We investigated the lithiation and delithiation properties of pure binary silicide electrodes in an ionic liquid electrolyte as novel anodes for lithium‐ion batteries. Some electrodes maintain a high reversible capacity in the electrolyte, whereas they show a poor cycling performance in an organic electrolyte. The superior performance results from the high affinity for the transition metal that composes the silicide with Li. Based on reaction behavior analysis, the crystal structure of silicide is maintained during the cycling, and phase separation does not occur. The ionic liquid electrolyte suppresses the formation of cracks and exfoliation of the silicide layer from a substrate. In addition, a surface film formed on the silicide electrode through the reductive decomposition of the electrolyte has different components than that on a Si electrode, even in the same ionic liquid electrolyte. Soft X‐ray emission spectroscopy demonstrates that the pure silicide itself reacts with Li. The obtained results will provide significant insights into novel alloy‐based anode materials for lithium‐ion batteries.

The combination of synthetically modified styrene‐butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) was studied as an aqueous binder for LiCoO2 composite electrodes under high‐voltage operation. Methyl methacrylate (MMA) and 2‐vinylpyridine (VP) substituted SBR copolymers were synthesized and examined as functional polymer binders. The electrolyte‐solvent uptake of the binder‐polymer film was increased by the introduction of the MMA units, but the solubility of the polymer in the solvent remained negligibly low. Hard‐X‐ray photoelectron spectroscopy revealed the formation of a relatively thick passivation layer on the LiCoO2 surface with MMA‐substituted SBR and CMC binder, which suppressed the self‐discharge of 4.5 V‐charged LiCoO2. The capacity retention during battery cycling experiments was similar for the LiCoO2 electrodes with MMA‐modified and unmodified SBR binders. While the effect of VP‐substitution was not significant, incorporation of the MMA unit enhanced the stability of the charged LiCoO2 electrode and provided improved self‐discharge performance.

A new combination of styrene acrylic rubber (SAR) and sodium carboxymethylcellulose was developed as a water-borne binder for LiCoO 2 composite electrodes operating at high voltages. Four novel SAR-based latex binders were synthesized with butyl acrylate or 2-ethylhexyl acrylate monomer and styrene via copolymerization with low and high crosslinking degrees. Composite electrodes prepared using lower-crosslinking-degree SAR binders became more stretchable and flexible. Surface analysis using electron microscopy and X-ray photoelectron spectroscopy revealed that the cycled LiCoO 2 electrode was covered with approximately 10-nanometer-thick decomposition products when a conventional poly(vinylidene fluoride) binder was used. The electrodes with SAR-based binders with low crosslinkage formed a stable passivation surface during the initial cycle, and further continuous electrolyte decomposition was successfully suppressed. This passivation improved the cycle stability of LiCoO 2 electrode up to 4.5 V, i.e., 87.1 % capacity retention, even after 100 cycles and suppressed self-discharge performance at 45 °C.