At present, the industry generally believes that the short-term goal of lithium battery technology is to achieve 300wh/kg through high nickel ternary anodes and silicon carbon anodes; the medium-term (2025) goal is based on lithium-rich manganese-based/high-capacity Si-C anodes to achieve single The body is 400wh/kg; in the long term, it is to develop lithium-sulfur and lithium-air batteries to achieve a specific energy of 500wh/kg. In the article "Why Lithium Sulfur/Lithium Air Battery Does Not Have Power Battery Application Prospects", Professor Ai Xinping of Wuhan University has recognized the feasibility of the short-term and medium-term goals and discussed in detail that lithium sulfur/lithium air batteries do not have power battery applications. The reason for the prospect; in the article "Where is the way out for the innovation of lithium battery core materials?", the next generation of lithium battery materials solutions are also discussed.

　　1. Battery safety issues.

　　Among them, the dissociation heat of the positive electrode is an important cause of thermal runaway of the battery. Taking three raw materials as an example, whether it is high nickel ternary or general ternary, their thermal stability is much worse than that of lithium iron phosphate. Not only does it emit a large amount of heat, but also has a low decomposition temperature, which will lead to the safety of our future batteries. The problem will be more serious. Of course, to solve the safety problem, we need to work in all directions from three aspects: materials, monomers, and systems.

　　Only a few solutions at the monomer level are discussed here.

　　The first idea is to develop battery self-excited thermal protection technology.

　　Lithium batteries have no temperature-sensitive features, and high temperature may cause thermal runaway. If there is a temperature-sensitive material in the battery that can effectively cut off the transmission of electrons and ions when the temperature is high, the battery will automatically shut down its reaction under abuse conditions to avoid further temperature rise.

　　The easiest way is to use PTC materials in batteries to achieve temperature sensitivity. In fact, PTC materials are used in many fields, but the batteries are not used. The main feature of PTC material is that it conducts well at room temperature; when it reaches a certain conversion temperature, the resistance rises sharply, changing from a conductor to an insulator, which cuts off the electron transmission on the electrode.

　　Research also found that some conductive polymers have PTC effect and are soluble. This material can be used to prepare very thin coatings. For example: P3OT polymer, the conductivity is relatively high at 30-80 degrees, but there will be three orders of magnitude change immediately at 90-110 degrees, the coating is less than 1 micron, about 600 nanometers, so Will not affect the energy density of the battery. This material exhibits thermal shutdown properties at 120 degrees, which significantly improves the safety of the battery under conditions such as overcharging, hot box, and acupuncture.

　　In addition, thermally closing the diaphragm is also a feasible method. The existing three-layer diaphragms all have a thermal shutdown function. For conventional diaphragms, its closed cell temperature is determined by the melting point of PE, which is about 135 degrees; the melting temperature is determined by the melting point of PP, which is about 165 degrees. Because the closed cell temperature is too high, after the heat is turned off, the thermal inertia can easily cause the battery temperature to continue to rise to 165 degrees, causing the diaphragm to melt and the battery to short-circuit. Therefore, the thermal protection effect of the conventional diaphragm is limited.

　　If a layer of plastic micropores is coated on the surface of the diaphragm, the surface microsphere layer will melt when the temperature reaches the melting point of the microspheres. After the ball is melted, the hole in the diaphragm is blocked. As a result, the holes on the surface of the electrode on which side the microspheres face are blocked, and the effect is very obvious. As the ion transmission is cut off, the battery reaction stops and the battery is safe.

　　The second idea to solve the safety problem is to develop all-solid-state batteries.

　　In fact, in terms of increasing the volumetric energy density, all-solid-state batteries are very promising. As battery density increases, volumetric energy density becomes more and more important for passenger cars. Judging from the feedback at the 57th Japan Battery Conference, some R&D institutions in South Korea and Japan are conducting research on solid-state batteries, and some large domestic battery companies such as ATL are also doing research in this area.

