Review—Materials Science Predictions of Thermal Runaway in Layered Metal-Oxide Cathodes: A Review of Thermodynamics

Abstract

Accurate models of thermal runaway in lithium-ion batteries require quantitative knowledge of heat release during thermochemical processes. A capability to predict at least some aspects of heat release for a wide variety of candidate materials a priori is desirable. This work establishes a framework for predicting staged heat release from basic thermodynamic properties for layered metal-oxide cathodes. Available enthalpies relevant to thermal decomposition of layered metal-oxide cathodes are reviewed and assembled in this work to predict potential heat release in the presence of alkyl-carbonate electrolytes with varying state of charge. Cathode delithiation leads to a less stable metal oxide subject to phase transformations including oxygen release when heated. We recommend reaction enthalpies and show the thermal consequences of metal-oxide phase changes and solvent oxidation within the battery are of comparable magnitudes. Heats of reaction are related in this work to typical observations reported in the literature for species characterization and calorimetry. The methods and assembled databases of formation and reaction enthalpies in this work lay groundwork a new generation of thermal runaway models based on fundamental material thermodynamics, capable of predicting accurate maximum cell temperatures and hence cascading cell-to-cell propagation rates.

From material properties to multiscale modeling to improve lithium-ion energy storage safety

“…As if the challenges associated with the reactivity of the lithium with electrolyte were not sufficient, the cathode can also transform exothermically and release oxygen that can react with the electrolyte. [21][22][23][24] The majority of cathodes are composed of layered transition-metal oxides of a form Li 1−x MO 2 where M is a transition metal; Ni, Co, Mn, and combinations of these are typical examples. When built in the discharged state, x = 0, but charging moves some Li to the anode, x > 0, giving the cathode a stronger oxidation potential.…”

“…The partially delithiated Li 1−x MO 2 might be thought of as a solution of the stable LiMO 2 and the less stable MO 2, with the latter having the potential to release O atoms. 21 Before proceeding further, we note another important class of cathode materials, olivines, with the general form Li x MPO 4 of which lithium iron phosphate (LFP) is the commercialized example. 23,24 Phosphate cathodes have oxygen bonded covalently in phosphate groups, and reaction with typical electrolytes is rare for LFP.…”

“…35 It is likely that the first exothermic cathode transformation observed is related to this formation of a lithium-containing spinel. 21,36,37 Subsequent heat release can occur with reactions between the electrolyte and oxygen atoms released from the cathode. This involves the conversion from MO 2 or LiM 2 O 4 to a spinel M 3 O 4 and/or a rock salt MO.…”

“…This involves the conversion from MO 2 or LiM 2 O 4 to a spinel M 3 O 4 and/or a rock salt MO. 21,[36][37][38][39] The oxygen release must occur at the surface and excess metal cations will need to move further into the bulk. 30 The exact limiting physics associated with this oxygen atom loss to react with the electrolyte is not well described at this point.…”

“…Thermodynamics indicates that the oxygen release itself is endothermic, but can be driven forward by the heat release and entropic gain associated with gas-phase products. 21,40 Figure 1b shows the global heat release (R1) as well as the heat release associated with the first spinel formation step (R4) and this second step (R6) where oxygen release combines with electrolyte oxidation for two typical cathode materials. Figure 1b values correspond to 50% delithiation (Li 0.5 MO 2 ), but greater heat release can occur at higher degrees of delithiation, as shown by the calorimetry measurements plotted on the left half of Figure 1c.…”