Silicon-Based Negative Electrode-Vapor Deposition Silicon Carbon

silicon-based negative electrode-vapor deposition of silicon carbon

Among the four main materials of lithium battery materials, namely positive electrode, negative electrode, separator and electrolyte, positive and negative electrode materials directly determine the performance of the battery and occupy the top layer of the material system value chain. The four main materials are like the limbs of a rock climber, pursuing strength and balance. For a long time, the progress of positive electrode materials is relatively ahead of the negative electrode materials. The pursuit of higher battery performance requires not only better positive electrodes, but also better negative electrode materials. WithWith the development and popularization of 8-series and 9-series high nickel batteries, the traditional graphite gram capacity is also close to the theoretical capacity ceiling, and the silicon negative electrode is recognized as the most effective and feasible material to improve the performance of lithium batteries with a theoretical energy density of 4200 mAh/g.

01.

Silicon-based anode, the most anticipated next-generation battery material

Silicon-based negative electrode has ultra-high theoretical energy density, low theoretical cost, excellent fast charging performance and better safety performance. In addition, the upstream and downstream industrial chain is mature, the source of raw materials is extensive, and the academic research foundation is sufficient and solid. It is considered to be the huge cake that is most likely to be the first to realize commercialization in the next generation of battery materials.

Research on silicon-based anode materials beganIn 1996, it was first invented by Hitachi, Japan, and began to push into the field of consumption and power batteries in 2015 and 2017. At present, the relevant technologies of Japan, South Korea and the United States started earlier and are also relatively leading. In addition to Hitachi, there are Japan's Shin-Vietnam Chemical, South Korea Caltex, South Korea Continent and the United States Anprius (Amprius).

In recent years, the industrialization of silicon anodes has accelerated.

From the demand and application of silicon-based negative, mainstream car companies, battery manufacturers and mobile phone manufacturers at home and abroad are investing heavily in the application of silicon negative materials. In recent years, the application of silicon anode has become a differentiated battery performance."The place of contention"

In 2017, Panasonic took the lead in applying silicon-based materials to power batteries in batches to supply Tesla. Subsequently, Samsung and LG Chemical gradually applied silicon-based anodes to the field of consumer batteries.

Since 2021, Tesla, Ningde Times, Yiwei Lithium Energy and other head enterprises have begun to mass produce power battery products using silicon-based negative electrodes, Huawei, Glory, Xiaomi and other head mobile phone manufacturers have also begun to use silicon carbon negative material technology on flagship models.

Up to now, domestic and foreign car companies have also laid out silicon-based negative electrodes. In the domestic market, Weilai, Zhiji, E'an and other brands of models began to carry silicon-based negative power batteries. In the international market, Mercedes-Benz electric bigG(EQG) has used Sila-based negative battery, Porsche has also reached a silicon-based negative supply agreement with Group14 Technologies, Tesla's push for the 4680 battery system, silicon-based negative is an indispensable key to performance improvement.

From the point of view of the supply and production and research of silicon-based negative electrodes, traditional lithium battery negative electrode enterprises, star start-up companies and industry chain related players also want to participate in and take a share of the pie.

Overseas start-up companies,The main vapor deposition of silicon carbon productsGroup14 Technologies Inc. Recently turned out, completed the post-investment valuation$3.114 billion for the latest round of funding (back-to-back rounds) of $0.614 billion.In its shareholder background, there is no shortage of such things as Porsche,ATL, BASF, SK Materials, Microsoft and other well-known industrial funds. As a company that does not currently have a certain income, the capital market can give such a high valuation, which shows that it has high expectations.Group14's flagship SCC55 fist product with a carbon-silicon ratio of 55:45 has been loaded by Tesla. Its cruising range has increased by 50% to 896km, and 0-80 charging can be completed in 10 minutes. If Sotredot fast charging and high voltage technology is adopted, it only takes 5 minutes.

Traditional anode material enterprises, there are almost no enterprises that do not announce the construction of silicon anode production line, such as Shanshan, Guoxuan Gaoke, Yan Tailai, Beitri, Zhengtuo Energy, Kaijin Energy, Shida Shenghua, Sibao Technology, Xiangfenghua, Zhongke Xingcheng, Snow and so on.​​​​​​​

Among the start-up companies, the leading silicon negative enterprises have won the favor of capital on the basis of almost no actual income, and the valuation is rising, so the market is not crazy.

