Abstract Hierarchical ZnFe2O4 yolk-shell spheres (YSs) assembled from primary nanosheets are synthesized via a simple one-step solvothermal method followed by a heat-treatment process. A polypyrrole (PPy) conductive network is formed in-situ on pristine ZnFe2O4 YSs via chemical oxidative polymerization to obtain ZnFe2O4@PPy YSs. Morphological and structural characterization confirms that the conductive PPy coating does not destroy the localized porous microenvironment of pristine ZnFe2O4 with rapid mass transport. The solvothermal reaction time-dependent structure evolution and formation mechanism of ZnFe2O4@PPy YSs have been elucidated. Furthermore, the electrochemical performance of the ZnFe2O4@PPy YSs is assessed and compared with that of pristine ZnFe2O4 YSs. The results reveal that ZnFe2O4@PPy YSs exhibit excellent rate capability and long-term cycling stability, achieving 541.7 mAh g−1 at 5 A g−1 after 1000 cycles. The improved electrochemical performances of ZnFe2O4@PPy YSs are attributed to not only the structural advantages of porous yolk-shell architecture, but also the conductivity enhancement and suppressed volume expansion induced by the PPy layer.

中文翻译：

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多孔纳米片组装的ZnFe2O4@聚吡咯蛋黄壳微球的合成作为高倍率锂离子电池负极材料

摘要 由初级纳米片组装而成的分层 ZnFe2O4 蛋黄壳球 (YSs) 通过简单的一步溶剂热法和热处理工艺合成。通过化学氧化聚合在原始的 ZnFe2O4 YSs 上原位形成聚吡咯 (PPy) 导电网络以获得 ZnFe2O4@PPy YSs。形态和结构表征证实，导电 PPy 涂层不会破坏具有快速质量传输的原始 ZnFe2O4 的局部多孔微环境。已经阐明了 ZnFe2O4@PPy YSs 的溶剂热反应时间依赖性结构演变和形成机制。此外，还评估了 ZnFe2O4@PPy YSs 的电化学性能，并与原始 ZnFe2O4 YSs 的电化学性能进行了比较。结果表明，ZnFe2O4@PPy YSs 表现出优异的倍率性能和长期循环稳定性，1000 次循环后在 5 A g-1 下达到 541.7 mAh g-1。ZnFe2O4@PPy YSs 电化学性能的改善不仅归因于多孔蛋黄-壳结构的结构优势，还归因于 PPy 层引起的导电性增强和抑制体积膨胀。