Synthesis, Structure Transformation, and Electrochemical Properties of Li₂MgSi as a Novel Anode for Li‐lon Batteries

Abstract

In this work, a novel hexagonal Li2MgSi anode is successfully prepared through a hydrogen‐driven chemical reaction technique. Electrochemical tests indicate significantly improved cycling stability for the as‐synthesized Li2MgSi compared with that of Mg2Si. Ball‐milling treatment induces a polymorphic transformation of Li2MgSi from a hexagonal structure to a cubic structure, suggesting that the cubic Li2MgSi is a metastable phase. The post‐24‐h‐milled Li2MgSi delivers a maximum capacity of 807.8 mAh g−1, which is much higher than that of pristine Li2MgSi. In particular, the post‐24‐h‐milled Li2MgSi retains 50% of its capacity after 100 cycles, which is superior to cycling stability of Mg2Si. XRD analyses correlated with CV measurements do not demonstrate the dissociation of metallic Mg and/or Li–Mg alloy involved in the lithiation of Mg2Si for the Li2MgSi anode, which contributes to the improved lithium storage performance of the Li2MgSi anode. The findings presented in this work are very useful for the design and synthesis of novel intermetallic compounds for lithium storage as anode materials of Li‐ion batteries.

A hybrid Si@FeSiy/SiOx anode structure for high performance lithium-ion batteries via ammonia-assisted one-pot synthesis

“…XRD analysis shows that the Fe powder is substantially disordered aer milling in NH 3 , whereas the one milled in Ar maintains mainly crystal structure, as shown also in Fig. S1 †.…”

“…As-received Si (1-2 mm, >99.99%, Shanghai ST-Nano) and Fe (10À50 mm, Sinopharm, Shanghai) powder particles, without further purication, were ball-milled in an NH 3 atmosphere by a planetary mill (QM-1SP04, Nanjing, China). A weight ratio of Si : Fe ¼ 2 : 1 was used.…”

“…To further clarify the formation mechanism of FeSi 2 , another experiment was conducted by milling the same ratio of Si and Fe powder particles in four different atmospheric environments (with the same pressure and other milling parameters as used for the atmosphere of NH 3 ): (1) in NH 3 for 40 h followed by another milling in a mixed gas atmosphere of N 2 and H 2 (1/3 by v/v) for 20 h, simulating the variation of the milling atmosphere of NH 3 during the 60 h of milling; (2) in NH 3 for 40 h followed by another milling in fresh NH 3 for 20 h, preserving the atmospheric environment to be mainly NH 3 ; (3) in a mixed gas atmosphere of N 2 and H 2 (1/3 by V/V) for 60 h, simulating the fully decomposed atmosphere of NH 3 ; (4) in Ar for 60 h, an inert atmosphere. The XRD patterns of these as-milled products without or with residual Fe removed by rinsing in HCl solution are also shown in Fig.…”

“…To further explore the essential factor for the formation of the FeSi 2 phase, the Fe powder was milled in NH 3 and Ar for 60 h, respectively. XRD analysis shows that the Fe powder is substantially disordered aer milling in NH 3 , whereas the one milled in Ar maintains mainly crystal structure, as shown also in Fig.…”

“…S1 †. In addition, elemental analysis of the Fe powder milled in NH 3 shows that the one milled in NH 3 contains 2.9 wt% of N, whereas there is no N detected in the one milled in Ar. EDS analysis under SEM (Fig.…”