All-Solid-State Batteries with a Limited Lithium Metal Anode at Room Temperature using a Garnet-Based Electrolyte

Interfacial study and modulation of high-voltage layered cathode based all-solid-state batteries

Employing layered materials as the cathodes for solid-state batteries (SSBs) is vital in enhancing the batteries' energy density, whereas numerous issues are present regarding the compatibilities between cathode electrode and modified solid electrolyte (ME) in this battery configuration. By investigating the electrochemical performance and interfacial properties of SSBs using various cathodes, the fundamental reason for the poor compatibility between layered cathodes, especially LiCoO2 with ME is revealed. Because of the Li(solvent)+ intercalation environments formed in the ME, the resultant weak-interacted TFSI- could be adsorbed and destabilized by Co ions on the surface. Besides, the high energy level offsets between LiCoO2 and ME lead to Li-ion transferring from the bulk electrode to the electrolyte, resulting in a pre-formed interface on the cathode particles before the electric current is applied, affects the formation of effective cathode-electrolyte interface (CEI) film during electrochemical process and deteriorated overall battery performance. From this view, an interlayer is pre-added on the LiCoO2 surface through an electrostatic adsorption method, to adjust the energy level offsets between the cathode and ME, as well as isolate the direct contact of surface Co ions to TFSI-. The cycling properties of the SSB using modified LiCoO2 are greatly enhanced, and a capacity retention of 68.72 % after 100 cycles could be achieved, against 8.28 % previously, certifying the rationality of the understanding and the effectiveness of the proposed modification method. We believe this research could provide basic knowledge of the compatibility between layered cathodes and MEs, shedding light on designing more effective strategies for achieving SSBs with high energy density.

Anode-Free Li Metal Batteries: Feasibility Analysis and Practical Strategy

Energy storage devices are striving to achieve high energy density, long lifespan, and enhanced safety. In view of the current popular lithiated cathode, anode-free lithium metal batteries (AFLMBs) will deliver the theoretical maximum energy density among all the battery chemistries. However, AFLMBs face challenges such as low plating-stripping efficiency, significant volume change, and severe Li-dendrite growth, which negatively impact their lifespan and safety. This study provides an overview and analysis of recent progress in electrode structure, characterization, performance, and practical challenges of AFLMBs. The deposition behavior of lithium is categorized into two stages: heterogeneous and homogeneous interface deposition. The feasibility and practical application value of AFLMBs are critically evaluated. Additionally, key test models, evaluation parameters, and advanced characterization techniques are discussed. Importantly, practical strategies of different battery components in AFLMBs, including current collector, interface layer, solid-state electrolyte, liquid-state electrolyte, cathode, and cycling protocol, are presented to address the challenges posed by the two types of deposition processes, lithium loss, crosstalk effect and volume change. Finally, the application prospects of AFLMBs are envisioned, with a focus on overcoming the current limitations and unlocking their full potential as high-performance energy storage solutions.

Cross-Linked Composite Solid Polymer Electrolyte Doped with Li6.4La3Zr1.4Ta0.6O12 for High Voltage Lithium Metal Batteries

Composite solid polymer electrolytes (CSPEs) are safer alternatives to liquid electrolytes and excellent candidates for high-voltage solid-state batteries. However, interfacial instabilities between the electrodes and CSPEs are one of the bottlenecks in pursuing these systems. In this study, a cross-linked CSPE was synthesized based on polypropylene carbonate, polyethylene glycol methyl ether acrylate, polyethylene glycol diacrylate with additives including lithium bis(trifluoromethane)sulfonimide salt, and tantalum-doped lithium lanthanum zirconium oxide (LLZTO). Mass fractions of 10, 20, and 40% LLZTO were added to the CSPE matrix. In a symmetric cell, lithium plating and stripping revealed that the interface between the lithium metal anode and CSPE with 10% of the LLZTO (CSPE-10LLZTO) shows the most stable interface. The CSPE-10LLZTO sample demonstrated high flexibility and showed no degradation over 800 h of cycling at varying current densities. The ionic conductivity for the CSPE-10LLZTO sample at 40 °C was 6.4 × 10-4 S/cm. An all-solid-state full cell was fabricated with LiNi0.5Mn0.3Co0.2O2 as the cathode, CSPE-10LLZTO as the electrolyte and separator, and Li metal as the anode, delivering approximately 140 mAh/g of capacity. Differential scanning calorimetry measurements on CSPE-xLLZTO showed high miscibility and the elimination of crystallinity. Raman spectroscopy revealed uniformity in the structure. These findings demonstrate the capability of the CSPEs to develop high-voltage solid-state lithium metal batteries.

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.

Revealing and reconstructing the 3D Li-ion transportation network for superionic poly(ethylene) oxide conductor

Understanding the Li-ions conduction network and transport dynamics in polymer electrolyte is crucial for developing reliable all-solid-state batteries. In this work, advanced nano- X-ray computed tomography combined with Raman spectroscopy and solid state nuclear magnetic resonance are used to multi-scale qualitatively and quantitatively reveal ion conduction network of poly(ethylene) oxide (PEO)-based electrolyte (from atomic, nano to macroscopic level). With the clear mapping of the microstructural heterogeneities of the polymer segments, aluminium-oxo molecular clusters (AlOC) are used to reconstruct a high-efficient conducting network with high available Li-ions (76.7%) and continuous amorphous domains via the strong supramolecular interactions. Such superionic PEO conductor (PEO-LiTFSI-AlOC) exhibites a molten-like Li-ion conduction behaviour among the whole temperature range and delivers an ionic conductivity of 1.87 × 10-4 S cm-1 at 35 °Ϲ. This further endows Li electrochemical plating/stripping stability under 50 μA cm-2 and 50 μAh cm-2 over 2000 h. The as-built Li|PEO-LiTFSI-AlOC|LiFePO4 full batteries show a high rate performance and a capacity retention more than 90% over 200 cycling at 250 μA cm-2, even enabling a high-loading LiFePO4 cathode of 16.8 mg cm-2 with a specific capacity of 150 mAh g-1 at 50 °Ϲ.

