In Situ Analysis of Interfacial Morphological and Chemical Evolution in All-Solid-State Lithium-Metal Batteries.

Visualizing lithium (Li) ions and understanding Li plating/stripping processes as well as evolution of solid electrolyte interface (SEI) are critical for optimizing all-solid-state Li metal batteries (ASSLMB). However, the buried solid-solid interfaces present a challenge for detection which preclude the employment of multiple analysis techniques. Herein, by employing complementary in situ characterizations, morphological/chemical evolution, Li plating/stripping dynamics and SEI dynamics were efficiently decoupled and Li ion behavior at interface between different solid-state electrolytes (SSE) was successfully detected. The innovative combining experiments of in situ atomic force microscopy and in situ X-ray photoelectron spectroscopy on Li metal anode revealed interfacial morphological/chemical evolution and decoupled Li plating/stripping process from SEI evolution. Though Li plating speed in Li10GeP2S12 (LGPS) was higher than Li3PS4 (LPS), speed of SSE decomposition was similar and ~85% interfacial SSE turned into SEI during plating and remained unchanged in stripping. To leverage strengths of different SSEs, an LPS-LGPS-LPS sandwich electrolyte was developed, demonstrating enhanced ionic conductivity and improved interfacial stability with less SSE decomposition (25%). Using in situ Kelvin Probe Force Microscopy, Li-ion behavior at interface between different SSEs was effectively visualized, uncovering distribution of Li ions at LGPS|LPS interface under different potentials.

Revealing the CO2 Conversion at Electrode/Electrolyte Interfaces in Li-CO2 Batteries via Nanoscale Visualization Methods.

Lithium-carbon dioxide (Li-CO2 ) battery technology presents a promising opportunity for carbon capture and energy storage. Despite tremendous efforts in Li-CO2 batteries, the complex electrode/electrolyte/CO2 triple-phase interfacial processes remain poorly understood, in particular at the nanoscale. Here, using in situ atomic force microscopy and laser confocal microscopy-differential interference contrast microscopy, we directly observed the CO2 conversion processes in Li-CO2 batteries at the nanoscale, and further revealed a laser-tuned reaction pathway based on the real-time observations. During discharge, a bi-component composite, Li2 CO3 /C, deposits as micron-sized clusters through a 3D progressive growth model, followed by a 3D decomposition pathway during the subsequent recharge. When the cell operates under laser (λ=405 nm) irradiation, densely packed Li2 CO3 /C flakes deposit rapidly during discharge. Upon the recharge, they predominantly decompose at the interfaces of the flake and electrode, detaching themselves from the electrode and causing irreversible capacity degradation. In situ Raman shows that the laser promotes the formation of poorly soluble intermediates, Li2 C2 O4 , which in turn affects growth/decomposition pathways of Li2 CO3 /C and the cell performance. Our findings provide mechanistic insights into interfacial evolution in Li-CO2 batteries and the laser-tuned CO2 conversion reactions, which can inspire strategies of monitoring and controlling the multistep and multiphase interfacial reactions in advanced electrochemical devices.

Self-Healable Solid Polymeric Electrolytes for Stable and Flexible Lithium Metal Batteries.

The key issue holding back the application of solid polymeric electrolytes in high-energy density lithium metal batteries is the contradictory requirements of high ion conductivity and mechanical stability. In this work, self-healable solid polymeric electrolytes (SHSPEs) with rigid-flexible backbones and high ion conductivity are synthesized by a facile condensation polymerization approach. The all-solid Li metal full batteries based on the SHSPEs possess freely bending flexibility and stable cycling performance as a result of the more disciplined metal Li plating/stripping, which have great implications as long-lifespan energy sources compatible with other wearable devices.

Revealing the Surface Effect of the Soluble Catalyst on Oxygen Reduction/Evolution in Li-O2 Batteries.

Understanding catalytic mechanisms at the nanoscale is essential for the advancement of lithium-oxygen (Li-O2) batteries. Using in situ electrochemical atomic force microscopy, we explored the interfacial evolution during the Li-O2 electrochemical reactions in dimethyl sulfoxide-based electrolyte, further revealing the surface catalytic mechanism of the soluble catalyst 2,5-di- tert-butyl-1,4-benzoquinone (DBBQ). The real-time views showed that during discharge flower-like Li2O2 formed in the electrolyte with DBBQ but small toroid without DBBQ. Upon charge, Li2O2 decomposes at a slow rate from bottom to top in the absence of DBBQ, yet with an outside-in approach in the presence of DBBQ. Bigger discharge products and more efficient decomposition pathways in the DBBQ-containing system reveal the catalytic activity of DBBQ straightforwardly. Our work provides a direct insight into the surface effect of soluble catalyst DBBQ on Li-O2 reactions at the nanoscale, which is critical for the performance optimization of Li-O2 batteries.

