Combating Li metal deposits in all-solid-state battery via the piezoelectric and ferroelectric effects.

All-solid-state Li-metal batteries (ASSLBs) are highly desirable, due to their inherent safety and high energy density; however, the irregular and uncontrolled growth of Li filaments is detrimental to interfacial stability and safety. Herein, we report on the incorporation of piezo-/ferroelectric BaTiO3 (BTO) nanofibers into solid electrolytes and determination of electric-field distribution due to BTO inclusion that effectively regulates the nucleation and growth of Li dendrites. Theoretical simulations predict that the piezoelectric effect of BTO embedded in solid electrolyte reduces the driving force of dendrite growth at high curvatures, while its ferroelectricity reduces the overpotential, which helps to regularize Li deposition and Li+ flux. Polarization reversal of soft solid electrolytes was identified, confirming a regular deposition and morphology alteration of Li. As expected, the ASSLBs operating with LiFePO4/Li and poly(ethylene oxide) (PEO)/garnet solid electrolyte containing 10% BTO additive showed a steady and long cycle life with a reversible capacity of 103.2 mAh g-1 over 500 cycles at 1 C. Furthermore, the comparable cyclability and flexibility of the scalable pouch cells prepared and the successful validation in the sulfide electrolytes, demonstrating its universal and promising application for the integration of Li metal anodes in solid-state batteries.

Revealing the Distribution of Lithium Compounds in Lithium Dendrites by Four-Dimensional Electron Microscopy Analysis.

Characterizing the microstructure of radiation- and chemical-sensitive lithium dendrites and its solid electrolyte interphase (SEI) is an important task when investigating the performance and reliability of lithium-ion batteries. Widely used methods, such as cryogenic high-resolution transmission electron microscopy as well as related spectroscopy, are able to reveal the local structure at nanometer and atomic scale; however, these methods are unable to show the distribution of various crystal phases along the dendrite in a large field of view. In this work, two types of four-dimensional electron microscopy diffractive imaging methods, i.e., scanning electron nanodiffraction (SEND) and scanning convergent beam electron diffraction (SCBED), are employed to show a new pathway on characterizing the sensitive lithium dendrite samples at room temperature and in a large field of view. Combining with the non-negative matrix factorization (NMF) algorithm, orientations of different lithium metal grains along the lithium dendrite as well as different lithium compounds in the SEI layer are clearly identified.

In Situ Polymerization Bi-Functional Gel Polymer Electrolyte for High Performance Quasi-Solid-State Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are expected to be the next-generation energy storage system due to the ultrahigh theoretical energy density and low cost. However, the notorious shuttle effect of higher-order polysulfides and the uncontrollable lithium dendrite growth are the two biggest challenges for commercially viable Li-S batteries. Herein, these two main challenges are solved by in situ polymerization of bi-functional gel polymer electrolyte (GPE). The initiator (SiCl4) not only drives the polymerization of 1,3-dioxolane (DOL) but also induces the construction of a hybrid solid electrolyte interphase (SEI) with inorganic-rich compositions on the Li anode. In addition, diatomaceous earth (DE) is added and anchored in the GPE to obtain PDOL-SiCl4-DE electrolyte through in situ polymerization. Combined with density functional theory (DFT) calculations, the hybrid SEI provides abundant adsorption sites for the deposition of Li+, inhibiting the growth of lithium dendrites. Meanwhile, the shuttle effect is greatly alleviated due to the strong adsorption capacity of DE toward lithium polysulfides. Therefore, the Li/Li symmetric cell and Li-S full cell assembled with PDOL-SiCl4-DE exhibit excellent cycling stability. This study offers a valuable reference for the development of high performance and safe Li-S batteries.

Porous Organic Framework Materials (MOF, COF, and HOF) as the Multifunctional Separator for Rechargeable Lithium Metal Batteries.

