Lithium-ion Pathways Research Articles

Development and Optimization of Thin-Lithium-Metal Anodes with a Lithium Lanthanum Titanate Stabilization Coating for Enhancement of Lithium-Sulfur Battery Performance.

Lithium-ion batteries are dominating high-energy-density energy storage for 30 years. However, their development approaches theoretical limits, spurring the development of lithium-sulfur cells that achieve high energy densities through reversible electrochemical conversion reactions. Nevertheless, the commercialization of lithium-sulfur cells is hindered by practical challenges associated primarily with the use of thick-lithium anodes, low-loading sulfur cathodes, and high electrolyte-to-sulfur ratios, which prevent realization of the cells' full potential in terms of electrochemical and material performance. To solve these extrinsic and intrinsic problems, the effect of lithium-metal thickness on the electrochemical behavior of lithium-sulfur cells with high-loading sulfur cathodes in lean-electrolyte configurations is investigated. Specifically, lithium lanthanum titanate (LLTO), a solid electrolyte, is utilized to form an ionically/electronically conductive coating to stabilize lithium-metal anodes, thereby enhancing their lithium-ion pathways and interfacial charge transfer. Electrochemical analyses reveal that an LLTO coating significantly reduces excessive reactions between lithium metal and an electrolyte, thereby minimizing lithium consumption and electrolyte depletion. Further, LLTO-stabilized lithium anodes improve lithium-sulfur cell performance, and most importantly, allow the fabrication of thin-lithium, high-loading-sulfur cells that open a pathway toward high-energy-density batteries.

Rational design of continuous and short-range lithium ion pathways based on polydopamine-anchored metal-organic frameworks for all-solid-state electrolytes

The immerging three dimensional (3D) metal-organic framework (MOF)-reinforced composite solid-state electrolytes have attracted great interest because of the enhanced ionic conductivity and mechanical properties. However, the defective spatial arrangement of MOFs restricted by fabrication methodology leads to insufficient lithium ion transport in electrolytes. Herein, a 3D interconnected MOF framework tailored for all-solid-state electrolytes is rationally designed by a universal polydopamine (PDA)-engineered “double-sided tape” strategy. The PDA serves as a double-sided tape, firmly adhering on the special single-layer Nylon grid as well as offering uniform nucleation sites to anchor the metal nodes to ensure continuous growth of well-ordered MOFs. Benefiting from the Lewis acid feature of MOFs and its cage effect toward TFSI−, a fast and homogeneous lithium ion transport can be achieved through the internal channels within neighboring MOFs and the continuous MOFs/polymer interfaces both along the short-range circumferential boundary of Nylon fiber. The resultant composite electrolytes exhibit high lithium ion conductivity and prominent mechanical properties, rendering excellent cyclic stability whether used in coin or pouch cells. This work demonstrates a widely applicable “double-sided tape” strategy for controllable spatial arrangement of MOF nanoparticles on optional substrates, which provides a scalable approach to rationally construct desired lithium ion pathways within composite electrolytes.

Solid-state rigid polymer composite electrolytes with in-situ formed nano-crystalline lithium ion pathways for lithium-metal batteries

Polymer-based solid-state electrolytes with excellent processability and flexibility are ideal candidates for commercialisation in lithium-metal batteries. However, the current polymer-based solid-state electrolytes still have many problems such as low ionic conductivity, limited Li+ transport number and high interfacial resistance with electrodes. To address the above challenges, a solid-state rigid polymer composite electrolyte with high ionic conductivity (2.8 mS cm−1) has been prepared based on the rigid polymer poly(2, 2′-disulfonyl-4, 4′-benzidine terephthalamide) (PBDT). Locally aligned PBDT-EMImN(CN)2 grains are interspersed with in-situ formed interconnected LiFSI to form the structure of the polymer composite electrolyte. The formation of defective LiFSI nanocrystals at grain boundaries inside the polymer electrolyte acts as additional conductive networks providing fast Li+ transportation (tLi+ = 0.59). The flexible region in the electrolyte gives excellent interfacial impedance (32.5 Ω cm2) with Li-metal electrode. The Li||Li batteries can be stably cycled for over 1000 cycles at 1 mA cm−2 (25 °C). The assembled Li||LiFePO4 batteries exhibit excellent cycling and multiplication performance over a wide operating temperature (from −20 to 60 °C). Moreover, this electrolyte material exhibits compatibility with high-voltage cathode LiNi0.6Mn0.2Co0.2O2 batteries. This electrolyte and design strategy is expected to inspire the realization of all-weather practical solid-state lithium-metal batteries.

