Na/K Diffusion in FeP as an Anode Material for Ion Batteries

Abstract

Potassium-and sodium-ion batteries (KIBs and SIBs) have attracted wide attention due to abundant potassium and sodium resources, low cost, and high safety. Therefore, in this work, FeP as an anode material is selected to study diffusions of Na/K using a density functional theory method in order to explain our experimental result that the rate performance of the FeP/C anode material in KIBs is much better than that in SIBs. The rate performance of the FeP/C anode material in KIBs and SIBs is related to diffusion activation energies including interaction energies between Na/K and FeP and migration energy barriers. Our calculations find that diffusion of Na/K in FeP is a multistep one. The most favorable one among various possible diffusion paths is obtained. A migration energy barrier is a key factor to distinguish between K and Na diffusions in FeP. Na−P/K−P bond lengths, consequent binding energies between Na/K and FeP, and local structures of transition states account for migration energy barriers. The calculated result of the larger migration energy barrier for Na in FeP than K in FeP can well explain our experimental phenomenon that the rate performance of FeP/C in KIBs is better than that in SIBs. This work provides a theoretical basis that iron phosphide can be used as a better, low-cost, and higher-energy-density anode material for KIBs.

Enhancement of Electrochemical Properties of SIBs by Generating a New Phase in Potassium-Doped NaV6O15 Film Electrodes

“…The increasing demand for energy is accelerating the consumption of all kinds of sources. In the past few decades, lithium-ion batteries (LIBs) have been widely used as an energy storage system due to their high energy density, environmental friendliness, and long lifetime . However, the nonabundance of lithium resources and the inferior rate capability will limit extensive application; they can be mined for less than 60 years according to the mining volume. , Hence, there is an urgent need to develop new energy materials with abundant resources and environmental friendliness .…”

“…21,22 However, their cycling stability is often unsatisfactory due to the lowest content of supporting metal ions. 6,22 The solutions to this problem are listed below: (1) modifying the structure such as the incorporation of dopants and morphological control to improve capacity fading; 22−26 (2) compounding to achieve a synergistic effect; 27−29 cycling stability. 10,30 Herein, doping has been chosen to improve the cycling stability of pure NaV 6 O 15 films in the work.…”