MINISTRY OF EDUCATION AND TRAINING VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY LA THI HANG SYNTHESIS OF LiFe1-xMxPO4/GRAPHENE NANOCOMPOSITE AS CATHODE MATERIAL TO IMPROVE ELECTROCHEMICAL PROPERTIES FOR LITHIUM-ION BATTERIES SUMMARY OF THESIS Major: Theoretical and Physical Chemistry Code: 9440119 HCMC-2019 The Thesis has been performed at: Institute of Applied Materials Science (IAMS) – Graduate University Science and Technology – Vietnam Academy of Science and Technology (VAST) …… ….………… Advisor 1: Assoc Prof Nguyen Nhi Tru Advisor 2: Assoc Prof Le My Loan Phung Reviewer 1: … Reviewer 2: … Reviewer 3: … The thesis was presented at National level Council of Doctoral Thesis Assessment held at Graduate University of Science and Technology – Vietnam Academy of Science and Technology at….on…… The Thesis can be stored at: - The Library of Graduate University of Science and Technology - -National Library of Vietnam INTRODUCTION The important role of thesis These days the seriousness surrounding and pertaining to the-renewable energy crisis can cause exploited demands to the surrounding ecosystems leading to depletion, pollution and climate change including the alarming negative effects such as eroded environments For these reasons, renewable energy should be increasingly promoted and developed further development and research such as: solar, wind and tide… thereby reducing our reliance on fossil fuels and the depletion of crucial ecosystems However, these resources have huge disadvantages that are intermittent and dependent on conditional factors related to the climate, so using them poses many challenges for its application Therefore, solving these problems requires the creation of efficient energy storage devices for the development of renewable energy transferred from chemical energy to electrical energy This is an important role and strategy toward the improvement of renewable energy for global solutions Since the advent of these technologies the rechargeable of Li-ion batteries were born, it brings many achievements for application science to contribute enhancement of new technology and various type of batteries for modern electrical and electronic technology Rechargeable batteries are devices which enable energy storage and release directly as electricity; by means of highly reversible electrochemical reactions Today, this storage dominates market in Portable mobile electronics with more potentials than other devices consideration: Large battery power, high energy density, light weight, safe and stability, as well as design flexibility With good characteristic, Li-ion batteries could replace traditional storage In recent years, Li-ion batteries have been considered the main structure to investigate electrochemical properties, especially, material electrode Actually, Commercial rechargeable LiCoO2 for Li-ion batteries with specific capacity: 248 mAh.g-1 has been the choice material in the predominate market with the electronic devices in this field since the commercialization by Sony Energitech in 1992 However, this compound using cathode material has met some limitations with respect to charge-discharge issue, additionally safe, unfriendly environments at expensive costs (rate of 0.001% Co, 1.5% Fe in the Earth) LiFePO4 structural olivine is excellent choice with prolonged it’s life time, deeply cycle stability, environmental friendliness, and advantageous low cost but olivine structure has only one channel of direction [010], the intrinsic electronic conductivity of LFP olivine structure Actually, LiFePO4 (LFP) has one huge drawback shown due to its rigid orthorhombic and Li+ diffusion rate is considerably low to reach it’s full theoretical capacity during battery operation Plainly, it’s oxidation properties from Fe2+ to Fe3+ make it a less suitable choice, these problems lead to poor performance with Li-ion batteries to meet some challenges due with commercialization To solve this problem, researchers in the world focus on improvement of ionic conductivity (10-9-10-10 S.cm-1) and diffusion coefficient (10-12-10-14 cm2.S-1) ion Li+ in order to enhance higher capacity in a high rate