Nonaqueous electrolyte secondary battery
View Patent ↗A nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a lithium ion conductive nonaqueous electrolyte, wherein the negative electrode contains graphite, an open circuit potential of the negative electrode in a fully charged state is 70 mV or less relative to lithium metal, the nonaqueous electrolyte contains a solvent, a cation, and an anion, the solvent contains a fluorine-containing cyclic carbonic acid ester, the cation includes lithium ions, and the anion includes an oxalate complex anion.
1. A nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a lithium ion conductive nonaqueous electrolyte, wherein
the negative electrode contains a carbon material that absorbs and releases lithium ions,
the negative electrode exerts a capacity by absorption and desorption of lithium ions and a capacity by deposition and dissolution of lithium metal,
an open circuit potential of the negative electrode in a fully charged state is less than 20 mV relative to lithium metal,
the nonaqueous electrolyte contains a solvent, a cation, and an anion,
the solvent contains a fluorine-containing cyclic carbonic acid ester,
the cation includes lithium ions, and
the anion includes an oxalate complex anion,
a concentration of the oxalate complex anion in the nonaqueous electrolyte is 0.8% by mass or more and 4.0% by mass or less, and
a concentration of the fluorine-containing cyclic carbonic acid ester in the nonaqueous electrolyte is 0.1% by mass or more and 20% by mass or less.
2. The nonaqueous electrolyte secondary battery according to claim 1 , wherein the oxalate complex anion is at least one selected from the group consisting of B(C 2 O 4 ) 2 —, BF 2 (C 2 O 4 )—, P(C 2 O 4 ) 3 —, PF 2 (C 2 O 4 ) 2 —, and PF 4 (C 2 O 4 )—.
3. The nonaqueous electrolyte secondary battery according to claim 1 , wherein the concentration of the oxalate complex anion in the nonaqueous electrolyte is 1.0% by mass or more and 4.0% by mass or less.
4. The nonaqueous electrolyte secondary battery according to claim 1 , wherein the concentration of the fluorine-containing cyclic carbonic acid ester in the nonaqueous electrolyte is 2% by mass or more and 20% by mass or less.
5. The nonaqueous electrolyte secondary battery according to claim 1 , wherein when the oxalate complex anion is derived from an oxalate complex salt, a mass ratio of the fluorine-containing cyclic carbonic acid ester to the oxalate complex salt in the nonaqueous electrolyte is 0.025 or more.
6. The nonaqueous electrolyte secondary battery according to claim 1 , wherein
the positive electrode contains a composite oxide represented by the following general formula: Li a Ni x Co y M 1-x-y O 2 ,
in the general formula,
0.97<a≤1.2,
0.5≤x≤1.0, and
0≤y≤0.1 are satisfied, and
M is at least one selected from the group consisting of Mn, Al, W, Mg, Mo, Nb, Ti, Si, and Zr.
7. The nonaqueous electrolyte secondary battery according to claim 6 , wherein 0.8≤x≤1.0 is satisfied.
8. The nonaqueous electrolyte secondary battery according to claim 6 , wherein
M includes Al, and
an atomic ratio Co/Al is 0 to 1.0.
9. The nonaqueous electrolyte secondary battery according to claim 1 , wherein the concentration of the oxalate complex anion in the nonaqueous electrolyte is 1.6% by mass or more and 4.0% by mass or less.
10. The nonaqueous electrolyte secondary battery according to claim 1 , wherein the concentration of the fluorine-containing cyclic carbonic acid ester in the nonaqueous electrolyte is 2% by mass or more and 5% by mass or less.