Marta Cabello

Enhancing the energy density of safer Li-ion batteries by combining high-voltage lithium cobalt fluorophosphate cathodes and nanostructured titania anodes

Recently, Li-ion batteries have been heavily scrutinized because of the apparent incompatibility between safety and high energy density. This work report a high voltage full battery made with TiO2/Li3PO4/Li2CoPO4F. The Li2CoPO4F cathode and TiO2 anode materials are synthesized by a sol–gel and anodization methods, respectively. X-ray diffraction (XRD) analysis confirmed that Li2CoPO4F is well-crystallized in orthorhombic crystal structure with Pnma space group. The Li3PO4-coated anode was successfully deposited as shown by the (011) lattice fringes of anatase TiO2 and (200) of γ-Li3PO4, as detected by HRTEM. The charge profile of Li2CoPO4F versus lithium shows a plateau at 5.0 V, revealing its importance as potentially high-voltage cathode and could perfectly fit with the plateau of anatase anode (1.8–1.9 V). The full cell made with TiO2/Li3PO4/Li2CoPO4F delivered an initial reversible capacity of 150 mA h g−1 at C rate with good cyclic performance at an average potential of 3.1–3.2 V. Thus, the full cell provides an energy density of 472 W h kg−1. This full battery behaves better than TiO2/Li2CoPO4F. The introduction of Li3PO4 as buffer layer is expected to help the cyclability of the electrodes as it allows a rapid Li-ion transport.

Reversible intercalation of aluminium into vanadium pentoxide xerogel for aqueous rechargeable batteries

Rechargeable batteries based on the intercalation of aluminium ions may be competitive against lithium-ion batteries, but their development and comprehension are full of difficulties. The charge/discharge processes are particularly complex in aqueous electrolyte solutions. The electrochemical behaviour of orthorhombic V2O5, obtained from xerogel, in an aluminium cell is studied here by using electrochemical cycling, impedance spectroscopy, XRD and XPS results. After electrochemical intercalation of aluminium, the resulting (Al3+)x/3[(V4+)x,(V5+)2−x]O5·nH2O is XRD-amorphous at approximately x = 0.5. The reversible capacity is ca. 120 mA h g−1 (equivalent to Al0.27V2O5). The loss of crystallinity induced by the electrochemical intercalation enhances the chemical exchange between the electrode material and the electrolyte solution. In the presence of acidic water solution, besides the faradic electrochemical process driven by the electrical current, aluminium, protons and water also can be intercalated into V2O5 by chemical reactions or ion exchange.

Electrochemical and chemical insertion/deinsertion of magnesium in spinel-type MgMn2O4 and lambda-MnO2 for both aqueous and non-aqueous magnesium-ion batteries

By using both chemical and electrochemical methods, magnesium has been reversibly removed from MgMn2O4 (s.g. I41/amd) with appropiate texture to form single-phase and nanocrystalline λ-MnO2 (s.g. Fdm). Cubic λ-MnO2 is not stable after annealing in both air and Ar atmospheres. The oxidation of Mn(III) to Mn(IV) eliminates the tetragonal distortion of the spinel-type lattice, but λ-MnO2 is more effectively obtained when powdered MgMn2O4 has a large specific surface area and a small particle size. In an aqueous solution of a magnesium salt, λ-MnO2 is formed by galvanostatic charge of MgMn2O4 and continuous Ar-flowing for removing oxygen from the solution. Starting from λ-MnO2, the tetragonal structure of MgMn2O4 and the cubic structure of LiMn2O4 are generated by electrochemical cycling in aqueous solutions containing salts of magnesium and lithium, respectively. In an aqueous solution cell, this material exhibits a reversible capacity of about 150 mA h g−1 and can be used in magnesium-ion batteries demonstrating it to be competitive against their lithium counterparts. In the absence of metallic Mg, the use of carbonate-based solvents can be a good choice for veritable non-aqueous magnesium-ion batteries, for example using positive electrode materials like MgMn2O4 (magnesium-ion source) and negative electrode materials like V2O5. In non-aqueous solvents (ethylene carbonate–diethyl carbonate mixture), the cubic phase λ-MnO2 is not formed, the tetragonal structure of MgxMn2O4 is preserved and its lattice cell is contracted.

On the Mechanism of Magnesium Storage in Micro- and Nano-Particulate Tin Battery Electrodes

This study reports on the electrochemical alloying-dealloying properties of Mg2Sn intermetallic compounds. 119Sn Mössbauer spectra of β-Sn powder, thermally alloyed cubic-Mg2Sn, and an intermediate MgSn nominal composition are used as references. The discharge of a Mg/micro-Sn half-cell led to significant changes in the spectra line shape, which is explained by a multiphase mechanism involving the coexistence of c-Mg2Sn, distorted Mg2−δSn, and Mg-doped β-Sn. Capacities and capacity retention were improved by using nanoparticulate tin electrodes. This material reduces significantly the diffusion lengths for magnesium and contains surface SnO and SnO2, which are partially electroactive. The half-cell potentials were suitable to be combined versus the MgMn2O4 cathodes. Energy density and cycling properties of the resulting full Mg-ion cells are also scrutinized.