Commercial Pouch Cells Research Articles

A Universal Plug-and-Play Approach to In Situ Multinuclear Magnetic Resonance Analysis of Electrochemical Phenomena in Commercial Battery Cells.

Advancing electrochemical energy storage devices relies on versatile analytical tools capable of revealing the molecular mechanisms behind the function and degradation of battery materials in situ. The nuclear magnetic resonance phenomenon plays a pivotal role in fundamental studies of energy materials and devices because of its exceptional sensitivity to local environments and the dynamics of many electrochemically relevant elements. The jelly roll architecture is one of the most energy-dense and, therefore, most popular concepts implemented in pouch, prismatic, and cylindrical Li- and Na-ion cells. Such widely commercialized designs, however, represent a significant obstacle for a range of powerful in situ magnetic resonance-based methodologies due to negligible radio frequency electromagnetic field penetration through conductive metal casings and current collectors. In this work, we introduce an experimental setup that enables direct RF wave transmission through the cell terminals and current collectors, and provides efficient excitation and detection of NMR signals. An RF adapter designed as a plug-and-play device effectively turns the battery cell into an NMR probe that can be tuned to a broad range of Larmor frequencies. Due to its exceptional sensitivity, versatility, and multinuclear capability, the proposed methodology is suitable for fundamental research and industrial high-throughput screening applications. In situ NMR lineshapes provide a direct quantitative description of the chemical environments of electrochemically active elements and enable new metrics for the accurate assessment of state-of-charge (SoC) and state-of-health (SoH). Specifically, in commercial pouch cells based on lithium cobalt oxide, lithium nickel manganese cobalt oxide, and sodium nickel iron manganese oxide chemistries, 7Li and 23Na NMR data unambiguously show electrochemical transformations between intercalated and metallic forms of charge carrier ions, and reveal anisotropic magnetic properties of the electrode coating.

Degradation mechanism and assessment for different cathode based commercial pouch cells under different pressure boundary conditions

Lithium-ion pouch cell exhibits expansion behavior during cycling, which determines the overall performance and external pressure evolution. It is significant to reveal the impact of pressure boundary conditions on battery degradation. This study investigated the degradation mechanism of different cathode-based pouch cells (LiFePO4 (LFP) and Li(Ni0.6Co0.2Mn0.2)O2 (NCM622)) under four distinct pressure boundary conditions (I-II. clamping with two foam pads having varying compression force deflection (CFD) respectively, III. without foam pad, IV. unpressurized). One hundred of pre-experiment cycles determined the optimal external pressure (12.5 kPa) to slow down the degradation process. Subsequently, multi-cell paralleled cycling experiments were conducted for 1000 cycles. The capacity degradation of LFP and NCM cells with the optimal condition was 6.0 % and 12.6 % less than that of unpressurized cells. The electrochemical tests indicated that unpressurized cells had the fastest rate of lithium-ion loss, which is related to solid electrolyte interface (SEI) film growth and lithium plating. Post-mortem characterization analysis further revealed that the pressure boundary condition is crucial for the electrode morphology, pressure distribution, and gas generation, which affect battery degradation. The pressurized cells’ surface exhibited fewer instances of lithium plating. With the stiff foam clamped, pouch cell swelling can be absorbed while maintaining contact between cell components, resulting in fewer electrode folds and cracks. This study provides valuable insights for designing long-lifespan battery modules or packs.

