Developing Lithium Ion Strategy

If we want to develop something, the basic concept that we should understand is the explorable part. In the lithium-ion battery, we have three improving aspects. The first one is increasing the Cell Voltage. The only way to increase the cell voltage is raising the operation voltage of the cathode as the present graphite anode. The three cathode structures (layered, spinel, and olivine) provide composition with operating voltage higher than the currently used voltages (~4.3 V). But, the cathode surface is not stable in contact with the organic solvents, like ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) used in the electrolyte. Fortunately, the development of new liquid or solid electrolytes with desired characteristics will enable the high-voltage utilization (> 4.3 V) that lead to better safety.

The second aspect is increasing the Charge-Storage Capacity. This related with conversion-reaction process. While the capacity of insertion-reaction electrodes is limited by the number of crsytallographic sites (available for reversible insertion/extraction of lithium), the conversion-reaction electrodes don't have a limitations. The example of conversion-reaction anodes are Si, Sn, Sb, Ge, P that offering higher capacities and operating voltages than graphite. And the examples of conversion-reaction cathodes are sulfur and oxygen that offer much higher capacities (figure 1).

Figure 1. Capacity and voltage ranges of anode and cathode materials for lithium-based batteries (Manthiram, 2017).

The last method is focusing on high-nickel layered oxides. As we know that the high-nickel cathodes are emerging as a trend for future technology. The characteristics of Ni are between Co and Mn in almost all the necessary aspects (chemical and structural stability, conductivity, toxicity, and cost). The driving force to successively increase the Ni content is the ability to increase the capacity and volumetric energy density; with Ni contents of ∼0.9, practical capacities as high as ~230 Ah/kg could be realized.

Date : 11 May 2021
Written by : NBRI
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