Dendrite-Free Lithium Metal Anodes in High Performance Lithium-Sulfur Batteries with Bifunctional Carbon Nanofiber Interlayers

A Review of Carbon Nanofiber Materials for Dendrite-Free Lithium-Metal Anodes

Lithium metal is regarded as ideal anode material due to its high theoretical specific capacity and low electrode potential. However, the uncontrollable growth of lithium dendrites seriously hinders the practical application of lithium-metal batteries (LMBs). Among various strategies, carbon nanofiber materials have shown great potential in stabilizing the lithium-metal anode (LMA) due to their unique functional and structural characteristics. Here, the latest research progress on carbon nanofibers (CNFs) for LMA is systematically reviewed. Firstly, several common preparation techniques for CNFs are summarized. Then, the development prospects, strategies and the latest research progress on CNFs for dendrite-free LMA are emphatically introduced from the perspectives of neat CNFs and CNF-based composites. Finally, the current challenges and prospects of CNFs for stabilizing LMA are summarized and discussed. These discussions and proposed strategies provide new ideas for the development of high-performance LMBs.

Lithium-Sulfur Batteries Meet Electrospinning: Recent Advances and the Key Parameters for High Gravimetric and Volume Energy Density

Lithium-sulfur (Li-S) batteries have been regarded as a promising next-generation energy storage technology for their ultrahigh theoretical energy density compared with those of the traditional lithium-ion batteries. However, the practical applications of Li-S batteries are still blocked by notorious problems such as the shuttle effect and the uncontrollable growth of lithium dendrites. Recently, the rapid development of electrospinning technology provides reliable methods in preparing flexible nanofibers materials and is widely applied to Li-S batteries serving as hosts, interlayers, and separators, which are considered as a promising strategy to achieve high energy density flexible Li-S batteries. In this review, a fundamental introduction of electrospinning technology and multifarious electrospinning-based nanofibers used in flexible Li-S batteries are presented. More importantly, crucial parameters of specific capacity, electrolyte/sulfur (E/S) ratio, sulfur loading, and cathode tap density are emphasized based on the proposed mathematic model, in which the electrospinning-based nanofibers are used as important components in Li-S batteries to achieve high gravimetric (WG ) and volume (WV ) energy density of 500 Wh kg-1 and 700 Wh L-1 , respectively. These systematic summaries not only provide the principles in nanofiber-based electrode design but also propose enlightening directions for the commercialized Li-S batteries with high WG and WV .

Graphene Oxide Induced Surface Modification for Functional Separators in Lithium Secondary Batteries

Functional separators, which have additional functions apart from the ionic conduction and electronic insulation of conventional separators, are highly in demand to realize the development of advanced lithium ion secondary batteries with high safety, high power density, and so on. Their fabrication is simply performed by additional deposition of diverse functional materials on conventional separators. However, the hydrophobic wetting nature of conventional separators induces the polarity-dependent wetting feature of slurries. Thus, an eco-friendly coating process of water-based slurry that is highly polar is hard to realize, which restricts the use of various functional materials dispersible in the polar solvent. This paper presents a surface modification of conventional separators that uses a solution-based coating of graphene oxide with a hydrophilic group. The simple method enables the large-scale tuning of surface wetting properties by altering the morphology and the surface polarity of conventional separators, without significant degradation of lithium ion transport. On the surface modified separator, superior wetting properties are realized and a functional separator, applicable to lithium metal secondary batteries, is demonstrated as an example. We believe that this simple surface modification using graphene oxide contributes to successful fabrication of various functional separators that are suitable for advanced secondary batteries.

A thin TiO2 NTs/GO hybrid membrane applied as an interlayer for lithium–sulfur batteries

Lithium–sulfur batteries hold great promise for serving as next generation high energy density batteries.

Dendrite formation in silicon anodes of lithium-ion batteries

Rechargeable lithium-ion batteries require a vigorous improvement if we want to use them massively for high energy applications. Silicon and metal lithium anodes are excellent alternatives because of their large theoretical capacity when compared to graphite used in practically all rechargeable Li-ion batteries. However, several problems need to be addressed satisfactorily before a major fabrication effort can be launched; for instance, the growth of lithium dendrites is one of the most important to take care due to safety issues. In this work we attempt to predict the mechanism of dendrite growth by simulating possible behaviors of charge distributions in the anode of an already cracked solid electrolyte interphase of a nanobattery, which is under the application of an external field representing the charging of the battery; thus, elucidating the conditions for dendrite growth. The extremely slow drift velocity of the Li-ions of ∼1 mm per hour in a typical commercial Li-ion battery, makes the growth of a dendrite take a few hours; however, once a Li-ion arrives at an active site of the anode, it takes an extremely short time of ∼1 ps to react. This large difference in time-scales allows us to perform the molecular dynamics simulation of the ions at much larger drift velocities, so we can have valuable results in reasonable computational times. The conditions before the growth are assumed and conditions that do not lead to the growth are ignored. We performed molecular dynamics simulations of a pre-lithiated silicon anode with a Li : Si ratio of 21 : 5, corresponding to a fully charged battery. We simulate the dendrite growth by testing a few charge distributions in a nanosized square representing a crack of the solid electrolyte interphase, which is where the electrolyte solution comes into direct contact with the LiSi alloy anode. Depending on the selected charge distributions for such an anode surface, the dendrites grow during the simulation when an external field is applied. We found that dendrites grow when strong deviations of charge distributions take place on the surface of the crack. Results from this work are important in finding ways to constrain lithium dendrite growth using tailored coatings or pre-coatings covering the LiSi alloy anode.

Dendrite formation conditions on a SEI crack exposing the silicon anode to the electrolyte during the charging of a LIB.