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Aluminum foil anodes have the potential to significantly improve the energy density, safety, cost, and sustainability of Li-ion batteries (LIB). However, their adoption is limited by their notoriously poor cycle life, and the dramatic structural transformations of Al foil anodes during formation and cycling remain poorly understood. In this work, we investigate how the nucleation and growth kinetics of LiAl control the microstructural evolution and cycle life of Al foil anodes. First, we demonstrate the unique sensitivity of Al foil anodes to the cell design and cycling conditions and emphasize the necessity of electrochemical testing in practical full cells. Operando electrochemical impedance spectroscopy (EIS) is combined with scanning electron microscope (SEM) imaging of the lithiated foils to elucidate the relationships between LiAl nucleation kinetics and the resulting LiAl microstructure. Particularly, we investigate the effects of annealing the pristine foils, and controlling the overpotential and temperature during formation, showing that as-rolled foils lithiated at high overpotentials give a columnar LiAl microstructure. Finally, we show that uncontrolled LiAl nucleation during cycling quickly destroys this favorable columnar structure, and a significant improvement in cycle life of LiFePO₄|| Al full cells is achieved by limiting the depth-of-discharge to <75%.

 

Gas evolution from high‐nickel layered oxide cathodes (>90% Ni) remains a major issue for their practical application. Gaseous species, such as CO₂, O₂, and CO, that are evolved at high states of charge (SOC) worsen the overall safety of batteries, as pressure build‐up within the cell may lead to cell rupture. Since these gasses are produced during cathode degradation, tracking the formation of gasses is also important in diagnosing cathode failure. Online electrochemical mass spectrometry (OEMS) is a powerful in situ technique to study gas evolution from the cathode during high‐voltage charge. However, the differences in the OEMS experimental setups between different groups make it challenging to compare results between groups. In this perspective, the various factors that influence gas evolution based on the OEMS results collected in this group are presented. The focus is on the conditions that lead to gas release, with a particular emphasis on reactive oxygen formation and subsequent chemical reactions with the electrolyte. Promising strategies, such as electrolytes, compositional tuning, and surface coatings that are effective at suppressing gas evolution from the cathode are highlighted. Critical insights into mitigating cathode degradation and gas evolution are provided to guide the development of safer, high‐energy batteries.

 

Enhancing the reversibility of Li is crucial for extending the cycle life of Li‐limited anode‐free lithium–sulfur (Li–S) batteries. Incorporating tellurium (Te) in the system has proven to be highly effective by its reaction with polysulfides and forming a passivating interfacial layer on Li surface, which reduces the Li‐ion diffusion barrier. However, due to the poor utilization of Te, a significant amount of Te is required to improve cell cycling performance. To address this, nanowire‐structured Te (TeNW) is synthesized via a hydrothermal method and applied to Li₂S‐based anode‐free cells to minimize the Te content in the system while extending the cell cycle life. Coating TeNW onto the separator greatly enhances Te utilization and demonstrates a significant cycle life improvement (38% retention over 300 cycles) with only 4 wt% TeNW content relative to the active material. The versatility of TeNW is further demonstrated by utilizing them with carbon nanotubes as the anode substrate. The exceptional performance of TeNW is attributed to the high‐surface‐area nanostructure and excellent conductive network, facilitating efficient electron transfer during cell cycling. These advantageous properties position TeNW as a promising material to enhance the cycle life of Li‐limited Li–S batteries.

 

The promise of secondary sulfur-based batteries as a sustainable and low-cost alternative to electrochemical energy storage has been long held back by the polysulfide shuttle problem. Herein, we demonstrate the utilization of electrolyte-soluble additives based on (oxo)thiomolybdate as a tool to mitigate the effect of the polysulfide shuttle in secondary sulfur-based batteries. Through a variety of techniques, it is shown that the Mo-containing anionic additives undergo spontaneous nucleophilic reactions with the highly soluble, long-chain polysulfides via a neutral S-atom transfer process, yielding higher S/Mo ratio complexes along with short-chain polysulfides. More importantly, it is shown how the O/S atomic substitution on the molybdenum center can induce enzymatic-level enhancement in the above reaction rate by lowering the homolytic S–S bond cleavage energy. Lastly, through anode-level inspections, it was realized that the dendritic electroplating of Li was suppressed considerably in the system with oxo/thiomolybdate, thereby reducing the cell impedance and overpotential, leading to significantly improved cycle-life. The positive influence of the increased polysulfide uptake reaction kinetics is evidenced by stable cycle-life and a low capacity-fade rate of 0.1% per cycle in Li–S cells with a high sulfur loading and lean electrolyte compositions. 

