Adaptive Cation Pillar Effects Achieving High Capacity in Li‐Rich Layered Oxide, Li₂MnO₃‐LiMeO₂ (Me = Ni, Co, Mn)

Abstract

Intensive research is underway to further enhance the performance of lithium‐ion batteries (LIBs). To increase the capacity of positive electrode materials, Li‐rich layered oxides (LLO) are attracting attention but have not yet been put to practical use. The structural mechanisms through which LLO materials exhibit higher capacity than conventional materials remain unclear because their disordered phases make it difficult to obtain structural information by conventional analysis. The X‐ray total scattering analysis reveals a disordered structure consisting of metal ions in octahedral and tetrahedral sites of Li layers as a result of cation mixing after the extraction of Li ions. Metal ions in octahedral sites act as rigid pillars. The metal ions move to the tetrahedral site of the Li layer, which functions as a Li‐layer pillar during Li extraction, and returns to the metal site during Li insertion, facilitating Li diffusion as an adaptive pillar. Adaptive pillars are the specific structural features that differ from those of the conventional layered materials, and their effects are responsible for the high capacity of LLO materials. An essential understanding of the pillar effects will contribute to design guidelines for intercalation‐type positive electrodes for next‐generation LIBs.

Structure and Charge Regulation Strategy Enabling Superior Cycling Stability of Ni-Rich Cathode Materials

“…Actually, the lattice collapse is caused by the oxidation of lattice O 2– ions at a high charging voltage due to the covalency between TM and oxygen ions. The O 2p band formed holes that released the anion–anion electrostatic repulsion between the neighboring oxygen layers, leading to the shrinkage of the c-lattice in the deep delithiation state. − By combining Rietveld refinements of in situ XRD, the variations of the c-lattice and the volume parameter are obtained, as shown in Figure c,d. With the continuous removal of Li + , the c value first increases and then decreases, which is in good accordance with the variation of the interlayer spacing between the two adjacent oxygen slabs mentioned above.…”

Reversible Tetrahedral-Site Migration Inducing an Additional Charge Compensation Reaction in Li-Rich Layered Oxide 0.4Li2MnO3–0.6LiNi0.5Mn0.5O2

“…For simplicity, the occupancies of Me were refined by assuming that only Ni migrated to the tetrahedral site and octahedral sites in the Li layer. 23 The equivalent analyses using Mn as the migrating cation validated this approach. Using Ni or Mn as the migrating cations gave almost identical results (Table S4).…”

A Mechanistic Insight into the Oxygen Redox of Li‐Rich Layered Cathodes and their Related Electronic/Atomic Behaviors Upon Cycling

“…[83] Hiroi et al concentrated on the role of native 3d metals in Li-rich NCM as pillars. [153] The X-ray total scattering showed that TMs moved to octahedral and tetrahedral sites in the Li layer upon charge. The TMs in the octahedral sites acted as rigid pillars, while the TMs in the tetrahedral sites acted as adaptive pillars moving back to the TM layer upon lithiation (Figure 11b).…”

“…Adapted under the terms of the CC‐BY Creative Commons Attribution 4.0 International license (https://creativecommons.org/licenses/by/4.0). [ 153 ] Copyright 2022, The Authors, published by Wiley‐VCH. c) Change of layer stacking order from the O3 to the O2 phase triggers reversible out‐of‐plane TM migration.…”

“…b) Migrated TM acting as adaptive and rigid pillars to avoid out-of-plane TM migration. Adapted under the terms of the CC-BY Creative Commons Attribution 4.0 International license (https://creativecommons.org/licenses/by/4.0) [153]. Copyright 2022, The Authors, published by Wiley-VCH.…”