Recently, Cui Guanglei, head of the bionic energy system team at the Qingdao Institute of Bioenergy and Process Research, Chinese Academy of Sciences, and a candidate for the "100 Persons Program" of the Chinese Academy of Sciences, have made a series of important progress in the research of electrode materials for energy storage batteries. The development of high-performance electrode materials is one of the core scientific issues in energy storage battery research.
Generally speaking, energy storage batteries (taking lithium ion batteries as an example) have three main dynamic processes: the transfer process of lithium ions in the electrolyte; the transition process of lithium ions in the electrolyte and the electrode surface; lithium ions in the electrode The chemical diffusion process in the material (Figure 1). Among them, the third process is the decisive step. In addition, this process must also meet the limitations of the diffusion equation. The diffusion time (Ï„) of lithium ions in the solid electrode material is proportional to the square of the diffusion length (L), that is: Ï„ = L2 / 2D (D is the diffusion of lithium ions coefficient). When the size of the electrode material becomes smaller, the diffusion time of lithium ions in the electrode material is reduced due to the shortened diffusion path, so that the rate performance of the electrode material is improved.
Cui Guanglei's team took nanostructured hybrid transmission (electron and ion) electrode materials as the core of the design, taking into account the construction of a fast and efficient transmission network and a favorable interface, and researched and developed high-performance energy storage battery electrode materials and new battery technologies (Figure 2). Based on titanium nitride (TiN) with good conductivity, high chemical stability and good economy, a new nanostructured TiN / MnO2 material was designed (Energy Environ. Sci., 2011, 4 (9), 3502 – 3508), mesoporous TiN nanospheres (ACS applied material interf. 2011, 3, 93-98) and coaxial TiN-VN materials (ACS applied material interf. 2011, DOI: 10.1021 / am200564b) are used as electrodes for high-energy capacitors material. The research results show that the above-mentioned composite materials can exhibit better mixed conductivity and exert higher capacity, which can take into account the energy and power density of the materials. Among them, the mesoporous TiN nanospheres can maintain an energy density of 45.0 Wh kg−1 at a higher power density.
Lithium-air secondary batteries theoretically have a very high energy density (more than ten times that of lithium-ion batteries). In order to meet the power battery's demand for lithium battery energy density, the team used nitrogen-doped graphene / MoN composites to construct a new type of air electrode material, which has excellent catalytic activity, greatly reduces discharge polarization, and improves energy utilization (Chem. Com. 2011, DOI: 10.1039 / C1CC14427H). At the same time, using a conductive array of biological enzymes and TiN to construct a biomimetic bio-empty battery (Biosensors and Bioelectronics 26 (2011) 4088–4094).
The team of Cui Guanglei also cooperated with Prof. Joachim Maier and Prof. Antonietti Markus of Solid State Institute, Metal Institute and Colloid Institute of the German Max Planck Association to carry out in-depth basic research on the lithium storage mechanism of materials. A new type of Ti-VN / C nano-composite with a multi-phase interface inside. This material exhibits good interfacial lithium storage properties, and at high currents, the material also exhibits good rate performance (ChemPhysChem 2010, 11, 3219–3223).
The team collaborated with academician Chen Liquan of the Chinese Academy of Sciences and Prof. Gu Lin to study the structure-effect relationship between nitrogen doping on the structure of graphene and the physical properties of lithium storage and the corresponding interface dynamics. The results show that nitrogen doping provides graphene sheets More lithium active sites, and nitrogen doping can greatly reduce the interface impedance (J. Mater. Chem., 2011, 21, 5430-5434). In-depth work found that Li3N (fast ion conductor) and its derivatives were generated on the interface It is the main reason for greatly reducing the interface impedance and forming a favorable SEI interface; in the process of studying nitrogen-doped graphene / VN composites, the use of EELS, external field XRD and high-resolution electron microscopy technology found that the composite (low VN activity) needs to be constantly After activation, it reacts with lithium, leading to a continuous increase in capacity (J. Mater. Chem., 2011, DOI: 10.1039 / c1jm11710f), and based on the above mechanism, developed an electrode material for high-power lithium-ion battery capacitors (Chinese invention patent ZL201010104003.1) .
Related research has been supported by the Ministry of Science and Technology's Major Research Program (973), the National Natural Science Foundation of China, the Chinese Academy of Sciences' "Hundred Talents Program", and the Shandong Outstanding Youth Fund.
Figure 1 The three main kinetic processes of lithium ion in lithium lithium ion secondary batteries [By Prof. Joachim Maier]
Figure 2 Nanostructured hybrid transmission (electron and ion) electrode material design concept
Figure 3 TEM (left) and EELS diagram of nitrogen-doped graphene / VN composite (indicating that lithium ions are continuously inserted into VN after cycling)
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