Editing Electrode (section)

=== Mechanical properties ===
A common failure mechanism of batteries is mechanical shock, which breaks either the electrode or the system's container, leading to poor conductivity and electrolyte leakage.<ref name="Why do batteries fail">{{cite journal |last1=Palacín |first1=M. R. |last2=de Guibert |first2=A. |date=2016-02-05 |title=Why do batteries fail? |url=https://www.science.org/doi/10.1126/science.1253292 |journal=Science |language=en |volume=351 |issue=6273 |pages=1253292 |doi=10.1126/science.1253292 |pmid=26912708 |hdl=10261/148077 |s2cid=11534630 |issn=0036-8075|hdl-access=free }}</ref> However, the relevance of mechanical properties of electrodes goes beyond the resistance to collisions due to its environment. During standard operation, the incorporation of ions into electrodes leads to a change in volume. This is well exemplified by Si electrodes in lithium-ion batteries expanding around 300% during lithiation.<ref>{{cite journal |last1=Li |first1=Dawei |last2=Wang |first2=Yikai |last3=Hu |first3=Jiazhi |last4=Lu |first4=Bo |last5=Cheng |first5=Yang-Tse |last6=Zhang |first6=Junqian |date=2017-10-31 |title=In situ measurement of mechanical property and stress evolution in a composite silicon electrode |journal=Journal of Power Sources |language=en |volume=366 |pages=80–85 |doi=10.1016/j.jpowsour.2017.09.004 |bibcode=2017JPS...366...80L |issn=0378-7753|doi-access=free }}</ref> Such change may lead to the deformations in the lattice and, therefore stresses in the material. The origin of stresses may be due to geometric constraints in the electrode or inhomogeneous plating of the ion.<ref name="doi.org">{{cite journal |last1=Xu |first1=Rong |last2=Zhao |first2=Kejie |date=2016-12-12 |title=Electrochemomechanics of Electrodes in Li-Ion Batteries: A Review |url=https://doi.org/10.1115/1.4035310 |journal=Journal of Electrochemical Energy Conversion and Storage |volume=13 |issue=3 |doi=10.1115/1.4035310 |issn=2381-6872}}</ref> This phenomenon is very concerning as it may lead to electrode fracture and performance loss. Thus, mechanical properties are crucial to enable the development of new electrodes for long lasting batteries. A possible strategy for measuring the mechanical behavior of electrodes during operation is by using [[nanoindentation]].<ref>{{cite journal |last1=de Vasconcelos |first1=Luize Scalco |last2=Xu |first2=Rong |last3=Zhao |first3=Kejie |date=2017 |title=Operando Nanoindentation: A New Platform to Measure the Mechanical Properties of Electrodes during Electrochemical Reactions |journal=Journal of the Electrochemical Society |language=en |volume=164 |issue=14 |pages=A3840–A3847 |doi=10.1149/2.1411714jes |s2cid=102588028 |issn=0013-4651|doi-access=free }}</ref> The method is able to analyze how the stresses evolve during the electrochemical reactions, being a valuable tool in evaluating possible pathways for coupling mechanical behavior and electrochemistry.

More than just affecting the electrode's morphology, stresses are also able to impact electrochemical reactions.<ref name="doi.org"/><ref>{{cite journal |last1=Zhao |first1=Kejie |last2=Pharr |first2=Matt |last3=Cai |first3=Shengqiang |last4=Vlassak |first4=Joost J. |last5=Suo |first5=Zhigang |date=June 2011 |title=Large Plastic Deformation in High-Capacity Lithium-Ion Batteries Caused by Charge and Discharge: Large Plastic Deformation in Lithium-Ion Batteries |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1551-2916.2011.04432.x |journal=Journal of the American Ceramic Society |language=en |volume=94 |pages=s226–s235 |doi=10.1111/j.1551-2916.2011.04432.x}}</ref> While the chemical driving forces are usually higher in magnitude than the mechanical energies, this is not true for Li-ion batteries.<ref>{{cite journal |last=Spaepen * |first=F. |date=2005-09-11 |title=A survey of energies in materials science |url=https://doi.org/10.1080/14786430500155080 |journal=Philosophical Magazine |volume=85 |issue=26–27 |pages=2979–2987 |doi=10.1080/14786430500155080 |bibcode=2005PMag...85.2979S |s2cid=220330377 |issn=1478-6435}}</ref> A study by Dr. Larché established a direct relation between the applied stress and the chemical potential of the electrode.<ref>{{cite journal |last1=Larché |first1=F |last2=Cahn |first2=J. W |date=1973-08-01 |title=A linear theory of thermochemical equilibrium of solids under stress |url=https://dx.doi.org/10.1016/0001-6160%2873%2990021-7 |journal=Acta Metallurgica |language=en |volume=21 |issue=8 |pages=1051–1063 |doi=10.1016/0001-6160(73)90021-7 |issn=0001-6160}}</ref> Though it neglects multiple variables such as the variation of elastic constraints, it subtracts from the total chemical potential the elastic energy induced by the stress.
<math display="block">\mu = \mu^\text{o} + k\cdot T\cdot\log (\gamma\cdot x)  + \Omega \cdot \sigma</math>

In this equation, ''μ'' represents the chemical potential, with ''μ''<sup>o</sup> being its reference value. ''T'' stands for the temperature and ''k'' the [[Boltzmann constant]]. The term ''γ'' inside the logarithm is the activity and ''x'' is the ratio of the ion to the total composition of the electrode. The novel term Ω is the partial molar volume of the ion in the host and ''σ'' corresponds to the mean stress felt by the system. The result of this equation is that diffusion, which is dependent on chemical potential, gets impacted by the added stress and, therefore changes the battery's performance. Furthermore, mechanical stresses may also impact the electrode's solid-electrolyte-interphase layer.<ref name="Why do batteries fail"/> The interface which regulates the ion and charge transfer and can be degraded by stress. Thus, more ions in the solution will be consumed to reform it, diminishing the overall efficiency of the system.<ref>{{cite journal |last1=Zhao |first1=Kejie |last2=Cui |first2=Yi |date=2016-12-01 |title=Understanding the role of mechanics in energy materials: A perspective |journal=Extreme Mechanics Letters |series=Mechanics of Energy Materials |language=en |volume=9 |pages=347–352 |doi=10.1016/j.eml.2016.10.003 |issn=2352-4316|doi-access=free |bibcode=2016ExML....9..347Z }}</ref>