Nonconventional Electrochemical Reactions in Rechargeable Lithium-Sulfur Batteries.

Rechargeable lithium-sulfur (Li-S) batteries are promising for high-energy storage. However, conventional redox reactions involving sulfur (S) and lithium (Li) can lead to unstable intermediates. Over the past decade, many strategies have emerged to address this challenge, enabling nonconventional electrochemical reactions in Li-S batteries. In our Perspective, we provide a brief review of these strategies and highlight their potential benefits. Specifically, our group has pioneered a top-down approach, investigating Li-S reactions at molecular and subatomic levels, as demonstrated in our recent work on stable S isotopes. These insights not only enhance understanding of charge transfer and storage properties but also offer exciting opportunities for advancements in battery materials research.

An ultralight, pulverization-free integrated anode toward lithium-less lithium metal batteries.

The high-capacity advantage of lithium metal anode was compromised by common use of copper as the collector. Furthermore, lithium pulverization associated with "dead" Li accumulation and electrode cracking deteriorates the long-term cyclability of lithium metal batteries, especially under realistic test conditions. Here, we report an ultralight, integrated anode of polyimide-Ag/Li with dual anti-pulverization functionality. The silver layer was initially chemically bonded to the polyimide surface and then spontaneously diffused in Li solid solution and self-evolved into a fully lithiophilic Li-Ag phase, mitigating dendrites growth or dead Li. Further, the strong van der Waals interaction between the bottommost Li-Ag and polyimide affords electrode structural integrity and electrical continuity, thus circumventing electrode pulverization. Compared to the cutting-edge anode-free cells, the batteries pairing LiNi0.8Mn0.1Co0.1O2 with polyimide-Ag/Li afford a nearly 10% increase in specific energy, with safer characteristics and better cycling stability under realistic conditions of 1× excess Li and high areal-loading cathode (4 milliampere hour per square centimeter).

Anchoring Active Li Metal in Oriented Channel by In Situ Formed Nucleation Sites Enabling Durable Lithium-Metal Batteries.

Lithium metal is the ultimate anode material for pursuing the increased energy density of rechargeable batteries. However, fatal dendrites growth and huge volume change seriously hinder the practical application of lithium metal batteries (LMBs). In this work, a lithium host that preinstalled CoSe nanoparticles on vertical carbon vascular tissues (VCVT/CoSe) is designed and fabricated to resolve these issues, which provides sufficient Li plating space with a robust framework, enabling dendrite-free Li deposition. Their inherent N sites coupled with the in situ formed lithiophilic Co sites loaded at the interface of VCVT not only anchor the initial Li nucleation seeds but also accelerate the Li+ transport kinetics. Meanwhile, the Li2 Se originated from the CoSe conversion contributes to constructing a stable solid-electrolyte interphase with high ionic conductivity. This optimized Li/VCVT/CoSe composite anode exhibits a prominent long-term cycling stability over 3000 h with a high areal capacity of 10 mAh cm-2 . When paired with a commercial nickel-rich LiNi0.83 Co0.12 Mn0.05 O2 cathode, the full-cell presents substantially enhanced cycling performance with 81.7% capacity retention after 300 cycles at 0.2 C. Thus, this work reveals the critical role of guiding Li deposition behavior to maintain homogeneous Li morphology and pave the way to stable LMBs.

A Fully Amorphous, Dynamic Cross-Linked Polymer Electrolyte for Lithium-Sulfur Batteries Operating at Subzero-Temperatures.

Solid-state lithium-sulfur batteries have shown prospects as safe, high-energy electrochemical storage technology for powering regional electrified transportation. Owing to limited ion mobility in crystalline polymer electrolytes, the battery is incapable of operating at subzero temperature. Addition of liquid plasticizer into the polymer electrolyte improves the Li-ion conductivity yet sacrifices the mechanical strength and interfacial stability with both electrodes. In this work, we showed that by introducing a spherical hyperbranched solid polymer plasticizer into a Li+ -conductive linear polymer matrix, an integrated dynamic cross-linked polymer network was built to maintain fully amorphous in a wide temperature range down to subzero. A quasi-solid polymer electrolyte with a solid mass content >90 % was prepared from the cross-linked polymer network, and demonstrated fast Li+ conduction at a low temperature, high mechanical strength, and stable interfacial chemistry. As a result, solid-state lithium-sulfur batteries employing the new electrolyte delivered high reversible capacity and long cycle life at 25 °C, 0 °C and -10 °C to serve energy storage at complex environmental conditions.

