All-Dry Synthesis of Single-Crystalline LiNi_0.6Mn_0.2Co_0.2O₂ Cathodes for High-Energy and Long-Life Li-Ion Batteries

Single-crystalline LiNi_0.6Mn_0.2Co_0.2O₂ cathodes (NMC622) synthesized by all-dry solid-phase synthesis (ADSPS) are promising candidates for high-voltage Li-ion batteries (LIBs) in virtue of their ecofriendly and cost-effective merits. However, serious Li/O loss at high sintering temperatures results in their structural and interfacial instabilities. Herein, a strontium/tantalum (Sr/Ta) codoped and lithium-borate (LBO) coated single-crystalline LiNi_0.6Mn_0.2Co_0.2O₂ (NMC622) with a superior layered structure is successfully prepared by ADSPS for the first time. Sr ions can reduce the sintering temperature by promoting grain-boundary fusion and particle growth, while Ta ions with a high Ta–O bond energy (839 kJ mol^–1) further alleviate oxygen loss to decrease Li/Ni mixing and oxygen vacancies. The LBO coating layer helps to remove surface residual alkali, enhancing interfacial stability and Li-ion transfer dynamics. Therefore, the resultant cathode displays a high capacity of 191.9 mAh g^–1 at 0.1C with a superior capacity retention of 81.6% at 1C within 2.7–4.5 V after 2000 cycles in pouch-type full cells.