Cell-like-carbon-micro-spheres for robust potassium anode

High-Voltage Cathode α-Fe2O3 Nanoceramics for Rechargeable Sodium-Ion Batteries

Previously, α-Fe2O3 nanocrystals are recognized as anode materials owing to their high capacity and multiple properties. Now, this work provides high-voltage α-Fe2O3 nanoceramics cathodes fabricated by the solvothermal and calcination processes for sodium-ion batteries (SIBs). Then, their structure and electrical conductivity were investigated by the first-principles calculations. Also, the SIB with the α-Fe2O3 nanoceramics cathode exhibits a high initial charge-specific capacity of 692.5 mA h g-1 from 2.0 to 4.5 V at a current density of 25 mA g-1. After 800 cycles, the discharge capacity is still 201.8 mA h g-1, well exceeding the one associated with the present-state high-voltage SIB. Furthermore, the effect of the porous structure of the α-Fe2O3 nanoceramics on sodium ion transport and cyclability is investigated. This reveals that α-Fe2O3 nanoceramics will be a remarkably promising low-cost and pollution-free high-voltage cathode candidate for high-voltage SIBs.

Novel Solid-State Sodium-Ion Battery with Wide Band Gap NaTi2(PO4)3 Nanocrystal Electrolyte

NaTi2(PO4)3 (NTP), a well-known anode material, could be used as a solid wide-band gap electrolyte. Herein, a novel solid-state sodium-ion battery (SSIB) with the thickness of electrolyte up to the millimeter level is proposed. The results of the difference in charge density investigated by the first-principles calculations imply that using the NTP nanocrystals as electrolytes to transport sodium ions is feasible. Moreover, the SSIB exhibits a high initial discharge capacity of 3250 mAh g-1 at the current density of 50 mA g-1. As compared with other previously reported SSIBs, our results are better than those reported and suggest that the NTP nanocrystals have potential application in SSIBs as solid electrolytes.

Enhanced Potassium Storage Capability of Two-Dimensional Transition-Metal Chalcogenides Enabled by a Collective Strategy

Potassium-ion batteries (PIBs) have been considered as a promising alternative to lithium-ion batteries due to their merits of high safety and low cost. Two-dimensional transition-metal chalcogenides (2D TMCs) with high theoretical specific capacities and unique layered structures have been proven to be amenable materials for PIB anodes. However, some intrinsic properties including severe stacking and unsatisfactory conductivity restrict their electrochemical performance, especially rate capability. Herein, we prepared a heterostructure of high-crystallized ultrathin MoSe₂ nanosheet-coated multiwall carbon nanotubes and investigated its electrochemical properties with a view to demonstrating the enhancement of a collective strategy for K storage of 2D TMCs. In such a heterostructure, the constructive contribution of CNTs not only suppresses the restacking of MoSe₂ nanosheets but also accelerates electron transport. Meanwhile, the MoSe₂ nanosheets loaded on CNTs exhibit an ultrathin feature, which can expose abundant active sites for the electrochemical reaction and shorten K⁺ diffusion length. Therefore, the synergistic effect between ultrathin MoSe₂ and CNTs endows the resulting nanocomposite with superior structural and electrochemical properties. Additionally, the high crystallinity of the MoSe₂ nanosheets further leads to the improvement of electrochemical performance. The composite electrode delivers high-rate capacities of 209.7 and 186.1 mAh g^-1 at high current densities of 5.0 and 10.0 A g^-1, respectively.

Molecular Regulation on Carbonyl-Based Organic Cathodes: Toward High-Rate and Long-Lifespan Potassium-Organic Batteries

Organic redox-active molecules have been identified as promising cathodes for practical usage of potassium-ion batteries (PIBs) but still struggle with serious dissolution problems and sluggish kinetic properties. Herein, we propose a pseudocapacitance-dominated novel insoluble carbonyl-based cathode, [2,6-di[1-(perylene-3,4,9,10-tetracarboxydiimide)]anthraquinone, AQ-diPTCDI], which possesses high reversible capacities of 150 mAh g^-1, excellent cycle stability with capacity retention of 88% over 2000 cycles, and fast kinetic properties. The strong intermolecular interactions of AQ-diPTCDI and in situ formed cathode electrolyte interphase films support it against the dissolution problem. The high capacitive-like contribution in capacities and fast potassium-ion diffusion enhance its reaction kinetics. Moreover, a symmetric organic potassium-ion battery (OPIB) based on AQ-diPTCDI electrodes also exhibits outstanding K-storage capability. These results suggest that AQ-diPTCDI is a promising organic cathode for OPIBs and provide a practicable route to realize high-performance K storage.

Red phosphorus embedded in TiO2/C nanofibers to enhance the potassium-ion storage performance

TiO₂-red phosphorus/C nanofibers (TiO₂-RP/CN) have been synthesized via electrospinning and then annealed with red phosphorus sublimation. Benefiting from the high electronic/ionic conductivity and robust stability of the unique structure, the TiO₂-RP/CN show high reversible capacities, as well as an outstanding cycling ability. In K half cells, the capacity decay of the TiO₂-RP/CN electrode mainly occurs in the first few cycles, and at 0.05 A g^-1 it delivers a high specific capacity of 257.8 mA h g^-1 after 500 cycles. K full cells were fabricated; these are well-matched with PTCDA (perylene-3,4,9,10-tetracarboxylic dianhydride) and also exhibited a good electrochemical performance (62 mA h g^-1 after 100 cycles). Therefore, the TiO₂-RP/CN are potential anode materials for use in K-ion batteries.

