The lithium NMR shifts of three paramagnetic materials important in the charging/discharging processes of lithium vanadium phosphate cathode materials have been studied by large-scale quantum-chemical methodology. Namely, the ⁷Li NMR shifts of the fully lithiated Li₃V₂(PO₄)₃ (LVP3.0), and of the partly delithiated Li_2.5V₂(PO₄)₃ (LVP2.5) and Li₂V₂(PO₄)₃ (LVP2.0), have been computed and analyzed using a recently proposed approach (A. Mondal, M. Kaupp J. Phys. Chem. C 123 (2019) 8387-8405) that accounts for the Fermi-contact, pseudo-contact, as well as orbital shifts, combining periodic computations with an incremental cluster model. LVP3.0 and LVP2.0 exhibit three and two unique Li sites, respectively, which could be assigned to their experimental ⁷Li NMR signals. In case of LVP2.0, the computations clearly assigned the signals at 143 ppm and 77 ppm to the Li(1) and Li(2) sites, respectively, even though the latter is connected to V_b^(+III d² sites and the former to V_a^(+IV) d¹ sites. LVP2.5 is the most complex of these three materials, exhibiting a 50% occupation of Li(3) sites, which generates much more complicated Li NMR spectra with seven peaks that partly are closely spaced. Exploring three different occupation patterns, the computations can clearly assign five of the seven signals to one type of Li site and give most probable assignments for the two remaining signals. Notably, the calculations support seven signals to be assigned to LVP2.5, while previous interpretations took two of the signals as being entirely due to contamination by LVP2.0. The accuracy of the computations could probably be improved further by full DFT optimization of large super-cell structures. This work suggests that first-principles computations of NMR shifts of extended paramagnetic solids provide an important tool for the analysis of even rather complex NMR spectra.

通过大规模量子化学方法研究了在磷酸钒锂正极材料的充电/放电过程中重要的三种顺磁性材料的锂NMR位移。即，完全锂化的Li ₃ V ₂（PO ₄）₃（LVP3.0）以及部分脱锂的Li _2.5 V ₂（PO ₄）₃（LVP2.5）和Li ₂ V ₂的⁷ Li NMR位移（PO ₄）₃（LVP2.0），已使用最近提出的方法（A.Mondal，M.Kaupp J.Phys.Chem.C 123（2019）8387-8405）进行了计算和分析，该方法说明了费米接触，伪接触以及轨道移位，将周期计算与增量聚类模型相结合。LVP3.0和LVP2.0分别显示三个和两个独特的Li位点，可以将其分配给它们的实验⁷ Li NMR信号。在LVP2.0的情况下，即使后者分别连接到V _b ^{（+ III} d ²位和前者为V _a ^{（+ IV）} d ¹网站。LVP2.5是这三种材料中最复杂的，展现出Li（3）位点占50％，它会生成更复杂的Li NMR谱图，其中七个峰之间的间隔很小。通过探索三种不同的占用模式，计算可以清楚地将七个信号中的五个分配给一种类型的Li站点，并为其余两个信号给出最可能的分配。值得注意的是，计算支持将七个信号分配给LVP2.5，而先前的解释则将其中两个信号完全归因于LVP2.0的污染。大型超级单元结构的完全DFT优化可能会进一步提高计算的准确性。