Entropy Regulation Quantified via Solvation Chemistry of Nonaqueous Electrolyte for Robust Lithium-Metal Batteries

The concept of high entropy is applied to various rechargeable batteries to improve the thermodynamic and kinetic behavior of electrolytes. However, the quantization and functionality of entropy are still ambiguous in liquid electrolytes. Herein, the regulation of entropy in non-aqueous electrolytes is quantitatively understood to construct robust Li metal batteries. Electrolyte entropy is first quantified through combining the Boltzmann statistical mechanics with the statistics of solvation structure configurations in the non-aqueous electrolyte. Entropy values do not necessarily increase with the increasing electrolyte components. Electrolytes with higher entropy dissociate ion aggregation to form homogeneous solvation structures, which effectively balance strong/weak solvation effects. This induces smaller cluster size, accelerating diffusion kinetics and desolvation process of Li + . An average Coulombic efficiency of 99.1% is obtained in Li||Cu batteries. Li||LiNi 0.5 Co 0.2 Mn 0.3 O 2 cells with a high cathode loading (19.7 mg cm −2 , 3.0 mAh cm −2 ) can maintain a capacity retention of 87.1% after 200 cycles. This finding offers novel understandings in the role of high-entropy effect, which is of great importance for the development of high-energy-density Li metal batteries.