Brief description of alternatives to power batteries

The energy density, cycle, and safety of power batteries are becoming a technical problem that restricts the further promotion of new energy vehicles.

Metal-air battery

At present, the lithium iron phosphate battery 330V/60Ah battery pack used in the market has only 19.8 kWh and weighs 230 kg, and the actual energy density is only 86Wh/kg. If the battery is scaled up to 60 KWH (about 400km) it will weigh an unacceptable 700kg. By the national standard committee designated as one of the two leading enterprises of high-power charging.

The domestic electric buses all claim to have a cruising range of up to 300 kilometers, but the pure electric bus currently uses 12 battery packs (about 3600kg). The pure electric bus can only drive 110-120 kilometers without air-conditioning. It can only continue for 80 kilometers, and the average daily operating mileage of the bus is 250 kilometers. Due to the safety of the battery, it is impossible to charge and discharge deeply. Therefore, the actual available energy is less than half the nominal energy of the battery.

The above facts indicate that there are currently insufficient domestic mobile batteries。

In China, metal and air batteries, aluminum and zinc-air batteries have been developed and entered the market, and the research of lithium-air batteries is still basically a blank.

Aluminum air battery

The aluminum air battery has the following features:

The energy density is high: the theoretical energy density is 8100Wh/Kg, and the actual energy density exceeds 350Wh/kg.

Easy to operate, long service life: metal electrodes can be mechanically replaced, battery management is simple, and the service life depends only on the working life of the oxygen electrode.

The battery has various structures: it can be designed as a primary battery or a secondary battery, and the metal positive electrode can be a plate type, a wedge type or a paste body, and the electrolyte can be circulated or not circulated.

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

Green and environmental protection: no poisonous gas, no pollution to the environment. Adequate raw materials: Aluminum is the most abundant metal element on the earth and has a low price. The global aluminum industry's industrial reserves exceed 25 billion tons, which can meet the needs of the automotive industry electric vehicle power battery.

The core technologies of aluminum-air battery research include: preparation of aluminum alloy electrode, research on corrosion and passivation of positive electrode; preparation of air diffusion electrode and research on oxygen reduction catalytic material; research on preparation and treatment system of electrolyte, inhibiting corrosion of positive electrode and reducing Polarization, improve battery efficiency; electrolyte circulation system, air circulation guarantee system and battery pack thermal management system; mechanical charging, mechanical replacement of new positive electrode after alloy positive discharge, discharge product and electrolyte centralized regeneration treatment, recycling.

According to reports, domestic academic research institutions have cooperated with enterprises to launch electric vehicle aluminum-air batteries with an energy density of more than 350Wh/Kg. The battery has been integrated and the capacity has reached more than 5000Ah, which can enter the market.

Zinc-air battery

At present, the power density of zinc-air battery developed by the institution is 101.4W/kg, the power fuel cell is 90.9W/kg, the former is 11.6% higher than the latter; the energy density of the zinc-air battery is 218.4Wh/kg, and the fuel cell is 197.7Wh. /kg, the former is 10.5% higher than the latter.

The zinc-air 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 the 2145Kw grid can produce 1 ton of zinc fuel. In 2010, China consumed 156 million tons of diesel and gasoline consumption of 71 million tons. If 50% of them are replaced by zinc fuel, they can reduce 317.78 million tons of CO2, 11.39 million tons of CO, 1.68 million tons of HC, and 1,140,500 tons of NOx.

Aluminium/magnesium-air batteries must address two challenges that are promising for electric vehicles: a five-fold increase in power density; eliminating aluminum/magnesium recycling contamination and significantly reducing the energy used in material preparation.

Hydrogen-oxygen fuel cells have the following problems: the electrolysis production of hydrogen consumes too much energy; the transportation of hydrogen vehicles is small and dangerous, such as pipeline transportation, the leakage can reach 40%; the hydrogen in the hydrogen storage tanks on the vehicle is currently only It accounts for 3 to 5% of the mass of the tank; there is no catalyst that can really replace platinum.

For example, the Mercedes-Benz Citaro oxyhydrogen fuel cell vehicle consumes 17hydrogen per 100 kilometers, and the electricity consumption per kilogram of fuel is 64-72 kWh, which translates to 1091 to 1227 kWh of electricity consumption per 100 kilometers. Therefore, it is necessary to greatly reduce the energy consumption of hydrogen production.

