Week 1 Understanding Different Battery Chemistry

Aim:

1.Prepare a table which includes materials & chemical reactions occurring at the anode and cathode of LCO, LMO, NCA, NMC, LFP and LTO type of lithium ion cells.Give your detailed explanation on it.

2.Compare the differences between each type of Li+ion batteries based on their characteristics.

Battery:

• A Battery is a device consisting of one or more electrochemical cells with external connections for powering electrical devices such as Flashlights, mobile phones and electric cars.
• When a battery is supplying electric power, its positive terminal is the cathode and its negative terminal is the anode. 
• The terminal marked negative is the source of electrons that will flow through an external electric circuit to the positive terminal.
• When a battery is connected to an external electric load, a Redox reaction converts high-energy reactants to lower-energy products, and the free energy difference is delivered to the external circuit as electrical energy.

There are two types of batteries,

       1. Primary cell    - These batteries are one time use batteries and they cannot be recharged for further usage.

       2. Secondary cell - These batteries can be recharged and can be used for multiple times.

1. Primary cell 

A primary cell is a cell that is designed to be used once and discarded, and not recharged with electricity and reused like a secondary cell.

In general, the electrochemical reaction occurring in the cell is not reversible, and so these cells cannot be recharged.

Examples of these Cells are dry Cells, Daniel Cells, etc.

2. Secondary cell

A secondary cell is a cell that is designed to be recharged with electricity and reused many times. In general, the electrochemical reaction occurring in the cell is reversible, and so these cells can be recharged.

Lithium ion Cell:

• The Lithium ion batteries are secondary type of batteries which can be recharged for further usage.
• Lithium ion batteries can be designed for optimal capacity with the drawback of limited loading, slow charging and reduced longevity. An industrial battery may have a moderate ampere rating but the focus is on durability. Specific energy only provides part of battery performance. 
• Before looking into the materials and chemical reactions of different types of lithium ion batteries. A battery is made up of an anode, cathode, separator, electrolyte and two current collectors (Positive and negative). The anode and cathode store the lithium.
• The electrolyte carries positively charged lithium ions from the anode to the cathode and vice versa through the separator. The movement of the lithium ions creates free electrons in the anode which creates a charge at the positive current collector. The electrical current then flows from the current collector through a device being powered to the negative current collector. The separator blocks the flow of electrons inside the battery.

The Lithium ion cells have four main Components in it and they are,

1. Cathode 
2.  Anode  
3.  Electrolyte 
4.  Separator                                    

1. Cathode:

They are the positive electrodes of the cell.

The cathode electrode is usually made up of, 

1. Layered Transition metal oxides - Has high Capacity but high in cost and poor in safety.
2. Spinels - High power Density but poor in conductivity and stability.
3. Olivine's - Lees capacity but has long life and are high in safety.

2. Anode:

They are the negative electrodes of the cell.

The anode electrode is usually made up of, 

1. Graphite
2. Hard Carbon, these anodes are less in cost and high in stability and specific capacity.

3. Electrolyte:

•  An electrolyte is a substance that produces an electrically conducting solution when dissolved in a polar solvent.
• The dissolved electrolyte separates into cations and anions, which disperse uniformly through the solvent. 
• Generally Lithium ion cells have electrolytes of Organic solvents such as, Ethylene carbonate, dimethyl carbonate, propylene carbonate and lithium salt as solute.

4. Separator:

• Battery separators provide a barrier between the anode (negative) and the cathode (positive) while enabling the exchange of lithium ions from one side to the other.
• They are materials that conducts ions but they do not conduct the electrons through them.
• Li-ion cells use polyolefin as a separator. This material has excellent mechanical properties, good chemical stability and is low-cost as well.

Working of Lithium ion cell:

While the battery is discharging and providing an electric current, the anode releases lithium ions to the cathode, generating a flow of electrons from one side to the other. When plugging in the device the opposite will happen that the lithium ions are released by the cathode and received by the anode. The charging and discharging processes are shown. 

• The battery is made up of an anode, cathode, separator, electrolyte, and two current collectors (positive and negative), the anode and cathode store the lithium.
• The electrolyte carries positively charged lithium ions from the anode to the cathode and vice versa through the separator.
• The movement of the lithium ions creates free electrons in the anode which creates a charge at the positive current collector.  
• The electrical current then flows from the current collector through a device being powered (cell phone, computer, Electric motor etc.) to the negative current collector. The separator blocks the flow of electrons inside the battery.
• While the battery is discharging and providing an electric current, the anode releases lithium ions to the cathode, generating a flow of electrons from one side to the other.
• When charging, the opposite happens, where Lithium ions are released by the cathode and received by the anode.
• This is the working principle of a lithium ion battery.

