RESEARCH

Research in Qiang’s group has been consisting of chemical engineering, material science, chemistry and electrical engineering to develop advanced materials using in sustainable energy conversion and storage technologies. Recent researches include: electrocatalysis, advanced materials synthesis and nanomanufacturing, energy storage devices and energy/mass conversion, large-scale fabrication technology of carbon materials used in energy storage.

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Safe and rechargeable lithium metal batteries have been difficult to achieve because of the formation of lithium dendrites. Herein an emerging electrolyte based on a simple solvation strategy is proposed for highly stable lithium metal anodes in both coin and pouch cells. Fluoroethylene carbonate (FEC) and lithium nitrate (LiNO3) were concurrently introduced into an electrolyte, thus altering the solvation sheath of lithium ions, and forming a uniform solid electrolyte interphase (SEI), with an abundance of LiF and LiNxOy on a working lithium metal anode with dendrite-free lithium deposition. Ultrahigh Coulombic efficiency (99.96%) and long lifespans (1000 cycles) were achieved when the FEC/LiNO3 electrolyte was applied in working batteries. The solvation chemistry of electrolyte was further explored by molecular dynamics simulations and first-principles calculations. This work provides insight into understanding the critical role of the solvation of lithium ions in forming the SEI and delivering an effective route to optimize electrolytes for safe lithium metal batteries.

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Rechargeable lithium-sulfur batteries have attracted tremendous scientific attention owing to their superior energy density. However, the sulfur electrochemistry involves multielectron redox reactions and complicated phase transformations, while the final morphology of solid-phase Li2S precipitates largely dominate the battery’s performance. Herein, a triple-phase interface among electrolyte/CoSe2/G is proposed to afford strong chemisorption, high electrical conductivity, and superb electrocatalysis of polysulfide redox reactions in a working lithium-sulfur battery. The triple-phase interface effectively enhances the kinetic behaviors of soluble lithium polysulfides and regulates the uniform nucleation and controllable growth of solid Li2S precipitates at large current density. Therefore, the cell with the CoSe2/G functional separator delivers an ultrahigh rate cycle at 6.0 C with an initial capacity of 916 mAh g(-1) and a capacity retention of 459 mAh g(-1) after 500 cycles, and a stable operation of high sulfur loading electrode (2.69-4.35 mg cm(-2)). This work opens up a new insight into the energy chemistry at interfaces to rationally regulate the electrochemical redox reactions, and also inspires the exploration of related energy storage and conversion systems based on multielectron redox reactions

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Lithium metal is among the most promising anode materials in next-generation energy-storage systems. However, Li dendrite growth and unstable solid electrolyte interphase have hindered its practical applications. Structured current collectors have been widely proposed to settle these issues, whereas the prefilling of Li metal into structured anode is challenging. We proposed a coralloid silver-coated carbon fiber-based composite Li anode (CF/Ag-Li) through Ag electroplating and molten Li infusion. The molten Li can be infused into the carbon fiber framework due to the lithiophilic nature of Ag. In addition, a dendrite-free morphology and extraordinary electrochemical performance are achieved in Li-LiFePO4 and Li-sulfur cells. The CF/Ag-LilLi symmetrical cells can cycle for 160 cycles at 10.0 mA cm(-2) and 10.0 mAh cm(-2). The CF/Ag-LiIS cells exhibited a high initial discharge capacity of 785 mAh g(-1) and a large capacity retention rate after 400 cycles at 0.5C.

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The lithium metal anode is regarded as a promising candidate in next-generation energy storage devices. Lithium nitrate (LiNO3) is widely applied as an effective additive in ether electrolyte to increase the interfacial stability in batteries containing lithium metal anodes. However, because of its poor solubility LiNO3 is rarely utilized in the high-voltage window provided by carbonate electrolyte. Dissolution of LiNO3 in carbonate electrolyte is realized through an effective solvation regulation strategy. LiNO3 can be directly dissolved in an ethylene carbonate/diethyl carbonate electrolyte mixture by adding trace amounts of copper fluoride as a dissolution promoter. LiNO3 protects the Li metal anode in a working high-voltage Li metal battery. When a LiNi0.80Co0.15Al0.05O2 cathode is paired with a Li metal anode, an extraordinary capacity retention of 53% is achieved after 300 cycles (13% after 200 cycles for LiNO3-free electrolyte) and a very high average Coulombic efficiency above 99.5% is achieved at 0.5C. The solvation chemistry of LiNO3-containing carbonate electrolyte may sustain high-voltage Li metal anodes operating in corrosive carbonate electrolytes.

