SEI Formation Research Articles

Dual-Salt Localized High-Concentration Electrolyte for Long Cycle Life Silicon-Based Lithium-Ion Batteries.

Silicon-based materials are considered the most promising anodes for next-generation lithium-ion batteries (LIBs) owing to their high specific capacity. However, poor interfacial stability due to enormous volume changes severely restricts their mass application in LIBs. Here, we design a fluoroethylene carbonate (FEC)-containing dual-salt (LiFSI-LiPF6) ether-based localized high-concentration electrolyte (D-LHCE-F) for enhancing the interfacial stability of silicon-based electrodes. It is revealed that the dominating LiFSI salt of superior chemical and thermal stability prevents the formation of corrosive HF, while the addition of FEC improves the interface stability by promoting the formation of protective LiF-rich SEI and increasing the flexibility of the interface. This robust and flexible SEI layer can adapt to substantial variations in the volume of silicon electrodes while preserving the integrity of the interface. The SiOx/C electrode using the unique D-LHCE-F retains up to 78.5% of its initial capacity after 500 cycles at 0.5C, well surpassing that of the control electrolyte (3.4% capacity retention). More notably, the cycle life of the SiOx/C||NCM90 (LiNi0.9Co0.05Mn0.05O2) full batteries is effectively enhanced thanks to the stabilized electrode/electrolyte interfaces. The key findings of this work offer crucial knowledge for rationally designing electrolyte chemistry to enable the practical application of high-energy-density LIBs adopting silicon-based anodes.

Combined, time-resolved, in situ neutron reflectometry and X-ray diffraction analysis of dynamic SEI formation during electrochemical N2 reduction

In situ neutron reflectometry and GI-XRD reveal the dynamics of SEI formation and layer composition during Li-NRR with current cycling.

A dual protection strategy for stable lithium metal anodes using Ag nanoseed decorated F-doped porous graphene current collectors

A dual protection strategy is proposed by fabricating a Ag decorated F-doped graphene (Ag@FG) current collector. The decorated Ag induces the uniform deposition of Li and F doping facilitates the formation of a stable LiF-enriched SEI.

Vinylene carbonate reactivity at lithium metal surface: first-principles insights into the early steps of SEI formation

Density Functional Embedding Theory (DFET) unveils the mechanism of Vinylene Carbonate (VC) degradation at the Li metal surface.

A transient component of the solid electrolyte interphase in the Li-ion battery

Schematic graphical representation of the SEI formation process accompanied by cointercalation of electrolyte components into graphite.

Co-substitution Strategy for Boosting Rate-Capability of Lithium-Superionic-Conductor (LISICON)-Type Anode Materials in γ-Li3VO4–Li4GeO4–Li3PO4 Quasi-Ternary-System

Using simple solid-state calcination, γ-Li3+x V1–x–y Ge x P y O4 (LVGePO) anode materials with lithium superionic conductor (LISICON)-related crystal structures have been successfully synthesized for next-generation energy storage applications with high-energy and high-power densities. The correlation among their chemical compositions, crystal-phase formations, and rate performances has been elucidated and mapped in the quasi-ternary phase diagram of the Li3VO4–Li4GeO4–Li3PO4 system. The crystal phase formation and surface stability can be controlled by the Ge4+- and/or P5+- substitution ratio; 5 at% or more Ge4+-substitution resulted in a pure γ-phase structure with high Li+ conductivity, while the presence of P5+ suppressed the SEI formation. Fine-tuning of the chemical composition brings about the highest charge (delithiation) capacity retention of ca. 62% of the theoretical capacity at 10 A g–1 (ca. 40C-rate) obtained in the typical chemical composition range of Li3.05–3.1V0.7–0.8Ge0.05–0.1P0.1–0.25O4 with the γ-phase crystal structure. Such co-substituted LVGePO anodes exhibited superior rate performances compared to any binary solid solutions of Li3+x V1–x Ge x O4 and Li3V1–y P y O4. The improvement in the electrochemical performances are induced by the distinct roles of co-substituted cations, viz., P5+ suppresses the reductive decomposition of electrolytes on the LVGePO crystal surfaces, while Ge4+ stabilizes the high Li+ conductive γ-phase structure.

