Formation Of Solid Electrolyte Interface Layer Research Articles

Electrolyte regulation achieving MoS2/C nanofiber for stable potassium-ion storage

Due to the pronounced expansion exhibited by sulfides in K-ion batteries (KIBs), achieving both high capacity and extended cycle life remains a formidable challenge. In our study, we utilized electrospinning to craft a self-standing MoS2/C electrode, and the incorporation of one-dimensional carbon was identified as a key factor significantly boosting its electronic conductivity. Addressing stability concerns, we meticulously regulated the salt concentration in ether solvents, revealing that the self-standing MoS2/C electrode exhibited outstanding electrochemical performance at a high-concentration electrolyte. After optimization, the MoS2/C electrode in 5 M ether electrolyte presents a capacity of 315 mA h g−1 after 50 cycles at 50 mA g−1. Impressively, even at 1 A g−1, the MoS2/C electrode still sustained a capacity of 200 mA h g−1 after 5000 cycles, exhibiting excellent electrochemical stability. According to our findings, decomposition occurs when the electrode material comes into contact with the electrolyte, resulting in the formation of a solid electrolyte interface (SEI) layer. In high-concentration electrolytes, a competitive mechanism between anions and ether solvent molecules takes place, with a tendency for preferential decomposition of highly concentrated anions. This behavior triggers the formation of a high-quality KF-rich SEI layer on the electrode interface, further suppressing the decomposition of subsequent electrolytes, which significantly improves the KIB’s electrochemical performance. We believe that this discovery will provide new insights for the development of high-performance KIBs.

Investigation and electrochemical analysis of SEI layer formation in natural graphite anode formation process in lithium-ion battery

The solid electrolyte interface (SEI) layer is a surface film formed by the decomposition of the electrolyte in a lithium-ion battery on the anode surface. A proper understanding of the SEI layer formation process in graphite anodes can provide a broader view of overcoming the challenges associated with these anodes, which will lead to better charge/discharge performance. In this research, cyclic voltammetry tests, electrochemical impedance spectroscopy and sequential charge/discharge tests have been used for cell to gain an accurate understanding of the SEI film formation process on the graphite anode surface. The results of the cyclic voltammetry test show that most of the SEI layer is formed in the first cycle and reaches stability with the continuation of the voltammetric cycles of the SEI layer. Also, the charge transfers resistance (Rct) has decreased from 123.5 Ω to 27.96 Ω after the electrochemical cycles, which indicates the facilitation of the charge transfer process after the formation of the SEI layer. The results of the consecutive charge/discharge test of anode graphite coin cell also show that the amount of non-reversible capacity in the first cycle is much higher than the amount of non-reversible capacity in subsequent cycles. This indicates the formation of a large part of the SEI layer in the first cycle. Considering that the SEI layer is almost stable after the second cycle, it can be said that the method of forming a lithium-ion cell with graphite anode can be done in two charge/discharge cycles.

High rate, high temperature, dendrite free plating/stripping of Li in 3-dimensional honeycomb boron carbon nitride to realize an ultrastable lithium metal anode

Lithium (Li) metal could be the anode of choice for energy dense Li-batteries owing to its high theoretical specific capacity. However, low coulombic efficiency and poor safety on account of the occurrence of the Li-dendrites during charging-discharging pose a bottleneck for practical applications. In this work, we report a high-rate plating and stripping of Li through host engineering to realize ultrastable Li metal anode (LMA). Benchmark plating/stripping efficiency could be achieved via uniquely structured, highly ordered honeycomb boron carbon nitride (HBCN) as a functional scaffold. Boron and nitrogen doping, large surface area and ordered mesoporous structure induce homogeneous solid electrolyte interface (SEI) layer formation and provide numerous nucleation sites with subsequent dendrite-free growth with 99.98 % coulombic efficiency at 8 mA cm−2 high current and 10 mAh cm−2 capacity over 3000 cycles. Via post-cycling advanced characterizations techniques of Ex-situ XPS, 3D X-ray micro-tomography analyses and FESEM, we demonstrate the formation of a stable SEI layer and morphological changes that occurred during Li plating cycles in the HBCN structure. Computational studies validate the high lithium plating-stripping efficacy of HBCN to its highly ordered porous nature, exothermic Li-binding and upshift in the Fermi levels. When tested at elevated temperature (50 °C), a stable Li plating-stripping in HBCN is realised at 4 mA cm−2 current and 10 mAh cm−2 capacity values with ∼100 % C.E.Furthermore, we report the results of testing a Li metal cell comprised of Li deposited HBCN anode and LiFePO4 (LFP) cathode.

