C = 26.8nm / M, n is the number of electrons, m is the quality of active substances, M is the molecular weight of the active substance
Into the battery, and some at room temperature into some high temperature into these two into the advantages and disadvantages:
The main difference between the thickness of the SEI film and dense, high temperature into the formation of SEI thick but not dense, lithium consumption, room temperature or low temperature the formation of dense thin cut.
Battery formula:
Negative formula: CMS: CMC: SBR: Super-P = 94.5:2.25:2.25:1
Electrolyte: 1M-of LiPF6 the EC / DMC / EMC
Negative design Capacity: 300mAh / g
Cathode design Capacity: 140mAh / g
Charge and discharge system: 1) constant current charging (1C, 4.2V)
2) constant voltage charging (4.2V, 20mA)
3) standing (10min)
4) constant current discharge (1C, 3.0V)
5) standing (10min)
6) cycles (350 weeks)
The dissolution of the polymer in a solvent to follow the three principles (polarity similar principle, the principle of solvation, the cohesive energy density similar principles), the three principles of combining polymer and solvent solubility parameter values, is the polymer good the basis of the solvent. PVDF / NMP was originally a good polymer / solvent with NMP is highly polar solvents and affinity for water well, so can easily absorb moisture, with increasing water content in the NMP, NMP / water mixed solvent solubility parameter, polarity, solvation, ability and so drift, while the corresponding value of PVDF has not changed, the PVDF / NMP binder solution system with the increase of water content, and gradually becomes unstable, the water content reached a certain value, PVDF can be precipitate from the solution, the nature of the solution in the process, including viscosity, bonding properties and will change. Dropwise to the solution of PVDF / NMP water, the local formation of the poor solvent environment will be PVDF precipitation.
And the corresponding formula combining different ingredients technology provides a common formula:
Of LiCoO2: 92% conductive graphite: 2.5% conductive agent: 2.5% of PVDF: 3.0%
80% of the cathode active material, acetylene black and 10% of PVDF10%.
Corporate formula:
Lithium cobalt oxide 94% conductive agent 1% 2% of the conductive agent of PVDF 3%
Negative surface of the SEI film can be roughly considered to be insoluble product of the organic solvent of the electrolyte reduction decomposition of get attached to the electrode surface, the results of different anode materials there will be some difference, but generally considered to be: lithium carbonate, alkyl ester lithium, lithium hydroxide, etc., of course, salt decomposition products, in addition to some of the polymer. Is generally believed that for lithium metal anode in the first lithium intercalation formation of SEI film formation voltage of 1.5V (relative to lithium), 0.8V near the formation of a large number of basically completed to 0.2V or so. In addition, studies have shown that the sequence 5 weeks after the first lithium insertion the main steps for the formation of SEI film, the SEI film formation process, but a very small. In addition, the SEI film is not static, there will be little change in the charge-discharge process, the main part of the organic reversible changes. In addition, the current density, different electrode surface formed by the composition of the SEI film is little difference.
Cathode surface of the SEI film, previously paid little attention to, like attention on the rise. A view that is the result of the deposition of oxidation products in the electrolyte, and Another view is due to partial dissolution of the SEI film of the cathode surface at the cathode surface deposition results. Relatively speaking, the electrolyte in the cathode surface oxide deposition evidence not of course do not rule out the possibility that the instrument accuracy can not be achieved due to low.
Why the negative use of copper foil cathode to use aluminum foil
1, both do the fluid collection is both good conductivity and relatively soft texture (this also may be conducive to bonding), are also relatively common and relatively inexpensive, while both the surface can form a layer of protective oxide film .
2, the copper surface oxide layer is a semiconductor, electronic conduction, oxide layer is too thick, the larger impedance; aluminum surface oxide layer of alumina is an insulator oxide does not conduct electricity, but because of its thin, the electronic conductivity through the tunnel effect. If the oxide layer is thick, aluminum foil conductive differential, and even insulation. Best to the general set of fluid before use after cleaning the surface of, on the one hand, to wash away the oil spill at the same time to remove the thick oxide layer.
3, the cathode potential is high, the thin aluminum oxide layer is very dense, to prevent set fluid oxidation. The copper oxidation layer, in order to prevent oxidation, relatively low potential good, Li difficult under the low potential of lithium intercalation alloys with Cu, but if the copper surface, hydrogen peroxide, in a slightly higher potential Li with oxidation compared to loose some copper occurrence of lithium intercalation hair should be. AL foil can not be used as a negative, low LiAl alloy.
Fluid collection requires ingredients pure. AL ingredients impure will result in the surface film is not dense occurrence of pitting corrosion than the destruction of the surface film causes the generation of LiAl alloy.
The weight of the pole piece, the weight of active substances the baseplates piece (aluminum or copper) weight, the weight of the positive pole piece theoretical design minus the substrate (aluminum density 2.7, copper 8.9) weight, the weight of active substances, multiplied by the weight of active substances 140mAh / g (lithium cobalt oxide), how many mAh capacity, negative capacity of 1.05-1.1 times according to the cathode, the method, the negative 300-330mAh / g, calculate the
Formula:
Lithium-ion battery theoretical capacity = (thickness of -2 * wall thickness) * (-2 width * thickness) * (length -2 * wall thickness) / positive and negative plus the estimates of parameters of the isolation film thickness / cathode design 100 * Tu fabric density parameter * capacity ratio
Of which:
0.0244 is the density of the coating of the cathode design, in fact, almost all
0.45, the positive and negative plus isolation estimates of parameters of the film thickness
140 capacity.
However, according to the previous calculation, the theoretical capacity of 063 048 is only 555 mA (thickness calculated according to 6.3), this capacity can only be set aside Ordnance Disposal.
(6.3-0.35 * 2) * (30-0.35 * 2) * (48-0.35 * 2) / 0.45/100 * 0.0244 * 140 = 555
In general, natural graphite coated negative and irreversible capacity is larger. mcmb a little better, this is the result of the experiment. There is also a film-forming potential of the SEI film is 1.2 ~ 0.8V (vs. Li / Li +), embedded lithium-bit 0.25 ~ 0v, this potential embedded in the lithium is reversible. If we make SEI film formed in the higher potential, it can prevent the further reduction of the solvent, to reduce the irreversible capacity, which is relatively large irreversible capacity of the polarization in the first charge curve, easily dropped to the lithium insertion platform, so the formation the reversible capacity is higher. SEI film a crucial role in the cycling performance of the battery, there is no good SEI film, each cycle has a large irreversible capacity loss, so the battery can usually can be seen from the electrolyte absorbent, or batteries that exist within the crystal water out.
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