"Name" for all solid state lithium batteries

Introduction: All solid-state lithium batteries have been studied since the 1950s and have lasted for more than half a century. In recent years, all-solid-state lithium batteries for electric vehicle applications have finally moved from the laboratory to industrialized small-volume manufacturing. At present, the frequency of “all-solid-state lithium batteries” in various public places in the field of new chemical power sources is getting higher and higher, and the industry has basically formed a consensus: all solid-state lithium batteries are expected to enter the market as the next-generation power source, but what is it all solid state lithium battery? I believe that there are many people who are confused. To this end, we have a close look at this article for the "synonym" of all solid-state lithium batteries for your reference. This article will be published in the first issue of 2018 in energy storage Science and Technology.

1 Overview of all solid state lithium batteries

An all-solid lithium battery is a lithium battery that uses a solid electrode material and a solid electrolyte material and does not contain any liquid, and mainly includes an all-solid lithium ion battery and an all-solid lithium metal battery. The difference is that the former negative electrode does not contain metallic lithium, and the latter The negative electrode is metallic lithium.

From the point of view of the time node, the all-solid metal lithium battery is earlier than the liquid lithium ion battery, but in the early stage, the electrochemical performance, safety and engineering manufacturing of the all-solid metal lithium battery have not been able to meet the application requirements. Liquid lithium-ion batteries have been continuously improved, and comprehensive technical indicators have gradually met the needs of consumer electronics market applications, and have been accepted by more markets. From the perspective of technology development, compared with liquid lithium-ion batteries, all-solid metal lithium batteries may have the advantages of good safety performance, high energy density and long cycle life. In recent years, solid electrolyte materials, especially sulfide electrolyte materials, have made major breakthroughs in ionic conductivity, so all-solid-state lithium battery technology has gradually begun to attract the attention of R&D institutions and large enterprises worldwide.

2. Classification of all solid lithium batteries

Along with the rise of all-solid-state lithium battery heat, various "all-solid" or "solid-state" lithium batteries have emerged, and there is a current state of confusion. The seven types of concepts related to solid-state lithium batteries have been sorted out and a preliminary summary has been made.

Liquid lithium battery:

The battery does not contain a solid electrolyte during the manufacturing process, and only a lithium battery containing a liquid electrolyte, including a liquid lithium ion battery and a liquid metal lithium battery.

Gel electrolyte lithium battery

The liquid electrolyte in the cell is in the form of a gel electrolyte, which does not contain a solid electrolyte, which is actually in the category of liquid lithium ion batteries.

Semi-solid lithium battery

In the cell electrolyte phase, half of the mass or volume is a solid electrolyte, and the other half is a liquid electrolyte; or one end of the cell is all solid and the other end contains a liquid.

Quasi-solid lithium battery

The electrolyte of the battery cell contains a certain solid electrolyte and a liquid electrolyte, and the mass or volume of the liquid electrolyte is smaller than that of the solid electrolyte.

Solid state lithium battery

A battery containing a high mass or volume ratio of a solid electrolyte and a small amount of liquid electrolyte is called "solid lithium battery" by some researchers, but it is not actually an all-solid lithium battery.

Mixed solid-liquid lithium battery

A solid electrolyte and a liquid electrolyte are simultaneously present in the cell. The above-mentioned semi-solid, quasi-solid, solid lithium battery and the like are all one of mixed solid-liquid lithium batteries. Since there is no need to artificially classify according to the ratio of solid-liquid, and there is no ambiguity, the term is recommended, and it can also be called "mixed solid-liquid electrolyte lithium battery".

All solid lithium battery

The battery cell is composed of a solid electrode and a solid electrolyte material. The battery core does not contain any mass and volume fraction of liquid electrolyte in the working temperature range, and can also be called "all solid electrolyte lithium battery". The charge and discharge cycle can be further referred to as an "all solid lithium secondary battery" or an "all solid electrolyte lithium secondary battery".

Table 1 Types and characteristics of mixed solid-liquid lithium batteries and all-solid lithium secondary batteries of different electrolyte types

In summary, lithium batteries can be divided into liquid lithium batteries, mixed solid-liquid lithium batteries and all-solid lithium batteries according to different electrolytes. According to the difference of the negative electrode, it can be classified into a lithium metal battery in which the negative electrode is metallic lithium and a lithium ion battery in which the negative electrode does not contain metallic lithium.

