Growth Of Solid Electrolyte Interphase Research Articles

Unveiling the Dynamics of Solid Electrolyte Interphase Evolution in Li-Ion Batteries Via Operando X-Ray Reflectivity: Experimental Insights for Advanced Energy Storage

The Solid-Electrolyte-Interphase (SEI) is a crucial component of Li-ion batteries (LIBs), as it passivates the highly reactive electrode from the electrolyte and helps to stabilize the electrode/electrolyte interface. However, the SEI formation and evolution can also limit the cycling performance and the capacity retention of the battery. Accurate electrochemical models must therefore account for the SEI and properly simulate it. In order to investigate experimentally the SEI, various techniques have been deployed, including electron microscopy1, X-ray photoelectron spectroscopy (XPS)2,3 and Nuclear magnetic resonance (NMR)4.Providing reliable information on the SEI evolution during cycling, and thus benchmarking models, is challenging with these ex-situ or destructive techniques, as they hardly allow in situ observation. On the other hand, synchrotron X-ray reflectivity (XRR) can be used for the operando investigation of interfacial phenomena. It provides information on the thickness, density, and roughness of the SEI, as well as their changes upon (de)lithiation or in out-of-equilibrium conditions. Moreover, operando XRR can be performed under controlled battery operating conditions, providing relevant information on the SEI. Recently, several works reported that operando XRR experiment can provide in situ structural information of the formation and the growth of SEI with sub-nanometer resolution during the cycling5–7.Herein, we report the results of operando XRR experiments performed at the beamline BM32 of the European Synchrotron Radiation Facility (ESRF) to investigate the SEI on Si anode using novel, sustainable fluorine-free electrolytes. Indeed, in the quest for environmentally friendly and safe LIBs, removing the fluorinated electrolytes that are toxic and release corrosive compounds is a necessary step. One way to enhance the safety and sustainability of LIBs is to replace the conventional fluorinated electrolytes by fluorine-free alternatives. A F-free composition based on the lithium bis(oxalato) borate (LiBOB) salt recently showed promising performance in commercially relevant cell configurations8. As with conventional electrolytes, the F-free electrolyte reacts at the surface of the electrodes during the first charge, thus forming the SEI. Characterizing the F-free SEI growth and stability is thus key to understand its behavior and to improve the cell performance for this promising green electrolyte.In this work, operando XRR experiments were performed in electrochemical cells with different electrolyte compositions: 1 M LiPF6 in ethylene carbonate (EC):ethyl methyl carbonate (EMC) = 3:7 vol % (LP57), 0.7 M LiBOB in EC:EMC = 3:7 vol % (LiBOB), and 0.7 M LiBOB in EC:EMC = 3:7 vol % with 2 wt% vinylene carbonate (LiBOB-VC) during at least three cycles. XRR data show that the formations of SEI layers and their evolutions during the cycling for these two types of electrolytes are different. Furthermore, a layer with low electron density (ED) is still present after total delithiation in the LiBOB-cells, while the ED evolutions are generally reversible for LP57 cell. This suggests that the F-free SEI has different properties during cycling than the SEI formed with conventional salt LiPF6.In summary, operando XRR is a powerful technique for investigating the impact of new electrolyte chemistry and formulation on the SEI properties, which significally influence batteries performances. Moreover, the in situ and in real-time experimental insights with sub-nanometer resolution from this technique provides valuable information for the development of more accurate and predictive models for the SEI evolution. Its unique capabilities make it an essential tool for advancing the understanding of SEI behavior and designing more efficient and stable energy storage systems.Figure 1: (a) Principle of operando X-ray reflectometry. (b) XRR data and fit-derived EDP of LiBOB cell upon lithiation. Figure 1

Revealing the aging process of solid electrolyte interphase on SiOx anode

As one of the most promising alternatives to graphite negative electrodes, silicon oxide (SiOx) has been hindered by its fast capacity fading. Solid electrolyte interphase (SEI) aging on silicon SiOx has been recognized as the most critical yet least understood facet. Herein, leveraging 3D focused ion beam-scanning electron microscopy (FIB-SEM) tomographic imaging, we reveal an exceptionally characteristic SEI microstructure with an incompact inner region and a dense outer region, which overturns the prevailing belief that SEIs are homogeneous structure and reveals the SEI evolution process. Through combining nanoprobe and electron energy loss spectroscopy (EELS), it is also discovered that the electronic conductivity of thick SEI relies on the percolation network within composed of conductive agents (e.g., carbon black particles), which are embedded into the SEI upon its growth. Therefore, the free growth of SEI will gradually attenuate this electron percolation network, thereby causing capacity decay of SiOx. Based on these findings, a proof-of-concept strategy is adopted to mechanically restrict the SEI growth via applying a confining layer on top of the electrode. Through shedding light on the fundamental understanding of SEI aging for SiOx anodes, this work could potentially inspire viable improving strategies in the future.

