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Intro to Lithium-ion

Lithium-ion batteries were invented in 1980 by John Goodenough; they were commercialized in 1991 by Sony. In the past decade, lithium-ion batteries have become the dominant rechargeable battery chemistry in nearly all industries. Lithium-ion, in comparison to previous popular chemistries, (Lead acid, Nickel-Cadmium, and Alkaline) is better in many ways. With the advancement in technology, a battery that is safe and powerful is in great need. Lithium is the most energy dense chemistry in use and with added features, can be the safest. Lithium energy is an active area of study, so new chemistries are being developed every year.

What Are Lithium-ion Batteries?

Intro

In the simplest terms, a lithium-ion battery refers to a battery with a negative electrode (anode) and a positive electrode (cathode) that transfers lithium ions between the two materials. Lithium ions move from the anode to the cathode during discharge and deposit themselves (intercalate) into the positive electrode, which is composed of lithium and other metals. During charge, this process is reversed.

Electron and ion flow during use

Within the cells, there are many layers of anode and cathode with a separator in between. Between the two plates, there is also an electrolyte solution, typically LiPF6 mixed with a liquid solution. This combination of materials can either be stacked (prismatic cells) or wound in a spiral (cylindrical cells). Cells vary in size and shape; some are encased in plastic while others are in aluminum cases. The casing is dependent on the environment they are going into and the size is determined by the amount of capacity needed for the application.

Each lithium-ion cell has a safe voltage range that it can be operated in. This range is dependent on the chemistry used in the battery. For example, an LFP battery at 0% State of Charge (SOC) is 2.5V and at 100% SOC is 3.6V. This is considered the safe operating range of this battery. Going below the stated 2.5V SOC can cause degradation of the electrodes. This is considered an over-discharge. If a cell is repeatedly over-discharged it can cause many issues that permanently damage the battery. The same is true for an over-charge, going above the stated 100% SOC. These two failures have led battery manufacturers to develop safety devices and features.

A battery is typically comprised of many cells working in conjunction with one another. Let’s consider an LFP cell with a nominal voltage of 3.2V and a capacity of 100 Ah. Most applications require a higher voltage and capacity, how would this be done? In order to increase the voltage of a battery, multiple cells must be connected in series. To increase the capacity, cells must be connected in parallel. For example, let's say we want a 12V battery with a capacity of 300 Ah. With the given LFP cell we would need 4 cells in series with 3 modules in parallel. This would produce a system that is 12.8V with a capacity of 300 Ah.

cell system diagram

 

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Definitions

Anode: The anode is the negative electrode in the cell. It is very common, in lithium-ion batteries, for it to be composed of lithium and carbon, usually a graphite powder. The current can be collected due to the copper film that is combined with the electrode. The purity, particle size, and uniformity of the anode all contribute to the aging behavior and capacity.

Cathode: The cathode is the positive electrode. This is where all the different chemistries come into play. The cathode is what determines the overall lithium chemistry. Like the anode, a current collector is combined with the material so the flow of electrons can occur. The cathode is typically combined with an aluminum film. As shown above there are many different chemistries. The key differences between them is temperature at which they react with the electrolyte (thermal runaway) and the voltages they produce.

Electrolyte: The electrolyte allows the transfer of the lithium ions between the plates. Typically, it is composed of different organic carbonates, such as ethylene, carbonate, and diethyl carbonate. The different mixtures and ratios vary depending on the application of the cell. For example, for a low temperature application the electrolyte solution will have a lower viscosity compared to one made for a room temperature environment. Lithium salts are essential in the mixture of the electrolyte, the salt determines the conductivity of the solution as well as aids in the formation of the solid electrolyte interface (SEI). In lithium batteries, lithium hexafluorophosphate (LiPF6) is the most common lithium salt. LiPF6 can produce hydrofluoric acid (HF) when mixed with water. The SEI is a chemical reaction between the lithium metal and electrolyte. Under normal conditions the cell manufacturer typically slow charges the cell to form an even SEI on the carbon anode.

Separator: Lithium-ion cell separators are porous plastic films that prevent direct contact of the anode and cathode. The films are usually 20 μm thick and have small pours that allow lithium ions to pass through during the charge and discharge process. A “shutdown” separator is the most common. This separator will close the pores to prevent lithium ions to pass through, once the cell is out of the temperature range or a short occurs. Separators continue to be developed today to improve safety, while also increasing the capacity of the cells.

Lithium-ion Vs Lead Acid Batteries

Intro

There are several reasons a company would opt to convert to lithium-ion power from their lead acid energy source.

