Selective Doping to Controllably Tailor Maximum Unit-Cell-Volume Change of Intercalating Li⁺ -Storage Materials: A...

Capacity decay of an intercalating Li⁺ -storage material is mainly due to the its particle microcracks from stress-causing volume change. To extend its cycle life, its unit-cell-volume change has to be minimized as much as possible. Here, based on a γ-Li₃ VO₄ model material, the authors explore selective doping as a general strategy to controllably tailor its maximum unit-cell-volume change, then clarify the relationship between its crystal-structure openness and maximum unit-cell-volume change, and finally demonstrate the superiority of "zero-strain" materials within 25-60 °C (especially at 60 °C). With increasing the large-sized Ge⁴⁺ dopant, the unit-cell volume of γ-Li_{3+ x} Ge_x V_{1- x} O₄ becomes larger and its crystal structure becomes looser, resulting in the decrease of its maximum unit-cell-volume change. In contrast, the doping with small-sized Si⁴⁺ shows a reverse trend. The tailoring reveals that γ-Li_3.09 Ge_0.09 V_0.91 O₄ owns the smallest maximum unit-cell-volume change of 0.016% in the research field of intercalating Li⁺ -storage materials. Consequently, γ-Li_3.09 Ge_0.09 V_0.91 O₄ nanowires exhibit excellent cycling stability at 25/60 °C with 94.8%/111.5% capacity-retention percentages after 1800/1500 cycles at 2 A g^-1 . This material further shows large reversible capacities, proper working potentials, and high rate capability at both temperatures, fully demonstrating its great application potential in long-life lithium-ion batteries.