Lithium-air, lithium-sulfur, and sodium-ion, which secondary battery category is more environmentally friendly and promising based on footprint family indicators?

The footprint family was used to assess the environmental impact of Li–S, sodium-ion and Li-air batteries, and predict the greenest battery model among these three batteries in this study. Besides, considering the assessment sensibility affected of different LCA methodologies, totally 13 methods were used to form a comprehensive assessment result. The ecological footprint of the Li–S, sodium-ion and Li-air batteries are 189.40 Pt, 182.58 Pt and 29.84 Pt, respectively; the carbon footprint of the Li–S, sodium-ion and Li-air batteries are 67.94 kg CO₂eq, 64.35 kg CO₂eq and 10.15 kg CO₂eq, respectively; and the water footprint of the Li–S, sodium-ion and Li-air batteries are 151.11 m³, 316.42 m³ and 21.15 m³, respectively. All methods show that Li-air battery is a more environmentally friendly battery model among these three new batteries. The footprint value of Li–S battery and Li-air battery mainly comes from the production of lithium-based materials. Also providing 1 kWh of electricity, far low demand for lithium resource is the main reason for Li-air battery to show its environmental advantages compared with Li–S battery. Besides, the close ecological and carbon footprints of sodium-ion battery are close to that of Li–S battery. And there is a far large water footprint of sodium-ion battery compared with Li–S battery. The low cost advantage of sodium resources is not enough to be reflected in the sodium-ion battery's environmental advantages. The demand for lithium and sodium resources per kWh largely determines their environmental impact.