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In this growing age of clean energy and the use of power storage to circumvent the use of traditional fossil fuel technologies, batteries of greater capacity, storage, and power are increasingly becoming indispensable. New chemistries are being developed to increase the capacity of traditional lithium ion batteries and to develop batteries beyond Lithium ion. Promising high capacity cathodes and anodes are developed however their large-scale deployment is hindered due to safety concerns. In this review, we summarize recent progress of lithium ion batteries safety, highlight current challenges, and outline the most advanced safety features that may be incorporated to improve battery safety for both lithium ion and batteries beyond lithium ion. Of particular interest is the issue of thermal runaway mitigation by incorporation of novel nano-materials and advanced technologies.

Sulfur remains in the spotlight as a future cathode candidate for the post-lithium-ion age. This is primarily due to its low cost and high discharge capacity, two critical requirements for any future cathode material that seeks to dominate the market of portable electronic devices, electric transportation, and electric-grid energy storage. However, before Li–S batteries replace lithium ion batteries, several technical challenges need to be solved. Among these challenges are polysulfide containment, the increase of sulfur loading (which must be ≥4–6 mg cm –2), the increase of sulfur fraction to ≥70%, the increase of sulfur utilization to ≥80%, the decrease of the electrolyte/sulfur weight ratio (which must be in the range of 3:1 or lower), and the stability of lithium anode material. Besides traditional carbon coating strategies, recent novel strategies addressing each of these challenges have been reported. The main purpose of this work is to review the state of the art and summarize and shed light on the most promising recent discoveries related to each challenge. This review also addresses the role of the electrolyte systems and electrocatalytic additives.

Hierarchical material nanostructuring is considered to be a very promising direction for high performance thermoelectric materials. In this work we investigate thermal transport in hierarchically nanostructured silicon. We consider the combined presence of nanocrystallinity and nanopores, arranged under both ordered and randomized positions and sizes, by solving the Boltzmann transport equation using the Monte Carlo method. We show that nanocrystalline boundaries degrade the thermal conductivity more drastically when the average grain size becomes smaller than the average phonon mean-free-path. The introduction of pores degrades the thermal conductivity even further. Its effect, however, is significantly more severe when the pore sizes and positions are randomized, as randomization results in regions of higher porosity along the phonon transport direction, which introduce significant thermal resistance. We show that randomization acts as a large increase in the overall effective porosity. Using our simulations, we show that existing compact nanocrystalline and nanoporous theoretical models describe thermal conductivity accurately under uniform nanostructured conditions, but overestimate it in randomized geometries. We propose extensions to these models that accurately predict the thermal conductivity of randomized nanoporous materials based solely on a few geometrical features. Finally, we show that the new compact models introduced can be used within Matthiessen's rule to combine scattering from different geometrical features within ~10% accuracy. . 3.7 Wm −1 K −1 for an average pore size of ~ 30 nm and grain sizes between 50 and 80 nm. 21 By reducing both pore and grain sizes, however, Basu et al. reported κ = 1.2 Wm −1 K −1 at 40% porosity in p-type silicon. 22 A recent work in SiGe nanomeshes, reported ultralow κ of 0.55 ± 0.10 Wm −1 K −1 for SiGe nanocrystalline nanoporous structures, a value well below the amorphous limit. 23 A significant amount of work can be found in the literature attempting to clarify these experimental observations. However, theoretical investigations of thermal conductivity in highly/hierarchically disordered nanostructures (which include not only crystalline boundaries, but also pores of random sizes placed at random positions) are very limited. Understanding the qualitative and quantitative details of such geometries on the thermal conductivity would allow the design of more efficient thermoelectrics and heat management materials in general. In this work, we solve the Boltzmann transport equation for phonons in disordered Si nanostructures using the Monte Carlo (MC) method. Monte Carlo, which can capture the details of geometry with relative accuracy, is widely employed to understand phonon transport in various nanostructures such as nanowires, 24,25,26 thin films, 27,28 nanoporous materials, 29,30,31,32,33 polycrystalline materials, 10,15,34,35,36 nanocomposites, 37,38 corrugated structures, 39,40,41,42 silicon-on-insulator devices, 43 etc. We consider geometries that include grai...