Scanning Electrochemical Microscopy for Chemical Imaging and Understanding Redox Activities of Battery Materials.

Improving the charge storage capacity and lifetime and charging/discharging efficiency of battery systems is essential for large-scale applications such as long-term grid storage and long-range automobiles. While there have been substantial improvements over the past decades, further fundamental research would help provide insights into improving the cost effectiveness of such systems. For example, it is critical to understand the redox activities of cathode and anode electrode materials and stability and the formation mechanism and roles of the solid-electrolyte interface (SEI) that forms at the electrode surface upon an external potential bias. The SEI plays a critical role in preventing electrolyte decay while still allowing charges to flow through the system while serving as a charge transfer barrier. While surface analytical techniques such as X-ray photoelectron (XPS), X-ray diffraction (XRD), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and atomic force microscopy (AFM) provide invaluable information on anode chemical composition, crystalline structure, and morphology, they are often performed ex situ, which can induce changes to the SEI layer after it is removed from the electrolyte. While there have been efforts to combine these techniques using pseudo-in situ approaches via vacuum-compatible devices and inert atmosphere chambers connected to glove boxes, there is still a need for true in situ techniques to obtain results with improved accuracy and precision. Scanning electrochemical microscopy (SECM) is an in situ scanning probe technique that can be combined with optical spectroscopy techniques such as Raman and photoluminescence spectroscopy methods to gain insights into the electronic changes of a material as a function of applied bias. This Review will highlight the potential of SECM and recent reports on combining spectroscopic measurements with SECM to gain insights into the SEI layer formation and redox activities of other battery electrode materials. These insights provide invaluable information for improving the performance of charge storage devices.

Unraveling the Interphasial Chemistry for Highly Reversible Aqueous Zn Ion Batteries

A robust solid electrolyte interface (SEI) is crucial to widen the electrochemical stability window of the electrolyte and enable sustainably stable electrode reactions in aqueous Zn ion batteries. Different from the SEI in nonaqueous electrolytes, it is of great importance to form a functional and stable SEI due to parasitic reactions with water in aqueous Zn ion batteries. However, the concrete SEI formation in aqueous electrolytes has been elusive so far. Here, we regulate and unravel the decomposition mechanisms of organic Zn salts at the Zn anode-electrolyte interface in the widely studied zinc triflate-based aqueous electrolytes. By introducing a buffering adsorption layer with an optimal concentration of acetate anions, the uncontrollable decomposition of organic zinc triflate salt is greatly inhibited on Zn anodes, resulting in a stable interface. The average Coulombic efficiency of the Zn anode thus can reach as high as 99.95% and stable cycling for 4200 h. With the cooperation of buffering adsorption layers, the tetraethyl ammonium trifluoromethanesulfonate additive as the decomposition promoter could further regulate the decomposition of triflate anions for the formation of robust SEI layers for Zn anodes in electrolytes with a dilute salt concentration. Zn-polyaniline (PANI) full cells demonstrate stable cycling with controlled N/P ratios in such electrolytes. This work proposes an insightful perspective on rational regulation of the decomposition pathway of electrolyte components by forming a stable electrode-electrolyte interface for improved electrochemical performance of aqueous Zn ion batteries.

A 3D Framework with Li3 N-Li2 S Solid Electrolyte Interphase and Fast Ion Transfer Channels for a Stabilized Lithium-Metal Anode.

