Johanna Weker | Stanford University (original) (raw)

Papers by Johanna Weker

Extreme fast charging (XFC) of commercial lithium-ion batteries (LIBs) in ≤10-15 minutes will sig... more Extreme fast charging (XFC) of commercial lithium-ion batteries (LIBs) in ≤10-15 minutes will significantly advance the deployment of electric vehicles globally. However, XFC leads to considerable capacity fade, mainly due to graphite anode degradation. Non-destructive three-dimensional (3D) investigation of XFC-cycled anodes is crucial to connect degradation with capacity loss. Here, we demonstrate the viability of simultaneous neutron and X-ray tomography (NeXT) for ex-situ 3D visualization of graphite anode degradation. NeXT is advantageous because of the sensitivity of neutrons to Li and H and X-rays to Cu. We combine the neutron and X-ray tomography with micron resolution for material identification and segmentation on one pristine and one XFC-cycled graphite anode, thereby underscoring the benefits of the simultaneous nature of NeXT. Our ex-situ results pave the way for the design of NeXT-friendly LIB geometries that will allow operando and/or in-situ 3D visualization of graph...

SSRN Electronic Journal, 2022

Review of Scientific Instruments, 2022

Laser powder bed fusion (LPBF) is a highly dynamic multi-physics process used for the additive ma... more Laser powder bed fusion (LPBF) is a highly dynamic multi-physics process used for the additive manufacturing (AM) of metal components. Improving process understanding and validating predictive computational models require high-fidelity diagnostics capable of capturing data in challenging environments. Synchrotron x-ray techniques play a vital role in the validation process as they are the only in situ diagnostic capable of imaging sub-surface melt pool dynamics and microstructure evolution during LPBF-AM. In this article, a laboratory scale system designed to mimic LPBF process conditions while operating at a synchrotron facility is described. The system is implemented with process accurate atmospheric conditions, including an air knife for active vapor plume removal. Significantly, the chamber also incorporates a diagnostic sensor suite that monitors emitted optical, acoustic, and electronic signals during laser processing with coincident x-ray imaging. The addition of the sensor s...

SSRN Electronic Journal, 2022

ECS Meeting Abstracts, 2020

Lithium-ion batteries (LIBs) capable of fast-charging are essential in the popularization of elec... more Lithium-ion batteries (LIBs) capable of fast-charging are essential in the popularization of electric vehicles. Typical fast-charge requirements are charging to 80% state of charge within 10 mins. However, such high rates cause active material degradation and undesired lithium plating, leading to capacity fading and safety hazards. These issues are impacted by charging conditions, e.g. charging protocol, temperature, external pressure, etc. Here, we focus on the pressure-dependence of fast-charge batteries using an in-house designed gas bladder cell configuration. Through a systematic study, we revealed correlations between externally applied electrode stack pressure and capacity fade. Additionally, we propose possible capacity fade mechanisms during fast charge and a way to mitigate it. We utilized single-layer pouch cell batteries with a graphite anode, LiNi0.5Mn0.3Co0.2O2 (NMC532) cathode, and organic liquid electrolyte solution. Electrode stack pressure is achieved by opposing p...

