Development of composite separators by coating hydrochloric acid-treated halloysite nanotubes on polypropylene separators for lithium-ion batteries.

In this study, polypropylene/halloysite nanotube (PP/HNT) composite separators were prepared by coating HNTs treated with hydrochloric acid (HCl) of different concentrations on both sides of a PP separator. The effect of HNTs treated with hydrochloric acid (HCl) of different concentrations on the properties of PP/HNT composite separators was investigated. The results indicate that the PP/HNT composite separator exhibits higher electrolyte uptake and wettability than a commercial PP separator, resulting in a better electrochemical performance in Li/LiFePO4 cells. In particular, the PP/HNTs-1.2 M composite separator with HNTs treated with 1.2 M HCl exhibits the highest electrolyte uptake (384%) and ionic conductivity (1.03 mS cm-1). The cells assembled with a PP/HNTs-1.2 M composite separator deliver discharge capacities of 166 mA h g-1 (0.5 C) and 131 mA h g-1 (3 C) with attractive cycling performance (87.6% capacity retention after 100 cycles). HNTs treated with HCl of appropriate concentrations can significantly improve the properties of PP/HNT composite separators for application in lithium-ion batteries.

1D hollow tubular/2D nanosheet hybrid dimensional porous carbon prepared by one-step carbonization using natural minerals as templates for supercapacitors.

The reasonable construction of one-dimensional (1D)/two-dimensional (2D) hybrid dimensional porous carbon materials with complementary advantages and disadvantages is an important approach to addressing the structural and performance deficiencies of single carbon materials, while also significantly improving the electrochemical performance of super-capacitors. In this study, 1D hollow tubular/2D nanosheet hybrid dimensional porous carbon was synthesized through one-step carbonization using 1D fibrous brucite and 2D layered magnesium carbonate hydroxide as templates. By adjusting the feed ratio of 1D fibrous and 2D layered templates, the morphology, pore structure and specific surface area (SSA) of the prepared 1D hollow tubular/2D nanosheet hybrid dimensional porous carbon were controlled. The prepared hybrid dimensional porous carbons were characterized using scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption-desorption. And their electrochemical performance was also studied by cyclic voltammograms (CV), galvanostatic charge/discharge (GCD) and electrochemical impedance spectroscopy (EIS). The results show that the use of templates with different dimensions significantly influences the morphology, pore structure, SSA and electrochemical performance of the synthesized hybrid dimensional porous carbon. The hybrid dimensional porous carbon (3F) exhibits a high specific capacitance and excellent cycling stability. 3F demonstrates the specific capacitance of 245.3 F g-1 at 1 A g-1. Furthermore, the capacity retention rate remains as high as 93.4% after 8000 cycles at 10 A g-1. This work reveals that hybrid dimensional porous carbon composed of 1D hollow carbon tubes and 2D carbon nanosheets has great potential for use in supercapacitor electrode materials.

Hierarchical hollow tubular fibrous brucite-templated carbons obtained by KOH activation for supercapacitors.

Hierarchical hollow tubular porous carbons have been widely used in applications of supercapacitors, batteries, CO2 capture and catalysis due to their hollow tubular morphology, large aspect ratio, abundant pore structure and superior conductivity. Herein, hierarchical hollow tubular fibrous brucite-templated carbons (AHTFBCs) were prepared using natural mineral fiber brucite as the template and KOH as the chemical activator. The effects of different KOH additions on the pore structure and capacitive performance of AHTFBCs were systematically studied. The specific surface area and micropore content of AHTFBCs after KOH activation were higher than those of HTFBC. The specific surface area of the HTFBC is 400 m2 g-1, while the activated AHTFBC5 has a specific surface area of up to 625 m2 g-1. In particular, compared with HTFBC (6.1%), a series of AHTFBCs (22.1% for AHTFBC2, 23.9% for AHTFBC3, 26.8% for AHTFBC4 and 22.9% for AHTFBC5) with significantly increased micropore content were prepared by controlling the amount of KOH added. The AHTFBC4 electrode displays a high capacitance of 197 F g-1 at 1 A g-1 and the capacitance retention of 100% after 10 000 cycles at 5 A g-1 in the three-electrode system. And an AHTFBC4//AHTFBC4 symmetric supercapacitor exhibits the capacitance of 109 F g-1 at 1 A g-1 in 6 M KOH and an energy density of 5.8 W h kg-1 at 199.0 W kg-1 in 1 M Na2SO4 electrolyte. In addition, the capacity retention of AHTFBC4 in the symmetric supercapacitor was maintained at 92% after 5000 cycles in both 6 M KOH and 1 M Na2SO4 electrolytes.

Silicon micron cages derived from a halloysite nanotube precursor and aluminum sacrificial template in molten AlCl3 as an anode for lithium-ion batteries.

Porous nanostructures have been proposed a promising strategy to improve the electrochemical performance of Si materials as anodes of lithium-ion batteries (LIBs). However, expensive raw materials and the tedious preparation processes hinder their widespread adoption. In this work, silicon micron cages (SMCs) have been synthesized in molten AlCl3 through using spherical aluminum particles as a sacrificial template, and the earth-abundant and low-cost natural halloysite clay as a precursor. The aluminum spheres (1-3 µm) not only act as a sacrificial template but also facilitate the formation of silicon branches, which connect together to form SMCs. As anodes for LIBs, the SMC electrode exhibits a high reversible capacity of 1977.5 mA h g-1 after 50 cycles at a current density of 0.2 A g-1, and 1035.1 mA h g-1 after 300 cycles at a current density of 1.0 A g-1. The improved electrochemical performance of SMCs could be ascribed to the micron cage structure, providing abundant buffering space and mesopores for Si expansion. This promising method is expected to offer a pathway towards the scalable application of Si-based anode materials in the next-generation LIB technology.

