Analyses of vanadium carbide as an anode for post-lithium batteries

Abstract

Today, lithium batteries dominate the market of rechargeable batteries, but lithium production is expensive and environmentally detrimental. Given increasing demand and rising costs, the search for alternative rechargeable batteries is critical. This work investigates the performance of a promising 2D MXene anode material, vanadium carbide (V₂C), for use in metal-ion batteries. We compare the properties of four promising alternative metal-ions (Na, Mg, Al, and Ag) with lithium (Li) using DFT. The comparison revealed that Na and Ag perform comparably to Li, with a respective OCV of 0.66–1.32 V and 0.91–1.23 V, with respective theoretical specific capacities of 627 mA h g⁻¹ and 967 mA h g⁻¹, compared to an OCV of 0.75–1.00 V and a capacity of 967 mA h g⁻¹ for Li. The diffusive barrier of Na is exceptionally low, 0.007 eV, and the barrier for Ag is 0.07 eV, while the barrier for Li is 0.02 eV. The Mg- and Al-ion batteries perform with a very high maximum charging capacity, 1883 mA h g⁻¹ and 2823 mA h g⁻¹ respectively, and a slightly lower OCV range of 0.39–0.45 V and 0.22–0.45 V respectively. Due to the good capacity, high OCV and low diffusive barriers of the ions, V₂C anodes are ideal for post-lithium metal-ion battery applications.

---

1 Introduction

Rechargeable batteries are an important technology that greatly influences our daily lives. Most rechargeable batteries used commercially are lithium ion batteries. However, lithium is a scarce resource that is expensive to mine and process. Its production also has a significant negative environmental impact. This impact is expected to intensify as the demand for more batteries continues to increase.^1,2 A new class of two-dimensional (2D) materials, called MXenes, has been shown to be a promising candidate for post-lithium-ion battery anodes.³ Two dimensional anode materials have been shown to offer significantly higher battery capacity than three-dimensional (3D) bulk materials.^4–7 The reason is their high surface area compared to their mass. Among 2D materials, MXene materials show great promise due to their rapid electron transfer and other suitable chemical properties.^8–11

MXenes are a class of 2D materials characterised by the formula M_n+1X_n, where M is a transition metal and X is carbon (C) or nitrogen (N). They have received a great deal of attention as a result of their unique physical and chemical properties.^12,13 For example, they exhibit low diffusion barriers for most ions and exhibit pseudo-capacitance that improves battery performance at high discharge rates.¹⁴ Among those materials are vanadium carbide MXenes and they have been shown to be theoretically and experimentally interesting materials for both lithium and post-lithium batteries. In a recent publication by Fan et al. from 2019 (ref. 15) they showed that V₃C₂ exhibits properties that make it a promising material for post-lithium anodes. It also possesses a significantly lower diffusion barrier than other 2D materials. The MXene of the vanadium carbide family with the theoretically highest capacity is V₂ C due to its low structural mass. In a publication by Xie et al. from 2014 (ref. 16) they calculated the maximum capacities of Li, Na, Mg, Al, K and Ca on the O and OH terminated V₂CT_X surfaces, where T_X is the termination along with bare V₂C showing promise as a high-capacity anode material for batteries. A later publication in 2020 by Li et al.¹⁷ reported the properties of V₂C with a vacancy. Another few studies have shown that pristine V₂C is a promising anode material for Li-ions.^18,19 There have also been quite a few experimental studies that support these claims for terminated V₂C for Li, Na, Al, and Zn.^20–26 A study from 2018 by Champagne et al. performed important calculations on the vibrational modes of V₂C for the identification and characterization of the material.²⁷ A recent review on the applications of vanadium-based MXenes in energy storage from 2024 by Hussain et al. goes nicely into technical details from previous articles on vanadium carbide anodes.²⁸

The ions Na¹⁺, Mg²⁺ and Al³⁺ are commonly recognised as promising replacements for lithium ions in lithium-ion batteries. Sodium-ion batteries are considered the most promising candidates for post-lithium batteries because of their similar electronic configuration and the low cost of sodium. Although lithium and sodium have the same electronic configuration, they often have vastly different electrochemistries due to sodium ions having a radius around 50% larger than that of lithium ions. Magnesium ion batteries are also very interesting because of their proximity to Li and Na in the periodic table, and they have shown high promise as a result of their conserved nature and theoretically higher capacity density due to their higher valence electron count. Aluminium ions are considered promising because of their even higher valence electron count which can lead to extremely high theoretical capacity.²⁹ Silver ions are also a promising candidate for replacing lithium ions, as they have the same electronic configuration as lithium ions while having a radius size more similar to lithium than to sodium.^30,31

In this study, we explored V₂C as an anode material for application in post-lithium batteries, by using density functional theory (DFT). We studied the theoretical possibility of using Na, Mg, Al, and Ag ions as replacements for Li in batteries. The main factors that can influence the ability of battery material are the maximum capacitance, the open circuit voltage (OCV) and the diffusion barrier, which we will calculate for all five ions. It is also important to determine whether the material is stable as an anode material, which is done in this study using phonon stability calculations and electronic calculations. The novelty of the current work lies in the fact that this is the first report where silver ions have been considered for metal-ion batteries, and we investigated the theoretical properties of post-lithium-ion batteries in a way deeper than has been done before, by considering the OCV profile of the charging process.