Nanostructured S@VACNTs Cathode with Lithium Sulfate Barrier Layer for Exceptionally Stable Cycling in Lithium-Sulfur Batteries

Lithium-sulfur technology garners significant interest due to sulfur’s higher specific capacity, cost-effectiveness, and environmentally friendly aspects. However, sulfur’s insulating nature and poor cycle life hinder practical application. To address this, a simple modification to the traditional sulfur electrode configuration is implemented, aiming to achieve high capacity, long cycle life, and rapid charge rates. Binder-free sulfur cathode materials are developed using vertically aligned carbon nanotubes (CNTs) decorated with sulfur and a lithium sulfate barrier layer. The aligned CNT framework provides high conductivity for electron transportation and short lithium-ion pathways. Simultaneously, the sulfate barrier layer significantly suppresses the shuttle of polysulfides. The S@VACNTs with Li2SO4 coating exhibit an extremely stable reversible areal capacity of 0.9 mAh cm−2 after 1600 cycles at 1 C with a capacity retention of 80% after 1200 cycles, over three times higher than lithium iron phosphate cathodes cycled at the same rate. Considering safety concerns related to the formation of lithium dendrite, a full cell Si-Li-S is assembled, displaying good electrochemical performances for up to 100 cycles. The combination of advanced electrode architecture using 1D conductive scaffold with high-specific-capacity active material and the implementation of a novel strategy to suppress polysulfides drastically improves the stability and the performance of Li-S batteries.

Effect of Nanostructured Inorganic Ceramic Filler on Poly(ethylene oxide)-Based Solid Polymer Electrolytes

In view of the ongoing changes in energy science and technology, the possibilities of energy storage are getting increasingly important. In particular, storing electrical energy is more complex than with fossil fuels.Lithium-Ion batteries are the most commonly used media for energy storage, but they also have some safety-related problems: toxic decomposition products can leak out and the devices can catch fire. Research is underway to find alternatives to minimize this potential hazards. Great improvements in safety matters can be achieved by replacing liquid electrolytes with ceramic/polymer hybrid electrolytes. These hybrid electrolytes combine the advantages of polymer electrolytes with the benefits of inorganic ceramic fillers.1 Flexibility, good contact ability and in addition the good processability is provided through the polymer. The inorganic ceramic filler in contrast adds mechanical stability, opens new pathways for the Lithium-Ions and can enhance the stability of the electrolyte.Figure 1: different Lithium-ion pathways in ceramic/polymer hybrid electrolytes dependent on different filler amounts. 2 In this work the impact of the manufacturing method on the conductivity of a series of electrolytes was examined. Therefore, hot pressing, solution casting and electrospinning were tested. Also, different distribution methods for the particles in the material were tested to monitor the influence of agglomeration on the conductivity. The materials were characterized regarding the crystallinity using X-Ray diffraction, the surface and particle distribution was monitored with SEM/EDX, the thermal character was investigated using DSC, the conductivity was determined using impedance spectroscopy and the electrochemical behavior was tested using cyclic voltammetry. Furthermore, the Arrhenius equation was used to interpret the results of impedance spectroscopy regarding their activation energy. The addition of inorganic ceramic fillers leads to an enhancement of the ionic conductivity in PEO based electrolytes and increases processability and stability of the electrolyte. In this work conductivities of 10-5 S/cm were reached at room temperature. The performance of the electrolyte was increased above three orders of magnitude compared to a PEO electrolyte without inorganic ceramic fillers. Walke, P.; Kirchberger, A.; Reiter, F.; Esken, D.; Nilges, T., Effect of nanostructured Al2O3 on poly(ethylene oxide)-based solid polymer electrolytes. Zeitschrift für Naturforschung B 2021, 76 (10-12), 615-624. Chen, L.; Li, Y.; Li, S.-P.; Fan, L.-Z.; Nan, C.-W.; Goodenough, J. B., PEO/garnet composite electrolytes for solid-state lithium batteries: From “ceramic-in-polymer” to “polymer-in-ceramic”. Nano Energy 2018, 46, 176-184. Figure 1

