Shulou(Shulou.com)11/24 Report--

Lithium battery as the current top industry topic, there is no doubt about the heat.

But when many people talk about lithium batteries, they are only talking about lithium batteries. At most, they extend their attention to the cathode materials that like to mention naming rights, and pay little attention to other aspects.

Cathode material is obviously not the only hero, behind the lithium battery, there are four kings. The protagonist of this article, lithium battery diaphragm, is one of them.

The topic of lithium battery diaphragm is not very high, and it starts late, but it is full of local enterprises working hard, overtaking in corners, high growth, high profits, invisible champions, domestic substitution, core patents, necks and other labels, which can be described as "full of elements".

This paper will analyze this inconspicuous good industry from four aspects: the basic technology, industry characteristics, market situation and development trend of lithium battery separator.

One of the four kings, lithium battery separator, is a porous film between the positive and negative electrodes of lithium battery, and is one of the four main materials of lithium battery (the other three are positive electrode, negative electrode and electrolyte). Its main function is to isolate the positive and negative electrodes of the battery, prevent short circuit, and ensure that lithium ions pass through the microporous channel normally during charge and discharge to ensure the normal operation of the battery. The performance of the separator has an important influence on the internal resistance, capacity, cycle performance, charge and discharge current density and safety of lithium-ion battery.

The industrial chain [1] of lithium battery separator industry in China has high technical content and many performance indexes. Generally speaking, high-end thin film products have reasonable pore size and distribution, which can reduce internal resistance, iron current, and effectively ensure battery energy density and cycle performance. In terms of safety, the improvement of anti-puncture strength and tensile strength can enhance the stability of the material, coupled with good thermal stability and spontaneous protection mechanism can avoid battery short circuit and other risk accidents.

Performance requirements of separator products [2] at present, the separators of commercial lithium batteries are mainly polyethylene (PE) diaphragm, polypropylene (PP) separator and PE and PP composite multilayer microporous membrane. PE diaphragm has high strength and wide processing range, and PP diaphragm has high porosity, air permeability and mechanical properties. The common 3C battery mainly uses single-layer PE film or single-layer PP film, while the power battery generally uses PE / PP double-layer film, PP / PP double-layer film or PP / PE / PP triple film.

The cost of diaphragm mainly includes raw material cost, energy cost, labor cost and depreciation amortization. Among them, the raw material cost accounts for the largest proportion, about 41%, mainly for the main materials and auxiliary materials needed for the production of diaphragms, including main materials PE, PP and auxiliary materials paraffin oil (white oil), dichloromethane, etc., accounting for a total of nearly 80%; high depreciation amortization is particularly affected by the high cost of equipment in the diaphragm industry, which will be detailed below [3].

The price gap between different levels of diaphragm is not small, so that its proportion in the cost of power batteries fluctuates to a certain extent, from single digits to nearly 20%, and the overall figure can be roughly estimated to be about 10% [3] [4] [5]. Considering that the proportion of battery cost of new energy vehicles is already very high, the diaphragm can be considered conspicuous in the composition of vehicle cost.

The production process of diaphragm is mainly divided into two categories: dry process and wet process, in which the dry process can be further divided into one-way and two-way:

Dry method: also known as melt drawing method, refers to the melt made by mixing polymer (mainly PP) and additive raw materials, extruding and casting to form lamellar structure, and then heat treatment to obtain hard elastic polymer film, which is stretched at a certain temperature to form slit-like micropores, and microporous films are prepared after heat setting.

Dry unidirectional stretching process [2] Wet method: also known as thermally induced phase separation method, is the high boiling point small molecules as pore-forming agent (white oil) added to polyolefin (polyethylene PE), heating and melting into a uniform system, by screw extrusion casting, after stretching with organic solvent (dichloromethane) extracted pore-forming agent, and then heat setting and other processes to get microporous membrane.

The core raw material of the wet process [2] dry process is PP, and the localization of the production equipment has been basically completed, so the cost is relatively low, and it has high safety because there is almost no thermal shrinkage, but the final product has poor transverse strength, uneven micropore size and distribution, and low stability. Dry diaphragms are suitable for applications that are cost-sensitive but do not require high energy density, such as energy storage markets. Biaxial stretching can only produce single-layer diaphragm, and all aspects of performance indicators are not outstanding, downstream usage is very small, the market share is very low.

