High-Performance Li-Ion Battery Anodes Based on Silicon-Graphene Self-Assemblies

Abstract

A series of Si/graphene sheet/carbon (Si/GS/C) composites was prepared by electrostatic self-assembly between amine-grafted silicon nanoparticles (SiNPs) and graphene oxide (GO). The Si/GS derived from carbonization of Si/GO assemblies showed limited cycling stability owing to loose cohesion between SiNPs and graphene, and increased impedances during cycling. To counteract the cycling instability of Si/GS, an additional carbon-gel coating was applied to the Si/GO assemblies in situ in solution followed by carbonization to yield dense three-dimensional particulate Si/GS/C composite with many internal voids. The obtained Si/GS/C composites showed much better electrochemical performances than the Si/GS owing to enhanced cohesion between the SiNPs and the carbon structures, which reduced the impedance buildup and protected the SiNPs from direct exposure to the electrolyte. A strategy for practical use of a high-capacity Si/GS/C composite was also demonstrated using a hybrid composite prepared by mixing it with commercial graphite. The hybrid composite electrode showed specific and volumetric capacities that were 200% and 12% larger, respectively, than those of graphite, excellent cycling stability, and CEs (>99.7%) exceeding those of graphite. Hence, electrostatic self-assembly of SiNPs and GO followed by in situ carbon coating can produce reliable, high-performance anodes for high-energy LIBs. Energy storage via rechargeable batteries will play an increasingly important role in the future not only to power advanced mobile electronic devices, power tools, sensors for internet-of-things devices, medical implants, military and aerospace devices, drones, e-bikes, many electrified vehicles, and so on, but also to store energy from intermittent renewable resources (solar and wind power) and for back-up energy supplies for smart electric grids.1-3 Among many rechargeable batteries, lithium-ion batteries (LIBs) offer the highest energy density to date and reasonably long cycle life and power capability. [4][5][6] Nonetheless, the demands for high-energy LIBs are increasing, especially the demand for electric vehicles to carry sufficient energy comparable to that of internal combustion vehicles. 1,2,[7][8][9] To further enhance the energy content of an LIB, electrode materials capable of delivering high capacity at a high working voltage (a higher-potential cathode coupled with a lower-potential anode vs. Li/Li + ) have to be incorporated, and the cell design has to be optimized to maximize the packing density. Noticeable progress has been made on the cathode side recently by optimizing the composition and structure of Ni-rich LiNi x Co y Mn z O 2 10,11 and Li-rich layered oxide 12,13 cathodes, which has resulted in LIBs with a much higher energy content. On the other hand, all LIB anodes are still made of graphite, whose theoretical capacity (372 mAh g −1 ) has been achieved since its first introduction in 1991. Therefore, a breakthrough in terms of the energy density of LIBs would require adoption of new anodes having a m...

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