Molecularly Engineered Li⁺ Microenvironment via Ester-Based Electrolytes for Plating-Free Fast-Charging Li-Ion Batteries

Liquid electrolytes in Li-ion batteries have been extensively developing to improve ionic conductivity, electrochemical stability, thermal stability, and safety by using various solvents, high concentration electrolytes, electrolyte additives, and lithium imide salts such as lithium bis (trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imde (LiFSI). The electrolytes extensively used in commercial Li-ion batteries are LiPF6 dissolved in some carbonate solvents such as propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC). Therefore, the optimal temperature range of the Li-ion batteries is a narrow range of 15℃-35 ℃ since Li-ion battery operated in the out of the comfortable temperature range will accelerate to degrade with serious risks of safety problems such a fire and explosion. The carbonate solvents occur the oxidation with CO2 gas generation on high-voltage cathodes such as LiCoO2, LiNi1-x-yCoxMnyO2, and LiNi0.5Mn1.5O4 under high-temperature conditions.In this work, we investigated the electrochemical and physicochemical properties of LiFSI/GBL-based electrolytes and effects of additives into the electrolytes on application to Li-ion batteries using LiNi0.8Co0.1Mn0.1O2 (NCM) cathode and TiNb2O7 (TNO) anode [1]. GBL has attractive properties of a low melting point of -43.6℃, a high boiling point of 204℃, and a high flash point of 98℃. However, Li-salt used for GBL-based electrolytes was not LiPF6 but LiBF4 [2] because LiBF4 is significantly chemical stable in GBL solvent. LiPF6 decomposes GBL, which is caused by HF generation from decomposition of LiPF6. Therefore, we have focused on LiFSI with chemical stability and high conductivity for the GBL-based electrolytes. Furthermore, we investigated the cosolvents for the GBL-based electrolyte for a decrease in the viscosity. Propyl propionate (PP) was used as the cosolvent because it has advantageous properties of only a low viscosity but also a very low melting point of -76℃ and a high boiling point of 122℃ compared to DMC and MEC. This paper reports on ionic conductivity, viscosity, self-diffusion coefficient (D Li) of Li+ ion of LiFSI/GBL-based electrolytes, and the performance of fabricated TNO/NCM pouch cells using the LiFSI/GBL/PP electrolytes with additives.Fig.1(a) and (b) show ionic conductivity of GBL electrolytes and other solvent electrolytes dependent on Li-salt concentration. The conductivity of LiFSI/GBL electrolyte was higher than that of LiTFSI/GBL and LiBF4/GBL electrolyte in all the concentration. A low-concentration LiFSI/GBL (1:10 by mol) electrolyte at a LiFSI molar fraction (XLiFSI) of 0.091exhibited the highest conductivity of 12.3 mS cm-1 at 25℃ compared to LiBF4/GBL, LiTFSI/GBL, and LiFSI-based electrolytes with other solvents of PC, DMC, DEC, and PP. Electrochemical stability of TNO and NCM electrode in the low-concentration LiFSI/GBL at XLiFSI=0.111 electrolyte was investigated by AC-impedance and liner sweep voltammetry (LSV) measurement. Impedance spectra as shown in Fig.2 indicated that a large interface resistance of the TNO electrode in the GBL electrolyte was significantly decreased by adding 2wt% fluoroethylene carbonate (FEC). The anodic dissolution of Al current collector for the NCM cathode in the electrolyte by LSV measurement was effectively suppressed by adding 2wt% lithium difluoro(oxalate)borate (LiDFOB), which overcame the strong corrosion of Al. Adding PP cosolvent into the LiFSI/GBL electrolyte decreased the viscosity and increased D Li in the electrolyte. We fabricated TNO/NCM pouch cells (70 ×100 ×1.2 mm) using LiFSI/GBL/PP and LiFSI/other solvent electrolytes at XLiFSI=0.111 with the additives. Charge-discharge cycling tests were conducted between 1.5 V and 3.0 V. The nominal capacity and voltage at 0.2 C were 900 mAh and 2.25 V, respectively. Fig.3 shows charge-discharge rate cycle performance at -20℃ of the cells with various electrolytes. Low-temperature rate capability of the cells using the LiFSI/GBL/PP electrolytes was superior to that using the DMC, PP, GBL, and PC electrolyte. It was demonstrated that the cells using the LiFSI/GBL/PP (1:2:6) electrolyte maintained high capacity with less gas generation by charge-discharge cycle tests between -20℃ and 45℃ compared to the cell using the LiFSI/DMC electrolyte. Fig.4 shows the amount and composition of each gas generated from the cells after 400 cycles at 45℃. The amount of CO2 generated from the LiFSI/GBL/PP electrolyte was 1/10th smaller than that from the DMC electrolyte, indicating that the LiFSI/GBL/PP electrolyte is electrochemical stable under a high-potential condition of the charged NCM cathode. We propose that low-concentration LiFSI/GBL/PP electrolytes with the additives of FEC and LiDFOB are promising electrolytes with high-rate, low-temperature performance, and good electrochemical stability with less gassing for wide temperature operation in Li-ion batteries.

