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SUMMARY:Electrochemical and mechanical modeling of lithium-ion batteries -
  Dr Ying Zhao\, CUED
DTSTART:20180202T140000Z
DTEND:20180202T143000Z
UID:TALK99874@talks.cam.ac.uk
CONTACT:Hilde Hambro
DESCRIPTION:Lithium-ion batteries\, with their high energy densities and l
 ight-weight designs\, have found broad applications in portable electronic
 s and electric vehicles. However\, their mechanisms and operation are not 
 yet fully understood\, which has motivated a wide span of multi-physical m
 odels from different disciplines. In this talk\, a thermodynamically consi
 stent phase-field framework is presented\, to investigate the electrochemi
 cal and mechanical behavior of lithium-ion battery electrode materials dur
 ing charge and discharge. Within this framework\, a series of coupled mode
 ls is developed sequentially towards the more realistic modeling. Firstly\
 , 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 the concentration-depende
 nt elastic properties are considered\, which has been proved in this thesi
 s to have a great impact on the phase separation. A more comprehensive mod
 el is formulated\, which deals additionally with the electrochemical react
 ion on the particle surface and the orthotropic phase separation. The reac
 tion rate is governed by a modified Butler–Volmer equation\, which takes
  both chemical and mechanical states into account. Based on this model\, w
 e further investigate the fracture in the particle by the phase-field appr
 oach\, where the reaction on the newly cracked surfaces is also taken into
  consideration. Finally\, the model of the particle embedded in a polymer 
 matrix is presented to study the interaction between the particle and the 
 surrounding materials. For the implementation two novel finite element met
 hods are used: isogeometric analysis and the B-Spline based finite cell me
 thod. Isogeometric analysis is employed in order to treat the fourth-order
  Cahn–Hilliard equation and the third-order drifting term in a straightf
 orward fashion. To deal with the additional boundary constraint\, which st
 ates that the normal gradient\nof the concentration equals to zero\, and w
 hich arises from the Cahn–Hilliard equation\, we propose two variational
  formulations based on the Lagrange multiplier method and the Nitsche meth
 od\, respectively\, as the weak imposition. Moreover\, we also employ fini
 te cell method with Cartesian B-Spline meshes to simulate the composite el
 ectrode with complex geometries. In this thesis\, the chemical and mechani
 cal fields are fully resolved in a variety of three dimensional simulation
 s. These simulations demonstrate the influence of the phase separation on 
 the stress field\, the fracture and the reaction rate. We find that the ph
 ase separation results in\, among others\, an intensified stress field and
  enhanced reaction rate near the phase interface\, and in severe cases it 
 also leads to crack propagation and branching. Moreover\, intensive discus
 sions are carried out to explore the factors that contribute to phase sepa
 ration and suppression\, such as the particle size\, charge rate and mater
 ial stiffness.
LOCATION:Oatley Seminar Room\, Department of Engineering
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