Ion Transport Network Research Articles

The Role of the Ionomer in the Catalyst Layer of Anion Exchange Membrane Water Electrolyzers

Anion exchange membrane water electrolyzers (AEMWE) have gained recent attention as a promising low temperature H2O electrolysis technology that combines the benefits of commercial liquid alkaline and proton exchange membrane water electrolyzers (PEMWE), while alleviating concerns over capital cost and materials criticality associated with these existing technologies.1,2 While AEMWEs have achieved significant performance advances in recent decades, overpotentials remain high relative to PEMWE counterparts,2 requiring AEMWE-specific catalyst layer design strategies to further advance this technology. Catalyst layers conventionally consist of catalyst particles which are co-deposited with an ion-conducting polymer or ionomer that is of the same chemistry as the ion-exchange polyelectrolyte phase.3 In PEMWEs, which are operated in pure water, this ionomer serves as the sole ion (H+) transport network through the catalyst layer. The ionomer further serves roles as a binding agent, adhering catalyst particles to the electrode, as well as an ink rheology agent.4 In contrast, AEMWEs often operate in dilute supporting electrolyte, raising questions about the role of the ionomer in AEMWE systems.In this work, we assess the specific roles of ionomers in supporting electrolyte fed AEMWEs using NiFe2O4, identified in our previous work as a strong candidate for a commercial alkaline oxygen evolution reaction (OER) catalyst, and PiperION TP85 from Versogen, a common commercially available AEM. Catalyst layers were constructed at variable ionomer contents (0 – 30 wt%) to investigate the role of the ionomer phase in supporting electrolyte-fed AEMWEs. Specifically, the role of the ionomer in catalyst structure and quality, catalyst adhesion, and ion transport were investigated via electrochemical and physical characterization of pristine and tested catalyst layers. Ex-situ scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM-EDS), x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS) measurements were employed to provide insights into catalyst and ionomer loss mechanisms over 200 h durability tests at different ionomer contents. Voltage breakdown analyses were used to further investigate the effects of ionomer content on cell overpotentials. Electrochemical impedance spectroscopy (EIS) and Tafel analyses were utilized to decouple thermodynamic, Ohmic, kinetic, and catalyst layer resistance contributions to overpotentials for each ionomer content.The results show that intermediate ionomer contents (5-10 wt%) provide the highest cell current densities. Intermediate ionomer contents were found to a achieve a balance of catalyst adhesion, catalyst layer porosity, and catalyst layer homogeneity, leading to improved site accessibility and decreased cell overpotentials. Testing with Nafion (a non-anion conducting polymer) further demonstrated that the ionomer is not required for ion conduction in AEMWE catalyst layers under supporting-electrolyte operation and therefore that ionomers do not need to match the chemistry of the anion exchange membrane. Instead, we find that, for initial performance, the ionomer is crucial for catalyst layer structure and quality, and for long-term stability, the ionomer is crucial to provide catalyst adhesion for long-term durability.[1] IRENA Green Hydrogen Cost Reduction - Scaling up Electrolyzers to Meet the 1.5C Climate Goal 2020, [2] Alia, S. et al., Electrochem. Soc. Interface 2021, [3] Volk, E. K. et al., EES Catalysis 2024, [4] Khandavalli, S. et al., ACS Appl. Mater. Interfaces 2019

Composite Polymer Electrolyte Enabled through 2D g-C3N4 for All Solid-State Sodium-Ion Batteries

