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Research Topics

The Pint Lab research effort combines a multidisciplinary team of the most talented and vision-driven researchers in the world to solve problems that require innovative solutions.  Our goal is not to improve existing systems, but to create new systems forged through guiding rationale, relentless hard work, and creative scientific insight.  Our efforts span across numerous fields, building upon the expertise of Prof. Pint and the team in areas of energy systems, carbon nanotechnology, and manufacturing.  Below is a discussion of research areas that our team has led forward, as well as a discussion of ongoing broad interests of the Pint lab. 

Energy Storage Materials and Systems

Our team has led key research thrusts in areas of battery research including lithium-sulfur batteries, sodium-sulfur batteries, sodium batteries, potassium batteries, and recently magnesium batteries.  One key advance from our team in this area has been the first "anode-free" sodium battery with low-cost processing and the highest > 400 Wh/kg energy density ever reported for sodium batteries [1].  Additionally, our work on lithium-sulfur batteries have demonstrated pathways for electrode processing to maintain combined high areal capacity of sulfur near 20 mAh/cm2 and high sulfur utilization enabling promise for Li-S batteries with energy density exceeding 500 Wh/kg [2-3].  Further, our work has used operando and in-situ methods for studying potassium ion battery anodes, highlighting ion staging processes in carbons and introducing doping as a mechanistic pathway to improve anodic capacity. [5-6].

Ongoing Interests: Our ongoing interests center in on studying and engineering key mechanistic limitations to reach batteries with significantly improved energy density, cost, and/or durability.  One area we are studying is the ability to control, modulate, and leverage nucleation processes during metal plating to enable new applications outside of batteries, as well as control key battery performance metrics such as charge and energy efficiency.  Additionally, we are actively pursuing research to multi-purpose or integrate components in batteries for increased information and monitoring capability, leading toward batteries that can be coupled with AI or machine learning algorithms.  

[1] A.P. Cohn, N. Muralidharan, R. Carter, K. Share, and C.L. Pint, “An anode-free sodium battery through in-situ plating of sodium metal,” Nano Letters, 17, 1296-1301 (2017).
[2] M. Li, R. Carter, A. Douglas, L. Oakes, C.L. Pint, “Sulfur vapor-infiltrated 3-D carbon nanotube foam for binder-free high areal capacity composite lithium sulfur battery cathodes,” ACS Nano 11, 4877-4884 (2017). 
[3] R. Carter, L. Oakes, N. Muralidharan, and C.L. Pint, “Isothermal sulfur condensation into carbon scaffolds: Improved loading, performance, and scalability for lithium sulfur battery cathodes,” Journal of Physical Chemistry C, 121, 7718-7727 (2017).
[4] R. Carter, L. Oakes, A. Douglas, N. Muralidharan, A.P. Cohn, and C.L. Pint, “A sugar derived room temperature sodium sulfur battery with long term cycling stability,” Nano Letters, 17, 1863-1869 (2017)
[5] K. Share, A.P. Cohn, R. Carter, B. Rodgers, and C.L. Pint, “Role of nitrogen doped graphene for improved high capacity potassium ion battery anodes,” ACS Nano 10, 9738-9744, (2016).
[6] K. Share, A.P. Cohn, R. Carter, and C.L. Pint, “Mechanism of Electrochemical Potassium Ion Intercalation Staging in Few Layered Graphene from In-Situ Raman Spectroscopy, Nanoscale 8, 16435-16439 (2016).

Beyond Batteries: Mechano-Chemistry and Energy Harvesting

Prof. Pint's team has led some of the first studies to evaluate how mechanical stresses can impact or control electrochemical processes in battery materials, providing a new intersection between mechanics and electrochemistry broadly relevant to energy storage and beyond. [1-3]   This is notable since whereas semiconductor manufacturing has utilized strain engineering as a tool for the last two decades to maintain synergy with Moore's law, battery researchers have focused efforts on studying strain only as an outcome or result of an electrochemical process, and not as an engineering input.  A key observation made by our work is that mechanical stresses can moderate the potential at which ions insert/extract from solid materials, which led us to demonstrate a new and novel platform that utilizes battery materials organized in a symmetric cell configuration to harvest energy from mechanical stresses instead of using those materials to store energy.  Our work in this area has highlighted the low-frequency response of this new energy harvesting platform where the long response times commonly greater than 100 seconds, are longer in duration than the low-frequency motions associated with human motion and movements.  In turn, we have highlighted this approach as a highly suitable method for both human motion energy harvesting and continuous sensing of the motions used for harvesting energy [4].

