Supratim Das

Authors: Daniel Remler, Supratim Das, Amritha Jayanti. Reviewers: Paul Shearing, Ju Li

Advancements in battery technology have been relatively slow due to the complex chemistry involved and the challenges to commercialize while maintaining safety. Improvements in battery technology, though, would mean enhanced energy availability and consumer electronics performance. The promises of emerging battery technology include enhanced smartphone battery life, reliable electric transportation… Show more

Authors: Daniel Remler, Supratim Das, Amritha Jayanti. Reviewers: Paul Shearing, Ju Li

Advancements in battery technology have been relatively slow due to the complex chemistry involved and the challenges to commercialize while maintaining safety. Improvements in battery technology, though, would mean enhanced energy availability and consumer electronics performance. The promises of emerging battery technology include enhanced smartphone battery life, reliable electric transportation, more efficient energy storage for large-scale buildings, and even energy storage for the grid. New designs could also address environmental and safety concerns regarding raw material sourcing, as well as battery disposal. However, it remains difficult for even the most promising battery experiments to find their way out of research labs and into the devices we carry. Despite these conditions, there are many researchers
and innovators working towards the cause.

At a national level, many countries have acknowledged the important role that novel battery technology will play in clean energy production, as well as competitiveness in the automotive sector. Though the United States has regulations of existing technology and investment plans for emerging technology research and development, there is still an observable gap in policy and the public sector engagement. With the emergence of competitive strategies from other nations and blocs, such as the European Union’s Strategic Action Plan on Batteries, it is increasingly important for the U.S. to focus and develop a public approach to battery technology investment that capitalizes on the promises of the technology, while minimizing foreseeable harms. Show less

Authors: Tao Gao*, Yu Han*, Dimitrios Fraggedakis, Supratim Das, Tingtao Zhou, Che-Ning Yeh, Shengming Xu, William C Chueh, Ju Li, Martin Z Bazant

Improving safety while increasing the charging rates and extending the lifetime is the grand challenge for lithium-ion batteries. The key challenge is to control lithium plating, a parasitic reaction on graphite anodes that competes with lithium intercalation. Here, we determine the fundamental mechanism for the onset of lithium plating on… Show more

Authors: Tao Gao*, Yu Han*, Dimitrios Fraggedakis, Supratim Das, Tingtao Zhou, Che-Ning Yeh, Shengming Xu, William C Chueh, Ju Li, Martin Z Bazant

Improving safety while increasing the charging rates and extending the lifetime is the grand challenge for lithium-ion batteries. The key challenge is to control lithium plating, a parasitic reaction on graphite anodes that competes with lithium intercalation. Here, we determine the fundamental mechanism for the onset of lithium plating on graphite particles. We perform in situ optical microscopy coupled with electrochemical measurements to resolve the spatial dynamics of lithiation and plating on the surface of a single graphite particle. We observe that the onset of plating is strongly coupled with phase separation in graphite and occurs only on the fully lithiated edges of the particles. The competition between Li insertion and plating is further elucidated by examining the energetics and kinetics of both reactions. Based on the physical insights drawn from the experiments, we propose a phase-field model that predicts the onset of Li plating. Show less

Authors: Donal P Finegan, Alexander Henry Quinn, David Wragg, Andrew Colclasure, Xuekun Lu, Chun Tan, Thomas Heenan, Rhodri Jervis, Dan Brett, Supratim Das, Tao Gao, Daniel Cogswell, Martin Z Bazant, Marco di Michiel, Stefano Checchia, Paul Shearing, Kandler Smith

The principal inhibitor of fast charging lithium ion cells is the graphite negative electrode, where
favorable conditions for lithium plating occur at high charge rates, causing accelerated degradation and
safety… Show more

Authors: Donal P Finegan, Alexander Henry Quinn, David Wragg, Andrew Colclasure, Xuekun Lu, Chun Tan, Thomas Heenan, Rhodri Jervis, Dan Brett, Supratim Das, Tao Gao, Daniel Cogswell, Martin Z Bazant, Marco di Michiel, Stefano Checchia, Paul Shearing, Kandler Smith

