Synthesis–structure relationships in Li- and Mn-rich layered oxides: phase evolution, superstructure ordering and stacking faults. Issue 11 (28th February 2022)

• Record Type: Journal Article
• Authors: Menon, Ashok S.; Khalil, Said; Ojwang, Dickson O.; Edström, Kristina; Gomez, Cesar Pay; Brant, William R.
• Is Part Of: Dalton transactions. Volume 51:Issue 11(2022)
• Page Start: 4435
• Page End: 4446
• Publication Date: 2022-02-28
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/d2dt00104g
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : Systematic investigation of synthesis-dependent structural changes in Li- and Mn-rich layered oxides. Abstract : Li- and Mn-rich layered oxides are promising positive electrode materials for future Li-ion batteries. The presence of crystallographic features such as cation-mixing and stacking faults in these compounds make them highly susceptible to synthesis-induced structural changes. Consequently, significant variations exist in the reported structure of these compounds that complicate the understanding of how the crystallographic structure influences its properties. This work investigates the synthesis–structure relations for three widely investigated Li- and Mn-rich layered oxides: Li2 MnO3, Li1.2 Mn0.6 Ni0.2 O2 and Li1.2 Mn0.54 Ni0.13 Co0.13 O2 . For each compound, the average structure is compared between two synthetic routes of differing degrees of precursor mixing and four annealing protocols. Furthermore, thermodynamic and synthesis-specific kinetic factors governing the equilibrium crystallography of each composition are considered. It was found that the structures of these compounds are thermodynamically metastable under the synthesis conditions employed. In addition to a driving force to reduce stacking faults in the structure, these compositions also exhibited a tendency to undergo structural transformations to more stable phases under more intense annealing conditions. Increasing the compositional complexity introduced a kinetic barrier to structural ordering, making Li1.2 Mn0.6 Ni0.2 O2 and Li1.2 Mn0.54 Ni0.13 Co0.13 O2 generally more faulted relative to Li2 MnO3 . Additionally, domains with different degrees of faulting were found to co-exist in the compounds. This study offers insight into the highly synthesis-dependent subtle structural complexities present in these compounds and complements the substantial efforts that have been undertaken to understand and optimise its electrochemical properties.