High capacity silicon (Si) is considered as a potential anode material for high performance lithium ion batteries (LIB). However, the large volume expansion during discharging/charging hinders its area capacity. In this paper, Professor Zhang Yafei's research group published the title "Binderless, Flexible and Self-supporting Nonwovens Based on Graphene/Silicon Hybrid Fibers for High Performance Lithium Ion Batteries", and designed a three-dimensional conductive network based on Flexible Graphene Fiber Fabric (GFF) to form the silicon negative electrode of self-supporting high performance lithium ion batteries without binder.
Si particles are firmly wrapped in graphene fibers. Graphene with a large number of holes caused by folds can effectively adapt to the volume change of silicon during lithium/lithium removal. The GFF/Si-37.5% electrode showed excellent cycling performance after 100 cycles at a current density of 0.4Ma cm-2, with a specific capacity of 920Ma Hg- 1. In addition, the GFF/Si-29. 1% electrode showed excellent reversible capacity of 580 Ma Hg-1after 400 cycles at a current density of 0.4 Ma cm-2. The capacity retention rate of GFF/Si-29. 1% electrode is as high as 96.5%. More importantly, the GFF/Si-37.5% electrode with a mass load of13.75 mg cm-2 achieves a high area capacity of14.3 Ma h cm-2, which is superior to the reported self-supporting Si anode. This work provides an opportunity to realize the adhesive-free, flexible and self-supporting silicon anode for high energy LIB.
Graphic reading guide
Figure 1. (a) Schematic diagram of manufacturing process of self-supporting GFF/Si-X electrode. The digital photographs of (b) GOF/Si, (c) Gof /Si and (d)GFF/Si- X in acetic acid solvent reveal their flexibility. (e) punching the GFF/Si-37.5% electrode into a small disk with an area of 1. 12 cm 2.
Figure 2. (a) the low magnification SEM image of GFF/Si-37.5% and (b) the partially magnified SEM image reveal that two independent fibers merge into one at the point where they meet. (c, d) SEM images of GFF/Si-37.5% surface and cross section.
Figure 3. Electrochemical characteristics of GFF/Si-X electrode with current density of 0.4 Ma cm-2: All specific capacities are calculated based on the total mass of independent electrodes. (a) Charge/discharge voltage curve of the first cycle. (b) Comparative analysis of ice. (c) Comparison of cycle performance. (d) Measure the CV of GFF/Si-37.5% electrode at a scanning rate of 0.2 mv s–1. (e) The GFF/Si ratio was -37.5%. (f) The area capacity of GFF/Si-37.5% electrodes with different anode weights.
Figure 4. Comparison of cycling performance of GFF/Si-Hi, GFF/Si-37.5% and GFF/Si-800 C electrodes.
Figure 5. Composition analysis of GFF/Si-HI, GFF/Si-37.5% and GFF/Si-800 C: (a) XRD pattern, (b) Raman spectrum, (c) TGA curve of GFF/Si-hi in N 2 atmosphere, and (d) FT-IR spectrum.
Figure 6. Raman spectra and XRD patterns of (a, b) GFF/Si-37.5% electrode before and after cycling. Study on the morphology of GFF/Si-37.5% electrode after 100 discharge/charge cycles: (c, d) low-power and high-power SEM images after lithiation/de-lithiation; The picture shows the digital photo of GFF/ silicon -37.5% electrode after cycling. Transmission electron microscope and HRTEM images; The illustration is a SAED image with low magnification; (g) element mapping.
summary
In this study, the three-dimensional conductive network based on GFF is designed for adhesive-free and free-standing silicon anodes. GFF structure successfully suppressed the volume expansion of Si during charging and discharging. A new method for preparing adhesive-free, flexible and self-supporting silicon anode for high performance lithium ion battery is proposed.
Literature:
https://doi . org/ 10. 102 1/ACS ami . 1c 04277