Core–Multishell‐Structured Digital‐Gradient Cathode Materials with Enhanced Mechanical and Electrochemical Durability

Abstract

Ni‐rich cathode materials provide high energy density, but their structural and surface instability limits their cyclability and thermal stability. As one of the approaches to mitigate this problem, cathode materials comprising Ni‐rich high‐capacity core wrapped in Mn‐rich multiple shells are produced successfully. In contrast to the conventional batch‐type process for concentration‐gradient materials, a digital‐gradient cascade coprecipitation process described here achieves the improvements in productivity and quality consistency needed to move toward large‐scale manufacturing. The core–multishell cathode materials produced in this manner not only have longer cycle life and improved rate performance compared to homogeneous Ni‐rich cathode materials having the same overall composition, but also show remarkably enhanced thermal stability and low impedance growth characteristics. In a novel attempt to determine the correlation between the mechanical properties of the core–multishell cathode particles and their electrochemical cyclabilities, their breaking force and elasticity were successfully measured using a statistical approach, which indicates that a cathode particle with stable surface composition as well as high breaking force has improved capacity retention and durability. These results guide the realization of long life and high thermal stability in Ni‐rich cathode materials through heterogeneous particle engineering.

Multiphase layered transition metal oxide positive electrodes for sodium ion batteries

“…A sample with homogeneous distribution of elements and/or phases could be compared to a core-shell material with the same overall composition to study the effect of the cathode-electrolyte interface and transport properties near the surface. 107 If the core-shell compositions are swapped (i.e., the original shell becomes new core, original core becomes new shell), this further elucidates the effect of surface phase properties on performance and simultaneously alters the mechanical coupling between phases within the particle. To study electrode materials with heterogeneous structure and composition, researchers must utilize methods that have sufficient spatial resolution to observe differences within individual secondary particles.…”

“…At the secondary particle scale, the spatial distribution of the phases/elements can then be altered. A sample with homogeneous distribution of elements and/or phases could be compared to a core‐shell material with the same overall composition to study the effect of the cathode‐electrolyte interface and transport properties near the surface 107 . If the core‐shell compositions are swapped (i.e., the original shell becomes new core, original core becomes new shell), this further elucidates the effect of surface phase properties on performance and simultaneously alters the mechanical coupling between phases within the particle.…”

Layered Cathode Materials: Precursors, Synthesis, Microstructure, Electrochemical Properties, and Battery Performance

“…Unfortunately, the synthesis of concentration-gradient precursors can be synthesized by the batch-type coprecipitation only. Recently, Shin et al [60] synthesized a core-multishellstructured digital-gradient precursor through a continuous process. In their protocol (Figure 11e), the matured core particles Ni 0.9 Mn 0.05 Co 0.05 (OH) 2 discharged from the first reactor were continuously fed into the second one and coated with a Ni 0.8 Mn 0.1 Co 0.1 (OH) 2 shell (step a to b).…”

“…e) Schematic illustration of continuous synthesis of digital-gradient precursor, together with f) the cycling performances of the digital-gradient cathodes and homogeneous LiNi 0.8 Co 0.1 Mn 0.1 O 2 . Reproduced with permission [60]. Copyright 2021, John Wiley and Sons.…”

3D Quantification of Elemental Gradients within Heterostructured Particles of Battery Cathodes

“…22,23 To bring the synthesis of such refined cathodes to manufacturing scales, Shin et al recently developed a "digital-gradient" process for precursors where a continuous-flow method through cascading continuous stirred tank reactors (CSTR) enabled increasingly complex compositional changes as additional layers on a baseline material. 24 The structures of representative multi-shell architectures made by this method are outlined in Figure 1. Starting from an initial baseline material, Ni0.9Co0.05Mn0.05(OH)2, the process was extended to grow a series of additional layers of hydroxide where the Ni:Co:Mn ratios of the synthesis feeds successively changed to 8:1:1, 6:2:2 and 1:1:1, targeting materials with increasing average Mn/Ni ratios and compositional differences between interior and surface.…”