Dissertations / Theses on the topic 'Lithium metal anode'

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Kyoto University (京都大学)
0048
新制・論文博士
博士(エネルギー科学)
乙第10221号
論エネ博第7号
新制||エネ||3(附属図書館)
UT51-99-S338
(主査)教授 伊藤 靖彦, 教授 八尾 健, 教授 尾形 幸生
学位規則第4条第2項該当

Since their commercialization in 1990, the electrodes of the lithium-ion battery have remained fundamentally the same. While energy density improvements have come from reducing the cell packaging, higher capacity electrodes are needed to continue this trend. A lithium metal anode, where the negative electrode half reaction is the plating and stripping of metallic lithium, is explored as an alternative to current graphite anodes. The specific capacity of the lithium metal anode is over ten times that of the graphite anode, making it a serious candidate to further improve the energy density of lithium batteries. Electrodeposited lithium metal forms dendrites, sharp needles that can grow across the separator and short circuit the battery. Thus, a chief goal is to alter lithium’s plating morphology. This was achieved in two separate ionic liquid electrolytes by co-depositing lithium with sodium. The co-deposited sodium is thought to block dendritic sites, leading to a granular deposit. A nucleation study confirmed that metal deposits from the ionic liquid electrolyte containing sodium, prevented dendritic growth from nucleation on, and not after dendrites had already grown. A model based on the geometry of the nuclei was used to gain insight into the effect of the solid electrolyte interface (SEI) that forms on freshly deposited lithium metal. In addition to sodium, the effect of alkaline earth metals on the lithium deposit morphology was also explored. While these metals did not deposit from the ionic liquid electrolyte, their addition also resulted in granular, dendrite free, deposits. The alkaline earth additives generally increased the overpotential for nucleating on the substrate and lowered the current density achievable. Strontium and barium showed the least of these negative effects while still providing a dendrite free deposit. A second hurdle for lithium metal anodes is the instability between the electrolyte and lithium metal. A protective SEI layer that prevents undesired side reactions is difficult to form because of the large volume change associated with cycling. Formation of a better SEI on lithium metal was attempted through the addition vinylene carbonate, which greatly improved the coulombic efficiency of lithium metal plating and stripping. The effect of gases, such as oxygen, nitrogen and carbon dioxide, on the SEI layer was also investigated. It was found that the presence of nitrogen and oxygen improved the coulombic efficiency by facilitating a thinner SEI layer. This work presents attempts at improving the lithium metal anode both by increasing the coulombic efficiency of the redox process and by eliminating dendrite growth. The coulombic efficiency was improved through the bubbling of gases and addition of organic additives but work remains to increase this value further. Dendritic growth, which poses a safety hazard, was completely eliminated by two methods: 1) co-deposition and 2) adsorption of a foreign metal. Both methods could potentially be applied to different electrolytes, making them promising methods for preventing dendritic growth in future lithium metal anodes.

Two novel lithium host materials were investigated using structural and electrochemical analysis; the cathode material Li₂CoSiO₄ and the LiMO₂ class of anodes (where M is a transition metal ion). Li₂CoSiO₄ materials were produced utilising a combination of solid state and hydrothermal synthesis conditions. Three Li₂CoSiO₄ polymorphs were synthesised; β[subscript(I)], β[subscript(II)] and γ₀. The Li₂CoSiO₄ polymorphs formed structures based around a distorted Li₃PO₄ structure. The β[subscript(II)] material was indexed to a Pmn2₁ space group, the β[subscript(I)] polymorph to Pbn2₁ and the γ₀ material was indexed to the P2₁/n space group. A varying degree of cation mixing between lithium and cobalt sites was observed across the polymorphs. The β[subscript(II)] polymorph produced 210mAh/g of capacity on first charge, with a first discharge capacity of 67mAh/g. It was found that the β[subscript(I)] material converted to the β[subscript(II)] polymorph during first charge. The γ₀ polymorph showed almost negligible electrochemical performance. Capacity retention of all polymorphs was poor, diminishing significantly by the tenth cycle. The effect of mechanical milling and carbon coating upon β[subscript(II)], β[subscript(I)] and γ₀ materials was also investigated. Various Li[subscript(1+x)]V[subscript(1-x)]O₂ materials (where 0≤X≤0.2) were produced through solid state synthesis. LiVO₂ was found to convert to Li₂VO₂ on discharge, this process was found to be strongly dependent on the amount of excess lithium in the system. The Li₁.₀₈V₀.₉₂O₂ material had the highest first discharge capacity at 310mAh/g. It was found that the initial discharge consisted of several distinct electrochemical processes, connected by a complicated relationship, with significant irreversible capacity on first discharge. Several other LiMO₂ systems were investigated for their ability to convert to layered Li₂MO₂ structures on low voltage discharge. While LiCoO₂ failed to convert to a Li₂CoO₂ structure, LiMn₀.₅Ni₀.₅O₂ underwent an addition type reaction to form Li₂Mn₀.₅Ni₀.₅O₂. A previously unknown Li₂Ni[subscript(X)]Co[subscript(1-X)]O₂ structure was observed, identified during the discharge of LiNi₀.₃₃Co₀.₆₆O₂.

