The 4680 large cylindrical battery improves battery safety and energy density through structural innovation and material system improvement. We expect that it is expected to usher in rapid development driven by domestic and foreign manufacturers such as Tesla / Panasonic / LG / Yiwei. It occupies a certain market share in the battery life electric vehicle.
The size of the cylindrical battery is increasing, and 4680 is expected to become one of the optimal solutions for the size of the cylindrical battery. From 18650 to 21700 batteries, Tesla is currently the most important user of cylindrical batteries. In 2020, Tesla research believes that 46mm is the best diameter for both economy and battery performance, and launches 4680 large cylindrical batteries. By increasing the diameter of cylindrical batteries, a higher proportion of active materials and higher energy density can be achieved, while reducing the amount of casing and reducing the difficulty of BMS management. We believe that it is expected to become the development direction of the next generation of cylindrical batteries.
Stepless ear technology innovation improves battery safety and is compatible with radical material systems. The cylindrical cells are in surface contact, which is not prone to thermal runaway conduction. Compared with the square soft pack battery, its structure has a natural high safety. On the other hand, the 4680 battery introduces the all-pole process, which shortens the electron flow path, directly reduces the internal resistance and heat generation of the cell, and the all-pole design increases the heat dissipation channel, improves the heat dissipation effect, and further enhances the safety of the battery. Higher safety is compatible with high nickel cathodes with poor thermal stability, and the internal force uniformity of the cylindrical shape can better adapt to the high expansion of silicon-based anodes. High nickel + silicon carbon will boost the energy density of 4680 cylindrical cells Further improvement, we believe that it is expected to become the potential development direction of high-end power batteries.
The industrialization development of 4680 batteries is accelerated, and the volume of new materials is promoted. At present, the leading companies in the layout of 4680 cylindrical batteries include Tesla, Panasonic, LG, Yiwei, etc. Among them, Tesla has started mass production of 4680 batteries in California and Texas factories, and Panasonic has started the pilot line. Mass production has been started, and LG and Yiwei have also planned large-scale production capacity to promote mass production. We expect that 2023 is expected to be the first year of 4680 battery discharge. Referring to the replacement rhythm of 21700 to 18650 batteries, we expect that the installed capacity of 4680 batteries is expected to exceed 20GWh in 2023 and 100GWh in 2024. The application of terminal OEMs is also expected to gradually penetrate from Tesla to high-end electric vehicle manufacturers such as BMW and Daimler. . At the same time, the rapid release of 4680 batteries will drive the demand for new materials to increase: we predict that by 2025, the demand for high nickel cathodes/silicon carbon anodes/LiFSI/lithium supplements/conductors/PVDF will reach 39.1/16.3/2.0/1.2 respectively /1.9/3.1 million tons.
risk
The industrialization of 4680 batteries has not advanced as expected.
4680 battery: a master of process and structural innovation, the time for industrial change
The history of the development of the cylindrical battery: Japan and South Korea lead, and gradually develop to large capacity
The world's first cylindrical lithium battery began in Japan. The technology development of Japanese and Korean battery companies is relatively mature. Tesla Roadster has opened the prelude to its commercialization in the field of electric vehicles. Throughout the brief history of cylindrical battery development, there are three important nodes:
►In 1991, the cylindrical battery was born, which was initially popular in the 3C market: In 1991, Sony Corporation of Japan invented the 18650 cylindrical battery, 18 is 18mm in diameter, 65 is 65mm in length, and 0 refers to the cylindrical battery. This model is also the first commercial battery in the world. of lithium-ion batteries. With the rapid development of the global 3C and small home appliance markets in the 1990s, cylindrical batteries became popular among Japanese and Korean lithium battery companies. Compared with lithium-ion batteries, the use of nickel-metal hydride materials in early cylindrical batteries is low-cost and safer, and has been used in Toyota hybrid vehicles.
►In 2008, Tesla opened the era of commercialization of cylindrical lithium batteries for vehicles: the winding process used in the production of cylindrical batteries is one of the most mature, automated, and stable quality battery processes so far. The cylindrical battery technology has accumulated early and deep, so when Tesla's first luxury coupe was launched in 2008, Panasonic's 18650 battery was used. At the beginning of 2017, Panasonic and Tesla launched a more efficient 2170 lithium battery mounted on the Model 3, using the NCA + silicon carbon solution, which increased the energy density of the monomer by 20%.
