40 Years of Low-Temperature Electrolytes for Rechargeable Lithium Batteries

Conjugated Nitroxide Radical Polymer with Low Temperature Tolerance Potential for High-Performance Organic Polymer Cathode

Low-temperature operation poses a significant challenge for current commercial rechargeable lithium-ion batteries (LIBs). Organic polymer electrode materials, exhibiting a nonintercalation redox mechanism, offer a viable solution to mitigate the decline in electrochemical performance at low temperatures in LIBs. Herein, a radical polymer P(DATPAPO-TPA) with a conjugated nitrogen-rich triphenylamine derivative as the backbone and high-density nitroxide pendants has been synthesized. Due to the large interstitial spaces between adjacent structural units and polymer chains, resulting from the significant torsion angle between the benzene rings in the P(DATPAPO-TPA) skeleton, ions could effectively transport. This structural feature demonstrated a notable discharge capacity of 143.3 mA h·g-1 and a high charge-discharge plateau at ∼3.75 V vs Li+/Li, outperforming most reported radical polymer cathode materials. In addition, its capacity retention could reach 83.1% after 2000 cycles at an ultrahigh current density of 50 C, showing excellent rate capability and promising cyclability. Also notable was P(DATPAPO-TPA)'s favorable low-temperature performance that maintains a high discharge capacity of 139.2 mA h·g-1 at 0 °C. The synthesized P(DATPAPO-TPA) is a tangible illustration of a viable design strategy for low-temperature electrode materials, thereby contributing to broadening applications for radical polymer electrode materials.

Delocalized electronic engineering of TiNb2O7 enables low temperature capability for high-areal-capacity lithium-ion batteries

High areal capacity and low-temperature ability are critical for lithium-ion batteries (LIBs). However, the practical operation is seriously impeded by the sluggish rates of mass and charge transfer. Herein, the active electronic states of TiNb2O7 material is modulated by dopant and O-vacancies for enhanced low-temperature dynamics. Femtosecond laser-based transient absorption spectroscopy is employed to depict carrier dynamics of TiNb2O7, which verifies the localized structure polarization accounting for reduced transport overpotential, facilitated electron/ion transport, and improved Li+ adsorption. At high-mass loading of 10 mg cm-2 and -30 °C, TNO-x@N microflowers exhibit stable cycling performance with 92.9% capacity retention over 250 cycles at 1 C (1.0-3.0 V, 1 C = 250 mA g-1). Even at -40 °C, a competitive areal capacity of 1.32 mAh cm-2 can be achieved. Such a fundamental understanding of the intrinsic structure-function put forward a rational viewpoint for designing high-areal-capacity batteries in cold regions.

Regulation of Interfacial Chemistry Enabling High-Power Dual-Ion Batteries at Low Temperatures

Interfacial chemistry plays a crucial role in determining the electrochemical properties of low-temperature rechargeable batteries. Although existing interface engineering has significantly improved the capacity of rechargeable batteries operating at low temperatures, challenges such as sharp voltage drops and poor high-rate discharge capabilities continue to limit their applications in extreme environments. In this study, an energy-level-adaptive design strategy for electrolytes to regulate interfacial chemistry in low-temperature Li||graphite dual-ion batteries (DIBs) is proposed. This strategy enables the construction of robust interphases with superior ion-transfer kinetics. On the graphite cathode, the design endues the cathode interface with solvent/anion-coupled interfacial chemistry, which yields an nitrogen/phosphor/sulfur/fluorin (N/P/S/F)-containing organic-rich interphase to boost anion-transfer kinetics and maintains excellent interfacial stability. On the Li metal anode, the anion-derived interfacial chemistry promotes the formation of an inorganic-dominant LiF-rich interphase, which effectively suppresses Li dendrite growth and improves the Li plating/stripping kinetics at low temperatures. Consequently, the DIBs can operate within a wide temperature range, spanning from -40 to 45 °C. At -40 °C, the DIB exhibits exceptional performance, delivering 97.4% of its room-temperature capacity at 1 C and displaying an extraordinarily high-rate discharge capability with 62.3% capacity retention at 10 C. This study demonstrates a feasible strategy for the development of high-power and low-temperature rechargeable batteries.

