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
Qingdao Industrial Energy Storage Research Institute, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, 266101, P. R. China.
School of Materials Science and Engineering, Shanghai University, Shanghai, 200444, P. R. China.
Adv Mater. 2020 Apr;32(14):e1907526. doi: 10.1002/adma.201907526. Epub 2020 Feb 20.
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 /Zn at both M1 and M2 when using NaV (PO ) (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 Zn in NVP, which is enabled by a concerted Na /Zn transfer mechanism. In addition, significant improvement of the electronic conductivity and mechanical properties is achieved in Zn -intercalated ZnNaV (PO ) in comparison with those of Na V (PO ) . This work not only provides in-depth insight into Zn intercalation and dynamics in NVP unlocked by activating the M1 sites, but also opens a new route toward design of improved NASICON cathodes.
长期以来，人们一直认为，作为锂/钠电池有前景的阴极材料，菱面体NASICON型化合物应具有不活跃的M1(6b)位点，离子（脱）嵌入仅发生在M2（18e）位点。特别重要的是，通常认为对充放电有活性的M1位点是不理想的，因为离子扩散往往会因通道的不规则占据而受到干扰，这会加速电池的劣化。然而，当使用NaV(PO)（NVP）作为锌离子电池的阴极时，发现通过在M1和M2处混合占据Na/Zn可以显著提高结构稳定性。原子尺度扫描透射电子显微镜的结果、从头算分子动力学模拟分析以及基于精确键价的结构模型表明，这种改进是由于NVP中Zn的容易迁移，这是由协同的Na/Zn转移机制实现的。此外，与NaV(PO)相比，插入Zn的ZnNaV(PO)的电子导电性和机械性能有显著提高。这项工作不仅深入洞察了通过激活M1位点解锁的NVP中Zn的嵌入和动力学，还为设计改进的NASICON阴极开辟了一条新途径。
