Investigation of carbon-coated SiO phase changes during charge/discharge by X-ray absorption fine structure

Practical implementation of Li doped SiO in high energy density 21700 cell

“…The different SiO-C grades studied in the present work are described in Table 1 : Grade A is the reference non pre-lithiated, carbon coated material. Detailed characterization of this grade can be found in previous literature [17,24]. Grade B and C have different levels of lithium doping [30,31], resulting in better first cycle efficiency (Figure 1).…”

“…Here new Li doped carbon coated SiO grades are evaluated (Li-SiO-C). Compared to the 72% efficiency with 1.2V vs. Li + /Li cutoff voltage of the reference material [24], they attain up to 90% first cycle efficiency, without sacrificing the reversible capacity of around 1400 mAh.g -1 . Moreover they are stable enough to be processed in standard aqueous based slurries.…”

“…During electrochemical lithiation, SiO2 domains irreversibly forms lithium silicate Li4SiO4, and a Si 0+ plus other lower valence SiO reversible part [14,15,16]. It was also shown by NMR that when charged above 0.7V vs. Li, Li4SiO4 is reactive, which causes capacity fading [24]. Indeed this reversed reaction induces disproportionation and segregation of silicon domains [17] which then may behave as pure silicon with crystallization of Li15Si4 known for poor cycle life.…”

“…nano clusters of SiO2 are crystalline and Si clusters amorphous in SiO. In ref 24,. crystalline Si is seen by XANES.…”

Revealing the size-dependent electrochemical Li-storage behaviors of SiO-based anodes

“…In this regard, the quantitative lithiation/delithiation process of SiO remains controversial despite years of experimental and theoretical efforts, even though various characterization technologies including NMR, XAFAS, Raman spectroscopy, XRD, and TEM have been introduced. [33][34][35][36][37][38][39][40][41][42] It is well accepted that the Si nanodomains contribute to the reversible capacity by forming amorphous Li-Si alloys (Li x Si, x = 3. 25, 3.44, 3.5, 3.75, 4.4, etc.).…”