共掺杂策略协同激活阴离子氧化还原构建高容量钠离子电池层状氧化物阴极材料

Synergistic activation of anionic redox via cosubstitution to construct high-capacity layered oxide cathode materials for sodium-ion batteries

作为锂离子电池的潜在替代品,钠离子电池由于成本、安全性等方面的优势吸引了广泛关注.但如何进一步提高其正极材料的能量密度仍是挑战,而通过激活阴离子氧化还原提供额外容量是一种可行的策略.本文报告了一种高性能锰基氧化物正极材料,Na_(0.67)Mg_(0.1)Zn_(0.1)Mn_(0.8)O_(2)(NMZMO).通过共掺杂策略协同激活阴离子氧化还原,此材料首圈可以放出~233 mAh g^(-1)的超高容量,明显高于Mg或Zn单掺杂的同类材料.综合多种光谱技术,作者证明了更高的容量源于更强的阴离子氧化还原活性.结合中子全散射以及共振非弹性X射线散射发现,Mg与Zn在高电压下会向面外迁移至四面体位点,诱导面内重排形成空位团簇,将氧阴离子以分子O_(2)的形式困于其中.Mg/Zn共存时,刺激了彼此更多的向面外迁移,为形成更多晶内分子O_(2)提供先决条件.本文提出了关于阴离子氧化还原的新见解,并为高容量钠电正极材料的开发提供了理论依据.

As a potential substitute for lithium-ion battery,sodium-ion batteries(SIBs)have attracted a tremendous amount of attention due to their advantages in terms of cost,safety and sustainability.Nevertheless,further improvement of the energy density of cathode materials in SIBs remains challenging and requires the activation of anion redox reaction(ARR)activity to provide additional capacity.Herein,we report a high-performance Mn-based sodium oxide cathode material,Na_(0.67)Mg_(0.1)Zn_(0.1)Mn_(0.8)O_(2)(NMZMO),with synergistic activation of ARR by cosubstitution.This material can deliver an ultra-high capacity of~233 mAh/g at 0.1 C,which is significantly higher than their single-cation-substituted counterparts and among the best in as-reported MgMn or ZnMn-based cathodes.Various spectroscopic techniques were comprehensively employed and it was demonstrated that the higher capacity of NMZMO originated from the enhanced ARR activity.Neutron pair distribution function and resonant inelastic X-ray scattering experiments revealed that out-of-plane migration of Mg/Zn occurred upon charging and oxygen anions in the form of molecular O_(2)were trapped in vacancy clusters in the fully-charged-state.In NMZMO,Mg and Zn mutually interacted with each other to migrate toward tetrahedral sites,which provided a prerequisite for further ARR activity enhancement to form more trapped molecular O_(2).These findings provide unique insight into the ARR mechanism and can guide the development of highperformance cathode materials through ARR enhancement strategies.