Synthesis Of LiFePO₄ By An Integrated Method With Precipitating In High Gravity Condition And Calcining In Microwave Field

The olivine-type LiFePO₄ has many excellent characteristics,such as stable performance,low price,environmental friendly,which were widely recognized by researchers and market since their discovery,and has become a new hot research area of cathode materials for lithium ion batteries.But LiFePO₄ have two defects,that is,low electrical conductivity and low bulk density which restrict their industrialized applications.Now high-temperature solid-state method is the main method to prepare LiFePO₄ industrially.This method is simple and reaction condition is easy to control,but it's difficult to control the particle size,and repeatability is bad,so it is not conducive to solve the above mentioned defects of LiFePO₄.The research and preparation of nanomaterials is one of the forefront of scientific and technological research,the latest studies have shown that nano-LiFePO₄ has excellent electrochemical performance.Therefore,research the new methods of preparation nano-LiFePO₄ material for the cathode material as well as the development of lithium-ion battery has important theoretical significance and great practical value.This paper aim at the nanocrystallization of LiFePO₄,proposing high gravity technology and microwave technology integration prepare nano-LiFePO₄.Co-precipitation,as the commonly used method to prepare nano materials,has obvious advantages in controlling the particle size and morphology over high-temperature solid-state method.To solve the problem of elements ratio imbalance of the products prepared by traditional co-precipitation,this paper has made the following improvements:firstly,the precursor was prepared by high gravity reaction device called Rotating Bed with Helix Channels?RBHC?.In the high gravity conditions,liquid-phase mass transfer process could be greatly intensified,mix intensity was improved,therefore,the mix of liquid phases could be attained at molecular level,and the precipitation particles formed was uniform and the agglomeration of crystalline grain could decrease obviously.Secondly,microwave calcinations were used instead of traditional calcinations.Considering the characteristics of microwave calcinations which is fast and even,it can simplify the sintering process,prevent the agglomeration of the crystalline grain,and moreover,can reduce energy consumption.This paper investigated the effects of the conditions of preparing nona-sized LiFePO₄ by combining high-gravity field with microwave field.Reaction conditions were optimized by TG/DSC,XRD,SEM and TEM etc.The results showed that:the molar ratio of raw materials was Li:Fe:P=4.2:1:1.4,reaction concentration was 0.1 mol/L,pH value=9.When high speed stirring for 30 min at 40?,stalling in water bath for 3 h,then the sage green precursor of LiFePO₄ was obtained.The performed precursor was put into the corundum crucible filled with activated carbon,microwave calcinations at 630 W for 30 min,and then spherical LiFePO₄ with complete crystal forms and good dispersion was obtained,its particle size was about 300 nm,tap density was up to 1.67 g/cm3.Then,the influences of carbon-coated and carbon-doped to pure phase of LiFePO₄ were investigated.LiFePO₄/C was prepared by doping glucose which was used as carbon source,and the quantity of doped carbon was 10wt%.The crystal structure of the obtained LiFePO₄ was not influenced by the doped carbon,the as-prepared particle was equal-fine and carbon was doped homogeneously on the surface of the particle.Carbon-doped could prevent the agglomeration of the grain and decrease particle size.The particle size was about 200 nm,the carbon-coated layer on the edge of the particle was about 3?6 nm.The tap density of the carbon-coated product was 1.46 g/cm3,which was a bit lower than not coated.