Purpose

Sodium-ion batteries (SIBs) are a promising emerging rechargeable battery technology. This study explores future cradle-to-gate and cradle-to-grave life cycle environmental impacts of SIB cells used in a stationary battery energy storage system (BESS). The SIB cells contain the commercially viable Prussian white (PW) and hard carbon (HC) as electrode active materials. Their environmental performance is benchmarked against previous results for SIB and lithium-iron-phosphate (LFP) lithium-ion battery (LIB) cells.

Methods

A prospective life cycle assessment (pLCA) is performed. Large-scale production and end-of-life treatment are modeled, and a cell production model specific to HC/PW SIB cells is developed by adjusting a LIB gigafactory model. Foreground system scenarios include different battery cell design choices, gigafactory electricity supply and end-of-life treatment options (incineration and direct recycling). A BESS is modeled in the use phase. Time-explicit inventory modeling of production, use, and end of life is applied. Different background system scenarios are applied, reflecting to different climate policies from the integrated assessment model REMIND.

Results and discussion

Cradle-to-gate results show that improvements in gravimetric energy density and a low-carbon electricity supply to the gigafactory together reduces the environmental impacts considerably. The HC/PW SIB-specific cell production requires less energy (-20%) as compared to a generic SIB cell production. Cradle-to-grave impacts are sensitive to the number of battery cell replacements during BESS operation. Direct recycling can reduce impacts considerably for most impact categories by reducing the need for primary materials. Time-explicit inventory modeling reduces impacts for some impact categories compared to a non-time-explicit modeling. Benchmarking shows that HC/PW SIBs are environmentally competitive compared to other SIB and LFP LIB cells, and even notably better if certain measures, such as increasing the technical performance of the battery cell, are implemented.

Conclusion and recommendations

The results show that cradle-to-gate and cradle-to-grave impacts can be considerably reduced. We recommend SIB cell developers and producers to prioritize increasing the technical performance of the battery cell (gravimetric energy density and cycle life) and supplying the gigafactory with low-carbon electricity, since these factors together have the largest influence on the results. Furthermore, time-explicit inventory modeling of production, use, and end of life has a notable effect on the results. We therefore recommend pLCA practitioners to apply such modeling, especially for long-lived products.