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Unveiling the thermodynamic and kinetic properties of NaxFe(SO4)2 (x = 0–2): toward a high-capacity and low-cost cathode material
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. (Materials Theory Division)
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. (Materials Theory Division)
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Royal Inst Technol KTH, Dept Mat & Engn, Appl Mat Phys, S-10044 Stockholm, Sweden. (Materials Theory Division)
2016 (Engelska)Ingår i: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 4, s. 17960-17969Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The mineral eldfellite, NaFe(SO4)2, was recently proposed as an inexpensive candidate for the next generation of cathode application in Na-based batteries. Employing the density functional theory framework, we have investigated the phase stability, electrochemical properties and ionic diffusion of this eldfellite cathode material. We showed that the crystal structure undergoes a volume shrinkage of ≈8% upon full removal of Na ions with no imaginary frequencies at the Γ point of phonon dispersion. This evokes the stability of the host structure. According to this result, we proposed structural changes to get higher specific energy by inserting two Na ions per redox-active metal. Our calculations indicate NaV(SO4)2 as the best candidate with the capability of reversibly inserting two Na ions per redox center and producing an excellent specific energy. The main bottleneck for the application of eldfellite as a cathode is the high activation energies for the Na+ ion hop, which can reach values even higher than 1 eV for the charged state. This effect produces a low ionic insertion rate.

Ort, förlag, år, upplaga, sidor
2016. Vol. 4, s. 17960-17969
Nationell ämneskategori
Fysik Den kondenserade materiens fysik
Identifikatorer
URN: urn:nbn:se:uu:diva-311345DOI: 10.1039/C6TA05330KISI: 000388505400007OAI: oai:DiVA.org:uu-311345DiVA, id: diva2:1059801
Forskningsfinansiär
VetenskapsrådetEnergimyndighetenStandUpTillgänglig från: 2016-12-23 Skapad: 2016-12-23 Senast uppdaterad: 2018-12-19Bibliografiskt granskad
Ingår i avhandling
1. Energy Storage Materials: Insights From ab Initio Theory: Diffusion, Structure, Thermodynamics and Design.
Öppna denna publikation i ny flik eller fönster >>Energy Storage Materials: Insights From ab Initio Theory: Diffusion, Structure, Thermodynamics and Design.
2017 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

The development of science and technology have provided a lifestyle completely dependent on energy consumption. Devices such as computers and mobile phones are good examples of how our daily life depends on electric energy. In this scenario, energy storage technologies emerge with strategic importance providing efficient ways to transport and commercialize the produced energy. Rechargeable batteries come as the most suitable alternative to fulfill the market demand due to their higher energy- and power- density when compared with other electrochemical energy storage systems. In this context, during the production of this thesis, promising compounds for advanced batteries application were investigated from the theoretical viewpoint. The framework of the density functional theory has been employed together with others theoretical tools to study properties such as ionic diffusion, redox potential, electronic structure and crystal structure prediction.

Different organic materials were theoretically characterized with quite distinct objectives. For instance, a protocol able to predict the redox potential in solution of long oligomers were developed and tested against experimental measurements. Strategies such as anchoring of small active molecules on polymers backbone have also been investigated through a screening process that determined the most promising candidates. Methods such as evolutionary simulation and basin-hopping algorithm were employed to search for global minimum crystal structures of small molecules and inorganic compounds working as a cathode of advanced sodium batteries. The crystal structure evolution of C6Cl4O2 upon Na insertion was unveiled and the main reasons behind the lower specific capacity obtained in the experiment were clarified. Ab initio molecular dynamics and the nudged elastic band method were employed to understand the underlying ionic diffusion mechanisms in the recently proposed Alluaudite and Eldfellite cathode materials. Moreover, it was demonstrated that electronic conduction in Na2O2, a byproduct of the Na-O2 battery, occurs via hole polarons hopping. Important physical and chemical insights were obtained during the production of this thesis. It finally supports the development of low production cost, environmental friendliness and efficient electrode compounds for advanced secondary batteries. 

