Search for New Anode Materials for High Performance Li-Ion Batteries

Polymer additives in liquid electrolytes for advanced lithium batteries

Compared to traditional energy storage devices, lithium-ion batteries (LIBs) have the advantages of high energy density, good cycling performance, and low self-discharge rate. Therefore, LIBs have been widely used as the main energy storage devices in various industries. As the blood of the battery, the electrolyte plays a key role in ion transport, formation of the interface layer, protection of electrode materials, etc. The commonly investigated electrolytes include liquid electrolytes, gel electrolytes, and solid or quasi-solid electrolytes. Liquid electrolytes have higher ionic conductivity, which is more conducive to the transport of lithium ions. Therefore, batteries based on liquid electrolytes often exhibit better electrochemical performance. In a liquid electrolyte, the additive is also an indispensable component to ensure the high efficiency of the electrolyte, which plays an important role in regulating the solvation structure of lithium ions, the formation of the solid-electrolyte interface layer, improving the safety performance of batteries, and maintaining operability under extreme conditions (such as low temperature). Unlike previous reviews that focused on small molecule additives, this review herein mainly reviews the application of polymer additives in liquid lithium batteries. Firstly, the functional mechanisms of different types of additives in liquid electrolytesfor lithium batteries are outlined and the advantages and disadvantages of different types of additives are summarized. Then, the research progress of polymers as additives in liquid lithium batteries in recent years is discussed in detail. According to the role of additives, the involved polymer additives are divided into five categories: molecular crowding agents, film-forming agents, HF scavengers, antifreeze agents, and flame retardants. A detailed explanation of the mechanisms related to the efficacy of polymers as additives is also provided. Finally, we present some perspectives on the limitations and future development trends of polymers as additives in liquid lithium batteries and other devices.

Controllable SiOx Coating Layer Promotes High Stable Si Anode for Lithium-Ion Batteries

Silicon (Si) is considered as one of the most promising candidates for next-generation lithium-ion batteries with high energy density. The main problems are the severe volume expansion and continuous interfacial side reaction of Si that hinder its further application. It can be an effective way by constructing a robust coating layer outside of Si to impede/alleviate the above effect. SiOx with high mechanical strength can largely promote the electrochemical performance of Si. Herein, Si@SiOx material with high specific surface area, high porosity, and controllable coating was synthesized via a simple solid-liquid reaction by LiOH solution etching effect. The etching/oxidation mechanism of Si under alkaline conditions was thoroughly investigated. The surface oxide layer of Si was beneficial to the formation of a solid electrolyte interphase (SEI) with excellent stability and high Li+ conductivity, while its high-porosity structure reduces the volume expansion of the material by approximately 110%. Under the synergistic effect of etching-oxidation, the modified material exhibited superior electrochemical properties. When employed as anode materials, the specific capacity was as high as 3101.5 mAh g-1 and maintained at 841.0 mAh g-1 after 500 cycles at 1 A g-1.

Graphene Quantum Dots from Agricultural Wastes: Green Synthesis and Advanced Applications for Energy Storage

Carbon nanostructures are highly promising materials for applications in a variety of different fields. Besides their interesting performances, the possibility to synthesize them from biowaste makes them an eco-friendly resource widely exploitable within a circular economy context. The present work deals with the green, one-pot synthesis of graphene quantum dots (GQDs) from carbon aerogels (CAs) derived from rice husk (RH). After having obtained CAs upon purification of RH, followed by gelification and carbonization of the resulting cellulose, the one-pot solventless production of GQDs was obtained by ball milling. This method determined the formation of crystalline nanostructures with a diameter of around 20 nm, which were analyzed via scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray diffraction, and Raman spectroscopy to obtain a full morphological and structural characterization. GQDs were used as electrode materials for supercapacitors and Li-ion batteries, showing the ability to both accumulate charges over the surface and intercalate lithium-ions. The reported results are a proof of principle of the possibility of exploiting GQDs as support material for the development of advanced systems for energy storage.

Pore-Free Single-Crystalline Particles for Durable Na-Ion Battery Cathodes

The O3-type Na[Ni1-x-yCoxMny]O2 cathodes have received significant attention in sodium-ion batteries (SIBs) due to their high energy density. However, challenges such as structural instability and interfacial instability against an electrolyte solution limit their practical use in SIBs. In this study, the single-crystalline O3-type Na[Ni0.6Co0.2Mn0.2]O2 (SC-NCM) cathode has been designed and synthesized to effectively relieve the degradation pathways of the polycrystalline O3-type Na[Ni0.6Co0.2Mn0.2]O2 (PC-NCM) cathode for SIBs. The mechanically robust SC-NCM due to the absence of pores in the particles enhances tolerance to particle cracking, resulting in stable cycling performance with a cycle retention of 73% over 350 cycles. Moreover, the proposed SC-NCM is synthesized using a simple and cost-effective molten-salt synthetic route without the complex quenching process typically associated with PC-NCM synthesis methods, showing good practical applicability. This study will provide an innovative direction for the development of advanced cathode materials for practical SIBs.

