How far is lithium from a "real" high energy battery?

The biggest obstacle to the large-scale industrialization of pure electric vehicles is "mileage anxiety". The essence of the problem is the energy density of the power battery system.

The existing lithium-ion battery system can only be considered as a "half" high-energy battery because its high specific energy is mainly based on the extremely low electrode potential. At present, several kinds of transition metal oxide positive electrode materials that are commercialized are not significantly superior to water secondary batteries in terms of operating voltage or specific capacity.

Therefore, there are only two ways to make lithium a "real" high-energy battery: to increase the operating voltage of the battery or to increase the specific capacity of the positive and negative materials. However, due to the constraints of many objective factors, the improvement of energy density of lithium-ion batteries has approached the bottleneck.

Theoretical calculations show that the existing maximum capacity positive and negative polar material system (high nickel ternary with Silicon carbon negative electrode) has a slightly higher energy density of about 300 W/Kg. Due to the strict restrictions of many technical indicators, large-scale power batteries are very different from 3C small batteries in the selection of electrode materials, system collocation, Polar technology, and core structure design. These factors make even the same positive and negative polar collocation system. The energy density of large power cells is much lower than that of small 3C batteries.

That is, in the foreseeable future, it is almost impossible for a high-energy lithium-ion power battery system that can be commercialized on a large scale to have an energy density of more than 250 W/Kg. This system energy density is for ordinary household passenger vehicles. In actual conditions and load conditions, it is a range of more than 300 Km.

The Beyond LIB has two dazzling "new stars": Li-S and Li-Air batteries. In fact, they are all old systems that have only been repackaged in recent years. If we look closely at these two electrochemical systems, their core problem is still the negative electrode of metal lithium.

The Li-S battery must solve the problem of the negative electrode of metal lithium, otherwise the Li-S battery basically loses the advantage of high energy. Coupled with the unique "sulfur ion shuttle effect" of Li-S batteries, the author does not think that Li-S batteries will have the possibility of practical application in electric vehicles. In the future, Li-S batteries may have certain applications in special areas such as military and wild areas.

The Li-Air battery's thinking and starting point are not the same as Li-S batteries. It belongs to the category of air batteries. But in my personal opinion, metal-air cells, especially secondary metal-air cells, actually combine the disadvantages of both secondary and fuel cells organically and magnify the disadvantages. Secondary Li-Air batteries involve more technical problems than Li-S batteries.

Personally, the next breakthrough for lithium-ion may lie in all-solid lithium-ion batteries, rather than Li-S and li-air or even graphene batteries, which are currently highly hyped. Due to the use of metallic lithium as a negative electrode, the energy density of all-solid lithium-ion batteries will be greatly improved compared to the current liquid lithium-ion batteries (the author estimates that the actual energy density can reach 350 Wh/kg). Good safety is another advantage of all-solid lithium-ion batteries.

However, due to the ion transfer characteristics of solid electrolytes and the interface resistance problems of solid electrolytes and positive and negative electrode materials, it is determined that the ratio performance must be its short plate. In addition, the recyclability and temperature performance of all-solid batteries still face great challenges.

Personally, the author believes that all-solid lithium-ion batteries may be used in 3C small electronic devices in the future, and large power cells may not be suitable for its application. According to the current research and development of all-solid lithium-ion batteries in the world, the author does not believe that there is a possibility of large-scale commercialization of all-solid lithium-ion batteries in the next 5-10 years.

What I want to emphasize here is that the above understanding and understanding of the safety and energy density of lithium electricity requires considerable electrochemical expertise and senior lithium electricity production practices. Due to space limitations, the author does not elaborate here.

Compared with lithium-ion power cells and fuel cells, we can see that there is very limited room for further increase in the energy density of lithium-ion power cells. If you think about it from the perspective of the most basic electrochemical principles, this problem is not difficult to understand. The increase in energy density of secondary batteries does not follow Moore's law.

The new chemical power supply system with higher energy density is still in the basic research stage, and the prospect of industrialization is still very uncertain. Relatively speaking, the energy density problem of PEMFC is not very prominent. Even if the number of hydrogen storage tanks is increased by the simplest to ensure the mileage, the operability is relatively easy.

We can also think from another perspective that the secondary battery must be developed into a fully sealed system and strive to be maintainable (for lithium power it is absolutely necessary), and precisely because the secondary battery is a sealed system, Which makes it impossible for it to have a high energy density. Otherwise, what's the difference between a closed high energy system and a bomb?

From the most basic law of conservation of energy does not make sense! From this point of view, it is easy to understand that the energy density increase of lithium-ion batteries (actually including all secondary battery systems) will be very limited. The fuel cell is an open system. The electric reactor is only an electrochemical reaction site. The energy density of the system mainly depends on the amount of hydrogen stored in the hydrogen storage system.

Because it is an open system, fuel cells have a greater potential for increasing energy density and are inherently safer. This advantage is exactly what any secondary battery does not have. From the perspective of electrochemical devices, fuel cells are a higher level of development of chemical power sources than secondary batteries.

Fundamentally, a secondary battery, including a lithium-ion battery, is an electrical energy storage device, and a fuel cell is an electrical energy production device. This most essential difference determines the different positioning of the two in the application field.

Many different characteristics of fuel cells and secondary cells determine that secondary cells are suitable for energy storage purposes of medium and small power, while fuel cells are more suitable for higher power applications. Therefore, the author personally believes that the positioning of lithium-ion batteries on electric vehicles is an auxiliary power device, and HEV and PHEV and small pure electric vehicles are its main application areas.

The PEMFC fuel cell has been developed as a large-scale power source from the very beginning and is a veritable "power cell." I would like to emphasize here that PEMFC fuel cells and lithium-ion batteries do not overlap in the application field. They are complementary relationships in electric vehicles, not who replaces whom.

The page contains the contents of the machine translation.