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.

Preparation and lithium storage of anthracite-based graphite anode materials

Several graphite samples with different microstructures were prepared from anthracite using an industrial silicon powder as a catalyst. The mechanism of the catalytic reaction and the electrochemical properties of the prepared coal-based graphite in lithium anodes were investigated. The correlation between the microstructure and the properties of the graphite was also discussed. Results show that the sample with 5% silicon (G-2800-5%) has the best lithium storage. It has the most graphitic structure with a degree of graphitization of 91.5% as determined from the interlayer spacing. When used as an anode material, a high reversible capacity of 369.0 mAh g−1 was achieved at 0.1 A g−1 and its reversible capacity was 209.0 mAh g−1 at a current density of 1 A g−1. It also had good cycling stability with a capacity retention of 92.2% after 200 cycles at 0.2 A g−1. The highly developed graphite structure, which is favorable for the formation of a stable SEI and therefore reduces lithium ion loss, is responsible for the superior electrochemical performance.

Electrode/Electrolyte Interphases of Sodium-Ion Batteries

The performance of sodium-ion batteries largely depends on the presence and properties of passive films formed on the electrode/electrolyte interfaces. Passive films on negative electrodes inevitably result from the reduction in electrolyte components (solvent and salt anion). They have the properties of a solid electrolyte with sodium ion conductivity and are insulators in terms of electronic conductivity. Usually, they are called SEI—solid electrolyte interphase. The formation of SEI is associated with the consumption of a certain charge, which is an irreversible capacity. Passive films on the surface of positive electrodes (CEI—cathode electrolyte interphase) arise as a result of electrolyte oxidation. The present review summarizes the literature of the recent 15 years concerning the effects of electrode nature (hard carbon, other carbon materials, various metals, oxides, chalcogenides, etc.), electrolyte composition, and other factors on composition and properties of SEIs in sodium-ion batteries. Literary data on CEIs are reviewed as well, although their volume is inferior to that of data on SEIs.

Benchmarking the Degradation Behavior of Aluminum Foil Anodes for Lithium‐Ion Batteries

AbstractAluminum is an attractive candidate for replacing graphite anodes in lithium‐ion batteries because of its high specific capacity and the potential for direct use as foil. However, achieving reversible reaction of aluminum is challenging due to volume changes, SEI formation, and sluggish ion transport. Although prior work has investigated electrochemical transformation behavior of aluminum, the effects of key variables, including areal capacity per cycle and alloy composition, are not well understood. Here, we carry out comprehensive electrochemical testing to benchmark the performance of two different aluminum foils (99.999 % Al and Al 8111). We find that for constant thickness, both foil compositions exhibit a power‐law dependence of cycle life on the lithiated areal capacity per cycle, revealing that degradation is significantly more rapid at higher areal capacities. This behavior is interpreted as an “electrochemical fatigue” mechanism, in analogy to mechanical fatigue. Additionally, the alloy composition was found to strongly affect the Coulombic efficiency (CE), with high‐purity foils exhibiting higher initial CE but reduced long‐term stability. Finally, operando optical microscopy revealed different spatiotemporal reaction mechanisms amongst the different materials. This improved understanding of aluminum foil anodes paves the way for efforts to engineer aluminum‐based foils with enhanced stability.

High-safety, wide-temperature-range, low-external-pressure and dendrite-free lithium battery with sulfide solid electrolyte

Li metal is considered to be the most ideal anode due to its highest energy density, but traditional lithium-metal liquid-electrolyte battery system suffers from low Coulombic efficiency, repetitive SEI formation, Li dendrite growth, etc. Herein, a new battery configuration is proposed to exploit room-temperature liquid lithium solutions (Li-BP-Ether) as anodes and argyrodite sulfide as solid electrolyte. Such liquid lithium solutions can deliver high safety performance, excellent dendrite suppression capability, low redox potentials, and high conductivity of 12 mS cm−1 at room temperature. Moreover, sulfide solid electrolyte has the highest room-temperature ionic conductivity among all solid electrolytes and ideal mechanical ductility for fully compact layer simply by cold pressing. This battery configuration combines the advantages of these materials and can operate at neglectable external pressure (3 kPa) in a wide temperature range (−20∼50 °C). As a result, a high reversible discharge capacity (140.4 mAh g−1) and high efficiencies (99.7% Coulombic efficiency and >96% energy efficiency after ∼100 cycles) are achieved. Furthermore, this battery demonstrates the best cycle stability and the highest efficiency among all the liquid lithium solution battery systems using solid cathodes reported so far. Overall, this class of battery configuration may open up a promising route for high-energy-density, cost-effective and safe rechargeable lithium batteries.

