A study of the lithium intercalation into nanoparticles of LiCoO2 from an aqueous solution

Abstract

Nanoparticles of lithium cobalt oxide (LiCoO 2 ) were synthesized by means of a citrate sol-gel combustion route. The particles were characterized by scanning and transmission electron microscopies (SEM and TEM), energy-dispersive X-ray spectroscopy, and X-ray diffraction (XRD) measurements. Near spherical nanoparticles of around 100 nm were observed in SEM and TEM micrographs. XRD data indicated that the as-prepared nanoparticles presented pure phase of LiCoO 2 with R-3m symmetry. The kinetics of electrochemical intercalation of lithium into the nanoparticles were investigated by means of cyclic voltammetry (CV), chronoamperometry, and electrochemical impedance spectroscopy (EIS) with special emphasis on the application potential as cathode material for aqueous rechargeable lithium batteries. CV studies of the nanoparticles at slow scan rate of 0.1 mV s -1 between 600 and 820 mV versus Ag/AgCl, demonstrated that the nanoparticles represented well-defined reversible peaks. The nonlinear chemical diffusion of lithium into the nanoparticles was explored by EIS. In this regards, the results were discussed based on an equivalent circuit, distinguishing the kinetic properties of lithium intercalation. The kinetic parameters of lithium intercalation were obtained using the equivalent circuit, which were in good agreement with the experimental results. The changes of kinetic parameters of lithium intercalation with potential were also discussed in detail.

Collision and Oxidation of Single LiCoO2 Nanoparticles Studied by Correlated Optical Imaging and Electrochemical Recording

“…Cyclic voltammogram of ensemble LiCoO 2 NPs immobilized on a regular gold electrode exhibited a pair of current peaks at 0.44/0.41 V (vs Ag/AgCl) in the presence of 1 M LiNO 3 aqueous solution (Figure a). This result was well consistent with previous studies on the aqueous electrochemistry of LiCoO 2 . , This pair of peaks corresponded to the first-order Mott transition from metallic to insulator phase. Our previous work has shown that delithiated Li 1– x CoO 2 (oxidized form) exhibited smaller RI compared with the lithiated state LiCoO 2 (reduced form), and the RI was nearly proportional to the lithiation state (1 – x ).…”

“…This result was well consistent with previous studies on the aqueous electrochemistry of LiCoO 2 . 32,33 This pair of peaks corresponded to the first-order Mott transition from metallic to insulator phase. Our previous work has shown that delithiated Li 1−x CoO 2 (oxidized form) exhibited smaller RI compared with the lithiated state LiCoO 2 (reduced form), 26 and the RI was nearly proportional to the lithiation state (1 − x).…”

Optical Imaging of Phase Transition and Li-Ion Diffusion Kinetics of Single LiCoO2 Nanoparticles During Electrochemical Cycling

“…Three pairs of current peaks can be clearly identified, which are in good agreements with previous reports on LiCoO 2 electrochemistry. , The first peak (0.47/0.44 V vs Ag/AgCl) indicated the first order insulator–metal phase transition . The second (0.62/0.60 V) and third (0.73/0.71 V) peaks were associated with the order–disorder transitions. , The current peaks accompanying the lithiation process were slightly broader and smaller, which was often observed in aqueous solution due to the slow desolvation process. , …”

“…The synthesis method of LiCoO 2 nanoparticles was adopted from ref . Briefly, a mixture consisting of 1 mM lithium acetate, 1 mM cobalt­(II) acetate, 20 mL of distilled water, and 2 mM citric acid anhydrous was first prepared.…”

Electronic and transport properties of LiCoO2

“…52 Further values from EIS are in the range 10 À10 to 10 À9 . 53 Larger values have also been obtained, such as 10 À10 to 10 À7 (ref. 54) (PSCA, EIS), 10 À9 (EVS), 55 and 10 À9 to 10 À8 (PITT).…”