3D‐Printing Electrolytes for Solid‐State Batteries

Solid‐state batteries have many enticing advantages in terms of safety and stability, but the solid electrolytes upon which these batteries are based typically lead to high cell resistance. Both components of the resistance (interfacial, due to poor contact with electrolytes, and bulk, due to a thick electrolyte) are a result of the rudimentary manufacturing capabilities that exist for solid‐state electrolytes. In general, solid electrolytes are studied as flat pellets with planar interfaces, which minimizes interfacial contact area. Here, multiple ink formulations are developed that enable 3D printing of unique solid electrolyte microstructures with varying properties. These inks are used to 3D‐print a variety of patterns, which are then sintered to reveal thin, nonplanar, intricate architectures composed only of Li₇La₃Zr₂O₁₂ solid electrolyte. Using these 3D‐printing ink formulations to further study and optimize electrolyte structure could lead to solid‐state batteries with dramatically lower full cell resistance and higher energy and power density. In addition, the reported ink compositions could be used as a model recipe for other solid electrolyte or ceramic inks, perhaps enabling 3D printing in related fields.     

Borohydride‐Scaffolded Li/Na/Mg Fast Ionic Conductors for Promising Solid‐State Electrolytes

Borohydride solid‐state electrolytes with room‐temperature ionic conductivity up to ≈70 mS cm^?1 have achieved impressive progress and quickly taken their place among the superionic conductive solid‐state electrolytes. Here, the focus is on state‐of‐the‐art developments in borohydride solid‐state electrolytes, including their competitive ionic‐conductive performance, current limitations for practical applications in solid‐state batteries, and the strategies to address their problems. To open, fast Li/Na/Mg ionic conductivity in electrolytes with BH₄ ^? groups, approaches to engineering borohydrides with enhanced ionic conductivity, and later on the superionic conductivity of polyhedral borohydrides, their correlated conductive kinetics/thermodynamics, and the theoretically predicted high conductive derivatives are discussed. Furthermore, the validity of borohydride pairing with coated oxides, sulfur, organic electrodes, MgH₂, TiS₂, Li₄Ti₅O₁₂, electrode materials, etc., is surveyed in solid‐state batteries. From the viewpoint of compatible cathodes, the stable electrochemical windows of borohydride solid‐state electrolytes, the electrode/electrolyte interface behavior and battery device design, and the performance optimization of borohydride‐based solid‐state batteries are also discussed in detail. A comprehensive coverage of emerging trends in borohydride solid‐state electrolytes is provided and future maps to promote better performance of borohydride SSEs are sketched out, which will pave the way for their further development in the field of energy storage.     

Graphene‐Analogues Boron Nitride Nanosheets Confining Ionic Liquids: A High‐Performance Quasi‐Liquid Solid Electrolyte

Solid electrolytes are one of the most promising electrolyte systems for safe lithium batteries, but the low ionic conductivity of these electrolytes seriously hinders the development of efficient lithium batteries. Here, a novel class of graphene‐analogues boron nitride (g‐BN) nanosheets confining an ultrahigh concentration of ionic liquids (ILs) in an interlayer and out‐of‐layer chamber to give rise to a quasi‐liquid solid electrolyte (QLSE) is reported. The electron‐insulated g‐BN nanosheet host with a large specific surface area can confine ILs as much as 10 times of the host's weight to afford high ionic conductivity (3.85 × 10^?3 S cm^?1 at 25 °C, even 2.32 × 10^?4 S cm^?1 at ?20 °C), which is close to that of the corresponding bulk IL electrolytes. The high ionic conductivity of QLSE is attributed to the enormous absorption for ILs and the confining effect of g‐BN to form the ordered lithium ion transport channels in an interlayer and out‐of‐layer of g‐BN. Furthermore, the electrolyte displays outstanding electrochemical properties and battery performance. In principle, this work enables a wider tunability, further opening up a new field for the fabrication of the next‐generation QLSE based on layered nanomaterials in energy conversion devices.     