Nonflammable Localized High-Concentration Electrolytes with Long-Term Cycling Stability for High-Performance Li Metal Batteries.

High-concentration electrolytes (HCEs) can effectively enhance interface stability and cycle performance of Li metal batteries (LMBs). However, HCEs suffer from low ionic conductivity, high viscosity, high cost, and high density. Herein, fluorobenzene (FB) diluted localized high-concentration electrolytes (LHCEs) consisting of lithium bis(fluorosulfonyl)imide (LiFSI)/triethyl phosphate (TEP)/FB are developed. 2.3 M LHCE can reserve concentrated Li+-FSI--TEP solvation structures. Diluent FB possesses low density, low viscosity, low cost, low dielectric constant, low LUMO, and a good fluorine-donating property, which can significantly reduce viscosity, improve ionic conductivity, promote the formation of LiF-rich SEI, and enhance interaction of Li+-TEP and Li+-FSI- ion-pairs of the electrolytes. 2.3 M LHCE is a highly safe nonflammable electrolyte. 2.3 M LHCE can effectively inhibit dendrite growth on Li metal anode. 2.3 M LHCE endows LiFePO4 cells with good rate capability (discharge capacity of 112.7 mAh g-1 at 5 C rate) and excellent cycling performance (capacity retention of 95.4% after 1000 cycles). 2.3 M LHCE also shows good compatibility with LiNi0.8Co0.1Mn0.1O2 and exhibits outstanding cycle stability (capacity retention of 86.4% after 500 cycles). Therefore, 2.3 M LHCE is a promising electrolyte for practical applications in LMBs.

Mechanical stress and morphology evolution in RuO2 thin film electrodes during lithiation and delithiation

RuO2 is a promising candidate for high-performance electrodes in thin film lithium-ion batteries, due to its large volumetric charge capacity, high rate capability, excellent cyclability and compatibility with silicon integrated circuit fabrication techniques. The evolution of mechanical stress associated with the lithiation and delithiation of RuO2 was investigated using in situ stress measurements, and the behavior was found to be fundamentally different from that of previously studied Si and Ge thin film electrodes. Most significantly, the tensile stress during delithiation of RuO2 was found to be very small, especially after the first cycle. The differences can be ascribed to the reversibility of SEI formation on RuO2, which does not occur in the case of Si and Ge. The decomposition of the SEI layer during delithiation allows freer interfacial sliding compared to Si or Ge, which accommodates the stress induced by significant volume changes during cycling. This might explain the relatively better cyclability of RuO2 films compared to Si or Ge films.

The Effect of Surface-Abundant Hydrogen Bonding on the Electrolyte Reduction for the Stable SEI in Lithium Metal Batteries

