On the Road to the Frontiers of Lithium‐Ion Batteries: A Review and Outlook of Graphene Anodes

Abstract

Graphene with fascinating physicochemical properties has been regarded as one of the most promising candidates to substitute the commercial graphite anode for next-generation lithium-ion batteries (LIBs). [1] As originally suggested by Dahn's group, Li ions can be adsorbed on each side of graphene, forming a Li 2 C 6 stoichiometry with a theoretical specific capacity of 744 mAh g −1 , twice that of graphite (372 mAh g −1 of the first-stage LiC 6 intercalation compound). [2] However, in situ Raman spectroscopy reveals that it is difficult to achieve high Li coverage on graphene because of the low binding energy of Li with carbon and the strong Coulombic repulsion between the adsorbed Li ions. [3] Using density functional theory (DFT) calculations, Lee et al. also found that Li cannot reside on the surface of pristine graphene since its adsorption energy is positive for the entire range of Li content. [4] Therefore, the Li storage capacity of pristine graphene is far from its theoretical value, and is even inferior to that of graphite. Accordingly, it was proposed that defective graphene presents superior Li adsorption because of the increased charge transfer between Li and the defects, and moreover, the specific capacity rises with the increase of defects densities. [5] In the case of the maximum divacancy defect density, the Li storage capacity can reach up to 1675 mAh g −1 . In this regard, reduced graphene oxide (rGO), a form of graphene prepared by a chemical oxidation-exfoliation-reduction process, has been proven to be a potential anode by virtue of its abundant defects and the residual O-containing functional groups. [6] On the other hand, rGO also exhibits the advantages of mass production from the reduction of graphene oxide (GO) with contained costs, which is an essential step for practical applications. [7] As a result, rGO anode is more frequently studied as compared to its pristine graphene counterpart.The groundbreaking work of graphene anodes was reported in 2008 by Honma's group, who demonstrated that the incorporation of carbonaceous materials, i.e., carbon nanotubes (CNTs) and fullerenes (C 60 ), into graphene sheets can efficiently expand the interlayer spacing, thus higher Li storage capacities. [8] Soon Graphene has long been recognized as a potential anode for next-generation lithium-ion batteries (LIBs). The past decade has witnessed the rapid advancement of graphene anodes, and considerable breakthroughs are achieved so far. In this review, the aim is to provide a research roadmap of graphene anodes toward practical LIBs. The Li storage mechanism of graphene is started with and then the approaches to improve its electrochemical performance are comprehensively summarized. First, morphologically engineered graphene anodes with porous, spheric, ribboned, defective and holey structures display improved capacity and rate performance owing to their highly accessible surface area, interconnected diffusion channels, and sufficient active sites. Surface-modified graphene anodes with less aggreg...

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“…Lithium-ion batteries have taken center stage in energy storage because of their applications in portable electronic devices. [1][2][3] Conventional anode materials such as graphite cannot meet the ever-going demands due to the limited specific capacity (372 mAh g À 1 ). [4] To develop high-performance anode materials, metal oxides, alloying materials, and organic compounds have been studied.…”