SEI Film Research Articles

New perspectives on spatial dynamics of lithiation and lithium plating in graphite/silicon composite anodes

Huge volume expansion, unstable SEI-film evolution and uncontrollable Li plating remain challenging issues for achieving high energy-density and fast charging graphite/silicon anodes. Unfortunately, less reports on Li plating in graphite/silicon anodes have been found up to now. Herein, for the first time, we report that the interfacial polarization of silicon dominates the co-lithiation process with graphite, thus determining the preferential Li-plating sites and SEI film evolution. Interestingly, the disturbance of local electrochemical potential due to consecutive volume variation of silicon upon cycling, indeed keep Li plating sites changing and deteriorate the battery performances. In a typical case of silicon, global electrochemical potential-equilibrium of electrons in silicon can be achieved by regulating Li-ion diffusion kinetic in silicon, thus delaying Li-plating on graphite. Comparing to commercial silicon, P-type photovoltaic silicon exhibits weaker disturbance of local electrochemical potential upon volume variation, resulting in smaller change in Li-plating sites and smaller re-growth SEI film. Therefore, our findings propose a new perspective on the competitive lithiation mechanism and Li plating for graphite/silicon anodes which is highly desirable for designing high-capacity and fast-charging graphite/silicon.

Pentafluoropyridine additive induced SEI film regulation and remarkable performance improvement of the lithium primary batteries

Lithium primary batteries with lithium metal anode are extensively applied in the portable appliances and electronic fields for the high specific energy and power, low self-discharge and wide operating temperature. However, the application of lithium metal anode causes the safety and stability issues. Herein, the pentafluoropyridine (C5F5N) was applied as an electrolyte additive in lithium primary battery, to construct a suitable surface layer on lithium anode to increase the stabilization and electrochemical performance. With C5F5N additive, the discharge capacity of the Li primary battery increases to 422.1 mAh/g at 0.01 C, compared to 62.2 mAh/g of the pristine battery. Meanwhile, the storage performance of the batteries was also greatly enhanced with the C5F5N additive. After stored for 60 days at room temperature, the Li primary battery with additive displays a specific discharge capacity of 180.7 mAh/g, much higher than the pristine battery without additive (43.6 mAh/g). The significant improvements in capacitive and storage performances are attributed to the additive induced inhibition of decomposition of solvents and lithium salts and tuning of SEI composition on lithium anode surface. The C5F5N is a promising electrolyte additive for the further development and application of high-performance Li primary batteries.

Enhanced cycle stability of aprotic Li-O2 batteries based on a self-defensed redox mediator

LiBr as a promising redox mediator (RM) has been applied in Li-O2 batteries to improve oxygen evolution reaction kinetics and reduce overpotentials. However, the redox shuttle of Br3− can induce the unexpected reactions and thus cause the degradation of LiBr and the corrosion of Li anode, resulting in the poor cyclability and the low round-trip efficiency. Herein, MgBr2 is firstly employed with dual functions for Li-O2 batteries, which can serve as a RM and a SEI film-forming agent. The Br– is beneficial to facilitating the decomposition of Li2O2 and thus decreasing the overpotential. Additionally, a uniform SEI film containing Mg and MgO generates on Li anode surface by the in-situ spontaneous reactions of Mg2+ and Li anode in an O2 environment, which can suppress the redox shuttle of Br3− and improve the interface stability of Li anode and electrolyte. Benefiting from these advantages, the cycle life of Li-O2 battery with MgBr2 electrolyte is significantly extended.

2D sp2-carbon-linked covalent organic frameworks as artificial SEI film for dendrite-free lithium metal batteries

2D sp2-carbon-linked covalent organic frameworks as artificial SEI film for dendrite-free lithium metal batteries

The effect of AlF3 as an electrolyte additive on Li anode in Li-O2 batteries

Li metal is considered as an ideal anode for Li-O2 batteries because of its unbeatably theoretical specific capacity and low electrode potential. Unfortunately, the growth of Li dendritic and the sensitivity to electrolyte and O2 hinder the practical applications of Li anode. Herein, AlF3 as an electrolyte additive is firstly employed in a Li-O2 battery, which can boost the formation of LiF@Al-Li@Al2O3-rich SEI film via in-situ spontaneous reactions of AlF3 with Li anode in O2 atmosphere. The generated SEI film contributes to inducing the homogeneous nucleation of Li and reducing the disgusting side reactions, which can suppress the growth of Li dendrite and improve the cyclability of Li anode. Benefiting from the rational design, both the Li-O2 and the Li|Li symmetric batteries with AlF3 electrolyte exhibit low overpotential and good cycling stability. We hope this work could provide a facile way to in-situ construct a stable SEI film to alleviate the uneven Li nucleation for Li-O2 batteries.

