Stable Solid Electrolyte Interface Research Articles

Tailoring the Size of Reduced Graphene Oxide Sheets to Fabricate Silicon Composite Anodes for Lithium-Ion Batteries.

The integration of a silicon (Si) anode into lithium-ion batteries (LIBs) holds great promise for energy storage, but challenges arise from unstable electrochemical reactions and volume changes during cycling. This study investigates the influence of reduced graphene oxide (rGO) size on the performance of rGO-protected Si composite (Si@rGO) anodes. Two sizes of graphene oxide (GO(L) and GO(S)) are used to synthesize Si@rGO composites with a core-shell structure by spray drying and thermal reduction. Electrochemical evaluations show the advantages of the Si@rGO(S) anode with improved cycle life and cycling efficiency over Si@rGO(L) and pure Si. The Si@rGO(S) anode facilitates the formation of a stable LiF-rich solid electrolyte interface (SEI) after cycling, ensuring enhanced capacity retention and swelling control. Rate capability tests also demonstrate the superior high-power performance of Si@rGO(S) with low and stable resistances in Si@rGO(S) over extended cycles. This study provides critical insights into the tailoring of graphene-protected Si composites, highlighting the critical role of rGO size in shaping structural and electrochemical properties. The Si material wrapped by graphene with an optimal lateral size of graphene emerges as a promising candidate for high-performance LIB anodes, thereby advancing electrochemical energy storage technologies.

Revealing the quasi-solid-state electrolyte role on the thermal runaway behavior of lithium metal battery

Replacing flammable non-aqueous organic liquid electrolyte (LE) with high thermal stability solid-state electrolyte (SSE) is considered to overcome the safety issues in lithium metal batteries (LMBs). However, both inorganic solid-state batteries (SSBs) with high mechanical strength and thermal stability, as well as flexible polymer-based SSBs, are not proven to be inherently safe yet. Currently, the reliability of SSBs still require continuous scientific verification. In this work, quasi-solid-state electrolyte (QSE) with practical application prospects was prepared through in-situ polymerization method. The effects of QSE and LE on the thermal runaway behavior of LMBs were systematically compared from four levels: electrolyte, electrolyte/electrode interface, coin cells, and pouch cells. The results showed that higher thermal stability of QSE was conducive for improving the reliability of quasi-solid-state batteries (QSBs) under different abused conditions. The stable and dense solid electrolyte interface (SEI) in QSB could not only inhibit the severe side-reactions of LMBs during cycling at elevated temperature, but also enhance the decomposition temperature with dead lithium. QSE's lower reaction activity towards Li reduced the exothermic reaction inside the battery had been proven to increase the self-exothermic onset temperature and thermal runaway trigger temperature of LMBs, which promoted the safety performance of LMBs. Thus, this study revealed the thermal runaway mechanism of QSE in LMBs, and provided a theoretical guideline for safe QSBs design.

Scalable Synthesis of SiOx-TiON Composite As an Ultrastable Anode for Li-Ion Half/Full Batteries.

Among various anode materials, SiOx is regarded as the next generation of promising anode due to its advantages of high theoretical capacity with 2680 mA h g-1, low lithium voltage platform, and rich natural resources. However, the pure SiOx-based materials have slow lithium storage kinetics attributed to their low electron/ion conductive properties and the large volume change during lithiation/delithiation, restricting their practical application. Optimizing the SiOx material structures and the fabricating methods to mitigate these fatal defects and adapt to the market demand for energy density is critical. Hence, SiOx material with TiO1-xNx phase modification has been prepared by simple, low-cost, and scalable ball milling and then combined with nitridation. Consequently, based on the TiO1-xNx modified layer, which boosts high ionic/electronic conductivity, chemical stability, and excellent mechanical properties, the SiOx@TON-10 electrode shows highly stable lithium-ion storage performance for lithium-ion half/full batteries due to a stable solid-electrolyte interface layer, fast Li+ transport channel, and alleviative volumetric expansion, further verifying its practical feasibility and universal applicability.

