Electric car, electric car, the world has suffered from the lack of range for too long.
Range anxiety has become another challenge for experienced drivers since the advent of new energy vehicles. While it may be manageable in the summer, some cars experience a range reduction of up to half in winter, catching many first-time buyers of new energy vehicles off guard.
So why is this "father" so difficult to serve? The root cause lies in the battery. The three major components of new energy vehicles that we usually talk about – the "three electric systems" – are actually quite mature in terms of electronic control and motors. Small motors with several hundred horsepower and electronic control that meets various road conditions and all terrains have already appeared in mass-produced vehicles. The only bottleneck is battery technology.
Even though the world's smartest minds and richest capitalists are working tirelessly on battery technology, its progress is not as fast as expected.
The content below mainly discusses why batteries have reached a bottleneck, sharing the current state of battery technology (focusing on commercially available or announced technologies) in a simple and easy-to-understand way, including the methods OEMs are using to maximize vehicle range. For those who are impatient, you can skip to the summary section at the end.
1. Why is everyone exploring solid-state batteries?
The principle of a nuclear battery is to convert the heat energy generated by the decay of isotopes into electrical energy. The reason why everyone thinks that a nuclear battery is equivalent to "unlimited power" is because the decay period of isotopes is very slow, so theoretically it can last for decades. Of course, putting aside the technical difficulties of miniaturizing the reactor, the price and radiation are already unacceptable to ordinary people.
Fuel cells convert the chemical energy of fuel into electrical energy. Currently, hydrogen is generally considered to be a suitable fuel. However, due to the many problems that still need to be solved in terms of the cost and technology of hydrogen production, storage, and transportation, commercialization is unlikely for the time being. Although Toyota has been working in this field for many years and used Toyota's hydrogen fuel cell vehicles at the 2022 Beijing Winter Olympics, this may only be a signal and does not mean that the problems have been solved.
Therefore, for a considerable period of time to come, batteries will remain a commercially viable and relatively clean energy source.
So what do ternary lithium batteries, lithium iron phosphate batteries, and the solid-state batteries that have become very popular in the last two years mean? What do they represent, and what are their characteristics?
First, let's clarify a concept: both lithium iron phosphate batteries and ternary lithium batteries belong to the category of lithium-ion batteries. They are mainly composed of positive and negative electrode materials, electrolyte, and separator. The main difference between lithium iron phosphate batteries and ternary lithium batteries lies in their positive electrode materials. The positive and negative electrode materials mainly determine the battery capacity, while the electrolyte is the medium for lithium-ion transfer.
As for solid-state batteries, the main difference lies in the electrolyte, which is solidified to replace both the electrolyte and the separator. This is because the electrolyte in traditional lithium-ion batteries is simply too heavy; for example, the 80kWh battery in the Mercedes-Benz EQC weighs over 700kg. In comparison, a V8 twin-turbocharged engine appears remarkably lightweight.
So, what exactly are the advantages of solid-state batteries that have sparked such heated discussions in the new energy sector?
Firstly, in terms of safety, because a solid electrolyte is used, there is no diaphragm, and there is no risk of short circuit between the positive and negative electrodes caused by puncture, overcharging or over-discharging, which greatly reduces the risk of spontaneous combustion. Even if it is punctured by needles, the solid electrolyte will remain unaffected.
Secondly, it can significantly improve energy density because liquid electrolytes have a large volume, with only 2% of the total lithium ions actually participating in charging and discharging. Solid-state electrolytes are thinner and lighter, allowing more cells to be packed into a unit volume. Furthermore, because solid-state electrolytes are more inert, they do not require large-scale thermal management systems. Moreover, since there is no waste liquid, solid-state batteries are also easier to recycle.
Given that solid-state batteries have so many advantages, why weren't they used in the first place for power batteries?
The main issues are cost and high-power application scenarios. Cost is a given; solid-state battery production is far more complex than lithium-ion battery production. For example, we all know that lithium-ion batteries outperform lead-acid batteries, but most low-end electric vehicles, two-wheeled electric vehicles, and electric vehicles for the elderly use lead-acid batteries, primarily because they are cheap enough.
As for the problems of high-power applications, they mainly lie in impedance and electron mobility. The problem with the former is that dendrites will precipitate on the negative electrode of the lithium battery during long-term charging and discharging. These dendrites are very troublesome in liquid electrolyte. After they accumulate to a certain extent, they will pierce the separator, causing a short circuit between the positive and negative electrodes and thus causing danger. Although solid electrolyte can effectively prevent dendrites from piercing the separator, it cannot prevent dendrites from accumulating. Over time, dead lithium will also occur, thereby reducing the battery capacity.
The issue of electron mobility stems primarily from the fact that lithium ions face greater difficulty flowing in solid-state electrolytes compared to liquid electrolytes. Previously, they could move from one liquid end to the other; now, they must traverse a solid medium. This is currently the biggest challenge facing solid-state batteries: insufficient high-current charging and discharging capabilities, while high-power discharging and charging are indispensable for future electric vehicles.