Plasticity analysis and a homogenized constitutive model of compressible multi-layer structure of battery

A homogenized constitutive model for the compressible multi-layer structure of battery (CMLSB) under external loading is essential for optimizing the structural design of electric assemblies. Currently, there is no specific constitutive model that is both mechanically explanatory and operationally applicable to CMLSB under varied loading conditions. In this study, due to limited understanding of the in-plane behavior of CMLSB, an analytical model was developed to investigate plasticity in this specific direction using the strain probing method. The observed plastic characteristics inspired the formulation of a novel two-dimensional constitutive framework for CMLSB in the in-plane direction.By integrating this new constitutive framework with one-dimensional plastic descriptions, a hybrid constitutive model was introduced and implemented in finite element software. Calibration and validation of the model were performed using a commercial pouch cell battery and its segments under various loading conditions. Finite element simulations with the hybrid model demonstrated remarkable accuracy in predicting the mechanical behavior of the cell under various in-plane and out-of-plane compression scenarios. Additionally, simulations were carried out to analyze the impact of cell packaging and air pressure. The new hybrid battery model is considered a user-friendly, physically interpretable, and high-fidelity tool, poised to significantly facilitate the comprehensive design of electric devices.

Protocol for Quantifying All Electrolyte Compositions in Aged Lithium‐ion Batteries

AbstractThe aging of lithium‐ion batteries (LIBs) typically accompanies the degradation of electrolyte, but the relationship between them remains unclear. Therefore, quantifying residual electrolyte in batteries at different states of health (SOH) is a crucial issue. Here, we have developed a comprehensive characterization method to quantitatively analyze the electrolyte salts, solvents, and additives in commercial pouch cell, achieving quantification of all electrolyte compositions with high accuracy. Compared to the reported external standard method used in gas chromatography‐mass spectrometry (GC‐MS), we developed an internal standard method, which offers higher accuracy and reliability, with the maximum error decreased from 9.54 % to 3.48 %. Moreover, the quantitative accuracy of the calibration curves remains unchanged after 2 months. Multi‐instruments analysis is also utilized for the extraction and quantitative analysis of electrolyte in practical battery systems, achieving less than 5 % quantification error for all compositions. With our proposed method, it becomes possible to determine the absolute amounts of all electrolyte compositions, rather than obtaining limited information such as concentration or relative content. It is believed that this protocol of quantifying electrolyte compositions in commercial cells could serve as a baseline for further studies to reveal the relationship between electrolyte degradation and battery aging.

Optimizing Structural Patterns for 3D Electrodes in Lithium-Ion Batteries for Enhanced Fast-Charging Capability and Reduced Lithium Plating

The most common pattern types for anode structuring, in particular the line, grid, and hexagonal-arranged hole pattern were evaluated in a comparable setup in full-cells and symmetrical cells. The cells with structured electrodes were compared to reference cells with unstructured anodes of similar areal capacity (4.3 mAh cm−2) and the onset of lithium plating during fast-charging was determined in situ by differential voltage analysis of the voltage relaxation and ex situ by post-mortem analysis. Furthermore, electrochemical impedance spectroscopy measurements on symmetrical cells were used to determine the ionic resistance of structured and unstructured electrodes of similar areal capacity. All cells with structured electrodes showed lower ionic resistances and an onset of lithium plating shifted to higher C-rates compared to cells with unstructured electrodes. The structure patterns with capillary structures, i.e., lines and grids, showed significant reduced lithium plating during fast-charging and a higher rate capability compared to reference cells with unstructured electrodes and cells with hole structured electrodes. The continuous rewetting of the electrode with liquid electrolyte by capillary forces and the reduced ionic resistance of the 3D electrode are identified as key factors in improving overall battery performance. The data of the studied cells were used to calculate the resulting energy and power densities of prospective commercial pouch cells and potential pitfalls in the comparison to cells with unstructured electrodes were identified.

