Ge Ji

Layered SnS2‐Reduced Graphene Oxide Composite – A High‐Capacity, High‐Rate, and Long‐Cycle Life Sodium‐Ion Battery Anode Material

Author(s): Qu, Baihua; Ma, Chuze; Ji, Ge; Xu, Chaohe; Xu, Jing; Meng, Ying Shirley; Wang, Taihong; Lee, Jim Yang | Abstract: A layered SnS2-reduced graphene oxide (SnS2-RGO) composite is prepared by a facile hydrothermal route and evaluated as an anode material for sodium-ion batteries (NIBs). The measured electrochemical properties are a high charge specific capacity (630 mAh g-1 at 0.2 A g-1) coupled to a good rate performance (544 mAh g-1 at 2 A g-1) and long cycle-life (500 mAh g-1 at 1 A g -1 for 400 cycles).

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

Graphene-encapsulated ordered aggregates of Fe(3)O(4) 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 Fe(3)O(4) nanoparticles electrically. The structure and morphology of the graphene-Fe(3)O(4) 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-Fe(3)O(4) 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.

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 (Ti(3+)) 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.

Nitrogen-doped carbon-encapsulation of Fe3O4 for increased reversibility in Li+ storage by the conversion reaction

One great challenge in designing anode materials for lithium-ion batteries is to satisfy the concurrent requirements for good capacity retention, high rate performance and low first cycle losses. We report here the design and synthesis of a nitrogen-doped carbon encapsulated Fe3O4 composite which performed very well in all these areas. The composite with the optimized carbon content not only showed a high reversible capacity of ∼850 mA h g−1 for 50 cycles at 100 mA g−1, but was also able to maintain a stable cycling performance at a twenty-fold increase in current density to 2000 mA g−1. More importantly, the composite significantly lowered the irreversible capacity loss in the first cycle compared with other iron oxide anodes reported in the literature. Characterization of the electrode/electrolyte interface indicated the presence of a protective solid electrolyte interface (SEI) layer in which chemically stable LiF and FeF3 were the major constituents. Thus, it is believed that the N-doped carbon coating had effectively modified the surface chemistry at the anode/electrolyte interface to increase the columbic efficiency of cycling and to reduce the secondary reactions in the first cycle of use.

In situ nitrogenated graphene–few-layer WS2 composites for fast and reversible Li+ storage

Two-dimensional nanosheets can leverage on their open architecture to support facile insertion and removal of Li(+) as lithium-ion battery electrode materials. In this study, two two-dimensional nanosheets with complementary functions, namely nitrogen-doped graphene and few-layer WS2, were integrated via a facile surfactant-assisted synthesis under hydrothermal conditions. The layer structure and morphology of the composites were confirmed by X-ray diffraction, scanning electron microscopy and high-resolution transmission microscopy. The effects of surfactant amount on the WS2 layer number were investigated and the performance of the layered composites as high energy density lithium-ion battery anodes was evaluated. The composite formed with a surfactant : tungsten precursor ratio of 1 : 1 delivered the best cyclability (average of only 0.08% capacity fade per cycle for 100 cycles) and good rate performance (80% capacity retention with a 50-fold increase in current density from 100 mA g(-1) to 5000 mA g(-1)), and may find uses in power-oriented applications.

Fe‐Doped MnxOy with Hierarchical Porosity as a High‐Performance Lithium‐ion Battery Anode

Fe-doped Mnx Oy with hierarchical porosity is prepared from a nanocasting technique using amine-functionalized bromomethylated poly (2,6-dimethyl-1,4-phenylene oxide) (BPPO) membranes as the sacrificial template. The synergistic coupling of a percolating macroporous network, uniformly distributed mesopores, and optimal iron doping is used to improve the electronic and ionic wirings of manganese oxides for Li(+) storage via the conversion reaction. Very impressive Li(+) storage capabilities are shown.

Facile solvothermal synthesis of anatase TiO2 microspheres with adjustable mesoporosity for the reversible storage of lithium ions

TiO2 microspheres with different morphologies and microstructures were synthesized by a facile solvothermal process. One of the mesoporous microspheres among the synthesized products exhibited high reversible capacity, good rate capability and long cycle life as an anode material for lithium ion batteries. The good electrochemical performance for Li+ storage could be attributed to the synergy of coupling ultra-fine anatase nanocrystallites (6–8 nm) to a uniform distribution of mesopores (pore size of 4–8 nm), leading to concurrent improvements in charge transfer kinetics and the transport of lithium ions and electrons in the material.

Synthesis of mixed-conducting carbon coated porous γ-Fe2O3 microparticles and their properties for reversible lithium ion storage

Disk-like α-Fe2O3 microparticles were synthesized by a facile hydrothermal method and transformed into iron oxide/carbon composites by chemical vapor deposition in an acetylene atmosphere. Through careful control of the reaction time, carbon-coated porous γ-Fe2O3 microparticles with reversible Li+ storage properties were produced. The measured specific capacity after 40 cycles of charge and discharge was in excess of 900 mA h g−1 and rate capability was very good up to a current density of 2000 mA g−1. The good performance in Li+ storage could be attributed to the combination of porosity and a uniform nanocarbon coating which provided mixed-conducting properties for the fast diffusion of both lithium ions and electrons.

Mitigating the initial capacity loss (ICL) problem in high-capacity lithium ion battery anode materials

For lithium ion batteries, some non-carbonaceous anode materials have shown the possibility of increasing the capacity of current anode materials (which are almost universally carbon) by two to ten folds. One of the greatest challenges in the acceptance of these high capacity anode materials is their high initial capacity loss (ICL) problem. A large ICL is undesirable in practice because it consumes, irreversibly, a large amount of lithium ions from the more expensive cathode material. This perspective article will review the current progresses in the research on ICL especially the likely mitigation methods.

High-Performance Lithium-Ion Cathode LiMn0.7Fe0.3PO4/C and the Mechanism of Performance Enhancements through Fe Substitution

LiMn1-xFexPO4/C (x = 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 LiMn0.7Fe0.3PO4/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.