Brief analysis of several cutting-edge technologies of lithium-ion batteries

　　With the widespread application of lithium-ion batteries in people’s daily life and military industry, many universities, research institutions, and enterprises are committed to the research and development of new lithium-ion battery technologies, which may be safer, higher capacity, and rechargeable in the near future. Faster lithium-ion batteries will become a reality. Next, please follow the editor to take a look at the 8 most popular research technologies in the field of lithium batteries in the near future.

　　1, all-solid-state lithium-ion battery 　　The currently commercialized lithium-ion battery electrolyte is liquid, so it is also called a liquid lithium-ion battery. Simply put, all-solid-state lithium-ion batteries mean that all components in the battery structure are in solid state, and the liquid electrolyte and diaphragm of traditional lithium-ion batteries are replaced with solid electrolytes.

　　Ternary material battery 　　 With people's pursuit of battery energy density, ternary cathode materials have attracted more and more attention. Ternary cathode materials have the advantages of high specific capacity, good cycle performance, and low cost, and generally refer to the layered structure of nickel cobalt lithium manganate materials. By increasing the battery voltage and the nickel content in the material, the energy density of the ternary cathode material can be effectively increased.

　　Theoretically speaking, the ternary material itself has the advantage of high voltage: the standard test voltage of the half-cell of the ternary cathode material is 4.35V, under this voltage, ordinary ternary materials can show good cycle performance; When the voltage is increased to 4.5V, the capacity of the symmetrical materials (333 and 442) can reach 190, and the cycleability is also good, while the cycleability of 532 is a little worse; when charged to 4.6V, the cycleability of the ternary material begins to decrease, causing flatulence. The phenomenon is getting worse. At present, the factor restricting the practical application of high-voltage ternary cathode materials is that it is difficult to find a matching high-voltage electrolyte.

　　Another way to increase the energy density of ternary materials is to increase the content of nickel in the material. Generally speaking, a high nickel ternary cathode material means that the mole fraction of nickel in the material is greater than 0.6. Such a ternary material has a high ratio of nickel. Features of capacity and low cost, but its capacity retention rate is low, and thermal stability is poor. The performance of this material can be effectively improved through the improvement of the preparation process. The micro-nano size and morphology have a great influence on the performance of the high nickel ternary cathode material. Therefore, most of the currently used preparation methods focus on uniform dispersion to obtain small-sized spherical particles with a large specific surface area.　　 Among many preparation methods, the combination of co-precipitation method and high temperature solid phase method is the mainstream method. First, the co-precipitation method is used to obtain a precursor with uniform raw material mixing and uniform particle size, and then high-temperature calcination to obtain a ternary material with a regular surface and an easy-to-control process. This is also the main method used in current industrial production. The spray-drying method is simpler than the co-precipitation method, and the preparation speed is faster. The morphology of the obtained material is no less than that of the co-precipitation method, which has the potential for further research. The shortcomings of high-nickel ternary cathode materials, such as cation mixing and phase change during charge and discharge, can be effectively improved through doping modification and coating modification. While suppressing the occurrence of side reactions and stabilizing the structure, improving the conductivity, cycle performance, rate performance, storage performance, and high temperature and high pressure performance will still be a research hotspot.　　3, high-capacity silicon carbon anode 　　 as an important part of lithium-ion batteries, negative electrode materials, directly affect the battery's energy density, cycle life and safety performance and other key indicators. Silicon is currently known as the anode material for lithium-ion batteries with the highest specific capacity (4200mAh/g). However, due to its volume effect exceeding 300%, the silicon electrode material will pulverize and peel off from the current collector during charging and discharging, making it active The electrical contact between the material and the active material, the active material and the current collector is lost, and at the same time, a new solid-phase electrolyte layer SEI is continuously formed, which ultimately leads to the deterioration of electrochemical performance. In order to solve this problem, researchers have made a lot of explorations and attempts, among which silicon-carbon composite materials are very promising materials.

　　Carbon material as a negative electrode material for lithium ion batteries has a small volume change during charging and discharging, has good cycle stability and excellent conductivity, so it is often used to compound with silicon. Among the carbon-silicon composite anode materials, it can be divided into two categories according to the types of carbon materials: silicon and traditional carbon materials and the composite of silicon and new carbon materials. The traditional carbon materials mainly include graphite, mesophase microspheres, and carbon black. And amorphous carbon; new carbon materials mainly include carbon nanotubes, carbon nanowires, carbon gels and graphene. Using silicon-carbon composite, the porous effect of carbon materials is used to restrict and buffer the volume expansion of silicon active centers, prevent particle agglomeration, prevent electrolyte penetration to the center, and maintain the stability of the interface and the SEI membrane. Many companies around the world have begun to devote themselves to this new type of anode material. For example, Shenzhen Beiterui and Jiangxi Zichen have taken the lead in launching a variety of silicon-carbon anode material products. Shanghai Shanshan is in the process of industrialization of silicon-carbon anode materials. Xingcheng Graphite The new silicon-carbon anode material has been taken as the direction of future product research and development. 4. High-voltage, high-capacity, lithium-rich materials, lithium-rich manganese-based (xLi[Li1/3-Mn2/3]O2; (1–x)LiMO2, M is a transition metal 0≤x≤1, and the structure is similar to LiCoO2). The high discharge specific capacity is about twice the actual capacity of the current cathode material, and therefore it has been widely studied for use in lithium battery materials. In addition, because the material contains a large amount of Mn, it is more environmentally friendly, safer and cheaper than LiCoO2 and the ternary material Li[Ni1/3Mn1/3Co1/3]O2. Therefore, xLi[Li1/3-Mn2/3]O2; (1–x)LiMO2 material is regarded by many scholars as an ideal choice for the next generation of lithium-ion battery cathode materials.

