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<p>In batteries, overpotentials control power and energy density. When particle overpotentials evolve as the square root of time, researchers attribute the mechanism to solid-state chemical diffusion. However, this practice has led to reported diffusivities ranging over four orders of magnitude. Here we demonstrate that modifying the liquid electrolyte increases the apparent diffusion overpotential of Li<sub><i>x</i></sub>Ni<sub>1/3</sub>Mn<sub>1/3</sub>Co<sub>1/3</sub>O<sub>2</sub> particles, even in thin electrodes. This finding challenges the conventional interpretation that equates square-root-of-time overpotentials to solid-state diffusion. We further show that electrolyte-penetrating pores in agglomerate particles can generate diffusion-like kinetics even without any diffusion processes. Electrolyte-penetrated pores produce a transmission-line configuration in chemical capacitance, leading to diffusion-like electrochemical behaviour. This demonstration highlights that square-root-of-time overpotentials are not exclusive to diffusion. Electroanalytical methods should therefore seek to identify specific physical origins rather than assume solid-state diffusion a priori. This finding suggests that the Li chemical diffusion coefficients and charge-transfer resistances reported in literature should be revisited.</p>

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Diffusion-like overpotentials from non-diffusion mechanisms in battery particles

  • 期刊论文

  • 发表日期：

    2026年7月31日

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  • Nidhi Kapate,
  • Shakul Pathak,
  • Hyukjin Kweon,
  • Jimmy J. Kuo,
  • Hongbo Zhao,
  • Seoyeon Jeong,
  • Martin Z. Bazant,
  • William C. Chueh,
  • Stephen Dongmin Kang

摘要

In batteries, overpotentials control power and energy density. When particle overpotentials evolve as the square root of time, researchers attribute the mechanism to solid-state chemical diffusion. However, this practice has led to reported diffusivities ranging over four orders of magnitude. Here we demonstrate that modifying the liquid electrolyte increases the apparent diffusion overpotential of LixNi1/3Mn1/3Co1/3O2 particles, even in thin electrodes. This finding challenges the conventional interpretation that equates square-root-of-time overpotentials to solid-state diffusion. We further show that electrolyte-penetrating pores in agglomerate particles can generate diffusion-like kinetics even without any diffusion processes. Electrolyte-penetrated pores produce a transmission-line configuration in chemical capacitance, leading to diffusion-like electrochemical behaviour. This demonstration highlights that square-root-of-time overpotentials are not exclusive to diffusion. Electroanalytical methods should therefore seek to identify specific physical origins rather than assume solid-state diffusion a priori. This finding suggests that the Li chemical diffusion coefficients and charge-transfer resistances reported in literature should be revisited.