A New Candidate in Polyanionic Compounds for a Potassium-Ion Battery Cathode: KTiOPO4

First-principles computations were performed to investigate the performance of KTiOPO₄ (KTP) as a cathode material for potassium-ion batteries (PIBs), including the stability and electronic properties of depotassiated structures and mechanisms of K deintercalation and diffusion. As depotassiation proceeds, oxygen hole polarons are produced, and there are not peroxides or superoxides formed after deep depotassiation. The anionic oxygen redox in KTP provides a voltage vs K/K⁺ over 4 V by the PBE+U method and over 5 V with the more reliable HSE06 hybrid functional. When all K in KTP is removed, the calculated volume compression is only 1.528%. The AIMD simulations at 300 K for TiOPO₄ verify its thermal stability. The PBE+U calculations predict a low ion diffusion barrier of 0.29 eV in bulk KTP, indicating a good charge-discharge rate for KTP as a cathode for PIBs. All of the calculated results indicate that KTP can be a promising cathode material for PIBs.

Enabling a Stable Room-Temperature Sodium-Sulfur Battery Cathode by Building Heterostructures in Multichannel Carbon Fibers

Room-temperature sodium-sulfur (RT Na-S) batteries are widely considered as one of the alternative energy-storage systems with low cost and high energy density. However, the both poor cycle stability and capacity are two critical issues arising from low conversion kinetics and sodium polysulfides (NaPSs) dissolution for sulfur cathodes during the charge/discharge process. Herein, we report a highly stable RT Na-S battery cathode via building heterostructures in multichannel carbon fibers. The TiN-TiO₂@MCCFs, fabricated by electrospinning and nitriding techniques, are loaded with the active material S, forming S/TiN-TiO₂@MCCFs as the cathode in a RT Na-S battery. At 0.1 A g^-1, the cathode produces the capacity of more than 640 mAh g^-1 within 100 cycles with a high Coulombic efficiency of nearly 100%. Even at 5 A g^-1, the battery still exhibites a capacity of 257.1 mAh g^-1 after 1000 cycles. Combining structural and electrochemical analyses with the first-principles calculations reveals that the incorporation of the highly electrocatalytic activity of TiN with the powerful chemisorption of TiO₂ well stabilizes S and also alleviates the shuttle effects of polysulfides. This work with simple processes and low cost is expected to promote the further development and application of metal-S batteries.

A new strategy for achieving high K+ storage capacity with fast kinetics: realizing covalent sulfur-rich carbon by phosphorous doping

Designing carbon anodes with rich heteroatoms and dilated graphitic interlayer spacing via a one-step synthesis process plays a vital role in accelerating the practical application of potassium ion batteries, but it is still a big challenge. Herein, P-doped S-rich mesoporous carbon (PSMC) is prepared by direct phosphate-assisted carbonization of carrageenan, and it exhibits excellent potassium storage capacity (449 mA h g-1 at 0.1 A g-1), superior rate performance (233 mA h g-1 at 2 A g-1) and long-term stability (97.3% capacity retention after 1000 cycles), due to the high sulfur doping (16.48 wt%) and the coexistence of ordered and disordered regions in the structure. Ex situ characterization, GITT and theoretical calculations reveal that the promotion of covalent sulfur can effectively increase the adsorption of K+ and enhance the K+ reaction kinetics. The proposed one-step synthesis strategy demonstrates the precise use of the composition in biomass, enabling large-scale production of high-performance anodes for K+ storage.

Iron Nitride@C Nanocubes Inside Core-Shell Fibers to Realize High Air-Stability, Ultralong Life, and Superior Lithium/Sodium Storages

Poor air stability and severe structure pulverization are crucial issues for metal nitrides in metal-ion batteries. Herein, core-shell hybrid fibers (CSHN fiber) filled with metal nitride@C hollow nanocubes are introduced to be a new self-supporting anode for sodium-ion and lithium-ion batteries. The hierarchical carbon network provides fast electronic pathways and gives high protection for iron nitrides. Meanwhile, the self-supporting electrode avoids the complicated electrode fabrication process and decreases the opportunity to air exposure. Moreover, its porous nature ensures high buffer to volumetric expansion and improves the cycling stability. Therefore, it is a good platform to realize fast kinetics and high durability. For the first time, Fe₂N@N-doped carbon CSHN hybrid fibers are constructed. Their influences on air stability and electrochemical behaviors are studied. Impressively, they achieve high stabilities in both lithium-ion (92.8%, at 5 A g^-1, 1000 cycles) and sodium-ion (95.6%, at 2 A g^-1, 2000 cycles) batteries. Therefore, this work introduces a new method to construct superior performance nitride anodes. Moreover, it also provides a new insight on the fabrication of highly efficient structures for diverse functional materials.

Al-doped H2TiO3 ion sieve with enhanced Li+ adsorption performance

H₂TiO₃ (HTO) is considered to be one of the most promising adsorbents for lithium recovery from aqueous lithium resources duo to its highest theoretical adsorption capacity. However, its actual adsorption capacity is much lower owing to its unknown structure and incomplete leaching of lithium. After Al is doped into H₂TiO₃ (HTO-Al), the adsorption capacity of HTO-Al is 32.12 mg g⁻¹ and the dissolution of Ti is 2.53%. HTO-Al has good adsorption selectivity, and all the separation factors α are ≫1. Furthermore, HTO-Al also exhibits good cyclic stability and solubility resistance. After 5 cycles, the adsorption capacity remains 29.3 mg g⁻¹ and the dissolution rate is 1.7%. Therefore, HTO-Al has potential application value for recovering Li⁺ from aqueous lithium resources.

H₂TiO₃ (HTO) is considered to be one of the most promising adsorbents for lithium recovery from aqueous lithium resources duo to its highest theoretical adsorption capacity.