Amy Marschilok, Stony Brook University
Progress Toward Safe Electrochemical Energy Storage Systems - The Benefits of Deliberate Materials-Focused Electrode Design and Operando Characterization
Written by Vignesh Murugadoss
Dr. Amy Marschilok initially quoted that “Anode, Cathode, and electrolyte play a crucial role in the overall safety of the electrochemical system.” She described this through a number of case studies and results from her research group that includes quantifying parasitic reactions; improving safety and power at the cathode through materials selection and electrode design; and fabricating solid-state batteries and improving safety and power at the anode through interface design. Starting from the quantification of parasitic reactions, their goal is to understand the conditions under which the system does useful work, and under which conditions the waste heat is generated from the system. Isothermal microcalorimetry coupled with fundamental electrochemistry measurement system is used to quantify the parasitic heat for Fe3O4 (insertion/conversion type) and nanocrystalline silicon (alloying type), thereby understanding the onset of side reactions which is detrimental to the capacity as well as safety of the system.
Secondly, one of the highest energy density cathode materials, carbon monofluoride, CFx (theoretical capacity = 865 mAh/g) is used in conjunction with carbon nanotubes to test the hypothesis to achieve higher rate capability power output and electrode level energy density along with a reduced inclination toward heat generation. Carbon nanotube-based electrode was effectively pulsed during pulsed intermittent discharge, whereas the aluminum foil substrate electrode was not functional. The quantitative difference measured from isothermal microcalorimetry revealed that aluminum foil generated more heat during the pulse and has a greater drop in voltage. This demonstrated that carbon nanotube-based electrodes improved rate capability higher output and reduced heat relative to the foil-based electrodes.
Thirdly, the team fabricated an all-solid-state battery using lithium iodide as the electrolyte with a lithium metal anode and iodine cathode to understand the factors governing the coulombic efficiency of the system. Impedance measured as a function of charge-discharge confirms that the impedance after charge/discharge is lower than the impedance before testing, implying an improved electrode/electrolyte interface. Furthermore, the lithium interfacial electrode system significantly increases the coulombic efficiency of the system when compared to the stainless steel and gold electrodes, which underlines the importance of the interface between the electrode and electrolyte.
Fourthly, improvement through safety and power at the anode through interface design is demonstrated by sputtering the Ni and Cu metal on graphite anode. Metal coatings reduced the Li-coating capacities by 30-40% compared to that of graphite without modifying the solid electrolyte interface chemistry. Also, the Ni-coated graphite system retained over 300 extreme fast charge cycles, which confirms the effectiveness of this approach to generate a high functioning Li-ion battery.
These examples demonstrated that materials-oriented electrode design and operando characterization contribute significantly to improve the kinetics of ion transport and safety, and bring us closer to the holy grail of concurrent high power and high energy in a safe electrochemical energy storage system.