Na-doped Ni-rich LiNi_0.5Co_0.2Mn_0.3O₂ cathode material, Li_0.97Na_0.03Ni_0.5Co_0.2Mn_0.3O₂, is synthesized by a hydroxide co-precipitation route. The structural characterization reveals that the substitution of Na for Li results in a more ordered α-NaFeO₂ structure, enlarges Li layer spacing, and reduces the degree of cation mixing. The Li_0.97Na_0.03Ni_0.5Co_0.2Mn_0.3O₂ material has a high tap density of 2.17 g cm⁻³ that meets the commercial requirement in lithium ion batteries (LIBs). The galvanostatic charge/discharge results show that the electrochemical performance of the Li_0.97Na_0.03Ni_0.5Co_0.2Mn_0.3O₂ is significantly improved. At 0.2, 1, 10, 30 and 50 C, the specific capacities of the Li_0.97Na_0.03Ni_0.5Co_0.2Mn_0.3O₂ are 228.43, 163.12, 121.43, 95.56 and 60.09 mA h g⁻¹, respectively, which are superior to those of the undoped LiNi_0.5Co_0.2Mn_0.3O₂ due to the enlargement of Li layer spacing, the decreased degree of cation mixing, and the rapid diffusion of Li-ion in the bulk lattice after the substitution of Na for Li. Therefore, the Na-doped Ni-rich LiNi_0.5Co_0.2Mn_0.3O₂ material is a promising cathode candidate for the next generation of LIBs.

Fe₃O₄@C nanoparticles were prepared by an in situ, solid-phase reaction, without any precursor, using FeSO₄, FeS₂, and PVP K30 as raw materials. The nanoparticles were utilized to decolorize high concentrations methylene blue (MB). The results indicated that the maximum adsorption capacity of the Fe3O4@C nanoparticles was 18.52 mg/g, and that the adsorption process was exothermic. Additionally, by employing H₂O₂ as the initiator of a Fenton-like reaction, the removal efficiency of 100 mg/L MB reached ~99% with Fe₃O₄@C nanoparticles, while that of MB was only ~34% using pure Fe₃O₄ nanoparticles. The mechanism of H₂O₂ activated on the Fe₃O₄@C nanoparticles and the possible degradation pathways of MB are discussed. The Fe₃O₄@C nanoparticles retained high catalytic activity after five usage cycles. This work describes a facile method for producing Fe₃O₄@C nanoparticles with excellent catalytic reactivity, and therefore, represents a promising approach for the industrial production of Fe₃O₄@C nanoparticles for the treatment of high concentrations of dyes in wastewater.

Rechargeable lithium–sulfur (Li–S) batteries are regarded as a promising option for electrochemical energy storage systems. However, one of the key issues hindering their practical application is lithium polysulfide (LiPS) shuttling, which results in severe capacity decay and self-discharge. Separator-decoration with oxides has been demonstrated to be an effective strategy and has attracted widespread attention. But there has been no report about intergrown multi-phase composite oxides for separator modification. Herein, spent layered cathode (LiNi_0.5Co_0.2Mn_0.3O₂) derived layered–spinel–rocksalt intergrown oxides were firstly introduced and investigated. Unexpectedly superior performance was obtained with high reversible capacity and outstanding stability, which could be contributed by the entrapping and catalysis of LiPSs. The Li–S batteries with the spent multi-phase composite LiNi_0.5Co_0.2Mn_0.3O₂ show a low fading rate of 0.053% per cycle over 550 cycles at 1C rate, and high discharge capacities of 976.1, 916.7, 865.2, and 795.1 mA h g⁻¹ at 0.5, 1, 2, and 3C rates, respectively. DFT calculation demonstrated that the spinel and rock-salt phases can provide more energetic reaction sites to strongly adsorb the LiPSs and accelerate the catalyzed conversion of LiPSs to Li₂S/Li₂S₂. Moreover, our systematic experimental and theoretical investigation produced intriguing results, indicating that there is a synergistic effect between the spinel, rock-salt and layered phases. This study not only provides a high-value application of spent LiNi_0.5Co_0.2Mn_0.3O₂ but also demonstrates the potential of multi-phase composites to boost the performance of Li–S batteries.