Capping Black Phosphorene by h‑BN Enhances Performances in Anodes for Li and Na Ion Batteries Chandra Chowdhury, Sharmistha Karmakar, and Ayan Datta* Department of Spectroscopy, Indian Association for the Cultivation of Science, Jadavpur 700032, West Bengal, India * S Supporting Information ABSTRACT: Black phosphorus (BP), despite possessing a favorable direct band gap, suffers from structural instability at ambient conditions that limits its utility for lithium ion batteries (LIB). In this Letter, we have proposed h- BN as an effective capping agent for black-phosphorene (Pn) for application as an anode material in both LIBs and sodium ion batteries (SIBs). The binding energy of Li/Na in the h-BN/black-Pn heterostructure is greatly enhanced (2.81 eV/2.55 eV) vis-a-vis pristine Pn (1.80 eV/1.59 eV) along with reduction in the barrier for movement of Li/Na within the layers. Significantly, lithiation/sodiation of these heterostructures does not alter the packing patterns due to insignificant volume changes (∼1.5-2.0%). The theoretical specific capacities for h-BN/black-Pn is 607 and 445 mA h g -1 for LIB and SIB, respectively, which are larger than those for existing commercial anode materials. Clearly, the high capacity, low open-circuit voltage, small volume change, and high mobility of Li/Na within the layers make h-BN- capped black-Pn an excellent anode material in LIBs/SIBs. The heterostructure exhibits an interesting semiconductor → metal electronic phase transition upon lithiation/sodiation. C hemical energy is the most appropriate form of energy storage in terms of energy density. Among the various available energy storage technologies, lithium ion batteries (LIBs) and sodium ion batteries (SIBs) have become prime candidates in next-generation energy storage devices. Due to their high energy density, enhanced rate capabilities, and good cycle life, LIBs are already in use for anode materials. 1 On the other hand, SIBs have generated interest due to their high abundance in the environment and low cost. Moreover, as Li and Na are physically/chemically similar, the existing technologies in LIBs can be directly translated to SIBs. Among the various hosts for anodes, two-dimensional (2D) materials, because of their large surface to volume ratio and short ion diffusion path, exhibit significantly improved electrochemical performances. 2,3 Graphite, the first material to be used as an anode in LIBs has a theoretical specific capacity of 372 mA h g -1 , which does not meet the requirement for future technologies. 4,5 Graphene, the most well-known 2D material, exhibits unique capacity in LIBs and has been utilized as both anode and cathode materials with great success. 6-8 Besides graphene, efforts have been made to fabricate LIBs from other 2D materials like silicene, transition-metal dichalcogenides (TMDs), and transition-metal carbides. 9-12 However, the weak binding of Li with graphene and other 2D materials impedes their applications in LIBs. 13,14 Although SIB anodes based on 2D materials have been studied along similar lines, the weak interactions between Na and atomic layers preclude their use in SIBs. 15,16 More recently, a new elemental 2D material, phosphorene (Pn) has generated excitement due to its finite direct band gap, high carrier mobility, and high drain current modulation. 17-19 Pn monolayers and bilayers have also been explored as anodes for LIBs and SIBs with high theoretical capacity. 20-23 Nevertheless, despite its stellar properties, the high tendency for air oxidation that significantly alters its electronic structure impedes its incorporation in advanced electronics. 24 Also, the chemical sensitivity of Pn to external adsorbates adversely affects device performances and reproducibility. Recent studies however show that structural and chemical degradation of Pn might be avoided by capping it with graphene or hexagonal boron nitride (h-BN). 25-28 In fact, Pn/graphene heterostruc- tures have been demonstrated to be good electrode materials for both LIBs and SIBs. 29,30 In this Letter, we show that capping of h-BN on Pn monolayers preserves the pristine electronic properties of Pn. The combined system additionally gains high chemical stability from the capping material (h-BN). Therefore, LIB/SIB anodes composed of h-BN-capped Pn can be protected from chemical degradation. By means of density Received: May 23, 2016 Accepted: June 13, 2016 Published: June 13, 2016 Letter http://pubs.acs.org/journal/aelccp © 2016 American Chemical Society 253 DOI: 10.1021/acsenergylett.6b00164 ACS Energy Lett. 2016, 1, 253-259