Operando Measurement of Cathode in Lithium Batteries Using a Laboratory-type XRD Instrument

An electrochemical cell with a specifically designed X-ray window was fabricated in order to evaluate the structural evolution of the cathode material under the operating condition. It enabled us to obtain strong signals from a positive electrode material without a significant loss of the battery function. With use of this system, the structure evolution during the charge-discharge process of a layered cathode material Li[Ni1/3Co1/3Mn1/3]O-2 and a high voltage spinel cathode LiMn1.5Ni0.5O4 was studied. It was found from the experimental results that the Li [Ni1/3Co1/3Mn1/3]O-2 cathode exhibited a single-phase reaction, where the lattice parameters continuously changed. In the case of LiMn1.5Ni0.5O4 cathode, the charge-discharge reaction proceeded in two continuous two-phase reactions. Especially for the latter, the phase evolution was reversible in the low- current density reaction. On the other hand, in the high current density charge-discharge reaction, asymmetric behavior was observed. This means that the kinetic limitation of the battery reaction is observable even in this laboratory X-ray diffraction system.