Overcoming the Interfacial Limitations Imposed by the Solid-Solid Interface in Solid-State Batteries Using Ionic Liquid-Based Interlayers

Enabling High-Performance Hybrid Solid-State Batteries by Improving the Microstructure of Free-Standing LATP/LFP Composite Cathodes

The phosphate lithium-ion conductor Li1.5Al0.5Ti1.5(PO4)3 (LATP) is an economically attractive solid electrolyte for the fabrication of safe and robust solid-state batteries, but high sintering temperatures pose a material engineering challenge for the fabrication of cell components. In particular, the high surface roughness of composite cathodes resulting from enhanced crystal growth is detrimental to their integration into cells with practical energy density. In this work, we demonstrate that efficient free-standing ceramic cathodes of LATP and LiFePO4 (LFP) can be produced by using a scalable tape casting process. This is achieved by adding 5 wt % of Li2WO4 (LWO) to the casting slurry and optimizing the fabrication process. LWO lowers the sintering temperature without affecting the phase composition of the materials, resulting in mechanically stable, electronically conductive, and free-standing cathodes with a smooth, homogeneous surface. The optimized cathode microstructure enables the deposition of a thin polymer separator attached to the Li metal anode to produce a cell with good volumetric and gravimetric energy densities of 289 Wh dm-3 and 180 Wh kg-1, respectively, on the cell level and Coulombic efficiency above 99% after 30 cycles at 30 °C.

Challenges and Recent Progress on Solid-State Batteries and Electrolytes, using Qualitative Systematic Analysis. A Short Review

The rise in the energy demand, the need to decrease the use of fossil fuels, expanding investments in renewable energy and boosting the electric vehicle market, opens the door to new technologies in clean energy accumulators. Lithium-ion batteries are the most advanced technology in the market but have safety concerns due to the flammability of the electrolyte, which opens the door to innovations. One of these innovations is the solid-state batteries (SSB), which, by using solid electrolytes, do not have the flammable risk, bringing safety to users while reaching similar energy and power densities. This work presents a review about SSB, based on qualitative and exploratory research, using the Web of Science (WoS) platform. Keywords used to gather information from the database were "solid state batteries" and "electrolytes". Only publications from 2018 to 2023 were selected. The main research focus is to solve the challenges posed by the different physical-chemical phenomena of the SSB. This work focuses on the general comprehension of the SSB batteries, what are the factors that can affect it and the main solutions presented in the literature the last five years.

Advancements in Quasi-Solid-State Li Batteries: A Rigid Hybrid Electrolyte Using LATP Porous Ceramic Membrane and Infiltrated Ionic Liquid

Despite the progress made in Li-ion battery components, technology still faces major challenges. Among them, the development of novel electrolytes with promising characteristics is required for next-generation energy storage devices. In this work, rigid hybrid electrolytes have been prepared by infiltration of an ionic liquid solution (Pyr14TFSI) with a lithium salt (LiTFSI) into a sintered LATP ion-conducting porous ceramic. The porous ceramic 3D network was obtained via solid-state sintering of LATP powders mixed with a small amount of corn starch as pore former. A synergetic effect between the ionic liquid and support was evidenced. The resultant quasi-solid-state hybrid electrolytes exhibit high ionic conductivity (∼10-3 S·cm-1 at 303 K), improved ion transfer number, tLi+, and a wide electrochemical window of 4.7-4.9 V vs Li+/Li. The LATP porosity plays a critical role in the free Li+ charge because it favors higher TFSI- confinement in the ceramic interfaces, which consequently positively influences tLi+ and ionic conductivity. Electrochemical tests conducted at room temperature for Li/LiFePO4 cells using the hybrid electrolyte exhibited a high capacity of 150 mAh·g-1LFP at C/30, and still retained 60 mAh·g-1LFP at 1 C, while bare LATP does not perform well at low temperatures. These findings highlight this hybrid electrolyte as a superior alternative to the ceramic LATP electrolyte and a safer option compared with conventional organic electrolytes.

