Lithium-ion batteries need to be applied on a large scale, and the manufacturing cost is "expensive", because online maintenance and recycling issues, battery life issues, system security issues, and sustainable development of the entire industry must be considered. To solve these problems, a new battery technology with low cost, long life, high safety and easy recycling should be developed.
Lithium-ion batteries have become the "sweet pastry" in the selection of power batteries for new energy vehicles because of their advantages such as high energy density, low self-discharge rate, and high cycle efficiency. Data show that in the first half of 2018, the installed capacity of new electrochemical energy storage projects in operation worldwide was 697.1 megawatts (MW), an increase of 133% year-on-year, and an increase of 24% compared with the end of 2017. From the perspective of technology distribution, lithium-ion battery installed capacity is the largest, with 690.2MW, accounting for 99%, an increase of 142% year-on-year. The installed capacity of new electrochemical energy storage projects put into operation in my country was 100.4MW, a year-on-year increase of 127%. The installed capacity of lithium-ion batteries was the largest, at 94.1MW.
"Using lithium-ion batteries to replace traditional diesel generators has very rich application scenarios in special exercises, hospital rescue, communications, emergency power traction, etc., and has more flexible and convenient applications." Qingdao Bioenergy and Process, Chinese Academy of Sciences Dong Shanmu, an associate researcher at the institute, described the "blueprint for the application of 'lithium' beyond electric vehicles" at the second seminar on the development direction of energy storage battery technology held recently. Liu Yong, secretary-general of the Energy Storage Application Branch of the China Chemical and Physical Power Supply Industry Association, said bluntly that with the rapid development of electric vehicles, the development potential of lithium-ion batteries in the next 3 to 5 years is huge.
"'Lithium' thinking" sounds particularly plump, but with the deepening of the industrialization of lithium batteries, some outstanding problems have become increasingly apparent, and the "reality" has begun to show a "skinny" side. While Dong Shanmu is optimistic about the application prospect of lithium batteries, he also expressed his concerns about its safety.
At present, the large battery technology on the market is still developed from the small battery technology, and the manufacturing cost is relatively "expensive". Because the problems of online maintenance and recycling are not considered, the cost of the entire industry chain is relatively high, and the service life of batteries is also limited. Along with system security issues, the development of the entire industry is unsustainable.Also read:24V 100Ah LiFePO4 Lithium Battery
How to solve these "skinny" problems? "We should develop new battery technologies with low cost, long life, high safety and easy recycling." Liu Hao said.
Let the electrolyte "hard and soft"
The most important safety hazard of lithium batteries comes from the electrolyte, and the liquid organic electrolyte currently selected is flammable and explosive. Dong Shanmu said that replacing liquid electrolyte with solid electrolyte is the most effective choice recognized by the industry to improve the safety performance of lithium batteries.
"The solid-state electrolytes currently used in solid-state batteries generally have performance shortcomings, which are still far from the requirements of high-performance lithium-ion battery systems. In addition, the failure behavior of the 'solid-solid contact interface' and the failure mechanism behind it also need to be elucidated urgently. "Dong Shanmu believes that building high-performance solid-state batteries needs to start from two aspects: building high-performance solid-state electrolytes and improving interface compatibility and stability.
Dong Shanmu introduced a design concept of "combining rigidity and flexibility", where "rigid" refers to the rigid polymer skeleton and rigid inorganic particles, and "soft" refers to the flexible polymer ion transport material. Through the Lewis acid-base interaction between polymers and between polymers and inorganic particles, new channels can be created for lithium ion transport and the overall performance of the electrolyte can be greatly improved. In addition, his team has also developed a series of lithium salts that are compatible with polymer electrolytes, which can increase the ion migration number of the electrolyte, thereby improving the ion transport performance of the solid electrolyte.
At present, the energy density of a single solid-state battery designed by Dong Shanmu’s team can reach 291.6 Wh/kg, and the capacity retention rate exceeds 85% after 850 cycles. It can pass five nail penetration tests without igniting or exploding. It can also recover quickly after a short fall.
