Enhancement of the electrochemical performance of silicon anodes through alloying with inert metals and encapsulation by graphene nanosheets

Pragmatic Approach to Design Silicon Alloy Anode by the Equilibrium Method

Silicon fascinates with incredibly high theoretical energy density as an anode material and considered as a primary candidate to replace well-established graphite. However, further commercialization is hindered by the abnormal volume changes of Si in every single cycle. Silicon embedded in a buffer matrix using the melt-spinning process is a promising approach; however, its metastable nature significantly reduces the microstructure homogeneity, the quality of the composition, and, therefore, the electrochemical performances. Herein, we developed a new approach to design a high-performance Si-alloy with improved microstructure uniformity and electrochemical properties. Namely, annealing at a certain temperature of the melt-spun amorphous alloy ribbon allowed us to evenly distribute Si nanocrystallites in the microstructure with control of average grain size. As a result, the Si-alloy electrode delivers an initial discharge capacity of 900 mAh g^-1 and exhibits a high coulombic efficiency of >99% from the second cycle with a capacity retention of ∼98% after 100 cycles. This study provides powerful insights and evidence for the successful application of the proposed approach for commercial purposes.

Architecturally Robust Graphene-Encapsulated MXene Ti2CT x@Polyaniline Composite for High-Performance Pouch-Type Asymmetric Supercapacitor

A harmonized three-component composite system which preserves the characteristics of individual components is of interest in the field of energy storage. Here, we present a graphene-encapsulated MXene Ti₂CT _x@polyaniline composite (GMP) material realized in a systematically stable configuration with different ternary nanomaterials for supercapacitor electrodes. Due to the different ζ-potentials in a high-pH solution, chemically converted graphene (negatively charged) is thoroughly unfolded to allow full encapsulation, but the MXene Ti₂CT _x@polyaniline composite with a low positive ζ-potential is easily attracted toward a counter-charged substance. The obtained GMP electrode exhibits improved cycling stability and better electrochemical performance owing to the use of mechanically robust and chemically inert graphene and the densely intercalated conductive polyaniline between the multilayer MXenes. The GMP electrode has a high gravimetric capacitance of 635 F g^-1 (volumetric capacitance of 1143 F cm^-3) at a current density of 1 A g^-1 with excellent cycling stability of 97.54% after 10 000 cycles. Furthermore, the asymmetric pouch-type supercapacitor assembled using the GMP as a positive electrode and graphene as a negative electrode yields a high energy density of 42.3 Wh kg^-1 at a power density of 950 W kg^-1 and remarkable cycling stability (94.25% after 10 000 cycles at 10 A g^-1).