Enhancing Electrode Performance through Triple Distribution Modulation of Active Material, Conductive Agent, and Porosity

The increasing demand for large-scale energy storage propels the development of lithium-ion batteries with high energy and high power density. Low tortuosity electrodes with aligned straight channels have proved to be effective in building such batteries. However, manufacturing such low tortuosity electrodes in large scale remains extremely challenging. In contrast, high-performance electrodes with customized gradients of materials and porosity are possible to be made by industrial roll-to-roll coating process. Yet, the desired design of gradients combining materials and porosity is unclear for high-performance gradient electrodes. Here, triple gradient LiFePO4 electrodes (TGE) are fabricated featuring distribution modulation of active material, conductive agent, and porosity by combining suction filtration with the phase inversion method. The effects and mechanism of active material, conductive agent, and porosity distribution on electrode performance are analyzed by experiments. It is found that the electrode with a gradual increase of active material content from current collector to separator coupled with the distribution of conductive agent and porosity in the opposite direction, demonstrates the best rate capability, the fastest electrochemical reaction kinetics, and the highest utilization of active material. This work provides valuable insights into the design of gradient electrodes with high performance and high potential in application.

Regulating Grafting Density to Realize High-Areal-Capacity Silicon Submicroparticle Anodes Under Ultralow Binder Content

Grafted biopolymer binders are demonstrated to improve the processability and cycling stability of the silicon (Si) nanoparticle anodes. However, there is little systematical exploration regarding the relationship between grafting density and performance of grafted binder for Si anodes, especially when Si particles exceed the critical breaking size. Herein, a series of guar gum grafted polyacrylamide (GP) binders with different grafting densities are designed and prepared to determine the optimal grafting density for maximizing the electrochemical performance of Si submicroparticle (SiSMP) anodes. Among various GP binders, GP5 with recommended grafting density demonstrates the strongest adhesion strength, best mechanical properties, and highest intrinsic ionic conductivity. These characteristics enable the SiSMP electrodes to sustain the electrode integrity and accelerate lithium-ion transport kinetics during cycling, resulting in high capacity and stable cyclability. The superior role of GP5 binder in enabling robust structure and stable interface of SiSMP electrodes is revealed through the PeakForce atomic force microscopy and in situ differential electrochemical mass spectrometry. Furthermore, the stable cyclabilities of high-loading SiSMP@GP5 electrode with ultralow GP5 content (1 wt%) at high areal capacity as well as the good cyclability of Ah-level LiNi0.8Co0.1Mn0.1O2/SiSMP@GP5 pouch cell strongly confirms the practical viability of the GP5 binder.

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.

Damage-Tolerant and Self-Repairing Web-Like Borate Type Binder Enable Stable Operation of Efficient Si-Based Anodes

Novel binder designs are shown to be fruitful in improving the electrochemical performance of silicon (Si)-based anodes. However, issues with mechanical damage from dramatic volume change and poor lithium-ion (Li+) diffusion kinetics in Si-based materials still need to be addressed. Herein, an aqueous self-repairing borate-type binder (SBG) with a web-like architecture and high ionic conductivity is designed for Si and SiO electrodes. The 3D web-like architecture of the SBG binder enables uniform stress distribution, while its self-repairing ability promotes effective stress dissipation and mechanical damage repair, thereby enhancing the damage tolerance of the electrode. The tetracoordinate boron ions (- BO 4 - $ - {\mathrm{BO}}_4^ - $ ) in the SBG binder boosts the Li transportation kinetics of Si-based electrodes. Based on dynamic covalent and ionic conductive boronic ester bonds, the diverse requirements of the binder, including uniform stress distribution, self-repairing ability, and high ionic conductivity, can be met by simple components. Consequently, the proposed straightforward multifunction design strategy for binders based on dynamic boron chemistry provides valuable insights into fabricating high-performance Si-based anodes.

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.

