Electrochemical kinetics of nanostructure LiFePO 4 /graphitic carbon electrodes

Abstract

a b s t r a c tLithium cation insertion/deinsertion reaction kinetics in a LiFePO 4 (LFP)/graphitic carbon composite material were electrochemically studied with a cavity microelectrode (CME). The LFP/graphitic carbon composite has a core LFP (crystalline/amorphous)/graphitic carbon shell structure. In the crystalline and amorphous LFP phase, different reaction mechanisms were observed and characterized. While the reaction mechanism in the crystalline LFP phase is controlled by Li + diffusion, the amorphous LFP phase shows a fast, surface-controlled, pseudocapacitive charge-storage mechanism. This pseudocapacitive behavior is extrinsic in origin since it comes from the presence of Fe 3+ defects in the structure. These features explain the ultrafast performance of the material which offers interesting opportunities as a positive electrode for assembling high power and high energy hybrid supercapacitors.

Immobilization of Polyiodide Redox Species in Porous Carbon for Battery-Like Electrodes in Eco-Friendly Hybrid Electrochemical Capacitors

“…Besides, the upshift of D- and G-bands indicated a charge transfer between the carbon host and the iodide species [23]. From the foregoing, it is clear that activated carbon can not only be used for storage charge at the EDL just like other reported materials [39,40,41], but it can also be used to design battery-like electrodes, similar to some of the previously reported materials [42,43,44,45,46,47].…”

Noncrystalline Nanocomposites as a Remedy for the Low Diffusivity of Multivalent Ions in Battery Cathodes

“…Therefore, smooth diffusion pathways through the solid are created, allowing even strongly interacting divalent magnesium ions to move through the solid phase. Our previous report demonstrated that the redox reaction in noncrystalline components exhibits no diffusion limitation within a large potential scan rate range . Here, the UC process results in nano-FePO 4 particles with a noncrystalline structure embedded in graphitic carbon, which provides an efficient environment for reversible electrochemical insertion and deinsertion of magnesium ions.…”

“…Our previous report demonstrated that the redox reaction in noncrystalline components exhibits no diffusion limitation within a large potential scan rate range. 50 Here, the UC process results in nano-FePO 4 particles with a noncrystalline structure embedded in graphitic carbon, which provides an efficient environment for reversible electrochemical insertion and deinsertion of magnesium ions. However, as shown in Figure 3a, the large hysteresis is still observed for magnesium charge−discharge, where the potential change at the beginning of the charging (magnesium deinsertion process) is obvious.…”

Recent Advances in Supercapacitors: Ultrafast Materials Make Innovations

“…Such nanocrystal composites can store and deliver energy at the highest rate attained to this date. In the following sections, we show two additional examples of uc-treated materials, Li 3 VO 4 (LVO) 8,10 and LiFePO 4 (LFP) 11,12 as negative and positive electrode materials for the SRC, respectively. We successfully transformed these two materials with typical battery characteristics into pseudocapacitive/ ultrafast materials via ultracentrifugation.…”

“…4c-d). 12 The electrochemical analysis shows two different behaviors and kinetic regimes in the core LFP (amorphous and crystalline). A surface charge storage pseudocapacitive mechanism drives the kinetics in the amorphous LFP phase containing Fe 3+ defects, while the Li + intercalation in the core crystalline LFP phase is a diffusion-limited process at a high scan rate (>120 mV s ¹1 ).…”