| Lithium-ion batteries（LIBs）have been widely used in traditional portable electronic products and emerging electric vehicles due to their high energy densities.However,the scarcity of lithium resources and uneven global distribution limit its large-scale application.Compared with lithium,sodium/potassium is abundant and low-cost.More importantly,the work mechanism of sodium/potassium ion batteries（SIBs/PIBs）is similar to that of lithium-ion batteries,so SIBs/PIBs are expected to replace lithium-ion batteries in large-scale energy storage applications.However,the larger ion radius of Na+/K+（compared with Li+）leads to the slower diffusion kinetics,and the insertion of Na+/K+will cause the huge volume expansion of active material,resulting in capacity decline of battery performance.Therefore,it is a great challenge to find a suitable electrode material with high performance for both SIBs/PIBs.Molybdenum disulfide is considered as a promising electrode material due to its high specific capacity(670 m Ah g-1)and unique two-dimensional layered structure.The weak interlayer van der Waals forces and large interlayer spacing facilitate the insertion of Na+/K+.Mo S2 has 2H,1T,and 3R phases.Among them,the conductivity of 2H-Mo S2is low,which is not conducive for electron transport.Compared to2H-Mo S2,1T-Mo S2 with octahedral coordination has obvious advantages:（1）the larger layer spacing（4?larger than that of 2H phase）is beneficial to the diffusion of Na+/K+,which can improve the diffusion kinetics;（2）the higher electrical conductivity（107 times of 2H-Mo S2）promotes the rapid electron transfer,thus improving the rate performance.However,as an electrode material,Mo S2 is prone to structural agglomeration and has poor cyclic stability.In this paper,1T-Mo S2 was used as the main active materials,which was modified by doped carbon material to prepare the hierarchical composite materials of 1T-Mo S2@doped carbon.The sodium/potassium storage performances were tested and the kinetic characteristics were studied.The main contents and research results of this paper are as follows:1.Preparation and sodium storage properties of microflower-like 1T/2H-Mo S2@NPC compositesFirst,the flower-like precursors were obtained by the chelating method,then P element was introduced by the calcination treatment,finally,1T/2H-Mo S2 and N/P co-doped carbon composites（1T/2H-Mo S2@PNC）were obtained by a hydrothermal method.By adjusting the reaction temperature and synthesis strategy,we have also prepared 2H-Mo S2@NPC,1T/2H-Mo S2@PC and other 1T/2H-Mo S2@PNC with different P doped contents composites.Then,the above composite materials were used as anode materials to assemble the SIBs,and the sodium storage performances were investigated.The experimental results showed that:1T/2H-Mo S2@PNC with P addition content of 20 mg shows the most excellent cycling performance(the reversible specific capacity remains at 261.1 m Ah g-1after 1000 cycles at 10.0 A g-1)and rate performance(the reversible specific capacity is up to 429.8 m Ah g-1 and346.7 m Ah g-1at 1 A g-1 and 10.0 A g-1),which is significantly better than1T/2H-Mo S2@NC and 2H-Mo S2@PNC.Moreover,the full cell using1T/2H-Mo S2@PNC-20 as anode materials and Na3V2（PO4）3as cathode materials is assembled to discuss the electrochemical performance.It provides a reversible capacity of 215.9 m Ah g-1 after 300 cycles at a current density of 0.5 A g-1.The excellent electrochemical results mainly depend on the synergistic effect of N,P co-doped carbon and 1T/2H-Mo S2.2.Preparation of 1T-Mo S2@NC microspheres and sodium/potassium storage properties1T-Mo S2@NC microspheres were prepared by a facile solvothermal method andsubsequent heat treatment.As the anode material for PIBs,due to the synergistic effect between active components and special hierarchical structure,the composite achieves high capacity,long cycle life and excellent rate capability(reversible specific capacities of 257.9/128.8 m Ah g-1at 0.05/0.5 A g-1).The cycle life can reach 400times at 0.8 A g-1.As anode materials for sodium storage,the reversible capacity of1T-Mo S2@NC can remain at 478 m A h g-1 after 1300 cycles at 2 A g-1.In addition,the kinetic characteristics and charge storage mechanism have also been studied for both two kinds of alkali ion batteries.Electrochemical results show that the high pseudocapacitive behavior of 1T-Mo S2 under a high rate and the synergistic effect between active materials with high conductivity jointly explain the excellent sodium/potassium storage performances.The simple synthesis strategy used in this experiment can be further extended to prepare other metal sulfides based composites,which is expected to realize the practical application in energy storage systems. |
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