Multifunctional Catalytic Hierarchical Interfaces of Ni12 P5 -Ni2 P Porous Nanosheets Enabled Both Sulfides Reaction Promotion and Li-Dendrite Suppression for High-Performance Li-S Full Batteries.

The development of lithium-sulfur (Li-S) batteries is very promising and yet faces the issues of hindered polysulfides conversion and Li dendrite growth. Different from using different materials strategies to overcome these two types of problems, here multifunctional catalytic hierarchical interfaces of Ni12 P5 -Ni2 P porous nanosheets formed by Ni2 P partially in situ converted from Ni12 P5 are proposed. The unique electronic structure in the interface endows Ni12 P5 -Ni2 P effective electrocatalysis effect toward both sulfides' reduction and oxidation through reducing Gibbs free energies, indicating a bidirectional conversion acceleration. Importantly, Ni12 P5 -Ni2 P porous nanosheets with hierarchical interfaces also reduced the Li nucleation energy barrier, and a dendrite-free Li deposition is realized during the overall Li deposition and stripping steps. To this end, Ni12 P5 -Ni2 P decorated carbon nanotube/S cathode showing a high capacity of over 1500 mAh g-1 , and a high rate capability of 8 C. Moreover, the coin full cell delivered a high capacity of 1345 mAh g-1 at 0.2 C and the pouch full cell delivered a high capacity of 1114 mAh g-1 at 0.2 C with high electrochemical stability during 180° bending. This work inspires the exploration of hierarchical structures of 2D materials with catalytically active interfaces to improve the electrochemistry of Li-S full battery.

Suppressing Dendrite Growth with Eco-Friendly Sodium Lignosulfonate Additive in Quasi-Solid-State Li Metal Battery.

The application of lithium metal batteries is limited by the drawbacks of safety problems and Li dendrite formation. Quasi-solid-state electrolytes (QSSEs) are the most promising alternatives to commercial liquid electrolytes due to their high safety and great compatibility with electrodes. However, Li dendrite formation and the slow Li+ diffusion in QSSEs severely hinder uniform Li deposition, thus leading to Li dendrite growth and short circuits. Herein, an eco-friendly and low-cost sodium lignosulfonate (LSS)-assisted PVDF-based QSSE is proposed to induce uniform Li deposition and inhibit Li dendrite growth. Li symmetric cells with 5%-LSS QSSE possess a high Li+ transfer number of 0.79, and they exhibit a long cycle life of 1000 h at a current density/areal capacity of 1 mA cm-2/5 mAh cm-2. Moreover, due to the fast electrochemical dynamics endowed by the improved compatibility of the electrodes and fast Li+ diffusion, the LFP/5%-LSS/Li full cells still maintain a high capacity of 110 mAh g-1 after 250 cycles at 6C. This work provides a novel and promising choice that uses eco-friendly LSS as an additive to PVDF-based QSSE in Li metal batteries.

Lithium Ion Repulsion-Enrichment Synergism Induced by Core-Shell Ionic Complexes to Enable High-Loading Lithium Metal Batteries.

A core-shell additive with anionic Keggin-type polyoxometalate (POM) cluster as core and N-containing cation of ionic liquid (IL) as shell is proposed to stabilize Li-metal batteries (LMBs). The suspended POM derived complex in ether-based electrolyte is absorbed around the protuberances of anode and triggers a lithiophobic repulsion mechanism for the homogenization of Li+ redistribution. The gradually released POM cores with negative charge then enrich Li+ and co-assemble with Li. The Li+ repulsion-enrichment synergism can compact Li deposition and reinforce solid electrolyte interphase. This sustained-release additive enables Li∥Li symmetric cells with a long lifetime over 500 h and 300 h at high current densities of 3 and 5 mA cm-2 respectively. The complex additive is also compatible with high-voltage Li∥LiNi0.8 Co0.15 Al0.05 O2 (NCA) cells. Even with a NCA loading as high as ca. 20 mg cm-2 , the additive contained Li∥NCA cell can still cycle for over 100 cycles at 2.6 mA cm-2 .

Progress on Lithium Dendrite Suppression Strategies from the Interior to Exterior by Hierarchical Structure Designs.

