Understanding and controlling the microstructure of zinc (Zn) metal electrodeposits are critical for advancing the next generation of rechargeable Zn batteries. In this study, we develop microelectrode arrays to systematically investigate the relationship among current density, morphology, and Coulombic efficiency (CE) during Zn electrodeposition from an ionic liquid electrolyte. By independently controlling the current density or voltage on each microelectrode, we identify three key deposition regimes. At lower current densities, Zn electrodeposition forms soft, loosely packed mossy structures with moderate CE between 80 and 90%. Increased current densities yield more compact morphologies, representing a transition zone where growth becomes more uniform and achieves 98-99% CE. Under constant voltage deposition, the Zn salt in the electrolyte near the microelectrode depletes, leading to sharp, filament-like dendrites with CE below 50%. These findings demonstrate the ability to control Zn electrodeposition morphology in nonaqueous electrolytes while highlighting the diffusion-limited kinetics that dictate deposition behavior and reversibility. The methodology provides mechanistic insights and offers viable strategies for designing dendrite-free Zn anodes for stable and efficient ZIBs.

This review provides a comprehensive overview of ultrasonic testing (UT) applied to battery research and development, bridging the gap between fundamental acoustic principles and practical applications. We begin by detailing the acoustic physics underlying UT and describing the hardware, software, and signal processing algorithms necessary to extract useful information from battery systems. We then summarize key academic findings and trends in UT analysis of lithium-based batteries, highlighting both foundational studies that have shaped the field and recent advancements pushing the boundaries of UT application. Following this, we provide an overview of lab-scale operando tools that complement UT analysis, illustrating how they can enhance and validate its findings. The discussion is extended beyond academic work to encompass UT applications in battery manufacturing, uniquely incorporating industry perspectives on the challenges and opportunities in this space. Finally, we conclude with a discussion of future directions in battery UT research. This review aims to provide a summary of the current state of UT applied to batteries, equip readers with the tools to contextualize new UT studies and applications, and serve as a practical guide for researchers and engineers seeking to implement UT in their work.

Solid-state electrolytes can enable pure Si anodes for high-energy-density battery applications due to improved interfacial stability over their liquid counterparts. Despite this, both systems suffer from large transient electrode volume changes that cause irreversible capacity losses. In all-solid systems, electrochemically induced strain causes stress on a brittle solid electrolyte, causing contact loss and/or cracking. As a result, tracking mechanics and stress evolution is especially important in developing protocols to mitigate these degradation modes. In this work, we utilize operando ultrasound transmission to study the chemomechanical and morphological dynamics of Si electrodes. We show that stress evolution within the bulk is nonlinearly a function of state of charge and depends on metastable Li x Si phases. We demonstrate operando and noninvasive visualization of porosity changes within all-solid-state Si|NMC full cells. We observe significant, irreversible changes in electrode packing density during the first cycle along with morphological dynamics that depend on the direction of current flow.

While thick electrodes may achieve good utilization at low charge and discharge rates (c-rates) used for diurnal grid storage, the widespread commercialization of thick electrodes across the electric vehicle and stationary storage industries is limited by their performance at higher c-rates. In thick electrodes, highly polarized concentration gradients form across the electrode to drive lithium ion transport through the thickness of the electrode, resulting in large overpotentials that limit capacity utilization at higher rates. It is well understood that depletion at one side of this concentration gradient results in a limiting current for the cell; our models show that for high-power thick electrode systems, salt accumulation at the other side of the concentration gradient can exceed the solubility of conventional carbonate electrolytes used in lithium-ion batteries. Both saturation and depletion phenomena are important to consider when defining the c-rates of operation as we move towards thicker electrodes, and analytical expressions for limiting currents in both scenarios are derived from first principles to facilitate the design of other electrode-electrolyte systems. Polarization in thick electrodes can drive electrolyte concentrations above their solubility limits.Electrolytes with higher diffusivity & solubility can mitigate saturation to improve rate performance & cycle life.Saturation & depletion limiting expressions are derived, and may aid the design & study of other systems.

