The residual Li and Li^(+)/Ni_(2)+cation mixing play essential roles in the electrochemical properties of Ni-rich cathodes.However,a general relationship between the residual Li conversion,cation mixing,and their effe...The residual Li and Li^(+)/Ni_(2)+cation mixing play essential roles in the electrochemical properties of Ni-rich cathodes.However,a general relationship between the residual Li conversion,cation mixing,and their effects on the Li^(+)kinetics and structural stability has yet to be established,due to the presence of cobalt in the cathode.Here,we explore the synergistic impact of the residual Li conversion and cation ordering on a Co-free Ni-rich cathode(i.e.,LiNi0.95Mn0.05O_(2)).It discloses that the rate capability is mainly affected by residual Li contents and operating voltage.Specifically,residual Li can be electrochemically converted to cathode electrolyte interphase(CEI)below 4.3 V,thus inducing high interphase resistance,and decomposes to produce CO_(2)-dominated gas at 4.5 V,causing temporary enhancement of Li^(+)diffusivity but severe surface degradation during cycling.Moreover,the cycling performance of Co-free Ni-rich cathode is not only determined by Li^(+)/Ni_(2)+cation-ordered superlattice,which enhances the structural stability as it functions as the pillar to impede lattice collapse at a highly charged state,but also by the robust CEI layers which protect the bulk from electrolyte attack under 4.3 V.These findings promote an in-depth understanding of residual Li conversion and Li^(+)/Ni_(2)+cation ordering on Co-free Ni-rich cathode.展开更多
Transition metal cation ordering is essential for controlling the electrochemical performance of cubic spinel LiNi_(0.5)Mn_(1.5)O_(4)(LNMO),which is conventionally adjusted by optimizing the high temperature sintering...Transition metal cation ordering is essential for controlling the electrochemical performance of cubic spinel LiNi_(0.5)Mn_(1.5)O_(4)(LNMO),which is conventionally adjusted by optimizing the high temperature sintering and annealing procedures.In this present work,multiple characterization techniques,including 6,7Li NMR,XRD and HRTEM,have been combined to trace the phase transformation and morphology evolution during synthesis.It has been illustrated that simultaneous formation of LiMn_(2)O_(4)(LMO)and LiNiO_(2)(LNO)binary oxides and their conversion into highly reactive LixNi^(3+)_(y)Mn_(3.5+)_(z)O ternary intermediate is a thermal dynamically difficult but crucial step in the synthesis of LNMO ternary oxide.A new strategy of modifying the intermediates formation pathway from binary mode to ternary mode using thermal regulating agent has been adopted.LNMO synthesized with thermal regulating agent exhibits supreme rate capability,long-cycling performance(even at elevated temperature)and excellent capacity efficiency.At a high rate of 100 C,the assembled battery delivers a discharge capacity of 99 mAh g^(-1).This study provides a way to control the formation pathway of complex oxides using thermal regulating agent.展开更多
基金supported by the National Natural Science Foundation of China(No.51774051)the Science and Technology Planning Project of Hunan Province(No.2019RS2034)+1 种基金the Hunan High-tech Industry Science and Technology Innovation Leading Plan(No.2020GK2072)the Changsha City Fund for Distinguished and Innovative Young Scholars(No.KQ1707014).
文摘The residual Li and Li^(+)/Ni_(2)+cation mixing play essential roles in the electrochemical properties of Ni-rich cathodes.However,a general relationship between the residual Li conversion,cation mixing,and their effects on the Li^(+)kinetics and structural stability has yet to be established,due to the presence of cobalt in the cathode.Here,we explore the synergistic impact of the residual Li conversion and cation ordering on a Co-free Ni-rich cathode(i.e.,LiNi0.95Mn0.05O_(2)).It discloses that the rate capability is mainly affected by residual Li contents and operating voltage.Specifically,residual Li can be electrochemically converted to cathode electrolyte interphase(CEI)below 4.3 V,thus inducing high interphase resistance,and decomposes to produce CO_(2)-dominated gas at 4.5 V,causing temporary enhancement of Li^(+)diffusivity but severe surface degradation during cycling.Moreover,the cycling performance of Co-free Ni-rich cathode is not only determined by Li^(+)/Ni_(2)+cation-ordered superlattice,which enhances the structural stability as it functions as the pillar to impede lattice collapse at a highly charged state,but also by the robust CEI layers which protect the bulk from electrolyte attack under 4.3 V.These findings promote an in-depth understanding of residual Li conversion and Li^(+)/Ni_(2)+cation ordering on Co-free Ni-rich cathode.
基金financially supported by the National Natural Science Foundation of China(Grant No.21673065 and 21875057)the Key-Area Research and Development Program of Guangdong Province(No.1934212200002)the Innovation and Entrepreneurship Team Project of Zhuhai(No.ZH01110405170016PWC)。
文摘Transition metal cation ordering is essential for controlling the electrochemical performance of cubic spinel LiNi_(0.5)Mn_(1.5)O_(4)(LNMO),which is conventionally adjusted by optimizing the high temperature sintering and annealing procedures.In this present work,multiple characterization techniques,including 6,7Li NMR,XRD and HRTEM,have been combined to trace the phase transformation and morphology evolution during synthesis.It has been illustrated that simultaneous formation of LiMn_(2)O_(4)(LMO)and LiNiO_(2)(LNO)binary oxides and their conversion into highly reactive LixNi^(3+)_(y)Mn_(3.5+)_(z)O ternary intermediate is a thermal dynamically difficult but crucial step in the synthesis of LNMO ternary oxide.A new strategy of modifying the intermediates formation pathway from binary mode to ternary mode using thermal regulating agent has been adopted.LNMO synthesized with thermal regulating agent exhibits supreme rate capability,long-cycling performance(even at elevated temperature)and excellent capacity efficiency.At a high rate of 100 C,the assembled battery delivers a discharge capacity of 99 mAh g^(-1).This study provides a way to control the formation pathway of complex oxides using thermal regulating agent.
