This article is from WeChat public account: car stuff (ID: chedongxi) , author: Bear
Samsung Advanced Research Institute and Samsung Japan Research Center recently published a title in “Nature Energy” (Nature Energy) For the paper “Achieving High Energy Density and Long-Life All-Solid-State Lithium Batteries Through Silver-Carbon Negative Electrodes”, Samsung’s solution to the lithium dendrite and charge-discharge efficiency problems that plagued the mass production of all-solid-state batteries.
Samsung publishes paper in Nature-Energy
It is understood that this solution will help Samsung ’s all-solid-state battery to achieve 900Wh / L (different from the unit of measurement of Wh / kg, due to different material densities Different, the two are not convertible) energy density, more than 1,000 charge and discharge cycles and 99.8% Coulombic efficiency (also known as charge and discharge Efficiency) . Although China’s more advanced solid-state battery technology can also achieve more than 1,000 charge and discharge cycles, the Coulomb efficiency is currently less than 100%.
According to the paper, Samsung introduced silver-carbon composite anodes, stainless steel (SUS) current collectors, pyroxene-type sulfide electrolytes, and special materials The coating has processed the negative electrode, electrolyte and positive electrode of the solid state battery, which effectively solved the lithium dendrite growth, low Coulomb efficiency and interface side reactions. These three core issues for mass production of solid state batteries promote Industrialization went further.
Breakthrough of key technologies means the start of the solid-state battery market card game, including players such as Panasonic, Ningde Times, Toyota, and BMW. It is foreseeable that in the next five years, solid-state battery technology will become the key to the technological confrontation and industrial layout of these companies.
Samsung will have a considerable lead in this competition because it took the lead in achieving technological breakthroughs.
Samsung is the first to make a breakthrough in the global battle for solid air batteries.
Solid battery was once considered the best battery technology for electric cars, but what kind of technology is it?
Literally, an all-solid-state battery means completely replacing the liquid electrolyte in the existing battery system with a solid-state electrolyte. However, in the definition of the battery industry, solid-state batteries have three major technical characteristics-solid-state electrolytes, high-energy positive and negative electrodes, and lightweight battery systems.
Solid electrolytes are well understood, and are different from liquid electrolytes such as ethylene carbonate, propylene carbonate, and diethyl carbonate used in traditional lithium batteries. Solid electrolytes are a new type of electrolyte that acts as ions between the positive and negative electrodes of a battery. The materials of the moving channel are currently divided into three categories-polymer materials, inorganic oxide materials, and inorganic sulfide materials.
Compared with liquid electrolytes, solid electrolytes have physical and chemical properties that are stable and non-flammable at high temperatures. At the same time, their mechanical structure can also inhibit the growth of lithium dendrites, preventing them from piercing the separator and causing battery short circuits.
At the same time, the characteristics of easy oxidation under the high pressure of conventional liquid electrolytes no longer exist for solid electrolytes, so solid batteries can use positive and negative solutions with higher energy density, higher discharge windows, and larger potential differences.
Since the solid-state battery cell contains no liquid, it can be assembled in series and then in parallel, which reduces the weight of the battery PACK;The characteristics of the stable nature of the battery can also eliminate the temperature control components inside the power battery to further reduce the weight of the power battery.
The three major characteristics correspond to the technical advantages of solid-state batteries over traditional lithium batteries. Simply put, it is higher energy density, larger discharge rate, longer cycle life, and more lightweight battery system design.
These technical advantages determine that solid-state batteries will be the most suitable power battery for electric vehicles in the next ten years. Based on the internal battery power industry’s research on the progress of mass production of solid-state batteries, after 2025, solid-state batteries will gradually Become a mainstream product in the field of power batteries.
It can be said that whoever wins the solid-state battery will seize the opportunity to develop the new energy industry in the next ten years.
