Binding FSI- to Construct a Self-Healing SEI Film for Li-Metal Batteries by In situ Crosslinking Vinyl Ionic Liquid.

The solid electrolyte interphase (SEI) membrane on the Li metal anode tends to breakdown and undergo reconstruction during operation, causing Li metal batteries to experience accelerated decay. Notably, an SEI membrane with self-healing characteristics can help considerably in stabilizing the Li-electrolyte interface; however, uniformly fixing the repairing agent onto the anode remains a challenging task. By leveraging the noteworthy film-forming attributes of bis(fluorosulfonyl)imide (FSI-) anions and the photopolymerization property of the vinyl group, the ionic liquid 1-vinyl-3-methylimidazolium bis(fluorosulfonyl)imide (VMI-FSI) was crosslinked with polyethylene oxide (PEO) in this study to form a self-healing film fixing FSI- groups as the repairing agent. When they encounter lithium metal, the FSI- groups are chemically decomposed into LiF & Li3N, which assist forming SEI membrane on lithium sheet and repairing SEI membrane in the cracks lacerated by lithium dendrite. Furthermore, the FSI- anions exchanged from film are electrochemically decomposed to generate inorganic salts to strengthen the SEI membrane. Benefiting from the self-healing behavior of the film, Li/LiCoO2 cells with the loading of 16.3 mg cm-2 exhibit the initial discharge capacities of 183.0 mAh ⋅ g-1 and are stably operated for 500 cycles with the retention rates of 81.4 % and the average coulombic efficiency of 99.97 %, operated between 3.0-4.5 V vs. Li+/Li. This study presents a new design approach for self-healing Li metal anodes and durable lithium metal battery.

Mobile Ions in Composite Solids.

Fast ion conduction in solid-state matrices constitutes the foundation for a wide spectrum of electrochemical systems that use solid electrolytes (SEs), examples of which include solid-state batteries (SSBs), solid oxide fuel cells (SOFCs), and diversified gas sensors. Mixing different solid conductors to form composite solid electrolytes (CSEs) introduces unique opportunities for SEs to possess exceptional overall performance far superior to their individual parental solids, thanks to the abundant chemistry and physics at the new interfaces thus created. In this review, we provide a comprehensive and in-depth examination of the development and understanding of CSEs for SSBs, with special focus on their physiochemical properties and mechanisms of ion transport therein. The origin of the enhanced ionic conductivity in CSEs relative to their single-phase parents is discussed in the context of defect chemistry and interfacial reactions. The models/theories for ion movement in diversified composites are critically reviewed to interrogate a general strategy to the design of novel CSEs, while properties such as mechanical strength and electrochemical stability are discussed in view of their perspective applications in lithium metal batteries and beyond. As an integral component of understanding how ions interact with their composite environments, characterization techniques to probe the ion transport kinetics across different temporal and spatial time scales are also summarized.

Core-Shell C@Sb Nanoparticles as a Nucleation Layer for High-Performance Sodium Metal Anodes.

Sodium metal anode (SMA) is one of the most favored choices for the next-generation rechargeable battery technologies owing to its low cost and natural abundance. However, the poor reversibility resulted from dendrite growth and formation of unstable solid electrolyte interphase has significantly hindered the practical application of SMAs. Herein, we report that a nucleation buffer layer comprising elaborately designed core-shell C@Sb nanoparticles (NPs) enables the homogeneous electrochemical deposition of sodium metal for long-term cycling. These C@Sb NPs can increase active sites for initial sodium nucleation through Sb-Na alloy cores and keep these cores stable through carbon shells. The assembled cells with this nucleation layer can deliver continuously repeated sodium plating/stripping cycles for nearly 6000 h at a high areal capacity of 4 mA h cm-2 with an average Coulombic efficiency 99.7%. This ingenious structure design of alloy-based nucleation agent opens up a promising avenue to stabilize sodium metal with targeted properties.

Real-Time TEM Study of Nanopore Evolution in Battery Materials and Their Suppression for Enhanced Cycling Performance.

