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Sodium titanate (NTO)/rGO electrode from Ti-MXene beautifully solved NTO’s poor conductivity, slow ion deintercalation reaction kinetics, and lattice expansion during charging/discharging, which achieved a good desalination performance.

V-doped T-Nb2O5 possesses reduced band gap, boosted ionic transportation and superior structural stability, resulting in excellent rate performance and cycling stability.

Combining the high operational security of magnesium-ion batteries (MIBs) and the fast Li intercalation mechanism of lithium-ion batteries (LIBs), Li+/Mg2+ hybrid-ion batteries (LMIBs) have been developed and are regarded as a promising source of stored power for applications. However, pristine MoS2 with an interplanar distance of 0.62 nm only allows Li+ intercalation, leading to limited energy densities and mediocre electrochemical performance. Herein, we designed and prepared a material consisting of hierarchical interlayer-expanded MoS2 nanosheets/hollow N-doped carbon nanofibers (O–MoS2/HN-CNFs) with interplanar expanded O–MoS2 (0.94 nm). HN-CNFs adequately conduct electrons, and the expanded interlayer spacing of O–MoS2 ensures that Mg2+ and Li+ simultaneously intercalate into the host, even at 1000 mA g−1. Additionally, O–MoS2/HN-CNFs can significantly reduce the ion diffusion barrier and increase the number of intercalated active sites. As a result, O–MoS2/HN-CNFs exhibited superior rate capabilities, good cycling performance, and long-term cycling stability, with a reversible capacity of 134.4 mA h g−1 at 1000 mA g−1 after 2000 cycles.

Mg2+/Li+ hybrid ion batteries (MLIBs) are regarded as an emerging candidate for next generation rechargeable batteries. However, realizing superior high-rate performance is still an unremitting challenge for further development of MLIBs. Herein, a rational design of the T-Nb2O5@MoO2 nanorod array heterostructure as the cathode of MLIBs is presented. The resulting heterostructure reinforces structural stability and induces the generation of a built-in electric field, which facilitates ionic transport kinetics, as verified by reaction kinetics analysis, ex situ characterization techniques and density functional theory calculations. As expected, the T-Nb2O5@MoO2 heterostructure delivers a reversible capacity of 250.3 mA h g−1 at 0.5C, excellent rate performance (68.8 mA h g−1 at 10C) and long cycling life (capacity retention of 76.0% at 5C after 1500 cycles). Thus, this strategy paves the way for designing advanced electrode materials with excellent electrochemical performance.

Undesirable lithium dendrite growth limits the application of lithium metal anodes in high-energy storage batteries. Here, multifunctional SnSe–C composite modified 3D scaffolds are constructed to achieve dendrite-free lithium deposition. During the initial lithiation stage, the porous SnSe–C composite converts into a Li–Sn alloy and Li2Se by lithium reduction. The lithiophilic Li–Sn alloy exhibits a low nucleation barrier and realizes homogeneous lithium nucleation. The reductive product Li2Se with a high ionic conductivity facilitates lithium ion transport, which helps realizing the homogeneous lithium ion flux and reducing concentration polarization. Benefitting from the synergistic effect of the Li–Sn alloy and Li2Se, the Li/SnSe–C anode exhibits an ultralong lifespan over 1100 h with a low overpotential of 18 mV. In full-cell configurations with LiFePO4 cathodes, the Li/SnSe–C anode demonstrates enhanced rate capability and cycle stability with a high-capacity retention of 85% over 750 cycles. This work prepares multifunctional SnSe–C composite modified 3D scaffolds to regulate lithium nucleation and transport, which offers new insights and opportunities for developing dendrite-free lithium metal battery technology.