In addition, from the upstream"Silicon source" enterprises, to the battery factory's own material research and development team, and then to the relevant equipment companies, the research groups of major universities, industry suppliers are flooding in, just to be in this huge but primary market, a share.

Although the current use of silicon negative electrodes is not large, and the penetration rate in the negative electrode is not high, the capital side and the client side have paved the way for it. The release of silicon-based negative electrodes is only a matter of time.

However, throughout the history of the industry, the clarion call for the industrialization of silicon anodes has been blowing for many years. Listed companies have used this theme to hype their stock prices. Star startups have emerged one after another, raising hundreds of millions of dollars, but they have also fallen in the change of technical routes. The industry has not ushered in the large-scale release of industrial demand for a long time, which shows the high threshold for the production and application of this material."Slogan entrepreneurship"-the fake it until make it approach may not be applicable in this field.

To really do a good job of a silicon anode material, we need to understand the scene, customer needs, academic research and development, enterprise management, raw materials and equipment supplier selection, mass production and cost control, which will directly determine the choice of the company's technical route, the construction of the team and the pace of financing and spending money.

Yuanlai Capital believes that at present, the power and energy storage battery material system still has a lot of room for improvement in key indicators such as energy density, fast charging performance, low temperature performance, cycle performance and safety performance. Among them, there are many application opportunities for related new materials. However, looking at all the next generation battery material systems, there are not many opportunities for start-up companies, such as lithium manganese iron phosphate for lithium iron phosphate and high nickel for lithium iron phosphate.523, sodium-electric layered to lithium-electric ternary, new materials and original materials have a high degree of academic and experience overlap at the level of research and development and mass production, coupled with closer binding with customers, research and development run-in more fully, more abundant talent and capital, start-up companies are difficult to stand out.Silicon-based materials and graphite materials are two completely different properties of materials, in academic research, mass production level and graphite experience almost no overlap, therefore, is one of the many new battery materials application opportunities to provide development opportunities for startups direction.

02.

Swelling Problem, Achilles Heel of Silicon-Based Negative Electrode

Despite being called the most anticipated next-generation battery material, silicon-based anodes also have their Achilles heel.-- Expansion problem. This is from the lithium negative electrode material charging principle.

Graphite is a layered structure of carbon simple substance, as a negative electrode material, the gap between the layers during charging can accommodate lithium ions, but the capacity is limited, generally formed.LiC6compounds, I .e.One carbon atom can absorb 0.17 Li ions to form a stable LiC6structure,Li is continuously deintercalated in the crystal structure, and the loss is small.

simple substanceThe lithium storage mechanism of Si is a typical alloying/dealloying mechanism in lithium ion batteries. When the reaction temperature is reached, Si and Li can form four equilibrium intermediate phases: Li12Si7,Li7Si3,Li13Si4andLi22Si5, among them,Li22Si5The theoretical specific capacity of the elemental silicon electrode material corresponding to the alloy product is the highest (4200 mAh/g）。

The alloying of lithium and silicon can be divided into two stages: (1) the first time in the lithium state, the crystalline state is transformed into amorphous lithium silicon;(2) the subsequent cycle of amorphous lithium silicon into crystalline Li15Si4.

Huge capacity for intercalation of lithium andThe complex phase transformation of LixSi alloy, and the loss of phase transition enthalpy during the transition from crystalline to amorphous after the first lithium insertion,will make the silicon anode material appear in the process of lithium insertion in the amplitude320 percent severe volume expansion compared to only 12 percent for graphite.Moreover, there are obvious anisotropic characteristics in the lithiation process of crystalline silicon.Y.Cui,H.Yang et al. studied the root causes of anisotropic expansion through in-situ SEM/TEM observation and theoretical modeling. It is believed that anisotropic expansion is caused by the directional selectivity of the reaction front movement between amorphous LixSi and crystalline Si interface, that is, the lithiation reaction rate of the reaction front is different in different crystal plane directions. By observing the Li ion flux distribution in Si nanowires with four different crystal plane directions, H.Yang found that the dominant flux of Li ions occurred in the <110> direction, which was consistent with the tendency of volume expansion along the <110> direction.