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Supramolecular materials, in which small organic molecules are assembled into regular structures by noncovalent interactions, attract tremendous interests because of their highly tunable functional groups and porous structure. Supramolecular adsorbents are expected to fully expose their abundant adsorptive sites in a dynamic framework. In this contribution, we introduced cucurbit[6] uril as a supramolecular capsule for reversible storage/delivery of mobile polysulfides in lithium-sulfur (Li-S) batteries to control undesirable polysulfide shuttle. The Li-S battery equipped with the supramolecular capsules retains a high Coulombic efficiency and shows a large increase in capacity from 300 to 900 mAhg(-1) at a sulfur loading of 4.2 mgcm(-2). The implementation of supramolecular capsules offers insights into intricate multielectron-conversion reactions and manifests as an effective and efficient strategy to enhance Li-S batteries and analogous applications that involve complex transport phenomena and intermediate manipulation.

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Lithium-sulfur (Li-S) batteries are strongly considered as the next-generation rechargeable cells. However, both the shuttle of lithium polysulfides (LiPSs) and sluggish kinetics in random deposition of lithium sulfides (Li2S) significantly degrade the capacity, rate performance, and cycling life of Li-S cells. Herein, bifunctional Ba0.5Sr0.5Co0.8Fe0.2O3-delta perovskite nanoparticles (PrNPs) are proposed as a promoter to immobilize LiPSs and guide the deposition of Li2S in a Li-S cell. The oxygen vacancy in PrNPs increases the metal reactivity to anchor LiPSs, and co-existence of lithiophilic (O) and sulfiphilic (Sr) sites in PrNP favor the dual-bonding (Li-O and Sr-S bonds) to anchor LiPSs. The high catalytic nature of PrNP facilitates the kinetics of LiPS redox reaction. The PrNP with intrinsic LiPS affinity serves as nucleation sites for Li2S deposition and guides its uniform propagation. Therefore, the bifunctional LiPS promoter in Li-S cell yields high rate performance and ultralow capacity decay rate of 0.062% (a quarter of pristine Li-S cells). The proposed strategy to immobilize LiPSs, promotes the conversion of LiPS, and regulates deposition of Li2S by an emerging perovskite promoter and is also expected to be applied in other energy conversion and storage devices based on multi-electron redox reactions.

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Water oxidation represents the core process of many sustainable energy systems, such as fuel cells, rechargeable metal-air batteries, and water splitting. Material surface defects with high-energy hanging bonds possess superb intrinsic reactivity, whose actual performance is limited by the dimension and conductivity of the electrocatalyst. Herein we propose a surface defect-rich perovskite electrocatalyst through a p-block metal regulation concept to achieve high performance for oxygen evolution. As a typical p-metal, Sn4+ dissolves from the solid phase from model SnNiFe perovskite nanodots, resulting in abundant surface defects with superior water oxidation performance. An oxygen pool model and a fusion-evolution mechanism are therefore proposed for the in-depth understanding of p-block metal regulation and the oxygen evolution reaction. The energy chemistry unveiled herein provides insights into water oxidation and helps to tackle critical issues in multi-electron oxygen electrocatalysis.

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Lithium metal is strongly regarded as a promising electrode material in next-generation rechargeable batteries due to its extremely high theoretical specific capacity and lowest reduction potential. However, the safety issue and short lifespan induced by uncontrolled dendrite growth have hindered the practical applications of lithium metal anodes. Hence, we propose a flexible anion-immobilized ceramic-polymer composite electrolyte to inhibit lithium dendrites and construct safe batteries. Anions in the composite electrolyte are tethered by a polymer matrix and ceramic fillers, inducing a uniform distribution of space charges and lithium ions that contributes to a dendrite-free lithium deposition. The dissociation of anions and lithium ions also helps to reduce the polymer crystallinity, rendering stable and fast transportation of lithium ions. Ceramic fillers in the electrolyte extend the electrochemically stable window to as wide as 5.5 V and provide a barrier to short circuiting for realizing safe batteries at elevated temperature. The anion-immobilized electrolyte can be applied in all-solid-state batteries and exhibits a small polarization of 15 mV. Cooperated with LiFePO4 and LiNi0.5Co0.2Mn0.3O2 cathodes, the all-solid-state lithium metal batteries render excellent specific capacities of above 150 mAh.g(-1) and well withstand mechanical bending. These results reveal a promising opportunity for safe and flexible next-generation lithium metal batteries.