The Li-metal anode has been recognized as the most promising anode for its high theoretical capacity and low reduction potential. However, the major drawbacks of Li metal, such as high reactivity and large volume expansion, can lead to dendrite growth and solid electrolyte interface (SEI) fracture. An in situ artificial inorganic SEI layer, consisting of lithium nitride and lithium sulfide, is herein reported to address the dendrite growth issues. Porous graphene oxide films are doped with sulfur and nitrogen (denoted as SNGO) to work as an effective lithium host. The SNGO film enables the in situ formation of an inorganic-rich SEI layer, which facilitates the transport of Li-ions, improves SEI mechanical strength, and avoids SEI fracture. In addition, COMSOL simulation results reveal that the microchannels fabricated by the 3D printing technique further shorten the Li-ion transfer pathways and homogenize heat and stress distribution in the batteries. As a result, the assembled anode shows low capacity fading of 0.1% per cycle at 2 C rate with the sulfur cathode. In addition, the high lithium utilization of the SNGO host enables the anode to provide a stable capacity at low negative/positive electrode ratios under 3 in LiS batteries.

Liquid cell electrochemical TEM: Unveiling the real-time interfacial reactions of advanced Li-metal batteries.

Li metal batteries (LMBs) reveal great application prospect in next-generation energy storage, because of their high energy density and low electrochemical potential, especially when paired with elemental sulfur and oxygen cathodes. Complex interfacial reactions have long been a big concern because of the elusive formation/dissolution of Li metal at the solid-electrolyte interface (SEI) layer, which leads to battery degradation under practical operating conditions. To precisely track the reactions at the electrode/electrolyte interfaces, in the past ten years, high spatio-temporal resolution, in situ electrochemical transmission electron microscopy (EC-TEM) has been developed. A preliminary understanding of the structural and chemical variation of Li metal during nucleation/growth and SEI layer formation has been obtained. In this perspective, we give a brief introduction of liquid cell development. Then, we comparably discuss the different configurations of EC-TEM based on open-cell and liquid-cell, and focus on the recent advances of liquid-cell EC-TEM and its investigation in the electrodes, electrolytes, and SEI. Finally, we present a perspective of liquid-cell EC-TEM for future LMB research.

Thiolate-Based Electrolytes with Anion-Dominated Solvation for Highly Stable Lithium Metal Batteries

Lithium metal has been regarded as one of the promising anodes due to its high theoretical specific capacity and low electrochemical potential. However, it is still hampered by the unstable solid electrolyte interface (SEI) and lithium dendrites. Herein, we report a class of thiolate-based salts with low dissociation but moderate ionic conductivity in ether mixture solvents for rechargeable lithium batteries, which leads to an anion-dominated solvation structure at standard concentration and is conducive to the formation of a dense LiF-rich SEI layer on the lithium metal anode surface, thereby inhibiting the continuous decomposition of the electrolyte. In addition, they are simple to prepare and have high solubility, low cost, and excellent lithium-ion transference number. Such an electrolyte is successfully applied in a Li/Li4Ti5O12 half-cell and shows promising battery performance. This work inspires a new direction to construct stable anion-derived SEI via designing the structure of lithium salts.

Enhanced Thermal Stability of Mesoporous Carbon Microbeads-Based Lithium-Ion Batteries by Propargyl Methacrylate as Electrolyte Additive.

In this current work, propargyl methacrylate (PMA) was successfully adopted to be an efficient electrolyte additive to stabilize the formation of a solid electrolyte interface (SEI) layer on mesoporous carbon microbeads (MCMB) in Li-ion batteries, especially at elevated temperatures. According to a series of material and electrochemical characterizations, the optimized concentration of PMA additive in the electrolyte was found to be 0.5 wt.%. The MCMB electrode cycled with the optimized 0.5 wt.% PMA-containing electrolyte exhibited impressive capacity retention of 90.3% after 50 cycles at 0.1C at elevated temperature, which was remarkably higher than that using the PMA-free electrolyte (83.5%). The improved electrochemical stability at elevated temperature could be ascribed to the rapid formation of stable and thin SEI layer on MCMB surface, which were investigated and suggested to be formed via PMA copolymerization reactions.

