Dr Emilia Olsson

Hard carbons are among the most promising materials for alkali‐ion metal anodes. These materials have a highly complex structure and understanding the metal storage and migration within these structures is of utmost importance for the development of next‐generation battery technologies. The effect of different carbon structural motifs on Li, Na, and K storage and diffusion are probed using density functional theory based on experimental characterizations of hard carbon samples. Two carbon structural models—the planar graphitic layer model and the cylindrical pore model—are constructed guided by small‐angle X‐ray scattering and transmission electron microscopy characterization. The planar graphitic layers with interlayer distance <6.5 Å are beneficial for metal storage, but do not have significant contribution to rapid metal diffusion. Fast diffusion is shown to take place in planar graphitic layers with interlayer distance >6.5 Å, when the graphitic layer separation becomes so wide that there is negligible interaction between the two graphitic layers. The cylindrical pore model, reflecting the curved morphology, does not increase metal storage, but significantly lowers the metal migration barriers. Hence, the curved carbon morphologies are shown to have great importance for battery cycling. These findings provide an atomic‐scale picture of the metal storage and diffusion in these materials.

In this paper, a computational study of Li, Na, and K adsorption and migration on pristine and defective graphene surfaces is conducted to gain insight into the metal storage and mobility in carbon-based anodes for alkali metal batteries. Atomic level studies of the metal adsorption and migration on the graphene surface can help address the challenges faced in the development of novel alkali metal battery technologies, as these systems act as convenient proxies of the crystalline carbon surface in carbon-based materials including graphite, hard carbons and graphene. The adsorption of Li and K ions on the pristine graphene surface is shown to be more energetically favourable than Na adsorption. A collection of defects expected to be found in carbonaceous materials are investigated in terms of metal storage and mobility, with N- and O-containing defects found to be the dominant defects on these carbon surfaces. Metal adsorption and migration at the defect sites show that defect sites tend to act as metal trapping sites, and metal diffusion around the defects is hindered when compared to the pristine surface. We identify a defect where two C sites are substituted with O and one C site with N as the dominant surface defect, and find that this defect is detrimental to metal migration and hence the battery cycling performance.

Hard carbons have shown considerable promise as anodes for emerging sodium-ion battery technologies. Current understanding of sodium-storage behaviour in hard carbons attributes capacity to filling of graphitic interlayers and pores, and adsorption at defects, although there is still considerable debate regarding the voltages at which these mechanisms occur. Here, ex situ23Na solid-state NMR and total scattering studies on a systematically tuned series of hard carbons revealed the formation of increasingly metallic sodium clusters in direct correlation to the growing pore size, occurring only in samples which exhibited a low voltage plateau. Combining experimental results with DFT calculations, we propose a revised mechanistic model in which sodium ions store first simultaneously and continuously at defects, within interlayers and on pore surfaces. Once these higher energy binding sites are filled, pore filling occurs during the plateau region, where the densely confined sodium takes on a greater degree of metallicity.

The need for sustainable and large-scale energy supply has led to significant development of renewable energy and energy storage technologies. Divalent metal ion (Mg, Ca, and Zn) batteries are promising energy storage technologies for the sustainable energy future, but the need for suitable electrode materials have limited their commercial development. This paper investigates, at the atomic scale, the adsorption and migration of Mg, Ca, and Zn on pristine and defective graphene surfaces, to bring insight into the metal storage and mobility in graphene and carbon-based anodes for divalent metal ion batteries. Such atomistic studies can help address the challenges facing the development of novel divalent metal battery technologies, and to understand the storage differences between divalent and monovalent metal-ion batteries. The adsorption of Ca on the graphene-based system is shown to be more energetically favorable than the adsorption of both Mg and Zn, with Ca showing adsorption behavior similar to the monovalent ions (Li, Na, and K). This was further investigated in terms of metal migration on the graphene surface, with much higher migration energy barriers for Ca than for Mg and Zn on the graphene systems, leading to the trapping of Ca at defect sites to a larger extent.

