Research and development of solid state battery -Lithium - Ion Battery Equipment

Research and development of solid state battery -Lithium - Ion Battery Equipment

All solid state lithium battery is a kind of lithium battery which uses solid electrode materials and solid electrolyte materials and does not contain any liquid. It mainly includes all solid state lithium ion battery and all solid metal lithium battery. The difference is that the negative pole of the former does not contain metal lithium, and the negative pole of the latter is metal lithium.

1、 Overview of solid state lithium battery

All solid state lithium battery is a kind of lithium battery which uses solid electrode materials and solid electrolyte materials and does not contain any liquid. It mainly includes all solid state lithium ion battery and all solid metal lithium battery. The difference is that the negative pole of the former does not contain metal lithium, and the negative pole of the latter is metal lithium.

Among the current various new battery systems, solid state batteries use new solid electrolyte to replace the current organic electrolyte and separator, which has high safety and high volume energy density. At the same time, they have extensive adaptability with different new high specific energy electrode systems (such as lithium sulfur system, metal air system, etc.), which can further improve the quality and energy density, and are expected to become the ultimate solution for the next generation of power batteries, causing Japan, the United States Germany and many other research institutions, start-ups and some auto enterprises pay extensive attention to it.(Lithium - Ion Battery Equipment)

2、 Advantages and technical defects of solid-state lithium batteries

Compared with traditional lithium ion batteries, solid-state lithium batteries have significant advantages:

(1) High safety performance: The traditional lithium ion battery uses organic liquid electrolyte. Under abnormal conditions such as overcharging and internal short circuit, the battery is easy to heat, causing electrolyte inflation, spontaneous combustion and even explosion. There are serious potential safety hazards. However, many inorganic solid electrolyte materials are nonflammable, non corrosive, non volatile, and free of leakage. Compared with liquid electrolyte containing flammable solvent, polymer solid electrolyte has greatly improved battery safety.

(2) High energy density: metal lithium can be used as the anode of solid state lithium battery, and the energy density of the battery is expected to reach 300~400Wh/kg or even higher; Its electrochemical stability window can reach above 5V, which can be matched with high voltage electrode materials to further improve the quality and energy density; There is no liquid electrolyte and diaphragm, reducing the weight of the battery, compressing the internal space of the battery, and improving the volume energy density; The safety is improved, the battery shell and cooling system module 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 by liquid electrolyte during charging and discharging and the problem of lithium dendrite piercing the diaphragm, greatly improving the cycle and service life of lithium metal battery.

(4) Wide operating temperature range: solid lithium battery has excellent acupuncture and high temperature stability. If all inorganic solid electrolytes are used, the maximum operating temperature is expected to reach 300 ℃, so as to avoid possible thermal runaway caused by the reaction of positive and negative electrode materials with electrolyte under high temperature.

(5) Production efficiency improvement: no need to encapsulate liquid, support serial stacking arrangement and bipolar mechanism, 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, they are easier and safer to package, and can be used in intelligent wearable and implantable medical devices in the future.

Although all solid state lithium batteries show obvious advantages in many aspects, there are also some problems that need to be solved urgently:

For the R&D of all solid state battery, the core to solve the above problems lies in the development of solid electrolyte materials and the regulation and optimization of interface performance.

3、 Technology Path and Research Focus of Solid State Lithium Battery

3.1 Technical path of solid electrolyte materials

The performance of electrolyte materials largely determines the power density, cycle stability, safety, high and low temperature performance and service life of the battery. Common solid electrolytes can be divided into polymer electrolytes and inorganic electrolytes.

Polymer solid electrolyte

As polyoxyethylene (PEO) has a stronger ability to dissociate lithium salts than other polymer matrices and is stable to lithium, the current research focuses on PEO and its derivatives.

