Hunter O. Ford

Alkali-rich transition-metal chalcogenides offer the opportunity to tap both cation- and anion-centered redox reactions for high-capacity, reversible charge-storage when used in the cathodes of advanced rechargeable batteries. A prime example is Li₂FeS₂, in which sulfide/persulfide redox augments Fe^2+/3+ reactions to support Li⁺-storage capacity >350 mAh g^–1 [1]. We recently introduced a new synthetic pathway to Li₂FeS₂ that is based on redox-mediated lithiation of FeS₂, as facilitated by select organic reducing agents [2]. With this approach, we are able to generate Li₂FeS₂ in nanometric and architecture-supported forms that are not achievable with conventional high-temperature, solid-state synthesis. We now extend such concepts to controlled chemical sodiation of FeS₂, with the goal of generating new Na₂FeS₂ structures that serve as high-capacity cathode materials for Na-ion batteries. The electrochemical characteristics of Na₂FeS₂ are evaluated in Na half-cells to determine fundamental and battery-relevant characteristics, including current–potential profile, capacity, reversibility, and rate capability. We assess the electronic and structural properties of these Na₂FeS₂ materials with X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD). In situ XAS and XRD measurements with prototype pouch cells and coin cells provide further insight to deconvolve multi-site redox mechanisms and track structural changes during Na-ion insertion/deinsertion reactions.

Straightforward low-temperature chemical synthesis of Na-ion storing compound Na ₂ FeS ₂ (>250 mAh g ⁻¹ ) that exhibits anion- and cation-sited redox.

Next-generation rechargeable zinc-based batteries require efficient deposition and stripping (D/S) of Zn in mild-pH aqueous electrolyte. With the move away from conversion of bulk Zn electrodes, the properties of D/S substrates, such as surface functionality and electrode architecture, can impact Zn redox processes. To investigate these effects, we adapt planar and 3D pyrolytic carbon (pyC) substrates previously reported for fundamental electroanalytical studies. Thin films of pyC are fabricated by benzene pyrolysis, yielding a low oxygen-content, oleophobic surface that can be further functionalized by plasma oxidation and nitridation or with heteroatom doping by adding precursors such as thiophene to the benzene feed. We evaluate Zn/Zn²⁺ redox at a series of pyC electrodes with varied surface characteristics, cycling in either zinc sulfate (ZnSO₄) or zinc acetate (Zn(OAc)₂) mild-pH aqueous electrolytes of relevance to “zinc-ion” batteries. Characteristics such as wettability, deposition morphology, Zn D/S reversibility, and coulombic efficiency are correlated with pyC surface functionality. Aromatic sulfur doping followed by plasma nitridation (pyC∼S:N) yields the best balance of uniform Zn electrodeposition and effective electrostripping from the substrate: a two-terminal cell charges/discharges at >98% coulombic efficiency for >350 cycles. We then conformally coat macroscale thick fiber-paper electrodes with pyC and plate Zn at 1, 5, and 10 mAh cm⁻². Even at 10 mAh cm⁻², 3D pyC electrodes deposit Zn without a charge-transfer resistance penalty, confirming the viability of such pyC architected electrodes for practical areal capacity.

This work is the first to describe an electrically conductive phthalonitrile (PN) polymer, extending novel properties to this class of high‐performance polymers. This novel resin was synthesized by integrating a conductive oligoaniline backbone with phthalonitrile termini, resulting in modest electrical conductivity (10 ⁻⁶ –10 ⁻⁵ S cm ⁻¹ ) in both uncured (heated only to 175°C) and cured (heated to 350+°C) states when doping with ≥ 25 mol% of a Lewis acid (e.g., CuCl ₂ ·2H ₂ O). The oligoaniline backbone imparts exceptional curing rates while retaining the thermal robustness associated with conventional phthalonitrile resins. Thermal analyses demonstrate excellent thermo‐oxidative stability with a char yield of 76% at 1000°C and good processability of the pre‐cured resin. The synergistic combination of electrical conductivity and superior thermal stability not only expands the scope of PN materials but also positions this new phthalonitrile resin as a promising candidate for next‐generation aerospace, military, and energy storage applications where both thermal stability and efficient electron transport are critical.

Synthesis of lithium-rich iron sulfide is achieved through redox-mediated chemical lithiation of pyrite FeS₂.

Decarbonizing our energy infrastructure will require implementing battery chemistries beyond lithium-ion that are safe-to-operate and contain non-strategic materials. Silver–zinc, a decades-old battery technology with competitive energy and power density to Li-ion, has been used in both the military and civilian sector, but its widespread adoption is hindered by its poor reversibility and short lifespan. Realizing highly reversible, long cycle life, rechargeable Ag–Zn batteries entails simultaneously addressing two challenges: (i) suppressing shape change at the Zn metal anode that leads to dendrite-driven short-circuits, and (ii) suppressing Ag dissolution and migration out of the cathode. With the issues of shape change at the Zn anode solved by recent advancements in electrode architecture by our group,¹ we turn our attention to the design of solid-state polymer electrolytes that suppress Ag dissolution and migration. We report on the synthesis and characterization of a suite of alkaline quaternary ammonium-based single-ion conducting polymer electrolytes suitable for use in Ag–Zn batteries. Specifically, we investigate the link between polymer chemistry and structure on ion transport via systematic tailoring of functional groups within the electrolyte. With these simple structural modifications, we can tune the Ag redox mechanism to shift equilibria away from the formation of Ag complexes responsible for dissolution and migration. By combining solid-state polymer electrolytes that suppress Ag transport with an NRL-patented Zn sponge anode, we demonstrate a high capacity, rechargeable Ag–Zn cell. These results serve as the foundation of a new class of solid-state polymer electrolytes to enable advanced rechargeable Ag–Zn batteries. (1) Parker, Joseph F., et al. "Wiring zinc in three dimensions re-writes battery performance–dendrite-free cycling." Energy & Environmental Science 7.3 (2014): 1117-1124.

The non-line-of-sight nature of initiated chemical vapor deposition (iCVD) makes it an amenable technique for depositing thin, conformal polymer films on three-dimensional (3D) high surface-area substrates. Adding to the versatility of iCVD, we process the deposited film in situ to impart additional functionality. Herein we describe fabricating submicron-thick positively charged polymer films with labile anions, a class of materials that brings ion-transport regulation to water desalination, gas separations, and energy-storage systems. Coatings of iCVD-deposited poly(4-dimethylaminomethylstyrene) (pDMAMS) on planar and 3D substrates are reacted with an alkylating/cross-linking reagent to yield quaternary ammonium-containing pDMAMS⁺. By optimizing deposition conditions, we demonstrate conformal coatings of pDMAMS and pDMAMS⁺ spanning a thickness range of 30–1000+ nm. Chemical and mechanical characterization confirms the successful quaternization of the iCVD-generated films, subsequent ion exchange of various counterions (Br⁻, HCO₃ ⁻, and OH⁻), and enhanced modulus of the crosslinked pDMAMS⁺ polymer. The use of grazing-incidence X-ray scattering reveals the films are noncrystalline and contain ion clusters with anion-dependent geometry. By understanding the impact of deposition conditions and functionalization on subsequent physicochemical-mechanical properties, we lay the groundwork for using iCVD-derived pDMAMS⁺ films in targeted applications.