Uncovering the Potential of M1‐Site‐Activated NASICON Cathodes for Zn‐Ion Batteries

There is a long‐standing consciousness that the rhombohedral NASICON‐type compounds as promising cathodes for Li+/Na+ batteries should have inactive M1(6b) sites with ion (de)intercalation occurring only in the M2 (18e) sites. Of particular significance is that M1 sites active for charge/discharge a...

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Bibliographic Details
Published in:Advanced materials (Weinheim) 2020-04, Vol.32 (14), p.e1907526-n/a
Main Authors: Hu, Pu, Zou, Zheyi, Sun, Xingwei, Wang, Da, Ma, Jun, Kong, Qingyu, Xiao, Dongdong, Gu, Lin, Zhou, Xinhong, Zhao, Jingwen, Dong, Shanmu, He, Bing, Avdeev, Maxim, Shi, Siqi, Cui, Guanglei, Chen, Liquan
Format: Article
Language:English
Subjects:
cathode materials
Cathodes
Computer simulation
Dynamic structural analysis
Intercalation
Ion diffusion
Materials science
Mechanical properties
Molecular dynamics
NASICON
occupation mechanism
Scanning transmission electron microscopy
Sodium
Structural stability
Zn‐ion batteries
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Summary:There is a long‐standing consciousness that the rhombohedral NASICON‐type compounds as promising cathodes for Li+/Na+ batteries should have inactive M1(6b) sites with ion (de)intercalation occurring only in the M2 (18e) sites. Of particular significance is that M1 sites active for charge/discharge are commonly considered undesirable because the ion diffusion tends to be disrupted by the irregular occupation of channels, which accelerates the deterioration of battery. However, it is found that the structural stability can be substantially improved by the mixed occupation of Na+/Zn2+ at both M1 and M2 when using NaV2(PO4)3 (NVP) as a cathode for Zn‐ion batteries. The results of atomic‐scale scanning transmission electron microscopy, analysis of ab initio molecular dynamics simulations, and an accurate bond‐valence‐based structural model reveal that the improvement is due to the facile migration of Zn2+ in NVP, which is enabled by a concerted Na+/Zn2+ transfer mechanism. In addition, significant improvement of the electronic conductivity and mechanical properties is achieved in Zn2+‐intercalated ZnNaV2(PO4)3 in comparison with those of Na3V2(PO4)3. This work not only provides in‐depth insight into Zn2+ intercalation and dynamics in NVP unlocked by activating the M1 sites, but also opens a new route toward design of improved NASICON cathodes. The concept for a novel storage mechanism for Zn2+ in NASICON is uncovered. The dynamic Na+/Zn2+ mixed occupation at the M1 and M2 sites of ZnxNaV2(PO4)3, enabled by their concerted migration, is proposed to improve the structural stability. This work may open a new route toward designing NASICON cathodes for Zn‐ion batteries for energy storage.
ISSN:0935-9648
1521-4095
DOI:10.1002/adma.201907526