Nonaqueous-electrolyte secondary battery

Abstract

A subject for the invention is to improve the cycle characteristics of a high-capacity secondary battery containing an active material packed at a high density, by using a particulate active material having a low aspect ratio. The invention relates to a nonaqueous-electrolyte secondary battery comprising a negative electrode and a positive electrode each capable of occluding/releasing lithium, a separator, and a nonaqueous electrolyte solution comprising a nonaqueous solvent and a lithium salt, characterized in that the separator comprises a porous film made of a thermoplastic resin containing an inorganic filler, and at least either of the following is satisfied: the active material contained in the negative electrode is a particulate active material having an aspect ratio of from 1.02 to 3; and the active material contained in the positive electrode is a particulate active material having an aspect ratio of from 1.02 to 2.2.

1 - 19 . (canceled) 
     
     
         20 . A nonaqueous-electrolyte secondary battery comprising a negative electrode and a positive electrode each capable of occluding/releasing lithium, a separator, and a nonaqueous electrolyte solution comprising a nonaqueous solvent and a lithium salt,
 wherein the separator comprises a porous film made of a thermoplastic resin containing an inorganic filler, and   the nonaqueous electrolyte solution comprises an aromatic compound having an exothermic property of 1.5 or higher.   
     
     
         21 . The nonaqueous-electrolyte secondary battery according to  claim 20 , wherein the aromatic compound having an exothermic property of 1.5 or higher is at least one member selected from the group consisting of cyclohexylbenzene, cyclohexylfluorobenzene, biphenyl, fluorobiphenyl, and diphenyl ether. 
     
     
         22 . The nonaqueous-electrolyte secondary battery according to  claim 20 , wherein the aromatic compound having an exothermic property of 1.5 or higher is contained in an amount of 0.1-8% by weight based on the nonaqueous electrolyte solution. 
     
     
         23 . The nonaqueous-electrolyte secondary battery according to  claim 20 , wherein the separator has a thickness of from 5 μm to 100 μm, a porosity of from 30% to 80%, an average pore diameter as provided for in ASTM F316-86 of from 0.05 μm to 10 μm, a Gurley air permeability as provided for in JIS P8117 of from 20 sec/100 cc to 700 sec/100 cc, and an average rate of change in retained-liquid amount of 15%/min or lower. 
     
     
         24 . The nonaqueous-electrolyte secondary battery according to  claim 20 , wherein the lithium salt is a fluorine-containing lithium salt and the nonaqueous solvent contains a cyclic carbonate and a chain carbonate. 
     
     
         25 . The nonaqueous-electrolyte secondary battery according to  claim 20 , wherein the negative-electrode active material is a carbon material. 
     
     
         26 . The nonaqueous-electrolyte secondary battery according to  claim 20 , wherein the positive-electrode active material is a lithium/transition metal composite oxide.