Rational design and in-situ formation of nickel–cobalt nitride multi-core/hollow N-doped carbon shell anode for Li-ion batteries

The construction of a carbon-encapsulated multi-core nanostructure based on transition metal nitride is a preferred approach to efficiently mitigate volume expansion with improved sustainability and to enhance conductivity with more active sites for Li-ion cell reaction. Herein, we report the in-situ formation of carbon-coated nickel–cobalt nitride multi-core nanoparticles encapsulated by hollow N-doped carbon shell via monodispersed Ni₃[Co(CN)₆]₂ Prussian blue analogue/polydopamine precursors using by simultaneous nitridation and calcination process. The (Ni/Co)₃N multi-core nanoparticles (Ni:Co = 3:2) were highly dispersed in conductive and hollow N-doped carbon shell, thereby (i) mitigating mechanical stress by volume change during the conversion reaction of nitrides, (ii) stabilizing the electrochemical reaction surface with a thin solid electrolyte interphase, and (iii) maintaining the original structure and hierarchical morphologies even after long cycles. The (Ni/Co)₃N multi-core@hollow N-doped carbon shell demonstrated better electrochemical performance than the (Ni/Co)₃N@carbon shell without the outer hollow N-doped carbon shell for the Li-ion battery anode, which has an excellent reversible capacity of ~440 mAh g⁻¹ and a stable cycle life of 130 cycles at 200 mA g⁻¹. The rational synthetic strategy of the unique hybrid nanoarchitecture via in-situ formation of polymer-coated metal–organic frameworks is key in improving the Li-ion storage capacity and cycle stability.