Mechanism of high Li-ion conductivity in poly(vinylene carbonate)-poly(ethylene oxide)cross-linked network based electrolyte revealed by solid-state NMR

Solid polymer electrolytes(SPEs)have become increasingly important in advanced lithium-ion batteries(LIBs)due to their improved safety and mechanical properties compared to organic liquid electrolytes.Cross-linked polymers have the potential to further improve the mechanical property without trading off Li-ion conductivity.In this study,focusing on a recently developed cross-linked SPE,i.e.,the one based on poly(vinylene carbonate)-poly(ethylene oxide)cross-linked network(PVCN),we used solid-state nuclear magnetic resonance(NMR)techniques to investigate the fundamental interaction between the chain segments and Li ions,as well as the lithium-ion motion.By utilizing homonuclear/heteronuclear correlation,CP(cross-polarization)kinetics,and spin-lattice relaxation experiments,etc.,we revealed the structural characteristics and their relations to lithium-ion mobilities.It is found that the network formation prevents poly(ethylene oxide)chains from crystallization,which could create sufficient space for segmental tumbling and Li-ion co nductio n.As such,the mechanical property is greatly improved with even higher Li-ion mobilities compared to the poly(vinylene carbonate)or poly(ethylene oxide)based SPE analogues.

Unique double-layer solid electrolyte interphase formed with fluorinated ether-based electrolytes for high-voltage lithium metal batteries

Li metal batteries using high-voltage layered oxides cathodes are of particular interest due to their high energy density.However,they suffer from short lifespan and extreme safety concerns,which are attributed to the degradation of layered oxides and the decomposition of electrolyte at high voltage,as well as the high reactivity of metallic Li.The key is the development of stable electrolytes against both highvoltage cathodes and Li with the formation of robust interphase films on the surfaces.Herein,we report a highly fluorinated ether,1,1,1-trifluoro-2-[(2,2,2-trifluoroethoxy)methoxy]ethane(TTME),as a cosolvent,which not only functions as a diluent forming a localized high concentration electrolyte(LHCE),but also participates in the construction of the inner solvation structure.The TTME-based electrolyte is stable itself at high voltage and induces the formation of a unique double-layer solid electrolyte interphase(SEI)film,which is embodied as one layer rich in crystalline structural components for enhanced mechanical strength and another amorphous layer with a higher concentration of organic components for enhanced flexibility.The Li||Cu cells display a noticeably high Coulombic efficiency of 99.28%after 300 cycles and Li symmetric cells maintain stable cycling more than 3200 h at 0.5 mA/cm^(2) and 1.0m Ah/cm^(2).In addition,lithium metal cells using LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2) and Li CoO_(2) cathodes(both loadings~3.0 m Ah/cm^(2))realize capacity retentions of>85%over 240 cycles with a charge cut-off voltage of 4.4 V and 90%for 170 cycles with a charge cut-off voltage of 4.5 V,respectively.This study offers a bifunctional ether-based electrolyte solvent beneficial for high-voltage Li metal batteries.

Incombustible solid polymer electrolytes:A critical review and perspective

Since the advent of the solid-state batteries,employing solid polymer electrolytes(SPEs)to replace routine flammable liquid electrolytes is regarded to be one of the most promising solutions in pursing highenergy-density battery systems.SPEs with superior thermal stability,good processability,and high mechanical modulus obtain increasing attentions.However,SPE-based batteries are not impenetrable due to their decomposition and combustibility under extreme conditions.Researchers believe incorporating appropriate flame-retardant additives/solvents/fragments into SPEs can intrinsically reduce their flammability to solve the battery safety issues.In this review,the recent research progress of incombustible SPEs,with special emphasis on flame-retardant structural design,is summarized.Specifically,a brief introduction of flame-retardant mechanism,evaluation index for safety of SPEs,and a detailed overview of the latest advances on diverse-types SPEs in various battery systems are highlighted.The deep insight into thermal ru naway process,the free-standing incombustible GPEs,and the ratio nal design of pouch cell structures may be the main directions to motivate revolutionary next-generation for safety batteries.

