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1804347 (1 of 8)
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Plasma Treatment for Nitrogen-Doped 3D Graphene
Framework by a Conductive Matrix with Sulfur for
High-Performance Li–S Batteries
Lianfeng Duan, Lijuan Zhao, Hui Cong, Xueyu Zhang, Wei Lü,* and Chunlai Xue*
Prof. L. F. Duan, L. J. Zhao, Dr. X. Y. Zhang, Prof. W. Lü
Key Laboratory of Advanced Structural Materials
Ministry of Education and Advanced Institute of Materials Science
Changchun University of Technology
Changchun 130012, P. R. China
E-mail: lvwei@ccut.edu.cn
Dr. H. Cong, Prof. C. L. Xue
State Key Laboratory on Integrated Optoelectronics
Institute of Semiconductors
Chinese Academy of Sciences
Beijing 100083, P. R. China
E-mail: clxue@semi.ac.cn
Dr. H. Cong, Prof. C. L. Xue
Center of Materials Science and Optoelectronics Engineering
University of Chinese Academy of Sciences
Beijing 100049, P. R. China
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/smll.201804347.
DOI: 10.1002/smll.201804347
Lithium ion batteries (LIBs) are widely used storage devices,
which have a wide range of applications in electrical devices,
hybrid electric vehicles, and for harvesting of renewable
energy.
[1]
However, increasing demands for high-performance
energy storage are unlikely to be satisfied by the theoretical
capacities of the LIBs.
[2]
In particular, alternative cathode mate-
rials are required.
[3]
Recently, lithium–sulfur (Li–S) batteries
have received attention owing to their high theoretical specific
Carbon materials have received considerable attention as host cathode
materials for sulfur in lithium–sulfur batteries; N-doped carbon materials
show particularly high electrocatalytic activity. Efforts are made to synthesize
N-doped carbon materials by introducing nitrogen-rich sources followed by
sintering or hydrothermal processes. In the present work, an in situ hollow
cathode discharge plasma treatment method is used to prepare 3D porous
frameworks based on N-doped graphene as a potential conductive matrix
material. The resulting N-doped graphene is used to prepare a 3D porous
framework with a S content of 90 wt% as a cathode in lithium–sulfur cells,
which delivers a specific discharge capacity of 1186 mAh g
−1
at 0.1 C, a
coulombic efficiency of 96% after 200 cycles, and a capacity retention of
578 mAh g
−1
at 1.0 C after 1000 cycles. The performance is attributed to the
flexible 3D structure and clustering of pyridinic N-dopants in graphene. The
N-doped graphene shows high electrochemical performance and the flexible
3D porous stable structure accommodates the considerable volume change
of the active material during lithium insertion and extraction processes,
improving the long-term electrochemical performance.
Lithium–Sulfur Batteries
capacity and energy (2600 Wh kg
−1
).
[4]
However, applications of Li–S batteries
suffer from multiple drawbacks, such as
poor electrical conductivity of the active
layer, large volume changes of the sulfur,
and the high solubility of lithium poly-
sulfide intermediates (Li
2
S
n
, 2 < n ≤ 8)
in organic electrolytes during charge/dis-
charge processes, leading to the shuttle
effect.
[5]
To overcome these issues and improve
the electrical conductivity of electrodes,
the element sulfur is often trapped in
electrically conductive host materials,
which limits dissolution of lithium sulfide
intermediates.
[6]
Typical hosts include
conducting metals, metal oxides, covalent
organic frameworks, polymers, and hybrid
carbon hosts.
[7]
Among carbon matrices,
hierarchically porous carbon, micro/
mesoporous carbon, carbon nanotubes,
and graphene are also considered to be
effective conductive frameworks for trap-
ping soluble polysulfides. Furthermore, carbon matrices with
a pore structure provide pathways for ion migration, improve
the reaction kinetics, and accommodate expansion.
[8]
Recently,
a freestanding porous interconnected 3D network based on
sulfur-graphene composites has been reported for lithium–
sulfur battery applications.
[9]
In particular, N-doped carbon
materials suppress the shuttle effect of lithium polysulfide
intermediates.
[10]
Nitrogen-doped graphene is a conductive
matrix material, which has excellent cycle life performance
[11]
and promotes effective anchoring of soluble Li polysulfides.
[12]
The binding energy (E
b
) of N-doped graphene with lithium
polysulfides has been calculated to be much greater than that
of pristine graphene with lithium polysulfides by density func-
tional theory.
[13]
However, there are no universal guidelines
that enable control over the morphology of N-doped graphene
with hybrid 3D structures as the host material. Additionally,
the mechanism for the formation of 3D N-doped graphene
for cathode materials and its morphological changes during
charging and discharging processes have yet to be reported on.
Herein, we prepared 3D N-doped graphene porous frame-
works (rNGO) through a novel method, namely, freeze-drying
followed by hollow cathode discharge (HCD) plasma discharge
in an Ar and N
2
flow (Figure 1). The HCD plasma treatment
is an efficient and environmentally friendly way of forming
a nanostructured surface, enabling plasma coating of many
kinds of materials (e.g., metals, glass, and composites). Such
Small 2019, 1804347