Atomic Layer Deposition of Al2O3-Ga2O3 Alloy Coatings for Li[Ni0.5Mn0.3Co0.2]O2 Cathode to Improve Rate Performance in Li-Ion Battery

Metal oxide coatings can improve the electro-chemical stability of cathodes and hence, their cycle-life in rechargeable batteries. However, such coatings often impose an additional electrical and ionic transport resistance to cathode surfaces leading to poor charge-discharge capacity at high C-rates. Here, a mixed oxide (Al2O3)(1-x)(Ga2O3)(x) alloy coating, prepared via atomic layer deposition (ALD), on Li[Ni0.5Mn0.3Co0.2]O-2 (NMC) cathodes is developed that has increased electron conductivity and demonstrated an improved rate performance in comparison to uncoated NMC. A "co-pulsing" ALD technique was used which allows intimate and controlled ternary mixing of deposited film to obtain nanometer-thick mixed oxide coatings. Co-pulsing allows for independent control over film composition and thickness in contrast to separate sequential pulsing of the metal sources. (Al2O3)(1-x)(Ga2O3)(x) alloy coatings were demonstrated to improve the cycle life of the battery. Cycle tests show that increasing Al-content in alloy coatings increases capacity retention; whereas a mixture of compositions near (Al2O3)(0.5)(Ga2O3)(0.5) was found to produce the optimal rate performance.