Flexible C6BN Monolayers As Promising Anode Materials for High-Performance K-Ion Batteries.

Pan Xiang,Jiang Wu,Udo Schwingenschlögl,Sitansh Sharma,Zhiming M Wang

doi:10.1021/acsami.0c09451

Abstract

K-ion batteries attract extensive attention and research efforts because of the high energy density, low cost, and high abundance of K. Although they are considered suitable alternatives to Li-ion batteries, the absence of high-performance electrode materials is a major obstacle to implementation. On the basis of density functional theory, we systematically study the feasibility of a recently synthesized C6BN monolayer as anode material for K-ion batteries. The specific capacity is calculated to be 553 mAh/g (K2C6BN), i.e., about twice that of graphite. The C6BN monolayer is characterized by high strength (in-plane stiffness of 309 N/m), excellent flexibility (bending strength of 1.30 eV), low output voltage (average open circuit voltage of 0.16 V), and excellent rate performance (diffusion barrier of 0.09 eV). We also propose two new C6BN monolayers. One has a slightly higher total energy (0.10 eV) than the synthesized C6BN monolayer, exhibiting enhanced electronic properties and affinity to K. The other is even energetically favorable due to B–N bonding. All three C6BN monolayers show good dynamical, thermal, and mechanical stabilities. We demonstrate excellent cyclability and improved conductivity by K adsorption, suggesting great potential in flexible energy-storage devices.

Highlights

The limited reserves of traditional energy sources and the environmental issues caused by them make the development of clean sustainable energy sources an urgent task.[1,2] these sources, such as solar energy and wind energy, are greatly affected by environmental and weather conditions, resulting in fluctuating output.[3]
In combination with fast ion transport in the electrolyte this makes them to promising alternatives for large scale energy storage systems and electric vehicles.[12,13]
It is essential to develop for K-ion batteries suitable low cost and high performance electrode materials, as they determine their electrochemical properties

Summary

■ INTRODUCTION

The limited reserves of traditional energy sources and the environmental issues caused by them make the development of clean sustainable energy sources an urgent task.[1,2] these sources, such as solar energy and wind energy, are greatly affected by environmental and weather conditions, resulting in fluctuating output.[3]. On the basis of first-principles calculations, the binding energy of a single K atom on graphene was found to be 1.05 eV, which is only slightly larger than the cohesive energy of K (0.93 eV), indicating potential risk of dendrite formation.[16] While the electrochemical performance of C-only anode materials is unsatisfactory for K-ion batteries, improvement is found for two-dimensional C3B.17. Still adopting the Perdew−Burke−Ernzerhof and Grimme schemes, the dynamic stability is investigated by calculating the phonon spectrum by the Phonopy[27] and VASP28 (projector augmented-wave potentials, 1 × 10−6 eV energy convergence threshold, Monkhorst− Pack 12 × 12 × 1 k-mesh) programs, and charge densities and electron localization functions are obtained by means of the CASTEP29 program (norm-conserving pseudopotentials, 5 × 10−7 eV/atom energy convergence threshold, Monkhorst−Pack 7 × 7 × 1 k-mesh)

■ RESULTS AND DISCUSSION

■ ACKNOWLEDGMENTS

■ REFERENCES