EMC refers to electromagnetic compatibility, which is the abbreviation of the English word Electro Magnetic Compatibility. This means that the electromagnetic interference caused by the equipment or system to the environment during normal operation cannot exceed a certain limit. a certain degree of immunity to electromagnetic interference present in the device, that is, electromagnetic susceptibility.
At the international level, most electrical components or devices are CEM certified. The aim is to ensure that electrical components or devices have the ability to function normally in the electromagnetic environment.
Detailed information
CEM certification process
1 Randomly select samples from the sampling matrix, where different samples are used for testing. and The company retains it for future reference.
2. Randomly select a unit from the samples used for EMC testing, and the test results will be judged by tightening the limit specified in the certification implementation standards by 2 dB.
3. If the measurement result of a single sample meets the requirement of being 2 dB stricter than the limit specified in the certification implementation standard, the sample is deemed to have passed inspection.
Baidu Encyclopedia-EMC
What is the structure of lithium battery?
Commonly used lithium-ion battery electrolytes are generally composed of organic solvents and electrolytes (lithium salts).
Requirements for solvents in lithium-ion batteries include safety, oxidation stability, negative electrode compatibility, conductivity, etc. The overall requirement is that the solvent has a high dielectric constant, low viscosity andother characteristics. . Lithium-ion batteries generally use aprotic polar solvents, and the carbonate series (including cyclic carbonates such as EC and PC and chain carbonates such as DMC and EMC) are widely used at this stage. Usually, the electrolytic solvent is a mixed solvent. Ethylene carbonate (EC) has become the main component of most electrolytes due to its excellent film-forming effect. The main solvent currently used in lithium batteries is binary or ternary mixed solvents. such as EC+DMC, EC+DEC, EC+DMC+EMC, etc.
The electrolyte is an essential component of lithium electrolyte. Currently, electrolytes include lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LIBF4), etc. Among them, lithium hexafluorophosphate has good conductivity properties and electrochemical stability, cis the current common electrolyte. However, lithium hexafluorophosphate also has two disadvantages: first, poor thermal stability; second, it is sensitive to moisture and hydrofluoric acid (HF) and is prone to decomposition reactions. Although people are working hard to find new electrolytes to achieve a better combination of conductivity, thermal stability and water resistance, no electrolyte capable of completely replacing lithium hexafluorophosphate has yet been found.
A small amount of certain additives may also be added to the electrolyte to improve certain aspects of performance. There are many types of additives that can be selected and used depending on the purpose of the battery.
First generation electrolyte: PC + DME + 1MLiPF6 has poor compatibility with negative graphite electrodes and co-intercalasolvent release is likely to occur.
The second generation electrolyte: EC + DMC (or DEC) + 1M LiPF6 has poor performance at low temperatures.
The third generation electrolyte: EC + DMC (DEC) + EMC + 1M LiPF6, the conductivity can reach 10-2S.cm-1, >50%.
Currently, most works focus on the selection of additives to improve the first charge and discharge efficiency of the battery and improve the stability of the SEI.
Liquid electrolyte solution: Lithium-ion batteries use an aprotic organic solvent dissolved in lithium salt as the electrolyte. The organic electrolyte participating in the formation of the SEI film on the surface of the negative electrode, it has a significant impact on the performance of the battery.
As an electrolyte for lithium-ion batteries, it must meet the following basic conditions:
① It has good chemical stability and a wide elect windowrochemical.
② High conductivity.
③ It has good compatibility with negative electrode materials and can form stable SEI film.
④ Wide operating temperature range (-40-60℃).
⑤ Low prices and easy to obtain materials.
⑥ Non-toxic, non-polluting.
★ Solvent part:
Aprotic organic solvent. To achieve the highest possible conductivity, binary or multi-component solvents are often used.
a. PC propylene carbonate (propylene carbonate).
b. Ethylene carbonate EC (ethylene carbonate).
c. DEC (dimethyl carbonate).
d. Propiolic acid methyl ester.
e. 1,4-Butyrolactone GBL (γ-Butyrolactone).
★ Solute part:
a. LiPF6 (mainly).
b.LiBF4.
c.LiClO4.
d. LiAsF6.
e, LiCF3SO3, etc.
A, cyclic carbonate (cyclic carbonate)
EC (ethylene carbonate) and PC (propylene carbonate) commoncommonly used:< /p> p>
① Phosgene method --- Using the reaction of the diol compound ﹝glycol﹞ with phosgene
CH2OHCH2OH + COCl2 -------> ( CH2O)2CO + 2 HCl
② Carbon dioxide synthesis method CH2OCH2 + CO2 -------> (CH2O)2CO
B. Chain carbonate compounds
C. Commonly used DMC (dimethyl carbonate) and DEC (diethyl carbonate):
① Carbon monoxide synthesis method: 2CH3OH. + CO + 1/2 O2 -------> (CH3O)2CO + H2O
② Transesterification method: C2H5OH + (CH3O)2CO -------> CH3OCOOC2H5 + CH3OH < /p>
★ Development of polymer electrolyte (polymer electrolyte):
① Dry polymer electrolyte: The polymer is doped with lithium salt to form a “polymer-lithium ion complex”.
Due to the low conductivity of lithium ions at room temperature (about 10-8s.cm-1), it is difficult to meet the application requirements
② Electrolyte plasticized polymer (electric plasticized polymertrolyte): Using the plasticization method of plasticized polymer electrolyte, the organic electrolyte solution is added as a plasticizer in the network structure formed by the polymer matrix material (such as polymethyl methacrylate PMMA, polyacrylonitrile PAN , polyvinylidene fluoride PVDF) and fixed.
The conductivity can reach 10-4——10-3s.cm-1, which is close to the conductivity of liquid phase solution, can meet practical requirements and has been put into application practical (marketed polymer lithium ion battery).