Defect-rich porous graphitic phase carbon nitride layer grafted MXene as desolvation promoter for efficient sulfur conversion in extremely harsh conditions.

Lithium-sulfur (Li-S) batteries exhibit superior theoretical capacity and energy density but are still hindered by the sluggish redox conversion kinetic of lithium polysulfides arising from the significant desolvation barrier, especially under high current density or low-temperature environments. Herein, a two-dimensional (2D) porous graphitic phase carbon nitride/MXene (CN-MX) heterostructure with intrinsic defects was designed via electrostatic adherence and in-situ thermal polycondensation. In the design, the defect-rich CN with abundant catalytic activity and porous structure could efficiently facilitate the lithium polysulfides capture, the dissociation of solvated lithium-ion (Li+), and fast Li+ diffusion. Concurrently, 2D MXene nanosheets with high electronic conductivity could act as charge transport channels and provide electrochemical active sites for sulfur redox reactions. The Li-S cells with CN-MX heterostructure modified separator demonstrated uncommon rate performance (945 mAh/g at 4.0 C) and satisfactory areal capacity (5.5 mAh cm-2 at 0.2 C). Most remarkably, even at 0 °C, the assembled Li-S batteries performed favorable cycle stability (91.6% capacity retention after 100 cycles at 0.5 C) and outstanding rate performance (695 mAh/g at 2.0 C), and superior high loading performance (5.1 mAh cm-2 at 0.1 C). This work offers exciting new insights to enable Li-S batteries to operate in extreme environments.

Superfast Zincophilic Ion Conductor Enables Rapid Interfacial Desolvation Kinetics for Low-Temperature Zinc Metal Batteries.

Low-temperature rechargeable aqueous zinc metal batteries (AZMBs) as highly promising candidates for energy storage are largely hindered by huge desolvation energy barriers and depressive Zn2+ migration kinetics. In this work, a superfast zincophilic ion conductor of layered zinc silicate nanosheet (LZS) is constructed on a metallic Zn surface, as an artificial layer and ion diffusion accelerator. The experimental and simulation results reveal the zincophilic ability and layer structure of LZS not only promote the desolvation kinetics of [Zn(H2O)6]2+ but also accelerate the Zn2+ transport kinetics across the anode/electrolyte interface, guiding uniform Zn deposition. Benefiting from these features, the LZS-modified Zn anodes showcase long-time stability (over 3300 h) and high Coulombic efficiency with ≈99.8% at 2 mA cm-2, respectively. Even reducing the environment temperature down to 0 °C, ultralong cycling stability up to 3600 h and a distinguished rate performance are realized. Consequently, the assembled Zn@LZS//V2O5-x full cells deliver superior cyclic stability (344.5 mAh g-1 after 200 cycles at 1 A g-1) and rate capability (285.3 mAh g-1 at 10 A g-1) together with a low self-discharge rate, highlighting the bright future of low-temperature AZMBs.

Engineering a Dynamic Solvent-Phobic Liquid Electrolyte Interphase for Long-Life Lithium Metal Batteries.

The heterogeneity, species diversity, and poor mechanical stability of solid electrolyte interphases (SEIs) in conventional carbonate electrolytes result in the irreversible exhaustion of lithium (Li) and electrolytes during cycling, hindering the practical applications of Li metal batteries (LMBs). Herein, this work proposes a solvent-phobic dynamic liquid electrolyte interphase (DLEI) on a Li metal (Li-PFbTHF (perfluoro-butyltetrahydrofuran)) surface that selectively transports salt and induces salt-derived SEI formation. The solvent-phobic DLEI with C-F-rich groups dramatically reduces the side reactions between Li, carbonate solvents, and humid air, forming a LiF/Li3PO4-rich SEI. In situ electrochemical impedance spectroscopy and Ab-initio molecular dynamics demonstrate that DLEI effectively stabilizes the interface between Li metal and the carbonate electrolyte. Specifically, the LiFePO4||Li-PFbTHF cells deliver 80.4% capacity retention after 1000 cycles at 1.0 C, excellent rate capacity (108.2 mAh g-1 at 5.0 C), and 90.2% capacity retention after 550 cycles at 1.0 C in full-cells (negative/positive (N/P) ratio of 8) with high LiFePO4 loadings (15.6 mg cm-2) in carbonate electrolyte. In addition, the 0.55 Ah pouch cell of 252.0 Wh kg-1 delivers stable cycling. Hence, this study provides an effective strategy for controlling salt-derived SEI to improve the cycling performances of carbonate-based LMBs.

