Robust Solid Electrolyte Interphase Research Articles

Rational Electrolyte Design for Elevated-Temperature and Thermally Stable Lithium-Ion Batteries with Nickel-Rich Cathodes.

As the energy density of lithium-ion batteries (LIBs) increases, the shortened cycle life and the increased safety hazards of LIBs are drawing increasing concerns. To address such challenges, a series of localized high-concentration electrolytes (LHCEs) based on a solvating-solvent mixture of tetramethylene sulfone and trimethyl phosphate and a high flash-point diluent 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether were designed. The LHCEs exhibited nonflammability and greatly suppressed heat release at elevated temperatures, which would potentially improve the safety performance of the LIBs. Moreover, the optimal LHCE achieved capacity retentions of 87.1% and 81.7% in graphite||LiNi0.8Mn0.1Co0.1O2 cells after 500 cycles at 25 and 45 °C, respectively, which were significantly higher than the conventional electrolyte, whose capacity retentions were only 75.2% and 38.5% under the same conditions. Mechanistic studies revealed that the LHCE not only formed a more robust solid electrolyte interphase but also exhibited improved anodic stability, compared with the conventional electrolyte. This work sheds light on rational electrolyte design for high-energy density LIBs with high battery performance and low safety concerns.

Engineering d-p Orbital Hybridization in a Single-Atom-Based Solid-State Electrolyte for Lithium-Metal Batteries.

Regulating lithium salt dissociation kinetics by enhancing the interaction between inorganic fillers and lithium salts is vital for enhancing the ionic conductivity in solid-state composite polymer electrolytes (CPEs). However, the influence of fillers' external electronic environments on lithium salt dissociation dynamics remains unclear. Here, we design single-atom sites in metal-organic framework fillers for poly(ethylene oxide) (PEO)-based CPEs, boosting lithium salt dissociation through an electrocatalytic strategy. This strategy enhances lithium-ion conductivity by tuning the coupling strength between the d and p orbitals of the fillers, as captured by a newly identified descriptor (λ) via high-throughput density functional theory (DFT) calculations and machine learning. The optimal single atom (Ti) sites are incorporated into a ZIF-8 matrix for PEO-based CPEs, achieving an ionic conductivity exceeding 10-3 S cm-1 at 30 °C. Additionally, the electrolyte forms a robust solid electrolyte interphase and is compatible with LiCoO2, LiNi0.9Co0.05Mn0.05O2, and sulfur cathodes. Consequently, the solid-state lithium metal battery with the electrolyte demonstrates excellent cycling stability, maintaining performance over 5000 cycles at 10 C with LiFePO4 cathodes and stable operation at -30 °C. These findings highlight the transformative potential of engineering d-p orbital hybridization by incorporating single-atom sites into inorganic fillers for designing highly ion-conductive CPEs.

Engineering d–p Orbital Hybridization in a Single‐Atom‐Based Solid‐State Electrolyte for Lithium‐Metal Batteries

Regulating lithium salt dissociation kinetics by enhancing the interaction between inorganic fillers and lithium salts is vital for enhancing the ionic conductivity in solid‐state composite polymer electrolytes (CPEs). However, the influence of fillers’ external electronic environments on lithium salt dissociation dynamics remains unclear. Here, we design single‐atom sites in metal‐organic framework fillers for poly(ethylene oxide) (PEO)‐based CPEs, boosting lithium salt dissociation through an electrocatalytic strategy. This strategy enhances lithium‐ion conductivity by tuning the coupling strength between the d and p orbitals of the fillers, as captured by a newly identified descriptor (λ) via high‐throughput density functional theory (DFT) calculations and machine learning. The optimal single atom (Ti) sites are incorporated into a ZIF‐8 matrix for PEO‐based CPEs, achieving an ionic conductivity exceeding 10⁻³ S cm⁻¹ at 30 °C. Additionally, the electrolyte forms a robust solid electrolyte interphase and is compatible with LiCoO₂, LiNi₀.₉Co₀.₀₅Mn₀.₀₅O₂, and sulfur cathodes. Consequently, the solid‐state lithium metal battery with the electrolyte demonstrates excellent cycling stability, maintaining performance over 5000 cycles at 10 C with LiFePO₄ cathodes and stable operation at ‐30 °C. These findings highlight the transformative potential of engineering d‐p orbital hybridization by incorporating single‐atom sites into inorganic fillers for designing highly ion‐conductive CPEs.

