Lithium-ion batteries, specifically Lithium Iron Phosphate (LiFePO4) and Ternary Lithium (NMC) batteries, are widely used as power sources for new energy vehicles due to their high energy density, broad operating temperature range, long cycle life, and high safety reliability. However, during the charging and discharging process, lithium batteries generate reversible reaction heat, ohmic heat, polarization heat, and side reaction heat. The amount of heat generated is primarily influenced by internal resistance and charging current.
Power batteries are remarkably "delicate." Temperature has a significant impact on their overall performance, primarily across three dimensions: operational performance, lifespan, and safety. In electric vehicle applications, the optimal operating range is generally determined by balancing performance, longevity, and safety based on thermal testing results. It is widely accepted that the ideal operating temperature for batteries is between 20°C and 30°C.
The Impact of Temperature on Capacity and Lifespan
Lithium battery capacity fluctuates with temperature. Testing reveals that for every 1°C increase in temperature, capacity rises by approximately 0.8%. However, elevated temperatures cause cumulative damage; both cycle life and capacity gradually decline. Research indicates that at a standard ambient temperature of 25°C, an increase of 6°C to 10°C can double the float charging current, effectively halving the battery's lifespan.
While capacity increases at higher temperatures (reducing the depth of discharge for the same total discharge), exceeding certain thresholds is hazardous. At 45°C, service life may temporarily seem extended, but charging above 50°C accelerates acid corrosion on the battery plates and speeds up the aging of the battery casing.
Available capacity decays at varying rates depending on the cold:
25°C: 100% available capacity
0°C: 85% available capacity
-10°C: 70% available capacity
When temperatures drop, discharge voltage also decreases significantly, causing the battery to reach its cut-off voltage faster. This results in low-temperature discharge capacity being markedly lower than room-temperature capacity.
Effects of Low Temperature on Performance
At low temperatures, available capacity is reduced and charge/discharge power is restricted. If power is not limited, lithium ions may precipitate internally, leading to irreversible capacity decay and safety hazards. Lower ambient temperatures lead to:
Reduced activity of active materials.
Increased internal resistance and viscosity of the electrolyte.
Slow ion diffusion, making it harder for ions to intercalate (embed) into electrodes.
It is a common experience that lithium batteries last shorter in winter. While discharge capacity loss at low temperatures is often reversible after returning to room temperature, low-temperature charging is much more dangerous. Charging below 0°C can cause lithium ions to plate onto the surface of the graphite anode rather than intercalating into it, forming metallic lithium dendrites. These dendrites consume recyclable lithium ions, permanently reducing capacity, and can pierce the separator, leading to internal short circuits and safety failures.
Effects of High Temperature on Safety
Safety risks increase significantly when temperatures exceed 45°C. Misuse or charger failure at high temperatures can trigger violent internal chemical reactions and rapid heat accumulation. This can lead to leakage, venting, smoke, or in extreme cases, combustion and explosion.
Key chemical reactions at high temperatures include:
SEI Film Decomposition: The protective layer decomposes exothermically between 90°C and 120°C.
Lithium-Electrolyte Reaction: Above 120°C, the anode contacts the electrolyte directly, causing exothermic reactions.
Electrolyte Decomposition: Occurs above 200°C, releasing heat.
Cathode Material Decomposition: In an oxidized state, cathode materials decompose, releasing oxygen which further reacts with the electrolyte.
Binder Reaction: Exothermic reactions between intercalated lithium and fluoride binders.
To ensure reliable performance in extreme environments, CM Batteries utilizes advanced wide temperature battery technology to provide stable power solutions that withstand both freezing winters and scorching summers.
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