In-situ polymerized PEO-based solid electrolytes contribute better Li metal batteries:Challenges,strategies,and perspectives

Polyethylene oxide(PEO)-based solid polymer electrolytes(SPEs)with good electrochemical stability and excellent Li salt solubility are considered as one of the most promising SPEs for solid-state lithium metal batteries(SSLMBs).However,PEO-based SPEs suffer from low ionic conductivity at room temperature and high interfacial resistance with the electrodes due to poor interfacial contact,seriously hindering their practical applications.As an emerging technology,in-situ polymerization process has been widely used in PEO-based SPEs because it can effectively increase Li-ion transport at the interface and improve the interfacial contact between the electrolyte and electrodes.Herein,we review recent advances in design and fabrication of in-situ polymerized PEO-based SPEs to realize enhanced performance in LMBs.The merits and current challenges of various SPEs,as well as their stabilizing strategies are presented.Furthermore,various in-situ polymerization methods(such as free radical polymerization,cationic polymerization,anionic polymerization)for the preparation of PEO-based SPEs are summarized.In addition,the application of in-situ polymerization technology in PEO-based SPEs for adjustment of the functional units and addition of different functional filler materials was systematically discussed to explore the design concepts,methods and working mechanisms.Finally,the challenges and future prospects of in-situ polymerized PEO-based SPEs for SSLMBs are also proposed.

PDOL-Based Solid Electrolyte Toward Practical Application:Opportunities and Challenges

Polymer solid-state lithium batteries(SSLB)are regarded as a promising energy storage technology to meet growing demand due to their high energy density and safety.Ion conductivity,interface stability and battery assembly process are still the main challenges to hurdle the commercialization of SSLB.As the main component of SSLB,poly(1,3-dioxolane)(PDOL)-based solid polymer electrolytes polymerized in-situ are becoming a promising candidate solid elec-trolyte,for their high ion conductivity at room temperature,good battery elec-trochemical performances,and simple assembly process.This review analyzes opportunities and challenges of PDOL electrolytes toward practical application for polymer SSLB.The focuses include exploring the polymerization mechanism of DOL,the performance of PDOL composite electrolytes,and the application of PDOL.Furthermore,we provide a perspective on future research directions that need to be emphasized for commercialization of PDOL-based electrolytes in SSLB.The exploration of these schemes facilitates a comprehensive and profound understanding of PDOL-based polymer electrolyte and provides new research ideas to boost them toward practical application in solid-state batteries.

Sandwich-type composited solid polymer electrolytes to strengthen the interfacial ionic transportation and bulk conductivity for all-solid-state lithium batteries from room temperature to 120℃

The insurmountable charge transfer impedance at the Li metal/solid polymer electrolytes(SPEs)interface at room temperature as well as the ascending risk of short circuits at the operating temperature higher than the melting point,dominantly limits their applications in solid-state batteries(SSBs).Although the inorganic filler such as CeO_(2)nanoparticle content of composite solid polymer electrolytes(CSPEs)can significantly reduce the enormous charge transfer impedance at the Li metal/SPEs interface,we found that the required content of CeO_(2)nanoparticles in SPEs varies for achieving a decent interfacial charge transfer impedance and the bulk ionic conductivity in CSPEs.In this regard,a sandwich-type composited solid polymer electrolyte with a 10%CeO_(2)CSPEs interlayer sandwiched between two 50%CeO_(2)CSPEs thin layers(sandwiched CSPEs)is constructed to simultaneously achieve low charge transfer impedance and superior ionic conductivity at 30℃.The sandwiched CSPEs allow for stable cycling of Li plating and stripping for 1000 h with 129 mV polarized voltage at 0.1 mA cm^(-2)and 30℃.In addition,the LiFePO_(4)/Sandwiched CSPEs/Li cell also exhibits exceptional cycle performance at 30℃and even elevated120℃without short circuits.Constructing multi-layered CSPEs with optimized contents of the inorganic fillers can be an efficient method for developing all solid-state PEO-based batteries with high performance at a wide range of temperatures.

