High Energy Density Batteries Research Articles

Pristine NASICON Electrolyte: A High Ionic Conductivity and Enhanced Dendrite Resistance Through Zirconia (ZrO2) Impurity-free Solid-Electrolyte Design.

Sodium batteries are considered a promising candidate for large-scale grid storage at tropical climate zone, and solid-state sodium metal batteries have a strong proposition as high energy density battery. The main challenge is to develop ultra-pure solid-state ceramic electrolyte and compatible metal interface. Here, a scalable and energy-efficient synthesis strategy of sodium (Na) Super Ionic CONductor, Na1+xZr2SixP3-xO12(x = 2, NZSP) solid electrolyte, has been introduced with the complete removal of unreacted zirconium oxide (ZrO2) impurities. Additionally, the reaction mechanism for the formation of pure phase NZSP is reported for the first time. The NZSP prepared by utilizing the Zr precursor, i.e., tetragonal zirconium oxide (t-ZrO2) derived from the Zr(OH)4 gets quickly and completely consumed in the synthesis process leaving no unreacted monoclinic ZrO2 impurities. The synthesis process only needs a minimum stay of 4 h, which is three times less than the conventional synthesis method. The elimination of ZrO2 impurities results in a 2.5-fold reduction in grain boundary resistivity, showcasing a total ionic conductivity of 1.75 mS cm-1 at room temperature and a relative density of 98%. The prepared electrolyte demonstrates remarkable resistance to dendrite formation, as evidenced by a high critical current density value of 1.4mA cm-2.

Design of CTP liquid cooling battery pack and thermal Characterization experiments

Range has emerged as a significant barrier to the advancement of electric vehicles, necessitating the development of high-energy–density battery packs. However, the conventional battery integration method, CTM (Cell to Module), has a relatively low space utilization rate, which presents a challenge to the enhancement of vehicle range. Consequently, a novel battery pack integration method, CTP (Cell to Pack), has emerged as a potential solution. In order to enhance the integration degree and effective energy density of the battery pack, a CTP and a symmetric serpentine runner liquid cooling plate are proposed in this paper. A thermal model of a single cell was constructed, and the cooling performance of the battery pack under different discharge conditions was analyzed. The optimal inlet water temperature and coolant mass flow rate were then determined. The findings indicate that the battery pack devised in this study exhibits commendable cooling capabilities and is capable of satisfying the cooling requirements associated with a 2C discharge scenario. Furthermore, when the battery pack is operated under Chinese Light Vehicle Driving Conditions (CLTC), the inlet flow rate of 2 L/min has been observed to reduce the maximum temperature differential by 1.31 °C in comparison to a scenario without internal coolant circulation.

Chitosan-derived N-doped porous carbon with fiber network structure for advanced lithium‑sulfur batteries

The flexible design and construction of advanced carbon-based sulfur hosts contribute to the rapid redox and reaction kinetics of lithium polysulfides (LiPSs) in lithium‑sulfur batteries (LSBs), laying the foundation for the next generation of high-energy density energy storage devices. Herein, chitosan (CS)-derived porous N-doped carbon with fiber network structure was prepared by a simple freeze-drying method combined with sintering process. The effect of inorganic salt additives on the morphology of CS-derived carbon was investigated by SEM. The types and contents of N-doping were investigated through XPS analysis. The influence of morphology and N content on the performance of LSBs has been explored in detail through cycling and CV testing. In addition, the true active sites in the CS-derived carbon were determined by XPS and first principles calculations. As an active species, pyrrolic N exhibits superior adsorption energy and the most suitable degradation energy barrier for LiPSs. As the optimal electrode, the performance of LSBs under different electrolyte to sulfur (E/S) conditions was further investigated to explore the potential application of CS-KOH electrodes in high-energy density batteries. The results unveil that the influence of E/S on Li2S deposition is quite significant, with a limit of 5 μL mg−1. This work provides a new strategy for the preparation of high-performance advanced carbon-based materials with fiber network structures from polysaccharide biomass, and also promotes the application of CS in energy storage.

