Introduction to the graphene materials
Graphene Oxide is a two-dimensional planar nanomaterial composed of carbon atoms with a hexagonal honeycomb lattice，the c-c bond length is 0.141nm, the theoretical density is about 0.77mg/m2, and the thickness is only about the diameter of a carbon atom. Carbon atoms participate in hybridization in the way of sp2, and electrons can smoothly conduct between layers, so graphene conducts electricity extremely well. It is the material with the smallest resistivity known, which is one of the reasons why graphene has a promising future in batteries.
Battery Graphene materials have excellent thermal conductivity, and their theoretical room temperature thermal conductivity of single layer is up to 3,000-5,000w/(m*K). This property can be used to study the heat dissipation during battery operation.It has excellent mechanical properties and is a material with excellent toughness and strength, which can be used to develop and study flexible electrode materials. In addition, the high specific surface area and high transmittance of graphene are also of great research value.
XIAMEN TOB NEW ENERGY is a technology company focused on the lithium battery equipment research and development and material improvement. We can provide high-quality products and the most professional technical services.
The Electrode Coating Machine is the key equipment for the production of lithium battery electrode. Because it directly affects the subsequent rolling operation, and even affects the performance of the entire battery. At present, the mainly lithium battery electrode coating process is: scraper type, roll to roll transfer coating type and a slit extrusion type. General speaking, laboratory equipment adopts the scraper type, the 3C battery adopts the roll to roll transfer coating type, and the power battery adopts the slit extrusion type.
Scraper coating: the foil substrate passes through the coating roller and directly contacts the slurry trough, and the excess slurry is coated on the foil substrate. The gap between the blade and the foil substrate determines the coating thickness, then the surface of the material forms a uniform coating.
Roll to roll transfer coating: The coating roller rotates to drive the slurry, the slurry transfer amount is adjusted by the comma scraper gap, and the slurry is transferred to the substrate by the rotation of the back roller and the coating roller.
Extrusion coating: As a precise wet coating technology, the working principle is that the coating liquid is sprayed out along the gap of the coating die at a certain pressure and transferred to the substrate. Compared with other coating methods, it has many advantages, such as fast coating speed, high precision and uniform thickness. The coating system is closed, which can prevent the entry of contaminants during the coating process. The slurry utilization rate is high and the slurry can be kept. It is stable in nature and can be coated at the same time. It can adapt to different slurry viscosity and solid content ranges, and has stronger adaptability than the transfer coating process.
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The main components of lithium ion battery include cathode, cathode, electrolyte, membrane, etc. The storage and release of lithium ion energy is realized in the form of REDOX reaction of electrode materials, and the cathode active material is the most critical core material of lithium ion battery.
Professor GOODENOUGH, the father of lithium battery, has made a great contribution to the research of lithium battery cathode materials. In 1980, while working at the university of Oxford in the United Kingdom, he discovered that lithium cobalt oxide (LCO) could be used as a lithium cathode. In 1981, he mentioned the feasibility of lithium nickelate (LiNiO2, also known as LNO) as a cathode material in the LCO patent. In 1983, he made his first attempt to use lithium manganate (LMO) as a cathode material for lithium-ion batteries. In 1997, he developed lithium iron phosphate (LiFePO4, or LFP), which is the cathode material of olivine structure. In addition, to solve the problem of unstable properties of lithium nickelate, a large amount of research has been conducted in the area of doping modification by Prof. DAHN from Canada and Prof. Sumika kosuki from Japan. In 1997, toda applied for the first patent of lini1-x-ycoxalyo2 (NCA). In 1999, liu zhaolin and yu aishui et al. from the university of Singapore introduced Mn modification on the basis of lithium ni-co (lini1-x-ycoxmnyo2, namely ternary material and NCM).
After nearly 30 years of rapid development, based on the above scientists research results. Lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt oxide (lini1-xcoxo2, also known as NC), lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium iron phosphate and other cathode materials have been industrialized, and have been expanded for many fields. With the demand of high energy density cathode materials for new energy vehicles, the nickel-cobalt lithium manganate ternary material has become the most important cathode material with the largest proportion.
Polyvinylidene fluoride binder(PVDF) is currently the most commonly used oil binder in the lithium ion battery industry. It is a non-polar chain polymer binder. It is characterized by strong oxidation resistance, good thermal stability and easy dispersion. N-methylpyrrolidone (NMP) is required as a solvent. This solvent has a high volatilization temperature, has a certain environmental pollution, and is expensive.