Nanoarchitectonics of lithium ion pathways through pores in a carbon framework for improving the storage capability and reversibility of lithium metal anode

The utilization of lithium (Li) metal as an anode has attracted significant attention for high‐energy Li batteries. Unfortunately, uncontrollable Li dendrite cannot be avoided during Li plating and stripping. Much intensive research has been conducted to suppress the dendritic growth by confinement of metallic Li in host architectures. Recently, zeolitic imidazolate frameworks (ZIFs) with a porous features have been used to explore a new approach to storing the Li metal with the advantages of their structural and chemical stability, large surface areas, and large pore cavities. Herein, we investigate the storage capability of metallic Li in a porous carbon framework derived from ZIFs as a function of carbonization temperature. Diversities in pore volumes and channels, the degree of crystallinity, the amount of residual zinc (Zn) metal, and the electrical conductivity can all be controlled by temperature. We demonstrate that well‐connected pore channels and adequate electrical conductivity secure the Li‐ion pathways and that well‐distributed Zn clusters in porous carbon trigger the outward growth of metallic Li from inside the frameworks, resulting in a relatively low overpotential and long‐lasting cyclability. Our findings can provide practical insight into advanced electrode design for next‐generation Li metal batteries.

Extended Lifespan of Low-Cost Metal Silicon Anodes via a One-Step Wet Ball-Milling Process for Ultra-Thin Polymer Protecting Layer and Optimal Particle Size

Silicon is a promising active material for lithium-ion batteries (LIBs) with a high theoretical capacity (∼4000 mA h g–1). However, there is a critical issue that the fabrication of the Si anode needs complicated and high-cost processes to alleviate the poor cyclic performance, such as nanostructuring. Furthermore, the Si anode requires a high component ratio of conductive agents and binder in the electrode. Herein, we report the fabrication of submicron Si particles coated by a polyacrylonitrile (PAN) layer with a highly polar nitrile group via a facile one-step wet ball-milling process. During the milling of Si particles in PAN solutions, PAN adheres to the Si surface and forms a nanometer coating layer. The nitrile groups of PAN enhance the electrolyte wettability and increase the lithium-ion pathways on the Si surface. These result in a stable solid electrolyte interphase (SEI) layer and reduce the internal resistance of the electrodes. Si anodes with an optimal particle size and PAN layer (SM-Si@PAN) exhibit a superior performance even at ultra-fast current density (50 A g–1). In addition, a full-cell with an NCM712 cathode shows an excellent performance.

Exploring the Nanoscale Origin of Performance Enhancement in Li1.1Ni0.35Mn0.55O2 Batteries Due to Chemical Doping

AbstractDespite significant potential as energy storage materials for electric vehicles due to their combination of high energy density per unit cost and reduced environmental and ethical concerns, Co‐free lithium ion batteries based on layered Mn oxides presently lack the longevity and stability of their Co‐containing counterparts. Here, a reduction in this performance gap is demonstrated via chemical doping, with Li1.1Ni0.35Mn0.54Al0.01O2 achieving an initial discharge capacity of 159 mAhg−1 at C/3 rate and a corresponding capacity retention of 94.3% after 150 cycles. The nanoscale origins of this improvement are subsequently explored through a combination of advanced diffraction, spectroscopy, and electron microscopy techniques, finding that optimized doping profiles lead to an improved structural and chemical compatibility between the two constituent sub‐phases that characterize the layered Mn oxide system, resulting in the formation of unobstructed lithium ion pathways between them. A structural stabilization effect of the host compound is also directly observed near the surface using aberration corrected scanning transmission electron microscopy and integrated differential phase contrast imaging.

