As an essential member of 2D materials, MXene (e.g., Ti3C2Tx) is highly preferred for energy storage owing to a high surface‐to‐volume ratio, shortened ion diffusion pathway, superior electronic conductivity, and neglectable volume change, which are beneficial for electrochemical kinetics. However, the low theoretical capacitance and restacking issues of MXene severely limit its practical application in lithium‐ion batteries (LIBs). Herein, a facile and controllable method is developed to engineer 2D nanosheets of negatively charged MXene and positively charged layered double hydroxides derived from ZIF‐67 polyhedrons into 3D hollow frameworks via electrostatic self‐assembling. After thermal annealing, transition metal oxides (TMOs)@MXene (CoO/Co2Mo3O8@MXene) hollow frameworks are obtained and used as anode materials for LIBs. CoO/Co2Mo3O8 nanosheets prevent MXene from aggregation and contribute remarkable lithium storage capacity, while MXene nanosheets provide a 3D conductive network and mechanical robustness to facilitate rapid charge transfer at the interface, and accommodate the volume expansion of the internal CoO/Co2Mo3O8. Such hollow frameworks present a high reversible capacity of 947.4 mAh g−1 at 0.1 A g−1, an impressive rate behavior with 435.8 mAh g−1 retained at 5 A g−1, and good stability over 1200 cycles (545 mAh g−1 at 2 A g−1).
Transition metal dichalcogenides
(TMDs), particularly molybdenum
diselenides (MoSe2), have the merits of their unique two-dimensional
(2D) layered structures, large interlayer spacing (∼0.64 nm),
good electrical conductivities, and high theoretical capacities when
applied in lithium-ion batteries (LIBs) as anode materials. However,
MoSe2 remains suffering from inferior stability as well
as unsatisfactory rate capability because of the unavoidable volume
expansion and sluggish charge transport during lithiation-delithiation
cycles. Herein, we develop a simultaneous reduction-intercalation
strategy to synthesize expanded MoSe2 (e-MoSe2) with an interlayer spacing of 0.98 nm and a rich 1T phase (53.7%)
by rationally selecting the safe precursors of ethylenediamine (NH2C2H4NH2), selenium dioxide
(SeO2), and sodium molybdate (Na2MoO4). It is noteworthy that NH2C2H4NH2 can effectively reduce SeO2 and MoO4
2– forming MoSe2 nanosheets;
in the meantime, the generated ammonium (NH4
+) efficiently intercalates between MoSe2 layers, leading
to charge transfer, thus stabilizing 1T phases. The obtained e-MoSe2 exhibits high capacities of 778.99 and 611.40 mAh g–1 at 0.2 and 1 C, respectively, together with excellent cycling stability
(retaining >90% initial capacity at 0.2 C over 100 charge–discharge
cycles). It is believed that the material design strategy proposed
in this paper provides a favorable reference for the synthesis of
other transition metal selenides with improved electrochemical performance
for battery applications.
Designing a thick electrode with
appropriate mass loading is a
prerequisite toward practical applications for lithium ion batteries
(LIBs) yet suffers severe limitations of slow electron/ion transport,
unavoidable volume expansion, and the involvement of inactive additives,
which lead to compromised output capacity, poor rate perforamnce,
and cycling instability. Herein, self-supported thick electrode composed
of vertically aligned two-dimensional (2D) heterostructures (V-MXene/V2O5) of rigid Ti3C2TX MXene and pliable vanadium pentoxide are assembled via an ice crystallization-induced strategy. The vertical channels prompt
fast electron/ion transport within the entire electrode; in the meantime,
the 3D MXene scaffold provides mechanical robustness during lithiation/delithiation.
The optimized electrodes with 1 and 5 mg cm–2 of
V-MXene/V2O5 respectively deliver 472 and 300
mAh g–1 at a current density of 0.2 A g–1, rate performance with 380 and 222 mAh g–1 retained
at 5 A g–1, and reliability over 800 charge/discharge
cycles.
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