4d transition metal doped lini0 5mn1 5o4 cathodes for high power lithium batteries

4d Transition Metal Doped LiNi0.5Mn1.5O4 Cathodes for High Power Lithium Batteries WANG HAILONG (B.Sc., M.Sc.) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF MECHANICAL ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2011 Acknowledgements I would like to express my deepest and heartfelt gratitude and appreciation to my supervisors, Professor Lu Li and Associate Professor Lai Man On, for their valuable guidance, continuous support and encouragement throughout the entire research work Their wise counsel, unique insights and perspectives and noteworthy talents and dedication, accompanied me throughout the research project I would like to thank Dr Yang Ping and Dr Zhang Jixuan for their precious advices on crystallography and TEM operation In addition, I want to express my appreciations to Dr Xiao Wei and Xia Hui for the many valuable discussions During the four years of research work, numerous encouraging supports and help were delivered by my friends I would like to acknowledge them: Dr Zhang Zhen, Wang Zhiyu, Mr Ye Shukai, Xiao Pengfei, Song Bohang, Lin Chunfu and Ms Zhu Jing I would also like to acknowledge the following staff member in the Materials Lab for their help, without which this project would not be successfully completed: Mr Thomas Tan, Abdul Khalim, Ng Hong Wei and Dr Maung Aye Thein Their professional work provides a good working environment for this research project A special appreciation goes to my wife He Miao, her endless support and understanding help me complete this work successfully I Table of contents Table of Contents Summary V List of Figures VII List of Tables XI List of Symbols XII Chapter Background, Motivation and Orientation 1.1 Introduction to Rechargeable Lithium Batteries 1.2 Literature review 1.2.1 Cathode materials with Layered structure 1.2.2 Cathode materials with Spinel structure 14 1.2.3 Cathode materials with Olivine structure 20 1.3 Limitations of High Power applications 25 1.4 Present Research Orientation on Spinel-structured oxides 28 Chapter Experimental Methodology 34 2.1 Material design 34 2.2 Material synthesis methods 37 2.3 Material characterization 39 2.3.1 Composition analysis 39 2.3.2 Crystal structure identification 40 2.3.3 Particle morphology observation 42 2.3.4 Conductivity measurement 42 2.4 Electrochemical performances tests 43 2.4.1 Battery assembly 43 2.4.2 Charge/discharge profiles at low current densities 44 2.4.3 Electrochemical reaction signal identification 44 2.4.4 Lithium diffusion coefficient measurement 45 2.4.5 Rate capability test 46 2.4.6 Cyclic performances at high current densities 46 II Table of contents Chapter Ru doped LiNi0.5Mn1.5O4 with spinel structure 47 3.1 Material design 47 3.1.1 Ru doped LiNi0.5Mn1.5O4 with perfect spinel structure 48 3.1.2 Ru doped LiNi0.5Mn1.5O4 with lattice defects 49 3.2 Material Characterization 51 3.2.1 Chemical Composition and Particle Morphology 51 3.2.2 Crystal Structure Analysis 54 3.2.3 