Direct Lithium Extraction Using Intercalation Materials.

Worldwide lithium demand has surged in recent years due to increased production of Li-ion batteries for electric vehicles and stationary storage. Li supply and production will need to increase such that the transition towards increased electrification in the energy sector does not become cost prohibitive. Many countries have taken policy steps such as listing Li as a critical mineral. Current commercial Li mining is mostly from dedicated mine sources, including ores, clays, and brines. The conventional ways to extract Li+ from those resources are through chemical processing and includes steps of calcination, leaching, precipitation, and purification. The environmental and economic sustainability of conventional Li processing has recently received increased scrutiny. Routes such as direct Li+ extraction may provide advantages relative to conventional Li+ extraction technologies, and one possible route to direct Li+ extraction includes leveraging intercalation materials. Intercalation material processing has recently demonstrated high selectivity towards Li+ as opposed to other cations. Reviews and reports of direct Li+ extraction with intercalation materials are limited, even as this technology has started to show promise in smaller-scale demonstrations. This paper will review selective Li+ extraction via intercalation materials, including both electrochemical and chemical methods to drive Li+ in and out, and efforts to characterize the Li+ insertion/deinsertion processes.

Stable Multicomponent Multiphase All Active Material Lithium-Ion Battery Anodes.

Due to their high energy density, lithium-ion batteries have been the state-of-the-art energy storage technology for many applications. Energy density can be further improved by engineering of the electrode architecture and microstructure, in addition to more common improvements via materials chemistry. All active material (AAM) electrodes consist of only the electroactive material that stores energy, and such electrodes have advantages to conventional composite processing with regards to improved mechanical stability at increased thicknesses and ion transport properties. However, the absence of binders and composite processing makes the electrode more vulnerable to electroactive materials with volume change upon cycling. Also, the electroactive material must have sufficient electronic conductivity to avoid large matrix electronic overpotentials during electrochemical cycling. TiNb2O7 (TNO) and MoO2 (MO) are electroactive materials with potential advantages as AAM electrodes due to relatively high volumetric energy density. TNO has higher energy density, and MO has much higher electronic conductivity, and thus a multicomponent blend of these materials was evaluated as an AAM anode. Herein, blends of TNO and MO as AAM anodes were investigated, where this is the first use of a multicomponent AAM anode. Electrodes that had both TNO and MO had the highest volumetric energy density, rate capability, and cycle life relative to single component TNO and MO anodes. Thus, using multicomponent materials provides a route to improve AAM electrochemical systems.

Thermodynamic Interactions as a Descriptor of Cross-Over in Nonaqueous Redox Flow Battery Membranes.

Grid-scale energy storage is increasingly needed as wind, solar, and other intermittent renewable energy sources become more prevalent. Redox flow batteries (RFBs) are well suited to this application because of the advantages in scalability and modularity over competing technologies. Commercial aqueous flow batteries often have low energy density, but nonaqueous RFBs can offer higher energy density. Nonaqueous RFBs have not been studied as extensively as aqueous RFBs, and the use of organic solvents and organic active materials in nonaqueous RFBs presents unique membrane separator challenges compared to aqueous systems. Specifically, organic active material cross-over, which degrades battery performance, may be affected by membrane/active material thermodynamic interactions in a fundamentally different way than ionic active material cross-over in aqueous RFB membranes. Hansen solubility parameters (HSPs) were used to quantify these interactions and explain differences in organic active material permeability properties. Probe molecules with a more unfavorable HSP-determined enthalpy of mixing with the membrane polymer exhibited lower permeability or cross-over properties. The HSP approach, which accounts for the uncharged polymer backbone and the charged side chain, revealed that interactions between the uncharged organic probe molecule and the hydrophobic polymer backbone were more important for determining permeability or cross-over properties than interactions between the probe molecule and the hydrophilic side chain. This result is significant for nonaqueous RFBs because it suggests a decoupling of ionic conduction expected to predominantly occur in charged polymer regions and cross-over of organic molecules via hydrophobic or uncharged polymer regions. Such decoupling is not expected in aqueous systems where active materials are often polar or ionic and both cross-over and conduction occur predominantly in charged polymer regions. For nonaqueous RFBs, or other membrane applications where selective organic molecule transport is important, HSP analysis can guide the co-design of the polymer separator materials and soluble organic molecules.

Thick Sintered Electrode Lithium-Ion Battery Discharge Simulations: Incorporating Lithiation-Dependent Electronic Conductivity and Lithiation Gradient Due to Charge Cycle.

