Magnetic, electronic, and electrochemical properties of high-voltage spinel cathodes for lithium-ion batteries



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Lithium-ion technology has revolutionized the electronics and electric vehicle industry in the past two decades. First commercialized by Sony in 1991, the lithium-ion battery is composed of three main components: (i) the cathode, (ii) the anode, and (iii) the electrolyte. Graphitic carbon remains the most widely used anode material due to its low voltage vs. the Li/Li+ redox couple and high specific capacity. However, there are several popular cathode materials, including layered oxides, spinel oxides, and polyanion materials.

In an effort to increase the energy density of lithium-ion batteries, much focus is given to improving the gravimetric charge capacity and the overall cell voltage. The latter must be accomplished by employing high-voltage cathodes, the most promising of which is the lithium manganese nickel oxide spinel with a specific capacity of 146 mAh/g and a redox voltage of 4.7 V vs. Li/Li+. However, there are still several problems with this material that must be understood and overcome in order to develop high-voltage spinel as a viable commercial cathode.

Physical property measurements can reveal the underlying electronic and atomic interactions in the solid in order to better understand high-voltage spinel and its odd behavior. Novel magnetic techniques have been developed, which reliably indicate the degree of Mn-Ni ordering and quantitative determination of the concentration of the Mn3+ ion. Measurements of several physical properties as a function of lithium content were also undertaken to determine the effects of Mn-Ni ordering on the electronic conductivity and the importance of electron-ion interactions.

In addition to understanding the physical properties of high voltage spinel, the understanding of the solid state chemistry and unique structure was utilized to realize a new full cell construction technique. The spinel structure offers a unique way to deal with first cycle irreversible capacity loss in full cells stemming from solid-electrolyte interphase (SEI) layer growth on the anode surface. To that end, a novel microwave-assisted chemical lithiation process was developed using non-toxic and air-stable chemicals. New composite anode chemistry was combined with a pre-lithiated spinel cathode to demonstrate the feasibility of this approach to realizing practical next-generation Li-ion cells.