Side Reactions/Changes in Lithium-Ion Batteries: Mechanisms and Strategies for Creating Safer and Better Batteries.

Lithium-ion batteries (LIBs), in which lithium ions function as charge carriers, are considered the most competitive energy storage devices due to their high energy and power density. However, battery materials, especially with high capacity undergo side reactions and changes that result in capacity decay and safety issues. A deep understanding of the reactions that cause changes in the battery's internal components and the mechanisms of those reactions is needed to build safer and better batteries. This review focuses on the processes of battery failures, with voltage and temperature as the underlying factors. Voltage-induced failures result from anode interfacial reactions, current collector corrosion, cathode interfacial reactions, overcharge, and over-discharge, while temperature-induced failure mechanisms include SEI decomposition, separator damage, and interfacial reactions between electrodes and electrolytes. The review also presents protective strategies for controlling these reactions. As a result, the reader is offered a comprehensive overview of the safety features and failure mechanisms of various LIB components.

Biosignals in the Gut-Brain Axis Transmission: Function and Detection.

The gut-brain axis (GBA) is an important information pathway connecting the brain, the central nervous system (CNS), and the gastrointestinal (GI) tract. On the one hand, gut microbiota can influence the function brain through GBA; on the other hand, the brain can also change the structural composition of gut microbiota via GBA. It contains a myriad of biosignals, such as monoamines, inflammatory cytokines, and macro-biomolecules, as the information carriers. Highly selective, sensitive, and reliable sensing techniques are essential to resolve the specific function of individual biosignals. This review summarizes the widely reported biosignals related to GBA and their functions, and organizes the latest sensing tools to provide feasible characterization ideas for GBA-related work. In addition, these low-cost, fast-responding sensors can also be used for early identification and diagnosis of GBA-related diseases (e.g., depression). Finally, the problems and deficiencies in this field are pointed out to provide a reference for the orientation of researchers in the sensing field.

Weak-Interaction Environment in a Composite Electrolyte Enabling Ultralong-Cycling High-Voltage Solid-State Lithium Batteries.

Poly(vinylidene fluoride) (PVDF)-based solid electrolytes with a Li salt-polymer-little residual solvent configuration are promising candidates for solid-state batteries. Herein, we clarify the microstructure of PVDF-based composite electrolyte at the atomic level and demonstrate that the Li+-interaction environment determines both interfacial stability and ion-transport capability. The polymer works as a "solid diluent" and the filler realizes a uniform solvent distribution. We propose a universal strategy of constructing a weak-interaction environment by replacing the conventional N,N-dimethylformamide (DMF) solvent with the designed 2,2,2-trifluoroacetamide (TFA). The lower Li+ binding energy of TFA forms abundant aggregates to generate inorganic-rich interphases for interfacial compatibility. The weaker interactions of TFA with PVDF and filler achieve high ionic conductivity (7.0 × 10-4 S cm-1) of the electrolyte. The solid-state Li||LiNi0.8Co0.1Mn0.1O2 cells stably cycle 4900 and 3000 times with cutoff voltages of 4.3 and 4.5 V, respectively, as well as deliver superior stability at -20 to 45 °C and a high energy density of 300 Wh kg-1 in pouch cells.

Fluorine Chemistry in Rechargeable Batteries: Challenges, Progress, and Perspectives.

