Samsung has made breakthrough progress on the mass production of all solid-state batteries!
A few days ago, Samsung Advanced Research Institute and Samsung Japan Research Center published a paper titled "Achieving High Energy Density and Long Life All-Solid Lithium Batteries through Silver Carbon Anode" in Nature Energy magazine, which showed Samsung's solution to the lithium dendrites and charging and discharging efficiency problems that plague the mass production of all solid-state batteries.
It is understood that this solution will help Samsung's all-solid-state battery achieve an energy density of 900Wh / L (different from the unit of measurement of Wh / kg, which is not convertible due to different material densities) and more than 1,000 charge and discharge cycles And 99.8% Coulomb 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 current Coulomb efficiency is still not close to 100%.
According to the paper, Samsung introduced a silver-carbon composite negative electrode, a stainless steel (SUS) current collector, a pyroxene sulfide electrolyte, and a special material coating to treat the negative electrode, electrolyte, and positive electrode of the solid-state battery, effectively solving the lithium dendrite Growth, low coulombic efficiency and interface side reactions, the core problems faced by the mass production of these three major solid-state batteries are pushing solid-state battery technology to go further from industrialization.
The breakthrough of key technologies means the opening of the card competition in the solid-state battery market, and players including Panasonic, Ningde Times, Toyota and BMW have sharpened their lives. 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.
And Samsung, because it took the lead in achieving a technological breakthrough, has a considerable lead in this competition.
Global competition for the new outlet of solid-state batteries Samsung took the lead in making breakthroughs
Solid-state batteries were once regarded as the most suitable battery technology for electric vehicles, but what kind of technology is it?
From a literal understanding, an all-solid-state battery means completely replacing the liquid electrolyte in the existing battery system with a solid electrolyte. However, in the definition of the battery industry, solid-state batteries have three major technical characteristics-solid electrolytes, high-energy compatible positive and negative electrodes, and lightweight battery systems.
The solid electrolyte is well understood, and is different from the liquid electrolytes such as ethylene carbonate, propylene carbonate, diethyl carbonate, etc. used in the traditional lithium battery. The solid electrolyte is a new type, which is used as the ion movement channel between the positive and negative electrodes of the battery. Materials 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 and prevent them from piercing the separator to cause a short circuit in the battery.
At the same time, the characteristics of the conventional liquid electrolyte that are easily oxidized under high pressure no longer exist for the solid electrolyte, so the solid-state battery can use positive and negative solutions with higher energy density, higher discharge window, and greater potential difference.
Since the solid-state battery cell does not contain liquid inside, it can be assembled in series first and then in parallel, reducing the weight of the battery PACK; the stable nature of the solid-state battery can also eliminate the temperature control element inside the power battery to further achieve power Battery weight loss.
Corresponding to the above three characteristics, it is the technical advantages of solid-state batteries over traditional lithium batteries. Simply put, it is higher energy density, greater discharge rate, longer cycle life and more lightweight battery system design.
These technical advantages determine that the solid-state battery will be the most suitable power battery for electric vehicles in the next ten years. Based on the research and judgment of the solid-state battery mass production progress within the power battery industry, after 2025, the solid-state battery will gradually become the mainstream of the power battery field. product.
It can be said that whoever grabs the solid-state battery will seize the opportunity for the development of the new energy industry in the next ten years.
Under the guidance of this idea, Toyota, BMW, Volkswagen and other international first-tier car companies, Panasonic, Samsung, Ningde Times and other power battery companies, and even Dyson, NGK | NTK and other giant players from across the border have poured in. In the field of solid-state batteries, we have tried to complete the card position before the industrialization of solid-state batteries through investment, mergers and acquisitions, technical cooperation, and independent research and development.
But when these players are actually going out, the technical difficulty of solid-state batteries is far beyond their imagination. At present, solid-state battery technology needs to solve many difficulties from mass production. Some studies have shown that the formation of lithium dendrites, the low Coulomb efficiency caused by the interface impedance, and the side reactions between the solid electrolyte and the positive and negative electrodes are particularly obvious in the solid-state battery experiment. .
Samsung recently published a paper in the "Nature-Energy" magazine, officially proposed solutions to these problems.