In efforts to increase the energy density of lithium-ion batteries, researchers have attempted to both increase the thickness of battery electrodes and increase the relative fractions of active material. One system that has both of these attributes are sintered thick electrodes comprised of only active material. Such electrodes have high areal capacities, however, detailed understanding is needed of their transport properties, both electronic and ionic, to better quantify their limitations to cycling at higher current densities. In this report, efforts to improve models of the electrochemical cycling of sintered electrodes are described, in particular incorporation of matrix electronic conductivity which is dependent on the extent of lithiation of the active material and accounting for initial gradients in lithiation of active material in the electrode that develop as a consequence of transport limitations during charging cycles. Adding in these additional considerations to a model of sintered electrode discharge resulted in improved matching of experimental cell measurements.

Probing transport limitations in thick sintered battery electrodes with neutron imaging.

Lithium-ion batteries have received significant research interest due to their advantages in energy and power density, which are important to enabling many devices. One route to further increase energy density is to fabricate thicker electrodes in the battery cell; however, careful consideration must be taken when designing electrodes as to how increasing the thickness impacts the multiscale and multiphase molecular transport processes, which can limit the overall battery operating power. Design of these electrodes necessitates probing the molecular processes when the battery cell undergoes electrochemical charge/discharge. One tool for in situ insights into the cell is neutron imaging, because neutron imaging can provide information of where electrochemical processes occur within the electrodes. In this manuscript, neutron imaging is applied to track the lithiation/delithiation processes within electrodes at different current densities for a full cell with a thick sintered Li4Ti5O12 anode and LiCoO2 cathode. The neutron imaging reveals that the molecular distribution of Li+ during discharge within the electrode is sensitive to the current density, or equivalently discharge rate. An electrochemical model provides additional insights into the limiting processes occurring within the electrodes. In particular, the impact of tortuosity and molecular transport in the liquid phase within the interstitial regions in the electrodes are considered, and the influence of tortuosity was shown to be highly sensitive to the current density. Qualitatively, the experimental results suggest that the electrodes behave consistent with the packed hard sphere approximation of Bruggeman tortuosity scaling, which indicates that the electrodes are largely mechanically intact but also that a design that incorporates tunable tortuosity could improve the performance of these types of electrodes.

Chemoresponsive assemblies of microparticles at liquid crystalline interfaces.

Assemblies formed by solid particles at interfaces have been widely studied because they serve as models of molecular phenomena, including molecular self-assembly. Solid particles adsorbed at interfaces also provide a means of stabilizing liquid-liquid emulsions and synthesizing materials with tunable mechanical, optical, or electronic properties. Whereas many past studies have investigated colloids at interfaces of isotropic liquids, recently, new types of intercolloidal interactions have been unmasked at interfaces of liquid crystals (LCs): The long-range ordering of the LCs, as well as defects within the LCs, mediates intercolloidal interactions with symmetries that differ from those observed with isotropic liquids. Herein, we report the decoration of interfaces formed between aqueous phases and nematic LCs with prescribed densities of solid, micrometer-sized particles. The microparticles assemble into chains with controlled interparticle spacing, consistent with the dipolar symmetry of the defects observed to form about each microparticle. Addition of a molecular surfactant to the aqueous phase results in a continuous ordering transition in the LC, which triggers reorganization of the microparticles, first by increasing the spacing between microparticles within chains and ultimately by forming two-dimensional arrays with local hexagonal symmetry. The ordering transition of the microparticles is reversible and is driven by surfactant-induced changes in the symmetry of the topological defects induced by the microparticles. These results demonstrate that the orderings of solid microparticles and molecular adsorbates are strongly coupled at the interfaces of LCs and that LCs offer the basis of methods for reversible, chemosensitive control of the interfacial organization of solid microparticles.

Characterization of the reversible interaction of pairs of nanoparticles dispersed in nematic liquid crystals.

Observations of reversible interactions between pairs of chemically functionalized nanoparticles dispersed in nematic liquid crystals (LCs) are reported. In contrast to the irreversible association of microparticles in nematic LCs, by using gold nanoparticles and darkfield microscopy, particle tracking reveals the pairwise interactions of the nanoparticles in nematic LCs to be long-ranged and reversible. The measured range and strength of the pairwise interaction of the nanoparticles in the LCs was found to differ substantially from past theoretical predictions of nanoparticle interactions in LCs. The observation of reversible interactions between nanoparticles in LCs suggests that nematic LCs may provide new routes to spontaneous formation of ordered nanoparticle arrays.

Single nanoparticle tracking reveals influence of chemical functionality of nanoparticles on local ordering of liquid crystals and nanoparticle diffusion coefficients.

