The nasicon-type titanium phosphates Ati2(PO4)3 (A=Li, Na) as electrode materials

Lithium and sodium have been intercalated in LiTi2(PO4)3 and NaTi2(PO4)3 respectively. Despite the low electronic conductivity of the NASICON framework the intercalation can be realized either chemically or electrochemically. The electrochemical study shows the reversibility of the process and the existence of large biphased domains in both systems. The observed phase separation reactions result from Li+(Na+) and e− migration without skeleton bond breaking and recombination. The large hexagonal c-parameter of Li3Ti2(PO4)3 results from a peculiar lithium ion distribution (M(1) empty, M(2) fully occupied) as shown by neutron diffraction.