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Peter Metz1 Peng Gao1 Robert Koch1 Madeleine Flint1 Scott Misture1

1, Alfred University, Alfred, New York, United States

Cyclic stability of electrochemical energy storage materials is a key challenge in the development of new electrochemical energy storage materials. This work demonstrates ex-situ and operando measurement of x-ray pair-distribution function (PDF) data from microgram quantities of electrochemically active δ-MnO2. Potassium birnessite was proton-exchanged and chemomechanically exfoliated using tetrabutylammonium hydroxide in an ultrasonic bath. Isolated nanosheets were electrostatically self-assembled and electrophoretically deposited on conductive substrates. PDFs reveals that the Mn-O coordination environment shows contracting bond lengths with increasing charge state, while electrode charging leads to a decrease in surface Frenkel defect concentration. Discharging reverses this process, creating more Mn3+ defects. Additionally, we see that interlayer water content varies with charge state: discharging the MnO2 electrode drives water from the interlayer gallery.

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