Popular Science Article: Solid-State Battery

Solid-state battery, this technical term has recently become a hot topic in the industry because of a live broadcast. Even in the A-share market, stocks related to the subject have seen a wave of rising prices. Today, let us learn about the ultimate goal of power batteries - solid-state batteries.

Let's first look at a report. In early April, Liu Tao, CEO of Zhiji brand, announced that the Zhiji L6 ( parameters | inquiry ) model has been equipped with the latest light-year solid-state battery, which can easily reach a range of 1,000 kilometers and the fast charging time is much faster than the current mainstream lithium batteries. As soon as this news came out, it immediately triggered a discussion about solid-state batteries. We will talk about the controversy about this solid-state battery later, but first let's understand what a solid-state battery is.

Zhiji's L6 semi-solid-state battery has a range of 1,000 km and quasi-900V fast charging

Solid-state batteries are relative to the liquid lithium-ion batteries that are currently in wide use. The liquid state refers to the form of electrolytes in lithium-ion or lithium iron phosphate batteries. Electrolytes play a vital role in batteries. Liquid electrolytes fill the space between the positive and negative electrodes of the battery. In the process of lithium ions moving from the positive electrode to the negative electrode and then back to the positive electrode, the battery's charging and discharging process is completed.

The structural difference between solid-state batteries and liquid batteries is mainly reflected in the form of the electrolyte

In principle, solid-state batteries use solid electrolytes. Since there is no diaphragm or liquid electrolyte, it has many inherent advantages, such as higher density and more compact structure of solid electrolytes, which can bring more charged ions together. These ions move faster in the solid medium, so they can generate larger currents and increase battery capacity.

The structural difference between solid-state batteries and liquid batteries is mainly reflected in the form of the electrolyte

At present, the driving range is the main bottleneck restricting the development of new energy vehicles, and this mainly depends on the energy density of the battery. In lithium-ion batteries, the energy density is determined by the positive and negative electrode materials. At present, the positive electrode materials of lithium-ion batteries have basically evolved to 811. This digital combination is actually the proportion of the three elements of nickel, cobalt, and manganese. It is called high-nickel ternary, which is basically the ceiling of the material. The evolution of negative electrode materials is not so smooth. At present, the main material used is the material upgraded from graphite to silicon-carbon negative electrode, and its energy density is capped at 400Wh/kg. However, if metallic lithium can be directly used as the negative electrode material, the energy density is expected to reach 2600-3500Wh/kg.

Solid-state batteries have good safety

Why can't it be used? Because in liquid electrolytes, during the charge and discharge process, metallic lithium easily produces a substance called lithium dendrites. The crystal shape of this substance is very sharp, and it may even pierce the diaphragm, causing a short circuit between the positive and negative electrodes. Solid electrolytes do not have such a problem. If metallic lithium is used as the negative electrode material, the energy density of the battery can be greatly improved, which is also the biggest advantage of solid-state batteries.

Traditional lithium-ion liquid batteries have a complex internal structure and require a large cooling system

In addition, since there is no liquid in the solid-state battery, its packaging becomes simpler, and there is no need to worry about leakage, and there is no need to add additional cooling pipes to cool down. In traditional lithium batteries, the volume of the diaphragm and electrolyte accounts for 40% of the entire battery, and the weight accounts for 25%. If solid electrolyte materials are used, the distance between the positive and negative electrodes can be reduced to more than ten microns, and the volume and weight of the entire battery pack will be greatly reduced. In terms of cycle life, due to overcoming the lithium dendrite phenomenon, the solid-state battery cycle performance can reach about 45,000 times under ideal conditions. In addition, it only takes more than ten minutes to fully charge the solid-state battery, and the operating temperature range has been expanded to more than three times.

High-performance ternary lithium battery pack is displayed in a fish tank with swimming fish

It can be seen that the advantages of solid-state batteries are obvious: high safety, high energy density, and stable performance at extreme temperatures. In fact, as early as 30 years ago, the Oak Ridge National Laboratory in the United States claimed to have developed solid-state batteries, but why have solid-state batteries not been widely popularized so far? We all know that the marketization of power batteries needs to meet five core indicators: energy density, charge and discharge performance, production cost, safety and cycle life. At present, the main bottleneck restricting solid-state batteries is still production cost. Some analysis agencies pointed out that by 2026, with the advancement of technology, the cost of solid-state batteries is expected to reach 6,000 yuan/kWh. If you buy a 70kWh solid-state battery car, the cost of the battery alone is as high as 420,000 yuan. The current price of lithium carbonate is 100,000 yuan per ton, which is converted into a ternary lithium battery cell cost of about 495 yuan/kWh. The battery cost of a 70kWh lithium battery car is only 35,000 yuan. This nearly ten-fold cost gap is currently the main factor hindering the development of solid-state batteries.

New ways to use and recycle lithium batteries

Let's go back to the beginning and talk about the Lightyear solid-state battery released by Zhiji. In fact, from the interpretation of the live video, we can see that this so-called solid-state battery has not completely gotten rid of the liquid electrolyte. It still needs a liquid component to wet the pole pieces to facilitate the movement of electrons between the pole pieces, and the mass of this "wetting agent" accounts for about 10% of the entire battery. So it is more reasonable to call it a semi-solid-state battery. However, even so, this battery has a capacity of 130KWh and an energy replenishment efficiency of replenishing 400km of driving range in 10 minutes, which is far ahead of the current mainstream lithium batteries. It can be seen that if the cost of solid-state batteries can be reduced to a level comparable to that of lithium-ion batteries in the future, the driving range of electric vehicles will be greatly increased, the safety of the battery will be significantly improved, and the pain points affecting the development of electric vehicles will be solved.