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The illustration highlights the role of the solid electrolyte interphase (SEI) in preventing lithium dendrite growth and stabilizing lithium metal. The cover showcases advancements in electrolyte design to engineer a more robust and stable SEI. This is a central theme of our review, which explores innovative approaches to achieving optimal SEI properties through tailored electrolyte formulations.image

Enhanced salt content and stabilized bilayer passivation interphase toward long-life and high-safety anode-free lithium battery

Anode-free lithium batteries (AFBs) offer optimal energy density, low cost, and simple manufacturing, making them desirable for next-generation high-energy-density batteries. However, the continuous consumption of electrolyte and Li metal through the undesirably constructed solid electrolyte interphase (SEI) significantly limits the cycling and thermal stability of AFBs. To address this challenge, dual-solvent localized high-LiFSI salt concentration electrolytes (DS-LHCEs) are designed by the addition of sulfolane (SF) due to its higher LiFSI solubility and highly consistent Li+-solvent binding energy with DME. High LiFSI content increases the salt-to-solvent concentration, decreases the amount of free solvent molecules, and restricts the side reaction between the free solvent and Li metal. As a result, a flat and dense Li metal with a robust LiF-rich SEI is deposited on Cu foil. Moreover, the introduction of trioxane (TO) constructs a high-strength outer organic SEI layer, which protects the weak grain boundaries of the inner inorganic SEI layer, further enhancing the stability of the Li metal anode. This results in assembled AFB pouch cells with a superior lifetime (206 cycles with 80 % capacity retention) and a much higher onset self-heating temperature (119 °C vs. 58 °C in the DME-based baseline electrolyte).

Robust Lif–Rich SEI Inducing Protective Layer for High Energy Density Si Anodes in Li–Ion Batteries

As the electric vehicle (EV) market has rapidly grown, the need for Li ion batteries (LIBs) with high energy density is increasing to achieve a longer driving range. However, since the graphite anodes in conventional LIBs have almost reached their theoretical capacity, it is urgently needed to develop a new battery chemistry to meet the demands for long-range EVs. In this regard, Si is considered as the most promising anode materials for high-energy-density LIBs owing to its high theoretical capacity (3579 mAh g-1), low operating potential (~ 0.4 V vs. Li/Li+), and earth abundance. Unfortunately, the employment of Si anodes is hindered by the large volume change (~ 300 %) during the lithiation/delithiation process, which accompanies with electrode pulverization, unstable solid electrolyte interphase (SEI), and continuous electrolyte decomposition.The SEI layer is the interface layer between the electrolyte and anode, which is formed via the reduction of the electrolyte components during the first lithiation process. Typically, the SEI layer is depicted as a mosaic structure that is mainly consisted of organic and inorganic constituents. The organic SEI constituents, which are the byproducts of the decomposition of the electrolytes, show poor Li ion conductivity with an unstable structure. In contrast, the inorganic SEI constituents are ideal SEI components owing to their excellent electrochemical stability. The ideal SEI layer should not only passivate the anode surface and prevent the direct contact of anode surface with the electrolyte, which causes continuous electrolyte decomposition, but also provide exhibit excellent Li ion transfer kinetics. In this respect, LiF is considered as the most ideal SEI component with its stability against the electrolyte and the high Li ion conductivity.To achieve a LiF-rich SEI layer on the Si anode, various strategies have been devised, such as electrolyte additive and LiF coating on the anode surface. The electrolyte additives such as FEC, has been widely used to construct a LiF-rich SEI layer. Unfortunately, the additives are continually consumed over repetitive cycling, which eventually results in a rapid capacity decay of the Si anodes, when they are exhausted. In case of the LiF coating, the coating layer indeed induces LiF-rich SEI layer during the first cycle. However, if the coating layer has insufficient mechanical strength, the severe volume change during the lithiation/delithiation process leads to the breakage of the SEI layer, resulting in uncontrollable electrolyte decomposition and following (re-)formation of the SEI layer. This causes a depletion of electrochemically available Li ions in the electrolyte and a thick-insulating SEI layer with poor Li ion kinetics. Therefore, not only forming an inorganic-rich SEI layer, but also constructing a robust interfacial layer with sufficient physicochemical stability is highly important to achieve stable cycle performances of the Si anodes.In this study, we propose a new strategy to construct a robust LiF-rich SEI layer on the Si anode by employing a LiF-rich SEI inducing protective layer (LPL) comprising of aluminum fluoride (AlF3) and poly(acrylic acid) (PAA) (LPL@Si). In the LPL@Si, the AlF3 induces a LiF-rich SEI layer with high Li ion conductivity, while the polymeric PAA provides a sufficient mechanical strength to alleviate the large volume change of the Si anode. In addition, the PAA in the LPL also acts a role of SEI stabilizer, which promotes the faster formation of the LiF-rich SEI layer owing to the abundant carboxyl groups, resulting in a rapid reduction of Li salts in the electrolyte. Due to these synergistic effects, the LPL@Si anode delivered significantly enhanced electrochemical performances in Li metal cell tests compared to that of the bare Si anode. Moreover, the LPL@Si anode exhibited an enhanced cycle performance than the bare Si anode in a full cell test with a NCM811 cathode. These results prove that our strategy for constructing a mechanically stable LiF-rich SEI layer would initiate further studies for achieving a highly stable Si anode in next-generation high energy density LIBs.

