Stable Solid Electrolyte Interphase Layer Research Articles

Robust Interfacial Chemistry Induced by B‐Doping Enables Rapid, Stable Sodium Storage

AbstractConstructing a stable solid electrolyte interphase (SEI) at the electrode–electrolyte interface is powerful for optimizing the battery performance. However, studies related to interface chemistry have particularly focused on engineering electrolytes and overlooked regulating electrode materials. Here, this study reports that the B‐doped Bi interconnected nanoparticles (B─Bi) are prepared by a facile and effective chemical reduction reaction. The B doping helps to catalyze the electrolyte decomposition and more NaF formation on the electrode surface, which facilitates a stable uniform SEI with enhanced mechanical stability. Such a robust SEI layer can inhibit the further decomposition of electrolytes and promote the interfacial Na+ transfer. The B─Bi offers a reversible capacity of 403.1 mAh g−1 at 1.0 A g−1 and a high rate capability of 203 mAh g−1 at 80 A g−1. Moreover, the B‐doping method also finds its viability to stabilize SEI in Sb material. This study demonstrates a new strategy for engineering the interface chemistry toward stable SEI and excellent performance.

The effect of Ti-based surface layer on AlSi thin film as a high-performance anode for the lithium-ion battery

Significant volume changes during cycling and the instability of the solid electrolyte interphase (SEI) are the main challenges that limit the practical application of silicon-based anodes. TiN and TiO2 were selected as surface layers and deposited on the HCl-etched AlSi (AlSi’) thin films by atomic layer deposition (ALD) to enhance the electrochemical performance of the anode. The surface layers with excellent mechanical strength can effectively suppress the volume expansion of the AlSi thin film and maintain excellent electrical contact between the film and the substrate during cycling. The effects of TiN and TiO2 surface layers on the composition and growth of the SEI layer on the AlSi’ film anode have been discussed in detail. The TiO2 surface layer was found to inhibit the continuous growth of the SEI layer and promote the formation of a mechanically robust and stable SEI layer. The AlSi’/TiO2(8 nm) anode shows a high initial discharge capacity of 2802 mA h g-1 with an initial coulomb efficiency (ICE) of 88% at 0.8 A g-1, and it maintains a capacity retention rate of 83% after 500 cycles. Moreover, the AlSi’/TiO2(8 nm) anode exhibits outstanding rate performance, as it sustains a capacity of 1710 mA h g-1 after 500 cycles at 5 A g-1, and maintains a capacity above 1032 mA h g-1 even at 30 A g-1.

Three dimensional titanium dioxide nanotube arrays induced nanoporous structures and stable solid electrolyte interphase layer for excellent sodium storage in ether-based electrolyte

The commercial feasibility of sodium ion batteries (SIBs) is currently limited by the lack of anode materials that simultaneously provide high-rate capability and long cycle stability. In this study, we report three-dimensional (3D) anatase TiO2 nanotube arrays (TiO2 NTAs) as an SIB anode for excellent sodium storage when paired with ether-based electrolyte. The TiO2 NTAs anode exhibits minimal capacity decay over 3000 cycles at 1C and 5000 cycles at 20C in ether-based electrolyte, demonstrating both excellent rate capability and long-term cycle stability. Structural analysis reveals novel discovery that the 3D TiO2 NTAs develop into unique nanoporous structures that sustain during repeated redox cycles in ether-based electrolyte. On the one hand, these nanoporous structures can provide more accessible areas for Na+ intercalation and de-intercalation, enabling fast Na+ intercalation. On the other hand, they also promote the formation of a thin and stable solid electrolyte interphase (SEI) in ether-based electrolyte that facilitates long-term cycle stability. Our investigation advances the performance of TiO2 as a promising SIBs anode material and also offers valuable insights into the impact of unique nanoporous structure to the excellent electrochemical performance.

Influence of LiNO3 on the Lithium Metal Deposition Behavior in Carbonate-Based Liquid Electrolytes and on the Electrochemical Performance in Zero-Excess Lithium Metal Batteries.