However, overall, the advantages of solid electrolytes over liquid electrolytes are still quite obvious. Compared to the two disadvantages mentioned earlier, high energy density, safety, and stability are the more important aspects for the development of electric vehicles today.
As for the solid-state battery that NIO mentioned at the ET7 launch event, it is not a pure solid-state battery. However, NIO has not mentioned the amount of electrolyte, nor has it announced whether the 70kWh and 100kWh vehicles can be upgraded, or what the price will be. As for whether the promised delivery can be made this year, only NIO knows.
2. Various patterns on the positive and negative terminals
If you haven't forgotten your middle school chemistry, you should remember that batteries are mainly composed of three parts: a positive electrode, a negative electrode, and an electrolyte. Having discussed the advantages and disadvantages of solid-state electrolytes for traditional power batteries, let's look at the various ways to utilize the positive and negative electrodes to further advance battery technology, and where our current challenges lie.
First, it's important to clarify that the materials and their ratio at the positive and negative electrodes both affect battery performance. For example, ternary lithium batteries use a mixture of nickel, cobalt, manganese, or aluminum as the positive electrode material. By adjusting the mixing ratio of each component, the battery can exhibit different characteristics. For instance, increasing the proportion of nickel can increase the battery's energy density; increasing the proportion of cobalt can extend the battery's lifespan and allow for faster charging; and increasing the proportion of manganese or aluminum can make the battery more stable.
Different models are derived from the mixing ratio, such as 523, 622, and 811. However, the evolution of this ratio shows that the proportion of nickel (80%) has been continuously increasing, while the proportion of cobalt has been decreasing. This is because nickel can directly increase the energy density of the battery. The reason for not using only nickel and retaining cobalt is that the latter helps maintain battery stability. However, correspondingly, increasing the cobalt content will also reduce the battery's energy density. Therefore, with high-energy-density batteries becoming the trend, ultra-low cobalt batteries or even cobalt-free batteries are the direction that engineers are currently striving for.
Currently, after continuous technological optimization, Tesla has reduced the cobalt content to about 3%. It is not impossible to reduce it to 1% or even cobalt-free in the future. However, for the sake of stability and safety, finding a substitute for the role played by cobalt has become crucial.
Great Wall Svolt Energy, which has been silent for a long time, is said to have achieved mass production of cobalt-free batteries. It has adopted a series of technologies that non-professionals cannot understand at all (nano-network coating, doping with cations, etc.) and achieved a single-cell energy density of 240Wh/kg.
As for the negative electrode, the most commonly used negative electrode material in lithium batteries is graphite, which is made of carbon. Since the negative electrode is responsible for discharging and needs to remove lithium ions from the electrolyte, the amount of lithium ions that the negative electrode can store becomes the upper limit of the battery capacity.
However, carbon's lithium storage performance is rather average. The reason why graphite can be widely used in anode materials is mainly due to its stable properties.
To further improve performance, the current mainstream technology is to add silicon to carbon. This is because silicon has nearly ten times the lithium storage capacity of carbon. However, if the proportion of silicon is too high, it will reduce the stability of the anode. For example, the charge-discharge expansion rate of an all-silicon anode reaches 300%, while that of graphite is only 10%. Therefore, most manufacturers try to achieve a balance, such as the "silicon-doped lithium supplement" of the Zhiji L7 and the sponge silicon anode sheet of the AION LX PLUS.
Of course, since the primary mission of the negative electrode is to release lithium ions into the electrolyte, the ultimate goal is obviously to directly use lithium metal as the negative electrode. However, the biggest danger of using lithium metal as the negative electrode is the dendrite problem mentioned earlier. When repeatedly charged and discharged, dendrites will precipitate on the negative electrode, which can puncture the separator and cause a short circuit. Theoretically speaking, solid electrolytes and lithium metal negative electrodes complement each other and satisfy each other. This is another reason why solid-state batteries are so popular.
Of course, the problems with lithium metal as an anode material are far more than just dendrites. Currently, this technology is still in the laboratory stage, and the first-generation lithium metal battery at SES Battery World has not yet been verified by the market and actual conditions. It is already very good that we can see the widespread adoption of high-silicon lithium batteries.
In conclusion
In conclusion, although battery technology is the slowest-progressing project in the three-electric system of electric vehicles, its future path is gradually becoming clearer in recent years with the continuous increase of capital and human resources.
Aside from fuel cells and nuclear batteries, the most perfect battery form we'll see in the future will likely be one using a pure solid-state electrolyte, lithium metal anode, and cobalt-free cathode. At that point, I estimate that mass production of Level 5 autonomous driving will be just around the corner. But regardless, we are ultimately a generation witnessing history.
