Ultrathin Electrolyte Research Articles

Advancements in Battery Materials: Bio-Based and Mineral Fillers for Next-Generation Solid Polymer Electrolytes.

The state-of-the-art all-solid-state batteries are expected to surpass conventional flammable Li-ion batteries, offering high energy density and safety in an ultrathin and lightweight solvent-free polymeric electrolyte (SPE). Nevertheless, there is an urgent need to boost the room-temperature ionic conductivity and interfacial charge transport of the SPEs to approach practical all-solid-state devices. Accordingly, loading filler grains into SPEs has been well-documented as a versatile strategy, promoting the overall electrochemical performance. In this era, using natural resources to extract filler additives has attracted tremendous attention to curb fossil fuel dependency. Also, there is a growing preference for materials that impose minimal environmental harm, are sustainable, and exhibit environmentally friendly characteristics. Therefore, mineral and biobased fillers, as natural-based additives, are strong candidates to replace traditional petroleum-based synthetic materials. Herein, we conduct a systematic investigation into the ion-transport mechanisms and fundamental properties of the filler-loaded SPEs. Additionally, recent advances in SPE architectures through embedding mineral and biobased fillers, as well as their hybrid compositions, are focused. Finally, the downsides and future directions are highlighted to facilitate further development and research toward revitalizing rechargeable battery-related technology. Overall, efficient methods for modifying SPEs through the use of natural resource organic and inorganic fillers are discussed, and technological advancements and related challenges are emphasized. Following the provided rational solutions to overcome major obstacles faced by SPEs, we hope to meet the demands of a greener future.

Molecular brush-based ultrathin polymer electrolytes with stable interfaces for high-voltage large-areal-capacity lithium metal batteries.

Polymer electrolytes hold great promise for long-cycling lithium metal batteries, but their unsatisfactory ionic conductivities and unstable interfacial contacts with electrodes greatly limit their practical applications under high cut-off voltage and large areal capacity conditions. Herein, a super-structured multifunctional molecular brush, BC-g-P(CCMA-co-TFEMA) (BC = bacterial cellulose; CCMA = (2-oxo-1,3-dioxolan-4-yl) methyl methacrylate; TFEMA = 2,2,2-trifluoroethyl methacrylate), has been designed to develop an ultrathin polymer electrolyte with superior ionic conductivity and stable electrolyte/electrode interfaces. The cyclic carbonate group in CCMA can weaken the binding of solvents and anions with lithium ions, thereby enhancing ionic transport. Meanwhile, the fluorine-containing group in TFEMA is beneficial for simultaneously constructing LiF-rich electrolyte/anode and electrolyte/cathode interfaces with enhanced stability. Moreover, the robust BC backbone provides the polymer electrolyte with outstanding mechanical properties. With such polymer electrolytes, a remarkable capacity retention of 83% has been demonstrated for Li/LiFePO4 cells at 1C after 1000 cycles. Remarkably, the solid-state full cell with a high-loading LiNi0.8Mn0.1Co0.1O2 cathode delivers a high discharge specific capacity of 204 mA h g-1 for more than 400 cycles at a high cut-off voltage of 4.5 V. This work provides a novel design principle for advanced electrolytes of high-voltage and large-areal-capacity lithium metal batteries.

Designing Cooperative Ion Transport Pathway in Ultra-Thin Solid-State Electrolytes toward Practical Lithium Metal Batteries.

Solid polymer electrolytes (SPEs) are promising for high-energy-density solid-state Li metal batteries due to their decent flexibility, safety, and interfacial stability. However, their development was seriously hindered by the interfacial instability and limited conductivity, leading to inferior electrochemical performance. Herein, we proposed to design ultra-thin solid-state electrolyte with long-range cooperative ion transport pathway to effectively increase the ionic conductivity and stability. The impregnation of PVDF-HFP inside pores of fluorinated covalent organic framework (CF3-COF) can disrupt its symmetry, rendering rapid ion transportation and inhibited anion imigration. The functional groups of CF3-COF can interact with PVDF-HFP to form fast Li+ transport channels, which enables the uniform and confined Li+ conduction within the electrolyte. The introduction of CF3-COF also enhances the mechanical strength and flexibility of SPEs, as well as ensures homogeneous Li deposition and inhibited dendrite growth. Hence, a remarkably high conductivity of 1.21×10-3 S cm-1 can be achieved. Finally, the ultra-thin SPEs with an extremely long cycle life exceed 9000 h can be obtained (the longest cycle life reported until now) while the NCM523/Li pouch cell demonstrates a high capacity of 760 mAh and 96% capacity retention after cycling, holding great promises to be utilized for practical solid-state Li metal batteries.

