Multiscale understanding of high-energy cathodes in solid-state batteries: from atomic scale to macroscopic scale

Abstract

In the crucial area of sustainable energy storage, solid-state batteries (SSBs) with nonflammable solid electrolytes stand out due to their potential benefits of enhanced safety, energy density, and cycle life. However, the complexity within the composite cathode determines that fabricating an ideal electrode needs to link chemistry (atomic scale), materials (microscopic/mesoscopic scale), and electrode system (macroscopic scale). Therefore, understiang solid-state composite cathodes covering multiple scales is of vital importance for the development of practical SSBs. In this review, the challenges and basic knowledge of composite cathodes from the atomic scale to the macroscopic scale in SSBs are outlined with a special focus on the interfacial structure, charge transport, and mechanical degradation. Based on these dilemmas, emerging strategies to design a high-performance composite cathode and advanced characterization techniques are summarized. Moreover, future perspectives toward composite cathodes are discussed, aiming to facilitate the develop energy-dense solid-state batteries.

A Quasi‐Multinary Composite Coating on a Nickel‐Rich NCM Cathode Material for All‐Solid‐State Batteries

“…SE oxidation, evident from the appearance of polysulfide and oxygenated sulfur/ phosphorus species, typically occurs at the contact points between the particles upon charging, with the degree of interfacial degradation being significantly different for coated and uncoated CAMs. [5][6][7][8]14,18,24,33,34] The same is to be expected here. However, from the available literature reports, it is apparent that there are no clear trends of what coating chemistry and/or morphology works best in terms of suppressing the formation of certain degradation products.…”

“…Interfacial degradation in lithium thiophosphate‐based SSBs has already been studied in detail using X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS), for example. SE oxidation, evident from the appearance of polysulfide and oxygenated sulfur/phosphorus species, typically occurs at the contact points between the particles upon charging, with the degree of interfacial degradation being significantly different for coated and uncoated CAMs [5–8,14,18,24,33,34] . The same is to be expected here.…”

“…Engineering of stable interfaces is one of the major challenges on the route to bulk‐type solid‐state batteries (SSBs) that are capable of competing with liquid electrolyte‐based Li‐ion batteries (LIBs) in terms of electrochemical performance [1–3] . Lithium thiophosphates, which exhibit the highest room‐temperature ionic conductivities [4] among the reported superionic solid electrolytes (SEs) along with favorable mechanical properties, have been shown to be unstable when in contact with energy‐dense cathode active materials (CAMs), such as LiNi x Co y Mn z O 2 (referred to as NCM), especially at the high voltages they are usually operated at [5–11] . Therefore, it is imperative to introduce a buffer layer between CAM and SE.…”

“…[1][2][3] Lithium thiophosphates, which exhibit the highest roomtemperature ionic conductivities [4] among the reported superionic solid electrolytes (SEs) along with favorable mechanical properties, have been shown to be unstable when in contact with energy-dense cathode active materials (CAMs), such as LiNi x Co y Mn z O 2 (referred to as NCM), especially at the high voltages they are usually operated at. [5][6][7][8][9][10][11] Therefore, it is imperative to introduce a buffer layer between CAM and SE. In the past, various protective CAM coatings prepared by different techniques have been reported.…”

Designing Cathodes and Cathode Active Materials for Solid‐State Batteries

“…In general, the fabrication of highperformance SSB cathodes presents challenges on different length scales, ranging from the micro-to the nano-scale which are related to the composite cathode, CAM particles, and interface between CAM and SE, respectively (Figure 1). [27] Besides optimizing the composite cathodes on a microscale level, the CAM itself needs to be tailored for application in SSBs to be (chemo-)mechanically compatible with the SE. In the following, we describe the different requirements for the CAM and composite cathodes from materials and processing perspectives.…”