Artificial SEI Layer Research Articles

Constructing Li‐Rich Artificial SEI Layer in Alloy–Polymer Composite Electrolyte to Achieve High Ionic Conductivity for All‐Solid‐State Lithium Metal Batteries

To achieve high ionic conductivity for solid electrolyte, an artificial Li-rich interface layer of about 60nm thick has been constructed in polymer-based poly(ethylene oxide)-lithium bis(trifluoromethanesulfonyl)imide composite solid electrolyte (briefly noted as PEOm ) by adding Li-based alloys. As revealed by high-resolution transmission electron microscopy and electron energy loss spectroscopy, an artificial interface layer of amorphous feature is created around the Li-based alloy particles with the gradient distribution of Li across it. Electrochemical analysis and theoretical modeling demonstrate that the interface layer provides fast ion transport path and plays a key role in achieving high and stable ionic conductivity for PEOm -Li21 Si5 composite solid electrolyte. The PEOm -5%Li21 Si5 composite electrolyte exhibits an ionic conductivity of 3.9 × 10-5 Scm-1 at 30°C and 5.6 × 10-4 Scm-1 at 45°C. The LiFePO4 | PEOm -5%Li21 Si5 | Li all-solid-state batteries could maintain a stable capacity of 129.2mAhg-1 at 0.2 C and 30°C after 100 cycles, and 111.3mAhg-1 after 200 cycles at 0.5 C and 45°C, demonstrating excellent cycling stability and high-rate capability.

An artificial hybrid interphase for an ultrahigh-rate and practical lithium metal anode

The present work theoretically and experimentally provides an insight into the internal mechanism of Li+ transport within an artificial hybrid SEI layer consisting of lithium-antimony (Li3Sb) alloy and lithium fluoride (LiF).

Lithium-activated SnS–graphene alternating nanolayers enable dendrite-free cycling of thin sodium metal anodes in carbonate electrolyte

Lithium activated SnS–graphene nanocomposite membrane is employed as an artificial Li-based SEI layer, allowing cyclability of record-thin 100 μm Na metal foils.

The lithium metal anode in Li–S batteries: challenges and recent progress

Critical challenges of Li–S batteries are related with the instability of Li metal during cycling. To overcome these issues, electrolyte modification and artificial SEI layer incorporation-based strategies have been here reviewed.

Surface Oxidation of Nano-Silicon as a Method for Cycle Life Enhancement of Li-ion Active Materials.

Among the many studied Li-ion active materials, silicon presents the highest specific capacity, however it suffers from a great volume change during lithiation. In this work, we present two methods for the chemical modification of silicon nanoparticles. Both methods change the materials’ electrochemical characteristics. The combined XPS and SEM results show that the properties of the generated silicon oxide layer depend on the modification procedure employed. Electrochemical characterization reveals that the formed oxide layers show different susceptibility to electro-reduction during the first lithiation. The single step oxidation procedure resulted in a thin and very stable oxide that acts as an artificial SEI layer during electrode operation. The removal of the native oxide prior to further reactions resulted in a very thick oxide layer formation. The created oxide layers (both thin and thick) greatly suppress the effect of silicon volume changes, which significantly reduces electrode degradation during cycling. Both modification techniques are relatively straightforward and scalable to an industrial level. The proposed modified materials reveal great applicability prospects in next generation Li-ion batteries due to their high specific capacity and remarkable cycling stability.

Li-B alloy with artificial solid electrolyte interphase layer for long-life lithium metal batteries

Rechargeable Li metal battery is an important option for the systems which required high energy densities, but it confronts some great issues, such as the potential formation of Li dendrites. Li-B alloy has been proven to be a potential alternative choice in lithium batteries, but the coulombic efficiency is still unacceptable. In this study, an artificial SEI layer was prepared on the surface of Li-B alloy using a simple method. Results infer the artificial layer may help to form a more stable SEI layer with consuming fewer lithium ions, which greatly improve the initial coulombic efficiency and the cycling stabilities. These results suggest that Li-B alloy with artificial solid electrolyte interphase layer may be a promising anode material for rechargeable lithium batteries.

