Dandelion-like Mesoporous SiOx@C Nanoparticles for High-Capacity and Ultralong Lifespan Lithium-Ion Battery Anode

Abstract

Silicon suboxide (SiOx, 0˂x˂2) is one of the promising anode materials for lithium-ion batteries (LIBs) due to its high specific capacity, low operating voltage (˂0.4 V) and rich natural resource [1]. SiOx converts to Si nanoparticles and inert components (lithium oxide and lithium silicate) during initial lithiation process, where the Si nanoparticles can reversibly store lithium ions and the inert components act as buffer matrix to accommodate the large volume variation of nano-sized Si. Compared to pure Si, SiOx electrode shows relatively good cycling stability while maintaining high specific capacity, thus is a promising anode material for high energy density Li-ion batteries. Nevertheless, bulk SiOx electrode cannot withstand long-term cycling due to the inevitable volume variation upon lithium uptake and removal. In addition, the poor intrinsic electrical conductivity of SiOx often limits the capacity utilization [2]. In this work, we prepared mesoporous SiOx@C nanoparticles with unique “dandelion flower” structure by a facile microemulsion method combined with a subsequent carbon coating process. The SiOx particles display a dandelion flower like porous structure with large void space and specific surface area. A uniform carbon layer wholly encapsulates the SiOx backbone, forming a 3D mono-dispersed SiOx@C particle with particle size of ~70 nm. The abundant mesopores inside particle can accommodate the volume expansion of SiOx during lithiation and lower the diffusion-induced stresses, which prevent from the electrode pulverization and thus maintain the structural integrity of SiOx@C electrode during repeated cycles. The 3D carbon network not only effectively facilitates the fast electron transport throughout the whole SiOx particle and thereby improving the electrode reaction kinetics, but also homogenizes the local current density of active particles and hence decreases the mechanical stress induced by volume change of SiOx. Benefiting from these advantages, the prepared SiOx@C anode exhibits ultrahigh reversible capacity (1261 mAh g-1 at 0.1 A g-1), ultralong lifespan (635 mAh g-1 at 2 A g-1 after 1000 cycles with retention of 88.6%), as well as superior rate capability (293 mAh g-1 at 10 A g-1). [1] Journal of Power Sources, 2017, 363: 126-144. [2] J. Mater. Chem. A, 2014, 2, 3521-3527.