Anode Materials For Metal-ion Batteries Research Articles

Theoretical investigation of the intercalation mechanism of VS2/MXene heterostructures as anode materials for metal-ion batteries

Ti2CO2 is one of the lightest MXenes, which is beneficial for achieving higher capacity as electrode material for batteries. However, its semiconductor conductivity has a negative effect on its charging/discharging rate and cyclability performance as electrode materials for batteries. Integrating two different two-dimensional materials to form heterostructures is an effective strategy to optimize the properties of materials. In this work, two heterostructures VS2/Ti2CT2 (T = O and S) are constructed and their electrochemical performances as anode materials for Li, Na and Mg-ion batteries are explored based on first-principles calculations. First of all, the lattice mismatch of these two heterostructures are relatively small, particularly, the lattice mismatch of VS2/Ti2CS2 is as low as 0.63%. Besides, compared with common graphene/Ti2CO2 and MoS2/Ti2CO2 heterostructures, VS2/Ti2CT2 simultaneously exhibit superior metal conductivities and stronger adsorption properties towards Li, Na and Mg atoms, thus achieving higher capacities. Considering the strong adsorption properties, suitable diffusion energy barriers, low open circuit voltages and high capacities, VS2/Ti2CO2 and VS2/Ti2CS2 are proposed to be promising high-performance anode materials for Mg-ion batteries, and VS2/Ti2CS2 is a preferable anode material for Na-ion batteries.

Molybdenum carbide nano-sheet as a high capacity anode material for monovalent alkali metal-ion batteries—Theoretical investigation

This contribution presents a theoretical investigation of monovalent metal-ion adsorption and diffusion on two-dimensional (2D) buckled nanostructure of molybdenum carbide (MoC) by using the first principle method. We find that buckled MoC nanostructure exhibits great stability, semiconducting electronic property, and high performance as electrode material. Interestingly, Crystal Orbital Hamilton population (COHP) method results show that buckled MoC is chemically stable in a wide range of temperatures, and various Li, Na, ions adsorbed configurations, which is beneficial for anode materials. Especially, single-layer MoC exhibits a superior theoretical capacity of 993.16 mAhg−1 for Li-ions and 496.58 mAhg−1 for Na/K-ions. The storage capacity of 1200 mAhg−1 is found for the adsorption of ions on multilayer bulk MoC. Moreover, migration energy barriers are predicted as 0.38 eV for Li, 0.32 eV for Na, and 0.24 eV for K; these remarkable results determine the applicability of buckled MoC as ideal anode material for metal-ion battery applications.

How does the active site in the MoSe2 surface affect its electrochemical performance as anode material for metal-ion batteries?

In this work, we implement density functional theory (DFT) simulations to study how active sites in the MoSe2 surface affect its electrochemical performance as anode material for metal-ion batteries (metal ions including Li, Na, K, Mg, and Al ions). Se vacancy MoSe2 (0 0 1) and MoSe2 (1 1 0) are considered to provide active sites for metal ions. The adsorption energies, diffusion energy barriers, electronic conductivity and open circuit voltage profile (OCV) are evaluated. According to our calculations, MoSe2 (0 0 1) with Se vacancy occupied by Mg ion shows similar diffusion energy barriers and comparable OCV to the pristine MoSe2 (0 0 1). Moreover, Mg ion shows much lower diffusion barriers than the other ions. Besides that, MoSe2 (1 1 0) shows much higher adsorption energies than the (0 0 1) section, indicating its high capacity for metal-ion batteries. However, MoSe2 (1 1 0) also exhibits much higher diffusion energy barriers, which would inhibit its rate capability. Comparatively, MoSe2 (0 0 1) with Se vacancies can improve the conductivity of MoSe2, and the conductivity increases with the number of Se vacancies increases. Consequently, MoSe2 (0 0 1) with single Se vacancy has comprehensive electrochemical performance for Mg-ion battery anode, including low Mg-ion diffusion energy, comparable OCV, and high electronic conductance.