Ultralong Cycling and Interfacial Regulation of Bilayer Heterogeneous Composite Solid-State Electrolytes in Lithium Metal Batteries

Under the background of "carbon neutral", lithium-ion batteries (LIB) have been widely used in portable electronic devices and large-scale energy storage systems, but the current commercial electrolyte is mainly liquid organic compounds, which have serious safety risks. In this paper, a bilayer heterogeneous composite solid-state electrolyte (PLPE) was constructed with the 3D LiX zeolite nanofiber (LiX-NF) layer and in-situ interfacial layer, which greatly extends the life span of lithium metal batteries (LMB). LiX-NF not only offers a continuous fast path for Li+, but also zeolite's Lewis acid-base interaction can immobilize large anions, which significantly improves the electrochemical performance of the electrolyte. In addition, the in-situ interfacial layer at the electrode-electrolyte interface can effectively facilitate the uniform deposition of Li+ and inhibit the growth of lithium dendrites. As a result, the Li/Li battery assembled with PLPE can be stably cycled for more than 2500 h at 0.1 mA cm-2. Meanwhile, the initial discharge capacity of the LiFePO4/PLPE/Li battery can be 162.43 mAh g-1 at 0.5 C, and the capacity retention rate is 82.74% after 500 cycles. These results emphasize that this bilayer heterogeneous composite solid-state electrolyte has distinct properties and shows excellent potential for application in LMB.

A Large-Scale Fabrication of Flexible, Ultrathin, and Robust Solid Electrolyte for Solid-State Lithium-Sulfur Batteries

All-solid-state lithium metal batteries (ASSLMBs) are considered as the most promising candidates for the next-generation high-safety batteries. To achieve high energy density in ASSLMBs, it is essential that the solid-state electrolytes (SSEs) are lightweight, thin, and possess superior electrochemical stability. In this study, a feasible and scalable fabrication approach to construct 3D supporting skeleton using an electro-blown spinning technique is proposed. This skeleton not only enhances the mechanical strength but also hinders the migration of Li-salt anions, improving the lithium-ion transference number of the SSE. This provides a homogeneous distribution of Li-ion flux and local current density, promoting uniform Li deposition. As a result, based on the mechanically robust and thin SSEs, the Li symmetric cells show outstanding Li plating/stripping reversibility. Besides, a stable interface contact between SSE and Li anode has been established with the formation of an F-enriched solid electrolyte interface layer. The solid-state Li|sulfurized polyacrylonitrile (Li|SPAN) cell achieves a capacity retention ratio of 94.0% after 350 cycles at 0.5 C. Also, the high-voltage Li|LCO cell shows a capacity retention of 92.4% at 0.5 C after 500 cycles. This fabrication approach for SSEs is applicable for commercially large-scale production and application in high-energy-density and high-safety ASSLMBs.

An electron-blocking interface for garnet-based quasi-solid-state lithium-metal batteries to improve lifespan

Garnet oxide is one of the most promising solid electrolytes for solid-state lithium metal batteries. However, the traditional interface modification layers cannot completely block electron migrating from the current collector to the interior of the solid-state electrolyte, which promotes the penetration of lithium dendrites. In this work, a highly electron-blocking interlayer composed of potassium fluoride (KF) is deposited on garnet oxide Li6.4La3Zr1.4Ta0.6O12 (LLZTO). After reacting with melted lithium metal, KF in-situ transforms to KF/LiF interlayer, which can block the electron leakage and inhibit lithium dendrite growth. The Li symmetric cells using the interlayer show a long cycle life of ~3000 hours at 0.2 mA cm-2 and over 350 hours at 0.5 mA cm-2 respectively. Moreover, an ionic liquid of LiTFSI in C4mim-TFSI is screened to wet the LLZTO|LiNi0.8Co0.1Mn0.1O2 (NCM) positive electrode interfaces. The Li|KF-LLZTO | NCM cells present a specific capacity of 109.3 mAh g-1, long lifespan of 3500 cycles and capacity retention of 72.5% at 25 °C and 2 C (380 mA g-1) with an average coulombic efficiency of 99.99%. This work provides a simple and integrated strategy on high-performance quasi-solid-state lithium metal batteries.

Composite Ionogel Electrodes for Polymeric Solid-State Li-Ion Batteries

Realizing rechargeable cells with practical energy and power density requires electrodes with high active material loading, a remaining challenge for solid-state batteries. Here, we present a new strategy based on ionogel-derived solid-state electrolytes (SSEs) to form composite electrodes that enable high active material loading (>10 mg/cm2, ~9 mA/cm2 at 1C) in a scalable approach for fabricating Li-ion cells. By tuning the precursor and active materials composition incorporated into the composite lithium titanate electrodes, we achieve near-theoretical capacity utilization at C/5 rates and cells capable of stable cycling at 5.85 mA/cm2 (11.70 A/g) with over 99% average Coulombic efficiency at room temperature. Finally, we demonstrate a complete polymeric solid-state cell with a composite anode and a composite lithium iron phosphate cathode with ionogel SSEs, which is capable of stable cycling at a 1C rate.