Confining Ionic Liquids in Developing Quasi-Solid-State Electrolytes for Lithium Metal Batteries

The concept of confining ionic liquids (ILs) in developing quasi-solid-state electrolytes (QSSEs) has been proposed, where ILs are dispersed in polymer networks/backbones and/or filler/host pores, forming the so-called confinement, and great research progress and promising research results have been achieved. In this review, the progress and achievement in developing QSSEs using IL-confinement for lithium metal batteries (LMBs), together with advanced characterizations and simulations, were surveyed, summarized, and analyzed, where the influence of specific parameters, such as IL (type, content, etc.), substrate (type, structure, surface properties, etc.), confinement methods, and so on, was discussed. The confinement concept was further compared with the conventional one in other research areas. It indicates that the IL-confinement in QSSEs improves the performance of electrolytes, for example, increasing the ionic conductivity, widening the electrochemical window, and enhancing the cycle performance of the assembled cells, and being different from those in other areas, that is, the IL-confinement concept in the battery area is in a broad extent. Finally, insights into developing QSSEs in LMBs with the confinement strategy were provided to promote the development and application of QSSE LMBs.

Interfacial Modification of Ga-Substituted Li7La3Zr2O12 against Li Metal via a Simple Doping Method

Garnet Li7La3Zr2O12 (LLZO) is considered a promising solid electrolyte for all-solid-state lithium-ion batteries due to its outstanding performance in which Ga-doped LLZO particularly exhibits excellent ionic conductivity. However, the application of Ga-doped LLZO is limited by the interfacial instability between Ga-doped LLZO and Li metal. In this study, Ga3+- and Sb5+-codoped LLZO is prepared using a conventional solid-state reaction method, and the effects of dual-doping on the crystal structure, microstructure, conductivity of LLZO, and battery cycle stability are investigated. The results demonstrate that the introduction of an appropriate amount of Sb5+ into Ga3+-stabilized cubic-phase LLZO promotes grain contact and enhances the total ionic conductivity. The optimized Li6.3Ga0.2La3Zr1.9Sb0.1O12 solid electrolyte exhibits the highest total ionic conductivity of 4.65 × 10-4 S cm-1 at room temperature. Additionally, the introduction of Sb5+ suppresses the formation of the LiGaO2 impurity phase, thereby improving the interface stability between Ga-doped LLZO and the Li metal. The assembled Li||Ga,Sb0.1-LLZO||Li symmetric cell demonstrates stable cycling for 500 h at room temperature under a current density of 0.13 mA cm-2. The Li||Ga,Sb0.1-LLZO||LiFePO4 full cell delivers a reversible capacity of about 140 mA h g-1, exhibiting negligible decay after 50 cycles. These findings suggest that the application of Ga-doped LLZO in all-solid-state lithium-ion batteries holds great promise by simply doping Zr sites with high-valence ions.

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.

Review of the Developments and Difficulties in Inorganic Solid-State Electrolytes

All-solid-state lithium-ion batteries (ASSLIBs), with their exceptional attributes, have captured the attention of researchers. They offer a viable solution to the inherent flaws of traditional lithium-ion batteries. The crux of an ASSLB lies in its solid-state electrolyte (SSE) which shows higher stability and safety compared to liquid electrolyte. Additionally, it holds the promise of being compatible with Li metal anode, thereby realizing higher capacity. Inorganic SSEs have undergone tremendous developments in the last few decades; however, their practical applications still face difficulties such as the electrode-electrolyte interface, air stability, and so on. The structural composition of inorganic electrolytes is inherently linked to the advantages and difficulties they present. This article provides a comprehensive explanation of the development, structure, and Li-ion transport mechanism of representative inorganic SSEs. Moreover, corresponding difficulties such as interface issues and air stability as well as possible solutions are also discussed.

