Nonstoichiometry of Li-rich cathode material with improved cycling ability for lithium-ion batteries.

We prepared nonstoichiometric Li-rich cathodes with stable capacity and median voltage for lithium-ion batteries. • The nonstoichiometry of Li-rich cathodes were firstly synthesized for lithium-ion batteries. • The nonstoichiometric cathodes exhibit stable capacity and median voltage upon cycling. • The improvement of cycling ability attributes to the production of Ni3+ ions in the nonstoichiometric samples. Lithium-rich layered oxides are considered as promising cathode materials for lithium-ion batteries due to its high capacity, but the rapid decay of capacity and operating voltage are great challenges to achieve its commercial application. In this work, the nonstoichiometry of Li-rich layered oxide Li 1.2 Mn 0.6 Ni 0.2 O 2 was designed by directly declining the Mn amounts in the form of Li 1.2 Mn x Ni 0.2 O 2 (x = 0.59, 0.57, 0.55). The nonstoichiometric sample Li 1.2 Mn 0.55 Ni 0.2 O 2 exhibits a capacity of 170.73 mAh g−1 at 0.5 C, a little lower than 187.29 mAh g−1 of Li 1.2 Mn 0.6 Ni 0.2 O 2 , however, better cycling stability of operating voltage and capacity is attained with the reduction of Mn amounts, compared to that of Li 1.2 Mn 0.6 Ni 0.2 O 2. The capacity retention of Li 1.2 Mn 0.55 Ni 0.2 O 2 is enhanced to 88.7% via 74.7% of Li 1.2 Mn 0.6 Ni 0.2 O 2 after 100 cycles at 0.5 C. The declining value of operating voltage for Li 1.2 Mn 0.55 Ni 0.2 O 2 is 0.200 V as compared to 0.559 V for Li 1.2 Mn 0.6 Ni 0.2 O 2. X-ray photoelectron spectra (XPS) was employed to confirm the existence of Ni3+ in the nonstoichiometric samples, and the amounts of Ni3+ increase along the Mn contents decrease. The improvement of electrochemical properties for nonstoichiometric samples is attributed to the presence of Ni3+ due to Ni3+ can defer the transition of layered-to-spinel structure through decreasing the Li/Ni mixing. [ABSTRACT FROM AUTHOR]