Electrolyte Interphase Formation Research Articles

(Invited) A Multifunctional Polynorbonene Binder System Enabling Next-Generation Lithium-Ion Batteries

Polynobornene (PNBE), a material commonly used in your shoes or for the tires of supercars, can also be highly influential to the development of next-generation batteries (Kim et al., 2022). When designing the batteries of tomorrow, we are interested in polymeric materials with precisely defined dynamic mechanical properties, increased ionic or conductivity, specific chemical interactions and moonshots like stable and healable interfaces (Lopez et al., 2019). PNBE provides high chemical and thermal stability, low shrinkage, and strong adhesion properties that lead to enhanced electrode stability and electrical conductivity(Le et al., 2020). Possessing a highly flexible nature allows PNBE to conform to the shape of an electrode – making PNBE an ideal multifunctional binder.Consider some persisting problems associated with batteries, for example Si electrodes typically fail due to cracks in the Si particles creating new surfaces for electrolyte decomposition/solid electrolyte interphase formation, and due to the Si becoming electrically disconnected from the rest of the electrode and ultimately terminating cycling (Ryu et al., 2004) . PNBE can address both aforementioned pain points, low shrinkage and flexibility can help mitigate the impact of cracking that occurs within an electrode over time by maintaining the structural integrity, and strong adhesion properties promote effective binding of the active material and the rest of the electrode. With increasing concerns about cobalt, there has been a move to replace oxides with phosphates. Substituting a substantial fraction of Mn, for Fe in LiFePO4 leads to a material with an energy density approaching that of the oxides, while substantially lessening environmental concerns. Unfortunately, Mn dissolution causes a poor cycle lifetime.In an effort to reduce Mn dissolution, a mixture of PNBE and PVDF was used as a binder system. The PNBE was designed to have ether-type comb-branch functionalities that aid in Mn trapping, while the PVDF had suitable viscosity and mechanical properties. Figure 1 shows cycle lifetime results conducted at 45°C on a 2Ah LMFP-Graphite cell containing a 4%PVDF/1%PNBE binder system. The results show very good lifetime, with the capacity retention nearly 90% after 1,000 cycles. Given the difficulty with cycling of LMFP due to Mn dissolution, these results show good promise for this approach.This talk will highlight the opportunities and challenges of custom and enabling PNBE binder systems for LMFP, and other battery systems. References Kim, N.-Y., Moon, J., Ryou, M.-H., Kim, S.-H., Kim, J.-H., Kim, J.-M., Bang, J., & Lee, S.-Y. (2022). Amphiphilic Bottlebrush Polymeric Binders for High-Mass-Loading Cathodes in Lithium-Ion Batteries. Advanced Energy Materials, 12(1), 2102109. https://doi.org/https://doi.org/10.1002/aenm.202102109Le, D., Samart, C., Lee, J.-T., Nomura, K., Kongparakul, S., & Kiatkamjornwong, S. (2020). Norbornene-Functionalized Plant Oils for Biobased Thermoset Films and Binders of Silicon-Graphite Composite Electrodes. ACS Omega, 5(46), 29678–29687. https://doi.org/10.1021/acsomega.0c02645Lopez, J., Mackanic, D. G., Cui, Y., & Bao, Z. (2019). Designing polymers for advanced battery chemistries. Nature Reviews Materials, 4(5), 312–330. https://doi.org/10.1038/s41578-019-0103-6Ryu, J. H., Kim, J. W., Sung, Y.-E., & Oh, S. M. (2004). Failure Modes of Silicon Powder Negative Electrode in Lithium Secondary Batteries. Electrochemical and Solid-State Letters, 7(10), A306. https://doi.org/10.1149/1.1792242 Figure 1

Operando Auger/XPS using an electron beam to reveal the dynamics/morphology of Li plating and interphase formation in solid-state batteries

Operando Auger using an e− beam allows revealing the dynamics/morphology of Li/solid electrolyte interphase formation and Li plating with chemical information for a model Li/Li6PS5Cl stack. Comparison with operando XPS using an e− beam was also performed.

