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Structural and Electrochemical Properties of Zn, Mn-based Metal Oxide Anode Materials for Lithium Ion Batteries

  • Min Seob Song (송민섭, 대학원 신소재공학과 신소재공학전공)

초록/요약

Lithium ion batteries are very promising fulfillment for such demands because of its outstanding characteristics such as light weight, high energy density, intrinsic discharge voltage and environmental friendly. From the first introduction into the market, in the last two decades, lithium ion batteries has become dominant from small rechargeable battery application like cellular phones, note book computers, and personal digital assistance to large applications such as satellites and electric vehicles. This growing demand has attracted researchers to develop lithium ion batteries with high voltage and capacity and low cost and safety. Extensive researches are underway an alternative electrode materials for lithium ion batteries. Graphite has been widely used as the anode material of commercial lithium ion batteries. With the growing demands of high capacity lithium ion batteries, the low capacity of graphite has been looked upon as the limiting factor in wide applications and new anode materials with high capacity have been sought. This present thesis details the study of structural and electrochemical properties of Zn, Mn-based metal oxide anode materials for lithium ion batteries. The ZnMn2O4 and ZnO-MnO composite metal oxide materials are studied as anode materials for lithium ion batteries. Their synthesis, physical characterization and electrochemical properties are discussed. Firstly, in order to reduce the solvothermal reaction time to prepare a pure phase of ZnMn2O4 as an anode material for lithium ion batteries, we have investigated the effect of the mixing times as an important reaction factor. It is found that the mixing times of zinc nitrate play an important role in removing the ZnO impurity phase which diminishes its electrochemical performance. The in-situ and ex-situ XRD for the pure phase of ZnMn2O4 during the first discharge and charge process showed that the crystalline ZnMn2O4 was converted to amorphous phase through a series of conversion reactions and the study of magnetic property revealed the MnO phase existed in the 1st cycled crystalline ZnMn2O4 electrode. Secondly, in order to improve its initial coulombic efficiency, ZnMn2O4 was transformed to ZnO-MnO composite by reduction process. To observe the phase change during the reduction process, the in-situ high temperature XRD was performed in vacuum condition. It is found that all of the ZnMn2O4 has been reduced to the ZnO-MnO composite phase between 500 oC and 700 oC. The electrochemical performance of reduced ZnO-MnO composite electrodes were evaluated by galvanostatic discharge-charge tests. When ZnMn2O4 was reduced to ZnO-MnO composite, the initial coulombic efficiency is significantly improved from 54.7 to 68.3%. Furthermore, in order to clarify the discharge-charge mechanism of ZnO-MnO composite electrode, the structural investigation was performed using ex-situ XRD and TEM. Finally, spherical ZnO-MnO composite material has been investigated as a anode material for lithium ion batteries. Spherical ZnO-MnO composite was synthesized by carbonate co-precipitation method. For preparing the carbon-coated ZnO-MnO composite, sucrose was selected as the carbon source. The obtained bare and carbon coated ZnO-MnO composite powders were characterized by X-ray diffraction, SEM and HR-TEM. The electrochemical performance of prepared ZnO-MnO composite electrodes, as an anode materials, were evaluated by galvanostatic discharge-charge tests. The carbon coated ZnO-MnO composite electrode indicated high initial reversible capacity of 728 mAh g-1 at 0.1 C and stable capacity retention (95%) of 625 mAh g-1 after 50 cycles. The carbon coated ZnO-MnO composite electrode also exhibits good rate capability of 595 and 539 mAh g-1 at 1 C and 5 C, respectively.

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목차

Chapter 1. Introduction 1
Chapter 2. Literature Survey 5
2-1. Lithium ion batteries 5
2-1-1. Charge/discharge mechanism of lithium ion batteries 9
2-1-2. Components of lithium ion batteries 10
2-2. Anode materials for lithium ion batteries 12
2-2-1. Anode materials 12
2-2-2. Ideal anode materials 14
2-3. Oxide-based anode materials 16
2-3-1. Anodes based on Li intercalation/de-intercalation reaction 16
2-3-2. Anodes based on alloying/de-alloying reaction 17
2-3-3. Anodes based on conversion reaction 18
2-3-4. Anodes based on both alloying/de-alloying and conversion reaction 21
Chapter 3. Experimental Procedure 25
3-1. ZnMn2O4 materials 25
3-1-1. Synthesis of ZnMn2O4 25
3-1-2. Characterization and electrochemical measurements 25
3-2. ZnO-MnO composite material 27
3-2-1. Preparation of ZnO-MnO composite 27
3-2-2. Characterization and electrochemical measurements 27
3-3. Modified ZnO-MnO composite material 29
3-3-1. Synthesis of [ZnMn2]CO3 precursor and ZnO-MnO composite 29
3-3-2. Preparation of Carbon-coated ZnO-MnO composite 30
3-3-3. Characterization and electrochemical measurements 30
Chapter 4. Results and Discussion 33
4-1. ZnMn2O4 material 33
4-1-1. Material caracterization 33
4-1-2. Electrochemical caracterization and reaction mechanism 45
4-2. ZnO-MnO composite material 62
4-2-1. Material caracterization 62
4-2-2. Electrochemical caracterization and reaction mechanism 71
4-3. Modified ZnO-MnO composite material 81
4-3-1. Material caracterization 81
4-3-2. Electrochemical caracterization 90
Chapter 5. Conclusions 97
References 99

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