The thickness of the wet diaphragm is thinner, the micropore is uniform, and the porosity is high, which can improve the energy density and cycle performance of the battery, which is more in line with the current development trend of the battery and the needs of the battery factory. The downstream demand is much larger than that of the dry film, and the gap is still widening. The disadvantage is that the wet process is more complex, the raw materials are more expensive, and the equipment investment is large, so the production cost is relatively high.

From the point of view of shipments, the current market share gap between wet diaphragm and dry diaphragm is huge. In 2021, the proportion of wet diaphragm shipments was as high as 74%, an increase of 3% over 2020; in the same period, the proportion of dry single pull / double pull was 24% 2% [6]. In the first half of 2022, the proportion of wet diaphragm increased by a further 5 percentage points to 79% [7]. This trend is mainly due to the continuous improvement of battery performance requirements of downstream power battery enterprises, the product advantage of wet diaphragm has been continuously magnified, and diaphragm enterprises continue to increase wet production capacity to meet the demand. although the dry process benefits from the expansion of the energy storage industry to a certain extent, the growth rate is still not as fast as the wet method, resulting in a continuous decline in the proportion of shipments. But on the whole, the diaphragm market is still a typical incremental market, both dry and wet are growing, and there is no decline in shipments.

Coating diaphragm is the most important evolution trend of diaphragm industry in recent years.

The so-called coating is the coating of specific materials on the polyolefin diaphragm to change the performance of the base membrane so that it can meet the more diversified needs of the downstream, which is essentially a means of modification. Through coating processing, it can not only improve the thermal stability of the diaphragm, improve its mechanical strength, prevent the contact between positive and negative maximum area caused by diaphragm shrinkage, but also improve the puncture resistance of the diaphragm and prevent the short circuit caused by lithium dendrite piercing the diaphragm under long-term battery cycle. At the same time, the coating process can enhance the liquid retention and wettability of the diaphragm, thus prolonging the cycle life of the battery. Generally speaking, the performance of coated diaphragm is obviously better than that of base membrane, which can better meet the growing performance needs of downstream battery factories, and the product premium is high, so it is an inevitable choice for the diaphragm industry. Data show that in 2021, coated membrane accounted for more than 45% of diaphragm shipments (including third-party coating) [8].

Coating diaphragm process [9] coating materials can be divided into two categories: inorganic and organic, inorganic materials are mainly ceramics (boehmite, alumina), organic materials are mainly PVDF, PMMA, aramid and so on. The main advantages of inorganic materials are that the technology is more mature, the production cost is lower, the performance-to-price ratio is high, and the economy is obviously better than organic coating; the biggest advantage of organic coating is good product performance, but the price is expensive.

In addition to the coating material, or a more accurate name, coating particles, the processing of the diaphragm also requires a coating solvent. Coating solvents can be divided into water-based (deionized water, ethanol, glycerol, etc.) and oily (acetone, NMP, etc.). Oil coating for organic coating particles, uniformity and adhesion are better than water coating, but the cost is high, mainly favored by high-end battery production line; water coating, although lacking in performance, but cost-effective, more cost-sensitive enterprises. The combination of coating solvent and coating particles determines the performance of the final film product [10].

Among the many materials, boehmite is the coating material that has attracted much attention at the present stage because of its better performance and economy. As a new ceramic coating material, the core performance index of boehmite is better than that of early mainstream alumina, and the degree of localization is high, but alumina has some problems, such as high hardness, high cost, serious wear to equipment and so on. it restricts its development potential, so boehmite is rapidly replacing alumina. In terms of cost, boehmite has become the processing route with the lowest unit cost in all coating processes because of its low material cost and the same low-cost water-based solvent, and the cost-effective advantage is quite outstanding.

In terms of organic materials, aramid is the most concerned, with good consistency and no particles, and the coating is very thin. at present, it is the only organic material that can be coated alone, and its light weight is not available in other materials, which accords with the long-term development trend that the diaphragm needs to take into account both safety and lightness. However, the price of aramid is very expensive, and boehmite has been able to meet most of the performance requirements, so aramid has not been widely used, mainly in high-end batteries.

At this stage, inorganic coated diaphragm occupies most of the market share and occupies a dominant position, which is far more than that of organic coated diaphragm. According to the data of the Institute of Lithium and electricity of High Industrial Research Institute, more than 95% of the shipments of coated diaphragms in 2021 were inorganic coatings, of which Boehmite shipped 18000 tons in 2021, an increase of 120% over the same period last year, and the penetration rate has exceeded 60% [8].

