Abstract:

5 Ⅴ-class LiNi_0.5Mn_1.5O₄ (LNMO) cathode material is emerging as a promising cobalt-free alternative to meet the growing demand for affordable, high-performance lithium-ion batteries (LIBs). However, LNMO faces significant electrochemical challenges, particularly interfacial instability with commercial electrolytes due to its high operating potentials. This instability leads to the dissolution of transition metals and consequently electrode crosstalk, which severely deteriorates electrochemical performance. Surface coating is extensively investigated to reduce interfacial side reactions for enhanced cycling stability. Traditional methods typically require multiple steps, including dispersion, mixing, drying, and calcination, which can be time-consuming and complex. Additionally, the resulting ceramic coatings are often rigid and unevenly distributed due to lattice mismatches, potentially leading to poor interfacial contact and increased resistance. In this study, tetraethyl orthosilicate (TEOS) is proposed as a streamlined slurry additive to in situ form an ethoxy-functional polysiloxane (EPS) film on the surface of LNMO particles during electrode preparation. Post-mortem X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma (ICP) analyses reveal the crucial role of the EPS film in addressing interfacial instability issues. First, the EPS film serves as an artificial cathode-electrolyte interface (CEI) with a robust Si―O―Si bonding network, which is less vulnerable under high potentials. Second, the remaining ethoxy-functional groups in EPS scavenge HF by forming stable Si―F bonds, thereby suppressing the detrimental transition metal dissolution and crosstalk. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) further confirm the stability of the EPS film and the enhanced structural stability of the modified LNMO. Galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) results demonstrate that EPS reduces the overall impedance and improves ion diffusion kinetics by forming stable electrode-electrolyte interfaces. As a result, compared to the baseline, the optimized LNMO cathode exhibits significantly improved cycling stability in both half cells (84.6% vs. 51.4% capacity retention after 1000 cycles) and full cells when paired with commercial graphite anodes (83.3% vs. 53.4% retention after 500 cycles). This strategy, further validated under elevated temperatures of 50 ℃ and in pouch-type cells, is expected to pave the way for the development of next-generation high-performance LIBs.

Key words: LiNi_0.5Mn_1.5O₄, High voltage, Cathode-electrolyte interface, Slurry additive, Transition metal dissolution, Lithium-ion battery