This letter reports that darkfield microscopy can be used to track the trajectories of chemically functionalized gold nanoparticles in nematic liquid crystals (LCs), thus leading to measurements of the diffusion coefficients of the nanoparticles in the LCs. These measurements reveal that the diffusion coefficients of the nanoparticles dispersed in the LC are strongly dependent on the surface chemistry of the nanoparticles. Because the changes in surface chemistry are measured to have negligible influence on the diffusion coefficients of the same nanoparticles dispersed in isotropic solvents, we conclude that surface chemistry-induced changes in the local order of LCs underlie the behavior of the diffusion coefficients of the nanoparticles in the LC. Surface chemistry-dependent ordering of the LCs near the surfaces of the nanoparticles was also found to influence diffusion coefficients measured when the LC was heated above the bulk nematic-to-isotropic transition temperature. These experimental measurements are placed into the context of past theoretical predictions regarding the impact of local ordering of LCs on diffusion coefficients. The results that emerge from this study provide important insights into the mobility of nanoparticles in LCs and suggest new approaches based on measurements of nanoparticle dynamics that can yield information on the ordering of LCs near nanoparticles.

Ordering of solid microparticles at liquid crystal-water interfaces.

We report a study of the organization of solid microparticles at oil-water interfaces, where the oil is a thermotropic liquid crystal (LC). The study was motivated by the proposition that microparticle organization and LC ordering would be coupled at these interfaces. Surfactant-functionalized polystyrene microparticles were spread at air-water interfaces at prescribed densities and then raised into contact with supported films of nematic 4-pentyl-4'-cyanobiphenyl (5CB). Whereas this method of sample preparation led to quantitative transfer of microparticles from the air-water interface to an isotropic oil-water interface, forces mediated by the nematic order of 5CB were observed to rapidly displace microparticles laterally across the interface of the water upon contact with nematic 5CB, thus leading to a 65% decrease in the density of microparticles at the LC-water interface. These lateral forces were determined to be caused by microparticle-induced deformation of the LC, the energy of which was estimated to be approximately 10(4) kT. We also observed microparticles transferred to the LC-water interface to assemble into chainlike structures that were not seen when using isotropic oils, indicating the presence of LC-mediated interparticle interactions at this interface. Optical textures of the LC in the vicinity of the microparticles were consistent with formation of topological defects with dipolar symmetry capable of promoting the chaining of the microparticles. The presence of microparticles at the interface also impacted the ordering of the LCs, including a transition from parallel to perpendicular ordering of the LC with increasing microparticle density. These observations, when combined, demonstrate that LC-mediated interactions can direct the assembly of solid microparticles at LC-water interfaces and that the ordering of the LC is also strongly coupled to the presence of microparticles.

Using localized surface plasmon resonances to probe the nanoscopic origins of adsorbate-driven ordering transitions of liquid crystals in contact with chemically functionalized gold nanodots.

We report that localized surface plasmon resonances (LSPRs) of gold nanodots immersed under liquid crystals (LCs) can be used to characterize adsorbate-induced ordering transitions of the LCs on the surfaces of the nanodots. The nanoscopic changes in ordering of the LCs, as measured by LSPR, were shown to give rise to macroscopic ordering transitions of the LCs that were observed by polarized light microscopy. The results reported herein suggest that (i) LCs may be useful for enhancing the sensitivity of LSPR-based detection of binding events and (ii) that LSPR measurements of gold nanodots provide a means to characterize the nanoscopic origins of macroscopic, adsorbate-induced LC ordering transitions.

Nanoparticles in nematic liquid crystals: interactions with nanochannels.

A mesoscale theory for the tensor order parameter Q is used to investigate the structures that arise when spherical nanoparticles are suspended in confined nematic liquid crystals (NLCs). The NLC is "sandwiched" between a wall and a small channel. The potential of mean force is determined between particles and the bottom of the channels or between several particles. Our results suggest that strong NLC-mediated interactions between the particles and the sidewalls of the channels, on the order of hundreds of k(B)T, arise when the colloids are inside the channels. The magnitude of the channel-particle interactions is dictated by a combination of two factors, namely, the type of defect structures that develop when a nanoparticle is inside a channel, and the degree of ordering of the nematic in the region between the colloid and the nanochannel. The channel-particle interactions become stronger as the nanoparticle diameter becomes commensurate with the nanochannel width. Nanochannel geometry also affects the channel-particle interactions. Among the different geometries considered, a cylindrical channel seems to provide the strongest interactions. Our calculations suggest that small variations in geometry, such as removing the sharp edges of the channels, can lead to important reductions in channel-particle interactions. Our calculations for systems of several nanoparticles indicate that linear arrays of colloids with Saturn ring defects, which for some physical conditions are not stable in a bulk system, can be stabilized inside the nanochannels. These results suggest that nanochannels and NLCs could be used to direct the assembly of nanoparticles into ordered arrays with unusual morphologies.