The LixMPn4 phases (M/Pn = Ti/P, V/As):: new negative electrode materials for lithium ion rechargeable batteries

LixTiP4 ternary phases (x = 7 and 9) show very close electrochemical behaviors versus lithium compared to the previously reported Li9VAs4 and Li7VP4. Up to seven lithium ions reversibly react with Li9TiP4, leading to specific and volumetric capacities of 970 mAh/g and 1650 mAh/cm(3), respectively, at average potentials close to 1V. Galvanostatic and potentiodynamic experiments reveal that lithium extraction/insertion follow different mechanisms: a two-phase process is evidenced on charge whereas a more complex process is achieved on discharge. Besides, in situ X-ray diffraction (XRD) patterns show that both Li9TiP4 and Li9VAs4 undergo a reversible crystalline to amorphous structural phase transition upon cycling. (C) 2004 Elsevier Ltd. All rights reserved.