Lithium-ion Full Cell Manufacturing Process Training--Cathode Electrode Materials Section
1.Principle of Lithium-ion Batteries
Note: EC and DEC are electrolyte solvents.In the diagram, the cathode is lithium cobalt oxide,
and the anode is graphite.
With Li+ as the ion conduction medium, the reaction of lithium ion insertion and extraction occurs between the anode and cathode, also known as a "rocking chair battery".
2.
The Composition of Lithium-ion Battery
Materials
2.1.Positive electrode materials refer to materials that can provide a source of lithium ions during the charging process.
For example: lithium compounds LiCoO2, LiNiO2, LiMnO2, LiNiCoMnO2, and LiFePO4.
2.2.Negative electrode materials are materials that provide a receiving site for lithium ions during the charging process.
For example: graphite (synthetic or natural), silicon alloys, tin alloys,etc.
2.3.Electrolyte is a material that provides a conduction medium for lithium ions.For example: organic solutions dissolved with lithium salts such as LiPF6, LiAsF6, etc.
2.4.Separator is a porous material that blocks the conduction of electrons between the positive and negative electrodes while allowing the conduction of ions.For example: PP, PE, non-woven fabric etc.
2.5.The current collector refers to a material carrier that provides a path for material coverage and a bundle of conductors for current.
For examples: copper foil (negative electrode), aluminum foil (for the positive electrode) etc.
2.6.The packaging shell refers to the composite material used to package and protect the battery cell.
Examples: aluminum-plastic film, stainless steel shell, and aluminum shell.
2.7.The conductive agent refers to a material that can enhance the electronic conductivity between active materials and between active materials and the current collector.Examples: conductive carbon black, carbon nanotube,etc.
2.8.The binder refers to a material that enhances the adhesion between materials and between materials and the current collector.
Examples: SBR and PVDF,etc.
2.9.Additives refer to special substances that enhance the safety and stability of the battery.Examples: film-forming additives and flame retardant additives,etc
3.Role and Selection Criteria of Cathode Electrode Materials
3.1.Requirements for the Selection of Cathode Electrode Materials
As an ideal cathode electrode material for lithium-ion batteries, lithium-ion insertion compounds must meet the following requirements:
3.1.1.Have a high redox potential to ensure the high voltage characteristics of lithium-ion batteries;
3.1.2.Allow a large amount of lithium ions to be inserted and extracted,
ensuring the high capacity characteristics of lithium-ion batteries;
Calculation of theoretical capacity: C0 = 26.8n m/M
Co---- theoretical capacity; n---- number of electrons gained or lost in the redox reaction;
m ---- mass of the active material completely reacting; M----molar mass of the active material
Using LiCoO2 as an example:
Co = 96500/M = 96500*1000/3600*98 = 273 mAh/g
LiNiO2has a capacity of 274 mAh/g;
LiMn2O4has a capacity of 148 mAh/g;
LiFePO4 has a capacity of 170 mAh/g.
3.1.3.Good reversibility during the insertion and extraction process, with minimal changes in material structure during charging and discharging;
3.1.4.Rapid insertion and extraction of lithium ions, with high electronic and ionic conductivity;
3.1.5.Good chemical stability in the electrolyte;
3.1.6.Low cost, easy to prepare, and environmentally friendly.
Currently, there are various cathode materials for lithium-ion batteries that are under extensive research, including LiCoO2, nickel-cobalt binary systems, nickel-cobalt-manganese, manganese compounds, and LiFePO4.
4.Classification of Cathode Materials
After process optimization and improvement, the gram capacity of lithium cobalt oxide and ternary materials has been significantly increased.