Low Coulombic Efficiency Research Articles

Interfacial electronic insulation strategy for high-performance Zinc-ion batteries

Aqueous rechargeable zinc metal batteries have garnered widespread attention due to their inherent high safety, high volumetric capacity, and low cost. However, the uncontrollable growth of zinc dendrites and severe hydrogen evolution reaction (HER) side reactions lead to low Coulombic efficiency and short lifespan of zinc metal anodes, hindering their practical application. We employed a plasma fluorination strategy to in-situ react on the surface of zinc metal to generate an electron-insulating ZnF2 coating, which reduces HER, suppresses dendrite growth, and enhances the wettability of the electrode with the electrolyte. Through density functional theory (DFT) and molecular dynamics (MD) simulations, we systematically studied the mechanism by which ZnF2 improves interfacial properties, suppresses the hydrogen evolution reaction (HER), and inhibits dendrite formation. Ultimately, symmetric batteries and Zn@ZnF2||Cu batteries assembled with Zn@ZnF2 electrodes exhibited significantly extended cycle life and high Coulombic efficiency. Full cells of Zn@ZnF2||MnO2@CNT achieved a cycle life of over 5000 cycles at a current density of 1 A g−1. This study provides a practical method for industrial treatment of the Zn surface and offers an in-depth analysis and discussion of the role of ZnF2 in inhibiting dendrite growth, HER, and improving interfacial wettability in zinc-ion batteries.

Revealing the degradation pathways of layered Li-rich oxide cathodes.

Layered lithium-rich transition metal oxides are promising cathode candidates for high-energy-density lithium batteries due to the redox contributions from transition metal cations and oxygen anions. However, their practical application is hindered by gradual capacity fading and voltage decay. Although oxygen loss and phase transformation are recognized as primary factors, the structural deterioration, chemical rearrangement, kinetic and thermodynamic effects remain unclear. Here we integrate analysis of morphological, structural and oxidation state evolution from individual atoms to secondary particles. By performing nanoscale to microscale characterizations, distinct structural change pathways associated with intraparticle heterogeneous reactions are identified. The high level of oxygen defects formed throughout the particle by slow electrochemical activation triggers progressive phase transformation and the formation of nanovoids. Ultrafast lithium (de)intercalation leads to oxygen-distortion-dominated lattice displacement, transition metal ion dissolution and lithium site variation. These inhomogeneous and irreversible structural changes are responsible for the low initial Coulombic efficiency, and ongoing particle cracking and expansion in the subsequent cycles.

In situ p-block protective layer plating in carbonate-based electrolytes enables stable cell cycling in anode-free lithium batteries.

'Anode-free' Li metal batteries offer the highest possible energy density but face low Li coulombic efficiency when operated in carbonate electrolytes. Here we report a performance improvement of anode-free Li metal batteries using p-block tin octoate additive in the carbonate electrolyte. We show that the preferential adsorption of the octoate moiety on the Cu substrate induces the construction of a carbonate-less protective layer, which inhibits the side reactions and contributes to the uniform Li plating. In the mean time, the reduction of Sn2+ at the initial charging process builds a stable lithophilic layer of Cu6Sn5 alloy and Sn, improving the affinity between the Li and the Cu substrate. Notably, anode-free Li metal pouch cells with tin octoate additive demonstrate good cycling stability with a high coulombic efficiency of ~99.1%. Furthermore, this in situ p-block layer plating strategy is also demonstrated with other types of p-block metal octoate, as well as a Na metal battery system, demonstrating the high level of universality.

Ultrafast and Highly Efficient Sodium Ion Storage in Manganese‐Based Tunnel‐Structured Cathode

AbstractNa0.44MnO2 with tunnel structure is considered a promising low‐cost cathode material for sodium‐ion batteries. However, the sluggish Na+ transport kinetics and low initial Coulombic efficiency restrict its practical applications in rechargeable sodium‐ion batteries. Herein, a manganese‐based tunnel‐structured cathode with high rate capability and high initial Coulombic efficiency is prepared by niobium doping and sodium compensation. Via materials characterizations and theoretical calculations, it is demonstrated that a proper amount of niobium doping in tunnel structure can effectively improve its structural stability and charge transport kinetics, resulting in outstanding rate capability (76.6% capacity retained from 0.5 to 30 C) and superior cycling performance (82.3% capacity retention after 800 cycles at 5 C) for the optimized Nb‐doped Na0.44MnO2 cathode (Na0.44Mn0.98Nb0.02O2). Furthermore, NaCrO2 is added into the Na0.44Mn0.98Nb0.02O2 cathode as a self‐sacrificing sodium compensation additive, and a high initial Coulombic efficiency close to 100% is achieved for the composite cathode. This work establishes a facile strategy to design advanced manganese‐based cathode materials for large‐scale energy storage applications.