Tailoring Practical Solid Electrolyte Composites Containing Ferroelectric Ceramic Nanofibers and All-Trans Block Copolymers for All-Solid-State Lithium Metal Batteries

Ion transport efficiency, the key to determining the cycling stability and rate capability of all-solid-state lithium metal batteries (ASSLMBs), is constrained by ionic conductivity and Li+-migration ability across the multicomponent phases and interfaces in ASSLMBs. Here, we report a robust strategy for the large-scale fabrication of a practical solid electrolyte composite with high-throughput linear Li+-transport channels by compositing an all-trans block copolymer PVDF-b-PTFE matrix with ferroelectric BaTiO3-TiO2 nanofiber films. The electrolyte shows a sustainable electromechanical-coupled deformability that enables the rapid dissociation of anions with Li+ to create more movable Li+ ions and spontaneously transform the battery internal strain into Li+-ion migration kinetic energy. The ceramic framework homogenizes the interfacial potential with electrodes, endowing the electrolyte with a high conductivity of 0.782 mS·cm-1 and stable ion transport ability in ASSLMBs at room temperature. The batteries of LiFePO4/Li can stably cycle 1000 times at 0.5 C with a high capacity retention of 96.1%, and Ah-grade pouch or high-voltage Li(Ni0.8Mn0.1Co0.1)O2/Li batteries also exhibit excellent rate capability and cycling performance.

Dual Interface Compatibility Enabled via Composite Solid Electrolyte with High Transference Number for Long-Life All-Solid-State Lithium Metal Batteries

The development of solid-state electrolytes (SSEs) effectively solves the safety problem derived from dendrite growth and volume change of lithium during cycling. In the meantime, the SSEs possess non-flammability compared to conventional organic liquid electrolytes. Replacing liquid electrolytes with SSEs to assemble all-solid-state lithium metal batteries (ASSLMBs) has garnered significant attention as a promising energy storage/conversion technology for the future. Herein, a composite solid electrolyte containing two inorganic components (Li6.25Al0.25La3Zr2O12, Al2O3) and an organic polyvinylidene difluoride matrix is designed rationally. X-ray photoelectron spectroscopy and density functional theory calculation results demonstrate the synergistic effect among the components, which results in enhanced ionic conductivity, high lithium-ion transference number, extended electrochemical window, and outstanding dual interface compatibility. As a result, Li||Li symmetric battery maintains a stable cycle for over 2500 h. Moreover, all-solid-state lithium metal battery assembled with LiNi0.6Co0.2Mn0.2O2 cathode delivers a high discharge capacity of 168 mAh g-1 after 360 cycles at 0.1 C at 25 °C, and all-solid-state lithium-sulfur battery also exhibits a high initial discharge capacity of 912 mAh g-1 at 0.1 C. This work demonstrates a long-life flexible composite solid electrolyte with excellent interface compatibility, providing an innovative way for the rational construction of next-generation high-energy-density ASSLMBs.

Insight into Multiple Intermolecular Coordination of Composite Solid Electrolytes via Cryo-Electron Microscopy for High-Voltage All-Solid-State Lithium Metal Batteries

Polymer/ceramic-based composite solid electrolytes (CSE) are promising candidates for all-solid-state lithium metal batteries (SLBs), benefiting from the combined mechanical robustness of polymeric electrolytes and the high ionic conductivity of ceramic electrolytes. However, the interfacial instability and poorly understood interphases of CSE hinder their application in high-voltage SLBs. Herein, a simple but effective CSE that stabilizes high-voltage SLBs by forming multiple intermolecular coordination interactions between polyester and ceramic electrolytes is discovered. The multiple coordination between the carbonyl groups in poly(ε-caprolactone) and the fluorosulfonyl groups in anions with Li6.5 La3 Zr1.5 Ta0.5 O12 nanoparticles is directly visualized by cryogenic transmission electron microscopy and further confirmed by theoretical calculation. Importantly, the multiple coordination in CSE not only prevents the continuous decomposition of polymer skeleton by shielding the vulnerable carbonyl sites but also establishes stable inorganic-rich interphases through preferential decomposition of anions. The stable CSE and its inorganic-rich interphases enable Li||Li symmetric cells with an exceptional lifespan of over 4800 h without dendritic shorting at 0.1 mA cm-2 . Moreover, the high-voltage SLB with LiNi0.5 Co0.2 Mn0.3 O2 cathode displays excellent cycling stability over 1100 cycles at a 1C charge/discharge rate. This work reveals the underlying mechanism behind the excellent stability of coordinating composite electrolytes and interfaces in high-voltage SLBs.

Lithiophilic and Eco-Friendly Nano-Se Seeds Unlock Dendrite-Free and Anode-Free Li-Metal Batteries

A 3D host design for lithium (Li)-metal anodes can effectively accommodate volume changes and suppress Li dendrite growth; nonetheless, its practical applicability in energy-dense Li-metal batteries (LMBs) is plagued by excessive Li loading. Herein, we introduced eco- and human-friendly Se seeds into 3D carbon cloth (CC) to create a robust host for efficient Li deposition/stripping. The highly lithiophilic nano-Se endowed the Se-decorated CC (Se@CC) with perfect Li wettability for instantaneous Li infusion. At an optimal Li loading of 17 mg, the electrode delivered an unprecedentedly long life span of 5400 h with low overpotentials <36 mV at 1 mA cm-2/1 mAh cm-2 and 1500 h at 5 mA cm-2/5 mAh cm-2. Furthermore, the uniform Se distribution and strong Li-Se binding allowed for further reduction in Li loading to 2 mg via direct Li electrodeposition. The corresponding LiNi0.8Co0.1Mn0.1O2 (NCM811)-based full cell afforded a high capacity retention rate of 74.67% over 300 cycles at a low N/P ratio of 8.64. Finally, the initial anode-free LMB using a NCM811 cathode and a Se@CC anode current collector demonstrated a high electrode-level specific energy of 531 Wh kg-1 and consistently high CEs >99.7% over 200 cycles. This work highlights a high-performance host design with excellent tunability for practical high-energy-density LMBs.