Experimental and Computational Study on SEI Composition and Electrochemical Performance of Lithium-Ion Battery with Silicon Oxide-Graphite Composite Electrode

Demand on batteries with high energy density is surging. Conventionally, carbon materials have been used as an anode active material, but recently silicon materials are likely to be incorporated to form a composite anode in lithium-ion batteries (LIBs) for higher energy density. However, LIBs which include silicon materials in anode tend to show a low cycle performance especially the ratio of silicon materials in the anode increases. Commercial LIBs still have difficulty in incorporating large amount of silicon materials especially under the requirements where multiple aspects like safety, charging rate and energy density should be totally met.One potential pathway to improve the cycle performance in LIBs with silicon materials is to tune the nature of solid electrolyte interphase (SEI), a thin film which forms at the interface between anode active material and electrolyte. The nature of SEI is particularly important for LIBs with silicon materials because such silicon active materials show large volume changes during battery operation and SEI is dynamically reconstructed. It has been qualitatively reported so far that LiF is an important component for better battery performance. Our work suggests that the ratio of LiF in initially formed SEI is a crucial factor to realize improved cycle performance in such LIBs.In our work, anode with silicon oxide (SiOx)-graphite composite is considered. We investigated the relationship between electrochemical performance of the cell with such composite electrode and the nature of the film estimated by characterization and molecular simulation. We systematically changed the composition of liquid electrolyte to form various types of SEI on anode surface. For characterization, both fresh and aged cells with different electrolytes were dismantled, and SEI components were extracted by designated solvents, then NMR (nuclear magnetic resonance) was applied to identify the SEI species and quantify the amounts of major SEI components. Comparison between the evolution of SEI amount and an impedance element in electrochemical impedance spectroscopy during aging indicates that degradation of the cells is closely related to the growth of SEI. To further deepen understanding the role of LiF, molecular dynamics simulation was carried out, where the mixture of LiF and typical organic SEI was modelled. Correlation between calculated mechanical property and measured electrochemical performance of the cells were revealed. In our presentation, the requirements that SEI should satisfy will be discussed from the insight of electrochemical measurements, NMR characterization and modeling approaches.

Sponge-Like Porous-Conductive Polymer Coating for Ultrastable Silicon Anodes in Lithium-Ion Batteries.

Urgent calls for reversible cycling performance of silicon (Si) requires an efficient solution to maintain the silicon-electrolyte interface stable. Herein, a conductive biphenyl-polyoxadiazole (bPOD) layer is coated on Si particles to enhance the electrochemical process and prolong the cells lifespan. The conformal bPOD coatings are mixed ionicelectronic conductors, which not only inhibit the infinite growth of solid electrolyte interphase (SEI) but also endow electrodes with outstanding ion/electrons transport capacity. The superior 3D porous structure in the continuous phase allows the bPOD layers to act like a sponge to buffer volume variation, resulting in high structural stability. The in situ polymerized bPOD coating and it-driven thin LiF-rich SEI layer remarkably improve the lithium storage performance of Si anodes, showing a high reversible specific capacity of 1600 mAh g-1 even after 500 cycles at 1 A g-1 along with excellent rate capacity of over 1500 mAh g-1 at 3 A g-1 . It should be noticed that a long cycle life of 800 cycles with 1065 mAhg-1 at 3 A g-1 can also be achieved with a capacity retention of more than 80%. Therefore, we believe this unique polymer coating design paves the way for the widespread adoption of next-generation lithium-ion batteries.

Enhancing High-Capacity and High-Rate Sodium-Ion Storage through Synergistic N, S Dual Doping of Hard Carbon.

