Understanding the Safety Advantages of Lithium Iron Phosphate vs Ternary Lithium Batteries

Lithium iron phosphate (LiFePO4) and ternary lithium batteries differ in several ways, particularly when it comes to "energy density" and "safety." While ternary lithium batteries offer higher energy density, their safety is often a concern. In comparison, lithium iron phosphate batteries have lower energy density, but they are widely regarded as safer.

For example, with 18650 cells (diameter: 18mm, height: 65mm), a ternary lithium battery can have a capacity of up to 3500mAh, while a LiFePO4 battery maxes out at around 2000mAh in the same volume.

Why Are Lithium Iron Phosphate Batteries Considered Safe?

LiFePO4 batteries use lithium iron phosphate as the cathode material. This composition, compared to others like lithium cobalt oxide or nickel-based materials, is much more stable. The P-O bond in LiFePO4 is difficult to break down, even under high temperatures or overcharge. This makes them less prone to heat-related issues and prevents the release of highly reactive substances, significantly improving safety.

Advantages of Lithium Iron Phosphate Batteries:

1. Long Lifespan: LiFePO4 batteries can last for more than 4000 cycles at 80% depth of discharge (DOD), giving them a lifespan of 10–15 years under normal use.
2. Safe to Use: Even in severe conditions such as car accidents, LiFePO4 batteries have passed stringent safety tests and won't explode.
3. Fast Charging: These batteries can be fully charged in 40 minutes using a special charger at 1.5C.
4. High Temperature Resistance: They can tolerate temperatures between 350–500°C without compromising safety.
5. Large Capacity and No Memory Effect: The battery doesn't suffer from the "memory effect" that reduces capacity over time.
6. Eco-Friendly: LiFePO4 batteries are non-toxic, have a low environmental impact, and are made from abundant, low-cost raw materials.

Are Ternary Lithium Batteries Safe?

Ternary lithium batteries, which typically use nickel, cobalt, and manganese (NCM), also have notable safety features:

1. Stable Cathode Material: The oxygen in the structure of ternary lithium materials is stable and doesn’t readily release, reducing the risk of fire or explosion.
2. Even Voltage Platform: During manufacturing, ternary lithium particles are made smaller, creating a more uniform internal arrangement. This promotes stability during operation.
3. Charge and Discharge Safety: While the oxidation ability of the materials is not strong, making it difficult for redox reactions to occur during charging and discharging, ternary batteries still operate in a relatively safe environment.

However, ternary lithium batteries can pose safety risks in extreme conditions:

• In high-impact situations, such as car accidents, the battery diaphragm could be damaged, causing a short circuit. The heat from this can cause thermal runaway, quickly raising the temperature beyond 300°C.
• The thermal stability of ternary lithium batteries is weaker than LiFePO4, as they can decompose at temperatures below 300°C, which could lead to a rapid deflagration.

Which Battery Is Safer?

The main safety difference between the two types lies in their cathode materials. Ternary lithium batteries begin to decompose at around 200°C, releasing oxygen and accelerating electrolyte combustion, which can lead to fire. In contrast, lithium iron phosphate batteries remain stable until 700-800°C and do not release oxygen molecules, making combustion less likely.

That said, safety isn't only about the materials. The overall safety of the battery system depends on the Battery Management System (BMS), which controls overcharge, over-discharge, temperature, and current to prevent accidents.

In conclusion, while ternary lithium batteries are more prone to catching fire in extreme conditions, the presence of a good BMS can mitigate these risks. LiFePO4 batteries are naturally safer due to their chemistry but still require proper system management to ensure complete safety. Therefore, it’s not accurate to say that ternary lithium batteries are inherently unsafe, or that LiFePO4 batteries are always completely safe—both rely heavily on proper design and management.

Edit by paco