In-situ organic SEI layer for dendrite-free lithium metal anode

Lithium metal (Li) is the most promising anode for high energy density secondary battery system, but the dendrite growth makes it very dangerous for commercial application. An artificial SEI layer with high ionic conductivity and low electronic conductivity has proven to be an effective way to improve the stability of Li anode. Organic layer is introduced on Li surface by in-situ spontaneous reaction between Li and carboxylic acid. The as-formed carboxylate layer can effectively limit the Li deposition under it and suppress the dendrite growth. And the uniformity of the organic layer is the key factor for achieving stable cycling performance. With a homogenous carboxylate layer of 1 ​μm, the Li electrode can sustain 1000 ​h of charge-discharge cycling at 0.5 ​mA ​cm−2. DFT calculation demonstrates that the enhanced absorption energy by oxygen atoms in lithium carboxylate contributes to the increased lithiophilicity and decreased depositing overpotential. This research provides a way for practical application of Li metal anode.

Facile ex situ formation of a LiF–polymer composite layer as an artificial SEI layer on Li metal by simple roll-press processing for carbonate electrolyte-based Li metal batteries

A facile and scalable process for the formation of artificial SEI layer is proposed by roll-press Li metal and fluoropolymer. The layer, composed of lithium fluoride and polymers, plays Li protection for highly stable lithium metal batteries.

An in situ formed LiF protective layer on a Li metal anode with solvent-less cross-linking

The artificial SEI layer that includes LiF can be fabricated simply through thermal curing of an F rich material on the surface of Li metal. The proposed artificial SEI layer design offers an alternative strategy for stabilizing the surface of Li metal.

Effective suppression of lithium dendrite growth using fluorinated polysulfonamide-containing single-ion conducting polymer electrolytes

A flexible artificial SEI layer with a 3D cross-linked network structure exhibits high ionic conductivity and single-ion conductive characteristics.

Constructing a liquid-metal based self-healing artificial solid electrolyte interface layer for Li metal anode protection in lithium metal battery

Uncontrollable Li dendrite growth and unstable SEI during repetitive Li deposition–dissolution processes severely impede the practical application of lithium metal batteries (LMBs). Herein, we create a novel artificial SEI layer by using liquid metal with self-healing property. The liquid metal could effectively facilitate the stable SEI layer formation by virtue of its self-healing property and regulate Li ion flus and inhibit the Li dendrite growth in the deposition process of Li. Electrochemical studies show that the LMNP-Li|LTO full-cell exhibits a superb rate capability and an excellent long-term cycling stability. This work offers a novel approach to achieve a stable Li metal anode with long cycle life.

Li Alginate-Based Artificial SEI Layer for Stable Lithium Metal Anodes.

Lithium metal anodes (LMAs) are critical for high-energy-density batteries such as Li-S and Li-O2 batteries. The spontaneously formed solid electrolyte interface on LMAs is fragile, which may not accommodate the cyclic Li plating/stripping. This usually will result in a low coulombic efficiency (CE), short cycle life, and potential safety hazards induced by the uncontrollable growth of lithium dendrites. In this study, we fabricate a Li alginate-based artificial SEI (ASEI) layer that is chemically stable and allows easy Li ion transport on the surface of LMAs, thus enabling the stable operation of lithium metal anodes. Compared to bare LMAs, the ASEI layer-protected LMAs exhibit a more stable Li plating/stripping behavior and present effective dendrite suppression. The symmetric Li∥Li cells with the ASEI layer-protected LMAs can stably run for 850 and 350 h at current densities of 0.5 and 1 mA cm-2, respectively. Additionally, the LiFePO4∥Li full cell with the ASEI layer-protected LMA exhibits a capacity retention of about 94.0% coupled with a CE of 99.6% after 1000 cycles at 4 C. We believe that this study of engineering an ASEI brings a new and promising approach to the stabilization of LMAs for high-performance lithium metal batteries.

