LIB USAGE GUIDELINES

Lithium ion battery is a type of rechargeable battery with wide domain of applications right from Mobile to Mobility along with portable electronic devices, laptops, tablets, etc.

Compared with the traditional batteries, lithium‐ion battery charge faster,last longer, is lighter and have more cycle life.

Cathode, Anode, Electrolyte, and Separator are four maajor components of LIBs. In all variants of LIB except LTO, graphite is commonly used at anode and an intercalated lithium compound at cathode.

The capacity and voltage of a LIB is dependent on the cathode chemistry, while the charge and discharge rate of a battery depends on the anode. Performance of LIB is limited by Anode.

Like any other batteries, life of Lithium ion battery is function of cyclic life associated with that relevant lithium ion battery chemistry. With every charge and discharge cycles, there is proposinate internal corrosion and electrolyte and electrode degradation deterioration, and this is finally leads to end of life for battery. Unlike most of other batteriesm in case of Lithium-Ion batteries the Charging and Discharging function requires strick control and subsequent monitoring to make them safer, and avoid premature failures.

The control and management system facilitating proper functioning of Lithium ion batteries within the predefined limits associated with relevant chemistry is referred to as BMS (Battery Management System). Also, Properly designed associated charging equipment is paramount for optimized performance of Lithium ion Battery Systems.

Due to thermal runaway isses associated with Lithium Ion Batteries (Lithium Titanate Battery is exception), comprehensive microprocesser based software assisted protection design for proper temperature sensing of lithium ion batteries during Charging and Discharging is very important.

Discharging LIBs....Guidelines

The minimum voltage at which a Lithium-ion battery can be considered to be "fully discharged" or "empty" depends on the specific chemistry and design of the battery. Depending on type of Chemistry of LIB manufacturer defines and recomends minimum voltage for a complete discharge which may be around 1.8 to 3.0 volts per cell. However, it is not recommended to fully discharge a lithium-ion battery, as this can damage the battery and reduce its lifespan.

It is important to note that fully discharging a lithium-ion battery can damage the battery and reduce its overall capacity, so it's recommended to recharge the battery before it gets too low.

Reason for Prematured degradation of LIBs.....

Lithium-Ion batteries, if subjected or used under stressed conditions namely high temperatures, overcharging, high current, over charging/discharging, high mechanical stress degrades Lithium Ion batteries, and may result in hazardous fire due to thermal runaway.

Temperature:LIBs if used under higher than rated temperature results in acceleration of chemical reactions in LIB resulting in substantial capacity loss and increase in internal resistance, and risk of thermal runaway.
Every 10 degree rise in working temperature of LIB reduces usable cycle life by 50%

High Current: LIBs if subjected to higher C rating then prescribed, results in overall rise of battery temperature giving rise to parasitic reactions within LIB. This sitiuation results in faster degradation of battery active material, and increases internal resistance of battery.

Over Charging/Discharging: Over Charging or Over Discharging LIBs results in change of structure of active electrode structure leading to unwanted side reactions and formation of solid electrolyte interface (SEI) layer on the electrode surface. This formed layuer reduces the battery capacity and increase of internal resistance of battery.

As excessive Over Charging/Discharging cycles results in increase in LIB temperature which subsequently results in decomposition of electrode material further resulting in generation of gases causing swelling and prematured failure of battery.

Also, high charging rate at low temperature can result in lithium plating on anode, leading to reduction of battery capacity and increasing risk of internal short circuit and subsiquent thermal runaway.

Mechanical Stress: Vibrations, Shocks, and other form of Physical Stress leads to mechanical failure of cell structure causing internal short circuit and therafter risk if thermal runaway.

Factors affecting Performance Efficiency of Lithium Ion Batteries

The efficiency of a Lithium-ion battery depends on several factors such as the manufacturing technology, the charging and discharging methods, the temperature, depth of discharge and storage conditions.

Actual efficiency of Lithium Ion Battery depends on its specific application and usage scenario. Generally, a Lithium-ion battery has over 80% to 90% of efficiency. The high efficiency is due to the low internal resistance of Lithium-ion batteries, which reduces the amount of energy lost as heat during charging and discharging. However, it's important to note that the efficiency can decrease over time and with usage, so proper maintenance and care are necessary to maintain it's efficiency.

