• Energy Research

High-performance permanent magnets (PM) are compounds with outstanding intrinsic magnetic properties. Most PMs are obtained from a favorable combination of rare earth metals (RE = Nd, Pr, Ce) with transition metals (TM = Fe, Co). Amongst them, CeFe11Ti claims considerable attention due to its large Curie temperature, saturation magnetization, and significant magnetocrystalline anisotropic energy. CeFe11Ti has several potential applications, in particular, in the development of electric motors for future automatic electrification. In this work, we shed some light on the mictrostructure of this compound by performing periodic hybrid-exchange density functional theory (DFT) calculations. We use a combined approach of atom-centered local orbitals, plane waves and full-potential linear muffin-tin orbital (LMTO) for our computations. The electronic configuration of the atoms involved in different steps of formation of the crystal structure of CeFe11Ti gives an explanation on the effect of Ce and Ti on its magnetic properties. While Ti stabilizes the structure, atomic orbitals of Ce hybridizes with Fe atomic orbitals to a significant extent and alters the electronic bands. Our calculations confirm a valence of 3+ for Ce, which has been deemed crucial to obtain a large magnetocrystalline anisotropy. In addition, we analyze several spin configurations, with the ferromagnetic configuration being most stable. We compare and contrast our data to those available and provide an insight for further development of optimized high-performance PMs. Moreover, we compute the Magnetocrystalline Anisotropy of this compound by means of two approaches: the Force Theorem and a full-potential LMTO method.

Lithium-titanium-sulfur cathodes have garnered interest due to their distinctive properties and potential applications in lithium-ion batteries. They present various benefits, including lower cost, enhanced safety, and greater energy density compared to the commonly used transition metal oxides. The current trend in lithium-ion batteries is to move to all-solid-state chemistries in order to improve safety and energy density. Several chemistries for solid electrolytes have been studied, tested, and characterized to evaluate the applicability in energy storage system. Among those, sulfur-based Argyrodites have been coupled with cubic rock-salt type Li2TiS3 electrodes. In this work, Li2TiS3 surfaces were investigated with DFT methods in different conditions, covering the possible configurations that can occur during the cathode usage: pristine, delithiated, and overlithiated. Interfaces were built by coupling selected Li2TiS3 surfaces with the most stable Argyrodite surface, as derived from a previous study, allowing us to understand the (electro)chemical compatibility between these two sulfur-based materials.

Thermo-electrochemical cells (or thermocells) represent a promising technology to convert waste heat energy into electrical energy, generating power with minimal material consumption and a limited carbon footprint. Recently, the adoption of ionic liquids has pushed both the operational temperature range and the power output of thermocells. This research discusses the design challenges and the key performance limitations that need to be addressed to deploy the thermocells in real-world applications. For this purpose, a unique up-scaled design of a thermocell is proposed, in which the materials are selected according to the techno-economic standpoint. Specifically, the electrolyte is composed of EMI-TFSI ionic liquid supplemented by [Co(ppy)]3+/2+ redox couples characterized by a positive Seebeck coefficient (1.5 mV/K), while the electrodes consist of carbon-based materials characterized by a high surface area. Such electrodes, adopted to increase the rate of the electrode reactions, lead to a thermoelectric performance one order of magnitude greater than the Pt electrode-based counterpart. However, the practical applications of thermocells are still limited by the low power density and low voltage that can be generated.

The development of long lifetime Li–S batteries requires new sulfur–carbon based composite materials that are able to suppress the shuttle effect—namely, the migration of soluble lithium polysulfides from the cathode to the anode of the cell. Graphene is one of the most promising carbon supports for sulfur, thanks to its excellent conductivity and to the possibility of tailoring its chemical–physical properties, introducing heteroatoms in its structure. By using first principle density functional theory simulations, this work aims at studying the effect of doping graphene with group III elements (B, Al, Ga) on its electronic properties and on its chemical affinity towards lithium polysulfides. Our results show that Al and Ga doping strongly modify the local structure of the lattice near heteroatom site and generate a charge transfer between the dopant and its nearest neighbor carbon atoms. This effect makes the substrate more polar and greatly enhances the adsorption energy of polysulfides. Our results suggest that Al- and Ga-doped graphene could be used to prepare cathodes for Li–S cells with improved performances and lifetime.

Since lithium-ion batteries seem to be the most eligible technology to store energy for e-mobility applications, it is fundamental to focus attention on kilometric ranges and charging times. The optimization of the charging step can provide the appropriate tradeoff between time saving and preserving cell performance over the life cycle. The implementation of new multistage constant current profiles and related performances after 1000 cycles are presented and compared with respect to a reference profile. A physicochemical (SEM, XRD, particle size analysis, etc.) and electrochemical (incremental capacity analysis, internal resistance measurements) characterization of the aged cells is shown and their possible implementation on board is discussed.

A density functional theory (DFT) study has been carried out on transition metal phosphates with olivine structure and formula LiMPO4 (M = Fe, Mn, Co, Ni) to assess their potential as cathode materials in rechargeable Li-ion batteries based on their chemical and structural stability and high theoretical capacity. The investigation focuses on LiMnPO4, which could offer an improved cell potential (4.1 V) with respect to the reference LiFePO4 compound, but it is characterized by poor lithium intercalation/de-intercalation kinetics. Substitution of cations like Co and Ni in the olivine structure of LiMnPO4 was recently reported in an attempt to improve the electrochemical performances. Here the electronic structure and lithium intercalation potential of Ni- and Co-doped LiMnPO4 were calculated in the framework of the Hubbard U density functional theory (DFT+U) method for highly correlated materials. Moreover, the diffusion process of lithium in the host structures was simulated, and the activation barriers in the doped and pristine structures were compared. Our calculation predicted that doping increases Li insertion potential while activation barriers for Li diffusion remain similar to the pristine material. Moreover, Ni and Co doping induces the formation of impurity states near the Fermi level and significantly reduces the band gap of LiMnPO4.