Lithium (Li) metal is promising for high energy density batteries due to its low electrochemical potential (-3.04 V) and high specific capacity (3860 mAh g-1 ). However, the safety issues impede the commercialization of Li anode batteries. In this work, research of hierarchical structure designs for Li anodes to suppress Li dendrite growth and alleviate volume expansion from the interior (by the 3D current collector and host matrix) to the exterior (by the artificial solid electrolyte interphase (SEI), protective layer, separator, and solid state electrolyte) is concluded. The basic principles for achieving Li dendrite and volume expansion free Li anode are summarized. Following these principles, 3D porous current collector and host matrix are designed to suppress the Li dendrite growth from the interior. Second, artificial SEI, the protective layer, and separator as well as solid-state electrolyte are constructed to regulate the distribution of current and control the Li nucleation and deposition homogeneously for suppressing the Li dendrite growth from exterior of Li anode. Ultimately, this work puts forward that it is significant to combine the Li dendrite suppression strategies from the interior to exterior by 3D hierarchical structure designs and Li metal modification to achieve excellent cycling and safety performance of Li metal batteries.

Solid Electrolyte Bimodal Grain Structures for Improved Cycling Performance.

The application of solid-state electrolytes in Li batteries is hampered by the occurrence of Li-dendrite-caused short circuits. To avoid cell failure, the electrolytes can only be stressed with rather low current densities, severely restricting their performance. As grain size and pore distributions significantly affect dendrite growth in ceramic electrolytes such as Li7La3Zr2O12 and its variants; here, a "detour and buffer" strategy to bring the superiority of both coarse and fine grains into play, is proposed. To validate the mechanism, a coarse/fine bimodal grain microstructure is obtained by seeding unpulverized large particles in the green body. The rearrangement of coarse grains and fine pores is fine-tuned by changing the ratio of pulverized and unpulverized powders. The optimized bimodal microstructure, obtained when the two powders are equally mixed, allows, without extra interface decoration, cycling for over 2000 h as the current density is increased from 1.0 mA·cm-2, and gradually, up to 2.0 mA·cm-2. The "detour and buffer" effects are confirmed from postmortem analysis. The complex grain boundaries formed by fine grains discourage the direct infiltration of Li. Simultaneously, the coarse grains further increase the tortuosity of the Li path. This study sheds light on the microstructure optimization for the polycrystalline solid-state electrolytes.

Dual-Component Interlayer Enables Uniform Lithium Deposition and Dendrite Suppression for Solid-State Batteries.

ß-Lithium thiophosphate (LPS) exhibits high Li+ conductivity and has been identified as a promising ceramic electrolyte for safe and high-energy-density all-solid-state batteries. Integrating LPS into solid-state lithium (Li) batteries would enable the use of a Li electrode with the highest deliverable capacity. However, LPS-based batteries operate at a limited current density before short-circuiting, posing a major challenge for the development of application-relevant batteries. In this work, we designed a dual-component interfacial protective layer called LiSn-LiN that forms in situ between the Li electrode and LPS electrolyte. The LiSn component, Li22Sn5, exhibits enhanced Li diffusivity compared with the metallic lithium and facilitates a more uniform lithium deposition across the electrode surface, thus eliminating Li dendrite formation. Meanwhile, the LiN component, Li3N, shows enhanced mechanical stiffness compared with LPS and functions to suppress dendrite penetration. This chemically robust LiSn-LiN interlayer provides a more than doubled deliverable critical current density compared to systems without interfacial protection. Through combined XPS and XAFS analyses, we determined the local structure and the formation kinetics of the key functional Li22Sn5 phase formed via the electrochemical reduction of a Sn3N4 precursor. This work demonstrates an example of the structural-specific design of a protective interlayer with a desired function - dendrite suppression. The structure of a functional protective layer for a given solid-state battery should be tailored based on the given battery configuration and its unique interfacial chemistry.

Unlocking solid-state conversion batteries reinforced by hierarchical microsphere stacked polymer electrolyte.