3D Printing of Customized Li‐Ion Batteries with Thick Electrodes

The growing demand for rechargeable lithium‐ion batteries (LIBs) with higher capacity in customized geometries underscores the need for new battery materials, architectures, and assembly strategies. Here, the design, fabrication, and electrochemical performance of fully 3D printed LIBs composed of thick semisolid electrodes that exhibit high areal capacity are reported. Specifically, semisolid cathode and anode inks, as well as UV curable packaging and separator inks for direct writing of LIBs in arbitrary geometries are created. These fully 3D printed and packaged LIBs, which are encased between two glassy carbon current collectors, deliver an areal capacity of 4.45 mAh cm^?2 at a current density of 0.14 mA cm^?2, which is equivalent to 17.3 Ah L^?1. The ability to produce high‐performance LIBs in customized form factors opens new avenues for integrating batteries directly within 3D printed objects.     

3D Interdigital Au/MnO2/Au Stacked Hybrid Electrodes for On‐Chip Microsupercapacitors

On‐chip microsupercapacitors (MSCs) have application in powering microelectronic devices. Most of previous MSCs are made from carbon materials, which have high power but low energy density. In this work, 3D interdigital Au/MnO₂/Au stacked MSCs have been fabricated based on laser printed flexible templates. This vertical‐stacked electrode configuration can effectively increase the contact area between MnO₂ active layer and Au conductive layer, and thus improve the electron transport and electrolyte ion diffusion, resulting in enhanced pseudocapacitive performance of MnO₂. The stacked electrode can achieve an areal capacitance up to 11.9 mF cm^?2. Flexible and all‐solid‐state MSCs are assembled based on the sandwich hybrid electrodes and PVA/LiClO₄ gel electrolyte and show outstanding high‐rate capacity and mechanical flexibility. The laser printing technique in this work combined with the physical sputtering and electrodeposition allows fabrication of MSC array with random sizes and patterns, making them promising power sources for small‐scale flexible microelectronic energy storage systems (e.g., next‐generation smart phones).     

Li‐Ion Cooperative Migration and Oxy‐Sulfide Synergistic Effect in Li14P2Ge2S16−6xOx Solid‐State‐Electrolyte Enables Extraordinary Conductivity and High Stability

Critical to the development of all‐solid‐state lithium‐ion batteries technology are novel solid‐state electrolytes with high ionic conductivity and robust stability under inorganic solid‐electrolyte operating conditions. Herein, by using density functional theory and molecular dynamics, a mixed oxygen‐sulfur‐based Li‐superionic conductor is screened out from the local chemical structure of β‐Li₃PS₄ to discover novel Li₁₄P₂Ge₂S₈O₈ (LPGSO) with high ionic conductivity and high stability under thermal, moist, and electrochemical conditions, which causes oxygenation at specific sites to improve the stability and selective sulfuration to provide an O‐S mixed path by Li‐S/O structure units with coordination number between 3 and 4 for fast Li‐cooperative conduction. Furthermore, LPGSO exhibits a quasi‐isotropic 3D Li‐ion cooperative diffusion with a lesser migration barrier (≈0.19 eV) compared to its sulfide‐analog Li₁₄P₂Ge₂S₁₆. The theoretical ionic conductivity of this conductor at room temperature is as high as ≈30.0 mS cm^?1, which is among the best in current solid‐state electrolytes. Such an oxy‐sulfide synergistic effect and Li‐ion cooperative migration mechanism would enable the engineering of next‐generation electrolyte materials with desirable safety and high ionic conductivity, for possible application in the near future.     

Sulfide‐Based Solid‐State Electrolytes: Synthesis,Stability, and Potential for All‐Solid‐State Batteries

Due to their high ionic conductivity and adeciduate mechanical features for lamination, sulfide composites have received increasing attention as solid electrolyte in all‐solid‐state batteries. Their smaller electronegativity and binding energy to Li ions and bigger atomic radius provide high ionic conductivity and make them attractive for practical applications. In recent years, noticeable efforts have been made to develop high‐performance sulfide solid‐state electrolytes. However, sulfide solid‐state electrolytes still face numerous challenges including: 1) the need for a higher stability voltage window, 2) a better electrode–electrolyte interface and air stability, and 3) a cost‐effective approach for large‐scale manufacturing. Herein, a comprehensive update on the properties (structural and chemical), synthesis of sulfide solid‐state electrolytes, and the development of sulfide‐based all‐solid‐state batteries is provided, including electrochemical and chemical stability, interface stabilization, and their applications in high performance and safe energy storage.     