Niobium-doped layered cathode material for high-power and low-temperature sodium-ion batteries

The application of sodium-based batteries in grid-scale energy storage requires electrode materials that facilitate fast and stable charge storage at various temperatures. However, this goal is not entirely achievable in the case of P2-type layered transition-metal oxides because of the sluggish kinetics and unfavorable electrode|electrolyte interphase formation. To circumvent these issues, we propose a P2-type Na0.78Ni0.31Mn0.67Nb0.02O2 (P2-NaMNNb) cathode active material where the niobium doping enables reduction in the electronic band gap and ionic diffusion energy barrier while favoring the Na-ion mobility. Via physicochemical characterizations and theoretical calculations, we demonstrate that the niobium induces atomic scale surface reorganization, hindering metal dissolution from the cathode into the electrolyte. We also report the testing of the cathode material in coin cell configuration using Na metal or hard carbon as anode active materials and ether-based electrolyte solutions. Interestingly, the Na||P2-NaMNNb cell can be cycled up to 9.2 A g−1 (50 C), showing a discharge capacity of approximately 65 mAh g−1 at 25 °C. Furthermore, the Na||P2-NaMNNb cell can also be charged/discharged for 1800 cycles at 368 mA g−1 and −40 °C, demonstrating a capacity retention of approximately 76% and a final discharge capacity of approximately 70 mAh g−1.

Insights into Reactivity of Silicon Negative Electrodes: Analysis Using Isothermal Microcalorimetry

Silicon offers high theoretical capacity as a negative electrode material for lithium-ion batteries; however, high irreversible capacity upon initial cycling and poor cycle life have limited commercial adoption. In this work, an operando isothermal microcalorimetry (IMC) study of a model system containing lithium metal and silicon composite film electrodes was reported on the first two cycles of (de)lithiation. The total heat flow data are analyzed in terms of polarization, entropic, and parasitic heat flow contributions to quantify and determine the onset of parasitic reactions. These parasitic reactions, which include solid−electrolyte interphase formation, contribute to electrochemical irreversibility. To complement the calorimetry, operando X-ray diffraction is used to track the phase evolution of silicon. During cycle 1 lithiation, crystalline Si undergoes transformation to amorphous lithiated silicon and ultimately to crystalline Li15Si4. The solid-state amorphization process is correlated to a decrease in entropic heat flow, suggesting that heat associated with the amorphization contributes significantly to the entropic heat flow term. This study effectively uses IMC to probe the parasitic reactions that occur during lithiation of a silicon electrode, demonstrating an approach that can be broadly applied to quantify parasitic reactions in other complex systems.

The Importance of Interphases in Energy Storage Devices: Methods and Strategies to Investigate and Control Interfacial Processes

Extended interphases are playing an increasingly important role in electrochemical energy storage devices and, in particular, in lithium-ion and lithium metal batteries. With this in mind we initially address the differences between the concepts of interface and interphase. After that, we discuss in detail the mechanisms of solid electrolyte interphase (SEI) formation in Li-ion batteries. Then, we analyze the methods for interphase characterization, with emphasis put on in-situ and operando approaches. Finally, we look at the near future by addressing the issues underlying the lithium metal/electrolyte interface, and the emerging role played by the cathode electrolyte interphase when high voltage materials are employed.

How the Binder/Solvent Formulation Impacts the Electrolyte Reactivity/Solid Electrolyte Interphase Formation and Cycling Stability of Conversion Type Electrodes

Conversion/alloying type materials are of great interests in term of electrochemical performance for Li-ion batteries and beyond. To address their large volume change (typically >200%) during cycling, tailoring the binder/solvent system used for the electrode formulation together with the use of electrolyte additives are the most used and efficient approaches. However, only few studies have investigated the role of the binder/solvent formulation on the electrolyte reactivity/solid electrolyte interphase (SEI) formation and its composition. To tackle this issue, gas chromatography coupled with electron impact mass spectrometry and X-ray photoelectron spectroscopy analysis were used to understand the long term cycling stability (100 cycles) of NbSnSb-based electrodes. It is showed that CMC-H2O and PAA-H2O formulations favored the formation of a more homogeneous SEI while maintaining efficient active/conducting particles bridging, which results in high cycling stability. PVDF-NMP and PAA-NMP led, however, to much lower coulombic efficiency and higher irreversible capacity correlated with the formation of thick SEI with a concomitant disconnection of active particles. These results highlight that CMC and PAA act as artificial SEI and/or as SEI stabilizers. Overall, this work should benefit to all researchers working on improving, through electrode formulation, the lifetime of Li-ion batteries and beyond.