Ultra–thin ePTFE–enforced electrolyte and electrolyte–electrode(s) assembly for high–performance solid–state lithium batteries

Challenges including low stability, excessive thickness, a low ionic conductivity of current solid–state electrolytes, and large interfacial resistance in solid–state lithium batteries (SSLBs) hinder their application. Herein, an ultra–thin electrolyte (∼20 μm) was prepared by using expanded porous polytetrafluoroethylene (ePTFE) as a framework and filling the pores with a hybrid electrolyte; it exhibited a high stability, mechanical strength, flexibility, and ionic conductivity (0.27 mS cm−1). A new mechanism for fast lithium-ion conduction in the composite electrolyte was creatively proposed, whereby the interface orients and concentrates lithium ions to accelerate ion transport. An electrolyte–electrode(s) assembly (EEA) was developed by directly spraying active material(s) with highly dispersed electrolytes on the electrolyte. EEA–based copper– and aluminum–free SSLBs with or without a low-dose liquid electrolyte achieved an excellent performance at room temperature. Furthermore, EEA–series–connected pouch batteries demonstrated high voltage, safety, and performance, making our ultra–thin electrolyte and EEA promising for the development of SSLBs.

Design of Ultrathin Asymmetric Composite Electrolytes for Interfacial Stable Solid-State Lithium-Metal Batteries.

Ultrathin composite electrolytes hold great promise for high energy density solid-state lithium metal batteries (SSLMBs). However, finding an electrolyte that can simultaneously balance the interfacial stability of the lithium anode and high-voltage cathode is challenging. The present study utilized the both-side tape casting technique to fabricate ultrathin asymmetric composite electrolytes reinforced with polyimide (PI) fiber membrane, with a thickness of 26.8 μm. The implementation of this asymmetric structural design enables SSLMBs to attain favorable interfacial characteristics, such as exceptional resistance to lithium dendrite puncture and compatibility with high voltages. The suppression of lithium dendrite growth and the extension of the cycle life of lithium symmetric batteries by 4000 h are both experimental and theoretically demonstrated under the dual confinement of PI fiber membrane and Li7La3Zr2O12 ceramic fibers. Furthermore, the integration of multicomponent solid electrolyte interphase and cathode electrolyte interface interfacial layers into the lithium anode and high-voltage cathode enhance theirs cycling stability. With a gravimetric/volumetric energy density of 333.1 Wh kg-1/713.2 Wh L-1, the assembled LiNi0.8Co0.1Mn0.1O2 pouch cell demonstrates exceptional safety. The extensive application of this design concept to SSLMBs enables the resolution of electrode/electrolyte interface issues.

Interfacial fusion-enhanced 11 µm-thick gel polymer electrolyte for high-performance lithium metal batteries

In the pursuit of ultrathin polymer electrolyte (<20 μm) for lithium metal batteries, achieving a balance between mechanical strength and interfacial stability is crucial for the longevity of the electrolytes. Herein, 11 μm-thick gel polymer electrolyte is designed via an integrated electrode/electrolyte structure supported by lithium metal anode. Benefiting from an exemplary superiority of excellent mechanical property, high ionic conductivity, and robust interfacial adhesion, the in-situ formed polymer electrolyte reinforced by titanosiloxane networks (ISPTS) embodies multifunctional roles of physical barrier, ionic carrier, and artificial protective layer at the interface. The potent interfacial interactions foster a seamless fusion of the electrode/electrolyte interfaces and enable continuous ion transport. Moreover, the built-in ISPTS electrolyte participates in the formation of gradient solid-electrolyte interphase (SEI) layer, which enhances the SEI’s structural integrity against the strain induced by volume fluctuations of lithium anode. Consequently, the resultant 11 μm-thick ISPTS electrolyte enables lithium symmetric cells with cycling stability over 600 h and LiFePO4 cells with remarkable capacity retention of 96.6% after 800 cycles. This study provides a new avenue for designing ultrathin polymer electrolytes towards stable, safe, and high-energy–density lithium metal batteries.