A Metal–Organic‐Framework‐Based Electrolyte with Nanowetted Interfaces for High‐Energy‐Density Solid‐State Lithium Battery

Solid‐state batteries (SSBs) are promising for safer energy storage, but their active loading and energy density have been limited by large interfacial impedance caused by the poor Li⁺ transport kinetics between the solid‐state electrolyte and the electrode materials. To address the interfacial issue and achieve higher energy density, herein, a novel solid‐like electrolyte (SLE) based on ionic‐liquid‐impregnated metal–organic framework nanocrystals (Li‐IL@MOF) is reported, which demonstrates excellent electrochemical properties, including a high room‐temperature ionic conductivity of 3.0 × 10^‐4 S cm^‐1, an improved Li⁺ transference number of 0.36, and good compatibilities against both Li metal and active electrodes with low interfacial resistances. The Li‐IL@MOF SLE is further integrated into a rechargeable Li|LiFePO₄ SSB with an unprecedented active loading of 25 mg cm^‐2, and the battery exhibits remarkable performance over a wide temperature range from ?20 up to 150 °C. Besides the intrinsically high ionic conductivity of Li‐IL@MOF, the unique interfacial contact between the SLE and the active electrodes owing to an interfacial wettability effect of the nanoconfined Li‐IL guests, which creates an effective 3D Li⁺ conductive network throughout the whole battery, is considered to be the key factor for the excellent performance of the SSB.     

3‐D Integrated All‐Solid‐State Rechargeable Batteries

Portable society urgently calls for integrated energy supplies. This holds for autonomous devices but even more so for future medical implants. Evidently, rechargeable integrated all‐solid‐state batteries will play a key role in these fields, enabling miniaturization, preventing electrode degradation upon cycling and electrolyte leakage. Planar solid‐state thin film batteries are rapidly emerging but reveal several potential drawbacks, such as a relatively low energy density and the use of highly reactive lithium. Thin film Si‐intercalation electrodes covered with a solid‐state electrolyte are found to combine a high storage capacity of 3500 mAh g^–1 with high cycle life, enabling to integrate batteries in Si. Based on the excellent intercalation chemistry of Si, a new 3D‐integrated all‐solid‐state battery concept is proposed. High aspect ratio cavities and features, etched in silicon, will yield large surface area batteries with anticipated energy density of about 5 mWh μm^–1 cm^–2, i.e. more than 3 orders of magnitude higher than that of integrated capacitors.     

Protected Lithium‐Metal Anodes in Batteries: From Liquid to Solid

High‐energy lithium‐metal batteries are among the most promising candidates for next‐generation energy storage systems. With a high specific capacity and a low reduction potential, the Li‐metal anode has attracted extensive interest for decades. Dendritic Li formation, uncontrolled interfacial reactions, and huge volume effect are major hurdles to the commercial application of Li‐metal anodes. Recent studies have shown that the performance and safety of Li‐metal anodes can be significantly improved via organic electrolyte modification, Li‐metal interface protection, Li‐electrode framework design, separator coating, and so on. Superior to the liquid electrolytes, solid‐state electrolytes are considered able to inhibit problematic Li dendrites and build safe solid Li‐metal batteries. Inspired by the bright prospects of solid Li‐metal batteries, increasing efforts have been devoted to overcoming the obstacles of solid Li‐metal batteries, such as low ionic conductivity of the electrolyte and Li–electrolyte interfacial problems. Here, the approaches to protect Li‐metal anodes from liquid batteries to solid‐state batteries are outlined and analyzed in detail. Perspectives regarding the strategies for developing Li‐metal anodes are discussed to facilitate the practical application of Li‐metal batteries.     

