The Influence of Solvents and Salts on the Properties of High-Voltage Cathode Materials at High Loads and High Temperatures

Lithium - ion batteries play an increasingly important role in the battery industry and they have become the dominant source of energy in the recnt years, especially for portable electronic devices due to their high gravimetric energy density. The new generations of lithium – ion battery cells are based on high-voltage cathode materials. These materials are characterized by a voltage near 5 V and higher energy density than the one currently used in lithium -ion cells. This advantage could help to increase battery expansion especially in transport. Representatives of this type of cathode materials are for example LiNi_0,5Mn_1,5O₄, LiCoPO₄ and Li₂CoPO₄F. The advantage of these materials is also their disadvantage - high working voltage means a big ballast for the electrolytes leading to deterioration of their stability. The stability of conventional carbonate electrolytes is strongly related to the stability and properties of cathode materials in the de-lithiated state. This article examines the influence of mixtures of solvents with different combinations of lithium salts on the stability of two types of high-voltage cathode materials: LiNi_0,5Mn_1,5O₄ and LiCr_0,1Ni_0,5Mn_1,5O₄ produced by a solid phase reaction. These materials were combined with several different electrolytes, cycled at various loads and elevated temperature. For these measurements various combinations of solvents ethylene carbonate (EC), dimethyl carbonate (DMC) and sulfolane were used. Salts LiPF₆ , LiNO₃ and LiTFSI were used.

Authors gratefully acknowledge financial support from the Centre for Research and Utilization of Renewable Energy under project No. CZ.1.05/2.1.00/01.0014, FEKT-S-11-7 and Company FEI.