Revising the pathways of the Li reaction with organic carbonates.

The metallic lithium electrode has major concerns such as extremely high reactivity and nonuniform needle-like electrodeposition, limiting its wide application as a negative electrode in secondary batteries. Its reactions with the electrolyte leading to solid electrolyte interphase (SEI) formation play an important role, and controlling its composition and properties can help to overcome both difficulties. Even though solid electrolyte interphase chemistry and properties seem to be well known, many surface chemistry experiments reported are not perfect with respect to the purity needed for Li studies and can be interpreted alternatively. Here, we studied reactions between lithium and propylene carbonate and ethylene carbonate in model reactions realized in an ultra-high vacuum. In addition to the already reported reaction pathway yielding lithium carbonate and semicarbonate, our theoretical (DFT) modeling confirms the preference of alternative routes. Along with the most beneficial final lithium carbonates, dilithium 1,2-dialkoxide (DD) can form barrierlessly as a final product by two-electron transfer. Experimental XPS/NEXAFS studies of gas phase and solid-gas model reactions revealed that in both cases DD is the main reaction product. Understanding of the discovered reaction pathway can also be essential for reactions in liquid electrolytes, although the low electric conductivity of the SEI makes it less probable.

Interaction between Li, Ultrathin Adsorbed Ionic Liquid Films, and CoO(111) Thin Films: A Model Study of the Solid|Electrolyte Interphase Formation

Aiming at a molecular-level understanding of the processes at the electrode|electrolyte interface (EEI), we investigated the interaction between the battery-relevant ionic liquid (IL) 1-butyl-1-met...

Cover Feature: Microgravimetric and Spectroscopic Analysis of Solid−Electrolyte Interphase Formation in Presence of Additives (ChemPhysChem 5/2019)

Cover Feature: Microgravimetric and Spectroscopic Analysis of Solid−Electrolyte Interphase Formation in Presence of Additives (ChemPhysChem 5/2019)

Adsorption of Ultrathin Ethylene Carbonate Films on Pristine and Lithiated Graphite and Their Interaction with Li.

Aiming at a better understanding of the solid-electrolyte interphase formation in Li-ion batteries, we have investigated the interaction of ultrathin films of ethylene carbonate (EC), which is a key solvent of battery electrolytes, with pristine and lithiated highly oriented pyrolytic graphite (HOPG) and with postdeposited Li. Employing X-ray and ultraviolet photoelectron spectroscopy as well as Fourier transform infrared spectroscopy under ultrahigh-vacuum conditions, in combination with density functional theory (DFT)-based calculations, we find that EC adsorbs molecularly intact on pristine HOPG in the entire temperature range between 80 K and desorption at 200 K. Features in the ultraviolet photoelectron spectra could be related to the molecular orbitals of EC obtained from DFT calculations, and a similar adsorption/desorption behavior is obtained also on lithiated HOPG. In contrast, stepwise postdeposition of ∼0.5 and one monolayer of Li0 on a preadsorbed EC adlayer leads not only to stabilization of Li+/Liδ+ at the surface, possibly as adsorbed Li+(EC) n species, but also to EC decomposition, forming products such as Li2CO3, ROCO2Li (CH2OCO2Li)2, and Li2O. Consequences on the electronic surface properties and on the stabilization of the resulting adlayer are discussed. Upon annealing up to room temperature, some residual Li-containing decomposition products remain on the surface, which is considered as the initial stage of the solid|electrolyte interphase formation at the electrode|electrolyte interface.

Micrometer-sized nano-structured silicon/carbon composites for lithium-ion battery anodes synthesized based on a three-step Hansen solubility parameter (HSP) concept

Abstract The processing towards Si/C composites, components and synthesis parameters were selected based on the concept of Hansen solubility parameters (HSP). Si/polymer composites were generated through modified bulk polymerization and subsequent pyrolysis transformed the polymer into the desired porous carbon matrix. Coulombic efficiencies (CE) in excess of 76% after the first cycle and 99.95% after solid electrolyte interphase (SEI) formation have been achieved. A notably high specific delithiation capacity of around 1600 mAh/g with an extremely stable cycling performance even after 400 cycles is obtained. This scalable and economical synthesis approach is readily applicable to the commercial production of anode materials.