It is not easy to make a diaphragm although the proportion of the diaphragm in the cost of power battery is not low, and it also has an important impact on the performance of the battery, the attention of the industry as a whole is obviously not high. Compared with other links of new energy vehicles, the most prominent feature of the diaphragm industry is that the industry barriers are quite high, and are reflected in almost every aspect.

First of all, battery separator is a very typical heavy asset industry, and the proportion of fixed assets is significantly higher than that of other battery main materials. Take Cinda Securities's 6 furniture representative battery main materials listed companies as an example, the proportion of fixed assets of diaphragm manufacturer Enjie and Xingyuan material is about 40%, which is much higher than that of enterprises in other sub-sectors [4].

The heavy asset characteristics of the diaphragm industry come from the very high investment in equipment in the industry. For example, Xingyuan's "High performance Lithium Ion Battery Wet diaphragm and coating diaphragm (Phase I) Project", with a total investment of 7.5 billion yuan and hardware investment of 5.061 billion yuan, accounted for 67% [4]. Enjie's "annual output of 400 million square meters of lithium-ion battery diaphragm project (phase I)", the total investment amount is 1.75 billion yuan, of which the equipment investment accounts for 81% [11].

Compared with other battery materials, the investment threshold of the diaphragm industry is also relatively high, the amount of money is quite astonishing. According to the institutional calculation, the investment of the diaphragm single GWh is usually more than 55 million, slightly higher than the ternary positive electrode, 2-3 times that of the negative electrode material and 7 times more than that of the electrolyte [11].

The characteristics of heavy assets and high investment determine that it is difficult to enter the diaphragm industry. the new participants are often large enterprises with a certain scale and the demand to get through the upstream and downstream of the supply chain, which are very unfriendly to startups. Within the industry, well-funded head manufacturers usually have a stronger ability to expand production lines and lock in the growing order demand downstream in advance, while second-and third-tier enterprises are difficult to keep up, leading to a competitive pattern of the strong.

Another important feature of the diaphragm is that it is difficult to produce, has high requirements for the technological level of enterprises, and has high technical barriers to the industry. The technological process of the diaphragm is far more complex than that of other battery main materials, and the process is not only very long, but also requires high precision in many links, which leads to poor average yield in the diaphragm industry, and there is a big gap between enterprises at different levels, ranging from 60% to nearly 90%. Far less than the average level of more than 90% in other links of the new energy vehicle industry chain [12]. Different yield will directly affect the production cost and profitability of enterprises, which is one of the core competitiveness of the diaphragm industry. There are still obvious losses in many links of the diaphragm production process, and the recovery of auxiliary materials in the process is more difficult, and the impact of the process level of the enterprise production line on the profit margin is particularly obvious.

Production process, take Enjie shares as an example [11] has high requirements for production process, in essence, it has high requirements for production equipment. The diaphragm production equipment is non-standardized to a large extent, and the equipment selection must be oriented and matched according to the process characteristics, which is usually designed and customized by the diaphragm manufacturer according to the production situation and the equipment manufacturer, which requires a very high manufacturing level of equipment suppliers. At present, the localization of dry process equipment in China has been basically completed, but the wet process equipment is highly dependent on import. There are not many diaphragm equipment suppliers around the world, and their production capacity is obviously insufficient, unable to keep up with the rapidly growing demand of upstream and downstream, which is one of the main constraints to the expansion of diaphragm production capacity.

The scarcity of equipment supply also increases the difficulty of competition for non-head enterprises. The current high-quality equipment suppliers have been deeply bound with the head diaphragm enterprises, the production capacity has long been locked, and the surplus capacity left to the second-tier enterprises is very limited. Take Enjie shares as an example, the company has a very close relationship with Nippon Steel, one of the major diaphragm equipment suppliers, and has locked its equipment orders for the next three years, and is expected to get 20 production lines in 2022, but it is still unable to meet the demand for production expansion; Xingyuan Materials has a long-term cooperation with Germany's Bruckner, the two sides have signed a separate supply agreement for China, equipment supply locked to 2026 [11]. And because the equipment determines the processing accuracy and quality rate of the diaphragm production line, and the production capacity of high-quality suppliers has been locked, the head enterprises have further compressed the production expansion space of the second-tier enterprises, indirectly hit the competitors and expanded their leading edge.

