Solid Electrolyte Interphase Research Articles

Rate Capability of Fluorinated Catholyte-Based Li Primary Batteries Governed by Interfacial and Bulk Li+ Transport

Fluorinated catholytes based on fluoro–organosulfur reactants have recently been shown to offer a compelling design space for high-energy lithium (Li) primary batteries with ability to compete with carbon monofluoride (CFx) at low rates and moderate cell temperatures. However, rate capability is hindered as the operating temperature is lowered to room temperature, warranting further investigation. Here, we examined the origin of such loss in detail via impedance spectroscopy and 3–electrode cells. As temperature decreases, the Li anode disproportionately contributes to discharge overpotentials at moderate to high rates (0.3–1 mA cm−2), indicating that the Li solid electrolyte interphase (SEI) plays a pivotal role in governing performance. Despite a modest temperature change, the chemical composition of the SEI is significantly different at 25 °C than at 50 °C, with a lower oxygen/fluorine ratio at room temperature that impedes SEI Li+ transport. Furthermore, continuous growth in ionic resistance/viscosity of the catholyte throughout discharge are found to be the cause of cell “sudden death” at lower temperature and higher rates. This analysis indicates that development of these energy–dense primary battery chemistries for moderate-to-high–rate applications must focus on enhancing SEI Li+ conductivity and maximizing diffusivity of reactant species under solvent–lean conditions.

Roll-to-roll Prelithiation of Li-ion Batteries Anodes Using Ultrathin Lithium Strips

The irreversible formation of solid electrolyte interphase (SEI) reduces lithium-ion batteries’ capacity and energy density (LIBs), prompting the prelithiation strategies to compensate for the Li loss. However, the accuracy of the prelithiation degree and the SEI formation under prelithiation conditions remain key issues, especially for practical industrial production. Herein, we demonstrate that roll-to-roll prelithiation of graphite anodes can be done using ultrathin lithium strips (6-μm-thick), and the prelithiation degree can be precisely tuned by the topological distribution. More importantly, the formation of SEI during the prelithiation process and its influence on the long-term cycling performance of the prelithiated LiFePO4 || graphite pouch cells was revealed. Afterward, the prelithiated pouch LiFePO4 || graphite cell at the optimized conditions exhibits the upgraded energy density after even 1200 cycles. This study shall provide an industrial-scale prelithiation technique for high-energy–density LIBs and a pioneering systematic investigation of SEI chemistry during prelithiation.

Microcrystalline-Fe2P4O12 as eco-friendly and efficient anode for high-performance dual-ion battery

Dual-ion batteries (DIBs) have garnered significant interest because of their cost-effectiveness and high level of safety. However, the anode typically utilized tends to show low cyclic stability in complete batteries when the only sources of lithium are primarily consumed in the electrolyte following the development of a solid electrolyte interphase (SEI) during the initial electrochemical process. Here, a simple approach is used to produce microcrystalline carbon-coated Fe2P4O12 at a mild temperature. This material has the ability to store lithium ions, resulting in a specific capacity of 215 mAh/g at a potential range of 1 to 2.5 V vs Li+/Li0. Furthermore, it demonstrates a remarkable coulombic efficiency of 99 % in the initial cycles, even in the absence of a solid electrolyte interphase (SEI) formation. On the other hand, the issue of the high voltage plateau of the graphite cathode is addressed by selecting a total of 4.2 V as the optimal voltage range in DIBs. Simultaneously, the composite Fe2P4O12 also demonstrates exceptional ion diffusion kinetics and reduced interfacial impedance due to its microcrystalline structure. The utilization of the proposed Fe2P4O12 anode addresses a crucial deficiency in the complete range of deep in-situ bioremediation techniques, hence expediting the industrialization process.