This study highlights the importance of the anion in the electrochemical uptake of lithium by metal phosphides. It is shown through a variety of in-situ and ex-situ analytical techniques that the redox active centers in three different systems (MnP₄, FeP₂, and CoP₃) are not necessarily cationic but can rest almost entirely upon the anionic network, thanks to the high degree of covalency of the metal-phosphorus bond and strong P-character of the uppermost filled electronic bands in the phosphides. The electrochemical mechanism responsible for reversible Li uptake depends on the transition metal, whether a lithiated ternary phase exists in the phase diagram with the same M:P stoichiometry as the binary phase, and on the structure of the starting phase. When both binary and lithiated ternary phases of the transition metal exist, as in the case of MnP₄ and Li₇MnP₄, a semi-topotactic phase transformation between binary and ternary phases occurs upon lithium uptake and removal. When only the binary phase exists two different behaviours are observed. In the FeP₂ system, lithium uptake leads to the formation of an amorphous material in which short-range order persists; removal of lithium reforms some the long-range order bonds. In the case of CoP₃, lithium uptake results in phase decomposition to metallic cobalt plus lithium triphosphide, which becomes the active material for the subsequent cycles.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2002.
Includes bibliographical references.
There has been great recent interest in lithium storage at the anode of Li-ion rechargeable battery by alloying with metals such as Al, Sn, and Sb, or metalloids such as Si, as an alternative to the intercalation of graphite. This is due to the intrinsically high gravimetric and volumetric energy densities of this type of anodes (can be over an order of magnitude of that of graphite). However, the Achilles' heel of these Li-Me alloys has been the poor cyclability, attributed to mechanical failure resulting from the large volume changes accompanying alloying. Me-oxides, explored as candidates for anode materials because of their higher cyclability relative to pure Me, suffer from the problem of first cycle irreversibility. In both these types of systems, much experimental and empirical data have been provided in the literature on a largely comparative basis (i.e. investigations comparing the anode behavior of some new material with older candidates). It is the belief of the author that, in order to successfully proceed with the development of better anode materials, and the subsequent design and production of batteries with better intrinsic energy densities, a fundamental understanding of the relationship between the science and engineering of anode materials must be achieved, via a systematic and quantitative investigation of a variety of materials under a number of experimental conditions. In this thesis, the effects of composition and processing on microstructure and subsequent electrochemical behavior of anodes for Li-ion rechargeable batteries were investigated, using a number of approaches.
(cont.) First, partial reduction of mixed oxides including Sb-V-O, Sb-Mn-O, Ag-V-O, Ag-Mn-O and Sn-Ti-O, was explored as a method to produce anode materials with high cyclability relative to pure metal anodes, and decreased first cycle irreversibility relative to previously produced metal-oxides. The highest cyclability was achieved with anode materials where the more noble metal of the mixed oxide was reduced internally, producing nanoscale active particles which were passivated by an inactive matrix. Second, a systematic study of various metal anode materials, including Si, Sn, Al, Sb and Ag, of different starting particle sizes was undertaken, in order to better understand the micromechanical mechanisms leading to poor cyclability in these pure metals. SEM of these materials revealed fracture in particles of > 1 pm after a single discharge/charge cycle, consistent with literature models which predict such fracture due to volumetric strains upon lithiation. However, TEM of these materials revealed a nanocrystalline structure after one cycle that in some metals was mixed with an amorphous phase. STEM of anode materials after 50 cycles revealed a dissociation of this nanostructure into nanoparticles, suggesting a failure mechanism other than volumetric strains, such as chemical attack. Finally, the appearance of the amorphous phase was investigated in lithiated Si, Sn, Ag and Al metal anode systems. A new mechanism, electrochemically-induced solid-state amorphization was proposed and explored via experiments using calibrated XRD and TEM. Experimental observations of these various Me systems subjected to different degrees of lithiation supported such phenomenon...
by Pimpa Limthongkul.
Ph.D.

