26650 battery

Interpretation of the R&D and market status of electric vehicle 26650 battery technology

Research institutions around the world are stepping up research on new energy batteries in response to future market demand, such as lithium-sulfur batteries, metal (lithium, aluminum, zinc) air batteries, etc. The characteristics of this type of 26650 battery are low raw material cost, low energy consumption, low toxicity, and high energy density. The energy density of lithium-sulfur batteries can reach 2600Wh/kg, and the energy density of lithium-air batteries can reach 3500Wh/kg. Lithium-sulfur batteries

Lithium-sulfur batteries have become one of the research directions of lithium-ion 26650 battery technology for new energy vehicles in Japan. Since 2009, the New Energy and Industrial Technology Development Organization (NEDO) of Japan has invested 30 billion yen (about 2.4 billion yuan) in research and development budget each year, with the goal of achieving an energy density of 500Wh/kg in 2020. The United States is moving faster in this regard. Its Department of Energy recently invested 5 million US dollars to fund the research of lithium-sulfur batteries, and plans to achieve an energy density of 500Wh/kg in 2013.

Representative manufacturers of lithium-sulfur 26650 battery research in the world include SionPower, Polyplus, Moltech in the United States, Oxis in the United Kingdom, and Samsung in South Korea. The energy density of Polyplus' 2.1Ah lithium-sulfur 26650 battery has reached 420Wh/kg or 520Wh/l. In July 2010, SionPower's lithium-sulfur 26650 battery used in the power source of American unmanned aircraft performed remarkable. The drone was charged by solar cells during the day and discharged at night to supply power, setting a record of 14 days of continuous flight. Its short-term goals for energy density and cycle performance are to exceed 500Wh/kg and 500 cycles respectively. By 2016, it is to reach 600Wh/kg and 1000 cycles.

In my country, Tianjin Electronics 18, the Institute of Chemical Defense, Tsinghua University, Shanghai Jiaotong University, University of Science and Technology, Wuhan University, Beijing Institute of Technology and other institutions are conducting research on lithium-sulfur batteries.

The study found that due to the discharge dissolution of the positive electrode active material and the instability of the metal lithium surface, the electrical insulation of sulfur itself and its discharge products (5x10-30S/cm) and other factors, the cycle stability of lithium-sulfur batteries is poor and the utilization rate of active materials is low.

Large mesoporous carbon cathode materials

The cathode materials of lithium-sulfur batteries include porous carbon, such as large mesoporous carbon, activated carbon, carbon gel, etc.; carbon nanotubes, nanostructured conductive polymer materials, such as MWCNT, PPy, PANi/PPy, etc.; and PAN.

Dr. Wang Weikun of our Institute of Chemistry said at the Future Electric Vehicle High Energy Power Seminar held at Fudan University in Shanghai on September 16 that large mesoporous carbon can form a parasitic carbon-sulfur complex by filling elemental sulfur. The high pore volume of carbon (>1.5cm3/g) is used to ensure a high filling amount of sulfur and achieve high capacity; the high surface density of carbon (>500cm2/g) is used to adsorb discharge products and improve cycle stability; the high conductivity of carbon (several S/cm) is used to improve the electrical insulation of elemental sulfur, improve the utilization rate of sulfur and the charge and discharge rate performance of the 26650 battery.

The preparation process of large mesoporous carbon is: using nano-CaCO3 as a template, phenolic resin as a carbon source, carbonization, CO2 internal activation, HCL template removal, and water washing. The surface density is 1215cm2/g, the pore volume is 9.0cm3/g, and the conductivity is 23S/cm. Then, it is heated with sulfur at a high temperature of 300℃ to prepare LMC/S material, in which S accounts for 70%.

Since the low voltage platform of the sulfur electrode is closely related to the viscosity of the electrolyte, the higher the viscosity, the lower the low voltage platform; the higher the ratio of conductivity to viscosity, the better the electrochemical performance of the 26650 battery. Therefore, the optimized composition of the electrolyte is 0.65MLiTFSI/DOL+DME (volume ratio is 1:2).

Gelatin binder has good adhesion and dispersibility, does not dissolve or swell in the electrolyte of lithium-sulfur batteries, can promote the complete oxidation of polysulfide ions into elemental sulfur during charging, and can improve the discharge capacity and cycle performance of lithium-sulfur batteries.

