Cnhl 6s lipo battery electrolyte, practical function and classic system construction
1. The actual role of cnhl 6s lipo battery electrolyte
Looking back at the development history of the cnhl 6s lipo battery (for the secondary cnhl 6s lipo battery, the rules are similar), we can see that the analysis of carriers - the study of electrodes - the invention and the improvement of the electrolyte system are linked together to promote The practicality and performance improvement of cnhl 6s lipo battery.
In the 1970s, British chemist Stanley Whittingham developed a cnhl 6s lipo battery with titanium disulfide as the positive electrode and lithium metal as the negative electrode, and the electrolyte was a lithium perchlorate-dioxane system. Compared with lead-acid cnhl 6s lipo battery, the better performance of cnhl 6s lipo battery begins to manifest. Since then, American physicist and chemist John B. Goodenough has replaced titanium disulfide with lithium cobalt oxide to obtain higher positive voltage and higher energy density of cnhl 6s lipo battery;
subsequent lithium manganate, lithium iron phosphate and Cathodes such as ternary materials are also available one after another. Japanese chemist Akira Yoshino used petroleum coke to replace lithium metal, which promoted the safety of cnhl 6s lipo battery and promoted the commercialization of lithium battery under the conditions at that time. In 1990, ethylene carbonate EC was used for the construction of electrolyte system, in 1993, the composite solvent system of EC and dimethyl carbonate DMC was developed; in 1994, the commercialized cnhl 6s lipo battery used graphite negative electrode.
Up to now, the carrier of high-performance (power, secondary) cnhl 6s lipo battery is determined to be lithium, and the positive and negative electrodes have entered a development stage where incremental innovation is the main focus, and subversive innovation is making unremitting efforts. The electrolyte has a very critical impact on the comprehensive performance of the cnhl 6s lipo battery, and it is also in the process of continuous evolution.
As the mainstream carrier of lithium transport in the internal circuit, the electrolyte needs to have the ability to conduct lithium efficiently and insulate electronically within a certain temperature range; the electrolyte directly contacts the positive and negative electrodes, so its electrochemical window, chemical stability, and positive and negative electrodes, The interfacial properties of the separator, etc. also need to meet the requirements of use; the electrolyte needs to resist thermal, electrical and mechanical abuse to a certain extent; such as environmental friendliness/easy post-processing is better.
Whenever the electrode material is improved, the adjustment and optimization of the electrolyte often reflects its importance and even irreplaceability.
Subject to the potential difference between the positive and negative electrodes far exceeding the water splitting voltage, and regardless of the expensive ionic liquids, the mainstream technical route of the electrolyte is a comprehensive system composed of suitable organic solvents and lithium salts.
2. cnhl 6s lipo battery electrolyte solvent system
The solvent itself is electronically insulating and is used to dissolve the lithium salt. The basic requirements of the cnhl 6s lipo battery electrolyte solvent system are: have a certain polarity (high dielectric constant) to dissolve lithium salts; wide electrochemical window (the electrochemical window of the cnhl 6s lipo battery electrolyte is mainly reflected in the electric power of the solvent. Chemical window), resistant to positive oxidation and negative reduction; low viscosity, easy to wet the electrode and improve low temperature performance; heat resistant. Up to now, there is no single-component solvent that can meet the above requirements at the same time, so the basic idea of constructing a mixed solvent system is very reasonable.
The basic consideration of the mixed solvent system of cnhl 6s lipo battery is to select the solvent components with high dielectric constant and low viscosity. The former corresponds to ethylene carbonate EC, propylene carbonate PC; the latter corresponds to dimethyl carbonate DMC, diethyl carbonate DEC, ethyl methyl carbonate EMC, etc.
Additional functions of the solvent, such as synergistic formation, stabilization of solid electrolyte membranes (SEI), assistance in flame retardancy, etc., also rely on solvent additives. cnhl 6s lipo battery solvent additives include conventional chain/cyclic esters (such as vinylene carbonate VC), fluorinated chain/cyclic/amino esters (such as fluoroethylene carbonate FEC), sulfate esters (such as Vinyl sulfate DTD, vinyl sulfite ES), sulfones, nitriles, phosphorus-based additives, silicon-based additives, ethers, heterocyclic compounds, etc.
3, cnhl 6s lipo battery electrolyte lithium salt selection
The lithium salt is dissolved in the solvent system and ionized, partially forming solvated lithium ions and corresponding anion groups, providing ion conductivity. The choice of lithium salt needs to consider the corresponding ion mobility, ion pair dissociation ability, solubility, thermal stability, chemical stability, solid electrolyte membrane formation ability, current collector passivation ability, environmental impact, etc.
Up to now, there is no single-component lithium salt that can meet the above requirements at the same time, so the basic idea of constructing a mixed lithium salt system is also very reasonable. On the other hand, lithium salt is the main cost source of the electrolyte system (more so if the mass percentage is considered), which makes lithium hexafluorophosphate LiPF6 with acceptable comprehensive performance and relatively low cost to become the most common electrolyte in the existing cnhl 6s lipo battery electrolyte. master salt.
In addition to the above lithium salts, lithium salt additives, including phosphates (such as lithium difluorophosphate LiDFP), borates (such as lithium bis-oxalate borate LiBOB, lithium bis-fluorooxalate borate LiDFOB), sulfonimide salts (except Lithium Bisfluorosulfonimide LiFSI, Lithium Bistrifluoromethylsulfonimide LiTFSI and other types), heterocyclic salts, aluminates, etc., can be used properly to improve the synthesis of lithium salt systems to varying degrees. performance.
Considering the performance and cost of both solvent and lithium salt, carbonate + lithium hexafluorophosphate has become the main component of the power cnhl 6s lipo battery electrolyte. But at the same time, in the process of improving the performance of the power cnhl 6s lipo battery, some other solvents/additives and lithium salts/additives are also emerging.
The above is the whole content of the cnhl 6s lipo battery electrolyte brought to you today, I hope it will help you, see you in the next issue.