Modification Of Manganese-based Cathode Materials For Sodium Ion Batteries

Manganese-based materials have become one of the most attractive cathode candidates in SIBs due to their high specific capacity,abundant resources,and relatively small environmental pollution.Although the electrochemical performance of manganese-based materials has been improved to a certain extent,their electrochemical performance under high voltage or high current is still unsatisfactory due to some defects of manganese-based materials themselves.In this paper,manganese-based cathode materials are used as the main research object,and three different methods are used to optimize its electrochemical performance in SIBs.（1）Was used to prepare the three-dimensional S-shaped tunnel structure Na_0.44MnO₂ micrometer rod as the matrix was prepared via the traditional solid-phase method,and then the Na_0.44MnO₂ micrometer rod coated with different amounts of In₂O₃ was prepared by the precipitation method as the modified material.Next,the characterization of the matrix material and the modified material were analyzed,while their electrochemical performance under 2-4.5 V were tested.At the same time,the optimal In₂O₃ coating amount was explored.The results show that Na_0.44MnO₂ with1wt.% In₂O₃ coating exhibits the best electrochemical performance.Even under the current density of 1 C,its maximum discharge capacity can still reach 108.1 m Ah g^-1with the capacity retention rate of 86.7% after 400 cycles.In addition,even at 10 C,it still retains 63.7 m Ah g^-1.These data are much higher than the uncoated base material,which indicates that the In₂O₃ coating improves the electrochemical performance of Na_0.44MnO₂.（2）In view of the relatively poor electrochemical performance of Na_0.67Mn_0.65Ni_0.2Co_0.15O₂（NMNCO）,the sodium storage capacity was improved by adding different surfactants（SDS、PVP、CTAB）.Firstly,NMNCO with（or without）different surfactants were prepared by hydrothermal method as the research objects,and then the characteristics and characteristics of these materials were compared and analyzed.The research results show that NMNCO prepared with PVP as a surfactant has the most uniform morphology and the best electrochemical performance.Under the condition of 0.1 C current density and votage range of 1.5-4.3 V,the initial specific capacity of NMNCO-PVP can reach 171 m Ah g^-1.After 100 cycles,the capacity of NMNCO-PVP can remain 116 m Ah g^-1.In addition,when the current density is increased by 5 C,the discharge capacity of other materials is close to 0m Ah g^-1,while NMNCO-PVP still has a discharge capacity of 55.5 m Ah g^-1.These data of NMNCO-PVP are far superior to those of NMNCO prepared without surfactant.Therefore,it can be determined that the addition of a suitable surfactant can well improve the electrochemical performance of Na_0.67Mn_0.65Ni_0.2Co_0.15O₂.（3）The Mg-doped Na_0.67Mn_0.75Ni_0.25O₂（NMNO）cathode materials with different amounts of sodium sites were prepared by the hydrothermal-calcination method.Then,the influence of Na-site Mg doping on the morphology was explored,and sodium storage capacity of NMNCO material was investigated.Finally,the optimal doping amount of Mg was researched.The results showed that the best sodium storage performance was obtained when the molar ratio of Na to Mg was 0.47:0.1.Under 20m Ah g^-1 the current density and the wide voltage range of 1.5-4.3 V,the NMNO-Mg0.1 has a high discharge specific capacity of 213 m Ah g^-1.Even at the high current density of 500 m A g^-1,NMNO-Mg0.1 still exists a discharge specific capacity of 88 m Ah g^-1.These data are much higher than the those of undoped NMNO matrix material.Therefore,it is certain that a proper amount of Mg doping can improve the sodium storage capacity of NMNO to a certain extent.