2 Methodology

This study was conducted using first-principle DFT calculations using the Vienna Ab initio Simulation Package (VASP).³² The ASE³³ package was extensively used to visualise and manipulate the structures, and Vesta³⁴ was used to create a detailed visualisation of the structure. Visualisation of the band structure and density of states calculations were performed via the SUMOplot package.³⁵ The calculations use the Perdew–Burke–Ernzerhof (PBE)³⁶ functional for the generalised gradient approximation (GGA) exchange–correlation functional. We used the DFT-D3 method of Grimme et al.³⁷ to simulate van der Waals forces between atoms in the structure. In the calculations, a 3 × 3 × 1 supercell with a 20 Å vacuum was used to minimise the interaction between the layers. For the phonon dispersion calculation we used a 4 × 4 × 1 supercell instead.

The kinetic energy cut-off used for the plane wave expansion of the valence electron wave functions was chosen to be 600 eV. The Brillouin zone was modelled using a Monkhorst–Pack k-point mesh scheme with a Γ-centered 5 × 5 × 1 mesh, which was used for the unit cell and the 3 × 3 × 1 supercell, while a denser 30 × 30 × 1 and 20 × 20 × 1 mesh was used for the density of states and band-structure calculations of the clean structure and fully adsorbed structures, respectively. An energy convergence criterion of 10⁻⁶ eV was used along with a force convergence criterion of 0.01 eV Å⁻¹.¹⁵ The method of climbing-image nudged elastic bands (CI-NEB)³⁸ was used to determine the diffusion energy barrier of the adsorbed ions on the structure. The adsorption energy E_ad for x ions adsorbed on the V₂C structure can be calculated with

where E_V2CMx is the total energy of the whole structure, E_V2C is the energy of the clean energy of the V₂C structure, and E_M is the total energy of Li, Na, Mg, Ag, and Al ions without being adsorbed on the surface. The open circuit voltage (OCV) can be calculated for the anode withwhere n is the number of valence electrons of the adsorbed atom.³⁹ In our case Li, Na, and Ag have one valence electron, while Mg and Al have two and three respectively. The theoretical maximum capacity is calculated withwhere x_Max is the maximum number of adsorbed ions on the anode, M_V2C is the molar mass of the clean V₂C anode structure, and F is the Faraday constant given as 26.8 A h mol⁻¹. The transfer of charge between adsorbed atoms and the V₂C anode material was determined using Bader charge analysis⁴⁰ and differential charge density analysis where the charge density difference Δρ is given as

Δρ = ρ_V2C+M − ρ_V2C − ρ_M, (4)

where ρ_V2C+M is the charge density of the total structure of one atom M adsorbed on the V₂C anode, ρ_V2C is the charge density of the V₂C anode, and ρ_M is the charge density of an unbound atom M.

3 Results

First, we studied the properties of the pristine V₂C structure, e.g. the structural properties, such as the lattice structure and structural stability and the electronic properties of the pristine structure. The monolayer of V₂C, shown in Fig. 1, is a hexagonal structure which is composed of two vanadium layers separated by a carbon layer. The calculated lattice parameters for the V₂C monolayer are a = b = 2.89 Å with thickness d = 2.19 Å, which is comparable to the lattice parameters in the experimental study by Bing Wu et al.²³ The V₂C MXene structure has also been shown to be stable in some other experimental studies.^20–22 But to show that the structure we simulated is stable, we simulated the phonon dispersion spectra of the unit cell using the phonopy code,^41,42 see Fig. 2. The lack of imaginary phonon modes in the first Brillouin zone suggests that the structure is stable. For V₂C to be a suitable anode material, it must have a high electronic conductivity.⁴³ By examining the electronic properties of the pristine structure, as shown in Fig. 3a and b, the structure is metallic and non-magnetic. This is because the electron bands cross the Fermi level, and the density of states is the same for up- and down-spins. These properties make V₂C a suitable anode candidate.

Fig. 1 Top and side views of the V₂C monolayer and all four adsorption sites: metal (M), bridge (B), hollow metal (H), and hollow carbon (C). The large blue atoms are vanadium atoms, while the small brown atoms are carbon atoms.