Battery materials, which store energy by combining mechanisms of intercalation, conversion, and alloying, provide promisingly high energy density but usually suffer from fast capacity decay due to the drastic volume change upon cycling. Particularly, the significant volume shrinkage upon mass (Li+, Na+, etc.) extraction inevitably leads to the formation of pores in materials and their final pulverization after cycling. It is necessary to explore the failure mechanism of such battery materials from the microscopic level in order to understand the evolution of porous structures. Here, prototyped Sb2Se3 nanowires are targeted to understand the structural failures during repetitive (de)sodiation, which exhibits mainly alloying and conversion mechanisms. The fast growing nanosized pores embedded in the nanowire during desodiation are identified to be the key factor that weakens the mechanical strength of the material and thus cause a rapid capacity decrease. To suppress the pore development, we further limit the cutoff charge voltage in a half-cell against Na below a critical value where the conversion reaction of such a material system is yet happening, the result of which demonstrates significantly improved battery performance with well-maintained structural integrity. These findings may shed some light on electrode failure investigation and rational design of advanced electrode materials with long cycling life.

Dendrite-Free Sodium Metal Anodes Enabled by a Sodium Benzenedithiolate-Rich Protection Layer.

Sodium metal is an ideal anode material for metal rechargeable batteries, owing to its high theoretical capacity (1166 mAh g-1 ), low cost, and earth-abundance. However, the dendritic growth upon Na plating, stemming from unstable solid electrolyte interphase (SEI) film, is a major and most notable problem. Here, a sodium benzenedithiolate (PhS2 Na2 )-rich protection layer is synthesized in situ on sodium by a facile method that effectively prevents dendrite growth in the carbonate electrolyte, leading to stabilized sodium metal electrodeposition for 400 cycles (800 h) of repeated plating/stripping at a current density of 1 mA cm-2 . The organic salt, PhS2 Na2 , is found to be a critical component in the protection layer. This finding opens up a new and promising avenue, based on organic sodium slats, to stabilize sodium metals with a protection layer.

Superior Conductive Solid-like Electrolytes: Nanoconfining Liquids within the Hollow Structures.

The growth and proliferation of lithium (Li) dendrites during cell recharge are currently unavoidable, which seriously hinders the development and application of rechargeable Li metal batteries. Solid electrolytes with robust mechanical modulus are regarded as a promising approach to overcome the dendrite problems. However, their room-temperature ionic conductivities are usually too low to reach the level required for normal battery operation. Here, a class of novel solid electrolytes with liquid-like room-temperature ionic conductivities (>1 mS cm(-1)) has been successfully synthesized by taking advantage of the unique nanoarchitectures of hollow silica (HS) spheres to confine liquid electrolytes in hollow space to afford high conductivities (2.5 mS cm(-1)). In a symmetric lithium/lithium cell, the solid-like electrolytes demonstrate a robust performance against the Li dendrite problem, preventing the cell from short circuiting at current densities ranging from 0.16 to 0.32 mA cm(-2) over an extended period of time. Moreover, the high flexibility and compatibility of HS nanoarchitectures, in principle, enables broad tunability to choose desired liquids for the fabrication of other kinds of solid-like electrolytes, such as those containing Na(+), Mg(2+), or Al(3+) as conductive media, providing a useful alternative strategy for the development of next generation rechargeable batteries.

Removal of interstitial H2O in hexacyanometallates for a superior cathode of a sodium-ion battery.

Sodium is globally available, which makes a sodium-ion rechargeable battery preferable to a lithium-ion battery for large-scale storage of electrical energy, provided a host cathode for Na can be found that provides the necessary capacity, voltage, and cycle life at the prescribed charge/discharge rate. Low-cost hexacyanometallates are promising cathodes because of their ease of synthesis and rigid open framework that enables fast Na(+) insertion and extraction. Here we report an intriguing effect of interstitial H2O on the structure and electrochemical properties of sodium manganese(II) hexacyanoferrates(II) with the nominal composition Na2MnFe(CN)6·zH2O (Na2-δMnHFC). The newly discovered dehydrated Na2-δMnHFC phase exhibits superior electrochemical performance compared to other reported Na-ion cathode materials; it delivers at 3.5 V a reversible capacity of 150 mAh g(-1) in a sodium half cell and 140 mAh g(-1) in a full cell with a hard-carbon anode. At a charge/discharge rate of 20 C, the half-cell capacity is 120 mAh g(-1), and at 0.7 C, the cell exhibits 75% capacity retention after 500 cycles.

Controlled synthesis of mesoporous carbon nanostructures via a "silica-assisted" strategy.

We have established a facile and generalizable "silica-assisted" synthesis for diverse carbon spheres-a category that covers mesoporous carbon nanospheres, hollow mesoporous carbon nanospheres, and yolk-shell mesoporous carbon nanospheres-by using phenolic resols as a polymer precursor, silicate oligomers as an inorganic precursor, and hexadecyl trimethylammoniumchloride as a template. The particle sizes of the carbon nanospheres are uniform and easily controlled in a wide range of 180-850 nm by simply varying the ethanol concentrations. All three types of mesoporous carbon nanospheres have high surface areas and large pore volumes and exhibit promising properties for supercapacitors with high capacitance and favorable capacitance retention.