In situ coordinated ultrathin MOF-polymer electrolyte membrane with vertically aligned transfer channels for solid lithium metal batteries

Metal organic framework (MOF)-polymer composite solid electrolyte membrane with novel microstructure is expected to show attractive prospect for solid state lithium metal batteries. But the reported MOF were usually regarded as an entirety in composite solid electrolyte resulting in tradeoff between ionic conductivity and lithium dendrite inhibition ability. Herein, MOF-polymer composite membrane with vertically aligned channels and ultrathin MOF layer is proposed to decrease lithium ion transportation resistance obtained by simple phase inversion and in situ coordinated growth methods. The vertically aligned highways can decrease tortuous pathways and intensify ion conduction. The embedded ultrathin MOF layer on membrane surface leads to homogeneous plating/stripping of lithium. This novel structured MOF-polymer composite solid electrolyte exhibits improved ionic conductivity of 0.55 mS cm−1 at 22 ° C and lithium ion transference number of 0.87. Furthermore, the Li/Li symmetrical cell shows stable lithium plating/stripping performance for 1100 h at 0.1 mA cm−2 and 0.1 mA h cm−2. LiFePO4/MOF-polymer/Li coin battery demonstrates good rate capability and cycling performance with capacity retention of 82 % after 100 cycles at 0.2C and the pouch cell can light up the “DLUT” blue light lamp under folding and cutting states. This work encourages a new avenue to develop composite solid electrolytes with ion transportation highways and uniform distribution plane for solid lithium metal batteries.

Fusion Bonding Technique for Solvent-Free Fabrication of All-Solid-State Battery with Ultrathin Sulfide Electrolyte.

For preparing next-generation sulfide all-solid-state batteries (ASSBs), the solvent-free manufacturing process has huge potential for the advantages of economic, thick electrode, and avoidance of organic solvents. However, the dominating solvent-free process is based on the fibrillation of polytetrafluoroethylene, suffering from poor mechanical property and electrochemical instability. Herein, a continuously solvent-free paradigm of fusion bonding technique is developed. A percolation network of thermoplastic polyamide (TPA) binder with low viscosity in viscous state is constructed with Li6PS5Cl (LPSC) by thermocompression (≤5MPa), facilitating the formation of ultrathin LPSC film (≤25µm). This composite sulfide film (CSF) exhibits excellent mechanical properties, ionic conductivity (2.1 mS cm-1), and unique stress-dissipation to promote interface stabilization. Thick LiNi0.83Co0.11Mn0.06O2 cathode can be prepared by this solvent-free method and tightly adhered to CSF by interfacial fusion of TPA for integrated battery. This integrated ASSB shows high-energy-density feasibility (>2.5 mAh cm-2 after 1400 cycles of 9200 h and run for more than 10 000 h), and energy density of 390 Wh kg-1 and 1020 Wh L-1. More specially, high-voltage bipolar cell (≥8.5V) and bulk-type pouch cell (326 Wh kg-1) are facilely assembled with good cycling performance. This work inspires commercialization of ASSBs by a solvent-free method and provides beneficial guiding for stable batteries.

5.1µm Ion-Regulated Rigid Quasi-Solid Electrolyte Constructed by Bridging Fast Li-Ion Transfer Channels for Lithium Metal Batteries.

An ultra-thin quasi-solid electrolyte (QSE) with dendrite-inhibiting properties is a requirement for achieving high energy density quasi-solid lithium metal batteries (LMBs). Here, a 5.1µm rigid QSE layer is directly designed on the cathode, in which Kevlar (poly(p-phenylene terephthalate)) nanofibers (KANFs) with negatively charged groups bridging metal-organic framework (MOF) particles are served as a rigid skeleton, and non-flammable deep eutectic solvent is selected to be encapsulated into the MOF channels, combined with in situ polymerization to complete safe electrolyte system with high rigidness and stability. The QSE withconstructed topological network demonstrates high rigidity (5.4GPa), high ionic conductivity (0.73 mS cm-1 at room temperature), good ion-regulated properties, and improved structural stability, contributing to homogenized Li-ion flux, excellent dendrite suppression, and prolonged cyclic performance for LMB. Additionally, ion regulation influences the Li deposition behavior, exhibiting a uniform morphology on the Li-metal surface after cycling. According to density-functional theory, KANFs bridging MOFs as hosts play a vital function in the free-state and fast diffusion dynamics of Li-ions. This work provides an effective strategy for constructing ultrathin robust electrolytes with a novel ionic conduction mode.

