In recent years, lithium secondary batteries, nickel hydrogen batteries and other secondary batteries have become increasingly important as vehicle-mounted power supplies or power supplies of personal computers and portable terminals. Lithium secondary batteries (and typically, lithium ion batteries) in particular are expected to be preferably used as high-output, vehicle-mounted power supplies since they are lightweight and allow the obtaining of high energy density.
In a typical configuration of this type of lithium secondary battery, an electrode is provided that employs a configuration in which a material capable of reversibly occluding and releasing lithium ions (electrode active material) is formed on an electroconductive member (electrode current collector). For example, typical examples of an electrode active material used in a negative electrode (negative electrode active material) include carbon-based materials such as graphite carbon or amorphous carbon. In addition, typical examples of an electrode current collector used in a negative electrode (negative electrode current collector) include sheet-like and foil-like members composed mainly of copper.
In a lithium secondary battery provided with this type of electrode active material, the electrode active material undergoes changes in volume due to expansion and contraction accompanying occlusion and release of lithium ions during charging and discharging. Due to these changes in volume, the electrode active material layer containing the electrode active material may lift from or slide off the electrode current collector causing a decrease in current collection performance of the electrode. In addition, there is the problem of the electrode active material coming off of the electrode current collector not only during charging and discharging, but also during the time from formation of the electrode active material layer to housing within the battery case (such as during the positive electrode, negative electrode and separator lamination steps). In order to deal with such problems, an electrode structure has been proposed in which a porous insulating layer is formed on the electrode active material layer. For example, Patent Document 1 discloses a secondary battery a porous protective film is formed on any of the surfaces of a positive electrode active material coating and negative electrode active material coating. In addition, Patent Documents 2 and 3 describe examples of the prior art relating to this type of porous protective film.    Patent Document 1: Japanese Patent Application Laid-open No. 117-220759    Patent Document 2: Japanese Patent Application Laid-open No. 2005-174792    Patent Document 3: Japanese Patent Application Laid-open No. 2005-327680
However, in the case of installing this type of lithium secondary battery in a vehicle such as an automobile, a battery assembly is constructed by connecting a plurality of the batteries in series in order to obtain high output. At that time, in addition to installation space being limited, since this battery is premised on use in the presence of vibrations, a battery assembly can be constructed in a state in which a large number of single batteries are arranged in a restrained state. Considerable pressure is applied to each battery that composes the battery assembly when restrained in this manner.