The shortage of energy sources and the global climate change crisis have become critical issues. Solving these problems with clean and sustainable energy sources (solar, wind, tidal, and so on) is a promising solution. In this regard, energy storage techniques need to be implemented to tackle with the intermittent nature of the sustainable energies. Among the next-generation energy storage systems, lithium sulfur batteries has gained prominence due to the low cost, high theoretical specific-capacity of sulfur. Extensive research has been conducted on this battery system. Nevertheless, several issues including the “shuttle effect” and the growth of lithium dendrites still exist, which could cause rapid capacity loss and safety hazards. Several methods are proposed to tackle the challenges in this dissertation, including cathode engineering, interlayer design, and lithium metal anode protection. An asymmetric cathode structure is first developed by a non-solvent induced phase separation (NIPS) method. The asymmetric cathode comprises a nanoporous matrix and ultrathin and dense top layer. The top-layer is a desired barrier to block polysulfides transport, while the sublayer threaded with cationic networks facilitate Li-ions transport and sulfur conversions. In addition, a conformal and ultrathin microporous membrane is electrodeposited on the whole surface of the cathode by an electropolymerization method. This strategy creates a close system, which greatly blocks the LiPS leakage and improves the sulfur utilization. A polycarbazole-type interlayer is deposited on the polypropylene (PP) separator via an electropolymerization method. This interlayer is ultrathin, continuous, and microporous, which defines the critical properties of an ideal interlayer that is required for advanced Li–S batteries. Meanwhile, a self-assembled 2D MXene based interlayer was prepared to offer abundant porosity, dual absorption sites, and desirable electrical conductivity for Li-ions transport and polysulfides conversions. A new 2D COF-on-MXene heterostructures is prepared as the lithium anode host. The 2D heterostructures has hierarchical porosity, conductive frameworks, and lithiophilic sites. When utilized as a lithium host, the MXene@COF host can efficiently regulate the Li+ diffusion, and reduce the nucleation and deposition overpotential, which results in a dendrite-free and safer Li–S battery.

