What is Battery Management System and why lithium Battery Needs it?

 

The winter of EVs is on its way and it’s called the summer season. Last year we saw various EVs and battery stations catching fire. When the government did the analysis, it was found that most of the batteries didn’t have any safety measures. So the government introduced AIS 156 amendments that mentioned smart batteries or batteries with BMS. But the question is what is BMS and why does your lithium battery need it?

What is BMS?

A BMS allows for continuous monitoring, data collection, and communication to an external interface where users can view the status of each cell as well as the overall health of the battery pack. A battery management system (BMS) monitors and manages a battery pack to protect it from damage, extend its life, and keep the battery operating within its safe limits. These functions are critical for efficiency, dependability, and safety.

Users can monitor individual cells within a battery pack using a battery management system. It is critical to maintaining stability throughout the pack as cells collaborate to release energy to the load.

 

What does a BMS measure?

A BMS can record data such as current, voltage, temperature, and coulomb count. Using these measurements, the system can assess the battery’s health and adjust operations as necessary to protect the pack.

A decrease in cell voltage at a given load, for example, can indicate an increase in internal resistance. This could indicate dry-out, corrosion, plate separation, or other diagnoses.

A sudden rise in the temperature of one cell may indicate the possibility of a thermal runaway event affecting the entire battery pack. The BMS could then stop the flow of energy and notify the user of a potential problem, allowing it to be contained before it becomes uncontrollable.

BMS with SoC and SoH

The state of charge (SoC) and state of health (SoH) of a battery are important indicators for determining its usability and capabilities. The SoC and SoH work together to provide a state of function, an overview of the battery, and an overview of the pack’s capabilities as a whole.

The most straightforward and common measure that a person would come across is the state of charge. The percentages of charge on phones and laptops are the states of charge. The SoC in electric vehicle batteries is used to calculate the remaining range of the car before it needs to be recharged. This, however, is not indicative of the battery’s overall health.

While SoC can show the battery’s short-term capability (how much energy is left), it cannot show the true capacity of the battery cell or pack. Cell capacity decreases with age, so while SoC may read 100%, the true capacity is likely to be less after a while.

Nonetheless, SoC remains an important metric in battery management. For example, to balance the load evenly across cells within the pack, the SoC of individual cells in the battery chain must be known.

In addition to SoC, the State of Health assesses the battery pack’s long-term capabilities.

SoH is an estimate of how long a battery can operate optimally based on charge acceptance, internal resistance, voltage, and self-discharge. It is usually measured against a new battery cell to determine where the cell is in its lifecycle.

There are no standard parameters for indicating SoH because it is determined by the function and applications of the battery cell. To calculate the overall SoH, different parameters such as cell resistance or self-discharge can be individually weighted.

Because SoH is typically measured against a new cell, the BMS must keep a record of the battery’s initial conditions as well as a log of measurements throughout the battery’s lifecycle to provide a more accurate indication of battery health.

 

Now the most important question is why BMS is so important.

A BMS is useful not only for indicating the health of a battery but also serves to protect the battery while it is in use.

Each battery cell and chemistry has a safe voltage, temperature, and current operating range. When a cell falls below or exceeds these limits, the BMS can detect and control it. Because lithium, for example, is a highly reactive substance, the BMS should monitor each lithium cell to ensure that it operates within predefined limits. This protects and preserves the battery in the long run.

Cell balancing is another important safety feature of a BMS. Individual cells in a battery pack do not operate in the same way. One cell in the chain may be weaker or stronger than another, charging or discharging faster. Without proper compensation, this could harm the overall health of the pack. If one cell short circuits or fails, the stability of the entire pack suffers. Cell balancing equalizes the charge of individual cells based on their capabilities. The BMS monitors and controls the charge demanded from each cell in the chain, ensuring that SoC is distributed evenly.

