Carbon and transition metal containing titanium phosphates as electrodes for lithium ion batteries

• Published in: Solid state ionics 2006-10, Vol.177 (26), p.2667-2674
• Main Authors: Santos-Peña, J., Cruz-Yusta, M., Soudan, P., Franger, S., Cuart-Pascual, J.J.
• Format: Article
• Language: English
• Subjects: Cobalt phosphate; Copper phosphate; Lithium ion battery electrodes; Mesoporous materials; Titanium phosphates
• ISSN: 0167-2738; 1872-7689
• DOI: 10.1016/j.ssi.2006.05.016

We prepared transition metal containing titanium phosphates obtained from mesoporous titanium phosphate treated with cobalt and copper acetates and subsequently heated at 573 K under either air or nitrogen atmospheres. The first treatment with acetates incorporates the metal and acetate ions in the system. Moreover, it partially extracts the director agent. Total extraction of the surfactant can be reached in the copper samples after heating twice. However, the surfactant is not removed from the cobalt samples under the thermal conditions therein used. The composition of the heated materials is close to NASICON structures with a formula close to M 1.5Ti 1.5(PO 4) 3 (M = Co,Cu). A certain content in elemental carbon is observed in the samples obtained under nitrogen atmosphere, which are also more conductive than those prepared under air. The first discharge of lithium cells based in these mesoporous materials show electrochemical activity of Ti 4+/Ti 3+, Co 2+/Co 0 and Cu 2+/Cu 0 couples in the OCV–1.0 V region. Below this voltage, the discharge profiles are typical of phosphate systems where Li 3PO 4 is a product of the electrochemical reaction with lithium and, moreover, electrolyte solvent is reduced. Electrolyte is more degraded when the samples contain carbon. Capacities as high as 1600 mA h g − 1 can be obtained at deep discharge. However, there is an irreversible capacity loss in the four systems due to the occurrence of insulating products as Li 3PO 4 and a solid electrolyte interface.