博士
國立臺灣科技大學
化學工程系
106
Abstract Inventing new materials and battery design to enable rechargeable lithium battery with higher capacity, cycle life, efficiency, and energy density is of paramount importance. In fulfilling these principles’ Lithium metal is the most promising anode material in lithium metal battery due to its highest theoretical capacity (3860 mAh/g), lowest reduction potential (-3.04 V) vs Li/Li+(V) and lowest density (0.534 g/cm3). To realize lithium metal rechargeable secondary battery, tremendous research efforts exerted and a remarkable progress has been made. However, the safety challenge, low Coulombic efficiency, shallow cycling conditions, and poor cycle life limit the practical application. To overcome those bottleneck challenges and effectively use lithium metal anode, an anode-free lithium metal battery designed. The new battery architecture constructed in discharge state by pre-storing lithium in the cathode and lithium metal anode generated in-situ on copper current collector while charging. Realizing such a battery is an effective strategy to boost energy density, minimize cost and ease cell fabrication with safety. However, like lithium metal battery in-situ plated lithium grow to moss and whiskers like lithium dendrites on bare copper current collector upon cycling resulting from uneven Li deposition and inability of solid electrolyte interface (SEI) to control the stress exerted by dendritic Li growth. The formation of lithium dendrite induces low Coulombic efficiency, infinite volume expansion, electrolyte decomposition and even penetration of separator and short circuiting cell. To realize a dendrite free high energy density in-situ plated battery new strategies such as nanostructured current collector anode, using stable SEI layer forming additives, high concentration electrolytes, optimizing electrolyte solvent and using lithium rich or pre-lithiated cathodes to compensate lithium loss can be implemented. Our strategy will allow the newly battery design to gain widespread acceptance in electric vehicles, electronics, communication devise as a result of its simplicity to scale up, low cost, increase safety and a means to potential market. In our first work, copper current collector coated with polyethylene oxide (PEO) film to stabilize lithium deposition and enhance cycle life. More importantly, the PEO film coating reinforces solid electrolyte interface (SEI) layer, encapsulate lithium film on copper and regulate the inevitable reaction of lithium with electrolyte. The modified electrode showed stable cycling of lithium with an average Coulombic efficiency of ~100% over 200 cycles and low voltage hysteresis (~30 mV) at a current density of 0.5 mA/cm2. Moreover, the anode-free battery proved experimentally by integrating it with the LiFePO4 cathode into a full cell configuration (Cu@PEO/LiFePO4). The new cell demonstrated stable cycling with average Coulombic efficiency of 98.6% and 49% capacity retention at 100th cycle. In contrary a capacity retention of ~35% obtained when bare copper paired with the same cathode. These impressive enhanced cycle life and capacity retention results from the synergy of PEO film coating and high electrode-electrolyte interface compatibility. Our result opens up a new route to realize the anode-free batteries by modifying the copper anode with PEO polymer to achieve ever demanding yet safe interfacial chemistry and controlled dendrite formation. The second motivation of this dissertation focus on engineering copper current collector with ultra-thin graphene layer with chemical vapor deposition (CVD) method as artificial layer to suppress lithium dendrite. Multilayer graphene film with superior strength, stability, and flexibility to facilitate uniform lithium-ion flux makes it an excellent choice to stabilize electrode interface. The new designed copper electrode with size higher than cathode size paired with commercial LiFePO4 cathode (mass loading ~12 mg/cm2), and ensures the first cycle discharge capacity of 147 and 151 mAh/g for bare and multilayer graphene protected electrode respectively which then alleviate the big hurdle (initial capacity loss) in an in-situ plated battery. After 100 round trip cycles, bare and multilayer graphene film protected copper retain ~ 46 and 61 % of their initial capacity respectively in an ether-based electrolyte at 0.1C rate. In final work, the viability of rechargeable in-situ plated lithium metal battery on bare copper anode demonstrated by using lithium bis(trifluoromethanesulfonyl)imide(LiTFSI) salt in dimethoxy ethane(DME)/1,3-dioxolane (DOL) solvent and 4 wt % LiNO3 additive. The reduction of LiNO3 into lower order nitrite LixNOx and lithium nitride (Li3N) facilitate the formation of robust solid electrolyte interface (SEI) layer with high mechanical strength and stability. By using Cu/LiFePO4 cell without any pre-lithiation, the feasibility of anode-free lithium metal battery could deliver areal capacity of ~1.60 mAh/cm2 in its first cycle and retains about 0.863 mAh/cm2 capacity even at 100th cycles. In contrary, Cu/LFP cell in ether electrolyte without LiNO3 showed a rapid capacity fading. Moreover, by using a 4 wt % graphite composite in LiFePO4 cathode the 100th and 200th cycle capacity retention improved to 65.6 % and 33 % of its initial capacity respectively when cycled at 0.2 mA/cm2.

碩士
國立臺灣大學
材料科學與工程學研究所
107
In this work, a poly(styrene-block-isoprene-block-sulfonated isoprene) triblock copolymer (denoted as SII-SO3Li) bearing pendant lithium sulfonate groups is synthesized via anionic polymerization and the following functional group conversion. Free standing membranes of SII-SO3Li with various thickness from 10 ~ 50 μm are fabricated from solvent-casting to serve as a protective layer for a lithium metal battery (LMB) by locating the membrane between the lithium metal anode and the mesoporous Celgard2400 separator to suppress lithium dendrite growth. The membranes show microphase separated nanostructure and good mechanical strength. The ion conductivity could reach 1 x 10-4 S cm-1 with merely 10 wt% liquid electrolyte uptake for the thin membrane (18 m thick), and which decreases with increasing thickness. The galvanostatic cycling studies on Li/SII-SO3Li/Celgard/Li cells and the cycling studies on Li/SII-SO3Li/Celgard/LFP batteries suggest thinner SII-SO3Li membrane would provide better charging/discharging performance due to higher conductivity. However, these SII-SO3Li membrane would lower the capacity of the LMB and not be able to stabilize the lithium metal surface, which are opposite to the expectation. It is suspected that the ion conductivity of the SII-SO3Li membrane is not high enough to provide satisfactory performance, requiring further work for the improvement.

