06-nature-2022-early-stop

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Abstract chars: 1427

Li- and Mn-rich (LMR) cathode materials that utilize both cation and anion redox can yield substantial increases in battery energy density 1-3 . However, although voltage decay issues cause continuous energy loss and impede commercialization, the prerequisite driving force for this phenomenon remains a mystery 3-6 Here, with in situ nanoscale sensitive coherent X-ray diffraction imaging techniques, we reveal that nanostrain and lattice displacement accumulate continuously during operation of the cell. Evidence shows that this effect is the driving force for both structure degradation and oxygen loss, which trigger the well-known rapid voltage decay in LMR cathodes. By carrying out micro- to macro-length characterizations that span atomic structure, the primary particle, multiparticle and electrode levels, we demonstrate that the heterogeneous nature of LMR cathodes inevitably causes pernicious phase displacement/strain, which cannot be eliminated by conventional doping or coating methods. We therefore propose mesostructural design as a strategy to mitigate lattice displacement and inhomogeneous electrochemical/ structural evolutions, thereby achieving stable voltage and capacity profiles. These findings highlight the significance of lattice strain/displacement in causing voltage decay and will inspire a wave of efforts to unlock the potential of the broad-scale commercialization of LMR cathode materials.

Sections

• Body (3150 chars)
• Initial structure/electrochemical properties (3079 chars)
• Strain evolution observed through BCDI (4062 chars)
• Origin and relaxation of tensile strain (4986 chars)
• Atomic observation of lattice displacement (3483 chars)
• A prospect for LMR cathode development (4066 chars)
• Online content (135 chars)
• Materials synthesis (2302 chars)
• Electrochemistry tests (1535 chars)
• BCDI and coherent multiple crystal diffraction (2447 chars)
• Synchrotron X-ray diffraction and absorption spectroscopy measurements (1594 chars)
• DFT calculation (1004 chars)
• Gas evolution analysis (935 chars)
• TEM measurement (549 chars)

