Fig. 4. Strategies to solve the issues in stage 2: Reliable cathodes.
(A) Schematic diagram of a positive electrode particle with a Ni-rich core surrounded by a concentration-gradient outer layer. Each particle has a Ni-rich central bulk Li(Ni0.8Co0.1Mn0.1)O2 and a Mn-rich outer layer [Li(Ni0.8Co0.1Mn0.1)O2] 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. The average composition is Li(Ni0.68Co0.18Mn0.18)O2. A scanning electron micrograph of a typical particle is also shown on the right. (B) Electron-probe x-ray microanalysis results of the final lithiated oxide Li(Ni0.64Co0.18Mn0.18)O2. The gradual concentration changes of Ni, Mn, and Co in the interlayer are evident. The Ni concentration decreases, and the Co and Mn concentrations increase toward the surface. (C) Differential scanning calorimetry (DSC) traces showing heat flow from the reaction of the electrolyte with concentration-gradient material Li(Ni0.64Co0.18Mn0.18)O2, the Ni-rich central material Li(Ni0.8Co0.1Mn0.1)O2, and the Mn-rich outer layer [Li(Ni0.46Co0.23Mn0.31)O2]. The materials were charged to 4.3 V. (A), (B), and (C) are reproduced with permission from Springer Nature. (D) Left: Transmission electron microscopy (TEM) bright-field image of the AlPO4 nanoparticle–coated LiCoO2; energy dispersive x-ray spectrometry confirms the Al and P components in the coating layer. Right: High-resolution TEM image showing the AlPO4 nanoparticles (~3 nm in diameter) in the nanoscale coating layer; the arrows indicate the interface between the AlPO4 layer and LiCoO2. (E) Left: A picture of a cell containing a bare LiCoO2 cathode after the 12-V overcharge test. The cell burned and exploded at that voltage. Right: A picture of a cell containing the AlPO4 nanoparticle–coated LiCoO2 after the 12-V overcharge test. (D) and (E) are reproduced with permission from John Wiley and Sons.