Higher power and charging rates are essential for large scale adoption of lithium-ion batteries in transportation applications. While lithium-ion batteries are ubiquitous in portable electronics, their performance and lifetime suffer during high rate charging and high power discharging. In such extreme electrochemical conditions, the mechanical response of electrode materials governs their degradation behavior. Here, we present a new technique to probe the electrochemically-induced mechanics of electrodes by calculating the electrochemical stiffness of electrodes via coordinated <i>in situ</i> stress and strain measurements.  Through electrochemical stiffness, we elucidate inherent and rate-dependent mechanical responses of graphitic battery electrodes. We find that stress and strain are asynchronous.  In particular, stress development is found to lead strain development as different graphite-lithium intercalation compounds are formed. Additionally, our analysis reveals inversely scaled rate-dependent behaviors for stress and strain responses. Stress scales as scan rate while strain scales with charge (or, equivalently, capacity).  These measurements provide a new paradigm for understanding mechanical effects in intercalation systems, such as batteries.  Stress arises as resistance to lithiation, while strain arises as a consequence of lithiation.  Electrochemical stiffness measurements provide new insights into the origin of the rate-dependent chemo-mechanical degradations, and provide a probe to evaluate advanced battery electrodes.  Application to both anode and cathode materials will be reported.<br/>

Electrochemical stiffness in lithium ion battery anodes and cathodes

251st National Meeting (2016)

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