Deciphering the Lithium-Ion Conduction Mechanism of LiH in Solid-Electrolyte Interphase.

Lithium hydride (LiH) has been widely recognized as the critical component of the solid-electrolyte interphase (SEI) in Li batteries. Although the formation mechanism and structural model of LiH in SEI have been extensively reported, the role in electro-performance of LiH in SEI is still ambiguous and has proven challenging to explored due to the complicated structure SEI and the lack of advanced in situ experimental technology. In this study, the isotopic exchange experiments combined with isotopic tracer experiments is applied to solidly illustrate the superior conductivity and Li+ conduction behavior of the LiH in natural SEI. Importantly, in situ transmission electron microscopy analysis is utilized to visualize the self-electrochemical decomposition of LiH, which is significantly distinctive from LiF and Li2O. The critical experimental evidence discovered by the work demonstrates ion transport behaviors of key components in the SEI, which is imperative for designing novel SEI and augurs a new area in optimizing the performance of lithium batteries.

Lithium Hydride in the Solid Electrolyte Interphase of Lithium-Ion Batteries as a Pulverization Accelerator of Silicon.

As a highly promising next-generation high-specific capacity anode, the industrial-scale utilization of micron silicon has been hindered by the issue of pulverization during cycling. Although numerous studies have demonstrated the effectiveness of regulating the inorganic components of the solid electrolyte interphase (SEI) in improving pulverization, the evolution of most key inorganic components in the SEI and their correlation with silicon failure mechanisms remain ambiguous. This study provides a clear and direct correlation between the lithium hydride (LiH) in the SEI and the degree of micron silicon pulverization in the battery system. The reverse lithiation behavior of LiH on micron silicon during de-lithiation exacerbates the localized stress in silicon particles and contributes to particle pulverization. This work successfully proposes a novel approach to decouple the SEI from electrochemical performance, which can be significant to decipher the evolution of critical SEI components at varied battery anode interfaces and analyze their corresponding failure mechanisms.

Revealing Capacity Degradation of Ge Anodes in Lithium-Ion Batteries Triggered by Interfacial LiH.

The Germanium (Ge), as a fast-charging and high specific capacity (1568 mAh g-1 ) alloy anode, is greatly hampered in practical application by poor cyclability. To date, the understanding of cycling performance degradation remains elusive. This study illustrates that, contrary to conventional beliefs, most of the Ge material in failed anodes still retains good integrity and does not undergo severe pulverization. It is revealed that capacity degradation is clearly correlated to the interfacial evolution of lithium hydride (LiH). Tetralithium germanium hydride (Li4 Ge2 H), as a new species derived from LiH, is identified as the culprit of Ge anode degradation, which is the dominant crystalized component in an ever-growing and ever-insulating interphase. The significantly increased thickness of the solid electrolyte interface (SEI) is accompanied by the accumulation of insulating Li4 Ge2 H upon cycling, which severely retards the charge transport process and ultimately triggers the anode failure. We believe that the comprehensive understanding of the failure mechanism presented in this study is of great significance to promoting the design and development of alloy anode for the next generation of lithium-ion batteries.

Robust Transport: An Artificial Solid Electrolyte Interphase Design for Anode-Free Lithium-Metal Batteries.

One of the most challenging issues in the practical implementation of high-energy-density anode-free lithium-metal batteries (AFLMBs) is the sharp capacity attenuation caused by the mechanical degradation of the solid electrolyte interphase (SEI). However, developing an artificial SEI to address this issue remains a challenge due to the trade-off between ionic conductivity and mechanical robustness for general ionic conducting films. In this study, a tenacious composite artificial SEI with integrated heterostructure of lithium fluoride (LiF) and lithium phosphorus oxynitride (LiPON) is prepared using a co-sputtering approach to achieve both high ionic conductivity and fracture toughness. The embedded LiF domain has an extremely high Young's modulus and surface energy compared with those of bulk LiPON film, enabling a significant increase in fracture toughness by an order of magnitude. Most importantly, the interface between LiPON and LiF in the integrated structure generates additional fast Li+ -transport pathways, providing the artificial SEI with a conductivity higher than 10-6 S cm-1 . Consequently, the artificial SEI implementation significantly increases the cycling lifetime of the corresponding AFLMBs by >250%. This study highlights the importance of fracture toughness for the structural integrity of batteries and provides suggestions for designing viable SEI materials for high-performance AFLMBs.

Water-Locked Eutectic Electrolyte Enables Long-Cycling Aqueous Sodium-Ion Batteries.

Aqueous sodium batteries are one of the awaited technologies for large-scale energy storage, but remain poorly rechargeable because of the reactivity issues of water. Here, we present a hydrated eutectic electrolyte featuring a water-locked effect, which is exceptional in that the O-H bond of water is essentially strengthened via weak hydrogen bonding (relative to the original H2O-H2O hydrogen bonds) to low-donor-number anions and ligands. Even without interphase protection, both the anodic and cathodic water electrodecomposition reactions are delayed, extending the aqueous potential window to 3.4 V. Combined with the alleviated electrode dissolution, Na2MnFe(CN)6||NaTi2(PO4)3 batteries deliver a high energy density of ∼80 W h kg-1 at 0.5 C and undergo over 1000 cycles with a 74.5% capacity retention and a 99.4% Coulombic efficiency at 4.2 C. This work may offer a general guide to ultimately exploit the water's innate stability for realizing the promise of aqueous battery technologies.

A Superior Polymer Electrolyte with Rigid Cyclic Carbonate Backbone for Rechargeable Lithium Ion Batteries.

The fabricating process of well-known Bellcore poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP)-based polymer electrolytes is very complicated, tedious, and expensive owing to containing a large amount of fluorine substituents. Herein, a novel kind of poly(vinylene carbonate) (PVCA)-based polymer electrolyte is developed via a facile in situ polymerization method, which possesses the merits of good interfacial compatibility with electrodes. In addition, this polymer electrolyte presents a high ionic conductivity of 5.59 × 10-4 S cm-1 and a wide electrochemical stability window exceeding 4.8 V vs Li+/Li at ambient temperature. In addition, the rigid cyclic carbonate backbone of poly(vinylene carbonate) endows polymer electrolyte a superior mechanical property. The LiFe0.2Mn0.8PO4/graphite lithium ion batteries using this polymer electrolyte deliver good rate capability and excellent cyclability at room temperature. The superior performance demonstrates that the PVCA-based electrolyte via in situ polymerization is a potential alternative polymer electrolyte for high-performance rechargeable lithium ion batteries.