Nanocolumns with different crystal plane orientations are completely lithiated (a)SEM cross-section, (B) model simulation results,(c) lithium flow distribution and sidewall crystal plane orientation of various nanopillars

If the expansion of the silicon negative electrode is not solved, it will cause a series of problems:

1) The silicon-based negative material will produce cracks until pulverization, destroying the contact between the electrode material and the current collector, making the active material detached from the pole piece, causing a significant loss of battery capacity;

2) Expansion will generate a lot of stress inside the battery, and the pole piece will be squeezed. With multiple cycles, the pole piece has the risk of breaking. This stress may also cause the reduction of the internal porosity of the battery, reduce the lithium ion movement channel, cause the precipitation of lithium metal, and affect the safety of the battery;

3) During the battery cycle, the expansion of the active material will squeeze the surrounding conductive material, and the squeezed conductive agent cannot return to its original position and state after the process of delithiation contraction, which eventually leads to capacity loss and poor electrical contact;

4) The volume change makes it impossible to form a stable SEI layer on the electrode surface, and the SEI layer is repeatedly broken and generated, consuming a large amount of Li ions. At the same time, the thickness of SEI increases with the electrochemical cycle, and the too thick SEI layer hinders the electron transfer and Li ion diffusion, the impedance increases and the polarization increases.

Failure mechanism of silicon anode

The expansion coefficient of silicon negative electrode material is highly related to the capacity retention rate during the battery cycle, and it is difficult for silicon negative electrode that cannot solve the expansion of the material to achieve excellent full battery cycle, which will not meet the procurement standards of lithium battery manufacturers for negative electrodes and cannot be released on a large scale,This is also why the current lithium negative mainstream silicon doped ratio has remainedWithin 3% (a few special scenes of consumer electronics scenes have achieved 5-10% mixing).

In addition to the expansion problem, the more realistic problem faced by silicon anodes is the cost performance.At present, the traditional silicon-based anode technology route is still facingThe dilemma of "increasing the cost by 10% and improving the performance by 5%.

So,How to solve the expansion problem of silicon-based negative electrode with reasonable cost, improve cycle stability, conductivity, and first cycle coulomb efficiency, has become a new battle that academia and industry must win.

03.

The technical route has changed, and the gas phase deposition of silicon carbon has become a consensus.

In order to solve the problems of expansion and failure of silicon-based negative electrodes, academia and industry have developed a variety of silicon-based negative electrode modification methods, including silicon oxidation, nanocrystallization, compounding, porous, alloying, pre-lithiation, pre-magnesium, etc., which are mainly divided into silicon oxygen and silicon carbon.

Among the subdivided technical routes, there are currently three routes that have been industrialized. The first is the grinding method nano-silicon carbon route, the second is the silicon oxygen route (first-generation silicon oxygen and pre-lithiated silicon oxygen), and the third isCVD Vapor Deposition Silicon Carbon Route.

In21 years ago, grinding silicon carbon was recognized by more industrial people.

For the abrasive silicon carbon material, the core is to buffer the comprehensive volume expansion of the material through the gaps between the silicon particles, providing a space for the volume change and stress release of the material expansion.​​​​​​​

Theoretically, if silicon particles can be groundBelow 20nm and without agglomeration, the problem of silicon negative electrode expansion can be solved to a great extent. However, facts have proved that this is beyond the limit of grinding process, and many manufacturers have failed to realize it for many years. Therefore, up to now, this product can only be applied to some rate batteries with low cycle requirements, and cannot be released on a large scale.​​​​​​​

And even if it can be achievedThe preparation of nano silicon below 20nm is also difficult to ensure that it does not reunite, and it is also very difficult to do carbon coating with too small nano silicon.​​​​​​​

Judging from the performance results that have been achieved, the cycle performance of the grinding method silicon carbon is not yet up to the standard, and it is difficult to further break through the technology, so the silicon-based anode has to find a new solution.

From 21 to 22 years, the technical route of the first generation of silicon oxygen and pre-lithiated silicon oxygen is expected to be high.

