The interplay between stack pressure, mechanical expansion and degradation pathways in lithium-ion batteries

Researchers from the Universities of Cambridge, Oxford, Warwick and Sydney have discovered a simple way to double the lifetime of commercial lithium-ion batteries without changing their chemistry. Published in Nature Energy, the research shows that optimising the pressure applied inside battery cells can dramatically improve battery durability while reducing degradation.

Most research into improving lithium-ion batteries focuses on developing new materials or electrolytes. However, far less attention has been paid to the mechanical forces acting inside a battery as it repeatedly charges and discharges. As batteries cycle, their electrodes expand and contract, creating internal stresses that contribute to degradation. Until now, researchers have struggled to study these effects because conventional testing methods cannot maintain a constant pressure as the battery changes shape.

To overcome this challenge, Professor Michael De Volder and colleagues developed a high-precision stack-pressure control system using pneumatic bellows—small air-filled cushions that act as self-adjusting clamps. The device maintained a constant pressure on commercial pouch cells while sensors continuously measured the tiny changes in battery thickness during charging and discharging. This allowed the team to investigate, for the first time, how constant stack pressure influences battery ageing.

Laboratory testing showed that increasing stack pressure to around four times the typical initial value doubled the cycle life of commercial graphite/NMC811 pouch cells without changing the battery’s active materials or electrolyte. The study also revealed why pressure matters. Too little pressure accelerated cracking within the cathode material, while excessive pressure promoted lithium plating. The findings identify an optimum pressure window that minimises degradation and significantly improves cycling stability.

Rather than requiring entirely new battery chemistries, the research demonstrates that improving the mechanical design of batteries could deliver substantial performance gains using existing commercial technologies.

The research has also resulted in a patent application filed through Cambridge Enterprise, supporting future commercial development of the technology.