Lithium metal internal short circuits are often implicated in thermal runaway despite a lack of direct, quantitative evidence supporting a causative link between these two events. A key barrier to quantifying heat release from lithium metal shorting is the challenge associated with isolating shorting from other physical and chemical processes that occur in common carbonate electrolytes. Herein, we develop a system that simultaneously measures heat and voltage using operando isothermal microcalorimetry (ITMC) during lithium metal short circuits. Measurements across various states-of-charge, especially at high voltage where oxygen provides fuel, show that lithium shorting produces very little heat (mu W/cm(2)) and minimal temperature rise (<2 degrees C), consistent with resistive, passivated lithium metal seen in (electro)chemical analyses. These results suggest that thermal runaway is not driven by the short circuit but aging-related phenomena, such as "dead" lithium buildup and gassing. Our findings support protocols to dissolve lithium filaments to improve battery safety.

In stationary storage, thick electrodes can minimize inactive material components to increase energy density and decrease cost, but they face challenges in performance and manufacturability. This work discusses a method to fabricate thick-format lithium-ion electrodes and a model to explore transport constraints for functional thick electrodes. Thick lithium iron phosphate (LFP) electrodes were fabricated using a solvent-free pressing process that adopts methods from alkaline electrode manufacturing for low-cost scale-up. LFP electrodes with thicknesses up to 1 mm and capacities up to similar to 15 mAh/cm(2) exhibited good rate performance (similar to 98 % utilization at C/10, similar to 95 % at C/5, similar to 76 % at C/2). A physics-based LFP half-cell model was developed to aid in characterizing transport within these thick electrodes, revealing opportunities to further improve performance by decreasing tortuosity.

The formation conditions of anode-free lithium metal batteries establish long-term cyclability. In this work, spatiotemporally-resolved ultrasound transmission is used to study the coupling between temperature, stack pressure, and current density during formation on Li plating dynamics in multilayered, anode-free Li metal batteries. Additionally, formed batteries undergo accelerated-rate cycling with simultaneous ultrasound transmission to determine the impact of formation protocols on electrochemical and chemo-mechanical performance. These operando techniques are validated with ex-situ optical and scanning electron microscopy imaging. Electrochemical analysis and X-ray photoelectron spectroscopy provide further insight into the relationship between electrochemical performance, Li mechanics, and the solid-electrolyte interphase. Our results indicate that increased temperature, stack pressure, and C-rate produce more uniform morphology across the anode during formation. Furthermore, improvements gained during formation lead to more stable chemo-mechanical behavior during cycling, though cathode dynamics and electrolyte side reactions convolute electrochemical performance.

The chemo-mechanics of lithium-sulfur (Li-S) batteries are unique in lithium-based batteries because sulfur undergoes a solid-liquid-solid transition during each half-cycle. The dissolution of sulfurous species in liquid electrolytes is a primary degradation mode in Li-S systems. While this challenge is well known, tracking and measuring sulfur liquefaction requires ex-situ experiments or hard-to-parallelize X-ray techniques. Here, we show that operando acoustic analyses can track both physicochemical phase changes and the mechanical dynamics of sulfur lithiation. We show time-of-flight can monitor sulfur phase changes during density and effective elastic moduli dynamics. Acoustic wave damping is highly sensitive to the state-of-matter transitions of the sulfur electrode. By accounting for cell dilation from Li plating and stripping, we show sulfur's chemo-mechanical phase changes dominate time-of-flight's nonlinear, non-monotonic signatures. By utilizing inter-cycle and intra-cycle time-of-flight trends, we develop a semi-quantitative method that can be calibrated to measure the dissolution of sulfur into the electrolyte and verify this with ex-situ TGA and XRD. Lastly, we pair acoustics with voltammetry to observe slow chemo-mechanical dynamics alongside the sluggish kinetics of sulfur utilization. Operando acoustic analyses can elucidate the chemo-mechanical dynamics of the sulfur electrode noninvasively and aid development efforts to slow and mitigate S migration.

Cell formation is an energy and time-intensive empirically-guided process crucial to manufacturing secondary lithium-ion batteries. As the rechargeable battery industry moves towards manufacturing lithium metal batteries—where a metallic lithium negative electrode is used instead of a porous graphite composite—the cell formation process may need reconsidering. The effects of formation rate and cycling protocol on lithium metal battery performance are poorly understood. In this work, we used operando acoustic transmission to measure physical changes during the formation cycles and the effect of formation cycling protocols on the long-term cycling of anode-free lithium metal pouch cells—where all the lithium inventory comes from the positive electrode and is deposited as metallic lithium on copper foil during initial charge. We show that a faster C/3 formation protocol results in comparable cycling performance and cell stiffness change to a slower C/10 formation step. Variations in acoustic metrics across different electrolytes tested are attributed to differences in gas formation, cell swelling, and lithium deposition morphology. NMC811 cathodes paired with a high-concentration ether electrolyte are shown to be particularly prone to gas formation, which is mitigated by using a localized high-concentration ether electrolyte and single-crystal NMC532. The results highlight differences in formation behavior between anode-free lithium metal cells and lithium-ion cells. These are important to consider when bringing new manufacturing plants online for lithium metal batteries.

