Thomas Alexander, Pohle Björn, Schmidt Marcus, Bischoff Henrik-Gerd, Lau Marius, Heubner Felix, Kaskel Stefan, Mikhailova Daria
Leibniz Institute for Solid State and Materials Research (IFW) Dresden e. V., Helmholtzstraße 20, 01069 Dresden, Germany.
Chemische Metallkunde, Max-Planck-Institut für Chemische Physik fester Stoffe, Nöthnitzer Straße 40, 01187 Dresden, Germany.
ACS Omega. 2025 Jan 14;10(3):2699-2711. doi: 10.1021/acsomega.4c08310. eCollection 2025 Jan 28.
Secondary reactions and solid-electrolyte interface (SEI) formation are crucial aspects for battery lifetime. We show that one part of a natural SEI consists of crystalline NaH, which is formed on the sodium surface when carbonate-based electrolytes are used. Its impact on the electrochemical performance was studied using room-temperature H-treated Na anodes and a NaH-Na composite anode. Depending on the preparation conditions, hydrogen was stored on the Na surface in the form of NaOH, enhancing the long-term performance of the cell with a layered Na-oxide cathode, or in the form of NaH, deteriorating the performance in comparison to a reference Na cell. With the help of thermogravimetry coupled with mass spectrometry, we identified an explosion-like thermal decomposition of fatigued Na anodes above approximately 120 °C, but H-treated anodes exhibited higher stability of 10-30 °C compared to the reference anode. The composite NaH-Na anode shows a lower electrochemical capacity but no thermally induced explosion. Therefore, for a highly reactive metallic sodium anode, an effective protective layer against liquid electrolyte components is necessary to achieve high capacities and stable long-term operation. This passivation layer must fulfill the requirement of inertness to hydrogen gas to ensure a long lifetime.
副反应和固体电解质界面（SEI）的形成是电池寿命的关键因素。我们发现，天然SEI的一部分由结晶态的NaH组成，当使用碳酸盐基电解质时，它在钠表面形成。使用室温下经过氢处理的钠阳极和NaH-Na复合阳极研究了其对电化学性能的影响。根据制备条件，氢以NaOH的形式存储在钠表面，增强了具有层状氧化钠阴极的电池的长期性能，或者以NaH的形式存储，与参考钠电池相比性能变差。借助热重分析与质谱联用技术，我们确定了疲劳钠阳极在约120°C以上会发生类似爆炸的热分解，但经过氢处理的阳极与参考阳极相比，在10 - 30°C时表现出更高的稳定性。复合NaH-Na阳极显示出较低的电化学容量，但没有热诱导爆炸。因此，对于高活性的金属钠阳极，需要一个有效的防止液体电解质成分的保护层来实现高容量和稳定的长期运行。该钝化层必须满足对氢气惰性的要求，以确保长寿命。