The renewable energy industry demands rechargeable batteries that can be manufactured at low cost using abundant resources while offering high energy density, good safety, wide operating temperature windows, and long lifespans. Utilizing fluorine chemistry to redesign battery configurations/components is considered a critical strategy to fulfill these requirements due to the natural abundance, robust bond strength, and extraordinary electronegativity of fluorine and the high free energy of fluoride formation, which enables the fluorinated components with cost effectiveness, nonflammability, and intrinsic stability. In particular, fluorinated materials and electrode|electrolyte interphases have been demonstrated to significantly affect reaction reversibility/kinetics, safety, and temperature tolerance of rechargeable batteries. However, the underlining principles governing material design and the mechanistic insights of interphases at the atomic level have been largely overlooked. This review covers a wide range of topics from the exploration of fluorine-containing electrodes, fluorinated electrolyte constituents, and other fluorinated battery components for metal-ion shuttle batteries to constructing fluoride-ion batteries, dual-ion batteries, and other new chemistries. In doing so, this review aims to provide a comprehensive understanding of the structure-property interactions, the features of fluorinated interphases, and cutting-edge techniques for elucidating the role of fluorine chemistry in rechargeable batteries. Further, we present current challenges and promising strategies for employing fluorine chemistry, aiming to advance the electrochemical performance, wide temperature operation, and safety attributes of rechargeable batteries.

Kirkendall effect-induced uniform stress distribution stabilizes nickel-rich layered oxide cathodes.

Nickel-rich layered oxide cathodes promise ultrahigh energy density but is plagued by the mechanical failure of the secondary particle upon (de)lithiation. Existing approaches for alleviating the structural degradation could retard pulverization, yet fail to tune the stress distribution and root out the formation of cracks. Herein, we report a unique strategy to uniformize the stress distribution in secondary particle via Kirkendall effect to stabilize the core region during electrochemical cycling. Exotic metal/metalloid oxides (such as Al2O3 or SiO2) is introduced as the heterogeneous nucleation seeds for the preferential growth of the precursor. The calcination treatment afterwards generates a dopant-rich interior structure with central Kirkendall void, due to the different diffusivity between the exotic element and nickel atom. The resulting cathode material exhibits superior structural and electrochemical reversibility, thus contributing to a high specific energy density (based on cathode) of 660 Wh kg-1 after 500 cycles with a retention rate of 86%. This study suggests that uniformizing stress distribution represents a promising pathway to tackle the structural instability facing nickel-rich layered oxide cathodes.

Molecular understanding of the critical role of alkali metal cations in initiating CO2 electroreduction on Cu(100) surface.

Molecular understanding of the solid-liquid interface is challenging but essential to elucidate the role of the environment on the kinetics of electrochemical reactions. Alkali metal cations (M+), as a vital component at the interface, are found to be necessary for the initiation of carbon dioxide reduction reaction (CO2RR) on coinage metals, and the activity and selectivity of CO2RR could be further enhanced with the cation changing from Li+ to Cs+, while the underlying mechanisms are not well understood. Herein, using ab initio molecular dynamics simulations with explicit solvation and enhanced sampling methods, we systematically investigate the role of M+ in CO2RR on Cu surface. A monotonically decreasing CO2 activation barrier is obtained from Li+ to Cs+, which is attributed to the different coordination abilities of M+ with *CO2. Furthermore, we show that the competing hydrogen evolution reaction must be considered simultaneously to understand the crucial role of alkali metal cations in CO2RR on Cu surfaces, where H+ is repelled from the interface and constrained by M+. Our results provide significant insights into the design of electrochemical environments and highlight the importance of explicitly including the solvation and competing reactions in theoretical simulations of CO2RR.

Deciphering the Formation and Accumulation of Solid-Electrolyte Interphases in Na and K Carbonate-Based Batteries.

The continuous solid-electrolyte interphase (SEI) accumulation has been blamed for the rapid capacity loss of carbon anodes in Na and K ethylene carbonate (EC)/diethyl carbonate (DEC) electrolytes, but the understanding of the SEI composition and its formation chemistry remains incomplete. Here, we explain this SEI accumulation as the continuous production of organic species in solution-phase reactions. By comparing the NMR spectra of SEIs and model compounds we synthesized, alkali metal ethyl carbonate (MEC, M = Na or K), long-chain alkali metal ethylene carbonate (LCMEC, M = Na or K), and poly(ethylene oxide) (PEO) oligomers with ethyl carbonate ending groups are identified in Na and K SEIs. These components can be continuously generated in a series of solution-phase nucleophilic reactions triggered by ethoxides. Compared with the Li SEI formation chemistry, the enhancement of the nucleophilicity of an intermediate should be the cause of continuous nucleophilic reactions in the Na and K cases.