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Bifunctional electrocatalysis for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) constitutes the bottleneck of various sustainable energy devices and systems like rechargeable metal-air batteries. Emerging catalyst materials are strongly requested toward superior electrocatalytic activities and practical applications. In this study, transition metal hydroxysulfides are presented as bifunctional OER/ORR electrocatalysts for Zn-air batteries. By simply immersing Co-based hydroxide precursor into solution with high-concentration S2-, transition metal hydroxides convert to hydroxysulfides with excellent morphology preservation at room temperature. The as-obtained Co-based metal hydroxysulfides are with high intrinsic reactivity and electrical conductivity. The electron structure of the active sites is adjusted by anion modulation. The potential for 10 mA cm(-2) OER current density is 1.588 V versus reversible hydrogen electrode (RHE), and the ORR half-wave potential is 0.721 V versus RHE, with a potential gap of 0.867 V for bifunctional oxygen electrocatalysis. The Co3FeS1.5(OH)(6) hydroxysulfides are employed in the air electrode for a rechargeable Zn-air battery with a small overpotential of 0.86 V at 20.0 mA cm(-2), a high specific capacity of 898 mAh g(-1), and a long cycling life, which is much better than Pt and Ir-based electrocatalyst in Zn-air batteries.

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Lithium (Li) metal is the most promising electrode for next-generation rechargeable batteries. However, the challenges induced by Li dendrites on a working Li metal anode hinder the practical applications of Li metal batteries. Herein, nitrogen (N) doped graphene was adopted as the Li plating matrix to regulate Li metal nucleation and suppress dendrite growth. The N-containing functional groups, such as pyridinic and pyrrolic nitrogen in the N-doped graphene, are lithiophilic, which guide the metallic Li nucleation causing the metal to distribute uniformly on the anode surface. As a result, the N-doped graphene modified Li metal anode exhibits a dendritefree morphology during repeated Li plating and demonstrates a high Coulombic efficiency of 98% for near 200 cycles.

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Lithium (Li) metal is regarded as the “Holy Grail” electrode because of its low electrochemical potential and high theoretical capacity. Unfortunately, uncontrolled dendritic Li growth induces low coulombic efficiency and poor safety during deposition. Here, we propose an ex situ electrochemical strategy for constructing an ultra-stable implantable solid electrolyte interphase (SEI) on a Li-metal anode. In our study, the SEI rendered dendrite-free Li deposits in a working battery. A Li-metal anode with a stable SEI can be transplanted into ether and ester electrolyte to cycle sulfur (S) and a LiNi0.5Co0.2Mn0.3O2 (NCM) cathode, respectively. The Li-S cell exhibited superb long-term cycling performance at 1.0 C with an initial capacity of 890 mAh g(-1) and capacity retention of 76% after 600 cycles. When matching the NCM cathode, the Li-metal anode with an implantable SEI avoided activation and increased capacity by 50% from 100 to 150 mAh g(-1). A Li-metal anode with implantable SEI protection delivers new insights into the rational design of Li-metal batteries with many alternative cathodes and electrolyte systems.