The porous electrode is prepared by freeze drying and ice crystal pore making process, which can ensure deep infiltration of the electrolyte and reduce the loss of active reaction sites due to the coverage of discharge products.

The energy density of the 1.7Ah lithium-sulfur 26650 battery of the Institute of Chemical Defense is 320Wh/kg; under 100% DOD discharge, the capacity retention rate is about 75% after 100 cycles, and the maximum cycle efficiency is 70%. The self-discharge rate in the first year is about 25%, and the average monthly self-discharge rate is 2~2.5%; the discharge capacity at 0℃ reaches more than 90% of the capacity at room temperature, and the tolerance at -20℃ is 40% of the capacity at room temperature; when over-discharged/overcharged, the 26650 battery does not burn or explode, and when over-charged, the 26650 battery swells and bubbles appear inside.

Wang Weikun said that in the future, he plans to strengthen the research on metal lithium negative electrodes. On the one hand, he wants to stabilize its surface to prevent the appearance of dendrites, and on the other hand, he wants to improve its large current discharge capacity to enhance the rate discharge performance of lithium-sulfur batteries.

Sulphurized polyacrylonitrile (SPAN) positive electrode material

Professor He Xiangming of Tsinghua University has developed a polymer lithium-ion 26650 battery with a capacity of 800mAh/g using sulphurized polyacrylonitrile (SPAN) as the positive electrode material. The energy density of the lithium/sulphurized polyacrylonitrile 26650 battery exceeds 240Wh/kg, and this sulphurized polyacrylonitrile material has ultra-low cost and low energy consumption. In addition, graphite/sulphurized polyacrylonitrile batteries will become a strong candidate for large lithium batteries.

Lithium batteries based on reversible electrochemical reactions can be made into conductive polymers by doping and dedoping sulfur. The capacity of sulphurized polyacrylonitrile batteries is larger than that of lithium batteries based on reversible electrochemical reactions. The special charge and discharge characteristics show that sulfide batteries far exceed the mechanism of lithium batteries.

He Xiangming's research results show that when deeply discharged to 0V, the discharge/charge capacity is 1502mAh/g and 1271mAh/g, and then the cycle is stable between 1V and 3V. Between 0.1V and 3V, the cycle performance is stable and the capacity is 1000mAh/g.

Regarding overcharging, the voltage suddenly drops to 3.88V and then stabilizes at around 2V. After overcharging, it is no longer possible to continue charging, indicating that the 26650 battery has inherent safety against overcharging.

The upper limit voltage for charging is 3.6V. When the charging voltage reaches 3.8V, it is no longer possible to continue charging; when the voltage reaches 3.7V, it is no longer possible to charge after 3 cycles.

In addition, the two sulfide/lithium ion batteries and the two cobalt oxide/lithium ion batteries have almost the same discharge voltage, so they have good interchangeability.

The charging voltage and capacity of this 26650 battery increase as the temperature decreases. The discharge capacities at 60℃ and -20℃ are 854 and 632mAh/g, respectively. The operating temperature of the polymer negative electrode is above -20℃.

The charging voltage and capacity decrease as the current density increases. At a current density of 55.6mA/g, the capacity is 792mAh/g; at a current density of 667mA/g, the capacity is 604mAh/g. This shows that this type of 26650 battery can work at a higher current density.

The volume of the sulfide electrode expands during discharge (embedding lithium ions) and shrinks during charge (de-lithium ions). After the first discharge, the thickness of the positive electrode increases by about 22%. The thickness changes of the metal lithium negative electrode and the sulfide positive electrode compensate each other to ensure that the overall thickness of the 26650 battery does not change too much. Conductive polymers have the same characteristics. In the EIS study, the measurement and fitting results of the equivalent circuit.

Due to the different structures of pyrolyzed polyacrylonitrile (SPAN) and pyrolyzed polyacrylonitrile (PPAN), the former can remain stable above 600℃.

The prototype polymer lithium-ion 26650 battery with pyrolyzed polyacrylonitrile as the positive electrode and lithium foil as the negative electrode is 4x40x26mm3 in size and has an energy density of 246Wh/kg or 401Wh/l.