(Invited) Advanced Processing Science for Low-Cost, High Energy Density Batteries

This project at the DOE Battery Manufacturing R&D Facility (BMF) at Oak Ridge National Laboratory (ORNL) has built research successes on advanced battery processing science and engineering (PSnE), cost reduction, and cell energy and power density improvements. Our goal is to perform the processing science and engineering needed to reduce high-risk, high-payoff technologies to lower risk levels, such that the U.S. industry will consider their integration in future products.Electron beam curing is demonstrated as a promising method for high speed, low cost and environmentally friendly battery electrode manufacturing. This work reports transfer of this process to pilot scale equipment and evaluation of electrochemical performance in prototype 1.5 Ah pouch cells. Thick NMC composite electrodes with an areal loading of 25 mg cm−2 (∼4 mAh cm−2) are successfully cured at a line speed of 500 feet per minute. This work demonstrates that electron beam curing is a promising method for manufacturing thick battery electrodes at high speeds and low capital/operation cost.

Improving Electrical Conductivity of LiFePO4 through Advanced Synthesis and Multidoping Techniques

Extensive research has been conducted to enhance the electrical conductivity of LiFePO4. Several techniques, including doping with metal cations, synthesizing nanocrystalline grains, and carbon coating, have been employed [1]. Recent advances in material synthesis have revolutionized LiFePO4, such as depositing conductive carbon coatings on active material particles and exploring surface doping techniques. These advanced approaches have significantly improved the mass transfer rate [2]. High-capacity LiFePO4 materials close to the theoretical specific capacitance have been obtained.Efforts are currently underway to improve the electronic and ionic conductivity of LiFePO4 to enhance its efficiency. However, before it can be widely used, the material's low electronic conductivity and suboptimal performance in high-speed regimes must be overcome. Doping with supervalent cations is an effective method for narrowing the energy gap and increasing the electrical conductivity of LiFePO4 [3]. Additionally, the synthesis of nanocrystalline grains and the deposition of conductive carbon coatings on the particle surface contribute to an increase in mass transfer rate, removing critical performance limitations of LiFePO4. Reducing the size of LiFePO4 to the nanoscale has been identified as a strategic method to shorten the diffusion length of Li-ions and accelerate electron-conducting pathways during charging and discharging cycles, ultimately improving the overall performance of the material.This work compares the doping process of LiFePO4 cathode material using two methods: solid-phase synthesis in a planetary ball mill and spray pyrolysis in an inert gas atmosphere. The studies on the synthesis and modification of LiFePO4 have significant potential to overcome existing limitations and unlock its full potential for integration into high energy density batteries. The above multidoping methods enable the production of doped LiFePO4 materials with specific capacitance approaching theoretical values. Acknowledgments This research was funded by the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan (Grant No. AP19677233).

Electrochemical Embrittlement Accelerates Dendrite Growth in Ceramic Electrolytes

Although solid-state batteries with metal anodes promise to enable safer, higher energy density batteries, metal protrusions (dendrites) grow when charging faster than a critical current density[1,2]. It is generally believed that dendrites grow when plating-induced stresses exceed that required for fracture of the solid-electrolyte[2–4]. Although the electrolyte's fracture toughness is commonly taken as a constant[2–4], here we show that the effective fracture toughness depends markedly upon the metal deposition current density. Based upon operando birefringence microscopy[5], we directly measure dendrite-induced stresses and obtain the mechanical driving force for failure, as well as the electrolyte fracture toughness. We find that increasing current densities embrittle the solid electrolyte—diminishing the fracture toughness by as much as 70%. Cryogenic Scanning Transmission Electron Microscopy (Cryo-STEM) reveals decomposed electrolyte phases at the dendrite tip. This decomposition is associated with a volume contraction consistent with embrittlement of the electrolyte. All experiments were conducted on the most electrochemically stable Li-ion conducting solid electrolyte (tantalum-doped lithium lanthanum zirconium oxide); the fracture toughness of less stable electrolytes (e.g., agryodites) may be even more susceptible to such embrittlement. The collective results indicate that “electrochemical embrittlement” markedly weakens the electrolyte, enabling dendrite growth—even when such degradation has negligible effect on bulk electrochemical properties.

