The effect of partial substitution of Mg for Ni on a high-sodium and lithium-free layered P2-type Na_(45/54)Mg_(6)/_(54)Ni_(12/54)Mn_(34/54)O_(2) cathode with high initial Coulombic efficiency and excellent cyclic sta...The effect of partial substitution of Mg for Ni on a high-sodium and lithium-free layered P2-type Na_(45/54)Mg_(6)/_(54)Ni_(12/54)Mn_(34/54)O_(2) cathode with high initial Coulombic efficiency and excellent cyclic stability has been investigated in this study.Based on the crystal structural analysis,the Mg doping can retain the P2 structure up to 4.3 V,thus restraining the detrimental phase transformation of P2-02during the Na-ion intercalation/deintercalation process.Therefore,the obtained Mg-doped P2-type cathode exhibits a reversible specific capacity of 109 mAh·g^(-1) at 0.1C between 2.0 and 4.3 V and a retention rate of 81.5% after 200cycles at 1C.In addition,the full cell consisting of Mg-doped P2-type cathode and hard carbon anode shows a capacity retention rate of 85.6% after 100 cycles.This study provides new insight into the development of durable cathode materials for sodium-ion batteries.展开更多
Due to their high capacity,the P2-type layered oxide cathodes containing oxygen redox reaction processes have attracted wide attention for sodium-ion batteries.However,these materials usually exhibit poor electro-chem...Due to their high capacity,the P2-type layered oxide cathodes containing oxygen redox reaction processes have attracted wide attention for sodium-ion batteries.However,these materials usually exhibit poor electro-chemical properties,resulting from irreversible oxygen redox reactions and phase transition processes at high voltages,and thus hinder their large-scale application.This work reveals the mechanism for the significantly improved cycle stability and rate performance of Co/Ni-free Na_(0.7)5Li_(0.25-2/3x)CuxMn_(0.75-1/3x)O_(2)via Cu doping.Ex-situ XPS demonstrates that Cu doping reduces the amount of Mn^(3+)that triggers the Jahn-Teller effect during the cycling.In addition,the electron enrichment of oxygen around Cu can alleviate the irreversible oxidation of oxygen,and thus suppressing the phase transition originates from the rapid weakening of the electrostatic repulsion between O-O.Meanwhile,in-situ XRD results verify that the Na_(0.7)5Li_(0.19)Cu_(0.09)Mn_(0.7)2O_(2)maintains the P2 phase structure during charging and discharging,resulting in a near-zero strain characteristic of 1.9%.Therefore,the optimized cathode delivers a high reversible capacity of 194.9 mAh g−1 at 0.1 C and excellent capacity retention of 88.6%after 100 cycles at 5 C.The full cell paired with commercial hard carbon anode delivers energy density of 240 Wh kg−1.Our research provides an idea for designing a new type of intercalated cathode for sodium-ion batteries with low cost and high energy density.展开更多
基金financially supported by the National Natural Science Foundation of China (No.21978193)the Natural Science Foundation of Shanxi Province (Nos.20210302123107, 20181102005, and 20181102019)。
文摘The effect of partial substitution of Mg for Ni on a high-sodium and lithium-free layered P2-type Na_(45/54)Mg_(6)/_(54)Ni_(12/54)Mn_(34/54)O_(2) cathode with high initial Coulombic efficiency and excellent cyclic stability has been investigated in this study.Based on the crystal structural analysis,the Mg doping can retain the P2 structure up to 4.3 V,thus restraining the detrimental phase transformation of P2-02during the Na-ion intercalation/deintercalation process.Therefore,the obtained Mg-doped P2-type cathode exhibits a reversible specific capacity of 109 mAh·g^(-1) at 0.1C between 2.0 and 4.3 V and a retention rate of 81.5% after 200cycles at 1C.In addition,the full cell consisting of Mg-doped P2-type cathode and hard carbon anode shows a capacity retention rate of 85.6% after 100 cycles.This study provides new insight into the development of durable cathode materials for sodium-ion batteries.
基金financially supported by the National Natural Science Foundation of China(22271211)the Natural Science Foundation of Shanxi Province(20210302123107 and 202202060301018)。
文摘Due to their high capacity,the P2-type layered oxide cathodes containing oxygen redox reaction processes have attracted wide attention for sodium-ion batteries.However,these materials usually exhibit poor electro-chemical properties,resulting from irreversible oxygen redox reactions and phase transition processes at high voltages,and thus hinder their large-scale application.This work reveals the mechanism for the significantly improved cycle stability and rate performance of Co/Ni-free Na_(0.7)5Li_(0.25-2/3x)CuxMn_(0.75-1/3x)O_(2)via Cu doping.Ex-situ XPS demonstrates that Cu doping reduces the amount of Mn^(3+)that triggers the Jahn-Teller effect during the cycling.In addition,the electron enrichment of oxygen around Cu can alleviate the irreversible oxidation of oxygen,and thus suppressing the phase transition originates from the rapid weakening of the electrostatic repulsion between O-O.Meanwhile,in-situ XRD results verify that the Na_(0.7)5Li_(0.19)Cu_(0.09)Mn_(0.7)2O_(2)maintains the P2 phase structure during charging and discharging,resulting in a near-zero strain characteristic of 1.9%.Therefore,the optimized cathode delivers a high reversible capacity of 194.9 mAh g−1 at 0.1 C and excellent capacity retention of 88.6%after 100 cycles at 5 C.The full cell paired with commercial hard carbon anode delivers energy density of 240 Wh kg−1.Our research provides an idea for designing a new type of intercalated cathode for sodium-ion batteries with low cost and high energy density.
