| Lithium ion batteries(LIBs)with long cycling life and high safety becomes one of the main concerns in buiding the better energy storage devices.At present,the Li4Ti5O12(LTO)spinel has drawn increasingly more attention due to its ultralong cycling life and outstanding safety performance.However,the LTO electrode suffers from the notorious package swelling,which a major challenge for LTO battery in practical applications.In this context,a systematic study is carried out on the material synthesis,surface modification,electrochemical performance and atomic-scale structural characteristics of LTO spinel,aimg to elucidate the working mechanism in LIBs.The LTO samples are prepared usng a high temperature solid state method The structure and morphology of the prepared materials are characterized by XRD,SEM,TEM and elemental scanning spectroscopy.And furthermore,the influences from the lithium salt,calcination temperature and reaction time on the structure,morphology and electrochemical performance of LTO are explored carefully.The results show that the best LTO electrode material can be prepared by calcining Li2CO3 as lithium salt at 850℃ for 16 hours.Next,the prepared material is subjected to surface modification treatment,and a carbon or aluminum oxide thin layer is coated on the as-prepared LTO sample by a liquid phase coating method.This surface modification is able to change the electrochemical activity of LTO surface.Electrochemical characterization shows that the surface coating of carbon or alumina on LTO not only shows the different interfacial Li diffusion kinetics,but also can block the adsorption of water and direct contact with the surface Ti-O dangling bond,thus determining the long cycle performance of LTO half-cell.Further,this paper reveals the phenomenon of synergistic gas releasing mechanism near surfacial structure of LTO,and clarifies the physical structure mechanism of LTO gas production from the perspective of surface structure change,The package swelling issues of LTO batteries is ascribed to the surfacial electrochemical activities,but the gas production process and incentives have been controversial.The structural relaxation/reconstruction leads to the formation of the Li-Ti antisites on the surface of LTO,which will Ti ions on the surface 16d migrate into the lithium insertion position of 16c,thereby causing the nagetive polarization of oxygens along the Ti-O dangling bonds.Therefore,the surface exposed oxygen atoms have strong Lewis basicity and act as a catalytic center,participating in the side reaction process of the electrode-electrolyte interface.The gas chromatography-mass(GC-MS)characterization shows that the Lewis basic centers catalyze the addition-elimination reaction of carbonate solvents in the liquid electrolyte that contains even trace amounts of water,resulting the CO2,CH3OH,etc..This intrinsic surface process can be suppressed by the surface modification,and the catalytic strength can be controlled via regulating the lattice distortion,controlling the water absorption and even the selective adsorption ability near the interface of the surface,and the gas production process can be suppressed.The gas production mechanism of LTO catalyzing electrolyte decomposition during electrochemical cycling was discussed.A series of important conclusions were obtained.It has guiding significance for lithium ion battery material design and mechanism knowledge,and deepened the interface of rechargeable battery Understanding. |
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