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 at least one chain carbonate represented by the following formula (I):
   ROCOOCH 3   (I)
 
   wherein R represents a methyl group or an ethyl group.   
     
     
         21 . The nonaqueous-electrolyte secondary battery according to  claim 20 , wherein the lithium salt is a fluorine-containing lithium salt and the nonaqueous solvent contains at least one cyclic carbonate. 
     
     
         22 . The nonaqueous-electrolyte secondary battery according to  claim 20 , wherein the content of the at least one chain carbonate represented by the following formula (I) in the nonaqueous electrolyte solution is 5-95% by volume. 
     
     
         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 negative-electrode active material is a carbon material. 
     
     
         25 . The nonaqueous-electrolyte secondary battery according to  claim 20 , wherein the positive-electrode active material is a lithium/transition metal composite oxide.