3. All solid state lithium battery may have advantages

The reason why all-solid-state lithium batteries will make international giants look because it is expected to solve the two "challenges" that currently plague the power battery industry - safety hazards and low energy density. The advantages of an all-solid lithium battery compared to a liquid lithium ion battery are as follows.

(1) High security performance

Since the liquid electrolyte contains a flammable organic solvent, the sudden rise in temperature during internal short circuit is likely to cause combustion or even explosion. It is necessary to install a safety device structure that is resistant to temperature rise and short circuit, which increases the cost, but still cannot completely solve the safety problem. . Known as BMS to achieve the best Tesla in the world, there have been two serious fires in the ModelS in China this year. Many inorganic solid electrolyte materials are non-flammable, non-corrosive, non-volatile, and have no leakage problems, and are also expected to overcome lithium dendrite. Therefore, all-solid lithium secondary batteries based on inorganic solid electrolytes are expected to have high safety characteristics. Polymer solid electrolytes still have a certain risk of burning, but the safety is also greatly improved compared to liquid electrolyte batteries containing flammable solvents.

(2) High energy density

At present, the energy density of lithium-ion battery cells used in the market is up to 260W·h/kg, and the energy density of lithium-ion batteries being developed can reach 300-320W·h/kg. For all-solid-state lithium batteries, if the negative electrode is made of metallic lithium, the energy density of the battery is expected to reach 300-400 W·h/kg or even higher. It should be noted that since the density of the solid electrolyte is higher than that of the liquid electrolyte, the lithium battery energy density of the liquid electrolyte is significantly higher than that of the all-solid lithium battery for the same system of the positive and negative materials. The reason why the all-solid lithium secondary battery has a high energy density is because the negative electrode may be made of a metallic lithium material.

(3) Long cycle life

The solid electrolyte is expected to avoid the problem of continuous formation and growth of the solid electrolyte interface film during the charging and discharging process of the liquid electrolyte and the problem of the lithium dendrite piercing the separator, which may greatly improve the cycle and service life of the metal lithium battery. The reported all-solid-state lithium metal battery can be cycled 45,000 times, but the current large-capacity lithium metal battery has not reported long cycle life, mainly the current cycle performance of high-surface capacity metal lithium electrode (>3mA·h/cm2) still poor.

(4) Wide operating temperature range

If all solid-state lithium batteries use inorganic solid electrolytes, the maximum operating temperature is expected to increase to 300 ° C or higher. At present, the low-temperature performance of large-capacity all-solid lithium batteries needs to be improved. The operating temperature range of a specific battery is mainly related to the high and low temperature characteristics of the electrolyte and the interface resistance.

(5) Electrochemical window width

The all-solid-state lithium battery has an electrochemically stable window width, which is likely to reach 5V, and is suitable for a high-voltage electrode material, which is advantageous for further increasing the energy density. At present, a thin film lithium battery based on lithium nitride phosphate can work at 4.8V.

(6) Flexibility advantage

All-solid-state lithium batteries can be fabricated into thin-film batteries and flexible batteries, which can be applied to smart wearable and implantable medical devices in the future. Compared to flexible liquid electrolyte lithium batteries, packaging is easier and safer.

(7) Easy to recycle

Battery recycling is generally two methods, one is wet and the other is dry. The wet method is to take out the toxic and harmful liquid core inside, and the dry method is, for example, crushing to extract the effective ingredients. The advantage of an all-solid-state lithium battery is that it has no liquid in itself, so theoretically there should be no waste liquid, which is relatively simple to handle.

4. Existing solid-state lithium battery defects and partial solutions

Although the all-solid lithium secondary battery shows obvious advantages in many aspects, there are also some problems that need to be solved urgently: the ionic conductivity of the solid electrolyte material is low; the interface impedance between the solid electrolyte/electrode is large, and the interface compatibility is poor. At the same time, the volume expansion and contraction of each material during charging and discharging, resulting in easy separation of the interface; the electrode material to be designed and constructed to match the solid electrolyte; the current cost of battery preparation is higher. In response to these problems, the researchers made various attempts and gave some possible solutions.