(Digital Presentation) Engineering Lithium Metal/Polymer Electrolyte Interface to Enhance Long-Term Stability and Cycle Performance of Lithium Metal Batteries

Unstable Li metal/solid polymer electrolyte (SPE) interface, or solid electrolyte interface (SEI), limits applications of SPEs in lithium metal batteries (LMBs). Arising from ultrahigh Li reducibility, parasitic reactions (for instance, reaction of Li with PEO to form C2H4, Li2O, and H2) inevitably take place at Li/PEO interface, harming the electrochemical performances of LMBs. Additionally, during the battery operation, the Li/SPE interface continuously thickens due to the repeated reactions between the Li metal and fresh SPE, leading to uneven surface morphology and large electrochemical impedance. These events occurring at the Li/PEO interface will lead to capacity loss and inferior battery lifespan. SEI is an ionically conducting and electronically insulating nanolayer which spontaneously forms on anodes as a result of reductive decomposition of an electrolyte in lithium batteries. The SEI layer plays a critical role in Li plating/stripping during charge/discharge processes and, hence, is a key factor in determining the morphology of Li electrochemical deposits, power capability, shelf life and cycle life, and safety of lithium batteries. The issue of an unstable Li/PEO-based SPE interface can also be addressed by engineering an interface rich in components with high Li ions conductivity and high stability against Li metal. Although the importance of the SEI layer is well-recognized, the structure, chemistry, and kinetics of the SEI layer formation and evolution are not well-understood, which is negatively impacting battery technology.Herein, we develop an LMB with superior electrochemical performance and a long lifespan enabled by an engineered Li/SPE interface. The SPE is made based on PEO-LiTFSI and a cyclic phosphazene compound as additive. The electrochemical degradation of the phosphazene compound during electrochemical cycling of the LMB can lead to an SEI layer rich in lithium nitride (Li3N), lithium phosphide (Li3P), and lithium phosphide (Li3PO4). Using cryo-TEM coupled with EDS and EELS characterization, detailed structure and chemistry of the SEI layer at Li/SPE interface is explored. The interface between the Li metal anode and the control SPE seems unstable, leading to significant fluctuations in overpotential followed by a sudden drop and finally a short-circuit. In contrast, a long-term stability could be observed for the symmetric Li/Li cell made using the engineered SPE, indicating the stable nature of the interface. A significant capacity loss is observed for the Li/LFP cell made using the control PEO-LiTFSI SPE. This can be correlated to the poor Li ions conductivity and instability against Li metal of the conventional SEI layer formed in the control PEO-LiTFSI SPE. On the other hand, and owing to the SEI layer rich in Li3N, Li3P, and Li3PO4 with high Li ions conductivity and stability against Li metal, a stable and long lifespan LMB made of the engineered PEO-LiTFSI-Phosphazene SPE is observed. The critical role of Li3N, Li3P and Li3PO4 in improving the electrochemical performance will be investigated by density functional theory (DFT) calculations. Reference [1] J. Liu, J. Liu, Z. Bao, Y. Cui, E. J. Dufek, J. B. Goodenough, P. Khalifah, Q. Li, B. Y. Liaw, P. Liu, A. Manthiram, Y. S. Meng, V. R. Subramanian, M. F. Toney, V. V. Viswanathan, M. S. Whittingham, J. Xiao, W. Xu, J. Yang, X.-Q. Yang, J.-G. Zhang, Nat. Energy 2019, 4 (3), 180–186.[2] O. Sheng, J. Zheng, Z. Ju, C. Jin, Y. Wang, M. Chen, J. Nai, T. Liu, W. Zhang, Y. Liu, X. Tao, Adv. Mater. 2020, 32 (34).[3] S. Li, S. Li, Q. Liu, X. Wang, Q. Wu, L. Fan, W. Zhang, Z. Shen, L. Wang, M. Ling, Y. Lu, ACS Mater. Lett. 2020, 2 (1), 1–8.

