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ReseaRch aRticle
Enabling Fast Na+ Transfer Kinetics in the Whole-Voltage-
Region of Hard-Carbon Anodes for Ultrahigh-Rate Sodium
Storage
Xiuping Yin, Zhixiu Lu, Jing Wang, Xiaochen Feng, Swagata Roy, Xiangsi Liu, Yong Yang,
Yufeng Zhao,* and Jiujun Zhang
X. P. Yin, Z. X. Lu, X. C. Feng, S. Roy, Y. F. Zhao, J. J. Zhang
College of Sciences & Institute for Sustainable Energy
Shanghai University
Shanghai 200444, China
E-mail: yufengzhao@shu.edu.cn
J. Wang
Key Laboratory of Applied Chemistry
Yanshan University
Qinhuangdao 066000, China
X. S. Liu, Y. Yang
State Key Laboratory for Physical Chemistry of Solid Surface
College of Chemistry and Chemical Engineering
Xiamen University
Xiamen 361005, China
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/adma.202109282.
DOI: 10.1002/adma.202109282
able energy exploitation of renewable
sources.[1–3] However, SIBs have to deal
with various challenges including infe-
rior rate capability, and condescending
lifetime, which generally instigated by the
lack of appropriate electrode materials,
especially the anodes.[4–7] Hard carbons
(HCs) have attracted extensive attention
with suitable potential versus Na+/Na,
good structural stability, decent coulombic
eciency, superior reversible capacity etc.,
and are considered as the most feasible
anode materials for further commerciali-
zation.[8–10] Nevertheless, the unsatisfied
rate capability of HCs (generally <5 A g–1)
represents the primary constraint in their
practical applications, as well as the under-
lying structure–performance correlation is
a substance of controversial discussion.
Typical HCs comprise a large number
of short-range-ordered graphitic domains
and internal micropore domains (or voids
between graphitic domains).[11] The gra-
phitic-domain with proper interlayer dis-
tance and the internal-nanopore-domain are both believed to be
capable of accommodating sodium ions.[12–17] Classic charge/dis-
charge curves of HCs comprise a high-potential slope (>0.10V)
and a low-potential plateau (0.01–0.10V). Various mechanisms
have been proposed to explicate the charge-storage behavior at
dierent potential regions, yet no conclusive outcome has been
accomplished.[18–25] A few studies correlate the charge-storage
behavior with the interlayer distance (d002), concluding that
short range ordered graphitic layers with d of 0.36–0.40nm are
capable of storing Na+ ions through “interlayer intercalation,”
providing a high plateau capacity,[26–29] whereas some other
studies contemplate that the filling of Na ions (or clusters) into
the internal micropores (or voids between graphitic domains) is
responsible for the plateau capacity.[12,13,30–32]
Despite the diverse opinions on the charge-storage mecha-
nism, it is a well-established fact that the low potential pla-
teau region represents the rate-determining step for HCs.
Various studies have unveiled that, HCs with obvious plateau
below 0.10V, encounter a dramatic drop of Na+ diusion coef-
ficient.[21,28,33–35] Generally, the Na+ diusion coecient at the
sloping area (3.00–0.10 V) is between 10–11 and 10–9 cm2 s–1,
which is of two orders lower (10–13 to 10–10 cm2 s–1) at the plateau
Ecient electrode materials, that combine high power and high energy, are
the crucial requisites of sodium-ion batteries (SIBs), which have unwrapped
new possibilities in the areas of grid-scale energy storage. Hard carbons
(HCs) are considered as the leading candidate anode materials for SIBs,
however, the primary challenge of slow charge-transfer kinetics at the low
potential region (<0.1V) remains unresolved till date, and the underlying
structure–performance correlation is under debate. Herein, ultrafast sodium
storage in the whole-voltage-region (0.01–2V), with the Na+ diusion coef-
ficient enhanced by 2 orders of magnitude (≈10–7 cm2 s–1) through rationally
deploying the physical parameters of HCs using a ZnO-assisted bulk etching
strategy is reported. It is unveiled that the Na+ adsorption energy (Ea) and
diusion barrier (Eb) are in a positive and negative linear relationship with
the carbon p-band center, respectively, and balance of Ea and Eb is critical
in enhancing the charge-storage kinetics. The charge-storage mechanism
in HCs is evidenced through comprehensive in(ex) situ techniques. The
as prepared HCs microspheres deliver a record high rate performance of
107 mAh g–1 @ 50 A g–1 and unprecedented electrochemical performance at
extremely low temperature (426 mAh g–1 @ −40 °C).
1. Introduction
Sodium-ion batteries (SIBs), owing to the abundant and cheap
sodium resources, have been surfaced as the next generation
large-scale energy storage systems to support the sustain-
Adv. Mater. 2022, 34, 2109282