Hard carbons, due to their relatively low cost and good electrochemical performance, are considered the most promising anode materials for Na-ion batteries. Despite the many reported structures of hard carbon, the practical use of hard carbon anodes is largely limited by low initial Coulombic efficiency (ICE), and the sodium storage mechanism still remains elusive. A better understanding of the sodium-ion behavior in hard carbon anodes is crucial to develop more efficient sodium-ion batteries. Here, a series of hard carbon materials with tailored morphology and surface functionality was synthesized via hydrothermal carbonization and subsequent pyrolysis from 1000 to 1900 °C. Electrochemical results revealed different sodiation-desodiation trends in the galvanostatic potential profiles and varying ICE and were compared with theoretical studies to understand the effect of the varying hard carbon structure on the sodium storage process at different voltages. Furthermore, electrode expansion during cycling was investigated by in situ dilatometry; to the best of our knowledge, this is the first time that the technique has been applied to hard carbons for ion storage mechanism investigation in Na-ion batteries. Combining experimental and theoretical results, we propose a model for sodium storage in our hard carbons that consist of Na-ion storage at defect sites and by intercalation in the high voltage slope region and via pore filling in the low voltage plateau region; these findings are important for the design of future electrode materials with high capacity and efficiency.

Lithium–sulfur batteries (LSBs) are a class of new‐generation rechargeable high‐energy‐density batteries. However, the persisting issue of lithium polysulfides (LiPs) dissolution and the shuttling effect that impedes the efficiency of LSBs are challenging to resolve. Herein a general synthesis of highly dispersed pyrrhotite Fe1−S nanoparticles embedded in hierarchically porous nitrogen‐doped carbon spheres (Fe1−S‐NC) is proposed. Fe1−S‐NC has a high specific surface area (627 m2 g−1), large pore volume (0.41 cm3 g−1), and enhanced adsorption and electrocatalytic transition toward LiPs. Furthermore, in situ generated large mesoporous pores within carbon spheres can accommodate high sulfur loading of up to 75%, and sustain volume variations during charge/discharge cycles as well as improve ionic/mass transfer. The exceptional adsorption properties of Fe1−S‐NC for LiPs are predicted theoretically and confirmed experimentally. Subsequently, the electrocatalytic activity of Fe1−S‐NC is thoroughly verified. The results confirm Fe1−S‐NC is a highly efficient nanoreactor for sulfur loading. Consequently, the Fe1−S‐NC nanoreactor performs extremely well as a cathodic material for LSBs, exhibiting a high initial capacity of 1070 mAh g−1 with nearly no capacity loss after 200 cycles at 0.5 C. Furthermore, the resulting LSBs display remarkably enhanced rate capability and cyclability even at a high sulfur loading of 8.14 mg cm−2.

Sodium ion batteries are a promising alternative to current lithium ion battery technology, providing relatively high capacity and good cycling stability at low cost. Hard carbons are today the anodes of choice but they suffer from poor rate performance and low initial coulombic efficiency. To improve the understanding of the kinetics of sodium mobility in these materials, muon spin rotation spectroscopy and density functional theory calculations were used to probe the intrinsic diffusion of sodium in a characteristic hard carbon sample. This revealed that atomic diffusion between sites is comparable to that observed in transition metal oxide cathode materials in sodium ion batteries, suggesting that the poor rate performance is not limited by site–site jump diffusion rates. In addition, diffusion was observed in the sodium that is irreversibly stored during the first cycle, suggesting that some of these sodium atoms are not immobilised in the solid electrolyte interface (SEI) layer but are still blocked from long range diffusion, thereby rendering the sodium electrochemically inactive.

Metal sulfides such as Bismuth sulfide (Bi2S3) hold immense potential to be promoted as anode materials for lithium-ion batteries (LIBs), owing to their high theoretical gravimetric and volumetric capacities. However, the poor electrical conductivity and volume expansion during cycling hinder the practical applications of Bi2S3. In this work, we used pyrrole and glucose as carbon source to design the surface carbon coating on the surface of Bi2S3 particles, to improve the structural stability of Bi2S3. Two composite materials were synthesized – Bi2S3 coated with nitrogen doped carbon (Bi2S3@NC), and Bi2S3 coated with carbon (Bi2S3@C). When used as anode active materials, both Bi2S3@NC and Bi2S3@C showed improved performance compared to Bi2S3, which confirms surface carbon coating as an effective and scalable way for the modification of Bi2S3 material. The electrode based on Bi2S3@NC materials demonstrated higher performance than that of Bi2S3@C, with an initial discharge capacity of 1126.5 mA h/g, good cycling stability (500 mA h/g after 200 cycles at 200 mA/g) and excellent rate capability. Finally, Li storage and migration mechanisms in Bi2S3 are revealed using first principle density functional theory calculations.

