Lithium-ion Li-ion) batteries are becoming popular in many portable electronic devices due to their high energy density, lack of memory effect, and high charge and discharge rate capabilities. Lithium-ion batteries are a relatively new technology, launched in 1990s, and research and development work is ongoing to improve safety and increase capacity, charge/discharge rate, and lifetime. Lithium-Ion batteries are mostly used in power banks, clocks and cameras.
Lithium-ion technology has its roots in primary batteries with metallic lithium negatives. Early attempts to produce rechargeable lithium batteries were thwarted by the poor cycling characteristics and safety issues associated with metallic lithium and it was not until an announcement by Sony in 1990 that the lithium-ion battery of today could be envisaged. Sony developed a carbon negative that allowed the intercalation of ionic lithium and paired it with a high-voltage positive material using lithiated cobalt oxide. Pioneer work with the lithium battery began in 1912 under G.N. Lewis but it was not until the early 1970s when the first non-rechargeable lithium batteries became commercially available. lithium is the lightest of all metals, has the greatest electrochemical potential and provides the largest energy density for weight.
The first commercial lithium-ion battery apperared in the year 1991. Though this was preceded by several separate inventions that included the owrk of Yazami and others. The use of the intercalated carbon and graphite anode eliminated the problems of poor lithium metal rechargeability due to the formation of denrites and mossy lithium metal deposits with only a small voltage penalty. It also greatly increased the safety aspects of the high energy battery system. The market of the Lithium-Ion batteries is driven by the demand of the portable electronic device market, especially power banks and the notebook computer.
Advantages of Lithium-Ion Batteries
The most important advantage of lithium-ion batteries is their high energy density. They have a long cycle life and do not suffer from the high self-discharge rate and memory effect of nickel-cadmium (NiCd) and nickel metal hydride (NiMH) batteries. Unlike sealed lead acid (SLA) and NiCd, Li-ion batteries do not contain toxic heavy metals. Lithium-ion is a low maintenance battery, an advantage that most other chemistries cannot claim. There is no memory and no scheduled cycling is required to prolong the battery’s life. In addition, the self-discharge is less than half compared to nickel-cadmium, making lithium-ion well suited for modern fuel gauge applications. lithium-ion cells cause little harm when disposed.
Some rechargeable cells need to be primed when they receive their first charge. There is no requirement for this with lithium ion cells and batteries. 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 batteries take a fraction of the time taken by other batteries to charge. This is one of the main reasons why these batteries are preferred over the others, especially in gadgets and other devices that require frequent charging.
Disadvantages of Lithium-Ion Batteries
Despite its overall advantages, lithium-ion has its drawbacks. It is fragile and requires a protection circuit to maintain safe operation. Li-ion batteries requires careful attention to safety. Overcharging, overheating, or short-circuiting a charged Li-ion battery can result in fire or explosion. For a safe and long-lasting product, Li-ion specific safety issues must be taken into account in product design.
Aging is a concern with most lithium-ion batteries and many manufacturers remain silent about this issue. Some capacity deterioration is noticeable after one year, whether the battery is in use or not. The battery frequently fails after two or three years. It should be noted that other chemistries also have age-related degenerative effects. This is especially true for nickel-metal-hydride if exposed to high ambient temperatures. At the same time, lithium-ion packs are known to have served for five years in some applications.
The production of lithium-ion batteries can be a rather expensive affair. In fact, the overall production cost of these batteries is around 40% higher than that of nickel-cadmium batteries. A lot of restrictions are in place for the transportation of lithium-ion batteries especially large quantities by air, although you can carry a small number of batteries along with you in your baggage when you fly. Lithium ion battery technology is 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.
Types of Lithium-Ion Batteries
Lithium-Ion battery refers to a diverse family of battery chemistries. All Li-ion batteries use a process known as intercalation, in which lithium ions are incorporated into the structure of the electrode material. Lithium ions move from the positive to the negative electrode during charging and from the negative to the positive electrode as the battery is discharged.
Positive Active Materials
The use of lithiated cobalt oxide (LiCoO2) by Sony has already been mentioned, and this material has remained the predominant positive material in the portable battery industry. Cells using LiCoO2 have high energy density and cycle life of around 500-700 deep discharge cycles, making them a good choice for many consumer applications. The main issue with this
material, as highlighted by the laptop battery recalls of 2006 and beyond, is that when abused it can release large amounts of energy, potentially resulting in a fire.