Electrodeposition Stability Landscape for Solid-Solid Interfaces

As solid-state batteries (SSBs) with lithium (Li) metal anodes gain increasing traction as promising next-generation energy storage systems, a fundamental understanding of coupled electro-chemo-mechanical interactions is essential to design stable solid-solid interfaces. Notably, uneven electrodeposition at the Li metal/solid electrolyte (SE) interface arising from intrinsic electrochemical and mechanical heterogeneities remains a significant challenge. In this work, the thermodynamic origins of mechanics-coupled reaction kinetics at the Li/SE interface are investigated and its implications on electrodeposition stability are unveiled. It is established that the mechanics-driven energetic contribution to the free energy landscape of the Li deposition/dissolution redox reaction has a critical influence on the interface stability. The study presents the competing effects of mechanical and electrical overpotential on the reaction distribution, and demarcates the regimes under which stress interactions can be tailored to enable stable electrodeposition. It is revealed that different degrees of mechanics contribution to the forward (dissolution) and backward (deposition) reaction rates result in widely varying stability regimes, and the mechanics-coupled kinetics scenario exhibited by the Li/SE interface is shown to depend strongly on the thermodynamic and mechanical properties of the SE. This work highlights the importance of discerning the underpinning nature of electro-chemo-mechanical coupling toward achieving stable solid/solid interfaces in SSBs.

Compressible and Elastic Reduced Graphene Oxide Sponge for Stable and Dendrite-Free Lithium Metal Anodes

Dendritic Li deposition, an unstable solid-electrolyte interphase (SEI), and a nearly infinite relative volume change during cycling are three major obstacles to the practical application of Li metal batteries. Herein, we introduce a compressible and elastic reduced graphene oxide sponge (rGO-S) to simultaneously eliminate Li dendrite growth, stabilize the SEI, and accommodate the volume change. The volume change is contained by compressing and expanding the rGO-S anode, which effectively releases the Li plating-induced stress during cycling. The smooth and dense Li metal is deposited on rGO-S without dendrites, which preserves the SEI, reduces consumption of the electrolyte, and prevents the formation of Li debris. The half-cells employing rGO-S show a steady and high Coulombic efficiency. The Li@rGO-S symmetric cells demonstrate excellent cycling stability over 1200 cycles with a low overpotential. When paired with LiFePO4 (LFP), the Li@rGO-S||LFP full cells exhibit a high specific capacity (150.3 mAh g-1 at 1C), superior rate performance, and good capacity retention.

A Solid-State Electrolyte Based on Li0.95 Na0.05 FePO4 for Lithium Metal Batteries

Solid-state electrolytes (SSEs) play a crucial role in developing lithium metal batteries (LMBs) with high safety and energy density. Exploring SSEs with excellent comprehensive performance is the key to achieving the practical application of LMBs. In this work, the great potential of Li0.95 Na0.05 FePO4 (LNFP) as an ideal SSE due to its enhanced ionic conductivity and reliable stability in contact with lithium metal anode is demonstrated. Moreover, LNFP-based composite solid electrolytes (CSEs) are prepared to further improve electronic insulation and interface stability. The CSE containing 50 wt% of LNFP (LNFP50) shows high ionic conductivity (3.58 × 10-4 S cm-1 at 25 °C) and good compatibility with Li metal anode and cathodes. Surprisingly, the LMB of Li|LNFP50|LiFePO4 cell at 0.5 C current density shows good cycling stability (151.5 mAh g-1 for 500 cycles, 96.5% capacity retention, and 99.3% Coulombic efficiency), and high-energy LMB of Li|LNFP50|Li[Ni0.8 Co0.1 Mn0.1 ]O2 cell maintains 80% capacity retention after 170 cycles, which are better than that with traditional liquid electrolytes (LEs). This investigation offers a new approach to commercializing SSEs with excellent comprehensive performance for high-performance LMBs.

Unveiling Challenges and Opportunities in Silicon-Based All-Solid-State Batteries: Thin-Film Bonding with Mismatch Strain

Li-metal and silicon are potential anode materials in all-solid-state Li-ion batteries (ASSBs) due to high specific capacity. However, both materials form gaps at the interface with solid electrolytes (SEs) during charging/discharging, resulting in increased impedance and uneven current density distribution. In this perspective, the different mechanisms of formation of these gaps are elaborated in detail. For Li-metal anodes, Li-ions are repeatedly stripped and unevenly deposited on the surface, leading to gaps and Li dendrite formation, which is an unavoidable electrochemical behavior. For Si-based anodes, Li-ions inserting/extracting within the Si-based electrode causes volume changes and a local separation from the SE, which is a mechanical behavior and avoidable by mitigating the strain mismatch of thin-film bonding between anode and SE. Si electro-chemical-mechanical behaviors are also described and strategies recommended to synergistically decrease Si-based electrode strain, including Si materials, Si-based composites, and electrodes. Last, it is suggested to choose a composite polymer-inorganic SE with favorable elastic properties and high ionic conductivity and form it directly on the Si-based electrode, beneficial for increasing SE strain to accommodate stack pressure and the stability of the interface. Thus, this perspective sheds light on the development and application of Si-based ASSBs.

Probing the Effectiveness in Stabilizing Lithium Metal Anodes through Functional Additives

A variety of electrolyte additives were comprehensively evaluated to understand their relative capability in stabilizing lithium metal anode. Although the Li||Cu test is an effective test to rule out ineffective additives, a reliable assessment of individual additives cannot be obtained just by a single evaluation method. Therefore, various methods must be combined to truly assess the stabilization of a lithium anode. Moreover, it was also discovered that a significant depletion of electrolytes occurred during the end-of-life of the lithium batteries, which partially contributed to the sudden failure of the lithium batteries during cycling. However, the main culprit of the sudden failure was identified as the significant increase in the resistance of the lithium metal anode. When used as an additive, cyclic fluorinated carbonates are the most effective in stabilizing the lithium anode and improving the cycling performance of lithium batteries among all the common additives. Despite its cost-effectiveness, the additive in the conventional electrolyte approach provides insufficient protection for lithium metal due to the complete consumption of the additive materials, which is necessary to repair the solid-electrolyte interphase (SEI). Therefore, it is suggested that a larger ratio (>15 wt %) of the SEI former should be employed to achieve effective lithium stabilization.

