Emerging Nonaqueous Aluminum‐Ion Batteries: Challenges,Status, and Perspectives

Aluminum‐ion batteries (AIBs) are regarded as viable alternatives to lithium‐ion technology because of their high volumetric capacity, their low cost, and the rich abundance of aluminum. However, several serious drawbacks of aqueous systems (passive film formation, hydrogen evolution, anode corrosion, etc.) hinder the large‐scale application of these systems. Thus, nonaqueous AIBs show incomparable advantages for progress in large‐scale electrical energy storage. However, nonaqueous aluminum battery systems are still nascent, and various technical and scientific obstacles to designing AIBs with high capacity and long cycling life have not been resolved until now. Moreover, the aluminum cell is a complex device whose energy density is determined by various parameters, most of which are often ignored, resulting in failure to achieve the maximum performance of the cell. The purpose here is to discuss how to further develop reliable nonaqueous AIBs. First, the current status of nonaqueous AIBs is reviewed based on statistical data from the literature. The influence of parameters on energy density is analyzed, and the current situation and existing problems are summarized. Furthermore, possible solutions and concerns regarding the construction of reliable nonaqueous AIBs are comprehensively discussed. Finally, future research directions and prospects in the aluminum battery field are proposed.     

Paving the Path toward Reliable Cathode Materials for Aluminum‐Ion Batteries

Aluminum metal is a high‐energy‐density carrier with low cost, and thus endows rechargeable aluminum batteries (RABs) with the potential to act as an inexpensive and efficient electrochemical device, so as to supplement the increasing demand for energy storage and conversion. Despite the enticing aspects regarding cost and energy density, the poor reversibility of electrodes has limited the pursuit of RABs for a long time. Fortunately, ionic‐liquid electrolytes enable reversible aluminum plating/stripping at room temperature, and they lay the very foundation of RABs. In order to integrate with the aluminum‐metal anode, the selection of the cathode is pivotal, but is limited at present. The scant option of a reliable cathode can be accounted for by the intrinsic high charge density of Al³⁺ ions, which results in sluggish diffusion. Hence, reliable cathode materials are a key challenge of burgeoning RABs. Herein, the main focus is on the insertion cathodes for RABs also termed aluminum‐ion batteries, and the recent progress and optimization methods are summarized. Finally, an outlook is presented to navigate the possible future work.     

静电纺丝法制备氧化锰纳米丝电极及其电化学性能

利用静电纺丝技术成功制备了φ60～80nm的氧化锰纳米纤维丝,并构建了三维纳米丝网状结构电极,应用于锂离子二次电池. 使用扫描电子显微镜、X射线衍射、循环伏安和电池充放电等研究手段,表征了纳米纤维丝的结构和电化学性能. 研究结果发现:氧化锰构建的纳米丝在嵌锂和脱锂的过程中没有出现纳米纤维丝的结构塌陷问题,在高能量密度下表现出较大的可逆循环容量,放电容量达到160mAh/g. 经过50次循环后, 容量可达132.5mAh/g, 平均每次循环的容量衰减在1%以下. 这些结果表明了氧化锰纳米纤维丝可作为三维锂离子电池中的阴极材料.     

Cathode Architectures for Rechargeable Ion Batteries: Progress and Perspectives

To satisfy the rising demand for energy, battery electrodes with higher loading, to simultaneously increase areal energy and power, are necessary. Nevertheless, in conventional thin-film electrodes, there is mutual exclusion between energy (capacity) and power. Increasing the thickness of electrodes alone is not feasible since this will lead to reductions in ion-diffusion efficiency, as well as electrode flexibility. To address this difficulty, 3D electrode architectures, especially cathode architectures, are proposed to pave a new path for the design and optimization of battery devices. Recent research suggests that 3D cathode architectures may optimize the configuration and engineering processes of battery technologies. Herein, the state-of-the-art progress of cathode architectures in various rechargeable-ion-battery technologies is summarized. Emphasis is placed on the different architecture strategies, areal loading, and mechanical understanding of 3D electrodes. Upcoming research directions are further outlined for future development in this field.     

