As everal atomic layers thick magnesium fluoride (MgF 2 )f ilm is successfully deposited onto each individual grain of an ultrahigh-potential LiMn 1.5 Ni 0.5 O 4 -powder material for Li-ion batteries. The resulting film has am arked protection action, as it does not compromise the cathode performance substantially,w hile it extends the cycle life of the cathodes prepared from the coatedp owder.T he protective effect is pronounceda t4 58Ca nd the catastrophicc apacity fading is halted. The essence of the protecting action is suggestedt ob ei nb lockingt he access of aggressive electrolyte-decompositionb yproducts to the cathode material surface.

The most promising LiMn 1.5 Ni 0.5 O 4 (LMNO) ultrahigh voltage cathode material is not yet commercialized because it is suffering from capacity fading during cycling, especially at elevated temperatures. Manganese ions dissolution from the cathode and their precipitation on the graphite anode are the main cause of failure of Li-ion batteries (LIBs) utilizing LMNO cathode material. In order to mitigate this issue, an AlF 3 layer was coated directly on LMNO powder particles via atomic layer deposition (ALD). A few nanometer thick coating was individually formed on each particle. The coating protected the particles from the corrosion-like phenomenon, when immersed in LIB electrolyte at room temperature (RT) and at 45 °C. Half-cell electrochemical measurements showed superior performance for the ALD coated AlF 3 material over the uncoated material. In the full-cell configuration enhanced capacity retention was observed for cells comprised from cathode materials coated by different AlF 3 ALD coatings. Complete Li-ion cells utilizing ALD coated cathode powder in the cathode and a graphite anode exhibited lower initial capacity, which was recovered continuously during cycling at RT and dramatically at 45 °C during the first ∼30 cycles. A different and modified formation process and cycling method significantly improved the lower initial capacity of the Li-ion cells on the expense of a rather shorter cycle life. Even with the new formation cycling, Li-ion cells utilizing ALD coated materials exhibited better cycling performance than cells utilizing pristine material. Fluorination of oxygen impurities in the coating layer or its lithiation are suggested as mechanisms for the recovered capacity. Li-ion cells utilizing ALD AlF 3 coated cathode powder were cycled up to 180 cycles, when 150 of them were at 45 °C. KEYWORDS: particle by particle, AlF 3 , ALD coating, LiMn 1.5 Ni 0.5 O 4 powder, Li-ion batteries

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