Widespread adoption of electric vehicles (EVs) largely depends on the development of efficient battery systems having high energy density with the capability of fast charging. In this regard, lithium (Li) metal-based batteries, such as Li-Oxygen and Li-Sulfur batteries, can provide much higher energy density compared to that of Li-ion batteries. However, low rate-capability of both Li-Oxygen and Li-Sulfur cells hinders their practical utilizations. It has been found that transport limitations in the electrolyte play a major role in affecting the rate-capability of the cells. Therefore, identifying a suitable electrolyte with high ionic conductivity is an essential requirement to improve the rate-capability of these batteries. Additionally, a desired electrolyte must also be stable toward the electrode processes in the cell. Glyme-ether based electrolytes, in these instances, are a preferred class of electrolytes for both Li-Oxygen and Li-Sulfur batteries due to their acceptable compatibility with Li metal as well as with the porous carbon electrodes. Nevertheless, the length of the glyme-ethers dramatically affects the ionic conductivities of the electrolytes and decides the rate-capability of the battery. Therefore, in this work we have investigated the viability of fast Li-plating in different glyme-ether electrolytes and critically analyzed the effects of ion-transport and also assessed the relative stabilities of the electrolytes during Li stripping/plating processes.The present study involves investigation of Li stripping/plating in six different electrolytes using three glyme-ethers, diglyme (G2), triglyme (G3) and tetraglyme (G4), as the electrolyte solvents with lithium nitrate (LiNO3) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the Li salts (1 M) and lithium bromide (LiBr) as an additive (0.05 M). It has been found that the ionic conductivity of the electrolyte increases as the glyme becomes smaller or highly associated LiNO3 is replaced with LiTFSI. As a result, both smaller glymes and LiTFSI help to achieve Li-plating at faster rates. However, unfortunately, stability of Li-plating in terms of Coulombic efficiency and overall cycle-life decreases in smaller glymes or in LiTFSI as the Li salt and detailed investigations reveal formation of unstable SEI to be responsible for lower stability of Li-plating in these electrolytes. Our results show that the consequences of increasing the ionic conductivity of the electrolyte by simply changing the glyme-ether solvent in Li-metal batteries are quite complex and warrant careful consideration of their relative stabilities with the electrode. All the results, in depth analyses and future perspectives of this work will be discussed during the presentation.