Mesoporous Prussian blue analogues: template-free synthesis and sodium-ion battery applications.

The synthesis of mesoporous Prussian blue analogues through a template-free methodology and the application of these mesoporous materials as high-performance cathode materials in sodium-ion batteries is presented. Crystalline mesostructures were produced through a synergistically coupled nanocrystal formation and aggregation mechanism. As cathodes for sodium-ion batteries, the Prussian blue analogues all show a reversible capacity of 65 mA h g-1 at low current rate and show excellent cycle stability. The reported method stands as an environmentally friendly and low-cost alternative to hard or soft templating for the fabrication of mesoporous materials.

Ambient lithium-SO2 batteries with ionic liquids as electrolytes.

Li-SO2 batteries have a high energy density but bear serious safety problems that are associated with pressurized SO2 and flammable solvents in the system. Herein, a novel ambient Li-SO2 battery was developed through the introduction of ionic liquid (IL) electrolytes with tailored basicities to solvate SO2 by reversible chemical absorption. By tuning the interactions of ILs with SO2, a high energy density and good discharge performance with operating voltages above 2.8 V were obtained. This strategy based on reversible chemical absorption of SO2 in IL electrolytes enables the development of the next generation of ambient Li-SO2 batteries.

Fast, reversible lithium storage with a sulfur/long-chain-polysulfide redox couple.

The cathodic reactions in Li-S batteries can be divided into two steps. Firstly, elemental sulfur is transformed into long-chain polysulfides (S8 ↔ Li2S4), which are highly soluble in the electrolyte. Next, long-chain polysulfides undergo nucleation reaction and convert into solid-state Li2S2 and Li2S (Li2S4 ↔ Li2S) by slow processes. As a result, the second-step of the electrochemical reaction hinders the high-rate application of Li-S batteries. In this report, the kinetics of the sulfur/long-chain-polysulfide redox couple (theoretical capacity=419 mA h g(-1)) are experimentally demonstrated to be very fast in the Li-S system. A Li-S cell with a blended carbon interlayer retains excellent cycle stability and possesses a high percentage of active material utilization over 250 cycles at high C rates. The meso-/micropores in the interlayer are responsible for accommodating the shuttling polysulfides and offering sufficient electrolyte accessibility. Therefore, utilizing the sulfur/long-chain polysulfide redox couple with an efficient interlayer configuration in Li-S batteries may be a promising choice for high-power applications.

An effective co-modification strategy to enhance the cycle stability of LiNi0.8Co0.1Mn0.1O2 for lithium-ion batteries.

Ni-rich cathode materials suffer from rapid capacity fading caused by interface side reactions and bulk structure degradation. Previous studies show that Co is conducive to bulk structure stability and sulfate can react with the residual lithium (LiOH and Li2CO3) on the surface of Ni-rich cathode materials and form a uniform coating to suppress the side reactions between the cathode and electrolyte. Here, CoSO4 is utilized as a modifier for LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode materials. It reacts with the residual lithium on the surface of the NCM811 cathode to form Li-ion conductive Li2SO4 protective layers and Co doping simultaneously during the high-temperature sintering process, which can suppress the side reactions between the Ni-rich cathode and electrolyte and effectively prevent the structural transformation. As a result, the co-modified NCM811 cathode with 3 wt% CoSO4 exhibits an improved cycling performance of 81.1% capacity retention after 200 cycles at 1C and delivers an excellent rate performance at 5C of 187.4 mA h g-1, which is 10.2% higher than that of the pristine NCM811 cathode.

Effect of LLZO on the in situ polymerization of acrylate solid-state electrolytes on cathodes.

The comprehensive performance of the state-of-the-art solid-state electrolytes (SSEs) cannot match the requirements of commercial applications, and constructing an organic-inorganic composite electrolyte in situ on a porous electrode is an effective coping strategy. However, there are few studies focused on the influence of inorganic ceramics on the polymerization of multi-organic components. In this study, it was found that the addition of Li6.4La3Zr1.4Ta0.6O12 (LLZO) weakens the interaction between different polymers and makes organic and inorganic components contact directly in the solid electrolyte. These suppress the segregation of components in the in situ polymerized composite SSE, leading to a decrease in the polymer crystallization and improvement of electrolyte properties such as electrochemical stability window and mechanical properties. The composite solid-state electrolyte can be in situ constructed on different porous electrodes, which can establish close contact with active material particles, showing an ionic conductivity 4.4 × 10-5 S cm-1 at 25 °C, and afford the ternary cathode stability for 100 cycles.