Linking the size of hard carbon particles with electrochemical response in sodium ion storage

Hard carbon is considered to be one of the most promising anodes for sodium-ion batteries (SIBs) owing to its high capacity and abundant resources. However, the role of particle size on sodium ion storage is unclear, which leads to low capacity and initial coulombic efficiency (ICE) in practical application. In this work, a series of hard carbons with different particle sizes were prepared by an “up to down” strategy using simple grinding and ball-milling method to investigate the effect of particle size on electrochemical response of sodium ion storage. The particle size of hard carbon has negligible effect on initial specific capacity. However, it has a strong effect on the ICE and rate capability. The ICE reduces as the particle size decreases, but the rate performance in reverse. Moreover, impedance analysis and electrochemical kinetics show huge differences for different particle sizes. In-situ Raman technique was also adopted to further illustrate the sodium ion storage mechanism of hard carbon, and an “adsorption-intercalation-pore filling” mechanism is proposed. This work could provide a new perspective for the design of hard carbon materials with suitable structure for efficient sodium ion storage, helping to develop high performance SIBs.

Interfacial Engineering of Polymer Membranes with Intrinsic Microporosity for Dendrite-Free Zinc Metal Batteries.

Metallic zinc has emerged as a promising anode material for high-energy battery systems due to its high theoretical capacity (820 mAh g-1), low redox potential for two-electron reactions, cost-effectiveness and inherent safety. However, current zinc metal batteries face challenges in low coulombic efficiency and limited longevity due to uncontrollable dendrite growth, the corrosive hydrogen evolution reaction (HER) and decomposition of the aqueous ZnSO4 electrolyte. Here, we report an interfacial-engineering approach to mitigate dendrite growth and reduce corrosive reactions through the design of ultrathin selective membranes coated on the zinc anodes. The submicron-thick membranes derived from polymers of intrinsic microporosity (PIMs), featuring pores with tunable interconnectivity, facilitate regulated transport of Zn2+-ions, thereby promoting a uniform plating/stripping process. Benefiting from the protection by PIM membranes, zinc symmetric cells deliver a stable cycling performance over 1500 h at 1 mA/cm2 with a capacity of 0.5 mAh while full cells with NaMnO2 cathode operate stably at 1 A g-1 over 300 cycles without capacity decay. Our work represents a new strategy of preparing multi-functional membranes that can advance the development of safe and stable zinc metal batteries.

Interfacial Engineering of Polymer Membranes with Intrinsic Microporosity for Dendrite‐free Zinc Metal Batteries

Metallic zinc has emerged as a promising anode material for high‐energy battery systems due to its high theoretical capacity (820 mA h g‐1), low redox potential for two‐electron reactions, cost‐effectiveness and inherent safety. However, current zinc metal batteries face challenges in low coulombic efficiency and limited longevity due to uncontrollable dendrite growth, the corrosive hydrogen evolution reaction (HER) and decomposition of the aqueous ZnSO4 electrolyte. Here, we report an interfacial‐engineering approach to mitigate dendrite growth and reduce corrosive reactions through the design of ultrathin selective membranes coated on the zinc anodes. The submicron‐thick membranes derived from polymers of intrinsic microporosity (PIMs), featuring pores with tunable interconnectivity, facilitate regulated transport of Zn2+‐ions, thereby promoting a uniform plating/stripping process. Benefiting from the protection by PIM membranes, zinc symmetric cells deliver a stable cycling performance over 1500 h at 1 mA/cm² with a capacity of 0.5 mAh while full cells with NaMnO2 cathode operate stably at 1 A g‐1 over 300 cycles without capacity decay. Our work represents a new strategy of preparing multi‐functional membranes that can advance the development of safe and stable zinc metal batteries.

