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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS2007

A Synopsis of Interfacial Phenomena in Lithium-Based Polymer Electrolyte Electrochemical Cells

The interfacial regions between electrode materials, electrolytes and other cell components play key roles in the overall performance of lithium-based batteries. For cell chemistries employing lithium metal, lithium alloy or carbonaceous materials (i.e., lithium-ion cells) as anode materials, a "solid electrolyte interphase" (SEI) layer forms at the anode/electrolyte interface, and the properties of this "passivating" layer significantly affect the practical cell/battery quality and performance. A thin, ionically-conducting SEI on the electrode surface can beneficially reduce or eliminate undesirable side reactions between the electrode and the electrolyte, which can result in a degradation in cell performance. The properties and phenomena attributable to the interfacial regions existing at both anode and cathode surfaces can be characterized to a large extent by electrochemical impedance spectroscopy (EIS) and related techniques. The intention of the review herewith is to support the future development of lithium-based polymer electrolytes by providing a synopsis of interfacial phenomena that is associated with cell chemistries employing either lithium metal or carbonaceous "composite" electrode structures which are interfaced with polymer electrolytes (i.e., "solvent-free" as well as "plasticized" polymer-binary salt complexes and single ion-conducting polyelectrolytes). Potential approaches to overcoming poor cell performance attributable to interfacial effects are discussed.

Baldwin, Richard S.↗

NASA NTRS2022

The Promise of Alloy Anodes for Solid-State Batteries

Solid-state batteries are anext-generation technology that could featureimproved safety and energy density, but reliably integrating high-capacity electrode materials to enable high energy while retaining stablelong-termcycling remains a challenge. Anode materials that alloy with lithium, such as silicon, tin, and aluminum,offer high capacity that canyield high-energy battery cells. The use of alloy anodes in solid-state batteries potentially offers major mechanistic benefits compared to other anode contendersand battery systems, such as lithium metal in solid-state architectures or alloys in liquid-electrolyte batteries. This perspective discusseskey advantagesof alloy anode materials for solid-state batteries, including the avoidance of the short circuiting observed with lithium metal and the chemo-mechanical stabilization of the solid-electrolyte interphase (SEI). We further discuss open research questions and challenges in engineering alloy-anode-based solid-state batteries, with the goal of advancing our understanding and control of alloy anode materialswithin solid-state architectures toward commercial application.

John A Lewis↗

NASA NTRS2009

The Effect of Electrolyte Additives upon the Lithium Kinetics of Li-Ion Cells Containing MCMB and LiNi(x)Co(1-x)O2 Electrodes and Exposed to High Temperatures

With the intent of improving the performance of lithium-ion cells at high temperatures, we have investigated the use of a number of electrolyte additives in experimental MCMB- Li(x)Ni(y)Co(1-y)O2 cells, which were exposed to temperatures as high as 80 C. In the present work, we have evaluated the use of a number of additives, namely vinylene carbonate (VC), dimethyl acetamide (DMAc), and mono-fluoroethylene carbonate (FEC), in an electrolyte solution anticipated to perform well at warm temperature (i.e., 1.0M LiPF6 in EC+EMC (50:50 v/v %). In addition, we have explored the use of novel electrolyte additives, namely lithium oxalate and lithium tetraborate. In addition to determining the capacity and power losses at various temperatures sustained as a result of high temperature cycling (cycling performed at 60 and 80 C), the three-electrode MCMB-Li(x)Ni(y)Co(1-y)O2 cells (lithium reference) enabled us to study the impact of high temperature storage upon the solid electrolyte interphase (SEI) film characteristics on carbon anodes (MCMB-based materials), metal oxide cathodes, and the subsequent impact upon electrode kinetics.

High Temperture Resilience↗

NASA NTRS2012

Fundamental Investigation of Silicon Anode in Lithium-Ion Cells

Silicon is a promising and attractive anode material to replace graphite for high capacity lithium ion cells since its theoretical capacity is ~10 times of graphite and it is an abundant element on Earth. However, there are challenges associated with using silicon as Li-ion anode due to the significant first cycle irreversible capacity loss and subsequent rapid capacity fade during cycling. Understanding solid electrolyte interphase (SEI) formation along with the lithium ion insertion/de-insertion kinetics in silicon anodes will provide greater insight into overcoming these issues, thereby lead to better cycle performance. In this paper, cyclic voltammetry and electrochemical impedance spectroscopy are used to build a fundamental understanding of silicon anodes. The results show that it is difficult to form the SEI film on the surface of a Si anode during the first cycle; the lithium ion insertion and de-insertion kinetics for Si are sluggish, and the cell internal resistance changes with the state of lithiation after electrochemical cycling. These results are compared with those for extensively studied graphite anodes. The understanding gained from this study will help to design better Si anodes, and the combination of cyclic voltammetry with impedance spectroscopy provides a useful tool to evaluate the effectiveness of the design modifications on the Si anode performance.

