Carbon-Encapsulated F‑Doped Li₄Ti₅O₁₂ as a High Rate Anode Material for Li⁺ Batteries

TiO₂ nanoparticles aggregated into a regular ball-in-ball morphology were synthesized by hydrothermal processing and converted to carbon-encapsulated F-doped Li₄Ti₅O₁₂ (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 TiO₂ 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 (Ti³⁺) 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^–1 at the 1 C rate with negligible capacity fading for 200 cycles and an extremely high rate performance up to 140 C

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 (Li₄Ti₅O₁₂, 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⁺ 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

Graphene-Encapsulated Hollow Fe₃O₄ Nanoparticle Aggregates As a High-Performance Anode Material for Lithium Ion Batteries

Graphene-encapsulated ordered aggregates of Fe3O4 nanoparticles with nearly spherical geometry and hollow interior were synthesized by a simple self-assembly process. The open interior structure adapts well to the volume change in repetitive Li+ insertion and extraction reactions; and the encapsulating graphene connects the Fe3O4 nanoparticles electrically. The structure and morphology of the graphene-Fe3O4 composite were confirmed by X-ray diffraction, scanning electron microscopy, and high-resolution transmission microscopy. The electrochemical performance of the composite for reversible Li+ storage was evaluated by cyclic voltammetry and constant current charging and discharging. The results showed a high and nearly unvarying specific capacity for 50 cycles. Furthermore, even after 90 cycles of charge and discharge at different current densities, about 92% of the initial capacity at 100 mA g–1 was still recoverable, indicating excellent cycle stability. The graphene-Fe3O4 composite is therefore a capable Li+ host with high capacity that can be cycled at high rates with good cycle life. The unique combination of graphene encapsulation and a hollow porous structure definitely contributed to this versatile electrochemical performance

High-Performance Lithium-Ion Cathode LiMn_0.7Fe_0.3PO₄/C and the Mechanism of Performance Enhancements through Fe Substitution

LiMn_1–<i>x</i>Fe_<i>x</i>PO₄/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_0.7Fe_0.3PO₄/C delivered an excellent rate performance as a LiMnPO₄ 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⁺ 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, MoS₂, the most studied TMD, does not have adequate rate performance even in the few-layer form or after compounding with nitrogen-doped graphene (NG). WS₂, a TMD with a higher intrinsic electronic conductivity, is more suitable for high rate applications but its theoretical capacity is lower than that of MoS₂. Hence, we hypothesize that a composition-optimized composite of MoS₂, WS₂, 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 (MoS₂/WS₂)-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^–1 at 100 mA·g^–1 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^–1 to 5000 mA·g^–1)