Li Symmetric Cells Research Articles

A functional SnS2-engineered separator for durable and practical lithium metal battery

Lithium (Li) metal is one of the most promising anodes for next-generation high-energy-density batteries. However, the practical application of Li metal anodes (LMAs) is hindered by uncontrollable solid electrolyte interphase (SEI) formation and detrimental Li dendrites growth. Herein, a well-designed SnS2 nanoflakes coating is utilized to modify the commercial polypropylene (PP) separator (denoted as SnS2@PP), providing a solution to tackle above issues. Impressively, an artificial SEI consisting of Li2S, Li5Sn2, and Li7Sn2 species with high ionic conductivity and superior Li affinity is generated on the Li surface to regulate homogeneous Li plating/stripping. Consequently, the Li||Li symmetric cells exhibit a stable cycling behavior of over 2700 h at 1 mA cm−2 for 1 mAh cm−2. Remarkably, SnS2@PP enables over 600 cycles at 2 C with a capacity retention of ∼80% in a Li||LiFePO4 coin cell and more than 110 cycles at 0.3 C with a capacity retention of ∼97% in a Li||LiFePO4 pouch cell under high cathode loading (13 mg cm−2), ultrathin Li foil (50 µm), and lean electrolyte (2.8 g Ah−1 after sealed) conditions. This work extends the scalable technology into a platform to control Li deposition and SEI formation toward practical Li metal batteries (LMBs) with ultralong life spans.

Skeleton-flesh shape of multipath Li+ transport and compatible interfacial composite solid electrolyte for stable Li-metal batteries

All solid-state battery (ASSB) as the breakthrough of the advanced lithium-ions battery owing to its superior energy density and safety. Solid electrolytes are required to possess excellent electrochemical and safety. However, the low ionic conductivity and the poor interfacial compatibility, respectively, limits the progress of polymer and ceramic electrolyte, which accelerate the development of composite solid electrolyte (CSE). Therefore, we demonstrate a hierarchy structure that PEO(polyethylene)-LLZO@NFPAN-SiO2, which consists of SiO2 particles encapsulated nanofibers (in-situ hydrolyzed by TEOS) and flexible membrane of PEO-LLZO to synergistically elevate the performance of CSE. This CSE exhibits broad electrochemical window (6 V vs. Li) and strong ionic conductivity (3.3 × 10−4 S cm−1, 30 °C), and also shows robust strength (5.1 MPa). The assembled Li-symmetric cells exhibit superior cycling life of 1000 h, with an extremely modest over potential of 45 mV. The full cell exhibits excellent cycle stability, 102 mA h g−1 after 100 cycles at 0.5C, and a high initial Coulomb efficiency of 68 %. Skeleton-flesh structure is constructed by in-situ particle-embedded nanofiber and covered polymer, which strengthened mechanical capability, compatibility, inhibition of lithium dendrites, and introduced multi-Li+ transport pathways, ensuring high safety and superior electrochemical performance for the applications of ASSBs.

Construction of a dense and N-rich solid electrolyte interface for dendrite-free lithium metal batteries

Lithium (Li) metal anode has attracted extensive research interest, while lithium dendrites and the resulting irreversible effects have restricted its development. In this study, a thin and dense solid electrolyte interface is constructed by introducing 3-(1-pyridinio)-1-propane sulfonate (PPS), a pyridine functional groups additive in DME/DOL based electrolyte to inhibit the lithium dendrite growth. The preferential decomposition of PPS has resulted in a reduction of gas generation. Subsequently, this process leads to forming of an N-rich solid electrolyte interface, which has been found to cause a decrease in polarization potential and change the behavior of lithium deposition from dendrites to a more cellular Li metal surface. As a result, our proposed electrolyte provides multiple functionalities, including remarkable rate capability, cyclic stability, and coulombic efficiency. Significantly, Li | Li symmetrical cells exhibited a stable cycle over 1200 h at a high current density and capacity of 5 mA cm−2/15 mAh cm−2. We are optimistic that our proposed method can be employed in future research to identify electrolytes appropriate for use in lithium metal anodes.

Post-synthetic Covalent Organic Framework to Improve the Performance of Solid-State Li+ Electrolytes.