Bilayer Dense-Porous Li7 La3 Zr2 O12 Membranes for High-Performance Li-Garnet Solid-State Batteries

Li dendrites form in Li₇ La₃ Zr₂ O₁₂ (LLZO) solid electrolytes due to intrinsic volume changes of Li and the appearance of voids at the Li metal/LLZO interface. Bilayer dense-porous LLZO membranes make for a compelling solution of this pertinent challenge in the field of Li-garnet solid-state batteries (SSB). Lithium is thus stored in the pores of the LLZO, thereby avoiding i) dynamic changes of the anode volume and ii) the formation of voids during Li stripping due to increased surface area of the Li/LLZO interface. The dense layer then additionally reduces the probability of short circuits during cell charging. In this work, a method for producing such bilayer membranes utilizing sequential tape-casting of porous and dense layers is reported. The minimum attainable thicknesses are 8-10 µm for dense and 32-35 µm for porous layers, enabling gravimetric and volumetric energy densities of Li-garnet SSBs of 279 Wh kg^-1 and 1003 Wh L^-1 , respectively. Bilayer LLZO membranes in symmetrical cell configuration exhibit high critical current density up to 6 mA cm^-2 and cycling stability of over 160 cycles at a current density of 0.5 mA cm^-2 at an areal capacity limitation of 0.25 mAh cm^-2 .

Enhancing the Interfacial Stability of the Li2S-SiS2-P2S5 Solid Electrolyte toward Metallic Lithium Anode by LiI Incorporation

Chalcogenide solid-state electrolytes (SEs) have been regarded as promising candidates for lithium dendrite suppression due to their high ionic conductivity, suitable mechanical strength, and large Li⁺ ion transference number. However, the wide applications of SEs in pragmatic all-solid-state batteries are still retarded by their limited interface stability, which leads to lithium dendrite growth and formation of interphase with high resistance. In addition, the interphase evolution mechanism between SEs and metallic Li anodes remains unclear. Herein, this work demonstrates that the interfacial stability of Li₂S-SiS₂-P₂S₅ SEs can be effectively enhanced by tuning the interphase through LiI incorporation. This strategy contributes to a high ionic conductivity of the SEs and electronic insulation interphase containing LiI. Thus, the 70(60Li₂S-28SiS₂-12P₂S₅)-30 LiI SEs prepared by melt-quenching exhibit a high ionic conductivity of 1.74 mS cm^-1 at room temperature and a larger critical current density of 1.65 mA cm^-2 at 65 °C. The cycling life of the symmetric Li|SEs|Li cell is up to 200 h without significant resistance growth at 0.1 mA cm^-2 at room temperature. This enhanced interface stability is revealed to originate from the in situ-formed LiI within the interphase, which prevents continual SEs degradation and suppresses lithium dendrite growth. This work provides a vital understanding of interphase evolution, which is valuable for designing SEs with long cycling stability.

Recent Advances in Polymers for Potassium Ion Batteries

Potassium-ion batteries (KIBs) are considered to be an effective alternative to lithium-ion batteries (LIBs) due to their abundant resources, low cost, and similar electrochemical properties of K⁺ to Li⁺, and they have a good application prospect in the field of large-scale energy storage batteries. Polymer materials play a very important role in the battery field, such as polymer electrode materials, polymer binders, and polymer electrolytes. Here in this review, we focus on the research progress of polymers in KIBs and systematically summarize the research status and achievements of polymer electrode materials, electrolytes, and binders in potassium ion batteries in recent years. Finally, based on the latest representative research of polymers in KIBs, some suggestions and prospects are put forward, which provide possible directions for future research.

