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Fast charging strategies in lithium-ion batteries : detection and control of lithium plating
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Koleti, Upender Rao (2020) Fast charging strategies in lithium-ion batteries : detection and control of lithium plating. EngD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3684289~S15
Abstract
The fast charging of lithium-ion (Li-ion) batteries is required as one means of reinforcing consumer acceptance of future electric vehicle (EV) technology. However, the useful life of a Li-ion battery is known to be closely related to the magnitude of applied current, the state of charge (SOC) range over which the current is applied and the temperature of the battery during the charging period. Lithium plating on the negative electrode (NE) is known to be one of the major ageing mechanisms associated with fast charging. Therefore, an optimal charging profile that avoids or minimizes lithium plating is necessary for Li-ion batteries to achieve fast charging while simultaneously maintaining a longer cycle life. The use of model-based lithium plating control techniques that employ electrochemical models is complex to deploy and still face significant challenges in their implementation. The aim of this research therefore primarily focuses on experimental approaches to detect lithium plating and to derive fast-charge protocols that avoid or minimize the occurrence of lithium plating.
Within this Engineering Doctorate Portfolio, lithium plating detection techniques and their application to control lithium plating are investigated. The contribution of this research is to provide knowledge that may underpin future fast charging algorithms for integration with a Battery Management System (BMS). This has been achieved through five related studies.
The experimental approaches such as neutron diffraction and voltage relaxation profiles (VRP) detect lithium plating based on the influence of lithium plating on the electrode lithiation levels and the cell terminal voltage. In this research, experimental evidence that establishes the influence of the CV phase of charging on the lithium plating detection ability (study 1) is presented for the first time. Further, in this study, it is identified that the VRP method that infers the occurrence of lithium plating using a two-stage voltage relaxation can false detect in some charge events because of the NE phase changes. A procedure to differentiate the plating induced two-stage recovery is suggested.
In study 2, a closed-loop control scheme is developed to derive a multi-stage charge profile for offline and online use with the support of existing approaches of lithium plating detection where the terminating voltage of the first stage CC is adjusted based on the occurrence of lithium plating. The Online approach bases on the improved and validated VRP method suitable for low-temperature applications. The second one utilizes the Coulombic efficiency method that is intended for identifying an offline charge profile. Although the developed charge profiles have improved the battery life compared to a standard CC-CV charge profile, many limitations are identified. One of them is their inability to detect and control lithium plating within a charging event.
In study 3, a detailed quantification of plating induced battery degradation modes in terms of Loss of lithium inventory (LLI) and loss of active material (LAM) at the electrodes is undertaken. The results in this work highlight that lithium plating results in significant LAM at the NE in addition to the LLI. This helps to improve our understanding of lithium plating and its effect on battery degradation.
In Study 4, a new approach to detect lithium plating while the battery is still undergoing charge is proposed and validated at near operating conditions (temperatures between 10 to 30 o C and Charge rates from 0.25 to 1.25C). Impact of lithium plating as a side reaction on the high-frequency impedance of the battery is utilized to identify the onset of plating with the proposed impedance tracking procedure. The new method is then utilised to develop two different charge control strategies- online and offline (study 5). Experimental validation of these charging approaches while cycling the cells has shown significant cycle life improvement (> 80%) at the cost of up to 20% increased charging time. The results indicate that both of these approaches can be improved to extend battery life further. Future work in this direction is outlined.
The primary area of novelty within this research is to detect the onset of lithium plating in-situ and control the charge current accordingly to minimize lithium plating. EV manufacturers to derive an optimal charging strategy can utilize the findings from this research.
Item Type: | Thesis (EngD) | ||||
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Subjects: | T Technology > TK Electrical engineering. Electronics Nuclear engineering T Technology > TL Motor vehicles. Aeronautics. Astronautics |
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Library of Congress Subject Headings (LCSH): | Electric vehicles -- Batteries, Electric vehicles -- Batteries -- Management, Lithium ion batteries, Lithium ion batteries -- Deterioration | ||||
Official Date: | 30 September 2020 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Warwick Manufacturing Group | ||||
Thesis Type: | EngD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Marco, James | ||||
Sponsors: | TVS Group (Firm) | ||||
Format of File: | |||||
Extent: | xv, 154 leaves : colour illustrations | ||||
Language: | eng |
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