Wen/Min Jiancheng Xi'an Slack Intelligent System Co., Ltd
From the overall point of view, the mainland new energy vehicles have developed rapidly, but there is still a gap in the maturity of technology compared with foreign advanced enterprises. New energy vehicles refer to cars that use other unconventional vehicle fuels as power sources in addition to gasoline and diesel engines, including pure electric vehicles, extended range electric vehicles, hybrid vehicles, fuel cell electric vehicles, hydrogen engine vehicles, and other new energy vehicles. According to the different power sources, domestic mainstream electric vehicles can be divided into three categories: pure electric vehicles (BEV), hybrid vehicles (PHEV), and fuel cell vehicles (FCEV).
Development of new energy vehicles
According to light Metal Age, a number of UK companies and institutions have jointly launched a major research project to design a new lightweight battery housing for the next generation of electric vehicles and ultra-low emission vehicles (ULEV). Members of the consortium include Kenneth, lmpression Technologies, BMW, Volvo, lnnoval, Technology, Brunel Centre for Advanced Solidification Technology (BCAST) Grainger & Worrall and WMG University. In addition, Lnnovate UK provided £3.3 million in funding to the project.
Over the past decade, China has become the world's largest new energy vehicle market. Factors such as policy support, technological innovation, and large scale have become the first-mover advantages of China's new energy vehicles to lead the world. According to relevant reports, as of 2020, China has the world's largest number of advanced cities for electric vehicle development, and China's cumulative sales of electric vehicles have accounted for 47% of the world's total. China's new energy automobile industry has taken the lead in the development of "from 0 to 1" and has an advantage in the industrial chain on a global scale. However, as foreign car companies step up their layout, the golden window period for China's new energy vehicles to "go global" has been compressed, and it will face more severe competition. International giants Panasonic, Samsung SDI, LG and other accelerated layout, domestic battery companies have also expanded the scale of production capacity, and the curtain of industry reshuffle has been opened.
In recent years, the state has issued a series of policies to guide the development of the mainland electric vehicle industry, proposing that by 2025, the sales volume of new energy vehicles will reach about 20% of the total sales of new vehicles, and by 2035, pure electric vehicles will become the mainstream of new sales vehicles, public domain vehicles will be fully electrified, fuel cell vehicles will be commercialized, and highly autonomous vehicles will be applied on a large scale, effectively promoting the level of energy conservation and emission reduction and the improvement of social operation efficiency. According to the planning requirements, it is expected that the mainland new energy automobile industry will usher in rapid development, and electric vehicles as the main driving new energy vehicle market growth space is larger.
Comparison of the three mainstream electric vehicles
At present, the lithium-ion batteries used in mainstream electric vehicles can be divided into square batteries, cylindrical batteries and button batteries according to their appearance; according to the outsourcing materials, there are aluminum shell batteries, steel shell batteries, soft pack batteries (aluminum-plastic film); according to the cathode materials, there are lithium cobalt oxide, lithium iron phosphate, lithium manganate, nickel cobalt manganese, lithium polymer and so on. Mainland China has set targets for new energy vehicles, including plug-in hybrids and hydrogen fuel cell vehicles, accounting for 20 percent of total vehicle sales by 2025, up from 5 percent now. According to the data of the Prospective Industry Research Institute, the comparative analysis of the three mainstream electric vehicles in China is shown in Table 1.
Table 1 Comparative analysis of the three mainstream electric vehicles in China
Battery case development
The development of battery shells is mainly divided into three stages. The first phase is before 2000, the second phase is from 2000 to 2010, and the third stage is from 2010 to the present. Among them, the battery type of the first stage is nickel-metal hydride battery, and the corresponding technical route is the strengthening of the terminals of the nickel-metal hydride battery pack housing and the strengthening of the pole column. As lithium-ion batteries gradually become a hot spot in patent applications in the industry, the second stage of battery types mainly involves the study of the housing of "18650" lithium-ion batteries. At this stage, the corresponding technical route is the lithium-ion battery monomer shell reinforcement and the lithium-ion battery pack end plate strengthening. The battery type of the third stage involves ternary lithium (nickel cobalt manganese) square monomer batteries, and its technical route involves square monomer battery terminal reinforcement. Square lithium battery is the research and development direction of various battery companies and automobile companies.
