Overview of solid-state lithium batteries
All-solid-state lithium battery is a lithium battery that uses solid electrode materials and solid electrolyte materials and does not contain any liquid. It mainly includes all-solid-state lithium-ion batteries and all-solid-state metal lithium batteries. The difference is that the negative electrode of the former does not contain metal lithium, and the latter The negative electrode is metallic lithium.
In the current various new battery systems, solid-state batteries use new solid-state electrolytes to replace the current organic electrolytes and separators, which have high safety and high volumetric energy density. Air system, etc.) has a wide range of adaptability, which can further improve the mass energy density, which is expected to become the ultimate solution for the next-generation power battery, which has attracted extensive attention from many research institutions, start-ups and some car companies in Japan, the United States, and Germany.
Second, the advantages of solid-state lithium batteries and the current technical defects
Compared with traditional lithium-ion batteries, solid-state lithium batteries have significant advantages:
(1) High safety performance: Traditional lithium-ion batteries use organic liquid electrolytes. Under abnormal conditions such as overcharging and internal short circuits, the batteries are prone to heat, causing electrolyte gas swelling, spontaneous combustion or even explosion, which poses serious safety hazards. However, many inorganic solid electrolyte materials are non-flammable, non-corrosive, non-volatile, and have no leakage problems. Compared with liquid electrolytes containing flammable solvents, polymer solid electrolytes have greatly improved battery safety.
(2) High energy density: Lithium metal can be used as the negative electrode of solid-state lithium batteries, and the energy density of the battery is expected to reach 300-400Wh/kg or even higher; its electrochemical stability window can reach more than 5V, which can be matched with high-voltage electrode materials to further improve the quality Energy density; there is no liquid electrolyte and separator, which reduces the weight of the battery, compresses the internal space of the battery, and improves the volumetric energy density; the safety is improved, the battery casing and cooling system modules are simplified, and the system energy density is improved.
(3) Long cycle life: It is expected to avoid the problem of continuous formation and growth of SEI film in the liquid electrolyte during charge and discharge and the problem of lithium dendrite piercing the separator, greatly improving the cycleability and service life of metal lithium batteries.
(4) Wide operating temperature range: solid-state lithium batteries have excellent acupuncture and high temperature stability. If all inorganic solid electrolytes are used, the maximum operating temperature is expected to reach 300 °C, so as to avoid the positive and negative electrode materials reacting with the electrolyte at high temperatures. of thermal runaway.
(5) Improved production efficiency: No need to encapsulate liquid, support serial stacking arrangement and bipolar mechanism, which can reduce the invalid space in the battery pack and improve production efficiency.
(6) Flexible advantages: All-solid-state lithium batteries can be prepared into thin-film batteries and flexible batteries. Compared with flexible liquid-electrolyte lithium batteries, packaging is easier and safer, and can be applied to smart wearables and implantable medical devices in the future.
Although all-solid-state lithium batteries show obvious advantages in many aspects, there are also some urgent problems that need to be solved:
For the research and development of all-solid-state batteries, the core of solving the above problems lies in the development of solid-state electrolyte materials and the regulation and optimization of interface properties.Also read:72v 200ah lithium battery pack
- Technical paths and research hotspots of solid-state lithium batteries
3.1 Technology Path of Solid Electrolyte Materials
The performance of the electrolyte material largely determines the power density, cycle stability, safety performance, high and low temperature performance and service life of the battery. Common solid electrolytes can be divided into two categories: polymer electrolytes and inorganic electrolytes.
polymer solid electrolyte
Compared with other polymer matrices, polyoxyethylene (PEO) has a stronger ability to dissociate lithium salts and is stable to lithium, so PEO and its derivatives are currently the main research hotspots.
The polymer electrolyte has poor ability to wet the electrode, and the active material must be transferred to the electrode surface through the electrode sheet, so that the capacity of the active material in the electrode sheet cannot be fully exerted during the battery operation. It is an effective method to improve the mobility of lithium ions in the pole piece and the performance of the battery capacity by bridging the agent, preparing it into a composite electrode material, filling the gaps between the electrode particles, and simulating the wetting process of the electrolyte. Due to the high crystallinity of PEO-based electrolytes, the conductivity is low at room temperature, so the operating temperature usually needs to be maintained at 60-85 °C, and the battery system needs to be equipped with a special thermal management system. In addition, PEO has a narrow electrochemical window and is difficult to match with high-energy-density cathodes, so it needs to be modified.