Continuous lithium (Li) depletion shadows the increase in energy density and safety properties promised by zero-excess lithium metal batteries (ZELMBs). Guiding the Li deposits toward more homogeneous and denser lithium morphology results in improved electrochemical performance. Herein, a lithium nitrate (LiNO3 ) enriched separator that improves the morphology of the Li deposits and facilitates the formation of an inorganic-rich solid-electrolyte interphase (SEI) resulting in an extended cycle life in Li||Li-cells as well as an increase of the Coulombic efficiency in Cu||Li-cells is reported. Using a LiNi0.6 Co0.2 Mn0.2 O2 positive electrode in NCM622||Cu-cells, a carbonate-based electrolyte, and a LiNO3 enriched separator, an extension of the cycle life by more than 50 cycles with a moderate capacity fading compared to the unmodified separator is obtained. The relative constant level of LiNO3 in the electrolyte, maintained by the LiNO3 enriched separator throughout the cycling process stems at the origin of the improved performance. Ion chromatography measurements carried out at different cycles support the proposed mechanism of a slow and constant release of LiNO3 from the separator. The results indicate that the strategy of using a LiNO3 enriched separator instead of LiNO3 as a sacrificial electrolyte additive can improve the performance of ZELMBs further by maintaining a compact and thus stable SEI layer on Li deposits.

Operando Investigation of Solid Electrolyte Interphase Formation, Dynamic Evolution, and Degradation During Lithium Plating/Stripping.

The solid electrolyte interphase (SEI) dictates the stability and cycling performance of highly reactive battery electrodes. Characterization of the thin, dynamic, and environmentally sensitive nature of the SEI presents a formidable challenge, which calls for the use of microscopic, time-resolved operando methods. Herein, we employ scanning electrochemical microscopy (SECM) to directly probe the heterogeneous surface electronic conductivity during SEI formation and degradation. Complementary operando electrochemical quartz crystal microbalance (EQCM) and ex situ X-ray photoelectron spectroscopy (XPS) provide comprehensive analysis of the dynamic size and compositional evolution of the complex interfacial microstructure. We have found that stable anode passivation occurs at potentials of 0.5 V vs Li/Li+, even in cases where anion decomposition and interphase formation occur above 1.0 V. We investigated the bidirectional relationship between the SEI and lithium plating-stripping, finding that plating-stripping ruptures the SEI. The current efficiency of this reaction is correlated to the anodic stability of the SEI, highlighting the interdependent relationship between the two. We anticipate this work will provide critical insights on the rational design of stable and effective SEI layers for safe, fast-charging, and long-lifetime lithium metal batteries.

Polymer Protective Layer Releasing Additives to Electrolyte of Lithium Metal Anode

As the need of batteries with high energy density raises, lithium metal anode has attracted considerable attention due to its high theoretical specific capacity and low reduction potential. However, there are several technical issues in practical use of lithium metal anode due to the growth of lithium dendrite and chemical instability with liquid electrolyte. It is essential to form the stable solid electrolyte interphase (SEI) layer on lithium metal anode to prevent lithium dendrite growth and minimize side reaction of liquid electrolyte. Designing the SEI with high Li+ ion conductivity and mechanical strength is imperative to stabilize lithium metal anode. Recently, various additives have been investigated to form a stable SEI layer on Li metal. However, during repetitive charge and discharge process, the additives in the electrolyte can be depleted by continuously forming SEI, which results in capacity fading of batteries. In this work, we developed the polymer protection layer containing excessive amount of additives that form the stable SEI layer. The additives can be stored in the polymeric layer, continuously released to the electrolyte during the repeated cycling. Electrochemical analyses such as linear sweep voltammetry and cyclic voltammetry were investigated, and the Li/Li symmetric cells showed the regulation of lithium deposition with small overpotential. The cycling performance of lithium metal batteries with protection layer was evaluated with high nickel NCM cathode.