charge-discharge by this method of expansion; instinct-LFP: doping metal as a new material LiFexM1-xPO4 (LFMP) or coating carbon (LFP/C) and reduced size Recently, the publication of these materials using cathode to enhancement of electrochemical properties for Li ion batteries have related to doping metals or coating graphene as individuality instead of linking together in recent decades Furthermore, the number of international publications on metal-doped LiFePO4 materials and coated and graphene has been limited with LiFexM1-xPO4/graphene composite nano materials less or none of researches studied deeply the differences with several kinds of electrochemical performance by evaluation of the kinetic element of Li+ ion diffusion process into olivine structure According to international publications in the world as well as inheriting previous research based knowledge, this thesis was chosen as its basis “Synthesis of LiFexM1-xPO4/graphene nanocomposite as cathode material to improve electrochemical properties for lithium-ion batteries In this study, therein, survey the influence various rate of metal-doped materials on diffusion kinetic process of ion Li+ to distinguish electrochemical properties before and after doping metals Besides, graphene coated-LiFe1-xMxPO4 materials as nanocomposite LiFe1-xMxPO4/graphene was investigated scope of olivine structure, morphology and the role of their improvement of electrochemial properties The research results offered considerable contributions of solving the urgent problems for LFP materials to offer new rechargeable batteries with at inexpensive price including safety and environmental friendliness LFP cathode is also a promising material for use in rechargeable batteries in electric vehicles compared to the lithium oxide layer structure materials using Co, Ni due to low toxicity and abundant in nature The target of thesis Nanocomposite material LiFe1-xMxPO4/Gr was successfully synthesized achieving it with single phase It’s response required electrochemical parameters of positive electrode materials for Li-ion batteries such as: improved diffusion coefficient and conductivity, higher capacity comparative with LFP in same conditional synthesis There are the specific ideas - Investigations relation of the process’s of synthesis in structural olivine LFP by the solvothermal method and investigation of different synthesized parameters such as: temperature, solvent and the ratio of precursors.… - Investigations in the process of structural olivine was synthesized by solvothermal method, analysis and appreciation of structure, morphology and the chemical components of compound - The Study of kinetic process of lithium extraction/insertion after doped metal-LFP with various ratio of weight Mn+ (Ni, Mn, Y) We also evaluate the linkage between graphene thin film materials, LiFe1xMxPO4/Gr structure as well as graphene's role in electrical conductivity and electrochemical properties of materials - Investigations in the performance of LiFe1-xMxPO4/Gr materials for cathode Li-ion batteries (capacity, cyclic) in in the model CR2032 NEW CONTRIBUTIONS OF THE THESIS LiFe1-xMxPO4/C nanocomposite was synthesized via solvothermal method by simultaneously doping various metals such as: Mn, Ni, Y, etc and carbon coating The carbon coating is itself from two separate sources: organic carbon (in situ) and graphene (ex situ) powder with LiFe1-xMxPO4/C material crystals of graphene honeycomb network based on the difference in electronegativity of the atoms creating the effect of charge attraction between graphene and LFMP hexagonal networks to create composite materials with structure sustainable structure and excellent electrochemical performance In contrast, previously published research only involves either graphene coating on LiFePO (LiFePO4/Gr) or doping M metals into the structure of material for LiFe1-xMxPO4 synthesis It was empirically shown that after doping with M metals, the structure of the resultant materials is linearly retained without alterations to the olivine structure, in accordance with Vegard’s Law With doping metal and coating graphene, the synthesized