(Invited) Nano-Engineered SEI Layers for Next Generation Lithium-Ion Batteries

The quest for high-performance lithium-ion batteries (LIBs) hinges on the continuous improvement of cathode materials. Dr. Marca Doeff's seminal contributions have propelled this approach, inspiring novel cathode materials. By studying the intricate interactions between cathode particles, coatings, and the solid electrolyte interphase (SEI) layer, we aim at engineering a high-energy-density and long-lasting next generation lithium-ion battery.We explore the latest advancements in cathode materials, with a focus on LiFePO4, LiMnFePO4, NCM811, and Li-S, introducing surface modifications by graphene and ALD coatings.Dr. Doeff's research has demonstrated the efficacy of carbon coatings in enhancing the rate capability and cycling stability of LFP-based batteries [1].NCM811 is the most promising cathode material due to its high specific capacity and energy density, however, issues such as structural instability and capacity fading hinder its practical application. Through meticulous optimization of ALD coatings, our group has mitigated these challenges, leading to enhanced electrochemical performance and prolonged cycle life [2].Li-S batteries offer a high theoretical specific capacity and low cost, making them attractive candidates for next-generation energy storage systems, however, polysulfide dissolution and shuttle effects pose significant challenges, limiting their practical viability.By leveraging ALD techniques, our group has engineered active coatings to enhance polysulfides conversion and stabilize the cathode cycling ability.The formation and stability of the SEI layer play a pivotal role in dictating the overall performance and safety of lithium-ion batteries. Graphene coatings and ALD treatments exert a profound influence on SEI layer formation, influencing ion transport kinetics, surface reactions, and interfacial stability.Graphene coatings not only enhance electronic conductivity but also modulate the SEI layer composition and morphology. Through synergistic interactions with electrolyte components, graphene coatings promote the formation of a robust and homogeneous SEI layer, thereby suppressing parasitic reactions and capacity degradation.ALD-enabled coatings offer precise control over film thickness and composition, enabling engineered interfaces with superior electrochemical performance. By depositing conformal ALD layers onto cathode surfaces, we can engineer SEI layers with enhanced chemical stability and ion permeability, leading to improved cyclability and safety.Dr. Marca Doeff's enduring legacy in lithium-ion battery research continues to inspire groundbreaking advancements in cathode material engineering. Through meticulous design and characterization of the cathode SEI layer, coupled with innovative materials engineering techniques, we are positioned at the forefront of electrochemistry to produce batteries with enhanced performance and cycle life.[1] MM Doeff et al. "Optimization of carbon coatings on LiFePO4," Journal of Power Sources 163 (1), 2006, 180-184.[2] D Mohanty et al. “Modification of Ni-Rich FCG NMC and NCA Cathodes by Atomic Layer Deposition: Preventing Surface Phase Transitions for High-Voltage Lithium-Ion Batteries,” Sci Rep 6, 26532 (2016).

Mitigating Gas Evolution in Electron Beam-Induced Gel Polymer Electrolytes through Bi-Functional Cross-Linkable Additives

