Tuning binder dissolution dynamics yields distinct structural states, promoting binder shell formation that confines sulfur and suppresses polysulfide loss.

The quest for high-performance lithium-ion batteries (LIBs) hinges on the continuous improvement of cathode materials. Dr. Marca Doeff's seminal contributions have propelled this approach, inspiring novel cathode materials. By studying the intricate interactions between cathode particles, coatings, and the solid electrolyte interphase (SEI) layer, we aim at engineering a high-energy-density and long-lasting next generation lithium-ion battery. We explore the latest advancements in cathode materials, with a focus on LiFePO4, LiMnFePO4, NCM811, and Li-S, introducing surface modifications by graphene and ALD coatings. Dr. Doeff's research has demonstrated the efficacy of carbon coatings in enhancing the rate capability and cycling stability of LFP-based batteries [1]. NCM811 is the most promising cathode material due to its high specific capacity and energy density, however, issues such as structural instability and capacity fading hinder its practical application. Through meticulous optimization of ALD coatings, our group has mitigated these challenges, leading to enhanced electrochemical performance and prolonged cycle life [2]. Li-S batteries offer a high theoretical specific capacity and low cost, making them attractive candidates for next-generation energy storage systems, however, polysulfide dissolution and shuttle effects pose significant challenges, limiting their practical viability. By leveraging ALD techniques, our group has engineered active coatings to enhance polysulfides conversion and stabilize the cathode cycling ability. The formation and stability of the SEI layer play a pivotal role in dictating the overall performance and safety of lithium-ion batteries. Graphene coatings and ALD treatments exert a profound influence on SEI layer formation, influencing ion transport kinetics, surface reactions, and interfacial stability. Graphene coatings not only enhance electronic conductivity but also modulate the SEI layer composition and morphology. Through synergistic interactions with electrolyte components, graphene coatings promote the formation of a robust and homogeneous SEI layer, thereby suppressing parasitic reactions and capacity degradation. ALD-enabled coatings offer precise control over film thickness and composition, enabling engineered interfaces with superior electrochemical performance. By depositing conformal ALD layers onto cathode surfaces, we can engineer SEI layers with enhanced chemical stability and ion permeability, leading to improved cyclability and safety. Dr. Marca Doeff's enduring legacy in lithium-ion battery research continues to inspire groundbreaking advancements in cathode material engineering. Through meticulous design and characterization of the cathode SEI layer, coupled with innovative materials engineering techniques, we are positioned at the forefront of electrochemistry to produce batteries with enhanced performance and cycle life. [1] MM Doeff et al. "Optimization of carbon coatings on LiFePO4," Journal of Power Sources 163 (1), 2006, 180-184. [2] D Mohanty et al. “Modification of Ni-Rich FCG NMC and NCA Cathodes by Atomic Layer Deposition: Preventing Surface Phase Transitions for High-Voltage Lithium-Ion Batteries,” Sci Rep 6, 26532 (2016).

The performance of Lithium-Sulfur (Li-S) batteries is significantly influenced by material selection and manufacturing processes, with conductive carbon and slurry formulation playing crucial roles. In this study, the impact of carbon morphology and solvent/solid ratio in slurry preparation on microstructure and electrochemical performance of sulfur cathodes was investigated. Various carbon structures, such as nanotubes, sheets, and particles, were explored, and the solvent volume was adjusted to assess their effects on electrode architecture and electrochemical performance. Our findings demonstrate that the binder dissolution process and consequent electrode architecture and performance are highly influenced by both the carbon structure and slurry solvent volume. Furthermore, it was observed that, contrary to common assumption, advanced carbon structures are not necessary for enhanced capacity and durability of Li-S cathodes. Accordingly, the best cycling durability was achieved by optimizing the slurry with 300 mu L/mgPVDF of NMP solvent and using Ketjen black as the conductive carbon, resulting in an initial capacity of 1029 mAh gS-1, with a retention of 830 mAh gS-1 after 500 cycles. These results, obtained at a high areal loading of 4.5 mgS cm-2, demonstrate the commercial potential of the proposed electrode formulation and processing method without reliance on advanced materials or techniques.