The ability of polymer electrolyte to wet the electrode is poor. The active material lithium must be transferred to the electrode surface through the electrode plate, so that the capacity of the active material in the electrode plate cannot be fully used during the battery operation. The electrolyte material is mixed into the electrode material or replaced by the binder to prepare a composite electrode material, fill the gap between the electrode particles, and simulate the electrolyte wetting process, It is an effective method to improve the lithium ion migration ability in the electrode sheet and the battery capacity. Due to the high crystallinity of PEO based electrolyte, the conductivity at room temperature is low, so the operating temperature usually needs to be maintained at 60~85 ℃, and the battery system needs to be equipped with a special thermal management system. In addition, PEO has a narrow electrochemical window, which is difficult to match with the high energy density cathode, so it needs to be modified.

At present, BOLLORE's PEO based electrolyte solid state battery with the highest maturity has been commercially available, and a small number of city rental vehicles have been put into use in the UK. Its operating temperature is required to be 60~80 ℃. LFP and LixV2O8 are used as positive electrodes. However, at present, the pack energy density is only 100Wh/kg.

Inorganic solid electrolyte

Inorganic solid electrolytes mainly include oxides and sulfides. According to the material structure, oxide solid electrolytes can be divided into two types: crystalline and amorphous. The research focus is LiPON type electrolytes used in thin film batteries.

The oxide battery prepared with LiPON as the electrolyte material has excellent multiplying performance and cycling performance. However, the positive and negative electrode materials must be made into thin film electrodes by means of magnetron sputtering, pulsed laser deposition, chemical vapor deposition, etc. At the same time, conductive materials cannot be added as in the ordinary lithium ion battery process, and the electrolyte cannot soak the electrode, resulting in poor lithium ion and electron mobility of the electrode. Only the positive and negative electrode layers are ultra-thin, The battery resistance can be reduced. Therefore, the capacity of a single battery of inorganic LiPON thin film solid state lithium battery is not high, and it is not suitable for the field of preparing Ah class power battery.

Sulfide solid electrolyte is derived from oxide solid electrolyte. Since the electronegativity of sulfur element is smaller than that of oxygen element, it has less binding on lithium ion, which is conducive to obtaining more free moving 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 to improve the conductivity. At present, Samsung, Panasonic, Hitachi Shipbuilding+Honda and Sony are all engaged in the research and development of sulfide inorganic solid electrolyte. However, the challenges brought by air sensitivity, easy oxidation, high interface resistance and high cost are not easy to be completely solved in a short time. Therefore, it is still a long way from the final application of all solid state lithium battery with sulfide electrolyte.

In a word, inorganic solid electrolyte gives play to the advantages of single ion conduction and high stability. It is used in all solid state lithium ion batteries and has the advantages of high thermal stability, low combustion and explosion, environmental friendliness, high cycle stability, and strong impact resistance. At the same time, it is expected to be used in lithium sulfur batteries, lithium air batteries, and other new lithium ion batteries, which is the main direction of electrolyte development in the future.

3.2 Adjustment and optimization of interface performance

The solid electrolyte has the problems of large interface impedance with the electrode, poor interface compatibility, and easy interface separation due to the volume expansion and contraction of various materials during the charging and discharging process. The use of lithium metal anode also has problems such as high solid contact impedance, interface reaction and low efficiency. At present, the main solutions are as follows:

4、 Industrialization progress of solid state lithium battery

4.1 Foreign giants have laid out solid 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 work in the field of solid-state lithium batteries. Japan has also promoted the research and development of solid state batteries to a national strategic height. In May 2017, the Ministry of Economy of Japan announced that it would invest 1.6 billion yen to jointly develop solid state batteries with Toyota, Honda, Nissan, Panasonic, GS Tangqian, Toray, Asahi, Mitsui Chemical, Mitsubishi Chemical and other domestic industrial chain forces, hoping to achieve the goal of 800 km endurance by 2030.

The EV "Bluecar" of Bollore Company in France is equipped with 30kwh lithium metal polymer battery produced by its subsidiary, Batscap. The Li-PEO-LFP material system is used. The Paris car sharing service "Autolib" uses about 2900 Bluecars, which is the first commercial all solid state battery used for EV in the world. Toyota has developed an all solid state lithium-ion battery with an energy density of 400Wh/kg and plans to commercialize it by 2020; The energy density of Panasonic's latest solid state battery is relatively increased by 3-4 times; Germany KOLIBRI battery is applied to Audi A1 pure electric vehicle, and has not been commercialized yet.