Silicon (Si) anodes paired with solid electrolytes have recently risen as a promising energy storage solution for energy-dense Li batteries. However, Si lithiation and delithiation can exacerbate electrochemical degradation due to its high mechanical dynamics, especially against a solid electrolyte. In this work, we utilize operando acoustic transmission to probe the chemo-mechanical dynamics of Si. Acoustic transmission utilizes ultrasound propagation to nondestructively monitor the electrode’s chemo-mechanics. The speed of sound through a material is proportional to its Young’s modulus (E) and inversely proportional to density. We show that in an all-solid-state system with a sulfide solid electrolyte, acoustic time of flight is highly sensitive to the mechanical dynamics of Li-Si alloying. We combine operando acoustics with ex-situ techniques such as FIB-SEM and XPS to gain physical insight into the fundamental electrode mechanics. We demonstrate that acoustics time of flight transmission is a useful tool in probing electrode dynamics that give further insight into the degradation modes of next-generation anode materials. Figure 1

Improving the performance and efficiency of batteries is key to enabling the broader adoption of electric vehicles and the effective use of intermittent renewable energy sources. However, this enhancement demands a more comprehensive understanding and improved surveillance of the essential mechanisms that control battery functionality over their entire lifespan. Unfortunately, from the moment batteries are sealed until their end of life, they remain a ‘black box’, and our knowledge of the health status of a commercial battery is limited to current (I), voltage (V), temperature (T) and impedance (R) measurements, at the cell or even module level during use, leading to an over-reliance on insufficient data to establish conservative safety margins and a systematic under-utilization of cells and batteries. Although the field of operando characterization is not new, the emergence of techniques capable of tracking commercial battery properties under realistic conditions has unlocked a trove of chemical, thermal and mechanical data that have the potential to revolutionize the development and utilization strategies of both new and used lithium-ion devices. In this Review, we examine the latest advances in non-destructive characterization techniques, including electrical sensors, optical fibres, acoustic transducers, X-ray-based imaging and thermal imaging (infrared camera or calorimetry), and their potential to improve our comprehension of degradation mechanisms, reduce time and cost, and enhance battery performance throughout their three main life stages: during the manufacturing process, during their utilization and, finally, at the end of their life. This Review examines the latest advances in non-destructive operando characterization techniques and their potential to improve our comprehension of degradation mechanisms and enhance battery performance during the manufacturing process, utilization and at the end of life.

This work demonstrates a minimal overhead storage technology exploiting, rather than compensating for, the innate physical properties of the zinc-bromide system. Using two symmetric planar electrodes and a homogenous electrolyte, we present a ZnBr2 cell with over 50 Wh/L energy density, over 70% roundtrip efficiency, and a lifetime limited by cell sealing quality. The scaled cell cost is estimated to be $40/kWh. The zinc-bromide system is known for its theoretically low cost, long lifetime, and high energy density. However, resolving this theory to practice has been difficult in active flow systems. Classic design goals work to “correct” the physical chemistry of the ZnBr systems, including rigorous separation of the charged Zn and Br2 phases, active phase control of the Br2/water mixture, and forced convection to maximize power density. But balance-of-plant support of concentrated halide electrolytes, complexing required to create reliable Br2 miscibility, and secondary safety systems required when running bromine through forced convection through manifolds conspire to increase the CAPEX and OPEX of the ZnBr2 system while decreasing its reliability. We have previously demonstrated a “static” ZnBr2 system that follows a traditional unit cell design, where zinc plates upon a carbon current collector and Br2 reside in a carbon foam's porosity. Here we present our new designs, where we remove the complexity of the “cathode carbon foam,” replacing it with a simple carbon surface and augmenting it with a better understanding of the native stratification and mixing behaviors of the ZnBr2 electrolyte at different concentrations/state of charge. We will also present learnings of the mixing/settling behavior of the electrolyte as a function of concentration (effective SoC) and orientation, as well as the kinetics of bromine oxidation and consumption on simple carbon electrodes. Figure 1