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Self-healing capability helps biological systems to maintain their survivability and extend their lifespan. Similarly, self-healing is also beneficial to next-generation secondary batteries because high-capacity electrode materials, especially the cathodes such as oxygen or sulfur, suffer from shortened cycle lives resulting from irreversible and unstable phase transfer. Herein, by mimicking a biological self-healing process, fibrinolysis, we introduced an extrinsic healing agent, polysulfide, to enable the stable operation of sulfur microparticle (SMiP) cathodes. An optimized capacity (similar to 3.7 mAh cm(-2)) with almost no decay after 2000 cycles at a high sulfur loading of 5.6 mg(S) cm(-2) was attained. The inert SMiP is activated by the solubilization effect of polysulfides whereas the unstable phase transfer is mediated by mitigated spatial heterogeneity of polysulfides, which induces uniform nucleation and growth of solid compounds. The comprehensive understanding of the healing process, as well as of the spatial heterogeneity, could further guide the design of novel healing agents (e.g., lithium iodine) toward high-performance rechargeable batteries.

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The oxygen reduction reaction (ORR) is the cornerstone of various sustainable energy-conversion technologies. Metal-free nanocarbon electrocatalysts with competitive activity, enhanced durability, and satisfactory cost, have been proposed as the most promising substitute for precious-metal catalysts. However, their further development is still primarily based on trial-and-error approaches due to the controversial knowledge of critical active sites and mechanisms. Herein, the activity origins of nanocarbon-based ORR electrocatalysts are comprehensively reviewed and correlated, considering the dopants, edges, and defects. Analogously, they can effectively modify the charge/ spin distribution on the sp2-conjugated carbon matrix, leading to optimized intermediate chemisorption and facilitated electron transfer. Specific doping at defective edges is expected to render practical applications for metal-free nanocarbon electrocatalysts.

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The uncontrollable growth of lithium (Li) dendrites seriously impedes practical applications of Li metal batteries. Various lithiophilic conductive frameworks, especially carbon hosts, are used to guide uniform Li nucleation and thus deliver a dendrite-free composite anode. However, the lithiophilic nature of these carbon hosts is poorly understood. Herein, the lithiophilicity chemistry of heteroatom-doped carbon is investigated through both first principles calculations and experimental verifications to guide uniform Li nucleation. The electronegativity, local dipole, and charge transfer are proposed to reveal the lithiophilicity of doping sites. Li bond chemistry further deepens the understanding of lithiophilicity. The O-doped and O/B–co-doped carbons exhibit the best lithiophilicity among single-doped and co-doped carbons, respectively. The excellent lithiophilicity achieved by O-doping carbon is further validated by Li nucleation overpotential measurement. This work uncovers the lithiophilicity chemistry of heteroatom-doped carbons and affords a mechanistic guidance to Li metal anode frameworks for safe rechargeable batteries.

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Lithium metal constitutes promising anode materials but suffers from dendrite growth. Lithiophilic host materials are highly considered for achieving uniform lithium deposition. Precise construction of lithiophilic sites with desired structure and homogeneous distribution significantly promotes the lithiophilicity of lithium hosts but remains a great challenge. In this contribution, a framework porphyrin (POF) material with precisely constructed lithiophilic sites in regard to chemical structure and geometric position is employed as the lithium host to address the above issues for dendrite-free lithium metal anodes. The extraordinary lithiophilicity of POF even beyond lithium nuclei validated by DFT simulations and lithium nucleation overpotentials affords a novel mechanism of favorable lithium nucleation to facilitate uniform nucleation and inhibit dendrite growth. Consequently, POF-based anodes demonstrate superior electrochemical performances with high Coulombic efficiency over 98%, reduced average voltage hysteresis, and excellent stability for 300 cycles at 1.0 mA cm ⁻² , 1.0 mAh cm ⁻² superior to both Cu and graphene anodes. The favorable lithium nucleation mechanism on POF materials inspires further investigation of lithiophilic electrochemistry and development of lithium metal batteries.