Overcoming the Na-ion conductivity bottleneck for the cost-competitive chloride solid electrolytes

Chloride solid electrolytes possess multiple advantages for the construction of safe,energy-dense allsolid-state sodium batteries,but presently the chlorides with sufficiently high cost-competitiveness for commercialization almost all exhibit low Na-ion conductivities of around 10^(-5)S cm^(-1)or lower.Here,we report a chloride solid electrolyte,Na_(2.7)ZFCl_(5.3)O_(0.7),which reaches a Na-ion conductivity of2.29×10^(-4)S cm^(-1)at 25℃without involving overly expensive raw materials such as rare-earth chlorides or Na_(2)S.In addition to the efficient ion transport,Na_(2.7)ZrCl_(5.3)O_(0.7)also shows an excellent deformability surpassing that of the widely studied Na_(3)PS_(4),Na_(3)SbS_(4),and Na_(2)ZrCl_(6)solid electrolytes.The combination of these advantages allows the all-solid-state cell based on Na_(2.7)ZrCl_(5.3)O_(0.7)and NaCrO_(2)to realize stable room-temperature cycling at a much higher specific current than those based on other non-viscoelastic chloride solid electrolytes in literature(120 mA g^(-1)vs.12-55 mA g^(-1));after 100 cycles at such a high rate,the Na_(2.7)ZFCl_(5.3)O_(0.7)-based cell can still deliver a discharge capacity of 80 mAh g^(-1)at25℃.

Advancements,strategies,and prospects of solid oxide electrolysis cells(SOECs):Towards enhanced performance and large-scale sustainable hydrogen production

Solid oxide electrolysis cells(SOECs)represent a crucial stride toward sustainable hydrogen generation,and this review explores their current scientific challenges,significant advancements,and potential for large-scale hydrogen production.In SOEC technology,the application of innovative fabrication tech-niques,doping strategies,and advanced materials has enhanced the performance and durability of these systems,although degradation challenges persist,implicating the prime focus for future advancements.Here we provide in-depth analysis of the recent developments in SOEC technology,including Oxygen-SOECs,Proton-SOECs,and Hybrid-SOECs.Specifically,Hybrid-SOECs,with their mixed ionic conducting electrolytes,demonstrate superior efficiency and the concurrent production of hydrogen and oxygen.Coupled with the capacity to harness waste heat,these advancements in SOEC technology present signif-icant promise for pilot-scale applications in industries.The review also highlights remarkable achieve-ments and potential reductions in capital expenditure for future SOEC systems,while elaborating on the micro and macro aspects of sOECs with an emphasis on ongoing research for optimization and scal-ability.It concludes with the potential of SOEC technology to meet various industrial energy needs and its significant contribution considering the key research priorities to tackle the global energy demands,ful-fillment,and decarbonization efforts.

Recent progresses in the development of tubular segmented-in-series solid oxide fuel cells:Experimental and numerical study

Solid oxide fuel cells(SOFCs)have attracted a great deal of interest because they have the highest efficiency without using any noble metal as catalysts among all the fuel cell technologies.However,traditional SOFCs suffer from having a higher volume,current leakage,complex connections,and difficulty in gas sealing.To solve these problems,Rolls-Royce has fabricated a simple design by stacking cells in series on an insulating porous support,resulting in the tubular segmented-in-series solid oxide fuel cells(SIS-SOFCs),which achieved higher output voltage.This work systematically reviews recent advances in the structures,preparation methods,perform-ances,and stability of tubular SIS-SOFCs in experimental and numerical studies.Finally,the challenges and future development of tubular SIS-SOFCs are also discussed.The findings of this work can help guide the direction and inspire innovation of future development in this field.