Tailoring chemical composition of solid electrolyte interphase by selective dissolution for long-life micron-sized silicon anode.

Micron-sized Si anode promises a much higher theoretical capacity than the traditional graphite anode and more attractive application prospect compared to its nanoscale counterpart. However, its severe volume expansion during lithiation requires solid electrolyte interphase (SEI) with reinforced mechanical stability. Here, we propose a solvent-induced selective dissolution strategy to in situ regulate the mechanical properties of SEI. By introducing a high-donor-number solvent, gamma-butyrolactone, into conventional electrolytes, low-modulus components of the SEI, such as Li alkyl carbonates, can be selectively dissolved upon cycling, leaving a robust SEI mainly consisting of lithium fluoride and polycarbonates. With this strategy, raw micron-sized Si anode retains 87.5% capacity after 100 cycles at 0.5 C (1500 mA g-1, 25°C), which can be improved to >300 cycles with carbon-coated micron-sized Si anode. Furthermore, the Si||LiNi0.8Co0.1Mn0.1O2 battery using the raw micron-sized Si anode with the selectively dissolved SEI retains 83.7% capacity after 150 cycles at 0.5 C (90 mA g-1). The selective dissolution effect for tailoring the SEI, as well as the corresponding cycling life of the Si anodes, is positively related to the donor number of the solvents, which highlights designing high-donor-number electrolytes as a guideline to tailor the SEI for stabilizing volume-changing alloying-type anodes in high-energy rechargeable batteries.

Refined Electrolyte and Interfacial Chemistry toward Realization of High-Energy Anode-Free Rechargeable Sodium Batteries.

Anode-free rechargeable sodium batteries represent one of the ultimate choices for the 'beyond-lithium' electrochemical storage technology with high energy. Operated based on the sole use of active Na ions from the cathode, the anode-free battery is usually reported with quite a limited cycle life due to unstable electrolyte chemistry that hinders efficient Na plating/stripping at the anode and high-voltage operation of the layered oxide cathode. A rational design of the electrolyte toward improving its compatibility with the electrodes is key to realize the battery. Here, we show that by refining the volume ratio of two conventional linear ether solvents, a binary electrolyte forms a cation solvation structure that facilitates flat, dendrite-free, planar growth of Na metal on the anode current collector and that is adaptive to high-voltage Na (de)intercalation of P2-/O3-type layered oxide cathodes and oxidative decomposition of the Na2C2O4 supplement. Inorganic fluorides, such as NaF, show a major influence on the electroplating pattern of Na metal and effective passivation of plated metal at the anode-electrolyte interface. Anode-free batteries based on the refined electrolyte have demonstrated high coulombic efficiency, long cycle life, and the ability to claim a cell-level specific energy of >300 Wh/kg.

Insights into Anion-Solvent Interactions to Boost Stable Operation of Ether-Based Electrolytes in Pure-SiOx ||LiNi0.8 Mn0.1 Co0.1 O2 Full Cells.

Ether solvents with superior reductive stability promise excellent interphasial stability with high-capacity anodes while the limited oxidative resistance hinders their high-voltage operation. Extending the intrinsic electrochemical stability of ether-based electrolytes to construct stable-cycling high-energy-density lithium-ion batteries is challenging but rewarding. Herein, the anion-solvent interactions were concerned as the key point to optimize the anodic stability of the ether-based electrolytes and an optimized interphase was realized on both pure-SiOx anodes and LiNi0.8 Mn0.1 Co0.1 O2 cathodes. Specifically, the small-anion-size LiNO3 and tetrahydrofuran with high dipole moment to dielectric constant ratio realized strengthened anion-solvent interactions, which enhance the oxidative stability of the electrolyte. The designed ether-based electrolyte enabled a stable cycling performance over 500 cycles in pure-SiOx ||LiNi0.8 Mn0.1 Co0.1 O2 full cell, demonstrating its superior practical prospects. This work provides new insight into the design of new electrolytes for emerging high-energy density lithium-ion batteries through the regulation of interactions between species in electrolytes.

A Self-Reconfigured, Dual-Layered Artificial Interphase Toward High-Current-Density Quasi-Solid-State Lithium Metal Batteries.

