Solvent-Mediated Electrolyte Design for Calcium Metal Batteries

Current electrolytes for calcium batteries (CaBs) rely on cumbersome salt synthesis, hindering research and development. As a subclass of CaBs, calcium metal batteries (CMBs) could potentially offer high energy density due to their use of a calcium anode. However, realizing this advantage remains difficult, largely due to calcium’s electrochemical instability. To address these challenges, we introduce a family of electrolytes made entirely from commercially accessible Ca-salts and solvent mixtures and further demonstrate stable cycling of symmetric Ca||Ca cells using only a solvent mixture, without added salt (i.e., not being an electrolyte on its own). Notably, this cycling stability extends to CMB full cells using low salt concentration electrolytes (e.g., 0.1 M Ca(OTf)2 in NMA:TMP), and similar full cell performance is also achieved using other combinations of salts and solvent mixtures. Extensive electrochemical testing confirms stable cycling under diverse and challenging conditions. Overall, our findings reframe electrolyte design principles and pave the way for practically useful CMB cells.

0.2 M Low Concentration Electrolytes (LCEs) for lithium‐based batteries formed from lithium salts with very weakly coordinating anions, i.e., the aluminate Li[Al{OC(CF 3 ) 3 } 4 ] and the gallate Li[Ga(C 2 F 5 ) 4 ] in ortho ‐difluorobenzene ( o ‐DFB), showed competitive conductivity to classical electrolytes of up to 5.0 mS cm −1 at 25 °C combined with electrochemical stability at least up to 4.5 V vs. Li/Li + . Given that a stoichiometric amount of 2 equivalents dimethoxyethane (DME) per lithium ion (as Li + complexing agent) and 2 wt.% fluoroethylene carbonate (as solid electrolyte interphase (SEI) former) were present in the LCEs, half and full‐cell measurements confirmed stable LCE cycling over 300 cycles in Lithium‐Ion‐Batteries. Even at high currents (5C), the discharge retained two thirds of the practical 1C capacities of NMC622. By contrast, a LCE made from 0.2 M LiPF 6 in EC/EMC 3:7 solution already led at a 2C rate to cell death, while a simple switch of the conducting salt to 0.2 M Li[Al{OC(CF 3 ) 3 } 4 ] led to stable cycling including rate tests for over 300 cycles and approached closely the values of the standard 1.0 M LiPF 6 electrolyte in EC/EMC 3:7 – attributed to the anions’ stability. The performance of the aluminate LCE was further evaluated in symmetrical Li‐Li cells and Lithium‐Metal‐Batteries containing 48 µm thin Lithium‐Metal‐Anodes (LMAs): LCEs improved the cell's lifetime by a factor of 3–6 at a current density of 1 mA cm −2 . Scanning electron microscope/energy‐dispersive X‐ray and potentiostatic electrochemical impedance spectroscopy measurements confirmed the exceptional stabilization of the LMAs by the aluminate LCE throughout the cycling, especially when combined with an artificial, adaptive and self‐healing SEI based on Li[PO 2 (OCH 2 CF 3 ) 2 ]. The solvation structure of standard and LCEs was investigated by NMR spectroscopic diffusion measurements and quantum chemical calculations. A three‐to‐fourfold increased Li ion mobility was found in LCEs compared to the system with 0.2 M LiPF 6 in standard carbonate solution. The presence of stable and compact Li(DME) 2 + structures as moving ions was shown and the relevance of Li + ions solvated with fluoro‐ethylene carbonate or o ‐DFB for SEI‐formation is discussed.

Density functional theory calculations for ethylene carbonate-based binary electrolyte mixtures in lithium ion batteries

