Role of Electronic Structure in Li Ordering and Chemical Strain in the Fast Charging Wadsley–Roth Phase PNb9O25,Chemistry of Materials

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Role of Electronic Structure in Li Ordering and Chemical Strain in the Fast Charging Wadsley–Roth Phase PNb9O25
Chemistry of Materials ( IF 7.2 ) Pub Date : 2021-09-20 , DOI: 10.1021/acs.chemmater.1c02059
Muna Saber ₁ , Molleigh B. Preefer ₂ , Sanjeev K. Kolli ₃ , William Zhang ₄ , Geneva Laurita ₅ , Bruce Dunn ₆ , Ram Seshadri _{3,

4} , Anton Van der Ven ₃

Affiliation

Wadsley–Roth crystallographic shear phases are a family of transition-metal oxides that show tremendous promise as electrode materials in Li-ion batteries. Despite their ability to intercalate lithium at high rates, little is known about their structural, thermodynamic, and electronic properties as a function of Li concentration. In this study, we use first-principles statistical mechanics methods to explore the lithium-site preference, lithiation strain, and electronic structure of PNb₉O₂₅, a Wadsley–Roth phase that has been shown to reversibly cycle at a rate of 60 C and that can accommodate more than one Li per Nb. We find that Li ions can occupy five symmetrically distinct interstitial sites within the PNb₉O₂₅ crystal structure, with three being pyramidal sites coordinated by five oxygen and two being window sites with square-planar oxygen coordination. The insertion of Li into PNb₉O₂₅ leads to a complex site filling sequence, with pyramidal sites preferred at low Li concentrations, followed by the filling of window sites at higher Li concentrations. Our findings are aided by neutron diffraction where pyramidal sites are found to be filled at low compositions. The order in which sites are filled is strongly influenced by the chemical strain due to Li insertion. The strain arises from the delocalization of donated electrons over the d orbitals of the structure’s edge-sharing niobium, which leads to a tetragonal distortion along the c-axis, thereby making vertical window sites favorable for Li occupancy at intermediate to high Li concentrations. Given the crystallographic similarities among different shear phases, we expect that the results of this study will also shed light on the electrochemical properties of other Wadsley–Roth chemistries.

中文翻译：

电子结构在快速充电 Wadsley-Roth 相 PNb9O25 中锂有序和化学应变中的作用

Wadsley-Roth 晶体剪切相是一类过渡金属氧化物，在锂离子电池中显示出巨大的电极材料前景。尽管它们能够以高速率嵌入锂，但对其作为锂浓度函数的结构、热力学和电子特性知之甚少。在这项研究中，我们使用第一性原理统计力学方法来探索 PNb ₉ O ₂₅的锂位偏好、锂化应变和电子结构，PNb ₉ O ₂₅是一种 Wadsley-Roth 相，已被证明以 60 C 的速率可逆循环并且每个 Nb 可以容纳一个以上的锂。我们发现锂离子可以占据 PNb ₉ O ₂₅内五个对称不同的间隙位点晶体结构，其中三个是由五个氧配位的金字塔位点，两个是具有方形平面氧配位的窗口位点。Li插入PNb ₉ O ₂₅导致复杂的位点填充顺序，在低Li浓度下优选锥体位点，随后在高Li浓度下填充窗口位点。我们的发现得到了中子衍射的帮助，其中发现金字塔位点以低成分填充。由于 Li 插入，位点填充的顺序受到化学应变的强烈影响。应变源于结构共享铌的 d 轨道上的捐赠电子离域，这导致沿c方向的四方畸变轴，从而使垂直窗口位点有利于在中到高浓度的锂离子中占据锂离子。鉴于不同剪切相之间的晶体学相似性，我们预计这项研究的结果也将阐明其他 Wadsley-Roth 化学物质的电化学性质。

更新日期：2021-10-12

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