Lithium (Li) metal anodes (LMAs) have been attracted world-wide attention as an ideal anode because of its extra-high theoretical capacity (3860 mAh g-1) and low electrode potential (-3.04 V vs S.H.E.). However, the dendritic growth of Li and low Coulombic efficiency (CE) are still hindering their practical uses [1]. To date, numerous methods such as construction of artificial solid electrolyte layer (ASEI) [2], adoption of 3D current collector [3], and tuning of the electrolyte composition [4] have been proposed to prevent Li dendrite growth and increase the CE. Among them, introducing functional additives is one of the most efficient approaches for practical application considering its cost-effectiveness. Until now, various functional additives were introduced to form stable and robust SEI layer in LMBs [4]. Among them, lithium nitrate (LiNO3) is considered as the most efficient electrolyte additive, ensuring high coulombic efficiency (CE) as well as long lifespan of LMBs. When LiNO3 is dissolved in the electrolyte, NO3 - anions are mainly reduced to form inorganic species such as Li3N, which has a high ionic conductivity and mechanical strength. As such species contribute to the construction of the robust and ionic-conductive SEI layer, and hence the reduction of NO3 - is important for stable Li cycling. In this regard, many researchers have focused on increasing reduction of NO3 - by using high-concentration LiNO3 [4], or adding solubilizer to increase more NO3 - in the electrolyte [5]. However, those remedies are still insufficient because most of them increase the viscosity of electrolyte leading to low kinetics, hence a novel and more efficient way to increase NO3 - reduction is needed for practical application.On the other hand, recent researches have reported that the preferential reduction of specific anions is possible by regulation of inner Helmholtz plane (IHP) structure [6]. For instance, Huang et al. reported that intermolecular force between PF6 - anions and surface adsorbent tris(trimethylsilyl) borate could derive in PF6 --abundant IHP, successfully resulted in LiF-rich SEI layer to increase the stability of LMA [6]. Inspired by those works, we expected that NO3 --derived SEI layer would be achieved by using surface adsorbent showing strong intermolecular interaction with NO3 -.In this context, we introduce the adoption of thiourea (TU) as a catalytic additive for the LiNO3 reduction during the SEI formation. Due to its unique molecular structure, addition of TU could induce NO3 - derived SEI layer. Firstly, TU could adsorb onto metallic surface by its S atom. Meanwhile, thiourea could form hydrogen bonding with NO3 - anion by its N-H bonds [7]. Hence in the presence of TU, we suggest that NO3 --abundant electrode surface would be achieved by interaction between TU-NO3 -, resulting in Li3N-rich SEI layer.The adsorption behavior of TU on the Cu electrode was investigated by potential of zero charge (PZC) measurement (Figure 1(a)). As the TU concentration increases, PZC decreases, indicating more surface coverage by TU. Figure 1(b) shows 1H NMR spectra of electrolytes with different components. Upshift displacement of N-H bond of TU were detected after addition of DME and LiTFSI, indicating that intramolecular H-bond of TU were weakened. By contrast, downshift displacement appeared when LiNO3 was added, which means NO3 - would form strong hydrogen bonding with TU. Furthermore, linear scanning voltammetry (LSV) curves at different concentration of TU were measured to investigate the effect of TU on electrolyte reduction (Figure 1(c)). The distinct peaks at 1.6 V and 1.3 V in the cell with 5 wt% LiNO3 indicate reduction of LiNO3 and LiTFSI, respectively. Interestingly, in the presence of TU, negative potential shift and increased current of those redox peaks were shown, indicating that the TU significantly increases the LiNO3 reduction.Importantly, from the XPS analysis, it was found that more abundant Li3N components are in the ASEI layer with TU than that without TU, implying that TU accelerates the reduction of LiNO3 (Figure 2(a-b)). As a result, Li|Cu@ASEI with TU shows better cyclability and higher average CE of 96.44% during 80 cycles compared to Li|Cu@NSEI and Li|Cu@ASEI w/o TU (Figure 3). In addition, morphological and chemical investigation on the favorable ASEI layers assisted by TU, and its electrochemical performance in LMBs will be discussed in this presentation.[1] Cheng et al, Chem. Rev, 117, 10403, 2017.[2] Lopez Jeffrey, et al. JACS 140.37 (2018): 11735-11744.[3] Yang Chun-Peng et al. Nature communications 6.1 (2015): 1-9.[4] Kang et al. Journal of Power Sources 490 (2021): 229504.[5] Zhang et al. Advanced Materials 32.24 (2020): 2001740.[6] Huang et al. Angewandte Chemie. 60.35 (2021): 19232-19240.[7] Nishizawa et al. Tetrahedron letters 36.36 (1995): 6483-6486. Figure 1