Stress-Relieving Carboxylated Polythiophene/Single-Walled Carbon Nanotube Conductive Layer for Stable Silicon Microparticle Anodes in Lithium-Ion Batteries.

Stress-relieving and electrically conductive single-walled carbon nanotubes (SWNTs) and conjugated polymer, poly[3-(potassium-4-butanoate)thiophene] (PPBT), wrapped silicon microparticles (Si MPs) have been developed as a composite active material to overcome technical challenges such as intrinsically low electrical conductivity, low initial Coulombic efficiency, and stress-induced fracture due to severe volume changes of Si-based anodes for lithium-ion batteries (LIBs). The PPBT/SWNT protective layer surrounding the surface of the microparticles physically limits volume changes and inhibits continuous solid electrolyte interphase (SEI) layer formation that leads to severe pulverization and capacity loss during cycling, thereby maintaining electrode integrity. PPBT/SWNT-coated Si MP anodes exhibited high initial Coulombic efficiency (85%) and stable capacity retention (0.027% decay per cycle) with a reversible capacity of 1894 mA h g-1 after 300 cycles at a current density of 2 A g-1, 3.3 times higher than pristine Si MP anodes. The stress relaxation and underlying mechanism associated with the incorporation of the PPBT/SWNT layer were interpreted by quasi-deterministic and quantitative stress analyses of SWNTs through in situ Raman spectroscopy. PPBT/SWNT@Si MP anodes can maintain reversible stress recovery and 45% less variation in tensile stress compared with SWNT@Si MP anodes during cycling. The results verify the benefits of stress relaxation via a protective capping layer and present an efficient strategy to achieve long cycle life for Si-based anodes for next-generation LIBs.

Lithiophilic Polymers of High Conjugation and Mesoporosity Enable Lean and Dendrite-Free Lithium Anode.

Lithiated Cu current collectors with a lean Li supply have been extensively explored as prospective composite anodes for constructing lithium metal batteries (LMBs) but suffer from low Coulombic efficiencies (CE) and uncontrollable dendrite growth. Herein, two hexaazanonaphthalene (HATN)-based compounds comprising rich conjugated aromatic rings and redox-active C═N groups are synthesized and exploited to modify the Cu surface for mediating smooth Li plating/stripping. Compared to the HATN compound interlinked through flexible sigma bonds, the one conjugated through dual sp2-carbon manifests a more rigid backbone, improved electric conductivity, and enhanced mesoporosity. As a result, Cu electrodes modified with the latter demonstrate enhanced CE and suppressed dendrites in both half and symmetric cells, apart from a stable operation over 250 cycles in the LiFePO4 full cells with a capacity retention of 94.9% at 1 C. This study signifies the tailoring of intramolecular conjugation and chain configuration of lithiophilic macromolecules to facilitate reversible Li deposition on Cu for achieving high-performance LMBs.

Entropy enhancement drived high initial Coulombic efficiency and capacity integrated SnS2 nanosheets for lithium-ion batteries

Layer SnS2 has been garnered significant attention for next-generation lithium-ion batteries (LIBs), due to its abundant resources and high theoretical capacity. However, the low initial Coulombic efficiency, large volume expansion and structural degradation have significantly hindered its application in LIBs. Herein, the layer Sn0.7(MoFeCoNiV)0.3S2 nanosheets (HE3-SnS2) grown on the conductive substrate carbon cloth (CC) is synthesized by one-step hydrothermal method. Multiple elements doping strategy not only increases the conformational entropy which will improve the structural stability of during cycling, but also enlarges the interlayer spacing which benefits for lithium-ion transfer. As a result, the additive-free integrated CC@HE3-SnS2 electrode achieves a high reversible specific capacity of 1204.9 mAh g−1 with a high initial Coulombic efficiency of 94.7 % at 1C, and maintains 1011.4 mAh g−1 after 100 cycles. Specifically, the CC@HE3-SnS2 anode exhibits excellent rate capability of 670.8 mAh g−1 at 10C. Moreover, the full cell based on CC@HE3-SnS2 anode and commercial LiCoO2 cathode displays a stable capacity retention of 862.7 mAh g−1 after 100 cycles at 1C. The entropy-stabilized SnS2-based anode with high initial Coulombic efficiency and rate capability has a competitive candidate for LIBs.