Currently, high-capacity LIBs commonly employ LiPF6-based liquid electrolytes (LEs) and high-nickel (Ni) layered oxide cathodes, such as Li[NixMnyCo1-x-y]O2 (NCM, x > 0.7). Although the LEs provide superior ionic conductivity, their intrinsic flammability and potential for leakage pose significant safety challenges. In addition, the generation of acidic species (e.g., POF3, PF5, and HF) from LiPF6 salt decomposition exacerbates the degradation of solid-electrolyte-interphase (SEI) and cathode-electrolyte-interface (CEI) layers. The high-Ni NCMs are particularly vulnerable to structural degradation and accelerate side reactions with the LEs under elevated voltages and temperatures, generating considerable gaseous byproducts, which, in turn, significantly increase the risk of battery explosion. Instead of LEs, solid-state electrolytes are considered safer alternatives owing to their enhanced safety. Yet, they have encountered obstacles such as unstable interface, low ionic conductivity, and the need for high processing temperatures exceeding 1000 °C. Therefore, designing a suitable electrolyte that simultaneously provides both safety and excellent interfacial compatibility is paramount.One of the emerging solutions is in-situ gel polymer electrolytes (GPEs), developed by incorporating a liquid precursor into the cell followed by polymerization, thus ensuring commendable electrode compatibility. Commonly, the production of in-situ GPEs employs a thermal curing process. However, its demand for an initiator, elevated temperatures exceeding 50 °C, and prolonged polymerization time can negatively impact battery components. Conversely, high-energy electron beam (E-beam) irradiation can initiate polymerization uniformly and rapidly within a minute without an initiator. Further, it can penetrate deeply into thick materials, even aluminum (Al)-based packaging of pouch-type batteries, making it an advantageous technique for widespread battery applications and conducive to mass production.In our research, we have developed a safe and commercially viable E-beam-induced GPE (E-Gel) with enhanced interfacial compatibility and minimal gas-related hazards using bi-functional cross-linkable additives (CIA). Dipentaerythritol hexaacrylate (DPH) is selected as a CIA for its proficiency in forming E-Gel with sufficient mechanical strength and Li-ion conductivity, achieving up to 80% of LEs with minimal addition of 3%.Key aspects of our work are as following. 1. Innovative GPE fabrication process Our work diverges fundamentally from existing methodologies by leveraging the bi-functional capability of DPH in a two-stage process involving initial electrochemical activation followed by E-beam-induced polymerization. Unlike conventional methods where a liquid precursor solution containing a monomer is injected and cured immediately after cell assembly, our process involves assembling a cell with a precursor solution and initiating the polymerization through electron beam irradiation after the first charge and discharge cycle. This sequence allows DPH to function as an additive during the initial cycle, establishing stable and robust polymeric SEI and CEI and as a crosslinker during the E-beam irradiation step, forming a polymer framework. Consequently,the DPH-derived SEI and CEI layers obtained by utilizing DPH as an additive had lower Young’s modulus values of 110.0 and 42 MPa, respectively, than the LE-derived SEI (289.2 MPa) and CEI (111.5 MPa). These findings suggest that the polymeric DPH-modified SEI and CEI layers possess soft and flexible attributes, enabling them to endure mechanical deformation during the Li-ion insertion-extraction processes occurring within the layered Gr and NCM811 materials. Enhanced interfacial compatibility at the electrode/E-Gel interfaces DPH first forms a stable, polymeric interface layer which acts as a protective shield for the electrodes during the first cycle. Then, during the E-beam irradiation step, the C=C bonds in the decomposition products of DPH on the electrode surface can be co-crosslinked with the acrylates within the residual DPH monomer. In other words, the polymer matrix within the GPE is integrated with cathode and anode surfaces, thereby augmenting the E-Gel's structural integrity and interfacial compatibility. Such an integrated system establishes continuous ion transport pathways at the GPE/electrode interphases, promoting ion conductivity and facilitating Li-ion migration. Improved safety and performance in practical applications Our research demonstrates that the E-Gel significantly reduces the release of hazardous gases by 2.5 times compared to LE, particularly during the initial formation stage. This is because the preferential decomposition of DPH to form stable SEI/CEI effectively alleviates the breakdown of EC. Outstandingly, the 1.2 Ah pouch cell incorporating E-Gel maintains a high capacity of 1.0 Ah after 200 cycles at 55 °C while preserving good contact between the electrodes with low gas generation.In summary, our research introduces a novel approach to the fabrication and application of gel polymer electrolytes for LIBs, leveraging the unique properties of DPH and a strategic E-beam irradiation process. Figure 1

Enhancing Anode-Free Lithium Battery Stability By One-Step Thermal Treatment of Porous Carbon Fibers for Controlled SEI Formation and Surface Activation

Anode-free lithium batteries (AFLBs) hold great promise for high energy density, yet challenges such as low coulombic efficiency and dendrite formation impede their practical use. Herein, we present an optimal defect design of a carbon current collector that markedly enhances stable cycling reactions in AFLBs. A one-step thermal treatment is introduced to create defective surfaces with nano-sized pores on carbon fibers, guided by a comparative analysis of defect evolution under varying thermal energy and oxidation conditions. The thermally derived atomic vacancies and functional groups on the graphitized surface create uniform edge planes on the basal background of graphite, thereby facilitating lithium-ion diffusion and electrolyte reduction. Additionally, molecular dynamics simulations are employed to model the lithiated nano-defects and calculate lithium adsorption energy according to the lithiation and defect configurations. The experimental/computational analyses demonstrate the beneficial role of carbon defects in inducing uniform lithium deposition and controlling the properties of a robust solid electrolyte interphase (SEI), which is crucial for suppressing lithium dendrite. Consequently, the highly defective carbon current collector exhibits much longer cycling stability and higher coulombic efficiency compared to pristine carbon current collector and copper foil in half-cell tests. Furthermore, it shows a stable high-rate capacity at the high cut-off voltage (4.5 V) in full cell with NMC cathode. The results suggest innovative design strategies for carbon-based electrodes, focusing on the correlations between intercalation and plating mechanisms. Moreover, the rapid yet systematic thermal process demonstrates significant utility in carbon treatment, indicating its promising potential for making next-generation lithium batteries.