Pursuing all-solid-state lithium metal batteries with dual upgrading of safety and energy density is of great significance. However, searching compatible solid electrolyte and reversible conversion cathode is still a big challenge. The phase transformation at cathode and Li deformation at anode would usually deactivate the electrode-electrolyte interfaces. Herein, we propose an all-solid-state Li-FeF3 conversion battery reinforced by hierarchical microsphere stacked polymer electrolyte for the first time. This g-C3N4 stuffed polyethylene oxide (PEO)-based electrolyte is lightweight due to the absence of metal element doping, and it enables the spatial confinement and dissolution suppression of conversion products at soft cathode-polymer interface, as well as Li dendrite inhibition at filler-reinforced anode-polymer interface. Two-dimensional (2D)-nanosheet-built porous g-C3N4 as three-dimensional (3D) textured filler can strongly cross-link with PEO matrix and LiTFSI (TFSI: bistrifluoromethanesulfonimide) anion, leading to a more conductive and salt-dissociated interface and therefore improved conductivity (2.5 × 10-4 S/cm at 60 °C) and Li+ transference number (0.69). The compact stacking of highly regular robust microspheres in polymer electrolyte enables a successful stabilization and smoothening of Li metal with ultra-long plating/striping cycling for at least 10,000 h. The corresponding Li/LiFePO4 solid cells can endure an extremely high rate of 12 C. All-solid-state Li/FeF3 cells show highly stabilized capacity as high as 300 mAh/g even after 200 cycles and of ~200 mAh/g at extremely high rate of 5 C, as well as ultra-long cycling for at least 1200 cycles at 1 C. High pseudocapacitance contribution (>55%) and diffusion coefficient (as high as 10-12 cm2/s) are responsible for this high-rate fluoride conversion. This result provides a promising solution to conversion-type Li metal batteries of high energy and safety beyond Li-S batteries, which are difficult to realize true "all-solid-state" due to the indispensable step of polysulfide solid-liquid conversion.

Robustness-Heterogeneity-Induced Ultrathin 2D Structure in Li Plating for Highly Reversible Li-Metal Batteries.

Anode interface modification is crucial for the stabilization of Li-metal batteries (LMBs), which have been considered as the most promising system for the electric vehicle market owing to their high energy density (500 W h kg-1). However, the biggest challenge for LMBs lies in the preservation of anode reversibility, including plated Li morphology control and dendritic Li inhibition during cycling. Here, we propose a nanostructure modulation strategy of Li grains and plating to activate the anode kinetics of LMBs without the compromise of anode stability. This modulation is triggered by the rapid deposition of ultrathin polydopamine coating on the Cu foil (PDA@Cu), which results in an unusual interlaced growth of vertical or lie-down two-dimensional Li nanoflakes on PDA. The high binding energy (>3 eV) between Li atoms and rich imino/carbonyl groups enables a superior lithiophilicity of PDA to homogenize the Li-ion flowing and Li-mass electroplating with negligible nucleation overpotential. The high Coulombic efficiency (98%) and low voltage hysteresis (∼20 mV) are stabilized for at least 300 cycles in the Li-PDA@Cu cell architecture. This PDA@Cu electrode can even tolerate much higher current densities of 5 and 10 mA cm-2 for 170 and 100 cycles, respectively. The interlaced network of Li nanosheets reinforces the electric contact and therefore charge transfer at the anode-electrolyte interface characterized by small interfacial resistance (<3 Ω cm2) and activation energy (0.28 eV). A viewpoint of robustness loss or mechanical heterogeneity in Li plating is discussed to disclose the evolution from column-like Li grains to porous Li sponges and then to compactly stacked Li nanoflakes with porosity shrinkage.

Metal-Organic Frameworks as Electrolyte Additives To Enable Ultrastable Plating/Stripping of Li Anode with Dendrite Inhibition.

Suppressing the extrusion of Li dendrites and alleviating the volume expansion of Li anode during long-term cycling are of great significance to achieve highly reversible Li metal batteries of high energy density potential. However, the exploration of facile and effective solutions to smoothen anode surface is still a big challenge. Here, we propose a solid additive strategy by blending tailored metal-organic framework (MOF) grains with typical carbonate electrolyte to enable an ultrastable plating/stripping cycling of Li anode for at least 1400 h with evident inhibition of anode roughening and voltage polarization. Zr-based MOF (UiO-66) additive enables the smallest nucleation and plateau overpotentials (∼80 mV) during Li plating especially under high current density (2 mA/cm2) and large areal capacity (4 mAh/cm2). The kinetic and cyclic advantages of Li anode modulated by UiO-66 not only benefit from its intrinsic features (high surface area/porosity and thermal/electrochemical stability) but also from the reinforced solid electrolyte interface with low resistance, which consists of concentrated LiF and robust Zr-O-C moieties. Li-Li4Ti5O12 cell based on MOF additive can achieve a high reversibility for at least 900 cycles.

