Abstract

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.

Highlights

  • Lithium-ion batteries (LIB) offer high gravimetric and volumetric energy densities which renders them suitable for mobile applications

  • Voltage range of Integrated andcapacities discharge for capacities for five cycles asfrom deduced from cyclic voltammograms (CVs) [32]

  • Electrochemical properties were studied by cyclic voltammetry (CV) and galvanostatic cycling with potential limitation (GCPL) in Swagelok-type cells [97]

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Summary

Introduction

Lithium-ion batteries (LIB) offer high gravimetric and volumetric energy densities which renders them suitable for mobile applications. Mechanical strain arising from volume changes is buffered by the hierarchical structures In this way, such materials optimally maintain the integrity of the bulk material while offering improved electrical conductivity owing to a carbon-based backbone structure [15,16,17,18,19,20,21,22,23,24,25,26,27,28]. A strong backbone structure improves the stability of the composite with respect to mechanical strain arising from volume changes during electrochemical cycling. Created network with Avogadro [29].(3) limitation of electrical the incorporated materialchemical to a stable conductive of CNT, direct electrolyte/active material contact yielding and improved chemical stability. The backbone network of CNT is unaffected by cracks of encapsulate which

Synthesis
The images clearly of is confirmed by exemplary and TEM studies presented in
Electrochemical Studies
Magnetization of pristine andelectrochemically electrochemically cycled
In the initial
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V withofa
O4 nanospheres cross-linked
O3 and Verwey oftransitions which enable unambiguously identify
O4 isreversible
Integrated
Material Characterization
Electrochemical Measurements
Findings
Conclusions
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