Tailored Electrolytes Enabling Practical Lithium–Sulfur Full Batteries via Interfacial Protection

The electroactivity of the sulfur composite cathode generally studied requires high electrode porosity, which brings many constraints to the design of lithium–sulfur (Li–S) batteries (e.g., electrolyte quantity and energy density). Here, we focus on electrolyte engineering for highly stable covalent-type sulfurized polyacrylonitrile (SPAN) to realize practical Li–S full batteries with jointly improved volumetric energy density (Ev) and cyclability. The conformal polycarbonate cathode-electrolyte interphase (CEI) derived by cyclic carbonate is determined to play a fundamental role in eliminating the fatal shuttle effect, thereby safeguarding the "solid-phase" mechanism of SPAN. The tailored electrolyte also induces a bilayered solid electrolyte interphase (SEI) with enhanced Li+ transport and mechanical strength, which unlocks the compatibility of an ultrathin Li anode. Practical Li-SPAN pouch cells, composed of high-capacity SPAN cathodes (4.08 mAh cm–2) and 1.2× excess Li anodes, can achieve an Ev of 615 Wh L–1 and show a cycle life at least 7 times that of the conventional carbonate-based electrolyte.