Interfacial Manipulation via In Situ Constructed Fast Ion Transport Channels toward an Ultrahigh Rate and Practical Li Metal Anode

The successful substitution of Li metal for the conventional intercalation anode can promote a significant increase in the cell energy density. However, the practical application of the Li metal anode has long been fettered by the unstable solid electrolyte interface (SEI) layer on the Li metal surface and notorious dendritic Li growth. Herein, a stabilized SEI layer with in situ constructed fast ion transport channels has successfully been achieved by a robust In2S3-cemented poly(vinyl alcohol) coating. The modified Li metal demonstrates significantly enhanced Coulombic efficiency, high rate performance (10 mA cm-2), and ultralong life cycling stability (∼4900 cycles). The Li|LiCoO2 (LCO) cell presents an ultralong-term stable operation over 500 cycles at 1 C with an extremely low capacity decay rate (∼0.018% per cycle). And the Li|LCO full cell with the ultrahigh loading cathode (∼25 mg cm-2) and ultrathin Li foil (∼40 μm) also reveals a prolonged cycling performance under the low negative-to-positive capacity ratio of 2.2. Furthermore, the Li|LCO pouch cell with a commercial cathode and ultrathin Li foil still manifests excellent cycling performance even under the harsh conditions of limited Li metal and lean electrolyte. This work provides a cost-effective and scalable strategy toward high performance practical Li metal batteries.

Highly Conductive Polyoxanorbornene-Based Polymer Electrolyte for Lithium-Metal Batteries

This present study illustrates the synthesis and preparation of polyoxanorbornene-based bottlebrush polymers with poly(ethylene oxide) (PEO) side chains by ring-opening metathesis polymerization for solid polymer electrolytes (SPE). In addition to the conductive PEO side chains, the polyoxanorbornene backbones may act as another ion conductor to further promote Li-ion movement within the SPE matrix. These results suggest that these bottlebrush polymer electrolytes provide impressively high ionic conductivity of 7.12 × 10-4 S cm-1 at room temperature and excellent electrochemical performance, including high-rate capabilities and cycling stability when paired with a Li metal anode and a LiFePO4 cathode. The new design paradigm, which has dual ionic conductive pathways, provides an unexplored avenue for inventing new SPEs and emphasizes the importance of molecular engineering to develop highly stable and conductive polymer electrolytes for lithium-metal batteries (LMB).

Cellulose-Assisted Vertically Heterostructured PEO-Based Solid Electrolytes Mitigating Li-Succinonitrile Corrosion for Lithium Metal Batteries

In the field of solid-state lithium metal batteries (SSLMBs), constructing vertically heterostructured poly(ethylene oxide) (PEO)-based solid electrolytes is an effective method to realize their tight contact with cathodes and Li anodes at the same time. Succinonitrile (SN) has been widely used in PEO-based solid electrolytes to improve the interface contact with cathodes, enhance the ionic conductivities, and obtain a high electrochemical stability window of PEO, but its application is still hindered by its intrinsic instability to Li anodes, which results in corrosion and side interactions with lithium metal. Herein, the cellulose membrane (CM) is introduced creatively into the vertically heterostructured PEO-based solid electrolytes to match the PEO-SN solid electrolytes at the cathode side. With the advantage of the interaction between -OH groups of CM and -C≡N groups in SN, the movement of free SN molecules from cathodes to Li anodes is limited effectively, resulting in a stable and durable SEI layer. In specific, the Li||LiFePO₄ battery with the CM-assisted vertically heterostructured PEO-based solid electrolyte by in situ preparation delivers a discharge capacity of around 130 mAh g^-1 after 300 cycles and capacity retention of 95% after 500 cycles at 0.5 C. Our work provides a solution to construct PEO-based solid electrolytes feasible to match cathodes and Li anodes effectively by intimate contact with electrodes.

Controlling Cell Components to Design High-Voltage All-Solid-State Lithium-Ion Batteries

All-solid-state batteries with solid ionic conductors packed between solid electrode films can release the dead space between them, enabling a greater number of cells to stack, generating higher voltage to the pack. This Review is focused on using high-voltage cathode materials, in which the redox peak of the components is extended beyond 4.7 V. Li-Ni-Mn-O systems are currently under investigation for use as the cathode in high-voltage cells. Solid electrolytes compatible with the cathode, including halide- and sulfide-based electrolytes, are also reviewed. Discussion extends to the compatibility between electrodes and electrolytes at such extended potentials. Moreover, control over the thickness of the anode is essential to reduce solid-electrolyte interphase formation and growth of dendrites. The Review discusses routes toward optimization of the cell components to minimize electrode-electrolyte impedance and facilitate ion transportation during the battery cycle.

Less is more: a perspective on thinning lithium metal towards high-energy-density rechargeable lithium batteries

Lithium (Li) metal, owing to its high specific capacity and low redox potential as a Li⁺ ion source in rechargeable lithium batteries, shows impressive prospects for electrochemical energy storage. However, engineering Li metal into thin foils has historically remained difficult, owing to its stickiness and fragility upon mechanical rolling. Consequently, using thick Li in battery systems betrays the original target for achieving higher energy density, results in material waste, and creates illusions on evaluating modification strategies for taming the highly reactive Li metal anode. Being apprehensive of this, in the tutorial review, we illustrate the argument of applying thin Li (<50 μm, preferably ≤30 μm) to achieve more realistic and advanced battery systems. A brief overview of Li is sketched first to help understand its role in batteries. Then, the reasons for pursuing thin Li are critically analyzed. Next, seminal technologies enabling the fabrication of thin Li are summarized and compared, which calls for the participation of experts from mechanical engineering, metallurgy, electrochemistry, and other fields. Subsequently, the possible applications of thin Li in batteries are presented. With the deployment of thin Li, there are new challenges and opportunities to encounter and an outlook is afforded thereof. Holy-grail Li metal anodes, combined with the subtraction operation in thickness and compatible modification strategies, would bring about a truly great leap forward in electrochemical energy storage.

