Loss Of Electrical Contact Research Articles

Modeling Durability of PGM-Free Active Site Structures at the Atomic Scale

The replacement of Pt group metal (PGM) electrocatalysts with earth-abundant PGM-free materials in polymer electrolyte fuel cell (PEFC) cathodes faces several technological hurdles, including the need for improved long-term durability. In PGM systems, catalyst durability is achieved by maintaining Pt catalyst surface area that is in electrical contact with the electrode (electrochemical surface area, ESA).1,2 This ESA can be probed directly by electrochemical methods. Loss of electrical contact (via carbon corrosion or Pt particle detachment) as well as Pt surface area loss (via Pt dissolution into ionomer, particle agglomeration, surface blocking, or Ostwald ripening) lead to a loss in oxygen reduction reaction (ORR) activity in aged PGM cathodes. State-of-the-art PGM-free catalysts are highly heterogeneous systems due to pyrolysis processing and contain a great diversity of atom-scale structures. As such, there is still much debate regarding the atomic scale structure of the ORR active site. It has been proposed that a number of sites in the materials are ORR active, with varying degrees of activity and durability, further complicating study. Unlike their PGM counterparts, PGM-free materials do not have an easily electrochemically probed property such as ESA that can be determined and correlated to measured activity loss. These complexities necessitate different approaches to identifying and predicting durability properties and degradation mechanisms in PGM-free systems. One proposed approach for understanding PGM-free catalyst durability3 is combining quantum chemical modeling with a TEM beam-damage model4 to identify how local atomic structure affects the kinetics of atom removal. Calculation of the knock-on displacement threshold energy (KODTE) could serve as a durability descriptor for a given atomic structure, similar to how thermodynamic limiting potential serves as a computationally-accessible activity descriptor of ORR active site structures. This descriptor would go beyond relative thermodynamic stability of active site structures and actively probe the kinetics of bond breaking in the system. As part of the DOE Electrocatalysis Consortium (ElectroCat), an automated workflow for calculating the KODTE for a given atomic scale structure using ab initio molecular dynamics has been developed and applied to a variety of possible PGM-free ORR active site structures as well as C-host materials. These methods have identified that N are most susceptible to removal and that edge-hosted structures are more susceptible than bulk-hosted structures. Utilized methodology, as well as identified trends from these calculations and comparisons to available experiments will be discussed.

Free Standing Silicon Microparticle and Self-Healing Polymer Composite for High-Energy Lithium-Ion Anode Applications

Developing a commercially viable silicon anode as a replacement for graphite has been the topic of intense research and discussion. Numerous attempts have been made including the use of nanoscale structures smaller than silicon’s critical fracture size (e.g. nanoparticles, nanowires, nanotubes, etc.). However, nanoscale structures, while sufficiently effective in lab scale, are difficult and expensive to scale up. To address this issue, applying a thin coat of polymer with self-healing chemistries has been reported as an effective remedy to enhance the cycle life of the silicon microparticle anode. The self-healing chemistry enabled mechanical fractures generated during the cycling process to self-heal. As a result, excellent cycle life was obtained compared to conventional microscale anodes. However, there still is room to improve the mechanical and electrochemical performances of the anode, most notably areal capacity and flexibility, while using large scale processes. In this study, a free standing silicon microparticle and self-healing polymer (SiSHP) composite is fabricated demonstrating long cycle life while still retaining high capacity (up to ~2,800mAhg-1 and ~3.5mAhcm-2) without a metal foil current collector. SiSHP composite is prepared by simple, inexpensive, and scalable approach. The SiSHP composite consists of silicon microparticles embedded within a self-healing polymeric matrix providing sufficient space for volume expansion during lithiation. The self-healing chemistry reduces irreversible loss of electric contact due to mechanical degradation prevalent in conventional slurry cast silicon electrode design. In addition, because the SiSHP composite eliminates the need for a metal current collector, adhesion issues between the electrode and current collector that arise with repeated bending are eliminated, thereby ensuring minimal loss in mechanical and electrochemical properties even after undergoing repeated bending. We found that a 1:1 Si/SHP weight ratio with 10 wt. % carbon conductive additive exhibits the optimal balance between high capacity and providing sufficient polymer matrix for stable cycling behavior. The fabricated SiSHP composite is moldable into the required shape and dimension ranging from millimeter to tens of centimeter-scale. The freestanding feature of the SiSHP composite anode eliminates the need for a metal foil current collector thereby reducing the non-active mass, which is beneficial to enhancing capacity and energy density of Lithium-ion cells.

