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Photocatalysis is a new type of renewable energy technology used in environmental treatment and hydrogen energy production. In this regard, a new class of photocatalysts, TiO2 aerogels, are attractive for having the chemical characteristics of TiO2 nanomaterials such as high catalytic activity, good stability, non-toxic, and non-polluting, and the structural characteristics of aerogels such as large specific surface area, high porosity, the 3-dimensional interconnected network structure composed of relatively uniform nanoparticles, and high light transmittance. Here we review the recent progress in TiO2 aerogels for photocatalysis, focusing on preparation techniques, the crystalline phases’ influence on photocatalytic properties, the modification of photocatalytic properties, and the analysis and discussion of future development. In particular, we first summarize various preparation techniques, including sol–gel method, nanoparticles self-assembly synthesis, and high-temperature aerosol technique, then detail the structure and composition of TiO2 crystalline phases that affect the photocatalytic properties. Subsequently, we discuss strategies to further enhance the photocatalytic properties of TiO2 aerogels by the composite of SiO2 aerogel semiconductors, the doping of metal dopants, and the doping or composite of non-metallic substances, and elaborate the modification mechanism and the modification effect achieved. Finally, combined with the research status of TiO2 aerogels and the development experience of other aerogels, we conduct a reasonable analysis and discussion on their further research directions and industrialization roads.

Lithium ion capacitors with liquid electrolyte are prone to leakage, combustion, explosion and other dangerous accidents. To solve these problems, the solid gel separator prepared by polyvinylidene fluoride - six fluoropropene (PVDF-HFP) is used in this work to improve the safety and stability of lithium ion supercapacitors. The PVDF-HFP based gel separator was used to replace the commercial separator and electrolyte in the lithium ion capacitor. The solid-state lithium ion supercapacitor was matched with porous carbon (PC) and hard carbon (HC). The maximum energy density of the device is 148.76 wh/kg, even at the power density of 33.6 kW/kg, which still retains 20.6 wh/kg. In addition, 83.3% capacity of solid-state lithium-ion supercapacitor is retained after 8000 times of charge and discharge. The requirements of high power energy density, high cycle stability and high safety are realized.

The NiCo2S4/C hybrid material was successfully prepared by a simple one-step hydrothermal method. Carbon composite increases the specific surface area of the material and provides more ion attachment points during the electrochemical process. Conducive to the ion transportation and transfer, the composition of carbon material greatly improves the conductivity of the hybrid material. Electric double-layer capacitor materials can accept transferred ions faster than pseudocapacitor materials, enable the hybrid materials better adapt to intensity current changes. Compared with a single carbon material or a pseudocapacitance material, it has a higher specific capacity. This discovery is of great significance to the research of pseudocapacitive materials and supercapacitors.

Spinel Li4Mn5O12 was successfully prepared by the wet chemical method to modify the surface of Li1.2Ni0.2Mn0.6O2. The results showed that an ultrathin spinel Li4Mn5O12 surface-modified layer with a thickness of approximately 10 nm was successfully constructed on the raw material surface, and that the cationic order was improved. In addition, the lithium ion diffusion coefficients (DLi+) of the raw materials and the modified materials were calculated using the EIS test and impedance fitting. The results indicated that the ultrathin Li4Mn5O12 surface modification shell can increase the lithium ion diffusion rate of the material and improve the rate capability of the material. So, the surface modification layer of spinel Li4Mn5O12 can reduce the oxygen loss of the first cycle and improve the cationic order of the material. Therefore, the first coulombic efficiency of Li4Mn5O12/Li1.2Ni0.2Mn0.6O2 material at the current density of 12.5 mA·g−1 reaches 80.46%, and the capacity retention rate reaches 91.74% after 50 cycles, which are 3.36% and 21.23% higher than those of the raw materials, respectively. It showed better electrochemical reversibility and cyclic stability. This study provides a straightforward and convenient modification method for improving the stability of cobalt-free lithium-rich manganese cathode materials and has a favorable application prospect. [ABSTRACT FROM AUTHOR]

Layered, Li-rich Mn-based oxides (LLMOs) are the most promising next-generation, high-energy batteries due to their relatively high specific capacities and high voltages. However, the practical application of LLMO cathodes is limited by low initial coulombic efficiencies (CEs) and poor cycling performance. Herein, we used the reaction of KMnO 4 and MnSO 4 under hydrothermal conditions to grow a nano-SCMO shell on the LLMO material surface (SCMO@LLMO). The unique particle/sheet compound structure of the SCMO shell is beneficial to the electrochemical reaction. SCMO has good Li storage characteristics and excellent surface structure stability in the single-crystal phase which further improves the reversible capacity, CE, and cyclic stability of the LLMO cathode. Therefore, the optimal coated sample (feedstock: 2 M KMnO 4 , SCMO@LLMO-2.0) exhibits a good initial discharge capacity (238.2 mA h g -1 at 1C and 173.8 mA h g -1 at 5C), initial CE (89.6% at 1C and 86.5% at 5C), and cycling performance (capacity retention of 84.67% at 1C and 62.72% at 5C after 200 cycles). This work adopts a hydrothermal method to synthesize a nano-single crystal composite material, laying a foundation for the preparation of the SCMO@LLMO cathodes for LLMO primary battery cathodes with high electrochemical performance., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)