Enhancing the safety of lithium-ion batteries: synthesis and performance evaluation of APP@UF microcapsule electrolyte additives

A B S T R A C T Ammonium polyphosphate was successfully encapsulated within a urea-formaldehyde resin shell via in-situ polymerization, yielding flame-retardant microcapsules. The synthesized microcapsules exhibited effective flame retardancy, as confirmed by various characterization techniques and ignition tests. The synthesized flame-retardant microcapsules (APP@UF) were uniformly integrated into the electrolyte matrix and subsequently assembled into electrochemical cells for performance evaluation. During thermal runaway in lithium-ion batteries, the internal temperature escalates. Upon reaching 210 °C, the microcapsule shell undergoes rupture, releasing APP to suppress the thermal runaway reactions within the battery, thereby achieving lithium-ion battery safety based on the concept of active protection. Furthermore, the microcapsules demonstrated stable dispersion in commercial lithium-ion electrolytes. Coin cells were assembled using electrolyte mixtures containing varying mass fractions of the microcapsules. At an addition level of 2 wt%, the battery retained 85.52 % of its capacity after 100 cycles under constant current charge-discharge conditions. The incorporation of microcapsules enhances battery safety without compromising electrochemical performance, presenting a viable strategy for improving the initial safety of lithium-ion batteries during thermal runaway.