Novel sandwich structured glass fiber Cloth/Poly(ethylene oxide)-MXene composite electrolyte

Recently,poly(ethylene oxide)(PEO)-based solid polymer electrolytes have been attracting great attention,and efforts are currently underway to develop PEO-based composite electrolytes for next generation high performance all-solid-state lithium metal batteries.In this article,a novel sandwich structured solid-state PEO composite electrolyte is developed for high performance all-solid-state lithium metal batteries.The PEO-based composite electrolyte is fabricated by hot-pressing PEO,LiTFSI and Ti_(3)C_(2)T_(x) MXene nanosheets into glass fiber cloth(GFC).The as-prepared GFC@PEO-MXene electrolyte shows high mechanical properties,good electrochemical stability,and high lithium-ion migration number,which indicates an obvious synergistic effect from the microscale GFC and the nanoscale MXene.Such as,the GFC@PEO-1 wt%MXene electrolyte shows a high tensile strength of 43.43 MPa and an impressive Young's modulus of 496 MPa,which are increased by 1205%and 6048%over those of PEO.Meanwhile,the ionic conductivity of GFC@PEO-1 wt%MXene at 60℃ reaches 5.01×10^(-2) S m^(-1),which is increased by around 200%compared with that of GFC@PEO electrolyte.In addition,the Li/Li symmetric battery based on GFC@PEO-1 wt%MXene electrolyte shows an excellent cycling stability over 800 h(0.3 mA cm^(-2),0.3 mAh cm^(-2)),which is obviously longer than that based on PEO and GFC@PEO electrolytes due to the better compatibility of GFC@PEO-1 wt%MXene electrolyte with Li anode.Furthermore,the solid-state Li/LiFePO_(4) battery with GFC@PEO-1 wt%MXene as electrolyte demonstrates a high capacity of 110.2–166.1 mAh g^(-1) in a wide temperature range of 25–60C,and an excellent capacity retention rate.The developed sandwich structured GFC@PEO-1 wt%MXene electrolyte with the excellent overall performance is promising for next generation high performance all-solid-state lithium metal batteries.

Synergistic coupling among Mg_(2)B_(2)O_(5),polycarbonate and N,Ndimethylformamide enhances the electrochemical performance of PVDF-HFP-based solid electrolyte

Polymer solid electrolytes(SPEs)based on the[solvate-Li+]complex structure have promising prospects in lithium metal batteries(LMBs)due to their unique ion transport mechanism.However,the solvation structure may compromise the mechanical performance and safety,hindering practical application of SPEs.In this work,a composite solid electrolyte(CSE)is designed through the organic-inorganic syner-gistic interaction among N,N-dimethylformamide(DMF),polycarbonate(PC),and Mg_(2)B_(2)O_(5) in poly(vinylidene fluoride-co-hexafluoropropylene)(PVDF-HFP).Flame-retardant Mg_(2)B_(2)O_(5) nanowires provide non-flammability to the prepared CSEs,and the addition of PC improves the dispersion of Mg_(2)B_(2)O_(5) nanowires.Simultaneously,the organic-inorganic synergistic action of PC plasticizer and Mg_(2)B_(2)O_(5) nanowires pro-motes the dissociation degree of LiTFSI and reduces the crystallinity of PVDF-HFP,enabling rapid Li ion transport.Additionally,Raman spectroscopy and DFT calculations confirm the coordination between Mg atoms in Mg_(2)B_(2)O_(5) and N atoms in DMF,which exhibits Lewis base-like behavior attacking adjacent C-F and C-H bonds in PVDF-HFP while inducing dehydrofluorination of PVDF-HFP.Based on the syner-gistic coupling of Mg_(2)B_(2)O_(5),PC,and DMF in the PVDF-HFP matrix,the prepared CSE exhibits superior ion conductivity(9.78×10^(-4) s cm^(-1)).The assembled Li symmetric cells cycle stably for 3900 h at a current density of 0.1 mA cm^(-2) without short circuit.The LFP||Li cells assembled with PDL-Mg_(2)B_(2)O_(5)/PC CSEs show excellent rate capability and cycling performance,with a capacity retention of 83.3%after 1000 cycles at 0.5 C.This work provides a novel approach for the practical application of organic-inorganic Synergistic CSEs in LMBs.