The separator is an important component in batteries, with the primary function of separating the positive and negative electrodes and allowing the free passage of ions. Porous organic framework materials have a stable connection structure, large specific surface area, and ordered pores, which are natural places to store electrolytes. And these materials with specific functions can be designed according to the needs of researchers. The performance of porous organic framework-based separators used in rechargeable lithium metal batteries is much better than that of polyethylene/propylene separators. In this paper, the three most classic organic framework materials (MOF, COF, and HOF) are analyzed and summarized. The applications of MOF, COF, and HOF separators in lithium-sulfur batteries, lithium metal anode, and solid electrolytes are reviewed. Meanwhile, the research progress of these three materials in different fields is discussed based on time. Finally, in the conclusion, the problems encountered by MOF, COF, and HOF in different fields as well as their future research priorities are presented. This review will provide theoretical guidance for the design of porous framework materials with specific functions and further stimulate researchers to conduct research on porous framework materials.

High-efficiency Lithium Metal Stabilization and Polysulfide Suppression in Li-S Battery Enabled by Weakly Solvating Solvent.

Lithium-sulfur batteries (LSBs) are considered a highly promising next-generation energy storage technology due to their exceptional energy density and cost-effectiveness. However, the practical use of current LSBs is hindered primarily by issues related to the "shuttle effect" of lithium polysulfide (LiPS) intermediates and the growth of lithium dendrites. In strongly solvating electrolytes, the solvent-derived solid electrolyte interphase (SEI) lacks mechanical strength due to organic components, leading to ineffective lithium dendrite suppression and severe LiPS dissolution and shuttling. In contrast, the weakly solvating electrolyte (WSE) can create an anion-derived SEI layer which can enhance compatibility with lithium metal anode, and restricting LiPS solubility. Herein, a WSE consisting of 0.4 Ð¼ LiTFSI in the mixture of 1,4-dioxane (DX):dimethoxymethane (DMM) is designed to overcome the issues associated with LSB. Surface analyses confirmed the formation of a beneficial SEI layer rich in LiF, enabling homogeneous lithium deposition with an average Coulombic efficiency CE exceeding 99% over 100 cycles. Implementing the low-concentration WSE in Li||SPAN cells yielded an impressive initial specific capacity of 671 mAh g-1. This research highlights the advantages of WSE and offers the pathway for cost-effective electrolyte development, enabling the realization of high-performance LSBs.

Dendrite-Free Dual-Phase Li-Ba Alloy Anode Enabled by Ordered Array of Built-in Mixed Conducting Microchannels.

The development and application of lithium (Li) anode is hindered by volumetric variation, dendritic Li growth, and parasitic reactions. Herein, a dual-phase Li-barium (Ba) alloy with self-assembled microchannels array is synthesized through a one-step thermal fusion method to investigate the inhibition effect of lithiophilic composite porous array on Li dendrites. The Li-rich Li-Ba alloy (BaLi24) as composite Li electrode exhibits an ordered porous structure of BaLi4 intermetallic compound after delithiation, which acts as a built-in 3D current collector during Li plating/striping process. Furthermore, the lithiophilic BaLi4 alloy scaffold is a mixed conductor, featuring with Li+ ions diffusion capability, which can efficiently transport the reduced Li to the interior of the electrode structure. This unique top-down growth mode can effectively prohibit Li dendrites growth and improve the space utilization of 3D electrode structure. The spin-polarized density functional theory (DFT) calculations suggest that the absorption capability of BaLi4 benefits the deposition of Li metal. As a result, the cell performance with the dual-phase Li-Ba alloy anode is significantly improved.

Intercepting Dendrite Growth With a Heterogeneous Solid Electrolyte for Long-Life All-Solid-State Lithium Metal Batteries.

