Dr. Tadhg Kennedy

Research Interests

There is an ever-growing demand for rechargeable batteries with reversible and efficient electrochemical energy storage and conversion. Lithium-ion batteries are by far the most popular on the market today and during the past three decades there has been great interest in developing active materials with improved electrochemical performance, particularly in alternatives to the graphite anode which has a relatively low maximum theoretical specific capacity of 372 mAh/g. Silicon and germanium based anodes are promising replacement candidates as they exhibit capacities that are multiples of graphite due to their ability to form lithium-rich alloys during charging. However, the formation of these high-capacity lithiated alloys, Li15Si4 (3579 mAh/g) and Li15Ge4 (1384 mAh/g), leads to considerable expansion of bulk Si and Ge electrodes (> 300%) which causes pulverisation of the material and loss of contact with the current collector, ultimately limiting the cycle life of Li-alloying anodes. By employing nanoscale materials this issue can be circumvented as the nano-dimensions can accommodate the large volume change without fracture, leading to a longer cycle life for the electrode.

My research involves the development of Si and Ge nanowire based electrodes as high-capacity anodes for next-generation Li-ion batteries. The unique morphology is well suited for lithium-ion battery applications as nanowires provide good electrical conductivity along their length, have a high interfacial area in contact with the electrolyte, have an optimal short diffusion distance for Li-ion transport, and can be grown directly from current collectors, eliminating the need for binders and conductive additives. These nanowire anodes have long cycle lives comparable to conventional graphitic anodes while delivering over three times the capacity over extended cycles. In particular in my research I look at:

· Development of rapid synthetic methods for substrate grown nanowires

· Identification of Li active catalyst materials for nanowire growth

· Electrochemical characterisation of Si and Ge nanowire electrodes

· Analysis of the effect of cycling on nanowire integrity and morphology

· Electrolyte development and characterisation