temperature impact to HEV lithium battery v.s. NiMH

If Lithium battery was used in HEV cars, how is the temperature change bringing impact to the Battery Pack during charge and discharge when driving? is it the same limit of 45°C as NiMH or there are more tolerance for Lithium battery?

Yes Lithium-ion batteries in hybrid electric vehicles (HEVs) are affected by temperature changes during charge and discharge cycles, and their performance differs from nickel-metal hydride (NiMH) batteries. Here's a breakdown:

Impact of Temperature on Lithium-Ion Battery Packs in HEVs

1. During Charging and Dischargingcycles:
   • Heat Generation: lithium-ion batteries generate heat due to internal resistance and electrochemical reactions. In HEVs, frequent charge-discharge cycles (e.g., during regenerative braking and acceleration) can elevate battery pack temperatures, especially under high load or rapid charging conditions.
   • Cold Temperatures: At low temperatures (below 0°C), lithium-ion batteries experience reduced capacity, slower chemical reactions, and increased internal resistance, leading to lower power output and efficiency. Charging at very low temperatures can also risk lithium plating on the anode, which degrades battery life.
   • High Temperatures: Elevated temperatures (above 40°C) accelerate chemical reactions, increasing capacity in the short term but causing faster degradation of the battery’s electrodes and electrolyte. This can lead to capacity fade and reduced lifespan. Extreme heat (e.g., >60°C) may trigger thermal runaway, a dangerous condition where the battery overheats uncontrollably.

2. Temperature Management:
   • HEVs use thermal management systems (e.g., air or liquid cooling) to maintain lithium-ion batteries within an optimal temperature range, typically 20–40°C, to balance performance and longevity. These systems are critical during driving, as the battery undergoes rapid charge-discharge cycles.

Comparison with NiMH Batteries

• NiMH Temperature Limit is 45°C:
  • NiMH batteries, commonly used in older HEVs like the Toyota Prius, have a practical upper temperature limit of around 45°C. Beyond this, their performance degrades significantly, and overheating can cause permanent damage or reduced cycle life.
  • NiMH batteries are less sensitive to low temperatures than lithium-ion but still lose efficiency in cold conditions.

3. Lithium-Ion Temperature Tolerance:
   • Lithium-ion batteries generally have a broader operating temperature range than NiMH, typically -20°C to 60°C, but their optimal performance is within 20–40°C.
   • They tolerate higher temperatures better than NiMH (up to ~60°C before severe degradation), but prolonged exposure to temperatures above 40°C accelerates aging. For example, at 45°C, lithium-ion batteries experience faster capacity fade than at 25°C, but they are less likely to suffer immediate damage compared to NiMH at the same temperature.
   • Lithium-ion batteries are more sensitive to low temperatures than NiMH, particularly during charging, where sub-zero temperatures can cause lithium plating.

Key Differences and Considerations 

• Tolerance: Lithium-ion batteries have a higher tolerance for elevated temperatures (up to ~60°C) compared to NiMH’s ~45°C limit, but their longevity is compromised if frequently exposed to high temperatures. Thermal management systems in HEVs are designed to keep lithium-ion batteries below 40°C to maximize lifespan.

• Performance: Lithium-ion batteries offer higher energy density and better efficiency than NiMH, making them more suitable for HEVs with demanding power needs. However, their performance is more sensitive to temperature extremes, requiring robust cooling/heating systems.
• Degradation: High temperatures accelerate electrolyte decomposition and electrode degradation in lithium-ion batteries, while NiMH batteries are more prone to electrolyte drying or crystal formation at high temperatures.

Practical Implications in HEVs

• In real-world driving, lithium-ion battery packs in HEVs are managed to stay within 20–40°C through active cooling (e.g., liquid cooling in modern HEVs like the Toyota RAV4 Hybrid or Ford Escape Hybrid). This ensures consistent performance and longevity.

• Unlike NiMH, lithium-ion batteries can handle short-term temperature spikes better but require careful monitoring to avoid long-term degradation.
• In extreme climates (e.g., very cold winters or hot summers), the thermal management system’s effectiveness is critical to maintaining lithium-ion battery performance.