Under the guidance of this idea, international first-tier car companies such as Toyota, BMW, and Volkswagen, power battery companies such as Panasonic, Samsung, and Ningde Times, and even giant players from across the world such as Dyson, NGK | NTK, They have poured into the field of solid-state batteries, and tried to complete the card slot before the industrialization of solid-state batteries through investment and mergers, technical cooperation, and independent research and development.
Volkswagen launched the Audi PB18 e-tron with solid-state battery
But when these players are really off the ground, the technical difficulty of solid-state batteries is far beyond their imagination. Current solid-state battery technology needs to solve many difficulties before mass production. Some studies have shown that the formation of lithium dendrites, low Coulomb efficiency caused by interface impedance, and side reactions between solid electrolytes and positive and negative electrodes have been tested in solid-state batteries China is especially obvious .
Samsung recently published a paper in the journal Nature-Energy that officially proposed solutions to these problems.
Samsung publishes paper in “Nature-Energy” magazine
First of all, Samsung reduced the excessive and uneven deposition of lithium ions in the negative electrode through the use of silver-carbon composite materials and stainless steel (SUS) Sulfide solid electrolyte with a higher ion migration number (Generally, the liquid electrolyte has a lithium ion migration number of 0.5, and the sulfide solid electrolyte has a lithium ion migration number of 1) , Reducing the deposition of lithium ions in the electrolyte, reducing the possibility of lithium dendrite formation in the two areas of the negative electrode and the electrolyte.
Second, Samsung applied the LZO coating to the NCM positive electrode layer, using 0.5nm LZO coating to separate the positive electrode material from the sulfide solid electrolyte, and realized by the good conductivity of the LZO coating itself The reduction of impedance is used to improve the coulomb efficiency of the battery system.
At the same time, the presence of the LZO coating and the silver-carbon composite material layer also blocked the possibility of side reactions between the sulfide solid electrolyte and the positive and negative electrodes, maximizing the normal performance of the solid-state battery during operation. And recyclability.
With this solution, Samsung ’s all-solid-state battery has achieved an energy density of 900Wh / L, more than 1,000 charge and discharge cycles, and a Coulomb efficiency of 99.8%.
The Toyota and Panasonic teams also studying solid-state batteries. Although the current solid-state battery technology can achieve higher levels of cycle times, its energy density is only 700Wh / L, and the Coulomb efficiency is also about 90%. The solid lithium battery of the Ningde era can theoretically achieve an energy density of more than 1000Wh / L, but in terms of Coulomb efficiency, it is also weaker than Samsung.
Samsung’s solutionEffectively overcome the technical difficulties of the industrialization of solid-state batteries. If you evaluate Samsung’s position among many opponents based on the idea of a card game, then Samsung’s breakthrough in key technologies of solid-state batteries will undoubtedly win the start-up advantage. .
Three methods for Samsung to solve the problem of lithium dendrite growth
The first problem that Samsung encountered in the research of all-solid-state batteries is the lithium dendrite problem. The formation of lithium dendrites is a problem that all lithium batteries have to face.
The generation principle is the uneven deposition of lithium ions in the negative electrode and the electrolyte, and the branch-like lithium ion crystals formed. These crystals are possible in discharge rates exceeding the battery design upper limit and in long-term charge and discharge cycles. appear.
Once the lithium dendrite appears, it means that the lithium ions inside the battery have irreversibly decreased. At the same time, the lithium dendrite will continue to adsorb free lithium ions to achieve growth, and may eventually pierce the separator, resulting in battery positive and negative electrodes. A direct contact causes a short circuit.
It has been thought that the mechanical properties of solid electrolytes can inhibit the growth of lithium dendrites and prevent their damage to the separator, but in reality, such a vision has not been realized.
Studies have shown that the position of lithium ions passing through the solid-state electrolyte ion channel when arriving at the negative electrode is more uneven, and there is also a gap between the solid electrolyte and the negative electrode interface, so it is easy to cause irregular deposition of lithium ions, thereby forming lithium dendrites. . And in this case, the voltage that causes the lithium dendrite to appear is even lower than that of traditional lithium batteries.
