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CATEGORIES:Engineering - Mechanics and Materials Seminar Seri
 es
SUMMARY:Electrochemical and mechanical modeling of lithium
 -ion batteries - Dr Ying Zhao\, CUED
DTSTART;TZID=Europe/London:20180202T140000
DTEND;TZID=Europe/London:20180202T143000
UID:TALK99874AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/99874
DESCRIPTION:Lithium-ion batteries\, with their high energy den
 sities and light-weight designs\, have found broad
  applications in portable electronics and electric
  vehicles. However\, their mechanisms and operatio
 n are not yet fully understood\, which has motivat
 ed a wide span of multi-physical models from diffe
 rent disciplines. In this talk\, a thermodynamical
 ly consistent phase-field framework is presented\,
  to investigate the electrochemical and mechanical
  behavior of lithium-ion battery electrode materia
 ls during charge and discharge. Within this framew
 ork\, a series of coupled models is developed sequ
 entially towards the more realistic modeling. Firs
 tly\, a mechanically coupled two-phase model of a 
 single particle is proposed\, based on a thorough 
 study of the chemical phase—separation of this par
 ticle. Thereby\, the effect of large strains and t
 he concentration-dependent elastic properties are 
 considered\, which has been proved in this thesis 
 to have a great impact on the phase separation. A 
 more comprehensive model is formulated\, which dea
 ls additionally with the electrochemical reaction 
 on the particle surface and the orthotropic phase 
 separation. The reaction rate is governed by a mod
 ified Butler–Volmer equation\, which takes both ch
 emical and mechanical states into account. Based o
 n this model\, we further investigate the fracture
  in the particle by the phase-field approach\, whe
 re the reaction on the newly cracked surfaces is a
 lso taken into consideration. Finally\, the model 
 of the particle embedded in a polymer matrix is pr
 esented to study the interaction between the parti
 cle and the surrounding materials. For the impleme
 ntation two novel finite element methods are used:
  isogeometric analysis and the B-Spline based fini
 te cell method. Isogeometric analysis is employed 
 in order to treat the fourth-order Cahn–Hilliard e
 quation and the third-order drifting term in a str
 aightforward fashion. To deal with the additional 
 boundary constraint\, which states that the normal
  gradient\nof the concentration equals to zero\, a
 nd which arises from the Cahn–Hilliard equation\, 
 we propose two variational formulations based on t
 he Lagrange multiplier method and the Nitsche meth
 od\, respectively\, as the weak imposition. Moreov
 er\, we also employ finite cell method with Cartes
 ian B-Spline meshes to simulate the composite elec
 trode with complex geometries. In this thesis\, th
 e chemical and mechanical fields are fully resolve
 d in a variety of three dimensional simulations. T
 hese simulations demonstrate the influence of the 
 phase separation on the stress field\, the fractur
 e and the reaction rate. We find that the phase se
 paration results in\, among others\, an intensifie
 d stress field and enhanced reaction rate near the
  phase interface\, and in severe cases it also lea
 ds to crack propagation and branching. Moreover\, 
 intensive discussions are carried out to explore t
 he factors that contribute to phase separation and
  suppression\, such as the particle size\, charge 
 rate and material stiffness.
LOCATION:Oatley Seminar Room\, Department of Engineering
CONTACT:Hilde Hambro
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