Coupling the advantages of sodium ion chemistry and solid-state batteries can circumvent challenges such as leakage, fire risk, cost, supply chain and better electrochemical performance compared to conventional non-aqueous Li-ion batteries. Here, the inherent low ionic conduction and poor mechanical strength of solid polymer electrolytes urges the necessity of coalescing of polymer with active or passive ceramic fillers to efficiently overcome the individual demerits by offering benefit of both counterparts. Hence, a composite polymer electrolyte through passive or functional fillers are explored due to their enhancements in the ionic conductivity, structural and electrochemical properties. It has been found that morphology, size, and shape of the fillers along with their concentration in the polymer host will have significant effect on the performance improvement of the electrolyte. Dimensional control such as aligned nanowires and two-dimensional clays have resulted in much improved ionic conductivity and battery performance. The filler addition firstly influences the crystallinity of the host and then ameliorates the mechanical strength to hinder dendrite growth and overall rigidity of the electrolyte. Furthermore, functional filler induced salt-filler interaction improves the dissociation ability, cation mobility and anion immobility. Morphology being a critical performance enabler, compared to 0D/1D/3D fillers, fillers with 2D morphology that possess abundant surfaces induce increased active interface that allows better transport network and mechanical strength.Herein, we have attempted to develop a unique functional filler, graphitic carbon nitride, g-C3N4 layered material based composite polymer electrolyte with PEO and salt for all solid-state sodium ion battery. As a two-dimensional filler, GCN synthesis is facile and scalable by simple thermal oxidative etching. Further, the functional N groups in the abundant surface of GCN allows increased interaction with Na salt that allows better ionization and transference. The 2D filler with high active surface properties can effectively create more nonslip region under load to augment the mechanical property. Additionally, unlike other 2D materials, GCN along with its high surface, also possess numerous defect regions that prospectively provide increased ion transport network for better ion migration through the created channels and thus efficiently improving the ionic conductivity of the composite electrolyte. Therefore, a ~60% increment in ionic conductivity (~4.5 × 10-6 S/cm) was observed for PEO-GCN composite compared to pure PEO electrolyte. Also, an assembled solid state sodium metal battery with the composite polymer electrolyte delivered an impressive discharge capacity of 102 mAh/g at 0.2 C operated at 60 °C using a functional composite NVP catholyte. References Ye, K. Liao, R. Ran, Z. Shao, Energy Fuels 2020, 34, 9189.Liu, W. Liu, D. Ba, Y. Zhao, Y. Ye, Y. Li, J. Liu, Advanced Materials 2023, 35, 2110423.Shen, Y. Cheng, S. Sun, X. Ke, L. Liu, Z. Shi, Carbon Energy 2021, 3, 482.Vijayakumar, M. Ghosh, K. Asokan, S. B. Sukumaran, S. Kurungot, J. Mindemark, D. Brandell, M. Winter, J. R. Nair, Advanced Energy Materials 2023, 13, 2203326.Wang, Y. Huo, Y. Fan, R. Wu, H. Wu, F. Wang, X. Xu, Journal of Photochemistry and Photobiology A: Chemistry 2018, 358, 61.

High-performance S cathode through a decoupled ion-transport mechanism

A high-performance sulfur (S) cathode is essential for advanced lithium-sulfur (LiS) batteries. Issues such as shuttle effect of polysulfides and low conductivity of S need to be resolved. Here, we report a S-cathode prepared via constructing unique decoupled ion-transport network formed from soy protein-based ionic conductor with well-dispersed graphene, leading to mitigated shuttle effect and excellent dual-conductive capabilities, i.e., high electronic and ionic conductivities. The decoupled ion-transport mechanism, which is unconventional in polymeric systems, is enabled by appropriately maintaining the denatured soy protein structure during the cathode preparation, facilitating polysulfide trapping and providing high adhesion for the S cathode, confirmed by the experiment and simulation results. Consequently, the LiS battery with the protein-based S cathode demonstrates excellent rate performance and long cycling stability. In specific, the LiS battery with the protein-based S cathode shows ∼70 % capacity retention (∼504 mAh g−1) after 600 cycles under the current density of 0.5 A g−1. This work will initiate new scientific studies on introducing an unconventional ion-transport mechanism into electrodes for producing high-performance batteries.

Highly Anion-Conductive Viologen-Based Two-Dimensional Polymer Membranes as Nanopower Generators.