5. Core materials introduction

5.1 Solid electrolyte

Solid electrolyte is the core component of all-solid lithium secondary battery, and its progress directly affects the industrialization process of all-solid lithium secondary battery. At present, research on solid electrolytes mainly focuses on three types of materials: polymers, oxides and sulfides.

Polymer solid electrolyte (SPE) consisting of polymer matrix (such as polyester, polyether and polyamine) and lithium salt (such as LiClO4, LiAsF6, LiPF6, etc.). Since 1973, WRIGHTPV was found in alkali metal salt complexes. After ionic conductivity, polymer materials have attracted extensive attention due to their solid-state electrochemical properties such as light weight, good elasticity, and excellent machinability. SPE was also the first solid electrolyte to achieve practical application. As early as 2011, the French company Bolure began to deliver Autolib electric cars to Paris, which is based on SPE-based all-solid lithium battery system.

Oxide solid electrolytes can be classified into crystalline and amorphous states according to their structure. Among them, crystalline electrolytes include perovskite, anti-perovskite, garnet, NASICON, LISICON, etc., amorphous oxidation. The research hotspots are LiPON type electrolytes and partially crystallized amorphous materials used in thin film batteries.

The sulfide solid electrolyte is derived from an oxide solid electrolyte in which an oxygen element in the oxide body is replaced by a sulfur element. Since the electronegativity of sulfur is smaller than that of oxygen, the binding of lithium ions is small which is beneficial to obtain more free-moving lithium ions. At the same time, the radius of the sulfur element is larger than that of the oxygen element. When the sulfur element replaces the oxygen element, the lattice structure is expanded to form a larger lithium ion channel and the conductivity is improved, and the room temperature can reach 10-2 to 10-4 S/cm. .

5.2 cathode material

The positive electrode of the all-solid lithium secondary battery generally adopts a composite electrode, and includes a solid electrolyte and a conductive agent in addition to the electrode active material, and functions to simultaneously transport ions and electrons in the electrode. LiCoO2, LiFePO4 and LiMn2O4 are more common. Later, it is possible to develop high-nickel layered oxides, lithium-rich manganese-based and high-voltage nickel-manganese spinel-type positive electrodes. At the same time, attention should be paid to the research and development of new cathode materials without lithium.

5.3 anode material

The anode materials of all-solid lithium secondary batteries are mainly concentrated in the metal lithium anode materials, carbon anode materials and oxide anode materials. The three materials have their own advantages and disadvantages, among which the metal lithium anode materials are high in capacity and low. The advantage of potential is one of the most important anode materials for all-solid lithium batteries.

6 all-solid lithium battery capacity division and corresponding application fields and preparation processes

From the form of the all-solid lithium secondary battery, it can be divided into two types of a film type and a large capacity type. The cell packaging technology of all types of all-solid lithium batteries is similar, and the main difference lies in the preparation of pole pieces and electrolyte membranes.

The thin film type all-solid lithium secondary battery sequentially prepares various elements of the battery in the order of the positive electrode, the electrolyte, and the negative electrode on the substrate, and finally encapsulates into a battery. In the preparation process, it is necessary to separately prepare the film layers of the battery by corresponding techniques. Generally, the negative electrode selects most of the metal lithium and is prepared by vacuum thermal vapor deposition (VD) technology; the negative electrode of the electrolyte and the positive electrode including the oxide can be used for various splashes. Injection techniques, such as RF sputtering (RFS), RF magnetron sputtering (RFMS), etc., have also been studied to produce films using 3D printing technology.

Large-capacity all-solid-state lithium secondary batteries, due to their wide application range and large market, require rapid and low-cost scale preparation, and high-speed extrusion coating or spraying technology widely used in liquid lithium ion batteries can be used for reference. The preparation of a large-capacity all-solid lithium secondary battery based on a polymer solid electrolyte is close to the winding process of the existing lithium ion battery. However, considering that the flexibility of the inorganic solid electrolyte membrane is currently poor, the lamination process is more often used in the preparation of the all-solid lithium secondary battery, and it is specifically used to separately prepare the electrolyte and the positive and negative membranes. The double-layer or multi-layer coating is used to prepare the composite layer of the electrolyte and the positive electrode, and the technical route suitable for large-scale production needs further research.