Review of Scientific Instruments, 2022

Microscopy and Microanalysis, 2021

Problem: The long charging times required for lithium-ion batteries (LIBs) constitute a major bot... more Problem: The long charging times required for lithium-ion batteries (LIBs) constitute a major bottleneck in the widespread deployment of battery electric vehicles (BEVs). Currently available BEVs cannot charge at rates that offer a similar experience to that of refueling a gasoline car at a gas station. Among the state-of-the-art BEVs, Tesla vehicles take ~ 1-12 hours to charge at the fastest recharge rates of 120 kW through Supercharger stations. 1 Therefore, there is a global push to enable extreme fast charging (XFC) that would reduce LIB charging times to 10-15 minutes. 2 However, existing LIBs cannot achieve this XFC goal without significantly reducing battery performance. One of the identified XFC failure pathways is a phenomenon known as "lithium (Li) plating," which severely limits battery capacity over lifetime and eventually leads to battery failure. 3 Thus, understanding the origin and characteristics of Li plating on graphite anodes is crucial to developing XFC batteries. Approach: In this work, we used simultaneous neutrons and X-ray-based tomography (NeXT) 4 as a non-destructive imaging modality to visualize Li plating across three dimensions on graphite anode ex-situ after XFC in LIBs. Since X-rays are sensitive to the electron density and neutrons to the nuclear density of the material, NeXT readily separates battery anode components such as Li, graphite, and copper, due to the complementary interaction of the two imaging probes with matter. Higher-energy X-rays are needed to penetrate the metallic components in a battery such as the copper current collector. However, X-rays lack the sufficient imaging contrast to differentiate low-Z elements, especially at high energies. Here, neutrons provide the sensitivity to differentiate graphite from Li due to the larger difference in their relative neutron crosssections. Methodology: We performed proof-of-concept multi-modal imaging experiments at the NeXT system located on the BT-2 imaging beamline at the National Institute of Standards and Technology Center for Neutron Research (NCNR). 4 We characterized pristine and cycled graphite anode strips containing plated Li. For cycled anode strips, we disassembled the battery pouch cells and harvested graphite anodes at fully discharged condition after these were cycled under XFC conditions, specifically 9 Crate for 450 cycles. 5 Our spatial resolution was ~15-20 μm, which was sufficient to pinpoint the location of Li plating within the thickness (80-100 μm) of the graphite anode. Data analysis/Discussion: For data analysis, we first denoised the neutron and X-ray images. Then, we used Livermore Tomography Toolbox, 6 a fast and user-friendly tomographic reconstruction package developed in LabView, for 3D iterative cone beam reconstruction. Next, we used bivariate histogram phase segmentation 7 on the reconstructed neutron and X-ray

ACS Applied Energy Materials, 2021

Advanced Energy Materials, 2021

Journal of The Electrochemical Society, 2020

Zinc continues to garner immense interest due to its versatility as an anode material in several ... more Zinc continues to garner immense interest due to its versatility as an anode material in several configurations utilizing either alkaline or mild-pH electrolytes. Current research on using mild-pH electrolytes has improved the rechargeability aspect of Zn-based batteries since Zn2+ is solely utilized for plating/stripping of Zn. Several studies have incorporated Zn metal foils, yet, dramatic improvements can be achieved by expressing Zn as a porous structure. Herein, we use a quasi-pulsed electrodeposition process to prepare a conformal Zn coating onto 3D porous copper foam. By tuning the electrodeposition parameters, we achieved an optimal Zn coating that undergoes reversible plating/stripping when tested in symmetric Zn cells, which supported a low overpotential of ∼60 mV for up to 100 cycles. We further investigated changes in the surface morphology by studying the Zn surface of both foil and 3D structure using scanning electron microscopy and X-ray micro-computed tomography. Bot...

Journal of Materials Chemistry A, 2020

Investigation of the mechanisms underlying control of electrodeposited lithium metal morphology u... more Investigation of the mechanisms underlying control of electrodeposited lithium metal morphology using electrolyte additives in lithium metal batteries.

Na 2 S was prepared from stoichiometric Na (Acros Organics, rod, 99.8%, mechanically cleaned prio... more Na 2 S was prepared from stoichiometric Na (Acros Organics, rod, 99.8%, mechanically cleaned prior to use) and S (see main text) in separate alumina crucibles (Almath) in an evacuated silica ampoule. The reactants were heated at 1°C min −1 to 300°C for 48 h and cooled ambiently to room temperature. The ground product was a fine powder of a slightly tan-color. The product was determined to be phase pure by XRD.

ECS Meeting Abstracts, 2016

ECS Meeting Abstracts, 2014

Ge anodes have very high theoretical lithium capacity (1600 mAhg-1) and are promising anodes for ... more Ge anodes have very high theoretical lithium capacity (1600 mAhg-1) and are promising anodes for Li batteries. Ge is more electronically conductive than Si and has a higher room temperature Li-ion diffusivity. However, because of their high capacity, Ge anodes suffer from large volume changes (up to 400%; similar to Si, at 4200 mAhg-1) during electrochemical cycling. Repeated expansion and contraction of these materials lead to fracturing and eventual pulverization resulting in the loss of electrical contact with the current collector and ultimately battery failure. In order to better understand these failures we have conducted the first 3D nanoscale in situ study of a Li battery system. We imaged Ge anodes with hard X-rays (11.2 keV, above the Ge K-edge) with transmission X-ray microscopy at 30 nm resolution. 2D images in operando were collected at several regions within the particles, and 3D tomography data was also collected at different time points within the fully operating bat...

