Triple battery storage capacity achieved by incorporating nanomaterials

Materials World magazine
,
25 Mar 2019

Using an ultra-thin nanomaterial a battery’s electrode could pervade three times storage capacity of conventional batteries. Shardell Joseph reports. 

The ever-increasing demand for the advancement of lithium-ion (Li-ion)batteries and greater storage capacity has pushed the search for more robust electrodes. Researchers at Trinity College Dublin, Ireland, found incorporating an ultra-thin nanomaterial into a battery’s electrode structure could significantly improve its storage capacity.

In High capacity silicon anodes enabled by MXene viscous aqueous ink, published in Nature Communications, the researchers highlight the issue of the electrodes in typical batteries.

‘The main problem with batteries is that we want to get them to store more energy so we can use them for longer between charges,’ said the university’s school of chemistry Professor of Nanomaterials and Advanced Microscopy, and study co-author, Valeria Nicolosi.

‘In a rechargeable lithium-ion battery you have electrodes where the charge is stored, and in order to store more charge we need to make these electrodes thicker. But they can only be manufactured to a certain thickness.

‘There is a threshold beyond which if we make the electrode too thick it starts cracking and the battery fails.’

In the paper, the research team identifies the need for strong electrodes with a high areal capacity, which can be achieved by producing thick electrodes from a high-performance active material. The researchers present ‘above critical thickness’ – solution-processed films that typically encounter electrical/mechanical problems – limiting the achievable areal capacity and rate performance as a result.

The researchers demonstrated how two-dimensional titanium carbide or carbonitride nanosheets, known as MXenes, could form a continuous metallic network, enable fast charge transport and provide good mechanical enforcement for thick electrodes.

Using nanosheets

MXenes are ceramics composed of a few atomic layers of transition metal carbides, nitrides or carbonitrides. First discovered in 2011, MXenes comprise one of the largest families of two-dimensional materials. This material derived from its 3D phase – a bulk crystal called MAX.

‘MXenes provide electrical conductivity and very importantly mechanical reinforcement,’ says Nicolosi. ‘The two-dimensional MXene material has the ability to prevent the silicon anode from expanding to its breaking point during charging – a problem that’s prevented its use for some time.’

Nicolosi explains how silicon anodes can replace graphite anodes in Li-ion batteries, hugely impacting the amount of energy stored. Substituting silicon for graphite as the primary material in the Li-ion anode would improve its capacity for taking in ions because each silicon atom can accept up to four lithium ions, whereas in graphite anodes, six carbon atoms can only take in one.

As it charges, however, silicon can expand up to 300%, causing it to break and the battery to malfunction. Therefore, electrodes are quickly pulverised with usage.

‘MXene nanosheets distribute randomly and form a continuous network while wrapping around the silicon particles, thus acting as conductive additive and binder at the same time’, says Nicolosi. ‘It’s the MXene framework that also imposes order on ions as they arrive and prevents the anode from expanding.’

The next step

The discovery of the efficient use of two-dimensional MXene nanosheets as a conductive binder for the silicon electrodes has been significant to the electrochemical energy storage field. The slurry-casting technique, which is highly scalable and low cost, can allow for large-area production of high performance silicon-based electrodes for advanced batteries, which could be incorporated into commercial battery manufacturing.

‘The way our prototypes are manufactured, it uses exactly the same manufacturing technology used by battery manufacturers – only in small scale,’ says Nicolosi. ‘Therefore, these new compositions should be easy to transfer to large-scale manufacturing.’