Electrolytes for Multivalent Metal-Ion Batteries: Current Status and Future Prospect

Electrochemical energy storage has experienced unprecedented advancements in recent years and extensive discussions and reviews on the progress of multivalent metal-ion batteries have been made mainly from the aspect of electrode materials, but relatively little work comprehensively discusses and provides an outlook on the development of electrolytes in these systems. Under this circumstance, this Review will initially introduce different types of electrolytes in current multivalent metal-ion batteries and explain the basic ion conduction mechanisms, preparation methods, and pros and cons. On this basis, we will discuss in detail the research and development of electrolytes for multivalent metal-ion batteries in recent years, and finally, critical challenges and prospects for the application of electrolytes in multivalent metal-ion batteries will be put forward.

Stabilizing High-Voltage Cathodes via Ball-Mill Coating with Flame-Made Nanopowder Electrolytes

LiMn1.5Ni0.5O4 (LMNO) spinel has recently been the subject of intense research as a cathode material because it is cheap, cobalt-free, and has a high discharge voltage (4.7 V). However, the decomposition of conventional liquid electrolytes on the cathode surface at this high oxidation state and the dissolution of Mn2+ have hindered its practical utility. We report here that simply ball-mill coating LMNO using flame-made nanopowder (NPs, 5-20 wt %, e.g., LiAlO2, LATSP, LLZO) electrolytes generates coated composites that mitigate these well-recognized issues. As-synthesized composite cathodes maintain a single P4332 cubic spinel phase. Transmission electron microscopy (TEM) and X-ray photoelectron spectra (XPS) show island-type NP coatings on LMNO surfaces. Different NPs show various effects on LMNO composite cathode performance compared to pristine LMNO (120 mAh g-1, 93% capacity retention after 50 cycles at C/3, ∼67 mAh g-1 at 8C, and ∼540 Wh kg-1 energy density). For example, the LMNO + 20 wt % LiAlO2 composite cathodes exhibit Li+ diffusivities improved by two orders of magnitude over pristine LMNO and discharge capacities up to ∼136 mAh g-1 after 100 cycles at C/3 (98% retention), while 10 wt % LiAlO2 shows ∼110 mAh g-1 at 10C and an average discharge energy density of ∼640 Wh kg-1. Detailed postmortem analyses on cycled composite electrodes demonstrate that NP coatings form protective layers. In addition, preliminary studies suggest potential utility in all-solid-state batteries (ASSBs).

Solid Electrolyte-Cathode Interface Dictates Reaction Heterogeneity and Anode Stability

Solid-state batteries (SSBs) employing a lithium metal anode are a promising candidate for next-generation energy storage systems, delivering higher power and energy densities. Interfacial instabilities due to non-uniform electrodeposition at the anode-solid electrolyte (SE) interface pose major constraints on the safety and endurance of SSBs. In this regard, non-uniform kinetic interactions at the anode-SE interface which are derived from cathode microstructural heterogeneity can have significant impact on anode stability. In this work, we present a comprehensive insight into microstructural heterogeneity-driven cathode-anode cross-talk and delineate the role of cathode architecture and SE separator design in dictating reaction heterogeneity at the anode-SE interface. We show that intrinsic and extrinsic parameters, such as cathode loading, separator thickness, particle morphologies of active material and SE, and temperature can have significant impact on reaction heterogeneity at the anode-SE interface and thus govern anode stability. Tradeoff between energy density and anode stability while achieving higher cathode loading and thinner SE separators is highlighted, and potential strategies to mitigate this problem are discussed. This work provides fundamental insights into cathode-anode cross-talk involving interfacial heterogeneities and enhancement in energy densities of SSBs via electrode engineering.

