summary
"Silicon-doped lithium supplement" is an important lithium battery technology, which represents the strength of research and development and financial strength, and can also solve the core anxiety of electric vehicles.
background
At present, the whole industry seems to be still looking forward to the progress of silicon-doped lithium supplementation technology. From the perspective of material companies, TDK, Tianqi Lithium, etc. began the research and development and preparation of lithium supplement materials 5 years ago; from the perspective of battery cell companies, Ningde Times, Guoxuan Hi-Tech, Sunwoda, A123, ATL, BYD, Zhongxin Aviation, Zhuhai Guanyu, Micro-Hong Power, etc. are involved in this technology; from the perspective of mobile phone companies, Xiaomi (11 Ultra high silicon pole sheet lithium supplement technology); from the perspective of car companies, Weilai Automobile / Tesla (pre-lithiumization + silicon anode) and so on are invariably starting from silicon anode materials or pre-lithiation technology, which also shows "Silicon anode, pre-lithium" will accelerate into the battery technology competition, and is expected to open the industry scale promotion and application in 2022.
The market is often ahead of technology or wider than technology, and a number of automakers have claimed that batteries can achieve 1000km endurance through new technologies, such as GAC Eian LX Plus's "sponge silicon anode sheet" battery, SAIC Zhiji's "silicon-doped lithium" battery, Xiaokang SF5's "solid-state battery", as well as Weilai ET7's "solid-state battery", Tesla Cyberruck's "pre-lithium" battery.
In fact, the pursuit of long mileage seems to be less important. On the contrary, the cost, safety and life of electric vehicles need to be considered. Based on existing lithium battery technology, cobalt and nickel are needed to improve power battery performance. Both of these are precious metals, which are generally used in high-end electric models. In 2022, Xiaopeng and Ideal will release Xiaopeng G9 and Ideal X01 respectively, and the expected price will be about 400,000 yuan. It just so happens that these high-end models are now willing to chase the "silicon-doped lithium" technology.
Silicon-doped lithium supplementation
Silicon-doped lithium supplementation is two technologies, and has been around for many years, the main role is to improve the performance (endurance and life of the battery). Silicon doped is anode doped silicon, increasing the specific energy; lithium supplementation, both from the negative electrode to supplement lithium, can also be supplemented from the positive electrode, can improve battery life. Often long life and energy density are intertwined, so "silicon-doped lithium" has become a representative of high-performance power battery technology.
Silicon-doped can significantly increase the energy density of power batteries.
From a technical point of view, if you want to improve the performance of the power battery, the modification of the material is the first step. Theoretically, the gram capacity of silicon is 4200mAh/g, which is 10 times that of graphite. Whether it is the positive NCM or NCA, the negative electrode adopts a graphite system, and the energy density of the lithium-ion battery has reached the ceiling of 300Wh/kg. If you want to further improve the energy density, you really need to do enough work on the silicon-based negative electrode.
Silicon materials| Images News | Wikipedia
According to Wikipedia information (pictured above), Silicon is a chemical element, the chemical symbol is Si, atomic number 14, relative atomic mass 28.0855, there are two allotropes of amorphous silicon and crystalline silicon, belonging to the third cycle on the periodic table, the metal-like elements of the IVA family.
As a common element, silicon rarely appears in nature in the form of elemental matter, but in the form of complex silicates or silica, which are widely present in rocks, gravel, and dust. In terms of abundance, silicon ranks 8th in the universe; in the crust, it is the second most abundant element, constituting 26.4% of the total mass of the crust, second only to oxygen in the 1st place (49.4%).
It should be pointed out that the higher the gram capacity of silicon materials (theoretically, the more silicon is incorporated) The better the lithium storage performance, but the high expansion rate (30 times that of graphite) is the fatal injury of the electrode material. In the process of charging and discharging, the volume of silicon will be greatly expanded and contracted, although the energy density of lithium batteries is improved, but it will affect the life of lithium batteries, so it is necessary to find a technical way to clamp the expansion of silicon materials.
