In recent years, secondary batteries have become important components that are essential as power sources for personal computers, video cameras, cellular phones and the like, or as power sources for automobiles and electric power storage.
Among secondary batteries, lithium ion secondary batteries in particular have the feature of higher capacity density than other secondary batteries, and the ability to operate at high voltage. They are therefore used in data-related devices and communication devices as secondary batteries that are suitable for size and weight reduction, and development has been progressing in recent years toward lithium ion secondary batteries with high output and high capacity, for electric vehicles or hybrid vehicles that constitute lower public hazards.
Lithium ion secondary batteries or lithium secondary batteries comprise a positive electrode layer and negative electrode layer, with an electrolyte comprising a lithium salt situated between them, where the electrolyte is composed of a nonaqueous liquid or solid. When a nonaqueous liquid electrolyte is used as the electrolyte, the electrolyte solution permeates into the positive electrode layer, readily forming an interface between the positive electrode active material of the positive electrode layer and the electrolyte, so that performance is easily improved. However, since the electrolyte solutions that are in wide use are combustible, it becomes necessary to install safety equipment to minimize temperature increase during short circuiting, or to mount a system for ensuring safety, such as preventing short circuiting. On the other hand, all-solid-state batteries, wherein the liquid electrolyte is replaced with a solid electrolyte to render the entire battery solid, do not employ combustible organic solvents in the batteries and thus allow safety equipment to be simplified and are considered to be superior in terms of production cost and productivity, and their development is also progressing.
As all-solid-state batteries there have been proposed all-solid-state batteries comprising a positive electrode collector/positive electrode active material layer/solid electrolyte layer/negative electrode active material layer/negative electrode collector, and a method for producing them has been also been proposed, by combining a positive electrode collector/positive electrode active material layer/solid electrolyte layer and pressing them to form a stack, or pressing a positive electrode collector/positive electrode active material layer/solid electrolyte layer/negative electrode active material layer/negative electrode collector to form a stack (PTL 1).