Li Adsorption Research Articles

Cation-vacancy induced Li+ intercalation pseudocapacitance at atomically thin heterointerface for high capacity and high power lithium-ion batteries

It is challenging to create cation vacancies in electrode materials for enhancing the performance of rechargeable lithium ion batteries (LIBs). Herein, we utilized a strong alkaline etching method to successfully create Co vacancies at the interface of atomically thin Co3−xO4/graphene@CNT heterostructure for high-energy/power lithium storage. The creation of Co-vacancies in the sample was confirmed by high-resolution scanning transmission electron microscope (HRSTEM), X-ray photoelectron spectroscopy (XPS) and electron energy loss near-edge structures (ELNES). The obtained Co3−xO4/graphene@CNT delivers an ultra-high capacity of 1688.2 mAh g−1 at 0.2 C, excellent rate capability of 83.7% capacity retention at 1 C, and an ultralong life up to 1500 cycles with a reversible capacity of 1066.3 mAh g−1. Reaction kinetic study suggests a significant contribution from pseudocapacitive storage induced by the Co-vacancies at the Co3−xO4/graphene@CNT interface. Density functional theory confirms that the Co-vacancies could dramatically enhance the Li adsorption and provide an additional pathway with a lower energy barrier for Li diffusion, which results in an intercalation pseudocapacitive behavior and high-capacity/rate energy storage.

The application of graphyne and its boron nitride analogue in Li-ion batteries

We discovered Li and Li+ adsorptions on graphyne and its BN analogues to survey their potential function as an anode in Li-ion batteries (LIBs), utilizing the computations of density functional theory. In B3LYP-D3/6-311G(d,p) level of theory, the stability of feasible isomers of one of the systems were surveyed. For studying the source of energy among multiple isomers of studying complexes, Shubin Liu's energy decomposition analysis (EDA-SBL) is utilized. Considering the results, we can deduce atomic and cationic lithium are preferentially adsorbed on a chosen nanostructures so that the Li+ adsorption is so stronger compared to Li adsorption. The computed ΔEint values were indicated the significant interaction between two fragments in I-isomer. These values were between −7.44 to −74.71 kcal/mol in the studied systems. As an anode in LIBs, the magnitude order of the cell voltage of nanostructures is as follows: G-I-BN > G-II-BN > G-II > G-I.

Point defects-induced adsorption and diffusion of lithium on monolayer titanium disulfide: A first-principles study

The impacts of point defects including single- and few-atom vacancies (VS, VTi, VS2, VTiS3, VTiS6) and antisites (STi, TiS) on the Li adsorption and diffusion in monolayer titanium disulfide (TiS2) are systematically investigated through first-principles calculations based on density functional theory for their underlying functions in Li-ion batteries. The calculations imply that Li adsorption and diffusion capabilities are strongly dependent on the defect types of TiS2. For example, defects VTi, VTiS3 and STi improve Li adsorption capability as their adsorption energies increase compared with the pristine TiS2, and VTi has the largest increase. VS, VS2 and VTi exhibit approximate Li diffusion energy barriers with the pristine TiS2 (0.21 eV), signifying that a neglected impact on the rate capability. More importantly, sulfur antisite STi reduces Li diffusion barrier by 0.03 eV, and thus enhances diffusion rates by 3.2 times. Interestingly, STi simultaneously enhances Li adsorption and diffusion capabilities in monolayer TiS2 to some degree, and VTi considerably favors Li adsorption without compromising diffusion rates, suggesting that the introduction of defects STi and VTi in TiS2 displays excellent properties for energy storage systems. This study benefits for comprehending the impacts of point defects and designing high-performance electrode materials for rechargeable batteries.

Model Studies on the Formation of the Solid Electrolyte Interphase: Reaction of Li with Ultrathin Adsorbed Ionic-Liquid Films and Co3 O4 (111) Thin Films.