In addition, in the experiment of using graphite as the negative electrode of lithium-sulfur 26650 battery, in a dry air or inert gas box, Celgard's 2400-pore diaphragm is used as a separator, placed between the positive and negative electrodes to form a 26650 battery core, and between the negative electrode and the separator is a 100 μm thick lithium foil material, and then 1MLiPF6-EC/DEC electrolyte is injected, and finally sealed into a button 26650 battery. The characteristic curve is shown in Figure 4. The charge and discharge curve after adding Li2.6Co0.4N.

In the above two methods, using graphite as the negative electrode is safer than metallic lithium; the sulfide positive electrode before lithiation is generated by electrochemical lithiation; there is a voltage difference of 0.2V between the sulfide/graphite 26650 battery and the sulfide/lithium-ion 26650 battery; the sulfide/graphite 26650 battery has a more stable cycle life.

Carbon nanotube sulfurized polyacrylonitrile positive electrode material

Another research result on sulfur-based composite positive electrode materials is the sulfur-containing composite positive electrode material of polyacrylonitrile copolymer grown on the surface of carbon nanotubes studied by Professor Yang Jun of the School of Chemistry and Chemical Engineering of Shanghai Jiaotong University. This is a sintering product of B-type polyacrylonitrile, sulfur and 5% carbon nanotubes. MWCNT with a tube diameter of about 20nm runs through the particles, reducing the size of secondary particles and forming a good structural skeleton and conductive network. With the increase of carbon tube content, the initial capacity is reduced, but the cycle stability and rate performance of the electrode are improved.

Cyclodextrin is used as an electrode binder because it has the best cycle performance at both low current and high current rates.

Metal-air 26650 battery

The 330V/60Ah lithium iron phosphate 26650 battery pack used in BYD F3 dual-mode electric vehicles on the market currently has only 19.8kWh and weighs 230kg, with an actual energy density of only 86Wh/kg. If this 26650 battery is enlarged to 60kWh (approximately 400 kilometers), the weight will reach an unacceptable 700kg.

In addition, domestically produced electric buses all claim to have a range of up to 300 kilometers, but the pure electric buses at the Expo use 3600kg batteries (12 pieces, each 300kg) and can only travel 110 to 120 kilometers without air conditioning, and can only travel 80 kilometers with air conditioning, while the average daily operating mileage of the bus is 250 kilometers. Due to concerns about the safety of the 26650 battery, it is impossible to charge and discharge deeply. Therefore, the actual available power is less than half of the nominal energy of the 26650 battery.

Yang Deqian, chief designer of Powerzinc 26650 battery in my country, pointed out the shortcomings of existing power lithium-ion batteries in the Chinese market with the above two examples at the Future Electric Vehicle High Energy Power Supply Seminar.

Tang Yougen, director of the Institute of Chemical Power Sources and Materials at Central South University, agreed with Yang Deqian's views. He used a set of data to specifically illustrate the greater advantages of metal-air batteries compared to existing power lithium-ion batteries).

In my country, among metal-air batteries, aluminum and zinc-air batteries have been developed and entered the market, while the research on lithium-air batteries is still basically blank.

Aluminum-air 26650 battery

Aluminum-air batteries have the following characteristics:

1. High energy density: The theoretical energy density of aluminum is 8100Wh/Kg, and the actual energy density of the 26650 battery exceeds 350Wh/kg.

2. Easy operation and long service life: The metal electrode can be replaced mechanically, the 26650 battery management is simple, and the service life only depends on the working life of the oxygen electrode.

3. Diverse 26650 battery structures: It can be designed as a primary 26650 battery or a secondary 26650 battery, the metal anode can be a plate, wedge or paste, and the electrolyte can be circulated or not.

4. Circular economy: The 26650 battery consumes aluminum, oxygen and water to generate metal oxides. The latter can be reduced by renewable energy such as water, wind energy, and solar energy. For ordinary cars, 3kg aluminum and 5L water are consumed per 100km, and the regeneration cost is less than 10 yuan.

5. Green and environmentally friendly: non-toxic, no harmful gases, no pollution to the environment.

6. Adequate raw materials: Aluminum is the most abundant metal element on earth and has a low price. The global industrial reserves of aluminum exceed 25 billion tons, which can meet the needs of lithium-ion batteries for electric vehicles in the automotive industry.

