Reactive surface area of the Lix(Co1/3Ni1/3Mn1/3)O2 electrode determined by μ+SR and electrochemical measurements

Abstract

The self-diffusion coefficient of Li(+) ions (D(Li)) in the positive electrode material Li(x)(Co(1/3)Ni(1/3)Mn(1/3))O2 has been estimated by muon-spin relaxation (μ(+)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, μ(+)SR provides an intrinsic D(Li) through the temperature dependence of the nuclear field fluctuation rate (ν) [Sugiyama et al., Phys. Rev. Lett., 2009, 103, 147601]. Both D(Li) at 300 K and activation energy (E(a)) were estimated to be ∼2.9 × 10(-12) cm(2) s(-1) and 0.074 eV for the x = 1 sample, ∼11.0 × 10(-12) cm(2) s(-1) and 0.097 eV for x = 0.70, and ∼8.9 × 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 Li(x)CoO2 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)(Co(1/3)Ni(1/3)Mn(1/3))O2 electrode in a liquid electrolyte was found to strongly depend on x particularly at x > 0.8.

Macroscopic Electrochemical Properties Clarified by Microscopic Measurements; Present and Future

“…This method gives a unique direct access to one of the most important material properties, namely the intrinsic Li-ion self-diffusion constant D Li . We have shown from our extensive measurements of Li-ion cathode materials [3][4][5][6][7][8]11] how the knowledge of such vital information will be crucial for the understanding of solid state ionics in these compounds. This is an important first step towards the materials development needed for future solid state batteries (SSB).…”

“…This is an important first step towards the materials development needed for future solid state batteries (SSB). Further, when the intrinsic D Li is clarified, we could also estimate density of mobile Li + [11] and reactive surface area of the electrode in a liquid electrolyte [8], which are also important parameters for increasing the performance of Li-ion batteries.…”

“…Furthermore, the QENS intensity is almost independent of x, being consistent with the µ + SR result. [8] re . Although almost all the electrochemical work have assumed that S m is independent of x, S m is highly likely to depend on x.…”

“…Recently, it was found that µ + SR detects a slight variation of an internal magnetic field (H int ) due to Li diffusion even for materials containing magnetic ions [3][4][5][6][7][8][9][10], since the implanted muons sense H int with a zero applied field (ZF) in contrast to Li-NMR. Furthermore, making comparison between µ + SR and neutron scattering for detecting D Li from a viewpoint of time window, µ + SR is a very good complementary technique to quasi-elastic neutron scattering (QENS) in the research of Li diffusion in solids (see Fig.…”

“…But at high temperatures, QENS provides direct information on the hopping distance of Li + . Particularly, when the intrinsic D Li is clarified, we could estimate carrier density [11] and reactive surface area of the electrode in a liquid electrolyte [8], which are also important parameter to prepare Li-ion batteries. When the ultra-slow muon microscope (USM) is available, we could further clarify the change in such parameters at a hidden interface between electrode and electrolyte.…”