LiFe1-xMxPO4/C material exhibits behaviors with Li+ ions’ movements through the olivine structure is predominantly controlled by the diffusion Warburg mechanism This is the theoretical basis for improving electrochemical efficiency through enhancing the diffusion coefficient and conductivity (5,1.10-3 S.cm-1) increasing 104-105 times (in comparison with LiFePO4 theory), resulting in specific capacity reaching 155-165 mAh.g-1 at C/10 remaining 96% after 20 cycles Using solvothermal method, LiFe0.8Mn0.2PO4/5%Gr has been successfully fabricated achieving specific capacity approximately equivalent to theoretical value of LiFePO4 The weight ratio of 20% Mn and 5% graphene can therefore be used to prepare LiFe1-xMxPO4/C as cathode materials for rechargeable Li-ion batteries, opening up new opportunities for expanding the scope of applications at a higher capacity PUBLICATIONS Huynh Le Thanh Nguyen, Nguyen Thi My Anh, Tran Van Man, La Thi Hang, Tran Thu Trang, Tran Thi Thuy Dung, Electrode composite LiFePO4@carbon: structure and electrochemical performances, Journal of Nanomaterials, 2019, 1-10 (SCI-E) La Thi Hang, Nguyen Thi My Anh, Nguyen Nhi Tru, Huynh Le Thanh Nguyen, Le My Loan Phung,Modification of nano-sized LiFePO4 via nickel doping and graphene coating, International Journal of Nanotechnology, 2019, 914-924(SCI-E) Dinh Duc Thanh, Nguyen Thi My Anh, Nguyen Nhi Tru, La Thi Hang, Le My Loan Phung, The impact of carbon additives on lithium ion diffusion kinetic of LiFePO4/C composites, The Science and Technology Development Journal, 22(1), 2019, 173 – 179 La Thi Hang, Nguyen Nhi Tru, Le My Loan Phung, Olivine structured LiFexYyPO4/C composite synthesized via solvothermal route as cathode material for lithium batteries, Vietnam Journal of Chemistry, 56(6E2), 2018, 267-271 Bui Thi Thao Nguyen, Doan Thi Kim Bong, La Thi Hang, Nguyen Nhi Tru, Hoang Xuan Tung, Nguyen Thi My Anh, -Modification of Ketjenblack EC-600JD carbon as filler in cathode material for lithium-ion battery, Vietnam Journal of Chemistry, 56(6E2), 2018, 262-266 Nguyen Thi My Anh, Doan Luong Vu, Nguyen Thai Hoa, Le My Loan Phung, Nguyen Ba Tai, La Thi Hang, Nguyen Ngoc Trung, Nguyen Nhi Tru- Characterization of LiFePO4 nanostructures synthesized by solvothermal method Journal of Science and Technology, Technical universities 118, 2017, 45-50 La Thi Hang, Le My Loan Phung, Nguyen Thi My Anh, Hoang Xuan Tung, Doan Phuc Luan, NguyenNhi Tru- Enhancement of li–ion battery capacity using nickel doped LiFePO4 as cathode material Journal of Science and Technology 55_1B, 2017, 267-283 La Thi Hang, Nguyen Nhi Tru, Nguyen Thi My Anh, Le My Loan Phung, Doan Luong Vu, Doan Phuc Luan, –Microwave-assisted solvothermal synthesis of LiFePO4/C nanostructures for lithium ion batteries, Proceedings of the 5th Asian Materials Data Symposium HaNoi 10, 2016, 343-352 CHAPTER INTRODUCTION This chapter expresses a brief overview of the Li-ion rechargeable battery and the history of it’s development and research in countries around the world This secondary rechargeable battery is of special interest with some advantages in electrochemical properties as well as durability and especially positive trends impacts on the environment as compared to other chemical traditional storage devices Studies surrounding the principles of operation the properties of fabrication of the battery Herein, analyzing the advantages and disadvantages of the battery to overcome the limitations of energy storage device Surveys show that recent studies focus on changing cathode material composition to increase it charging efficiency and durable battery Statistics and collection of documents from various publications about various types of cathode electrode materials and improvement directions Specifically, highly studied cathode materials in which the olivine LiFePO4 (LFP) is considered as the most famous candidate for the family of olivine-type lithium transition metal phosphates by a relative specific capacity for the cathodes lithium-ion batteries High capacity (170 mAh.g-1), flat voltage (3.45 V vs Li+/Li), slight weight, inexpensive (18-20 USD/kg of powder material) due to the amount of