Lattice Boltzmann simulation study of anode degradation in solid oxide fuel cells during the initial aging process

For present solid oxide fuel cells(SOFCs),rapid performance degradation is observed in the initial aging process,and the dis-cussion of the degradation mechanism necessitates quantitative analysis.Herein,focused ion beam-scanning electron microscopy was em-ployed to characterize and reconstruct the ceramic microstructures of SOFC anodes.The lattice Boltzmann method(LBM)simulation of multiphysical and electrochemical processes in the reconstructed models was performed.Two samples collected from industrial-size cells were characterized,including a reduced reference cell and a cell with an initial aging process.Statistical parameters of the reconstructed microstructures revealed a significant decrease in the active triple-phase boundary and Ni connectivity in the aged cell compared with the reference cell.The LBM simulation revealed that activity degradation is dominant compared with microstructural degradation during the initial aging process,and the electrochemical reactions spread to the support layer in the aged cell.The microstructural and activity de-gradations are attributed to Ni migration and coarsening.

Boosting oxygen reduction activity and CO_(2) resistance on bismuth ferrite-based perovskite cathode for low-temperature solid oxide fuel cells below 600℃

Developing efficient and stable cathodes for low-temperature solid oxide fuel cells(LT-SOFCs) is of great importance for the practical commercialization.Herein,we propose a series of Sm-modified Bi_(0.7-x)Sm_xSr_(0.3)FeO_(3-δ) perovskites as highly-active catalysts for LT-SOFCs.Sm doping can significantly enhance the electrocata lytic activity and chemical stability of cathode.At 600℃,Bi_(0.675)Sm_(0.025)Sr_(0.3)FeO_(3-δ)(BSSF25) cathode has been found to be the optimum composition with a polarization resistance of 0.098 Ω cm^2,which is only around 22.8% of Bi_(0.7)Sr_(0.3)FeO_(3-δ)(BSF).A full cell utilizing BSSF25 displays an exceptional output density of 790 mW cm^(-2),which can operate continuously over100 h without obvious degradation.The remarkable electrochemical performance observed can be attributed to the improved O_(2) transport kinetics,superior surface oxygen adsorption capacity,as well as O_(2)p band centers in close proximity to the Fermi level.Moreover,larger average bonding energy(ABE) and the presence of highly acidic Bi,Sm,and Fe ions restrict the adsorption of CO_(2) on the cathode surface,resulting in excellent CO_(2) resistivity.This work provides valuable guidance for systematic design of efficient and durable catalysts for LT-SOFCs.

Construction of a High‑Performance Composite Solid Electrolyte Through In‑Situ Polymerization within a Self‑Supported Porous Garnet Framework

Composite solid electrolytes(CSEs)have emerged as promising candidates for safe and high-energy–density solid-state lithium metal batteries(SSLMBs).However,concurrently achieving exceptional ionic conductivity and interface compatibility between the electrolyte and electrode presents a significant challenge in the development of high-performance CSEs for SSLMBs.To overcome these challenges,we present a method involving the in-situ polymerization of a monomer within a self-supported porous Li_(6.4)La_(3)Zr_(1.4)Ta_(0.6)O_(12)(LLZT)to produce the CSE.The synergy of the continuous conductive LLZT network,well-organized polymer,and their interface can enhance the ionic conductivity of the CSE at room temperature.Furthermore,the in-situ polymerization process can also con-struct the integration and compatibility of the solid electrolyte–solid electrode interface.The synthesized CSE exhibited a high ionic conductivity of 1.117 mS cm^(-1),a significant lithium transference number of 0.627,and exhibited electrochemical stability up to 5.06 V vs.Li/Li+at 30℃.Moreover,the Li|CSE|LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2) cell delivered a discharge capacity of 105.1 mAh g^(-1) after 400 cycles at 0.5 C and 30℃,corresponding to a capacity retention of 61%.This methodology could be extended to a variety of ceramic,polymer electrolytes,or battery systems,thereby offering a viable strategy to improve the electrochemical properties of CSEs for high-energy–density SSLMBs.

