Recently, lithium-ion batteries have been attracting more interest for use in automotive applications. Lithium resources are confi rmed to be unevenly distributed in South America, and the cost of the lithium raw materials has roughly doubled from the fi rst practical application in 1991 to the present and is increasing due to global demand for lithium-ion accumulators. Since the electrochemical equivalent and standard potential of sodium are the most advantageous after lithium, sodium based energy storage is of great interest to realize lithium-free high energy and high voltage batteries. However, to the best of our knowledge, there have been no successful reports on electrochemical sodium insertion materials for battery applications; the major challenge is the negative electrode and its passivation. In this study, we achieve high capacity and excellent reversibility sodium-insertion performance of hard-carbon and layered NaNi 0.5 Mn 0.5 O 2 electrodes in propylene carbonate electrolyte solutions. The structural change and passivation for hard-carbon are investigated to study the reversible sodium insertion. The 3-volt secondary Na-ion battery possessing environmental and cost friendliness, Na + -shuttlecock hard-carbon/NaNi 0.5 Mn 0.5 O 2 cell, demonstrates steady cycling performance as next generation secondary batteries and an alternative to Li-ion batteries.

High-capacity SiO powder composite electrodes for rechargeable lithium-ion batteries are prepared with different polymer binders of poly(acrylic acid) (PAA), poly(vinyl alcohol) (PVA), sodium carboxymethyl cellulose (CMCNa), and conventional poly(vinylidene fluoride) (PVdF). Electrode performance of the SiO composites highly depends on selection of binders, and their electrochemical reversibility is drastically improved by using PAA as the binder in comparison to the PVdF, CMCNa, and PVA binders. Coulombic efficiency at the initial cycle is improved for the SiOÀPAA composite electrode, and the reversible capacity reaches 700À750 mAh g À1 for continuous fifty cycling test at a rate of 100 mA g À1 . The improvement mechanism of SiOÀPAA composite electrode is characterized by X-ray diffraction, electron microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, self-discharge test, and adhesive strength test. Amorphous PAA polymer not only tightly binds but also covers the individual SiO particles. Moreover, the PAA binder suppresses swelling of the composite electrode with the electrolyte solution compared to the PVdF binder. Through-thickness electric resistance of the PAA composite electrode is much lower than that of the PVdF when it is wet with the electrolyte. It is proposed that these characters of the PAA binder effectively suppress isolation of the SiO powders in the composite electrode associated with the large volume expansion/shrinkage during the lithiation/delithiation processes.

To study the effect of different polymer binders on electrochemical performance of the Si composite electrode in rechargeable lithium-ion batteries, sodium polyacrylate (PAANa), sodium carboxymethyl cellulose (CMCNa), and poly(vinylidene fluoride) (PVdF) are utilized as the polymer binders for the preparation of composite electrodes consisting of powdery silicon, graphite, and Ketjen black. The electrodes are examined by cross-sectional observation using a scanning electron microscope after a focused ion beam process, X-ray photoelectron spectroscopy, micro Raman spectroscopy, X-ray diffraction, and a peel test. We report that electrode performance of the Si composites depends on a selection of binders, and PAANa binder remarkably improves the electrochemical lithiation and delithiation performance of the Si–graphite composite electrode compared to that of conventional binders of PVdF and CMCNa. When the electrode is prepared with 30 wt % PAANa binder, the higher initial efficiency is obtained with much improved cyclability. Furthermore, the specific capacity of the electrode reaches 1000 mAh g–1 and exceeds 800 mAh g–1 of reversible capacity during the 30 continuous cycling test. The PAANa polymer binder increases the mechanical strength and adhesive strength as composite electrodes. Furthermore, the polymer layer reduces the electrolyte decomposition at the Si particles and suppresses the capacity deterioration by volume change and pulverization due to Si–Li alloying, compared with PVdF, leading to the better electrochemical reversibility.

Graphite/silicon composite electrodes are prepared with PANa polymer as a binder. Morphological characters and electrode performance are compared with those of PVdF. The PANa layer behaves like SEI at the interface with ionic liquid, resulting in the highly reversible electrode performance.

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