With the global energy reduction and environmental degradation, the development of environmentally friendly new energy sources has received widespread attention. Among them, new energy materials play a great role in guiding and supporting. Battery materials mainly involve positive electrode, negative electrode, electrolyte and phase diaphragm, which are important parts of electricity storage and power supply. At present, battery materials are developing to the nanometer level, and nanomaterials have special microscopic shape and structure, high embedded lithium capacity and energy density, and long cycle life. However, the problems of nanoparticle agglomeration and size control, the small contact area between electrode materials and electrolyte, and the corrosion inhibition of electrolyte need to be solved by surfactants.
Surfactants can change the crystalline shape of metal oxides, inhibit hydrogen precipitation, dendrite growth and corrosion, delay electrode passivation, and act as a “microreaction cell” and prevent the agglomeration of nanoparticles in emulsions. The research of surfactants in the preparation of battery materials and the recycling of used batteries is reviewed. Surfactant molecules consist of hydrophobic and hydrophilic groups, which can form ordered assemblies of micelles, anti-micelles, vesicles, etc. in solution, and the ordered assemblies can be used as “microreactors” to prepare nanoparticles. The surfactants can prevent the agglomeration of nanoparticles, control the size of nanoparticles, and improve the electrical properties of the electrodes made by forming an oriented arrangement of carriers. Surfactants play an important role in the production of battery catalysts, electrode materials, as corrosion inhibitors, and in battery recycling.
- Application to battery catalyst production
Surfactants play an important role in the production of ion-exchange membrane fuel cell catalysts, which are mainly made by microemulsion method. There are orthogel microemulsion systems and antigel microemulsion systems. The main disadvantage of the ortho-micellar microemulsion system is that the particles are difficult to be separated and purified from the microemulsion, and a large amount is consumed in the production process. The inverse micellar method is used in the production of proton exchange membrane fuel cell electrocatalysts, compared with other chemical methods, the prepared particles are not easy to agglomerate, the size can be controlled, and the dispersion is good. This method is a promising method for nanoparticle preparation with simple equipment and process. The role of surfactants in the preparation of nanoparticles by the inverse micelle method is mainly: (1) to form the inverse micelle system and control the particle size; (2) to reduce particle agglomeration; (3) to control the shape and crystal shape of the particles, etc.
- Application in the preparation of electrode materials
The main surfactants used in the preparation of electrode materials are CTAB, sodium 2-ethylhexane sulfosuccinate, nonylphenol polyoxyethylene ether (NPE), ethylene oxide (EO) and propylene oxide (PO) triblock copolymer EO100PO70EO100, P123 (E020P070EO20), PEO600, Tween 80, Span, TritonX-100, sorbitan monooleate anhydrous, SDBS, SDS, cyclohexane and fluoroalkyl quaternary ammonium salts, oleic acid and sodium 4-styrenesulfonate.
The commonly used methods are phase transfer method, precipitation method, self-assembly method, template method, sol-gel method, etc. 1, the production of cathode materials with SDBS, CTAB, TritonX-100 and Brij56[C16H33 (OCH2CH2)8H] can be made of different structures and electrochemical properties of MnO2. The MnO2 produced by using SDBS as the stencil had a hindering effect on the battery cycling performance, CTAB only slightly improved the battery cycling performance, TritonX-100 had a good discharge capacity and cycling performance, while the nanoscale MnO2 cathode material produced by electro-precipitation using Brij56 as the electrolyte showed a good cycling performance and high discharge capacity. P123, sodium 4-styrenesulfonate, CTAB, oleic acid and kerosene mixed melt solution can be used to prepare LiCoO2 positive electrode materials for lithium batteries, respectively. The sulfur-polypyrrole (S-PPy) composite was made by using sodium 4-styrenesulfonate as the stencil and FeCl3 as the oxidizer, and was used as the positive electrode of Li/S-PPy battery. When LiFePO4 was used as battery cathode by hydrothermal method using CTAB as template, its discharge capacity was improved, cost was reduced and toxicity was decreased. The LiFePO4/TiO2 composite electrode made of LiFePO4 and nano-scale TiO2/graphite composite material by mixed molten liquid of oleic acid and kerosene has lower energy density, almost no loss in 700 cycles, current efficiency up to 100%, durability, low cost and good safety than conventional lithium batteries.
