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.

Nanoscale Visualization of Lithium Plating/Stripping Tuned by On-site Formed Solid Electrolyte Interphase in All-Solid-State Lithium-Metal Batteries.

The interfacial processes, mainly the lithium (Li) plating/stripping and the evolution of the solid electrolyte interphase (SEI), are directly related to the performance of all-solid-state Li-metal batteries (ASSLBs). However, the complex processes at solid-solid interfaces are embedded under the solid-state electrolyte, making it challenging to analyze the dynamic processes in real time. Here, using in situ electrochemical atomic force microscopy and optical microscopy, we directly visualized the Li plating/stripping/replating behavior, and measured the morphological and mechanical properties of the on-site formed SEI at nanoscale. Li spheres plating/stripping/replating at the argyrodite solid electrolyte (Li6 PS5 Cl)/Li electrode interface is coupled with the formation/wrinkling/inflating of the SEI on its surface. Combined with in situ X-ray photoelectron spectroscopy, details of the stepwise formation and physicochemical properties of SEI on the Li spheres are obtained. It is shown that higher operation rates can decrease the uniformity of the Li+ -conducting networks in the SEI and worsen Li plating/stripping reversibility. By regulating the applied current rates, uniform nucleation and reversible plating/stripping processes can be achieved, leading to the extension of the cycling life. The in situ analysis of the on-site formed SEI at solid-solid interfaces provides the correlation between the interfacial evolution and the electrochemical performance in ASSLBs.

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.

Topological Hydrogels for Long-Term Brain Signal Monitoring, Neuromodulation, and Stroke Treatment.

Stroke is the primary cause of disability without effective rehabilitation methods. Emerging brain-machine interfaces offer promise for regulating brain neural circuits and promoting the recovery of brain function disorders. Implantable probes play key roles in brain-machine interfaces, which are subject to two irreconcilable tradeoffs between conductivity and modulus match/transparency. In this work, mechanically interlocked polyrotaxane is incorporated into topological hydrogels to solve the two tradeoffs at the molecular level through the pulley effect of polyrotaxane. The unique performance of the topological hydrogels enables them to acquire brain neural information and conduct neuromodulation. The probe is capable of continuously recording local field potentials for eight weeks. Optogenetic neuromodulation in the primary motor cortex to regulate brain neural circuits and control limb behavior is realized using the probe. Most importantly, optogenetic neuromodulation is conducted using the probe, which effectively reduces the infarct regions of the brain tissue and promotes locomotor function recovery. This work exhibits a significant scientific advancement in the design concept of neural probes for developing brain-machine interfaces and seeking brain disease therapies.

High-Yield Synthesis of Colloidal Carbon Rings and Their Applications in Self-Standing Electrodes of Li-O2 Batteries.

The use of carbon materials in porous electrodes has impressive advantages. However, precisely tailoring the multilevel pore structure of carbon electrodes remains an unsolved challenge. Here, we report a highly efficient site-selective growth strategy to synthesize colloidal carbon rings by templating patchy droplets. Carbon rings are used for the direct fabrication of self-standing porous electrodes with hierarchical pores for lithium-oxygen batteries (LOBs). In situ atomic force microscopy reveals that during discharge the discharge products densely nucleate and grow on carbon rings, demonstrating that such rings are a very potential electrode material in LOBs. The hollow carbon ring electrode (HCRE) possesses micrometer-scale channels formed by random packing of rings and nanochannels consisting of ring-shaped hollow cavities connected by nanosized pores in the wall. Both channels contribute to ion transportation and gas diffusion, but the storage of the discharge products mainly lies in micrometer-scale channels, leading to a high discharge capacity of LOBs (20 658 mAh/g). Our work paves a new way to construct hierarchically porous electrodes for application in electrocatalysis and electrochemical energy storage.

Numerical Simulation on Preparing Uniform and Stable Perovskite Wet Film in Slot-Die Coating Process.

