Probing Lithiation Kinetics of Carbon-Coated ZnFe₂O₄ Nanoparticle Battery Anodes

Abstract

The investigation of the lithiation−delithiation kinetics of anodes comprising carbon-coated ZnFe 2 O 4 nanoparticles is reported in here. The study confirmed that, as occurring with other conversion electrodes, lithiation of ZnFe 2 O 4 nanoparticles is a multistep process involving the presence of intermediate Li−Zn−Fe−O phases as precursors for the formation of amorphous Li 2 O. A detailed knowledge on the reaction kinetics of the involved electrochemical mechanisms has been achieved by using impedance spectroscopy. It has been observed that lithiation reactions introduce a long delay that limits the electrode charging, not related to diffusion mechanisms. The sloping curve following the conversion plateau of the galvanostatic discharge is connected to a retardation effect in the reaction kinetics. This limitation is seen as an additional resistive process originated by the specific lithiation microscopic features. It is concluded that capacitance spectra allow distinguishing two separate processes: formation of kinetically favored intermediate Li−Zn−Fe−O phases and subsequent reaction to produce highly dispersed LiZn and Fe 0 in an amorphous Li 2 O matrix. A detailed electrical model is provided accounting for the overall electrode lithiation process. ■ INTRODUCTIONLi-ion batteries have become core devices for the consumer electronics industry. Materials for commercial battery electrodes are mostly chosen from a set of intercalation compounds that reversibly accommodate lithium ions in host sites in the lattice without severely distorting the structure. In most transition metal compounds such as LiCoO 2 , LiNi 1−y−z Mn y Co z O 2 , LiFePO 4 , and Li 4 Ti 5 O 12, redox activity is restricted to a few exchanged electrons. Therefore, intercalation materials exhibit intrinsic limitations that make them unviable when high capacity requirements have to be fulfilled as in the case of large scale or automotive applications.1−3 During the past decades a new family of electrode materials operating under the so-called conversion reaction has been intensely studied.4 For these compounds lithiation occurs through the reaction that involves a complete metal reduction as M a X b + (bn)Li ↔ aM + bLi n X, where M = transition metal, X = anion (O, S, N, P, and F), and n = anion formal oxidation state. Conversion reaction is able to accommodate larger amount of Li atoms into the lithium binary compound Li n X, which explains specific capacities exceeding 1000 mAh g −1 as reported for many compounds. Interestingly, conversion materials usually show good reversibility because of the formation of a nanostructured matrix that comprises metallic nanoparticles surrounded by amorphous Li n X phases. Intimate phase contact facilitates reactivity as evidenced by the observation of remaining metallic nanoparticles after extended oxidation/ reduction cycling. 4 Despite their potentialities, conversion compounds present a series of performance limitations that hinders their straightforward application in commercial devices. There...

Facile kinetics of Li-ion intake causes superior rate capability in multiwalled carbon nanotube@TiO2 nanocomposite battery anodes

“…In this study, MWCNT were included as a blank and to support the discussion derived from these results. case Li x TiO 2 [12,13]. It is worth mentioning that for TiO 2 at high voltage for charging and discharging, the charge transfer resistance is so high that it does not allow detecting other processes in the frequency range employed in the characterization as observed in Fig.…”

“…Recently, we have proposed a model to study the lithiation kinetic through equivalent circuit analysis of the experimentally obtained electrochemical impedance spectroscopy (EIS) spectra [12,13]. This approach facilitates the extraction of resistances involved in the overall lithium ion storage, as well as the insertion-extraction process occurring during the cycling of the battery.…”

SEI Growth and Depth Profiling on ZFO Electrodes by Soft X‐Ray Absorption Spectroscopy

“…As a consequence Fe, LiZn, Li 2 O are formed upon lithiation, which are fi nely dispersed into a carbonaceous matrix, [ 7 ] according to a reversible reaction involving nine lithium ions per formula unit of ZFO and resulting in a capacity of ≈1000 mAh g −1 . [ 7 ] While the lithiation kinetics have already been probed by electrochemical impedance spectroscopy (EIS) and X-ray diffraction (XRD) analysis, [ 5,7 ] very little is known about the evolution of passivation layer properties on ZFO-C.The aim of this work is to study the evolution of the SEI in this innovative anode material at selected charging steps by exploiting the surface sensitivity [10][11][12] of the soft X-ray absorption spectroscopy (XAS). This technique requires synchrotron radiation and was never used before for such a purpose, although it appears to be very suitable for a detailed depth profi ling of the SEI of advanced electrodes.…”

“…As a consequence Fe, LiZn, Li 2 O are formed upon lithiation, which are fi nely dispersed into a carbonaceous matrix, [ 7 ] according to a reversible reaction involving nine lithium ions per formula unit of ZFO and resulting in a capacity of ≈1000 mAh g −1 . [ 7 ] While the lithiation kinetics have already been probed by electrochemical impedance spectroscopy (EIS) and X-ray diffraction (XRD) analysis, [ 5,7 ] very little is known about the evolution of passivation layer properties on ZFO-C.…”

LiFePO 4 particle conductive composite strategies for improving cathode rate capability

“…Recently, we have proposed a model to study the lithiation/delithiation kinetics through equivalent circuit analysis of the experimentally obtained electrochemical impedance spectroscopy (EIS) spectra 22,23 . This approach facilitates the extraction of resistances involved in the overall lithium ion storage that allows establishing mechanisms for rate capability reduction, as well as the insertion-extraction process occurring during the battery cycling.…”