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NEWS MEDIA ADVISORY EMBARGOED FOR RELEASE: Sunday, April 7, 2013, 8 a.m. Eastern Time
Note to journalists: Please report that this research was presented at a meeting of the American Chemical Society.
Newswise — NEW ORLEANS, April 7, 2013 — With lithium-ion batteries in the news for grounding the Boeing 787 Dreamliner fleet — and as a fixture in many consumer electronics products — li-ion technology is the topic of dozens of potentially newsworthy scientific reports that begin here today. The presentations are part of the 245th National Meeting & Exposition of the American Chemical Society, the world’s largest scientific society.
Abstracts of some key reports scheduled for the meeting appear below.
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Abstracts
High efficiency low temperature recycling technology for lithium ion batteries
Lithium ion (Li ion) batteries are extensively used because of their high energy density, good cycle life, high capacity, etc. The rechargeable Li ion battery market was ~ $4.6 billion in 2006 and is expected to grow to more than $6.3 billion by 2012. Also lithium ion batteries are gradually being used for large applications, such as hybrid or electrical vehicles and grid systems. At present, Li ion batteries such as the ones used in cell phones and laptops are not widely recycled. We believe that such an open loop industrial cycle is not sustainable; it is our strong conviction that we must develop and establish viable Li ion battery recycling methodologies. In this project, we recycle Li ion batteries through low temperature chemical methods and active materials can be synthesized during recycling process; this will reduce energy usage, environmental damage, lead to economically viable processes, and strengthen our national security position.
Potential induced structural changes and solid electrolyte interphase (SEI) decomposition in Sn anodes for Li ion batteries
We report measurements of electrochemical surface stress of thin film Sn electrodes for Li-ion battery anodes at potentials
In contrast, Sn surfaces exhibit significant changes in compressive and tensile surface stress even before Li insertion. Since these features occur in potential regions where there is no major interaction between Li and Sn, these features originate in changes in the Sn material itself. During the cathodic scan, an intense compressive feature at ca. 0.7 V vs. Li/Li+ is observed. A major tensile release at ca. 0.6 V vs. Li/Li+ follows this compressive feature. These features have a structural origin in a phase change in the Sn anode. This phase change impacts the ability of Sn and its alloys to serve as an anode material for a Li ion battery.
We also report the results of matrix assisted laser desorption (MALDI) time of flight (TOF) mass spectrometry (MS) analysis of Sn electrodes. In a mixture of ethylene carbonate and dimethyl carbonate, long chain oligomers are observed following the first cycle. These oligomers decompose in the subsequent cycles showing that Sn surfaces form an unstable SEI. This decomposition produces oligomerized species, which are different from those formed at the end of the first cycle. We discuss potential and solvent dependent oligomerization mechanisms and their effect on the mechanical properties of Sn electrodes.
Chemically induced stresses in Li ion battery electrodes
Lithiation induced volume changes in battery electrode materials lead to a variety of chemo-mechanical phenomena. It is difficult to investigate these mechanisms directly in complex electrode microstructures that consist of powdered active components, conductive filler, and binders. Thin films provide an opportunity to more directly investigate fundamental processes, by combining in situ stress data with conventional in situ electrochemical measurements. Three examples that demonstrate this approach will be highlighted: (1) the formation of the solid-electrolyte interphase (SEI) layer on graphitic carbon films, where disruption of the near surface leads to stresses that impact the SEI stability; (2) the stress-induced response of interfaces in model Si-based nanocomposite structures, (3) the role of stress and oxygen non-stoichiometry on phase transformations in vanadium oxide films.
New low-temperature, non-flammable polyelectrolyte systems for lithium ion batteries
Renewable lithium-ion batteries are promising sustainable alternatives to non-renewable energy resources like petroleum. However, safety concerns, electrochemical stability, and narrow temperature range of operation remain persisting challenges that impede their prominence. In order to circumvent these shortcomings, we will describe herein a new class of lithium ion electrolytes composed of perfluoropolyethers (PFPE) and poly(ethylene oxide) (PEO) mixtures. These polymeric blends are amphiphilic, transparent, homogeneous and demonstrate the ability to solvate different lithium salts. The flammability, degree of crystallinity, ionic conductivity and electrochemical stability of these carbonate-free systems will be discussed.