Low Coverage Blocks

• p1 metadata coverage=0.0: 1Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, IL, USA. 2School of Advanced Materials, Peking University, Shenzhen Graduate School, Shenzhen, China. 3X‐ray Science Division, Argonne National Laboratory, Lemont, IL, USA. 4Cent
• p2 scientific_body coverage=0.0: Regular ‘bright–bright–dark’ arrangements are identified as Li2MnO3 domains, which are characterized by the well-known honeycomb Li–Mn ordering. LiTMO2 domains are identified with no distinguished dark spots in the bright spot columns. e, Schematic structure o
• p3 scientific_body coverage=0.0: respectively. The strain evolution in each state is detailed by the spatial location of the slices along the y axis. m, In situ differential electrochemical mass spectroscopy measurements for the LMR primary particle. n, Formation energy of O vacancies in Li2M
• p5 scientific_body coverage=0.0: delithiated sample (4.5 V) at a certain angle of rotation. h, Low-magnification TEM image of the LMR cathode charged to 4.8 V. i, j, EELS line-scan of O K edge (i) and Mn L2,3 edge (j) of the LMR cathode charged to 4.8 V. k, 2D EELS mapping of Mn–L3/L2. The hi
• p6 scientific_body coverage=0.286: which results in tensile strain at the nanoscale. The accumulated tensile strain severely affects the structural stability of the composite LMR cathode, which may trigger the decomposition of Li2MnO3 domains, oxygen release and transition metal (TM) migration.
• p10 back_matter coverage=0.005: Acknowledgements We gratefully acknowledge support from the US Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Office. This work was also supported by the Clean Vehicles, US–China Clean Energy Research Centre
• p10 back_matter coverage=0.0: Author contributions T.L., J. Liu, L.L., J. Lu, F.P. and K.A. conceived the idea and designed the experiments. T.L., J. Liu, R.Q. and S.X. synthesized all the materials and conducted electrochemical measurements. J. Liu, L.Y., T.Z., Y.X., W.Z. and J.W. carried
• p10 scientific_body coverage=0.0: Additional information Correspondence and requests for materials should be addressed to Jun Lu, Feng Pan or Khalil Amine. Peer review information Nature thanks Doron Aurbach and the other, anonymous, reviewer(s) for their contribution to the peer review of thi
• p11 scientific_body coverage=0.0: corresponding BET plot of LMR. The nitrogen adsorption/desorption isotherm and the corresponding BET plot of the as-prepared LMR cathode indicate that its specific surface area is calculated to be 2.804 m2 g−1. f SEM-EDS results of the pristine LMR cathode. Th
• p11 scientific_body coverage=0.0: Extended Data Fig. 1 | The morphology, particle distribution, surface area and composition of the LMR cathode. a, b The SEM image of the LMR powder. The particle size ranges from 200–600 nm. c The particle size distribution of the as-prepared LMR cathode. The
• p12 scientific_body coverage=0.061: extraction and at this stage oxygen is oxidized (at high potentials) to per-oxo species: (2O2− ↔ [O2]2− + 2e−). c, d The galvanostatic intermittent titration technique (GITT) test of the first charge. The Li-ion diffusion coefficient keeps stable in stage 1 bu
• p12 scientific_body coverage=0.108: Extended Data Fig. 2 | The electrochemical properties of the LMR cathode. a, b The first charge/discharge curve and corresponding dQ/dV curve of LMR cathode. The first charge profile exhibits two distinct electrochemical stages at different voltage ranges. Sta
• p13 scientific_body coverage=0.018: Extended Data Fig. 3 | The morphology, particle distribution, surface area and in situ DEMS of the Li2MnO3 cathode. a The SEM image of the as-prepared Li2MnO3 powder. The as-prepared Li2MnO3 exhibits a single-particle morphology with average particle size of 1
• p14 scientific_body coverage=0.0: (1C = 250 mA g-1). The obvious lattice parameter changes can be observed from in situ XRD patterns, particularly in the 2 theta range of 1.3–1.5°. Generally, the structure evolution observed in in situ XRD is completely consistent with that in ex situ XRD (Fig
• p14 scientific_body coverage=0.046: Extended Data Fig. 4 | The ex situ and in situ XRD and ex situ XAS of the LMR cathode. a The ex situ XRD patterns of the first charge/discharge for the LMR cathode. The superlattice evolution of the LMR cathode can be observed in the 2 theta range of 1.5–1.8°.
• p15 scientific_body coverage=0.1: Extended Data Fig. 5 | Visible lattice displacement observations using TEM of the LMR charged to 4.47 V. High magnification TEM image of the LMR charged to 4.47 V. Although the layered structure is maintained, lattices in the marked areas are deformed signific
• p16 scientific_body coverage=0.0: cathode charged to 4.5 V. The lattice displacements are highlighted with yellow marks. k, l and m The corresponding FFT images of Extended Data Fig. 6h, i and j. Obvious lattice displacements are observed in the different particles and the corresponding FFT im
• p18 scientific_body coverage=0.0: Extended Data Fig. 8 | Lattice displacement and structure changes observed from 3D-rED and SAED. a, b The reciprocal lattice viewed along the a* axis of the LMR cathode at 4.5 V. c The selected area electron diffraction (SAED) image of the sample charged to 4.
• p19 metadata coverage=0.0: Extended Data Fig. 9 | Visible structural observations and chemical state changes of the LMR charged to 4.8 V. a, b Low and High magnification TEM image of the LMR charged to 4.8 V. A clear reconstruction surface layer with the spinel phase can be visualized.
• p19 metadata coverage=0.077: substantially reduces from the interior to the exterior and almost disappears near the surface. Concurrently, Mn L-edge shows left shift near the surface. d Electron energy loss spectroscopy line scans of the O K-edge, Mn L-edge, Co & Ni L-edge for the LMR cha
• p20 scientific_body coverage=0.028: being aggregated to form a Li2MnO3-like domain. c The charge/discharge profiles of O2 phase-based LMR cathode. The cells were activated at C/10 within first 3 cycles and then cycled at C/3. The smooth charging behaviour with no apparently differentiated voltag
• p20 scientific_body coverage=0.0: Extended Data Fig. 10 | Structure and electrochemical properties of O2 phase-based LMR. a The XRD pattern of as-prepared LixNi0.13Mn0.54Co0.13O2. The diffraction peaks belonging to an O2 phase with P63mc symmetry are indexed by blue marks, while some tiny peak