Laminar Composite Solid Electrolyte with Poly(Ethylene Oxide)-Threaded Metal-Organic Framework Nanosheets for High-Performance All-Solid-State Lithium Battery

Developing laminar composite solid electrolyte with ultrathin thickness and continuous conduction channels in vertical direction holds great promise for all-solid-state lithium batteries.Herein,a thin,laminar solid electrolyte is synthesized by filtrating–NH 2 functionalized metal-organic framework nanosheets and then being threaded with poly(ethylene oxide)chains induced by the hydrogen-bonding interaction from–NH_(2) groups.It is demonstrated that the threaded poly(ethylene oxide)chains lock the adjacent metal-organic framework nanosheets,giving highly enhanced structural stability(Young’s modulus,1.3 GPa)to 7.5-μm-thick laminar composite solid electrolyte.Importantly,these poly(ethylene oxide)chains with stretching structure serve as continuous conduction pathways along the chains in pores.It makes the non-conduction laminar metal-organic framework electrolyte highly conductive:3.97×10^(−5) S cm^(−1) at 25℃,which is even over 25 times higher than that of pure poly(ethylene oxide)electrolyte.The assembled lithium cell,thus,acquires superior cycling stability,initial discharge capacity(148 mAh g^(−1) at 0.5 C and 60℃),and retention(94% after 150 cycles).Besides,the pore size of nanosheet is tailored(24.5–40.9˚A)to evaluate the mechanisms of chain conformation and ion transport in confined space.It shows that the confined pore only with proper size could facilitate the stretching of poly(ethylene oxide)chains,and meanwhile inhibit their disorder degree.Specifically,the pore size of 33.8˚A shows optimized confinement effect with trans-poly(ethylene oxide)and cis-poly(ethylene oxide)conformation,which offers great significance in ion conduction.Our design of poly(ethylene oxide)-threaded architecture provides a platform and paves a way to the rational design of next-generation high-performance porous electrolytes.

Pulsed electrolysis of carbon dioxide by large-scale solid oxide electrolytic cells for intermittent renewable energy storage

CO_(2) electrolysis with solid oxide electrolytic cells(SOECs)using intermittently available renewable energy has potential applications for carbon neutrality and energy storage.In this study,a pulsed current strategy is used to replicate intermittent energy availability,and the stability and conversion rate of the cyclic operation by a large-scale flat-tube SOEC are studied.One hundred cycles under pulsed current ranging from -100 to -300 mA/cm^(2) with a total operating time of about 800 h were carried out.The results show that after 100 cycles,the cell voltage attenuates by 0.041%/cycle in the high current stage of−300 mA/cm^(2),indicating that the lifetime of the cell can reach up to about 500 cycles.The total CO_(2) conversion rate reached 52%,which is close to the theoretical value of 54.3% at -300 mA/cm^(2),and the calculated efficiency approached 98.2%,assuming heat recycling.This study illustrates the significant advantages of SOEC in efficient electrochemical energy conversion,carbon emission mitigation,and seasonal energy storage.

Rational Design of High-Performance PEO/Ceramic Composite Solid Electrolytes for Lithium Metal Batteries

Composite solid electrolytes(CSEs)with poly(ethylene oxide)(PEO)have become fairly prevalent for fabricating high-performance solid-state lithium metal batteries due to their high Li~+solvating capability,flexible processability and low cost.However,unsatisfactory room-temperature ionic conductivity,weak interfacial compatibility and uncontrollable Li dendrite growth seriously hinder their progress.Enormous efforts have been devoted to combining PEO with ceramics either as fillers or major matrix with the rational design of two-phase architecture,spatial distribution and content,which is anticipated to hold the key to increasing ionic conductivity and resolving interfacial compatibility within CSEs and between CSEs/electrodes.Unfortunately,a comprehensive review exclusively discussing the design,preparation and application of PEO/ceramic-based CSEs is largely lacking,in spite of tremendous reviews dealing with a broad spectrum of polymers and ceramics.Consequently,this review targets recent advances in PEO/ceramicbased CSEs,starting with a brief introduction,followed by their ionic conduction mechanism,preparation methods,and then an emphasis on resolving ionic conductivity and interfacial compatibility.Afterward,their applications in solid-state lithium metal batteries with transition metal oxides and sulfur cathodes are summarized.Finally,a summary and outlook on existing challenges and future research directions are proposed.

