MDPI - Publisher of Open Access Journals

14 pages, 4845 KiB

Open AccessArticle

Capacity Measurements for Second Life EV Batteries

by Ngalula Sandrine Mubenga and Thomas Stuart

Electricity 2022, 3(3), 396-409; https://doi.org/10.3390/electricity3030021 - 13 Aug 2022

Cited by 6 | Viewed by 4202

After they reached the end of their useful EV life, lithium-ion batteries are still satisfactory for second life (SL) energy storage applications. However, the spread in their SL cell capacities may be much wider than in the EV, and this raises a question as to what type of cell voltage equalizer (EQU) should be used. Most users plan to retain the same passive EQU (PEQ) from the EV, but this means the battery capacity will be the same as the worst cell in the battery, just as it was in the EV. Unfortunately, the SL cell capacity spread may be much wider than it was in the EV, and if so, most of the cells will be under-utilized. This can be corrected by using an active EQU (AEQ) or a hybrid, such as the bilevel EQU (BEQ), to provide a capacity close to the cell average; but first, measured data is needed on the actual size of the cell capacity spread. To simplify and reduce the cost of these measurements, a new method is proposed that provides the capacities of the worst cell and the cell average. Full article

► Show Figures

Figure 1

14 pages, 3095 KiB

Open AccessArticle

Bilevel vs. Passive Equalizers for Second Life EV Batteries

by Ngalula Sandrine Mubenga, Boluwatito Salami and Thomas Stuart

Electricity 2021, 2(1), 63-76; https://doi.org/10.3390/electricity2010004 - 7 Feb 2021

Cited by 10 | Viewed by 4891

Abstract

Once lithium-ion batteries degrade to below about 80% of their original capacity, they are no longer considered satisfactory for electric vehicles (EVs), but they are still adequate for second-life energy storage applications. However, once this level is reached, capacity fade increases at a much faster rate, and the spread between the cell capacities becomes much wider. If the passive equalizer (PEQ) from the EV is still used, battery capacity remains equal to that of the worst cell in the stack, just like it was in the EV. Unfortunately, the worst cell eventually becomes much weaker than the cell average, and the other cells are not fully utilized. If operated while the battery is in use, an active equalizer (AEQ) can increase the battery capacity to a much higher value close to the cell average, but AEQs are much more expensive and are not considered cost effective. However, it can be shown that the bilevel equalizer (BEQ), a PEQ/AEQ hybrid, also can provide a capacity very close to the cell average and at a much lower cost than an AEQ. Full article

► Show Figures

Figure 1

11 pages, 2228 KiB

Open AccessArticle

A Bilevel Equalizer to Boost the Capacity of Second Life Li Ion Batteries

by Ngalula Sandrine Mubenga, Kripa Sharma and Thomas Stuart

Batteries 2019, 5(3), 55; https://doi.org/10.3390/batteries5030055 - 1 Aug 2019

Cited by 17 | Viewed by 9857

Abstract

There is a strong interest in second life applications for the growing number of used electric vehicle (EV) batteries, but capacity variations amongst these used cells present a problem. Even when these cells are matched for capacity, some imbalance is bound to remain, and a few lower capacity cells are also likely to develop after the pack begins its second life. Conventional cell voltage equalizers (EQU) do not address this problem, and they only provide a battery discharge capacity that is exactly equal to that of the weakest cell in the pack. This can easily result in a capacity loss of perhaps 20% to 25%, or more. This indicates the need for a new class of EQUs that can provide a discharge capacity that is close to the average of the cells, instead of the weakest cell. It is proposed to call these “capacity EQUs”, and the properties they must have are described. One such EQU is the bilevel equalizer (BEQ), described previously. This present paper provides an enhanced analysis of the BEQ and improved modelling methods. It also presents more details that are necessary to implement the microcontroller algorithm for the BEQ hardware. Full article

► Show Figures

Graphical abstract

13 pages, 4232 KiB

Open AccessArticle

A Bilevel Equalizer for Large Lithium Ion Batteries

by Ngalula Sandrine Mubenga, Zachary Linkous and Thomas Stuart

Batteries 2017, 3(4), 39; https://doi.org/10.3390/batteries3040039 - 7 Dec 2017

Cited by 9 | Viewed by 14119

Abstract

Due to variations among the cells, large lithium ion batteries (LIB) such as those in battery energy storage stations (BESS) and electric vehicles (EVs) must have an equalizer (EQU) circuit to balance the cell voltages. In spite of their significant losses and other limitations, passive equalizers (PEQ) are used in most applications because they are relatively simple and low cost. Active equalizers (AEQ) reduce these PEQ problems, but are not as widely used due to their much higher cost and complexity. A new hybrid circuit called the Bilevel EQU (BEQ) combines the PEQ and AEQ to provide much higher performance than a pure PEQ but at a much lower cost than a pure AEQ. Full article

► Show Figures

Figure 1

Search Results (4)

Further Information

Guidelines

MDPI Initiatives

Follow MDPI

Saved Queries

Search Filter Reset All

Years

Feature Papers

Subjects

Journals

Article Types

Countries / Regions

Search Results (4)

Further Information

Guidelines

MDPI Initiatives

Follow MDPI