Obvious deficiencies include:
1） Young’s modulus is relatively high, between 1-4GPa, the flexibility of the pole piece is not good enough;
2） When PVDF absorbs water, the molecular weight decreases and the viscosity becomes poor, so the humidity requirement for the environment is relatively high;
3） For ion and electronic insulation, there is a certain degree of swelling in the electrolyte. It reacts exothermically with lithium metal and LixC6 at higher temperatures, which is detrimental to the safety of the battery.
Conventional PVDF, the main mechanism of action is van der Waals force, that is, the intermolecular force acts as a bonding force, and some modified PVDF, the mechanism of action has two parts, one part is the van der Waals force brought by high molecular weight. On the other hand, it is due to the chemical bond between the foil and the foil.
Current synthetic methods include suspension polymerization and emulsion polymerization.
For different cathode materials, PVDF synthesized by different methods can be applied, and also combined with the corresponding homogenization process, in order to achieve a good effect.
The vacuum drying oven is designed for drying heat sensitive, easily decomposable and easily oxidizable materials. It can be filled with an inert gas, which can make some ingredients with complex ingredients dry quickly.
Scope of application:
High Temperature Vacuum drying ovens are widely used in research and application fields such as biochemistry, chemical pharmacy, medical and health, agricultural research, and environmental protection. For powder drying, baking and disinfection and sterilization of various glass containers. It is especially suitable for fast and efficient drying of heat sensitive, easily decomposable, oxidizable substances and complex ingredients.
It has the following advantages over conventional drying technology:
1) The vacuum environment greatly reduces the boiling point of the liquid to be repelled, so vacuum drying can be easily applied to heat sensitive substances;
2) For samples that are not easy to dry, such as powder or other granular samples, vacuum drying can effectively shorten the drying time;
3) Various mechanical parts or other porous samples with complicated structure are cleaned and vacuum dried, leaving no residual material after complete drying;
4) Safer to use – completely eliminate the possibility of oxide explosion during vacuum or inert conditions;
5) Powdered samples are not blown or moved by flowing air compared to ordinary drying by air circulation;
6) Control features: parameter memory protected by power failure and data loss of the crash state, call recovery function.
The lithium-air battery is a new type of high-capacity lithium-ion battery developed by the Japan Industrial Technology Research Institute 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 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 transmitted to the positive electrode through the wire, and oxygen and water in the air react on the surface of the fine carbonized carbon. Hydrogen peroxide is formed and combined with lithium ions in an aqueous electrolyte solution of the positive electrode to form water-soluble lithium hydroxide. When charging, electrons are transmitted to the negative electrode through a wire, and lithium ions pass through the solid electrolyte of the positive electrode to the surface of the negative electrode through the solid electrolyte, and react to form metallic lithium on the surface of the negative electrode; the hydroxide of the positive electrode loses electron-generating oxygen.
The lithium-ion battery can be replaced by a positive electrode electrolyte and a negative electrode lithium. The discharge capacity is as high as 50,000 mAh/g, and the energy density is high. Theoretically, 30 kg of metal lithium and 40 L of gasoline release the same energy; the product lithium hydroxide is easy to recycle and environmentally friendly. However, cycle stability, conversion efficiency, and rate performance are disadvantages.
Although high-voltage lithium battery materials are getting more and more attention, these high-voltage anode materials are still unable to achieve good results in practical production and application. The biggest limiting factor is that the electrochemical stability window of the carbonate-based electrolyte is low. When the battery voltage reaches about 4．5（vs．Li/Li＋）, the electrolyte begins to produce violent oxidation decomposition, causing the lithium-intercalation and lithium-deintercalation for the battery not working properly. The development of electrolytic liquid systems that can withstand high voltage is an important step to promote the application of this new material.
The development and application of new high voltage electrolyte systems or high voltage film forming additives to improve the stability of electrode/electrolyte interface is an effective way to develop high voltage electrolyte. Economically, the latter is often preferred. Such additives to improve the voltage tolerance of electrolyte generally include boron, organic phosphorus, carbonates, sulfur, ionic liquids and other types of additives. Boron additives include trimethylalkanes borase, lithium borate dioxalate, lithium borate difluoroxalate, tetramethylborate, trimethyl borate and trimethylcyclotriboroxane. Organic phosphorus additives include phosphite esters, phosphite esters. Carbonate additives include fluorinated anhydryl compounds. Sulfur-containing additives include propionic acid lactone, dimethyl sulfonyl methane, trifluoromethyl phenyl sulfide, etc. Ionic liquid additives include imidazole and quaternary phosphate salts.
