Nonaqueous electrolyte and nonaqueous electrolyte secondary battery

A nonaqueous electrolyte secondary battery, comprising:

• a case having a wall thickness not larger than 0.3 mm;
• a positive electrode provided in said case;
• a negative electrode provided in said case;
• and
• a nonaqueous electrolyte provided in said case and comprising a nonaqueous solvent and a solute dissolved in said nonaqueous solvent, the nonaqueous solvent containing ethylene carbonate (EC) and γ-butyrolactone (BL) and at least one selected from the group consisting of ethylene sulfite, phenylethylene carbonate, 2-methylfuran, furan, thiophene, catechol carbonate, and vinylethylene carbonate, as a third solvent,
• wherein, when a charge-discharge cycle test satisfying conditions (A) to (D) given below is performed under an environment of 45° C., the capacity retention rate at 100-th charge-discharge cycle is at least 85% based on the discharge capacity in the first charge-discharge cycle:
• (A) for the charging, the constant current-constant voltage charging to 4.2V is performed for 3 hours under a current of 1C;
• (B) the discharging is performed to 3V under a current of 1C;
• (C) after the charging, the secondary battery is left to stand for 10 minutes, followed by performing the discharging;
• and
• (D) after the discharging, the secondary battery is left to stand for 10 minutes, followed by performing the charging.

A nonaqueous electrolyte secondary battery, comprising:

• a case having a wall thickness not larger than 0.3 mm;
• a positive electrode provided in said case;
• a negative electrode provided in said case;
• and
• a nonaqueous electrolyte which is provided in said case and comprises a nonaqueous solvent and a solute dissolved in said nonaqueous solvent, said nonaqueous solvent containing ethylene carbonate (EC), γ-butyrolactone (BL), and at least one selected from the group consisting of ethylene sulfite, phenylethylene carbonate, catechol carbonate and vinylethylene carbonate as a third solvent, the EC content falling withing a range of 20 to 50% by volume based on the total amount of the EC and the BL, and the BL content falling within a range of 40 to 80% by volume based on the total amount of the EC and the BL.

A nonaqueous electrolyte secondary battery, comprising:

• a case having a wall thickness not larger than 0.3 mm;
• a positive electrode provided in said case;
• a negative electrode provided in said case;
• and
• a nonaqueous electrolyte layer which is arranged between said positive electrode and said negative electrode and comprises a nonaqueous electrolyte and a polymer for gelling said nonaqueous electrolyte, said nonaqueous electrolyte comprising a nonaqueous solvent containing ethylene carbonate (EC), γ-butyrolactone (BL), and at least one selected from the group consisting of ethylene sulfite, phenylethylene carbonate, catechol carbonate and vinylethylene carbonate, as a third the EC content falling within a range of 20 to 50% by volume based on the total amount of the EC and the BL, and the BL content falling within a range of 40 to 80% by volume based on the total amount of the EC and the BL.