The importance of BMS for protecting battery health

This article originally appeared in the July '22 magazine issue of Electronic Specifier Design – see ES's Magazine Archives for more featured publications.

Most of the lithium-ion (Li-Ion) batteries used to power equipment and machinery rely on a battery management system (BMS) to protect the battery’s internal chemistry. The BMS safeguards the longevity of the battery by preventing damage to the core elements of the cells.

Without a BMS there is a real risk of damage due to the uncontrolled and unmanaged flow of energy through the battery. This can result in damaged electrodes, significant degradation, and the longevity of the Li-Ion battery can be greatly hampered. The BMS runs constant diagnostics on the health of the battery to ensure that the power needs of the user can be achieved without compromising battery health. When it comes to selecting a battery partner, ensuring that they operate with an effective BMS should be an absolute priority.

The role of the BMS Within the battery casing, the BMS operates as the battery brain by controlling all functions. At its most basic, the BMS evaluates the battery in relation to the equipment or charger, ensuring that the correct flow of energy occurs based on internal and external conditions, such as charge/discharge parameters and temperature. The BMS connects to the thermistors that constantly monitor individual cell and pack temperatures, allowing the BMS to control the energy flow and keep the battery within its optimal operating window.

The BMS uses a power map that governs all the rules and boundaries for safe, long-life battery operation. The power map determines the flow of energy throughout the battery enabling the BMS to optimise the charge and discharge rates based on cell temperature, state-of-charge (SoC) and state-of-health (SoH). Combined, the BMS and the power map are crucial for protecting the overall battery health and preventing long term battery degradation.

The BMS enables users to gather data on the health of the battery, and is crucial for diagnosing the internal health of the battery. Recording data on temperature, charging speed, and charge status allows the user to understand the overall health of the battery and protects user safety.

Protecting the internal chemistry

Throughout the charging process, the BMS controls the transfer rate of lithium-ions within the battery, to minimise dendrite growth (a form of lithium plating) on the negative electrode. When charging a Li-Ion battery, the charge moves from the cathode to the anode, but if the process is not controlled, dendrite growth can build-up on the anode impacting the effectiveness of the flow of electrons. Without a BMS – or with an inadequate power map – dendrite growth will more quickly limit the useful energy (capacity) of the battery, which can lead to a dangerous shorting of the battery.

The temperature at which the battery is stored, charged and discharged can also significantly impact its degradation. Operating or storing a battery at high temperatures can shorten its life by limiting capacity. Overcharging, deep discharging or charging more quickly than recommended (high C rate) can also shorten life expectancy. The BMS’s control of energy flow makes it crucial to protecting the internal chemistry and preventing dendrite growth.

Temperature control

The BMS also helps to maintain battery temperature by controlling the flow of energy. It does this by constantly monitoring and measuring the temperature and the charge and discharge currents, alongside the voltages of each individual cell bank. When a Li-Ion battery exceeds its maximum temperature it can go into a thermal runaway event, whereby the temperature rises rapidly releasing the battery’s energy. This will not occur, however, when the battery is properly managed and protected with a BMS.

Temperature operating windows have greatly increased for Li-Ion batteries due to the data that is collected by the BMS. It enables them to be used from −40˚C to +70˚C, dependent on the battery cell, by adjusting the discharge rate to counter external conditions. Low temperatures reduce the rate of reaction within the battery cells causing a slower discharge rate. A BMS can compute lower temperatures and carefully control the rate of discharge to avoid damaging the cell.

In ambient temperatures, the BMS controls charging and discharging to prevent dendrite growth to reduce the risk of lithium plating, which impacts the effectiveness of the battery. Whilst the controlled charging process can result in a slow charge rate for the user, the health of the battery is maintained allowing for its power capacity to remain constant regardless of the change in external conditions.