Recent developments in natural mineral-based separators for lithium-ion batteries.

Lithium-ion batteries (LIBs) are currently the most widely used portable energy storage devices due to their high energy density and long lifespan. The separator plays a key role in the battery, and its function is to prevent the two electrodes of the battery from contacting, causing the internal short circuit of the battery, and ensuring the lithium ions transportation. Currently, lithium ion battery separators widely used commercially are polyolefin separators, such as polyethylene (PE) and polypropylene (PP) based separators. However, polyolefin separators would shrink at high temperatures, causing battery safety issues, and also causing white pollution. To solve these issues, the use of natural minerals to prepare composite separators for LIBs has attracted widespread attention owing to their unique nano-porous structure, excellent thermal and mechanical stability and being environmentally friendly and low cost. In this review, we present recent application progress of natural minerals in separators for LIBs, including halloysite nanotubes, attapulgite, sepiolite, montmorillonite, zeolite and diatomite. Here, we also have a brief introduction to the basic requirements and properties of the separators in LIBs. Finally, a brief summary of recent developments in natural minerals in the separators is also discussed.

Nacre-Inspired Composite Electrolytes for Load-Bearing Solid-State Lithium-Metal Batteries.

Solid-state lithium-metal batteries with solid electrolytes are promising for next-generation energy-storage devices. However, it remains challenging to develop solid electrolytes that are both mechanically robust and strong against external mechanical load, due to the brittleness of ceramic electrolytes and the softness of polymer electrolytes. Herein, a nacre-inspired design of ceramic/polymer solid composite electrolytes with a "brick-and-mortar" microstructure is proposed. The nacre-like ceramic/polymer electrolyte (NCPE) simultaneously possesses a much higher fracture strain (1.1%) than pure ceramic electrolytes (0.13%) and a much larger ultimate flexural modulus (7.8 GPa) than pure polymer electrolytes (20 MPa). The electrochemical performance of NCPE is also much better than pure ceramic or polymer electrolytes, especially under mechanical load. A 5 × 5 cm2 pouch cell with LAGP/poly(ether-acrylate) NCPE exhibits stable cycling with a capacity retention of 95.6% over 100 cycles at room temperature, even undergoes a large point load of 10 N. In contrast, cells based on pure ceramic and pure polymer electrolyte show poor cycle life. The NCPE provides a new design for solid composite electrolyte and opens up new possibilities for future solid-state lithium-metal batteries and structural energy storage.

Use of a diatomite template to prepare a MoS2/amorphous carbon composite and exploration of its electrochemical properties as a supercapacitor.

A MoS2/amorphous carbon composite was prepared using diatomite as a template and ammonium thiomolybdate/sucrose as starting materials. The composite perfectly inherits the template morphology with a porous structure, in which MoS2 possesses a structure with several layers, and amorphous carbon is partially inserted into the interlayer spaces of the MoS2, inhibiting the restacking of the MoS2 nanosheets along the (002) plane. The interlaminar distance of the adjacent MoS2 nanosheets in the composite is 1.03 nm, which is approximately twice that between adjacent MoS2 and carbon layers. The supercapacitor utilizing this composite exhibits a high specific capacitance, 167.3 F g-1 at the current density of 0.5 A g-1 and high rate capability, 96.4 F g-1 at 10 A g-1. Moreover, the capacitance retention is maintained at 93.2% after 1000 cycles, indicating excellent cycling stability. In contrast, the capacities of pure AC and MoS2 are much lower, and also the cyclability of MoS2. The overall improvement in electrochemical performance could be ascribed to the unique microstructure and the close combination of MoS2 and amorphous carbon.

[Spectroscopy Characterization of Anthracite Oxide].

With high degree of metamorphism and carbon content, anthracite is commonly used for activated carbon. The structural properties of anthracite play a decisive role in its materialization, while with chemical oxidation, anthracite structure can be purposefully improved. The anthracite oxide was prepared via acid leaching and oxidizing, using high carbon content and low ash content anthracite from Zhaotong, Yunnan Province, China. The structural and spectroscopy characteristics of anthracite and anthracite oxide were acquired with X-ray diffraction (XRD), Raman spectroscopy and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). The results show that crystallites in anthracite have intermediate structures between graphite and amorphous. Compared with bitumite and lignite, its structure order degree lies between graphite and low metamorphic coals with relatively high average diameter of coal crystallites(La) and average height of coal crystallites (Lc). The process of anthracite oxidation can be modeled in two steps, the edge of crystal was curled and destroyed with strong oxidation, with the generation of CO group and intercalation of HNO3/H2SO4 into the edge layers, leading to the reducing of lateral sizes; HNO3/H2SO4 were continually intercalated into crystals, resulted in the increase of interlayer spacing (d(002)) from 0.351 to 0.361 nm, and the number of stacked layers dropped to 4.5 from 6 due to exfoliate. ID1/IG in Raman spectroscopy increased from 1.9 to 2.0, with full width at half maximum (FWHM) of G bond and intensity of D2 bond increasing from 63 to 68 and 10.26 to 13.78. Numbers of new ­C­O­, CO, ­NO2 groups generated, leading to the decrease of oxygen-containing functional groups content from 0.11 to 0.42. After HNO3/H2SO4 oxidation, the aromaticity (fa) of anthracite oxide increases, with the decrease of structure order degree and more-over a lot of active reaction sites generates in the process. The oxidation of anthracite enables anthracite has great potential in the application of porous carbon preparation.