Reactive surface area of the Li-x(Co1/3Ni1/3Mn1/3)O-2 electrode determined by mu+SR and electrochemical measurements

The self-diffusion coefficient of Li+ ions (D-Li) in the positive electrode material Li-x(Co1/3Ni1/3Mn1/3)O-2 has been estimated by muon-spin relaxation (mu+SR) using powder samples with x = 1-0.49, which were prepared by an electrochemical reaction in a Li-ion battery. Here, since the implanted muons sense a slight change in the internal magnetic field due to Li-diffusion, mu+SR provides an intrinsic D-Li through the temperature dependence of the nuclear field fluctuation rate (nu) [Sugiyama et al., Phys. Rev. Lett., 2009, 103, 147601]. Both D-Li at 300 K and activation energy (E-a) were estimated to be similar to 2.9 x 10(-12) cm(2) s(-1) and 0.074 eV for the x = 1 sample, similar to 11.0 x 10(-12) cm(2) s(-1) and 0.097 eV for x = 0.70, and similar to 8.9 x 10(-12) cm(2) s(-1) and 0.062 eV for x = 0.49, assuming that the diffusing Li+ ions mainly jump from a regular occupied site to a regular vacant site. The estimated D-Li was smaller by roughly one order of magnitude than those for LixCoO2 in the whole x range measured. Furthermore, by making comparison with D-Li obtained by electrochemical measurements, the reactive surface area of the Li-x(Co1/3Ni1/3Mn1/3)O-2 electrode in a liquid electrolyte was found to strongly depend on x particularly at x > 0.8.