According to the domestic and foreign studies that have been published, the introduction of high-voltage additives can make the electrolyte withstand the voltage of 4.4-4.5v. However, when the charging voltage reaches 4.8v or even more than 5V, it is necessary to develop the electrolyte that can withstand higher voltage.
The battery separator plays a major role in lithium ion battery conduction lithium ions and isolation between the positive and negative electrode electronic contact. It is an important component to support the battery to complete the electrochemical process of charge and discharge.
In the use of lithium batteries, when the battery overcharge or at higher temperatures, the separator need to have enough thermal stability (thermal deformation temperature > 200 ℃), to effectively isolate the battery positive and negative electrode contact, prevent short circuit, such as thermal runaway and even explosion accidents. Currently widely used polyolefin Separator, its melting point and low softening temperature (< 165 ℃), it is difficult to effectively guarantee the safety of the battery, and its low porosity and low surface energy, limiting the battery performance ratio. Therefore, it is very important to develop high safety high temperature Separator.
Xiamen TOB technology research department has developed a new type of high temperature resistant porous membrane by adopting the wet process primary molding technology, which is low-cost to prepare and easy to quantify production. Preliminary study results show that thermal deformation temperature of the Separator is much higher than 200 ℃, and the thermal stability of the commercialization of non-woven Separator, can effectively guarantee the battery safety.
The 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) has a high discharge specific capacity. It is about twice the actual capacity of the cathode material currently used, and is therefore widely studied for lithium battery materials. In addition, since the material contains a large amount of Mn element, it is more environmentally safe 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 considered by many scholars as the ideal material 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, hydrothermal method and other processes to prepare, but the obtained material properties are not as stable as the co-precipitation method.
Although this material has a high specific capacity, there are still several problems in its practical application:
1）The irreversible capacity of the first cycle is up to 40 ~ 100mAh/g;
2）Poor rate capability, 1C capacity under 200mAh/g;
3）High charging voltage causes electrolyte decomposition, making the cycling performance less than ideal.
4）And security issues in use.
By means of metal oxide coating, composite with other anode materials, surface treatment, special structure construction, low upper limit voltage precharge and discharge treatment and other measures, the above problems of lithium-manganese rich materials can be well solved.
TOB Machine is a lithium enterprise full of vitality and creativity. We can provide you with a full set of solutions of the lithium-ion battery, provide lithium-ion battery equipment, materials, lithium-ion battery project planning, manufacturing technology, plant program design and management system.
As an important component of lithium ion battery, negative electrode material has a direct impact on the energy density, cycle life and safety performance of the battery and other key indicators. Silicon is the anode material of lithium ion battery with the highest specific capacity (4200mAh/g) known at present. However, due to its over 300% volume effect, The silicon electrode material will pulverize during charging and discharging, and flake off from the collector fluid. caused the loss of electrical contact between active matter and active matter, the active matter, and the stream of fluid, and forming a new layer of solid electrolyte layers, which ultimately leads to the deterioration of electrochemical properties. In order to solve this problem, researchers have made a lot of explorations and attempts, among which silicon-carbon composites are very promising materials.
Carbon material, as the cathode material of lithium ion battery, has a small volume change in the charging and discharging process, and has good cycling stability and excellent conductivity, so it is often used to compound with silicon. Among the carbon-silicon composite cathode materials, according to the types of carbon materials, they can be divided into two categories: The combination of silicon and traditional carbon materials and silicon and new materials, The traditional carbon materials mainly include graphite, intermediate phase microspheres, carbon black and amorphous carbon. New carbon materials mainly include carbon nanotubes, carbon nanowires, carbon gels and graphene. Silicon carbon composite is adopted to restrain and buffer the volume expansion of silicon active center by utilizing the porous effect of carbon material, prevent particle agglomeration, prevent electrolyte from penetrating into the center, and maintain the stability of interface and SEI film.
Many enterprises around the world have begun to work on this new type of cathode material, silicon carbon new cathode material as the direction of future product research and development.