Two-dimensional polymers (2DPs) and their layer-stacked 2D covalent organic frameworks (2D COFs) membranes hold great potential for harvesting sustainable osmotic energy. The nascent research has yet to simultaneously achieve high ionic flux and selectivity, primarily due to inefficient ion transport dynamics. This is directly related to ultrasmall pore size (<3 nm), much smaller than the duple Debye length in the diluted electrolyte (6-20 nm), as well as low charge density (<4.5 mC m-2). Here, we introduce a π-conjugated viologen-based 2DP (V2DP) membrane possessing a large pore size of 4.5 nm, strategically enhancing the overlapping of the electric double layer, coupled with an exceptional positive surface charge density (~6 mC m-2). These characteristics enable the membrane to facilitate high anion flux while maintaining ideal selectivity. Notably, V2DP membranes realize an impressive current density of 5.5×103 A m-2, surpassing benchmarks set by previously reported nanofluidic membranes. In the practical application scenario involving the mixing of artificial seawater and river water, the V2DP membranes exhibit a considerable ion transference number of 0.70 towards Cl-, contributing to an outstanding power density of ~55 W m-2. Theoretical calculations reveal the important role of the large quantity of anion transport sites, which act as binding sites evenly located in the positively charged N-containing pyridine rings. These binding sites enable kinematic coupling and decoupling between anions and the V2DP skeleton, establishing a continuous Cl- ion transport pathway. This work demonstrates the great promise of large-area ultrathin 2DP membranes featuring highly organized charged ion transport networks when applied for osmotic energy conversion.

Spatially Confined Engineering Toward Deep Eutectic Electrolyte in Metal-Organic Framework Enabling Solid-State Zinc-Ion Batteries.

Uncontrollable interfacial side reactions generated from common aqueous electrolytes, just like the hydrogen evolution reaction (HER) and dendrite growth, have severely prevented the practical application of zinc-ion batteries (ZIBs). Solid-state ZIBs are considered to be an efficient strategy by adopting high-quality solid-state electrolytes (SSEs). Here, by confining deep eutectic electrolyte (DEE) into the nanochannels of metal-organic framework (MOF)-PCN-222, a stable DEE@PCN-222 SSE with internal Zn2+ transport channels was obtained. A distinctive ion-transport network composed of DEE and PCN-222 in the interior of DEE@PCN-222 realizes the efficient Zn2+ conduction, contributing to high ionic conductivity of 3.13×10-4 S cm-1 at room temperature, low activation energy of 0.12 eV, and a high Zn2+ transference number of 0.74. Furthermore, experimental and theoretical investigations demonstrate that DEE@PCN-222 with its unique channel structure could homogeneously regulate the Zn2+ distribution and effectively alleviate the side reactions. Highly reversible Zn plating/stripping performance of 2476 h can be realized by the SSE. The solid-state ZIBs show a specific capacity of 306 mAh g-1 and display cycling stability of 517 cycles. This unique design concept provides a new perspective in realizing the high-safety and high-performance ZIBs.

Highly Anion‐Conductive Viologen‐Based Two‐Dimensional Polymer Membranes as Nanopower Generators

AbstractTwo‐dimensional polymers (2DPs) and their layer‐stacked 2D covalent organic frameworks (2D COFs) membranes hold great potential for harvesting sustainable osmotic energy. The nascent research has yet to simultaneously achieve high ionic flux and selectivity, primarily due to inefficient ion transport dynamics. This is directly related to ultrasmall pore size (&lt;3 nm), much smaller than the duple Debye length in the diluted electrolyte (6–20 nm), as well as low charge density (&lt;4.5 mC m−2). Here, we introduce a π‐conjugated viologen‐based 2DP (V2DP) membrane possessing a large pore size of 4.5 nm, strategically enhancing the overlapping of the electric double layer, coupled with an exceptional positive surface charge density (~6 mC m−2). These characteristics enable the membrane to facilitate high anion flux while maintaining ideal selectivity. Notably, V2DP membranes realize an impressive current density of 5.5×103 A m−2, surpassing benchmarks set by previously reported nanofluidic membranes. In the practical application scenario involving the mixing of artificial seawater and river water, the V2DP membranes exhibit a considerable ion transference number of 0.70 towards Cl−, contributing to an outstanding power density of ~55 W m−2. Theoretical calculations reveal the important role of the large quantity of anion transport sites, which act as binding sites evenly located in the positively charged N‐containing pyridine rings. These binding sites enable kinematic coupling and decoupling between anions and the V2DP skeleton, establishing a continuous Cl− ion transport pathway. This work demonstrates the great promise of large‐area ultrathin 2DP membranes featuring highly organized charged ion transport networks when applied for osmotic energy conversion.

