A solid, amorphous, lithiated carbon phosphonitride displaying lithium ion conductivity

Thermal runaway reactions resulting in catastrophic battery failure and combustion have invigorated a search for non-flammable electrolytes. We report the synthesis of non-flammable inorganic lithiated carbon phosphonitride (Li–C–P–N) amorphous solids in various solvents, their spectroscopic and other characterization aimed at greater molecular structure understanding, and their ionic conductivities. The resin precursor to this polymeric material is the product of reacting solvated P(CN)3 and LiN(CN)2 ​at room temperature. The resulting resin can be cast from various polar aprotic solvents and produces Li–C–P–N films upon drying. The reaction mechanism was studied by time-resolved 31P solution NMR. A fully cured sample was studied by 31P, 13C and 7Li MAS NMR, including variable temperature 7Li MAS NMR observations of changes in satellite transitions arising from Li ​+ ​ion motions. Films dried at room temperature under inert atmosphere were temperature cycled as high as 250 ​°C to measure conductivity as a function of temperature and thermal curing. Thermally treated, partially solvated Li–C–P–N films cast from pyridine and dimethoxyethane/acetonitrile exhibit ionic conductivities as high as 10−5 ​S ​cm−1 above 100 ​°C, depending on temperature and cure procedure, although conductivity drops dramatically in films held above 150 ​°C. We propose that the conductivity of Li+ ions through the films is highly dependent on the presence and identity of tightly-bound solvent, the presence of excess LiN(CN)2 retained in the Li–C–P–N matrix, as well as the structure of the cross-linked Li–C–P–N network.