Swelling-Controlled Double-Layered SiO_x/Mg₂SiO₄/SiO_x Composite with Enhanced Initial Coulombic Efficiency for Lithium-Ion Battery

Abstract

Si-based anode materials are considered as potential materials for high-energy lithium-ion batteries (LIBs) with the advantages of high specific capacities and low operating voltages. However, significant initial capacity loss and large volume variations during cycles are the primary restrictions for the practical application of Si-based anodes. Herein, we propose an affordable and scalable synthesis of double-layered SiO x /Mg2SiO4/SiO x composites through the magnesiothermic reduction of micro-sized SiO with Mg metal powder at 750 °C for 2 h. The distinctive morphology and microstructure of the double-layered SiO x /Mg2SiO4/SiO x composite are beneficial as they remarkably improve the reversibility in the first cycle and completely suppress the volume variations during cycling. In our material design, the outermost layer with a highly porous SiO x structure provides abundant active sites by securing a pathway for efficient access to electrons and electrolytes. The inner layer of Mg2SiO4 can constrain the large volume expansion to increase the initial Coulombic efficiency (ICE). Owing to these promising structural features, the composite prepared with a 2:1 molar ratio of SiO to Mg exhibited initial charge and discharge capacities of 1826 and 1381 mA h g–1, respectively, with an ICE of 75.6%. Moreover, it showed a stable cycle performance, maintaining high capacity retention of up to >86.0% even after 300 cycles. The proposed approach provides practical insight into the mass production of advanced anode materials for high-energy LIBs.

Micrometer‐Sized SiMgyOx with Stable Internal Structure Evolution for High‐Performance Li‐Ion Battery Anodes

“…To further investigate the improved rate performance of SiMg y O x @C, galvanostatic intermittent titration technique (GITT) was employed to determine the diffusion coefficient of Li + (Figure S15, Supporting Information). After first cycle, the diffusion coefficient of Li + in SiMg y O x @C (1.99 × 10 −12 cm 2 s −1 ) is much higher than that of SiO x @C (1.50 × 10 −13 cm 2 s −1 ), and the superiority is maintained in the following cycles, which could be ascribed to the existence of magnesium silicate and the distinct internal constituent of SiMg y O x @C. [ 46 ] Cycling stability is another significant parameter for anode materials in addition to ICE and rate performance. Figure 3d,e shows the Coulombic efficiency of 50 cycles and the long‐term cycling performance of SiMg y O x @C and SiO x @C, respectively.…”

Crystallinity‐controlled SiO x anode material prepared through a salt‐assisted magnesiothermic reduction for lithium‐ion batteries

“…Figure 1A presents a schematic of the morphologies of the SiO x particles synthesized using different heat absorbents via the scalable magnesiothermic reduction process. The micron‐sized SiO particles were thoroughly mixed with the Mg powder and KCl or NaCl powders, which were the heat absorbents 25 . The mixtures were placed in a tube furnace and heated at 750°C for 2 hour in inert (Ar) environment.…”

“…Two symmetric peaks occurred when the binding energy was 99.0 and 103.5 eV, corresponding to the orbitals of Si 2p 3/2 and Si 2p 1/2 , respectively. These peaks can be deconvoluted into the oxidation states of Si 0 (99.0 eV), Si + (101.5 eV), Si 2+ (102.9 eV), Si 3+ (103.5 eV), and Si 4+ (104.5 eV) 25 . SiO x ‐NaCl exhibited a stronger signal for metallic Si than that exhibited by SiO x ‐KCl, as NaCl absorbed less heat during the exothermic reaction based on the binding energy of 99.0 eV.…”

“…In our previous work, we confirmed that the microstructural evolution of SiO x depends significantly on the temperature of the magnesiothermic reduction. In addition to the synthesis temperature, heat control influences the morphology and microstructure of SiO x , which governs the electrochemical performance 16‐25 …”

“…In addition to the synthesis temperature, heat control influences the morphology and microstructure of SiO x , which governs the electrochemical performance. [16][17][18][19][20][21][22][23][24][25] During magnesiothermic reduction, massive heat is released from the exothermic reaction (Mg [g], ΔH = À586.7 kJ mole À1 for SiO 2 ), 26 thereby increasing the temperature to a few hundred degrees higher than the set temperature. As a result, microstructural changes in SiO x , such as the formation of secondary phases (eg, Mg 2 Si and Mg 2 SiO 4 ) and abnormal growth of Si crystals, are induced.…”