New Insights into the All-Dry Synthesis of NMC622 Cathodes Using a Single-Phase Rock Salt Oxide Precursor

Abstract

In this study, new insights into the all-dry synthesis of the LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) cathode using a singlephase rock-salt (RS) oxide precursor are provided. It was found that use of a larger amount of excess Li content not only can enhance the electrochemical performance of NMC made from the RS-precursor but also increase the degree of homogeneity of the NMC cathode material. In situ XRD analysis showed that lithiation of the RS-precursor (i.e., formation of the O3-phase) starts at a higher synthesis temperature (∼450 °C) than that is required when using a hydroxide precursor (HP) and lithium carbonate (∼350 °C). Consequently, Li 2 CO 3 was consumed by the reaction with the HP at low temperatures before the temperature reached the Li 2 CO 3 melting point. In contrast, the reduced lithiation kinetics of the RS-precursor results in the presence of liquid Li 2 CO 3 during the synthesis, which rapidly increases the rates of precursor lithiation and increases the NMC primary particle size.

All-Dry Solid-Phase Synthesis of Single-Crystalline Ni-Rich Co-Poor Ternary Cathodes for Li-Ion Batteries

“…Single-crystalline Ni-rich Co-poor ternary cathode materials can achieve high energy density, long cycle life, and low-cost properties; thus, it is regarded as a prospective cathode material for lithium-ion batteries (LIBs). − At present, a majority of commercially produced single-crystalline Ni-rich Co-poor ternary materials are manufactured by presynthesis of hydroxide precursors through coprecipitation followed by high-temperature calcination. − However, the process of synthesizing hydroxide precursors by coprecipitation is complex and generates wastewater contaminated with heavy metals, which is not suitable for green and sustainable development. − Recently, all-dry solid-phase synthesis (ADSPS) has emerged as an attractive strategy to fabricate single-crystalline-layered materials. − The ADSPS eliminates the synthesis step of the hydroxide precursor and directly calcines Ni, Co, and Mn raw materials with lithium salts to obtain single-crystalline materials. , Therefore, it is deemed to be an eco-friendly and cost-effective route for the synthesis of single-crystalline ternary cathode materials.…”

All-Dry Synthesis of NMC from [Ni,Mn,Co]3O4 Spinel Precursors

“…5,9 Analysis shows that this lithiation process proceeds via direct conversion of the RS structure into the O3 layered oxide, but that this process is hindered by slow kinetics. 11 Increased lithiation kinetics and an improved NMC results if the RS precursor is oxidized, resulting in the formation of a spinel phase (containing most of the Mn and Co from the original RS, and some but not most of the Ni), mixed with a RS NiO phase that contains the excess Ni not transferred into the spinel. 12 This reduces the amount of energy consumed in the synthesis process, and partially alleviates a known issue of Li 2 O 2 evaporation during the heating process.…”

“…All-dry synthesis of NMC may result in lower transition metal homogeneity compared to NMC synthesized from hydroxide precursors. 5,9,11,16 Homogeneity may be improved if intense milling methods are used or if small particle feedstock particles are employed. However, such processing steps can introduce impurities and can increase costs when used on a large scale.…”