Interpretation of the development of CR2032 button cell batteries technology

1. The current ternary and lithium iron phosphate battery technologies are highly mature

1. Ternary and lithium iron phosphate batteries are the focus of enterprise layout

In the field of automotive power batteries, lithium batteries have become mainstream. At present, the main battery types of international mainstream power battery companies are basically lithium iron phosphate and ternary lithium batteries.

2. Lithium iron phosphate and ternary lithium batteries still have a period of development

After a period of development, the technical level of lithium iron phosphate and ternary lithium batteries has been significantly improved. In terms of cost, the price of lithium iron phosphate battery packs has dropped from 1.8-1.9 yuan/Wh at the beginning of 2017 to 1.45-1.55 yuan/Wh at the end of the year. The price of ternary power battery packs has dropped from 1.7-1.8 yuan/Wh at the beginning of the year to 1.4-1.5 yuan/Wh at the end of the year.

In terms of energy density, at the end of 2017, the energy density of the battery cell based on NCM622 material exceeded 200Wh/kg, and the system energy density was 160Wh/kg. In 2018, the energy density of the battery cell is expected to reach 230~250Wh/kg.

There is still room for improvement for these two types of batteries, especially the role of new generation materials in improving battery performance. For example, the research and development of positive electrode material 811 and silicon-carbon negative electrode will further improve the energy density of lithium power batteries. The energy density of the single cell is expected to reach 300Wh/kg. In addition, the industrial foundation of these two types of batteries is strong, and the competition in the industry will continue for a certain period of time.

2. Solid-state batteries have become the current focus of layout

From the perspective of technical potential, the theoretical energy density of lithium iron phosphate system is about 170Wh/kg, and the theoretical energy density of ternary lithium battery is 300-350Wh/kg. At the same time, there are safety issues such as low thermal decomposition temperature and easy combustion and explosion. The energy density of the two is relatively small. However, the energy density of all-solid-state lithium batteries has great potential for improvement, which is more feasible in theory.

1. Potential technical advantages of solid-state lithium batteries

Compared with traditional lithium batteries, the biggest feature of solid-state lithium batteries is that they use solid electrolyte materials. When the electrodes and electrolyte materials used are solid and do not contain any liquid components, they are all-solid-state lithium batteries. Solid-state electrolytes have changed the traditional structure of lithium batteries. Diaphragms and liquid electrolytes are no longer necessary components, bringing huge potential for technical advantages

The main technical advantages of solid-state lithium batteries are reflected in the following aspects: first, they are highly safe, do not contain flammable, volatile and toxic organic solvents, do not have leakage problems, are expected to avoid the generation of lithium dendrites, and greatly reduce the risk of battery combustion and explosion. Second, they have a long cycle life. There is no problem of liquid electrolytes generating solid electrolyte interface films during the charge and discharge cycle. The expected life span of current research and development is 15,000-20,000 times. Third, they have high energy density. In traditional lithium batteries, the volume of diaphragms and electrolytes accounts for 40%. Solid-state electrolytes can greatly reduce the distance between the positive and negative electrodes of the battery and increase the volume specific energy. The estimated maximum potential value of the energy density of all-solid-state lithium batteries is 900Wh/kg. Fourth, the system has a high specific energy density, and the solid electrolyte has no fluidity, which can realize the internal series connection to form a high-voltage monomer, which is conducive to improving the grouping efficiency and energy density of the power battery system. Fifth, the range of positive and negative electrode materials is wide, and new technologies such as metal lithium negative electrode and high potential positive electrode materials can be used at the same time. All-solid-state metal lithium batteries are the research and development direction of new batteries in the future. In addition, solid-state batteries have a wide operating temperature range and electrochemical stability window, and have the potential for thin film and flexibility.

2. Global companies are deploying solid-state batteries to compete for the first opportunity

Due to the current bottlenecks of lithium iron phosphate and ternary lithium batteries themselves, as well as the potential advantages of solid-state batteries, many companies in the industrial chain involving power batteries, automobiles and energy in Europe, the United States, Japan, South Korea, China and other countries are actively deploying and developing solid-state batteries.

In general, European and American countries are mainly entrepreneurial companies based on solid-state battery technology, and Japan is mainly based on traditional car companies and machinery companies. Battery technology innovation. Chinese companies entered the field of solid-state lithium batteries relatively late, and are mainly supported by scientific research institutions or colleges and universities, and the industrialization process is slow.

In terms of R&D, the main force in China is the scientific research institutions of the Chinese Academy of Sciences, which have accumulated a certain amount of experience and are basically at the same level as foreign countries. However, there is still a lot of room for improvement in energy density from the theoretical value, and ionic conductivity and cycle life also need to be further improved. Solid-state lithium batteries are divided into three technical routes according to solid electrolytes, namely polymer, oxide and sulfide solid electrolytes, and the technical routes adopted by various scientific research institutions are not the same. Among them, the Qingdao Institute of Energy of the Chinese Academy of Sciences and the Institute of Chemistry of the Chinese Academy of Sciences focus on polymer solid-state lithium batteries. The energy density of the former's experimental samples reached 300Wh/kg, and deep-sea tests were completed for the first time, while the latter broke through the bottleneck of low conductivity of polymer solid electrolytes at room temperature; the research feature of the Institute of Physics of the Chinese Academy of Sciences lies in mastering the in-situ formation technology, and the 10Ah soft-pack battery developed has an energy density of 310-390Wh/kg and a volume specific energy of 800-890Wh/L; the Ningbo Institute of Materials of the Chinese Academy of Sciences and the Shanghai Institute of Silicates focus on the research of inorganic solid-state lithium batteries and composite solid-state lithium batteries respectively.