　　Comparing all solids and liquids, the main advantage is high safety. Another feature is the ability to achieve internal series connection, which is beneficial to the improvement of the energy density of the module and the system. However, its interface stress is large and its stability is poor. The solid electrolyte must be in full contact with the active material particles, otherwise the transmission of lithium ions cannot be realized. However, any electrode material, whether it is graphite or ternary material, will change in volume during charging and discharging. Once the volume change causes solid/solid separation, the conduction of lithium ions will be hindered, and the battery performance will drop rapidly.

　　Therefore, one of the key points of the whole R&D of solid battery is the choice of solid electrolyte. From now on, sulfide is more suitable because sulfide is relatively soft; the second is the construction technology and stabilization technology of solid/solid interface. There is a knack, if it is definitely not possible to do it with pure solid electrolyte, the best way is a hybrid of inorganic and polymer; the third is the development of production technology and special equipment. The production process of solid-state batteries is definitely different from our current business format.

　　2. Design technology of high-capacity electrode.

　　After the energy density increases, the problem of electrode design becomes more prominent. The proportion of active materials in the battery is an important factor that affects the specific energy of the battery. The same positive and negative materials, the same gram capacity, if the active material in a battery accounts for a relatively small mass, the energy density of the battery will be low. Therefore, to increase the energy density, it is necessary to fill as much active material as possible from the battery of the same weight. More active materials must be less auxiliary materials, copper foil should be reduced, and aluminum foil should be reduced; in fact, the most important thing is to make the electrode thicker. If the electrode is thicker, the amount of current collector and diaphragm will be reduced.

　　However, lithium ion electrodes cannot be made thick. After thickening, the electrode surface polarization becomes larger, and the utilization rate of the electrode in the thickness direction decreases, and it will cause problems such as lithium ionization in the negative electrode and decomposition of the positive electrode during the charging process. In terms of increasing energy density, it is hoped that the thicker the better; but the polarization theory tells us that the thinner the electrode, the better, the two are completely contradictory. As the energy density increases, for example, a single unit of 100wh/kg now becomes 300wh/kg, which means that the current per unit weight of the material increases simultaneously. Therefore, it is very difficult to maintain power performance for future high energy density batteries. , So high-capacity electrode design technology is becoming more and more important.　　 There is actually a way to resolve this contradiction. The liquid phase current increases as it gets closer to the diaphragm, and this current is the external current; along the thickness of the pole piece, the liquid phase current gradually decreases, and the solid phase current gradually increases. Therefore, the closer the diaphragm to the electrode, the higher the pores, and the closer to the electrode's polar fluid, the lower the electrode pores can be. Therefore, in order to ensure high energy density and power performance, it is necessary to design an electrode with a gradient pore distribution. With the application of new materials and the improvement of battery energy density, the design of gradient pore electrodes becomes more and more important. As for the degree of gradient, it is difficult to find out by experiment. It is necessary to establish a polarization model.

　　Finally, a summary by Professor Ai Xinping of Wuhan University:

　　1) Lithium-ion batteries are still the focus of power battery development. To solve the problems of low cycle coulombic efficiency of silicon anodes and voltage attenuation of lithium-rich manganese bases, it is expected that advanced lithium-ion power batteries with specific energy exceeding 400wh/kg will be developed.

　　2) From a long-term perspective, innovative lithium-ion batteries are more realistic and feasible than lithium sulfur and lithium air. The development of a high-capacity lithium-rich oxide positive electrode based on the anion charge compensation mechanism can develop a power battery with a specific energy greater than 500wh/kg.　　3) Safety determines the prospects of high specific energy battery loading applications. The development of self-heating control technology and all-solid-state batteries is a feasible solution, and it is necessary to step up research.

　　4) High-capacity electrodes are the basis for achieving high specific energy of batteries. According to the new polarization, the development of gradient porosity electrodes has an important role and significance for the development of high specific energy batteries.