Irin Sultana

High capacity potassium-ion battery anodes based on black phosphorus

Potassium-ion batteries are a new class of high voltage electrochemical energy storage cells that may potentially complement or replace lithium-ion batteries in many applications. Graphite is considered as a prospective anode material for these batteries but its demonstrated capacity is only 270 mA h g−1. This manuscript studies a novel type of nanocomposite anodes based on black phosphorus as their main active component, with a much higher capacity in potassium-ion batteries. These anode materials are able to deliver a first cycle capacity as high as 617 mA h g−1, more than twice the capacity of graphite in potassium cells. Quick depotassiation is achievable in the electrodes under certain conditions. Based on the data of X-ray diffraction analysis, it is proposed that black phosphorus operates via an alloying–dealloying mechanism with potassium and the end product of the electrochemical transformation is a KP alloy (implying a theoretical capacity of 843 mA h g−1 for phosphorus in potassium cells). This work emphasizes the feasibility of potassium-ion battery anode materials with high gravimetric capacities, comparable with those of high capacity anode materials for lithium-ion and sodium-ion batteries.

Self-assembled V2O5 interconnected microspheres produced in a fish-water electrolyte medium as a high-performance lithium-ion-battery cathode

Interconnected microspheres of V2O5 composed of ultra-long nanobelts are synthesized in an environmental friendly way by adopting a conventional anodization process combined with annealing. The synthesis process is simple and low-cost because it does not require any additional chemicals or reagents. Commercial fish-water is used as an electrolyte medium to anodize vanadium foil for the first time. Electron microscopy investigation reveals that each belt consists of numerous nanofibers with free space between them. Therefore, this novel nanostructure demonstrates many outstanding features during electrochemical operation. This structure prevents self-aggregation of active materials and fully utilizes the advantage of active materials by maintaining a large effective contact area between active materials, conductive additives, and electrolyte, which is a key challenge for most nanomaterials. The electrodes exhibit promising electrochemical performance with a stable discharge capacity of 227 mAh·g–1 at 1C after 200 cycles. The rate capability of the electrode is outstanding, and the obtained capacity is as high as 278 at 0.5C, 259 at 1C, 240 at 2C, 206 at 5C, and 166 mAh·g–1 at 10C. Overall, this novel structure could be one of the most favorable nanostructures of vanadium oxide-based cathodes for Li-ion batteries.

Understanding Structure-Function Relationship in Hybrid Co3O4-Fe2O3/C Lithium-Ion Battery Electrodes.

A range of high-capacity Li-ion anode materials (conversion reactions with lithium) suffer from poor cycling stability and limited high-rate performance. These issues can be addressed through hybridization of multiple nanostructured components in an electrode. Using a Co3O4-Fe2O3/C system as an example, we demonstrate that the cycling stability and rate performance are improved in a hybrid electrode. The hybrid Co3O4-Fe2O3/C electrode exhibits long-term cycling stability (300 cycles) at a moderate current rate with a retained capacity of approximately 700 mAh g(-1). The reversible capacity of the Co3O4-Fe2O3/C electrode is still about 400 mAh g(-1) (above the theoretical capacity of graphite) at a high current rate of ca. 3 A g(-1), whereas Co3O4-Fe2O3, Fe2O3/C, and Co3O4/C electrodes (used as controls) are unable to operate as effectively under identical testing conditions. To understand the structure-function relationship in the hybrid electrode and the reasons for the enhanced cycling stability, we employed a combination of ex situ and in situ techniques. Our results indicate that the improvements in the hybrid electrode originate from the combination of sequential electrochemical activity of the transition metal oxides with an enhanced electronic conductivity provided by percolating carbon chains.

Lithium Germanate (Li2GeO3): A High-Performance Anode Material for Lithium-Ion Batteries

A simple, cost-effective, and easily scalable molten salt method for the preparation of Li2 GeO3 as a new type of high-performance anode for lithium-ion batteries is reported. The Li2 GeO3 exhibits a unique porous architecture consisting of micrometer-sized clusters (secondary particles) composed of numerous nanoparticles (primary particles) and can be used directly without further carbon coating which is a common exercise for most electrode materials. The new anode displays superior cycling stability with a retained charge capacity of 725 mAh g-1 after 300 cycles at 50 mA g-1 . The electrode also offers excellent rate capability with a capacity recovery of 810 mAh g-1 (94 % retention) after 35 cycles of ascending steps of current in the range of 25-800 mA g-1 and finally back to 25 mA g-1 . This work emphasizes the importance of exploring new electrode materials without carbon coating as carbon-coated materials demonstrate several drawbacks in full devices. Therefore, this study provides a method and a new type of anode with high reversibility and long cycle stability.