Two-dimensional nanoporous graphene (NPG) with uniformly distributed nanopores has been synthesized recently and shown remarkable electronic, mechanical, thermal, and optical properties with potential applications in several fields. Here, we explore the potential application of NPG as an anode material for Li-, Na-, K-, Mg-, and Ca-ion batteries. We use density functional theory calculations to study structural properties, defect formation energies, metal binding energies, charge analysis, and electronic structures of NPG monolayers. Pristine NPG can bind effectively K+ cations but cannot sufficiently bind the other metal cations strongly, which is a prerequisite of an efficient anode material. However, upon substitution with oxygen-rich functional groups (e.g., O, OH, and COOH) and doping with heteroatoms (B, N, P, and S), the metal binding ability of NPG is significantly enhanced. Of the considered systems, the S-doped NPG (S-NPG) binds the metal cations most strongly with binding energies of −3.87 (Li), −3.28 (Na), −3.37 (K), −3.68 (Mg), and −4.97 (Ca) eV, followed by P-NPG, O-NPG, B-NPG, and N-NPG. Of the substituted NPG systems, O-substituted NPG exhibits the strongest metal binding with binding energies of −3.30 (Li), −2.62 (Na), −2.89 (K), −1.67 (Mg), and −3.40 eV (Ca). Bader charge analysis and Roby–Gould bond indices show that a significant amount of charge is transferred from the metal cations to the functionalized NPG monolayers. Electronic properties were studied by density of states plots, and all the systems were found to be metallic upon the introduction of metal cations. These results suggest that functionalized NPG could be used as a global anode material for Li-, Na-, K-, Mg-, and Ca-ion batteries.Two-dimensional nanoporous graphene (NPG) with uniformly distributed nanopores has been synthesized recently and shown remarkable electronic, mechanical, thermal, and optical properties with potential applications in several fields. Here, we explore the potential application of NPG as an anode material for Li-, Na-, K-, Mg-, and Ca-ion batteries. We use density functional theory calculations to study structural properties, defect formation energies, metal binding energies, charge analysis, and electronic structures of NPG monolayers. Pristine NPG can bind effectively K+ cations but cannot sufficiently bind the other metal cations strongly, which is a prerequisite of an efficient anode material. However, upon substitution with oxygen-rich functional groups (e.g., O, OH, and COOH) and doping with heteroatoms (B, N, P, and S), the metal binding ability of NPG is significantly enhanced. Of the considered systems, the S-doped NPG (S-NPG) binds the metal cations most strongly with binding energies of −3.87 (Li), −3.28 (Na), −3.37 (K), −3.68 (Mg), and −4.97 (Ca) eV, followed by P-NPG, O-NPG, B-NPG, and N-NPG. Of the substituted NPG systems, O-substituted NPG exhibits the strongest metal binding with binding energies of −3.30 (Li), −2.62 (Na), −2.89 (K), −1.67 (Mg), and −3.40 eV (Ca). Bader charge analysis and Roby–Gould bond indices show that a significant amount of charge is transferred from the metal cations to the functionalized NPG monolayers. Electronic properties were studied by density of states plots, and all the systems were found to be metallic upon the introduction of metal cations. These results suggest that functionalized NPG could be used as a global anode material for Li-, Na-, K-, Mg-, and Ca-ion batteries.

High capacity electrode materials are the key for high energy density Li-ion batteries (LIB) to meet the requirement of the increased driving range of electric vehicles. Here we report the synthesis of a novel anode material, Bi 2 MoO 6/palm-carbon composite, via a simple hydrothermal method. The composite shows higher reversible capacity and better cycling performance, compared to pure Bi 2 MoO 6. In 0–3 V, a potential window of 100 mA/g current density, the LIB cells based on Bi 2 MoO 6/palm-carbon composite show retention reversible capacity of 664 mAh· g− 1 after 200 cycles. Electrochemical testing and ab initio density functional theory calculations are used to study the fundamental mechanism of Li ion incorporation into the materials. These studies confirm that Li ions incorporate into Bi 2 MoO 6 via insertion to the interstitial sites in the MoO 6-layer, and the presence of palm-carbon improves the electronic conductivity, and thus enhanced the performance of the composite materials. 

