Single Crystal Layered Oxide Cathodes: The Relationship between Particle Size, Rate Capability, and Stability

Abstract

With the increasing demand for safer, more stable, and energy dense batteries, investigations into single crystal layered oxide cathodes have gained momentum. However, translating considerations from polycrystalline to single‐crystalline particles and their ensembles is not one‐to‐one. Lithium diffusion path length, surface, dopants and coatings, as well as the synthetic methods used take on different dimensions for single‐crystalline particles. In this concept article, we review key considerations that must be made when developing well‐performing single crystal layered oxide cathodes. We discuss how diffusion limitations can affect material stability in addition to how improvements to diffusivity can act as a method to simultaneously improve rate capability and surface stability. In addition, we briefly discuss how the unique feature of faceting and the synthetic design space for single‐crystalline particles should be conceptualized.

The role of niobium in layered oxide cathodes for conventional lithium-ion and solid-state batteries

“…Single-crystalline LTMOs are ideally composed of individual crystallites but practically consist of 3–5 agglomerated grains. 143 As noted elsewhere, 144 increasing particle (grain) size leads to a reduction in surface area per unit mass, which helps mitigate surface reactions and whose deagglomerated character can alleviate the issue of intergranular cracking commonly observed in polycrystalline NCM CAMs. Nevertheless, they present balance of limitations related to an increased path length for lithium diffusion.…”

Seesaw Effect of Substitutional Point Defects on the Electrochemical Performance of Single-Crystal LiNiO2 Cathodes

“…Another aspect is their relation to the first-cycle capacity loss, as reported by Arai et al, Delmas et al, and Bianchi et al In particular, they emphasized the need for lowering the defect density for decreasing the first-cycle loss. − Subsequent studies did not find this correlation and instead proposed a direct link between the first-cycle loss and primary particle size of the active material. ,, However, since the Ni Li • defects affect the lithium transport properties through vacancy trapping and by acting as a diffusion barrier, it is difficult to distinguish between the influence of the point defects and size effects, which arise at different calcination temperatures . This intrinsic convolution of particle size and defect density contributions to the electrochemical performance demands further study, as diffusion-induced capacity loss can be substantial particularly for single-crystalline morphologies. , …”

Grain‐growth Inhibitor with Three‐section‐sintering for Highly Dispersed Single‐crystal NCM90 Cubes

“…[8] To solve these issues, some strategies were developed, such as molten-salt sintering and hydrothermal method. [9][10][11][12] In the molten-salt sintering, large amount of salts are adopted as fluxing agents to lower the grain-growth temperature and separate NCM particles, which however need to be washed off using water and so cause Li + /H + exchange. [11] A post-annealing procedure is required, making this method time-consuming and cost boosting.…”

“…The hydrothermal method prepared NCM are mainly nano-sized particles, not conducive to reduce the interfacial reactions with electrolytes. [12] In addition, poor C-rate performance of SC-NCM is another challenge, owing to the elimination of internal void and elongated Li + -migration distance. Therefore, although SC-NCM materials are starting to be applied in market, more efficient preparation methods for highly dispersed SC-NCM with improved C-rate performance are intensely desired.…”