Analysis of the Lithium Storage Mechanism in the SiO_x/C Composite Based on the Performance Variation Applied to a Lithium-Ion Battery

Abstract

The SiO x /C composite, as a form of silicon-based materials, has been considered as an attractive alternative anode for next-generation lithium-ion batteries. The porous SiO 0.71 C 1.95 N 0.47 anode material exhibiting robust Si−O skeletons wrapped by carbon layers is successfully prepared and delivers an initial capacity of over 1700 mAh g −1 with an initial coulombic efficiency of 69.4% and favorable cycle life. Both Si (2p) X-ray photoelectron spectroscopy (XPS) and 29 Si nuclear magnetic resonance (NMR) demonstrate the existence of SiO 4 and SiO 3 C units as main lithium storage sites in the original state. The XPS curve moved toward the direction of the binding energy decreasing with NMR spectra shifting to a high field after the first lithiation process. The massive capacity loss during the first discharge and charge cycle results from the formation of irreversible Li silicate (Li 2 SiO 4 ). The fluctuation of the charge and discharge capacity, including a persistent decline during the first 30 cycles and a continuous elevation in the following 400 cycles, could be attributed to the participated degree of reversible Li silicate (Li 2 SiO 3 and Li 2 Si 2 O 5 ) in the delithiation process. The Si−O skeletons are gradually corroded and ultimately destroyed in the final 400 cycles, leading to the sharp drop of the cycling performance of the half-cell.

Amorphous SiO2 Nanoparticles Encapsulating a SiO Anode with Strong Structure for High-Rate Lithium-Ion Batteries

“…There has been a significant surge in demand for lithium-ion batteries (LIBs) in the market, primarily driven by their exceptional characteristics, including long cycle life, high energy density, and environmental sustainability. These features make LIBs particularly desirable for a wide range of applications such as mobile electronic devices and electric cars. − Nonetheless, traditional graphite anodes have a lower theoretical capacity (372 mA h g –1 ) than silicon (Si), which offers an extremely high theoretical capacity (4200 mA h g –1 for Li 22 Si 4 ), rich resources, and a suitable operating voltage (≈0.4 V vs Li/Li + ), making Si one of the highest potential anode materials. ,− However, the commercialization of Si is constrained by the large volume expansion (≈300%) during the lithiation and delithiation processes, along with poor intrinsic conductivity leading to difficulties in achieving high-cycle performance. , As an alternative, silicon monoxide (SiO) has gained broader interest among researchers since they have a more suitable volume expansion (≈160%) due to the production of Li 2 O and lithium silicates. ,, Unfortunately, two crucial issues still need to be addressed. First, the volume expansion of SiO cannot be overlooked, as it results in the pulverization and detachment of electrode materials.…”