Covalent triazine frameworks crosslinked microporous polymer membranes with fast and selective ion transport for ultra-stable vanadium redox flow batteries

The vanadium redox flow batteries (VRFBs) are an essential pathway to long-duration energy storage with the merits of power and energy decoupling, long lifetime and safety. However, low coulombic efficiency stemming from vanadium crossover across the membrane together with notable ohmic loss originated from low proton conductivity of the membrane still limits high performance operation of the VRFBs. Herein, we proposed 2,2′-bipyridine-based covalent triazine frameworks (bipCTF) crosslinked sulfonated-poly (4,4′-diphenylether-5,5′-bibenzimidazole) (SOPBI) (bipCTF/SP-100) for use as the membrane in VRFBs, which synergistically prevents vanadium crossover and enhances proton conductivity. By delicately tuning the sulfonation degree and properly incorporate bipCTF, the bipCTF/SP-100 membrane is successfully synthesized based on OPBI polymers, which delivers a reduced area resistance of 0.3 Ω cm2 and a low VO2+ permeability of 19.05 × 10−9 cm2 s−1, affording an excellent trade-off between proton conductivity and ion selectivity. Theoretical calculation further corroborates that the high proton conductivity of bipCTF/SP-100 is attributed to the ionic channels formed by bipCTF, while the superior ion selectivity is assigned to protonated imidazole and pyridine. Benefiting from microporous bipCTF/SP-100 membrane, the VRFB exhibits a high CE of 99.8 % and an excellent EE of 78.3 % at 250 mA cm−2 and meanwhile yields a high capacity retention of 94.8 % after 200 cycles at 200 mA cm−2, which shows enormous potential for high power density operation of the VRFBs.

Molecular Filter Net Synergy with Regulation in Ion Percolation for High-Performance Zn Metal Batteries.

The uncontrollable dendrite growth and complex parasitic reactions of Zn metal anodes cause short cycle lives and low Coulombic efficiency, which seriously affect their applications. To address these issues, this research proposes an efficient ion percolating interface constituted by a hydrogen-bonded organic framework (HND) for a highly stable and reversible Zn anode. The hydrogen-bonded skeleton acts as a molecular filter net, capturing water molecules by forming targeted hydrogen-bonding systems with them, sufficiently inhibiting parasitic reactions. Additionally, the interaction of the rich-N and -O electrochemically active sites with Zn2+ effectively regulates its percolation, which greatly enhances the diffusion kinetics of Zn2+, thus facilitating rapid and uniform migration of Zn2+ at the anode surface. Through the above synergistic effect, dendrite-free anodes with highly reversible Zn plating/stripping behaviors can be achieved. Hence, the modified Zn anode (HND@Zn) performs a steady cycling time of more than 1700 h at 1 mA cm-2. Moreover, the HND@Cu||Zn asymmetric cell exhibits a stable charge/discharge process of over 1600 cycles with an average Coulombic efficiency of up to 99.6% at 5 mA cm-2. This work provides some conceptions for the evolution and application of high-performance Zn metal batteries.

Comprehensive Review of Li-Rich Mn-Based Layered Oxide Cathode Materials for Lithium-Ion Batteries: Theories, Challenges, Strategies and Perspectives.

Lithium-rich manganese-based layered oxide cathode materials (LLOs) have always been considered as the most promising cathode materials for achieving high energy density lithium-ion batteries (LIBs). However, in practical applications, LLOs often face some key problems, such as low initial coulombic efficiency, capacity/voltage decay, poor rate performance and poor cycle stability. It seriously shortens the lifespan of lithium-ion batteries and hinder the large-scale commercial application of LLOs. Herein, firstly, the basic theories of LLOs were systematically reviewed, including the structural characteristics, the working mechanism of LLOs, the preparation methods of LLOs (liquid phase co-precipitate method, sol-gel method, hydrothermal synthesis method, solid phase method, low heat solid-phase method, high temperature solid-state method etc.), and electrochemical characteristics of LLOs (first charge discharge characteristics and reversible efficiency, cycling performance, high and low temperature performance and thermal stability etc.). Then, key challenges faced by LLOs were systematically discussed. Finally, the LLOs modification strategies used to address these challenges (element doping, surface modification, defect engineering, structural and morphological control etc.) were elaborated in detail. This important review provides potential insights and directions for further improving the electrochemical performance of LLOs, and provides a necessary theoretical basis for accelerating the large-scale commercial application of LLOs. It possesses important scientific research value and far-reaching social significance.

