F-doped carbon layer coating is an effective surface
modification
method to enhance the intrinsic conductivity of active materials and
facilitate the accommodation of solvated Li+ ions near
the carbon surface. Furthermore, it induces the formation of an effective
LiF-rich solid electrolyte interface with high electrochemical stability
and facile surface diffusion of Li+ ion owing to its low
energy barrier. Therefore, by employing a cost-effective coating material
poly(vinylidene fluoride) (PVDF), high electrochemical performance
in rate capability, cyclability, and energy/power density can be easily
achieved without using expensive materials. A uniform and thin coating
of an F-doped amorphous carbon layer was fabricated on the natural
graphite (NG) surface using 1 wt % of PVDF (NG-F1), followed by a
carbonization step. This process resulted in a high energy density
of 59.8 Wh kg–1 at a current density of 5.0 A g–1 (100C) in a full cell configuration for lithium-ion
capacitors (LICs). In comparison, the pristine NG demonstrated an
energy density of 47.3 Wh kg–1. Furthermore, this
LIC full cell with NG-F1 showed a lower charge-transfer resistance
and a higher capacity retention of 99.4% than pristine NG, even after
500 charge–discharge cycles at 3C.
Mixed transition metal oxides are promising anodes to meet high‐performance energy storage materials; however, their widespread uses are restrained owing to limited theoretical capacity, restricted synthesis methods and templates, low conductivity, and extreme volume expansion. Here, Mn3‐xFexO4 nanosheets with interconnected conductive networks are synthesized via a novel self‐hybridization approach of a facile, galvanic replacement‐derived, tetraethyl orthosilicate‐assisted hydrothermal process. An exceptionally high reversible capacity of 1492.9 mAh g−1 at 0.1 A g−1 is achieved by producing Li‐rich phase through combined synergistic effects of amorphous phases with interface modification design for fully utilizing highly spin‐polarized surface capacitance. Furthermore, it is demonstrated that large surface area can effectively facilitate Li‐ion kinetics, and the formation of interconnected conductive networks improves the electrical conductivity and structural stability by alleviating volume expansion. This leads to a high rate capability of 412.3 mAh g−1 even at an extremely high current density of 10 A g−1 and stable cyclic stability with a capacity up to 921.9 mAh g−1 at 2 A g−1 after 500 cycles. This study can help to overcome theoretically limited electrochemical properties of conventional metal oxide materials, providing a new insight into the rational design with surface alteration to boost Li‐ion storage capacity.
Nowadays, thickness optimization
of an electrode is considered
an effective approach to achieve a high energy density or high areal
capacity of Li-ion batteries. In this paper, we report a simple electrospinning
technique to develop free-standing sheet bundles of lithium titanium
oxide (LTO) nanowires with a readily controlled thickness of electrodes.
The LTO nanowire sheet bundles (LNSBs) can show a very high areal
capacity as an anode due to its microscale layer-by-layer configuration
in which the nanoscale LTO nanowires are networked in each microscale
layer. Such unique structures with interspaces formed between the
multiple stacked sheet layers should promote electrolytes to efficiently
penetrate through the thick electrode layer. Nanoscale wire assemblies
can also increase the transfer rates of ions and electrons during
the lithiation/delithiation processes. Consequently, the fabricated
LNSB electrode delivers an ultrahigh areal capacity of up to ca. 14.2
mA h cm–2 for the first cycle and ca. 6.5 mA h cm–2 for the 500th cycle at 0.2C rate current density,
which is a much larger areal capacity than the commercial graphite
anode (ca. 3.5 mA h cm–2). Such a high areal discharge
capacity on a novel free-standing electrode design could provide an
idea for advanced energy storage applications.
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