Types of cathode materials for lithium-ion batteries

Types of cathode materials for lithium-ion batteries

This article describes the six most common lithium ion battery electrode materials.

#1 Lithium Cobalt Oxide (LiCoO2) - LCO

Its high specific energy makes batteries with lithium cobalt oxide as the cathode material a popular choice for cell 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 current is reversed during charging. The disadvantages of Li-Co are a relatively short lifetime, low thermal stability, and limited load capacity (specific power).When lithium-ion batteries were introduced in 1991, they used LiCoO2 cathodes (60% Co) and graphite anodes, with a standard voltage of 3. 6 V and an operating voltage range of 3. 0-4. 2 V. The specific energy is 150-200 Wh/kg, and the number of charge/discharge cycles is 500-1000, depending on the battery discharge depth. 1000 times, which is related to the battery discharge depth, load and temperature.LiCoO2 has a high specific energy, but exhibits moderate performance in terms of specific power, safety and lifetime.

#2 Lithium manganese oxide (LiMn2O4) - LMO

Lithium manganese oxide was commercialized as a cathode material for lithium-ion batteries in 1996. The material is a three-dimensional spinel structure, which improves ion flow at the electrode, which leads to lower internal resistance. Another advantage of spinel is high thermal stability and strong safety, but limited cycling and lifetime.

The low internal resistance of the battery allows for fast charging and high current discharging. In 18650 (a battery type formulated by Sony) batteries, lithium manganese cells can be discharged at a current of 20- 30 A. The current of the lithium manganese cells is not very high, but they can be discharged at a high current. Sustained high loads at this current can lead to heat buildup and the battery temperature should not exceed 80°C. Li-Mn batteries are used in power tools, medical devices, and hybrid and electric vehicles.

Li-Mn batteries have a capacity approximately one-third lower than that of Li-Co batteries (100-150 Wh/kg) and are standardized at 3.7 or 3.8 V. Design flexibility allows engineers to maximize battery life, maximum load current, or high capacity. Lithium manganese batteries have moderate overall performance, but newer designs can be improved in terms of specific power, safety and life.

Most Li-Mn batteries are blended with Li-Ni-Mn-Co (NMC) batteries to increase specific energy and extend life. This combination brings out the best in each system, with LMO (NMC) being chosen for most electric vehicles such as the Nissan Leaf, Chevrolet Volt, and BMW i3. The LMO portion of the battery (which makes up about 30%) provides high current during acceleration, and the NMC portion is responsible for long-range range.

Lithium-manganese batteries typically favor a combination of cobalt, nickel, manganese and or aluminum as the active cathode material. In some studies, a small amount of silicon has been added to the anode to provide a 25% capacity boost, however, since silicon deforms with charging and discharging, high capacity is usually accompanied by a short cycle life.

#3 Lithium-Nickel-Manganese-Cobalt Oxide (LiNiMnCoO2) - NMC

Lithium-Nickel-Manganese-Cobalt Oxide (LiNiMnCoO2) is one of the most successful lithium-ion systems. Similar to lithium manganese, these systems can be customized as either energy or power cells. For example, the NMC in an 18650 battery for medium load conditions has a capacity of about 2800 mAh and can be discharged at currents of 4A to 5A. An NMC in the same cell optimized for a specific power has a capacity of only about 2,000 mAh, but can deliver a continuous discharge current of 20 A. The NMC in the same cell is optimized for a specific power. Using a silicon-based anode will achieve 4000 mAh or more, but with reduced load capacity and shorter cycle life. Silicon added to graphite deforms during charging and discharging, making the battery mechanically unstable.

NMC is the battery of choice for power tools, e-bikes, and other electric powertrains with the lowest self-heating rate. The cathode combination is typically one-third nickel, one-third manganese and one-third cobalt, also known as 1-1-1. cobalt is expensive and in limited supply. Battery manufacturers are reducing the cobalt content while making some compromises on performance. A successful combination is the NCM 532; other combinations are the NMC 622 and NMC 811.

NMC batteries have a standard voltage of 3.6 or 3.7V and can be charged up to 4.4V using special electrolytes, with a specific energy of 150-220Wh/kg and 1000-2000 cycles.

#4 Lithium iron phosphate (LiFePO4) - LFP

In 1996, the University of Texas (and other researchers) discovered phosphate as a cathode material for rechargeable lithium batteries. Lithium phosphate has good electrochemical properties with low electrical resistance, and its main advantages are high current rating and long cycle life, as well as good thermal stability, enhanced safety and tolerance. Lithium phosphate is more tolerant and less stressed than other Li-ion systems if held at high voltages for extended periods of time. However, its lower standard voltage of 3.2 V gives it a lower specific energy (90-120 Wh/kg). For most batteries, low temperatures reduce performance and high storage temperatures shorten service life, and lithium phosphate is no exception. Lithium phosphate batteries have a higher self-discharge than other Li-ion batteries, which can lead to aging.

#5 Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2) - NCA

Lithium-Nickel-Cobalt-Aluminum-Oxide (NCA) was first used in lithium-ion batteries in 1999. It is similar to NMC in that it offers high specific energy, fairly good specific power and long life, but safety and cost are not so good.

#6 Lithium Titanate (Li2TiO) - LTO

In the 1980s, lithium titanate was used as a battery anode. Later lithium titanate replaced graphite anodes in lithium-ion batteries, which have a spinel structure. The cathode can be LMO or NMC. lithium titanate has a standard cell voltage of 2.40 V, a specific energy of 50-80 Wh/kg, can be recharged quickly, and has a cycle count that is said to be higher than that of other lithium ion batteries. Lithium Titanate has high safety performance and excellent low temperature discharge characteristics, with 80% capacity still available at -30 ° C. The lithium titanate battery is also available in a range of different sizes and sizes.

By comparing the specific energy of lead-based, nickel-based and lithium-based, NCA is the clear winner as it has the highest specific energy. In terms of specific power and thermal stability, LMO and LFP are the best. LTO has a lower capacity but outperforms most other batteries in terms of lifetime and also has the best low temperature performance.