A Lithium‐Affinitive Covalent Organic Polymer Network Functionalized Separator for Dendrite‐Free and High‐Durability Lithium–Sulfur Batteries under Harsh Conditions

AbstractLithium–Sulfur (Li─S) batteries are renowned for their high theoretical specific capacity and cost‐effectiveness. Nevertheless, their performance could be impeded by obstacles including lithium dendrite growth and lithium polysulfide (LiPS) shuttle, particularly under harsh conditions. Herein, an economical strategy is reported for modifying polyolefin separators (PP) with covalent organic polymer networks (TPE) to alter Li solvent structure, enhance lithium‐ion transport, and suppress shuttle effects. Combining in situ/ex situ characterization and theoretical calculations, it is demonstrated that the lithiophilic groups (‐C═N‐) in the TPE@PP separator form strong interaction with lithium, facilitating the dissociation of Li─Solvent/LiPS‐solvent to release freer lithium ion and shape a stable solid electrolyte interface rich in LiF and Li3N. The polymer network serves as a “highway” that accelerates Li transport and promotes uniform nucleation behavior. Therefore, the Li|TPE@PP|CNT/S cell enables 60% capacity retention after 2000 cycles at 1.0 C and exhibits stable cycling performance of 100 cycles from ‐40 to 80 °C. Moreover, the pouch cell maintains a capacity of more than 600 mA h g−1 after 30 cycles at 0 °C. This study provides a promising avenue for the application of high‐performance batteries in harsh environment from the perspective of separator engineering.

Three-dimensional cross-linked network deep eutectic gel polymer electrolyte with the self-healing ability enable by hydrogen bonds and dynamic disulfide bonds

Solid polymer electrolytes (SPEs) are effective solutions for the development of high-performance and flexible lithium metal batteries (LMBs). However, the key problems of SPEs including low ionic conductivity and inability to repair damage have hindered their industrialization process. In this work, a three-dimensional (3D) cross-linked network gel polymer electrolyte (CNGPE) is designed. The addition of deep eutectic solvent (DES) improves the ionic conductivity of CNGPE. The hydrogen bonds and dynamic disulfide bonds in the 3D cross-linked network endow CNGPE rapid self-healing ability at ambient temperature. In addition, the addition of lithium difluoro(oxalato)borate (LiDFOB) and lithium nitrate (LiNO3) helps to form a stable solid electrolyte interface (SEI). Due to the ingenious design, the Li/CNGPE/Li symmetrical cell exhibits excellent interface stability and no short circuit occurs for more than 800 h. The assembled LiFePO4/CNGPE/Li cell exhibits a discharge specific capacity of 126 mAh g−1 after 960 cycles at 0.5C. This work has shown that the self-healing gel polymer electrolyte containing DES provides an effective and feasible method for the development of high-performance LMBs.

Reconstructing Solvation Structure by Steric Hindrance-Coordination Push-Pull of Dipolymer-H2O-Zn2+ toward Long-life Aqueous Zinc-Metal Batteries.

Aqueous zinc-metal batteries are prospective energy storge devices due to their intrinsically high safety and cost effectiveness. Yet, uneven deposition of zinc ions in electrochemical reduction and side reactions at the anode interface significantly hinder their development and application. Here, we propose a solvation-interface attenuation strategy enabled by a frustrated tertiary amine amphiphilic dipolymer electrolyte additive. The configuration of superhydrophilic segments with covalently bonded lipophilic spacers enables coupled steric hindrance/coordination, which establishes a balanced push-pull dynamic of dipolymer-H2O-Zn2+. Such interplay reconstructs the solvation structure of Zn2+ and allows the formation of a stable dipolymer-inorganic hybrid solid electrolyte interface (SEI) layer. This SEI layer effectively shields the zinc-metal anode from water and anions, significantly reducing side reactions. In addition, the dipolymer adsorbed at the zinc-metal anode interface regulates the interfacial electrochemical reduction kinetics and ensures uniform zinc deposition. As a result, the Zn-Zn symmetric cells with dipolymer-containing electrolyte exhibit remarkable cycling stability exceeding 5800 h (242 days). The Zn-NVO batteries and Zn-AC hybrid ion supercapacitors also deliver stable cycling for up to 1440 h (60 days) with high-capacity retention over 80%. This research demonstrates the potential to facilitate the development and commercialization of zinc-based energy storage devices.