Adsorption mechanisms of Mo2CrC2 MXenes as potential anode materials for metal-ion batteries: A first-principles investigation

Two dimensional MXene are attracting increasing interests as electrode materials for metal ion batteries (MIBs) because metal ions can diffuse in a 2D lattice surface. In this work, first-principles calculations were carried out to investigate the adsorption performance of monolayer Mo2CrC2 for Li, Na, and K. The results show strong storage ability for various metal cations. There are three layers of Li, two layers of Na, one layer of K, and four layers of Mg on both sides of the monolayer. The electrochemical and thermodynamics of the intercalation of metal ions on the Mo2CrC2 Mxene have been intensively investigated. There is no band gap at the Fermi level of any configuration indicating that it has excellent electronic conductivity leading to an asymmetric electron localization distribution. The binding energy of metal ions decreases as the ion concentration increases. The adsorption of metal ions on a mono-layer of Mo2CrC2 has been studied, and the results indicate that the metal ions obviously improved the diffusion of metal ions. The CI-NEB method was used to study the diffusion of a cation on a Mo2CrC2 surface and search for its lowest energy along the diffusion pathway. Their structural transformations were studied via ab initio molecular dynamic (AIMD) simulations at a series of temperatures. The metal ions gradually evolved via thermal motion with increasing temperature. These results suggest that Mo2CrC2 could be a promising electrode material for Li- and Na-ion batteries in terms of Mo2CrC2 specific capacity, diffusion dynamics, and structural stability.

Boron based layered electrode materials for metal-ion batteries.

Graphite is the most commonly used electrode material, which is mainly due to two key advantages, i.e., its layered structure acts a perfect framework for the accommodation and migration of ions, and the light atomic mass of carbon is conducive to obtaining a high specific capacity. As a neighbor of carbon in the periodic table, boron is even lighter than carbon, and it can also form various layered structures. Here, we systematically investigate boron-based layered compounds to explore their potential applications as electrode materials by means of first-principle calculations. Among various types of boron compounds, MXB4 (M = Li, Na, Mg; X = Al, Ga) with the YCrB4-type structure are found to be potentially excellent electrode materials for metal-ion batteries. The adsorption and migration of Li/Na/Mg in MXB4 have been presented, and migration barriers comparable with conventional electrode materials are observed. In particular, Li2AlB4 and Li2GaB4 are found to exhibit quite high specific capacities of 754 mA h g-1 and 470 mA h g-1 compared to the theoretical value of graphite (372 mA h g-1) as well as low average voltages of 0.71 V and 0.79 V, respectively, revealing that they may be good anode materials for Lithium ion batteries.

New Phosphate Framework for Facile Reversible Alkali Metal Ion De/Insertion

Phosphate-based cathode materials are considered safe, reliable and commercially viable for perfecting the next generation of metal-ion batteries for grid applications. Contrary to oxides, phosphates tend to form more sophisticated and diverse crystal structures thus expanding playground for designing and tuning electrochemical properties. Coupled with fluoride anions phosphates might offer not only even higher electrode potentials but also a richer crystal chemistry and then ampler opportunities in developing new cathode materials. Recently we proposed a novel series of vanadium-based AVPO4F (A = Li, Na, K, Rb) cathode materials crystallizing in a unique KTiOPO4 (KTP)-type structure. The target materials were synthesized via different soft-chemistry routes including hydrothermal method and freeze-drying. The KTP-type “VPO4F” framework featured outstanding rate capability and capacity retention especially in Li cells: the material maintained more than 75% of the initial specific capacity at the 40C rate with an average potential of 4.0 V vs. Li/Li+ [1]. The structural evolution during Li de/insertion was examined by operando X-ray diffraction and ex situ electron tomography. The material experienced a series of phase transitions characterized by a volume variation just within 2%. Another quality of this framework is supporting reversible Na+, K+ and even Rb+ ions de/insertion sustaining the host structure [2]. The experimental electrochemical performance and ion transport properties were different for various alkali ions. The ion diffusion coefficients obtained by PITT were the lowest for Li+ (10-12 – 10-14 cm2/s) and the highest for K+ (10-11 – 10-12 cm2/s), with the latter anticipating high-power applications of KVPO4F in K-ion batteries [3]. According to DFT calculations, the “VPO4F” framework manifested extremely low energy barriers for K+ and Rb+ migration of less than 0.2 eV in accordance with experimental transport properties. Furthermore, the full extraction of K+ in KVPO4F occurred at the highest potential of ~4.6 V vs. K/K+ compared to Li+, Na+ and Rb+. At the same time the average potential of the material (4.3 V vs. K/K+) lay within a stability window of commercial electrolytes that validates KVPO4F as the most prospective cathode material for high-voltage K-ion batteries [4]. Additionally, the “VPO4F” framework demonstrated reversible electrochemical activity in the low-voltage domain (below 1.8 V vs. A/A+) in Li, Na and K cells thus opening prospects for creating anode materials for metal-ion batteries. In this talk we will focus on our recent activities on the KTP-type fluoride-phosphates as promising electrode materials for metal-ion rechargeable batteries.