Altering the Solid Electrolyte Interface Through Surface-Modification of Lithium Metal Anode for High-Voltage Lithium Battery

The physical structure and chemical composition of the solid electrolyte interphase (SEI) affect the performance of the lithium metal anode. The tuning of the chemical composition and structure of the SEI through the surface modification of the lithium metal anode has been conducted. A series of dicarboxylic acids, oxalic acid, malonic acid, succinic acid, glutaric acid, and adipic acid have been utilized to modify the surface of the lithium anode. Physical characterization methods have been employed to study the surface morphology and chemical composition of the SEI. Symmetrical (Li/Li) and asymmetrical (NMC622/Li) cells with pristine lithium and surface modified lithium electrodes have been assembled and tested. NMC622/Li cell with surface modified lithium shows improved performance compared to that of pristine lithium. Malonic acid-treated lithium outperforms all the electrodes by retaining 141 mAh g−1 specific capacity even after 100 cycles of charge-discharge. XPS depth profiling analysis reveals that the SEI on the MA-Li contains evenly distributed organic and inorganic components which are responsible for the performance of MA-Li.

Pyrrolic and pyridinic nitrogen-rich carbon microspheres derived from polydopamine as advanced anodes for sodium ion batteries

This study presents an efficient approach for designing hard carbon electrodes through the synthesis of nitrogen-doped carbon microspheres (NCS) via an eco-friendly high-temperature pyrolysis of polydopamine. By precisely modulating the pyrolysis temperature, the nitrogen content and bonding configurations are carefully optimized. NCS treated at 1000 °C demonstrate exceptional electrochemical performance, including an initial Coulombic efficiency of 73.4 %, a reversible capacity of 386.6 mA h g−1, a rate capability of 180.1 mA h g−1 at 10 A g−1, and 75.3 % capacity retention after 1500 cycles. The abundant pyrrolic-N dopants effectively expand interlayer spacing, facilitating efficient and reversible Na⁺ intercalation. Additionally, pyridinic-N and pyrrolic-N functionalities significantly increase surface defect density, promoting rapid electron and ion transport. The spherical morphology, characterized by a low surface area, further reduces irreversible Na⁺ consumption during solid electrolyte interphase (SEI) formation, thereby ensuring high initial coulombic efficiency (ICE).

Lithium-ion comb—artificial self-regulating lithium-storage film on aluminum anode enabling long cycles of batteries

Al anode can increase battery energy density, but its non-wettability and high Li nucleation hindrance cause uneven Li nucleation to deteriorate the anode structure. Herein, we present a novel in-situ synthesis method for the deposition of molybdenum oxide nanospheres (NMO) onto the surface of Al foil, that is, molybdenum oxide/aluminum (M-Al), which demonstrates a two-stage propulsion effect on Li-ion migration to address the issue at hand. The high wettability and low Li nucleation hindrance of the NMO layer drive the first stage of Li-ion migration. NMO acted as a comb to deliver Li ions uniformly with minor volume expansion. Subsequently, the formation of Li2O-rich solid electrolyte interphase (SEI) film with exceptional desolvation capability, facilitated by the NMO layer and electrochemically activated M-Al to Li molybdate/aluminum (Li-M-Al), represents the second stage in the advancement of Li−ion migration. The embedding of lithium ions makes molybdenum oxide evolve into lithium molybdate, thereby enabling Mo to regulate the storage of Li ions through the valence state. Hence, the Li nucleation overpotential of M-Al is decreased by 0.32 V, leading to a significant enhancement in the cycling performance of the Li-M-Al||LiFePO4 (LFP) battery, with a capacity retention rate of 78.5 % after 400 cycles at 1C.

Robust polymer electrolytes with fast ion-transport nanochannels constructed by carbon dots for long lifespan Li metal batteries

As an anode material in energy storage systems, Li metal has exceptional merits, including high specific capacity, low density, and low redox potential. However, challenges such as lithium dendrites and unstable solid electrolyte interphase (SEI) hinder the practical application of lithium metal batteries (LMBs). Solid polymer electrolytes (SPEs), notably PVDF-HFP, are expected to overcome the above problems because of their mechanical merits and safe features, but their limited ion transportation behaviors result in insufficient ionic conductivity at room temperature. Herein, we invent an approach to prepare high performance electrolytes composed by porous PVDF-HFP and functionalized carbon dots (CDs). Such porous PVDF-HFP polymer membranes are created by a subtle phase inversion process, possessing a sponge-like structure, vertical lithium-ion transport channels and CDs decorated surfaces, thus able to uptake the liquid electrolyte (LE) to form gel polymer electrolytes (GPEs). The CDs fillers are produced in large scale with adjustable surface states, which can enhance Li salts disassociation to release free Li ions. As a result, the optimal conductivity of the as-prepared GPEs at room temperature is up to 8.7 mS cm−1 and the lithium transference number reaches 0.64. Our GPEs endow Li symmetric batteries with very stable SEI and long cycling life over 2200 h, and help realize high capacities and retention rates of the LMBs using LiFePO4(LFP) or LiCoO2(LCO) cathodes.