Types of Lithium ion battery:

There are some types of lithium ion cells based on their chemical compositions.

These 6 commonly used lithium ion batteries are listed below.

• Lithium cobalt oxide (LiCoO2) - LCO.
• Lithium Manganese oxide (LiMn2O4) - LMO.
• Lithium Nickel Manganese cobalt oxide (liNiMnCoO2) - NMC.
• Lithium Iron phosphate (LiFePO4) - LFP.
• Lithium Nickel Cobalt Aluminium Oxide (LiNiCoAlO2) - NCA.
• Lithium Titanate (Li2TiO3) - LTO.

Each Lithium ion batteries provides different characteristics and are used in different applications accordingly.  

• Lithium cobalt oxide (LCO) battery was invented in the year 1991. Also known as lithium cobalt or lithium-ion cobalt batteries, lithium cobalt oxide batteries are made from lithium carbonate and cobalt. Its anode (negative electrode) material is graphite carbon (LiaC6), the cathode (positive electrode) material is cobalt oxide  (LibCoO2 ) and the carrier is Li+. During discharge, lithium ions move from anode to cathode, with the flow reversing when the battery is charging. It is used in various applications ranging from electronic devices to all laptops and phone batteries. The majority of lithium ion batteries for portable devices are cobalt based. This type of battery has some drawbacks, including a relatively short battery life and limited specific power.  additionally, these batteries are not as safe as other types.

• Lithium manganese oxide battery (LMO) is a lithium ion cell that uses manganese dioxide MnO2 as a cathode material. The first commercial lithium-ion cells made with lithium manganese oxide as a cathode material were produced in 1996 by Moli Energy. They function through the same intercalation/ de-intercalation mechanism as other commercialised secondary battery technologies such as LiCoO2. Cathodes based on manganese oxide components are earth - abundant, inexpensive, non - toxic and provide better thermal stability. Lithium manganese oxide batteries are notable for their high temperature stability and are also safer than other lithium-ion battery types. For this reason, they are often used in medical equipment and devices, but they may also be used in power tools, electric bikes and more. It is also possible to use lithium manganese oxide batteries to power laptops and electric powertrain cars.

             MnO2 + Li + +e--->LiMnO4 

• Lithium Nickel Manganese Cobalt Oxide (NMC) battery offer a combination a nickel, Manganese and cobalt. They are sometimes known as Lithium Manganese Cobalt oxide batteries. NMC batteries have a high specific energy or power.They cannot, however, have both properties. NMC batteries, include a cathode made of a combination of nickel, manganese and cobalt.The cathode combination ratio is usually 60 percent nickel, 20 percent manganese and 20 percent cobalt. This means that the raw material cost is lower than it is for other lithium-ion battery options, as cobalt can be quite expensive.These batteries may come down in price further in the future, as some battery makers are planning to switch their battery chemistry to a higher % of Nickel, so that they can use less cobalt. This battery type is most common in power tools and in powertrains for vehicles. This battery type is commonly preferred for electric vehicles due to its very low self-heating rate. 

• Lithium iron phosphate battery (LiFePO4) LFP. batteries which is known as Li - phosphate batteries as well. They use phosphate as cathode material. In addition they benefit from the low resistance properties that enhance their thermal stability and safety. Other benefits include durability and a long lifecycle — fully charged batteries can be stored with little change to the total lifespan of the battery’s charge. Li-phosphate batteries are often the most cost-effective option as well when their long battery life is taken into consideration. However, the lower voltage of the li-phosphate battery means that it has less energy than other types of lithium batteries. Accordingly, these batteries are often used in electric motorcycles as well as other applications that need a long lifecycle and significant safety.  

• Lithium Nickel cobalt aluminium oxides (NCA) battery has been around since 1999 for special applications. It shares similarities with NMC by offering high specific energy, reasonably good specific power and a long life span. NCA batteries are becoming increasingly important in electric powertrains and in grid storage.NCA batteries are not common in the consumer industry, but are promising for the automotive industry. NCA batteries provide a high-energy option with a good lifespan, but they are not as safe as they could be compared to other lithium-ion battery types and are quite costly.

• Lithium Titanate oxide (LTO) batteries is a type of rechargeable battery which has the advantage of being faster to charge than other lithium ion batteries but its disadvantage of having a much lower energy density. However, these batteries have lower inherent voltage, or lower energy density, than other lithium-ion battery varieties, which can present issues with powering vehicles efficiently. Even so, the density of lithium titanate batteries is still higher than other non-lithium-ion batteries, which is a plus. Currently, manufacturers of electric vehicles and bikes use li-titanate batteries, and there is potential for this type of battery to be used in electric buses for public transportation.

