Nian-Wu Li

Accommodating lithium into 3D current collectors with a submicron skeleton towards long-life lithium metal anodes

Lithium metal is one of the most attractive anode materials for electrochemical energy storage. However, the growth of Li dendrites during electrochemical deposition, which leads to a low Coulombic efficiency and safety concerns, has long hindered the application of rechargeable Li-metal batteries. Here we show that a 3D current collector with a submicron skeleton and high electroactive surface area can significantly improve the electrochemical deposition behaviour of Li. Li anode is accommodated in the 3D structure without uncontrollable Li dendrites. With the growth of Li dendrites being effectively suppressed, the Li anode in the 3D current collector can run for 600 h without short circuit and exhibits low voltage hysteresis. The exceptional electrochemical performance of the Li-metal anode in the 3D current collector highlights the importance of rational design of current collectors and reveals a new avenue for developing Li anodes with a long lifespan.

An Artificial Solid Electrolyte Interphase Layer for Stable Lithium Metal Anodes

A Li3PO4 solid electrolyte interphase (SEI) layer is demonstrated to be stable in the organic electrolyte, even during the Li deposition/dissolution process. Thus, the Li-conducting Li3PO4 SEI layer with a high Youngs modulus can effectively reduce side reactions between Li metal and the electrolyte and can restrain Li dendrite growth in lithium-metal batteries during cycling.

Advanced Micro/Nanostructures for Lithium Metal Anodes

Owning to their very high theoretical capacity, lithium metal anodes are expected to fuel the extensive practical applications in portable electronics and electric vehicles. However, unstable solid electrolyte interphase and lithium dendrite growth during lithium plating/stripping induce poor safety, low Coulombic efficiency, and short span life of lithium metal batteries. Lately, varies of micro/nanostructured lithium metal anodes are proposed to address these issues in lithium metal batteries. With the unique surface, pore, and connecting structures of different nanomaterials, lithium plating/stripping processes have been regulated. Thus the electrochemical properties and lithium morphologies have been significantly improved. These micro/nanostructured lithium metal anodes shed new light on the future applications for lithium metal batteries.

Graphitized Carbon Fibers as Multifunctional 3D Current Collectors for High Areal Capacity Li Anodes

The Li metal anode has long been considered as one of the most ideal anodes due to its high energy density. However, safety concerns, low efficiency, and huge volume change are severe hurdles to the practical application of Li metal anodes, especially in the case of high areal capacity. Here it is shown that that graphitized carbon fibers (GCF) electrode can serve as a multifunctional 3D current collector to enhance the Li storage capacity. The GCF electrode can store a huge amount of Li via intercalation and electrodeposition reactions. The as-obtained anode can deliver an areal capacity as high as 8 mA h cm-2 and exhibits no obvious dendritic formation. In addition, the enlarged surface area and porous framework of the GCF electrode result in lower local current density and mitigate high volume change during cycling. Thus, the Li composite anode displays low voltage hysteresis, high plating/stripping efficiency, and long lifespan. The multifunctional 3D current collector promisingly provides a new strategy for promoting the cycling lifespan of high areal capacity Li anodes.

Passivation of Lithium Metal Anode via Hybrid Ionic Liquid Electrolyte toward Stable Li Plating/Stripping

Hybrid electrolyte of ionic liquid and ethers is used to passivate the surface of Li metal surface via modification of the as‐formed solid electrolyte interphase with N‐propyl‐N‐methylpyrrolidinium bis(trifluoromethanesulfonyl)amide (Py13TFSI), thereby reducing the side reactions between the Li metal and electrolyte, leading to remarkably suppressed Li dendrite growth and mitigating Li metal corrosion.

Stable Li Metal Anodes via Regulating Lithium Plating/Stripping in Vertically Aligned Microchannels

Li anodes have been rapidly developed in recent years owing to the rising demand for higher-energy-density batteries. However, the safety issues induced by dendrites hinder the practical applications of Li anodes. Here, Li metal anodes stabilized by regulating lithium plating/stripping in vertically aligned microchannels are reported. The current density distribution and morphology evolution of the Li deposits on porous Cu current collectors are systematically analyzed. Based on simulations in COMSOL Multiphysics, the tip effect leads to preferential deposition on the microchannel walls, thus taking full advantage of the lightening rod theory of classical electromagnetism for restraining growth of Li dendrites. The Li anode with a porous Cu current collector achieves an enhanced cycle stability and a higher average Coulombic efficiency of 98.5% within 200 cycles. In addition, the resultant LiFePO4 /Li full battery demonstrates excellent rate capability and stable cycling performance, thus demonstrating promise as a current collector for high-energy-density, safe rechargeable Li batteries.