(Invited) Interfacial Dynamics of Anode-Free Solid-State Batteries

There is significant interest in solid-state batteries (SSBs) as an alternative to traditional Li-ion batteries, as they can potentially eliminate the flammable liquid electrolyte and enable Li-metal anodes. However, manufacturing of SSBs with Li metal anodes poses a significant challenge, owing to the highly reactive nature of Li metal. Therefore, there has been a recent increase in interest in “anode-free” configurations, where the Li metal anode is formed in situ using the pre-existing inventory in the cathode. In addition to manufacturing considerations, anode-free configurations also enhance energy density compared to batteries with excess Li metal in the anode. However, compared to pre-formed Li metal/solid electrolyte interfaces, the nucleation, growth, and stripping of Li metal in anode-free SSBs has not been widely studied, and poses unique electro-chemo-mechanical phenomena.To probe the dynamic interfacial evolution of anode-free SSBs, in this study, I will present results using a complimentary set of in situ/operando methodologies. First, I will describe the morphological evolution of Li nucleation and growth at garnet LLZO solid electrolytes, using a newly developed platform for operando 3-D video microscopy [1]. In particular, the influence of mechanical stresses on both the thermodynamic and kinetic properties of Li will be discussed, and unique electrochemical signatures of anode-free plating will described. A mechanistic framework for these electro-chemo-mechanics will be presented, which results in design rules for improving the homogeneity of Li plating during anode formation.To compliment this morphological information, I will also present results using operando x-ray photoelectron spectroscopy (XPS) on sulfide solid electrolytes. This allows for direct observation of SEI formation during in situ anode formation. In particular, we observe a transition in reaction pathways from SEI formation to nucleation of Li metal, which is a function of both the charging protocol and the presence of interlayer coatings [2-3]. Finally, these results will be compared and contrasted to anode-free Li plating in liquid electrolytes, and a discussion will be presented on how to optimize plating morphology and reversibility.[1] E. Kazyak, M. Wang, K. Lee, S. Yadavalli, A. J. Sanchez, M. D. Thouless, J. Sakamoto, N. P. Dasgupta, Submitted (2022).[2] A. L. Davis, R. Garcia-Mendez, K. N. Wood, E. Kazyak, K.-H. Chen, G. Teeter, J. Sakamoto, N. P. Dasgupta, J. Mater. Chem. A 8, 6291 (2020).[3] A. L. Davis, E. Kazyak, D. W. Liao, K. N. Wood, N. P. Dasgupta, J. Electrochem. Soc. 168, 070557 (2021).

Electrochemically Dealloyed 3D Porous Copper Nanostructure As High-Performance Anode Current Collector of Li-Metal Batteries

Li metal anode is the ultimate choice for Li batteries owning to its highest theoretical capacity (3806 mAh/g) and lowest redox potential (-3.04 V vs. standard hydrogen electrode) among possible candidates.[1] However, despite the advantages of Li metal anodes, a number of remaining challenges must be addressed before its commercialization: undesired dendrite growth of Li, and irreversible parasitic reactions between Li and electrolyte, etc.Stabilization of Li metal is essential for commercial application of Li metal anodes. In the past few years, several strategies have been developed to suppress Li dendrite growth and stabilize SEI formation during Li plating/stripping processes. Among these strategies, 3D current collectors showed its high potential in Li anode stabilization due to its much larger surface area, which can provide much more Li nucleation sites, alleviate volumetric changes of Li anode, and decrease practical current density. Thus, compared to flat Cu foil used in commercial Li-ion batteries, 3D Cu current collectors can facilitate uniform Li deposition, mitigate Li dendrite growth, and enhance Li cycling stability.[2]Our previous work reported a 3D porous Cu current collector fabricated via a facile one-step electrodeposition method directly on commercial Cu foil. [3] The fabricated 3D porous Cu current collector showed stable long-term cycling with a high areal capacity of 6 mAh/cm2 and no Li dendrite growth was observed during cycling process. However, for the one-step electrodeposition method, the thickness of the porous Cu deposition layer is limited. Thus, preparation of 3D porous Cu layers with both high thickness and high porosity is necessary to further improve the areal capacity of this current collector. Recently, we developed a new two-step electrochemical process to fabricate thick and porous Cu layer: a thick Cu-Zn alloy was first electrodeposited on commercial Cu foil, and Zn was then removed electrochemically, leaving a thick and highly porous 3D Cu layer. Compared to our previous method, this 3D Cu layer has a high thickness of ~14 um and porosity of ~72%. This new 3D Cu current collector can achieve stable Li cycling up to 230 h at high areal capacity of ~10 mAh/cm2 at a high current density of 10 mA/cm2, demonstrated its high commercial application potential in Li-metal batteries. Tarascon, J.M. and M. Armand, Issues and challenges facing rechargeable lithium batteries. Nature, 2001. 414(6861): p. 359-367.Yang, C.P., et al., Accommodating lithium into 3D current collectors with a submicron skeleton towards long-life lithium metal anodes. Nature Communications, 2015. 6.Ma, X., Z. Liu, and H. Chen, Facile and scalable electrodeposition of copper current collectors for high-performance Li-metal batteries. Nano Energy, 2019. 59: p. 500-507.