3. Technical and industrial barriers need to be broken through

After the efforts of enterprises and research institutions, solid-state battery technology has achieved breakthroughs, with energy density exceeding 300Wh/kg, but they are basically laboratory products and are still a long way from industrialization.

At the technical level, solid electrolyte ion conductivity, solid/solid interface compatibility and stability are still two major constraints. The conductivity of polymer electrolytes is low at room temperature, and generally needs to be heated to above 60oC to work normally. For example, Bolloré in France uses the technical route of polymer electrolyte and battery heating; the conductivity of sulfide electrolytes is currently comparable to that of traditional lithium batteries, but the interface phase problem still needs to be broken through, mainly through material synthesis and nanolayer technology to increase the amount of active substances and reduce the interface layer resistance. At the same time, metal lithium negative electrodes and new composite positive electrode materials are still under development, and it is expected to realize the application of all-solid-state lithium metal batteries, by which time there will be huge breakthroughs in energy density, capacity, rate performance, safety performance and cycle life.

At the industrialization level, the difficulties in achieving large-scale production mainly lie in production equipment, production processes and production line environment. For example, the stacking, coating, and packaging processes in the preparation of solid-state batteries require customized high-precision equipment, and the production line environment also needs to maintain a higher level of drying room. Only when large-scale production achieves an increase in output and capacity can the cost of solid-state lithium batteries be reduced.

Overall, the maturity of the production and preparation of solid-state lithium batteries needs to be strengthened, and large-scale, automated production lines need further research and development. It is still in the industry accumulation period. The overall development path of solid-state batteries is that, subject to the problem of solid/solid interface stability, the content of liquid electrolytes gradually decreases, and the transition from liquid → semi-solid → solid-liquid mixture → solid → all-solid-state batteries; in the development of all-solid-state lithium metal batteries, subject to the problem of the rechargeability of metal lithium negative electrodes, the negative electrode material will transition from graphite → alloyed negative electrode (such as Si/C) → metal lithium negative electrode. With the development of R&D technology and industrial production, the performance and production of solid-state batteries will be gradually optimized, ushering in opportunities in the power battery market.

3. Potential technology substitutes still exist

In addition to the improvement of current lithium batteries and the layout of solid-state batteries, domestic and foreign companies and institutions/universities have made different attempts in the innovation of power battery technology. Some indicators have been greatly improved compared with the current level, providing a strong reference for the improvement of power battery performance.

By sorting out the technical indicators of typical innovative cases collected, it can be found that the key indicators of some products have been improved. In terms of energy density, the energy density of aluminum-air batteries reaches 780Wh/kg, lithium-sulfur batteries reach 350Wh/kg, and solid-state batteries reach 360Wh/kg; in terms of charging rate, the highest charging rate of typical innovative products has exceeded 100C. In terms of cycle life, typical innovative products can already exceed 15,000 times.

New batteries have many advantages. First, in terms of technology, for example, lithium-sulfur batteries use sulfur as the positive electrode material, and the theoretical specific energy of the battery can reach up to 2600Wh/kg. Lithium-air batteries are also a very promising high-capacity battery technology. They use the reversible reaction of lithium metal and oxygen, and the theoretical energy density limit reaches 11000Wh/kg. Second, the industry can reduce dependence on scarce resources. For example, sodium-ion batteries have the advantages of abundant reserves and low costs compared to lithium-ion batteries.

However, at present, innovative power battery products are generally laboratory products, and new batteries still face many challenges in the next step of industrialization. For example, lithium-sulfur batteries have low safety, low volume specific energy, low discharge rate, low energy conversion efficiency and low number of cycles, and it is difficult to be used in the automotive field in a short time. In general, although these studies are currently in the experimental stage and are far from industrialization, whether they can replace existing system batteries in a certain period of time is also controversial in the industry. But there is no doubt that these batteries are expected to break some technical bottlenecks of current power batteries, reduce battery costs, and create longer driving range. In the development of the power battery industry, these batteries cannot be ignored.

IV. Summary

From the perspective of technological development, ternary and lithium iron phosphate batteries have dominated the automotive power battery market. Ternary and lithium iron phosphate batteries have become the main technical routes of mainstream enterprises, and enterprises are further deploying these two technical routes. From the perspective of development, ternary and lithium iron phosphate battery technologies have made breakthroughs, but there is still room for further improvement in technology, and it will continue for some time in the industry competition.

From the perspective of new battery technology layout, solid-state batteries have technical advantages and can solve many problems facing the current industry. Domestic and foreign companies are competing to layout and have achieved technological breakthroughs. However, from the perspective of industrial development, solid-state batteries are currently in the industry accumulation period, and there are still many technical and industrial supporting issues to be solved.

On the other hand, in addition to the improvement of current lithium batteries and the layout of solid-state batteries, many research institutions are also developing new generation batteries such as lithium sulfur and lithium air batteries, and have made breakthroughs in some technical aspects, providing a favorable reference for the development of the battery industry. But in general, these studies are basically in the experimental stage, far from industrialization, and there are also many controversies in the industry, but it is undeniable that these batteries are expected to break some bottlenecks of current power batteries, and they cannot be ignored in industrial development.

While improving the performance of products along the existing technology route, battery companies should also actively plan the research and development of the next generation of batteries in order to take the lead in the next round of competition. Government departments should encourage enterprises, research institutions and universities to develop key materials, battery cells and system key technologies for power batteries through various channels such as science and technology plans (special projects, funds), relevant innovation projects and high-tech industry development projects, and actively promote the engineering and industrialization of key technologies and equipment such as the preparation, production process and testing of new products and new materials such as solid-state batteries, lithium-sulfur batteries and metal-air batteries, promote the construction of engineering and technical capabilities of the entire industry chain, and promote the application of new technologies and new products for power batteries in demonstration and promotion projects.

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