Lithium secondary battery

A lithium secondary battery for an engine starter which can be discharged at −30 degrees centigrade and quickly charged at 25 degrees centigrade by repeatedly occluding and releasing lithium ions in a construction in which an organic electrolytic solution is permeated into a wound or stacked electrode group or said electrode group is immersed in said organic electrolytic solution with a separator being interposed between a positive electrode having a positive electrode material formed on a metal foil and a negative electrode having a negative electrode material formed on a metal foil,

• wherein said positive electrode material consists of a mixture of olivine lithium iron phosphate (LiFePO4) particles whose surfaces are coated with an amorphous carbon material and a conductive carbon material to form positive electrode surface carbon materials in which atoms of said positive electrode surface carbon materials are chemically bonded to one another;
• wherein the conductive carbon material contains a conductive carbon powder and a conductive carbon fiber;
• said negative electrode material contains (a) graphite particles having a specific surface area of not less than 6 m2/g and (b) soft carbon particles, in which said graphite particles and said soft carbon particles are coated with an amorphous carbon material;
• said soft carbon particles form negative electrode surface carbon materials in which atoms of said negative electrode surface carbon materials are chemically bonded to one another;
• said metal foil for the positive electrode has a plurality of through-holes, formed therethrough, each having a projected portion on at least one surface thereof;
• said organic electrolytic solution consists of an organic solvent and a mixed electrolyte dissolved therein, said organic solvent is a mixed carbonic acid ester and said mixed electrolyte consists of lithium hexafluorophosphate and lithium bis fluorosulfonyl imide;
• said separator consists of a fibrous nonwoven cloth having at least one of a hydrophilic group and oxide ceramics on a surface thereof;
• said mixed carbonic acid ester contains ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate;
• a mixing ratio between said lithium hexafluorophosphate and said lithium bis fluorosulfonyl imide in said mixed electrolyte being set to lithium hexafluorophosphate/lithium bis fluorosulfonyl imide in a molar ratio equal to 1/0.2 to 0.4/0.8;
• and
• said fibrous nonwoven cloth is cellulose fibrous nonwoven cloth.

A lithium secondary battery for an engine starter which can be discharged at −30 degrees centigrade and quickly charged at 25 degrees centigrade by repeatedly occluding and releasing lithium ions in a construction in which an organic electrolytic solution is permeated into a wound or stacked electrode group or said electrode group is immersed in said organic electrolytic solution with a separator being interposed between a positive electrode having a positive electrode material formed on a metal foil and a negative electrode having a negative electrode material formed on a metal foil,

• wherein said positive electrode material consists of a mixture of olivine lithium iron phosphate (LiFePO4) particles whose surfaces are coated with an amorphous carbon material and a conductive carbon material to form positive electrode surface carbon materials in which atoms of said positive electrode surface carbon materials are chemically bonded to one another;
• wherein the conductive carbon material contains a conductive carbon powder and a conductive carbon fiber;
• said negative electrode material contains (a) graphite particles having a specific surface area of not less than 6 m2/g and (b) soft carbon particles, in which said graphite particles and said soft carbon particles are coated with an amorphous carbon material;
• said soft carbon particles form negative electrode surface carbon materials in which atoms of said negative electrode surface carbon materials are chemically bonded to one another;
• said metal foil for the positive electrode has a plurality of through-holes, formed therethrough, each having a projected portion on at least one surface thereof;
• said organic electrolytic solution consists of an organic solvent and a mixed electrolyte dissolved therein, said organic solvent consists of mixed carbonic acid ester and said mixed electrolyte consists of lithium hexafluorophosphate and lithium bis fluorosulfonyl imide;
• said separator consists of a fibrous nonwoven cloth having at least one of a hydrophilic group and oxide ceramics on a surface thereof;
• said mixed carbonic acid ester contains ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate;
• a mixing ratio between said lithium hexafluorophosphate and said lithium bis fluorosulfonyl imide in said mixed electrolyte being set to lithium hexafluorophosphate/lithium bis fluorosulfonyl imide in a molar ratio equal to 1/0.2 to 0.4/0.8;
• and
• said fibrous nonwoven cloth is cellulose fibrous nonwoven cloth.