A monitoring assembly for an electrochemical cell of a secondary lithium battery includes a porous sensory structure and a transducer. The porous sensory structure includes a sensory layer disposed on a major surface of a porous separator and a buffer layer disposed between the sensory layer and a facing surface of a negative electrode layer. The buffer layer electrically isolates the sensory layer from the facing surface of the negative electrode layer. The sensory layer includes an electrically conductive material and is configured to produce a response to an input signal or to a physical stimulus received within the electrochemical cell. The transducer is configured to process the response produced by the sensory layer to generate an output signal indicative of a diagnostic condition within the electrochemical cell.