We previously speculated that Tesla might make a fuss about cathode materials and use single crystal technology; Maxwell dry electrode technology+pre-lithiation can also be used on the anode material, or new additives can be added to the electrolyte. As a result, Tesla's nano-material forecast tells us that we still have the killer of battery technology! .
In fact, Amprius, which cooperated with Tesla, put this new battery into use as early as last year. Zephyr UAV has been flying in the stratosphere for more than 25 days after being equipped with silicon nanowire batteries.
This company is also very interesting, and now it has sneaked away with Tesla. The picture shows that Amprius has moved to a secret place with Tesla? Tera？ The battery factory has become a neighbor, and Tesla Battery Day will also be held here. Ok, getting the moon first is really an advantage. No wonder Maxwell had to step back a little.
On the other hand, what is this so-called "silicon nanowire" battery? Pay attention to the sentence, silicon/nanowires. In fact, this kind of battery essentially uses silicon nanowires to replace graphite, the negative electrode material in traditional lithium-ion batteries.
Then why not use ordinary silicon? Silicon is environmentally friendly and rich in resources. Its working voltage is close to that of graphite, and its theoretical specific capacity reaches 4200mAh/g, which is also the highest among alloy anode materials at present. Silicon is cheap and common. Doesn't it smell good?
Of course-it's no use. During the cycle, the volume of silicon will change seriously. The capacity of lithium ion batteries is related to the number of lithium ions that can be embedded in anode materials. The more lithium ions are embedded, the greater the battery capacity. The charging process is a lithium ion embedding process, and the silicon material expands accordingly; When the battery is discharged, lithium ions are extracted from the silicon material.
The main problem of silicon is that when lithium is embedded, its volume expands by nearly 400% compared with its original size. Compared with the previous battery, the battery with silicon as the negative electrode may expand four times after expansion. Therefore, it is difficult for silicon to return to its original form after lithium removal.
Volume expansion will put extra stress on silicon material, leading to material damage and fracture. This process is called electrode pulverization. Generally speaking, it is the process of subjective confrontation of the electrode to make it expand. As a result, the battery was broken. In the process of pulverization, the broken silicon material will fall off the electrode, which will also lead to poor cycle stability of the battery and a sharp decline in battery capacity. Silicon can be regarded as a reaction vessel. Without the reaction container, the battery can't react normally.
This kind of silicon nanowire refers to a material with a width of about 10 nm and an unlimited length, which can be imagined as a silicon nanobelt. This is a new type of one-dimensional semiconductor nano-material, the core is monocrystalline silicon, and the outside is a layer of silicon dioxide.
By consulting patents, we can probably know the manufacturing process of Amprius' silicon nanowires: silicon nanowires are directly grown on conductive substrates by PECVD process or thermal CVD method using silicon-coated nanostructure templates. Nanowires have a core-shell structure, and this preparation method is also suitable for compounding or doping other substances on silicon nanowires to enhance their conductivity and strength.
Silicon nanowires can release stress well by lateral expansion, and will not cause cracking or damage of nanowires, thus preventing electrode pulverization. There is a certain gap between silicon nanowires, and there is also a certain space for them to expand when the volume expands, so that they will not squeeze each other.
In addition, the direct growth of nanowires on the current collector can also enhance the physical and electrical contact between nanowires and the substrate. Generally speaking, the electrode material is adhered to the electrode by adhesive, which is equivalent to "growing" silicon from the electrode, and the electrons on each nanowire can be well transmitted to the external circuit. The conductivity of nanowires can also be improved by doping, alloying, core-shell materials and other different ways, so there is no need to worry about the conductivity of silicon nanowires.
Up to now, although silicon nanowires have so many advantages, I still insist that Tesla may use this kind of silicon nanowire battery, but we can't attribute all the increase in capacity to this. Why?
From the cost point of view, although the reserves of silicon are large and the cost is low, the cost of the above preparation process is not low. The above mentioned nanocrystallization and chemical vapor deposition (CVD) both increase the cost of silicon nanowire cathode invisibly.
This process is a high energy consumption process, and the processing difficulty and manufacturing cost are higher than those of artificial graphite. If it is really mass-produced, the cost will be unacceptable. Batteries in new energy vehicles are different from those in the aerospace field and need mass production, but it is normal to burn tens of billions of aerospace materials casually. If the cost cannot be reduced, it will eventually be passed on to consumers.
In terms of performance, although Amprius' patent shows that the energy density of silicon nanowires can still reach 1.000 mAh/g after 1.80 cycles, it is not only the negative electrode material that decides the integration into the battery. What is the maximum capacity and cycle performance of silicon nanowire battery with positive electrode and electrolyte? Whether the cost is directly proportional to this degree of improvement will not be known until after mass production.
Another key problem is that it is not the negative electrode material that restricts the upper limit of battery capacity of pure electric vehicles, but the positive electrode material. From NCM523 to NCM622 to NCM8 1 1, the development trend of the battery is to increase the proportion of nickel in the battery. Even the lithium ferrous phosphate blade battery that caught fire this year has only been upgraded from the module level.
Although the anode material has not been tossed, GAC New Energy has also publicized the advantages of graphene as a cathode some time ago, but it has not revealed more information so far, but major manufacturers are really stupid enough to think of improving the cathode to improve the battery capacity.
The contribution of negative electrode capacity to the total specific capacity of the battery is far from as great as everyone thinks. Theoretical capacity of graphite is 372mAh/g, Tesla model? The capacity of graphite anode doped with 3 10% silicon-based material is about 550 mAh/g ... What about the model? Is the cruising range of 3 significantly improved?
Tesla's "love rat" attitude is, don't admit it, don't deny it, don't know, I can hint that Amprius and I have cooperated and adopted silicon nanowire technology, but as long as I don't admit it, you won't know what's going on until battery day on September 22nd. What can we do? Let's wait for Musk to reveal it.
This article comes from car home, the author of the car manufacturer, and does not represent car home's position.