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Downsizing well-established materials to the nanoscale is a key route to novel functionalities, in particular if different functionalities are merged in hybrid nanomaterials. Hybrid carbon-based hierarchical nanostructures are particularly promising for electrochemical energy storage since they combine benefits of nanosize effects, enhanced electrical conductivity and integrity of bulk materials. We show that endohedral multiwalled carbon nanotubes (CNT) encapsulating high-capacity (here: conversion and alloying) electrode materials have a high potential for use in anode materials for lithium-ion batteries (LIB). There are two essential characteristics of filled CNT relevant for application in electrochemical energy storage: (1) rigid hollow cavities of the CNT provide upper limits for nanoparticles in their inner cavities which are both separated from the fillings of other CNT and protected against degradation. In particular, the CNT shells resist strong volume changes of encapsulates in response to electrochemical cycling, which in conventional conversion and alloying materials hinders application in energy storage devices. (2) Carbon mantles ensure electrical contact to the active material as they are unaffected by potential cracks of the encapsulate and form a stable conductive network in the electrode compound. Our studies confirm that encapsulates are electrochemically active and can achieve full theoretical reversible capacity. The results imply that encapsulating nanostructures inside CNT can provide a route to new high-performance nanocomposite anode materials for LIB. [ABSTRACT FROM AUTHOR]

We demonstrate three different synthesis procedures to fill carbon nanotubes with main group IV-elements in their metallic state. We demonstrated, that filling CNT with nanoparticles really demands an adjusted procedure. After finding the best filling method, we tuned the morphology of filling particles, degree of filling and sample purity, in terms of coating-to-filling-ratio, by variation of the reaction parameters. A mass fraction of up to 30% of a highly crystalline filling material and a pure outer nanotube surface at once, can address conditions for application. Using the template CNT, we prepared chemically stable, metallic nanoparticles with a well-defined size distribution and high rates of filling. Such materials are promising candidates for sensoric and energy storage applications. [ABSTRACT FROM AUTHOR]