Manipulating the Host-Guest Chemistry of Cucurbituril to Propel Highly Reversible Zinc Metal Anodes.

Rechargeable aqueous zinc-ion batteries are practically plagued by the short lifespan and low Coulombic efficiency (CE) of Zn anodes resulting from random dendrite deposition and parasitic reactions. Herein, the host-guest chemistry of cucurbituril additive with Zn2+ to achieve longstanding Zn anodes is manipulated. The macrocyclic molecule of cucurbit[5]uril (CB[5]) is delicately designed to reconstruct both the CB[5]-adsorbed electric-double layer (EDL) structure at the Zn interface and the hydrated sheath of Zn2+ ions. Especially benefiting from the desirable carbonyl rims and suitable hydrophobic cavities, the CB[5] has a strong host-guest interaction with Zn2+ ions, which exclusively permits rapid Zn2+ flux across the EDL interface but retards the H2O radicals and SO4 2-. Accordingly, such a unique particle redistributor warrants long-lasting dendrite-free deposition by homogenizing Zn nucleation/growth and significantly improved CE by inhibiting side reactions. The Zn anode can deliver superior reversibility in CB[5]-containing electrolyte with a ninefold increase of cycle lifetime and an elevated CE of 99.7% under harsh test conditions (10 mA cm-2/10 mA h cm-2). The work opens a new avenue from the perspective of host-guest chemistry to propel the development of rechargeable Zn metal batteries and beyond.

A Lithium Intrusion-Blocking Interfacial Shield for Wide-Pressure-Range Solid-State Lithium Metal Batteries.

Lithium garnets are considered as promising solid-state electrolytes for next-generation solid-state Li metal batteries (SSLBs). However, the Li intrusion driven by external stack pressure triggers premature of Li metal batteries. Herein, for the first time, an in situ constructed interfacial shield is reported to efficiently inhibit the pressure-induced Li intrusion in SSLBs. Theoretical modeling and experimental investigations reveal that high-hardness metallic Mo nanocrystals inside the shield effectively suppress Li dendrite growth without alloy hardening-derived interfacial contact deterioration. Meanwhile the electrically insulated Li2 S as a shield component considerably promotes interfacial wettability and hinders Li dendrite penetration into the bulk of garnet electrolyte. Interfacial shield-protected Li6.4 La3 Zr1.4 Ta0.6 O12 (LLZTO)-based cells exhibit significantly enhanced cyclability without short circuits under conventional pressures of ≈0.2 MPa and even at high pressure of up to 70 MPa; which is the highest endurable stack pressure reported for SSLBs using garnet electrolytes. These key findings are expected to promote the wide-pressure-range applications of SSLBs.

pH buffer KH2PO4 boosts zinc ion battery performance via facilitating proton reaction of MnO2 cathode.

Zinc-ion batteries (ZIBs) are rapidly emerging as safe, cost-effective, nontoxic, and environmentally friendly energy storage systems. However, mildly acidic electrolytes with depleted protons cannot satisfy the huge demand for proton reactions in MnO2 electrodes and also cause several issues in ZIBs, such as rapidly decaying cycling stability and low reaction kinetics. Herein, we propose a pH-buffering strategy in which KH2PO4 is added to the electrolyte to overcome the problems caused by low proton concentrations. This strategy significantly improves the rate and cycle stability performance of zinc-manganese batteries, delivering a high capacity of 122.5 mAh/g at a high current density of 5 A/g and enabling 9000 cycles at this current density, with a remaining capacity of 70 mAh/g. Ex-situ X-ray diffraction and scanning electron microscopy analyses confirmed the generation/dissolution of Zn3PO4·4H2O and Zn4(OH)6(SO4)·5H2O, byproducts of buffer products and proton reactions. In-situ pH measurements and chemical titration revealed that the pH change during the electrochemical process can be adjusted to a low range of 2.2-2.8, and the phosphate distribution varies with the pH range. Those results reveal that H2PO4- provides protons to the cathode through the chemical balance of HPO42-, HPO42-, and Zn3PO4·4H2O. This study serves as a guide for studying the influences and mechanisms of buffering additives in Zn-MnO2 batteries.

