Phase Stability and Fast Ion Conductivity in the Hexagonal LiBH4-LiBr-LiCl Solid Solution

This study shows a flexible system that offers promising candidates for Li-based solid-state electrolytes. The Br− substitution for BH4 − stabilizes the hexagonal structure of LiBH4 at room temperature (RT), whereas Cl− is soluble only at higher temperatures. Incorporation of chloride in a hexagonal solid solution leads to an increase in the energy density of the system. For the first time, a stable hexagonal solid solution of LiBH4 containing both Cl− and Br-halide anions has been obtained at RT. The LiBH4−LiBr−LiCl ternary phase diagram has been determined at RT by X-ray diffraction coupled with a Rietveld refinement. A solubility of up to 30% of Cl− in the solid solution has been established. The effect of halogenation on the Li-ion conductivity and electrochemical stability has been investigated by electrochemical impedance spectroscopy and cyclic voltammetry. Considering the ternary samples, h-Li(BH4)0.7(Br)0.2(Cl)0.1 composition showed the highest value for conductivity (1.3 × 10−5 S/cm at 30 °C), which is about 3 orders of magnitude higher than that for pure LiBH4 in the orthorhombic structure. The values of Li-ion conductivity at RT depend only on the BH4 − content in the solid solution, suggesting that the Br/Cl ratio does not affect the defect formation energy in the structure. Chloride anion substitution in the hexagonal structure increases the activation energy, moving from about 0.45 eV for samples without Cl− ions in the structure up to about 0.63 eV for h-Li(BH4)0.6(Br)0.2(Cl)0.2 compositions, according to the Meyer−Neldel rule. In addition to increasing Li-ion conductivity, the halogenation also increases the thermal stability of the system. Unlike for the Liion conductivity, the Br/Cl ratio influences the electrochemical stability: a wide oxidative window of 4.04 V versus Li+/Li is reached in the Li−Br system while further addition of Cl is a trade-off between oxidative stability and weight reduction. The halogenation allows both binary and ternary systems operating below 120 °C, thus suggesting possible applications of these fast ion conductors as solid-state electrolytes in Li-ion batteries

Detection of lithium plating in li-ion cell anodes using realistic automotive fast-charge profiles

The widespread use of electric vehicles is nowadays limited by the “range anxiety” of the customers. The drivers’ main concerns are related to the kilometric range of the vehicle and to the charging time. An optimized fast-charge profile can help to decrease the charging time, without degrading the cell performance and reducing the cycle life. One of the main reasons for battery capacity fade is linked to the Lithium plating phenomenon. This work investigates two methodologies, i.e., three-electrode cell measurement and internal resistance evolution during charging, for detecting the Lithium plating conditions. From this preliminary analysis, it was possible to develop new Multi-Stage Constant-Current profiles, designed to improve the performance in terms of charging time and cells capacity retention with respect to a reference profile. Four new profiles were tested and compared to a reference. The results coming from the new profiles demonstrate a simultaneous improvement in terms of charging time and cycling life, showing the reliability of the implemented methodology in preventing Lithium plating