Before the above problems were solved, it seems impossible for oxyhydrogen fuel cells to be commercialized. In addition, the United States and Canada have stopped research and development of automotive oxyhydrogen fuel cells.

Lithium-air batteries are still in the early stages of research. The problems to be solved include: preventing the chronic leakage of the diaphragm using the two electrolytes; increasing the usable temperature of the organic electrolyte; finding a gold and platinum catalyst that can replace the current use; How to prevent the intrusion of water vapor to cause explosion when replacing lithium fuel; how to recycle unused lithium and lithium hydroxide; how to reduce the energy consumption of circulating lithium hydroxide.

Based on the above situation, some experts believe that a zinc-air battery is not the best battery, but it is the most practical battery.

Lithium-sulfur battery

Representative manufacturers of lithium-sulfur battery research in the world include Sion Power, Polyplus, Moltech in the United States, Oxis in the United Kingdom, and Samsung in South Korea. Polyplus' 2.1Ah lithium-sulfur battery has an energy density of 420Wh/kg or 520Wh/l.

In China, Tianjin Electronics 18, Chemical Research Institute, Tsinghua University, Shanghai Jiaotong University, National Defense University of Science and Technology, Wuhan University, Beijing Institute of Technology are conducting research on lithium-sulfur batteries. It was found that the cycle stability of lithium-sulfur batteries was caused by the discharge dissolution of the positive active material and the instability of the surface of the metallic lithium, the electrical insulation of the sulfur itself and its discharge products (5x10-30S/cm). Poor, the utilization of active materials is low.

The cathode material of lithium-sulfur battery includes 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.

Large mesoporous carbon

Large mesoporous carbon can form a parasitic carbon-sulfur complex by filling elemental sulfur. Using high pore volume (>1.5cm³/g) of carbon to ensure the high filling capacity of sulfur to achieve high capacity; use high carbon surface density (>500cm²/g) to adsorb discharge products, improve cycle stability. Utilize high conductivity of carbon (Several S/cm) Improves the electrical insulation of elemental sulfur, improves the utilization of sulfur and the charge and discharge rate performance of the battery.

The preparation process of large mesoporous carbon is: using nano CaCO3 as a template, phenolic resin as carbon source, carbonization, activation in CO2, HCL stenciling, and water washing. The surface density was 1215 cm² /g, the pore volume was 9.0 cm³ /g, and the electrical conductivity was 23 S/cm. Then, it was co-headed with sulfur at a high temperature of 300 ° C to prepare an LMC/S material in which S accounted 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 battery. Therefore, the optimum composition of the electrolyte is 0.65 M LiTFSI/DOL + DME (volume ratio 1:2).

Gelatin adhesive has good adhesion and dispersibility. It does not dissolve or melt in the electrolyte of lithium-sulfur battery. It can promote the complete oxidation of polysulfide ions into elemental sulfur during charging, which can improve the discharge capacity of lithium-sulfur batteries.

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

Taking a 1.7Ah lithium-sulfur battery as an example, the energy density is 320Wh/kg and in100% DOD discharge, the cycle is 100 times, the capacity retention rate is about 75%, and the cycle efficiency is up to 70%. In the first year, the self-discharge rate is about 25%, and the average monthly self-discharge rate is 2 to 2.5%; the 0°C discharge capacity reaches 90% of the normal temperature capacity, and the tolerance at -20 °C is 40% of the normal temperature capacity; When the battery is discharged/overcharged, the battery does not ignite or explode. When the battery is overcharged, the battery bulges and bubbles are generated inside.

Vulcanized polypropylene

A kind of polymer lithium battery with 800mAh/g of sulfide polypropylene (SPAN) as the positive electrode material, the energy density of lithium/sulfide polypropylene fine battery exceeds 240Wh/kg, and this sulfide polypropylene fine material has ultra-low cost and low energy consumption. In addition, graphite/sulfide polypropylene batteries will be a strong candidate for large lithium batteries.

A lithium secondary battery based on a reversible electrochemical reaction can be a conductive polymer by doping and dedoping sulfur, and vulcanizing the pyrolyzed polypropylene.

The capacity of the vulcanized polypropylene battery is larger than that of the lithium battery based on the reversible electrochemical reaction. The special charge and discharge characteristics indicate that the sulfide battery far exceeds the lithium battery mechanism.

