Structural Reorganization-Based Nanomaterials as Anodes for Lithium-Ion Batteries: Design, Preparation, and Performance

In recent years, with the growing demand for higher capacity, longer cycling life, and higher power and energy density of lithium ion batteries (LIBs), the traditional insertion-based anodes are increasingly considered out of their depth. Herein, attention is paid to the structural reorganization electrode, which is the general term for conversion-based and alloying-based materials according to their common characteristics during the lithiation/delithiation process. This Review summarizes the recent achievements in improving and understanding the lithium storage performance of conversion-based anodes (especially the most widely studied transition metal oxides like Mn-, Fe-, Co-, Ni-, and Cu-based oxides) and alloying-based anodes (mainly including Si-, Sn-, Ge-, and Sb-based materials). The synthesis schemes, morphological control and reaction mechanism of these materials are also included. Finally, viewpoints about the challenges and feasible improvement measures for future development in this direction are given. The aim of this Review is to shed some light on future electrode design trends of structural reorganization anode materials for LIBs.

Si@void@C Nanofibers Fabricated Using a Self-Powered Electrospinning System for Lithium-Ion Batteries

In recent years, research in lithium-ion batteries (LIBs) has been focused on improving their performance in various ways, such as density, capacity, and lifetime, but little attention has been paid to the energy consumption cost in the manufacturing process. Herein, we report an energy-efficient preparation method of anode materials for LIBs based on a self-powered electrospinning system without an external power source, which consists of a rotatory triboelectric nanogenerator (r-TENG), a power management circuit, and an electrospinning unit. By harvesting kinetic energy from a handle rotation, the r-TENG is able to fully power the electrospinning system to fabricate nanofibers for LIBs. The as-obtained Si@void@C nanofibers present outstanding cyclic performance with a discharge capacity of 1045.2 mA h g^-1 after 100 cycles and 88% capacity retention, along with an excellent high rate capacity of 400 mA h g^-1 at a current density of 5 A g^-1, which are completely comparable with those made by commercial electrospinning equipment. Our study demonstrates an innovative and distinct approach toward an extremely low-cost preparation procedure of electrode materials, leading to a great breakthrough for the LIB production industry.

Uniform MnCo2O4 Porous Dumbbells for Lithium-Ion Batteries and Oxygen Evolution Reactions

Three-dimensional (3D) binary oxides with hierarchical porous nanostructures are attracting increasing attentions as electrode materials in energy storage and conversion systems because of their structural superiority which not only create desired electronic and ion transport channels but also possess better structural mechanical stability. Herein, unusual 3D hierarchical MnCo₂O₄ porous dumbbells have been synthesized by a facile solvothermal method combined with a following heat treatment in air. The as-obtained MnCo₂O₄ dumbbells are composed of tightly stacked nanorods and show a large specific surface area of 41.30 m² g^-1 with a pore size distribution of 2-10 nm. As an anode material for lithium-ion batteries (LIBs), the MnCo₂O₄ dumbbell electrode exhibits high reversible capacity and good rate capability, where a stable reversible capacity of 955 mA h g^-1 can be maintained after 180 cycles at 200 mA g^-1. Even at a high current density of 2000 mA g^-1, the electrode can still deliver a specific capacity of 423.3 mA h g^-1, demonstrating superior electrochemical properties for LIBs. In addition, the obtained 3D hierarchical MnCo₂O₄ porous dumbbells also display good oxygen evolution reaction activity with an overpotential of 426 mV at a current density of 10 mA cm^-2 and a Tafel slope of 93 mV dec^-1.

Nanostructured (Co, Mn)3O4 for High Capacitive Supercapacitor Applications

Nanostructured Co doped Mn₃O₄ spinel structure ((Co, Mn)₃O₄) were prepared by co-precipitation under O₃ oxidizing conditions and post-heat treatment. The product was composed of nanogranules with a diameter of 20-60 nm. The electrochemical performance of (Co, Mn)₃O₄ electrode was tested by cyclic voltammetry, impedance, and galvanostatic charge-discharge measurements. A maximum specific capacitance value of 2701.0 F g^-1 at a current density of 5 A g^-1 could be obtained within the potential range from 0.01 to 0.55 V versus Hg/HgO electrode in 6 mol L^-1 KOH electrolyte. When at high current density of 30 A g^-1, the capacitance is 1537.2 F g^-1 or 56.9% of the specific capacitance at 5 A g^-1, indicating its good rate capability. After 500 cycles at 20 A g^-1, the specific capacitance remains 1324 F g^-1 with a capacitance retention of 76.4%.

Recovery of lithium from the effluent obtained in the process of spent lithium-ion batteries recycling

A novel process of lithium recovery as lithium ion sieve from the effluent obtained in the process of spent lithium-ion batteries recycling is developed. Through a two-stage precipitation process using Na₂CO₃ and Na₃PO₄ as precipitants, lithium is recovered as raw Li₂CO₃ and pure Li₃PO₄, respectively. Under the best reaction condition (both the amounts of Na₂CO₃ and Li₃PO₄vs. the theoretical ones are about 1.1), the corresponding recovery rates of lithium (calculated based on the concentration of the previous stage) are 74.72% and 92.21%, respectively. The raw Li₂CO₃ containing the impurity of Na₂CO₃ is used to prepare LiMn₂O₄ as lithium ion sieve, and the tolerant level of sodium on its property is studied through batch tests of adsorption capacity and corrosion resistance. When the weight percentage of Na₂CO₃ in raw Li₂CO₃ is controlled less than 10%, the Mn corrosion percentage of LiMn₂O₄ decreases to 21.07%, and the adsorption capacity can still keep at 40.08 mg g^-1. The results reveal that the conventional separation sodium from lithium may be avoided through the application of the raw Li₂CO₃ in the field of lithium ion sieve.

Metal-Organic Frameworks Derived Okra-like SnO2 Encapsulated in Nitrogen-Doped Graphene for Lithium Ion Battery

A facile process is developed to prepare SnO₂-based composites through using metal-organic frameworks (MOFs) as precursors. The nitrogen-doped graphene wrapped okra-like SnO₂ composites (SnO₂@N-RGO) are successfully synthesized for the first time by using Sn-based metal-organic frameworks (Sn-MOF) as precursors. When utilized as an anode material for lithium-ion batteries, the SnO₂@N-RGO composites possess a remarkably superior reversible capacity of 1041 mA h g^-1 at a constant current of 200 mA g^-1 after 180 charge-discharge processes and excellent rate capability. The excellent performance can be primarily ascribed to the unique structure of 1D okra-like SnO₂ in SnO₂@N-RGO which are actually composed of a great number of SnO₂ primary crystallites and numerous well-defined internal voids, can effectively alleviate the huge volume change of SnO₂, and facilitate the transport and storage of lithium ions. Besides, the structural stability acquires further improvement when the okra-like SnO₂ are wrapped by N-doped graphene. Similarly, this synthetic strategy can be employed to synthesize other high-capacity metal-oxide-based composites starting from various metal-organic frameworks, exhibiting promising application in novel electrode material field of lithium-ion batteries.

Effect of storage environment on hydrogen generation by the reaction of Al with water

Water vapor rather than oxygen is responsible for the degradation of Al activity during storage in atmospheric environment.