Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 10, Issue 26, Pages 22580-22590Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsami.8b05057
Keywords
Li4Ti5O12; nanoparticles; mesoporous fiber; mesoporous film; size effects; interfacial charge storage; pair distribution function
Funding
- DFG via the GRK (Research Training Group) [2204]
- LOEWE program of excellence of the Federal State of Hessen (project initiative STORE-E)
- China Scholarship Council (CSC) [2011631008]
- Diamond Light Source [EE13560, SP13560]
- Center for Materials Research (LaMa) at Justus Liebig University Giessen
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Lithium titanate Li4Ti5O12 (LTO) is regarded as a promising alternative to carbon-based anodes in lithium-ion batteries. Despite its stable structural framework, LTO exhibits disadvantages, such as the sluggish lithium-ion diffusion and poor electronic conductivity. To modify the performance of LTO as an anode material, nanosizing constitutes a promising approach and the impact is studied here by a systematical experimental approach. Phase-pure polycrystalline LTO nanoparticles (NPs) with high crystallinity and crystallite sizes ranging from 4 to 12 nm are prepared by an optimized solvothermal protocol and characterized by several state-of-the-art technologies, including high-resolution transmission electron microscopy, X-ray diffraction (XRD), pair distribution function (PDF) analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy. Through a wide array of electrochemical analyses, including charge/discharge profiles, cyclic voltammetry, and electrochemical impedance spectroscopy, a crystallite size of approx. 7 nm is identified as the optimum particle size. Such NPs exhibit as good reversible capacity as the ones with larger crystallite sizes but with a more pronounced interfacial charge storage. By decreasing the crystallite size to about 4 nm, the interfacial charge storage increases remarkably, however resulting in a loss of reversible capacity. An in-depth structural characterization using the PDF obtained from synchrotron XRD data indicates an enrichment in Ti for NPs with the small crystallite sizes, and this Ti-rich structure enables a higher Li storage. The electrochemical characterization confirms this result and furthermore points to a plausible reason as to why a higher Li storage in very small nanoparticles (4 nm) results in a loss in the reversible capacity.
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