<p>The degradation of lithium-ion batteries has become a concerning issue. One problem is metal ion dissolution from the cathode material, such as Mn²⁺ dissolution from spinel-type LiMn₂O₄ (LMO). However, direct observation of the dissolution process has yet to be reported. Here, we establish in-situ ¹H nuclear magnetic resonance imaging (MRI) measurement as an efficient technique to observe Mn²⁺ dissolution from a model lithium battery with LMO as the cathode. We observe an increase in the MRI signal intensity near the cathode, confirming the dissolution of Mn²⁺ from the cathode to the electrolyte. Moreover, we show that Mn²⁺ dissolution from LMO can be suppressed using an appropriate choice of electrolytes. We believe the method developed here can answer the long-time unanswered question of when, where, and how the metal ion dissolution occurs in the lithium-ion battery electrode and can be extended to other electrochemical systems.</p><p></p>