Conductivity Measurement 60 3.3 Electrochemical Performances 65 3.3.1 Charge/Discharge performance at 0.2 C 66 3.3.2 Redox reaction analysis 68 3.3.3 Rate Capability 73 3.3.4 Cyclic performance at 10 C 76 3.4 Summary 78 Chapter Rh doped LiNi0.5Mn1.5O4 with spinel structure 80 4.1 Material design 80 4.2 Material Characterization 82 4.3 Electrochemical performances 86 4.3.1 Charge/Discharge performance at 0.2 C 87 4.3.2 Redox reaction analysis 88 4.3.3 Rate capability 90 4.3.4 Cyclic performance at 10 C 91 4.4 Summary 92 Chapter Nb doped LiNi0.5Mn1.5O4 with spinel structure 94 5.1 Material design 94 5.2 Material Characterization 95 5.3 Electrochemical performances 99 5.3.1 Charge/discharge performance at 0.2 C 99 5.3.2 Redox reaction analysis 101 5.3.3 Rate capability 102 III Table of contents 5.3.4 Cyclic performance at 10 C 104 5.4 Summary 106 Chapter LiNi0.5-2zRuzMn1.5O4 with submicron sized particles 107 6.1 Material preparation and comparison 108 6.2 Material Characterization 113 6.3 Electrochemical performances 117 6.3.1 Charge/Discharge performance at 0.2 C 117 6.3.2 Redox reaction analysis and lithium diffusivity 120 6.3.3 Rate capability 123 6.3.4 Cyclic performance at 10 C 127 6.5 Summary 131 Chapter Conclusions and Recommendations 133 7.1 Conclusions 133 7.2 Limitations and Recommendations 135 References 137 Journal Papers Published 157 IV Summary Summary Cathode materials for lithium batteries with high power density are in great demand to power electric vehicles and hybrid electric vehicles Hence, spinel-structured LiNi0.5Mn1.5O4 cathode has received great attentions due to its high operation voltage of around 4.7 V However, its poor high rate performances cannot satisfy with high power applications Many strategies have been employed to improve its high rate performances The aim of this research was to firstly design and synthesis LiNi0.5Mn1.5O4 cathodes modified by 4d transition metals; and then thoroughly investigate their crystal structures, particle morphologies, charge transportation properties as well as electrochemical performances Ru, Rh and Nb doped LiNi0.5Mn1.5O4 spinels have been synthesized by solid state reactions Ru doped LiNi0.5Mn1.5O4 exhibited the best electrochemical performances and can deliver a capacity of 117 mAh g-1 even at an extremely high discharge rate of 1470 mA g-1 (10 C rate), and excellent cyclic performances at the 10 C charge/discharge rate for 500 cycles are achieved The electronic conductivties of Ru doped LiNi0.5Mn1.5O4 can be as high as 3.2 times of that of the LiNi0.5Mn1.5O4 Delocalized 4d orbitals and large 4d orbitals‟ radius overlapping with O 2p orbitals have been proposed to be main mechanisms for enhanced electronic conductivity Lithium diffusivity has also been improved through Ru doping Ru doped LiNi0.5Mn1.5O4 synthesized by solid state reactions exhibited much better electrochemical performances at high rates compared to pristine V Summary LiNi0.5Mn1.5O4, which can be attributed to greatly enhanced charge transportation properties Although