Utilizing FeS2 Deposition on 3D Printed Carbon Microlattices as Free-Standing Electrodes in Lithium-Ion Batteries

Free-standing electrodes are a great alternative to slurry-coated battery electrodes as they eliminate the need for inactive components and shorten the fabrication process. In this work, carbon microlattice templates are designed and fabricated through the use of 3D stereolithography followed by pyrolysis to create a well-defined carbon template with a resolution >35 µm. Iron disulfide, a material with a high specific theoretical capacity, is then deposited on the surface and used as electrode material in lithium-ion batteries. To date, there have been no reports of FeS2 combined with 3D printed free-standing electrodes. The design utilizes controlled microchannels along the thickness direction to facilitate efficient ion transfer and interconnected carbon skeletons for electron transfer throughout the entire electrode. When directly applied in a lithium-ion battery, the composite material displayed a specific capacity of 562.5 mAh g-1 after 200 cycles with a current density of 500 mA g-1. A high-rate capability was also achieved. Stepwise cyclic voltammetry and Dunn Method confirm that the dominant mechanism guiding the excellent electrochemical performance is diffusion-controlled process, further highlighting the benefits of the organized microchannels. These results will advance the development of composite electrodes as well as shine light on the immense potential to develop high energy density batteries utilizing 3D printing, advocating for sustainable energy from both a research-driven and practical stance.

Understanding Organic Components of Solid Electrolyte Interphase on the Lithium Metal Anode

Lithium ion batteries have become the dominant form of energy storage used in consumer electronics and, recently, electric vehicles. However, high costs have prevented widespread deployment of lithium ion batteries for applications other than portable electronics, and the safety issues associated with liquid organic electrolytes remain to be addressed. In order to enable the greater utilization of electric vehicles, allow for grid scale energy storage, and meet the demands of new electronic applications, new materials for high energy density batteries must be developed. High capacity electrode materials like lithium metal have the potential to facilitate these technologies, but lithium metal electrodes are presently limited by significant side reactions, poor quality deposition, and the potential to form hazardous dendrites. Therefore, it is important to develop a clear understanding of the surface reactivity and growth behavior of the lithium metal at the interface with the electrolyte in order to enable stable long-term cycling.The products that form as a result of electrolyte decomposition reactions at the electrode interface are known to be extremely important in determining the final cell performance, yet characterizing the organic components of the solid electrolyte interphase (SEI) proves to be challenging with typical techniques. In this presentation we will discuss a combination of in operando and ex situ techniques developed in efforts to more comprehensively characterize the reaction intermediates and organic SEI products of electrolyte reduction reactions. Specifically, we employ electron paramagnetic resonance (EPR) spectroscopy to identify radical intermediates and clarify electrolyte reduction mechanisms. Furthermore, SEI product formation with respect to electrochemical potential and time will be described using data obtained from in operando ATR-FTIR. ATR-FTIR is a powerful method for characterizing organic species, but typical materials such as Ge, Si, and ZnSe react with lithium metal during deposition. In this talk, the development of a diamond based operando cell and its application to the characterization of organosulfur and fluorinated electrolytes will be discussed. With the understanding developed from these two techniques we provide new insights into the formation and chemical nature of SEI components that promote stable cycling of lithium metal electrodes.

Unlocking the Multi-Redox (Nb5+/Nb4+/Nb3+) Reactions in Nasicon- Nb2(PO4)3 Anode for Li- and Na-Ion Batteries

