Whether it is new energy vehicles or energy storage equipment, one of the most important key components is the battery. One of the challenges in the battery industry in recent years is to increase energy density and pursue safer methods, whether it is trying new positive and negative electrodes. materials; or increasing the proportion of nickel in nickel manganese cobalt (NMC) ternary batteries; there are also people working on developing technologies that are different from traditional lithium batteries, such as hydrogen energy vehicles using hydrogen fuel cells. Solid-State Battery is regarded as the next generation of battery technology. What is a solid-state battery? What kind of technology is an all-solid-state battery? In layman's terms, an all-solid-state battery is a battery with no gas or liquid inside, and all materials exist in solid form. Considering that the most common battery in people's daily life is lithium-ion battery, we will default to "all-solid-state lithium-ion battery" as the representative of all-solid-state battery (ignore all-solid-state lithium-sulfur and other new batteries for the time being). Generally speaking, lithium-ion batteries are mainly composed of positive electrodes, negative electrodes, separators, electrolytes, structural shells and other parts. The electrolyte allows current to be conducted in the form of ions inside the battery. Electrolyte technology is one of the core technologies of lithium batteries and is also a highly profitable component of the current battery industry. Schematic diagram of the structure of a lithium-ion battery. Li+ (lithium ions) are in the internal circuit and are conducted through the electrolyte. However, some lithium batteries will bulge after being used for a long time, and in more extreme and small-probability events, some may even be dangerous. (For example, the recent battery explosion of the twist car caused related manufacturing companies and battery companies to encounter comprehensive difficulties). In addition, generally speaking, the operating temperature range of current lithium-ion batteries is limited. At high temperatures above 40 degrees, the life will be shortened sharply, and the safety performance will also have big problems (so Tesla MODELS will have a strict battery temperature range. control system, that’s why). In fact, the safety issues mentioned above are directly related to the electrolyte of the organic system used in our current batteries. In order to solve battery safety problems and increase energy density, the scientific research community and industry are currently developing and producing all-solid-state batteries, which means replacing the separators and electrolytes of traditional lithium-ion batteries with solid electrolyte materials. So let's talk about it, compared to the most common ordinary lithium-ion batteries in our lives, what are the main advantages of all-solid-state batteries? One of the advantages of solid-state batteries: thin - small size. In fact, the volumetric energy density is Battery is a very important parameter. In terms of application fields, the requirements from high to low are consumer electronics > household electric vehicles > electric buses. In layman's terms, the volumetric energy density is high, so batteries of the same mass can be made smaller. The available space in electronic products is often very limited. Nearly 1/3 of the volume and mass of many products (such as mobile phones and tablets) has been occupied by batteries. Moreover, the majority of manufacturers and consumers hope to further increase the battery capacity (increase the battery capacity). Under the requirements of battery life) and compressed volume (portable, beautiful and easy to design), lithium cobalt oxide (LCO) batteries with high compactness and the highest volume energy density are still the mainstream products. In traditional lithium-ion batteries, separators and electrolytes are required, which together account for nearly 40% of the battery's volume and 25% of its mass. And if they are replaced with solid electrolytes (mainly organic and inorganic ceramic material systems), the distance between the positive and negative electrodes (traditionally filled with separator electrolyte, now filled with solid electrolyte) can be shortened to even just a few to More than ten microns, the thickness of the battery can be greatly reduced - therefore all-solid-state battery technology is the only way to miniaturize and thin the battery. Not only that, many all-solid-state batteries prepared by physical/chemical vapor deposition (PVD/CVD) may have an overall thickness of only a few dozen microns, so they can be made into very small power devices and integrated into MEMS (microelectromechanical systems). in the field. The ability to make very small batteries is also a major feature of all-solid-state battery technology, which can facilitate the battery to adapt to the application of various new small-sized smart electronic devices, which is difficult to achieve with traditional lithium-ion battery technology. of. (The (a) volume proportion and (b) mass proportion of each component of the current lithium-ion battery) A key obstacle to the practical use of many nanomaterials is their large specific surface area and too low volume density. As a result, if they are made based on these materials, Finished products often occupy too large a volume under the same mass, that is, the volumetric energy density is low, completely unable to meet the requirements of general industrial products. Therefore, current scientific research on nanometer (battery) materials often chooses not to report parameters in this area. The reason is not difficult to understand. Advantage 2: The prospect of flexibility. All-solid-state batteries can be further optimized and turned into flexible batteries, thereby bringing more functions and experiences. In fact, even brittle ceramic materials can often be bent when the thickness is reduced to less than a millimeter, and the material becomes flexible. Correspondingly, the flexibility of all-solid-state batteries will also be significantly improved after being thinned and light. By using appropriate packaging materials (not steel shells), the manufactured batteries can withstand hundreds to thousands of bends and ensure There is basically no degradation in performance. In fact, flexible electronic devices represented by various wearable devices are an important direction for the development of next-generation electronic products, and this requires that the components in the products also need to be flexible. Therefore, flexible all-solid-state batteries are an important topic in scientific research and industry. , a very promising star of tomorrow. (Typical laminated structure flexible all-solid-state battery prepared by KAIST, South Korea) Not only that, the potential of functionalized all-solid-state batteries is far more than the above flexible batteries. After the battery material structure is optimized, it can be made into a transparent battery, or the stretching range can be up to 300% stretchable batteries, or integrated power generation-storage devices that can be integrated with photovoltaic devices, etc. - all-solid-state batteries have many functional innovative application prospects. In this regard, researchers and engineers Our imagination will bring us more and more