Week 1 Understanding Different Battery Chemistry
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.
1.LCO(Lithium Cobalt Oxide): Its high specific energy makes Li-cobalt the popular choice for mobile phones, laptops and digital cameras. The battery consists of a cobalt oxide cathode and a graphite carbon anode. The cathode has a layered structure and during discharge, lithium ions move from the anode to the cathode. The flow reverses on charge. The drawback of Li-cobalt is a relatively short life span, low thermal stability and limited load capabilities (specific power). Below figure illustrates the structure.
Anode material is graphite and the Cathode material is LiCoO2.
Electrolyte used is Ethylene Carbonate.
Chemical Reactions occuring during the discharging at anode and the cathode is as follows,
At anode: LiC6------>xLi+ +xe- + C6
At Cathode: Li1-xCoO2 +xLi+ +xe--------->LiCoO2
The drawback of Li-cobalt is a relatively short life span, low thermal stability and limited load capabilities. Like other cobalt-blended Li-ion, Li-cobalt has a graphite anode that limits the cycle life by a changing SEI, thickening on the anode and lithium plating while fast charging and charging at low temperature. Newer systems include nickel, manganese and/or aluminum to improve longevity, loading capabilities and cost.
2. LMO(Lithium Manganese Oxide): Li-ion with manganese spinel was first published in the Materials Research Bulletin in 1983. In 1996, Moli Energy commercialized a Li-ion cell with lithium manganese oxide as cathode material. The architecture forms a three-dimensional spinel structure that improves ion flow on the electrode, which results in lower internal resistance and improved current handling. A further advantage of spinel is high thermal stability and enhanced safety, but the cycle and calendar life are limited.Low internal cell resistance enables fast charging and high-current discharging. In an 18650 package, Li-manganese can be discharged at currents of 20–30A with moderate heat buildup. It is also possible to apply one-second load pulses of up to 50A. A continuous high load at this current would cause heat buildup and the cell temperature cannot exceed 80°C (176°F). Li-manganese is used for power tools, medical instruments, as well as hybrid and electric vehicles.
Anode material is graphite and the Cathode material is LiMn2O4.
Electrolyte used is Lithium Halide.
Chemical Reactions occuring during the discharging at anode and the cathode is as follows,
At anode: LiC6------>xLi+ +xe- + C6
At Cathode: Li1-xMn2O4 +xLi+ +xe- -------->LiMn2O4
These three active metals, as well as the silicon enhancement can conveniently be chosen to enhance the specific energy, specific power (load capability) or longevity. While consumer batteries go for high capacity, industrial applications require battery systems that have good loading capabilities, deliver a long life and provide safe and dependable service.
3. NCA(Lithium Nickel Cobalt Aluminum Oxide):Lithium nickel cobalt aluminum oxide battery, or NCA, 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. Less flattering are safety and cost. NCA is a further development of lithium nickel oxide; adding aluminum gives the chemistry greater stability.High energy and power densities, as well as good life span, make NCA a applicable to EV powertrains. High cost and marginal safety are negatives.
Anode material is graphite and the Cathode material is LiNiCoAlO2.
Electrolyte used is Ethylene Carbonate.
Chemical Reactions occuring during the discharging at anode and the cathode is as follows,
At anode: LiC6------>xLi+ +xe- + C6
At Cathode: Li1-xMO2 +xLi+ +xe- -------->LiMO2.
4. NMC(Lithium Nickel Manganese Cobalt Oxide):One of the most successful Li-ion systems is a cathode combination of nickel-manganese-cobalt (NMC). Similar to Li-manganese, these systems can be tailored to serve as power cells. For example, NMC in an 18650 cell for moderate load condition has a capacity of about 2,800mAh and can deliver 4A to 5A; NMC in the same cell optimized for specific power has a capacity of only about 2,000mAh but delivers a continuous discharge current of 20A. A silicon-based anode will go to 4,000mAh and higher but at reduced loading capability and shorter cycle life. Silicon added to graphite has the drawback that the anode grows and shrinks with charge and discharge, making the cell mechanically unstable.The secret of NMC lies in combining nickel and manganese. An analogy of this is table salt in which the main ingredients, sodium and chloride, are toxic on their own but mixing them serves as seasoning salt and food preserver. Nickel is known for its high specific energy but poor stability; manganese has the benefit of forming a spinel structure to achieve low internal resistance but offers a low specific energy. Combining the metals enhances each other strengths.
Anode material is graphite and the Cathode material is LiNiMnCoO2.
Electrolyte used is Lithium Salt.
Chemical Reactions occuring during the discharging at anode and the cathode is as follows,
At anode: LiC6------>xLi+ +xe- + C6
At Cathode: Li1-xMO2 +xLi+ +xe- -------->LiMO2.
NMC is the battery of choice for power tools, e-bikes and other electric powertrains. The cathode combination is typically one-third nickel, one-third manganese and one-third cobalt, also known as 1-1-1. This offers a unique blend that also lowers the raw material cost due to reduced cobalt content. Another successful combination is NCM with 5 parts nickel, 3 parts cobalt and 2 parts manganese (5-3-2). Other combinations using various amounts of cathode materials are possible.
5. LPF(Lithium Iron Phosphate): In 1996, the University of Texas (and other contributors) discovered phosphate as cathode material for rechargeable lithium batteries. Li-phosphate offers good electrochemical performance with low resistance. This is made possible with nano-scale phosphate cathode material. The key benefits are high current rating and long cycle life, besides good thermal stability, enhanced safety and tolerance if abused.Li-phosphate is more tolerant to full charge conditions and is less stressed than other lithium-ion systems if kept at high voltage for a prolonged time.
