Lithium secondary battery

Abstract

A lithium secondary battery of the present invention has a positive electrode is provided with a positive electrode mix layer that includes a positive electrode active material and a conductive material. The positive electrode mix layer has two peaks, large and small, of differential pore volume over a pore size ranging from 0.01 μm to 10 μm in a pore distribution curve measured by a mercury porosimeter. A pore size of the smaller peak B of the differential pore volume is smaller than a pore size of the larger peak A of the differential pore volume.

1 . A lithium secondary battery, comprising
 a positive electrode that has a positive electrode collector and a positive electrode mix layer that includes, on a surface of the collector, a positive electrode active material and a conductive material, wherein   the positive electrode mix layer has two peaks, large and small, of differential pore volume over a pore size ranging from 0.01 μm to 10 μm, in a pore distribution curve measured by a mercury porosimeter, and   from among the large and small peaks, a pore size in a smaller peak B of the differential pore volume is smaller than a pore size in a larger peak A of the differential pore volume.   
     
     
         2 . The lithium secondary battery according to  claim 1 , wherein in the pore distribution curve, a pore size P [μm] of a minimum value between the large and small peaks lies in a range from 0.1 μm to 0.7 μm. 
     
     
         3 . The lithium secondary battery according to  claim 2 , wherein in the pore distribution curve, a total pore volume per unit mass of the conductive material for pores having a pore size smaller than the pore size P [μm] and encompassing the small pore size peak B satisfies a range of 0.18 cm 3 /g to 0.8 cm 3 /g. 
     
     
         4 . The lithium secondary battery according to  claim 2 , wherein in the pore distribution curve, a total pore volume Sb [cm 3 /g] of pores having a pore size smaller than the pore size P [μm] and encompassing the small pore size peak B is smaller than a total pore volume Sa [cm 3 /g] of pores having a pore size larger than the pore size P [μm] and encompassing the large pore size peak A. 
     
     
         5 . The lithium secondary battery according to  claim 1 , wherein in the pore distribution curve, a ratio (Sb/Sa) of the total pore volume Sb [cm 3 /g] to the total pore volume Sa [cm 3 /g] satisfies 0.4<(Sb/Sa)<1. 
     
     
         6 . The lithium secondary battery according to  claim 1 , wherein as the conductive material included in the positive electrode mix layer, at least one type selected from the group consisting of acetylene black, furnace black, Ketchen black and graphite powder is used. 
     
     
         7 . The lithium secondary battery according to  claim 1 , wherein a layer density of the positive electrode mix layer ranges from 1.5 g/cm 3  to 2.8 g/cm 3 . 
     
     
         8 . A method for producing a lithium secondary battery that is provided with a positive electrode that has a positive electrode collector and a positive electrode mix layer that includes, on a surface of the collector, a positive electrode active material and a conductive material,
 the method comprising the steps of:   forming the positive electrode mix layer on a surface of the positive electrode collector;   measuring a pore distribution of the positive electrode mix layer in use of a mercury porosimeter, and selecting a positive electrode such that the pore distribution curve obtained on the basis of the measurement satisfy the conditions below:   there are two peaks, large and small, of differential pore volume in a pore size ranging from 0.01 μm to 10 μm; and   from among the large and small peaks, a pore size in a smaller peak B of the differential pore volume is smaller than a pore size in a larger peak A of the differential pore volume; the method further including   constructing a lithium secondary battery by using the selected positive electrode.   
     
     
         9 . The production method according to  claim 8 , wherein a positive electrode is selected that exhibits a pore size P [μm] of a minimum value between the large and small peaks in the pore distribution curve obtained by the measurement ranging from 0.1 μm to 0.7 μm. 
     
     
         10 . The production method according to  claim 9 , wherein a positive electrode is selected that exhibits, as a further condition, a total pore volume per unit mass of the conductive material for pores having a pore size smaller than the pore size P [μm] and encompassing the small pore size peak B, in the pore distribution curve obtained by the measurement, satisfying a range of 0.18 cm 3 /g to 0.8 cm 3 /g. 
     
     
         11 . A vehicle, comprising the lithium secondary battery according to  claim 1 .