As a new class of crystalline materials, covalent organic frameworks (COFs) have long-range ordered channels and feasibility to functionalize. The well-arranged pores make it possible to contain and transport ions. Here, we designed a novel functionalized anionic COF-SS-Li by a post-synthetic method utilizing the Povarov reaction of BDTA-COF, anchoring -SO3- groups to the COF backbone and converting the imine linkage to a more stable quinoline unit. The grafted -SO3- groups and directional channels can promote the lithium-ion transport through a hopping mechanism. As a solid-state lithium-ion electrolyte, COF-SS-Li exhibits the conductivities of 9.63 × 10-5 S cm-1 at 20 °C and 1.28 × 10-4 S cm-1 at 40 °C and a wide electrochemical window of 4.85 V. The assembled Li|COF-SS-Li|Li symmetric cell can cycle stably for 600 h at 0.1 mA cm-2. Also, the Li|COF-SS-Li|LiFePO4 cell delivers an initial capacity of 117 mAh g-1 at 0.1 A g-1 and retains a capacity rate of 56.7% after 500 cycles. The research enriches the solid-state electrolytes for lithium-ion batteries.

Achieving multi-dimensional Li+ transport nanochannels via spatial-partitioning in crystalline ionic covalent organic frameworks for highly stable lithium metal anode

The fragile solid electrolyte interphase (SEI) and anisotropic dendrite growth during Li plating/stripping have posed as intractable handicaps to the practical implementation of lithium metal batteries (LMBs). The Li+ uniform distribution and unimpeded transfer play significant roles to enable protuberance-free Li textures. Herein, the highly-crystalline TFSI− ionic-covalent organic framework (I-COF) endowed with designated mixed-dimensional channels was constructed as an artificial SEI layer via anionic post-modification. Benefiting from the desirable spatial-partitioning effect triggered by nanochannels reconfiguration, the I-COF with expanded multi-dimensional Li+ transport channels and scaled-down pore volume could effectively disperse the local concentration gradient of Li+ flux and inhibit growth of Li dendrites. Besides, the coordinated TFSI− anions with a high tLi+ of 0.76 can selectively restrict the delivery and decomposition of homogeneous ions. To understand the interfacial charge transfer mechanisms, the lithophilic properties and the energy barriers for Li+ migration were also calculated. Correspondingly, the I-COF(TI−) modified Li|Li symmetric cell showed superb durability over 5500 h at 4 mA cm−2 with extraordinary overpotential. The Li|S full cell also displayed prolonged lifespan and excellent rate performance. The comprehension of the mixed-dimensional interfacial strategy via spatial-partitioning provides new insights into the fabrication of solid–solid interfaces, which can aid in the improved design and development of advanced lithium-metal batteries (LMBs).

Separator‐Free In Situ Dual‐Curing Solid Polymer Electrolytes with Enhanced Interfacial Contact for Achieving Ultrastable Lithium‐Metal Batteries

AbstractSolid polymer electrolytes (SPEs) are expected to possess high ionic conductivity and conformal interfacial contact with all cell components for all‐solid‐state lithium‐ion batteries. However, the commonly used in situ separator‐assisted approach reduces the ionic conductivity because of the use of inert and non‐ion‐conducting separators. Here, a facile separator‐free dual‐curing strategy combining UV‐curing outside the cell and subsequent thermal‐curing inside the cell is reported, in which the second thermal polymerization process provides improved interfacial properties without sacrificing ionic conductivity. The resulting DC‐SPEs possess high ionic conductivity (0.3 mS cm−1 at 25 °C), a wide electrochemical stability window (4.64 V vs Li/Li+), and improved interfacial properties. The in situ‐formed DC‐SPE can effectively suppress the growth of Li dendrites and achieve stable Li symmetric cell cycling performance at high current density (over 700 h at 0.2 mA cm−2 and 0.2 mAh cm−2). The all‐solid‐state lithium metal batteries (LMBs) with LiFePO4 demonstrate high coulombic efficiency (>99.93%) and ultrastable cycling stability (900 cycles) at 1C rate under 40 °C. The dual‐curing strategy provides a brand new in situ processing method to avoid the use of expensive and inert separators, which can be widely applied to the development of all‐solid‐state LMBs.