Poly(p-terphenyl-piperidine-bromoacetophenone) anion exchange membranes with pendant N-spirocyclic cations: Cations synergistic build efficient ion transport networks

The establishment of well-developed ionic conduction channels and the preparation of excellent chemical stability are urgent needs for anion exchange membranes. In this study, we successfully prepared poly (p-terphenyl-piperidine-bromoacetophenone) polymers using superacid catalysis. Then a series of QPTPP-N-ASU-x AEMs were prepared by introducing N-spirocyclic side chain cations (N-ASU) with different grafting rates. The introduction of N-spirocyclic cations with better alkali resistance increases multiple OH− transport sites, contributes to the microphase separation structure, and is synergistic with piperidine cations to rapidly construct ion transport networks, giving the membranes good conductivity and alkali resistance stability. The AFM showed that QPTPP-N-ASU-5% AEM had a remarkable microstructure and formed large ionic domains, the conductivity of the membrane was 121.2 mS cm−1, corresponding to a peak power density of 477.25 mW cm−2. The conductivity residual of QPTPP-N-ASU-5% AEM was 94.15 % and 87.71 % after immersion in 2 M and 4 M NaOH at 80 °C for 1440 h. It shows that membrane has good potential for application.

Flexible phase change film with motion sensing and tactile recognition for wearable thermal management

Phase change materials (PCMs) have gained significant interest in personal thermal management technologies owing to high latent heat capacity and isothermal phase transitions. However, achieving simultaneous thermal and wearing comfort remains a formidable challenge due to their solid rigidity and liquid leakage. In this work, a polyetheramine-based conductive phase change film was developed by introducing ion transport network and tetradecanol as phase change components encapsulated within the skeleton network. The film possesses adjustable heat storage density (79.5–163.4 J/g) and exceptional flexibility at room temperature. On the basis of desirable thermal regulation ability and ideal wearability, the film was successfully applied in the personal thermal management field and effectively regulated the human body temperature. Moreover, the film realized human motion sensing and object tactile recognition in real time with construction of the inner ion transport channels. This successful exploration provides a promising and scalable route towards intelligent wearable thermal management.

Highly Efficient Aligned Ion-Conducting Network and Interface Chemistries for Depolarized All-Solid-State Lithium Metal Batteries

HighlightsThis study introduces an innovative 3D-printed electrolyte with vertically aligned ion transport network, which contains well-dispersed nanoscale Ta-doped Li7La3Zr2O12 in a poly(ethylene glycol) diacrylate matrix.The 3DSE architecture enables efficient ion transport across the Li/electrolyte and electrolyte/cathode interfaces, which allows for increased active material mass loading and enhanced interfacial adhesion.The p-3DSE Li symmetric cell displays an impressive critical current density value of 1.92 mA cm−2 and stable operation for 2600 h at room temperature. Full cells using p-3DSE achieve notable areal capacities.

Vanadium pentoxide interfacial layer enables high performance all-solid-state thin film batteries.

