| As a common electrochemical energy storage device,lithium ion batteries have been widely used in the 3C and electric vehicle markets.With the rapid development of electric vehicles in recent years,requirements for the safety of lithium-ion batteries become a serious issue.At present,graphite is still a common anode material of lithium ion battery.Graphite has a relatively high capacity and excellent cyclic stability.However,the low operating voltages leads to the deposition of lithium and formation of lithium dendrites,which will result in the serious safety problems.As an alternative to current carbon-based anode,Li4Ti5O12 has drawn much attention because of its several intrinsic advantages such as the zero-volume change during charge-discharge cycles and relatively high potential plateau(1.55 V vs.Li/Li+),which can prohibit the formation of dendritic lithium and provide a stable long cycle life.Unfortunately,the high potential plateau also results in the low energy density in full batteries compared with graphite.Therefore,it is significant to develop new titanium based anode materials with a lower operating potential.Recently,the Ruddlesden-Popper phase perovskite compound LiEuTiO4 was proposed as a promising material for LIB anodes.Among the many new Ti-based anode materials,LiEuTiO4 has many advantages like better capacity,lower operating potential and more stable cycling performances.However,LiEuTiO4 still meet some disadvantage like poor conductivity and rate performance.This paper was focused on researching methods to improve LiEuTiO4 poor electrochemical performances.The main contents are described as follows:(1)The NaEuTi04 precursors were respectively synthesized by solid phase synthesis,spray drying and sol-gel methods.The XRD results showed that the samples synthesized by sol gel and spray drying were pure phase,while the samples synthesized by solid phase had some impurities.SEM results showed that the solid-phase synthesis and sol-gel method respectively finally got bulk LiEuTiO4 materials,while the spray drying method finally got aggregated LiEuTiO4 materials.The electrochemical properties proved that the LiEuTiO4 synthesized by the sol-gel method had the best electrochemical performances,including the highest first cycle coulombic efficiency(76.47%),cycle capacity(146.6 mA h g-1 after 200 cycles)and rate performance(108.2 mA h g-1 at high current density of 1600 mAg-1).(2)A facile strategy was proposed to improve electrochemical performances of LiEuTiO4 by surface modification via pyrolysis of urea.The effects of surface modification on structure and electrochemical performances were extensively studied.SEM and TEM results indicated the pyrolysis of urea surface modification successfully lead to the formation of a nitrogen-carbon co-existed coating layer.XPS analysis confirmed the presence of N-doped carbon and TiN.The modified LiEuTiO4(C&N-Leto-50)exhibited excellent electrochemical performances,including high capacity(166.3 mA h g-at 100 mA g-1 at 1st cycle),high rate capability(129.4 mA h g-1 at 1600 mA g-1),and long cyclic stability(149.8 mA h g-1 after 650 cycles at 500 mA g-1).(3)NaEuTiO4 precursor was treated with acid,and effect of acid treatment time on the morphology,structure and electrochemical properties of the material was also studied.EDAX results showed that with the increase of acid treatment time,Na+was gradually replaced by H+in NaEuTiO4.At the same time,XRD results showed that the crystallinity of the material was better when the acid treatment time was over 6 hours.The Neto-acid-12h sample showed the best electrochemical performances among the other samples,including best cycle capacity(192.9 mA g h-1 after 300 cycles),rate performance(142.7 mA g h-1 at 2000 mA g-1). |
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