Fig. 2 The phonon dispersion spectra of the V₂C unit cell calculated using phonopy.

Fig. 3 Electronic density of states and band structure of the pristine V₂C unit cell, plotted using SUMOplot.

The most active adsorption sites of the Li/Na/Mg/Ag/Al ions on V₂C, along with the respective adsorption strength, are found by adsorbing the ions onto a 3 × 3 × 1 supercell, calculating the relaxed adsorption energy, and performing Bader charge analysis at different adsorption sites. In this study, we consider four different adsorption sites on the anode material, as shown in Fig. 1a and b. The adsorption sites are the metal site (M) located above the top vanadium atom, the bridge site (B) located between two metal sites, the hollow site (H) located above the bottom vanadium atom and between three metal sites, and the hollow carbon site (C) located above the carbon atom and between three metal sites. The calculated adsorption energy of the Li/Na/Mg/Ag/Al ions at different adsorption sites determines which site is favoured as seen in Fig. 4 and Table 1. There is not much difference between the binding energies at different sites. Numerically, the most exergonic sites for the ions are C for Li/Mg/Al, M for Na, and H for Ag. Fig. 5 shows the relaxed configurations of the most exergonic sites. The most exergonic sites correspond to the most active sites for the ions, except Na, which does not adsorb onto the surface in simple 3 × 3 layers. Notably, only the Na ion remained adsorbed across all four adsorption sites, the other ions migrated to other sites from the e.g. bridge site, as seen in Table 1. However, the adsorption energy difference for the different adsorption sites of Na is very small, which can predict the low diffusion barrier of the ion, which will be calculated later.

Fig. 4 Adsorption energy of a single ion adsorbed on the V₂C monolayer. The missing bars correspond to ions that did not adsorb at the site and instead migrated to another site. Both the graphs show the same data in a different way for clarity.

Table 1 Adsorption properties on different sites between the adsorbed single respective ion and the V₂C anode. The @ site means that the ion moved to the respectively mentioned site during relaxation

System	E ad (eV)				Charge transfer q (e^−)				h (Å)
	M	B	H	C	M	B	H	C	M	B	H	C
Li–V2C	−0.98	@C	−1.00	−1.01	0.85	@C	0.85	0.85	2.50	@C	2.60	2.58
Na–V2C	−1.32	−1.32	−1.31	−1.32	0.73	0.72	0.72	0.72	2.77	2.78	2.90	3.01
Mg–V2C	@H	@C	−0.79	−0.82	@H	@C	0.75	0.77	@H	@C	2.47	2.49
Ag–V2C	@H	@H	−0.91	−0.88	@H	@H	−0.42	−0.39	@H	@H	2.44	2.41
Al–V2C	@C	@C	−0.62	−0.65	@C	@C	−0.15	−0.13	@C	@C	2.26	2.27

---

Fig. 5 Visualization of relaxed single-ion adsorption sites. Sub figures (a)–(e) show Li, Na, Mg, Ag and Al respectively.

The adsorption process can be visualized with the method of charge density difference. Fig. 6 shows how the charge density changes with bonding. The light blue colour shows charge depletion, which is equivalent to electron accumulation, while the yellow colour shows electron depletion and charge accumulation.

Fig. 6 Charge difference density of adsorbing a single ion on V₂C. The light blue and yellow surfaces show charge depletion and accumulation respectively during the adsorption. Sub figures (a)–(e) show Li, Na, Mg, Ag and Al respectively.

The magnitude of charge transfer on each site can be seen in Table 1, as well as a comparison of the adsorption energy and height of the adsorbed ions for each site. We can see two different adsorption behaviours. The first is where the charge transfer is positive, as is the case for Na, Li, and Mg. Positive charge transfer means that the charge goes from the anode to the ion and thus the ions share electrons with the anode material. This indicates how the ions bind to the anode during the electrochemical reaction and that the ions become positively charged after adsorption. The latter one is where the charge transfer is negative, like for Ag and Al. This means that the charge goes from the ion to the surface. This indicates that the ion becomes slightly negatively charged during the electrochemical reaction, which indicates a slight cathode behaviour. However, this does not necessarily mean that the ion is not suitable for the anode since the charge value is small. For the single-ion adsorptions, there is almost no visible difference between these adsorption patterns, but it becomes visible during the multi-ion adsorptions. In these case of ions with positive charge transfer adsorb with a higher adsorption energy, for example; the second lithium ion adsorbs on the C site, which is further away from the first ion, with E_ad = −0.90 eV, which is higher than the adsorption energy for the first lithium ion adsorbing on the C site with E_ad = −1.01 eV. This behaviour is opposite for negative charge-transfer ions, where the second adsorption energy of the ions is lower than that of the first one. For example, the second adsorption for Al is on the closest C site to the first ion, then both the ions migrate closer to each other by going respectively to their closest B sites, and there they are adsorbed with energy E_ad = −0.79 eV, which is much more exergonic than the first adsorption on the C site with energy E_ad = −0.65 eV. This means that for the negative charge transfer case, the ions attract each other and the interaction between the ions strengthens the bond to the anode, but for the positive charge transfer case, the ions repel each other and weaken the bond to the anode.

