CATL's new patent: a hard carbon composite particle negative electrode material with a gram capacity of up to 486mAh/g

For lithium battery negative electrode materials, although there are many materials under research, graphite is still the main material that can be commercially produced on a large scale.

Graphite as the negative electrode has high conductivity and high stability, but low theoretical capacity. The current performance of graphite negative electrode is almost close to its theoretical maximum value of 372 mAh/g. Faced with the demand for high-power fast charging, the expansion problem of graphite negative electrode is more serious, which reduces the life and reliability of the battery.

Silicon has become a new type of negative electrode material that has attracted widespread attention due to its capacity advantage of up to 4200 mAh/g, but it faces problems such as poor cycle performance and severe volume expansion.

Hard carbon is also a new type of negative electrode material. It is a type of carbon that is difficult to graphitize. It has a similar lithium potential to graphite and a higher specific capacity, generally 500-700 mAh/g, and can even be as high as 1000 mAh/g or more. However, hard carbon materials have disadvantages such as potential hysteresis (i.e., the lithium insertion potential is lower than the lithium extraction potential) and large irreversible capacity in the first cycle, which affects the commercialization of hard carbon materials in negative electrodes.

What kind of material will the next generation of negative electrodes be made of? CATL’s recent patent shows that it is focusing on the “great integration” of several materials.

In an invention patent titled "Negative Electrode Active Materials, Secondary Batteries and Electronic Devices" published on August 2, CATL proposed a composite particle negative electrode active material consisting of a first active material and a second active material. The first active material is mainly hard carbon with a disordered carbon structure, and the second active material is composed of at least one of graphite, graphene, carbon nanotubes, lithium oxide or transition metal oxide, which is disorderly distributed or layered.

The composite particle size of the negative electrode active material in the patent is between 3μm and 12μm, the average particle size of graphite is 10~1000nm, the average sheet size of graphene is 10~2000nm, the average length of carbon nanotubes is 10~2000nm, the average particle size of lithium oxide is 10nm~1000nm, and the average particle size of transition metal oxide is 10nm~1000nm.

According to the experimental data given in the patent, when hard carbon and nanographite are used to form a composite material, the gram capacity is as high as 486 mAh/g. Among them, Example 1 with an average particle size of 100 nm of nanographite has the largest lithium ion diffusion coefficient at high SOC, the highest CC segment capacity at 3C rate, and has better fast charging capability.

By using the materials in the patent, the gram capacity of the negative electrode active material and the diffusion coefficient of the active ions inside it can be increased, thereby increasing the energy density of the secondary battery and improving its cycle performance, rate performance and fast charging capability.

Previously, the Kirin battery released by CATL, in addition to a volume utilization rate of up to 72%, also has an extremely surprising performance: 5 minutes of hot start, 10 minutes of fast charge to 80%. To achieve such a speed, the negative electrode must no longer use traditional graphite materials.

Will hard carbon be one of the options? This patent was only applied for on June 24 this year. Judging from the time, it should not be, because the research and development time is usually earlier than the official press conference, and the patent application time should also be earlier. It may also be another technical route for CATL to explore negative electrode materials.