Li-ion batteries have become the more dominant battery type used in portable electronic devices such as cell phones, computers and more recently their application in full electric vehicles (EV). Li-ion batteries have many advantages over the traditional rechargeable systems (Pb-acid and Ni-MH) such as their higher energy density, low self-discharge, long capacity cycle life and relatively maintenance free. Due to their commercial advantages, a lot of research is done in developing new novel Li-ion electrode materials, improving existing ones and to reduce manufacturing costs in order to make them more cost effective in their applications. This study looked at the cathode material chemistry that has a typical spinel manganese oxide (LiMn2O4) type structure. For comparison the study also considered the influence of doping the phase with various metals such as Al, Mg, Co and Ni that were made as precursors using various carboxylic acids (Citric, Ascorbic, Succinic and Poly-acrylic acid) from a sol-gel process. Traditional batch methods of synthesizing the electrode material is costly and do not necessarily provide optimized electrochemical performance. Alternative continuous less energy intensive methods would help reduce the costs of the preparation of the electrode materials. This study investigated the influence of two synthesis techniques on the materials physical and electrochemical characteristics. These synthesis methods included the use of a typical batch sol-gel method and the continuous spray-drying technique. The spinel materials were prepared and characterized by Powder X-Ray Diffraction (PXRD) to confirm the formation of various phases during the synthesis process. In addition, in-situ PXRD techniques were used to track the phase changes that occurred in the typical batch synthesis process from a sol-gel mixture to the final crystalline spinel oxide. The materials were also characterized by thermal gravimetric analysis (TGA), whereby the materials decomposition mechanisms were observed as the precursor was gradually heated to the final oxide. These synthesized materials prepared under various conditions were then used to build suitable Li-ion coin type of cells, whereby their electrochemical properties were tested by simple capacity tests and electrochemical impedance spectroscopy (EIS). EIS measurements were done on the built cells with the various materials at various charge voltages. TG analysis showed that the materials underwent multiple decomposition steps upon heating for the doped lithium manganese oxides, whereas the undoped oxide showed only a single decomposition step. The results showed that all the materials achieved their weight loss below 400 °C, and that the final spinel oxide had already formed. The in-situ PXRD analysis showed the progression of the phase transitions where certain of the materials changed from a crystalline precursor to an amorphous intermediate phase and then finally to the spinel cathode oxide (Li1.03Mg0.2Mn1.77O4, and LiCo1.09Mn0.91O4). For other materials, the precursor would start as an amorphous phase, and then upon heating, convert into an impure intermediate phase (Mn2O3) before forming the final spinel oxide (Li1.03Mn1.97O4 and LiNi0.5Mn1.5O4). The in-situ study also showed the increases in the materials respective lattice parameters of the crystalline unit cells upon heating and the significant increases in their crystallite sizes when heated above 600 °C. Hence the results implied that a type of sintering of the particles would occur at temperatures above 600 °C, thereby increasing the respective crystallite size. The study showed that the cathode active materials made by the sol-gel spray-drying method would give a material that had a significantly larger surface area and a smaller crystallite size when compared to the materials made by the batch process. The electrochemical analysis showed that there was only a slight increase in the discharge capacities of the cells made with the spray-drying technique when compared to the cells made with the materials from the batch sol-gel technique. Whereas, the EIS study showed that there were distinct differences in the charging behavior of the cells made with the various materials using different synthesis techniques. The EIS results showed that there was a general decrease in the cells charge transfer resistance (Rct) as the charge potential increased regardless of the synthesis method used for the various materials. The results also showed that the lithium-ion diffusion coefficient (DLi) obtained from EIS measurements were in most of the samples higher for the cathode materials that had a larger surface area. This implied that the Li-ion could diffuse at a faster rate through the bulk material. The study concluded that by optimizing the synthesis process in terms of the careful control of the thermal parameters, the Li-ion batteries‟ cathode active material of the manganese spinel type could be optimized and be manufactured by using a continuous flow micro spray process.

