Deep Cycling for High-Capacity Li-Ion Batteries

Efficient mitigation of lithium dendrite by two-dimensional A-type molecular sieve membrane for lithium metal battery

Uneven lithium deposition poses a primary challenge for lithium-ion batteries, as it often triggers the growth of lithium dendrites, thereby significantly compromising battery performance and potentially giving rise to safety concerns. Therefore, the high level of safety must be guaranteed to achieve the large-scale application of battery energy storage systems. Here, we present a novel separator design achieved by incorporating a two-dimensional A-type molecular sieve coating onto the polypropylene separator surface, which functions as an effective lithium ion redistribution layer. The results demonstrated that even after undergoing 1000 cycles, the cell equipped with a two-dimensional A-type molecular sieve-Polypropylene (2D-A-PP) separator still maintains an impressive capacity retention rate of 70 %. In contrast, cells equipped with Polypropylene (PP) separators exhibit capacity retention rates below 50 % after only 500 cycles. Additionally, the incorporation of a two-dimensional molecular sieve enhances the mechanical properties of the PP separator, thereby bolstering battery safety. This study proposes a novel concept for the design of lithium-ion battery separator materials, offering a fresh perspective on the development of separators with exceptional thermal stability, enhanced porosity, superior electrolyte affinity, and effective inhibition of lithium dendrite formation.

Electrochemical Activation Inducing Rocksalt-to-Spinel Transformation for Prolonged Service Life of LiMn2O4 Cathodes

LiMn2O4 spinel is emerging as a promising cathode material for lithium-ion batteries, largely due to its open framework that facilitates Li+ diffusion and excellent rate performance. However, the charge-discharge cycling of the LiMn2O4 cathode leads to severe structural degradation and rapid capacity decay. Here, an electrochemical activation strategy is introduced, employing a facile galvano-potentiostatic charging operation, to restore the lost capacity of LiMn2O4 cathode without damaging the battery configuration. With an electrochemical activation strategy, the cycle life of the LiMn2O4 cathode is extended from an initial 1500 to an impressive 14 000 cycles at a 5C rate with Li metal as the anode, while increasing the total discharge energy by ten times. Remarkably, the electrochemical activation enhances the diffusion kinetics of Li+, with the diffusion coefficient experiencing a 37.2% increase. Further investigation reveals that this improvement in capacity and diffusion kinetics results from a transformation of the redox-inert LiMnO2 rocksalt layer on the surface of degraded cathodes back into active spinel. This transformation is confirmed through electron microscopy and corroborated by density functional theory simulations. Moreover, the viability of this electrochemical activation strategy has been demonstrated in pouch cell configurations with Li metal as the anode, underscoring its potential for broader application.

Revealing Hydrogen Bond Effect in Rechargeable Aqueous Zinc-Organic Batteries

The surrounding hydrogen bond (H-bond) interaction around the active sites plays indispensable functions in enabling the organic electrode materials (OEMs) to fulfill their roles as ion reservoirs in aqueous zinc-organic batteries (ZOBs). Despite important, there are still no works could fully shed its real effects light on. Herein, quinone-based small molecules with a H-bond evolution model has been rationally selected to disclose the regulation and equilibration of H-bond interaction between OEMs, and OEM and the electrolyte. It has been found that only a suitable H-bond interaction could make the OEMs fully liberate their potential performance. Accordingly, the 2,5-diaminocyclohexa-2,5-diene-1,4-dione (DABQ) with elaborately designed H-bond structure exhibits a capacity of 193.3 mAh g-1 at a record-high mass loading of 66.2 mg cm-2 and 100 % capacity retention after 1500 cycles at 5 A g-1. In addition, the DABQ//Zn battery also possesses air-rechargeable ability by utilizing the chemistry redox of proton. Our results put forward a specific pathway to precise utilization of H-bond to liberate the performance of OEMs.