It can be seen that surfactants play a great role in the preparation of positive electrode materials, especially the LiFePO4/TiO2 composite electrode prepared by oleic acid and kerosene mixed with molten liquid surfactant has good performance. 2. making negative electrode materials Surfactants can not only control the particle size and order the crystal arrangement, but also control the porosity to improve the electrical properties of the electrode made. The surface of CuO modified by the anionic surfactant CTAB has an ordered needle-like crystal structure, which increases the contact area between CuO and electrolyte. Adjusting the amount of CTAB can control the porosity of tin-phosphate material and improve the battery cycle performance. The compound surfactant has a synergistic effect on corrosion inhibition. TritonX-100 and n-ethanol were used to control the size of Cu-Sn particles, and the resulting Cu-Sn nanoparticles were assembled into lithium-ion battery anodes with high cycling capacity and reversible specific capacity. The non-ionic surfactant containing polyoxyethylene and indium hydroxide additive can significantly slow down the self-discharge of the battery and improve the electrochemical performance of the rechargeable alkaline-manganese battery. The nano-tin dioxide/carbon composites and nano-tin oxide/carbon composites were fabricated in ethanolic solution containing P123, and showed better cycling performance compared with general nano-tin-based materials as the anode of lithium-ion batteries.
- Self-discharge of zinc electrode in alkaline manganese battery used as organic substitute for mercury corrosion inhibitor is one of the main reasons affecting the working life of the battery. Nowadays, people generally use mercury or mercury salt to suppress self-discharge. Mercury is not only highly toxic and a serious environmental hazard, but also accelerates the deformation of the zinc electrode. Therefore, it is necessary to eliminate or replace the toxic mercury in the battery. At present, there are two main measures for mercury-free alkaline manganese batteries: adding corrosion inhibitors to the electrolyte and adding corrosion inhibitors to the zinc negative electrode. The buffers used in the study are mainly inorganic corrosion inhibitors and organic mercury substitution inhibitors, of which organic mercury substitution inhibitors are mainly anti-corrosive surfactants. The corrosion inhibition performance of zinc in KOH solution was studied by six different hydrophilic chain surfactants, among which decyl(octa)oxyethylene ether phosphate potassium salt could reduce the hydrogen precipitation of zinc powder by 70.6% and the corrosion inhibition efficiency could reach 78.7%. However, it is difficult to improve the electrochemical performance of zinc electrodes with a single additive, and most researchers are now focusing on the search for efficient compounding additives with good results. By comparing the corrosion inhibition effects of organic additives YLZX (alkyl trimethyl ammonium bromide with alkyl numbers from 12 to 16), YZ (alkyl phenol ethoxylates with alkyl ethoxy sulfate with alkyl numbers from 10 to 17), lauryl ethoxylates with alkyl ethoxy sulfate, PEO400, SDS, and Tween-20 on zinc electrodes, it can be seen that YLZX and YZ have significantly SDBS and Tween-20 have excellent corrosion inhibition, delayed passivation effect and obvious synergistic effect, and the discharge capacity of zinc electrode is significantly improved, and the corrosion inhibition efficiency reaches 83.26% with the best compound addition. The above is the study of corrosion inhibitor added in electrolyte on the corrosion inhibition effect of zinc electrode, but the study of adding in electrode material is less. However, the addition of organic corrosion inhibitors in the negative electrode can reduce the self-discharge of zinc-nickel batteries, but still cannot meet the requirements of commercialization of zinc-nickel batteries.
- Application in battery recycling
The surfactant formed an emulsion to improve the mobility of some metals. An emulsion film formed by (kerosene), surfactant (Span80), carrier and ammonia in the internal aqueous phase was used to separate and enrich cadmium ions from used nickel-cadmium batteries, and an industrial scale-up experiment was conducted in a 100-L reactor, and the migration rate of cadmium was 93.3%, while that of nickel was only 14.6%. This method can better achieve the separation of cadmium and nickel ions. The surfactant can also reduce the activation energy of the reaction between carbon and manganese oxide interface, which has a great influence on the reduction rate. After sorting the waste batteries, crushing and sieving, the manganese dioxide is made into pellets with the reducing agent carbon, and then sintered and reduced in an induction furnace to make manganese steel. The experimental results show that the process can be directly applied to the treatment of waste batteries in the production of cast steel.
- Conclusion and Outlook
Surfactants have important applications in batteries, which can change the crystalline shape of metal oxides, inhibit hydrogen precipitation and dendrite growth, play a role in corrosion inhibition, and act as a “micro-reaction cell” in emulsions to prevent agglomeration. The surfactants used are mainly anionic, cationic, nonionic and special surfactants, which are mainly used in proton exchange membrane fuel cells, lithium-ion batteries, alkaline manganese batteries, zinc-air batteries and nickel-cadmium batteries. The composite electrode prepared by mixed molten liquid active agent of oleic acid and kerosene is more ideal. The nano lithium-ion battery anode made in ethanol solution containing P123 showed more excellent cycling performance, but there are still some problems. Although the surfactant has improved the cycle performance and charge/discharge efficiency of the electrode, there is still a certain distance from the practical use, such as the charge/discharge efficiency is still not more than 99.5% for many electrodes.
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