What are the power secondary batteries for vehicles?

Other types of secondary batteries, including vanadium-lithium batteries, sodium-ion batteries, magnesium-ion batteries, and lithium-air batteries, are currently researched and applied, and the following will briefly summarize these secondary batteries.

When the secondary lithium battery technology was first developed, technicians generally used lithium metal as the negative electrode material. However, due to technical problems such as lithium dendrites (which are easy to cause short circuits), it was difficult to solve. Currently, lithium alloys are mainly used in lithium ion batteries. Or lithium compounds as negative electrode materials. Despite this, there are still companies and researchers who have adhered to the technological development route of metal lithium as the negative electrode for many years, such as Japan's Fuji Heavy Industries, France's BarCap, etc., which use vanadium oxide as the positive electrode material, and have launched vanadium-lithium batteries for application.

In 2006, Japan's Fuji Heavy Industries released a lithium battery using vanadium pentoxide (V₂O₅) as a positive electrode material with an energy density of up to 200Wh/kg. The technical principle of the vanadium-lithium battery is as follows: when the battery is made, the lithium metal is electrolyzed, so that lithium ions are doped on the negative electrode. Since there are a lot of lithium ions on the negative electrode side, although V₂O₅ as the positive electrode material does not contain lithium, it can also be used as an electrode with lithium ions doped on the negative electrode. The technology of vanadium-lithium battery is still under further research and development, and its stability still cannot meet the requirements. The lithium metal polymer battery (LMP lithium battery) product developed by French Barcap uses metal lithium as the negative electrode material, while the positive electrode material uses a resin composite material composed of vanadium oxide, carbon and polymer, and uses solid polymer as the negative electrode material. electrolyte. The LMP lithium battery developed by RatScap has been applied to the electric vehicle product Lucar ev developed by Bollore. The 30kWh IMP lithium battery pack equipped in the Bluccar ev is laid under the floor of the entire cabin and weighs 300kg. Compared with the Nissan Leaf ev, which can store 24kWh of electricity but weighs 280kg, it has a slightly higher energy density. The battery pack voltage is 200~435V. The battery pack can work normally when the external temperature is -20°C~60°C and the internal temperature is 60°C-80°C. The battery pack's warranty coverage is 200,000 km. The BlueCar EV is additionally equipped with supercapacitors as auxiliary equipment, and it is equipped with a motor with a maximum output of 45kW. By using the hybrid power mode of LMP lithium battery and supercapacitor, the BlueCar EV can reach a top speed of 130km/h and a continuous driving distance of 250km. A full charge takes 6 hours, and a 2-hour fast charge restores 50% of the battery's capacity.

2.Sodium batteries

The global reserves of lithium resources are not high. In comparison, sodium is cheap, non-toxic and abundant, so it has received widespread attention. Previous secondary batteries using sodium include the commercial sodium-sulfur battery developed by Japan's NGK company and the sodium-nickel chloride battery developed by Switzerland's MES-DEA company. These batteries use sodium and ceramic solid electrolytes and require an operating temperature of at least 300°C.

1) Sodium Nickel Chloride battery

The sodium nickel chloride (Na-NiCI₂) battery was invented by Dr. J Coetger of Zebra power systems in South Africa, so it is called Zebra battery. Germany's AEG Zebra Battery Marketing Gmbh is the main company that studies and trial-produces Zebra batteries. It has carried out trial production of 1-3 generations of battery products, and has been tested and used in cars, trucks and buses. Tests have proved that Zebra batteries have excellent It can meet the requirements of electric vehicle power performance and driving range.

The specific energy of sodium-nickel chloride battery is high, which can theoretically exceed 700Wh/kg. At present, the specific energy of the actual product has reached 100Wh/kg. Therefore, it has great potential for development. The open circuit voltage of sodium-nickel chloride batteries is higher, up to 2.58V. The improved sodium-nickel chloride battery has a higher peak power, which is beneficial to improve the power of electric vehicles. In addition, the sodium-nickel chloride battery also has a high energy conversion rate, no self-discharge, resistance to overcharge and overdischarge, and the battery has Wide operating temperature range and good stability, the cycle life can reach more than 1000 times of charge and discharge. The sodium-nickel-chloride battery adopts a fully sealed structure, which will not burn or explode when subjected to vibration and shock, and is easy to maintain.

In the experimental demonstration area established by Germany on the island of Regen, Mercedes-Benz's 190-type electric car and A-class electric car, BMW's 3-series electric car, and Volkswagen's (VW) Golf electric car , Kadett's electric cars of Opel Company and buses of MAN Company are equipped with zebra power battery as a hybrid battery pack, which effectively increases the mileage of the vehicle. Zbra batteries can be maintenance-free for five years, and some of the experimental vehicles have a range of more than 10,000km. Tests show that Zebra sodium-nickel-chloride battery is a very promising new type of high-energy battery for electric vehicles.

2) Na-ion batteries.

Sodium ion batteries have also received extensive attention from researchers. Although the characteristics of sodium ion batteries are similar to those of lithium ion batteries, the radius of sodium ions is at least 35% larger than that of lithium ions. The limitation of physical size makes sodium ions intercalate and desorb at the positive and negative electrodes. The reaction rate is lower, and the stability of the cathode material for sodium-ion batteries is also higher. The latest research progress of sodium-ion batteries is shown in Figure 1.

