Potential for porous silicon in batteries of the future

In the 21st century we’re all using batteries but we need faster charging, longer life and new storage materials. A new review from the Department of Chemical and Biological Engineering evaluates existing academic literature on silica to silicon for lithium-ion battery applications.

Silicon has extensive storage capacity and has significant advantages over current materials used in commercial lithium-ion batteries, but what is the potential for porous silicon? Lithium-ion battery chemistries, and particularly silicon anodes (which make up batteries), are highly topical due to the scientific interests and commercial potential.

A review of magnesiothermic reduction of silica to porous silicon for lithium-ion battery applications and beyond” Authors Jake Entwistle, Anthony Renniea and Siddharth Patwardhan.

Author Dr Siddharth Patwardhan outlines further;

“What is new in this review is that we’ve identified the gaps and the potential. We’ve shown aspects where other researchers can go in the future.”

“There’s a huge scientific and commercial need for this in regards to batteries. Silicon has enormous capacity over what is currently used in batteries which is graphite, but the problem using silicon is that it under goes expansion and contraction in use.”

“Every time we charge and discharge a battery the silicon expands/contracts and then eventually breaks – its life is much shorter. We get high capacity but only for a short period, researchers have suggested we use a porous material, so it expands into the core of the battery without cracking and contracting.”

“This review discusses how important silicon is and how porous silicon will solve that problem. The challenge is how do we make that porous silicon? There are multiple methods which are existing to make silicon but we are highlighting on one particular method, which is using a much lower temperature to others. Current existing methods use 1500 – 2000 Celsius which is very energy consuming.  The methods we are talking about in this review is ‘magnesiothermic reduction’, it’s a one step process taking the pre cursor (which is oxide) of silicon to its reduced form, which is reduced silicon and it operates at around 600 – 800 Celsius.”

“The gap in our current scientific knowledge is how do we control the properties of porous silicon from starting materials and the process parameters? People haven’t linked the properties of the materials that they start with which is oxide to the processing conditions (temperature, time, concentrations) to the actual final product properties. That is what we’ve identified as the key gap in this area which people should address in the future.”

“This is really important to making this material in a commercial way and scalable way for future batteries.”

Abstract

Increasing demands for portable power applications are pushing conventional battery chemistries to their theoretical limits. Silicon has potential as an anode material to increase lithium-ion cell capacity. The associated volume change during lithiation/delithiation leads to a decline in capacity during cycling and low lithium diffusion rates within silicon limit high rate performance.

Porous silicon can potentially address the poor cyclability and rate capabilities simultaneously by minimising stresses and providing smaller silicon substructures for lithium diffusion. Template assisted synthesis and magnesiothermic reduction of silica to silicon offers a facile and scalable route for the production of porous silicon structures even when using a non-porous feedstock.

This review collates the available literature concerning the effects of reaction conditions through the reduction reaction. We highlight that it is important to report in detail all reaction conditions and complete characterisation of both the reactant and the product. The battery performance of these porous silicon structures is discussed and future research directions are identified. These outcomes will enable the identification of a clear design pathway for the bespoke production of porous silicon.