Electron transmission matrix and anion regulation strategy-derived oxygen-deficient δ-MnO2 for a high-rate and long-life aqueous zinc-ion battery.

Ion migration and electron transmission are vital for manganese dioxides in zinc ion batteries. δ-MnO2 is believed to be more suitable for zinc ion storage due to its layered structure. However, the performance of δ-MnO2 is still hampered by the frustrating conductivity and sluggish reaction kinetics. Herein, atomic engineering is adopted to modify δ-MnO2 at the atomic level to obtain oxygen-deficient δ-MnO2 (N-MnO2). Meanwhile, hollow carbon microtubes (HCMTs) obtained from green and renewable energy grass are proposed as cross-connected electron transmission matrices (CETMs) for MnO2. The biomass-derived CETMs not only optimize reaction kinetics but also facilitate the ion storage performance of MnO2. The as-prepared N-MnO2@HCMTs exhibit high rate capability and enhanced pseudocapacitve behavior contributed by the oxygen-deficient N-MnO2 and CETMs. Ex situ analysis reveals the reversible insertion/extraction of H+ and Zn2+ in N-MnO2@HCMTs during charge/discharge processes. Moreover, the quasi-solid-state N-MnO2@HCMTs//Zn cells are assembled and they deliver extraordinary discharge capacity and a long cyclic lifespan. This study may provide insights for further exploration of cathode materials in AZIBs and promote the large-scale production of aqueous Zn-MnO2 batteries.

Nanostructure and Advanced Energy Storage: Elaborate Material Designs Lead to High-Rate Pseudocapacitive Ion Storage.

The drastic need for development of power and electronic equipment has long been calling for energy storage materials that possess favorable energy and power densities simultaneously, yet neither capacitive nor battery-type materials can meet the aforementioned demand. By contrast, pseudocapacitive materials store ions through redox reactions with charge/discharge rates comparable to those of capacitors, holding the promise of serving as electrode materials in advanced electrochemical energy storage (EES) devices. Therefore, it is of vital importance to enhance pseudocapacitive responses of energy storage materials to obtain excellent energy and power densities at the same time. In this Review, we first present basic concepts and characteristics about pseudocapacitive behaviors for better guidance on material design researches. Second, we discuss several important and effective material design measures for boosting pseudocapacitive responses of materials to improve rate capabilities, which mainly include downsizing, heterostructure engineering, adding atom and vacancy dopants, expanding interlayer distance, exposing active facets, and designing nanosheets. Finally, we outline possible developing trends in the rational design of pseudocapacitive materials and EES devices toward high-performance energy storage.

Unlocking the Potential of Vanadium Oxide for Ultrafast and Stable Zn2+ Storage Through Optimized Stress Distribution: From Engineering Simulation to Elaborate Structure Design.

Compared with lithium-ion batteries (LIBs), aqueous zinc batteries (AZIBs) have received extensive attention due to their safety and cost advantages in recent years. The cathode determines the electrochemical performance of AZIBs to a large extent. Vanadium-based materials exhibit excellent capacity when used as AZIB cathodes. However, unexpected structural stress is inevitably induced during cycling and high current densities, which can gradually lead to structural deterioration and capacity decay. In fact, the stress/strain distribution in nanomaterials is crucial for electrochemical performance. In this work, the optimized stress distribution of the hierarchical hollow structure is verified by the finite element simulation of COMSOL software firstly. Guided by this model, a simple solvothermal method to synthesize hierarchical hollow vanadium oxide nanospheres (VO-NSs), consisting of ≈10 nm ultrathin nanosheets and ≈500 nm hollow inner cavities, is employed. And a highly disordered structure is introduced to the VO-NSs by in situ electrochemical oxidation, which can also weaken the structural stress during Zn2+ insertion and extraction. Benefiting from this unique structure, VO-NSs exhibit high-rate and stable Zn2+ storage capability. The strategy of engineering-driven material design provides new insights into the development of AZIB cathodes.

Balanced Crystallinity and Nanostructure for SnS2 Nanosheets through Optimized Calcination Temperature toward Enhanced Pseudocapacitive Na+ Storage.

Sodium ion batteries (SIBs) are expected to take the place of lithium ion batteries (LIBs) as next-generation electrochemical energy storage devices due to the cost advantages they offer. However, due to the larger ion radius, the reaction kinetics of Na+ in anode materials is sluggish. SnS2 is an attractive anode material for SIBs due to its large interlayer spacing and alloying reactions with high capacity. Calcination is usually employed to improve the crystallinity of SnS2, which could affect the Na+ reaction kinetics, especially the pseudocapacitive storage. However, excessively high temperature could damage the well-designed nanostructure of SnS2. In this work, we uniformly grow SnS2 nanosheets on a Zn-, N-, and S-doped carbon skeleton (SnS2@ZnNS). To explore the optimal calcination temperature, SnS2@ZnNS is calcined at three typical temperatures (300, 350, and 400 °C), and the electrochemical performance and Na+ storage kinetics are investigated specifically. The results show that the sample calcined at 350 °C exhibited the best rate capacity and cycle performance, and the reaction kinetics analysis shows that the same sample exhibited a stronger pseudocapacitive response than the other two samples. This improved Na+ storage capability can be attributed to the enhanced crystallinity and the intact nanostructure.