SiO2-Decorated-Montmorillonite reinforced Poly(1,3-dioxolane) as a multifunctional solid electrolyte for High-Performance lithium batteries

Solid polymer electrolytes (SPEs) have garnered considerable attention owing to their remarkable flexibility, manufacturability, and cost-effectiveness. However, SPEs are hampered by critical limitations such as inadequate ionic conductivity at room temperature and issues related to lithium-ion migration, which curtail their practical applications. To tackle these challenges, the incorporation of inorganic additives into SPEs is considered as an effective strategy. Montmorillonite (MMT), a typical two-dimensional material, has emerged as an advanced filler for SPEs, displaying increased ionic conductivity, lithium-ion transference, and electrochemical stability. Herein, siliconized-modified montmorillonite (SiO2-MMT) nanosheets are synthesized and incorporated into poly(1,3-dioxolane) (PDOL)-based SPEs, resulting in a multifunctional composite solid electrolyte (CSE). The CSE shows an ionic conductivity as high as 5.58 × 10−4 S cm−1 at 30 °C, with a lithium-ion transference number close to 0.58. Symmetrical Li||Li cells utilizing the CSE exhibits stable performance for over 1200 h at a current density of 0.2 mA cm−2. Additionally, the CSE contributes to the stability of electrolytes, facilitates superior Li+ mobility and uniform deposition, thereby forming a stable solid electrolyte interface (SEI). Density functional theory (DFT) simulation confirms that SiO2-MMT, containing a large number of adsorption sites, facilitated fast reaction kinetics and effective anchoring of lithium polysulfides (LiPSs). As a result, the composite electrolyte is cycled in Lithium-sulfur (Li-S) batteries at 200 mA g−1 and 30 °C for 250 cycles, achieving a high coulombic efficiency (CE > 99.4 %) and a capacity decay rate of 0.15 %. Additionally, when paired with high-voltage Li(Ni0.8Co0.1Mn0.1)O2 (NCM811) cathodes and LiFePO4 (LFP) cathodes, both display excellent electrochemical performance. This research presents a highly promising approach for constructing multifunctional solid electrolytes for high-performance lithium batteries.

Water/DMSO-Based Hybrid Electrolyte and Urea Additive Engineering for Performance Regulation in Aqueous Sodium Batteries

Electrochemical energy storage devices are of interest, especially aqueous sodium ion batteries (ASIBs), due to their safety, low-cost, and environmental friendliness. However, ASIBs suffer from poor cyclic stability and a narrow electrochemical window, which hinders their large-scale application. Compared to the traditional dilute saline electrolytes, high concentration electrolytes show a wider potential window. In this study, we designed a novel NaClO4-H2O/DMSO-Urea hybrid electrolyte to suppress these problems, in which DMSO and Urea create a synergistic effect. The formation of hydrogen bonds between DMSO and H2O reduced water activity, thereby suppressing the hydrogen evolution reaction. The addition of DMSO resulted in the reduction from −1.2 to −1.6 V for the hydrogen evolution potential. Therefore, we were able to expand the electrochemical window on the basis of reducing the concentration of sodium salts. Moreover, the addition of Urea facilitated formation of a stable solid electrolyte interface on the electrode surface, which improved the cycling stability of NVP/C (Na3V2(PO3)4/C) symmetric cell which exhibited a specific capacity of 59.7 mAh g−1 with the retention capacity of 80.1% after 200 cycles at 1 C. This work points out a promising strategy for developing stable and wide voltage aqueous electrolyte.