Advanced Engineering Materials, 2019

Chemistry of Materials, 2018

Magnesium-sulfur batteries are one of the most promising next-generation battery systems due to t... more Magnesium-sulfur batteries are one of the most promising next-generation battery systems due to their high energy density, low cost, and high level of safety. However, the reaction mechanisms are not well understood, and in particular, the discharge reaction products have not yet been identified. Here we show that zinc blende magnesium sulfide is observed as a reaction product after discharging in magnesium-sulfur batteries. When magnesium reacts electrochemically with sulfur in a sulfone-based magnesium electrolyte, sulfur becomes amorphous consisting of magnesium and sulfur in the cathode. In this study, it has been found that the amorphous material has an unusual local structure, which is not related to the most stable rock salt phase of magnesium sulfide but rather the metastable zinc blende phase. It was indicated that this material realizes the reversibility of magnesium-sulfur batteries.

Nature Communications, 2019

Laser powder bed fusion additive manufacturing is an emerging 3D printing technique for the fabri... more Laser powder bed fusion additive manufacturing is an emerging 3D printing technique for the fabrication of advanced metal components. Widespread adoption of it and similar additive technologies is hampered by poor understanding of laser-metal interactions under such extreme thermal regimes. Here, we elucidate the mechanism of pore formation and liquidsolid interface dynamics during typical laser powder bed fusion conditions using in situ X-ray imaging and multi-physics simulations. Pores are revealed to form during changes in laser scan velocity due to the rapid formation then collapse of deep keyhole depressions in the surface which traps inert shielding gas in the solidifying metal. We develop a universal mitigation strategy which eliminates this pore formation process and improves the geometric quality of melt tracks. Our results provide insight into the physics of laser-metal interaction and demonstrate the potential for science-based approaches to improve confidence in components produced by laser powder bed fusion.

Extreme fast charging (XFC) of commercial lithium-ion batteries (LIBs) in ≤10-15 minutes will sig... more Extreme fast charging (XFC) of commercial lithium-ion batteries (LIBs) in ≤10-15 minutes will significantly advance the deployment of electric vehicles globally. However, XFC leads to considerable capacity fade, mainly due to graphite anode degradation. Non-destructive three-dimensional (3D) investigation of XFC-cycled anodes is crucial to connect degradation with capacity loss. Here, we demonstrate the viability of simultaneous neutron and X-ray tomography (NeXT) for ex-situ 3D visualization of graphite anode degradation. NeXT is advantageous because of the sensitivity of neutrons to Li and H and X-rays to Cu. We combine the neutron and X-ray tomography with micron resolution for material identification and segmentation on one pristine and one XFC-cycled graphite anode, thereby underscoring the benefits of the simultaneous nature of NeXT. Our ex-situ results pave the way for the design of NeXT-friendly LIB geometries that will allow operando and/or in-situ 3D visualization of graph...

SSRN Electronic Journal, 2022

Review of Scientific Instruments, 2022

Laser powder bed fusion (LPBF) is a highly dynamic multi-physics process used for the additive ma... more Laser powder bed fusion (LPBF) is a highly dynamic multi-physics process used for the additive manufacturing (AM) of metal components. Improving process understanding and validating predictive computational models require high-fidelity diagnostics capable of capturing data in challenging environments. Synchrotron x-ray techniques play a vital role in the validation process as they are the only in situ diagnostic capable of imaging sub-surface melt pool dynamics and microstructure evolution during LPBF-AM. In this article, a laboratory scale system designed to mimic LPBF process conditions while operating at a synchrotron facility is described. The system is implemented with process accurate atmospheric conditions, including an air knife for active vapor plume removal. Significantly, the chamber also incorporates a diagnostic sensor suite that monitors emitted optical, acoustic, and electronic signals during laser processing with coincident x-ray imaging. The addition of the sensor s...