Investigation of Gas Evolution by Operando GC/MS from SEI Forming Additives in Lithium-Ion-Batteries

Due to the chemical reactivity of the electrolyte, electrolyte decomposition often occurs at the electrode-electrolyte interface during cycling, which can lead to a loss in LIB performance. On the anode side, however, the formation of a stable Solid Electrolyte Interphase (SEI) is essential for the safe operation of Lithium-ion batteries (LIBs). The SEI layer, which is permeable for Li+ ions, protects the electroactive materials from direct contact with the electrolyte, thereby inhibiting further electrolyte decomposition. In the formation cycles of fresh cells, electrolyte degradation is primarily attributed to the SEI formation processes at the anode. Several literature reports have confirmed that the newly formed interphase consists of organic and inorganic decomposition products of the electrolyte.1 To increase battery performance, cycle life and safety, it is essential to form a stable SEI.2 A common strategy to stabilize the SEI is to use additives in the electrolyte composition. The additives should exhibit higher reduction potentials than other electrolyte components to enable preferential reduction and incorporation into the SEI. The most common SEI forming additives are fluoroethylene carbonate (FEC) and vinylene carbonate (VC). They both decompose during the formation cycle to form a polymeric layer at the electrode surface.The electrolyte decomposition reactions which lead to SEI formation are usually accompanied by gaseous side products. The evolving gas species form a complex gas mixture which can be separated by gas chromatography (GC) into their individual components and subsequently identified by mass spectrometry (MS). While operando GC/MS gives information on the volatile side products of the electrolyte decomposition reactions, X-ray photoelectron spectroscopy (XPS) can be used to identify the degradation products that form on the surface of the electrode and are incorporated into the SEI. The combination of the two techniques allows a more comprehensive picture of SEI formation processes to be drawn.In this work, operando GC/MS of Lithium-ion full cells with NMC 811 cathodes and graphite anodes was used to compare the gas species evolving during the formation reactions in an electrolyte with the composition of 1M LiPF6 in EC/DEC 1:1 with FEC and VC electrolyte additives in a ratio of 1w%, respectively. In a comparative study we present the decomposition pathways of the electrolytes with and without SEI forming additives by analysing the composition of the gas phase as a function of cell potential. We observe that the complex gas mixture consists of carbonate components originating from transesterification reactions and evaporation of the volatile electrolyte. In addition, inorganic components such as carbon monoxide and carbon dioxide are produced, which mainly stem from the degradation of cyclic carbonates. Furthermore, the gas phase consists of saturated and unsaturated hydrocarbons which can be ascribed to the linear carbonate components as well as ether and carbonyl components. We have also observed that it is possible to distinguish between volatile compounds which form during the charge and discharge processes, respectively. The increased gas evolution at the beginning of the formation cycle confirms that a substantial part of the passivation layer is formed during charge. Finally, operando GC/MS was also used to monitor the evolution of the decomposition products during battery operation at overcharge conditions.Acknowledgement:The author gratefully acknowledges the FFG (Austrian Research Promotion Agency) for funding this research within project No. 879613

Synthesis of Free-Standing Tin Phosphide/Phosphate Carbon Composite Nanofibers as Anodes for Lithium-Ion Batteries with Improved Low-Temperature Performance.

Free-standing tin phosphide/phosphate carbon composite nanofiber mats of unique nanostructure have been successfully synthesized by electrospinning and partially reducing the phosphate-containing precursors. An unusual effect of the Sn:P molar ratio in the precursor solution on the structure and physical-electrochemical properties of the material is observed. Physical characterizations, including X-Ray diffraction (XRD), Raman spectroscopy, X-Ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), confirm the formation of tin phosphide/phosphate nanoparticles of P-rich inner Snx P layer and Sn-rich outer layer uniformly distributed within carbon nanofiber matrix when the Sn:P=1:1. The prepared material is tested as an anode material for lithium-ion batteries and it retains 1141 mAh g-1 charge capacity after 300 cycles at a current density of 250mA g-1 with almost 100% Coulombic efficiency at room temperature. Furthermore, it demonstrates six times higher capacity (846 mAh g-1 ) at 0°C compared to a commercial graphite anode and stable cyclability at -20 °C and 50mA g-1 . Post-mortem ex situ XRD and SEM analyses confirm the structural stability of the designed material and the formation of a uniform stable solid electrolyte interphase layer even after 100 cycles at 50mA g- 1 .