Advantages of battery improvement and shape change
As one of the core components of pure electric vehicles, power batteries are closely related to the vehicle's range, overall quality, power performance, and handling performance. In terms of the manufacturing cost of pure electric vehicles, the proportion of batteries is also the highest, generally more than 30%, which leads to higher prices for electric vehicles and post-maintenance costs. Therefore, reducing the unit cost of the battery and increasing the energy density of the battery has always been the main direction of the development of electric vehicle technology. According to BYD, after the replacement of ternary lithium (nickel cobalt manganese) batteries with higher energy density, higher discharge voltage and better low temperature performance, the core competitiveness of BYD's EV model series has been greatly improved. The battery cell shell made of magnesium aluminum alloy is lighter and lower cost than the stainless steel housing used in cylindrical batteries, which is conducive to improving the energy density of the battery cell and the manufacturing cost is also lower. Moreover, the structure of the square shell can accommodate more electrolyte, the expansion stress of the cell pole piece is lower, and the battery life is more than 2 times higher than that of the cylindrical shape. Pro EV500 adopts BYD's self-developed nickel-cobalt-manganese ternary lithium battery, that is, on the basis of lithium cobalt oxide, it has been improved to use nickel-cobalt-manganese as the battery cathode material, and reasonably match the ratio of nickel-cobalt-manganese. While optimizing cost and ensuring safety, the battery has excellent electrochemical properties such as high capacity, good thermal stability performance, and wide charge and discharge voltage. And effectively improve the battery energy density, reaching 160.9Wh/kg. Achieve NEDC cruising range of 420km and 60km/h constant speed cruising range of 500km, thus effectively alleviating users' worries about cruising range. And thanks to the high energy density of the battery pack, it effectively reduces the battery load of the car, thereby reducing the weight of the car.
Tesla recently released the "infinity ear" new battery, the size of this battery is only 46mm×80mm, so it is also known as the "4680" battery, it will tesla electric vehicle battery energy density directly increased by 5 times, while the output power increased by 6 times, and made tesla cars mileage increased by 16%, while the production cost and investment cost of the battery were reduced by 56% and 69% respectively. The battery is now in pilot production.
Ternary lithium batteries: nickel-cobalt-manganese ternary lithium batteries, because of their use of rare earth elements, the price is expensive. Toyota of Japan will show its solid-state battery in 2021, and its energy density is 2 to 3 times that of lithium batteries.
On March 29, 2020, BYD announced that lithium iron phosphate "blade battery". Its thermal runaway resistance and thermal diffusion are better than that of ternary lithium batteries, and its safety is excellent. Because of its thin square shape, it is called: "blade battery". Tesla also prefers lithium iron phosphate batteries.
At present, more than half of the batteries on the market use cylindrical battery housings (such as Tesla's electric vehicles) or square battery housings (such as Batteries used by Toyota, Mitsubishi, Honda, BMW, Volkswagen, Audi, Chrysler, BYD, Ford and other manufacturers). Although cylindrical batteries are less expensive and more commercialized, they require complex battery management systems. Square batteries, on the other hand, have optimal scalability and longer cycle life, but production costs are still high.
Battery case forming process
Stand-alone production line process
Open press mainframe, equipped with unwinding, leveling, feeding, press forming, receiving (material frame), scrap shearing, scrap conveying, and waste collection. The process is still used by some enterprises. The open press battery case production line is shown in Figure 1.
Figure 1 Open press battery case production line
Adopt closed double-point press main engine, equipped with unwinding, leveling, feeding, press multi-station forming, receiving (material frame), scrap shearing, scrap conveying, waste collection, mainly producing round diameter large or square battery shells (aluminum shells). This process is currently used by most battery companies. The closed two-point press battery case production line is shown in Figure 2.
