Li2ZnCu3 modified Cu current collector to regulate Li deposition.

Rationally designing a current collector that can maintain low lithium (Li) porosity and smooth morphology while enduring high-loading Li deposition is crucial for realizing the high energy density of Li metal batteries, but it is still challengeable. Herein, a Li2ZnCu3 alloy-modified Cu foil is reported as a stable current collector to fulfill the stable high-loading Li deposition. Benefiting from the in-situ alloying, the generated numerous Li2ZnCu3@Cu heterojunctions induce a homogeneous Li nucleation and dense growth even at an ultrahigh capacity of 12 mAh cm-2. Such a spatial structure endows the overall Li2ZnCu3@Cu electrode with the manipulated steric hindrance and outmost surface electric potential to suppress the side reactions during Li stripping and plating. The resultant Li||Li2ZnCu3@Cu asymmetric cell preserves an ultrahigh average Coulombic efficiency of 99.2% at 3 mA cm-2/6 mAh cm-2 over 200 cycles. Moreover, the Li-Li2ZnCu3@Cu||LiFePO4 cell maintains a cycling stability of 87.5% after 300 cycles. After coupling with the LiCoO2 cathode (4 mAh cm-2), the cell exhibits a high energy density of 407.4 Wh kg-1 with remarkable cycling reversibility at an N/P ratio of 3. All these findings present a doable way to realize the high-capacity, dendrite-free, and dense Li deposition for high-performance Li metal batteries.

A Low-Temperature Na-MoS2 Rechargeable Battery.

It is generally accepted that the low-temperature environment typically augments electrolyte viscosity and impedes electrochemical kinetics, thereby diminishing battery performance. However, this prevailing notion, while valid in certain contexts, lacks universality, particularly regarding cycling stability. In this context, the Na-MoS2 batteries serve as a model to elucidate the impacts of low temperatures. By significantly suppressing the pulverization and amorphization of MoS2, the low-temperature milieu effectively mitigates the risk of micro-short circuits induced by the mass shuttling to the Na metal anode, thereby averting performance degradation by self-discharge. Upon cycling, the generated NaxMo3S4 intermediates only at low temperatures benefit the structural and electrochemical stabilizations to counteract the intrinsic performance degradation. The attenuation of kinetics at low temperatures facilitates the accumulation of Na2S, akin to a sustained-release agent within the electrode, steadily furnishing the capacity in long cycling. Moreover, the suppression of polysulfide dissolution and shuttling emerges as a pivotal factor contributing to the cycling stability at low-temperature. These findings provide a rewarding avenue toward understanding of the influence of low temperature on battery performance, as well as the design of practical electrodes and batteries for low-temperature applications.

Hierarchical Li electrochemistry using alloy-type anode for high-energy-density Li metal batteries.

Exploiting thin Li metal anode is essential for high-energy-density battery, but is severely plagued by the poor processability of Li, as well as the uncontrollable Li plating/stripping behaviors and Li/electrolyte interface. Herein, a thickness/capacity-adjustable thin alloy-type Li/LiZn@Cu anode is fabricated for high-energy-density Li metal batteries. The as-formed lithophilic LiZn alloy in Li/LiZn@Cu anode can effectively regulate Li plating/stripping and stabilize the Li/electrolyte interface to deliver the hierarchical Li electrochemistry. Upon charging, the Li/LiZn@Cu anode firstly acts as Li source for homogeneous Li extraction. At the end of charging, the de-alloy of LiZn nanostructures further supplements the Li extraction, actually playing the Li compensation role in battery cycling. While upon discharging, the LiZn alloy forms just at the beginning, thereby regulating the following Li homogeneous deposition. The reversibility of such an interesting process is undoubtedly verified from the electrochemistry and in-situ XRD characterization. This work sheds light on the facile fabrication of practical Li metal anodes and useful Li compensation materials for high-energy-density Li metal batteries.

Quasi-In Situ XPS Insights into the Surface Chemistry of Garnet-Type Li6.4La3Zr1.4Ta0.6O12 Solid-State Electrolytes: The Overlooked Impact of Pretreatments and a Direct Observation of the Formation of LiOH.

Garnet-type Li6.4La3Zr1.4Ta0.6O12 (LLZTO) is a highly promising solid-state lithium metal battery electrolyte due to its exceptional ionic conductivity and electrochemical stability. However, when exposed to air, a passivation layer can be spontaneously formed on the garnet-type electrolyte, deteriorating its wettability with metallic lithium (Li) and impeding the lithium ion transfer at the Li-garnet electrolyte interface. The passivation layer is considered a critical issue for garnet-type solid electrolytes. Despite intensive research, the formation mechanism of the passivation film remains poorly understood. The key to elucidating the formation mechanism is to obtain a pristine garnet electrolyte surface and study how the pristine garnet electrolyte interacts with air. In this study, different passivation layer removal pretreatments were performed to expose pristine garnet electrolytes, and their impacts on the samples were systematically studied. The results reveal the overlooked negative impacts of vacuum annealing and acid treatment on LLZTO, which are indicated by the severe loss of Li and O and the formation of additional Li-depleted metal oxides. It was confirmed that argon annealing is the only viable approach to remove the passivation layer without introducing concomitant contaminations to LLZTO. Based on this method, we directly evidenced the formation of LiOH on LLZTO under rarefied air using quasi-in situ X-ray photoelectron spectroscopy. It was confirmed that the loss of Li and O ions, rather than Li+/H+ exchange, drives the formation of LiOH in the passivation layer. These results not only provide a better understanding of the surface and interface chemistry of LLZTO but also reveal a reliable surface treatment for the LLZTO sample.