By considering multi-ion adsorption on V₂C, it allows finding the important values of open-circuit voltage (OCV) and the theoretical specific capacity. The OCV was determined by iteratively adsorbing the ions to the anode at the four different sites, and at each iteration we chose the most exergonic site to continue with, and then eqn (2) is used to calculate the OCV for that step. The maximum theoretical specific capacity is calculated using eqn (3) using the maximum number of ions adsorbed on the anode. We were able to adsorb up to four layers of ions on the anode, that is, two layers on top and two on the bottom, as can be seen in Fig. 7 where each layer consists of 9 ions for the supercell, leading to 36 ions being adsorbed in total. However, the Na ion behaves differently; it has a bigger radius than the other ions, so 9 ions do not fit on the anode, so we stopped adsorbing after 24 ions, i.e., just before the third layer formed on each side. The active sites for the multilayer adsorption on Li are the hollow carbon (C) for the first layer and the hollow carbon (H) for the second. For Mg and Al: the hollow (H) site for the first layer and metal (M) site for the second layer, and for Ag: hollow (H) and metal (M).

Fig. 7 Comparison of multilayer adsorption of Li (a) and (d) and Na (b) and (c). The other ions Mg, Al and Ag show the same behaviour as Li.

Fig. 8a shows the adsorption energy per atom as a function of ion coverage x on the anode, while Fig. 8b shows how the OCV changes with the ion coverage. It shows that the OCV for Li lies in the range 0.75–1.00 V, while the OCV for Na and Ag lies in the ranges 0.66–1.32 V and 0.91–1.23 V, respectively. So, the OCV of Na and Ag is comparable to or even better than the OCV of Li. However, the OCV for Mg and Al lies in the ranges 0.39–0.45 V and 0.22–0.45 V, respectively. This is a comparatively lower OCV than that of the other ions; however, what they lack in OCV, they make up for in maximum capacity as can be seen from Fig. 8c showing the relationship between OCV and capacity for the different ions. The maximum capacity for Mg and Al is 1883 mA h g⁻¹ and 2823 mA h g⁻¹, respectively, while for both Li and Ag it is 967 mA h g⁻¹ and only 627 mA h g⁻¹ for Na. For comparison, the most commonly used commercial anode graphite has a theoretical maximum capacity of 372 mA h g⁻¹.⁴⁴ From Fig. 8b it is also possible to see how the adsorption energy and the OCV change as a function of the number of adsorbed ions, for both positive (Li, Na, and Mg) and negative charge transfer cases (Ag and Al). In the negative charge-transfer cases, the OCV gets lower as the ion coverage of the anode is increased, while for the positive charge-transfer cases, such as Ag and Al, the OCV increases until the anode is covered by one layer on top and another on the bottom. Magnesium shows the behaviour of both cases, as at the start the OCV decreases with the second ion but then increases after the third ion. After adsorbing the ions on the anode we ensured that the anode has good conductivity throughout the process by calculating the density of states after the adsorption process and making sure that they are all metallic, as shown in Fig. 9. In Fig. 9, the orbitals are colour coded by atoms, where the vanadium atom orbitals are shades of green, the carbon atoms are blue, and the adsorbed atoms are red.

Fig. 8 OCV and adsorption energy of each ion investigated as a function of the anode ion coverage (capacity). The coverage x is equal to the number of adsorbed ions in a unit cell.

Fig. 9 The total and partial density of states for the V₂C anode fully adsorbed corresponding to two layers on both sides. They all show metallic behaviour, which is suitable for anodes.

Another important estimator for theoretical battery anode analysis is the diffusion barrier of the ion. The diffusion barrier is used to estimate the ion mobility during the charging process.⁴⁵ In this study, the diffusion barrier is calculated using the climbing-image nudged elastic band (CI-NEB) method.³⁸ We examine the diffusion over two different diffusion paths that are independent of each other, as shown in Fig. 10. In 2D hexagonal materials, the paths chosen are usually called armchair (AB) and zigzag (AC) directions. The path is chosen to be between two neighbouring sites of the most exergonically adsorbed sites for each ion. Fig. 11 shows the energy diagram along the pathways for the ions and a bar diagram that compares the diffusion barrier for the ions. The energy barrier on path AC is lower than that on path AB for all the considered ions.

