The solid-electrolyte-interphase ͑SEI͒ layers formed on the electrodes of pristine Si and carbon-coated Si ͑C-Si͒ particles in Li cells have been studied. The counter electrode is Li, and the electrolyte is LiPF 6 in the mixture of ethylene carbonate and ethyl methyl carbonate. Other than those, such as Li carbonates and fluoride, already known to the SEI of graphite electrode, there were detected significant amounts of SEI species unique to each of the Si electrodes. On the pristine Si electrode, there was concurrence of abundance of C and Si fluorides after long cycles. Coating the Si particles with a graphitized carbon layer has significant effects on the SEI formation. It helps to keep the Si particles remaining integrated after cycling, resulting in a smooth superficial SEI layer. It removes the native oxide layer not only to reduce humidity contamination but also to significantly change the SEI compositions. The SEI of the C-Si electrode shows the absence of Si and C fluorides but the presence of siloxane species. Reaction mechanisms leading to the formation of the fluoride and siloxane species have been proposed, elucidating an important role played by the native Si oxide layer. Si possesses a maximum capacity exceeding 3000 mAh/g for being a negative electrode for Li-ion batteries.1,2 Two issues are considered critical to realize this application. The first critical issue is the dramatic volume expansion and shrinkage of the Si particles during lithiation and delithiation, [3][4][5] respectively. Such cyclic volumetric variations tend to cause fast mechanical failure of the electrode structure, resulting in a very poor cycle life. A fairly large amount of literature adopting different approaches to enhance the structural robustness of the electrode has been dedicated to tackle this crucial problem. In the case of the conventional thick-film electrode made of particulate materials, for example, studies 3-8 have coated the Si particles with different conducting materials, which may serve either to enhance the conductivity of the electrode or to act as a buffer to partially accommodate the volumetric variations during cycling. In particular, coating with a carbon/graphite surface layer 3-6 has shown a significant beneficial effect on enhancing cycle life.The second critical issue is the properties of the surface layer on Si in contact with the Li + -containing electrolyte, also known as the solid-electrolyte-interphase ͑SEI͒. The SEI properties, on either cathode or anode, have been well recognized to play an important role in, among others, the safety, power capability, and cycle life of Li-ion-based batteries. It is believed to be equally important to the electrochemical performance of Si anode. Unfortunately, study on this critical issue is scarce. Choi et al.9,10 once reported preliminary results on the effects of certain electrolyte additive and salt on the SEI compositions of Si thin-film electrodes.In this work, the morphology and composition of the SEI formed on the electrodes containing either pris...
Carbon-coating of sub-lm SiO particles (d max = 0.36 lm, d 50 = 0.69 lm) by a fluidized-bed chemical-vapor-deposition process has produced unique nano-porous SiO/C secondary particles within which the SiO primary particles are ''glued'' together by carbon to form a network that possesses randomly distributed pores with sizes in the nano-meter range and a bulk porosity of [30%. Upon lithiation/delithiation cycling in an organic Li-ion electrolyte, the electrode made of the SiO/C particles exhibited reduced polarization, smaller irreversible electrode expansion, and remarkably enhanced cycling performance, as compared with that of pristine SiO particles. The reduced electrode expansion exhibited by the SiO/ C electrode can be attributed to the combination of diluted SiO content and presence of pre-set voids, which could partially accommodate volume expansion arising from lithiation of the SiO primary particles. These effects render the SiO/C electrode structurally more robust than the SiO electrode against volumetric variations upon cycling.
The evolution of the interior microstructures of SnO during electrochemical lithiation/de-lithiation has been visualized by in situ transmission X-ray microscopy (TXM), complemented by in situ X-ray diffraction (XRD) to reveal phase information. A SnO secondary particle consisting of plates of primary particles has been shown to homogeneously expand during the first lithiation in two stages, including the first producing Li 2 O matrix that bears most original particle morphology and the second involving full lithiation of the precipitated Sn nano-particles from the first stage. Only the second stage is reversible upon de-lithiation, and the particle undergoes the reversible second-stage deformation during subsequent cycles. The results indicate clear advantages of using such a porous secondary SnO as the anode material in comparison with dense Sn particle previously revealed, including fast lithiation/de-lithiation kinetics, reduced overall volume expansion and enhanced mechanical robustness of the particle, supported by the Li 2 O backbones.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.