Aluminium-ion batteries- moving beyond lithium-ion!

Shalini Divya¹, Jim Johnston¹, Thomas Nann²

¹School of Chemical and Physical Sciences, Victoria University of Wellington

²The University of Newcastle, Australia

Lithium-ion batteries (LIBs) are a common battery-choice for most applications. However, future battery demand will put pressure on lithium and cobalt reserves as these metal oxides (LiCoO₂) form the fundamental component of LIB electrodes. Moreover, the electrolyte typically used in LIBs is flammable, making them unsafe. As a result, any damage to the cell (like thermal runaway or electrode contact) leads to short circuits, sometimes leading to an explosion. Therefore, there is a need for alternative and more sustainable ion battery systems.

Rechargeable aluminium-ion batteries (AIBs) are promising alternatives to meet the growing energy storage requirements. They are low in cost, with low flammability and high volumetric energy density [1]. The aluminium anodes are not prone to ‘dendrite’ formation. To date, researchers have broadly focused on cathodes of AIBs such as various forms of graphite [2], vanadium oxides [3], and a few metal sulphides [4]. These non-aqueous batteries use an ionic liquid made of aluminum chloride (AlCl₃) and imidazolium chlorides (e.g., EMIC) as the electrolyte. The chloroaluminates (Al_xCl_y) ions from the electrolyte intercalate into the cathode layers during charging. During my Ph.D., I screened different cathode materials, focusing on 2D layered materials, natural carbon-based materials, transition metal dichalcogenides [5], nitrides, and carbides a better performing AIB than state-of-the-art. A few new cathode materials were found that had high stability and long cycle life and outperformed the existing ones. One of the cathodes was patented, and we are on our way to commercialising it and manufacturing AIBs soon through a spin-out company 'TasmanION'.

1. Ambroz et al., Adv. Energy Mater., 2017, 7.

2. Lin et al., Nature, 2015, 520.

3. Jayaprakash et al., Chem. Commun., 2011, 47.

4. Geng et al., Chem. Mater., 2015, 27.

5. Divya et al., Energy Technology, 2020, 8.

Bismuth and antimony 2D-nanostructures

Sara Salehi^1,2, Pawel Kowalczyk³, Tobias Maerkl^1,2, Maxim Le Ster^1,2, Ishan Mahajan^1,2, Guang Bian⁴, Xiaoxiong Wang⁵, Tai Chiang⁶, Simon Brown^1,2

¹School of Physical and Chemical Sciences, University of Canterbury

²MacDiarmid Institute for Advanced Materials and Nanotechnology

³Department of Solid State Physics, University of Lodz, Poland

⁴Department of Physics and Astronomy, University of Missouri, USA

⁵College of Science, Nanjing University of Science and Technology, China

⁶Department of Physics, University of Illinois at Urbana-Champaign, USA

Atomically thin materials, referred to as 2D-materials, are characterized by confinement in one dimension, strong in-plane bonds and weak van der Waals (VDW)-type interlayer coupling. Owing to the reduction of size and quantum confinement effects, 2D-Materials gain exotic, robust, rich and more importantly tuneable electrical and optical properties, different from those of their bulk counterparts [1]. 2D-materials are proposed to be promising candidates to revolutionize current technologies in various fields such as quantum computing, spintronics, energy conversion/storage and sensing [1].

Various 2D-materials ranging from graphene and transition metal dichalcogenides (TMDs) to compounds such as hexagonal boron nitrides (h-BN) have been thoroughly investigated in the past decade [1]. Black phosphorus (BP) 2D-structures (a rectangular allotrope of the elements of group-V in the periodic table), however, have gained less attention compared to the others [2]. We present an overview of our ongoing research on bismuth [3, 4] and antimony [5] BP-2D-nanostructures and the approaches which allow us to engineer their van der Waals heterostructures with a range of interesting electronic and morphological properties.

[1]M. Zeng et al., Chem. Rev. 2018, 118, 13, 6236–6296

[2]S. Wu et al. Adv Sci. 2018, 5, 5, 1700491

[3] S. A. Scott, M. V. Kral and S.A. Brown, PhysRevB, 2006, 73(20), 205424.