Dielectric Filler-Induced Hybrid Interphase Enabling Robust Solid-State Li Metal Batteries at High Areal Capacity.

The fillers in composite solid-state electrolyte are mainly responsible for the enhancement of the conduction of Li ions but barely regulate the formation of solid electrolyte interphase (SEI). Herein, a unique filler of dielectric NaNbO3 for the poly(vinylidene fluoride) (PVDF)-based polymer electrolyte, which is subjected to the exchange of Li+ and Na+ during cycling, is reported and the substituted Na+ is engaged in the construction of a fluorinated Li/Na hybrid SEI with high Young's modulus, facilitating the fast transport of Li+ at the interface at a high areal capacity and suppressing the Li dendrite growth. The dielectric NaNbO3 also induces the generation of high-dielectric ß phase of PVDF to promote the dissociation of Li salt. The Li/Li symmetrical cell exhibits a long-term dendrite-free cycling over 600 h at a high areal capacity of 3 mA h cm-2. The LiNi0.8Mn0.1Co0.1O2/Li solid-state cells with NaNbO3 stably cycle 2200 times at 2 C and that paired with high-loading cathode (10 mg cm-2) can stably cycle for 150 times and exhibit excellent performances at -20 °C. This work provides a novel design principle of fillers undertaking interfacial engineering in composite solid-state electrolytes for developing the safe and stable solid-state lithium metal battery.

Fluorinating All Interfaces Enables Super-Stable Solid-State Lithium Batteries by In Situ Conversion of Detrimental Surface Li2CO3.

Li-stuffed battery materials intrinsically have surface impurities, typically Li2CO3, which introduce severe kinetic barriers and electrochemical decay for a cycling battery. For energy-dense solid-state lithium batteries (SSLBs), mitigating detrimental Li2CO3 from both cathode and electrolyte materials is required, while the direct removal approaches hardly avoid Li2CO3 regeneration. Here, a decarbonization-fluorination strategy to construct ultrastable LiF-rich interphases throughout the SSLBs by in situ reacting Li2CO3 with LiPF6 at 60 °C is reported. The fluorination of all interfaces effectively suppresses parasitic reactions while substantially reducing the interface resistance, producing a dendrite-free Li anode with an impressive cycling stability of up to 7000 h. Particularly, transition metal dissolution associated with gas evolution in the cathodes is remarkably reduced, leading to notable improvements in battery rate capability and cyclability at a high voltage of 4.5 V. This all-in-one approach propels the development of SSLBs by overcoming the limitations associated with surface impurities and interfacial challenges.

Multifunctional Liquid Metal-Bridged Graphite Nanoplatelets/Aramid Nanofiber Film for Thermal Management.

Miniaturization of modern micro-electronic devices urges the development of multi-functional thermal management materials. Traditional polymer composite-based thermal management materials are promising candidates, but they suffer from single functionality, high cost, and low fire-resistance. Herein, a multifunctional liquid metal (LM)-bridged graphite nanoplatelets (GNPs)/ aramid nanofibers (ANFs) film is fabricated via a facile vacuum-assisted self-assembly approach followed by compression. ANFs serve as interfacial binders to link LM and GNPs together via hydrogen bondings and π-π interactions, while LM bridges the adjacent layer of GNPs to endow a fast thermal transport by phonons and electrons. The resultant composite films exhibit a high bidirectional thermal conductivity (In-plane: 29.5 W m-1 K-1 and through-plane: 5.3 W m-1 K-1 ), offering a reliable and effective cooling. Moreover, the as-fabricated composite films exhibit superior flame-retardance (peak of heat release rate of 4000J g-1 ), outstanding Joule heating performance (200 °C at supplied voltage of 3.5 V), and excellent electromagnetic interference shielding effectiveness (EMI SE of 62 dB). This work provides an efficient avenue to fabricate multifuntional thermal management materials for micro-electronic devices, battery thermal management, and artificial intelligence.