From the perspective of product characteristics, the scale effect of the base membrane is obvious, and the shipment volume has a direct impact on the unit cost of the enterprise. Large-scale dilution of hydropower, manpower, equipment depreciation expenses and so on is one of the necessary conditions to improve profitability. The advantage of the head enterprise is obvious.

But the coating process is different. At present, the coating is still dominated by technology and patents, and the core patents are mainly controlled by overseas enterprises such as LG and Teijin, while the authorization is locked by domestic leading enterprises, which is similar to equipment and is exclusive, which will interfere with the expansion of related business by competitors.

Finally, the diaphragm has a very critical impact on the performance of power batteries, downstream battery manufacturers are often very cautious, the certification of products is relatively strict, the certification cycle is relatively long. The product certification cycle of domestic battery manufacturers is usually 6 to 12 months, while abroad is as long as 18 to 24 months, and will not be replaced in the short term once integrated into the supply chain [11]. This makes the leading diaphragm enterprises that have established stable downstream customers have a stronger ability to obtain orders continuously, can occupy the new demand in advance, have higher performance certainty, and have more advantages in competition with backward enterprises.

But high industry barriers also have their own rich returns: the average profit level of the basement membrane industry is significantly higher than that of all other segments of the electric vehicle field, and the profit margins of the head companies are amazing.

According to statistics from Guojin Securities, in 2021, the overall average gross profit margin of the electric vehicle industry was 27.8%, and that of the diaphragm industry was 36.1%, significantly higher than that of most subdivided tracks [12].

The profitability gap of enterprises within the diaphragm industry is also very large. First-tier leaders rely on comprehensive advantages, profit margins are often ten or even dozens of percentage points higher than second-and third-tier enterprises, and this advantage is usually based on the premise that the product itself has a price advantage, and there is no need to sacrifice profit space. This differentiation of profitability further consolidates the competitiveness of the head enterprises and aggravates the catch-up difficulty of the second and third-tier enterprises.

Relying on lithium power, growth does not worry about diaphragm as a key component of lithium battery, the industry has significantly benefited from the booming power battery market and energy storage market in recent years, showing a trend of rapid growth. and under the premise that there will not be a major turn in the global green economy in the short term, this growth has a certain degree of sustainability.

Data show that China's lithium diaphragm shipments in 2021 were 7.8 billion square meters, an increase of more than 100 percent over the same period last year. In the first half of 2022, lithium diaphragm shipments were 5.4 billion square meters, an increase of more than 55 percent over the same period last year [7] (the statistical caliber only calculates basement membrane shipments).

It is not difficult to understand that the prosperity of the diaphragm market is driven by the downstream power battery market: in 2021, China's power battery market shipments reached 220GWh, with a synchronous growth rate of more than 170%; only in the first half of 2022, domestic power battery shipments exceeded 200GWh, a year-on-year growth rate of more than 150%, and its corresponding demand for main materials is the key support of the diaphragm industry. At the same time, with the strengthening of the competitiveness of Chinese diaphragm enterprises, the growth of overseas battery shipments is also driving the export volume of domestic internal diaphragm products to increase significantly [6] [7].

In terms of market share, thanks to the comprehensive advantages of capital, technology, cost and customers, domestic diaphragm accounts for a high proportion of the global market and is still expanding rapidly. In 2021, global diaphragm shipments were 10.8 billion square meters, an increase of 72 percent over the same period last year. China's diaphragm shipments accounted for 72 percent, an increase of 12 percentage points over 2020, of which Enjie, Xingyuan and Sinopec combined shipments reached 4.9 billion square meters, accounting for 45 percent of the global share. Local Chinese companies also contribute most of the increase in the global diaphragm industry: the increment of global diaphragm shipments in 2021 was 4.52 billion square meters, of which 4.08 billion square meters, about 90 percent came from domestic enterprises [11].

Specific to the domestic diaphragm market, affected by the industry characteristics mentioned above, leading enterprises have omni-directional advantages over tail enterprises, resulting in a high degree of market concentration, while undercompetitive backward enterprises are continuously integrated (Suzhou Jie Li, Celgard, Numi Technology, etc.) or directly eliminated (Henan Yiteng, Donggao diaphragm, Hongtu diaphragm, etc.) [3]. Even in the case of tight supply, full production and sales of head enterprises and spillover of orders, the trend of increasing industry concentration has not changed.

