Whether the process of positive pole lithium supplement can replace the process of negative pole lithium supplement

Currently the most common methods of lithium technology is lithium tonic, both using lithium powder and lithium foil complement the irreversible capacity loss in the process of charging for the first time, in addition, another is studying the fill is the positive electrode lithium method, not only in the anode add a small amount of high capacity lithium oxide, Li5FeO4 materials, for example, using the positive store extra Li, Li loss in the process of discharge for the first time to replenish. Both lithium methods have their own advantages, today let's together to explore and compare the two methods of lithium supplement.

Development: silicon anode effect problem

Pure Si in the condition of fully embedded lithium, specific capacity can reach 4200 mah/g (Li4.4 Si), but also accompanied by up to 300% of the volume expansion, which can result in pure silicon materials will happen in the process of the intercalated-li grain breakage and differentiation, the cathode material, cause in the process of material circulation capacity failure is very serious. In order to overcome the silicon anode materials this difficult problem, people will try to make pure silicon nanoparticles with the expansion of the inhibition of Si particles, but in fact, this strategy was not successful, the relevant calculation shows that only when the pure Si particle size less than cell size could inhibit the volume expansion of Si particles completely, this is clearly impossible, so Nano is only did ease Si anode particles volume expansion, nanoparticles larger specific surface area at the same time also can cause side effects between the cathode and the electrolyte increased significantly. In addition, another strategy is to Si materials "raisin bread" structure, which is spread Si nanoparticles in graphite oceans, absorb the use of graphite Si particles in the process of charging and discharging volume expansion, but also the method is not perfect, the first material of specific capacity is very low, because of the high concentration of graphite, so most of this kind of silicon carbon negative specific capacity is only 400-500 mah/g, at the same time this kind of silicon carbide materials cycle life also does not get much improved.

Because pure Si material all of these problems, people begin to try to use another kind of silicon oxide, SiOX as anode materials, Si - O can key in the key is the double of Si - Si keys can, at the same time in the process of embedded lithium, Li will react with material of the O elements, generate LiXO, the Li oxide is inactive, then in the interior of the oxidation of silicon particles as a buffer layer, which can restrain the materials in good charge and discharge process of volume expansion, improve the cycle performance of materials. For the first time because of SiOx intercalated-li will be generated in the process of metallic lithium oxide LiXO, resulting in the silicon oxide materials of coulomb efficiency is only 70% or so, for the first time after a lot of technical improvement in recent years, about 80% for the first time efficiency was raised, there is a big gap between the with graphite material is 90%, so in order to play the advantages of high specific capacity of SiOx material, need to fill with lithium technology, added for the first time in the process of the intercalated-li irreversible capacity loss.

The anode for lithium compared with cathode for lithium

Now fill the lithium technology mainly is divided into two categories;1) cathode for lithium technology;2) positive electrode for lithium technology, including the cathode for lithium technology is our most common lithium methods, such as lithium powder filling lithium and lithium foil, is currently the major manufacturers are focus on the development of lithium technology. Lithium powder filling process first proposed by FMC company, FMC company developed inert lithium powder, through spraying and homogenate in adding the right amount of lithium powder into the cathode. Lithium foil cover for lithium technology of lithium is emerging in recent years, to be addressed to the lithium metal foil rolling several microns thickness, and then with the cathode compound, rolling. The battery after injection liquid metal Li quickly react with the cathode, anode materials embedded in, and thus improve material efficiency for the first time. But these methods all have to face a problem -- the safety problems of metallic lithium, lithium metal is a high reaction activity of alkali metal, to intense reaction with water, makes the metal lithium is very high to the requirement of environment, which makes the two anode for lithium technology have invested heavily on the production line, purchasing expensive lithium equipment, at the same time to ensure the effect of lithium, still need to adjust the existing production process.

Compared to the difficult, high investment of the cathode for lithium process, the anode for lithium is more simple, the positive complement of the typical lithium technology is in the process of the anode homogenate, add a small amount of high capacity anode material, in the process of charging, redundant Li elements from these high capacity anode material of emergence, embedded in the cathode of complement the irreversible capacity of the charge and discharge for the first time. Such as XinSu argonne national laboratory, just by adding 7% in LiCoO2 positive Li5FeO4 (LFO) materials, make the battery for the first time efficiency increased by 14%, and significantly improve the cycle performance of battery.Li5FeO4 material theoretical specific capacity is 700 mAh/g, and almost all of the irreversible capacity, rapid deactivation after taking off lithium materials, no longer participate in the charge and discharge reaction, take off the lithium equation: Li5FeO4?4 li + + 4 e - + LiFeO2 + O2.

GiulioGabrielli etc. are taken from Germany will two positive active material: LiNi0.5 Mn1.5 and Li1 + m1 XNi0.5 Mn1.5 mixing method, m1 Li1 + XNi0.5 Mn1.5 m1 in the process of battery charge for the first time can provide extra Li, make up for the loss in the process of first intercalated-li anode Li, after completely off lithium Li1 + XNi0.5 Mn1.5 into a fully active LiNi0.5 m1 Mn1.5 m1, therefore this method has no effect to the positive electrode composition completely, Li1 + XNi0.5 Mn1.5 m1 can be seen as a temporary storage redundant Li anode materials, by changing the Li1 + XNi0.5 Mn1.5 and m1 LiNi0.5 Mn1.5 m1, the proportion of the number of Li can provide extra for the anode can control, so as to adapt to different efficiency of negative electrode for the first time.

Process struggle: the anode for lithium technology can replace the cathode for lithium process?

Through the analysis of the above, we can found that the anode for lithium process the biggest advantage is simple, don't need to existing lithium ion batteries production process to change, also do not need to modify the existing production workshop, do not need to purchase expensive lithium equipment, more important is the anode for lithium process will greatly improve the safety of the supplement, but in the process of the positive for lithium appears to cause a decline in the proportion of positive active material, for example, when using Li5FeO4 need the content of 7%, and the product of lithium is not active, thus has affected the lithium ion battery for improving the energy density.

Compared to two kinds of lithium methods, the author is more bullish on the anode for lithium. The cathode for lithium technology conditions of rigid, large investment, and the use of metallic lithium cause larger security risks, by contrast, the anode for lithium technology is simple, no need to modification of existing production line and process, small investment, no security risk, GiulioGabrielli people such as the development of the anode for lithium technology has solved the problems influencing the anode for lithium products, although at present the technology application in LiNi0.5 only Mn1.5 m1 material, but through the related technology research and development, fill the lithium technology believe that also can be used such as sliding and NCA ternary material, promote efficiency of the battery for the first time.

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