Failure mechanism of bulk silicon anode electrodes for lithium-ion batteries

Silicon has been investigated extensively as a promising anode material for rechargeable lithium-ion bat- teries. Understanding the failure mechanism of silicon-based anode electrodes for lithium-ion batteries is essential to solve the problem of low coulombic efficiency and capacity fading on cycling and also to further commercialize this very new energetic material in cells. To reach this goal, the structure changes of bulk silicon particles and electrode after cycling were studied using ex-situ scanning electron microscopy （SEM） and X-ray diffraction （XRD） techniques. The SEM images indicated that the microstructural changes of the bulk silicon particles during cycling led to a layer rupture of the electrode and then the breakdown of the conductive network and the failure of the electrode. The result contributes to the basic understanding of the failure mechanism of a bulk sil- icon anode electrode for lithium-ion batteries.

Thermal behavior analysis of a pouch type Li[Ni0.7Co0.15Mn0.15]O2-based lithium-ion battery

Since lithium-ion battery with high energy density is the key component for next-generation electrical vehicles, a full understanding of its thermal behaviors at different discharge rates is quite important for the design and thermal management of lithium-ion batteries （LIBs） pack/module. In this work, a 25 Ah pouch type Li[Ni0.7 Co0.15Mn0.15]O2/graphite LIBs with specific energy of 200 Wh.kg-1 were designed to investigate their thermal behaviors, including temperature distribution, heat generation rate, heat capacity and heat transfer coefficient with environment. Results show that the temperature increment of the charged pouch batteries strongly depends on the discharge rate and depth of discharge. The heat generation rate is mainly influenced by the irreversible heat effect, while the reversible heat is important at all discharge rates and contributes much to the middle evolution of the tem- perature during discharge, especially at low rate. Subse- quently, a prediction model with lumped parameters was used to estimate the temperature evolution at different discharge rates of LIBs. The predicted results match well with the experimental results at all discharge rates. Therefore, the thermal model is suitable to predict the average temperature for the large-scale batteries under normal operating conditions.

Improvement of cycle behavior of Si/Sn anode composite supported by stable Si–O–C skeleton

A Si/Sn/SiOC/graphite(SSSG) composite with high efficiency and long-term cycling stability was synthesized by a cost-effective and scalable method, including the processes of mechanical milling and pyrolysis. The composite was characterized by X-ray diffraction(XRD),scanning electron microscope(SEM) and energy dispersive X-ray spectrometry(EDX). The electrochemical properties were investigated until the 25th cycle. As a result, the SSSG composite anode exhibits excellent long-term cycling stability and capacity. Such SSSG composite anode shows excellent cycling stability with a specific capacity of 568.2 mAh·g^(-1) and ~80% capacity retention over 25 cycles at 0.3C rate. The reasons for good electrochemical characteristics are considered that the SiOC net with favorable chemical stability acts as a skeleton to support and segregate Si/Sn nanostructures, and the graphitic mixing in the composite is used as conductive material to enhance the electrical conductivity in this composite. The results suggest that the design of this new structure has the potential to provide a way for the other functional composite materials.

Electrochemical preparation of silicon nanowires from porous Ni/SiO2 blocks in molten CaCl2

Silicon nanowires(SiNWs)with diameter distributions ranging from 80 to 350 nm were prepared by electrochemical reduction of Ni/SiO2 in molten CaCl2.The effect of the content of nickel additives on the morphology of produced silicon was investigated.Large quantities of SiNWs are obtained by the electrochemical reduction of Ni/SiO2 blocks with SiO2 to Ni molar ratio of 20 and 10.Nickel additives repress the growth of irregular branches and promote longitudinal growth of SiNWs.Wire morphologies and surfaces are influenced by the electrolysis temperature.SiNWs become thicker with the increase of the electrolysis temperature.The optimum temperature to prepare single crystal SiNWs with high aspect ratio and extraordinary surface quality seems to be 1173 K.The amorphous layer of the silicon nanowire is thinner compared to the SiNWs obtained from the pure SiO2 pellets.The produced SiNWs show a photoluminescence emission peak at about 758 nm at room temperature.This work demonstrates the potentiality for the electrochemical reduction process to obtain large quantities of SiNWs with high quality.