NASICON (Natrium Super-Ionic CONductor) type materials are known for their high structural, and thermal stability and superior sodium ion mobility which make this framework an efficient electrode material for Na-ion batteries.1 In recent times NASICON-type compounds have been widely explored as Li- and Na-ion cathodes and solid-state electrolytes but are largely ignored as anodes due to their lower capacities and higher intercalation voltages, which reduce the overall energy densities of Li- and Na-ion batteries (LIBs and SIBs). NASICON structure has a general molecular formula of NaxMM′(PO4)3, where two MO6 octahedra corners are shared with three PO4 tetrahedra along the c-direction resulting in the “lantern units” and each lantern unit joins six other lantern units, generating a large interstitial space that can accommodate up to four alkali cations per formula unit.2 In the NASICON family usually all members contain Na/Li ions in terms of synthesis and electrochemical/chemical oxidation routes must be employed to remove the Na from the parent compound.Herein, for the first time we will present a comprehensive study on the structural and electrochemical properties of the empty NASICON-type (contains no Li or Na ions in its pristine state) mixed valance Nb2(PO4)3 and its potential application as an anode in LIBs and SIBs. Due to the multi-redox activity of Nb, it is possible to attain high insertion capacity (~ 150 mAh g-1 for SIBs and ~ 170 for LIBs) and relatively lower voltages (1.8 V vs. Li+/Li0 and 1.4 V vs. Na+/Na0) compared to Ti or V-based NASICON anodes.3,4 Our in-situ XRD measurements revealed multiple-phase transformations during Li and Na intercalation with the formation of short-range ordered Li3Nb2(PO4)3 and triclinic (P-1)-Na3Nb2(PO4)3 at the end of discharge. The distinct electrochemical Li and Na intercalation behavior of the Nb2(PO4)3 anode can be ascribed to the relative differences in size, filling of crystallographic sites, and chemical characters of Li and Na ions. Our density functional theory calculations are also in agreement with the in-situ XRD measurements in predicting a stable Na3Nb2(PO4)3 composition in the Na-Nb2(PO4)3 pseudo-binary system. X-ray absorption spectroscopy confirms the participation of multi-redox Nb5+/Nb4+/Nb3+ couples. Although the micron-sized anode showed moderate storage capacities (~106 and 84 mAh g-1 for Li and Na cells, respectively) at 1C rate after 200 cycles, further optimization of electrode and electrolytes is expected to produce better performance. In the future, pairing Nb2(PO4)3 anode with suitable cathodes can enable high-energy density batteries.5

3D lithiophilic collector coated by amorphous g-C3N4 enabling Ultra-Stable cycling Li metal batteries

Lithium metal batteries (LMB) are thought of the most promising candidates for the next generation of high energy density batteries, but the problems of interface instability and uncontrollable dendrite growth are key constraints to the commercial application. Herein, we constructed an amorphous graphitic carbon nitride (g-C3N4) “outerwear” modified lithiophilic 3D Au/CoO nanoarray matrix (CACM) as a multifunctional dual-layer host, achieving dendrite-free and cycling stabilized Li metal anode. The density functional theory (DFT) calculations show that the reaction between CACM and Li atoms has a strong binding energy and a large amount of charge transfer. The lithiophilic 3D host induces Li metal uniform deposition with a low nucleation barrier within the 3D skeleton. The amorphous g-C3N4 “outerwear” can effectively avoid direct contact between the electrolyte and Li and reduce the irreversible side reaction. Meanwhile, the g-C3N4 layer has abundant Li ion transport channels, which facilitated fast Li+ transfer and modulate the ion concentration over the anode surface. Thus, the half-cell equipped with the CACM electrode has ultra-high cyclic stability, maintaining a CE value of 99.6 % over 230 cycles at 1 mA cm−2 with 1 mAh cm−2. The symmetric-cell can maintain a low overpotential stable run 1300 cycles at 10 mA cm−2. Similarly, the full cell also showed outstanding long-term cycle stability (capacity maintained at 96.3 % after 400 cycles at 1C) and superior rate capability. The in-situ visualization cell test and ex-situ SEM also demonstrated that the multifunctional host inhibits volume expansion and the dendritic growth of Li.

Micrometer-sized 3D porous structure decorated with uniform InSb alloy layer towards dendrite-free Li metal electrode

Li metal electrode is expected to be one promising anode to construct high energy density batteries because of its high theoretical specific capacity and the lowest electrode potential. However, uncontrollable dendrite growth and large volume changes cause batteries failure and safety risks. Here, an InSb alloy modified three-dimensional porous Cu (3D Cu@InSb) is constructed by electroless plating coupled with electroplating to stabilize the Li metal electrode. The suitable 3D porous structure with pore size of several micrometers can provide uniform current distribution, rapid ionic transferring channels, and effectively accommodate volumetric changes and release stress as well, avoiding the limited modifying effect using too large pores and poor ionic transport kinetics using too small pores. Moreover, the InSb alloy modified layer with high binding energy to Li+ reduces the nucleation overpotential and enhances the Li plating/stripping reversibility. Under the synergistic effects of InSb alloy modified layer and suitable 3D porous structure, Li metal is uniformly plated/stripped in pores with almost thorough flat surface even under a high area capacity of 4 mAh cm−2. The full battery assembled using LiFePO4 (LFP) cathode demonstrates a long life of 600 cycles at 2 C with a capacity retention of 86 %.