In 2021, the top three companies of lithium diaphragm in China had a market share (CR3) of 64% and 81% respectively. In the first half of 2022, with the commissioning of new production lines and further increase in industry concentration, CR3 / CR6 increased to 65% and 83% respectively [12].

From the perspective of market segmentation, the pattern of the wet diaphragm industry is "one super and many strong", while the dry pattern is "tripod": Enjie shares, as a well-deserved industry leader, accounts for more than half of the wet market, while CR5 is close to 89%; dry market CR3 is less than 70%, ZTE new materials, Xingyuan materials, Huiqiang new materials three head enterprises have a small gap, but far more than the tail enterprises [4]. Considering that Enjie has cooperated with Ningde era in the layout of dry film projects (20 billion ping / year), the pattern of this market segment is likely to change greatly in the future [13].

The future trend of the diaphragm industry although China's diaphragm industry has a high market share in the global market, there is also a demand for domestic alternatives in some sectors.

As we have mentioned above, dry diaphragm production has basically been localized, but wet equipment is still heavily dependent on imports, and the localization rate of new equipment production capacity in 2020 is only about 15% to 16% [12]. The low localization rate not only limits the capacity expansion, but also brings a higher burden of equipment investment for enterprises.

Replacing imports with domestic equipment is a very clear cost reduction route for the diaphragm industry, and it is also the direction of efforts of local diaphragm enterprises at present. According to securities firms, it is expected to reduce costs by 30% [11] [12] if localization is fully realized. Take Enjie shares as an example, although the company vigorously purchases imported equipment, it is also promoting the process of localization substitution; the company acquires Suzhou Jieli, Fuqiang Technology, and JOT to promote the localization of diaphragm equipment, and the first plant is expected to be completed in the second half of 2022. It is expected that it will be involved in extraction and other units during the year, and it will transition to full-line manufacturing in the future, and plans to have a self-research production line in 2023.

There is also a demand for localization of coating. The current high-end diaphragm patents and formulations are still highly dependent on overseas companies' licenses, and the risk of patent attack persists, especially at a time when companies are seeking to go out to sea. It is essential to strengthen self-research and create localized intellectual property rights to cope with the competition of overseas enterprises.

Another trend of coating diaphragm is integration, that is, the vertical development of enterprises, the production of base membrane, and coating. In the early stage, the shipping volume of the coated diaphragm is small, which is mainly produced by OEM coating (Pu Tailai) or self-built battery factory (BYD), but with the continuous growth of demand, the new industry trend is for the diaphragm faucet to build its own production line and deliver the coated film directly to the downstream cover. Integration can not only reduce the production cost of coating diaphragm, but also improve the profit space of diaphragm enterprises, and facilitate the diaphragm factory to improve quality control, which is the second clear growth curve of the industry.

The concept of integration brings about a new production process called "online coating". On-line coating technology refers to the integration of two-stage production process in which a coating is directly added at the end of the base film main line to make the base film production line and the coating workshop independent of each other. Because the process of winding and slitting before coating is reduced, on the one hand, the production efficiency can be improved, on the other hand, the winding fold can be avoided and the waste can be formed by slitting, thus improving the yield, and the effect on the cost is obvious.

However, although the upstream raw materials of diaphragm production (PE, PP) also have room for localization, because they do not account for a particularly high proportion of costs and are all very common commodities, diaphragm plants develop upstream, the production capacity of self-built raw materials is relatively rare, and the economy is not outstanding.

As for the impact of technical iteration on the diaphragm industry, it can only be regarded as a long-term possibility, which does not exist at this stage.

This concern comes from the solid-state battery, which is considered to be the technical route of the future form of the battery, which can upgrade and replace the diaphragm functionally because of the high mechanical strength of the solid-state electrolyte it uses. this means that there will be no diaphragm position in the future industrial chain.

But on the whole, the iterative risk of battery technology faced by the diaphragm industry is not prominent, at least in the short term, the development of the industry does not pose a threat.

At present, the maturity of solid-state battery is very low, it still faces a large number of technical problems, it is still far away from mass production and commercialization, and the uncertainty is very strong, and it may not be the optimal solution of battery technology. based on this, it is emphasized that the development risk of the diaphragm industry is open to question.