►In 2020, the 4680 will be launched, and the large-scale cylindrical battery will go further: In September 2020, Tesla announced the 4680 battery on the battery day, and the battery diameter has been further increased to 46mm. The cost of metal-clad structural parts and conductive connectors is reduced by about 14% per kWh. At the same time, the 4680 adopts the laser engraving electrodeless ear technology. The electrodeless ear structure greatly shortens the electronic movement distance and reduces the internal resistance, making it possible for safer and higher capacity batteries, and the energy density can reach 300Wh/kg.
From the perspective of shipment structure, Japanese and Korean companies dominate the global cylindrical battery market, and electric vehicles are the largest application scenario. According to B3 data from Japan, global cylindrical lithium-ion battery shipments will reach 6.225 billion units in 2021, a year-on-year increase of 27%. From the perspective of companies, the three Japanese and Korean battery factories, Panasonic, LG and Samsung SDI, account for 80% of the global share of cylindrical battery shipments, and the pattern is highly concentrated; from the perspective of application scenarios, electric vehicles are the largest application scenario, accounting for 43%. , followed by power tools (including garden tools) accounting for 24%.
The diameter of 46mm is the best result of the comprehensive balance between performance and economy, and the height can be adjusted flexibly. Increasing the diameter of the cylindrical battery enables:
►Increase the proportion of active substances in battery cells and improve battery energy density.
►Under the same battery pack energy, the number of cells can be reduced, the amount of casing and production costs can be reduced, and the difficulty of BMS management can be reduced.
However, large cells will affect the safety and fast charging performance of lithium batteries. A larger battery diameter will directly increase the battery internal resistance and battery heat generation, and put forward higher requirements for the battery thermal management system. At the same time, a larger battery cell capacity will also affect the rate performance and fast charging efficiency of lithium batteries.
Therefore, Tesla research believes that 46mm is the best diameter for both economy and battery performance. In terms of height, it can be flexibly adjusted according to the needs of the model. For example, BAK's 46 family battery has a height ranging from 80 to 120mm, and BMW chooses a 4695 size lithium battery.
Compared with the 18650 and 2170, the biggest innovation of the 4680 battery is the use of a poleless ear structure, also known as full pole ear. The tab is a metal conductor that leads the positive and negative electrodes from the cylindrical battery. The main components are aluminum and copper, and it is the contact point for the battery to charge and discharge. The electrons in the lithium battery move between the positive and negative lugs, and the flow path is proportional to the internal resistance, and the internal resistance is positively related to the internal loss and heat generation of the battery. Therefore, shortening the electron flow path can directly reduce the internal resistance and heat generation of the cell.
The stepless ear structure greatly reduces the internal resistance of the lithium battery. The 4680's all-pole tab is a change of the original tab structure that leads out the metal conductor. The entire current collector tail is used as the tab to design a collector plate structure, and the electron flow path is from the original cell winding length (2170 battery). The winding length is about 1000mm) into the height of the lithium battery (4680 is 80mm), the flow path is greatly shortened, and the internal resistance of the battery is reduced. According to the estimation of "Power Battery 4680 All-Ear Technology Scan" [1], the internal resistance of the 21700 battery of the traditional ear is about 23mΩ, while the internal resistance of the 4680 battery with the stepless ear structure is only 2mΩ, which achieves an order of magnitude reduction in internal resistance.
The stepless ear structure brings battery safety and performance improvement:
►Lower heat production and higher safety: The lower internal resistance will directly reduce the heat production of the battery during charging and discharging, and improve the safety of the battery. At the same time, the all-pole lugs have increased heat dissipation channels, and the heat dissipation has changed from the original two-pole lugs to a larger area of the all-pole lugs. The heat transmission channel is wide, which improves the heat dissipation effect and further enhances the safety of the battery.
►Higher output power and fast charging performance: Due to the reduction of the internal resistance of the battery, the internal loss is reduced, which can bring higher output power and better fast charging performance, and the battery can be charged from 0 to 15 minutes within 15 minutes. 80%, and the peak power density can reach more than 1000W/kg.