Studies have shown that when the deep discharge reaches 0V, the discharge/charge capacity is 1502mAh/g and 1271mAh/g, after which the cycle is stabilized between 1V and 3V. The cycle performance is stable between 0.1 V and 3 V, and the capacity is 1000mAh/g.

For 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 battery has the inherent safety of overcharging.

The upper limit voltage for charging is 3.6V. When the charging voltage reaches 3.8V, it can no longer continue charging; when the voltage reaches 3.7V, it cannot be recharged after 3 cycles.

In addition, the two sulfides/ lithium batteries have almost the same discharge voltage as the lithium cobaltate/lithium batteries, so they have good interchangeability.

The charging voltage and capacity of such a battery increase as the temperature decreases. The discharge capacities at 60 ° C and -20 ° C were 854 and 632mAh/g, respectively. The polymer anode has an operating temperature above -20 °C.

The charging voltage and capacity will decrease as the current density increases. At a current density of 55.6mA/g, the capacity was 792mAh/g; when the current density was 667mA/g, the capacity was 604mAh/g. This indicates that the battery can operate in a state where the current density is high.

The sulfide electrode expands in volume when discharged (intercalated with lithium ions) and shrinks when charged (de-lithium ion). After the first discharge, the positive electrode thickness increases by about 22%. The thickness variations of the metal lithium negative electrode and the sulfide positive electrode compensate each other to ensure that the overall thickness of the battery does not change too much. Conductive polymers also have the same properties. In the EIS study, the equivalent circuit was measured and fitted.

Due to the different structure of sulfidation pyrolyzed polypropylene (SPAN) and pyrolytic polypropylene (PPAN), the former can remain stable above 600 °C.

A prototype polymer lithium battery using a sulfided polypropylene as a positive electrode and a lithium foil as a negative electrode have a size of 4x40x26 mm3 and an energy density of 246Wh/kg or 401Wh/l.

In addition, in the experiment of using graphite as the negative electrode of the lithium-sulfur battery, in dry air or inert gas box, Celgard's 2400-hole diaphragm is used as a separator, which is placed between the positive and negative electrodes to form a cell, and the negative electrode and the separator are separated. Between the sheets is a 100μm thick lithium foil material, which is then filled with 1 M LiPF6-EC/DEC electrolyte and finally sealed into a button cell. The characteristic curve is shown. It’s charge and discharge curves after addition of Li2.6Co0.4N.

Among the above two methods, it is safer to use graphite as the negative electrode than metal lithium; the sulfide positive electrode before lithiation is formed by electrochemical lithiation; there is a voltage of 0.2V between the sulfide/graphite battery and the sulfide/lithium battery. Poor; sulfide/graphite batteries have a more stable cycle life.

Carbon nanotube vulcanized polyacrylonitrile

The sulfur-containing composite positive electrode material of the polyacrylonitrile copolymer grown on the surface of the carbon nanotube is a sintered product of B-type polyacrylonitrile, sulfur and 5% carbon nanotubes. MWCNTs with a diameter of about 20 nm penetrate between the particles, reducing the size of the secondary particles, forming a good structural skeleton and a conductive network. As the carbon tube content increases, the initial capacity decreases, but the cycle stability and rate performance of the electrode are improved.

In summary, in addition to lithium iron phosphate, countries around the world are actively researching more batteries with high energy density, such as metal-air batteries and lithium-sulfur batteries. Such batteries are low in cost, low in energy consumption, and high in energy density. The metal-air battery has an energy density of 3,500Wh/kg, and the lithium-sulfur battery has an energy density of 2,600Wh/kg.

The US Laiden Energy Company has developed a current collector that can work safely at high temperature on the basis of higher energy density than existing lithium batteries and is very suitable for electric vehicles.

Leiden Energy replaced the aluminum collector and lithium hexafluorophosphate used in traditional battery electrolytes with graphite collectors and sodium sulfite to improve battery life while operating at temperatures above 60 °C. Moreover, the energy density of the new battery is 50% higher than that of lithium batteries used in electric vehicles.

New battery with sodium sulfinamide

The US Laiden Energy Company has developed a current collector that can work safely at high temperatures on the basis of higher energy density than existing lithium batteries and is very suitable for electric vehicles.

Leiden Energy replaced the aluminum collector and lithium hexafluorophosphate used in traditional battery electrolytes with graphite collectors and sodium sulfite to improve battery life while operating at temperatures above 60 °C. Moreover, the energy density of the new battery is 50% higher than that of lithium batteries used in electric vehicles.

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