First, Samsung reduced the uneven deposition of excessive lithium ions in the negative electrode through silver-carbon composite materials and stainless steel (SUS) current collectors, and adopted a sulfide solid electrolyte with a higher lithium ion migration number (generally the liquid electrolyte lithium ion migration number is 0.5, sulfide The number of lithium ions in the solid electrolyte is 1), which reduces the deposition of lithium ions in the electrolyte and reduces the possibility of lithium dendrite formation in the two areas of the negative electrode and the electrolyte.
Secondly, Samsung applied the NZO cathode layer with an LZO coating, using a 0.5nm LZO coating to separate the cathode material from the sulfide solid electrolyte, and using the good electrical conductivity of the LZO coating to reduce impedance Small, to improve the coulombic efficiency of the battery system.
At the same time, the presence of the LZO coating and the silver-carbon composite material layer also blocks the possibility of side reactions between the sulfide solid electrolyte and the positive and negative electrodes, which maximizes the normal performance and cycleability of the solid-state battery during operation. Sex.
Through this solution, Samsung's all-solid-state battery achieves an energy density of 900Wh / L, more than 1,000 charge and discharge cycles, and a 99.8% Coulomb efficiency.
The Toyota and Panasonic teams that are also working on solid-state batteries. Although the current solid-state battery technology can achieve a higher level of cycle times, its energy density is only 700Wh / L, and the Coulomb efficiency is also about 90%. The solid-state 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 solution effectively overcomes the technical difficulties of industrialization of solid-state batteries. If Samsung ’s position among many opponents is evaluated by the idea of ​​a card-bit game, then Samsung ’s breakthrough in key technologies of solid-state batteries will undoubtedly win. The advantage of the starting stage.
Three methods for Samsung to solve the problem of lithium dendrite growth
The first problem encountered by Samsung 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 formation of branch-shaped lithium ion crystals, which may appear in the discharge rate exceeds the upper limit of the battery design and long-term charge and discharge cycles.
Once the lithium dendrites appear, it means that the lithium ions inside the battery have irreversibly decreased. At the same time, the lithium dendrites will continue to adsorb free lithium ions to achieve growth, which may eventually puncture the separator, resulting in direct contact between the positive and negative electrodes of the battery. Cause a short circuit.
There was a point of view that the mechanical properties of solid electrolytes can inhibit the growth of lithium dendrites and prevent their damage to the separator, but in fact, this assumption has not been realized.
Studies have shown that the position of lithium ions through the solid electrolyte ion channel when reaching 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 lithium dendrites to appear is even lower than traditional lithium batteries.
Faced with this problem, Samsung proposed a three-in-one solution:
1. Silver carbon composite material layer
Samsung added a layer of silver-carbon composite material between the sulfide solid electrolyte and the anode material.
The working principle of the charging process is to combine lithium ions with 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, reducing the nucleation energy of lithium ions (which can be simply understood as the accumulation of Together), so that lithium ions are deposited evenly on the anode material.
â–² The schematic diagram of the silver-carbon composite layer (red line part) in the battery structure
During the discharge process, the lithium ions completely disappeared in the silver-lithium metal coating originally deposited on the negative electrode material, and returned to the positive electrode. The silver ions will be distributed between the negative electrode material and the silver-carbon composite material layer, waiting for the next charging process The arrival of lithium ions.
The Samsung team conducted a controlled experiment to determine whether the silver-carbon composite layer produced an effect during the lithium ion deposition process.
First, the team studied the case where the silver-free carbon composite layer and the negative electrode were in direct contact with the sulfide solid electrolyte.
When the charge rate (SOC) is 50% and the charge rate is 0.05C (0.34mAh / cm2), although the deposition of lithium ions on the negative electrode is not dense, the deposits are thick and random in shape, with the ability to generate lithium dendrites possibility.
â–² The deposition of lithium ions on the negative electrode without silver carbon layer
In addition, after 10 full charge and discharge cycles, the battery capacity has 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.
â–² Attenuation of battery power of silver-free carbon layer battery
According to the analysis of the Samsung research team, this situation is most likely due to the generation of lithium dendrites inside the battery, resulting in a significant reduction in the number of active lithium ions, thereby reducing the battery's discharge capacity.
In the case of the silver-carbon composite layer, during the first charging process (0.1C, 0.68mAh / cm2), after the lithium ions pass through the silver-carbon layer, a dense and uniform deposit is formed on the negative electrode.