Lithium-sulfur has been identified as one of the most promising lithium battery chemistries to achieve performance requirements that enable next-generation electrified applications, such as satellite miniaturization and long duration electrified aviation, with a completely U.S.-centric supply-chain [1] . In general, the dissolution and shuttling of intermediate lithium polysulfide (Li2Sx, 4 < x < 8) phases in current- and prior-generation Li-S batteries have limited sulfur utilization (<60%) and led to rapid lifetime degradation [2] . Substantial progress has occurred in C/S composites with sulfur utilization exceeding 60% using various sulfur dispersion and carbon support selection [3] [4] , though commercialization has been fraught with difficulties. NantG Power is pursuing novel routes to overcome many of the cell-scaling issues with the use of carbon substrate materials modified with sub-nanometer thick catalyst coatings to both accelerate the Solid -> Liquid and Liquid -> Solid phase transformations, as well as act as polar tethering sites for polysulfides. ALD has been shown to improve cathode stability in traditional Li-ion [5] and has been used to cap traditional C/S composite particles and electrodes [6] . These coatings, prepared with powder atomic-layer deposition (ALD), immobilize the intermediate polysulfides while simultaneously catalyzing their otherwise sluggish reaction kinetics of the multi-phase reactions. With this method, long-term sulfur utilization above 60% can be demonstrated in multi-Ah cells with >5mg/cm2/>60% sulfur loading and E:S < 5, exceeding 400 Wh/kg. This talk will outline a combination of computational modeling approaches (MD, AIMD, DFT, etc.) that predicts the energetic and lattice matching of highly disordered, sub nanometer ALD coatings coupled with electrochemical/chemical/physical interrogation and 1Ah test cell builds to highlight the promise of this reasonably novel direction. References: [1] Z. W. Seh, Y. Sun, Q. Zhang, and Y. Cui, “Designing high-energy lithium-sulfur batteries,” Chemical Society Reviews, vol. 45, no. 20. 2016. doi: 10.1039/c5cs00410a. [2] L. Peng et al., “A fundamental look at electrocatalytic sulfur reduction reaction,” Nat Catal, vol. 3, no. 9, 2020, doi: 10.1038/s41929-020-0498-x. [3] M. K. Song, Y. Zhang, and E. J. Cairns, “A long-life, high-rate lithium/sulfur cell: A multifaceted approach to enhancing cell performance,” Nano Lett, vol. 13, no. 12, 2013, doi: 10.1021/nl402793z. [4] Y. Hwa et al., “Three-Dimensionally Aligned Sulfur Electrodes by Directional Freeze Tape Casting,” Nano Lett, vol. 19, no. 7, 2019, doi: 10.1021/acs.nanolett.9b01805. [5] D. M. King, J. E. Trevey, P. R. Lichty, S.-J. Cho, K. Dahlberg, and F. Albano, “Low-Cost Manufacturing of Safe, Long-Life Battery Materials Using Atomic Layer Deposition,” ECS Meeting Abstracts, vol. MA2016-03, no. 2, 2016, doi: 10.1149/ma2016-03/2/241. [6] B. Yan et al., “A review of atomic layer deposition providing high performance lithium sulfur batteries,” Journal of Power Sources, vol. 338. 2017. doi: 10.1016/j.jpowsour.2016.10.097.

