Study Of Structural Regulation And Stability In High Performance Lithium Manganese Oxide Cathode Materials

In recent years,with the proposal of"emission peak and carbon neutrality"dual carbon goals,it has become a consensus to promote industrial structure upgrading and economic structure reform,as well as to promote the clean and green industrial chain.Lithium-ion batteries were favored by the market due to their advantages of high energy density,long life-span,high safety and environmentally friendly,and now are widely used in electronics,electric vehicles,large-scale energy storage systems and so on.Compared with the current widely used commercial lithium-ion batteries cathode materials,which are mostly relied on the high cost transition metal elements of cobalt(Co)and nickel(Ni),manganese(Mn)-based layered oxides due to its abundant,cheap and non-toxic Mn resources,as well as high practical capacity,were considered as the most promising materials for the next generation lithium-ion batteries cathode materials.However,Mn-based layered oxide cathode materials are suffered from lattice oxygen(O)loss and structure migration during cycling,which caused severe electrochemical decay and greatly hindered their practical applications.In this thesis,we carried out the studies from basic composition and structural design issues,then addressing a deep scientific understanding of the intrinsic structural instability of Mn-based layered oxide cathode materials,and also provide new design concepts and approaches for the development of Mn-based cathode materials with both high cycling stability and high specific capacity.Firstly,following with the rational composition regulation,the Mn-based layered oxides with different Co and Ni elemental substitution contents were synthesized,and the influences of elemental composition on the structural characterization and stability of the materials were systematically studied.We found that Co-substituted Mn-based cathode material suffered from serious phase separation and lattice O loss behavior at high charge voltage,while the Ni substitution could effectively improve the phase structure and lattice O stability.These basic elemental chemical understandings highlight the regulatory roles of elemental components on material structure and influenced the structural stability and electrochemical behavior,and further provide a new guideline for the composition choice for the development of high-performance layered Mn-based cathode materials.Subsequently,the effects of the arrangement of structural units in the transition metal layers on the lattice oxygen and structural stability of the layered Li-rich Mn-based cathode materials were investigated.We synthesized a layered Li-rich Mn-based cathode material with delocalized Li@Mn₆ superstructure units in the transition metal layers,and found the prepared material exhibits suppressed structural deterioration originated from transition metals migration and lattice O loss upon cycling,and thus shows decent structural stability.This study deepens our understanding of the relationship between microstructure changes and material properties,and provides new concepts for the exploration of next generation high performance lithium-ion batteries cathode materials with reversible anionic redox behavior.Finally,we revealed the important role of the antisites in the structural stability of layered Mn-based cathode materials with tetrahedral sites Li⁺ions storage.It was found that antisites-rich structure was generated in the bulk after initial activation process of the as-prepared layered Mn-based cathode material and constructed a stable structural framework.The elastic lattice with rich antisites structure can withstand the huge lattice change caused by excessive Li⁺ions insertion,thus the material can achieve an ultra-high reversible specific capacity with long-term cyclic stability.This study extends our understanding of the roles of anti-site structure,and provides a new strategy for the development of new generation layered lithium-ion batteries cathode materials with both high capacity and high stability.In general,this thesis systematically studied the influences of the microstructure change on the electrochemical properties in layered Mn-based cathode materials.These studies not only deepen the understanding of the structure characteristics and stability of layered Mn-based cathode materials from the perspective of the underlying structure of materials,but also provide new guidelines and feasible paths for the exploration of high-performance cathode materials.