Li_xSi_yO_z coating for LiCoO₂ cathode material using atomic layer deposition (ALD)

With a high theoretical capacity of 274 mAh, LiCoO₂ (LCO) is commonly used as a cathode material in portable devices and different Li-ion batteries (LIBs) applications. However, its practical capacity is lower than the theoretical value due to interfacial degradation pathways that limit the cathode operating voltage. In this work, we demonstrate an advanced and efficient methodology for surface coating of Li_xSi_yO_z over LiCoO₂ (LCO) cathodes by atomic layer deposition (ALD). To get an in-depth understanding of the Li_xSi_yO_z growth mechanism, density functional theory (DFT) was used. The DFT calculations indicate that the surface precursor material, 3-aminopropyl triethoxysilane (APTES), is covalently bonded to the cathode surface in a thermodynamically favorable process before its further oxidation in the ALD sequence. We demonstrate the efficacy of two types of Li_xSi_yO_z surface coating as protective layers that improve the electrochemical performance of the LCO cathode. Both Li_xSi_yO_z coatings enabled high-voltage operation of the LCO cathode (> 4.5 V), especially thin layers of Li-rich Li_xSi_yO_z coated samples. After 100 charge–discharge cycles, the Li-rich coated LCO cathode outperformed the untreated LCO, showing a 23.4% higher discharge capacity.