Iron oxide (Fe2O3) has a high theoretical capacity (~1000 mAh-1), abundant resources and environmental friendliness, so it is considered to be one of the most promising new lithium ion battery anode materials. However, problems such as poor conductivity of Fe2O3 and slow diffusion of lithium ions will inevitably lead to poor capacity and low rate capability. More seriously, the volume expansion of Fe2O3 during the process of deintercalating lithium causes the electrode to pulverize, resulting in poor cycle stability. In order to improve the electrochemical performance of Fe2O3, nanostructured Fe2O3 has been extensively studied in combination with various carbon materials. For example, the anchoring of Fe2O3 nanoparticles on graphene can simultaneously prevent re-agglomeration of nanoparticles and buffer volume expansion during charge and discharge of Fe2O3. In addition, graphene provides a highly conductive substrate for Fe2O3 nanoparticles, ensuring fast conduction of electrons. Inspired by this, MXene is used as a new two-dimensional material for lithium-ion battery anode composites due to its unique physical and chemical properties.

Recently, Guangdong University of Technology, Yan Yonggang and Cai Junjie (corresponding author) synthesized a nanocomposite (N–Ti3C2/Fe2O3) with well-dispersed iron oxide nanoparticles (NPs) anchored on wrinkled nitrogen-doped MXene nanosheets. Compared with the conventional multilayer MXene, the wrinkled N-doped MXene nanosheet has a larger specific surface area and pore volume and a large number of active sites, which can better fix the Fe2O3 nanoparticles uniformly on the MXene substrate. Prevent agglomeration of nanoparticles and buffer volume changes. This composite material combines the high conductivity of MXene and the high lithium ion storage capacity of iron oxide nanoparticles. Therefore, the N–Ti3C2/Fe2O3 composite has excellent rate performance, high capacity and long cycle life as the negative electrode of lithium ion battery. Related research results are published in the Journal of Power Sources under the title "Highly-dispersed iron oxide nanoparticles anchored on crumpled nitrogen-doped MXene nanosheets as anode for lithium-containing batteries with enhanced cyclic and rate performance". The first author of the paper is Zhang Zengyao.

[Graphic introduction]

Figure 1. Schematic diagram of direct preparation of N–Ti3C2/Fe2O3 nanocomposites by solventless thermal decomposition



Figure 2. SEM topography



(a-b) SEM image of Ti3C2TX;

(c–d) an SEM image of N–Ti3C2;

SEM image of (e–f)N–Ti3C2/Fe2O3 nanocomposites.

Figure 3. Physical properties of N–Ti3C2/Fe2O3 nanocomposites



(a-b) N-Ti3C2/Fe2O3 nanocomposite X-ray diffraction pattern (a) and XPS spectrum (b);

(c-d) High resolution XPS spectra of N–Ti3C2/Fe2O3 nanocomposites N 1s(c) and Fe 2p(d).

Figure 4. TEM analysis of N–Ti3C2/Fe2O3 nanocomposites



TEM image (a-b) of the (a-c)N–Ti3C2/Fe2O3 nanocomposite and the corresponding HRTEM image (c);

(d) STEM image and element mapping image of the N–Ti3C2/Fe2O3 nanocomposite (d 1 –d 5).

Figure 5. Electrochemical performance of N–Ti3C2/Fe2O3 nanocomposites



(a) Cyclic voltammetry of the N–Ti3C2/Fe2O3 electrode;

(b) comparing the rate performance of N–Ti3C2/Fe2O3 and Ti3C2/Fe2O3 samples;

(c) constant current charge and discharge curves of N–Ti3C2/Fe2O3 at different current densities;

(d) EIS curves from different samples.

Figure 6. Long cycle performance of N–Ti3C2/Fe2O3 nanocomposites



(a) Comparison of cycle performance at a current density of 1 A g-1;

(b) Constant current discharge/charge curve of the N–Ti3C2/Fe2O3 composite electrode at a current density of 2 A g-1; (c) Corresponding long-circulation performance at a current density of 2 A g-1.

【summary】

In summary, nanocomposites with well-dispersed iron oxide nanoparticles anchored on highly conductive N-doped MXene nanosheets have better electrochemical performance than samples prepared with Ti3C2, mainly due to N–Ti3C2 The unique wrinkle structure has a high specific surface area and nitrogen doping increases the electron conductivity of the entire electrode. In addition, the N–Ti3C2 nanosheet acts as a barrier in the nanocomposite to effectively prevent the aggregation of nanoparticles and the re-stacking of MXene nanosheets, thereby effectively buffering large volume changes of the active material. The N-Ti3C2/Fe2O3 anode has good reversible capacity and long-term cycle stability, indicating that N-Ti3C2/Fe2O3 is expected to be the anode material for the next generation of lithium ion batteries.

Literature link: "Highly-dispersed iron oxide nanoparticles anchored on crumpled nitrogen-doped MXene nanosheets as anode for Li-ion batteries with enhanced cyclic and rate performance" (Journal of Power Sources, 2019, DOI: 10.1016/j.jpowsour.2019.227107 )