Slot-die coating is regarded as a reliable and potential technology for preparing large-area perovskite solar cells with high efficiency and low cost. Therein, the formation of continuous and uniform wet film is of significance to obtain a high-quality solid perovskite film. In this work, the rheological properties of the perovskite precursor fluid are analyzed. Then, the ANSYS Fluent is introduced to establish an integrated model of internal and external flow fields during the coating process. The model is applicable to all perovskite precursor solutions with near-Newtonian fluids. Based on the theoretical simulation of finite element analysis, the preparation of 0.8 M-FAxCs1-xPbI3, one of the typical large-area perovskite precursor solutions, is explored. Accordingly, this work indicates that the coupling process parameters like the fluid supply velocity (Vin) and coating velocity (V) determine the uniformity that the solution flows out of the slit and is coated onto the substrates, and the coating windows for a uniform and stable perovskite wet film is obtained. For the upper boundary range of the coating windows, the maximum value of V and Vin follows V = 0.003 + 1.46Vin (Vin ≤ 0.1 m/s), while for its lower boundary range, the minimum value of V and Vin is V = 0.002 + 0.67Vin (Vin ≤ 0.1 m/s). When Vin is higher than 0.1 m/s, the film will break due to the excessive V. Finally, the real experiment verifies the accuracy of the numerical simulation. Hopefully, this work is of reference value for the development of the slot-die coating forming process on the perovskite precursor solution approximating Newtonian fluid.

In Situ Insight into the Interfacial Dynamics in "Water-in-Salt" Electrolyte-Based Aqueous Zinc Batteries.

Water-in-salt (WIS) electrolyte is considered as one of most promising systems for aqueous zinc batteries (AZBs) due to its dendrite-free plating/stripping with nearly 100% Coulombic efficiency. However, the understanding of the interfacial mechanisms remains elusive, which is crucial for further improvements in battery performance. Herein, the interfacial processes of solid electrolyte interphase (SEI) formation and subsequent Zn plating/stripping are monitored by in situ atomic force microscopy and in situ optical microscopy. The live formation of uniform and compact LiF-rich SEI in WIS systems could induce the uniform hexagonal Zn deposition with preferential orientation growth in the (002) crystal plane, showing excellent plating/stripping reversibility. In contrast, the SEI formed in 1 m zinc bis(trifluoromethylsulfonyl)imide (Zn(TFSI)2 ) is uneven and rich in inert ZnO, adversely triggering the dendrite propagation and successive "dead" Zn accumulation in repeated deposition/dissolution cycles. This work provides an in-depth understanding of the relationship between SEI evolution and Zn-deposited behaviors in AZBs, possibly stimulating more research on rational composition design and structural optimization of solid/liquid interface for advanced rechargeable aqueous multivalent-ion batteries.

Electron Conductive and Transparent Hydrogels for Recording Brain Neural Signals and Neuromodulation.

Recording brain neural signals and optogenetic neuromodulations open frontiers in decoding brain neural information and neurodegenerative disease therapeutics. Conventional implantable probes suffer from modulus mismatch with biological tissues and an irreconcilable tradeoff between transparency and electron conductivity. Herein, a strategy is proposed to address these tradeoffs, which generates conductive and transparent hydrogels with polypyrrole-decorated microgels as cross-linkers. The optical transparency of the electrodes can be attributed to the special structures that allow light waves to bypass the microgel particles and minimize their interaction. Demonstrated by probing the hippocampus of rat brains, the biomimetic electrode shows a prolonged capacity for simultaneous optogenetic neuromodulation and recording of brain neural signals. More importantly, an intriguing brain-machine interaction is realized, which involves signal input to the brain, brain neural signal generation, and controlling limb behaviors. This breakthrough work represents a significant scientific advancement toward decoding brain neural information and developing neurodegenerative disease therapies.

In situ visualization of synergistic effects between electrolyte additives and catalytic electrodes in Li-O2 batteries.

