Template-assisted synthesis of high packing density SrLi2Ti6O14 for use as anode in 2.7-V lithium-ion battery

doi:10.1016/j.jpowsour.2010.11.011

Journal of Power Sources

Volume 196, Issue 5, 1 March 2011, Pages 2871-2874

https://doi.org/10.1016/j.jpowsour.2010.11.011 Get rights and content

Abstract

SrLi₂Ti₆O₁₄ has been prepared by using mesoporous TiO₂ brookite as a template and reactant. The prepared particles retained the rounded shape of the precursor, leading to high dispersivity and high packing density. The material has been further electrochemically characterized in both half and full cells. It shows good cycling stability and rate capability. A 2.7-V cell has been built by combining a SrLi₂Ti₆O₁₄ anode with a 4-V spinel cathode of LiMn₂O₄. This cell has a higher voltage compared to the 2.5-V LiMn₂O₄/Li₄Ti₅O₁₂ system.

Research highlights

▶ This work deals with the preparation and characterization of an alternative anode material to graphite and lithium titanate, namely SrLi₂Ti₆O₁₄. ▶ To reduce agglomeration issue related to the use of high temperature synthesis, the complex titanate has been prepared by using mesoporous TiO₂ as template and reactant. The as prepared material displayed high purity, well defined particle shape (rounded) leading to high packing density material. ▶ Furthermore, the prepared material was combined with the spinel 4-V cathode leading to a 2.7-V lithium ion cell. The cell displayed high cycling stability and good rate capability which makes it a suitable candidate for high power applications.

Introduction

The safety concern related to the use of a carbonaceous-based electrode in lithium-ion batteries (LIBs) has driven ample research directed toward improving the cell abuse tolerance via engineering and cell chemistry solutions. Within the latter approach, the use of less reducing anodes can mitigate the thermal instability of the solid-electrolyte interface, thus improving the safety of the battery. Titanium-based oxides, including the commercially available Li₄Ti₅O₁₂, are suitable anodes because they operate at 1.5–1.8 V within the electrolyte stability zone [1]. Nevertheless, it is of interest to investigate other systems that can display a lower operating voltage in order to increase the overall energy density of the cell while operating within the electrolyte stability region. In this regard, the complex titanates SrLi₂Ti₆O₁₄ and BaLi₂Ti₆O₁₄ were considered as potential candidates to replace Li₄Ti₅O₁₂ due to their low operating voltage, around 1.3–1.4 V [2]. Later, Na₂Li₂Ti₆O₁₄ was reported to display an even lower potential of 1.25 V [3]. A comparative study of sol-gel synthesized MLi₂Ti₆O₁₄ (M = Ba, Sr, 2Na) compounds has shown that SrLi₂Ti₆O₁₄ exhibited the most promising properties [4]. Additionally, these materials possess less inactive lithium atoms as compared to Li₄Ti₅O₁₂, which can help reducing the cost, especially if an “all electric” vehicle is to be developed [5].

The synthesis of complex metal oxides with a defined shape is challenging, mostly because of the calcination at high temperature that is required for the preparation of pure crystalline phases. High temperature calcinations often lead to the formation of agglomerates, which prevent the growth of well-defined particles. Template-directed synthesis is a powerful route to tune the morphology and, hence, the physical properties of advanced materials. This technique has been widely used for the preparation of electrode materials using soft and hard templates [6]. An alternative to the use of organic (surfactants, co-polymer, etc.) or inorganic membranes (anodic aluminum oxide, silica, etc.) is a template that combines a pre-existing and well-defined shape structure and also plays the role of a chemical reagent. Such a method was presently adopted for the preparation of the complex titanate SrLi₂Ti₆O₁₄ by using mesoporous TiO₂ with a well-defined shape as both a template and reactant. Recently, we reported on the synthesis of mesoporous TiO₂ brookite prepared by thermal decomposition of an oxalate precursor obtained by an aqueous precipitation method [7].

Criteria for the selection of an electrode material are tightly related to its morphology. For high rate performance, nano-structured materials are undoubtedly more suitable than micron-sized particles. Nevertheless, nano-particles display several drawbacks related to their tendency to form agglomerates, leading to inhomogeneous electrodes. On the contrary, micron-sized and well-defined particles, especially rounded ones, exhibit a better dispersibility and, more important, have higher volumetric energy density. In the present work, mesoporous and micron-size particles of TiO₂ were used as a template for the synthesis of the complex titanate SrLi₂Ti₆O₁₄. The latter was characterized for use as the anode for lithium-ion batteries.

Section snippets

Experimental procedure

A two-step process was used for the synthesis of SrLi₂Ti₆O₁₄. First, the TiO₂ precursor, the oxalate-based compound Ti₂O₃(H₂O)₂(C₂O₄)·H₂O, was synthesized by an aqueous precipitation method performed at 90 °C for 3 h. Titanium oxysulfate (Sigma–Aldrich, Supelco) and Li₂C₂O₄ were used as chemicals. After washing and drying the titanium oxalate hydrate, it was decomposed at 400 °C, leading to pure TiO₂. Thereafter, TiO₂ was dispersed in an ethanol/acid acetic solution containing the strontium

Results and discussion

The synthesis conditions were selected to achieve rounded and micron-sized TiO₂ particles offering suitable dispersibility and high packing density. X-ray diffraction analysis (Fig. 1) confirmed the phase purity of the oxalate phase whose pattern was indexed within the Cmca space group [8]. After thermal decomposition at 400 °C, the titanium oxalate phase transformed to TiO₂ brookite, as confirmed by XRD (Fig. 1). Due the removal of the oxalate/water species during the decomposition of Ti₂O₃(H₂O)

Conclusion

Particles of SrLi₂Ti₆O₁₄ that are dispersable and possess high packing density have been synthesized using mesoporous TiO₂ as template and reactant. The prepared material reversibly inserts three lithium atoms per unit formula. When a SrLi₂Ti₆O₁₄ anode is combined with a 4-V cathode, the 2.7 V cell shows good cycling stability and rate capability. This makes SrLi₂Ti₆O₁₄ a promising anode for high power applications.

Acknowledgments

This research was funded by the U.S. Department of Energy, FreedomCAR and Vehicle Technologies Office. Argonne National Laboratory is operated for the U.S. Department of Energy by UChicago Argonne, LLC, under contract DE-ACO2-06CH11357.

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Short communicationTemplate-assisted synthesis of high packing density SrLi2Ti6O14 for use as anode in 2.7-V lithium-ion battery

Abstract

Research highlights

Introduction

Section snippets

Experimental procedure

Results and discussion

Conclusion

Acknowledgments

J. Power. Sources

Electrochem. Commun.

Electrochem. Commun.

Solid State Sci.

Short communication
Template-assisted synthesis of high packing density SrLi₂Ti₆O₁₄ for use as anode in 2.7-V lithium-ion battery