Zincophilic group-rich aminoglycosides for ultra-long life and high-rate zinc batteries

The application of environmentally friendly and economical aqueous zinc (Zn) metal batteries (ZMBs) is severely limited by critical issues associated with Zn anodes, including dendrite growth, hydrogen evolution reaction and corrosion. Hence, many improvement methods, such as electrolyte additives, mainly focus on the protection of Zn anodes. Herein, owing to the abundance of zincophilic functional groups, aminoglycosides represented by amikacin are introduced as sulfates to solve these problems. The presence of zincophilic functional groups, such as amino and hydroxyl, enables amikacin to effectively replace H2O molecules, thereby altering the solvation structure of Zn2+. Additionally, amikacin preferentially adsorbs on the anode surface and facilitates the formation of solid electrolyte interphase (SEI), achieving highly conductive and uniformly deposited Zn anodes. Therefore, the Zn||Zn symmetric cell with the modified electrolyte can work stably with a long cycle lifespan of up to 3300 h at 1 mA cm−2, 1 mAh cm−2. It is worth mentioning that the symmetric cells deliver excellent cycle lifespans of 1000 h (5 mA cm−2, 5 mAh cm−2), 790 h (10 mA cm−2, 10 mAh cm−2) and 330 h (20 mA cm−2, 20 mAh cm−2). Besides, the Zn-based full cell, in conjunction with NaV3O8·1·5H2O cathode, also demonstrates exceedingly good cycling stability with a remarkable capacity retention rate of 95.92 % after 3000 cycles at 5 A g-1. More encouragingly, ZMBs supplemented with the other aminoglycoside sulfates, namely gentamicin sulfate (GS) and neomycin sulfate (NS), also show excellent performance, confirming the universality of the improvement by these aminoglycosides.

Constructing stable solid electrolyte interphases to enhance the calendar life of anode-free lithium metal batteries

Advancement of anode-free lithium metal batteries (AFLMBs) has been appreciated due to their exceptional volumetric energy density and manufacturing simplicity. However, AFLMBs suffer from poor cycle performance due to the absence of excess lithium and current research lacks an understanding of lithium corrosion and calendar aging in AFLMBs. Here, we investigate the practical effects of chemical and galvanic corrosion on battery performance (calendar life) through a modified full-cell cycling experiment. The impact of galvanic corrosion is negligible, whereas chemical corrosion during a rest period reduces the capacity retention (CR) from 47% to 32% over 100 cycles. Consequently, a corrosion control strategy is implemented, substituting 1,2-dimethoxyethane with 1,2-dimethoxypropane (DMP), which has weaker lithium ion solvation properties due to its inductive effect. This approach results in the formation of a Li2O-rich solid-electrolyte interphase (SEI) layer, which effectively prevents direct contact of lithium with the electrolyte and the formation of additional SEI layers. Consequently, the decrease in CR due to chemical corrosion is considerably mitigated in DMP-based electrolyte, with only a slight decrease from 51% to 49%. This study provides insights into lithium corrosion in practical AFLMBs and offers guidelines for designing less-corrosive electrolytes to improve AFLMB performance for diverse industrial applications as energy-storage devices.

Multidimensional core-shell nanocomposite of iron oxide-carbon tube and graphene nanosheet: A lithium-ion battery anode with enhanced performance through structural optimization

