Effects of Doping on Lithium Rich NMC Cathode Prepared Via Spray Pyrolysis

Li_xMO₂(M= Mn, Ni, Co) materials with layered structures have received attention as high-capacity, low cost and safe cathode materials for lithium-ion batteries (1, 2). Various synthesis methods have been developed for the production of these materials, including co-precipitation, solid-state synthesis and ball milling. Recently a spray pyrolysis synthesis method has been developed by this group for producing cathode materials with porous morphologies and high tap density (3). Spray pyrolysis has certain advantages compared to other methods: the short residence time in the reactor allows large throughput; the process is scalable, no further post-synthesis purification steps are required and the product is inherently purified throughout the synthesis. Most importantly, each particle is synthesized with precise stoichiometry because each droplet behaves as a mini-reactor. This allows for accurate control of composition.  

The layered lithium-nickel-manganese-cobalt oxides, such as Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ or 0.5 NMC are known to demonstrate a voltage fade over cycling. This effect has been attributed to a layered-spinel transformation (4). This study will focus on doping Li_1.2Mn_0.54Ni_0.13Co_0.13O₂using trace level dopants and exploring their effects on voltage fade and cycling stability.

Figure 1 shows a typical SEM result of lithium rich material prepared via spray pyrolysis, demonstrating the uniform and spherical morphology. Figure 2 compares the effect of synthesis method for dopant free material synthesized via co-precipitation and spray pyrolysis, indicating distinct advantages both in terms of capacity and voltage fade for the material synthesized via spray pyrolysis, due to the superior uniformity of the synthesis method (5-7). Figure 3 shows the cycle test results for 0.5 NMC with Al doping. Al doping clearly improves the cycle stability of the sample.

Acknowledgements:

The authors are grateful to the NSF and X-tend Energy LLC for support. RLA and Washington University may receive income based on a license of related technology by the University to X-tend Energy LLC.

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