All Dry in One Step (ADIOS to Water) Synthesis of W-Coated Li1+X(Ni0.7Mn0.3)1-XO2

Abstract

Cathode powders for lithium-ion batteries are typically made from hydroxide precursors with the intended transition metal composition and calcined with a lithium source at high temperatures to make LiMO2, where M = Ni, Mn, Co. However, large amounts of process water and salts like NaOH are used in the co-precipitation process employed to make these hydroxide precursors1. Purifying and drying the precursors after co-precipitation requires additional energy input and produces waste streams that are difficult to treat, as illustrated in Fig. 1a. In this work, we introduce a simple, solvent-free method to produce tungsten (W) coated Li1+x(Ni0.7Mn0.3)1-xO2 (NM73) materials from a mixture of Ni, MnO2, LiOH·H2O and W precursors. NM73 was chosen as the primary focus of investigation so that cobalt is avoided due to its scarcity and high cost.The starting reagents are dry mixed and calcined, followed by jet-milling. An extra reheating step after jet-milling is advantageous for minimizing cation disorder and lithium surface impurities. Pure phase, R -3m single crystal NM73 materials can be made with this method and Rietveld refinement analysis showed that low Ni/Li mixing was achieved. W is believed to remain at the surface, forming a separate LixWyOz phase2. The addition of W was found to reduce the mean particle size and improve both the initial discharge capacity and first cycle efficiency. Small amounts of W increase the initial discharge capacity up to 197 mAh/g. Full coin cells were made from both coated and uncoated materials. Their cycling performance is shown in Fig. 1b, revealing improved capacity retention as another improvement afforded by the W coating.The proposed method simplifies the current production process of LiMO2 by eliminating the need for hydroxide precursors entirely. Cobalt-free single crystal materials with excellent electrochemical performance can be made all-dry in one step, potentially reducing the cost of cathode materials significantly and eliminating waste streams.