Ga-Doped LLZO Solid-State Electrolyte with Unique "Plate-like" Morphology Derived from Water Hyacinth (Eichhornia crassipes) Aquatic Weed: Waste to Wealth Conversion

An attempt has been made for the first time to convert waste biomass such as water hyacinth (WH) to a functional energy material in a cost-effective way. The present research describes a novel exo-templating methodology to develop engineered microstructure of Ga-doped Li₇La₃Zr₂O₁₂ (Li_6.25La₃Ga_0.25Zr₂O₁₂, referred as WH-Ga-LLZO) solid-state electrolyte for its use in all solid-state lithium batteries (ASSLBs) by mimicking the intercellular structure of water hyacinth (Eichhornia crassipes), an invasive and noxious aquatic plant. The developed exo-templated methodology offers a low calcination temperature of 1000 °C in air where all the major peaks could be indexed as cubic garnet, as confirmed by XRD. The FESEM micrographs revealed a unique "plate-like" morphology that mimicked the intercellular structure of water hyacinth fiber. The bulk lithium-ion conductivity in the WH-Ga-LLZO electrolyte was found to be 3.94 × 10^-5 S/cm. Li/WH-Ga-LLZO/Li cells were galvanostatically cycled for a continuous 295 h with increasing step current densities from 28 μA/cm² without a short circuit. The highest current density as measured for maximum polarization in a symmetric cell was found to be 452 μA/cm². The WH exo-templated methodology was thus developed and optimized and can be extended for synthesizing any application-specific multifunctional materials.

Metal-Organic Framework Confined Solvent Ionic Liquid Enables Long Cycling Life Quasi-Solid-State Lithium Battery in Wide Temperature Range

Solid-state Li batteries are receiving increasing attention as a prospective energy storage system due to the high energy density and improved safety. However, the high interfacial resistance between solid-state electrolyte and electrode results in sluggish Li⁺ transport kinetics. To tackle the interfacial problem and prolong the cycle life of solid-state Li batteries, a quasi-solid-state electrolyte (QSSE) based on a solvate ionic liquid (SIL) space-restricted in nanocages of UIO-66 (SIL/UIO-66) is prepared in this study. Benefiting from the effective spatial confinement of the TFSI^- by the pore UIO-66 and the strong chemical interactions between the SIL and metal atoms, SIL/UIO-66 QSSE exhibits high ionic conductivity and good compatibility with electrodes. As a result, Li|QSSE|LFP cells demonstrate excellent rate capability and cycle stability in a wide temperature range of 25-90 °C. This study provides a realistic strategy for the fabrication of safe solid electrolytes with excellent compatibility and long cycle life for high-performance QSSE Li-ion batteries.

Inorganic–Organic Hybrid Electrolytes Based on Al-Doped Li7La3Zr2O12 and Ionic Liquids

Organic–inorganic hybrid electrolytes based on Al-doped Li7La3Zr2O12 (LLZO) and two different ionic liquids (ILs), namely N-ethoxyethyl-N-methylpiperidinium bis(fluorosulfonyl)imide (FSI IL) and N-ethoxyethyl-N-methylpiperidinium difluoro(oxalato)borate (DFOB IL), were prepared with the aim of improvement of inherent flexibilities of inorganic solid electrolytes. The composites were evaluated in terms of thermal, spectroscopical, and electrochemical properties. In the impedance spectra of LLZO composites with 15 wt% ILs, a semi-circle due to grain boundary resistances was not observed. With the sample merely pressed with 1 ton, without any high-temperature sintering process, the ionic conductivity of 10−3 S cm−1 was achieved at room temperature. Employing a ternary composite of LLZO, FSI IL, and LiFSI as an electrolyte, all-solid-state lithium metal batteries having LiFePO4 as a cathode were assembled. The cell exhibited a capacity above 100 mAh g−1 throughout the course of charge–discharge cycle at C/20. This confirms that FSI IL is an effective additive for inorganic solid electrolytes, which can guarantee the ion conduction.