In Situ Construction of Zn2Mo3O8/ZnO Hierarchical Nanosheets on Graphene as Advanced Anode Materials for Lithium-Ion Batteries

Transition-metal oxides as anodes for lithium-ion batteries (LIBs) have attracted enormous interest because of their high theoretical capacity, low cost, and high reserve abundance. Unfortunately, they commonly suffer from poor electronic and ionic conductivity and relatively large volume expansion during discharge/charge processes, thereby triggering inferior cyclic performance and rate capability. Herein, a molybdenum-zinc bimetal oxide-based composite structure (Zn2Mo3O8/ZnO/rGO) with rectangular Zn2Mo3O8/ZnO nanosheets uniformly dispersed on reduced graphene oxide (rGO) has been prepared by using a simple and controllable cyanometallic framework template method. The Zn2Mo3O8/ZnO rectangular nanosheets with desirable porous features are composed of nanocrystalline subunits, facilitating the exposure of abundant active sites and providing sufficient contact with the electrolyte. Benefiting from the composition and structural merits as well as the induced synergistic effects, the Zn2Mo3O8/ZnO/rGO composite as LIB anodes delivers superior electrochemical properties, including high reversible capacity (960 mA h g-1 after 100 cycles at 200 mA g-1), outstanding rate performance (417 mA h g-1 at 10,000 mA g-1), and admirable long-term cyclic stability (862 mA h g-1 after 400 cycles at 1000 mA g-1). The mechanism of lithium storage and the formation of SEI film are systematically elucidated. This work provides an effective strategy for synthesizing promising Mo-cluster compound-based anodes for high-performance LIBs.

LiF-Rich Interfaces and HF Elimination Achieved by a Multifunctional Additive Enable High-Performance Li/LiNi0.8Co0.1Mn0.1O2 Batteries.

Li-metal batteries (LMBs), especially in combination with high-energy-density Ni-rich materials, exhibit great potential for next-generation rechargeable Li batteries. Nevertheless, poor cathode-/anode-electrolyte interfaces (CEI/SEI) and hydrofluoric acid (HF) attack pose a threat to the electrochemical and safety performances of LMBs due to aggressive chemical and electrochemical reactivities of high-Ni materials, metallic Li, and carbonate-based electrolytes with the LiPF6 salt. Herein, the carbonate electrolyte based on LiPF6 is formulated by a multifunctional electrolyte additive pentafluorophenyl trifluoroacetate (PFTF) to adapt the Li/LiNi0.8Co0.1Mn0.1O2 (NCM811) battery. It is theoretically illustrated and experimentally revealed that HF elimination and the LiF-rich CEI/SEI films are successfully achieved via the chemical and electrochemical reactions of the PFTF additive. Significantly, the LiF-rich SEI film with high electrochemical kinetics facilitates Li homogeneous deposition and prevents dendritic Li from forming and growing. Benefiting from the collaborative protection of PFTF on the interfacial modification and HF capture, the capacity ratio of the Li/NCM811 battery is boosted by 22.4%, and the cycling stability of the symmetrical Li cell is expanded over 500 h. This provided strategy is conducive to the achievement of high-performance LMBs with Ni-rich materials by optimizing the electrolyte formula.

Boosting the Low-Temperature Performance for Li-Ion Batteries in LiPF6-Based Local High-Concentration Electrolyte

LiPF6-based commercial electrolytes are widely used in lithium-ion batteries (LIBs). However, due to the low ion conductivity that originated from the high freezing point of EC, sluggish desolvation process, and large interface resistance, LIBs with the currently commercial electrolyte based on LiPF6 demonstrate unsatisfactory performance in low-temperature operation. Herein, a LiPF6-based local high-concentration electrolyte with lithium difluorobis(oxalato)phosphate (LiDFBOP) additive is designed to enhance the performance of LIBs at low temperature. Higher-concentration LiPF6 in EC-free solvent improve the overall ionic conductivity of electrolyte. The Li+–solvent–PF6– structure can be obtained to reduce the desolvation energy; meanwhile, LiDFBOP is introduced to construct an effective SEI film with high ionic conductivity and cycle stability. The graphite/Li cells demonstrate good rate performance and low-temperature performance (ca. 240 mAh g–1 at −20 °C (0.1 C)). This work provides a feasible strategy for developing a commercial LiPF6-based electrolyte to improve the operation of LIBs at low temperature.

