Study On Modification And Electrochemical Performance Of Lithium Iron Phosphate Synthesized By Phosphorous Iron Through The Method Of Hydrothermal In-situ Coating

At present,lithium iron phosphate cathode materials occupy a large share in the field of the applications of lithium-ion batteries.However,the problems of low electronic conductivity and ion transmission rate,and the search for cheaper and more efficient synthesis path restrict its further development.In this paper,on the one hand,the use of Fe1.5P as the raw material reduced the production cost,on the other hand,the in-situ coating method can overcome the problem of unevenness coated carbon layer of Li Fe PO4.In addition,during the modification process,it was found that the prepared lithium iron phosphate composite materials exceed the theoretical specific capacity,and the cause of this phenomenon was analyzed.In this paper,on the one hand,the stepwise in-situ coating preparation of lithium iron phosphate composite Li Fe PO4/C?recorded as LFP/C?with Fe1.5P as material and under acidic system by the surfactant-assisted hydrothermal method.The intermediate Fe PO4 prepared with Fe1.5P only in the acidic system of phosphoric acid and nitric acid,the particle agglomeration of LFP/C is serious,and the electrochemical performance needs to be improved further,so we studied the different addition amounts of the cationic surfactant CTAB,the anionic surfactant SDS and the non-ionic surfactant PEG400 as soft template agents under the acidic conditions assist synthesis of LFP/C material.The experimental results show that the particle agglomeration of the synthesized LFP/C is decreased when m?CTAB?=2.0 g,and the electrochemical performance is the best.The specific discharge capacity of the first discharge at 0.1C rate reaches 174.5 m Ah g^-1,which exceeds the theoretical specific capacity(170 m Ah g^-1)of lithium iron phosphate.On the other hand,one-step hydrothermal in-situ synthesis of LFP/C synthesized by Fe1.5P was carried out.Because lithium iron phosphate cannot exist under acidic conditions,Na2CO3 can promote the conversion of Fe1.5P.In the preparation of LFP/C under the above acid system,PEG400 can be used as reducing agent,and Fe1.5P,Li NO3,NH4H2PO4,Na2CO3,PEG400,C6H12O6·H2O were selected as raw materials,exploring the effects of the adding amount of Na2CO3,PEG400,glucose,ball milling before reaction,reaction time on the physical and chemical and electrochemical properties for one-step in-situ coating synthetic materials.It was found that under the condition of the hydrothermal reaction of 180?/36 h,n?Fe?:n?P?:n?Li?:n?C?=1:2:1:1.25,n?Fe1.5P?:n?Na2CO3?=1:1,V?PEG400?=10 m L prepared LFP/C has the best electrochemical performance,and the first discharge specific capacity is 128.0m Ah g^-1.