Vanadium oxide mesocrystals: Synthesis, formation mechanism, and application in lithium-ion battery
An additive and template free process was developed for the synthesis of mesocrystalline VO2(B) nanostars via the solvothermal reaction of oxalic acid and V2O5. Microscopy results demonstrate that the six-armed star architectures are composed of stacked nanosheets that are homoepitaxially oriented along the [100] crystallographic register with respect to one another. The mesocrystal formation mechanism is proposed to proceed through classical as well as non-classical crystallization processes and was possibly facilitated or promoted by the presence of a reducing/chelating agent. The product was tested as cathode for lithium-ion batteries and show good capacity at discharge rates ranging from 150-1500 mA g-1 and a cyclic stability of 195 mA h g-1 over fifty cycles. The exposed (100) facets lead to fast lithium intercalation, and the homoepitaxial stacking of nanosheets offers a strong inner-sheet binding force that leads to better accommodation of the strain induced during cycling.
High-performance lithium-ion battery anode based on core-shell heterostructure of silicon-coated vertically aligned carbon nanofibers
A high-performance hybrid lithium-ion anode material was developed using coaxially coated Si shells on vertically aligned carbon nanofiber (VACNF) cores. The bush-like VACNFs serve as conductive cores to effectively interface with Si shells for Li+ storage. The open core-shell nanowire structure allows the Si shells to freely expand/contract in the radial direction during Li+ insertion/extraction. A high specific capacity of 3000-3650 mAh(gSi)-1, comparable to the maximum value of amorphous Si, has been achieved. About 89% of capacity is retained after 100 charge-discharge cycles at C/1 rate. After long cycling, the electrode material becomes even more stable, showing the invariant Li+ storage capacity as the charge-discharge rate is increased by 20 times from C/10 to C/0.5 (or 2C). The ability to obtain high capacity at significantly improved power rates while maintaining the extraordinary cycle stability demonstrates that this novel structure could be a promising anode material for high-performance Li-ion batteries.
Used Li-ion batteries recycling: Lithium recovery for a new utilization
The French Alternative Energies and Atomic Energy Commission has been starting a key program on the development of Li-ion technologies for applications such as green transportation and stationary energy storage. Among them, the technologies based on LFP and LTO active materials are now transferring at industrial scale. In parallel, the recycling has to be considered for production scrap and batteries end of life.
In this domain, two main issues arise:
- The European regulation fixes at 50% the minimal recycling rate,
- The economical balance of current recycling processes is threatened by materials without Co, Ni or Mn.
A study has been initiated on the recycling of such materials by hydrometallurgy in order to maximize the value of main elements by reintroducing them in the new active materials synthesis. Lithium and Iron were recovered, separated and turned into phosphates or carbonates with high purity and high recovery rate.
Redox Shuttle Additives for High Voltage Lithium-Ion Battery Cathodes
Preventing overcharge in lithium-ion batteries is critical for extending battery lifetimes and preventing safety issues. When batteries connected in series have non-equivalent capacities, one or more batteries will become fully charged before the battery pack is completely charged, thus resulting in an overcharged state, which lead to irreversible reactions of the electrode and electrolyte. Redox shuttles can mitigate excess charge by acting as an internal shunt for excess current. We are developing new redox shuttles with the aim of increasing oxidation potentials for higher voltage cathodes. It is also critical to have long cycle lifetimes to ensure many overcharge cycles. We report new N-ethylphenothiazine derivatives as redox shuttle additives. The presentation will include synthesis of new derivatives, comparisons of oxidation potentials from cyclic voltammetry to energy levels obtained from DFT calculations, and battery cycling studies.
Non-flammable electrolytes for high performance lithium-ion batteries
Rechargeable lithium-ion batteries with improved safety and high performance are needed for numerous applications including electric vehicles and consumer electronics. Current lithium-ion batteries utilize a flammable electrolyte which can combust and release highly toxic chemicals. Non-flammable electrolytes based on ionic liquids, phosphates, phosphonates, and other fire retardant additives have been developed, however, most non-flammable electrolytes developed to date result in decreased battery performance particularly under high rate and low temperature conditions. Compositions were developed to allow the electrolyte to be both non-flammable and provide high performance under wide temperature ranges and high rates. The electrolyte properties and electrochemical performance of cells containing the electrolyte were evaluated. Testing showed that electrolytes containing specific flame retardant additives and components provide batteries with significantly lower flammability and similar capacities, rates, cycle lives, and temperature ranges as batteries containing conventional flammable electrolytes.