The principal inhibitor of fast charging lithium ion cells is the graphite negative electrode, where
favorable conditions for lithium plating occur at high charge rates, causing accelerated degradation and
safety concerns. The local response of graphite, both at the electrode and particle level, when exposed
to fast charging conditions of around 6C is not well understood. Consequently, the conditions that lead
to the onset of lithium plating, as well as the local dynamics of lithium plating and stripping, have also
remained elusive. Here, we use high-speed (100 Hz) pencil-beam X-ray diffraction to repeatedly raster
along the depth of a 101 mm thick graphite electrode in 3 mm steps during fast (up to 6C) charge and
discharge conditions. Consecutive depth profiles from separator to current collector were each
captured in 0.5 seconds, giving an unprecedented spatial and temporal description of the state of the
electrode and graphite’s staging dynamics during high rate conditions. The electrode is preferentially
activated near the separator, and the non-uniformity increases with rate and is influenced by freeenergy barriers between graphite’s lithiation stages. The onset of lithium plating and stripping was
quantified, occurring only within the first 15 mm from the separator. The presence of lithium plating
changed the behavior of the underlying graphite, such as causing co-existence of LiC6 and graphite in
the fully discharged state. Finally, the staging behavior of graphite at different rates was quantified,
revealing a high dependency on rate and drastic hysteresis between lithiation and delithiation. Show less

Authors: William Huang, Peter M. Attia, Hansen Wang, Sara E. Renfrew, Norman Jin, Supratim Das, Zewen Zhang, David T. Boyle, Yuzhang Li, Martin Z. Bazant, Bryan D. McCloskey, William C. Chueh*, and Yi Cui*

The stability of modern lithium-ion batteries depends critically on an effective solid–electrolyte interphase (SEI), a passivation layer that forms on the carbonaceous negative electrode as a result of electrolyte reduction. However, a nanoscopic understanding of how the SEI evolves… Show more

Authors: William Huang, Peter M. Attia, Hansen Wang, Sara E. Renfrew, Norman Jin, Supratim Das, Zewen Zhang, David T. Boyle, Yuzhang Li, Martin Z. Bazant, Bryan D. McCloskey, William C. Chueh*, and Yi Cui*

The stability of modern lithium-ion batteries depends critically on an effective solid–electrolyte interphase (SEI), a passivation layer that forms on the carbonaceous negative electrode as a result of electrolyte reduction. However, a nanoscopic understanding of how the SEI evolves with battery aging remains limited due to the difficulty in characterizing the structural and chemical properties of this sensitive interphase. In this work, we image the SEI on carbon black negative electrodes using cryogenic transmission electron microscopy (cryo-TEM) and track its evolution during cycling. We find that a thin, primarily amorphous SEI nucleates on the first cycle, which further evolves into one of two distinct SEI morphologies upon further cycling: (1) a compact SEI, with a high concentration of inorganic components that effectively passivates the negative electrode; and (2) an extended SEI spanning hundreds of nanometers. This extended SEI grows on particles that lack a compact SEI and consists primarily of alkyl carbonates. The diversity in observed SEI morphologies suggests that SEI growth is a highly heterogeneous process. The simultaneous emergence of these distinct SEI morphologies highlights the necessity of effective passivation by the SEI, as large-scale extended SEI growths negatively impact lithium-ion transport, contribute to capacity loss, and may accelerate battery failure. Show less

Authors: Peter M Attia, Supratim Das, Stephen J Harris, Martin Z Bazant, William C Chueh

Growth of the solid electrolyte interphase (SEI) is a primary driver of capacity fade in lithium-ion batteries. Despite its importance to this device and intense research interest, the fundamental mechanisms underpinning SEI growth remain unclear. In Part I of this work, we present an electroanalytical method to measure the dependence of SEI growth on potential, current magnitude, and current… Show more

Authors: Peter M Attia, Supratim Das, Stephen J Harris, Martin Z Bazant, William C Chueh