Silica-based resistive random access memory devices have become an active research area due to complementary metal–oxide–semiconductor compatibility and recent dramatic increases in their performance and endurance. In spite of both experimental and theoretical insights gained into the electroforming process, many atomistic aspects of the set and reset operation of these devices are still poorly understood. Recently a mechanism of electroforming process based on the formation of neutral oxygen vacancies (VO0) and interstitial O ions (Oi2–) facilitated by electron injection into the oxide has been proposed. In this work, we extend the description of the bulk (Oi2–) migration to the interface of amorphous SiO2 with the polycrystaline TiN electrode, using density functional theory simulations. The results demonstrate a strong kinetic and thermodynamic drive for the movement of Oi2– to the interface, with dramatically reduced incorporation energies and migration barriers close to the interface. The arrival of Oi2– at the interface is accompanied by preferential oxidation of undercoordinated Ti sites at the interface, forming a Ti–O layer. We investigate how O ions incorporate into a perfect and defective ∑5(012)[100] grain boundary (GB) in TiN oriented perpendicular to the interface. Our simulations demonstrate the preferential incorporation of Oi at defects within the TiN GB and their fast diffusion along a passivated grain boundary. They explain how, as a result of electroforming, the system undergoes very significant structural changes with the oxide being significantly reduced, interface being oxidized, and part of the oxygen leaving the system.

Rare earth oxides have shown great promise in a variety of applications in their own right, and as the building blocks of complex oxides. A great deal of recent interest has been focused on Sm2O3, which has shown significant promise as a high-k dielectric and as a ReRAM dielectric. Experimentally, these thin films range from amorphous, through partially crystalline, to poly-crystalline, dependent upon the synthetic conditions. Each case presents a set of modelling challenges that need to be defined and overcome. In this work, the problem of modelling amorphous Sm2O3 is tackled, developing an atomistic picture of the effect of amorphization on Sm2O3 from a structural and electronic structure perspective.

This study reports the potential application of Ni2P as highly effective catalyst for chemical CO2recycling via dry reforming of methane (DRM). Our DFT calculations reveal that the Ni2P (0001) surface is active toward adsorption of the DRM species, with the Ni hollow site being the most energetically stable site and Ni–P and P contributing as coadsorption sites in DRM reaction steps. Free-energy analysis at 1000 K found CH–O to be the main pathway for CO formation. The competition of DRM and reverse water gas shift (RWGS) is also evidenced with the latter becoming important at relatively low reforming temperatures. Very interestingly, oxygen seems to play a key role in making this surface resistant toward coking. From microkinetic analysis, we have found greater oxygen surface coverage than that of carbon at high temperatures, which may help to oxidize carbon deposits in continuous runs. The tolerance of Ni2P toward carbon deposition was further corroborated by DFT and microkinetic analysis. Along with the higher probability of C oxidation, we identify poor capacity of carbon diffusion on the Ni2P (0001) surface with very limited availability of C nucleation sites. Overall, this study opens avenues for research in metal-phosphide catalysis and expands the application of these materials to CO2 conversion reactions.

One of the main challenges facing solid oxide fuel cell (SOFC) technology is the need to develop materials capable of functioning at intermediate temperatures (500–800 °C), thereby reducing the costs associated with SOFCs. Here, Sm0.75A0.25MnxCo1−xO2.88 (A = Ca, or Sr) is investigated as a potential new cathode material to substitute the traditional lanthanum–strontium manganate for intermediate temperature SOFCs. Using a combination of density functional theory calculations and molecular dynamics simulations, the crucial parameters for SOFC performance, such as the electronic structure, electronic and ionic conductivity, and thermal expansion coefficient, were evaluated. An evaluation of the results illustrates that the conductivity and thermal match of the materials with the electrolyte is dramatically improved with respect to the existing state-of-the-art.

