Abstract
Aqueous binders are highly recommended in battery production for (i) reducing the costs and, (ii) increasing the safety due to the absence of an organic solvent. Unfortunately, the impact of water during the electrode formulation on sodiated phases is still unclear and deserves investigation. In this work, we used carboxymethylcellulose (Na-CMC) binder to prepare electrodes of a high energy density P2-layered oxide material, Na0.67Mn0.6Fe0.25Co0.15O2 (NaMFC). We investigated the effects of water-based electrode preparation on the electrochemical performance, by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), and neutron diffraction. The water leads to degradation of the material limiting the reversible specific charge at 90 mAh·g−1 instead of 120 mAh·g−1 obtained with N-methyl pyrrolidone (NMP) solvent with polyvinylidene fluoride (PVDF) as binder. The protons exchanged in the structure, occurring during electrode preparation, are assumed to disrupt the Na ions extraction mechanism limiting the specific charge of such a material.
Highlights
The electric vehicles market is constantly growing due to its positive impact on the environment aimed at the reduction of greenhouse gas emission
Electrode preparation usually requires an efficient drying process generating additional costs and major safety issues appear with the use of the carcinogenic N-methyl pyrrolidone (NMP) solvent for designing polyvinylidene fluoride (PVDF) based electrodes
Efforts are being put into electrode preparation with aqueous binders such as carboxymethylcellulose (Na-carboxymethylcellulose sodium salt (CMC))
Summary
The electric vehicles market is constantly growing due to its positive impact on the environment aimed at the reduction of greenhouse gas emission. Li-ion batteries are the only energy sources for powering such engines and the efforts being made by both companies and researchers to provide more energetic and safer batteries are tremendous. The positive impact on the environment is generally counter balanced by the production of such batteries generating toxic and hazardous products. Interest in Na-ion batteries has been growing due to the crustal abundance of Na compared to Li, which could decrease the overall price of the battery and allow new chemistry to be explored [4]. For high energy density Na-ion batteries, the attention has been focused on layered oxide materials which were first investigated by the Delmas’s group [5]. Two structures have been mainly investigated in the literature: the P2 structure, which has a low Na content and
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