Although the production equipment of all-solid lithium secondary batteries is quite different from the traditional lithium-ion battery cell production equipment, there is no revolutionary innovation from the objective point of view. It is possible that 80% of the equipment can continue the production equipment of lithium-ion batteries. It only has higher requirements in the production environment and needs to be produced in a higher-level drying room. It is sensitive to air with super capacitors, lithium ion capacitors, nickel-cobalt aluminum, pre-lithiation, lithium titanate, etc. For companies with devices or materials, the manufacturing environment is compatible, but the corresponding production environment costs are significantly higher.

7 Outlook for all solid state lithium batteries

At present, the development of new energy vehicles has clearly risen to the national strategic level, in which power batteries are the most critical core components of new energy vehicles, and the key level can be seen.

According to China's "Technology Roadmap for Energy Saving and New Energy Vehicles", the energy density target of pure electric vehicle power battery in 2020 is 300W·h/kg, the target for 2025 is 400W·h/kg, and the target for 2030 is 500W·h/ Kg. According to public data, the current energy density limit of liquid electrolyte-powered lithium-ion battery using ternary cathode material and graphite anode material is about 250W·h/kg, while silicon-based composite material is introduced instead of pure graphite as anode material, liquid electrolyte-powered lithium. The energy density of the ion battery cell can reach 300W·h/kg, and the upper limit is about 350W·h/kg (the Panasonic 21700 battery has been used on the Tesla Model3, the positive electrode is made of nickel-cobalt-aluminum ternary material, and the negative electrode is made of silicon. Composite materials, claiming energy density has exceeded 300W·h/kg).

"If the energy density is further improved, we must consider all-solid-state lithium batteries from now on." Academician Chen Liquan of the Chinese Academy of Engineering said in a recent public speech that "the long-term development of the electric vehicle industry requires technical reserves, and all-solid lithium batteries are expected." to become the leading technology route for the next generation of vehicle power batteries in China. It is imperative to develop all-solid-state lithium batteries!

From a global perspective, almost all of the old powerhouses have already established new energy vehicle development plans. On September 7, the Scottish National Party (SNP) leader Nikola Stukkin said in the parliament that it will fight for 2032. The sale of gasoline and diesel vehicles was stopped in the year to reduce air pollution. In fact, not only Scotland, Norway, the Netherlands, Germany, the United Kingdom, and Belgium have all introduced or are preparing policies for abolishing fuel vehicles. Therefore, we can imagine that by 2050, traveling to Europe, traveling, looking around running new energy vehicles on the road. On the other hand, our country has made relevant development plans based on actual conditions. In the already published "Long-term Plan for the Automotive Industry", China's automobile industry aims to achieve 30 million vehicle sales and sales by 2020, including 2 million new energy vehicles. By 2025, the production and sales volume of automobiles will reach 35 million, including 7 million new energy vehicles, accounting for 20%.

In response to the increasingly urgent high-performance demands of new energy vehicles, countries have begun to deploy high-energy-density lithium batteries. As proposed by the Japanese government, the energy density of power battery cells will reach 250W·h/kg in 2020 and 500W in 2030. · h/kg; The United States Advanced Battery Association (USABC) proposed to increase the energy density of batteries in 2020 from 220W·h/kg to 350W·h/kg; the “Made in China 2025” issued by the State Council of China clearly stated that In 2020, the specific energy of China's power battery cells reached 300W·h/kg, reached 400W·h/kg in 2025, and reached 500W·h/kg in 2030. The Battery500 project in the United States proposed to develop a power battery sample with an energy density of 500 W·h/kg in 2020. To improve the energy density of the battery core, it is inevitable to take into consideration the safety. Therefore, the development of all-solid lithium secondary battery technology is of great significance.

Under the guidance of national policies, a global all-solid lithium secondary battery technology competition has been launched. It is expected that hybrid solid-liquid lithium secondary batteries will be the first to enter the terminal market in 2020, and all solid-state lithium secondary batteries will enter the country in 2022. In the end market, with the improvement of comprehensive technical indicators such as cycle, rate, high and low temperature and safety, it gradually entered the electric vehicle market, and the swarming research institutions and enterprise alliances may bring the all-solid lithium secondary battery to the market. Time ahead!

Fortunately, the research progress of China's all-solid lithium secondary battery in the background of national rejuvenation is already in a stage of rapid development. It is expected that China's battery industry will be able to seize the opportunity of battery technology iteration to achieve the run and lead in the battery and automotive fields.

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