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Progress in Safety Technology for Lithium-ion Power Batteries

May 18 , 2022

Traditional methods such as ion lithium power pack safety design and manufacturing, PTC current limiting devices, pressure safety valves, thermally closed diaphragms, and improving the thermal stability of battery materials have limitations and can only reduce the likelihood of lithium ion battery unsafe behavior to a limited extent. To build an ion lithium power pack self-excitation safety prevention system, new technologies to avoid short circuit, overcharge, thermal runaway, combustion, and non-combustible electrolyte should be explored.


Ⅰ. Internal short circuit protection in ion lithium power packs


Ceramic diaphragm and negative heat resistance layer are examples of protective coatings.


Ⅱ. Overcharge technique for anti-ion lithium power packs


1. Additive redox electric couple R is oxidized to O at the positive electrode when the ion lithium battery pack is overcharged, and subsequently O diffuses to the negative electrode and is reduced to R. The charging voltage is kept at a safe level by this internal cycle, which also prevents electrolyte breakdown and other electrode reactions.


2. Dimethoxybenzene compounds have a steady voltage clamping capacity of less than 0.5C owing to limited solubility; ion lithium power packs have a substantial self-discharge. Shuttle's molecular structure requires more investigation.


3. Reversible overcharge prevention not only solves the battery's overcharge problem but also contributes to the capacity balance of each individual cell in a lithium battery pack, lowering battery consistency needs while also extending battery life.


4. Voltage-sensitive diaphragm for rechargeable lithium battery packs. In the normal charging and discharging voltage range, the diaphragm part of the microporous filled with an electroactive polymer is insulated, allowing only ion conduction; when the charging voltage reaches a controlled value, the polymer is oxidized and doped to become electronically conductive, forming a polymer conductive bridge between the positive and negative electrodes, preventing the charging current bypass, ion lithium power pack.


Ⅲ. Ion lithium power pack thermal runaway prevention technology


1. temperature-sensitive electrode for ion lithium power packs (PTC electrode). When the temperature rises to the Curie conversion temperature of the complex, the polymer matrix expands, conductive carbon black out of contact, and the composite material has a high electronic conductivity; when the temperature rises to the Curie conversion temperature of the complex, the polymer matrix expands, conductive carbon black out of contact, and the complex loses its electronic conductivity. The electrical conductivity rapidly decreases.


(1) At high temperatures, the resistance of the PTC coating, which is embedded between the PTC electrode collector and the electrode activator coating, sharply increases, cutting off current transfer, terminating the battery reaction, and preventing thermal runaway of the ion lithium power pack, resulting in safety issues.


(2) For example, testing results reveal that the PTC lithium cobaltate (LiCoO2) electrode has an excellent self-excited thermal blocking effect at high temperatures of 80120°C, which may protect ion lithium power packs from safety issues caused by overcharge and external short circuit.


(3) Internal short circuits, on the other hand, render the PTC electrode useless. Additionally, the polymer PTC material's temperature response properties must be improved.


2. Thermally closed electrodes in an ion lithium power pack. On the surface of the electrode or diaphragm, a layer of nano-spherical thermosoluble substance is changed. When the temperature rises to the melting temperature of the spherical material, the spheres melt into a dense film, cutting off ion transport and potentially terminating the battery reaction; when the temperature rises to the melting temperature of the spherical material, the spheres melt into a dense film, cutting off ion transport and potentially terminating the battery reaction.


3. Lithium ion power pack that has been thermally cured. A monomer capable of heat polymerization is introduced to the electrolyte. When the temperature rises, polymerisation occurs, hardening the electrolyte and shutting off ion transit, thereby ending the ion lithium power pack operation. Experiments have demonstrated that BMI electrolyte additions have no effect on battery charging and discharging and that BMI can hinder battery charging and discharging at high temperatures.


Ⅳ. A non-flammable electrolyte prevents the ion lithium power pack from catching fire


Organic phosphate ester is a flame retardant compound with high solubility in electrolyte salt. For example, DMMP (dimethoxymethyl phosphate) has a low viscosity (cP 1.75 at 25°C), a low melting point, and a high boiling temperature (-50 to 181°C), significant flame retardancy (P-content: 25%), and high lithium salt solubility.


In practice, however, ion lithium power pack flame-retardant solvents have the following issues: poor matching with the negative electrode and low Coulomb efficiency while charging and discharging the battery. As a result, the right film-forming ingredients must be discovered.