The low energy density and capacity fading of δ-MnO₂ electrode limit the practical applications for supercapacitors. Herein, Li doped δ-MnO₂ electrode (δ-Li_0.17Mn_0.83O₂) is successfully synthesized to improve the electrochemical performance. It is found that Li doping (δ-Li_0.17Mn_0.83O₂) dramatically enhances the specific capacitance(40 % enhancement at 0.2 A g^-1) and cycling stability(15 % enhancement after 5000 cycles) These improvements can be attributed to the modulation of redox chemistry and morphology optimization of δ-MnO₂ electrode. First-principles calculations suggest that the substitution of Mn by Li atom can modify oxygen redox chemistry, which stimulates electrochemical activity of oxygen and enhances electric-conductivity of the system, leading to the improvement of capacitance. Moreover, Li insertion can also reduce the valence state of Mn and optimize interlayer space, inhibiting Jahn–Teller effect and improving cycling stability of δ-MnO₂. Additionally, Brunauer Emmett and Teller analysis reveals that δ-Li_0.17Mn_0.83O₂ possesses a larger specific surface area(150.1 m² g^-1) and a wide range of pore sizes(50 nm) than that of δ-MnO₂(85.3 m² g^-1, 20 nm), leading to increased electrolyte ions’ adsorption/migration and improved capacitance. These results show that modulation of redox chemistry in δ-MnO₂ by ions inserting is an important strategy to develop layered transition-metal oxide based-electrode materials.

中文翻译：

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通过插入锂调节 δ-MnO2 电极的氧化还原化学：实验和第一性原理计算


δ-MnO₂ 电极的低能量密度和容量衰减限制了超级电容器的实际应用。本文成功合成了掺锂的 δ-MnO₂ 电极 （δ-Li_0.17Mn_0.83O₂），以提高电化学性能。研究发现，锂掺杂 （δ-Li_0.17Mn_0.83O₂） 显着提高了比电容（在 0.2 A ^g-1 时提高了 40%）和循环稳定性（5000 次循环后提高了 15%）这些改进可归因于氧化还原化学的调制和 δ-MnO₂ 电极的形态优化。第一性原理计算表明，Li原子取代Mn可以改变氧氧化还原化学，从而刺激氧的电化学活性并增强系统的导电性，从而提高电容。此外，Li 插入还可以降低 Mn 的价态并优化层间空间，抑制 Jahn-Teller 效应并提高 δ-MnO₂ 的循环稳定性。此外，Brunauer Emmett 和 Teller 分析表明，δ-Li_0.17Mn_0.83O₂ 比 δ-MnO₂ （85.3 m^{2 g-1}， 20 nm） 具有更大的比表面积 （150.1 m^{2 g-1}） 和更宽的孔径范围 （50 nm），导致电解质离子的吸附/迁移增加并提高了电容。这些结果表明，通过离子插入调节 δ-MnO₂ 中的氧化还原化学是开发层状过渡金属氧化物基电极材料的重要策略。