A thermodynamic and crystal structure study of thermally aged lithium ion cells

Lithium ion batteries in the coin-cell form factor (2032) initially charged to 4.2 V at ambient temperature are stored at 60 °C and 70 °C for up to 8 weeks. The cells discharge capacity (Qd) and thermodynamic properties, including open-circuit potential (OCP), entropy (ΔS) and enthalpy (ΔH) are measured after each completed ageing week. Post-mortem analysis of aged anodes and cathodes is investigated by X-ray diffractometry (XRD) and Raman Scattering spectrometry (RS) in an attempt to correlate thermodynamic data to changes in the crystal structure characteristics. It is found that degradation of the electrode materials' crystal structure accounts for most of the observed changes in the cells' thermodynamics with well quantified and distinct contributions from anode and cathode.