The electrochemistry of stable sulfur isotopes versus lithium.

Sulfur in nature consists of two abundant stable isotopes, with two more neutrons in the heavy one (34S) than in the light one (32S). The two isotopes show similar physicochemical properties and are usually considered an integral system for chemical research in various fields. In this work, a model study based on a Li-S battery was performed to reveal the variation between the electrochemical properties of the two S isotopes. Provided with the same octatomic ring structure, the cyclo-34S8 molecules form stronger S-S bonds than cyclo-32S8 and are more prone to react with Li. The soluble Li polysulfides generated by the Li-34S conversion reaction show a stronger cation-solvent interaction yet a weaker cation-anion interaction than the 32S-based counterparts, which facilitates quick solvation of polysulfides yet hinders their migration from the cathode to the anode. Consequently, the Li-34S cell shows improved cathode reaction kinetics at the solid-liquid interface and inhibited shuttle of polysulfides through the electrolyte so that it demonstrates better cycling performance than the Li-32S cell. Based on the varied shuttle kinetics of the isotopic-S-based polysulfides, an electrochemical separation method for 34S/32S isotope is proposed, which enables a notably higher separation factor than the conventional separation methods via chemical exchange or distillation and brings opportunities to low-cost manufacture, utilization, and research of heavy chalcogen isotopes.

Sodium layered oxide cathodes: properties, practicality and prospects.

Rechargeable sodium-ion batteries (SIBs) have emerged as an advanced electrochemical energy storage technology with potential to alleviate the dependence on lithium resources. Similar to Li-ion batteries, the cathode materials play a decisive role in the cost and energy output of SIBs. Among various cathode materials, Na layered transition-metal (TM) oxides have become an appealing choice owing to their facile synthesis, high Na storage capacity/voltage that are suitable for use in high-energy SIBs, and high adaptivity to the large-scale manufacture of Li layered oxide analogues. However, going from the lab to the market, the practical use of Na layered oxide cathodes is limited by the ambiguous understanding of the fundamental structure-performance correlation of cathode materials and lack of customized material design strategies to meet the diverse demands in practical storage applications. In this review, we attempt to clarify the fundamental misunderstandings by elaborating the correlations between the electron configuration of the critical capacity-contributing elements (e.g., TM cations and oxygen anion) in oxides and their influence on the Na (de)intercalation (electro)chemistry and storage properties of the cathode. Subsequently, we discuss the issues that hinder the practical use of layered oxide cathodes, their origins and the corresponding strategies to address their issues and accelerate the target-oriented research and development of cathode materials. Finally, we discuss several new Na layered cathode materials that show prospects for next-generation SIBs, including layered oxides with anion redox and high entropy and highlight the use of layered oxides as cathodes for solid-state SIBs with higher energy and safety. In summary, we aim to offer insights into the rational design of high-performance Na layered oxide cathode materials towards the practical realization of sustainable electrochemical energy storage at a low cost.

Reduced Volume Expansion of Micron-Sized SiOx via Closed-Nanopore Structure Constructed by Mg-Induced Elemental Segregation.

The inherently huge volume expansion during Li uptake has hindered the use of Si-based anodes in high-energy lithium-ion batteries. While some pore-forming and nano-architecting strategies show promises to effectively buffer the volume change, other parameters essential for practical electrode fabrication, such as compaction density, are often compromised. Here we propose a new in situ Mg doping strategy to form closed-nanopore structure into a micron-sized SiOx particle at a high bulk density. The doped Mg atoms promote the segregation of O, so that high-density magnesium silicates form to generate closed nanopores. By altering the mass content of Mg dopant, the average radii (ranged from 5.4 to 9.7 nm) and porosities (ranged from 1.4 % to 15.9 %) of the closed pores are precisely adjustable, which accounts for volume expansion of SiOx from 77.8 % to 22.2 % at the minimum. Benefited from the small volume variation, the Mg-doped micron-SiOx anode demonstrates improved Li storage performance towards realization of a 700-(dis)charge-cycle, 11-Ah-pouch-type cell at a capacity retention of >80 %. This work offers insights into reasonable design of the internal structure of micron-sized SiOx and other materials that undergo conversion or alloying reactions with drastic volume change, to enable high-energy batteries with stable electrochemistry.

