Fatigue Process in Li-Ion Cells: An In Situ Combined Neutron Diffraction and Electrochemical Study

Abstract

In-situ and operando neutron powder diffraction is well established method for studying structural changes in Li-ion electrode materials in real time during battery operation. Quality of diffraction data obtained in operando experiments depends on characteristics of diffractometer (brightness, space resolution) and design and assembly of electrochemical cell. Operando neutron diffraction experiments can be successfully performed with real batteries; however using special designed electrochemical cell allows us to exclude some undesirable reflexes of battery components from diffraction pattern, use Li-metal as counter electrode, decrease background from incoherent scattering elements, be almost independent from commercial machines for battery preparation and considerably reduce a mass of investigated materials. In this report we present special designed electrochemical cells developed for operando study of Li-ion electrode materials at time-of-flight neutron diffractometers at the IBR-2 neutron source (Dubna, Frank Laboratory of Neutron Physics). The cells are easily assembled in a glove box and demonstrate the excellent parameters of cyclabilities (with graphite electrodes, more than 700 cycles) and absence of leakage current. In dependence of scattering properties of studied materials the measured diffraction patterns can be analyzed by Rietveld method or Peak's profile data analysis. Several successful operando experiments on Li-ion electrode materials using these cells have been performed. In particular, investigation of LiNi0.8Co0.15Al0.05O2 (NCA) cathode material in the electrochemical cell allowed us to reveal the microstructural reasons of phase separation that occurs in cycled NCA during the first charge. The work is supported by Russian Science Foundation (project №14-12-00896). [1] A.

Low-temperature performance of Li-ion batteries: The behavior of lithiated graphite

“…It might be associated with a more rapid cell fatigue at low temperatures than cycling at ambient conditions, where a drop of 2.2% in capacity is observed after approx. 30e40 cycles of charge/discharge at 293 K [24]. Comparing this to only 7 discharge cycles at different temperatures performed in the current study, cell fatigue can be expected to be a factor of ca.…”

Fundamental degradation mechanisms of layered oxide Li-ion battery cathode materials: Methodology, insights and novel approaches

“…This allows for in operando studies on 18650-type cells, and fatigue can be studied under exactly the same conditions as in the established applications of Li-ion batteries [32]. Neutron diffraction has one more advantage against X-ray and even high-energy synchrotron radiation: The light elements, like H, Li, C, O and F, which are important components in battery materials, are well localized within structure models, because of the much stronger scattering power of these elements for neutrons than for photons.…”

“…In combination with flammable electrolytes an overheating at high charge levels results in this ongoing exothermal reaction, known as "thermal runaway". Li-occupation levels as low as 40% are observed in commercial LiCoO 2 -based fatigued batteries [32]. Advanced materials have been derived by replacing some of the Co by other transition metals or Al, like Li(Ni 1/3 Co 1/3 Mn 1/3 )O 2 (NCM) or Li(Ni 0.8 Co 0.15 Al 0.05 )O 2 (NCA).…”

In-Situ Neutron Studies of Electrodes for Li-Ion Batteries Using a Deuterated Electrolyte: LiCoO2as a Case Study

“…Rodriguez et al [53] determined the variations in the lattice parameters of a LiCoO2-type material as a function of charge state, also in a commercial Liion cell, whilst changes in both the lattice parameters and lithium occupancies with repeated cell cycling were shown to be correlated with the degradation of cell performance [54]. In the case of in-situ X-ray powder diffraction studies, Reimers et al [55] and Morcrette et al [56] showed that LixCoO2 undergoes multiple phase transitions on removal of Li  .…”