Fe in Earth's crust and nontoxic lead to environmental friendness However, commercializing this material is a major barrier because the element Fe is easily oxidized, the + Li ion is less flexible because it moves a single diffraction direction [010] in the olivine tunnel structure, resulting in poor electrical conductivity (10-14 S.cm-1) and low diffusion coefficients (10-12-10-14 cm2.s-1) The author has surveyed and collected documents from published works, to improve the disadvantages of LFP materials with various approaches as a key in the electrochemistry The following consideratiions and mentions are applicable Control particle size (i) nanometer (nm) with nano size (100-350 nm) and well-shape crystals are important for enhancing the electrochemical properties because of shortening the amplitude of redox potential Besides, reducing particle size increases electron density, shortening the distance of Li+ ion diffusion can increase diffusion coefficients Another improvement that is of interest is metal doping (ii) electronic density enrichment that displaces the potential and increases the electrical conductivity of the material Doping is good way for stabilizing the lattice structure of this class of inorganic electroactive materials Lastly, It is well-known that carbon as a reducing agent prevents the formation of Fe3+ impurity and the agglomeration of particles during the preparation of LFP, but it also can significantly improve the battery performance Coated-carbon (iii) on the material is also appreciated because it conducts electricity well on large surface contact areas as a conductive bridge and preventage corrosion of the electrode and limits exposure to the atmosphere CHAPTER EXPERIMENT 2.1 The route of synthesis LiFePO4, LiFe1-xMxPO4, LiFe1-xMxPO4/Gr The chemical precursors using synthesis of LFP, LiFe1-xMxPO4, LiFe1-xMxPO4/Gr as: LiOH.H2O (98%, Fisher); FeSO4.7H2O (99,9%, Fisher); Mn(NO3)2.4H2O (99,98%, Merck); Y(NO3)2.6H2O (99,9%, Merck), H3PO4 (99,98%, Merck), ascorbic acid (99,87%, Merck); H3PO4 (99,98%, Fisher) ethylene glycol (99, 87%, Merck), graphene (Merck) The precursors was weighted and measured basing on the rate of chemical formula of the material synthesis by an analytical balance of odd numbers based on the ratio of Li: Fe: P and the number of moles of Li was chosen random: 0.03, 0.027, 0.025 mol The author was defined ratio of Li:Fe:P = 3:1:1 achieving a single-phase material with high quality crystallization; ascorbic acid as a agent prevented oxidation Fe2+ and a reducing agent transferring Fe3+ to Fe2+ This mixture was dissolved in solvent with ethylene glycol/water (ratio volume: 4:1 stirring under ultrasonication until clear solution) in nitrogen atmosphere The solution was finally transferred into autoclave under the argon atmosphere to perform the solvothermal reaction in 180 °C for h After reaction, the greyish precipitate was centrifuged, rinsed repeatedly with ethanol and dried in vacuum at 70 °C for 7-9 hours After that, the powder product is stored in desiccator at room temperature to avoid the moisture in the environment Lastly, the sample was finally calcined at 550-600 °C in nitrogen atmosphere for h to remove impurities The mass and volume of precursors used for LFP synthesis are shown in Table 2.3; to synthesize doped LFP Mn, Ni, Y and to synthesize doped-LFP and graphene-coated LFP materials respectively Table 2.4, 2.5 Table 2.3 The mass/ volume of precursor expenditure for synthesis of LFP A ST01 ST02 ST03 LiOH.H2O (g) 41.96 1.2588 1.1329 1.0490 FeSO4.7H2O (g) 278.01 2.7801 2.7801 2.7801 ST00 1.2588 2.7801 Samples C6H8O6 (g) 176.12 0.2202 0.2202 0.2202 - H3PO4 (g) 97.99 1.1596 1.1596 1.1596 1.1596 C2H4(OH)2 (ml) 80 80 80 - H2O (ml) 20 20 20 100 Tỉ lệ Li: Fe: P 3.0:1:1 2.7:1:1 2.5:1:1 3.0:1:1 Table 2.4 The mass/ volume of precursor expenditure for synthesis of metal dopant -LFP Samples FeSO4.7H2O (g) 278.01 2.6970 2.6411 2.5029 STM1 LiOH.H2O (g) 41.96 1.2588 1.2588 1.2588 1.2588 2.2241 M(NO3)n.6H2O (g) 0.0872 0.1454 0.2908 0.5740 C6H8O6 (g) 176.12 0.22015 0.22015 0.22015 0.22015 H3PO4 (g) 97.99 1.1596 1.1596 1.1596 1.1596 STM2 1.2588 2.0851 0.4305 