To the best of my knowledge, Li Ping has never revealed the source of the LiFePO4 cells used in his arrays. Li Ping has always maintained there isn't a LiFePO4 cell made anywhere in China that he is not aware of, or has not tested for suitabilty. Given this, I think it's unlikely that better cells than his are available.
It has always been believed, the reason his batteries are so reliable, is his deep understanding of how the cells perform, and this is why he designs his own BMS. In fact, I would think the reason his batteries are so successful is due mainly to his management system.
The original V1's were limited to around 0.5C charge/discharge on a 10ah array, this was fine for us guys pulling no more than 15amps, but the Americans quickly ran into trouble trying to pull 20+ amps. The immediate solution for them, was to purchase an array of higher capacity than would normally be needed for a given range per charge.
The later V2.5's and above are capable of higher C rates, again, entirely due to his new improved BMS.
As for your question, by all means ask, Li Ping speaks excellent English and is also very polite and courteous.
All the best
Bob