Performance of interstitial thermal barrier materials on containing sidewall rupture and thermal runaway propagation in a lithium-ion battery module

Containing thermal runaway propagation in lithium-ion battery packs is a pertinent problem that is exacerbated when considering high energy density batteries and severe battery failure modes, such as sidewall rupture. This work investigates five different passive thermal barrier materials for their performance with respect to containing sidewall rupture and mitigating thermal runaway propagation between high energy density 21,700 cells. Along with propagation rate and total count of sidewall rupture failures, two new key performance indicators are introduced, the temperature reduction value and the sidewall rupture ratio, to quantify a material's performance. Overall, a stainless steel thermal barrier coated with an intumescent flame-retardant fabric performs best out of the five materials investigated. Evidence is given for the count of sidewall ruptures being linearly correlated to the propagation rate. It is shown that cells that fail with sidewall rupture have an average maximum surface temperature of 919 °C compared to 653 °C for cells that fail with top cap rupture. Evidence is also presented that sidewall rupture propagates to adjacent cells in a module. This work aims to provide battery pack designers with information to aid them in determining a strategy for containing thermal runaway propagation and sidewall rupture, including a method to evaluate the performance of thermal barrier materials against this objective.

Revisiting porous foam Cu host based Li metal anode: The roles of lithiophilicity and hierarchical structure of three-dimensional framework

Lithium (Li) metal anode (LMA) is one of the most promising anodes for high energy density batteries. However, its practical application is impeded by notorious dendrite growth and huge volume expansion. Although the three-dimensional (3D) host can enhance the cycling stability of LMA, further improvements are still necessary to address the key factors limiting Li plating/stripping behavior. Herein, porous copper (Cu) foam (CF) is thermally infiltrated with molten Li-rich Li-zinc (Li-Zn) binary alloy (CFLZ) with variable Li/Zn atomic ratio. In this process, the LiZn intermetallic compound phase self-assembles into a network of mixed electron/ion conductors that are distributed within the metallic Li phase matrix and this network acts as a sublevel skeleton architecture in the pores of CF, providing a more efficient and structured framework for the material. The as-prepared CFLZ composite anodes are systematically investigated to emphasize the roles of the tunable lithiophilicity and hierarchical structure of the frameworks. Meanwhile, a thin layer of Cu-Zn alloy with strong lithiophilicity covers the CF scaffold itself. The CFLZ with high Zn content facilitates uniform Li nucleation and deposition, thereby effectively suppressing Li dendrite growth and volume fluctuation. Consequently, the hierarchical and lithiophilic framework shows low Li nucleation overpotential and highly stable Coulombic efficiency (CE) for 200 cycles in conventional carbonate based electrolyte. The full cell coupled with LiFePO4 (LFP) cathode demonstrates high cycle stability and rate performance. This work provides valuable insights into the design of advanced dendrite-free 3D LMA toward practical application.

Compositionally Tunable Mn-V-Fe Phosphoselenide Nanorods with Minimal Ion-Diffusion Barrier as High Energy Density Battery Electrode Materials.

The design and synthesis of novel heterostructured electrode materials are crucial to enable the fabrication of efficient supercapacitor devices. In this regard, transition metal phosphochalcogenides (S, Se) are promising candidates owing to their exotic electronic properties. Herein, a facile two-step hydrothermal protocol was used to synthesize binary and ternary metal phospho-selenide electrodes (Mn-Fe-P-Se, V-Fe-P-Se, Mn-V-P-Se, and Mn-Fe-V-P-Se). The chemical composition, morphology, and structure of the as-fabricated materials were fully investigated. The three-electrode electrochemical evaluation at 1.0 A g-1 demonstrated that the ternary metal electrode (MFVP-Se) exhibits a high capacity of 1968.63 C g-1. To assess the practical value of the rationally designed Mn-Fe-V-P-Se electrode material, Mn-Fe-V-P-Se was used as a positive electrode coupled with activated carbon (AC) as a negative electrode to assemble a hybrid supercapacitor device. This Mn-Fe-V-P-Se//AC device delivers a power density of 1999.96 W kg-1 with a high energy density of 149.88 Wh kg-1 coupled with no capacity loss after 5000 charging/discharging cycles. Additionally, density functional theory calculations revealed that our electrode exhibits suitable adsorption energy for OH- ions with a minimal diffusion barrier for ions.

