The present application relates to a nonaqueous electrolyte secondary battery.
Among nonaqueous electrolyte batteries, a lithium ion secondary battery is rapidly developing as a power source of portable electronic appliances such as a mobile phone and a portable personal computer. In the power source for such a portable electronic appliance, an energy density, namely an energy storage capacity per unit volume is the most necessary characteristic, and how long the portable electronic appliance can be used attracts interest. In recent years, a lithium iron phosphate compound (LiFePO4) having an olivine structure is watched from the viewpoint of safety.
JP-A-2004-22336 discloses that a lithium secondary battery having not only excellent characteristics in energy density, electromotive force and the like but excellent cycle life and safety is obtained using an electrolytic solution containing a sulfonic acid anhydride in an aprotic organic solvent.
JP-A-2002-134170 discloses that in a nonaqueous electrolytic solution secondary battery using a cobalt-containing positive electrode active material, by adding a compound capable of forming a complex with cobalt to an electrolytic solution to stabilize a cobalt ion eluted in the electrolytic solution and to suppress deposition thereof on a negative electrode, thereby reducing a reaction area of the negative electrode and suppressing the generation of a gas due to a catalytic reaction of cobalt, a nonaqueous electrolytic solution secondary battery which is excellent in high-temperature storage characteristic and high-temperature charge and discharge cycle characteristic can be provided.
However, for example, when a portable personal computer is allowed to stand in a continuously connected state to a power source, the battery within a battery pack is exposed in a charged state, and the battery capacity is abruptly deteriorated. This is caused due to the fact that iron contained in the positive electrode active material is easily eluted in an oxidizing atmosphere, or the film growth on the surface of the positive electrode active material in a charging atmosphere is promoted, whereby the interfacial resistance increases, and at the same time, the capacity is lowered by a change in the layered structure. Furthermore, an increase in the circumferential temperature following drive of the portable personal computer is a factor in acceleration of the deterioration.
As reform measures, for example, JP-A-2002-134170 discloses a technology in which even when Co is eluted from a lithium cobalt complex oxide, it is stabilized by an additive of the electrolytic solution, thereby avoiding an adverse influence against the negative electrode. A phenomenon of elution of a metal ion from not only the lithium cobalt complex oxide but an iron olivine phosphate or the like is common as a basic mechanism. However, though the adverse influence against the negative electrode to be caused due to the elution of Fe can be avoided, the positive electrode resistance increases by a change in the positive electrode structure, and the capacity is deteriorated. Namely, a battery with high reliability is not obtainable unless the elution of Fe itself is suppressed.
That is, a nonaqueous electrolyte secondary battery which is further excellent in a floating characteristic is desirable.