Lithium-ion batteries (LIBs) play a significant role in our highly electrified world and will continue to lead technology innovations. Millions of vehicles are equipped with or directly powered by LIBs, mitigating environmental pollution and reducing energy use. This rapidly increasing use of LIBs in vehicles will introduce a large quantity of spent LIBs within an 8- to10-year span and proper handling of end-of-life (EOL) vehicle LIBs is required. Over the last several years, the Worcester Polytechnic Institute (WPI) team in the Department of Mechanical Engineering has developed a closed-loop lithium ion battery recycling process and it has been demonstrated that the recovered NMC 111 has similar or better electrochemical properties than the commercial control powder with both coin cells and pouch cells, which have been independently tested by A123 Systems and Argonne National Laboratory. In addition, the different chemical compositions of the incoming recycling streams were shown to have little observed effects on the recovered precursor and resultant cathode material. Therefore, the WPI-developed process applies to different spent Li-ion battery waste streams and is, therefore, general. During the last few years, industry has the tendency to employ higher-nickel and lower-cobalt cathode material since it can provide higher capacity and energy density and lower cost. However, higher-nickel cathode material has the intrinsic unstable properties and surface modifications can be applied to slow down its degradation. Here, two facile scalable Al2O3 coating methods (dry coating and wet coating) were applied to recycled NMC 622 and the resultants were systematically studied. The Al-rich layer from the dry coating process imparted improved structural and thermal stability in accelerated cycling performed at 45 °C between 3.0 and 4.3 V, and the capacity retention of pouch cells with dry coated NMC 622 (D-NMC) cathode increased from 83% to 91% compared to Al-free NMC 622 after 300 cycles. However, for wet coated NMC 622 (W-NMC), the increased surface area accompanying by formation of NiO rock-salt like structure could have negative impacts on the cycling performance. There exist three challenges for current LIBs’ recycling research. First of all, most of the research is done in lab-scale and the scale-up ability needs to be proven. The scale-up ability of our recycling process has been verified by our scale-up experiments. The second challenge resides in the flexibility, here once again, with our intentionally designed experiments that having various incoming chemistries, the flexibility is validated. The last challenge is the lack of reliable testing because most of the testing is conducted with coin cells. Coin cells are relatively simple format and lacks persuasion. Here, with various industrial-level cell formats that ranging from coin cell, single layer pouch cell, 1Ah cell and 11Ah cell, a reliable and trustworthy testing is established. With this validation, the hesitation of recruiting recycled materials into industry shouldn’t exist.

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Lithium-alloying anode materials have attracted much attention as an alternative to carbon due to their high theoretical gravimetric capacities (e.g. Li4.4Si: 4200 mAh g-1, Li4.4Sn: 990 mAh g-1, and Li3Sb: 660 mAh g-1). An additional benefit of lithium alloying metals is that some of the react at a higher potentials vs. Li/Li+ than carbon, which can mitigate safety issues caused by solid-electrolyte interface layer formation and lithium plating. One of the most promising lithium -alloying anode materials that are being pursued are Sn-based materials due to their high capacity and tap density. This thesis investigates the synthesis and characterization of Sn-based lithium-ion battery anodes. SnSb-TiC-C and FeSn2-TiC nanocomposite alloy anodes for lithium-ion batteries have been synthesized by a mechanochemical process involving high-energy mechanical milling of Ti/Sn, Ti/M (M = Fe or Sb), and C. Characterization of the nanocomposites formed with x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) reveals that these alloys are composed of crystalline nanoparticles of FeSn2 and SnSb dispersed in a matrix of TiC and carbon. The SnSb-TiC-C alloy shows an initial gravimetric capacity of 653 mAh g-1 (1384 mAh cm-3), an initial coulombic efficiency of 85%, and a tap density of 1.8 g cm-3. The FeSn2-TiC alloy shows an initial gravimetric capacity of 510 mAh g-1 (1073 mAh cm-3), an initial coulombic efficiency of 71%, and a tap density of 2.1 g cm-3. The TiC-C buffer matrix in the nanocomposite alloy anodes accommodates the large volume change occurring during the charge-discharge process and leads to good cyclability compared to pure FeSn2 and SnSb anodes. / text