钠离子电池铁基正极材料的研究进展

随着锂电池在新能源汽车和大型定置装备上的应用,稀有金属锂(Li)供应短缺问题日益凸显。因而发展钠离子可充电池尤其是室温钠离子电池受到了全球范围内的重视。相比于其他正极材料,铁基正极材料具有电位高,储量丰富等优势。综述了当前国内外各类钠离子铁基正极材料最新研究进展,介绍了其结构特征和电化学性能,总结了各类型铁基正极材料应用于钠离子电池的优缺点。最后提出新型的高电压聚硫酸根离子铁基正极材料具有诱人的应用前景。     

Chemically Prelithiated Hard‐Carbon Anode for High Power and High Capacity Li‐Ion Batteries

Hard carbons (HC) have potential high capacities and power capability, prospectively serving as an alternative anode material for Li‐ion batteries (LIB). However, their low initial coulombic efficiency (ICE) and the resulting poor cyclability hinder their practical applications. Herein, a facile and effective approach is developed to prelithiate hard carbons by a spontaneous chemical reaction with lithium naphthalenide (Li‐Naph). Due to the mild reactivity and strong lithiation ability of Li‐Naph, HC anode can be prelithiated rapidly in a few minutes and controllably to a desirable level by tuning the reaction time. The as‐formed prelithiated hard carbon (pHC) has a thinner, denser, and more robust solid electrolyte interface layer consisting of uniformly distributed LiF, thus demonstrating a very high ICE, high power, and stable cyclability. When paired with the current commercial LiCoO₂ and LiFePO₄ cathodes, the assembled pHC/LiCoO₂ and pHC/LiFePO₄ full cells exhibit a high ICE of >95.0% and a nearly 100% utilization of electrode‐active materials, confirming a practical application of pHC for a new generation of high capacity and high power LIBs.     

Superresilient Hard Carbon Nanofabrics for Sodium‐Ion Batteries

Developing supermechanically resilient hard carbon materials that can quickly accommodate sodium ions is highly demanded in fabricating durable anodes for wearable sodium‐ion batteries. Here, an interconnected spiral nanofibrous hard carbon fabric with both remarkable resiliency (e.g., recovery rate as high as 1200 mm s^?1) and high Young's modulus is reported. The hard carbon nanofabrics are prepared by spinning and then carbonizing the reaction product of polyacrylonitrile and polar molecules (melamine). The resulting unique hard carbon possesses a highly disordered carbonaceous structure with enlarged interlayer spacing contributed from the strong electrostatic repulsion of dense pyrrolic nitrogen atoms. Its excellent resiliency remains after intercalation/deintercalation of sodium ions. The outstanding sodium‐storage performance of the derived anode includes excellent gravimetric capacity, high‐power capability, and long‐term cyclic stability. More significantly, with a high loading mass, the hard carbon anode displays a high‐power capacity (1.05 mAh cm^?2 at 2 A g^?1) and excellent cyclic stability. This study provides a unique strategy for the design and fabrication of new hard carbon materials for advanced wearable energy storage systems.     

Antipulverization Electrode Based on Low‐Carbon Triple‐Shelled Superstructures for Lithium‐Ion Batteries

The realization of antipulverization electrode structures, especially using low‐carbon‐content anode materials, is crucial for developing high‐energy and long‐life lithium‐ion batteries (LIBs); however, this technology remains challenging. This study shows that SnO₂ triple‐shelled hollow superstructures (TSHSs) with a low carbon content (4.83%) constructed by layer‐by‐layer assembly of various nanostructure units can withstand a huge volume expansion of ≈231.8% and deliver a high reversible capacity of 1099 mAh g^?1 even after 1450 cycles. These values represent the best comprehensive performance in SnO₂‐based anodes to date. Mechanics simulations and in situ transmission electron microscopy suggest that the TSHSs enable a self‐synergistic structure‐preservation behavior upon lithiation/delithiation, protecting the superstructures from collapse and guaranteeing the electrode structural integrity during long‐term cycling. Specifically, the outer shells during lithiation processes are fully lithiated, preventing the overlithiation and the collapse of the inner shells; in turn, in delithiation processes, the underlithiated inner shells work as robust cores to support the huge volume contraction of the outer shells; meanwhile, the middle shells with abundant pores offer sufficient space to accommodate the volume change from the outer shell during both lithiation and delithiation. This study opens a new avenue in the development of high‐performance LIBs for practical energy applications.     

