In recent years, the energy crisis has attracted global attention. Electric vehicles such as Tesla have become more and more popular in the public eye. Smart digital products such as Apple's mobile phones have been pursuing longer standby times and lighter weight. The fuselage, all this needs to focus on one technology-lithium-ion batteries.
Lithium-ion batteries, commonly known as "lithium batteries", are a type of secondary battery that was first mass-produced by Sony Corporation in Japan in the 1990s. At that time, lithium-ion batteries used carbon material as the negative electrode and lithium cobaltate (LiCoO2) as the positive electrode . The layered structure of lithium ion positive and negative electrode materials can reversibly intercalate and deintercalate lithium ions, and rely on the movement of lithium ions to achieve charge and discharge.
Lithium-ion batteries have significant advantages such as small size, long life, high operating voltage, long cycle life, and no memory effect, so they are widely used in smart phones, notebook computers, digital cameras, and electronic watches. In addition to portable electronic devices, in recent years, people have faced the needs of energy storage batteries, car lithium cylindrical battery and hybrid vehicles, which has also repeatedly made it into people's vision.
The electrode and electrolyte materials largely determine the performance of the battery. For high temperature resistance lithium ion batteries, carbon materials are used for the negative electrode, and there are not many patterns in terms of types, but the research on positive electrode materials can be described as a contention . Cathode materials are not only a battlefield for researchers to improve the performance of lithium batteries, but also a major bottleneck that limits the cost and safety of lithium-ion batteries. Therefore, the research of cathode materials has also become the focus and focus of lithium ion research and development.
First, the structure of the lithium ion battery anode material
LiCoO2 is currently the most common cathode material for lithium-ion batteries. Figure 1 shows its layered crystal structure . The overlapping cobalt and lithium layers exert different forces and directions on the oxygen atoms, forming a twisted three-dimensional structure. This layered three-dimensional structure provides a very suitable two-dimensional tunnel for the movement of lithium ions in and out, thereby enabling the LiCoO2 material to obtain a higher conductivity.
2. Lithium nickelate (LiNiO2)
Like LiCoO2, LiNiO2 crystals also have a layered salt rock structure. Figures 1 and 2 are schematic diagrams of its structure . The oxygen atoms are densely packed in cubes, and the octahedral voids of each oxygen atom are alternately occupied by nickel and lithium atoms, respectively. Similarly, the two-dimensional layered structure of the nickel layer and the lithium layer formed thereon also enables the LiNiO2 material to have lithium ion intercalation and deintercalation activities.
3. Lithium manganate (LiMn2O4)
The spinel-type LiMn2O4 has tetragonal symmetry, and a unit cell contains 16 Mn3 + / 4 + atoms, 32 O2- atoms, and 8 Li + atoms. In the crystal [Mn2] O4 frame (as shown in Figure 3), the distribution ratio of the Mn3 + cationic layer to the cation layer without Mn3 + is 3: 1. This cubic close-packed alternating layers between oxygen planes build a three-dimensional channel for lithium ion diffusion, helping lithium ions to diffuse quickly between layers.
5. Lithium vanadium phosphate [Li3V2 (PO4) 3]
Li3V2 (PO4) 3 has two types of structures, and it is a monoclinic system commonly used in lithium ion batteries. Its crystal structure is shown in Fig. 5 and consists of PO4 tetrahedron, metal octahedron and common oxygen atoms. Every 6 tetrahedron P atoms surround a metal V atom, and every 4 V octahedra surround an atom, forming a three-dimensional structure . Lithium ions are intercalated and removed through holes in this structure.
2200mah Li-Ion Battery
Outlook: As the bottleneck of the 2200mAh Li-ion battery research in recent years, the cathode material is also the focus. It is a barrier that researchers must pass on the road to continuously pursue higher performance lithium-ion batteries.
The two clearing paths for the research of cathode materials, one is to explore materials, and constantly look for new elements, new materials, organic or inorganic, layered or 3D. Lithium-ion battery cathode materials are in full bloom today, and new types are bound to emerge in the future. The second is modification. By doping metal ions and conductive agents, and controlling the particle size of particles, the electrochemical performance of the original cathode material can also be significantly improved.
From the recent literature, new hotspots have appeared in lithium-ion battery cathode materials. Presumably, in the next few years, high energy density, high conductivity, and good cycle materials will continue to emerge. This will also be a highlight of the enduring topic of "energy" in the entire human world!