Lithium cobalt oxide (LiCoO2) is considered as one of the promising building blocks that can be used to fabricate all-solid-state thin film batteries (TFBs) because of its easy accessibility, high working voltage, and high energy density. However, the slow interfacial dynamics between LiCoO2 and LiPON in these TFBs results in undesirable side reactions and severe degradation of cycling and rate performance. Herein, amorphous vanadium pentoxide (V2O5) film was employed as the interfacial layer of a cathode-electrolyte solid-solid interface to fabricate all-solid-state TFBs using a magnetron sputtering method. The V2O5 thin film layer assisted in the construction of an ion transport network at the cathode/electrolyte interface, thus reducing the electrochemical redox polarization potential. The V2O5 interfacial layer also effectively suppressed the side reactions between LiCoO2 and LiPON. In addition, the interfacial resistance of TFBs was significantly decreased by optimizing the thickness of the interfacial modification layer. Compared to TFBs without the V2O5 layer, TFBs based on LiCoO2/V2O5/LiPON/Li with a 5 nm thin V2O5 interface modification layer exhibited a much smaller charge transfer impedance (Rct) value, significantly improved discharge specific capacity, and superior cycling and rate performance. The discharge capacity remained at 75.6% of its initial value after 1000 cycles at a current density of 100 μA cm-2. This was mainly attributed to the enhanced lithium ion transport kinetics and the suppression of severe side reactions at the cathode-electrolyte interface in TFBs based on LiCoO2/V2O5/LiPON/Li with a 5 nm V2O5 thin layer.

Regulating Ceramic-Polymer Interphase in Composite Solid Electrolytes

Exhibiting satisfactory safety and high energy density, all-solid-state lithium-ion batteries (ASSLBs) is considered as the next-generation energy storage device for green power. Composite solid electrolytes (CSEs) consisting of polymer matrix and active inorganic fillers have shown great potential for practical applications owing to desirable mechanical properties and improved ionic conductivity. However, mechanisms of how different active fillers enhance the ion transport in CSEs still remain inconclusive and comprehensive properties of CSEs need to be improved to meet the demand for high-performance ASSLBs. Our work focuses on the mechanism of Li ion transportation in CSEs and the interaction among polymer matrix, inorganic active fillers and Li-salts. Further, the specific insights into the improving mechanism are applied to the design of CSEs with ideal overall performance.First, NASICON-type (LATP) and garnet-type (LLZTO) inorganic solid electrolytes are utilized as active fillers to incorporate with poly (ethylene oxide) PEO matrix. The experimental and computational results shown that the high affinity between LATP and PEO facilitates unhindered interfacial Li+ transfer, so that LATP functions as bulk-active filler to provide additional inorganic ion pathway. Instead, anion-trapping LLZTO mainly improves the ion conductivity by dissociating lithium salt, making it an interface-active filler. Therefore, the as-prepared PEO-LATP CSEs achieve the highest ion conductivity with medium filler content (50wt%) due to the well-built synergistic ion transport tunnels. By contrast, PEO-LLZTO peak at low filler content (10wt%) attributed to the maximized interfacial interactions.Next, based on the above findings, surface defects are introduced to interface-active LLZTO to not only enhance the anion-trapping effect, but also serve as anchoring points for polymer chains, forming a firmly bonded polymer-ceramic interface. The as-prepared OV-LLZTO/PEO composite exhibits high mechanical strength, reduced interfacial resistance with electrodes as well as improved Li+ conductivity.Further, Li-salt combination in CESs is optimized to improve the electrode compatibility for higher energy density. With the interaction of interface-active LLZTO and main lithium salt, functional additive has access to more preferable coordination. As a result, robust inorganic-rich electrode/electrolyte interface with high ionic conductivity can be synergistically constructed. More importantly, stable and fast ion transport network is built inside the high-volt LCO cathode, thus high rate performance and high capacity retentions achieved in Li|PEO-LLZTO|LCO cells with charging cut-off of 4.2 V.To summarize, we have first revealed ion conduction mechanisms in CSEs, then optimization approaches such as surface defects introduction on the active fillers and Li-salt modification are employed to improve the critical properties of CSE (e.g. ionic conductivity, mechanical strength, interfacial contact and interfacial stability between electrode and electrolyte). These works jointly point out a new principle for the design of high-performance CSEs via regulating the ceramic-polymer interphases. Figure 1

Highly ion-conducting, robust and environmentally stable poly(vinyl alcohol) eutectic gels designed by natural polyelectrolytes for flexible wearable sensors and supercapacitors