surprises. (Schematic diagram of the structure of an all-solid-state battery with a tensile deformation degree of up to 300%) (Schematic diagram of a fiber-shaped device integrating solar cells and supercapacitors) Advantage three: safer As an energy storage device, in fact all batteries are thermodynamically essentially None can be absolutely safe. However, there are many factors that determine the true safety of a battery in its actual application. The influencing factors include the characteristics of the electrode material of the battery, the properties of the electrolyte, and the battery management system in electronic products. At present, the safety of generally commercial lithium ions is the focus of everyone's concern. Here, using "not ideal" to evaluate the safety of current batteries should be a more appropriate evaluation. Advantage 4: Light - high energy density. After using all-solid-state electrolytes, the applicable material system of lithium-ion batteries will also change. The core point is that it is not necessary to use lithium-embedded graphite negative electrodes, but to directly use metallic lithium. Making the negative electrode can significantly reduce the amount of negative electrode material and significantly increase the energy density of the entire battery. In addition, many new high-performance electrode materials may not have good compatibility with existing electrolyte systems before, but this problem can be alleviated to a certain extent after using all-solid electrolytes. Taking the above two factors into consideration, the energy density of all-solid-state batteries can be greatly improved compared to ordinary lithium-ion batteries: many laboratories can now produce small-scale batch trials with energy densities of 300-400Wh. /kg all-solid-state battery (generally lithium-ion batteries are 100-220Wh/kg). Judging from the energy density data, perhaps all-solid-state batteries really have hope to upgrade our lives from "one charge a day" to "one charge every two days." Technical routes of solid-state batteries There are different technical routes in the field of solid-state batteries. Solid electrolytes can be roughly divided into three categories: inorganic electrolytes, solid polymer electrolytes (SPE, Solid Polymer Electrolyte), and composite electrolytes. The materials currently being researched by many industries include solid polymers, sulfides, oxides, thin films, etc. For example, the solid-state battery factories Sakti3 and Infinite Power Solutions acquired by Dyson and Apple respectively are mainly based on thin films, but the manufacturing process is complicated and mass production is difficult. Previously, there were rumors in the market that Dyson and Apple intend to give up, so the current development situation is not clear. , while Toyota, Panasonic, Samsung, BMW, and CATL have invested in sulfide electrolytes, while Huineng and Sony have focused on oxides. Apple has been actively developing patents for solid-state batteries and charging technology since 2012, and acquired Infinite Power Solutions in 2013. In the past two or three years, news about automobile factories deploying solid-state batteries has come to the fore. For example, Toyota announced that it will sell electric vehicles equipped with solid-state batteries in 2022. In addition, Volkswagen invested in QuantumScape, a solid-state battery startup co-founded by MIT Technology Review TR35 young entrepreneur Jagdeep Singh. In June last year, it increased its investment and became a director of QuantumScape. It is expected to establish a solid-state lithium battery company in 2025. Battery production line. Japan, a big battery country in the past, has shifted its research focus to solid-state batteries after gradually abandoning lithium batteries. The Japan Science and Technology Agency (JST) and the Japan New Energy Industry Technology Development Organization (NEDO) are actively promoting these developments. These developments have caused the outside world to start Pay attention to this technology. Players investing in solid-state batteries (Photo source: Yole Développement) Solid-state battery companies that the market is paying attention to: A look at the technical bottlenecks of solid-state batteries. Currently, many battery and automobile manufacturers, including South Korea's Samsung, Japan's Toyota, and my country's CATL, have increased their investment in solid-state batteries. With investment in R&D, some batteries have entered the vehicle testing stage. Although the prospects are promising, the road to developing solid-state batteries is by no means smooth sailing due to various technical and process problems. First, there is a lack of efficient electrolyte material systems. At present, solid-state battery materials are developing rapidly, but comprehensive applications are lacking. As the core material of solid-state batteries, there has been a breakthrough in the single indicator of solid lithium-ion conductors, but the comprehensive performance cannot yet meet the needs of large-scale energy storage. The solid-state electrolytes used in today's solid-state batteries generally have performance shortcomings, and there is still a big gap between the requirements of high-performance lithium-ion battery systems. 1. The interface treatment between solid electrolyte and electrode is also a major problem currently faced by solid-state batteries. In solid electrolytes, the transmission impedance of lithium ions is very large, and the contact area of the rigid interface with the electrode is small. Changes in the volume of the electrolyte during the charge and discharge process can easily destroy the stability of the interface. 2. In solid-state lithium batteries, in addition to the interface between the electrolyte and the electrode, there are also complex multi-level interfaces inside the electrode. Factors such as electrochemistry and deformation will cause contact failure and affect battery performance. Thirdly, unsatisfactory stability during long-term use is also a bottleneck in the development of long-life energy storage solid-state batteries. The structure and interface of solid-state batteries will degrade over time during service. However, the impact of degradation on the overall performance of the battery is still unclear, making it difficult to achieve long-term application. Therefore, to build high-performance solid-state batteries, we need to start from two aspects. One is to build a high-performance solid-state electrolyte, and the other is to improve the compatibility and stability of the interface. In a sense, the evolution of cars is the evolution of batteries. In terms of origin, electric vehicles have a history of more than 180 years, and their emergence is about the same as that of fuel vehicles. However, neither lead-acid batteries nor nickel-metal hydride batteries have made a breakthrough in the status of electric vehicles. It was not until the upgrade of lithium iron phosphate batteries and ternary lithium batteries that some consumers gradually accepted electric vehicles. If solid-state batteries become commercially available, electric vehicles will accelerate the pace of replacing internal combustion locomotives. Whoever masters this technology first will have a greater say in the future competitive landscape.

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