What are the advances in solid-state lithium batteries?

All solid state lithium ion batteries with the replacement of traditional organic liquid electrolyte and solid electrolyte is expected to be fundamentally solved battery security issues, is the ideal chemical power electric cars and large-scale energy storage. In order to realize the large capacity and long service life, thus to promote practical of all solid state lithium ion battery, the battery of the development of key materials and performance optimization is urgently needed, including the preparation of high room temperature conductivity and electrochemical stability of solid electrolyte and used throughout the high energy of solid state lithium ion battery electrode materials, the improvement of electrode/solid electrolyte interface compatibility.

Solid-state batteries are introduced

Traditional lithium-ion batteries use organic liquid electrolyte, such as overcharge, internal short circuit under the condition of abnormal, battery easy fever, electrolyte flatulence, spontaneous combustion and explosion, there are serious security hidden danger.Developed in the 1950 s all solid state based on solid electrolyte lithium battery, as a result of using solid electrolyte, does not contain flammable, volatile components, eliminate cells due to the leakage cause of smoke, fire and other safety concerns, known as the safest battery system.For energy density, the government of China, the United States and Japan hope that developed in 2020, 400 ~ 500 wh/kg of prototype devices, realize the mass production from 2025 to 2030, in order to achieve this goal, now recognized as the most likely is the use of lithium metal anode, and lithium metal exist in the traditional liquid lithium ion battery dendrite, pulverization, the SEI (solid electrolyte interface film) is not stable, surface side reaction and so on many technical challenges, and the solid electrolyte and compatibility of metallic lithium makes it possible to use lithium as negative, thus realize the ascension of the energy density significantly.

Different kinds of electrolytes and compare the properties of lithium ion battery system

Solid electrolyte are reviewed

For solid-state batteries, solid electrolyte is core component of its different from other battery system, solid electrolyte should have ideal working temperature range (especially at room temperature) maintain high lithium ionic conductivity;Can be ignored or there is no grain boundary impedance;With the thermal expansion coefficient of the electrode materials;The battery charge and discharge process, the anode electrode materials for maintaining good chemical stability, especially lithium metal or lithium alloy anode;Electrochemical wide mouth wide, high breakdown voltage;Not easy to moisture absorption, low cost, preparation technology is simple, environmentally friendly.

At present, the production of polymer solid polymer electrolyte in the battery material system is polyethylene oxide (PEO).PEO polymer electrolyte is characteristic of high ionic conductivity at high temperature, easy to film, easy to machining, and the anode can be formed after composite continuous ion conductive channel, the anode surface resistance is small.PEO oxidation potential of 3.8 V, cobalt acid lithium, layered oxides and spinel oxides such as high energy density anode is hard to match, need to modification;Second, the PEO base electrolyte temperature in 60 ~ 85 ℃, battery system need thermal management, the need for power and energy storage applications special battery system design;Again, this kind of lithium battery used directly in the process of charging and discharging uneven sedimentation still exist at the interfaces of lithium dendrite across the polymer membrane caused by short circuit inside the hidden trouble, in addition ratio characteristics also needs to be improved.Development of resistance to high voltage, high ionic conductivity at room temperature and has a blocking mechanism of lithium dendrite, good mechanical properties of polymer electrolyte is a key research direction.

Inorganic solid electrolyte consists of oxide and sulfide.Has been small batch production of solid-state batteries are mainly amorphous Lipton as electrolyte thin film batteries.Inorganic solid electrolyte has the advantage of some of the material body, high ionic conductivity can tolerate high voltage, electrochemical, chemical and thermal stability, inhibition of lithium dendrite has a certain effect.

Relative to the oxide and sulfide due to relatively soft, it is easier to processing, by hot pressing method preparation of all solid state lithium battery.Recently showed solid state lithium battery may even be able to work under 60 c at room temperature, while the volume and quality will be a significant reduction in the energy density, but at least the results reflected the solid-state batteries in high power output potential.Sulfide electrolyte is air sensitive, easy oxidation, the water is easy to produce the harmful gas such as hydrogen sulfide.Through in sulfide compound oxide or doping, this problem can improve to a certain extent, but in the end can satisfy the application requirement for safety, environment friendly features experimental verification is needed.At this stage, the use of inorganic ceramic solid electrolyte solid-state large capacity battery batteries quality and volume energy density is significantly lower than the existing liquid lithium ion battery.