Hard carbon, as the most promising commercial anode materials of sodium-ion batteries (SIBs), has suffered from the coupling limitations on initial Coulombic efficiency (ICE), capacity, and rate capability. Herein, to break such coupling limitations, sulfur-rich nitrogen-doped carbon nanomaterials (S-NC) were synthesized by a synergistic modification strategy, including structure/morphology regulation and dual heteroatom doping. The small specific surface area of S-NC is beneficial for inhibiting excessive growth of solid electrolyte interphase (SEI) film and irreversible interfacial reaction. The covalent S can serve as active electrochemical sites by Faradaic reactions and provide extra capacity. Benefit by N, S co-doping, S-NC shows large interlayer spacing, high defects, good electronic conductivity, strong ion adsorption performance, and fast Na+ ion transport, which combined with a more significant pore volume result in speedier reaction kinetics. Hence, S-NC possesses a high reversible specific capacity of 464.7 mAh g-1 at 0.1 A g-1 with a high ICE of 50.7%, excellent rate capability (209.8 mAh g-1 at 10.0 A g-1), and superb long-cycle capability delivering a capacity of 229.0 mAh g-1 (85% retention) after 1800 cycles at 5.0 A g-1.

Atomic Layer Deposition of Ultrathin Al2O3 Layer on Carbon Nanotube Anodes for Potassium Ion Batteries with High Initial Coulombic Efficiency and Electrochemical Performance

AbstractPotassium ion batteries (PIBs) have emerged as one of the most attractive alternatives to lithium‐ion batteries (LIBs) to satisfy the burgeoning energy demand. The continuous growth of solid electrolyte interphase (SEI) and consumption of potassium resources cause poor initial Coulombic efficiency (ICE), unstable cycling performance, and even safety issues. Herein, the fabrication of an artificial SEI of an ultrathin Al2O3 layer by atomic layer deposition (ALD) on a multi‐walled carbon nanotubes (MWCNTs) anode for high‐performance PIBs is reported. The SEI resistance and the charge transfer resistance in the MWCNTs electrode are significantly reduced according to electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration (GITT) measurements. The MWCNT electrode with a 2‐nm Al2O3 layer exhibits a much higher ICE of up to 85.9% than that of the uncoated one (20.8 %). It also maintains a remarkably high reversible capacity of 284 mA h g−1 at 100 mA g−1 after 100 cycles. In particular, the anode delivers superior rate capability of 558, 303, 251, 203, and 154 mAh g−1 at a current density of 50, 100, 200, 400, and 800 mA g−1, respectively. This work offers an effective approach for fabricating PIBs with high ICE and electrochemical performance.

Comprehensive analysis on aging behavior and safety performance of LiNixCoyMnzO2/graphite batteries after slight over-discharge cycle

Over-discharge is one of the common abuse conditions for lithium-ion batteries (LIBs), while the safety hazard of over-discharged cell is still unclear. In this work, the aging behavior and safety performance of commercial Li(Ni0.5Co0.2Mn0.3)O2/graphite LIBs under 1.5, 1.0, 0.5, and 0.0 V over-discharge cycles are investigated. The cells experience capacity decay and structural damage during over-discharge cycle. Compare to the normal cycled cells, the increased impedance after over-discharge cycle leads to more heat generation during operating, which further accelerates the inconsistency of LIB module. Moreover, the thermal runaway behavior of the over-discharged cell was studied using Extended Volume Accelerating Rate Calorimeter. The kinetics of self-heating reaction is obtained, and the criticality of thermal runaway under different heat dissipation conditions was analyzed based on Semenov model. The thermal stability and maximum safe storage temperature of the LIB were decreased after over-discharge cycle, especially for the cell over-discharged to 0.0 V. Based on the electrochemical impedance spectroscopy, the loss of lithium inventory relate to the growth of solid electrolyte interphase (SEI) film is found to be the primary aging contribution. Moreover, the post-mortem test implied the dissolution of Cu initiated when over-discharged to 0.5–0.0 V.

