Application of Acrylic-Rubber-Based Latex Binder to High-Voltage Spinel Electrodes of Lithium-Ion Batteries

Acrylic rubber (AR) is studied as a new aqueous latex binder for a high-voltage positive electrode material, spinel-type LiNi0.5Mn1.5O4, for lithium-ion batteries (LIBs). The electrode with AR and sodium carboxymethyl cellulose (CMC) as a composite binder delivers a reversible capacity of 138 mAh g(-1) at the first cycle and 128 mAh g(-1) at 50th cycle in non-aqueous Li cells within a voltage range of 3.0 to 5.0 V. As well as capacities higher than 120 mAh g(-1), in the case of conventional poly(vinylidene fluoride) (PVdF) binder, the AR/CMC electrode exhibits better cycle stability than that with PVdF. An initial coulombic efficiency of the AR/CMC electrode of 91 % is higher than 78 % for the styrene-butadiene rubber (SBR)/CMC electrode, because irreversible anodic oxidation of a C=C bond in the SBR molecule is avoided in the AR molecular structure. In addition, comprehensive analyses with AC impedance spectroscopy, cross-sectional scanning electron microscopy, X-ray diffraction, time-of-flight secondary-ion mass spectrometry, as well as hard and soft X-ray photoelectron spectroscopy reveal uniform dispersion of LiNi0.5Mn1.5O4 particles and acetylene black in the AR/CMC electrode and sufficient coverage of AR/CMC on LiNi0.5Mn1.5O4 particles due to good affinity of aqueous binder to them.