Influence of milling time in solid-state synthesis on structure, morphology and electrochemical properties of Li4Ti5O12 of spinel structure

doi:10.1016/j.powtec.2014.06.056

Powder Technology

Volume 266, November 2014, Pages 372-377

https://doi.org/10.1016/j.powtec.2014.06.056 Get rights and content

Highlights

•
Successfully synthesized phase-pure Li₄Ti₅O₁₂ of spinel structure.
•
Raman spectroscopy studies confirmed XRD analysis.
•
Extending synthesis time slightly improved electrochemical performance of Li₄Ti₅O₁₂.

Abstract

A high-energy ball-milling process was used for the solid-state synthesis of single phase powders of spinel-structured lithium-titanium oxide (Li₄Ti₅O₁₂). The influence of the high-energy ball-milling time on the structure, morphology, and electrochemical performance of synthesized powders was investigated. Remarkably, the electrochemical tests performed at high rates showed significantly improved specific capacity of the powders obtained with extended synthesis times. In particular, after 50 charging/discharging cycles at the current rate of 1C, the samples retained more than 94% of their initial specific capacity.

Graphical abstract

Introduction

Recently, there has been an increasing interest in the development of lithium–titanium oxide (Li₄Ti₅O₁₂; LTO) of spinel (cubic) structure as a potential negative electrode (anode) material for application in lithium-ion batteries and hybrid supercapacitors. Lithium–titanium oxide shows a number of improved characteristics compared with carbon-based anode materials [1], [2], [3]. In particular, it has good structural stability, with practically negligible volume change during the Li⁺ insertion and extraction processes, which potentially means superior capacity retention and very long cycle life. Li₄Ti₅O₁₂ exhibits also a flat operating potential of about 1.55 V vs. Li/Li⁺ i.e., higher than the reduction potential of the most electrolyte solvents. This prevents SEI formation and metallic lithium plating on the electrode's surface. All these mentioned characteristics make Li₄Ti₅O₁₂ an advantageous anode material for use in lithium-ion batteries, when the electrode's safety, long lifetime, and reliability, are concerned [4], [5], [6]. However, the major problem of lithium titanium oxide is its poor rate capability, mainly due to low electronic conductivity and slow diffusion of lithium ions. Various strategies have been proposed to address these problems. For example, the conductivity of lithium–titanium oxide can be greatly improved by surface modifications, cation doping or selecting different methods of LTO preparation. On the other hand, using Li₄Ti₅O₁₂ in a nano-scale form is the best way to overcome the inefficient mobility of Li⁺ cations, as the lithium diffusion pathways are significantly reduced [7].

A variety of synthesis methods have been employed to obtain single-phase, ultrafine and homogenous powders of Li₄Ti₅O₁₂. Among them, the solid state synthesis is considered the most economical, efficient and simple way for the mass production of Li₄Ti₅O₁₂ [7], [8], [9], [10], [11], [12], [13], [14]. The solid state synthesis has been often combined with additional processing methods such as high-energy ball-milling (HEBM) [8], [12], [13], [14], addition of carbon to the starting materials [10], or so-called two stage thermal treatment [11]. While there are few other approaches to obtain nano-sized Li₄Ti₅O₁₂ spinel powders, such as sol–gel [7], [15], [16], [17] or combustion methods [18], [19], they are more complicated and require expensive reagents. Thus, the solid-state synthesis remains unrivaled when the scaling-up and mass production of lithium titanium oxide are considered.

In this work we present a new solid state synthesis approach to obtain nano-scale Li₄Ti₅O₁₂, which involves the use of a two-stage thermal treatment preceded by high-energy ball-milling (HEBM). The main focus of the current study is the influence of the milling time on structure, morphology and electrochemical performance of Li₄Ti₅O₁₂ obtained using this method.

Section snippets

Synthesis of Li₄Ti₅O₁₂

The solid-state synthesis was used to obtain single-phase lithium-titanium oxide powders of the spinel structure. The synthesis was carried out under high-energy ball-milling (HEBM) process, using ethanol as a medium and zirconia balls in a Planetary Mono Mill PULVERISETTE 6 (Fritsch, Germany). The starting reagent used was titanium dioxide TiO₂ (99%, Sigma-Aldrich) mixed with lithium carbonate Li₂CO₃ (synthesized in-house, at the Institute of Electronic Materials Technology) at the Ti:Li molar

XRD results

The XRD analysis shows that all synthesized Li₄Ti₅O₁₂ powders (Fig. 2) are single phase materials, and all have the spinel-type Fd3m structure with no other phases observed in the diffraction patterns. As shown in Fig. 2, all 6 characteristic XRD peaks observed for these LTO powders, i.e. peaks at the 2θ angles of 18.35, 35.60, 27.24, 43.28, 47.39 and 57.27°, are successfully indexed using the cubic structure of lithium–titanium oxide (ICDD-49-0207). These peaks correspond to the (111), (311),

Conclusions

We successfully obtained Li₄Ti₅O₁₂ material using high-energy ball-milling process with alcohol medium. With longer high-energy ball-milling time, we observed smaller powders' grains, smaller crystallite sizes and better electrochemical results.