Covalent Organic Frameworks as Electrode Materials for Alkali Metal-ion Batteries

Covalent organic frameworks (COFs) are a class of porous crystalline polymeric materials constructed by linking organic small molecules through covalent bonds. COFs have the advantages of strong covalent bond network, adjustable pore structure, large specific surface area and excellent thermal stability, and have broad application prospects in various fields. Based on these advantages, rational COFs design strategies such as the introduction of active sites, construction of conjugated structures, and carbon material composite, etc. can effectively improve the conductivity and stability of the electrode materials in the field of batteries. This paper introduces the latest research results of high-performance COFs electrode materials in alkali metal-ion batteries (LIBs, SIBs, PIBs and LSBs) and other advanced batteries. The current challenges and future design directions of COFs-based electrode are discussed. It provides useful insights for the design of novel COFs structures and the development of high-performance alkali metal-ion batteries.

PPy-Coated Mo3S4/CoMo2S4 Nanotube-like Heterostructure for High-Performance Lithium Storage

Heterostructured materials show great potential to enhance the specific capacity, rate performance and cycling lifespan of lithium-ion batteries owing to their unique interfaces, robust architectures, and synergistic effects. Herein, a polypyrrole (PPy)-coated nanotube-like Mo3S4/CoMo2S4 heterostructure is prepared by the hydrothermal and subsequent in situ polymerization methods. The well-designed nanotube-like structure is beneficial to relieve the serious volume changes and facilitate the infiltration of electrolytes during the charge/discharge process. The Mo3S4/CoMo2S4 heterostructure could effectively enhance the electrical conductivity and Li+ transport kinetics owing to the refined energy band structure and the internal electric field at the heterostructure interface. Moreover, the conductive PPy-coated layer could inhibit the obvious volume expansion like a firm armor and further avoid the pulverization of the active material and aggregation of generated products. Benefiting from the synergistic effects of the well-designed heterostructure and PPy-coated nanotube-like architecture, the prepared Mo3S4/CoMo2S4 heterostructure delivers high reversible capacity (1251.3 mAh g-1 at 300 mA g-1), superior rate performance (340.3 mAh g-1 at 5.0 A g-1) and excellent cycling lifespan (744.1 mAh g-1 after 600 cycles at a current density of 2.0 A g-1). Such a design concept provides a promising strategy towards heterostructure materials to enhance their lithium storage performances and boost their practical applications.

Promoted kinetics and capacity on the Li2CuTi3O8/C anode by constructing a one dimensional hybrid structure for superior performance lithium ion batteries

Notably, spinel Li2CuTi3O8 with higher theoretical capacity inherits the characteristics of Li4Ti5O12, which is a promising anode material for lithium ion batteries with high energy density. However, the reversible migration of Cu2+ in Li2CuTi3O8 during the discharge process limits the diffusion of Li+, resulting in poor electrochemical performance. Space confinement is a desirable successful strategy to reduce the size of electroactive materials in return for getting improved kinetics and capacity for secondary ion batteries. Here, we develop a strategy by controlling the precursor of Li2CuTi3O8 in the walls of sulfonated polymer nanotubes, and the highly crosslinked copolymer network in the process of pyrolysis caused strong space confinement for the nanoparticles, which effectively prevented the agglomeration of Li2CuTi3O8 during the calcination process. The hybrid porous nanotubes consisting of Li2CuTi3O8 nanoparticles (5-50 nm) embedded in carbon nanotubes exhibit superior performance (402.8 mA h g-1 at 0.2 A g-1, 101 mA h g-1 at 10 A g-1 after 1000 cycles). This work provides a rapid and durable Li2CuTi3O8 electrochemistry, holding great promise in developing a practically viable Li2CuTi3O8 anode and enlightening material engineering in related energy storage and conversion areas.

Quantum dot heterostructures on N-doped graphene with accelerated diffusion kinetics for stable lithium-ion storage

The high energy density and low self-discharge rate of lithium-ion batteries make them promising for large-scale energy storage. However, the practical development of such electrochemical energy storage systems relies heavily on the development of anode materials with high multiplier capacity and stable cycle life. Here, a simple and efficient one-step hydrothermal method is used to obtain stannide heterostructures, which are loaded on N-doped graphene (SnS2/SnO2@NG) that promotes Li+ diffusion for fast charge transfer. It is demonstrated that the built-in electric field generated by the electron transfer from electron-rich SnS2 to SnO2 in the stannide heterojunction collectively provides abundant cation adsorption sites, accelerating the migration of Li+ thus improving the electrochemical reaction kinetics. Besides, the SnS2/SnO2 nanoparticles have high structural stability, and the heterojunction compressive stresses obtained from density functional theory (DFT) calculations can significantly limit the structural damage. When applied as anodes in Li+ batteries with 300 cycles at 0.5 A/g, we achieved a high reversible capacity of 892.73 mAh/g. The rational design of low-cost batteries for energy storage and conversion can benefit from the quantitative design of fast and persistent charge transfer in a stannide heterostructure.

