@article{THESIS,
      recid = {14508},
      author = {Wang, Jing},
      title = {Understanding the Chemo-Mechanical Evolution of Single  Crystal Nickel-Rich Cathodes},
      publisher = {University of Chicago},
      school = {Ph.D.},
      address = {2025-03},
      number = {THESIS},
      abstract = {The ever-increasing demand for electric-vehicle and  grid-storage markets necessitates advances in lithium-ion  batteries (LIBs) with higher energy density and longer  cycling life. Single-crystal nickel (Ni)-rich cathodes  (SC-NMCs) have garnered widespread attention in the LIB  community, due to their high tap density, mechanical  robustness, and boundary-free architecture. While SC-NMC  cathodes have shown exceptional stability and performance  at low Ni content, they exhibit pronounced capacity  degradation and structural instability as Ni content  increases beyond 80% or under high-voltage cycling  conditions. Furthermore, numerous studies have adopted a  trial-and-error approach to modifying SC cathodes, often  relying on degradation indicators and modification  strategies developed for conventional polycrystalline (PC)  NMC cathodes, despite the fundamentally distinct  chemo-mechanical degradation pathways of SC materials. This  thesis systematically investigates the chemo-mechanical  evolution in SC-NMC cathodes to identify the critical  factors limiting their performance, to evaluate the  compositional effects, and to provide effective guidelines  for their optimization and future development. In Chapter  1, we explore the performance gap between PC- and SC-NMC  cathodes under high-Ni-content conditions. Multi-scale  operando techniques reveal that the degradation in SC-NMC  cathodes is primarily driven by internal bulk strain rather  than surface reactions. The heterogeneous Ni oxidation in  the micron-sized SC particles during cycling generates  non-uniform strain distributions and irreversible oxygen  redox activity, resulting in intragranular cracking and  phase transformation. Therefore, unlike PC cathodes, which  demonstrate better chemo-mechanical stability despite more  severe surface reconstruction, SC cathodes suffer from poor  cycling performance due to more strain-driven microcrack  formation within a single particle. These findings  highlight the critical role of Ni redox behavior in  influencing the mechanical stability and electrochemical  performance of Ni-rich cathodes.  Building on these  insights, Chapter 2 focuses on unraveling the nanoscopic  strain evolution in SC-NMC cathodes, challenging  traditional composition-driven strategies derived from PC  systems. Through a combination of advanced diagnostics and  modeling, we reveal that mechanical degradation in SC-NMC  is decoupled from lattice volume changes, instead driven by  kinetic heterogeneities and multiple-dimension lattice  distortions. Our study identifies manganese (Mn) as a major  contributor to localized strain accumulation in SC  cathodes, exacerbating structural degradation, while cobalt  (Co) mitigates these effects by enhancing structural  integrity and diffusion pathways. These findings not only  redefine the compositional requirements for SC-NMC  cathodes, but also emphasize the need for tailored strain  modulation strategies distinct from those applied to PC  materials. This thesis advances the understanding of  chemo-mechanical evolution mechanisms in SC-NMC cathodes,  facilitating the refinement of existing strategies and  driving innovation in cathode design. By bridging the gap  between degradation behaviors and material design, this  work offers a comprehensive framework to guide the future  improvement of SC-NMC cathodes, paving the way for  next-generation LIBs with improved longevity and  performance.},
      url = {http://knowledge.uchicago.edu/record/14508},
      doi = {https://doi.org/10.6082/uchicago.14508},
}