Solid-state batteries: The critical role of mechanics.

Solid-state batteries with lithium metal anodes have the potential for higher energy density, longer lifetime, wider operating temperature, and increased safety. Although the bulk of the research has focused on improving transport kinetics and electrochemical stability of the materials and interfaces, there are also critical challenges that require investigation of the mechanics of materials. In batteries with solid-solid interfaces, mechanical contacts, and the development of stresses during operation of the solid-state batteries, become as critical as the electrochemical stability to keep steady charge transfer at these interfaces.

Role of Pairwise Reactions on the Synthesis of LiLaTiO and the Resulting Structure-Property Correlations.

The performance of single-ion conductors is highly sensitive to the material's defect chemistry. Tuning these defects is limited for solid-state reactions as they occur at particle-particle interfaces, which provide a complex evolving energy landscape for atomic rearrangement and product formation. In this report, we investigate the (1) order of addition and (2) lithium precursor decomposition temperature and their effect on the synthesis and grain boundary conductivity of the perovskite lithium lanthanum titanium oxide (LLTO).

Local electronic structure variation resulting in Li 'filament' formation within solid electrolytes.

Solid electrolytes hold great promise for enabling the use of Li metal anodes. The main problem is that during cycling, Li can infiltrate along grain boundaries and cause short circuits, resulting in potentially catastrophic battery failure. At present, this phenomenon is not well understood.

Study of the Segmental Dynamics and Ion Transport of Solid Polymer Electrolytes in the Semi-crystalline State.

Solid polymer electrolytes are promising in fulfilling the requirements for a stable lithium metal anode toward higher energy and power densities. In this work, we investigate the segmental dynamics, ionic conductivity, and crystallinity of a polymer electrolyte consisting of poly(ethylene oxide) (PEO) and lithium triflate salt, in the semi-crystalline state. Using quasi-elastic neutron scattering, the segmental dynamics of PEO chains confined between the crystalline lamellae is quantified, using Cole-Cole analysis.

Elucidating Interfacial Stability between Lithium Metal Anode and Li Phosphorus Oxynitride via Electron Microscopy.

Li phosphorus oxynitride (LiPON) is one of a very few solid electrolytes that have demonstrated high stability against Li metal and extended cyclability with high Coulombic efficiency for all solid-state batteries (ASSBs). However, theoretical calculations show that LiPON reacts with Li metal. Here, we utilize electron microscopy to observe the dynamic evolutions at the LiPON-Li interface upon contacting and under biasing.

Plasma Synthesis of Spherical Crystalline and Amorphous Electrolyte Nanopowders for Solid-State Batteries.

Here, we demonstrate the theory-guided plasma synthesis of high purity nanocrystalline LiSiPO and fully amorphous LiSiPON. The synthesis involves the injection of single or mixed phase precursors directly into a plasma torch. As the material exits the plasma torch, it is quenched into spherical nanocrystalline or amorphous nanopowders.

Resolving the Amorphous Structure of Lithium Phosphorus Oxynitride (Lipon).

Lithium phosphorus oxynitride, also known as Lipon, solid-state electrolytes are at the center of the search for solid-state Li metal batteries. Key to the performance of Lipon is a combination of high Li content, amorphous character, and the incorporation of N into the structure. Despite the material's importance, our work presents the first study to fully resolve the structure of Lipon using a combination of  ab initio molecular dynamics, density functional theory, neutron scattering, and infrared spectroscopy.

Interfacial Stability of Li Metal-Solid Electrolyte Elucidated via in Situ Electron Microscopy.

Despite their different chemistries, novel energy-storage systems, e.g., Li-air, Li-S, all-solid-state Li batteries, etc.

Unravelling the Impact of Reaction Paths on Mechanical Degradation of Intercalation Cathodes for Lithium-Ion Batteries.

The intercalation compounds are generally considered as ideal electrode materials for lithium-ion batteries thanks to their minimum volume expansion and fast lithium ion diffusion. However, cracking still occurs in those compounds and has been identified as one of the critical issues responsible for their capacity decay and short cycle life, although the diffusion-induced stress and volume expansion are much smaller than those in alloying-type electrodes. Here, we designed a thin-film model system that enables us to tailor the cation ordering in LiNi(0.