Graphene-based flexible supercapacitors and lithium ion batteries
Graphene has high specific surface area, good chemical stability, high electrical and thermal conductivity, and excellent flexibility. Therefore, graphene and its composite materials can be used as free-standing and binder-free electrodes for flexible energy storage devices.
First, flexible graphene/polyaniline paper was prepared by in situ anodic electropolymerization of polyaniline on a graphene membrane, and it shows a stable large electrochemical capacitance and excellent cyclibility. Second, we fabricated graphene-cellulose paper membranes which are used as freestanding and binder-free electrodes for flexible supercapacitors with good performance. Finally, we developed template-directed CVD to synthesize a three-dimensional interconnected graphene framework (GF). An anode and cathode were made by coating active materials on the GF to assemble a thin, lightweight and flexible lithium ion battery. The battery has high rate capability and capacity, and can be repeatedly bent down to
Silicon nanowire core aluminum shell coaxial nanocomposites for lithium ion battery anodes grown with and without a TiN interlayer
We investigated the effect of aluminum coating layers and of the support growth substrates on the electrochemical performance of silicon nanowires (SiNWs) used as negative electrodes in lithium ion battery half-cells. Extensive TEM and SEM analysis was utilized to detail the cycling induced morphology changes in both the Al-SiNW nanocomposites and in the baseline SiNWs. We observed an improved cycling performance in the Si nanowires that were coated with 3 and 8 wt.% aluminum. After 50 cycles, both the bare and the 3 wt.% Al coated nanowires retained 2600 mAh/g capacity. However beyond 50 cycles, the coated nanowires showed higher capacity as well as better capacity retention with respect to the first cycle. Our hypothesis is that the nanoscale yet continuous electrochemically active aluminum shell places the Si nanowires in compression, reducing the magnitude of their cracking/disintegration and the subsequent loss of electrical contact with the electrode. We combined impedance spectroscopy with microscopy analysis to demonstrate how the Al coating affects the solid electrolyte interface (SEI). A similar thickness alumina (Al2O3) coating, grown via atomic layer deposition (ALD), was shown not to be as effective in reducing the long-term capacity loss. We demonstrate that an electrically conducting TiN barrier layer present between the nanowires and the underlying stainless steel current collector leads to a higher specific capacity during cycling and a significantly improved coulombic efficiency. Using TiN the irreversible capacity loss was only 6.9% from the initial 3581 mAh/g, while the while the first discharge (lithiation) capacity loss was only 4%. This is one of the best combinations reported in literature.
Materials challenges and opportunities of lithium-ion batteries
Lithium-ion batteries have revolutionized the portable electronics market, but their adoption for transportation and stationary electrical energy storage applications is hampered by high cost and safety concerns. The success of lithium-ion technology for these applications relies heavily on the development of low-cost, safe cathode and anode materials with high energy and power along with long cycle life. After providing an overview of the pros and cons of the existing cathode and anode materials, this presentation will focus on high-capacity, high-voltage layered and spinel oxide cathodes as well as nano-engineered alloy anodes. With the oxide cathodes, the importance of surface structure and chemistry to realize a robust electrode-electrolyte interface and superior electrochemical performance will be focused. With the alloy anodes, the importance of nanoarchitectures to avoid particle growth and realize long cycle life will be discussed.
Silicon and Germanium nanowires for next generation high capacity lithium ion batteries
Lithium (Li)-ion batteries have the highest energy and power density of any available rechargeable battery technology and they are widely used to power portable electronics. Still, Li-ion batteries are needed with lower cost, lighter weight, higher energy density, and better performance at fast charge/discharge rates. The most demanding Li-ion batteries applications of in battery-powered electric vehicles and large-scale (or grid) energy storage require unprecedented enhancements in energy and power density. One way to increase the energy density of a Li-ion battery is to replace the graphite anode with silicon (Si) or germanium (Ge). Si and Ge have significantly higher lithium storage capacities than graphite (3,579 mA h g-1 and 1,384 mA h g-1 compared to 373 mA h g-1). Si and Ge, however, undergo massive volume expansions when lithiated—by about 280%. Nanowires are being explored for Li-ion batteries because they can more or less tolerate these volume changes without degradation. Battery performance, however, relies on all of the constituents of the anode, including electrolyte and binder formulations. Seeds used to grow the nanowires can also influence the battery performance. Here, we present battery results using large quantities of Si and Ge nanowires grown by solution-based methods. The highest performance Si nanowires have been grown using tin seeds, which is also electrochemically active, and Ge nanowires have exhibited the best rate capability with capacities near the theoretical capacity due to its reasonably high electrical conductivity and fast Li diffusion.