A Silica‐Aerogel‐Reinforced Composite Polymer Electrolyte with High Ionic Conductivity and High Modulus

High‐energy all‐solid‐state lithium (Li) batteries have great potential as next‐generation energy‐storage devices. Among all choices of electrolytes, polymer‐based systems have attracted widespread attention due to their low density, low cost, and excellent processability. However, they are generally mechanically too weak to effectively suppress Li dendrites and have lower ionic conductivity for reasonable kinetics at ambient temperature. Herein, an ultrastrong reinforced composite polymer electrolyte (CPE) is successfully designed and fabricated by introducing a stiff mesoporous SiO₂ aerogel as the backbone for a polymer‐based electrolyte. The interconnected SiO₂ aerogel not only performs as a strong backbone strengthening the whole composite, but also offers large and continuous surfaces for strong anion adsorption, which produces a highly conductive pathway across the composite. As a consequence, a high modulus of ≈0.43 GPa and high ionic conductivity of ≈0.6 mS cm^?1 at 30 °C are simultaneously achieved. Furthermore, LiFePO₄–Li full cells with good cyclability and rate capability at ambient temperature are obtained. Full cells with cathode capacity up to 2.1 mAh cm^?2 are also demonstrated. The aerogel‐reinforced CPE represents a new design principle for solid‐state electrolytes and offers opportunities for future all‐solid‐state Li batteries.     

Advances and Prospects of Sulfide All‐Solid‐State Lithium Batteries via One‐to‐One Comparison with Conventional Liquid Lithium Ion Batteries

Owing to the safety issue of lithium ion batteries (LIBs) under the harsh operating conditions of electric vehicles and mobile devices, all‐solid‐state lithium batteries (ASSLBs) that utilize inorganic solid electrolytes are regarded as a secure next‐generation battery system. Significant efforts are devoted to developing each component of ASSLBs, such as the solid electrolyte and the active materials, which have led to considerable improvements in their electrochemical properties. Among the various solid electrolytes such as sulfide, polymer, and oxide, the sulfide solid electrolyte is considered as the most promising candidate for commercialization because of its high lithium ion conductivity and mechanical properties. However, the disparity in energy and power density between the current sulfide ASSLBs and conventional LIBs is still wide, owing to a lack of understanding of the battery electrode system. Representative developments of ASSLBs in terms of the sulfide solid electrolyte, active materials, and electrode engineering are presented with emphasis on the current status of their electrochemical performances, compared to those of LIBs. As a rational method to realizing high energy sulfide ASSLBs, the requirements for the sulfide solid electrolytes and active materials are provided along through simple experimental demonstrations. Potential future research directions in the development of commercially viable sulfide ASSLBs are suggested.     

Composition Modulation and Structure Design of Inorganic‐in‐Polymer Composite Solid Electrolytes for Advanced Lithium Batteries

Owing to their safety, high energy density, and long cycling life, all‐solid‐state lithium batteries (ASSLBs) have been identified as promising systems to power portable electronic devices and electric vehicles. Developing high‐performance solid‐state electrolytes is vital for the successful commercialization of ASSLBs. In particular, polymer‐based composite solid electrolytes (PCSEs), derived from the incorporation of inorganic fillers into polymer solid electrolytes, have emerged as one of the most promising electrolyte candidates for ASSLBs because they can synergistically integrate many merits from their components. The development of PCSEs is summarized. Their major components, including typical polymer matrices and diverse inorganic fillers, are reviewed in detail. The effects of fillers on their ionic conductivity, mechanical strength, thermal/interfacial stability and possible Li⁺‐conductive mechanisms are discussed. Recent progress in a number of rationally constructed PCSEs by compositional and structural modulation based on different design concepts is introduced. Successful applications of PCSEs in various lithium‐battery systems including lithium–sulfur and lithium–gas batteries are evaluated. Finally, the challenges and future perspectives for developing high‐performance PCSEs are proposed.     

Nanostructured Metal–Organic Framework (MOF)‐Derived Solid Electrolytes Realizing Fast Lithium Ion Transportation Kinetics in Solid‐State Batteries

