High-voltage charge type nonaqueous electrolyte secondary cell
View Patent ↗The preservation performance of a nonaqueous electrolyte secondary cell charged to high potential is improved while the initial capacity and the cycle property of the cell are also improved. The nonaqueous electrolyte secondary cell includes: a positive electrode having lithium phosphate and a positive electrode active material containing lithium cobalt compound oxide and lithium manganese nickel compound oxide having a layer structure, the lithium cobalt compound oxide having at least zirconium and magnesium added in LiCoO 2 ; a negative electrode having a negative electrode active material; and a nonaqueous electrolyte having a nonaqueous solvent and an electrolytic salt. The potential of the positive electrode is more than 4.3 V and 5.1 V or less based on lithium. The nonaqueous electrolyte contains vinylene carbonate as the nonaqueous solvent and, as the electrolytic salt, at least one of lithium bis(pentafluoroethane sulfonyl)imide and lithium bis(trifluoromethane sulfonyl)imide at 0.1 M or more and 0.5 M or less. The nonaqueous electrolyte contains 1,3-dioxane.
1. A nonaqueous electrolyte secondary cell comprising:
a positive electrode having a positive electrode active material containing a lithium element;
a negative electrode having a negative electrode active material; and
a nonaqueous electrolyte having a nonaqueous solvent and an electrolytic salt, wherein:
the positive electrode active material is a mixture of lithium cobalt compound oxide and lithium manganese nickel compound oxide having a layer structure, the lithium cobalt compound oxide containing at least one element selected from the group consisting of Mg, Al, Ti, and Zr;
a potential of the positive electrode is more than 4.3 V and 5.1 V or less based on lithium; and
the nonaqueous electrolyte contains 1,3-dioxane.
2. The nonaqueous electrolyte secondary cell according to claim 1 , wherein the positive electrode contains lithium phosphate.
3. The nonaqueous electrolyte secondary cell according to claim 2 , wherein a ratio of the lithium phosphate to a total mass of the positive electrode active material and the lithium phosphate is 0.01 mass % or more and 5 mass % or less.
4. The nonaqueous electrolyte secondary cell according to claim 1 , wherein:
the negative electrode active material is made of noncrystalline carbon-covered graphite particles, a surface of each of the graphite particles being covered with a covering layer containing noncrystalline carbon; and
the noncrystalline carbon-covered graphite particles have a heating peak at 550° C. or higher and 620° C. or lower according to a differential thermal analysis in an air atmosphere, the heating peak having a peak area of 100 μVs/mg or more and 500 Vs/mg or less at a temperature rising rate of 5° C/min.
5. The nonaqueous electrolyte secondary cell according to claim 1 , wherein the nonaqueous solvent contains vinylene carbonate at 0.5 mass % or more and 5 mass % or less relative to a total mass of the nonaqueous solvent.
6. The nonaqueous electrolyte secondary cell according to claim 1 , wherein:
the nonaqueous solvent contains ethylene carbonate at 5 mass % or more and less than 30 mass % relative to a sum of the mass of the nonaqueous solvent,
the nonaqueous electrolyte contains 1,3-dioxane at 0.3 to 3 mass % relative to a total mass of the nonaqueous electrolyte.
7. The nonaqueous electrolyte secondary cell according to claim 1 , wherein the nonaqueous electrolyte contains as the electrolytic salt at least one of lithium bis(pentafluoroethane sulfonyl)imide and lithium bis(trifluoromethane sulfonyl)imide at 0.1 M or more and 0.5 M or less.
8. The nonaqueous electrolyte secondary cell according to claim 1 , wherein the potential of the positive electrode is 4.4 V or more and 4.6 V or less based on lithium.