Mechanical Stability of the Heterogenous Bilayer Solid Electrolyte Interphase in the Electrodes of Lithium–Ion Batteries

Mechanical stability of the solid electrolyte interphase (SEI) is crucial to mitigate the capacity fade of lithium–ion batteries because the rupture of the SEI layer results in further consumption of lithium ions in newly generated SEI layers. The SEI is known as a heterogeneous bilayer and consists of an inner inorganic layer connecting the particle and an outer organic layer facing the electrolyte. The growth of the bilayer SEI over cycles alters the stress generation and failure possibility of both the organic and inorganic layers. To investigate the probability of mechanical failure of the bilayer SEI, we developed the electrochemical-mechanical coupled model with the core–double-shell particle/SEI layer model. The growth of the bilayer SEI is considered over cycles. Our results show that during charging, the stress of the particle changes from tensile to compressive as the thickness of bilayer SEI increases. On the other hand, in the SEI layers, large compressive radial and tensile tangential stress are generated. During discharging, the compressive radial stress of the bilayer SEI transforms into tensile radial stress. The tensile tangential and radial stresses are responsible for the fracture and debonding of the bilayer SEI, respectively. As the thickness ratio of the inorganic to organic layers increases, the fracture probability of the inorganic layer increases, while that of the organic layer decreases. However, the debonding probability of both layers is decreased. In addition, the SEI covering large particles is more vulnerable to fracture, while that covering small particles is more susceptible to debonding. Therefore, tailoring the thickness ratio of the inorganic to organic layers and particle size is important to reduce the fracture and debonding of the heterogeneous bilayer SEI.

A microcrack propagation-based life prediction model for lithium-ion batteries with Ni-rich cathode materials

The formation and growth of solid electrolyte interphase (SEI) on the anode are key parameters governing battery life prediction models of lithium-ion batteries (LiBs). However, as conventional battery life prediction models do not reflect other degradation parameters such as crack formation and propagation in Ni-rich cathode materials, their accuracy is greatly reduced as the nickel content increases in layered oxide cathode materials. Herein, we propose an advanced prediction model that includes both crack propagation and SEI growth. The reliability of this microcrack propagation-based life prediction model is verified using experimental data of over 50 commercial 18650 LiB cells, which are tested under depths of discharge and current rates, from 500 to 5000 cycles. The proposed model predicts capacity retention values with less than 5 % error, even in practical operations of energy storage systems and electric vehicles, providing a standard solution for predicting the cycle life of LiBs with Ni-rich cathode materials.

Carbon Encapsulated Silicon for High-Capacity Durable Anodes

One of the biggest challenges of the near future is how to meet the increasing energy demand without any adverse environmental impact. Lithium-Ion batteries (LIBs) are one of the promising alternative energy storage systems to replace conventional non-rechargeable batteries. LIBs are becoming one of the most widely used energy storage devices because of their relatively high specific energy density (~300 Wh/kg), excellent stability over a wide temperature range, and lower cost than other battery systems. Intense research is in progress to increase the capacity of anode electrodes for realizing high-energy LIBs. In this context, silicon (Si) has a great potential to replace commercial graphitic anode active materials mainly due to its high theoretical specific capacity (4200 mAh/g) and low working potential (0.37 to 0.45 V vs. Li/Li+). To harness and maintain a high capacity from Si-based anodes, we must deal with two main challenges: (i) volume changes of Si (>300%) during charging and discharging, which cause pulverization of the material and loss of electrical contact, and (ii) unstable growth of solid-electrolyte interphase (SEI) layer, which can cause early degradation of performance in Si-anode batteries. To overcome these challenges, different approaches have been taken. This includes developing graphite/Si anodes with limited amounts of Si (<30 wt.%), conformal coating of Si active materials (e.g., CVD carbon coating), etc. However, these challenges still could not be fully overcome.To advance the use of Si materials in LIB anodes, we developed a viable technology to create a hybrid silicon-carbon material, called Si@C, in which a soybean-derived carbon cloud protects Si nanoparticles during the battery operation. We employed soybean oil in a scalable oil-in-water emulsion polymerization technique to produce Si-containing polymeric particles. In this method, we emulsified two immiscible solutions. One contains a homogeneous Si mixture in epoxidized soybean oil (ESO), and another contains a uniform dispersion of ball-milled lignin or soyhull powders in water. Citric acid, a crosslinking agent, was used to help polymerize the ESO and integrate carbon-rich lignin/soyhull with polymerized particles. The final Si@C product was achieved by carbonizing the polymerized solid product at 500 °C (under argon) and ball milling to get a fine powder. Several Si@C hybrid materials containing 20 wt.% to 50 wt.% Si were successfully prepared and utilized for anode preparation. Electrodes were made by coating a slurry of Si@C active material, carbon black, and binder with a mass ratio of 60:20:20 onto an ion-permeable Bucky Paper (BP, a flexible and conductive paper made of carbon nanotubes). Anodes with different binding systems were prepared to determine an appropriate binder for Si@C based batteries. The 2032-type coin cells were assembled for battery testing using 1M LiPF6 in EC:DMC in a volume ratio of 1:1 as the electrolyte, Li chips as the counter electrode, and Celgard 2325 as the separator. The coin cells were cycled at a current rate of 0.1C (420 mA/gSi) over the potential range of 0.01 – 1.0 V at room temperature.Battery results showed that Si@C hybrid materials increased the capacity of Si anodes by a factor of >2. At Si mass loading of 1.0 mg/cm2, implementing our carbon cloud approach led to an increase in the discharge capacity of anodes from 0.5 mAh (corresponding to anode with bare Si) to >1.0 mAh (corresponding to anode with Si@C hybrids). Results from battery cycling at 0.1C demonstrated excellent capacity retention of >95% after 130 cycles for anodes prepared using our Si@C active materials. The Si content of Si@C hybrid particles was also found to be an influential factor in the cycling performance of anodes. Finally, we observed that the use of water-based polyacrylic acid (PAA) and carboxymethyl cellulose (CMC) binders improve the electrochemical performance of Si@C based anodes. These water-based binders are ideal for preparing Si-based slurries, and the need for using toxic solvents (e.g., NMP) to prepare slurries can be averted. In conclusion, we innovated a viable technology that uses biomass (soybean oil and soyhulls) to enhance Si-based batteries' performance. We demonstrated that our Si@C materials with a carbon cloud protecting the Si nanoparticles are promising active materials to improve the capacity and cycling stability of LIB anodes.