Small Functional Molecules As Slurry Additives for Si-Alloy Coatings with CMC/SBR Binder

Si-alloy based anodes are attractive for use in Li-ion batteries because of their high volumetric capacity. Polyacrylic acid (PAA) [1] binder is often used in such anodes, which contains carboxyl groups that bind to alloy surfaces, maintaining electrode integrity and forming an artificial SEI layer [2]. Aromatic binders like PI can decompose during lithiation, forming a conductive carbon network [3]. However, these binders have disadvantageous for their practical use, including superhydrophilicity, in the case of PAA; and high irreversible capacity and the cost and use of NMP solvent, in the case of PI. Sodium carboxymethyl cellulose/styrene-butadiene rubber (CMC/SBR) is currently the binder system of choice for Li-ion cell makers. Enabling the use of CMC/SBR binders with alloys could enable wider implementation of alloy electrodes. In this work, several small molecule compounds containing carboxyl groups were evaluated as slurry additives. It was found that some slurry additives could significantly improve alloy cycle life in CMC/SBR coatings. Figure 1 shows the capacity retention versus cycle number for each slurry additive. Tremendous variations in capacity retention are observed for different additives. In particular, the addition of 5% sodium mellitate and sodium citrate resulted in a large increase in cycling performance of the CMC/SBR coating beyond even that of a coating with PAA binder. This work shows that the cycle life of alloy coatings using CMC/SBR binder can be improved by the use of small molecule slurry additives. This could help enable the use of alloy based electrodes in Li-ion batteries using practical binder systems. Reference s : [1] Magasinski, Alexandre, et al. "Toward efficient binders for Li-ion battery Si-based anodes: polyacrylic acid." ACS applied materials & interfaces 2.11 (2010): 3004-3010. [2] Chen, Hao, et al. "Exploring chemical, mechanical, and electrical functionalities of binders for advanced energy-storage devices." Chemical reviews 118.18 (2018): 8936-8982. [3] Wilkes, B. N., et al. "The electrochemical behavior of polyimide binders in Li and Na cells." Journal of The Electrochemical Society 163.3 (2016): A364-A372. Figure 1

High Performance Li‐ion battery Anodes based on Si Nano core in an LATP Matrix with better Electrolyte Compatibility and Temperature Resistance

AbstractNovel core/matrix morphologies of Silicon nanostructures/ LATP ceramics are synthesized through a sol ‐ gel assisted method. The Li1.3 Al0.3 Ti1.7(PO4)3 powders were coated on Si nanoparticles as an artificial SEI layer selectively conducting Li cations, which also prevents the formation of the thick natural SEI layer formation, improving the cyclic stability. The composite anodes exhibited a specific capacity of discharge capacities of 1789 mA h g−1 at 0.1 C in the ionic liquid electrolyte LiTFSI‐Pyr14TFSI. They cycle 500 times with a capacity retention of more than 75%. It is assumed that the promising electrochemical characteristics of the composite anode films are due to the absence of direct contact between the Si nanoparticles and the electrolyte and the presence of LATP providing an efficient and quick pathway for lithium ion transport and acts as a Li ion reservoir. The electrodes also show promising results with suitable ionic liquid based electrolytes at high temperature. Hence the conclusions from the present study projects LATP−Si composite films as a promising anode material for LIBs, with high capacities and long cycling stabilities at room temperature as well as high temperature.

A Lithiophilic Scaffold of Three-Dimensional Free-Standing Silver Nanowire Aerogels for Stable Lithium Metal Batteries: In Operando xrd Investigation

Although lithium metal is the most attractive anode materials in rechargeable batteries because of its high theoretical specific capacity (3,860 mAh g-1) and lowest electrochemical potential (-3.04 V), three problems including inhomogeneous lithium deposition, high chemical reactivity with electrolyte, and infinite relative volume expansion during lithium plating and stripping processes still hinder its practical applications. Several methods have been introduced to solve these problems including the use of artificial SEI layer, solid-state electrolytes, host materials. However, all such approaches mainly focused on the final stage of dendritic lithium with less consideration on the initial stage of lithium nucleation. Herein, we propose a new strategy to encapsulate metallic lithium within a lithiophilic scaffold of three-dimensional free-standing silver nanowire aerogel electrode (AgNWAs) which can control the position and morphology of plated lithium at the initial nucleation stage leading to a good coulombic efficiency of 98% after 100 cycles (400 h) in a corrosive carbonate-based electrolyte without any additives. The phase transformation mechanism of Li-AgNWA alloy half-cell and lithiated-AgNWA//LFP full-cell during lithiation/de-lithiation processes is also fundamentally investigated by in operando XRD measurement. In addition, the lithiophilic properties comparing between the bare AgNWAs, Li-AgNWA alloy, and planar Cu electrode are also confirmed by means of DFT calculation. This proposed strategy demonstrates the possible practical use of high-energy rechargeable lithium-metal battery in the next-generation energy storage technologies.