Boron nitride nanofibers enhanced composite PEO-based solid-state polymer electrolytes for lithium metal batteries

Polyethylene oxide (PEO)-based solid-state polymer electrolytes (SPEs) are limited by their poor cyclic stability and inferior ionic conductivity for applicating in high-safety, long-cycling and high-energy-density lithium metal batteries. Herein, porous boron nitride nanofibers (BNNFs) are filled into PEO-based SPE, which significantly suppresses Li dendrites growth and enhances the electrochemical performance of Li metal battery. BNNFs with high porosity have more active sites to connect with PEO, which can effectively reduce the crystallinity of the PEO matrix and enhance its ionic conductivity. Moreover, owing to the hardness and good stability of BNNFs, BNNFs/PEO/LiTFSI electrolyte exhibits a wider electrochemical window, better mechanical property and higher thermal stability compared with PEO/LiTFSI electrolyte. Consequently, the Li symmetric cell composed of 1% BNNFs/PEO/LiTFSI performs good cyclic stability (>1800 h), and the Li||1% BNNFs/PEO/LiTFSI||LFP full battery shows obviously improved performances in charge-discharge polarization voltage, discharge specific capacity, rate performance and cyclic stability than the Li||PEO/LiTFSI||LFP battery.

Surface modification of lithium metal anode with lithium silicate-lithium phosphate composite layer for enhanced cycling stability

Lithium metal anode with exceptionally high capacity is very attractive for next-generation anode material of lithium rechargeable batteries, but the safety problems and low Coulombic efficiency have retarded its commercialization. Despite the enormous efforts made to solve the problem of lithium metal anode, its practical use still appears to have a long way to go. In this study, to expedite the problem-solving, we suggest the use of a lithium silicate-lithium phosphate (SP) composite layer to suppress the dendritic growth of lithium and the formation of dead lithium. The composite layer is formed by simply dipping lithium metal in a mixed solution of tetraethyl orthosilicate and phosphoric acid. The synergistic effect of lithium silicate and lithium phosphate – high Li-ion conductivity and high Young's modulus of the inorganic layer – results in enhanced cycling stability of Li || Li symmetric cell and LiFePO4 || Li cell. The change in morphology of the lithium metal anode surface after cycling confirms that the SP layer mitigates the excessive dendritic growth of lithium and dead lithium formation, stabilizing the interface of lithium metal anode/electrolyte.

Regulation of Lithium‐Ion Flux by Nanotopology Lithiophilic Boron‐Oxygen Dipole in Solid Polymer Electrolytes for Lithium‐Metal Batteries

Inhomogeneous lithium‐ion (Li+) deposition is one of the most crucial problems, which severely deteriorates the performance of solid‐state lithium metal batteries (LMBs). Herein, we discovered that covalent organic framework (COF‐1) with periodically arranged boron‐oxygen dipole lithiophilic sites could directionally guide Li+ even deposition in asymmetric solid polymer electrolytes. This in situ prepared 3D cross‐linked network Poly(ACMO‐MBA) hybrid electrolyte simultaneously delivers outstanding ionic conductivity (1.02 × 10−3 S cm−1 at 30 °C) and excellent mechanical property (3.5 MPa). The defined nanosized channel in COF‐1 selectively conducts Li+ increasing Li+ transference number to 0.67. Besides, The COF‐1 layer and Poly(ACMO‐MBA) also participate in forming a boron‐rich and nitrogen‐rich solid electrolyte interface to further improve the interfacial stability. The Li‖Li symmetric cell exhibits remarkable cyclic stability over 1000 h. The Li‖NCM523 full cell also delivers an outstanding lifespan over 400 cycles. Moreover, the Li‖LiFePO4 full cell stably cycles with a capacity retention of 85% after 500 cycles. the Li‖LiFePO4 pouch full exhibits excellent safety performance under pierced and cut conditions. This work thereby further broadens and complements the application of COF materials in polymer electrolyte for dendrite‐free and high‐energy‐density solid‐state LMBs.

Synergized Tricomponent All-Inorganics Solid Electrolyte for Highly Stable Solid-State Li-Ion Batteries.