The surface double-coupling on single-crystal LiNi0.8Co0.1Mn0.1O2 for inhibiting the formation of intragranular cracks and oxygen vacancies

Single-crystal LiNi0.8Co0.1Mn0.1O2 (SC-811), which prevents grain-boundary fracture and offers better cycle performance compared to the polycrystalline morphology, has gained great attention as cathode materials for lithium-ion batteries. However, the single-crystal Ni-rich LiNixCoyMnzO2 (x+y+z=1) (NCM) is suffering from oxygen vacancy, intragranular crack, and ion diffusion in large particles that hinder its electrochemical performance. Herein, a double coupling of surface La2Li0.5Al0.5O4 coating and concentration-gradient Al3+ doping is exploited on SC-811 cathode by facile sol-gel method. The synergistic impacts endow the SC-811 with excellent capacity retentions: 90.9%, after 200 cycles at 1 C. In a pouch-type full battery, the graphite/LLA modified SC-811 exhibits a capacity retention of 90.1% after 500 cycles at 1 C in the 2.8-4.25 V range at 25°C. Multiple characterizations reveal that the excellent electrochemical performance are mainly attributed to double-coupling that successfully inhibits the attenuation of H2-H3 phase, intragranular cracks, oxygen vacancies, the serious rock salt phase transition, and alleviates the growth of solid electrolyte interphase (SEI) and the side reaction of electrode/electrolyte during cycling. This work demonstrates that doping combined with coating is a critical pathway for the further development of single-crystal ternary cathode materials.

A Hierarchical Si/C Nanocomposite of Stable Conductive Network Formed Through Thermal Phase Separation of Asphaltenes for High-Performance Li-Ion Batteries.

Silicon is one of the most promising anode materials for lithium-ion batteries. However, the huge volume change of silicon during lithiation/delithiation triggers continuous growth of solid-electrolyte interphase, loss of conductive contacts and structural collapse of the electrode, which causes a rapid deterioration of battery capacities. Inspired by the polyaromatic molecular nature and phase separation of asphaltenes in bitumen during thermal cracking, a hierarchical Si/C nanocomposite of robust carbon coatings and a firmly connected carbon framework on the silicon surface is synthesized by controlling the concentration of asphaltenes as carbon source and hence desired phase separation during the subsequent carbonization. The electrode made using this special Si/C nanocomposite exhibits a high reversible capacity of 1149 mAh g-1 after 600 cycles with a capacity retention of 98.5% and the operation ability at a high mass loading over 10mg cm-2 or an area capacity of 23.8 mAh cm-2 , which represents one of the highest area capacities reported in open literature but with much more stable and prolonged operations. This simple and efficient strategy is easy to scale up for commercial production to meet the rapid growth of the electric vehicle industry.

