Microwave Plasma Synthesis of Cathode Material for Lithium-Ion Batteries
Authors: DeWees Rachel , Noudari Abhinav , Thapa Arjun , Sunkara Mahendra 
Published: February 2024

Among LiB cathode materials, lithiated NMC (Li1Ni(1-x-y)MnxCoyO2) formulations with ≥90% nickel have the potential to increase the specific capacity of LiBs, which is the most direct route to increasing the energy density of the battery. Lithiated NMC (LiNixMnyCo (1-x-y)) has the α-NaFeO2-type crystal structure of LiCoO2, but is chemically more evolved; nickel and manganese are substituted for cobalt, decreasing toxicity and expense, and increasing specific capacity [1-3]. Pristine 90% Nickel-rich cathode material frequently performs with a baseline cycling stability of ~75% over 50 cycles, regardless of synthesis method [4, 5]. NMC morphology is described as having secondary particles made up of many smaller primary particles, which is advantageous to packing density when in application- the best performing materials report secondary particle size of up to 20 μm, with primary particle size of ≤ 1 μm [6].

Fig. 1. Particle morphology of secondary particles up to ~20μm made up of primary particles ≤1μm.

Microwave plasma at atmospheric pressure provides a facile method for cathode material fabrication. With a working gas of air, ionized gas catalyzed immediate reaction to form cathode precursors from metal salts. This commercializable synthesis method provides a solution to the excessive time and energy waste as well as the environmental and health hazards which are inherent in the coprecipitation manufacturing method that dominates the current NMC production market. In this work, high capacity NMC compositions are produced using the plasma fabrication method. Method produced desired “meat-ball” particle morphology of secondary particles up to ~20μm made up of primary particles ≤1μm.

Ni rich Ni-Mn-Co (NMC) cathode materials were characterized for their lithium-ion capacity. Specifically, pristine cathode material with 955 and 811 compositions were prepared and tested using coin cells. Li-NMC with 955 (90% Ni; 5% Mn; 5% Co) cycled with initial specific capacity of 215 mAhg-1, with coulombic efficiency 99% at 20 cycles. Similarly, Li-NMC with 811 composition (80% Ni, 10% Mn and 10% Co) exhibited 190 mAhg-1 capacity and coulombic efficiency >99% over 20 cycles. Cyclic voltammetry confirmed three expected phase changes upon lithiation and delithiation, with clear durability and reversibility after first cycle. Layered crystal structure is confirmed with highly desired particle morphology for best packing density. NMC particles as synthesized by the atmospheric plasma method exhibit baseline NMC performance characteristics.

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