Effect Of Treatment To Precursor On Performance Of LINI_0.5 MN_1.5O₄ , Cathode Material Li-ion Battery

In all cathode materials of Lithium-ion batteries, LiNi_0.5Mn_1.5O₄ attracted a great of interests due to its special properties, such as low product-cost, high special capacity, high discharge voltage, no environmental pollution, good cyclic property, et al. Based on my survey of researches on LiNi_0.5Mn_1.5O₄, this thesis carried out a series of studies in order to resolve the present remaining problems. Accordingly, some meaningful results were obtained. Main points of thesis are listed as below:1. Synthesis of LiNi_0.5Mn_1.5O₄ precursor with high density: The precursor of LiNi_0.5Mn_1.5O₄ cathode material with high density was synthesized by two-dryness co-precipitation method. The optimized parameters were found out by studying the relationship between the density of precursor and concentration of reactants, manner of adding agglomerating agent, remaining water in filter cake and manner of dryness. Our results provide an important reference on synthesis of high density cathode materials of Li-ion Batteries. Besides, the content of Ni and Mn in precursor was analyzed, by which the ratio of Ni and Mn was kept at 1: 3.2. Effect on performance of LiNi_0.5Mn_1.5O₄ by treating precursor with oxidation or reduction: Oxidant (H₂O₂) or reductant (hydrazine) was added in while synthesizing LiNi_0.5Mn_1.5O₄ precursor by two dryness co-precipitation method. Great difference of structure and electrochemical performance were showed on LiNi_0.5Mn_1.5O₄ materials from different precursors with oxidant treated or reductant treated. Results revealed the LiNi_0.5Mn_1.5O₄ from hydrazine treated precursor shows higher special capacity, better cyclic activities and high-discharge-rate performance. However, LiNi_0.5Mn_1.5O₄ from H₂O₂ treated precursor shows bad electrochemical properties.3. Effect of remaining sodium ion on performance of LiNi_0.5Mn_1.5O₄: On the view of Na+ content in cathode, we studied the performance of LiNi_0.5Mn_1.5O₄ from precursor treated with reductant (hydrazine) or oxidant (H₂O₂). Furthermore, for comparison, performance of LiNi_0.5Mn_1.5O₄ synthesized with LiOH or NH₄HCO₃ (to replace NaOH) was also studied. Results of XRD, SEM and electrochemical tests show the content of remaining Na+ takes a great effect on properties of LiNi_0.5Mn_1.5O₄: the less remaining Na+, the better electrochemical performance of samples. Our results show that LiNi_0.5Mn_1.5O₄ sample with well-crystallization and pure phase could be obtained, which shows better electrochemical performance accordingly, if the content of remaining sodium ion can be reduced as clear as possible in synthesis of precursor by two dryness co-precipitation method.4. Performance of LiNi_0.5Mn_1.5O₄ at high temperature (55 oC): By comparing electrochemical properties of LiNi_0.5Mn_1.5O₄ cathode materials under high temperature and room temperature, we found that LiNi_0.5Mn_1.5O₄ synthesized from hydrazine treated precursor shows higher discharge special capacity and better cyclic performance (Special capacity keeps almost unchanged within 50 charge/discharge cycles). Our results indicated that cathode material from hydrazine treated precursor has a good high-temperature resistance, which might resolve the security problem of lithium-ion batteries at high temperature.