Garnet-type oxide Li6.4 La3 Zr1.4 Ta0.6 O12 (LLZTO) features superior ionic conductivity and good stability toward lithium (Li) metal, but requires high-temperature sintering (≈1200°C) that induces high fabrication cost, poor mechanical processability, and high interface resistance. Here, a novel high-performance tricomponent composite solid electrolyte (CSE) comprising LLZTO-4LiBH4 /xLi3 BN2 H8 is reported, which is prepared by ball milling the LLZTO-4LiBH4 mixture followed by hand milling with Li3 BN2 H8 . Green pellets fabricated by heating the cold-pressed CSE powders at 120°C offer ultrafast room-temperature ionic conductivity (≈1.73×10-3 Scm-1 at 30°C) and ultrahigh Li-ion transference number (≈0.9999), which enable the Li|Li symmetrical cells to cycle over 1600h at 30°C with only 30mV of overpotential. Moreover, the Li|CSE|TiS2 full cells deliver 201mAhg-1 of capacity with long cyclability. These outstanding performances are due to the low open porosity in the electrolyte pellets as well as the high intrinsic ionic conductivity and easy deformability of Li3 BN2 H8 .

A sandwich-structured ceramic-gel hybrid electrolyte to realize practical long cycle life Li-air batteries

Lithium-air batteries (LABs) have been regarded as the pinnacle of energy storage field owing to their ultrahigh energy density. However, most research focuses on lithium-oxygen batteries that work in pure oxygen instead of ambient air due to Li anode corrosion by the moisture in air atmosphere. Inspired by soft properties of gel polymer electrolyte (GPE) and dense structure characteristics of Li1.5Al0.5Ge1.5(PO4)3 ceramic, a sandwich-structured ceramic/gel hybrid electrolyte is successfully constructed via ultraviolet-irradiation method in this work, in which Li1.5Al0.5Ge1.5(PO4)3 ceramic is helpful in inhibiting Li anode corrosion while GPE is good at optimizing interface compatibility of electrolyte│electrode. The results show that the Li anode in LABs maintains metallic luster even after cycling in ambient air at 10–20% relative humidity (RH) for more than 100 h. Moreover, the interface resistance of Li symmetric cell is sharply reduced (from over 20 kΩ–1 kΩ), and it exhibits an ultralong lifespan (2000 h). Therefore, the lithium-air coin cell with this hybrid electrolyte has achieved more than 4-times the lifetime of that of conventional GPEs. A ‘3.5 cm × 3.5 cm’ pouch cell based on this hybrid electrolyte has also obtained an excellent cycle life of 750 h, further proving its application prospects in LABs.

Long‐life lithium batteries enabled by a pseudo‐oversaturated electrolyte

AbstractThe specific energy of Li metal batteries (LMBs) can be improved by using high‐voltage cathode materials; however, achieving long‐term stable cycling performance in the corresponding system is particularly challenging for the liquid electrolyte. Herein, a novel pseudo‐oversaturated electrolyte (POSE) is prepared by introducing 1,1,2,2‐tetrafluoroethyl‐2,2,3,3‐tetrafluoropropyl ether (TTE) to adjust the coordination structure between diglyme (G2) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Surprisingly, although TTE shows little solubility to LiTFSI, the molar ratio between LiTFSI and G2 in the POSE can be increased to 1:1, which is much higher than that of the saturation state, 1:2.8. Simulation and experimental results prove that TTE promotes closer contact of the G2 molecular with Li+ in the POSE. Moreover, it also participates in the formation of electrolyte/electrode interphases. The electrolyte shows outstanding compatibility with both the Li metal anode and typical high‐voltage cathodes. Li||Li symmetric cells show a long life of more than 2000 h at 1 mA cm−2, 1 mAh cm−2. In the meantime, Li||LiNi0.8Co0.1Mn0.1O2 (NCM811) cell with the POSE shows a high reversible capacity of 134.8 mAh g−1 after 900 cycles at 4.5 V, 1 C rate. The concept of POSE can provide new insight into the Li+ solvation structure and in the design of advanced electrolytes for LMBs.