A novel multidimensional composite of 1D iron oxide (Fe3O4)-carbon tube and 2D graphene nanosheet (GNS) was demonstrated to be used as the anode material for lithium-ion batteries (LIBs). Fe3O4-carbon tube-GNS manifested a unique core–shell composite structure, where the Fe3O4 nanoparticles were embedded in the carbon tube with the GNS. The material characterization confirmed that the Fe3O4 nanoparticles were embedded in the highly graphitized carbon tube with the dispersed GNS. Fe3O4-carbon tube-GNS exhibited a high porosity (surface area: 62.3 m2/g, pore volume: 0.112 m3/g). It also exhibited an excellent electrochemical performance with a high reversible capacity (900 mAh/g at 1 A/g), a high coulombic efficiency (∼100 % for 100 cycles), and good rate capability (491 mAh/g at 5 A/g). The excellent electrochemical performance of our composite is attributed to the suppressed/accommodated volume expansion of Fe3O4 and formation of a stable solid electrolyte interphase (SEI) layer during lithiation/delithiation caused by unique multidimensional composite structure of Fe3O4-carbon tube-GNS with a continuous transport path for electrons and Li+. In addition, such the enhanced lithium storage of our composite is confirmed with the kinetic characterization at various scan rates by analyzing their storage and capacitive contributions.

Unraveling the Complex Temperature-Dependent Performance and Degradation of Li-Ion Batteries with Silicon-Graphite Composite Anodes

Competing effects of graphite and Si result in a complex temperature dependent performance and degradation of Li-ion batteries with Si-graphite composite anodes. This study examines the influence of varying the Si content (0 to 20.8 wt%) in Si-graphite composite anodes with consistent areal capacity and N/P ratio in full cells containing NMC622 cathodes. One hundred pilot-scale double-layer pouch cells were built and cycle aged in the temperature range from −10 to 55 °C. Electrochemical characterization demonstrated that increasing Si contents enhance capacity and mitigate internal resistance at low temperatures. On the other hand, high Si contents decrease charge-discharge energy efficiency and cycle life, particularly at elevated temperatures. Post-mortem analysis of aged electrodes, including physico-chemical characterization (scanning electron microscopy, energy-dispersive X-ray analysis, thickness measurements) and cell reconstruction revealed significant solid electrolyte interphase growth and increased loss of active material in anodes with high Si content. The optimum temperature for longest cycle life as derived from Arrhenius plots decreased from 30 °C for graphite anodes to 10 °C for cells with moderate Si content up to 5.8 wt%. These findings allow the design of optimized cells by balancing the Si content versus operating temperature in order to achieve lowest cell aging.

The electrochemical performance deterioration mechanism of LiNi0.83Mn0.05Co0.12O2 in aqueous slurry and a mitigation strategy

Integrating high-nickel layered oxide cathodes with aqueous slurry electrode preparation routes holds the potential to simultaneously meet the demands for high energy density and low-cost production of lithium-ion batteries. However, the influence of dual exposure to air and liquid water as well as the heating treatment during aqueous slurry electrode processing on the high-nickel layered oxide electrode is yet to be understood. In this study, we systematically investigate the structural evolution and electrochemical behaviors when LiNi0.83Mn0.05Co0.12O2 (NMC83) is subjected to aqueous slurry processing. It was observed that the crystal structure near the surface of NMC83 is partially reconstructed to contain a mixture of rock-salt and layered phases when exposed to water, leading to the deteriorated rate capability of the NMC83 electrodes. This partial surface reconstruction layer completely converts into a pure rock-salt phase upon cycling, accompanied by the release of O2, Ni leaching, catalyzed decomposition of the electrolyte, and the formation of a thick cathode electrolyte interphase layer. The byproducts of the electrolyte and dissolved Ni could shuttle to the Li metal side, causing a crosstalk effect that results in a thick and unstable solid electrolyte interphase layer on the Li surface. These in combination severely undermined the cycling stability of the NMC83 electrodes obtained from the aqueous slurry. A mitigation strategy using molecular self-assembly technique was demonstrated to enhance the surface stability of water-treated NMC83. Our findings offer new insights for tailoring ambient environment stability and aqueous slurry processability for ultra-high nickel layered oxide and other water-sensitive cathode materials.

