Carbon-coated LiTi2(PO4)3 composites synthesized through tannic acid with high rate performance for aqueous lithium-ion batteries

Carbon-coated LiTi2(PO4)3 (LTP-1) was synthesized by sol-gel and in-situ coating method, with tannic acid as carbon source. To compare the electrochemical performance, LTP-2 and LTP-3 were synthesized by the same method with citric acid and lactic acid as carbon sources, respectively. After calcination, the amorphous carbon layers were coated on the surface of LiTi2(PO4)3 crystal. Carbon contents of all the samples were controlled around 9.0%. The primary particles of LTP-1 are 20–50 nm, which agglomerate into irregular micron-sized secondary particles. The primary particles of LTP-2 and LTP-3 are 60–100 nm. As anode in aqueous lithium-ion batteries (LIBs), LTP-1 presented high cyclic stability and rate performance. The initial discharge capacity of LTP-1 is 60.9 mAh·g−1 at rate of 10 C. After cycling for 1000 cycles, the capacity retention rate of LTP-1 is 72.8%. As for LTP-2 and LTP-3, the initial specific discharge capacity is 46.0 mAh·g−1 and 44.0 mAh·g−1, the corresponding capacity retention rates are 45.4% and 16.4%, respectively, with the same testing parameters.