Lithium-ion batteries: Ageing processes and surface/interface phenomena
Lithium-ion batteries are the well-established power source of portable electronic devices. Research efforts are now mainly motivated by the quest for improved energy storage systems for renewable energies and urban transportation. Future Li-ion battery applications such as electric vehicles require higher energy or power densities. Other applications require a good electrochemical behavior at high temperatures.
The reactivity at electrode/electrolyte interfaces is a very important issue. Common Li-ion batteries can work only because a passivation layer is formed at the surface of graphite that prevents this electrode from side reactions towards electrolyte. The use of new nanosized electrode materials, or operating at unusual temperatures, increases the importance of these electrode/electrolyte interface issues that directly impact the safety and the life span of batteries. In this presentation I will show some of the latest results obtained in the study of ageing processes in Li-ion batteries by X-ray Photoelectron Spectroscopy (XPS).
Lithium single-ion conducting polymers with unusual high-voltage stabilities for battery applications
Polymeric lithium single-ion conductors (PLSICs), in which mobile Li-ions are associated with a polyanionic backbone, mitigate problems with electrolyte polarization in Li-ion batteries. We have synthesized an electrochemically stable PLSIC by acyclic diene metathesis (ADMET) polymerization of a diolefin monomer containing a lithium bis(malonato)borate functionality. Electrochemical studies of this polymer reveal moderate lithium conductivity and an unusually wide electrochemical window (0.05-8.0 V vs. Li/Li+) due to the formation of a stable solid-electrolyte interphase (SEI) layer.
Nanosheets of layered transition metal dichalcogenides for lithium-ion batteries
Layered transition metal dichalcogenides, MX2, where M is a transition metal from groups 4 to 6 and X is S, Se, or Te, have potential as high discharge capacity materials in lithium-ion batteries. In these materials, individual layers of MX2 are held together by van der Waals forces, which permits the intercalation of ions or small molecules, as well as separation into mono- or multilayer nanomaterials. To date, studies with MoS2 nanoplatelets (>10 nm thickness) have shown that this MX2 material does not performed as well as expected in lithium-ion battery applications. We propose that the higher surface area of MX2 nanosheets (
Conversion reactions for lithium ion battery cathodes
Materials that undergo a conversion reaction with lithium (e.g., metal fluorides) often accommodate more than one Li atom per transition-metal, and are promising candidates for high-capacity electrodes for lithium batteries. However, little is known about the mechanisms involved in the conversion process, the origins of the large polarization during electrochemical cycling, and why some materials are reversible (FeF2) while others are not (CuF2). A better understanding of the conversion reaction mechanism requires tracking the local phase nucleation and evolution with lithiation, which is extremely challenging due to the complexity of the reaction and presence of multiple phases within nano-scale domains. This work provides new insights into the inter- and intra-particle Li transport and kinetics of lithium conversion reactions, and may help to pave the way to develop high-energy conversion electrodes for lithium-ion batteries.
Fundamental microstructural designing concepts for high capacity and long cycle life of anode materials based on carbon and silicon for lithium ion battery
For lithium ion battery, a range of materials has a high theoretical capacity, while in reality, this type of materials cannot be used directly due to a fast capacity fading. It is believed that the capacity fading and short cycle life of the battery using this type of materials are directly related to the overall large volume expansion and anisotropic accommodation of the volume change. Carbon is a commonly used conductor additive in the lithium electrode materials and it has a range of tailorable structures, ranging from nanofiber, graphene, and particles. Therefore, it is a natural approach to rationally design a composite materials based on Si and carbon. Due to their nanoscale dimensions, the lithiation induced volume expansion and shape change can be accommodated, therefore, reducing the chance of the failure of the battery. In this presentation, we review some of the fundamental designing concepts and associated challenges for tailoring composite materials based on Si and carbon as anode materials with high capacity and long cycle life.
Nanostructured electrodes for lithium ion batteries
Lithium-ion batteries store electrical energy in the form of chemical potential like primary batteries; however, the charge-discharge process in lithium-ion batteries is more complex as it involves not only Faradaic reactions at the interface between electrodes and electrolyte, but also is accompanied with mass and charge transport and volume change of the electrodes that commonly possess low electrical conductivity. Electrodes away from thermodynamic equilibrium include nanostructures with high surface energy, poor-crystalline materials, and materials with significant surface or bulk defects. Such materials are in higher energy state and, thus, easier for phase transfer and nucleation; such materials also have less closely packed structure, permitting faster mass transport and accommodating more lithium-ions as well as tolerating more volume change. This presentation will take vanadium pentoxide and lithium titanate as two model materials to illustrate the influences of doping, surface defects and carbon coating, and nanostructures on the lithium-ion intercalation properties.