Nanostructured Li-Rich Fluoride Coated by Ionic Liquid as High Ion-Conductivity Solid Electrolyte Additive to Suppress Dendrite Growth at Li Metal Anode.

Blending additive with electrolyte is a facile and effective method to suppress anode dendrite growth in Li metal batteries (LMBs), especially when a LiF-rich solid electrolyte interface (SEI) is formed as a consequence of additive decomposition or deposition. However LiF still suffers from poor bulk ion conductivity as well as the difficult access to tailored nanostructure. Exploring new Li fluoride of high Li-ion conductivity as SEI component is still a big challenge in view of the lacking of desired structure prototype or mineral phase. Here, we propose a Li-rich Li3AlF6 derivative from cryolite phase as solid electrolyte additive, which is characterized by textured nanoporous morphology and ionic liquid coating. Its room temperature ion conductivity is as high as ∼10-5 S/cm with a low activation energy of 0.29 eV, the best level among fluoride-based solid electrolytes. These features guarantee a homogenization of Li+ fluxing through bulk and grain boundary of Li3AlF6-rich SEI and reinforce the effect on Li dendrite suppression. Li3AlF6 additive enables a stable cyclability of Li∥Li symmetric cells for at least 100 cycles even under a high areal capacity of 3 mA h/cm2 and a significant improvement on capacity retention for various LMBs based on LiFePO4, FeS2, and S cathodes.

Self-Healing Wide and Thin Li Metal Anodes Prepared Using Calendared Li Metal Powder for Improving Cycle Life and Rate Capability.

The commercialization of Li metal electrodes is a long-standing objective in the battery community. To accomplish this goal, the formation of Li dendrites and mossy Li deposition, which cause poor cycle performance and safety issues, must be resolved. In addition, it is necessary to develop wide and thin Li metal anodes to increase not only the energy density, but also the design freedom of large-scale Li-metal-based batteries. We solved both issues by developing a novel approach involving the application of calendared stabilized Li metal powder (LiMP) electrodes as anodes. In this study, we fabricated a 21.5 cm wide and 40 µm thick compressed LiMP electrode and investigated the correlation between the compression level and electrochemical performance. A high level of compression (40% compression) physically activated the LiMP surface to suppress the dendritic and mossy Li metal formation at high current densities. Furthermore, as a result of the LiMP self-healing because of electrochemical activation, the 40% compressed LiMP electrode exhibited an excellent cycle performance (reaching 90% of the initial discharge capacity after the 360th cycle), which was improved by more than a factor of 2 compared to that of a flat Li metal foil with the same thickness (90% of the initial discharge capacity after the 150th cycle).

Li4SiO4-Based Artificial Passivation Thin Film for Improving Interfacial Stability of Li Metal Anodes.

An amorphous SiO2 (a-SiO2) thin film was developed as an artificial passivation layer to stabilize Li metal anodes during electrochemical reactions. The thin film was prepared using an electron cyclotron resonance-chemical vapor deposition apparatus. The obtained passivation layer has a hierarchical structure, which is composed of lithium silicide, lithiated silicon oxide, and a-SiO2. The thickness of the a-SiO2 passivation layer could be varied by changing the processing time, whereas that of the lithium silicide and lithiated silicon oxide layers was almost constant. During cycling, the surface of the a-SiO2 passivation layer is converted into lithium silicate (Li4SiO4), and the portion of Li4SiO4 depends on the thickness of a-SiO2. A minimum overpotential of 21.7 mV was observed at the Li metal electrode at a current density of 3 mA cm-2 with flat voltage profiles, when an a-SiO2 passivation layer of 92.5 nm was used. The Li metal with this optimized thin passivation layer also showed the lowest charge-transfer resistance (3.948 Ω cm) and the highest Li ion diffusivity (7.06 × 10-14 cm2 s-1) after cycling in a Li-S battery. The existence of the Li4SiO4 artificial passivation layer prevents the corrosion of Li metal by suppressing Li dendritic growth and improving the ionic conductivity, which contribute to the low charge-transfer resistance and high Li ion diffusivity of the electrode.