We show that the lithium atoms in the inverse spinel, LiNiVO4, can be electrochemically removed and reinserted in nonaqueous electrochemical cells at about 4.8 V vs. metallic Li. Using in situ x-ray diffraction methods, we prove that this is an intercalation reaction. To our knowledge, this is the Li intercalation reaction with the highest voltage known. The isostructural compound LiCoVO4, also shows reversible lithium intercalation, but only near 4.2 V vs. Li.