Accelerated Aging in Lithium-ion batteries for Electric Vehicles
Lead Research Organisation:
University of Oxford
Department Name: Engineering Science
Abstract
Lithium-ion batteries have become one of the most popular energy storage devices for electric vehicles(EVs). The rise in popularity of EVs has indicated the need to explore the energy storage device in depth. One of the major factors contributing to the reduced efficiency of the Li-ion battery is the degradation effects caused due to various stress factors. The degradation within batteries results in negative effects such as loss of active material, formation of solid electrolyte interface and an increase in impedance which can lead to accelerated aging within the cell. For these reasons it is vital to research the accelerated aging in Li-ion batteries as it will allow the identification of the weaknesses of the cells which can be used to improve efficiency in the future.
There are two types of aging that the Li-ion battery faces throughout its lifespan which are cyclic aging and calendar aging. Cyclic aging is caused when the cell is subject to charge and discharge cycles. Stress factors such as state of charge and depth of discharge can affect the reversibility of the active materials within the battery causing the formation of solid electrolyte interface which results in capacity fade and power fade. These degradation factors in turn lead to the limitation of efficiency of Lithium-ion cells. The effects in the cells that occurs while not cycling leads to calendar aging which aggravates the cyclic degradation. Calendar aging has been seen to be significantly accelerated by elevated storage temperature and state of charge. Another perspective which is yet to be thoroughly studied is the effects of calendar aging when the cell is left as an open circuit to self-discharge as compared to when the battery is supplied with a float charge in order to maintain the state of charge of the battery.
The objective of my research is to clearly identify the causes of accelerated cyclic and calendar aging in Lithium-ion cells in relation to stress factors in order to create an aging model which can lead to improved efficiency of the cell. This can provide EV cell manufacturers with a clearer idea of the capability of the battery and as a result the turnover rate of the batteries can be predicted and reduced. To conduct the research, I plan to continue to read prior studies while setting up experiments in order to obtain a data set. The initial study will focus on calendar aging as it is a less explored field of aging and tests will be conducted in order to collect information on the effects of the state of charge, temperature, time dependency, open circuit and float charging on aging of the cell. Experimental techniques such as open circuit voltage tests, electrochemical impedance spectroscopy and pulsed techniques will be used in order to collect the required information. This data will then be studied in order to identify links between the stress factors which will lead to the creation of a model specifically for calendar aging. Similar tests will be conducted for cyclic aging and a correlation between the two aging models will be found in order to combat accelerated aging within lithium-ion batteries.
This project is in line with the scope of the EPRSC's aim to introduce more efficient fuel cells into the transportation sector and falls within the EPRSC, Energy - Alternate Fuel Cells and Fuel Cells research area.
This project is in collaboration with Jaguar Land Rover.
There are two types of aging that the Li-ion battery faces throughout its lifespan which are cyclic aging and calendar aging. Cyclic aging is caused when the cell is subject to charge and discharge cycles. Stress factors such as state of charge and depth of discharge can affect the reversibility of the active materials within the battery causing the formation of solid electrolyte interface which results in capacity fade and power fade. These degradation factors in turn lead to the limitation of efficiency of Lithium-ion cells. The effects in the cells that occurs while not cycling leads to calendar aging which aggravates the cyclic degradation. Calendar aging has been seen to be significantly accelerated by elevated storage temperature and state of charge. Another perspective which is yet to be thoroughly studied is the effects of calendar aging when the cell is left as an open circuit to self-discharge as compared to when the battery is supplied with a float charge in order to maintain the state of charge of the battery.