In principle, silicon oxygen is in the process of lithium intercalation and lithium removal of the material.SiOxwithLi reacts first to generate elemental Si, Li2O and lithium silicate (Li4SiO4,Li2SiO3andLi2SiO5etc.), simple substanceSi further reacts with Li to form LixSi alloy, which in turn produces a reversible capacity. The generated Li2The O and lithium silicates no longer participate in the reaction during subsequent electrochemical cycling. The essence is through a chemical reaction, rather than physical grinding, so that the silicon oxygen material in the elemental silicon particle size reached 5nm below, the particle gap is more abundant, at the same time, the formation of Li2O and lithium silicate do not participate in the subsequent reaction and have no expansion, thus providing a larger stress buffer space and reducing the overall expansion coefficient of the material.​​​​​​​

However, the formationLi2The process of O and lithium silicate consumes a large amount of lithium ions, which not only causes the cost to soar but also causes the first effect of the material to be very low, only about 75%, compared with 95% for graphite, which is far from meeting the requirements of the whole battery for negative electrode materials.​​​​​​​​​​​​​​

Therefore, the industryBy adding lithium metal, lithium carbonate, magnesium metal, etc. as pre-lithiation agents for the first time in charge and discharge, the first effect of the pre-lithiated silicon-oxygen negative electrode can be increased to about 86-90%, but the problem of high product cost is inevitably brought about.​​​​​​​

Pre-magnesium silicon oxygen negative electrode is to solve the low first effect of silicon oxygen material came into being, but pre-magnesium products generally gram capacity is not high, pre-magnesium chemical process will increase.The material cost of 10-150000/ton can only increase the first effect to about 82%-83%, which is very low cost performance for the battery core factory. At present, it is generally considered to be an embarrassing technical solution in the industry, and patents are almost monopolized by South Korea continents.​​​​​​​

Pre-lithiated silicon oxide is a better solution than pre-magnesium.21-22 years were expected. According to our recent survey, the specific capacity of the market is 1400 mAh/g, and the selling price of 93% of the first-effect pre-lithiated silicon oxide has exceeded 1 million/ton (the actual selling price is highly related to the first-effect, and the selling price of about 90% of the first-effect products is also in the range of 80-900000/ton).​​​​​​​

Pre-lithiated silicon oxide has good deduction performance, but the cost is too high, and the residual alkali problem has not been able to be solved stably, which will lead to poor material processability and battery gas production problems. At the same time, it is also faced with the problem of patent disputes with Japan's Shin Yue, so it has not been applied in large-scale industrialization for a long time, and the shipment volume is greatly limited.

Now,On the basis of the other two silicon anode technology routes facing certain bottlenecks, with the breakthrough of vapor deposition silicon carbon products and the verification of full battery performance, downstream cell factories began to gradually shift their focusCVD vapor deposition of silicon carbon. According to Yuanlai Capital, this year, many battery core factories have made it clear that they will only test silicon-based negative electrode samples of vapor-deposited silicon carbon. At the same time, almost all customers of power and consumer battery enterprises are looking for excellent domestic vapor-deposited silicon carbon samples in order not to fall behind in this wave of technical competition.

For vapor-deposited silicon carbon, the core is to store silicon by producing a porous carbon skeleton at low cost, and to buffer the volume expansion of silicon during lithium insertion through the voids inside the porous carbon,Therefore, the expansion rate is low and the cycle is excellent.. The carbon skeleton not only has low production cost, but also has good lithium storage capacity. In addition, the carbon skeleton itself has low density and light weight, making itThe material has high energy density.​​​​​​​

and,Required for CVD vapor deposition of siliconShort production process, less equipment, low theoretical costTherefore, it is a silicon negative solution with final significance by various battery cell factories.With the future decline in silane prices, the increase in silane utilization and the scale-up of vapor deposition equipment., vapor deposition of silicon carbon will further open the cost gap with other silicon anode routes,Final production costs are expected to be reducedBelow 200000/ton.​​​​​​​

In terms of the buckle and full battery test results that have been achieved, U.S. manufacturersThe specific capacity of the Group14 can reach 2000 mAh/g, and the first effect can reach 90%. As of now,Each battery cell customer has receivedGroup14 samples and full battery testing, its full battery performance and cycle excellent, product stability, good consistency, low expansion rate, excellent processability, shocked the industry.. The customer's preference for the technical route of vapor deposition silicon carbon has soared, which directly affects the technical route choice of upstream manufacturers.​​​​​​​​​​​​​​

In summary, whether it is from the performance, cost and product stability that has been achieved so far, or from the future potential of the technical route, vapor deposition of silicon carbon is considered to be the most advantageous final direction of the three technical routes.Vapor deposition of silicon carbon can be used to pre-lithium silicon oxygen products.50% of the cost, to achieve 130 of its performance, to be fully mature industrialization, is expected to lead the silicon negative industry to achieve real large-scale mixing and release.

