Please pay attention to the safety issues related to lithium-ion batteries. Lithium-ion batteries are prone to short circuits during charging. Although most lithium-ion batteries have short-circuit protection circuits and explosion-proof wires, these circuits may not function under various circumstances. The effectiveness of explosion-proof wires is also limited. So, what conditions should lithium-ion batteries meet in terms of safety performance?
I. Safety Characteristics of Lithium-ion Batteries
Internationally, very strict standards have been established for assessing the safety performance of lithium-ion batteries. A qualified lithium-ion battery should meet the following safety performance requirements:
1. Short circuit: No fire, no explosion
2. Overcharge: No fire, no explosion
3. Hot box test: No fire or explosion (150℃ constant temperature for 10 minutes)
4. Needle puncture: No explosion (using a Ф3mm nail to pierce the battery)
5. Flat plate impact: No fire or explosion (10kg weight dropped on the battery from a height of 1m)
II. Advantages of Lithium-ion Batteries
1. High voltage: The working voltage of a single cell is as high as 3.7-3.8V. The working voltage of lithium iron phosphate is 3.2V, which is 3 times that of Ni-Cd and Ni-MH batteries.
2. The actual specific energy that can be achieved is about 555Wh/kg, which means that the material can achieve a specific capacity of more than 150mAh/g, which is 3-4 times that of Ni-Cd and 2-3 times that of Ni-MH, which is close to about 88% of its theoretical value.
3. Long cycle life: Batteries typically last for over 500 cycles, even exceeding 1000 cycles, with lithium iron phosphate batteries reaching over 2000 cycles. For appliances with low-current discharge, a longer battery life significantly increases the appliance's competitiveness.
4. Excellent safety performance, pollution-free, and no memory effect. As the predecessor of Li-ion, lithium-ion batteries have limited applications because metallic lithium is prone to dendrite formation and short circuits. Li-ion does not contain elements such as cadmium, lead, and mercury that pollute the environment. A major drawback of some processes, such as sintered Ni-Cd batteries, is the "memory effect," which severely restricts the use of the battery. However, Li-ion does not have this problem at all.
5. The self-discharge rate of Li-ion at room temperature after one month of storage is about 2%, which is much lower than that of Ni-Cd (25-30%) and Ni-MH (30-35%).
6. Fast charging: 1C charging for 30 minutes can reach more than 80% of the nominal capacity, while phosphorus iron batteries can reach 90% of the nominal capacity in 10 minutes.
7. Operating temperature: The operating temperature is -25~45°C. With improvements in the electrolyte and positive electrode, it is expected that the operating temperature range can be extended to -40~70°C.
8. Burning: No explosion (gas flame used to roast the battery)
III. Disadvantages of Lithium-ion Batteries
1. Aging: Unlike other rechargeable batteries, lithium-ion batteries experience a slow capacity decline, which is related to the number of uses and temperature. This decline can be represented by a decrease in capacity or an increase in internal resistance. Because it is temperature-dependent, it is more noticeable in electronic products with high operating currents. Replacing graphite with lithium titanate seems to extend the battery's lifespan. The relationship between storage temperature and the rate of permanent capacity loss:
2. Recycling rate: Approximately 1% of new products need to be recycled for various reasons.
3. Not tolerant of overcharging: When overcharged, excessively embedded lithium ions will be permanently fixed in the crystal lattice and cannot be released, which can lead to a short battery life.
4. Not tolerant of over-discharge: During over-discharge, too many lithium ions are de-intercalated or de-intercalated in the electrode, which can lead to lattice collapse and thus shorten the lifespan.
