Archive for category: News

New paper published in ChemSusChem in collaboration with the Kickelbick-Group at Saarland University. We have developed an exciting new class of inorganic-organic hybrid materials with redox-active components that have great potential for use in lithium-ion batteries (LIBs). The materials were prepared using an aqueous precipitation reaction of ammonium heptamolybdate (AHM) with para-phenylenediamine (PPD), and a low-energy continuous wet chemical synthesis process known as the microjet process. By varying the ratio of molybdate to organic ligand and pH, we were able to produce two different crystalline hybrid products with large surface areas in the submicrometer range and high purity and reproducibility on a large scale. The first product, [C₆H₁₀N₂]₂[Mo₈O₂₆] ⋅ 6 H₂O, was obtained by using a ratio of para-phenylenediamine to ammonium heptamolybdate from 1 : 1 to 5 : 1. The second product, [C₆H₉N₂]₄[NH₄]₂[Mo₇O₂₄] ⋅ 3 H₂O, was obtained by using higher PPD ratios from 9 : 1 to 30 : 1. Our electrochemical testing revealed that the second product showed exceptional battery performance, with a high capacity of 1084 mAh/g at 100 mA/g after 150 cycles. The product reached maximum capacity after an induction phase, which can be explained by a combination of a conversion reaction with lithium to Li₂MoO₄ and an additional in situ polymerization of PPD. We are excited about the potential of this hybrid material for use in LIB applications.

After a lot of work by our Ph.D. students Stefanie Arnold and Lei Wang, our invited article in the Wiley journal SMALL on the dual-use of seawater batteries for energy storage and water desalination. Seawater batteries are a unique type of device that capitalizes, in the most common design, on a ceramic separator, an electrocatalytic reaction on one electrode side, and reversible sodium-ion electrochemistry on the other side. Since simple seawater can be used as the aqueous electrolyte in the system, the system has become known as seawater batteries. In our opinion, this technology can do more than contribute toward beyond-lithium energy storage by also being used for desalination.

new paper published in ACS Energy Letters on continuous electrochemical lithium-ion extraction. We used a redox electrolyte “engine” to drive the ion transfer (in our case: potassium ferricyanide). Employing a pair of ceramic lithium superionic conductor (LISICON) membranes meant that only Lithium ions were accessible to the redox electrolyte for charge compensation. And to complement the design, we used an anion exchange membrane to separate the inflow (e.g., seawater) from a recovery solution. By this way, we obtained an electrochemical system for the continuous extraction of Lithium ions. This sets this technology apart from earlier works (including our contributions) that relied on a cyclic operation to obtain ion separation. Yet, this is just one of many more steps towards seeing such technology toward application; future research must critically address cell design, optimization of the Li-membranes, and investigating the robustness and durability of continuous operation.

This work was the result of the collaboration of our Ph.D. students Lei Wang, Stefanie Arnold, Panyu Ren, and our former Postdoc (now group leader at Bavarian Center for Battery Technology (BayBatt)) Qingsong Wang, as well as our Chinese collaborators Jun Jin and Zahoyin Wen (Chinese Academy of Sciences).

New paper published in Desalination on the ion selectivity of carbon nanopores. It is well known that electrolyte confinement inside carbon nanopores strongly affects ion electrosorption in capacitive deionization. A thorough understanding of the intricate pore size influence enables enhanced charge storage performance and desalination in addition to ion separation. In subnanometer pores, where the pore size is smaller than hydrated ion size, a dehydration energy barrier must be overcome before the ions can be electrosorbed into the pores. Ion sieving is observed when the dehydration energy is larger than the applied energy. However, when a high electrochemical potential is used, the ions can desolvate and enter the pores. Capitalizing on the difference in size and dehydration energy barriers, this work applies the subnanometer porous carbon material, and a high electrochemical ion selectivity for Cs⁺ and K⁺ over Na⁺, Li⁺, Mg²⁺, and Ca²⁺ is observed. This establishes a viable way for selective heavy metal removal by varying pore and solvated ion sizes. Our work also shows the transition from double-layer capacitance to diffusion-limited electrochemical features in narrow ultramicropores.