Switching Electrolyte Interfacial Model to Engineer Solid Electrolyte Interface for Fast Charging and Wide-Temperature Lithium-Ion Batteries

A Weakly Solvating Ether Electrolyte Enables Fast-Charging and Wide-Temperature Lithium-Ion Pouch Cells

Graphite-based lithium-ion batteries have succeeded greatly in the electric vehicle market. However, they suffer from performance deterioration, especially at fast charging and low temperatures. Traditional electrolytes based on carbonated esters have sluggish desolvation kinetics, recognized as the rate-determining step. Here, a weakly solvating ether electrolyte with tetrahydropyran (THP) as the solvent is designed to enable reversible and fast lithium-ion (Li+) intercalation in the graphite anode. Unlike traditional ether-based electrolytes which easily cointercalate into the graphite layers, the THP-based electrolyte shows fast desolvation ability and can match well with the graphite anode. In addition, the weak interconnection between Li+ and THP allows more anions to come into the solvating shell of Li+, inducing an inorganic-rich interface and thus suppressing the side reactions. As a result, the lithium iron phosphate/graphite pouch cell (3 Ah) with the THP electrolyte shows a capacity retention of 80.3% after 500 cycles at 2 C charging, much higher than that of the ester electrolyte system (7.6% after 200 cycles). At 4 C charging, the discharging capacity is increased from 2.29 Ah of esters to 2.96 Ah of THP. Furthermore, the cell can work normally over wide working temperatures (-20 to 60 °C). Our electrolyte design provides some understanding of lithium-ion batteries at fast charging and wide temperatures.

Low-Temperature and Fast-Charging Lithium Metal Batteries Enabled by Solvent-Solvent Interaction Mediated Electrolyte

Lithium metal batteries utilizing lithium metal as the anode can achieve a greater energy density. However, it remains challenging to improve low-temperature performance and fast-charging features. Herein, we introduce an electrolyte solvation chemistry strategy to regulate the properties of ethylene carbonate (EC)-based electrolytes through intermolecular interactions, utilizing weakly solvated fluoroethylene carbonate (FEC) to replace EC, and incorporating the low-melting-point solvent 1,2-difluorobenzene (2FB) as a diluent. We identified that the intermolecular interaction between 2FB and solvent can facilitate Li+ desolvation and lower the freezing point of the electrolyte effectively. The resulting electrolyte enables the LiNi0.8Co0.1Mn0.1O2||Li cell to operate at -30 °C for more than 100 cycles while delivering a high capacity of 154 mAh g-1 at 5.0C. We present a solvation structure and interfacial model to analyze the behavior of the formulated electrolyte composition, establishing a relationship with cell performance and also providing insights for the electrolyte design under extreme conditions.

Wide Temperature Electrolytes for Lithium Batteries: Solvation Chemistry and Interfacial Reactions

Improving the wide-temperature operation of rechargeable batteries is crucial for boosting the adoption of electric vehicles and further advancing their application scope in harsh environments like deep ocean and space probes. Herein, recent advances in electrolyte solvation chemistry are critically summarized, aiming to address the long-standing challenge of notable energy diminution at sub-zero temperatures and rapid capacity degradation at elevated temperatures (>45°C). This review provides an in-depth analysis of the fundamental mechanisms governing the Li-ion transport process, illustrating how these insights have been effectively harnessed to synergize with high-capacity, high-rate electrodes. Another critical part highlights the interplay between solvation chemistry and interfacial reactions, as well as the stability of the resultant interphases, particularly in batteries employing ultrahigh-nickel layered oxides as cathodes and high-capacity Li/Si materials as anodes. The detailed examination reveals how these factors are pivotal in mitigating the rapid capacity fade, thereby ensuring a long cycle life, superior rate capability, and consistent high-/low-temperature performance. In the latter part, a comprehensive summary of in situ/operational analysis is presented. This holistic approach, encompassing innovative electrolyte design, interphase regulation, and advanced characterization, offers a comprehensive roadmap for advancing battery technology in extreme environmental conditions.

Electrolyte-Induced Morphology Evolution to Boost Potassium Storage Performance of Perylene-3,4,9,10-tetracarboxylic Dianhydride

Organic materials have attracted extensive attention for potassium-ion batteries due to their flexible structure designability and environmental friendliness. However, organic materials generally suffer from unavoidable dissolution in aprotic electrolytes, causing an unsatisfactory electrochemical performance. Herein, we designed a weakly solvating electrolyte to boost the potassium storage performance of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA). The electrolyte induces an in situ morphology evolution and achieves a nanowire structure. The weakly dissolving capability of ethylene glycol diethyl ether-based electrolyte and unique nanowire structure effectively avoid the dissolution of PTCDA. As a result, PTCDA shows excellent cycling stability (a capacity retention of 89.1% after 2000 cycles) and good rate performance (70.3 mAh g-1 at 50C). In addition, experimental detail discloses that the sulfonyl group plays a key role in inducing morphology evolution during the charge/discharge process. This work opens up new opportunities in electrolyte design for organic electrodes and illuminates further developments of potassium-ion batteries.