Resolving Deactivation of Low-Spin Fe Sites by Redistributing Electron Density toward High-Energy Sodium Storage.

Prussian blue (PB) has been an emerging class of cathode material for sodium-ion batteries due to its low cost and high theoretical capacity. However, their working voltage and capacity are substantially restricted due to the deactivation of low-spin Fe sites. Herein, we demonstrate a universal strategy to activate the low-spin Fe sites of PB by hybridizing them with the π-π conjugated electronic conductors. The redistribution of electron density between π-π conjugated conductors and PB effectively promotes the participation of low-spin Fe sites in sodium storage. Consequently, the low-spin Fe-induced plateau is greatly aroused, resulting in a high specific capacity of 148.4 mAh g-1 and remarkable energy density of 444.2 Wh kg-1. In addition, the excellent structural stability enables superior cycling stability over 2500 cycles and outstanding rate performance. The work will provide fundamental insight into activating the low-spin Fe sites of PB for advanced battery technologies.

Stabilizing non-iridium active sites by non-stoichiometric oxide for acidic water oxidation at high current density.

Stabilizing active sites of non-iridium-based oxygen evolution reaction (OER) electrocatalysts is crucial, but remains a big challenge for hydrogen production by acidic water splitting. Here, we report that non-stoichiometric Ti oxides (TiOx) can safeguard the Ru sites through structural-confinement and charge-redistribution, thereby extending the catalyst lifetime in acid by 10 orders of magnitude longer compared to that of the stoichiometric one (Ru/TiO2). By exploiting the redox interaction-engaged strategy, the in situ growth of TiOx on Ti foam and the loading of Ru nanoparticles are realized in one step. The as-synthesized binder-free Ru/TiOx catalyst exhibits low OER overpotentials of 174 and 265 mV at 10 and 500 mA cm-2, respectively. Experimental characterizations and theoretical calculations confirm that TiOx stabilizes the Ru active center, enabling operation at 10 mA cm-2 for over 37 days. This work opens an avenue of using non-stoichiometric compounds as stable and active materials for energy technologies.

Investigating K+ Storage Behavior of Highly Graphitized Carbon Fibers as Anodes for a Potassium-Ion Battery.

Many problems of potassium-ion batteries (PIBs) are hidden under a low mass load of the active material. However, developing research based on areal capacity is challenging for PIBs, due to the lack of an anode capable of delivering a stable capacity of more than 1 mAh cm-2. This work investigates the K+ storage behavior of highly graphitized carbon fibers (HG-CF), which exhibit automatic structural adjustments to mitigate voltage polarization. The created defects and residual K+ in the structure favor the reversible insertion/deinsertion of K+. HG-GF after structural adjustment realizes a capacity of 2 mAh (1.13 cm-2) without K deposition and a stable cyclic stability (>500 h). In situ X-ray diffraction and in situ Raman spectra were used to detect defect formation and structural evolution during cycles. This work demonstrates the feasibility of HG-GF as an anode for PIBs and provides a suitable anode for further research of PIBs based on areal capacity.

Tetraphenylporphyrin-based Chelating Ligand Additive as a Molecular Sieving Interfacial Barrier toward Durable Aqueous Zinc Metal Batteries.

The sustained water consumption and uncontrollable dendrite growth strongly hamper the practical applications of rechargeable zinc (Zn) metal batteries (ZMBs). Herein, for the first time, we demonstrate that trace amount of chelate ligand additive can serve as a "molecular sieve-like" interfacial barrier and achieve highly efficient Zn plating/stripping. As verified by theoretical modeling and experimental investigations, the benzenesulfonic acid groups on the additive molecular not only facilitates its water solubility and selective adsorption on the Zn anode, but also effectively accelerates the de-solvation kinetics of Zn2+ . Meanwhile, the central porphyrin ring on the chelate ligand effectively expels free water molecules from Zn2+ via chemical binding against hydrogen evolution, and reversibly releases the captured Zn2+ to endow a dendrite-free Zn deposition. By virtue of this non-consumable additive, high average Zn plating/stripping efficiency of 99.7 % over 2100 cycles together with extended lifespan and suppressed water decomposition in the Zn||MnO2 full battery were achieved, thus opening a new avenue for developing highly durable ZMBs.