To know more about our batteries, contact us

Join the EV Revolution with Ipower Batteries

 

Reducing reliance on fossil fuels has been a priority as India works to fulfill its commitment to achieving net-zero carbon emissions by the year 2070. India is actively promoting the use of electric vehicles (EVs) to achieve its goal of having 30% of private cars, 70% of commercial vehicles, and 80% of two- and three-wheelers powered by electricity by the year 2030. To promote the use of EVs, the government has introduced incentives for both manufacturers and end users. Although EV adoption is increasing, recent incidents of EV batteries catching fire have caused a great deal of fear and hesitation to buy EVs.

 

What is a thermal management system in EV and why it is important?

The effectiveness and longevity of batteries depend on proper thermal management. It’s crucial to keep your thermal management strategy in mind when choosing how to package and integrate a battery pack into a vehicle.

Batteries are like Goldilocks; they don’t work well in extreme temperatures. To achieve the performance, dependability, and safety that OEMs are looking for, they must maintain the precisely right temperature. The battery pack’s capacity, cell balancing, capacity, charging speed, and service life will all be impacted by poor thermal management. A sound cooling plan will guarantee a uniform temperature distribution and get rid of any dangers that could arise from uncontrolled battery temperatures.

EV-specific Thermal Management System (TMS) maintains the vehicle’s operation at an ideal temperature to preserve the vehicle’s safety and effectiveness.

There are other factors as well, with safety being the most important. The batteries are higher energy density, high voltage Li-Ion batteries. Due to the increased density, even a slight temperature change could cause a fire hazard.

 

Active thermal management: keeping cool or maintaining control?

Active thermal management systems come in different varieties, and what sets those apart most is what they are used for. Some are intended to cool the battery, while others stabilize temperature extremes. There are mainly 3 types of active thermal management systems and they are as follows:

 

• Air cooling 

• Liquid cooling 

• Thermoelectric coolers

 

Air Cooling:

Active air-cooling systems use convection to cool the battery pack by blowing air across it, typically from an AC unit or air drawn in from the outside.

The simplicity and low cost of air-cooling systems are their main benefits. They are only meant to cool and stop overheating, though. They are unable to control a wide range of ambient temperatures as a result. Warm or even mild climates don’t have a problem with this, but colder climates can cause battery deterioration because EVs don’t like driving in the snow! Due to its low specific heat capacity, the air is not particularly effective at transferring heat away from the battery, even at moderate temperatures.

There are concerns about the safety of using an air-cooling system for high-power applications as batteries grow in strength and charge capacity.

 

Liquid Cooling:

Liquid cooling, which involves pumping and circulating a liquid coolant, like glycol, around the battery in a closed loop, offers a more precise way to control thermal conditions and keeps them within a desirable range.

To dissipate heat, heat is typically transferred to liquids through thermally conductive metal pipes that pull the heat away from the source. Since liquid-based cooling is so much more effective, it enables smaller, lighter, and more compact systems without requiring additional power or mass.

This is very helpful because the automotive industry wants to use the lightest systems possible.

 

Thermoelectric coolers:

Another technique of thermal management that is causing a stir in the automotive sector involves sandwiching semiconductors between a heat sink and a heat source (in this case, a battery). When a voltage is applied, a temperature difference between the source and sink is created, which causes heat to be transferred through conduction. In situations where heat is needed, the direction of heat transfer could be changed by reversing the current. This enables precise control of temperatures by a straightforward change in voltage.

 

Why passive thermal management system is required?

The biggest drawback of all active BTMS is that they drain the battery of valuable power, which is regrettably their biggest drawback. Therefore, passive cooling or passive thermal management is required. The objective of passive thermal management is to allow the battery to control its temperature without the use of an external energy source.

There are many passive cooling strategies in development, even though active management strategies are currently preferred for their effectiveness.

For instance, heat pipes, which use a closed cycle of liquid evaporation and condensation to transfer heat from a battery, are very effective at doing so in smartphones. However, these solutions can only absorb heat from the battery, not draw it away from the source. Expect to see more of these passive techniques employed in the future due to the ongoing push to reduce parasitic power consumption in EVs.

In a world full of changes, there are a few universal constants that cannot be altered. One of them is “Energy can neither be created nor be destroyed, it can only be converted from one form to another”. This very statement by Julius Robert Mayer is the basis of energy storage solutions.