The objective of my research is to clearly identify the causes of accelerated cyclic and calendar aging in Lithium-ion cells in relation to stress factors in order to create an aging model which can lead to improved efficiency of the cell. This can provide EV cell manufacturers with a clearer idea of the capability of the battery and as a result the turnover rate of the batteries can be predicted and reduced. To conduct the research, I plan to continue to read prior studies while setting up experiments in order to obtain a data set. The initial study will focus on calendar aging as it is a less explored field of aging and tests will be conducted in order to collect information on the effects of the state of charge, temperature, time dependency, open circuit and float charging on aging of the cell. Experimental techniques such as open circuit voltage tests, electrochemical impedance spectroscopy and pulsed techniques will be used in order to collect the required information. This data will then be studied in order to identify links between the stress factors which will lead to the creation of a model specifically for calendar aging. Similar tests will be conducted for cyclic aging and a correlation between the two aging models will be found in order to combat accelerated aging within lithium-ion batteries.
This project is in line with the scope of the EPRSC's aim to introduce more efficient fuel cells into the transportation sector and falls within the EPRSC, Energy - Alternate Fuel Cells and Fuel Cells research area.
This project is in collaboration with Jaguar Land Rover.
People |
ORCID iD |
| Trishna Raj (Student) |
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| EP/N509310/1 | 01/10/2015 | 30/03/2021 | |||
| 1802014 | Studentship | EP/N509310/1 | 01/10/2016 | 31/03/2021 | Trishna Raj |
| Description | This study aims to investigate and quantify the impact that path dependency has on lithium ion cell degradation. Experimental studies have been seen in the literature that investigate the influence of calendar and cyclic aging on cell lifetime individually. It has also been determined that the impact of each degradation mechanism cannot be isolated due to the interaction between the mechanisms and products formed. Due to the lack of data collected using controlled combined profiles, a relationship between path dependency, degradation and cell lifetime has not been formed. Looking at the models in the literature being used to predict cell degradation, most models do not factor in the influence of degradation path dependency. The research conducted will provide the data to support the statement that path dependency will influence the rate with which the cell ages. The data will lead to modifications to the cell lifetime models that can be made in order to obtain power and capacity predictions with greater accuracy. The updated models will be beneficial to cell manufacturers and electric vehicle manufacturers as they will be able to attain a more realistic view of cell lifetime and power capabilities as the cell ages. The data collected so far shows the degradation paths diverging which suggests that path dependency does have an impact on degradation and that the current lifetime predictions that superimpose calendar and cyclic aging may be inaccurate. |
| Exploitation Route | The results from the study can be used to improve the accuracy with which lifetime and state of health predictions for lithium ion batteries are made. By incorporating the impact of path dependency on degradation, battery manufacturers and electric vehicle manufacturers can improve the reliability of their cells/vehicles with greater lifetime prediction accuracy. This will result in better use of resources and batteries as well as encourage the use of electric vehicles. |
| Sectors | Energy,Transport |
| Title | Path Dependent Battery Degradation Dataset Part 1 |
| Description | Models that predict battery lifetime require knowledge of the causes of degradation and operating conditions that accelerate it. Batteries experience two aging modes: calendar aging at rest and cyclic aging during the passage of current. Existing empirical aging models treat these as independent, but degradation may be sensitive to their order and periodicity - a phenomenon that has been called 'path dependence'. This long-term dataset was collected to study the influence of path dependence in commercially available lithium-ion 18650 cells with nickel cobalt aluminium oxide (NCA) positive electrodes and graphite negative electrodes. Four groups of 3 cells each were subjected to combined load profiles comprising fixed periods of calendar and cyclic aging applied in various orders. Cells in groups 1 and 2 were exposed to one day of cycling followed by five days of calendar aging at C/2 and C/4 respectively. Cells in groups 3 and 4 were exposed to two days of cycling followed by ten days of calendar aging at C/2 and C/4 respectively. The data collected while the cells were exposed to the combined profiles as well as the reference performance tests and electrochemical impedence spectroscopy data is included in this dataset. |