The uncontrollable dendrite growth and unstable solid electrolyte interphase have long plagued the practical application of Li metal batteries. Herein, a dual-layered artificial interphase LiF/LiBO-Ag is demonstrated that is simultaneously reconfigured via an electrochemical process to stabilize the lithium anode. This dual-layered interphase consists of a heterogeneous LiF/LiBO glassy top layer with ultrafast Li-ion conductivity and lithiophilic Li-Ag alloy bottom layer, which synergistically regulates the dendrite-free Li deposition, even at high current densities. As a result, Li||Li symmetric cells with LiF/LiBO-Ag interphase achieve an ultralong lifespan (4500 h) at an ultrahigh current density and area capacity (20 mA cm-2 , 20 mAh cm-2 ). LiF/LiBO-Ag@Li anodes are successfully applied in quasi-solid-state batteries, showing excellent cycling performances in symmetric cells (8 mA cm-2 , 8 mAh cm-2 , 5000 h) and full cells. Furthermore, a practical quasi-solid-state pouch cell coupling with a high-nickel cathode exhibits stable cycling with a capacity retention of over 91% after 60 cycles at 0.5 C, which is comparable or even better than that in liquid-state pouch cells. Additionally, a high-energy-density quasi-solid-state pouch cell (10.75 Ah, 448.7 Wh kg-1 ) is successfully accomplished. This well-orchestrated interphase design provides new guidance in engineering highly stable interphase toward practical high-energy-density lithium metal batteries.

Mitigating Swelling of the Solid Electrolyte Interphase using an Inorganic Anion Switch for Low-temperature Lithium-ion Batteries.

In overcoming the Li+ desolvation barrier for low-temperature battery operation, a weakly-solvated electrolyte based on carboxylate solvent has shown promises. In case of an organic-anion-enriched primary solvation sheath (PSS), we found that the electrolyte tends to form a highly swollen, unstable solid electrolyte interphase (SEI) that shows a high permeability to the electrolyte components, accounting for quickly declined electrochemical performance of graphite-based anode. Here we proposed a facile strategy to tune the swelling property of SEI by introducing an inorganic anion switch into the PSS, via LiDFP co-solute method. By forming a low-swelling, Li3 PO4 -rich SEI, the electrolyte-consuming parasitic reactions and solvent co-intercalation at graphite-electrolyte interface are suppressed, which contributes to efficient Li+ transport, reversible Li+ (de)intercalation and stable structural evolution of graphite anode in high-energy Li-ion batteries at a low temperature of -20 °C.

Noncoordinating Flame-Retardant Functional Electrolyte Solvents for Rechargeable Lithium-Ion Batteries.

In Li-ion batteries, functional cosolvents could significantly improve the specific performance of the electrolyte, for example, the flame retardancy. In case the cosolvent shows strong Li+-coordinating ability, it could adversely influence the electrochemical Li+-intercalation reaction of the electrode. In this work, a noncoordinating functional cosolvent was proposed to enrich the functionality of the electrolyte while avoiding interference with the Li storage process. Hexafluorocyclotriphosphazene, an efficient flame-retardant agent with proper physicochemical properties, was chosen as a cosolvent for preparing functional electrolytes. The nonpolar phosphazene molecules with low electron-donating ability do not coordinate with Li+ and thus are excluded from the primary solvation sheath. In graphite-anode-based Li-ion batteries, the phosphazene molecules do not cointercalate with Li+ into the graphite lattice during the charging process, which helps to maintain integral anode structure and interface and contributes to stable cycling. The noncoordinating cosolvent was also applied to other types of electrode materials and batteries, paving a new way for high-performance electrochemical energy storage systems with customizable functions.

Hydrogen Isotope Effects on Aqueous Electrolyte for Electrochemical Lithium-Ion Storage.

As two stable hydrogen isotopes, protium and deuterium show magnified isotope effects in physicochemical properties due to the significantly varied atomic masses. In this work, aqueous electrolytes based on heavy water (D2 O) and light water (H2 O) were prepared to reveal the electrochemical isotope effects between the hydrogen isotopes. The covalent hydrogen-oxygen bond and intermolecular hydrogen bond in D2 O are much stronger than those in H2 O, making them thermodynamically more stable. Compared with the H2 O-based electrolyte, the D2 O-based electrolyte shows a broader electrochemical window, a higher percentage of coordinated water and a longer lifetime of hydrogen bond. Because of the above electrochemical isotope effects, the D2 O-based electrolyte shows high anodic stability against operation of high-voltage layered oxide cathode materials including LiCoO2 and LiNi0.8 Co0.1 Mn0.1 O2 , which enables long cycle life and favorable rate performance of aqueous Li-ion batteries.