Directional Ion Transport Enabled by Self‐Luminous Framework for High‐Performance Quasi‐Solid‐State Lithium Metal Batteries

Composite gel polymer electrolyte (CGPE), derived from ceramic fillers has emerged as one of the most promising candidates to improve the safety and cycling stability of lithium metal batteries. However, the poor interface compatibility between the ceramic phase and polymer phase in CGPE severely deteriorates lithium-ion pathways and cell performances. In this work, a fluorescent ceramic nanowire network that can palliate the energy barrier of photoinitiators and contribute to preferential nucleation and growth of polymer monomers is developed, thus inducing polymer segment orderly arrangement and tightly combination. A proof-of-concept study lies on fabrications of poly(ethylene oxide) closely coating on the ceramic nanowires, thus dividing the matrix into mesh units that contribute to directional lithium-ion fluxand dendrite-free deposition on the metallic anode. The CGPE, based on the state-of-the-art self-luminous framework, facilitates high-performance quasi-solid-state Li||LiFePO4 cell, registering a high capacity of 143.3 mAh g-1 after 120 cycles at a mass loading of 12mg cm-2 . X-ray computed tomography provides an insight into the relationship between directional lithium-ion diffusion and lithium deposition behavior over the electrochemical processes. The results open a door to improve the electrochemical performances of composite electrolytes in various applications.

(Battery Division Early Career Award Sponsored by Neware Technology Limited) Design, Synthesis, and Characterization of Cathode Microstructures in Lithium Batteries

The propagation of redox reactions governs the electrochemical properties of battery materials and their critical performance metrics in battery cells. The recent research progress, especially aided by advanced analytical techniques, has revealed that incomplete and heterogeneous redox reactions prevail in many electrode materials. Advanced high-capacity cathode materials are mostly polycrystalline materials that exhibit complex charge distribution (the valence state distribution of the redox-active cations) due to the presence of numerous constituting grains and grain boundaries. The redox reactions in individual grains typically do not proceed concurrently due to their distinct geometric locations in polycrystalline particles. As a result, these unsynchronized local redox events collectively induce heterogeneous and anisotropic charge distribution, building up intergranular and intragranular stress. Therefore, these polycrystalline materials may exhibit weak mechanical stability, leading to undesired chemomechanical breakdown during battery operation. Grain engineering in polycrystalline materials provides a large playground to modulate the materials properties beyond controlling the chemical composition, and electronic and crystal structures. In particular, the anisotropic ion-conducting pathways in layered oxides make the grain crystallographic orientation a critical factor in determining the modality of the redox reactions in these materials.This presentation will discuss our recent progress in the design, synthesis, and characterization of cathode microstructures in lithium batteries.First, we will discuss how the charge distribution is guided by grain crystallographic orientations in polycrystalline battery materials. We elucidate the spatially resolved charge distribution in lithium layered oxides with different grain crystallographic arrangements and establish a model to quantify their charge distributions. While the holistic “surface-to-bulk” charge distribution prevails in polycrystalline particles, the crystallographic orientation-guided redox reaction governs the charge distribution in the local charged nanodomains. Compared to the randomly oriented grains, the radially aligned grains exhibit a lower cell polarization and higher capacity retention upon battery cycling. The radially aligned grains create less tortuous lithium-ion pathways, thus improving the charge homogeneity as statistically quantified from over 20 million nanodomains in polycrystalline particles. This study provides an improved understanding of the charge distribution and chemomechanical properties of polycrystalline battery materials.Second, we will discuss how the grain arrangement affects the thermal stability of polycrystalline cathode materials in rechargeable batteries. We performed a systematic in situ study on the Ni-rich polycrystalline cathode materials to investigate the fundamental degradation mechanism of charged cathodes at elevated temperatures, which is essential for tailoring material properties and improving performance. Using multiple microscopy, scattering, thermal, and electrochemical probes, we decoupled the major contributors to the thermal instability from intertwined factors. Based on our findings, the cathode grain microstructure has a forgotten yet important role in the thermal stability of polycrystalline rechargeable batteries. Oxygen release, as an important process during the thermal runaway, can be regulated through engineering grain arrangements. The grain arrangement can modulate the macroscopic crystallographic transformation pattern and oxygen diffusion length in layered cathodes to offer more possibilities for cathode material design and synthesis.Third, we will discuss our new understanding of particle behaviors in composite cathodes. We capture and quantify the particle motion during the solidification of battery electrodes and reveal the statistics of the dynamically evolving motion in the drying process, which has been challenging to resolve. We discover that the particle motion exhibits a strong dependence on its geometric location within a drying electrode. Our results also imply that the final electrode quality can be controlled by balancing the solvent evaporation rate and the particle mobility in the region close to the drying surface. We formulate a network evolution model to interpret the regulation and equilibration between electrochemical activity and mechanical damage of these particles. Through statistical analysis of thousands of particles using x-ray phase-contrast holotomography in a Ni-rich cathode, we found that the local network heterogeneity results in asynchronous activities in the early cycles, and subsequently the particle assemblies move toward a synchronous behavior. Our study pinpoints the chemomechanical behavior of individual particles and enables better designs of the conductive network to optimize the utility of all the particles during operation.