Micro-Mesoporous Carbons from Cyclodextrin Nanosponges Enabling High-Capacity Silicon Anodes and Sulfur Cathodes for Lithiated Si-S Batteries.

Manufactured globally on industrial scale, cyclodextrins (CD) are cyclic oligosaccharides produced by enzymatic conversion of starch. Their typical structure of truncated cone can host a wide variety of guest molecules to create inclusion complexes; indeed, we daily use CD as unseen components of food, cosmetics, textiles and pharmaceutical excipients. The synthesis of active material composites from CD resources can enable or enlarge the effective utilization of these products in the battery industry with some economical as well as environmental benefits. New and simple strategies are here presented for the synthesis of nanostructured silicon and sulfur composite materials with carbonized hyper cross-linked CD (nanosponges) that show satisfactory performance as high-capacity electrodes. For the sulfur cathode, the mesoporous carbon host limits polysulfide dissolution and shuttle effects and guarantees stable cycling performance. The embedding of silicon nanoparticles into the carbonized nanosponge allows to achieve high capacity and excellent cycling performance. Moreover, due to the high surface area of the silicon composite, the characteristics at the electrode/electrolyte interface dominate the overall electrochemical reversibility, opening a detailed analysis on the behavior of the material in different electrolytes. We show that the use of commercial LP30 electrolyte causes a larger capacity fade, and this is associated with different solid electrolyte interface layer formation and it is also demonstrated that fluoroethylene carbonate addition can significantly increase the capacity retention and the overall performance of our nanostructured Si/C composite in both ether-based and LP30 electrolytes. As a result, an integration of the Si/C and S/C composites is proposed to achieve a complete lithiated Si-S cell.

Gradient SEI layer induced by liquid alloy electrolyte additive for high rate lithium metal battery

Current energy storage device has fallen short behind from the fast growing requirement for (hybrid) electric vehicles and portable devices including mobile phones, which drives the lithium metal anode to be a research hot topic. However, the large volume change of lithium metal anode induces instable solid electrolyte interface (SEI) layer, which prevents its further development. A stable SEI layer required flexible surface to accommodate the large volume variation and inorganic core with low Li + partial molar volume for dendrite suppression. Herein, we achieved a gradient SEI which is composed of flexible surface-rich polycarbonate moieties and low Li + partial molar volume inorganic LiF-rich core by applying liquid alloy GaSnIn as electrolyte additive. Initially, the calculation verified that liquid alloy GaSnIn as electrolyte additive would facilitate the initial decomposition of LiPF 6 , and lead to the formation of the gradient SEI layer. In the Li||Li half‐cell test, we successfully achieved dense deposition of Li metal and in this way, the cycling performance with liquid alloy GaSnIn as electrolyte additive is greatly improved especially at high rate (10 mA cm −2 ). Voltage polarization was greatly reduced and Coulombic efficiency was effectively improved due to the gradient SEI layer achieved in the interface of Li anode and electrolyte. In the Li||LFP cell, high average coulombic efficiency (99.06%) at long cycle life (＞2500 cycles) is achieved for the liquid alloy GaSnIn‐protected Li metal anode at high areal capacity (3 mAh/cm 2 ). These results deepen our understanding on liquid alloy as a promising electrolyte additive for efficient dendrite suppressing, enabling the practical lithium metal batteries (LMBs). • We successfully achieved a gradient SEI layer through liquid alloy for lithium dendrite suppression. • Gradient SEI layer is composed of flexible surface-rich polycarbonate moieties and inorganic LiF-rich inside. • Liquid alloy GaSnIn as electrolyte additive facilitates the initial decomposition of LiPF6, facilitating the gradient SEI layer.

Highly Stable Cycling of Silicon-Nanographite Aerogel-Based Anode for Lithium-Ion Batteries.