CoO/Co3O4 Hybrid Oxide Anode Synthesis Techniques and Performance Improvement for Super-Theoretical Capacity in Lithium-Ion Batteries

The electrochemical instability of transition metal oxide (TMO)-based electrodes has hindered their broader adoption in lithium-ion batteries (LIBs), primarily due to rapid performance degradation. Addressing this challenge requires the development of TMO materials with enhanced lithium storage capacities and improved cycling stability. In this study, we report a facile hydrothermal synthesis of a CoO/Co₃O₄ hybrid oxide, followed by high-temperature calcination, aimed at boosting the electrochemical performance of these electrodes. Fluoroethylene carbonate (FEC) and vinylene carbonate (VC) additives were introduced to stabilize the Co₃O₄ interface, minimizing electrolyte decomposition and enhancing the electrode/electrolyte interface. At an optimized concentration of 2 wt%, these additives significantly improved cycling stability and capacity retention.To further address common issues like grain boundary cracking and void formation, calcination at 800°C with 2% FEC was employed, resulting in improved Li⁺ transport and structural stability. This optimized synthesis and additive strategy led to remarkable improvements in the CoO/Co₃O₄ anode’s electrochemical performance, achieving a super-theoretical capacity (STC) phenomenon. After 400 cycles at 0.5 C, the CoO/Co₃O₄ anode exhibited an extraordinary capacity of 1427.35 mAh g⁻¹, a significant increase from its initial capacity of 925 mAh g⁻¹.The observed STC is attributed to enhanced additive-driven electrolyte stabilization, the formation of a robust solid electrolyte interphase (SEI), and the mitigation of electrode surface cracking. Structural characterization via SEM, TEM, and BET analyses confirmed increased porosity and structural stability after prolonged cycling, further supporting the STC phenomenon. This study highlights the critical importance of tailored material synthesis and electrolyte engineering in overcoming the limitations of TMO-based anodes, paving the way for high-performance, long-lasting LIBs. Figure 1

The Effect of Solvating Ability and Diffusivity of Electrolyte Solutions for Solid Electrolyte Interphases in Lithium Metal Batteries

Lithium (Li)-metal batteries (LMBs) have been extensively investigated owing to the higher capacity of metallic Li anode compared to graphite employed in the current Li-ion batteries (LIBs). However, the surface stability of the Li electrode has not yet been fully addressed, attributed to the imperfect solid electrolyte interphase (SEI) layer and electrolyte solution. Many efforts have focused on seeking the pertinent electrolytes forming stable inorganic SEI layers on Li. For example, fluorinated ether solvents coordinate Li+ ion weakly, leading to Li+ - anion ion pairing and the formation of anion-derived SEI.[1] In addition, the utilization of diluent, which does not solvate Li+ but forms locally concentrated anions around Li+, further led to ion-pairing.[2] These approaches are promising to create (electro)chemically and mechanically robust SEI layers and have demonstrated improved cell cycling performance. Nonetheless, the weakly coordinating Li+ system has suffered from low ionic conductivity. In addition, the specific condition for the formation of ideal SEI composites, such as LiF, Li2S, Li3N, and Li2O, as the form of fully reduced anion (e.g., bis(fluorosulfonyl)imide (FSI-), has not been fully addressed.Here, we present the understanding of weakly solvating Li+ conditions correlated with the SEI composites and diffusivity of the electrolyte solution. We used 1 M lithium bis(fluorosulfonyl)imide (LiFSI) and fluorinated 1,4-dimethoxylbutane (FDMB) as a main weakly coordinating solvent and added diluent either tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) or bis (2,2,2-trifluoroethyl) ether (BTFE). Comparing FDMB and FDMB and TTE (1/1 v/v) co-solution, 1 M LiFSI in FDMB and BTFE (1/1 v/v) electrolyte solution exhibited the best cycling performances in both Li|Li coin cells and Li|NCM811 pouch cells (>100 cycles). Notably, the BTFE-involving electrolyte formed the ideal LiF, Li2S, and Li3N composites in the SEI layers, whereas other electrolytes created partially decomposed FSI species and formed more organic-rich composites arising from the solvent decomposition. The desired SEI layer from the BTFE-containing electrolyte offered insignificant Li corrosion and the lowest presence of dead Li residue. In addition, the thinnest interphasial layer on NMC811 was observed, leading to no cathode crack after cycling.NMR analysis revealed that the addition of diluents, both BTFE and TTE, led to an increased amount of aggregated ion pairing, causing the formation of the anion-derived SEI layer. However, it may not explain the different degrees of anion reduction, thus forming different SEI composites. We address this disparity from ion diffusivity. BTFE has the lowest viscosity (0.7 cP at 25 oC) among FDMB (1.40 cP) and TTE (1.40 cP) and resulted in forming a small ionic cluster with a hydrodynamic radius of 0.49 pm, measured by NMR analysis. It contrasted with the large-size TTE, enhancing the solution viscosity despite no Li+ solvation and forming a large cluster with a hydrodynamic radius of 0.65 pm. Considering the Stoke-Einstein equation, the smaller hydrodynamic radius and low viscosity increase the Li+ and FSI- diffusion coefficients, supported by measured ionic conductivity and voltage hysteresis in Li|Li symmetric cells. In this presentation, I will discuss the details of the BTFE and TTE roles and the correlation between ion diffusivity and the SEI composite.