Capturing Solid Solutions during a First-Order Phase Transition of Li1+XMn2O4

Lithium-ion batteries (LIBs) offering the highest energy density among the known battery chemistries are the major contenders for both transportation and stationary storage applications. In order to satisfy the demands of energy density for these applications, new full cell configuration with either improved working voltage or specific capacity is needed to further enlarge its energy density. One candidate that has received a great deal of attention is the spinel cathode LiMn2O4, which offers the advantages of a high operating voltage (4.0 V vs. Li+/Li) and an excellent rate capability. Nonetheless, the relatively low specific capacity of 125 mAh·g-1 is mainly due to the restricted operating voltage between 3 and 4.5 V. In theory, LiMn2O4 cathode can deliver a capacity of ∼297 mAh·g-1 when 2 mole of lithium ions are inserted/extracted into/from both 8a tetrahedral and 16c octahedral sites of the spinel lattice at the voltages of, respectively, ∼4.0 and ∼2.7 V.1 Phase transition related to 4.0 V plateau is highly reversible, involving only two similar cubic spinel phases. However, phase transition related to 2.7 V plateau is partly reversible because a cubic spinel transforms to a tetragonal spinel with Jahn-Teller distortion occurring as a result of Mn3+ formation. The increase in the axial ratio from c/a = 1.0 in the cubic phase to c/a = 1.6 in the tetragonal phase due to the cooperative Jahn-Teller distortion leads to a fracture of large particles, which induces a loss of electrical contact with the current collector upon cycles.2 These effects cause serious capacity fading. However, the dynamic process of this phase transition has never been fully understood due to a lack of characterization techniques. Based on the above considerations, we report an in operando neutron diffraction study to fully understand the ~2.7 V related phase transition in the Li1+xMn2O4 spinel upon electrochemical cycling. We found solid solution formation upon reversible discharge and charge process, although a first-order phase transition is widely believed. The solid solution formation is possibly due to a thick electrode configuration that we applied and a large overpotential it could generate, which is cosistent with the phenomenon that observed under high-rate charging/discharging of LiFePO4 using in situ synchrotron XRD.3 J. B. Goodenough, M. M. Thackeray, W. I. F. David, P. G. Bruce, Rev. Chim. Miner., 1984, 21, 435.S.-H. Kang, J. B. Goodenough, and L. K. Rabenberg, Chemistry of Materials, 2001, 13, 1758-1764.H. Liu, F. C. Strobridge, O. J. Borkiewicz, K. M. Wiaderek, K. W. Chapman, P. J. Chupas, C. P. Grey, Science 344, 7 (2014).

Graphene Coated Ni Foam As a Current Collector for N-Type Doped Si Thin Film Anode for Li-Ion Batteries

Thin film silicon (Si) has gained a significant attention as an anode material for Li-ion batteries (LIBs), since its nanostructure retains structural integrity through minimizing the volume variation. However, 2D Si thin film experiences delamination from the current collector, and loss of electrical contact leads to further capacity fading. To overcome this issue, recent scientific investigations have shown that the 3D structure of electrodes (porous, rough-surface, etc.) is capable of suppressing volume changes upon lithiation/delithiation and providing large contact area between active material and current collector. Here, we propose a novel electrode material for LIBs that comprises of Si on graphene coated Ni foam (G-Ni). Porous Ni foam serves as 3D structured highly electroconductive network, and graphene layer was employed with the purpose of improving adhesion and electrochemical stability of Si thin film electrode. Magnetron sputtering was used to deposit n-type doped amorphous Si thin film on G-Ni. Chemical vapor deposition (CVD) was applied to obtain a few layer graphene (FLG) on catalytic Ni foam. The as-grown anode material was tested in a half-cell configuration with metallic lithium as a counter and reference electrode. The results were compared with n-type doped amorphous Si thin film on pristine Ni foam. Galvanostatic cycling performance was evaluated in the voltage range from 0.1 to 1.5 V at a current density of ~ 32 µA cm-2. Si-G-Ni anode exhibited the initial areal capacity of around 141 µA cm-2 and the stable reversible areal capacity of around 80 µA cm-2 over 100 cycles. Si-Ni anode shows an initial capacity of 91 µA/cm-2 with a rapid capacity fading to approximately 30 µA cm-2 at 100th cycle. The results of characterization and electrochemical tests will be presented at the conference. Figure 1

Effects of Carboxylated Polythiophenes in Fe3O4 Li-Ion Battery Anodes

The high energy/power density of Li-ion batteries elicits intensive research efforts related to high capacity anode materials. The main obstacles which retard the practical employment of high-capacity electrochemically active particles including Si, Sn, metal oxide and their derivatives, stem from large volume changes associated with Li insertion/extraction and the resultant electrical contact loss, thereby leading to poor cycling performance. Efforts have been made to circumvent the breakdown of electron pathways through the introduction of electrical conducting functionalities to the surface of active materials, such as carbon coatings and conductive polymeric binders, or the fabrication of a stable battery anode with electrically inactive polymeric binders that enable the system to maintain its integrity. These approaches are reasonably effective, however, incorporation of a porous entity which helps ion transport, into a composite electrode is also essential for improved performance. In principle, electrochemical reactions that occur within the electrode, reveal the intrinsic energy capacity when a Li ion encounters an electron inside an active site. Electron and ion transport are both critical factors to determine the internal resistance of the electrodes, which in turn influences their electrochemical performance. Here we present how to improve both electronic and ionic transport in Li-ion battery electrodes using conjugated polymers. The approach includes poly[3-(potassium-4-butanoate)thiophene] (PPBT) — a water-soluble, carboxylate substituted polythiophene — as a binder component, and polyethylene glycol (PEG) as a surface coating on active material, namely, Fe3O4 nanoparticles. Additionally, carbon nanotubes (CNTs) are considered for use as the conducting networks to facilitate design of a light-weight, flexible web electrode. To enhance the electronic conduction in the electrodes, connection between active materials (PEG- Fe3O4) and conducting agents (or CNTs) through binding components is of importance. PEG coating and carboxylated polythiophenes play an important role in dispersing the Fe3O4 nanoparticles and conducting agents (or CNTs), respectively, in a water medium, which allow for well-developed and interconnected electrode structures. Furthermore, carboxylated polythiophenes (e.g. PPBT) can boost electronic conduction, based on their high conducting properties and through electrochemical doping during electrochemical testing. The presence of carboxylic moieties on the side chain of polythiophenes such as PPBT could facilitate the formation of stable electrodes via chemical interactions between PPBT moieties (COO-) and the Fe3O4 surface (–OH). The results will show that this methodical consideration of both ion and electron transport through introduction of a carboxylated PPBT component, can remarkably enhance the performance of Fe3O4 based high-capacity anodes.