Silicon anodes are considered as promising electrode materials for next-generation high capacity lithium-ion batteries (LIBs). However, the capacity fading due to the large volume changes (∼300%) of silicon particles during the charge–discharge cycles is still a bottleneck. The volume changes of silicon lead to a fracture of the silicon particles, resulting in recurrent formation of a solid electrolyte interface (SEI) layer, leading to poor capacity retention and short cycle life. Nanometer-scaled silicon particles are the favorable anode material to reduce some of the problems related to the volume changes, but problems related to SEI layer formation still need to be addressed. Herein, we address these issues by developing a composite anode material comprising silicon nanoparticles and nanographite. The method developed is simple, cost-efficient, and based on an aerogel process. The electrodes produced by this aerogel fabrication route formed a stable SEI layer and showed high specific capacity and improved cyclability even at high current rates. The capacity retentions were 92 and 72% of the initial specific capacity at the 171st and the 500th cycle, respectively.

Carbon Composite Anodes with Tunable Microstructures for Potassium‐Ion Batteries

AbstractAmong the post‐lithium battery technologies, potassium‐ion batteries are promising for cost‐effective large‐scale energy storage, as potash is an abundant resource. However, a major challenge is to understand the structure‐performance relationships of carbon anodes for potassium‐ion storage. In this study, we have designed a variety of carbon composite materials from 100 % graphite to 100 % soft carbon and in between, with tunable structural features to fundamentally understand the roles of different carbon structural features in potassium ion insertion. We have found that the graphite‐soft carbon composites (G‐SC) show a high charge capacity of 280.2 mAh g−1 with an increased initial coulombic efficiency, representing the best reversibility among different carbon composites. Electrochemical impedance spectroscopy, cyclic voltammetry, and ex‐situ structural characterizations have been applied to substantiate that the presence of soft carbon in G‐SC inhibits the solid electrolyte interface layer formation and provides structural protection to the graphitic layers.

In-Situ Electrochemical Dilatometry Study for Understanding Volume Changes of the Graphite Electrodes for Lithium-Ion Battery

In-situ electrochemical dilatometry is applied as an analytical technique to investigate the effect of both solid electrolyte interface (SEI) formation and the microstructure of the electrode on the dilation behavior of the graphite electrodes during lithium ion intercalation at the same time. It was found that the dilation and contraction behavior of the graphite electrode was dependent on the microstructure of the graphite electrode. The relationship between the microstructure, such as preferred orientation of graphite particles and the pore structure, and the volume changes of the graphite electrode were investigated by half-cell type in-situ electrochemical dilatometer during cycling. Dilation behavior of graphite electrodes monitored by in-situ dilatometer clearly showed the volume changes of the graphite electrodes induced by Li ion intercalation/de-intercalation as well as the SEI layer formation, and how the microstructure of the electrodes affects their volume expansion upon lithium ion intercalation. It was also found that differential dilation plots of the graphite electrodes upon lithiation and delithiation gave us more detailed information of dilation and contraction behaviors with respect to the amount of Li ion intercalated into graphite.

(Invited) High Coulombic Efficiency Electrolyte Enables Li||Span Batteries with Superior Cycling Performance