Multi-functions of amino thiophenol additives for shielding lithium metal anode in advanced Li-S battery

Lithium-sulfur (Li-S) batteries have been considered as a promising candidate for the next generation of battery systems due to their high specific capacity and energy density. However, some barriers impede the application of Li-S batteries, such as the “shuttle effects” of lithium polysulfides (LPS), the poor electrical conductivity of sulfur, and lithium dendrite formation on lithium metal electrodes. Herein, we investigated a series of amino thiophenol as electrolyte additives: 2-amino thiophenol (2-ATP), 3-amino thiophenol (3-ATP), and 4-amino thiophenol (4-ATP); as well as p-phenylenediamine (PPD). These additives react with Li to form a stable and uniform solid electrolyte interphase (SEI) to protect the Li anode and minimize the interaction of Li with soluble LPS. Initial specific capacity at 0.1C and reversible specific capacity after 100 cycles are 1420 and 1043 mAh/g, 1429 and 982 mAh/g, 1148 and 871 mAh/g, 1317 and 791 mAh/g for 4-ATP, 3-ATP, 2-ATP, and PPD, respectively. Long-term cycling testing of Li-S cells was conducted at 0.2C and the cell with 4-ATP additives deliver an initial specific capacity of 1159 mAh/g and capacity retention of 77% after 300 cycles. The morphology and composition of the after-cycled SEI layers were examined by SEM and XPS. The findings suggest amino thiophenols (ATPs) form stable and smooth closed-packed SEI layers, that ameliorate lithium dendrite problems and LPS reactions with Li metal. 4-ATP is found to exhibit the best electrochemical performance followed by 3-ATP, 2-ATP, and PPD, which are in good agreement with the surface morphology. In addition, the amine group can assist the reaction between the thiol group and S8 on the cathode and modify the redox pathway of polysulfide.

Comparative study of different lithium salts as electrolyte additives of Li/SiOx–Si–C half-cells for lithium sulfur batteries

Silicon oxide and its derivatives (SiOx, 0 < x < 2) are drawing significant interest as electrode material for Li-ion and Li–S batteries owing to their unique properties of high specific capacity, low working potential, high abundance, and environmental friendliness. In-depth research is done on the effects of electrolyte additives on the electrochemical and interfacial characteristics of SiOx-based anodes for Li–S batteries. Two different electrolyte additives namely lithium bis (fluorosulfonyl imide) (LiFSI) and lithium bis (oxalatoborate) (LiBOB) were incorporated in the supporting electrolyte containing 1 M lithium bis (trifluoromethanesulfonyl imide) (LiTFSI) in tetraethylene glycol dimethyl ether (TEGDME): 1,3 dioxolane (DOL) in the ratio of 1:1 (v/v). The Li/SiOx–Si–C 2032-type half-cells were assembled, and their charge–discharge properties were explored at 0.1 C-rate. Surface morphology and electrochemical impedance investigations of the electrode materials have been performed after cycling. The interfacial properties of SiOx-based electrodes were examined by FTIR and XPS. Among the electrolytes studied LiFSI-added electrolytes offer superior charge–discharge properties, which was attributed to the formation of a stable solid electrolyte interphase (SEI) layer on the electrode surface. The surface chemistry studies revealed the formation of Li2CO3 and ROCO2Li peaks on the lithium metal surface. The formation of Li2CO3 and ROCO2Li compounds are identified on lithium surface by XPS data and complemented by NMR analysis.

Catalytic Chemistry Derived Artificial Solid Electrolyte Interphase for Stable Lithium Metal Anodes Working at 20 mA cm-2 and 20 mAh cm-2.

A stable solid electrolyte interphase (SEI) layer is crucial for lithium metal anode (LMA) to survive in long-term cycling. However, chaotic structures and chemical inhomogeneity of natural SEI make LMA suffering from exasperating dendrite growth and severe electrode pulverization, which hinder the practical application of LMAs. Here, we design a catalyst-derived artificial SEI layer with an ordered polyamide-lithium hydroxide (PA-LiOH) bi-phase structure to modulate ion transport and enable dendrite-free Li deposition. The PA-LiOH layer can substantially suppress the volume changes of LMA during Li plating/stripping cycles, as well as alleviate the parasitic reactions between LMA and electrolyte. The optimized LMAs demonstrate excellent stability in Li plating/stripping cycles for over 1000 hours at an ultra-high current density of 20 mA cm-2 in Li||Li symmetric cells. A high coulombic efficiency up to 99.2 % in Li half cells in additive-free electrolytes is achieved even after 500 cycles at a current density of 1 mA cm-2 with a capacity of 1 mAh cm-2 .

