A new type of electrolyte additive, the hyperbranched polyimine derivative (p-BPMI) is prepared from 1,3-dimethyl-barbituric acid (1,3-DBTA), copolymerizing of bismaleamic acyl imide (BMI) and N-phenylmaleimide(PMI). The p-BPMI powder is dissolvable in electrolyte (1M LiPF₆ in EC+DMC+EMC 1:1:1 V/V %), and administered similarly as other electrolyte additives. The interface composition and SEI structure after pre-cycling the coin cells using the Li(Ni_1/3Mn_1/3Co_1/3)O₂/Li half cell were characterized by SEM、EIS and XPS techniques and confirmed that the hyper-branched p-BPMI participated with the growth of SEI, where both the electrolytes and salt decomposition are reduced, leading to the formation of thinner and more robust SEI coating.

With addition of 1wt% p-BPMI in electrolyte, the capacity retention is improved from 85.21% to 96.53% compared with the base electrolyte after 0.5C-rate for 80 cycles at 25°C. Cycling at 0.5C-rate at 60^oC for 30 cycle, the capacity retention is improved from 93.71% to 96.43% when compared with 1wt% VC.  NMC/graphite pouch full cell (500mA) with 1wt% p-BPMI-added electrolyte in the fully charged state at 4.3V shows no sign of combustion or explosion after induce internal shortage by puncturing the cell, while the regular cell with only VC additive is exploded.  This new type of electrolyte additive p-BPMI not only improved the room and high temperature cycling performance, it also assured LIBs safety.