AFM: Preparation of 3DMXene by Spray-Freezing Method for Enhanced Potassium Storage Properties

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In modern society, lithium-ion batteries have achieved great success as energy storage systems in electric vehicles and wearable electronic devices. However, with the rapid development of renewable energy sources such as wind and solar, new battery technologies for grid-scale energy storage are in urgent need of development, especially in the face of limited resources and rising lithium costs. Benefiting from its abundant source and low redox potential of potassium (-2.93 V vs. standard hydrogen electrode), potassium-ion batteries are regarded as strong competitors for next-generation energy storage systems and have received continuous attention from researchers . Nonetheless, conventional "rocking-chair" batteries suffer from sluggish reaction kinetics due to the double slow semi-diffusion confinement of large-radius potassium ions in the anode and cathode. Recently, researchers have proposed a potassium-ion hybrid capacitor technology composed of a battery-type negative electrode and a capacitive-type positive electrode, which have Faraday and Faraday reaction mechanisms, respectively. This recombination mechanism and the "accordion"-type reaction process can achieve high power and energy density with good cycle life.

Ti3C2Tx MXene, as one of the most popular 2D materials, has been widely studied and applied in Li-ion and Na-ion batteries due to its high metallic conductivity and abundant surface functional groups. However, the application of Ti3C2Tx for potassium storage is largely affected by the stacking problem that cannot be ignored. Addressing the stacking problem shared by Ti3C2Tx and other 2D materials is necessary to facilitate their widespread applications. Among them, the introduction of "pillars" or the use of templates are effective strategies, but not only the process is complicated, but also some low-active substances may be introduced. Therefore, it is very necessary and promising to develop a general and simple 3D construction method that does not destroy the original properties of 2D materials.

Recently, the team of Professor Cao Dianxue and Professor Zhu Kai of Harbin Engineering University published a research paper titled: Aggregation-Resistant 3D Ti3C2Tx MXene with Enhanced Kinetics for Potassium Ion Hybrid Capacitors Batteries in the international high-level academic journal Advanced Functional Materials, proposing a simple The spray-freeze strategy successfully prepared a 3D-structured Ti3C2Tx that can effectively prevent the stacking problem. The first author of this paper is Dr. Fang Yongzheng.

Figure 1. Morphology and structural characterization of 3D-Ti3C2.

Figure 2. 3D morphologies of Ti3C2, Ti2C and graphene oxide 2D materials.

Figure 3. Electrochemical characterization of the 3D-Ti3C2 electrode.

Figure 4. Kinetic analysis of electrochemical polarization and concentration polarization of 3D-Ti3C2 and 2D-Ti3C2.

Figure 5. Electrochemical performance of potassium-ion hybrid capacitors composed of 3D-Ti3C2 and HPAC.

This paper presents a novel scalable spray-freeze strategy that can be used to assemble 2D nanosheets into 3D structures. A 3D macroporous sphere/tube Ti3C2Tx, a microporous Ti2CTx tube and a nano-rolled GO were successfully prepared, which successfully solved the stacking problem of 2D materials in energy storage and electrode fabrication. The as-prepared 3D Ti3C2Tx has a shorter ion transport path and larger specific surface area, and exhibits outstanding rate performance and cycling stability. After 10,000 cycles at a current of 1 A g-1, it has a specific capacity of 122 mAh g-1. In addition, the assembled potassium ion capacitor with 3D Ti3C2Tx as the negative electrode and HPAC as the positive electrode exhibited a high energy density of 98.4 Wh kg-1 and a power density of 7015.7 W kg-1. This work provides a new idea for the realization of higher potassium storage capacity.

Literature link:

https://doi.org/10.1002/adfm.202005663