By using in situ atomic force microscopy, Li-O2 interfacial reactions promoted synergistically by the electrolyte additive K+ and Pt nanoparticles electrode are visualized. The Pt nanoparticles electrode promotes the formation of the intermediate lithium superoxide (LiO2) and K+ assists its diffusion into the electrolyte, thereby promoting the formation of large-sized discharge products during discharging and increasing the discharge capacity of the Li-O2 battery. These results provide direct evidence for clarifying the interfacial synergy mechanism of electrolyte additives and solid catalysts.

Revealing the High Salt Concentration Manipulated Evolution Mechanism on the Lithium Anode in Quasi-Solid-State Lithium-Sulfur Batteries.

Lithium-sulfur batteries are promising candidates of energy storage devices. Both adjusting salt/solvent ratio and applying quasi-solid-state electrolytes are regarded as effective strategies to improve the lithium (Li) anode performance. However, reaction mechanisms and interfacial properties in quasi-solid-state lithium-sulfur (QSSLS) batteries with high salt concentration are not clear. Here we utilize in-situ characterizations and molecular dynamics simulations to unravel aforesaid mysteries, and construct relationships of electrolyte structure, interfacial behaviour and performance. The generation mechanism, formation process, and mechanical/chemical/electrochemical properties of the anion-derived solid electrolyte interphase (SEI) are deeply explored. Li deposition uniformity and dissolution reversibility are further tuned by the sustainable SEI. These straightforward evidences and deepgoing studies would guide the electrolyte design and interfacial engineering of QSSLS batteries.

Highly Tunable, Broadband, and Negative Photoresponse MoS2 Photodetector Driven by Ion-Gel Gate Dielectrics.

Revealing the light-matter interaction of molybdenum disulfide (MoS2) and further improving its tunability facilitate the construction of highly integrated optoelectronics in communication and wearable healthcare, but it still remains a significant challenge. Herein, polyvinylidene fluoride and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (PVDF-EMIM-TFSI) ion-gel are employed to replace the oxide to fabricate a MoS2-based phototransistor. The high capacitance enables a large tunability of the carrier concentration that results in ambipolar transport of MoS2. It is found that the photoelectrical effect of the MoS2 ion-gel phototransistor can be greatly tuned by the gate voltage including its photoresponsivity, detectivity, and response wavelength. An abnormal negative photoelectrical effect in both the electron branch and the hole branch is observed which is due to the adsorption/desorption of the C2F6NO4S2- ion. By tuning the carrier concentration, the photoresponse can be extended from the visible region to the short infrared region. At 1200 nm, the photoresponse and detectivity can be tuned as large as 0.90 A/W and 1.88 × 1011 Jones, respectively. Ultimately, by combining the tunability of gate voltage and wavelength, it is demonstrated that the photoelectrical effect is dominated by the photogating effect in the hole carrier, while it is coregulated by a photogating and photothermal effect in electron carrier. This study provides new insights for developing a highly tunable broadband photodetector with low consumption.

Interfacial Evolution of the Solid Electrolyte Interphase and Lithium Deposition in Graphdiyne-Based Lithium-Ion Batteries.

All-carbon graphdiyne (GDY)-based materials have attracted extensive attention owing to their extraordinary structures and outstanding performance in electrochemical energy storage. Straightforward insights into the interfacial evolution at GDY electrode/electrolyte interface could crucially enrich the fundamental comprehensions and inspire targeted regulations. Herein, in situ optical microscopy and atomic force microscopy monitoring of the GDY and N-doped GDY electrodes reveal the interplay between the solid electrolyte interphase (SEI) and Li deposition. The growth and continuous accumulation of the flocculent-like SEI is directly tracked at the surface of GDY electrode. Moreover, the nanoparticle-shaped SEI homogeneously propagates at the interface when N configurations are involved, providing a critical clue for the N-doping effects of stabilizing interfaces and homogenizing Li deposition. This work probes into the dynamic evolution and structure-reactivity correlation in detail, creating effective strategies for GDY-based materials optimization in lithium-ion batteries.

Direct Visualization of Dynamic Mobility of Li2O2 in Li-O2 Batteries: A Differential Interference Microscopy Study.