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Hydrogen peroxide (H2O2) is a green oxidizer widely involved in a vast number of chemical reactions. Electrochemical reduction of oxygen to H2O2 constitutes an environmentally friendly synthetic route. However, the oxygen reduction reaction (ORR) is kinetically sluggish and undesired water serves as the main product on most electrocatalysts. Therefore, electrocatalysts with high reactivity and selectivity are highly required for H2O2electrosynthesis. In this work, a synergistic strategy is proposed for the preparation of H2O2 electrocatalysts with high ORR reactivity and high H2O2 selectivity. A Co−Nx−C site and oxygen functional group comodified carbon‐based electrocatalyst (named as Co–POC–O) is synthesized. The Co–POC–O electrocatalyst exhibits excellent catalytic performance for H2O2 electrosynthesis in O2‐saturated 0.10 m KOH with a high selectivity over 80% as well as very high reactivity with an ORR potential at 1 mA cm−2 of 0.79 V versus the reversible hydrogen electrode (RHE). Further mechanism study identifies that the Co−Nx−C sites and oxygen functional groups contribute to the reactivity and selectivity for H2O2 electrogeneration, respectively. This work affords not only an emerging strategy to design H2O2 electrosynthesis catalysts with remarkable performance, but also the principles of rational combination of multiple active sites for green and sustainable synthesis of chemicals through electrochemical processes.

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Because of the high capacity of lithium (Li) metal and the intrinsic safety of solid-state electrolyte, solid-state Li-metal batteries are regarded as a promising candidate for next-generation energy storage. However, uncontrollable dendrite growth and large interfacial resistance severely hamper the practical applications. This review summarizes the issues generated by the marriage of Li-metal anodes and solid-state electrolytes. First, the current challenges are underscored. Specific attention is paid to the large interfacial resistance, uncontrolled dendrite growth, and low operation current or capacity. The second section is dedicated primarily to understanding the ionic channels in the composite electrolyte and the space charge layers in the interfacial region. Based on these dilemmas and working principles, emerging strategies to render solid-state Li-metal batteries are summarized. Finally, the general conclusion and perspective on the current limitations and recommended research of solid-state Li-metal batteries are presented.

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Lithium-sulfur (Li-S) batteries are considered as promising candidates for next-generation energy storage devices due to their ultrahigh theoretical gravimetric energy density, cost-effectiveness, and environmental friendliness. However, the application of Li-S batteries remains challenging, mainly due to a lack of understanding of the complex chemical reactions and associated equilibria occurring in a working Li-S system. In this review, the typical applications of computational chemistry in Li-S battery studies, correlating to characterization techniques, such as X-ray diffraction, infra-red & Raman spectra, X-ray absorption spectroscopy, binding energy, and nuclear magnetic resonance, are reviewed. In particular, high-accuracy calculations and large-scale models, materials genome, and machinelearning approaches are expected to further advance computational design for the development of Li-S batteries and related fields.

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The lithium metal battery is strongly considered to be one of the most promising candidates for high-energy-density energy storage devices in our modern and technology-based society. However, uncontrollable lithium dendrite growth induces poor cycling efficiency and severe safety concerns, dragging lithium metal batteries out of practical applications. This review presents a comprehensive overview of the lithium metal anode and its dendritic lithium growth. First, the working principles and technical challenges of a lithium metal anode are underscored. Specific attention is paid to the mechanistic understandings and quantitative models for solid electrolyte interphase (SEI) formation, lithium dendrite nucleation, and growth. On the basis of previous theoretical understanding and analysis, recently proposed strategies to suppress dendrite growth of lithium metal anode and some other metal anodes are reviewed. A section dedicated to the potential of full-cell lithium metal batteries for practical applications is included. A general conclusion and a perspective on the current limitations and recommended future research directions of lithium metal batteries are presented. The review concludes with an attempt at summarizing the theoretical and experimental achievements in lithium metal anodes and endeavors to realize the practical applications of lithium metal batteries.

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Owing to high specific energy, low cost, and environmental friendliness, lithium-sulfur (Li-S) batteries hold great promise to meet the increasing demand for advanced energy storage beyond portable electronics, and to mitigate environmental problems. However, the application of Li-S batteries is challenged by several obstacles, including their short life and low sulfur utilization, which become more serious when sulfur loading is increased to the practically accepted level above 3-5 mg cm(-2). More and more efforts have been made recently to overcome the barriers toward commercially viable Li-S batteries with a high sulfur loading. This review highlights the recent progress in high-sulfur-loading Li-S batteries enabled by hierarchical design principles at multiscale. Particularly, basic insights into the interfacial reactions, strategies for mesoscale assembly, unique architectures, and configurational innovation in the cathode, anode, and separator are under specific concerns. Hierarchy in the multiscale design is proposed to guide the future development of high-sulfur-loading Li-S batteries.

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