Hassan Mohamed H, Fu Jintao, Liu Jiaxin, Detsi Eric
Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA, 19104, USA.
Mater Horiz. 2025 Sep 29;12(19):7636-7647. doi: 10.1039/d5mh00656b.
To achieve high specific capacities in sodium-ion batteries (SIBs) containing P2-type Na[NiMn]O (NNMO) cathodes, researchers have increasingly explored cycling batteries beyond the conventional 2-4 V voltage range. However, crossing this voltage boundary at either the upper or lower limits causes phase transitions that result in structural instability. This opinion article primarily focuses on the performance of NNMO in the higher voltage region, where P2-O2 phase transition occurs (≥4.2 V Na/Na). This transition is accompanied by metal oxide layer gliding and lattice oxygen loss, leading to structural degradation. Among the various strategies to mitigate this effect, NNMO doping has been shown to minimize structural degradation and reduce capacity fading to a certain extent. In this opinion article, we argue that regardless of the doping elements, doped-NNMO does not yield satisfactory results for practical applications. This raises the question of whether doping NNMO is the right approach to mitigate structural instability issues during the P2-O2 phase transition between 2 and 4.5 V. In this opinion article, we clarify some misconceptions about NNMO doping strategies in mitigating the P2-O2 phase transition. Finally, we discuss a strategy beyond doping that might help address the aforementioned issues.
为了在含P2型Na[NiMn]O（NNMO）阴极的钠离子电池（SIBs）中实现高比容量，研究人员越来越多地探索在传统2-4V电压范围之外对电池进行循环。然而，在上限或下限越过这个电压边界会导致相变，从而导致结构不稳定。这篇观点文章主要关注NNMO在较高电压区域的性能，在该区域会发生P2-O2相变（≥4.2V Na/Na）。这种转变伴随着金属氧化物层滑动和晶格氧损失，导致结构退化。在减轻这种影响的各种策略中，NNMO掺杂已被证明能在一定程度上最小化结构退化并减少容量衰减。在这篇观点文章中，我们认为无论掺杂元素如何，掺杂的NNMO在实际应用中都不能产生令人满意的结果。这就引出了一个问题，即掺杂NNMO是否是减轻2至4.5V之间P2-O2相变过程中结构不稳定问题的正确方法。在这篇观点文章中，我们澄清了一些关于NNMO掺杂策略在减轻P2-O2相变方面的误解。最后，我们讨论了一种超越掺杂的策略，该策略可能有助于解决上述问题。