4680+ high nickel silicon base + high voltage + CTC collaborative application
Due to the large cylindrical structure of 4680 and the innovation of stepless ears, the overall safety factor of the battery has been greatly improved. We believe that active materials with high specific capacity such as high nickel positive electrode and silicon-based negative electrode can better exert the advantages of 4680 battery; at the same time, cylindrical batteries are highly consistent The advantages of performance make the 4680 battery more suitable for 800V high voltage and solve the problem of fast charging of electric vehicles; combined with the better structural support of cylindrical batteries than square and soft pack batteries, 4680 will also promote the industrial transformation of CTC.
Why is 4680 more suitable for high nickel + silicon base? 1) Compared with the graphite negative electrode, the silicon-based negative electrode has a higher expansion coefficient, and the inner stress distribution of the cylindrical cell is more uniform than that of the square cell, which is not easy to cause damage to the internal material; 2) The square or soft-packed cells are in surface contact, When a single cell is thermally out of control, it is easy to spread to the surrounding cells to produce a chain reaction, while the cylindrical cell is in line contact, which can better avoid thermal runaway conduction; 3) The disadvantage of cylindrical cells is that the group efficiency is low (cylindrical cells are about 70 %, the square battery can reach 80%), so if the cylindrical battery wants to achieve the same energy density as the square battery, a more radical solution must be used at the monomer level, so the structure of the 4680 complements the high nickel + silicon-based negative electrode, which is more adaptation.
Why 4680 batteries can better adapt to 800V high voltage? The voltage of a single cell is only 3-4V. To achieve a higher voltage, more cells need to be connected in series. For example, an 800V high-voltage platform needs about 200 cells to be connected in series. higher. Compared with square and soft package packaging, cylindrical batteries have outstanding advantages in terms of standardization of production and monomer consistency, and can better adapt to 800V high-voltage platforms.
Why 4680 and CTC also have a certain synergy? In the integrated design of CTC (Cell to Chassis), the battery pack design is cancelled, and the battery cells or modules are directly installed on the body. The battery is not only an energy device to provide battery life, but also acts as a structural hardware to provide a certain strength. Compared with square and soft-coated cells, the shells of all single cells of cylindrical cells can provide a certain structural rigidity, and their honeycomb structure can better prevent deformation from affecting the internal structure of the cells when subjected to external impacts. In terms of space, Tesla canceled the battery cover on the 4680 battery array. The parts on the upper surface of the battery are connected to the body structure to integrate the functions of seat fixing and body beams, and at the same time assume the sealing function of the battery, thus saving one layer. The design of the upper cover plate increases the space utilization rate. In terms of manufacturing costs, Musk said that after adopting the CTC+ integrated die-casting technology, 370 parts can be saved, the body weight can be reduced by 10%, and the battery cost per kWh can be reduced by 7%.
On the whole, Tesla has achieved multi-link synergy through the unique 4680 cell structure, matching high-capacity silicon anodes and high-nickel materials, simplifying production processes and CTC solutions, thereby achieving battery energy density and cruising range. Substantial increase, unit cost and investment amount dropped significantly. According to the data released by Tesla Battery Day: Compared with 2170, the synergy of 4680+ high specific capacity positive and negative electrodes + CTC scheme can increase the comprehensive cruising range by 54%, of which the battery cell design accounts for 16%, the negative electrode material 20%, The cathode material is 4%, and the cell chassis integration accounts for 14%. The unit manufacturing cost decreased by 56%, with cell design accounting for 14%, cell factory accounting for 18%, negative electrode material 5%, positive electrode material accounting for 12%, and battery cell chassis integration accounting for 7%.
Tab welding is difficult, and the yield rate continues to increase
The innovation of the full-tab process brings many process difficulties in the battery production process: 1) Slitting link: The cutting and stacking method is mainly the full-pole production process adopted by Tesla. When stacked together, the surface undulations are relatively large, which may easily lead to poor consistency of internal resistance of the tabs due to inconsistent contact degrees. 2) Liquid injection link: Since both ends are closed by the polar ears, it is difficult to continuously inject liquid for production. 3) Kneading and leveling link: The kneading and leveling method is a kind of full-ear solution widely used in China. During the flattening process, the tabs are prone to produce metal debris, which leads to excessive self-discharge of the cell, and even an internal short circuit. In addition, the rear end surface of the flattening is relatively dense, and it is difficult for the electrolyte to enter the inside of the cell. 4) Laser welding process: From the traditional spot welding of two pole lugs to full-pole lug surface welding, the welding process and welding volume increase, the laser intensity and focal length are not easy to control, and it is easy to weld through the inside of the cell or without welding. Complete. At present, the difficulties of 4680 batteries in various enterprises are mainly concentrated in the welding process, which directly affects the yield of 4680 batteries.
