Scalable lignin/graphite electrodes formed by mechanochemistry

Abstract

Lignin is a promising candidate for energy storage because of its abundance, wide geographic distribution, and low cost as it is mainly available as a low value product from processing of wood into paper pulp. Lignin contains large amounts of potential quinone groups, which can be oxidized and reduced in a two electron process. This redox reaction makes lignin suitable for charge storage. However, lignin is insulating and therefore conductive materials are necessary in lignin electrodes, for whom the cost of the conductive materials hinders the scalable application. Among the organic conductive materials, graphite is one of the cheapest and is easily acquired from nature. In this work, we combine graphite and lignosulfonate (LS) and fabricate LS/graphite organic electrodes under a solvent-free mechanical milling method, without additives. The graphite is sheared into small particles with a size range from 50 nm to 2000 nm. Few-layer graphene is formed during the ball milling process. The LS/graphite hybrid material electrodes with primary stoichiometry of 4/1 (w/w) gives a conductivity of 280 S m À1 and discharge capacity of 35 mA h g À1 . It is a promising material for the scalable production of LS organic electrodes.

Renewable and Scalable Energy Storage Materials Derived from Quinones in Biomass

“…[14] For thin-layer electrode, or if only the adsorbed species on the electrode contribute to the current, there is no diffusion limitation from the electroactive species and Ip is proportional to the scan rate but not to the square root of scan rate. As observed in paper I in this thesis, [17] the lignin/graphite hybrid material electrodes display a changing Ep and a growing peak separation at increasing potential scan rate, indicating the electrode redox reactions to be quasi-reversible at high scan rate; while for the humic acid/graphite hybrid material electrode in paper II, [18] Ep and the peak separation do not vary as the scan rate increases. It is due to the limited amount of redox active species confined in the electrode and the redox reactions are not limited by the diffusion process.…”

“…Though the discharge capacity and cycling stability of these electrodes are moderate, however, the low-cost original materials and facile processing method enable these electrodes to be scalable. [17] The detail about the processing methodmechanicalmillingwill be introduced in chapter 4. a: The specific capacitance of some electrodes are recalculated into discharge capacity for a better comparison; b: the increase of capacity/capacitance.…”

“…In paper I, the blackish LS/graphite mixture obtained from ball-milling is dispersed into water; however, drop-casting of this dispersion creates separate aggregates instead of homogeneous films. [17] The as-prepared dispersion is therefore centrifuged resulting in a pellet and a supernatant that are separated. The films formed from the supernatant display cracks upon drying and partly dissolve into the aqueous electrolyte (0.1 M HClO4).…”

“…On the other hand, the materials collected in pellets successfully create homogeneous films without cracks and are stable to electrolytes. [17] Usually to get a carbon paste it is essential to utilize a liquid binder, which is, however, electrically insulating and does not contribute to the charge storage. Binders can further decrease the conductivity of electrodes which is vital in our case since large fraction of lignin is favorable.…”

“…Therefore, the materials in the supernatant are discarded and that in the pellets are collected and coated onto gold substrates via an automated blade coater, creating an electrode. [17] The whole procedure of the electrodes preparation is presented in Figure 4.2.…”