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Synthesis, characterisation and modification of materials for Na-ion batteries

Driscoll, Laura Louise (2017)
Ph.D. thesis, University of Birmingham.

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Abstract

This thesis describes the synthesis, characterisation and modification of a range of sulfate materials, of interest for applications as cathodes for Na-ion batteries. The successful synthesis and doping of sodium transition metal sulfate hydrates is reported. Two structures are possible for Na2M(SO4)2·2H2O: a monoclinic structure, favoured by larger divalent transition metal cations (e.g. Mn, Fe, Co and Cu) and a triclinic structure, which is only naturally adopted by the smaller Ni2+. The effect of substitution of (SO4)2- by isoelectronic dopants such as (PO3F)2- and (SeO4)2- was explored. The structure obtained after doping was found to be strongly dependent on the cation selected to form the framework and level/type of dopant used. In addition, the products of dehydration were also examined and it was found that systems that naturally adopt a Na2M(SO4)2 phase after dehydration, can adopt a novel alluaudite-type phase Na3M1.5(SO4)3-x(SeO4)x, once a threshold concentration of selenate is reached.

The langbeinite system, K2MII2(SO4)3, has also been investigated as a potential host structure for sodium due to its structural similarity to the well-established NaSICON systems. A Na substitution study was conducted on K2Mg2(SO4)3, which showed that up to 88% of the K could be replaced by Na. This study was later extended to examine langbeinite systems containing common transition metals used in battery materials (Mn, Fe, Co and Ni). Lower sodium levels could be accommodated in these latter systems, although the amount of Na incorporation could be increased by partial substitution of the transition metal by Mg.

In addition, this thesis reports an alternative synthetic approach to obtain a small family of Na-V-S-O systems. The method proposed in this work consistently produces high purity samples at relatively low temperatures (<400°C).

Type of Work:Ph.D. thesis.
Supervisor(s):Slater, Peter and Wright, Adrian
School/Faculty:Colleges (2008 onwards) > College of Engineering & Physical Sciences
Department:School of Chemistry
Additional Information:

Embargo till 31 July 2019

Subjects:QD Chemistry
Institution:University of Birmingham
ID Code:7144
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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