Lightweight electrolyte design for Li/sulfurized polyacrylonitrile (SPAN) batteries.

Sulfurized polyacrylonitrile (SPAN) has recently emerged as a promising cathode for high-energy Li metal batteries owing to its high capacity, extended cycle life, and liberty from costly transition metals. As the high capacities of both Li metal and SPAN lead to relatively small electrode weights, the weight and specific energy density of Li/SPAN batteries are particularly sensitive to electrolyte weight, highlighting the importance of minimizing electrolyte density. In addition, the large volume changes of Li metal anode and SPAN cathode require inorganic-rich interphases that can guarantee intactness and protectivity throughout long cycles. This work addresses these crucial aspects with an electrolyte design in which lightweight dibutyl ether (DBE) is used as diluent for concentrated LiFSI-triethyl phosphate (TEP) solution. The designed electrolyte (d = 1.04 g mL-1) is 40-50% lighter than conventional localized high-concentration electrolytes (LHCEs), leading to 12-20% extra energy density at the cell level. Besides, the use of DBE introduces substantial solvent-diluent affinity, resulting in a unique solvation structure with strengthened capability to form favorable anion-derived inorganic-rich interphases, minimize electrolyte consumption, and improve cell cyclability. Our electrolyte also exhibits lower volatility than carbonate electrolytes and offers enhanced protection to both Li metal anode and SPAN cathode under thermal abuse. This article is protected by copyright. All rights reserved.

Wide Temperature Electrolytes for Lithium Batteries: Solvation Chemistry and Interfacial Reactions.

Improving the wide-temperature operation of rechargeable batteries is crucial for boosting the adoption of electric vehicles and further advancing their application scope in harsh environments like deep ocean and space probes. Herein, recent advances in electrolyte solvation chemistry are critically summarized, aiming to address the long-standing challenge of notable energy diminution at sub-zero temperatures and rapid capacity degradation at elevated temperatures (>45°C). This review provides an in-depth analysis of the fundamental mechanisms governing the Li-ion transport process, illustrating how these insights have been effectively harnessed to synergize with high-capacity, high-rate electrodes. Another critical part highlights the interplay between solvation chemistry and interfacial reactions, as well as the stability of the resultant interphases, particularly in batteries employing ultrahigh-nickel layered oxides as cathodes and high-capacity Li/Si materials as anodes. The detailed examination reveals how these factors are pivotal in mitigating the rapid capacity fade, thereby ensuring a long cycle life, superior rate capability, and consistent high-/low-temperature performance. In the latter part, a comprehensive summary of in situ/operational analysis is presented. This holistic approach, encompassing innovative electrolyte design, interphase regulation, and advanced characterization, offers a comprehensive roadmap for advancing battery technology in extreme environmental conditions.

Revealing the Anion-Solvent Interaction for Ultralow Temperature Lithium Metal Batteries.

Anion solvation in electrolytes can largely change the electrochemical performance of the electrolytes, yet has been rarely investigated. Herein, three anions of bis(trifluoromethanesulfonyl)imide (TFSI), bis(fluorosulfonyl)imide (FSI), and derived asymmetric (fluorosulfonyl)(trifluoro-methanesulfonyl)imide (FTFSI) are systematically examined in a weakly Li+ cation solvating solvent of bis(3-fluoropropyl)ether (BFPE). In-situ liquid secondary ion mass spectrometry demonstrates that FTFSI- and FSI- anions are associated with BFPE solvent, while weak TFSI- /BFPE cluster signals are detected. Molecular modeling further reveals that the anion-solvent interaction is accompanied by the formation of H-bonding-like interactions. Anion solvation enhances the Li+ cation transfer number and reduces the organic component in solid electrolyte interphase, which enhances the Li plating/stripping Coulombic efficiency at a low temperature of -30 °C from 42.4% in TFSI-based electrolytes to 98.7% in 1.5 m LiFTFSI and 97.9% in LiFSI-BFPE electrolytes. The anion-solvent interactions, especially asymmetric anion solvation also accelerate the Li+ desolvation kinetics. The 1.5 m LiFTFSI-BFPE electrolyte with strong anion-solvent interaction enables LiNi0.8 Mn0.1 Co0.1 O2 (NMC811)||Li (20 µm) full cell with stable cyclability even under -40 °C, retaining over 92% of initial capacity (115 mAh g-1 , after 100 cycles). The anion-solvent interactions insights allow to rational design the electrolyte for lithium metal batteries and beyond to achieve high performance.

