Reconfiguring Hard Carbons with Emerging Sodium‐Ion Batteries: A Perspective

Abstract

Hard carbons, an important category of amorphous carbons, are non‐graphitizable and are widely accepted as the most promising anode materials for emerging sodium‐ion batteries (SIBs)， because of their changeable low‐potential charge/discharge plateaus. However, their microstructures are not fixed and are difficult to accurately demonstrate as graphites do. The successful use of hard carbons in SIBs revives the interest to clearly picture their complicated microstructures that are in close relevance to sodium storage. In this review, the past definitions and structural models of hard carbons are revisited first, and a renewed understanding of their sodium storage is presented. Three critical structural features are highlighted for hard carbons, namely crystallites, defects, and nanopores, which are directly responsible for the presence of the low‐potential plateaus and their reversible extension. The impact of these structural features upon the sodium storage is then deeply discussed and sieving carbons is finally proposed as an ideal configuration of carbon anode for superhigh sodium storage. This review is expected to offer a clear picture of hard carbons, and help realize a truly rational design of high‐capacity carbon anodes, driving the industrialization of SIBs, and more promisingly open up a window for exploring their possible new uses.

Toward High Performance Anodes for Sodium-Ion Batteries: From Hard Carbons to Anode-Free Systems

“…HC is considered to be the most promising anode material for SIBs due to its low operating voltage, high capacity, and low cost . However, the long calendar life, rate capability, and initial Coulombic efficiency (ICE) are far from satisfactory.…”

“…HC is considered to be the most promising anode material for SIBs due to its low operating voltage, high capacity, and low cost. 6 However, the long calendar life, rate capability, and initial Coulombic efficiency (ICE) are far from satisfactory. From the prospective of pursuing higher energy densities, the Na metal anode deserves to be refocused due to the high theoretical specific capacity (1166 mA h g −1 ) and low redox potential (−2.714 V versus standard hydrogen electrode potential).…”

Theoretical Prediction of Janus TQ-Graphene as a Metallic Two-Dimensional Carbon Allotrope with Negative Poisson’s Ratios for High Capacity Sodium-Ion Batteries

“…Its two-dimensional (2D) counterpart graphene is inert toward Na-ion storage because of the giant delocalized π electron system . Therefore, substantial efforts have been made to enhance the chemical reactivity of graphene by breaking the hexagonal symmetry. − For example, honeycomb-kagome FSL-graphene, nonbenzenoid biphenylene monolayer, and pentagraphyne are predicted to have high theoretical Na storage capacity (680–3347.1 mA h g –1 ).…”

Flexible Precursor Modulation toward Selective Heteroatom Doping in a Hard-Carbon Anode for Sodium-Ion Batteries

“…Similar to the lithium-ion intercalation chemistry, sodium-ion batteries (SIBs) are expected to be an alternative solution for grid-scale energy storage systems and low-speed electric vehicles due to natural abundance. − Theoretically, the energy density/power output and cycle stability of battery structures depend on the rational design of cation storage sites in electrodes. Among all the anode candidates, hard carbon (HC) is one of the most viable choices for SIBs due to its readily available resources, abundant storage sites, and large interplanar spacing for Na + diffusion.…”