Sustainable lithium extraction enabled by responsive metal-organic frameworks with ion-sieving adsorption effects.

Metal-organic frameworks (MOFs) are superior ion adsorbents for selectively capturing toxic ions from water. Nevertheless, they have rarely been reported to have lithium selectivity over divalent cations due to the well-known flexibility of MOF framework and the similar physiochemical properties of Li+ and Mg2+. Herein, we report an ion-sieving adsorption approach to design sunlight-regenerable lithium adsorbents by subnanoporous MOFs for efficient lithium extraction. By integrating the ion-sieving agent of MOFs with light-responsive adsorption sites of polyspiropyran (PSP), the ion-sieving adsorption behaviors of PSP-MOFs with 6.0, 8.5, and 10.0 Å windows are inversely proportional to their pore size. The synthesized PSP-UiO-66 with a narrowest window size of 6.0 Å shows high LiCl adsorption capacity up to 10.17 mmol g-1 and good Li+/Mg2+ selectivity of 5.8 to 29 in synthetic brines with Mg/Li ratio of 1 to 0.1. It could be quickly regenerated by sunlight irradiation in 6 min with excellent cycling performance of 99% after five cycles. This work sheds light on designing selective adsorbents using responsive subnanoporous materials for environmentally friendly and energy-efficient ion separation and purification.

X-ray Spectroscopy Study of Defect Contribution to Lithium Adsorption on Porous Carbon.

Lithium adsorption on high-surface-area porous carbon (PC) nanomaterials provides superior electrochemical energy storage performance dominated by capacitive behavior. In this study, we demonstrate the influence of structural defects in the graphene lattice on the bonding character of adsorbed lithium. Thermally evaporated lithium was deposited in vacuum on the surface of as-grown graphene-like PC and PC annealed at 400 °C. Changes in the electronic states of carbon were studied experimentally using surface-sensitive X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. NEXAFS data in combination with density functional theory calculations revealed the dative interactions between lithium sp2 hybridized states and carbon π*-type orbitals. Corrugated defective layers of graphene provide lithium with new bonding configurations, shorter distances, and stronger orbital overlapping, resulting in significant charge transfer between carbon and lithium. PC annealing heals defects, and as a result, the amount of lithium on the surface decreases. This conclusion was supported by electrochemical studies of as-grown and annealed PC in lithium-ion batteries. The former nanomaterial showed higher capacity values at all applied current densities. The results demonstrate that the lithium storage in carbon-based electrodes can be improved by introducing defects into the graphene layers.

Calix[4]arene-Decorated Covalent Organic Framework Conjugates for Lithium Isotope Separation.

Lithium isotope separation has attracted extensive interest due to its important role in fusion and fission reactions. Up to now, it is still a great challenge to separate lithium isotopes (6Li and 7Li) in an efficient manner due to the low capture ability for lithium ions of related materials and highly similar physicochemical properties between lithium isotopes. In this work, three calix[4]arene-decorated crystalline covalent organic frameworks (COFs) with wave-like extension and AA-stacking configuration were designed and utilized for lithium adsorption and its isotope separation. Experimental studies show that these COFs exhibit an outstanding lithium adsorption capacity up to 94.66 mg·g-1, which is about 2 times beyond that of adsorbents reported in the literature. The high adsorption capacity of COFs could be attributed to the abundant adsorption sites from calix[4]arene unit. More importantly, this study demonstrates for the first time that calixarene groups can separate lithium isotopes with an excellent separation factor up to 1.053 ± 0.002, comparable to the most successful solid-phase lithium separation adsorbent. The calculation based on density functional theory showed that calixarene played an important role in the lithium adsorption. Interestingly, the lithium isotope separation performance is mainly affected by the amine bridging units. This work demonstrated that calixarene COFs are promising adsorbents for lithium isotope separation.

MnO2-decorated biochar composites of coconut shell and rice husk: An efficient lithium ions adsorption-desorption performance in aqueous media.

Lithium (Li+) is used in various applications involving pharmaceuticals, textile dyes, and batteries. Therefore, the demand for environmentally friendly and effective materials for Li+ uptake and recovery continues to increase. Herein, rice husk (RH) and coconut shell (CS) biomasses were used to fabricate honeycomb-networked biochar (BC) precursors via slow pyrolysis. RHBC- and CSBC-based MnO2 composites were synthesized by depositing MnO2 in various ratios onto RHBC and CSBC by varying the KMnO4 concentration (2%, 3%, and 4%), followed by simple ultrasonication and heat-treatment methodologies. The structural and physicochemical properties of all of the fabricated composites were analyzed using several different instrumental methods. The batch adsorption experiments were performed for comparative Li+-adsorption studies of RHBC-Mnx and CSBC-Mnx composites by optimizing several parameters (pH, adsorbent dose, Li+ initial concentration, and contact time). The comparative adsorption analysis revealed that the RHBC-Mnx composites exhibited stronger Li+-adsorption ability than the CSBC-Mnx composites and that increasing the MnO2 deposition to 3% in both cases led to maximum Li+ adsorption capacities (62.85 mg g-1 and 57.8 mg g-1), respectively. The kinetic studies show that Li+ adsorption proceeds through the pseudo-second-order mechanism. Li+ recovery was successfully carried out using HCl (eluting agent), thereby demonstrating the benefits of synthesized composites at the industrial scale. The current work indicates that the fabricated RHBC-Mnx and CSBC-Mnx composites may have potential for use as economical composites in eco-friendly applications such as Li+ adsorption and recovery from aqueous media.

