  As global energy demands escalate, and the use of non-renewable resources
become untenable, renewable resources and electric vehicles require far better
batteries to stabilize the new energy landscape. To maximize battery
performance and lifetime, understanding and monitoring the fundamental
mechanisms that govern their operation throughout their life cycle is crucial.
Unfortunately, from the moment batteries are sealed until their end-of-life,
they remain a black box, and our current knowledge of a commercial battery s
health status is limited to current (I), voltage (V), temperature (T), and
impedance (R) measurements, at the cell or even module level during use.
Electrochemical models work best when the battery is new, and as state
reckoning drifts leading to an over-reliance on insufficient data to establish
conservative safety margins resulting in the systematic under-utilization of
cells and batteries. While the field of operando characterization is not new,
the emergence of techniques capable of tracking commercial battery properties
under realistic conditions has unlocked a trove of chemical, thermal, and
mechanical data that has the potential to revolutionize the development and
utilization strategies of both new and used lithium-ion devices. In this
review, we examine the latest advances in non-destructive operando
characterization techniques, including electrical sensors, optical fibers,
acoustic transducers, X-ray-based imaging and thermal imaging (IR camera or
calorimetry), and their potential to improve our comprehension of degradation
mechanisms, reduce time and cost, and enhance battery performance throughout
its life cycle.

Materials Science