Overcharging, over-discharging, or using a mixture of lithium batteries can lead to the following problems:
Overcharging hazards
Thermal runaway: Electrolyte decomposition produces gas, increasing internal pressure and triggering an explosion. Experimental data shows that continuous overcharging can increase battery internal resistance by 37% and accelerate capacity decay by 5 times.
Structural damage: The positive electrode material collapses, and sharp lithium dendrites form on the negative electrode, piercing the separator and causing an internal short circuit.
Shortened lifespan: A test of a certain brand of mobile phone battery showed that the swelling rate reached 8.2% after 200 overcharge cycles.
Over-discharge hazards
Material damage: The crystal lattice of the positive electrode material collapses, and the copper current collector in the negative electrode dissolves, forming a conductive path and causing a short circuit.
Permanent capacity degradation: Multiple deep discharges (<5% charge) can reduce battery capacity to 62% of its initial value.
Safety hazard: If the voltage drops below 2.5V, repair costs could reach as high as 120,000 yuan.
Risks of mixed use
Accelerated aging: When different types of lithium batteries (such as lithium iron phosphate and ternary lithium) are used together, mismatched charging voltages may lead to overcharging or over-discharging.
Safety Hazard: Aging or improperly modified wiring can easily cause short circuits, leading to fires and explosions.
Recommended measures:
Unplug the power cord immediately after it is fully charged;
Charge immediately when the battery level drops below 20%;
Avoid charging in high-temperature (>35℃) or low-temperature (<-5℃) environments;
Use the original charger and check the battery health value regularly.
Over-discharge vs. Overcharge of Lithium-ion Batteries: Which is More Prone to Lithium Plating? | Lithium-ion batteries are a crucial energy source for modern electronic devices, and their performance stability directly impacts the safety and lifespan of these devices. However, in practical use, lithium-ion batteries may experience lithium plating due to over-discharge or overcharge, leading to performance degradation or even damage. So, which is more likely to cause lithium plating in lithium-ion batteries: over-discharge or overcharge?
I. The impact of over-discharge of lithium batteries on lithium plating
Over-discharge of a lithium battery refers to the state where the voltage drops too low during the discharge process. Over-discharge causes irreversible changes in the positive and negative electrode materials inside the battery, thus affecting the battery's capacity and performance. It can also lead to safety issues such as internal short circuits or thermal runaway. Although lithium plating may occur in an over-discharged state, the risk is relatively lower compared to overcharging.
II. The impact of overcharging lithium batteries on lithium plating
Overcharging a lithium battery refers to the state where the battery voltage exceeds its design limit during charging. Overcharging is extremely harmful to lithium batteries, potentially causing damage to the positive electrode material structure, electrolyte decomposition, and increased internal battery temperature. Among these, damage to the positive electrode material structure and electrolyte decomposition are the main causes of lithium plating. Damage to the positive electrode material structure prevents lithium ions from effectively embedding into the crystal lattice during charging, leading to the formation of lithium dendrites on the electrode surface. Electrolyte decomposition generates gas and heat, further exacerbating lithium plating. Therefore, lithium batteries are more prone to lithium plating when overcharged.
III. How to avoid lithium plating in lithium batteries
For lithium plating due to overcharging:
1. Hard voltage cutoff: The BMS sets a redundancy voltage limit (e.g., NCM battery ≤ 4.18V);
2. Charging optimization:
The constant voltage to constant current (CV→CC) switching point has been improved to 0.05C (traditionally 0.1C);
Charging current is halved in low-temperature environments (≤0.3C at 0℃);
3. Material modification:
The negative electrode surface is coated with a Li₄Ti₅O₁₂ (LTO) buffer layer (lithium intercalation potential 1.55V, to avoid lithium plating at 0V);
Adding FEC (fluoroethylene carbonate) to the electrolyte promotes a uniform SEI film.
Regarding over-discharge:
1. Voltage monitoring: Initiates hibernation after deep discharge (e.g., power off LFP batteries when <2.8V);
2. Repair mechanism: Low voltage and low current (0.01C) activation and recovery.
Definitions and hazards of overcharging and over-discharging
Overcharging of a lithium battery refers to the internal voltage exceeding the design standard voltage. In this case, the internal chemical reactions become unstable, generating heat and gas, which can lead to safety issues such as leakage, short circuits, and explosions. Over-discharging refers to the internal charge of the battery falling below the standard capacity, resulting in reduced battery capacity, shortened service life, or even inability to recharge. Both overcharging and over-discharging negatively impact battery life and safety, making them crucial considerations for lithium batteries.
Under what circumstances will overcharging and over-discharging occur?
1. Improper use: Overcharging due to failure to disconnect power in time during charging, or over-discharging due to failure to charge in time during discharging.
2. Battery aging: Lithium batteries will gradually age over time, which will lead to a reduction in battery capacity or safety hazards.
3. High temperature environment: High temperature will accelerate the chemical reaction inside the lithium battery, which can easily lead to overcharging and over-discharging.
4. Circuit failure: Problems such as malfunctions in the battery's internal protection circuit or loose connectors.
How to prevent overcharging and over-discharging
1. Use a professional charger: A professional charger can automatically control charging and discharging according to the battery status, avoiding overcharging and over-discharging.
2. Use high-quality batteries: High-quality batteries have better safety performance and longer service life.
3. Do not leave the battery in a high-temperature environment for a long time: Pay attention to the storage environment of the battery and avoid leaving it in a high-temperature environment for a long time.
4. Immediate troubleshooting: Once a battery malfunction is detected, it should be addressed promptly, such as replacing the battery or repairing the battery's protection circuit.
Overcharging and over-discharging are issues that need attention during the use of lithium batteries, as neglecting them may affect battery life and safety. Following the methods described above can effectively prevent overcharging and over-discharging.
Summarize
Overcharging is the main cause of lithium plating: its essence is that the lithium intercalation capacity of the negative electrode is saturated, which forces ions to be reduced and deposited on the surface; over-discharge does not trigger lithium plating: the core risks of this process are copper dendrite short circuits and SEI film decomposition.