New Insights in the Prolonged Cycle Life of Si Electrodes Prepared in Aqueous Buffered Media at Low pH

Silicon as an anode material in lithium-ion batteries (LIB) has the 10-fold storage capacity of lithium ions than graphite and is thus an interesting candidate for next generation LIB.[1] However, due to the sever volume expansion during the alloying reaction of Si with Li, the physical inter-particle connections mediated by the electrode binder are broken. As a result the electrode disintegrates and its capacity fades rapidly. The mechanical and interfacial properties can be enhanced when the Si electrodes are prepared in an aqueous solution of a citric acid buffer at pH=3, instead of neutral pH, such as water.[2] This behavior was previously ascribed to the acid-catalyzed formation of a silyl ester between binder and the native silicon oxide surface.[3] However, many questions still remain unanswered, e.g. what is the impact of the pH or how does the type of acid affect the surface functionalization? Additionally, recent results suggest that citric acid itself interacts strongly with the Si surface, thus forming an artificial SEI layer.[3] In our study we are providing a deeper insight in the role of the carboxylic acids by examining a series of different carboxylic acids, namely glycolic acid (GlyAc), malic acid (MalAc) and citric acid (CitAc) (Figure 1). The carboxylic acids carry a different number of functional groups, which helps to interpret the rather complex FTIR spectra (Fig. 1a) of these silicon:acid:binder composites. The impact of the carboxylic acid on other cell components (e.g. electrolyte salt or current collectors) was investigated by on-line mass spectroscopy, electron microscopy and electrochemical techniques (e.g. Fig. 1b). Our aim is to evaluate how the capacity retention of acid-treated Si electrodes could be further improved by rational choice of the buffer chemistry and to identify the key control parameters in the functionalization process and during slurry preparation (e.g. pH and acid strength) in order to advance the slurry fabrication process and the performance of Si-containing electrodes.

Tuning Interfacial Processes in Mn-Based Li-Ion Systems Though Vapor Phase Modification

Among the different rechargeable battery technologies available, Co/Ni/Mn-based Li-ion systems appear to be a leading contender for automotive applications as a result of their high specific energy. However, the high operating potential of this system is outside the thermodynamic stability window of standard organic carbonate-based electrolytes. This results in electrolyte oxidation with transition metal dissolution and gas formation at the electrode/electrolyte interface during cycling, which leads to severe loss of electrochemical performance. To address these challenges, many strategies are currently being investigated, ranging from the development of new electrodes and electrolytes to the improvement of commercial Li-ion systems by surface engineering of the interfaces.In this work, we mitigate parasitic interfacial processes in start/stop batteries by atomic layer deposition (ALD). We develop an Al2O3 or LiPON conformal artificial SEI layer on LMO and LTO electrodes and study its effect on the Li-ion batteries failure modes with differential electrochemical mass spectroscopy (DEMS), X-ray Photoelectron Spectroscopy (XPS) and ICP measurements. The beneficial impact of the protection layer on the kinetics of the gassing, metal dissolution and associated chemical cross-talk was clearly identified. The presence of a protection layer at the LMO surface, in particular of a 10 nm LiPON conformal layer, mitigate the electrolyte oxidation at high voltage at 60°C with a significant reduction of the amount of H2 produced. The formation of metal complexes and subsequent poisoning of the SEI is also attenuated. Interestingly, counter intuitively, the ratio of the inorganic to organic components of the SEI is lowered by the presence of an inorganic protection layer. The correlation between the nature of the electrode protection layer, the electrode’s surface activity, and associated organic electrolyte oxidation pathways will be presented and discussed. Acknowledgement This work was supported by SAFT and as part of the Nanostructures for Electrical Energy Storage (NEES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science.

An artificial TiO2/lithium n-butoxide hybrid SEI layer with facilitated lithium-ion transportation ability for stable lithium anodes.

