Lithium-ion secondary battery
A positive electrode of a lithium-ion secondary battery contains first positive electrode active material particles and second positive electrode active material particles. The first positive electrode active material particles have a first composition represented by a compositional formula LiNi x1 Co y1 Mn z1 O 2 (here, x1, y1, and z1 are numerical values satisfying 0<x1<1, 0<y1<1, 0.3<z1<0.5, and x1+y1+z1=1). The second positive electrode active material particles have a second composition represented by a compositional formula LiNi x2 Co y2 Mn z2 O 2 (here, x2, y2, and z2 are numerical values satisfying 0<x2<1, 0<y2<1, 0<z2<0.2, and x2+y2+z2=1). The surface of at least one of the first positive electrode active material particles and the second positive electrode active material particles is coated with a transition metal oxide.
1. A lithium-ion secondary battery comprising:
a housing;
a pressure operated safety mechanism configured to operate in response to an internal pressure of the housing;
a positive electrode accommodated in the housing;
a negative electrode accommodated in the housing; and
an electrolytic solution stored in the housing, wherein:
the positive electrode contains first positive electrode active material particles and second positive electrode active material particles;
the first positive electrode active material particles and the second positive electrode active material particles satisfy a relationship of first positive electrode active material particles:second positive electrode active material particles=74:26 to 48:52 in terms of mass ratio;
the first positive electrode active material particles have a first composition represented by a compositional formula as follows,
LiNi x1 Co y1 Mn z1 O 2 ,
here, x1, y1, and z1 are numerical values satisfying 0<x1<1, 0<y1<1, 0.3<z1<0.5, and x1+y1+z1=1;
the second positive electrode active material particles have a second composition represented by a compositional formula as follows,
LiNi x2 Co y2 Mn z2 O 2 ,
here, x2, y2, and z2 are numerical values satisfying 0<x2<1, 0<y2<1, 0<z2<0.2, and x2+y2+z2=1;
a surface of at least one of the first positive electrode active material particles and the second positive electrode active material particles is coated with a transition metal oxide;
the transition metal oxide contains a transition metal other than Ni, Co, and Mn; and
the electrolytic solution contains an overcharge additive.
2. The lithium-ion secondary battery according to claim 1 , wherein the surface of the first positive electrode active material particles is coated with the transition metal oxide.
3. The lithium-ion secondary battery according to claim 1 , wherein:
x1 and y1 are numerical values satisfying 0.3<x1<0.5 and 0.1<y1<0.3; and
x2 and y2 are numerical values satisfying 0.3<x2<0.5 and 0.4<y2<0.6.
4. The lithium-ion secondary battery according to claim 1 , wherein the transition metal oxide has a lower resistivity than the first positive electrode active material particles and the second positive electrode active material particles.
5. The lithium-ion secondary battery according to claim 1 , wherein the transition metal oxide is at least one selected from the group consisting of titanium oxide, tungsten oxide, and molybdenum oxide.
6. The lithium-ion secondary battery according to claim 1 , wherein, in the first positive electrode active material particles or the second positive electrode active material particles coated with the transition metal oxide, a mass ratio of the transition metal oxide to a total mass of the first positive electrode active material particles or the second positive electrode active material particles and the transition metal oxide is 2 mass % or more and 6 mass % or less.
7. The lithium-ion secondary battery according to claim 1 , wherein the overcharge additive is at least one selected from the group consisting of cyclohexylbenzene, biphenyl, methylphenyl carbonate, diphenyl carbonate, and triphenyl phosphate.