Adjusting Oxygen Redox Reaction and Structural Stability of Li- and Mn-Rich Cathodes by Zr-Ti Dual-Doping.

Li- and Mn-rich cathodes (LMRs) with cationic and anionic redox reactions are considered as promising cathode materials for high-energy-density Li-ion batteries. However, the oxygen redox process leads to lattice oxygen loss and structure degradation, which would induce serious voltage fade and capacity loss and thus limit the practical application. High-valent and electrochemical inactive d0 element doping is an effective method to tune the crystal and electronic structures, which are the main factors for the electrochemical stability. Herein, noticeably inhibited oxygen loss, reduced voltage fade, enhanced rate performance, and improved structure stability and thermal stability of LMRs have been realized by Ti4+ and Zr4+ dual-doping. The underlying modulation mechanisms are unraveled by combining differential electrochemical mass spectrometry, soft X-ray absorption spectroscopies, in situ XRD measurements, etc. The dual-doping reduces the covalency of the TM-O bond, mitigates the irreversible oxygen release during the oxygen redox, and stabilizes the layered framework. The expanded lithium layer facilitates the lithium diffusion kinetics and structure stability. This study may result in the fundamental understanding of crystal and electronic structure evolution in LMRs and contribute to the development of high capacity cathodes.

Electrochemically fabricated polypyrrole-cobalt-oxygen coordination complex as high-performance lithium-storage materials.

Current lithium-ion battery (LIB) technologies are all based on inorganic electrode materials, though organic materials have been used as electrodes for years. Disadvantages such as limited thermal stability and low specific capacity hinder their applications. On the other hand, the transition metal oxides that provide high lithium-storage capacity by way of electrochemical conversion reaction suffer from poor cycling stability. Here we report a novel high-performance, organic, lithium-storage material, a polypyrrole-cobalt-oxygen (PPy-Co-O) coordination complex, with high lithium-storage capacity and excellent cycling stability. Extended X-ray absorption fine structure and Raman spectroscopy and other physical and electrochemical characterizations demonstrate that this coordination complex can be electrochemically fabricated by cycling PPy-coated Co(3)O(4) between 0.0 V and 3.0 V versus Li(+)/Li. Density functional theory (DFT) calculations indicate that each cobalt atom coordinates with two nitrogen atoms within the PPy-Co coordination layer and the layers are connected with oxygen atoms between them. Coordination weakens the C-H bonds on PPy and makes the complex a novel lithium-storage material with high capacity and high cycling stability.

Enhanced Electrochemical Performance of Ni-Rich Cathodes by Neutralizing Residual Lithium with Acid Compounds.

Surficial residual LiOH and/or Li2CO3 on Ni-rich cathodes arouse troubles for their practical applications, such as slurry gelling and durability degrading. To assure acceptable performance, the strategy of "washing and heat treatment" is generally utilized to remove them in industry, which is unavoidable to generate plenty of wastewater. In this work, we investigated the mechanism of slurry gelling caused by residual lithium on Ni-rich materials and then proposed a simple and efficient method to convert the detrimental residual lithium to the useful surface layer of LiF or LiBOB at 220 °C without water washing. As a result, the basicity of modified samples is lowered to 11.48 and 11.60 from 12.05 of the pristine, respectively. Owing to the beneficial effect of the surface layer, the treated samples deliver a discharge capacity of 189.5 and 187.9 mA h g-1 and retain 84.1 and 82.8% of the initial capacity under 1 C after 300 cycles, which is much better than that of the untreated material (57.8%). The comprehensive performances of the modified samples in this work are very close to those of the material treated with the industrial method, demonstrating the advantage of this strategy to further reduce the cost of material production.

Addressing Unfavorable Influence of Particle Cracking with a Strengthened Shell Layer in Ni-Rich Cathodes.

