LiNi_0.5Mn_1.5O₄ (LNMO) with a spinel crystal structure presents a compelling avenue towards the development of economic cobalt-free and high voltage (~ 5 V) lithium-ion batteries. Nevertheless, the elevated operational voltage of LNMO gives rise to pronounced interfacial interactions between the distorted surface lattices characterized by Jahn–Teller (J–T) distortions and the electrolyte constituents. Herein, a localized crystallized coherent LaNiO₃ and surface passivated Li₃PO₄ layer is deposited on LNMO via a one-step calcination process. As evidenced by transmission electron microscopy (TEM), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and density functional theory (DFT) calculation, the epitaxial growth of LaNiO₃ along the LNMO lattice can effectively stabilize the structure and inhibit irreversible phase transitions, and the Li₃PO₄ surface coating can prevent the chemical reaction between HF and transition metals without sacrificing the electrochemical activity. In addition, the ionic conductive Li₃PO₄ and atomic wetting inter-layer enables fast charge transfer transport property. Consequently, the LNMO material enabled by the lattice bonding and surface passivating features, demonstrates high performance at high current densities and good capacity retention during long-term test. The rational design of interface coherent engineering and surface coating layers of the LNMO cathode material offers a new perspective for the practical application of high-voltage lithium-ion batteries.

Solid-state batteries (SSBs) will potentially offer increased energy density and, more importantly, improved safety for next generation lithium-ion (Li-ion) batteries. One enabling technology is solid-state composite cathodes with high operating voltage and area capacity. Current composite cathode manufacturing technologies, however, suffer from large interfacial resistance and low active mass loading that with excessive amounts of polymer electrolytes and conductive additives. Here, we report a liquid-phase sintering technology that offers mixed ionic-electronic interphases and free-standing electrode architecture design, which eventually contribute to high area capacity. A small amount (~ 4 wt.%) of lithium hydroxide (LiOH) and boric acid (H₃BO₃) with low melting point are utilized as sintering additives that infiltrate into single-crystal Ni-rich LiNi_0.8Mn_0.1Co_0.1 (NMC811) particles at a moderately elevated temperature (~ 350 °C) in a liquid state, which not only enable intimate physical contact but also promote the densification process. In addition, the liquid-phase additives react and transform to ionic-conductive lithium boron oxide, together with the indium tin oxide (ITO) nanoparticle coating, mixed ionic-electronic interphases of composite cathode are successfully fabricated. Furthermore, the liquid-phase sintering performed at high-temperature (~ 800 °C) also enables the fabrication of highly dense and thick composite cathodes with a novel free-standing architecture. The promising performance characteristics of such composite cathodes, for example, delivering an area capacity above 8 mAh·cm⁻² within a wide voltage window up to 4.4 V, open new opportunities for SSBs with a high energy density of 500 Wh·kg⁻¹ for safer portable electronic and electrical transport.