Interfacial Properties of Copper-coated Graphite Electrodes: Coating Thickness Dependence (original) (raw)
Related papers
The basic electroanalytical behavior of practical graphite–lithium intercalation electrodes
Electrochimica Acta, 1998
AbstractÐThe electrochemical behavior of practical carbon electrodes comprising arti®cial graphite particles of dierent sizes and PVDF binder in EC-DMC Li salt solutions was studied using simultaneously slow scan rate cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and potentiostatic intermittent titration (PITT). The theme of this work was to study the eect of the particle size of the graphite on the electroanalytical response of these electrodes during intercalation with lithium. At slow enough scan rates, the CV of these electrodes probe mostly the accumulation Ð consumption of lithium and phase transition between intercalation stages, perturbed by slow kinetics and solid state diusion. Impedance spectra of these electrodes re¯ect clearly a separation among dierent time constants which relate to migration of Li through surface ®lms, charge transfer, solid state diusion, and ®nally Ð accumulation of Li in the bulk. The diusion coecient of Li in graphite was found to be a peak shaped function of the potential and the intercalation level. The peaks of Àlog D vs E, X (X Li in Li X C 6 ) correspond to the CV peaks (which re¯ect phase transitions). The particle size and the solution composition in¯uence very strongly the resolution of all the above electroanalytical tools in the separation of the various processes which occur during intercalation of lithium into graphite. The eect of the particle size and the solution composition on the electroanalytical response of these electrodes is discussed. #
Journal of Electroanalytical Chemistry, 1997
Using slow scan rate (4 to 80 p,Vs-i) cyclic voltammetry for thin graphite electrodes (8 to 10 Ixm thick), two limiting cases for the intercalation mechanism of Li ion in graphite in aprotic solvents have been observed: (i) quasi-equilibrium, capacitive-like step at very slow potential scan rates and (ii) semi-inf'mite diffusion of Li + ions inside the graphite matrix at higher scan rates. Each of these two limiting types of behavior has been appropriately modeled, and from the comparison of experimental and simulated voltammetric curves quantitative information has been extracted, including (a) the effective heterogeneous rate constants for Li* ion transfer through the graphitelsolution interface; (b) the lateral attraction parameter for the intercalated species; (c) half-peak width and peak potential separation; and (d) diffusion coefficients of the intercalated ions.
The electrochemical behavior of composite anodes prepared either by mixing partially oxidized graphite and Cu powders or by coating the pristine partially oxidized graphite electrodes with few-nanometerthick Cu layers has been studied by slow-scan-rate cyclic voltammetry (SSCV) and galvanostatic charge/discharge cycles over the temperature range of −30 • C to 20 • C. The interfacial intercalation/ deintercalation kinetics has also been investigated using electrochemical impedance spectroscopy (EIS).
Metal-oxidized graphite composite electrodes for lithium-ion batteries
Electrochimica Acta, 2005
The electrochemical behavior of composite electrodes obtained by mixing graphite (Timrex KS-15 by Timcall), partially oxidized by thermal treatment, with nanometric metal particles (Au, Ag, Ni, Cu, Al, Sn) at about 1% (w/o) is presented. The charge-discharge properties of the composite electrodes have been studied in the temperature range 20 to −30 • C in 1 M LiPF 6 EC-DEC-DMC (1:1:1). The main effect is a general improvement of the cycling behavior at any temperature. In particular, at −30 • C about 30% of the theoretical intercalation capacity is retained by electrodes containing Cu, Al and Sn. At the same temperature, the composites containing the above metals show evidences of lithium staging. This may indicate that certain metals affect the kinetics of phase transformation that, together with other effects including charge transfer resistance, lithium diffusion coefficient and polarization due to SEI and solvent conductivities, seems to be the main cause of the poor intercalation capacity of graphite anodes at low temperature.
The study of electrochemical properties and lithium deposition of graphite at low temperature
Journal of Power Sources
The electrochemical properties of graphite with various degrees of graphitization, contents of rhombohedral phase, and surface areas were electrochemically investigated at 25 • C and −5 • C. The degree of graphitization and the amount of rhombohedral phase affected the samples' lithium intercalation/deintercalation and surface deposition. The reductions of electrolyte conductivity and lithium ion diffusion in the graphite interlayer at −5 • C lowered the graphite's capacity. Lithium deposition also occurred on the graphite's surface. Highly graphitized samples were affected greatly by temperature, showing large capacity loss at low temperature. Increased rhombohedral phase facilitated lithium deposition on the graphite's surface as lithium ions did not insert into the graphite interlayers and accumulated at its edged planes. Increasing the pathways for lithium ion intercalation could facilitate lithium intercalation and reduce lithium deposition.
Journal of The Electrochemical Society, 2003
The open-circuit voltage ͑OCV͒ of graphite-coated copper foil electrodes in Li-ion battery electrolytes was found to vary over time. A detailed study showed that the OCV first rapidly decreased until reaching a minimum, and then gradually increased until reaching a steady state. These results were compared with OCV studies of graphite-coated aluminum foil and copper foil without graphite coating. The influence of hydrofluoric acid and thermal treatment of the graphite coating was also studied. Combined with copper dissolution studies using atomic absorption spectroscopy, it was found that the interaction of the graphite coating with electrolyte solution was the main causative factor that resulted in the OCV variation.
Effect of Graphite Crystal Structure on Lithium Electrochemical Intercalation
Journal of The Electrochemical Society, 1999
The electrochemical intercalation of lithium into various graphite materials has been examined in LiPF 6 solutions of ethylene carbonate (EC)/dimethyl carbonate (DMC) or EC/DMC/propylene carbonate (PC). When the graphite powder samples contained at least 30% of the rhombohedral form, no exfoliation was observed, even with electrolytes containing a large amount (80%) of PC. However, when the graphites were heat-treated at temperatures above 1000ЊC, the faradaic losses due to the exfoliation reappeared, even though the rhombohedral phase content was unchanged. From Raman spectroscopy measurements, a correlation was found between the irreversible capacity due to the exfoliation and the ratio, R, of the integrated intensity of the disorder-induced line at 1350 cm Ϫ1 to the Raman-allowed line at 1580 cm Ϫ1 . This suggests that structure defects, probably localized in grain boundaries between rhombohedral and hexagonal domains, hinder the layer opening necessary for the intercalation of solvated lithium species at the beginning of the first electrochemical cycle.
The Role of Carbonate Solvents on Lithium Intercalation into Graphite
Journal of The Electrochemical Society, 2007
Lithium intercalation into graphite was investigated using a graphite with a spheroidal particle morphology and propylene carbonate ͑PC͒-based electrolytes containing LiPF 6 , NaPF 6 , or ͑C 4 H 10 ͒ 4 NPF 6 as the supporting electrolyte. The data from Li/C cells utilizing these electrolytes showed that reduction of PC on the graphite electrode occurs at about 0.9 V vs Li + /Li. The PC reduction potentials showed no dependence on the supporting electrolyte salt present in the electrolyte. Furthermore, there was no evidence of graphite exfoliation in PC electrolyte. This was supported by the observation that graphite electrodes retrieved from the Li/C cells, after PC reduction, and reassembled and tested with standard Li-ion battery electrolyte exhibited Li intercalation capacities identical to those exhibited by fresh graphite electrodes. The potentials at which PC is reduced are very similar to those previously found with graphite electrodes in which PC was reported to cointercalate into graphite as Li + ͑PC͒ n , leading to its exfoliation at about the same potentials as found in this study. The data presented here are useful for the systematic design and optimization of electrolytes based on organic carbonate solvents to tailor Li-ion battery performance.