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2017. s. 83
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1584
Nyckelord
Density Functional Theory, Defects Diffusion, Thermodynamics and Batteries.
Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:uu:diva-331399 (URN)978-91-513-0122-8 (ISBN)
Disputation
2017-12-07, Polhemsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 13:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2017-11-15 Skapad: 2017-10-19 Senast uppdaterad: 2018-03-07
2. Materials Modelling for Energy Harvesting: From Conversion to Application through Storage
Öppna denna publikation i ny flik eller fönster >>Materials Modelling for Energy Harvesting: From Conversion to Application through Storage
2019 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

In this Ph.D. thesis, ab initio density functional theory along with molecular dynamics and global optimization methods are used to unveil and understand the structures and properties of energy relevant materials. In this connection, the following applications are considered: i. electrocatalyst for solar fuel production through water splitting, ii. hybrid perovskite solar cell for generation of electrical energy and iii. Battery materials to store the electrical energy. The water splitting mechanism in terms of hydrogen evolution and oxygen evolution reactions (HER and OER) on the catalytic surfaces has been envisaged based on the free energy diagram, named reaction coordinate, of the reaction intermediates. The Ti-functionalized two-dimensional (2D) borophene monolayer has been emerged as a promising material for HER and OER mechanisms as compared to the pristine borophene sheet. Further investigation in the series of this noble metal free monolayer catalyst is 2D Al2C monolayer both in form of pristine and functionalized with nitrogen (N), phosphorous (P), boron (B), and sulphur (S). It has been observed that only B substituted Al2C shows very close to thermoneutral, that could be the most promising candidate for HER on functionalized Al2C monolayer. The adsorption of O* intermediate is stronger in S-substituted Al2C, whereas it is less strongly adsorbed on N-substituted Al2C. The subsequent consideration is being the case of n-type doping (W) along with Ti codoped in BiVO4 to enhance the efficiency of BiVO4 photoanode for water splitting. The determined adsorption energy and corresponding Gibbs free energies depict that the Ti site is energetically more favorable for water splitting. Moreover, the Ti site possesses a lower overpotential in the W–Ti codoped sample as compared to the mono-W doped sample. We have also explored the effect of mixed cation and mixed anion substitution in the hybrid perovskite in terms of structural stability, electronic properties and optical response of hybrid perovskite crystal structures. It has been found that the insertion of bromine (Br) into the system could modulate the stability of the Guanidinium lead iodide (GAPbI3) hybrid perovskite.  Moreover, the band gap of the mixed hybrid perovskite is increased with the inclusion of smaller Br anion while replacing partially the larger iodine (I) anion. Finally the electrochemical storage mechanism for Sodium (Na) and lithium (Li) ion insertion has been envisaged in inorganic electrode (eldfellite, NaFe(SO4)2) as well as in more sustainable organic electrode (di-lithium terephthalate, Li2TP). The full desodiation capability of the eldfellite enhances the capacity while the activation energies (higher than 1 eV) for the Na+ ion diffusion for the charged state lower the ionic insertion rate. The key factor as the variation of Li-O coordination in the terephthalate, for the disproportionation redox reaction in Li2TP is also identified.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2019. s. 96
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1760
Nyckelord
Materials Modelling, DFT, Energy Materials, Photocatalysis, HER and OER, Hybrid Perovskite Solar Cells, Stability, Thermodynamics and Kinetics in Na-ion battery, Organic Crystal Battery
Nationell ämneskategori
Den kondenserade materiens fysik Atom- och molekylfysik och optik
Identifikatorer
urn:nbn:se:uu:diva-369695 (URN)978-91-513-0544-8 (ISBN)
Disputation
2019-02-15, 80101, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2019-01-24 Skapad: 2018-12-19 Senast uppdaterad: 2019-02-18

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