Lithium metal is being extensively studied as an anode to replace graphite due to its high capacity and the low electrochemical potential.Current research focus is to mitigate lithium dendrite growth and to increase coulomb efficiency during electrochemical cycling by using various surface coatings and electrolyte additives.1 , 2 In addition, a 3D host can be beneficial due to the reduced volume change.3 While sulfur or metal oxide intercalation cathodes can both in principle achieve full-cell energy densities of 500 Wh kg-1, sulfur-based cathodes are particularly appealing due to their low cost, abundant supply, and high storage capacity. Among these, the SPAN (sulfurized polyacrylonitrile) cathode is particularly promising due to the physical confinement of the small molecular sulfur in the conductive polymer network which provides a high specific capacity of > 550 mAh g-1 and an average discharge potential of ~ 1.8 V. We have recently focused on designing novel electrolyte solution chemistry that enables Li||SPAN batteries with superior cycling performance.In the first example, we designed a high-concentration, ether-based electrolyte with LiTFSI and LiNO3 as the co-salts. In addition to providing excellent protection for lithium metal anodes by forming the solid electrolyte interface (SEI), the electrolyte promotes the formation of a crystalline cathode electrolyte interface (CEI) on the SPAN surface composed of LiF and LiNO2. The CEI effectively prevents the formation of soluble polysulfide species and enables stable cycling of the Li||SPAN battery. The benefit of having effective CEI and SEI layers is also demonstrated in Li||SPAN cells with limited lithium supply, which exhibit lithium cycling efficiency values consistent with or exceeding Li||Cu test results, reaching 99.5%. The development of electrolyte chemistries to enable the formation of effective CEI layers is a promising approach to long-life lithium metal batteries.In another example, we formulated a highly concentrated salt/ether electrolyte diluted in a fluorinated ether, which realized an average lithium coulombic efficiency of 99.37% at 0.5 mA cm−2 and 1 mAh cm−2 for more than 900 cycles. This electrolyte also maintained a record coulombic efficiency of 98.7% at 10 mA cm−2, indicative of its ability to provide fast-charging with high cathode loadings. Morphological studies reveal dense, dendrite free Li depositions after prolonged cycling, while surface analyses confirmed the formation of a robust LiF-rich SEI layer on the cycled Li surface. Moreover, this ether-based electrolyte is highly compatible with the SPAN cathode, where the constructed Li||SPAN cell exhibited reversible cathode capacity of 579 mAh g-1 and no capacity decay after 1200 cycles. A cell where a high areal loading SPAN electrode (3.5 mAh cm−2) is paired with only one-fold excess Li was constructed and cycled at 1.75 mA cm−2, maintaining a coulombic efficiency of 99.30% for the lithium metal. This study provides a path to enable high energy density Li||SPAN battery with stable cycling. Acknowledgements This work was supported by the Office of Vehicle Technologies of the U.S. Department of Energy through the Advanced Battery Materials Research Program (Battery 500 Consortium) under Contract DE-EE0007764. Part of the work used the UCSD-MTI Battery Fabrication Facility and the UCSD-Arbin Battery Testing Facility. H. Liu, X. Wang, H. Zhou, H.-D. Lim, X. Xing, Q. Yan, Y. S. Meng and P. Liu, ACS Applied Energy Materials, 2018, DOI: 10.1021/acsaem.8b00348.H. Liu, H. Zhou, B.-S. Lee, X. Xing, M. Gonzalez and P. Liu, Acs Applied Materials & Interfaces, 2017, 9, 30635-30642.H. Liu, X. Yue, X. Xing, Q. Yan, J. Huang, V. Petrova, H. Zhou and P. Liu, Energy Storage Materials, 2018, DOI: https://doi.org/10.1016/j.ensm.2018.09.021.

Boosting Coulombic Efficiency of Conversion‐Reaction Anodes for Potassium‐Ion Batteries via Confinement Effect

AbstractPotassium‐ion battery anode materials with high capacity always hold one or more K ions and are companied by large volume swelling, which threatens the stability of solid‐electrolyte‐interface (SEI) layers, and results in low coulombic efficiency as well as inferior cycling stability. Herein, an avenue that induces the rapid formation of continuous SEI layers by the confinement effect to boost K ions storage property is proposed. CuS nanoplates are dispersed on the core layer of carbon nanofibers and further confined by the Nb2O5‐C shell layer, constructing core–shell structure CuS‐C@Nb2O5‐C nanofibers (NFs). The shell layer protects the CuS nanoplates from immediate contact with the electrolyte and brings about volume expansion, assisting the rapid formation of continuous SEI layers. As a result, the capacity retention of the CuS‐C@Nb2O5‐C NFs electrode remains at 93.1% after 100 cycles, much larger than that of the CuS‐C NF electrode (74.6%); the process that coulombic efficiency stabilized above 99.0% shortens to 5 cycles from 30 cycles. This progress is also found in the CoS2‐C@Nb2O5‐C and NiS2‐C@Nb2O5‐C NFs electrodes. The improved coulombic efficiency and cycling stability brought about by the confinement effect offer a facile approach to boost the K ion storage property of conversion reaction anodes.