The effect of using alternative binders and second life graphite materials on the electrochemical performance of lithium-ion battery electrodes

Lithium-ion battery anodes were produced and tested using gelatin and sodium alginate (NaAlg) biopolymers, modified with a deep eutectic solvent (DES). Anodes created with these alternative binder systems showed comparable capacities and Coulombic efficiencies to cells assembled using commercial PVDF and CMC/SBR binders. Rate tests of these cells found that DES-NaAlg possessed a higher rate capability than PVDF, showing a greater capacity (∼70 mAh.g−1 higher) when cycled at 1C. Anodes using gelatin materials exhibited lower rate stability, showing significant capacity fade at cycling rates <0.5C. EIS measurements showed that NaAlg anodes were similar to the cells using conventional binders, but gelatin possessed an extra impedance contribution relating to a polymeric coating of the graphite active materials. NaAlg binders were incorporated into graphite anodes reclaimed from a commercial pouch cell using an ultrasound delamination technique. These cells showed reduced rate performance, brought about by ultrasonic fracturing and particle agglomeration. The capacities at low cycling rates were, however, comparable to pristine materials and evidence of key processes such as SEI formation were observed.

Unilateral RF sensors based on parallel-plate architecture for improved surface-scan MRI analysis of commercial pouch cells

Rapid expansion of the Li-ion pouch cell market is driven by the looming problem of permanent depletion of natural gas reservoirs and by the growing demand for high-performance portable devices and electric vehicles. Safety and performance of Li-ion cells have been two main focal points of the extensive battery research. Surface-scan Magnetic Resonance Imaging (MRI) is an operando method designed for the accurate detection of substandard battery cells and for monitoring electrochemical processes with high spatial and temporal resolutions. Intercalation-dependent magnetism and charge transfer processes in the cell's electrodes give rise to characteristic magnetic field patterns outside the cell. For accurate mapping of such patterns, we proposed the concept of a unilateral radio-frequency (RF) sensor, a flat thin resonator encapsulating a proton-rich solid-state detection medium. When the pouch cell is placed in direct contact with the sensor, the magnetic field patterns propagate inside the detection medium, and the corresponding spatial distribution of Larmor precession frequencies can be detected with MRI. In this work, we developed and evaluated a series of RF sensor configurations based on parallel-plate architecture enhanced by arrays of distributed capacitors. The parallel-plate approach does not suffer from RF interference with pouch cells and provides excellent sensitivity and B1-field homogeneity. The optimal configuration of the parallel-plate sensor depends on the dimensions of the pouch cell and the distribution of parallel capacitors. This article includes the results of experimental tests, RF-field simulations, and strategies to further improve the surface-scan MRI method.

Hierarchical implementation of electrochemical techniques to provide a reliable diagnosis of commercial lithium-ion pouch cells under selected operational conditions

Understanding the performance of commercial Lithium-Ion batteries (LIBs) under various operational conditions is a paramount concern for ensuring their long-term stability. While numerous methodologies exist from a materials perspective to enhance comprehension of fundamental phenomena, electrochemical engineers often rely only on charge/discharge curves. Although these curves provide valuable insights, their information can be enriched through the systematic implementation of electrochemical protocols. This approach offers more nuanced data that can facilitate swift diagnostics of LIB conditions and enable in-depth analysis of underlying physicochemical processes. In this study, a comprehensive methodology is proposed for assessing the reversibility, stability, dominant processes, and degradation effects of LIBs. This involves combining charge/discharge curves with complementary electrochemical techniques and specific methodologies to extract maximum information from the data; for this purpose the following strategies are sequentially applied: Galvanostatic Cycling with Potential Limitation (GCPL), Galvanostatic Electrochemical Impedance Spectroscopy (GEIS), Distribution of Relaxation Time protocols (DRT), and Differential Capacitance (DC) analysis to a range of commercial pouch cell LIBs under diverse conditions. By correlating the results obtained through these techniques, we established meaningful interpretations of battery performance, thorough specialized protocols based on DRT and DC analysis, under various operational case scenarios, the effect of temperature, C-rate, and extended cycling. These protocols yielded crucial electrochemical parameters and relevant characteristics, enabling advanced diagnostics. The proposed framework serves as a guide for methodologically analyzing commercial batteries, it underscores that traditional characterization techniques can be augmented with additional analyses to comprehensively grasp the performance of commercial LIBs.

