Li₂ZrO₃-Coated NCM622 for Application in Inorganic Solid-State Batteries: Role of Surface Carbonates in the Cycling Performance

Abstract

All-inorganic solid-state batteries (SSBs) currently attract much attention as nextgeneration high-density energy storage technology. However, to make SSBs competitive with conventional Li-ion batteries, several obstacles and challenges must be overcome, many of which are related to interface stability issues. Protective coatings can be applied to the electrode materials to mitigate side reactions with the solid electrolyte, with lithium transition metal oxides, such as LiNbO3 or Li2ZrO3, being well established in research. In addition, it has been recognized lately that carbonates incorporated into the coating may also positively affect the interface stability. In this work, we studied the effect that surface carbonates in case of Li2ZrO3-coated Li1+x(Ni0.6Co0.2Mn0.2)1−xO2 (NCM622) cathode material have on the cyclability of pellet stack SSB cells with Li6PS5Cl and Li4Ti5O12 as solid electrolyte and anode, respectively. Both carbonate-rich and carbonate-poor hybrid coatings were produced by altering the synthesis conditions. The best cycling performance was achieved for the carbonate-deficient Li2ZrO3-coated NCM622, due to decreased degradation of the argyrodite solid electrolyte at the interfaces, as determined by ex situ X-ray photoelectron spectroscopy and in situ differential electrochemical mass spectrometry. The results emphasize the importance of tailoring the composition and nature of protective coatings to improve the cyclability of bulk SSBs.

Operando Characterization Techniques for All‐Solid‐State Lithium‐Ion Batteries

“…The discussed studies show that DEMS is a valuable tool to test and understand the stabilizing effect of CAM coatings in SSBs, recently also shown for Li 2 CO 3 /Li 2 ZrO 3 ‐coated NCM622. [ 73 ] This has been further demonstrated in the study of a system containing a poly(ethylene oxide) (PEO)‐based SE and LCO CAM. [ 74 ] As known from literature, such polymer SEs have a narrow electrochemical stability window.…”

“…While the initial studies have been focused on the cathode side, such investigations need to be extended to the anode side (note that observations of H 2 evolution and CO 2 evolution at the very beginning of the initial charge cycle have been assigned to reactions possibly occurring at the anode). [ 67,71–73 ] Future studies aiming to create a more complete picture of interface/interphase formation in SSB cells could benefit from the combination of DEMS with X‐ray‐based techniques to reveal solid decomposition products along with gaseous species.…”

On the role of surface carbonate species in determining the cycling performance of all-solid-state batteries

“…Previous literature reports revealed that this hybrid coating concept is also compatible with other materials than LiNbO 3 , for example, Li 2 ZrO 3 and Li 3 BO 3 , demonstrating the great versatility in terms of chemical composition (coating formulation) and properties [45][46][47]. In all of these cases, the coating was capable of suppressing to different extents interfacial decomposition of the solid electrolyte at the contact points with the CAM secondary particles, which otherwise would lead to impedance buildup due to formation of insulating degradation products (oxygenated sulfur and phosphorus species etc) and capacity fade.…”

In Search of the Best Solid Electrolyte-Layered Oxide Pairing for Assembling Practical All-Solid-State Batteries

“…10,11 The degree of advancement of such decomposition reactions depends upon the quality of oxide coating but more so on the nature of the solid ionic conductor used. [12][13][14] Nowadays, a wide panel of fast Li + conductors for solid-state battery applications are known. The lithium thiophosphate family is probably the largest and one of the most attractive for practical applications.…”