The application of lithium metal anode in all-solid-state batteries has the potential to achieve both high energy density and safety performance. However, the presence of serious dendrite issues hinders this potential. Here, the ion transport pathways and orientation of dendrite growth are regulated by utilizing the differences of ionic conductivity in heterogeneous electrolytes. The in situ formed Li-Ge alloy phases from the spontaneous reaction between Li10GeP2S12 and the attracted dendrites greatly enhance the ability to resist dendrite growth. As an outcome, the heterogeneous electrolyte achieves a high critical current density of 2.1 mA cm-2 and long-term stable symmetrical battery operation (0.3 mA cm-2 for 17 000 h and 1.0 mA cm-2 for 2000 h). Besides, due to the superior interfacial stability and low interface impedance between the heterogeneous electrolyte and lithium anode, the Li||LiNi0.8Co0.1Mn0.1O2 full battery exhibits great cycling stability (80.5% after 500 cycles at 1.0 mA cm-2) and rate performance (125.4 mAh g at 2.0 mA cm-2). This work provides a unique strategy of interface regulation via heterogeneous electrolytes design, offering insights into the development of state-of the-art all-solid-state batteries.

A New Method for In-Situ Characterization of Solid-State Batteries Based on Optical Coherence Tomography.

With the in-depth study of solid-state batteries (SSBs), various in situ and ex situ characterization technologies have been widely used to study them. The performance and reliability of SSBs are limited by the formation and evolution of lithium dendrites at the interfaces between solid electrodes and solid electrolytes. We propose a new method based on optical coherence tomography (OCT) for in situ characterization of the internal state of solid-state batteries. OCT is a low-loss, high-resolution, non-invasive imaging technique that can provide real-time monitoring of cross-sectional images of internal structures of SSBs. The morphology, growth, and evolution of lithium dendrites at different stages of cycling under various conditions can be visualized and quantified by OCT. Furthermore, we validate and correlate the OCT results with scanning electron microscopy (SEM) and XPS, proving the accuracy and effectiveness of the OCT characterization method. We reveal the interfacial phenomena and challenges in SSBs and demonstrate the feasibility and advantages of OCT as a powerful tool for in situ and operando imaging of battery interfaces. This study provides new insights into the mechanisms and factors that affect SSB performance, safety, and lifetime, and suggests possible solutions for improvement and application in the field of applied energy.

Review of the Real-Time Monitoring Technologies for Lithium Dendrites in Lithium-Ion Batteries.

Lithium-ion batteries (LIBs) have the advantage of high energy density, which has attracted the wide attention of researchers. Nevertheless, the growth of lithium dendrites on the anode surface causes short life and poor safety, which limits their application. Therefore, it is necessary to deeply understand the growth mechanism of lithium dendrites. Here, the growth mechanism of lithium dendrites is briefly summarized, and the real-time monitoring technologies of lithium dendrite growth in recent years are reviewed. The real-time monitoring technologies summarized here include in situ X-ray, in situ Raman, in situ resonance, in situ microscopy, in situ neutrons, and sensors, and their representative studies are summarized. This paper is expected to provide some guidance for the research of lithium dendrites, so as to promote the development of LIBs.

Low-Solvent-Coordination Solvation Structure for Lithium-Metal Batteries via Electric Dipole-Dipole Interaction.

Unveiling inherent interactions among solvents, Li+ ions, and anions are crucial in dictating solvation-desolvation kinetics at the electrode/electrolyte interface. Developing an electrolyte with a low ion-transport barrier and minimal solvent coordination in its interfacial solvation structure is essential for forming an anion-derived solid-electrolyte interface, a key component for high-performance Li-metal batteries. In this study, we harness electric dipole-dipole synergistic interactions to formulate an electrolyte with significantly reduced interfacial solvent coordination. Operando characterization and theoretical analysis reveal that 2-fluoropyridine (FPy) with high dipole preferentially adsorbs onto the Li metal surface. The adsorbed FPy molecule squeezes succinonitrile in the primary solvation sheath through steric hindrance, leading to the formation of an inorganic-rich interphase. Consequently, the introduction of FPy enhances the reversible capacity of the LiCoO2||Li cell, which maintains a capacity of 143 mAh g-1 after 500 cycles at a 1C rate. Moreover, the cycle life of LiCoO2 batteries with a limited supply of lithium extends from 120 cycles to over 200 cycles. These findings offer a strategy that can be applied broadly to design interfacial solvation structures for various metal-ion/metal-based batteries.

