Rechargeable Potassium-Ion Full Cells Operating at -40 °C.

Potassium-ion batteries (PIBs) are promising for cryogenic energy storage. However, current researches on low-temperature PIBs are limited to half cells utilizing potassium metal as an anode, and realizing rechargeable full cells is challenged by lacking viable anode materials and compatible electrolytes. Herein, a hard carbon (HC)-based low-temperature potassium-ion full cell is successfully fabricated for the first time. Experimental evidence and theoretical analysis revealed that potassium storage behaviors of HC anodes in the matched low-temperature electrolyte involve defect adsorption, interlayer co-intercalation, and nanopore filling. Notably, these unique potassiation processes exhibited low interfacial resistances and small reaction activation energies, enabling an excellent cycling performance of HC with a capacity of 175 mAh g-1 at -40 °C (68 % of its room-temperature capacity). Consequently, the HC-based full cells demonstrated impressive rechargeability and high energy density above 100 Wh kg-1 cathode at -40 °C, representing a significant advancement in the development of PIBs.

Low-Temperature High-Areal-Capacity Rechargeable Potassium-Metal Batteries.

High mass loading and high areal capacity are key metrics for commercial batteries, which are usually limited by the large charge-transfer impedance in thick electrodes. This can be kinetically deteriorated under low temperatures, and the realization of high-areal-capacity batteries in cold climates remains challenging. Herein, a low-temperature high-areal-capacity rechargeable potassium-tellurium (K-Te) battery is successfully fabricated by knocking down the kinetic barriers in the cathode and pairing it with stable anode. Specifically, the in situ electrochemical self-reconstruction of amorphous Cu1.4 Te in a thick electrode is realized simply by coating micro-sized Te on the Cu collector, significantly improving its ionic conductivity. Meanwhile, the optimized electrolyte enables fast ion transportation and a stable K-metal anode at a large current density and areal capacity. Consequently, this K-Te battery achieves a high areal capacity of 1.25 mAh cm-2 at -40 °C, which greatly exceeds those of most reported works. This work highlights the significance of electrode design and electrolyte engineering for high areal capacity at low temperatures, and represents a critical step toward practical applications of low-temperature batteries.

Rechargeable Aqueous Aluminum Organic Batteries.

Aqueous aluminum-ion batteries (AABs) are regarded as promising next-generation energy storage devices, and the current reported cathodes for AABs mainly focused on inorganic materials which usually implement a typical Al3+ ions (de)insertion mechanism. However, the strong electrostatic forces between Al3+ and the host materials usually lead to sluggish kinetics, poor reversibility and inferior cycling stability. Herein, we employ an organic compound with redox-active moieties, phenazine (PZ), as the cathode material in AABs. Different from conventional inorganic materials confined by limited lattice spacing and rigid structure, the flexible organic molecules allow a large-size Al-complex co-intercalation through reversible redox active centers (-C=N-) of PZ. This co-intercalation behavior can effectively reduce desolvation penalty, and substantially lower the Coulombic repulsion during the ion (de)insertion process. Consequently, this organic cathode exhibits a high capacity and excellent cyclability, which exceeds those of most reported electrode materials for AABs. This work highlights the anion co-intercalation chemistry of redox-active organic materials, which is expected to boost the development of high-performance multivalent-ion battery systems.

Facile and Scalable Modification of a Cu Current Collector toward Uniform Li Deposition of the Li Metal Anode.

The development of lithium metal anodes has been severely impeded by the detrimental lithium (Li) dendrite growth which can largely shorten the lifespan of the battery. Here, we propose a one-step redox strategy to fabricate reduced graphene oxide (rGO) and Cu2O co-modified Cu current collector (rGO-Cu2O/Cu), which can guide the uniform Li ion nucleation and suppress the formation of the Li dendrite. The lithiophilic Cu2O in situ grown on the Cu substrate via direct chemical oxidation of Cu foil by the GO solution can decrease the Li nucleation overpotential and regulate the preferential nucleation of Li ions, while the rGO produced at the same time can facilitate the electron transport. As the consequence of the synergistic effects, rGO-Cu2O/Cu could be fully discharged with largely enhanced Coulombic efficiency of 98% and extended cycling life of the symmetrical cell up to 300 h. The full battery assembled with LiFePO4 also exhibits satisfying electrochemical performance, indicating the promising practical application of this Li-plated rGO-Cu2O/Cu anode. Furthermore, the processable rGO-Cu2O/Cu which can make Li metal anode moldable into various shapes with a controllable size will be favorable to manufacture diverse device architectures.

A novel and fast method to prepare a Cu-supported α-Sb2S3@CuSbS2 binder-free electrode for sodium-ion batteries.

Antimony sulfide (Sb2S3) is a promising anode material for sodium-ion batteries due to its low cost and high theoretical specific capacity. However, poor stability and a complex preparation process limit its large-scale application. Herein, we prepare a binder-free composite electrode composed of amorphous (α-) Sb2S3 and copper antimony sulfide (CuSbS2) through a simple closed-space sublimation (CSS) method. When applied as the anode in sodium-ion batteries, the α-Sb2S3@CuSbS2 electrode exhibits excellent performance with a high discharge capacity of 506.7 mA h g-1 at a current density of 50 mA g-1 after 50 cycles. The satisfactory electrochemical performance could be ascribed to the α-Sb2S3-CuSbS2 composite structure and binder-free electrode architecture, which not only retain the structural stability of the electrode but also improve the electrical conductivity. Consequently, CSS, as a scalable and environmentally friendly method, can produce a binder-free electrode in just a few minutes, demonstrating its great potential in the industrial production of sodium-ion batteries. This study may open an avenue to preparing binder-free commercial electrodes.

