Lithium Silicide Nanocrystals: Synthesis, Chemical Stability, Thermal Stability, and Carbon Encapsulation

Abstract

Lithium silicide (LixSi) is the lithiated form of silicon, one of the most promising anode materials for the next generation of lithium-ion batteries (LIBs). In contrast to silicon, LixSi has not been well studied. Herein we report a facile high-energy ball-milling-based synthesis of four phase-pure LixSi (x = 4.4, 3.75, 3.25, and 2.33), using hexane as the lubricant. Surprisingly, the obtained Li3.75Si phase shows significant downward shifts in all X-ray diffraction peak positions, compared with the standard. Our interpretation is that the high-energy ball-mill-synthesized Li3.75Si presents smaller internal pressures and larger lattice constants. The chemical-stability study reveals that only surface reactions occur after Li4.4Si and Li3.75Si are immersed in several battery-assembly-related chemicals. The thermal-stability study shows that Li4.4Si is stable up to 350 °C and Li3.75Si is stable up to 200 °C. This remarkable thermal stability of Li3.75Si is in stark contrast to the long-observed metastability for electrochemically synthesized Li3.75Si. The carbon encapsulation of Li4.4Si has also been studied for its potential applications in LIBs.

Systematic Investigation of Prelithiated SiO2 Particles for High-Performance Anodes in Lithium-Ion Battery

“…It has been reported that Li 21 Si 5 is the most thermally stable phase among the crystalline lithium silicates [21]. The XRD patterns of the four Li x Si/Li 2 O composites are similar, indicating that pristine particle size does not have a big effect on the formation of crystalline Li 21 Si 5 . As calculated by the Scherrer equation, the crystalline sizes of the four composites are 28.2, 29.3, 31.9 and 37.5 nm, indicating that the SiO 2 microparticles produce relatively large Li 21 Si 5 domains.…”

“…A home-made sealed sample holder was used to avoid exposing the products to the air. The diffraction peaks of Li 2 O and Li 21 Si 5 are shown in the Figure 3a, demonstrating the formation of Li 2 O (PDF# 04-001-893) and Li 21 Si 5 (PDF# 00-018-747) phases. It has been reported that Li 21 Si 5 is the most thermally stable phase among the crystalline lithium silicates [21].…”

“…The diffraction peaks of Li 2 O and Li 21 Si 5 are shown in the Figure 3a, demonstrating the formation of Li 2 O (PDF# 04-001-893) and Li 21 Si 5 (PDF# 00-018-747) phases. It has been reported that Li 21 Si 5 is the most thermally stable phase among the crystalline lithium silicates [21]. The XRD patterns of the four Li x Si/Li 2 O composites are similar, indicating that pristine particle size does not have a big effect on the formation of crystalline Li 21 Si 5 .…”

“…This process consumes an excess amount of cathode materials [6][7][8]13,18,19], which significantly reduces the total energy density of full-cells, thereby preventing their practical applications. In order to tackle this issue, researchers have proposed prelithiation of the electrode material, which directly compensates for the irreversible loss of lithium during the first cycle [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. For example, Tarascon's…”

Composite lithium metal anode by melt infusion of lithium into a 3D conducting scaffold with lithiophilic coating

“…This "lithiophobic" effect possibly originates from the lack of bonding interaction between surface (carbon or Cu) and molten Li (27,28). For surface-modified objects, the Si coating reacts with molten Li to create a binary alloy phase-lithium silicide with some bonding interactions to pure Li (29)(30)(31). This reaction drives and guides molten Li to wet the entire surface and fill in the porous structure (28).…”