In recent years, the energy crisis has become increasingly prominent, and new energy has become the focus of development. As a rising star in the automotive industry, new energy vehicles have attracted the attention of major car companies. Compared with fuel vehicles, electric vehicles have significantly reduced energy consumption and exhaust emissions, which is in line with current energy conservation and emission reduction policies. It is the best choice for urban public transportation, and the key to the development of electric vehicles is energy storage devices, which we usually call traditional batteries. It is a kind of energy storage device.
Emerging supercapacitors have the advantages of long service life, short charging time, clean and pollution-free, high current discharge capability and high power density, which have become the development of electric vehicle energy storage devices. Supercapacitor pure electric vehicles are zero-emission and zero-pollution, and they are becoming popular with super-capacitor pure electric vehicles. However, the specific energy of super capacitors is still relatively low. The lithium ion secondary battery has been greatly developed. The negative electrode of the battery generally uses a carbon material such as graphite, and the positive electrode uses a lithium-containing metal oxide such as lithium cobaltate or lithium manganate. After the battery is assembled, the positive electrode supplies lithium ions to the negative electrode during charging, and the lithium ion of the negative electrode returns to the positive electrode during discharge, so it is called a "rocking chair type battery". Compared with lithium batteries using lithium metal, this battery is characterized by high safety and high cycle life. The specific power of the battery is low, and people are trying to solve this problem in two aspects: (1) using the battery in combination with the supercapacitor, when the normal operation, the battery provides the required power; when starting or requiring a large current discharge, It is provided by a capacitor, on the one hand, it can improve the shortcomings of poor low-temperature performance of the battery; it can solve the application for high-power pulse current, such as GSM, GPRS, etc. The combination of capacitors and batteries can extend the life of the battery, but this will increase the battery accessories, contrary to the current development of energy equipment such as short and thin. (2) Using the principle of electrochemical capacitors and batteries, hybrid capacitors were developed as new energy storage components.
In 1990, Giner introduced a so-called tantalum capacitor or Pseudo-capacitor with noble metal oxide as the electrode material. To further increase the specific energy of electrochemical capacitors, 1995, D. A. Evans et al. proposed the concept of combining an ideal polarization electrode with a Faraday reaction electrode to form a hybrid capacitor (Electrochemical Hybrid Capacitor, EHC or Hybrid capacitor). In 1997, ESMA announced the concept of NiOOH/AC hybrid capacitors, revealing new technologies for battery material and electrochemical capacitor material combinations. In 2001, G. G. Amatucci reported that Li4Ti5012/AC electrochemical hybrid capacitors with organic lithium-ion battery materials and activated carbon are another milestone in the development of electrochemical hybrid capacitors. However, this electrochemical hybrid capacitor has a problem of low power density and low energy density. Therefore, it has been an effort to provide a supercapacitor battery having both high specific power characteristics and high specific energy characteristics.
At present, there are two ways to combine the supercapacitor and the lithium ion secondary battery energy storage system: one is “external combination”, that is, the two monomers are combined into one energy storage device or system through the power management system. The other is "inner bonding", which combines the two organically in the same monomer. A hybrid power system consisting of a supercapacitor and a battery in parallel ("external combined" power system), although it can provide power for electric vehicles, is less complex than the power, weight and volume, and system management and control is too complicated Disadvantages, so the effect is not ideal. The "in-combined" power supply system has the advantages of high specific power, small weight and small volume, low cost, and can ensure the consistency of the unit and reduce the complexity of the management system, so it has become the focus of current research.
Supercapacitor batteries are those that have both electric double layer energy storage and lithium ion deintercalation for energy storage. They also have the advantages of supercapacitors and lithium ion batteries. The current research direction of this system is roughly divided into the following four types:
The first direction is that the positive electrode is lithium ion energy storage and the negative electrode is double electric layer energy storage. The advantage of this method is that the combination is simple, the electrochemical problems to be solved are less, the positive and negative electrode ratio, electrolyte and current collector are selected. For the research core of this kind of device, this kind of device has also realized commercial application. The typical representative patent is the hybrid water-based lithium ion battery of Xia Yongyao of Fudan University, but the voltage of this system is generally 1.8V, even if the electrolyte The organic electrolyte voltage is also selected within 2. 7V, which limits the increase in power and energy.