In this work we aim towards the molecular understanding of the solid electrolyte interphase (SEI) formation at the electrode electrolyte interface (EEI). Herein, we investigated the interaction between the battery‐relevant ionic liquid (IL) 1‐butyl‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMP‐TFSI), Li and a Co3O4(111) thin film model anode grown on Ir(100) as a model study of the SEI formation in Li‐ion batteries (LIBs). We employed mostly X‐ray photoelectron spectroscopy (XPS) in combination with dispersion‐corrected density functional theory calculations (DFT‐D3). If the surface is pre‐covered by BMP‐TFSI species (model electrolyte), post‐deposition of Li (Li+ ion shuttle) reveals thermodynamically favorable TFSI decomposition products such as LiCN, Li2NSO2CF3, LiF, Li2S, Li2O2, Li2O, but also kinetic products like Li2NCH3C4H9 or LiNCH3C4H9 of BMP. Simultaneously, Li adsorption and/or lithiation of Co3O4(111) to LinCo3O4 takes place due to insertion via step edges or defects; a partial transformation to CoO cannot be excluded. Formation of Co0 could not be observed in the experiment indicating that surface reaction products and inserted/adsorbed Li at the step edges may inhibit or slow down further Li diffusion into the bulk. This study provides detailed insights of the SEI formation at the EEI, which might be crucial for the improvement of future batteries.

Redistributing Li-ion flux and homogenizing Li-metal growth by N-doped hierarchically porous membranes for dendrite-free Lithium metal batteries

Safety hazards caused by lithium dendrites significantly impedes the practical applications of Li metal batteries. However, the previously reported materials with low porosity can be easily filled up by the deposition of Li and loss of regulating effect for lithium dendrites as a Li metal protecting interlayer. Herein, scalable N-doped hierarchically porous membranes (NHPM) with significant porosity of about 90% are reported. The interconnecting porous networks with carbon nanotubes (CNTs) as the cores and N-doped carbon coating as the crosslinked shells allow the uniform distribution of Li+ ions. It also facilitates the rapid diffusion of Li ions and promotes the reversible Li plating and stripping processes. The first-principle calculations reveal that the N active sites that promote Li adsorption can greatly reduce the energy barrier for Li-ion transfer and diffusion on the carbon-coated surface. The protected Li anode exhibits a high Coulombic efficiency of ~99% and presents dendrite free morphology even when repeated Li plating/stripping processes are conducted over 500 h under condition of high current density (8 mA cm−2). A full cell battery with LiFePO4 as the cathode and protected Li as the anode exhibits high cycling stability (up to 600 cycles). The capacity decay rate is as low as 0.03% per cycle.

Half-metallicity and enhanced magnetism in monolayer T-CrTe2 by lithium adsorption

Based on first-principle calculations, we investigate the electronic and magnetic properties of Li-adsorbed monolayer T-CrTe2, named LixCrTe2. We find that as the adsorption concentration x increases from 0.25 to 1.0 and then to 1.25, the monolayers change from metal to semiconductor and then to half-metal. We demonstrate that Li adsorption tuning the electronic properties mainly through electron doping and lattice expansion. The former raises the band filling level, while the latter significantly enhances the ferromagnetic coupling and help open energy gaps. Besides, we find the Curie temperature qualitatively increases as x increases from 0.25 to 1.0 and then decreases at x=1.25, which is caused by the joint effect of the direct exchange, the superexchange and the increased band filling level. Our work provides an efficient strategy to tailor magnetism and produce two-dimensional magnetic semiconductors and half-metals from metals.

GeP3/NbX2 (X=S, Se) Nano-Heterostructures: Promising Isotropic Flexible Anodes for Lithium-Ion Batteries with High Lithium Storage Capacity.

A new trend is emerging that flexible batteries will play an indispensable role in the progress of social science and technology. However, flexibility exists only in a single direction for the existing electrode material. Searching for flexible battery materials has attracted more and more attention from researchers. In this article, the lattice structural stability, electronic structure modulation, and the Li adsorption properties of the heterostructures designed by assembling GeP3 and NbX2 (X = S, Se) together were methodically explored based on van der Waals. We found that diffusion barrier of the GeP3/NbS2 heterostructure with metallic properties is 0.21 eV for Li. It greatly improves the charge and discharge performance of the battery. The predicted heterostructure shows quite high theoretical specific capacity with 540.24 mA h/g, which is higher than the traditional graphite anode (372 mA h/g). It demonstrates superior isotropic flexibility with a considerable small Young’s modulus (151.98–159.02 N/m), which has promising application as flexible electrodes for rechargeable battery equipment.