Composition regulation of polyacrylonitrile-based polymer electrolytes enabling dual-interfacially stable solid-state lithium batteries

The polyacrylonitrile (PAN) is an attractive matrix of polymer electrolytes owing to its wide electrochemical window and strong coordination with Li salts. However, the PAN-based electrolytes undergo severe interfacial problems from both cathode and anode sides, including uneven ionic transfer induced by high rigidity of dry PAN-based polymer, as well as inferior stability against Li-metal anode. Herein, the composition regulation of PAN-based electrolytes is proposed by introducing succinonitrile (SN) plastic crystal and LiNO3 salt for the construction of interfacially stable solid-state lithium batteries. The plastic nature of SN enables the rapid ionic transfer in electrolytes, along with the establishment of conformally interfacial contacts. Meanwhile, a stable solid-electrolyte-interface (SEI) layer consisting of Li3N and LiNO2 is in-situ formed at Li/electrolyte interface, contributing to the inhibition of uncontrol reactions between PAN and Li-metal. Consequently, the resultant Li symmetric cell delivers an extended critical current density of 1.7 mA cm−2 and an outstanding cycling lifespan of 700 h at 0.1 mA cm−2. Moreover, the corresponding solid-state LiNi0.6Co0.2Mn0.2O2/Li full cell shows an initial discharge capacity of 161 mAh/g followed by an outstanding capacity retention of 88.7 % after 100 cycles at 0.1C. This work paves the way for application of PAN-based electrolytes in the field of solid-state batteries by facile composition regulation.

Configuration design toward sustainably-released polymer electrolytes for enhancing ionic transport and cycle stability of solid lithium batteries

Poly(vinylidene difluoride) (PVDF)-based solid polymer electrolytes (SPEs) hold great promise in the practical deployment of solid lithium batteries (SLBs), but suffer from low ionic conductivity, poor interfacial compatibility, and unstable anode interface, especially without liquid wetting. Herein, we utilize poly (propylene carbonate) (PPC), which degrades into propylene carbonate (PC) when being contacted with alkaline Li-metal to construct the PVDF-based composite SPEs. Blended and bi-layered PVDF/PPC configurations are designed, of which the sustain-release effect of PPC, the ionic transport, and the cycle stability are compared. The evenly swelling of PC on PVDF enables a high ionic conductivity (1.2 × 10−4 S cm−1) and a low interfacial resistance (42 Ω cm−2) of bi-layered SPEs at 30 °°C and contributes to the homogeneous distribution of high current density inside electrolytes. Besides, the produced PC can accelerate the dissociation and decomposition of Li-salts, leading to the generation of a stable and uniform solid electrolyte interface. Consequently, the Li/LiFePO4 and Li/LiNi0.6Co0.2Mn0.2O2 cells with bi-layered SPEs deliver a capacity of 163.1 and 151.4 mAh g−1 for 100 cycles at 0.2 C and 30 °C. This study provides a rational protocol for the design of PVDF SPEs and promotes the practical application of PVDF-based SLBs with desirable performances.

Selective construction of amorphous/crystalline heterostructure high entropy oxide for Li-ion batteries

High entropy oxides (HEO) are widely used as anode for lithium-ion batteries due to their exceptional chemical stability and mechanical strength. However, HEO encounters challenges such as low initial coulomb efficiency (ICE) and poor capacity. To address these issues, a simple mechanochemical method is employed to selectively amorphized and densely embed LiF within the HEO matrix. Taking advantage of the differing chemical properties of LiF and HEO, the transformation of LiF’s crystal structure not only overcomes its poor ionic conductivity but also successfully constructs an amorphous LiF/crystalline HEO heterostructure, which also improves the transport capacity of lithium ions. Additionally, the presence of abundant defects (e.g., oxygen vacancies, dislocations, and stacking faults) boosts the material's lithium transport and storage capacity. Furthermore, LiF facilitates the formation of a stable solid electrolyte interface (SEI) film on the HEO surface, preventing the corrosion of active materials and minimizing side reactions, effectively improving the ICE. The as-prepared LiF/HEO-48 demonstrates a superior initial capacity of 1632.9/1158.5 mAh g−1, along with an ICE of 70.9%. It maintains a high reversible capacity of 552.2 mAh g−1 after 1000 cycles at 0.5 A g−1, and even after 400 cycles at 2 A g−1, it retains 99.4% of its capacity. This study may open up new ways to selectively construct amorphous/heterostructures to improve the ICE and capacity of lithium-ion anodes.

