Zeolites as multifunctional additives stabilize high-voltage Li-batteries based on LiNi_0.5Mn_1.5O₄ cathodes, mechanistic studies

The work reported herein discusses the improved electrochemical and thermal behavior of LiNi_0.5Mn_1.5O₄ (LNMO) spinel cathodes via surface engineering using a series of zeolites. The limiting issues of these high voltage electrodes are phase transition during Li-ions intercalation/de-intercalation processes, weakening the active material's structure. Besides, it initiates harmful interfacial side reactions, including solution species oxidation and Ni & Mn dissolution, affecting their long-term cycling stability severely and detrimentally. Therefore, we propose a zeolite-based surface modification of LNMO involving a simple surface coating strategy that includes liquid-phase (ethanol) mixing followed by heat treatment at 200 °C under nitrogen gas flow. The cathodes comprising LNMO coated with 2 wt% zeolites exhibited significantly improved cycling stability than the reference cathodes with the uncoated material. Furthermore, we discovered that the zeolite species adsorbed to the LNMO surface act as buffer interphase that enhance the electrodes' redox kinetics, trapping dissolved-TMs ions and serving as local Li⁺-ions reservoirs. Pouch cells containing graphite anodes and zeolite-coated LNMO cathodes demonstrated impressively improved electrochemical behavior in capacity retention during prolonged cycling, enhanced rate capability, lower voltage hysteresis, and direct current internal resistance (DCIR) evolution. The zeolite-based surface coating participates in (i) lowering HF formation in battery solutions by absorbing trace water, (ii) HF scavenging, and (iii) lowering TMs cations dissolution. Furthermore, Si and Al constituents of the zeolites can deposit on Li-anodes and possibly increase their stability, later established by additional electrochemical studies of full-pouch cells comprising uncoated LNMO cathodes vs. zeolite-coated graphite anodes. Other pivotal findings of this work are the coherent structural, morphological, and thermal stabilization of zeolite-coated LNMO cathodes during prolonged cycling experiments.