Objective: The goals of this article are to (1) identify the incidence of reported laboratory abnormalities in patients in the medical intensive care unit (ICU); (2) characterize the relationship between reported laboratory abnormalities and Acute Physiology and Chronic Health Evaluation III (APACHE III) score, length of stay, and mortality; and (3) evaluate therapeutic replacement in patients with electrolyte abnormalities. Design: Retrospective chart review of all patients admitted to the medical ICU between April 1, 1993 and June 30, 1993. Setting: Large teaching institution. Participants: Patients admitted to the medical ICU (n = 116). Interventions: The following data were collected: age, sex, admitting diagnosis, serum electrolyte and laboratory parameters, APACHE HI score, length of ICU stay, and mortality. Results: Ten individual laboratory abnormalities were found in more than 30% of all patients in the medical ICU (range 32.8–59.5%). Abnormalities in four laboratory parameters were associated with undesirable patient outcomes. Patients with hypoalbuminemia had a significantly higher APACHE HI score (p < 0.05). Hypocalcemia, hypomagnesemia, and hypoalbuminemia all were associated with an increased length of stay in the ICU (p < 0.05). Overall mortality was significantly higher in patients with alkalosis (p = 0.002). Therapeutic replacement in those with low electrolyte concentrations often was delayed or missed. Fifteen to 75% of patients who had abnormally low serum electrolyte concentrations were not treated. Conclusions: A high incidence of laboratory abnormalities is reported in patients admitted to the medical ICU. Several of these abnormalities are associated with undesirable outcomes such as an increased length of ICU stay in patients with hypoalbuminemia, hypocalcemia, and hypomagnesemia and increased mortality in patients with alkalosis. Therapeutic replacement of electrolytes in patients with abnormalities often was delayed or missed.

Electrochemical instability of room-temperature ionic liquids with LiTFSI at elevated temperature and its consequences in Li/Li-ion based half-cells and full-cells

While the formation of an inorganic-rich solid electrolyte interphase (SEI) plays a crucial role, the persistent challenge lies in the formation of an organic-rich SEI due to the high solvent ratio in low-concentration electrolytes (LCEs), which hinders the achievement of high-performance lithium metal batteries. Herein, by incorporating di-fluoroethylene carbonate (DFEC) as a non-solvating cosolvent, a solvation structure dominated by anions is introduced in the innovative LCE, leading to the creation of a durable and stable inorganic-rich SEI. Leveraging this electrolyte design, the Li||NCM83 cell demonstrates exceptional cycling stability, maintaining 82.85% of its capacity over 500 cycles at 1 C. Additionally, Li||NCM83 cell with a low N/P ratio (≈2.57) and reduced electrolyte volume (30µL) retain 87.58% of its capacity after 150 cycles at 0.5 C. Direct molecular information is utilized to reveal a strong correlation between solvation structures and reduction sequences, proving the anion-dominate solvation structure can impedes the preferential reduction of solvents and constructs an inorganic-rich SEI. These findings shed light on the pivotal role of solvation structures in dictating SEI composition and battery performance, offering valuable insights for the design of advanced electrolytes for next-generation lithium metal batteries.

Sulfide-based lithium (Li)-ion conductors represent one of the most popular solid electrolytes (SEs) for solid-state Li metal batteries (SSLMBs) with high safety. However, the commercial application of sulfide SEs is significantly limited by their chemical instability in air and electrochemical instability with electrode materials (metallic Li anode and oxide cathodes). To address these difficulties, here, we design and successfully demonstrate a novel sulfide-incorporated composite electrolyte (SCE) through the combination of inorganic sulfide Li argyrodite (Li7PS6) with poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) polymer. In this composite structure, Li7PS6 is embedded in PVDF-HFP polymer matrix, making the SCE flexible and air-stable and achieve great chemical and electrochemical stability. Meanwhile, the presence of sulfide facilitates Li-ion transport in SCE, leading to a superior room-temperature ionic conductivity of 1.1 × 10-4 S cm-1. Using the SCE with enhanced stability while maintaining high conductivity, Li||Li symmetric cells achieved stable cycling up to 1000 h at 0.2 mA cm-2. In addition, LiFePO4 (LFP)||SCE||Li cells can deliver an impressive specific capacity of 160 mAh g-1 over 150 cycles. These features indicate that Li7PS6/PVDF-HFP SCE is a promising candidate to contribute to the practical development of SSLMBs.

