Influence of sputtering carbon top-layer on lithium storage performance of amorphous Ni–P films from ionic liquid

Amorphous Ni–P–C films are fabricated by combining the electrodeposition of Ni–P films from a eutectic-based ionic liquid and the direct current magnetron sputtering of amorphous carbon top-layer. The carbon top-layer with a thickness of about 10   nm is homogeneously coated on the surface of the Ni–P films. A comparison study is undertaken between Ni–P and Ni–P–C films to evaluate the microstructure and the electrochemical performances of the composite films as anode materials for lithium ion batteries , which allow the decoupling of the effect of the carbon layer . It is found that at lower discharge–charge current densities, the cyclability of both Ni–P and Ni–P–C films is similar. As the discharge–charge current density increases, the Ni–P–C film exhibits improved capability and reversibility over the Ni–P film. The Ni–P–C film delivers an initial discharge capacity of 1060   mAh   g −1 at 250   mA   g −1 and the capacity retention after 50 cycles is 62%, much higher than that of the Ni–P film (51%). The cyclability of Ni–P–C film at different discharge–charge current densities from 200 to 500   mA   g −1 is also much better than those of Ni–P film. This study indicates that the introduction of a carbon top-layer on Ni–P film could significantly improve the electrochemical performances due to the decreased interface electric resistance and the structure stability.