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

In situ analysis of Li plating/stripping processes and evolution of solid electrolyte interphase (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 directly detected. As a mixed ionic-electronic conducting interface, Li|Li10GeP2S12 (LGPS) performed distinct interfacial morphological/chemical evolution and dynamics from ionic-conducting/electronic-isolating interface like Li|Li3PS4 (LPS), which were revealed by combination of in situ atomic force microscopy and in situ X-ray photoelectron spectroscopy. Though Li plating speed in LGPS was higher than 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.

A Fast-Charge Graphite Anode with a Li-Ion-Conductive, Electron/Solvent-Repelling Interface.

Graphite has been serving as the key anode material of rechargeable Li-ion batteries, yet is difficultly charged within a quarter hour while maintaining stable electrochemistry. In addition to a defective edge structure that prevents fast Li-ion entry, the high-rate performance of graphite could be hampered by co-intercalation and parasitic reduction of solvent molecules at anode/electrolyte interface. Conventional surface modification by pitch-derived carbon barely isolates the solvent and electrons, and usually lead to inadequate rate capability to meet practical fast-charge requirements. Here we show that, by applying a MoOx-MoNx layer onto graphite surface, the interface allows fast Li-ion diffusion yet blocks solvent access and electron leakage. By regulating interfacial mass and charge transfer, the modified graphite anode delivers a reversible capacity of 340.3 mAh g-1 after 4000 cycles at 6 C, showing promises in building 10-min-rechargeable batteries with a long operation life.

Quantification of Charge Transport and Mass Deprivation in Solid Electrolyte Interphase for Kinetically-Stable Low-Temperature Lithium-Ion Batteries.

Graphite (Gr)-based lithium-ion batteries with admirable electrochemical performance below -20 °C are desired but are hindered by sluggish interfacial charge transport and desolvation process. Li salt dissociation via Li+-solvent interaction enables mobile Li+ liberation and contributes to bulk ion transport, while is contradictory to fast interfacial desolvation. Designing kinetically-stable solid electrolyte interphase (SEI) without compromising strong Li+-solvent interaction is expected to compatibly improve interfacial charge transport and desolvation kinetics. However, the relationship between physicochemical features and temperature-dependent kinetics properties of SEI remains vague. Herein, we propose four key thermodynamics parameters of SEI potentially influencing low-temperature electrochemistry, including electron work function, Li+ transfer barrier, surface energy, and desolvation energy. Based on the above parameters, we further define a novel descriptor, separation factor of SEI (SSEI), to quantitatively depict charge (Li+/e-) transport and solvent deprivation processes at Gr/electrolyte interface. A Li3PO4-based, inorganics-enriched SEI derived by Li difluorophosphate (LiDFP) additive exhibits the highest SSEI (4.89×103) to enable efficient Li+ conduction, e- blocking and rapid desolvation, and as a result, much suppressed Li-metal precipitation, electrolyte decomposition and Gr sheets exfoliation, thus improving low-temperature battery performances. Overall, our work originally provides visualized guides to improve low-temperature reaction kinetics/thermodynamics by constructing desirable SEI chemistry.

Vertically Fluorinated Graphene Encapsulated SiOx Anode for Enhanced Li+ Transport and Interfacial Stability in High-Energy-Density Lithium Batteries.

Achieving high energy density has always been the goal of lithium-ion batteries (LIBs). SiOx has emerged as a compelling candidate for use as a negative electrode material due to its remarkable capacity. However, the huge volume expansion and the unstable electrode interface during (de)lithiation, hinder its further development. Herein, we report a facile strategy for the synthesis of surface fluorinated SiOx (SiOx@vG-F), and investigate their influences on battery performance. Systematic experiments investigations indicate that the reaction between Li+ and fluorine groups promotes the in-situ formation of stable LiF-rich solid electrolyte interface (SEI) on the surface of SiOx@vG-F anode, which effectively suppresses the pulverization of microsized SiOx particles during the charge and discharge cycle. As a result, the SiOx@vG-F enabled a higher capacity retention of 86.4% over 200 cycles at 1.0 C in the SiOx@vG-F||LiNi0.8Co0.1Mn0.1O2 full cell. This approach will provide insights for the advancement of alternative electrode materials in diverse energy conversion and storage systems.