At present, BOLLORE's PEO-based electrolyte solid-state battery with the highest maturity has been commercialized, and a small number of urban rental cars have been put into the UK. Its operating temperature is required to be 60~80 °C, and the positive electrode uses LFP and LixV2O8, but the current Pack energy density is only 100Wh/kg.Also read:12V 100AH lifepo4 battery Manufacturer
Inorganic solid electrolyte
Inorganic solid-state electrolytes mainly include oxides and sulfides. Oxide solid electrolytes can be divided into two types: crystalline and amorphous according to their material structure, among which the research focus is LiPON electrolytes used in thin-film batteries.
The oxide battery prepared with LiPON as the electrolyte material has excellent rate performance and cycle performance, but the positive and negative electrodes must be made of thin-film electrodes by magnetron sputtering, pulsed laser deposition, chemical vapor deposition, etc. The same conductive materials are added to the ion battery process, and the electrolyte cannot infiltrate the electrode, which makes the lithium ion and electron migration ability of the electrode poor. Only when the positive and negative layers are ultra-thin, the battery resistance can be reduced. Therefore, the single battery capacity of inorganic LiPON thin-film solid-state lithium batteries is not high, and it is not suitable for the preparation of Ah-level power batteries.
Sulfide solid electrolytes are derived from oxide solid electrolytes. Since the electronegativity of sulfur is smaller than that of oxygen, the binding of lithium ions is smaller, which is beneficial to obtain more freely mobile lithium ions. At the same time, the radius of sulfur element is larger than that of oxygen element, which can form a larger lithium ion channel and improve the conductivity. At present, Samsung, Panasonic, Hitachi Shipbuilding + Honda, and Sony are all conducting research and development of sulfide inorganic solid electrolytes. However, the challenges brought by air sensitivity, easy oxidation, high interface resistance, and high cost are not easy to be completely solved in the short term, so there is still a long way to go before the final application of all-solid-state lithium batteries with sulfide electrolytes.
In short, inorganic solid electrolytes have the advantages of single ion conduction and high stability, and are used in all-solid-state lithium-ion batteries. At the same time, it is expected to be applied to new lithium-ion batteries such as lithium-sulfur batteries and lithium-air batteries, which is the main direction of electrolyte development in the future.
3.2 Control and optimization of interface performance
The solid electrolyte has problems such as high interface impedance with electrodes, poor interface compatibility, and volume expansion and contraction of each material during charge and discharge, resulting in easy interface separation. The use of lithium metal negative electrodes also has problems such as large solid-phase contact resistance, interface reaction, and low efficiency. The main directions of the current solution are as follows:
Fourth, the industrialization progress of solid-state lithium batteries
4.1 Foreign giants have laid out the solid-state lithium battery industry
In order to make lithium batteries have higher energy density and better safety, foreign lithium-ion battery manufacturers and research institutes have carried out a lot of research and development in solid-state lithium batteries. In Japan, the research and development of solid-state batteries has been elevated to a national strategic level. In May 2017, the Ministry of Economic Affairs of Japan announced that it would invest 1.6 billion yen to join Toyota, Honda, Nissan, Panasonic, GS Yuasa, Toray, Asahi Kasei, Mitsui Chemicals, and Mitsubishi. Chemical and other domestic industrial chain forces will jointly develop solid-state batteries and hope to achieve the 800-kilometer endurance goal by 2030.
The EV "Bluecar" of the French company Bollore is equipped with a 30kwh metal lithium polymer battery produced by its subsidiary Batscap, using the Li-PEO-LFP material system, and the Paris car-sharing service "Autolib" uses about 2900 Bluecars, which is the first time in the world Commercial all-solid-state batteries for EVs. Toyota has developed an all-solid-state lithium-ion battery with an energy density of 400Wh/kg, which is planned to be commercialized in 2020; Panasonic's latest solid-state battery has a relatively increased energy density of 3 to 4 times; German KOLIBRI batteries are used in Audi A1 pure electric vehicles, It has not yet been commercialized.
