Graphite as a negative electrode material for lithium ion batteries
Graphite as a negative electrode material for lithium ion batteries
Initial studies focused upon obtaining reproducible results, and identifying the various different graphite intercalation compounds (GIC's) formed. This was investigated using pulsed coulometric titration, differential capacitance plots and slow scan cyclic voltammetry. The kinetics of lithium diffusion in graphite are complicated by the phase changes as different GIC's are formed. The phase change for a stage I' to a stage 4 has been used as a case study. The kinetics of lithium insertion in both the single and two phase region were studied using potential step technique. It has been demonstrated that it is not possible to analyse the data using a simple Cottrell behaviour. A new model has been proposed which considers the case of finite diffusion into a single graphite particle with cylindrical geometry having significant interfacial resistance at the surface. The diffusion coefficient (D) in stage 4 is found by application of a new model for a two phase system, in which the rate determining step is diffusion through an outer layer of stage 4 material surrounding a particle of stage 1' material. Two values of D have been calculated Dα~4 x 10-7 cm2 s-1 and Dβ ~1.5 x 10-8 cm2 s-1(for stage 1' and stage 4 materials respectively).
The second aspect of this project considers the two main sources of first cycle irreversible capacity loss in graphite composite electrodes (i) poor particle contact and (ii) surface film formation. Several modifications in the electrode fabrication procedure have been tested and optimised. It has been demonstrated that particle contact is improved by addition of a high surface area carbon black, or by deposition of a thin copper film. It has also been shown that it is possible to prepare a chemically grown film prior to cycling which has similar passivating properties to that obtained electrochemically from electrolyte reduction during the first cycle. SEM analysis has proved to be an invaluable tool in determining changes in surface morphology, and has complemented the data obtained from electrochemical techniques.
University of Southampton
Gray, Melanie Grace
85255dd1-e717-40f2-838e-49afd77bf7dd
1999
Gray, Melanie Grace
85255dd1-e717-40f2-838e-49afd77bf7dd
Gray, Melanie Grace
(1999)
Graphite as a negative electrode material for lithium ion batteries.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Initial studies focused upon obtaining reproducible results, and identifying the various different graphite intercalation compounds (GIC's) formed. This was investigated using pulsed coulometric titration, differential capacitance plots and slow scan cyclic voltammetry. The kinetics of lithium diffusion in graphite are complicated by the phase changes as different GIC's are formed. The phase change for a stage I' to a stage 4 has been used as a case study. The kinetics of lithium insertion in both the single and two phase region were studied using potential step technique. It has been demonstrated that it is not possible to analyse the data using a simple Cottrell behaviour. A new model has been proposed which considers the case of finite diffusion into a single graphite particle with cylindrical geometry having significant interfacial resistance at the surface. The diffusion coefficient (D) in stage 4 is found by application of a new model for a two phase system, in which the rate determining step is diffusion through an outer layer of stage 4 material surrounding a particle of stage 1' material. Two values of D have been calculated Dα~4 x 10-7 cm2 s-1 and Dβ ~1.5 x 10-8 cm2 s-1(for stage 1' and stage 4 materials respectively).
The second aspect of this project considers the two main sources of first cycle irreversible capacity loss in graphite composite electrodes (i) poor particle contact and (ii) surface film formation. Several modifications in the electrode fabrication procedure have been tested and optimised. It has been demonstrated that particle contact is improved by addition of a high surface area carbon black, or by deposition of a thin copper film. It has also been shown that it is possible to prepare a chemically grown film prior to cycling which has similar passivating properties to that obtained electrochemically from electrolyte reduction during the first cycle. SEM analysis has proved to be an invaluable tool in determining changes in surface morphology, and has complemented the data obtained from electrochemical techniques.
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Published date: 1999
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Local EPrints ID: 463999
URI: http://eprints.soton.ac.uk/id/eprint/463999
PURE UUID: 3c4a0bcd-3ab1-4184-930c-f256308efbb2
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Date deposited: 04 Jul 2022 21:00
Last modified: 23 Jul 2022 02:15
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Author:
Melanie Grace Gray
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