Ongoing Interests: We are actively working toward extending this new battery material enabled energy conversion platform to textiles and wearable materials that can usher in a new era of smart, biocompatible, and functional fabrics and clothing.  We are also broadly interested in the other areas where coupling between electrochemical processes and mechanics can be technologically useful, such as in actuation and alloying and dealloying processes for material processing. 

[1] L. Oakes, R. Carter, T. Hanken, A.P. Cohn, K. Share, B. Schmidt, and C.L. Pint, “Interface strain in vertically stacked two-dimensional heterostructured carbon-MoS2 nanosheets controls electrochemical reactivity,”  Nature Communications 7, 11796 (2016).
[2] N. Muralidharan, R. Carter, L. Oakes, A.P. Cohn, and C.L. Pint, “Strain engineering to modify the electrochemistry of energy storage electrodes,” Scientific Reports 6, 27542 (2016).
[3] N. Muralidharan, C. Brock, A.P. Cohn, D. Schauben, R.E. Carter, L. Oakes, D.G. Walker, and C.L. Pint, “Tunable MechanoChemistry of Lithium Battery Electrodes,” ACS Nano 11, 6243-6251 (2017).
[4] N. Muralidharan, M. Li, R. Carter, N. Galioto, and C.L. Pint, “Ultralow Frequency Electrochemical – Mechanical Strain Energy Harvester using 2D Black Phosphorus Nanosheets,” ACS Energy Letters 2, 1797-1803 (2017).

Sustainable Conversion of CO2 into Carbon Nanomaterials

Many recent efforts have demonstrated conversion of CO2 into various products including fuels, solid carbons, etc.  However, to be practical, these efforts must be benchmarked to sustain energy efficiency such that the capture and conversion of CO2 doesn't produce more grid-scale emissions assuming the energy is drawn from the electric grid.  In this manner, the Pint lab has been focused on converting CO2 captured directly from the atmosphere into highly valuable, crystalline carbon nanomaterials, such as small diameter multi-walled carbon nanotubes, single-walled carbon nanotubes, and few- and single-layered graphene with high yield of CO2 to solid carbon formation (> 85%), high purity of materials (90-99%), and with 95%+ Faradaic energy conversion efficiency of CO2. Our early collaborative work demonstrated the first carbon nano/micro tubes with diameters > 100 nm using an electrochemical manufacturing process in molten carbonates that produces only O2 as a process byproduct. [1]  However, focusing on mechanistic design of electrodes and catalysts inspired from over 10 years of Pint's experience in single-walled carbon nanotube synthesis [2], our team demonstrated the importance of iron catalyzed CNTs in this process, producing crystalline multi-walled CNTs with diameters near or below 30 nm [3], which is comparable to high volume (and low quality) CNTs industrially produced through fluidized bed and other gas phase synthesis methods.  Most recently, we have demonstrated the importance of controlling Ostwald ripening of catalysts in this process and shown multi-walled CNTs with small diameters < 10 nm with significant technological value, [4] and also the presence of some double-walled CNTs.  A key focus of our work that sets us apart from others working in CO2 conversion (other solid carbons, fuels, etc.) is the aim toward a highly energy efficient carbon neutral or negative process without needing to justify the necessity of geothermal or solar power sources that have no post-production carbon footprint, and the ability to tune the materials we produce based on scientific underpinnings combining electrochemistry and catalysis to target materials with value > $200/kg, which is the case with CNTs having high crystalline quality and small diameters.  

Ongoing Interests: We are working to overcome the scientific limitations of synthesizing single-walled CNTs and single-layered graphene, the most atomically precise and valuable materials in the world, from atmospheric carbon dioxide.  We are also exploring how electrochemistry tools can convert other greenhouse gases into carbon nanotubes, and how electrochemistry can be the golden bullet for a long-standing challenge of metallic carbon nanotube cloning, as originally envisioned by the late Prof. Richard Smalley.