NaSn2F5 nanocluster composed of nanoparticles with matched lattices induced by dislocations: Accelerated sodium-ion transport via in situ oxidation in solid-state sodium metal battery

Na metal batteries using inorganic solid-state electrolytes (SSEs) have attracted extensive attention due to their superior safety and high energy density. However, their development is plagued by the unclear structural/volumetric evolution of SSEs and the corresponding Na+ migration mechanisms. In this work, NaSn2F5 (NSF) clusters are composed of nanoparticles (NPs) with matched lattices induced by dislocations, which can mitigate the volume swelling/shrinkage of the NPs. NSF behaves like a single ion conductor with a high Na+ transference number (tNa+) of 0.79. Specially, the ionic conductivity (σ) of NSF is increased from 7.64 × 10-6 to 5.42 × 10-5 S cm−1 after partial irreversible oxidation of Sn2+ (0.118 Å) → Sn4+ (0.069 Å) with the shrunk ionic radius during the charge process, giving more spaces for Na+ migration. Furthermore, a poly(acrylonitrile)-NaSn2F5-NaPF6 composite polymer electrolyte (NSF CPE) was fabricated with a σ of 4.13 × 10-4 S cm−1 and a tNa+ of 0.60. The NSF CPE-based symmetric cell can operate over 3000 h due to the couplings between the different components in NSF CPE, which is beneficial for ion transfer and the construction of stable solid electrolyte interface. And the quasi-solid-state Na|NSF CPE|Na3V2(PO4)3 full cell displays excellent electrochemical performance.

BF4- Tailoring Solvation Chemistry of Ether-Based Electrolytes to Construct Stable Electrode/Electrolyte Interfaces for Sodium-Ion Full Batteries.

The ether-based electrolytes show excellent performance on anodes in sodium-ion batteries (SIBs), but they still show poor compatibility with the cathodes. Here, ether electrolytes with NaBF4 as the main salt or additive were applied in NFM//HC full cells and showed enhanced performance than the electrolyte with NaPF6. Then, BF4- was found to have a stronger interaction with Na+, which could reduce the solvation of Na+ with the solvent, thus inducing the formation of the cathode electrolyte interface (CEI) and solid electrolyte interface (SEI) layers rich in inorganic species. Moreover, the morphology, structure, composition, and solubility of CEI and SEI were explored, concluding that NaBF4 could induce more stable CEI and SEI layers rich in B-containing species and inorganics. This work proposes using NaBF4 as the main salt or additive to improve the performance of ether electrolytes in NFM//HC full cells, which provides a strategy to improve the compatibility of ether-based electrolytes and cathodes.

Constructing flame retardant microspheres for safe and stable poly (ethylene oxide) based All-Solid-State batteries at high voltage

