Discovering Cathodic Biocompatibility for Aqueous Zn-MnO2 Battery: An Integrating Biomass Carbon Strategy

Developing high-performance aqueous Zn-ion batteries from sustainable biomass becomes increasingly vital for large-scale energy storage in the foreseeable future. Therefore, γ-MnO2 uniformly loaded on N-doped carbon derived from grapefruit peel is successfully fabricated in this work, and particularly the composite cathode with carbon carrier quality percentage of 20 wt% delivers the specific capacity of 391.2 mAh g-1 at 0.1 A g-1, outstanding cyclic stability of 92.17% after 3000 cycles at 5 A g-1, and remarkable energy density of 553.12 Wh kg-1 together with superior coulombic efficiency of ~ 100%. Additionally, the cathodic biosafety is further explored specifically through in vitro cell toxicity experiments, which verifies its tremendous potential in the application of clinical medicine. Besides, Zinc ion energy storage mechanism of the cathode is mainly discussed from the aspects of Jahn-Teller effect and Mn domains distribution combined with theoretical analysis and experimental data. Thus, a novel perspective of the conversion from biomass waste to biocompatible Mn-based cathode is successfully developed.

Advanced Li/Na-CO2 Batteries Enabled by the γ-MnO2 Catalyst with Enhanced Carbonate Decomposition

Metal-CO₂ batteries, especially Li-CO₂ and Na-CO₂ batteries, are regarded as ideal new-generation energy storage systems owing to their high energy density and extraordinary CO₂ capture capability. However, the advancement of metal-CO₂ batteries is still at an early stage. The problems caused by accumulation of carbonates during charge-discharge cycles, such as large polarization and poor reversibility, restrict their practical application. Therefore, designing efficient catalysts is crucial for promoting the decomposition of carbonate to improve the electrochemical performance of metal-CO₂ batteries. Herein, we first adopted sea urchin-like γ-MnO₂ as the cathode material for Li/Na-CO₂ batteries. Benefiting from the unique structure and excellent catalytic activity of γ-MnO₂, the as-prepared Li-CO₂ and Na-CO₂ batteries can achieve low overpotentials of 1.28 and 1.36 V, respectively, at a current density of 100 mA g^-1 with a cutoff capacity of 1000 mA h g^-1. The overpotentials are lower than those of most of the state-of-the-art catalysts in previous reports. After 100 and 50 cycles of Li-CO₂ and Na-CO₂ batteries, respectively, their charging termination voltages remain at around 4.1 and 3.9 V, respectively; such a low charging platform indicates the excellent catalytic activity of the γ-MnO₂ cathode on the discharge products. Our findings offer a promising guideline to design efficient electrocatalysts for high-performance metal-CO₂ batteries.

Core-Shell Structure and Interaction Mechanism of γ-MnO2 Coated Sulfur for Improved Lithium-Sulfur Batteries

Lithium-sulfur batteries have attracted worldwide interest due to their high theoretical capacity of 1672 mAh g^-1 and low cost. However, the practical applications are hampered by capacity decay, mainly attributed to the polysulfide shuttle. Here, the authors have fabricated a solid core-shell γ-MnO₂ -coated sulfur nanocomposite through the redox reaction between KMnO₄ and MnSO₄ . The multifunctional MnO₂ shell facilitates electron and Li⁺ transport as well as efficiently prevents polysulfide dissolution via physical confinement and chemical interaction. Moreover, the γ-MnO₂ crystallographic form also provides one-dimensional (1D) tunnels for the Li⁺ incorporation to alleviate insoluble Li₂ S₂ /Li₂ S deposition at high discharge rate. More importantly, the MnO₂ phase transformation to Mn₃ O₄ occurs during the redox reaction between polysulfides and γ-MnO₂ is first thoroughly investigated. The S@γ-MnO₂ composite exhibits a good capacity retention of 82% after 300 cycles (0.5 C) and a fade rate of 0.07% per cycle over 600 cycles (1 C). The degradation mechanism can probably be elucidated that the decomposition of the surface Mn₃ O₄ phase is the cause of polysulfide dissolution. The recent work thus sheds new light on the hitherto unknown surface interaction mechanism and the degradation mechanism of Li-S cells.