Flexible conductive materials have received a lot of attention due to their versatility in wearable devices, etc. Eutectic gels are expected to replace the traditional hydrogel as a new generation of soft conductors. Here, sodium alginate (SA), a polysaccharide polyelectrolyte with surface charge, was ingeniously used to construct the energy dissipation and ion transport network. Thus, a double-network polyvinyl alcohol composite eutectic gel with various physical effects was prepared by salting out and solvent replacement process. The obtained gels showed excellent mechanical properties, frost resistance and stability; the maximum fracture strain and toughness can reach 3.87 MPa and 9.87 MJ/m3, respectively. Surprisingly, the –COO− contained in SA plays an active role in the ion transport, and the conductivity (0.30 S/m) was improved by 5 times. Based on this composite gel, a supercapacitor with a wide operating window of 1.7 V and good cyclic charging and discharging stability (capacitance retention at 82.1 % after 1500 cycles) was prepared. And the prepared sensor can sensitively monitor the movement of human joints and perform handwriting recognition. This strategy realizes the balance between mechanical properties and conductivity of eutectic gel and opens up the application of natural polyelectrolytes in the construction of high-performance ion-transport networks.

In-situ coupling construction of interface bridge to enhance electrochemical stability of all solid-state lithium metal batteries

Polymer-based composite electrolytes composed of three-dimensional Li6.4La3Zr2Al0.2O12 (3D-LLZAO) have attracted increasing attention due to their continuous ion conduction and satisfactory mechanical properties. However, the organic/inorganic interface is incompatible, resulting in slow lithium-ion transport at the interface. Therefore, the compatibility of organic/inorganic interface is an urgent problem to be solved. Inspired by the concept of “gecko eaves”, polymer-based composite solid electrolytes with dense interface structures were designed. The bridging of organic/inorganic interfaces was established by introducing silane coupling agent (3-chloropropyl)trimethoxysilane (CTMS) into the PEO-3D-LLZAO (PL) electrolyte. The in-situ coupling reaction improves the interface affinity, strengthens the organic/inorganic interaction, reduces the interface resistance, and thus achieves an efficient interface ion transport network. The prepared PEO-3D-LLZAO-CTMS (PLC) electrolyte exhibits enhanced ionic conductivity of 6.04 × 10−4 S cm−1 and high ion migration number (0.61) at 60 °C and broadens the electrochemical window (5.1 V). At the same time, the PLC electrolyte has good thermal stability and high mechanical properties. Moreover, the LiFePO4|PLC|Li battery has excellent rate performance and cycling stability with a capacity decay rate of 2.2% after 100 cycles at 60 °C and 0.1 C. These advantages of PLC membranes indicate that this design approach is indeed practical, and the in-situ coupling method provides a new approach to address interface compatibility issues.

Confined amphipathic ionic-liquid regulated anodic aluminum oxide membranes with adjustable ion selectivity for improved osmotic energy conversion

To attain carbon neutrality and carbon peaking, there is an urgent need to convert the vast amount of blue energy present between seawater and river water into usable electricity. Reverse electrodialysis based on ion-exchange membranes is a promising way to efficiently achieve osmotic energy conversion. Anodic aluminum oxide (AAO) membranes are frequently used for osmotic energy harvesting because of their uniform nanopore channels, high flux, and excellent stability. However, the existing surface modification methods are complex and inefficient. In this study, an amphiphilic ionic liquid was selected to modify a porous anodic alumina membrane via simple capillary insertion. Due to the abundance of pH-dependent amphiphilic OH groups on the surface of AAO pore channels, the ionic liquids not only provide abundant surface charge but can also intelligently adjust its surface charge to different environments. In addition, it fills the AAO nanochannels to provide a continuous ion transport network. The modified hybrid membrane achieves efficient and stable osmotic energy conversion performance. This simple and feasible strategy paves the way for further improvements in commercial membranes.