Capacity Loss/Aging evaluation of Lithium Ion Batteries

The capacity loss of the battery is a non-linear process containing complex aging mechanism. However, the aging mechanism of batteries cannot be precisely described, especially for the decay rules of cycle life. To properly analyze the Lithium-ion battery aging, the degradation is divided into two form namely Calendar aging and Cyclic aging.

Calender Aging: Calendar aging refers to the capacity loss during storage, which is mainly influenced by high temperature and SOC. Degradation occuring over aperiod of time irrespective of usage, resulting in capacity fade, and ability of LIB to deliver power due to increase in internal resistance of battery.

Cyclic Aging: Degradation caused due to regular charging /dicharging cycles resulting in capacity fade, and ability of LIB to deliver power due to increase in internal resistance of battery.
However, cycling aging is always accompanied by calendar aging in an actual application, which makes it complicated to clarify the degradation procedure. Cycling aging is dominant reason for battery aging.

Benifits of Discharging LIBs below C Rating

If LIB is discharged at a rate that is below its specified C rating, it is typically more efficient in terms of usable energy compared to discharging it at a higher rate. By discharging the battery at 50% of its C rating, the battery is being used within its design specifications, and will therefore experience less stress and operate more efficiently.

At lower discharge rates, the battery can maintain a higher average voltage during discharge, which means that it can deliver more usable energy and higher capacity.

At lower discharge rates, LIB experiences less self-heating and is able to maintain a higher average voltage during discharge, which can help to preserve its usable energy, therby increasing the efficiency of LIB.

It is important to note that the exact improvement in efficiency will depend on the specific battery chemistry and design and also the discharge cycle characteristics.

Effect of Discharging LIB above specified C Rating

Discharging LIB above it's C rating is generally not recommended and can have a negative impact on the usable energy density. It's important to adhere to the manufacturer's recommended operating practices and discharge the battery at or below its rated C rate to ensure optimal performance and maximum usable energy density.

Discharging a battery above its C rating causes the battery to experience higher levels of stress and degrade more quickly than if it were discharged at or below its rated C rate it was designed for, resulting in......

Capacity loss: Discharging a battery above its C rating can cause it to lose capacity more quickly than if it were discharged at a lower rate, leading to a decrease in usable energy density.

Voltage Sag: Discharging a battery above its C rating can cause voltage sag, which is a temporary decrease in voltage that occurs when high current is drawn from the battery. This can reduce the amount of usable energy that can be extracted from the battery, as the voltage will recover only once the discharge rate is reduced.

Temperature rise: Discharging a battery above its C rating can cause it to generate more heat than intended, which can damage the battery and lead to a decrease in its usable energy density. Every 10 degree rise in working temperature of LIB reduces usable cycle life by 50%

Thermal Runaway in LIB explained.

Thermal runaway is a self-accelerating exothermic process that can occur in lithium-ion batteries under certain conditions. It is characterized by an increase in temperature and pressure within the battery that can lead to the release of flammable gases or even explosion.

The thermal runaway occurance may get initiated by a number of factors such as overcharging, mechanical damage, high temperature, and internal cell shorts. Once initiated, the heat generated by the reaction causes neighboring cells to undergo the same process, causing a chain reaction and leading to a rapid increase in temperature and pressure.

The reason for this phenomenon is that lithium-ion batteries store a large amount of energy in a small volume. When this energy is rapidly released, it can result in a buildup of heat and pressure that cannot be dissipated quickly enough, leading to thermal runaway.

To prevent thermal runaway, lithium-ion batteries are designed with safety mechanisms such as thermal management systems, voltage monitoring, and current limiting, popularly referred as BMS (Battery Management System).
Additionly, proper handling, storage, and charging practices can also help to minimize the risk of thermal runaway in lithium-ion batteries.

