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      The lithium battery industry has developed from cutting-edge technology into the public life. This year, the Nobel Prize in chemistry was awarded to three pioneers in the invention of lithium-ion batteries. With the rapid development of new energy vehicles, the scale of power battery application has expanded rapidly, which has driven the market to strengthen, but also caused public concern for safety. Based on the existing material system and technology framework, how to ensure the simultaneous improvement of energy density and safety of lithium battery? What challenges will lithium battery industry face in the future? Some people in the industry put forward that the industrialization of solid-state battery has stepped into the era of 2.0.            Nan Qiwen, an academician of the Chinese Academy of Sciences and professor of Tsinghua University, was interviewed by this magazine recently. He believed that solid-state battery products have entered the public vision, and the industrialization of solid-state lithium battery is a natural choice for lithium battery to gradually go to the market. The academic and industrial circles should jointly promote this process, and China will certainly lead in this field before coming to China.            Why solid state lithium battery            Energy review: in the recently disclosed new energy vehicle industry development plan (2021-2025) (Draft for comments), it is clearly proposed to "accelerate the research and development and industrialization of all solid state power battery technology". What do you think of this?            Nancewen: solid state batteries are getting attention from all walks of life. Now it is not only the universities, institutions and enterprises engaged in battery research, but also many seemingly unrelated people, such as financial investment institutions, who are also interested in battery research, and gradually enter. This means that the solid-state battery industry is facing the opportunity of change, indicating that the solid-state battery technology and industrialization are worth looking forward to.            Energy review: the great development of lithium battery industry, fundamentally or because of the increasing market demand, where do you think the main driving force comes from?            Nancewen: from the perspective of the market, the demand for lithium batteries is very large in recent years. Some areas that we were not familiar with before are beginning to need lithium batteries. According to the white paper on the development of lithium-ion battery industry (2019) issued by China Institute of electronic information industry development, in 2018, the global scale of lithium-ion battery industry (excluding battery related materials) reached US $41.2 billion, a year-on-year increase of 18%; in terms of capacity, the global scale reached 200 GWH, a year-on-year increase of 25%. Of course, the biggest market driving force is still from the field of electric vehicles. In this respect, China is undoubtedly the fastest-growing and largest in the world.            Energy review: with the rapid growth of market scale, electric vehicle users have put forward higher requirements for endurance mileage, and there are many safety problems with lithium battery. How do you think to solve them?            Nancewen: lithium battery is a complex composite system, multi-level composite material or composite system. In terms of technology, there are many goals to be achieved, including long endurance, long life, high safety, low cost and fast charging.            At present, the focus is more on long endurance and high safety. Long endurance requires high battery energy density. The development goal of our country is very clear. At present, the progress of academia and industry is also very fast. The current energy density of lithium battery can be 240-260 watt hours / kg; according to the current material system and technology, it can be barely 300 watt hours / kg, but this has reached the limit. If we follow the original technology development roadmap, the current material system may be limited, which needs new ideas to solve.            At the same time, safety is the most concerned problem, but the hidden danger is the inherent problem of liquid lithium battery. There have been many fire and explosion accidents of lithium battery (energy storage station) in South Korea this year. If there are always safety problems of lithium battery, it will hit consumer confidence, and the lithium battery industry may also be hit. For example, Samsung mobile phone battery explosion has seriously affected the Samsung mobile phone market. High security and high energy density are a pair of contradictions.            How to break through the bottleneck of energy and safety under the existing conditions, the natural choice is solid-state.            Energy review: there are many ways to solve the above problems. Why is it bound to be solid?            Nancewen: because using solid electrolyte to replace the electrolyte in lithium-ion battery can solve the original potential safety hazard caused by low flash point electrolyte itself and achieve intrinsic safety. In addition, solid-state batteries have other advantages, such as: don't forget the original heart, use lithium metal as the negative pole, the positive pole can touch the high-voltage material, so as to improve the energy density of the battery; don't worry about the high-temperature storage problem, there will be no more explosion risk. In a word, solid-state battery can not only significantly improve energy density and safety, but also make battery packaging simpler. At the same time, it can realize the flexibility and heteromorphism of battery, and can design different shapes according to different application scenarios.            It can be tested in advance from polymer based composite system            Energy review: what do you think of the research and industrialization process of solid-state batteries?            Nancewen: solid state batteries must be practical and large-scale. If you keep talking on paper, you can't. When a new technology comes out, after a period of heat, we must slowly move towards the direction of industrial application, even if we take a small step, but we can't go out without it. At present, many large companies, especially well-known international automobile enterprises, have announced to mass produce solid-state batteries, and have formulated their own development route plans.            Energy review: what are the key issues and technologies to promote the development of solid-state lithium batteries?            Nancewen: in