Al-Doped Co-Free Layered-Spinel Mn/Ni Oxides as High-Capacity Cathode Materials for Advanced Li-Ion Batteries

Li- and Mn-rich layered-spinel integrated cathodes exhibit a high specific capacity, ≥200 mAh g^-1, in a wide potential range; however, the low initial capacity of Li[Ni_1/3Mn_2/3]O₂is a drawback for their application in Li-ion batteries. Two Al-doped layered-spinel Li[Ni_0.33Mn_0.63Al_0.03]O₂and Li[Ni_0.33Mn_0.60Al_0.06]O₂cathode materials which were synthesized by self-combustion reaction, having less monoclinic and more active spinel phases, could show a much higher initial capacity compared to the undoped reference material. These cathode materials exhibit an initial specific capacity of 188 mAh g^-1vs ∼110 mAh g^-1when cycled at 20 mA g^-1between 2.3 and 4.9 V vs Li. Their capacity gradually increases to 210 mAh g^-1during initial cycling in standard electrolyte solutions and stabilizes thereafter. The average discharge voltage decreases from around 3.6 to 3.2 V after 200 cycles. Electrochemical impedance spectroscopic measurements clearly indicate the lower impedance due to lower surface film and charge-transfer resistance of the cathodes comprising the Al-doped materials compared to cathodes comprising the reference, undoped material. The high specific capacity and excellent cycling stability of Li[Ni_0.33Mn_0.60Al_0.06]O₂render it a promising cathode material for high-energy Li-ion batteries.