NH₄PF₆ as a Structural Modifier for Building a Robust Carbon-Coated Natural Graphite Anode for Lithium-Ion Batteries

To improve the electrochemical performance of natural graphite anodes, we have designed a facile, scalable carbon-coating process using coal-tar pitch and ammonium hexafluorophosphate (NH₄PF₆) as a structural modifier. NH₄PF₆ effectively modifies the microstructure of amorphous carbon, coated on the surface of the natural graphite, leading to better, reversible Li⁺-storage characteristics within a wide operating-temperature range (from -20 to 60°C). The C-O-P linkage introduced as a result of the thermal decomposition of NH₄PF₆ assists the formation of open nanopores in the amorphous carbon layer. The integrated nanopores act as additional reversible Li⁺-storage sites, which minimize the reversible capacity loss and improve the cycle performance of natural graphite. Moreover, the thermal stability of natural graphite can also be improved while maintaining the improved electrochemical performance. Thus, this approach is a step toward the practical use of natural graphite anodes for lithium-ion batteries for electric-vehicle applications.