Ni-rich layered materials are widely accepted as pivotal cathode materials to realize low-cost high-energy-density batteries. However, they still suffer from the intrinsic mechanically induced degradation due to the large lattice deformation. Here, we fabricate a strengthened shell layer on polycrystalline secondary particles to address the unfavorable influence of particle cracking instead of suppressing their bulky pulverization. This tough layer, constructed via welding LiNi0.8Co0.1Mn0.1O2 primary particles with a Nb-based ceramic, increases Young's modulus of the particles 2.6 times. This layer allows the particles work properly with the intact spherical morphology even after bulk cracking. It seems that this tough skin stops the bulky flaws growing into perforated fissures and keeps the electrodes from quick polarization. This approach demonstrates that, besides addressing the intrinsic challenges directly, appropriate particle engineering is another efficient way to exploit the potentials of Ni-rich cathodes and power batteries made out of them.

Improving the Durability of Lithium-Metal Anode via In situ Constructed Multilayer SEI.

In this work, a novel multilayer solid electrolyte interphase (SEI) is demonstrated to prolong the durability of a lithium-metal anode. It is in situ generated via reducing lithium bis(oxalate) borate (LiBOB) and fluoroethylene carbonate (FEC) in the electrolyte containing them as additives. The as-obtained SEI could be roughly divided into three layers: the polycarbonates surface membrane, LiF-rich middle layer, and B-containing polymer bottom film corresponding to their sequentially reductive potentials of 0.8, 1.55, and 1.8 V vs Li+/Li, respectively. This special structure prolongs the durability of lithium-metal anode since the elastic bottom layer could buffer the influence of volumetric variation and the LiF-rich middle layer could suppress Li dendrite growth and electrolyte permeation. Benefiting from the protection of this multilayer SEI, LiNi0.88Co0.09Al0.03O2/Li batteries with ultrahigh cathode loading of ∼4.5 mAh cm-2 stably operate for 200 cycles with the accumulated capacity of 750 mAh cm-2 and the coulombic efficiency of 99.78%. This approach provides a simple and efficient strategy to hover lithium-metal anode.

A Polymer-Assisted Spinodal Decomposition Strategy toward Interconnected Porous Sodium Super Ionic Conductor-Structured Polyanion-Type Materials and Their Application as a High-Power Sodium-Ion Battery Cathode.

A general polymer-assisted spinodal decomposition strategy is used to prepare hierarchically porous sodium super ionic conductor (NASICON)-structured polyanion-type materials (e.g., Na3 V2 (PO4 )3 , Li3 V2 (PO4 )3 , K3 V2 (PO4 )3 , Na4 MnV(PO4 )3 , and Na2 TiV(PO4 )3 ) in a tetrahydrofuran/ethanol/H2 O synthesis system. Depending on the boiling point of solvents, the selective evaporation of the solvents induces both macrophase separation via spinodal decomposition and mesophase separation via self-assembly of inorganic precursors and amphiphilic block copolymers, leading to the formation of hierarchically porous structures. The resulting hierarchically porous Na3 V2 (PO4 )3 possessing large specific surface area (≈77 m2 g-1 ) and pore volume (≈0.272 cm3 g-1 ) shows a high specific capacity of 117.6 mAh g-1 at 0.1 C achieving the theoretical value and a long cycling life with 77% capacity retention over 1000 cycles at 5 C. This method presented here can open a facile avenue to synthesize other hierarchically porous polyanion-type materials.

A Hybrid Ionic and Electronic Conductive Coating Layer for Enhanced Electrochemical Performance of 4.6 V LiCoO2.

The LiCoO2 cathode undergoes undesirable electrochemical performance when cycled with a high cut-off voltage (≥4.5 V versus Li/Li+). The unstable interface with poor kinetics is one of the main contributors to the performance failure. Hence, a hybrid Li-ion conductor (Li1.5Al0.5Ge1.5P3O12) and electron conductor (Al-doped ZnO) coating layer was built on the LiCoO2 surface. Characterization studies prove that a thick and conductive layer is homogeneously covered on LiCoO2 particles. The coating layer can not only enhance the interfacial ionic and electronic transport kinetics but also act as a protective layer to suppress the side reactions between the cathode and electrolyte. The modified LiCoO2 (HC-LCO) achieves an excellent cycling stability (77.1% capacity retention after 350 cycles at 1C) and rate capability (139.8 mAh g-1 at 10C) at 3.0-4.6 V. Investigations show that the protective layer can inhibit the particle cracks and Co dissolution and stabilize the cathode electrolyte interface (CEI). Furthermore, the irreversible phase transformation is still observed on the HC-LCO surface, indicating the phase transformation of the LiCoO2 surface may not be the main factor for fast performance failure. This work provides new insight of interfacial design for cathodes operating with a high cut-off voltage.