The transition towards renewable energy sources necessitates the development of efficient and cost-effective energy storage solutions to mitigate the intermittent nature of these resources. Static zinc-bromine batteries (ZBBs) have emerged as a promising, safe, and low-cost grid electrochemical energy storage device. However, their long-term cycling performance suffers from undesirable side reactions, specifically, a precipitation reaction at the cathode during cycling. This precipitate, identified as layered polycrystalline zinc hydroxide bromide (ZHB) for the first time, increases charge transfer resistance and reduces efficiency and capacity. While its formation mechanism remains unclear, our study investigates the effects of electrolyte composition, pH variation, and charging conditions on the precipitation using electroanalytical techniques. We propose that electrolyte pH changes caused by concentration polarization at the cathode surface during charging and hydrogen ion loss are major drivers of ZHB formation. Controlling these parameters can potentially suppress this detrimental precipitate, improving the long-term performance of ZBB.

Wetting is a critical step of lithium-ion battery manufacturing. Following electrolyte filling and sealing, the electrolyte percolates through the porous matrix of the electrodes to encapsulate and penetrate the active particles. This impregnation facilitates necessary ionic conductivity and passivation on formation, resulting in maximum capacity retention during cycling. Unfortunately, incumbent electrochemical techniques fail to fully elucidate this process, particularly in multilayered cells. In this work, we leverage acoustics to demonstrate that the wetting process is not simply a function of thermotemporal conditions but invariably continues into the formation cycles. In particular, transmitted acoustic signal energy is shown to be a function of wetting and a predictor for subsequent cycling performance. The spatial extent of wetting is probed using a purpose-built acoustic scanning apparatus, and a high-throughput fixed-location jig yields a statistical distribution for multiple cells under various wetting and formation conditions. These insights indicate that the two-step pre-cycling conditions should not be considered two separate processes but rather intimately entangled.

Acoustic waves can assess the wetting extent of a porous material by sending sound waves through the material and analyzing how those waves are reflected, refracted, or absorbed. Using modeling and analytical tools developed by the seismology community and correlating with traditional impedance measurements, we have shown that the wetting extent can be understood for many cycles. In this study, we determine where and when the electrolyte moves during Na-ion formation. Further, we discuss how the SEI varies as a function of the adsorption, intercalation, and pore-filling modes of sodium storage observed by the community in hard carbon electrodes.

Electrochemical degradation of solid electrolytes is a major roadblock in the development of solid-state batteries. Combining X-ray absorption spectroscopy characterization, first -principles simulations, and machine learning, here we report the atomic -scale oxidative degradation mechanisms of sulfide electrolytes using Li 3 PS 4 (LPS) as a model system. The degradation begins with a decrease of Li neighbor affinity to S atoms, followed by the formation of S -S bonds as the PS 4 tetrahedron deforms. After the first cycle, the PS 4 motifs become strongly distorted, and PS 3 motifs start to form. The distortion of PS 4 and the formation of S -S bonds are correlated with an increased interfacial impedance. We identify the spectral fingerprints of the local structural evolution and use them as a proxy for the electrochemical stability of phosphorus sulfide electrolytes, as demonstrated in argyrodite Li 6 PS 5 Cl. This study provides guidance for controlling macroscopic reactions through microstructural engineering and can advance the rational design of sulfide electrolytes.

The superionic solid-state argyrodite electrolyte Li6PS5Br can improve lithium and lithium-ion batteries' safety and energy density. Despite many reports validating the conductivity of this electrolyte, it still suffers from passivating electrode degradation mechanisms. At first analysis, lithium iron phosphate (LFP) should be more thermodynamically stable in contact with sulfide electrolytes. However, without substantial improvements to interfacial engineering, we find that LFP is not inherently stable against Li6PS5Br. We hypothesize argyrodite oxidation favorably competes with LFP's delithiation, insulating the electrolyte-electrode interface and causing large overpotential losses. We show that compared to LiNixMnyCozO2, LFP has no actual electrochemical stability advantage despite operating at a lower voltage. We utilize tender energy XAS and XPS to show that chemical reactions occur between LFP and the Li6PS5Br solid electrolyte and these reactions are exacerbated by cycling. We also show that electrochemical degradation occurs at the interface between the solid electrolyte ion conductor and any electron conductor, namely, the active material and carbon additives. We further demonstrate that LiNbO3 cathode coatings on LFP can delay electrochemical degradation by electronically insulating the LFP-sulfide electrolyte interface but not prevent its occurrence at the carbon-electrolyte interface.