Increased Efficiencies: Thanks to technological advances, like BMS and opportunity charging, lithium-ion-powered equipment can help improve a facility’s efficiencies and reduce downtime due to needing to recharge battery-powered equipment.

Boosted Productivity: Operators can worry less about charging their equipment and focus more on the task at hand. Lithium-ion battery technology also empowers companies to invest in automation and robotic solutions to bypass the need for human labor.

Easier Charging & Storage Protocols: Lithium-ion batteries can be opportunity charged - and thrive on it! That means you can charge when it is convenient for you.

Lithium-ion batteries also don’t need their own charging/storage space since they don’t come with the same hazardous/environmental risks that lead acid batteries do.

No Required Maintenance: Unlike lead acid batteries, lithium-ion batteries do not require tedious watering and maintenance. 

Improve Operational Safety: Lithium-ion batteries improve a facility’s operational safety in several ways.

1. They do not need to be removed as often since they can be opportunity charged.

2. Lithium-ion batteries are also environmentally safer because there is less risk of overheating, exploding, or discharging hazardous and toxic fumes or liquids.


State of Charge Comparison Over Time

Website-Discharge Voltage

 

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Definitions

UL Listed/Certification: Underwriters Laboratories (UL) Listed/Certification means that UL has evaluated samples of products to ensure that they meet specific requirements. This includes testing samples that cover functional safety and use cases.

Internal Combustion Forklift: A forklift with an engine that uses fuel to run. The fuel is burned within the engine which produces power directly to the forklift. Fuel is typically gasoline, diesel, liquified petroleum gas, or compressed natural gas.

Opportunity Charging: The practice of using natural periods of downtime, like operator meal breaks, to charge the battery for short periods of time throughout the day. This allows operators the continuous use of the same battery throughout multiple shifts.

Equalization Charging: Overcharging the battery after a full charging cycle at a higher-than-normal voltage. This step is necessary help remove built-up sulfate and balance the voltage of each cell in lead acid batteries.

Battery Degradation: The process that reduces the amount of energy a battery can store. Temperature, charge, and discharge voltage, current and the depth of charge and discharge can affect how much a battery’s capacity is reduced over time.

Battery Lifespan: How long a battery can operate during its life. Lifespan is measured by the number of completed charge and discharge.

Battery Cycle Count: The cumulative number of charges and discharges if the battery completes one charge and discharge as a cycle. The battery cycle is comprised of 100% discharge and charge.

Battery Operating Temperature: The acceptable temperature of the surrounding environment at which a battery operates. The battery may fail if the operating temperature is outside of the range.

Types Of Lithium-ion Battery Chemistries

Intro

Lithium energy is an active area of study so new chemistries are being developed every year. Some of the most popular chemistries are:

1. Lithium titanate (LTO)
2. Lithium cobalt oxide (LCO)
3. Lithium nickel manganese cobalt (NMC)
4. Lithium iron phosphate (LFP)

While these are all lithium batteries, there are key differences between them.

LTO has a very long life and a wide temperature range. They are capable of handling large charge currents greater than 10C. They have one of the lowest energy densities (2.4V/Cell) of all lithium batteries and are one of the most expensive.


LCO became very popular because of its high energy density (3.6 V/Cell). Cobalt is a very energy-dense material but is extremely volatile and expensive. It is a resource that is depleting quickly due to its recent increase in consumption. LCO has many negatives, it cannot handle large charge currents, are very sensitive to temperature, and have a short cycle life.


NMC is a rapidly developing chemistry, at the time this is written. The blending of nickel, manganese, and cobalt produces a very well-rounded battery. With a high energy density (3.6V/Cell) and a decreased use of cobalt, it has become one of the most desired batteries in the industry. Due to its lower cobalt concentration, it is safer than LCO. Its life cycle is longer than LCO but shorter than LTO. It can handle charge currents up to 2C and a greater range in temperature. It is also important to know that batteries that contain cobalt require more safety features which make the batteries more expensive.


LFP is popular in industries with heavy use and rough environments. While this chemistry has a slightly lower energy density (3.2V/Cell), it can withstand a lot of abuse. It has a long lifespan, it is less costly and much safer because it does not contain cobalt. It can even withstand a very wide range of temperatures. LFP can also withstand discharge currents up to 20C but typical usage patterns include 1C. Overall this is the safest and most reliable chemistry.

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Comparison of LTO, LCO, NMC and LFP

FP-battery-comparison-chart

Definitions

TPPL Battery: Thin Plate Pure Lead (TPPL) batteries are a type of lead acid battery which have electrodes that are thinner than traditional lead acid battery designs. TPPL batteries have a high rate of charge and discharge which increases the level of internal heat. This causes the life of a TPPL battery to deplete faster than other types of lead acid batteries.