Facing this problem, Samsung proposed a three-in-one solution:
1, silver-carbon composite material layer
Samsung added a silver-carbon composite material layer between the sulfide solid electrolyte and the anode material.
The working principle during charging is to reduce the nucleation energy of lithium ions by combining them with the silver ions in the middle of the silver-carbon material layer during the final deposition of lithium ions through the electrolyte to the negative electrode. (can be simply understood as the ability to gather together) , so that lithium ions are uniformly deposited on the anode material.
Silver-carbon composite layer (red line) in the battery structure diagram
During the discharge process, the lithium ions in the silver-lithium metal coating originally deposited on the negative electrode material completely disappeared and returned to the positive electrode, and the silver ions will be distributed between the negative electrode material and the silver-carbon composite material layer, waiting for the next time The arrival of lithium ions during charging.
Samsung ’s team conducted a controlled experiment to determine whether the silver-carbon composite material layer had an effect during the lithium ion deposition process.
First, the team investigated the case where the negative electrode was in direct contact with the sulfide solid electrolyte in the silver-free carbon composite layer.
When the charging rate is (SOC) 50%, and the charging rate is 0.05C (0.34mAh / cm2) , although the deposition of lithium ions on the negative electrode is not dense, its deposits are thick and random in shape, which has the possibility of generating lithium dendrites.
Deposition of lithium ions on the negative electrode without silver-carbon layer
In addition, after 10 full charge and discharge cyclesAfter the ring, the battery capacity dropped significantly compared with the initial capacity. After about 25 charge and discharge cycles, the battery capacity has dropped to about 20% of the initial capacity.
Attenuation of the silver-free carbon layer battery
According to the analysis of Samsung research team, this situation is likely that lithium dendrites were generated inside the battery, resulting in a significant reduction in the number of active lithium ions, thereby reducing the battery’s discharge capacity.
In the presence of a silver-carbon composite layer, during the first charging process, (0.1C, 0.68mAh / cm2) , lithium ions pass through After the silver-carbon layer, a dense and uniform deposit was formed on the negative electrode.
According to Samsung’s research team, the silver in the silver-carbon layer combines with lithium ions when lithium ions pass through to form a silver-lithium alloy, which reduces the nucleation energy of lithium ions and forms a solid solution when it reaches the anode. , So that lithium ions are uniformly deposited on the negative electrode material.
The distribution of silver ions after multiple cycles
while inDuring the subsequent discharge, the image under the electron microscope showed that 100% of the lithium ions were returned to the positive electrode material, and there was no residue in the negative electrode material. This means that during the charge and discharge process, almost no loss of lithium ions occurred, No deposits remain, avoiding the formation of lithium dendrites.
2, SUS collector negative electrode
The silver-carbon composite material layer largely solves the problem of uneven deposition of lithium ions, but in order to reduce the formation of lithium dendrites as much as possible, the “excess” lithium in the battery needs to be reduced.
The reason for this statement is that Samsung has found that it is rumored to be suitable as a high-energy-density (3,860 mAh g−1) Metal lithium is not suitable for solid-state batteries.
Excessive lithium is likely to aggregate spontaneously under the action of high voltage, forming lithium dendrites.
Samsung therefore uses lithium-free stainless steel in its all-solid-state battery solutions. For the carrier of ions and the structure of the battery, the mechanical strength of the SUS material is very reliable.
Also, since the negative electrode material does not contain lithium, the formation of lithium dendrites can also be suppressed.
3. Pyrite solid sulphide electrolyte
Another place where lithium dendrites are formed is the electrolyte. Because the number of lithium ion migration in traditional electrolytes is usually 0.5, a large amount of lithium ion migration caused by excessive discharge will cause lithium ions to be deposited in the ion channel. Lithium dendrites may form.
