基于阳离子势设计高性能P2/O3共生复合相储钠正极材料

Cationic-potential tuned biphasic layered cathodes for stable desodiation/sodiation

含钠层状氧化物比容量高、结构多样、组分可调、制备简单,是极具前景的钠离子电池正极材料之一.其中,P2型和O3型层状氧化物因结构的差异表现出了不同的性能特点,制备P2/O3复合相材料可在一定程度上耦合二者的优势.然而,这种复合相材料的形成机制尚不明确,材料设计缺乏指导依据.对此,本文基于阳离子势观点系统研究了P2/O3复合相的形成机制,证明了P2/03双相结构本质上源于反应热力学/动力学因素导致的元素分布不均匀性及其引起的局部阳离子势差异,进一步提出了具有普适性的“临界阳离子势+调控组分熵”材料设计原则,并阐释了以P2/O3相竞争反应为主的复合相“协同效应”,为钠离子电池新型氧化物正极材料的设计开发提供了理论依据.

Sodium layered oxides generally suffer from deep-desodiation instability in P2 structure and sluggish kinetics in O3 structure.It will be great to design P2/O3 biphasic materials that bring the complementary merits of both structures.However,such exploration is hindered by the ambiguous mechanism of material formation.Herein,supported by theoretical simulations and various spectroscopies,we prove that P2/O3 biphasic structures essentially originate from the internal heterogeneity of cationic potential,which can be realized by constraining the temperature-driven ion diffusion during solid-state reactions.Consequently,P2/O3 biphasic Na_(0.7)Ni_(0.2)Cu_(0.1)Fe_(0.2)Mn_(0.5)O_(2)-δ with well-designed quaternary composition is successfully obtained,exhibiting much-improved rate capabilities(62 mAh g^(-1)at 2.4 A g^(-1)) and cycling stabilities(84%capacity retention after 500 cycles)than its single-phase analogues.Furthermore,synchrotron-based diffraction and X-ray absorption spectroscopy are employed to unravel the underlying sodium-storage mechanism of the P2/O3 biphasic structure.This work presents new insights toward the rational design of advanced layered cathodes for sodium-ion batteries.