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Preparation, Modification And Electrochemical Performance Of LiNiO2Cathode Material Of Lithium Ion Battery

Posted on:2014-07-06Degree:MasterType:Thesis
Country:ChinaCandidate:Z L GuoFull Text:PDF
GTID:2251330401972229Subject:Physical chemistry
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Lithium-ion battery has many advantages such as high specific energy, no memory effect, light weight, low self-discharge and so on. It is widely used in the field of mobile communication equipment, electric vehicles, defense technology. However, lithium-ion battery manufacturing process is still not mature enough, the main reason is that the preparation of appropriate positive and negative material is not easy.Currently, the most widely used cathode material in lithium-ion battery is still LiCoO2. Due to its high price and toxin, the development of LiCoO2is limited. Compared to Co, Ni has a richer source. LiNiO2also has higher theoretical specific capacity and low self-discharge, thus is seen as the potential to replace LiCoO2. Nevertheless, LiNiO2still has disadvantages, including:(1) synthesis of difficulties;(2) instability of layered structure in the charge-discharge process, resulting in poor cycle performance. Lots of researchers have done a lot of related work to overcome these shortcomings. This paper aims to solve the synthesis problem of LiNiO2and improve the electrochemical performance by doping with other elements. We used the mixture of trivalent nickel compound and LiOH·H2O as precursor, then LiNiO2was prepared by calcined the precursor at low temperature in air. At the same time, we did a lot of work for the doping modification of LiNiO2in order to improve the electrochemical properties of the material and get the following conclusions:1. LiNiO2particles with good layered structure and electrochemical properties were synthesized by low temperature solid method. At first, we prepared NiOOH by chemical oxidation, and then get precursor by mixing NiOOH and LiOH. LiNiO2was obtained by calcined the precursor at600℃for15hours and characterized by XRD, SEM and so on. The results show that the stoichiometric formula of prepared samples is Li0.92Ni1.08O2and the particles were spherical. The particles size was400nm. Then the charge/discharge cycling was examined in order to test its electrochemical properties. The result shows the initial discharge capacity of the LiNiO2can reach122mAh g-1at current density of28mA g-1. Impedance techniques and cyclic voltammetry also show the material has good electrochemical properties.2. Explored the preparation method and its electrochemical properties of LiNi0.7Co0.3O2. We prepared Ni0.7Co0.3OOH by chemical oxidation and then mixed it with LiOH. The mixture was calcined at600℃for15hours thus we get LiNi0.7Co0.3O2at last. XRD analysis shows characteristic peaks can correspond standard cards. SEM shows the it appears as irregular tabular grains with a certain degree of agglomeration. At a current density of28mA g-1, its initial discharge capacity can reach155mAh g-1, higher than LiNiO2. However, its capacity retention rate is lower than LiNiO2at a current density of140mA g-1. The possible reasons may be that:(1) the layered structure of the prepared material is unstable;(2) the poor morphology of the material causes the material easy to desorb from the collector thus result in the degradation of the cycle.3. La doping of LiNiO2(LiLaxNi1-xO2) was prepared and tested to get its physical properties and electrochemical properties. The research shows it can improve the layered structure of the material and reduce the size of particles resulting in the improvement of its electrochemical properties by doping a small amount of La to LiNiO2. Compared with LiNiO2, XRD characterization shows the layered structures of LiLa0.01Ni0.99O2and LiLa0.02Ni0.9gO2have improved. At the same time, SEM images show the material doping with a small amount of La element is still spherical. The particles turn smaller and the surface is much rougher. The charge/discharge cycling tests show the initial discharge capacity of LiLa0.01Ni0.99O2and LiLa0.02Ni0.98O2have improved compared to LiNiO2. At a current density of28mA g-1, their discharge capacity respectively reached131.9mAh g-1and129.8mAh g-1. Their cycling performance also improved. After40cycles, the capacity retention rate still kept73.9%and88.3%. The impedance of the material was smaller through EIS tests. This tells us that the conductivity of the material enhanced by doping a small amount of La element.
Keywords/Search Tags:LiNiO2, La, doping, lithium battery, electrochemical performance
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