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This work demonstrates the effect of coating LiMn 1.5 Ni 0.5 O 4 with MgO and ZnO by a sono-chemical method. It was found that the sonochemical process results in a coating that serves as a buffer, yet allows the easy transport of Li + ions to and from the active mass. Both the ZnO and MgO coatings modify the particles' surface chemistry and help to inhibit the dissolution of Mn and Ni ions from the active mass into the solution phase at elevated temperatures and thus managed to improve the stability of LiMn 1.5 Ni 0.5 O 4 as an high voltage cathode material. MgO was found to be more effective than ZnO in this regard. The MgO coated cathodes demonstrated better electrochemical performance than the uncoated material. Lastly, the ZnO-coated material indicated a reduction in thermal stability in standard solutions, while the MgO coating did not affect the material's thermal stability.

The conductivity of 0.38–1.9MnormalCafalse(AlCl4)2‐normalthionyl chloride solutions was determined at temperatures from −30° to +60°C. The maximum specific conductivities at −30°, 30°, and 60°C were found to be 3.25, 6.7, 8.7 mmho cm−1, respectively. The discharge performance of sandwich‐like glass laboratory cells was determined at rates of 0.8–13 mA cm−2over this temperature range. Cell capacity at 25°C was 38 mA‐hr cm−2 at 1 mA cm−2 and 22 mA‐hr cm−2 at 11 mA cm−2. There was no loss of capacity on discharge at 60°C. At −20°C and 0.8 mA cm−2 the cell delivers 80% of its 25°C capacity. It was estimated that the energy density of a “jelly‐roll” type cell will be 250–300 W‐hr kg−1. The safety features of the cell were excellent as it was practically impossible to charge or overdischarge the cell. At a charging or a reversal voltage of 30V the corresponding current densities were smaller than 0.1 mA cm−2.

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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