[4] P. J. Kowalczyk, O. Mahapatra, S.A Brown, G. Bian, X. Wang and T. C. Chiang, Nano Letters, 2012, 13(1), 43-47.

[5] T. Märkl, P. Kowalczyk, M. Le Ster, I.V. Mahajan, H. Pirie, Z. Ahmed, G. Bian, X. Wang and T. C. Chiang and S.A. Brown, 2D Materials, 2017, 5(1)-011002.

Two-dimensional allotropes of gallium oxide (Ga₂O₃): a first-principles study

Bushra Anam¹, Nicola Gaston¹

¹Department of Physics, University of Auckland

Rapidly emerging two-dimensional (2D) materials exhibit exotic physical and chemical properties compared to their bulk counterparts. Among these 2D materials, metallic layers are attracting tremendous interest due to their extraordinary properties and promising potential applications in bio sensing and imaging, catalysis, gas sensing, and magnetic recordings. However, they are largely unexplored. To date only few 2D metal oxides have been studied and their experimental synthesis has been stated.

In this project, we report on the stability of various 2D structures of Gallium oxide by using ab-initio density functional calculations. The electronic structure and bonding characteristics have been calculated using VASP software, and thermodynamic properties have been studied based on phonon properties by using PHONOPY code under the harmonic approximation [1-5]. We will present initial results on the relative stability of the 2D allotropes of Gallium oxide and this will demonstrates a new avenue to the discovery of thermodynamically stable 2D metallic layers with properties potentially suitable for electronic and optoelectronic applications.

1. G. Kresse and J. Hafner. Ab initio molecular dynamics for liquid metals. Phys. Rev. B, 1993, 47, 558.

2. G. Kresse and J. Hafner. Ab initio molecular-dynamics simulation of the liquid-metal-amorphous-semiconductor transition in germanium. Phys. Rev. B, 1994, 49, 14251.

3. G. Kresse and J. Furthmüller. Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Comput. Mat. Sci.,1996, 6, 15.

4. G. Kresse and J. Furthmüller. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B, 1996, 54, 11169.

5. A. Togo and I. Tanaka. First principles phonon calculations in materials science. Scr. Mater., 2015, 108, 1-5.

NaMgF₃:Ce,Sm nanoparticles suitable for radiation dose monitoring and real-time dose measurements

Hellen Nalumaga¹, Joe Schuyt¹, Grant Williams¹, Dave Clarke², Shen Chong¹

¹School of Chemical and Physical Sciences, Victoria University of Wellington

²Callaghan Innovation, New Zealand

NaMgF₃ is a near tissue-equivalent (Zeff = 10.39) host material that when doped with luminescent ions exhibits optically stimulated luminescence, radioluminescence (RL) and radiophotoluminescence (RPL) suitable for radiation dose measurement and monitoring [1, 2]. However, the majority of studies have focused on the bulk material with relatively few studies on nanoparticles. Studies on nanoparticles are encouraged as they have distinct properties in comparison to their bulk counterparts [1]. Additionally, they possess tunable optical properties and their luminescence can be enhanced through functionalisation. Furthermore, nanoparticles exhibit minimal light scattering that is useful for 2D dosimetry [3].

Previous research on bulk NaMgF₃:Sm has demonstrated that the material can be used for radiation dose monitoring via the RPL of the radiation-induced valence conversion Sm³⁺ to Sm²⁺ [2]. However, Sm³⁺ ions typically show weak photoluminescence (PL) due to the low oscillator strengths of their forbidden intraconfigurational 4f transitions. The Sm³⁺ luminescence can be enhanced by co-doping the compound with a sensitising ion and the allowed 4f → 5d transitions of Ce³⁺ can be used in this regard, where Ce³⁺ excitation in the UV can lead to energy transfer to Sm³⁺ ions. Herein, we present an analysis of the luminescence properties of Ce,Sm-doped NaMgF₃ nanoparticles, before, during and after stimulation with X-rays. We observed Ce³⁺ sensitisation of the Sm³⁺ PL emissions. X-ray irradiation caused the conversions of Sm³⁺ and Ce³⁺ to Sm²⁺ and Ce⁴⁺, respectively, and these RPL signals could be used for cumulative dose monitoring. Furthermore, the dose-history independence of the Sm²⁺ RL after a priming dose renders the material favourable for real-time dose measurements.

