Ruijun Ma

Chemical Preinsertion of Lithium: An Approach to Improve the Intrinsic Capacity Retention of Bulk Si Anodes for Li-ion Batteries

Silicon represents one of the most promising anodes for next-generation Li-ion batteries due to its very high capacity and low electrochemical potential. However, the extremely poor cycling stability caused by the huge volume change during charge/discharge prevents it from the commercial use. In this work, we propose a strategy to decrease the intrinsic volume change of bulk Si-based anodes by preinsertion Li into Si with a chemical reaction. Amorphous Li12Si7 was successfully synthesized by a hydrogen-driven reaction between LiH and Si associated with subsequent energetic ball milling. The as-prepared amorphous Li12Si7 anode exhibits significantly improved lithium storage ability as ∼70.7% of the initial charge capacity is retained after 20 cycles. This finding opens up the possibility to develop bulk Si-based anodes with high capacity, long cycling life and low fabrication cost for Li-ion batteries.

Superior Dehydrogenation/Hydrogenation Kinetics and Long-Term Cycling Performance of K and Rb Cocatalyzed Mg(NH2)2-2LiH system

The coaddition of KH and RbH significantly improves the hydrogen storage properties of the Mg(NH2)2-2LiH system. An Mg(NH2)2-2LiH-0.04KH-0.04RbH composite was able to reversibly store 5.2 wt % H2 when the dehydrogenation operates at 130 °C and the hydrogenation operates at 120 °C. The isothermal dehydrogenation rate at 130 °C was approximately 43 times that of a pristine sample. During ball-milling, KH reacts with RbH to form a K(Rb)H solid solution. Upon heating, RbH first separates from the K(Rb)H solid solution and participates in the first step of dehydrogenation reaction, and then the remaining KH participates in the second dehydrogenation reaction. The presence of RbH and KH provide synergetic effects, which improve the thermodynamics and kinetics of hydrogen storage in the Mg(NH2)2-2LiH system. In particular, more than 93% of the hydrogen storage capacity (4.4 wt %) remains after cycling a sample with 0.04 mol of KH and RbH for 50 cycles, indicating notably better cycling stability compared with any presently known Li-Mg-N-H systems.

Mg2Si anode for Li-ion batteries: Linking structural change to fast capacity fading

This work reports on the underlying mechanism of the fast capacity fading of Mg2Si. The linking of the structural change and degradation behavior that occurs during cycling shows that the dissociation and irreversible lithiation of Mg is the critical factor for the capacity fading of a Mg2Si anode. This mechanism was further proven by designing a ternary Li2MgSi that exhibited significantly improved cycling stability because of the elimination of the intermediate Mg upon charging/discharging. This finding is useful as a general guideline and inspiration for improving the cycling stability of Mg2Si anodes and designing anode materials with long-term cyclability.