Study On Preparation And Electrochemical Energy Storage Performance Of New Layered Metal Phosphides

Compared to Sn₄P₃ anode material with a theoretical lithium-storage capacity of 1255mAhg^-1,Sn₃P₄ anode demonstrates a higher theoretical capacity of 1517mAhg^-1 that is four times of graphite.In contrast to the complex synthesis methods of other phosphides,Sn₃P₄ material can be prepared by a simple high-temperature solid-state reaction,and the obtained material has a layered crystal structure that empowers it as a new type anode material.After investigating the literature in details,we selected Sn₃P₄ as the target material.The Sn₃P₄/Sn₄P₃ composite materials were synthesized by high-temperature solid-state reaction method with Sn₃P₄ material as the main phase.The morphologies of Sn₃P₄/Sn₄P₃ powders were observed under high-resolution scanning electron microscope.The material displays an obvious layered microstructure.It was found that the material in the oil binder PVDF exhibited poor cycle stability and severe capacity decay.Afterwards,the electrochemical performance of the Sn₃P₄/Sn₄P₃ material on the negative electrode of the lithium-ion battery was effectively improved by replacing the binder and coating carbon black.In order to explore the lithium storage performance of this new material,we firstly prepared oil-based negative electrode maded from Sn₃P₄/Sn₄P₃ materials,carbon black(Super P),PVDF,and N-methylpyrrolidone(NMP).It can be seen that although the oil-based negative electrode made of Sn₃P₄/Sn₄P₃ material has a high initial discharge capacity,its capacity decay is also very serious.Then we will focus on improving its electrochemical performance later afterwards.After carrying out various improvement methods,we found that the water-based binder sodium carboxymethyl cellulose(CMC-Na)can significantly improve the cycle stability of the Sn₃P₄/Sn₄P₃ anode material.Thereby the Sn₃P₄/Sn₄P₃ material was blended with CMC-Na in water to form water-based negative electrodes(denoted as Sn₃P₄/Sn₄P₃-CMC-Na).This electrode shows good cycle reversibility.Firstly,this is mainly because Sn₃P₄/Sn₄P₃ is a layered structural material.Secondly,the CMC-Na binder is more rigid than the PVDF binder.Due to the synergistic effect of layered structure and CMC-Na binder,the volume change of the anode material during cycling was suppressed.In addition,the reaction activity at the heterointerface is higher,and the existence of this structure can accelerate ion transmission and result in better electrochemical performance.Based on the finding that CMC-Na binder can effectively enhance the cycle performance of Sn₃P₄/Sn₄P₃ anode,we continued to explore other strategies to further improve its electrochemical performance.In order to obtain Sn₃P₄/Sn₄P₃ battery anode material with more stable cyclability and better electrochemical properties,we conducted the coating experiment on Sn₃P₄/Sn₄P₃ powders.Through high-energy ball milling,conductive carbon black Super P was mixed with Sn₃P₄/Sn₄P₃ to form the Sn₃P₄/Sn₄P₃@C anode material.It can be inferred from the above experiment that the CMC-Na binder renders anode materials with better electrochemical performance.So the Sn₃P₄/Sn₄P₃@C-CMC-Na andoe was prepared by mixing the active material,super P and CMC-Na binder.Sn₃P₄/Sn₄P₃@C anode presented the best electrochemical performance among these three electrodes.