Transition metal oxides are promising electrode candidates for supercapacitor because of their low cost, high theoretical capacity, and good reversibility. However, intrinsically poor electrical conductivity and sluggish reaction kinetics of these oxides normally lead to low specific capacity and slow rate capability of the devices. Herein, a commonly used cobalt oxide is used as an example to demonstrate that lithiation process as a new strategy to enhance its electrochemical performance for supercapacitor application. Detailed characterization reveals that electrochemical lithiation of Co 3 O 4 crystal reduces the coordination of the CoO band, leading to substantially increased oxygen vacancies (octahedral Co 2+ sites). These vacancies further trigger the formation of a new electronic state in the bandgap, resulting in remarkably improved electrical conductivity and accelerated faradic reactions. The lithiated Co 3 O 4 exhibits a noticeably enhanced specific capacity of 260 mAh g −1 at 1 A g −1 , approximately fourfold enhancement compared to that of pristine Co 3 O 4 (66 mAh g −1). The hybrid supercapacitor assembled with lithiated Co 3 O 4 //N-doped activated carbon achieves high energy densities in a broad range of power densities, e.g., 76.7 Wh kg −1 at 0.29 kW kg −1 , 46.9 Wh kg −1 at a high power density of 18.7 kW kg −1 , outperforming most of the reported hybrid supercapacitors.

lithium-sulfur, sodium-, magnesium-, and aluminum-based batteries. [2] Among these competitors, lithium-sulfur battery (LSB) is a promising candidate since the earth-abundant sulfur has a high theoretical capacity of 1675 mAh g −1 and LSB provides a high theoretical energy density of 2600 Wh kg −1 or 2800 Wh l −1 . [3] Nevertheless, the practical application of LSB is still limited by the poor electric/ionic conductivity of sulfur and the "shuttle effect" caused by the dissolution and diffusion of lithium polysulfides (LiPSs), resulting in an uncompetitive capacity, rate performance, and cycling life. [4] To address these issues, intensive studies have been done, such as cathode design, separator modification, electrolyte optimization, and anode protection. [5] LiPSs immobilization and LiPSs ↔ Li 2 S 2 /Li 2 S conversion acceleration are two major considerations for LSB cathode design. [6] The anchoring and catalyzing effect of various candidates (such as metal oxides/sulfide/nitride) have been investigated by first principle calculations [7] or quantitative adsorption experiments. [8] Although some species show strong chemical interactions with LiPSs or effective catalysis on the conversion reaction, battery performances have been largely restrained by the poor electronic/ionic conductivity As the lightest member of transition metal dichalcogenides, 2D titanium disulfide (2D TiS 2 ) nanosheets are attractive for energy storage and conversion. However, reliable and controllable synthesis of single-to few-layered TiS 2 nanosheets is challenging due to the strong tendency of stacking and oxidation of ultrathin TiS 2 nanosheets. This study reports for the first time the successful conversion of Ti 3 C 2 T x MXene to sandwich-like ultrathin TiS 2 nanosheets confined by N, S co-doped porous carbon (TiS 2 @NSC) via an in situ polydopamine-assisted sulfuration process. When used as a sulfur host in lithium-sulfur batteries, TiS 2 @NSC shows both high trapping capability for lithium polysulfides (LiPSs), and remarkable electrocatalytic activity for LiPSs reduction and lithium sulfide oxidation. A freestanding sulfur cathode integrating TiS 2 @NSC with cotton-derived carbon fibers delivers a high areal capacity of 5.9 mAh cm −2 after 100 cycles at 0.1 C with a low electrolyte/sulfur ratio and a high sulfur loading of 7.7 mg cm −2 , placing TiS 2 @NSC one of the best LiPSs adsorbents and sulfur conversion catalysts reported to date. The developed nanospace-confined strategy will shed light on the rational design and structural engineering of metal sulfides based nanoarchitectures for diverse applications.

Li‐rich layered oxides are promising cathode materials for next‐generation Li‐ion batteries because of their extraordinary specific capacity. However, the activation process of the key active component Li2MnO3 in Li‐rich materials is kinetically slow, and the complex phase transformation with electrode/electrolyte side reactions causes fast capacity/voltage fading. Herein, a simple thermal treatment strategy is reported to simultaneously tackle these challenges. The introduction of a urea thermal treatment on Li‐rich material Li1.87Mn0.94Ni0.19O3 leads to oxygen deficiencies and partially reduced Mn ions on the oxide surface for activating the Li‐rich phase. In situ synchrotron study confirms that the urea‐treated cathode shows much faster Li extraction from both Li and transition metal layers with less oxygen evolution upon charging than that of untreated counterparts. Moreover, the decomposition products of urea during thermal treatment subsequently deposit on the surface of cathode material, leading to a unique passivation layer against side reactions between electrode and electrolyte. Soft X‐ray absorption spectroscopy reveals the structural evolution mechanism with a significantly suppressed dissolution of Mn species over cycling measurement. The urea‐treated Li1.87Mn0.94Ni0.19O3 shows accelerated activation kinetics to reach high capacity of 270 mA h g–1 and demonstrates excellent capacity retention of 98.49% over 300 cycles with slower voltage decay.

Providing sufficient driving force for charge separation and transfer (CST) is a critical issue in photoelectrochemical (PEC) energy conversion. Normally, the driving force is derived mainly from band bending at the photoelectrode/electrolyte interface but negligible in the bulk. To boost the bulky driving force, we report a rational strategy to create effective electric field via controllable lattice distortion in the bulk of a semiconductor film. This concept is verified by the lithiation of a classic TiO 2 (Li-TiO 2) photoelectrode, which leads to significant distortion of the TiO 6 unit cells in the bulk with well-aligned dipole moment. A remarkable internal builtin electric field of~2.1 × 10 2 V m −1 throughout the Li-TiO 2 film is created to provide strong driving force for bulky CST. The photoelectrode demonstrates an over 750% improvement of photocurrent density and 100 mV negative shift of onset potential upon the lithiation compared to that of pristine TiO 2 film.

Lead halide perovskites have witnessed significant progress in low-cost and high-efficiency photovoltaics, with a rapid increase in photovoltaic efficiencies from 3.8% to a certified record of 25.2% in the past decade. [1-4] However, the viability and practical scale-up implementation are limited by the stability and toxicity of the lead halide perovskites. [5,6] To circumvent these two

No abstract

Recently, Sn 4 P 3 has emerged as a promising anode for sodium-ion batteries (SIBs) due to the high specific capacity. However, the use of Sn 4 P 3 has been impeded by capacity fade and an inferior rate performance. Herein, a biomimetic heterostructure is reported by using a simple hydrothermal reaction followed by thermal treatment. This bottlebrush-like structure consists of a stem-like carbon nanotube (CNT) as the electron expressway and mechanical support; fructus-like Sn 4 P 3 nanoparticles as the active material; and the permeable stoma-like thin carbon coating as the buffer layer. Having benefited from the biomimetic structure, a superior electrochemical performance is obtained in the SIBs. It exhibits a high capacity of 742 mA h g −1 after 150 cycles at 0.2C, and superior rate performance with 449 mA h g −1 at 2C after 500 cycles. Moreover, the sodium storage mechanism is confirmed by cyclic voltammetry and ex situ X-ray diffraction and transmission electron microscopy. In situ electrochemical impedance spectroscopy was adopted to analyze the reaction dynamics. This research represents a further step toward figuring out the inferior electrochemical performance of other metal phosphide materials.

No abstract