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Building ultraconformal protective layers on both secondary and primary particles of layered lithium transition metal oxide cathodes


Despite their relatively high capacity, layered lithium transition metal oxides suffer from crystal and interfacial structural instability under aggressive electrochemical and thermal driving forces, leading to rapid performance degradation and severe safety concerns. Here we report a transformative approach using an oxidative chemical vapour deposition technique to build a protective conductive polymer (poly(3,4-ethylenedioxythiophene)) skin on layered oxide cathode materials. The ultraconformal poly(3,4-ethylenedioxythiophene) skin facilitates the transport of lithium ions and electrons, significantly suppresses the undesired layered to spinel/rock-salt phase transformation and the associated oxygen loss, mitigates intergranular and intragranular mechanical cracking, and effectively stabilizes the cathode–electrolyte interface. This approach remarkably enhances the capacity and thermal stability under high-voltage operation. Building a protective skin at both secondary and primary particle levels of layered oxides offers a promising design strategy for Ni-rich cathodes towards high-energy, long-life and safe lithium-ion batteries.

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Research at the Argonne National Laboratory was funded by the US Department of Energy, Vehicle Technologies Office. Use of the Advanced Photon Source and the Centre for Nanoscale Materials, both Office of Science user facilities, was supported by the US Department of Energy, Office of Science and Office of Basic Energy Sciences, under contract no. DE-AC02-06CH11357. Research in Hong Kong was funded by the Hong Kong Research Grant Council (PolyU163208/16P), a postgraduate studentship from HKUST and the area of Excellence fund of HKPolyU (1-ZE30). G.-L.X., Z.C. and K.A. gratefully acknowledge support fromt the US department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Office. K.A., F.P. and M.O. also thank Clean Vehicles, US–China Clean Energy Research Centre (CERC-CVC2), for support.

Author information

K.A., G.C. and G.-L.X. initiated this research project. Q.L. carried out oCVD with help from K.K.S.L. and performed the half-cell performance test with the help of J.L. and M.S. G.-L.X. performed the full-cell performance test. Q.L. and G.-L.X. performed morphology and physical structure analysis. G.-L.X., H.G., M.Z., F.P., Z.C. and Y.R. conducted in situ HEXRD measurement and analysis. G.-L.X., X.Z. and Y.L. conducted focused ion beam TEM characterization and analysis. X.L. and M.O. performed thermal stability and oxygen evolution characterization on charged cathodes. G.-L.X., Q.L., K.A. and G.C. prepared the manuscript with input from all authors.

Competing interests

The authors declare no competing interests.

Correspondence to Khalil Amine or Guohua Chen.

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Fig. 1: The oCVD process and particle structural differences between different coatings.
Fig. 2: Surface characterization confirming the formation of PEDOT skin.
Fig. 3: TEM results confirming PEDOT coating on secondary/primary particles of NCM cathodes.
Fig. 4: In situ synchrotron HEXRD characterization of bare NCM111 and 60-PEDOT@NCM111 cathodes during charge–discharge.
Fig. 5: The effects of PEDOT coating on electrochemical performance.
Fig. 6: The structural stability of the 60-PEDOT@NCM111 cathode after cycling.
Fig. 7: The effect of PEDOT coating on stabilizing the cathode–electrolyte interface.
Fig. 8: Effect of PEDOT coating on thermal stability of NCM111 cathode.