Designing electrolytes and interphases for high-energy lithium batteries.

High-energy and stable lithium-ion batteries are desired for next-generation electric devices and vehicles. To achieve their development, the formation of stable interfaces on high-capacity anodes and high-voltage cathodes is crucial. However, such interphases in certain commercialized Li-ion batteries are not stable. Due to internal stresses during operation, cracks are formed in the interphase and electrodes; the presence of such cracks allows for the formation of Li dendrites and new interphases, resulting in a decay of the energy capacity. In this Review, we highlight electrolyte design strategies to form LiF-rich interphases in different battery systems. In aqueous electrolytes, the hydrophobic LiF can extend the electrochemical stability window of aqueous electrolytes. In organic liquid electrolytes, the highly lithiophobic LiF can suppress Li dendrite formation and growth. Electrolyte design aimed at forming LiF-rich interphases has substantially advanced high-energy aqueous and non-aqueous Li-ion batteries. The electrolyte and interphase design principles discussed here are also applicable to solid-state batteries, as a strategy to achieve long cycle life under low stack pressure, as well as to construct other metal batteries.

Electrolyte Design for Low-Temperature Li-Metal Batteries: Challenges and Prospects.

Electrolyte design holds the greatest opportunity for the development of batteries that are capable of sub-zero temperature operation. To get the most energy storage out of the battery at low temperatures, improvements in electrolyte chemistry need to be coupled with optimized electrode materials and tailored electrolyte/electrode interphases. Herein, this review critically outlines electrolytes' limiting factors, including reduced ionic conductivity, large de-solvation energy, sluggish charge transfer, and slow Li-ion transportation across the electrolyte/electrode interphases, which affect the low-temperature performance of Li-metal batteries. Detailed theoretical derivations that explain the explicit influence of temperature on battery performance are presented to deepen understanding. Emerging improvement strategies from the aspects of electrolyte design and electrolyte/electrode interphase engineering are summarized and rigorously compared. Perspectives on future research are proposed to guide the ongoing exploration for better low-temperature Li-metal batteries.

Synthesis of Multiple Emission Carbon Dots from Dihydroxybenzoic Acid via Decarboxylation Process.

Carbon dots (CDs), as a new zero-dimensional carbon-based nanomaterial with desirable optical properties, exhibit great potential for many application fields. However, the preparation technique of multiple emission CDs with high yield is difficult and complex. Therefore, exploring the large-scale and straightforward synthesis of multicolor CDs from a simple carbon source is necessary. In this work, the solvent-free method prepares a series of multicolor emission CDs from dihydroxybenzoic acid (DHBA). The maximum emission wavelengths are 408, 445, 553, 580, and 610 nm, respectively, covering the visible light region. The 2,4- and 2,6-CDs possess the longer emission wavelength caused by the 2,4-, and 2,6-DHBA easily undergo decarboxylation to form the larger sp2 domain graphitized structure. These CDs incorporated with g-C3N4 can significantly improve the photocatalytic water-splitting hydrogen production rate by extending the visible light absorption and enhancing the charge separation efficiency. The long-wavelength emission CDs can further enhance photocatalytic activity primarily by improving visible light absorption efficiency.

Electrolyte design for Li-ion batteries under extreme operating conditions.

The ideal electrolyte for the widely used LiNi0.8Mn0.1Co0.1O2 (NMC811)||graphite lithium-ion batteries is expected to have the capability of supporting higher voltages (≥4.5 volts), fast charging (≤15 minutes), charging/discharging over a wide temperature range (±60 degrees Celsius) without lithium plating, and non-flammability1-4. No existing electrolyte simultaneously meets all these requirements and electrolyte design is hindered by the absence of an effective guiding principle that addresses the relationships between battery performance, solvation structure and solid-electrolyte-interphase chemistry5. Here we report and validate an electrolyte design strategy based on a group of soft solvents that strikes a balance between weak Li+-solvent interactions, sufficient salt dissociation and desired electrochemistry to fulfil all the aforementioned requirements. Remarkably, the 4.5-volt NMC811||graphite coin cells with areal capacities of more than 2.5 milliampere hours per square centimetre retain 75 per cent (54 per cent) of their room-temperature capacity when these cells are charged and discharged at -50 degrees Celsius (-60 degrees Celsius) at a C rate of 0.1C, and the NMC811||graphite pouch cells with lean electrolyte (2.5 grams per ampere hour) achieve stable cycling with an average Coulombic efficiency of more than 99.9 per cent at -30 degrees Celsius. The comprehensive analysis further reveals an impedance matching between the NMC811 cathode and the graphite anode owing to the formation of similar lithium-fluoride-rich interphases, thus effectively avoiding lithium plating at low temperatures. This electrolyte design principle can be extended to other alkali-metal-ion batteries operating under extreme conditions.