A 3D Hierarchical Host with Gradient-Distributed Dielectric Properties toward Dendrite-free Lithium Metal Anode.

The conventional conductive three-dimensional (3D) host fails to effectively stabilize lithium metal anodes (LMAs) due to the internal incongruity arising from nonuniform lithium-ion gradient and uniform electric fields. This results in undesirable Li "top-growth" behavior and dendritic Li growth, significantly impeding the practical application of LMAs. Herein, we construct a 3D hierarchical host with gradient-distributed dielectric properties (GDD-CH) that effectively regulate Li-ion diffusion and deposition behavior. It comprises a 3D carbon fiber host modified by layer-by-layer bottom-up attenuating Sb particles, which could promote Li-ion homogeneously distribution and reduce ion concentration gradient via unique gradient dielectric polarization. Sb transforms into superionic conductive Li3Sb alloy during cycling, facilitating Li-ion dredging and pumps towards the bottom, dominating a bottom-up deposition regime confirmed by COMSOL Multiphysics simulations and physicochemical characterizations. Consequently, a stable cycling performance of symmetrical cells over 2000 h under a high current density of 10 mA cm-2 is achieved. The GDD-CH-based lithium metal battery shows remarkable cycling stability and ultra-high energy density of 378 Wh kg-1 with a low N/P ratio (1.51). This strategy of dielectric gradient design broadens the perspective for regulating the Li deposition mechanism and paves the way for developing high-energy-density lithium metal anodes with long durability.

Fe3 C/nanocarbon-Enabled Lithium Dendrite Mitigation in Lithium-Sulfur batteries.

Lithium dendrite-induced short circuits and material loss are two major obstacles to the commercialization of lithium-sulfur (Li-S) batteries. Here, a nanocarbon composite consisting of cotton-derived Fe3 C-encapsulated multiwalled carbon nanotubes (Fe3 C-MWCNTs) and graphene effectively traps polysulfides to suppress lithium dendrite growth is reported. Machine learning combined with molecular dynamics (MD) simulations unveils a new polysulfide-induced lithium dendrite formation mechanism: the migration of polysulfides away from the anode drags out lithium protrusions through localized lattice distortion of the lithium anode and traps lithium ions in the surrounding electrolyte, leading to lithium dendrite formation. The Li-S battery, constructed using the composite of cotton-derived Fe3 C-MWCNTs and graphene that serves as both the sulfur host and the anode interlayer, exhibits exceptional cycling stability, impressive capacity retention, and effective mitigation of lithium dendrite formation. The findings offer valuable strategies to prevent lithium dendrite formation and enhance understanding of lithium dendrite growth in Li-S batteries.

Interface Design Enabling Stable Polymer/Thiophosphate Electrolyte Separators for Dendrite-Free Lithium Metal Batteries.

Organic/inorganic interfaces greatly affect Li+ transport in composite solid electrolytes (SEs), while SE/electrode interfacial stability plays a critical role in the cycling performance of solid-state batteries (SSBs). However, incomplete understanding of interfacial (in)stability hinders the practical application of composite SEs in SSBs. Herein, chemical degradation between Li6 PS5 Cl (LPSCl) and poly(ethylene glycol) (PEG) is revealed. The high polarity of PEG changes the electronic state and structural bonding of the PS4 3- tetrahedra, thus triggering a series of side reactions. A substituted terminal group of PEG not only stabilizes the inner interfaces but also extends the electrochemical window of the composite SE. Moreover, a LiF-rich layer can effectively prevent side reactions at the Li/SE interface. The results provide insights into the chemical stability of polymer/sulfide composites and demonstrate an interface design to achieve dendrite-free lithium metal batteries.

Grain Boundary Electronic Insulation for High-Performance All-Solid-State Lithium Batteries.

