Preparation And Performance Control Of Spinel-structured Manganese Oxide-based Semi-solid Flow Electrode Materials

In recent years,with the development of the global economy,energy problems have become increasingly serious,developing green and sustainable energy technologies is urgent.The energy storage technology currently used has problems such as high cost and weak applicability,which is not suitable for large-scale energy storage.Semi-solid flow capacitor,which combines the advantages of the independent adjustable energy density and power density of the flow battery and good cycle stability of supercapacitors,shows great potential in the field of large-scale energy storage.However,the semi-solid flow electrode used for energy storage mainly has the problems of high viscosity and low conductivity.In particular,the preparation of a semi-solid flow electrode with both low viscosity and high conductivity is still a huge challenge,which related to its structure closely.Herein,from the perspective of semi-solid flow electrode microstructure design,we synthesized the spinel structure lithium manganate microspheres(LMO_(sph))by co-precipitation method and high-temperature calcination method.On this basis,we prepared the LMO_(sph)/PANI(polyaniline)composite materials and analyzed the composition,phase,structure and electrochemical properties of LMO_(sph)and LMO_(sph)/PANI by using multiple characterization techniques.Semi-solid flow electrodes of different microstructures were prepared with LMO_(sph),LMO_(sph)/PANI and spinel structure LMO with irregular morphology purchased from the market(LMO_(com))as the active material,and the effect of microstructure on the conductivity,rheology and electrochemical performance of the semi-solid flow electrodes were studied.The following results were achieved:1.Single phase spinel structure lithium manganate porous microspheres with uniform particle size distribution was synthesized.By adjusting the mass ratio of LMO_(sph)to aniline hydrochloride,LMO_(sph)/PANI composites were prepared.It was found that when mass ratio of LMO_(sph)to aniline hydrochloride is 2:1,the LMO_(sph)/PANI(2:1)sample has a porous spherical morphology and the particle size is basically the same as that of LMO_(sph).The thickness of the PANI coating on the surface of LMO_(sph)was about 5-20 nm.The content of PANI in LMO_(sph)/PANI(2:1)sample is about 10 wt%.LMO_(sph)/PANI(2:1)has a high specific capacity of91.2 m A h g^-1,which is 5%higher than that of LMO_(sph)(86.6 m A h g^-1).2.By controlling the morphology of the LMO particles and coating the PANI conductive layer on its surface,the viscosity of the semi-solid fluid electrode is effectively reduced,and its conductivity is improved at the same time.When the shear rate is 100 s^-1,the viscosity of the flow electrode made of spherical LMO is 4.5 times lower than that of the flow electrode made of irregular LMO;The electronic conductivity of the flow electrode coated the PANI conductive layer is 15.2 m S cm^-1,which is 10 times higher than that of the flow electrode without the PANI coating.3.Under static conditions,the semi-solid flow capacitor demonstrated in this paper has a high volume energy density of 27.4 W h L^-1,which is the highest value ever reported for aqueous semi-solid flow capacitors.In addition,the capacitor showed excellent cycle stability,the coulombic efficiency is 97.6%after 500 cycles,and it can operate stably in intermittent flow mode.The strategies developed in this work can also provide references for other flow electrochemical energy storage systems.