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- Proceedings of the National Academy of Sciences
- Medium: X
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- National Science Foundation
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Abstract Electrochemical intercalation can enable lithium extraction from dilute water sources. However, during extraction, co-intercalation of lithium and sodium ions occurs, and the response of host materials to this process is not fully understood. This aspect limits the rational materials designs for improving lithium extraction. Here, to address this knowledge gap, we report one-dimensional (1D) olivine iron phosphate (FePO 4 ) as a model host to investigate the co-intercalation behavior and demonstrate the control of lithium selectivity through intercalation kinetic manipulations. Via computational and experimental investigations, we show that lithium and sodium tend to phase separate in the host. Exploiting this mechanism, we increase the sodium-ion intercalation energy barrier by using partially filled 1D lithium channels via non-equilibrium solid-solution lithium seeding or remnant lithium in the solid-solution phases. The lithium selectivity enhancement after seeding shows a strong correlation with the fractions of solid-solution phases with high lithium content (i.e., Li x FePO 4 with 0.5 ≤ x < 1). Finally, we also demonstrate that the solid-solution formation pathway depends on the host material’s particle morphology, size and defect content.more » « less
Due to the high capacity of the three‐electron redox mechanism, Al‐ions‐based energy‐storage devices have the potential to provide a viable solution to meet the growing demand for powering electronic products. However, discovering suitable electrode materials for reversible insertion of Al ions remains a difficult task. Herein, it is reported that a classical conductive polymeric material poly(3,4‐ethylenedioxythiophene):poly(4‐styrenesulfonate) (PEDOT:PSS) can perform the reversible Al‐ions intercalation for aqueous electrochemical capacitors. The as‐prepared PEDOT:PSS film on a carbon cloth composite electrode exhibits a large magnitude of faradaic currents and sharp redox peaks in cyclic voltammetry (CV) curves in aluminum sulfate electrolyte, and delivers a high capacitance of 269 F g−1(78 mAh g−1). Diffusion‐controlled Al‐ions intercalation/deintercalation as the charge‐storage mechanism is demonstrated here, which is not observed in other ions‐based electrolytes (H+, Mg2+, Li+, Na+). An asymmetric electrochemical capacitor based on Al ions, composed of such an electrode and activated carbon electrode is assembled and displays a high energy density of 41.6 Wh kg−1at a power density of 0.24 kW kg−1, demonstrating a promising aqueous electrochemical capacitor with an advanced energy density via polyvalent ions intercalation.
The selective uptake of lithium ions is of great interest for chemists and engineers because of the numerous uses of this element for energy storage and other applications. However, increasing demand requires improved strategies for the extraction of this element from mixtures containing high concentrations of alkaline impurities. Here, we study solution phase interactions of lithium, sodium, and potassium cations with polyoxovanadate-alkoxide clusters, [V 6 O 7 (OR) 12 ] (R = CH 3 , C 3 H 7 , C 5 H 11 ), using square wave voltammetry and cyclic voltammetry. In all cases, the most reducing event of the cluster shifts anodically as the ionic radius of the cation decreases, indicating increased stability of the reduced cluster and further suggesting that these assemblies might be useful for the selective uptake of Li + . Exploring the consequence of ligand length, we found that the short-chain cluster, [V 6 O 7 (OCH 3 ) 12 ], irreversibly binds Li + in the presence of excess potassium (K + ) and exhibits an electrochemical response in titration experiments similar to that observed upon the addition of Li + to the POV–alkoxide in the presence of non-coordinating tetrabutylammonium ions. However, in the presence of excess sodium (Na + ), the cluster showed only a modest preference for lithium, with exchange between sodium and lithium ions governed by equilibrium. Extending these studies to [V 6 O 7 (OC 5 H 11 ) 12 ], we found that the presence of the pentyl ligands allows the assembly to irreversibly bind Li + in the presence of Na + or K + . The change in mechanism caused by surface functionalization of the clusters increases the differential binding affinity for more compact cations, translating to improved selectivity for Li + uptake in these molecular assemblies.more » « less
