Pressure‐Induced Vapor Synthesis of Carbon‐Encapsulated SiO_x/C Composite Spheres with Optimized Composition for Long‐Life, High‐Rate, and High‐Areal‐Capacity Lithium‐Ion Battery Anodes

Abstract

SiOx exhibits a high specific capacity as anode materials for lithium‐ion batteries. However, it is still a challenge to achieve long life, high rate performance, and high areal capacity for the SiOx materials. Herein, carbon‐encapsulated SiOx/C composite spheres are prepared by a high pressure caused by heating SiOx/C spheres in pure dimethylformamide in a sealed vessel. The SiOx/C spheres with different compositions are synthesized by pyrolysis of different liquid siloxanes and hexamethyldisilane in a sealed vessel and subsequent heat treatment. The electrochemical performances are strongly dependent on the composition of the SiOx/C spheres. The specific capacity and initial coulombic efficiency (ICE) greatly increase, and cyclability slightly decreases with a decrease in the x value from 1.28 to 0.59. However, the capacity, ICE, and cyclability greatly decrease with a further decrease in the x value because of the formation of SiC. The carbon‐encapsulated SiO0.59/C spheres exhibit a high reversible capacity (1561.3 mAh g−1), an outstanding cyclability (0.0332% capacity loss per cycle during 500 cycles at 1 A g−1), a good rate performance (245.3 mAh g−1 at 10 A g−1), and a high areal capacity (4.08 mAh cm−2). Formation of the spherical morphology and carbon‐encapsulating layers is a result of the high vapor pressure generated at a high temperature.

Nanoscopically and uniformly distributed SnO2@TiO2/C composite with highly mesoporous structure and bichemical bonds for enhanced lithium ion storage performances

“…Different from the first charge/discharge curve of TiO 2 /C, SnO 2 @TiO 2 /C exhibits two potential plateaus below 0.6 V in the charge/discharge curves, attributed to the delithiation/ lithiation of SnO 2 . 21,31 Additionally, SnO 2 @TiO 2 /C does not show obvious delithiation plateaus of anatase TiO 2 at 2.15 V, probably due to the contribution of SnO 2 and higher carbon content. 15 The reversible capacity of the active material has been reported to be associated with the relative content of each component, the particle size, and the number of phase boundaries and chemical bonds at the interface.…”

“…15 The reversible capacity of the active material has been reported to be associated with the relative content of each component, the particle size, and the number of phase boundaries and chemical bonds at the interface. 15,21 Due to low theoretical capacity of anatase TiO 2 , adding high-capacity active material can greatly enhance the capacity of TiO 2 -based anodes, such as SnO 2 and amorphous carbon. Owing to the low electrical conductivity (EC) of anatase TiO 2 , adding materials with higher EC can considerably improve the electrical connectivity of the whole electrode, enabling more active materials to react with lithium ions and thus increasing the specific capacity.…”

“…1a, TiO 2 /C exhibits a spherical shape with an average size of 2.5 mm due to the high vapor pressure, with its formation mechanism being discussed in detail in our previous reports. 20,21 Interestingly, adding MO into TOT led to the formation of nanoparticles with an average size of 15 nm (Fig. 1b), indicating that MO addition facilitates nanocomposite formation in the vapor pressureinduced reaction process.…”

Pressure‐Induced Synthesis of Homogeneously Dispersed Sn/SnO2/C Nanocomposites as Advanced Anodes for Lithium‐Ion Batteries

“…Both results show that sample‐II has the highest carbon content (14.5 wt%) and higher oxygen content (11.1 wt%). At 400 °C, C 2 H 6 OSn has totally decomposed (Figure S4, Supporting Information), which can release a large amount of gaseous substances in the sealed vessel, thus producing the elevated pressure . At this moment, due to low reaction temperature, the pressure produced by the decomposition of C 2 H 6 OSn is not enough to make carbon‐containing gaseous substance completely converted into solid carbon.…”

“…Elevated pressure caused by the gaseous free radicals under high temperature promotes complete conversion of SnO into Sn and SnO 2 . While Sn and SnO 2 are formed, the gaseous free radicals transform to solid carbon material under the elevated pressure . Then, Sn and SnO 2 grains are efficiently separated and further growth of Sn and SnO 2 nanocrystals and coalescence of the liquid Sn are stopped.…”