In Situ Construction of Bimetallic Selenides Heterogeneous Interface on Oxidation-Stable Ti3C2Tx MXene Toward Lithium Storage with Ultrafast Charge Transfer Kinetics.

Ti3C2Tx (MXene) is widely acknowledged as an excellent substrate for constructing heterogeneous structures with transition metal chalcogenides (TMCs) for boosting the electrochemical performance of lithium-ion storage. However, conventional synthesis strategies inevitably lead to poor electrochemical charge transfer due to Ti3C2Tx-derived TiO2 at the heterogeneous interface between Ti3C2Tx and TMCs. Here, an innovative in situ selenization strategy is proposed to replace the originally generated TiO2 on Ti3C2Tx with metallic TiSe2 interphase, clearing the bottleneck of slow charge transfer barrier caused by MXene oxidation. The construction of bimetallic selenide formed by CoSe2 and TiSe2 generates intrinsic electric fields to guide the fast ion diffusion kinetics in a heterogeneous interface. Additionally, the CoSe2/TiSe2/Ti3C2Tx heterogeneous structure with enhanced structural stability and improved rate performance is confirmed by both experiments and theoretical calculations. The engineered heterogeneous structure exhibits an ultra-high pseudocapacitance contribution (73.1% at 0.1 mV s-1), rendering it well-suited to offset the kinetics differences between double-layer materials. The assembled lithium-ion capacitor based on CoSe2/TiSe2/Ti3C2Tx possesses a high energy density and an ultralong life span (89.5% after 10 000 times at 2 A g-1). This devised strategy provides a feasible solution for utilizing the performance advantages of MXene substrates in lithium storage with ultrafast charge transfer kinetics.

Self-Templating Synthesis of Mesoporous Carbon Cathode Materials for High-Performance Lithium-Ion Capacitors.

Lithium-ion capacitors (LICs) have attracted considerable interest because of their excellent power and energy densities. However, the development of LICs is limited by the low capacity of the cathode and the kinetics mismatch between the cathode and anode. In this work, mesoporous carbon materials (MCs) with uniform pore sizes were prepared using magnesium citrate as the raw material through a self-templating method. During the carbonization process, MgO nanoparticles generated from magnesium citrate act as a template, resulting in a more orderly pore structure. The resultant MCs demonstrate a high specific surface area of 1673 m2 g-1 and an abundance of small mesopores, which significantly accelerated ion migration within the electrolyte and expedited the formation of electric double layers. Benefiting from these advantages, the MCs cathode demonstrates a high reversible specific capacity, excellent cycling stability, and rate performance. The assembled MCs-based LIC provides a high energy density of 152.2 Wh kg-1 and a high power density of 14.3 kW kg-1. After 5000 cycles, a capacity retention rate of 80% at the current density of 1 A g-1 is obtained. These results highlight the excellent potential of MCs as a cathode material for LICs.

Tracing the geographical origin of endangered fungus Ophiocordyceps sinensis, especially from Nagqu, using UPLC-Q-TOF-MS.

Ophiocordyceps sinensis (OS), known as "soft gold", played an important role in local economic development. OS from different producing areas was difficult to be discriminated by the appearance. Nagqu OS, a distinguished and safeguarded geographical indication product, commands a premium price in market. The real claim of OS geographical origins is urgently required. Here, 81 OS samples were collected from Tibetan Plateau in China to explore markers for tracing origins. OS from Xigazê can be distinguished by dark color of head of caterpillar. Then 57 samples, a fully representative training-sample set, were used to set up OPLS-DA models by nontargeted metabolomics from UPLC-QTOF-MS. Certain markers were successfully identified and validation using 21 blind test samples confirmed that the markers can trace the geographical origin of OS, especially Nagqu samples. It was affirmed that UPLC-QTOF-MS-based untargeted metabolomics coupled with OPLS-DA was a reliable strategy to trace the geographical origins of OS.

Rapid Ion Transport Induced by the Enhanced Interaction in Composite Polymer Electrolyte for All-Solid-State Lithium-Metal Batteries.

