Relay-Type Catalysis by a Dual-Metal Single-Atom System in a Waste Biomass Derivative Host for High-Rate and Durable Li-S Batteries

An environmental-friendly and sustainable carbon-based host is one of the most competitive strategies for achieving high loading and practicality of Li-S batteries. However, the polysulfide conversion reaction kinetics is still limited by the nonuniform or monofunctional catalyst configuration in the carbon host. In this work, we propose a catalysis mode based on "relay-type" co-operation by adjacent dual-metal single atoms for high-rate and durable Li-S batteries. A discarded sericin fabric-derived porous N-doped carbon with a stacked schistose structure is prepared as the high-loading sulfur (84 wt %) host by a facile ionothermal method, which further enables the uniform anchoring of Fe/Co dual-metal single atoms. This multifunctional host enables superior lithiophilic-sulfiphilic and electrocatalytic capabilities contributed by the "relay-type" single-atom modulation effects on different conversion stages of liquid polysulfides and solid Li2S2/Li2S, leading to the suppression of the "shuttle effect", alleviation of nucleation and decomposition barriers of Li2Sx, and acceleration of polysulfide conversion kinetics. The corresponding Li-S batteries exhibit a high specific capacity of 1399.0 mA h g-1, high-rate performance up to 10 C, and excellent cycling stability over 1000 cycles. They can also endure the high sulfur loading of 8.5 mg cm-2 and the lean electrolyte condition and yield an areal capacity as high as 8.6 mA h cm-2. This work evidentially demonstrates the potential of waste biomass reutilization coupled with the design of a single-atom system for practical Li-S batteries with high energy density.

A Covalent Heterostructure of Metal Phosphide Quantum Dots Anchored in N, P Co-doped Carbon Nanocapsules for Fast and Durable Lithium Storage

Transition-metal phosphides (TMPs) anodes for lithium ion batteries (LIBs) usually show poor rate capability and rapid capacity degradation owing to their low electronic conductivities, huge volumetric changes, as well as inferior reversibility of the discharge product Li₃P. Herein, a covalent heterostructure with TMPs quantum dots anchored in N, P co-doped carbon nanocapsules (NPC) has been prepared in which the P element in TMPs is simultaneously doped into the carbon matrix. As a proof of concept, Co₂P quantum dots covalently anchored in NPC (Co₂P QDs/NPC) is prepared and evaluated as an anode for LIBs. The Co₂P QDs/NPC electrode not only demonstrates a high capacity and an extraordinary rate performance but also delivers an impressive cyclability with a high capacity retention of 102.5% after 1600 cycles, one of the best reported values for TMPs-based electrode materials for LIBs. The covalent heterostructure can facilitate the electron/ion transfer and maintain the structural stability during the intensive cycles. Moreover, density functional theory calculations demonstrate that the interfacial covalent coupling can enhance the electrochemical reversibility of the discharge product Li₃P in the charge processes via lowering the conversion reaction energies. This work presents an effective interfacial engineering strategy for developing high-performance TMPs anodes for advanced LIBs.

Atomically Dispersed and O, N-Coordinated Mn-Based Catalyst for Promoting the Conversion of Polysulfides in Li2S-Based Li-S Battery

Nowadays, Li-S batteries are facing many thorny challenges like volume expansion and lithium dendrites on the road to commercialization. Due to the peculiarity of complete lithiation and the capability to match non-lithium anodes, Li₂S-based Li-S batteries have attracted more and more attention. Nevertheless, the same notorious shuttle effect of polysulfides as in traditional Li-S batteries and the poor conductivity of Li₂S lead to sluggish conversion reaction kinetics, poor Coulombic efficiency, and cycling performance. Herein, we propose the interconnected porous carbon skeleton as the host, which is modified by an atomically dispersed Mn catalyst as well as O, N atoms (named as ON-MnPC) via the melt salt method, and introduce the Li₂S nanosheet into the carbon host with poly(vinyl pyrrolidone) ethanol solution. It has been found that the introduction of O, N to bind with Mn atoms can endow the nonpolar carbon surface with ample unsaturated coordination active sites, restrain the shuttle effect, and enhance the diffusion of Li⁺ and accelerate the conversion reaction kinetics. Besides, due to the ultra-high catalyst activity of atomically dispersed Mn catalysts, the Li₂S/ON-MnPC cathode shows good electrochemical performance, e.g., an initial capacity of 534 mAh g^-1, a capacity of 514.18 mAh g^-1 after 100 cycles, a high retention rate of 96.23%, and a decay rate of 0.04% per cycle. Hence, use of atomically dispersed Mn catalysts to catalyze the chemical conversion reactions of polysulfides from multiple dimensions is a significant exploration, and it can provide a brand-new train of thought for the development and commercialization of the economical, high-performance Li₂S-based Li-S batteries.