Abnormal Overcharging during Lithium-Ether Co-Intercalation in a Graphite System: Formation of Shuttling Species by the Reduction of the TFSI Anion.

Materializing an ultrafast charging system is one of the crucial technologies for next-generation Li-ion batteries (LIBs). Among many studies aimed at achieving fast charging systems, Li-ether solvent cointercalation into the graphite electrodes in LIB has been identified as a novel concept for achieving high power performance because this system does not consist of the sluggish desolvation step and a resistive solid-electrolyte interface (SEI) layer. Interestingly, while studying the Li-ether solvent cointercalation into graphite electrodes, employing lithium bis-trifluoromethane sulfonimide (LiTFSI) as the Li salt, we observed an abnormal overcharging phenomenon. Here, we screened the specific conditions, under which the abnormal overcharging occurred, and revealed that this abnormal overcharging was attributable to the shuttling mechanism. The formation of shuttling species could have been derived by the reduction of TFSI- anion. With this understanding of the underlying mechanism, we efficiently suppressed the abnormal overcharging by adding LiNO3 to the electrolyte. The shuttling and resulting overcharging could be prevented by the synergistic contributions of LiNO3 and SxOy, dissolved in the electrolyte, to the formation of a dense solid LiSxOy SEI layer on Li-metal. We expect that this work could be a great reference in analyzing many unsolved phenomena in systems utilizing TFSI-.

Surface chemistry of LiFePO4 cathode material as unraveled by HRTEM and XPS

During the first cycle of lithium-ion batteries, a passivation layer is formed on the surface of electrode due to electrolyte decomposition, which is called solid electrolyte interface (SEI). In this study, the evolution of LiFePO4 cathode surface and components of SEI layer are investigated in different states by high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The results suggest that SEI layer is mainly formed during the first cycle and remains stable in the following cycles. Furthermore, SEI layer can be divided into two parts, and components of these two parts are different. The outer layer that is near to electrolyte is composed of organic components, and the inner layer that is near to active material is composed of inorganic components. Taken together, the study reveals SEI layer formation process on LiFePO4 cathode surface, which is of significance for understanding the influence of SEI layer on electrochemical performance.

Functional lithiophilic polymer modified separator for dendrite-free and pulverization-free lithium metal batteries

Severe performance drop and fire risk due to the uneven lithium (Li) dendrite formation and growth during charge/discharge process has been considered as the major obstacle to the practical application of Li metal batteries. So inhibiting dendrite growth and producing a stable and robust solid electrolyte interface (SEI) layer are essential to enable the use of Li metal anodes. In this work, a functional lithiophilic polymer composed of chitosan (CTS), polyethylene oxide (PEO), and poly(triethylene glycol dimethacrylate) (PTEGDMA), was homogeneously deposited on a commercial Celgard separator by combining electrospraying and polymer photopolymerization techniques. The lithiophilic environment offered by the CTS-PEO-PTEGDMA layer enables uniform Li deposition and facilitates the formation of a robust homogeneous SEI layer, thus prevent the formation and growth of Li dendrites. As a result, both Li/Li symmetric cells and LiFePO4/Li full cells deliver significantly enhanced electrochemical performance and cycle life. Even after 1000 cycles, the specific capacity of the modified full cell could be maintained at 65.8 mAh g−1, twice which of the unmodified cell (32.8 mAh g−1). The long-term cycling stability in Li/Li symmetric cells, dendrite-free anodes in SEM images and XPS analysis suggest that the pulverization of the Li anode was effectively suppressed by the lithiophilic polymer layer.