Electrochemically anodized porous silicon: Towards simple and affordable anode material for Li-ion batteries

Silicon is being increasingly studied as the next-generation anode material for Li-ion batteries because of its ten times higher gravimetric capacity compared with the widely-used graphite. While nanoparticles and other nanostructured silicon materials often exhibit good cyclability, their volumetric capacity tends to be worse or similar than that of graphite. Furthermore, these materials are commonly complicated and expensive to produce. An effortless way to produce nanostructured silicon is electrochemical anodization. However, there is no systematic study how various material properties affect its performance in LIBs. In the present study, the effects of particle size, surface passivation and boron doping degree were evaluated for the mesoporous silicon with relatively low porosity of 50%. This porosity value was estimated to be the lowest value for the silicon material that still can accommodate the substantial volume change during the charge/discharge cycling. The optimal particle size was between 10–20 µm, the carbide layer enhanced the rate capability by improving the lithiation kinetics, and higher levels of boron doping were beneficial for obtaining higher specific capacity at lower rates. Comparison of pristine and cycled electrodes revealed the loss of electrical contact and electrolyte decay to be the major contributors to the capacity decay.

Mechanical Investigation of Various Stack Designs for Solid Oxide Cells

Stress development in metallic interconnects during operational cycles of solid oxide cells (SOCs) could create permanent plastic deformations, which can cause contact losses in the interface between the interconnect and cells. The magnitude of these stresses and their distribution within the SOC stack are dependent on the overall design of the stack and its operational parameters/conditions. In this study, analysis of stress generation in metallic interconnects due to temperature and stack assembly loadings for different types of generic SOC stack designs operated under the same operational cycles is performed. The analysis includes stack design concepts with and without contact layers having cross-shaped and/or corrugated metallic interconnect. To consider the effect of thermal gradient over the surface of the stacks (due to electro-chemical reaction), stacks with two types of temperature profiles are studied. The analysis is performed numerically using finite element modeling of a standard repeating unit of SOC stack. Special focus is given to stresses that can cause possible delamination of the interconnect from the cell that subsequently leads to loss of electrical contact. Comparison of stress for different types of stack design concepts are presented. An effective way to minimize stresses in the interconnect is found to be through designing the micro-architectures of the interconnect and us eof contact layers materials. Key words: Solid oxide fuel cells, Metalic interconnect, Creep, finite element modeling

Carbon coated mesoporous Si anode prepared by a partial magnesiothermic reduction for lithium-ion batteries

Owing to its high theoretical capacity, Si based anode materials have been regarded as the most promising alternative anode materials for lithium-ion batteries. Unfortunately, the commercial application of Si based anode materials has been greatly hindered, due to the large volume change of Si materials during their lithiation/delithiation process, which results in severe pulverization, loss of electrical contact and rapid capacity fading. To address these issues, we reported a partial magnesiothermic reduction method by adjusting the proportion of added Mg powder to convert SiO2 into Si/SiO2 and subsequently to coat such a composite with a carbon layer. After removing unreacted SiO2 using HF, carbon-coated mesoporous Si (p-Si@C) can be obtained. The internal pores could accommodate the volume changes of Si and the carbon coating layer could effectively stabilize the interface during cycling. With this design, the as-prepared p-Si@C shows superior electrochemical performance compared with bare Si. When the p-Si@C electrode evaluated at a rate of 0.5 A g−1, a reversible capacity of 1146 mAh g−1 could still be maintained after 100 cycles.

Electrochemical Characterization of Silicon Nanocrystals Embedded in Alloy Matrix As Anode Materials for Lithium-Ion Cells

Silicon has been regarded as one of the most promising anode materials to increase the energy density of lithium-ion batteries by replacing graphite materials due to its high theoretical capacity.1 However, the practical application of silicon materials in lithium-ion batteries is hampered by the large volume changes that occur during repeated cycling, which result in the cracking of the electrode, loss of electrical contact, unstable solid electrolyte interphase (SEI) formation, and eventually rapid capacity fading upon cycling.2,3 The promising approach to overcome the above problems is the utilization of active-inactive alloy systems, where the electrochemical reaction occurs in the active phase and the inactive phases help to improve electronic conductivity and act as a volume buffer. In the present work, we synthesized silicon alloys composed of silicon nanoparticles embedded in Cu-Al-Fe matrix phases. The matrix phases have a mechanical property to endure the stress generated by the volume expansion of Si during cycling in addition to high electrical conductivity for fast electron transfer to silicon. This strategy resulted in enhanced cycling performance in terms of discharge capacity, capacity retention and rate capability. These superior performances could be attributed to its unique structure with silicon particle embedded by alloy matrix, which could effectively accommodate the large volume change during cycling and provide continuous electronic pathway in the electrode. Detailed characterization of the silicon alloy materials along with their electrochemical performance as anode in lithium-ion cells will be presented.