Effects of excessive lithium deintercalation on Li+ adsorption performance and structural stability of lithium/aluminum layered double hydroxides.

Lithium/aluminum layered double hydroxides (Li/Al-LDHs) have been industrially proven to be recyclable lithium adsorbents that do not dissolve upon elution, although they are hypersensitive to lithium deintercalation. In this study, the Li+ adsorption performances and structural stabilities of Li/Al-LDHs samples with different lithium deintercalation intensities are comprehensively investigated and compared to expose the influence of excessive lithium deintercalation. The characterization results demonstrate that Li/Al-LDHs are inclined to transform to gibbsite under excessive lithium deintercalation. Moreover, this transformation is enhanced by a long deintercalation time at 80 °C in deionized water because the layered structure of Li/Al-LDHs collapses upon reduction of the lithium content. The Li+ adsorption kinetics and isotherms reveal that excessive lithium deintercalation has no effect on the adsorption pathway and rate, while the adsorption capacity fluctuates with increased lithium loss on account of the conflict between the generation of Li+ active sites and structural damage. Adsorption experiments at different pH values show that a neutral pH is more favorable because an acidic or alkaline condition leads to the undesirable formation of a gibbsite or amorphous phase in Li/Al-LDHs during adsorption. In addition, the presence of Mg2+ has a significant effect on the lithium adsorption capacity of Li/Al-LDHs. The adsorption capacities of Li/Al-LDHs samples with different lithium deintercalation intensities are all dramatically enhanced by a high Mg2+ concentration, reflecting the promising potential application of Li/Al-LDHs in Li+ extraction from low-grade brines with high Mg/Li ratios.

Suppressing Sponge-Like Li Deposition via AlN-Modified Substrate for Stable Li Metal Anode.

Sponge-like lithium (Li) deposition results in high-surface-area morphology that harmfully accelerates the side reactions between Li and electrolyte, arousing serious safety issues of next high energy density Li metal batteries (LMBs). Herein, we propose a strategy to suppress the sponge-like Li deposition by plating Li metal on aluminum nitride (AlN)-modified substrates. For a practical Li deposition of 4 mAh cm-2 on a AlN-modified copper (Cu) electrode, the roughness and thickness of the as-deposited Li layer are only ∼10% and ∼50% of those for the Li layer deposited on bare Cu. Only based on the compacted Li deposition layer without any other protective remedies, the AlN-modified Cu electrode could provide a Li cycling life of 5 times longer than that on bare Cu, and an AlN-modified carbon felt was proved as an efficient interlayer to boost the cycling stability of Li||LiFePO4 batteries. These results demonstrate the high importance of suppressing the sponge-like Li deposition for high energy density LMBs.

Ab initio study of adsorption and diffusion of lithium on transition metal dichalcogenide monolayers.

Using first principles calculations, we studied the stability and electronic properties of transition metal dichalcogenide monolayers of the type MX2 (M = Ti, Zr, Hf, V, Nb, Ta, Mo, Cr, W; X= S, Se, Te). The adsorption and diffusion of lithium on the stable MX2 phase was also investigated for potential application as an anode for lithium ion batteries. Some of these compounds were found to be stable in the 2H phase and some are in the 1T or 1T' phase, but only a few of them were stable in both 2H/1T or 2H/1T' phases. The results show that lithium is energetically favourable for adsorption on MX2 monolayers, which can be semiconductors with a narrow bandgap and metallic materials. Lithium cannot be adsorbed onto 2H-WS2 and 2H-WSe2, which have large bandgaps of 1.66 and 1.96 eV, respectively. The diffusion energy barrier is in the range between 0.17 and 0.64 eV for lithium on MX2 monolayers, while for most of the materials it was found to be around 0.25 eV. Therefore, this work illustrated that most of the MX2 monolayers explored in this work can be used as promising anode materials for lithium ion batteries.

Ultrafast and directional diffusion of lithium in phosphorene for high-performance lithium-ion battery.

Density functional theory calculations have been performed to investigate the binding and diffusion behavior of Li in phosphorene. Our studies reveal the following findings: (1) Li atom forms strong binding with phosphorus atoms and exists in the cationic state; (2) the shallow energy barrier (0.08 eV) of Li diffusion on monolayer phosphorene along zigzag direction leads to an ultrahigh diffusivity, which is estimated to be 10(2) (10(4)) times faster than that on MoS2 (graphene) at room temperature; (3) the large energy barrier (0.68 eV) along armchair direction results in a nearly forbidden diffusion, and such strong diffusion anisotropy is absent in graphene and MoS2; (4) a remarkably large average voltage of 2.9 V is predicted in the phosphorene-based Li-ion battery; and (5) a semiconducting to metallic transition induced by Li intercalation of phosphorene gives rise to a good electrical conductivity, ideal for use as an electrode. Given these advantages, it is expected that phosphorene will present abundant opportunities for applications in novel electronic device and lithium-ion battery with a high rate capability and high charging voltage.