One-step preparation of large-size 1.5-μm-thick robust YSZ electrolyte for high CH4 conversion SOFCs at 600 °C

Ultrathin electrolytes can lower the operating temperature of yttria-stabilized zirconia (YSZ)-based solid oxide fuel cells (SOFCs) to below 600 °C, accelerating their commercialization. However, current technologies for fabricating robust electrolytes with large areas and a thickness of a few microns for SOFCs suffer from substantial practical limitations, including high manufacturing costs, intricate technical demands, and multistep fabrication processes. This study introduces a low-cost, high-yield, and facile one-step phase inversion technology to fabricate large-area and shape-variable ultrathin YSZ electrolyte-based SOFCs (disc diameter >12 cm and area of 10 cm × 10 cm). An integrated form of SOFCs with dendritic YSZ microchannels supporting a 1.5-μm-thick dense YSZ thin film was fabricated. The ultrathin electrolyte layer lowered ohmic and polarization losses, enhancing SOFC electrochemical performance. The integrated anode/electrolyte structure overcame the interfacial thermal mismatch, resulting in more than 210 h of long-term stability even with cells operating in rapidly changing environments. The single cell also exhibited a high CH4 conversion efficiency (55%), which was attributed to the fast gas diffusion and excellent catalytic activity within the integrated anode. In addition, our 4 cm × 4 cm flat SOFCs exhibited a high power output (5.1 W) at 600 °C, paving the way for the mass production of ultrathin and robust YSZ electrolytes.

Lignin Derived Ultrathin All-Solid Polymer Electrolytes with 3D Single-Ion Nanofiber Ionic Bridge Framework for High Performance Lithium Batteries.

The lignin derived ultrathin all-solid composite polymer electrolyte (CPE) with a thickness of only 13.2µm, which possess 3D nanofiber ionic bridge networks composed of single-ion lignin-based lithium salt (L-Li) and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) as the framework, and poly(ethylene oxide)/lithium bis(trifluoromethanesulfonyl)imide (PEO/LiTFSI) as the filler, is obtained through electrospinning/spraying and hot-pressing. t. The Li-symmetric cell assembled with the CPE can stably cycle more than 6000h under 0.5mA cm-2 with little Li dendrites growth. Moreover, the assembled Li||CPE||LiFePO4 cells can stably cycle over 700 cycles at 0.2 C with a super high initial discharge capacity of 158.5 mAh g-1 at room temperature, and a favorable capacity of 123 mAh g-1 at -20°C for 250 cycles. The excellent electrochemical performance is mainly attributed to the reason that the nanofiber ionic bridge network can afford uniformly dispersed single-ion L-Li through electrospinning, which synergizes with the LiTFSI well dispersed in PEO to form abundant and efficient 3D Li+ transfer channels. The ultrathin CPE induces uniform deposition of Li+ at the interface, and effectively inhibit the lithium dendrites. This work provides a promising strategy to achieve ultrathin biobased electrolytes for solid-state lithium ion batteries.

Hybrid ion/electron interfacial regulation stabilizes the cobalt/oxygen redox of ultrahigh-voltage lithium cobalt oxide for fast-charging cyclability

High-voltage and fast-charging LiCoO2 (LCO) is key to high-energy/power-density Li-ion batteries. However, unstable surface structure and unfavorable electronic/ionic conductivity severely hinder its high-voltage fast-charging cyclability. Here, we construct a Li/Na-B-Mg-Si-O-F-rich mixed ion/electron interface network on the 4.65 V LCO electrode to enhance its rate capability and long-term cycling stability. Specifically, the resulting artificial hybrid conductive network enhances the reversible conversion of Co3+/4+/O2−/n− redox by the interfacial ion–electron cooperation and suppresses interface side reactions, inducing an ultrathin yet compact cathode electrolyte interphase. Simultaneously, the derived near-surface Na+/Mg2+/Si4+-pillared local intercalation structure greatly promotes the Li+ diffusion around the 4.55 V phase transition and stabilizes the cathode interface. Finally, excellent 3 C (1 C = 274 mA g−1) fast charging performance is demonstrated with 73.8% capacity retention over 1000 cycles. Our findings shed new insights to the fundamental mechanism of interfacial ion/electron synergy in stabilizing and enhancing fast-charging cathode materials.