The development of all-solid-state polymer electrolytes (ASSPE) based on poly (ethylene oxide) (PEO) is facing a series of challenges, such as poor ionic conductivity, low Li+ transference number, flammability, and the limited electrochemical windows of 4 V. Herein, we report our recent effort to meet these challenges by introducing flame retardant microspheres (TH) into PEO-based ASSPE to form stable solid cathode electrolyte interface (CEI) films and enhance safety performance. TH is constructed by reacting tetrabromobisphenol A (TBBA) with hexachlorocyclotriphosphazene (HCCP). With the presence of only 5 wt% TH, the LiNi0.8Mn0.1Co0.1O2 (NCM811)//Li cell achieves a high capacity retention rate of 77.61 % after 100 cycles at the cutoff voltage of 4.3 V and 0.5C, and achieves a capacity retention of 75.7 % at the voltage range of 3–4.5 V after 50 cycles at 0.5C. In addition, the PEO-based ASSPE with TH (TH-PEO/PE) shows excellent flame retardancy, which endows the NCM811//Li pouch cell with good resistance to fire and mechanical abuse. This simple process is compatible with the existing production lines in the battery industry, which exhibits enormous promise in manufacturing commercialized all-solid-state lithium metal batteries (ASSLMBs) with high energy density and safety capabilities.

Improving the conductivity of silicon anode and the stability of solid electrolyte interface by Si/Bi2S3 nanocomposite

In the field of lithium battery research, silicon has received extensive attention due to its high specific capacity and abundant reserves, but the factors such as large volume expansion and low electrical conductivity limit its further development. In this work, Si/Bi2S3 composites with a heterogeneous structure is obtained by using a hydrothermal reaction. The heterogeneous structure can promote the rapid transfer of charge, and the interfacial coupling effect of the heterogeneous structure has an adsorption effect on Li2S generated by the conversion reaction of Bi2S3, and Li2S is distributed on the surface of the Si/Bi2S3 composite to become an effective component of solid electrolyte interface (SEI), promoting the stability of the SEI film. The Bi and LixBi (x = 1, 3) produced during the conversion and alloying reactions of Bi2S3 can reduce the internal resistance of the Si/Bi2S3 composite. Thus, at a current density of 500 mA g−1, the initial charge-discharge specific capacity of Si/Bi2S3 is 2240.5/2767.8 mAh g−1. After 200 cycles, the discharge specific capacity can achieve 1443.3 mAh g−1, with a capacity retention of 52.1 %.

Designing Compatible Ceramic/Polymer Composite Solid-State Electrolyte for Stable Silicon Nanosheet Anodes.

The commercialization of silicon anode for lithium-ion batteries has been hindered by severe structure fracture and continuous interfacial reaction against liquid electrolytes, which can be mitigated by solid-state electrolytes. However, rigid ceramic electrolyte suffers from large electrolyte/electrode interfacial resistance, and polymer electrolyte undergoes poor ionic conductivity, both of which are worsened by volume expansion of silicon. Herein, by dispersing Li1.3 Al0.3 Ti1.7 (PO4 )3 (LATP) into poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP) and poly(ethylene oxide) (PEO) matrix, the PVDF-HFP/PEO/LATP (PHP-L) solid-state electrolyte with high ionic conductivity (1.40 × 10-3 Scm-1 ), high tensile strength and flexibility is designed, achieving brilliant compatibility with silicon nanosheets. The chemical interactions between PVDF-HFP and PEO, LATP increase amorphous degree of polymer, accelerating Li+ transfer. Good flexibility of the PHP-L contributes to adaptive structure variation of electrolyte with silicon expansion/shrinkage, ensuring swift interfacial ions transfer. Moreover, the solid membrane with high tensile limits electrode structural degradation and eliminates continuous interfacial growth to form stable 2D solid electrolyte interface (SEI) film, achieving superior cyclic performance to liquid electrolytes. The Si//PHP-L15//LiFePO4 solid-state full-cell exhibits stable lithium storage with 81% capacity retention after 100 cycles. This work demonstrates the effectiveness of composite solid electrolyte in addressing fundamental interfacial and performance challenges of silicon anodes.

