Novel nanomaterials based on electronic and mixed conductive glasses
Introduction
Lithium–nickel–cobalt oxides, lithium–manganese-oxides, vanadium oxides or phosphates and phospho-olivines belong to the most studied materials for cathodes in Li–ion rechargeable batteries [1], [2], [3], [4]. Majority of these materials are polycrystalline. Substantially less is known about glasses [5] or glassy-crystalline nanomaterials suitable for battery applications. It was shown [6], that glasses of the Li2O–V2O5–P2O5 system are mixed electronic–ionic conductors in which the proportions of the electronic-to-ionic components of the total conductivity depend on the ratio between the contents of a glass modifier (Li2O) and glass formers (V2O5 + P2O5). Use of these glasses as potential cathode materials for lithium batteries requires that the conduction is mainly electronic. An increase in electronic conductivity of these materials can be achieved after their nanocrystallization, induced by an appropriate annealing process.
The aim of this paper was to demonstrate that electric conductivity of potential glassy cathode materials may be substantially improved by their nanocrystallization. We have studied lithium–vanadate-phosphate (LVP) and lithium–iron-phosphate (LFP) glasses. The latter glasses are amorphous analogs of polycrystalline phospho-olivines intensively studied recently. Unfortunately, besides all their advantages [1], polycrystalline olivines have one serious deficiency—very low electrical conductivity at room temperature (ca. 10− 10 S cm− 1). This low conductivity may be considerable increased in nanocrystalline olivines.
In our studies we have used impedance spectroscopy (IS), thermal analyses (DSC/DTA), X-ray diffractometry (XRD) and scanning electron microscopy (SEM).
Section snippets
Experimental
Lithium–vanadate-phosphate (LVP) and lithium–iron-phosphate (LFP) glasses were synthesized by a standard press quenching technique.
Two series of vanadate–phosphate glasses were prepared—one containing lithium and one lithium-free. Their compositions were described by respective formulas: i) xLi2O·(100 − 2x)V2O5·xP2O5, for 15 ≤ x ≤ 45, and ii) xV2O5·(100 − x)P2O5, for 60 ≤ x ≤ 90. Samples were prepared from pre-dried and mixed chemicals: V2O5 (ABCR, 99.9%), NH4H2PO4 (POCh, 99.9%) and LiNO3 (Aldrich,
Results and discussion
Use of mixed conductive LVP or LFP glasses as potential cathode materials for lithium batteries requires that the electric conduction is mainly electronic. This occurs in V2O5-rich LVP glasses and all LFP glasses under study.
Conclusions
Electronic and mixed conductive glasses can be promising starting compounds to prepare attractive nanostructured materials. The annealing of LVP glasses leads to their nanocrystallization. The resulting nanomaterials exhibit much higher electronic conductivity (10− 1 S·cm− 1 at 300 °C), lower activation energy and better thermal stability than the initial glasses. It was found that thermal nanocrystallization of LFP glasses also leads to the electronic conductivity enhancement and therefore it
Acknowledgements
The authors thank Dr. I.Gorzkowska (Department of Chemistry, Warsaw University of Technology) for her assistance in DTA measurements and Dr. S.Gierlotka (Institute of High Pressure Physics PAS) for his help in SEM studies.
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Glasses: Phosphates
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2018, Journal of Non-Crystalline SolidsEffect of conditional glass former variation on electrical transport in Li<inf>2</inf>O-P<inf>2</inf>O<inf>5</inf> glassy and glass-ceramic ionic system
2014, Solid State IonicsCitation Excerpt :Therefore, mainly two approaches have been used to increase the ionic transport, viz., (i) addition of salt to provide mobile ions and (ii) use of mixed glass formers. Salt addition (Li2SO4, LiCl etc.) [7–9] leads to an increase in the number of charge carries, whereas, use of mixed glass formers (e.g. P2O5–B2O3) essentially increases the free volume of the glass matrix [11–23]. Typical glass formers e.g. SiO2, P2O5, and B2O3form a glassy state naturally, following the Zachariasen rules [10].