electrochemical results show that Rh doping can improve the high rate performances of LiNi0.5Mn1.5O4, it cannot compete with the effects of Ru doping Synthesis of phase pure Nb doped LiNi0.5Mn1.5O4 spinels are not successful LiNbO3 impurity with poor electronic conductivity presents in Nb doped samples Suffering from LiNbO3, Nb doped LiNi0.5Mn1.5O4 exhibit poor electrochemical performances even at low rates Several methods attempting to obtain Ru doped LiNi0.5Mn1.5O4 spinels with reduced particle size were investigated Phase pure spinel-structured LiNi0.5-2zRu zMn1.5O4 particles have been successfully synthesized by polymer assisted method (PA) With reduced particle size, the high rate electrochemical performances have been further improved compared to micron sized LiNi0.5-2zRu zMn1.5O4 The results presented here have demonstrated the ability of 4d transition metals doping to improve high-rate electrochemical performances of spinel-structured LiNi0.5Mn1.5O4 cathode materials We believe that this strategy may pave the way for the practical application of spinel-structured transition metal oxides as cathode materials for next generation of high power lithium-ion batteries VI List of Figures List of Figures Fig 1.1 Illustration of lithium ion battery Fig 1.2 Crystal structure of LiMO2 with layered structure (M=transition metal) Fig 1.3 Charge and discharge curves of LiCoO2: (a) Li/LiCoO2, and (b) Li/graphite cell Fig 1.4 Energy vs density of states of Co3+/4+ for LiCoO2 Fig 1.5 Crystal structure of spinel LiMn2O4 15 Fig 1.6 Charge and discharge curves of LiMn2O4 15 Fig 1.7 Crystal structure of LiFePO4 21 Fig 1.8 Charge and discharge curves of LiFePO4 [59] 21 Fig 1.9 Illustration of damage of LiNi0.5Mn1.5O4 particle at high rate discharge caused by low conductivity 31 Fig 3.1 Illustration of LiNi0.5Mn1.5O4 spinel structure ( Fig 3.2 Illustration of LiNi0.5-2zRuzMn1.5O4 spinel structure ( space group) 48 space group) 50 Fig 3.3 SEM morphology of (a) LiNi0.5Mn1.5O4, (b) Li1.1Ni0.35Ru0.05Mn1.5O4, (c) LiNi0.48Ru0.01Mn1.5O4, (d) LiNi0.44Ru0.03Mn1.5O4 and (e) LiNi0.4Ru0.05Mn1.5O4 53 Fig 3.4 TEM observation and EDX spectrum of (a) LiNi 0.5Mn1.5O4, (b) Li1.1Ni0.35Ru0.05Mn1.5O4 and (c) LiNi0.4Ru0.05Mn1.5O4 54 Fig 3.5 XRD profiles and Rietveld refinement results of (a) LiNi 0.5Mn1.5O4, (b) Li1.1Ni0.35Ru0.05Mn1.5O4, (c) LiNi0.48Ru0.01Mn1.5O4, (d) LiNi0.44Ru0.03Mn1.5O4 and (e) LiNi0.4Ru0.05Mn1.5O4 55 Fig 3.6 Lattice constant variation with Ru doping 58 Fig 3.7 Selected area electron diffraction patterns in [100] zone of (a) LiNi0.5Mn1.5O4, (b) Li1.1Ni0.35Ru0.05Mn1.5O4, (c) LiNi0.48Ru0.01Mn1.5O4, (d) LiNi0.44Ru0.03Mn1.5O4 and (e) LiNi0.4Ru0.05Mn1.5O4 59 Fig 3.8 The impedance spectra of LiNi0.5Mn1.5O4 and Ru doped LiNi0.5Mn1.5O4 measured at room temperature 60 VII List of Figures Fig 3.9 dc conductivity results of LiNi0.5Mn1.5O4 and Ru doped LiNi0.5Mn1.5O4 measured at room temperature 62 Fig 3.10 Calculated electronic and electrical conductivities of LiNi 0.5-2zRuzMn1.5O4 (z=0, 0.01, 0.03 and 0.05) 63 Fig 3.11 