Enhancing the sodium storage performance of hard carbon by constructing thin carbon coatings via esterification reactions

Hard carbons derived from pitch are considered a competitive low-cost anode for sodium-ion batteries. However, the preparation of pitch-based hard carbon (PHC) requires the aid of a pre-oxidation strategy, which introduces unnecessary defects and oxygen elements, which leads to low initial Coulombic efficiency (ICE) and poor cycling stability. Herein, we demonstrate a new surface engineering strategy by grafting chemically active glucose molecules on the PHC surface via esterification reactions, which can achieve low-cost nano-scaled carbon coating. Thin glucose coating can be carbonized at a lower temperature, which results in a more closed pore structure and fewer functional groups. The as prepared PHC exhibits a high reversible capacity of 328.5 mAh/g with a high ICE of 92.08 % at 0.02 A/g. It is noteworthy that the PHC can be adapted to a variety of cathode materials for full-cell assembling without pre-sodiation, which maintains the characteristics of high capacity and excellent cycling stability. The performance of resin-based hard carbon coated with a similar method was also improved, demonstrating the universality of the technique.

Regulating the Electrochemical Performance of Simple Halogen-Free Electrolyte Using Ammonium Bromide Additive for Magnesium-Sulfur Battery Applications

Magnesium-sulfur (Mg-S) batteries are a promising energy storage system; however, the short cycle life, low coulombic efficiency, and the shuttle effect of polysulfide hinder its practical application. Applying electrolyte additives is a powerful technique to optimize the electrochemical performance of Mg-S electrolytes. Herein, ammonium bromide (NH4Br) is used as an inorganic electrolyte additive in the halogen-free electrolyte (HFE) to guide homogeneous Mg deposition. It can be noticed that the addition of NH4Br decreases the activation energy values from 0.14 eV to 0.10 eV and reduces the value of Mg2+ stripping/plating overpotential. It is found that the introduction of NH4Br to HFE enhances the cycle life and the initial discharge capacity (~1662 mAhg-1) of the Mg-S cells compared with the cells using free NH4Br that deliver initial discharge capacity of ~ 184 mAh g-1, low coulombic efficiency, and short cycle life. Further efforts have been devoted by implementing a BaTiO3 (BTO) as a modified separator to overcome the polysulfide dissolution issue in the cell. The surface of the cell's anode applying a modified separator shows half wt.% S content compared with the bare cell after cycling. This study opens further research for developing novel electrolyte schemes for magnesium-sulfur battery applications.

Li-Sn Alloyed Layer Containing Artificial SEI on Li-Metal Anode for Superior Lithium Metal Batteries: Development and Understanding of Anode/Electrolyte Interfacial Phenomena

