A high-performance rechargeable Mg2+/Li+ hybrid battery using CNT@TiO2 nanocables as the cathode

Catalyzing Desolvation at Cathode-Electrolyte Interface Enabling High-Performance Magnesium-Ion Batteries

Magnesium ion batteries (MIBs) are expected to be the promising candidates in the post-lithium-ion era with high safety, low cost and almost dendrite-free nature. However, the sluggish diffusion kinetics and strong solvation capability of the strongly polarized Mg2+ are seriously limiting the specific capacity and lifespan of MIBs. In this work, catalytic desolvation is introduced into MIBs for the first time by modifying vanadium pentoxide (V2 O5 ) with molybdenum disulfide quantum dots (MQDs), and it is demonstrated via density function theory (DFT) calculations that MQDs can effectively lower the desolvation energy barrier of Mg2+ , and therefore catalyze the dissociation of Mg2+ -1,2-Dimethoxyethane (Mg2+ -DME) bonds and release free electrolyte cations, finally contributing to a fast diffusion kinetics within the cathode. Meanwhile, the local interlayer expansion can also increase the layer spacing of V2 O5 and speed up the magnesiation/demagnesiation kinetics. Benefiting from the structural configuration, MIBs exhibit superb reversible capacity (≈300 mAh g-1 at 50 mA g-1 ) and unparalleled cycling stability (15 000 cycles at 2 A g-1 with a capacity of ≈70 mAh g-1 ). This approach based on catalytic reactions to regulate the desolvation behavior of the whole interface provides a new idea and reference for the development of high-performance MIBs.

Construction of TiO2/TiOF2 heterojunction as a cathode material for high-performance Mg2+/Li+ hybrid-ion batteries

Anatase TiO₂ has attracted significant interest as a cathode material for Mg-ion batteries or Mg²⁺/Li⁺ hybrid-ion batteries. However, owing to the semiconductor property and slower Mg²⁺ diffusion kinetics it still suffers from poor electrochemical performance. Herein, a TiO₂/TiOF₂ heterojunction consisting of in situ formed TiO₂ sheets and TiOF₂ rods, was prepared by adjusting the amount of HF in the hydrothermal process, and used as cathode of Mg²⁺/Li⁺ hybrid-ion battery. The TiO₂/TiOF₂ heterojunction prepared by adding 2 mL HF (TiO₂/TiOF₂-2) exhibits high electrochemical performance, with a high initial discharge capacity (378 mAh/g at 50 mA/g), an outstanding rate performance (128.8 mAh/g at 2000 mA/g), and good cycle stability (capacity retention of 54 % after 500 cycles), which is much superior to that of Pure TiO₂ and Pure TiOF₂. The reactions of Li⁺ intercalation/detercalation in the TiO₂/TiOF₂ heterojunction are revealed by investigating the evolution of the hybrids during different electrochemical states. Moreover, theoretical calculations prove that the Li⁺ formation energy in the TiO₂/TiOF₂ heterostructure is much lower than that of TiO₂ and TiOF₂, demonstrating that the heterostructure plays a crucial role in the enhanced electrochemical performance. This work provides a novel method to design cathode materials with high performance by constructing heterostructure.

High-Performance Mg-Li Hybrid Batteries Based on Pseudocapacitive Anatase Ti1-x Cox O2-y Nanosheet Cathodes

Despite the proposed safety, performance, and cost advantages, practical implementation of Mg-Li hybrid batteries is limited due to the unavailability of reliable cathodes compatible with the dual-ion system. Herein, a high-performance Mg-Li dual ion battery based upon cobalt-doped TiO₂ cathode was developed. Extremely pseudocapacitance-type Ti_1-x Co_x O_2-y nanosheets consist of an optimum 3.57 % Co-atoms. This defective cathode delivered exceptional pseudocapacitance (maximum of 93 %), specific capacities (386 mAh g^-1 at 25 mA g^-1 ), rate performance (191 mAh g^-1 at 1 A g^-1 ), cyclability (3000 cycles at 1 A g^-1 ), and coulombic efficiency (≈100 %) and fast charging (≈11 min). This performance was superior to the TiO₂ -based Mg-Li dual-ion battery cathodes reported earlier. Mechanistic studies revealed dual-ion intercalation pseudocapacitance with negligible structural changes. Excellent electrochemical performance of the cation-doped TiO₂ cathode was credited to the rapid pseudocapacitance-type Mg/Li-ion diffusion through the disorder generated by lattice distortions and oxygen vacancies. Ultrathin nature, large surface area, 2D morphology, and mesoporosity also contributed as secondary factors facilitating superior electrode-electrolyte interfacial kinetics. The demonstrated method of pseudocapacitance-type Mg-Li dual-ion intercalation by introducing lattice distortions/oxygen vacancies through selective doping can be utilized for the development of several other potential electrodes for high-performance Mg-Li dual-ion batteries.

Self-supporting V2O5 nanofiber-based electrodes for magnesium-lithium-ion hybrid batteries

The increasing demand for high energy, sustainable and safer rechargeable electrochemical storage systems for portable devices and electric vehicles can be satisfied by the use of hybrid batteries. Hybrid batteries, such as magnesium-lithium-ion batteries (MLIBs), using a dual-salt electrolyte take advantage of both the fast Li+ intercalation kinetics of lithium-ion batteries (LIBs) and the dendrite-free anode reactions. Here we report the utilization of a binder-free and self-supporting V2O5 nanofiber-based cathode for MLIBs. The V2O5 cathode has a high operating voltage of ∼1.5 V vs. Mg/Mg2+ and achieves storage capacities of up to 386 mA h g-1, accompanied by an energy density of 280 W h kg-1. Additionally, a good cycling stability at 200 mA g-1 over 500 cycles is reached. The structural integrity of the V2O5 cathode is preserved upon cycling. This work demonstrates the suitability of the V2O5 cathode for MLIBs to overcome the limitations of LIBs and MIBs and to meet the future demands of advanced electrochemical storage systems.