In the second direction, the positive electrode is the electric double layer energy storage, and the negative electrode is the lithium ion energy storage. The system is characterized by high voltage to achieve high power, but since the positive electrode is only the electric double layer energy storage, the energy density is increased. One difficulty is that, since the negative active material is lithium storage and the positive electrode has no lithium source, the core of the system is the negative pre-doped lithium ion design. There are many researches on this system, but there is still a big gap between the energy density that can be achieved and the lithium-ion battery.
Fuji Heavy Industries proposes a new type of battery that combines the characteristics of both capacitors and lithium-ion rechargeable batteries: the positive electrode is made of activated carbon material, and the negative electrode is made of lithium-filled carbon material. The mass ratio energy is 30Wh/kg, and the volume specific energy is reached. 52Wh / L, greatly exceeds the electric double layer capacitor. At the 16th International Electrochemical Conference in 2006, Hatozaki O et al. reported a lithium-ion capacitor. The negative electrode of the lithium-ion capacitor is a lithium-intercalated carbon material treated with a metal lithium plate, and the positive electrode has a double The activated carbon stored in the electric layer has a working voltage of 3. 8V, a specific energy of 30Wh/kg, and a specific power of up to 6kw/kg, but the process of treating the carbon material with the metal lithium sheet is complicated.
Hongyu Wang used different types of graphite as the negative electrode, and the positive electrode used activated carbon. The effects of electrolyte anion and cation, ratio of positive and negative materials on the performance of supercapacitor cells were studied. The results showed that graphite was used instead of activated carbon as the negative electrode, and the discharge capacitance was very large. Increasing, the discharge voltage is also greatly improved, so the energy density is greatly improved compared with the electric double layer supercapacitor.
The third direction is that the positive electrode has both lithium ion energy storage and electric double layer energy storage function, and the negative electrode also has lithium ion energy storage and electric double layer energy storage, but due to the voltage limitation of the negative electrode electric double layer energy storage, It is theoretically difficult to obtain the same energy storage potential interval in an electrolytic cell. The system is difficult to be practical, and it is rarely reported.
The fourth direction is that the positive electrode has both lithium ion energy storage and electric double layer energy storage function, and the negative electrode is lithium ion energy storage. The high voltage of the system can achieve high power, and the positive electrode has double layer energy storage and lithium ion chemistry. Energy storage, therefore, can increase the specific energy at the same time, is the most ideal system, but because the positive electrode has different energy storage methods, and the potential of the stored energy is not completely matched, these technical problems constrain the development of the system.
At present, the internal combined supercapacitor battery, the positive electrode material adopts the composite technology of lithium metal oxide and activated carbon material, the negative electrode material selects hard carbon, through the positive and negative energy storage potential matching technology, the positive and negative current collectors respectively adopt the porous cathode The foil has a holed copper foil, and the negative electrode hard carbon is electrochemically pre-doped by the third electrode, so that the initial state of charge of the hard carbon reaches 30%-80%. The resulting supercapacitor battery greatly improves the specific energy while maintaining the high specific power, long life and fast charging characteristics of the supercapacitor, and has a larger application than the conventional button ion capacitor, and at the same time The characteristics of ultra-high cycle life are retained. Its working voltage can reach 4. 2V, the specific energy can reach 50Wh/kg, and the specific power reaches about 100W/kg. The cycle life reaches 50,000 times.
Driven by the rapid growth of market demand, the existing supercapacitor manufacturers in China are actively financing and expanding production. The international supercapacitor production predators have also targeted the strategic investment in China. As emerging companies continue to emerge, supercapacitor batteries are in China. The large-scale application is gradually getting closer. Domestic suppliers are actively responding to the problems faced by scale applications from different perspectives. At present, the supercapacitor industry is still in the early stage of rapid development, and its future development space is huge.