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Silicon-Few Layer Graphene (Si-FLG) composite electrodes are investigated using a scalable electrode manufacturing method. A comprehensive study on the electrochemical performance and the impedance response is measured using electrochemical impedance spectroscopy. The study demonstrates that the incorporation of few-layer graphene (FLG) results in significant improvement in terms of cyclability, electrode resistance and diffusion properties. Additionally, the diffusion impedance responses that occur during the phase changes in silicon is elucidated through Staircase Potentio Electrochemical Impedance Spectroscopy (SPEIS): a more comprehensive and straightforward approach than previous state-of-charge based diffusion studies.

Polymer binders are a key component for long-lasting silicon (Si)-based electrodes, and they should be mechanically robust and electrochemically stable, with the ability to accommodate the large volume expansion of Si during the lithiation/delithiation process. The combination of poly(acrylic acid) (PAA) and poly(vinyl alcohol) (PVA) utilizes the strong adhesion properties of PAA and mechanical robustness of PVA, which can potentially overcome the current technical challenges faced by the traditional polyvinylidene-fluoride-based binder systems, e.g., poor interfacial adhesion, brittleness, and short service life. This study has investigated the PAA/PVA (60/40 wt %) blend for Si anodes and compared its performance with the effects of PAA and partially neutralized PAA/PVA (60/40 wt %). The PAA/PVA blends were further thermally cross-linked in order to improve the mechanical properties. The PAA/PVA binder shows higher stiffness, adhesion strength, and electrochemical performance (100 cycles with 240 mA/g and 40 cycles with 400 mA/g) compared with those of unmodified PAA (38 cycles with 240 mA/g and 25 cycles with 400 mA/g). The partially neutralized PAA/PVA blend shows further improved performance (over 140 cycles with 240 mA/g and over 60 cycles with 400 mA/g). The working mechanism of the partially neutralized PAA/PVA binder is discussed.

Copies of full items can be used for personal research or study, educational, or not-for-profit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. Publisher statement:First published by Royal Society of Chemistry 2016 http://dx.doi.org/10.1039/C6CP06788C A note on versions:The version presented here may differ from the published version or, version of record, if you wish to cite this item you are advised to consult the publisher's version. Please see the 'permanent WRAP URL' above for details on accessing the published version and note that access may require a subscription. Hybrid anode materials consisting of micro-sized silicon (Si) interconnected with few-layer graphene (FLG) nanoplatelets and sodium-modified poly (acrylic acid) (PAA) as a binder were evaluated for Li-ion batteries. The hybrid film has demonstrated a reversible discharge capacity of ~1800 mAh/g with a capacity retention of 97% after 200 cycles. The superior electrochemical properties of the hybrid anodes are attributed to a durable, hierarchical conductive network formed between Si particles and the multi-scale carbon additives, with enhanced cohesion by the functionalized polymer binder. Furthermore, improved SEI stability is achieved from the electrolyte additives, due to the formation of a kinetically stable film on the surface of the Si.

While silicon-based negative electrode materials have been extensively studied, to develop high capacity lithium-ion batteries, implementing a large-scale production method that can be easily transferred to industy, has been a crucial challenge. Here, a scalable wet-jet milling method was developed to prepare a silicon-graphene hybrid material to be used as negative electrode in lithium-ion batteries. This synthesized composite, when used as an anode in lithium cells, demonstrated high Li ion storage capacity, long cycling stability and high-rate capability. In particular, the electrode exhibited a reversible discharge capacity exceeding 1763 mAh g-1 after 450 cycles with a capacity retention of 98% and a coulombic efficiency of 99.85% (with a current density of 358 mA g-1). This significantly supersedes the performance of a Si-dominant electrode structures. The capacity fade rate after 450 cycles was only 0.005% per cycle in the 0.05-1 V range. This superior electrochemical performance is ascribed to the highly layered, silicon-graphene porous structure, as investigated via focused ion beam in conjunction with scanning electron microscopy (FIB-SEM) tomography. The hybrid electrode could retain 89% of its porosity (under a current density of 358 mA g-1) after 200 cycles compared with only 35% in a Si-dominant electrode. Moreover, this morphology can not only accommodate the large volume strains from active silicon particles, but also maintains robust electrical connectivity. This confers faster transportation of electrons and ions with significant permeation of electrolyte within the electrode. Physicochemical characterisations were performed to further correlate the electrochemical performance with the microstructural dynamics. The excellent performance of the hybrid material along with the scalability of the synthesizing process is a step forward to realize high capacity/energy density lithium-ion batteries for multiple device applications.

Multiple heteroatom-doped core/shell carbonaceous framework materials showed a rapid charge–discharge capacity and excellent cycling stability, demonstrating great potential for anode materials for lithium ion batteries.

Hierarchically porous carbon nanostructures with intrinsically doped heteroatoms and metal elements are attractive for electrochemical energy storage applications.

Silicon remains a promising anode material for next generation lithium-ion batteries, despite the well-documented issues associated with it, due to its abundance and high capacity (3579mAh/g: almost 10 times higher than the capacity of graphite).  The problems still facing Si-based battery commercialization are volume expansion, which results in rapid capacity fade, and continued Li loss through SEI formation from electrolyte decomposition.  To address this problem, effective binders are considered to be one solution, and could help to maintain good contact between the active material and current collector but also to generate effective, stable networks between silicon particles and conductive carbon additives. This work will introduce a new binder system: Polyacrylic Acid-Styrene Butadiene Rubber (PAA-SBR). PAA is an aqueous-based polymer and possesses a high concentration of carboxyl group, which effectively bonds with the surface of silicon but also can H-bond with other polar species contributing to a good cohesive composite. SBR (Styrene Butadiene Rubber) is well known for its good flexibility, which can improve the tensile property of the electrode towards volume expansion. Therefore, it is hypothesized that the binary binder PAA-SBR can help Si anode achieve an improved, more stable performance because it can preserve good adhesion and flexibility simultaneously under the stress of the Si expansion. A preliminary study was conducted on Si vs.Li/Li+ half cells with different binder systems: PAA, PAA-SBR (2:1 mass ratio) and PAA-SBR (5:1 mass ratio), where PAA-only is used as the control binder. Cells are tested under the maximum lithiation capacity of 1200mAh/g at a C rate of C/5. Electrochemical cycling data indicates that for first 100 charge-discharge cycles, the PAA-SBR (2:1) showed a similar level of performance compared with PAA in terms of specific capacity (~1194mAh/g) and columbic efficiency (~99.5%), while the PAA-SBR (5:1) displayed capacity fade after 80 cycles, as shown in Fig.1. We anticipate that an optimized PAA-SBR ratio will generate superior composite durability during longer-term electrochemical testing. To further approve the hypothesis, a comprehensive study based on PAA-SBR (2:1) will be followed including polymer stability in electrolyte solvents, tensile properties, adhesion and impedance testing. Figure 1