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.

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.

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.

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 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.

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.

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.

A polycarboxylic/ether composite polymer electrolyte via in situ UV-curing for all-solid-state lithium battery.

A polycarboxylic/ether composite polymer electrolyte derived from two-arm monomer and polyethylene oxide (PEO) was in situ synthesized on the cathode. The composite electrolyte exhibits a high ionic conductivity of 3.6 × 10-5 S cm-1, high oxidation stability, excellent stability towards Li metal and makes Li/LiFePO4 present good cyclic and rate performance at 25°C.

Amide-Based Interface Layer with High Toughness In Situ Building on the Li Metal Anode.

Lithium metal is considered to be the ultimate anode for lithium-ion batteries (LIBs) because of its ultrahigh capacity and lowest electrochemical potential. However, the high reactivity of the lithium metal triggers continuous electrolyte consumption and dendrite growth, resulting in short cycle lifetime and serious safety issues. Massive efforts have been made to stabilize the surface of the lithium metal anode. Here, we propose an amide-based passivation layer to serve as an electrochemically stable and highly tough SEI on the lithium metal anode by in situ generation. The SEI layer presents a high elasticity modulus of 10 GPa and enables stable cycling in 2500 h. Furthermore, based on our strategy, the Li/LiFePO4 cell with a cathode loading of ∼19 mg cm-2 exhibits a long lifespan of 400 cycles. Our approach establishes a meaningful guideline for building a highly strong electrolyte/electrode interface in high-energy density lithium metal batteries.

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.

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.

Narrowing Working Voltage Window to Improve Layered GeP Anode Cycling Performance for Lithium-Ion Batteries.

Layered germanium phosphide (GeP), a recently developed two-dimensional material, promises highly attractive theoretical capacity for use as a lithium-ion battery anode. Here, we comprehensively investigate its electrochemical performance and the modification mechanism. GeP flakes demonstrate large initial discharge/charge capacity and high initial Coulombic efficiency. However, the cycling performance is disappointing in the potential window of 0.001-3 V in which capacity retention is only ∼18% after 100 cycles. In situ transmission electron microscopy reveals that the poor cycling behavior results in the unexpected large volume change induced by complex reaction processes in cycles. Serious cracking and fracture appear clearly on the electrode surface after cycling. Narrowing the working voltage window to 0.001-0.85 V, cycling stability will be greatly enhanced, with 75% capacity retaining after 100 cycles and ∼50% left after 350 cycles due to the absence of the dealloying of Li3P in the narrowed working voltage window. Additionally, the electric contact among the electrode components has been enhanced by the alleviation of the electrode volume change in the narrowed working voltage window. Our work provides one effective method to give a deep understanding of the high-energy-density electrode failure and helps to narrow the huge gap between the microstructure and the performance of the electrode.

Enhanced Surface Chemical and Structural Stability of Ni-Rich Cathode Materials by Synchronous Lithium-Ion Conductor Coating for Lithium-Ion Batteries.

Ni-rich cathode materials LiNixCoyMn1-x-yO2 (x ≥ 0.6) have attracted much attention due to their high capacity and low cost. However, they usually suffer from rapid capacity decay and short cycle life due to their surface/interface instability, accompanied by the high Ni content. In this work, with the Ni0.9Co0.05Mn0.05(OH)2 precursor serving as a coating target, a Li-ion conductor Li2SiO3 layer was uniformly coated on Ni-rich cathode material LiNi0.9Co0.05Mn0.05O2 by a precoating and syn-lithiation method. The uniform Li2SiO3 coating layer not only improves the Li-ion diffusion kinetics of the electrode but also reduces mechanical microstrain and stabilizes the surface chemistry and structure with a strong Si-O covalent bond. These results will provide further in-depth understanding on the surface chemistry and structure stabilization mechanisms of Ni-rich cathode materials and help to develop high-capacity cathode materials for next-generation high-energy-density Li-ion batteries.

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.

Dense PVDF-type polymer-in-ceramic electrolytes for solid state lithium batteries.

Li7La3Zr1.4Ta0.6O12 (LLZTO) and polyvinylidene fluoride (PVDF) composite electrolytes (LPCEs) with a high ceramic content up to 80 wt% have been developed. Hot pressing can significantly reduce the porosity of LPCEs and increase the conductivity to 1.08 × 10-4 S cm-1 at 60 °C, then the LPCEs can sustain Li plating/stripping cycling for over 1500 h, and make LiFePO4/LPCE/Li cell display a capacity retention of 86% in 200 cycles.

Tailored architectures of FeNi alloy embedded in N-doped carbon as bifunctional oxygen electrocatalyst for rechargeable Zinc-air battery.

As one type of bifunctional oxygen electrocatalyst for Zn-air battery, herein, FeNi alloy was successfully embedded into N-doped carbon with tailored architectures by integrating MOF precursor method and polymer coating/encapsulation strategy. The content of Fe in primary precursor has been proven to be able to obviously affect the morphology of the final catalyst. Benefiting from the mature active site (e.g. FeNi alloy) and the stable carbon matrix, a series of catalysts exhibited good performance towards ORR and OER. Of great significance, a particular ratio of Fe/Ni happened to be able to catalyze the growth of 1D bamboo-like carbon nanotubes, giving rise to a conductive network to diffuse ORR/OER-relevant species. Apparently, a low discharge-charge voltage gap (1.1 V) was acquired in a liquid Zn-air battery with 1.5FeNi@NCNT air cathode. Moreover, the solid-state Zn-air battery assembled on it also displayed a high open circuit voltage (1.38 V) and yielded a high power density of 81 mW cm-2 at 0.83 V. This would leverage a choice to tailor carbon geometry of FeNi alloy-based active sites for ORR/OER and further serve for devices of practical significance.

Hard carbon micro-nano tubes derived from kapok fiber as anode materials for sodium-ion batteries and the sodium-ion storage mechanism.

Hard carbon materials are considered as the most promising anode for sodium-ion batteries (SIBs). However, the high cost and poor rate performance hinder their application in SIBs. Moreover, the controversial mechanism of Na-ion storage restricts the improvement of hard carbon anodes. Herein, hard carbon micro-nano tubes (HCMNTs) from low-cost biomass kapok fibers are prepared as a promising anode for SIBs. Benefitting from the micro-nano structure, which offers low surface area and short Na+ diffusion path, 1400HCMNT possesses a good initial Coulombic efficiency of 80%, a high reversible capacity of 290 mA h g-1, and an excellent rate capacity. Furthermore, electron paramagnetic resonance and thermogravimetric analysis were applied to investigate the Na-ion storage mechanism in the HCMNTs. Sodium is stored in the hard carbon in an ionic state in the slope region and as quasi-liquid metallic sodium clusters in the low-voltage plateau.

Simplifying the Electrolyte Systems with the Functional Cosolvent.

The state-of-the-art electrolytes utilized in lithium-ion batteries are based on liquid carbonates combining a number of additives to fulfill the practical requirements including safety and low temperature. The plenty of components result in the quadruple times of probable radical groups involved into the interfacial reactions, rendering it too difficult to control the surface layer. This work tends to simplify the system with the fluorine-substituted ether as the functional cosolvent to expand the functions of basic electrolytes. The incorporation of this solvent enables the electrolyte to self-extinguish, reduces its freezing point to ∼75 °C lower, and assists in the formation of LiF-rich protective interlayers, resulting in the improvement of the rate capability, cryogenic performance, and cyclic stability for the LiNi1/3Co1/3Mn1/3O2 cathode. This novel design could significantly diminish the amount of necessary additives and possess the acceptable cost, which provides a probability to revitalize the development of liquid electrolytes.