New structural applications of graphene materials in flexible lithium-ion batteries

Recently, Professor Hui Ying Yang from the University of Science and Technology of Singapore and Professor Sun Kening from Harbin Institute of Technology jointly published an article on Nature Communications. The article describes a use of germanium quantum dots/nitrogen-doped graphene nano-core-shell The structure-encapsulated three-dimensional nitrogen-doped graphene interconnected porous foam is used in lithium-ion battery electrodes.

This three-dimensional structure material combines the advantages of the stable structure of the graphene carbon material and the advantages of the metal germanium capacity, and overcomes the huge volume expansion of the previous electrode materials in the battery charging and discharging process. The problem of capacity attenuation comes. Among them, through the use of germanium quantum dots composite nitrogen-doped graphene carbon nanotubes, the prepared flexible lithium ion battery has a specific capacity of 1220mAh·g-1, and the rate performance still has 800mAh·g-1 at a large rate of 40C. The capacity retention rate reaches 97% after 1000 cycles.

Figure 1. Schematic diagram of the preparation method of Ge-QD@NG/NGF/PDMS nano core-shell structure

The picture shows Ge-QD@NG/NGF /PDMS nano core-shell structure preparation process: firstly deposit a layer of nitrogen-doped graphene on the foamed nickel template by CVD, and heat treatment in Ar/H2 atmosphere; then conduct hydrothermal treatment in GeCl4, and then chemically on its surface Nickel is plated, and germanium quantum dots are deposited by CVD; finally, the foamed nickel template is etched away, and PDMS is coated to form a core-shell structure.

Figure 2. Physical performance characterization of Ge-QD@NG/NGF

(a, b) Flexible Ge-QD@NG/NGF core shell Photograph of electrode (7×4cm)

(c) SEM image of Ge-QD@NG/NGF core-shell nanostructure

(d) EDS of Ge, C and N elements Distribution map

(e) TEM image of Ge-QD@NG/NGF core-shell nanostructures

(f) High resolution of Ge-QD@NG/NGF core-shell nanostructures TEM image

(g) Electron diffraction pattern of germanium quantum dots

(h, i) Ge-QD@NG/NGF core-shell nanostructure and (h) XRD pattern of NGF And (i) Raman spectrum

Figure 3. Electrochemical performance of Ge-QD@NG/NGF/PDMS

(a) The first battery Constant current charge-discharge curve for 1, 2, 10, 100 and 1000 cycles, the voltage window is 0.01-1.5V, and the rate is 1C

(b) Ge-QD@NG/NGF/PDMS core shell The discharge cycle performance and coulombic efficiency of the structure, the Ge/NGF/PDMS and Ge/Cu electrode at the 1000th cycle at 1C magnification

(c) In-situ Raman microscopic measurement of 'transparent' half-cell Schematic diagram

(d) Ge-QD@NG/NGF/PDMS core-shell nanostructure and selected area Raman spectrum of constant current lithiation process, magnification C/10, laser power 2.5mW, collection time A total of 10 Raman spectra were collected for 30 seconds.

Comparison of electrode design of electrodes formed by (e, f) Ge coated on Cu foil and NGF-based flexible substrates

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Figure 4. Ge-QD@NG/NGF/PDMS flexibility test

(a) Typical stress and strain of self-supporting three-dimensional electrode structure with and without Ge-QD@NG Curve

(b) The tensile strength and modulus diagrams of the self-supporting three-dimensional electrode structure of composite and uncomposited Ge-QD@NG, the error range is shown in the data

(c ) The constant current charging and discharging curve of the battery, the red and blue lines respectively represent the constant current charging and discharging curve of a flat battery after 20 cycles and a bent battery after 20 cycles of repeated bending (the bending angle is not 90°)< /p>

(d) The cycle performance of the battery in the straight state and the curved state. The red line and the gray line represent the charge and discharge performance when the charge and discharge rate is less than 1C.

Figure 5. Ge-QD@NG/NGF/PDMS magnification performance and morphological changes

(a) Ge-QD@NG/NGF/PDMS core-shell structure magnification performance, where Ge /NGF/PDMS and Ge/Cu electrodes at different current densities Bottom

(b) Nyquist diagram of Ge-QD@NG/NGF/PDMS core-shell structure electrode, respectively 1, 2, 10, 100 and 1000 cycles under 1C magnification

(ce)Ge-QD@NG/NGF/PDMS core-shell structure electrode in the state of lithium ion intercalation (c) SEM, (d, e) TEM image, magnification 1C, cycle 1000th

(f) Schematic diagram of Ge-QD@NG/NGF/PDMS core-shell structure during charging and discharging process

Summary

This work uses a negative electrode composed of germanium quantum dot matrix and graphene material The material is used in lithium-ion batteries, and a porous interconnected three-dimensional graphene foam material is obtained through a reasonable three-dimensional structure design. After that, it is heat-treated in a nitrogen atmosphere to introduce nitrogen-doped sites that combine with lithium ions. This structure provides a suitable space for the insertion of lithium ions, so that the half-cell capacity reaches 1220mAh·g-1, and the capacity retention rate is still 96% after 1000 cycles. At the same time, the battery is at a high rate (40C). The capacity still has 800mAh·g-1.