Poly(vinylidene fluoride)-based dual-salt composite polymer electrolytes for superior room-temperature solid-state lithium batteries

Polymer electrolytes are one of the most promising candidates for advancing the development of solid-state lithium metal batteries (SLMBs) due to their easy preparation process, high flexibility, and lightweight. However, the low ionic conductivity at room temperature limits their practical applications. In this study, we propose a strategy of dual-salt modification of polyvinylidene fluoride (PVDF)-based polymer electrolytes to enhance lithium ion transport channels, specifically through the introduction of Lithium bis(trifluoromethanesulphonyl)imide (LiTFSI), lithium bis(oxalate)borate (LiBOB), and Li6.4La3Zr1.4Ta0.6O12 (LLZTO) into polyvinylidene fluoride-polyvinyl acetate (PVDF-PVAC) polymer chain to form a dual-salt composite polymer electrolyte (DS-CPE), which effectively control the dehydrofluorination of the PVDF skeleton and eliminate the PVDF gel discoloration phenomenon. The newly developed DS-CPE shows high ionic conductivity at room temperature (4.96 × 10−4 S cm−1), sufficient Li+ transference number (tLi+ = 0.57), excellent oxidation resistance (5.4 V vs. Li/Li+), and favorable interfacial compatibility. Moreover, Li|DS-CPE|Li symmetric cell stably cycles 1300 h at 0.1 mA cm−1, and the Li|DS-CPE|LFP cell delivers excellent rate performance, maintaining a capacity retention of 91.4 % over 450 cycles.

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.

Stack Pressure Dependence of Li Stripping/Plating Performance in All-Solid-State Li Metal Cells Containing Sulfide Glass Electrolytes.

Sulfide-based all-solid-state Li/S batteries have attracted considerable attention as next-generation batteries with high energy density. However, their practical applications are limited by short-circuiting due to Li dendrite growth. One of the possible reasons for this phenomenon is the contact failure caused by void formation at the Li/solid electrolyte interface during Li stripping. Herein, we studied the operating conditions, such as stack pressure, operating temperature, and electrode composition, that could potentially suppress the formation of voids. Furthermore, we investigated the effects of these operating conditions on the Li stripping/plating performance of all-solid-state Li symmetric cells containing glass sulfide electrolytes with a reduction tolerance. As a result, symmetric cells with Li-Mg alloy electrodes instead of Li metal electrodes exhibited high cycling stability at current densities above 2.0 mA cm-2, a temperature of 60 °C, and stack pressures of 3-10 MPa. In addition, an all-solid-state Li/S cell with a Li-Mg alloy negative electrode operated stably for 50 cycles at a current density of 2.0 mA cm-2, stack pressure of 5 MPa, and temperature of 60 °C, while its measured capacity was close to a theoretical value. The obtained results provide guidelines for the construction of all-solid-state Li/S batteries that can reversibly operate at high current densities.

Promotion of Li+ desolvation and efficient cathode interphase formation by 4-aminobenzoic multifunctional electrolyte additive

The application of Li metal anode in high energy density batteries is hindered by uncontrolled dendrites growth and rapid capacity decline. In this study, 4-aminobenzoic acid (4-ABA) is used as a multifunctional electrolyte additive to effectively stabilise Li anode and extend the cycling life of LiNi0.8Co0.15Al0.05O2 (NCA) cathode in carbonate electrolyte. It is found that 4-ABA facilitates the desolvation of Li+ and increases the Li+ transference number, leading to an increase in Li+ flux on the surface of the Li anode, and finally the growth of Li dendrites is inhibited. The cycling performance of Li||Li symmetric cell is extended from < 400 h to more than 600 h at 1 mA cm−2 with a capacity of 1 mAh cm−2. For the NCA cathode, 4-ABA is involved in the formation of a thin and uniform cathode electrolyte interphase (CEI) layer, which is conducive to inhibiting the corrosion of electrolyte on NCA cathode and reducing the dissolution of the transition metals Ni and Co. Thus, the electrochemical performances of the Li||NCA cell with the electrolyte containing 0.5% 4-ABA are significantly improved. In particular, the discharge capacity of the cells with the electrolyte containing 0.5% 4-ABA are still 164.9 and 150.7 mAh g−1compared to only 126.3 and 116.0 mAh/g for the cells with the baseline electrolyte after 200 cycles at 1C and 5C. This study provides a simple and effective strategy for improving the electrochemical performances of Li anodes and NCA cathodes by optimising the electrolyte.