Catalytic Chemistry Derived Artificial Solid Electrolyte Interphase for Stable Lithium Metal Anodes Working at 20 mA cm−2 and 20 mAh cm−2

AbstractA stable solid electrolyte interphase (SEI) layer is crucial for lithium metal anode (LMA) to survive in long‐term cycling. However, chaotic structures and chemical inhomogeneity of natural SEI make LMA suffering from exasperating dendrite growth and severe electrode pulverization, which hinder the practical application of LMAs. Here, we design a catalyst‐derived artificial SEI layer with an ordered polyamide‐lithium hydroxide (PA‐LiOH) bi‐phase structure to modulate ion transport and enable dendrite‐free Li deposition. The PA‐LiOH layer can substantially suppress the volume changes of LMA during Li plating/stripping cycles, as well as alleviate the parasitic reactions between LMA and electrolyte. The optimized LMAs demonstrate excellent stability in Li plating/stripping cycles for over 1000 hours at an ultra‐high current density of 20 mA cm−2 in Li||Li symmetric cells. A high coulombic efficiency up to 99.2 % in Li half cells in additive‐free electrolytes is achieved even after 500 cycles at a current density of 1 mA cm−2 with a capacity of 1 mAh cm−2.

Extended Lifespan of Low-Cost Metal Silicon Anodes via a One-Step Wet Ball-Milling Process for Ultra-Thin Polymer Protecting Layer and Optimal Particle Size

Silicon is a promising active material for lithium-ion batteries (LIBs) with a high theoretical capacity (∼4000 mA h g–1). However, there is a critical issue that the fabrication of the Si anode needs complicated and high-cost processes to alleviate the poor cyclic performance, such as nanostructuring. Furthermore, the Si anode requires a high component ratio of conductive agents and binder in the electrode. Herein, we report the fabrication of submicron Si particles coated by a polyacrylonitrile (PAN) layer with a highly polar nitrile group via a facile one-step wet ball-milling process. During the milling of Si particles in PAN solutions, PAN adheres to the Si surface and forms a nanometer coating layer. The nitrile groups of PAN enhance the electrolyte wettability and increase the lithium-ion pathways on the Si surface. These result in a stable solid electrolyte interphase (SEI) layer and reduce the internal resistance of the electrodes. Si anodes with an optimal particle size and PAN layer (SM-Si@PAN) exhibit a superior performance even at ultra-fast current density (50 A g–1). In addition, a full-cell with an NCM712 cathode shows an excellent performance.

Surface engineering of core-shell MoS2@N-doped carbon spheres as stable and ultra-long lifetime anode for sodium-ion batteries

MoS2 is regarded as a hopeful anode candidate for sodium-ion batteries (SIBs) due to their various merits such as high specific capacity, abundant raw material reserves and low cost. However, their practical application is impeded by unsatisfied cycling ability due to the intense mechanical stress and unstable solid electrolyte interphase (SEI) during Na+ insertion/extraction process. Herein, spherical MoS2@polydopamine derived highly conductive N-doped carbon (NC) shell composites (MoS2@NC) are designed and synthesized to promote the cycling stability. The internal MoS2 core is optimized and restructured from the original micron-sized block to the ultra-fine nanosheets during initial 100–200 cycles, which not only improves the utilization of electrode materials but also shortens the ion transport distance. The outer flexible NC shell effectively maintains the original spherical structure of the overall electrode material and prevents the occurrence of large-scale agglomeration, which is conducive to form a stable SEI layer. Therefore, the core–shell MoS2@NC electrode presents a remarkable cyclic stability and a capable rate performance. Under a high rate of 20 A g−1, the high capacity of 428 mAh g−1 can be acquired after over ultra-long 10,000 cycles without obvious capacity loss. Moreover, the MoS2@NC‖Na3V2(PO4)3 full-cell assembled by employing commercial Na3V2(PO4)3 cathode can achieve a high capacity retention of 91.4% after 250 cycles at 0.4 A g−1. This work reveals the promising prospect of MoS2-based materials as anode of SIBs, and also has some inspirations on the structural design for conversion-type electrode materials.

