β-LiVP2O7 as a positive electrode material for Li-ion batteries

• Novel pyrophosphate-based electrode material for Li-ion batteries is presented. • β-LiVP 2 O 7 demonstrates ≈100 mAh g −1 at 4.0-4.2 V vs. Li/Li + . • Capacity of 93 mAh g −1 was gained at 10C discharge current density. • Overall capacity of β-LiVP 2 O 7 exceeds 200 mAh g −1 within 1.5-4.5 V vs. Li/Li + range. A novel polymorph of lithium vanadium pyrophosphate has been obtained using electrochemical Na + for Li + exchange in β-NaVP 2 O 7 . β-LiVP 2 O 7 has a triclinic KAlP 2 O 7 -type structure with large tunnels along the [100] direction and demonstrates electrochemical capacity of 100 mAh g −1 within a high-voltage region of 4.0-4.2 V vs. Li/Li + with excellent C-rate capability: increasing discharge current density from C/10 to 10C results in a capacity drop of only 7%. The (de)intercalation process is characterized by a solid solution-like behavior with the diffusion coefficient amounting to 10 −12 – 10 −11 cm 2 s −1 . A redox process at ~ 1.8 V vs. Li/Li + leads to 200 mAh g −1 of the overall intercalation capacity within the extended voltage range that corresponds to “β-VP 2 O 7 ↔ β-Li 2 VP 2 O 7 ” two-electron process.