High-efficient sodium compensation enabled by dual-carbon coupling catalyst strategy for sodium-ion batteries

Sodium oxalate (Na2C2O4), a green, cost-effective, and high-capacity additive candidate, suffers from a decomposition voltage that largely exceeds the cutoff voltage of currently common layered oxides and polyanionic compounds, limiting its availability. This work constructs a composite structure of carbon-coated Na2C2O4 coupled with a catalyst-loaded Ketjen black (NCO@C@MMNKB) using a low-temperature carbon-coated assisted ball milling technique. The results show that the decomposition potential of Na2C2O4 is significantly reduce from 4.42 to 3.91 V. Meanwhile, correspondingly the full cell energy density is enhanced from 135.0 to 236.4 Wh Kg−1. Further investigations show that the by-products of the sodium compensation additive exhibit different “gas effects” on the formation of the cathode and anode solid electrolyte interphase (CEI and SEI) films. This provides a practical thought to promote similar additives towards practicality to improve the overall performance of SIBs.

Effects of Main Aging Mechanism and State of Charge on the Safety of 21700 Li-Ion Battery Cells with Ni-Rich NMC Cathode

It is known that both the material used in Li-ion battery cells, as well as their aging history and state of charge (SOC), strongly impact the safety of such cells. This study investigates the safety characteristics of new or aged 21700 cells containing silicon-graphite blend anodes together with Ni-rich NMC cathodes by accelerating rate calorimetry (ARC) at different SOC. Cells underwent cyclic aging at 0 °C, room temperature, or 50 °C to induce different aging mechanisms including Li plating and solid electrolyte interphase growth. The quasi-adiabatic heat-wait-seek ARC tests show lower temperatures for self-heating (SH), CID triggering, venting, and thermal runaway (TR) with increasing SOC, indicating reduced safety levels. Furthermore, the mass loss and TR intensity increase as the SOC of the cell increases. Aged cells show a similar SOC dependence as new cells in view of venting and TR, although both temperatures are reduced. The onset of SH at around 35 °C, independent of SOC, reveals a significant safety issue in cells with Li plating. Additional cell voltage monitoring and on-line mass spectrometry provide further insights into the decomposition processes. Our findings provide essential knowledge to improve the safety and design of Li-ion battery cells by identifying unsafe states.

A CaI2-Based Electrolyte Enabled by Borate Ester Anion Receptors for Reversible Ca-Organic and Ca-Se Batteries.

Passivating solid electrolyte interphases (SEIs) in Ca metal anodes constitute a long-standing challenge, as they block Ca2+ transport and inhibit reversible Ca deposition/stripping. Current solutions focus primarily on boron/aluminum-based electrolytes to mitigate such interfacial issues by producing Ca2+-conductive species, yet the complex synthetic procedure of these salts restricts the widespread application. Moreover, whether any inorganic phases possess decent Ca2+ conductivity within SEIs remains ambiguous. Herein, we report that a commercially available CaI2-dimethoxyethane electrolyte supports reversible Ca/Ca2+ redox reactions via forming CaI2-involved SEI, inspired by our density functional theory calculations where CaI2 species is predicted to possess the lowest Ca2+ diffusion barrier among a range of inorganic phases. We further materialize this finding by introducing a serial of borate ester anion receptors, resulting in the formation of CaI2/borides hybrid SEIs with an enhanced Ca2+ conductivity. Consequently, the resultant electrolytes realize a 7-fold reduction in deposition/stripping overpotential compared to anion receptor-free one, allowing for the construction of reversible Ca-metal full cells with high-capacity selenium and organic cathodes.

A CaI2‐Based Electrolyte Enabled by Borate Ester Anion Receptors for Reversible Ca−Organic and Ca−Se Batteries

AbstractPassivating solid electrolyte interphases (SEIs) in Ca metal anodes constitute a long‐standing challenge, as they block Ca2+ transport and inhibit reversible Ca deposition/stripping. Current solutions focus primarily on boron/aluminum‐based electrolytes to mitigate such interfacial issues by producing Ca2+‐conductive species, yet the complex synthetic procedure of these salts restricts the widespread application. Moreover, whether any inorganic phases possess decent Ca2+ conductivity within SEIs remains ambiguous. Herein, we report that a commercially available CaI2‐dimethoxyethane electrolyte supports reversible Ca/Ca2+ redox reactions via forming CaI2‐involved SEI, inspired by our density functional theory calculations where CaI2 species is predicted to possess the lowest Ca2+ diffusion barrier among a range of inorganic phases. We further materialize this finding by introducing a serial of borate ester anion receptors, resulting in the formation of CaI2/borides hybrid SEIs with an enhanced Ca2+ conductivity. Consequently, the resultant electrolytes realize a 7‐fold reduction in deposition/stripping overpotential compared to anion receptor‐free one, allowing for the construction of reversible Ca‐metal full cells with high‐capacity selenium and organic cathodes.

