Design & Preparation Of High-performance P-based Anode Materials And Research On Their Electrochemical Behavior

Since the radius of sodium ion and potassium ion are larger than that of lithium ion,the electrode materials for lithium battery are difficult to be directly applied to sodium?potassium?ion battery.The main research bottleneck is to find suitable sodium?potassium?ion battery electrode materials.Thus,phosphorus-based materials are considered to be promising anode materials due to their high specific capacity and abundant reserves.However,whether it is in lithium-ion battery or next-generation sodium?potassium?ion battery,large capacity often causes a problem of large volume expansion.In this study,the strategy of the nanostructure structure and the design of ternary materials were adopted to solve the common problems of anode materials in alkali metal ion batteries.Finally,the phosphorus-based high performance anode materials were developed.Their electrochemical properties and energy storage mechanisms were also investigated.In addition,the single crystal structure of ternary Sb₂MoO₆ was also studied for the first time as the negative electrode of sodium ion batteries in this research.The main findings are as follows:?1?The organic conductive polymer PPy coated CoP₃ cubic porous structure was designed and prepared by a one-step high temperature heat treatment using a special MOF as precursor followed by PPy coating.This porous cubic structure has a first reversible specific capacity up to 1310 mAh/g at a current of 100 mA/g.After 220 cycles at 500 mA/g,the capacity can still be maintained at 650 mAh/g.Moreover,this composite structure has excellent rate performance with capacities of 1000,980,950 and 900 mAh/g at 200,500,1000 and 2000 mA/g,respectively.Even at high current density up to 4000 mA/g,the capacity can still reach 800 mAh/g.Full batteries using commercial Li Fe PO4 as cathode material were assembled with capacity of 540 mAh/g after 100 cycles at 100 mA/g.The excellent cycle and rate performance of this composite is attributed to its unique porous structure,while the PPy coating also plays critical role in conduction and buffering volume expansion during the electrochemical reaction.?2?A new ternary FeSi₄P₄ anode material was designed and prepared.The electrochemical properties and lithium storage mechanism of this ternary material were studied for the first time.As the anode material of lithium ion battery,the first reversible capacity of the ternary anode material reaches 1800 mAh/g with first coulombic efficiency up to 88%.After a simple carbon coating,its cycle life and rate performance are further improved.The test results show that the lithium storage mechanism of this new ternary phosphorus-based material is based on the conversion reaction.The FeSi₄P₄ anode material has the advantages of low working potential,excellent specific capacity,good thermal stability,simple preparation,low raw material cost,etc.,and is a promising next-generation lithium ion battery anode material.?3?For the first time,the electrochemical properties and sodium storage mechanism of the new ternary FeSi₄P₄ material as the anode of sodium ion battery were further studied.The results show that the FeSi₄P₄ electrode material has a first reversible charging capacity of 180 mAh/g.After 100 cycles,the capacity remains above 180 mAh/g without attenuation.Even at current densities up to 4000 mA/g,the specific capacity of this negative electrode material can be maintained above 54 mAh/g.By combining experimental analysis with firstprinciples calculations,we found that,unlike lithium-ion batteries,the sodium-storing behavior of this particular FeSi₄P₄ anode is achieved by highly reversible sodium ion deintercalation.The small volume change caused by the electrochemical reaction between sodium ion and FeSi₄P₄ negative electrode,coupled with its high ion diffusion coefficient,are beneficial to the migration and diffusion of sodium ions,making this ternary FeSi₄P₄ negative electrode have excellent cycle life and rate performance.?4?The ternary amorphous CuSeP₂ was designed and prepared as the anode material of potassium ion battery for the first time,and its electrochemical performance was also investigated.After ball-milling with commercial graphene powder,it is used as the anode material for potassium ion battery with first reversible charging capacity up to 300 mAh/g,and the corresponding initial coulombic efficiency is close to 60%.The capacity remains above 180 mAh/g after 100 cycles at 200 mA/g,and the CuSeP₂/graphene electrode material still has a potassium storage capacity of up to 100 mAh when the current density is increased to 1000 mA/g.When the current drops to 50 mA/g,the specific capacity quickly recover to 280 mAh/g.Our results show that the potassium storage mechanism of the ternary CuSeP₂ anode material is also a typical conversion reaction.Finally,the study also shows that the introduction of Cu can not only buffer the volume expansion during the subsequent electrochemical reaction,but also effectively enhance the electrochemical reversibility of potassium ion.?5?The composites of single crystal Sb₂MoO₆ with reduced graphene oxide were synthesized by simple hydrothermal method.The growth process of the single crystal was also studied in detail.It was found that graphene oxide plays a critical role in purity of the product and the preferential growth of single crystal.As a sodium ion battery,the electrode material has a first reversible capacity of 421 mAh/g,and the capacity retention rate is as high as 93.2% after 200 cycles at 200 mA/g.At a current of up to 4 A/g,the capacity of the composite can be maintained at around 270 mAh/g.Combined with in-situ XRD,ex-situ TEM and XPS analysis,the results show that the amorphous Na2O/Mo Ox formed in the reaction of Sb₂MoO₆ with sodium ions after the first discharge will encapsulate the active element Sb in situ to inhibit volume expansion in subsequent cycles and to increase ion mobility.Through structural construction and new material system design,we investigated the structure and multi-component synergistic effects of the above materials on their electrochemical stability and kinetics.The research results may offer some guidance for the design,synthesis and analysis of other multi-energy storage materials.