lithium batteries
The working principle of a lithium battery is shown in the figure below. During discharge, the anode loses electrons, while lithium ions migrate from the electrolyte to the negative electrode; during charging, the opposite occurs, with lithium ions migrating to the anode.
Charging and discharging is a process of lithium delithiation and lithium insertion, and the reaction process is as follows:
Lithium-ion batteries have higher energy-to-weight ratio and energy-to-volume ratio; longer lifespan, with charge/discharge cycles well exceeding 500 under normal operating conditions; they are typically charged with a current of 0.5 to 1 times their capacity, reducing charging time; they do not contain heavy metals, thus causing no environmental pollution; and they can be used in parallel with easy capacity adjustment. However, their cost is relatively high, mainly due to the high price of the cathode material LiCoO2 (Co resources are scarce), the difficulty in purifying the electrolyte system, and the inability to discharge at high currents. Furthermore, due to the organic electrolyte system and other factors, their internal resistance is relatively higher than other types of batteries.
lead-acid batteries
The principle of a lead-acid battery is as follows: During the discharge process when the battery is connected to a load, dilute sulfuric acid reacts chemically with the active materials on the anode and cathode to produce a new compound, lead sulfate. As the battery discharges, the sulfuric acid is released from the electrolyte; the longer the discharge lasts, the lower its concentration becomes. Therefore, by measuring the concentration of sulfuric acid in the electrolyte, the remaining charge can be determined. During charging, the lead sulfate produced on the anode and cathode plates is decomposed and reduced back to sulfuric acid, lead, and lead oxide. Therefore, the concentration of sulfuric acid gradually increases. When the lead sulfate at both electrodes is reduced to its original form, the charging process is complete, and the battery awaits the next discharge cycle.
Lead-acid batteries have the longest history of industrialization, resulting in the most mature technology, good stability, and wide applicability. They use dilute sulfuric acid as the electrolyte, which is non-flammable and offers high safety. They also have a wide operating temperature and current range and good storage performance. However, their energy density is relatively low, their cycle life is relatively short, and they pose a lead pollution problem.
Gel batteries
Gel batteries utilize the principle of cathode absorption to achieve a sealed battery. During charging, oxygen is released at the positive electrode, and hydrogen is released at the negative electrode. Oxygen evolution at the positive electrode begins when the charge reaches 70%. The released oxygen reaches the negative electrode and undergoes the following reaction, achieving the purpose of cathode absorption.
2Pb + O2 = 2PbO
2PbO + 2H2SO4 : 2PbSO4 + 2H2O
Hydrogen evolution at the negative electrode begins when the charge reaches 90%. In addition, the reduction of oxygen at the negative electrode and the increase in the hydrogen overpotential of the negative electrode itself prevent a large amount of hydrogen evolution reaction.
For AGM sealed lead-acid batteries, although the AGM separator retains most of the electrolyte, it is essential to prevent electrolyte from entering through 10% of the separator pores. Oxygen generated at the positive electrode reaches the negative electrode through these pores and is absorbed by the negative electrode.
The gel electrolyte in gel batteries forms a solid protective layer around the plates, preventing capacity loss and extending lifespan. They are safe to use, environmentally friendly, and truly green power sources. They also exhibit low self-discharge, good deep-discharge performance, strong charge acceptance, small potential difference, and large capacity. However, their production technology is challenging and costly.
Through the above introduction to the three types of batteries, we should have a certain understanding of them. Lead-acid batteries have a relatively mature manufacturing process and low cost, but a shorter lifespan. Lithium-ion batteries, as a recent development, have a significantly longer lifespan than lead-acid batteries and are smaller in size, but are relatively more expensive. Gel batteries also have a longer lifespan, but their technology is more complex, so they are not price-competitive.
