Mesoporous TiO2/TiC@C Composite Membranes with Stable TiO2-C Interface for Robust Lithium Storage

摘要

class="head no_bottom_margin" id="sec1title">IntroductionLithium-ion batteries (LIBs) are widely used in portable electric devices and electric vehicles (, , ). Extensive research has been carried out to develop transition metal oxides (TMOs)-based composite materials as LIB anodes (, , , , , , , , , , , ). In most cases, carbon materials including mesoporous carbon, carbon nanotubes, and graphene are employed as ideal matrixes for TMOs anodes owing to their unique properties such as excellent conductivity and flexibility, which can facilitate stable and fast lithium storage (href="#bib39" rid="bib39" class=" bibr popnode">Zhang et al., 2014, href="#bib9" rid="bib9" class=" bibr popnode">Fang et al., 2016, href="#bib24" rid="bib24" class=" bibr popnode">Mo et al., 2017). However, current TMOs/C composite anodes still suffer from poor cycling stability due to unstable TMOs-C interfaces resulting from the volume change difference between carbon and TMOs upon Li⁺ insertion/extraction. The unstable TMOs-C interfaces may cause aggregation of TMOs nanoparticles as well as collapse of carbon frameworks. As a result, the cycling life over 1,000 cycles based on TMOs/carbon composites have been extremely limited. Therefore the construction of stable TMOs-carbon interfaces is the key for stable and robust lithium storage, which remains a considerable challenge.Among the different kinds of TMOs, TiO2 is an attractive material for LIBs owing to its natural abundance, low cost, and environmental benignancy (href="#bib20" rid="bib20" class=" bibr popnode">Liu and Chen, 2014, href="#bib21" rid="bib21" class=" bibr popnode">Liu et al., 2015a, href="#bib38" rid="bib38" class=" bibr popnode">Zhang et al., 2012). TiO2/C composite anode materials with various dimensions and structures have been fabricated, which include hierarchical TiO2/C nanocomposite monoliths (href="#bib13" rid="bib13" class=" bibr popnode">Huang et al., 2016), ordered mesoporous TiO2/C nanocomposites (href="#bib37" rid="bib37" class=" bibr popnode">Zeng et al., 2013), graphitic carbon conformal coating of mesoporous TiO2 hollow spheres (href="#bib22" rid="bib22" class=" bibr popnode">Liu et al., 2015b), and mesoporous TiO2 coating on flexible graphitized carbon (href="#bib23" rid="bib23" class=" bibr popnode">Liu et al., 2016). However, all TiO2/C composites also suffer from severe structural collapse stemming from unstable TiO2-C interfaces. In this regard, TiO2/C composite represents a typical class of LIB anode materials facing the problem of serious structure disintegration. Therefore there is a pressing need to solve the aforementioned problem of TiO2/C composite.Herein, to construct stable TiO2-C interfaces, TiC nanodots with high conductivity and electrochemical inactivity (href="#bib32" rid="bib32" class=" bibr popnode">Wang et al., 2016b, href="#bib33" rid="bib33" class=" bibr popnode">Yao et al., 2011, href="#bib26" rid="bib26" class=" bibr popnode">Peng et al., 2016, href="#bib1" rid="bib1" class=" bibr popnode">Allcorn and Manthiram, 2015) are introduced to TiO2-C interfaces by an in situ carbothermic reduction (href="#bib34" rid="bib34" class=" bibr popnode">Yu et al., 2007) that occurs in TiO2-nanocrystals-embedded mesoporous carbon framework (TiO2@C) membranes. The designed strategy leads to the formation of stable TiO2-C interfaces where TiC nanodots act as a bridge to link TiO2 nanocrystals and carbon frameworks accurately. The obtained mesoporous TiO₂/TiC@C composite membranes have a conductive, robust, and mesoporous framework. Besides, TiO₂ nanocrystals and TiC nanodots are interconnected and highly dispersed in the mesoporous carbon frameworks. When used as additive-free and binder-free electrodes, the TiO₂/TiC@C membranes deliver a high capacity of ∼237 mA⋅h⋅g⁻¹ at a current density of 0.4 A⋅g⁻¹. More importantly, an ultra-long cycling life (up to 5,000 cycles with over 68.4% reversible capacity retention) and superior rate performance can be achieved. Furthermore, a flexible full battery with impressive battery performance was assembled by using the TiO₂/TiC@C membranes as the anode, highlighting the great potential of the composite membranes in flexible devices.