Sulfide electrolytes with high ionic conductivities are one of the most highly sought for all-solid-state lithium batteries (ASSLBs). However, the non-negligible electronic conductivities of sulfide electrolytes (≈10-8  S cm-1 ) lead to electron smooth transport through the sulfide electrolyte pellets, resulting in Li dendrite directly depositing at the grain boundaries (GBs) and serious self-discharge. Here, a grain-boundary electronic insulation (GBEI) strategy is proposed to block electron transport across the GBs, enabling Li-Li symmetric cells with 30 times longer cycling life and Li-LiCoO2 full cells with three times lower self-discharging rate than pristine sulfide electrolytes. The Li-LiCoO2 ASSLBs deliver high capacity retention of 80 % at 650 cycles and stable cycling performance for over 2600 cycles at 0.5 mA cm-2 . The innovation of the GBEI strategy provides a new direction to pursue high-performance ASSLBs via tailoring the electronic conductivity.

Li Plating Regulation on Fast-Charging Graphite Anodes by a Triglyme-LiNO3 Synergistic Electrolyte Additive.

Graphite anodes are prone to dangerous Li plating during fast charging, but the difficulty to identify the rate-limiting step has made a challenging to eliminate Li plating thoroughly. Thus, the inherent thinking on inhibiting Li plating needs to be compromised. Herein, an elastic solid electrolyte interphase (SEI) with uniform Li-ion flux is constructed on graphite anode by introducing a triglyme (G3)-LiNO3 synergistic additive (GLN) to commercial carbonate electrolyte, for realizing a dendrite-free and highly-reversible Li plating under high rates. The cross-linked oligomeric ether and Li3 N particles derived from the GLN greatly improve the stability of the SEI before and after Li plating and facilitate the uniform Li deposition. When 51 % of lithiation capacity is contributed from Li plating, the graphite anode in the electrolyte with 5 vol.% GLN achieved an average 99.6 % Li plating reversibility over 100 cycles. In addition, the 1.2-Ah LiFePO4 | graphite pouch cell with GLN-added electrolyte stably operated over 150 cycles at 3 C, firmly demonstrating the promise of GLN in commercial Li-ion batteries for fast-charging applications.

Phase Separation-Controlled Assembly of Hierarchically Porous Aramid Nanofiber Films for High-speed Lithium-Metal Batteries.

The growth of lithium (Li) dendrites reduces the lifespan of Li-metal batteries and causes safety issues. Herein, hierarchically porous aramid nanofiber separators capable of effectively suppressing the Li dendrite growth while maintaining highly stable cycle performances at high charge/discharge rates are reported. A two-step solvent exchange process combined with reprotonation-mediated self-assembly is utilized to control the bimodal porous structure of the separators. In particular, when ethanol and water are used sequentially, aramid nanofibers form hierarchical porous structures containing nanopores in macroporous polymer frameworks to yield a mechanically robust membrane with high porosity of 97% or more. The optimized samples exhibit high ionic conductivities of 1.87-4.04 mS cm-1 and high Li-ion transference numbers of 0.77-0.84 because of the ultrahigh porosity and selective affinity to anions. Li-metal symmetric cells do not show any noticeable presence of dendrites after 100 cycles, and they operate stably for more than 1500 cycles even under extreme conditions with a high current density of >20 mA cm-2 . In addition, the LiFePO4 /Li full cell retains 86.3% of its capacity after 1000 cycles at a charge rate of 30 C.

An All-Solid-State Battery Based on Sulfide and PEO Composite Electrolyte.

Replacing liquid electrolytes with solid polymer electrolytes (SPEs) is considered as a vital approach to developing sulfur (S)-based cathodes. However, the polysulfides shuttle and the growth of lithium (Li) dendrites are still the major challenges in polyethylene oxide (PEO)-based electrolyte. Here, an all-solid-state Li metal battery with flexible PEO-Li10 Si0.3 PS6.7 Cl1.8 (LSPSCl)-C-lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) composite cathode (FCC) and PEO-LSPSCl-LiTFSI composite electrolyte (S-CPE) is designed. The initial capacity of the Li|S-CPE|FCC battery is 414 mAh g-1 with 97.8% capacity retention after 100 cycles at 0.1 A g-1 . Moreover, the battery displays remarkable capacity retention of 80% after 500 cycles at 0.4 A g-1 . Cryo-transmission electron microscopy (Cryo-TEM) reveals rich large-sized Li2 CO3 particles at the Li/PEO interface blocking the Li+ transport, but the layer with rich Li2 O nanocrystals, amorphous LiF and Li2 S at the Li/S-CPE interface suppresses the growth of lithium dendrite and stabilizes the interface. In situ optical microscopy demonstrates that the excellent cyclic stability of FCC is ascribed to the reversible shuttle of P-S-P species, resulting from the movement of ether backbone in PEO. This study provides strategies to mitigate the polysulfide shuttle effect and Li dendrite formation in designing high energy density solid-state Li-S-based batteries.

