Even with the many desirable properties, natural abundance and low cost of α-MnO₂, its application as the anode in lithium-ion batteries has been limited because of its low intrinsic electrical conductivity and large volume expansion occurring during charge/discharge cycles. In this work, a ternary composite electrode consisting of MnO₂-polypyrrole (PPy) core–shell arrays is grown on graphene foam (GF) to address the above critical issues. The freestanding MnO₂–PPy/GF electrode exhibits a high reversible capacity of 945 mA h g⁻¹ at 0.1 A g⁻¹ after 150 cycles with a coulombic efficiency of over 98%, far better than 550 mA h g⁻¹ for the uncoated counterpart. An in situ TEM examination reveals several functional features of the PPy coating that ameliorate the MnO₂ conversion reaction kinetics, and thus the electrochemical performance of the electrode. The PPy coated MnO₂ nanowires have a lithiation speed three times faster than that of the uncoated MnO₂ along with improved electronic conduction and a stable structure against volume expansion. Such a rational design of an electroactive core and a highly conductive polymer shell on a GF conductive substrate offers a potential solution to developing novel MnO₂-based electrodes with enhanced electrochemical performance.

中文翻译：

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原位锂化的TEM研究成聚吡咯涂覆α-MnO的₂ /石墨烯泡沫独立电极†

即使有许多期望的性质，天然丰度和α-MnO的成本低₂，其作为锂离子电池阳极的申请已由于其低的本征导电率，并且在充电/放电循环中发生大的体积膨胀的限制。在这项工作中，在石墨烯泡沫（GF）上生长了由MnO _2-聚吡咯（PPy）核-壳阵列组成的三元复合电极，以解决上述关键问题。独立的MnO ₂ –PPy / GF电极在150次循环后，在0.1 A g ^-1时表现出945 mA hg ^-1的高可逆容量，库仑效率超过98％，远优于未镀膜的550 mA hg ^-1。一种原位TEM检查揭示了PPy涂层的几个功能特性，这些功能特性改善了MnO ₂转化反应动力学，从而改善了电极的电化学性能。PPy涂覆的MnO ₂纳米线的锂化速度是未涂覆的MnO _2的三倍，具有改进的电子传导性和稳定的抗体积膨胀结构。GF导电基板上的电活性核和高导电聚合物壳的这种合理设计为开发具有增强的电化学性能的新型MnO ₂基电极提供了潜在的解决方案。