Abstract
Systematic first-principles calculations were performed to investigate the adsorption and diffusion of Li on different graphene layers with B/N-doping and/or C-vacancy, so as to understand why doping heteroatoms in graphene anode could significantly improve the performance of lithium-ion batteries. We found that the formation of single or double carbon vacancies in graphene are critical for the adsorption of Li atoms. While the N-doping facilitates the formation of vacancies, it introduces over binding issue and hinders the Li diffusion. The presence of B takes the excessive electrons from Li and N and reduces the energy barrier of Li diffusion on substrates. We perceive that these clear insights are crucial for the further development of graphene based anode materials for lithium-ion batteries.
Highlights
With excellent characters of high energy density, long cycling life and environmental friendliness, lithium-ion batteries (LIBs) have been widely used in portable electronic devices[1,2,3,4,5]
We first studied the adsorption configurations and energies of one Li atom on the decorated graphene cells with x N-atoms and y VC, G_NxVy (x = 0–4 and y = 0–2), corresponding to a N-concentration of ~1.4–5.6%, comparable with the experimental range for graphene samples synthesized via the thermal reaction between graphene oxide and NH3 at high temperature[33]
We see that for y = 0, i.e., N-substituted graphene without VC, N atoms prefer to stay far away from each other to minimize the perturbation to the graphene π-electron bonds, as depicted in Table S1 in the supplementary material (SM)
Summary
Properties of Lithium on B,N,VCdecorated Graphene received: 14 September 2016 accepted: 03 November 2016 Published: 29 November 2016. The presence of B takes the excessive electrons from Li and N and reduces the energy barrier of Li diffusion on substrates We perceive that these clear insights are crucial for the further development of graphene based anode materials for lithium-ion batteries. Liu et al found that the substitutional B atoms cause slight electron deficiency, which makes the adsorption of Li on the C3B monolayer easy[26] These pictures are not much beyond intuition and the synergy between effects of B,N-dopants and C-vacancy decorations on the improvement of Li storage capacity and conductivity remains vague, which hinders the development of graphene as anode materials in LIBs. In the present work, we performed systematic density functional theory (DFT) calculations for the structures and energetics of different B/N/VC-decorated graphene geometries, as well as the Li adsorption and diffusion.
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