A lithium-ion secondary battery which is lightweight and which has a high voltage and a large capacity, and an electrical double layer capacitor having excellent charge/discharge rate characteristics have been put into practical use as a power source for mobile electric devices, such as a cell phone and a laptop computer. However, in the use of battery as power supply for vehicle and others, which needs to discharge and charge a large current in a short time upon starting and stopping the vehicle and others, the conventional battery has a high internal resistance so that it cannot exhibit practically satisfactory high-rate charge/discharge cycle characteristics. In addition, the conventional battery is unsatisfactory in respect of the charge/discharge capacity from the viewpoint of the running distance, and further unsatisfactory in respect of the adhesion properties between the electrode active material layer and the metal current collector from the viewpoint of the safety.
One of the reasons why the battery cannot exhibit satisfactory properties as mentioned above resides in that the resistance between the battery current collector and the active material layer is high, and in that the adhesion force between the battery current collector and the active material layer is not satisfactory. As a method for solving the above problem, a method has been proposed in which a battery current collector is provided with a conductive coating layer, and an active material layer is formed on the surface of the conductive coating layer to reduce the resistance at the interface between the battery current collector and the active material layer, thus improving the adhesion force between the current collector and the active material layer (patent document 1).
Especially, a conductive coating layer of a type including a polymer compound incorporated as a binder, wherein the polymer compound is crosslinked, has excellent solvent resistance and excellent adhesion properties (patent documents 2, 3, and 4).
However, when the battery obtained by the above methods is used as power supply for vehicle and others, the battery cannot achieve practically satisfactory high-rate charge/discharge cycle characteristics. Particularly, when the battery obtained by the above methods is subjected to long-term charge/discharge cycle test or high-temperature shelf test, the deterioration of the battery characteristics cannot be satisfactorily prevented.