Al based alloy powders (Al₈₅Ni₅Y₆Co₂Fe₂) are produced by spray atomization method. High energy ball milling is done to modify the surface topology and particle size for better electrochemical performance. X ray diffraction (XRD), differential scanning calorimeter (DSC), scanning electron microscope (SEM) and transmission electron microscope (TEM) were conducted to characterize the microstructure of the alloys after ball milling. It is found that 5 hours ball milling gives the minimum crystallization and structure change. Thin film sample is also deposited on stainless steel substrate by pulsed laser deposition (PLD) method for electrochemical test. The capacity and reversibility for different samples are compared and discussed. A capacity of 200mAh/g is obtained for the battery with thin film sample as anode and a capacity of 140mAh/g is obtained for that with electrode from powder sample. Both of the batteries give up to 94% capacity retention after 20 cycles.
Singapore-MIT Alliance (SMA)

博士
國立臺灣科技大學
化學工程系
107
Lithium (Li) metal is regarded as an ultimate negative electrode (anode) for energy storage system due to its very high specific capacity (3860 mAh g-1), the most negative electrochemical potential (-3.04V vs. Standard hydrogen electrode, SHE) and a low gravimetric density (0.534 g cm−3). Rechargeable lithium metal batteries (LMBs) have been extensively studied since the last four decades and received high attention currently due to increasing demand for high energy density batteries for consumer electronics, electric vehicles (EVs), and smart grid energy storage. To realize lithium metal rechargeable secondary batteries, tremendous research efforts exerted and remarkable progress has been made. However, the safety challenge, low Coulombic efficiency, shallow cycling conditions, and poor cycle life limit the practical application. To overcome these challenges and effectively use lithium metal anode, an anode-free (AFB) is battery designed. The new battery configuration is constructed by pre-storing lithium in the cathode and lithium metal anode generated in-situ onto anode current collector while charging. AFB is an effective strategy to uplift the energy density, reduce cost and simplify cell fabrication process with safety should be taken into account. Anode-free batteries (AFBs) are impressive and recent phenomena in the era of energy storage devices due to their high energy density and relative ease of production compared to the traditional Lithium metal batteries (LMBs). However, dendrite formation during plating and stripping and low coulombic efficiency (CE) are the main challenges that impede practical implementation of these batteries. Here we report an extremely stable dual-salt electrolyte, 2M LiFSI+1M LiTFSI (2FSI+1TFSI)) in DME/DOL (1:1, v/v), system in comparison to the single salt 3M LiTFSI (3TFSI) in DME/DOL (1:1, v/v), to effectively stabilize AFB composed of LiFePO4 cathode and bare Cu-foil anode for the first time. The electrolyte stabilized anode-free cell with the configuration Cu||LiFePO4 via reductive decomposition of its anions and enabled the cell to be cycled with CE of 98.9% for 100 cycles. This results from the formation of stable, ion conductive and electrically insulating inorganic components rich Solid Electrolyte Interface (SEI) layer on the surface of in-situ deposited Li-metal that blocks the undesirable parasitic reaction between the deposited Li and the electrolyte. Thus, aforesaid SEI mitigates the formation of dead lithium and dissolution of the in-situ deposited Li surface during repeated cycling and prolongs cycle life of the battery. The combined effect of concentrated salt electrolyte and resting protocol on the cyclic performance of anode free battery (AFB) is evaluated systematically. In-situ deposition of Li in the AFB configuration in the presence of a concentrated electrolyte containing fluorine donating salt and resting the deposit at higher voltage enables the formation of stable and uniform SEI. The SEI intercepts undesirable side reaction between the deposit and solvent in the electrolyte and reduces electrolyte and Li consumption during cycling. The synergy between the laboratory prepared concentrated 3M LiFSI in the ester-based electrolyte and our resting protocol significantly enhanced cyclic performances of AFBs in comparison to the commercial carbonate-based dilute electrolyte, 1M LiPF6. Benefitting from the combined effect, Cu||LiFePO4 cells delivered excellent cyclic performance at 0.5 mA/cm2 with average CE of up to 98.78% retaining reasonable discharge capacity after 100 cycles. Furthermore, the AFB can also be cycled at a high rate up to 1.0 mA/cm2 with a high average CE and retaining encouraging discharge capacity after 100 cycles. The fast cycling and stable performance of these cells are attributed to the formation robust, flexible and tough F-rich conductive SEI on the surface of the in-situ deposited Li by benefiting from the combined effect of the resting protocol and the concentrated electrolyte. A condescending understanding of the mechanism of SEI formation and material choice could facilitate the development of AFBs as a future advanced energy storage devices. The effects of lithium imide and fluorinated lithium orthoborate dual-salt electrolytes of different salt composition in a mixture of ether and carbonate solvents on the cycling stability of anode free batteries are comparatively investigated. The compositions of the dual-salt electrolyte were optimized using the anode free battery configuration and found that the 0.9M LiTFSI+0.3M LiDFOB in FEC/TTE (2:3, v/v) is the best among all. The electrochemical performance of AFB in this optimized dual-salt electrolyte is intensively investigated in comparison to the single salt electrolyte, 1.2M LiTFSI, in the same solvent ratio. Accordingly, the cyclic performance of Cu||NMC cell in the dual-salt electrolyte surpassed that of the single salt. The relative better performance of the anode free battery in the dual salt electrolyte is attributed to the co-existence of dual ion (TFSI- and DFOB-) in the electrolyte, which enhanced conductivity and introduces entirely new interphases via preferential decomposition mechanisms. The newly formed interface is stable, ionically conductive, and be able to intercept parasitic side reaction between the solvent in the electrolyte and deposited Li by blocking electron and solvent flow towards the deposit. As a result of the unique interfacial chemistry brought by this dual-salt system, this electrolyte supports an unprecedented CE (98.6%) and capacity retention (63%) in 4.5V Cu||NMC cell at 0.5 mA/cm2 and >27% improvement over the single salt electrolyte after 50 cycles.

