In Situ Electrochemical Lithiation/Delithiation Observation of Individual Amorphous Si Nanorods

Abstract

In situ electrochemical lithiation and delithiation processes inside a nanobattery consisting of an individual amorphous Si nanorod and ionic liquid were explored. Direct formation of the crystalline Li(22)Si(5) phase due to the intercalation of Li ions was observed. In addition, the role of the electrolyte-nanorod interface was examined. It was observed that the lithiation of Si nanorods is dominated by surface diffusion. Upon the delithiation process, partial decomposition of Li(22)Si(5) particles was observed which can explain the irreversible capacity loss that is generally seen in Si anodes. This study shows that the radial straining due to lithiation does not cause cracking in nanorods as small in diameter as 26 nm, whereas cracks were observed during the lithiation of 55 nm Si nanorods.

Nanocomposites of silicon and carbon derived from coal tar pitch: Cheap anode materials for lithium-ion batteries with long cycle life and enhanced capacity

“…It shows high reversibility and stable capacity with prolonged cycling, but the reversible capacity has reached its theoretical limit (~372 mAh g ) [5][6][7], and tin (994 mAh g -1 ) [8][9][10][11].…”

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

“…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. This approach differs from other practical strategies to improve capacity retention that limit the Si cycling regimes to B1,200-1,500 mAh g À 1 , cycling at higher potentials between different a-Li x Si compositions 3,28 .…”

“…A range of in situ and ex situ mechanistic studies have recently been reported to investigate the Li-Si system, including in situ nuclear magnetic resonance (NMR) [29][30][31] , in situ X-ray diffraction (XRD) 23,24,27 , in situ transmission electron microscopy (TEM) studies 5,12,22,26,[32][33][34][35][36] and ex situ pair distribution function analysis 30 . These studies show that crystalline Si (c-Si) is converted into a-Li x Si phases during the first lithiation, which transform into a metastable crystalline phase c-Li 3.75 Si at low voltages (o70 mV versus Li) 5,12,[22][23][24][25][26][27] , and possibly over-lithiated phases such as c-Li 3.75 þ d Si 24,29 or Li 4.4 Si/Li 4.2 Si 2, 22 .…”

“…These studies show that crystalline Si (c-Si) is converted into a-Li x Si phases during the first lithiation, which transform into a metastable crystalline phase c-Li 3.75 Si at low voltages (o70 mV versus Li) 5,12,[22][23][24][25][26][27] , and possibly over-lithiated phases such as c-Li 3.75 þ d Si 24,29 or Li 4.4 Si/Li 4.2 Si 2, 22 . The formation of the crystalline phase is associated with a large overpotential particularly on charge, which is energetically inefficient in an operating cell and results in a lower operating voltage.…”

Atomic resolution observation of conversion-type anode RuO2during the first electrochemical lithiation

“…[15][16][17] Meanwhile, the Coulomb efficiency of the first cycle is of critical importance to most anode materials and determines the cycling behavior afterwards. 18,19 Therefore, it is crucial to uncover what exactly happens in the first lithiation.…”