Lithium manganese ternary oxide Li Mn.sub.2 0.sub.4+x is produced, where 0.ltoreq..times..ltoreq.0.2, by adding carbon to a manganese-containing solution such as manganese acetate and reacting the solution in an inert atmosphere with a lithium-containing compound such as lithium hydroxide and ammonia. Carbon is added in a proportion up to 8 percent of the weight of the Li Mn.sub.2 0.sub.4+x produced, and preferably the proportion of carbon added is in the range 2 to 6 percent by weight of Li Mn.sub.2 0.sub.4+x. The carbon is preferably carbon powder such as carbon black. Preferably, the Li Mn.sub.2 0.sub.4+x produced as a gelatinous precipitate is dried and heat treated. Alternatively, lithium manganese ternary oxide Li Mn.sub.2 0.sub.4+x is produced by reacting a manganese-containing compound with lithium carbonate. The reaction takes place in water and a precipitate is formed which is dried. The dried precipitate may be heat treated. The manganese-containing compound comprises manganese acetate. Carbon such as carbon powder may be added to the mixture before the reaction occurs.
Hydrothermal treatment of at least one manganese source material, for example, an oxide of manganese, such as Mn.sub.2 O.sub.3, MnO, or MnO.sub.2, in an aqueous solution containing at least one water-soluble lithium salt, such as lithium hydroxide, lithium chloride, lithium nitrate, lithium fluoride, or lithium bromide, and an alkaline metal hydroxide, such as potassium hydroxide, at 130 to 300.degree. C. can realize the preparation of a lithium manganese oxide (LiMnO.sub.2) having a layered rock-salt structure in a single stage.
A method of making lithium manganese oxide of spinel structure is disclosed. The method involves the step of prelithiating a manganese oxide by reacting it with lithium hydroxide or lithium salt and then reacting the prelithiated manganese oxide in a second step at elevated temperature, for example, with lithium carbonate to form a lithium manganese oxide spinel. The spinel product may be used advantageously in secondary (rechargeable) batteries. The spinel product may be admixed with a partially substituted nickelite, preferably, LiNi.sub.x Co.sub.1-x O.sub.2 (0.1<x<0.9) or LiNi.sub.x Mg.sub.1-x O.sub.2 (0.85<x<0.97) and mixtures thereof to form the active material for the positive electrode of a rechargeable lithium ion cell. A preferred mixture for the positive electrode of lithium ion cells comprises lithium manganese oxide spinel and LiNi.sub.x Co.sub.1-x O.sub.2 (0.1<x<0.9). The positive electrode for lithium ion cells may also be formed of a layer comprising active material of lithium manganese oxide spinel overlayed with a second layer comprising active material formed of a partially substituted nickelite, preferably LiNi.sub.x Co.sub.1-x O.sub.2 (0.1<x<0.9) or LiNi.sub.x Mg.sub.1-x O.sub.2 (0.85<x<0.97) and mixtures thereof.
A nonaqueous electrolyte secondary cell, wherein a lithium-containing metal oxide capable of binding and releasing lithium is used as a positive electrode, and a nonaqueous electrolyte containing a lithium salt is used as an electrolyte, in which a spinel type lithium manganese oxide which satisfies the formula: wherein 0.ltoreq.x.ltoreq.0.05, and -0.025.ltoreq..delta..ltoreq.0.050, and wherein the average valency of Mn is within a range of from 3.501 to 3.535, is used as the lithium-containing metal oxide.
A process for preparing a compound that includes the steps of: (a) preparing a solution comprising (i) a chromium source, (ii) a manganese source, (iii) a lithium source, and (iv) an oxygen source, where the relative amounts of each of the sources is selected to yield, following step (c), a compound having the formula Li.sub.y Cr.sub.x Mn.sub.2-x O.sub.4+z where y.gtoreq.2, 0.25<x<2, and z.gtoreq.0; (b) treating the solution to form a gel; and (c) heating the gel under an inert atmosphere for a time and at a temperature sufficient to yield a compound having the formula Li.sub.y Cr.sub.x Mn.sub.2-x O.sub.4+z where y.gtoreq.2, 0.25<x<2, and z.gtoreq.0. The invention also features a compound having the formula Li.sub.y Cr.sub.x Mn.sub.2-x O.sub.4+z where y>2, 0.25<x<2, and z.gtoreq.0, and an electrode composition containing this compound.
Active materials of the invention contain at least one alkali metal and at least one other metal capable of being oxidized to a higher oxidation state. Preferred other metals are accordingly selected from the group consisting of transition metals (defined as Groups 4-11 of the periodic table), as well as certain other non-transition metals such as tin, bismuth, and lead. The active materials may be synthesized in single step reactions or in multi-step reactions. In at least one of the steps of the synthesis reaction, reducing carbon is used as a starting material. In one aspect, the reducing carbon is provided by elemental carbon, preferably in particulate form such as graphites, amorphous carbon, carbon blacks and the like. In another aspect, reducing carbon may also be provided by an organic precursor material, or by a mixture of elemental carbon and organic precursor material.