A novel perspective on behavior and improvement of Li-rich cathodes in commercial pouch cells

A novel perspective on behavior and improvement of Li-rich cathodes in commercial pouch cells

State Estimation for Battery Populations by Holistic Analysis of Ultrasonic Waveforms

Battery inspection using ultrasonic waves has gained popularity since 2015 [1] as a non-electrochemical method to estimate battery states. The propagation of sound through the internal structure of a battery is influenced by the mechanical properties and geometry of its constituent layers, which are known to vary during cycling and as the battery ages. In particular, alterations in the stiffness, density, thickness and porosity of the layers affect the speed of sound, its attenuation and length-of-travel. As a result, ultrasonic waveforms recorded during battery operation can be correlated to its internal states, and the accuracy of this mapping is subject to the modelling method used.Most attempts at modelling the acoustic signatures of batteries simplify the task by isolating specific waveform peaks, most commonly the final peak which is an ‘echo’ originating at the posterior side of the cell [2]–[5]. However, different battery layers will influence different waveform portions disproportionately, and such localisations in the analysis could lead to imprecision. More importantly, such localisations do not produce consistent trends across different cells, as shown in the accompanying figure. The figure depicts results from acoustic experiments conducted on seven commercial pouch cells (cells A to G). The cells were of the same type (product id) and chemistry, comprising a graphite negative electrode and a lithium cobalt oxide (LCO) positive electrode. The cells were tested for a total of 45 cycles using CC-CV protocols, out of which 25 cycles were performed at a rate of 1C and are the ones plotted. The remaining 20 cycles were performed at different rates, at intermediate times, and are not shown. The second and last acoustic peaks were isolated and their amplitude and Time-of-Flight (ToF) are plotted for each cell against battery capacity (Q). It is evident that the cell-to-cell variation of these localised acoustic characteristics is large, to the extent that a model relying on these features alone will be unable to generalise to the entire population. It should be noted that the temperature variation among experiments was 8 °C (18.8 - 26.8 °C) which does not explain the cell-to-cell variation seen.Alternative analysis methods that can utilise waveforms in their entirety were proposed in previous work [6]. Artificial neural networks were used to estimate battery state-of-charge (SoC) using multiple features from the time and frequency domains. In the present study we explore extensions of this machine learning approach to exploit feature spaces of even higher dimensions, and we assess the generalisation performance of these state estimators compared to methods based on peak selection.[1] A. G. Hsieh et al., “Electrochemical-acoustic time of flight: in operando correlation of physical dynamics with battery charge and health,” Energy Environ. Sci., vol. 8, no. 5, pp. 1569–1577, May 2015, doi: 10.1039/C5EE00111K.[2] P. Ladpli, F. Kopsaftopoulos, and F. K. Chang, “Estimating state of charge and health of lithium-ion batteries with guided waves using built-in piezoelectric sensors/actuators,” J. Power Sources, vol. 384, pp. 342–354, Apr. 2018, doi: 10.1016/J.JPOWSOUR.2018.02.056.[3] L. Gold et al., “Probing lithium-ion batteries’ state-of-charge using ultrasonic transmission – Concept and laboratory testing,” J. Power Sources, vol. 343, pp. 536–544, Mar. 2017, doi: 10.1016/J.JPOWSOUR.2017.01.090.[4] G. Davies et al., “State of Charge and State of Health Estimation Using Electrochemical Acoustic Time of Flight Analysis,” J. Electrochem. Soc., vol. 164, no. 12, p. A2746, Sep. 2017, doi: 10.1149/2.1411712JES.[5] R. E. Owen et al., “Operando Ultrasonic Monitoring of Lithium-Ion Battery Temperature and Behaviour at Different Cycling Rates and under Drive Cycle Conditions,” J. Electrochem. Soc., vol. 169, no. 4, p. 40563, Apr. 2022, doi: 10.1149/1945-7111/ac6833.[6] E. Galiounas, T. G. Tranter, R. E. Owen, J. B. Robinson, P. R. Shearing, and D. J. L. Brett, “Battery state-of-charge estimation using machine learning analysis of ultrasonic signatures,” Energy AI, vol. 10, p. 100188, Nov. 2022, doi: 10.1016/J.EGYAI.2022.100188. Figure 1

