Crystalline Domain Battery Materials

The development of next-generation energy storage materials for secondary batteries relies more and more on the delicate design and tailoring of their local structures and properties. Crystalline domain battery materials (CDBMs) are defined as a family of materials that are hierarchically engineered primarily by bonding selective atoms in certain space groups with short-range order to form nanoscale crystal domains as fundamental constructive and functional units, secondarily by integrating these interactive crystal domains under certain configurations into grains to implement electrochemical synergy, and finally by optimizing grains through nanoengineering toward advanced electrode materials. In CDBMs, adjacent crystal domains can undergo structural co-transformations with noticeable interrelationships, and the overall electrochemical performance is determined not only by the intrinsic structure of each crystal domain (element, bonding, valence, stacking, orientation, etc.) but also by the configuration of crystal domains (size, ratio, interface, distribution, interaction, etc.). Pioneering studies have shown significant enhancement of electrochemical performance by controlling crystal domains, suggesting the prospect of developing novel electrode materials through crystal-domain engineering. However, fundamental understanding and delicate fabrication of this material family, in terms of structural identification, electrochemical structure evolution, reaction mechanism, design and adjustment, and structure-performance relationship, among others, still face great challenges to meet the compelling requirements of high-performance electrode materials for secondary batteries. This Account systematically introduces the structure and electrochemistry of CDBMs. The efficient structural identification of crystal domains, which is still challenging due to their structural complexity, is demonstrated using prototype materials by advanced characterization techniques such as high-energy X-ray diffraction combined with Rietveld refinement and spherical aberration-corrected transmission electron microscopy. Investigations on the structural evolution of CDBMs in electrochemical reactions by ex-situ and in-situ techniques provide insights into reaction scenarios such as how ions migrate in and across crystal domains and how these crystal domains transform synergistically. A crystal-domain reaction mechanism is thus proposed to explain the electrochemistry of these materials. Design principles and adjustment strategies for designated crystal-domain structures including their components, ratios, distributions, and interfaces are deduced from the structural identification, evolution and reaction mechanism. The relationship between crystal-domain structures and electrochemical performance can further be elucidated, inspiring us to explore efficient strategies for optimizing the electrochemical performance, as validated by examples of high-performance batteries using materials with controlled crystal-domain structures. Based on these systematic studies, the trends in the rapid enrichment, deep investigation, and practical application of CDBMs are envisioned to promote continuous studies on this nascent energy storage material family.