Did the lithium battery hit the ceiling?

On March 1, the four ministries and commissions issued the Action Plan for the Development of the Automobile power battery Industry, which set out clear requirements for battery performance, production capacity, safety, materials, and equipment. Faced with the prospect of a100 billion watt hours of leapfrogging development, how should industry face the "endless" new technologies?

The reporter recently interviewed Nan Ceven, an academician of the Chinese Academy of Sciences and dean of the Institute of Materials Science and Engineering at Tsinghua University. He believes that all-solid-state lithium batteries will greatly improve safety and performance, but before industrialization, it is still necessary to continuously improve There are technologies. In the future, with the continuous discovery of new materials, lithium battery technology and industry development space is infinite.

The "Golden Key" to Solve Security Problems

Reporter: In 2017, with the rapid expansion of electric vehicles, safety has received unprecedented attention. What do you think is the advantage of all-solid lithium-ion batteries over traditional lithium-ion batteries?

Nan Cewen: In simple terms, the traditional lithium-ion battery is a structure in which the positive and negative poles are separated by the diaphragm and poured into the organic electrolyte. Electrolytic fluids are prone to seepage, especially when they are short-circuited or overcharged by positive and negative poles, which will lead to a rapid increase in temperature, evaporation, and decomposition of electrolytes, resulting in a large amount of gas, which will cause safety problems in the battery and even lead to battery combustion explosions.

All-solid lithium batteries use all-solid electrolytes to perform a two-in-one effect, replacing the diaphragm and electrolyte in traditional batteries to solve safety problems. At the same time, with the use of all-solid electrolytes, metallic lithium can be used as a negative electrode to increase energy density.

Safety is the key and foundation of industrial development, and it also relates to the survival of the battery industry. Energy density is the core of industry research and development and the prospect of industry development. From the point of view of solving safety problems and using existing materials to increase energy density, all-solid lithium batteries can be expected to meet the needs of industrial development and deserve to be vigorously developed.

Reporter: Based on the existing technology, can we solve the safety problem better?

Nan Cewen: There are a variety of technical tools available to improve the safety of lithium-ion batteries, such as the battery management system(BMS). However, BMS is a means of "governance", and "treatment" also needs to start with the battery material itself. Among them, the use of ceramic diaphragm is a good direction to improve the safety of lithium-ion batteries. It is on the substrate of the diaphragm that a layer of Nano ceramic (Al2O3) particle coating is applied to increase the mechanical strength and heat resistance of the diaphragm, reducing the possibility of direct short-circuit of the positive and negative poles, thereby improving safety. The new generation ceramic diaphragm product is a Nano ceramic fiber coating diaphragm(Jiangsu Qingtao energy production), which has better heat resistance and other properties and is more effective in improving the safety of lithium-ion batteries. The second-generation product is an active ceramic fiber coated diaphragm. The use of ceramic electrolyte fibers, in addition to improving safety, will also increase the conduction rate of lithium ions, thereby improving battery doubling performance. The overall idea is to improve the safety of existing lithium-ion batteries through the ceramic diaphragm and gradually develop it to replace the diaphragm and electrolytes with all-solid electrolytes in order to completely solve the safety problem.

Journalist: So, all-solid electrolytes can be called the "golden key" to solve battery safety. Based on the current industrial layout and R&D situation, what kind of development strategy should the industry choose?

Nan Cewen: At present, Bolloré in France, Sakti3 in the United States, and Toyota in Japan represent the research and development directions of three major solid electrolytes: polymers, oxides, and sulfide. In fact, the combination of several methods is also a way of thinking. For example, combining inorganic materials with organic materials, the overall principle is to try between multiple solutions. The more likely development strategy in the future is to slowly transition and gradually reduce the number of electrolytes, for example, from 20 % to 30 % to 5 % to 10 %, or even 0, and gradually develop from semi-solid to all-solid.

Although the current all-solid battery type is "far from hydrolyzing to near-thirst" and it is not yet possible to achieve industrialization, before that, the industry has been continuously improving existing technologies and gradually improving the safety and energy density of existing batteries. For example, improve the existing material ratio, improve electrolyte performance, battery management system(BMS) and so on.

Research and industrialization: from 1 % to 100 %

Interviewer: What are your expectations for the industrialization of all-solid lithium-ion batteries?