Thermal Runaway event oocurance step-wise scenario

1. SEI Layer Decomposition starts at 60 deg C to 70 deg C

2. Anode Reaction: Decomposition of SEI layer further increases temperature and at 110 deg C, Solvent starts reacting with Anode

3. Separator Melting: Owing toon going Anode-Solvent reaction the temperature within LIB cell further rises, and at 130 deg C Separator melts down

4. Electrolyte decomposition:LIB electrolyte decomposition gets initiated upon temperature reaching 150 deg C

5. Cathode Reaction: Depending on Chemistry of Cathod active material composition Cathode-Solvent reaction gets initiated from 170 deg C to 300 deg C, and this is final stage.

Broadly Thermal Runaway occurance can be classified in 3 Stages

Stage-1: Decomposition of SEI Layer

Stage-2: Melting of Separator

Stage-3: Cathode Decomposition + Electrolyte Oxidation

Safety, Efficiency and Life of LIB-Pack is BMS dependent

Battery Management System (BMS) enhances efficiency and performance of LIB by getting most out of battery pack ensuring safety and extension of usable life of LIBs.

Incorporation of Battery Management System (BMS) improves battery life and efficiency through continous monitoring of battery's voltage and current, preventing overcharging or discharging of LIB beyond its rated voltage, thus avoiding damage to the battery.

In addition, BMS also monitors individal cells to ensure that each individual cell in the battery pack is working at the same voltage and capacity, which helps to improve the overall performance and longevity of the battery.

BMS also controls the charging rate of the battery, preventing it from charging too quickly or too slowly. This functionality ensures that the battery is working in a safe and stable manner.

Temperature management is key function of BMS. BMS continously monitors the temperature of the battery through specific algorithium methodology, and is programmed to take protective measures such as shutting down charging or discharging to ensure saftey and prevention of damages in case of any abnormal thermal proile caused by overheating or extreme cold.

Battery Management System (BMS) for LIBs....an Overview

Lithium ion battery Power-Pack consist of large number of individual Lithium ion cells. Ideally it is expected that all individual cells in power-pack should at same voltage level. However, due to mismatch in leakage currents in the cells, the cell voltages begin to diverge over time and the cells acquire unequal voltages.

Lithium-ion batteries are known for their high energy density, but they can be dangerous if not handled carefully. Lithium batteries are particularly sensitive to over charging and extreme temperatures. Prolonged operation of the battery in sub-optimal conditions can result in safety hazards and also reduce the battery life significantly.

To mitigate the narrated problem statement Battery Management System (BMS) an electronic device is incorporated with a multi-cell battery pack of LIB to ensure safe operation of the battery and monitor its operational state. BMS monitors the battery's voltage, temperature, and current to ensure that LIB pack operates within safe limits and prevents overcharging, over-discharging, and overheating.

Battery Management System safeguards the battery pack by protecting it from over charging, deep discharging, over current, over temperature, etc. Apart from providing safety, a BMS also increases the operational life of a battery. The most important features of the BMS include.......

Over charge protection

Deep discharge protection

Over current protection

Short circuit protection

Over temperature protection

Cell voltage balancing

BMS should also equiped with capability of digital communication ports for communicating real time battery parameters to an external computer system or a master controller.

Various types BMS Communication Protocol.

A Lithium-ion battery pack management system (BMS) uses various protocols to communicate and transmit data between the battery cells and the battery management unit (BMU). The following are some commonly used protocols in the Lithium-ion battery pack BMS:

1. CAN Bus: Controller Area Network (CAN) Bus is a widely used protocol for the communication between the battery cells and the BMU. It is an efficient and reliable protocol that can handle large amounts of data and supports long-distance communication between the battery cells.

2. SMBus: System Management Bus (SMBus) is a simple and low-speed protocol that is used to communicate between the battery cells and the BMU. SMBus enables the BMU to monitor the battery cells' voltage, temperature, and state of charge.

3. I2C: Inter-Integrated Circuit (I2C) is a low-speed serial protocol that is used to communicate between the battery cells and the BMU. I2C is an efficient protocol that can handle small amounts of data and supports two-way communication between the devices.

4. RS485: RS485 is a serial protocol that is used in medium to long-distance communication between the battery cells and the BMU. RS485 is a reliable and flexible protocol that can handle multiple devices on the same bus and supports a high data transfer rate.

