Recently, intensive efforts are dedicated to convert and store the solar energy in a single device. Herein, dye-synthesized solar cell technology is combined with lithium-ion materials to investigate light-assisted battery charging. In particular we report the direct photo-oxidation of lithium iron phosphate nanocrystals in the presence of a dye as a hybrid photo-cathode in a two-electrode system, with lithium metal as anode and lithium hexafluorophosphate in carbonate-based electrolyte; a configuration corresponding to lithium ion battery charging. Dye-sensitization generates electron–hole pairs with the holes aiding the delithiation of lithium iron phosphate at the cathode and electrons utilized in the formation of a solid electrolyte interface at the anode via oxygen reduction. Lithium iron phosphate acts effectively as a reversible redox agent for the regeneration of the dye. Our findings provide possibilities in advancing the design principles for photo-rechargeable lithium ion batteries.

Most of the current commercialized lithium batteries employ liquid electrolytes, despite their vulnerability to battery fire hazards, because they avoid the formation of dendrites on the anode side, which is commonly encountered in solid-state batteries. In a review two years ago, we focused on the challenges and issues facing lithium metal for solid-state rechargeable batteries, pointed to the progress made in addressing this drawback, and concluded that a situation could be envisioned where solid-state batteries would again win over liquid batteries for different applications in the near future. However, an additional drawback of solid-state batteries is the lower ionic conductivity of the electrolyte. Therefore, extensive research efforts have been invested in the last few years to overcome this problem, the reward of which has been significant progress. It is the purpose of this review to report these recent works and the state of the art on solid electrolytes. In addition to solid electrolytes stricto sensu, there are other electrolytes that are mainly solids, but with some added liquid. In some cases, the amount of liquid added is only on the microliter scale; the addition of liquid is aimed at only improving the contact between a solid-state electrolyte and an electrode, for instance. In some other cases, the amount of liquid is larger, as in the case of gel polymers. It is also an acceptable solution if the amount of liquid is small enough to maintain the safety of the cell; such cases are also considered in this review. Different chemistries are examined, including not only Li-air, Li–O2, and Li–S, but also sodium-ion batteries, which are also subject to intensive research. The challenges toward commercialization are also considered.

The increasing need for energy storage has been the motivation for intensive research in batteries with different chemistries in the recent past. Among the elements of the batteries, the salts and their solvent play an important role. In particular, the cathodic stability at low potential depends importantly on the choice of the cation, while the stability at high potentials is mainly due to oxidation of anions and the ion mobility and dissociation depend primarily on the delocalization of the anion, so that many attempts are made to find the optimum choice of both the cations and anions of the salts, and their solvents. Although lithium-based batteries are almost exclusively used today, efforts are currently made to explore batteries based on sodium, aluminum, magnesium, calcium, potassium. The purpose of the present work is to review the salts and solvents that have been proposed in these different batteries and discuss their properties and their ability to be used in the near future and in the next generation of batteries.

We report a phosphine-free colloidal synthesis of CuIn x Ga 1−x S 2 (CIGS) nanocrystals (NCs) by heating a mixture of metal salts, elemental sulfur, octadecene, and oleylamine. In contrast with the more commonly used hot injection, this procedure is highly suitable for large-scale NC production, which we tested by performing a gram-scale synthesis. The composition of the CIGS NCs could be tuned by varying the In and Ga precursor ratios, and the samples showed a composition-dependent band gap energy. The average particle size was scaled from 13 to 19 nm by increasing the reaction temperature from 230 to 270 °C. Two concomitant growth mechanisms took place: in one, covellite (CuS) NCs nucleated already at room temperature and then incorporated increasing amounts of In and Ga until they evolved into chalcopyrite CIGS NCs. In the second mechanism, CIGS NCs directly nucleated at intermediate temperatures. They were smaller than the NCs formed by the first mechanism, but richer in In and Ga. In the final sample, obtained by prolonged heating at 230−270 °C, all NCs were homogeneous in size and composition. Attempts to replace the native ligands on the surface of the NCs with sulfur ions (following literature procedures) resulted in only around 50% exchange. Films prepared using the partially ligand exchanged NCs exhibited good homogeneity and an ohmic dark conductivity and photoconductivity with a resistivity of about 50 Ω•cm.

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