AGM Battery: Absorbent Glass Mat (AGM) batteries are a type of lead acid battery which contain a glass mat separator. This separator absorbs the electrolyte solution between the battery plates like a sponge which keeps the battery water levels down so you don’t have to water them as constant as other lead acid batteries. However, if the battery is overcharged, gas pressure builds within the cell and will cause the battery to dry out and fail.

Battery Energy Density: The measure of how much energy a battery contains in proportion to its weight. This measurement is typically presented in Watt-hours per kilogram (Wh/kg). A watt-hour is a measure of electrical energy that is equivalent to the consumption of one watt for one hour.

Flooded: A flooded battery has plates, separators, and a high-density paste material. It uses a liquid electrolyte that submerges the plates. The liquid solution can be damaged in extreme temperatures due to evaporation or freezing. This requires watering and maintenance of the battery.

Battery Discharge Rate: The amount of current divided by the time it takes to discharge a battery. It is defined as the stable current in amperes (A) that is taken from a battery of specified capacity (Ah) over a period of time.

Battery Charge Rate: The amount of current divided by time it takes to charge a battery. It is the amount of charge added to the battery per unit time.

C-rating: The rate of time it takes to charge or discharge a battery. C-rating is another way of representing the charge or discharge rates, where 1C is equivalent to charging or discharging the entire capacity of the battery in one hour.

Battery Efficiency: The amount of energy that a battery delivers compared to the amount of energy that is put into it during charging. Factors that affect battery efficiency include charge current, internal resistance, battery temperature, and battery age.

Battery Overcharging: Overcharging a battery is charging a battery more than its designed capacity. This can create unstable conditions inside the battery, increase pressure, and cause thermal runaway. This can be damaging to the battery, the equipment, and the operator.

Battery Regulator: A battery regulator limits or controls the rate at which current is added to or drawn from batteries. This keeps the voltage in a circuit relatively close to the desired value of the battery.

Why Flux Power Uses LFP

Intro

We take pride in being experts in energy storage solutions. This is why we chose a superior battery chemistry that has been proven through decades of research and deployment in multiple applications. In addition, the energy storage solution chosen has numerous advantages over current lead acid technology.

Capacity & Cycle Life
All lithium chemistries have higher energy density compared to lead acid batteries. We use lithium-ion technology because of the dramatic increase in energy density over current lead acid battery solutions. We chose lithium iron phosphate (LiFePO4) because it has a specific energy of ~110 watt-hours per kilogram, compared to lead acids ~40 watt-hours per kilogram. What does this mean? Our batteries can be ~1/3 the weight for similar amp-hour ratings.

Not only do lithium-ion battery packs store more energy, but the cycle-lifetime far exceeds that of lead acid and many other lithium chemistries.

Every battery cell chemistry is affected by the depth of discharge, and the deeper the discharge, the shorter the lifespan. Our lithium-ion can be discharged to 80% while still maintaining long cycle lifetimes (>3500 cycles). Lead acid batteries experience drastic reductions in cycle life. In fact, at an 80% depth of discharge, lead acid batteries only last 1000-1500 cycles, meaning our batteries last 3x longer.


Speed & Efficiency
Our lithium-ion batteries are fast. They can be fast-charged completely and can handle ultra-fast charging up to 1C (a full charge in 1 hour). Lead acid can only be fast-charged up to 80% after which the charging current drops dramatically. In addition, our battery packs maintain excellent performance under discharge rates as high as 3C continuous (full discharge in 1/3 an hour) or 5C pulsed. Lead acid experiences dramatic voltage sag and capacity reduction by comparison. In fact, the discharge profile of a lithium-ion battery shows how voltage and power remain almost constant throughout its discharge, unlike lead acid. This means that even when the battery runs low, performance stays high.

There are also no memory issues, discharge and charge the battery at any point without consequence. With lead acid, failure to fully charge leads to sulfation which damages the batteries. This also occurs when storing lead acid while not fully charged. With our lithium-ion, store the battery pack at any state of charge except near zero.


Safety & Reliability
There are a wide variety of chemistries to choose from when looking at advanced lithium batteries. We chose lithium iron phosphate (LiFePO4) because it has three advantages that make it the obvious choice for tough jobs.

  1. It is thermally stable up to very high temperatures, meaning no thermal runaway. The batteries can be used safely in ambient temperatures up to 55°C (131°F). Operating lead acid batteries at this temperature reduces their cycle life by a whopping 80%.