In situ construction of an ultra-thin and flexible polymer electrolyte for stable all-solid-state lithium-metal batteries

By integrating polyethylene fiber and a rationally designed, in situ formed polymer network, an ultra-thin, flexible and high mechanical robustness solid polymer electrolyte with a thickness of ≈5 μm is constructed.

Construction of an ultrathin multi-functional polymer electrolyte for safe and stable all-solid-state batteries.

The ever-increasing demand for safe and high-energy-density batteries urges the exploration of ultrathin, lightweight solid electrolytes with high ionic conductivity. Solid polymer electrolytes (SPEs) with high flexibility, reduced interfacial resistance and excellent processability have been attracting significant attentions. However, reducing the thickness of SPEs to be comparable with that of commercial separators increases the risk of short-circuiting. Herein, an ultrathin (≈7 μm), flexible and mechanical robust SPE was constructed from a rationally designed multi-functional polymer network, i.e., poly[2,2,2-trifluoroethyl methacrylate-r-(2-ethylhexyl acrylate)-r-methyl methacrylate-r-1,4-bis(acryloyloxy)butane] (PTEM) and porous polyethylene (PE). The resultant PTEM@PE electrolyte possesses a high tensile strength of 128.0 MPa with extensibility up to 34.8%, which could effectively prevent short-circuiting and minimize the interfacial resistance of cells. The obtained all-solid-state Li|PTEM@PE|LiFePO4 cell exhibited stable cycling performance over 1500 cycles at 0.5 C with a capacity retention of 74.4%. With high-voltage NCM811 as the cathode, the cell fabricated with PTEM@PE showed a remarkable capacity retention of 84.2% over 500 cycles. Even with the high-mass loading (≈3 mA h cm-2) NCM811 cathode, the cell could be operated at ambient temperature, demonstrating superior ion-migration kinetics. The current design provides a promising strategy to develop ultrathin and multifunctional solid electrolytes for safe, long-cycling and high-energy-density all-solid-state batteries.

Electrolyte-supported solid oxide fuel cells with ultra-thin honeycomb structure prepared by digital light processing 3D printing technology

A significant challenge in electrolyte-supported solid oxide fuel cells (SOFCs) pertains to the substantial thickness of the electrolyte, resulting in elevated operational temperatures that hinder commercial viability. In this research, we utilized digital light processing (DLP) 3D printing technology to fabricate ultra-thin honeycomb electrolyte-supported SOFCs and subsequently evaluated their performance. Through the use of ultraviolet absorbers, we achieved a shallow curing depth (60.3 μm), which facilitated the creation of ultra-thin electrolyte samples. We investigated the mechanical properties of electrolytes with various honeycomb structures, finding that the square honeycomb structure exhibited the highest mechanical integrity, with an average failure load of 1.01 N. Finally, we assessed the electrochemical performance, observing a substantial power density of 215.4 mW/cm2, representing a twofold increase compared to the 114 mW/cm2 achieved by the same method in a flat primary cell.

An ultra-thin composite electrolyte with vertical aligned Li ion transport pathways for all-solid-state lithium metal battery