Solid‐state batteries are hindered from practical applications, largely due to the retardant ionic transportation kinetics in solid electrolytes (SEs) and across electrode/electrolyte interfaces. Taking advantage of nanostructured UIO/Li‐IL SEs, fast lithium ion transportation is achieved in the bulk and across the electrode/electrolyte interfaces; in UIO/Li‐IL SEs, Li‐containing ionic liquid (Li‐IL) is absorbed in Uio‐66 metal–organic frameworks (MOFs). The ionic conductivity of the UIO/Li‐IL (15/16) SE reaches 3.2 × 10^?4 S cm^?1 at 25 °C. Owing to the high surface tension of nanostructured UIO/Li‐IL SEs, the contact between electrodes and the SE is excellent; consequently, the interfacial resistances of Li/SE and LiFePO₄/SE at 60 °C are about 44 and 206 Ω cm², respectively. Moreover, a stable solid conductive layer is formed at the Li/SE interface, making the Li plating/stripping stable. Solid‐state batteries from the UIO/Li‐IL SEs show high discharge capacities and excellent retentions (≈130 mA h g^?1 with a retention of 100% after 100 cycles at 0.2 C; 119 mA h g^?1 with a retention of 94% after 380 cycles at 1 C). This new type of nanostructured UIO/Li‐IL SEs is very promising for solid‐state batteries, and will open up an avenue toward safe and long lifespan energy storage systems.     

Aliphatic Polycarbonate‐Based Solid‐State Polymer Electrolytes for Advanced Lithium Batteries: Advances and Perspective

Conventional liquid electrolytes based lithium‐ion batteries (LIBs) might suffer from serious safety hazards. Solid‐state polymer electrolytes (SPEs) are very promising candidate with high security for advanced LIBs. However, the quintessential frailties of pristine polyethylene oxide/lithium salts SPEs are poor ionic conductivity (≈10⁻⁸ S cm⁻¹) at 25 °C and narrow electrochemical window (<4 V). Many innovative researches are carried out to enhance their lithium‐ion conductivity (10⁻⁴ S cm⁻¹ at 25 °C), which is still far from meeting the needs of high‐performance power LIBs at ambient temperature. Therefore, it is a pressing urgency of exploring novel polymer host materials for advanced SPEs aimed to develop high‐performance solid lithium batteries. Aliphatic polycarbonate, an emerging and promising solid polymer electrolyte, has attracted much attention of academia and industry. The amorphous structure, flexible chain segments, and high dielectric constant endow this class of polymer electrolyte excellent comprehensive performance especially in ionic conductivity, electrochemical stability, and thermally dimensional stability. To date, many types of aliphatic polycarbonate solid polymer electrolyte are discovered. Herein, the latest developments on aliphatic polycarbonate SPEs for solid‐state lithium batteries are summarized. Finally, main challenges and perspective of aliphatic polycarbonate solid polymer electrolytes are illustrated at the end of this review.     

An Electron/Ion Dual‐Conductive Alloy Framework for High‐Rate and High‐Capacity Solid‐State Lithium‐Metal Batteries

The solid‐state Li battery is a promising energy‐storage system that is both safe and features a high energy density. A main obstacle to its application is the poor interface contact between the solid electrodes and the ceramic electrolyte. Surface treatment methods have been proposed to improve the interface of the ceramic electrolytes, but they are generally limited to low‐capacity or short‐term cycling. Herein, an electron/ion dual‐conductive solid framework is proposed by partially dealloying the Li–Mg alloy anode on a garnet‐type solid‐state electrolyte. The Li–Mg alloy framework serves as a solid electron/ion dual‐conductive Li host during cell cycling, in which the Li metal can cycle as a Li‐rich or Li‐deficient alloy anode, free from interface deterioration or volume collapse. Thus, the capacity, current density, and cycle life of the solid Li anode are improved. The cycle capability of this solid anode is demonstrated by cycling for 500 h at 1 mA cm^?2, followed by another 500 h at 2 mA cm^?2 without short‐circuiting, realizing a record high cumulative capacity of 750 mA h cm^?2 for garnet‐type all‐solid‐state Li batteries. This alloy framework with electron/ion dual‐conductive pathways creates the possibility to realize high‐energy solid‐state Li batteries with extended lifespans.     