Constructing multifunctional solid electrolyte interface via in-situ polymerization for dendrite-free and low N/P ratio lithium metal batteries

Stable solid electrolyte interface (SEI) is highly sought after for lithium metal batteries (LMB) owing to its efficient electrolyte consumption suppression and Li dendrite growth inhibition. However, current design strategies can hardly endow a multifunctional SEI formation due to the non-uniform, low flexible film formation and limited capability to alter Li nucleation/growth orientation, which results in unconstrained dendrite growth and short cycling stability. Herein, we present a novel strategy to employ electrolyte additives containing catechol and acrylic groups to construct a stable multifunctional SEI by in-situ anionic polymerization. This self-smoothing and robust SEI offers multiple sites for Li adsorption and steric repulsion to constrain nucleation/growth process, leading to homogenized Li nanosphere formation. This isotropic nanosphere offers non-preferred Li growth orientation, rendering uniform Li deposition to achieve a dendrite-free anode. Attributed to these superiorities, a remarkable cycling performance can be obtained, i.e., high current density up to 10 mA cm−2, ultra-long cycle life over 8500 hrs operation, high cumulative capacity over 4.25 Ah cm−2 and stable cycling under 60 °C. A prolonged lifespan can also be achieved in Li-S and Li-LiFePO4 cells under lean electrolyte content, low N/P ratio or high temperature conditions. This facile strategy also promotes the practical application of LMB and enlightens the SEI design in related fields.

Porous hydrogen substituted graphyne as a promising anode for lithium-ion batteries.

Porous hydrogen substituted graphyne (HsGY) has been considered as a promising candidate for anode material due to its excellent electrochemical properties. In this work, we found that monolayer and bilayer HsGY are good electrodes for high charge capacity lithium-ion batteries based on density functional theory calculations. Mechanical tests reveal that monolayer and bilayer HsGY exhibit excellent mechanical properties, including large critical strains (>25%) and high in-plane stiffness (>200 N m−1). The bilayer HsGY displays ultrahigh stiffness (400.27 N m−1). Li adsorption on bilayer HsGY is stronger than that on the monolayer HsGY. Moreover, Li diffusion on the surfaces of monolayer and bilayer HsGY has low energy barriers (<0.5 eV). Our calculation results suggest that HsGY may contain the highest theoretical charge capacity among two-dimensional (2D) materials studied so far, with ultrahigh Li capacities of 3378 and 2895 mA h g−1 for monolayer and bilayer HsGY, respectively. Given these advantages, including large critical strain, high mechanical stiffness, strong adsorption, low diffusive energy barrier, and high charge capacity, we conclude that both monolayer and bilayer HsGY could be promising anode materials for lithium-ion batteries.

Unoccupied 3d orbitals make Li-unalloyable transition metals usable as anode materials for lithium ion batteries

This work reports the use of Fe which is unalloyable with Li as the anode for LIBs. DFT calculations indicate that the unoccupied 3d orbitals of Fe can accept electrons from Li, making the surface of Fe nanoparticles active for Li adsorption.

First-principles study of structural stability and lithium storage property of Si&lt;sub&gt;&lt;i&gt;n&lt;/i&gt;&lt;/sub&gt; clusters (&lt;i&gt;n&lt;/i&gt; ≤ 6) adsorbed on graphene