The reversibility and the discharge/charge performance in nonaqueous lithium-oxygen (Li-O2) batteries are critically dependent on the kinetics of interfacial reactions. However, the interfacial reaction dynamic behaviors, especially the quantitative analysis, are still far from deep understanding. Using the method of laser confocal microscopy combined with differential interference contrast microscopy (LCM-DIM), we monitored the Li-O2 interfacial reaction and in situ traced the Li2O2 migration processes promoted by the solution catalyst. Different dynamic behaviors exist when regulating the concentration of the redox mediator. Quantitative analysis of the discharged Li2O2 particles shows high mobility at the early discharge stage and decayed motion in the subsequent process, indicating the solution-mediated pathway participating Li2O2 formation in the low-concentration redox mediator addition, while particles/aggregates confined into the amorphous film demonstrate simultaneous solution and surface route-mediated pathway participation in the high-concentration case. These distinctive observations of Li2O2 formation and decomposition processes present the advantage of LCM-DIM to fundamentally understand the dynamic evolution in Li-O2 batteries.

Revealing the Correlations between Morphological Evolution and Surface Reactivity of Catalytic Cathodes in Lithium-Oxygen Batteries.

Lithium-oxygen batteries suffer from the degradation of the catalytic cathode during long-term operation, which limits their practical use. Understanding the direct correlations between the surface morphological evolution of catalytic cathodes at nanoscale and their catalytic activity during cycling has proved challenging. Here, using in situ electrochemical atomic force microscopy, the dynamic evolution of the Pt nanoparticles electrode in a working Li-O2 battery and its effects on the Li-O2 interfacial reactions are visualized. In situ views show that repeated oxidation-reduction cycles (ORCs) trigger the increase in the size of Pt nanoparticles, eventually causing the Pt nanoparticles to fall off the electrode. In 0-80 ORCs, the grown Pt nanoparticles promote the conversion of the Li-O2 reaction route from the surface-mediated pathway to the solution-mediated pathway during discharging and significantly increase the discharge capacity. After 250 ORCs, accompanied by the part of the Pt nanoparticles detaching from the electrode, the nucleation potential of reaction product decreases, and the reaction dynamic slows down, which cause the performance to degrade. Modification of a proper amount of Au nanoparticle on the Pt nanoparticles electrode could improve its stability and maintain the high catalytic activity. These results provide a direct evidence for clarifying the correlations between morphological evolution and surface reactivity of catalytic cathodes during cycling, which is critical for developing high-performance catalysts.

Cooperative Shielding of Bi-Electrodes via In Situ Amorphous Electrode-Electrolyte Interphases for Practical High-Energy Lithium-Metal Batteries.

Solid-state Li-metal batteries offer a great opportunity for high-security and high-energy-density energy storage systems. However, redundant interfacial modification layers, intended to lead to an overall satisfactory interfacial stability, dramatically debase the actual energy density. Herein, a dual-interface amorphous cathode electrolyte interphase/solid electrolyte interphase CEI/SEI protection (DACP) strategy is proposed to conquer the main challenges of electrochemical side reactions and Li dendrites in hybrid solid-liquid batteries without sacrificing energy density via LiDFOB and LiBF4 in situ synergistic conversion. The amorphous CEI/SEI products have an ultralow mass proportion and act as a dynamic shield to cooperatively enforce dual electrodes with a well-preserved structure. Thus, this in situ DACP layer subtly reconciles multiple interfacial compatibilities and a high energy density, endowing the hybrid solid-liquid Li-metal battery with a sustainably brilliant cycling stability even at practical conditions, including high cathode loading, high voltage (4.5 V), and high temperature (45 °C) conditions, and enables a high-energy-density (456 Wh kg-1) pouch cell (11.2 Ah, 5 mA h cm-2) with a lean electrolyte (0.92 g Ah-1, containing solid and liquid phases). The compatible modification strategy points out a promising approach for the design of practical interfaces in future solid-state battery systems.

Keystone species determine the "selection mechanism" of multispecies biofilms for bacteria from soil aggregates.