"Based on the above monomer technology, we cooperated with the Institute of Deep Ocean Research, Chinese Academy of Sciences, and successfully demonstrated the application of the solid-state battery system 'Qingneng-1' full-sea deep power supply (withstanding 100 MPa) in the Mariana Trench. The blockade of the deep sea power technology makes my country the second country after Japan to master the deep lithium power technology of the whole sea." Dong Shanmu said proudly.
Breakthrough from basic design
The concept of lithium slurry battery technology was formally proposed in a 2015 patent by the Energy Storage Technology Research Group of the Institute of Electrical Engineering, Chinese Academy of Sciences. Lithium slurry battery means that all or part of the electrodes of the battery are composed of slurry state lithium storage active material, conductive agent and electrolyte. Lithium slurry battery has two significant technical characteristics of ultra-thick slurry electrode and maintainable regeneration.
"The current connection method used by lithium-ion batteries generally has a thickness of 100 to 200 microns. If the thickness is increased, the electrode sheet will be severely cracked, the electrode material will fall off during use, the battery capacity will decrease, and the cycle performance will decay." Liu Hao said.
Lithium paste itself has a dynamic contact conductive network, there is no risk of falling off, and the thickness of the electrode can reach the millimeter level, which is 10 to 50 times that of ordinary lithium-ion batteries. Therefore, lithium paste batteries may be more suitable for providing large-capacity energy storage power output. The lithium slurry battery has made some structural designs, combined with the characteristics of the slurry electrode, it is very convenient for rehydration, liquid replacement and plasma replacement operations.
"After the battery has been used for a period of time and its performance has declined, the internal interface of the battery can be repaired and regenerated to re-enhance the battery's vitality and prolong its service life. In addition, when the battery is scrapped, the slurry is very easy to recycle, and the material can be used for new products after regeneration. production of batteries."
Good raw material recycling
"If you look at the whole life cycle of lithium batteries, reducing the cost of battery materials requires research and development from raw materials." Li Li, a professor at Beijing Institute of Technology, said, "The recycling of raw materials can reduce to a certain extent the battery field or other material fields. pressure."
At present, battery recycling technologies mainly include pretreatment process, living method and wet method. In recent years, many enterprises and research institutes have paid more and more attention to the pretreatment process. Li Li said that the dismantling and crushing process mainly releases volatiles from the electrolyte. In addition, the density screening in the early stage will have a direct impact on the leaching rate of various metals in the later stage.Also read:48V 500AH Lithium Battery
Li Li said that an important task in the lithium battery recycling technology is to analyze the failure mechanism of lithium iron phosphate. "We hope that for each material, it is best to use a different method, just like a patient seeing a doctor. Lithium iron phosphate The structure is very stable, and the position of lithium will be missing after charging, so elemental analysis can show the function of lithium iron phosphate material after failure or thousands of cycles."
"Materials such as iron phosphate and iron oxides lead to a direct decrease in the performance and capacity of iron phosphate. Based on this failure mechanism, 'replenishing lithium' can be performed in the mixture of later materials, which can be supplemented in the form of carbonate or aluminum hydroxide. Calcined at high temperature, the material properties will recover to a certain extent." Li Li said.
In addition, the traditional wet technology mainly uses a mixed solution of acid to separate the metal elements of the material from the solid phase to the liquid phase. Most of them are positive electrode materials. The recovery of negative electrodes and electrolytes has been neglected in the past few decades.
"Maybe because negative electrode graphite is very cheap, everyone thinks it is not worth adding." Li Li expressed her opinion, "At present, we hope to regenerate and recycle different components in an all-round way. Graphite can be generated after recycling negative electrode materials. Graphene materials, and in the battery field or other fields, the attraction of graphene's high conductivity is very large."
Recycling of electrolyte is also technically feasible. The connection and extraction of carbon dioxide is used to re-match the electrolyte, and its conductivity can meet the current commercial requirements.