Coupling 3D vertical graphene skeleton with lithophilic ZnO Interface to enable highly stable lithium metal anode

Lithium metal has been considered as the most promising anode material for high energy density batteries owing to its high theoretical capacity and low reduction potential. Unfortunately, the uncontrollable growth of lithium dendrites and unrestrained volume expansion seriously hinder its practical applications. Designing 3D skeletons with high electronic conductivity, and superior lithophilicity to control the lithium plating/stripping process has been proven to be an effective strategy to alleviate these two issues. In this study, ZnO-decorated 3D vertical graphene skeleton (ZnO@VG) was developed as the host material to regulate lithium nucleation and dendrite growth. Attributing to the unique cavity arrangement, enlarged specific surface area, and numerous lithiophilic sites of ZnO@VG, a remarkable coulombic efficiency of 99.12 % after 350 cycles is achieved. Furthermore, symmetric cells based on ZnO@VG/Li electrodes demonstrate lower voltage polarization and enhanced cycling stability (over 1800 h) at 0.5 mA cm−2 and 1 mA h cm−2. Notably, when coupled with a LiFePO4 cathode, the full cell exhibits a discharge specific capacity of 100.33 mA h cm−2 at 5 C and maintains a high capacity retention of 89.1 % after 740 cycles at 1 C.

Ligand‐to‐Metal Charge Transfer Motivated the Whole‐Voltage‐Range Anionic Redox in P2‐Type Layered Oxide Cathodes

AbstractAnionic redox in layered transition metal oxides (TMOs) cathodes presents significant opportunities for achieving high energy density batteries. However, the O 2p non‐bonding state can only undergo redox at high voltages and is often accompanied by severe structural distortion. In this study, the whole‐voltage‐range anionic redox has successfully been achieved in Metal‐organic frameworks (MOF) derived chemically homogeneous P2‐Na0.67Ni0.2Mg0.2Mn0.6O2 (NNMMO). Through a systematic analysis of the orbital combinations of TMs and O, it is found that the Mg‐induced O 2p non‐bonding state as an electron donor, forming strong π‐type interactions between Ni 3d spin‐down t2g orbitals. The resulting π‐configurational oxygen occupies an anti‐bonding state just below the Fermi level, exhibiting high oxidation activity and stability. Additionally, the high covalency between Mn and O increases the strength of the Mn–O bond, mitigating the structural aberration of NNMMO. As a result, NNMMO demonstrates a high capacity of 216 mAh g−1 at 0.1 C and stable battery performance, with a capacity retention of ≈90% after 500 cycles at 2 C. This π‐type anionic redox and intrinsic competition mechanism present an alternative strategy for achieving advanced cathode materials for sodium‐ion batteries.

A model for the prediction of thermal runaway in lithium–ion batteries

The increasing popularity of electric vehicles is driving research into lithium-ion batteries (LIBs). Thermal runaway (TR) in LIBs is a serious concern for the safe operation of these high–energy-density batteries that is yet to be overcome. A reliable model is needed to predict voltage variation, heat generation, temperature rise, and the process leading to TR of a LIB battery under its operating conditions (charging–discharging). Such a model can be used to design battery packs more resilient to thermal runaway or assess how a battery pack would perform under hazardous conditions. Furthermore, it can be used for generating a warning signal if there is a possibility of the battery going towards TR. This paper presents an approach to solving this problem, which is not currently well addressed in the literature. The approach adopted in this paper is based on a numerical analysis of a multilayered electrochemical–thermal model of LIB. Tuning the parameters of a LIB for accurate results from this numerical model is presented, as well as the details of the approach in the paper. Experiments are performed under several LIBs, and their voltage and surface temperature variations are measured under various operating conditions, including thermal runaway. The results of the experiments are compared with the predictions of the numerical simulations. An excellent agreement is observed with the experimental results, proving the accuracy of the proposed approach. This approach can be configured to give results in a few minutes. The paper also discusses how the developed approach can be used to create a TR warning during operating conditions or to change the mode of operation of a LIB before a hazard occurs.