Lithium-Sulfur (Li-S) batteries are among the popular candidates for next-generation rechargeable energy storage devices due to their high specific capacity and superior energy storage capabilities. However, commercialization of Li-S batteries has been hindered by several challenges such as the insulating nature of sulfur, and the shuttling of soluble lithium polysulfides and accumulation of insulating deposits on the electrodes – leading to capacity degradation over extended cycling1. Several research efforts have been devoted to mitigating these challenges. Among the different approaches, many studies focus on addressing the poor conductivity of sulfur and lithium polysulfide shuttling simultaneously by developing conductive carbon hosts2,3. While improvements have been achieved in the development of host structures with better electronic conductivity and improved polysulfide trapping capability, many of those structures have advanced architectures that demand complex processing, expensive precursors, and often lower gravimetric sulfur loading (<70 wt%).This leads to expensive-to-produce electrodes that have lower true energy density than desired. What is needed are simple preparation methods that address the issues discussed above without overly complicated processing, and preferably already commercialized materials. In this work, we systematically investigate the effect of different electrode components, including various common carbons and polymeric binders. The effect of carbon type and loading is discussed. The effect of solvent to binder ratio in the electrode slurry preparation is also studied. By tuning the binder composition, types of conductive carbon black, and the amount of solvent, we observed a difference in the structure of the host medium and consequently the sulfur electrode. Specifically, a shell covering surrounding the sulfur particles was observed at low solvent/binder ratio. Increasing the solvent/binder ratio led to the disappearance of the shell coverings and particle agglomeration, which resulted in lower achieved capacity and reduced cycle life. Ketjen black offered the highest specific capacity, while the presence of shell covering achieved at a low solvent/binder ratio was found necessary for cycling stability. This work demonstrates the importance of electrode processing parameters on the structure and electrochemical performance of sulfur cathode in Li-S batteries. The new understandings from this work can provide guidance on electrode designs to achieve Li-S batteries with enhanced capacity and longevity. References G. Li et al., Adv. Mater., 30, 1705590 (2018). D.-W. Wang et al., J. Mater. Chem. A, 1, 9382 (2013). Y. Li and S. Guo, Matter, 4, 1142–1188 (2021).

Polynobornene (PNBE), a material commonly used in your shoes or for the tires of supercars, can also be highly influential to the development of next-generation batteries (Kim et al., 2022). When designing the batteries of tomorrow, we are interested in polymeric materials with precisely defined dynamic mechanical properties, increased ionic or conductivity, specific chemical interactions and moonshots like stable and healable interfaces (Lopez et al., 2019). PNBE provides high chemical and thermal stability, low shrinkage, and strong adhesion properties that lead to enhanced electrode stability and electrical conductivity(Le et al., 2020). Possessing a highly flexible nature allows PNBE to conform to the shape of an electrode – making PNBE an ideal multifunctional binder. Consider some persisting problems associated with batteries, for example Si electrodes typically fail due to cracks in the Si particles creating new surfaces for electrolyte decomposition/solid electrolyte interphase formation, and due to the Si becoming electrically disconnected from the rest of the electrode and ultimately terminating cycling (Ryu et al., 2004) . PNBE can address both aforementioned pain points, low shrinkage and flexibility can help mitigate the impact of cracking that occurs within an electrode over time by maintaining the structural integrity, and strong adhesion properties promote effective binding of the active material and the rest of the electrode. With increasing concerns about cobalt, there has been a move to replace oxides with phosphates. Substituting a substantial fraction of Mn, for Fe in LiFePO 4 leads to a material with an energy density approaching that of the oxides, while substantially lessening environmental concerns. Unfortunately, Mn dissolution causes a poor cycle lifetime. In an effort to reduce Mn dissolution, a mixture of PNBE and PVDF was used as a binder system. The PNBE was designed to have ether-type comb-branch functionalities that aid in Mn trapping, while the PVDF had suitable viscosity and mechanical properties. Figure 1 shows cycle lifetime results conducted at 45°C on a 2Ah LMFP-Graphite cell containing a 4%PVDF/1%PNBE binder system. The results show very good lifetime, with the capacity retention nearly 90% after 1,000 cycles. Given the difficulty with cycling of LMFP due to Mn dissolution, these results show good promise for this approach. This talk will highlight the opportunities and challenges of custom and enabling PNBE binder systems for LMFP, and other battery systems. References Kim, N.-Y., Moon, J., Ryou, M.-H., Kim, S.-H., Kim, J.-H., Kim, J.-M., Bang, J., & Lee, S.-Y. (2022). Amphiphilic Bottlebrush Polymeric Binders for High-Mass-Loading Cathodes in Lithium-Ion Batteries. Advanced Energy Materials , 12 (1), 2102109. https://doi.org/https://doi.org/10.1002/aenm.202102109 Le, D., Samart, C., Lee, J.-T., Nomura, K., Kongparakul, S., & Kiatkamjornwong, S. (2020). Norbornene-Functionalized Plant Oils for Biobased Thermoset Films and Binders of Silicon-Graphite Composite Electrodes. ACS Omega , 5 (46), 29678–29687. https://doi.org/10.1021/acsomega.0c02645 Lopez, J., Mackanic, D. G., Cui, Y., & Bao, Z. (2019). Designing polymers for advanced battery chemistries. Nature Reviews Materials , 4 (5), 312–330. https://doi.org/10.1038/s41578-019-0103-6 Ryu, J. H., Kim, J. W., Sung, Y.-E., & Oh, S. M. (2004). Failure Modes of Silicon Powder Negative Electrode in Lithium Secondary Batteries. Electrochemical and Solid-State Letters , 7 (10), A306. https://doi.org/10.1149/1.1792242 Figure 1

