New spin-casting technique for high-performance silicon nanoparticle/graphene materials for Li-ion electrodes
21 October 2012
|A binder-free silicon nanoparticles/graphene electrode exhibits a high capacity, a superior rate capability, and strong cycle life. Credit Zhou et al. Click to enlarge.|
A team at the Beijing National Laboratory for Molecular Sciences (BNLMS), Chinese Academy of Sciences reports a new method to construct binder-free silicon/graphene electrode materials for Li-ion batteries with high capacity, superior rate capability and strong cycle life. A paper on their work is published in the journal Nano Research.
The binder-free, spin-coated Si nanoparticles/graphene (SC-Si/G) electrode shows a high capacity of 1611 mAh g-1 at 1 A g-1 after 200 cycles, a superior rate capability of 648 mAh g-1 at 10 A g-1, and a cycle life of 200 cycles with 74% capacity retention.
Energy storage has become a critical technology for large scale applications including portable electronics, electric vehicles (EVs), and utility grids...To further improve the energy density of LIBs, the development of new electrode materials with higher capacity or voltage plateau are essential. As for anode materials, silicon stands out as a very attractive candidate in merit of its low lithium-uptake potential (<0.5 V vs Li+/Li) and the highest theoretical capacity (4200 mA h g-1), which is 10 times higher than those of the commercial graphite anodes. Furthermore, silicon is low cost, abundant in nature, and beneficial in mature mass production.
However, the practical applications of Si as anode materials have been severely hampered by two major problems. First, substantial volume changes (>300%) during lithium insertion and extraction from Si result in dramatic pulverization of Si and loss of electrical contact between Si and conducting networks, such as carbon black, leading to a rapid capacity fading upon extended cycling. Second, the huge volume changes will destroy solid electrolyte interphase (SEI) films on the surface of Si, resulting in the Si to be repeatedly exposed to the electrolyte. This causes a continuous formation of SEI films and consumption of the electrolyte and lithium ions. The excessive growth of SEI films lead to higher resistance for lithium ion transportation, lower electronic conductivity, and worse Coulombic efficiency of the Si-based anode. Consequently, the cycling performance will be significantly impaired.—Zhou et al.
Numerous research groups are working on solutions to those barriers to commercialization, including the use of various Si nanostructures and carbon-coated Si nanocomposites. In their work, Zhou et al. from BNLMS propose a simple and efficient fabrication procedure. Using a stable suspension of Si nanoparticles and graphene oxide in ethanol as a starting point, they use spin-coating to cast a composite film of Si/graphene on a copper (Cu) foil, which can later on be directly used as anode with the film as the active material while the Cu foil as the current collector.
The SC-Si/G electrode shows several advantages compared to Si electrodes prepared in more conventional ways, the team suggests:
The facile solution-based spin-coating technique can be successfully applied to prepare high quality Si/graphene films with favorable structures for its application in LIBs. Proper treatment of Si nanoparticles results in their stable dispersal in ethanol, making the spin-coating technique possible.
The existence of graphene in the electrode acts as both an efficient electronic conductor and effective binder. No binder, such as polyvinylidenefluride (PVDF) or polytetrafluoroethylene (PTFE), is needed for the formation of a high-performance Si/graphene film benefiting from the high flexibility of graphene sheets, which can effectively cover and permeate through the Si nanoparticles.
The film has a unique nanostructure that can accommodate the large volume changes of Si nanoparticles during cycling, improve electronic conductivity of Si nanoparticles via the graphene, and possess enough void spaces around the Si nanoparticles for lithium ion diffusion and volume expansion of Si nanoparticles.
This successful materials design for Si-based anode could also be extended to other high capacity anode and cathode materials with large volume changes for advanced LIBs, the authors conclude.
Xiaosi Zhou, An-Min Cao, Li-Jun Wan, and Yu-Guo Guo (2012) Spin-Coated Silicon Nanoparticles/Graphene Electrode as a Binder-Free Anode for High-Performance Lithium-Ion Batteries. Nano Res. doi: 10.1007/s12274-012-0268-4
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