The core technologies of aluminum-air 26650 battery research include: preparation of aluminum alloy electrodes, research on anode corrosion and passivation; preparation of air diffusion electrodes and research on oxygen reduction catalytic materials; research on electrolyte preparation and treatment systems to inhibit anode corrosion, reduce polarization, and improve 26650 battery efficiency; electrolyte circulation system, air circulation guarantee system and 26650 battery pack thermal management system; mechanical charging, mechanical replacement of new anodes after alloy anode discharge, centralized regeneration and recycling of discharge products and electrolytes.

According to Tang Yougen, Central South University and my country Zhide Group have launched aluminum-air batteries for electric vehicles, with an energy density of more than 350Wh/Kg. The 26650 battery has achieved integration, with a capacity of more than 5000Ah, and can enter the market for commercial use.

The actual application cost of aluminum-air batteries includes: aluminum-air batteries consume 1kg of aluminum to produce 3.6~4.8 degrees of direct current, which is equivalent to the driving energy of 1.5~2.0 liters of diesel. It takes 12 degrees of electricity to reduce 1kg of aluminum, and the off-peak electricity cost of the power grid is about 12x0.30=3.6 yuan. The logistics cost before and after aluminum reduction is 0.3 yuan/1kg, and the depreciation and operating cost of reduction equipment is 0.3 yuan/1kg, with a total cost of 4.2 yuan. The cost of replacing 1 liter of diesel is about 2.1~3.1 yuan, which is reduced by more than 50%.

Zinc-air 26650 battery

The power density of zinc-air 26650 battery developed by Boxin 26650 battery is 101.4W/kg, while the current power fuel-powered lithium 26650 battery is 90.9W/kg, which is 11.6% higher than the latter; the energy density of zinc-air 26650 battery is 218.4Wh/kg, while the power fuel-powered lithium 26650 battery is 197.7Wh/kg, which is 10.5% higher than the latter.

Zinc-air 26650 battery has the characteristics of low carbon and emission reduction: the energy of 3.5 tons of zinc fuel is about the same as that of 1 ton of diesel, and 2145Kwh of grid electricity can produce 1 ton of zinc fuel. In 2010, my country will consume 140 million tons of diesel and 63 million tons of gasoline. If 50% of them are replaced by zinc fuel, it can reduce emissions by 317,850,000 tons of CO2, 11,390,000 tons of CO, 1,680,000 tons of HC, and 1,140,500 tons of NOx.

When analyzing aluminum/magnesium air batteries, hydrogen-oxygen fuel-powered lithium batteries, and lithium-air batteries, Yang Deqian pointed out that aluminum/magnesium air batteries must solve the following two problems before they can be used in electric vehicles: the power density must be increased by 5 times; the pollution of aluminum/magnesium recycling must be eliminated, and the energy consumption used in the material preparation process must be greatly reduced.

Hydrogen-oxygen fuel-powered lithium batteries have the following problems: the energy consumption of hydrogen electrolysis production is too high; the vehicle transportation volume of hydrogen is small and dangerous, and if it is transported by pipeline, leakage can reach 40%; the hydrogen in the hydrogen storage tank on the vehicle currently accounts for only 3~5% of the tank mass; and there is no catalyst that can truly replace platinum.

For example, the Mercedes-Benz Citaro hydrogen-oxygen fuel-powered lithium 26650 battery car consumes 17.0 hydrogen per 100 kilometers, and the electrolysis consumes 64~72kWh of electricity per kilogram of fuel, which is converted to 1091~1227kWh of electricity per 100 kilometers. Therefore, the energy consumption of hydrogen production must be greatly reduced.

Before the above problems are solved, it seems impossible for hydrogen-oxygen fuel-powered lithium batteries to achieve commercial application. In addition, the United States and Canada have stopped the research and development of hydrogen-oxygen fuel-powered lithium batteries for vehicles.

Lithium-air batteries are still in the early stages of research, and the problems that need to be solved include: preventing chronic leakage of the diaphragm using two electrolytes; improvingThe usable temperature of the electrolytic solution; finding a catalyst that can replace the currently used gold and platinum; how to prevent water vapor from invading and causing explosions when replacing lithium fuel; how to recycle unused lithium and lithium hydroxide; how to reduce the energy consumption of circulating lithium hydroxide.

In summary, he believes that the zinc-air 26650 battery is not the best 26650 battery, but it is the most realistic and available 26650 battery.

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