(1) J. Schuyt, G. Williams, J. Lumin., 2018, 204, 472-479.

(2) J. Schuyt, G. Williams, Mater. Res. Bull., 2018, 106, 455-458.

(3) G. Williams, S. Janssens, C. Gaedtke, S. Raymond, D. Clarke, J. Lumin., 2013, 143, 219-225.

A study of upconversion thermometry using Yb³⁺/Er³⁺ Co-doped KY₃F₁₀ nanoparticles

Pratik Solanki¹, Sangeetha Balabhadra¹, Michael Reid¹, Vladimir Golovko¹, Jon-Paul Wells¹

¹School of Physical and Chemical Sciences, University of Canterbury

We report high-sensitivity luminescence thermometry using Yb³⁺/Er³⁺ co-doped KY₃F₁₀ core and core-shell upconverting nanoparticles. The highest thermal sensitivity of 1.51 and 1.38 % K^-1 and temperature uncertainty of 0.11 K (for core only nanoparticles) was achieved by tuning the excitation wavelength from 975 to 980 nm from in-to-near resonant with optical transitions of the Yb³⁺ ion. The observed thermal sensitivity is not strongly dependent upon the excitation wavelength. High-resolution Yb³⁺ excitation spectra were measured by monitoring the Er³⁺ 4S3/2,4F9/2→4I15/2 upconversion fluorescence, with the highest fluorescence yield obtained at 10254 cm^-1 (975 nm) for both nanoparticles. This coincides with the ground state absorption maximum at 297 K. However, at 10 K, the Yb³⁺ upconversion excitation spectra also show evidence of excited state absorption peaks. The Yb³⁺ absorption spectra for the core and core-shell nanoparticles is dominated by single ion centres (of C4v symmetry). Resonant excitation of both the core and core-shell nanoparticles is observed to yield a five-fold increase in Er³⁺ upconversion intensity relative to excitation at 980 nm, increasing the fluorescence intensity ratio and the thermal sensitivity of a KY₃F₁₀ nanothermometer operating at the physiological temperatures.

Photoluminescence originating from silica defects in the diatom frustules

Jiazun Wu¹, Gerald Smith¹, Grant Williams¹

¹School of Chemical and Physical Sciences, Victoria University of Wellington

Diatoms are unicellular algae with nanoporous cell shells (frustules) made of hydrated amorphous silica. Photoluminescence (PL) was observed when excited with UV radiation even after using oxidising chemicals to remove the contents of the diatoms and exterior adherent molecules. Although the PL excitation and emission spectra of various defects overlap, their PL lifetimes that are mainly in the microsecond range allow partial separation and identification of some luminescent species.

Point defects in amorphous silica are of three general types: (i) intrinsic structural defects, (ii) trace adventitious impurities and (iii) structural alteration induced by radiation [1].

The excitation and emission spectra and luminescence lifetimes from chemically cleaned diatom frustules were compared with those originating from commercially-obtained fused silica and high-purity silica nanoparticles. When frustules were excited at ~265 nm, emission with a maximum at ~420 nm was observed with a lifetime ~4 µs. This is in good agreement with that observed from the mechanically-ground fused silica sample. TEM/EDS mapping examination showed both of these materials contained some aluminium ions replacing silicon in the silica matrix. The aluminium-impurity defects exhibited PL with these spectral distributions. Emission with a maximum at ~620 nm when excited at ~280 nm was observed in all forms of the amorphous/fused silica studied and was attributed to non-bridging oxygen hole centres. Emission with a maximum in the 530-550 nm range has been previously reported from frustules excited by intense UV at 325 nm from a laser. In this work, although this emission was not apparent in the emission spectrum, it was evident in lifetime measurements carried out at 530 nm using excitation with a less intense pulsed LED source. This behaviour is consistent with the formation of photoinduced defects.

1 L. Skuja, J. Non. Cryst. Solids, 1998, 239, 16-48.