锂离子电池磷酸铁锂正极材料的制备及改性研究进展

橄榄石型磷酸铁锂(LiFePO4)由于安全性能好、循环寿命长、原材料来源广泛、无环境污染等优点被公认为是最具发展潜力的锂离子动力与储能电池正极材料。综述了近年来磷酸铁锂正极材料在制备和改性方面的最新进展。在此基础上,提出了磷酸铁锂正极材料未来的主要研究和发展方向。     

Highly Electrochemically‐Reversible Mesoporous Na2FePO4F/C as Cathode Material for High‐Performance Sodium‐Ion Batteries

As promising cathode materials, iron‐based phosphate compounds have attracted wide attention for sodium‐ion batteries due to their low cost and safety. Among them, sodium iron fluorophosphate (Na₂FePO₄F) is widely noted due to its layered structure and high operating voltage compared with NaFePO₄. Here, a mesoporous Na₂FePO₄F@C (M‐NFPF@C) composite derived from mesoporous FePO₄ is synthesized through a facile ball‐milling combined calcination method. Benefiting from the mesoporous structure and highly conductive carbon, the M‐NFPF@C material exhibits a high reversible capacity of 114 mAh g^?1 at 0.1 C, excellent rate capability (42 mAh g^?1 at 10 C), and good cycling performance (55% retention after 600 cycles at 5 C). The high plateau capacity obtained (>90% of total capacity) not only shows high electrochemical reversibility of the as‐prepared M‐NFPF@C but also provides high energy density, which mainly originates from its mesoporous structure derived from the mesoporous FePO₄ precursor. The M‐NFPF@C serves as a promising cathode material with high performance and low cost for sodium‐ion batteries.     

Atomic Fe–Nx Coupled Open‐Mesoporous Carbon Nanofibers for Efficient and Bioadaptable Oxygen Electrode in Mg–Air Batteries

The recently emerging metal–air batteries equipped with advanced oxygen electrodes have provided enormous opportunities to develop the next generation of wearable and bio‐adaptable power sources. Theoretically, neutral electrolyte‐based Mg–air batteries possess potential advantages in electronics and biomedical applications over the other metal–air counterparts, especially the alkaline‐based Zn–air batteries. However, the rational design of advanced oxygen electrode for Mg–air batteries with high discharge voltage and capacity under neutral conditions still remains a major challenge. Inspired by fibrous string structures of bufo‐spawn, it is reported here that the scalable synthesis of atomic Fe–N_x coupled open‐mesoporous N‐doped‐carbon nanofibers (OM‐NCNF‐FeN_x) as advanced oxygen electrode for Mg–air batteries. The fabricated OM‐NCNF‐FeN_x electrodes present manifold advantages, including open‐mesoporous and interconnected structures, 3D hierarchically porous networks, good bio‐adaptability, homogeneously coupled atomic Fe–N_x sites, and high oxygen electrocatalytic performances. Most importantly, the assembled Mg–air batteries with neutral electrolytes reveal high open‐circuit voltage, stable discharge voltage plateaus, high capacity, long operating life, and good flexibility. Overall, the discovery on fabricating atomic OM‐NCNF‐FeN_x electrode will not only create new pathways for achieving flexible, wearable, and bio‐adaptable power sources, but also take a step towards the scale‐up production of advanced nanofibrous carbon electrodes for a broad range of applications.     

Azo Compounds Derived from Electrochemical Reduction of Nitro Compounds for High Performance Li‐Ion Batteries

Organic compounds are desirable alternatives for sustainable lithium‐ion battery electrodes. However, the electrochemical properties of state‐of‐the‐art organic electrodes are still worse than commercial inorganic counterparts. Here, a new chemistry is reported based on the electrochemical conversion of nitro compounds to azo compounds for high performance lithium‐ion batteries. 4‐Nitrobenzoic acid lithium salt (NBALS) is selected as a model nitro compound to systemically investigate the structure, lithiation/delithiation mechanism, and electrochemical performance of nitro compounds. NBALS delivers an initial capacity of 153 mAh g^?1 at 0.5 C and retains a capacity of 131 mAh g^?1 after 100 cycles. Detailed characterizations demonstrate that during initial electrochemical lithiation, the nitro group in crystalline NBALS is irreversibly reduced into an amorphous azo compound. Subsequently, the azo compound is reversibly lithiated/delithiated in the following charge/discharge cycles with high electrochemical performance. The lithiation/delithiation mechanism of azo compounds is also validated by directly using azo compounds as electrode materials, which exhibit similar electrochemical performance to nitro compounds, while having a much higher initial Coulombic efficiency. Therefore, this work proves that nitro compounds can be electrochemically converted to azo compounds for high performance lithium‐ion batteries.     