Stabilizing the Li1.3 Al0.3 Ti1.7 (PO4 )3 |Li Interface for High Efficiency and Long Lifespan Quasi-Solid-State Lithium Metal Batteries

To tackle the poor chemical/electrochemical stability of Li_1+x Al_x Ti_2-x (PO₄ )₃ (LATP) against Li and poor electrode|electrolyte interfacial contact, a thin poly[2,3-bis(2,2,6,6-tetramethylpiperidine-N-oxycarbonyl)norbornene] (PTNB) protection layer is applied with a small amount of ionic liquid electrolyte (ILE). This enables study of the impact of ILEs with modulated composition, such as 0.3 lithium bis(fluoromethanesulfonyl)imide (LiFSI)-0.7 N-butyl-N-methylpyrrolidinium bis(fluoromethanesulfonyl)imide (Pyr₁₄ FSI) and 0.3 LiFSI-0.35 Pyr₁₄ FSI-0.35 N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr₁₄ TFSI), on the interfacial stability of PTNB@Li||PTNB@Li and PTNB@Li||LiNi_0.8 Co_0.1 Mn_0.1 O₂ cells. The addition of Pyr₁₄ TFSI leads to better thermal and electrochemical stability. Furthermore, Pyr₁₄ TFSI facilitates the formation of a more stable Li|hybrid electrolyte interface, as verified by the absence of lithium "pitting corrosion islands" and fibrous dendrites, leading to a substantially extended lithium stripping-plating cycling lifetime (>900 h). Even after 500 cycles (0.5C), PTNB@Li||LiNi_0.8 Co_0.1 Mn_0.1 O₂ cells achieve an impressive capacity retention of 89.1 % and an average Coulombic efficiency of 98.6 %. These findings reveal a feasible strategy to enhance the interfacial stability between Li and LATP by selectively mixing different ionic liquids.

Unveiling the Cation Exchange Reaction between the NASICON Li1.5Al0.5Ge1.5(PO4)3 Solid Electrolyte and the pyr13TFSI Ionic Liquid

Recently, the formation of the ceramic-ionic liquid composite has attracted huge interest in the scientific community. In this work, we investigated the chemical reactions occurring between NASICON LAGP ceramic electrolyte and ionic liquid pyr13TFSI. This study allowed us to identify the cation exchange reaction pyr13-Li occurring on the LAGP surface, forming a LiTFSI salt that was detected by the nuclear magnetic resonance analysis. In addition, using ⁶Li foils, we succeeded in demonstrating that both LAGP and LiTFSI:pyr13TFSI participate in the diffusion of Li ions by the formation of an ionic bridge between two species.

On the feasibility of all-solid-state batteries with LLZO as a single electrolyte

Replacement of Li-ion liquid-state electrolytes by solid-state counterparts in a Li-ion battery (LIB) is a major research objective as well as an urgent priority for the industry, as it enables the use of a Li metal anode and provides new opportunities to realize safe, non-flammable, and temperature-resilient batteries. Among the plethora of solid-state electrolytes (SSEs) investigated, garnet-type Li-ion electrolytes based on cubic Li₇La₃Zr₂O₁₂ (LLZO) are considered the most appealing candidates for the development of future solid-state batteries because of their low electronic conductivity of ca. 10⁻⁸ S cm⁻¹ (RT) and a wide electrochemical operation window of 0–6 V vs. Li⁺/Li. However, high LLZO density (5.1 g cm⁻³) and its lower level of Li-ion conductivity (up to 1 mS cm⁻¹ at RT) compared to liquid electrolytes (1.28 g cm⁻³; ca. 10 mS cm⁻¹ at RT) still raise the question as to the feasibility of using solely LLZO as an electrolyte for achieving competitive energy and power densities. In this work, we analyzed the energy densities of Li-garnet all-solid-state batteries based solely on LLZO SSE by modeling their Ragone plots using LiCoO₂ as the model cathode material. This assessment allowed us to identify values of the LLZO thickness, cathode areal capacity, and LLZO content in the solid-state cathode required to match the energy density of conventional lithium-ion batteries (ca. 180 Wh kg⁻¹ and 497 Wh L⁻¹) at the power densities of 200 W kg⁻¹ and 600 W L⁻¹, corresponding to ca. 1 h of battery discharge time (1C). We then discuss key challenges in the practical deployment of LLZO SSE in the fabrication of Li-garnet all-solid-state batteries.

