Enhanced Performance of P2‐Na0.66(Mn0.54Co0.13Ni0.13)O2 Cathode for Sodium‐Ion Batteries by Ultrathin Metal Oxide Coatings via Atomic Layer Deposition. (7th August 2017) - Kaliyappan, Karthikeyan
Abstract : Sodium‐ion batteries are widely considered as promising energy storage systems for large‐scale applications, but their relatively low energy density hinders further practical applications. Developing high‐voltage cathode materials is an effective approach to increase the overall energy density of sodium‐ion batteries. When cut‐off voltage is elevated over 4.3 V, however, the cathode becomes extremely unstable due to structural transformations as well as metal dissolution into the electrolytes. In this work, the cyclic stability of P2‐Na0.66 (Mn0.54 Co0.13 Ni0.13 )O2 (MCN) electrode at a cut‐off voltage of 4.5 V is successfully improved by using ultrathin metal oxide surface coatings (Al2 O3, ZrO2, and TiO2 ) deposited by an atomic layer deposition technique. The MCN electrode coated with the Al2 O3 layer exhibits higher capacity retention among the MCN electrodes. Moreover, the rate performance of the MCN electrode is greatly improved by the metal oxide coatings in the order of TiO2 < Al2 O3 < ZrO2, due to increased fracture toughness and electrical conductivity of the metal oxide coating layers. A ZrO2 ‐coated MCN electrode shows a discharge capacity of 83 mAh g −1 at 2.4 A g −1, in comparison to 61 mAh g −1 for a pristine MCN electrode. Cyclic voltammetry and electrochemical impedance analysis disclose the reduced charge transfer resistance from 1421 to 760.2 Ω after cycles, suggesting that the metal oxide coating layer can effectively minimize the undesirable phase transition, buffer inherent stress and strain between the binder, cathode, and current collector, and avoid volumetric changes, thus increasing the cyclic stability of the MCN electrode. Abstract : Different metal oxide coatings by atomic layer deposition are employed to stabilize the electrochemical stability of P2‐Na0.66 (Mn0.54 Co0.13 Ni0.13 )O2 cathodes for sodium‐ion batteries. The cyclic stability is extremely enhanced after the coating process. Moreover, the P2 materials coated with ZrO2 have improved rate performance with TiO2, Al2 O3 layer, due to increased fracture toughness and electrical conductivity of ZrO2 layers.