Nan Cewen: for industrialization, the domestic formulation is generally achieved by 2020 ~ 2025, and some experts have proposed to strive for industrialization within five years. That goal will be possible only if we work together. Of course, it also depends on the degree and scale of industrialization standards. For example, it is reported that BMW's goal is not to announce a commercialization agenda by 2028, but it has invested heavily in all-solid batteries earlier and has been working hard.

Interviewer: What areas will all-solid lithium-ion batteries be used in the future?

Nan Cewen: all-solid batteries are currently used in special industries such asspecial and medical care that have absolute safety requirements. The future has good prospects in the fields of power and energy storage.

Reporter: As a new technology, all-solid lithium-ion batteries will inevitably have problems such as immature technology and high cost. How do you evaluate the view that high cost is the biggest bottleneck in its industrialization?

Nan Cewen: all-solid lithium-ion battery doubling performance overall low and other issues, are science and technology problems, need to be solved slowly. Cost is not the biggest bottleneck. In fact, any new technology or new product has just begun to come out, and the cost is higher. Once the production technology is mature and the output is up, the cost will naturally come down. Therefore, the cost is a matter for the industry to solve, not a problem that the academic community can solve.

At the same time, the goal of laboratory research and industrialization is not the same. Doing research to pursue the possibility and feasibility of 1 %, you can find new materials through continuous trial and error innovation, as long as there is a possibility, even 1 % can be; The industry pursues 99 % or even 100 % reliability and consistency. It cannot be poor, and it must be considered in all aspects. Therefore, it is necessary to change by 1 % to 99 % or even 100 %. In the middle, there is a bridge and process of transformation. It is necessary to gradually perfect from the laboratory and the middle test and then enlarge and mature to achieve complete control.

Development without "ceiling"

Journalist: The breakthrough of the chemical battery depends on the innovation of material technology. From this point of view, how do you evaluate the direction of development of all-solid lithium batteries?

Nan Cewen: unlike most people, lithium-ion batteries are not the same as ordinary electronic components. They are actually complex systems. For example, positive and negative poles are compounded by a variety of materials, and electrolytes and membranes are also a variety of mixtures.

All-solid batteries look simple, but they're complicated. For example, the positive layer of a liquid lithium-ion battery contains a variety of components such as a positive polar active substance, a conductive agent, an electrolyte, and a binder. If it is replaced with a fully solid electrolyte, because there is no electrolytic infiltration in the positive layer, The combination of components will be complex. Making liquid lithium-ion batteries is like mixing cement with sand on the ground. Adding water can make stones, sand, and cement, but in all-solid batteries, there is no liquid material involved. How to solve the interface problem between solid and solid materials and ensure the activity of effective substances is a great challenge.

Journalist: What kind of evolution pattern would you think from lithium iron phosphate, ternary, high nickel ternary to all-solid battery?

Nan Cewen: The energy density of a single battery must reach 300 watt/kg, and it is not difficult to develop new products on the existing technology system. Once more than 400 to 500 watts/kg, new breakthroughs are needed. Technically speaking, the evolution route is based on time, but batteries at different levels of technology are not deadly relationships and maybe coexisting patterns. This means that it is not the emergence of a new generation of batteries that will completely eliminate other batteries. It may be a gradual process of alternation, and it may also coexist for a long time.

In the case of lead-acid batteries, although their energy density is low and their pollution is large, so far lead-acid batteries have not been completely replaced by lithium-ion batteries, and they have developed well. The reason is that its cost is low, its safety is good, and it has solved the problems such as recycling and recycling, so it has been coexisting with lithium-ion batteries. Different batteries have different characteristics and exist in different application fields suitable for themselves.

Journalist: As far as energy density is concerned, as an element ranked third in the periodic table, lithium metal batteries can theoretically reach 700 watt/kg. Is this the limit of battery energy storage?

Nan Cewen: This is certainly not the limit. The energy density of the battery needs to consider both positive and negative materials. If new positive material is found, the energy density of the battery will increase if the capacity and voltage are much higher than three yuan or the existing material. The limits of lithium batteries, or ceilings, are not technically visible, at least for the time being. If you want to determine the relative limit, As a lithium-air battery that is more than one order of magnitude higher than the current lithium-ion battery energy density, it may be imagined as the limit(theoretical energy density is about 3500 watt/kg), but 700 watt/kg is not the limit.

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