Abstract
Rechargeable lithium-ion batteries require a vigorous improvement if we want to use them massively for high energy applications. Silicon and metal lithium anodes are excellent alternatives because of their large theoretical capacity when compared to graphite used in practically all rechargeable Li-ion batteries. However, several problems need to be addressed satisfactorily before a major fabrication effort can be launched; for instance, the growth of lithium dendrites is one of the most important to take care due to safety issues. In this work we attempt to predict the mechanism of dendrite growth by simulating possible behaviors of charge distributions in the anode of an already cracked solid electrolyte interphase of a nanobattery, which is under the application of an external field representing the charging of the battery; thus, elucidating the conditions for dendrite growth. The extremely slow drift velocity of the Li-ions of ∼1 mm per hour in a typical commercial Li-ion battery, makes the growth of a dendrite take a few hours; however, once a Li-ion arrives at an active site of the anode, it takes an extremely short time of ∼1 ps to react. This large difference in time-scales allows us to perform the molecular dynamics simulation of the ions at much larger drift velocities, so we can have valuable results in reasonable computational times. The conditions before the growth are assumed and conditions that do not lead to the growth are ignored. We performed molecular dynamics simulations of a pre-lithiated silicon anode with a Li : Si ratio of 21 : 5, corresponding to a fully charged battery. We simulate the dendrite growth by testing a few charge distributions in a nanosized square representing a crack of the solid electrolyte interphase, which is where the electrolyte solution comes into direct contact with the LiSi alloy anode. Depending on the selected charge distributions for such an anode surface, the dendrites grow during the simulation when an external field is applied. We found that dendrites grow when strong deviations of charge distributions take place on the surface of the crack. Results from this work are important in finding ways to constrain lithium dendrite growth using tailored coatings or pre-coatings covering the LiSi alloy anode.
Highlights
Lithium-ion batteries are devices that transform available electrical energy into chemical energy, so the energy can be transformed back and delivered as electrical energy when needed
Classical molecular dynamics (MD) simulations are performed using the Large-Scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) program developed by Plimpton et al.[40]
An equilibration at 5 K is performed for 1 ns, the temperature is increased from 5 K to 300 K for 2 ns, and nally an equilibration at 300 K for 7 ns is done with a relaxation time of 10 fs
Summary
Lithium-ion batteries are devices that transform available electrical energy into chemical energy, so the energy can be transformed back and delivered as electrical energy when needed. A typical lithium-ion battery (LIB) consists mainly of a graphite anode, a LiCoO2 cathode, an electrolyte solution made of ethylene carbonate (EC)[1,2] with a dissolved LiPF6 salt, a separator, and two metallic current collectors. There are strong efforts to design more powerful, more efficient, and more environmentally compatible materials for batteries. Silicon and Li-metal have been proposed as promising anode materials for rechargeable LIB3,4 because of their high. There is a lot of recent experimental and computational work being reported on dendrites.[28,29,30,31,32,33,34,35,36,37,38]
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