High-Entropy Layered Oxide Cathode Enabling High-Rate for Solid-State Sodium-Ion Batteries.

Na-ion O3-type layered oxides are prospective cathodes for Na-ion batteries due to high energy density and low-cost. Nevertheless, such cathodes usually suffer from phase transitions, sluggish kinetics and air instability, making it difficult to achieve high performance solid-state sodium-ion batteries. Herein, the high-entropy design and Li doping strategy alleviate lattice stress and enhance ionic conductivity, achieving high-rate performance, air stability and electrochemically thermal stability for Na0.95Li0.06Ni0.25Cu0.05Fe0.15Mn0.49O2. This cathode delivers a high reversible capacity (141 mAh g-1 at 0.2C), excellent rate capability (111 mAh g-1 at 8C, 85 mAh g-1 even at 20C), and long-term stability (over 85% capacity retention after 1000 cycles), which is attributed to a rapid and reversible O3-P3 phase transition in regions of low voltage and suppresses phase transition. Moreover, the compound remains unchanged over seven days and keeps thermal stability until 279 ℃. Remarkably, the polymer solid-state sodium battery assembled by this cathode provides a capacity of 92 mAh g-1 at 5C and keeps retention of 96% after 400 cycles. This strategy inspires more rational designs and could be applied to a series of O3 cathodes to improve the performance of solid-state Na-ion batteries.

Introducing a conductive pillar: a polyaniline intercalated layered titanate for high-rate and ultra-stable sodium and potassium ion storage.

A novel electrode material, TiO2-coated polyaniline intercalated layered titanate, is synthesized. Polyaniline is tri-functional: stabilizing the layered titanate structure, enlarging the interlayer spacing and enhancing the electronic conductivity. Such a composite can deliver high capacities of 258 and 219 mA h g-1 in sodium and potassium-ion batteries, respectively. Its high-rate capability and long cycle life are also impressive.

In situ carbon coated flower-like VPO4 as an anode material for potassium-ion batteries.

Here we design a novel carbon coating method for phosphate-based VPO4 with three different morphologies, via the intercalation of isobutanol to layered VOPO4·2H2O combined with thermal reduction. The well-constructed flower-like VPO4 delivers a high reversible capacity of 400 mA h g-1 with a long cycle-life of more than 500 cycles, proving that the special structure is suitable to accommodate the large volume expansion during the electrochemical charge-discharge process.

A vanadium-based metal-organic phosphate framework material K2[(VO)2(HPO4)2(C2O4)] as a cathode for potassium-ion batteries.

Herein, we report a layered material K2[(VO)2(HPO4)2(C2O4)] with a large interplanar lattice spacing. Highly reversible K+ extraction and insertion in the layers are achieved, with a good cycling stability of up to 200 cycles (83% of retention). And the structural evolution of this material during the electrochemical processes is explored.