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Everything You Need to Know about Cathode Materials in Lithium-Ion Batteries

2020-05-09

The cathode materials are the key material to determine the battery performance and there is multiple choice of cathode materials within the Li-ion battery. Originally, the main active component of the cathode was cobalt. Currently, cobalt is partially being substituted by other component like nickel. The cathode materials which have been used to achieve battery performance include Cobalt-based lithium-ion (LCO), Lithium iron phosphate (LFP), lithium manganate (LiMn2O4), ternary materials such as Nickel Cobalt Aluminum (NCA) and Nickel Cobalt Manganate (NCM or NMC). 

Lithium ion batteries (LIBs) represent one of the most promising solutions for environmentally friendly transportation such as electric vehicles. The demand for high energy density, low cost and environmentally friendly batteries makes high-capacity cathode materials very attractive for future LIBs.

Today, we will explore some common cathode material within lithium-ion battery in the following article.

Cobalt-based lithium-ion (LCO): Suitable for small batteries

Lithium cobalt oxide, with the benefits of high discharge voltage plateau, good capacity and cycle performance, simple manufactured process, is the first commercialized cathode material in li-ion battery. However, due to the relative shortage of cobalt resource, and the noxious effect of material on the environment, the long-term development of LCO is greatly limited. Additionally, the poor safety performance of this cathode material also limits the application of this batteries. At present, lithium cobalt oxide is mainly used in small batteries for electronic products. The compacted density of LCO cathode material is greater than that of ternary material, which means that more capacity can be contained per volume. Therefore, it is a better choice in small batteries which focus more on volume density. 

Figure 1Snapshot of an average Li-cobalt battery.
Li-cobalt excels on high specific energy but offers only moderate performance specific power, safety and life span.
Source:  Battery University

Lithium iron phosphate (LFP, LiFePO4): High safety performance, Low energy density

Lithium iron phosphate is one of the cathode material that drawing people's attention nowadays. High safety and long cycle life are two major advantage of LFP cathode material. The olivine structure of lithium iron phosphate leads to its good performance on safety. This structure slows down the capacity of ion diffusion in the battery, but it has a good stability of high temperature and ideal cycle performance on the other hand. Besides, with the feature of eco-friendly, the LFP batteries gain some market share in the energy storage and electric vehicle fields.

Nevertheless, low energy density is a main shortage of LFP cathode material. The voltage of lithium iron phosphate material is about 3.3V, lower than the other material, which makes LiFePO4 battery store less energy than the other batteries. The conductivity of LFP material is not as good as the other cathode material, which makes the material become “fluffy” and has a low compacted density. Although the energy density affects the application range of LFP battery, it is still preferred in some of the electric vehicles because of its high safety performance, especially in electric buses which a large number of lives are involved. Recently, LiFePO4 battery also get more popularity in the telecommunication field. China Mobile and China Tower both announced their procurement plan of LiFePO4 battery as backup power in telecom tower. LiFePO4 battery has come into play in energy storage. A superior quality LiFePO4 battery such as UFO LiFePO4 battery is good to choose. 



Figure 2: Snapshot of a typical Li-phosphate battery.

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

Ternary materials (NCM, NCA): Battery safety is the vital issue need to be solved

Ternary material, including Nickel Cobalt Aluminum(NCA) and Nickel Cobalt Manganate ( NCM or NMC), which has integrated the benefits of LiCoO2、LiNiO2 and LiMnO2, has the highest energy density among the three main cathode materials.

The different proportions of nickel, cobalt, and manganese can bring various performance to the batteries. The higher the elements of Ni, the higher the energy density of cells while the lower safety of cells. The existence of cobalt can improve the structure stability but too much cobalt will also lower the battery capacity. The manganese is the element which can improve the safety performance of battery and reduce the cost of battery as well, but it could damage the layered structure of battery if there are too much manganese inside the lithium-ion battery. Because of the pursuit of high energy density in lithium-ion battery for many applications, the proportion of Ni is increasing for NCM and NCA batteries.

The shortcoming of ternary materials is the safety problem. When the thermal runaway phenomenon occurring during operating process of li-ion battery, it will contain a large amount of gas which greatly improves the risk of accidents. As there is a increasing growth in ternary material for batteries, the improvement of safety performance for battery is the heart of the matter making ternary cathode material such as NCM and NCA batteries be utilized in more market fields. Significant safety advancements have become essential as the technology ripples through grid storage and electric vehicles.

                 

Figure 3: Snapshot of NMC.
NMC has good overall performance and excels on specific energy. This battery is the preferred candidate for the electric vehicle and has the lowest self-heating rate.

Source: Battery University


                 

Figure 4: Snapshot of NCA.
High energy and power densities, as well as good life span, make NCA a candidate for EV powertrains. High cost and marginal safety are negatives.

Source: Battery University







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