In terms of yield rate, the yield rate of Tesla's 4680 test line will be about 80% in 2021. At the beginning of 2022, according to information from Tesla motors clubs, on January 22, 2022, Tesla's Fremont factory produced a total of There are 6813 4680 cells with an average yield of 92%, which is a significant increase compared to 2021. However, compared with the 95%+ yield of 21700 cylindrical batteries, there is still a certain gap. We expect that the yield of 4680 batteries is expected to continue to increase with the improvement of processes and production lines of various companies.
Since Tesla released the 4680 battery, various domestic and foreign manufacturers have rapidly advanced the layout. At present, Tesla and Panasonic are leading the production capacity layout. We expect that 2023 is expected to be the first year of 4680 battery release.
►Tesla: 1) Kato Road Factory, California: In 2020, Tesla will establish a "pilot factory" on Kato Road, Fremont, California, to trial production of 4680 batteries, with a planned target annual production capacity of 10GWh. In January 2022, Tesla announced that it had manufactured 1 million 4680 batteries and delivered the first electric vehicles (Model Y) equipped with 4680 batteries in 1Q22. 2) Austin, Texas factory: Tesla's Austin, Texas factory will hold a "Cyber Rodeo" event on April 7, 2022 to celebrate the start of production of its factory. It has officially started production of 4680 batteries, and the future total plan is 100GWh. 3) Berlin factory in Germany: 4680 battery production line equipment is currently being installed. The company expects to start production from the end of 2022 to 2023, with a total planned production capacity of 50GWh.
►Panasonic: In 2021, Panasonic will build a new 4680 production line in its Gigafactory in Nevada and start mass production. At the same time, it will start the construction of the 4680 pilot line in the Japanese factory and test production in early 2022; in February 2022, Panasonic decided to start production in Japan The Wakayama factory in the west has established a 4680 production base, which is expected to be mass-produced from March 2023 to March 2024.
►LG: At the beginning of 2021, it will start the renovation of its Ochang factory in South Korea and build the 4680 test line. The company expects to achieve mass production in 2023 at the earliest.
► Yiwei Lithium Energy: cooperated with the Israeli startup StoreDot (focusing on fast charging technology) to develop 4680 and 4695. In November 2021, the company announced that it would invest 3.2 billion yuan to build a 20GWh large cylindrical battery capacity. production; in March 2022, the company announced that it will deploy large cylindrical production capacity in Hungary overseas, aiming to meet the order needs of local customers, form nearby supporting facilities, and strengthen customer services.
From the perspective of terminal demand, Tesla is the main driver in the short term. In the medium and long term, we believe that manufacturers such as BMW and Daimler are expected to gradually apply it. We review the replacement rhythm of Panasonic 21700 to 18650 batteries: In 2017, Panasonic began mass production of 21700 cylindrical batteries at its Nevada factory, and after 2018, the volume increased rapidly. As of 2020, the output of Panasonic 21700 batteries has reached 3 billion, accounting for about 3/7 of its total cylindrical output.
We expect Tesla's production to exceed 1.5 million/2 million units respectively in 2022/2023. Referring to the rhythm of Panasonic's 21700 cylindrical battery volume, we assume that the penetration rate of 4680 in Tesla's ternary battery in 2022/2023 will be 5%/20% respectively , corresponding to about 4.4/25.5GWh of 4680 battery demand. By 2025, we expect that the penetration rate of 4680 is expected to reach 70%, and the corresponding installed capacity demand is expected to exceed 150GWh.
The 4680 large cylindrical solution is expected to gradually penetrate into other car factories, promoting the increase of the installed capacity of cylindrical batteries. In addition to Tesla, BMW has also clarified its 4695 large cylindrical battery research and development plan. It is expected to achieve mass production in 2024, and plans to mass produce 100-120GWh 4695 large cylindrical batteries within seven years. In addition, we expect that as the yield rate of large cylindrical batteries increases and the cost decreases, the advantages of long cruising range and fast charging performance will be fully reflected. It is expected that other car companies are also expected to introduce 4680 batteries and promote the penetration rate of cylindrical batteries. We predict that by 2025, the total installed capacity of large cylindrical batteries such as 4680 is expected to exceed 200GWh, accounting for about 16% of the total installed capacity of power batteries.