The cathode materials of sodium-ion batteries include oxide type and polyanion type; the anode materials include carbon-based materials, titanium-based materials and alloy materials; the electrolytes mainly include organic solvent electrolytes and gel polymer electrolytes. Although various materials have their own advantages and limitations, many researchers believe that the sodium secondary battery system may gradually replace the lithium ion battery. The main problem of the current sodium ion battery research is how to match the different material systems. Cheap and high-performance materials are the key to the commercialization of sodium-ion batteries. While learning from the development experience of lithium-ion batteries, it is also necessary to understand the major differences between the two. A large number of research results on different types of positive and negative electrode materials and structural systems show that the continued in-depth exploration of sodium salt compounds is the key to sodium-ion batteries. important path for rapid development.

Pelion Technologies of the United States is actively developing magnesium secondary batteries with high energy density. The company uses computer technology to analyze and predict material properties to accelerate the process of material synthesis and electrolyte optimization, thereby identifying new magnesium anode materials with high energy density and compatible electrolyte materials. According to a statement from the U.S. Department of Energy's Advanced Research Projects Agency, Pelion Technologies is expected to break through current battery technology for electric and hybrid vehicles.

Lithium-air battery is a battery with metal lithium as the negative electrode and oxygen in the air as the positive electrode reactant. During the discharge process, the metal lithium of the negative electrode releases electrons to form lithium ions (Li⁺), and Li⁺ passes through the electrolyte material to combine with oxygen and electrons flowing from the external circuit at the positive electrode to form lithium oxide (Li₂O) or lithium peroxide (Li₂O₂) , and remain in the porous carbon substrate of the positive electrode. The open circuit voltage of the lithium-air battery cell is 2.91V.

The lithium-air battery has a high energy density, and its specific energy can reach 5210Wh/kg (with oxygen mass), or 11140Wh/kg (without oxygen mass). It needs to be stored in the positive electrode. Theoretically, since there is no material limit for oxygen as a positive reactant, the capacity of the lithium-air battery depends only on the lithium metal electrode, and its isothermal value is 40.1M/kg, which is similar to the gasoline's 44MU/kg. Therefore, Li-air batteries are very attractive from the point of view of specific energy.

In 1996, KMAbrahan and his colleagues demonstrated for the first time a practical non-aqueous lithium-air battery. This battery uses metallic lithium as the negative electrode, porous carbon as the positive electrode substrate material, and a gel-like electrolyte film between the positive and negative electrodes as the battery. Separators and media for ion transport, electrolyte materials include gel-like electrolytes such as polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF), and materials such as organic solvents, dry organic polymers, and inorganic metal electrolytes can also be used. Oxygen from the environment enters the cathode region through the pores of the porous carbon and acts as the cathode active material. During the discharge process of the lithium-air battery, the oxygen in the carbon-based pores is consumed, and the generated discharge products are subsequently filled in the carbon-based pores.

Since the cathode of a lithium-air battery is constructed in the same way as a fuel cell, the electrode needs to have the ability to use a catalyst to react with oxygen. At the same time, as a secondary rechargeable battery, it must also have the function of reducing reaction products such as Li₂O₂, which needs to be further solved in practical application. The Japan Institute of Industrial Technology developed a new type of large-capacity lithium-air battery in 2009. The negative electrode material of the battery is metal lithium, which is immersed in an organic solvent electrolyte containing lithium salts, and the positive electrode uses an aqueous electrolyte, which has a similar structure. For fuel cells, the oxygen in the air reacts with the water-based electrolyte of the positive electrode under the action of the catalyst in the porous carbon material to form an alkaline solution at the positive electrode, which completely avoids the formation of lithium oxide at the positive electrode of the original lithium-air battery. The problem of plugging porous carbon. The separator of the battery uses lithium zinc germanate (LISICON) wafer as the solid electrolyte to prevent the two electrolytes from mixing, and the open circuit voltage of the battery is about 3V. Experiments show that the battery has a very high specific capacity, the value is as high as 50000mAh/g, and the highest is 80000mAh/g. In 2010, Toyota Motor Corporation of Japan released the trial production results of a lithium-air battery with a positive electrode composed of ketjen black, electrolytic manganese dioxide and fluororesin powder (PTFE), and a negative electrode composed of metal lithium materials.

Research and development in lithium-air batteries in the United States is also continuing. For example, IBM has rich experience in material science, nanotechnology, chemistry and supercomputer, so it has obvious advantages in the development of lithium-air batteries. The company plans to use nano-diaphragm technology to develop a water purification system to combine oxygen in the air with water material isolated. Using experience with nanostructures can also distribute the oxygen in the battery to each cell to prevent clogging. Supercomputers can conduct modeling research that effectively guarantees that individual atoms can pass through the nanomembranes in batteries. A technology consortium led by IBM hopes to manufacture lithium-ion power batteries that combine lithium and oxygen elements, and double the performance of current lithium batteries, which can drive electric vehicles for 500 to 800 kilometers on a single charge.

Although many countries and companies have made progress and produced samples in the field of lithium-air batteries, so far, the development of lithium-air batteries is still very difficult. The urgent problems to be solved in this battery technology mainly include how to prevent the two Chronic penetration of electrolyte outside the diaphragm; how to increase the usable temperature range of organic electrolyte, improvement of catalysts, safety issues of lithium materials, and how to recycle unused lithium metal and lithium hydroxide, etc.