Highly Flexible Hydrogen Boride Monolayers as Potassium-Ion Battery Anodes for Wearable Electronics

Abstract

The rapid development of wearable electronics has revealed an urgent need for low-cost, highly flexible, and high-capacity power sources. In this sense, emerging rechargeable potassium-ion batteries (KIBs) are promising candidates owing to their abundant resources, low cost, and lower redox potential in nonaqueous electrolytes compared to lithium-ion batteries. However, the fabrication of flexible KIBs remains highly challenging because of the lack of high-performance flexible electrode materials. In this work, we investigated the mechanical properties and electrochemical performance of a recently developed hydrogen boride (BH) monolayer as a high-performance anode material on the basis of density functional theory formalism. We demonstrated that (i) BH presents ultralow out-of-plane bending stiffness, rivaling that of graphene, which endows it with better flexibility to accommodate the repeated bending, rolling, and folding on wearable device operation; (ii) high in-plane stiffness (157 N/m along armchair and 109 N/m along zigzag) of BH makes the electrode stable against pulverization upon external and internal strains. More importantly, a BH electrode delivers a low voltage of ∼0.24 V in addition to desired K-ion affinity and hopping resistance, which remains very stable with the bending curvature. Emerged H vacancies in electrodes were found to improve both the K-ion intercalation and K-ion hopping, yielding a high theoretical capacity (1138 mAh/g), which was among the highest reported values in the literature for K-ion anode materials. All of the presented results suggested that a BH electrode could be used as a brand-new flexible and lightweight KIB anode with high capacity, low voltage, and desired rate performance.

Vacancy in Ultrathin 2D Nanomaterials toward Sustainable Energy Application

“…The situation for K + storage is similar to that of Na + 2b. Density functional theory (DFT) calculations have revealed that H‐vacancies in a curved BH monolayer lower the migration energy barrier of K + ions on the boron‐concave side to E bar (0.03–0.28 eV) relative to that of pristine BH (0.32 eV), which decreases even further with proximity to the H vacancy (Figure c,d) 41a. Note that the structural features of a BH monolayer are more similar to an M a X b structure than to a X a Y b structure.…”

“…Several emerging energy‐related electrocatalytic reactions, such as carbon dioxide reduction and nitrogen fixation, have recently received close attention due to their potential for clean and convenient energy production and/or storage. The unique characteristics of ultrathin 2D materials with X a &X a Y b , M a X b , and M a X b Y c structures are well‐suited for these applications. In addition, depending on the structure of these materials, vacancy engineering can be used to fine‐tune or tailor properties according to the specific needs of the application.…”

“…(Inset: The corresponding diffusion paths.) Reproduced with permission 41a. Copyright 2019, American Chemical Society.…”

A New Monolayer B4C4 with Robust Stability and Excellent Performance for Spontaneous Water Splitting Under Visible Light

“…[ 53 ] The elastic constants are listed in Table S1 in the Supporting Information and the elastic moduli is 300.65 and 221.44 N m −1 in the a and b direction, respectively. These exceeds those of hydrogen boride (BH) monolayer (157 and 109 N m −1 ), [ 54 ] MoS 2 (133 and 133 N m −1 ), [ 55 ] β 12 borophene (123 and 147 N m −1 ). [ 56 ] And the elastic constant of a direction is even close to graphene (342 N m −1 in the a direction).…”

New Findings on an Old Question: Can Defect‐Free Graphene Monolayers be Superior Metal‐Ion Battery Anodes?

“…Thus, a 3 × 3 × 1 graphene supercell could hold four layers of K atoms with a total 12 atoms, corresponding to the stoichiometric ratio of K 2 C 3 and a maximum K capacity on defect‐free graphene of 1487.7 mA h g −1 . The capacity is larger than most 2D electrodes, such as Θ‐graphene (956 mA h g −1 ), [ 14 ] xgraphene (744 mA h g −1 ), [ 15 ] hydrogen boride (1138 mA h g −1 ), [ 16 ] blue phosphorene (865 mA h g −1 ), [ 17 ] VS 2 (466 mA h g −1 ), [ 13 ] Ti 3 C 2 (192 mA h g −1 ), [ 18 ] and MoN 2 (432 mA h g −1 ). [ 19 ] Such a high specific capacity may be attributed to the multilayer adsorption of K atoms and light weight of C atoms.…”