Electrochemical and mechanical properties of LiMn2O4 according to particle morphology

Abstract

Lithium-ion battery (LIB) is currently used as a power source in mobile devices and electric vehicles. One of the requirements for those uses is high volumetric energy density and it can be realized by a step in electrode making process called pressing. Pressing can, however, damage active materials with the high pressure applied to them, and this particle breakage phenomenon can cause side effects in LIBs. In this work, the effect of pressing on particle breakage and LIB performance is studied. Active material used in this study is spinel structured LiMn2O4. Using LiMn2O4 it was confirmed from FE-SEM image, high temperature cycle and storage performance that pressing can induce particle breakage and it can degrade cell performance. To alleviate this problem, the relation between particle morphology and breaking property was studied. First the effect of morphology was checked in the level of particle by micro compression test. A criterion established from hard carbon system was used to interpret the results of micro compression test. As a result, spherical LiMn2O4 showed more resistance to breakage based on the criterion. Next, the experiment was performed for electrodes. Electrodes whose active materials are either spherical or non-spherical LiMn2O4s were compared based on FE-SEM images and high temperature storage test. The result agreed with that of micro compression test, showing that spherical LiMn2O4s are more resistant to breakage during pressing and preferable also in respect of electrode performance. This study has found that particle breakage during pressing should be considered an important factor in LIB using LiMn2O4 as active material and morphology control can handle this problem. Micro compression test was suggested as a tool for studying mechanical properties of LIB active materials with proper criteria. It is expected that the results and methodologies used in the study can also be used for various active materials other than spinel LiMn2O4.