Negative electrode and nonaqueous electrolyte secondary battery
The herein disclosed negative electrode is a negative electrode for a nonaqueous electrolyte secondary battery that includes a current collector, and a negative electrode active material layer disposed on a single surface or both surfaces of the current collector. The negative electrode active material layer includes a negative electrode active material and a binder. A graphite particle and a Si-containing particle are included as the negative electrode active material. A carboxymethyl cellulose (CMC), a poly acrylic acid (PAA), and a styrene butadiene rubber (SBR) are included as the binder. A spring constant in a thickness direction of the negative electrode is equal to or more than 70 kN/mm and not more than 400 kN/mm, and a yield loop height on a stiffness test is equal to or less than 13 mm.
1 . A negative electrode for a nonaqueous electrolyte secondary battery, comprising:
a current collector; and
a negative electrode active material layer disposed on a single surface or both surfaces of the current collector, wherein
the negative electrode active material layer comprises a negative electrode active material and a binder,
the negative electrode active material comprises graphite particles and Si-containing particles,
the binder comprises carboxymethyl cellulose (CMC), poly acrylic acid (PAA), and styrene butadiene rubber (SBR),
a spring constant in a thickness direction of the negative electrode is equal to or more than 70 kN/mm and not more than 150 kN/mm, and
on a correlation graph for a stress of a sample and a loop height of the sample which are obtained when an outer circumference surface of the sample is pressed, the sample with a 80 mm outer circumference being formed in a loop shape and being obtained by rounding a negative electrode plate in a single fold, the negative electrode plate comprising the negative electrode active material layer on a single surface of the current collector, to make the outer circumference surface become the negative electrode active material layer, a yield loop height is equal to or less than 13 mm, the yield loop height being the loop height corresponding to a first inflexion point at which the stress is reduced after being substantially and continuously risen.
2 . The negative electrode according to claim 1 , wherein
the negative electrode active material includes:
0.3 to 4 parts by mass of the CMC,
0.5 to 5 parts by mass of the PAA, and
0.5 to 5 parts by mass of the SBR, relative to 100 parts by mass of the negative electrode active material.
3 . The negative electrode according to claim 1 , wherein
the negative electrode active material includes 3 to 5 parts by mass of the SBR, relative to 100 parts by mass of the negative electrode active material.
4 . The negative electrode according to claim 3 , wherein
the negative electrode active material includes a total of 3.5 to 6 parts by mass of the CMC and the PAA, relative to 100 parts by mass of the negative electrode active material.
5 . The negative electrode according to claim 1 , wherein
the negative electrode active material layer further comprises carbon nanotubes as a conductive material, and the negative electrode active material includes 0.05 to 1 part by mass of the carbon nanotubes, relative to 100 parts by mass of the negative electrode active material.
6 . The negative electrode according to claim 1 , wherein
the Si-containing particles include a Si—C composite.
7 . A nonaqueous electrolyte secondary battery, comprising:
an electrode assembly provided with a positive electrode and a negative electrode, and a nonaqueous electrolyte, wherein
the negative electrode is the negative electrode according to claim 1 .
8 . The negative electrode according to claim 1 , wherein the negative electrode active material includes 3 to 5 parts by mass of the SBR, relative to 100 parts by mass of the negative electrode active material.
9 . The negative electrode according to claim 1 , wherein a ratio of a total mass of the CMC and PAA to a mass of SBR is 0.5 or more and 2 or less.