Metal-ion batteries (e.g., lithium and sodium ion batteries) are the promising power sources for portable electronics, electric vehicles, and smart grids. Recent metal-ion batteries with organic liquid electrolytes still suffer from safety issues regarding inflammability and insufficient lifetime.1 As the next generation energy storage devices, all-solid-state batteries (ASSBs) have promising potentials for the improved safety, higher energy density, and longer cycle life than conventional Li-ion batteries.2 The nonflammable solid electrolytes (SEs), where only Li ions are mobile, could prevent battery combustion and explosion since the side reactions that cause safety issues as well as degradation of the battery performance are largely suppressed. However, their practical application is hampered by the high resistance arising at the solid–solid electrode–electrolyte interface (including cathode-electrolyte interface and anode-electrolyte interface).3 Several methods have been introduced to optimize the contact capability as well as the electrochemical/chemical stability between the metal anodes (i.e.: Li and Na) and the SEs, which exhibited decent results in decreasing the charge transfer resistance and broadening the range of the stable energy window (i.e., lowing the chemical potential of metal anode below the highest occupied molecular orbital of the SEs).4 Nevertheless, mitigation for the cathode in ASSB is tardily developed because: (1) the porous structure of the cathode is hard to be infiltrated by SEs;5 (2) SEs would be oxidized and decomposed by the high valence state elements at the surface of the cathode at high state of charge.5 Herein, we demonstrate a universal cathode design strategy to achieve superior contact capability and high electrochemical/chemical stability with SEs. Stereolithography is adopted as a manufacturing technique to realize a hierarchical three-dimensional (HTD) electrode architecture with micro-size channels, which is expected to provide larger contact areas with SEs. Then, the manufactured cathode is sintered at 700 °C in a reducing atmosphere (e.g.: H2) to accomplish the carbonization of the resin, delivering sufficiently high electronic conductivity for the cathode. To avoid the direct exposure of the cathode active materials to the SEs, oxidative chemical vapor deposition technique (oCVD) is leveraged to build conformal and highly conducting poly(3,4-ethylenedioxythiophene) (PEDOT) on the surface of the HTD cathode.6 To demonstrate our design strategy, both NCM811 and Na3V2(PO4)3 is selected as active materials in the HTD cathode, then each cathode is paired with organic (polyacrylonitrile-based) and inorganic (sulfur-based) SEs assembled into two batteries (total four batteries). SEM and TEM reveal the micro-size HTD structure with built-in channels. Featured by the HTD architecture, the intrinsic kinetic and thermodynamic conditions will be enhanced by larger surface contact areas, more active sites, improved infusion and electrolyte ion accessibility, and larger volume expansion capability. Disclosed by X-ray computed tomography, the interface between cathode and SEs in the four modified samples demonstrates higher homogeneity at the interface between the cathode and SEs than that of all other pristine samples. Atomic force microscopy is employed to measure the potential image of the cross-sectional interface by the peak force tapping mode. The average potential of modified samples is lower than that of pristine samples, which confirms a weakened space charge layer by the enhanced contact capability. In addition, through Electron Energy Loss Spectroscopy coupled with Scanning Transmission Electron Microscopy, the preserved interface between HTD cathode and SE is identified; however, the decomposing of the pristine cathode is clearly observed. In addition, Finite element method simulations validate that the diffusion dynamics of lithium ions is favored by HTD structure. Such a demonstrated universal strategy provides a new guideline to engineer cathode electrolyte interface by reconstructing electrode structures that can be applicable to all solid-state batteries in a wide range of chemical conditions.more » « less
Transition metal dichalcogenides (TMDs) are a class of 2D materials demonstrating promising properties, such as high capacities and cycling stabilities, making them strong candidates to replace graphitic anodes in lithium-ion batteries. However, certain TMDs, for instance, MoS2, undergo a phase transformation from 2H to 1T during intercalation that can affect the mobility of the intercalating ions, the anode voltage, and the reversible capacity. In contrast, select TMDs, for instance, NbS2and VS2, resist this type of phase transformation during Li-ion intercalation. This manuscript uses density functional theory simulations to investigate the phase transformation of TMD heterostructures during Li-, Na-, and K-ion intercalation. The simulations suggest that while stacking MoS2layers with NbS2layers is unable to limit this 2H → 1T transformation in MoS2during Li-ion intercalation, the interfaces effectively stabilize the 2H phase of MoS2during Na- and K-ion intercalation. However, stacking MoS2layers with VS2is able to suppress the 2H → 1T transformation of MoS2during the intercalation of Li, Na, and K-ions. The creation of TMD heterostructures by stacking MoS2with layers of non-transforming TMDs also renders theoretical capacities and electrical conductivities that are higher than that of bulk MoS2.