Low-Concentration Flame-Retardant PC-Based Electrolytes for Wide-Temperature and High-Voltage Lithium-Ion Batteries

Propylene carbonate (PC) is regarded as a promising solvent for replacing ethylene carbonate due to its high dielectric constant and wide working temperature range. However, the co-intercalation behavior between PC and Li+ on graphite poses limitations to its further application. In this study, a weakly solvating solvent of methyl trifluoromethyl carbonate (FEMC) and lithium bis(oxalato)difluorophosphate (LiDODFP) synergistically enable reversible cycling of low-concentration PC-based electrolytes on graphite. Nuclear magnetic resonance spectroscopy and theoretical calculations indicate that FEMC partially substitutes PC in the solvation structure and interacts with PC through intermolecular forces, facilitating desolvation of Li+. Moreover, the utilization of LiDODFP enhances the solvation structure of Li+, effectively resolving the compatibility issue between graphite and PC. This electrolyte exhibits exceptional oxidative stability and nonflammability properties. At a cut-off voltage of 4.5 V, the NCM811/graphite full cell exhibits 88.86% capacity retention after 300 cycles at 25 °C, and retains 76.23% capacity after 100 cycles at 60 °C; even at -40 °C, it still delivers a capacity of 67 mAh g-1. This work presents a novel strategy for developing low-concentration, wide-temperature-applicable, high-safety, and high-voltage PC-based electrolytes.

Precise Synthesis of 4.75 V-Tolerant LiCoO2 with Homogeneous Delithiation and Reduced Internal Strain

The rapid advancements in 3C electronic devices necessitate an increase in the charge cutoff voltage of LiCoO2 to unlock a higher energy density that surpasses the currently available levels. However, the structural devastation and electrochemical decay of LiCoO2 are significantly exacerbated, particularly at ≥4.5 V, due to the stress concentration caused by more severe lattice expansion and shrinkage, coupled with heterogeneous Li+ intercalation/deintercalation reactions. Herein, employing the molten-salt synthesis technique, we propose a universal morphology-shaping strategy to attain bulk reaction homogeneity and reduce internal strains, even at extremely high charge voltages. The newly designed flattened polygon prismlike LiCoO2 (P-LCO) particle, featuring a regular symmetrical arrangement along the c-axis, demonstrates a more homogeneous Li+ extraction/insertion reaction, which results in a restrained transformation to detrimental O1 phase and reduced variation in lattice volume throughout the (de)lithiation processes. This benefits the mitigation of the local stress accumulation misfit dislocations and particle cracking, ultimately maintaining the mechanical stability of the cathode. Consequently, P-LCO is capable of breaking the voltage ceiling and exhibits exceptional long-term cycling capability at an ultrahigh voltage of 4.75 V. This work offers a brand-new perspective for the rational design of cathode morphology to address capacity deterioration caused by inhomogeneous delithiation and internal strain, thus inspiring the development of high-energy-density cathodes with improved durability.

Multipoint Anionic Bridge: Asymmetric Solvation Structure Improves the Stability of Lithium-Ion Batteries

In this study, a novel concept of multipoint anionic bridge (MAB) is proposed and proved, which utilizes anions with different sites to connect with the asymmetric solvation structure (ASS). Compared to usual solvation structures, this study utilizes the multifunctional groups of difluoro(oxalate)borate anion (ODFB-), which can connect with Li+. By tailoring the concentration, the anion serves as a bridge between different solvated structures. The electrolyte is investigated through in situ techniques and simulations to draw correlations between different solvation structures and reaction pathways. The proposed design demonstrates remarkable high-temperature performance on both the anode and cathode sides, enabling stable cycling of LCO||graphite (0.5 Ah, 1.0 C) pouch cell for over 200 cycles at 80 °C and facilitating Li||MCMB and Li||LFP cells to deliver stable performance for 200 cycles at 100 °C. This work paves the way for the development of high-performance electrolyte systems by designing and using new multipoint anions to construct ASSs.

Molecule Design for Non-Aqueous Wide-Temperature Electrolytes via the Intelligentized Screening Method

Operating a lithium-ion battery (LIB) in a wide temperature range is essential for ensuring a stable electricity supply amidst fluctuating temperatures caused by climate or terrain changes. Electrolyte plays a pivotal role in determining the temperature durability of batteries. However, specialized electrolytes designed for either low or high temperatures typically possess distinct features. Therefore, wide-temperature electrolytes (WTEs) are necessary as they encompass a combination of diverse properties, which complicates the clear instruction of WTE design. Here we represent an artificial intelligence (Al)-assisted workflow of WTE design through stepwise parameterizations and calculations. Linear mono-nitriles are identified as ideal wide-liquidus-range solvents that can "softly" solvate lithium ions by weak interactions. In addition, the explainable modules revealed the halogenoid similarity of cyanide as fluorine on the electrolyte properties (e.g. boiling point and dielectric constant). With the further introduction of an ether bond, 3-methoxypropionitrile (MPN) has been eventually determined as a main electrolyte solvent, enabling the battery operation from -60 to 120 °C. Particularly, a LiCoO2/Li cell using the proposed WTE can realize stable cycling with capacity retention reaching 72.3 % after 50 cycles under a high temperature of 100 °C.

