Sn is a promising metal anode for aqueous batteries, with up to four-electron redox available per atom (903 mAh g⁻¹_Sn). However, practically harnessing the four-electron Sn(OH)₆²⁻/Sn reversibility remains challenging due to limited mechanistic understanding. Here, we reveal a kinetically asymmetric redox pathway involving a successive four-electron plating and a stepwise 2 + 2 electron stripping through a Sn(OH)₃⁻ intermediate. The crossover of Sn(OH)₃⁻ induces a reversible self-discharge that reduces Coulombic efficiency but does not impact cyclability, demonstrated by four-electron Sn-Ni full cells that sustain >800 h of stable cycling. By tuning the ion selectivity of the separator to suppress Sn(OH)₃⁻ crossover while allowing OH⁻ transport, we further demonstrate high Sn utilization (67%) and high energy density (143.1 Wh L⁻¹_cell). The results provide key understandings of the tradeoffs in engineering reversible multi-electron metal anodes and define a new benchmark for practical energy density that exceeds any Sn-based aqueous batteries to date.

中文翻译：

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可逆四电子锡金属水电池


Sn是一种很有前景的水系电池金属阳极，每个原子最多可进行四电子氧化还原（903 mAh g ^-1 _Sn ）。然而，由于对机理的理解有限，实际利用四电子 Sn(OH) ₆ ²⁻ /Sn 可逆性仍然具有挑战性。在这里，我们揭示了一个动力学不对称氧化还原途径，涉及连续的四电子电镀和通过 Sn(OH) ₃ ^-中间体的逐步 2 + 2 电子剥离。 Sn(OH) ₃ ⁻的交叉会引起可逆的自放电，从而降低库仑效率，但不会影响循环性能，四电子 Sn-Ni 全电池可维持 >800 小时的稳定循环证明了这一点。通过调整隔膜的离子选择性以抑制Sn(OH) ₃ ^-交叉，同时允许OH ^-传输，我们进一步证明了高Sn利用率（67%）和高能量密度（143.1 Wh L ^-1_电池）。研究结果提供了对设计可逆多电子金属阳极的权衡的关键理解，并为实际能量密度定义了新的基准，该能量密度超过了迄今为止任何锡基水系电池。