SmCoO3 is a promising perovskite material for the next generation of intermediate temperature solid oxide fuel cells (SOFC), but its potential application is directly linked to, and dependent on, the presence of dopant ions. Doping on the Co-site is suggested to improve the catalytic and electronic properties of this cathode material. Fe, Mn, Ni, and Cu have been proposed as possible dopants and experimental studies have investigated and confirmed the potential of these materials. Here we present a systematic DFT+ study focused on the changes in electronic, magnetic, and physical properties with B-site doping of SmCoO3 to allow cathode optimization. It is shown that doping generally leads to distortion in the system, thereby inducing different electron occupations of the Co d-orbitals, altering the electronic and magnetic structure. From these calculations, the 0 K electronic conductivity (e) was obtained, with SmMnCo1−O3 having the highest e, and SmFeCo1−O3 the lowest e, in agreement with experiment. We have also investigated the impact of dopant species and concentration on the oxygen vacancy formation energy (f), which is related to the ionic conductivity (O). We found that the f values are lowered only when SmCoO3 is doped with Cu or Ni. Finally, thermal expansion coefficients were calculated, with Mn-doping showing the largest decrease at low  and at  = 0.75. Combining these results, it is clear that Mn-doping in the range  = 0.125–0.25 would imbue SmCoO3 with the most favorable properties for IT-SOFC cathode applications.

The substitutional doping of Ca2+, Sr2+, and Ba2+ on the Sm-site in the cubic perovskite SmCoO3 is reported to improve both electronic and ionic conductivities for applications as solid oxide fuel cell (SOFC) cathodes. Hence, in this study we have used density functional theory (DFT) calculations to investigate dopant configurations at two different dopant concentrations: 25 and 50%. To preserve the electroneutrality of the system, we have studied two different charge compensation mechanisms: the creation of oxygen vacancies, and electronic holes. After examining the electronic structure, charge density difference, and oxygen vacancy formation energies, we concluded that oxygen vacancy charge compensation is the preferred mechanism to maintain the electroneutrality of the system. Furthermore, we found that the improvement of the electronic conduction is not a direct consequence of the appearance of electron holes, but a result of the distortion of the material, more specifically, the distortion of the Co–O bonds. Finally, molecular dynamics were employed to model ionic conduction and thermal expansion coefficients. It was found that all dopants at both concentrations showed high ionic conduction comparable to experimental results.

SmCoO3 is a perovskite material that has gained attention as a potential substitute forLa1 xSrxMnO3 d as a solid oxide fuel cell cathode. However, a number of properties have remained unknown due to the complexity of the material. For example, we know from experimental evidence that this perovskite exists in two different crystal structures, cubic and orthorhombic, and that the cobalt ion changes its spin state at high temperatures, leading to a semiconductor-to-metal transition. However, little is known about the precise magnetic structure that causes the metallic behavior or the spin state of the Co centers at high temperature. Here, we therefore present a systematic DFT+U study of the magnetic properties of SmCoO3 in order to determine what magnetic ordering is the one exhibited by the metallic phase at different temperatures. Similarly, mechanical properties are difficult to mea- sure experimentally, which is why there is a lack of data for the two different phases of SmCoO3. Taking advantage of our DFT calculations, we have determined the mechanical properties from our calculated elastic constants, finding that both polymorphs exhibit similar ductility and brittleness, but that the cubic structure is harder than the orthorhombic phase.

Doped LaMnO3 and SmCoO3 are important solid oxide fuel cell cathode materials. The main difference between these two perovskites is that SmCoO3 has proven to be a more efficient cathode material than LaMnO3 at lower temperatures. In order to explain the difference in efficiency, we need to gain insight into the materials’ properties at the atomic level. However, while LaMnO3 has been widely studied, ab initio studies on SmCoO3 are rare. Hence, in this paper, we perform a comparative DFT + U study of the structural, electronic, and magnetic properties of these two perovskites. To that end, we first determined a suitable Hubbard parameter for the Co d–electrons to obtain a proper description of SmCoO3 that fully agrees with the available experimental data.We next evaluated the impact of oxygen and cation vacancies on the geometry, electronic, and magnetic properties. Oxygen vacancies strongly alter the electronic and magnetic structures of SmCoO3, but barely affect LaMnO3. However, due to their high formation energy, their concentrations in the material are very low and need to be induced by doping. Studying the cation vacancy concentration showed that the formation of cation vacancies is less energetically favorable than oxygen vacancies and would thus not markedly influence the performance of the cathode. Published