Electrochemical and mechanical properties of LiMn2O4 according to particle morphology

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dc.description학위논문 (석사)-- 서울대학교 대학원 : 화학생물공학부, 2015. 2. 오승모.-
dc.description.abstractLithium-ion battery (LIB) is currently used as a power source in mobile devices and electric vehicles. One of the requirements for those uses is high volumetric energy density and it can be realized by a step in electrode making process called pressing. Pressing can, however, damage active materials with the high pressure applied to them, and this particle breakage phenomenon can cause side effects in LIBs.
In this work, the effect of pressing on particle breakage and LIB performance is studied. Active material used in this study is spinel structured LiMn2O4. Using LiMn2O4 it was confirmed from FE-SEM image, high temperature cycle and storage performance that pressing can induce particle breakage and it can degrade cell performance.
To alleviate this problem, the relation between particle morphology and breaking property was studied. First the effect of morphology was checked in the level of particle by micro compression test. A criterion established from hard carbon system was used to interpret the results of micro compression test. As a result, spherical LiMn2O4 showed more resistance to breakage based on the criterion.
Next, the experiment was performed for electrodes. Electrodes whose active materials are either spherical or non-spherical LiMn2O4s were compared based on FE-SEM images and high temperature storage test. The result agreed with that of micro compression test, showing that spherical LiMn2O4s are more resistant to breakage during pressing and preferable also in respect of electrode performance.
This study has found that particle breakage during pressing should be considered an important factor in LIB using LiMn2O4 as active material and morphology control can handle this problem. Micro compression test was suggested as a tool for studying mechanical properties of LIB active materials with proper criteria. It is expected that the results and methodologies used in the study can also be used for various active materials other than spinel LiMn2O4.
dc.description.tableofcontentsAbstract i
List of Figures iii
List of Tables v

1. Introduction 1
2. Background 3
2.1. Fundamentals of lithium-ion batteries 3
2.2. Components of lithium ion batteries 5
2.2.1. Negative electrode materials 5 Carbonaceous materials 6 Li-alloy materials 7
2.2.2. Positive electrode materials 8 Layered structure 8 Spinel structure 9 Olivine structure 11
2.2.3. Electrolyte 11 Organic electrolyte 11 Polymer electrolyte 12
3. Experimental 13
3.1. Fabrication of electrode 13
3.2. Fabrication of coin-type cell 14
3.3. Charge-discharge cycling test 14
3.4. Electrode storage test 15
3.5. Synthesis of hard carbon 15
3.5.1. Synthesis of spherical hard carbon 17
3.5.2. Synthesis of non-spherical hard carbon 17
3.6. Micro compression test 18
3.7. Other instrument and analysis method 20
4. Results and discussions 21
4.1. Effect of electrode pressing on LiMn2O4 electrode 21
4.1.1. Confirmation of particle breakage induced by pressing 21
4.1.2. Effect of particle breakage on electrochemical properties at high temperature 24
4.1.3. Effect of particle breakage on manganese dissolution after storage at high temperature 27
4.2. Establishing criterion for breaking property under compression 28
4.2.1 Suggestion of the criterion for breaking property 30
4.2.2 Verification of the criterion for constant α and St 31
4.2.3 Verification of the criterion for different values of St 34
4.2.4 Verification of the criterion for different values of α 34
4.3. Effect of morphology on breakage of LiMn2O4 particle under compression 40
4.3.1. Micro compression test on LiMn2O4 particles according to its morphology 40
4.3.2. Effect of morphology on breakage of LiMn2O4 particles in electrode 43
5. Conclusions 47

References 48
Abstract (Korean) 50
dc.format.extent2922712 bytes-
dc.publisher서울대학교 대학원-
dc.subjectlithium-ion battery-
dc.titleElectrochemical and mechanical properties of LiMn2O4 according to particle morphology-
dc.citation.pagesⅶ, 51-
dc.contributor.affiliation공과대학 화학생물공학부-
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College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Chemical and Biological Engineering (화학생물공학부)Theses (Master's Degree_화학생물공학부)
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