Controlling Intermolecular Interaction and Interphase Chemistry Enabled Sustainable Water-tolerance LiMn2 O4 ||Li4 Ti5 O12 Batteries.

Solid electrolyte interphase (SEI) formation and H2 O activity reduction in Water-in-Salt electrolytes (WiSE) with an enlarged stability window of 3.0 V have provided the feasibility of the high-energy-density aqueous Li-ion batteries. Here, we extend the cathodic potential of WiSE by rationally controlling intermolecular interaction and interphase chemistry with the introduction of trimethyl phosphate (TMP) into WiSE. The TMP not merely limits the H2 O activity via the strong interaction between TMP and H2 O but also contributes to the formation of reinforced SEI involving phosphate and LiF by manipulating the Li+ solvation structure. Thus, water-tolerance LiMn2 O4 (LMO)||Li4 Ti5 O12 (LTO) full cell with a P/N ratio of 1.14 can be assembled and achieve a long cycling life of 1000 times with high coulombic efficiency of >99.9 %. This work provides a promising insight into the cost-effective practical manufacture of LMO||LTO cells without rigorous moisture-free requirements.

Critical Review on cathode-electrolyte Interphase Toward High-Voltage Cathodes for Li-Ion Batteries.

The thermal stability window of current commercial carbonate-based electrolytes is no longer sufficient to meet the ever-increasing cathode working voltage requirements of high energy density lithium-ion batteries. It is crucial to construct a robust cathode-electrolyte interphase (CEI) for high-voltage cathode electrodes to separate the electrolytes from the active cathode materials and thereby suppress the side reactions. Herein, this review presents a brief historic evolution of the mechanism of CEI formation and compositions, the state-of-art characterizations and modeling associated with CEI, and how to construct robust CEI from a practical electrolyte design perspective. The focus on electrolyte design is categorized into three parts: CEI-forming additives, anti-oxidation solvents, and lithium salts. Moreover, practical considerations for electrolyte design applications are proposed. This review will shed light on the future electrolyte design which enables aggressive high-voltage cathodes.

Salt-in-Salt Reinforced Carbonate Electrolyte for Li Metal Batteries.

The instability of carbonate electrolyte with metallic Li greatly limits its application in high-voltage Li metal batteries. Here, a "salt-in-salt" strategy is applied to boost the LiNO3 solubility in the carbonate electrolyte with Mg(TFSI)2 carrier, which enables the inorganic-rich solid electrolyte interphase (SEI) for excellent Li metal anode performance and also maintains the cathode stability. In the designed electrolyte, both NO3 - and PF6 - anions participate in the Li+ -solvent complexes, thus promoting the formation of inorganic-rich SEI. Our designed electrolyte has achieved a superior Li CE of 99.7 %, enabling the high-loading NCM811||Li (4.5 mAh cm-2 ) full cell with N/P ratio of 1.92 to achieve 84.6 % capacity retention after 200 cycles. The enhancement of LiNO3 solubility by divalent salts is universal, which will also inspire the electrolyte design for other metal batteries.

Enhancing Li+ Transport in NMC811||Graphite Lithium-Ion Batteries at Low Temperatures by Using Low-Polarity-Solvent Electrolytes.

LiNix Coy Mnz O2 (x+y+z=1)||graphite lithium-ion battery (LIB) chemistry promises practical applications. However, its low-temperature (≤ -20 °C) performance is poor because the increased resistance encountered by Li+ transport in and across the bulk electrolytes and the electrolyte/electrode interphases induces capacity loss and battery failures. Though tremendous efforts have been made, there is still no effective way to reduce the charge transfer resistance (Rct ) which dominates low-temperature LIBs performance. Herein, we propose a strategy of using low-polarity-solvent electrolytes which have weak interactions between the solvents and the Li+ to reduce Rct , achieving facile Li+ transport at sub-zero temperatures. The exemplary electrolyte enables LiNi0.8 Mn0.1 Co0.1 O2 ||graphite cells to deliver a capacity of ≈113 mAh g-1 (98 % full-cell capacity) at 25 °C and to remain 82 % of their room-temperature capacity at -20 °C without lithium plating at 1/3C. They also retain 84 % of their capacity at -30 °C and 78 % of their capacity at -40 °C and show stable cycling at 50 °C.

