STUDY OF PARTICULARIZED PROTECTIVE METAL FLUORIDES FILMS DEVELOPED ON LiMn_1.5Ni_0.5O_{4 CATHODE POWDER MATERIALS}

Li-ion batteries (LIBs) utilizing LiMn_1.5Ni_0.5O₄ (LMNO) spinel type cathode material have high voltage (4.8 V) and most reasonable specific capacity. Therefore, they are most appealing materials in high energy density LIB. However, this promising material suffers from a low cyclability, particularly at elevated temperatures. Among the reasons for the capacity fading is the leaching of manganese (Mn) from the cathode material. Eliminating (or substantially reducing) Mn dissolution from the cathode matrix via the formation of a stable and durable coating layer (under a battery operation condition) that will prevent Mn passage from the cathode and will also be permeable to Li⁺ ion is a desired research direction.

LMNO powder was coated uniformly with a several atomic layers thick magnesium fluoride (MgF₂) and aluminum fluoride (AlF₃) films using atomic layer deposition (ALD) process. At the same time, MgF₂ and AlF₃ coatings were also deposited on the same LMNO material using wet chemistry methods.

We plan to report on the capacity fading of the coated materials at room temperature cycling as well as at 45⁰C. Correlation of the electrochemical performance with the surface morphology developed at the LMNO surface subsequent to the coating procedure will be reported. High resolution scanning electron microscopy (HRSEM) and transmission electron microscopy (TEM) showed a uniform several nanometer layer of metal fluorides on the LMNO powder in the ALD process, whereas the wet coating process showed a non-uniform coating. In addition, HRSEM images showed crystallinity of the wet coatings after annealing at elevated temeratures.