In addition to these several mainstream silicon-based anode routes, the technical routes of silicon anode also include: liquid phase nano-silicon route, plasma route, pre-magnesium silicon oxygen route, porous silicon route, etc. Among them, the liquid phase method of nano-silicon carbon and the plasma method of nano-silicon carbon can only provide laboratory-level samples at present, in the mass production of materials and the application of materials is still relatively early. As for other technical routes, it has not yet been paid attention to by the industry.

According to the source of capital observation,This year, at the request of customers of electric core factories, large domestic silicon-oxygen material factories and grinding silicon-carbon head enterprises that have accumulated for many years have transformed and laid out the technical route of vapor deposition of silicon-carbon. Some silicon-based negative electrode start-up companies with more sensitive information have also begun to transform, spending tens to millions of dollars to purchase Chinese-style equipment for vapor deposition of silicon-carbon to develop vapor deposition of silicon-carbon. As the source of capital has been continuously concerned about the silicon-based negative track, there is a very intuitive feeling. From the scorn of the route to the standard, the change of the silicon-based anode technology route and the arrival of the turning point of the industry change have made the players on the silicon anode track embark on a new journey.

However, as the highest technical threshold in silicon-based anodes and the most difficult route for mass production, it is not easy to transform and do this product well. At present, the industrialization of domestic vapor deposition silicon carbon still faces many difficulties, which puts forward extremely high requirements for companies and teams that want to get involved in this field.

04.

Revolution has not been successful, the difficulties of industrialization of vapor deposition silicon carbon

The technical barriers and industrialization difficulties of vapor deposition of silicon carbon mainly lie in the selection of porous carbon, deposition equipment and deposition process.

The selection of carbon involves the preparation of the carbon skeleton, the definition of the scene, and the test scheme.The quality of the carbon skeleton directly determines the mass production capacity of future products. Different porous carbons need to be matched with different graphites to show good performance at the core end. The carbon skeleton pore size, pore volume and porosity requirements are different in different scenarios, and the performance varies greatly, requiring the cooperation of professional cell designers to complete the development. The test scheme is also a key point in the development of carbon materials. How to efficiently and accurately evaluate the performance of porous carbon and understand its performance in silicon carbon materials and whole batteries determines the accuracy and efficiency of the company's research and development.The selection of carbon is closely related to the full battery performance of the material.​​​​​​​

Deposition equipment is also one of the difficulties in the industrialization of vapor deposition of silicon and carbon..Among them, the application of rotary kiln equipment in this field is more mature, but it is easy to cause poor performance due to uneven deposition and imperfect coating. At the same time, the low utilization rate of silane in the rotary kiln will directly lead to the high cost of its mass-produced silicon carbon products and the loss of certain competitiveness. However, although the deposition of fluidized bed is more uniform and the utilization rate of silane is higher, the equipment needs to meet the high tightness and high pressure in order to meet the gaseous coating of small particles, and it is difficult to realize the difficulty of mass production and amplification. How to develop deposition equipment with good deposition effect, high utilization rate of silane, large-scale and continuous production is one of the difficulties in the industrialization of vapor deposition of silicon carbon materials, which has not been completely solved at present.​​​​​​​

Apart from that,Advances in deposition processes also require constant trial and error by the industry.Among them, the small-scale deposition process has relatively small barriers, but the consistency requirements of the mass production process are extremely high. A large number of simulations are also required for mixing materials of 100kg, temperature partition of the furnace chamber, partial pressure of the chamber, and residence time of deposition in the chamber.The conquering of deposition processes and deposition equipment is closely related to the reduction in the application cost of materials.

According to the actual visit and research of the source capital,At present, domestic manufacturers are overcoming the above problems, the industry has no completed and bulk shipments of large-scale production line.."The revolution has not yet succeeded, and comrades still need to work hard". With the joint promotion of capital and battery customers, we believe that the day of large-scale industrialization of silicon carbon vapor deposition will come.

According to IICC data,Silicon negative electrode mix (finished negative electrode mixed with a large amount of graphite) inDemand will exceed 500000 tons in 2025, and assuming a price of $80000 per ton, the market size of silicon anode mixes will reach 44 billion in 2025.

With the maturity of technology and the gradual improvement of downstream recognition, silicon-based negative products are expected to take the lead in the next few years in the field of high-capacity lithium-ion batteries large-scale application, and with the cost reduction gradually expanded to the general field, the comprehensive cost-effective of vapor deposition silicon carbon also has the possibility of exceeding graphite, the market prospects are broad.