Gel polymer electrolytes for rechargeable batteries toward wide-temperature applications

Rechargeable batteries, typically represented by lithium-ion batteries, have taken a huge leap in energy density over the last two decades. However, they still face material/chemical challenges in ensuring safety and long service life at temperatures beyond the optimum range, primarily due to the chemical/electrochemical instabilities of conventional liquid electrolytes against aggressive electrode reactions and temperature variation. In this regard, a gel polymer electrolyte (GPE) with its liquid components immobilized and stabilized by a solid matrix, capable of retaining almost all the advantageous natures of the liquid electrolytes and circumventing the interfacial issues that exist in the all-solid-state electrolytes, is of great significance to realize rechargeable batteries with extended working temperature range. We begin this review with the main challenges faced in the development of GPEs, based on extensive literature research and our practical experience. Then, a significant section is dedicated to the requirements and design principles of GPEs for wide-temperature applications, with special attention paid to the feasibility, cost, and environmental impact. Next, the research progress of GPEs is thoroughly reviewed according to the strategies applied. In the end, we outline some prospects of GPEs related to innovations in material sciences, advanced characterizations, artificial intelligence, and environmental impact analysis, hoping to spark new research activities that ultimately bring us a step closer to realizing wide-temperature rechargeable batteries.

Hygroscopic Solutes Enable Non-van der Waals Electrolytes for Fire-Tolerant Dual-Air Batteries

Thermal safety issues of batteries have hindered their large-scale applications. Nonflammable electrolytes improved safety but solvent evaporation above 100 °C limited thermal tolerance, lacking reliability. Herein, fire-tolerant metal-air batteries were realized by introducing solute-in-air electrolytes whose hygroscopic solutes could spontaneously reabsorb the evaporated water solvent. Using Zn/CaCl2 -in-air/carbon batteries as a proof-of-concept, they failed upon burning at 631.8 °C but self-recovered then by reabsorbing water from the air at room temperature. Different from conventional aqueous electrolytes whose irreversible thermal transformation is determined by the boiling points of solvents, solute-in-air electrolytes make this transformation determined by the much higher decomposition temperature of solutes. It was found that stronger intramolecular bonds instead of intermolecular (van der Waals) interactions were strongly correlated to ultra-high tolerance temperatures of our solute-in-air electrolytes, inspiring a concept of non-van der Waals electrolytes. Our study would improve the understanding of the thermal properties of electrolytes, guide the design of solute-in-air electrolytes, and enhance battery safety.

Electrolyte Design for Lithium-Ion Batteries for Extreme Temperature Applications

With increasing energy storage demands across various applications, reliable batteries capable of performing in harsh environments, such as extreme temperatures, are crucial. However, current lithium-ion batteries (LIBs) exhibit limitations in both low and high-temperature performance, restricting their use in critical fields like defense, military, and aerospace. These challenges stem from the narrow operational temperature range and safety concerns of existing electrolyte systems. To enable LIBs to function effectively under extreme temperatures, the optimization and design of novel electrolytes are essential. Given the urgency for LIBs operating in extreme temperatures and the notable progress in this research field, a comprehensive and timely review is imperative. This article presents an overview of challenges associated with extreme temperature applications and strategies used to design electrolytes with enhanced performance. Additionally, the significance of understanding underlying electrolyte behavior mechanisms and the role of different electrolyte components in determining battery performance are emphasized. Last, future research directions and perspectives on electrolyte design for LIBs under extreme temperatures are discussed. Overall, this article offers valuable insights into the development of electrolytes for LIBs capable of reliable operation in extreme conditions.

Hygroscopic Chemistry Enables Fire-Tolerant Supercapacitors with a Self-Healable "Solute-in-Air" Electrolyte

High-temperature-induced fire is an extremely serious safety risk in energy storage devices; which can be avoided by replacing their components with nonflammable materials. However; these devices are still destroyed by the high-temperature decomposition; lacking reliability. Here, a fire-tolerant supercapacitor is further demonstrated that recovers after burning with a self-healable "solute-in-air" electrolyte. Using fire-tolerant electrodes and separator with a semiopen device configuration; hygroscopic CaCl₂ in the air ("CaCl₂ -in-air") is designed as a self-healable electrolyte; which loses its water solvent at high temperatures but spontaneously absorbs water from the air to recover by itself at low temperatures. The supercapacitor is disenabled at 500 °C; while it recovers after cooling in the air. Especially; it even recovers after burning at around 647 °C with enhanced performance. The study offers a self-healing strategy to design high-safety; high-reliability; and fire-tolerant supercapacitors; which inspires a promising way to deal with general fire-related risks.

Concentrated Electrolytes Widen the Operating Temperature Range of Lithium-Ion Batteries

The operating temperatures of commercial lithium-ion batteries (LIBs) are generally restricted to a narrow range of -20 to 55 °C because the electrolyte is composed of highly volatile and flammable organic solvents and thermally unstable salts. Herein, the use of concentrated electrolytes is proposed to widen the operating temperature to -20 to 100 °C. It is demonstrated that a 4.0 mol L^-1 LiN(SO₂ F)₂ /dimethyl carbonate electrolyte enables the stable charge-discharge cycling of a graphite anode and a high-capacity LiNi_0.6 Co_0.2 Mn_0.2 O₂ cathode and the corresponding full cell in a wide temperature range from -20 to 100 °C owing to the highly thermal stable solvation structure of the concentrated electrolyte together with the robust and Li⁺ -conductive passivation interphase it offered that alleviate various challenges at high temperatures. This work demonstrates the potential for the development of safe LIBs without the need for bulky and heavy thermal management systems, thus significantly increasing the overall energy density.