Decomposition Pathways of EC and Effects of Additives: Accounting for Liquid, Gas, and Solid Phase Reactions during the First Charge

The majority of lithium-ion batteries (LIBs) utilize carbonate-based electrolytes, due to the good lithium solvation, electrochemical stability, and electrode passivation.1 Studies regarding decomposition pathways and other reaction mechanisms2-4 of carbonates in LIBs are abundant in the literature but few attempt to quantify total losses of these solvents. Quantitative measurement of solvent loss from the electrolyte would significantly inform the comprehensive picture of electrolyte reaction mechanisms in the cell. Furthermore, this approach allows for the study of any effects additives may have on carbonate solvent decomposition. For example, organosilicon (OS) additives have been shown to reduce gassing and improve high temperature cycling in carbonate-based LIBs,5 but their quantitative impact on EC decomposition is not known.In this poster, we detail our methodology for quantitatively tracking and characterizing different forms of ethylene carbonate (EC) decomposition in a LIB pouch cell as well as the effects of organosilicon additives on these reactions. This study focused on the loss of EC after the first charge when the majority of SEI formation occurs. Liquid phase composition, including both EC and its decomposition products, was quantified by NMR analysis (1H and 19F) of extracted electrolyte using internal standards (LiPF6 and 1,4-bis(trifluoromethyl)benzene). Gas phase decomposition was characterized by a combination of the Archimedes method (to quantify gas volume) and GC-MS analysis (to determine gas composition). Finally, the impact of OS additives on the decomposition pathways of EC was examined. Inclusion of OS molecules reduces EC decomposition during the first charge, predominately by reducing the amount of liquid phase decomposition. 1Xu, K. Chem. Rev. 2004, 104, 4303-4417. 2 Campion, C.; Li, W.; Lucht, B. Thermal Decomposition of LiPF6-Based Electrolytes for Lithium-Ion Batteries. Journal of the Electrochemical Society 2005, 152, A2327. 3 Seo, D.; Chalasani, D.; Parimalam, B.; Kadam, R.; Nie, M.; Lucht, B. Reduction Reactions of Carbonate Solvents for Lithium Ion Batteries. EC Electrochemistry Letters 2014, 3, A91-A93. 4 Xing, L.; Li, W.; Wang, C.; Gu, F.; Xu, M.; Tan, C.; Yi, J. Theoretical Investigation on Oxidative Stability of Solvents and Oxidative Decomposition Mechanism of Ethylene Carbonate for Lithium Ion Battery Use. J. Phys. Chem. 2009, 113, 16596-16602. 5 Guillot, S.L.; Usrey, M.L.; Peña-Hueso, A.; Kerber, B.M.; Zhou, L.; Du, P.; Johnson, T. Reduced Gassing in Lithium-Ion Batteries with Organosilicon Additives. J. Electrochem. Soc. 2021, 168, 030533-030543.

