Reduction of Electronic Conductivity within Secondary Particles Revealing a Degradation Mechanism of Ni-Rich Cathode for Lithium Ion Batteries

Abstract

A locally reduction in electronic conductivity in the core region of secondary particles is proposed as a capacity-fading mechanism of a Ni-rich cathode. This is investigated by measuring the electronic conductivity of the secondary particles of Li[Ni0.98Co0.01Mn0.01]O2 using the scanning spreading resistance microscopy (SSRM) mode of atomic force microscopy. SSRM analysis reveals that a much thicker rocksalt phase, which is transformed from the original layered structure, on the surface of the primary particles in the core region electronically disconnects the primary particles from the neighboring particles. Intercalation and deintercalation of Li are hindered in the electronically insulated primary particles. Thus, detecting of the local electronic conductivity in the secondary particles confirms that the loss of electronic conductivity in the core region of the secondary particle is a important factor in the degradation mechanism of a Ni-rich cathode for lithium ion batteries.