Fabrication of dense anion exchange membranes by filling polymer matrix into quaternized branched polyethyleneimine @cellulose aerogel through in-situ polymerization

In order to construct interconnected three-dimensional ion transport structures within anion exchange membranes (AEMs), we proposed the idea of preparing AEMs by filling the aerogel three-dimensional network skeleton by in-situ polymerization. First, quaternized branched polyethyleneimine (QBPEI) with a large number of quaternary ammonium groups was cross-linked with cellulose to construct an aerogel with a three-dimensional network. Then, poly(4-vinylbenzyl chloride) (PVBC) was filled into the aerogel network through in-situ polymerization. Finally, dense AEMs with internal three-dimensional ion transport networks were prepared by hot pressing PVBC/QBPEI@cellulose. The prepared AEMs have low ion exchange capacity (IEC) values and high ionic conductivities, with the membrane with the best overall performance (IEC value of 1.58 meq./g) having a maximum hydroxide conductivity of 38.88 mS/cm at 80 °C. In addition, the optimized membrane has good chemical and dimensional stability, and the maximum power density of the fuel cell assembled based on it is 46.32 mW/cm2. Although the performance of the prepared composite membranes needs to be further improved due to the preparation process, the design idea in this work provides a feasible solution for the construction of continuous ion fast transport channels in AEMs.

Design and Optimization of Composite Cathodes for Solid-State Batteries Using Hybrid Carbon Networks with Facile Electronic and Ionic Percolation Pathways.

Solid-state batteries (SSBs) have emerged as a promising alternative to conventional liquid electrolyte batteries due to their potential for higher energy density and improved safety. However, achieving high performance in SSBs is difficult because of inadequate contact and interfacial reactions that generate high interfacial resistance, as well as inadequate solid-solid contact between electrodes. These chronic issues are associated with inhomogeneous ion and electron transport networks owing to imperfect solid-solid interfacial contact. This study developed an optimal interfacial engineering strategy to facilitate an ion-electron transport network by designing an active material (NCM622) uniformly filled with a thin layer of a solid electrolyte (garnet-type Li6.25Ga0.25La3Zr2O12) and conductive additives. The optimal composite electrode architecture enhanced the high capacity, high rate capability, and long-term cycle stability, even at room temperature, owing to the percolating network for facile ionic conduction that assured a homogeneous reaction. In addition to mitigating the mechanical degradation of the cathode electrode, it also reduced the crosstalk effects on the anode-solid electrolyte interface. Effectively optimizing the selection and use of conductive additives in composite electrodes offers a promising approach to addressing key performance-limiting factors in SSBs, including interfacial resistance and solid-solid contact issues. This study underscores the critical importance of cathode architecture design for achieving high-performance SSBs by ensuring that the interfaces are intact with solid electrolytes at both the cathode and anode interfaces while promoting uniform reactions. This study provides valuable insights into the development of SSBs with improved performance, which could have significant implications for a wide range of applications.

Oriented Porous NASICON 3D Framework via Freeze-Casting for Sodium-Metal Batteries.

Sodium-metal batteries are promising candidates for low-cost, large-format energy storage systems. However, sodium-metal batteries suffer from high interfacial resistance between the electrodes and the solid electrolyte, leading to poor electrochemical performance. We demonstrate a sodium superionic conductor (NASICON) with an oriented porous framework of sodium aluminum titanium phosphate (NATP) fabricated by the freeze-casting technique, which shows excellent properties as a solid electrolyte. Using X-ray computed tomography, we confirm the uniform low-tortuosity channels present along the thickness of the scaffold. We infiltrated the porous NATP scaffolds with sodium vanadium phosphate (NVP) cathode nanoparticles achieving mass loadings of ∼3-4 mg cm-2, which enables short sodium ion diffusion path lengths. For the resulting hybrid cell, we achieved a capacity of ∼90 mAh g-1 at a specific current of 50 mA g-1 (∼300 Wh kg-1) for over 100 cycles with ∼94% capacity retention. Our study offers valuable insights for the design of hybrid solid electrolyte-cathode active material structures to achieve improved electrochemical performance through low-tortuosity ion transport networks.