　　At present, the co-precipitation method is mainly used to prepare lithium-rich manganese-based materials, and some researchers use sol-gel method, solid phase method, combustion method and hydrothermal method to prepare them, but the material properties obtained are not as stable as co-precipitation method. Although this material has a high specific capacity, its practical application still has several problems: the first cycle irreversible capacity is as high as 40-100 mAh/g; the rate performance is poor, and the 1C capacity is below 200 mAh/g; high charging voltage causes electrolyte Decomposition makes the cycle performance unsatisfactory and the safety of use. The above-mentioned problems of lithium-rich manganese-based materials can be well solved by adopting metal oxide coating, composite with other positive electrode materials, surface treatment, special structure structure, and low-limit voltage pre-charge and discharge treatment. In 2013, Ningbo Institute of Materials developed a novel gas-solid interface modification technology to form uniform oxygen vacancies on the surface of lithium-rich manganese-based cathode material particles, thereby greatly improving the first charge and discharge efficiency, discharge specific capacity and cycle of the material. Stability has strongly promoted the practical process of lithium-rich manganese-based cathode materials.　　5. High-voltage withstand electrolyte 　　 Although high-voltage lithium battery materials have received more and more attention, in actual production and application, these high-voltage cathode materials still cannot achieve good results. The biggest limiting factor is the low electrochemical stability window of the carbonate-based electrolyte. When the battery voltage reaches about 4.5 (vs. Li/Li+), the electrolyte will begin to undergo violent oxidation and decomposition, resulting in the insertion and removal of lithium in the battery. The reaction cannot proceed normally. The development of an electrolyte system that withstands high voltage has become an important link in promoting the practical application of this new material.

　　Improving the stability of the electrode/electrolyte interface through the development and application of new high-pressure electrolyte systems or high-pressure film-forming additives is an effective way to develop high-voltage electrolytes. From an economic point of view, the latter is often more popular. Such additives to improve the voltage withstand capability of the electrolyte generally include boron-containing, organic phosphorus, carbonate, sulfur, ionic liquid and other types of additives. The boron-containing additives include tris(trimethylalkane)boronidase, lithium bisoxalate borate, lithium bisfluorooxalate borate, tetramethyl borate, trimethyl borate, and trimethylcycloboroxane. Organic phosphorus additives include phosphites and phosphates. Carbonate-based additives include fluorine-containing Anhui based compounds. Sulfur-containing additives include 1,3-propane sultone, dimethylsulfonyl methane, trifluoromethyl phenyl sulfide and the like. Ionic liquid additives include imidazole and quaternary phosphorus salts. According to the domestic and foreign studies that have been publicly reported, the introduction of high-voltage additives can make the electrolyte withstand voltages of 4.4 to 4.5V. However, when the charging voltage reaches 4.8V or even more than 5V, it is necessary to develop higher voltage resistance. Electrolyte.　　6. High temperature resistant diaphragm 　　 Lithium battery diaphragm mainly plays a role in conducting lithium ions and isolating the electronic contact between the positive and negative electrodes in lithium-ion batteries, and is an important component that supports the battery to complete the electrochemical process of charging and discharging. During the use of lithium batteries, when the battery is overcharged or the temperature rises, the separator needs to have sufficient thermal stability (heat distortion temperature> 200℃) to effectively isolate the contact between the positive and negative electrodes of the battery and prevent short circuits and heat. Accidents such as loss of control or even explosions. Currently, the widely used polyolefin separators have low melting point and softening temperature (<165°C), which makes it difficult to effectively ensure the safety of the battery, and its low porosity and low surface energy limit the performance of the battery's rate performance. Therefore, it is very important to vigorously develop high-safety high-temperature resistant diaphragms.

