Lithium-Ion Conductor Li2ZrO3-Coated Primary Particles To Optimize the Performance of Li-Rich Mn-Based Cathode Materials.

A lithium-rich manganese-based cathode material (LRMC) is currently considered as one of the most promising next-generation materials for lithium-ion batteries, which has received much attention, but the LRMC still faces some key scientific issues to break through, such as poor rate capacity, rapid voltage, capacity decay, and low first coulomb efficiency. In this work, homogeneous Li2ZrO3 (LZO) was successfully coated on the surface of Li1.2Mn0.54Ni0.13Co0.13O2 (LRO) by molten salt-assisted sintering technology. Li2ZrO3 has good chemical and electrochemical stability, which can effectively inhibit the side reaction between electrode materials and electrolytes and reduce the dissolution of transition metal ions. Thus, the as-prepared LRO@LZO composites are expected to improve the cycling performance. It can be found that the discharge specific capacity of LRO is 271 mAh g-1 at 0.1 C, and the capacity retention rate is still 93.7% after 100 cycles at 1 C. In addition, Li2ZrO3 is an excellent lithium-ion conductor, which is prone to increasing the lithium-ion transfer rate and improving the rate capacity of LRO. Therefore, this study provides a new solution to improve the structure stability and electrochemical performance of LRMCs.

Engineering a TiNb2O7-Based Electrocatalyst on a Flexible Self-Supporting Sulfur Cathode for Promoting Li-S Battery Performance.

Lithium-sulfur (Li-S) batteries are considered a prospective energy storage system because of their high theoretical specific capacity and high energy density, whereas Li-S batteries still face many serious challenges on the road to commercialization, including the shuttle effect of lithium polysulfides (LiPSs), their insulating nature, the volume change of the active materials during the charge-discharge process, and the tardy sulfur redox kinetics. In this work, double transition metal oxide TiNb2O7 (TNO) nanometer particles are tactfully deposited on the surface of an activated carbon cloth (ACC), activating the surface through a hydrothermal reaction and high-temperature calcination and finally forming the flexible self-supporting architecture as an effective catalyst for sulfur conversion reaction. It has been found that ACC@TNO possesses many catalytic activity sites, which can inhibit the shuttle effect of LiPSs and increase the Coulombic efficiency by boosting the redox reaction kinetics of LiPS transformation reaction. As a consequence, the ACC@TNO/S cathode exhibits an impressive electrochemical performance, including a high initial discharge capacity of 885 mAh g-1 at a high rate of 1 C, a high discharge specific capacity of 825 mAh g-1 after 200 cycles with a prominent capacity retention rate of 93%, and a small decay rate of 0.034% per cycle. Although TNO is extensively used in the fields of lithium ion batteries and other rechargeable batteries, it is first introduced as sulfur host materials to boost the redox reaction kinetics of the LiPS transformation reaction and increase the electrochemical performance of Li-S batteries. Therefore, studies of the synergistic effect on the chemical absorption and catalytic conversion effect of TNO for LiPSs of Li-S batteries provide a good strategy for boosting further the comprehensive electrochemical performances of Li-S batteries.

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.

Li2S In Situ Grown on Three-Dimensional Porous Carbon Architecture with Electron/Ion Channels and Dual Active Sites as Cathodes of Li-S Batteries.

Li2S-based Li-S batteries are taken as promising energy storage systems due to the high theoretical specific capacity/energy density and nature of a matching Li-metal-free anode. However, the cyclic stability of the Li2S-based Li-S battery is seriously prevented by the shuttle effect of lithium polysulfides (LiPSs). Meanwhile, due to the poor electrical conductivity of Li2S, the Li-S battery displays slow reaction kinetics. In this work, we design 3D-porous carbon (PC) architecture as a host for inhabiting the LiPS shuttle based on physical capture. Furthermore, this porous carbon architecture is modified by introducing two kinds of heteroatoms (N and S) to form dual active sites (named as NSPC) for chemically binding LiPSs and accelerating their conversion. The polyvinyl pyrrolidone-coated Li2SO4·H2O is embedded in the NSPC skeleton and further forms the Li2S/NSPC cathode via a carbothermal reduction process. In consequence, the NSPC architecture possesses continuous electron/ion channels and abundant active sites, which are beneficial to the fast diffusion of Li+ and timely conversion of sulfur species. As a result, the as-prepared Li2S/NSPC cathode exhibits a high initial discharge capacity of 690 mAh g-1 at a high rate of 1C and keeps a capacity of 587 mAh g-1 after 200 cycles with a good capacity retention rate of 85% and low fading rate of 0.075% per cycle. Therefore, this work offers a brand-new platform to understand the synergistic effects of promoting reaction kinetics for Li2S-based Li-S batteries.

Photo-induced self-catalysis of nano-Bi2MoO6 for solar energy harvesting and charge storage.

Efficient, sustainable, and integrated energy systems require the development of novel multifunctional materials to simultaneously achieve solar energy harvesting and charge storage. Bi-based oxysalt aurivillius phase materials are potential candidates due to their typical photovoltaic effect and their pseudo-capacitance charge storage behavior. Herein, we synthesized nano-Bi2MoO6 as a material for both solar energy harvesting and charge storage due to its suitable band gap for absorption of visible light and its well-defined faradaic redox reaction from Bi metal to Bi3+. The irradiation of visible light significantly affected the electrochemical processes and the dynamics of the Bi2MoO6 electrode. The photo-induced self-catalytic redox mechanism was carefully explored by adding sacrificial agents in photocatalysis reaction. In accordance with the rule of energy matching, the photo-generated holes oxidized the Bi metal to Bi3+, and the corresponding peak current increased by 79.5% at a scanning rate of 50 mV s-1. More importantly, the peak current retention rate remained higher than 92.5% during the entire 200 cycles. The photo-generated electrons facilitated a decrease of 184 mV in the overpotential of the reduction process. Furthermore, the irradiation of visible light also accelerated the ionic diffusion of the electrolyte. These investigations provide a unique perspective for the design and development of new multifunctional materials to synergistically realize solar energy harvesting and charge storage.