Synergetic Effect of LiNO3 and Fluorine-Containing Additives on Stabilizing Electrode-Electrolyte Interfaces in Lithium Metal Batteries

Lithium metal batteries (LMBs) are regarded as an ideal candidate for next-generation batteries to meet the increasing demand for high energy density batteries. Due to the high theoretical capacity (3860 mAh g-1) and the low electrochemical redox potential (- 3.04 V vs Standard Hydrogen Electrode (SHE)) of lithium metal anodes, lithium metal batteries can achieve a high energy density. However, the poor compatibility of conventional carbonate electrolytes with lithium metal anodes has limited the commercialization of LMBs. The unstable solid-electrolyte interphase (SEI) generated from the charging and discharging process leads to the dendritic growth of lithium and the continuous depletion of the electrolyte, limiting the cycle life of LMBs. Furthermore, the unstable cathode-electrolyte interphase (CEI) limits the charge transfer kinetics of Li+ and decomposes at high voltage operation of LMBs. Therefore, the formation of stable electrode-electrolyte interfaces is crucial for the adoption of LMBs. Numerous studies have been attempted to regulate the electrode-electrolyte interfaces by introducing additives to the electrolyte. Lithium nitrate (LiNO3) is an effective additive for regulating the SEI layers through the formation of a highly lithium ion-conductive SEI components derived from the reduction of NO3 - ions such as Li3N (2~4 x 10-4 S cm-1). However, it is vulnerable to volume expansion, leading to continuous consumption of the additive itself. Fluorine-containing additives such as fluoroethylene carbonate (FEC) and lithium difluoro(oxalate)borate (LiDFOB) can promote the formation of a robust, high mechanical strength (64.7 GPa) LiF-rich SEI layer to enhance the mechanical strength of the SEI layer to mitigate the lithium dendrite growth. Nevertheless, LiF can hinder the lithium ion transport, due to its low ionic conductivity (10-9 ~ 10-14 cm-2). The synergetic effect of LiF and Li3N as SEI components may be able to enable highly reversible LMBs. In addition, the LiDFOB additive have been reported to form a thin and stable CEI via B-O bonds with anchoring transition metal ions in the cathode, preventing the degradation of the cathode. The electrolyte system with FEC and LiDFOB is able to increase the cycle life of LMBs by the formation of robust SEI and CEI layer. Herein, the synergetic effects of LiNO3, FEC, and LiDFOB additive is discussed to further enhance the stability of the electrode-electrolyte interfaces for high energy density LMBs. The LiNO3 additive is sustainably released through the use of a porous film which consists of LiNO3 embedded polyacrylonitrile (PAN) nanofibers (LiNO3/PAN) to overcome the low solubility of LiNO3 in the carbonate electrolyte. Moreover, fluorine containing additives, LiDFOB and FEC are introduced with LiNO3 in order to form a LiF/Li3N-rich SEI to lengthen the life cycle of LMBs. LiDFOB-derived CEI also contributed to the enhanced stability of the cathode. Consequently, through the synergetic effects of LiNO3 and fluorine-containing additives, the capacity retention of ultra-thin Li (20 μm)||nickel-rich NCM811 cells is improved.

The Regulation of Solid Electrolyte Interphase on Composite Lithium Anodes in Solid-State Batteries.

Solid-state lithium metal batteries (SSLMBs) with solid polymer electrolyte (SPE) are highly promising for next-generation energy storage due to their enhanced safety and energy density. However, the stability of the solid electrolyte interphase (SEI) on the lithium metal/SPE interface is a major challenge, as continuous SEI degradation and regeneration during cycling lead to capacity fading. This article investigates the SEI formation on lithium anodes (l-SEI) and composite lithium anodes (c-SEI) in solid-state lithium metal batteries. The composite anodes form a uniform Li2S-rich inorganic SEI layer and a thinner organic SEI layer, effectively passivating the interface for enhanced cycling stability. Specifically, the full cells with c-SEI anodes sustain over 400 cycles at 0.5 C under a high areal capacity of 2.0 mAh cm-2. Moreover, the reversible high-loading solid-state pouch cells exhibit exceptional safety even after curling and cutting. These findings offer valuable insights into developing composite electrodes with robust SEI for solid-state polymer-based lithium metal batteries.

