Electroconductive Gold Deposited Silicon Nanoparticles for Lithium Ion Battery Anode Prepared by Immersion Plating Method

INTRODUCTION

For the application of lithium ion batteries in hybrid cars, electrical cars and a smart grid, there is an urgent need for next-generation batteries with higher energy densities.

It has been known that silicon is a candidate for the anode material in lithium ion batteries, due to its high theoretical energy capacity (4200 mAh/g) compared to carbon (372 mAh/g) in current commercially available lithium ion batteries. Silicon also has low electroconductivity and short cycle life due to large volume changes during the charge-discharge cycle¹⁾.

A number of studies have been carried out to overcome these problems. The use of nano-sized silicon has been shown to produce better cyclability to a certain degree¹⁾. Using additive such as carbon black to overcome the low electroconductivity, or applying a carbon coating using thermal vapor deposition²⁾ to improve anode electroconductivity are widely used.

Previously, by depositing gold on the surface of silicon nanoparticles using electroless plating with a reducing agent, we were able to obtain better electroconductivity³⁾. In the present study, we propose gold deposited silicon nanoparticles as a new electrode material. We also describe a silicon alkaline immersion plating method to deposit gold on the silicon nanoparticle surface, based on the silicon alkaline etching method⁴⁾.

EXPERIMENTAL

We used commercially available silicon nanoparticles (50 nm particle size). An immersion plating bath containing 2 g/L Si and 0.0125 M NaAuCl₄·2H₂O was prepared, and 10 g/L KOH was then added. The silicon nanoparticles were dispersed using ultrasonic irradiation. The reaction time was 2 hours and the reaction was carried out in a water bath to maintain the temperature at 25 °C. The silicon nanoparticles were then collected on a filter by suction filtration and dried in vacuum at 110 °C for 2 hours.

The microstructure of the samples was observed using field-emission scanning electron microscopy (FE-SEM) and scanning-transmission electron microscopy (STEM). The phase structure of the deposited material was analyzed by X-ray diffraction (XRD). A chemical composition analysis was performed using X-ray fluorescence spectrometry (XRF).

Finally, charge-discharge cycle tests of the prepared samples were performed in a glove box in order to evaluate the characteristics of batteries incorporating these materials.

RESULTS AND DISCUSSION

We deposited gold on the silicon nanoparticles surface using an alkaline immersion plating method without the need for a catalyst. Compared to gold deposited with a reducing agent in the electroless plating method, we were able to produce more uniform deposits using alkaline immersion plating (see Fig. 1, deposited gold are shown by the white area).

In the electroless plating method, the electrons needed to reduce gold ions to solid gold are provided by the reducing agent. In the immersion plating method, electrons released when the silicon nanoparticles are etched, are also used to reduce the gold ions to solid gold. The gold ions are thus selectively deposited on the silicon nanoparticles surface. With this method, we can expect better electroconductivity while using the same amount or less of gold compared to the electroless plating method.

We will present the charge-discharge characteristics of the samples at the meeting.

REFERENCES

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