Light element (B, N) co-doped graphitic films on copper as highly robust current collectors for anode-free Li metal battery applications

Abstract

We have examined the case of light atom (B, N) doped and co-doped graphitic films grown on copper for the anode-free Li Metal Battery (AFLMB) application. For nitrogen doping, the depositions were carried out by laser ablating pure graphite (Gr) in the presence of Nitrogen (N2) or Ammonia (NH3). In another interesting case, 5 wt. % Boron nitride (BN) was added into the graphite target itself to obtain BN-doped graphite films. It was found that the growth condition mediated film constitution and properties significantly influence the Coulombic efficiency and cycling stability of the cells when tested for AFLMB. The cycle life demonstrated by the cells of pure graphitic film (Gr) was only about 110 cycles, while the N-doped graphite films obtained using N2 gas (N2–Gr) exhibited stability up to about 300 cycles. Interestingly the N-doped films obtained using NH3 gas (NH3–Gr) exhibited a stability of 715 cycles and B, N co-doped graphite (BN–Gr) film resulted in an even longer cycle life of 795 cycles. Density functional theory calculations were also performed to deeply understand the interaction and binding energy of Lithium within the undoped and doped graphene sheets modeled through the addition of light elements. It was found that the binding of Li is stronger in the (B, N) co-doped graphene as compared to the N-doped graphene and undoped graphene but much weaker than the B-doped graphene. Therefore, an improved lateral Li diffusion in the (B, N) co-doped graphene is observed where the Li binding strength is optimum resulting in better cycling stability.