An insight into the electro-chemical properties of halogen (F, Cl and Br) doped BP and BN nanocages as anodes in metal-ion batteries

Here, electro-chemical properties of BN and BP nanocages as anodes in metal-ion batteries are examined. The effect of halogens adoption of BN and BP-NCs on electro-chemical properties of M-IBs are investigated. Results showed that the BP nanocages as anode electrode in M-IBs has higher efficiency than BN nanocages and the K-IB has higher cell voltage than N-IBs. Results indicated that the halogens adoption of BN and BP-NCs are improved the cell voltage of M-IBs. Results proved that the F-doped M-IBs have higher cell voltage than M-IBs. Finally, F-B17P18 as anodes in K-IB is proposed as suitable electrodes.

In previous studies, the chemical and physical properties of boron nitride nanocages (BN-NC) and boron phosphide nanocages (BP-NC) have been investigated [1][2][3] . The results of previous studies confirmed that nanocages have acceptable properties as anodes and cathode materials in batteries due to low band gap energies and high potential to transfer the electrons and ions [4][5][6][7] .
Results of previous studies indicated that the formation heat and formation heat of per atom of B 18 N 18 , B 24 N 24 and B 36 N 36 are decreased when the number of atoms are increased. Results of previous studies confirmed that the formation heat and formation heat of per atom of B 18 P 18 is higher than those of B 24 P 24 and B 36 P 36 , significantly [8][9][10][11] . Results of previous studies showed that the formation heat of B 18 [8][9][10][11] .
Results of previous studies indicated that the halogen (F, Cl and Br) adoption of nanocages are decreased the band gap energies of nanocages and halogen (F, Cl and Br) adoption are improved the electro-chemical properties (cell voltage) of nanocages as anodes and cathode materials in batteries [12][13][14][15] . The potential of graphite, nanotubes and nanocages as anodes of metal-ion batteries (M-IBs) have been studied and results showed that nanocages have higher potential rather graphite and nanotubes [16][17][18] .
In previous studies, the electro-chemical properties (cell voltage) of B 12 N 12 as anodes in L-IBs and Na-IBs are examined and results confirmed that the F and Br are improved the properties of L-IBs and Na-IBs [19][20][21] . In previous studies, the metal adsorption on BN-NCs are investigated and results indicated that the lithium and potassium atoms are increased the properties of NC in M-IBs. The electronic properties of B 16  www.nature.com/scientificreports/ In this study, electro-chemical properties of BN and BP-NCs as anodes in L-IBs, N-IBs and K-IBs are examined. The effects of F, Cl and Br doping of BN and BP-NCs on their electro-chemical properties (cell voltage) as anode electrodes in M-IBs are examined. The main goals of this study are to (1) find the cell voltages of LIBs made of BP and BN nanocages as anodes; (2) compare the cell voltages of LIBs and NIBs made of BP and BN nanocages as anodes; (3) find the effects of halogen adoption on cell voltages of LIBs made of BP and BN nanocages as anodes; (4) propose the metal-ion batteries with high cell voltage values.
The Gibbs free energy of structures are calculated as follow: G = E 0 + ZPE + ∆H trans + ∆H rot + ∆H vib + RT-TS. The Gibbs free energy of adsorption of halogens on nanocages are calculated as follow: . The Gibbs free energy of adsorption of M and M + on nanocages are calculated as follow: [44][45][46][47] .
The  Table 1.
The V cell of K-B 18 N 18 is higher than Li-B 18 N 18 and Na-B 18 N 18 and V cell of K-B 18 P 18 is higher than Li-B 18 P 18 and Na-B 18 P 18 . The V cell of Li, Na and K on B 18 P 18 are higher than B 18 N 18 . Here, interactions of atoms on B atom in BN and BP-NCs are examined. The structures of M atoms with BN and BP-NCs via N and P sites are showed in Fig. 1. Calculated V cell of BN and BP-NCs with M atoms via N and P sites by M06-2X and HSE06 functional are reported in Table 1.
The |G ad | of M atoms with BN and BP-NCs via N and P sites are higher than |G ad | of B site ca 0.13 kcal/mol. The |G ad | of M + with BN and BP-NCs via N and P sites are higher than |G ad | of B site ca 0.75 kcal/mol.
The |G ad | of M atoms on BN and BP-NCs via N and P sites are higher than |G ad | of bridge B-N and B-P ca 0.28 kcal/mol. The |G ad | of M + with BN and BP-NCs via N and P sites are higher than |G ad | of bridge B-N and B-P site ca 1.45 kcal/mol. Results showed that the trends of calculated G ad by M06-2X and HSE06 functional are same for studied nanocages.
The V cell of M atoms with BN and BP-NCs via N and P sites are higher than V cell of B site and bridge site ca 0.03 and 0.05 V. Finally, M atoms on BN and BP-NCs via N and P sites are more stable than B site and bridge site.
The calculated orbital energies of metal with BN and BP-NCs by M06-2X and HSE06 functional are described in Supplementary Table 2S

Data availability
The calculated G ad of nano-structures by M06-2X and HSE06 functional are presented in Table 1S and calculated energies of orbitals and q of nano-structures by M06-2X and HSE06 functional are presented in Table 2S.