Gas-mediated defect engineering in earth-abundant Mn-rich layered oxides for non-aqueous sodium-based batteries

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Abstract
Gases are often by-products of battery materials during cell formation and degradation, affecting the cycle life and safety of rechargeable batteries. However, understanding gas-mediated (electro)-chemical reactions and nanoscale structural transformations during the synthesis of battery electrode materials remains challenging because of the lack of suitable characterization routes and the complexity of the interplay between thermodynamics and kinetics. Here we use operando synchrotron X-ray diffraction, in situ transmission X-ray microscopy and multiscale modelling to elucidate the reaction pathways and microstructural defect development of earth-abundant Mn-rich layered oxides as positive electrode materials for sodium-based batteries. In particular, we demonstrate the dominant role of CO2 over O2 and H2O(g) in modulating the competition between entropy and enthalpy during solid-state synthesis. Using Ni0.25Mn0.75CO3 as a model precursor, we reveal that CO2 generation favours the formation of entropy-driven metastable intermediates, suppresses closed pore/nanovoids formation and decreases chemical heterogeneity and residual lattice strain of Mn-rich layered oxides during the synthesis. This result motivates a fast-sintering strategy to promote CO2 release, which ultimately leads to improved chemo-mechanical and electrochemical stability of the Mn-rich positive electrodes when tested in non-aqueous Na metal coin cells.
Funding Information
  • DOE | Office of Energy Efficiency & Renewable Energy | Vehicle Technologies Office (DE-AC02-06CH11357, DE-AC02-06CH11357, DE-AC02-06CH11357, DE-AC02-06CH11357, DE-AC02-06CH11357, DE-AC02-06CH11357, DE-AC02-06CH11357, DE-AC02-06CH11357, DE-AC02-06CH11357)
  • DOE | SC | Basic Energy Sciences (DE-AC02-06CH11357, DE-AC02-06CH11357, DE-AC02-06CH11357, DE-AC02-06CH11357, DE-AC02-06CH11357, DE-SC0012704, DE-SC0012704, DE-SC0012704)

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