Fused aromatic heterocycles for overcharge protection in lithium-ion batteries
Derivatives of the aromatic molecule phenothiazine have been used in batteries due to their ability to form the corresponding radical with minimal degradation, allowing them to redirect excess energy and prevent overcharge. This project aimed to find more efficient molecules for use as overcharge protectors in batteries. Specifically, oxidation potential, determined via cyclic voltammetry, was used to identify derivatives that could be used for higher end-of-charge potential cathodes, and the reversibility of the oxidation was examined. Derivatives of phenothiazine were synthesized in which alternate groups were substituted for the hydrogen molecules at junctions two and seven, as were molecules with 2,7-cyano groups but alternate base compounds. More broadly, the x-ray crystal structure was determined for each molecule to determine relative planarity in the hopes of discovering a relationship between planarity and efficiency. This experiment provides a basis for determining the accuracy of planarity as an indicator of a compound's effectiveness as an overcharge protector; results may also suggest the most efficient base molecules to serve as said additives.
Ultrathin coating of Al2O3 on negative electrode for lithium ion batteries
Next generation lithium ion batteries have required the high energy/power density and long cycling stability for powering transportation and grid systems. The silicon has been expected as a suitable negative electrode to apply these areas due to high theoretical energy capacity (4200 mAh/g). However, the silicon suffers from huge volume expansion, which cause loss of electrical contact among active materials and finally capacity fading. Here, we demonstrated the ultrathin coating of Al2O3 on patterned silicon wafer (p-Si) as a negative electrode for lithium ion batteries by surface sol-gel method. Al2O3 coated p-Si was characterized by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The TEM and XPS data revealed that the p-Si was conformably coated with 5 nm of Al2O3. The electrochemical behavior and cycle performance were examined by cyclic voltammetry, electrochemical impedance spectroscopy, and battery cycler.
Bicyclic-borate synthesis for use in lithium ion batteries
Bicyclic-borate complexes have been synthesized for use as an alternative anion for lithium ion batteries in hopes that they will provide insight into more flame retardant types of ions, or FRIons. This synthesis has been done through azeotropic distillations and solvent-free methods utilizing boronic acids. The current bicyclic compounds being produced were inspired by creating derivatives of lithium bis(oxalato) borate, also known as LiBOB.
Carbon cross-linked Si/SiC nanosphere as advanced anode of lithium-ion batteries
Silicon-based materials have been demonstrated as promising alternative anode materials with a specific capacity as high as around 4,200 mAh g-1 at a relative low discharge potential; however, the conventional Si-based anode suffers from rapid degradation in capacity due to its poor electrical conductivity and huge volume change during charging-discharging processes. We herein report a rational design and controllable route to fabricate carbon cross-linked Si/SiC nanospheres, in which the carbon not only functions as the network building block but also acts as a conducting film. The preparation was realized through thermal reduction of cross-linked SiO2@C using magnesium powders as a reducing agent. The hierarchical Si/SiC/C nanostructures exhibited a capacitance of around 860 mAh g-1 after cycling for 100 cycles with capacity retention of above 65%. The as-developed method is envisaged to pave a promising way to prepare high performance Si-based anode materials for lithium-ion batteries.
Stability and reactivity of redox shuttle additives for lithium-ion batteries
Derivatives of fused heteroaromatic molecules have been studied as electrolyte additives, also called redox shuttles, for overcharge protection in lithium-ion batteries with varying degrees of success. These additives fail as they decompose in their radical cation state, reacting with other shuttle molecules, electrodes, or electrolyte. Our goal is to study new redox shuttles that can undergo extended overcharge cycles. Therefore we are studying the stability of the radical cations formed in situ through spectroscopic techniques and performing DFT calculations simultaneously in order to observe a trend between experimental and computational results. The lack of extended cycles is not only due to stability of radical cations, but can also originate from possible reactions that can occur in battery conditions—intramolecular or intermolecular. Here we report results on radical cation stability and reactivity for possible redox shuttles in order to understand the possible mechanisms for the shuttle reaction in batteries.