Tuning Reaction Kinetics of Fluorinated Molecules to Construct Robust Solid Electrolyte Interphases on SiOx Anode.

Introducing fluorinated electrolyte additives to construct LiF-rich solid-electrolyte interphase (SEI) on Si-based anodes is proven an effective strategy for coping with its massive volume changes during cycling. However, most current research on fluorine-containing additives focuses on their thermodynamics of decomposition, lacking studies on the correlation between the molecular structure of additives and their decomposition kinetics. Herein, two fluorinated ester additives, diethyl fluoromalonate (F1DEM) and diethyl 2,2-difluoromalonate (F2DEM) were designed and synthesized. Through combining a wealth of characterizations and simulations, it is revealed that despite the similar reduction thermodynamics, the favorable reduction kinetics of single-fluorinated F1DEM facilitate a LiF-rich layer during the early stage of SEI formation, contributing to the formation of a more robust SEI on SiOx anode compared to the difluorinated F2DEM. Consequently, the proposed additive achieves excellent cycling stability (84 % capacity retention after 1000 cycles) for 5 Ah 21700 cylindrical batteries under practical testing conditions. By unveiling the role of reaction kinetics, a long-overlooked aspect for the study of electrolyte additives, this work sheds light on how to construct a stable SEI on Si-based anodes.

Tuning Reaction Kinetics of Fluorinated Molecules to Construct Robust Solid Electrolyte Interphases on SiOx Anode

AbstractIntroducing fluorinated electrolyte additives to construct LiF‐rich solid‐electrolyte interphase (SEI) on Si‐based anodes is proven an effective strategy for coping with its massive volume changes during cycling. However, most current research on fluorine‐containing additives focuses on their thermodynamics of decomposition, lacking studies on the correlation between the molecular structure of additives and their decomposition kinetics. Herein, two fluorinated ester additives, diethyl fluoromalonate (F1DEM) and diethyl 2,2‐difluoromalonate (F2DEM) were designed and synthesized. Through combining a wealth of characterizations and simulations, it is revealed that despite the similar reduction thermodynamics, the favorable reduction kinetics of single‐fluorinated F1DEM facilitate a LiF‐rich layer during the early stage of SEI formation, contributing to the formation of a more robust SEI on SiOx anode compared to the difluorinated F2DEM. Consequently, the proposed additive achieves excellent cycling stability (84 % capacity retention after 1000 cycles) for 5 Ah 21700 cylindrical batteries under practical testing conditions. By unveiling the role of reaction kinetics, a long‐overlooked aspect for the study of electrolyte additives, this work sheds light on how to construct a stable SEI on Si‐based anodes.

Stabilizing the Solid Electrolyte Interphase of SiOx Negative Electrodes: The Role of Fluoroethylene Carbonate in Enhancing Electrochemical Performance

Stabilizing the Solid Electrolyte Interphase of SiOx Negative Electrodes: The Role of Fluoroethylene Carbonate in Enhancing Electrochemical Performance

A multifunctional separator as sustained release Carrier of NaNO3 to Address the low solubility of Nitrate in Electrolyte

In the face of modern large-scale energy storage needs, sodium metal batteries (SMBs) with high energy density have received widespread attention. However, safety and cycle stability issues have become obstacles to the practical application of SMBs. In this paper, we present a multifunctional and high-performance SMBs separator (NNP91) utilizing the nonwoven composite NaNO3@PVDF. NNP91 has good tensile properties and offers possibilities for flexible batteries. In addition, NNP91 has a dense separator layer that can physically block sodium dendrites to prevent short-circuit of the cell. More importantly, NNP91 brings NaNO3 into the cell, which is insoluble in conventional electrolytes. NaNO3 and Na metal form a nitride-rich solid electrolyte interphase (SEI) that inhibits the disordered growth of sodium dendrites, increases the rate of ionic shuttling and exhibits excellent electrochemical performance. NNP91 offers a new approach to inorganic materials insoluble in electrolytes.