Ultrathin CuF2‐Rich Solid‐Electrolyte Interphase Induced by Cation‐Tailored Double Electrical Layer toward Durable Sodium Storage

AbstractSolid‐electrolyte interphase (SEI) seriously affects battery's cycling life, especially for high‐capacity anode due to excessive electrolyte decomposition from particle fracture. Herein, we report an ultrathin SEI (3–4 nm) induced by Cu+‐tailored double electrical layer (EDL) to suppress electrolyte consumption and enhance cycling stability of CuS anode in sodium‐ion batteries. Unique EDL with SO3CF3‐Cu complex absorbing on CuS in NaSO3CF3/diglyme electrolyte is demonstrated by in situ surface‐enhanced Raman, Cyro‐TEM and theoretical calculation, in which SO3CF3‐Cu could be reduced to CuF2‐rich SEI. Dispersed CuF2 and F‐containing compound can provide good interfacial contact for formation of ultrathin and stable SEI film to minimize electrolyte consumption and reduce activation energy of Na+ transport. As a result, the modified CuS delivers high capacity of 402.8 mAh g−1 after 7000 cycles without capacity decay. The insights of SEI construction pave a way for high‐stability electrode.

Gradient design for constructing artificial SEI layer towards high-performace Lithium metal batteries

The construction of artificial interfacial layer on Li anode is one of the most effective methods to block Li dendrite growth and volume expansion. The charge transport and ion diffusion behavior can be regulated due to the variation of component gradients and diffusion kinetics at different depths. However, there are few researches on the regulation of components’ distribution in artificial interfacial layer (SEI layer), which is of great significance for enhancing the electrochemical performance of Li anode. Herein, a gradient-design SEI layer is constructed on the Li anode to regulate charge transport and Li ion diffusion behavior in the interface, which could optimize the lithium deposition process. Based on this gradient structure, the gradient distribution of inorganic and organic components in the as-constructed SEI can effectively regulate the Li+ configuration and hinder the volume change during Li plating/stripping progress. With this hybrid interfacial layer, an improved cycling performance of Li-Li symmetric cell is achieved over 1750 h with a low overpotential under an ultrahigh current density of 10 mA cm−2, and ultrahigh capacity of 10 mAh cm−2. Based on the gradient-design artificial SEI film, the pouch cells matched with high-loading LiFePO4 cathode (21 mg cm−2) demonstrates extremely long cycling life with almost no capacity fade, which is superior compared with previous reports.

Aging diagnosis-oriented three-scale impedance model of lithium-ion battery inspired by and reflecting morphological evolution

Numerous mutually coupled factors contribute to the aging of lithium-ion battery (LIB). Inspired by the observation of microscopic morphological changes and their mechanistic analysis, this paper considers the evolving agglomerate fracture and growing SEI film as the main driving forces, and the aging of LIB and consequential impedance changes are represented with the fracture expansion of secondary particle and thickness growth of SEI layer, leading to a full-cell impedance model suitable for describing aging behavior of LIB, which is capable of effectively approximating the electrochemical impedance spectrum (EIS) throughout the usable life. By analyzing the identified parameters with regard to the state of health (SOH), the fracture depth of cathode agglomerate and the thickness of anode SEI film exhibit trends consistent with the morphological development on electrode materials and the deduction of multi-physical mechanisms, and such strong correlation is conveniently used to estimate the SOH of LIB. A large number of qualitative studies are emerging regarding the aging of LIB, and this paper aims to supplement research on the aging modeling and diagnosis of SOH in the frequency-domain by unifying the cause and effect from a quantitative perspective.

Uracil-based additives for enabling robust interphases of high-voltage Li-ion batteries at elevated temperature by substituent effects

SEI films were formed on both electrodes of the NCM523‖graphite pouch cell by employing UC and TUC as bifunctional electrolyte additives, and further optimization of the substituent effects improving the high-voltage performances at 45 °C.