Electronic configurations of Ni2+ and Ru4+ 64 Fig 3.12 Charge/discharge profiles at 0.2 C of (a) LiNi 0.5Mn1.5O4, (b) Li1.1Ni0.35Ru0.05Mn1.5O4, (c) LiNi0.48Ru0.01Mn1.5O4, (d) LiNi0.44Ru0.03Mn1.5O4 and (e) LiNi0.4Ru0.05Mn1.5O4 67 Fig 3.13 dQ/dV curve of (a) LiNi0.5Mn1.5O4, (b) Li1.1Ni0.35Ru0.05Mn1.5O4, (c) LiNi0.48Ru0.01Mn1.5O4, (d) LiNi0.44Ru0.03Mn1.5O4 and (e) LiNi0.4Ru0.05Mn1.5O4 69 Fig 3.14 Rate capability of (a) LiNi0.5Mn1.5O4, (b) Li1.1Ni0.35Ru0.05Mn1.5O4, (c) LiNi0.48Ru0.01Mn1.5O4, (d) LiNi0.44Ru0.03Mn1.5O4 and (e) LiNi0.4Ru0.05Mn1.5O4 73 Fig 3.15 Discharge capacity retention at different discharge rates 75 Fig 3.16 Cyclic performance of LiNi0.5Mn1.5O4 and Ru doped LiNi0.5Mn1.5O4 charged/discharged at 1470 mAh g-1 (10 C) 76 Fig 4.1 XRD profiles of LiNi0.5Mn1.5O4, LiNi0.425Rh0.05Mn1.5O4 and LiNi0.4Rh0.05Mn1.5O4 82 Fig 4.2 SEM morphology of (a) LiNi0.5Mn1.5O4, (b) LiNi0.4Rh0.05Mn1.5O4 and (c) LiNi0.425Rh0.05Mn1.5O4 86 Fig 4.3 Charge/discharge profiles of (a) LiNi0.5Mn1.5O4, (b) LiNi0.4Rh0.05Mn1.5O4 and (c) LiNi0.425Rh0.05Mn1.5O4 87 Fig 4.4 dQ/dV curve of (a) LiNi0.5Mn1.5O4, (b) LiNi0.4Rh0.05Mn1.5O4 and (c) LiNi0.425Rh0.05Mn1.5O4 88 Fig 4.5 Rate capability of (a) LiNi0.5Mn1.5O4, (b) LiNi0.4Rh0.05Mn1.5O4 and (c) LiNi0.425Rh0.05Mn1.5O4 90 Fig 4.6 Cyclic performance of LiNi0.5Mn1.5O4 and Rh doped LiNi0.5Mn1.5O4 at 1470 mAh g-1 (10 C) 91 Fig 5.1 XRD profiles of LiNi0.5Mn1.5O4, LiNi0.425Nb0.03Mn1.5O4, LiNi0.4Nb0.04Mn1.5O4 and LiNi0.4Nb0.05Mn1.5O4 96 Fig 5.2 SEM morphology of (a) LiNi0.5Mn1.5O4, (b) LiNi0.425Nb0.03Mn1.5O4, (c) LiNi0.4Nb0.04Mn1.5O4 and (d) LiNi0.4Nb0.05Mn1.5O4 98 VIII List of Figures Fig 5.3 Charge/discharge profiles of (a) LiNi0.5Mn1.5O4, (b) LiNi0.425Nb0.03Mn1.5O4, (c) LiNi0.4Nb0.04Mn1.5O4 and (d) LiNi0.4Nb0.05Mn1.5O4 100 Fig 5.4 dQ/dV curve of (a) LiNi0.5Mn1.5O4, (b) LiNi0.425Nb0.03Mn1.5O4, (c) LiNi0.4Nb0.04Mn1.5O4 and (d) LiNi0.4Nb0.05Mn1.5O4 101 Fig 5.5 Rate capability of (a) LiNi0.5Mn1.5O4, (b) LiNi0.425Nb0.03Mn1.5O4, (c) LiNi0.4Nb0.04Mn1.5O4 and (d) LiNi0.4Nb0.05Mn1.5O4 103 Fig 5.6 Cyclic performance of LiNi0.5Mn1.5O4 and Nb doped LiNi0.5Mn1.5O4 at 1470 mAh g-1 (10 C) 104 Fig 6.1 SEM morphology of (a) PE-LiNi0.5Mn1.5O4, (b) PE-LiNi0.4Ru0.05Mn1.5O4, (c) RF-LiNi0.5Mn1.5O4, (d) RF-LiNi0.4Ru0.05Mn1.5O4, (e) PA-LiNi0.5Mn1.5O4 and (f) PA-LiNi0.4Ru0.05Mn1.5O4 109 Fig 6.2 XRD results of (a) PE-LiNi0.5Mn1.5O4, PE-LiNi0.4Ru0.05Mn1.5O4, (b) RF-LiNi0.5Mn1.5O4, RF-LiNi0.4Ru0.05Mn1.5O4, and (c) PA-LiNi0.5Mn1.5O4 and PA-LiNi0.4Ru0.05Mn1.5O4 111 Fig 6.3 SEM morphology of PA-LiNi0.5-2zRuzMn1.5O4 with (a) z=0, (b) z=0.01, (c) z=0.03 and (d) z=0.05 113 Fig 6.4 XRD results of LiNi0.5-2zRuzMn1.5O4 (z=0, 0.01, 0.03 and 0.05) 115 Fig 6.5 FTIR results of LiNi0.5-2zRuzMn1.5O4 (z=0, 0.01, 0.03 and 0.05) 115 Fig 6.6 Charge/discharge profiles of PA-LiNi0.5-2zRuzMn1.5O4 at 0.2 C with (a) z=0, (b) z=0.01, (c) z=0.03 and (d) z= 0.05 118 Fig 6.7 dQ/dV curve of PA-LiNi0.5-2zRuzMn1.5O4 with (a) z=0, (b) z=0.01, (c) z=0.03 and (d) z= 0.05 120 Fig 6.8 The 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