Lithium/sodium-selenium (Li/Na-Se) batteries are promising energy storage systems due to their relatively low cost and high volumetric energy density of Se cathode. Rechargeable lithium-ion batteries (LIBs) play a critical role in portable devices, electric vehicles and large-scale stationary energy storage, due to their relatively high energy density and low cost among available technologies [1]. Sodium-selenium (Na-Se) batteries have also drawn much attention, because of the large abundance and low cost of sodium and decent energy density of Se [2]. As a cathode material, Se provides a moderate gravimetric capacity of 678 mAh g−1, a high volumetric capacity of 3270 mAh cm−3, and possesses a high electronic conductivity of 1 ×10 −3 S m−1 [3, 4]. These advantages of Se have stimulated growing research in developing Li-Se and Na-Se batteries over the past years. However, the practical application of these batteries has been hindered by the polyselenides dissolution (or shuttle effect phenomena), which could cause low Coulombic efficiency and poor cycling lifetime. Microporous carbon (MPC) has been fabricated through a facile carbonization method from polyvinylidene fluoride (PVDF) and used without any further activation as selenium host to produce MPC/Se composite employed as cathode in rechargeable lithium/sodium-selenium (Li/Na-Se) batteries and the electrochemical properties of the prepared cell have been investigated in Li-Se batteries. (figures 1 and 4).Basically, in linear carbonate-containing electrolytes, the metal readily decomposes at the anode side, causing capacity drop over cycling. To address this problem, electrolyte design should accompany manifested cathode structure. Hence, fluoroethylene carbonate (FEC) has been used as an additive in the electrolyte solution for stabilizing the capacity in Na-Se batteries. Our investigation showed that exceptional cell stability could be reached by using the FEC in carbonate-based electrolyte. In lithium/sodium-selenium batteries, diethyl carbonate (DEC) electrolyte decomposes in contact with metal, producing some radicals and metal alkyl carbonates. These radicals start a chain reaction, causing the destruction of over cycles. By adding the FEC to the electrolyte solution, this side reaction will be prohibited. [5] FEC readily decomposes on the surface of the metal prior to any reduction of linear carbonates, making the protective and stable surface film on the metal. This layer makes the capacity much more stable for the cell contains FEC in the electrolyte. For the cell without FEC in the electrolyte, the capacity starts to fade from initial cycles and continue fading during the cycling. In sodium/selenium batteries, at the current rate of 0.1 C, the cell contains no FEC in the electrolyte, showed a capacity of 317 and 245 mAh g-1 after 100 and 200 cycles, respectively. However, the cell with an electrolyte solution containing 3% FEC, showing excellent cyclability by way of delivering 382 and 350 mAh g-1 capacity at those above-mentioned cycles, respectively (figures 2 and 5). Another important finding was that the use of FEC additive could prevent the corrosion of metal anode from soluble polyselenides, and preserve the structural integrity of metal anode, contributing to the enhanced cycling stability and specific capacity of Na-Se batteries.The utilization of nanoscale Al2O3 surface coating by atomic layer deposition (ALD) to protect a MPC/Se cathode and reduce polyselenide dissolution was also investigated in another stage. It was found that Al2O3 surface coating effectively suppressed the polyselenide dissolution from the MPC/Se cathode, thus reducing the loss of Se active material and improving the overall performance of Na-Se batteries. Compared to the pristine MPC/Se, Al2O3-coated MPC/Se cathode exhibited improved discharge capacity, cycling stability, and rate capability in Na-Se batteries (figures 3 and 6). Keywords: Fluoroethylene carbonate; lithium/sodium−selenium batteries; ALD coating; carbonate-based electrolyte; microporous carbon

This review paper provides a comprehensive analysis of electric vehicles (EVs) and the various factors influencing fast charging technology. The surge in EV adoption has necessitated advancements in charging infrastructure, particularly in fast charging solutions. We delve into the technical aspects of fast charging, including its impact on battery life, charging station architecture, power grid integration, and charging protocols. Moreover, we discuss the influence of battery chemistry, temperature management, and charging infrastructure on the efficacy of fast charging. By synthesizing current research findings and industry trends, this paper offers insights into the challenges and opportunities for enhancing fast charging efficiency and accessibility, thereby accelerating the widespread adoption of electric vehicles.