Fig. 10 The two possible CI-NEB diffusion paths. They were chosen between two of the most exergonically adsorbed sites for an ion. The blue path marks the zigzag (AC) path, while the red path marks the armchair (AB) path.

Fig. 11 The results of the CI-NEB calculation between the two diffusion paths armchair (AB) and zigzag (AC), along with a bar diagram showing the diffusion barrier for the respective ions.

The diffusion barrier of the ions are all low, especially Li and Na, which are respectively 0.02 eV and 0.007 eV. This is even lower than the diffusive barrier of V₃C₂, which is considerably lower than that of other typical 2D materials. For comparison, the diffusive barrier of other typical 2D materials is in the order 0.1 eV.¹⁵ The diffusive barriers of Mg, Al, and Ag are slightly higher; they are 0.07 eV, 0.1 eV, and 0.07 eV, respectively.

During charging and discharging, the adsorption of ions on the anode material can affect the volume of the electrode and its capacity may decline over a few cycles and become unusable quickly, leading to unfavourable cycle count. We can qualitatively estimate the stress on the anode from the compression and dilatation ratio ΔL/L, where L is the length of the pristine structure and ΔL is the length deviation of the adsorbed structure. The compression and dilation ratio in the zigzag and armchair directions of the anode lattice is around 1% for Ag, Al, Li, and Na, while for Mg it is around 4%. In the out-of-plane direction, ΔL/L is around 2% for Ag and Li and around 5% for Mg and Al. However, for Na it is around 38%, which is very high and predicts a poor cycle count for Na-ions. The volume compression and dilation ratio ΔV/V is under 3% for all the ions except Na where it is 41%. Thermal stability is also important for good cycle count, but that is calculated using AIMD. These calculations have been done for V₂C at 300 K by Xu et al. in a study from 2017 and in a study from 2019 by Nyamdelger et al. for lithinated V₂C at 300 K and 500 K. Those calculations show that V₂C is thermally stable.^18,19

These results for V₂C make it a very competitive prospective post-lithium anode material. In Table 2 we have compiled some competitive results of previous DFT studies on 2D anode materials to compare with our results. We also included the theoretical values for a graphite anode, which is currently commercially used. Our lithium and sodium results are very competitive because they have a very high specific capacity, good OCV, and a very low diffusion barrier. However, sodium shows very high stress during the charging process, which predicts a poor cycle count. The magnesium results are also very good and comparable to the highly competitive results of previous work, as it has a good combination of high specific capacity, a low diffusion barrier, and good OCV. The aluminium-based metal-ion battery results show the highest capacity compared to its OCV, while having a low but slightly higher diffusion barrier, which makes it a very competitive battery anode prospect. This is the first study showing the possibility of using silver ions in metal ion batteries, and the results are of a quality similar to that of lithium ion batteries. However, although silver is a scarce resource, it is more readily available than lithium and might be a suitable substitute.

Table 2 Comparison of specific capacity, diffusion barrier, and OCV for various anode materials

Anode material	Ion	Specific capacity (mA h g^−1)	Diffusion barrier (eV)	OCV (V)	Reference
V2C	Li	967	0.02	0.75–1.00	This work
V2C	Na	627	0.007	0.66–1.32	This work
V2C	Mg	1883	0.07	0.39–0.45	This work
V2C	Al	2823	0.1	0.22–0.45	This work
V2C	Ag	967	0.07	0.91–1.23	This work
V2N	Li	925	0.025	0.32	46
V3C2	Li	606.42	0.04	0.85–1.15	15
Graphite	Li	372	0.22	0.11	47
MoS2	Li	335	0.22	0.5–0.25	47
VS2	Li	466	0.25	0.93	47
Ti2N	Li	484	0.021	0.67	48
V2N	Na	463	0.014	0.24	46
V3C2	Na	606.42	0.02	0.75–1.25	15
Ti2N	Na	484	0.014	0.44	48
V2N	Mg	1850	0.058	0.43	46
Ti2N	Mg	2930	0.076	0.13	48
Ti2NO2	Al	1134	0.4	0.09	48