As global energy demands escalate, and the use of non-renewable resources become untenable, renewable resources and electric vehicles require far better batteries to stabilize the new energy landscape. To maximize battery performance and lifetime, understanding and monitoring the fundamental mechanisms that govern their operation throughout their life cycle is crucial. Unfortunately, from the moment batteries are sealed until their end-of-life, they remain a black box, and our current knowledge of a commercial battery s health status is limited to current (I), voltage (V), temperature (T), and impedance (R) measurements, at the cell or even module level during use. Electrochemical models work best when the battery is new, and as state reckoning drifts leading to an over-reliance on insufficient data to establish conservative safety margins resulting in the systematic under-utilization of cells and batteries. While the field of operando characterization is not new, the emergence of techniques capable of tracking commercial battery properties under realistic conditions has unlocked a trove of chemical, thermal, and mechanical data that has the potential to revolutionize the development and utilization strategies of both new and used lithium-ion devices. In this review, we examine the latest advances in non-destructive operando characterization techniques, including electrical sensors, optical fibers, acoustic transducers, X-ray-based imaging and thermal imaging (IR camera or calorimetry), and their potential to improve our comprehension of degradation mechanisms, reduce time and cost, and enhance battery performance throughout its life cycle.

To enable the use of renewable energy in place of fossil fuels for grid-scale electricity generation, low-cost, long-duration (3 hr charge, 12 hr discharge) energy storage systems must be developed to bridge the intermittency of these resources. This present work explores the adoption of thick-format lithium-ion electrodes to minimize inactive material cost and achieve <$100/kWh of storage. Thick lithium iron phosphate (LFP) pellets were fabricated using a dry pressing process, and the effects of composition, thickness/porosity balance, and electrolyte choice on the performance of the LFP half cells were explored. LFP electrodes with thicknesses up to 1 mm and capacities up to ~15 mAh/cm 2 exhibited good rate performance (~90% utilization at a C/10 rate) and stable cycling over 100 cycles. A physics-based model was used to study transport within these thick electrodes. As thickness increases, large concentration gradients form across the electrode, with salt depletion at the current collector and salt accumulation at the separator exceeding the solubility limit of conventional electrolytes. Unlike fast-charging thin electrodes where kinetic overpotentials dominate inefficiencies, thick electrode performance is diffusion-limited, suggesting that methods for minimizing tortuosity and increasing ionic conductivity will be key in enabling low-cost thick electrodes. Figure 1

Silicon anodes have emerged as a viable strategy for a negative material in solid-state batteries to balance their reactivity with high energy density. Compared to conventional graphite electrodes, silicon anodes have a large theoretical capacity of 3600 mAh/g compared to 372 mAh/g in graphite. This large capacity comes from the fact that lithiated silicon (Si 4 Li 15 ) can accommodate 15 Li atoms per 4 Si atoms as opposed to LiC 6 . As a result, silicon anodes experience large volumetric expansions up to ~300% as Li ions alloy into the Si negative electrode. Acoustic transmission utilizes sound propagation to nondestructively probe electrode chemo-mechanics in operando. c = √(E/ρ) The speed of sound through a material is proportional to its Young’s modulus (E) and inversely proportional to density. Previous works have shown that acoustic transmission can detect gas formation and dewetting in commercial Li-ion cells and Li metal cells. There has also been a study showing acoustics can detect void formation during Li stripping in solid-state Li symmetric cells. To the best of our knowledge, there has not been an acoustic study of an all solid state Li full cell. This work intends to show that acoustic transmission can monitor Si expansion and contraction as a function of waveform damping and the Young’s modulus of the Si electrode. This works gives insight into the mechanical considerations and possible loss of contact as Si lithiates and delithiates repeatedly. The reliance of Si anodes on stack pressure is not well understood and is further elucidated in this work. We hope to give a better understanding of the intersection between the electrochemical reactions at the Si electrode and the mechanical stresses induced on the cell. Figure 1