Developing a Diamine-Assisted Polymerization Method To Synthesize Nano-LiMnPO4 with N-Doped Carbon from Polyamides for High-Performance Li-Ion Batteries

A diamine-assisted polymerization method is invented to synthesize nano-LiMnPO4 coated with highly homogeneous polyamides. The additive, p-phenylenediamine with a diamine and an aromatic group, enters the whole reaction, effectively adsorbed on the LiMnPO4. p-Phenylenediamine suppresses the particle growth and maintains the reaction pH value that promotes the formation of impurity-free LiMnPO4. When carbon is prepared with sucrose, the LiMnPO4/C prepared with large amounts of p-phenylenediamine exhibits a capacity of 134 mAhg–1 at 0.1C. To further synthesize a more homogeneous and conductive carbon, p-phenylenediamine and acyl chloride are in situ polymerized to two types of polyamide, aromatic (known as, aramid) and semialiphatic polyamide. The N-doped carbon pyrolyzed from the polyamide allows a fast Li-ion migration into the LiMnPO4. Lithium ions are favorable for being adsorbed/desorbed on the N-doped carbon as compared with the nondoped carbon. It is demonstrated that N is bonding with P and Mn on the LiMnPO4 surface, decreasing the contact resistance of carbon. Thus, LiMnPO4/N-doped C exhibits better cycling performance and rate capability than the LiMnPO4/C prepared with sucrose.