Atomistic Mechanism and Long-Term Stability of Using Chlorinated Graphdiyne Film to Reduce Lithium Dendrites in Rechargeable Lithium Metal Batteries.

The formation of lithium dendrites remains one of the biggest challenges of commercializing rechargeable lithium metal batteries. Here, we combine classical molecular dynamics simulations and first-principles calculations to study the possibility of utilizing modified graphdiyne film, which possesses intrinsic nanopores, as a stable "nanosieve" to reduce the lithium dendrites on anode. We find that through a mechanism resembling the hydraulic jump in fluid dynamics, graphdiyne film can enforce the concentration uniformity of lithium ions even under a highly non-uniform electric field and thus can induce a uniform nucleation of lithium metal. We further show that bare graphdiyne film can be gradually metalized by lithium metal, but the chlorination of graphdiyne significantly increases its resistance to the metalization and easily conducts the lithium ions. These properties together suggest that the chlorinated graphdiyne can potentially be used as a stable membrane to reduce the lithium dendrites in rechargeable lithium metal batteries.

A Dual Functional Artificial SEI Layer Based on a Facile Surface Chemistry for Stable Lithium Metal Anode.

Solid electrolyte interphase (SEI) on a Li anode is critical to the interface stability and cycle life of Li metal batteries. On the one hand, components of SEI with the passivation effect can effectively hinder the interfacial side reactions to promote long-term cycling stability. On the other hand, SEI species that exhibit the active site effect can reduce the Li nucleation barrier and guide Li deposition homogeneously. However, strategies that only focus on a separated effect make it difficult to realize an ideal overall performance of a Li anode. Herein, a dual functional artificial SEI layer simultaneously combining the passivation effect and the active site effect is proposed and constructed via a facial surface chemistry method. Simultaneously, the formed LiF component effectively passivates the anode/electrolyte interface and contributes to the long-term stable cycling performance, while the Li-Mg solid solution alloy with the active site effect promotes the transmission of Li+ and guides homogeneous Li deposition with a low energy barrier. Benefiting from these advantages, the Li||Li cell with the modified anode performs with a lower nucleation overpotential of 2.3 mV, and an ultralong cycling lifetime of over 2000 h at the current density of 1 mA cm-2, while the Li||LiFePO4 full battery maintains a capacity retention of 84.6% at rate of 1 C after 300 cycles.

WSe2 Flakelets on N-Doped Graphene for Accelerating Polysulfide Redox and Regulating Li Plating.

The practical application of lithium-sulfur batteries is still limited by the lithium polysulfides (LiPSs) shuttling effect on the S cathode and uncontrollable Li-dendrite growth on the Li anode. Herein, elaborately designed WSe2 flakelets immobilized on N-doped graphene (WSe2 /NG) with abundant active sites are employed to be a dual-functional host for satisfying both the S cathode and Li anode synchronously. On the S cathode, the WSe2 /NG with a strong interaction towards LiPSs can act as a redox accelerator to promote the bidirectional conversion of LiPSs. On the Li anode, the WSe2 /NG with excellent lithiophilic features can regulate the uniform Li plating/stripping to mitigate the growth of Li dendrite. Taking advantage of these merits, the assembled Li-S full batteries exhibit remarkable rate performance and stable cycling stability even at a higher sulfur loading of 10.5 mg cm-2 with a negative to positive electrode capacity (N/P) ratio of 1.4 : 1.