Wu, James J.↗

NASA NTRS2018

Ionic Liquids at Electrified Interfaces: From Double Layers to Decomposition

Ionic liquids are versatile electrolytes whose properties at electrified interfaces have the potential to enable technologies such as supercapacitors and Li-metal battery anodes. At electrified carbon surfaces, ionic liquids form an electric double layer that stores energy and provides the foundation for supercapacitors. At electrified lithium surfaces, ionic liquids decompose to form a solid electrolyte interphase that has the potential to stabilize Li-metal anodes in rechargable batteries. The behavior of two ionic liquids of technological importance, [pyr14][TFSI] and [EMIM][BF4], are examined at these electrified interfaces through molecular dynamics and ab initio techniques.

Haskins, Justin B.↗

NASA NTRS2018

Ionic Liquids at Electrified Interfaces: from Double Layers to Decomposition

Haskins, Justin B.↗

NASA NTRS2018

Ionic Liquids at Electrified Interfaces: from Double Layers to Decomposition

Haskins, Justin B.↗

NASA NTRS2017

Factors Limiting Li+ Charge Transfer Kinetics in Li-ion Batteries

Understanding the factors limiting Li+ charge transfer kinetics in Li-ion batteries is essential in improving the rate performance, especially at lower temperatures. The Li+ charge transfer process involved in the lithium intercalation of graphite anode includes the step of de-solvation of the solvated Li+ in the liquid electrolyte and the step of transport of Li+ in the preformed solid electrolyte interphase (SEI) on electrodes until the Li+ accepts an electron at the electrode and becomes a Li in the electrode. Whether the de-solvation process or the Li+ transport through the SEI is a limiting step depends on the nature of the interphases at the electrode and electrolyte interfaces. Several examples involving the electrode materials such as graphite, lithium titanate (LTO), lithium iron phosphate (LFP), lithium nickel cobalt aluminum oxide (NCA) and solid Li+ conductor such as lithium lanthanum titanate or Li-Al-Ti-phosphate are reviewed and discussed to clarify the conditions at which either the de-solvation or the transport of Li+ in SEI is dominating and how the electrolyte components affect the activation energy of Li+ charge transfer kinetics. How the electrolyte additives impact the Li+ charge transfer kinetics at both the anode and the cathode has been examined at the same time in 3-electrode full cells. The resulting impact on Li+ charge transfer resistance, Rct, and activation energy, Ea, at both electrodes are reported and discussed.

Delp, Samuel A.↗

NASA NTRS2012

Wide Operating Temperature Range Electrolytes for High Voltage and High Specific Energy Li-Ion Cells

A number of electrolyte formulations that have been designed to operate over a wide temperature range have been investigated in conjunction with layered-layered metal oxide cathode materials developed at Argonne. In this study, we have evaluated a number of electrolytes in Li-ion cells consisting of Conoco Phillips A12 graphite anodes and Toda HE5050 Li(1.2)Ni(0.15)Co(0.10)Mn(0.55)O2 cathodes. The electrolytes studied consisted of LiPF6 in carbonate-based electrolytes that contain ester co-solvents with various solid electrolyte interphase (SEI) promoting additives, many of which have been demonstrated to perform well in 4V systems. More specifically, we have investigated the performance of a number of methyl butyrate (MB) containing electrolytes (i.e., LiPF6 in ethylene carbonate (EC) + ethyl methyl carbonate (EMC) + MB (20:20:60 v/v %) that contain various additives, including vinylene carbonate, lithium oxalate, and lithium bis(oxalato)borate (LiBOB). When these systems were evaluated at various rates at low temperatures, the methyl butyrate-based electrolytes resulted in improved rate capability compared to cells with all carbonate-based formulations. It was also ascertained that the slow cathode kinetics govern the generally poor rate capability at low temperature in contrast to traditionally used LiNi(0.80)Co(0.15)Al(0.05)O2-based systems, rather than being influenced strongly by the electrolyte type.

Li-ion Battery↗

NASA NTRS2012

Solid State Multinuclear Magnetic Resonance Investigation of Electrolyte Decomposition Products on Lithium Ion Electrodes

Solid electrolyte interphase (SEI) formation in lithium ion cells prepared with advanced electrolytes is investigated by solid state multinuclear (7Li, 19F, 31P) magnetic resonance (NMR) measurements of electrode materials harvested from cycled cells subjected to an accelerated aging protocol. The electrolyte composition is varied to include the addition of fluorinated carbonates and triphenyl phosphate (TPP, a flame retardant). In addition to species associated with LiPF6 decomposition, cathode NMR spectra are characterized by the presence of compounds originating from the TPP additive. Substantial amounts of LiF are observed in the anodes as well as compounds originating from the fluorinated carbonates.

Li-ion battery electrolytes↗