Surface engineering of inorganic solid-state electrolytes via interlayers strategy for developing long-cycling quasi-all-solid-state lithium batteries

Lithium metal batteries (LMBs) with inorganic solid-state electrolytes are considered promising secondary battery systems because of their higher energy content than their Li-ion counterpart. However, the LMB performance remains unsatisfactory for commercialization, primarily owing to the inability of the inorganic solid-state electrolytes to hinder lithium dendrite propagation. Here, using an Ag-coated Li_6.4La₃Zr_1.7Ta_0.3O₁₂ (LLZTO) inorganic solid electrolyte in combination with a silver-carbon interlayer, we demonstrate the production of stable interfacially engineered lab-scale LMBs. Via experimental measurements and computational modelling, we prove that the interlayers strategy effectively regulates lithium stripping/plating and prevents dendrite penetration in the solid-state electrolyte pellet. By coupling the surface-engineered LLZTO with a lithium metal negative electrode, a high-voltage positive electrode with an ionic liquid-based liquid electrolyte solution in pouch cell configuration, we report 800 cycles at 1.6 mA/cm² and 25 °C without applying external pressure. This cell enables an initial discharge capacity of about 3 mAh/cm² and a discharge capacity retention of about 85%.

Microstructure of the Li-Al-O Second Phases in Garnet Solid Electrolytes

The microstructure of the Li₇La₃Zr₂O₁₂ (LLZO) garnet solid electrolyte is critical for its performance in all-solid-state lithium-ion battery. During conventional high-temperature sintering, second phases are generated at the grain boundaries due to the reaction between sintering aids and LLZO, which have an enormous effect on the performances of LLZO. However, a detailed structure study of the second phases and their impact on physical properties is lacking. Here, crystal structures of the second phases in LLZO pellets are studied in detail by transmission electron microscopy. Three different crystal structures of Li-Al-O second phases, γ-LiAlO₂, α-Li₅AlO₄, and β-Li₅AlO₄ were identified, and atomic-scale lattice information was obtained by applying low-dose high-resolution imaging for these electron-beam-sensitive second phases. On this basis, the structure-property relationship of these structures was explored. It was found that sintering aids with a higher Li/Al ratio are beneficial to form Li-rich second phases, which result in more highly ionic conductive LLZO.

Stable Anode-Free All-Solid-State Lithium Battery through Tuned Metal Wetting on the Copper Current Collector

A stable anode-free all-solid-state battery (AF-ASSB) with sulfide-based solid-electrolyte (SE) (argyrodite Li₆ PS₅ Cl) is achieved by tuning wetting of lithium metal on "empty" copper current-collector. Lithiophilic 1 µm Li₂ Te is synthesized by exposing the collector to tellurium vapor, followed by in situ Li activation during the first charge. The Li₂ Te significantly reduces the electrodeposition/electrodissolution overpotentials and improves Coulombic efficiency (CE). During continuous electrodeposition experiments using half-cells (1 mA cm^-2 ), the accumulated thickness of electrodeposited Li on Li₂ Te-Cu is more than 70 µm, which is the thickness of the Li foil counter-electrode. Full AF-ASSB with NMC811 cathode delivers an initial CE of 83% at 0.2C, with a cycling CE above 99%. Cryogenic focused ion beam (Cryo-FIB) sectioning demonstrates uniform electrodeposited metal microstructure, with no signs of voids or dendrites at the collector-SE interface. Electrodissolution is uniform and complete, with Li₂ Te remaining structurally stable and adherent. By contrast, an unmodified Cu current-collector promotes inhomogeneous Li electrodeposition/electrodissolution, electrochemically inactive "dead metal," dendrites that extend into SE, and thick non-uniform solid electrolyte interphase (SEI) interspersed with pores. Density functional theory (DFT) and mesoscale calculations provide complementary insight regarding nucleation-growth behavior. Unlike conventional liquid-electrolyte metal batteries, the role of current collector/support lithiophilicity has not been explored for emerging AF-ASSBs.

Negating Na‖Na3Zr2Si2PO12 interfacial resistance for dendrite-free and "Na-less" solid-state batteries

Solid electrolytes hold promise in safely enabling high-energy metallic sodium (Na) anodes. However, the poor Na‖solid electrolyte interfacial contact can induce Na dendrite growth and limit Na utilization, plaguing the rate performance and energy density of current solid-state Na-metal batteries (SSSMBs). Herein, a simple and scalable Pb/C interlayer strategy is introduced to regulate the surface chemistry and improve Na wettability of Na3Zr2Si2PO12 (NZSP) solid electrolyte. The resulting NZSP exhibits a perfect Na wettability (0° contact angle) at a record-low temperature of 120 °C, a negligible room-temperature Na‖NZSP interfacial resistance of 1.5 Ω cm2, along with an ultralong cycle life of over 1800 h under 0.5 mA cm-2/0.5 mA h cm-2 symmetric cell cycling at 55 °C. Furthermore, we unprecedentedly demonstrate in situ fabrication of weight-controlled Na anodes and explore the effect of the negative/positive capacity (N/P) ratio on the cyclability of SSSMBs. Both solid-state Na3V2(PO4)3 and S full cells show superior electrochemical performance at an optimal N/P ratio of 40.0. The Pb/C interlayer modification demonstrates dual functions of stabilizing the anode interface and improving Na utilization, making it a general strategy for implementing Na metal anodes in practical SSSMBs.

