Isophorone Diisocyanate: An Effective Additive to Form Cathode-Protective-Interlayer and Its Influence on LiNi0.5Co0.2Mn0.3O2 at High Potential.

In this work, we propose a novel electrolyte additive, isophorone diisocyanate (IPDI), to construct the surface protective interlayer. This membrane is produced via nucleophilic addition between the IPDI's diisocyanate groups and the free-radical-onium ion oxidative intermediate of propylene carbonate (PC). In the electrolyte with IPDI added between 10-20 mM, LiNi0.5Co0.2Mn0.3O2 presents the excellent performance, demonstrating the relative wide operational window to form the optimal protective membrane. This protective membrane ameliorates the cyclic stability. Although all systems deliver ∼185 mAh g-1 under 1 C between 2.5-4.6 V (vs Li+/Li), the cells in the suitable electrolyte maintain 90.4% in the 50 cycles and 83.2% in the 200 cycles, whereas the control cells are seriously dropped to 73.4% and 69.8%. The cells in the electrolyte with the appropriate IPDI also present the good rate capability, attaining ∼143 mAh g-1 under 5 C, much higher than the cells in the control electrolyte(92.4 mAh g-1). The additive proposed in this work is helpful to augment the energy density of lithium ion battery and prolong the one-drive distance of electric vehicles.