Uncovering Unique Interfacial Properties in Different Lithium Fluoride Phases: A First-Principles Prediction

Electrolytes are susceptible to reductive decomposition on the surface of negative electrodes leading to the formation and growth of solid-electrolyte interphase (SEI) layer [1]. Stable SEI can be beneficial as a protective layer, given that it can provide insulation to electron transport from the anode to electrolyte, prevent solvent molecules from reaching the anode, and at the same time allow transport of Li+ [2]. Thus, the SEI can contribute critically to the safety and operability of lithium-ion batteries (LIBs), but its functionality heavily depends on the conditions under which it gets synthesized [3]. This can have a significant effect on battery performance. For instance, nucleation and growth of lithium dendrites during cycling is known to result in continuous electrolyte degradation, destruction of the SEI, agglomeration of so-called “dead lithium”, and short-circuiting of the battery [4]. This greatly affects next-generation electric vehicles (EVs), for which all-solid-state lithium-metal batteries (ASSLMBs) have garnered significant attention due to their superior energy storage capacity and safety over LIBs [5]. However, the considerable interfacial impedance originating from poor physical contact and/or parasitic reactions at the Li/SSE interface hinders the development of ASSLMBs. Alternative approaches towards achieving a stable protective interface have been pursued: like use of electrolyte additives to manipulate the constituents and compositions of SEI or designing artificial protective layers to improve performance. For instance, admixture of optimum amounts of fluorine-rich additives like fluoroethylene carbonate (FEC) to traditional carbonate electrolytes (like EC/DMC) has been seen to generate a robust LiF-rich SEI. However, the intrinsic role of LiF remains a topic of uncertainty. Conventional understanding would posit that dominance of LiF leaves the SEI susceptible to poor lithium-ion transport properties. Previously, theoretical works reported significantly lower ionic conductivities in crystalline LiF when compared to other common inorganic SEI materials like Li2O and Li2CO3. Underwhelming transport properties pose serious rate limitations in its effectiveness as a serious candidate for interfacial protection in ASSLMBs. To potentially overcome such bottleneck, this study systematically investigates different phases of LiF: their structures, stabilities and interfacial properties are described using first principles calculations. Careful analysis of the structural models reveals that unlike the widely studied rock salt ordered counterpart, certain phases of LiF exhibit excellent Li+ transport properties with a high predicted diffusivity at room temperature. Mechanically too, improved interfacial qualities are demonstrated with increased flexibility and fracture resistance, opening up important avenues for structural and compositional stability over cell cycling while maintaining its desirable electron-blocking characteristics. However, it is also important to take a step back and note that the rock salt phase is the most energetically stable among LiF phases, which thereby exhibit a propensity for phase transformation under ambient conditions. To overcome this, a strategy of incorporating hetero dopants as impurities to stabilize the host matrix is discussed. By increasing the dopant concentration up to an optimum amount, relative thermodynamic stability of the interface-friendly phases of LiF is achieved. Our examination of the structure reveals unique lithium-dopant interactions which help sustain such LiF phases in the host matrix. The combination of excellent Li-ion transport properties and electron blocking ability makes such LiF-rich composites an excellent candidate for use as an interfacial protective layer that can effectively suppress electrolyte decomposition and Li dendrite propagation, while simultaneously improving the contact and compatibility of the electrode/electrolyte interface. These unique and exceptional traits make them materials of great promise for protecting critical interfaces in ASSLMBs and LIBs.[1] M. Gauthier, T.J. Carney, A. Grimaud, L. Giordano, N. Pour, H.-H. Chang, D.P. Fenning, S.F. Lux, O. Paschos, C. Bauer, F. Maglia, S. Lupart, P. Lamp, Y. Shao-Horn, Electrode−Electrolyte Interface in Li-Ion Batteries: Current Understanding and New Insights, J. Phys. Chem. Lett. 6 (2015) 4653−4672. https://doi.org/10.1021/acs.jpclett.5b01727[2] D. Bedrov, O. Borodin, J.B. Hooper, Li+ Transport and Mechanical Properties of Model Solid Electrolyte Interphases (SEI): Insight from Atomistic Molecular Dynamics Simulations, J. Phys. Chem. C 121 (2017) 16098–16109. https://doi.org/10.1021/acs.jpcc.7b04247[3] D. Aurbach, B. Markovsky, I. Weissman, E. Levi, Y. Ein-Eli, On the Correlation Between Surface Chemistry and Performance of Graphite Negative Electrodes for Li Ion Batteries, Electrochim. Acta 45 (1999) 67−86. https://doi.org/10.1016/S0013-4686(99)00194-2[4] W. Xu, J. Wang, F. Ding, X. Chen, E. Nasybulin, Y. Zhang, J.G. Zhang, Lithium Metal Anodes for Rechargeable Batteries, Energy Environ. Sci. 7 (2014) 513−537. https://doi.org/10.1039/C3EE40795K[5] J. G. Kim, B. Son, S. Mukherjee, N. Schuppert, A. Bates, O. Kwon, M. J. Choi, H. Y. Chung, S. Park, A review of lithium and non-lithium based solid state batteries, J. Power Sources 282 (2015) 299−322. https://doi.org/10.1016/j.jpowsour.2015.02.054