---

4 Conclusion

In conclusion, we have investigated the performance of V₂C as an anode material for the ions Na, Mg, Al and Ag compared to Li. First, we showed the stability of the pristine structure and calculated its electronic properties to show that V₂C is a non-magnetic metal. We also ensured that the fully adsorbed anode structure shows good electronic conductivity throughout the charging/discharging cycle for all the ions, by confirming that the structure stays a nonmagnetic metal. We compared the OCV and the theoretical capacity of the ions with that of Li, which has an OCV in the range of 0.75–1.00 V and a capacity of 967 mA h g⁻¹. The results are that Na and Ag show similar performance to Li; therefore, V₂C is a suitable anode material for post-lithium metal ion batteries using Na and Ag. Na has an OCV in the range of 0.66–1.32 V and a capacity of 627 mA h g⁻¹, while Ag has a higher and more stable OCV in the range 0.91–1.23 V and the same capacity as that of Li 967 mA h g⁻¹. The performance of Ag ions on V₂C is interesting as the choice of using Ag ions for metal ion batteries is novel, and they outperform Li ions for V₂C. The possibility of using Ag ions might be a new research direction in post-lithium metal ion batteries, and further research is needed. The performance of Mg- and Al-ions on V₂C is also good as both offer very high capacity compared to Li ions, despite their comparatively lower OCVs. Mg has a capacity of 1883 mA h g⁻¹ and an OCV in the range of 0.39–0.45 V, while Al has the highest capacity of 2823 mA h g⁻¹ with an OCV in the range of 0.22–0.45 V. We also calculated the diffusion energy barrier to predict the charge/discharge rate, and all the ions have low diffusive barriers. Li has a diffusive barrier of 0.02 eV, while Ag and Mg have a barrier of 0.07 eV. Al has the highest diffusive barrier of 0.1 eV and therefore the slowest charging speed, while Na has the lowest barrier of only 0.007 eV, which is extremely low. All of the materials are predicted to have a good cycle count, except Na, which exhibits significant lattice dilation during the charging process. Based on these findings, we conclude that V₂C is a suitable anode material for replacing Li ions in metal-ion batteries with Mg, Al, and Ag.

Data availability

The calculations have been performed using the Vienna ab initio simulation package VASP (6.3.2 version).⁴⁹ The data that supports the article has been presented in the manuscript in the form of free energy diagrams.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

We would like to acknowledge financial support from the NSN Fund of Rannis, grant No. 2412434-1101.