Vertical-Channel Cathode Host Enables Rapid Deposition Kinetics toward High-Areal-Capacity Sodium-Chlorine Batteries

Rechargeable sodium chloride (Na-Cl2) batteries have emerged as promising alternatives for next-generation energy storage due to their superior energy density and sodium abundance. However, their practical applications are hindered by the sluggish chlorine cathode kinetics related to the aggregation of NaCl and its difficult transformation into Cl2. Herein, the study, for the first time from the perspective of electrode level in Na-Cl2 batteries, proposes a free-standing carbon cathode host with customized vertical channels to facilitate the SOCl2 transport and regulate the NaCl deposition. Accordingly, electrode kinetics are significantly enhanced, and the deposited NaCl is distributed evenly across the whole electrode, avoiding the blockage of pores in the carbon host, and facilitating its oxidation to Cl2. With this low-polarization cathode, the Na-Cl2 batteries can deliver a practically high areal capacity approaching 4 mAh cm-2 and a long cycle life of over 170 cycles. This work demonstrates the significance of pore engineering in electrodes for mediating chlorine conversion kinetics in rechargeable alkali-metal-Cl2 batteries.

Covalent Bonding of MXene/COF Heterojunction for Ultralong Cycling Li-Ion Battery Electrodes

Covalent organic frameworks (COFs) have emerged as promising renewable electrode materials for LIBs and gained significant attention, but their capacity has been limited by the densely packed 2D layer structures, low active site availability, and poor electronic conductivity. Combining COFs with high-conductivity MXenes is an effective strategy to enhance their electrochemical performance. Nevertheless, simply gluing them without conformal growth and covalent linkage restricts the number of redox-active sites and the structural stability of the composite. Therefore, in this study, a covalently assembled 3D COF on Ti3C2 MXenes (Ti3C2@COF) is synthesized and serves as an ultralong cycling electrode material for LIBs. Due to the covalent bonding between the COF and Ti3C2, the Ti3C2@COF composite exhibits excellent stability, good conductivity, and a unique 3D cavity structure that enables stable Li+ storage and rapid ion transport. As a result, the Ti3C2-supported 3D COF nanosheets deliver a high specific capacity of 490 mAh g-1 at 0.1 A g-1, along with an ultralong cyclability of 10,000 cycles at 1 A g-1. This work may inspire a wide range of 3D COF designs for high-performance electrode materials.

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.

Temperature-Tunable Operando Nondestructive Detection of Electronic and Geometrical Structures in Battery Electrodes

Real-time monitoring of the structural evolution of battery materials is crucial for understanding their underlying reaction mechanisms, which cannot be satisfied by the typically used post-mortem analysis. While more and more operando techniques were constructed and employed, they are all based on ambient working conditions that are not generally the case for real-world applications. Indeed, batteries work in an environment where self-heat dissipation increases the surrounding temperature, and extreme temperature applications (<-20 °C or >60 °C) are also frequently proposed. Operando characterization techniques under variable temperatures are therefore highly desired for tracking battery reactions under real-working conditions. Here, we develop a methodology to operando monitor the electronic and geometrical structures of battery materials over a wide range of temperatures based on X-ray spectroscopies. It is substantiated with data collected on a model LiNi0.90Co0.05Mn0.05O2/Si@C pouch cell under operando quick X-ray absorption fine structure spectroscopy, by which we found a temperature-dependent structure evolution behavior that is highly correlated with the electrochemical performance. Our work establishes an exemplary protocol for analyzing battery materials under temperature-variable environments that can be widely used in other related fields.

