Clean Energy Forum: San Diego, California

Siyi Liu

University of Alabama

Understanding Internal Short Circuit Caused Thermal Runaway of Li-ion Cells through In Situ Diagnosis

Internal short circuit (ISC) caused thermal runaway is a major cause of Li-ion battery fires in various applications such as electric vehicles and cell phones. However, the mechanisms of how an ISC triggers thermal runaway are still not well understood despite extensive research. Many methods have been developed to trigger ISCs in Li-ion cells but lack the capability of in situ diagnosis of critical parameters. Because ISC is a highly localized and transient phenomenon, in situ diagnosis is important for understanding its behaviors. To address this challenge, our group developed a method for simultaneous in situ measurement of the ISC temperature, ISC current, and ISC resistance in large-format Li-ion cells during slow nail penetration tests. Multiple ISC temperature peaks were observed before thermal runaway while the surface temperature showed much less detail. It was found that those ISC temperature peaks were caused by the change in ISC current and heat generation rate, which was further caused by the dynamic change in ISC resistance. These findings can enhance the understanding of ISC-triggered thermal runaway, which could inspire novel mitigation or prevention strategies.

Jyotishman Pathak

Indian Institute of Technology Guwahati (IITG)

Post Life Analysis of Lithium Cobalt Oxide Cathode Composition in a Recyclable Lithium-Ion Battery

The present research addresses the compositional analysis of a lithium cobalt oxide (LCO) layer on an aluminum current collector to understand the recyclable state of the lithium-ion battery (LiB) battery used in a drone after 120 cycles. Raman spectroscopy was employed to investigate the existence of the pure cobalt oxide layer with additional layers evolved from the parasitic reactions in the cathode surface, the correlation of Raman peaks in between the 400 cm-1-700 cm-1 provides significant insight of the LCO layer’s deformation process. Also, XRD analysis identified the combination of graphite percolation network crystalline properties along with the LCO degrade layers. Further, the surface morphology of the LCO layers are identified through FESEM imaging to extract the surface quality at nanoscale resolution. Impedance spectroscopy of the cathode film also provides the variation landscape of electrical resistance with respect to the various sub-micron regions of LCO layers. The overall studies combine meaningful sets of information to reveal the actual LCO coating and carbon network quality after 120 cycles of LiB operation.

Shuang Bai

UCSD

Quantifying and Understanding Electron Beam Radiation Induced Degradation of Lithium Battery Materials

The investigation of the solid electrolyte interphase (SEI) in Li metal batteries is crucial for advancing battery technology, improving safety, extending battery lifespans, and unlocking the full potential of Li metal as an anode material. Spatially resolved techniques, such as transmission electron microscopy (TEM), are widely applied to understand the continuous composition and structure evolution of SEI during battery cycling. However, electron beam-induced damage poses challenges to accurate data interpretation. In this study, we quantify the beam dosage limit for commonly reported SEI components, including Li2CO3, LiF, Li2S, LiOH, LiH, and Li2O, demonstrating their chemical and structural evolution under electron beam irradiation. Our results reveal that these components exhibit varying susceptibility to electron beam damage, with Li2CO3 being the most easily damaged and Li2O the least. The observed effects of repeated electron beam irradiation include surface atomic displacement, mass loss, and chemical reactions. To preserve pristine chemical environments, minimizing electron beam damage becomes crucial, and cryogenic protection during imaging proves to be an effective approach. Moreover, our study highlights the potential misinterpretation of experimental results due to electron beam damage, providing examples of SEI formed in two different electrolytes. This calls for special attention to ensure accurate characterization of SEI in Li metal batteries.

Thomas Marchese

University of Chicago

Spatial and Spectral Characterization of Energy Material Interfaces

Advancements in interfacial engineering of energy materials is enabling integration of next-generation batteries, fuel cells, and photovoltaics for higher efficiency green energy. The interfaces comprised of solids, liquids, and gases undergo dynamic changes under operation via interaction with triggers such as photons, electrons, and ions. It is important that a mechanistic understanding is achieved for the role of evolving interface morphology on performance. Fitting such a purpose, scanning transmission electron microscope (STEM) characterization of the cross-section of devices provides the ability to resolve the two-dimensional structural relationship between components below an angstrom. In combination with techniques like high-resolution electron energy loss spectroscopy and energy dispersive X-ray spectroscopy, STEM experiments can additionally reveal precise chemical information about the location of elements within an ordered or disordered interface. The combination of hyperspectral and structural information is important to understanding degradation pathways that currently limit the operational lifetime of engineered devices. The acquisition and analysis of this data with due diligence is not trivial as these devices often include reactive materials and phases including lithium and sulfur, which can be highly sensitive to beam damage mechanisms. As such, careful experimental design must be employed for controlling the environment during sample preparation and to maximize the signal-to-noise ratio of data obtained through low-dose STEM experiments preformed at cryogenic temperatures.