References

1. J. A. Llamas-Orozco, F. Meng, G. S. Walker, A. F. N. Abdul-Manan, H. L. MacLean and I. D. Posen, et al., Estimating the environmental impacts of global lithium-ion battery supply chain: a temporal, geographical, and technological perspective, PNAS Nexus, 2023, 2(11), pgad361.
2. M. Gutsch and J. Leker, Costs, carbon footprint, and environmental impacts of lithium-ion batteries – from cathode active material synthesis to cell manufacturing and recycling, Appl. Energy, 2024, 353, 122132.
3. Y. Guo, Z. Du, Z. Cao, B. Li and S. Yang, MXene Derivatives for Energy Storage and Conversions, Small Methods, 2023, 7(8), 2201559.
4. S. Kaviani, I. Piyanzina, O. V. Nedopekin and D. A. Tayurskii, First-principles outlook of two-dimensional B3O3 monolayer as an anode material for non-lithium ion (K+, Ca2+, and Al3+) batteries, Comput. Theor. Chem., 2023, 1228, 114246.
5. S. Kaviani, D. A. Tayurskii, O. V. Nedopekin, I. Piyanzina and E. Shakerzadeh, Unveiling potential of thiophene-functionalized C3N3 nanosheet as an anode for Li-ion batteries: a DFT-D3 study, Inorg. Chem. Commun., 2024, 165, 112491.
6. S. Kaviani, I. Piyanzina, D. A. Tayurskii and O. V. Nedopekin, A DFT modeling of 4-cyclohexene-1,3-dione embedded in covalent triazine framework as a stable anode material for Li-ion batteries, Mater. Chem. Phys., 2024, 322, 129592.
7. S. Kaviani, I. Piyanzina, O. V. Nedopekin, D. A. Tayurskii and R. Rahimi, A DFT-based design of B/N/P-co-doped oxo-triarylmethyl as a robust anode material for magnesium-ion batteries, J. Power Sources, 2024, 604, 234425.
8. M. Q. Long, K. K. Tang, J. Xiao, J. Y. Li, J. Chen and H. Gao, et al., Recent advances on MXene based materials for energy storage applications, Mater. Today Sustain., 2022, 19, 100163.
9. N. Ashraf, M. Isa khan, A. Majid, M. Rafique and M. B. Tahir, A review of the interfacial properties of 2-D materials for energy storage and sensor applications, Chin. J. Phys., 2020, 66, 246–257.
10. M. Isa Khan, A. Majid, N. Ashraf and I. Ullah, A DFT study on a borophene/boron nitride interface for its application as an electrode, Phys. Chem. Chem. Phys., 2020, 22, 3304–3313.
11. N. Ashraf and Y. Abghoui, Borophene Potential for Developing Next-Generation Battery Applications: A Comprehensive Review, Energy Fuels, 2023, 37(19), 14589–14603.
12. U. Fatima, M. B. Tahir, M. Sagir, N. Fatima, T. Nawaz and M. P. Bhatti, et al., Two-dimensional materials and synthesis, energy storage, utilization, and conversion applications of two-dimensional MXene materials, Int. J. Energy Res., 2021, 45(7), 9878–9894.
13. V. Chaudhary, N. Ashraf, M. Khalid, R. Walvekar, Y. Yang and A. Kaushik, et al., Emergence of MXene–Polymer Hybrid Nanocomposites as High-Performance Next-Generation Chemiresistors for Efficient Air Quality Monitoring, Adv. Funct. Mater., 2022, 32(33), 2112913.
14. M. H. Hossain, M. A. Chowdhury, N. Hossain, M. A. Islam and M. H. Mobarak, Advances of lithium-ion batteries anode materials—A review, Chem. Eng. J. Adv., 2023, 16, 100569.
15. K. Fan, Y. Ying, X. Li, X. Luo and H. Huang, Theoretical Investigation of V3C2 MXene as Prospective High-Capacity Anode Material for Metal-Ion (Li, Na, K, and Ca) Batteries, J. Phys. Chem. C, 2019, 123(30), 18207–18214.
16. Y. Xie, Y. Dall'Agnese, M. Naguib, Y. Gogotsi, M. W. Barsoum and H. L. Zhuang, et al., Prediction and Characterization of MXene Nanosheet Anodes for Non-Lithium-Ion Batteries, ACS Nano, 2014, 8(9), 9606–9615.
17. Y. M. Li, Y. L. Guo and Z. Y. Jiao, The effect of S-functionalized and vacancies on V2C MXenes as anode materials for Na-ion and Li-ion batteries, Curr. Appl. Phys., 2020, 20(2), 310–319.
18. Z. Xu, X. Lv, J. Chen, L. Jiang, Y. Lai and J. Li, DFT investigation of capacious, ultrafast and highly conductive hexagonal Cr2C and V2C monolayers as anode materials for high-performance lithium-ion batteries, Phys. Chem. Chem. Phys., 2017, 19, 7807–7819.
19. S. Nyamdelger, T. Ochirkhuyag, D. Sangaa and D. Odkhuu, First-principles prediction of a two-dimensional vanadium carbide (MXene) as the anode for lithium ion batteries, Phys. Chem. Chem. Phys., 2020, 22, 5807–5818.
20. A. VahidMohammadi, A. Hadjikhani, S. Shahbazmohamadi and M. Beidaghi, Two-Dimensional Vanadium Carbide (MXene) as a High-Capacity Cathode Material for Rechargeable Aluminum Batteries, ACS Nano, 2017, 11(11), 11135–11144.
21. Y. Liu, Y. Jiang, Z. Hu, J. Peng, W. Lai and D. Wu, et al., In-Situ Electrochemically Activated Surface Vanadium Valence in V2C MXene to Achieve High Capacity and Superior Rate Performance for Zn-Ion Batteries, Adv. Funct. Mater., 2021, 31(8), 2008033.
22. S. Behl, V. Lahariya, P. P. Pandey and R. Kumar, Recent developments in V2C MXene as energy storage materials: Promises, challenges and future prospects, J. Energy Storage, 2024, 92, 112176.