Effective coating of polydopamine-mediated polyacrylamide on SiOx microparticles enables stable interface chemistry

Functional polymer coating is one of effective strategies to achieve high performance Si-based anodes for lithium-ion batteries (LIBs). Unfortunately, many functional polymers are incompatible with carbon layer which are important for electrical conductivity of Si-based composites, especially for carbon-coated SiOx microparticles (SiOC). Here, we present a polydopamine (PDA)-mediated strategy that enables a robust polyacrylamide (PAM) polymer to effectively couple with SiOC microparticles through the PDA bridge. As a robust barrier, the PDA-PAM coating effectively inhibits electrolyte corrosion while promoting the formation of a stable solid electrolyte interface layer. The resulting SiOC@PDA-PAM microparticles display enhanced cycling stability without sacrificing their rate performance. The pouch cell incorporated with 10 wt% SiOC@PDA-PAM in graphite anode has a superior capacity retention of 85.1% after 800 cycles and an improved storage performance due to the stable interfacial chemistry of SiOC@PDA-PAM. Considering the strong adhesion and easy functionalization of PDA for surface modification, this work spotlights the prospect of developing more functional polymer coating to extend the cycling life of Si-based anodes.

Synergistic regulation of Li deposition on F-doped hollow carbon spheres toward dendrite-free lithium metal anodes.

The notorious issues of lithium (Li) dendrite growth and volume change hinder the practical applications of Li metal anodes. LiF as a key component of the solid electrolyte interface (SEI) governs Li+ transport and deposition, yet the formation of LiF consumes the anions (PF6-/TFSI-) in the electrolyte, preventing the stable cycling of Li anodes. Herein, fluorine (F)-doped hollow carbon (FHC) was synthesized and used to construct a composite current collector with FHC as an F-rich buffer layer for modifying the Cu foil. The F content provided by FHC not only mitigates the anion (PF6-/TFSI-) consumption but also enhances the stability of SEI. The hollow structure of FHC with abundant internal space can accommodate deposited Li to relieve the volume change during cycling. Besides, the significantly improved specific surface area of the electrode effectively reduces the local current density to achieve a homogeneous Li deposition. Due to the above cooperation, the symmetrical cell of Cu@FHC-Li||Cu@FHC-Li maintains stable cycling for more than 1800 h with a hysteresis voltage of 19 mV. In addition, full cell coupling with LiFePO4 cathode delivers excellent long-term cycling and rate performance. This work provides an effective route for developing stable Li metal anodes.

Tuning the Interfacial Chemistry for Stable and High Energy Density Aqueous Sodium-Ion/Sulfur Batteries

