Hydrothermal Synthesis Of LiMnPO₄ As Cathode Material For Lithium Ion Batteries

The performance of battery depends largely on the performance of cathode materials.The performance of cathode materials improving is batter for the overall performance of battery.Based on reviewing the development of lithium cathode materials in detail,olivine structured LiMnPO4 cathode with high safety performance and high voltage platform was selected as the research object of cathode material in this thesis work.Study the traditional rich-lithium hydrothermal synthesis of LiMnP04 cathode materials.Design a kind of equal amounts of reactants hydrothermal synthesis.Preparationof LiMnPO4 acthode materials.Improve the yield of the product which with equal amounts of reactants hydrothermal by rich-phosphorous hydrothermal.For the traditional synthesis method of LiMnPO4 cathod materials,investigate the influence of Li/Mn molar ratio of reactant,reaction temperature,concentration of reactants and the feeding sequence of reactants on synthesis of LiMnPO4 cathode materals.The result show that appropriate excess of LiOH·H2O is good for synthesis LiMnPO4 cathode material vai hydrothermal method.However,the pH value of the mixture has a vital effect on the synthesis of LiMnPO4 cathode material.The concentration of reactants has no significant effect on the synthesis of materials,but it has some effect on the particle size of the material.Under the condiction of our experiment parameters and equipments,the critical temperature of synthesis LiMn.PO4 cathode material is?120?.Various feeding sequence of reactants will lead to various intermediate phase productions.The intermediate phase product translate into NH4MnPO4 H2O at the end of feeding reactants.And then intermediate phase product NH4MnPO4 H2O generate target product LiMnPO4 by cation exchange reaction during hydrothermal.Independent experiments were conducted to synthesis the intermediate phase product NH4MnPO4·H2O and Li3PO4,respectively.And then,they are used as precursor to reacte respectively with lithium salt and manganese salt to synthesis LiMnPO4 cathode materials.We found that NH4+ with strong complexation ability was easy combination with Mn2+ and PO43-to form NH4MnPO4·H2O.There are obviously inhibiting effect for synthesis LiMnPO4 cathode materials,because the solubility product constant of NH4MnPO4·H2O is very low.For new synthesis idea,independent experiments were conducted where the raw material was exchange.The result show that the pure phase LiMnPO4 can be synthesis with equal molar weight reactants when the NH4+ does not exist in reaction system.However,there was low yield for production LiMnPO4,In order to improve the yield,independent experiments were conducted where excess phosphate was used to participate in the reaction.The result show that it can effectively improve the yield of the product,up to about 95%.We aslo can synthesis the LiMnPO4 cathode materials with excess(NH4)2 HPO4 as phosphate by change the kinetic conditions of the reaction system,such as increase the reaction temperature,prolong the reaction time,when there are NH4+ in the reaction system.