According to Samsung ’s research team, the silver in the silver-carbon layer combines with lithium ions when passing through lithium ions to form a silver-lithium alloy, reducing the nucleation energy of lithium ions, and forming a solid solution during the process of reaching the negative electrode Ions are deposited uniformly on the anode material.
â–² The distribution of silver ions after multiple cycles
In the subsequent discharge process, the image under the electron microscope showed that 100% of the lithium ions returned to the positive electrode material, and there was no residue in the negative electrode material, which means that there is almost no loss of lithium ions during the charging and discharging process. There is no remaining deposit to avoid the formation of lithium dendrites.
2. SUS collector negative electrode
The silver-carbon composite layer largely solves the problem of uneven deposition of lithium ions, but in order to minimize the formation of lithium dendrites, it is also necessary to reduce the "excess" lithium in the battery.
The reason for this statement is because Samsung found that metal lithium, which is rumored to be suitable as a high energy density (3,860 mAh g−1) negative electrode material, is not suitable for solid state batteries.
Excessive lithium is likely to spontaneously aggregate under the action of high voltage to form lithium dendrites.
Therefore, Samsung uses a lithium-free stainless steel (SUS) current collector as its negative electrode in its all-solid battery solution. As a lithium ion deposition carrier and battery structure, the mechanical strength of SUS material is very reliable.
And since the negative electrode material does not contain lithium, the formation of lithium dendrites can also be suppressed.
3. Pyroxene sulfide solid electrolyte
Another location for the formation of lithium dendrites is the electrolyte. Since the migration number of lithium ions in traditional electrolytes is usually 0.5, a large amount of lithium ion migration caused by excessive discharge will cause lithium ions to deposit in the ion channel, and lithium may be formed in a long-term cycle. Dendrite.
The electrolyte used by Samsung in the all-solid-state battery solution is a pyroxene sulfide solid electrolyte with a lithium ion migration number of 1. Its lithium ion migration number is larger than that of a general electrolyte, and it is not easy to deposit lithium ions in it, so it can also Inhibit the formation of lithium dendrites.
Through the above three methods, Samsung's all-solid-state battery solution effectively avoids the formation of lithium dendrites. In its thousands of cycles, the solid-state battery using this scheme did not form lithium dendrites.
The special coating solves the impedance problem with a Coulomb efficiency of 99.8%
For two other difficulties in the research and development of all-solid-state batteries-the Coulomb efficiency problem caused by high interface impedance, and the problem of side reactions between the solid electrolyte and the positive and negative electrodes, Samsung also gave a solution.
In a solid-state battery, a solid-solid interface is formed between a solid electrode and a solid electrolyte. Unlike the solid-liquid interface of a conventional battery, which has good contact properties, direct contact between solids and solids is difficult to achieve seamlessly. That is to say, 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 greater the impedance.
At the same voltage, the greater the impedance, the lower the current, and the lower the Coulomb efficiency of the battery.
Not only that, the solid electrolyte also produces side reactions at the interface during contact with the active cathode material.
According to the research results of the University of California, San Diego, the oxygen generated during the deintercalation of the positive electrode lithium ion will have a strong electrostatic effect with the lithium in the sulfide solid electrolyte, and the interdiffusion of the cation between the electrolyte and the positive electrode material will form the SEI film ( A kind of passivation layer covering the surface of the electrode), and thickened and blocked the ion transport in repeated cycles.
This phenomenon will also cause the battery's coulombic efficiency to decrease.
In order to deal with the above two problems, Samsung has dealt with both positive and negative electrodes.
For the positive electrode, Samsung applied a 5nm thick LZO (Li2O–ZrO2) coating to the positive electrode NCM material to improve the impedance performance of the solid-solid interface between the positive electrode and the electrolyte.
â–² NZO cathode material coated with LZO coating
At the same time, the coated LZO coating blocks the side reaction between the positive electrode material and the sulfide solid electrolyte, which prevents the SEI film from appearing between the two, the Coulomb efficiency is improved, and the discharge capacity is also reduced. Significantly slowed down.
In the negative electrode, the sulfide solid electrolyte is indirectly contacted with the negative electrode through the silver carbon layer, the interface impedance is also improved, silver ions can also help lithium ions to complete the uniform deposition on the negative electrode, and the impedance is further reduced.
