Thrinathreddy Ramireddy

Phosphorus–carbon nanocomposite anodes for lithium-ion and sodium-ion batteries

With the expected theoretical capacity of 2596 mA h g−1, phosphorus is considered to be the highest capacity anode material for sodium-ion batteries and one of the most attractive anode materials for lithium-ion systems. This work presents a comprehensive study of phosphorus–carbon nanocomposite anodes for both lithium-ion and sodium-ion batteries. The composite electrodes are able to display high initial capacities of approximately 1700 and 1300 mA h g−1 in lithium and sodium half-cells, respectively, when the cells are tested within a larger potential windows of 2.0–0.01 V vs. Li/Li+ and Na/Na+. The level of demonstrated capacity is underpinned by the storage mechanism, based on the transformation of phosphorus to Li3P phase for lithium cells and an incomplete transformation to Na3P phase for sodium cells. The capacity deteriorates upon cycling, which is shown to originate from disintegration of electrodes and their delamination from current collectors by post-cycling ex situ electron microscopy. Stable cyclic performance at the level of ∼700 and ∼350–400 mA h g−1 can be achieved if the potential windows are restricted to 2.0–0.67 V vs. Li/Li+ for lithium and 2–0.33 vs. Na/Na+ for sodium half-cells. The results are critically discussed in light of existing literature reports.

Stable anode performance of an Sb–carbon nanocomposite in lithium-ion batteries and the effect of ball milling mode in the course of its preparation

Materials that alloy with lithium (Si, Ge, Sn, Sb, and P) are considered as alternatives to graphitic anodes in lithium-ion batteries. Their practical use is precluded by large volume changes (200–370%) during cycling. Embedding nanoparticles into carbon is being investigated as a way to tackle that, and ball milling is emerging as a technique to prepare nanocomposites with enhanced capacity and cyclic stability. Using Sb as a model system, we investigate the preparation of Sb–carbon nanocomposites using a reconfigurable ball mill. Four distinctive milling modes are compared. The structure of the composites varies depending on the mode. Frequent strong ball impacts are required for the optimal electrochemical performance of the nanocomposite. An outstanding stable capacity of 550 mA h g−1 for 250 cycles at a current rate of 230 mA g−1 is demonstrated in a thin electrode (1 mg cm−2) and a capacity of ∼400 mA h g−1 can be retained at 1.15 A g−1. Some capacity fade is observed in a thicker electrode (2.5 mg cm−2), i.e. the performance is sensitive to mass loading. The electrochemical stability originates from the nanocomposite structure containing Sb nanoparticles (5–15 nm) dispersed in a carbon component.

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.

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.

Preparation of composite electrodes with carbon nanotubes for lithium-ion batteries by low-energy ball milling

Some of the prospective electrode materials for lithium-ion batteries are known to have electronic transport limitations preventing them from being used in the electrodes directly. In many cases, however, these materials may become practical if they are applied in the form of nanocomposites with a carbon component, e.g. via incorporating nanoparticles of the phase of interest into a conducting network of carbon nanotubes. A simple way to prepare oxide–carbon nanotube composites suitable for the electrodes of lithium-ion batteries is presented in this paper. The method is based on low-energy ball milling. An electrochemically active but insulating phase of LiFeTiO4 is used as a test material. It is demonstrated that the LiFeTiO4–carbon nanotube composite is not only capable of having significantly higher capacity (∼105–120 mA h g−1 vs. the capacity of ∼65–70 mA h g−1 for the LiFeTiO4 nanoparticles) at a slow current rate but may also operate at reasonably high current rates.