Efficient Anion Fluoride-Doping Strategy to Enhance the Performance in Garnet-Type Solid Electrolyte Li7La3Zr2O12

Garnet-type solid-state electrolyte Li₇La₃Zr₂O₁₂ (LLZO) is expected to realize the next generation of high-energy-density lithium-ion batteries. However, the severe dendrite penetration at the pores and grain boundaries inside the solid electrolyte hinders the practical application of LLZO. Here, it is reported that the desirable quality and dense garnet Li_6.8Al_0.2La₃Zr₂O_11.80F_0.20 can be obtained by fluoride anion doping, which can effectively facilitate grain nucleation and refine the grain; thereby, the ionic conductivity increased to 7.45 × 10^-4 at 30 °C and the relative density reached to 95.4%. At the same time, we introduced a transition layer to build the Li_6.8Al_0.2La₃Zr₂O_11.80F_0.20-t electrolyte in order to supply a stable contact; as a result, the interface resistance of Li|Li_6.8Al_0.2La₃Zr₂O_11.80F_0.20-t decreases to 12.8 Ω cm². The Li|Li_6.8Al_0.2La₃Zr₂O_11.80F_0.20-t|Li symmetric cell achieved a critical current density of 1.0 mA cm^-2 at 25 °C, which could run stably for 1000 h without a short circuit at 0.3 mA cm^-2 and 25 °C. Moreover, the Li|LiFePO₄ battery exhibited a high Coulombic efficiency (>99.5%), an excellent rate capability, and a great capacity retention (123.7 mA h g^-1, ≈80%) over 500 cycles at 0.3C and 25 °C. The Li|LiNi_0.8Co_0.1Mn_0.1O₂ cell operated well at 0.2C and 25 °C and delivered a high initial discharge capacity of 151.4 mA h g^-1 with a good capacity retention (70%) after 195 cycles. This work demonstrates that the anion doping in LLZO is an effective method to prepare a dense garnet ceramic for the high-performance lithium batteries.

High Performance Single-Crystal Ni-Rich Cathode Modification via Crystalline LLTO Nanocoating for All-Solid-State Lithium Batteries

Sulfide-based all-solid-state lithium batteries (ASSLBs) assembled with Ni-rich layered cathodes are currently promising candidates for achieving high-energy-density and high-safety energy storage systems. However, the interfacial challenges between sulfide electrolyte and Ni-rich layered cathode, such as space charge layer, side reaction, and poor physical contact, greatly limit the practicality of all-solid-state batteries. In this work, an optimal crystalline Li_0.35La_0.55TiO₃ (LLTO) surface coating with a thickness of roughly 6 nm and a high Li ion conductivity of 0.3 mS cm^-1 was adopted to enhance the structural stability of the single-crystal LiNi_0.6Co_0.2Mn_0.2O₂ (S-NCM622) cathode in ASSLBs. Furthermore, due to the high ionic conductivity and chemical stability of the LLTO coating layer, the interfacial problems, involving interfacial reaction and a space charge layer, in sulfide-based all-solid-state batteries have been effectively solved. As a result, the assembled ASSLBs with the S-NCM622@LLTO cathode exhibit high initial capacity (179.7 mAh g^-1) at 0.05 C and excellent cycling performance with 84.5% capacity retention after 100 cycles at 0.1 C at room temperature. This work proposes an effective strategy to enhance the performance of Ni-rich layered cathodes for next-generation high-energy-density sulfide-based lithium batteries.