4680 battery
We believe that Tesla's first application of 4680 will have a demonstration effect in the industry, and 4680 will bring energy density/fast charging performance improvement, cost reduction and BMS threshold reduction (reduced cylinder consumption), which is expected to be introduced to more OEMs and become a A structural main line of battery technology development is expected to usher in heavy volume in 2023. The 4680 large cylinder is quite different from the original 18650/21700 system in material system, battery structure and manufacturing process. In particular, the design of all-pole lugs brings difficulties in the laser welding process and becomes the main bottleneck for the current yield improvement. The structure is non-standard and the solutions of various manufacturers are different (there are patent barriers), which brings high barriers to the entry of battery factories. We are optimistic about the top and high-quality second-tier manufacturers. With the advantages of technology, manufacturing, industrial chain and cost, we are expected to grasp the structural line of the development of 4680 large cylinders and increase the global share.
Thermal runaway propagation within a battery pack is a major concern for safety issues. At present, power battery packs are grouped in series and parallel by many small-capacity cells to meet the requirements of high energy. Considering the thermal runaway problem of the battery pack, it is mainly solved from two dimensions: 1) the problem of thermal runaway of the single cell; 2) the problem of heat conduction to other grouped batteries after the single thermal runaway. Considering that the thermal stability of high nickel is poorer than that of medium and low nickel, and the safety requirements are more stringent, we believe that 4680 is a more suitable packaging process for high nickel:
►Cylinders have a natural advantage in suppressing thermal runaway. 1) Cylindrical battery cells have small capacity and low thermal runaway release energy of a single battery, which is less likely to cause thermal runaway spread than square and soft packs; 2) Cylindrical battery cells are in line contact, with slow thermal conduction and arc-shaped On the surface, natural heat dissipation gaps are reserved, while square and soft packs are in surface contact, with a large contact area and small heat dissipation space. Once the single battery has thermal runaway, it is easy to spread to the battery pack.
►Cylinder from 21700 to 4680, high nickel safety upgrade. The 4680 large cylinder achieves higher safety through the design of full pole lugs: 1) Reduces internal resistance and heat generation. During battery operation, the existence of internal resistance will reduce the output power, reduce the charging and discharging rate, and the generated ohmic heat will easily lead to thermal runaway of the battery. The larger the contact area of the tabs, the shorter the distance between the tabs, the smaller the internal resistance, and the lower the probability of thermal runaway of the battery. The 4680 all-tab battery turns the entire positive/negative current collector into a tab, and the entire area of the current collector is connected to the battery shell or current collector plate, which greatly reduces the internal resistance of the battery and reduces the generation of ohmic heat. 2) Increase the cooling channel. The heat dissipation of cylindrical batteries is mostly axial, and the heat is dissipated from the tabs. Traditional cylindrical batteries such as 21700 have only two tabs, and the heat transfer channel is narrow, so the heat dissipation effect is not good. The heat dissipation effect is improved and the thermal stability of the battery is enhanced.
Silicon carbon anode
4680 is an important starting point for the promotion of silicon-based anodes
The structural advantages of ►4680 make silicon-based anodes the first to be applied. The traditional graphite negative electrode accommodates lithium ions through an intercalation reaction. On average, every 6 carbon atoms can accommodate 1 lithium ion, while the silicon negative electrode accommodates lithium ions through an alloying reaction. Each silicon atom is combined with a maximum of 4.4 lithium ions to form a lithium-silicon alloy, and then The theoretical specific capacity of the silicon anode material reaches about 4200 mAh/g, which is ten times that of the traditional graphite anode. But at the same time, its volume change rate also reaches 300%-400%, far exceeding 12% of traditional graphite. The large cylindrical steel shell scheme of 4680 has more advantages in structural stress distribution, and also makes silicon-based negative electrodes the first to be applied.