Unraveling SEI formation and cycling behavior of commercial Ni-rich NMC Li-ion pouch cells through operando optical characterization

Lithium-ion batteries, relying on Ni-rich NMC (LiNixMnyCo1−x−yO2) phases, are widely used in various applications due to their high energy density and extended cycle life. However, further improvements are possible with a deeper understanding of their internal chemistry in real-world conditions. Here, using optical fiber Bragg grating sensors placed inside commercial pouch cells, we demonstrate the feasibility of monitoring the heat release during the formation cycles and real-driving cycling. By collecting temperature data for Li-ion cells using different types of NMCs, we were able to extract the contribution of the anode and the impact of additives on overall heat generation. We also present a comparison of the heat generation of NMC-based batteries under varying power and voltage levels, which provides insights into battery safety in dynamic, real-world environments. Our study reveals the importance of continuously monitoring batteries heat release throughout its lifespan to enhance our understanding of the interconnected materials surfaces and electrolyte reactions.

An efficient multi-state evaluation approach for lithium-ion pouch cells under dynamic conditions in pressure/current/temperature

The current analytical and simulation models for lithium-ion pouch cells encounter challenges in accuracy and efficiency for battery management applications. This paper proposes an analytical model and decoupling algorithm for lithium-ion pouch cells. It can evaluate the multi-state distribution and evolution in gas/heat generation, temperature, pressure, and deformation. Analytic differential equations are formulated, including mechanical, thermal circuit and reaction sub-models. The analysis framework considers dynamic conditions (e.g., mechanical pressure, charging/discharging, heat dissipation) and uniform characteristics (e.g., local heating, anisotropic heat conduction, shell deformation). A sequential decoupling algorithm from the global to the local is proposed to address the convergence issue from the high-dimensional and strongly nonlinear equations. Iterative mechanisms are established to determine the solving parameters for eliminating confusion in engineering applications. The numerical and experimental results on three commercial pouch cells verified the approach performances, including stable convergence, millisecond efficiency, and 2% temperature error. The performances suggest its application prospects in energy storage and vehicle power systems.

Change of safety by main aging mechanism – A multi-sensor accelerating rate calorimetry study with commercial Li-ion pouch cells

The safety of Li-ion batteries is the most critical of many important characteristics and must be carefully considered. However, depending on the aging conditions, safety of batteries can change drastically. We had recently introduced ARC-MS as a new tool for safety investigations, which is an updated accelerating rate calorimeter (ARC) combined with a mass spectrometer (MS). Additionally, our ARC-MS setup is equipped by seven more low cost sensors (temperature, voltage, resistance, audio, strain, and transmitted and reflected ultrasound). In this paper, the dependence of safety on the dominant aging mechanism as a function of aging temperature, and state-of-health (SOH) is investigated on the example of 3.3 Ah commercial pouch cells. The ambient temperature during aging has a strong influence on the dominant aging mechanism (Li plating or SEI growth) of this cell as shown by Arrhenius plots of the aging rate and Post-Mortem analyses (ICP-OES, SEM, EDX, Hg porosimetry, STA) of aged cells. Our in-depth evaluation shows that different sensors can provide indications of safety relevant events (onset of swelling, onset of self-heating, cell venting, stable exothermic reactions, separator melting, and thermal runaway) in the cells independently. Combining these low-cost sensors might be a solution for detection of unsafe cells in applications.

