The commercial uptake of lithium-sulfur (Li-S) batteries is undermined by their rapid performance decay and short cycle life. These problems originate from the dissolution of lithium polysulfide in liquid electrolytes, causing charge and active material to shuttle between electrodes. The dynamics of intractable polysulfide migration at different length scales often tend to escape the probing ability of many analytical techniques. Spatial and temporal visualization of Li in Li-S electrodes and direct mechanistic understanding of how polysulfides are regulated across Li-S batteries starting from current collector and active layer coating to electrode-electrolyte interface are still lacking. To address this we employ neutron depth profiling across Li-S electrodes using the naturally occurring isotope, 6Li, which yields direct spatial information on Li-S electrochemistry. Using three types of Li-S electrodes, namely, carbon-sulfur, carbon-sulfur with 10% lithium titanium oxide (LTO), and carbon-sulfur with LTO membrane, we provide direct evidence for the migration, adsorption, and confinement of polysulfides in Li-S cells at work. Our findings further provide insights into the dynamics of polysulfide dissolution and re-utilization in relation to Li-S battery capacity and longevity to aid rational electrode designs toward high-energy, safe, and low-cost batteries.

Enabling the transition to renewable power sources requires further optimization of batteries in terms of energy/power density and cost-effectiveness. Increasing the practical thickness of Li ion battery electrodes not only can improve energy density on cell level but reduces manufacturing cost. However, thick electrodes exhibit sluggish charge-transport kinetics and are mechanically less stable, typically resulting in substandard battery performance compared to the current commercial standards (~50 μm). Here we disclose a novel method based on immersion precipitation by employing a non-solvent to solidify the battery binder, instead of solvent evaporation. This method allows for the fabrication of thick and suitable density electrodes (>100 μm with ultra-high mass loading) offering excellent electrochemical performance and mechanical stability. Using commercial electrode active materials at a remarkable mass-loading of 24 mg cm⁻², the electrodes processed via immersion method are shown to deliver 3.5 mAh cm⁻² at a rate of 2C and operate at rates up to 10C. As additional figure of merit, this method produces electrodes that are both stand-alone and highly flexible, which have been evaluated in flexible full-cells. Furthermore, via immersion precipitation the commonly used more toxic N-Methyl-2-pyrrolidone can be supplanted by environmentally benign dimethyl sulfoxide as solvent for processing electrode layers.

Computational modeling is vital for the fundamental understanding of processes in Li-ion batteries. However, capturing nanoscopic to mesoscopic phase thermodynamics and kinetics in the solid electrode particles embedded in realistic electrode morphologies is challenging. In particular for electrode materials displaying a first order phase transition, such as LiFePO₄, graphite, and spinel Li₄Ti₅O₁₂, predicting the macroscopic electrochemical behavior requires an accurate physical model. Herein, a thermodynamic phase field model is presented for Li-ion insertion in spinel Li₄Ti₅O₁₂ which captures the performance limitations presented in literature as a function of all relevant electrode parameters. The phase stability in the model is based on ab initio density functional theory calculations and the Li-ion diffusion parameters on nanoscopic nuclear magnetic resonance (NMR) measurements of Li-ion mobility, resulting in a parameter free model. The direct comparison with prepared electrodes shows good agreement over three orders of magnitude in the discharge current. Overpotentials associated with the various charge transport processes, as well as the active particle fraction relevant for local hotspots in batteries, are analyzed. It is demonstrated which process limits the electrode performance under a variety of realistic conditions, providing comprehensive understanding of the nanoscopic to microscopic properties. These results provide concrete directions toward the design of optimally performing Li₄Ti₅O₁₂ electrodes.

Li and Na metals have the highest theoretical anode capacity for Li/Na batteries, but the operational safety hazards stemming from uncontrolled growth of Li/Na dendrites and unstable electrode-electrolyte interfaces hinder their real-world applications. Recently, the emergence of 3D conductive scaffolds aimed at mitigating the dendritic growth to improve the cycling stability has gained traction. However, while achieving 3D scaffolds that are conducive to completely prevent dendritic Li/Na is challenging, the routes proposed to fabricate 3D scaffolds to date are often complex and expensive. This not only leads to sub-optimal battery performance but can make the manufacturing nearly unachievable, compromising their commercial viability. We herein introduce a facile and single-step route to honeycomb-like 3D porous Ni@Cu scaffolds via a hydrogen bubble dynamic template (HBDT) electrodeposition method. The current collectors fabricated by this method offer highly stable cycling performance of Li plating/stripping (>300 cycles at 0.5 mAh cm⁻² and over 200 cycles at 1.0 mAh cm⁻²), attributed to their ability to effectively accommodate Li/Na deposits in their porous networks and to delocalize the charge distribution. The beneficial role of LiNO₃ as an electrolyte additive in improving the mechanical integrity of solid electrolyte interface (SEI) and mechanistic insights into how the 3D porous structure facilitates Li/Na plating/stripping are comprehensively presented. Finally, with an outstanding cycling performance of reversible Na deposition (over 240, 110 and 50 cycles for 0.5, 1.0 and 2.0 mAh cm⁻² at 1.0 mA cm⁻²), our findings open new doors to expedite the development of Li/Na metal battery technology.

Nanostructured silicon has been intensively investigated as a high capacity Li-ion battery anode. However, the commercial introduction still requires advances in the scalable synthesis of sophisticated Si nanomaterials and electrodes. Moreover, the electrode degradation due to volume changes upon de-/lithiation, low areal electrode capacity, and application of large amounts of advanced conductive additives are some of the challenging aspects. Here we report a Si electrode, prepared from direct deposition of Si nanoparticles on a current collector without any binder or conducting additives, that addresses all of the above issues. It exhibits an excellent cycling stability and a high capacity retention taking advantages of what appears to be a locally protective, yolk-shell reminiscent, solid electrolyte interphase (SEI) formation. Cycling an electrode with a Si nanoparticle loading of 2.2 mg cm⁻² achieved an unrivalled areal capacity retention, specifically, up to 4.2 mAh cm⁻² and ~ 1.5 mAh cm⁻² at 0.8 mA cm⁻² and 1.6 mA cm⁻², respectively.

Li₄Ti₅O₁₂ is well known to be a safe and efficient anode material for Li-ion batteries. A metal-organic chemical vapor deposition process has been developed for the synthesis of Li₄Ti₅O₁₂ thin film anodes on planar and 3D substrates. The influences of various deposition parameters, including precursor flow rates and post-annealing temperatures, have been investigated by material and electrochemical analyses. Li₄Ti₅O₁₂ thin films deposited at the optimized process parameters showed a high crystallinity and high electrochemical activity. A reversible storage capacity of 151 mAh/g was achieved at a current of 0.5 C, corresponding to 86.3% of the theoretical specific capacity of Li₄Ti₅O₁₂. Up to almost 600 cycles, the electrodes showed no significant capacity loss. Furthermore, the deposited thin film anodes also showed excellent rate performance. Compared to the storage capacity at 0.5 C, 93% of the capacity was maintained at 10 C. Thin films were also deposited on highly structured substrates to investigate the uniformity and electrochemical performance. With the same footprint area, the 3D Li₄Ti₅O₁₂ film anode showed a 2.5 times higher storage capacity than planar electrode.