Lithiophilic Mo2C Clusters‐Embedded Carbon Nanofibers for High Energy Density Lithium Metal Batteries

AbstractLithium metal anodes are widely regarded as the ideal candidate for the next generation of high‐energy‐density lithium batteries. Here, a 3D host made of lithiophilic Mo2C clusters‐embedded carbon nanofibers (Mo2C@CNF) is developed. The uniformly dispersed clusters and large specific surface areas of Mo2C@CNF provide numerous nucleation sites for lithium deposition. Mo2C clusters exhibit ultralow nucleation overpotential compared to MoO2, which is also supported by density functional theory calculations. Furthermore, the transition metal element serves as a catalyst for the formation of a stable and robust solid electrolyte interphase layer containing LiF on Mo2C@CNF, effectively mitigating the occurrence of dead lithium and enhancing the Coulombic efficiency during prolonged operation. As a result, the Mo2C@CNF composite delivers superior electrochemical performance (&gt;1600 h) at 1 mA cm−2 and lower nucleation overpotential (13 mV) for lithium plating. The Li/Mo2C@CNF anode coupled with the commercial LiFePO4 cathode exhibits excellent cycling stability (300 cycles at 1 C) and high rate capability at low N/P ratios.

Visualizing Water Reduction with Diazonium Grafting on a Glassy Carbon Electrode Surface in a Water-in-Salt Electrolyte.

Aqueous batteries are regaining interest, thanks to the extended working stability voltage window in a highly concentrated electrolyte, namely the water-in-salt electrolyte. A solid-electrolyte interphase (SEI) forms on the negative electrode to prevent water access to the electrode surface. However, we further reported that the formed SEI layer was not uniform on the surface of the glassy carbon electrode. The SEI after passivation will also show degradation during the remaining time of open-circuit voltage (OCV); hence, it calls for a more stable passivation layer to cover the electrode surface. Here, a surface modification was successfully achieved via artificial diazonium grafting using monomers, such as poly(ethylene glycol), α-methoxy, ω-allyloxy (PEG), and allyl glycidyl cyclocarbonate (AGC), on glassy carbon. Physical and electrochemical measurements indicated that the hydrophobic layer composed of PEG or AGC species was well grafted on the electrode surface. The grafted hydrophobic coatings could protect the electrode surface from the water molecules in the bulk electrolyte and then suppress the free water decomposition (from LSV) but still migrating lithium ions. Furthermore, multiple cycles of CV with one-hour resting OCV identified the good stability of the hydrophobic grafting layer, which is a highlight compared with our precious work. These findings relying on the diazonium grafting design may offer a new strategy to construct a stable artificial SEI layer that can well protect the electrode surface from the free water molecule.

Two-dimensional silica enhanced solid polymer electrolyte for lithium metal batteries

Solid polymer electrolytes (SPEs) are promising substitutes for current flammable liquid electrolytes to achieve high-safety and high-energy-density lithium metal batteries. Polyethylene oxide (PEO) based solid polymer electrolytes have attracted increasing attention because of their excellent flexibility, manufacturability, light weight, and low-cost processing, while they often suffer from low ionic conductivity at room temperature, low lithium transference number and unsatisfactory interfacial resistance, which largely restrain their practical application. Herein, two-dimensional holey silica nanosheets (2D-HSN) as the fillers, together with LiNO3 as the electrolyte additive, are introduced in a PEO/poly(vinylidene fiuoride-co-hexafluoropropylene) (PVDF-HFP) blended polymer matrix to obtain a SPE. The incorporation of HSN filler creates supplementary channels for lithium ion migration and lowers the crystallinity of the polymer, thereby facilitating the movement of lithium ions. The HSN-based SPE demonstrates higher ionic conductivity up to 3.7 × 10−4 S cm−1 at 30 °C, larger Li+ transference number close to 0.34, and more stable lithium plating/stripping than that without the fillers, and HSN can promote the formation of more stable solid electrolyte interphase (SEI) layer. The as-assembled LiFePO4||Li batteries deliver a high specific capacity of 159 mA h g−1 with the capacity retention of 95.5% after 200 cycles at 30 °C, as well as superior rate performance and cycling stability compared to that using the blank SPE.