Despite the potential to become the next‐generation energy storage technology, practical lithium–sulfur (Li–S) batteries are still plagued by the poor cyclability of the lithium‐metal anode and sluggish conversion kinetics of S species. In this study, lithium tritelluride (LiTe₃), synthesized with a simple one‐step process, is introduced as a novel electrolyte additive for Li–S batteries. LiTe₃quickly reacts with lithium polysulfides and functions as a redox mediator to greatly improve the cathode kinetics and the utilization of active materials in the cathode. Moreover, the formation of a Li₂TeS₃/Li₂Te‐enriched interphase layer on the anode surface enhances ionic transport and stabilizes Li deposition. By regulating the chemistry on both the anode and cathode sides, this additive enables a stable operation of anode‐free Li–S batteries with only 0.1 mconcentration in conventional ether‐based electrolytes. The cell with the LiTe₃additive retains 71% of the initial capacity after 100 cycles, while the control cell retains only 23%. More importantly, with high utilization of Te, the additive enables significantly better cyclability of anode‐free pouch full‐cells under lean electrolyte conditions.

 

Real‐time onboard state monitoring and estimation of a battery over its lifetime is indispensable for the safe and durable operation of battery‐powered devices. In this study, a methodology to predict the entire constant‐current cycling curve with limited input information that can be collected in a short period of time is developed. A total of 10 066 charge curves of LiNiO₂‐based batteries at a constant C‐rate are collected. With the combination of a feature extraction step and a multiple linear regression step, the method can accurately predict an entire battery charge curve with an error of < 2% using only 10% of the charge curve as the input information. The method is further validated across other battery chemistries (LiCoO₂‐based) using open‐access datasets. The prediction error of the charge curves for the LiCoO₂‐based battery is around 2% with only 5% of the charge curve as the input information, indicating the generalization of the developed methodology for predicting battery cycling curves. The developed method paves the way for fast onboard health status monitoring and estimation for batteries during practical applications.

 

The electrochemical behavior of sulfur-based batteries is intrinsically governed by polysulfide species. Here, we compare the substitutions of selenium and tellurium into polysulfide chains and demonstrate their beneficial impact on the chemistry of lithium–sulfur batteries. While selenium-substituted polysulfides enhance cathode utilization by effectively catalyzing the sulfur/Li 2 S conversion reactions due to the preferential formation of radical intermediates, tellurium-substituted polysulfides improve lithium cycling efficiency by reducing into a passivating interfacial layer on the lithium surface with low Li + -ion diffusion barriers. This unconventional strategy based on “molecular engineering” of polysulfides and exploiting the intrinsic polysulfide shuttle effect is validated by a ten-fold improvement in the cycle life of lean-electrolyte “anode-free” pouch cells. Assembled with no free lithium metal at the anode, the anode-free configuration maximizes the energy density, mitigates the challenges of handling thin lithium foils, and eliminates self-discharge upon cell assembly. The insights generated into the differences between selenium and tellurium chemistries can be applied to benefit a broad range of metal–chalcogen batteries as well as chalcogenide solid electrolytes. 

Sodium–sulfur (Na–S) batteries with durable Na‐metal stability, shuttle‐free cyclability, and long lifespan are promising to large‐scale energy storages. However, meeting these stringent requirements poses huge challenges with the existing electrolytes. Herein, a localized saturated electrolyte (LSE) is proposed with 2‐methyltetrahydrofuran (MeTHF) as an inner sheath solvent, which represents a new category of electrolyte for Na–S system. Unlike the traditional high concentration electrolytes, the LSE is realized with a low salt‐to‐solvent ratio and low diluent‐to‐solvent ratio, which pushes the limit of localized high concentration electrolyte (LHCE). The appropriate molecular structure and solvation ability of MeTHF regulate a saturated inner sheath, which features a reinforced coordination of Na⁺to anions, enlarged Na⁺‐solvent distance, and weakened anion‐diluent interaction. Such electrolyte configuration is found to be the key to build a sustainable interphase and a quasi‐solid–solid sulfur redox process, making a dendrite‐inhibited and shuttle‐free Na–S battery possible. With this electrolyte, pouch cells with decent cycling performance under rather demanding conditions are demonstrated.