Anodes

Conductive Polymer Binder Improves Silicon Anode Cyclability

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).

Gao — Figure 1. (Left) Traditionally, composite anodes using silicon (blue spheres) contain a polymer binder such as PVDF (light brown) and a conductive carbon additive (dark brown spheres). Silicon swells and shrinks while acquiring and releasing lithium ions, and this repeated volume change eventually breaks electrical contacts to the carbon particles. (Right) The new Berkeley Lab polymer (purple) is itself conductive and continues to bind tightly to the silicon particles despite repeated volume change, thus maintaining conductivity in the electrode over many hundreds of cycles.

[Read more…]

From Particles to Wires: Shaping Silicon Cyclability

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.

Cui_Fig1 — Figure 1. (Left) TEM image of interconnected hollow Si spheres. (Right) SEM image of hollow Si nanospheres scraped using a sharp razor blade, revealing the interior empty space in the spheres and their interconnected shells.

[Read more…]

In-situ SEM: Seeing Battery Cycling in Action

Real-time Observation of Morphology Changes in SiO_x Anodes for Lithium-ion Batteries

The Zaghib Group at Hydro-Québec has used in situ SEM to see SiO_x particles grow and shrink during cycling. SiO_x 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 SiO_x particles provides insight into the failure mode associated with capacity fade on cycling. [Read more…]

Nanoscale Heterostructures for Low-Cost, High-Capacity Lithium-Ion Batteries

Figure 1. Transmission electron microscopy image of a carbon nanotube covered with Si nanoclusters.

Approaches toward Silicon-Based High-Capacity Anodes for Lithium-Ion Batteries

The Kumta Lab is developing low-cost methods for producing nanoscale silicon composites as lithium-ion anodes. These heterostructures comprise nanocrystalline or amorphous Si and may contain a variety of carbon precursors. The Si provides high capacity while the graphitic and disordered carbon acts as an electrically-conductive matrix as well as a mechanically compliant phase. The Kumta Lab’s multi-pronged approach towards anode fabrication includes chemical vapor deposition (CVD), high-energy mechanical milling (HEMM), and electro-reduction.

[Read more…]