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Doped Modification Of LiMnO2 As Cathode Materials For Lithium-ion Batteries And Properties Research

Posted on:2017-04-24Degree:MasterType:Thesis
Country:ChinaCandidate:S J FanFull Text:PDF
GTID:2271330482494901Subject:Materials engineering
Abstract/Summary:PDF Full Text Request
The rapid development of electronic science and technology puts forward higher requirements on portable rechargeable batteries, lithium ion batteries with high power, high capacity and excellent circulation property, is the most ideal secondary battery. However, at present, the research progress of lithium ion battery cathode materials is relatively slow, which restricts the development of the whole battery industry. LiMnO2 is a traditional high specific capacity cathode material whose theoretical specific capacity is as high as 285 mAh/g, and manganese resources is abundant, low cost, no toxicity. However, it is still not realistic for LiMnO2 to be produced as cathode material in large-scale. In the process of preparation, Mn3+is oxidized attribute to J-T effect, which results in structural transformation, moreover, Mn dissolved in organic electrolyte solution, and cause specific capacity dramatically reduced.According to the above problems, this paper uses the high temperature solid phase-low temperature hydrothermal two-step method, synthesized metal elements doping LiMnO2 phase and improved the comprehensive performance of cathode materials. Doping precursor phases were synthesized by high temperature solid-state method and then end-products were obtained with hydrothermal synthesis. Main doping element was Ni and Cr, on this basis, the effect of the dual doping on the properties of cathode materials was further studied, mainly for Cr, Mg and Cr, Ni. The phase composition, crystal structure, microtopography, physical and chemical properties were characterized by using XRD, SEM and TEM. Charging and discharging circulation, cyclic voltammetry, ac impedance were tested to analyze the electrochemical properties. Combined physical, chemical and electrochemical performance to determine the optimal doping ratio, and the modification mechanism of doping elements were analyzed.The results show that though the high temperature solid phase-low temperature hydrothermal two-step method, nanoscale LiMnO2 and doping modification phases were synthesized, compare with the traditional synthesis method, product particle size is smaller and comprehensive performance is better. The optimal Ni-doping ratio is 20%, the highest discharge specific capacity reaches 129.8 mAh/g, improves the charging voltage of the battery,but to a certain extent, restricts the cycle property. The optimal doping ratio of Cr is 10%, the discharge specific capacity up to 154.2 mAh/g, after 50 cycles, the capacity retention rate maintains 85.9%, significantly improves the performance of cathode materials. Because part of Mn3+was replaced by doped Cr3+in crystal structure of LiMnO2, changed the layer structure, reduced the grain size. On the basis of Cr doping, the influence of Mg and Ni element on the properties of materials were studied. The co-doped Cr and Mg further improved the cycle stability of the material.Through the above research, this paper provides a new method to obtain the modified Li Mn O2 phase with excellent electrochemical performance,and the optimal doping ratio was determined, which has a certain guiding role for future large-scale industrial production of lithium ion battery cathode material.
Keywords/Search Tags:Lithium-ion batteries, LiMnO2, Doping modification, Electrochemistry
PDF Full Text Request
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