Increasing Li-ion battery energy density by implementing high-voltage cathodes
Elise Ramleth Østli*, Nils Peter Wagner**, Ann Mari Svensson*, Fride Vullum-Bruer*
*Norwegian University of Science and Technology, Department of Materials Science and Engineering, 7491 Trondheim
**SINTEF Industry, 7491 Trondheim, Norway
Summary. High-voltage cathode materials, such as LiNi0.5Mn1.5O4, can increase the energy density of state of the art Li-ion batteries due to their high operating potential. But exactly how does a high operating potential lead to increased energy density? And what are the main challenges related to the use of these materials? By using LiNi0.5Mn1.5O4 as an example, the possibilities and limitations of high-voltage cathode materials will be discussed.
Abstract. In order to meet the energy demands of the future, particularly in the transportation sector, environmentally friendly batteries with high energy density must be developed. The energy density of a battery is determined by the voltage of the cell, e.g. the difference in operating potential between the two electrodes, and the capacity of the electrodes, e.g. how many lithium ions that can be stored in each electrode. The energy density of the Li-ion battery is mainly limited by the cathode. This is due to the fact that commercial cathode materials have much lower capacities than anode materials such as graphite. However, a high-voltage cathode material can compensate for the low capacity with its high operating potential, and in this way increase the energy density of state of the art Li-ion batteries1.
LiNi0.5Mn1.5O4 is an interesting high-voltage cathode material due to its high operating potential of 4.7 V vs Li/Li+, high safety, and economical and environmental advantages compared to other materials2. However, some challenges need to be solved before the material can be fully commercialized. The loss of Ni and Mn from the electrode during cycling due to a lack of a stable electrode/electrolyte interface is causing problems on the anode3, and the high operating voltage leads to decomposition of the electrolyte on the cathode surface. Both these effects reduce the lifetime and durability of the batteries. Therefore, efforts to stabilize the cathode/electrolyte interface are necessary. Strategies like protective surface coatings and alternative electrolytes with wider electrochemical stability windows will be used as examples of how we in the future can commercialize high-voltage cathode materials such as LiNi0.5Mn1.5O4.
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