An ethyl bromofluoroacetate redox mediator enables a robust LiF-rich solid electrolyte interphase for advanced lithium–oxygen batteries

An ethyl bromofluoroacetate redox mediator has been introduced into lithium–oxygen batteries to achieve high performance in long-term cycling by reducing the charging overpotential and simultaneously forming a LiF-rich SEI film.

A CF4 plasma functionalized polypropylene separator for dendrite-free lithium metal anodes

A simple and effective plasma functionalization technique for grafting fluorine-containing functional groups on commercial PP separators to induce the formation of LiF-rich SEI films has been proposed.

Room temperature solid-state deformation induced high-density lithium grain boundaries to enhance the cycling stability of lithium metal batteries.

Due to its high theoretical capacity and low anode potential advantages, lithium is becoming the ideal high-capacity anode of next generation batteries. Nevertheless, the satisfactory long-term cyclability of lithium metal batteries is still not achieved. Inspired by the intrinsic soft nature of the lithium metal, we have developed a simple room temperature solid-state deformation route to overcome the lithium dendrite issue, and the cycle life of the deformation treated lithium anode is 5 times that of the untreated lithium anode. It is demonstrated that microscale lithium grains are divided into nanoscale lithium grains by directional friction forces of solid-state deformation. The lithium grain boundaries are lithiophilic active sites towards Li ions, which regulate homogeneous deposition of Li ions to form a thin and stable SEI film, eventually overcoming the lithium dendrite issue and enhancing the cyclability of lithium batteries. Overcoming the challenges in conventional tedious chemical routes to grow high-density grain boundary active sites for catalysis, the room temperature solid-state deformation route will pave a new road to grow high-density grain boundaries for fuel cells and metal-based batteries.

Recovery and regeneration of anode graphite from spent lithium-ion batteries through deep eutectic solvent treatment: Structural characteristics, electrochemical performance and regeneration mechanism

Recovery of graphite from spent lithium-ion batteries (LIBs) as new anode materials in the LIBs after regeneration can not only promote the recycling of spent LIBs, but also help to alleviate its environmental risks. However, the removal of the impurities in spent graphite is unsatisfying and its electrochemical performance need to be further improved when using conventional regeneration methods (such as acid treatment). Herein, we proposed a novel deep eutectic solvent (DES) leaching method to recover and regenerate waste graphite from spent LIBs under mild condition. The result showed that DES leaching could not only effectively remove the impurities in spent graphite, but also restore its crystal structure and morphology. The regenerated graphite obtained by DES treatment (DRG) exhibited a high specific capacity of 449.4 mAh/g for the first cycle at 0.1C and 285.4 mA h/g even after 500 cycles at 1C. In addition, the retention rate and coulombic efficiency of DRG were as high as 96.0 % and 100 %, respectively. These results demonstrated the excellent electrochemical performance of DRG, which was even comparable to that of commercial graphite. The regeneration mechanism of the proposed method was also elucidated. The organic binder was dissolved in DES by forming hydrogen bonds (OH…F and CH…Cl−). The Li coordination complex formed between SEI film and DES contributed to the dissolution of SEI film, and the residual electrolytes were removed based on the similarity-intermiscibility theory. This study provides a facile and green method to accomplish the closed-loop utilization of spent graphite in spent LIBs.

Criticality of solid electrolyte interphase in achieving high performance of sodium-ion batteries

Sodium-ion batteries (SIBs) have shown tremendous application prospects for large-scale energy storage system in recent years due to the abundant natural sodium resources. Notably, the ideal SEI film on the anode of SIBs plays an indispensable role in realizing excellent electrochemical performance. In this work, we report the CoSe2/Fe3C composite derived from Prussian blue analogue as an anode of SIBs, which forms a favorable SEI film within ether-based electrolytes and exhibits excellent electrochemical performance of ultrahigh initial Coulombic efficiency (96.4 % at 2 A/g) as well as long-term cycling life (412.4 mAh/g at 10 A/g over 2000 cycles). We unveil that the favorable SEI layer formed within ether-based electrolytes is rich in inorganics, and thin and dense in microstructure, all of which promote Na+ transport. The formed SEI also has a high Young’s modulus to resist the volume variation of active materials during cycling. Moreover, the theoretical molecular orbital analysis suggests that the SEI formation process with ether-based electrolytes is driven by the preferential decomposition of sodium salt prior to the solvent decomposition. Overall, this work underscores the significance and origin of forming a friendly SEI layer to achieve rapid and stable sodium storage.