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Aluminum based amorphous metallic glass powders were produced and tested as the anode materials for the lithium ion rechargeable batteries. Ground Al₈₀Ni&#x2081₀La&#x2081₀ was found to have a low first cycle capacity of about 100 Ah/Kg. The considerable amount of intermetallic formed in the amorphous glass makes the aluminum inactive towards the lithium. The ball milled Al₈₈Ni₉Y₃ powders contain pure aluminum crystalline particles in the amorphous matrix and have first cycle capacity of about 500 Ah/Kg. Nevertheless, polarization was caused by oxidation introduced by the ball-milling process. The electrochemical performances of these amorphous metallic glasses need to be further investigated. Their full lithium insertion capacities cannot be confirmed until the compositions and particle size inside the metallic glass anodes, the conformation of the electrodes and the mechanical milling processes are optimized. / Singapore-MIT Alliance (SMA)

Colloidally synthesized silicon (Si) and germanium (Ge) were explored as high capacity anode materials in lithium ion batteries. a-Si:H particles were synthesized through the thermal decomposition of trisilane in supercritical n-hexane. Precise control over particle size and hydrogen content was demonstrated. Particles ranged in size from 240-1500 nm with hydrogen contents from 10-60 atomic%. Particles with low hydrogen content had some degree of local ordering and were easily crystallized during Raman spectroscopy. The as-synthesized particles did not perform well as an anode material due to low conductivity. Increasing surface conductivity led to enhanced lithiation potential. Cu nanoparticles were deposited on the surface of the a-Si:H particles through a hydrogen facilitated reduction of Cu salts. The resulting Cu coated particles had a lithiation capacity seven times that of pristine a-Si:H particles. Monophenylsilane (MPS) grown Si nanowire paper was annealed under forming gas to reduce a polyphenylsilane shell into conductive carbon. The resulting paper required no binder or carbon additive and achieved capacities of 804 mA h/g vs 8 mA h/g for unannealed wires. Si and Ge heterostructures were explored to take advantage of the higher inherent conductivity of Ge. Ge nanowires were successfully coated with a-Si by thermal decomposition of trisilane on their surface, forming Ge@a-Si core shell structures. The capacity increased with increasing Si loading. The peak lithiation capacity was 1850 mA h/g after 20 cycles – higher than the theoretical capacity of pure Ge. MPS additives created a thin amorphous shell on the wire surfaces. By incubating the wires after MPS addition the shell was partially reduced, conductivity increased, and a 75% increase in lithiation capacity was observed for the nanowire paper. The syntheses of Bi and Au nanoparticles were also explored. Highly monodisperse Bi nanocrystals were produced with size control from 6-18 nm. The Bi was utilized as seeds for the SLS synthesis of Ge nanorods and copper indium diselenide (CuInSe2) nanowires. Sub 2 nm Au nanocrystals were synthesized. A SQUID magnetometer probed their magnetic behavior. Though bulk Au is diamagnetic, the Au particles were paramagnetic. Magnetic susceptibility increased with decreasing particle diameter. / text

Manganese spinel cathodes LiMn₂O₄ offer the advantage of a strong, edge-shared octahedral framework with fast, 3-dimensional Li⁺-ion conduction. To better understand the safety of these materials, the thermal stability characteristics of spinel oxide and oxyfluoride cathodes Li[subscript 1.1]Mn[subscript 1.9-y]M[subscript y]O₄[subscript-z]F[subscript z] (M = Ni and Al, 0 ≤ y ≤ 0.3, and 0 ≤ z ≤ 0.2) have been investigated systematically. The thermal characteristics are assessed in terms of the onset temperature and reaction enthalpy for the exothermic reaction. The thermal stability increases with decreasing lithium content in the cathode in the charged state. High-voltage spinel cathodes LiMn[subscript 1.5]Ni[subscript 0.5]O₄ are promising candidates for electric vehicles and stationary storage of electricity produced by renewable energies due to their high power