碩士
國立臺灣大學
化學研究所
90
There is an increasing demand for higher capacity and longer cycle life for lithium ion battery. The performance of lithium ion batteries is governed by the intrinsic chemistry of electrode materials. Large interest is focused on new electrode and electrolyte materials in the present lithium ion battery technology. In particular, large effort is directed to replace the carbonaceous anode with higher energy density and better stability materials. Transition metals usually include many oxidation states and interchange these states through the redox reactions. CoO reacts with Li through a redox mechanism that differs from the conventional intercalation/deintercalation or alloy one in a lithium ion battery. The reaction may be written as CoO + 2Li D Li2O + Co. Cobalt oxide (CoO) reacts with lithium to form a nanocomposite consisting of reduced Co metal and Li2O during the first discharge. Further cycling proceeds via the formation of CoO during charge and again a nanocomposite of Co metal and Li2O during discharge. In this work, we demonstrate the chemical reactions and phase transitions of CoO and Fe3O4 electrodes during discharge by the combination of in-situ X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS) and X-ray diffraction (XRD). Here, we also utilized particle size analyzer (BET), scanning electron microscope (SEM), cyclic voltammeter (CV), transmission electron microscope (TEM) etc. to investigate the mechanisms therein. For CoO and Fe3O4 electrodes, they have reversible specific capacity up to 700 mAh/g and 1000 mAh/g respectively and exhibit good capacity retention over 100 cycles. Their capacity are twice or more than the commercial carbon powder (mesophase carbon micro bead; MCMB). Furthermore, new composites of metal oxides and MCMB with equal amounts were also found. Besides, the surface modification was performed on MCMB to obtain an improved capacity. A part of results in this research has been applied for the patents.

In this dissertation, a meso-scale computational model, using the smoothed particle hydrodynamics (SPH) numerical method, is used to simulate the deposition process at the electrolyte/anode interface of a lithium metal battery. The SPH model simulates the physics at this interface by solving the governing equations for diffusion, migration, and potential distribution in a binary electrolyte and near a reactive, moving interface and dendrite surfaces. The model is implemented in the LAMMPs code base and includes the ability to model charge/discharge cycles. Using the SPH model, the effect of various structures in the electrolyte on mass transport and dendrite growth are investigated. The first goal is to understand the effects of local transport through battery separators on dendrite growth by explicitly representing commercial battery separator structures taken from SEM images. Using SPH, the geometrical parameters of the separator are characterized based on their effect on mass transport and dendrite growth. The findings from the simulations suggest that the tortuosity of the separator is a key property affecting transport. Additionally, despite the characterization of battery separators using bulk properties, the heterogeneity of the separators lead to vastly different local transport outcomes. Building upon these insights and in collaboration with experimental groups, the effect of the structure of novel coatings and electrolytes on the mass transport to the anode and subsequent dendrite morphology are investigated. The computational studies demonstrate the mechanisms by which these novel techniques improve the performance of lithium metal batteries such as reducing the pore size in carbon nanomembranes reduces dendrite length and increases deposition density; ionic liquid crystal supramolecular assemblies oriented perpendicular to the anode increase the uniformity of Li+ deposition at the anode; the effects of homogeneity of ionic conductivity of protective coatings on the anode to enable uniform Li+ deposition. Additionally, the model is used to explore how the local conditions in the electrolyte change during battery cycling. During standard charging, the Li+ concentrations at the anode create reaction rate limited conditions that lead to more uniform Li+ deposition. However, during “fast” charging, the local Li+ concentrations rapidly decrease leading to mass transport limited conditions which result in dendrite growth and lower battery performance.