　　The Power Lithium Battery Engineering Laboratory of Ningbo Institute of Materials and the Energy Storage Technology Research Department of Dalian Institute of Chemical Physics, using wet process one-step molding technology, jointly developed a new type of high-temperature resistant porous diaphragm. This porous diaphragm has a low production cost and is easy to quantify Production. Preliminary research results show that the thermal deformation temperature of the separator is much higher than 200°C, which is equivalent to the thermal stability of a commercial non-woven separator, which can effectively ensure the safety of the battery. At the same time, this porous membrane has a pore structure with high porosity and high curvature, which can effectively avoid battery short-circuit and self-discharge while ensuring battery capacity. In addition, Ningbo Institute of Materials has also developed heat-resistant composite membranes with ultra-thin ion-exchangeable functional layers, gel composite membranes based on three-dimensional heat-resistant frameworks, and ceramic membranes.　　 In addition to Ningbo Institute of Materials, in 2015, Mitsubishi Resin coated high heat-resistant inorganic fillers on the diaphragm, so that the diaphragm can still maintain an appropriate resistance value at a temperature of 220 ℃, blocking the flow of current.　　7. Lithium-sulfur battery 　　Lithium-sulfur battery is a kind of lithium battery in which sulfur is used as the positive electrode of the battery and metal lithium is used as the negative electrode. The biggest difference from general lithium-ion batteries is that the reaction mechanism of lithium-sulfur batteries is electrochemical reaction, not lithium ion deintercalation. The working principle of lithium-sulfur batteries is based on complex electrochemical reactions. So far, the intermediate products formed during the charging and discharging process of sulfur electrodes have not been characterized by a breakthrough. It is generally believed that during discharge, the negative electrode reacts as lithium loses electrons and becomes lithium ions, and the positive electrode reacts as sulfur reacts with lithium ions and electrons to generate sulfide. The potential difference between the positive electrode and the negative electrode is the discharge voltage provided by the lithium-sulfur battery. Under the action of an external voltage, the positive and negative electrodes of the lithium-sulfur battery react in reverse, which is the charging process.

　　The biggest advantage of lithium-sulfur batteries is that their theoretical specific capacity (1672mAh/g) and specific energy (2600Wh/kg) are higher, much higher than other types of lithium-ion batteries currently widely used in the market, and due to the abundant elemental sulfur reserves, This battery is inexpensive and environmentally friendly. However, lithium-sulfur batteries also have some disadvantages: elemental sulfur has poor electronic and ionic conductivity; the intermediate discharge products of lithium-sulfur batteries will dissolve in the organic electrolyte, and polysulfide ions can migrate between the positive and negative electrodes, resulting in activity Material loss; metal lithium negative electrode will change in volume during charging and discharging, and it is easy to form dendrites; sulfur positive electrode has up to 79% volume expansion/shrinkage during charging and discharging.

　　The main methods to solve the above problems generally start from two aspects: electrolyte and cathode material: In terms of electrolyte, ether electrolyte is mainly used as the electrolyte of the battery. Adding some additives to the electrolyte can effectively relieve lithium polysulfide. The problem of dissolution of compounds; in terms of positive electrode materials, it is mainly the combination of sulfur and carbon materials, or the combination of sulfur and organic matter, which can solve the problem of non-conductivity and volume expansion of sulfur. Lithium-sulfur batteries are still in the laboratory research and development stage. The research institutes, Nanyang Technological University, Stanford, Japan Institute of Industrial Technology and University of Tsukuba are in a leading position, and SionPower has carried out significant research in the field of notebooks and drones. Application try.　　8. Lithium-air battery 　　 Lithium-air battery is a new type of large-capacity lithium-ion battery, jointly developed by the Japan Institute of Industrial Technology and the Japan Society for the Promotion of Science (JSPS). The battery uses lithium metal as the negative electrode, oxygen in the air as the positive electrode, and the two electrodes are separated by a solid electrolyte; the negative electrode uses an organic electrolyte, and the positive electrode uses an aqueous electrolyte.

　　During discharge, the negative electrode is dissolved in the organic electrolyte in the form of lithium ions, and then migrates through the solid electrolyte to the aqueous electrolyte of the positive electrode; electrons are transferred to the positive electrode through the wire, and oxygen and water in the air react on the surface of the micronized carbon. Hydroxide is generated, which combines with lithium ions in the aqueous electrolyte of the positive electrode to generate water-soluble lithium hydroxide. During charging, electrons are transported to the negative electrode through the wire. Lithium ions pass through the solid electrolyte from the positive electrode's aqueous electrolyte to the negative electrode surface, and react on the negative electrode surface to generate metal lithium; the hydroxide radical of the positive electrode loses electrons to generate oxygen.

　　Lithium-air battery can be replaced by the positive electrolyte and negative electrode lithium without charging. The discharge capacity is as high as 50000mAh/g, and the energy density is high. Theoretically, 30kg lithium metal can release the same energy as 40L gasoline; the product lithium hydroxide is easy to recycle and is environmentally friendly. But cycle stability, conversion efficiency and rate performance are its shortcomings.　　 In 2015, Cambridge University Gray developed a high-energy density lithium-air. The number of recharges was "more than 2000", and the energy efficiency theoretically exceeded 90%, which made the practical use of lithium-air batteries one step forward. As early as 2009, IBM launched a sustainable transportation project to develop a lithium-air battery suitable for household electric vehicles. It hopes to travel about 500 miles on a single charge. Recently, Japan’s Asahi Kasei and Chuo Glass Co. Joining this project, the research and development of scientific research institutions and well-known companies in the field of lithium-air batteries will greatly promote the application of this battery technology.