With increasing global pollution, energy conservation and environmental protection have finally become a top priority. Currently, there are calls from all sectors to promote the use of energy-saving and environmentally friendly products, and my country has introduced numerous related policies to encourage the research and development and use of such products. In the battery market, lithium batteries have rapidly gained market share due to their advantages such as safety, long lifespan, low maintenance costs, light weight, complete charge and discharge, and no memory effect, becoming the leader in the battery industry and gradually replacing traditional lead-acid batteries. A friend asked me, what is the maximum discharge voltage of a lithium battery? Let's take a look at the discharge voltage of lithium batteries.
What is the maximum discharge voltage of a lithium battery?
Regarding the over-discharge voltage of lithium batteries, we contacted two lithium battery manufacturers as developers; out of respect, we will refer to them as Manufacturer A and Manufacturer B for now. Manufacturer A's over-discharge protection trip voltage is 2.75V, while Manufacturer B's is 2.3V.
Regarding over-discharge voltage
Manufacturer A informed us that the over-discharge protection voltage for lithium batteries is not different depending on the manufacturer, but is limited by the chemical characteristics of lithium-ion (polymer) batteries. Under normal temperature conditions, a discharge voltage below 2.75V will cause irreversible damage to lithium-ion batteries.
Manufacturer B told us that they had not heard of any issue regarding over-discharge voltage exceeding 2.75V damaging the battery. However, they were certain that the over-discharge protection tripped at 2.3V for all their batteries, and that they used a very large quantity of these batteries, so they should meet the standard. We found the following line in Manufacturer B's battery specification sheet: "When the voltage of any cell drops below 2.3V, the over-discharge protection function should function to prevent deep discharge of the cell."
During the assembly process of lithium batteries, slight differences in the constituent materials of the lithium battery cells and varying levels of assembly technology can lead to inconsistent functional performance of the lithium battery cells during use and storage. This is known as the dispersion phenomenon of lithium batteries. The quantitative indicator describing this dispersion phenomenon is the dispersion degree, which is obtained by the functional relationship of several parameters. The main factors that cause changes in the dispersion degree are: resistance, voltage, capacity, and temperature.
1. Inconsistent internal resistance of the battery, especially polarization resistance, causes drastic voltage changes in individual batteries during charging and discharging, resulting in drastic changes in the voltage of the entire battery pack;
2. Inconsistent voltages in individual ultra-thin battery cells will affect the peak-shaving capability of the battery pack, resulting in a reduction in the overall energy released by the battery pack;
3. Because ultra-thin batteries undergo heat release and absorption processes during operation, their temperature constantly changes. Overheating can lead to performance degradation and safety hazards. In recent years, it has been proven that the triggers for fires in electric vehicles during operation and testing have all been due to inadequate overheat protection causing battery overheating and fires. This applies not only to lithium manganese oxide batteries but also to lithium iron phosphate batteries.
4. Capacity is the most serious factor in the dispersion. Inconsistent capacity mainly causes two performance problems. First, some batteries will be in an overcharged and over-discharged state, leading to safety hazards such as combustion and explosion. Second, low-capacity individual cells will stop working early, affecting the energy of other individual cells in the entire ultra-thin battery pack, thus causing the lifespan of the entire battery pack to decline.
