MnO₂-based zinc-ion batteries have emerged as a promising candidate for next-generation energy storage systems. Despite extensive research on MnO₂ electrodes, the charging mechanism in mildly acidic electrolytes remains debated. Most studies have focused on α-MnO₂, and this study aims to shed light on the identity of the charge carrier in β-MnO₂ and the role of the Mn²⁺ cations. By employing in situ EQCM-D measurements, along with ssNMR, XRD, TEM, and in situ pH monitoring, we demonstrated that the charging mechanism is primarily governed by proton de/intercalation. Compared to α-MnO₂, with its larger 2 × 2 tunnels that accommodate hydronium ions, the β-phase has smaller 1 × 1 tunnels, permitting only the insertion of bare protons. During cycling, we observed the formation of new phases on β-MnO₂ originating from the repetitive electrodeposition/dissolution of Mn²⁺. In addition, these phases can reversibly host hydronium ions, resulting in a mixed charging mechanism that involves the insertion of both H₃O⁺ and H⁺.

中文翻译：

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揭示 β-MnO2 在水性锌电解质中的电荷储存机制


MnO₂ 基锌离子电池已成为下一代储能系统的有前途的候选者。尽管对 MnO₂ 电极进行了广泛的研究，但弱酸性电解质中的充电机制仍然存在争议。大多数研究都集中在 α-MnO₂ 上，本研究旨在阐明 β-MnO₂ 中电荷载流子的身份以及 Mn²⁺ 阳离子的作用。通过采用原位 EQCM-D 测量以及 ssNMR、XRD、TEM 和原位 pH 监测，我们证明了充电机制主要由质子去/插层控制。与 α-MnO₂ 相比，β相具有更大的 2 × 2 个容纳水合氢离子的隧道，而 相具有较小的 1 × 1 个隧道，只允许插入裸质子。在循环过程中，我们观察到 β-MnO₂ 上形成的新相源于 Mn²⁺ 的重复电沉积/溶解。此外，这些相可以可逆地承载水合氢离子，从而产生涉及 H₃O⁺ 和 H⁺ 插入的混合充电机制。