Study of induced liquid-phase sintering effect in lithium-ion battery cathode upcycling

<h2>Summary</h2> As concerns over the sustainability of lithium-ion batteries (LIBs) intensify, direct upcycling has emerged as a promising alternative to conventional recycling methods. However, its practical adoption is hindered by the need for high-pressure processing and the limited particle size of regenerated materials. Here, we present a new upcycling method, direct exposure heating (DEH), which selectively accelerates beneficial reaction kinetics while suppressing detrimental side reactions. DEH prevents liquid-phase depletion by eliminating the non-equilibrium heating ramp stage and minimizes irreversible phase transitions by bypassing prolonged intermediate temperatures. Under mild pressure (∼5 MPa), this process transforms secondary particles from spent LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) into large, structurally stable single-crystal LiNi_0.6Co_0.2Mn_0.2O2 (NCM622) particles. Grounded in thermodynamic and kinetic control, DEH resolves the long-standing trade-off between particle size and structural integrity, offering a scalable strategy not only for accelerating LIB upcycling commercialization but also for broadening advanced material synthesis.