Emerging Chemistry for Wide-Temperature Sodium-Ion Batteries

The shortage of resources such as lithium and cobalt has promoted the development of novel battery systems with low cost, abundance, high performance, and efficient environmental adaptability. Due to the abundance and low cost of sodium, sodium-ion battery chemistry has drawn worldwide attention in energy storage systems. It is widely considered that wide-temperature tolerance sodium-ion batteries (WT-SIBs) can be rapidly developed due to their unique electrochemical and chemical properties. However, WT-SIBs, especially for their electrode materials and electrolyte systems, still face various challenges in harsh-temperature conditions. In this review, we focus on the achievements, failure mechanisms, fundamental chemistry, and scientific challenges of WT-SIBs. The insights of their design principles, current research, and safety issues are presented. Moreover, the possible future research directions on the battery materials for WT-SIBs are deeply discussed. Progress toward a comprehensive understanding of the emerging chemistry for WT-SIBs comprehensively discussed in this review will accelerate the practical applications of wide-temperature tolerance rechargeable batteries.

A Fully Methylated Cyclic Ether Solvent Enables Graphite Anode Cycling at Low Temperatures

Graphite anode suffers from great capacity loss and larger cell polarization under low-temperature conditions in lithium-ion batteries (LIBs), which are mainly caused by the high energy barrier for the Li+ desolvation process and sluggish Li+ transfer rate across the solid electrolyte interface (SEI). Regulating an electrolyte with an anion-dominated solvation structure could synchronously stabilize the interface and boost the reaction kinetics of the graphite anode. Herein, a highly ionic conductive electrolyte consisting of a fully methylated cyclic ether solvent of 2,2,4,4,5,5-hexamethyl-1,3-dioxolane (HMD) and fluoroethylene carbonate (FEC) cosolvent was designed. The high electron-donating effect and steric hindrance of -(CH3)2 in HMD endow the HMD-based electrolyte with high ionic conductivity but lower coordination numbers with Li+, and an anion-dominated solvation structure was formed. Such configuration can accelerate the desolvation process and induce the forming of a LiF-rich SEI film on the anode, avoiding the solvent coembedding into graphite and enhancing the ion migration rate under low temperatures. The assembled Li||graphite cell with the tame electrolyte outperformed the conventional carbonates-based cell, showing 93.8% capacity retention after 227 cycles for the DF-based cell compared to 64.7% after 150 cycles. It also exhibited a prolonged cycle life for 200 rounds with 81% capacity retention under -20 °C. Therefore, this work offers a valuable thought for solvent design and provides approaches to electrolyte design for low-temperature LIBs.

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.

Li3V2(PO4)3 Cathode Material: Synthesis Method, High Lithium Diffusion Coefficient and Magnetic Inhomogeneity

Li3V2(PO4)3 cathodes for Li-ion batteries (LIBs) were synthesized using a hydrothermal method with the subsequent annealing in an argon atmosphere to achieve optimal properties. The X-ray diffraction analysis confirmed the material's single-phase nature, while the scanning electron microscopy revealed a granular structure, indicating a uniform particle size distribution, beneficial for electrochemical performance. Magnetometry and electron spin resonance studies were conducted to investigate the magnetic properties, confirming the presence of the relatively low concentration and highly uniform distribution of tetravalent vanadium ions (V4+), which indicated low lithium deficiency values in the original structure and a high degree of magnetic homogeneity in the sample, an essential factor for consistent electrochemical behavior. For this pure phase Li3V2(PO4)3 sample, devoid of any impurities such as carbon or salts, extensive electrochemical property testing was performed. These tests resulted in the experimental discovery of a remarkably high lithium diffusion coefficient D = 1.07 × 10-10 cm2/s, indicating excellent ionic conductivity, and demonstrated impressive stability of the material with sustained performance over 1000 charge-discharge cycles. Additionally, relithiated Li3V2(PO4)3 (after multiple electrochemical cycling) samples were investigated using scanning electron microscopy, magnetometry and electron spin resonance methods to determine the extent of degradation. The combination of high lithium diffusion coefficients, a low degradation rate and remarkable cycling stability positions this Li3V2(PO4)3 material as a promising candidate for advanced energy storage applications.

