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In this work, Ni2+ was doped into the crystal lattice of LiFePO4 to improve the electrochemical performance. Lengths of the Li–O bonds in LiFe0.98Ni0.02PO4/C (2% NiSO4-doped LiFePO4) is longer than that of the bare LiFePO4 sample, the micromorphology of LiFe0.98Ni0.02PO4/C sample becomes uniform, and the Ni2+ doped into LiFePO4 expands the crystal plane spacing, which is conducive to Li+ diffusion. Amongst all the doped samples, the Li+ diffusion coefffcient of LiFe0.98Ni0.02PO4/C is the largest, and the redox peak of LiFe0.98Ni0.02PO4/C is more symmetrical, sharper and narrower, indicating that the proper amount of Ni2+-modified LiFePO4 can improve the electrochemical performance. Specific discharge capacity at 1C is 152 mAh g−1 when the doping amount is 2%. Additionally, after 200 cycles at 2C, the discharge specific capacity can be attained at 140 mAh g−1 and capacity retention rate reached 98%. [ABSTRACT FROM AUTHOR]

Iron oxalate (FeC2O4) is a promising candidate as an anode material for lithium-ion batteries (LIBs) with its advantages of low cost and high capacity. However, its commercial application is limited by its poor electrical conductivity, which leads to slow chemical reaction kinetics. Herein, a novel FeC2O4-based composite (FeC2O4/Gs) with dual-level structured graphene sheets (Gs) was constructed via electrostatic adherence technology, which enhanced the combination form and composite effect for two discrepant materials. Based on the dual-level structured Gs in FeC2O4/Gs composites, micro-based Gs (∼5 μm) was dispersed between the FeC2O4 particles. Meanwhile, the nano-based (∼50 nm) Gs was coated and embedded on the surface of rod-like FeC2O4 particles. Because of the special structure of FeC2O4/Gs, it has a dual promotion of electron transport both within and on the surface of the FeC2O4 particles, favoring electrochemical activity and efficiently inducing the conversion reaction. Consequently, the FeC2O4/Gs composite achieved a high reversible capacity of 820 mA h g−1 and excellent cycling stability with a capacity retention of 41% after 200 cycles under 10C. This study provides a novel opportunity to design composites and electrodes with electronic conductivity, excellent electrochemical activity and ultrahigh cycling stability for lithium storage. [ABSTRACT FROM AUTHOR]