Li7La3Zr2O12 Protonation as a Means to Generate Porous/Dense/Porous-Structured Electrolytes for All-Solid-State Lithium-Metal Batteries

Enhanced Solid Electrolyte Interphase Layer in Li-Ion Batteries with Fluoroethylene Carbonate Additives Evidenced by Liquid-Phase Transmission Electron Microscopy

The solid electrolyte interphase (SEI) layer is essential for battery performance and safety due to its electron insulation and Li-ion conduction. However, issues such as ongoing electrolyte decomposition and Li dendrite growth often arise. The most common strategy for improving the SEI is using electrolyte additives. However, the growth mechanism of the SEI with additives remains unclear. In this study, we use operando electrochemical liquid cell scanning transmission electron microscopy (ec-LC-STEM) to monitor in real time the nanoscale processes at the electrode-electrolyte interface during battery operation. We investigate how the additive fluoroethylene carbonate (FEC) influences the formation and properties of the SEI, as well as the growth and dissolution of Li dendrites. Our study shows that FEC decomposes early, allowing the nucleation and growth of LiF nanoparticles (NPs) that create a dense, uniform, and thin SEI layer. Interestingly, our analysis reveals that these NPs have structural defects that could influence ionic and electronic conductivity. The real-time observations show that the FEC-based SEI facilitates the formation of dense and short Li metals, whereas the FEC-free SEI leads to the growth of long Li whiskers with thinner roots than tips. This structural difference influences their dissolution mechanism: in FEC-rich electrolytes, the strong contact between Li metal and the electrode ensures complete dissolution, while in FEC-free electrolytes, partial dissolution occurs, leaving behind inactive Li metal. These findings emphasize the crucial role of additives in shaping the growth mechanism and the local structure of the SEI, thereby regulating the growth and dissolution of Li metal.

In-Situ Construction of Electronically Insulating and Air-Stable Ionic Conductor Layer on Electrolyte Surface and Grain Boundary to Enable High-Performance Garnet-Type Solid-State Batteries

Lithophobic Li2CO3/LiOH contaminants and high-resistance lithium-deficient phases produced from the exposure of garnet electrolyte to air leads to a decrease in electrolyte ion transfer ability. Additionally, garnet electrolyte grain boundaries (GBs) with narrow bandgap and high electron conductivity are potential channels for current leakage, which accelerate Li dendrites generation, ultimately leading to short-circuiting of all-solid-state batteries (ASSBs). Herein, a stably lithiophilic Li2ZO3 is in situ constructed at garnet electrolyte surface and GBs by interfacial modification with ZrO2 and Li2CO3 (Z+C) co-sintering to eliminate the detrimental contaminants and lithium-deficient phases. The Li2ZO3 formed on the modified electrolyte (LLZTO-(Z+C)) surface effectively improves the interfacial compatibility and air stability of the electrolyte. Li2ZO3 formed at GBs broadens the energy bandgaps of LLZTO-(Z+C) and significantly inhibits lithium dendrite generation. More Li+ transport paths found in LLZTO-Z+C by first-principles calculations increase Li+ conductivity from 1.04×10-4 to 7.45×10-4 S cm-1. Eventually, the Li|LLZTO-(Z+C)|Li symmetric cell maintains stable cycling for over 2000 h at 0.8 mA cm-2. The capacity retention of LiFePO4|LLZTO-(Z+C)|Li battery retains 70.5% after 5800 ultralong cycles at 4 C. This work provides a potential solution to simultaneously enhance the air stability and modulate chemical characteristics of the garnet electrolyte surface and GBs for ASSBs.

Review of the Developments and Difficulties in Inorganic Solid-State Electrolytes

All-solid-state lithium-ion batteries (ASSLIBs), with their exceptional attributes, have captured the attention of researchers. They offer a viable solution to the inherent flaws of traditional lithium-ion batteries. The crux of an ASSLB lies in its solid-state electrolyte (SSE) which shows higher stability and safety compared to liquid electrolyte. Additionally, it holds the promise of being compatible with Li metal anode, thereby realizing higher capacity. Inorganic SSEs have undergone tremendous developments in the last few decades; however, their practical applications still face difficulties such as the electrode-electrolyte interface, air stability, and so on. The structural composition of inorganic electrolytes is inherently linked to the advantages and difficulties they present. This article provides a comprehensive explanation of the development, structure, and Li-ion transport mechanism of representative inorganic SSEs. Moreover, corresponding difficulties such as interface issues and air stability as well as possible solutions are also discussed.