  2. Lithium iron phosphate provides a remarkably long cycle life, with competing chemistries being either too expensive (lithium titanate), or too unstable (lithium nickel cobalt aluminum oxide).

  3. Lithium iron phosphate provides more power and more energy density than lead acid and many other lithium chemistries, so it’s perfect for demanding jobs, and efficient energy storage solutions.

Not all lithium batteries are created equal. There are several factors that go into creating a battery that is high-performing, long-lasting, and most importantly, safe. One major factor to consider is UL certification, or at a minimum making sure the battery is designed to UL standards.

Did you know lithium-ion battery packs are maintenance-free? No electrolyte must be added and there is no danger of acid spills or dangerous vapors. In our case studies, fewer batteries were needed when compared to lead acid, so no storage room is required.

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Five Year Savings with Lithium-ion Batteries

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Definitions

Ergonomic Risk: Situations that may present risks to people. These include any physical wear and tear on the body or injury related accidents.

UL Recognized: UL Recognized does not apply approval for complete products. Instead, it focuses on components and parts that are used within other products. It certifies that a component within a larger mechanism meets UL standards. UL Recognized is easier to attain than UL Listed.

Class 1 Forklift: Also known as electric motor ride forklifts, Class 1 forklifts can be stand up or sit-down models. These forklifts can include counterbalanced or three-wheel trucks. These forklifts can handle a capacity of 8,000 lbs. or more, making them essential when lifting heavy materials throughout a facility.

Class 2 Forklift: These forklifts are used for multiple applications and can include order pickers, turret trucks, narrow aisle forklifts and more. Many of these forklifts are designed to operate in tight spaces and narrow aisles.

Class 3 Forklift: These forklifts include pallet jacks, walkie stackers, end riders and center riders. Class 3 forklifts are designed to lift loads a few inches off the ground for transportation. They have minimal lift capabilities (i.e. lifting a pallet off the ground) used to transport materials throughout a facility.

Current Rating: The maximum current that a fuse will hold for an amount of time without degrading the fuse.

Thermal Stability: Stability of a fluid and its ability to resist breaking down under heat stress. If the heat reaches max temperatures, the fluid will deteriorate.

SEI Film: SEI film (solid electrolyte interphase) is a layer that is formed from the decomposition or breaking up of the electrolyte of the battery. This is important for lithium-ion batteries because it affects the cycle life.

Internal Resistance: Internal resistance is the resistance in a battery which causes a drop in the source voltage when there is a current. Internal resistance restricts the voltage delivery and determines the battery’s runtime.

Battery Management System

Intro

All of our energy storage solutions use a patented Battery Management System (BMS) which monitors the battery life and provides valuable information to the end user. The system uses a Battery Management System Module (BMSM) to monitor up to 4 individual lithium iron phosphate cells. The BMSMs then report to the Battery Control Module (BCM), which can manage up to 28 BMSMs. This means our lithium-ion is a scalable solution for almost any application.

A State of Charge LED indicator tells the end user how much energy is left in the battery pack and can display several diagnostic trouble codes for monitoring battery and system health. It will also notify the user if recommended operating temperature is exceeded, or if battery servicing is required. In addition, a warning buzzer sounds when the battery is close to empty, so you will know when to plug it in.

When the battery charges, the BMS performs an auto-balancing of the cells near the top of charge and notifies the end user when finished. This auto-balancing feature is a vital component and enables the end user to get the longest cycle lifetime and best performance out of our batteries. At times balancing may be required. In these cases, the LED indicator notifies the end user, and the system should be fully charged until all cells are balanced. Finally, if for any reason the user needs to interface with the BMS, it uses the robust automotive standard CAN protocol.

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Industry 4.0

Industry 4.0 graphic

Definitions

Battery Management System: The brain of the battery pack. It manages the operation of a battery pack. The BMS also allow users to monitor cells within a battery pack. It can provide the status and health of a battery.

Forklift Telematics Systems: Forklift tracking devices that send, receive, and store data on one forklift or up to an entire fleet of forklifts. This lets users monitor forklifts to make operative decisions.

Industry 4.0: The fourth industrial revolution. It is the automation of conventional manufacturing and industrial applications. Industry 4.0 will use modern smart technologies including artificial intelligence (AI), robotics, Internet of Things (IoT), genetic engineering, quantum computing, and others.

Industrial Internet of Things: The interconnected sensors, instruments, and other devices connected together with computers’ industrial applications, including manufacturing and energy management. In use cases, smart devices may be deployed in vehicles, robotics, power systems, and more.

Cell Balancing: The equalization of voltages and state of charge among the cells within a battery when they are at full charge. This is a practice that preserves the capacity of a battery pack with multiple cells.