碩士
國立成功大學
化學系
102
Gel polymer electrolytes (GPE) have been attractive for the development of plastic Li ion batteries since they combine the advantages of liquid electrolytes (high ionic conductivity) and polymers (free from leaks, good mechanical strength). Gel polymer electrolytes (GPEs) were prepared by dipping a solid polymer electrolyte in 1.0M LiPF6 in ethylene carbonate (EC)/ dimethyl carbonate (DMC)/diethyl carbonate (DEC)(1:1:1 wt% + 2wt% VC) liquid electrolyte. Compare to commercial liquid electrolyte (LE). GPE has a stable electrochemical window up to 5 V vs. Li/Li+. Higher ionic conductivity up to above 1×10-3S/cm from 10 to 90 degrees C. Better lithium ion dissociation ability and higher transfer number (0.6). The performance test are evaluated in half-cell configurations (Li/GPE/LiFePO4)with different discharge rates. The specific half-cell capacities of GPE membraneis similar to commercial separator LE (from 0.1 to 1 C). Moreover, GPE has good cycling stability at room temperature. The specific properties of the polymer electrolyte membrane allow it to act as both an ionic conductor and separator.

碩士
國立臺北科技大學
化學工程研究所
102
The anode materials are usually carbon in commercial lithium ion batteries. However, the main drawback for carbonaceous materials has a large irreversible capacity loss , and there is still some safty problem. The crystal size of Li4Ti5O12 does not change during charge and discharge process. Therefore,this material is call zero strain material which has properties of long life and safety. It has the problem of poor rate capability due to its low electronic conductivity. 　　In studies, we tried to use sol-gel method to synthesize Li4Ti5O12 and searched for optimal synthetic process. First, we change the calcination temperature, heating rate of calcination,and calcination duration in order to synthesis, and find the best conditions. Second, the same proportion of different metal ion doped on Li4Ti5O12, and electrochemical performance analysis. 　　The result shows that calcination temperature must reach 800℃ maintaining 14 hours and the rate is 4℃/min to keep better crystallinity. The discharge capacity of Li4Ti5O12 is 152.2 mAh/g and 58mAh/g at 0.1C and 10C. The discharge capacity of Li4Al0.05Ti4.95O12 is 157 mAh/g and 79 mAh/g at 0.1 C and 10 C. And the discharge capacity of Li4La0.05Ti4.95O12 is 160.2 mAh/g and 112.6 mAh/g at 0.1 C and 10 C. In addition the discharge capacity of Li4Ce0.05Ti4.95O12 is 165.6 mAh/g and 122.8 mAh/g at 0.1 C and 10 C.

碩士
國立高雄應用科技大學
化學工程與材料工程系博碩士班
103
This study is divided into two parts: the first part is the preparation of expanded mesocarbon microbeads (EMCMB) by chemical oxidation of mesocarbon microbeads (MCMB). By use of mixed acid, a strong oxidant, and sufficient heating time, the EMCMB powder could be formed. The spacing between graphitic layers increased after chemical expansion, which was in favor of diffusion of the electrolyte and thus enhanced the storage of lithium ions, leading to an increase in the specific capacity. Its reversible capacity in the first cycle reached 650 mAh g-1. The EMCMBs were easily restacked in a solvent, resulting in an increase in the stacking layers of graphite, the compact packing hindered the diffusion of lithium ions and led to a significant hysteresis phenomenon in the lithiation delithiation processes, resulting in a considerable decay in cycling capacity. The second part is the preparation of nickel-organic framework (NiOF) electrode with different carbonization temperatures. Mesoporous carbon structures could be formed after the carbonization, which were used as anode materials for lithium-ion battery and their electrochemical properties were systematically explored. NiOF electrode carbonized at 400C exhibited the highest reversible capacity of 916 mAh g-1 in the first cycle. NiOF electrode carbonized at 600C showed the highest capacity retention of 75% after 80 charge/discharge cycles.