All-solid-state lithium metal batteries employing composite electrolytes can fundamentally settle the safety issues of commercial liquid electrolytes. However, the thick thickness and low ionic conductivity as well as unregulated ion transport of current composite electrolytes pose great obstacles in further promoting their applicability and compatibility with Li metal anode. Herein, an ultra-thin composite electrolyte with vertical aligned Li ion transport pathways is rationally designed via filling polyethylene glycol-perfluoropolyether polymer electrolyte into the nanochannels of an alumina template via vacuum infusion and in-situ polymerization. The strong Lewis acid-base effect that existed between ions and composite electrolytes can construct numerous fast channels for Li+ transport. A restrained vertical direction of ion immigration can facilitate the uniform deposition of Li+ on metallic Li anode. The shortened Li ion conductive distance and superior electrolyte/electrode interfaces contribute to the improved electrochemical performance of the assembled solid-state batteries. An ionic conductivity of 1.21 × 10−4 S cm−1 and a transference number of 0.37 at room temperature are achieved for the designed composite electrolytes, which is superior to those of the conventional composite electrolytes reinforced with Al2O3 or garnet nanoparticles. The corresponding Li symmetrical cell can stably work for over 1200 h without short-circuit and the LiFePO4 || Li full cell exhibits a high initial discharge capacity of 164.8 mAh g−1 with capacity retention of 93.7 % after 100 cycles with a coulombic efficiency close to 100 %. This work offers an effective tactic to develop ultra-thin composite electrolytes for high-performance all-solid-state lithium metal batteries.

A Novel Ultrathin Multiple‐Kinetics‐Enhanced Polymer Electrolyte Editing Enabled Wide‐Temperature Fast‐Charging Solid‐State Zinc Metal Batteries

AbstractThe sluggish ion transport kinetics and poor interface compatibility are the major challenges for developing high‐performance solid‐state zinc metal batteries. Here, using the densified polyacrylonitrile/silicon dioxide (PAN‐SiO2) nanofiber membrane as a unique multifunctional mediator, a novel mediator‐bridged type of ultrathin (28.6 µm) polymer electrolyte that is rationally designed. The PAN/SiO2 /polyethylene oxide/Zn(OTf)2(PSPZ) polymer electrolyte is demonstrated to significantly enhance multiple kinetics. In addition to superior mechanical properties, the efficient thermal conductive effect endows it with good high‐temperature structural stability. Interestingly, a unique PAN skeleton‐locking‐anion‐enabled fast ion transport mechanism is uncovered to achieve a high Zn2+ migration number (0.71). Moreover, an efficient dendrite‐free Zn deposition guided by a flat dense SEI is demonstrated. In this case, highly reversible Zn metal anodes can be realized in the temperature range extending to −25–80 °C, as well as an impressive 4800 h‐cycle lifespan at the condition of 0.1 mA cm−2. Beyond that, wide‐temperature, high‐rate, durable PSPZ‐based solid‐state Zn/VO2 batteries are also successfully verified. This brand‐new concept of multiple‐kinetics‐enhanced polymer electrolyte design can provide a new perspective for developing all‐climate fast‐charging solid‐state batteries, including but not limited to zinc metal batteries.

LATP-coated LiNi0.8Co0.1Mn0.1O2 cathode with compatible interface with ultrathin PVDF-reinforced PEO-LLZTO electrolyte for stable solid-state lithium batteries

LiNi0.8Co0.1Mn0.1O2 (NCM811) is considered as a promising cathode for high-energy-density solid-sate Li metal battery for its high theoretical capacity. However, the high oxidizability and structural instability during charge limit its practical applications. In this work, 1% (in mass) of nanosized Li1.3Al0.3Ti1.7(PO4)3 (LATP) was coated on NCM811 to enhance its electrochemical stability with a ceramic/polymer composite electrolyte. A robust, ultrathin (11 μm) composite electrolyte film was prepared by combining poly(vinylidene fluoride) (PVDF) with polyethylene oxide (PEO)-Li6.5La3Zr1.5Ta0.5O12 (LLZTO). An in-situ polymerization process was used to enhance the interface between the PVDF/PEO-LLZTO (PPL) composite electrolyte and the LATP-coated NCM811 (LATP-NCM811). Coin-type Li|LATP-NCM811 cell with the PPL electrolyte exhibits stable cycling with an 81% capacity retention after 100 cycles at 0.5 C. Pouch-type cell was also fabricated, which can be stably cycled for 70 cycles at 0.5 C/1.0 C (80% retention), and withstand abuse tests of bending, cutting and nail penetration. This work provides an applicable method to fabricate solid-state Li metal batteries with high performance.

