Effect of aqueous binders formulation in the performance of high capacity silicon nanoparticles-based anodes for lithium-ion batteries

EMILIANO N. PRIMO; GUILLERMINA L. LUQUE; DANIEL E. BARRACO

San Salvador de Jujuy

Workshop; IWLiME 2016: 3rd International Workshop on Lithium, Industrial Minerals and Energy; 2016

Universidad Nacional de Jujuy - Centro de Investigación Avanzada del Litio y Minerales Industriales

Silicon is a promising and attractive anode material to replace graphite for the next generation lithium ion batteries (LIB) since its theoretical capacity is 10 times of graphite and its widespread abundance on Earth?s crust. Although this remarkable high capacity, Si-based anodes suffer from rapid degradation with each cycle due to electrode volume expansion of 400% during lithiation, producing stress and strain on the Si particles and causing cracks and breakage. Solving the high capacity fading during cycling is a complex issue with multiple aspects to take into account, being one of them the binder formulation. These polymers hold the electrode together as they maintain its structure and has been recently acknowledged as one of the key features for achieving a repeatable LIB operation.In the present work we study the performance and properties of SiNPs-based anodes prepared with aqueous polymeric binders (shown in the image below) in various conditions. Specifically, we conduct a comparative performance analysis of slurries prepared with sodium alginate (ALG), poly(acrylic acid) (PAA) and sodium carboxymethylcellulose (CMC) at different pHs (2.50 and 10.00), relative to the standard PVDF binder. The slurries were made by ball milling a mixture of 40:45:15 wt% of SiNPs:superP carbon:binder and adding the proper solvent.We found that slurries made with aqueous binders exhibited higher specific capacities and better cycling stability than the conventional PVDF, as the latter one can only establish weak van der Waals interactions with the electrode constituents. Furthermore, the comparison of cyclic voltammetry profiles and charge-discharge curves revealed that acid pH conditions are preferred to alkaline ones, as both cyclability and electrochemical response towards lithium alloying is greater in the case of acidic pHs.By SEM micrographs we found that the slurry coverage and SiNPs distribution in the electrode are homogeneous and relatively independent of the binder identity and pH. This suggests that the cyclability and capacity differences are related to mechanical and/or rheological properties of the dissolved binder.In conclusion, we showed that the performance Si-based anodes for LIBs strongly depend on the polymer binder and its preparation conditions. As the binder is meant to help reduce the level of pulverization of SiNPs and keep contact with the surrounding conducting material, the key of the differences observed rely on the interactions of the polymer chains and the SiNPs surfaces.