Tradeoff between the Ion Exchange-Induced Residual Stress and Ion Transport in Solid Electrolytes

Rapid filament growth of lithium is limiting the commercialization of solid-state lithium metal anode batteries. Recent work demonstrated that lithium filaments grow into pre-existing or nascent cracks in the solid electrolyte, suggesting that increasing the fracture toughness of the solid electrolytes will inhibit filament penetration. It has been suggested that introducing residual compressive stresses at the surface of the solid electrolyte can provide this additional fracture toughness. One of the ways to induce these residual compressive stresses is by exchanging lithium ions (Li+) with larger isovalent ions such as potassium (K+). On the other hand, incorporation of too much potassium can alter the lithium-ion diffusion pathway and lower the diffusivity, thus limiting the performance of the solid-state electrolyte. Using multiscale modeling methods, we optimize this tradeoff and predict that exchanging 3.4% potassium ions up to a depth twice the grain sizes in Li7La3Zr2O12 solid electrolyte can induce a maximum residual compressive stress of around 1.1 GPa, corresponding to an increase in fracture strength by ∼8 times, while lowering the diffusivity in the ion-exchanged region by a factor of 5 at room temperature. The reduction of lithium diffusivity is due to K+-induced stress and (mainly) blockage of lithium ion pathways in the shallow ion-exchanged layer.

Nerve network-inspired solid polymer electrolytes (NN-SPE) for fast and single-ion lithium conduction

The low lithium-ion conductivity is current the bottleneck in developing solid-state electrolytes (SSEs) that are expected to be a key component in the next generation of lithium batteries. Inspired by the high connectivity of the biological nerve network, we designed a mimic architecture inside a polymer electrolyte to provide fast lithium-ion pathways. Detailed experimental and simulation studies revealed that the mimic nerve network could efficiently form the bi-continuous structure at very low percolation threshold, and rendered an unprecedentedly non-linear increment by order of magnitudes in the lithium-ion conductivity, with a superior lithium-ion conductivity up to 0.12 mS·cm−1, transference number up to 0.974 and robust mechanical strength of 10.3 MPa. When applied in lithium metal batteries, good rate and cycling performance were achieved at both room and elevated temperatures.

Grain Boundaries and Dislocations in Layered Cathodes

Crystallographic defects exist in many redox active energy materials, e.g., battery and catalyst materials, which significantly alter their chemical properties for energy storage and conversion. In this presentation, we will address how these defects, e.g., grain boundaries and geometrically necessary dislocations, govern the charge distribution and battery performance of layered oxide cathodes. Architecting grain crystallographic orientation can modulate charge distribution and chemomechanical properties for enhancing the performance of polycrystalline battery materials. However, probing the interplay between charge distribution, grain crystallographic orientation, and performance remains a daunting challenge. Herein, we elucidate the spatially resolved charge distribution in lithium layered oxides with different grain crystallographic arrangements and establish a model to quantify their charge distributions. While the holistic “surface-to-bulk” charge distribution prevails in polycrystalline particles, the crystallographic orientation-guided redox reaction governs the charge distribution in the local charged nanodomains. Compared to the randomly oriented grains, the radially aligned grains exhibit a lower cell polarization and higher capacity retention upon battery cycling. The radially aligned grains create less tortuous lithium ion pathways, thus improving the charge homogeneity as statistically quantified from over 20 million nanodomains in polycrystalline particles. This study provides an improved understanding of the charge distribution and chemomechanical properties of polycrystalline battery materials. Crystallographic defects, such as geometrically necessary dislocations, are reported to influence the redox reactions in battery particles through single-particle, multimodal, in situ synchrotron measurements. Through Laue X-ray microdiffraction, many crystallographic defects are spatially identified and statistically quantified from a large quantity of diffraction patterns in many layered oxide particles, including geometrically necessary dislocations, tilt boundaries, and mixed defects. The in situ and ex situ measurements, combining microdiffraction and X-ray spectroscopic imaging, reveal that LiCoO2 particles with a higher concentration of geometrically necessary dislocations provide deeper charging reactions, indicating that dislocations may facilitate redox reactions in layered oxides during initial charging. The present study illustrates that a precise control of crystallographic defects and their distribution can potentially promote and homogenize redox reactions in battery materials.