Modern civilization and cutting-edge technologies and tools are highly dependent on energy storage devices and demand efficient and long-lasting high-energy-density storage devices. Lithium metal batteries have surpassed their competitors concerning energy density due to their inherent high specific capacity (3860 mAh/g) and the lowest electrochemical potential (-3.04 V vs. standard hydrogen electrode), proving to be one of the most favorable energy storage devices for smart and mobile gadgets, electric automobiles, grid storage, etc. However, safety-threatening and performance-decay challenges associated with lithium metal anodes, such as lithium dendrite formation, uncontrolled parasitic reactions between Li-metal and electrolyte, low coulombic efficiency, dead Li-formation, etc., restrict its employment in practical batteries. The root cause of the dendrite formation is poor Li-ion conductivity of bulk lithium metal, which results in an uneven electric field distribution, leading to non-uniform Li deposition/stripping upon repeated charge/discharge. Herein, a facile chemical reduction process is being opted to fabricate a highly Li-ion diffusive Li-Sn-based artificial SEI layer on the lithium metal surface to prevail over the above-mentioned issues. Therefore, upon careful concentration investigation of reactants, 25 mM precursor concentration (SnCl4 in EC: DMC in 1:1 volume ration) demonstrated the best electrochemical performance, revealing a cumulative capacity of over 700 mAh/cm2 at a current density of 1 mA/cm2 for 1 h in a symmetric cell. Physical characterizations (XRD and SEM-EDS) showed a thin layer containing Li-Sn alloys along with LiCl formed at the lithium metal surface. Possessing high Li-ion diffusivity, Li-Sn alloyed hybrid anode illustrated a gradual decrease in the charge transfer resistance on increasing the concentration, thus, lower overpotential in symmetric cells, in contrast to pristine Li-metal. However, an increase in the electrical resistance has been observed on increasing the precursor concentration due to the presence of the insulating LiCl phase in the protective layer. Moreover, in-situ optical microscopy demonstrated more uniform and on-surface Li-deposition for the hybrid electrode, whereas mossy and dendritic growth on bare Li-metal. Full cells prepared with Li-Sn alloyed anode against NMC532 cathode illustrated stable cycling up to 150 cycles; contrastingly, the cell with pristine Li-metal showed a drastic capacity fade just after 100 cycles, demonstrating the inclination towards safer lithium metal batteries.

A Sustainable Process for Rare Earth Electrowinning in Chloride Based Molten Salts

Neodymium production has become increasingly important due to use of neodymium–iron–boron (NdFeB) magnets in green energy, consumer technology and defense applications. The state-of-the-art practice features a neodymium fluoride and lithium fluoride molten salt with a consumable carbon anode converting dissolved neodymium oxide and carbon to neodymium metal and CO2.1-2 The anode effect results in PFCs and CO emissions, which make the current neodymium electrowinning process unsustainable.3-4 Some attempts have been made to electrolyze the chloride salt of neodymium to produce chlorine at the anode. Chlorine is a value-added product which neither consumes the anode nor produces other deleterious GHGs. Additionally, the chloride of neodymium can be non-carbothermically produced through a spontaneous reaction with hydrochloric acid, producing only water as a side product. However, a common problem in chloride rare earth electrowinning is the low Coulombic efficiency (10-50%) obtained in lab-scale and pilot-scale efforts.5 The neodymium chloride electrolysis process notoriously encounters a two-step reduction producing an intermediate divalent (Nd2+) oxidation state which is stable in the chloride media.6-7 The intermediate neodymium species diffuses away from the cathode leading to Coulombic efficiency loss. Additionally, the kinetics of the chlorine evolution reaction (CER) in chloride molten salts are known to be relatively sluggish, causing significant anodic overpotentials which elevate the specific energy consumption during electrowinning. Furthermore, electrowinning from molten salts often produces spongy or dendritic deposits of metal requiring energy-intensive purification. In this talk, we will address all aforementioned technical hurdles and report on our efforts achieving high Coulombic efficiency (~85%), and compact deposits with superior as-electrowon neodymium metal purity (>99 wt.%). Furthermore, we will report the development of a new anode which catalyzes chlorine evolution, lowering the anodic overpotential considerably during electrolysis at high current densities of practical interest for electrowinning. Specific energy consumption is calculated for some example cases and found to be between 2.1 and 3.5 kWh/kg representing a significant improvement over the conventional oxyfluoride process. Figure 1

Mechanistic Understanding of the Role of Bis(4-nitrophenyl) Carbonate (BNC) As Additive on the Solvation Structure and Polysulfides Shuttling Effect Towards Capacity Improvement in Lithium-Sulfur Batteries

