Comprehensive understanding of aqueous polymer as effective binders for silicon nanoparticles-based anodes for lithium-ion batteries

E. PRIMO; D. BARRACO; G. LUQUE

Buenos Aires

Simposio; 20th Topical Meeting of the International Society of Electrochemistry; 2017

International Society of Electrochemistry

Comprehensive understanding of aqueous polymers as effective binders for silicon nanoparticles-based anodes for lithium-ion batteriesEmiliano N. Primo1, Guillermina L. Luque2, Daniel E. Barraco11IFEG, Facultad de Matemática Astronomía y Física, Universidad Nacional de Córdoba, CONICET, Ciudad Universitaria, 5000 Córdoba, Argentina.2INFIQC, Departamento de Química Teórica y Computacional, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, CONICET, Ciudad Universitaria, 5000 Córdoba, Argentina.Since capacity of conventional graphite anode is low for large-scale applications, there has been a great interest to develop new and better materials with a high capacity and low lithiation potential. At present, silicon is potentially the best replacement because of its elevated theoretical capacity of 3590 mAh g-1 and widespread abundance in the Earth?s crust. However, the practical application in lithium ion batteries (LIB) suffers from poor cycling performance, which is induced by poor conductivity of bulk Si and structural deterioration resulting from the large volume changes during the alloying/dealloying process with Li ions. Amongst the various strategies for solving the rapid capacity fading, the binder nature and formulation has been recently acknowledged due to its role in the mechanical stability and inter-particle contact between the different phases of the slurries [1,2].In the present work we study the performance and properties of SiNPs-based anodes prepared with aqueous polymeric binders in various conditions. Specifically, we conduct a comparative electrochemical 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. Also, the effect of the polymers backbone functional groups and viscosity properties was also investigated. 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 can only establish weak van der Waals interactions with the anode 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. A direct parallelism can be made with the viscosity of the polymers solutions as a function of its identity and pH.SEM images revealed that the slurry coverage and laminate morphology in the electrode are homogeneous and relatively independent of the binder identity and pH. Nevertheless, changes in the degree of segregation between the SiNPs and the superP carbon are observed. This suggests that the cyclability and capacity differences are related to the different abilities of the binders to mix and distribute the SiNPs with the conductive carbon. IR spectroscopic and rheological measurements were made to correlate the electrochemical performance with the interactions of the polymers with SiNPs.In conclusion, we showed that the performance of SiNP-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 and its mechanical properties.[1] D. Mazouzi, Z. Karkar, C. Reale Hernandez, P. Jimenez Manero, D. Guyomard, L. Roué, B. Lestriez, Journal of Power Sources, 280 (2015) 533-549[2] A. Casimir, H. Zhang, O. Ogoke, J. C. Amine, J. Lu, G. Wu, Nano Energy, 27 (2016) 359-376