| In recent years,energy storage devices have developed rapidly and lithium-ion batteries have gradually dominated the market,but the massive use of lithium resources has led to a shortage of their reserves.As the most promising next-generation alkaline ion battery,sodium ion batteries are recognized to work similarly to lithium ion batteries and have application advantages such as wide source,high safety and environmental friendliness.The development of cathode materials has become a key link in the application of sodium ion batteries.Sodium-manganese-nickel base oxide is a promising cathode material for sodium-ion batteries due to its simple preparation process,low cost and high theoretical capacity.This paper focuses on the key challenges of composition design and preparation of sodium-manganese-nickel base-like oxides.The layered cathode electrode material with relatively excellent electrochemical performance were obtained through the rational design of transition metal elements.The microstructure,sodium storage performance and mechanism of sodium-manganese-nickel layered oxides were systematically investigated using structural characterisation and electrochemical testing techniques,and full cell construction and scenario application analysis were carried out.1.Series of P2-NaxLi0.05(Mn0.65Ni0.20Fe0.15)0.95O2（x=0.70-0.85）materials were synthesized using a continuous co-precipitation-high temperature fast cooling method.The transition metal layer was constructed using Li,Mn,Fe,and Ni elements.The effects of sodium content on capacity contribution and ion diffusion of the materials were characterized by constant current charge/discharge tests,cyclic voltammetry tests and so on.XRD,SEM were used to determine the phase structure differences caused by different sodium content.Systematic studies led to the discovery of the high capacity characteristics of P2-type materials and the high cycling stability of P2/O3-composite materials.These findings offer valuable insights for future research in this field.2.Based on the study of P2-NaxLi0.05(Mn0.65Ni0.20Fe0.15)0.95O2（x=0.70-0.85）,a series of Na0.85Lix(Mn0.65Ni0.20Fe0.15)1-xO2（x=0.10-0.20）materials were constructed by adjusting the proportion of elements in the transition metal layer Through XRD and TEM characterization,the crystal structure of Na0.85Lix(Mn0.65Ni0.20Fe0.15)1-xO2 was determined as P2/O3 composite phase.Additionally,the GITT test revealed that the Na+diffusion order of P2/O3-Na0.85Lix(Mn0.65Ni0.20Fe0.15)1-xO2 was 10-10 cm2 s-1.The phase transition mechanism of L015 was determined by in situ-XRD as P2/O3→P2/P3→OP4/OP2.In terms of performance,the L015 material boasted an initial discharge specific capacity of 154.40 m Ah g-1,a first turn Coulomb efficiency of 84.41%,and a retention rate of 64.51%for 100 turns at a current density of 20 m A g-1.L015//hard carbon whole battery exhibit a reversible first cycle specific capacity of 125.40 m Ah g-1,and the first cycle Coulomb efficiency of 95.50%,and the cycle retention rate is 85.37%after undergoing 100 charge/discharge cycles at a current density of 200 m A g-1 under test conditions.The full battery has also been effectively employed in scenario applications.3.In order to further reduce the cost,to optimize the electrolyte formula and adjust the transition metal formula,NaMn2/3-x-yNi1/3Mgx CuyO2（x=0,y=0;x=1/6,y=0;x=0,y=1/6;x=1/12,y=1/12）were obtained.When copper and magnesium elements were introduced,the MN compound exhibited a composite crystal structure of P2/O3/P3.The contribution to capacity from the NaMn2/3-x-yNi1/3Mgx CuyO2 cathode material was controlled by the diffusion of sodium ions.The diffusion coefficient of NaMn2/3-x-yNi1/3Mgx CuyO2cathode can remain stable at around 10-10 cm2 s-1.Among all the materials,MNC had an initial discharge specific capacity of 110.87 m Ah g-1 at a current density of 20 m A g-1.After undergoing 100cycles,it had demonstrated a remarkable cycle retention rate of over 80%and exhibited exceptional rate performance. |
PDF Full Text Request