1. Material Differences
Cathode (Positive Electrode):
- Li-ion batteries offer a broader selection, including ternary, lithium iron phosphate, and lithium cobalt oxide materials.
- Na-ion batteries primarily utilize layered transition metal oxides, polyanions, and Prussian blue.
- Cost disparity: Lithium carbonate (Li-ion) is significantly more expensive (69x) than sodium carbonate (Na-ion).
Anode (Negative Electrode):
- Li-ion batteries commonly use artificial or natural graphite and silicon-based materials.
- Na-ion batteries primarily rely on hard carbon, currently more expensive than Li-ion anodes (artificial and natural graphite).
Electrolyte:
- Both battery types use solvents, solutes, and additives, but Na-ion batteries replace lithium hexafluorophosphate with sodium hexafluorophosphate or sodium perchlorate.
- While Na-ion electrolytes have lower raw material costs, large-scale production hasn't materialized yet, making them currently more expensive than Li-ion equivalents.
Current Collectors:
- Li-ion batteries require copper foil for the negative electrode due to lithium's alloying reaction with aluminum at low potentials.
- Na-ion batteries can utilize cheaper aluminum foil for both positive and negative electrodes as sodium doesn't react with aluminum at low potentials.
Separators:
- Li-ion battery separators (polyethylene and polypropylene) work for Na-ion batteries but aren't ideal due to average adaptability. New separators specifically designed for Na-ion systems are under development.
2. Performance Differences
Energy Density:
- Na-ion batteries fall short of high-performance ternary Li-ion batteries but are comparable to lithium iron phosphate batteries in terms of energy storage capacity per unit weight.
Temperature Range:
- Na-ion batteries excel in wide-temperature operation, functioning from -40°C to 80°C.
- They maintain impressive discharge capacity at both extremes:
- Over 100% of rated capacity at 55°C and 80°C (high temperature)
- Over 70% of rated capacity at -40°C (low temperature)
- They can also achieve efficient charging (nearly 100%) at -20°C, outperforming Li-ion batteries in low-temperature functionality.
Applications:
- Li-ion batteries, due to their higher energy density, cater to fields demanding high battery performance, like energy storage and electric vehicles.
- Na-ion batteries, with their cost-effectiveness and exceptional low-temperature performance, are suitable for energy storage applications, low-speed electric vehicles, and two-wheeled electric vehicles.
3. Conclusion:
While both Na-ion and Li-ion batteries serve as rechargeable options, their material distinctions lead to different strengths and weaknesses. Na-ion batteries offer a cost-effective and low-temperature-tolerant alternative, especially for applications where high energy density isn't the primary concern. As research and development progress, Na-ion batteries have the potential to become even more competitive in the future.