0.22015 1.1596 STM3 1.2588 2.2241 0.4305, 0.1454 0.22015 1.1596 STY1 1.2588 2.6970 0.1149 0.22015 1.1596 STY2 1.2588 2.7245 0.0766 0.22015 1.1596 STY3 1.2588 2.7523 0.0383 0.22015 1.1596 Khối lượng mol STN1 STN2 Ni2+ STN3 Mn2+ Mn2+, Ni2+ Y3+ Ni(NO3)2.6H2O = 290,8; Mn(NO3)2.6H2O = 287,04; Y(NO3)3.6H2O = 383 Bảng 2.5 The mass/volume of precursor using for synthesis of LiFe1-xMxPO4/Gr FeSO4.7H2O (g) 278.01 2.6411 2.6411 2.2241 STM2-G2 LiOH.H2O (g) 41.96 1.2588 1.2588 1.2588 1.2588 2.2241 M(NO3)n.6H2O (g) (*) 0.1454 0.1454 0.5740 0.5740 C6H8O6 (g) 176.12 0.22015 0.22015 0.22015 0.22015 H3PO4 (g) 97.99 1.1596 1.1596 1.1596 1.1596 Graphene (g) 12 0.08605 0.1721 0.0859 0.1718 STY1-G1 1.2588 2.7245 0.0766 0.22015 1.1596 0.08633 STY2-G2 1.2588 2.7245 0.0766 0.22015 1.1596 0.17266 STM3-G1 1.2588 2.2241 0.4305, 0.1454 0.22015 1.1596 0.08453 Samples M STN1-G1 STN2-G2 STM1-G1 2.2 The Analysis Method Iron contents in LFP and nickel doped LFP were analyzed by the volumetric titration method using KMnO4 in concentrated H2SO4 medium to fully oxidized-Fe2+ to Fe3+ The LFP and LFNP samples were stirred with 50 mL H2SO4 until the formation of a clear green solution was created The solution was then titrated with 0.0125N KMnO4 The LFP, LiFe1-xMxPO4, LiFe1-xMxPO4/Gr crystalline structure, phase purity and the particles size were characterized using a Rigaku/max 2500Pc and D8 Brucker X-ray diffractometer (XRD) with Cu-Kα radiation (λ=1.5418 Å, 2: 0° to 90° at a scan rate 0.25 -1.00 °/s) Raman measurements were performed using Horiba Jobin Yvon LabRAM HR300 system with 514.5 nm laser radiation, and the resolution of the measurement system was cm-1 Raman spectra ranges from 1003000 cm-1 With µm penetration, the vibration of LFNP bonds was determined and its structure and thin nanographene was identified The system uses two excitation lasers and magnetic ways (600 lines / mm to 2400 lines/mm) The controled heat speed is completed by software with an error of ± 0.1oC, measuring materials in powder form Thermogravimetric analysis (TGA) technique with the type of Seratam LABSYS Evo TG-DSC at a heating rate of 10 oK/min in argon environment was implemented to determine the impurities phase contents in the samples The mass in a sample of 100-150 mg its decreases it’s following when heating from 100 -1200 o C, rate scan 5-10 oC/minutes, time for scan reaching 50 minutes was performed at HCM City University Department of Education This method was used as a predication of thermal stability with the calculation of crystallization content with the sample Flame Atomic Absorption Spectrometry (FAAS) on AA-6800 machine (Shimadzu, Japan) ionte in air-acetylene flame at about 2700 °C This technique is typically used for determinations in the mg/ L range, and may be extended down to a few μg /L with radiation wavelength: 253.7 nm, sensitivity: 0.1 ppm, operation mode: CV-AAS at HCM city University of Science Energy dispersive X-rays (EDX - Hitachi SU6600, pressure < 10 pA, time lines: 30- 40 s, resolution: 127 eV) analysis was conducted to identify the elements occurring in structure And using EDS Edax Team software analyzed data The composite morphology and particle size were characterized by Scanning Electron Microscopy (SEM– type of 4800 machine: kV, 8.5 mm x 20.0 k, the SEM images was studied at National Institute of Hygiene and Epidemiology), Field Emission Scanning Electron Microscopy (FESEM-Hitachi SU6600 equipment with machine parameters: 10 kV, 9.8 mm x 20 k at Institute for Nanotechnology in HCM city) and Transmission Electron Microscope (TEM-JEM-1400 with resolution of 0.2-0.38 nm, capacity of 100 kW, magnification of 2-3 Å), High-Resolution Transmission Electron Microscopy (HRTEM-FEI T20 at Singapore) Those methods was deeply investigated determination of particle morphology as well as analyzing the graphene film coating structure on material particles In addition, with high-resolution HR-TEM technique, it’s possible to identify graphene film image and thickness and number of layers (sheet) X-ray Photoelectron spectroscopy (XPS) is well-method was used to determine the percentage of elements on the thin layer of materials (