The automotive industry is rapidly transitioning to electric vehicles (EVs) in response to the global efforts to reduce greenhouse gas emissions. Lithium-ion battery (LIB) has emerged as the main tool for energy storage in electric vehicles. A widespread adoption of EVs, however, requires a fast-charging technology that can significantly reduce charging time while avoiding any unsafe conditions including short circuits due to failure of the separator in an LIB cell. Therefore, it is necessary to understand the mechanical stresses during fast charging and their long-term effect on the integrity of the separator. This paper presents a novel hybrid model for the prediction of the stress distribution in the separator of a pouch cell under various charging speeds, ambient temperatures, and pack assembly conditions, such as compressive pressures. The proposed hybrid model consists of three sub-models, namely, an electrochemical cell model, a lumped-parameter model, and a solid mechanics model. A robust parameter identification scheme is implemented to determine the model parameters using the experimental data. The separator within the test setup will experience maximum von Mises stress of 74 MPa during 4C charging, i.e., when the charge current in A is four times as high as the capacity of the battery cell in Ah. To assess the evolution of the damage in the separator under the estimated stress during fast charging, creep and fatigue tests are conducted on the separator. Their results indicate a progressive accumulation of damage in the separator, further emphasizing the importance of understanding and mitigating mechanical degradation in separator materials.

A “dual-fluorinated” electrolyte consisting of fluoroethylene carbonate (FEC), 1H,1H,5H-Perfluoropentyl-1,1,2,2-tetrafluoroethylether (F-EAE) was investigated for 5V-class LiNi0.5Mn1.5O4 (LNMO)-based batteries. It is found that the synergistic effect of two fluorinated solvents brings about high oxidation durability of exceeding 5 V (vs Li+/Li), and then excellent cycle performance with the capacity retention of ∼92% after 200 cycles at the cutoff voltage of 5 V, far beyond conventional carbonate-based electrolyte and another “mono-fluorinated” electrolyte merely with F-EAE. The SEM, TEM and XPS test reveal that a uniform and F/P-contained surface film exists in the cycled LNMO cathode in the “dual-fluorinated” electrolyte, possibly derived from the interactivity of two fluorinated solvents under the high voltage environment. It is further stressed that that the suitable interface modification on the cathode is another important factor for the long-term and stable cycling at 5 V operation besides the oxidation-resistivity of the electrolyte self.

Promoting electrochemical rates by concurrent ionic-electronic conductivity enhancement in high mass loading cathode electrode

Li metal batteries (LMBs) employing high voltage cathodes show promise as next generation batteries for electric vehicles due to their high energy density. However, the cycling stability of such energy-dense LMBs at high charge rates has seldom been explored. In this work, Li Coulombic efficiency (CE) as a function of current density (i.e., C-rate) and temperature was investigated in ether-based highly concentrated electrolytes (HCEs). We found that Li metal anodes can be stably cycled in the HCEs at elevated temperatures with a high Li CE of >99.4% for a plating capacity of 3 mAh cm−2 at a high C-rate greater than 1 C. The cycling stability of LMB full cells with Li(Ni0.8Co0.1Mn0.1)O2 (NMC811) cathodes was also investigated at different charge rates (1 C to 3 C) at 40 and 60 °C. The LMBs with high areal capacity (∼3.2 mAh cm−2) NMC811 cathodes and minimal Li excess anodes (negative/positive capacity ratio (N/P ratio) <3.1) can achieve ∼189 stable cycles with an average efficiency of ∼99.86% at 1 C charge and C/3 discharge at 60 °C.

Fast charging (at rates greater than 4 C) is essential for high-energy lithium-ion batteries in electric vehicles yet remains challenging owing to a lack of understanding of fast-charging barriers. Conventional optimization strategies concentrate on shortening lithium-ion transport pathways through electrode structure modification, which often compromises energy densities. In this work, we demonstrate that thick-electrode fast charging is constrained by solvent withdrawal within porous electrodes and the resulting electro-osmotic drag polarization, which is driven by cation-induced electro-osmotic drag. To reduce electro-osmotic drag polarization, we designed electrolytes with weak cation solvation and strong anion solvation, where a difluorinated solvent weakens lithium-cation solvation and its difluoromethyl hydrogen atoms enhance anion solvation through hydrogen bonding. This electrolyte enables thick-electrode, energy-dense batteries to achieve 80% charge within 13 minutes.