Silicon/carbon composite is one of the most potential high-capacity anode materials for lithium-ion batteries. The interface state between silicon and carbon of silicon/carbon composite is an important factor affecting its electrochemical performance. In this paper, Si&lt;sub&gt;&lt;i&gt;n&lt;/i&gt;&lt;/sub&gt; (&lt;i&gt;n&lt;/i&gt; ≤ 6) clusters with different numbers of Si atoms are constructed on graphene as a structural unit of carbon material. The geometric configuration, structure stability and electronic property of Si&lt;sub&gt;&lt;i&gt;n&lt;/i&gt;&lt;/sub&gt; clusters adsorbed on graphene (Si&lt;sub&gt;&lt;i&gt;n&lt;/i&gt;&lt;/sub&gt;/Gr) are studied by the first-principles method based on density functional theory (DFT). The results show that when the number of Si atoms &lt;i&gt;n&lt;/i&gt; ≤ 4, the Si&lt;sub&gt;&lt;i&gt;n&lt;/i&gt;&lt;/sub&gt; clusters are preferentially adsorbed on graphene in a two-dimensional configuration parallel to graphene. When &lt;i&gt;n&lt;/i&gt; ≥ 5, the Si&lt;sub&gt;&lt;i&gt;n&lt;/i&gt;&lt;/sub&gt; clusters are preferentially adsorbed on graphene in a three-dimensional configuration. With the increase of the number of Si atoms &lt;i&gt;n&lt;/i&gt;, the thermodynamic stability of Si&lt;sub&gt;&lt;i&gt;n&lt;/i&gt;&lt;/sub&gt; clusters on graphene decreases significantly, the interface binding strength between Si&lt;sub&gt;&lt;i&gt;n&lt;/i&gt;&lt;/sub&gt; clusters and graphene decreases, and the charge transfer between Si&lt;sub&gt;&lt;i&gt;n&lt;/i&gt;&lt;/sub&gt; clusters and graphene becomes less. At the same time, the storage capacity of Li atoms in Si&lt;sub&gt;&lt;i&gt;n&lt;/i&gt;&lt;/sub&gt;/Gr complex is also studied. Li atoms are mainly stored on the graphene surface near Si&lt;sub&gt;&lt;i&gt;n&lt;/i&gt;&lt;/sub&gt; clusters and around Si&lt;sub&gt;&lt;i&gt;n&lt;/i&gt;&lt;/sub&gt; clusters. The complex synergistic effect of Si&lt;sub&gt;&lt;i&gt;n&lt;/i&gt;&lt;/sub&gt; clusters and graphene enhances the thermodynamic stability of Li adsorption. When &lt;i&gt;n&lt;/i&gt; ≤ 4, storing two Li atoms is beneficial to improving the thermodynamic stability of &lt;i&gt;x&lt;/i&gt;Li-Si&lt;sub&gt;&lt;i&gt;n&lt;/i&gt;&lt;/sub&gt;/Gr system, and the thermodynamic stability decreases with the increase of Li atom number. When &lt;i&gt;n&lt;/i&gt; ≥ 5, the thermodynamic stability of &lt;i&gt;x&lt;/i&gt;Li-Si&lt;sub&gt;&lt;i&gt;n&lt;/i&gt;&lt;/sub&gt;/Gr system decreases with the increase of Li atom number. In the &lt;i&gt;x&lt;/i&gt;Li-Si&lt;sub&gt;5&lt;/sub&gt;/Gr system, the C-C bond and Si-Si bond are mainly covalent bonds, while the Li-C bond and Li-Si bond are mainly ionic bonds with certain covalent properties.

Lattice-distorted lithiation behavior of a square phase Janus MoSSe monolayer for electrode applications.

Janus transition metal dichalcogenides with unique physical properties have recently attracted increasing research interest for their energy and catalytic applications. In this paper, we investigate the lithiation behavior of a square phase Janus MoSSe monolayer (1S-MoSSe) using first-principles calculations. Computational results show that a single Li atom energetically prefers to adsorb on the central site of the octagonal ring (O site) and on the S-layer side of 1S-MoSSe. The predicted energy barriers for Li diffusion are surface dependent and in the range of 0.33 to 0.51 eV, indicating the acceptable Li migration kinetics on 1S-MoSSe in comparison with other 2D TMD materials. Further thermodynamic analysis demonstrates that Li adsorption on 1S-MoSSe is energetically stable up to a Li concentration of x = 1.0, above which the lithiation process becomes unstable with a negative charging potential. Phonon calculations also confirm that Li adsorption (0.25 ≤ x ≤ 0.75) results in the lattice distortion of 1S-MoSSe in order to suppress the structural instability of the lithiated monolayer 1S-LixMoSSe with imaginary phonon frequencies. The less symmetric nature of 1S-MoSSe is believed to destabilize Li adsorption at much smaller x than 1H-MoSSe does, regardless of the higher dipole moment of 1S-MoSSe. This computational study provides a fundamental understanding of the electrochemical performance of 1S-MoSSe, as well as useful insight into the material design of Janus TMD anodes for Li-ion batteries.