Tuning the Solid Electrolyte Interphase for Selective Li‐ and Na‐Ion Storage in Hard Carbon

Solid‐electrolyte interphase (SEI) films with controllable properties are highly desirable for improving battery performance. In this paper, a combined experimental and theoretical approach is used to study SEI films formed on hard carbon in Li‐ and Na‐ion batteries. It is shown that a stable SEI layer can be designed by precycling an electrode in a desired Li‐ or Na‐based electrolyte, and that ionic transport can be kinetically controlled. Selective Li‐ and Na‐based SEI membranes are produced using Li‐ or Na‐based electrolytes, respectively. The Na‐based SEI allows easy transport of Li ions, while the Li‐based SEI shuts off Na‐ion transport. Na‐ion storage can be manipulated by tuning the SEI layer with film‐forming electrolyte additives, or by preforming an SEI layer on the electrode surface. The Na specific capacity can be controlled to < 25 mAh g^?1; ≈ 1/10 of the normal capacity (250 mAh g^?1). Unusual selective/preferential transport of Li ions is demonstrated by preforming an SEI layer on the electrode surface and corroborated with a mixed electrolyte. This work may provide new guidance for preparing good ion‐selective conductors using electrochemical approaches.     

Emerging application of 3D-printing techniques in lithium batteries: From liquid to solid

There is rapid progress in the field of 3D printing technology for the production of electrodes, electrolytes, and packages of batteries due to the technique’s low cost, a wide range of geometries printable, and rapid prototyping speed by combining computer-aided design with advanced manufacturing procedures. The most important part of 3D printing applied in batteries is the printing of electrodes, electrolytes, and packages. These will affect the battery energy/power density. However, there are still several challenges that need to be overcome to print active and stable electrodes/electrolytes for energy storage systems that can rival that of the state-of-the-art. In this review, the printing materials, and methods for batteries from liquid to solid-state batteries are discussed and recent examples of this technique applied in high power/energy batteries are highlighted. This review for batteries will cover 3D printing technologies, printed cathode, and anode in conventional batteries, and printed solid-state electrolytes in solid-state batteries. The working principles, advantages, and limitations for solid-state batteries via the 3D printing method will be discussed before highlighting the printing materials for electrodes and electrolytes. We will then discuss how to modify the electrode and solid-state electrolyte to raise the electrochemical performance of solid-state batteries using 3D printing. Finally, we will give our insights into the future perspectives of this printing technique for fabricating batteries.     

3D‐Printed Transparent Glass

Silica inks are developed, which may be 3D printed and thermally processed to produce optically transparent glass structures with sub‐millimeter features in forms ranging from scaffolds to monoliths. The inks are composed of silica powder suspended in a liquid and are printed using direct ink writing. The printed structures are then dried and sintered at temperatures well below the silica melting point to form amorphous, solid, transparent glass structures. This technique enables the mold‐free formation of transparent glass structures previously inaccessible using conventional glass fabrication processes.     

Extended Electrochemical Window of Solid Electrolytes via Heterogeneous Multilayered Structure for High‐Voltage Lithium Metal Batteries

In response to the call for safer high‐energy‐density storage systems, high‐voltage solid‐state Li metal batteries have attracted extensive attention. Therefore, solid electrolytes are required to be stable against both Li anode and high‐voltage cathodes; nevertheless, the requirements still cannot be completely satisfied. Herein, a heterogeneous multilayered solid electrolyte (HMSE) is proposed to broaden electrochemical window of solid electrolytes to 0–5 V, through different electrode/electrolyte interfaces to overcome the interfacial instability problems. Oxidation‐resistance poly(acrylonitrile) (PAN) is in contact with the cathode, while reduction tolerant polyethylene glycol diacrylate contacts with Li metal anode. A Janus and flexible PAN@Li_1.4Al_0.4Ge_1.6(PO₄)₃ (80 wt%) composite electrolyte is designed as intermediate layer to inhibit dendrite penetration and ensure compact interface. Paired with LiNi_0.6Co_0.2Mn_0.2O₂ and LiNi_0.8Co_0.1Mn_0.1O₂ cathodes, which are rarely used in solid‐state batteries, the solid‐state Li metal batteries with HMSE exhibit excellent electrochemical performance including high capacity and long cycle life. Besides, the Li||Li symmetric batteries maintain a stable polarization less than 40 mV for more than 1000 h under 2 mA cm^?2 and effective inhibition of dendrite formation. This study offers a promising approach to extend the applications of solid electrolytes for high‐voltage solid‐state Li metal batteries.