Improving electrochemical performance of lithium ion batteries using a binder-free carbon fiber-based LiNi_0.5(1-x)Mn_1.5(1-x/3)Cr_xO₄ cathode with a conventional electrolyte

A binder-free LiNi_0.5(1-x)Mn_1.5(1-x/3)Cr_xO₄ (Cr-doped LNMO)/carbon fiber (CF) cathode with carbon paper as the current collector is developed via a process that involves electrochemical deposition, hydrothermal reaction, and vacuum filtration. The composite material properties are thoroughly characterized using scanning electron microscopy/transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The Cr-doped LNMO active materials are composed of submicron particles with polyhedral and spinel crystal structures with good crystallinity. The LiNi_0.5(1-x)Mn_1.5(1-x/3)Cr_xO₄ (x = 0.2) configuration is found to have a higher Mn⁴⁺/Mn³⁺ ratio and is capable of delivering a reversible capacity of ~137 mAh g⁻¹ at 0.2 C, due to the active Ni²⁺/Ni³⁺/Ni⁴⁺ and Cr³⁺/Cr⁴⁺ redox reactions. Furthermore, it exhibits an enhanced rate capability with 118 mAh g⁻¹ at 5 C. This is evidenced by a reduction in charge transfer resistance at the solid/electrolyte interface, and accelerated ion diffusion in the host material corresponding to a high degree of cation disordering in Cr-doped LNMO. Overall, the binder-free electrode, which integrates Cr-doped LNMO and a 3D CF-based framework, facilitates the electrochemical activity of the active material. This leads to improved cycling stability with 99% capacity retention over 200 cycles against high voltage (4.9 V vs. Li/Li⁺).