Which is better, graphene batteries or graphene lithium batteries?

1 Introduction

The growing energy demand in advanced communications equipment and electric vehicles has caused great interest in the development of high energy density lithium-ion batteries. Silicon-based materials can be used as cathodes for next-generation lithium-ion batteries due to their ultra-high specific capacity, large reserves, and relatively low lithium insertion potential. However, significant changes in volume during continuous lithium intercalation and delithiation (300%) can cause the active material to break and fall off, which in turn causes severe capacity decay. Many studies have shown that silicon-carbon composites obtained by introducing certain carbon materials such as graphene can exhibit many excellent properties of carbon (such as electrical conductivity and mechanical flexibility), so that this problem can be effectively solved.

2 results introduction

Recently, Peking University academician Zhongfan Liu, in collaboration with professor Hailin Peng (co-communications), proposed a vertical graphene-coated silica particle (d-sio@vg) that can be used as a stable negative electrode for lithium ion batteries and has a high specific capacity. Graphene grown vertically on the surface of silicon monoxide (SiO) particles by chemical vapor deposition can not only significantly enhance the electrical conductivity of the particles, but also provide a large number of transport channels for lithium ions. It was found that even at high loads (1.5mg/cm2), the resulting composites remained stable (100 cycles, retention rate 93%) with a capacity of up to 1600mAh/g. This results in "VerTIcalGrapheneGrowthonSiOMicroparTIclesforStableLithiumIonBatteryAnodes entitled" published in the journal NanoLetter on May 4.

3. Picture and text guide

Mechanism figure 1. Design of vertical graphene-coated silicon-based particles

a. Electrical insulation of the silicon-based electrode caused by volume change during continuous battery cycling.

b. The surface-covered vertical graphene provides a stable conductive connection between the silicon oxide particles during battery cycling.

Figure 1, Vertical graphene growth on SiO particles

(ab) TEM image of the interconnected d-SiO@vG particles and a white square selected partially enlarged image.

(c) A high resolution TEM image of a triangular vertical graphene film, the inner view being a cross-sectional view of the marked area.

(d) Raman spectrum of d-SiO@vG particles.

(e-f) the peak of Si2p in the XPS spectra of d-sio@vg particles and SiO particles and the C1sXPS spectra of d-sio@vg particles.

During the heating process, the silica obtained by the disproportionation reaction on the surface of the silicon oxide can provide a catalytic site for the growth of graphene. From the Raman map, the characteristic peaks of graphene (D: ~1359cm-1, G:~2699cm-1, 2D: ~2690cm-1) can be seen. The XPS spectrum shows that the surface of the composite particles is mainly amorphous silica. There are CO bonds in the structure without C-Si bonds, indicating that oxygen plays an important role in the growth of graphene.

Figure 2, Conductivity test of d-SiO@vG particles

(a) A circuit for particle current-voltage testing under an optical microscope.

(b) IV curves of individual SiO particles, a single d-SiO@vG particle, and a plurality of interconnected d-SiO@vG particles.

(c) Schematic representation of different forms of conductive contact between active materials.

(df) Two-dimensional scanning images of SiO, d-SiO@hG (horizontal graphene) and d-SiO@vG composite electrode film on PI film.

When the SiO particles are coated with about 2.5% by weight of graphene, the resistance is reduced from ~4.0 & times; 1012 Ω to ~3.1 & times; 104 Ω, and the contact resistance and sheet resistance between the particles are also greatly reduced.

Figure 3, electrochemical performance of d-SiO@vG anode

(a) Typical CV curves of d-sio@vg electrodes (including the first, second and fifth cycles), with a sweep rate of 0.05mvs-1.

(b) Nyquist curve of the d-SiO@vG electrode before and after scanning.

(c) Charge-discharge performance at 160 mag-1 current density.

(d) Specific capacity and circulation efficiency of d-sio electrodes and d-sio @vg electrodes at 320 mag-1 current density.

The first cycle cyclic voltammetry curve has a peak at 0.65 V, indicating the formation of a solid electrolyte membrane, which results in an increase in charge transport resistance, but the value remains substantially unchanged after ten rotations. The presence of the solid electrolyte membrane and graphene increases the specific surface area of the particles (from 3 m 2 /g to 12 m 2 /g), thereby increasing the charge and discharge capacity. At the same time, vertical graphene encapsulation also improves the cycle performance of the electrode.

Figure 4, In situ TEM characterization of d-SiO@vG particles during lithium insertion

(a-b) schematic diagram and TEM image of nano-electrochemical device for in-situ lithium implantation test.

(cd) d-SiO@vG particle image before and after lithium intercalation.

(ef) corresponds to the surface topography of the graphene-modified layer in the regions marked in Figures c and d, respectively.

After lithium intercalation, the length of the composite particles is increased by about 15%, and in the same case, the unmodified SiO particles are increased by 200%. High-powered photographs show that the graphene base remains unchanged before and after particle expansion, indicating that it provides a stable conductive path.

Figure 5, d-SiO@vG/graphite-NCA full battery performance test

(a) Photograph of 18650 full-cell battery assembled with d-SiO@vG/graphite as the negative electrode and NCA as the positive electrode.

(b) Assembly battery rate performance at different charging rates from 5C to 5C.

(c) Cyclic performance of the assembled full battery at a charge/discharge rate of 5C/1C.

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