Electrolytes for High Nickel Lithium-Ion Batteries

We have shown different strategies1, 2 in improving capacity retention and reducing impedance rise in modifying additives: in situ electrolyte additives to synthesize the beneficial lithium tetrafluorophosphate components3, 4 or dual-salt electrolytes1 for reducing cathodic impedance.The cathodes we have tested have a LiNiO2 structure with an ultra-low amount of Co/Mn. An improved structural stability compared to that of LiNiO2 can be achieved while maintaining the high Ni content and high specific capacity. Using an optimal ratio of Ni/Mn/Co of 90/5/5 for a LiNi90Mn5Co5O2 cathodes,5 we here report the reduced reactivity of electrolytes using a combinatorial approach of reducing EC and introducing effective additives, targeting both a more robust SEI formation and a less resistive cathode electrolyte interface.Multifaceted posttest analytical methods were used to understand the failure mechanism of the baseline cells and how additives/solvents approaches help the performance. For example, the new electrolytes prevent the transesterification reactions on anode surface, form a stable cathode interface, and mitigate structural damage on the cathode surface. Further analysis also investigated the how electrolytes protect the cathode bulk structure.[1] J. Yang, M.-T. Fonseca Rodrigues, S.-B. Son, J. C. Garcia, K. Liu, J. Gim, H. Iddir, D. P. Abraham, Z. Zhang and C. Liao, ACS Applied Materials & Interfaces, 2021.[2] J. Yang, I. Shkrob, K. Liu, J. Connell, N. L. Dietz Rago, Z. Zhang and C. Liao, Journal of The Electrochemical Society, 2020, 167, 070533.[3] J. Yang, I. Shkrob, Q. Liu, N. L. Dietz Rago, Y. Liu, K. Liu, Z. Zhang and C. Liao, Journal of Power Sources, 2019, 438, 227039.[4] I. A. Shkrob, B. Han, R. Sahore, A. P. Tornheim, L. Zhang, D. P. Abraham, F. Dogan, Z. Zhang and C. Liao, Chemistry of Materials, 2019, 31, 2459-2468.[5] C. S. Yoon, M. H. Choi, B.-B. Lim, E.-J. Lee and Y.-K. Sun, Journal of The Electrochemical Society, 2015, 162, A2483-A2489.

