Performance Characterization & Degradation of Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are seen as a sustainable alternative to lithium-ion batteries, as they are derived from cheaper and abundant raw materials. However, state-of-the-art SIBs remain uncompetitive for electric vehicles and other demanding applications because of their low energy densities and a poor understanding of aging. Research is needed to develop electrode materials that deliver high capacities and voltages in SIBs without excessive degradation. Layered oxide (NFM111, NaNi 1/3 Fe 1/3 Mn 1/3 O 2 ) | hard carbon (HC) cells represent a prototypical SIB for further study. Here, we study NFM111|HC cell degradation under different aging conditions, including at various voltage cutoffs and cycling rates. Recent techno-economic analyses have argued that charging sodium layered oxides to high voltages is required for SIBs to compete with commercial lithium iron phosphate (LFP) | graphite batteries, but doing so triggers severe structural irreversibility in the cathode. 1,2 This is because sodium layered oxides undergo complex phase changes during cycling, involving interlayer gliding, which do not regularly occur in their lithium counterparts. A particular focus of this work is to understand the impedance growth and capacity loss mechanisms when this occurs. This is done using a three-electrode cell developed in-house to deconvolute the contribution of the cathode and anode, as shown in the figure below. Identifying the dominant degradation modes of sodium-ion full cells will highlight the next steps for SIB development. [1] A. Yao, et al., Nat. Energy, 10 , 404–416 (2025). [2] K. Fang, et al., J. Am. Chem. Soc., 146 31860–31872 (2024) Figure 1