The electric vehicle's most crucial component is its battery, which provides the vehicle with power. A key element of electric vehicles (EVs) is the battery management system (BMS), which ensures the safe and efficient functioning of the battery pack. Previous research on electric vehicles has identified some drawbacks, such as lengthy charging times and the need for different charging methods depending on battery capacity and temperature. In the proposed work, the battery's state of charge and remaining capacity will be estimated by measuring the voltage and current with the use of a current sensor and temperature monitor. The novelty of the work lies in its ability to increase the range of electric vehicles. This is achieved through higher energy densities in high-voltage batteries, which allow for longer driving distances between charges. Additionally, faster charging systems can handle higher charging power levels, resulting in quicker charging times. These improvements in performance are made possible by the use of high-voltage batteries, which provide the necessary power for greater peak speeds and improved acceleration. As electric mobility becomes more widespread, the ability to accurately predict charging times based on layout becomes crucial in building user confidence, optimizing energy grid management, and promoting the widespread adoption of electric vehicles.

Automotive manufacturers are working to improve cell and pack design by increasing their performance, durability, and range. One of the critical factors to consider as the industry moves towards materials with higher energy density is the ability to consider the irreversible volume change characteristic of the accelerated SEI layer growth tied to the large volume change and particle cracking typically associated with active material strain. Here, we add to a previously developed mechano-electrochemical model[1-8] to more practically understand the impact of irreversible volume change, primarily assigned to SEI layer growth. As the time from initial design to manufacture of electric vehicle is decreased in order to rapidly respond to consumer demands and widespread adoption of electric vehicles, the ability to link aging and volume change to end of life vehicle requirements using virtual tools is critical.[9] In this study[10], we apply a model to determine the irreversible volume change at the electrode and cell level, allowing for virtual design iterations to predict the volume change at battery cell aged states, and probe possible changes in the SEI layer over life.

Fast charging of lithium-ion battery using multistage charging and optimization with Grey relational analysis

With the rapid advancement of energy storage technologies and the widespread adoption of electric vehicles (EVs), the demand for high-energy-density rechargeable batteries is growing exponentially. Lithium metal batteries (LMBs) have emerged as promising candidates for next-generation energy storage due to their high specific energy, exceeding 350 Wh kg⁻¹. However, conventional LMBs employing liquid electrolytes suffer from limited cycle life and poor safety, primarily due to non-uniform lithium deposition and dendritic lithium growth. Therefore, constructing a robust and stable solid electrolyte interphase (SEI) is crucial to suppress parasitic side reactions and inhibit dendrite formation. Gel polymer electrolytes (GPEs) have gained attention as an effective strategy, as they can modulate the Li⁺ solvation sheath through interactions with functional groups in the polymer matrix, facilitating the formation of a stable, anion-derived, inorganic-rich SEI. In this study, a multifunctional acrylate crosslinker-based GPE was designed to regulate the Li⁺ solvation environment and promote the formation of a stable SEI. Fourier-transform infrared (FT-IR), Raman, and nuclear magnetic resonance (NMR) spectroscopy revealed a more aggregated solvation configuration of Li⁺ in the GPE. This optimized solvation structure leads to enhanced lithium plating morphology and stable SEI formation, as confirmed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Furthermore, the acrylate-based GPE exhibits a higher Li⁺ transference number than conventional liquid electrolytes. As a result, Li/GPE/LiNi₀.₈Co₀.₁Mn₀.₁O₂ cells achieved superior electrochemical performance, retaining 70% of their initial capacity after 160 cycles at 1.0 C under a high mass loading of 20 mg cm⁻² at 25 °C. These findings underscore the potential of acrylate-based GPEs to enable the practical application and commercialization of high-energy-density LMBs.

