Preparation And Modification Investigation Of P2 Type Ni-Mn Base Layered Oxide Cathode Materials For Sodium Ion Batteries

The development of renewable energy has put forward higher and higher requirements for energy storage devices.However,as the most successful energy storage device at present,the application of lithium-ion battery has been seriously restricted due to the resource constraints of lithium and cobalt in recent years.Sodium ion battery,as an alternative of lithium ion battery,has attracted much attention due to its high sodium abundance,low cost and similar working mechanism with lithium ion battery.However,the lack of suitable cathode materials has greatly limited its commercialization process.Among numerous cathode materials,P2 type nickel manganese base layered oxide cathode material Na_0.67Ni_0.33Mn_0.67O₂ possess the advantages of high specific capacity and operating voltage,low cost and good air stability,which is considered as a potential cathode material of sodium ion battery.However,a P2-O₂ phase transition occurs in the high voltage region,which causes serious structural damage and makes its electrochemical performance unsatisfactory.Moreover,the interface side reactions and sluggish dynamic behavior of Na⁺ diffusion also aggravate the degradation of its electrochemical performance,which severely limits its practical application.To solve the above problems,this paper adopted a series of modification methods,which effectively improve its electrochemical performance,and also many characterization methods are performed to analyze its mechanism.The relevant research results are as follows:1).A dual strategy of Mg²⁺doping integrated with ZrO₂ surface modification has been developed,which improves the structure and interface stability simultaneously.The research shows that the P2-O₂ phase transition of P2-type Na_0.67Ni_0.33Mn_0.67O₂ is effectively suppressed after Mg²⁺doping,and transforms into a P2-OP4 phase transition with better structural stability.Besides,the side reactions between cathode and electrolyte are also suppressed due to the introduction of ZrO₂ surface modification.At half cell configuration,the material after such a dual strategy modification can deliver a specific capacity of 121.9 mAh g^-1 at 0.1C as well as 81.9%capacity retention after 150 cycles at 1C.And the full cell matched with hard carbon anode can output a high operating voltage of 3.57 V and high energy density of 238.91 Wh kg^-1 under the power density of 36.73 W kg^-1.2).A dedicate multi component modulation strategy was designed,which effectively improved the electrochemical performance of P2 type Na_0.67Ni_0.33Mn_0.67O₂ by replacing Ni²⁺ with Li⁺and Mn⁴⁺with Ti⁴⁺ as well as adjusting the Na+content to make the charge balance.The research shows that the modified material exhibits an inhibited P2-O₂ phase transition and better Na⁺/vacancy disordering,and the electrochemical performance also get improved significantly.Specifically,the specific capacity can reach 128 mAh g^-1 at 0.1C,and can deliver a capacity retention of 80%after 200 cycles at 1C.The full cell matched with hard carbon anode can output a high energy density of 263.4 Wh kg^-1 at the power density of 37.3 W kg^-1.