(Digital Presentation) Stable Passivation Layer of Oxygen Deficient α-MoO3-X Nanobelts Suppress Li Dendrites to Achieve High-Capacity Li-S Battery

The high energy density lithium metal batteries (LMBs) are considered promising energy storage devices for future development. The Li metal reacts with electrolyte and forms an unstable solid electrolyte interphase (SEI), such SEI break down upon cycles and exposes fresh Li metal to the electrolyte which further initiate the growth of Li dendrites. The Li dendrites eventually penetrate the separator and can cause catastrophic battery failure. To suppress the growth of Li dendrites, we have formed a passivation layer on Li metal anode by using oxygen-deficient α-MoO3 nanobelts (MNBs) via a simple spray coating method. The MNBs were synthesized by simple ball milling method. The porous net-like interconnected structure formed by MNBs accommodates the excess Li, provides shorter diffusion pathways to Li+ ions and avoids the dendritic growth and pulverization of SEI. The Li-Li symmetrical cells with MNBs coated Li electrodes (MNB-Li) operated at current density of 1 mA cm–2 with a deposition capacity of 1 mAh cm–2 shows lower overpotential (~30 mV) than the cells with pristine Li (~45mV) after 100 hours of cycling. Oxygen vacancies present on the surface of MNBs act as shallow donors and boost carrier concentration, resulting in increased surface conductivity. The MNB-Li paired up with sulfur expanded graphite (SEG) cathode and activated expanded graphite (AEG) coated separator offers ~1077 mAh g-1 initial capacity at 0.5C (1C=1600 mAh g-1) and ~99 % coulombic efficiency for 100 cycles. Figure 1

Electrochemical Protocols to Assess the Effects of Dissolved Transition Metal in Graphite/LiNiO2 Cells Performance

The deployment of energy dense positive electrode materials such as Ni-rich NMC (LiNixMnyCozO2 with 0 < x, y, z < 1 and x + y + z = 1) for Li-ion batteries is plagued by numerous interfacial limitations. Among them, dissolution of transition metals (TMs) was shown to trigger deleterious growth of solid electrolyte interphase (SEI) and/or lithium plating at the anode. Although numerous post-mortem analysis and cycling data showed a causal relationship between TMs deposition and capacity fading, quantifying and discriminating the major source of degradation proves tedious. Herein, using graphite/LiNiO2 chemistry, we quantitatively demonstrate that TMs in solution permeate inside the SEI to be reduced, which precipitates cell aging following a loss of lithium inventory at the anode. This loss induces a change in intercalation staging at the graphite anode, allowing the recovery of LiNiO2 intercalation plateau at high potential, thus leading to a “S”-shape evolution of capacity as function of cycling. Furthermore, aging study in temperature show that TMs do not favor lithium plating but rather destabilize the SEI, especially at high temperature. Beyond the sole understanding of the graphite/LiNiO2 chemistry, this work offers practical routes towards evaluating LIBs degradations using electrochemical diagnosis methods.

Structural Restoration of Degraded LiFePO 4 Cathode with Enhanced Kinetics Using Residual Lithium in Spent Graphite Anodes

Structural Restoration of Degraded LiFePO ₄ Cathode with Enhanced Kinetics Using Residual Lithium in Spent Graphite Anodes

Interfacial Evolution of the Solid Electrolyte Interphase and Lithium Deposition in Graphdiyne-Based Lithium-Ion Batteries.

