Sn- and SnO2-graphene flexible foams suitable as binder-free anodes for lithium ion batteries

With the objective of developing new advanced composite materials that can be used as anodes for lithium ion batteries (LIBs), herein we describe the synthesis of novel three dimensional (3D) macroporous foams formed by reduced graphene oxide (rGO) and submicron tin-based particles. The aerogels were obtained by freeze/freeze-drying a suspension of graphene oxide (GO) in the presence of a tin precursor and its subsequent thermal reduction under an argon atmosphere. The materials exhibited a 3D-macroporous structure formed by the walls of rGO decorated with Sn or SnO2 particles depending on the temperature of calcination. Self-standing compressed foams were directly assembled into coin cells without using any metallic support to be evaluated as binder-free anodes for LIBs. The homogeneous dispersion and intimate contact between the Sn-based particles and graphene walls were confirmed by scanning electron microscopy (SEM). The performance of SnO2-rGO composite materials as anodes for LIBs showed higher specific capacity compared with rGO and metallic Sn-containing samples, reaching a reversible capacity of 1010 mA h g(-1) per mass of the electrode at 0.05 A g(-1) and good capacity retention (470 mA h g(-1)) even at 2 A g(-1) (similar to 2 C), among the highest reported for similar systems. The SEM images of selected electrodes after 50 charge-discharge cycles showed that even though SnO2 submicron particles were pulverized into small nanoparticles they remain intact upon cycling.