Jialiang Tang

Pushing the theoretical capacity limits of iron oxide anodes: capacity rise of γ-Fe2O3 nanoparticles in lithium-ion batteries

Nanoparticles (NPs) of γ-Fe2O3 are successfully prepared via facile hydrolysis of a complex iron iodide precursor with subsequent oxidation under mild conditions. When evaluated as an anode material in lithium ion half-cells, electrodes made with γ-Fe2O3 NPs exhibit excellent rate capabilities with high capacities and good coulombic efficiencies. Electrodes of γ-Fe2O3 NPs initially deliver capacities of 1100 mA h g−1 at 100 mA g−1 current density and 980 mA h g−1 at 1000 mA g−1. Following an activation step of the electrodes, the capacities increase by up to ∼300 mA h g−1 while coulombic efficiencies also improve slightly. At a high current density of 4000 mA g−1, a stable capacity of 770 mA h g−1 is achieved. In this study, dQ/dv plots are employed to graphically illustrate the capacity breakdown of each cycle into intercalation, conversion, and extra capacity regions. Upon prolonged cycling, the extra capacity region expands to yield higher capacities; this phenomenon has been attributed to both pulverization-induced particle size reduction and high-rate lithiation-induced activation processes. This study concludes that γ-Fe2O3 NPs could serve as a promising anode material with comparable results to widely studied α-Fe2O3 and Fe3O4 NPs.

From Allergens to Battery Anodes: Nature-Inspired, Pollen Derived Carbon Architectures for Room- and Elevated-Temperature Li-ion Storage.

The conversion of allergic pollen grains into carbon microstructures was carried out through a facile, one-step, solid-state pyrolysis process in an inert atmosphere. The as-prepared carbonaceous particles were further air activated at 300 °C and then evaluated as lithium ion battery anodes at room (25 °C) and elevated (50 °C) temperatures. The distinct morphologies of bee pollens and cattail pollens are resembled on the final architecture of produced carbons. Scanning Electron Microscopy images shows that activated bee pollen carbon (ABP) is comprised of spiky, brain-like, and tiny spheres; while activated cattail pollen carbon (ACP) resembles deflated spheres. Structural analysis through X-ray diffraction and Raman spectroscopy confirmed their amorphous nature. X-ray photoelectron spectroscopy analysis of ABP and ACP confirmed that both samples contain high levels of oxygen and small amount of nitrogen contents. At C/10 rate, ACP electrode delivered high specific lithium storage reversible capacities (590 mAh/g at 50 °C and 382 mAh/g at 25 °C) and also exhibited excellent high rate capabilities. Through electrochemical impedance spectroscopy studies, improved performance of ACP is attributed to its lower charge transfer resistance than ABP. Current studies demonstrate that morphologically distinct renewable pollens could produce carbon architectures for anode applications in energy storage devices.

In situ sonochemical synthesis of luminescent Sn@C-dots and a hybrid Sn@C-dots@Sn anode for lithium-ion batteries

A facile sonochemical approach is employed for the in situ formation of C-dots via ultrasonic irradiation of polyethylene glycol (PEG) solvent and its decomposition. Metallic bulk tin was added to the reaction vessel and heated to its melting point (234 °C) in the presence of polyethylene glycol 400. The two-phase mixture was sonicated to yield Sn@C-dots and subsequently to achieve Sn nanoparticles decorated with Sn@C-dots (Sn@C-dots@Sn). The fluorescence (luminescence) properties of Sn@C-dots are different from those of the C-dots alone and change as a function of excitation wavelength. The as-synthesized Sn@C-dots@Sn nanoparticles were directly deposited on the copper foil current collector as a promising anode for Li-ion batteries. Encouraging lithiation and delithiation properties are obtained with high coulombic efficiency and enhanced rate capabilities for the hybrid Sn@C-dots@Sn nanoparticles, owing to the conducting carbon dot network on the tin nanoparticles minimizing pulverization effects. Methodical studies on morphology (SEM, TEM), structure (XRD, HR-TEM) and compositions (XPS, EDS) are carried out on the Sn@C-dots and electroactive Sn@C-dots@Sn nanoparticles to understand the reaction mechanism and their luminescence and battery anode properties.

Cobalt Nanoparticles Chemically Bonded to Porous Carbon Nanosheets: A Stable High-Capacity Anode for Fast-Charging Lithium-Ion Batteries

A two-dimensional electrode architecture of ∼25 nm sized Co nanoparticles chemically bonded to ∼100 nm thick amorphous porous carbon nanosheets (Co@PCNS) through interfacial Co-C bonds is reported for the first time. This unique 2D hybrid architecture incorporating multiple Li-ion storage mechanisms exhibited outstanding specific capacity, rate performance, and cycling stabilities compared to nanostructured Co3O4 electrodes and Co-based composites reported earlier. A high discharge capacity of 900 mAh/g is achieved at a charge-discharge rate of 0.1C (50 mA/g). Even at high rates of 8C (4 A/g) and 16C (8 A/g), Co@PCNS demonstrated specific capacities of 620 and 510 mAh/g, respectively. Integrity of interfacial Co-C bonds, Co nanoparticles, and 90% of the initial capacity are preserved after 1000 charge-discharge cycles. Implementation of Co nanoparticles instead of Co3O4 restricted Li2O formation during the charge-discharge process. In situ formed Co-C bonds during the pyrolysis steps improve interfacial charge transfer, and eliminate particle agglomeration, identified as the key factors responsible for the exceptional electrochemical performance of Co@PCNS. Moreover, the nanoporous microstructure and 2D morphology of carbon nanosheets facilitate superior contact with the electrolyte solution and improved strain relaxation. This study summarizes design principles for fabricating high-performance transition-metal-based Li-ion battery hybrid anodes.