Lithium plating-free 1 Ah-level high-voltage lithium-ion pouch battery via ambi-functional pentaerythritol disulfate

Elevating the charge cut-off voltage beyond traditional 4.2 V is a commonly accepted technology to increase the energy density of Li-ion batteries (LIBs) but the risk of Li-dendrites and fire hazard increases as well. The use of ambi-functional additive, which forms stable solid electrolyte interphase (SEI) simultaneously at both cathode and anode, is a key to enabling a dendrites-free and well-working high-voltage LIB. Herein, a novel ambi-functional additive, pentaerythritol disulfate (PEDS), at 1 wt% without any other additive is demonstrated. We show the feasibility and high impacts of PEDS in forming lithium sulfate-incorporated robust SEI layers at NCM523 cathode and graphite anode in 1 Ah-level pouch cell under 4.4 V, 25 °C and 0.1 C rate, which mitigates the high-voltage instability, metal-dissolution and cracks on NCM523 particles, and prevents Li-dendrites at graphite anode. Improved capacity retention of 83% after 300 cycles is thereby achieved, with respect to 69% with base electrolyte, offering a promising path toward the design of practical high-energy LIBs.

Optimized Solid Electrolyte Interphase and Solvation Structure of Potassium Ions in Carbonate Electrolytes for High-Performance Potassium Metal Batteries.

The introduction of electrolyte additives is one of the most potential strategies to improve the performance of potassium metal batteries (PMBs). However, designing an additive that can alter the K+ solvation shell and essentially inhibit K dendrite remains a challenge. Herein, the amyl-triphenyl-phosphonium bromide wasintroduced as an additive to build a stable solid electrolyte interphase layer. The amyl-TPP cations can form a cation shielding layer on the metal surface during the nucleation stage, preventing K+ from gathering at the tip to form Kdendrites. Besides, the cations can be preferentially reduced to form Kx Py with fast K+ transport kinetics. The Br- anions, as Lewis bases with strong electronegativity, can not only coordinate the Lewis acid pentafluoride to inhibit the formation of HF, but also change the K+ solvation structure to reduce solvent molecules in the first solvation structure. Therefore, the symmetrical battery exhibits a low deposition overpotential of 123mV at 0.1mAcm-2 over 4200h cycle life. The full battery, paried with a perylene-tetracarboxylic dianhydride (PTCDA) cathode, possesses a cycle life of 250 cycles at 2C and 81.9% capacity retention. This work offers a reasonable electrolyte design to obtain PMBs with long-term stablity and safety.

Integrated design of multifunctional all-in-one polymer electrolyte membranes with 3D crosslinking networks toward high-performance lithium metal batteries

Gel polymer electrolytes (GPEs) are highly worthwhile for constructing high-energy-density lithium metal batteries (LMBs) because of their good flexibility and manufacturability. But, it is still challenging to prepare GPEs with excellent electrochemical performance, good flame retardancy, and good compatibility with electrodes for safe and dendrite-free LMBs application. Herein, a well-designed GPE with three-dimensional (3D) crosslinking network containing –CN and -PO(OC2H5)2 functional groups (3D-ADCL) with synergistic effect is prepared via thermal-initiated in-situ polymerization. Concretely, the -PO(OC2H5)2 segment enhances the flame resistance of polymer electrolyte, and the –CN segment grants improved Li-ion conductivity. In addition, the 3D crosslinking networks in the whole LMBs are incredibly favorable for improving the physical stability of both polymer electrolyte membrane/electrode bulks and electrolyte/electrode interface. Furthermore, the 3D-ADCL-based polymer electrolyte (3D-ADCL-PE) demonstrates an enhanced Li-ion transference number (tLi+) of 0.58 because the –CN groups possess strong coordination with Li-ion and electrostatic repulsion with PF6− anion. It is also confirmed that the –CN group can enable the formation of stable Li3N-rich solid electrolyte interphase (SEI) and high-quality cathode electrolyte interphase (CEI) layers to inhibit Li dendrite growth and stabilize the LiFePO4 cathode, respectively. Consequently, the 3D-ADCL-PE based LiFePO4/Li cells exhibit a remarkable capacity of 106.4 mA h g−1 at 6 C-rate with a high capacity retention of 90.3% after long 1000 cycles.