[1] S. Licht, A. Douglas, J. Ren, R. Carter, M. Lefler, and C.L. Pint, “Carbon nanotubes produced from ambient carbon dioxide for environmentally sustainable lithium-ion and sodium-ion battery anodes,”  ACS Central Science 2, 162-168 (2016).
[2] A. Douglas and C.L. Pint, “Review – Electrochemical growth of carbon nanotubes and graphene from ambient carbon dioxide: Synergy with conventional gas-phase growth mechanisms,” ECS Journal of Solid State Science and Technology, 6, M3084-M3089 (2017).
[3] A. Douglas, R. Carter, N. Muralidharan, L. Oakes, and C.L. Pint, “Iron catalyzed growth of crystalline multi-walled carbon nanotubes from ambient carbon dioxide mediated by molten carbonates,” Carbon, 116, 572-578 (2017).
[4] A. Douglas, N. Muralidharan, R. Carter, and C.L. Pint, “Sustainable Capture and Conversion of Carbon Dioxide into Valuable Multi-Walled Carbon Nanotubes using Metal Scrap Materials,” ACS Sustainable Chemistry & Engineering, accepted (2017).

Multifunctional and Integrated Energy Systems

In modern battery research, researchers strive to improve the performance of a battery that will eventually be externally integrated into a system.  However, a passion that Prof. Pint has been pursuing for nearly a decade is to update how we think about system optimization with energy storage, for example.  In other words, can we design a system so that on the basis for which the individual components of that system are evaluated (e.g. gravimetric performance for batteries, mechanical performance for structural materials, etc.), can multiple externally situated components become integrated to improve or enhance the total overall system performance.  A key aspect of our efforts have been in the area of structural energy storage, e.g. combining active materials for energy storage into a structural composite material framework.  Pint's early team in this area has studied the importance of robust interfaces that dually function for reinforcement and energy storage in this framework and developed critical assessment routes for the simultaneous mechanical - electrochemical testing necessary for assessment of multifunctional energy storage[1].  Building from this, Pint's team has demonstrated practical design methods for a new class of structural supercapacitors, where carbon nanotubes grown onto and adhered to a structural framework can both reinforce a structural laminate and facilitate energy storage.  However, a key limitation of this approach is the low energy density of supercapacitors that has led the Pint team to focus on batteries.  The first battery template Pint's team has demonstrated is a structural Fe-Ni battery, which is coined an ultrabattery based on the use of nanoscale active materials that can charge/discharge very quickly.  This yielded a high energy density of active + inactive composite materials near 1.4 Wh/kg, which was the highest result reported to date in this area.  Most recently, Pint's team has overcome the many obstacles of producing the world's first carbon fiber reinforced lithium-ion structural battery.  This battery utilized traditional LFP and graphite electrode materials and demonstrated a phenomenal 35 Wh/kg energy density benchmarked against both the active energy storage materials and inactive composite materials.  Pint's team worked along with a team at NASA KSC to demonstrate the viability of this approach by designing a CubeSat satellite frame where the batteries where integrated into the panels of the structural frame, instead of contained on the interior of the satellite as a payload.  

Ongoing Interests: We are aggressively working to develop and design new methods for structural batteries by exploring how different methods for reinforcement can boost the mechanical properties and designing interfaces that maintain integrity under mechanical load cycling.  We are also working toward a vision for cohesive integration of multifunctional energy storage (and harvesting) materials and wireless energy transfer for what we envision as a core future technology for smart, autonomous systems in a world powered by big data.  

[1] A.S. Westover, J.W. Tian, S. Bernath, L. Oakes, R. Edwards, F.N. Shabab, S. Chatterjee, A. Anilkumar, and C.L. Pint, “A multifunctional load-bearing solid-state supercapacitor,” Nano Letters, 14, 3197-3202 (2014).
[2] A.S. Westover, B. Baer, B.H. Bello, H. Sun, L. Oakes, L. Bellan, and C.L. Pint, “Multifunctional high strength and high energy epoxy composite structural supercapacitors with wet-dry operational stability,” Journal of Materials Chemistry A  3, 20097-20102 (2015).
[3] A.P. Cohn, W.R. Erwin, K. Share, L. Oakes, A.S. Westover, R.E. Carter, R. Bardhan, and C.L. Pint, “All silicon electrode photo-capacitor for integrated energy storage and conversion,” Nano Letters 15, 2727-2731, (2015).
[4] A.S. Westover, K. Share, R. Carter, A.P. Cohn, L. Oakes, and C.L. Pint, “Direct integration of a supercapacitor into the backside of a silicon photovoltaic device,” Applied Physics Letters 104, 213905 (2014).
[5] T. Metke, A.S. Westover, R. Carter, L. Oakes, A. Douglas, and C.L. Pint, “Particulate-free porous silicon networks for efficient capacitive deionization water desalination,” Scientific Reports 6, 24680 (2016).