Mechano-Electrochemical Interaction Gives Rise to Strain Relaxation in Sn Electrodes

Abstract

Tin (Sn) anode active particles were electrochemically lithiated during simultaneous imaging in a scanning electron microscope. Relationships among the reaction mechanism, active particle local strain rate, particle size, and microcrack formation are elucidated to demonstrate the importance of strain relaxation due to mechano-electrochemical interaction in Sn-based electrodes under electrochemical cycling. At low rates of operation, due to significant creep relaxation, large Sn active particles, of size 1 μm, exhibit no significant surface crack formation. Microcrack formation within Sn active particles occurs due to two different mechanisms: (i) large concentration gradient induced stress at the two-phase interface, and (ii) high volume expansion induced stress at the surface of the active particles. From the present study, it can be concluded that majority of the microcracks evolve at or near the particle surface due to high volume expansion induced tension. Concentration gradient induced damage prevails near the center of the active particle, though significantly smaller in magnitude. Comparison with experimental results indicates that at operating conditions of C/2, even 500 nm sized Sn active particles remain free from surface crack formation, which emphasizes the importance of creep relaxation. A phase map has been developed to demonstrate the preferred mechano-electrochemical window of operation of Sn-based electrodes. High energy-density lithium-ion batteries use intercalation of lithium into solid active particles as the primary mechanism of energy storage.1 Traditional electrochemical systems used to store energy through surface reactions, which was a major barrier against achieving high specific capacity.2 Insertion and extraction of the secondary species during charge and discharge must occur through minimal irreversible change in the structure of the solid electrode material. Mitigation of mechanisms responsible for degradation of storage capacity is necessary for long-term battery cycling with good capacity retention. 3Most of the commercially available lithium ion batteries use electrode active materials (graphite as anode and lithium-cobalt-oxide/lithiumnickel-manganese-cobalt-oxide/lithium-manganese-oxide as cathode) that store lithium ions through intercalation mechanism.4,5 During lithiation and delithiation processes, these active materials experience very small strain and associated structural change, which results in capacity retention over many cycles. 6,7 However, the specific capacity of the intercalation materials is limited due to the weight of the atomic framework. Alloying anodes have received significant attention, as high capacity alternatives to intercalation anodes, due to their relatively high specific capacity (e.g. 3579 mAh g −1 for Li in Si).3 To accommodate Li atoms, this material undergoes a large volume expansion that can lead to particle failure. 8,9 Even small volume expansion cathode materials (such as, LiCoO 2 and LiFePO 4 ) experiences mechanical failure due to anisot...

The effect of electrochemical cycling on the strength of LiCoO2

“…While the quantitative extent of the impact of particle fracture on cycle life in traditional composite electrodes remains unclear, growing interest in all solid‐state batteries requires that the mechanics of cathode particles be better understood . Fracture mechanics models have been developed to treat different lithiation problems such as stress and strain developed during single‐phase reactions, two‐phase reactions, and reactions in anisotropic polycrystals . However, the database of underlying materials properties as a function of Li composition and cycle number is limited …”

Mechanistic Analysis of Mechano-Electrochemical Interaction in Silicon Electrodes with Surface Film

“…Detailed illustration of the lattice spring methodology amalgamating large deformation has been provided in Barai et al 40,41 The salient features of this framework are summarized here along with the modifications required to incorporate surface film mechanics.…”

“…29,34 Lattice spring model based high volume expansion modeling has been shown to replicate the deformation of silicon and tin electrodes. 40,41 However, there are no detailed numerical analyses investigating the effect of the diffusion mechanism on fracture tendencies inside silicon particle with surface film mimicking solid electrolyte interphase or secondary phase layer.In this work, we have extended the computational methodology developed in our group 40,41 to analyze and contrast the effect of the diffusion mechanism on the fracture methodology inside silicon active material with a surface film. Lithiation of crystalline silicon via two-phase diffusion process has been reported to cause large strain inhomogeneity between lithium rich and lithium poor phase exacerbating fracture.…”

Nickel‐Based Transition Metal Nitride Electrocatalysts for the Oxygen Evolution Reaction

“…The oxygen evolution reaction (OER), given by 2H 2 O!4H + + O 2 + 4e À (E 0 = 1.23 Vv s. RHE), is ac rucial half reaction in overall water splitting (2 H 2 O!2H 2 + O 2 , DE = 01.23 V). [7] Metal-air batteries are promising, but their performance is drastically hindered by sluggish kineticsa nd large ORR/OER overpotentials through discharging and recharging at the air-cathode interface. H 2 ; E 0 = 0.00 Vv s. RHE).…”

“…For instance, the same electrode material with different facets can exhibit rather different reaction pathways andr esult in distinctly differentm echanisms. [7] Metal-air batteries are promising, but their performance is drastically hindered by sluggish kineticsa nd large ORR/OER overpotentials through discharging and recharging at the air-cathode interface. This resultsi nl ow effectiveness and short cyclability.…”