Review on Interface and Interphase Issues in Sulfide Solid-State Electrolytes for All-Solid-State Li-Metal Batteries

All-solid-state batteries have emerged as promising alternatives to conventional Li-ion batteries owing to their higher energy density and safety, which stem from their use of inorganic solid-state electrolytes instead of flammable organic liquid electrolytes. Among various candidates, sulfide solid-state electrolytes are particularly promising for the development of high-energy all-solid-state Li metal batteries because of their high ionic conductivity and deformability. However, a significant challenge remains as their inherent instability in contact with electrodes forms unstable interfaces and interphases, leading to degradation of the battery performance. In this review article, we provide an overview of the key issues for the interfaces and interphases of sulfide solid-state electrolyte systems as well as recent progress in understanding such interface and interphase formation and potential solutions to stabilize them. In addition, we provide perspectives on future research directions in this field.

Recent Advances and Perspectives on the Polymer Electrolytes for Sodium/Potassium-Ion Batteries

Owing to the low cost of sodium/potassium resources and similar electrochemical properties of Na⁺ /K⁺ to Li⁺ , sodium-ion batteries (SIBs) and potassium-ion batteries (KIBs) are regarded as promising alternatives to lithium-ion batteries (LIBs) in large-scale energy storage field. However, traditional organic liquid electrolytes bestow SIBs/KIBs with serious safety concerns. In contrast, quasi-/solid-phase electrolytes including polymer electrolytes (PEs) and inorganic solid electrolytes (ISEs) show great superiority of high safety. However, the poor processibility and relatively low ionic conductivity of Na⁺ and K⁺ ions limit the further practical applications of ISEs. PEs combine some merits of both liquid-phase electrolytes and ISEs, and present great potentials in next-generation energy storage systems. Considerable efforts have been devoted to improving their overall properties. Nevertheless, there is still a lack of an in-depth and comprehensive review to get insights into mechanisms and corresponding design strategies of PEs. Herein, the advantages of different electrolytes, particularly PEs are first minutely reviewed, and the mechanism of PEs for Na⁺ /K⁺ ion transfer is summarized. Then, representative researches and recent progresses of SIBs/KIBs based on PEs are presented. Finally, some suggestions and perspectives are put forward to provide some possible directions for the follow-up researches.

Pyrrolidinium Containing Ionic Liquid Electrolytes for Li-Based Batteries

Ionic liquids are potential alternative electrolytes to the more conventional solid-state options under investigation for future energy storage solutions. This review addresses the utilization of IL electrolytes in energy storage devices, particularly pyrrolidinium-based ILs. These ILs offer favorable properties, such as high ionic conductivity and the potential for high power drain, low volatility and wide electrochemical stability windows (ESW). The cation/anion combination utilized significantly influences their physical and electrochemical properties, therefore a thorough discussion of different combinations is outlined. Compatibility with a wide array of cathode and anode materials such as LFP, V₂O₅, Ge and Sn is exhibited, whereby thin-films and nanostructured materials are investigated for micro energy applications. Polymer gel electrolytes suitable for layer-by-layer fabrication are discussed for the various pyrrolidinium cations, and their compatibility with electrode materials assessed. Recent advancements regarding the modification of typical cations such a 1-butyl-1-methylpyrrolidinium, to produce ether-functionalized or symmetrical cations is discussed.

Wetting Phenomena and their Effect on the Electrochemical Performance of Surface-Tailored Lithium Metal Electrodes in Contact with Cross-linked Polymeric Electrolytes

Li metal batteries (LMBs) containing cross-linked polymer electrolytes (PEs) are auspicious candidates for next-generation batteries. However, the wetting behavior of PEs on uneven Li metal surfaces has been neglected in most studies. Herein, it is shown that microscale defect sites with curved edges play an important role in a wettability-dependent electrodeposition. The wettability and the viscoelastic properties of PEs are correlated, and the impact of wettability on the nucleation and diffusion near the Li|PE interface is distinguished. It is found that the curvature of the edges is a key factor for the investigation of wetting phenomena. The appearance of microscale defects and phase separation are identified as main causes for erratic nucleation. It is emphasized that the implementation of stable and consistent long-term cycling performance of LMBs using PEs requires a deeper understanding of the "soft-solid"-solid contact between PEs and inherently rough Li metal surfaces.