High surface area to volume ratio electrodes in lithium sulphur batteries

Lithium ion batteries has the highest energy density of commercially available portable rechargeable batteries. But, in practical use, numerous problems concerning safety, progressive loss of charge capacity with increase in charge cycles, and inadequate energy density for high power consuming smartphones, tablets and laptops, motivated the development of new generations of lithium ion batteries with different designs and chemistries.

 

Current lithium ion batteries use graphite electrodes for storing charge, which are on the lithium ions. However, graphite electrodes have finite capacity not sufficient for higher charge density required for high energy consuming devices. Finding alternative electrodes for housing lithium ions in batteries is a major area of research, and one promising electrode material is sulphur.

 

Based on theoretical calculations, lithium sulphur batteries offer a charge density 5 times that of lithium ion batteries. The question is how do we construct a sulphur electrode capable of realising the theoretical charge density as well as circumvent the problem of polysulphide formation on the electrode.

 

A recent article featured in BBC News (http://www.bbc.com/news/science-environment-37788436) highlighted the utility of increasing the surface area to volume ratio of sulphur electrode for increasing the efficiency in which lithium ions can diffuse to and be stored on the electrode (with potential for fast charging) as well as the charge capacity per unit weight of sulphur electrode. The latter is an important consideration since there has been much focus on reducing the weight of current lithium ion batteries for various portable applications such as embedded batteries in clothing and smart wearable devices.

 

Shaped like the microvilli of the intestine, the new sulphur electrode offers significant enhancement in charge density and ease of diffusion of lithium ions to the electrode over other designs of lithium sulphur batteries. But, given the intricate nature of the long and thin micro sulphur electrodes and the high density at which they must be packed together to realise greater charge capacity per unit weight, the technique used to produce these microstructures must be further optimised and translated to the battery industry for mass producing lithium sulphur batteries of the microvilli electrode design. This highlights, once again, the precision engineering nature of lithium ion battery manufacturing (https://ngwenfa.wordpress.com/2016/10/21/understanding-the-precision-engineering-aspects-of-lithium-ion-batteries/) where, in the case of the proposed lithium ion batteries, new methods capable of high volume production with high precision must be developed to precisely grow the sulphur electrode microstructures to desired dimensions.

 

Collectively, the new electrode design (reminiscent of the microvilli of the intestine) is a positive way forward in enhancing the charging speed and capacity of future lithium sulphur batteries. But, it also highlights one facet of the difficulty in moving the myriad designs and improvements in lithium ion batteries reported in the literature into the commercial space: the great leap needed to develop the manufacturing processes and precision to mass produce microstructure electrodes at cost suitable for use in the mid-end of the consumer market.

 

Interested readers can find a downloadable copy of the featured image at https://figshare.com/articles/Surface_area_to_volume_ratio_concept_in_microvilli-like_sulphur_electrode_of_lithium_sulphur_batteries/4233203

 

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