Cell Balancing: Improving EV Battery’s Performance and Lifecycle

Cell Balancing: Improving EV Battery’s Performance and Lifecycle

Advancements in battery technology and their environmental benefits have boosted the global demand for electric vehicles (EVs), making it a $786 billion market in 2024. The swelling demand for EVs has played a key role in increasing the adoption of batteries worldwide. 

The global demand for electric vehicle batteries surpassed 750 GWh in 2023 – a 40% growth from 2022, and this trend is expected to continue in the upcoming years. 

While different battery systems exist and are likely to gain traction in the future, lithium-ion batteries dominate the EV space due to their high power density and low self-discharge current. 

Despite these benefits, battery manufacturers and stakeholders have realized the need to boost cell uniformity and focus on cell balancing to augment performance, improve safety, and increase the battery’s lifespan. 

This article examines cell balancing and why it matters for optimal EV performance. It also taps into the different cell balancing techniques and how battery management systems can overcome the current barriers. 

What is Cell Balancing?

Cell balancing is primarily used to equalize the state of charge and voltages in various cells connected together in a battery pack when they’re completely charged.

  • It is important to note that every cell is unique and varies from one another. 
  • There are also minor differences, including self-discharge rate, state of charge, temperature-related characteristics, impedance, and capacity. 
  • This is also true for cells manufactured by the same company in the same production batch. 

Therefore, manufacturers ensure different cells in a battery pack have the same voltage value and chemistry. However, these parameters tend to change once the batteries are in use, resulting in cell unbalancing. 

Efficient cell balancing promotes optimal battery performance by preventing deep discharging and overcharging and tackling other aforementioned issues. 

Key Cell Balancing Techniques

Cell balancing techniques can be classified into two main categories. Let’s discuss them in detail. 

1. Passive Cell Balancing

Passive cell balancing is arguably the most straightforward cell balancing technique and is an excellent option where cost and the size of a battery pack are the primary constraints. 

There are two types of passive cell balancing: charge shunting and charge limiting. 

Charge Shunting

In this method, a resistor or dummy load is employed to divert excess voltage, ensuring all cells are balanced. Each cell within a battery pack is equipped with its bypass resistor, which is connected through a switch.

Charge Limiting

Charge limiting is another type of cell balancing wherein the battery’s efficiency is compromised in favor of its safety and lifetime. 

The voltage levels of all the cells are individually monitored, and the charging or discharging is stopped when even a single cell reaches the maximum and minimum cut-off voltage, respectively. It is cost-effective and suitable for compact batteries. 

2. Active Cell Balancing

One of the main reasons why passive cell balancing is not very efficient is because the excess charge isn’t utilized. On the flip side, the excess charge is transferred to a low-charge cell in active balancing to equalize the state of charge using storing components, including inductors and capacitors. 

Some of the most common types of active cell balancing include charge shuttles, inductive converters, and inductive converters. 

Why is Cell Balancing Important?

Let’s discuss a few reasons why cell balancing is so important and plays an important role in ensuring batteries perform optimally and last longer. 

Thermal Runway 

Lithium cells are highly sensitive to overcharging and overcharging. For example, in a cell pack, if one cell is 3.5V and the other cell is 3.3V, the 3.5V cell is likely to be overcharged above its threshold since the other cell is undercharged. 

This can overheat the cells, leading to thermal runaway and reinforcing the need for cell balancing to ensure pack safety and stability.

Cell Degradation

The lifecycle and efficiency of a cell are heavily compromised even when they are slightly overcharged above the optimal or recommended level. Therefore, accurate cell balancing is important to prevent cell degradation and improve a battery’s lifetime. 

Incomplete Pack Charging

Some cells within a battery start getting weaker over time when they start getting older. Weaker cells often charge and discharge faster than normal cells, which typically leads to the termination of the charging cycle since charging stops when even a single cell touches the maximum voltage limit. 

Therefore, since weak cells in a battery pack will charge faster, the healthy cells will never charge to their maximum limit, resulting in incomplete utilization of a battery’s optimal capacity.

Parting Notes

As the sales of EVs continue to move upward, it is safe to assume that the demand for batteries will grow as well. As the battery market becomes increasingly crowded, manufacturers need to go above and beyond to develop durable and high-performing battery packs and stay ahead of the curve.

Cell balancing can fulfill these requirements, and advanced cell balancing has emerged as a promising technology to ensure high performance and extended battery life. 

In addition, research and development will also play a key role in improving and discovering new cell-balancing solutions in the near future.