Self-supported Porous Silicon Nanotube Arrays As Anode Material for Li-ion Batteries

Li-ion batteries (LIBs) have been used as a power source ranging from microelectronics to electrical vehicles. However, the use of graphite as anode material for next generation LIBs is unsuitable because of the low Li+ storage capacity (372 mAh.g-1). Various alternative, such as Si, Sn, Ge, has been considered as alternative due to their superior specific gravimetric capacity (for example Si = 4200 mAh.g-1) resulting in high power/energy densities1. However, these materials are intrinsically prone to large volume change during alloying/dealloying mechanism resulting in pulverization, thick SEI formation, loss of electrical contact and active material2. The use of nanostructure has been widely studied to address this problem. Recently, our group has developed techniques to fabricate ultrathin crystalline silicon nanotube arrays (Si NTAs). In comparison to previous works which focus on sealed SiNTs3 and larger size SiNTs (> 400 nm)4, our Si NTAs are ultrathin (10 nm) with porous side walls5. Fig.1 a & b, shows the SEM and TEM images of the Si NTAs fabricated by three step template directed method. The first step is the formation of sacrificial ZnO into stainless steel substrates followed by the deposition of Si onto the ZnO nanowires. The last step is the removal of the sacrificial ZnO nanowire templates to obtain the Si NTAs with porous side wall structure. Fig. 1 (a) SEM and (b) TEM image of Si NTAs. Fig. 2 shows the gravimetric capacity of Si NTAs as a function of cycle number. The electrochemical tests were performed in two electrode Swagelok cell. The half-cells were assembled by using Si NTAs as a working electrode, Li foil as a counter electrode, and a Whatman glass microfiber soaked in 1 M LiPF6 in EC:DEC electrolyte as separator. The cell was cycled at C/20 in a potential window of 0.01 – 1.75 V vs Li/Li+. It delivers a specific capacity of 1670 mAh.g-1 after 30 cycles. The high capacity values are attributed to the 3D porous structure of the Si NTAs. During this work, the improved electrochemical performance of Si NTAs will be discussed. Fig. 2. Gravimetric capacity vs cycle number for Si NTAs at C/20. Reference 1. Liang, B.; Liu, Y.; Xu, Y., Silicon-based materials as high capacity anodes for next generation lithium ion batteries. Journal of Power Sources 2014, 267, 469-490. 2. Kasavajjula, U.; Wang, C.; Appleby, A. J., Nano- and bulk-silicon-based insertion anodes for lithium-ion secondary cells. Journal of Power Sources 2007, 163 (2), 1003-1039. 3. Song, T.; Xia, J.; Lee, J.-H.; Lee, D. H.; Kwon, M.-S.; Choi, J.-M.; Wu, J.; Doo, S. K.; Chang, H.; Park, W. I., Arrays of sealed silicon nanotubes as anodes for lithium ion batteries. Nano letters 2010, 10 (5), 1710-1716. 4. Wu, H.; Chan, G.; Choi, J. W.; Yao, Y.; McDowell, M. T.; Lee, S. W.; Jackson, A.; Yang, Y.; Hu, L.; Cui, Y., Stable cycling of double-walled silicon nanotube battery anodes through solid-electrolyte interphase control. Nature nanotechnology 2012, 7 (5), 310-315. 5. Huang, X.; Gonzalez-Rodriguez, R.; Rich, R.; Gryczynski, Z.; Coffer, J. L., Fabrication and size dependent properties of porous silicon nanotube arrays. Chemical Communications 2013, 49 (51), 5760-5762. Figure 1

Ultrafine Sn nanoparticles embedded in shell of N-doped hollow carbon spheres as high rate anode for lithium-ion batteries

A novel reversible interaction in polymeric nanoparticles is used to induce hollow Sn4+-MOPs. Then ultrafine Sn nanoparticles uniformly embedded in shell of N-doped hollow carbon spheres is successfully synthesized by pyrolysis of the Sn4+-MOPs precursor. In this architecture, the N-doped carbon shells can effectively avoid the direct exposure of embedded Sn nanoparticles to the electrolyte and efficiently accommodate the volume change of Sn nanoparticles. Furthermore, the hollow structure of carbon sphere can prevent Sn nanoparticles aggregation over repeated cycling and shorten the diffusion path of both electrons and ions. As a consequence, this N-doped hollow Sn/C anode delivers a reversible capacity of 606mAhg−1 at a current density of 0.2Ag−1 after 250 cycles and a reversible capacity of 221mAhg−1 even at a much higher current density of 10Ag−1, which are much better than those of pure Sn nanoparticles. The desirable cyclic stability and rate capability were attributed to the unique architecture that provided fast pathway for electron transport and simultaneously solved the major issues of Sn-based anodes, such as pulverization, aggregation and loss of electrical contact.

