Three fundamental challenges for the development of technologically relevant Sodium-ion batteries (SIB) and Sodium-ion capacitors (SIC) are the lower cell voltage, decreased ionic-diffusivity and larger volume of sodium-ion relative to their Lithium-ion analogues. Using first-principles computation, we show that, two dimensional BxCyNz with nitrogen-excess trigonal BxNz-domain (TN) meets the requirements of a superior anode for SIB. Variation in shape of the BxNz-domain and B-N charge-imbalance in BxCyNz results in tunable anodic properties. Monolayer TN-sheet can store Na (Li) up to Na2.2C6 (Li1.8T6) composition which corresponds to a specific capacity as high as 810 (668) mAhg-1 for SIB (LIB). The average open circuit voltage is ~1.25 V vs. Na/Na+ for wide range of chemical stoichiometry of NaxTN which is also beneficial to the overall cell-voltage. Enhanced electronic transport and fast diffusion kinetics of the Na-ions is particular for TN-anode which can result in high power efficiency in SIB, even better than that of graphite electrode in conventional LIB. Charge-storage upon layer-wise accumulation of Na-ion on TN surface is also appealing for application to “Sodium-ion capacitor,” as an alternative to the lithium-ion capacitor. These features are in contrast to the conventional layered materials, where the voltage drops quickly as Na-ions are removed from the matrix. Hence, this article may serve as a guiding step for designing the borocarbonitride electrode for SIB (SIC) with controlled experimental behaviour.
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