DFT design and study of lithium-ion battery electrolytes and anode
The modification of edges in both graphene and graphite can significantly alter the electronic properties as well as the lithium diffusion mechanism. Our finding illustrate the importance of controlling the edges of these carbonaceous materials with atomic precision in order to take full advantage of their potential for high density applications in lithium ion batteries.
With regard to the electrolyte, the thermodynamic and kinetic data for the oxidative decomposition of PC show that the major oxidative decomposition products are independent of the type of lithium salt. Furthermore, the most possible components of the film formed on the cathode surface are polycarbonate, acetone, diketone, 2-(ethan-1-ylium-1-yl)-4-methyl-1,3-dioxolan-4-ylium and CO2. Similarly the major products which are responsible for the formation of protective SEI film when ES is used as an additive are Li2SO3, (CH2OSO2Li)2, CH3CH(OSO2Li)CH2OCO2Li and ROSO2Li. While, the products from the termination reactions of the primary radical of PS would build up an effective solid electrolyte interphase.
Investigating the voltage fading mechanism in Li1.2Co0.1Mn0.55Ni0.15O2 lithium-ion battery cathode by in situ x-ray diffraction studies
In this study, in situ x-ray diffraction (XRD) technique was implemented to investigate the voltage fading pathways in lithium-rich Li1.2Co0.1Mn0.55Ni0.15O2 cathode in a lithium-ion battery. A custom designed coin-cell with Kapton® film window of ~ 13mm in diameter opening was fabricated for in situ XRD experiment. The in situ XRD was collected during electrochemical charge/discharge process performed in 2.4-4.8 V voltage window at 10 mA/g rate in fist cycle and after subsequent cycles (16 and 36). The collected in situ XRD patterns were simulated and lattice parameters were calculated to correlate with the electrochemical profile. The results show increase in c-lattice parameter during initial charging up to 4.4 V and subsequently decreases beyond 4.4 V. The a-lattice parameter remains constant at the first cycle plateau region. After 16(36) cycles, (440) cubic spinel reflections were observed which indicate a layer to spinel-like phase transformation and believed to suppress the voltage profile.
Nanodiamond-derived carbon nano-onions as negative electrode materials for lithium-ion batteries
Nanodiamond-derived carbon nano-onions (N-CNOs) were prepared by annealing of nanodiamonds at 1650 °C under flow of helium. The morphology and structure of N-CNOs were investigated by high-resolution transmission electron microscopy (HRTEM), X-ray diffraction, Raman spectroscopy and BET nitrogen adsorption. Due to their smaller size and number of surface defects, they exhibit higher surface area (520 m2/g) and mesoporosity. Due to their smaller size, high surface area and number of surface defects, these N-CNOs exhibit high capacity and stable cycling performance as anode materials for lithium-ion batteries at slower (C/10) and higher (C) charge-discharge rates compared with that of mesocarbon microbead (MCMB) graphite particles.
High energy density silicon anodes for lithium-ion batteries: Combining hollow nanospheres with conductive polymer binder
The alloying reaction of Si with lithium causes significant volume expansion during lithiation process and lead to the fracture of Si particles because of huge lithiation-induced mechanical stress. Various approaches with different focus, such as nanoengieering Si anode structures, stabilizing solid-electrolyte interphases between Si and organic electrolyte, and synthesizing new polymer binders to accommodate the volume change, have been shown successfully improving the energy density and cycle life, bringing Si anodes one step closer into practical Li-ion batteries. In this preprint, we show that both the active hollow nanospheres Si anode structure and the inactive conductive polymer binder have significant impact on the anode cycling performance. Combining the hollow nanospheres with conductive polymer binder, long cycle life Si anode is demonstrated at high energy density.
Porous structured silicon for lithium-ion battery anode
Silicon is a promising anode material for lithium ion battery, because of its highest theoretical capacity (4200 mAh/g). However, intrinsic drawbacks of silicon, e.g. pulverization due to repeating volume change in cycling, and low lithium ion diffusivity in silicon, set hindrances for silicon to be used in high power-density battery. Here we find porous structured silicon a promising anode material for lithium ion battery. Theoretical study shows the pores can help to stabilize the structure by means of providing additional spaces to accommodate large volume change during cycling, and therefore release the stress and strain inside silicon. In addition, the large surface area that accessible to electrolyte helps to shorten the diffusion length for lithium ions, which enables fast charge/discharge. Experimentally, we have employed porous silicon nanowires as a prototype to show the advantages of using porous structured silicon as lithium-ion battery anode. By combining with alginate binder, the porous silicon nanowire shows capacity larger than 1000 mAh/g after 2000 cycles at current rate of 4 A/g. Beyond that, we have developed a scalable and cost-efficient method to produce nano and micron porous silicon particles, which shows decent battery performance.