Fig. 2 Closed two-point press battery case production line
Closed double-point large tonnage press main engine is adopted. A special press is adopted for blanking and stacking; another closed double-point large-tonnage press host, equipped with a feeding machine, a depalletizing machine (with piece of depalletizing detection), double crossbar clamp feeding, multi-station forming, receiving (material frame), scrap shearing, scrap conveying, and receiving waste; the process is mainly used by enterprises producing large-diameter battery shells (steel shells). The square shell production line of closed double-point large tonnage press is shown in Figure 3.
Figure 3 Closed double-point large tonnage press square shell production line
Cupping + drawing process (this process is mainly used for aluminum shells)
The process adopts a closed double-point double-action high-speed precision press for cup punching, equipped with unwinding, feeding machine, press cup punching, cup conveying, scrap shearing, to cup extension machine, cup mouth shearing, waste receiving waste (material frame). When the port is required, the closing process is included. Battery casing conveying, testing, cleaning, conveying, packing, bundling, conveying, warehousing. At present, the process is used more in foreign developed countries, and less used by domestic enterprises. Suzhou Slack lower transmission cup production line is shown in Figure 4.
Figure 4 Suzhou Slack lower transmission cup production line
Cup material impact extrusion molding process (from Schuler, Germany)
The raw material of the battery shell is made of aluminum material block, which is made by impact extrusion, and processed by forming, processing, cutting edge, cleaning and other processes. When the punch squeezes the block, the material flows in the opposite direction. After that, the preform is scanned from both sides to detect cracks or deformations. Products that exceed specifications will be removed to prevent downtime in the next process. In the next step, the preformed cup will pass through four channels into a one-die four-piece mold of a 300-ton aftertreatment press. In addition to thinning and drawing depth, functions such as fine drawing or shaping calibration can also be integrated. Then, the housing is inverted in the trimmer. The cutting head works in a wobbly motion from the inside to the outside, avoiding burrs on the inside. After cleaning, drying and visual inspection, it is ready for use. The line produces up to 5 times faster than current solutions, while also saving materials. The production lines provided by the German company Schuler are shown in Figure 5. This high-speed extrusion process is currently in use in a large battery manufacturer's factory and is capable of producing more than 30 million battery cases per year. Schuler also offers punching presses for the manufacture of battery covers. It uses progressive dies and contains 12 forming stations such as punching, trimming, embossing and sharding. The Schuler square battery case is shown in Figure 6.
Fig. 5 Schuler square battery case forming production line
Figure 6 Schuler square battery case
Horizontal stretching machine
The steel battery shell of Jiangsu Qili Forging Machine Tool Co., Ltd. adopts vertical and horizontal extension machines, with a tonnage of 600 ~ 12500kN. Suzhou Slack uses the can process to produce battery shells, using horizontal extender, Suzhou Slack horizontal extension machine as shown in Figure 7.
Figure 7 Suzhou Slack horizontal extending machine
The design concept of Suzhou Slack battery case draws on the production process of cans, and the processing process is similar to that of the can. This cutting-edge technology makes the timeliness and material utilization rate of processing metal materials very high, greatly reducing production costs. The process first uses a closed double-action high-speed precision press cup punch, and then one or more tensile machines multi-channel deep drawing, the purpose of the first cup is to save processing materials, the overall calculation, the utilization rate of the process materials reached 87.0% ~ 87.5%. The utilization rate of traditional processing materials is only 60% to 65%. In terms of processing speed, the process speed is very fast, can be a cupping machine with 6 sets, or even 10 or so tensile machines, so calculated, the production line per minute about 1200 ~ 3000 cylindrical battery shells. The square battery case can produce 200 to 600 per minute.