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.

Reviving Fatigue Surface for Solid-State Upcycling of Highly Degraded Polycrystalline LiNi1-x-yCoxMnyO2 Cathodes.

The ongoing tide of spent lithium-ion batteries (LIBs) urgently calls for high-value output in efficient recycling. Recently, direct regeneration has emerged as a novel recycling strategy but fails to repair the irreversible morphology and structure damage of the highly degraded polycrystalline layered oxide materials. Here, this work carries out a solid-state upcycling study for the severely cracked LiNi1-x-yCoxMnyO2 cathodes. The specific single-crystallization process during calcination is investigated and the surface rock salt phase is recognized as the intrinsic obstacle to the crystal growth of the degraded cathodes due to sluggish diffusion in the heterogeneous grain boundary. Accordingly, this work revives the fatigue rock salt phase by restoring a layered surface and successfully reshapes severely broken cathodes into the high-performance single-crystalline particles. Benefiting from morphological and structural integrity, the upcycled single-crystalline cathode materials exhibit an enhanced capacity retention rate of 93.5% after 150 cycles at 1C compared with 61.7% of the regenerated polycrystalline materials. The performance is also beyond that of the commercial cathodes even under a high cut-off voltage (4.5 V) or high operating temperature (45 °C). This work provides scientific insights for the upcycling of the highly degraded cathodes in spent LIBs.

A Plastic-Crystal Electrolyte Layer Promotes Interfacial Stability of Ni-Rich Oxide Cathode in Li6PS5Cl-Based All-Solid-State Rechargeable Li Batteries.

Unfavorable parasitic reactions between the Ni-rich layered oxide cathode and the sulfide solid electrolyte have plagued the realization of all-solid-state rechargeable Li batteries. The accumulation of inactive by-products (P2Sx, S, POx n- and SOx n-) at the cathode-sulfide interface impedes fast Li-ion transfer, which accounts for sluggish reaction kinetics and significant loss of cathode capacity. Herein, we proposed an easily scalable approach to stabilize the cathode electrochemistry via coating the cathode particles by a uniform, Li+-conductive plastic-crystal electrolyte nanolayer on their surface. The electrolyte, which simply consists of succinonitrile and Li bis(trifluoromethanesulphonyl)imide, serves as an interfacial buffer to effectively suppress the adverse phase transition in highly delithiated cathode materials, and the loss of lattice oxygen and generation of inactive oxygenated by-products at the cathode-sulfide interface. Consequently, an all-solid-state rechargeable Li battery with the modified cathode delivers high specific capacities of 168 mAh g-1 at 0.1 C and a high capacity retention >80 % after 100 cycles. Our work sheds new light on rational design of electrode-electrolyte interface for the next-generation high-energy batteries.

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).

Boosting Sodium Compensation Efficiency via a CNT/MnO2 Catalyst toward High-Performance Na-Ion Batteries.

The formation of a solid electrolyte interphase on carbon anodes causes irreversible loss of Na+ ions, significantly compromising the energy density of Na-ion full cells. Sodium compensation additives can effectively address the irreversible sodium loss but suffer from high decomposition voltage induced by low electrochemical activity. Herein, we propose a universal electrocatalytic sodium compensation strategy by introducing a carbon nanotube (CNT)/MnO2 catalyst to realize full utilization of sodium compensation additives at a much-reduced decomposition voltage. The well-organized CNT/MnO2 composite with high catalytic activity, good electronic conductivity, and abundant reaction sites enables sodium compensation additives to decompose at significantly reduced voltages (from 4.40 to 3.90 V vs Na+/Na for sodium oxalate, 3.88 V for sodium carbonate, and even 3.80 V for sodium citrate). As a result, sodium oxalate as the optimal additive achieves a specific capacity of 394 mAh g-1, almost reaching its theoretical capacity in the first charge, increasing the energy density of the Na-ion full cell from 111 to 158 Wh kg-1 with improved cycle stability and rate capability. This work offers a valuable approach to enhance sodium compensation efficiency, promising high-performance energy storage devices in the future.