Fluorinated boron nitride nanosheet enhanced ultrathin and conductive polymer electrolyte for high‐rate solid‐state lithium metal batteries

AbstractPolyethylene oxide (PEO)‐based polymer solid electrolytes (PSE) have been pursued for the next‐generation extremely safe and high‐energy‐density lithium metal batteries due to their exceptional flexibility, manufacturability, and lightweight nature. However, the practical application of PEO‐PSE has been hindered by low ionic conductivity, limited lithium‐ion transfer number (tLi+), and inferior stability with lithium metal. Herein, an ultrathin composite solid‐state electrolyte (CSSE) film with a thickness of 20 μm, incorporating uniformly dispersed two‐dimensional fluorinated boron nitride (F‐BN) nanosheet fillers (F‐BN CSSE) is fabricated via a solution‐casting process. The integration of F‐BN effectively reduces the crystallinity of the PEO polymer matrix, creating additional channels that facilitate lithium‐ion transport. Moreover, the presence of F‐BN promotes an inorganic phase‐dominated electrolyte interface film dominated by LiF, Li2O, and Li3N on the lithium anode surface, greatly enhancing the stability of the electrode‐electrolyte interface. Consequently, the F‐BN CSSE exhibits a high ionic conductivity of 0.11 mS cm−1 at 30°C, high tLi+ of 0.56, and large electrochemical window of 4.78 V, and demonstrates stable lithium plating/striping behavior with a voltage of 20 mV for 640 h, effectively mitigating the formation of lithium dendrites. When coupled with LiFePO4, the as‐assembled LiFePO4|F‐BN CSSE|Li solid‐state battery achieves a high capacity of 142 mAh g−1 with an impressive retention rate of 82.4% after 500 cycles at 5 C. Furthermore, even at an ultrahigh rate of 50 C, a capacity of 37 mAh g−1 is achieved. This study provides a novel and reliable strategy for the design of advanced solid‐state electrolytes for high‐rate and long‐life lithium metal batteries.

Tunable Conformal Electrodeposition of Ultra-Thin Polymeric Films for Electrolyte Interphases

Functional coatings and interphases influence the stability and performance parameters of electrodes in various applications. Polymer thin films offer a wide range of molecular structures and compositions for tunable functionalities that can be custom designed to the needs of an application. In solid-state energy storage devices in particular, electrolyte-type polymeric interfaces between battery components and materials with disparate functions, such as the active electrode material and solid electrolyte could overcome some of these incompatibility detriments and the increase in contact resistance over long-term operation. In high-performance micro scale power sources, 3D thin-film all-solid-state batteries show great potential as they take advantage of both short ion diffusion distances for high-rate capability with low heat generation, as well as the third dimension for high material loading and energy density. Therefore, conformal deposition methods for ultra-thin polymeric electrolyte interphases on the interior surface of electrodes with mesoscale 3D architectures and complex porosity are in demand. Here, we report a molecular design concept of dual-functional molecules that contain electrochemically active end groups for self-limiting electropolymerization, and a core molecular motif that determines the thin film functionality. The electrodeposition of this monomer represents a non-line-of-sight coating method for polymer thin films with independently tailorable functionalities and tunable properties on conductive substrates with arbitrary shape. We exemplify this method using monomers with poly(ethylene glycol) (PEG) as the core motif for lithium-ion transport and phenol as electrochemically active end groups. We studied the electrodeposition of the monomers, poly(ethylene glycol) diphenol (PEGDP), and demonstrate their self-limiting film formation mechanism (Figure 1a) which originates from the insulating nature of resulting poly(PEGDP) film that confines the charge transfer reaction. We present an exhaustive exploration of their material-processing-structure-property relationships that reveals the multi-scale control over the ultrathin-film properties. For example, the uniform film thickness is tunable from 10 to 100s of nanometer through electrodeposition conditions and molecular design, while their molecular permeability and electronic resistance can be tailored from pervious to fully blocking. We show that the electrodeposited functional interphases fully coat complex 3D electrode architectures (Figure 1b top: uncoated carbon electrode, bottom: film coated carbon electrode) with retention of their functionality in a battery. This work demonstrates that rational molecular design enables the conformal electrodeposition of ultrathin functional coatings with solid polymer electrolyte properties on 3D structured electrodes that will enable designer interphases in various solid-state battery architectures and chemistries. Figure 1