Available Technology

BSA 15-10: Hybrid Design for Improved Cathode Energy Density

In the past two decades, the chemistries of the lithium ion battery technologies have been intensely studied and the active material utilization is close to their theoretical limit. The graphite anode in conventional Li-ion batteries has already reached its theoretical capacity (372 mAh/g) with little room for improvement. The same limitation also applies to the layered transition metal oxides intercalation cathodes (~250-300 mAh/g). While much effort have been devoted to the discovery of the new high energy density materials in recent years, such as alloy type of anodes (e.g. Si or Sn) and Sulfur cathode, as well as multivalent conversion reaction cathodes, the cell systems utilizing these new materials do not perform satisfactorily, especially in terms of cycle life, long term stability and reliability. This invention is geared toward the reduction/elimination of non-active carbon additive by introducing the electronic conductive secondary cathode component in the hybrid composite cathode. The hybrid cathodes may enable versatile and tailor-made properties with electrochemical performances beyond those of the individual cathode.
Patent Abstract: 
The hybrid cathode design is aimed to replace the non-active carbon conductive additive with an electronic conductive and electrochemically active transition metal sulfide additive as a secondary cathode without changing the well behaved primary lithium ion intercalation cathodes, such as layered LiN1/3M1/3C1/3, spinel LiMn2O4 and olivine LiFePO4. By introducing transition metal sulfide cathode to replace carbon additive, this approach could retain the good safety and cycling behavior of the conventional cathode materials, and at the same time may boost the cathode theoretical energy density by up to 20% without sacrificing the power capability of the cathode. The electronic conductivities of LiCoO2, LiFePO4 and LiMn2O4 are several orders of magnitude lower than transition metal sulfides, therefore, the presence of transition metal sulfides as secondary cathode additive may enable the reduction or even elimination of the carbon additive within the cathode metrics. Furthermore, the selected transition metal sulfides/Li couples also have their theoretical energy densities (Wh/kg or Wh/L) comparable or higher than the traditional intercalation cathode/graphite (or Li metal) couple systems. Thus, without changing the % of 1st cathode in the composite, any carbon additive replacement by transition metal sulfide will represent a net gain of cell energy density.
The benefits of this technology include, i) minimization of conductive additives unnecessary in the battery cell manufacturing process and lends it to higher flexibility in the cathode composition. This flexibility might make it possible to balance the requirement for high energy loading per unit area and good mechanical property and high power responses. ii) With simple replacement of carbon by transition metal sulfide, the same existing equipment and electrode process conditions can be utilized without the need for new equipment or process investment.
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