All MOF-derived-carbon material-based integrated electrode constructed by carbon nanosheet sulfur host and Fe microparticles with carbon nanofiber network interlayer for lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries are promising future-generation portable electronic devices due to the outstanding energy density of S. However, the serve problems of Li–S batteries originating from the intrinsic poor conductivity of S and the dissolution and diffusion of dissoluble polysulfides in electrolytes are a major limitation. Herein, we demonstrated an all metal–organic framework (MOF)-derived carbon material-based integrated sulfur cathode, which was constructed with 3D carbon nanofiber network with Fe microparticles (MIL1000) as interlayer on a polypropylene (PP) separator and 2D nanosheets (MIL900-H) as S host. Notably, the MIL900-H carbon nanosheets with many mesopores and doping oxygen possessed lithium-ion pathways and chemical adsorption of soluble polysulfides, and the MIL1000 interlayer could chemically adsorb, physically block polysulfide, and facilitate the kinetics of the cathode reaction. As a result, the integrated electrode that avoided the use of a metal current collector exhibited a high initial capacity of 1244.6 mAh/g at 0.1 C, fast Li2S nucleation, and excellent cycle stability with the capacity retention of 69.3% after 500 cycles at 1 C. Therefore, this rationale strategy of constructing an all MOF-derived-carbon material-based integrated electrode can be extended to other abundant MOF-derived materials for high energy density Li–S batteries.

(Invited) Grain Boundaries and Dislocations in Layered Cathodes

Crystallographic defects exist in many redox active energy materials, e.g., battery and catalyst materials, which significantly alter their chemical properties for energy storage and conversion. In this presentation, we will address how these defects, e.g., grain boundaries and geometrically necessary dislocations, govern the charge distribution and battery performance of layered oxide cathodes.Architecting grain crystallographic orientation can modulate charge distribution and chemomechanical properties for enhancing the performance of polycrystalline battery materials. However, probing the interplay between charge distribution, grain crystallographic orientation, and performance remains a daunting challenge. Herein, we elucidate the spatially resolved charge distribution in lithium layered oxides with different grain crystallographic arrangements and establish a model to quantify their charge distributions. While the holistic “surface-to-bulk” charge distribution prevails in polycrystalline particles, the crystallographic orientation-guided redox reaction governs the charge distribution in the local charged nanodomains. Compared to the randomly oriented grains, the radially aligned grains exhibit a lower cell polarization and higher capacity retention upon battery cycling. The radially aligned grains create less tortuous lithium ion pathways, thus improving the charge homogeneity as statistically quantified from over 20 million nanodomains in polycrystalline particles. This study provides an improved understanding of the charge distribution and chemomechanical properties of polycrystalline battery materials.Crystallographic defects, such as geometrically necessary dislocations, are reported to influence the redox reactions in battery particles through single-particle, multimodal, in situ synchrotron measurements. Through Laue X-ray microdiffraction, many crystallographic defects are spatially identified and statistically quantified from a large quantity of diffraction patterns in many layered oxide particles, including geometrically necessary dislocations, tilt boundaries, and mixed defects. The in situ and ex situ measurements, combining microdiffraction and X-ray spectroscopic imaging, reveal that LiCoO2 particles with a higher concentration of geometrically necessary dislocations provide deeper charging reactions, indicating that dislocations may facilitate redox reactions in layered oxides during initial charging. The present study illustrates that a precise control of crystallographic defects and their distribution can potentially promote and homogenize redox reactions in battery materials.

