Multilevel carbon architecture of subnanoscopic silicon for fast‐charging high‐energy‐density lithium‐ion batteries

Silicon(Si)is widely used as a lithium‐ion‐battery anode owing to its high capacity and abundant crustal reserves.However,large volume change upon cycling and poor conductivity of Si cause rapid capacity decay and poor fast‐charging capability limiting its commercial applications.Here,we propose a multilevel carbon architecture with vertical graphene sheets(VGSs)grown on surfaces of subnanoscopically and homogeneously dispersed Si–C composite nanospheres,which are subsequently embedded into a carbon matrix(C/VGSs@Si–C).Subnanoscopic C in the Si–C nanospheres,VGSs,and carbon matrix form a three‐dimensional conductive and robust network,which significantly improves the conductivity and suppresses the volume expansion of Si,thereby boosting charge transport and improving electrode stability.The VGSs with vast exposed edges considerably increase the contact area with the carbon matrix and supply directional transport channels through the entire material,which boosts charge transport.The carbon matrix encapsulates VGSs@Si–C to decrease the specific surface area and increase tap density,thus yielding high first Coulombic efficiency and electrode compaction density.Consequently,C/VGSs@Si–C delivers excellent Li‐ion storage performances under industrial electrode conditions.In particular,the full cells show high energy densities of 603.5 Wh kg^(−1)and 1685.5 Wh L^(−1)at 0.1 C and maintain 80.7%of the energy density at 3 C.

Flexible bifunctional electrocatalyst (Ni@(Ni,Fe)Se_(2)/Ni@CC) by adjusting d-band center for high-efficiency HER and overall water splitting

Nickel foam is widely used as a collector for electrocatalysts because of its excellent electrical conductivity;however,it is prone to react with elements such as oxygen,sulfur,and phosphorus during the growth of electrode materials,which makes it brittle and fragile,thus limiting its large-scale application.In this study,bifunctional electrocatalysts with flexible multilevel Ni-based nanoclusters Ni@(Ni,Fe)Se_(2)/Ni@CC were synthesized on carbon cloth(CC)by hydrothermal and electrodeposition methods;these flexible electrocatalysts are convenient for subsequent industrial applications.At a current density of 10 mA cm^(−2),the overpotentials of the hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)reached 98 and 224 mV,respectively,exceeding the catalytic effects of most metal-based collectors.The overall water-splitting potential of the catalyst was only 1.56 V at 10 mA cm^(−2),and the performance was maintained after a 24 h stability test.Ni@(Ni,Fe)Se_(2)/Ni@CC significantly improved the activity in alkaline environments by modulating the center of the d-band,thereby increasing the adsorption capacity of the catalyst for H ions.In this study,we improved the intrinsic activity and charge transfer of transition metal electrocatalysts by modifying the carbon cloth and constructing multilevel Ni-based nanoclusters,which provided some insights into the rational design of flexible bifunctional electrocatalysts.