Probing battery chemistry with liquid cell electron energy loss spectroscopy.

We demonstrate the ability to apply electron energy loss spectroscopy (EELS) to follow the chemistry and oxidation states of LiMn2O4 and Li4Ti5O12 battery electrodes within a battery solvent. This is significant as the use and importance of in situ electrochemical cells coupled with a scanning/transmission electron microscope (S/TEM) has expanded and been applied to follow changes in battery chemistry during electrochemical cycling. We discuss experimental parameters that influence measurement sensitivity and provide a framework to apply this important analytical method to future in situ electrochemical studies.

Nanoscale imaging of fundamental li battery chemistry: solid-electrolyte interphase formation and preferential growth of lithium metal nanoclusters.

The performance characteristics of Li-ion batteries are intrinsically linked to evolving nanoscale interfacial electrochemical reactions. To probe the mechanisms of solid electrolyte interphase (SEI) formation and to track Li nucleation and growth mechanisms from a standard organic battery electrolyte (LiPF6 in EC:DMC), we used in situ electrochemical scanning transmission electron microscopy (ec-S/TEM) to perform controlled electrochemical potential sweep measurements while simultaneously imaging site-specific structures resulting from electrochemical reactions. A combined quantitative electrochemical measurement and STEM imaging approach is used to demonstrate that chemically sensitive annular dark field STEM imaging can be used to estimate the density of the evolving SEI and to identify Li-containing phases formed in the liquid cell.

Direct visualization of solid electrolyte interphase formation in lithium-ion batteries with in situ electrochemical transmission electron microscopy.

Complex, electrochemically driven transport processes form the basis of electrochemical energy storage devices. The direct imaging of electrochemical processes at high spatial resolution and within their native liquid electrolyte would significantly enhance our understanding of device functionality, but has remained elusive. In this work we use a recently developed liquid cell for in situ electrochemical transmission electron microscopy to obtain insight into the electrolyte decomposition mechanisms and kinetics in lithium-ion (Li-ion) batteries by characterizing the dynamics of solid electrolyte interphase (SEI) formation and evolution.

Artificial solid electrolyte interphase to address the electrochemical degradation of silicon electrodes.

Electrochemical degradation on silicon (Si) anodes prevents them from being successfully used in lithium (Li)-ion battery full cells. Unlike the case of graphite anodes, the natural solid electrolyte interphase (SEI) films generated from carbonate electrolytes do not self-passivate on Si, causing continuous electrolyte decomposition and loss of Li ions. In this work, we aim at solving the issue of electrochemical degradation by fabricating artificial SEI films using a solid electrolyte material, lithium phosphorus oxynitride (Lipon), which conducts Li ions and blocks electrons.

Quantitative electrochemical measurements using in situ ec-S/TEM devices.

Insight into dynamic electrochemical processes can be obtained with in situ electrochemical-scanning/transmission electron microscopy (ec-S/TEM), a technique that utilizes microfluidic electrochemical cells to characterize electrochemical processes with S/TEM imaging, diffraction, or spectroscopy. The microfluidic electrochemical cell is composed of microfabricated devices with glassy carbon and platinum microband electrodes in a three-electrode cell configuration. To establish the validity of this method for quantitative in situ electrochemistry research, cyclic voltammetry (CV), choronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) were performed using a standard one electron transfer redox couple [Fe(CN)6]3-/4--based electrolyte.

Direct visualization of initial SEI morphology and growth kinetics during lithium deposition by in situ electrochemical transmission electron microscopy.

Deposition of Li is a major safety concern existing in Li-ion secondary batteries. Here we perform the first in situ high spatial resolution measurement coupled with real-time quantitative electrochemistry to characterize SEI formation on gold using a standard battery electrolyte. We demonstrate that a dendritic SEI forms prior to Li deposition and that it remains on the surface after Li electrodissolution.

Lithium polysulfidophosphates: a family of lithium-conducting sulfur-rich compounds for lithium-sulfur batteries.

Sulfur-rich lithium polysulfidophosphates (LPSPs) act as an enabler for long-lasting and efficient lithium-sulfur batteries. LPSPs have ionic conductivities of 3.0×10(-5)  S cm(-1) at 25 °C, which is 8 orders of magnitude higher than that of Li2S.

