As scientific exploration gradually enters unknown fields such as the Earth's core and deep space that are difficult to charge, high-energy density primary batteries have once again become a focus of attention for scientists. Among all current batteries, lithium sulfur batteries have a very high theoretical energy density of 2600 Wh/kg, making them one of the promising primary battery systems. However, lithium sulfur primary batteries face two challenges and have not yet achieved practicality. One is lower than expected actual energy density: excessive addition of inactive substances (electrolyte and conductive carbon) to promote sulfur conversion increases the quality burden of the system; The slow solid-liquid solid conversion reduces capacity utilization. The second is the unsatisfactory energy storage performance: elemental sulfur continuously dissolves from the positive electrode and diffuses through a concentration gradient to the negative electrode, corroding the metal lithium and producing Li2Sx (S8sol+Li → Li2Sx), resulting in continuous loss of capacity between the positive and negative electrodes during storage. These fundamentally interrelated problems occur throughout the entire battery system (positive electrode side, electrolyte side, and negative electrode side), so traditional local optimization methods such as adding positive electrode catalysts or strengthening negative electrode SEI often cannot balance the actual energy density and storage performance requirements. Given the bridging role of electrolytes in the entire battery system, scientists have started with electrolytes and gradually solved the two major difficulties mentioned above as a starting point. The excessive quality of lithium sulfur batteries mainly comes from the electrolyte, and reducing the electrolyte quality without affecting performance has become the top priority in improving energy density. For this, the traditional solution is to reduce the volume of the electrolyte. However, the solid liquid solid conversion mechanism of porous positive electrodes and sulfur has essential requirements for the amount of electrolyte. Unlimited reduction of electrolyte volume can cause insufficient positive electrode infiltration, damage capacity release, and ultimately have the opposite effect. On the contrary, the mass formula m= ρ X V indicates that as the decrease in electrolyte volume approaches the marginal effect, reducing density can further effectively reduce electrolyte quality.

The Huairou Research Department of the Chinese Academy of Sciences/National Research Center for Condensed Matter Physics, and the Suo Liumin Research Group of the Beijing Clean Energy Frontier Research Center, together with the Mao Huican Research Group of the University of Science and Technology Beijing, proposed an ultra light electrolyte strategy with a packaging solvation structure for the two challenges of the practical application of lithium sulfur primary batteries. The study aimed to introduce chain like monooxymethyl tert butyl ether to construct an ultra light electrolyte, which reduced the electrolyte quality by 23.1% and increased capacity utilization by 38.1%. In addition, the energy density of the system was further improved by combining the composite sulfur based cathode strategy with the introduction of fluorinated graphite (CFx). During a 31 day static experiment, the S-CFx | | UE | | Li system exhibited excellent storage performance. In the evaluation at the soft pack level, the 300 mAh level battery assembled by this system achieved a breakthrough energy density of 661 Wh/kg and low self discharge rate.

The relevant research results are titled Ultralight Electrolyte with Protective Encapsulation Solvation Structure Enabling Hybrid Sulfur Based Primary Batteries Exceeding 660 Wh/kg and published in the Journal of the American Chemical Society (JACS). The research work was supported by the Young Talents Program of the Chinese Academy of Sciences and the "Huairou Science City" clean energy materials testing, diagnosis and research and development platform.

Paper link:论文链接