Lithiophilic diffusion barrier layer on stainless steel mesh for dendrite suppression and stable lithium metal anode

Lithium metal battery has high theoretical specific capacity but suffers from dendrite growth that leads to low Columbic Efficiency (CE) and uncontrolled volume expansion during cycling. Here, we develop a method for fabrication of a nitrogen-doped carbon-coating as a lithophilic diffusion barrier layer, by carbonizing polydopamine (PDA) on three-dimensional (3D) porous stainless steel (called Nitrogen-doped carbon stainless steel, N-C-SS) mesh, and used it as the current collector for Li metal anode. With this layer, we observed significant suppression of Li dendrite formation during Li deposition. More specifically, the N-C-SS/Li anode in symmetric cells exhibit stable cycling for over 1800 h, 4 times longer than the bare Li electrode. Similarly, the fabricated half cells retain an average CE of 98.1% after cycling 400 times and show a low overpotential of 12 mV, while for fabricated full cells, they retain 98.6% of their initial capacity 140 mA h g−1 after 200 cycles at 3C. Density functional theory (DFT) calculation results show that N-C-SS surface enables higher diffusion barrier, with more negative Li adsorption energy than the untreated SS surface or Cu or Li substrate, which guides Li nucleation and suppresses dendrite growth on the barrier layer. An additional advantage of SS framework is that the 3D SS mesh skeleton distributes Li along with the mesh uniformly and provides ample voids to accommodate high Li loading (>10 mA h cm−2), while simultaneously minimizes local current density.

First-principles investigation of the structure and electronic properties of graphene toward Li adsorption

ABSTRACT The first-principles calculation is performed to investigate the possibility of applying pristine, defected, N-doped, Al-doped and N-Al co-doped graphene in the feasible materials of lithium ion battery. Defected, monoatomic doped and diatomic doped graphene have different effects for Li adsorption. For monoatomic doped graphene, the adsorption energy of Al-doped graphene is the lowest, and its final adsorption distance is the shortest. Among the three types of diatomic doped graphene, N–Al para co-doped graphene is more suitable for the lithium ion battery anode material. Furthermore, the band structures of graphene absorbed with Li are analysed in detail, which indicates that pristine graphene adsorbed with Li belongs to physical adsorption while defected and doped graphene adsorbed with Li belongs to chemical adsorption. What’s more, Mulliken population analysis is applied to investigate the interaction between graphene and Li. According to the calculation results, it will provide a theoretical basis for the future application of graphene in lithium ion battery.

First-principles study of heterostructures of MXene and nitrogen-doped graphene as anode materials for Li-ion batteries

Two-dimensional heterostructures have attracted considerable attention as promising anode materials for lithium-ion batteries (LIBs). Here, we investigated the geometric and electronic properties of heterostructures composed of Ti2CT2 (T=O, F, OH) and N-doped graphene via first-principles density functional theory. Further, we investigated the Li adsorption and diffusion in heterostructures. We demonstrated that electron transfer between the two building blocks of the heterostructures dictates the strength of the adsorption of Li ions on surfaces. The direction and magnitude of electron transfer vary with the functional groups of MXene and N-doping types in N-doped graphene, which in turn influences the adsorption and diffusion of Li ions. We found that the heterostructure composed of Ti2CO2 and N-doped graphene has the strongest adsorption capacity for Li ions. Theoretical capacitances were estimated to be 378 and 417 mAhg−1 for Ti2CO2/GNG (graphitic N doping) and Ti2CO2/GNP (pyridinic N doping), respectively, which were larger than those of pristine Ti2CO2. These results suggest that heterostructures are promising anode materials for LIBs.

Li adsorption on nitrogen-substituted graphyne for hydrogen storage

The adsorptions of hydrogen on Li-decorated nitrogen-substituted graphyne are investigated by density functional theory. The substitutional doping of nitrogen atoms can change the electronic structure of graphyne, which is beneficial to the adsorption of Li atoms. The results show that isolate Li atom is preferred to locate hollow site above the center of the acetylenic ring with binding energies more than 3.10 eV. A maximum of three hydrogen molecules can bind to Li atom decorated graphyne on one side. The average binding energy per H2 molecule for Li-decorated nitrogen-substituted graphyne is higher than that of pure graphyne.

