Innovative High-Voltage Cathode Architectures for Doped Ammonium Vanadium Oxide: Overcoming Limitations and Boosting Energy Density

Abstract

Sodium-ion batteries are emerging as a feasible substitute to lithium-ion batteries due to natural abundance and cost of their raw materials. Cathode materials with high operating voltage window are highly investigated in order to attain a high specific capacity and energy density. Because of its larger ionic size and lower standard electrochemical potential of Na, research on suitable cathodes with rich electrochemistry and high energy density is of utmost importance. NH4V4O10 (Ammonium Vanadium Oxide) is one such cathode with rich electrochemistry in terms of high sodium-ion storage along with a low-cost proposition. It is synthesized feasibly using a one-step hydrothermal process at lower temperatures (160o). However, the low conductivity and structural distortion during extended cycling pose a significant challenge. In this study, we present a high-rate cathode based on NH4V4O10, which employs a doping strategy to address the structural changes that cause distortion, while simultaneously improving ionic conductivity and electrochemical performance. By introducing dopants into NH4V4O10, the mobility of carriers is increased as the lattice spacing is expanded. This modification facilitates easier movement of Na-ions within the crystal lattice during electrochemical cycling, ultimately leading to enhanced Na-ion diffusion. As a result, the doped NH4V4O10 electrode exhibits superior high-rate performance compared to the pristine NH4V4O10. Furthermore, this doped NH4V4O10 cathode can be operated effectively at High voltage (1 V to 4.2 V ) and thus increasing the energy density. In addition to enhancing the ionic conductivity and Na-ion diffusion coefficient, the incorporation of dopants into NH4V4O10 also results in improved morphology, which contributes to the maintenance of a stable structure. As a result, the doped- NH4V4O10 cathode exhibits a specific capacity of 250 mAh/g with 0.1 A/g after 100 cycles, along with a Coulombic efficiency of 98%, whereas NH4V4O10 only achieves a 70% efficiency and within a restricted working potential window. With its unique properties, including superior conductivity, high Na-ion diffusion coefficient, and stable capacity over extended cycling, this newly modified doped NH4V4O10 material holds promise as a novel class of cathode for next-generation high-performance sodium-ion batteries.