Interfacial Design for a 4.6 V High-Voltage Single-Crystalline LiCoO2 Cathode.

Single-crystalline cathode materials have attracted intensive interest in offering greater capacity retention than their polycrystalline counterparts by reducing material surfaces and phase boundaries. However, the single-crystalline LiCoO2 suffers severe structural instability and capacity fading when charged to high voltages (4.6 V) due to Co element dissolution and O loss, crack formation, and subsequent electrolyte penetration. Herein, by forming a robust cathode electrolyte interphase (CEI) in an all-fluorinated electrolyte, reversible planar gliding along the (003) plane in a single-crystalline LiCoO2 cathode is protected due to the prevention of element dissolution and electrolyte penetration. The robust CEI effectively controls the performance fading issue of the single-crystalline cathode at a high operating voltage of 4.6 V, providing new insights for improved electrolyte design of high-energy-density battery cathode materials.

Solvation sheath reorganization enables divalent metal batteries with fast interfacial charge transfer kinetics.

Rechargeable magnesium and calcium metal batteries (RMBs and RCBs) are promising alternatives to lithium-ion batteries because of the high crustal abundance and capacity of magnesium and calcium. Yet, they are plagued by sluggish kinetics and parasitic reactions. We found a family of methoxyethyl-amine chelants that greatly promote interfacial charge transfer kinetics and suppress side reactions on both the cathode and metal anode through solvation sheath reorganization, thus enabling stable and highly reversible cycling of the RMB and RCB full cells with energy densities of 412 and 471 watt-hours per kilogram, respectively. This work provides a versatile electrolyte design strategy for divalent metal batteries.

An Inorganic-Rich Solid Electrolyte Interphase for Advanced Lithium-Metal Batteries in Carbonate Electrolytes.

In carbonate electrolytes, the organic-inorganic solid electrolyte interphase (SEI) formed on the Li-metal anode surface is strongly bonded to Li and experiences the same volume change as Li, thus it undergoes continuous cracking/reformation during plating/stripping cycles. Here, an inorganic-rich SEI is designed on a Li-metal surface to reduce its bonding energy with Li metal by dissolving 4m concentrated LiNO3 in dimethyl sulfoxide (DMSO) as an additive for a fluoroethylene-carbonate (FEC)-based electrolyte. Due to the aggregate structure of NO3 - ions and their participation in the primary Li+ solvation sheath, abundant Li2 O, Li3 N, and LiNx Oy grains are formed in the resulting SEI, in addition to the uniform LiF distribution from the reduction of PF6 - ions. The weak bonding of the SEI (high interface energy) to Li can effectively promote Li diffusion along the SEI/Li interface and prevent Li dendrite penetration into the SEI. As a result, our designed carbonate electrolyte enables a Li anode to achieve a high Li plating/stripping Coulombic efficiency of 99.55 % (1 mA cm-2 , 1.0 mAh cm-2 ) and the electrolyte also enables a Li||LiNi0.8 Co0.1 Mn0.1 O2 (NMC811) full cell (2.5 mAh cm-2 ) to retain 75 % of its initial capacity after 200 cycles with an outstanding CE of 99.83 %.

Solvation Structure Design for Aqueous Zn Metal Batteries.

Aqueous Zn batteries are promising energy storage devices for large-scale energy-storage due to low cost and high energy density. However, their lifespan is limited by the water decomposition and Zn dendrite growth. Here, we suppress water reduction and Zn dendrite growth in dilute aqueous electrolyte by adding dimethyl sulfoxide (DMSO) into ZnCl2-H2O, in which DMSO replaces the H2O in Zn2+ solvation sheath due to a higher Gutmann donor number (29.8) of DMSO than that (18) of H2O. The preferential solvation of DMSO with Zn2+ and strong H2O-DMSO interaction inhibit the decomposition of solvated H2O. In addition, the decomposition of solvated DMSO forms Zn12(SO4)3Cl3(OH)15·5H2O, ZnSO3, and ZnS enriched-solid electrolyte interphase (SEI) preventing Zn dendrite and further suppressing water decomposition. The ZnCl2-H2O-DMSO electrolyte enables Zn anodes in Zn||Ti half-cell to achieve a high average Coulombic efficiency of 99.5% for 400 cycles (400 h), and the Zn||MnO2 full cell with a low capacity ratio of Zn:MnO2 at 2:1 to deliver a high energy density of 212 Wh/kg (based on both cathode and anode) and maitain 95.3% of the capacity over 500 cycles at 8 C.

