Magnetic and Transport Properties of Heat-Treated Polyparaphenylene-Based Carbons

<jats:title>ABSRACT</jats:title><jats:p>Electron spin resonance (ESR), magnetic susceptibility, and transport measurements were recently performed on a set of heat-treated polyparaphenylene (PPP)-based carbon samples, which are of significant interest as novel carbon-based anode electrodes in Li-ion batteries. Attention is focused on the evolution of the carbonaceous structures formed at low heat-treatment temperatures (<jats:italic>T</jats:italic><jats:sub><jats:italic>HT</jats:italic></jats:sub>) in the regime of 600° C ≤ <jats:italic>T</jats:italic><jats:sub><jats:italic>HT</jats:italic></jats:sub> ≤ 800° C, where percolative transport behavior is observed. At the percolation threshold, <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="gif" xlink:type="simple" xlink:href="S1946427400252871_inline1" /> the coexistence of two spin centers with peak-to-peak Lorentzian linewidths of Δ<jats:italic>H</jats:italic><jats:sub><jats:italic>pp</jats:italic></jats:sub>(300K) = 0.5 and 5.0 G is observed. The relatively high ratio of hydrogen. carbon (H/C) near <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="gif" xlink:type="simple" xlink:href="S1946427400252871_inline2" /> is believed to influence the ESR results through an unresolved hyperfine interaction. Curie-Weiss temperaures are found from measurements of [<jats:italic>I</jats:italic><jats:sub><jats:italic>pp</jats:italic></jats:sub>(Δ<jats:italic>H</jats:italic><jats:sub><jats:italic>pp</jats:italic></jats:sub>)<jats:sup>2</jats:sup>]<jats:sup>–1</jats:sup>, where <jats:italic>I</jats:italic><jats:sub><jats:italic>pp</jats:italic></jats:sub> is the peak-to-peak lineheight, yielding results that are in agreement with static susceptibility, χ(<jats:italic>T</jats:italic>), measurements. At low <jats:italic>T</jats:italic><jats:sub><jats:italic>HT</jats:italic></jats:sub>, PPP-based materials exhibit a large amount of disorder and this is evidenced by the high density of localized spins, <jats:italic>N</jats:italic><jats:sub><jats:italic>c</jats:italic></jats:sub>, which is obtained from a Curie-Weiss fit to χ(<jats:italic>T</jats:italic>) assuming a spin quantum number of <jats:italic>S</jats:italic> = ½. A model explaining the microstructure and high electrochemical doping capacity of PPP samples heat-treated to 700° C can be related to Li-ion battery performance.</jats:p>