In addition, Samsung, Mitsubishi, BMW, Hyundai, Dyson and other enterprises have also stepped up the layout of solid-state battery reserve research and development through independent research and development or combined mergers and acquisitions. Toyota announced its cooperation with Panasonic in the development of solid state batteries; BMW announced to cooperate with SolidPower to develop solid state lithium battery; Bosch, together with the famous GSYUASA (Tangqian) battery company in Japan and Mitsubishi Heavy Industries, has established a new factory focusing on solid state anode lithium ion batteries; The organization established by Honda and Hitachi Shipbuilding has developed and issued Ah battery, which is expected to be mass produced in three years.

4.2 Domestic research institutions take the lead in setting foot in the solid lithium battery industry

In China, the basic research on solid-state lithium batteries started early. During the "Sixth Five Year Plan" and "Seventh Five Year Plan", the Chinese Academy of Sciences has listed solid lithium batteries and fast ion conductors as key topics. At present, five R&D teams have made different progress. In addition, Peking University, 18 institutes of China Electronics Technology Group in Tianjin and other institutions have also set up projects to conduct research on solid lithium electrolyte.

Domestic enterprises engaged in the development of solid lithium battery include CATL, Guojia Star (Jiawei), Jiangsu Qingtao Energy, Huineng, AVIC Lithium, etc. CATL takes sulfide electrolyte as the main research and development direction, and uses positive electrode coating to solve the interface reaction problem between positive electrode materials and solid electrolyte. At present, the cycle of polymer lithium metal solid state battery has reached more than 300 weeks, and the capacity retention rate has reached 82%. Qingtao Energy has developed all ceramic membranes and inorganic solid electrolytes with high solid content, and has cooperated with BAIC for pilot test. Guojia Interstellar uses material genome technology to determine the optimal composition of polymer solid electrolyte through high-throughput testing technology. In addition, Ganfeng Lithium, BYD, Wanxiang 123 and others have also announced their plans in the field of solid-state batteries, but most enterprises are still in the stage of "oral research and development".

5、 Prospect of solid state lithium battery industry

At present, there are two research and development directions for solid state batteries. One is the solid-state of lithium ion batteries. There are mature plans for other industries in this direction, but the grafting of lithium batteries requires secondary research and development. There are few mass production enterprises of solid electrolyte abroad, and none in China, which restricts the development progress of solid battery to a certain extent. The gelled battery successfully developed by the Japanese laboratory has been sampled by domestic universities and scientific research institutes for a long time, but most of them remain at the level where the energy ratio meets the standard and the cycle is only a few hundred times. In addition, the cost is very high, and the yield is very low, which cannot be mass produced.

Another technology research and development direction is metal solid state battery, the most common is lithium sulfur battery. When the electrolyte is replaced with a solid, the lithium battery system is transformed from the solid-liquid interface of electrode material electrolyte to the solid-liquid interface of electrode material solid electrolyte. There is no wettability between solid and solid, and its interface is easy to form higher contact resistance, so the battery circulation will become worse, and it is impossible to charge quickly. The production environment of lithium sulfur battery is vacuum. Once oxygen is mixed, it will explode, which brings great challenges to equipment enterprises.

As one of the future battery technology directions to replace traditional lithium batteries, all solid state lithium batteries have attracted many research institutions and enterprises at home and abroad to carry out research and development. However, there is still a long way to go in terms of solid electrolyte materials, interface performance optimization, electrode material selection, cost and process. Both the production process and the surrounding environment of the production line need a lot of capital investment and strict parameter control, For less advanced start-ups, the road from the laboratory to the mass production line is long, far and expensive. Of course, in the face of its huge commercial value space, there will certainly be more outstanding automobile manufacturers and battery enterprises like BMW to invest in it. I believe that with the promotion and deepening of research and development technology, the pace of solid-state battery industrialization will gradually accelerate.



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