Grain Boundary Engineering in Ta-Doped Garnet-Type Electrolyte for Lithium Dendrite Suppression

Solid-state lithium batteries (SSLBs) based on Ta-doped Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZTO) suffer from lithium dendrite growth, which hinders their practical application. Herein, first principles simulations indicate that the Ta element prefers to segregate along grain boundaries in the form of Ta₂O₅ precipitates due to a high energy difference induced by Ta doping. Grain boundary engineering is employed to regulate the distribution of the Ta element and enhance the density of LLZTO by introducing the La₂O₃ additive. The sufficient La₂O₃ additive reacts with the Ta₂O₅ precipitates, while the residual La₂O₃ nanoparticles fill up void defects, promoting the homogeneous distribution of the Ta element and improving the relative density to ∼98%. Critical current density of the symmetric Li battery reaches 2.12 mA·cm^-2 at room temperature with the solid-state electrolyte (LLZTO + 5 wt % La₂O₃), which increases by 41% compared to pure LLZTO. SSLBs with the LiFePO₄ cathode achieve a stable cycling performance with a discharge capacity of 138.6 mA·h·g^-1 after 400 cycles at 0.2 C. This work provides theoretical insights into the distribution of Ta-doped LLZTO and inhibits lithium dendrite growth through grain boundary engineering.

Ultrafast Sintering for Ceramic-Based All-Solid-State Lithium-Metal Batteries

Long processing time and high temperatures are often required in sintering ceramic electrolytes, which lead to volatile element loss and high cost. Here, an ultrafast sintering method of microwave-induced carbothermal shock to fabricate various ceramic electrolytes in seconds is reported. Furthermore, it is also possible to integrate the electrode and electrolyte in one step by simultaneous co-sintering. Based on this ultrafast co-sintering technique, an all-solid-state lithium-metal battery with a high areal capacity is successfully achieved, realizing a promising electrochemical performance at room temperature. This method can extend to other various ceramic multilayer-based solid devices.

Issues Concerning Interfaces with Inorganic Solid Electrolytes in All-Solid-State Lithium Metal Batteries

All-solid-state batteries have attracted wide attention for high-performance and safe batteries. The combination of solid electrolytes and lithium metal anodes makes high-energy batteries practical for next-generation high-performance devices. However, when a solid electrolyte replaces the liquid electrolyte, many different interface/interphase issues have arisen from the contact with electrodes. Poor wettability and unstable chemical/electrochemical reaction at the interfaces with lithium metal anodes will lead to poor lithium diffusion kinetics and combustion of fresh lithium and active materials in the electrolyte. Element cross-diffusion and charge layer formation at the interfaces with cathodes also impede the lithium ionic conductivity and increase the charge transfer resistance. The abovementioned interface issues hinder the electrochemical performance of all-solid-state lithium metal batteries. This review demonstrates the formation and mechanism of these interface issues between solid electrolytes and anodes/cathodes. Aiming to address the problems, we review and propose modification strategies to weaken interface resistance and improve the electrochemical performance of all-solid-state lithium metal batteries.

Stabilizing Metallic Na Anodes via Sodiophilicity Regulation: A Review

This review focuses on the Na wetting challenges and relevant strategies regarding stabilizing sodium-metal anodes in sodium-metal batteries (SMBs). The Na anode is the essential component of three key energy storage systems, including molten SMBs (i.e., intermediate-temperature Na-S and ZEBRA batteries), all-solid-state SMBs, and conventional SMBs using liquid electrolytes. We begin with a general description of issues encountered by different SMB systems and point out the common challenge in Na wetting. We detail the emerging strategies of improving Na wettability and stabilizing Na metal anodes for the three types of batteries, with the emphasis on discussing various types of tactics developed for SMBs using liquid electrolytes. We conclude with a discussion of the overlooked yet critical aspects (Na metal utilization, N/P ratio, critical current density, etc.) in the existing strategies for an individual battery system and propose promising areas (anolyte incorporation and catholyte modifications for lower-temperature molten SMBs, cell evaluation under practically relevant current density and areal capacity, etc.) that we believe to be the most urgent for further pursuit. Comprehensive investigations combining complementary post-mortem, in situ, and operando analyses to elucidate cell-level structure-performance relations are advocated.

Room temperature all-solid-state lithium batteries based on a soluble organic cage ionic conductor

All solid-state lithium batteries (SSLBs) are poised to have higher energy density and better safety than current liquid-based Li-ion batteries, but a central requirement is effective ionic conduction pathways throughout the entire cell. Here we develop a catholyte based on an emerging class of porous materials, porous organic cages (POCs). A key feature of these Li+ conducting POCs is their solution-processibility. They can be dissolved in a cathode slurry, which allows the fabrication of solid-state cathodes using the conventional slurry coating method. These Li+ conducting cages recrystallize and grow on the surface of the cathode particles during the coating process and are therefore dispersed uniformly in the slurry-coated cathodes to form a highly effective ion-conducting network. This catholyte is shown to be compatible with cathode active materials such as LiFePO4, LiCoO2 and LiNi0.5Co0.2Mn0.3O2, and results in SSLBs with decent electrochemical performance at room temperature.

