Secondary cell electrode and fabrication method, and secondary cell, complex cell, and vehicle

The present application is a divisional of U.S. application Ser. No. 10/565,171, filed Jan. 19, 2006, which is the national stage entry of PCT/JP2004/011021, filed Jul. 27, 2004, which in turn claims benefit of priority to Japanese application Nos. 2003-283974 and 2003-283975, both filed Jul. 31, 2003, the entire contents of which are incorporated herein by reference.

The present invention relates to a secondary cell electrode, and particularly, to a nonaqueous electrolyte electrode and a gel electrolyte electrode, and further to a fabrication method of the same, as well as to a secondary cell employing the secondary cell electrode, a complex cell employing the secondary cell, and a vehicle employing the secondary cell or the complex cell.

Recent years have observed, on the background with a rising trend for environmental protection, demands for a promoted introduction of an electric vehicle (EV), a hybrid vehicle (HEV), and a fuel cell powered vehicle (FCV), as well as developments of cells for their drive motors.

For objectives needing high output and high energy density such as for driving a motor of EV, HEV, or FCV, it practically is difficult to cope with a big-scale simplex cell, and a typical measure is the use of a complex cell composed of a plurality of serially connected cells. For use to such a complex cell, Japanese Patent Application Laid-Open Publication No. 2003-151526 has proposed a thin laminate cell.

This laminate cell has a positive or negative polarized electrode formed with an electrode active material spread over a collector or foil, by using a coater or the like, thus having a three-dimensionally uniform concentration of solid material or electrolyte ingredients.

As will be discussed later, such a laminate cell suffers an unfavorable tendency for Li ions to be exhausted in a charge or discharge at a high current rate, resulting in a reduced cell performance such as charge or discharge capacity.

The present invention has been made with such points in view. It therefore is an object of the invention to provide a secondary cell electrode that works even at a high current rate, and a fabrication method therefor, as well as a secondary cell, a complex cell, and a vehicle employing such a secondary cell.

The present inventors have found using such an electrode that has an electrode active material layer low of the resistance to diffusion of Li ions supplied from an electrolyte layer, with a changed constitution of electrolyte in a patterning of the layer.

To achieve the object, a first aspect of the invention provides a secondary cell electrode comprising an electrode active material layer having a density gradient.

Another aspect of the invention provides a fabrication method comprising fabricating a secondary cell electrode comprising an electrode active material layer having a density gradient.

Another aspect of the invention provides a secondary cell comprising the secondary cell electrode.

Another aspect of the invention provides a complex cell comprising a plurality of secondary cells connected to each other.

Another aspect of the invention provides a complex cell comprising a plurality of secondary cells fabricated by the fabrication method, connected to each other.

Another aspect of the invention provides a vehicle including the secondary cell.

Another aspect of the invention provides a vehicle including a secondary cell fabricated by the fabrication method.

Other and further features, advantages, and benefits of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.