All-carbon graphdiyne (GDY)-based materials have attracted extensive attention owing to their extraordinary structures and outstanding performance in electrochemical energy storage. Straightforward insights into the interfacial evolution at GDY electrode/electrolyte interface could crucially enrich the fundamental comprehensions and inspire targeted regulations. Herein, in situ optical microscopy and atomic force microscopy monitoring of the GDY and N-doped GDY electrodes reveal the interplay between the solid electrolyte interphase (SEI) and Li deposition. The growth and continuous accumulation of the flocculent-like SEI is directly tracked at the surface of GDY electrode. Moreover, the nanoparticle-shaped SEI homogeneously propagates at the interface when N configurations are involved, providing a critical clue for the N-doping effects of stabilizing interfaces and homogenizing Li deposition. This work probes into the dynamic evolution and structure-reactivity correlation in detail, creating effective strategies for GDY-based materials optimization in lithium-ion batteries.

Ferroelectric Engineered Electrode-Composite Polymer Electrolyte Interfaces for All-Solid-State Sodium Metal Battery.

To enhance the compatibility between the polymer‐based electrolytes and electrodes, and promote the interfacial ion conduction, a novel approach to engineer the interfaces between all‐solid‐state composite polymer electrolyte and electrodes using thin layers of ferroelectrics is introduced. The well‐designed and ferroelectric‐engineered composite polymer electrolyte demonstrates an attractive ionic conductivity of 7.9 × 10–5 S cm–1 at room temperature. Furthermore, the ferroelectric engineering is able to effectively suppress the growth of solid electrolyte interphase (SEI) at the interface between polymer electrolytes and Na metal electrodes, and it can also enhance the ion diffusion across the electrolyte‐ferroelectric‐cathode/anode interfaces. Notably, an extraordinarily high discharge capacity of 160.3 mAh g–1, with 97.4% in retention, is achieved in the ferroelectric‐engineered all‐solid‐state Na metal cell after 165 cycles at room temperature. Moreover, outstanding stability is demonstrated that a high discharge capacity retention of 86.0% is achieved over 180 full charge/discharge cycles, even though the cell has been aged for 2 months. This work provides new insights in enhancing the long‐cyclability and stability of solid‐state rechargeable batteries.

A significant enhancement of cycling stability at fast charging rate through incorporation of Li3N into LiF-based SEI in SiOx anode for Li-ion batteries

SiOx has attracted significant attention as an advanced anode material for next-generation lithium-ion batteries for electric vehicles. However, low Li-ion conductivity, chemical instability, morphological inhomogeneity, and the subsequent uneven growth of solid electrolyte interphase (SEI) are still unresolved and hinder its practical application. The LiF-rich SEI obtained using a conventional electrolyte with vinyl carbonate (VC) additive generally exhibits enhanced mechanical rigidity and low ionic conductivity. Herein, we report the use of octadecylamine (ODA) as additional electrolyte additives to enhance the ionic conductivity and physicochemical stability of the SEI by incorporating Li3N into the LiF-based SEI of SiOx anode. The Li3N with high ionic conductivity obtained by addition of ODA provides excellent lithium storage stability and fast charge/discharge performance; the NCM-811||Ti-SiOx@C full cell with VC and ODA additives exhibits approximately 2 times increased capacity retention even after 1000 cycles at 5 C-rate compared to the conventional electrolyte with VC additive only (approximately 5 times compared to the electrolyte without an additive).

Understanding electrolyte salt chemistry for advanced potassium storage performances of transition‐metal sulfides

AbstractMolybdenum disulfide/carbon nanotubes assembled by ultrathin nanosheets are synthesized to illustrate the electrolyte salt chemistry via potassium bis‐(fluorosulfonyl)imide (KFSI) versus potassium hexafluorophosphate (KPF6). Compared to the case of KPF6, the electrochemical performances using KFSI as the electrolyte salt are greatly improved: ~275 mAh g−1after 15,000 cycles at 1 A g−1, or ~172 mAh g−1even at 40 A g−1. These results represent one of the best performances for the reported anode materials. The enhanced performances could be attributed to the FSI‐induced changes in the solvate structures, that is, a large solvation energy, a high lowest unoccupied molecular orbital, and a small bonding dissociation energy of S–F. In this case, a uniform and robust solid–electrolyte interphase (SEI) is produced, improving the mechanical properties and the interface integrity. Then, the uncontrollable fracture and repeated growth of SEI, which always lead to the dissolution of sulfur species and the blockage of charge transfer in the case of KPF6, are well inhibited. This similar enhancement works for other sulfides by KFSI, demonstrating the general importance of this electrolyte salt chemistry.