EFFECTS OF ELECTROLYTE SOLUTION TO THE PROPERTIES OF RECHARGEABLE BATTERY lani4 5 ge0 5

VIETNAM NATIONAL UNIVERSITY, HANOI VNU UNIVERSITY OF SCIENCE FACULTY OF PHYSICS Nguyen Thi Thu Huyen EFFECTS OF ELECTROLYTE SOLUTION TO THE PROPERTIES OF RECHARGEABLE BATTERY LaNi4.5 Ge0.5 International Standard Program Hanoi - 2016 VIETNAM NATIONAL UNIVERSITY, HANOI VNU UNIVERSITY OF SCIENCE FACULTY OF PHYSICS Nguyen Thi Thu Huyen EFFECTS OF ELECTROLYTE SOLUTION TO THE PROPERTIES OF RECHARGEABLE BATTERY LaNi4.5 Ge0.5 International Standard Program Supervisor: Prof Dr Luu Tuan Tai Hanoi - 2016 ACKNOWLEDGEMENT First and foremost, I would like to express my special thanks of gratitude to my teacher Prof Dr Luu Tuan Tai who gave me the precious opportunity to and finish this wonderful project My sincere thanks for your continuous support, your patience, enthusiasm and immense knowledge I could not have imagined having better advisors for my study My sincere thanks also go to teachers, officers and friends at Faculty of Physics University of Natural Sciences for always supply best conditions to me to this thesis Finally I would like to thank all relatives and friends for all the support and active my staff when I made this thesis Ha Noi, June 2016 Student Nguyen Thi Thu Huyen Numerical calculation and graphed Figure 1.1: Crystal structure of LaNi5 intermetallic compound[9] Figure 1.2: Dependence of LnPH2 to 1/T Figure 1.3: Shematic representation of an interphase for a hydrogen absorbing metal (a)absorption plan; (t) charge tranfer plane; (l) lattice[9] Figure 1.4: Schematic charge/discharge of Ni-MH battery[8] Figure 1.5: Schematic representation of the concept of a sealed rechargeable Ni- MH battery[8] Figure 1.6: Charge characteristics of Ni-MH battery Figure 1.7 : Discharge characteristic of Ni-MH battery Figure 1.8: Schematic representation of the hydride formation/decomposition via a gas phase(a) and electrochemical charge transfer reaction(b) Figure 1.9 : Reaction scheme proposed by Bode et al[8] for the Ni electrode reactions in alkaline solutions Figure 1.10: Schematized solid- state transition mechanism for the Ni(OH)2/NIOOH charge transfer reaction Figure 2.1: Making sample system using arc melting(ITIMS) Figure 2.2: X-diffraction device Figure 2.3: Three electrodes electrochemical cell Figure 2.4 : E0 measurement of an working electrode Figure 2.5: Charge- discharge measurement schema Figure 2.6 Cyclic Voltammetric measurement system Table 3.1: Lattice parameters of sample before and after charge/discharge cycles Figure 3.1 The sites for H in lattice LaNi5 intermetallic compound Figure 3.2 : X-ray diffraction spectra of LaNi4.5Ge0.5 and its hydride Figure 3.3: Magnetization curve of LaNi4.5 Ge0.5 before charge/ discharge Figure 3.4: Magnetization curve of LaNi4.5 Ge0.5 after 5th cycle in KOH (6M) Figure 3.5: Magnetization curve of LaNi4.5 Ge0.5 after 5th cycle in KOH(5M)and LiOH(1M) Figure 3.6: Magnetization curve of LaNi4.5 Ge0.5 after 5th cycle in KOH(5,1M)and LiOH(0.9M) Figure 3.7: Cycle performance of LaNi4.5Ge0.5 in KOH (6M ) and LiOH(1M) Figure 3.8: Cycle performance of LaNi4.5Ge0.5 in KOH(5M) and LiOH(1M) Figure 3.9: Cycle performance of LaNi4.5Ge0.5 in KOH(6M) Figure 3.10: Cycle performance of LaNi4.5Ge0.5 in KOH (5.1M ) and LiOH(0.9M) Content Introduction Chapter 1: Intermetallic hydride material and rechargeable nickel- metal hydride battery 1.1 The intermetallic hydride material 1.1.1Crystal structure of intermetallic compounds base on LaNi5 .2 1.1.2 Kinetics of sorption and desorption of hydrogen .3 1.1.3 Hydrogen adsorption capability of intermetallic compounds 1.1.4 Hydro sorption in electrochemical systems .5 1.1.5 Magnetic properties 1.2 Rechargeable Nickel-Metal hydride (Ni-MH) battery 1.2.1 The reactions 1.2.2 Structure of nickel Hydride Batteries 1.2.3 Charge charateristics 1.2.4 Discharge characteristics 1.2.5 Discharge characteristics 1.2.6 The nickel oxide electrode .12 Chapter 2: Experimental techniques 16 2.1 Sample preparation 16 2.2 X-ray diffraction measurement .17 2.3 Magnetic measurements 18 2.4 Electrochemical studies 18 2.4.1 Three electrodes electrochemical system 18 2.4.2 Open- circuit potential measurement .19 2.4.3 Galvanostatic charge-discharge cycles .20 2.4.4 Cyclic Voltammetric technique 21 