Electrochemical and structural studies of the carbon-coated Li[CrxLi(1/3−x/3)Ti(2/3−2x/3)]O2 (x = 0.3, 0.35, 0.4, 0.45)

A series of carbon-coated layered structured LiCr_xLi_(1/3−x/3)Ti_(2/3−2x/3)]O₂ samples (0.3 ≤ x ≤ 0.45) were prepared. Among them, the sample of x = 0.4 shows the highest initial reversible capacity of 207 mAh g⁻¹ at 30 mA g⁻¹ in 2.5–4.4 V. The reversible Li-storage capacities for the samples with high x values (x = 0.4, 0.45) faded slightly while the samples with low Cr content (x = 0.3 and 0.35) showed a capacity increase upon cycling. It was found that the relative intensity ratio of (0 0 3) peak to (1 0 4) peak (R_(0 0 3) = I_(0 0 3)/I_(1 0 4)) is influenced strongly by x value in as-prepared samples. The samples of x = 0.35 and 0.4 turn to a similar structure with low R_(0 0 3) value during cycling. These phenomena indicate that the cation mixing of Cr³⁺ in the lithium layer occurs in as-prepared samples and became more significant upon delithiation and lithiation. This is supposed being a necessary process for Cr-based layered structure materials possessing electrochemical reactivates. The occurrence of the cation mixing is beneficial from the local lattice distortion caused by the short-range ordering between Ti and Li. This is supposed to be helpful for the migration of Cr⁶⁺ and Cr³⁺ at tetrahedral and octahedral sites. Different from the case of LiNiO₂, the cation mixing is essential for the transport and storage of lithium in the carbon-coated Li–Cr–Ti–O layered compounds.