摘要
Na-ion diffusion kinetics is a key factor that decided the charge/discharge rate of the electrode materials in Na-ion batteries.In this work,two extreme concentrations of NaMnO_(2) and Na_(2/3)Li_(1/6)Mn_(5/6)O_(2) are considered,namely,the vacancy migration of Na ions in the fully intercalated and the migration of Na ions in the fully de-intercalated.The Na-vacancy and Na^(+)distribution in NaMnO_(2) migrated along oxygen dumbbell hop(ODH)and tetrahedral site hop(TSH),and the migration energy barriers were 0.374 and 0.296 eV,respectively.In NaLi_(1/6)Mn_(5/6)O_(2),the inhomogeneity of Li doping leads to the narrowing of the interlayer spacing by 0.9%and the increase of the energy barrier by 53.8%.On the other hand,due to the alleviation of Jahn-Teller effect of neighboring Mn,the bonding strength of Mn-O was enhanced,so that the energy barrier of path 2-3 in Mn-L1 and Mn-L2 was the lowest,which was 0.234 and 0.424 eV,respectively.In Na_(1/6)Li_(1/6)Mn_(5/6)O_(2),the migration energy barriers of Na-L2 and Na-L3 are 1.233 and 0.779 eV,respectively,because Li+migrates from the transition(TM)layer to the alkali metal(AM)layer with Na^(+)migration,which requires additional energy.
钠离子扩散动力学是决定钠离子电池电极材料充放电速率的关键因素。本文考虑了NaMnO_(2)和Na_(2/3)Li_(1/6)Mn_(5/6)O_(2)的两种极端浓度,即完全嵌入的Na^(+)空位迁移和完全脱嵌的Na^(+)迁移。NaMnO_(2)中的空位和钠离子分布沿着氧哑铃位迁移和四面体位迁移,迁移能垒分别为0.374和0.296 eV。在NaLi_(1/6)Mn_(5/6)O_(2)中,一方面由于Li掺杂的不均匀性导致被掺杂层的层间距变窄0.9%,能垒增加53.8%;另一方面由于缓解邻近Mn的Jahn-Teller效应强化了Mn—O成键强度,使得Mn-L1和Mn-L2中path2-3能垒最低,分别为0.234和0.424 eV。在Na_(1/6)Li_(1/6)Mn_(5/6)O_(2)中,Na-L2和Na-L3迁移能垒分别为1.233和0.779 eV,这是因为随着Na^(+)迁移,Li+会从过渡金属层向碱金属层迁移,从而需要额外的能量。
基金
Projects(51602352,51974373,51874358,51772333,61533020) supported by the National Natural Science Foundation of China
Project(2019JZZY020123) supported by the Major Scientific and Technological Innovation Projects of Shandong Province,China。
