Lithiation Methods to Fabricate Li2S Cathodes for Future Li-ion Sulfur Battery 将来型 Li-S 二次電池用 Li2S 正極形成のための 電極リチエーション手法 July, 2018 Yunwen WU 呉 蘊雯 Lithiation Methods to Fabricate Li2S Cathodes for Future Li-ion Sulfur Battery 将来型 Li-S 二次電池用 Li2S 正極形成のための 電極リチエーション手法 July, 2018 Waseda University Graduate School of Advanced Science and Engineering Department of Applied Chemistry Research on Applied Electrochemistry Yunwen WU 呉 蘊雯 Principal referee: Prof. Dr. Toshiyuki Momma (Waseda University) Referees: Prof. Dr. Yoshiyuki Sugahara (Waseda University) Prof. Dr. Takayuki Homma (Waseda University) I sincerely appreciate their reviewing this dissertation Contents Chapter 1 General Introduction ................................................................ 1 1.1 Rechargeable Lithium-Sulfur Battery ................................................................... 2 1.2 Challenges of Li-S battery .................................................................................... 5 1.2.1 Dissolution of polysulfide ............................................................................... 5 1.2.2 Formation of Li dendrite ................................................................................. 8 1.2.3 Degradation of Li anode ................................................................................. 9 1.2.4 Other challenges ............................................................................................ 11 1.3 Li2S based cathode .............................................................................................. 13 1.3.1 Challenges in Li2S based cathode ................................................................. 13 1.3.2 Fabrication of Li2S cathode using commercial Li2S ..................................... 15 1.3.3 Thermal reaction method to fabricate Li2S ................................................... 17 1.3.4 Chemically fabricate Li2S cathode by organolithium reagents ..................... 20 1.4 Full Cell Systems Based on a Li2S Cathode ....................................................... 22 1.4.1 Li2S-Sn full cell system ................................................................................ 22 1.4.2 Li2S-Si full cell system ................................................................................. 24 1.4.3 Li2S-graphite full cell system ........................................................................ 25 1.5 Objective for this dissertation ............................................................................. 28 1.6 References ........................................................................................................... 29 Chapter 2 Direct contacting lithiation method to fabricate Li2S cathode ................................................................................................................... 37 2.1 Introduction ......................................................................................................... 38 2.2 Experimental ....................................................................................................... 40 2.2.1 Preparation .................................................................................................... 40 2.2.2 Characterization ............................................................................................ 41 2.2.3 Electrochemical measurement ...................................................................... 41 2.3 Results and Discussion ....................................................................................... 42 2.3.1 Characterization of the S/KB cathode. .......................................................... 42 2.3.2 Material analysis of the lithiated Li2S cathode ............................................. 43 2.3.3 Cathode performance dependence on PPy thickness .................................... 52 2.3.4 Li metal free full cell ..................................................................................... 55 i 2.4 Summary ............................................................................................................. 60 2.5 References ........................................................................................................... 61 Chapter 3 Electrochemical lithiation method to lithaite S cathode ....... 63 3.1 Introduction ......................................................................................................... 64 3.2 Experimental ....................................................................................................... 65 3.2.1 Preparation .................................................................................................... 65 3.2.2 Lithiation process .......................................................................................... 65 3.2.3 Characterization ............................................................................................ 66 3.2.4 Electrochemical measurement ...................................................................... 66 3.3 Results and Discussions ...................................................................................... 67 3.3.1 Theoretical foundation for the p-stat lithiation method ................................ 67 3.3.2 Influence of applied potential in p-stat lithiation .......................................... 70 3.3.3 Comparison of the p-stat lithiation and the g-stat lithiation methods ........... 73 3.4 Summary ............................................................................................................. 79 3.5 References ........................................................................................................... 80 Chapter 4 Fabrication of Li2S cathode using the organolithium reagent ................................................................................................................... 83 4.1 Introduction ......................................................................................................... 84 4.2 Experimental ....................................................................................................... 85 4.2.1 Preparation .................................................................................................... 85 4.2.2 Characterization ............................................................................................ 86 4.2.3 Electrochemical measurement ...................................................................... 87 4.3 Results and Discussion ....................................................................................... 87 4.3.1 On-site lithiation of Li2S cathode ................................................................. 87 4.3.2 Synthesis of Li2S@KB nanostructured cathode ........................................... 98 4.4 Summary ........................................................................................................... 112 4.5 References ......................................................................................................... 113 Chapter 5 General Conclusions ............................................................ 115 List of Achievements……………………………………………………………..119 Acknowledgement ……………………………………………...….…………….123 ii Chapter 1 General Introduction 1 1.1 Rechargeable Lithium-Sulfur Battery The energy crisis due to the quick consumption of fossil fuels and the environmental issues causing by the burning of fuels are the two main crises in today’s world 1, 2. Wind, solar, geothermal and other renewable sources can produce a sustainable amount of energy. As a result, the energy storage device for the storage of the renewable energy is the key issue for the widespread application of the renewable energy 3-5. Fig. 1.1 illustrates the typical gravimetric and volumetric energy density of different rechargeable batteries. The secondary rechargeable batteries have been developed from lead acid battery, which shows very low gravimetric energy density around 50 Wh kg-1 to nickel–cadmium battery (NiCd). In 1989 nickel-metal hydrogen batteries (NiMH) were developed and had a longer life than NiCd batteries. However, the gravimetric energy density of the NiCd and NiMH batteries are still lower than 100 Wh kg-1, which is still far from the requirements in the state-of-art electronic devices 6. Li-ion battery with a rather high energy density and high diversity of battery systems is the most common used attainable energy storage systems for electronic devices. Li- ion battery shows advantages in high energy density, low self-discharge and small memory effect, which contribute to its wide application in home electronics and portable electronics 5, 7. The concept of Li-ion battery in which the Li could migrate through the battery from one electrode to the other as a Li+ ion is firstly raised in 1980s. Subsequently, commercialized Li-ion battery was assembled by pairing LiCoO2 with graphite anode in 1990s. The LiCoO2-graphite battery material is still dominate the Li- ion battery market in nowadays. However, it cannot match the increasing demand for the development of a new generation of secondary battery with high capacity and long cycle life to meet the application in portable electronics, electronic vehicles and consumer devices 4, 8. 2 Fig. 1.1 Development of various energy storage devices in function of gravimetric energy density and volumetric density. As shown in Fig. 1.2, there are various types of Li-ion battery nowadays 6, 8-10, typically, the LiMnO2/ LiCoO2-graphite system shows a theoretical energy density around 420