Threefold Increase in the Young’s Modulus of Graphite Negative Electrode during Lithium Intercalation

Abstract

Density functional theory (DFT) is used to reveal that the polycrystalline Young’s modulus (E) of graphite triples as it is lithiated to LiC6 . This behavior is captured in a linear relationship between E and lithium concentration suitable for continuum-scale models aimed at predicting diffusion-induced deformation in battery electrode materials. Alternatively, Poisson’s ratio is concentration-independent. Charge-transfer analyses suggest simultaneous weakening of carbon–carbon bonds within graphite basal planes and strengthening of interlayer bonding during lithiation. The variation in bond strength is shown to be responsible for the differences between elasticity tensor components, Cij , of lithium–graphite intercalation (Li-GIC) phases. Strain accumulation during Li intercalation and deintercalation is examined with a core–shell model of a Li-GIC particle assuming two coexisting phases. The requisite force equilibrium uses different Young’s moduli computed with DFT. Lithium-poor phases develop tensile strains, whereas Li-rich phases develop compressive strains. Results from the core–shell model suggest that elastic strain should be defined relative to the newest phase that forms during lithiation of graphite, and Li concentration-dependent mechanical properties should be considered in continuum level models.

The effect of lithium-intercalation on the mechanical properties of carbon fibres

“…3 and 7, respectively. In the same time, increasing Li-concentration in graphite intercalation compounds was reported to significantly strengthen the interlayer bonding but slightly soften the intralayer bonding [24]. This improvement in the filament lateral cohesion at high capacities could explain a limited drop of strength and the higher total strain at failure than in virgin fibres shown in Fig.…”

Effect of Electrochemical Charging on Elastoplastic Properties and Fracture Toughness of LiXCoO2

“…19,[21][22][23][24][25][26][27] Mechanical property variations of this magnitude affect the stress distributions developed in electrochemically active materials. 29,33 Thus, the design and selection of mechanically robust battery electrode materials requires knowledge of how mechanical properties change during electrochemical cycling.Here, we investigate the mechanical properties of the model lithium intercalation compound, Li X CoO 2 (LCO), as a function of electrochemical delithiation. The coupling between material chemistry and mechanical behavior is referred to as chemomechanics; with the added dimension of electrochemical control of composition, we refer to this coupling as electro-chemo-mechanics.…”

Structural evolution of electrodes in the NCR and CGR cathode-containing commercial lithium-ion batteries cycled between 3.0 and 4.5 V: An operando neutron powder-diffraction study

“…During overcharge, the graphite negative electrode converts to single-phase LiC 6 , in contrast to conventional charge which results in the two-phase LiC 12 and LiC 6 composition 22,23 where the crystallographic structure of the LiC 12 and LiC 6 phases were determined using NPD. Another lithiated phase intermediate between the graphite and LiC 12 phase has been reported, and although this is thought to be of LiC 24 or LiC 18 composition, [22][23][24][25][26][27][28][29] the LiC x composition and structure has not been fully established. Neutron radiography was used to elucidate lithium distribution under overcharging conditions in a coin cell with a carbon anode, 30 showing that lithium deposition is more likely to occur at the anode.…”