The general practice of battery manufacturers is to choose a compromise route to improve the particle size of silicon materials, such as incorporating nanoscale silicon materials into the carbon anode to form a carbon-silicon anode - "graphite + silicon", and "SBR" + "PPA" + "PVDF" on the adhesive.
Silicon-based anodes are divided into two broad categories:
One is the silicon carbon anode, that is, nano-silicon and graphite blending, the gram capacity exceeds 3000mAh/g, but the actual gram capacity exceeds 2000mAh/g;
The other is the silicon oxygen anode, silica oxide mixed graphite as the negative electrode, the gram capacity of 1400-1800mAh / g.
In terms of application, domestic 3C consumer electronic products generally use more silicon carbon anode; while vehicle power batteries generally use more silicon oxygen anode.
The problem now is that 1) the proportion of silicon doped can not be too high, generally 5% to 10%; 2) the price of silicon-based anode materials is expensive, and the current silicon anode materials made of 5% silicon are currently more than 100,000 yuan / ton at domestic prices, and even overseas prices are more than 1 million yuan / ton. How to industrialize on a large scale, how good and fast, how much and how cheap is a problem that needs to be solved urgently.
Lithium supplementation can significantly improve the cycle life of the power battery.
In order to improve the performance of power batteries, in addition to "doping silicon" in the negative electrode, engineers in the lithium battery industry also thought of "lithium supplementation". Lithium battery common sense tells us that when the battery is charged for the first time, Li+ swims from the positive pole to the negative electrode, and the negative electrode film generally produces about 10% of the irreversible capacity loss.
In order to solve this problem, the general practice of the industry is to pre-prepare a part of the lithium on the electrode material, which may be a negative electrode or a positive electrode to make up for this part of the loss. The positive electrode supplement is generally based on lithium sulfate (also used Li3N, the core meaning is that lithium ions from the positive electrode to the negative electrode. The negative electrode supplement lithium is made of lithium powder or lithium tape (punching - evaporation - rolling), or a technical trend. Other methods include electrochemical lithium supplementation and vacuum lithium plating, but they are similar.
However, it is certain that lithium supplementation can be regarded as tailor-made for "eating lithium", which can not only supplement the loss caused by the first circle of film formation, but also be used as a follow-up SEI/CEI membrane growth.
From an academic point of view, the lithium band is a metal lithium beaten into a thin band, the purity of metal lithium is not less than 98%, each piece is about 15cm, after passivation will float in the liquid paraffin wax, can be pressed with a relatively heavy plastic sheet; lithium powder preparation needs to be added to the first solvent (paraffin oil) under an inert atmosphere, the first solvent does not react with the metal lithium, heated to the metal lithium melting, stirring to make the molten metal lithium dispersed passivation, cooling after cleaning and drying, and then obtain lithium powder particles.
According to Wikipedia information (pictured below), lithium has atomic number 3 and atomic weight 6.94 and is the lightest alkali metal element. The main lithium minerals in nature are spodumene, hem mica, lithium permeene feldspar and phosphorite. Lithium metal is a silvery-white light metal with a melting point of 180.54 °C, a boiling point of 1342 °C, a density of 0.534 g/cm, and a hardness of 0.6. Lithium metal is soluble in liquid ammonia. Lithium is easily combined with oxygen, nitrogen, sulfur, etc. The nitrogen oxide film on the surface of the lithium is dissolved, making the reaction more intense.
Several lithium supplementation technologies have progressed
There are three kinds of lithium supplementation technology: 1) vacuum winding evaporation lithium supplementation; 2) lithium-rich cathode, chemical lithium supplement; 3) calendered lithium belt lithium supplementation.
1) Vacuum winding evaporation lithium supplement technology. The basic principle is that the use of vacuum coating and automated design, roll-to-roll cycle operation. This method can achieve good uniformity of lithium plating and mass production, but there is still a distance from commercialization, and it needs to be driven by market demand.
