LITHIUM INSERTION INTO LI3CRO4 AND RELATED LISICON MATERIALS

The electrochemical intercalation of lithium into chromium (V)-contain ing oxides isostructural with beta- and gamma-Li3PO4 has been studied. beta-Li3CrO4 can reversibly intercalate around 1 mole of Li ions per formula unit to give Li3+xCrO4:0 < x < 1 with a discharge capacity of 196 mAh g-L; electrochemical data indicate the possible existence of a two-phase region in the approximate range 0.3 <x < 0.8. Fully interca lated material appears to have a gamma-related structure. gamma-Li3.5C r0.5Ge0.5O4 with a LISICON structure can reversibly intercalate up to 0.5 moles of Li ions per formula unit to give Li3.5+xCr0.5Ge0.5O4: 0 < x < 0.5. During intercalation, the gamma-phase transforms into a beta -phase which is retained on deintercalation. The volume changes associ ated with (de)intercalation of both beta and gamma structures are smal l, much less than 1%. During the beta --> gamma transition, the orthor hombic c axis, and the unit cell volume, increase by similar to 2%.