Molten Guest-Mediated Metal-Organic Frameworks Featuring Multi-Modal Supramolecular Interaction Sites for Flame-Retardant Superionic Conductor in All-Solid-State Batteries.

The development of solid-state electrolytes (SSEs) with outstanding comprehensive performance is currently a critical challenge for achieving high energy density and safer solid-state batteries (SSBs). In this study, a strategy of nano-confined in situ solidification is proposed to create a novel category of molten guest-mediated metal-organic frameworks, named MGM-MOFs. By embedding the newly developed molten crystalline organic electrolyte (ML20) into the nanocages of anionic MOF-OH, MGM-MOF-OH, characterized by multi-modal supramolecular interaction sites and continuous negative electrostatic environments within nano-channels, is achieved. These nanochannels promote ion transport through the successive hopping of Li+ between neighbored negative electrostatic environments and suppress anion movement through the chemical constraint of the hydroxyl-functionalized pore wall. This results in remarkable Li+ conductivity of 7.1 × 10-4 S cm-1 and high Li+ transference number of 0.81. Leveraging these advantages, the SSBs assembled with MGM-MOF-OH exhibit impressive cycle stability and a high specific energy density of 410.5Wh kganode + cathode + electrolyte -1 under constrained conditions and various working temperatures. Unlike flammable traditional MOFs, MGM-MOF-OH demonstrates high robustness under various harsh conditions, including ignition, high voltage, and extended to humidity.

Pre-impregnated protective layer for high energy density Li metal batteries using aqueous electrolyte

Aqueous electrolytes have been considered as alternatives for solving thermal safety issues of batteries caused by the high flammability of non-aqueous electrolytes. However, the use of low-potential anodes for high energy density batteries using aqueous electrolytes is limited by the narrow electrochemical stability window of water (1.23 V). Therefore, an artificial protective layer is required to compensate for the potential difference between the electrolyte and anode: however, using selectively conducting Li ions while suppressing water penetration during cycling tests in batteries is a key problem that has not yet been solved. In this study, a pre-impregnated protective layer using a Li ion conductive high concentration solution in a hydrophobic polymer framework (PIPL-H) was developed for the reversible use of Li metal in batteries using aqueous electrolyte. PIPL-H minimizes hydrogen evolution reactions by preventing direct contact between the water molecules and the Li metal. PIPL-H enabled a Li symmetric cell without increasing polarization for 1000 h, as well as a full cell using LiMn2O4 with 88.2 % capacity retention for up to 60 cycles. These results provide a new perspective into protective layers that enable stable operation without being constrained by the limited cathodic stability of aqueous electrolytes.

Novel Cu(II)-based metal–organic framework STAM-1 as a sulfur host for Li–S batteries

Due to the increasing demand for energy storage devices, the development of high-energy density batteries is very necessary. Lithium–sulfur (Li–S) batteries have gained wide interest due to their particularly high-energy density. However, even this type of battery still needs to be improved. Novel Cu(II)-based metal–organic framework STAM-1 was synthesized and applied as a composite cathode material as a sulfur host in the lithium–sulfur battery with the aim of regulating the redox kinetics of sulfur cathodes. Prepared STAM-1 was characterized by infrared spectroscopy at ambient temperature and after in-situ heating, elemental analysis, X-ray photoelectron spectroscopy and textural properties by nitrogen and carbon dioxide adsorption at − 196 and 0 °C, respectively. Results of the SEM showed that crystals of STAM-1 created a flake-like structure, the surface was uniform and porous enough for electrolyte and sulfur infiltration. Subsequently, STAM-1 was used as a sulfur carrier in the cathode construction of a Li–S battery. The charge/discharge measurements of the novel S/STAM-1/Super P/PVDF cathode demonstrated the initial discharge capacity of 452 mAh g−1 at 0.5 C and after 100 cycles of 430 mAh g−1, with Coulombic efficiency of 97% during the whole cycling procedure at 0.5 C. It was confirmed that novel Cu-based STAM-1 flakes could accelerate the conversion of sulfur species in the cathode material.