Polymer-Inorganic Nanocomposite Coating with High Ionic Conductivity and Transference Number for Stable Lithium Metal Anode

Lithium metal is an ideal candidate for battery anodes due to its high specific capacity (3860 mAh g–1) and low electrochemical potential (–3.04 V). However, non-uniform lithium electrodeposition causes low Coulombic efficiency, poor cycling stability, potential safety issues, and has hindered the commercialization of lithium metal batteries at scale. The parasitic reaction of lithium metal with liquid electrolytes results in the formation of a solid electrolyte interphase (SEI). During cycling, the SEI tends to break continuously, exposing unreacted lithium metal to the electrolyte. This not only promotes non-uniform lithium plating and stripping, but also leads to further SEI formation, which consumes the liquid electrolyte. In addition, the detachment of dendritic lithium from the bulk lithium electrode produces electrically isolated 'dead' lithium during lithium stripping, which no longer participates in the cell reaction. Dendritic lithium and 'dead' lithium formed during cycling largely increase the surface area of the lithium metal anode and consequently accelerates electrolyte consumption. These mechanisms lead to rapid capacity fading and cell failure due to either the complete consumption of the electrolyte or the complete conversion of the lithium metal anode to 'dead' lithium. The formation of lithium metal dendrites can also causes abrupt cell short circuit, which results in thermal runaway. Therefore, a stable interface on lithium metal electrode that enables uniform lithium electrodeposition is the key for the development of lithium metal batteries.Here, we report a nanocomposite coating for the lithium metal protection, which consists of nano-sized LiF particles embedded into a PEO polymer matrix as shown in the inset of the following figure. The nano-sized LiF particles ensure high interface area, which provides lithium-ion pathway throughout the composite. The LiF/PEO nanocomposite coating offers exceptionally high ionic conductivity of 0.97 mS cm–1 and high lithium-ion transference number of 0.77 at room temperature in contact with a carbonate-based liquid electrolyte. Both properties are key to realize uniform lithium plating and stripping and prevent lithium dendrite formation. Lithium metal electrodes coated with this protective coating enable stable lithium plating and stripping at 1 mA cm–2 for over 1000 h. As shown in the following figure, a full cell with the coated lithium metal anode and a NMC622 cathode with an areal capacity of 1 mAh cm–2 shows much improved specific capacity and cycling stability. The cell exhibits a high initial capacity of 135 mAh g–1 and a capacity retention of 83% after 500 cycles at 1 mA cm–2. Even at a high current density of 3 mA cm–2, the full cell shows an initial capacity of 125 mAh g–1 and a capacity retention of 74% after 300 cycles. Figure 1

Separators Modified Using MoO2@Carbon Nanotube Nanocomposites as Dual-Mode Li-Polysulfide Anchoring Materials for High-Performance Anti-Self-Discharge Lithium–Sulfur Batteries

The commercialization of lithium–sulfur batteries (LSBs) remains difficult owing to the shuttle effect of soluble lithium–polysulfide and the poor redox kinetics of a traditional cell configuration without a sophisticated cathode design. To resolve these difficulties, we developed modified separators with electrically exploded MoO2@carbon nanotube (MoO2@CNT) nanocomposites. The embedded MoO2 nanoparticles demonstrated strong chemical anchoring properties with polysulfides; meanwhile, a porous CNT scaffold supported suppression of the shuttle effect and acted as an upper current collector. In addition, the mesoporous textural properties of a MoO2@CNT nanocomposite provide a suitable lithium-ion pathway with enhanced ionic conductivity and additional active sites for active sulfur during cycling; finally, a high utilization of sulfur is achieved in a reversible manner. The LSBs using the modified separator with the optimized MoO2@CNT nanocomposite exhibit high discharge capacities of 1067 mA h g–1 at 0.2 C after 100 cycles and significant cycling stability at 1 C. Also, an impressive anti-self-discharge feature and improved rate capabilities were achieved through the introduction of a MoO2@CNT nanocomposite. We believe that our approach can be used as a proof-of-concept for further research into effective methods to prepare modified separators with various electrically exploded carbon–metal oxide nanocomposites that can used in high-performance LSBs.