SSRN Electronic Journal, 2022

ECS Meeting Abstracts, 2020

Lithium-ion batteries (LIBs) capable of fast-charging are essential in the popularization of elec... more Lithium-ion batteries (LIBs) capable of fast-charging are essential in the popularization of electric vehicles. Typical fast-charge requirements are charging to 80% state of charge within 10 mins. However, such high rates cause active material degradation and undesired lithium plating, leading to capacity fading and safety hazards. These issues are impacted by charging conditions, e.g. charging protocol, temperature, external pressure, etc. Here, we focus on the pressure-dependence of fast-charge batteries using an in-house designed gas bladder cell configuration. Through a systematic study, we revealed correlations between externally applied electrode stack pressure and capacity fade. Additionally, we propose possible capacity fade mechanisms during fast charge and a way to mitigate it. We utilized single-layer pouch cell batteries with a graphite anode, LiNi0.5Mn0.3Co0.2O2 (NMC532) cathode, and organic liquid electrolyte solution. Electrode stack pressure is achieved by opposing p...

Review of Scientific Instruments, 2022

Microscopy and Microanalysis, 2021

Problem: The long charging times required for lithium-ion batteries (LIBs) constitute a major bot... more Problem: The long charging times required for lithium-ion batteries (LIBs) constitute a major bottleneck in the widespread deployment of battery electric vehicles (BEVs). Currently available BEVs cannot charge at rates that offer a similar experience to that of refueling a gasoline car at a gas station. Among the state-of-the-art BEVs, Tesla vehicles take ~ 1-12 hours to charge at the fastest recharge rates of 120 kW through Supercharger stations. 1 Therefore, there is a global push to enable extreme fast charging (XFC) that would reduce LIB charging times to 10-15 minutes. 2 However, existing LIBs cannot achieve this XFC goal without significantly reducing battery performance. One of the identified XFC failure pathways is a phenomenon known as "lithium (Li) plating," which severely limits battery capacity over lifetime and eventually leads to battery failure. 3 Thus, understanding the origin and characteristics of Li plating on graphite anodes is crucial to developing XFC batteries. Approach: In this work, we used simultaneous neutrons and X-ray-based tomography (NeXT) 4 as a non-destructive imaging modality to visualize Li plating across three dimensions on graphite anode ex-situ after XFC in LIBs. Since X-rays are sensitive to the electron density and neutrons to the nuclear density of the material, NeXT readily separates battery anode components such as Li, graphite, and copper, due to the complementary interaction of the two imaging probes with matter. Higher-energy X-rays are needed to penetrate the metallic components in a battery such as the copper current collector. However, X-rays lack the sufficient imaging contrast to differentiate low-Z elements, especially at high energies. Here, neutrons provide the sensitivity to differentiate graphite from Li due to the larger difference in their relative neutron crosssections. Methodology: We performed proof-of-concept multi-modal imaging experiments at the NeXT system located on the BT-2 imaging beamline at the National Institute of Standards and Technology Center for Neutron Research (NCNR). 4 We characterized pristine and cycled graphite anode strips containing plated Li. For cycled anode strips, we disassembled the battery pouch cells and harvested graphite anodes at fully discharged condition after these were cycled under XFC conditions, specifically 9 Crate for 450 cycles. 5 Our spatial resolution was ~15-20 μm, which was sufficient to pinpoint the location of Li plating within the thickness (80-100 μm) of the graphite anode. Data analysis/Discussion: For data analysis, we first denoised the neutron and X-ray images. Then, we used Livermore Tomography Toolbox, 6 a fast and user-friendly tomographic reconstruction package developed in LabView, for 3D iterative cone beam reconstruction. Next, we used bivariate histogram phase segmentation 7 on the reconstructed neutron and X-ray

ACS Applied Energy Materials, 2021

Advanced Energy Materials, 2021

Journal of The Electrochemical Society, 2020

Zinc continues to garner immense interest due to its versatility as an anode material in several ... more Zinc continues to garner immense interest due to its versatility as an anode material in several configurations utilizing either alkaline or mild-pH electrolytes. Current research on using mild-pH electrolytes has improved the rechargeability aspect of Zn-based batteries since Zn2+ is solely utilized for plating/stripping of Zn. Several studies have incorporated Zn metal foils, yet, dramatic improvements can be achieved by expressing Zn as a porous structure. Herein, we use a quasi-pulsed electrodeposition process to prepare a conformal Zn coating onto 3D porous copper foam. By tuning the electrodeposition parameters, we achieved an optimal Zn coating that undergoes reversible plating/stripping when tested in symmetric Zn cells, which supported a low overpotential of ∼60 mV for up to 100 cycles. We further investigated changes in the surface morphology by studying the Zn surface of both foil and 3D structure using scanning electron microscopy and X-ray micro-computed tomography. Bot...