Soil aggregates are integral parts of soil structure and play paramount roles in supporting microbial diversity, nutrient cycling and water retention. The formation of multispecies biofilms is a survival strategy for bacterial adaptation to the environment and help microorganisms access more complex nutrient sources via labor sharing, especially in soil aggregates. However, very little is known about the effect of species richness and composition on bacterial multispecies biofilms formation in different size soil aggregates. A random partition design strategy was used to identify the relative importance of bacterial richness and composition in driving multispecies biofilms. The strategy can separate the effects of species richness and composition from the soil aggregates occurring bacterial assemblage. Increasing species richness was found to be always positively correlated with multispecies biofilms productivity for bacteria from the same aggregate fractions. General linear model analysis revealed that species composition contributed more than species richness to forming multispecies biofilms, suggesting that "selection mechanism" plays a more important role than "complementarity mechanism". This "selection mechanism" relies mainly on culturable keystone species that can significantly enhance the formation of multispecies biofilms. The co-occurrence network was investigated to explore whether the culturable keystone species from the random partitions experiment are consistent with the keystone taxa. Four out of 10 culturable keystone species isolated from soil aggregates were matched the keystone taxa. It is concluded that the culturable keystone species determine the multispecies biofilms formation for bacteria residing in soil aggregates. This study provides insights into the role of culturable keystone species in multispecies biofilms. Understanding the formation of multispecies biofilms is fundamental to decipher how microbes interact with each other in soil aggregates. Meanwhile, it will enhance our knowledge of the quorum behavior of complex bacterial communities.

Surface Mechanism of Catalytic Electrodes in Lithium-Oxygen Batteries: How Nanostructures Mediate the Interfacial Reactions.

The use of catalysts is the key to boost electrode reactions in lithium-oxygen (Li-O2) batteries. In-depth understanding of the nanoscale catalytic effect at electrode/electrolyte interfaces is of great significance for guiding a design of functionally optimized catalyst. Here, using electrochemical atomic force microscopy, we present the real-time imaging of interfacial evolution on nanostructured Au electrodes in a working battery, revealing that the nanostructure of Au is directly related to the catalytic activity toward oxygen reduction reaction (ORR)/oxygen evolution reaction (OER). In situ views show that nanoporous Au with a size of ∼14 nm for ligaments and ∼5 nm for nanopores promote the nucleation and growth of discharge product Li2O2 with large size at a high discharge voltage, yet densely packed Au nanoparticles with a diameter of ∼15 nm could catalyze Li2O2 to fully decompose via the top-bottom approach at a low charge potential. In addition, the difference in the nucleation potential of Li2O2 on the electrode with hybrid nanostructures could result in an uneven distribution of discharge products, which is alleviated at a large discharge rate and the capacity of the battery is improved significantly. These observations provide deep insights into the mechanisms of Li-O2 interfacial reaction catalyzed by nanostructured catalysts and strategies for improving Li-O2 batteries.

Nitriding-Interface-Regulated Lithium Plating Enables Flame-Retardant Electrolytes for High-Voltage Lithium Metal Batteries.

Safety concerns are impeding the applications of lithium metal batteries. Flame-retardant electrolytes, such as organic phosphates electrolytes (OPEs), could intrinsically eliminate fire hazards and improve battery safety. However, OPEs show poor compatibility with Li metal though the exact reason has yet to be identified. Here, the lithium plating process in OPEs and Li/OPEs interface chemistry were investigated through ex situ and in situ techniques, and the cause for this incompatibility was revealed to be the highly resistive and inhomogeneous interfaces. Further, a nitriding interface strategy was proposed to ameliorate this issue and a Li metal anode with an improved Li cycling stability (300 h) and dendrite-free morphology is achieved. Meanwhile, the full batteries coupled with nickel-rich cathodes, such as LiNi0.8 Co0.1 Mn0.1 O2 , show excellent cycling stability and outstanding safety (passed the nail penetration test). This successful nitriding-interface strategy paves a new way to handle the incompatibility between electrode and electrolyte.

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.