4 research outputs found
Improving the Performance of High Capacity Li-Ion Anode Materials by Lithium Titanate Surface Coating
Current methods for improving the electrochemical performance
of
lithium-ion battery electrode materials mostly depend on materials
design and synthesis. We propose that the unique electrochemical properties
of spinel lithium titanate (Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub>, LTO) make it suitable as a protective coating to improve the performance
of high capacity anode materials. In this study, tin oxide was coated
with LTO to reduce the initial irreversible capacity loss because
of solid electrolyte interface (SEI) formation and to improve the
reversibility (capacity and rate performance) of tin oxide for Li<sup>+</sup> storage. The LTO coating was applied to porous hollow tin
oxide particles by a two-step process. Experimental measurements showed
that the LTO coating shielded most of the direct contact between tin
oxide and the electrolyte and hence the ICL due to SEI formation was
reduced to mostly that of LTO, which is much lower than tin oxide.
In addition the coated tin oxide also showed notable improvements
in material cyclability and rate performance
Carbon-Encapsulated F‑Doped Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> as a High Rate Anode Material for Li<sup>+</sup> Batteries
TiO<sub>2</sub> nanoparticles aggregated into a regular ball-in-ball morphology were synthesized by hydrothermal processing and converted to carbon-encapsulated F-doped Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> (LTO) composites (C-FLTO) by solid state lithiation at high temperatures. Through the careful control of the amount of carbon precursor (d(+)-glucose monohydrate) used in the process, LTO encapsulated with a continuous layer of nanoscale carbon was formed. The carbon encapsulation served a dual function: preserving the ball-in-ball morphology during the transformation from TiO<sub>2</sub> to LTO and decreasing the external electron transport resistance. The fluoride doping of LTO not only increased the electron conductivity of LTO through trivalent titanium (Ti<sup>3+</sup>) generation, but also increased the robustness of the structure to repeated lithiation and delithiation. The best-performing composite, C-FLTO-2, therefore delivered a very satisfying performance for a LTO anode: a high charge capacity of ∼158 mA h g<sup>–1</sup> at the 1 C rate with negligible capacity fading for 200 cycles and an extremely high rate performance up to 140 C
High-Performance Lithium-Ion Cathode LiMn<sub>0.7</sub>Fe<sub>0.3</sub>PO<sub>4</sub>/C and the Mechanism of Performance Enhancements through Fe Substitution
LiMn<sub>1–<i>x</i></sub>Fe<sub><i>x</i></sub>PO<sub>4</sub>/C (<i>x</i> = 0 and 0.3) with a uniform carbon
coating and interspersed carbon particles was prepared by a high-energy
ball-milling (HEBM)-assisted solid-state reaction. The as-synthesized
LiMn<sub>0.7</sub>Fe<sub>0.3</sub>PO<sub>4</sub>/C delivered an excellent
rate performance as a LiMnPO<sub>4</sub> class of materials. Specifically,
the specific discharge capacity was 164 mAh/g (96% of theoretical
value) at the 0.05 C rate and 107 mAh/g at the 5 C rate (1 C = 170
mA/g). Electrochemical impedance spectroscopy (EIS) and galvanostatic
intermittent titration technique (GITT) measurements indicated improvements
in the transport of electrons and Li<sup>+</sup> as well as the emergence
of a single-phase region in lithium extraction and insertion reactions
Double Transition-Metal Chalcogenide as a High-Performance Lithium-Ion Battery Anode Material
Transition-metal
dichalcogenides (TMDs) are a recent addition to
a growing list of anode materials for the next-generation lithium-ion
battery (LIB). The actual performance of TMDs is however constrained
by their limited electronic conductivity. For example, MoS<sub>2</sub>, the most studied TMD, does not have adequate rate performance even
in the few-layer form or after compounding with nitrogen-doped graphene
(NG). WS<sub>2</sub>, a TMD with a higher intrinsic electronic conductivity,
is more suitable for high rate applications but its theoretical capacity
is lower than that of MoS<sub>2</sub>. Hence, we hypothesize that
a composition-optimized composite of MoS<sub>2</sub>, WS<sub>2</sub>, and NG may provide high capacity concurrently with good rate performance.
This is a report on the design and preparation of double transition-metal
chalcogenide (MoS<sub>2</sub>/WS<sub>2</sub>)-nitrogen doped graphene
composites where the complementarity of component functions may be
maximized. For example the best sample in this study could deliver
a high discharge capacity of 1195 mAh·g<sup>–1</sup> at
100 mA·g<sup>–1</sup> concurrently with good cycle stability
(average of 0.02% capacity fade per cycle for 100 cycles) and high
rate performance (only 23% capacity reduction with a 50 fold increase
in current density from 100 mA·g<sup>–1</sup> to 5000
mA·g<sup>–1</sup>)