This invention relates to lithium-ion batteries.
Lithium-ion batteries typically include an anode, an electrolyte, and a cathode that contains lithium atoms intercalated within a lithium transition metal oxide. Examples of transition metal oxides that have been used include lithium cobalt dioxide, lithium nickel dioxide, and lithium manganese dioxide. None of these materials, however, exhibits an optimal combination of high initial capacity, high thermal stability, and good capacity retention after repeated charge-discharge cycling.
In a first aspect, the invention features a lithium-ion battery that includes a cathode, an anode other than a lithium metal anode, and an electrolyte. The cathode comprises particles that include (i) transition metal grains having a grain size no greater than about 50 nanometers; and (ii) lithium-containing grains selected from the group consisting of lithium oxides, lithium sulfides, lithium halides (e.g., chloride, bromides, iodides, or fluorides), and combinations thereof.
In a second aspect, the invention features a lithium-ion battery that includes a cathode, an anode, and an electrolyte in which the cathode comprises particles that include (i) transition metal grains having a grain size no greater than about 50 nanometers; and (ii) lithium-containing grains selected from the group consisting of lithium sulfides, lithium halides (e.g., chloride, bromides, iodides, or fluorides), and combinations thereof.
In preferred embodiments, the cathode particles have diameters ranging from about 0.01 microns to about 30 microns. The lithium-containing grains preferably have a grain size no greater than about 50 nanometers. The transition metal grains preferably have a grain size no greater than about 20 nanometers. Examples of useful transition metals include iron, cobalt, chromium, nickel, vanadium, manganese, copper, zinc, zirconium, molybdenum, niobium, and combinations thereof.
In one useful embodiment, the particles are used as an additive in a lithium-transition metal oxide-based cathode such as a lithium cobalt dioxide-based cathode. The particles can provide a high capacity lithium source in cells, such as cells having graphite anodes, which would otherwise suffer from high irreversible capacity losses.
The invention also features a process for preparing a lithium-ion battery that includes (a) preparing a cathode comprising particles that include (i) transition metal grains having a grain size no greater than about 50 nanometers, and (ii) lithium-containing grains selected from the group consisting of lithium oxides, lithium sulfides, lithium halides, and combinations thereof; and (b) combining the cathode with an electrolyte and an anode to form the battery. In one embodiment, the cathode is prepared by ball milling a mixture that includes a transition metal and a lithium-containing compound selected from the group consisting of lithium oxides, lithium sulfides, lithium halides, and combinations thereof.
The lithium-ion batteries exhibit high initial capacities and good capacity retention after repeated charge-discharge cycling. In addition, they are readily manufactured because all of the lithium atoms needed to support the cell reaction can be incorporated in the cathode, which, unlike most anodes, is relatively stable in air in its lithium-containing (i.e., discharged) state.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.