Chapter 3: Results and discussion .24 3.1 Crystal structure analysis 24 3.3 The electrochemical results .27 Conclusion 32 Introduction Hydrogen absorption capacity of the inter-metallic diatomic compounds materials were first discovered in the late 60s of the 20th century Since then, the compounds RT5 have been known and studied a lot because of the ability to absorb and disabsorb the very large amounts of hydrogen at atmospheric pressure and room temperature [9] which does not damage the lattice structure Hydrogen accumulation in the crystal lattice of the material creates a permanent-form hydrogen container and energy reserves This feature has been applied in many fields of science and technology, one of the applications that is built rechargeable battery cathode Ni-MH[[3,4] The advantages of Ni-MH battery are high-capacity battery and its waste does not pollute the environment[7] On the other hand, compared with Ni-Cd or the lithium battery are familiar products in the electronics and communications handed, Ni-MH battery have longer lifetime and lower cost.[7] Currently, NiMH batteries are widely used, thus improving the quality and innovation are necessary There are many ways to improve the battery performance has been studied as: doping 3d elements capable of absorbing hydrogen, reducing particle size which increase the surface area of the electrode in contact with the electrolyte solution to increase the level of hydrogen absorption, changes capable of releasing hydrogen absorption and by acting on the electrolyte solution.The third way takes very few interested, earlier with NiCd batteries, the electrolyte solution has been carefully studied and selected by the 6M KOH electrolyte solution thus selected now for the same type of positive electrode is NaOH In this work, we focus on the influence of the electrolyte solution to the electrochemical properties of the LaNi4,5Ge0,5 compound The thesis contains three chapters and some conclusions: Chapter 1: Intermetallic hydride material and rechargeable nickelmetal hydride battery Chapter 2: Experimental technique Chapter 3: Results and discussion Chapter 1: Intermetallic hydride material and rechargeable nickel- metal hydride battery 1.1 The intermetallic hydride material 1.1.1Crystal structure of intermetallic compounds base on LaNi5 The intermetallic compound system LaNi5 crystallizes with the hexagonal CaCu5- type structure The structure consists of two alternating types of plane: the basal plane with Lanthanum and Nickel atom which occupy the 1a and 2c sites respectively the z=1/2 plane with only Nickel atoms on the 3g site[[1] Lanthanum 1a NickelI 2c NickelII 3g Figure 1.1: Crystal structure of LaNi5 intermetallic compound[9] The studies of the absorption and the disabsorption have been carried out on their compounds showed that in the process of hydrogenation material, elements entered the hole tetrahedron, octahedron and network failures filled interstitial mechanism alters the lattice constant without changing the material structure 1.1.2 Kinetics of sorption and desorption of hydrogen Hydrogen absorption process can be studied by isotherm of pressure balance as a function of concentration (x) of the oxidizing compound However, according to Bureau, Planagan and Oast, its kinetic process can be studied by a simpler way When hydrogenation occurs with 2-phases to distinguish the values ΔH and ΔF can be obtained from the temperature dependence of the pressure balance Hydrogenation reaction occurs between LaNi5 and hydrogen compounds are represented as follows: LaNi5 + mH2 = LaNi5H2m In thermodynamics, kinetics Vanhoff equation is represented: LnPH2 = -ΔF/R + ΔH/RT where R is the gas constant, the value of ΔH and ΔF is the thermodynamic quantities corresponding to mol hydrogen Considering the temperature range can be considered small enough isothermal, then ΔH and ΔF will not depend on the temperature By plotting the dependence of RnH2 with the inverse of temperature (1 / T) will be obtained superlative line Based on the graph it is easy to find the value of ΔH (corresponding to the slope of the line) and the value ΔS ΔH can get different values, it can have a positive or negative value Hydrogenation occurs in two phases: the first phase to the process of decomposition of hydrogen molecules into atoms, this process consumes energy (ΔH> 0) The second stage occurs as hydrogenation, the process is radiating energy (ΔH [...]