锂离子电池炭负极材料结构的研究进展

综述了近年来锂离子电池碳负极材料结构的研究情况,着重总结了石墨材料、炭材料以及纳米碳材料结构方面的研究进展.     

Dual‐Functionalized Double Carbon Shells Coated Silicon Nanoparticles for High Performance Lithium‐Ion Batteries

To address the challenge of huge volume change and unstable solid electrolyte interface (SEI) of silicon in cycles, causing severe pulverization, this paper proposes a “double‐shell” concept. This concept is designed to perform dual functions on encapsulating volume change of silicon and stabilizing SEI layer in cycles using double carbon shells. Double carbon shells coated Si nanoparticles (DCS‐Si) are prepared. Inner carbon shell provides finite inner voids to allow large volume changes of Si nanoparticles inside of inner carbon shell, while static outer shell facilitates the formation of stable SEI. Most importantly, intershell spaces are preserved to buffer volume changes and alleviate mechanical stress from inner carbon shell. DCS‐Si electrodes display a high rechargeable specific capacity of 1802 mAh g⁻¹ at a current rate of 0.2 C, superior rate capability and good cycling performance up to 1000 cycles. A full cell of DCS‐Si//LiNi_0.45Co_0.1Mn_1.45O₄ exhibits an average discharge voltage of 4.2 V, a high energy density of 473.6 Wh kg⁻¹, and good cycling performance. Such double‐shell concept can be applied to synthesize other electrode materials with large volume changes in cycles by simultaneously enhancing electronic conductivity and controlling SEI growth.     

Carbon Nanotube–CoF2 Multifunctional Cathode for Lithium Ion Batteries: Effect of Electrolyte on Cycle Stability

Transition metal fluorides (MF_x) offer remarkably high theoretical energy density. However, the low cycling stability, low electrical and ionic conductivity of metal fluorides have severely limited their applications as conversion‐type cathode materials for lithium ion batteries. Here, a scalable and low‐cost strategy is reported on the fabrication of multifunctional cobalt fluoride/carbon nanotube nonwoven fabric nanocomposite, which demonstrates a combination of high capacity (near‐theoretical, ) and excellent mechanical properties. Its strength and modulus of toughness exceed that of many aluminum alloys, cast iron, and other structural materials, fulfilling the use of MF_x‐based materials in batteries with load‐bearing capabilities. In the course of this study, cathode dissolution in conventional electrolytes has been discovered as the main reason that leads to the rapid growth of the solid electrolyte interphase layer and attributes to rapid cell degradation. And such largely overlooked degradation mechanism is overcome by utilizing electrolyte comprising a fluorinated solvent, which forms a protective ionically conductive layer on the cathode and anode surfaces. With this approach, 93% capacity retention is achieved after 200 cycles at the current density of 100 mA g⁻¹ and over 50% after 10 000 cycles at the current density of 1000 mA g⁻¹.     

树脂炭包覆石墨作为锂离子电池负电极的研究

以液相浸渍法在天然鳞片石墨（ＮＦＧ）表面包覆酚醛树脂后进行热处理,制备了酚醛树脂炭包覆石墨材料．将这种材料作为锂离子电池的负极材料,运用恒电流充、放电法,粉末微电极循环伏安法考察了其在１Ｍ　ＬｉＰＦ_６／ＥＣ＋ＤＥＣ（１：１）电解液中的充、放电性能,并分析了工艺条件中不同热处理温度（ＨＴＴ）对其充、放电性能的影响．实验结果表明,经ＨＴＴ＝９００℃热处理的酚醛树脂炭包覆石墨材料的第三次稳定放电容量（Ｄ_３）为 ２１３．７５ｍＡｈ／ｇ,第三次充、放电效率（η_３）为８８．６９％;并且循环寿命较长,可作为高性能锂离子电池的负极材料．