Printed Nanochain-Based Colorimetric Assay for Quantitative Virus Detection.

Fast and ultrasensitive detection of pathogens is very important for efficient monitoring and prevention of viral infections. Here, we demonstrate a label-free optical detection approach that uses a printed nanochain assay for colorimetric quantitative testing of viruses. The antibody-modified nanochains have high activity and specificity which can rapidly identify target viruses directly from biofluids in 15 min, as well as differentiate their subtypes. Arising from the resonance induced near-field enhancement, the color of nanochains changes with the binding of viruses that are easily observed by a smartphone. We achieve the detection limit of 1 PFU µL-1 through optimizing the optical response of nanochains in visible region. Besides, it allows for real-time response to virus concentrations ranging from 0 to 1.0×105  PFU mL-1 . This low-cost and portable platform is also applicable to rapid detection of other biomarkers, making it attractive for many clinical applications.

Formulating the Electrolyte Towards High-Energy and Safe Rechargeable Lithium-Metal Batteries.

Rechargeable lithium-metal batteries with a cell-level specific energy of >400 Wh kg-1 are highly desired for next-generation storage applications, yet the research has been retarded by poor electrolyte-electrode compatibility and rigorous safety concerns. We demonstrate that by simply formulating the composition of conventional electrolytes, a hybrid electrolyte was constructed to ensure high (electro)chemical and thermal stability with both the Li-metal anode and the nickel-rich layered oxide cathodes. By employing the new electrolyte, Li∥LiNi0.6 Co0.2 Mn0.2 O2 cells show favorable cycling and rate performance, and a 10 Ah Li∥LiNi0.8 Co0.1 Mn0.1 O2 pouch cell demonstrates a practical specific energy of >450 Wh kg-1 . Our findings shed light on reasonable design principles for electrolyte and electrode/electrolyte interfaces toward practical realization of high-energy rechargeable batteries.

Large-Scale Synthesis of the Stable Co-Free Layered Oxide Cathode by the Synergetic Contribution of Multielement Chemical Substitution for Practical Sodium-Ion Battery.

The O3-type layered oxide cathodes for sodium-ion batteries (SIBs) are considered as one of the most promising systems to fully meet the requirement for future practical application. However, fatal issues in several respects such as poor air stability, irreversible complex multiphase evolution, inferior cycling lifespan, and poor industrial feasibility are restricting their commercialization development. Here, a stable Co-free O3-type NaNi0.4Cu0.05Mg0.05Mn0.4Ti0.1O2 cathode material with large-scale production could solve these problems for practical SIBs. Owing to the synergetic contribution of the multielement chemical substitution strategy, this novel cathode not only shows excellent air stability and thermal stability as well as a simple phase-transition process but also delivers outstanding battery performance in half-cell and full-cell systems. Meanwhile, various advanced characterization techniques are utilized to accurately decipher the crystalline formation process, atomic arrangement, structural evolution, and inherent effect mechanisms. Surprisingly, apart from restraining the unfavorable multiphase transformation and enhancing air stability, the accurate multielement chemical substitution engineering also shows a pinning effect to alleviate the lattice strains for the high structural reversibility and enlarges the interlayer spacing reasonably to enhance Na+ diffusion, resulting in excellent comprehensive performance. Overall, this study explores the fundamental scientific understandings of multielement chemical substitution strategy and opens up a new field for increasing the practicality to commercialization.

Building an Air Stable and Lithium Deposition Regulable Garnet Interface from Moderate-Temperature Conversion Chemistry.

Garnet-type electrolytes suffer from unstable chemistry against air exposure, which generates contaminants on electrolyte surface and accounts for poor interfacial contact with the Li metal. Thermal treatment of the garnet at >700 °C could remove the surface contaminants, yet it regenerates the contaminants in the air, and aggravates the Li dendrite issue as more electron-conducting defective sites are exposed. In a departure from the removal approach, here we report a new surface chemistry that converts the contaminants into a fluorinated interface at moderate temperature <180 °C. The modified interface shows a high electron tunneling barrier and a low energy barrier for Li+ surface diffusion, so that it enables dendrite-proof Li plating/stripping at a high critical current density of 1.4 mA cm-2 . Moreover, the modified interface exhibits high chemical and electrochemical stability against air exposure, which prevents regeneration of contaminants and keeps high critical current density of 1.1 mA cm-2 . The new chemistry presents a practical solution for realization of high-energy solid-state Li metal batteries.

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.

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.