The lithium-sulfur (Li-S) batteries are considered as one of the most promising devices for next-generation energy storage applications, owing to its exceptional theoretical capacity and energy density. However, persistent challenges have hampered its performance, notably the sluggish polysulfides conversion kinetics and the polysulfides shuttling phenomenon. These issues lead to irreversible active material loss, rapid capacity decay, low coulombic efficiency, and a limited cycle life. This study demonstrates that bis(4-nitrophenyl) carbonate (BNC) can serve as an effective agent in anchoring dissolved polysulfides, thereby preventing their migration to the anode. Furthermore, this investigation indicates that BNC has the capability to modify the solvation structure of polysulfides in the electrolyte. The presence of 0.01M BNC induces a downfield shift in the 7Li NMR spectrum, signifying a strengthened solvation structure on Li-ion. This solvation modification results in altered kinetics, specifically a reduced Li2S2/Li2S conversion without sacrificing capacity, as confirmed by operando X-ray absorption spectroscopy (XAS). Operando Raman spectroscopy reveals the suppression of long-chain polysulfides (at 400 cm-1) and intermediate polysulfides (at 453 cm-1) with 0.01M BNC, mitigating sulfur shuttling to the anode. This observation is corroborated by X-ray fluorescence (XRF) mapping. Analysis of the corresponding X-ray absorption near-edge structure (XANES) demonstrates that both anodes and cathodes with 0.01M BNC exhibit lower levels of unconverted polysulfides over extended cycles. This improvement is attributed to the kinetic consequences resulting from solvation structure alteration. However, this investigation cautions against an indiscriminate increase in BNC concentration, as higher concentrations may lead to the over-conversion of soluble polysulfides. This nuanced understanding of the solvation structure's intrinsic mechanism, coupled with chemical reactions, provides valuable insights for practical design of Li-S batteries Figure 1

(Invited) A Facile Three-Dimensional Lightweight Current Collector Strategy for High Energy Density Lithium Metal Batteries

Despite the great achievement in the development of rechargeable lithium (Li) metal batteries (LMBs) with high energy densities, their practical application is still facing difficulties due to the intrinsic issues of Li metal anode (LMA) including high reactivity and dendritic Li formation which cause low Coulombic efficiency, constant loss of Li and electrolyte, and unstable solid electrolyte interphase (SEI) layer, etc. Additionally, from the structural point of view, LMA which consists of Li foil on the two-dimensional copper (Cu) current collector brings the formidable loss of the areal capacity that leads to less specific energy density since Cu is non-faradaic and one of the heavy metals. Further, the “hostless” feature of LMA induces more issues like volume expansion and limited utilization of Li. To address such issues, a metal-coated polymeric three-dimensional (3D) scaffold is designed here. In this study, Cu is selected as an electronic conductivity provider, and electrospun polyimide (PI) is chosen as a 3D scaffold because of its high thermal stability and good mechanical properties. Cu-coated PI (Cu@PI) was produced via a facile electroless process. Driven by the structural/material uniqueness, the developed 3D Cu@PI current collector enables a uniform/continuous Li-ion conduction pathway thus leading to dense Li deposition and enhancing the electrochemical performance of LMBs containing the electrochemically deposited Li on Cu@PI and the specific energy density due to the great reduction in substrate weight. We anticipate the suggested new strategy of 3D structured LMAs would lead to a facile route toward the high energy density LMBs beyond the conventional technologies.

Optimizing the Electrolyte Additive Content in Practical Li-Ion Cells with Si-Dominant Anodes

Due to their high capacity, Silicon (Si) anodes are very promising for the next generation of lithium-ion batteries. However, Si materials suffer from a high volume expansion, which cause cracking and accumulated growth of the solid electrolyte interphase (SEI), resulting in low coulombic efficiencies and lifetime of the Si anodes. Applying additives in the electrolyte is a facile and straightforward approach to improve the composition of the SEI and reduce cracking. For Si-containing anodes, fluoroethylene carbonate (FEC) and vinylene carbonate (VC) are considered the most effective electrolyte additives. The salt lithium difluorophosphate (LiDFP) is known to improve the interphases of cathode materials and graphite when applied as additive, but has been poorly investigated for Si anodes. In our study, we combine VC, FEC, and a variation of LiDFP concentrations to investigate the effect on Si-dominant anodes in detail. We conducted detailed electrochemical testing in half coin cells and Si/NCM pouch cells, including long-term cycling, rate capability tests, potential monitoring of the anode and electrochemical impedance spectroscopy. For the latter two, we applied a novel perforated reference electrode concept, which allows for broad and precise measurement in pouch cells, while avoiding a blocking effect of the lithium ions. Furthermore, post-mortem analysis was conducted to gain detailed insights into the SEI formation and microstructure influenced by the different additive concentrations.