The anode materials are reviewed

In addition to a solid electrolyte and electrode materials is also the key factors influencing the performance of solid-state batteries.Although a solid electrolyte and electrode material interface basic does not exist solid electrolyte decomposition side effects, but solid feature makes the electrode/electrolyte interface compatibility, high interface has been affected by the impedance of the ion transport, leads to the low cycle life, ratio of solid state battery performance is poor.In addition, the development and application of all solid state lithium ion batteries in the future will inevitably from small solid-state thin-film batteries to large solid-state battery energy storage type, however traditional electrode materials have been unable to meet the requirements of high energy density.Based on the above reasons, on the study of electrode materials are mainly concentrated in two aspects: one is to modification of electrode materials and its interface, improve the electrode/electrolyte interface compatibility;The second is to develop new electrode material, so as to further enhance the electrochemical properties of the solid-state batteries.

High energy density of the anode material has larger intercalated-li capacity and high voltage, there will be significant in the process of charging and discharging volume change.Using solid electrolyte, in the anode and the interface of solid electrolyte membrane, and the positive internal contact with solid electrolyte interface, contact variation is likely to happen.The solution including the positive particles in the surface in situ or ex situ deposits or hot pressing a solid electrolyte layer;Or the positive particle pore filling in a certain elastic solid electrolyte, form continuous ion conductive phase, similar to the liquid electrolyte;Or in liquid, introduced the positive side, solid-liquid composite system.Because it is difficult to separate liquid injection to the anode, the introduction of the liquid, whether can have the advantages of solid state lithium battery with high energy density and safety is the key, it depends on the introduction of the electrochemical properties of liquid and security features, and lithium metal electrode is fully protected in advance.Now that the security of the existing liquid electrolyte has been basically meet the requirements, therefore, in the solid-state batteries, add the liquid to reduce the positive side, contact resistance should be a can both dynamics and security solutions.But can find work in high voltage, good wettability, security, good liquid electrolyte additive also is not easy, it is in itself a liquid lithium ion battery is one of the main research direction and the bottleneck technique.

Anode materials are reviewed

Metal because of its high capacity and low potential advantages into solid-state batteries one of the main anode materials, lithium metal in the process of circulation, however, has the production of lithium dendrite, not only can make to reduce the amount of lithium the embedded/take off, more serious is that can cause safety problem such as short circuit.Other metal Li is very lively, easy to react with oxygen in the air and water, etc, and is not capable of high temperature metallic lithium, brings to the battery assembly and application of the difficulties.Join other of lithium metal and alloy is one of the main methods to solve these problems, the alloy material are usually has high theoretical capacity, and the activity of metallic lithium and decreased by the participation of other metals, can effectively control the production of lithium dendrite and the electrochemical reaction, thus promotes the interface stability.Lithium alloy anode, however, there are some obvious flaws, mainly is the electrode in the process of circulation volume change is big, will lead to serious electrode pulverization, cycle performance fell sharply, at the same time, due to the lithium is still an electrode active material, so the corresponding safety problems still exist.At present, can improve these problems mainly include the synthesis of new alloy materials, the preparation of ultrafine nano alloy and composite alloy system (such as active/inactive, active/active, carbon composite and porous structure), etc.

Carbon group of carbon, silicon and tin based material is another important group of all solid state battery anode materials.Carbon is typical representative with graphite materials, graphite carbon is suitable for lithium ion embedding and emergence of layered structure, has a good platform for the voltage, charge and discharge efficiency over 90%, but theoretical capacity is low (only about 372 ma ˙ h/g) is one of the largest, this kind of material and the practical application has been basically achieved theoretical limit, cannot meet the needs of high energy density.

conclusion

To replace the traditional organic solid electrolyte electrolyte preparation of solid-state batteries, can fundamentally solve the problem of the safety of the lithium ion battery.At present a lot of work focused on the development of higher energy and power density of all solid state lithium ion batteries, in promoting the high security, high energy storage battery in the process of industrialization, the key materials (such as solid electrolyte, the positive and negative) of research and development and the preparation is crucial one annulus.

Solid electrolyte developed system of PEO and its derivatives polymer electrolyte, Lipton film electrolyte, oxides and sulfides and amorphous electrolyte and sulfide glass electrolyte system, ionic conductivity was promoted continuously.For now, most likely to be applied to all solid state lithium ion battery of the solid electrolyte materials including the PEO base polymer electrolyte, electrolyte NASICON and garnet oxide and sulfide electrolyte.

In terms of electrode, in addition to the traditional transition metal oxide anode, metal lithium, graphite anode, a series of high-performance anode materials are, are being developed, including sulfide anode oxide anode high voltage, high capacity, good stability of composite cathode, etc.

Battery is the key material of optimization for large capacity of all solid state lithium ion battery industry laid a solid foundation, but there are still some problems to be solved, and become the development direction of the future, although there are many problems, in general, solid-state batteries development prospects are very bright, replace existing lithium ion battery become the mainstream in the future energy storage power supply is also the trend of The Times.

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