## 1 Introduction  
The energy transition is a necessary path toward the transformation of the worldwide energy sector from fossil-based to zero carbon by 2050, which is fundamental to reduce energy-related CO\({}_{2}\) emissions to limit climate change [1]. One of the main pillars for the energy transition is the global spread of the use of solar energy, being basically endless and free [2]. However, its diurnal nature, weather conditions, and seasonality might make solar energy unavailable when required. This time lag between energy supply and demand is a critical point to be addressed for renewable solar energy development and replacement of fossil-based energy. For this aim, thermal energy storage (TES) is an efficient and effective means to store solar energy when in excess, thus shifting the peak load demand into off-peak hours. Among TES technologies, the thermochemical one exploits materials with a large reaction enthalpy and reversibility. Inorganic salt hydrate (M\({}_{\rm n}\)A\({}_{\rm m}\)\(\cdot\)XH\({}_{2}\)O) is a widely used class and one of the most promising investigated classes of materials for thermochemical heat storage [3; 4], which is based on the following storage reaction:  
\[\mathrm{M_{n}A_{m}\cdot nH_{2}O+heat\leftrightarrow M_{n}A_{m}\cdot(n-x)H_{2}O+xH_{2}O}\]  
Heat is transferred from a selected source to the material and the dehydration reaction takes place (storage step). The heat is stored for as long as the salt is in the dehydrated form. When heat is required, water is made accessible to the salt, the reversible hydration takes place, and heat is released (release step). One of the main advantages of this technology is, indeed, the possibility to control the heat release by controlling the water vapor accessibility to the dehydrated salt, thus making the heat discharge available and controllable on-demand [5]. Due to this great potential, several pure salt hydrates and composite systems with different salts were investigated: e.g., LiBr [6], MgSO\({}_{4}\)[7], CaCl\({}_{2}\)[8], SrCl\({}_{2}\)[9], and LiCl [10]. Among them, LiCl is one of the salts that raised more interest for low/medium temperature (i.e., below 120 \({}^{\circ}\)C) TES application [11]. Indeed, the high-energy density of the LiCl-based system makes it an attractive candidate from the heat storage capacity cost perspective, thus resulting in one of the materials with a lower cost per kWh stored (\(\sim\)6 \(\mathrm{\upxi}\)/kWh) [12]. Nevertheless, lithium chloride is one of the most hygroscopic salts known and it incurs the phenomenon of deliquescence. Deliquescence is a first-order phase transformation of the solid to a saturated solution, which occurs at a specific relative humidity (RH) inherent to the properties of the solid and the temperature [13]. When this RH is reached, the aqueous solution is the thermodynamically favored phase and dissolution begins, whereby liquid patterns or patches of solution form on the surface. As the humidity further increases, these patches merge and form a thin liquid film, which gradually thickens; the entire solid particle dissolves and transforms into a solution drop; and its radius abruptly grows. In a closed environment, a saturated solution of lithium chloride will form an equilibrium at a relative humidity of about 12.4% (20 \({}^{\circ}\)C). The reverse process to deliquescence is called efflorescence. Efflorescence is the process of the crystallization and expulsion of water from the crystallized material when the decreasing humidity reaches another threshold value, called efflorescence relative humidity (ERH). Several issues arise due to the deliquescence phenomenon in TES technologies. The liquid film that forms on the surface of the salt crystal inhibits the rehydration reaction (e.g., in the case of the LiCl, LiBr, and CaCl\({}_{2}\)) [14; 15].