【Research Background】

With the development of wearable electronics and electric vehicles, lithium-ion batteries have achieved great success. Limited lithium resources have forced people to research alternative options to ensure the requirements of sustainable and ecological development. Today, potassium ion batteries (KIBs) have aroused great interest and are expected to replace lithium batteries due to their abundant natural resources and similar working potentials of potassium ( E K ⁺ / K = -2.93V,  E Li ⁺ / Li =- 3.04 V vs. E ^o ). The larger ionic radius of K ⁺ may weaken its solvation ability and higher ion mobility in the electrolyte and the electrode / electrolyte interface. On the other hand, a larger K ⁺radius will cause larger volume changes during potassium insertion and removal, which will affect its performance.

Among the many negative electrode materials, carbon negative electrodes have excellent cycle stability and rate performance. However, the lower theoretical (300 mAh g ^-1 ) capacity offsets its advantages. Antimony (Sb) can form K3Sb at a relatively safe operating voltage to produce a higher reversible specific capacity, higher electrical conductivity and higher physical density (6.7 g cm ^-3 ), which means that Great potential as a potassium anode. In addition, the earth‘s Sb resources are rich, and its low cost and environmental friendliness have more advantages. However, Sb anodes will experience greater volume expansion during alloying and de-alloying, which will lead to powdering and poor contact, so the capacity will rapidly decline. Most electrode materials are coated on the current collector by slurrying, which will introduce non-conductive binders and conductive agents, which will seriously weaken the actual capacity.

MXenes, as a new two-dimensional material, represented by Ti 3 C 2 T x , has attracted great attention from researchers due to its high electrical conductivity, negative surface charge, and outstanding intercalation effects. At the same time, monovalent or polyvalent metals (such as Li ⁺ , K ⁺  and Al ³⁺ ) can achieve intercalation between Ti 3 C 2 T x layers and occupy electrochemically active sites for energy storage.

Recently, Professor Feng Jinkui of Shandong University published a research paper titled A general method for constructing robust, flexible and freestanding MXene @ metal anodes for high performance potassium-ion batteries in the internationally renowned academic journal Journal of Materials Chemistry A. In this paper, by using highly conductive flexible MXene paper as a current collector, a high-speed electron transmission path is provided to promote electron transmission and limit volume expansion during cycling. MXenes @ Sb has a high reversible capacity: 516.8 mAh g ^-1 , high rate performance, a capacity of 270 mAh g ^-1 at 500 mA g ^-1 and a stable capacity retention rate, and only loses each charge and discharge cycle 0.042%.

[Picture and text guide]

Figure 1.  Preparation process of flexible self-supporting film

Figure 2.  Characterization of physical composition and micromorphology.

Figure 3.   MXene @ Sb for electrochemical performance testing of potassium anodes.

Figure 4.   Digital photo, twisted histogram and SEM image of the composite membrane after 100 cycles.

Figure 5.  Schematic diagram of potassium ion insertion.

Figure 6.  Characterization of the physical composition of MXene @ Bi, MXene @ Sn composite membranes.

[Summary of this article]

In summary, this work successfully prepared a layered porous Sb on MXenes as a stable, flexible self-supporting binder-free potassium ion battery anode. It has a reversible capacity of 516.8 mAh g ^-1 at a spot density of 50 mA g ^-1 and an initial capacity retention rate of 79.14% after 500 cycles. In addition, this universal simple electrodeposition method can be extended to other flexible self-supporting MXene @ metal electrodes (MXene @ Bi, MXene @ Sn). This flexible self-supporting electrode can also be applied to other rechargeable batteries, catalysis and Sensor field.

Literature link:

DOI: 10.1039 / c9ta02233c

Source: MXene Frontier