The thermodynamic origin of hysteresis in insertion batteries

Abstract

Lithium batteries are considered the key storage devices for most emerging green technologies such as wind and solar technologies or hybrid and plug-in electric vehicles. Despite the tremendous recent advances in battery research, surprisingly, several fundamental issues of increasing practical importance have not been adequately tackled. One such issue concerns the energy efficiency. Generally, charging of 10(10)-10(17) electrode particles constituting a modern battery electrode proceeds at (much) higher voltages than discharging. Most importantly, the hysteresis between the charge and discharge voltage seems not to disappear as the charging/discharging current vanishes. Herein we present, for the first time, a general explanation of the occurrence of inherent hysteretic behaviour in insertion storage systems containing multiple particles. In a broader sense, the model also predicts the existence of apparent equilibria in battery electrodes, the sequential particle-by-particle charging/discharging mechanism and the disappearance of two-phase behaviour at special experimental conditions.

Current-induced transition from particle-by-particle to concurrent intercalation in phase-separating battery electrodes

“…Our data suggest that the current homogeneity is not only dependent on the cycling rate but also on the direction (i.e., charge vs. discharge). By showing that the active population of an LFP electrode depends strongly on the cycling condition, our experiments reconcile the seemingly contradictory reports of particle-byparticle [13][14][15][16][17] and concurrent intercalation pathways 18,19 : the differing experimental observations result from different sample preparation routes. Fast, chemically delithiated particles, where the complete delithiation occurs within 2 minutes 38 , resulted in concurrent intercalation, while electrochemically-prepared samples at lower rates resulted in particle-by-particle intercalation.…”

“…A seemingly contradictory observation is the fraction of actively-intercalating particles, with reports ranging from around 0% (particle-by-particle) [13][14][15][16][17] to 100% (concurrent intercalation) 18,19 .…”

“…On the one hand, the so-called "mosaic" particle-byparticle intercalation mechanism has been reported in studies using X-ray diffraction 13 , electron microscopy 14,15 , and X-ray microscopy 16 . Dreyer et al proposed that the thermodynamic origin of this behaviour arises from the non-monotonic chemical potential of Li as a function of the particle's composition 17 . On the other hand, a concurrent intercalation pathway, whereby most particles intercalate at once, has also been observed in LFP 18,19 .…”

Design and use of multisine signals for Li-ion battery equivalent circuit modelling. Part 2: Model estimation

“…The difference between the charge and discharge OCV curve is the battery hysteresis voltage. While lithium iron phosphate cathode batteries are known to exhibit hysteresis ( [19,20]), the work in [18] experimentally demonstrated the presence of a non-negligible level of hysteresis in other Li-ion systems. For the 3.03Ah LiNiCoAlO 2 batteries tested a 10-20 mV magnitude of hysteresis voltage is measured over 5 % -95 % SoC.…”

In operando tracking phase transformation evolution of lithium iron phosphate with hard X-ray microscopy

“…As a result, the homogeneous and concurrent phase transformation on the multiple-particle scale has become increasingly inadequate. For example, based on theoretical calculation, a new multiple-particle delithiation mechanism was recently suggested where LiFePO 4 particles were delithiated sequentially, not concurrently 14 . In addition to the insufficient understanding of the multi-particle mechanism, more disputes focus on the single-particle delithiation model.…”