Since the discovery of carbon nanotubes by Ijima, the research on the application of carbon nanotubes in secondary batteries has not stopped. Due to its special tubular graphite structure and unique ballistic electron conduction effect, the conductivity of carbon nanotubes at room temperature can reach as high as 10 3 s/cm/(MK), the thermal conductivity can reach 5800W/(MK), and the thermal conductivity of MWCNTs (multi-walled carbon nanotubes) can reach 3000W/(MK). At the same time, the directional growth of three-dimensional carbon nanotube arrays has excellent mechanical properties.
Carbon nanotubes are also widely used, including electronic fields (transistors, sensors, etc.), biomedical fields, Aerospace (research spacecraft lenses, composite reinforcement, functional materials), military Field (biochemical protective clothing and mine, explosive detector), Energy Field (supercapacitor, lithium ion battery and solar thermal photovoltaic equipment) and laser, etc. Today, let's take a look at the application of carbon nanotubes in lithium ion batteries.
Application of carbon nanotubes in cathode materials of lithium ion batteries
Carbon nanotubes are used as conductive agents in cathode materials, which are mainly used to improve the capacity, magnification, circulation and other properties of batteries.
◆Lithium cobalt/carbon nanotube composite anode material
Wang et al compared the application of multi-walled carbon nanotubes (MWCNTs), carbon black (CB) and carbon fiber (CF) as conductive agents in LiCoO 2 when the battery performance difference, at a magnification of 2 C, LiCoO 2 the capacity of/MWCNT battery attenuates very little during the cycle, while the battery containing carbon black and carbon fiber attenuates 10% and 30% respectively after 20 cycles. Tests show that the battery containing MWCNT has the lowest impedance and the highest conductivity.
◆ Lithium permanganate/carbon nanotube composite anode material
Liu et al. synthesized multi-walled carbon nanotubes/Lithium permanganate nanocomposites by solution gel method. After 20 cycles, the capacity retention rate of the Composite reached 99%, while pure limnox 4 the capacity retention rate of nanoparticles after 20 cycles is 90%, which indicates that the composite material has better cycle stability. This is because MWCNT forms a conductive network inside the electrode, which makes charge transfer easier, at the same time, the AC impedance test results show that the impedance of the composite material is lower.
◆ lithium iron phosphate/carbon nanotube composite anode material
Li et al studied LiFePO 4 the electrochemical performance of the composite electrode prepared by mixing particles with MWCNT, scanning electron microscope diagram shows that one-dimensional MWCNT and LiFePO 4 particles form a three-dimensional network, effectively improving the conduction ability of electrons between active substances and collector.
Application of carbon nanotubes in cathode materials of lithium ion batteries
◆Pure carbon nanotubes as negative electrode material
The unique morphology and high specific capacity of carbon nanotubes are very beneficial to their application in lithium ion batteries. When lithium ions can be inserted into the tubes, the electrode capacity will be greatly improved. Therefore, some people try to directly use carbon nanotubes as negative electrode materials.
Wu et al made the Carbon Nanotubes synthesized by template method into nano porous carbon film, making the inside and outside of the carbon nano tube be embedded by lithium ion. Carbon nanotube thin film electrode shows 490m Ah · g -1.
The structure and graphitization degree of carbon nanotubes determine the specific capacity and cycle life of carbon nanotube films. Low-grade graphitized carbon nanotubes show higher specific capacity, but their stability is worse than that of highly graphitized carbon nanotubes. This is because lithium is often preferentially inserted into areas with low graphitization, such as the boundary of stone ink layer or the surface of single-layer graphite. However, graphite carbon nanotubes are generally better than amorphous carbon nanotubes in lithium dissolution. Different preparation conditions lead to different microstructure and chemical components of carbon nanotubes, thus determining their electrochemical properties.
However, due to the large specific surface area of carbon nanotubes, when it is directly used as negative electrode material, the formation of SEI film leads to a huge loss of specific capacity of the first circle, which makes the final capacity of carbon nanotubes very limited. Therefore, people have to find ways to compound carbon nanotubes with other materials to improve the material performance.
◆Carbon nanotube composite negative electrode material
The chemical inertness of carbon nanotubes makes it still maintain its structural stability in many chemical reactions, so many researchers grow negative electrode materials on carbon nanotubes in situ to synthesize composite electrode. In order to successfully prepare carbon nanotube composite electrode, van der Waals's attraction between carbon nanotubes needs to be overcome, so surface dispersant or weak oxidant is essential, they can reduce the interaction between carbon nanotubes. The cathode material grown in situ is coated on the surface of carbon nanotubes to further modify its surface, this not only promotes the dispersion of carbon nanotubes but also strengthens the chemical force between carbon nanotubes and electrode materials.
In addition, researchers have also tried to prepare tin dioxide/carbon nanotubes composite negative electrode materials and transition metal oxide/carbon nanotubes composite negative electrode materials, which have successfully improved the electrochemical performance of electrode materials, for large capacity, the development of highly stable lithium ion batteries provides possible solutions.