In addition, several companies such as Samsung, Mitsubishi, BMW, Hyundai, Dyson, etc. have also stepped up the research and development of solid-state batteries through independent research and development or combined mergers and acquisitions. Toyota announced to cooperate with Panasonic to develop solid-state batteries; BMW announced to cooperate with SolidPower to develop solid-state lithium batteries; Bosch and Japan's famous GSYUASA (Yuasa) battery company and Mitsubishi Heavy Industries jointly established a new factory, focusing on solid-state anode lithium-ion batteries; Honda and The organization established by Hitachi Shipbuilding has developed Ah-class batteries, which are expected to be mass-produced in three years.
4.2 Domestic research institutions lead to set foot in the solid-state lithium battery industry
my country's basic research on solid-state lithium batteries started earlier. During the "Sixth Five-Year Plan" and "Seventh Five-Year Plan" period, the Chinese Academy of Sciences listed solid-state lithium batteries and fast ion conductors as key topics. At present, the five R&D teams have made different progress. In addition, Peking University, Tianjin 18 Institutes of China Electronics Technology Group and other institutes have also established projects to conduct research on solid-state lithium battery electrolytes.Also read:lithium battery manufacturer
Domestic companies that are developing solid-state lithium batteries include CATL, Guojia Interstellar (Jiawei), Jiangsu Qingtao Energy, Huineng, and AVIC Lithium. CATL takes sulfide electrolyte as the main research and development direction, and uses positive electrode coating to solve the problem of interface reaction between positive electrode material and solid electrolyte. At present, the polymer lithium metal solid state battery has a cycle of more than 300 cycles and a capacity retention rate of 82%. Qingtao Energy has developed high-solid content all-ceramic separators and inorganic solid electrolytes, and has cooperated with BAIC for pilot testing. Guojia Interplanetary uses material genome technology to determine the optimal composition of polymer solid electrolytes through high-throughput testing technology. In addition, Ganfeng Lithium, BYD, Wanxiang 123, etc. have also announced the layout of the solid-state battery field, but most companies are still in the "oral research and development" stage.
Five, solid-state lithium battery industry prospects
At present, there are two research and development directions for solid-state batteries. One is the solidification of lithium-ion batteries. There are mature solutions in other industries in this direction, but secondary research and development is required for grafting to lithium batteries. There are very few companies that mass-produce solid-state electrolytes abroad, and none in China, which restricts the research and development progress of solid-state batteries to a certain extent. The gel battery successfully developed by the Japanese laboratory has long been sampled by domestic universities and research institutes, but most of them stay at the level of energy ratio reaching the standard and only a few hundred cycles. In addition, the cost is high, and the yield is very low. Produce.
Another technology research and development direction is metal solid-state batteries, the most common being lithium-sulfur batteries. When the electrolyte is changed to a solid, the lithium battery system is transformed from the solid-liquid interface of the electrode material-electrolyte to the solid-solid interface of the electrode material-solid electrolyte. There is no wettability between solid and solid, and its interface is easy to form higher contact resistance, the battery cycle will be worse, and the charging cannot be fast. The production environment of lithium-sulfur batteries is a vacuum. Once mixed with oxygen, it will explode, which brings great challenges to equipment companies.
As one of the future battery technology directions to replace traditional lithium batteries, all-solid-state lithium batteries have attracted many domestic and foreign research institutions and enterprises for research and development. Whether it is the production process or the surrounding environment of the production line requires a lot of capital investment and strict parameter control, for the backward start-up companies, the road from the laboratory to the mass production line is very long and very long. far more expensive. Of course, in the face of its huge commercial value space, there will definitely be more excellent car manufacturers and battery companies like BMW to invest in it. It is believed that with the promotion and deepening of R&D technology, the industrialization of solid-state batteries will gradually accelerate.