Exploring Novel Cathode Materials For Potassium Ion Batteries By First-principles Studies

In recent years,the rapid consumption of petroleum fuel and corresponding environmental problems have aroused people’s attention to the grid-scale energy storage system.Among various electrochemical energy storage devices,Lithium-ion batteries(LIBs)have been widely used as important storage devices because of their high energy density and long cycle life.However,the low content of lithium in the earth’s crust and the year-on-year increase in price limit the further development of lithium-ion batteries in large-scale energy storage systems.Due to low cost and abundant resources,potassium ion batteries(KIBs),as a substitute for lithium ion batteries,have received more and more attention in recent years.Because of the large radius of potassium ions,there is a lack of suitable cathode substrate materials that can accommodate K without large strain or volume change.Therefore,it is essential to explore novel cathode materials for potassium ion batteries.In this paper,a general method for high-throughput screening of novel KIBs cathode materials is proposed,and some potential electrode materials have been obtained.And we have thoroughly studied the feasibility of three-dimensional KFe O2 as a KIBs cathode material,and that provides a new strategy for identifying suitable cathode materials.An important challenge of K-ion batteries lies in exploring earth-abundant and safe cathode materials that can provide high capacity with high migration rate of K ions.Here,we propose a simple and efficient method for searching potential K cathode materials with first principles calculations.Our screening is based on combinations of weight capacity,K ion occupation ratio,volume of per K,and valence limit.With this screening method we predicted a series of potential KIBs cathodes with favorable electrochemical performance,such as K2VPO4CO3-like structures with 1D diffusion channels,3D channel structures K2 Co Si O4,layered materials KCo O2,KCr O2,KVF4 and K5V3F14,and others.These potential cathodes have small volume changes,suitable voltage,high capacity and small diffusion barriers.They may be useful in KIBs with high energy density and high-rate performance.Next,we further explored the potential application of three-dimensional KFe O2 as a KIBs cathode material.We use first-principles calculations and cluster expansion method to analyze the structural changes during the intercalation/deintercalation of potassium ions.We found that the pore frame structure of Fe O2 was stable through the charge/discharge process.A voltage window of 3.0–4.0 V and a theoretical capacity of172 m Ah/g were found.The diffusion barriers at high and low concentrations of K were analyzed and found to be 0.13-0.26 e V,implying high-rate of charging-and discharging-performance.The research on KFe O2 provides a new strategy to access suitable potential KIBs cathode materials with high capacity and high-rate performance.