Design criteria for electrochemical shock resistant battery electrodes

Abstract

Mechanical degradation of electrode active materials (''electrochemical shock'') contributes to impedance growth of battery electrodes, but relatively few design criteria have been developed to mitigate fracture. Using micromechanical models and in situ acoustic emission experiments, we demonstrate and explain C-rate independent electrochemical shock in polycrystalline electrode materials with anisotropic Vegard coefficients. We conclude that minimizing the principal shear strain, rather than minimizing net volume change as previously suggested, is an important new design criterion for crystal chemical engineering of electrode materials for mechanical reliability. Polycrystalline particles of anisotropic Li-storage materials should be synthesized with primary crystallite sizes smaller than a material-specific critical size to avoid fracture along grain boundaries. Finally, we revise the electrochemical shock map construction to incorporate the material-specific critical microstructure feature sizes for C-rate independent electrochemical shock mechanisms, providing a simple tool for designing long-lived battery electrodes.

High electrochemical performance of high-voltage LiNi0.5Mn1.5O4 by decoupling the Ni/Mn disordering from the presence of Mn3+ ions

“…Furthermore, in the bare sample, the LNMO, L 0.5 NMO and NMO phases coexisted at x~0. 25. The extended existence of the LNMO may cause the three phases to coexist, because that phase was observed up to x = 0.25.…”

“…Therefore, a large particle size makes phase-separation behaviors difficult and thereby leads to poor electrochemical activity. Recently, Woodford et al 25 reported that the critical particle size for coherency stress for spinel phases such as LiMn 2 O 4 and LNMO is~1 μm. This indicates that a particle size 41 μm can cause incoherent interfaces between the two phases and the formation of cracks or dislocations High electrochemical performance of high-voltage LNMO J Lee et al that slow the phase transformation.…”

Chemomechanics of ionically conductive ceramics for electrical energy conversion and storage

“…In contrast to the advantageous effects of strain in SOFC cathodes, the electro-chemo-mechanical couplings in LIB cathodes are manifested primarily as large shape changes that induce severe and heterogeneous stress states, ultimately leading to fracture of active particles. As a result, the active particle microstructures must be chosen to minimize or avert particle fracture under specified duty cycles of the battery [13,14]. To consider and quantify this coupling in SOFCs and LIBs, we will next outline the experimental and computational methods that have been developed for both fundamental study and practical design of the ionically conductive compounds.…”

“…Finally, beyond direct observation of cracks in materials or devices, acoustic emission has emerged as a tool for non-destructive, in situ monitoring of particle-level fracture in battery materials. Acoustic emission has been used to study conversion-type materials [74], silicon anodes [75], electrolytic MnO 2 , [76][77][78], and LiCoO 2 [14]; similar measurements were also used to study fracture of metal-hydride battery electrodes [79].…”

“…While concentration-gradient stresses develop in proportion to the applied electrochemical cycling rate (C-ratedependent), coherency and compatibility stresses persist even to arbitrarily slow cycling rates and may be considered C-rate-independent. One way of summarizing these mechanisms and the microstructure design criteria resulting from them is with an electrochemical shock map [13,14], which graphically summarizes the microstructure and duty cycle combinations which avert electrochemical shock. Figure 8 shows these maps for the mechanisms discussed above.…”