New directions in rechargeable lithium-ion batteries: Lessons from in situ electron microscopy
Nanostructured anode materials have received considerable attention in energy storage devices due to the enhanced electrochemical reactions at the surface and their unique electrical and mechanical properties. Silicon and titanate nanostructures are promising anode materials because of their energy capacity and safer performance for Li-ion batteries. One of the hurdles in developing better and long lasting batteries is the lack of scientific knowledge on the electrochemical reactions that happen inside a battery under charging and discharging conditions. Using real-time microscopy at atomic resolutions should shed light into some of the fundamental questions in this field. This presentation focuses on the in-situ observation of lithiation and delithiation in Si nanorods and TiO2 nanotubes. The electrochemical testing of these low dimensional structures were conducted inside a transmission electron microscope equipped with a novel in-situ electrical probing holder. The intercalation of Li-ions in Si nanorods was monitored during charging and the fracture of nanorods was quantified in terms of size. In addition, the intercalation of crystalline anatase and amorphous TiO2 was studied and their fracture events were monitored in real time.
Quino(triazene)s: A new class of organic cathode materials for the lithium ion battery
There has been much interest in the development of organic cathode materials for lithium ion batteries as a green alternative to the expensive lithium cobalt oxide. Previously, our group has reported a novel class of compounds derived from the reaction of quino(imidazolylidene)s and a variety of azidoarenes. In this presentation, we report the synthesis and characterization of a series of quino(triazene)s as cathodes for lithium ion batteries. Furthermore, we describe their solid state structure, electrochemistry, electrochromic properties, and battery performance.
First principles atomistic modeling of surface and interfacial effects in lithium ion battery materials
Surfaces and interfaces play an important role in the performance of lithium ion batteries, including such effects as surface orientation-dependent lithiation, surface chemistry-dependent lithiation capacity, and the formation of the solid-electrolyte interphase (SEI). Computational modeling, especially first principles atomistic approaches, provides significant insight into these surface and interfacial effects. A significant challenge in such modeling is the construction of atomistic models to accurate describe the complexity of the surfaces and interfaces.
In this talk, I will discuss using a variety of first principles approaches to tackle the challenge of building accurate atomistic models of surfaces and interfaces in lithium ion battery materials. I will describe how such approaches are used to study: orientation-dependence, and the lack thereof, of lithiation in silicon and germanium; the effects of surface chemistry on the lithiation of silicon; the deposition of lithium on gold; and the formation of SEI on silicon.
Enhanced lithium ion battery energy density with carbon nanotube current collectors
Traditional battery electrodes consist of composites coated onto high density, inactive metal current collectors which can limit battery energy density. Conventional methods of increasing energy density include the use of higher capacity materials. However, when electrodes are paired in a full battery, only a small increase in energy density is realized due to the capacity limited cathode compared to novel anode materials. A more significant increase in energy density can be realized by reducing or eliminating the mass of the current collector. This work investigates the replacement of metal current collectors with carbon nanotube (CNT) papers using traditional composites to reduce electrode mass and increase energy density. The results show that CNTs can replace metal current collectors on both the anode and cathode and achieve expected specific capacities. The electrode specific capacity, including current collector mass, increased up to 28% for the cathode and 188% for the anode using CNTs.
Surface-disordered hydrogenated TiO2 nanocrystals for lithium ion battery
TiO2, mainly known for photocatalysis, has also been studied as a safer anode material for lithium ion batteries compared to graphite, while with the limited lithium ion diffusion within the host and the structural distortion during lithium insertion/extraction. Here, we demonstrate that a thin layer of hydrogenated surface disorder on the crystalline TiO2 electrode may induce better electrochemical energy storage performance, better charge/discharge rate performance, larger capacity and longer stability. The reasons for these improvements are proposed in terms of the facilitation of easier lithium ion transport within the disordered layer and the less structural distortion during the lithium insertion/extraction process.
