Evolution of ternary Li_xSn_yO_z artificial cathode-electrolyte interphase (ACEI) through ALD: a surface strengthened NCM811 with enhanced electrochemical performances for Li-ion batteries

[(LiNi_0·8Co_0·1Mn_0.1)O₂], or NCM811, a member of the Li_xNi_1−y−zCo_yMn_zO₂ (NCM) family of cathode active materials (CAMs), is gaining recognition in the battery community as the CAM of choice for future high energy density lithium-ion batteries, given its high nickel content of c. 80%. Yet, its commercialization is impeded by its mechanochemical instability at a high state of charge (SOC), which results in severe capacity fading and active lithium loss during cycling. In this contribution, we report conformal nanometer-thick (c. 4–7 nm) lithiated tin-oxide ternary coatings (Li_xSn_yO_z) deposited on NCM811 cathode powder using the atomic layer deposition (ALD) technique. The first-of-its-kind ALD coating, where Li is being accompanied by a second metal ion (Sn); provides a combination of benefits: (i) it stabilizes the crystal structure, (ii) suppresses electrode polarization, (iii) lowers the voltage hysteresis, and (iv) reduces interfacial and bulk resistance. These improvements all contribute to prolonging the cycling stability of the NCM811 cathode in half-cells (vs. Li/Li⁺) at 30 °C and 55 °C and full pouch cells (vs. graphite) at 30 °C. Furthermore, this coating approach is compatible with large-scale production methods and provides a bridge between lab-scale demonstration and industrial manufacturing, thus facilitating the adoption of the developed coating technology by the automobile industry.