2) Compare the differences between each type of Li+ion batteries based on their characteristics

 The Major 6 types of lithium ion batteries was discussed early, Now the major differences in the characteristics can be found when choosing a battery. The major things that can be differentiated from one another.

• Nominal voltage : It is the system voltage at which the device is designed to operate. The rated voltage is usually higher than the nominal voltage to ensure the safe operation of the device.
• Cycle : The charge and discharge when took place for a single time makes a cycle. The higher the cycles can take place, the higher the cycles can takes place than the lifespan is higher.
• Thermal runway : The thermal runway begins when the heat generated within a battery exceeds the amount of heat that is dissipated to its surroundings.Internal battery temperature will continue to rise, causing the battery current to rise creating a domino effect. The rise in temperature in a single battery will begin to affect other batteries nearby and the pattern will continue.
• Specific energy : It is the amount of energy stored per unit mass (Wh/Kg). This is a very important deciding factor that decides how much energy or power from different batteries with the same amount of weight. 

• Nominal Voltage : Most of the batteries are very close when it comes to characteristics. LMO (3.7) has the highest range and LTO (2.4) has the lowest range in volts.
• Cycle life : They differ by a significant amount from each other. LTO battery has the longest life cycle so that it can last longer period of time and it is exactly opposite for the LMO type batteries.
• Charge current rate : Higher the charge current, the less time the battery will take to get fully charged. LTO and LTP are highest NCA comes close to its condensers.
• Discharge current rate : If we need higher discharge rates and faster charging times we should choose a high rated battery instead. LTO has a discharge rate 10 times higher than the others and it is one of the safest batteries.
• Thermal runaway : A thermal runaway occurs in situations where an increase in temperature changes the conditions in a way that causes increase in temperature often leading a destructive result. LTO has the highest temperature rating in this and NCA and LCP has its lowest.
• Specific energy : The specific energy density can be calculated by integrating from 0 to cutoff. We can obtain the specific energy density in Wh/Kg. Lithium ion with cobalt cathodes offer the highest energy densities. This types of applications are cell phones, laptops and digital cameras. Power density indicates how much power a battery can deliver on demand.

For ease of choosing a battery from layman's perspective, the 6 key features are given a value within 0-5 range for all of the, are given with the same parameters which are considered in case of 5 point hexagonal analysis of the batteries. They are

1. Specific energy.
2. Specific power.
3. Safety.
4. Performance.
5. Life span.
6. Cost.

LCO :

Li-cobalt excels on high specific energy but offers only moderate performance specific power, safety and life span.

 

LMO :

Although moderate in overall performance, newer designs of Li-manganese offer improvements in specific power, safety and life span. 

NMC :

NMC has good overall performance and excels on specific energy. This battery is the preferred choice for the electric vehicle and has the lowest self heating rate. 

LFP :

Li-phosphate has excellent safety and long life span but moderate specific energy and elevated self discharge.

NCA :

High energy and power densities as well as a good life span make NCA a choice for EV powertrains. High cost and marginal safety are negative.

 

LTO :

Li-titanate excels in safety, low temperature performance and life span. Efforts are being made to improve the specific energy and lower the cost 

• These types of lithium ion batteries are some of the most popular. As technology is continuously seeing more development, new lithium technologies are always being developed and those which exists are being developed. 

