors affecting cycle life

Charge and discharge depth: Charge and discharge depth refers to the percentage of the battery's discharge capacity to its rated capacity. Frequent deep discharges will accelerate the sulfation of the plates and the shedding of active substances, thereby shortening the cycle life of the battery. Generally speaking, the charge and discharge depth of forklift lead-acid batteries should be controlled below 80% to extend the battery life.

Charging methods: Unreasonable charging methods, such as overcharging and undercharging, can cause damage to the battery and reduce its cycle life. By using appropriate charging equipment and methods and charging according to the charging characteristics of the battery, the cycle life of the battery can be effectively extended.

Operating ambient temperature: The ambient temperature has a significant impact on the cycle life of batteries. High-temperature environments can accelerate the chemical reactions inside the battery, leading to problems such as plate corrosion and water loss, and shortening the battery's lifespan. Low-temperature environments will reduce the capacity and charging and discharging performance of batteries, increase their internal resistance, and are also detrimental to their cycle life. The optimal operating temperature for forklift lead-acid batteries is around 25℃. In actual use, it is necessary to avoid the battery working in an environment with excessively high or low temperatures as much as possible.

Conclusion

The structural composition and performance parameters of forklift lead-acid batteries are closely related, jointly determining the battery's performance and service life. The reasonable design and selection of structural components such as plates, separators, electrolytes and casings are the basis for ensuring that batteries have good performance. Performance parameters such as rated voltage, rated capacity, discharge characteristics, charging characteristics, cycle life and energy density provide important basis for forklift users when choosing and using batteries. In practical applications, lead-acid batteries should be reasonably selected based on the operating conditions and operational requirements of forklifts, and scientific usage and maintenance methods should be adopted to fully leverage the performance advantages of the batteries, extend their service life, and reduce operating costs. Meanwhile, with the continuous advancement of technology, lead-acid battery technology is also constantly developing. In the future, it is expected to further enhance its performance by improving materials and structural design, etc., to meet the growing demands of industrial applications.