Multi-role TiO2 layer coated carbon@few-layered MoS2 nanotubes for durable lithium storage

The combination of transitional-metal dichalcogenides with rigid TiO2 has been proved to be an effective strategy to improve their structural stability but the poor long-term cycling stability at high current density still hinders their practical applications. In this paper, a smart structure consisting of multi-role TiO2 coated on carbon@few-layered MoS2 (CMT) nanotubes was synthesized to achieve superior long-term cycling performance. In this unique structure, the anatase/rutile TiO2 is explored as a coating layer of MoS2, which not only accommodates the volume change resulting from the phase transformation from S to Li2S but also alleviates the “shuttle effect” caused by the dissolution of long-chain lithium polysulfides. Moreover, the carbon nanotubes serve as a conductive backbone for MoS2 to improve the electron transport ability of electrode and the few-layered MoS2 nanosheets with expanded interlayers can shorten the lithium-ion pathway and improve the lithium-ion diffusion mobility. Benefitting from the synergetic effects of TiO2 layer, carbon and MoS2, when applied as anode of LIBs, the CMT demonstrates an extraordinary long-term cycling performance (528.5 mAh g−1 at 1000 mA g−1 and 455.2 mAh g−1 at 2000 mA g−1 after 1000 cycles), which outperforms most of the MoS2-TiO2 based anode materials reported before. This work should offer new perspectives into exploring high-performance MoS2-TiO2 based anode materials for efficient lithium storage.

Solid Polymer Electrolytes with Flexible Framework of SiO2 Nanofibers for Highly Safe Solid Lithium Batteries.

Composite electrolytes consisting of polymers and three-dimensional (3D) fillers are considered to be promising electrolytes for solid lithium batteries owing to their virtues of continuous lithium-ion pathways and good mechanical properties. In the present study, an electrolyte with polyethylene oxide–lithium (bis trifluoromethyl) sulfate–succinonitrile (PLS) and frameworks of three-dimensional SiO2 nanofibers (3D SiO2 NFs) was prepared. Taking advantage of the highly conductive interfaces between 3D SiO2 NFs and PLS, the total conductivity of the electrolyte at 30 °C was approximately 9.32 × 10−5 S cm−1. With a thickness of 27 μm and a tensile strength of 7.4 MPa, the electrolyte achieved an area specific resistance of 29.0 Ω cm2. Moreover, such a 3D configuration could homogenize the electrical field, which was beneficial for suppressing dendrite growth. Consequently, Li/LiFePO4 cells assembled with PLS and 3D SiO2 NFs (PLS/3D SiO2 NFs), which delivered an original specific capacity of 167.9 mAh g−1, only suffered 3.28% capacity degradation after 100 cycles. In particular, these cells automatically shut down when PLS was decomposed above 400 °C, and the electrodes were separated by the solid framework of 3D SiO2 NFs. Therefore, the solid lithium batteries based on composite electrolytes reported here offer high safety at elevated temperatures.

Charge distribution guided by grain crystallographic orientations in polycrystalline battery materials

Architecting grain crystallographic orientation can modulate charge distribution and chemomechanical properties for enhancing the performance of polycrystalline battery materials. However, probing the interplay between charge distribution, grain crystallographic orientation, and performance remains a daunting challenge. Herein, we elucidate the spatially resolved charge distribution in lithium layered oxides with different grain crystallographic arrangements and establish a model to quantify their charge distributions. While the holistic “surface-to-bulk” charge distribution prevails in polycrystalline particles, the crystallographic orientation-guided redox reaction governs the charge distribution in the local charged nanodomains. Compared to the randomly oriented grains, the radially aligned grains exhibit a lower cell polarization and higher capacity retention upon battery cycling. The radially aligned grains create less tortuous lithium ion pathways, thus improving the charge homogeneity as statistically quantified from over 20 million nanodomains in polycrystalline particles. This study provides an improved understanding of the charge distribution and chemomechanical properties of polycrystalline battery materials.