Microstructure and surface moieties of porous carbons play a significant role in affecting their performance in a variety of applications. While it is well known that high-temperature treatments of porous carbons can influence the microstructure, no systematic studies have been done on carbide-derived carbons. We show that vacuum annealing increases the pore volume and specific surface area of titanium carbide-derived carbon with no significant change in the pore size up to 1500°C. This treatment produces porous carbons with subnanometer porosity and a specific surface area up to 2000m2/g, while treating the samples at temperatures above 1600°C increases the pore size above 1nm because of graphitization and collapse of the micropore structure. The results demonstrate that vacuum treatment can be used to further tune the pore structure and potentially the surface functionality of carbide-derived carbons for supercapacitor electrodes, gas chromatography, sorption, sensing and other applications. Vacuum annealing of carbide-derived carbon is therefore a suitable alternative to conventional microstructure modification methods, such as gas or liquid phase activation, which are subject to substantial sample loss and result in additional surface functionalization.

Microbatteries with dimensions of tens to hundreds of micrometers that are produced by common microfabrication techniques are poised to provide integration of power sources onto electronic devices, but they still suffer from poor cycle lifetime, as well as power and temperature range of operation issues that are alleviated with the use of supercapacitors. There have been a few reports on thin-film and other micro-supercapacitors, but they are either too thin to provide sufficient energy or the technology is not scalable. By etching supercapacitor electrodes into conductive titanium carbide substrates, we demonstrate that monolithic carbon films lead to a volumetric capacity exceeding that of micro- and macroscale supercapacitors reported thus far, by a factor of 2. This study also provides the framework for integration of high-performance micro-supercapacitors onto a variety of devices.

This paper presents the results from the investigation of the influence of ion size on the capacitance behaviour of TiC-derived carbon (CDC) powders in the ethyl-methylimmidazolium-bis(trifluoro-methane-sulfonyl)imide ionic liquid (EMI, TFSI) used as neat electrolyte at 60°C or as salt dissolved in acetonitrile and tested at room temperature. These studies were carried out with the assembly of conventional 3-electrode electrochemical cells as well as using the Cavity-MicroElectrode (CME) technique. The issues regarding the extents of desolvation of the electrolyte ions when adsorbed in the pores of the CDCs under applied potential were studied, the CME technique was found to be particularly efficient in the deduction of the effective ion size under solvated conditions.

Supercapacitors have the ability to deliver an order of magnitude more power than batteries. However, at the present, they are more expensive than batteries and not widely available. Supercapacitors have the capability to be more energy efficient and powerful than batteries and in some cases they will complement or displace batteries. The goal of this project was to develop a method of simple assembly of efficient yet cheap supercapacitors, which could be assembled outside a laboratory by anyone. These supercapacitors could be used as demonstrations or models of simple devices for capacitive energy storage, but in the future could be used in homes or in developing countries and remote locations.