PEO-based solid-state electrolyte modified by cationic covalent organic frameworks enabling high-performance all-solid-state Li metal and graphite anode batteries

Covalent organic frameworks (COFs) with regular and ordered channels have been proved that they could offer extra space to accommodate ions and fast conduction pathways for ion motion. However, the ion conductivities of their own are not high because of most of them have no enough active segmental motion of polymer chains for ion transport. Polyethylene oxide (PEO) is the most typical and efficient solid-state polymer material for Li+ migration by the segmental motion of molecular chains. Herein, we propose a simple and effective strategy of introducing a small quantity of cationic COF additive EB-COF-TFSI into the PEO of low glass transition temperature to obtain high-performance solid-state electrolyte (SSEs) and Li batteries. The cationic COF structure not only provides fast pathway for Li+ but also these cations on it accelerate Li salt dissociation and Li+ conduction. As a result, the cycling time of Li symmetrical cells increases to triplication at a same test condition; the corresponding all-solid-state LFP and NMC//Li metal cells are stimulated to release higher specific capacities, exhibit an enhanced cycling stability and better rate capability. It is surprising that all-solid-state LFP//graphite cells show excellent charging and discharging performance no matter on longtime cycling or rate performance test which are both much better than that of Li metal cells and provide a great strategy for building commercial all-solid-state Li battery based the current structure of it.

Prolonged Life Lithium Metal Batteries Enabled by Introducing Abundant Lithium Nitrate in Commercial Carbonate Electrolytes

AbstractCarbonate electrolytes have been extensively used as commercial electrolytes in lithium‐ion batteries (LIBs) because of its high oxidative stability. However, the organic‐inorganic solid electrolyte interphase (SEI) formed on the lithium (Li) metal surface is too fragile to endure huge volume fluctuation during Li plating/stripping cycles in carbonate electrolytes. Herein, a chemically stable inorganic‐rich SEI was constructed on Li metal anodes by dissolving 5.5 M LiNO3 in N,N‐dimethylformamide (DMF) into carbonate electrolytes as an additive. The Li+ solvation structure coordinated with NO3− and DMF molecules favors the formation of LixNy, LiNxOy, and LiF in the SEI film, which have been proved to increase the interfacial energy and improve the ionic diffusion as well as the mechanical strength of the SEI. Therefore, the designed carbonate electrolyte enhances the stable cycling of Li symmetric cells up to 700 h, with a high Coulombic efficiency (CE) of 99.0 % by Aurbach CE test. When paired with LiFePO4 cathode, the coin cells achieve an outstanding average CE of 99.5 % and 86.5 % retention of initial capacity after 300 cycles.

Highly Conductive Iodine and Fluorine Dual-Doped Argyrodite Solid Electrolyte for Lithium Metal Batteries

Sulfide-type argyrodite solid electrolytes (SEs) with halide doping have attracted serious interest. Although other halides such as Cl and Br have been found to enhance Li-ion transport in argyrodites, the direct synthesis of efficiently conductive Li6PS5I without postprocessing has rarely been investigated. In this work, we report the one-step synthesis of highly conductive Li6PS5I with an impressive ionic conductivity of 2.5 × 10–4 S cm–1 at room temperature through a solvent-based method. Moreover, by introducing F– to partially replace I–, hybrid-doped argyrodites Li6PS5FxI1–x (x = 0.25, 0.5, 0.75) have been synthesized. Li6PS5F0.25I0.75 achieves the highest conductivity of 3.5 × 10–4 S cm–1 due to the energetic preference for anion-disordering among F–/I– and S2–, which facilitate faster Li transport as supported by density functional theory (DFT) calculations. With higher F content in argyrodites, Li6PS5F0.75I0.25 displays the best electrochemical stability toward Li metal, as evidenced by long-term stable cycling in Li symmetric cells up to 1100 h. Solid-state Li metal batteries with an active cathode of Li4Ti5O12 (LTO) display an initial specific capacity of 140 mAh g–1 and remain at 105 mAh g–1 after 200 cycles, suggesting great battery cycling performance. This research has developed new compositions in the argyrodite SE family which could lead to advancements in the development of solid-state Li metal batteries.