Before talking about or predicting the future of lithium batteries, it’s very important to understand their past. We have to understand the significance of the fact that the entire concept of energy storage came from a frog experiment done by Luigi Galvani who was an Italian physicist.

Although lithium batteries were not made commercially available until the late 20th century, Gilbert Newton Lewis was the first to experiment with them.

These batteries were made possible by three significant developments:

1. The LiCoO2 cathode was discovered by John Goodenough in 1980.
2. Graphite anode was discovered in 1982 by RachidYazami.
3. Asahi Chemicals created a prototype for a rechargeable lithium battery in 1985.

After that, it was Sony Company that commercialized lithium-ion batteries.

Now let’s head toward the future of lithium batteries via the roads of the present.

Lithium batteries offer a chance to change the transportation industry, which currently emits a lot of carbon into the atmosphere. They also provide a remedy for the erratic energy generated by solar and wind power, making these environmentally friendly options more practical.

New and cutting-edge chemistries and technologies have been developed and adopted over the past few years in the energy storage industry. One of the most recent adopters, lithium-ion batteries have gained popularity and respect for their chemistry, performance, and features. Lithium-ion batteries have a significantly higher energy density in joules per kilogram than earlier battery technologies like nickel-cadmium (NiCd) and nickel-metal hydride (NiMH).

But the question is what the future of lithium-ion batteries is.

 

Solid State Batteries:

In terms of technology, solid-state batteries represent a paradigm shift. In all-solid-state batteries, the liquid electrolyte is swapped out for a solid substance that still permits lithium ions to move around inside of it.

This idea is not new, but over the past ten years, extensive global research has led to the discovery of new families of solid electrolytes with extremely high ionic conductivity, comparable to the liquid electrolyte, enabling the removal of this particular technological hurdle.

Pros of solid-state batteries

• High thermal and impact safety because the liquid electrolyte is replaced by a solid
• Reduced dendrite growth issues extend service lifetime
• High-specific energy and low cost

Cons of solid-state batteries

• Cycle life is highly dependent on the specific anode-cathode mix (currently less than 1,000 cycles)
• Not commercially viable currently; expected to reach the mass market in 3–5 years

 

Lithium-sulphur Batteries:

Lithium ions are stored in active materials that serve as stable host structures in li-ion batteries during charge and discharge. The host structures in lithium-sulphur (Li-S) batteries are absent. The lithium anode is consumed during discharging, and sulphur is converted into several different chemical compounds during charging.

Pros of Lithium sulphur batteries

• Higher specific energy and power discharge compared with conventional LiBs
• High tolerance for extreme temperatures
• Uses low-cost and easily disposable input material

Cons of lithium-sulphur batteries

• Low cycle life and longevity

 

Lithium-Air batteries:

The lithium-air batteries would function by producing lithium peroxide on the cathode during the discharge phase by fusing lithium already present in the anode with air oxygen.

The area where air enters the battery is known as the cathode. Theoretically, lithium and oxygen can be combined to create electrochemical cells with the highest potential specific energy, comparable to the potential specific energy of gasoline.

This is almost five times more powerful than a Li-ion battery. However, before becoming widely used, Li-air batteries’ useful power and life cycle require significant improvements. The market for electric vehicles is a significant market driver for batteries.

Pros of Lithium-air batteries

• Very high theoretical energy density
• Uses abundant, low-cost materials for electrodes, offering a lower bill of materials

Cons of Lithium-air batteries

• Technology is still in the R&D stage, currently limited by low efficiency and poor cycle life

 

Lithium-carbon Batteries:

An emerging method of energy conversion and storage is the lithium-carbon dioxide battery. Even though these batteries are still in the early stages of development, researchers need to have a clear understanding of the major obstacles they must overcome to fulfill their potential as innovative energy storage systems.

Researchers have focused their attention on carbon capture and storage because carbon dioxide is a significant factor in the cycles of the earth’s temperature. Lithium-CO2 batteries present an intriguing alternative for the storage of electricity generated by renewable energy sources as well as for the conversion of waste carbon dioxide into products with added value.

