If Σ={0,1}
Σ+ = {0, 1, 00, 11, 01, 10, 000, 001,………..} : All combinations of 0 and 1 except ε(null string).
L is a language for given alphabet set (Σ). So, L can be anything (e.g. , L= {00, 11} then L.L*=L+ = all combination of 00 and 11)
There is no such relation between Σ+ and L.L*