Compared with the strategy of expanding MoS2 interlayer spacing, constructing van der Waals heterostructures of MoS2 and graphene (MoS2/G) has proven to be a more effective method to facilitate the ion diffusion rate in host materials. However, the reduced adsorption energy of intercalated metal ions at the active sites of MoS2/G interlamination causes a rapid voltage drop during discharge processes, resulting in an inferior energy density. Herein, we constructed anion vacancy-rich MoSSe and graphene van der Waals heterostructures (v-MoSSe/G). By adjusting the Se doping amount, v-MoSSe/G with an S : Se ratio of 1 : 1 exhibits the most anion vacancies. Compared with MoS2/G heterostructures, density functional theory calculations proved that more anion vacancies in v-MoSSe/G can further reduce the ion diffusion barriers and increase the adsorption energy of the intercalated ions, thereby greatly enhancing the ion diffusion rate and suppressing the rapid voltage drop during discharge processes. Therefore, for rechargeable Mg–Li hybrid-ion batteries, v-MoSSe/G realizes a Mg2+/Li+ co-intercalation even at 1000 mA g−1, and also delivers excellent cycling performance, rate capability, and long-term cycling stability with a reversible capacity of 164.6 mA h g−1 at 1000 mA g−1 after 3000 cycles.

The most critical issue hindering the practical application of lithium metal anodes in secondary batteries is the uncontrollable growth of dendrites, which is caused by the uneven supply of lithium ions transported from the inevitably inhomogeneous solid electrolyte interface (SEI) layer on the electrode surface. During lithium deposition, the intrinsically uneven distribution of lithium ions on the anode surface causes the lithium to be liable to deposit at tips and humps, and this results in uncontrollable dendrite growth. Herein, CuO–C modified glass fiber films with a mixed ion and electron-conducting network are proposed to realize homogenized lithium ion flux via providing widespread inner lithium ion transport channels in the skeleton. The improved lithium ion transport in the anodes can remarkably weaken the polarization of lithium plating, further contributing to uniform lithium deposition and high cycling stability. Owing to the high-performance mixed ion and electron transport frameworks, the resultant half cells achieve a long lifespan of over 500 cycles at 1 mA cm−2. Moreover, a full battery coupled with LiFePO4 shows enhanced rate capabilities and high cycle stability, with retention of 81.1% at 1C over 400 cycles compared with a Cu–C modified glass fiber film scaffold.

To realize the industrial feasibility of capacitive deionization (CDI), many efforts have been made to improve the desalination performance. Since investment and daily maintenance issues have to be considered in the actual operation of CDI, which are related to the long-term operational stability of the system, the decline in the performance of electrode materials in long-term operation has seriously impeded the practical application of CDI systems. In this paper, we propose a binder-free Alk-Ti3C2Tx MXene (Alk-Ti3C2Tx-M) using 2D delaminated Ti3C2Tx MXene (d-Ti3C2Tx) nanosheets and 3D porous Alk-Ti3C2Txvia a simple vacuum-assisted filtration strategy. The alkali induces MXene to form a three-dimensional (3D) porous structure, which improves the stability of the electrode with open interconnected pores, while the high surface area guarantees fast ionic diffusion and high Na+ loading. Moreover, d-Ti3C2Tx sheets as a conductive binder replaces traditional conductive adhesives, which enhance the capacity and stability of the electrode by effectively accommodating the volume change and eliminating electrochemically inactive components of traditional conductive binders. As a result, the integrated Alk-Ti3C2Tx-M cathode could be directly used for CDI and exhibited a high capacity (50 ± 3 mg g−1 at 30 mA g−1) and a long-life cycle stability (∼250 cycles, over more than 10 days). Therefore, this strategy of assembling electrodes can be readily extended to constructing a large number of 2D-derived materials for electrochemical applications.

Capacitive deionization (CDI) is a novel technology for desalinating feed water because of its low cost and easy regeneration and in spite of its low desalination capacity and charge efficiency. One of the most promising methods to address these issues is replacing traditional carbon materials with materials that can store ions via faradaic reactions (here known as faradaic electrode materials). Faradaic electrode materials have three main advantages over carbon materials: high capacity, low energy loss, and selective separation; thus, faradaic materials have attracted the interest of many scholars. However, there has not been a comprehensive review of the advances in faradaic materials in desalination and ion separation. In this paper, we present an overview of three kinds of architectures of faradaic deionization cells and analyze their advantages and disadvantages. A variety of faradaic materials are introduced in terms of their structures, merits, drawbacks, and methods to address their deficiencies are discussed. The performance of faradaic electrode materials in desalination, the removal of heavy metals and ion separation is also presented. The issues related to performance are identified, and ways to address them are proposed.