Diyi Cheng

Lawrence Berkeley National Laboratory

Free-Standing LiPON: From the Fundamentals to Uniformly Dense Lithium Metal Deposition with no External Pressure

Lithium phosphorus oxynitride (LiPON) is an amorphous solid electrolyte that has been extensively studied over the last three decades. Despite the promise of pairing it with various electrode materials, LiPON’s rigidity and air sensitivity set limitations to understanding its intrinsic properties. Here we report a methodology to synthesize LiPON in a free-standing form that manifests remarkable flexibility and a Young’s modulus of ∼33 GPa. We use solid-state nuclear magnetic resonance and differential scanning calorimetry to quantitatively reveal the chemistry of the Li/LiPON interface and the presence of a well-defined LiPON glass-transition temperature of 207°C. Combining interfacial stress and a gold seeding layer, our free-standing LiPON shows a uniformly dense deposition of lithium metal without the aid of external pressure. This free-standing LiPON film offers opportunities to study fundamental properties of LiPON for interface engineering for solid-state batteries.

Min-Huei Chiou

Helmholtz-Institute Münster, Forschungszentrum Jülich GmbH

Compatibility of Polymer Segments Impacts Electrolyte Membrane Homogeneity and Electrochemical Performance

A reversible exploitation of high-energy density lithium metal batteries requires homogeneous lithium deposition upon cell cycling, where copolymer electrolytes based on their good balance of mechanical strength and achievable ionic conductivity are viable candidates for mitigating high-surface-area lithium growth. Thus, in this work1, in-depth analysis of (polarity-derived) compatibility among polymer segments that affect the distribution of membrane properties and lithium deposition is presented, introducing PTMC- and PEO-based copolymer systems2. The corresponding morphology of lithium deposits appeared severely localized in cases where the electrostatic fields and number of lithium-ion coordination sites at the polymer segment species were highly different, exhibiting sudden cycling failure and poor cell longevity. In contrast, copolymer electrolytes comprised of more compatible segment species (as reflected by similar molecular dipole moments) afforded superior cell performance (e.g., cycling at rates of 1C even with higher mass-loaded cathodes (6.3 mg cm−2)). Combined with computational efforts, the present work contributes to more comprehensive understanding of cell failure mechanisms and the design of tailored electrolytes that could avoid lithium protrusion of the membranes, in this way yielding feasible concepts for a development of high-performance copolymer electrolytes.

1. M.-C. Chiou et al., ACS Applied Energy Materials 2023, 6, 4422

2. M.-C. Chiou et al., Journal of Power Sources 2022, 538, 231528

Andrea Bowring

Mitra Chem

From Atoms to Tons: High-Throughput and In-Situ Characterization to Accelerate Cathode Material Development and Commercialization

Mitra Chem’s aims to develop and scale domestic, iron-based cathode materials production at an unprecedented lab-to-market timeline. Utilizing our proprietary “atoms-to-tons” materials acceleration platform, which integrates end-to-end machine learning within numerous functions and scales, we are able to reduce industry-conventional lab-to-market timelines of 8 to 10 years by a factor of 10. Critical to the platform is our development of accelerated, automated, and in-depth materials characterization serving as a linking node between materials synthesis and electrochemical properties and thereby enabling efficient downselection of materials for characterizing, classifying, and predicting materials performance.

In this work, we highlight our work on developing high-throughput automated SEM and powder X-ray diffraction, which are used to efficiently characterize structural, chemical, and electrochemical materials properties. This is complemented by our in-house development multivariate Bayesian optimization models that have been demonstrated to accurately predict critical but time-consuming metrics such as cell performance from characterization-derived powder properties. Within our suite of characterization techniques, we have built integrated data-driven, multi-modal functionality to go beyond surface level analysis. For example, with our Thermo Scientific™ Phenom™ Desktop SEM, we have been building automated one-click image collection and analysis pipelines allowing us to image up to 30 samples in an automated fashion while leveraging image analysis that can deliver fast, quantitative data into key powder properties such as grain size. These new methodologies have the potential to replace more traditional and time-consuming particle size analysis techniques such as laser scattering/diffraction. Furthermore, operator time saved by creating human-free automated characterization and analysis pipelines allows our team to focus on high-value, high-insight techniques such as the development of in-situ and operando X-ray diffraction during which calcination and electrochemical cycling are performed to establish fundamental microstructural insights that are used to fine-tune material synthesis and performance at scale.