Pros of Lithium-carbon batteries

• Combines benefits of traditional LiBs with capacitors —good energy/power density and fast recharging
• Promises low carbon footprint
• Low-cost, relatively abundant materials
• it does not need an external cooling system

Cons of Lithium-carbon batteries

Technology is in a very early stage, with a limited number of makers

The Ministry of Road Transport and Highway established an Expert Committee with members from the DRDO, IITs, IISc, and ARCI to recommend additional safety requirements in the existing battery safety standards notified under CMV Rules in the wake of numerous fire incidents involving electric two-wheelers in various parts of the nation.

On August 29, 2022, the Ministry published Amendment 2 to AIS 156, Specific Requirements for Motor Vehicles of the L Category. This was done in response to the expert committee report’s recommendations.

Amendment 2 to AIS 038 Rev. 2 – Specific Requirements for Electric Power Trains of Motor Vehicles of the M Category and N Category is also included, along with electric power trains.

Additional safety requirements for battery cells, BMS, onboard chargers, battery pack design, thermal propagation due to internal cell short circuits causing fire, etc. are included in these amendments.

With effect from 1st October 2022, the current battery safety standards recommend additional safety requirements.

Let’s talk about the most recent notification that will force modified AIS156 and AIS038 Rev.2 standards for the relevant categories of electric vehicles starting on October 1st, 2022.

The requirement strengthened safety in three key areas of the battery pack that are cell, BMS, and pack design. It also addresses the onboard/offboard charger, which was broadly covered by the AIS 156 and AIS 038 Rev.2 standards.

• Cell Level
• BMS (Battery Management system)
• Pack Level
• Charger

 

Cell Level:

• The manufacture date should be written in DDMMYY format on every cell. There are no acceptable codes.
• Based on their form factors, there should be enough room or distance between each cell.
• Cells from a NABL-accredited lab are in compliance with AIS 16893 Parts 2 and 3.
• A minimum of 5 charge and discharge cycles should be recorded for each cell.
• Cells need to be safeguarded in case of regeneration stops.

 

BMS (Battery Management system) Level:

• Microprocessor/Microcontroller circuits should be used to create BMS.
• All necessary safeguards against overcurrent, over-discharge, overvoltage, short circuit, and overtemperature must be present in a BMS.
• According to AIS 004 Part 3 or AIS 004 Part 3 Rev 1, as appropriate, BMS must pass the EMC testing.
• According to IS 17387, BMS should have a data logging feature.
• BMS ought to be able to read and write RF.

 

Pack Level:

• The pack needs to comply with IPx7.
• The Pressure Relief Valve (PRV) or a pressure vent should be incorporated into the pack’s design.
• Additionally, traceability documents are needed at the pack, cell, BMS, and charger levels.
• Test for thermal propagation.
• If a thermal event occurs, the system should have an audio-visual warning.
• The Pack must have four temperature sensors at the very least.
• FUSE or a circuit breaker should be used in the pack’s electrical architecture.
• There should be a paralleling circuit active in the pack.

 

Charger Level:

• A charge voltage cut-off for the charger is required for REESS.
• There must be a time-based charge cut-off feature on the charger.
• To begin charging, the charger needs to have a soft-start feature.
• To identify the over-discharge condition of the battery, the charger must have a pre-charge function.
• The charger must have a way to detect earth leaks.
• The battery must be able to communicate with the onboard or portable charger (BMS).

Automotive Research Association of India (ARAI) Ministry of Road Transport & Highways – India

 

Major Challenges:

• Time to upgrade the system based on the above changes.
• RFID tag implementation within the specified timeline.
• Rugged Testing of the required BMS features.
• Cyclic test on Cells

Summer is approaching fast. In every summer, scorching heat makes our life miserable. Making the matter worse, the frequency of power cuts increases in summer. Without any doubt, your inverter is your only savior in hot months of summer. Therefore, you should make sure that everything is fine with your inverter. Else, you will not get a proper backup from your inverter.