Journal of Materials Chemistry A, 2020

Investigation of the mechanisms underlying control of electrodeposited lithium metal morphology u... more Investigation of the mechanisms underlying control of electrodeposited lithium metal morphology using electrolyte additives in lithium metal batteries.

Na 2 S was prepared from stoichiometric Na (Acros Organics, rod, 99.8%, mechanically cleaned prio... more Na 2 S was prepared from stoichiometric Na (Acros Organics, rod, 99.8%, mechanically cleaned prior to use) and S (see main text) in separate alumina crucibles (Almath) in an evacuated silica ampoule. The reactants were heated at 1°C min −1 to 300°C for 48 h and cooled ambiently to room temperature. The ground product was a fine powder of a slightly tan-color. The product was determined to be phase pure by XRD.

ECS Meeting Abstracts, 2016

ECS Meeting Abstracts, 2014

Ge anodes have very high theoretical lithium capacity (1600 mAhg-1) and are promising anodes for ... more Ge anodes have very high theoretical lithium capacity (1600 mAhg-1) and are promising anodes for Li batteries. Ge is more electronically conductive than Si and has a higher room temperature Li-ion diffusivity. However, because of their high capacity, Ge anodes suffer from large volume changes (up to 400%; similar to Si, at 4200 mAhg-1) during electrochemical cycling. Repeated expansion and contraction of these materials lead to fracturing and eventual pulverization resulting in the loss of electrical contact with the current collector and ultimately battery failure. In order to better understand these failures we have conducted the first 3D nanoscale in situ study of a Li battery system. We imaged Ge anodes with hard X-rays (11.2 keV, above the Ge K-edge) with transmission X-ray microscopy at 30 nm resolution. 2D images in operando were collected at several regions within the particles, and 3D tomography data was also collected at different time points within the fully operating bat...

Advanced Engineering Materials, 2019

Chemistry of Materials, 2018

Magnesium-sulfur batteries are one of the most promising next-generation battery systems due to t... more Magnesium-sulfur batteries are one of the most promising next-generation battery systems due to their high energy density, low cost, and high level of safety. However, the reaction mechanisms are not well understood, and in particular, the discharge reaction products have not yet been identified. Here we show that zinc blende magnesium sulfide is observed as a reaction product after discharging in magnesium-sulfur batteries. When magnesium reacts electrochemically with sulfur in a sulfone-based magnesium electrolyte, sulfur becomes amorphous consisting of magnesium and sulfur in the cathode. In this study, it has been found that the amorphous material has an unusual local structure, which is not related to the most stable rock salt phase of magnesium sulfide but rather the metastable zinc blende phase. It was indicated that this material realizes the reversibility of magnesium-sulfur batteries.

Nature Communications, 2019

Laser powder bed fusion additive manufacturing is an emerging 3D printing technique for the fabri... more Laser powder bed fusion additive manufacturing is an emerging 3D printing technique for the fabrication of advanced metal components. Widespread adoption of it and similar additive technologies is hampered by poor understanding of laser-metal interactions under such extreme thermal regimes. Here, we elucidate the mechanism of pore formation and liquidsolid interface dynamics during typical laser powder bed fusion conditions using in situ X-ray imaging and multi-physics simulations. Pores are revealed to form during changes in laser scan velocity due to the rapid formation then collapse of deep keyhole depressions in the surface which traps inert shielding gas in the solidifying metal. We develop a universal mitigation strategy which eliminates this pore formation process and improves the geometric quality of melt tracks. Our results provide insight into the physics of laser-metal interaction and demonstrate the potential for science-based approaches to improve confidence in components produced by laser powder bed fusion.