Mesoporous Ti4 O7 Nanosheets with High Polar Surface Area for Catalyzing Separator to Reduce the Shuttle Effect of Soluble Polysulfides in Lithium-sulfur Batteries.

In the effort to accelerate adsorption and catalytic conversion of lithium polysulfides (Li-PSs) and suppress the shuttle effect of lithium-sulfur batteries (LSBs), the Ti4 O7 nanosheets/carbon material-modified separator is successfully fabricated to reducing soluble Li-PSs' crossover from cathode to anode. The catalyst of mesoporous Ti4 O7 nanosheets with O-Ti-O units synthesized at low temperature shows both excellent conductivity and high surface area. The modified separator can serve as a diffusion barrier of Li-PSs and catalyst for converting soluble low-chain sulfides into insoluble ones and then remarkably enhance the sulfur utilization and electrochemical performance of the LSB. This work provides a feasible avenue in both design and synthesis of mesoporous catalyst materials for suppressing the shuttle effect of lithium-sulfur batteries.

Corrosion Resistance of Waterborne Epoxy Resin Coating Cross-Linked by Modified Tetrabutyl Titanate.

The development of waterborne coating is essentially important for environmental protection, and cross-linking agent is of great significance for ensuring corrosion resistance of the coating. In this work, tetrabutyl titanate was modified by ethylene glycol and tris(2-hydroxyethyl) amine and used for the solidification of waterborne acrylic-epoxy resin. Fourier-transform infrared spectroscopy (FTIR) analysis revealed that the agent reacted with OH groups first to cross-link the resin preliminarily, and then, when the amount of agent was further increased, the amino groups opened epoxide rings resulting in a secondary cross-link. Field emission scanning electron microscope (FESEM) observation and electrochemical impedance spectroscopy (EIS) test found that, when the cross-linking agent was used at 6%, the coating remains intact and kept an impedance of as high as 108 Ωcm2 even after being immersed in NaCl solution for 30 days. Copper-accelerated acetic acid-salt spray (CASS) test confirmed that the coating containing 6% cross-linking agent provided the best protection for the carbon steel substrate.

MnO2 nanoflowers grown on a polypropylene separator for use as both a barrier and an accelerator of polysulfides for high-performance Li-S batteries.

The separator modification has been considered to be the most effective approach to obtain high-stability lithium-sulfur batteries (LSBs). Therefore, a separator with an ultralight modification layer plays an indispensable role to obtain LSBs with high specific capacity and high energy density. Herein, we report a novel modified separator with an ultrathin and lightweight MnO2 functional layer (500 nm, 0.1 mg cm-2), which was grown in situ on a Celgard-2400 separator (MnO2@PP) via a facile hydrothermal reaction. The MnO2@PP separator effectively suppressed the shuttle of lithium polysulfides (LiPSs) and improved the redox process. In addition, the strong chemical affinity of MnO2 for LiPSs was also verified by first-principles calculations. Benefiting from these advantages, the cell with the MnO2@PP separator delivered a high rate performance of 759 mA h g-1 at 2.5 C and an initial capacity of 825 mA h g-1 with a retention of 684 mA h g-1 after 400 cycles at 1.25 C. Even with a high sulfur loading of 6 mg cm-2, the obtained cell exhibited a reversible capacity of 747 mA h g-1 after 150 cycles.

A novel 3D porous pseudographite/Si/Ni composite anode material fabricated by a facile method.

A novel 3D porous pseudographite/Si/Ni (PG/Si/Ni) composite was prepared by a facile low-temperature calcination method using saturable starch and NiCl2·6H2O as precursors. The pseudographite matrix of PG/Si/Ni was obtained from the reaction between starch and NiCl2·6H2O during the calcination process. Compared to the C/Si electrode, the PG/Si/Ni electrode delivers a high reversible specific capacity of 659.66 mA h g-1 at a current density of 1 A g-1 even after 2000 cycles. In addition, the PG/Si/Ni electrode shows superior rate performance and still maintains a high specific capacity of 1324.01 mA h g-1 when the cycle current density returns to 0.1 A g-1. The porous pseudographite structure is able to improve Li+ diffusion efficiency, reduce pulverization and lead to the formation of stable SEI layers during the cycling process. Therefore, these results suggest that the 3D porous pseudographite/Si/Ni composite is a promising novel anode material. Besides, the low-temperature synthesis method of the pseudographite matrix can be applied for further modification of carbon-based Si anode materials.