Anode material is graphite and the Cathode material is LiFePO4.
Electrolyte used is Ethylene Carbonate.
Chemical Reactions occuring during the discharging at anode and the cathode is as follows,
At anode: LiC6------>xLi+ +xe- + C6
At Cathode: LiFe(IIII)PO4+xLi+ +xe- ---------->LiFe(II)PO4
Li-phosphate is often used to replace the lead acid starter battery. Four cells in series produce 12.80V, a similar voltage to six 2V lead acid cells in series. Vehicles charge lead acid to 14.40V (2.40V/cell) and maintain a topping charge. Topping charge is applied to maintain full charge level and prevent sulfation on lead acid batteries.With four Li-phosphate cells in series, each cell tops at 3.60V, which is the correct full-charge voltage. At this point, the charge should be disconnected but the topping charge continues while driving. Li-phosphate is tolerant to some overcharge; however, keeping the voltage at 14.40V for a prolonged time, as most vehicles do on a long road trip, could stress Li-phosphate. Time will tell how durable Li-Phosphate will be as a lead acid replacement with a regular vehicle charging system. Cold temperature also reduces performance of Li-ion and this could affect the cranking ability in extreme cases.
6. LTO (Lithium Titanate): Batteries with lithium titanate anodes have been known since the 1980s. Li-titanate replaces the graphite in the anode of a typical lithium-ion battery and the material forms into a spinel structure. The cathode can be lithium manganese oxide or NMC. Li-titanate has a nominal cell voltage of 2.40V, can be fast charged and delivers a high discharge current of 10C, or 10 times the rated capacity. The cycle count is said to be higher than that of a regular Li-ion. Li-titanate is safe, has excellent low-temperature discharge characteristics and obtains a capacity of 80 percent at –30°C (–22°F).
Anode material is Lithium titanate and the Cathode material is lithium manganese oxide.
Electrolyte used is Lithium Salt.
Chemical Reactions occuring during the discharging at anode and the cathode is as follows,
At anode: LiC6------>xLi+ +xe- + C6
At Cathode: 4Mn2O4+4Li+ +4e- -------->4LiMn2O4.
LTO (commonly Li4Ti5O12) has advantages over the conventional cobalt-blended Li-ion with graphite anode by attaining zero-strain property, no SEI film formation and no lithium plating when fast charging and charging at low temperature. Thermal stability under high temperature is also better than other Li-ion systems; however, the battery is expensive. At only 65Wh/kg, the specific energy is low, rivalling that of NiCd. Li-titanate charges to 2.80V/cell, and the end of discharge is 1.80V/cell. Figure 13 illustrates the characteristics of the Li-titanate battery. Typical uses are electric powertrains, UPS and solar-powered street lighting.
2.Compare the differences between each type of Li+ion batteries based on their characteristics
1. LCO
The above figure shows the 6 different parameters of LCO.We can conclude from the figure that Li-cobalt excels on high specific energy but offers only moderate performance specific power, safety and life.Since as the matter of safety they are not advaisable for EV applications.The Li-cobalt is losing favor to Li-manganese, but especially NMC and NCA because of the high cost of cobalt and improved performance by blending with other active cathode materials.
2.LMO
Above figure shows the spider web of a typical Li-manganese battery. The characteristics appear marginal but newer designs have improved in terms of specific power, safety and life span. Pure Li-manganese batteries are no longer common today; they may only be used for special applications.Most Li-manganese batteries blend with lithium nickel manganese cobalt oxide (NMC) to improve the specific energy and prolong the life span. This combination brings out the best in each system, and the LMO (NMC) is chosen for most electric vehicles, such as the Nissan Leaf, Chevy Volt and BMW i3. The LMO part of the battery, which can be about 30 percent, provides high current boost on acceleration; the NMC part gives the long driving range.
3.NMC
NMC has good overall performance and excels on specific energy and the specific power. This battery is the preferred choice for the electric vehicle and has the lowest self-heating rate.There is a move towards NMC-blended Li-ion as the system can be built economically and it achieves a good performance. The three active materials of nickel, manganese and cobalt can easily be blended to suit a wide range of applications for automotive and energy storage systems (EES) that need frequent cycling. The NMC family is growing in its diversity.
4.LPF
Li-phosphate has excellent safety and long life span but moderate specific energy and elevated self-discharge.This cell might not be applicable to EV's.Performance is also poor. Used in Portable and stationary needing high load currents and endurance.Li-phosphate is more tolerant to full charge conditions and is less stressed than other lithium-ion systems if kept at high voltage for a prolonged time.
5.NCA
From the above figure we can conclude that,high energy and power densities, as well as good life span, make NCA a choice for EV powertrains. High cost and marginal safety are negatives.It shares similarities with NMC by offering high specific energy, reasonably good specific power and a long life span. Less flattering are safety and cost. NCA is a further development of lithium nickel oxide; adding aluminum gives the chemistry greater stability.
6.LTO
From the above figure we can conclude that Li-titanate excels in safety, low-temperature performance and life span. Efforts are being made to improve the specific energy and lower cost.LTO has advantages over the conventional cobalt-blended Li-ion with graphite anode by attaining zero-strain property, no SEI film formation and no lithium plating when fast charging and charging at low temperature.