Search

Nano-structures on the surface of graphite based carbon particles have been investigated by means of high resolution transmission electron microscopy. The surfaces consist of “closed-edge” structures in a similar manner as carbon nano-tube. That is, they are composed of coaxial carbon tubes consisting of adequate coupling of graphite layer edges. These graphite particles are chemically stable and, therefore, applicable for lithium-ion secondary battery anodes. Molecular dynamics simulations based on the Tersoff potential reveal that the vibrations of the graphite layers at the free edges play an important role in the formation of the closed-edge structures. In lithium-ion secondary batteries, Li ions can intrude into bulk carbon anodes through these closed-edge structures. In order to clarify this intrusion mechanism, we have studied the barrier potentials of Li intrusion through these closed edges using the first-principles cluster calculations. From electrochemical measurements, the carbon anodes compos...

We report microstructures on the surface of graphite particles found in practicable carbon anodes by means of high-resolution transmission electron microscopy. The surfaces consist of “closed-edge” structures constructed in a similar manner as carbon nano-tube. We have also investigated the formation mechanism of these nano-structures using molecular dynamics simulations based on the Tersoff potential. From electrochemical measurements, the carbon anodes composed of these “closed-edge” structures show actually high battery performance with a large discharge capacity and a small irreversible capacity.

Cathodes composed of layered transition metal oxides LiMO2 (M = Co, Ni) and spinel manganese oxide LiMn2O4, carbon anodes, and nonaqueous electrolyte solutions have been investigated with the aim of achieving higher energy density. The lithium-ion rechargeable cell using the LiCoO2 cathode and the propylene carbonate(PC)-diethyl carbonate (DEC)/ LiPF6 electrolyte solution exhibits excellent characteristics. Furthermore, non-graphitizable carbon such as polyfurfuryl alcohol derived carbon has larger capacity and better cycleability than graphitizable carbon such as coke.

Combined with renewable energy harvesting technologies, such as solar panels or wind turbines, energy storage is the key to keeping up with the ever-increasing demand for electric energy and reducing the world dependency on fossil fuels. Over the last three decades lithium-ion batteries (LiBs), starting with the first commercialized cell by Sony in 1990 [1], have evolved from the most promising energy-storage technologies [2] to the most widely used nowadays. Not only can LiBs be found in portable devices such as laptops, they are also used in larger scale applications such as electric vehicles. Since the first commercialization of LiBs, graphite (372 mAh.g-1) has been the usual negative electrode material. Nevertheless, the continuous demand, in the automotive industry in particular, for more performant, light, safe and cheap LiBs drives research towards the design and development of new electrode materials characterized in particular by high energy densities and a longer capacity retention during cycling. Among the candidates for high specific gravimetric capacity is silicon (3579 mAh.g-1) [3]. However, two major problems hamper the use of this material as a LiB electrode material. The first is its high volumetric change (297 % [4]) during lithiation, which causes particle cracking and pulverization during cycling which in turn leads to a quick fading of the cell capacity. The second is its high first cycle irreversible capacity. Reducing the particle size to the nanoscale and thus reducing the mechanical strain on the particle by attenuating its volumetric expansion/contraction helps alleviate pulverization. However, because of poor electrode structural stability during cycling this approach alone does not stop capacity degradation [5]. Using a dual-phase composite material that contains an inactive host matrix in which the active material is well-dispersed also alleviates pulverization. The FeSi2/Si/graphite anode material is particularly interesting due to its low-cost, high reversible capacity and good cycling stability [6]. This material is composed of a dual-phase FeSi2 (inactive)/amorphous Si (active) composite and graphite, a conductive matrix to accommodate the Si volumetric expansion, and is seen as well suited for the development of high capacity LiBs. Be that as it may, it is still unclear how this complex material functions and what makes it so performant. With the aim of accessing the lithiation/delithiation mechanism of a FeSi2/Si/graphite negative LiB electrode, we performed simultaneous operando Small and Wide Angle X-Ray Scattering (SAXS and WAXS) measurements on a cycling NMC//FeSi2/Si+graphite pouch-cell filled with a 1 mol.L-1 LiPF6 in FEC/EMC (30/70 wt%) electrolyte at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. Through WAXS we were able to investigate the local structure (10-1 nm) of the cell materials and in particular observe the lithiation/delithiation of the graphite phase by following its corresponding Bragg peak and those of its different lithiated phases (LiC30, LiC24, LiC18, LiC12 and LiC6). Simultaneously, we gained information on the active silicon state of lithiation/delithiation by observing the morphology changes occurring at the nano-scale (1 nm to 10 nm) during the volumetric expansion/contraction of the silicon through SAXS measurements. The combined information give us insight on the lithiation/delithiation mechanism of the negative electrode and enabled us to dissociate the capacity contribution of the silicon phase from that of the graphite phase as a function of potential, time and capacity. By cycling the cell at several current-rates and by repeating the same experiment on an aged cell cycled 300 times, we were also able to enquire into the impact of fast-charging and ageing on the lithiation/delithiation mechanism of the negative electrode. In this talk, we will present those results after proposing a lithiation/delithiation mechanism for the FeSi2/Si/graphite composite electrode. Yoshio Nishi, H.A., Atsuo Omaru Non aqueous electrolyte cell, in US Patent1990, Sony Corp United States of America. Armand, M. and J.M. Tarascon, Building better batteries. Nature, 2008. 451: p. 652. Goriparti, S., et al., Review on recent progress of nanostructured anode materials for Li-ion batteries. Journal of Power Sources, 2014. 257: p. 421-443. Tian, H., et al., High capacity group-IV elements (Si, Ge, Sn) based anodes for lithium-ion batteries. Journal of Materiomics, 2015. 1(3): p. 153-169. Li, H., et al., A High Capacity Nano Si Composite Anode Material for Lithium Rechargeable Batteries. Electrochemical and Solid-State Letters, 1999. 2(11): p. 547-549. Li, T., et al., Cycleable graphite/FeSi6 alloy composite as a high capacity anode material for Li-ion batteries. Journal of Power Sources, 2008. 184(2): p. 473-476. Figure 1