Enhancing the performance of cylindrical Li-ion batteries via mechanical preload and optimization of impedance

Abstract

Pouch and prismatic battery cells are usually mechanically preloaded for their use in electric vehicles to improve the performance and service life of battery cells. Although these positive effects are well known and studied in literature, only these cell formats continue to be mechanically preloaded excluding cylindrical battery cells. In this study, the impact of mechanical preload in the range of 0 MPa to 18 MPa was applied to the mantle surface of cylindrical battery cells. Subsequently, the battery impedance and its persistent impact on cycling behavior upon the first cycle was investigated. Revealing that moderate pressure (≤ 9 MPa) reduced ohmic resistance up to −0.00884 mΩ (−0.34%), whereas pressures exceeding 9 MPa led to an increase up to 0.462 mΩ (5.58%). CT-scans illustrated that applying external pressure up to 18 MPa induced buckling of the battery cell can and the outer jelly roll layers but did not compromise functionality when cycled afterwards. This led to an average increase in discharge capacity of 0.88%. This preliminary findings demonstrated that applying mechanical preload to cylindrical battery cells similar to the approach commonly used for pouch and prismatic battery cells can yield beneficial effects for moderate pressures.