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Atomically thin layers of nitrides are a subject of interest due to their novel applications. In this paper, we focus on GaN multilayers, investigating their stability and the effects of stacking and electric fields on their electronic properties in the framework of density functional theory. Both bilayers and trilayers prefer a planar configuration rather than a buckled bulk-like configuration. The application of an external perpendicular electric field induces distinct stacking-dependent features in the electronic properties of nitride multilayers: the band gap of a monolayer does not change whereas that of a trilayer is significantly reduced. Such a stacking-dependent tunability of the band gap in the presence of an applied field suggests that multilayer GaN is a good candidate material for next generation devices at the nanoscale.

the ultimate choice with no competition [2] because of its ultrahigh specific capacity (3860 mAh g −1), lightweight (0.53 g cm-3) and the lowest electrochemical potential (−3.040 V versus standard hydrogen electrode). [1,3] Replacing graphite anodes in Li-ion batteries with Li metal would lead to an immediate increase of energy density by 40%. [1,2] In a broader context, Li anodes are also indispensable components for next-generation concept battery chemistries such as Li-sulfur and Li-air couples, whose energy density are expected to exceed 370 and 1700 Wh kg −1 , respectively. [4-6] The major obstacle impeding the electrochemical cycling of Li metal is its high reactivity with electrolytes, which results in uncontrolled growth of Li dendrites and incessant formation of dead lithium. These reactions not only consume lithium resource at the expense of reversibility, but also often induce safety hazards. [1,5,6,7] In the past decades, many strategies have been proposed to suppress the parasitic reactions between Li metal and electrolytes, with focus frequently directed at the dendrite growth. [8-13] These strategies include: i) designing high-concentration salt liquid electrolytes to mitigate the inhomogeneous distribution of Li ions; [14] ii) optimizing electrolyte additives to stabilize Lithium (Li) metal offers the highest projected energy density as a battery anode, however its extremely high reactivity induces dendrite growth and dead Li formation during repeated charge/discharge processes, resulting in both poor reversibility and catastrophic failure. Approaches reported to date often seek to suppress dendrites formation at the expense of energy density. Here, a strategy that resolves the above conflict and achieves a dendritefree and long-term reversible Li metal anode is reported. A self-organized core-shell composite anode, comprising an outer sheath of lithiated liquid metal (Li x LM y) and an inner layer of Li metal, is developed, which posesses high electrical and ionic conductivity, and physically separates Li from the electrolyte. The introduction of Li x LM y not only prevents dendrite formation, but also eliminates the use of copper as an inert substrate. Full cells made of such composite anodes and commercially available LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM 622) cathodes deliver ultrahigh energy density of 1500 Wh L −1 and 483 Wh kg −1. The high capacity can be maintained for more than 500 cycles, with fading rate of less than 0.05% per cycle. Pairing with LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM 811) further raises the energy density to 1732 Wh L −1 and 514 Wh kg −1. The rapid development of mobile electronics, internet-of-things and electrical vehicles imposes an insatiable demand for highenergy-density rechargeable batteries, which relies on the discoveries of better electrodes, electrolytes and interphases. [1] Among all possible anode material candidates, [1] Li metal is

Silicon is a promising candidate for negative electrodes due to its high theoretical specific capacity (~3579 mAh g -1 ) and low lithiation potential (~0.40 V vs Li). However, its practical applications in battery have been inhibited by the large volume change (~400%) induced by Li + -insertion into Si lattices. Here, we attempt to resolve this issue at a fundamental level, and report for the first time a novel liquid metal (LM)-mediated spontaneous repairing conductive-additive-free Si anode for Li-ion battery. The fluidity of LM ensures the eternal contact between Si and the conducting-network during its repeated electrochemical reactions.The as-prepared nano-composite of LM/Si leads to superior performances as characterized by high capacity utilization (2300 mAh g -1 at 500 mA g -1 ), long-term stability (968 mAh g -1 after 1500 charge-discharge cycles at 8 A g -1 with 81.3% retention), high rate capability (360 mAh g -1 at 20 A g -1 , equivalence of 55 C, or full charge/discharge in 65 seconds), and, in particular, an extra-ordinarily high initial coulombic efficiency (95.92%), which is not only the highest reported for Si to the best of our knowledge, but also higher than the mature graphitic carbon anodes. The unique approach described in this work not only resolves the basic stress challenges faced by the promising but often problematic alloy-type materials; in broader context it also provides a universal inspiration to all electrode materials whose electric properties suffer from extreme mechanic upheavals induced by the electrochemical strains during the cell reactions.