Cathode electrode architecture with facile ion percolating network assuring interfacial integrity for high-performance solid-state batteries

Although solid-state batteries (SSBs) are promising next-generation energy-storage devices owing to their high safety and energy density, their wide application is hindered by critical issues such as poor power density and rapid performance degradation. These issues are related to the limit of electronic and lithium percolation networks with imperfect solid–solid interfacial contact. This study develops an optimal strategy to facilitate an ion-transport network by designing a simple core–shell–like cathode covered by an inorganic solid electrolyte (garnet-type Li6.25Ga0.25La3Zr2O12) for polymer-based SSBs, ensuring the high capacity, high rate capability, and long-term cycle stability even in practical pouch cell at room temperature. Encapsulated cathode electrode architecture via a simple dry-coating strategy provides a percolating network for facile ionic conduction, assuring the homogeneous reaction in the cathode electrode. It alleviates not only the mechanical degradation of the cathode electrode but also the subsequent crosstalk effect on the anode–solid electrolyte interface. Our study highlights that the design of the cathode architecture considering the ion-conducting network is crucial to secure the high performance of polymer-based SSBs by maintaining the interfaces intact with solid electrolytes in both the cathode and anode interfaces.

Inhibiting Formation and Reduction of Li2 CO3 to LiCx at Grain Boundaries in Garnet Electrolytes to Prevent Li Penetration.

Poor ion and high electron transport at the grain boundaries (GBs) of ceramic electrolytes are the primary reasons for lithium filament infiltration and short-circuiting of all-solid-state lithium metal batteries (ASLMBs). Herein, it is discovered that Li2 CO3 at the GBs of Li7 La3 Zr2 O12 (LLZO) sheets is reduced to highly electron-conductive LiCx during cycling, resulting in lithium penetration of LLZO. The ionic and electronic conductivity of the GBs within LLZO can be simultaneously tuned using sintered Li3 AlF6 . The generated LiAlO2 (LAO) infusion and F-doping at the GBs of LLZO (LAO-LLZOF) significantly reduce the Li2 CO3 content and broaden the energy bandgap of LLZO, which decreases the electronic conductivity of LAO-LLZOF. LAO forms a 3D continuous ion transport network at the GB that significantly improves the total ionic conductivity. Lithium penetration within LLZO is suppressed and an all-solid-state LiFePO4 /LAO-LLZOF/Li battery stably cycled for 5500 cycles at 3C. This work reveals the chemistry of Li2 CO3 at the LLZO GBs during cycling, presents a novel lithium penetration mechanism within garnet electrolytes, and provides an innovative method to simultaneously regulate the ion and electron transport at the GBs in garnet electrodes for advanced ASLMBs.

Enhanced ionic conductivity in a novel composite electrolyte based on Gd-doped SnO2 nanotubes for ultra-long-life all-solid-state lithium metal batteries

All-solid-state electrolytes are exceedingly attractive because of the outstanding inherent safety and energy density compared to liquid electrolytes. Whereas, it is still formidable to simultaneously design solid electrolytes with favorable electrode/electrolyte interface compatibility and high ionic conductivity in a simple and scalable manner. Hence, the oxygen-vacancy-rich Gd-doped SnO2 nanotubes (GDS NTs) are innovatively prepared and applied to the electrolyte of all-solid-state lithium metal batteries for the first time. The addition of GDS NTs can validly construct long-range continuous ion transport networks in the poly(ethylene oxide) (PEO)-based system and greatly improve the mechanical properties of the electrolyte. Compared to the PEO-based electrolyte, the composite electrolyte displays a higher lithium ion conductivity of 2.41 × 10–4 S cm−1 at 30 ℃, a higher lithium ion transference number up to 0.62 and a wider electrochemical window of 5 V at 50 ℃. In addition, the composite electrolyte manifests outstanding compatibility with high-voltage LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode, LiFePO4 cathode and lithium metal anode. The assembled Li/Li symmetric battery exhibits stable Li plating/stripping cycling performance, which can cycle steadily for 1500 h at a capacity of 0.3 mA h cm−2. And Li/LiFePO4 battery still maintains a high capacity of 131.54 mA h g−1 at 0.5C after 800 cycles, which has a superior capacity retention rate of 93.2%. The obtained novel composite electrolyte has promising application prospects in the field of all-solid-state lithium metal cells.