The technical route of semi-solid battery, which is considered to be a compromise, that is, solid-liquid mixed battery with solid electrolyte and liquid electrolyte, is much less different from traditional battery than solid-state battery. Compared with the current solid-state battery, its R & D difficulty, cost and comprehensive price ratio have obvious advantages, the commercial prospect is clearer, the industrialization difficulty is lower, and it is a more realistic upgrade route. At the same time, the manufacturing process and process of semi-solid battery are highly compatible with traditional liquid battery, and the incompatible parts can also be realized by transforming the existing production line, without complex omni-directional upgrade [14]. In other words, the diaphragm is still one of the main materials of semi-solid batteries, and Enjie shares said at the performance presentation that the dosage is not different from the traditional process [15]. This means that even if the battery industry enters the semi-solid era, the support of the diaphragm industry is also guaranteed.

However, new technology will inevitably bring about a new industry pattern. Although the base membrane of semi-solid battery does not change much, the coating material changes from conventional inert inorganic materials such as alumina and boehmite to active materials with ionic conductivity, and the coating formula and process need to be upgraded. the new battery also puts forward higher requirements for lithium dendrite resistance of the diaphragm, and the coating material needs a new design to meet the performance requirements. This is likely to further enhance the technical barriers of the diaphragm industry, strengthen the competitive advantages of existing leading enterprises, provide new opportunities for late entrants with stronger R & D capabilities, and mean a worse competitive environment for backward enterprises. at that time, the industry may still face a reshuffle.

References:

[1] head Leopard Research Institute: an overview of China's lithium battery diaphragm industry in 2019, 2020.09.07

[2] Xingyuan material: IPO prospectus for initial public offering and listing on gem (application draft), 2016.08.22

[3] Yingda Securities: diaphragm products are becoming more and more popular, and the pace of industry production expansion is speeding up. 2022.04.15

[4] Cinda Securities: "diaphragm Industry Special report: the trend of vertical integration, the head advantage is more obvious", 2022.09.25

[5] Hua Fangyuan: a super and multi-strong pattern is gradually emerging-- carding of domestic suppliers with battery diaphragm | Future energy venture vane, 36 krypton, 2022.10.17 https://36kr.com/ phand 1952781336533124

[6] GGII: "China's lithium diaphragm shipments of 7.8 billion square meters in GGII:2021, a year-on-year increase of more than 100%", New Industry think Tank, 2022.01.12 https://mp.weixin.qq.com/ s/1WTrNhjBGB-ZKRNBC9spQA

[7] GGII: "GGII:2022H1 China lithium diaphragm shipments of 5.4 billion square meters, year-on-year growth of more than 55%", new industry think tank, 2022.08.02 https://mp.weixin.qq.com/ s / QxytRPzjWpNAQ-CMcwbMYg

[8] GGII: "China shipped 18000 tons of boehmite for lithium battery diaphragm in GGII:2021", Gao Gong Lithium, 2022.10.15 https://mp.weixin.qq.com/ s / PjuQ7vJASu-gT2B08tLMYA

[9] Pu Tai Lai: initial public offering prospectus (application draft), 2022.07.14

[10] Guojin Securities: series of Special reports on Lithium Battery coating Materials: small and firm coating Materials, promising prospects for escort batteries, 2022.04.11

[11] Huaan Securities: battery profit repair, focus on new diaphragm entrants and upstream lithium links, 2022.08.27

[12] Guojin Securities: Enjie shares: industry characteristics determine the competitive pattern, leading advantages protect excess returns, 2022.04.17

[13] High-tech lithium power grid: behind the deployment of diaphragm supply chain in Ningde era, 2021.11.12 https://www.gg-lb.com/ art-43827.html

[14] Dimension C: solid-liquid hybrid semi-solid battery, which may be the ultimate route of electric vehicle, Vico, 2022.05.30 https://libattery.ofweek.com/ 2022-05 / ART-36001-8420-30562775.html

[15] Interactive Investor announcement-Shenzhen: "Enjie shares: 2021 results presentation", flush Finance, 2022.04.14 http://news.10jqka.com.cn/ 20220414 / c35425465.shtml

This article comes from the official account of Wechat: fruit Shell hard Technology (ID:guokr233), author: Chen Julei, Editor: Li Tuo

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