... performance of LaNi4. 5Ge0 .5 in KOH (5. 1M ) and LiOH(0.9M) The results in Figure 3.10 indicate that the sample LaNi4. 5Ge0 .5 is charged/discharge in solution KOH (5, 1M) and LiOH( 0,9M) gives the highest performance and most stable, corresponding to the greatest magnetic has been shown By acting on the components of the electrolyte solution, we can get the ratio Cp/Cn to approximately 100% This shows that the electrolyte. .. (6M) In figure3 .5, it shows the magnetization curve after 5 th charge/discharge cycle in electrolyte solution KOH(5M) and LiOH(1M) The maximum value is over 0.3 emu/g Figure 3 .5: Magnetization curve of LaNi4. 5 Ge0 .5 after 5th cycle in KOH(5M)and LiOH(1M) 26 The Figure 3.6 indicate that the sample LaNi4. 5Ge0 .5 is charged/discharged in solution KOH (5. 1) and LiOH(0.9) after 5 cycles gives the highest magnetization... around 55 % 28 Figure 3.8: Cycle performance of LaNi4. 5Ge0 .5 in KOH(5M) and LiOH(1M) In figure 3.9, the percentage Cp/Cn reaches steady state ( around 55 %) after only 13 cycles, and this state lasts until the 50 th cycle To be compared with two solution before, in this electrolyte solution ( KOH(6M)), the electrode works more stable and gets ratio Cp/Cn better Figure 3.9: Cycle performance of LaNi4. 5Ge0 .5. .. versus the applied potential is generally referred to as a voltammogram The magnitude of the current flow will depend on the rate of the slowest reaction step, which may be eithern the mass transport of the analysis to the electrode or the electron tranfer process at the electrode surface If the rate of the reaction can be made sufficiently fast so taht the surface concentration becomes zero, then the. .. for the Ni(OH)2/NIOOH charge transfer reaction During charging both protons and electrons are liberate within the β – Ni(OH)2 solid: Ni(OH)2 =NiOOH +H+ +e- (7) The electrons are transported to the current collector at the back of the electrode On the other hand, protons are transported through the solid by means of diffusion to the solid by means of diffusion to the solid /solution interface, where they... of adsorbed hydrogen into the bulk of the electrode material results in the formation of MH alloy and the MH alloy undergo volumetric deformation Figure 3.1 The sites for H in lattice LaNi5 intermetallic compound 24 We release that the partial substitution of Ni by Ge remains the crystal structure of LaNi5 compounds but makes the lattice expand Figure 3.2 : X-ray diffraction spectra of LaNi4. 5Ge0 .5. .. the RT5 compound through which the hydride is formed Had↔Habs And transport of OH- ions into the bulk of the electrolyte OH-s↔OH-b iv Depending on the materials composition and on the hydrogen concentration in the solid, either an α phase is formed Habs(α) ↔Habs(β) v Recombination of two Had atoms has to be taken into account This lead to the formation of H2, Which is released, from the electode surface... linearly to a more negative potential, and then ramped in reverse back to the staring voltage The forward scan produces a current peak for any analyses that can be reduced through the range of potential scan The current will increase as the potential reaches the reduction potential of the analysis, but then falls off as the concentration of the analysis is depleted close to the electrode surface As the. .. curve of LaNi4. 5 Ge0 .5 after 5th cycle in KOH (5, 1M)and LiOH(0.9M) After 5 charge/discharge cycles in the different solutions the magnetic moment of these sample have been increase significant It is due to during repeated charge/discharge cycling this materials were undergone volumetric deformation, broken and oxidized lead to the Ni decomposed on the surface, this amount of Ni is the main cause of magnetic... decreases quickly to about 45% at some last cycles The fluctuating range from 40 to 70 is quite large, and it shows that the battery with this solution work unstablely Similar to KOH(6M) and LiOH(1M), in Fig 3.8, the ratio Cp/Cn reaches to approximately 50 % within some first cycles, but this percentage drop rapidly to bottom ( about 35% ), then it gets maximium value of 57 % at 34th cycle After 25 cycles, this