Cell-nucleus structured electrolyte for low-temperature aqueous zinc batteries

Lithium-Sulfur-Batteries (LSBs) have been discussed as one of the most promising post-lithium-ion-battery technologies in literature for the last decade due to their high theoretical specific energy of 2600 Wh/kg. However, several drawbacks still exist in case of liquid LSB-concepts, especially cycling stability with low electrolyte excess in combination with a reasonable sulfur utilization plus cycle stability still hinders the commercial breakthrough of this battery technology. One main reason for both issues is the dissolution of the active material, sulfur, as polysulfides in the electrolyte, which leads to the so-called polysulfide shuttle that comprises polysulfide diffusion through the cell to the lithium metal anode resulting in decomposition reactions, and therefore, loss of active material. Several electrolyte approaches in order to limit polysulfide dissolution have been developed over the last 5-10 years, however, those electrolyte formulations usually lead to a strong lithium metal corrosion. Electrolytes that enable stable cycling of lithium metal batteries in combination with a nickel manganese cobalt oxide cathode have been successfully developed, however, they are ususally not compatible with the polysulfides of Li-S batteries. Hence, decoupling the anolyte from the catholyte has been much desirable. Recently introduced solid-state lithium sulfur batteries based on sulfidic solid electrolytes might overcome some challenges of conventional liquid LSBs since no formation or diffusion of polysulfide species can take place, and very high sulfur utilization have been already reached. However, solid-state LSBs have not been cycleable so far when a thin layer of solid electrolyte and lithium metal anode (without indium) were employed, especially in pouch cells, due to the formation of lithium dendrites, resulting in short circuits.Herein, a completely new battery design, a “semi-solid”-LSB, is presented. The concept combines the advantages of liquid and solid state LSBs. On the cathode side, an electrode comprising carbon, sulfur and sulfidic solid electrolyte (argyrodite) enables a solid to solid conversion of sulfur resulting in a complete suppression of the polysulfide shuttle.On the anode side, a liquid electrolyte enabling stable cycling of a lithium metal anode is employed. A careful design of the liquid electrolyte is crucial in order to obtain high stability of the liquid electrolyte against the lithium metal anode as well as to avoid side reaction between the solid electrolyte of the cathode and the liquid electrolyte. Different electrolytes are discussed for the new cell design and proof of concept was successfully reached in coin cells leading to 100 cycles with a stable coulombic efficiency of over 99 % which outperforms the majority of previously published Li-S cycling data. In addition, the concept was also transferred into first semi-solid lithium sulfur-pouch cells which is an important step in the direction of practical applications.

The practical application of solid polymer electrolytes in high-energy Li metal batteries is hindered by Li dendrites, electrochemical instability and insufficient ion conductance. To address these issues, flexible composite polymer electrolyte (CPE) membranes with three dimensional (3D) aramid nanofiber (ANF) frameworks are facilely fabricated by filling polyethylene oxide (PEO)-lithium bis(trifluoromethylsulphonyl)imide (LiTFSI) electrolyte into 3D ANF scaffolds. Because of the unique composite structure design and the continuous ion conduction at the 3D ANF framework/PEO-LiTFSI interfaces, the CPE membranes show higher mechanical strength (10.0 MPa), thermostability, electrochemical stability (4.6 V at 60°C) and ionic conductivity than the pristine PEO-LiTFSI electrolyte. Thus, the CPEs display greatly improved interfacial stability against Li dendrites (≥1000 h at 30°C under 0.10 mA cm−2 ), compared with the pristine electrolyte (short circuit in 13 h). The CPE-based all-solid-state LiFePO4/Li cells also exhibit superior cycling performance (e.g., 130 mA h g−1 with 93% retention after 100 cycles at 0.4 C) than the ANF-free cells (e.g., 82 mA h g−1 with 66% retention). This work offers a simple and effective way to achieve high-performance composite electrolyte membranes with 3D nanofiller framework for promising solid-state Li metal battery applications.

Ternary metal oxide filled PEO-based polymer electrolyte for solid-state lithium metal battery: The role of filler particle size

