A NEW MNO2 TUNNEL RELATED PHASE AS HOST LATTICE FOR LI INTERCALATION

A long range disordered alpha-MnO2 phase has been synthesized from the reduction of an aqueous K+ permanganate solution by fumaric acid in a cidic medium. Its formula is K0.062MnO2 . 0.43H(2)O. From XRD measurem ents on heat-treated samples, it has been assumed a hollandite-type st ructure for this new phase. The high oxidation state of Mn and the low content of K+ ions within the channels of the structure raise the pos sibility of utilizing this alpha-MnO2 framework as a rechargeable cath odic material for secondary lithium batteries. With a theoretical fara daic yield of 0.9 F.mol(-1) leading to a specific capacity of 280 Ah.k g(-1) available between 4.1 and 2.3 V, this material exhibits the best performances of alpha-MnO2 forms. Lithium insertion occurs in one sin gle electrochemical step and the presence of structural water is shown to ensure the rechargeability of the insertion process. During galvan ostatic cycling at C/20, in the potential range 4.1 V-2.3 V, with an i nitial d.o.d of Delta x = 0.6, the specific capacity rapidly decreases to 120 Ah.kg(-1) after which it stabilizes for at least 20 cycles. Cy cling experiments can be performed by involving higher d.o.d but witho ut obtaining similar results.