Gao Liu at LBNL has developed a new kind of composite anode based on silicon that can absorb eight times the lithium of current Li-ion batteries and maintains a high capacity of 2100 mAh/g in Si after 650 cycles. The key to such improved cyclability is a tailored polymer with dual functionality: it conducts electricity and binds closely to silicon particles as they undergo more than a 300% volume change during the lithiation process (Figure 1).
Understanding volume change and conductivity in Si nanostructures for Li-ion anodes
Silicon is a promising next-generation anode material for high-energy lithium-ion batteries due to its high specific capacity, which is theoretically 10 times greater than graphite. However, its cycle life is limited due to volume expansion and fracture during lithium reaction. This degradation of the Si results in loss of electrical connection and pulverization of the electrode. Several fundamental studies still need to be conducted to develop viable Si electrodes for batteries. Yi Cui’s group at Stanford University is working on understanding the properties of various Si nanostructures and is designing new ones based on particles and wires that target improving Si cyclability.
Predicting the Properties of Ionic Liquids from a Polarizable Force Field in Molecular Dynamics Simulations
Oleg Borodin at the Army Research Laboratory has developed and validated a polarizable force field for a wide class of ionic liquids (ILs), which are being explored as additives to lithium-battery electrolytes for improved stability. The developed force field for a wide range of anions shown in Figure 1 will serve as a starting point for molecular dynamics simulations (MD) of liquid electrolytes doped with variety of conventional and novel lithium salts. This force field, when used in MD simulations, is a tool for predicting thermodynamic and transport properties of conceptual ILs and IL-solvent mixtures and may shed light on structure-property relationships. Using predictions of promising properties to direct materials design can accelerate the development of ILs suitable for battery applications.
High-Rate NMC Cathodes Achieved with Carbon Nanotube Additive
Through a collaborative effort, the Dillon Group at NREL and the Whittingham Group at SUNY -Binghamton have enhanced the conductivity of NMC cathodes to improve their rate capability in Li-ion batteries. These layered cathodes usually suffer from poor electrical conductivity and capacity fade at high charge/discharge rates. To mitigate these problems, the researchers have incorporated single-wall carbon nanotubes (SWNTs) into the NMC cathodes (LiNi0.4Mn0.4Co0.2O2). The resultant composite cathodes exhibit stable high-rate capacities, ~130 mAh/g at 5C and nearly 120 mAh/g at 10C for over 500 cycles, which are significantly higher than those achieved with conventional NMC cathodes.
The Zaghib Group at Hydro-Québec has used in situ SEM to see SiOx particles grow and shrink during cycling. SiOx is a promising anode material for Li-ion batteries due to a high theoretical specific capacity of 1338 mAh/g and less volume change than Si upon charge-discharge. Analysis of the morphology changes in SiOx particles provides insight into the failure mode associated with capacity fade on cycling. [Read more…]