Application of nanotechnology in lithium ion battery
Lithium ion battery, as high-efficiency energy storage components, have been widely used in the field of consumer electronics. Lithium-ion batteries have been used in mobile phones and laptops. Lithium-ion batteries have achieved such brilliant results thanks to their ultra-high energy storage density. And good safety performance. With the continuous development of technology, the energy density and power density of lithium-ion batteries have also been continuously improved, among which nanotechnology has made an indelible contribution. Because LiFePO4 has poor conductivity, in order to improve its conductivity, people have prepared it into nanoparticles, which greatly improves the electrochemical performance of LiFePO4. In addition, the silicon negative electrode is also a beneficiary of nanotechnology. Nano-silicon particles can well suppress the volume expansion of Si during lithium intercalation and improve the cycle performance of Si materials.
Cathode material
1.LiFePO4 material
LiFePO4 material has good thermal stability and low cost. Due to the unique covalent bond structure inside the LiFePO4 material, the electronic conductivity of the LFP material is very low, which limits its high rate charge and discharge performance. To this end, LFP materials are made into nanoparticles and coated with materials such as conductive materials, conductive polymers, and metals. In addition, by incorporating a non-stoichiometric solid solution doping method into the nano-LFP particles, the electronic conductivity of the LFP nano-particles can be increased by 108, so that the LFP material can be charged and discharged within 3 minutes. This is particularly important for electric vehicles.
2.Inhibit LiMn2O4 material decomposition
LMO materials have three-dimensional Li + diffusion channels and therefore have a high ion diffusion coefficient. However, Mn3 + is formed in a low SoC state. Due to the existence of the Jonh-Teller effect, the LMO structure is unstable. Part of the Mn element is dissolved into the electrolyte and finally deposited on the surface of the negative electrode, which destroys the structure of the SEI film. Some low-cost main group metal ions can be added in the LMO to replace part of Mn, thereby increasing the valence state of the Mn element and reducing Mn3 + in a low SoC. The surface of the LMO material particles can also be coated with a layer of oxides and fluorides with a thickness of 10-20 nm.
3. Inhibit NMC chemical activity
The specific capacity of NMC materials, especially high-nickel NMC materials, can be as high as 200mAh / g or more, and they have very good cycle performance. However, the NMC material is extremely susceptible to oxidation of the electrolyte in the charged state. In order to suppress the reactivity of the high nickel NMC material and the electrolyte, the material is coated with nanoparticles to avoid direct contact between the material particles and the electrolyte. Greatly improved the cycle life of the material. In addition, nanoparticles with core-shell structure are also an effective method to reduce the reactivity. The high Mn shell has good stability, but the capacity is low, and the high nickel core capacity is high, but the reactivity is large.
Anode material
1.Graphite material protection
Graphite material has low lithium insertion voltage, which is very suitable as a negative electrode material for lithium ion batteries. The lithium-doped graphite has a strong reactivity and will react with organic electrolytes, causing the graphite sheet to fall off and the electrolyte to decompose. Although the SEI film can suppress the decomposition of the electrolyte, the SEI film is not 100% resistant to the graphite negative electrode. Form protection. Common graphite surface protection methods include surface oxidation and nano-coating technology.
Nano-coating technologies include three categories: amorphous carbon, metals and metal oxides. Among them, amorphous carbon is mainly obtained by a vacuum chemical deposition CVD method, which is low cost and suitable for large-scale production. Metal and metal oxide nano-coatings are mainly obtained by wet chemical methods, which can well protect graphite and prevent electrolyte decomposition.
2.Improve the rate performance of lithium titanate LTO and TiO2 materials
The LTO material has high safety, no stress will be generated during Li intercalation and deintercalation, and the lithium intercalation potential is high, which will not cause decomposition of the electrolyte. It is a very excellent anode material. However, LTO materials have low specific capacity and low electronic and ionic conductivity. At present, nanotechnology mainly uses particle nanotechnology, nanocoating technology, and LTO nanomaterials and conductive materials composite applications on LTO. LTO material nano-ization can effectively reduce the diffusion distance of Li +, increase the contact area with the electrolyte, strengthen the charge exchange, and improve the rate performance.
3. Increase the energy density of the silicon anode
The theoretical specific capacity of Si material reaches 3572mAh / g, which is much higher than that of graphite material. However, Si has a volume expansion of 300% during the process of lithium intercalation and delithiation, resulting in particle breakage and active material shedding. The Si material is made into nanoparticles in order to relieve the mechanical stress caused by the expansion of the Si particles.