Battery State of Health: This refers to the battery’s life and reflects the ability of a battery to deliver and receive charge. The SOH is the comparison of a battery’s releasable capacity compared to the capacity of an identical new battery.

Cathode Electrolyte Oxidation: The electrochemical reaction that occurs in the cell of a battery. The cathode oxidizes the electrode which acquires electrons from the circuit and the cathode is reduced during the electrochemical reaction. The electrolyte acts as a medium that provides the ion transport mechanism between the cathode and anode.

Thermal Runaway: When heat generated in a battery exceeds the amount of heat that is dissipated to its surroundings. In batteries this occurs when a cell exceeds a specific high temperature which varies by chemical composition, because of thermal failure, mechanical failure, short circuiting, and electrochemical abuse.

Equivalent State of Charge: The level of charge for a battery related to its capacity. The SOC determines the remaining capacity and energy available in a battery pack.

Predictive Maintenance: Using data to analyze the condition of equipment and forecast when maintenance is needed.

Lithium-ion Battery Applications

Intro

Lithium-ion batteries are used across multiple sectors, from industry to medical, automotive and electronics.

There are at least a dozen different chemistries that comprise lithium-ion batteries. Because of its high energy density, however, lithium-ion batteries that feature a lithium iron phosphate chemistry are most often used in material handling operations.

Material handling equipment powered by this type of lithium-ion battery include:

  • Counterbalanced forklifts

  • Narrow aisle forklifts

  • Walkie stackers and pallet jacks

  • End and center riders

  • 3 Wheel Forklifts

Lithium-ion batteries with lithium iron phosphate chemistry also play an important role in ensuring airport operations run smoothly and efficiently. While this leading-edge technology reduces long-term costs and improves workflow, lithium-ion batteries also provide a cleaner technology that many airports are seeking today. The use of this green technology also helps reduce human impacts on the airport environment.

Electric ground support equipment powered by lithium-ion batteries include:

  • Pushback tugs

  • Airport belt loaders

  • Airport container loaders

  • Airport luggage tugs

  • Airport baggage carts

Lithium-ion batteries featuring a chemistry of lithium nickel manganese cobalt oxide (NMC) also are found in some equipment fleets, though this type of battery is a more popular choice in electric vehicles such as:

  • E-bikes

  • Buses

  • Other electric powertrains

The future of electric-powered products is already here. The advantages of switching from conventional power sources are too good to ignore. As more industries and businesses become aware of the benefits of lithium-ion technology, the business decision to switch over is becoming a much easier one to make.

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Definitions

Airport Ramp Equipment: Used for the loading and unloading of cargo and passenger bags in airports. It is also used to transport baggage, mail, and other cargo to and from the airport terminal and plane.

Ground Support Equipment: The support equipment used at an airport to provide service. This includes refueling, towing airplanes, towing luggage, loading luggage, transporting passengers, and other airport services.

Electric GSE: Electrical equipment that is used at an airport to service airplanes between flights. Electric GSE offers benefits such as energy efficiency, zero emissions, and others.

Battery Cooldown Period: Batteries produce a considerable amount of heat when charging, so they require a battery cooldown period. This allows the battery temperature to decrease after charging for a prolonged amount of time.

Ideal Temperature Range: All batteries have defined operating temperature to maximize their lifespan and ensure safety. Lithium-ion batteries should be charged within a range of 32°F to 131°F, and discharged between -4°F to 131°F.

Voluntary Airport Low Emissions Infrastructure Program: The Voluntary
Airport Low Emissions Infrastructure Program (VALE) is a national program designed to reduce sources of airport ground support emissions. This program improves current airport air quality.

Voluntary Airport Zero Emissions Vehicle Infrastructure Program: A program that facilitates the use of zero emissions technologies to improve airport air quality. The program allows airport sponsors to use funds to buy zero emissions vehicles and to build or improve infrastructure which is necessary to use zero emissions vehicles.

AGV: Automated guided vehicles (AGV) are vehicles designed to perform material handling or load carrying without the use of an operator or driver. AGVs are guided by sensors, markers, tape, or wires in the facility and have a fixed navigational route.

AMR: Autonomous mobile robots (AMR) are more technologically advanced than AGVs. They move around the facility based on the most efficient path using sensors and cameras. AMRs can navigate around obstacles, adapt to its surroundings, and avoid anything in their way.

Warehouse Automation: The process of automating warehouse activities with minimum human assistance. Warehouse Automation solutions include automated storage retrieval systems (AS/RS), automated guided vehicles, Autonomous mobile robots, automated sortation systems, picking systems, and more.

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