NaAlH4 Nanoconfinement in a Mesoporous Carbon for Application in Lithium Ion Batteries

Alanates have recently attracted attention as new anodic materials for lithium ion batteries. The electrochemical activity of sodium alanate has been already reported and the conversion mechanism explained. Through a complex conversion reaction, this compound is able to develop almost all the theoretical capacity, achieving more than 1700 mAh/g upon first discharge with an efficiency of 70%. Nevertheless alanate undergoes to capacity fade in few cycles. This is mainly due to the severe structural reorganization following the conversion reaction, that results in electrode pulverization and loss of electric contact. Here, we present a nanocomposite material consisting of NaAlH4 confined in the nanoporous of a carbon matrix able to mitigate the effect of volume expansion and improve the cyclability. Specifically, the nanocomposite has been studied in terms of structure, morphology and hydrogen content by the means of Infrared Spectroscopy, solid state NMR, electronic microscopy and thermal analysis. Finally, its performance in lithium cells is presented.

Investigations on the electrochemical decomposition of the electrolyte additive vinylene carbonate in Li metal half cells and lithium ion full cells

Abstract In this study, the decomposition of vinylene carbonate (VC) additive and its effect on the aging behavior is investigated in Li metal half cells and lithium ion full cells. Four electrolyte systems, the reference electrolyte with three VC additive amounts, i.e., 1, 5 and 10 vol% are examined with commercial LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC 111) cathode material and mesophase carbon microbeads (MCMB) anode material. The thickness changes of the cathode electrolyte interphase (CEI) and of the solid electrolyte interphase (SEI) after 5 constant current cycles at 0.1C and 200 constant current/constant voltage (potential) cycles at 1C are investigated for cells containing different amounts of VC. With the help of X-ray photoelectron spectroscopy (XPS) and high-performance liquid chromatography (HPLC), a correlation between CEI thickness change and electrolyte decomposition is figured out. The addition of VC leads to a thin CEI layer and a high capacity retention in a lithium metal half cell. A strong dependence of the performance on the VC concentration is found for half cells that results from the continuous consumption of electrolyte and the electrolyte additive at the Li metal counter electrode. In contrast, for full cells, even 1 vol% of VC helps to form both a stable CEI and SEI, while a larger amount of VC increases the CEI thickness, electric contact loss and the internal resistance.

Structural and Chemical Synergistic Encapsulation of Polysulfides Enables Ultralong-Life Lithium-Sulfur Batteries

The fast depletion of fossil fuels and deterioration of environment have led to increasing demand for renewable energies and efficient energy storage technologies. Lithium-sulfur (Li-S) batteries have been regarded as one of the most promising high-energy power sources in broad applications ranging from electric vehicles to large-scale grid energy storage. Li-S batteries deliver a theoretical energy of 2600 W h kg-1 that is an order of magnitude higher than that of the current lithium-ion batteries (LIBs), and utilize naturally abundant sulfur as the cathode material which significantly reduces the cost. The major challenge for the practical implementation of Li-S batteries resides in the dramatic capacity decay. The intermediate lithium polysulfides (Li x S n , 3≤n≤8) formed during cycling dissolve in the liquid electrolyte, migrate through the separator, and deposit on Li metal anode, causing “shuttle effect”. In addtion, the utilization of the active material is strongly hampered by the intrinsic insulating of S and its discharge product Li2S, leading to a low capacity and poor rate capability. Furthermore, the S cathode suffers from the volume variation (~80%) during lithiation/de-lithiation, causing the loss of electrical contact and the structure instability. Herein, we demonstrate an innovative strategy to efficiently entrap Li x S n from synergistic effect of structural restriction and chemical encapsulation using metal oxide-decorated hollow sulfur spheres. The significance of this strategy lies in that we purposely design a material architecture with both structural and chemical encapsulation effect, and that the material architecture provides a prolonged cycling stability. MnO2 is selected as a model and the MnO2 nanosheets-decorated hollow S spheres (hollow S-MnO2) nanocomposites are achieved through a facile synthesis. The nanocomposites with unique structure possess several features favoring highly stable S electrodes: i) the hollow spheres with inner void space not only alleviate the volume expansion of S on lithiation but also structurally restrict soluble Li x S n within the spherical structure; ii) the decorated MnO2 nanosheets with large surface area efficiently and chemically minimize the polysulfides dissolution by forming strong bonding; iii) the small dimensions of hollow S-MnO2 nanocomposites facilitate both ion and electron transport, leading to a better utilization of the S. This design presents a new strategy to prevent loss of polysulfides by structural and chemical dual-encapsulation, and can be expanded to other metal oxides or metal hydroxides. The unique material architecture enables high-performance S cathodes with high capacity, high sulfur loading and extremely low capacity decay of only 0.028% per cycle over 1500 cycles at 0.5 C-rate. Figure 1

Poly(fluorene phenylene) Graft Copolymer As a Novel Binder with Polyvinylpyrrolidone for High-Capacity Silicon Anode in Lithium-Ion Batteries

