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/00%/l0ICYS Annual Report 2023 ycneiciffeegrahcsiDcibmouoC1-ghAmyticapac1.5−4.8 V-130 mA g1M LiPF6 in EC/EMC 3:71M LiPF6 in EC/EMC 5:51M LiPF6 in EC/EMC 7:31M LiPF6 in EC/EMC 3:7 with coatingβ−MnO21M LiPF6 in EC/EMC 3:71M LiPF6 in EC/EMC 5:51M LiPF6 in EC/EMC 7:31M LiPF6 in EC/EMC 3:7 with coatingβ−MnO21.5−4.8 V-130 mA g30025020015010050104102100989694255075100Cycle number255075100Cycle number(a)(b)1. Outline of Research2. Research ActivitiesChia-Ching LINFig. 1. Electrochemical performances of β-MnO2 with different electrolytes and 2 wt% Li3PO4 coating: (a) cycle performance and (b) Coulombic efficiency in a voltage range of 1.5-4.8 V at 30 mA g−1.Fig. 2. The degradation mechanism of MnO2 as cathode for lithium-ion batteriesReferences 1) C.C. Lin, C.T. Hsu, W. Liu, S.C. Huang, M.H. Lin, U. Kortz, A. S. Mougharbel, T.Y. Chen, C.W. Hu, J.F. Lee, C.C. Wang, Y.F. Liao,L.L Li, L. Li, S. Peng, U. Stimming, H.Y. Chen, ACS Appl. Mater. Interfaces 2020, 12, 40296-40309 2) C.C. Lin, H.Y Liu, J.W. Kang, C.C. Yang, C.C. Li, H.Y.T. Chen, S.C. Huang, C.S. Ni, Y.C. Chuang, B.H. Chen, C.K. Chang, H.Y. Chen, Energy Storage Mater. 51 (2022) 159-171Energy storage technologies play a crucial role in various applications, ranging from portable electronics to electric vehicles and grid storage. Among these, lithium-ion batteries (LIBs) stand out for their impressive energy density, extended cycle life, and efficiency, earning them widespread attention. In contrast, sodium-ion batteries (SIBs) are considered promising candidates for large-scale energy storage due to their lower cost, abundant raw materials, and the more even global distribution of sodium compared to lithium. However, a major challenge in advancing LIBs/SIBs is identifying suitable host electrode materials that can deliver high capacity and reversibility. To improve the performance them, it is crucial to develop cathode materials and understand the degradation mechanism that can optimize their operation. [1-2] LIBs are costly due to the use of expensive transition metals like traditional cathode materials such as Co and Ni LiNi0.8Co0.1Mn0.1O2 (NCM) and LiCoO2. The presence of these toxic metals also complicates recycling efforts. As a result, finding next-generation, environmentally friendly, and high-performance cathode materials is essential. Tunnel-type manganese dioxide (MnO2) is commonly used as a cathode in commercial lithium metal primary batteries due to its low cost, non-toxicity, and high capacity of 308 mAh g−1. However, recharging these batteries can lead to lithium dendrite formation on the anode, causing short circuits and safety risks. Recently, interest in using lithium metal as an anode to boost LIB energy density has led to strategies like surface coating, electrolyte design, and lithophilic structures to minimize dendrite formation.in In this study, we systematically investigate the electrochemical performance and structural evolution of β-MnO2 as a function of electrolyte composition and voltage range. The results reveal that the cycle stability of β-MnO2 is influenced by both structural changes and manganese (Mn) dissolution, with their relative contributions being dependent on the upper cutoff voltage. Specifically, structural changes account for approximately 30-40% of the capacity decay after 100 cycles when the upper cutoff voltage is set at 4.2 V. However, this contribution decreases to around 10-20% when the upper cutoff voltage is increased to 4.8 V. This observation suggests that a higher cutoff voltage induces greater Mn dissolution, which can be attributed to side reactions between the active material and the electrolyte.Notably, our results indicate that ethylene carbonate (EC) in the electrolyte plays a significant role in Mn dissolution. A more substantial capacity loss is observed in MnO2 electrodes tested with electrolytes containing higher EC concentrations, highlighting the detrimental effects of EC on Mn stability. To mitigate this, we surface-coated the MnO2 electrodes with Li3PO4, which significantly improves the capacity retention of the material during cycling. This enhancement is attributed to the Li3PO4 coating, which prevents direct contact between the active material and the electrolyte, thereby reducing Mn dissolution. importance of electrolyte the Our findings underscore composition, voltage window, and surface coating in controlling the electrochemical stability and phase evolution of β-MnO2. Additionally, this study identifies the key factors influencing the degradation mechanisms of the active material and emphasizes the necessity for optimizing cycling conditions, electrolyte formulations, and surface modifications the performance and lifespan of Mn-based cathodes in lithium-ion batteries.to enhance Research Digest 17Investigate Electrode Materials for High Energy Density Lithium/Sodium-Ion Batteries