Lithium ion batteries have dominated the portable electronics market and have the potential to dominate large-scale battery applications including hybrid and electric vehicles as well as grid storage because of their high energy and power densities.[1] It is well known that conventional electrolytes (such as 1.2 M LiPF6 in EC/EMC 3/7) show poor anodic stabilities above 4.5 V versus Li/Li+.[2] However, high voltage electrolytes play an intrinsic role in many applications such as hybrid and electrical vehicles, aerospace uses and power grids. As a result, high voltage electrolytes are essential for the development of next generation lithium ion batteries. One possible solution is to develop fluorinated electrolytes which not only form kinetically stable SEI interphase, but also are resistant to oxidative decomposition due to their high oxidation potential. [3] In this work, a novel fluorinated electrolyte was introduced in a graphite-LiNi0.5Mn0.3Co0.2O2 full cell operated between 3.0 - 4.6 V. The electrolyte contains 1.0 M LiPF6 dissolved in a mixture of FEC and HFDEC solvent with 1wt % LiDFOB used as the additive. Compared to a conventional EC and EMC based electrolyte, the fluorinated electrolyte shows an excellent cycle life under a 4.6V cut off voltage. NMR and GC-MS were used to analyze the harvested electrolyte post-cycling while SEM, XPS and FTIR were employed to study the interface between the electrolyte and the bulk electrodes. Most importantly, HR-XRD and XANS were conducted to investigate and compare the cycled bulk cathode electrode in different electrolytes. To the best of our knowledge, the structural change of the cycled cathode material in different electrolytes has never been reported. Therefore, we believe this research is a crucial breakthrough for studying the interaction between the electrolyte and electrode. The methodology developed could be fundamental in the design and investigation of better electrolytes for next generation lithium ion batteries. [1]Xu, Kang. "Nonaqueous liquid electrolytes for lithium-based rechargeable batteries." Chemical reviews 104.10 (2004): 4303-4418. [2] Xu, Kang. "Electrolytes and interphases in Li-ion batteries and beyond." Chemical reviews 114.23 (2014): 11503-11618. [3] Zhang, Zhengcheng, et al. "Fluorinated electrolytes for 5 V lithium-ion battery chemistry." Energy Environ. Sci. 6.6 (2013): 1806-1810.

Electrolytes are essential for the proper functioning of any battery technology and the emerging Na-ion technology is no exception. Hence, a major focus on battery research is to identify the most appropriate formulation so as to minimize interface reactions and enhance both cell performances and safety aspects. In order to identify suitable electrolyte formulations for Na-ion chemistry we benchmarked various electrolytes containing diverse solvent mixtures (cyclic, acyclic carbonates, glymes) and Na-based salts having either F-based or perchlorate anions and measured viscosity, ionic conductivity, and thermal and electrochemical stability. The binary EC:PC solvent mixture has emerged as the best solvent formulation and has been used to test the performance of Na/hard carbon cells with both NaClO4 and NaPF6 as dissolved salts. Hard carbon electrodes having reversible capacities of 200 mA h g−1 with decent rate capability and excellent capacity retention (>180 cycles) were demonstrated. Moreover, DSC heating curves demonstrated that fully sodiated hard carbon cycled in NaPF6–EC:PC exhibits the highest exothermic onset temperature and nearly the lowest enthalpy of reaction, thus making this electrolyte most attractive for the development of Na-ion batteries.

A route to a more sustainable nickel composite electrodeposit, using turmeric and a new low nickel ion concentration electrolyte

Properties of the solid-electrolyte interphase (SEI) strongly effects the morphology, features and overall performance of the Lithium metal anode (LMA). It is well accepted but least understood that the formation mechanism of SEI is correlated with the electrolyte solvation structure. Here, synchrotron X-ray diffraction (XRD), pair distribution function (PDF) analysis, and molecular dynamic (MD) simulation are employed to obtain direct insight to the correlation between electrolyte solvation structure and interphasial chemistry. Systems of lithium bis(fluorosulfonyl)imide in propylene carbonate, dimethyl carbonate, and dimethoxyethane at both low (1M) and high (5 M) salt concentrations are studied. While solvents dominate in the solvation structure for low concentration electrolytes (LCE), a large number of anions enter the solvation shell in high concentration electrolytes (HCE). Quantification of crystalline phases in the bulk SEI reveal that while dendrites are the dominant phases for SEI of LCE, their formation is significantly suppressed in SEI of HCE. Highly nano-sized LiF, Li2O, and LiOH are dominant crystalline phases in SEI of HCE. The SEI of HCE is also very rich in oligomers resulting from anion decomposition. The small crystallites and amorphous oligomers promise fast Li ion conduction in the SEI and therefore a superior electrochemical performance of LMA.