High‐Density Monolith of N‐Doped Holey Graphene for Ultrahigh Volumetric Capacity of Li‐Ion Batteries

Abstract

To solve the aforementioned problems, emerging graphene agglomerates with crumpled morphologies obtained by the stacking of graphene sheets seem to be promising for increasing the packing density and energy density in energystorage devices. [ 23,24 ] Unfortunately, they usually exhibit a rather low packing density, and consequently a relatively low volumetric capacity. Additionally, the closely stacked graphene agglomerate electrodes generally decrease the ion-accessible surface area and electrolyte ion diffusion, which inevitably compromises its lithium storage capacity. Thus, both a high density and porous structure should be taken into consideration when seeking a strategy for the synthesis of novel carbon-based LIB anodes.Recently, holey graphene, as a new class of graphene derivatives, has attracted extensive attention because of its high intrinsic electrical conductivity, open ion channels, and edge activity useful for applications in electrochemistry-related fi elds. [ 8,25 ] In our previous study, we have demonstrated a lightweight porous graphene foam as advanced electrode material for electrochemical processes (e.g., hydrogen evolution reaction, oxygen reduction reaction, ethanol oxidation reaction, and as electrochemical capacitor). [26][27][28][29][30] Herein, we report a N-doped holey-graphene monolith (NHGM) with a dense microstructure and high density of 1.1 g cm −3 . The holey structure in the individual graphene sheets could not only provide effi cient diffusion channels for Li ions and a highly conductive pathway for electrons, but also provided more edges on the sheet to enhance Li intercalation. [ 31,32 ] NHGM was obtained by conjugating N-containing holey-graphene sheets into a 3D hydrogel, followed by evaporation of the trapped water under vacuum at room temperature and an annealing treatment under Ar atmosphere. This highly compact but porous architecture with heteroatom doping is favorable for ion diffusion, Li ion storage, and maximizing the LIB properties; the NHGM had a volumetric capacity of 1052 mAh cm −3 , which is nearly three times that of commercial graphite anodes (370 mAh cm −3 ), [ 33 ] and exhibited competitive characteristics over the existing Si-based and carbon/sulfur hybrid electrode materials (see Table S1 in the Supporting Information). This makes our graphene-based electrode material an important step toward practical applications.To prepare the N-doped, high-density, holey-graphene monolith (NHGM), we fi rst produced the N-containing holeygraphene hydrogel (NHGH) by a one-pot hydrothermal process with simultaneous etching of nanopores in the graphene sheets and co-assembly of graphene and pyrrole to form a 3D hydrogel. During the hydrothermal process, a controlled amount of H 2 O 2

Hierarchical Structures Based on Two‐Dimensional Nanomaterials for Rechargeable Lithium Batteries

“…[43,128,129] In this strategy, GO sheets were reduced and self-assembled into hydrogels with interconnected 3D macroporous network with the pore sizes ranging from submicrometres to several micrometres and the pore walls consisting of single-or few-layer graphene sheets (Figure 4a,b). As a typical example, holey graphene and its derivatives hydrogels can be prepared by one-pot hydrothermal process with simultaneous H 2 O 2 -etching reaction in the graphene sheets.…”

Isolated Fe Single Atomic Sites Anchored on Highly Steady Hollow Graphene Nanospheres as an Efficient Electrocatalyst for the Oxygen Reduction Reaction

“…[23][24][25] Unfortunately, the irreversible stacking of 2D graphene nanosheets would diminish the accessible surface, bury the catalytically active sites and obstruct the mass diffusion/transport, thereby posing a negative effect to electrocatalytic performance. Among various substrates, 2D graphene-based nanosheets are regarded as a class of promising candidate because of their large surface area, outstanding mechanical robustness and superior electrical conductivity.…”

Holey 2D Nanomaterials for Electrochemical Energy Storage

“…Similarly, N-doped holey-graphene monolith (NHGM) was reported by Wang et al as electrodes with a dense microstructure and high density. [49] The NHGM was produced by a one-pot hydrothermal process to form the N-doped holeygraphene hydrogel (NHGH) and followed by thermal treatment to convert NHGH to NHGM. NHGH was formed by the coassembly of graphene and pyrrole, in which pyrrole provided the N source and prevented the possible self-stacking of the hydrogel.…”