Li-S batteries have high energy density and low cost, and are very promising next-generation energy storage batteries. However, the main problems Li-S batteries currently face are the low conductivity of S and the problem of dissolution of lithium intercalation products. By compounding S with porous hollow carbon or metal oxide oxide nanoparticles, the stability of S can be significantly improved and the cycling performance of the electrode can be improved. In addition, the compounding of S and graphene materials can also significantly improve the cycling performance of S negative electrodes.
Cathode material
1.LiFePO4 material
LiFePO4 material has good thermal stability and low cost. Due to the unique covalent bond structure inside the LiFePO4 material, the electronic conductivity of the LFP material is very low, which limits its high rate charge and discharge performance. To this end, LFP materials are made into nanoparticles and coated with materials such as conductive materials, conductive polymers, and metals. In addition, by incorporating a non-stoichiometric solid solution doping method into the nano-LFP particles, the electronic conductivity of the LFP nano-particles can be increased by 108, so that the LFP material can be charged and discharged within 3 minutes. This is particularly important for electric vehicles.
2.Inhibit LiMn2O4 material decomposition
LMO materials have three-dimensional Li + diffusion channels and therefore have a high ion diffusion coefficient. However, Mn3 + is formed in a low SoC state. Due to the existence of the Jonh-Teller effect, the LMO structure is unstable. Part of the Mn element is dissolved into the electrolyte and finally deposited on the surface of the negative electrode, which destroys the structure of the SEI film. Some low-cost main group metal ions can be added in the LMO to replace part of Mn, thereby increasing the valence state of the Mn element and reducing Mn3 + in a low SoC. The surface of the LMO material particles can also be coated with a layer of oxides and fluorides with a thickness of 10-20 nm.
3. Inhibit NMC chemical activity
The specific capacity of NMC materials, especially high-nickel NMC materials, can be as high as 200mAh / g or more, and they have very good cycle performance. However, the NMC material is extremely susceptible to oxidation of the electrolyte in the charged state. In order to suppress the reactivity of the high nickel NMC material and the electrolyte, the material is coated with nanoparticles to avoid direct contact between the material particles and the electrolyte. Greatly improved the cycle life of the material. In addition, nanoparticles with core-shell structure are also an effective method to reduce the reactivity. The high Mn shell has good stability, but the capacity is low, and the high nickel core capacity is high, but the reactivity is large.
Anode material
1.Graphite material protection
Graphite material has low lithium insertion voltage, which is very suitable as a negative electrode material for lithium ion batteries. The lithium-doped graphite has a strong reactivity and will react with organic electrolytes, causing the graphite sheet to fall off and the electrolyte to decompose. Although the SEI film can suppress the decomposition of the electrolyte, the SEI film is not 100% resistant to the graphite negative electrode. Form protection. Common graphite surface protection methods include surface oxidation and nano-coating technology.
Nano-coating technologies include three categories: amorphous carbon, metals and metal oxides. Among them, amorphous carbon is mainly obtained by a vacuum chemical deposition CVD method, which is low cost and suitable for large-scale production. Metal and metal oxide nano-coatings are mainly obtained by wet chemical methods, which can well protect graphite and prevent electrolyte decomposition.
2.Improve the rate performance of lithium titanate LTO and TiO2 materials
The LTO material has high safety, no stress will be generated during Li intercalation and deintercalation, and the lithium intercalation potential is high, which will not cause decomposition of the electrolyte. It is a very excellent anode material. However, LTO materials have low specific capacity and low electronic and ionic conductivity. At present, nanotechnology mainly uses particle nanotechnology, nanocoating technology, and LTO nanomaterials and conductive materials composite applications on LTO. LTO material nano-ization can effectively reduce the diffusion distance of Li +, increase the contact area with the electrolyte, strengthen the charge exchange, and improve the rate performance.
3. Increase the energy density of the silicon anode
The theoretical specific capacity of Si material reaches 3572mAh / g, which is much higher than that of graphite material. However, Si has a volume expansion of 300% during the process of lithium intercalation and delithiation, resulting in particle breakage and active material shedding. The Si material is made into nanoparticles in order to relieve the mechanical stress caused by the expansion of the Si particles.
Li-S batteries have high energy density and low cost, and are very promising next-generation energy storage batteries. However, the main problems Li-S batteries currently face are the low conductivity of S and the problem of dissolution of lithium intercalation products. By compounding S with porous hollow carbon or metal oxide oxide nanoparticles, the stability of S can be significantly improved and the cycling performance of the electrode can be improved. In addition, the compounding of S and graphene materials can also significantly improve the cycling performance of S negative electrodes.
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