Enhanced electrochemical performance of LiNi0.8Co0.1Mn0.1O2 with a 3D-SiO2 framework by a new negative pressure immersion method.

LiNi0.8Co0.1Mn0.1O2 is one of the most promising cathode materials for lithium ion batteries; however, during the charge/discharge process, it suffers from capacity fading, which is considered to be due to intergranular cracking. Herein we develop an original concept to alleviate this problem via negative pressure immersion treatment. A 3D-SiO2 framework is formed in the intergranular voids and at grain boundaries (functioning as the buffer zone and transfer-bridge) and the SiO2 protective layer is completely and homogeneously coated on the surfaces of the pristine particles through a hydrolytic condensation reaction involving tetraethoxysilane (TEOS). The 3D-SiO2 framework has two advantages: firstly, acting as a buffer zone, the framework can effectively inhibit the generation and extension of intergranular cracking; secondly, like the SiO2 protective layer on the surface of the particles, the 3D-SiO2 framework can impede side reactions between primary particles (grains) and electrolyte inside the particles. As a result, the as-modified LiNi0.8Co0.1Mn0.1O2 exhibits enhanced cycling performance with 92.4% capacity retention after 100 cycles at 1 C (200 mA h·g-1), while the capacity retention values for the pristine particles and normal coating treatment particles are only 55.4% and 82.6%, respectively. Moreover, the thermal stability (60 °C) is distinctly enhanced and the rate performance is significantly improved at high rates (2, 3 and 5 C).

Synthesis of High-performance LiNi0.6Co0.2Mn0.2O2 Cathode Material for Lithium-ion Batteries by Using a Four Times Liquid Nitrogen Quenching Method and an Al2O3 Coating Method.

Based on the normal co-precipitation method to synthesize LiNi0.6Co0.2Mn0.2O2 cathode material, we propose a novel approach using a liquid nitrogen quenching method to synthesize Al2O3 coated LiNi0.6Co0.2Mn0.2O2 cathode material. In the whole process, liquid nitrogen was used four times to quench the materials from high temperatures (50 °C, 750 °C, 90 °C, 500 °C) to -196 °C rapidly in four stages. Various characterizations proved that this method could help to improve the electrochemical performance of lithium-ion batteries. Especially at 5 C rate current, after 100 cycles, the specific discharge capacities were 24.5 mAh/g (LNCM 622), 43.8 mAh/g (LNCM 622-LN), and 53.9 mAh/g (LNCM 622-LN@Al2O3). Liquid N2 quenching increased the charge/discharge capacities and the Al2O3 layer increased the cycle stability at high current, to finally obtain improved electrochemical properties.

A facile in situ synthesis of SiC&Si@CNT composite 3D frameworks as an anode material for lithium-ion batteries.

SiC&Si@CNT composite 3D frameworks were successfully synthesized via an in situ reduction method of a C@SiO2@CNT precursor. Owing to the extremely large amount of heat derived from magnesiothermic reduction, SiC particles of the SiC&Si@CNT composite were obtained by a reaction between Si and C. The amount of SiC could be adjusted by changing the poly-dopamine coating time. The SiC&Si@CNT composite is composed of reduced nano Si, fine SiC and CNTs. The as-prepared materials, particularly the SiC&Si@CNT-1 sample, show superior cycling performance and electrochemical characteristics as anode materials for lithium-ion batteries. In particular, the specific capacity of the SiC&Si@CNT-1 electrode reaches 1051.44 mA h g-1 at 1 A g-1 even after 880 cycles. Furthermore, the SiC&Si@CNT-1 electrode delivered ideal reversible capacities of 671.58 mA h g-1 and 476.71 mA h g-1 at high current densities of 4 A g-1 and 8 A g-1, respectively. The porous nanostructure of the SiC&Si@CNT composite 3D framework is beneficial for shortening the path of lithium-ion diffusion inside the electrode, alleviating the volume expansion and contraction during the cycling process. These results suggest that the SiC&Si@CNT composite 3D frameworks can be used as appropriate anode materials for lithium-ion batteries.