Iodine encapsulated in mesoporous carbon enabling high-efficiency capacitive potassium-Ion storage.

The development of potassium-ion batteries (KIBs) are hampered by the lack of appropriate electrode materials allowing for the reversible insertion/de-insertion of the large K-ion. Iodine, as a conversion-type cathode for rechargeable batteries, has high theoretical capacity and excellent electrochemical reversibility, making it a potential cathode material for KIBs. However, due to the defects of iodine with the poor electronic conductivity and easy dissolution in the electrolyte, an intensive quest for iodine-based KIBs enabling high-performance potassium-ion storage is still underway. In this work, a high-efficiency capacitive K-I2 battery has been successfully achieved by constructing a nanocomposite of iodine encapsulated in mesoporous carbon (CMK-3). The as-prepared CMK-3/iodine nanocomposite exhibites excellent rate performance (89.3 mA h g-1 at 0.5 A g-1) and superior cycling stability, which remarkably exceeds most of reported KIBs cathode materials. Such a excellent electrochemical performance can be ascribed to the engineered structure of CMK-3/iodine hybridized electrode which can alleviate the impact of the shuttle phenomenon, improve electronic conductivity and facilitate ion diffusion. As a consequence, iodine within the conductive protecting CMK-3 can afford an extraordinary pseudo-capacitive potassium-ion storage, which sheds light on the development prospect of conversion-type electrode materials to meet urgent demand for advanced KIBs.

Few-Layer Bismuthene with Anisotropic Expansion for High-Areal-Capacity Sodium-Ion Batteries.

Bismuth is a promising anode material for state-of-the-art rechargeable batteries due to its high theoretical volumetric capacity and relatively low working potential. However, its charge storage mechanism is unclear, hindering further improvement of the cell performance. Here, using in situ transmission electron microscopy and X-ray diffraction techniques as well as theoretical analysis, it is found that a large anisotropic volume expansion of 142% occurs along the z-axis largely due to the alloy reaction during sodiation, significantly reducing the electrochemical performance of bismuth electrodes. To address this problem, ultrathin few-layer bismuthene with a large aspect ratio is rationally synthesized, and can relieve the expansion strain along the z-axis. A free-standing bismuthene/graphene composite electrode with tunable thickness achieves a strikingly stable and high areal sodium storage capacity of 12.1 mAh cm-2 , which greatly exceeds that of most reported electrode materials. The clarification of the charge storage mechanism and the superior areal capacity achieved should facilitate the development of bismuth-based high-performance anodes for practical electrochemical energy-storage applications.

In Situ Atomic-Scale Study of Particle-Mediated Nucleation and Growth in Amorphous Bismuth to Nanocrystal Phase Transformation.

Understanding classical and nonclassical mechanisms of crystal nucleation and growth at the atomic scale is of great interest to scientists in many disciplines. However, fulfilling direct atomic-scale observation still poses a significant challenge. Here, by taking a thin amorphous bismuth (Bi) metal nanosheet as a model system, direct atomic resolution of the crystal nucleation and growth initiated from an amorphous state of Bi metal under electron beam inside an aberration-corrected transmission electron microscope is provided. It is shown that the crystal nucleation and growth in the phase transformation of Bi metal from amorphous to crystalline structure takes place via the particle-mediated nonclassical mechanism instead of the classical atom-mediated mechanism. The dimension of the smaller particles in two contacted nanoparticles and their mutual orientation relationship are critical to governing several coalescence pathways: total rearrangement pathway, grain boundary migration-dominated pathway, and surface migration-dominated pathway. Sequential strain analyses imply that migration of the grain boundary is driven by the strain difference in two Bi nanocrystals and the coalescence of nanocrystals is a defect reduction process. The findings may provide useful information to clarify the nanocrystal growth mechanisms of other materials on the atomic scale.

Role of carbon quantum dots in titania based photoelectrodes: Upconversion or others?

Carbon quantum dots (CQDs) were synthesized by a facile and green pyrolysis method. The as-prepared CQDs show wide light absorption, tunable downconversion photoluminescence (PL) properties and excellent "upconversion" luminescence properties. CQDs were used to design the TiO2/CdS/C photoelectrodes for photoelectrochemical hydrogen evolution. The role of the CQDs was investigated based on the TiO2/CdS/C photoelectrodes. The results reveal that CQDs can enhance light-harvesting efficiency and improve their charge separation and transfer properties when coupled with conventional QD-sensitized photoelectrodes. Nevertheless, the contribution of "upconversion" luminescence of CQDs to the enhanced photoelectrochemical performance is negligible.

Facile synthesis of an urchin-like Sb2S3 nanostructure with high photocatalytic activity.

Herein, an urchin-like Sb2S3 nanostructure has been synthesized without a surfactant via a wet chemical method. The crystal structure, morphology, composition and optical properties were characterized using XRD, TEM, SEM, EDS, Raman spectroscopy, and diffuse reflectance absorption spectroscopy. The factors, including the reaction time, temperature, and ratio of the raw materials, influencing the evolution of the urchin-like morphology have been discussed, and a plausible formation mechanism for the urchin-like Sb2S3 has been proposed. The urchin-like Sb2S3 micro/nanostructure exhibits high catalytic performance towards the degradation of MB under visible light irradiation. The photodegradation ratio of MB is up to 99.32% under visible light irradiation of 130 min. Our synthesis method will be extended to prepare other photocatalysts.