Thermal-Stable Separators: Design Principles and Strategies Towards Safe Lithium-Ion Battery Operations

Lithium-ion batteries (LIBs) are momentous energy storage devices, which have been rapidly developed due to their high energy density, long lifetime, and low self-discharge rate. However, the frequent occurrence of fire accidents in laptops, electric vehicles, and mobile phones caused by thermal runaway of the inside batteries constantly reminds us of the urgency in pursuing high-safety LIBs with high performance. To this end, this Review surveyed the state-of-the-art developments of high-temperature-resistant separators for highly safe LIBs with excellent electrochemical performance. Firstly, the basic properties of separators (e. g., thickness, porosity, pore size, wettability, mechanical strength, and thermal stability) in constructing commercialized LIBs were introduced. Secondly, the working mechanisms of advanced separators with different melting points acting in the thermal runaway stage were discussed in terms of improving battery safety. Thirdly, rational design strategies for constructing high-temperature-resistant separators for LIBs with high safety were summarized and discussed, including graft modification, blend modification, and multilayer composite modification strategies. Finally, the current obstacles and future research directions in the field of high-temperature-resistant separators were highlighted. These design ideas are expected to be applied to other types of high-temperature-resistant energy storage systems working under extreme conditions.

Lithium-Ion Batteries under Low-Temperature Environment: Challenges and Prospects

Lithium-ion batteries (LIBs) are at the forefront of energy storage and highly demanded in consumer electronics due to their high energy density, long battery life, and great flexibility. However, LIBs usually suffer from obvious capacity reduction, security problems, and a sharp decline in cycle life under low temperatures, especially below 0 °C, which can be mainly ascribed to the decrease in Li⁺ diffusion coefficient in both electrodes and electrolyte, poor transfer kinetics on the interphase, high Li⁺ desolvation barrier in the electrolyte, and severe Li plating and dendrite. Targeting such issues, approaches to improve the kinetics and stability of cathodes are also dissected, followed by the evaluation of the application prospects and modifications between various anodes and the strategies of electrolyte design including cosolvent, blended Li salts, high-concentration electrolyte, and additive introduction. Such designs elucidate the successful exploration of low-temperature LIBs with high energy density and long lifespan. This review prospects the future paths of research for LIBs under cold environments, aiming to provide insightful guidance for the reasonable design of LIBs under low temperature, accelerating their widespread application and commercialization.

A Figure of Merit for Fast-Charging Li-ion Battery Materials

Rate capability is characterized necessarily in almost all battery-related reports, while there is no universal metric for quantitative comparison. Here, we proposed the characteristic time of diffusion, which mainly combines the effects of diffusion coefficients and geometric sizes, as an easy-to-use figure of merit (FOM) to standardize the comparison of fast-charging battery materials. It offers an indicator to rank the rate capabilities of different battery materials and suggests two general methods to improve the rate capability: decreasing the geometric sizes or increasing the diffusion coefficients. Based on this FOM, more comprehensive FOMs for quantifying the rate capabilities of battery materials are expected by incorporating other processes (interfacial reaction, migration) into the current diffusion-dominated electrochemical model. Combined with Peukert's empirical law, it may characterize rate capabilities of batteries in the future.

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.

Commercialization-Driven Electrodes Design for Lithium Batteries: Basic Guidance, Opportunities, and Perspectives

Current lithium-ion battery technology is approaching the theoretical energy density limitation, which is challenged by the increasing requirements of ever-growing energy storage market of electric vehicles, hybrid electric vehicles, and portable electronic devices. Although great progresses are made on tailoring the electrode materials from methodology to mechanism to meet the practical demands, sluggish mass transport, and charge transfer dynamics are the main bottlenecks when increasing the areal/volumetric loading multiple times to commercial level. Thus, this review presents the state-of-the-art developments on rational design of the commercialization-driven electrodes for lithium batteries. First, the basic guidance and challenges (such as electrode mechanical instability, sluggish charge diffusion, deteriorated performance, and safety concerns) on constructing the industry-required high mass loading electrodes toward commercialization are discussed. Second, the corresponding design strategies on cathode/anode electrode materials with high mass loading are proposed to overcome these challenges without compromising energy density and cycling durability, including electrode architecture, integrated configuration, interface engineering, mechanical compression, and Li metal protection. Finally, the future trends and perspectives on commercialization-driven electrodes are offered. These design principles and potential strategies are also promising to be applied in other energy storage and conversion systems, such as supercapacitors, and other metal-ion batteries.