►The positive electrode of the 4680 battery is mainly made of high nickel, and the combination of the silicon-based negative electrode is expected to greatly improve the energy density of the battery. According to the corresponding relationship between the energy density of the full battery and the specific capacity of the positive and negative electrodes, when the fixed positive electrode capacity is 180 mAh/g, if the negative electrode capacity reaches 500 mAh/g, the energy density will increase by 10%; if the negative electrode capacity reaches 800 mAh/g, the energy density will increase by 24%.
The silicon-based negative electrode has large expansion, high potential, and low first effect, corresponding to a package of supporting improvement solutions such as structural design, pre-lithiation, and conductive agent. From the perspective of structural design, the current two major technical paths of silicon-based anodes are silicon-carbon composite materials and silicon-oxygen composite materials. Among them, silicon-carbon anodes mainly reduce the influence of material expansion by reducing the size of silicon to nanometer level, while silicon-based anodes The Si clusters, SiO2 clusters and their oxidation interfaces in the oxygen anode can play a role in buffering the volume expansion during the alloying reaction.
New Lithium Salt LiFSI
The performance of the new lithium salt LiFSI can better suit the chemistry/structural system of the 4680 battery, and we expect that the addition ratio is expected to increase from the current about 2-6% to nearly 10%. 4680 uses more aggressive positive and negative materials to achieve high energy density, but faces thermal stability problems caused by high nickel. Adding a new lithium salt LiFSI to the electrolyte can improve the thermal stability of the electrolyte, and can be used with 4680 full-pole lugs Further improve the fast charging performance of the battery. Compared with LiFSI and lithium hexafluorophosphate, the electrolyte added with LiFSI has the following advantages over the electrolyte containing only LiPF6:
►Good thermal stability and higher safety. When the temperature is greater than 200 °C, LiFSI can still exist stably with good heat resistance. At the same time, LiFSI mixed electrolyte has lower impedance, generates less heat under special circumstances, and is not prone to explosion. And when heated, LiFSI can inhibit the generation of HF gas and improve the problem of battery inflation.
►Better low temperature discharge and high temperature performance retention. The electrolyte with LiFSI as the electrolyte maintains good compatibility with the positive and negative materials, improving the performance of lithium batteries under extreme temperature conditions.
►Higher conductivity and good high-rate discharge performance. The electrolyte added with LiFSI has higher conductivity and lower viscosity, higher discharge capacity, and improves the instantaneous output power of the power battery.
►Improve the thermal stability of SEI film and prolong battery cycle life. Compared with LiPF6, LiFSI can form a more thermally stable SEI film with the graphite anode, reduce the possibility of side reactions between the electrode and the electrolyte, and improve the cycle performance and service life of the battery.
Note: Oxidation voltage refers to the highest charging voltage that the electrolyte can withstand without being oxidized and decomposed. The parameters obtained from the test of 1.0M lithium salt when the viscosity and conductivity are 25℃. Source: Enabling fast charging of high energy density Li-ion cells with high lithium ion transport electrolytes, Kangpeng Technology, Research Department of CICC
Lithium supplement
Lithium supplementation technology will promote the process of silicon carbon industrialization, further improve battery energy density and prolong cycle life. The growth of SEI on the surface of the negative electrode during the formation of Li-ion batteries will consume active lithium, resulting in battery energy loss. At present, the irreversible capacity loss of the most widely used graphite anode is greater than 6%, while the irreversible capacity of silicon-based anode is as high as 10% to 20% [3], which limits the advantages of high gram capacity of the silicon-carbon system. The active lithium can be compensated by the lithium supplement technology, which can improve the short board of the low first-efficiency silicon carbon anode and give full play to its high capacity advantage. At present, there are two types of lithium supplementation methods: negative electrode lithium supplementation and positive lithium supplementation:
►Lithium supplementation for negative electrodes started early, but industrialization is difficult. The research and development of negative electrode lithium supplementation technology has been carried out earlier, including physical mixed lithium supplementation based on metal lithium and chemical lithium supplementation. American FMC Company was the first to develop stabilized lithium metal
The powder product (97% lithium and 3% lithium carbonate coating layer constitutes a core-shell structure), is added to the negative electrode by spraying or homogenizing addition to realize lithium supplementation. Compared with lithium powder, the safety of lithium foil supplementation is improved. The metal lithium foil is rolled to a thickness of several microns, and then combined with the negative electrode and rolled. After the battery is injected, the metallic lithium rapidly reacts with the negative electrode and is embedded in the negative electrode material, thereby improving the first cycle efficiency of the material. The negative electrode lithium supplementation method is simple and efficient, but due to the safety risks and technological difficulties of metal lithium itself, it cannot be applied on a large scale for the time being.
