RESUMO
Current research has found the amorphous/crystal interface has some unexpected electrochemical behaviors. This work designed a surface modification strategy using NaBH4 to induce in situ conversion of the surface structure of Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) into TM-B-O amorphous interface layer. Oxidizing the surface from transition metals (TM) with high valence and reductive BH4- in a weak polar medium of ethanol results in an easy redox reacton. A TM-B-O amorphous structure is formed on NCM811 surface. The action of reactive wetting ensures a complete and uniform structure evolution of the surface crystals. The complete coverage protects the outer crystal and the heterogeneous interface impedance between the modified layer and bulk is reduced. More importantly, this amorphous interface layer through in situ conversion enhances the heterogeneous link at interface and its own structural stability. The modified NCM811 (TB2@NCM) treated with 1 wt % NaBH4 shows excellent electrochemical performance, especially cyclic stability. At a high cutoff voltage of 4.5 V, the capacity retention was 72.5% at 1 C after 500 cycles. The electrode achieves 173.7 mAh·g-1 at 10 C. This work creates a modifying strategy with potential application prospect due to simple technology with low-cost raw material under mild operating conditions.
RESUMO
The increasing demand for graphite and the higher lithium content than environment abundance make the recycling of anode in spent lithium-ion batteries (LIBs) also become an inevitable trend. This work proposes a simple pathway to convert the retired graphite to high-performance expanded graphite (EG) under mild conditions. After the oxidation and intercalation by FeCl3 for the retired graphite, H2O2 molecules are more likely to penetrate into the extended layers. And the gas phase diffusion caused by the produced O2 from the redox reaction between FeCl3 and H2O2 further promotes lattice expansion of interlayers (0.535 nm), which is beneficial to the stripping of graphene oxide (GO) with fewer layers. The EG exhibits excellent electrochemical performances in both LIBs and sodium-ion batteries (SIBs). It delivers 331.5 mAh g-1 at 3C (1C = 372 mA g-1) in LIBs, while it achieves 176.8 mAh g-1 at 3C (1C = 120 mA g-1) in SIBs. Then the capacity retains 753.6 (LIBs) and 201.6 (SIBs) mAh g-1 after a long-term cycling of 500 times at 1C, respectively. The full cells with the EG electrodes after prelithium/presodiation also show excellent cycle stability. Thus, this work offers another referable strategy for the recycling of waste graphite in spent LIBs.
