An Investigation In Synthesis Of High Performance Lithium Manganate Cathode Materials For Lithium Ion Batteries

The theoretical capacity of spinel lithium manganate(LiMn2O4)is 148 mAh/g.It has been widely applied as lithium-ion battery material in the fields of electric tools and bicycles due to its good safety,low cost and environmental friendliness.However,during the charge and discharge processes,the structure changes of LiMn2O4 induced by Jahn-Teller effect take place,leading to poor cycle performance of the battery.Meanwhile,at the end of discharge process,the increase of trivalent manganese ion(Mn3+)results in disproportionate reaction and Mn3+ dissolution,causing irreversible capacity loss.In particular,the Mn3+disproportionate reaction will be obviously accelerated at higher temperatures,and the cycle performance of battery and specific capacity of LiMn2O4 will be significantly reduced.It is,therefore,very important to solve for the problems induced by Jahn-Teller effect and Mn3+dissolution involved in spinel LiMn2O4 in order to expand application fields.In this work,the high-temperature pretreatment of manganese dioxide(MnO2)was introduced to improve the properties of raw material with the low specific surface area of LiMn2O4 and the inhibited electrolyte corrosion in batteries to reduce the required activation energy without raising preparation temperature and to achieve the enhanced cycle performance.The spinel LiMn2O4 materials were then synthesized by using the products of high-temperature pretreated MnO2 as raw materials.The effects of molar ratio of lithium to manganese(Li:Mn)metals and aluminum(Al)doping on the crystal structure,surface morphology and electrochemical performance of spinel LiMn2O4 materials were preliminarily investigated.The result showed that at an air atmosphere manganic oxide(Mn2O3)was obtained after pretreated MnO2 at 560??960 ?,while trimanganese tetraoxide(Mn3O4)after pretreated MnO2 at the temperature exceeding 960?.The products of MnO2 being pretreated at 600 ?and 1000 ? were used as raw materials,respectively,and mixed uniformly with lithium carbonate(Li2CO3).The spinel LiMn2O4 cathode materials were then prepared at the sintering temperature of 750 ?.The first charge capacities of 108.5 mAh/g and 104.64 mAh/g under 0.1C were achieved,respectively,with the first charge and discharge efficiencies of 98.24%and 92.51%,respectively.Furthermore,the Al doped spinel LiMn2O4 material was also prepared using the product of pretreated MnO2 at 600 ? as the raw material with the metal molar ratio of Li:Mn being 1.12:2,the AI doping content of 0.04 mol(Li1.098Mn1.96Al0.04O4)and the sintering temperature of 750 ? for 20 h.The charge and discharge capacities of 122 mAh/g and 116.51 mAh/g were obtained,respectively,under 0.1C with the charge and discharge efficiencies of 95.5%.The cycle performance was not apparently improved when the Al doping content was over 0.03 mol,however,remarkably enhanced below 0.03 mol with Al doping.On the other hand,the cycle performance was greatly reduced when the Li:Mn value was smaller than 1.12:2.Although the cation ion doping caused the capacity loss of the material,the Mn ions might be substituted by Al ions with a smaller radius,which led to not only the shrinkage of unit cells,but also the reduction in the amount of Mn3+ ions.Accordingly,the disproportionate reaction of Mn3+ could be controlled,and finally,the Jahn-Teller effect of spinel LiMn2O4 material might be minimized.