High-energy cathode material for long-life and safe lithium batteries

Layered lithium nickel-rich oxides, Li[Ni1-xMx]O-2 (M = metal), have attracted significant interest as the cathode material for rechargeable lithium batteries owing to their high capacity, excellent rate capability and low cost(1-7). However, their low thermal-abuse tolerance and poor cycle life, especially at elevated temperature, prohibit their use in practical batteries(4-6). Here, we report on a concentration-gradient cathode material for rechargeable lithium batteries based on a layered lithium nickel cobalt manganese oxide. In this material, each particle has a central bulk that is rich in Ni and a Mn-rich outer layer with decreasing Ni concentration and increasing Mn and Co concentrations as the surface is approached. The former provides high capacity, whereas the latter improves the thermal stability. A half cell using our concentration-gradient cathode material achieved a high capacity of 209m Ah g 1 and retained 96% of this capacity after 50 charge-discharge cycles under an aggressive test profile (55 degrees C between 3.0 and 4.4V). Our concentration-gradient material also showed superior performance in thermal-abuse tests compared with the bulk composition Li[Ni0.8Co0.1Mn0.1]O-2 used as reference. These results suggest that our cathode material could enable production of batteries that meet the demanding performance and safety requirements of plug-in hybrid electric vehicles.