Differential Analysis of Galvanostatic Cycle Data from Li-Ion Batteries: Interpretative Insights and Graphical Heuristics

Differentiation of a Li-ion battery cycling profile (galvanostatic voltage vs charge) yields a pair of complementary measures: differential capacity (dQ/dV vs voltage, also called incremental capacity) and differential voltage (dV/dQ vs charge). These metrics, especially when obtained under experimental conditions approximating cell equilibrium, are widely used to diagnose cell state and mechanisms related to cell aging. Central to the resulting diagnosis is the understanding of how the chemistry of individual electrode materials manifests in the full-cell differential plots. In this article, a fundamental theory of differential analysis is advanced from the starting point of idealized single electrode (half-cell) measurements, building up to the nontrivial translation to full cell data, with consideration of cell balancing and degradation. Various complementary approaches from the existing literature are harmonized with the aid of a novel graphical heuristic in which cell voltage and differential capacity data are superimposed on a 2D representation (“square plot”) of the cell thermodynamic state. Interpretative analysis based on the new approach is demonstrated using data from a commercial pouch cell with the well-characterized LiCoO2|graphite chemistry. A brief review of current literature on practical uses of differential analysis is also provided.

Fluorinated ether decomposition in localized high concentration electrolytes

Localized high concentration electrolytes (LHCEs) are a promising class of battery materials to enable stable cycling of the lithium metal anode. Here, we report the use of operando nuclear magnetic resonance (NMR) spectroscopy to observe electrolyte decomposition during Li stripping/plating and identify the influence of individual components in LHCEs on Li metal battery performance. Data from operando19F solution NMR indicates that both bis(fluorosulfonyl)imide (FSI−) salt and bis(2,2,2-trifluoroethyl) ether (BTFE) diluent molecules play a key role in solid electrolyte interphase (SEI) formation. Three-electrode electrochemical impedance spectroscopy (EIS) of commercial pouch cells also shows differences in interfacial resistances between LHCE and standard high concentration electrolytes (HCEs) that may be explained by incorporation of BTFE and BTFE reaction products into the SEI. Based on solid-state NMR and X-ray photoelectron spectroscopic characterization, we find that BTFE diluents decompose to form CF2- and CF3-containing fragments within a LiF-rich SEI deposited on the anode surface. The CEI on the cathode (here, LiNi0.8Mn0.1Co0.1O2) side of the battery also contains higher quantities of LiF and trapped LiFSI after cycling in the LHCE compared to a HCE that are attributed to diluent decomposition and correlated with lower impedance at the cathode. Overall, this work provides a new framework to consider highly fluorinated ether molecules—instead of functioning purely as diluting agents in LHCEs, these fluorinated ethers exhibit tunable interfacial reactivity that can be leveraged to control Li deposition behavior.

Potential of ultrasonic time-of-flight and amplitude as the measurement for state of charge and physical changings of lithium-ion batteries

Lithium-ion battery is an electrochemical energy storage device with high reliability safety and efficiency requirements, it is necessary to obtain and evaluate the battery performance in time. In this study, ultrasound is applied as a timely measuring method for the state-of-charge (SoC) of lithium-ion battery. In experimental presentation, the ultrasonic measurement is performed on commercial pouch cell, to identify the relationship between its SoC and the ultrasonic signals. The ultrasonic time-of-flight (ToF) and amplitude are sensitive to changes in physical properties of cell's layers during charging and discharging. Analyses of ultrasonic ToF signals present that sound velocity is influenced by the cell's temperature, the charging/discharging current and voltage, as well as the changing in layered materials. Analysis of ultrasonic amplitude shows that amplitude is properly correlated with physical (volume) changing in anode and cathode layers, as a function of the SoC. This ultrasonic amplitude measurement shows the potential application as one real-time diagnostic technique for lithium-ion battery.

