Revealing the Design Principles of Ni‐Rich Cathodes for All‐Solid‐State Batteries

Abstract

The highly percolated ionic/electronic pathways are the primary factors enabling the fast kinetics in electrochemical systems. [4] The composite cathodes microstructure engineering plays a critical role in building the ionic/electronic conductive channels. [5] This composite cathode microstructure can be regulated by the main components of cathode active materials (CAM) and SEs. Distinguished with the good wettability of liquid electrolytes, the rigid SEs particles lead to the insufficient contact area between CAM and SEs, leading to reducing active surfaces. [4a,6] For that reason, it is especially important for the SEs mass fraction to be optimized for effective ionic transport pathways in composite cathodes. [7] However, the achievement of both fast ionic and electronic conduction pathways is extremely difficult because the electronic transport networks are supported only by the interconnected CAM particles. This leads to the importance of composite cathode microstructure engineering. [8] There are several key factors of CAM particle size, CAM-to-SEs particle size ratio, and SEs mass fraction that have great impacts on CAM utilization and electrochemical performance. [5a,6,9] However, the effects on the electrode design of these factors are not comprehensively studied, especially on their correlations between these aspects.Herein, we studied the critical effects in terms of the particle size distribution and composition of the composite cathodes on the electrochemical properties. Two advanced popular materials of Ni-rich layered oxides LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM) with different particle sizes and sulfide fast ion conductors Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 (LSPSC) are selected to reveal these effects. The cathode composites are prepared by pressing NCM and LSPSC into a thick pellet with different component ratios. Optimized electrochemical performance suggests an approximate positive relationship between CAM particle size and electrode component ratio. The interfacial impedance changes raised from the varying electrode microstructure were also revealed by electrochemical impedance spectroscopy (EIS) techniques. In the optimized composite cathodes, effective ionic and electronic percolation networks building on highly interconnected CAM particles and highly interconnected SEs particles were demonstrated by cross-section analysis of the composite electrode. As is proved by the direct current (DC) polarization techniques, a compromise between the ionic conductivities and electronic conductivities in composite cathodes Electrode microstructure is one of the primary factors determining the electrochemical properties of all-solid-state batteries (ASSBs). However, the key principles of electrode design to realize fast ionic/electronic transport pathways are not well elucidated. Herein, the correlation between electrode microstructure and electrochemical behaviors is studied through different electrode design in terms of energy-density-related electrode composition and Ni-rich layered oxides particle siz...

Low-cobalt active cathode materials for high-performance lithium-ion batteries: synthesis and performance enhancement methods

“…18 (a) Schematic illustration demonstrating the inter-dependence between the particle size, wt% of CAM with electronic and ionic conductivity in SSBs (adapted with permission. 220 Copyright 2022, Wiley-VCH. ), (b) surface energy profiles of NCM811 and solid-electrolytes with and without interface engineered with Li 3 PO 4 (adapted with permission.…”

“…The particle size and mass fraction of CAMs also have a signicant role in achieving promising electrochemical performance of SSBs. 220,223 Jiang et al have well depicted the competitive nature of the electronic and ionic conductivity through Fig. 18a.…”

“…However, a decreased contact area, crystallographic imparity and high reactivity of solid electrolytes (SEs) with cathode active This journal is © The Royal Society of Chemistry 2023 materials (CAMs) at high voltage, etc., are a few of the primary challenges to use Ni-rich NCMs as the cathode of SSBs. 220,221 The crystallographic mismatch of SEs and CAMs adversely affects the Li + diffusion through the interfaces. It is already discussed in the previous section that Ni-rich NCMs undergo volume shrinkage during the delithiation process, which creates severe stress problems at the interface of rigid SEs.…”

“…18a. 220 Ni-rich NCMs with a small particle size demand a higher mass fraction of solid electrolytes to achieve facile ionic diffusion, whereas with the increase of particle size the CAM wt% is required to be increased to obtain effective electronic transportation. Several efforts have been made to improve the structural compatibility and electrochemical performance of Ni-rich NCM based solid state batteries.…”

Design of densified nickel-rich layered composite cathode via the dry-film process for sulfide-based solid-state batteries

“…These SSEs were generally required in signicant amounts within the composite cathodes for proper Li + diffusion (SSEs 20% of the weight fraction), decreasing the energy density. [15][16][17] However, composite cathodes suffer from sluggish charge transport kinetics owing to agglomeration of SSEs in the microstructure, resulting in poor contact between particles with the formation of pore volume and/or particle isolation. [18][19][20] Although numerous studies have identied the issue mentioned above, few have examined the relationship between the improvement in connectivity of particles through densication and the electrochemical characteristics of composite cathodes for SSBs.…”