The electrolyte used by Samsung in all-solid-state battery solutions is a pyroxene-type sulfide solid electrolyte with a lithium ion migration number of 1. Its lithium ion migration number is larger than that of ordinary electrolytes, and it is not easy for lithium ions to be deposited therein. Therefore, formation of lithium dendrites can also be suppressed.
Samsung ’s all-solid-state battery solution effectively avoids the formation of lithium dendrites through the above three methods. In its thousands of cycle tests, solid-state batteries using this solution did not form lithium dendrites. .
Special coating solves the impedance problem, the Coulomb efficiency reaches 99.8%
For the other two difficulties in the research and development of all-solid-state batteries-the problem of Coulomb efficiency caused by high interface impedance, and the problem of side reactions between solid electrolyte and positive and negative electrodes, Samsung also gave solutions.
In solid-state batteries, solid-solid interfaces are formed between solid-state electrodes and solid electrolytes. Unlike solid-liquid interfaces in traditional batteries, which have good contact properties, direct contact between solids and solids is difficult to achieve seamlessly. . That is, the contact area of the solid-solid interface is smaller than that of the solid-liquid interface of the same specification.
According to the principle that the contact area affects the ionic conductivity, the smaller the contact area, the lower the ionic conductivity between the interfaces and the larger the impedance.
At the same voltage, the larger the impedance, the smaller the current, and the lower the Coulomb efficiency of the battery.
Not only that, the solid electrolyte also produces interface side reactions during contact with the active cathode material.
According to the research results of the University of California, San Diego, the oxygen generated during the lithium ion deintercalation of the positive electrode will produce a strong electrostatic effect with the lithium in the sulfide solid electrolyte, and the mutual diffusion of cations between the electrolyte and the positive electrode material will form The SEI film is (a passivation layer covering the surface of the electrode) , and the phenomenon of thickening and hindering ion transport occurs in repeated cycles.
This phenomenon will also cause the coulomb efficiency of the battery to decrease.
To address the above two issues, Samsung has addressed both the positive and negative electrodes.
For the positive electrode, Samsung coated the positive NCM material with a 5nm layer of LZO (Li2O–ZrO2) , Used to improve the impedance performance of the solid-solid interface of the positive electrode and the electrolyte.
LZO coating on NCM cathode material
At the same time, the coated LZO coating blocked the side reaction between the positive electrode material and the sulfide solid electrolyte, which prevented the SEI film from appearing between them, the Coulomb efficiency was improved, and the discharge capacity was reduced. At the same time, it was significantly slowed.
In the negative electrode, the sulfide solid electrolyte is indirectly in contact with the negative electrode through the silver-carbon layer, and the interface impedance is also improved. Silver ions can also help lithium ions to complete uniform deposition on the negative electrode, and the impedance is further reduced.
Another reason why Samsung uses SUS current collectors as anode materials is because SUS current collectors have almost no reaction with sulfides, which means that the possibility of side reactions between the anode and sulfide solid electrolyte is also cut off. .
In addition, Samsung’s choice of pyroxene sulfide solid electrolyte has the same ionic conductivity as ordinary liquid electrolytes (1-25ms / cm) , therefore, the conductivity of the electrolyte itself is very strong, which is also helpful to improve the coulomb efficiency.
The average Coulomb efficiency of this battery solution is more than 99.8% during 1000 charge and discharge cycles of Samsung research team. In July last year, among the solid-state battery solutions published by the Chinese Academy of Sciences Physics, the battery’s Coulomb efficiency was about 93.8%.
Samsung is one step ahead, other players still have a five-year window period
Samsung’s all-solid-state battery solution has, to a certain extent, solved the three major technical difficulties of the current industrialization of solid-state batteries. The breakthrough of key technologies means that solid-state batteries are moving closer to industrialization, and the days when electric vehicles can use solid-state batteries are getting closer.