Li2MoO4 Tailored Anion‐enhanced Solvation Sheath Layer Promotes Solution‐phase Mediated Li‐O2 Batteries

AbstractThe high overpotential of Li‐O2 batteries (LOBs) is primarily triggered by sluggish charge transfer kinetics at the reaction interfaces. A typical LiBr redox mediator (RM) catalyst can effectively reduce the battery's overpotential. However, it is prone to shuttling and corroding the Li anode, leading to RM loss and reduced energy efficiency. To address these challenges, we introduced Li2MoO4 into the LiBr‐containing electrolyte to promote the solution‐phase mediated LOBs. This addition tailors the anion‐enhanced Li+ solvation sheath layer and forms a robust anion‐derived solid electrolyte interphases (SEI) on the Li anode. The robust SEI effectively mitigates the corrosion of soluble Br3−/Br2 and attacks by highly reactive oxygen species. Additionally, the dispersed and high‐density Li2MoO4 exhibits strong adsorption capabilities for O2/LiO2 and Br‐related species during the discharge/charge process, thereby promoting the growth and decomposition of Li2O2 in the solution phase and inhibiting the shuttle effect of Br‐related species in LOBs. Consequently, the LOBs demonstrate exceptional cycling stability (415 cycles) and high energy efficiency (86.2 %), paving the way for the sustainable development and practical application of these battery systems.

The Regulation of Solid Electrolyte Interphase on Composite Lithium Anodes in Solid‐State Batteries

AbstractSolid‐state lithium metal batteries (SSLMBs) with solid polymer electrolyte (SPE) are highly promising for next‐generation energy storage due to their enhanced safety and energy density. However, the stability of the solid electrolyte interphase (SEI) on the lithium metal/SPE interface is a major challenge, as continuous SEI degradation and regeneration during cycling lead to capacity fading. This article investigates the SEI formation on lithium anodes (l‐SEI) and composite lithium anodes (c‐SEI) in solid‐state lithium metal batteries. The composite anodes form a uniform Li2S‐rich inorganic SEI layer and a thinner organic SEI layer, effectively passivating the interface for enhanced cycling stability. Specifically, the full cells with c‐SEI anodes sustain over 400 cycles at 0.5 C under a high areal capacity of 2.0 mAh cm−2. Moreover, the reversible high‐loading solid‐state pouch cells exhibit exceptional safety even after curling and cutting. These findings offer valuable insights into developing composite electrodes with robust SEI for solid‐state polymer‐based lithium metal batteries.

Li2MoO4 Tailored Anion-enhanced Solvation Sheath Layer Promotes Solution-phase Mediated Li-O2 Batteries.

The high overpotential of Li-O2 batteries (LOBs) is primarily triggered by sluggish charge transfer kinetics at the reaction interfaces. A typical LiBr redox mediator (RM) catalyst can effectively reduce the battery's overpotential. However, it is prone to shuttling and corroding the Li anode, leading to RM loss and reduced energy efficiency. To address these challenges, we introduced Li2MoO4 into the LiBr-containing electrolyte to promote the solution-phase mediated LOBs. This addition tailors the anion-enhanced Li+ solvation sheath layer and forms a robust anion-derived solid electrolyte interphases (SEI) on the Li anode. The robust SEI effectively mitigates the corrosion of soluble Br3 -/Br2 and attacks by highly reactive oxygen species. Additionally, the dispersed and high-density Li2MoO4 exhibits strong adsorption capabilities for O2/LiO2 and Br-related species during the discharge/charge process, thereby promoting the growth and decomposition of Li2O2 in the solution phase and inhibiting the shuttle effect of Br-related species in LOBs. Consequently, the LOBs demonstrate exceptional cycling stability (415 cycles) and high energy efficiency (86.2 %), paving the way for the sustainable development and practical application of these battery systems.

Monofluorinated Phosphate with Unique P-F Bond for Nonflammable and Long-Life Lithium-Ion Batteries.

Lithium-ion batteries (LIBs) with conventional carbonate-based electrolytes suffer from safety concerns in large-scale applications. Phosphates feature high flame retardancy but are incompatible with graphite anode due to their inability to form a passivated solid electrolyte interphase (SEI). Herein, we report a monofluorinated co-solvent, diethyl fluoridophosphate (DEFP), featuring a unique P-F bond that allows a trade-off between safety and electrochemical performance in LIBs. The P-F bond in DEFP weakens ion-dipole interactions with Li+ ions, lowering the desolvation barrier, and simultaneously reduces the lowest unoccupied molecular orbital (LUMO) of DEFP, promoting the formation of a robust and inorganic-rich SEI. Additionally, DEFP exhibits improved thermal stability due to both robust SEI and the inherent flame-retardant properties of the P-F bond. Consequently, the optimized DEFP-based electrolyte exhibits improved cyclability and rate capacity in LiNi0.8Co0.1Mn0.1O2||graphite full cells compared with triethyl phosphate-based electrolytes and commercial carbonate electrolytes. Even at a low E/C ratio of 3.45 g Ah-1, the 1.16 Ah NCM811||Gr pouch cells achieve a high capacity retention of 94.2 % after 200 cycles. This work provides a promising approach to decouple phosphate safety and graphite compatibility, paving the way for safer and high-performance lithium-ion batteries.

