Negative electrode including lithium and fluorine containing coating film covering negative electrode active material layer
A nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a nonaqueous electrolyte having a lithium ion conductivity, and the negative electrode includes a negative electrode collector, a negative electrode active material layer provided on a surface of the negative electrode collector, and a coating film which at least partially covers a surface of the negative electrode active material layer and which has a lithium ion permeability. The coating film contains a lithium compound which contains an element M, an element A, an element F, and lithium; the element M is at least one selected from the group consisting of P, Si, B, V, Nb, W, Ti, Zr, Al, Ba, La, and Ta; and the element A is at least one selected from the group consisting of S, O, N, and Br.
1. A nonaqueous electrolyte secondary battery comprising:
a positive electrode; a negative electrode; and a nonaqueous electrolyte having a lithium ion conductivity,
wherein the negative electrode includes a negative electrode collector, a negative electrode active material layer provided on a surface of the negative electrode collector, and a coating film covering at least a part of a surface of the negative electrode active material layer,
the coating film which has a lithium ion permeability,
the coating film contains a lithium compound which contains an element M, an element A, an element F representing fluorine, and lithium,
the element M is at least one selected from the group consisting of P, Si, B, V, Nb, W, Ti, Zr, Al, Ba, La, and Ta,
the element A is at least one selected from the group consisting of S, O, N, and Br,
the nonaqueous electrolyte contains a lithium salt and a nonaqueous solvent dissolving the lithium salt, and
the nonaqueous solvent contains a compound having a fluoro group,
wherein in a vicinity of a surface of the coating film, a molar ratio: (F/A) 1 of the element F with respect to the element A contained in the lithium compound satisfies an equation of 0.3≤(F/A) 1 ≤6, and
wherein in a vicinity of an interface between the coating film and the surface of the negative electrode active material layer, a molar ratio: (F/A) 2 of the element F with respect to the element A contained in the lithium compound satisfies an equation of 1.2≤F/A) 1 /(F/A) 2 ≤10.
2. The nonaqueous electrolyte secondary battery according to claim 1 , wherein a thickness of the coating film is 0.5 to 200 nm.
3. The nonaqueous electrolyte secondary battery according to claim 1 , wherein the lithium salt contains at least one selected from the group consisting of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.
4. The nonaqueous electrolyte secondary battery according to claim 1 , wherein the compound having a fluoro group contains at least one selected from the group consisting of a trifluoropropionate ester and a fluorinated carbonate ester.
5. The nonaqueous electrolyte secondary battery according to claim 4 , wherein the trifluoropropionate ester includes methyl 3,3,3-trifluoropropionate.
6. The nonaqueous electrolyte secondary battery according to claim 4 , wherein the fluorinated carbonate ester includes fluoroethylene carbonate.
7. The nonaqueous electrolyte secondary battery according to claim 1 ,
wherein
the coating film partially covers the surface of the negative electrode collector.
8. The nonaqueous electrolyte secondary battery according to claim 7 ,
wherein the negative electrode active material layer contains carbon material particles as a negative electrode active material, and
the coating film at least partially covers surfaces of the carbon material particles.
9. The nonaqueous electrolyte secondary battery according to claim 8 , wherein on interfaces between the lithium compound and the carbon material particles, a compound having a bond between the element M and carbon is formed.