Abstract
This study is devoted to the confinement effects on freezing and melting in electrochemical systems containing nanomaterial electrodes and liquid electrolytes. The melting of nanoparticles formed upon freezing of liquids confined in pores of disordered nanostructured n-type silicon has been studied by low-temperature differential scanning calorimetry. Experimental results obtained for deionized water, an aqueous solution of potassium sulfate, and n-decane are presented. A model is proposed for predicting the melting point of nanoparticles formed during freezing of liquids inside the pores of a disordered nanostructured material. The model is based on the classical thermodynamic concept of the phase transition temperature dependence on the particle size. It takes into account the issues arising when a liquid is dispersed in a matrix of another material: the effect of mechanical stress resulted from the difference in the thermal linear expansion coefficients at a temperature gradient, the effect of the volumetric liquid content in the matrix, the presence of a nonfreezing liquid layer inside the pores, and the effect of wettability of the matrix with the liquid. Model calculations for water and n-decane confined in nanostructured silicon matrix have been carried out considering the volumetric liquid content. The results obtained have been compared with the differential scanning calorimetry data.
Highlights
Over the last decades, silicon-based anode materials for metal–ion batteries have been of great interest due to their tremendous theoretical specific capacity, accessibility of raw materials, economy, and environmental friendliness [1,2]
We proposed the model for predicting the melting point of nanoparticles formed during freezing of liquids inside the pores of a disordered nanostructured material accounting the bulk density of strain energy
Model calculations have shown that the contribution of mechanical stresses resulted from the difference in the thermal linear expansion coefficients at a temperature gradient to the melting point change is negligible compared to surface contribution
Summary
Silicon-based anode materials for metal–ion batteries have been of great interest due to their tremendous theoretical specific capacity, accessibility of raw materials, economy, and environmental friendliness [1,2]. The DSC-method was applied to investigate phase behavior of water inside pores of silica gel [22] and to examine some other liquids under nanoconfinement [23,24], as well as to determine pore size of different materials on the basis of Gibbs–Thomson equation [25,26,27] This method, known as DSC-based thermoporosimetry, is applicable only with reference measurements with standard samples. It is known that, in the case of a substantial temperature gradient, the confinement phenomena can be affected by the bulk density of strain energy [28,29] This physico-chemical characteristic is caused by the mechanical stress resulting from the difference in the thermal linear expansion coefficients (TLECs) of contacting phases. The influence of the measurement conditions and the matrix wettability with various liquids on the experimental results is discussed
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