5. Modbus: Modbus is a serial communication protocol that is widely used in industrial applications. It is a simple and efficient protocol that can handle large amounts of data and supports communication between multiple devices on the same bus.

Note: Selection of the protocol for use in BMS is based on the application-specific requirements such as data transfer rates, distance, and the number of devices on the bus.

Mitigation of Hacking/Cyberattack concerns associated with BMS Protocol.

Any protocol that is not properly secured, encrypted, or authenticated can be vulnerable to hacking attacks. However, some protocols may be more susceptible to attacks than others due to their design or implementation, due care and extra precautions should be taken for high end LIB Power-packs for Grid, Defense, and other important utility applications.

CAN Bus has been identified as a potential security risk for lithium-ion battery pack BMS systems. CAN Bus was designed for use in automotive and industrial applications and was not intended to provide security or encryption. As a result, it is vulnerable to various types of attacks, including denial of service, spoofing, message injection, and man-in-the-middle attacks.

SMBus and I2C protocols can also be vulnerable to hacking attacks if they are not properly secured. These protocols lack encryption and authentication, making them susceptible to various types of attacks, including snooping, injection, and replay attacks.

RS485 and Modbus protocols is generally considered to be secure for lithium-ion battery pack BMS systems. However, the security of these protocols depends on the implementation of the system and the measures in place to prevent unauthorized access and ensure data integrity.

Note: Overall, security of the lithium-ion battery pack BMS system depends not only on the protocol used but also on the implementation of the system's security measures, such as encryption, authentication, access controls, and regular updates.
A well-designed and properly secured BMS system can help ensure the safety and reliability of the battery pack while mitigating the risks of hacking and cyber attacks.

Battery Pack Cooling Requirement/Conditions.

Like any other batteries, Lithium-ion batteries stores energy and releases the same on demand, it is during these activity LIBs generate heat. This generated heat can affect LIBs performance, lifespan, and more importantly Safety may get compromised. Normally, air cooling/liquid cooling is deployed as part of thermal management mechansim.

There is no size/capacity related thumb rule for incorporation of cooling mechansim for Lithium-Ion battery Power Pack. In general smaller LIB packs such as those used in portable consumer electronics or low-power electric vehicles, typically do not require cooling. These packs typically have a capacity ranging from a few hundred millamperes per hour to a few kilowatt-hours.

Larger Lithium-ion battery packs used in high-power applications such as electric vehicles, grid storage, aerospace, etc may require cooling due to the high heat generated during operation. These packs typically range from several kilowatt-hours to hundreds of megawatt-hours.

The requirement of cooling in LIB pack depends on several factors, including the chemistry of the battery, the size of the pack, the operating environment, and the desired/required performance is also a critical deciding factor.

Types of Cooling Mechanism deployed for Lithium-ion Battery Packs.

Depending on Type of LIB Chemistry, Size of LIB Pack, Operating environment, and load power density requirement, desired thermal management mechanism is deployed. The different type of cooling/Thermal management mechanism for Lithium Power pack is as below:

Forced Air Cooling: This is the basic mechanism predominately deployed for cooling of LIB pack. Air cooling is simple and cost-effective thermal system, but due to it's low heat transfer capability it is not very efficient, and cannot be deployed for high-performance applications.

Liquid Cooling: In this type of thermal management mechansim Water-Glycol based coolant liquid, an isolated flow-away path is incorporated around the cells within the power-pack. When compared with Air cooling, this liquid cooling exhibits better heat transfer capability, but increases system complexity, weight and cost. It is obsereved that LIB packs equiped with Liquid Cooling system typically suffers from uneven cooling resulting in temperature gradients within the LIB pack, and thereby resulting in uneven aging of the cells and loss of performance and capacity thereof.

Immersion Cooling: Limitations of liquid cooling can be effectively addressed by submerging the battery cells directly into a dielectric liquid coolant. This liquid coolant is electrically non-conductive with superior heat transfer characteristics. This type of cooling system is known as Immersion Cooling.
Immersion Cooling mechansim offers better overall temperature uniformity amongst cells, and system's self consumption of energy can be controlled and optimized by coolant's flow rate, specific heat capacity, viscosity and by addition of thermally conductive additives in this coolant.