Lithium Sulfur (Li-S) batteries are one of the most promising next generation battery chemistries with potential to achieve 500-600 Wh/kg in the next few years. Yet understanding the underlying mechanisms of operation remains a major obstacle to their continued improvement. From a review of a range of analytical studies and physical models, it is clear that experimental understanding is well ahead of state-of-the-art models. Yet this understanding is still hindered by the limitations of available techniques and the implications of experiment and cell design on the mechanism. The mechanisms at the cor e of physical models for Li-S cells are overly simplistic compared to the latest thinking based upon experimental results, but creating more complicated models will be difficult, due to the lack of and inability to easily measure the necessary parameters. Despite this, there are significant opportunities to improve models with the latest experimentally derived mechanisms. Such models can inform materials research and lead to improved high fidelity models for controls and application engineers.

Prevention and mitigation of thermal runaway presents one of the greatest challenges for the safe operation of lithium-ion batteries. Here, we demonstrate for the first time the application of high-speed synchrotron X-ray computed tomography and radiography, in conjunction with thermal imaging, to track the evolution of internal structural damage and thermal behaviour during initiation and propagation of thermal runaway in lithium-ion batteries. This diagnostic approach is applied to commercial lithium-ion batteries (LG 18650 NMC cells), yielding insights into key degradation modes including gas-induced delamination, electrode layer collapse and propagation of structural degradation. It is envisaged that the use of these techniques will lead to major improvements in the design of Li-ion batteries and their safety features.

This is a pre-print version of: Offer, G.J., et al., Comparative analysis of battery electric, hydrogen fuel cell and hybrid vehicles in a future sustainable road transport system. Energy Policy (2009Policy ( ), doi:10.1016Policy ( /j.enpol.2009 AbstractThis paper compares battery electric vehicles (BEV) to hydrogen fuel cell electric vehicles (FCEV) and hydrogen fuel cell plug-in hybrid vehicles (FCHEV). Qualitative comparisons of technologies and infrastructural requirements, and quantitative comparisons of the lifecycle cost of the powertrain over 100,000 miles are undertaken, accounting for capital and fuel costs. A common vehicle platform is assumed. The 2030 scenario is discussed and compared to a conventional gasoline-fuelled internal combustion engine (ICE) powertrain. A comprehensive sensitivity analysis shows that in 2030 FCEVs could achieve lifecycle cost parity with conventional gasoline vehicles. However, both the BEV and FCHEV have significantly lower lifecycle costs. In the 2030 scenario, powertrain lifecycle costs of FCEVs range from $7,360 to $22,580, whereas those for BEVs range from $6,460 to $11,420 and FCHEVs, from $4,310 to $12,540. All vehicle platforms exhibit significant cost sensitivity to powertrain capital cost. The BEV and FCHEV are relatively insensitive to electricity costs but the FCHEV and FCV are sensitive to hydrogen cost. The BEV and FCHEV are reasonably similar in lifecycle cost and one may offer an advantage over the other depending on driving patterns. A key conclusion is that the best path for future development of FCEVs is the FCHEV.

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A picture of the challenges faced by the lithium-sulfur technology and the activities pursued by the research community to solve them is synthesized based on 1992 scientific articles. It is shown that, against its own advice of adopting a balanced approach to development, the community has instead focused work on the cathode. To help direct future work, key areas of neglected research are highlighted, including cell operation studies, modelling, anode, electrolyte and production methods, as well as development goals for real world target applications such as high altitude unmanned aerial vehicles. Lithium Sulfur (Li-S) batteries are one of the most promising next generation battery technologies 1 due to their high theoretical energy density, low materials cost, and relative safety.2 Li-S has the potential to achieve significantly higher gravimetric energy density than intercalation based lithium ion technologies, 3 with some companies already reporting 400 Wh/kg cells. 4,5 However, Li-S has a lower comparable volumetric energy, 6 suggesting that applications where minimising mass is more important than volume will adopt it faster. Li-S technology is close to industrial production, 7 with a number of companies scaling up manufacturing capabilities for large capacity cells. 4,5 Meanwhile, the number of Li-S research papers published per year has increased dramatically from less than 50 in 2010 to over 900 in 2016. We have reviewed almost two thousand articles to identify the major gaps in research and discussed how targeting them could speed up the development and adoption of Li-S technology. We also discuss how from an industry/applied research viewpoint focussing on a performance metric, such as power density, would speed up development iterations, getting products to market sooner and help unlock further research funding. Current StatusLi-S cells are already commercially viable in niche applications. In order to expand their market potential, however, there are still many challenges to overcome, such as limited cycle life, high self-discharge rates and over-heating at end of charge. Many of these are thought to be caused by the shuttle, where cathode species diffuse to the anode and react directly with the metallic lithium.8 Multiple solutions have therefore been proposed to prevent shuttle, such as physically 9,10 or chemically 11-13 encapsulating the sulfur, designing tailored carbon structures, 14 using electrolyte additives, 15,16 separators, 17 protective layers, 18 or solid electrolytes to physically protect the anode. 19-21However, many of these solutions affect energy or power density adversely or do not function in practical commercial cells. Li-S batteries also undergo significant volume changes during operation, which poses a particular challenge for battery pack system designers and is being studied only since recently. 22 These observations have only been possible since large form factor pouch cells are available. The effect of precipitation on useable capacity and reversible capacity loss, 23 and ...