Tin dioxide (SnO2) is considered one of the most promising anode materials for Lithium ion batteries (LIBs), due to its large theoretical capacity and natural abundance. However, its low electronic/ionic conductivities, large volume change during lithiation/delithiation and agglomeration prevent it from further commercial applications. In this thesis, we investigate modified SnO2 as a high energy density anode material for LIBs. Specifically two approaches are presented to improve battery performances. Firstly, SnO2 electrochemical performances were improved by surface modification using Atomic Layer Deposition (ALD). Ultrathin Al2O3 or HfO2 were coated on SnO2 electrodes. It was found that electrochemical performances had been enhanced after ALD deposition. In a second approach, we implemented a layer-by-layer (LBL) assembled graphene/carbon-coated hollow SnO2 spheres as anode material for LIBs. Our results indicated that the LBL assembled electrodes had high reversible lithium storage capacities even at high current densities. These superior electrochemical performances are attributed to the enhanced electronic conductivity and effective lithium diffusion, because of the interconnected graphene/carbon networks among nanoparticles of the hollow SnO2 spheres.

abstract: This dissertation will investigate two of the most promising high-capacity anode materials for lithium-based batteries: silicon (Si) and metal lithium (Li). It will focus on studying the mechanical behaviors of the two materials during charge and discharge and understanding how these mechanical behaviors may affect their electrochemical performance. In the first part, amorphous Si anode will be studied. Despite many existing studies on silicon (Si) anodes for lithium ion batteries (LIBs), many essential questions still exist on compound formation, composition, and properties. Here it is shown that some previously accepted findings do not truthfully reflect the actual lithiation mechanisms in realistic battery configurations. Furthermore the correlation between structure and mechanical properties in these materials has not been properly established. Here, a rigorous and thorough study is performed to comprehensively understand the electrochemical reaction mechanisms of amorphous-Si (a-Si) in a realistic LIB configuration. In-depth microstructural characterization was performed and correlations were established between Li-Si composition, volumetric expansion, and modulus/hardness. It is found that the lithiation process of a-Si in a real battery setup is a single-phase reaction rather than the accepted two-phase reaction obtained from in-situ TEM experiments. The findings in this dissertation establish a reference to quantitatively explain many key metrics for lithiated a Si as anodes in real LIBs, and can be used to rationally design a-Si based high-performance LIBs guided by high-fidelity modeling and simulations. In the second part, Li metal anode will be investigated. Problems related to dendrite growth on lithium metal anodes such as capacity loss and short circuit present major barriers to the next-generation high-energy-density batteries. The development of successful mitigation strategies is impeded by the incomplete understanding of the Li dendrite growth mechanisms. Here the enabling role of plating residual stress in dendrite initiation through novel experiments of Li electrodeposition on soft substrates is confirmed, and the observations is explained with a stress-driven dendrite growth model. Dendrite growth is mitigated on such soft substrates through surface-wrinkling-induced stress relaxation in deposited Li film. It is demonstrated that this new dendrite mitigation mechanism can be utilized synergistically with other existing approaches in the form of three-dimensional (3D) soft scaffolds for Li plating, which achieves superior coulombic efficiency over conventional hard copper current collectors under large current density.
Dissertation/Thesis
Doctoral Dissertation Mechanical Engineering 2018

碩士
國立清華大學
材料科學工程學系
103
In our work, anatase TiO2 nanostructures on Ti foil transformed from sodium titanate were synthesized by a facile hydrothermal reaction. Under different hydrothermal conditions, diverse morphologies including nanowire, nanosheet and nanobelt can be obtained. The rate of sodium ion intercalating into TiO6 structure during the hydrothermal reaction will influence the morphology of sodium titanate. High intercalation rate occurring at high temperature and high sodium ion concentration environment leads to the formation of nanowire TiO2. On the contrary, lamellar TiO2 including nanosheet and nanobelt were obtained in low intercalation rate condition. Anatase TiO2 on conductive Ti foil can be used as a binder-free anode material for lithium ion batteries. Nanowire exhibits the best lithium ion batteries performance among three different morphologies and retains 220.95 mAh/g after 100 cycles at the rate of 1 C (335 mA/g). In variable current test, at the rate of 20 C (6.7 A/g), anatase TiO2 nanowire still remains 99.04 mAh/g. The extraordinary performance can be attributed to high specific surface area and low charge transfer resistance. This result suggests that anatase TiO2 growing on Ti foil can be a promising candidate for high performance lithium ion batteries.