High safety and cycling stability of ultrahigh energy lithium ion batteries

High-nickel layered oxide Li-ion batteries (LIBs) dominate the electric vehicle market, but their potentially poor safety and thermal stability remain a public concern. Here, we show that an ultrahigh-energy LIB (292 Wh kg⁻¹) becomes intrinsically safer when a small amount of triallyl phosphate (TAP) is added to standard electrolytes. TAP passivates the electrode-electrolyte interfaces and limits the maximum cell temperature during nail penetration to 55°C versus complete cell destruction (>950°C) without TAP. The downside of this reliable safety solution is higher interfacial impedance and hence lower battery power; however, thermal modulation for battery operation around 60°C can restore power completely. When cycled at 60°C, the cell stabilized with TAP achieved 2,413 cycles at 76% capacity retention. Such an unconventional combination of interface-passivating electrolyte additive with cell thermal modulation renders the most energy-dense LIBs even safer than LiFePO₄ chemistry, while enjoying high power and cycling stability concurrently.