In situ construction of a stable composite solid electrolyte interphase for dendrite-free Zn batteries

Building a stable solid electrolyte interphase(SEI)has been regarded to be highly effective for mitigating the dendrite growth and parasitic side reactions of Zn anodes.Herein,a robust inorganic composite SEI layer is in situ constructed by introducing an organic cysteine additive to achieve long lifetime Zn metal batteries.The chemisorbed cysteine derivatives are electrochemically reduced to trigger a local alkaline environment for generating a gradient layered zinc hydroxide based multicomponent interphase.Such a unique interphase is of significant advantage as a corrosion inhibitor and Zn^(2+)modulator to enable reversible plating/stripping chemistry with a reduced desolvation energy barrier.Accordingly,the cells with a thin glass fiber separator(260μm)deliver a prolonged lifespan beyond 2000 h and enhanced Coulombic efficiency of 99.5%over 450 cycles.This work will rationally elaborate in situ construction of a desirable SEI by implanting reductive additives for dendrite-free Zn anodes.

Bifunctional flame retardant solid-state electrolyte toward safe Li metal batteries

Solid polymer electrolytes(SPEs)are one of the most promising alternatives to flammable liquid electrolytes for building safe Li metal batteries.Nevertheless,the poor ionic conductivity at room temperature(RT)and low resistance to Li dendrites seriously hinder the commercialization of SPEs.Herein,we design a bifunctional flame retardant SPE by combining hydroxyapatite(HAP)nanomaterials with Nmethyl pyrrolidone(NMP)in the PVDF-HFP matrix.The addition of HAP generates a hydrogen bond network with the PVDF-HFP matrix and cooperates with NMP to facilitate the dissociation of Li TFSI in the PVDF-HFP matrix.Consequently,the prepared SPE demonstrates superior ionic conductivity at RT,excellent fireproof properties,and strong resistance to Li dendrites.The assembled Li symmetric cell with prepared SPE exhibits a stable cycling performance of over 1200 h at 0.2 m A cm^(-2),and the solid-state LiFePO_4||Li cell shows excellent capacity retention of 85.3%over 600 cycles at 0.5 C.

Solid polymer electrolytes in all-solid-state lithium metal batteries:From microstructures to properties

All-solid-state lithium(Li)metal batteries(ASSLMBs)are considered one of the most promising secondary batteries due to their high theoretical capacity and high safety performance.However,low room-temperature ionic conductivity and poor interfacial stability are two key factors affecting the practical application of ASSLMBs,and our understanding of the mechanisms behind these key problems from microscopic perspective is still limited.In this review,the mechanisms and advanced characterization techniques of ASSLMBs are summarized to correlate the microstructures and properties.Firstly,we summarize the challenges faced by solid polymer electrolytes(SPEs)in ASSLMBs,such as the low roomtemperature ionic conductivity and the poor interfacial stability.Secondly,several typical improvement methods of polymer ASSLMBs are discussed,including composite SPEs,ultra-thin SPEs,SPEs surface modification and Li anode surface modification.Finally,we conclude the characterizations for correlating the microstructures and the properties of SPEs,with emphasis on the use of emerging advanced techniques(e.g.,cryo-transmission electron microscopy)for in-depth analyzing ASSLMBs.The influence of the microstructures on the properties is very important.Until now,it has been difficult for us to understand the microstructures of batteries.However,some recent studies have demonstrated that we have a better understanding of the microstructures of batteries.Then we suggest that in situ characterization,nondestructive characterization and sub-angstrom resolution are the key technologies to help us further understand the batteries'microstructures and promote the development of batteries.And potential investigations to understand the microstructures evolution and the batteries behaviors are also prospected to expect further reasonable theoretical guidance for the design of ASSLMBs with ideal performance.