Lithium superionic sulfide cathode for all-solid lithium-sulfur batteries.

This work presents a facile synthesis approach for core-shell structured Li2S nanoparticles with Li2S as the core and Li3PS4 as the shell. This material functions as lithium superionic sulfide (LSS) cathode for long-lasting, energy-efficient lithium-sulfur (Li-S) batteries. The LSS has an ionic conductivity of 10(-7) S cm(-1) at 25 °C, which is 6 orders of magnitude higher than that of bulk Li2S (∼10(-13) S cm(-1)).

Anomalous high ionic conductivity of nanoporous β-Li3PS4.

Lithium-ion-conducting solid electrolytes hold promise for enabling high-energy battery chemistries and circumventing safety issues of conventional lithium batteries. Achieving the combination of high ionic conductivity and a broad electrochemical window in solid electrolytes is a grand challenge for the synthesis of battery materials. Herein we show an enhancement of the room-temperature lithium-ion conductivity by 3 orders of magnitude through the creation of nanostructured Li(3)PS(4).

In situ ambient pressure X-ray photoelectron spectroscopy studies of lithium-oxygen redox reactions.

The lack of fundamental understanding of the oxygen reduction and oxygen evolution in nonaqueous electrolytes significantly hinders the development of rechargeable lithium-air batteries. Here we employ a solid-state Li(4+x)Ti(5)O(12)/LiPON/Li(x)V(2)O(5) cell and examine in situ the chemistry of Li-O(2) reaction products on Li(x)V(2)O(5) as a function of applied voltage under ultra high vacuum (UHV) and at 500 mtorr of oxygen pressure using ambient pressure X-ray photoelectron spectroscopy (APXPS). Under UHV, lithium intercalated into Li(x)V(2)O(5) while molecular oxygen was reduced to form lithium peroxide on Li(x)V(2)O(5) in the presence of oxygen upon discharge.

Local detection of activation energy for ionic transport in lithium cobalt oxide.

Local activation energy for ionic diffusion is probed on the nanometer level in LiCoO(2) thin films using variable temperature electrochemical strain microscopy (ESM). The high spatial resolution of ESM allows one to extract information about ionic activation energies on the level of individual grains and grain facets, thus bridging the lengths scales of atomistic calculations and traditional macroscopic experiments. A series of control experiments have been performed and possible signal generating mechanisms are discussed to explain the temperature-dependent ESM measurements.

Influence of Lithium Salts on the Discharge Chemistry of Li-Air Cells.

In this work, we show that the use of a high boiling point ether solvent (tetraglyme) promotes the formation of Li2O2 in a lithium-air cell. However, another major constituent in the discharge product of a Li-air cell contains halides from the lithium salts and C-O from the tetraglyme used as the solvent. This information is critical to the development of Li-air electrolytes, which are stable and promote the formation of the desired Li2O2 products.

Direct mapping of ionic transport in a Si anode on the nanoscale: time domain electrochemical strain spectroscopy study.

Local Li-ion transport in amorphous silicon is studied on the nanometer scale using time domain electrochemical strain microscopy (ESM). A strong variability of ionic transport controlled by the anode surface morphology is observed. The observed relaxing and nonrelaxing response components are discussed in terms of local and global ionic transport mechanisms, thus establishing the signal formation mechanisms in ESM.

Decoupling electrochemical reaction and diffusion processes in ionically-conductive solids on the nanometer scale.

We have developed a scanning probe microscopy approach to explore voltage-controlled ion dynamics in ionically conductive solids and decouple transport and local electrochemical reactivity on the nanometer scale. Electrochemical strain microscopy allows detection of bias-induced ionic motion through the dynamic (0.1-1 MHz) local strain.

Real space mapping of Li-ion transport in amorphous Si anodes with nanometer resolution.

The electrical bias driven Li-ion motion in silicon anode materials in thin film battery heterostructures is investigated using electrochemical strain microscopy (ESM), which is a newly developed scanning probe microscopy based characterization method. ESM utilizes the intrinsic link between bias-controlled Li-ion concentration and molar volume of electrode materials, providing the capability for studies on the sub-20 nm scale, and allows the relationship between Li-ion flow and microstructure to be established. The evolution of Li-ion transport during the battery charging is directly observed.