The reason for the distance from commercialization has also been proven recently. Industry common sense tells us that adding rich lithium materials in mixing is the safest way to supplement lithium. However, the vacuum winding distillation technology of lithium supplementation was once denied in the previous test, and lithium powder and lithium belt are too dangerous, and the price is not cheap, such as a roll of lithium tape 100,000-500,000. In addition, it should be emphasized that the current vacuum winding evaporation lithium supplement, the focus of the problem is still the passivation of the lithium metal surface and the inhibition of the growth of lithium dendrites, but it remains to be seen how effective it is.
The representative enterprises of this technology are still CATL (Ningde Era), ATL (Dongguan/Ningde New Energy), Zhongxin Aviation, Zhuhai Guanyu, Hefei Guoxuan, Weihong Power and so on.
2) Lithium-rich cathode, chemical synthesis lithium supplement technology. The basic principle is that the lithium-rich cathode is used, including the core and carbon coating, the carbon coating covers the core, and the kernel covers lithium fluoride and metal elemental particles (M). When formed, the lithium-rich positive electrode provides additional lithium ions to the negative electrode.
The advantage of this method is that it can compensate for the loss of lithium ions of the irreversible capacity of the negative electrode, thereby improving the positive gram capacity and ultimately increasing the energy density of the secondary lithium battery. However, the method has limited effect on exerting the gram capacity, and it has finally been proved to be impossible in the short term. In addition, the preparation of lithium-rich cathode materials also has certain technical difficulties and capital thresholds.
The representative enterprise is still ATL (Dongguan / Ningde New Energy).
3) Calendered lithium belt lithium supplement technology. The basic principle is: in the stirring of enriched lithium material, calendering equipment module will be lithium tape calendered into lithium foil and attached to the release film, forming a lithium belt. Then, under vacuum drying conditions, store the lithium patch. The overlay module then attaches the lithium foil to the negative electrode sheet by calendering the lithium strip on the pole piece. The advantage of this technology is that the calendering module and the overlay module are independent of each other. It can avoid mutual restraint between the running speed of the calendering module and the running speed of the overlay module, thereby ensuring the production capacity of the pole plate lithium supplement device and improving the utilization rate of the calendering module.
Although the technology is harsh on the environment, either insufficient lithium supplementation leads to an insignificant increase in energy density, or excessive lithium supplementation, forming a lithium coating or even lithium dendrites, losing battery performance. In addition, the technology can also be in the existing equipment and industrial chain, the use of pressure rollers, testing instruments, auxiliary reagents and other devices, can be precise control, can solve the problem of insufficient lithium supplementation. In fact, the calendered lithium belt lithium supplement technology is the first successful lithium supplement technology. The success of this technology is not only because the lithium supplementation process is simple and can realize automated production, but also because it can take into account the cost of materials, equipment and plant management.
The representative enterprise of this technology is still CATL (Ningde Era) and so on.
Future development
There is no doubt that "silicon-doped lithium supplementation" is an important lithium battery technology, which also represents the strength of research and development and financial strength, and can also solve the core anxiety of electric vehicles. However, with the gradual development of solid-state battery technology, hydrogen fuel cells and other lithium ferromanganese phosphate, sodium-ion batteries, high-manganese batteries, and aluminum-air batteries, fast charging and the acceleration of 800V platform technology, the life anxiety and performance anxiety of electric vehicles will be solved. Therefore, the supply side should guide market demand, rather than blindly over-designing, or even "overnutrition". In the case of considering the shortage of resources, silicon-doped lithium supplement technology can only be as far as possible to support high-end electric vehicle models, rather than universal use.
It should be pointed out that any technology has technical feasibility and economic feasibility, rather than "public theory is reasonable, the wife is reasonable", and the "silicon-doped lithium supplement" technology is also incomparable. Although the entire industry is paying attention to this technology, with the diversified development of lithium-ion power battery technology and the simultaneous advancement of supporting facilities, the shortage of lithium resources and the safety of lithium batteries need more attention.
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