New [3+2+1] Iridium Complexes as Effective Phosphorescent Sensitizers for Efficient Narrowband Saturated-Blue Hyper-OLEDs.

Two newly designed and synthesized [3+2+1] iridium complexes through introducing bulky trimethylsiliyl (TMS) groups are doped with a terminal emitter of v-DABNA to form an coincident overlapping spectra between the emission of these two phosphors and the absorption of v-DABNA, creating cascade resonant energy transfer for efficient triplet harvesting. To boost the color quality and efficiency, the fabricated hyper-OLEDs have been optimized to achieve a high external quantum efficiency of 31.06%, which has been among the highest efficiency results reported for phosphor sensitized saturated-blue hyper-OLEDs, and pure blue emission peak at 467 nm with the full width at half maxima (FWHM) as narrow as 18 nm and the CIEy values down to 0.097, satisfying the National Institute of Standards and Technology (NIST) requirement for saturated blue OLEDs display. Surprisingly, such hyper-OLEDs have obtained the converted lifetime (LT50 ) up to 4552 h at the brightness of 100 cd m-2 , demonstrating effective Förster resonance energy transfer (FRET) process. Therefore, employing these new bulky TMS substituent [3+2+1] iridium(III) complexes for effective sensitizers can greatly pave the way for further development of high efficiency and stable blue OLEDs in display and lighting applications.

Si/Organic Integrated Narrowband Near-Infrared Photodetector.

Spectrally selective narrowband photodetection is critical for near-infrared (NIR) imaging applications, such as for communicationand night-vision utilities. It is a long-standing challenge for detectors based on silicon, to achieve narrowband photodetection without integrating any optical filters. Here, this work demonstrates a NIR nanograting Si/organic (PBDBT-DTBT:BTP-4F) heterojunction photodetector (PD), which for the first time obtains the full-width-at-half-maximum (FWHM) of only 26 nm and fast response of 74 µs at 895 nm. The response peak can be successfully tailored from 895 to 977 nm. The sharp and narrow response NIR peak is inherently attributed to the coherent overlapping between the NIR transmission spectrum of organic layer and diffraction enhanced absorption peak of patterned nanograting Si substrates. The finite difference time domain (FDTD) physics calculation confirms the resonant enhancement peaks, which is well consistent with the experiment results. Meanwhile, the relative characterization indicates that the introduction of the organic film can promote carrier transfer and charge collection, facilitating efficient photocurrent generation. This new device design strategy opens up a new window in developing low-cost sensitive NIR narrowband detection.

Irremovable Mn-Bi Site Mixing in MnBi2Te4.

MnBi2Te4, an antiferromagnetic topological insulator, was theoretically predicted to have a gapped surface state on its (111) surface. However, a much smaller gapped or even gapless surface state has been observed experimentally, which is thought to be caused by the defects in MnBi2Te4. Here, we have theoretically identified the antisite MnBi and BiMn as dominant defects and revealed their evolution during the phase transition from MnTe/Bi2Te3 to MnBi2Te4. We found that the complete elimination of MnBi and BiMn defects in MnBi2Te4 by simple annealing is almost impossible due to the high migration barrier in kinetics. Moreover, the gap of the Dirac point-related bands in a MnBi2Te4 monolayer would be eliminated with an increasing concentration of MnBi and BiMn defects, which could explain the experimentally unobserved large-gap surface state in MnBi2Te4. Our results provide an insight into the theoretical understanding of the quality and the experimentally measured topological properties of the synthesized MnBi2Te4.