Samsung’s research team bluntly stated in the thesis: “The all-solid-state battery we have developed has a capacity of more than 900Wh / L.Energy density and charge-discharge cycle life of more than 1,000 times, and excellent performance make this solution a key breakthrough in the field of solid-state batteries. It is likely to help all-solid-state batteries become the choice of high-energy density and high-safety batteries for electric vehicles in the future. . “
However, it should be noted that when a company announces the completion of a breakthrough in key difficulties in forward-looking technology, it also means that the company’s technical barriers are being established, and opportunities for other companies are correspondingly reduced. Especially in industries where the technological advantages such as batteries are extremely high, it is self-evident that it is difficult to break through technical barriers.
Before, Hitachi Chemical, a Japanese lithium battery material maker, completed the research and development of carbon-based anode technology, and the blockade of China’s material companies has lasted for 30 years.
Samsung, LG Chem, SKI and other companies have early deployed batteries, electrolytes, electrodes and other fields upstream of the battery. While cultivating their own supplier system, they have received a large number of patents and formed other battery companies Of the blockade.
Samsung is the first to break through the technical difficulties of solid-state batteries. It is bound to block patents on other battery companies. China, Japan, South Korea and other power battery companies have one more technical path to break through the difficulties of solid-state batteries.
This is the result of Samsung’s first-mover advantage in the solid-state battery card race.
But for Samsung, a first mover advantage doesn’t mean winning. Mass production of solid-state batteries still has many difficulties for Samsung.
First, the sulfide solid electrolyte has extremely high requirements on the production process. It is prone to oxidation when exposed to air, and it is prone to produce harmful gases such as H2S when exposed to water. The production process needs to be isolated from moisture and oxygen.
Second, the large-scale production of silver carbon layer requires the purchase of precious silver, which is not small in scale, and the cost is quite high.
For Samsung ’s battery business, which has not been profitable in recent years, the input-output ratio formed between the cost of purchasing precious metals in new production lines and the market after mass production of solid-state batteries is worth measuring.
Therefore, before the air outlet of solid-state batteries has arrived, (the industry believes that they will be mass-produced in 2025) , other power battery companies Still has a window of market and technology, the first spot of solid-state batteries is still empty.
In Japan, Panasonic has formed an alliance with Toyota and came up with a solid-state battery solution with an energy density of 700Wh / L two years ago.
The patent recently announced by Ningde Times in China shows that the energy density of its all-solid-state lithium metal battery can theoretically exceed 1000Wh / L. The Institute of Physics of the Chinese Academy of Sciences has also completed the development of materials that can improve the coulomb efficiency of solid-state batteries to more than 93% .
Solid Power, an American power battery startup, has received investment from Hyundai, BMW, Ford and other automakers and announced that it will mass produce solid-state batteries for electric vehicles in 2026.
It is foreseeable that in the next five years, the power battery industry will start a dark battle around the key technology of solid state batteries. Power battery companies in China, Japan, the United States, and South Korea have already entered the market, and are preparing to compete for the leading position in this field when the solid-state battery vent comes.
Conclusion: Difficulties in solid-state batteries were overcome by Samsung
In the previous research and development of solid-state batteries, lithium dendrite problems, Coulomb efficiency problems, and interface side reaction problems have stumped R & D teams in many battery fields.
But this time, Samsung successfully solved the problem of lithium dendrite formation through the silver-carbon composite material and the negative electrode of the SUS current collector. The coating of the positive electrode by the LZO coating also made the Coulomb efficiency of the battery system reach 99.8%.
It can be considered that the key difficulties of solid-state battery technology have been overcome by Samsung, and solid-state battery products are one step closer to mass production.
This phenomenon means that in the next five years, car companies, power battery suppliers and cross-border players who are deploying solid-state battery fields will follow this line of research to promote the realization of solid-state battery fields from research and development to Breakthrough in mass production.
In terms of the number of players, the capital boost, and the demand of the electric vehicle industry, the outlet of the solid-state power battery industry may soon come.
This article is from the WeChat public account: car stuff (ID: chedongxi) , Author: Bear