ShanghaiTech University successfully constructed a self-driven lithium extraction nonwoven material

On July 19, 2022, the team of Professor Liu Wei of ShanghaiTech University published a research paper entitled “Self-driven lithium extraction by directional liquid transport nonwoven” in the journal Matter.

By combining a layer of hydrophobic fiber layer containing lithium ion sieve particles and a layer of hydrophilic fiber layer, the research group constructs a lithium extraction nonwoven material with a wetting gradient, directly relies on the difference between the gravity of the aqueous solution and the capillary pressure of the material itself, guides the aqueous solution to penetrate the zigzag pores in the material and contacts the ion sieve particles, and realizes the extraction of lithium ions without any external driving force.

Dr. Xin Chen of the School of Materials, ShanghaiTech University of Science and Technology is the first author of the paper, and Professor Liu Wei of the School of Materials of ShanghaiTech University is the sole corresponding author of the paper.

Under the grand mission of “carbon peaking” and “carbon neutrality”, lithium is becoming a strategic resource as the most indispensable energy metal in the fields of new energy vehicles, 3C consumer electronics and energy storage. Commercial lithium is mainly derived from terrestrial lithium mines, and there are limited quantities and uneven geographical distribution. As a large and geographically independent lithium resource, marine and salt lake brines contain huge lithium reserves. Therefore, extracting lithium from seawater/brine is considered the most promising method.

The lithium ion sieve membrane based on the ion displacement adsorption method of the existing lithium extraction process can realize the extraction of Li+, while the structure of the traditional lithium ion sieve membrane is dense, and the liquid lithium source (seawater/brine) must apply external pressure as the driving force to achieve liquid penetration. Therefore, traditional lithium-ion screen membranes cause additional energy consumption problems during the lithium extraction process.

Recently, Professor Liu Wei’s team developed a composite asymmetric nonwoven (CAN) with directional water permeation function, WHICH is composed of a hydrophobic (polyvinylidene fluoride, PVDF) fiber layer containing lithium-ion sieve (lithium titanate, Li4T5O12) particles and a hydrophilic (cotton, cotton) fiber layer (Figure 1). The cotton fiber layer (hydrophilic layer) is prepared by spunlace nonwoven processing, then the PVDF nanofiber layer containing lithium-ion sieve (hydrophobic layer) is prepared by electrospinning on its surface, and finally the hydrophilic layer and the hydrophobic layer are recombined by hot rolling (Figure 2). This work enables the extraction of lithium ions without any external driving force, which is expected to bring hope for saving energy costs for lithium extraction in seawater/salt lakes.

Figure 1: Schematic diagram of the structure and application of CAN with directional water infiltration function.

Figure 2: Preparation process and associated characterization of CAN.

The asymmetric hydrophilic/hydrophobic structure of CAN and the characteristics of directional water penetration. CAN exhibits completely different wettability on both sides (Figure 3), with a contact angle of ~35° for the pro-water surface and ~115° for the surface of the thin water, an asymmetrical wetting structure that causes the can to exhibit different capillary effects on both sides. The wetting gradient is constructed by using the differences in the eigenform and wettability of hydrophilic/hydrophobic fibers, and when the liquid comes into contact with the surface of the hydrophobic water, under the action of the difference between gravity and the capillary pressure of the material itself, the liquid completes the self-penetration through the internal through-hole of the hydrophobic lithium extraction layer and the diversion of hydrophilic fibers; When the liquid comes into contact with the pro-water surface, the liquid quickly spreads to the entire surface, unable to form a sufficient height to overcome the surface of the thin water capillary pressure, and thus unable to penetrate the CAN. Thus, this directional water permeation property can drive an aqueous solution containing Li+ to penetrate CAN without any external forces.

Figure 3: Asymmetric hydrophilic/hydrophobic structure of CAN and characteristics of directional water penetration.

Lithium extraction properties of CAN in alkaline Li+ solutions. Based on ion displacement adsorption, after CAN is acidified, Li+ in the litrenic lattice of the hydrophobic layer Li4T5O12 is replaced by H+ displacement. When in contact with an alkaline lithium-containing solution, ion substitution occurs between CAN and Li+ in contact with the lithium-depleted state to complete Li+ adsorption. The results showed that the adsorption capacity of CAN on Li+ solution (pH = 12, CLi+ = 400 mg L-1) could reach ~30.5 mg m-2, in addition, CAN showed good stability during multiple cycles. Compared with other lithium extraction technologies, the energy consumption ratio of lithium extraction is only ~1.63 J mg-1, and CAN is highly cost-effective in the field of adsorption method for lithium extraction.

Figure 4: Lithium extraction characteristics of CAN in alkaline Li+ aqueous solution.

(Source: Science Network)

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