Sodium and aluminum are a natural combination of inexpensive, abundant elements as a redox pair for battery energy storage. Recent explorations pairing a sodium anode and aluminum cathode have demonstrated reversible, energy dense Na-Al cells with excellent rate capability using the electrochemical reaction between a molten Na anode and a NaAlCl₄/Al cathode. In this work, the NaAlCl₄/Al cathode is extended beyond the neutral NaAlCl₄ composition by unlocking the NaCl-AlCl₃ phase diagram to explore the extra accessible capacity hidden in acidic chloroaluminate melts up to and beyond the composition NaAl₂Cl₇. This enables higher specific capacity and average discharge voltages than previous Na-Al batteries, utilizing two distinct cell reaction mechanisms in one battery. Fundamental aspects of the NaAlCl₄-NaAl₂Cl₇ reaction chemistry are investigated, and Na-metal/chloroaluminate batteries with excellent reversibility and areal capacity are demonstrated. Increasing the voltage window of the chloroaluminate Na-Al battery takes advantage of the higher voltage (∼ 2 V vs ∼1.6 V for neutral NaAlCl₄) contributed by the acidic chloroaluminate cathode reaction, unlocking an additional specific energy of ∼119 Wh kg⁻¹ by utilizing the conversion of NaAlCl₄ to NaAl₂Cl₇, which adds to the neutral melt reaction between NaAlCl₄/Al and Na (∼493 Wh kg⁻¹ theoretical). By significantly increasing the cathode thickness and therefore accessible areal capacity up to 131.7 mAh cm⁻², a discharge duration of 28.2 h is achieved with an estimated raw active materials cost of $7.02 kWh⁻¹. These metrics show the great potential of this unlocked chloroaluminate battery for future low-cost, long-duration electrochemical energy storage.

钠和铝是廉价、丰富元素的天然组合，作为电池储能的氧化还原对。最近将钠阳极和铝阴极配对的探索表明，利用熔融钠阳极和 NaAlCl ₄ /Al 阴极之间的电化学反应，可逆、能量密集的 Na-Al 电池具有出色的倍率性能。在这项工作中，NaAlCl ₄ /Al 阴极通过解锁 NaCl-AlCl ₃相图扩展到中性 NaAlCl ₄成分之外，以探索隐藏在酸性氯铝酸盐熔体中的额外可访问容量，直至和超过成分 NaAl ₂ Cl ₇. 这使得比以前的 Na-Al 电池具有更高的比容量和平均放电电压，在一个电池中利用两种不同的电池反应机制。研究了 NaAlCl ₄ -NaAl ₂ Cl ₇反应化学的基本方面，并展示了具有出色可逆性和面积容量的钠金属/氯铝酸盐电池。增加氯铝酸盐 Na-Al 电池的电压窗口利用了酸性氯铝酸盐阴极反应提供的更高电压（∼ 2 V vs ∼1.6 V 中性 NaAlCl ₄），释放了∼119 Wh kg ⁻¹的额外比能通过利用 NaAlCl ₄到 NaAl ₂ Cl的转化₇，它增加了 NaAlCl ₄ /Al 和 Na 之间的中性熔融反应（~493 Wh kg ^-1理论值）。通过显着增加阴极厚度并因此将可及面积容量增加到高达 131.7 mAh cm ^-2，实现了 28.2 小时的放电持续时间，估计原材料成本为 7.02 美元 kWh ^-1。这些指标显示了这种未锁定的氯铝酸盐电池在未来低成本、长期电化学储能方面的巨大潜力。