Tanja Kallio1,Seyedabolfazl Mousavihashemi1,Katja Lahtinen1
Aalto University1
Tanja Kallio1,Seyedabolfazl Mousavihashemi1,Katja Lahtinen1
Aalto University1
Enhancing lithium batteries cycle life and efficiency are essential from both economic and sustainability perspective. On the other hand, battery energy and power densities have to be improved to meet increased energy storage capacity expectations for portable and mobile applications. Today LiNi<sub>0.6</sub>Co<sub>0.2</sub>Mn<sub>0.2</sub>O<sub>2</sub> is the most popular lithium battery positive electrode active material because of its relatively high energy density. However, it suffers from relative low conductivity limiting the achieved power density and efficiency at high power operation. Moreover, durability of nickel rich active material calls for enhancement. Preparing a 3D composite electrode form the active material and single-walled carbon nanotubes (SWNTs) is an attractive approach to solve these issues as SWNTs can offer the electrode such desired properties as high electrical conductivity and excellent mechanical and (electro)chemical durability.<br/><br/>In this study, we have investigated implications of incorporating SWNTs in a lithium battery positive electrode. The focused is on optimizing performance of LiNi<sub>0.6</sub>Co<sub>0.2</sub>Mn<sub>0.2</sub>O<sub>2</sub> based battery electrodes by adjusting the SWNT amount, but also SWNT surface treatment is considered. The relevance of adding SWNTs in the composite electrode structure is verified in various electrochemical half cell experiments. The origin of the favorable properties and effects brought by SWNTs have been investigated using various structural analysis methods and in-situ electrochemical characterizations.<br/><br/>By optimizing the composite electrode structed, a 3D SWNT network around the active battery material particles is shown to improve the wiring between the particles, and the particles to the current collector. This results in enhanced electron transfer leading to an increment in the positive electrode power density and energy efficiency. That is relflected as enhanced electrochemical lithium (de)insertion reactions, in particularly at high charge/discharge currents. The best performance is reached when the SWNTs are subjected to a mildly oxidizing pre-treatment to increase the electrode wetting tough this has an adverse effect on the electron transfer properties.<br/><br/>Our investigations reveal that another benefit brought by SWNTs for the 3D composite electrode is mitigation of mechanochemical aging. This results from hindering electrode volume changes during lithium (de)insertion in the active battery material as SWNTs entangled around the LiNi<sub>0.6</sub>Co<sub>0.2</sub>Mn<sub>0.2</sub>O<sub>2</sub> particles decreases irreversible height changes occurring during both the formation cycle and continuous cycling. Our results suggests that this is also reflected as suppression of harmful side reactions indicated by an increase in the coulombic efficiency.<br/>Summarizing, incorporating an optimized amount of modified SWNTs in a LiNi<sub>0.6</sub>Co<sub>0.2</sub>Mn<sub>0.2</sub>O<sub>2 </sub>based lithium battery positive electrode simultaneously enhances electrode power and energy density and cycling stability. Hence, all the above-mentioned important properties can be improved by incorporating highly conductive and durable carbon nanomaterials in a battery positive electrode structure.