23. B. Wu, M. Li, V. Mazánek, Z. Liao, Y. Ying and F. M. Oliveira, et al., In Situ Vanadium-Deficient Engineering of V2C MXene: A Pathway to Enhanced Zinc-Ion Batteries, Small Methods, 2024, 8(9), 2301461.
24. A. A. Sijuade, V. O. Eze, N. Y. Arnett and O. I. Okoli, Vanadium MXenes materials for next-generation energy storage devices, Nanotechnology, 2023, 34(25), 252001.
25. Y. Guan, B. Xiao, X. Zhang, L. Xiong, J. Liu and Y. Ding, et al., Two-dimensional vanadium carbide (V2C) MXene derived heterostructures for high-performance lithium storage, J. Alloys Compd., 2025, 1010, 177171.
26. S. M. Bak, R. Qiao, W. Yang, S. Lee, X. Yu and B. Anasori, et al., Na-Ion Intercalation and Charge Storage Mechanism in 2D Vanadium Carbide, Adv. Energy Mater., 2017, 7(20), 1700959.
27. A. Champagne, L. Shi, T. Ouisse, B. Hackens and J. C. Charlier, Electronic and vibrational properties of V₂C-based MXenes: from experiments to first-principles modeling, Phys. Rev. B, 2018, 97, 115439.
28. I. Hussain, O. J. Kewate, A. Hanan, F. Bibi, M. S. Javed and P. Rosaiah, et al., V-MXenes for Energy Storage/Conversion Applications, ChemSusChem, 2024, 17(15), e202400283.
29. M. Walter, M. V. Kovalenko and K. V. Kravchyk, Challenges and benefits of post-lithium-ion batteries, New J. Chem., 2020, 44, 1677–1683.
30. A. Kramida, Y. Ralchenko, J. Reader and NIST ASD Team, NIST Atomic Spectra Database (ver. 5.11), available: https://physics.nist.gov/asd, [2024, October 18], National Institute of Standards and Technology, Gaithersburg, MD, 2023.
31. J. C. Slater, Atomic Radii in Crystals, J. Chem. Phys., 1964, 41(10), 3199–3204.
32. G. Kresse and J. Furthmüller, Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set, Phys. Rev. B:Condens. Matter Mater. Phys., 1996, 54(16), 11169–11186.
33. A. Hjorth Larsen, J. Jørgen Mortensen, J. Blomqvist, I. E. Castelli, R. Christensen and M. Dułak, et al., The atomic simulation environment—a Python library for working with atoms, J. Phys.: Condens. Matter, 2017, 29(27), 273002.
34. K. Momma and F. Izumi, VESTA3 for three-dimensional visualization of crystal, volumetric and morphology data, J. Appl. Crystallogr., 2011, 44, 1272–1276.
35. A. M. Ganose, A. J. Jackson and D. O. Scanlon, sumo: Command-line tools for plotting and analysis of periodic ab initio calculations, J. Open Source Softw., 2018, 3, 717.
36. J. P. Perdew, K. Burke and M. Ernzerhof, Generalized Gradient Approximation Made Simple, Phys. Rev. Lett., 1996, 77(18), 3865–3868.
37. S. Grimme, J. Antony, S. Ehrlich and H. Krieg, A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu, J. Chem. Phys., 2010, 132(15), 154104.
38. G. Henkelman, B. P. Uberuaga and H. Jónsson, A climbing image nudged elastic band method for finding saddle points and minimum energy paths, J. Chem. Phys., 2000, 113(22), 9901–9904.
39. M. K. Aydinol, A. F. Kohan and G. Ceder, Ab initio calculation of the intercalation voltage of lithium-transition-metal oxide electrodes for rechargeable batteries, J. Power Sources, 1997, 68(2), 664–668.
40. W. Tang, E. Sanville and G. A. Henkelman, A grid-based Bader analysis algorithm without lattice bias, J. Phys.: Condens. Matter, 2009, 21, 084204.
41. A. Togo, First-principles Phonon Calculations with Phonopy and Phono3py, J. Phys. Soc. Jpn., 2022, 92(1), 012001.
42. A. Togo, L. Chaput, T. Tadano and I. Tanaka, Implementation strategies in phonopy and phono3py, J. Phys.: Condens. Matter, 2023, 35(35), 353001.
43. W. Li, Y. Yang, G. Zhang and Y. W. Zhang, Ultrafast and Directional Diffusion of Lithium in Phosphorene for High-Performance Lithium-Ion Battery, Nano Lett., 2015, 15(3), 1691–1697.
44. J. Niu and S. Kang, New High-energy Anode Materials, in Future Lithium-ion Batteries, The Royal Society of Chemistry, 2019.
45. V. Etacheri, R. Marom, R. Elazari, G. Salitra and D. Aurbach, Challenges in the development of advanced Li-ion batteries: a review, Energy Environ. Sci., 2011, 4(9), 3243–3262.
46. H. Liu, Y. Cai, Z. Guo and J. Zhou, Two-Dimensional V2N MXene Monolayer as a High-Capacity Anode Material for Lithium-Ion Batteries and Beyond: First-Principles Calculations, ACS Omega, 2022, 7(21), 17756–17764.
47. Y. Jing, Z. Zhou, C. R. Cabrera and Z. Chen, Metallic VS2 Monolayer: A Promising 2D Anode Material for Lithium Ion Batteries, J. Phys. Chem. C, 2013, 117(48), 25409–25413.
48. D. Wang, Y. Gao, Y. Liu, D. Jin, Y. Gogotsi and X. Meng, et al., First-Principles Calculations of Ti2N and Ti2NT2 (T = O, F, OH) Monolayers as Potential Anode Materials for Lithium-Ion Batteries and Beyond, J. Phys. Chem. C, 2017, 121(24), 13025–13034.
49. G. Kresse and D. Joubert, Phys. Rev. B: Condens. Matter Mater. Phys., 1999, 59, 1758.

---

Footnote

† Present address: The Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, 2100 Copenhagen Ø, Denmark.

---