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The highest voltage lithium ion battery why not break through the 4. 2V?

by:UFO      2020-05-10
Expression of lithium ion battery energy storage parameters are the size of the energy density, mathematically equivalent to about the product of voltage and lithium battery capacity, in order to effectively improve the capacity of lithium-ion batteries, people tend to use way to increase the battery capacity to achieve purpose. However, limited to the nature of the raw materials used, capacity improvement is always limited, and improve the voltage value of higher lithium battery storage capacity in another way. As we all know, lithium battery nominal voltage is 3. 6 v or 3. 7 v, the highest voltage is 4. 2V。 So, lithium battery voltage what why can't we get a bigger breakthrough? , in the end, this is decided by the lithium battery materials and structural properties. The lithium battery voltage is determined by the electrode potential. Also known as electric potential difference or voltage potential difference, it is to measure charge in electrostatic field because of potential energy difference generated by the different physical quantities. Electrode potential is about 3 v lithium ion, lithium battery voltage with different materials have change. Like, the lithium ion battery rated voltage is 3. 7 v, full electric voltage is 4. 2V; The lithium iron phosphate battery rated voltage is 3. 2 v, full electric voltage to 3. 65V。 In other words, in the practical lithium ion battery electric potential difference between the positive and negative can't more than 4. 2 v, this is a kind of based on the needs of material and the use of security. If Li/Li + the reference potential was A mu A relative on anode materials for electrochemical potential, mu C relative electrochemical potential as the anode material, Eg for electrolyte electrolyte potential interval minimum electronic did not possess the energy levels and the highest level difference. So, decided to lithium battery voltage value is highest mu, mu C, Eg these three factors. Mu A and mu C difference for lithium ion battery open circuit voltage ( The highest voltage value) When the voltage value in Eg interval, can guarantee the normal work of the electrolyte. 'Work' means: lithium-ion batteries through the electrolyte in the positive and negative electrode movement back and forth, but will not happen with the electrolyte REDOX reaction, thus ensuring the stability of cell structure. And electrochemical potential on anode materials are causing abnormal electrolyte work has two forms: 1, the lowest when the cathode electrochemical potential is higher than the electrolyte electronic not possess energy level, the cathode electron will be seized, electrolyte and electrolyte was oxidized, reaction products in anode materials particles form a solid-liquid interface layer, which can lead to negative may be damaged. 2, when the anode electrochemical potential high electronics has a level below the electrolyte, the electrons in the electrolyte can be the positive, so as to be electrolytic liquid oxygen, and reaction products in the anode material particles form a solid-liquid interface layer, which leads to the positive may be damaged. However, the possibility of damage to the positive or negative, however, because of the existence of the solid-liquid interface layer and prevent the electron in further movement of the electrolyte and the positive and negative electrode, instead to protect the electrode material, that is, to a lesser degree of solid-liquid interface layer is 'protective'. The premise is: protective anode electrochemical potential is can a bit more than Eg interval, too much but not beyond. Now, for example, the lithium ion battery anode materials are mostly use graphite, is because the graphite relative to Li/Li + electrode electrochemical potential is about 0. 2 v, slightly beyond the (Eg interval 1 v ~ 4。 5 v) , but because of the 'protective' 'solid-liquid interface layer', the electrolyte will not be further reduction, to stop the development of polarization reaction. 5 v high voltage anode material, however, is beyond the commercial organic electrolyte Eg interval too much now, and therefore vulnerable to oxidation in the process of charging and discharging, as with the increase of number of charging and discharging capacity drops, reduce the service life. Now understand that the open circuit voltage of lithium ion battery was chosen to 4. 2 v, because the existing commercial lithium battery electrolyte Eg range of 1 v ~ 4. 5 v, if the open circuit voltage set to 4. 5 v may improve lithium battery output power, but also increase the risk of battery charge, and the harm of overcharge has shown considerable data, there is no longer say more. According to the above principle, people want to by raising the voltage value to improve the energy density of lithium-ion batteries, only two roads, one is found with high voltage anode material that matches the electrolyte, the second is for battery protective surface modification.
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