High-quality solid electrolyte is the key to developing high-performance all-solid-state lithium-metal batteries (ASSLMBs). Herein, we report a thin composite polymer electrolyte (CPE) based on nanosized Li6.4La3Zr1.4Ta0.6O12 (N-LLZTO) and the PVDF-HFP matrix through a simple film-casting method. N-LLZTO induces partial dehydrofluorination of the poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) matrix that activates the coordination of Li+ with PVDF-HFP and LLZTO due to Lewis acid-base interactions, which facilitates dissociation of lithium salt to increase the Li+ carrier density. As a result, the as-fabricated composite polymer electrolyte with a 20 wt % N-LLZTO (CPE-20) membrane possesses high ionic conductivity (1.7 × 10-4 S cm-1), a high lithium-ion transference number (0.57), a wide electrochemical window (∼4.8 V), and good thermal stability. Moreover, the CPE-20 membrane displays excellent electrochemical stability to suppress the lithium dendrite and serves more than 2000 h. The solid-state Li|CPE-20|LiFePO4 pouch cells exhibit excellent cycling and rate performance, as well as high energy density. This study presents an effective strategy to design promising solid-state electrolyte for next-generation ASSLMBs.

Scalable Production of Wearable Solid-State Li-Ion Capacitors from N-Doped Hierarchical Carbon.

Smart and wearable electronics have aroused substantial demand for flexible portable power sources, but it remains a large challenge to realize scalable production of wearable batteries/supercapacitors with high electrochemical performance and remarkable flexibility simultaneously. Here, a scalable approach is developed to prepare wearable solid-state lithium-ion capacitors (LICs) with superior performance enabled by synergetic engineering from materials to device architecture. Nitrogen-doped hierarchical carbon (HC) composed of 1D carbon nanofibers welded with 2D carbon nanosheets is synthesized via a unique self-propagating high-temperature synthesis (SHS) technique, which exhibits superior electrochemical performance. Subsequently, inspired by origami, here, wave-shaped LIC punch-cells based on the above materials are designed by employing a compatible and scalable post-imprint technology. Finite elemental analysis (FEA) confirms that the bending stress of the punch-cell can be offset effectively, benefiting from the wave architecture. The wearable solid-state LIC punch-cell exhibits large energy density, long cyclic stability, and superior flexibility. This study demonstrates great promise for scalable fabrication of wearable energy-storage systems.

Three-Dimensional Carbon Current Collector Promises Small Sulfur Molecule Cathode with High Areal Loading for Lithium-Sulfur Batteries.

With the high energy density of 2600 W h kg-1, lithium-sulfur (Li-S) batteries have been considered as one of the most promising energy storage systems. However, the serious capacity fading resulting from the shuttle effect hinders its commercial application. Encapsulating small S2-4 molecules into the pores of ultramicroporous carbon (UMC) can eliminate the dissolved polysulfides, thus completely inhibiting the shuttle effect. Nevertheless, the sulfur loading of S2-4/UMC is usually not higher than 1 mg cm-2 because of the limited pore volume of UMC, which is a great challenge for small sulfur cathode. In this paper, by applying ultralight 3D melamine formaldehyde-based carbon foam (MFC) as a current collector, we dramatically enhanced the areal sulfur loading of the S2-4 electrode with good electrochemical performances. The 3D skeleton of MFC can hold massive S2-4/UMC composites and act as a conductive network for the fast transfer of electrons and Li+ ions. Furthermore, it can serve as an electrolyte reservoir to make a sufficient contact between S2-4 and electrolyte, enhancing the utilization of S2-4. With the MFC current collector, the S2-4 electrode reaches an areal sulfur loading of 4.2 mg cm-2 and performs a capacity of 839.8 mA h g-1 as well as a capacity retention of 82.5% after 100 cycles. The 3D MFC current collector provides a new insight for the application of Li-S batteries with high areal small sulfur loading and excellent cycle stability.

Rational design of nano-architecture composite hydrogel electrode towards high performance Zn-ion hybrid cell.

In this paper, we developed a novel Zn-ion hybrid cell based on a graphene-conducting polymer composite hydrogel (capacitor-type) cathode and a zinc metal (battery-type) anode. The pseudocapacitive-type cathode materials can effectively boost the capacity of Zn-ion hybrid cell compared to that of electrical double layer cathode materials. In particular, the composite hydrogel with rational designed three-dimensional (3D) nano-architecture combining 3D porous nanostructure with hydrogel, can significantly enlarge the active interfaces between the electrode and electrolyte. According to our experiments, the 3D graphene@PANI composite hydrogel electrode exhibits a large capacity of 154 mA h g-1, a superior rate capability and excellent capacity retention of 80.5% after 6000 charge-discharge cycles in a Zn-ion hybrid cell. The outstanding electrochemical properties demonstrate that the 3D nanostructure composite hydrogel materials can effectively promote the material utilization, transport of charges, and reduce the degradation of conducting polymers, leading to a highly efficient, fast and stable electrochemical process. Based on our results, Zn-ion hybrid cells based on a composite hydrogel electrode could be an extremely promising candidate for next generation electrochemical energy storage devices.