Bridging Ionic Field Strength Disparity Stabilizes High-Voltage Sodium-Ion Battery Cathodes
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Summary
A quantitative design strategy could improve the cycling stability of high-voltage sodium-ion batteries (SIBs) by mitigating ionic field strength disparities among transition-metal (TM) ions in O3-type layered oxide cathodes. The researchers introduce an ionic field strength disparity coefficient (η), defined as the standard deviation of ionic field strength (Φ) divided by its mean, where Φ = Z/r2(Z and r represent the ionic charge and radius, respectively). This descriptor enables quantitative evaluation of chemical-field heterogeneity within TM layers. By incorporating electrochemically inactive ions with intermediate ionic field strengths to compensate for disparities among redox-active ions, the strategy reduces η and mitigates local structural distortion during deep desodiation. The low-η cathode retains approximately 80% of its capacity after 500 cycles at 10C, compared with 22% for its high-η counterpart. The approach also establishes a quantitative framework for screening inact
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