Influence of lithium content on the electrochemical performance of Li1+x(Mn0.533Ni0.233Co0.233)1−xO2 cathode materials

► Pure phase can be obtained when Li-excessive value x keeps between 0.045 and 0.18. ► The initial efficiency (Q1d/Q1c) keeps the same low-level of 70% for different samples. ► Li1.045Mn0.509Ni0.223Co0.223O2 sample (x = 0.045) expresses highest initial discharge capacity of 259.8 mA h g−1. ► The Li-excessive value x of 0.09 sample exhibits the best rate capability in 100 mA g−1 and 200 mA g−1. ► Almost no reduction is observed after 24-time cycles in all for Li1.09Mn0.486Ni0.212Co0.212O2 sample.