Suppression of staging in lithium-intercalated carbon by disorder in the host

Abstract

We report electrochemical and x-ray-diffraction studies of the intercalation of lithium in graphite and in disordered carbons. The phase diagram of electrochemically intercalated graphite agrees well with previous work on samples prepared by chemical methods. The we11-known staged phases present in intercalated graphite are absent in intercalated petroleum coke. Furthermore, the voltage V(x) of Li/Li"C6 cells differs greatly when graphite or coke is used as the host. By heating coke to successively higher temperatures, we are able to increase the graphitization or crystalline order of the host in a continuous fashion and study the effect of this variation on the phase diagram of Li"C, and on V(x). We find that staged phases are suppressed at room temperature for hosts less ordered than a "critical disorder. " A lattice-gas model with random site energies is used to model the effects of host disorder and qualitatively explains the suppression of staged phases and the changes in V(x) with increasing disorder in the host. For a rectangular "density of sites, " staged phases are suppressed when the width of the site energy distribution is greater than the magnitude of the mean-field attractive Li-Li interaction, which causes island growth and staging in intercalated graphite.

Revealing lithium–silicide phase transformations in nano-structured silicon-based lithium ion batteries via in situ NMR spectroscopy

“…5c,d), there are three distinct processes both on discharge and charge with a capacity of B300 mAh g À 1 : dQ/ dV peaks at 200 mV (namely C#d1, 84 mAhg À 1 LiC 27 ), 110 mV (C#d2, 171 mAhg À 1 LiC 13 ) and 80 mV(C#d3, 300 mAhg À 1 LiC 7.4 ) on discharge, and at 90 mV(C#c1, 171 mAhg À 1 LiC 13 ), 140 mV(C#c2, 80 mAhg À 1 LiC 28 ), and 230 mV (C#c3) on charge. These dQ/dV processes are in good agreement with those in graphite 20,21 , even though our CFGDL is partially disordered.…”

“…An alternative practical strategy involves the use of Si/graphite composite structures that couple the good capacity and cyclability of graphite with a small fraction of the Si capacity (of an all-Si electrode) to provide modest but still significant increases in capacity. One problem with this strategy is that it requires the electrode to be cycled to low voltages 20,21 to access the full graphite capacity. At these low voltages, the amorphous Li-silicides (a-Li x Si) formed on lithiation are converted to crystalline phases such as crystalline Li 3.75 Si (c-Li 3.75 Si) 5,12,[22][23][24][25][26][27] , a process that is associated with a large overpotential on delithiation.…”

Approaching the limits of transparency and conductivity in graphitic materials through lithium intercalation

“…As shown in Fig. 3c-g, a clear lithiated (LiC 36 ) and dilute stage (LiC 72 ) interface (that is, a lithiation front) is observed within 100 s, and the lithiated area becomes more transparent and the LiC 36 area increases linearly with time ( Fig. 3h).…”

“…During the Li intercalation process, the volume of ultrathin graphite gradually expands because of the insertion of lithium atoms. The layer spacing of LiC 6 is B10% larger than that of pristine graphite 36 . Therefore, the narrow metal electrodes fabricated by the normal method of thermal evaporation on top of ultrathin graphite usually crack after intercalation.…”

“…Note that R S measured on both stage I and II is inversely proportional to the sample thickness (before intercalation) as indicated by the dashed lines. Considering the expansion of the graphite-layer spacing during Li intercalation 36 , we can estimate that r(LiC 6 )B3.1 Â 10 À 6 and r(LiC 12 )B1.4 Â 10 À 5 O cm À 1 . The intrinsic limit of the conductivity for doped graphene at room temperature is set by electron-acoustic phonon scattering and is approximately s dc,phonon ¼ 33 mS per layer 26,37 for Fermi energies in the linear portion of the band structure, while we observe a DC sheet conductivity s dc E11 mS per layer in LiC 6 .…”