Growth of the solid electrolyte interphase (SEI) is a primary driver of capacity fade in lithium-ion batteries. Despite its importance to this device and intense research interest, the fundamental mechanisms underpinning SEI growth remain unclear. In Part I of this work, we present an electroanalytical method to measure the dependence of SEI growth on potential, current magnitude, and current direction during galvanostatic cycling of carbon black/Li half cells.We find that SEI growth strongly depends on all three parameters; most notably, we find SEI growth rates increase with nominal C rate and are significantly higher on lithiation than on delithiation. We observe this directional effect in both galvanostatic and potentiostatic experiments and discuss hypotheses that could explain this observation. This work identifies a strong coupling between SEI growth and charge storage (e.g., intercalation and capacitance) in carbon negative electrodes. Show less

Authors: Supratim Das, Peter M Attia, William C Chueh, Martin Z Bazant

Mathematical models of capacity fade can reduce the time and cost of lithium-ion battery development and deployment, and growth of the solid-electrolyte interphase (SEI) is a major source of capacity fade. Experiments in Part I reveal nonlinear voltage dependence and strong charge-discharge asymmetry in SEI growth on carbon black negative electrodes, which is not captured by previous models. Here, we present a… Show more

Authors: Supratim Das, Peter M Attia, William C Chueh, Martin Z Bazant

Mathematical models of capacity fade can reduce the time and cost of lithium-ion battery development and deployment, and growth of the solid-electrolyte interphase (SEI) is a major source of capacity fade. Experiments in Part I reveal nonlinear voltage dependence and strong charge-discharge asymmetry in SEI growth on carbon black negative electrodes, which is not captured by previous models. Here, we present a theoretical model for the electrochemical kinetics of SEI growth coupled to lithium intercalation, which accurately predicts experimental results with few adjustable parameters. The key hypothesis is that the initial SEI is a mixed ion-electron conductor, and its electronic conductivity varies approximately with the square of the local lithium concentration, consistent with hopping conduction of electrons along percolating networks. By including a lithium-ion concentration dependence for the electronic conductivity in the SEI, the bulk SEI thus modulates the overpotential and exchange current of the electrolyte reduction reaction. As a result, SEI growth is promoted during lithiation but suppressed during delithiation. This new insight establishes the fundamental electrochemistry of SEI growth kinetics. Our model improves upon existing models by introducing the effects of electrochemical SEI growth and its dependence on potential, current magnitude, and current direction in predicting capacity fade. Show less

Authors: Supratim Das, Chaitanya Narayanam, Shantanu Roy, Rajesh Khanna

Wetting of partially wettable porous solids is encountered in many and diverse applications such as imbibition of liquid reactants into pores of porous catalysts and adsorbents in reactor beds, water vapor condensation on porous substrates like leaves, and spreading of liquid condensate on fuel cell membranes. This wetting is a combination of liquid spreading/retraction on the external surface and imbibition into the… Show more

Authors: Supratim Das, Chaitanya Narayanam, Shantanu Roy, Rajesh Khanna

Wetting of partially wettable porous solids is encountered in many and diverse applications such as imbibition of liquid reactants into pores of porous catalysts and adsorbents in reactor beds, water vapor condensation on porous substrates like leaves, and spreading of liquid condensate on fuel cell membranes. This wetting is a combination of liquid spreading/retraction on the external surface and imbibition into the pores. In this paper, we establish the basic “building block” of this problem, i.e., the dynamics of wetting and retraction of a thin film in the vicinity of a single infinite pore of a porous solid and show the way forward by discussing the case of two such adjacent pores.

The coupled process described by a unified and simple model derived from equations of motion under the lubrication approximation for thin film flow on the external surface and Hagen-Poiseulle flow inside the pores. A single final evolution equation tracks the externally wetted region in time by solving for the height of the liquid surface starting from an initial liquid droplet. The wetted area initially expands as the droplet spreads and then contracts as droplet retracts due to imbibition in the pore. The liquid surface becomes increasingly liable to rupture under the influence of intermolecular forces as it thins because of imbibition. The governing equation can track the rupture and subsequent dewetting of the surface also. The liquid morphology and kinetics of wetting show good agreement with the reported experiments implying that the description of a spreading liquid as a thin film indeed manages to incorporate the most important physics governing the internal wetting of liquids on porous substrates at the micro scale. The model shows a possible way to develop wetting correlations for larger scales of flow in industrial trickle bed reactors in a bottom-up manner. Show less