Electrode Materials for Lithium-Ion Batteries with Surface Modification by Advanced Hybrid Polymers

The main challenges in the development of lithium-ion batteries for automotive applications are the improvement of energy density and cycling stability. For this purpose the electrodes have to be protected from irreversible reactions with the electrolyte which occur especially at high operating voltages. 

A very promising approach to prevent this degradation process is the surface coating of electrode materials with protective layers. To achieve these protective layers a new nanosized multifunctional coating was designed. The coating (shown in Fig. 1) consists of an inorganic-organic hybrid polymer, named ORMOCER^® (trademark of Fraunhofer ISC). Due to its specific design of inorganic and organic networks on the molecular level, several remarkable material properties could be generated. These properties include an electrochemical stability up to at least 5.0 V. This enables the stabilization of high-voltage materials like LiMn_1.6Ni_0.4O₄. The hybrid polymer also displays a high elasticity, which provides a long-term mechanical stability of the coating during cycling. Moreover, the coating material has a good ionic conductivity of 10^‑4 S/cm to facilitate the ion transport into the electrode material.

Based on these properties, the new core-shell nanocomposite approach can be applied to various electrode materials to improve their cycling performance, especially on materials with high operating voltages to achieve a high energy density of the batteries. Fig. 2 shows such an improvement, expressed in a significantly reduced capacity fade of coated LiMn_1.6Ni_0.4O₄ electrodes during cycling.

This work was supported by the Bavarian State Ministry of Economics, Infrastructure, Traffic and Technology.