Electrochemical behavior of graphite anode at elevated temperatures in organic carbonate solutions (original) (raw)
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Journal of Electroanalytical Chemistry, 2004
We report on the potential and temperature dependences of the differential intercalation capacitance, C dif , and the chemical diffusion coefficient, D, during Li intercalation into a graphite anode by a combined application of slow-scan rate cyclic voltammetry (SSCV) and the potentiostatic intermittent titration technique (PITT). Drastically different behavior was observed within the shorttime ranges of the PITT response measured for a two-phase coexistence domain and a solid solution of phases 4 and 3. Electroanalytical evidence for small droplet formation (nucleation) of a new phase in the bulk of the old one was found for the former domain, showing good correlation with in situ XRD studies. SSCV data obtained in the 25-80°C temperature range were in excellent agreement with the published temperature-concentration phase diagrams built on the basis of detailed XRD characterizations. The simultaneous appearance of maxima on C dif versus E plots and minima on the related log D versus E plots in the twophase domains was rationalized in terms of a lattice gas model with single site energy, and highly attractive interactions between the intercalated guest atoms. The electroanalytical behavior of graphite within the solid-solution domain (a mixture of phases 4 and 3) was interpreted semi-quantitatively on the basis of a model that took into account the presence of two sub-lattices of different energy (a model of ''energetic heterogeneity'') for Li accommodation, and attractive interactions between the guest atoms on each sublattice, or, alternatively, due to in-plane order-disorder transitions because of short-range repulsive interactions between the intercalated guest species.
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 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. #
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.
Journal of The Electrochemical Society, 2020
The effect of temperature on the kinetics of electrochemical insertion/removal of lithium in graphite is analyzed by kinetic Monte Carlo methods. Different electrochemical techniques are simulated at different temperatures and responses are compared with experimental results. Simulated voltammograms show, similarly to experiment, how the behavior of the system becomes closer to equilibrium as temperature increases. Calculated chronoamperometric profiles show a different qualitative behavior in the current at different temperatures, especially in the Cottrell representation peaks, explained in terms of the relative importance of diffusive versus charge transfer processes at different temperatures. Results at room temperature are in good agreement with experiment, and we further evaluate trends at elevated temperature that have not yet been described in experimental or theoretical works. Exchange current densities for different degrees of lithium intercalation at different temperature...
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.
Journal of energy storage, 2018
The performance of graphite electrodes in various electrolytes containing ethylene carbonate (EC) and mixtures of EC and propylene carbonate (PC) was studied at temperatures between 0 and 40°C. Included in the study was also the addition of ethyl acetate (EA). Differential scanning calorimetry (DSC) was employed to investigate phase transitions at low temperature (down to −80°C) and decomposition at elevated temperatures. Capacity loss was compared for graphite electrodes cycled at varying temperatures between 0 and 40°C for these electrolytes. Based on the results, suitable electrolytes able to work in a wide temperature range could be identified. Addition of EA improved the low temperature properties of the electrolyte and the graphite electrode, but the electrodes failed upon cycling at +40°C. Addition of PC to a multi-component system, making the total amount of cyclic carbonates 40% (i.e. 20% EC and 20% PC), increased the liquid temperature range of the electrolyte. However, the addition of PC, led to very high initial irreversible capacity loss of the graphite electrode, and reduced the capacity considerably at 0°C, most likely related to a higher resistance of the solid electrolyte interphase. Thus, mixtures of EC and linear carbonates like dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) were found to perform best in this temperature range.
Effect of co-intercalated organic solvents in graphite on electrochemical Li intercalation
Synthetic Metals, 2001
Electrochemical properties of graphite in propylene carbonate based electrolytes containing various organic solvents have been studied by cyclic voltammetry and charge±discharge measurements. Good correlation between solvent co-intercalation and electrochemical lithium intercalation into graphite was found. Effect of co-intercalated organic solvents in graphite on electrochemical Li intercalation was discussed.
Journal of Power Sources, 1997
Electrochemical hthium intercalation into graphite was studied by cyclic voltammetry and a.c. impedance spectroscopy. Highly oriented pyrolytic graphite was used as a model graphite material to distinguish the difference in electrochemical behavior between the basal and the edge planes at graphite. A comparison between cyclic voltammograms of the basal plane and the whole surface of highly ortented pyrolytic graphite revealed that electrochemical lithium intercalation proceeds predominantly at the edge plane/electrolyte interface. The charge-transfer resistance changed continuously with electrode potential, and no significant change was observed at stage transition potentials (210, 120, and 90 mV versus Li/Li +). From the variations of the Warburg impedance of samples of different sizes, it was concluded that lithium diffuses from the edge plane to the interior in the direction parallel to the basal plane and that its dlffusivity changes with the stage structure of the bulk lithium-graphite intercalation compound.
Electrochemical investigation of lithium intercalation into graphite from molten lithium chloride
Journal of Electroanalytical Chemistry, 2002
In this paper we report on the lithium reversible storage in titanium dioxide (TiO 2 ) prepared by metal-organic chemical vapor deposition (MOCVD). Electrochemical properties in terms of lithium reversible insertion depend on the deposited microstructure. For thick films deposited on silicon wafer electrochemical activity of the anatase type of TiO 2 is registered in the potential range 1.8-2.1 V vs. Li. For thinner films the intercalation reaction takes place in two potential ranges: 1.8-2.1 V vs. Li and below 1.4 V vs. Li. The second electroactivity range is attributed to lithium insertion into rutile. We found that the decrease of the lower potential limit (0.5 V instead of commonly used 1 V) leads to an increase of the recovered capacity. In consequence the investigated MOCVD TiO 2 demonstrates high reversible capacity of about 300 mAhg -1 .