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Research Background

With the rapid development of electronic devices, electric vehicles, and large-scale power grids, lithium-ion batteries have become one of the most important energy storage devices for commercial applications in the past few decades. In commercial applications, improving the capacity and cycle life of lithium batteries is the primary task of related research. In terms of capacity, Si-based materials have ultra-high theoretical capacity (~4200 mAh g-1 is almost ten times the capacity of graphite electrodes), lower discharge range (less than 0.5V vs. Li/Li+), and lower The electrode polarization has become the most potential anode material in lithium batteries. However, the severe volume expansion of Si during lithium intercalation limits its widespread use, and the volume expansion of Li15Si4 even exceeds 300%. This leads to the formation of an unstable solid-state electrolyte interface (SEI), which in turn leads to rapid capacity decay. In addition, the low conductivity of Si itself affects the electron transfer between the current collector and the active material, which in turn affects the electrochemical performance.
Recently, the team of Prof. Chen Xiaohong and Prof. Song Huaihe from Beijing University of Chemical Technology published the research titled: Three-Dimensional Hierarchical Porous Structures Constructed by Two-Stage MXene-Wrapped Si Nanoparticles for Li-Ion Batteries in the international high-level academic journal ACS Applied Materials and Interfaces In this paper, an efficient strategy is proposed to fabricate a 3D hierarchically porous MXene-protected Si-based anode. The positively charged modified Si and MXene nanosheets self-assemble through electrostatic force to form a composite structure.

Figure 1. Schematic diagram of the synthesis method of SiNP@MX1/MX2.

Figure 2. Micromorphological characterization of SiNP@MX1/MX2.

Figure 3. Nitrogen adsorption and desorption curves, pore size distribution and XRD patterns of SiNP@MX1/MX2.

Figure 4. XPS spectra of SiNP@MX1/MX2.

Figure 5. Electrochemical performance test and kinetic analysis of SiNP@MX1/MX2 for lithium battery.

Figure 6. Electrochemical AC impedance and delithiation and intercalation process of SiNP@MX1/MX2.

Figure 7. SEM images of SiNP@MX1/MX2, SiNP@MX1 and SiNP@MX2 samples after cycling for 200 cycles.
In this paper, 3D porous composite structures of Si nanoparticles and MXene nanosheets were successfully prepared by hydrothermal and electrostatic self-assembly. After 200 cycles at a current density of 0.5 A g-1, it still has a reversible capacity of 1422 mA h g-1, excellent rate performance, high Coulombic efficiency and long cycle life. The excellent performance benefits from the protection from MXene and the good electronic conductivity and fast Li-ion transport from the 3D hierarchical porous structure. It is a very useful preparation strategy.
Literature link:

DOI: https://dx.doi.org/10.1021/acsami.0c15527