Fabricating an artificial solid electrolyte interphase (SEI) layer on a lithium metal surface has become an available strategy to prevent highly active lithium directly contacting the organic electrolyte, which could avoid the spontaneous formation of an inhomogeneous and unstable SEI film on the lithium surface. However, the poor Li-ion transport capability of the traditional SEI films greatly limited the application of the artificial SEI for lithium metal anodes. In this work, we proposed an artificial TiO2/lithium n-butoxide hybrid SEI layer with facilitated Li-ion transport ability to enhance the cycling stability of lithium metal anodes. The artificial SEI film is mainly composed of amorphous titanium dioxide and lithium n-butoxide (ROLi, R = C4H9) which were in situ formed on the lithium metal surface via the hydrolytic process of tetrabutyl titanate. The obtained SEI exhibited not only efficient mechanical strength but also facilitated Li-ion transport ability, ensuring the long cycling stability of the lithium metal anode. As a consequence, the symmetrical battery with a TiO2/ROLi-Li electrode showed outstanding electrochemical performance in terms of a low potential hysteresis of 50 mV and long cycling stability over 600 hours with a flat voltage plateau. Li-LiFePO4 full cells also show greatly improved electrochemical performance with a high capacity retention of ∼100% for 200 cycles and a high capacity of 140 mA h g-1 at 0.5C.

Engineering Artificial SEI for Improving Performance of Anode Free Batteries

Practical implementation of a lithium battery or an anode-free battery with promising high capacity is hampered by dendrite formation and low coulombic efficiency [1,2]. Most notably, these challenges stem from non-uniform lithium platting and unstable SEI layer formation. Here, we revealed a homogeneous lithium deposition and effective dendrite suppression with engineering artificial SEI layer. Surface coating reinforces a thin and robust artificial SEI layer film formation via hosting lithium and regulating the inevitable reaction of lithium with electrolyte. The cell with engineered SEI layer showed stable cycling of lithium with an average coulombic efficiency of ~100% over 200 cycles and low voltage hysteresis (~30 mV) at current density of 0.5 mA cm-2. Moreover, we have proved the anode-free battery experimentally by integrating it with various cathodes into a full cell configuration. The new cell demonstrated stable cycling with excellent average coulombic efficiency. These impressive enhanced cycle life and capacity retention results from the synergy of electrode modification, high electrode-electrolyte interface compatibility, and stable artificial SEI formation. Our result opens up a new route to realize the anode-free batteries by engineering artificial SEI layer to achieve safe interfacial chemistry and controlled dendrite formation. Reference s : [1] A.M. Tripathi, W.N. Su and B.J. Hwang, Chem. Soc. Rev., 47, 736–851 (2018). [2] J.H. Cheng, A.A. Assegie, C.J. Huang, M.H. Lin, A.M. Tripathi, C.C. Wang, M.T. Tang, Y.F. Song, W.N. Su, and B.J. Hwang, J. Phys. Chem. C, 121, 7761–7766 (2017).

A step towards understanding the beneficial influence of a LIPON-based artificial SEI on silicon thin film anodes in lithium-ion batteries.

In this work, we present a comprehensive study on the influence of lithium phosphorus oxynitride (LIPON) as a possible "artificial SEI layer" on the electrochemical performance of pure silicon (Si) thin film electrodes for a possible application in microbatteries or on-chip batteries. Si thin film anodes (140 nm) with and without an additional amorphous LIPON surface layer of different thicknesses (100-300 nm) were prepared by magnetron sputter deposition. The LIPON surface coating was characterized thoroughly by means of electrochemical impedance spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy. In situ electrochemical dilatometry and ex situ cross-section analysis of the electrodes after cycling could prove that the LIPON coating greatly diminishes the volume expansion of the Si electrode and, therefore, significantly improves the cycling stability and capacity retention. Furthermore, the LIPON coating remarkably reduces parasitic electrolyte decomposition reactions that originate from the Si volume expansion and contribute to the overall electrode volume expansion, as observed by the enhanced Coulombic efficiency over ongoing charge/discharge cycling. Overall, this article focuses on the preparation of optimized Si-based thin film electrodes in combination with LIPON solid electrolyte coatings for use in high-energy lithium ion batteries.