Nonaqueous electrolyte secondary battery
A nonaqueous electrolyte secondary battery according to an embodiment of the present disclosure includes a negative electrode mixture layer which contains a first region located in a flat part of an electrode body and second regions located in a pair of curved parts of the electrode body, the ratio (B/A) of the packing density (B) in each of the second regions to the packing density (A) in the first region being 0.75 or more and 0.95 or less. Further, in a section passing through the center in the axial direction of the electrode body and being perpendicular to the axial direction, the ratio (SB/SA) of the sectional area (SB) of the pair of curved parts to the sectional area (SA) of the flat part is 0.28 or more and 0.32 or less.
1. A nonaqueous electrolyte secondary battery comprising:
a wound electrode body which is obtained by winding a positive electrode, containing a positive electrode mixture layer, and a negative electrode containing a negative electrode mixture layer, and a separator interposed between the positive electrode and the negative electrode, and which is formed into a flat shape having a flat part and a pair of curved parts;
a nonaqueous electrolyte; and
a battery case which houses the electrode body and the nonaqueous electrolyte,
wherein the negative electrode mixture layer contains a first region located in the flat part of the electrode body and second regions located in the pair of curved parts, the ratio B/A of the packing density B in each of the second regions to the packing density A in the first region being 0.75 or more and 0.95 or less: and
in a section passing through the center in the axial direction of the electrode body and being perpendicular to the axial direction, the ratio SB/SA of the cross-sectional area SB of the pair of curved parts to the cross-sectional area SA of the flat part is 0.28 or more and 0.32 or less, wherein SA is equal to d×(W−d), and SB is equal to (d/2) 2 π where d represents a thickness of the wound electrode body and W represents a width in the direction perpendicular to the axial direction and the thickness direction of the wound electrode body.
2. The nonaqueous electrolyte secondary battery according to claim 1 ,
wherein the ratio K/W of the length K of the positive electrode mixture layer along the axial direction of the electrode body to the width W in the direction perpendicular to the axial direction and the thickness direction of the electrode body is 1.6 or more.
3. The nonaqueous electrolyte secondary battery according to claim 1 ,
wherein the ratio B/A is 0.78 or more and 0.93 or less.
4. The nonaqueous electrolyte secondary battery according to claim 1 ,
wherein the porosity of the first region is 38% or more and 48% or less; and
the porosity of the second regions is 48% or more and 59% or less.
5. The nonaqueous electrolyte secondary battery according to claim 1 ,
wherein the negative electrode mixture layer contains particles of a negative electrode active material having a volume-based median diameter of 8 μm or more and 12 μm or less, and wherein the negative electrode mixture layer further contains styrene-butadiene rubber, and carboxymethyl cellulose or a salt thereof.
6. The nonaqueous electrolyte secondary battery according to claim 1 ,
wherein the battery case houses the nonaqueous electrolyte in an amount of 55 g or more and 75 g or less.