| Type Of Material | Database/Collection of data |
| Year Produced | 2020 |
| Provided To Others? | Yes |
| Impact | - |
| URL | https://ora.ox.ac.uk/objects/uuid:de62b5d2-6154-426d-bcbb-30253ddb7d1e |
| Title | Path Dependent Battery Degradation Dataset Part 2 |
| Description | Batteries experience two aging modes: calendar aging at rest and cyclic aging during the passage of current. Existing empirical aging models treat these as independent, but degradation may be sensitive to their order and periodicity - a phenomenon that has been called 'path dependence'. This long-term dataset was collected to study the influence of path dependence in commercially available lithium-ion 18650 cells with nickel cobalt aluminium oxide (NCA) positive electrodes and graphite negative electrodes. Four groups of 3 cells each were subjected to combined load profiles comprising fixed periods of calendar and cyclic aging applied in various orders. Cells in groups 1 and 2 were exposed to one day of cycling followed by five days of calendar aging at C/2 and C/4 respectively. Cells in groups 3 and 4 were exposed to two days of cycling followed by ten days of calendar aging at C/2 and C/4 respectively. All cycling in the combined load profiles was conducted under constant current (CC) conditions and calendar aging was conducted at 90% state of charge (SoC). Cells in group 5 were exposed to continuous CC cycling at C/2 while group 6 consists of a single cell calendar aged at 90% SoC. This dataset is a continuation of the 'Path Dependent Battery Degradation Dataset Part 1, DOI: 10.5287/bodleian:v0ervBv6p ' dataset. Path Dependent Battery Degradation Dataset Part 1 includes data collected over 1.5 years from the beginning of life to the middle of life. Path Dependent Battery Degradation Dataset Part 2 covers the remaining 1.5 years of data from the middle of life to end of life. The data collected while the cells were exposed to the combined profiles as well as the reference performance tests and electrochemical impedance spectroscopy data is included in this dataset. |
| Type Of Material | Database/Collection of data |
| Year Produced | 2021 |
| Provided To Others? | Yes |
| Impact | - |
| URL | https://ora.ox.ac.uk/objects/uuid:be3d304e-51fd-4b37-a818-b6fa1ac2ba9d |
| Title | Path Dependent Battery Degradation Dataset Part 3 |
| Description | Batteries experience two aging modes: calendar aging at rest and cyclic aging during the passage of current. Existing empirical aging models treat these as independent, but degradation may be sensitive to their order and periodicity - a phenomenon that has been called 'path dependence'. This dataset was collected to study the influence of path dependence in commercially available lithium-ion 18650 cells with nickel cobalt aluminium oxide (NCA) positive electrodes and graphite negative electrodes. It was collected in order to support the data presented in 'Path Dependent Battery Degradation Dataset Part 1, https://doi.org/10.5287/bodleian:v0ervBv6p' and 'Path Dependent Battery Degradation Dataset Part 2, https://doi.org/10.5287/bodleian:2zvyknyRg' by investigating the impact that modified calendar/cyclic conditions has on path dependence. Four groups of 3 cells each were subjected to combined load profiles comprising fixed periods of calendar and cyclic aging applied in various orders. Cells in groups 7 were exposed to 1 day of constant current constant voltage (CCCV) cycling at C/2 followed calendar aging at 90% state of charge (SoC) for 5 days which was compared to group 8 that was exposed to 2 days of CCCV cycling at C/2 followed by 10 days of calendar aging at 90% SoC. Groups 9 and 10 were designed to understand the influence of calendar aging conditions on path dependence. Group 9 was exposed to 1 day of CCCV cycling at C/2 followed by calendar aging at 4.2V (100% SoC) for 5 days while cells in group 10 were subjected to 2 days of CCCV cycling at C/2 and 10 days of calendar aging at 4.2V. The data collected while the cells were exposed to the combined profiles as well as the reference performance tests and electrochemical impedance spectroscopy data is included in this dataset. |
| Type Of Material | Database/Collection of data |
| Year Produced | 2021 |
| Provided To Others? | Yes |
| Impact | - |
| URL | https://ora.ox.ac.uk/objects/uuid:78f66fa8-deb9-468a-86f3-63983a7391a9 |