A Flexible Solid Electrolyte Interphase Layer for Long-Life Lithium Metal Anodes

Lithium (Li) metal is a promising anode material for high-energy density batteries. However, the unstable and static solid electrolyte interphase (SEI) can be destroyed by the dynamic Li plating/stripping behavior on the Li anode surface, leading to side reactions and Li dendrites growth. Herein, we design a smart Li polyacrylic acid (LiPAA) SEI layer high elasticity to address the dynamic Li plating/stripping processes by self-adapting interface regulation, which is demonstrated by in situ AFM. With the high binding ability and excellent stability of the LiPAA polymer, the smart SEI can significantly reduce the side reactions and improve battery safety markedly. Stable cycling of 700 h is achieved in the LiPAA-Li/LiPAA-Li symmetrical cell. The innovative strategy of self-adapting SEI design is broadly applicable, providing opportunities for use in Li metal anodes.

Three-dimensional sandwich-type graphene@microporous carbon architecture for lithium–sulfur batteries

The commercial applications of lithium–sulfur batteries are hindered by several issues including the poor electronic/ionic conductivity of sulfur and discharge products, the dissolution of lithium polysulfides in organic electrolytes, and the volume change during charge/discharge processes. In this study, a three-dimensional (3-D) sandwich-type graphene@microporous carbon (G@MC) architecture with large pore volume (2.65 cm3 g−1) and ultrahigh surface area (3374 m2 g−1) was designed to encapsulate sulfur and polysulfides in the hierarchical microporous structure. The G@MC materials with a lot of sp2 hybrid carbon atoms can provide 3-D electron transfer pathways for sulfur and discharge products. Furthermore, the G@MC materials with the novel hierarchical structure can absorb a lot of polysulfides and restrain the polysulfide diffusion, and provide adequate nanospace for sulfur expansion ensuring the structural integrity during the cycling. Thus, the optimized G@MC–S nanocomposite with high sulfur loading (75.4 wt%) retains a discharge capacity of 541.3 mA h g−1 after 500 cycles at 0.5C. This design strategy is simple and broadly applicable, providing new opportunities for materials design that can be extended to various electrode materials.

Self-Powered Electrospinning System Driven by a Triboelectric Nanogenerator

Broadening the application area of the triboelectric nanogenerators (TENGs) is one of the research emphases in the study of the TENGs, whose output characteristic is high voltage with low current. Here we design a self-powered electrospinning system, which is composed of a rotating-disk TENG (R-TENG), a voltage-doubling rectifying circuit (VDRC), and a simple spinneret. The R-TENG can generate an alternating voltage up to 1400 V. By using a voltage-doubling rectifying circuit, a maximum constant direct voltage of 8.0 kV can be obtained under the optimal configuration and is able to power the electrospinning system for fabricating various polymer nanofibers, such as polyethylene terephthalate (PET), polyamide-6 (PA6), polyacrylonitrile (PAN), polyvinylidene difluoride (PVDF), and thermoplastic polyurethanes (TPU). The system demonstrates the capability of a TENG for high-voltage applications, such as manufacturing nanofibers by electrospinning.

Ultra-robust triboelectric nanogenerator for harvesting rotary mechanical energy

Triboelectric nanogenerators (TENGs) for harvesting rotary mechanical energy are mostly based on in-plane sliding or free-standing mode. However, the relative displacement between two contacting triboelectric layers causes abrasion, which lowers the output power and reduces service life. Therefore, it is important to develop a method to minimize abrasion when harvesting rotary mechanical energy. Here, we report a scale-like structured TENG (SL-TENG), in which two triboelectric layers work under a contact-separation mode to avoid in-plane relative sliding in order to minimize abrasion. As a result, the SL-TENG exhibits outstanding robustness. For example, the output voltage of the SL-TENG does not exhibit any measurable decay although this output has been continuously generated through more than a million cycles. Moreover, at a very low rotation rate of 120 rpm, the SL-TENG can generate a maximum short-circuit current of 78 μA, delivering an instantaneous power density of 2.54 W/m2 to an external load. In relation to this, a Li-ion battery was charged using the SL-TENG. After a 30-min charging time, the battery achieved a discharge capacity of 0.1 mAh. Through a power management circuit integrated into the SL-TENG, a continuous direct current (DC) of 5 V is outputted, providing sufficient DC power for driving a radio-frequency wireless sensor and other conventional electronics.