While the idea that fast charging batteries could be utilized in electric vehicles is enticing, current fast charging batteries face significant challenges that must be mitigated before this application is realized. Fast charging batteries currently suffer from capacity loss and degradation over time which not only affects battery life but poses a safety hazard. The current electrolyte, 1.2 M LiPF6 in 3:7 wt.% EC/EMC (Gen2), contains the salt LiPF6 that when exposed to moisture can form dangerous hydrofluoric acid and contains a carbonate-based solvent that when exposed to oxygen can ignite. In addition, batteries experience degradation over many cycles of fast charging which results in capacity fade and poor battery performance. However, previous studies have shown the potential for other electrolyte systems to mitigate these problems, specifically by using highly concentrated electrolytes1. These studies claim that using these electrolytes results in the formation of a solid electrolyte interphase (SEI) that passivates Li ions better than the Gen2 electrolyte. The SEI is a layer that forms on the anode within the battery and serves as a protective layer that allows for Li intercalation into graphite and can therefore protect against degradation. By using different electrolytes, a different SEI is formed, and different degradation mechanisms are observed. In this way, the SEI can be tuned to improve Li passivation and ionic conductivity by changing the electrolyte’s composition and concentration2. This research focuses on such alternative electrolyte systems and aims to characterize the different degradation mechanisms corresponding to each electrolyte. Favorable performance has been observed using 1.2 M LiFSI in 3:7 wt.% EC/EMC as an electrolyte. We are studying LiFSI in acetonitrile (AN) at higher concentrations than traditional Gen2 to quantify the SEI. We expect AN to form an anion derived SEI, a composition of which results in improved passivation of Li ions1. In this study, we characterize degradation of alternative electrolyte systems through x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Through these methods we can observe and quantify both crystalline, amorphous degradation products due to loss of Li inventory and loss of active material. XPS allows quantification of compositional changes in the SEI layer at the surface of the electrode. The SEM provides qualitative information on degradation such as visualizing lithium plating and dendrite formation. We implement quantitative XRD to measure the crystalline phases of the graphite anode, showing the degree of lithium intercalation and further quantifying degradation such as Li plating. Putting the results of these three characterization techniques together in tandem with electrochemical cycling data paints a picture of the degradation that happens on the anode of a fast-charging lithium-ion battery with respect to electrolyte composition.[1] Yamada, Y., Wang, J., Ko, S., Watanabe, E., & Yamada, A. (2019). Advances and issues in developing salt-concentrated battery electrolytes. Nature Energy. [2] Logan, E. R., & Dahn, J. R. (2020). Electrolyte Design for Fast-Charging Li-ion Batteries. Trends in Chemistry.

To meet the growing demand for energy storage, lithium-ion batteries (LIBs) with fast charging capabilities has emerged as a critical technology. The electrode materials affect the rate performance significantly. Organic electrodes with structural flexibility support fast lithium-ion transport and are considered promising candidates for fast-charging LIBs. However, it is a challenge to create organic electrodes that can cycle steadily and reach high energy density in a few minutes. To solve this issue, accelerating the transport of electrons and lithium ions in the electrode is the key. Here, it is demonstrated that a ferrocene-based polymer electrode (Fc-SO3Li) can be used as a fast-charging organic electrode for LIBs. Thanks to its molecular architecture, LIBs with Fc-SO3Li show exceptional cycling stability (99.99% capacity retention after 10 000 cycles) and reach an energy density of 183Wh kg-1 in 72 seconds. Moreover, the composite material through insitu polymerization with Fc-SO3Li and 50 wt % carbon nanotube (denoted as Fc-SO3Li-CNT50) achieved optimized electron and ion transport pathways. After 10000 cycles at a high current density of 50C, it delivered a high energy density of 304Wh kg-1. This study provides valuable insights into designing cathode materials for LIBs that combine high power and ultralong cycle life.