A systematic approach to resolve high impedance of multifunctional energy storage composites

Previous work has proposed and characterized the structural and electrical performance of Multifunctional Energy Storage Composite (MESC) structures: structural elements with embedded lithium-ion batteries which were developed by the Structures and Composite Laboratory (SACL) at Stanford University. This work conducts a comprehensive parametric study over the design variables in the manufacturing process to determine the root cause of increased DC impedance compared to commercial pouch cell batteries. Several MESC samples were assembled under various controlled environmental temperatures and pressures. The samples underwent Hybrid Peak Pulse Characterization (HPPC) to approximate the DC impedance as a function of state of charge (SOC). Failure limits of the battery with respect to assembly temperature and pressure were tested, and an MESC manufacturing simulation model was constructed in Abaqus to validate the manufacturing limits. Samples assembled without enough temperature or pressure failed due to a lack of structural integrity or hermetic seal. Conversely, samples which underwent elevated temperatures and pressures resulted in high DC impedance due to nonuniform electrolyte wetting. This work resolves the primary concern of MESC by achieving comparable DC impedance to commercial pouch cells of the same chemistry and testing procedure.

Ultralow‐Expansion Lithium Metal Composite Anode via Gradient Framework Design

AbstractImproving the stability of lithium (Li) anodes is critical for the safety and reliability of Li metal batteries. Developing a 3D conductive Li host is suggested as one of the most promising strategies in this context, especially for suppressing the pulverization of the electrode. However, the material consistency and volume expansion of the electrodes (&lt;15%) represent significant challenges for their applications in commercial pouch cells. In this work, dual‐gradient architecture, combining rigidity and flexibility through the synergistic effect of silver wires and carbon nanotubes, is fabricated by a facile suction filtration method. This unique network shows a volume expansion of only 5.4%, outperforming all previously reported composite Li anodes. In addition, the online digital holography clearly monitors the preferential deposition of metallic Li at the lithiophilic layer. Consequently, the present gradient host effectively prevents the deposition of metallic Li at the electrode/separator interface, resulting in excellent cycling stability in both symmetric and full cells.

Sodium Borates: Expanding the Electrolyte Selection for Sodium‐Ion Batteries

AbstractSodium‐ion batteries (SIBs) are a promising grid‐level storage technology due to the abundance and low cost of sodium. The development of new electrolytes for SIBs is imperative since it impacts battery life and capacity. Currently, sodium hexafluorophosphate (NaPF6) is used as the benchmark salt, but is highly hygroscopic and generates toxic HF. This work describes the synthesis of a series of sodium borate salts, with electrochemical studies revealing that Na[B(hfip)4]⋅DME (hfip=hexafluoroisopropyloxy, OiPrF) and Na[B(pp)2] (pp=perfluorinated pinacolato, O2C2(CF3)4) have excellent electrochemical performance. The [B(pp)2]− anion also exhibits a high tolerance to air and water. Both electrolytes give more stable electrode‐electrolyte interfaces than conventionally used NaPF6, as demonstrated by impedance spectroscopy and cyclic voltammetry. Furthermore, they give greater cycling stability and comparable capacity to NaPF6 for SIBs, as shown in commercial pouch cells.

Sodium Borates: Expanding the Electrolyte Selection for Sodium-Ion Batteries.

Sodium‐ion batteries (SIBs) are a promising grid‐level storage technology due to the abundance and low cost of sodium. The development of new electrolytes for SIBs is imperative since it impacts battery life and capacity. Currently, sodium hexafluorophosphate (NaPF6) is used as the benchmark salt, but is highly hygroscopic and generates toxic HF. This work describes the synthesis of a series of sodium borate salts, with electrochemical studies revealing that Na[B(hfip)4]⋅DME (hfip=hexafluoroisopropyloxy, OiPrF) and Na[B(pp)2] (pp=perfluorinated pinacolato, O2C2(CF3)4) have excellent electrochemical performance. The [B(pp)2]− anion also exhibits a high tolerance to air and water. Both electrolytes give more stable electrode‐electrolyte interfaces than conventionally used NaPF6, as demonstrated by impedance spectroscopy and cyclic voltammetry. Furthermore, they give greater cycling stability and comparable capacity to NaPF6 for SIBs, as shown in commercial pouch cells.