Rechargeable lithium ion batteries (LIB) have been vastly used in portable devices like cellular phones, laptops, tablets and also in electric vehicles because of their relatively high energy density, good power performance and cycle life. Carbonaceous negative electrode materials, especially graphitic carbons are conventionally used as anode materials at LIBs due to their good cycle-ability and low stable discharge voltage plateau. However, graphite has a low Li atomic density at full Li capacity in carbon intercalation compound (LiC6) which leads to lower theoretical capacity (372 mAh/g). Therefore, different types of anode active materials have been investigated as an alternative to graphite in order to achieve higher capacities. Among them, silicon (Si) is one of the most promising candidate as an anode active material because of its high theoretical capacity (more than 3500 mAh/g at room temperature) and low average discharge potential (∼0.5 V vs Li/Li+).Unfortunately, huge volume expansion (310% at full lithiation of Si) due to the lithium ion diffusion during the lithiation/delithiation process causes drastic capacity fade because of the high internal stresses, loss of electrical contact and the formation of non-electronic and ionic conductive passivation film between the anode surface and electrolyte. Low electrical conductivity of silicon is also another problem that remarkably hinders the rate performance. In the present work, above mentioned shortcomings are overwhelmed by incorporating tri(ethylene glycol) (TEG) groups over phenylene base units as side chains on the framework of the PFP based conductive polymer. Polyvinylpyrrolidone (PVP) was also used as adhesive to enhance the property of binding, thus decreasing stress-induced cracks. The synthesis was achieved through Suzuki polycondensation reaction in the presence of Pd(PPh3)4 catalyst by using independently prepared TEG functionalized dibromo benzene in conjunction with dioctylfluorene-diboronic acid bis(1,3-propanediol) ester. The obtained conductive and flexible polymer was used as a binder for Si-anode with high performance. It was demonstrated that the designed and fabricated binder polymer with multi-functionality displays a high electronic conductivity, mechanical strength, high polarity, adhesion, and more importantly, the electrolyte uptake arising from its excellent ductility. Figure 1

Surface Modification Strategies of High Capacity Anodes Towards Exceptional Robust Cycling

Pulverization of electrode materials and loss of electrical contact have been identified as the main causes for the performance deterioration of alloy anodes. In this talk, we describe the hierarchical arrangement of spatially confining silicon nanocrystals within several different physical insulting capsules for alleviating these issues. Firstly, an elastic, highly oriented graphene monolith was engineered to fully encapsulate the silicon nanoparticles, serving as a robust framework with the well-accessible thoroughfares for electrolyte percolation, as well as an electrolyte blocking layer to restrain Si from direct exposure to electrolyte without sacrificing the high-efficiency electron/Li ion transport channels; in return, the pillar effect of Si NPs prevents the graphene sheets from re-stacking. Secondly, we also attempted to develop a F-doped TiO2-x layer on the silicon surface with additional possibility of the in-situ etching of the native oxide layer into a hollow interior. When evaluated as binder-free anodes, both type of the electrodes exhibit a remarkable cycle life for more than 1000 cycles with average coulombic efficiency higher than 99.5%. Operando XRD and synchrotron-based XPS confirmed the formation of the most volume expanded lithiated phase Li15Si4, suggesting the effective buffering of the volume variation upon cycling. Furthermore, we also develop a GF/Si free-standing film through re-adjusting the pore size in GF/Si monolith. Thanks to electrical conductivity, the elasticity and structural integrity of GF monoliths, the as-developed GF/Si free-standing film showcases the potential use in the flexible electronic devices.

Electrochemically Synthesized Sn Nanodendrites As High-Performance Na-Ion Batteries Anodes

Because of their high energy density, Li-ion batteries have attracted attention as large storage systems over their traditional use for portable and electric vehicle applications. However, there are some concerns about the scarcity, uneven global distribution and high cost of lithium resourced. Compared with Li, Na has the advantages of natural abundance and low cost. Furthermore, Na and Li are in the same main group, exhibiting similar chemical properties, which translates to a resemblance between operational characteristics in Li-ion batteries and Na-ion batteries. Therefore, Na-ion batteries have been suggested for the alternatives to Li-ion batteries for large-scale systems. For the practical use of Na-ion batteries, studies for finding suitable electrode materials with high energy density, good cyclability and rate performance for Na-ion batteries have been actively conducted. Although several cathode materials have been suggested, the anode choices are severely limited because of the unique characteristic of Na. Na-ion cannot be stored much in commercial layered graphite because of its large radius. Si based materials are expected to be the most promising anode for Li-ion batteries, but it is electrochemically inactive with Na. On the contrary, Sn can store 3.75 Na/host-atom (Na15Sn4) resulting a maximum storage capacity of 847 mAh g-1 as an anode for Na-ion battery. Besides the high theoretical capacities, Sn also has advantages as an anode material for Na-ion battery such as low reaction potential and non-toxicity. However, pure Sn anode exhibits poor cyclability due to a loss of electrical contact with the current collector, resulting from a severe volume change (up to approximately 420%) during sodiation/desodiation. To improve the cyclability of Sn electrode, several strategies have been suggested such as introducing carbon or designing Sn-M intermetallic compounds for providing an active or inactive phase that acts as buffer matrix, and synthesizing a micro/nanostructured electrode for facilitating the relaxation of material stress. Among these strategies, synthesizing a nanostructured pure Sn, especially using electrodeposition, should be ideal solution. The material fracture is presumably due to the repeated non-uniform expansion and contraction during alloying and de-alloying. Because of a sluggish kinetic of sodium ion, the diffusion time is large compared to the charge/discharge time for the large sized particles which results uneven sodiation and desodiation states (different phases with different mechanical strengths) inside one particle. These variations in phase lead to stress, which can lead to crack propagation and pulverization. For this reason, nanostructured Sn could greatly reduce the stress induced during sodiation/desodiation by reducing the diffusion time of sodium ions in the electrode. Furthermore, using electrodeposition process, theoretical specific capacity of Sn can be fully used because the Sn anode are deposited directly on the current collector without mixing and drying processes for binder and conductive agent. Recently, we synthesized Sn nanodendrites with nano-sized branches. The Sn nanodendrites exhibited a high reversible capacities and excellent cycle performances. The maximum capacity was measured to be 783.88 mAh g-1 and the charge capacity at 100th cycle was measured to be 759.27 mAh g-1 that correspond to 96.86% of the maximum value. After cycling, the Sn nanodendrites exhibits no loss of active materials and it was attributed to the nano-sized branches greatly reducing the internal stress during sodiation/desodiation.