The adverse safety aspects of LiCoO2 have led researchers to search for alternative materials for the positive electrode. One such material that is in limited production for consumer applications is lithiated manganese oxide, LiMn2O4, also known as spinel for its crystal structure. This material yields cells with similar voltage characteristics and energy density to cobalt-based cells. Safety is much improved but unfortunately these cells exhibit rather rapid capacity fading.
Negative electrode materials
Graphite is by far the most common material for the negative electrode, but some other technologies are under development. Lithium Titanate offers very high cycle life, faster charging, and better safety than graphite, but at a cost of much lower energy density. These batteries are starting to become available commercially, mainly for electric vehicles and grid energy storage.
An additional benefit for lithium titanate is seen in fast charging. Conventional graphite negatives operate at a voltage only about 150 mV higher than that of lithium metal. The SEI on those negatives has a certain resistance to passing lithium ions and if the charge current exceeds a value that would result in a 150 mV drop across the SEI, lithium ions will be deposited on the surface of the SEI instead of passing through. When not taken to extremes, this lithium plating process does not constitute a safety risk but nevertheless damages the cell and reduces its life. The higher voltage of lithium titanate negatives allows them to be charged at a much higher rate, sometimes in as little as five minutes. Of course, higher negative electrode voltage leads to lower cell voltage, so energy and power density suffers accordingly. Thus cells with lithium titanate negatives will be of little practical value except in the few applications in which fast charging is vitally important.
Charging And Discharging in Lithium-Ion Batteries
- During charging the battery, the lithium ions flow from the positive electrode to the negative electrode through the electrolyte. Electrons tend to flow in the opposite direction around the outer circuit.
- When all the ions stop flowing, the battery is supposed to be fully charged and ready to use.
- During discharging the battery, the ions flow back from the negative electrode to the positive electrode. Electrons tend to flow the opposite way through the outer circuit , powering our laptop
Safety factor in Lithium Ion Batteries
Battery safety is a matter of crucial importance to the lithium battery industry. In large size batteries the safety problems are more serious as compared to the small size batteries i.e. batteries for electric vehicle would have more risk of catching fire or explosion as compared to batteries for laptops and power banks. When phosphate is used as cathode material in a lithium iron phosphate battery, we get very safe battery. Phosphates can withstand high temperatures and hence they are extremely stable in overcharge or short circuit conditions. Charging lithium ion batteries to above 4.6 V cell, when using lithium metal oxide cathodes and flammable liquid electrolyte cathodes can lead to unsafe events, possibly due to lithium deposition or to oxidation of solvents at these high potentials.
Overheating affects the negative electrode. The safety issue relates to decomposition of the SEI above about 110 °C and the resulting exothermic reaction between lithium ions and the electrolyte. The heat source may be internal, through Joule heating, or external, from excessively high ambient temperatures or phenomena such as brush fires. In the case of Joule heating safety issues can be avoided through the use of active cooling systems or by inhibiting charge or discharge of the battery. For external heating there is little that can be done; insulation around the battery may protect it from short spikes in temperature that might be experienced from a fast-moving brush fire, but it is important to balance the amount of insulation used with the need to be able to dissipate Joule heat from normal charging and discharging operations.
Overcharging is hazardous because the charged positive electrode material can begin to react with the electrolyte, resulting in electrolyte venting, smoke, fire, or explosion. Some positive electrode materials are more stable and thus safer than others; LFP is the safest, followed by NMC, LMO, and LCO. The battery protection circuitry protects against overcharging by opening a switch if the voltage exceeds the limit. If the circuit fails and the battery continues to charge, a safety vent opens to release the pressure in the battery.
Lithium Ion battery has the wide range of characteristics due to which variety of different sizes of batteries can be produced and they found major areas of application:
- Consumer electronics: power banks, notebook, laptops and watches
- Big electric vehicles: buses, electric cars, tour buses, hybrid vehicles and other attractions.
- Light electric vehicles: Electric bikes, golf carts, small cars, forklifts, electric vehicle cleaning wheelchairs, etc.
- Power tools: Lawn movers, electric saws, electric drills.
- Remote control toys: cars, boats, planes, etc
- Wind energy storage and solar equipment.
- Warning lights, UPS, miner’s lamp, emergency lights, etc