Another reason Samsung uses SUS current collectors as negative electrode materials is also because SUS current collectors hardly react with sulfides, which means that the possibility of side reactions between negative electrodes and sulfide solid electrolytes is also cut off.
In addition, the pyroxene sulfide solid electrolyte selected by Samsung has the same ion conductivity (1-25ms / cm) as the general liquid electrolyte. Therefore, the conductivity of the electrolyte itself is very strong, which is effective for improving the Coulomb efficiency. Also help.
In the 1,000 charge-discharge cycles of the Samsung research team, the average coulombic efficiency of this battery solution is greater than 99.8%. In July last year, in the solid-state battery solution published by the Institute of Physics of the Chinese Academy of Sciences, the battery's coulombic efficiency was about 93.8%.
Samsung is one step ahead and other players still have a five-year window
Samsung's all-solid-state battery solution, to a certain extent, has solved the three major technical difficulties in the industrialization of solid-state batteries. The key technology is overcome, which means that solid-state batteries are further from industrialization, and the days when electric vehicles can use solid-state batteries have also become closer.
The Samsung research team bluntly stated in the paper: "The all-solid-state battery we developed has an energy density of more than 900Wh / L and a charge-discharge cycle life of more than 1,000 times. The excellent performance makes this solution a key breakthrough in the field of solid-state batteries. It is likely to promote all-solid-state batteries to 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 key breakthrough in forward-looking technology, it also means that the company ’s technical barriers are being established, and the opportunities for other companies are reduced accordingly. Especially in industries where the technical advantages of batteries are far greater than the sky, the difficulty of breaking through technical barriers is self-evident.
Prior to this, the Japanese lithium battery material manufacturer Hitachi Chemical completed the research and development of carbon-based anode technology, and the blockade of China's material enterprises has reached 30 years.
And Samsung, LG Chem, SKI and other companies are early in the field of battery separators, electrolytes, electrodes and other fields, while cultivating their own supplier system, they have received a lot of patents in the hands, forming a blockade of other battery companies. Momentum.
This time Samsung is the first to break through the difficulties of solid-state battery technology, and it will inevitably also block patents for other battery companies. Power battery companies such as China, Japan and South Korea have one less 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 competition.
But for Samsung, the first mover advantage does not mean winning. Mass production of solid-state batteries still has many difficulties for Samsung.
First of all, sulfide solid electrolytes have extremely high requirements on the production process. When exposed to air, they are susceptible to oxidation, and H2S and other harmful gases are easily generated in water. The production process needs to be isolated from moisture and oxygen.
Secondly, the large-scale production of silver carbon layer requires the purchase of precious metal silver, which is quite large, and the cost is quite high.
For the Samsung battery business with poor profitability 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 tuyere of solid-state batteries has arrived (the industry believes that it will be mass-produced in 2025), other power battery companies still have a window of market and technology, and the first spot of solid-state batteries is still waiting.
In Japan, Panasonic has formed an alliance with Toyota and took out a solid-state battery solution with an energy density of 700Wh / L two years ago.
The patents recently published by Ningde Times in China show that the energy density of its all-solid-state lithium metal batteries can theoretically exceed 1000Wh / L. The Institute of Physics of the Chinese Academy of Sciences has also completed the research and development of materials that can increase the Coulomb efficiency of solid-state batteries to more than 93%.
American power battery startup Solid Power has received investment from Hyundai, BMW, Ford and other car companies and announced that it will mass produce solid-state batteries that can be used in electric vehicles by 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 all entered the market layout and are ready to compete for the leading position in this field when the solid-state battery outlet comes.
Conclusion: The difficulty of solid-state batteries was overcome by Samsung
In the previous solid-state battery research and development, lithium dendrite problems, Coulomb efficiency problems and interface side reaction problems have stumped many battery research and development teams.
But this time, Samsung effectively solved the problem of lithium dendrite formation through the silver-carbon composite material and the SUS collector negative electrode. The LZO coating on the positive electrode also made the battery system's Coulomb efficiency 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 in the field of solid-state batteries will conduct research along this line of thought, and promote the realization of solid-state batteries from R & D to mass production. breakthrough.
Based on the three points of the incoming player volume, capital boost and the demand of the electric vehicle industry, the outlet of the solid-state power battery industry may soon come.
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