Rational Design of Statically and Dynamically Stable Lithium–Sulfur Batteries with High Sulfur Loading and Low Electrolyte/Sulfur Ratio

The primary challenge with lithium–sulfur battery research is the design of sulfur cathodes that exhibit high electrochemical efficiency and stability while keeping the sulfur content and loading high and the electrolyte/sulfur ratio low. With a systematic investigation, a novel graphene/cotton‐carbon cathode is presented here that enables sulfur loading and content as high as 46 mg cm^?2 and 70 wt% with an electrolyte/sulfur ratio of as low as only 5. The graphene/cotton‐carbon cathodes deliver peak capacities of 926 and 765 mA h g^?1, respectively, at C/10 and C/5 rates, which translate into high areal, gravimetric, and volumetric capacities of, respectively, 43 and 35 mA h cm^?2, 648 and 536 mA h g^?1, and 1067 and 881 mA h cm^?3 with a stable cyclability. They also exhibit superior cell‐storage capability with 95% capacity‐retention, a low self‐discharge constant of just 0.0012 per day, and stable poststorage cyclability after storing over a long period of six months. This work demonstrates a viable approach to develop lithium–sulfur batteries with practical energy densities exceeding that of lithium‐ion batteries.     

Thermodynamics and Kinetics of Sulfur Cathode during Discharge in MgTFSI2–DME Electrolyte

Rechargeable magnesium/sulfur battery is of significant interest because its energy density (1700 Wh kg^?1 and 3200 Wh L^?1) is among the highest of all battery chemistries (lower than Li/O₂ and Mg/O₂ but comparable to Li/S), and Mg metal allows reversible operation (100% Coulombic efficiency) with no dendrite formation. This great promise is already justified in some early reports. However, lack of mechanistic study of sulfur reaction in the Mg cation environment has severely hindered our understanding and prevents effective measures for performance improvement. In this work, the very first systematic fundamental study on Mg/S system is conducted by combining experimental methods with computational approach. The thermodynamics and reaction pathway of sulfur cathode in MgTFSI₂–DME electrolyte, as well as the associated kinetics are thoroughly investigated. The results here reveal that sulfur undergoes a consecutive staging pathway in which the formation and chain‐shortening of polysulfide occur at early stage accompanied by the dissolution of long‐chain polysulfide, and solid‐state transition from short‐chain polysulfide to magnesium sulfide occurs at late stage. The former process is much faster than the latter due to the synergetic effect of the mediating effect of dissolved polysulfide and the fast diffusion of Mg ion in the amorphous intermediate.     

强电场下高聚物绝缘中的应力转化与补偿效应

研究了高分子聚合物绝缘材料在强电场下发生的应力转化与补偿现象。发现外加电场可以转化为材料耐受的机械应力,形成机械应变;反之,外加机械应力或残余应力又可以补偿电场作用,影响材料的击穿电压和场强。这种转化和补偿的定量关系与材料的松弛特性有关,由此导出的材料击穿场强公式可用于定量评估应力/应变以及杨氏模量对材料介电性能的影响。     

Atomic Engineering Catalyzed MnO2 Electrolysis Kinetics for a Hybrid Aqueous Battery with High Power and Energy Density

Research interest and achievements in zinc aqueous batteries, such as alkaline Zn//Mn, Zn//Ni/Co, Zn–air batteries, and near-neutral Zn-ion and hybrid ion batteries, have surged throughout the world due to their features of low-cost and high-safety. However, practical application of Zn-based secondary batteries is plagued by restrictive energy and power densities in which an inadequate output plateau voltage and sluggish kinetics are mutually accountable. Here, a novel paradigm high-rate and high-voltage Zn–Mn hybrid aqueous battery (HAB) is constructed with an expanded electrochemical stability window over 3.4 V that is affordable. As a proof of concept, catalyzed MnO₂/Mn²⁺ electrolysis kinetics is demonstrated in the HAB via facile introduction of Ni²⁺ into the electrolyte. Various techniques are employed, including in situ synchrotron X-ray powder diffraction, ex situ X-ray absorption fine structure, and electron energy loss spectroscopy, to reveal the reversible charge-storage mechanism and the origin of the boosted rate-capability. Density functional theory (DFT) calculations reveal enhanced active electron states and charge delocalization after introducing strongly electronegative Ni. Simulations of the reaction pathways confirm the enhanced catalyzed electrolysis kinetics by the facilitated charge transfer at the active O sites around Ni dopants. These findings significantly advance aqueous batteries a step closer toward practical low-cost application.