Silicon Nanofiber Paper Battery

Patent Status

Full Description

Background

High theoretical capacity, availability abundance, non-toxicity and environmental benignity make Silicon (Si) the preferred choice of anode for next generation Lithium-ion batteries. Large volumetric expansion (~300%), achievement of Si nanostructures (characteristic dimension below 150 nm) and pragmatic fabrication process are critical obstacles to overcome to build Lithium-Silicon batteries for real world applications. Electrospinning of polymers, dissolved in organic solvents along with active material such as Si, is a feasible fabrication process. However, current electrospinning methods:

• Require lengthy, thermal oxidative stabilization and carbonization steps.
• Build electrodes with reduced capacity because the weight percentage of active material can be less than 50%.

Current Invention

Prof. Cengiz Ozkan and his research team have developed a patented, binderless, freestanding, Silicon Nanofiber (SiNF) paper with Si weight percentage in excess of 80%. SiNF paper is synthesized via magnesiothermic reduction of SiO₂ nanofiber (SiO₂NF) paper which is produced by an in situ acid-catalyzed polymerization of tetraethyl orthosilicate (TEOS) in flight. To enhance the surface conductivity of the electrode, a 4 nm carbon coating is applied to the SiNF paper.

Schematic illustration of the electrospinning and the subsequent reduction process.

Cycling data for carbon-coated SiNF compared to uncoated SiNF at C/10 rate.

Advantages

The novel aspects and benefits of their invention are:

• Existence of a 1-2 nm thickness, native SiO2 shell on all the Silicon nanoparticles (SiNP) serves to mitigate volume expansion effects during lithiation.
• The diameter of the SiNPs are 8 – 25 nm, well below the critical dimension.
• Reduced bulk diffusion length for Lithium.
• Excellent electrochemical stability and high degree of scalability.
• No carbon black, metallic current collectors or polymer binders.
• Magnesiothermic reduction process requires lower operating temperatures (700 deg. C).

Suggested uses

• Lithium-ion and Lithium-Silicon batteries

Testing

The team fabricated 2032 type coin cells with SiNF electrodes. After 650 cycles, the SiNF electrodes deliver a reversible capacity of 802 mAh/gram and a coulombic efficiency of 99.9%.

Related Materials

• Towards Scalable Binderless Electrodes: Carbon Coated Silicon Nanofiber Paper via Mg Reduction of Electrospun SiO2 Nanofibers