In Situ Construction of a Polymer Coating Layer on the LiNi0.8Co0.1Mn0.1O2 Cathode for High-Performance Lithium-Ion Batteries

Lithium-ion batteries (LIBs) are known for their high energy density but exhibit poor cyclic stability and safety risks due to side reactions between the electrode and electrolyte. To address these issues, a novel approach involving construction of a polymer coating layer (PCL) via in situ self-polymerization using 2,2,3,4,4,4-hexafluorobutyl methacrylate (HFBM) as an electrolyte additive on the cathode is proposed. The PCL endows the electrolyte with a high onset oxidation potential (4.78 V) and lithium-ion transference number (0.52). The uniform and robust in situ constructed PCL can effectively inhibit the severe irreversible side reactions and suppress harmful reactions, thus providing a protective barrier against degradation. The resulting Li||LiNi0.8Co0.1Mn0.1O2 batteries exhibit an improved discharge capacity retention of 80% at 1C over 100 cycles. These results demonstrate that the in situ self-polymerization strategy holds promising potential for enhancing LIB performance and long-term stability, especially when high-voltage cathode materials are used.

An Ultrastable Low-Temperature Na Metal Battery Enabled by Synergy between Weakly Solvating Solvents

The low ionic conductivity and high desolvation barrier are the main challenges for organic electrolytes in rechargeable metal batteries, especially at low temperatures. The general strategy is to couple strong-solvation and weak-solvation solvents to give balanced physicochemical properties. However, the two challenges described above cannot be overcome at the same time. Herein, we combine two different kinds of weakly solvating solvents with a very low desolvation energy. Interestingly, the synergy between the weak-solvation solvents can break the locally ordered structure at a low temperature to enable higher ionic conductivity compared to those with individual solvents. Thus, facile desolvation and high ionic conductivity are achieved simultaneously, significantly improving the reversibility of electrode reactions at low temperatures. The Na metal anode can be stably cycled at 2 mA cm-2 at -40 °C for 1000 h. The Na||Na3V2(PO4)3 cell shows the reversible capacity of 64 mAh g-1 at 0.3 C after 300 cycles at -40 °C, and the capacity retention is 86%. This strategy is applicable to other sets of weak-solvation solvents, providing guidance for the development of electrolytes for low-temperature rechargeable metal batteries.

A Two-dimensional Metal-Organic Framework as Promising Cathode for Advanced Lithium Storage

Anthraquinone electrode materials are promising candidates for lithium-ion batteries (LIBs) due to the abundance of anthraquinone and the high theoretical capacity, and good reversibility of the anthraquinone electrodes. However, the active anthraquinone materials are soluble in organic electrolytes, resulting in a sharp decay of capacity during the charge and discharge processes. Herein, we report on a two-dimensional calcium anthraquinone 2,3-dicarboxy metal-organic framework (2D CaAQDC MOF) fabricated using a simple hydrothermal method. The 2D CaAQDC MOF not only effectively inhibits the dissolution of active electrode substances into the electrolyte, but also promotes the diffusion of lithium ion into the pores of the MOF. When used as a cathode for the LIBs, the resulting CaAQDC electrode delivers a high specific capacity of ~100 mAh g-1 at a current density of 50 mA g-1 after 200 cycles, demonstrating its good cycle stability. Even at a high current density of 200 mA g-1 , the CaAQDC electrode exhibits a specific capacity of ~60 mAh g-1 . The fabricated 2D coordination polymers effectively restrains the dissolution of anthraquinone into the organic electrolyte and enhances the structural stability, which greatly improves the electrochemical performance of anthraquinone. These research results offer a rational molecular design strategy to address the dissolution of this and other active organic electrode materials.

Electrolyte Design for Low-Temperature Li-Metal Batteries: Challenges and Prospects

Electrolyte design holds the greatest opportunity for the development of batteries that are capable of sub-zero temperature operation. To get the most energy storage out of the battery at low temperatures, improvements in electrolyte chemistry need to be coupled with optimized electrode materials and tailored electrolyte/electrode interphases. Herein, this review critically outlines electrolytes' limiting factors, including reduced ionic conductivity, large de-solvation energy, sluggish charge transfer, and slow Li-ion transportation across the electrolyte/electrode interphases, which affect the low-temperature performance of Li-metal batteries. Detailed theoretical derivations that explain the explicit influence of temperature on battery performance are presented to deepen understanding. Emerging improvement strategies from the aspects of electrolyte design and electrolyte/electrode interphase engineering are summarized and rigorously compared. Perspectives on future research are proposed to guide the ongoing exploration for better low-temperature Li-metal batteries.