Lithium ion battery advantages

• High energy density:   The high energy density is one of the chief advantages of lithium ion battery technology. With electronic equipment such as mobile phones needing to operate longer between charges while still consuming more power, there is always a need to batteries with a much higher energy density.
  For example, NiMH batteries would not be able to provide the charge capacity required for a modern smartphone. Using Nickel Metal Hydride battery technology a smartphone would not last long enough, especially if the battery needed to keep within the same size constraints.
  In addition to this, there are many power applications from power tools to electric vehicles. The much higher power density offered by lithium ion batteries is a distinct advantage. Electric vehicles also need a battery technology that has a high energy density.
• Self-discharge:   One issue with many rechargeable batteries is the self discharge rate. Lithium ion cells is that their rate of self-discharge is much lower than that of other rechargeable cells such as Ni-Cad and NiMH forms. It is typically around 5% in the first 4 hours after being charged but then falls to a figure of around 1 or 2% per month.
• Low maintenance:   One major lithium ion battery advantage is that they do not require and maintenance to ensure their performance.
  Ni-Cad cells required a periodic discharge to ensure that they did not exhibit the memory effect. As this does not affect lithium ion batteries and cells. This process or other similar maintenance procedures are not required.
  Likewise lead acid cells require maintenance, some needing the battery acid to be topped up periodically.
  Fortunately one of the advantages of lithium ion batteries is that there is no active maintenance required.
• Cell voltage:   The voltage produced by each lithium ion cell is about 3.6 volts. This has many advantages. Being higher than that of the standard nickel cadmium, nickel metal hydride and even standard alkaline cells at around 1.5 volts and lead acid at around 2 volts per cell, the voltage of each lithium ion cell is higher, requiring less cells in many battery applications. For smartphones a single cell is all that is needed and this simplifies the power management.
• Load characteristics:   The load characteristics of a lithium ion cell or battery are reasonably good. They provide a reasonably constant 3.6 volts per cell before falling off as the last charge is used.
• No requirement for priming:   Some rechargeable cells need to be primed when they receive their first charge. One advantage of lithium ion batteries is that there is no requirement for this they are supplied operational and ready to go.
• Variety of types available:   There are several types of lithium ion cell available. This advantage of lithium ion batteries can mean that the right technology can be used for the particular application needed. Some forms of lithium ion battery provide a high current density and are ideal for consumer mobile electronic equipment. Others are able to provide much higher current levels and are ideal for power tools and electric vehicles.

Lithium ion battery disadvantages

• Protection / battery management system required:   Lithium ion cells and batteries are not as robust as some other rechargeable technologies. They require protection from being over charged and discharged too far. In addition to this, they need to have the current maintained within safe limits. Accordingly one lithium ion battery disadvantage is that they require protection circuitry incorporated to ensure they are kept within their safe operating limits.
  Fortunately with modern integrated circuit technology, this can be relatively easily incorporated into the battery, or within the equipment if the battery is not interchangeable. Incorporation of the battery management circuitry enables li-ion batteries to be used without any special knowledge. They can be left on charge and after the battery is fully charged the charger will cut the supply to it.
  The battery management system built into lithium ion batteries monitors a number of aspects of their operation. The protection circuit limits the peak voltage of each cell during charge as excessive voltage can damage the cells. They are typically charged in series as there is normally only one connection for a battery and therefore as different cells may require different levels of charge there is a possibility of one cell experiencing a higher than required voltage.
  Also the battery management or protection circuitry prevents the cell voltage from dropping too low on discharge. Again this can happen if one cell can store less charge than others on the battery and its charge becomes exhausted before the others.
  A further aspect of the battery management system is that the cell temperature is monitored to prevent temperature extremes. The maximum charge and discharge current on most packs is limited to between 1°C and 2°C. That said, some do become a little warm on occasions when fast charging.
• Ageing:   One of the major lithium ion battery disadvantages for consumer electronics is that lithium ion batteries suffer from ageing. Not only is this time or calendar dependent, but it is also dependent upon the number of charge discharge cycles that the battery has undergone.
  Often batteries will only be able to withstand 500 - 1000 charge discharge cycles before their capacity falls. With the development of li-ion technology, this figure is increasing, but after a while batteries may need replacing and this can be an issue if they are embedded in the equipment.
  Lithium ion batteries also age whether they are in use or not. Despite the usage there is also a time related element to the reduction in capacity.
  When a typical consumer lithium cobalt oxide, LCO battery or cell needs to be stored it should be partially charged - around 40% to 50% and kept in a cool storage area. Storage under these conditions will help increase the life.
• Transportation:   This li-ion battery disadvantage has come to the fore in recent years. Many airlines limit the number of lithium ion batteries they take, and this means their transportation is limited to ships.
  For air travellers, lithium ion batteries often need to be in carry-on luggage, although with the security position, this may change from time to time. But the number of batteries may be limited. Any lithium ion batteries carried separately must be protected against short circuits by protective covers, etc. It is particularly important where some of the large lithium ion batteries like those used in large power banks.
  It is necessary to check before flying whether a large power bank can be carried or not. Sadly the guidance is not always particularly clear.
• Cost:   A major lithium ion battery disadvantage is their cost. Typically they are around 40% more costly to manufacture than Nickel cadmium cells. This is a major factor when considering their use in mass produced consumer items where any additional costs are a major issue.
• Developing technology:   Although lithium ion batteries have been available for many years, it can still be considered an immature technology by some as it is very much a developing area. This can be a disadvantage in terms of the fact that the technology does not remain constant. However as new lithium ion technologies are being developed all the time, it can also be an advantage as better solutions are coming available.