Department of Material Science and Engineering , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States.
State Key Laboratory of Advanced Technology for Materials Synthesis and Processing , Wuhan University of Technology , Wuhan 430070 , P. R. China.
ACS Appl Mater Interfaces. 2018 Dec 26;10(51):44376-44384. doi: 10.1021/acsami.8b13376. Epub 2018 Dec 11.
Cryptomelane-type α-MnO has been demonstrated as a promising anode material for high-energy Li-ion batteries because of its high capacity and intriguing [2 × 2] tunnel structure. However, applications of MnO electrode, especially at high current rates and mass active material loading, are limited by the poor mechanical stability, unstable solid electrolyte interphase layer, and low reversibility of conversion reactions. Here, we report a design of homogeneous core-shell MnO nanowires (NWs) created by near-surface gradient Ti doping (Ti-MnO NWs). Such a structurally coherent core-shell configuration endowed gradient volume expansion from the inner core to the outer shell, which could effectively release the stress of the NW lattice during cycling and avoid pulverization of the electrode. Moreover, the gradiently doped Ti is able to avoid the Mn metal coarsening, reducing the metal particle size and improving the reversibility of the conversion reaction. In this way, the Ti-MnO NWs achieved both high reversible areal and volumetrical capacities (2.3 mA h cm and 991.3 mA h cm at 200 mA g, respectively), a superior round-trip efficiency (Coulombic efficiency achieved above 99.5% after only 30 cycles), and a long lifetime (a high capacity of 742 mA h g retained after 3000 cycle at 10 A g) at a high mass loading level of 3 mg cm. In addition, the detailed conversion reaction mechanism was investigated through in situ transmission electron microscopy, which further evidenced that the unique homogeneous core-shell structure could largely suppress the separation of core and shell upon charging and discharging. This new NW configuration could benefit the design of other large-volume-change lithium battery anode materials.
钙钛矿型α-MnO 由于其高容量和有趣的[2×2]隧道结构，已被证明是高能量锂离子电池的有前途的阳极材料。然而，MnO 电极的应用，特别是在高电流速率和高质量活性材料负载下，受到其较差的机械稳定性、不稳定的固体电解质界面层和转换反应的低可逆性的限制。在这里，我们报告了一种通过近表面梯度 Ti 掺杂（Ti-MnO NWs）设计均匀核壳结构 MnO 纳米线（NWs）的方法。这种结构上连贯的核壳结构赋予了从内核到外壳的梯度体积膨胀，这可以在循环过程中有效地释放 NW 晶格的应力，避免电极的粉碎。此外，梯度掺杂的 Ti 能够避免 Mn 金属粗化，减小金属颗粒尺寸，提高转换反应的可逆性。通过这种方式，Ti-MnO NWs 实现了高的可逆面积和体积容量（在 200 mA g 时分别为 2.3 mA h cm 和 991.3 mA h cm），高的往返效率（仅 30 次循环后库仑效率达到 99.5%以上）和长寿命（在 10 A g 下 3000 次循环后保持 742 mA h g 的高容量），在高质量负载水平为 3 mg cm 时。此外，通过原位透射电子显微镜研究了详细的转换反应机制，进一步证明了独特的均匀核壳结构可以在很大程度上抑制充电和放电时核壳的分离。这种新的 NW 结构可以有益于其他大容量变化的锂电池阳极材料的设计。