Emerging Multiscale Porous Anodes toward Fast Charging Lithium-Ion Batteries

With the accelerated penetration of the global electric vehicle market, the demand for fast charging lithium-ion batteries (LIBs) that enable improvement of user driving efficiency and user experience is becoming increasingly significant. Robust ion/electron transport paths throughout the electrode have played a pivotal role in the progress of fast charging LIBs. Yet traditional graphite anodes lack fast ion transport channels, which suffer extremely elevated overpotential at ultrafast power outputs, resulting in lithium dendrite growth, capacity decay, and safety issues. In recent years, emergent multiscale porous anodes dedicated to building efficient ion transport channels on multiple scales offer opportunities for fast charging anodes. This review survey covers the recent advances of the emerging multiscale porous anodes for fast charging LIBs. It starts by clarifying how pore parameters such as porosity, tortuosity, and gradient affect the fast charging ability from an electrochemical kinetic perspective. We then present an overview of efforts to implement multiscale porous anodes at both material and electrode levels in diverse types of anode materials. Moreover, we critically evaluate the essential merits and limitations of several quintessential fast charging porous anodes from a practical viewpoint. Finally, we highlight the challenges and future prospects of multiscale porous fast charging anode design associated with materials and electrodes as well as crucial issues faced by the battery and management level.

Aluminene as a Low-Cost Anode Material for Li- and Na-Ion Batteries

Two-dimensional (2D) materials are promising candidates for next-generation battery technologies owing to their high surface area, excellent electrical conductivity, and lower diffusion energy barriers. In this work, we use first-principles density functional theory to explore the potential for using a 2D honeycomb lattice of aluminum, referred to as aluminene, as an anode material for metal-ion batteries. The metallic monolayer shows strong adsorption for a range of metal atoms, i.e., Li, Na, K, and Ca. We observe surface diffusion barriers as low as 0.03 eV, which correlate with the size of the adatom. The relatively low average open-circuit voltages of 0.27 V for Li and 0.42 V for Na are beneficial to the overall voltage of the cell. The estimated theoretical specific capacity has been found to be 994 mA h/g for Li and 870 mA h/g for Na. Our research highlights the promise of aluminene sheets in the development of low-cost, high-capacity, and lightweight advanced rechargeable ion batteries.

Constructing a Low-Cost Si-NSs@C/NG Composite by a Ball Milling-Catalytic Pyrolysis Method for Lithium Storage

Silicon-based composites are promising candidates as the next-generation anode materials for high-performance lithium-ion batteries (LIBs) due to their high theoretical specific capacity, abundant reserves, and reliable security. However, expensive raw materials and complicated preparation processes give silicon carbon anode a high price and poor batch stability, which become a stumbling block to its large-scale practical application. In this work, a novel ball milling-catalytic pyrolysis method is developed to fabricate a silicon nanosheet@amorphous carbon/N-doped graphene (Si-NSs@C/NG) composite with cheap high-purity micron-size silica powder and melamine as raw materials. Through systematic characterizations such as XRD, Raman, SEM, TEM and XPS, the formation process of NG and a Si-NSs@C/NG composite is graphically demonstrated. Si-NSs@C is uniformly intercalated between NG nanosheets, and these two kinds of two-dimensional (2D) materials are combined in a surface-to-surface manner, which immensely buffers the stress changes caused by volume expansion and contraction of Si-NSs. Attributed to the excellent electrical conductivity of graphene layer and the coating layer, the initial reversible specific capacity of Si-NSs@C/NG is 807.9 mAh g^-1 at 200 mA g^-1, with a capacity retention rate of 81% in 120 cycles, exhibiting great potential for application as an anode material for LIBs. More importantly, the simple and effective process and cheap precursors could greatly reduce the production cost and promote the commercialization of silicon/carbon composites.

Intercalation pseudocapacitance in 2D N-doped V2O3 nanosheets for stable and ultrafast lithium-ion storage

2D N-doped V2O3 (N-V2O3) is synthesized as an anode material for Li-ion batteries by a facile strategy. Benefiting from the 3D V–V tunnel structure, sufficient active sites and N modifications, N-V2O3 exhibits stable and ultrafast Li-ion storage.