• Energy Research

Using an operando optical scattering technique, we identify markedly asymmetric Li-ion flux in aged single crystalline NMC cathodes, primarily caused by an uneven growth of rocksalt phase across the particle surface.

Understanding how lithium-ion dynamics affect the (de)lithiation mechanisms of state-of-the-art nickel-rich layered oxide cathodes is crucial to improving electrochemical performance. Here, we directly observe two distinct kinetically-induced lithium heterogeneities within single-crystal LiNixMnyCo(1-x-y)O2 (NMC) particles using recently developed operando optical microscopy, challenging the notion that uniform (de)lithiation occurs within individual particles. Upon delithiation, a rapid increase in lithium diffusivity at the beginning of charge results in particles with lithium-poor peripheries and lithium-rich cores. The slow ion diffusion at near-full lithiation states – and slow charge transfer kinetics – also leads to heterogeneity at the end of discharge, with a lithium-rich surface preventing complete lithiation. Finite-element modelling confirms that concentration-dependent diffusivity is necessary to reproduce these phenomena. Our results show that diffusion limitations cause first-cycle capacity losses in Ni-rich cathodes.

Sodium-ion batteries (SIBs) offer a sustainable alternative to lithium-ion batteries but face cathode instability. This work emphasizes the low state of charge phase transition and shows improved cycling performance via calcium substitution.

AbstractConducting polymers have been considered for use as cathode materials in rechargeable lithium‐ion batteries (LIBs) since 1981 but problems with poor cycling stability, rapid self‐discharge, and low energy and power densities have so far limited their applicability. Herein it is shown that nanostructured freestanding conducting polymer composites [e.g., polypyrrole (PPy) and polyaniline (PANI)] can be used to circumvent these shortcomings. Freestanding and binder‐free PPy and cellulose‐based composites can straightforwardly be used as versatile organic cathode materials for LIBs. The composite, reinforced with chopped carbon filaments (CCFs), exhibited a large active mass loading of approximately 10 mg cm−2, an areal capacity of 1.0 mAh cm−2(corresponding to 102 mAh g−1), and stable cycling. With an active mass loading of 4.4 mg cm−2, a capacity of 0.22 mAh cm−2(corresponding to 58 mAh g−1) was found for current densities of 5 A g−1yielding discharge times of approximately 40 seconds, and a capacity retention of 91 % over 100 cycles was obtained at 0.2 A g−1. The present method constitutes a straightforward approach for the manufacturing of high‐performance freestanding electroactive conducting‐polymer‐based paper‐like electrodes for use in inexpensive and sustainable, high‐performance organic LIBs.

Li-ion battery (LIB) full cells comprised of TiO2-nanotube (TiO2-nt) and LiFePO4 (LFP) electrodes and either a conventional organic solvent based liquid electrolyte or an ionic liquid based electrolyte have been cycled at 80 °C. While the cell containing the ionic liquid based electrolyte exhibited good capacity retention and rate capability during 100 cycles, rapid capacity fading was found for the corresponding cell with the organic electrolyte. Results obtained for TiO2-nt and LFP half-cells indicate an oxidative degradation of the organic electrolyte at 80 °C. In all, ionic liquid based electrolytes can be used to significantly improve the performance of LIBs operating at 80 °C.