Effect of Ce incorporation into carbon layer on the performance of silicon-carbon composite as anode for LIBs

Volume expansion of silicon during lithiation limits its use as a commercial anode material. Carbon coating on silicon surfaces can buffer the phase change stress of silicon and enhance conductivity. In this work, the effect of the incorporation of rare earth element Ce in the carbon layer on the electrochemical properties of silicon-carbon composites was investigated. After mixing according to a particular procedure, cerium nitrate, micron silicon, and sodium alginate (SA) were calcined to obtain the silicon-carbon composite coated carbon layer incorporation Ce. The tests found that the incorporation of Ce into the carbon layer had the following effects on the performance of LIBs anode: (1) enhanced the toughness of the carbon layer and improved the cycle performance, (2) reduced the formation of SEI film and increased the first Coulombe efficiency (ICE), (3) boosted the lithium-ion conductivity of silicon-carbon composite and improved the rate capability. As a result, the electrochemical properties of Ce incorporated silicon-carbon composites (Si@C/CeO2) are significantly improved. The initial specific capacity of Si@C/CeO2 was 1848.6 mAh g-1, even micro silicon engendered strong phase change stress, still maintained 502.2 mAh g-1 after 180 cycles, and the ICE was higher than most of the silicon-carbon composites reported.

Drastically enhancing the cycle stability of copper-dicarboxylate as an anode material for lithium-ion batteries by rational fluorination

Metal-organic frameworks (MOFs) are extensively investigated in lithium-ion batteries because of their large specific surface area, adjustable chemical properties, porous structure, and rich reaction sites. However, the severe capacity attenuation of MOF electrodes has been one of the hardest obstacles hindering the further application of MOFs, due to the embedding and de-embedding of lithium ions during the cycles leading to the structural disintegration and volume fluctuation. Inspired by the wide application of fluorinated additives in commercial electrolytes, a typical carboxylate MOF, copper 1,4-benzenedicarboxylate is fluorinated molecularly to improve its cycle stability. Without enough fluorine source for a robust SEI film, the performance of fluorine-free copper 1,4-benzenedicarboxylate degrades rapidly to 99.5 mAh/g in the initial 21 cycles at a current density of 100 mA g−1, while its fluorinated counterpart, copper tetrafluoroterephthalate, delivers drastically enhanced cycle stability and maintains a reversible specific capacity of 575.5 mAh/g after 500 cycles, due to the SEI-promoting effect of fluorine in the framework. The present fluorination strategy is proved effective and can be extended in much wider applications of MOF materials.

A yolk-shell eGaSn@Void@SiO2 nanodroplet design for high-performance cathodes in room temperature liquid metal batteries

Gallium-based liquid alloys that exhibit high capacity and self-healing properties have been demonstrated to be promising cathodes for room temperature liquid metal batteries (RTLMBs). However, the electrochemical performances of these alloys are poor due to severe volume expansion and an unstable solid electrolyte interface layer during the lithiation process. Here, a sol-gel strategy was performed to construct yolk-shell structure nanodroplets (eGaSn@Void@SiO2) that contain sufficient void space by amorphous silicon oxide, which generated a liquid metal electrode with a high performance. The amorphous SiO2 shells not only play an important role in building stable SEI films, providing efficient electron/ion conduction channels and preventing agglomeration of active substances, but exhibit good elastic behavior during charging/discharging. Due to the appropriate voids in the yolk-shell structure, the eGaSn nanodroplets can expand freely without breaking or disrupting the electrode structure; thus, the resulting eGaSn@Void@SiO2 NDs exhibited high capacities of 538, 454, and 338 mA h g−1 at current rates of 0.2, 1 and 5 C, respectively. No obvious decay was observed with more than 500 cycles and a capacity of 377 mA h g−1 at 2 C. Interestingly, the density functional theory (DFT) calculations revealed that the effective chemisorption between the discharge products and SiO2 provides sufficient electrical contact sites with a significant drop in electrochemical impedance during cycling. The causes of the superior electrodes performance were investigated in depth using in situ X-ray diffraction and theoretical calculations. Our rational design may shed unprecedented light on the development of liquid alloy-based cathodes for high-performance RTLMBs.