40 Years of Low-Temperature Electrolytes for Rechargeable Lithium Batteries

Rechargeable lithium batteries are one of the most appropriate energy storage systems in our electrified society, as virtually all portable electronic devices and electric vehicles today rely on the chemical energy stored in them. However, sub-zero Celsius operation, especially below -20 °C, remains a huge challenge for lithium batteries and greatly limits their application in extreme environments. Slow Li+ diffusion and charge transfer kinetics have been identified as two main origins of the poor performance of RLBs under low-temperature conditions, both strongly associated with the liquid electrolyte that governs bulk and interfacial ion transport. In this review, we first analyze the low-temperature kinetic behavior and failure mechanism of lithium batteries from an electrolyte standpoint. We next trace the history of low-temperature electrolytes in the past 40 years (1983-2022), followed by a comprehensive summary of the research progress as well as introducing the state-of-the-art characterization and computational methods for revealing their underlying mechanisms. Finally, we provide some perspectives on future research of low-temperature electrolytes with particular emphasis on mechanism analysis and practical application.

Full-Dimensional Analysis of Electrolyte Decomposition on Cathode-Electrolyte Interface: Establishing Characterization Paradigm on LiNi0.6Co0.2Mn0.2O2 Cathode with Potential Dependence

Cathode electrolyte interphase (CEI) layers derived from electrolyte oxidative decomposition can passivate the cathode surface and prevent its direct contact with electrolyte. The inorganics-dominated inner solid electrolyte layer (SEL) and organics-rich outer quasi-solid-electrolyte layer (qSEL) constitute the CEI layer, and both merge at the junction without a clear boundary, which assures the CEI layer with both ionic-conducting and electron-blocking properties. However, the typical "wash-then-test" pattern of characterizations aiming at the microstructure of CEI layers would dissolve the qSEL and even destroy the SEL, leading to an overanalysis of electrolyte decomposition pathway and misassignment of CEI architecture (e.g., component and morphology). In this study, we established a full-dimensional characterization paradigm (combining Fourier transform infrared, solution NMR, X-ray photoelectron spectroscopy, and mass spectrometry technologies) and reconstructed the original CEI layer model. Besides, the feasibility of this characterization paradigm has been verified in a wide operating voltage range on a typical LiNi_xMn_yCo_zO₂ cathode.

Non-Flammable Electrolyte Enables High-Voltage and Wide-Temperature Lithium-Ion Batteries with Fast Charging

Electrolyte design has become ever more important to enhance the performance of lithium-ion batteries (LIBs). However, the flammability issue and high reactivity of the conventional electrolytes remain a major problem, especially when the LIBs are operated at high voltage and extreme temperatures. Herein, we design a novel non-flammable fluorinated ester electrolyte that enables high cycling stability in wide-temperature variations (e.g., -50 °C-60 °C) and superior power capability (fast charge rates up to 5.0 C) for the graphite||LiNi_0.8 Co_0.1 Mn_0.1 O₂ (NCM811) battery at high voltage (i.e., >4.3 V vs. Li/Li⁺ ). Moreover, this work sheds new light on the dynamic evolution and interaction among the Li⁺ , solvent, and anion at the molecular level. By elucidating the fundamental relationship between the Li⁺ solvation structure and electrochemical performance, we can facilitate the development of high-safety and high-energy-density batteries operating in harsh conditions.

Inner Lithium Fluoride (LiF)-Rich Solid Electrolyte Interphase Enabled by a Smaller Solvation Sheath for Fast-Charging Lithium Batteries

Fast-charging lithium-ion batteries (LIBs) have been severely hampered by the slow development of their electrolytes. Herein, we demonstrate that the size effect of solvent sheath would pose a great effect on the fast-charging performance of LIBs. Three similar ethers, including diethyl ether (DEE), dipropyl ether (DPE), and dibutyl ether (DBE), were mixed with 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) and lithium bis(fluorosulfonyl)imide (1 M) to form an electrolyte for fast-charging LIBs, respectively. The results showed that it is more difficult to form ternary graphite intercalation compounds (GICs) in the electrolyte with a larger solvation sheath. The DEE electrolyte can form stable GICs and generate an inner LiF-rich solid electrolyte interphase (SEI), lowering the diffusion barrier of Li⁺. Therefore, the graphite anode powered by the DEE electrolyte can maintain a capacity of 190 mAh g^-1 at 4 C after 500 cycles. This kind of size effect of solvation sheath is also applicable to lithium metal batteries.