Interfacial Mechanism in Lithium-Sulfur Batteries: How Salts Mediate the Structure Evolution and Dynamics.

Lithium-sulfur batteries possess favorable potential for energy-storage applications because of their high specific capacity and the low cost of sulfur. Intensive understanding of the interfacial mechanism, especially the polysulfide formation and transformation under complex electrochemical environment, is crucial for the buildup of advanced batteries. Here, we report the direct visualization of interfacial evolution and dynamic transformation of the sulfides mediated by the lithium salts via real-time atomic force microscopy monitoring inside a working battery. The observations indicate that the lithium salts influence the structures and processes of sulfide deposition/decomposition during discharge/charge. Moreover, the distinct ion interaction and the diffusion in electrolytes manipulate the interfacial reactions determining the kinetics of the sulfide transformation. Our findings provide deep insights into surface dynamics of lithium-sulfur reactions revealing the salt-mediated mechanisms at nanoscale, which contribute to the profound understanding of the interfacial processes for the optimized design of lithium-sulfur batteries.

High-Temperature Formation of a Functional Film at the Cathode/Electrolyte Interface in Lithium-Sulfur Batteries: An In†Situ AFM Study.

Lithium-sulfur (Li-S) batteries have been attracting wide attention for their promising high specific capacity. A deep understanding of Li-S interfacial mechanism including the temperature (T) effect is required to meet the demands for battery modification and systematic study. Herein, the interfacial behavior during discharge/charge is investigated at high temperature (HT) of 60 °C in an electrolyte based on lithium bis(fluorosulfonyl) imide (LiFSI). By in situ atomic force microscopy (AFM), dynamic evolution of insoluble Li2 S2 and Li2 S is studied at the nanoscale. An in situ formed functional film can be directly monitored at 60 °C after Li2 S nucleation. It retards side reactions and facilitates interfacial redox. The insight into the interfacial processes at HT provides direct evidence of the existence of the film and reveals its dynamic behavior, providing a new avenue for electrolyte design and performance enhancement.

Insight into the Interfacial Process and Mechanism in Lithium-Sulfur Batteries: An In Situ AFM Study.

Lithium-sulfur (Li-S) batteries are highly appealing for large-scale energy storage. However, performance deterioration issues remain, which are highly related to interfacial properties. Herein, we present a direct visualization of the interfacial structure and dynamics of the Li-S discharge/charge processes at the nanoscale. In situ atomic force microscopy and ex situ spectroscopic methods directly distinguish the morphology and growth processes of insoluble products Li2 S2 and Li2 S. The monitored interfacial dynamics show that Li2 S2 nanoparticle nuclei begin to grow at 2 V followed by a fast deposition of lamellar Li2 S at 1.83 V on discharge. Upon charging, only Li2 S depletes from the interface, leaving some Li2 S2 undissolved, which accumulates during cycling. The galvanostatic precipitation of Li2 S2 and/or Li2 S is correlated to current rates and affects the specific capacity. These findings reveal a straightforward structure-reactivity correlation and performance fading mechanism in Li-S batteries.

Click and Patterned Functionalization of Graphene by Diels-Alder Reaction.

Chemical functionalization is a promising approach to controllably manipulate the characteristics of graphene. Here, we designed cis-dienes, featuring two dihydronaphthalene backbones, to decorate a graphene surface via Diels-Alder (DA) click reaction. The installation of a diene moiety into a nonplanar molecular structure to form cis-conformation enables a rapid (∼5 min) DA reaction between graphene and diene groups. Patterned graphene of sub-micrometer resolution can be obtained by easily soaking poly(methyl methacrylate)-masked graphene in solution of hydroxyl-substituted cis-diene at room temperature. The functionalization degree can be further controlled by carrying out the reaction at higher temperature. The present result gives important insight into the effect of molecular conformation on the graphene functionalization process, and provides an effective and facile method for graphene functionalization.