LiFePO4is one of most promising cathode materials for lithium-ion batteries (LIB) due to its superior rate handling ability, reduced cost, low environmental hazards, and safe long-term cyclability. Application of electrochemical quartz crystal admittance (EQCA) method to LIB electrodes provides direct access to potential-driven shifts of frequency (∆fexp) and width (∆Γ) of the resonance peaks simultaneously with the charge due to Li-ions insertion/extraction. In addition to conventional monitoring of mass changes in the electrode coating, the parameters ∆fexpand ∆Γreflect via hydrodynamic solid-liquid interactions, in-situ mechano-structural changes in the composite electrodes occurring during the operation of a LIB. Applying the model that takes into account such interactions, potential-induced changes of the effective thickness and permeability of the composite electrode have been determined which are evident of non-uniform deformation of the electrode coating caused by ions insertion/extraction process. Using EQCA as a unique mechanical probe of the insertion-type electrodes, the dynamic effect of the local host environment on the foreign Na+-ions insertion/extraction has been studied in mixed solution of Li and Na salts. As a highly reliable and quantitative tool, EQCA methodology may provide surprisingly wide scope for further investigations resulting in a broader understanding of coupled electrochemical and mechanical events in LIB during their long-term operation. This includes information about the distortion/deformation of the electrode intercalation particles and the entire composite electrode under polarization, and is able to clarify the role of polymeric binder in the composite electrodes as the factor stabilizing long-term cyclability of Li-ions batteries.