Constraining Si Particles within Graphene Foam Monolith: Interfacial Modification for High‐Performance Li+ Storage and Flexible Integrated Configuration

Pulverization of electrode materials and loss of electrical contact have been identified as the major causes for the performance deterioration of alloy anodes in Li‐ion batteries. This study presents the hierarchical arrangement of spatially confining silicon nanoparticles (Si NPs) within graphene foam (GF) for alleviating these issues. Through a freeze‐drying method, the highly oriented GF monolith is engineered to fully encapsulate the Si NPs, serving not only as a robust framework with the well‐accessible thoroughfares for electrolyte percolation but also a physical blocking layer to restrain Si from direct exposure to the electrolyte. In return, the pillar effect of Si NPs prevents the graphene sheets from restacking while preserving the highly efficient electron/Li+ transport channels. When evaluated as a binder‐free anode, impressive cycle performance is realized in both half‐cell and full‐cell configurations. Operando X‐ray diffraction and in‐house X‐ray photoelectron spectroscopy confirm the pivotal protection of GF to sheathe the most volume‐expanded lithiated phase (Li15Si4) at room temperature. Furthermore, a free‐standing composite film is developed through readjusting the pore size in GF/Si monolith and directly integrated with nanocellulose membrane (NCM) separator. Because of the good electrical conductivity and structural integrity of the GF monolith as well as the flexibility of the NCM separator, the as‐developed GF/Si‐NCM electrode showcases the potential use in the flexible electronic devices.

Technologies and Materials to Enable Advanced Anode and Cathode Materials

The increased adoption of electric vehicle technologies is driving the demand for higher energy density batteries. Since the lithium ion battery was first commercialized 25 years ago in 1991, significant improvements have been achieved through both battery design and material innovations. However, even as these past achievements are celebrated, current research and industry targets are focused on higher energy and lower cost batteries. It is necessary to consider advanced materials on both the cathode and anode sides of the battery to achieve these goals. Commercially available electric vehicles have achieved driving ranges in excess of 200 miles (320 km) per charge (1). This has been made possible in part through the use of high nickel cathode materials. Nickel-rich layered cathode materials such as LiNi0.8Co0.15Al0.05O2 (NCA) and nickel-rich LiNixCo(1-x)/2Mn(1-x)/2O2 (NCM) can deliver high specific capacities of over 200 mAh g-1. However, the issues surrounding synthesis of these materials are well documented (2), (3), (4). It is established that synthesis of NCA requires use of lithium hydroxide as the lithium precursor. Additional research efforts have been focused on nickel-rich NCM materials (Ni ≥ 0.6 moles) in an effort to balance high specific capacity with battery safety. The choice of lithium precursor, LiOH.H2O or Li2CO3, can have a dramatic effect on the performance of these materials. We will discuss the advantages of using lithium hydroxide on the performance of nickel-rich cathode materials. On the anode side, silicon-based materials offer the potential for very high energy density (5). However, fundamental properties of silicon materials are hindering their commercialization (6). Extensive efforts are being undertaken to overcome issues such as loss of electrical contact and conductivity caused by material disintegration due to volume expansion and contraction during cycling, and a lot of progress has been reported (7). Nevertheless, it is generally accepted that successful commercialization of silicon-based anode materials will require pre-lithiation to overcome the issue of inherent large first cycle irreversible capacity loss. FMC’s innovative technology and material, Lectro® Max Powder (SLMP®), enables a new high energy density generation of lithium ion batteries by providing an independent source for lithium (8), (9) . Significant research has been directed toward developing stable, deployable SLMP pre-lithiation systems and processes (10), (11). In our presentation, we will show energy density improvements with SLMP in LIB as well as discuss its use for beyond lithium ion applications (12). References Straubel, J. B. "Driving Range for the Model S Family." Tesla Motors, 30 Dec. 2014. Web. B. H. Kim, et al., The effect of oxygen pressure on the synthesis of LiNiO2. Solid State Phenomena, Vols. 124-126, (2007), p. 1043-1046 P. Kalyani, N. Kalaiselvi, Various aspects of LiNiO2 chemistry: A Review. Science and Technology of Advanced Materials, 6, (2005), p. 689–703 Kim, M.-H., Shin, H.-S., Shin, D. & Sun, Y.-K., Synthesis and electrochemical properties of Li[Ni0.8Co0.1Mn0.1]O2 and Li[Ni0.8Co0.2]O2 via co-precipitation. Journal of Power Sources, (2006), 159, p. 1328-1333 Yushin, G. et al., High-performance Lithium-ion Anodes Using a Hierarchical Bottom-up Approach. Nature Materials, 9, (2010), 353-58. <www.nature.com>. Koratkar, Nikhil et al., Nanostructured Silicon Anodes for Lithium Ion. Small Journal, 20, (2009), p. 2236-242. Hui Zhao, Wei Yang, Ruimin Qiao, Chenhui Zhu, Ziyan Zheng, Min Ling, Zhe Jia, Ying Bai, Yanbao Fu, Jinglei Lei, Xiangyun Song, Vincent Battaglia, Wanli Yang, Phillip Messersmith, and Gao Liu, Conductive polymer binder for high-tap-density nano-silicon material for lithium ion battery negative electrode application. Nano Letters, (2015), 15, p. 7927-7932. C. R. Jarvis, M.J. Lain, Y. Gao, and M. Yakovleva, J. Power Sources, 146, 331 (2005). Y. Li, B. Fitch, Electrochem. Commun., 13, (2011) 664. Guo Ai, Zhihui Wang, Hui Zhao, Wenfeng Mao, Yanbao Fu, Vincent Battaglia, Sergey Lopatin, and Gao Liu, Scalable process for application of stabilized lithium metal powder in Li-ion batteries. Journal of Power Sources, (2016). Zhihui Wang , Yanbao Fu , Zhengcheng Zhang , Shengwen Yuan , Khalil Amine,Vincent Battaglia , Gao Liu, Application of Stabilized Lithium Metal Powder (SLMP) in graphite anode-A high efficient prelithiation method for lithium-ion batteries, Journal of Power Sources, 260, (2014), 57e61 Margret Wohlfahrt-Mehrens, Manuel Weinberger, Novel strategies towards the realization of larger lithium sulfur/silicon pouch cells. Electrochimica Acta, Volume 191, 10, February (2016), p. 124–132. Figure 1

