Despite significant advancements in lithium battery technology, lead-acid batteries remain the primary choice for railway locomotives. However, as renewable energy battery technologies evolve, polymer lithium batteries, lithium iron phosphate (LFP) batteries, and ternary lithium batteries are expected to gradually replace lead-acid batteries. So, which battery is best for railway locomotives?

Railway locomotive batteries mainly include lead-acid batteries, nickel-cadmium batteries, and lithium batteries. Below is a comparative analysis of these batteries based on capacity, charge-discharge life, safety, and technological maturity.

Raw Materials for Battery Production

The upstream materials for locomotive batteries include various raw materials:

• Lead-Acid Batteries: Primarily lead and lead products (including lead, lead alloys, plates, terminals), plastics for battery casings, separators, and grids, as well as sulfuric acid.

• Nickel-Cadmium Batteries: Composed mainly of nickel powder and electrolytes.

• Lithium-Ion Batteries: Consist of cathode and anode materials, electrolytes, electrode substrates, separators, and casing materials.

As global railway operation mileage increases, the market for locomotive batteries is also growing. For example, in 2016, the global market size for railway locomotive batteries was approximately 3.05 billion yuan, reflecting a year-on-year increase of 5.24% from 2015. With initiatives like the Belt and Road Initiative promoting infrastructure development in China, the global railway battery market is expected to continue expanding.

However, the use of lead-acid batteries raises serious environmental pollution issues, as both the electrolyte and lead materials pose significant risks to the environment and human health. Thus, developing alternative renewable batteries has become crucial. Currently, lithium battery technology, especially lithium iron phosphate batteries, shows promise as a replacement for lead-acid batteries.

Advantages of Lithium Iron Phosphate Batteries Over Lead-Acid Batteries

1. Application Areas:

• Lead-acid batteries are used in electric forklifts, traction vehicles, electric bicycles, and sightseeing cars.

• Lithium iron phosphate batteries are utilized in electric bicycles, electric vehicles, buses, and backup power supplies. Essentially, lithium iron phosphate batteries can replace lead-acid batteries in most applications.

2. Voltage Comparison:

• Lead-acid batteries have a nominal voltage of 2.0V, while lithium iron phosphate batteries have a nominal voltage of 3.2V. Lead-acid batteries experience a drop in voltage as capacity decreases, leading to higher fuel consumption, whereas lithium batteries maintain a stable voltage during discharge.

3. Raw Materials:

• Lead-acid battery materials: positive electrode made of lead oxide, negative electrode made of lead, electrolyte is sulfuric acid.

• Lithium iron phosphate battery materials: positive electrode made of lithium iron phosphate, negative electrode made of graphite, electrolyte is organic. From an environmental standpoint, lead and sulfuric acid are highly polluting, while lithium iron phosphate batteries are non-toxic and environmentally friendly.

4. Size and Weight:

• Lead-acid batteries have an energy density of 100–150 Wh/kg, while lithium iron phosphate batteries range from 30–50 Wh/kg. For the same capacity, lithium iron phosphate batteries are significantly lighter, weighing about one-fourth of lead-acid batteries.

5. Charge and Discharge:

• Lead-acid batteries allow float charging, are easy to control, but have longer charging times. Lithium iron phosphate batteries can charge quickly and handle high current discharges, but they are less stable and harder to control.

6. Service Life:

• Lead-acid batteries have a theoretical cycle life of 300–500 times, while lithium iron phosphate batteries exceed 2000 cycles. Additionally, lithium batteries have a self-discharge rate of less than 3% per month, compared to 15–30% for lead-acid batteries, making them more suitable for long-term storage.

7. Temperature Range:

• Lead-acid batteries operate at 5℃–45℃ for charging and -20℃–45℃ for discharging.

• Lithium iron phosphate batteries can charge at -20℃–55℃ and discharge at -30℃–70℃, offering a wider temperature adaptability.

Conclusion

Overall, while lead-acid batteries have been the traditional choice for railway locomotives due to their established technology, lithium iron phosphate batteries present several advantages, including higher efficiency, longer lifespan, and better environmental compatibility. As technology progresses, lithium batteries are likely to become the preferred option for railway locomotive applications.