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We will describe a methodology to prepare nano-Si / natural graphite composite using an established transformation manufacturing process without significant changes to the initial process flow, thus minimizing the cost of implementation. First, a baseline was established by investigating half-cells made with anode using a mixture of coated spherical natural graphite, nano-Si and LiPAA binder. Then, a composite of graphite / nano-Si was prepared by carbonizing a dry mixture of spherical graphite, nano-Si and petroleum pitch. The silicon content was below 20 wt.% toward graphite and the pitch-to-nano-Si was optimized. Following these guidelines, a series of Si/graphite composites were prepared by first performing a spheronization process to a dry mixture of natural graphite flakes, nano-Si and carbon precursors to disperse the silicon in the core and on the surface of the graphite matrix. Followed by a carbonization step to form the amorphous carbon coating simultaneously on the graphite and nano-Si surface. The morphology and chemical composition of the composites' surface was investigated using XPS, SEM and HRTEM and the possible formation of silicon oxides or carbides was evaluated by XRD. Tap density, surface area and PSD were performed to assess if the prepared powders reached the battery grade specifications. The composites show very high reversible capacity when evaluated in coin-type, Li-ion half cells.

Increasing the energy density for Li ion batteries is very crucial for the success of EVs, grid-scale energy storage and next generation of power electronics. A holistic approach is required where the performance of the electrodes and electrolyte needs to be improved simultaneously. On the anode side, Si has been considered as the best candidate to give much higher capacities reaching, in theory, 10 times those of graphite. [1,2] However, in practice Si alone cannot deliver this high capacity reversibly due to many problems associated with volume expansion/shrinking during lithiation/de-lithiation. Also, current cathode materials have limited specific capacity to 150-200 mAh/g and can only be coated up to certain thickness before fracture or polarization takes place. A composite of silicon and graphite with capacities between 500 and 1000 mAh/g has been considered as a transient and practical alternative. In this work we have conducted theoretical and experimental study of silicon, graphite, and binder composite electrodes. We have calculated the percentage of improvement in capacity of composites and in energy density of full cells. We have tested more than 50 compositions in half cells with different ratios, binder type and silicon (shape, size and surface chemistry). Also, we have tested full cells using NMC cathode, a carbonate solvent mixture and various additives. We will show the result of our theoretical and experimental findings and demonstrate the actual parameters that need to be optimized in order to reach real improvements in practical energy density of Li-ion full cells. [1] Chae-Ho Yim, Fabrice M Courtel, Yaser Abu-Lebdeh,Journal of Materials Chemistry, 1(28), 2013 8234. [2] Nuha Salem, Matt Lavrisa and Yaser Abu-Lebdeh, 2015, Energy Technology, DOI 10.1002/ente.201500250.

Graphene and its composites have great potential as anode materials for Li-ion batteries (LIB) since their capacity was reported to exceed that of graphite, currently used as anode in most LIB [1].There are many methods to synthesize graphene, but there are still challenges to produce graphene at a large scale with desired properties that suit its perspective applications. Since there is yet no universal method for graphene production, especially that gives high yield, it would be reasonable to develop methods adjusted to specific applications e.g. electrochemical energy storage. Liquid ultrasonic exfoliation of graphene is very popular technique however satisfactory yield of exfoliation is usually achieved with either toxic organic solvents or in the water solutions of surfactants, the latter results in contaminated final product, which is unacceptable for electrochemical applications. In our work we used sodium carboxymethyl cellulose (NaCMC) as a water soluble “green” exfoliating agent for the high-yield graphene preparation. Since NaCMC is known to be a good binder for active electrode masses there is no need to remove it from as prepared graphene. Such approach allowed us simultaneous synthesis of graphene and preparation of electrode material for LIB. Microwave assisted method for the liquid phase graphite exfoliation was developed in the present work. Addition of microwave heating step to sonication of graphite dispersions in solutions of sodium carboxymethyl cellulose (NaCMC) resulted in formation of concentrated graphene dispersions of up to 4.3 mg/ml after 10 hours of sonication; concentration of graphene was increased for 34% compared to using sonication alone. HRTEM and Raman spectroscopy revealed formation of few-layer graphene (3-4 layers). It was found as well that graphene yield depends on the molecular weight of the NaCMC – the higher molecular weight the higher graphene yield (up to 59% increase of graphene yield was observed for NaCMC with 250000 molecular weight compared to NaCMC with 90000 molecular weight). Drying of prepared dispersions resulted in the graphene/NaCMC composites with graphene content up to 38.65%. Yield and concentration of graphene can further be improved by increasing sonication time and recycling of sediment. Graphene/NaCMC composite was tested as electrochemically active binder for using with Si nanoparticles in LIB electrodes. Si showed up to 51% capacity increase in the presence of graphene/NaCMC binder comparing to conventional NaCMC binder. N. Lavoie et al. in Y. Abu-Lebdeh and I. Davidson (eds) Nanotechnology for Lithium-ion batteries,117 (Springer, NY, 2013). A. Cieselski, P. Samori, Chem. Soc. Rev. 43, 381 (2014).