►The industrialization of cathode lithium supplementation is coming soon. Lithium supplementation for the positive electrode is the addition of a lithium-containing compound with high irreversible capacity to the positive electrode. According to the type of compound, it can be divided into binary lithium-containing compounds represented by Li2O, Li2O2 and Li2S, and ternary lithium-containing compounds represented by Li6CoO4 and Li5FeO4. Lithium-containing compounds and organic lithium-containing compounds represented by Li2DHBN and Li2C2O4. The positive electrode lithium supplement material can be directly added in the homogenization process of the positive electrode slurry, without additional process improvement and low cost, so it is more suitable for the current lithium ion battery manufacturing process.
4680 mainly adopts the "silicon base + high nickel" solution, and the addition of carbon nanotube conductive agent improves the battery energy density, cycle, rate and other performance. The amount of carbon nanotube conductive agent is only 1/6~1/2 of the traditional conductive agent, and the minimum addition ratio can reach 0.4% [5], thereby reducing the amount of PVDF and so on to indirectly improve the energy density of the battery. In addition, due to the one-dimensional tubular structure of carbon nanotubes, the aspect ratio and specific surface area are larger, and the conductivity is better than that of traditional conductive agents.
From the perspective of 4680 increments, we believe that with the increase in the permeability of silicon-based anodes, the demand for single-wall tubes is also expected to gradually increase.
►For a single wall with more walls, it has higher advantages in aspect ratio and mechanical strength. Single-walled carbon nanotubes are formed by rolling a layer of graphene. According to the data of Xinyu Lithium Battery, the diameter of single-walled carbon nanotubes is about 1-2nm, while the diameter of multi-walled carbon nanotubes is about 7-100nm. The single-walled carbon nanotubes have a better aspect ratio, resulting in lower impedance and higher rate performance in battery applications.
►Single-walled carbon nanotubes can effectively improve the cycling and mechanical properties of silicon-based anodes. Compared with multi-walled carbon nanotubes, single-walled carbon nanotubes have a very high aspect ratio, providing better mechanical strength and flexibility, and can generate 3-4 times volume expansion in silicon-based negative electrodes at low doses. It still provides a stable and rich conductive network in the case of a stable and abundant conductive network, and establishes a tight and long-lasting connection between the silicon particles, thereby improving the cycle life. In addition, tightly wrapping the surface of the silicon-based negative electrode can improve the mechanical properties of the pole piece.
4680 brings a new cylindrical structure design, and the manufacturing and processing barriers are higher than 21700:
►The size and wall thickness of the 4680 shell are increased (4680 wall thickness is about 0.6mm, 2170 wall thickness is about 0.2mm), and the material is changed to pre-nickel-plated stainless steel, with higher strength than 21700 aluminum alloy, which makes the overall stamping of 4680 shell Increased difficulty (to ensure that the nickel-plated layer does not break during the stamping process);
►4680 adopts a new cap structure, and both head and bottom are designed with explosion-proof valve. The traditional 21700 and 18650 caps include top cover, explosion-proof disc, isolation ring, connecting piece, sealing ring and other components. The top cover connects the explosion-proof disc, isolation ring and connecting piece in turn. There are many structural parts, and when the internal pressure of the battery is too large , Under the constraints of the top cover structure, if the weakening line on the explosion-proof disc is not disconnected in time, it is easy to cause a short circuit of the battery. The 4680 adopts a new cap that adapts to the design of all pole lugs. The whole cap includes explosion-proof valve, isolation ring, connecting piece and sealing ring. The design of the top cover is cancelled, the amount of structural parts is reduced, and the pressure relief failure of the top cover is also reduced. risks and internal resistance. And, due to the 4680 all-pole design, the bottom of the positive collector plate and the pole are directly welded, and caps with explosion-proof valves are designed at the top and bottom, while the traditional 21700 and 18550 are only designed for directional blasting at the top.
4680 The structure of each manufacturer is different, and the structural parts are non-standard, which requires the structural parts suppliers to have strong development, design and manufacturing capabilities; For better synergy in the process, manufacturers are more inclined to fix the cap and shell at the same time.
