US 9,059,478 to Semiconductor Energy Laboratory Co., Ltd. titled Lithium-ion secondary battery with graphene and composite oxide layered electrode

The first claim of US Patent No. 9,059,478:


A lithium-ion secondary battery comprising: a positive electrode comprising: a positive electrode current collector; and a positive electrode active material layer comprising a graphene layer stacked with a layer comprising a plurality of single crystal particles, the positive electrode active material layer provided over the positive electrode current collector, a negative electrode; and an electrolyte between the positive electrode and the negative electrode, wherein each of the plurality of single crystal particles comprises a lithium-containing composite oxide which is expressed by a general formula LiMPO.sub.4, where M is one or more of Fe(II), Mn(II), Co(II), and Ni(II), wherein a part of the plurality of the single crystal particles does not overlap with the graphene layer which is in direct contact with the positive electrode current collector, wherein in each of the plurality of single crystal particles, a length in a b-axis direction is shorter than each of lengths in an a-axis direction and a c-axis direction, and wherein each of the plurality of single crystal particles is provided over the positive electrode current collector so that the b-axis of the single crystal particle intersects with a surface of the positive electrode current collector.




From the specification:


However, lithium-containing composite oxides included in a lithium-ion secondary battery have high resistance, so that there has been a limit on the increase of the discharge capacity and the energy density.

In view of the above problems, an object of one embodiment of the present invention is to provide a lithium-ion secondary battery having higher discharge capacity and higher energy density and a method for manufacturing such a lithium-ion secondary battery.

One embodiment of the present invention is a lithium-ion secondary battery including a positive electrode, a negative electrode, and an electrolyte provided between the positive electrode and the negative electrode. The positive electrode includes a positive electrode current collector and a positive electrode active material layer provided over the positive electrode current collector. The positive electrode active material layer includes graphenes and lithium-containing composite oxides. Specifically, in the positive electrode active material layer, the plurality of lithium-containing composite oxides is provided between the different graphenes. The lithium-containing, composite oxide is expressed by a general formula LiMPO.sub.4 (M is one or more of Fe(II), Mn(II), Co(II), and N(II)). The lithium-containing composite oxide is a flat single crystal particle in which the length in the b-axis direction is shorter than each of the lengths in the a-axis direction and the c-axis direction. The length in the b-axis direction is typically longer than or equal to 5 nm and shorter than or equal to 50 nm. Further, the lithium-containing composite oxide is provided over the positive electrode current collector so that the b-axis of the single crystal particle intersects with a surface of the positive electrode current collector. Typically, the b-axis of the single crystal particle intersects with the surface of the positive electrode current collector at any angle from 60.degree. to 90.degree..