Facile Dry Coating Method of High‐Nickel Cathode Material by Nanostructured Fumed Alumina (Al₂O₃) Improving the Performance of Lithium‐Ion Batteries

Abstract

Surface coating is a crucial method to mitigate the aging problem of high‐Ni cathode active materials (CAMs). By avoiding the direct contact of the CAM and the electrolyte, side reactions are hindered. Commonly used techniques like wet or ALD coating are time consuming and costly. Therefore, a more cost‐effective coating technique is desirable. Herein, a facile and fast dry powder coating process for CAMs with nanostructured fumed metal oxides are reported. As the model case, the coating of high‐Ni NMC (LiNi0.7Mn0.15Co0.15O2) by nanostructured fumed Al2O3 is investigated. A high coverage of the CAM surface with an almost continuous coating layer is achieved, still showing some porosity. Electrochemical evaluation shows a significant increase in capacity retention, cycle life and rate performance of the coated NMC material. The coating layer protects the surface of the CAM successfully and prevents side reactions, resulting in reduced solid electrolyte interface (SEI) formation and charge transfer impedance during cycling. A mechanism on how the coating layer enhances the cycling performance is hypothesized. The stable coating layer effectively prevents crack formation and particle disintegration of the NMC. In depth analysis indicates partial formation of LixAl2O3/LiAlO2 in the coating layer during cycling, enhancing lithium ion diffusivity and thus, also the rate performance.

A Dry‐Processed Al2O3/LiAlO2 Coating for Stabilizing the Cathode/Electrolyte Interface in High‐Ni NCM‐Based All‐Solid‐State Batteries

“…It is worth noting that the Al 2 O 3 ‐dry coating is very effective in improving the electrochemical performance of liquid electrolyte‐based cells, as recently shown by Herzog et al. [ 34 ] One main reason is that the liquid electrolyte can penetrate into the highly porous Al 2 O 3 coating, which facilitates the transport of lithium ions through the surface layer. In contrast, the solid electrolyte used in ASSBs is not able to reach the interior of the pores of the coating (Alu‐NCM), i.e., the porous coating impedes lithium‐ion transport between active material and electrolyte due to its insulating properties and the reduced contact area.…”

“…For a better comparison, Figure 6b also shows the normalized discharge capacity, i.e., the specific discharge capacity of each cell was normalized to the CAM mass and related to the initial specific discharge capacity. The initial specific discharge capacity of the P‐NCM cells (136 mAh g −1 ) is found significantly lower compared to cells with liquid electrolytes (≈ 180 mAh g −1 ) [ 34,39 ] indicating a higher interfacial degradation of the SSE than for cells with liquid electrolytes (as the achievable theoretical capacity of NCM is ≈ 180 mAh g −1 ) as reviewed by Jena et al. [ 56 ] The Alu‐coated NCM material shows a slightly lower initial specific capacity (130 mAh g −1 ) than the P‐CAM.…”

“…In order to reduce ecological and economic costs, a new dry coating procedure on CAM was recently introduced by Herzog et al. [ 34 ] It has been shown that by using a high energy mixer, fumed nanostructured Al 2 O 3 physically absorb on the surface of NCM particles and form a porous Al 2 O 3 ‐coating layer, which significantly improves the electrochemical rate performance and capacity retention in liquid‐electrolyte‐based LIBs. [ 34 ]…”

Multi‐Element Surface Coating of Layered Ni‐Rich Oxide Cathode Materials and Their Long‐Term Cycling Performance in Lithium‐Ion Batteries

“…[10,11,12] Aluminum oxide has emerged as an inexpensive, yet effective coating material, applied through a variety of methods, including atomic layer deposition (ALD), wet-chemistry, and dry coating routes with different protective mechanisms proposed. [13][14][15][16][17] Mechanistically, these coatings are reported to protect the CAM by scavenging HF, [13] by forming beneficial electrolyte additives in a reaction with LiPF 6 , [14] by suppressing surface phase transformations [15] or by reducing resistance and improving lithium diffusivity. [16] The energy density of layered oxide cathode materials increases with their Ni content, while the stability decreases and degradation becomes more severe.…”

“…[13][14][15][16][17] Mechanistically, these coatings are reported to protect the CAM by scavenging HF, [13] by forming beneficial electrolyte additives in a reaction with LiPF 6 , [14] by suppressing surface phase transformations [15] or by reducing resistance and improving lithium diffusivity. [16] The energy density of layered oxide cathode materials increases with their Ni content, while the stability decreases and degradation becomes more severe. A common strategy to mitigate or prevent degradation is the application of protective coatings on the particle surfaces.…”