Efficient Mutual-Compensating Li-Loss Strategy toward Highly Conductive Garnet Ceramics for Li-Metal Solid-State Batteries

Garnet-type Li₇La₃Zr₂O₁₂ (LLZO) is a promising solid-state electrolyte (SSE) due to its high Li⁺ conductivity and stability against lithium metal. However, wide research and application of LLZO are hampered by the difficulty in sintering highly conductive LLZO ceramics, which is mainly attributed to its poor sinterability and the hardship of controlling the Li₂O atmosphere at a high sintering temperature (∼1200 °C). Herein, an efficient mutual-compensating Li-loss (MCLL) method is proposed to effectively control the Li₂O atmosphere during the sintering process for highly conductive LLZO ceramics. The Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZTO) ceramic SSEs sintered by the MCLL method own high relative density (96%), high Li content (5.54%), high conductivity (7.19 × 10^-4 S cm^-1), and large critical current density (0.85 mA cm^-2), equating those sintered by a hot-pressing technique. The assembled Li-Li symmetric battery and a Li-metal solid-state battery (LMSSB) show that the as-prepared LLZTO can achieve a small interfacial resistance (17 Ω cm²) with Li metal, exhibits high electrochemical stability against Li metal, and has broad potential in the application of LMSSBs. In addition, this method can also improve the sintering efficiency, avoid the use of mother powder, and reduce raw-material cost, and thus it may promote the large-scale preparation and wide application of LLZO ceramic SSE.

Confronting the Challenges in Lithium Anodes for Lithium Metal Batteries

With the low redox potential of -3.04 V (vs SHE) and ultrahigh theoretical capacity of 3862 mAh g-1 , lithium metal has been considered as promising anode material. However, lithium metal battery has ever suffered a trough in the past few decades due to its safety issues. Over the years, the limited energy density of the lithium-ion battery cannot meet the growing demands of the advanced energy storage devices. Therefore, lithium metal anodes receive renewed attention, which have the potential to achieve high-energy batteries. In this review, the history of the lithium anode is reviewed first. Then the failure mechanism of the lithium anode is analyzed, including dendrite, dead lithium, corrosion, and volume expansion of the lithium anode. Further, the strategies to alleviate the lithium anode issues in recent years are discussed emphatically. Eventually, remaining challenges of these strategies and possible research directions of lithium-anode modification are presented to inspire innovation of lithium anode.

Tailoring Stress and Ion-Transport Kinetics via a Molecular Layer Deposition-Induced Artificial Solid Electrolyte Interphase for Durable Silicon Composite Anodes

Silicon is considered as a blooming candidate material for next-generation lithium-ion batteries due to its low electrochemical potential and high theoretical capacity. However, its commercialization has been impeded by the poor cycling issue associated with severe volume changes (∼380%) upon (de)lithiation. Herein, an organic-inorganic hybrid film of titanicone via molecular layer deposition (MLD) is proposed as an artificial solid electrolyte interphase (SEI) layer for Si anodes. This rigid-soft titanicone coating with Young's modulus of 21 GPa can effectively relieve stress concentration during the lithiation process, guaranteeing the stability of the mechanical structure of a Si nanoparticles (NPs)@titanicone electrode. Benefiting from the long-strand (Ti-O-benzene-O-Ti-) unit design, the optimized Si NPs@70 cycle titanicone anode delivers a high Li⁺ diffusion coefficient and a low Li⁺ diffusion barrier, as revealed by galvanostatic intermittent titration (GITT) investigations and density functional theory (DFT) simulations, respectively. Ultimately, the Si NPs@70 cycle titanicone electrode shows high initial Coulombic efficiency (84%), long cycling stability (957 mAh g^-1 after 450 cycles at 1 A g^-1), a stable SEI layer, and good rate performances. The molecular-scale design of the titanicone-protected Si anodes may bring in new opportunities to realize the next-generation lithium-ion batteries as well as other rechargeable batteries.

Electrocatalytic NiCo2O4 Nanofiber Arrays on Carbon Cloth for Flexible and High-Loading Lithium-Sulfur Batteries

Lithium-sulfur batteries have ultrahigh theoretical energy densities, which makes them one of the most promising next-generation energy storage systems. However, it is still difficult to achieve large-scale commercialization because of the severe lithium polysulfide (LiPS) shuttle effect and low sulfur loading. Here, we report a flexible lithium-sulfur battery of a high sulfur loading with the assistance of NiCo₂O₄ nanofiber array grown carbon cloth. The NiCo₂O₄ nanofibers are ideal electrocatalysts for accelerating LiPS conversion kinetics through strong chemical interactions. Therefore, the composite cathode delivers a high specific capacity of 1280 mAh g^-1 at 0.2 C with a sulfur loading of 3.5 mg cm^-2, and it can maintain a high specific capacity of 660 mAh g^-1 after 200 cycles, showing a good cycle stability. The "layer-by-layer" stacking strategy enables the Li-S battery with a high S loading of ∼9.0 mg cm^-2 to deliver a high areal capacity of 8.9 mAh cm^-2.

Interfacial Atomistic Mechanisms of Lithium Metal Stripping and Plating in Solid-State Batteries

All-solid-state batteries based on a Li metal anode represent a promising next-generation energy storage system, but are currently limited by low current density and short cycle life. Further research to improve the Li metal anode is impeded by the lack of understanding in its failure mechanisms at lithium-solid interfaces, in particular, the fundamental atomistic processes responsible for interface failure. Here, using large-scale molecular dynamics simulations, the first atomistic modeling study of lithium stripping and plating on a solid electrolyte is performed by explicitly considering key fundamental atomistic processes and interface atomistic structures. In the simulations, the interface failure initiated with the formation of nano-sized pores, and how interface structures, lithium diffusion, adhesion energy, and applied pressure affect interface failure during Li cycling are observed. By systematically varying the parameters of solid-state lithium cells in the simulations, the parameter space of applied pressures and interfacial adhesion energies that inhibit interface failure during cycling are mapped to guide selection of solid-state cells. This study establishes the atomistic modeling for Li stripping and plating, and predicts optimal solid interfaces and new strategies for the future research and development of solid-state Li-metal batteries.