A rationally designed 3D interconnected porous tin dioxide cube with reserved space for volume expansion as an advanced anode of lithium-ion batteries.

To work against the volume expansion (∼300%) of SnO2 during lithiation, here a sub-micro sized, interconnected, and porous SnO2 cube with rationally designed reserved space (∼375%) is synthesized via an artful topochemistry route (CaSn(OH)6-CaSnO3-SnO2). Owing to its microstructure, this novel material harvests enhanced lithium-storage performance.

Boron-Induced Nitrogen Fixation in 3D Carbon Materials for Supercapacitors.

Nitrogen-rich carbon materials attract great attention because of their admirable performance in energy storage and electrocatalysis. However, their conductivity and nitrogen content are somehow contradictory because good conductivity requires high-temperature heat treatment, which decomposes most of the nitrogen species. Herein, we propose a facile method to solve this problem by introducing boron (B) to fix the nitrogen in a three-dimensional (3D) carbon material even at 1000 °C. Besides, this N-rich carbon material has a high content of pyrrolic nitrogen due to the selective stabilization of B, which is favorable in electrochemical reactions. Density functional theory (DFT) investigation demonstrates that B reduces the energy level of neighboring N species (especially pyrrolic nitrogen) in the graphene layer, making it difficult to escape. Thus, this carbon material simultaneously, achieves high conductivity (30 S cm-1) and nitrogen content (7.80 atom %), thus showing an outstanding capacitance of 412 F g-1 and excellent rate capability.

In Situ Synthesis of MoC1- x Nanodot@Carbon Hybrids for Capacitive Lithium-Ion Storage.

In this study, in situ synthesis of carbon-coated MoC1- x nanodots anchored on nitrogen-doped carbon (MoC1- x@C) for lithium storage is reported. The obtained MoC1- x@C hybrids exhibit intriguing structural characteristics including ultrafine particle size (ca. 1.2 nm) of MoC1- x nanodots, porous structure of nitrogen-doped carbon matrix, and good robustness. When evaluated as anodes for lithium-ion batteries, the optimized MoC1- x@C sample demonstrates a superior specific capacity (1099.2 mA h g-1 at 0.1 A g-1) and good rate capability (369.1 mA h g-1 at 5 A g-1). The MoC1- x@C anode also presents remarkable cycling stability with a much higher specific capacity (657.9 mA h g-1) than that of commercial bulk MoC (91.4 mA h g-1) after 500 cycles at 1 A g-1. Kinetics analysis of the anodes reveals the charge storage mechanism, which demonstrates the existence of capacitive redox reactions occurring at the shallow surface of the MoC1- x nanodots and closely relating to the particle size. The outstanding electrochemical performance results from the synergistic effect of the elastic carbonaceous encapsulation to accommodate the huge volume expansion and the ultrafine MoC1- x nanodots to provide more reactive sites for capacitive lithium storage.

Dismutation of Titanium Sub-oxide into TiO and TiO2 with Structural Hierarchy Assisted by Ammonium Halides.

Black TiO2-x attracts enormous attention due to its large solar absorption and improved conductivity. In this work, a novel structure of TiO2-x with conductive TiO layer, performing full-spectrum absorption, was synthesized in one step by the unforeseen dismutation reaction of titanium sub-oxides (Tin O2n-1 ) in ammonium halide atmosphere. For this new reaction, a possible mechanism of decomposition-etching-disproportionation-rehydrolysis process was proposed. The vital intermediate reactant TiCl4 , which verifies the assumption, has been captured in the form of (NH4 )2 TiCl6 , especially where Ti2 O3 is the reactant. Furthermore, this work not only can nominate TiO as an alternative for noble metals or carbon materials in the aim to improve the electron conductivity and solar absorption of black TiO2-x , which are important in electrochemistry and optoelectronics fields, but also can be a new route to synthesize special structures for other multivalent transition metals.

Self-templated synthesis of heavily nitrogen-doped hollow carbon spheres.

Nitrogen-doped hollow carbon spheres with a well-defined shape, uniform diameter, and high doping concentration (11 at%) are synthesized via space-confined thermal decomposition of a single source precursor zinc carbodiimide, which can serve as both carbon and nitrogen sources and also a self-template.