Future battery development research
CATL explores the cutting-edge technology of batteries
According to the official report of CATL Times, the technologies explored by CATL include: CTC structural innovation technology, which can integrate the battery cell into the chassis, and the estimated cruising range can reach 1000km; high specific energy technology, battery system energy density of 215Wh/kg; CTP technology, high nickel technology, high voltage technology, ultra-thin substrate technology; long-life technology, life of 16 years, 2 million kilometers; low lithium power consumption, passivation cathode, bionic self-healing electrolyte, polar microstructure design, expansion force adaptive management, life compensation Ultra-fast charging technology, 15 minutes charging 80% SOC; ultra-electronic network, fast ion ring, isotropic graphite, superconducting electrolyte, high-altitude gap diaphragm, multi-gradient polar piece, multi-pole ear, anode potential monitoring; true safety technology, four-dimensional safety protection, to create aerospace-grade safety batteries; temperature-resistant cathode, safety coating, high-safety electrolyte, aerospace-grade thermal barrier, self-cooling, big data early warning; self-controlled temperature technology, temperature rise 2 °C/min; battery cell weak short circuit, cell temperature control, platformization, SOC rapid repair, power compensation, Hardy graphite, hardy cathode, hardy electrolyte.
Intelligent management technology
Battery 24-hour full-cycle all-round monitoring, cell health detection, residual value assessment, cloud-edge collaboration; battery detection platform; replacement station within 3 minutes; intelligent robot charging workshop; tens of thousands of batteries back to the smart station to charge; intelligent emergency replacement of trams; accelerate the arrangement of charging piles, such as Volkswagen will use its joint venture company Kaimeis (CAMS) to lay 500 charging stations, 6,000 charging piles in the Chinese market, covering 8 cities across the country; by 2025 will cover the vast majority of cities, With 17,000 charging piles and a charging power of 120 to 300 kW, VW plans to recycle 95% of lithium battery material batteries in the future. One plant has already begun to recycle batteries in 2021.
Development of a new type of battery housing
Germany's SGL Carbon announced that it has reached a partnership with Chinese automaker NIO, the former of which will develop a prototype of a carbon fiber reinforced plastic (CFRP) battery shell for the latter, which is 40% lighter than traditional aluminum or steel battery housings, has high rigidity, and is 200 times lower than aluminum's thermal conductivity. The battery housing is particularly light, stable and safe, and the entire battery box including the battery can be replaced within three minutes of the WEILAI replacement power station.
Reduce battery costs and increase battery energy density
Volkswagen announced the 2030 battery technology and charging technology route planning: reduce the cost of batteries to 50%, and do a good job in the technical layout of lithium iron phosphate, gaomeng, nickel cobalt manganese and solid-state batteries. The company plans to reduce battery cost reduction distribution: 15% reduction in optimized battery design, 10% reduction in production links (dry electrode technology), 20% reduction in positive and negative electrode materials, 5% reduction in battery system integration optimization (CTP, CTC), and a total reduction of 50% (Figure 8). The company plans to unify 80% of the batteries into the same model by 2030, reaching battery consistency and modularity, and Volkswagen aims to simplify production, enhance economies of scale, save costs and reduce battery costs by 50% through the popularization of such batteries.
Figure 8 Volkswagen battery technology in 2030
Increased security
In addition to the cost and mileage of the battery is the focus of user concern, battery safety has also been included in the key issues to be solved by electric vehicles. The 811 ternary battery system developed by CATL can easily pass the battery heat test, the time is not 5 minutes, but never fire, which will be the magic weapon for the rapid growth of electric vehicles. South Korea has built the thinnest photovoltaic cell, with a thickness of one percent of the diameter of a hair.
In summary, whether it is the ternary lithium battery technology route or the lithium iron phosphate technology route, the development of battery technology affects the battery shell forming technology. Therefore, battery shell forming technology should closely follow the development of batteries, work hard in materials, molds, equipment, processes, control technologies and recycling, and improve the whole life chain of battery shells. If China wants to take the lead in battery shell forming technology, it must unify specifications and interface sizes as soon as possible, reduce specifications, and carry out intensive production; establish intelligent workshops, intelligent factories, integrate into digital platforms, master battery shell forming intellectual property rights, and make comprehensive breakthroughs in technology, quality and quantity; and meet the needs of various types of users.
——Article excerpted from: Forging and Stamping, No. 2, 2022