Sulfurized Electrolyte Additives for Stable Lithium Metal Anodes

Researchers around the world are striving to develop new materials for energy-efficient and high energy density lithium-ion batteries [1]. Lithium metal with a theoretical specific capacity of 3860 mAh/g, low density (0.534 g/cm3), and the lowest potential (−3.040 V vs. standard hydrogen electrode) is consider the ultimate anode material for high specific energy batteries [2]. However, various issues remain to be address that hinder its use in commercial batteries, namely, cycling stability, Coulombic efficiency, and safety aspects associated with dendritic growth [3]. Inactive lithium, also known as “dead lithium,” originating from the dendrites that become separated from the surface over prolonged cycling contribute to anode capacity loss and require high negative to positive electrode capacity ratio (N/P). In addition, due to the extremely low standard redox potential of lithium, electrolytes readily react with the lithium metal surface even without any potential polarization. These reactions lead to the formation of mostly insoluble species in a layer often referred to as solid electrolyte interface, SEI. Ideally, the SEI layer is self-terminating; however, as fresh lithium gets exposed via dendritic growth, SEI formation continues. The steady and uncontrollable growth of SEI throughout the functional life of the battery leads to gradual resistant growth responsible for the capacity fade and eventual “death” of the battery.In previous art, alternative electrolytes, electrolyte additives, and artificial SEIs were studied [4] [5]. For example, the electrolyte additive lithium fluoride (LiF) was used in carbonate electrolytes and provided a strong protective layer that reduced side reactions and improved the life capacity of the battery [6]. Recently, 3-dimensional design of the anode’s current collector was shown to accommodate Li deposition resulting in suppressed SEI growth and volume expansion during cycling [7].In the present work, we use sulfur-containing compounds as additives at a very low concentration (1 – 50 mM) in standard 1M LiPF6 EC:DMC (v:v = 1:1). Coin cells (2032) were assembled using lithium foil (100 mm thick), separator (Celgard), and NMC811 cathode (> 10 mg/cm2). Cells were first rested and activated at a slow rate then cycled at C/3 and 1C for charge and discharge respectively in prescribed voltage cutoff window. As shown in Figure 1, the sulfur-containing cell had more than 300 cycles before 90% capacity retention relative to the beginning of life (BOL) capacity. The sulfur-free control cell lasted less than 150 cycles above the 90% retention line. Electrochemical impedance spectroscopy (EIS) measurements for cycled cells showed lower interfacial resistance for cells with sulfur-containing additives compared to control cells. The reason for the improved cycle stability can be attributed to the stability afforded by the additives to the SEI layer. Figure 1: A comparison of cell performance between control (black) and sulfur-containing additive (green). The Red line indicates the 90% retention of the battery. References Yoshio, Masaki, Ralph J. Brodd, and Akiya Kozawa. Lithium-ion batteries. Vol. 1. New York: Springer, 2009.Liu, Bin, Ji-Guang Zhang, and Wu Xu. "Advancing lithium metal batteries." Joule2, no. 5 (2018): 833-845.Xiao, Jie, Qiuyan Li, Yujing Bi, Mei Cai, Bruce Dunn, Tobias Glossmann, Jun Liu et al. "Understanding and applying coulombic efficiency in lithium metal batteries." Nature Energy5, no. 8 (2020): 561-568.Tikekar, Mukul D., Snehashis Choudhury, Zhengyuan Tu, and Lynden A. Archer. "Design principles for electrolytes and interfaces for stable lithium-metal batteries." Nature Energy1, no. 9 (2016): 1-7.Wang, Qian, Chengkai Yang, Jijin Yang, Kai Wu, Cejun Hu, Jing Lu, Wen Liu, Xiaoming Sun, Jingyi Qiu, and Henghui Zhou. "Dendrite‐free lithium deposition via a superfilling mechanism for high‐performance Li‐metal batteries." Advanced Materials31, no. 41 (2019): 1903248.Choudhury, Snehashis. "Lithium fluoride additives for stable cycling of lithium batteries at high current densities." In Rational Design of Nanostructured Polymer Electrolytes and Solid–Liquid Interphases for Lithium Batteries, pp. 81-94. Springer, Cham, 2019.Yun, Qinbai, Yan‐Bing He, Wei Lv, Yan Zhao, Baohua Li, Feiyu Kang, and Quan‐Hong Yang. "Chemical dealloying derived 3D porous current collector for Li metal anodes." Advanced Materials28, no. 32 (2016): 6932-6939. Figure 1

Thermal Runaway Reactions Modeling in Lithium-Ion Batteries

Lithium-ion batteries are ubiquitously used as power source in a variety of applications due to their superior performance and reliability. However, thermal runaway of Li-ion batteries is a serious concern due to risks associated with such catastrophic event, and hence elucidating the different chemical reactions involved in the thermal runaway phenomenon is a highly active area of research. It is both cost and time prohibitive to experimentally assess the different battery pack designs for the possibility of thermal runaway event, and hence mathematical models play critical role in the battery safety research. Thermal runaway of battery pack is usually initiated by one or a small group of cells which are affected by abuse conditions such as internal short circuit, nail penetration, overcharging, etc., and then depending on the battery pack design and thermal management, thermal runaway can propagate to neighboring cells resulting in fires that can sustain for long time. Since understanding chemistry leading to thermal runaway at cell level is crucial, many studies, both experimental and modeling, have focused on this topic.Some of the important reactions involved in the onset of thermal runaway are primary SEI decomposition, secondary SEI formation due to reaction between electrolyte and intercalated lithium ions, electrolyte decomposition, separator melting, and cathode decomposition. Since it is difficult to directly measure the different species involved in these reactions, calorimetric based approaches are used to determine the reaction parameters; DSC and ARC are widely used for this purpose. The model consists of system of differential equations which can be solved as a function of time for species fractions and cell temperature. In this work, we have developed flexible and easy to use framework for solving thermal runaway model equations. Both the electrochemical reactions and thermal runaway reactions are solved together with the aim of tighter two-way coupling between these two different processes. Using this model, we analyze the different reaction mechanisms proposed in the literature. We discuss the models for pressure build up in the cell, venting, and combustion of the vented gases.