Cathode material for lithium ion batteries

What is the cathode material of lithium-ion batteries? Next, the cathode material of the lithium-ion battery will be introduced in detail.

Cathode material is an important part of lithium-ion batteries, which provides the lithium needed for the reciprocating intercalation and deintercalation between the positive and negative lithium intercalation compounds during the lithium ion charge and discharge process. Lithium-ion battery cathode materials are generally intercalation compounds. As an ideal cathode material, the following requirements should be met:

①The metal lithium ion should have a high redox potential in the intercalation compound, so as to ensure the high and stable output voltage of the battery;

②There should be enough places to accept lithium ions, and a large amount of lithium can be reversibly intercalated and deintercalated, so that the electrode has a higher specific capacity;

③In the process of lithium ion insertion and extraction, the material structure has no or little change, so that the battery has good cycle performance;

④ The intercalation compound should have high electronic conductivity and ion conductivity, thereby reducing polarization and being able to charge and discharge with high current;

⑤In the entire charge and discharge voltage range, it should have high chemical stability and not react with the electrolyte;

⑥ From a practical point of view, it should also take into account the rich resources of embedded compounds, low production costs and no pollution to the environment.

Currently commonly used cathode materials for lithium-ion batteries mainly include layered LiMO2 (M=Co, Ni, Mn) and Li[Co, Ni, Mn]O2, and LiMPO4 with olivine structure (M=Fe, V, Co, Ni). , Mn, Cu), spinel structure of LiMn2O4 and vanadium pentoxide (V2O5) and so on.

Among the layered structural materials, LiCoO2 is the most mature and commercialized. LiCoO2 belongs to a two-dimensional layered structure, the theoretical specific capacity is 273mA•h/g, the actual specific capacity is only 130~140mA•h/g, and the discharge voltage is 3.9V. As a cathode material, LiCoO2 has the advantages of high specific capacity and discharge platform, mature production technology, etc., so it is widely used in electronic products such as portable computers and multifunctional smart phones. However, lithium borate has disadvantages such as high cost, high toxicity, and serious environmental pollution. These shortcomings limit its application in the field of power batteries, so it is not suitable for the needs of future energy storage development.

The structure of LiNiO2 is similar to LiCoO2, the theoretical specific capacity is 275mA•h/g, the actual specific capacity is 190~210mA•h/g, and the working voltage is 2.5~4.1V. Compared with LiCoO2, it has a higher capacity, is environmentally friendly and the price of raw materials is cheap, but the disadvantage is that the thermal stability is poor, the capacity decay is still very fast, and the synthesis is very difficult. This makes LiNiO2 no commercial application so far.

The structure of Li[Co, Ni, Mn]O2 is similar to that of LiCoO2, and the three elements have their own influence on the electrochemical performance of the material. Co can improve the stability of the material structure and arrange the cations of the layered structure in an orderly manner; Ni can improve the electrochemical activity of the material and make the material larger than the specific capacity; Mn can increase the specific capacity and safety of the material and reduce the cost. Compared with unary materials, the ternary composite material Li[Co, Ni, Mn]O2 has the advantages of low cost, less environmental hazard, stable structure, good cycle performance, and high capacity. It has commercialization potential and broad application prospects.

Olivine structure LiMPO4, (M=Fe, V, Co, Ni, Mn, Cu) phosphate materials can be used as the positive electrode of lithium-ion batteries, and different elements have different specific capacities and discharge voltage platforms. At present, LiMPO4 is more commonly used. The theoretical specific capacity is 170mA•h/g, the actual capacity is 160mA•h/g, the working voltage is 3.5V, and the thermal stability and cycle performance are good. LiMPO4 is transformed into FePO4 with similar structure and volume after delithiation, which makes its structure very stable and excellent cycle performance. Although its electrical conductivity and ion mobility are not high, it can be improved by preparing nano-scale electrode materials. The disadvantage of LiMPO4 is that the tap density is low during the packaging process, so it is difficult to produce LiMPO4 batteries with high energy density, which limits its application in electric vehicles and other large-scale energy storage.

In contrast, LiMn2O4 with a spinel structure has a three-dimensional tunnel structure, with a theoretical capacity of 148mA•h/g, and an actual capacity of more than 130mA•h/g. LiMn2O4 has excellent high-current charging and discharging performance, abundant raw material resources, low price and non-toxic. It is an environmentally friendly material and has a relatively high voltage platform. However, its actual capacity is relatively low (less than 120mA•h/g), resulting in low energy density, and its cycle performance is unstable. The Jahn-teller type distortion effect that causes the electron spin state to change during the charge and discharge process is reduced. The reversible electrochemical activity of electrode materials therefore limits its large-scale application in the future.

Compared with the above-mentioned cathode materials, researchers have found that vanadium oxide cathode materials have higher theoretical lithium insertion capacity and specific capacity, and have the advantages of abundant resources and low price. Therefore, vanadium oxide has become the most promising kind of development. Lithium-ion battery cathode material. Among the transition metal elements, the price of vanadium is lower than that of diamond and manganese, and it is a multivalent metal element. Its chemical properties are relatively active. It can form a variety of lithium-intercalating oxides with lithium, such as: V2O5, VO2, V3O8, etc. . However, since V has three stable oxidation states (v5+, v4+, V3+), which can form an oxygen close-packed distribution, vanadium oxide has a good application prospect as a cathode material for intercalation of lithium-ion batteries.

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