Herein, we developed three-dimensional pristine titanium dioxide (TiO₂) photo-electrocatalyst material (PEM) with homogeneous distribution of oxygen vacancies (OV) for lithium-oxygen (Li-O₂) battery system (denoted as LOBs) under illumination. This rationally designed OV-TiO₂ photoelectrode-catalyst has exhibited excellent capacity, small overpotential, long-term cycle stability, and higher rate capability performance according to our electrochemical experiment study. In short, OV as photoinduced charge separation centers (inert surface atomic modification method) fascinate the effective separation of electrons (e⁻) and holes (h⁺). In turn, induced e⁻ and h⁺ are beneficial to the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) process. More importantly, machine learning (ML) algorithms to analyze and optimize battery performance are innovative in the photoelectrical field. The utility of ML analysis is extensively shown to be effective in learning the in/output connection of interest. Based on ML analysis results, the OV-TiO₂ cathode is indeed the key point to extend the LOB life span. More importantly, our brilliant anatase OV-TiO₂ revealed the optimization of electrode material for high performance and reversibility in LOBs. We expect that it will bring special OV-TiO₂ and some other hierarchical hollow nanomaterials, a big step toward battery technology no matter in cost-effectiveness and environmentally friendly aspects.

Aiming at inhibiting the irreversible P2–O2 phase transition of conventional P2-type cathode materials at high voltage and enhancing the cycling stability of sodium-ion batteries, in this article, based on a strategy of adjusting the Na⁺ ion occupancy within the crystal structure, Na_0.67Ni_0.33Mn_0.67–xFe_xO₂ (NM–xFe, x = 0.10, 0.15, 0.20) cathode materials were synthesized by high shear mixer (HSM)-assisted co-precipitation method and evaluated the electrochemical performance at high voltage (4.35 V). The optimal sample NM–0.15Fe exhibits an initial discharge capacity of 130.8 mAh/g (0.1 C), with exceptional retention of 95.9% after 100 cycles (1 C). XRD analysis reveals that Fe intercalation promotes the more amount of Nae-similar occupation; the Nae/Naf ratio equals 1.93 for NM–0.15Fe versus 1.62 for NM, which enhances Na⁺ diffusion kinetics, as confirmed by GITT tests. Through characterizations of in situ XRD, XPS, HRTEM, CV, etc., it is illustrated that the Fe³⁺ intercalation can effectively disrupt the Na⁺/vacancy ordering and inhibit the harmful P2–O2 phase transition, and then improve the cycling stability of the cathode. DFT calculations disclose that intercalated Fe can reduce the electron densities of adjacent transition metallic elements, generating more repulsive forces impacted on sodium and consequently appearance of more Nae sites, leading to a lower Na⁺ diffusion energy barrier. Such strategy of modulating Na occupation sites in crystal structure is conducive to the development of low-cost and high-performance layered cathode materials for sodium-ion batteries.

NiFe(oxy)hydroxide (NiFeOOH) has been widely studied as a catalyst for oxygen evolution reaction (OER), but its activity is still not satisfactory. Although metal doping has been employed as a promising strategy for addressing this issue, the instability and leaching of the high-valence dopant metals remain considerable challenges. Herein, an array of Cr-doped NiFeOOH nanosheets was in situ synthesized on nickel foam via a one-step hydrothermal method. The doping of NiFeOOH with Cr was found to induce partial electron transfer from Ni and Fe to Cr atoms, thereby modulating the electronic structure of the catalyst and enhancing its intrinsic activity. Electrochemical and in situ Raman spectroscopy analyses showed that Fe active sites with lower charge density enhance the adsorption of *OH and reduce the formation energy barrier of the *OOH intermediate during OER, thereby accelerating the OER. Moreover, Fe was found to promote the transfer of additional electrons to Cr, leading to electron accumulation at Cr sites. This electron accumulation effectively prevents Cr from excessive oxidation and leaching under anode potentials, thereby maintaining the structural stability of the catalyst. The optimized Cr-doped NiFeOOH self-supported electrode exhibited a current density of 50 mA/cm² with an overpotential of only 239 mV and remained stable for 100 h at 600 mA/cm² in 1 mol/L KOH.

The development of high-performance lithium-ion batteries (LIBs) hinges on searching for advanced anode materials with large specific capacities as well as high cycling stability. However, traditional graphite anodes have not met the demand for higher energy storage owing to the deficiency of low lithium storage capacity. In the current work, we focus on designing one composite anode material with multiscale porous (MP) structure and phosphorus (P) doping. The coupling effects of three-dimensional (3D) interconnected skeleton, hollow pore channels, and P doping can facilitate the electrolyte diffusion and the mass transfer, as well as accommodate the volume changes during lithiation/delithiation processes. As expected, the as-prepared MP-SiGeSnSbPAl composite exhibits superior lithium storage performance, achieving a specific capacity of 827.9 mAh/g after 150 cycles at 200 mA/g and maintaining the high capacity of 456.7 mAh/g after 400 cycles at 1 A/g. Contrastively, the corresponding surplus capacities are only 590.3 and 225.7 mAh/g for the non-doped counterparts, respectively. In particular, MP-SiGeSnSbPAl displays much more stable cycling performances under the measurement of high areal mass loading of ~ 3 mg/cm² and the full-cell tests with the lithium iron phosphate as the cathode. This work witnesses one scalable protocol for preparing multinary Si-based composite in terms of facile operation and high lithium storage performances.

The membrane, one of the key components of flow batteries, ideally has high selectivity, conductivity, and stability. However, porous membranes prepared by conventional non-solvent-induced phase separation (NIPS) commonly suffer from low selectivity and poor mechanical stability. Here, we used rigid naphthalene-containing polybenzimidazole (NPBI) to prepare a porous membrane with unique egg-shaped pores by adjusting solvent/non-solvent exchange in NIPS. The dense pores with a size of 3.6 Å arranged dispersedly between egg-shaped pores. The rigid NPBI and 3.6-Å small pores enabled the membrane high mechanical strength. The thickness was thus decreased to 1.4 μm, which exhibited an ultrahigh tensile strength of 463.54 MPa. The dense pores were also smaller than hydrated vanadium ions, achieving a low permeability of 2.28 × 10^‒7 cm²/h, indicating high selectivity. This is the first time to prepare such a highly selective and mechanically stable ultrathin porous membrane by NIPS. Importantly, the ion-transport pathways in the 1.4 μm membrane were shortened, decreasing the area resistance to as low as 0.015 Ω cm². Demonstrated in a vanadium flow battery, its coulombic efficiency was 98.57% and energy efficiency reached 81.72% at 200 mA/cm². This study proposes an effective strategy to prepare high-performance ultrathin porous membranes for flow batteries.