Constructing a Functional Fast‐Ion Conductor Interface for Vertically Aligned Titanium Boride Nanosheets to Achieve Superior Sodium‐Ion Storage Performances

AbstractDesigning excellent anode materials to enhance the sluggish interfacial kinetics of Na+ is a key challenge in improving the electrochemical performance of sodium‐ion batteries (SIBs). Herein, an ultra‐thin fast‐ionic conductor NaB5C coating TiB2 nanoflowers with vertically aligned nanosheet arrays to form yolk–shell TiB2@NaB5C (TBNBC) nanospheres as an anode material for SIBs. The unique structure creates direct and short ion/electron transfer pathways and reserves enough space to prevent the uneven electrochemical reactions from TiB2 nanosheets aggregation and stacking, thus ensuring the long‐term cycling stability of SIBs. Additionally, the NaB5C coating with fast‐ionic conductor functional interphase provides rapid Na+ transport channels and effectively reduces the Na+ de‐solvation barrier, accelerating Na+ reaction kinetics. Furthermore, a homogeneous and robust solid electrolyte interphase (SEI) film including inorganic boron species and fluorine‐rich inner layer is constructed on the TBNBC electrode to delocalize stress and induce a uniform Na+ flux, further promoting fast Na+ interphase reaction kinetics. Consequently, the optimized composites achieve ultrastable cycling performances of 173 mAh g−1 over 5000 cycles at 10 A g−1. More importantly, they also exhibit an outstanding capacity of 182.2 mAh g−1 at −20 °C. This work offers opportunities for the energy storage use of transition metal borides under extreme conditions.

Monofluorinated Phosphate with Unique P−F Bond for Nonflammable and Long‐Life Lithium‐Ion Batteries

AbstractLithium‐ion batteries (LIBs) with conventional carbonate‐based electrolytes suffer from safety concerns in large‐scale applications. Phosphates feature high flame retardancy but are incompatible with graphite anode due to their inability to form a passivated solid electrolyte interphase (SEI). Herein, we report a monofluorinated co‐solvent, diethyl fluoridophosphate (DEFP), featuring a unique P−F bond that allows a trade‐off between safety and electrochemical performance in LIBs. The P−F bond in DEFP weakens ion‐dipole interactions with Li+ ions, lowering the desolvation barrier, and simultaneously reduces the lowest unoccupied molecular orbital (LUMO) of DEFP, promoting the formation of a robust and inorganic‐rich SEI. Additionally, DEFP exhibits improved thermal stability due to both robust SEI and the inherent flame‐retardant properties of the P−F bond. Consequently, the optimized DEFP‐based electrolyte exhibits improved cyclability and rate capacity in LiNi0.8Co0.1Mn0.1O2||graphite full cells compared with triethyl phosphate‐based electrolytes and commercial carbonate electrolytes. Even at a low E/C ratio of 3.45 g Ah−1, the 1.16 Ah NCM811||Gr pouch cells achieve a high capacity retention of 94.2 % after 200 cycles. This work provides a promising approach to decouple phosphate safety and graphite compatibility, paving the way for safer and high‐performance lithium‐ion batteries.

Machine Learning-Assisted Bayesian Optimization for the Discovery of Effective Additives for Dendrite Suppression in Lithium Metal Batteries.

In the pursuit of enhancing the performance and safety of lithium (Li)-metal batteries, the discovery of effective electrolyte additives to suppress Li dendrites has emerged as a paramount objective. In this study, we employ an inverse design strategy to identify potential additives for dendrite mitigation. Two key mechanisms, namely, the formation of robust solid electrolyte interphase layers and the leveling mechanism, serve as the foundation for our investigation. Our inverse design strategy is guided by molecular properties such as the lowest unoccupied molecular orbital energy and interaction energy upon Li surface adsorption. An active learning process utilizing Bayesian optimization (BO) was utilized to identify potential molecules with ideal properties. Through this screening process, we uncover a collection of 62 molecules with the potential to act as SEI-forming additives, along with 106 molecules for leveling additives, both surpassing the performance of established additives reported in the literature. This work highlights the potential of BO methods in computationally based inverse design of materials for many applications, and the discovered additives could potentially boost the commercialization of Li-metal batteries.