How the Conditions of Preparation Process Affect the Electrochemical Properties of C/Sn Anode Materials?

How the conditions of preparation process affect the electrochemical properties of C/Sn anode materials? The application of tin in commercially available Li-ion batteries is limited by the poor cyclic performance due to the pulverization caused by cyclic volume changes of elementary cell, during the insertion and extraction processes of lithium ions [1]. Consequently, it results in loss of electrical contact between active material and current collector. One of the ways to overcome this issue is development of tin-carbon nanocomposite, in which nanometric tin grains are encapsulated in a flexible and conductive carbon layers. Such nanocomposites are able to provide appropriate electrochemical properties, only if the formed carbon layer is flexible, has appropriate porosity which featuring local free space to compensate volume changes. The goal of the presented studies is to examine the effects of carbonization temperature as well as origin and content of carbon on the electrochemical performance of carbon-tin nanocomposites. Electrode materials consisted of tin-based nanograins encapsulated in carbon buffer matrix of different origins (starch or water soluble polymer) were obtained in a simple and inexpensive process. The tin precursor (SnO2) was prepared using a modified reverse nanoemulsion method (w/o) and then was coated by a various source of carbon (potato starch or modified poly(N-vinylformamide)) [2,3]. The carbon-tin precursors were pyrolyzed, providing formation of tin-based nanograins encapsulated in buffer matrix. The optimal condition for preparation process was studied using thermal analysis method (EGA-TGA/DTG/SDTA). The structure and the morphology of the samples were characterized by X-Ray diffraction analysis (XRD), low-temperature nitrogen adsorption method (N2-BET) and transmission electron microscopy (TEM) as well. The quality of carbon matrix in resulting composites was determined by Raman spectroscopy (RS) measurements. The working electrodes were prepared from a carbon-tin active material and polyvinylidene fluoride (PVDF) binder in N-methylpyrrolidone (NMP) solvent on copper foil. R-2032 coin type cells were assembled using obtained electrodes combined with Li metal discs as a counter electrode. The electrolyte consisted of a solution of 1M LiPF6in a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with EC/DEC molar ratio of 1:1. The lithium cells were characterized by cyclic voltammetry (CV), charge-discharge tests (CELL TEST) as well as electrochemical impedance spectroscopy (EIS). The thermal analysis results enabled determination of the optimal carbonization temperature for obtaining carbon-tin anode materials. N2-BET data as well as TEM images indicated that samples, in which the potato starch was used as a carbon source, have high specific surface area and pore volume as well as reveal presence of the opened pores through the composites. The electrochemical tests showed that better encapsutation of tin nanograins in carbon buffer matrix resulted in higher gravimetric capacity and better cell performance. The C/Sn material in which carbon matrix was fabricated from modified polymer exhibited higher gravimetric capacity and better cell performance (589 mAh g-1 after 70 cycles). The authors acknowledge a financial support from the National Science Centre of Poland under research grant No. 2012/07/N/ST8/03725. [1] S. Ding, X.W. Lou, Nanoscale, 3 (2011) 3586[2] M. Molenda, A. Chojnacka, M. Bakierska, R. Dziembaj, Mater. Technol., 29 (2014) A88[3] A. Chojnacka, M. Molenda, M. Bakierska, R. Dziembaj, Procedia Eng., 98 (2014) 2