The environmental-related issues arising from the fossil fuel assorted industrial revolution and worldwide development have prompted the quest for rechargeable batteries. In these predicaments, lithium-ion batteries (LIBs) took ownership to reshape our lives. However, the limited abundance, non-uniform geographical distribution and severe flammability of organic electrolytes, increase the uncertainty over their large-scale application. Recently, aqueous rechargeable sodium-ion batteries (ARSIBs) have gained considerable curiosity for large-scale energy storage due to their much-assured safety, environment friendliness, high-rate capacity, and low cost. However, the prospects of ARSIBs seeing commercial success remained remote due to the narrow water stability window (1.23 V), which translates into low cell voltage (< 1.6 V), low energy density (< 70 Wh Kg-1), and compromised cycling stability. The aforesaid dilemmas can be resolved by generating a protective layer known as a solid electrolyte interface (SEI) like in organic electrolytes. However, the SEI concept in aqueous electrolytes is relatively unexplored, as water dissociation leads to O2 and H2, and will enhance the parasitic reactions. The SEI formed in WiSE due to salt reduction is often inhomogeneous with a porous mosaic structure and is susceptible to mechanical cracking, and increase the overall cost. Hence, high-capacity electrodes and high voltage electrolytes capable of forming a stable SEI are urgently required to fulfill the dream of the large-scale application of ARSIBs.Recently low cost, highly abundant sulfur-based electrode material has attracted significant research attention due to its high theoretical capacity (1675 mA h g-1) and energy density. However, sluggish sulfur redox kinetics, acute polysulfide shutting, dendritic growth on the metal-based anode and low conductivity of sulfur and its discharge products proves to be a major roadblock for its commercialization. Utilizing abundant sulfur in an aqueous electrolyte along with abundant Na+ can resolve the kinetics and conductivity anxieties and leads to a new greener and safer Na-ion/S batteries chemistry. However lower order polysulfide dissolution in water is more feasible, leading to the rapid capacity decay and active sulfur loss due to H2S formation. Polysulfide dissolution is an interfacial mechanism occurring at the electrode-electrolyte interface and depends on both electrode and electrolyte merits. Therefore, an effective approach will be to couple efficient sulfur host with an electrolyte capable of generating a stable SEI on the electrode surface to prevent the direct attack of water on polysulfide.Herein we have explored urchin-like CoWO4 as a sulfur host coupled with Na-W-U-D electrolyte. The CoWO4 exhibits high conductivity, strong chemical interaction for sulfur and its discharge products, and urchin-like morphology having exposed edges facilitate the charge transport results in excellent polysulfide redox kinetics. The high voltage Na-W-U-D electrolyte was prepared by mixing NaClO4, urea, and N, N-dimethylformamide DMF in 1:2:1 ratio in water. Each component in the electrolyte plays an important role. Urea has very high water solubility and tends to form stable SEI, while DMF has a high dielectric constant, good solvation ability, and develop stabilize SEI. As a result, Na-W-U-D shows a stability window close to the 3.1 V regime due to reduced water activity resulting from complex ion solvent interaction and stable and uniform SEI formation, consisting of Na2CO3, polyurea, and reduction products of DMF. Despite the addition of DMF, non-flammable features of aqueous electrolytes remain well maintained. Herein for the first time, the SEI concept was successfully used for the aq. Na-ion/S battery. We discovered that the lower water activity of Na-W-U-D electrolyte hindered polysulfide dissolution and stable SEI prevent the direct attack of water on polysulfide and results in extended cycling stability. At the same time, the urchin-like CoWO4 host enhances the sluggish polysulfide redox kinetics and provides an abundant anchoring site for polysulfide adsorption. We investigate the effect of time, C-rate, depth of discharge, and dissolved oxygen on polysulfide dissolution and self-discharge of the negative electrode. The high electrode capacity combined with the safety and stable SEI of Na-W-U-D electrolyte translated into a record high initial capacity of 834 mA h g-1 w.r.t sulfur, with remarkable cycling stability up to 500 cycles @ 0.5 C. Post analysis by SEM and XPS, evident that the stable SEI consists of Na2CO3, polyurea, and reduced products of DMF (CO and NHMe2), which also prevent the negative electrode from self-discharge by mitigating the parasitic reaction of dissolved oxygen in the electrolyte. Moreover, a full cell assembled by integrating S@CoWO4 anode and Na0.44MnO2 cathode showed remarkable stability and a high energy density of 119 Wh kg-1, making it a promising candidate for a future energy storage system. Figure 1

High Rate Performance of Li Metal Anode in Na-Containing so2-Based Inorganic Electrolyte

Lithium metal anode is one of the best candidates for the next generation energy storage systems due to the lowest electrochemical potential (- 3.04 V vs. standard hydrogen electrode) and the highest theoretical capacity (3860 mAh g-1). However, lithium metal anode have critical problems including dendritic growth of Li deposits during cycling, poor stability of solid electrolyte interface (SEI) on lithium metal anode and severe chemical reaction between Li metal and the electrolyte. Recently, stable artificial interface layers on the Li metal anode have been proposed to solve these problems. In this work, surface modification of Li metal with a Na-containing SO2-based inorganic electrolyte was investigated as an effective way to prevent lithium dendritic growth during cell operation. The surface-modified lithium metal anode effectively prevented the dendritic deposits of Li deposits even at high current density (3 mA cm-2). More detailed reaction chemistry of Li metal with Na-containing inorganic electrolyte will be discussed in the presentation.