This research hydrothermal process in autoclaves using Finite Element Analysis (FEA) to evaluate transient thermal behaviour and its effects on pressure and stress distribution. Simulations indicate that during the 600-s hydrothermal process using an oven, the surface temperature of the Teflon liner ranges from 185 °C to 218 °C with outward-inward heat transfer. The process reaches 200 °C within 200 seconds, rising to 400 °C, generating pressure variations between 1 and 5 MPa and resulting in a maximum stress of 100–200 MPa with deformation reaching 0.86 mm. Material characterisation reveals spherical LiNMC particles, while LiNMC-Nd particles exhibit porosity. X-ray diffraction (XRD) confirms the crystallite sizes of LiNMC-Nd in the 20–50 nm range, and Fourier transform infrared spectroscopy (FTIR) validates the formation of LiNMC-Nd bonds. In the symmetric configuration (LiNMC | KOH | LiNMC), a specific capacitance of 12.98 F·g−1 at 1 mA·cm−2 is achieved, with corresponding specific power and energy values of 65.33 W. g−1 and 1.96 Wh·kg−1, respectively. However, specific capacitance diminishes by 66,7% after 500 cycles, indicating a moderate level of cyclic stability. In the symmetric configuration (LiNMC-Nd | KOH | LiNMC-Nd), a specific capacitance of 164.83 F·g−1 at 1 mA·cm−2 is achieved, with corresponding specific power and energy values of 61.90 W·g−1 and 22.28 Wh·kg−1, respectively. © 2025 Informa UK Limited, trading as Taylor & Francis Group.