Enhanced properties of olivine LiFePO4/graphene co-doped with Nb5 + and Ti4 + by a sol–gel method

• Nb and Ti co-doping LiFePO4/graphene is first synthesized successfully by sol–gel method.
• Among all samples, Li0.99Nb0.01Fe0.97Ti0.03PO4/G shows the best rate capability and cycling stability.
• Nb and Ti co-doping and graphene coating can enhance LiFePO4 properties greatly.

Nanostructured LiFePO4 powder with a narrow size distribution (~ 100 nm) has been obtained using a sol–gel method with graphene as coating, and applied in high efficiency lithium-ion battery cathode. During preparation of LiFePO4 precursor, Nb5 + and Ti4 + were added to get a sufficient and homogenous doping. Through X-ray diffraction (XRD), scanning electron microscope (SEM), charge/discharge tests, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) characterization, the influence of supervalent metal doping and graphene coating on the structure and performance of LiFePO4 was studied. Li0.99Nb0.01Fe0.97Ti0.03PO4/graphene cathode delivers a discharge capacity (163 mAh g− 1 at 0.1 C) close to the theoretical value with excellent capacity retention (99.1% after 30 cycles) and rate capability (140 mAh g− 1 after discharged at 0.1 C, 2 C, 5 C stepwise). The results indicate that both ion-doping and graphene-coating are effective to improve the electrochemical performance of lithium ion battery.