The first-principles study on the performance of the graphene/WS2 heterostructure as an anode material of Li-ion battery

The development of high-performance anode materials for rechargeable Li-ion batteries(LIBs) requires not only a large storage capacity, but also the excellent electrical conductivity and high cycle stability. The van der Waals heterostructure can retain the character of the components, and dramatically improve the properties due to the interlayer coupling. In this paper, the electronic structure and stability of the graphene/WS2(G/WS2) heterostructure as well as the Li adsorption and diffusion within the structure are systematically studied by the first-principles calculations. The G/WS2 heterostructure can realize a direct band gap of only 0.01 eV, which is similar to that of graphene (0 eV) and much smaller than that of WS2 (1.89 eV), indicating the metallic property and the amazing electrical conductivity. Moreover, the G/WS2 heterostructure has the much higher stiffness (463.1 N/m) than the 340.5 N/m of graphene and the 106.4 N/mof the WS2 monolayer. The diffusion energy barrier (0.37 eV) of the Li atom in the G/WS2 heterostructure is much lower than that in other anode materials. The in-plane diffusion coefficient (5.54 × 10−10 m2/s) of Li atoms in the G/WS2 heterostructure at 300 K is higher than that on graphene(2.0 × 10−11 m2/s). The largest volume expansion ratio of the G/WS2 heterostructure anode is only 7.4% at the largest Li capacity and ensures the LIB to avoid rapid performance degradation during the charge/discharge cycle. These results can provide conclusive evidence for exploring that the G/WS2 heterostructure should be the promising anode for LIBs.

Adsorption induced magnetic anisotropy in the two-dimensional magnet CrCl3

Two-dimensional (2D) CrCl3 has attracted much attention as it is reported to be a ferromagnetic semiconductor. By performing first-principles calculations, we investigate the effects of Li and F adsorption on the saturation magnetization and magnetic anisotropy energy (MAE) of CrCl3. It is observed that Li adsorption can dramatically enhance its saturation magnetization, and tune its easy magnetization axis to the in-plane direction from original out-of-plane. The monotonic enhancement of in-plane magnetism in CrCl3 as the coverage of Li increases are attributed to electrostatic doping induced by charge transfer between Li atoms and Br atoms. By contrast, the F adsorption reduces the out-of-plane magnetism in CrCl3 as the coverage of F increases but keeps the original easy magnetization. These findings will benefit for further understanding of the tunable magnetic properties of CrCl3 and push 2D spintronics applications.

Metallic VS2/blue phosphorene heterostructures as promising anode materials for high-performance lithium ion batteries: A first principles study

In this work, based on first principles calculations and molecular dynamics simulation, we systematically investigated the VS2/blue phosphorene (BlueP) heterostructures as potential anodes for LIBs. Our results show that both H-VS2/BlueP and T-VS2/BlueP heterostructures exhibit metallic characteristics, ensuring good electrical conductivity for the fast electron transport. The Young’s moduli (187.3 N/m for H-VS2/BlueP and 183.4 N/m for T-VS2/BlueP), mechanical flexibility (ultimate strains > 16%) and adsorption energy of VS2/BlueP heterostructures are remarkably improved in comparison with pristine BlueP. Such improved mechanical property and adsorption energy are of great significance to suppress the anode pulverization on the whole lithium intercalation–deintercalation process. Moreover, the specific capacities of VS2/BlueP heterostructures are up to 1211.34 mA h/g (multi-layer Li adsorption), which are much higher than pristine BlueP and commercial graphite anodes. In addition, diffusion barriers in the H-VS2/BlueP and T-VS2/BlueP heterostructures are 0.17, 0.16 eV, respectively, implying high mobility of Li. All these encouraging results indicate that VS2/BlueP heterostructures are promising anodes to achieve advanced LIBs.

Theoretical study of enhanced ferromagnetism and tunable magnetic anisotropy of monolayer CrI3 by surface adsorption

Magnetic anisotropy energy (MAE) plays a key role for 2D magnetic materials, which have attracted significant attention for their promising applications in spintronic devices. Based on first-principles calculations, we have investigated the influence of surface adsorption on the ferromagnetism and MAE of monolayer CrI3. We find that Li adsorption can dramatically enhance its ferromagnetism, and tune its easy magnetization axis to the in-plane direction from original out-of-plane at certain coverage of Li. The monotonic enhancement of in-plane magnetism in CrI3 as the coverage of Li increases are attributed to electrostatic doping induced by charge transfer between Li atoms and I atoms, as supported by the charge doping simulation. The tunable robust magnetic anisotropy may open new promising applications of CrI3–based materials in spintronic devices.