capability. However, widespread adoption of this high-voltage spinel cathode is hampered by severe capacity fade resulting from aggressive reaction with the electrolyte to form a thick solid-electrolyte interphase (SEI) layer. The synthesis conditions of the co-precipitation method are found to influence the microstructure and morphology through nucleation and growth of crystals in solution. Two samples prepared by similar wet-chemical routes have been characterized by microscopy and electrochemical methods to determine the role of microstructure and morphology on the electrochemical performance. It is found that the surface crystal planes play a key role in the capacity retention and rate performance. In order to achieve consistent electrochemical properties essential for the commercialization of the high-voltage spinel cathode LiMn[subscript1.5]Ni[subscript 0.5]O₄, the relationship between cation ordering, presence of impurity phase, and particle morphology must be elucidated. Accordingly, comparison of the stoichiometric LiMn[subscript1.5]Ni[subscript 0.5]O₄ cathodes with a Mn/Ni ratio of 3.0 prepared by different methods having varying morphologies and degrees of cation ordering is presented. It is found that although an increase in the degree of cation ordering decreases the rate capability, the crystallographic planes in contact with the electrolyte have a dominant effect on the electrochemical properties. To examine the effect of cation substitution on morphology, an investigation of the nucleation and growth of doped co-precipitated mixed-metal hydroxide precursor particles and the resulting stabilization of preferred crystallographic surface planes in the final spinel samples are presented. It is found that doping with certain cations stabilizes the growth of low-energy (111) surface planes, facilitating a long cycle life and fast high-rate performance. With an aim to develop a better understanding of the factors influencing the electrochemical properties, a systematic investigation of LiMn[subscript 1.5]Ni[subscript0.5-x]M[subscript x]O₄ (M = Cu and Zn and x = 0.08 and 0.16), in which Ni²⁺ ions are substituted by divalent Cu2+ and Zn2+ ions, is presented. It is found that although both Zn and Cu are divalent with ionic radii similar to that of Ni2+, they behave quite differently with respect to cation ordering and site occupancy, and higher levels of doping leads to distinct differences in cycling and rate performances. / text

There is a growing interest for relying on cleaner and more sustainable energy sources due to the negative side-effects of the dominant fossil-fuel based energy storage and conversion systems. Cleaner, electrochemical energy storage through lithium-ion batteries has gained considerable interest and market value for applications such as electric vehicles and renewable energy storage. However, capacity and rate (power) limitations of current lithium-ion battery technology hinder its ability to meet the high energy demands in a competitive and reliable fashion. Silicon is an element with very high capacity to Li-ion storage although commercially impractical due to its poor stability and rate capabilities. Nevertheless, it has been heavily researched with more novel electrode nanostructures to improve its stability and rate capability. It was found that silicon nanomaterials such as silicon nanowires have inherently higher stability due to mitigation of cracking and higher rate capability due to the short Li-ion diffusion distance. However, electrode compositions based only on silicon nanowires without additional structural features and a high conductive support do not have enough stability and rate capability for successful commercialization. One structural and conductive support of silicon materials studied in literature is graphene. Graphene-based electrodes have been reported as material capable of rapid electron transport enabling new strides in rate capabilities for Li ion batteries. This thesis presents a novel electrode nanostructure with a simple, inexpensive, scalable method of silicon nanwire synthesis on graphene nanosheets via nickel catalyst. The research herein shows the different electrode compositions and variables studied to yield the highest achievable capacity, stability and rate capability performance. The carbon coating methodology in addition to enhancing the 3D conductivity of the electrode by replacing typical binders with pyrolyzed polyacrylonitrile provided the highest performance results.