The critical role of carbon in marrying silicon and graphite anodes for high-energy lithium-ion batteries

Increasing the energy density of conventional lithium-ion batteries(LIBs)is important for satisfying the demands of electric vehicles and advanced electronics.Silicon is considered as one of the most-promising anodes to replace the traditional graphite anode for the realization of high-energy LIBs due to its extremely high theoretical capacity,although its severe volume changes during lithiation/delithiation have led to a big challenge for practical application.In contrast,the co-utilization of Si and graphite has been well recognized as one of the preferred strategies for commercialization in the near future.In this review,we focus on different carbonaceous additives,such as carbon nanotubes,reduced graphene oxide,and pyrolyzed carbon derived from precursors such as pitch,sugars,heteroatom polymers,and so forth,which play an important role in constructing micrometersized hierarchical structures of silicon/graphite/carbon(Si/G/C)composites and tailoring the morphology and surface with good structural stability,good adhesion,high electrical conductivity,high tap density,and good interface chemistry to achieve high capacity and long cycling stability simultaneously.We first discuss the importance and challenge of the co-utilization of Si and graphite.Then,we carefully review and compare the improved effects of various types of carbonaceous materials and their associated structures on the electrochemical performance of Si/G/C composites.We also review the diverse synthesis techniques and treatment methods,which are also significant factors for optimizing Si/G/C composites.Finally,we provide a pertinent evaluation of these forms of carbon according to their suitability for commercialization.We also make far-ranging suggestions with regard to the selection of proper carbonaceous materials and the design of Si/G/C composites for further development.

Iridic oxide nanoparticles grown in situ on BCN nanotubes as highly efficient dual electrocatalyst for rechargeable lithium-O2 batteries

Oxygen cathode catalysts can significantly address the issues faced by Li-O2 battery.In this research,a composite of IrO2 nanoparticles grown in situ on BCN nanotubes(IrO2@BCNNTs)has been synthesized by facile hydrothermal method,which is initially fabricated as cathode catalyst for Li-O2 battery.The results indicate that IrO2@BCNNTs nanocomposite has a better effect on improving the actual discharge capacity,voltage gap and cyclability of Li-O2 battery.In addition,it is also demonstrated that the Ir O2@BCNNTs composite exhibits bifunctional characteristics for both the oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)through rotating disk electrode(RDE)measurements.The excellent performances of the synthesized catalyst may be attributed to the unique interconnected tubular structure and strong synergistic effect,which can provide more charged sites and defect sites and then facilitate reversible Li2 O2 formation and decomposition.Therefore,it is promising for applying the rational design of the bifunctional catalyst to Li-O2 battery.