Structural analysis by XRD and Raman spectroscopy yielded consistent results. Both methods show good crystal quality and decrease in average grain size with the increase of milling time. The shape of the Raman spectrum does not change with milling time

Acknowledgments

This work was supported by The National Centre for Research and Development through the research grant PBS1 (contract no. PBS1/A1/4/2012). The work of D. Ziolkowska was supported by the Foundation for Polish Science International PhD Projects Programme co-financed by the EU European Regional Development Fund. M. Krajewski, D. Ziolkowska and B. Hamankiewicz would like to thank for the scholarship awarded by the Mazovia Voivodeship Office.

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Citation Excerpt :
All mentioned above properties make Li4Ti5O12 an excellent anode material used in high-rate, high safety, high voltage, and long cycle life lithium-ion batteries [1–18]. One of the major factors which limits the wide practical applications of the pristine LTO material is the low electronic (<10−13 S·cm−1) and sluggish Li+ diffusion coefficient (10−9–10−13 cm2·s−1) resulting in poor electrochemical rate performances [1–18]. Various strategies have been utilized to solve these problems, like surface modification of pristine material, doping with ions or creation of new techniques to get a LTO material with better electrochemical properties [7–18].
Lithium titanium oxide (Li₄Ti₅O₁₂) particles were surface-modified with 1–5% wt. of multi-walled carbon nanotubes (MWCNT) using a new low temperature method (LTM). Subsequent techniques have been applied to characterize all materials: X-ray powder diffraction (XRD), Raman and X-ray photoelectron (XPS) spectroscopy, scanning electron (SEM), transmission (STEM), and atomic force (AFM) microscopy. The selected materials have been subjected to preliminary electrochemical analysis. The effect of the synthesis conditions on the obtained series of LTO/1–5% wt. MWCNT nanocomposites was analyzed. X-ray diffraction showed that the crystal structure of LTO is not affected by the multi-walled carbon nanotubes (MWCNT) modification. Raman spectroscopy confirms the XRD results that the MWCNTs do not affect the LTO structure and all nanocomposites show similar levels of defects and/or degree of graphitization. The XPS measurements showed the most intense line at the binding energy of 284.5 eV, which corresponds to the C=C/C-C bonding in carbon atoms in the graphitic structure on the surface of the LTO material. Additionally, the peak at 285.3 eV was attributed to aliphatic structures, edges, and defects in the graphitic nanotube structure, whereas the peaks at 286.1, 287.6, 289.0 and 290.1 eV, correspond to CO, CO, HO-C=O, and OCOO, carbon atoms attached to different oxygen-containing moieties, respectively. CNTs were well distributed between LTO particles, as revealed by STEM observations. Single CNTs or agglomerates by joining LTO particles created cross-links for electron transfer. The relationship and effect between the structural and morphological analysis of spinel Li₄Ti₅O₁₂ structure modified with carbon nanotubes was examined for the first time in this work. The performed preliminary electrochemical measurements revealed that the best electrochemical properties was obtained for LTO powder modified with 1%wt. of MWCNT. After 50 cycles of charge/discharge processes at the current rate of 1 C, the LTO/1%wt. MWCNT powder retained more than 98% of its specific capacity.

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Influence of milling time in solid-state synthesis on structure, morphology and electrochemical properties of Li4Ti5O12 of spinel structure

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Synthesis of Li4Ti5O12

XRD results

Conclusions

Acknowledgments

Int. J. Electrochem. Sci.

Int. J. Electrochem. Sci.

J. Power Sources

Electrochim. Acta

J. Power Sources

Solid State Ionics

J. Power Sources

Electrochem. Commun.

Solid State Ionics

J. Alloys Compd.

J. Phys. Chem. Solids

J. Alloys Compd.

J. Power Sources

Electrochim. Acta

J. Alloys Compd.

Solid State Ionics

Influence of milling time in solid-state synthesis on structure, morphology and electrochemical properties of Li₄Ti₅O₁₂ of spinel structure

Synthesis of Li₄Ti₅O₁₂