Synthesis, Regeneration And Performance Research Of Lithium Iron Phosphate Cathode Materials

Lithium iron phosphate cathode material has a theoretical specific capacity of 170mAh·g^-1 and a 3.5V lithium charging platform.It has many advantages such as wide range of raw materials,outstanding safety performance,good cycling performance,good thermal stability and low cost.It is an ideal cathode material for power lithium-ion batteries.With the rapid development of energy industry,lithium iron phosphate battery is about to enter a large-scale decommissioning period.If numbers of waste lithium-ion batteries without economic and effective treatment methods,it will not only bring potential environmental pollution,but also lose a large number of valuable elements such as lithium,phosphorus,iron,etc.The spent LiFePO₄ recycling technology needs urgently.In order to realize the recovery of lithium iron phosphate battery,a new technology featured by H₃PO₄ leaching was proposed by Institute of Process Engineering.In this paper,the product obtained from the recovery process was used as the raw material,and the feasibility of the synthesis of regenerated lithium iron phosphate was analyzed by thermodynamic calculation.The high-temperature solid-state method and hydrothermal method were studied to respectively synthesize regenerated LiFeO₄.The main research results are as follows:?1?The thermodynamics of roasting and hydrothermal synthesis of regenerated lithium iron phosphate was systematically analyzed.The results show that the high-temperature solid-state method using FePO₄ as the raw material can be carried out spontaneously within 300?1000?;the hydrothermal method using LiH₂PO₄ and FeC₂O₄·H₂O can proceed spontaneously.?2?LiFePO₄ cathode material was synthesized by roasting method using FePO₄ and Li₂CO₃ as raw materials.At 750? and 15% glucose as carbon source,LiFePO₄ cathode materials with 3.5% carbon residue were obtained.The first discharge capacity is 158.5mAh·g^-1 at 0.1C,the capacity of 65 cycles is almost no loss,and the cycle performance is excellent.?3?LiFePO₄ cathode material was synthesized by hydrothermal method with LiH₂PO₄ solution and FeC₂O₄·H₂O as raw materials.The optimal reaction conditions as follows:reaction temperature 230?,reaction time 8h,pH value of precursor 5.5,control over 20%of Liin raw materials;when the concentration of Li⁺is about 1 mol/L,the yield of LiFePO₄ is the highest.The electrochemical performance of LiFePO₄ was further improved by adding surfactant,adjusting pH value and high temperature calcination with carbon.The results showed that the first discharge capacity was 143.8mAh·g^-1 with 0.3 mmol CTAB,and the capacity retention rate of 65 cycles was 98.26% at 0.1C.The electrochemical performance of the sample is improved when the samples of the solid phase method and the hydrothermal method are evenly mixed.