Next generation polymer nanocomposite electrolytes for lithium ion batteries
Polymer electrolytes offer many advantages compared to liquid electrolytes used in lithium ion batteries, including safety, stability and thin film manufacturability. Nanoscale fillers can enhance Li ion conductivity as well as the mechanical properties of polymer electrolytes. In this study, we investigate the role of nanofillers in enhancing ion conductivity including experimental results as well as insights from our continuum-level model and molecular dynamics (MD) simulations. Novel nanoscale fillers including hybrid clay-carbon nanotubes (CNTs) for next generation polymer electrolytes will also be discussed. We show that CNTs grown and insulated within clay layers can work as effective hybrid 3D nanofillers and improve Li ion conductivity of PEO electrolyte by almost two orders of magnitude with significant enhancement in tensile strength. Ion conductivity enhancement can be attributed to the high surface density of the hybrid fillers and the strong interactions between the CNT's negative electron cloud and positive lithium ions.
Increasing redox shuttle oxidation potentials to match high voltage cathodes in lithium-ion batteries
Electrolyte additives called redox shuttles can protect batteries in series from experiencing overcharge, a condition in which one or more fully charged cells continue to receive applied current. Derivatives based on 1,4-dimethoxybenzene, N-alkylphenothiazine, and TEMPO cores have been reported as superior additives for overcharge protection. Eventually these electrolyte additives fail, presumably due to decomposition of their radical cation forms. Increased electron deficiency makes radical cations more susceptible to nucleophilic attack, which may result in reactions with electrolyte components. Few examples of stable redox shuttles for high voltage cathodes have been reported, presumably due to their high reactivity. Our work focuses on improving the stability of redox shuttles for high voltage cathodes. We have synthesized a variety of carbazole, diphenylamine, phenothiazine, and phenoxazine derivatives containing electron-withdrawing groups. This study focuses on the electrochemical analysis of the new derivatives and the stability of their radical cation forms.
Multiscale multiphysics lithium-ion battery model with multidomain modular framework
Lithium-ion batteries (LIBs) powering recent wave of personal ubiquitous electronics are also believed to be a key enabler of electrification of vehicle powertrain on the path toward sustainable transportation future. Over the past several years, National Renewable Energy Laboratory (NREL) has developed the Multi-Scale Multi-Domain (MSMD) model framework, which is an expandable platform and a generic modularized flexible framework resolving interactions among multiple physics occurring in varied length and time scales in LIB[1]. NREL has continued to enhance the functionality of the framework and to develop constituent models in the context of the MSMD framework responding to U.S. Department of Energy's CAEBAT program objectives. This talk will introduce recent advancements in NREL's LIB modeling research in regards of scale-bridging, multi-physics integration, and numerical scheme developments.
Solvothermal synthesis, growth mechanism, and performance of LiFePO4 nanorods used as a cathode material in lithium ion batteries
We report the use of water-triethylene glycol (TEG) as a solvent to synthesize LiFePO4 (LFP) nanorods with uniform size. TEG, a reducing agent in the reaction, promotes the formation of LiFePO4. Crystal phase and growth behavior were monitored by powder X-ray diffraction (XRD), synchrotron X-ray Diffraction, as well as transmission electron microscopy (TEM), while particles morphologies were investigated with scanning electron microscope (SEM). Three crystal growth mechanisms during the synthesis were interpreted based on the time study of the samples. Initially, the nucleation of LFP (20nm thick sheets) occurred accompanying with the formation of Fe3(PO4)2•8H2O (vivianite). This metastable phase evolved into spindle-like olivine LiFePO4 through oriented attachment (OA) of LFP primary nanosheets. With the increasing reaction time, the pH decreased with the concurrent formation of LiFePO4. The dissolution-recrystallization process, i.e. Ostwald ripening (OR), results in evenly distributed
LiFePO4 nanorods due to the increased solubility of LiFePO4. The mechanism (from nanosheet to spindle to rod) revealed by this study will help develop guidelines to control the size and morphological features of LFP more precisely.
Safe collection and high value recycling of li-ion batteries
German collection scheme
- Legal obligations for producers and distributors of batteries in Germany
- Collection and recycling of batteries in Germany
Risks and safety issues
- Potential risks in end-of-live chain
- First nationwide take-back system for industrial Li batteries in Europe
- Logistic solutions: collection, packaging, transport of Li batteries
Recycling strategy for Li batteries
Market volumes
- Li batteries: applications and end-of-life volumes
Material contents
- Content of valuable materials in Li batteries
Recycling technologies
- Thermo metallurgical technologies
- Hydro metallurgical technologies
- Mechanical chemical technologies
- Mechanical technologies
- Recycling products and markets
Economical valuation
Conclusions for European recycling strategy
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