Zhaoyang Chen

University of Houston

Constructing Favouable Microstructures of Solid-State Organic Cathodes via Mechanical Property Manipulation

Organic electrode materials have recently emerged as competitive alternatives to inorganic cathode materials for solid-state batteries (SSBs). One advantage of organic electrode materials is their soft nature, which ensures intimate contact with sulfide-based electrolytes during cycling and therefore improved battery longevity. However, the same softness leads to the formation of unfavorable composite microstructures where particles of solid electrolytes are islanded by organic materials, the result of the soft organic materials deforming under pressure and the hard solid electrolytes being surrounded. This mismatch in mechanical property prevents a high fraction of organic compounds from being used in a solid-state cathode, limiting the energy density of organic SSBs. Here we report the formation of favorable microstructures of organic cathodes by simultaneously “softening” solid electrolytes and “hardening” organic materials. Solvent treatment of the sulfide electrolyte Li6PS5Cl reduces its Young’s modulus to less than half, while partial lithiation of the organic material pyrene-4,5,9,10-tetraone (PTO) more than triple its Young’s modulus. As a result, the mass fraction of PTO can be improved from 20 to 40 wt.% while maintaining high utilization (85.7%) via grinding with electrolyte precursor. Compared with cells using the pristine and re-hardened Li6PS5Cl, the utilization of PTO is increased by 90.8% and 133.6%, respectively. The mechanical manipulation of sulfide-based electrolyte provides a way to obtain the ideal organic electrode microstructure for effective ion transport. This strategy is applicable to mechanically processed composites with multiple solid components.

Charles Soulen

UCSD

Bridging the Gap Between Pouch and Coin Cell Electrochemical Performance in Lithium Metal Batteries

Applied stack pressure has been shown to be a critical variable in nearly every type of battery studied. However, the structures used to apply the stack pressure are rarely studied. For example, two of the most common battery structures—pouch cells and coin cells—are known to produce substantially different results even when identical chemistries are used. While this discrepancy is commonly attributed to poor pressure control in coin cells, there is no definite study on the topic. Here, we utilize both experimental and computational results to investigate this issue and bridge the gap between pouch cell and coin cell performance. We show that coin cells suffer from a severe pressure inhomogeneity due to the geometry of the wave spring used to apply pressure to the cell stack. Replacing the wave spring with a continuous elastic rubber disc applies a uniform force to the cell stack, resulting in a homogeneous pressure distribution. Li/Cu half cells and NMC/Cu full cells using the updated structure show performance metrics on par with chemically identical pouch cells. This solution retains the quick, easy nature of coin cells while producing pouch cell-level results.

Jie Zheng

University of Houston

Understanding the Chemo-Mechanical Instability of Halide-Based Solid Electrolytes in All-Solid-State Batteries

All-solid-state batteries (ASSBs) using solid electrolytes (SEs) have been widely acknowledged as the next-generation critical energy-storage systems due to their potentially higher energy density and safety performances. Halide-based SEs are gaining popularity as a new candidate for ASSBs. Compared to sulfide and oxide SEs, halide SEs have decent Li+ conductivity, high-voltage stability, good deformability, unique moisture stability, and potentially enabling scale-up manufacturing. Most studies on halide solid-state batteries require operation at high stack pressures and low current densities to achieve long cycle life. However, a comprehensive and systematic understanding of the underlying mechanisms remains elusive.

In this study, we reveal the effect of chemo-mechanical instability at the cathode-electrolyte and anode-electrolyte interfaces on cell longevity. We examined Li-In alloy|Li6PS5Cl|Li3InCl6|NMC811 full cells utilizing Li3InCl6 synthesized via wet-chemistry methods using various volatile solvents. We also evaluated the impact of synthesis methods (ball milling vs. wet chemistry) on the particle size of Li3InCl6 and its influence on cell electrochemical performance. Then, Li|Li6PS5Cl|Li3YCl6|NMC811 full cells were tested under different stacking pressures. We characterized the microstructure of composite electrode and electrolyte after cycling with scanning electron microscopy (SEM) on cryo-polished cross-section samples. The correlation between morphology, stack pressure, and cycling performance were systematically studied. We evaluated the mechanical compatibility of NMC with Li3YCl6 electrolytes featuring different particle sizes by assessing electrochemistry and morphology. In situ electrochemical impedance spectroscopy (EIS) was used to assess the interfacial stability of the cathode-electrolyte and anode-electrolyte interface during cycling. Our investigation reveals that capacity decay in halide-based ASSBs may originate from void formation within the cathode, interfacial incompatibility toward the anode, and SE layer delamination from the cathode. Our research further shed light on the design of long-cycle-life ASSBs.

Robert Kuphal

Michigan State University

Enabling High-Energy Hybrid Lithium-Ion/Lithium-metal Batteries

The key to enabling higher energy dense secondary batteries often points towards the utilization of the alternative Li-metal or anode free battery over graphite anodes. However, many conventional lithium-ion battery electrolytes used with the graphite anode are incapable of purely enabling the use of the Li-metal and anode free configurations as both yield low cycle life, uncontrolled surface reactions, and potential safety issues. A different strategy for increasing the energy density looks towards the incorporation of various amounts of Li-metal within the graphite anode system. Here, we systematically screen the Li-ion mode capabilities under various N/P ratios to probe the standard cycling stability. We then implement an interval protocol to enable Li-ion mode and Li-metal mode capabilities that rely on the physicochemical properties of the electrolyte to improve the overall energy density and stability of the hybrid system.