Nonaqueous electrolyte secondary battery, nonaqueous electrolyte, and charging method therefor
View Patent ↗A nonaqueous electrolyte secondary battery of the invention has a positive electrode having a positive electrode active material, a negative electrode, and a nonaqueous electrolyte having electrolyte salt in a nonaqueous solvent. The electric potential of the positive electrode active material is 4.4 to 4.6 V relative to lithium, and the nonaqueous electrolyte contains a compound expressed by structural formula (I) below. The quantity of compound added is preferably 0.1% to 2% by mass. Also, the positive electrode active material preferably comprises a mixture of a lithium-cobalt composite oxide which is LiCoO 2 containing at least both zirconium and magnesium and a lithium-manganese-nickel composite oxide that has a layer structure and contains at least both manganese and nickel. Thanks to such structure, a nonaqueous electrolyte secondary battery can be provided that is charged to charging termination potential of 4.4 to 4.6 V relative to lithium and that has enhanced overcharging safety. [Chemical Formula 1]
1. A nonaqueous electrolyte secondary battery comprising:
a positive electrode that has a positive electrode active material;
a negative electrode; and
a nonaqueous electrolyte that has electrolyte salt in a nonaqueous solvent;
the electric potential of said positive electrode active material being 4.4 to 4.6 V relative to lithium, and
said nonaqueous electrolyte containing
a compound given by structural formula (I) below in a content of 0.1% to 2% by mass of said nonaqueous electrolyte,
methyl ethyl carbonate content of 30% to 80% by volume, and
LiPF 6 content of 1.0 mol/L to 2.0 mol/L in said nonaqueous solvent,
and said positive electrode active material comprises a mixture of a lithium-cobalt composite oxide which is LiCoO 2 containing at least both zirconium and magnesium and a lithium-manganese-nickel composite oxide that has a layer structure and contains at least both manganese and nickel.
2. The nonaqueous electrolyte secondary battery according to claim 1 , wherein said nonaqueous electrolyte further contains vinylene carbonate.
3. The nonaqueous electrolyte secondary battery according to claim 1 , wherein the compound given by structural formula (I) decomposes to deactivate the battery when the battery charged to higher than 4.6 V.
4. A method for charging a nonaqueous electrolyte secondary battery including:
a positive electrode having a positive electrode active material;
a negative electrode; and
a nonaqueous electrolyte with electrolyte salt contained in a nonaqueous solvent;
said nonaqueous electrolyte containing as an additive
a compound given by structural formula (I) below in a content of 0.1% to 2% by mass of said nonaqueous electrolyte,
methyl ethyl carbonate content of 30% to 80% by volume, and
LiPF 6 content of 1.0 mol/L to 2.0 mol/L in said nonaqueous solvent,
said positive electrode active material comprises a mixture of a lithium-cobalt composite oxide which is LiCoO 2 containing at least both zirconium and magnesium and a lithium-manganese-nickel composite oxide that has a layer structure and contains at least both manganese and nickel
said method comprising:
charging so that the electric potential of said positive electrode active material is 4.4 to 4.6 V relative to lithium.
5. The method for charging a nonaqueous electrolyte secondary battery according to claim 4 , wherein the content of said compound given by said structural formula (I) is 0.1% to 2% by mass of said nonaqueous electrolyte.