98% charge in less than 10 minutes. What technology is 3D structure silicon base
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2022/07/20 17:38:59
Silicon negative lithium battery, ushered in the latest progress: American battery manufacturer Enovix in a 0.27Ah silicon negative power battery unit, successfully achieved 0-80% charge only 5.2 minutes; 0-98% charge 6C fast charge in less than 10 minutes. That's nearly two-thirds less than the current USABC target.
Moreover, this data is achieved under the premise of ensuring battery life. Official cycle life data: after 1000 cycles, the battery capacity can still remain at 93%, while the mainstream ternary lithium battery after 1000 cycles, the capacity can only remain about 80%. The feasibility of fast charging and battery cycle of silicon anode lithium battery is proved theoretically.
The technology behind this is Enovix's proprietary 3D Silicon cell structure.
How to balance service life and speed?
In the official press release, Enovix gave two key pieces of information: Silicon anode material and Enovix's exclusive patent: 3D Silicon cell structure.
Let's start with the silicon anode material
As we all know, silicon-based anode materials have two advantages over the current mainstream graphite anode materials:
First of all, the unit capacity is high, the data show that the lithium battery using silicon as the anode material, the theoretical capacity can reach 4200mAh/g, compared to the current mainstream lithium battery unit capacity is 365mAh/g, the gap between the two is more than 10 times.
The simple derivation of the formula "battery capacity = unit energy density x volume/mass" means that the energy density of silicon-based batteries can be more than 10 times that of graphite anode materials.
Second, silicon has an economic and environmental advantage because it is more environmentally friendly because of its abundant mineral reserves on Earth.
Finally, in the charging and discharging process of graphite negative lithium battery, dendrites will be formed due to the lithium electroplating process, which may penetrate the diaphragm and cause short circuit and other safety problems, which is also an important factor affecting the charging speed of lithium battery, while silicon element can inhibit the growth of dendrites, thus forming an advantage in charging speed.
Based on the above advantages, silicon anode battery is also regarded as the future development direction of lithium battery.
"Future" is both a trend and an open question, and when it comes to silicon negative batteries, one of the most important obstacles needs to be removed if they are to be successfully commercialized in electric vehicles:
Charging expansion problem. Data show that the volume expansion can reach 300%-400% in the process of forming silicon lithium alloy compound by lithium silicon embedded in silicon, which is much higher than the graphite anode material battery.
This feature has two hidden dangers: silicon negative battery in the charging process will lead to the separation of silicon material and conductive agent, reducing the conductivity, the result is a rapid decay of battery capacity, reduce the cycle life.
Huge expansion changes will make the electrode film bigger and crack, and finally make the active material fall off from the collector, resulting in the increase of battery internal resistance and heat, which brings serious battery safety problems.
So the advantages of silicon anode materials are obvious, the battery capacity and energy density have huge advantages, but the disadvantages are also obvious: short life. These two problems, from the current pure electric vehicle power battery demand point of view, almost original sin.
So how does Enovix solve this?
This brings us to the second key point: 3D Silicon. The traditional wound battery structure consists of stacking the positive and negative electrodes of the battery together with the diaphragm, and then rolling them up like a roll of paper.
The disadvantage of conventional structures is that to avoid short-circuiting inside the battery, the diaphragm is usually made wider than the anode and cathode, wasting storage space.
According to official information, the design of the structure refers to the manufacturing process of the chip. Specifically, the cell is made of silicon wafers 1 mm thick, and grooves are made on the silicon wafers by photolithography, and then the conductive layer of the battery is plated in the grooves by electroplating, and then the positive electrode material and diaphragm are filled in the grooves.
According to official data, this structure can improve the space efficiency of the energy storage material by up to 75%, which can reduce the battery size per unit of capacity. In addition to improving the volume, this kind of battery structure has the greater advantage of improving the cycle times and safety of silicon negative battery while ensuring high energy density and fast charging rate.
Enovix doesn't disclose this, but when we looked at enoVIx-related papers and patents, we found two key points:
On the one hand, at the micro level, when 3D Silicon battery etches grooves on the Silicon plate, it will pre-bury the gap for the Silicon negative electrode in advance, which is used to solve the problem that the expansion can be digested internally in the process of Silicon embedding lithium, rather than squeezing the battery space and forming a short circuit.
3D Silicon, on the other hand, uses a technology called BrakeFlow to prevent thermal runaway in the event of a short circuit.
Specifically, in the case of multiple panels superimposed, a fixed resistance is set on the bus connected to each unit, so that in the case of internal short circuit, the current through the short circuit can be adjusted through BrakeFlow, limiting the overheating of the short-circuit area and thermal control. However, Enovix did not disclose the mechanism and principle behind BrakeFlow.
Finally, based on the silicon anode material and unique battery structure design, how does the silicon cathode battery perform? Enovix gives the results:
Based on a 0.27ah battery unit, under the condition of 4.2-2.5V voltage and 6C charging rate (6 times of battery capacity), the 0-80% charging time is 5.2 minutes, and the charging time of 98% charge is kept within 10 minutes.
At the same time, it can still maintain 93% of the battery capacity after more than 1000 cycles of charging, much higher than the current mainstream ternary lithium battery capacity of about 80% after 1000 cycles of data.
Of course, this is only experimental data achieved in 0.27ah small cell, and whether it can be commercialized is still unknown. However, according to the official business, a silicon negative lithium battery with the same structure has been commercially applied in the field of 3C consumption. It is reported that the energy density of its product can reach 900Wh/L. Enovix previously planned to enter the field of electric vehicle power batteries in 2023-2024.
Eastchem's main products: electron-grade N-methylpyrrolidone (NMP) and single-walled carbon nanotubes (SWCNT).
N-methyl pyrrolidone (NMP) belongs to nitrogen heterocyclic compound, is a non-toxic, high boiling point, strong polarity, low viscosity, small corrosion, large solubility, low volatility, good stability, easy recovery of highly selective solvent. It is a very important auxiliary material in the production of lithium ion battery, generally used as a positive electrode coating solvent, or as a lithium battery conductive slurry solvent.
Single walled carbon nanotubes (SWCNT) is a new conductive agent for lithium ion batteries. It can reduce the internal resistance of electrodes, improve the circulation at room temperature and high temperature, improve the energy density, and provide excellent conductivity for lithium ion batteries.
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