Study On CVD Preparation Techniques And Performances Of Flexible Electrodes

Future wearable electronic devices require advanced fabrication techniques to achieve more favorable performances.However,one of the common issues for these devices is to keep the robust connection between the active material and the conductive matrix while the device undergoes severe deformation.Chemical Vapor Deposition?CVD?is a widely used technique that can produce conformal surface coatings on other matrices and keep strong attachment during deformation.In this study,a variety of flexible electrodes were prepared using CVD.The electrochemical properties of the as-prepared electrodes were tested in lithium/sodium-ion batteries.By building up the relationship between physiochemical and theoretical parameters,the effects of processing on the performance of flexible electrodes were discussed.The main conclusions are as follows:?1?The effects of CVD parameters on the morphologies and mass loadings of iron phosphate?FP?coated electrodes used in lithium battery were studied.The relationship between the phase,thickness and electrochemical performance was systematically discussed.The amorphous FP film can be uniformly coated on the surface of carbon nanotubes at the suitable deposition conditions.With the increase of reaction time and the decrease of deposition pressure,the mass loading of FP in the composites increased simultaneously with the growing of thickness and density of FP film.The amorphous iron phosphate?a-FP?provides important kinetic advantages.The thicker FP coating showed inferior rate performance due to the delamination of the FP layer,while the thin FP coating provided the short paths for Li-ion diffusivity within the active FP materials and excellent rate performance can be achieved.?2?A successful chemical vapor deposition approach for coating a conformal amorphous iron?III?phosphate?a-FP?on the surface of flexible CNT fabric was proposed.The effect of FP thickness on their electrochemical performance of sodium?Na?battery and mechanical properties was studied.The electrodes with thicker FP coatings showed very low initial capacity,which may potentially be related to poor initial electrolyte wetting.Yet,with continuous cycling,their overall electrochemical performance increased,which can be explained by the FP electrode swelling possibly originating from the stresses within the electrodes during insertion and extraction of large Na⁺.In addition,the combination of FP film and CNT can effectively prevent active materials falling off from substrates under bending and stretching conditions.?3?Polymer-infiltrated CNT@FP electrodes were fabricated.The effects of infiltrated polymer on the mechanical properties of the CNT@FP electrodes were evaluated.The electrochemical properties of polymer-infiltrated CNT@FP flexible electrodes in solid-state battery were studied by adjusting the content of Al₂O₃nanofiber in polymer membranes.The strain of CNT@FP electrode was increased due to the addition of PEO.Due to the coordination of Li with O atoms on the surface of Al₂O₃ nanofibers,the stability of cycling performances was increased and the electrochemical stability windows of separators was broadened.The all solid-state polymer battery showed an excellent capacity at 50 ^oC.?4?A Li_xFePO₄?CNT@L_xFP?conformal layer was deposited on CNT fabric by CVD technique,the phase composition and electrochemical performance were studied.The Li_xFePO₄ layer was composed of FP and LFP.An amorphous FP coated crystallized LFP structure was obtained after annealing.The amorphous FP coating released the inner stress of LFP particles,therefore the cycling performance of CNT@L_xFP flexible electrode was optimized when compared to that of commercial LFP electrode.