Shrivastava Aniruddh, Do Vu Q, Smith Kyle C
Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana 61801, Illinois, United States.
Computational Science and Engineering Program, University of Illinois at Urbana-Champaign, Urbana 61801, Illinois, United States.
ACS Appl Mater Interfaces. 2022 Jul 13;14(27):30672-30682. doi: 10.1021/acsami.2c03261. Epub 2022 Jul 1.
NASICON (sodium superionic conductor) materials are promising host compounds for the reversible capture of Na ions, finding prior application in batteries as solid-state electrolytes and cathodes/anodes. Given their affinity for Na ions, these materials can be used in Faradaic deionization (FDI) for the selective removal of sodium over other competing ions. Here, we investigate the selective removal of sodium over other alkali and alkaline-earth metal cations from aqueous electrolytes when using a NASICON-based mixed Ti-V phase as an intercalation electrode, namely, sodium titanium vanadium phosphate (NTVP). Galvanostatic cycling experiments in three-electrode cells with electrolytes containing Na, K, Mg, Ca, and Li reveal that only Na and Li can intercalate into the NTVP crystal structure, while other cations show capacitive response, leading to a material-intrinsic selectivity factor of 56 for Na over K, Mg, and Ca. Furthermore, electrochemical titration experiments together with modeling show that an intercalation mechanism with a limited miscibility gap for Na in NTVP mitigates the state-of-charge gradients to which phase-separating intercalation electrodes are prone when operated under electrolyte flow. NTVP electrodes are then incorporated into an FDI cell with automated fluid recirculation to demonstrate up to 94% removal of sodium in streams with competing alkali/alkaline-earth cations with 10-fold higher concentration, showing process selectivity factors of 3-6 for Na over cations other than Li. Decreasing the current density can improve selectivity up to 25% and reduce energy consumption by as much as ∼50%, depending on the competing ion. The results also indicate the utility of NTVP for selective lithium recovery.
NASICON（钠超离子导体）材料是用于可逆捕获钠离子的有前景的主体化合物，此前已在电池中用作固态电解质和阴极/阳极。鉴于它们对钠离子的亲和力，这些材料可用于法拉第去离子化（FDI），以选择性地去除钠而非其他竞争性离子。在此，我们研究了使用基于NASICON的混合Ti-V相作为插层电极，即钠钛钒磷酸盐（NTVP）时，从水性电解质中选择性去除钠而非其他碱金属和碱土金属阳离子的情况。在含有Na、K、Mg、Ca和Li的电解质的三电极电池中进行的恒电流循环实验表明，只有Na和Li可以插入NTVP晶体结构中，而其他阳离子表现出电容响应，导致材料对Na相对于K、Mg和Ca的固有选择性因子为56。此外，电化学滴定实验与建模表明，NTVP中Na的混溶间隙有限的插层机制减轻了在电解质流动下运行时相分离插层电极容易出现的充电状态梯度。然后将NTVP电极并入具有自动流体再循环的FDI电池中，以证明在含有浓度高10倍的竞争性碱/碱土阳离子的流中，钠的去除率高达94%，显示出Na相对于除Li以外的阳离子的过程选择性因子为3-6。根据竞争性离子不同降低电流密度可将选择性提高多达25%，并将能耗降低多达约50%。结果还表明了NTVP用于选择性锂回收的效用。
